review article allotropic carbon nanoforms as advanced metal-free catalysts … · 2019. 7. 31. ·...

Review ArticleAllotropic Carbon Nanoforms as Advanced Metal-FreeCatalysts or as Supports

Hermenegildo Garcia

Instituto Universitario de Tecnologıa Quımica CSIC-UPV Universidad Politecnica de Valencia Avenida De Los Naranjos sn46022 Valencia Spain

Correspondence should be addressed to Hermenegildo Garcia hgarciaqimupves

Received 19 May 2014 Revised 14 July 2014 Accepted 28 July 2014 Published 15 September 2014

Academic Editor Davut Avci

Copyright copy 2014 Hermenegildo Garcia This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

This perspective paper summarizes the use of three nanostructured carbon allotropes as metal-free catalysts (ldquocarbocatalystsrdquo) or assupports of metal nanoparticles After an introductory section commenting the interest of developingmetal-free catalysts andmainfeatures of carbon nanoforms the main body of this paper is focused on exemplifying the opportunities that carbon nanotubesgraphene and diamond nanoparticles offer to develop advanced catalysts having active sites based on carbon in the absence oftransition metals or as large area supports with special morphology and unique properties The final section provides my personalview on future developments in this field

1 Introduction From Active Carbons toCarbon Allotropes

In classical heterogeneous catalysis active carbons (ACs)have been widely used as supports for noble metal and metaloxides [1ndash3] ACs are high surface area materials havingcarbon as predominant element in their composition thatare obtained by pyrolysis of available biomass wastes uponaddition of inorganic reagents to promote the carbonisationprocess For instance one popular active carbon comes fromcoconut shells adequately powdered pyrolyzed at 600∘Cunder N

2 mixed with phosphoric acid for activation and

then baked at temperatures below 300∘C [4 5] In otherrecipes olive seeds or almond shells are used as AC pre-cursors and other mineral acids or oxidizing chemicals areemployed as additives [6ndash8]

The structure of ACs is poorly defined with domains ofamorphous carbon and the presence of condensed polycyclicaromatic compounds forming platelets of nanometric dimen-sions that are interconnected by bridges that can be CH

2and

heteroatoms such as O NH and S In certain regions ACshave graphitic domains when the platelets are large enoughand stacking of the imperfect graphene (G) sheets can take

place Besides oxygen and other elements such as nitrogen orsulphur metal traces such as iron zinc and copper are veryfrequently present in the final composition of the materialbecause these transition metals have been introduced asadditives in the pyrolysis process and they remain in residualsometimes not negligible percentages

Understanding themechanism in heterogeneous catalysislargely depends on the exhaustive characterization of thesolid catalyst and on the knowledge on the architecture ofthe active sites [9] In this sense while ACs are available andaffordable materials exhibiting high adsorption capacity thisproperty being suitable for their use as support they are toocomplex and ill-defined to allow structural characterizationand moreover they make impossible the preparation ofsingle-site catalysts

One of the main problems in heterogeneous catalysisderives from the fact that solids contain a wide distributionof centers in which the architecture of the sites and thesurroundings change from one specific site to another andas result the activity and selectivity may change from onesite to the neighbor Optimal solid catalysts would requirea material in which all the sites are identical (ldquosingle siterdquo)all of them exhibiting the same selectivity and desirably the

Hindawi Publishing CorporationAdvances in ChemistryVolume 2014 Article ID 906781 20 pageshttpdxdoiorg1011552014906781

2 Advances in Chemistry

maximal activity Design and synthesis of single-site catalystshas been a continued task in heterogeneous catalysis with thelong-term aim of the development of solid catalysts with thehighest activity and selectivity [10ndash12]

In the last decades carbon allotropes with nanometricparticle dimension have been characterized and have becomecommercially available Since their structure is much betterdefined than ACs there has been a continued growinginterest in the application of these carbon nanoforms incatalysis as a logical evolution of the use of ACs [13ndash15]The interest of allotropic carbon nanoforms in catalysis istherefore a logical evolution of the continued use of ACsfor the preparation of heterogeneous catalysts but goes muchbeyond ACs since the point is now to incorporate the activesites on the carbon structure

As in the case of ACs the simplest possibility has beenthe use of these carbon allotropes as large area supports ofactive sites [16ndash18] but the most recent research front is toimplement the catalytic sites on the carbon allotrope itselfin the absence of metals (ldquocarbocatalysisrdquo) Starting from anideal structure of the carbon allotrope it should be possibleto introduce sites by creating carbon vacancies carbon withdangling bonds structural defects due to carbon vacanciesand oxygenated functional groups or by replacing carbonatoms by other elements (ldquodopingrdquo)

The term ldquocarbocatalystsrdquo refers to the development ofcatalysts based exclusively or predominantly on the use ofcarbon materials avoiding or minimizing the dependency ofcatalysis on the use of metals [19ndash25] While the use of metalsis considered not ldquosustainablerdquo due to the limited availableresources carbonaceous catalysts particularly those derivedfrom biomass are renewable and affordable and consideredas ldquosustainablerdquo materials

Among the different carbon allotropes that have beenapplied in heterogeneous catalysis the initial studies werebased on carbon nanotubes (CNTs) because these materialsbecome commercially available earlier than other carbonmaterials [26 27] Preparation of CNTs requires catalystsand special equipment CNTs typically are obtained in smallbatch quantities and impurified with the catalyst used intheir synthesis typically iron or iron-cobalt alloys dispersedin a matrix to maintain the particle size small This makesnecessary in commercial CNTs several steps of purificationoxidation and other modification processes before theycan be used as catalysts After CNTs the use of diamondnanoparticles (DNPs) has also become possible DNPs can beobtained by milling of diamond powders or by explosive det-onation [28] In the last caseDnanocrystals are embedded ona soot matrix of amorphous carbon that has to be removedbefore the use of the DNPs as supports [29] More recentlya new line of research has appeared trying to exploit theopportunities of G-basedmaterials in catalysis [20 21 30 31]

Allotropic carbon nanoforms can be dispersed in sus-pension in a liquid phase as inks that allow the recoveryof the carbonaceous materials by filtration or centrifugationafter their use The term ldquopseudohomogeneous catalysisrdquo hasbeen used to denote the fact that during the reaction thereis no apparent phase differentiation between substrates andcatalysts but after the reaction the carbonaceous material

Carbon nanoforms in catalysis

Carbon Graphene

Diamond

nanotubes nanoparticles

Scheme 1 Structure of the three carbon allotropes whose use ascarbocatalysts or as supports of metal nanoparticles will be the topicof the present perspective paper

can be easily separated and recovered as is characteristic inheterogeneous catalysis [32]

In the present spotlight paper I will comment on someof the possibilities that nanometric carbon allotropes offer ascatalysts or as supports showing the logic of the evolutionfrom ACs or from other supports to these carbonaceousnanomaterials as catalysts Scheme 1 contains the type andstructure of the carbon nanoforms whose catalytic activitywill be commented on in this perspective paper Whenpossible comparison between the performance of differentcarbon allotropes will be made but I will try to highlight thefeatures of each type of carbon nanoform thatmake thembestsuited for certain catalytic applications I will start with thepossibilities and limitations of CNTs followed by the use ofG-basedmaterials in catalysis and finishing with applicationsof DNPs as supports In this paper I will cover a broad rangeof articles in this area with emphasis on the use of thesematerials as carbocatalysts in the absence of metals with theaim of illustrating the broad potential that carbon nanoformsoffer in catalysis In the last section I will summarize themajor points and will provide my view on possible futuredevelopments and targets in this area

2 Catalysts Based on CNTs as Supports

CNTs are characterized by their long aspect ratio in whichone or several concentric hexagonal arrangements of sp2carbons (ldquographene sheetsrdquo) form a cylinder with nanometricdiameter but lengths that can reach tens of micrometersThelong aspect ratio and the curvature of the graphene walls arethe main characteristics of CNTs

The synthesis of CNTs either single wall (SWCNTs) ormultiple wall (MWCNTs) is difficult to control and relieson the use of a metal catalyst typically Fe and Co alloys inthe form of small metal NPs to decompose in the pyrolyticprocess at temperatures about 500∘C or above the organicprecursor in the absence of oxygen and effect the nucleationand growth of CNTs from elemental carbon atoms generatedunder these reductive conditions (Scheme 2) [34]

Due to the use of a catalyst in the preparation of CNTsthe amount of CNTs that is available in each batch is limitedcompared to other carbon nanoforms [36] MWCNTs canbe prepared in larger quantities than SWCNTs because the

Advances in Chemistry 3

PrecursorCH4

DehydrogenationMetal NPnucleation

Growth

CNT

Support

Scheme 2 Pictorial illustration of the synthesis of CNT by dehydro-genative carbonisation of methane on hot metal nanoparticles Onthe surface of themetal carbon atoms are continuously being formedat high temperatures due to the dehydrogenative decomposition ofthe precursors (methane in this case) and these atoms condense inan hexagonal arrangement leading to the graphene wall with diam-eter commensurate with the dimensions of the metal nanoparticlecatalyst and growing outside these nanoparticles

control on the particle size of the metal alloy is not so strictIn general terms the advantages of using single wall withrespect to multiwall have not been clearly demonstrated incatalysis and therefore the use of more stable and affordableMWCNTs can be advantageous with respect to SWCNTsHowever from the point of view of achieving the highestcatalytic activity and having well-defined structure SWCNTscan be preferable since all the carbons are exposed at thesurface and their morphology and structure is well definedand can be determined by electron microscopy Also fromthe catalytic point of view there are no examples showingdifferences between the properties of conductive or semicon-ductive SWCNTs as catalysts [37 38] Electrical conductivityin CNTs depends on the way in which the hexagons of thegraphene wall are aligned along the long axis either spiral(semiconductive) or perpendicular (conductive)

During the purification of CNTs to remove the metalcatalyst employed in the synthesis of CNTs strong inorganicacids are generally needed HNO

3is one of the preferred

reagents for CNT purification and then at the same timethat the acid dissolves inorganic impurities mild oxidationof the graphene wall forming oxygenated functionalities andparticularly carboxylic acid groups can also be produced Byperforming treatment with HNO

3under harsh conditions

of concentration temperature and time purification of theorganic residues can be accompanied by cutting of the CNTsfrom micrometers to hundreds of nanometers [39 40] thecut taking place preferentially by oxidation of the graphenewall at defects One consequence of the shorter length andformation of oxygenated functional groups is an increaseon the dispersability of CNTs in liquid media and water in

MetalNPs

HO2C

HO2C

HO2C

HO2CHO2C

Defects

CO2H

CO2H

CO2HCO2H

CO2H

Doping

Carboxylicacids

X X

XX

Scheme 3 Possible sites present in CNTs that can exhibit catalyticactivity

particular [41 42] Preparation of permanent suspensionsof short CNTs is very adequate for the development ofpseudohomogeneous catalysis

CNTs can contain active sites due to the presence ofcarboxylic acid groups at the rims and wall defects thatcan be functionalized Also CNTs can be doped with someheteroatoms the most common one being N atoms Otherpossible defects include carbon vacancies and doping withsome heteroatoms replacing carbon atoms in the wall CNTscan also be the support of metal NPs that can be the activesites in the reaction Scheme 3 summarizes some of thepossibilities that CNTs offer to incorporate active centers

However as commented earlier the cumbersome prepa-ration and purification of CNTs explain why these carbonnanoforms have not become as widely available and afford-able for the catalytic community as desirable Since it isexpected that the activity of these modified CNTs as acidcarbocatalysts would be similar to that of more easily avail-able Gmaterials or that of polymeric resins having carboxylicacids there is no special reasons beyond morphology andthe possibility to encapsulate metal NPs inside the tubes toprefer CNTs in catalysis with respect to G Thus althoughit would be desirable much more information about thecatalytic activity of CNTs it is unlikely that this research frontwill develop strongly in the near future and perhaps themajor point of interest will be to compare the catalytic activityof CNTs having curved graphene walls with that of other G-based catalysts

CNTs in the absence of any metal have been found tobe suitable catalysts for the oxidative dehydrogenation ofhydrocarbons (Scheme 4) [43ndash45] This process has consid-erable interest in petrochemical industry for the transfor-mation of propane into propene and butanes into butenesand butadiene CNTs have defects that typically correspondto oxygenated functional groups namely carboxylic acidsquinone-like carbonyl groups and hydroxyl groups As I


HH O2

CNTs+ H2O

Scheme 4 Oxidative dehydrogenation of propane catalysed byCNTs

will comment along this paper one of the issues that stillhas to be clarified in many reactions is the nature of theactive sites responsible for promoting the reaction In thepresent case using an elegant strategy the catalytic activityof CNTs for the oxidative dehydrogenation of light alkaneswas compared to that of analogous CNTs samples that havebeenmodified tomask selectively each type of the oxygenatedfunctional groups [46] In this way carboxylic and hydroxylgroups were selectively protected by esterification or sub-stitution respectively while quinone-like carbonyl groupswere transformed into imines Comparison of the catalyticactivity of these modified CNTs having selectively maskedone of the three possible functional groups has shown thatthe catalytic activity of pristine CNTs and that of the esterifiedor hydroxyl substituted CNTs are almost identical and aboutfour times higher than that of the imine functionalized CNTs(Scheme 5) This decrease in the catalytic activity for themodified CNTs that do not contain quinone-like carbonylsbut contain carboxylic and hydroxyl groups has led to theconclusion that quinone carbonyls are the functional groupsthat are responsible for promoting this dehydrogenation [46]This type of studies shed light on the nature of the catalyticallyrelevant sites and can serve to prepare carbocatalysts with themaximum density of these functional groups and presum-ably with the optimal catalytic activity and selectivity

Considering that the aim of carbocatalysis is to developcatalysts to replace metals one challenging reaction that isknown to be promoted by transition and noble metals ishydroperoxide decomposition Using transition metal ionshydroperoxide decomposition can consume stoichiometricamounts leading to the formation of considerable amounts ofwastes in the reaction One example of this type of reactionsis the Fenton decomposition of H

2O2by Fe2+ ions in water

at acidic pH values [47 48] Therefore there is an increasinginterest in developing catalytic versions of this hydroperoxidedecomposition [47 48]

In the simplest mechanism the presence of redox sitesthat can reversibly donate one electron reducing hydroper-oxide and producing the reductive cleavage of the OndashObond and then become reoxidized by other hydroperoxidemolecules rendering oxygen should catalyze hydroperoxidedecomposition Scheme 6 illustrates the catalytic cycle ofhydroperoxide decomposition by the presence of a redox sitethat really can be considered as hydroperoxide dismutationHydroperoxides have oxygen atoms in the minusI oxidationstate and can undergo disproportionation to the 0 and minusIIoxidation states Transition metals having different oxidationstates and binding strongly to hydroperoxides have been thepreferred catalyst for this process

However carbon materials can also have other typesof redox sites for instance those based on quinone-hydroquinone pairs having adequate redox potential to pro-mote the process In this context not surprisingly it has beenreported that CNTs can promote benzene hydroxylation tophenol byH

2O2with high selectivity [49ndash51]Theprocess still

requires deeper study and understanding in order to increasethe efficiency and particularly to assess the nature of theactive site but it is interesting to note that the curvature of thegraphene wall inMWCNTs has been invoked as playing a keyrole in the reactionmechanism [49] It would be important tocheck this hypothesis by comparing the process with CNTs ofdifferent diameters or even other G-based materials

In the previous process the synthesis of a chemicalcompound phenol frombenzene is the target of the reactionHowever most frequently peroxide decomposition is used todegrade organic compounds present in aqueous phase AlsoMWCNTs have been reported to act as catalysts for this typeof reaction Thus peroxy monosulfate can decompose by thepresence of MWCNTs leading to the formation of sulfateradicals that are able to initiate the aerobic decolorizationof methylene blue and decomposition of 24-dichlorophenol[52] For this reaction active carbons also exhibit catalyticactivity but it has been found that reduced graphene oxide(GO) can exhibit even higher activity than MWCNTs [52]

Doping can be a viable general strategy to introduceactive sites in CNTs As a general observation the presenceof N increases the stability of the carbon nanoforms againstoxidation and therefore N doping makes CNTs moresuitable as oxidation catalysts [53 54] N-doped MWCNTsare also able to promote the aerobic oxidation of benzylalcohols at moderate temperatures [55 56] These N-dopedMWCNTs exhibit for this reaction similar catalytic activityas G materials

Although in general similar performance as catalystsshould be expected for CNTs andGmaterials one peculiarityof CNTs is the possibility to include inside the tube ofnanometric dimension some metal nanoparticles (NPs) ofsize smaller than the diameter of the tubes In this regardFe NPs have been confined inside CNTs and the resultingmaterial used for the aerobic oxidation of cyclohexane toadipic acid a process of large industrial relevance (Scheme 7)[57] However the study has to show conclusively thatthe system based on the inclusion of Fe NPs on CNTs isstable under the reaction conditions and does not undergoself-degradation during the course of the reaction Carbonnanoforms can be oxidized under various conditions Thisoxidation leads to the formation of oxygenated functionalgroups resulting in the creation of defects In the case ofCNTs oxidation can result in a shortening of their length asconsequence of the oxidative cutting of the tube Thus it isvery likely that CNTs could undergo an increasing degree ofoxidation that eventually could lead to the release of Fe NPsand the deactivation of the catalyst but this issue of catalyststability in aerobic oxidations has not been yet addressed

Besides oxidation carbon nanoforms and also CNTshave attracted interest as catalyst for reversible hydrogenreleaseuptake from metal hydrides [58ndash61] In the contextof hydrogen storage one of the possibilities that has been


Ph (O=C) O2CPh (O=C) O O

O

O O

N

N

O

O OO

O

2C

(PhCO)2O

O

OH

HO

OH

OHOH

OHCO2COPh

CH2COPh

CH2COPh

CNT-anhydride

HO

HOPh

Ph

OH

OH

OHOH

CH2COPh CH2COPh

Ph-NH2

CNT-ether

CNT

CNT-imine

PhCOCH2BrCO2H

CO2H

CO2HHO2CHO2C

HO2C

HO2CHO2C

HO2C

ndash ndashndash ndash

Scheme 5 Derivatisation of CNTs to mask selectively oxygenated functional groups to assess the nature of the active sites It was found thatCNT CNT-anhydride and CNT-ether perform with similar catalytic activity four times higher than that of CNT-imine

H2O + 12O2

HOOH

HOOHReduced

Oxidized siteHOminus + ∙OH

site

Scheme 6 Catalytic hydrogen peroxide decomposition (dismuta-tion) mediated by a redox site that could be present in a carbonnanoform

O2

(Fe NP)CNT

COOHCOOH

Adipic acid

Scheme 7 Aerobic oxidation of cyclohexane to adipic acid catalysedby Fe NPs incorporated inside CNTs ((Fe NP)CNT)

subjected to intensive study has been storage of hydrogeninto a chemical compound that can release hydrogen ondemand at moderate temperatures with the assistance of acatalyst After being used the residual product resulting fromhydrogen release should also regain catalytically hydrogenforming the initial hydride One of the preferred metalhydrides for this process has been LiBH

4(1) It has been

found that CNTs can release up to 88 wt of hydrogen fromLiBH4under mild conditions [61] However comparison

with GO and r-GO indicates that the hydrogen release usingG-basedmaterials is about 1higher than that of usingCNTsThis comparison suggests that defects and residual oxygenfunctionalities are acting as catalytic centers in this processand that CNTs could have a lower density of this type of sites

LiBH4999445999468 LiH + B + 15H

2(1)

One of the possibilities that CNTs offer in catalysis istheir use as supports of metal NPs Pd NPs supported onMWCNTs have been employed as catalyst for hydrogenationoxidation and CndashC coupling reactions [62ndash66] The activityof PdMWCNTs has been compared to that of palladiumsupported on ACs (PdC) and it was found that the turnovernumber with respect to Pd was higher for PdMWCNTsthan that for PdC for some of these reactions [33] It wasconsidered that the interaction between the graphene wallof the support with Pd together with the morphology ofthe nanotubes is beneficial to increase the catalytic activityof Pd NPs for those reactions in which the Pd particlesize is a key parameter controlling the catalytic activity Incontrast Pd supported on MWCNTs were much less activethan Pd supported on charcoal for those reactions such ashydrogenation of cinnamaldehyde and oxidation of benzylalcohol that are less sensitive to the average particle size ofPd (Scheme 8)

The strong metal-support interaction arising from over-lapping of the extended 120587 system of the graphene wall ofCNTs and the orbitals of metal clusters has also been claimedas being responsible for the formation and stabilization


Hydrogenation of cinnamaldehyde

(PdC more active than PdMWCNT)

C-C coupling reaction (PdMWCNT more active than PdC)

O

O

O

OH OH

OHO2

X

+

Oxidation of benzyl alcohol


Reactions catalyzed by palladium supported on MWCNTs

Scheme 8 Comparison of the catalytic activity of Pd NPs supported on MWCNTs or on ACs (based on [33])

CO + O2 CO2

Scheme 9 Pictorial representation of Au NPs supported on modi-fied SWCNT acting as catalyst for the aerobic oxidation of CO

of small Au clusters on SWCNTs and for the remarkablecatalytic activity towards molecular oxygen dissociation(Scheme 9) [67 68] Supported Au NPs are highly activeand selective catalysts for the aerobic oxidations of variousfunctional groups [69] and the experimental data indicatethat the support always plays an important role in the catalyticactivity of Au NPs and in the reaction mechanism In thepresent case Au NPs supported on SWCNTs are highlyactive for the low temperature CO oxidation and theoreticalcalculations at the DFT level indicate that this remarkablecatalytic activity should be mainly due to the ability of Au

NPs on SWCNTs for molecular oxygen dissociation resultingin the generation of Au oxide clusters highly dispersed on thematerial Recently Corma et al have shown that it is possibleto prepare and characterize clusters of a few Au atoms on thesurface ofmodifiedMWCNTs and that these clusters between5 and 10Au atoms are exceedingly active for the aerobicoxidation of thiophenol to diphenyldisulfide [70] It is clearthat this type of interaction120587-d betweenCNTs andmetal NPsis currently underestimated and other remarkable examplesobserving an increase in the catalytic activity can similarly beachieved in other cases The curvature of the graphene wallsand the presence of defects (oxygen functional groups andcarbon vacancies) or heteroatoms should constitute powerfultools to tune the electron density on the metal NP

Besides the use as support of metal NPs CNTs can alsobe employed as platforms to anchormetal complexes that canact as catalytic sites CNTs conveniently cut and purified canform permanent inks in aqueous solutions or organic mediabut once used as catalysts they can be recovered by filtrationIn this way the active sites will be highly dispersed in thereaction media during the reaction but can be recovered atthe end of the process and the catalyst recycled (ldquopseudo-homogeneous catalystrdquo) An example of this strategy has beenthe anchoring of a vanadyl salen complex that has been usedas catalyst for the cyanosilylation of aldehydes (Scheme 10)[71 72]

An important point in this approach is characterizationof the integrity of the metal complex and this is betterguaranteed if anchoring of the metal complex to SWCNTs iscarried out in the last step of the preparation of the material


(i) (ii)

(iii)

SWNT COClSWNT

SHSWNT

AIBN

VO(salen)SWNT

O

CI

O

O OO

O

N

V

V

N N

N N

H

NH

S

SH

As statistical mixture

O OO

Scheme 10 Synthesis of a vanadyl salen complex anchored to SWCNTs Reagents and conditions (i) 3M HNO3

reflux 24 h (ii) SOCl2

DMF 60∘C 24 h and (iii) 2-aminoethanethiol hydrochloride Et

3

N CH2

Cl2

45∘C 48 h

since all the previous intermediates can be purified and fullycharacterized by routine analytical and spectroscopic toolscommonly employed in organic chemistry Compared to ACthe use of short SWCNTs has the advantage of a well-definedmorphology and chemistry for covalent functionalizationthat can be based on the reactivity of carboxylic groupspresent predominantly at the tips andwall defects of theCNTsor on the reactivity of the graphene wall through specificcycloadditions such as the so-called Prato reaction or radicaladdition (Scheme 11) [73] In the case of the vanadyl salenSWCNTs it was found that the system is reusable and thechiral version can induce the preferential formation of oneenantiomer of the 120572-cyano trimethylsilyl ether with highenantiomeric excess [71] This area however still needs to bedeveloped and further work is necessary to fully exploit thepossibilities that CNTs offer as scaffolds to anchor covalentlymetal complexes including high dispersability easiness ofrecovery the interaction of substrates and sites with thegraphene walls either conducting or semiconducting andthe special morphology with long aspect ratio and highcurvature of the graphene wall

3 G-Based Materials in Catalysis

Compared to CNTs that are obtained by pyrolysis of adequatevolatile carbon precursors on transition metal-containingcatalysts (Fe and Co alloys or other possible metals) or byarc-discharge on graphite electrodes prepared adequately insuch a way that they already contain the metal catalyst [3674 75] Gs can be prepared by many other ways some of

them are chemical methods [76] Chemical procedures canbe preferable because they generally allow the preparationof large quantities Thus one of the most popular waysto prepare G-based materials starts with graphite that isdeeply oxidized using KMnO

4and H

2O2under strong acid

conditions (H2SO4 HNO

3) followed by exfoliation and

dispersion in an adequate solvent leading to GO suspensions[77] GO has a tendency to undergo chemical reductionleading to a decrease in its oxygen percentage typicallyabout 50wt oxygen content for GO obtained from graphiteoxidation forming suspendedmaterials with residual oxygencontent that are generally denoted as reduced graphene oxide(rGO) [76]

Recently we have reported a greener alternative to obtainG and doped Gs consisting in the pyrolysis in the absenceof oxygen of biomass precursors such as modified alginatesor chitosan (Scheme 12) [35 78 79] Chitosan acts as singlesource of carbon and nitrogen and depending on the pyrol-ysis temperature N-doped G can be obtained with variouspercentages of nitrogen up to 8wt that decreases as thepyrolysis temperature increases Also alginate modified byboric acid leads upon heating at temperatures higher than600∘C in the absence of oxygen to B-doped G the percentageof boron depends on the amount of borate in the precursorand on the pyrolysis temperature (Scheme 12) [35]

Pyrolysis of natural biopolymers tends to form graphiticcarbon residues with loose stacking of the graphene sheets asevidenced by XRD These graphitic carbon residues can besubsequently easily exfoliated without the need of oxidation[80] Thus no liquid chemical wastes are generated in theformation of doped G by biomass pyrolysis and in addition


Toluene refluxCH3

CH3

N

N

+

minusH2OminusCO2

OH

OO H

HHN +

Cminus

Scheme 11 Covalent functionalization of CNTs by dipolar cycloaddition (ldquoPrato reactionrdquo) to the graphene walls forming a pyrrolidinelinkage

H H

HH H

H

H

H

HH

OH OH

G

M

CH

120572

120573HO

4

41

1

O

O

O

O OO

O(a)

(c)(b)

Alginate

Alginate

Doped

precursor+ dopant graphene

Ominus

Ominus

Scheme 12 General route for the synthesis of doped G by using alginate as G precursor that is modified by addition of a compound of thedopant element (a) followed by pyrolysis of the modified biopolymer in the absence of oxygen (b) and sonication in the presence of a liquidphase (c) The letters G and M correspond to the guluronic and maluronic monosaccharides of alginate

only a natural biopolymer (typically considered as a valuelessbiomass waste) in combination or not of other dopantprecursors is employed in the synthesis In summary eitherstarting from graphite and submitting it to deep oxidation orstarting from other precursors G materials are more easilyavailable than CNTs and can be prepared in larger scalebasically because they do not require catalysts to nucleate thedehydrogenative carbonisation of the walls

One advantage of G-based materials is their large diver-sity and the opportunities to modify the G sheet by oxidationand doping with heteroatoms In this sense the group ofBielawski has pioneered in showing that GO can be acarbocatalyst for oxidation reactions (Scheme 13) [21]

Benzyl alcohols can undergo aerobic oxidation promotedby GO in the absence of metal [81] Also GO as acidcarbocatalyst promotes dimerization and oligomerizationof styrene [82 83] However it has to be mentioned thatimpurities present in GO have to be surveyed as possibleactive sites responsible for the catalytic activity Since GOpreparation employs a large excess of KMnO

4and H

2SO4

it could be possible that these chemicals (or some impu-rities accompanying them) may not have been removedcompletely from GO and that these impurities at the ppmlevel or above could be responsible for the catalysis in thesereactions For instance our group has shown that GO cancatalyze the room-temperature acetalization of aldehydes bymethanol and the epoxide ring aperture (Scheme 14) andthat this activity is related to the presence of sulphate groups

anchored to G [84 85] In accordance with the presenceof impurities on GO and their role in catalysis it has beenfound that exhaustive GO washings to the point in whichthe sulfur content becomes below ppms reduces significantlythe catalytic activity of GO for these two processes [84 85]Based on this it has been proposed that ndashOSO

2OH groups

anchored on GO sheets should be the active sites for thesetwo acid-catalyzed reactions The excellent activity of GOis a consequence of the high surface area easy accessibilityand excellent dispersability of GO sheets Comparison of thecatalytic activity of GO obtained from Hummers oxidationwith that of acetic acid reveals that HOAc is much lessefficient to promote these two reactions that probably requiresites of strong acidity However ndashOSO

2OH groups are not

permanently bonded to the GO sheets and can undergohydrolysis Therefore upon reuse a gradual decrease in thecatalytic activity is observed [84] In this sense the needof complete analytical data of G-based materials should beemphasized since their catalytic activity can arise from MnFe or other metal impurities or adventitious acid sites welldispersed on the large surface area characteristic on single-layer GOs

More recently our group has found that N-dopedG or (BN-) codoped G are suitable carbocatalysts to promote aerobicoxidations [35] Comparison of these doped G materialswith the catalytic activity of undoped G prepared followingthe same procedure suggests that this catalytic activity isdue to the presence of the dopant elements In comparison


HOOCOH

OH

H

OH

O

O

O O

OOO

O

OO

O

O

O

HO

HOHO

COOH

COOH

COOH

COOH

OH

OH

+ O2

GO

Scheme 13 Catalytic activity of GO to promote the aerobic oxidation of benzylic alcohols and cis-stilbene

O

O

HH CH3OH

CH3OH

OH

OSO3H

OSO3H

H3CO OCH3

OCH3

Scheme 14 Catalytic activity of rGO for the room temperatureformation of dimethyl acetal and epoxide ring aperture due to thepresence of residual sulfate groups anchored to the G sheet

with N-doping doping with B atoms leads to a materialwith lower activity [35] IR monitoring of the interactionof molecular oxygen with (N)G shows the appearance of anew band that has been attributed to some peroxyl groupson G [35] Formation of this peroxyl group is reversible andmild heating and evacuation under reduced pressure leadto the disappearance of this band [35] Other studies havealso shown the ability of N atoms on G to activate molecularoxygen [86] and how this interaction can serve to promote

aerobic oxidations of benzylic alcohols and hydrocarbonsalthough theymay require the use of tert-butylhydroperoxideas initiator [35] Overall the above data shows the potentialthat the incorporation of dopants on the G sheet can have toproduce active sites on the carbocatalysts as I have alreadypointed out for the case of CNTs (Scheme 3) [35]

Besides benzylic alcohols and hydrocarbons styrene canalso undergo aerobic oxidation by doped G leading tooxidative C=C bond degradation forming benzaldehyde orC=C bond epoxidation accompanied by rearrangement ofthe epoxide to 2-phenylacetaldehyde (Scheme 15) [35] Theimportant observation here is that the product selectiv-ity changes along styrene conversion Thus benzaldehydeis formed initially with almost complete selectivity whilestyrene oxide appears at higher conversions but can reachselectivities over 60 at final reaction times [35]

These changes in product selectivity as well as the for-mation of benzaldehyde without induction period have ledto proposing a mechanism for styrene oxide formation thatis similar to the one assumed for oxidation with molecularoxygen using a transitionmetal complex or salt and aldehydesas cocatalysts [87] According to this mechanism when theconcentration of benzaldehyde is sufficiently high reactionof oxygen with benzaldehyde promoted by doped G in theabsence of metals will lead to the formation of benzoyl


O2

Dopedgraphene

O OH + +

CHO

Scheme 15 Product distribution in the aerobic oxidation of styrenepromoted by doped G

10

20

30

40

50

0

Con

vers

ion

()

Time (h)

(a)

(b)

(c)

0 1 2 3 4 5 6

Figure 1 Time-conversion plots for the aerobic oxidation of styreneusing (N)Gas catalyst in the absence (a) and in the presence of 25 (b)and 5wt (c) of benzaldehyde Reaction conditions styrene (1mL)(N)G (10mg) and oxygen purging through a balloon 100∘C Plottaken with permission from [35]

peroxides and peracids that will be the real oxidizing speciesleading to C=C epoxidation Experiments in which variousamounts of benzaldehyde were added since the beginning ofthe reaction show that under these conditions styrene oxideis formed without any induction period (Figure 1)

As commented in the section of CNTs also G-basedcatalysts exhibit activity for the decomposition of peroxidemonosulfate and other peroxides [52 88] The main applica-tion of these reactions has been decolorization of dyes presentin aqueous solution Peroxide monosulfate as reagent hasthe advantage over hydrogen peroxide in that the processcan take place at neutral pH values and that the resultingsulfates radicals are highly reactive species attacking most ofthe organic compounds that could be present in water

Besides oxidations G can also be used for reductionAlthough obviously this reaction type has been much morefrequently performed with catalysts containing noble metalsG in the absence of any metal can have also some activityOne of the favorite reactions for which the catalytic activityof G has been tested is the reduction of nitrobenzene andderivatives with NaBH

4[89ndash91] In most of the cases a large

excess of NaBH4(over 300 equivalents) was used Although

this large excess of NaBH4is unrealistic for any application

due to the relatively high price of this commodity chemicalit can be used as a benchmark reaction to rank the activityof the G catalysts by using reaction conditions in whichthe kinetics becomes apparently of first order In this waythe value of the rate constant can quantitatively assess theactivity of the catalyst Another advantage of the reduction

HOOC

HOOC

HOOC

HOOC

O

O

O

O

O

O OO

OO

O

O

O

O

OO

HO

HOHO

HO

HO

HO

HO

HO

OH OH

OH

OH

OH OH

OH

OH

OH

OH

OHOH

OH

OH

COOH

COOH

Figure 2Model forGO showing the possible oxygenated functionalgroups and their location on the sheet

of nitrobenzene to aniline as a model reaction is that usingnitrophenol as probe under basic pH values the reactioncan be carried out in aqueous solution highly compatiblewith GO and r-GO and the course of the reaction can besimply monitored by following in UVvisible spectroscopythe decay and growth of the specific bands corresponding tonitrophenol and hydroxyaniline respectively

As commented previously in the case of CNTs oxidativedehydrogenation of alkanes is a reaction that can becarried out also using G-based materials as catalyst [92]In particular GOhas been reported as catalyst for the processIt should be commented that there are different models ofGO that try to fit with spectroscopic and analytical data forthis material These models indicates the type of oxygenatedfunctional groups that should be present in highly oxidizedGO (Figure 2) The functional groups include epoxide etherhydroxyl and carboxylic acid functionalities and basicallyhave to explain the high oxygen content of GO that can beeven above 50 in weight as I have already pointed out Thishigh oxygen content present in GOdetermines that the activesites that have been proposed for the oxidative dehydrogena-tion of propane on CNTs (quinone-like moieties) could notbe the same as those responsible for the same reaction in GO

In fact it has been proposed that in the case of GO epoxygroups should be mainly responsible for the process [92]In a certain way GO would act in the reaction mechanismfor the oxidative dehydrogenation analogously to the well-established Mars van Krevelen mechanism occurring innonstoichiometric metal oxides In these nonstoichiometricoxides oxygen from the solid lattice is reversibly transferredto the substrate causing its oxidation and then is replenishedby the oxidizing reagent [93] According to this analogyoxygen atoms of the epoxide groups present on GOwill formwater by reaction with the propane but in a subsequent stepepoxides will be formed again by reaction with molecularoxygen

One interesting application of G-based materials is to actas catalyst in the combustion of nitromethane and other highenergy fuels for rocketry thus increasing the power that thefuel can deliver to the engine Combination of theoreticaland experimental data indicates that defects on the G sheetand dangling bonds are responsible for the generation of


nitromethyl radicals that subsequently react with adsorbedoxygen and also for the decomposition of peroxide interme-diates [94 95] It could be interesting also to determine if thiscatalytic activity of G in combustion reactions can be appliedto conventional fuels such as gasoline or diesel where thecombustion of G could boost the octane or cetane number offuels

Although the use of G materials as carbocatalysts isdeveloping currently at a very fast pace it is clear thatat the present the most widely use of G in catalysis isas support of metal NPs In this type of reactions G cancooperate to the process at least in four different ways Thefirst one is providing a material with a very large surface areaallowing a good dispersion of themetal NPs (estimated about2630m2 times gminus1 for fully exfoliated single-layer material) [96]In addition a second possible effect is the strong metal-Ginteraction that takes place particularly at defects and in theposition in which heteroatoms are located in doped Gs [9798] The extended 120587 orbital of G especially in certain areasis particularly suitable for overlapping with the d orbitalsof transition metals leading to charge transfer phenomenabetween the metal and the support This orbital overlapalso determines a high affinity of G for metals minimizingleaching of the metal from the surface to the liquid phaseand also reducing particle growth and agglomeration In thiscase the key point is to show how the presumably strong 120587-dinteraction between theG sheet and themetal atomsmodifiesthe intrinsic catalytic activity of themetal NPs with respect toother supports

A third general effect that has been frequently claimed torationalize the excellent performance of the catalytic activityof metal NPs supported on G has been the strong adsorptioncapacity of G for substrates and reagents bringing them inclose proximity to the active sites and even also transferringelectrons to them

A fourth way in which G can contribute to the catalysisin which metal NPs are the main active sites is by providingacid base or other types of sites that can cooperate in certainsteps of the reaction mechanism The frequently observedconsequence of the use of G as support of metal NPs isa very good dispersability of the material in the reactionmedium that derives from the single-layer morphology andsubnanometric dimensions of the G

Comparison of the activity and selectivity of G-supportedmetal NPs with that exhibited by other related materials andparticularly metal supported on ACs is necessary in order tofully delineate the advantages of using G sheets as supportsThe presence of active sites on the G sheet combined withthe catalysis by the metal could lead to the development ofbifunctional catalysts with activity in tandem reactions inwhich two or more processes occur in a single step

The flat surface of G sheets is particularly suitable forthe interaction with metal NPs and Pd Au Pt and Ru havebeen among the preferred examples for their use in catalysis[99] At the moment although there is a large number ofexamples for preparation of supported metal NPs on G theirapplication in catalysis is still relatively limited It is expectedthat the numbers of examples will grow in the near future

applying Gs not only as catalysts oxidation reductionsand couplings but also for novel reactions in the field ofreversible hydrogen releaseuptake In the case of Au NPssupported on Gs there are some examples showing theiractivity as reduction catalysts for the transformation ofaromatic nitro groups into amines using sodium borohydrideas reagent [100] Similarly Pt NPs have been supportedon G and used as oxidation and hydrogenation catalyststhat are reaction types of general importance in industryand organic chemistry [101] Pd NPs supported on Gs havebeen the preferred pseudohomogeneous catalyst for couplingreactions [102]

Theoretical studies suggest that defects on G shouldfavour the interaction with supported Pt NPs [103] Compu-tational ab initio calculations have led to proposing that Ptsupported on defect-engineered G should be more tolerantcompared to free Pt NPs to the poisoning by CO sinceit should show a higher affinity for H

2[104] This lower

tendency to CO poisoning is of importance for the develop-ment of fuel cells and must be corroborated by experimentalmeasurements [105]

Pt NPs supported on rGO can be obtained by solvolysisusing ethylene glycol as reductant and stabilising agent[106ndash108] The average particle size of Pt NPs prepared inethylene glycol can be around 3 nm and they can exhibitoriented 111 facetsThismaterial performs for hydrogenationof nitrobenzene to aniline over 12 times more efficientlythan an analogous Pt catalyst using MWCNTs as supportFurthermore the catalytic activity at 0∘C of Pt-rGO is about20 times higher than the activity of Pt supported on ACThisenhanced catalytic activity of Pt-rGO is proposed to arisefrom the high dispersion of Pt clusters on rGO and from thedispersability of this material in the reaction mixture [101]

Electrical conductivity is one of the main properties ofsp2-forms of carbon allotropes and particularly of G-basedmaterials This electrical conductivity can serve to developelectrocatalysts [86 109] Pt NPs supported on G sheets ofsmall dimensions (G quantum dots (GQDs)) have also beenprepared by solvolysis with ethylene glycol of PtCl

4

minus onnanosized GQDs obtained by acid etching of carbon fibers[110]The resultingmaterial exhibits high activity as electrodefor the electrochemical oxygen reduction where the target isto reduce as much as possible the overpotential needed forthis electrochemical process [111] It was found that Pt-GQDshows an onset potential for oxygen reduction of +105V thatis 70mVmore positive than the onset potential observed foran analogous electrode prepared with Pt supported on AC[111] In fact due to the electrical conductivity G materialscontaining or not metal NPs have been widely used aselectrocatalysts but this area has been covered extensivelyin recent reviews and the reader is addressed to them for acomplete coverage [112ndash115]

4 Diamond Nanoparticles (DNPs) as Support

DNPs are affordable and commercially available (AldrichCAS 7782-40-3) DNPs can be prepared by milling ofdiamond powders or by explosive detonation [28] In the last


case the commercial samples have DNPs embedded in amatrix of amorphous carbon (ldquosootrdquo) and it is necessary totreat the samples to etch this amorphous soot matter DNPsfrom milling have generally much larger particle size thansamples obtained by detonation that are smaller than 10 nmConsidering the importance of having small particle sizesDNPs from detonation should be preferred as support incatalysis provided that they are liberated from the soot

In the previous shown cases of CNTs and G allotropicforms the carbon atoms have sp2 atomic orbitals and a stronginteraction due to the overlap of extended 120587 orbitals of CNTsor G materials with substrates or metal NPs should play akey role in the catalytic activity In contrast in the case ofDNPs the carbons are mainly sp3 with surface OH groupsand no 120587-120587 or 120587-d overlapping can take place Moreover alarge percentage of the surface of DNPs can be highly inertand can be envisioned better as devoid of interactions withthe active sites or metal NP This robustness and inertness ofDNPs can be however beneficial for their use as support topromote some reactions in which highly aggressive speciesthat can react with the support are going to be formedThus the current state of the art does not consider DNPs ascarbocatalysts since there is no a clear view of which type ofsites could be present in sp3 carbons but on the other handthey complement CNTs andGs as support since they provideand inert and robust surface that however can immobilizemetal NPs by the presence of occasional OH groups

One example of the beneficial use of DNPs as supportsof metal NPs is in the catalytic Fenton reaction for thedegradation of the organic pollutants in water by hydrogenperoxide [116 117] DNPs can be hydrophilic materials whenthe population of surface hydroxyl groups is large It is inthese surface OH nests where metal NPs are anchored Thedensity of these hydroxyl groups can be diminished to meetthe optimal density required to interact with the metal NPsby reductive treatments with hydrogen at temperatures above300∘C that converts CndashOH into CndashH groups [118] Turnovernumbers as high as 500000 have been determined for Ausupported on DNPs in the degradation of phenol taken asmodel pollutant [116 117 119] For this reaction at acid pHvalues almost quasistoichiometric 5 1 equivalents of H

2O2

to substrate are needed [116 117 119] These conditions areremarkable since very frequently reported Fenton catalystsuseH

2O2excesses as large as 10000 [116 117 119] Apparently

the key point of the excellent catalytic activity of the Au-DNPas catalyst is the combination of the lack of spurious H

2O2

decomposition characteristic of the catalytic behavior of AuNPs and the fact that ∙OH radicals formed in the process arefree to diffuse into the solution not remaining surface-boundas it happens withmany other solid Fenton catalysts based onmetal (typically Fe) supported on inorganic or organic solids(Scheme 16) [120 121]

One of the undesirable limiting conditions of the Fentonchemistry that should be overcome is the need of acidicpH values typically below 5 units to occur [122] For manyapplications it will be important to effect the Fenton reactionat neutral pH since it is not possible to adjust the pH valuefor large water volumes or stream flows Operation of Fenton

HO-OHSurface bound

radicalOH

MMMMM MMMMM

HO-OH ∙OH (free radical)

Au-DNPs(a)

(b)

Scheme 16 Pictorial illustration of the characteristic catalytic activ-ity of Au-DNP generating free ∙OH radicals due to the inertness ofits surface (a) in contrast to surface-bound ∙OH radicals (b)

Phen

ol d

egra

datio

n (

)

100

80

60

40

20

0

Initial pH = 7

Induction period

Time (h)

Low pH

0 1 2 3 4 5

Figure 3 Representative example of an ideal time conversion plotfor the phenol disappearance in the catalytic Fenton degradation byH2

O2

using Au-DNP as catalyst in the dark in the absence of buffersThe reaction is initiated at neutral pH exhibiting an inductionperiod Once the reaction starts there is a decrease in the pH valueup to 35 due to the formation of polycarboxylic acids that acceleratesthe reaction

catalysis at neutral pH can only be achieved using a verylarge excess of H

2O2and if there are not buffers in the

solution and for batch reactions it is frequently observed thatafter an induction period characterized by a slow start upof the reaction an acceleration occurs (Figure 3) This oftenremarkable increase in the reaction rate is mainly due to thefact that the pH of the solution becomes spontaneously acidicas soon as some phenol decomposes due to the formation ofcarboxylic acids that are the degradation byproducts It washowever observed that in the case of Au-DNPs the reactioncan take place at initial neutral pH values if the reaction isilluminated with solar light or artificial visible light [116 117]The reason for this photoinduced process is that Au NPsexhibit a surface plasmon band at 120582max 560 nm and visiblelight absorption at this wavelength can promote electroninjection from excited Au NPs to H

2O2 leading to ∙OH

radicals even in this unfavourably high pH range (Scheme 17)[116 117]


eminus

eminuseminus

O2 + H+

= Au0

E0 =

E0 =

E0 = 18 V18 V

= Au

Reduction

minusOH + ∙OH

Oxidation

Highly reactive

H2O2 H2O2

∙OOH + H+

semi-reaction

hydroxyl radical

semi-reactionh

120575+

28V

Scheme 17 Proposed mechanism for the photoinduced catalyticFenton generation of ∙OH radicals at neutral pH values by visiblelight irradiation of Au-DNPs The light is absorbed by Au NPs thatexhibit a visible band at about 560 nm (surface plasmon band) Lightabsorption triggers electron ejection that causes the reduction ofH2

O2

and formation of ∙OH radical

NH2-NH2O2

O2

SH S S

CuD

Scheme 18 Catalytic activity of Cu-DNP for the C=C double bondhydrogenation by hydrazine in the presence of oxygen and theaerobic oxidative coupling of thiophenol to diphenyldisulfide

Alternatively or coincidentally irradiation at the Ausurface plasmon band can induce local heating near the AuNPs that initiate a thermally induced Fenton reaction [116117] It has been reported based on estimation of the reactionrates and activation energies that irradiation can induce in thesubmillisecond time scale local temperatures as high as 300∘C[123]

Recently the use of DNPs as supports of metal NPs hasbeen extended by developing DNP-supported Cu NPs thatare efficient catalysts for the aerobic oxidation of thiols todisulfides [124] and for the hydrogenation of C=C doublebonds by hydrazine (Scheme 18) [125] As in the case ofthe Au-DNPs the key feature to understand the excellent

H H

H H

H

H

HN N N

H

H HHHN N

N CatO2

R1

R2 R3

R1

R2 R3

Hydrazine Diimide

H2O

+

+

Scheme 19 Proposed mechanism for the hydrogenation of C=Cdouble bonds by hydrazine under aerobic conditions promoted byCu-DNP as catalyst

catalytic activity of Cu DNPs is the small particle size of themetal NP (in the subnanometric size) and the inertness ofthe surface Thus using hydrazine as reducing agent for thehydrogenation of styrene Cu-DNPs is far more active thanother metal NPs including Pd and Pt or other supports suchas ACs [126] This higher activity of Cu NPs over preciousmetals is interesting from the point of view of reducingthe dependency of catalysis on expensive noble metalsThe reaction mechanism of Cu-DNP catalysed hydrazinereduction involves presumably the intermediacy of diimidegenerated by aerobic oxidation of hydrazine (Scheme 19) Infact even though this reaction is a reduction it requiresthe presence of oxygen to occur Diimide (Scheme 19) is ahighly reactive intermediate that spontaneously decomposesand can be envisioned as the precursor of H

2+ N2 The

use of hydrazine combined with Cu-DNPs as catalyst can beconvenient for some applications avoiding manipulation ofhydrogen gas

Cu-DNPs have also been found to be a recyclable catalystfor the selective oxidation of thiols to disulfides by molecularoxygen [124] The interesting point here is that on onehand thiols are typical poisons of noble metals such aspalladium and gold and on the other hand they tend to formdifferent oxidation products including sulfenic and sulfonicacids Thus Cu-DNPs appear to be ideal catalyst that doesnot undergo deactivation and exhibits selectivity towardsdisulfide TONvalues as high as 5700 have beenmeasured forthe oxidation of thiophenol to diphenyl disulfidewith the Cu-DNP catalyst being reusable at least in four cycles at PhSHCumol ratio of 5772 with turnover frequency of 825 hminus1 [124]

This behavior of Cu-DNPs and its stability contrastsfor instance with the performance of Cu-containing metalorganic frameworks such as Cu

3(BTC)

2(BTC 135-ben-

zenetricarboxylate) that undergoes complete decompositionunder similar conditions [127ndash129] Metal organic frame-works are microporous crystalline solids that are used ascatalysts for a wide range of organic [130] reactions includingalcohol [131] and alkane aerobic oxidations [132] Howevermetal organic frameworks and in particular Cu

3(BTC)

2may

not be stable in the presence of thiols [133] This comparisonillustrates again the robustness of metal supported DNPscatalysts with regard to other alternative solids

Besides being used as supports of noble metal and CuNPs oxidized DNPs have been also been used as supports ofother first-row transition metal oxides that exhibit catalytic


++ COH H

HHH

HH H

HH

Cr22

O3-DNPCO + H2O

Scheme 20 Oxidative dehydrogenation of ethane by CO2

activity for hydrocarbon dehydrogenation or oxidation usingCO2as oxidizing reagent I have shown previously that

commercially available DNPs samples should preferably beoxidized to remove amorphous soot matter This processgenerates a large density of oxygenated surface functionalgroups that can be undesirable to stabilize small metal NPsFor this reason another alternative to remove this amorphouscarbon contaminating DNPs could be initial hydrogenationof commercial diamond powder at high temperatures underpure hydrogen stream and then the process should befollowed by oxidation with diluted molecular oxygen at450∘CThis pretreatment is very important in order to controlthe properties of the external DNP surface that after thetreatment contains carbonyl groups and ethers It is howeververy likely that partial combustion of DNP surface could leadalso to hydroxyl and carboxylic groups that can interact bysharing the oxygen with metal oxide clusters on the surfaceand therefore the conditions and time of the treatmentcan have a considerable impact on the performance of theresulting DNP as catalyst

Using this type of DNP powders obtained by hydro-genation and oxidation as support Nakagawa et al havedeposited metal NPs on the surface by wet impregnationof the corresponding metal salt followed by calcination at450∘C under air [134] Depending on the nature of themetal oxide the resulting DNP containing metal oxide NPsexhibits distinctive catalytic properties for various reactionsof hydrocarbons with CO

2

For instance Ni-DNP is able to promote dry reforming ofmethane (see (2)) making methane conversion reach about25 at 600∘C without deposition of elemental carbon onthe catalyst [134] It was proposed the catalytically activespecies in this dry reforming should be Ni NPs that mustbe formed from NiO at the initial stages of the reactionThe weak interaction of NiO with the surface of DNPswill be responsible for the easy generation of Ni NPs inthe course of the reaction and therefore of the catalyticactivity

CH4+ CO2997888997888997888997888997888997888997888997888997888rarrNiO-DNPs

2CO + 2H2

(2)

In another work the partial oxidation of methane hasbeen carried out using as catalyst Ni or Co NPs supported onDNPs The catalysts were prepared by impregnation of DNPpowders with the required amount of the metal salt followedby water evaporation and calcination at open air at 450∘CThe catalytic activity data show that Ni-DNP performs betterthan Co-DNP and significantly better than other analogouscatalysts of these two metals on different supports reaching

conversions of 32 at temperatures of 700∘C [135] It wasdetermined that at this temperature no carbon depositionon the catalyst occurs and therefore the activity of thecatalyst remains steady without deactivation Concerningthe reaction mechanism it was proposed that the overallpartial oxidation is the combination of the total combustionof methane coupled with hydrogen reduction of CO

2[135]

CH4+ 2Osurf 997888rarr CO

2+ 2H2

(3)

CO2+H2997888rarr CO +H

2O (4)

CO2997888rarr CO +Osurf (5)

When instead of methane ethane or light alkanes arereacted with CO

2using Cr

2O3-DNPs then dehydrogenation

of ethane and light alkanes takes place (Scheme 20) [136]The yield of C

2H4increases along of the oxidation state of

chromiumoxide present on theDNP catalyst It was observedthat the presence of oxygenated functional groups on thesurface of diamond plays a key role in the dehydrogenation byacting as oxygen supplier in the formation of water Oxygenbecomes subsequently replenished by CO

2 According to this

reaction mechanism CO2under the reaction conditions will

transfer oxygen atoms toDNPs becoming converted into CO[136]

V2O5supported on DNPs is also able to promote the

reaction of methane and ethane with CO2but exhibits in

general a different reactivity than Ni NPs or Cr2O3NPs

[137] In the case of V2O5-DNPs the result of the reaction

is the corresponding aldehyde indicating that there is atransfer of an oxygen atom to the alkane (see (6)) Cat-alytic measurements have shown that formaldehyde yieldincreases with the increase of the partial pressure of CO

2

and with the increase of the space velocity [137] The laterobservation was explained as derived from the fact thatlong residence time of formaldehyde on the catalyst leads toits decomposition The optimal V

2O5-DNP contains 2wt

of V2O5loading and the maximum TOF measured was

27 molHCHOtimeshminus1timesmolV2O5

minus1 [137] Similar trends wereobserved for the formation of acetaldehyde by oxidationof ethane by CO

2 As in the related dehydrogenation with

Cr2O3-DNP it was proposed that the oxygen atoms of V

2O5

and on the surface of DNP are transferred to C2H6to form

CH3CHO and that the role of CO

2is replenishing surface

oxygen atoms to DNP

CH3CH3+ 2CO

2997888997888997888997888997888997888997888997888997888997888rarrV2O5-DNP

CH3CHO + 2CO +H

2O

(6)

The role of CO2providing oxygen atoms to the surface of

DNPs avoids deposition of elemental C on the catalyst that isthe main cause of the lack of selectivity and deactivation ofthe catalyst If Ni-DNP or Pd-DNP are used as catalysts forthe pyrolysis of ethane or methane then filamentous carbonnanotubes are formed by decomposition of this hydrocarbon[138 139] As it is usually observed due to the higher strengthof CndashH bonds dehydrogenative decomposition of methanerequires temperatures higher than those for the case of ethane


+ H2ORRR 998400(H)R998400(H)H

OOH

Pd-CeO2-DNP+ 1

2O2

Scheme 21 Aerobic oxidation of alcohols

that can be decomposed at temperatures between 400 and600∘C in the case Ni-DNP or 500 to 800∘C in the case of Pd-DNP It was observed that temperatures above 650∘C lead todeactivation of Ni-DNP due to the formation of NiC

119909phases

[138] In fact the morphology of the metal NPs changesunder the reaction conditions from spherical particles tofaceted thin flat particles under operation conditions [138]Annealing of the resulting thin carbon filaments at 800∘C for5 h under argon also changes the morphology of the carbonfilaments to CNTs with high diameters in the range from 80to 130 nm

Oxidation of alcohols to carbonyl compounds is a processof large importance in organic synthesis as well as for thepreparation of commodities and fine chemicals A long goalin this area is to develop a general catalyst that can promoteselectively alcohol oxidation using molecular oxygen or airIn this regard it has been reported that Pd NPs combinedwith CeO

2NPs supported on diamond is able to catalyze this

reaction (Scheme 21) [140] As in other cases preparation ofthematerial was performed by two consecutive impregnationcycles first with Pd(OAc)

2and then Ce(NH

4)2(NO3)6 fol-

lowed by solvent removal and air calcination at 450∘C for 5 h[140] Before using as catalyst it was necessary to treat the Pd-CeO2-DNP with a hydrogen stream at 85∘C for 1 h to reduce

Pd(II) to Pd NPs In this way conversions of 95 of benzylalcohol to afford 78 benzaldehyde were achieved [140] TheTOF value of the catalyst was 850 hminus1 It was proposed thatDNP as support contributes to the catalysis by providing ahydrophobic environment to the active sites avoiding strongwater adsorption on the sites In addition the lack of porosityof DNP determines that the reaction takes place on a fullyaccessible external surface Comparison of the performanceof Pd-CeO

2-DNP with analogous Pd-DNP catalyst lacking

CeO2for the oxidation of 1-phenylethanol shows that the role

of CeO2should be neutralization of the adventitious acid

sites on the catalyst surface that are responsible for the lackof selectivity leading to the formation of undesirable methylbenzyl ether and ethyl benzene as secondary products Otherbasic metal oxides such as Y

2O3perform similarly to CeO

2

avoiding the acidity introduced by Pd [140] Also comparisonof the average particle size for Pd-DNP and Pd-CeO

2-DNP

shows that an additional role of CeO2is to favor Pd dispersion

reducing the average particle size from 47 (Pd-DNP) to39 nm (Pd-CeO

2-DNP) [140]

Fischer-Tropsch synthesis of hydrocarbons is a well-proven technology for the production of fuels from CO andH2mixtures of different origins DNPs have also been used

as supports of Co NPs that have high activity for the Fischer-Tropsch synthesis [141] Two different metal salts eitherCo(NO

3)26H2OorCo(OAc)

2 were used in the impregnation

of DNPs as cobalt precursors Impregnation can be carried

out either in aqueous solution (Co(NO3)26H2O) or in ace-

tone (Co(OAc)2) An interesting aspect of this work has been

to show the superior performance of DNPs as support ofCo NPs compared to graphite or ACs even though DNPshave lower surface area than the other two carbon supportsTo rationalize this higher activity of DNPs it was proposedthat sp2 carbons exert a negative influence on the Co atomsat the interface by transferring electron density from thesupport to the metal decreasing its catalytic activity [141]This proposal is again in line with the general fact that forsome reactions the inertness of DNP surface can be beneficialfor some processes

Several factors play a key role in the catalytic activity forthe Fischer-Tropsch transformation of Co-DNP such as thereduction temperature in the catalyst pretreatment that influ-ences Co particle size the reaction temperature that deter-mines the selectivity for methane and C

5+hydrocarbons and

the partial pressure of H2and CO All these parameters

includingmetal precursor salt and Co loading determine thecatalytic activity of the Co-DNP catalyst and the selectivity ofthe process that in general has to be adjusted to optimize theproduct distribution in C

5+hydrocarbons that can be used

as fuels and gasoline alternative Under optimal conditionsCo-DNP becomes a very stable catalyst maintaining a steadyconversion for one day of continuous flow operation

Besides being used as supports of metal NPs DNPs offerother possibilities in catalysis Due to the high density ofsurface OH groups DNPs can also be used advantageouslyto anchor covalently some moieties for instance by usingacyl chlorides or alkoxysilane reagents as reactive functionalgroups to attach the moiety to the surface [29] This strategyhas however still to be further exploited in catalysis foranchoring transition metal complexes as it has been alreadyreported for CNTs and G [142] In comparison to the lastmaterials DNPs offering inert surfaces should in principleexhibit a reactivity of the transitionmetal complexmore aliketo that observed for homogeneous phase analogues

5 Summary and Future Prospects

In the above sections I have illustrated the potential thatnanostructured allotropic carbon materials offer in catalysiseither as carbocatalysts or as supports of active sites In thosecases in which thematerial can be suspended indefinitely thesystem can work similarly to a homogeneous catalyst withthe added advantage of being recoverable at the end of thereaction It has been found that the CNTs and Gs havingextended 120587 orbitals can interact strongly with substratesand metal NPs and in this way these carbon supports caninfluence the catalytic activity by favoring the contact ofsubstrates with the active sites

Another aspect is that CNTs and G can assist by epitaxialinteractions the preferential growth of certain crystallo-graphic facets in the metal NPs while maintaining their smallaverage particle size and influencing their electronic densityon the metal NP These factors can exert strong influence inthe catalytic activity exposing themost activemetal facets andtuning the electronic density on the metal atoms


However these carbonmaterials constituted by sp2 atomsmay suffer from poor stability when highly reactive interme-diates are generated due to the single-layer G structure or dueto the tendency to undergo oxidation and degradation Incontrast in the other extreme DNPs conveniently purifiedfrom amorphous soot matrix offer an intrinsically robustand inert surface while still allowing anchoring of NPs andstabilization of very small average size particles due to thepresence of ndashOH nests on the surface Thus DNPs are moresuited for those reactions in which the role of the support is toprovide a high dispersion of themetal NP without possessingdirectly any intrinsic catalytic activity

Considering the availability of new allotropic nanostruc-tured carbon materials and their unique properties derivedfrom well-defined morphologies high surface area andpredictable interactions it can be anticipated that their use incatalysis will grow in the near future [17 21 30] ParticularlyG materials can have some advantage over CNTs due to thewider availability and their more convenient preparation andmodification [30] Similarly the use of DNPs will also growand will be particularly suited for reactions carried out underharsh conditions and in where highly aggressive and reactiveintermediates are generated

Conflict of Interests

The author declares that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

Financial support by the Spanish Ministry of Economyand Competitiveness (Severo Ochoa and CTQ-201232315)and Generalitat Valenciana (Prometeo 2012014) is gratefullyacknowledged

References

[1] A E Aksoylu M Madalena A Freitas M F R Pereira andJ L Figueiredo ldquoEffects of different activated carbon supportsand supportmodifications on the properties of PtAC catalystsrdquoCarbon vol 39 no 2 pp 175ndash185 2001

[2] H Juntgen ldquoActivated carbon as catalyst support A review ofnew research resultsrdquo Fuel vol 65 no 10 pp 1436ndash1446 1986

[3] K Kohler R G Heidenreich J G E Krauter and J PietschldquoHighly active palladiumactivated carbon catalysts for Heckreactions correlation of activity catalyst properties and PdleachingrdquoChemistrymdashAEuropean Journal vol 8 no 3 pp 622ndash631 2002

[4] J Laine A Calafat and M labady ldquoPreparation and charac-terization of activated carbons from coconut shell impregnatedwith phosphoric acidrdquo Carbon vol 27 no 2 pp 191ndash195 1989

[5] O S Amuda A A Giwa and I A Bello ldquoRemoval of heavymetal from industrial wastewater using modified activatedcoconut shell carbonrdquo Biochemical Engineering Journal vol 36no 2 pp 174ndash181 2007

[6] O Ioannidou and A Zabaniotou ldquoAgricultural residues as pre-cursors for activated carbon production-a reviewrdquo Renewableand Sustainable Energy Reviews vol 11 no 9 pp 1966ndash20052007

[7] W K Lafi ldquoProduction of activated carbon from acorns andolive seedsrdquo Biomass and Bioenergy vol 20 no 1 pp 57ndash622001

[8] A Zabaniotou G Stavropoulos and V Skoulou ldquoActivatedcarbon from olive kernels in a two-stage process industrialimprovementrdquo Bioresource Technology vol 99 no 2 pp 320ndash326 2008

[9] D Astruc F Lu and J R Aranzaes ldquoNanoparticles as recyclablecatalysts the frontier between homogeneous and heteroge-neous catalysisrdquo Angewandte Chemie - International Editionvol 44 no 48 pp 7852ndash7872 2005

[10] G W Coates ldquoPrecise control of polyolefin stereochemistryusing single-site metal catalystsrdquoChemical Reviews vol 100 no4 pp 1223ndash1252 2000

[11] G G Hlatky ldquoHeterogeneous single-site catalysts for olefinpolymerizationrdquo Chemical Reviews vol 100 no 4 pp 1347ndash1376 2000

[12] J M Thomas R Raja and D W Lewis ldquoSingle-site hetero-geneous catalystsrdquo Angewandte ChemiemdashInternational Editionvol 44 no 40 pp 6456ndash6482 2005

[13] G Centi and S Perathoner ldquoOpportunities and prospects in thechemical recycling of carbon dioxide to fuelsrdquo Catalysis Todayvol 148 no 3-4 pp 191ndash205 2009

[14] P Chawla V Chawla R Maheshwari S A Saraf and S KSaraf ldquoFullerenes fromcarbon to nanomedicinerdquoMini-Reviewsin Medicinal Chemistry vol 10 no 8 pp 662ndash677 2010

[15] R Schloegl ldquoCarbon in catalysisrdquo inAdvances in Catalysis B CGates and F C Jentoft Eds vol 56 pp 103ndash185 2013

[16] R Puskas A Sapi A Kukovecz and Z Konya ldquoComparisonof nanoscaled palladium catalysts supported on various carbonallotropesrdquo Topics in Catalysis vol 55 no 11ndash13 pp 865ndash8722012

[17] E Auer A Freund J Pietsch and T Tacke ldquoCarbons as sup-ports for industrial precious metal catalystsrdquo Applied CatalysisA General vol 173 no 2 pp 259ndash271 1998

[18] M Kang Y-S Bae and C-H Lee ldquoEffect of heat treatmentof activated carbon supports on the loading and activity of Ptcatalystrdquo Carbon vol 43 no 7 pp 1512ndash1516 2005

[19] N Keller N I Maksimova V V Roddatis et al ldquoThe cat-alytic use onion-like carbon materials for styrene synthesis byoxidative dehydrogenation ethylbenzenerdquo Angewandte ChemieInternational Edition vol 41 no 11 pp 1885ndash1888 2002

[20] L Tan BWang andH Feng ldquoComparative studies of grapheneoxide and reduced graphene oxide as carbocatalysts for poly-merization of 3-aminophenylboronic acidrdquo RSC Advances vol3 no 8 pp 2561ndash2565 2013

[21] D R Dreyer H-P Jia and C W Bielawski ldquoGraphene oxidea convenient carbocatalyst for facilitating oxidation and hydra-tion reactionsrdquo Angewandte Chemie vol 49 no 38 pp 6813ndash6816 2010

[22] D R Dreyer and C W Bielawski ldquoCarbocatalysis heteroge-neous carbons finding utility in synthetic chemistryrdquo ChemicalScience vol 2 no 7 pp 1233ndash1240 2011

[23] J Pyun ldquoGraphene oxide as catalyst application of carbonmaterials beyond nanotechnologyrdquo Angewandte Chemie vol50 no 1 pp 46ndash48 2011

[24] C Su and K P Loh ldquoCarbocatalysts Graphene oxide and itsderivativesrdquo Accounts of Chemical Research vol 46 no 10 pp2275ndash2285 2013

[25] D S Su S Perathoner and G Centi ldquoNanocarbons for thedevelopment of advanced catalystsrdquo Chemical Reviews vol 113no 8 pp 5782ndash5816 2013


[26] M S Dresselhaus and M Terrones ldquoCarbon-based nanomate-rials from a historical perspectiverdquo Proceedings of the IEEE vol101 no 7 pp 1522ndash1535 2013

[27] M Endo T Hayashi Y-A Kim M Terrones and M S Dres-selhaus ldquoHistory and structure in carbon nanotuberdquo ChimicaOggimdashChemistry Today vol 23 no 2 pp 29ndash32 2005

[28] V Y Dolmatov ldquoDetonation synthesis ultradispersed dia-monds properties and applicationsrdquoRussian Chemical Reviewsvol 70 no 7 pp 607ndash626 2001

[29] R Martın P C Heydorn M Alvaro and H Garcia ldquoGeneralstrategy for high-density covalent functionalization of diamondnanoparticles using fenton chemistryrdquo Chemistry of Materialsvol 21 no 19 pp 4505ndash4514 2009

[30] C Huang C Li and G Shi ldquoGraphene based catalystsrdquo Energyand Environmental Science vol 5 no 10 pp 8848ndash8868 2012

[31] D R Dreyer K A Jarvis P J Ferreira and C W BielawskildquoGraphite oxide as a carbocatalyst for the preparation offullerene-reinforced polyester and polyamide nanocompositesrdquoPolymer Chemistry vol 3 no 3 pp 757ndash766 2012

[32] M Boronat and A Corma ldquoMolecular approaches to catalysisnaked gold nanoparticles as quasi-molecular catalysts for greenprocessesrdquo Journal of Catalysis vol 284 no 2 pp 138ndash147 2011

[33] A Corma H Garcia and A Leyva ldquoCatalytic activity of pal-ladium supported on single wall carbon nanotubes comparedto palladium supported on activated carbon study of the Heckand Suzuki couplings aerobic alcohol oxidation and selectivehydrogenationrdquo Journal of Molecular Catalysis A Chemical vol230 no 1-2 pp 97ndash105 2005

[34] E Flahaut A Govindaraj A Peigney C Laurent A Roussetand C N R Rao ldquoSynthesis of single-walled carbon nanotubesusing binary (Fe Co Ni) alloy nanoparticles prepared in situ bythe reduction of oxide solid solutionsrdquoChemical Physics Lettersvol 300 no 1-2 pp 236ndash242 1999

[35] A Dhakshinamoorthy A Primo P Concepcion M Alvaroand H Garcia ldquoDoped graphene as a metal-free carbocatalystfor the selective aerobic oxidation of benzylic hydrocarbonscyclooctane and styrenerdquo Chemistry vol 19 no 23 pp 7547ndash7554 2013

[36] T W Ebbesen and P M Ajayan ldquoLarge-scale synthesis ofcarbon nanotubesrdquoNature vol 358 no 6383 pp 220ndash222 1992

[37] P M Ajayan ldquoNanotubes fromCarbonrdquo Chemical Reviews vol99 no 7 pp 1787ndash1799 1999

[38] D S Bethune C H Kiang M S de Vries et al ldquoCobalt-catalysed growth of carbon nanotubes with single-atomic-layerwallsrdquo Nature vol 363 no 6430 pp 605ndash607 1993

[39] C Aprile R Martin M Alvaro J C Scaiano and H GarcialdquoNear-infrared emission quantum yield of soluble short single-walled carbon nanotubesrdquo Chemphyschem vol 10 no 8 pp1305ndash1310 2009

[40] R Martın M Alvaro and H Garcıa ldquoPhotoresponsivecovalently-functionalized short single wall carbon nanotubesrdquoCurrent Organic Chemistry vol 15 no 8 pp 1106ndash1120 2011

[41] M F Islam E Rojas D M Bergey A T Johnson and A GYodh ldquoHigh weight fraction surfactant solubilization of single-wall carbon nanotubes in waterrdquo Nano Letters vol 3 no 2 pp269ndash273 2003

[42] M Zheng A Jagota E D Semke et al ldquoDNA-assisted disper-sion and separation of carbon nanotubesrdquoNatureMaterials vol2 no 5 pp 338ndash342 2003

[43] X Liu B Frank W Zhang T P Cotter R Schlogl and D SSu ldquoCarbon-catalyzed oxidative dehydrogenation of n-butane

selective site formation during sp3-to-sp2 lattice rearrange-mentrdquo Angewandte Chemie vol 50 no 14 pp 3318ndash3322 2011

[44] W Qi W Liu B Zhang X Gu X Guo and D Su ldquoOxidativedehydrogenation on nanocarbon identification and quantifica-tion of active sites by chemical titrationrdquo Angewandte Chemievol 52 no 52 pp 14224ndash14228 2013

[45] J Zhang X Liu R Blume A Zhang R Schlogl and S SDang ldquoSurface-modified carbon nanotubes catalyze oxidativedehydrogenation of n-butanerdquo Science vol 322 no 5898 pp73ndash77 2008

[46] X Liu D S Su and R Schlogl ldquoOxidative dehydrogenation of1-butene to butadiene over carbon nanotube catalystsrdquo Carbonvol 46 no 3 pp 547ndash549 2008

[47] A Dhakshinamoorthy S Navalon M Alvaro and H GarcialdquoMetal nanoparticles as heterogeneous fenton catalystsrdquo Chem-SusChem vol 5 no 1 pp 46ndash64 2012

[48] S Navalon A Dhakshinamoorthy M Alvaro and H GarcialdquoHeterogeneous Fenton catalysts based on activated carbon andrelated materialsrdquo ChemSusChem vol 4 no 12 pp 1712ndash17302011

[49] Z H Kang E B Wang B D Mao et al ldquoHeterogeneoushydroxylation catalyzed by multi-walled carbon nanotubes atlow temperaturerdquo Applied Catalysis A General vol 299 no 1-2pp 212ndash217 2006

[50] S Song H Yang R Rao H Liu and A Zhang ldquoDefectsof multi-walled carbon nanotubes as active sites for benzenehydroxylation to phenol in the presence of H

2

O2

rdquo CatalysisCommunications vol 11 no 8 pp 783ndash787 2010

[51] H Zhang X Pan X Han et al ldquoEnhancing chemical reactionsin a confined hydrophobic environment an NMR study ofbenzene hydroxylation in carbon nanotubesrdquoChemical Sciencevol 4 no 3 pp 1075ndash1078 2013

[52] H Sun S Liu G Zhou H M Ang M O Tade and S WangldquoReduced graphene oxide for catalytic oxidation of aqueousorganic pollutantsrdquo ACS Applied Materials and Interfaces vol4 no 10 pp 5466ndash5471 2012

[53] C Chen J Zhang B Zhang C Yu F Peng and D SuldquoRevealing the enhanced catalytic activity of nitrogen-dopedcarbon nanotubes for oxidative dehydrogenation of propanerdquoChemical Communications vol 49 no 74 pp 8151ndash8153 2013

[54] B Frank J Zhang R Blume R Schlogl and D S Su ldquoHet-eroatoms increase the selectivity in oxidative dehydrogenationreactions on nanocarbonsrdquoAngewandte ChemiemdashInternationalEdition vol 48 no 37 pp 6913ndash6917 2009

[55] J Luo H Yu H Wang H Wang and F Peng ldquoAerobicoxidation of benzyl alcohol to benzaldehyde catalyzed bycarbon nanotubes without any promoterrdquoChemical EngineeringJournal vol 240 pp 434ndash442 2014

[56] J Luo F Peng H Wang and H Yu ldquoEnhancing the catalyticactivity of carbon nanotubes by nitrogen doping in the selectiveliquid phase oxidation of benzyl alcoholrdquo Catalysis Communi-cations vol 39 pp 44ndash49 2013

[57] Y Cao X Luo H Yu F Peng H Wang and G Ning ldquoSp2-and sp3-hybridized carbon materials as catalysts for aerobicoxidation of cyclohexanerdquoCatalysis Science and Technology vol3 no 10 pp 2654ndash2660 2013

[58] Z-Z Fang X-D Kang P Wang and H-M Cheng ldquoImprovedreversible dehydrogenation of lithium borohydride by millingwith as-prepared single-walled carbon nanotubesrdquo Journal ofPhysical Chemistry C vol 112 no 43 pp 17023ndash17029 2008


[59] P-J Wang Z-Z Fang L-P Ma X-D Kang and P WangldquoEffect of carbon addition on hydrogen storage behaviors of Li-Mg-B-H systemrdquo International Journal of Hydrogen Energy vol35 no 7 pp 3072ndash3075 2010

[60] X B Yu ZWuQRChen Z L Li B CWeng andT SHuangldquoImproved hydrogen storage properties of LiBH4 destabilizedby carbonrdquo Applied Physics Letters vol 90 no 3 Article ID034106 2007

[61] Y ZhangW-S Zhang A-QWang et al ldquoLiBH4

nanoparticlessupported by disorderedmesoporous carbon hydrogen storageperformances and destabilization mechanismsrdquo InternationalJournal of Hydrogen Energy vol 32 no 16 pp 3976ndash3980 2007

[62] P Serp M Corrias and P Kalck ldquoCarbon nanotubes andnanofibers in catalysisrdquo Applied Catalysis A General vol 253no 2 pp 337ndash358 2003

[63] J-P Tessonnier L Pesant G Ehret M J Ledoux and C Pham-Huu ldquoPd nanoparticles introduced inside multi-walled carbonnanotubes for selective hydrogenation of cinnamaldehyde intohydrocinnamaldehyderdquo Applied Catalysis A General vol 288no 1-2 pp 203ndash210 2005

[64] X R Ye Y Lin and C MWai ldquoDecorating catalytic palladiumnanoparticles on carbon nanotubes in supercritical carbondioxiderdquo Chemical Communications vol 9 no 5 pp 642ndash6432003

[65] G-Y Gao D-J Guo andH-L Li ldquoElectrocatalytic oxidation offormaldehyde on palladium nanoparticles supported on multi-walled carbon nanotubesrdquo Journal of Power Sources vol 162 no2 pp 1094ndash1098 2006

[66] B Yoon and C M Wai ldquoMicroemulsion-templated synthesisof carbon nanotube-supported Pd and Rh nanoparticles forcatalytic applicationsrdquo Journal of theAmericanChemical Societyvol 127 no 49 pp 17174ndash17175 2005

[67] F Ding P Larsson J A Larsson et al ldquoThe importance ofstrong carbon-metal adhesion for catalytic nucleation of single-walled carbon nanotubesrdquo Nano Letters vol 8 no 2 pp 463ndash468 2008

[68] L Alves B Ballesteros M Boronat et al ldquoSynthesis andstabilization of subnanometric gold oxide nanoparticles onmultiwalled carbon nanotubes and their catalytic activityrdquoJournal of the American Chemical Society vol 133 no 26 pp10251ndash10261 2011

[69] A Abad A Corma and H Garcıa ldquoCatalyst parameters deter-mining activity and selectivity of supported gold nanoparticlesfor the aerobic oxidation of alcohols The molecular reactionmechanismrdquo ChemistrymdashA European Journal vol 14 no 1 pp212ndash222 2008

[70] A Corma P Concepcion M Boronat et al ldquoExceptionaloxidation activity with size-controlled supported gold clustersof low atomicityrdquo Nature Chemistry vol 5 no 9 pp 775ndash7812013

[71] C Baleizao B Gigante H Garcıa and A Corma ldquoChiralvanadyl salen complex anchored on supports as recoverablecatalysts for the enantioselective cyanosilylation of aldehydesComparison among silica single wall carbon nanotube acti-vated carbon and imidazolium ion as supportrdquoTetrahedron vol60 no 46 pp 10461ndash10468 2004

[72] C Baleizao B Gigante H Garcia and A Corma ldquoVanadylsalen complexes covalently anchored to single-wall carbonnanotubes as heterogeneous catalysts for the cyanosilylation ofaldehydesrdquo Journal of Catalysis vol 221 no 1 pp 77ndash84 2004

[73] D Tasis N Tagmatarchis A Bianco and M Prato ldquoChemistryof carbon nanotubesrdquo Chemical Reviews vol 106 no 3 pp1105ndash1136 2006

[74] J L Hutchison N A Kiselev E P Krinichnaya et al ldquoDouble-walled carbon nanotubes fabricated by a hydrogen arc dischargemethodrdquo Carbon vol 39 no 5 pp 761ndash770 2001

[75] J Kong A M Cassell and H Dai ldquoChemical vapor depositionof methane for single-walled carbon nanotubesrdquo ChemicalPhysics Letters vol 292 no 4ndash6 pp 567ndash574 1998

[76] S Stankovich D A Dikin R D Piner et al ldquoSynthesis ofgraphene-based nanosheets via chemical reduction of exfoli-ated graphite oxiderdquo Carbon vol 45 no 7 pp 1558ndash1565 2007

[77] W S Hummers Jr and R E Offeman ldquoPreparation of graphiticoxiderdquo Journal of the American Chemical Society vol 80 no 6p 1339 1958

[78] A Primo P Atienzar E Sanchez J M Delgado and H GarcıaldquoFrom biomass wastes to large-area high-quality N-dopedgraphene catalyst-free carbonization of chitosan coatings onarbitrary substratesrdquo Chemical Communications vol 48 no 74pp 9254ndash9256 2012

[79] P Atienzar A Primo C Lavorato R Molinari and H GarcıaldquoPreparation of graphene quantum dots from pyrolyzed algi-naterdquo Langmuir vol 29 no 20 pp 6141ndash6146 2013

[80] A Primo A Forneli A Corma and H Garcıa ldquoFrom biomasswastes to highly efficient CO

2

adsorbents graphitisation ofchitosan and alginate biopolymersrdquo ChemSusChem vol 5 no11 pp 2207ndash2214 2012

[81] C Su M Acik K Takai et al ldquoProbing the catalytic activity ofporous graphene oxide and the origin of this behaviourrdquoNatureCommunications vol 3 article 2315 8 pages 2012

[82] D R Dreyer S Park C W Bielawski and R S Ruoff ldquoThechemistry of graphene oxiderdquoChemical Society Reviews vol 39no 1 pp 228ndash240 2010

[83] N Wu X She D Yang X Wu F Su and Y Chen ldquoSynthesisof network reduced graphene oxide in polystyrene matrix bya two-step reduction method for superior conductivity of thecompositerdquo Journal of Materials Chemistry vol 22 no 33 pp17254ndash17261 2012

[84] A Dhakshinamoorthy M Alvaro P Concepcion V Fornesand H Garcia ldquoGraphene oxide as an acid catalyst for the roomtemperature ring opening of epoxidesrdquo Chemical Communica-tions vol 48 no 44 pp 5443ndash5445 2012

[85] A Dhakshinamoorthy M Alvaro M Puche V Fornes andH Garcia ldquoGraphene oxide as catalyst for the acetalizacion ofaldehydes at room temperaturerdquo ChemCatChem vol 4 no 12pp 2026ndash2030 2012

[86] L Qu Y Liu J-B Baek and L Dai ldquoNitrogen-doped grapheneas efficient metal-free electrocatalyst for oxygen reduction infuel cellsrdquo ACS Nano vol 4 no 3 pp 1321ndash1326 2010

[87] A Corma and H Garcia ldquoSupported gold nanoparticles ascatalysts for organic reactionsrdquo Chemical Society Reviews vol37 no 9 pp 2096ndash2126 2008

[88] W Peng S Liu H Sun Y Yao L Zhi and S Wang ldquoSynthesisof porous reduced graphene oxide as metal-free carbon foradsorption and catalytic oxidation of organics in waterrdquo Journalof Materials Chemistry A vol 1 pp 5854ndash5859 2013

[89] Y Gao D Ma C Wang J Guan and X Bao ldquoReducedgraphene oxide as a catalyst for hydrogenation of nitrobenzeneat room temperaturerdquo Chemical Communications vol 47 no 8pp 2432ndash2434 2011


[90] X-K Kong Z-Y Sun M Chen C-L Chen and Q-WChen ldquoMetal-free catalytic reduction of 4-nitrophenol to 4-aminophenol by N-doped graphenerdquo Energy and Environmen-tal Science vol 6 no 11 pp 3260ndash3266 2013

[91] X K Kong Q W Chen and Z Y Lun ldquoProbing the influenceof different oxygenated groups on graphene oxidersquos catalyticperformancerdquo Journal of Materials Chemistry A vol 2 no 3pp 610ndash613 2014

[92] V Schwartz W Fu Y-T Tsai et al ldquoOxygen-functionalizedfew-layer graphene sheets as active catalysts for oxidativedehydrogenation reactionsrdquo ChemSusChem vol 6 no 5 pp840ndash846 2013

[93] A Corma and H Garcia ldquoLewis acids from conventionalhomogeneous to green homogeneous and heterogeneous catal-ysisrdquo Chemical Reviews vol 103 no 11 pp 4307ndash4366 2003

[94] L-M Liu R Car A Selloni D M Dabbs I A Aksay and R AYetter ldquoEnhanced thermal decomposition of nitromethane onfunctionalized graphene sheets Ab initio molecular dynamicssimulationsrdquo Journal of the American Chemical Society vol 134no 46 pp 19011ndash19016 2012

[95] J L Sabourin D M Dabbs R A Yetter F L Dryer and I AAksay ldquoFunctionalized graphene sheet colloids for enhancedfuelpropellant combustionrdquoACSNano vol 3 no 12 pp 3945ndash3954 2009

[96] G Eda G Fanchini and M Chhowalla ldquoLarge-area ultrathinfilms of reduced graphene oxide as a transparent and flexibleelectronic materialrdquo Nature Nanotechnology vol 3 no 5 pp270ndash274 2008

[97] G Blanita and M D Lazar ldquoReview of graphene-supportedmetal nanoparticles as new and efficient heterogeneous cata-lystsrdquoMicro and Nanosystems vol 5 no 2 pp 138ndash146 2013

[98] M Ding Y Tang and A Star ldquoUnderstanding interfacesin metal-graphitic hybrid nanostructuresrdquo Journal of PhysicalChemistry Letters vol 4 no 1 pp 147ndash160 2013

[99] S Sharma A Ganguly P Papakonstantinou et al ldquoRapidmicrowave synthesis of CO tolerant Reduced graphene oxide-supported platinum electrocatalysts for oxidation of methanolrdquoJournal of Physical Chemistry C vol 114 no 45 pp 19459ndash19466 2010

[100] K Jasuja J Linn S Melton and V Berry ldquoMicrowave-reduceduncapped metal nanoparticles on graphene tuning catalyticelectrical and raman propertiesrdquo Journal of Physical ChemistryLetters vol 1 no 12 pp 1853ndash1860 2010

[101] R Nie J Wang L Wang Y Qin P Chen and Z HouldquoPlatinum supported on reduced graphene oxide as a catalystfor hydrogenation of nitroarenesrdquo Carbon vol 50 no 2 pp586ndash596 2012

[102] G M Scheuermann L Rumi P Steurer W Bannwarth and RMulhaupt ldquoPalladium nanoparticles on graphite oxide and itsfunctionalized graphene derivatives as highly active catalysts forthe Suzuki-Miyaura coupling reactionrdquo Journal of the AmericanChemical Society vol 131 no 23 pp 8262ndash8270 2009

[103] D-H Lim and J Wilcox ldquoMechanisms of the oxygen reductionreaction on defective graphene-supported Pt nanoparticlesfrom first-principlesrdquo Journal of Physical Chemistry C vol 116no 5 pp 3653ndash3660 2012

[104] F H Yang A J Lachawiec Jr and R T Yang ldquoAdsorptionof spillover hydrogen atoms on single-wall carbon nanotubesrdquoJournal of Physical Chemistry B vol 110 no 12 pp 6236ndash62442006

[105] N Shang P Papakonstantinou P Wang and S R P SilvaldquoPlatinum integrated graphene for methanol fuel cellsrdquo Journalof Physical Chemistry C vol 114 no 37 pp 15837ndash15841 2010

[106] C Xu X Wang and J Zhu ldquoGraphenemdashmetal particlenanocompositesrdquo Journal of Physical Chemistry C vol 112 no50 pp 19841ndash19845 2008

[107] L Dong R R S Gari Z Li M M Craig and SHou ldquoGraphene-supported platinum and platinum-rutheniumnanoparticles with high electrocatalytic activity for methanoland ethanol oxidationrdquo Carbon vol 48 no 3 pp 781ndash787 2010

[108] Y Li W Gao L Ci C Wang and P M Ajayan ldquoCatalyticperformance of Pt nanoparticles on reduced graphene oxide formethanol electro-oxidationrdquo Carbon vol 48 no 4 pp 1124ndash1130 2010

[109] C Li and G Shi ldquoThree-dimensional graphene architecturesrdquoNanoscale vol 4 no 18 pp 5549ndash5563 2012

[110] J Peng W Gao B K Gupta et al ldquoGraphene quantum dotsderived from carbon fibersrdquoNano Letters vol 12 no 2 pp 844ndash849 2012

[111] G He Y Song K Liu AWalter S Chen and S Chen ldquoOxygenreduction catalyzed by platinum nanoparticles supported ongraphene quantum dotsrdquo ACS Catalysis vol 3 no 5 pp 831ndash838 2013

[112] Y Shao J Wang H Wu J Liu I A Aksay and Y LinldquoGraphene based electrochemical sensors and biosensors areviewrdquo Electroanalysis vol 22 no 10 pp 1027ndash1036 2010

[113] D A C Brownson D K Kampouris and C E BanksldquoGraphene electrochemistry fundamental concepts through toprominent applicationsrdquo Chemical Society Reviews vol 41 no21 pp 6944ndash6976 2012

[114] F Cheng and J Chen ldquoMetal-air batteries from oxygen reduc-tion electrochemistry to cathode catalystsrdquo Chemical SocietyReviews vol 41 no 6 pp 2172ndash2192 2012

[115] V Georgakilas M Otyepka A B Bourlinos et al ldquoFunction-alization of graphene covalent and non-covalent approachesderivatives and applicationsrdquo Chemical Reviews vol 112 no 11pp 6156ndash6214 2012

[116] S Navalon M de Miguel R Martin M Alvaro and HGarcia ldquoEnhancement of the catalytic activity of supported goldnanoparticles for the fenton reaction by lightrdquo Journal of theAmerican Chemical Society vol 133 no 7 pp 2218ndash2226 2011

[117] S Navalon R Martin M Alvaro and H Garcia ldquoSunlight-assisted fenton reaction catalyzed by gold supported on dia-mond nanoparticles as pretreatment for biological degradationof aqueous phenol solutionsrdquo ChemSusChem vol 4 no 5 pp650ndash657 2011

[118] R Martın M Alvaro J R Herance and H Garcıa ldquoFenton-treated functionalized diamond nanoparticles as gene deliverysystemrdquo ACS Nano vol 4 no 1 pp 65ndash74 2010

[119] S Navalon R Martin M Alvaro and H Garcia ldquoGold ondiamond nanoparticles as a highly efficient fenton catalystrdquoAngewandte Chemie vol 49 no 45 pp 8403ndash8407 2010

[120] J Feng X Hu and P L Yue ldquoEffect of initial solution pH on thedegradation of Orange II using clay-based Fe nanocompositesas heterogeneous photo-Fenton catalystrdquo Water Research vol40 no 4 pp 641ndash646 2006

[121] M B Kasiri H Aleboyeh and A Aleboyeh ldquoDegradation ofacid blue 74 using Fe-ZSM5 zeolite as a heterogeneous photo-Fenton catalystrdquoApplied Catalysis B Environmental vol 84 no1-2 pp 9ndash15 2008


[122] P Wardman and L P Candeias ldquoFenton chemistry an intro-ductionrdquo Radiation Research vol 145 no 5 pp 523ndash531 1996

[123] C Aliaga D R Stuart A Aspee and J C Scaiano ldquoSolventeffects on hydrogen abstraction reactions from lactones withantioxidant propertiesrdquo Organic Letters vol 7 no 17 pp 3665ndash3668 2005

[124] A Dhakshinamoorthy S Navalon D Sempere M Alvaro andH Garcia ldquoAerobic oxidation of thiols catalyzed by coppernanoparticles supported on diamond nanoparticlesrdquo Chem-CatChem vol 5 no 1 pp 241ndash246 2013

[125] A Dhakshinamoorthy S Navalon D Sempere M Alvaroand H Garcıa ldquoReduction of alkenes catalyzed by coppernanoparticles supported on diamond nanoparticlesrdquo ChemicalCommunications vol 49 no 23 pp 2359ndash2361 2013

[126] Y Wang Z Xiao and L Wu ldquoMetal-nanoparticles supportedon solid as heterogeneous catalystsrdquoCurrentOrganic Chemistryvol 17 no 12 pp 1325ndash1333 2013

[127] L Huang H Wang J Chen et al ldquoSynthesis morphologycontrol and properties of porous metal-organic coordinationpolymersrdquo Microporous and Mesoporous Materials vol 58 no2 pp 105ndash114 2003

[128] C Z-J Lin S S-Y Chui S M-F Lo et al ldquoPhysical stability vschemical lability in microporous metal coordination polymersa comparison of [Cu(OH)(INA)]

119899

and [Cu(INA)2

]119899

INA =14-(NC

5

H4

CO2

)rdquo Chemical Communications no 15 pp 1642ndash1643 2002

[129] T M Reineke M Eddaoudi M OrsquoKeeffe and O M YaghildquoA microporous lanthanidendashorganic frameworkrdquo AngewandteChemie International Edition vol 38 pp 2590ndash2594 1999

[130] J Lee O K Farha J Roberts K A Scheidt S T Nguyen andJ T Hupp ldquoMetal-organic framework materials as catalystsrdquoChemical Society Reviews vol 38 no 5 pp 1450ndash1459 2009

[131] A Dhakshinamoorthy M Alvaro and H Garcia ldquoMetal-organic frameworks as heterogeneous catalysts for oxidationreactionsrdquo Catalysis Science and Technology vol 1 no 6 pp856ndash867 2011

[132] A Dhakshinamoorthy M Alvaro and H Garcia ldquoAerobicoxidation of styrenes catalyzed by an iron metal organicframeworkrdquo ACS Catalysis vol 1 no 8 pp 836ndash840 2011

[133] A Dhakshinamoorthy M Alvaro and H Garcıa ldquoAerobicoxidation of thiols to disulfides using ironmetal-organic frame-works as solid redox catalystsrdquo Chemical Communications vol46 no 35 pp 6476ndash6478 2010

[134] K Nakagawa H Nishimoto Y Enoki et al ldquoOxidized dia-mond supported Ni catalyst for synthesis gas formation frommethanerdquo Chemistry Letters no 5 pp 460ndash461 2001

[135] H-A Nishimoto K Nakagawa N-O Ikenaga M Nishitani-Gamo T Ando and T Suzuki ldquoPartial oxidation of methaneto synthesis gas over oxidized diamond catalystsrdquo AppliedCatalysis A General vol 264 no 1 pp 65ndash72 2004

[136] K Nakagawa C Kajita N-O Ikenaga et al ldquoThe role ofchemisorbed oxygen on diamond surfaces for the dehydrogena-tion of ethane in the presence of carbon dioxiderdquo Journal ofPhysical Chemistry B vol 107 no 17 pp 4048ndash4056 2003

[137] K Okumura K Nakagawa T Shimamura et al ldquoDirectformation of acetaldehyde from ethane using carbon dioxideas a novel oxidant over oxidized diamond-supported catalystsrdquoThe Journal of Physical Chemistry B vol 107 no 48 pp 13419ndash13424 2003

[138] N-O Higashi H-A Ichi-oka T Miyake and T SuzukildquoGrowth mechanisms of carbon nanofilaments on Ni-loaded

diamond catalystrdquo Diamond and Related Materials vol 17 no3 pp 283ndash293 2008

[139] N-O Higashi N-O Ikenaga T Miyake and T SuzukildquoCarbon nanotube formation on Ni- or Pd-loaded diamondcatalystsrdquo Diamond and Related Materials vol 14 no 3ndash7 pp820ndash824 2005

[140] T Yasu-eda R Se-ike N-O Ikenaga T Miyake and TSuzuki ldquoPalladium-loaded oxidized diamond catalysis for theselective oxidation of alcoholsrdquo Journal of Molecular CatalysisA Chemical vol 306 no 1-2 pp 136ndash142 2009

[141] T-O Honsho T Kitano T Miyake and T Suzuki ldquoFischer-Tropsch synthesis over Co-loaded oxidized diamond catalystrdquoFuel vol 94 pp 170ndash177 2012

[142] P V Kamat ldquoGraphene-based nanoarchitectures anchoringsemiconductor and metal nanoparticles on a two-dimensionalcarbon supportrdquo Journal of Physical Chemistry Letters vol 1 no2 pp 520ndash527 2010

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


maximal activity Design and synthesis of single-site catalystshas been a continued task in heterogeneous catalysis with thelong-term aim of the development of solid catalysts with thehighest activity and selectivity [10ndash12]

In the last decades carbon allotropes with nanometricparticle dimension have been characterized and have becomecommercially available Since their structure is much betterdefined than ACs there has been a continued growinginterest in the application of these carbon nanoforms incatalysis as a logical evolution of the use of ACs [13ndash15]The interest of allotropic carbon nanoforms in catalysis istherefore a logical evolution of the continued use of ACsfor the preparation of heterogeneous catalysts but goes muchbeyond ACs since the point is now to incorporate the activesites on the carbon structure

As in the case of ACs the simplest possibility has beenthe use of these carbon allotropes as large area supports ofactive sites [16ndash18] but the most recent research front is toimplement the catalytic sites on the carbon allotrope itselfin the absence of metals (ldquocarbocatalysisrdquo) Starting from anideal structure of the carbon allotrope it should be possibleto introduce sites by creating carbon vacancies carbon withdangling bonds structural defects due to carbon vacanciesand oxygenated functional groups or by replacing carbonatoms by other elements (ldquodopingrdquo)

The term ldquocarbocatalystsrdquo refers to the development ofcatalysts based exclusively or predominantly on the use ofcarbon materials avoiding or minimizing the dependency ofcatalysis on the use of metals [19ndash25] While the use of metalsis considered not ldquosustainablerdquo due to the limited availableresources carbonaceous catalysts particularly those derivedfrom biomass are renewable and affordable and consideredas ldquosustainablerdquo materials

Among the different carbon allotropes that have beenapplied in heterogeneous catalysis the initial studies werebased on carbon nanotubes (CNTs) because these materialsbecome commercially available earlier than other carbonmaterials [26 27] Preparation of CNTs requires catalystsand special equipment CNTs typically are obtained in smallbatch quantities and impurified with the catalyst used intheir synthesis typically iron or iron-cobalt alloys dispersedin a matrix to maintain the particle size small This makesnecessary in commercial CNTs several steps of purificationoxidation and other modification processes before theycan be used as catalysts After CNTs the use of diamondnanoparticles (DNPs) has also become possible DNPs can beobtained by milling of diamond powders or by explosive det-onation [28] In the last caseDnanocrystals are embedded ona soot matrix of amorphous carbon that has to be removedbefore the use of the DNPs as supports [29] More recentlya new line of research has appeared trying to exploit theopportunities of G-basedmaterials in catalysis [20 21 30 31]

Allotropic carbon nanoforms can be dispersed in sus-pension in a liquid phase as inks that allow the recoveryof the carbonaceous materials by filtration or centrifugationafter their use The term ldquopseudohomogeneous catalysisrdquo hasbeen used to denote the fact that during the reaction thereis no apparent phase differentiation between substrates andcatalysts but after the reaction the carbonaceous material

Carbon nanoforms in catalysis

Carbon Graphene

Diamond

nanotubes nanoparticles

Scheme 1 Structure of the three carbon allotropes whose use ascarbocatalysts or as supports of metal nanoparticles will be the topicof the present perspective paper

can be easily separated and recovered as is characteristic inheterogeneous catalysis [32]

In the present spotlight paper I will comment on someof the possibilities that nanometric carbon allotropes offer ascatalysts or as supports showing the logic of the evolutionfrom ACs or from other supports to these carbonaceousnanomaterials as catalysts Scheme 1 contains the type andstructure of the carbon nanoforms whose catalytic activitywill be commented on in this perspective paper Whenpossible comparison between the performance of differentcarbon allotropes will be made but I will try to highlight thefeatures of each type of carbon nanoform thatmake thembestsuited for certain catalytic applications I will start with thepossibilities and limitations of CNTs followed by the use ofG-basedmaterials in catalysis and finishing with applicationsof DNPs as supports In this paper I will cover a broad rangeof articles in this area with emphasis on the use of thesematerials as carbocatalysts in the absence of metals with theaim of illustrating the broad potential that carbon nanoformsoffer in catalysis In the last section I will summarize themajor points and will provide my view on possible futuredevelopments and targets in this area

2 Catalysts Based on CNTs as Supports

CNTs are characterized by their long aspect ratio in whichone or several concentric hexagonal arrangements of sp2carbons (ldquographene sheetsrdquo) form a cylinder with nanometricdiameter but lengths that can reach tens of micrometersThelong aspect ratio and the curvature of the graphene walls arethe main characteristics of CNTs

The synthesis of CNTs either single wall (SWCNTs) ormultiple wall (MWCNTs) is difficult to control and relieson the use of a metal catalyst typically Fe and Co alloys inthe form of small metal NPs to decompose in the pyrolyticprocess at temperatures about 500∘C or above the organicprecursor in the absence of oxygen and effect the nucleationand growth of CNTs from elemental carbon atoms generatedunder these reductive conditions (Scheme 2) [34]

Due to the use of a catalyst in the preparation of CNTsthe amount of CNTs that is available in each batch is limitedcompared to other carbon nanoforms [36] MWCNTs canbe prepared in larger quantities than SWCNTs because the


PrecursorCH4


Growth

CNT

Support








MetalNPs

HO2C

HO2C

HO2C

HO2CHO2C

Defects

CO2H

CO2H

CO2HCO2H

CO2H

Doping

Carboxylicacids

X X

XX







HH O2

CNTs+ H2O
















O

O O

N

N

O

O OO

O

2C

(PhCO)2O

O

OH

HO

OH

OHOH

OHCO2COPh

CH2COPh

CH2COPh

CNT-anhydride

HO

HOPh

Ph

OH

OH

OHOH

CH2COPh CH2COPh

Ph-NH2

CNT-ether

CNT

CNT-imine

PhCOCH2BrCO2H

CO2H

CO2HHO2CHO2C

HO2C

HO2CHO2C

HO2C



H2O + 12O2

HOOH

HOOHReduced


site


O2

(Fe NP)CNT

COOHCOOH

Adipic acid



4(1) It has been



LiBH4999445999468 LiH + B + 15H

2(1)







O

O

O

OH OH

OHO2

X

+





CO + O2 CO2







(i) (ii)

(iii)

SWNT COClSWNT

SHSWNT

AIBN

VO(salen)SWNT

O

CI

O

O OO

O

N

V

V

N N

N N

H

NH

S

SH


O OO




3

N CH2

Cl2

45∘C 48 h





4and H








Toluene refluxCH3

CH3

N

N

+

minusH2OminusCO2

OH

OO H

HHN +

Cminus


H H

HH H

H

H

H

HH

OH OH

G

M

CH

120572

120573HO

4

41

1

O

O

O

O OO

O(a)

(c)(b)

Alginate

Alginate

Doped


Ominus

Ominus





4and H

2SO4



2OH groups


2OH groups are not




HOOCOH

OH

H

OH

O

O

O O

OOO

O

OO

O

O

O

HO

HOHO

COOH

COOH

COOH

COOH

OH

OH

+ O2

GO


O

O

HH CH3OH

CH3OH

OH

OSO3H

OSO3H

H3CO OCH3

OCH3







O2

Dopedgraphene

O OH + +

CHO


10

20

30

40

50

0

Con

vers

ion

()

Time (h)

(a)

(b)

(c)

0 1 2 3 4 5 6









HOOC

HOOC

HOOC

HOOC

O

O

O

O

O

O OO

OO

O

O

O

O

OO

HO

HOHO

HO

HO

HO

HO

HO

OH OH

OH

OH

OH OH

OH

OH

OH

OH

OHOH

OH

OH

COOH

COOH















2[104] This lower




4








2O2




2O2



HO-OHSurface bound

radicalOH

MMMMM MMMMM


Au-DNPs(a)

(b)


Phen

ol d

egra

datio

n (

)

100

80

60

40

20

0

Initial pH = 7

Induction period

Time (h)

Low pH

0 1 2 3 4 5


O2








eminus

eminuseminus

O2 + H+

= Au0

E0 =

E0 =

E0 = 18 V18 V

= Au

Reduction

minusOH + ∙OH

Oxidation

Highly reactive

H2O2 H2O2

∙OOH + H+

semi-reaction

hydroxyl radical

semi-reactionh

120575+

28V


O2


NH2-NH2O2

O2

SH S S

CuD




H H

H H

H

H

HN N N

H

H HHHN N

N CatO2

R1

R2 R3

R1

R2 R3

Hydrazine Diimide

H2O

+

+



2+ N2 The




3(BTC)

2(BTC 135-ben-


3(BTC)

2may




++ COH H

HHH

HH H

HH

Cr22

O3-DNPCO + H2O





2



2CO + 2H2

(2)



2[135]


2+ 2H2

(3)


2O (4)



2using Cr





2 According to this








2








2O5




oxygen atoms to DNP

CH3CH3+ 2CO

2997888997888997888997888997888997888997888997888997888997888rarrV2O5-DNP

CH3CHO + 2CO +H

2O

(6)




+ H2ORRR 998400(H)R998400(H)H

OOH

Pd-CeO2-DNP+ 1

2O2



119909phases





2and then Ce(NH

4)2(NO3)6 fol-








2


2-DNP



2-DNP) [140]



3)26H2OorCo(OAc)







5+hydrocarbons and














Acknowledgments


References





















































2

O2


































2




















































119899

and [Cu(INA)2

]119899

INA =14-(NC

5

H4

CO2


























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


PrecursorCH4


Growth

CNT

Support








MetalNPs

HO2C

HO2C

HO2C

HO2CHO2C

Defects

CO2H

CO2H

CO2HCO2H

CO2H

Doping

Carboxylicacids

X X

XX







HH O2

CNTs+ H2O
















O

O O

N

N

O

O OO

O

2C

(PhCO)2O

O

OH

HO

OH

OHOH

OHCO2COPh

CH2COPh

CH2COPh

CNT-anhydride

HO

HOPh

Ph

OH

OH

OHOH

CH2COPh CH2COPh

Ph-NH2

CNT-ether

CNT

CNT-imine

PhCOCH2BrCO2H

CO2H

CO2HHO2CHO2C

HO2C

HO2CHO2C

HO2C



H2O + 12O2

HOOH

HOOHReduced


site


O2

(Fe NP)CNT

COOHCOOH

Adipic acid



4(1) It has been



LiBH4999445999468 LiH + B + 15H

2(1)







O

O

O

OH OH

OHO2

X

+





CO + O2 CO2







(i) (ii)

(iii)

SWNT COClSWNT

SHSWNT

AIBN

VO(salen)SWNT

O

CI

O

O OO

O

N

V

V

N N

N N

H

NH

S

SH


O OO




3

N CH2

Cl2

45∘C 48 h





4and H








Toluene refluxCH3

CH3

N

N

+

minusH2OminusCO2

OH

OO H

HHN +

Cminus


H H

HH H

H

H

H

HH

OH OH

G

M

CH

120572

120573HO

4

41

1

O

O

O

O OO

O(a)

(c)(b)

Alginate

Alginate

Doped


Ominus

Ominus





4and H

2SO4



2OH groups


2OH groups are not




HOOCOH

OH

H

OH

O

O

O O

OOO

O

OO

O

O

O

HO

HOHO

COOH

COOH

COOH

COOH

OH

OH

+ O2

GO


O

O

HH CH3OH

CH3OH

OH

OSO3H

OSO3H

H3CO OCH3

OCH3







O2

Dopedgraphene

O OH + +

CHO


10

20

30

40

50

0

Con

vers

ion

()

Time (h)

(a)

(b)

(c)

0 1 2 3 4 5 6









HOOC

HOOC

HOOC

HOOC

O

O

O

O

O

O OO

OO

O

O

O

O

OO

HO

HOHO

HO

HO

HO

HO

HO

OH OH

OH

OH

OH OH

OH

OH

OH

OH

OHOH

OH

OH

COOH

COOH















2[104] This lower




4








2O2




2O2



HO-OHSurface bound

radicalOH

MMMMM MMMMM


Au-DNPs(a)

(b)


Phen

ol d

egra

datio

n (

)

100

80

60

40

20

0

Initial pH = 7

Induction period

Time (h)

Low pH

0 1 2 3 4 5


O2








eminus

eminuseminus

O2 + H+

= Au0

E0 =

E0 =

E0 = 18 V18 V

= Au

Reduction

minusOH + ∙OH

Oxidation

Highly reactive

H2O2 H2O2

∙OOH + H+

semi-reaction

hydroxyl radical

semi-reactionh

120575+

28V


O2


NH2-NH2O2

O2

SH S S

CuD




H H

H H

H

H

HN N N

H

H HHHN N

N CatO2

R1

R2 R3

R1

R2 R3

Hydrazine Diimide

H2O

+

+



2+ N2 The




3(BTC)

2(BTC 135-ben-


3(BTC)

2may




++ COH H

HHH

HH H

HH

Cr22

O3-DNPCO + H2O





2



2CO + 2H2

(2)



2[135]


2+ 2H2

(3)


2O (4)



2using Cr





2 According to this








2








2O5




oxygen atoms to DNP

CH3CH3+ 2CO

2997888997888997888997888997888997888997888997888997888997888rarrV2O5-DNP

CH3CHO + 2CO +H

2O

(6)




+ H2ORRR 998400(H)R998400(H)H

OOH

Pd-CeO2-DNP+ 1

2O2



119909phases





2and then Ce(NH

4)2(NO3)6 fol-








2


2-DNP



2-DNP) [140]



3)26H2OorCo(OAc)







5+hydrocarbons and














Acknowledgments


References





















































2

O2


































2




















































119899

and [Cu(INA)2

]119899

INA =14-(NC

5

H4

CO2


























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


HH O2

CNTs+ H2O
















O

O O

N

N

O

O OO

O

2C

(PhCO)2O

O

OH

HO

OH

OHOH

OHCO2COPh

CH2COPh

CH2COPh

CNT-anhydride

HO

HOPh

Ph

OH

OH

OHOH

CH2COPh CH2COPh

Ph-NH2

CNT-ether

CNT

CNT-imine

PhCOCH2BrCO2H

CO2H

CO2HHO2CHO2C

HO2C

HO2CHO2C

HO2C



H2O + 12O2

HOOH

HOOHReduced


site


O2

(Fe NP)CNT

COOHCOOH

Adipic acid



4(1) It has been



LiBH4999445999468 LiH + B + 15H

2(1)







O

O

O

OH OH

OHO2

X

+





CO + O2 CO2







(i) (ii)

(iii)

SWNT COClSWNT

SHSWNT

AIBN

VO(salen)SWNT

O

CI

O

O OO

O

N

V

V

N N

N N

H

NH

S

SH


O OO




3

N CH2

Cl2

45∘C 48 h





4and H








Toluene refluxCH3

CH3

N

N

+

minusH2OminusCO2

OH

OO H

HHN +

Cminus


H H

HH H

H

H

H

HH

OH OH

G

M

CH

120572

120573HO

4

41

1

O

O

O

O OO

O(a)

(c)(b)

Alginate

Alginate

Doped


Ominus

Ominus





4and H

2SO4



2OH groups


2OH groups are not




HOOCOH

OH

H

OH

O

O

O O

OOO

O

OO

O

O

O

HO

HOHO

COOH

COOH

COOH

COOH

OH

OH

+ O2

GO


O

O

HH CH3OH

CH3OH

OH

OSO3H

OSO3H

H3CO OCH3

OCH3







O2

Dopedgraphene

O OH + +

CHO


10

20

30

40

50

0

Con

vers

ion

()

Time (h)

(a)

(b)

(c)

0 1 2 3 4 5 6









HOOC

HOOC

HOOC

HOOC

O

O

O

O

O

O OO

OO

O

O

O

O

OO

HO

HOHO

HO

HO

HO

HO

HO

OH OH

OH

OH

OH OH

OH

OH

OH

OH

OHOH

OH

OH

COOH

COOH















2[104] This lower




4








2O2




2O2



HO-OHSurface bound

radicalOH

MMMMM MMMMM


Au-DNPs(a)

(b)


Phen

ol d

egra

datio

n (

)

100

80

60

40

20

0

Initial pH = 7

Induction period

Time (h)

Low pH

0 1 2 3 4 5


O2








eminus

eminuseminus

O2 + H+

= Au0

E0 =

E0 =

E0 = 18 V18 V

= Au

Reduction

minusOH + ∙OH

Oxidation

Highly reactive

H2O2 H2O2

∙OOH + H+

semi-reaction

hydroxyl radical

semi-reactionh

120575+

28V


O2


NH2-NH2O2

O2

SH S S

CuD




H H

H H

H

H

HN N N

H

H HHHN N

N CatO2

R1

R2 R3

R1

R2 R3

Hydrazine Diimide

H2O

+

+



2+ N2 The




3(BTC)

2(BTC 135-ben-


3(BTC)

2may




++ COH H

HHH

HH H

HH

Cr22

O3-DNPCO + H2O





2



2CO + 2H2

(2)



2[135]


2+ 2H2

(3)


2O (4)



2using Cr





2 According to this








2








2O5




oxygen atoms to DNP

CH3CH3+ 2CO

2997888997888997888997888997888997888997888997888997888997888rarrV2O5-DNP

CH3CHO + 2CO +H

2O

(6)




+ H2ORRR 998400(H)R998400(H)H

OOH

Pd-CeO2-DNP+ 1

2O2



119909phases





2and then Ce(NH

4)2(NO3)6 fol-








2


2-DNP



2-DNP) [140]



3)26H2OorCo(OAc)







5+hydrocarbons and














Acknowledgments


References





















































2

O2


































2




















































119899

and [Cu(INA)2

]119899

INA =14-(NC

5

H4

CO2


























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



O

O O

N

N

O

O OO

O

2C

(PhCO)2O

O

OH

HO

OH

OHOH

OHCO2COPh

CH2COPh

CH2COPh

CNT-anhydride

HO

HOPh

Ph

OH

OH

OHOH

CH2COPh CH2COPh

Ph-NH2

CNT-ether

CNT

CNT-imine

PhCOCH2BrCO2H

CO2H

CO2HHO2CHO2C

HO2C

HO2CHO2C

HO2C



H2O + 12O2

HOOH

HOOHReduced


site


O2

(Fe NP)CNT

COOHCOOH

Adipic acid



4(1) It has been



LiBH4999445999468 LiH + B + 15H

2(1)







O

O

O

OH OH

OHO2

X

+





CO + O2 CO2







(i) (ii)

(iii)

SWNT COClSWNT

SHSWNT

AIBN

VO(salen)SWNT

O

CI

O

O OO

O

N

V

V

N N

N N

H

NH

S

SH


O OO




3

N CH2

Cl2

45∘C 48 h





4and H








Toluene refluxCH3

CH3

N

N

+

minusH2OminusCO2

OH

OO H

HHN +

Cminus


H H

HH H

H

H

H

HH

OH OH

G

M

CH

120572

120573HO

4

41

1

O

O

O

O OO

O(a)

(c)(b)

Alginate

Alginate

Doped


Ominus

Ominus





4and H

2SO4



2OH groups


2OH groups are not




HOOCOH

OH

H

OH

O

O

O O

OOO

O

OO

O

O

O

HO

HOHO

COOH

COOH

COOH

COOH

OH

OH

+ O2

GO


O

O

HH CH3OH

CH3OH

OH

OSO3H

OSO3H

H3CO OCH3

OCH3







O2

Dopedgraphene

O OH + +

CHO


10

20

30

40

50

0

Con

vers

ion

()

Time (h)

(a)

(b)

(c)

0 1 2 3 4 5 6









HOOC

HOOC

HOOC

HOOC

O

O

O

O

O

O OO

OO

O

O

O

O

OO

HO

HOHO

HO

HO

HO

HO

HO

OH OH

OH

OH

OH OH

OH

OH

OH

OH

OHOH

OH

OH

COOH

COOH















2[104] This lower




4








2O2




2O2



HO-OHSurface bound

radicalOH

MMMMM MMMMM


Au-DNPs(a)

(b)


Phen

ol d

egra

datio

n (

)

100

80

60

40

20

0

Initial pH = 7

Induction period

Time (h)

Low pH

0 1 2 3 4 5


O2








eminus

eminuseminus

O2 + H+

= Au0

E0 =

E0 =

E0 = 18 V18 V

= Au

Reduction

minusOH + ∙OH

Oxidation

Highly reactive

H2O2 H2O2

∙OOH + H+

semi-reaction

hydroxyl radical

semi-reactionh

120575+

28V


O2


NH2-NH2O2

O2

SH S S

CuD




H H

H H

H

H

HN N N

H

H HHHN N

N CatO2

R1

R2 R3

R1

R2 R3

Hydrazine Diimide

H2O

+

+



2+ N2 The




3(BTC)

2(BTC 135-ben-


3(BTC)

2may




++ COH H

HHH

HH H

HH

Cr22

O3-DNPCO + H2O





2



2CO + 2H2

(2)



2[135]


2+ 2H2

(3)


2O (4)



2using Cr





2 According to this








2








2O5




oxygen atoms to DNP

CH3CH3+ 2CO

2997888997888997888997888997888997888997888997888997888997888rarrV2O5-DNP

CH3CHO + 2CO +H

2O

(6)




+ H2ORRR 998400(H)R998400(H)H

OOH

Pd-CeO2-DNP+ 1

2O2



119909phases





2and then Ce(NH

4)2(NO3)6 fol-








2


2-DNP



2-DNP) [140]



3)26H2OorCo(OAc)







5+hydrocarbons and














Acknowledgments


References





















































2

O2


































2




















































119899

and [Cu(INA)2

]119899

INA =14-(NC

5

H4

CO2


























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





O

O

O

OH OH

OHO2

X

+





CO + O2 CO2







(i) (ii)

(iii)

SWNT COClSWNT

SHSWNT

AIBN

VO(salen)SWNT

O

CI

O

O OO

O

N

V

V

N N

N N

H

NH

S

SH


O OO




3

N CH2

Cl2

45∘C 48 h





4and H








Toluene refluxCH3

CH3

N

N

+

minusH2OminusCO2

OH

OO H

HHN +

Cminus


H H

HH H

H

H

H

HH

OH OH

G

M

CH

120572

120573HO

4

41

1

O

O

O

O OO

O(a)

(c)(b)

Alginate

Alginate

Doped


Ominus

Ominus





4and H

2SO4



2OH groups


2OH groups are not




HOOCOH

OH

H

OH

O

O

O O

OOO

O

OO

O

O

O

HO

HOHO

COOH

COOH

COOH

COOH

OH

OH

+ O2

GO


O

O

HH CH3OH

CH3OH

OH

OSO3H

OSO3H

H3CO OCH3

OCH3







O2

Dopedgraphene

O OH + +

CHO


10

20

30

40

50

0

Con

vers

ion

()

Time (h)

(a)

(b)

(c)

0 1 2 3 4 5 6









HOOC

HOOC

HOOC

HOOC

O

O

O

O

O

O OO

OO

O

O

O

O

OO

HO

HOHO

HO

HO

HO

HO

HO

OH OH

OH

OH

OH OH

OH

OH

OH

OH

OHOH

OH

OH

COOH

COOH















2[104] This lower




4








2O2




2O2



HO-OHSurface bound

radicalOH

MMMMM MMMMM


Au-DNPs(a)

(b)


Phen

ol d

egra

datio

n (

)

100

80

60

40

20

0

Initial pH = 7

Induction period

Time (h)

Low pH

0 1 2 3 4 5


O2








eminus

eminuseminus

O2 + H+

= Au0

E0 =

E0 =

E0 = 18 V18 V

= Au

Reduction

minusOH + ∙OH

Oxidation

Highly reactive

H2O2 H2O2

∙OOH + H+

semi-reaction

hydroxyl radical

semi-reactionh

120575+

28V


O2


NH2-NH2O2

O2

SH S S

CuD




H H

H H

H

H

HN N N

H

H HHHN N

N CatO2

R1

R2 R3

R1

R2 R3

Hydrazine Diimide

H2O

+

+



2+ N2 The




3(BTC)

2(BTC 135-ben-


3(BTC)

2may




++ COH H

HHH

HH H

HH

Cr22

O3-DNPCO + H2O





2



2CO + 2H2

(2)



2[135]


2+ 2H2

(3)


2O (4)



2using Cr





2 According to this








2








2O5




oxygen atoms to DNP

CH3CH3+ 2CO

2997888997888997888997888997888997888997888997888997888997888rarrV2O5-DNP

CH3CHO + 2CO +H

2O

(6)




+ H2ORRR 998400(H)R998400(H)H

OOH

Pd-CeO2-DNP+ 1

2O2



119909phases





2and then Ce(NH

4)2(NO3)6 fol-








2


2-DNP



2-DNP) [140]



3)26H2OorCo(OAc)







5+hydrocarbons and














Acknowledgments


References





















































2

O2


































2




















































119899

and [Cu(INA)2

]119899

INA =14-(NC

5

H4

CO2


























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


(i) (ii)

(iii)

SWNT COClSWNT

SHSWNT

AIBN

VO(salen)SWNT

O

CI

O

O OO

O

N

V

V

N N

N N

H

NH

S

SH


O OO




3

N CH2

Cl2

45∘C 48 h





4and H








Toluene refluxCH3

CH3

N

N

+

minusH2OminusCO2

OH

OO H

HHN +

Cminus


H H

HH H

H

H

H

HH

OH OH

G

M

CH

120572

120573HO

4

41

1

O

O

O

O OO

O(a)

(c)(b)

Alginate

Alginate

Doped


Ominus

Ominus





4and H

2SO4



2OH groups


2OH groups are not




HOOCOH

OH

H

OH

O

O

O O

OOO

O

OO

O

O

O

HO

HOHO

COOH

COOH

COOH

COOH

OH

OH

+ O2

GO


O

O

HH CH3OH

CH3OH

OH

OSO3H

OSO3H

H3CO OCH3

OCH3







O2

Dopedgraphene

O OH + +

CHO


10

20

30

40

50

0

Con

vers

ion

()

Time (h)

(a)

(b)

(c)

0 1 2 3 4 5 6









HOOC

HOOC

HOOC

HOOC

O

O

O

O

O

O OO

OO

O

O

O

O

OO

HO

HOHO

HO

HO

HO

HO

HO

OH OH

OH

OH

OH OH

OH

OH

OH

OH

OHOH

OH

OH

COOH

COOH















2[104] This lower




4








2O2




2O2



HO-OHSurface bound

radicalOH

MMMMM MMMMM


Au-DNPs(a)

(b)


Phen

ol d

egra

datio

n (

)

100

80

60

40

20

0

Initial pH = 7

Induction period

Time (h)

Low pH

0 1 2 3 4 5


O2








eminus

eminuseminus

O2 + H+

= Au0

E0 =

E0 =

E0 = 18 V18 V

= Au

Reduction

minusOH + ∙OH

Oxidation

Highly reactive

H2O2 H2O2

∙OOH + H+

semi-reaction

hydroxyl radical

semi-reactionh

120575+

28V


O2


NH2-NH2O2

O2

SH S S

CuD




H H

H H

H

H

HN N N

H

H HHHN N

N CatO2

R1

R2 R3

R1

R2 R3

Hydrazine Diimide

H2O

+

+



2+ N2 The




3(BTC)

2(BTC 135-ben-


3(BTC)

2may




++ COH H

HHH

HH H

HH

Cr22

O3-DNPCO + H2O





2



2CO + 2H2

(2)



2[135]


2+ 2H2

(3)


2O (4)



2using Cr





2 According to this








2








2O5




oxygen atoms to DNP

CH3CH3+ 2CO

2997888997888997888997888997888997888997888997888997888997888rarrV2O5-DNP

CH3CHO + 2CO +H

2O

(6)




+ H2ORRR 998400(H)R998400(H)H

OOH

Pd-CeO2-DNP+ 1

2O2



119909phases





2and then Ce(NH

4)2(NO3)6 fol-








2


2-DNP



2-DNP) [140]



3)26H2OorCo(OAc)







5+hydrocarbons and














Acknowledgments


References





















































2

O2


































2




















































119899

and [Cu(INA)2

]119899

INA =14-(NC

5

H4

CO2


























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


Toluene refluxCH3

CH3

N

N

+

minusH2OminusCO2

OH

OO H

HHN +

Cminus


H H

HH H

H

H

H

HH

OH OH

G

M

CH

120572

120573HO

4

41

1

O

O

O

O OO

O(a)

(c)(b)

Alginate

Alginate

Doped


Ominus

Ominus





4and H

2SO4



2OH groups


2OH groups are not




HOOCOH

OH

H

OH

O

O

O O

OOO

O

OO

O

O

O

HO

HOHO

COOH

COOH

COOH

COOH

OH

OH

+ O2

GO


O

O

HH CH3OH

CH3OH

OH

OSO3H

OSO3H

H3CO OCH3

OCH3







O2

Dopedgraphene

O OH + +

CHO


10

20

30

40

50

0

Con

vers

ion

()

Time (h)

(a)

(b)

(c)

0 1 2 3 4 5 6









HOOC

HOOC

HOOC

HOOC

O

O

O

O

O

O OO

OO

O

O

O

O

OO

HO

HOHO

HO

HO

HO

HO

HO

OH OH

OH

OH

OH OH

OH

OH

OH

OH

OHOH

OH

OH

COOH

COOH















2[104] This lower




4








2O2




2O2



HO-OHSurface bound

radicalOH

MMMMM MMMMM


Au-DNPs(a)

(b)


Phen

ol d

egra

datio

n (

)

100

80

60

40

20

0

Initial pH = 7

Induction period

Time (h)

Low pH

0 1 2 3 4 5


O2








eminus

eminuseminus

O2 + H+

= Au0

E0 =

E0 =

E0 = 18 V18 V

= Au

Reduction

minusOH + ∙OH

Oxidation

Highly reactive

H2O2 H2O2

∙OOH + H+

semi-reaction

hydroxyl radical

semi-reactionh

120575+

28V


O2


NH2-NH2O2

O2

SH S S

CuD




H H

H H

H

H

HN N N

H

H HHHN N

N CatO2

R1

R2 R3

R1

R2 R3

Hydrazine Diimide

H2O

+

+



2+ N2 The




3(BTC)

2(BTC 135-ben-


3(BTC)

2may




++ COH H

HHH

HH H

HH

Cr22

O3-DNPCO + H2O





2



2CO + 2H2

(2)



2[135]


2+ 2H2

(3)


2O (4)



2using Cr





2 According to this








2








2O5




oxygen atoms to DNP

CH3CH3+ 2CO

2997888997888997888997888997888997888997888997888997888997888rarrV2O5-DNP

CH3CHO + 2CO +H

2O

(6)




+ H2ORRR 998400(H)R998400(H)H

OOH

Pd-CeO2-DNP+ 1

2O2



119909phases





2and then Ce(NH

4)2(NO3)6 fol-








2


2-DNP



2-DNP) [140]



3)26H2OorCo(OAc)







5+hydrocarbons and














Acknowledgments


References





















































2

O2


































2




















































119899

and [Cu(INA)2

]119899

INA =14-(NC

5

H4

CO2


























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


HOOCOH

OH

H

OH

O

O

O O

OOO

O

OO

O

O

O

HO

HOHO

COOH

COOH

COOH

COOH

OH

OH

+ O2

GO


O

O

HH CH3OH

CH3OH

OH

OSO3H

OSO3H

H3CO OCH3

OCH3







O2

Dopedgraphene

O OH + +

CHO


10

20

30

40

50

0

Con

vers

ion

()

Time (h)

(a)

(b)

(c)

0 1 2 3 4 5 6









HOOC

HOOC

HOOC

HOOC

O

O

O

O

O

O OO

OO

O

O

O

O

OO

HO

HOHO

HO

HO

HO

HO

HO

OH OH

OH

OH

OH OH

OH

OH

OH

OH

OHOH

OH

OH

COOH

COOH















2[104] This lower




4








2O2




2O2



HO-OHSurface bound

radicalOH

MMMMM MMMMM


Au-DNPs(a)

(b)


Phen

ol d

egra

datio

n (

)

100

80

60

40

20

0

Initial pH = 7

Induction period

Time (h)

Low pH

0 1 2 3 4 5


O2








eminus

eminuseminus

O2 + H+

= Au0

E0 =

E0 =

E0 = 18 V18 V

= Au

Reduction

minusOH + ∙OH

Oxidation

Highly reactive

H2O2 H2O2

∙OOH + H+

semi-reaction

hydroxyl radical

semi-reactionh

120575+

28V


O2


NH2-NH2O2

O2

SH S S

CuD




H H

H H

H

H

HN N N

H

H HHHN N

N CatO2

R1

R2 R3

R1

R2 R3

Hydrazine Diimide

H2O

+

+



2+ N2 The




3(BTC)

2(BTC 135-ben-


3(BTC)

2may




++ COH H

HHH

HH H

HH

Cr22

O3-DNPCO + H2O





2



2CO + 2H2

(2)



2[135]


2+ 2H2

(3)


2O (4)



2using Cr





2 According to this








2








2O5




oxygen atoms to DNP

CH3CH3+ 2CO

2997888997888997888997888997888997888997888997888997888997888rarrV2O5-DNP

CH3CHO + 2CO +H

2O

(6)




+ H2ORRR 998400(H)R998400(H)H

OOH

Pd-CeO2-DNP+ 1

2O2



119909phases





2and then Ce(NH

4)2(NO3)6 fol-








2


2-DNP



2-DNP) [140]



3)26H2OorCo(OAc)







5+hydrocarbons and














Acknowledgments


References





















































2

O2


































2




















































119899

and [Cu(INA)2

]119899

INA =14-(NC

5

H4

CO2


























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


O2

Dopedgraphene

O OH + +

CHO


10

20

30

40

50

0

Con

vers

ion

()

Time (h)

(a)

(b)

(c)

0 1 2 3 4 5 6









HOOC

HOOC

HOOC

HOOC

O

O

O

O

O

O OO

OO

O

O

O

O

OO

HO

HOHO

HO

HO

HO

HO

HO

OH OH

OH

OH

OH OH

OH

OH

OH

OH

OHOH

OH

OH

COOH

COOH















2[104] This lower




4








2O2




2O2



HO-OHSurface bound

radicalOH

MMMMM MMMMM


Au-DNPs(a)

(b)


Phen

ol d

egra

datio

n (

)

100

80

60

40

20

0

Initial pH = 7

Induction period

Time (h)

Low pH

0 1 2 3 4 5


O2








eminus

eminuseminus

O2 + H+

= Au0

E0 =

E0 =

E0 = 18 V18 V

= Au

Reduction

minusOH + ∙OH

Oxidation

Highly reactive

H2O2 H2O2

∙OOH + H+

semi-reaction

hydroxyl radical

semi-reactionh

120575+

28V


O2


NH2-NH2O2

O2

SH S S

CuD




H H

H H

H

H

HN N N

H

H HHHN N

N CatO2

R1

R2 R3

R1

R2 R3

Hydrazine Diimide

H2O

+

+



2+ N2 The




3(BTC)

2(BTC 135-ben-


3(BTC)

2may




++ COH H

HHH

HH H

HH

Cr22

O3-DNPCO + H2O





2



2CO + 2H2

(2)



2[135]


2+ 2H2

(3)


2O (4)



2using Cr





2 According to this








2








2O5




oxygen atoms to DNP

CH3CH3+ 2CO

2997888997888997888997888997888997888997888997888997888997888rarrV2O5-DNP

CH3CHO + 2CO +H

2O

(6)




+ H2ORRR 998400(H)R998400(H)H

OOH

Pd-CeO2-DNP+ 1

2O2



119909phases





2and then Ce(NH

4)2(NO3)6 fol-








2


2-DNP



2-DNP) [140]



3)26H2OorCo(OAc)







5+hydrocarbons and














Acknowledgments


References





















































2

O2


































2




















































119899

and [Cu(INA)2

]119899

INA =14-(NC

5

H4

CO2


























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










2[104] This lower




4








2O2




2O2



HO-OHSurface bound

radicalOH

MMMMM MMMMM


Au-DNPs(a)

(b)


Phen

ol d

egra

datio

n (

)

100

80

60

40

20

0

Initial pH = 7

Induction period

Time (h)

Low pH

0 1 2 3 4 5


O2








eminus

eminuseminus

O2 + H+

= Au0

E0 =

E0 =

E0 = 18 V18 V

= Au

Reduction

minusOH + ∙OH

Oxidation

Highly reactive

H2O2 H2O2

∙OOH + H+

semi-reaction

hydroxyl radical

semi-reactionh

120575+

28V


O2


NH2-NH2O2

O2

SH S S

CuD




H H

H H

H

H

HN N N

H

H HHHN N

N CatO2

R1

R2 R3

R1

R2 R3

Hydrazine Diimide

H2O

+

+



2+ N2 The




3(BTC)

2(BTC 135-ben-


3(BTC)

2may




++ COH H

HHH

HH H

HH

Cr22

O3-DNPCO + H2O





2



2CO + 2H2

(2)



2[135]


2+ 2H2

(3)


2O (4)



2using Cr





2 According to this








2








2O5




oxygen atoms to DNP

CH3CH3+ 2CO

2997888997888997888997888997888997888997888997888997888997888rarrV2O5-DNP

CH3CHO + 2CO +H

2O

(6)




+ H2ORRR 998400(H)R998400(H)H

OOH

Pd-CeO2-DNP+ 1

2O2



119909phases





2and then Ce(NH

4)2(NO3)6 fol-








2


2-DNP



2-DNP) [140]



3)26H2OorCo(OAc)







5+hydrocarbons and














Acknowledgments


References





















































2

O2


































2




















































119899

and [Cu(INA)2

]119899

INA =14-(NC

5

H4

CO2


























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of





2O2




2O2



HO-OHSurface bound

radicalOH

MMMMM MMMMM


Au-DNPs(a)

(b)


Phen

ol d

egra

datio

n (

)

100

80

60

40

20

0

Initial pH = 7

Induction period

Time (h)

Low pH

0 1 2 3 4 5


O2








eminus

eminuseminus

O2 + H+

= Au0

E0 =

E0 =

E0 = 18 V18 V

= Au

Reduction

minusOH + ∙OH

Oxidation

Highly reactive

H2O2 H2O2

∙OOH + H+

semi-reaction

hydroxyl radical

semi-reactionh

120575+

28V


O2


NH2-NH2O2

O2

SH S S

CuD




H H

H H

H

H

HN N N

H

H HHHN N

N CatO2

R1

R2 R3

R1

R2 R3

Hydrazine Diimide

H2O

+

+



2+ N2 The




3(BTC)

2(BTC 135-ben-


3(BTC)

2may




++ COH H

HHH

HH H

HH

Cr22

O3-DNPCO + H2O





2



2CO + 2H2

(2)



2[135]


2+ 2H2

(3)


2O (4)



2using Cr





2 According to this








2








2O5




oxygen atoms to DNP

CH3CH3+ 2CO

2997888997888997888997888997888997888997888997888997888997888rarrV2O5-DNP

CH3CHO + 2CO +H

2O

(6)




+ H2ORRR 998400(H)R998400(H)H

OOH

Pd-CeO2-DNP+ 1

2O2



119909phases





2and then Ce(NH

4)2(NO3)6 fol-








2


2-DNP



2-DNP) [140]



3)26H2OorCo(OAc)







5+hydrocarbons and














Acknowledgments


References





















































2

O2


































2




















































119899

and [Cu(INA)2

]119899

INA =14-(NC

5

H4

CO2


























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


eminus

eminuseminus

O2 + H+

= Au0

E0 =

E0 =

E0 = 18 V18 V

= Au

Reduction

minusOH + ∙OH

Oxidation

Highly reactive

H2O2 H2O2

∙OOH + H+

semi-reaction

hydroxyl radical

semi-reactionh

120575+

28V


O2


NH2-NH2O2

O2

SH S S

CuD




H H

H H

H

H

HN N N

H

H HHHN N

N CatO2

R1

R2 R3

R1

R2 R3

Hydrazine Diimide

H2O

+

+



2+ N2 The




3(BTC)

2(BTC 135-ben-


3(BTC)

2may




++ COH H

HHH

HH H

HH

Cr22

O3-DNPCO + H2O





2



2CO + 2H2

(2)



2[135]


2+ 2H2

(3)


2O (4)



2using Cr





2 According to this








2








2O5




oxygen atoms to DNP

CH3CH3+ 2CO

2997888997888997888997888997888997888997888997888997888997888rarrV2O5-DNP

CH3CHO + 2CO +H

2O

(6)




+ H2ORRR 998400(H)R998400(H)H

OOH

Pd-CeO2-DNP+ 1

2O2



119909phases





2and then Ce(NH

4)2(NO3)6 fol-








2


2-DNP



2-DNP) [140]



3)26H2OorCo(OAc)







5+hydrocarbons and














Acknowledgments


References





















































2

O2


































2




















































119899

and [Cu(INA)2

]119899

INA =14-(NC

5

H4

CO2


























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


++ COH H

HHH

HH H

HH

Cr22

O3-DNPCO + H2O





2



2CO + 2H2

(2)



2[135]


2+ 2H2

(3)


2O (4)



2using Cr





2 According to this








2








2O5




oxygen atoms to DNP

CH3CH3+ 2CO

2997888997888997888997888997888997888997888997888997888997888rarrV2O5-DNP

CH3CHO + 2CO +H

2O

(6)




+ H2ORRR 998400(H)R998400(H)H

OOH

Pd-CeO2-DNP+ 1

2O2



119909phases





2and then Ce(NH

4)2(NO3)6 fol-








2


2-DNP



2-DNP) [140]



3)26H2OorCo(OAc)







5+hydrocarbons and














Acknowledgments


References





















































2

O2


































2




















































119899

and [Cu(INA)2

]119899

INA =14-(NC

5

H4

CO2


























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


+ H2ORRR 998400(H)R998400(H)H

OOH

Pd-CeO2-DNP+ 1

2O2



119909phases





2and then Ce(NH

4)2(NO3)6 fol-








2


2-DNP



2-DNP) [140]



3)26H2OorCo(OAc)







5+hydrocarbons and














Acknowledgments


References





















































2

O2


































2




















































119899

and [Cu(INA)2

]119899

INA =14-(NC

5

H4

CO2


























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of






Acknowledgments


References





















































2

O2


































2




















































119899

and [Cu(INA)2

]119899

INA =14-(NC

5

H4

CO2


























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




























2

O2


































2




















































119899

and [Cu(INA)2

]119899

INA =14-(NC

5

H4

CO2


























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

























2




















































119899

and [Cu(INA)2

]119899

INA =14-(NC

5

H4

CO2


























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










































119899

and [Cu(INA)2

]119899

INA =14-(NC

5

H4

CO2


























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of










Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

review article allotropic carbon nanoforms as advanced metal-free catalysts … · 2019. 7. 31. ·...

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