Edited byMartin H. G. Prechtl

Nanocatalysis in Ionic Liquids

Edited by Martin H. G. Prechtl

Nanocatalysis in Ionic Liquids

Editor

Dr. Martin H. G. PrechtlUniversität zu KölnInstitut für Anorganische ChemieGreinstr. 650939 KölnGermany

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V

Contents

List of Contributors XIPreface XVForeword XIXSymbols and Abbreviations XXI

Part I Synthesis, Characterization, and Evaluation ofNanocatalysts in Ionic Liquids 1

1 Fe, Ru, and Os Nanoparticles 3Madhu Kaushik, Yuting Feng, Nathaniel Boyce, and Audrey Moores

1.1 Introduction 31.2 Synthesis of Fe, Ru, and Os NPs in ILs 41.2.1 Synthesis via Reduction of Metal Precursors or Ligands 61.2.2 Synthesis via Decomposition of Metal Precursors 71.2.3 The Use of Additional Stabilizers and Functional ILs 81.3 Ionic Liquid Stabilization of Metal Nanoparticles 91.3.1 Ionic Liquid Properties 91.3.2 Molecular Aspects of Ionic Liquid Stabilization of Metal

Nanoparticles 101.4 Applications of Ru, Fe, and Os Nanoparticles to Catalysis 111.4.1 Applications of Ru NPs in ILs to Catalysis 121.4.1.1 Hydrogenation of Olefins 121.4.1.2 Hydrogenation of Arenes 161.4.1.3 Other Types of Hydrogenations 171.4.1.4 Biomass Conversion 181.4.1.5 Miscellaneous Reactions 201.4.2 Applications of Fe Nanoparticles to Catalysis 201.5 Conclusion 21

Acknowledgments 21References 21

VI Contents

2 Co, Rh, and Ir Nanoparticles 25Jackson D. Scholten and Muhammad I. Qadir

2.1 Introduction 252.2 Chemical Routes for the Synthesis of Metal NPs in ILs 262.2.1 Chemical Reduction 262.2.2 Thermal/Microwave Decomposition 292.3 Catalytic Application of Metal NPs in ILs 312.3.1 Hydrogenation Reaction 312.3.2 Miscellaneous Reactions 342.4 Conclusions 37

References 37

3 Ni and Pt Nanoparticles 41Carla Weber Scheeren

3.1 Introduction 413.2 Synthesis and Characterization of Pt NPs in ILs 423.3 Catalytic Applications of Pt NPs in ILs 473.4 Synthesis and Characterization of Ni NPs in ILs 483.5 Catalytic Applications of Ni NPs in ILs 533.6 Summary and Conclusions 58

Symbols and Abbreviations 59Characterization Methods 59Ionic Liquids 59References 59

4 Pd Nanoparticles for Coupling Reactions and Domino/TandemReactions 63Anna M. Trzeciak

4.1 Introduction 634.2 Formation of Pd NPs in ILs 654.3 The Heck Coupling 684.4 The Suzuki Reaction 744.5 The Stille Coupling 754.6 The Sonogashira Coupling 764.7 Summary and Conclusions 78

Acknowledgments 79References 79

5 Soluble Pd Nanoparticles for Catalytic Hydrogenation 83Ran Zhang and Zhenshan Hou

5.1 Introduction 835.2 Synthesis of Pd Nanoparticles in ILs 855.2.1 Reduction of Pd NPs in ILs 865.2.2 Type of Metal Precursor 87

Contents VII

5.2.3 Reducing Agents and Ionic Liquids 875.3 Pd Nanoparticles for Hydrogenation 885.3.1 Hydrogenation of Alkene, Alkynes, and Dienes 885.3.2 Hydrogenation of Aldehydes and Aromatic Nitro

Compounds 905.3.3 Hydrogenation of Phenols 915.3.4 Hydrogenation of Ketones 915.3.5 Hydrogenation of Biomass 925.4 Summary and Conclusions 93

Ionic Liquid Abbreviations 93References 94

6 Au, Ag, and Cu Nanostructures 97Abhinandan Banerjee and Robert W. J. Scott

6.1 Introduction 976.2 Au NPs in the Presence of ILs 986.2.1 Early Examples and Chemical Synthesis Protocols 986.2.2 Advances in IL-Phase Au NP Synthesis: Physical Methods 1026.2.3 Electrochemical Applications of AuNP/IL Composites 1046.2.4 AuNP/IL Composites in Sensing 1046.2.5 Miscellaneous Applications of AuNP/IL Composites 1056.3 Catalytic Applications of AuNP/IL Composites 1066.4 Ag NPs in the Presence of ILs 1086.4.1 Novel Approaches for IL-Phase Synthesis of Ag NPs 1086.4.2 IL-Phase Ag NPs for Sensors 1106.4.3 Plasmonic Nanocatalysis with Ag NPs in ILs 1116.4.4 Anti-pathogenic Applications of Ag NPs in ILs 1126.5 Cu NPs in the Presence of ILs 1136.5.1 Synthesis of IL-Phase Cu NPs for Miscellaneous Applications 1136.5.2 Catalysis with IL-Phase Cu NPs 1166.6 Summary and Conclusions 118

Acronyms 119References 119

7 Bimetallic Nanoparticles in Ionic Liquids: Synthesis and CatalyticApplications 125Isabelle Favier, Emmanuelle Teuma, and Montserrat Gómez

7.1 Introduction 1257.2 Synthesis of Bimetallic Nanoparticles in Ionic Liquids 1277.2.1 Bottom-Up Methodologies 1277.2.1.1 Chemical Reduction 1277.2.1.2 Thermal Decomposition 1327.2.1.3 Electrochemical Methods 1347.2.2 Top-Down Methodology 135

VIII Contents

7.3 Applications in Catalysis 1377.3.1 Reactions under Hydrogen Pressure:

Hydrogenation–Hydrogenolysis–Dehalogenation 1377.3.1.1 Hydrogenation Reactions 1377.3.1.2 Hydrogenolysis Reactions 1407.3.1.3 Dehalogenation Reactions 1407.3.2 Oxidation 1417.4 Summary and Outlook 143

Acknowledgments 144References 144

8 Synthesis and Application of Metal Nanoparticle Catalysts in IonicLiquid Media using Metal Carbonyl Complexes as Precursors 147Raquel Marcos Esteban and Christoph Janiak

8.1 Introduction 1478.2 Metal Carbonyls – Synthesis, Structure, and Bonding 1508.3 Metal Carbonyls for the Synthesis of Metal Nanoparticles

(M-NPs) 1528.3.1 Synthesis in Ionic Liquids 1538.3.2 Synthesis in ILs with Deposition on Support 1578.4 Catalytic Applications of Metal Nanoparticles from Metal Carbonyls

in ILs 1608.5 Conclusions 163

Acknowledgment 164References 164

9 Top-Down Synthesis Methods for Nanoscale Catalysts 171Tsukasa Torimoto, Tatsuya Kameyama, and Susumu Kuwabata

9.1 Introduction 1719.2 Sputter Deposition of Metals in RTILs 1729.2.1 Uniformly Dispersed Nanoparticles in RTILs via Sputter Deposition

of a Single Element 1729.2.2 Synthesis Mechanism of Nanoparticles via RTIL/Metal

Sputtering 1789.2.3 Preparation of Alloy Nanoparticles and Control of Their

Composition 1829.2.4 Sequential Sputter Deposition for Synthesizing Nanocomposite

Particles 1859.2.5 Film Preparation on the Surfaces of RTILs 1869.2.6 Immobilization of Nanoparticles Sputter-Deposited in RTILs 1879.2.7 Application/Plasmonic Materials 1899.2.8 Application/Photoluminescence Materials 1929.2.9 Application/Electrocatalysts 1929.2.10 Application/Catalysts for Organic Syntheses 195

Contents IX

9.3 Thermal Vapor Deposition on RTILs for Preparation of MetalNanoparticles 196

9.4 Laser-Induced Downsizing and Ablation of Materials 1979.5 Preparation of Single Crystals by Vapor Deposition onto RTILs 1999.6 Conclusion 202

References 203

10 Electrochemical Preparation of Metal Nanoparticles in IonicLiquids 207Yasushi Katayama

10.1 Introduction 20710.2 Basics of Electrodeposition 20810.3 Electrodeposition of Silver and Formation of Silver Nanoparticles in

Ionic Liquids 21010.4 Electrochemical Formation of the Nanoparticles of Various

Metals 21510.4.1 Iron, Cobalt, and Nickel 21510.4.2 Palladium 21810.4.3 Gold 22010.4.4 Platinum 22210.5 Summary and Conclusions 225

References 227

Part II Perspectives for Application of Nanocatalysts in IonicLiquids 231

11 Tailoring Biomass Conversions using Ionic Liquid Immobilized MetalNanoparticles 233Srinidhi Narayanan, Jiaguang Zhang, and Ning Yan

11.1 Introduction 23311.2 Cellulose 23411.3 Lignin 23811.4 Fatty Acid and Its Derivatives 24111.5 Other Biomass Substrates 24311.6 Conclusion 245

References 245

12 Nanoparticles on Supported Ionic Liquid Phases – Opportunities forApplication in Catalysis 249Pedro Migowski, Kylie L. Luska, and Walter Leitner

12.1 Introduction 24912.2 Synthesis of Supported Ionic Liquid Phases (SILPs) 25012.3 Nanoparticles Immobilized onto Supported Ionic Liquid Phases

(NPs@SILPs) 25212.3.1 Nanoparticles Supported onto Physisorbed SILPs 254

X Contents

12.3.2 Nanoparticles Supported onto Chemisorbed SILPs 25512.4 Catalytic Applications of NPs@SILPs 25612.4.1 C–C Coupling 25712.4.1.1 Nonfunctionalized ILs 25712.4.1.2 Functionalized ILs 25912.4.2 Hydrogenation 26212.4.2.1 Nonfunctionalized ILs 26212.4.2.2 Functionalized ILs 26412.5 Summary and Conclusions 268

Acknowledgments 269References 269

13 Photovoltaic, Photocatalytic Application, and Water Splitting 275Adriano F. Feil, Heberton Wender, and Renato V. Gonçalves

13.1 Introduction 27513.2 Photovoltaic Cells 27613.2.1 Working Principles of a DSSC 27613.2.2 ILs in Photovoltaic Cells 27713.3 Photocatalytic Processes 28113.3.1 Principles of Photocatalysis 28113.3.2 ILs in Photocatalysis 28213.4 Water Splitting 28513.4.1 Principles of Photocatalytic and Photoelectrochemical Water

Splitting 28613.4.2 Nanostructured Semiconductor for Photocatalytic WS

Reaction 28713.4.3 Nanostructured Semiconductor for the PEC WS Reaction 28913.5 Summary and Conclusions 291

References 292

Index 295

XI

List of Contributors

Abhinandan BanerjeeUniversity of CalgaryNanoScience Program2500 University Drive NWCalgary, AB T2N 1N4Canada

Nathaniel BoyceMcGill UniversityDepartment of ChemistryCentre for Green Chemistryand Catalysis801 Sherbrooke Street WestMontreal, QC H3A 0B8Canada

Isabelle FavierUniversité de Toulouse 3 – PaulSabatierLaboratoire HétérochimieFondamentale et AppliquéeUMR CNRS 5069118 route de Narbonne31062 Toulouse Cedex 9France

Adriano F. FeilPUCRSCentro Interdisciplinar deNanociência eMicro-NanotecnologiaAv. Ipiranga, 6681CEP 90619-900, Porto AlegreRSBrazil

Yuting FengMcGill UniversityDepartment of ChemistryCentre for Green Chemistryand Catalysis801 Sherbrooke Street WestMontreal, QC H3A 0B8Canada

Montserrat GómezUniversité de Toulouse 3 – PaulSabatierLaboratoire HétérochimieFondamentale et AppliquéeUMR CNRS 5069118 route de Narbonne31062 Toulouse Cedex 9France

XII List of Contributors

Renato V. GonçalvesUniversidade de São PauloInstituto de Física de São Carlos13560-970, São CarlosSPBrazil

Zhenshan HouEast China University of Scienceand TechnologySchool of Chemistry andMolecular EngineeringKey Laboratory for AdvancedMaterialsMeilong Road 130Xuhui DistrictShanghai 200237China

Christoph JaniakHeinrich-Heine-UniversitätDüsseldorfInstitut für AnorganischeChemie und StrukturchemieUniversitätsstrasse 140225 DüsseldorfGermany

Tatsuya KameyamaNagoya UniversityDepartment of CrystallineMaterials ScienceGraduate School of EngineeringFuro-cho, Chikusa-kuNagoya 464-8603Japan

Yasushi KatayamaKeio UniversityDepartment of AppliedChemistryFaculty of Science andTechnology3-14-1 Hiyoshi, Kohoku-kuYokohamaKanagawa 223-8522Japan

Madhu KaushikMcGill UniversityDepartment of ChemistryCentre for Green Chemistryand Catalysis801 Sherbrooke Street WestMontreal, QC H3A 0B8Canada

Susumu KuwabataOsaka UniversityDepartment of AppliedChemistryGraduate School of Engineering2-1 Yamada-okaSuita, Osaka 565-0871Japan

Walter LeitnerRWTH Aachen UniversityInstitut für Technische undMakromolekulare ChemieWorringerweg 252074 AachenGermany

and

Max-Planck-Institut fürKohlenforschung45470 Mülheim an der RuhrGermany

List of Contributors XIII

Kylie L. LuskaRWTH Aachen UniversityInstitut für Technische undMakromolekulare ChemieWorringerweg 252074 AachenGermany

Raquel Marcos EstebanHeinrich-Heine-UniversitätDüsseldorfInstitut für AnorganischeChemie und StrukturchemieUniversitätsstrasse 140225 DüsseldorfGermany

Pedro MigowskiRWTH Aachen UniversityInstitut für Technische undMakromolekulare ChemieWorringerweg 252074 AachenGermany

Audrey MooresMcGill UniversityDepartment of ChemistryCentre for Green Chemistryand Catalysis801 Sherbrooke Street WestMontreal, QC H3A 0B8Canada

Srinidhi NarayananNational University of SingaporeDepartment of Chemical andBiomolecular Engineering4 Engineering Drive 4Blk E5, #02-37Singapore 117585Singapore

Muhammad I. QadirUFRGSInstituto de QuímicaAvenida Bento Gonçalves9500, Agronomia91501-970 Porto Alegre, RSBrazil

Jackson D. ScholtenUFRGSDepartamento de QuímicaInorgânicaInstituto de QuímicaAvenida Bento Gonçalves9500, Agronomia91501-970 Porto Alegre, RSBrazil

Robert W. J. ScottUniversity of SaskatchewanDepartment of Chemistry110 Science PlaceSaskatoon, SK S7N 5C9Canada

Emmanuelle TeumaUniversité de Toulouse 3 – PaulSabatierLaboratoire HétérochimieFondamentale et AppliquéeUMR CNRS 5069118 route de Narbonne31062 Toulouse Cedex 9France

Tsukasa TorimotoNagoya UniversityDepartment of CrystallineMaterials ScienceGraduate School of EngineeringFuro-cho, Chikusa-kuNagoya 464-8603Japan

XIV List of Contributors

Anna M. TrzeciakUniversity of WrocławDepartment of InorganicChemistryFaculty of Chemistry14 Fryderyka Joliot-Curie50-383 WrocławPoland

Carla Weber ScheerenFederal University of Rio GrandeSchool of Chemistry and FoodRua Barão do Caí, 125 sala 09Santo Antônio da PatrulhaRS 95500000Brazil

Heberton WenderUniversidade Federal de MatoGrosso do Sul (UFMS)Instituto de FísicaLaboratório de Nanomateriais eNanotecnologia Aplicada(LNNA) Av. Costa e Silva s/nCEP 79070-900, Campo GrandeMSBrazil

Ning YanNational University of SingaporeDepartment of Chemical andBiomolecular Engineering4 Engineering Drive 4Blk E5, #02-37Singapore 117585Singapore

Jiaguang ZhangNational University of SingaporeDepartment of Chemical andBiomolecular Engineering4 Engineering Drive 4Blk E5, #02-37Singapore 117585Singapore

Ran ZhangEast China University of Scienceand TechnologySchool of Chemistry andMolecular EngineeringKey Laboratory for AdvancedMaterialsMeilong Road 130Xuhui DistrictShanghai 200237China

XV

Preface

The first room-temperature organic molten salt was reported by Peter Waldenover 100 years ago in 1914 [1]. In the next decades, molten salts have been testedas solvents for biomass processing (1920s), and later as electrolytes (1950s) forthe electrodeposition of aluminum. Interestingly it took again more than 20 yearsuntil molten salts, now also called ionic liquids, were reported as solvents fororganic synthesis in the 1980s [2]. The first applications of ionic liquids (ILs)in catalysis was reported just in 1990, when Yves Chauvin (Nobel laureate2005; 1930–2015) published the first nickel-catalyzed olefin dimerization reac-tion performed in water-sensitive organochloroaluminate molten salts underbiphasic reaction conditions [3]. Later, in the mid-1990s, two manuscripts weresubmitted almost simultaneously (26 June 1995 and 18 August 1995) aboutrhodium-catalyzed hydrogenation in biphasic systems using for the first timeair and water-stable ILs [4, 5]. Both Yves Chauvin and Jairton Dupont focusedon imidazolium-based ionic liquids for the immobilization of the catalysts.Already these early works reported promising turnover numbers (15 000) andgood catalyst recyclability. The robustness of these systems in terms of air- andmoisture stability was a crucial factor for the later and wide spread application ofsuch ILs. However, it has taken some more years, until for the new millenniummore perspectives and future directions have been envisioned and propagatedespecially in review articles [6–8].

Contrary to the advent of the ILs application, the use of colloidal metals,hence solvated nanoparticles, goes back at least 2000 years and had been subjectof scientific researches early as in the nineteenth century by Michael Faraday[9]. Nanoscale metals have been synthesized from chemical vapor in 1927 byRoginsky and Schalnikoff, [10] and applied in catalysis in the 1940s by Nord andcoworkers [11]. Since then, the synthesis and uses of metal nanoparticles hasspread over all fields of chemistry. Again in the 1990s, Manfred Reetz reportedthe synthesis of metal nanoparticles in zwitterionic surfactants [12] and the use ofpalladium nanoclusters stabilized by propylene carbonate for their use as activecatalysts for the Mizoroki-Heck reaction [13]. At the same institute, alreadyin 1991 Helmut Bonnemann reported the synthesis of metal nanoparticles

XVI Preface

using tetraalkyl ammonium hydrotriorganoborates as reducing agent for metalsalts and the formed ammonium salts acted as stabilizing agent for the metalnanoparticles [14]. At about the same time, Bradley, Chaudret and colleaguesturned their attention from synthesis of organometallic complexes to a novelapproach toward the controlled decomposition of organometallics for the definedsynthesis of metal nanoparticles for industrial application [15].

These early observations and applications about “laboratory curiosities”such as the use of molten salts in organic synthesis and the decomposition ofmetal precursors obviously have not fully revealed their potential. The above-mentioned contributions are examples of the vivid research activities towardthe end of the last century and of course many other researchers were activeas well.

It was only in the early 2000s that the above mentioned aspects of (i) multi-phase catalysis in ionic liquids and (ii) controlled decomposition of metal precur-sors for metal nanoparticle formation started to merge into a single application:nanocatalysis in ionic liquids. These nanocatalysts revealed properties betweensingle-site catalysts in homogeneous catalysis and multisite catalysts in hetero-geneous catalysis. It was again Dupont et al. who presented a pioneering workabout the use of ionic liquids as template for the synthesis of nanomaterials inionic liquids and hybrid systems consisting of nanoparticles as catalysts and ionicliquids for multiphase catalysis [16]. In the next years, this new field started totake full ride and the field of application of those nanocatalysts in ILs broadenedits diversity. Nowadays there are many examples in literature for different reactiontypes including hydrogenation, dehydrogenation, cross-coupling, C–H activation,and applications such as in organic synthesis (drug design, fine chemicals), newmaterials, biomass conversion, hydrogen storage, energy conversion, industrialimplementation, flow processes, and so on.

This book presents a collection of selected topics about the progress ofnanocatalysis in ionic liquids. The individual chapters are divided into twosections: (i) metals and (ii) specific applications. The chapters cover pioneer-ing works, recent achievements, and discussion for future advancements insustainable synthetic methods, technologies, and energy research. Besides hydro-genation and cross-coupling reactions, that is, hydrogen storage, water-splitting,biomass processing are subject to discussion as well as bottom-up and top-downsynthetic methods for the preparation of metal nanoparticles.

It has been a pleasure and an inspiration to act as editor in this book. I am grate-ful to all the authors for their efforts in the production of this informative collec-tion about nanocatalysis in ionic liquids. Thirty authors working in eight differentcountries contributed to 13 chapters reflect international diversity. Nanocatalysisand ionic liquids have become promising research fields in the last 20 years andthere are many interesting things to investigate in the future.

Moreover, I am thankful to Dr Claudia Ley who has taken the initiative to discusswith me the adventure and idea for this book project in March 2014. Moreover,

Preface XVII

I thank Mrs Samanaa Srinivas as supportive project editor along the project. Lastbut not least, I am grateful to all my current and former collaboration partners,coauthors, students, mentors, family, and friends over the years.

March 2016 Martin H. G. PrechtlKöln

References

1. Walden, P. (1914) Bull. Acad. Impér. Sci.St. Pétersbourg, 8, 405–422.

2. Plechkova, N.V. and Seddon, K.R. (2008)Chem. Soc. Rev., 37, 123–150.

3. Chauvin, Y., Gilbert, B., and Guibard, I.(1990) J. Chem. Soc., Chem. Commun.,1715–1716.

4. Suarez, P.A.Z., Dullius, J.E.L., Einloft,S., de Souza, R.F., and Dupont, J. (1996)Polyhedron, 15, 1217–1219.

5. Chauvin, Y., Mussmann, L., and Olivier,H. (1995) Angew. Chem. Int. Ed. Engl.,34, 2698–2700.

6. Welton, T. (1999) Chem. Rev., 99,2071–2083.

7. Wasserscheid, P. and Keim, W.(2000) Angew. Chem. Int. Ed., 39,3772–3789.

8. Dupont, J., de Souza, R.F., andSuarez, P.A.Z. (2002) Chem. Rev., 102,3667–3691.

9. Faraday, M. (1857) Phil. Trans. R. Soc.London, 147, 145–181.

10. Roginsky, S. and Schalnikoff, A. (1927)Kolloid Z., 43, 67.

11. Rapino, L.D. and Nord, F.F. (1941) J. Am.Chem. Soc., 63, 2745 and 3268.

12. Reetz, M.T. and Quaiser, S.A. (1995)Angew. Chem. Int. Ed. Engl., 34,2240–2241.

13. Reetz, M.T. and Lohmer, G. (1996)Chem. Commun., 1921–1922.

14. Bonnemann, H., Brijoux, W., Brinkmann,R., Dinjus, E., Joussen, T., and Korall, B.(1991) Angew. Chem. Int. Ed. Engl., 30,1312–1314.

15. Bradley, J.S., Hill, E.W., Behal, S., Klein,C., Duteil, A., and Chaudret, B. (1992)Chem. Mater., 4, 1234–1239.

16. Dupont, J., Fonseca, G.S., Umpierre, A.P.,Fichtner, P.F.P., and Teixeira, S.R. (2002)J. Am. Chem. Soc., 124, 4228–4229.

XIX

Foreword

Metal nanoparticles are only kinetically stable and consequently nanoparticlesthat are freely dissolved in solution must be stabilized in order to prevent theiragglomeration. Unchecked, they can diffuse together and coalesce, eventuallyleading to the formation of the thermodynamically favored bulk metal. Indeed,since Faraday, various capping agents have been used to stabilize metal nanopar-ticles in aqueous or organic solvent solutions, rendering the investigation ofthe properties of freely dissolved metal nanoparticles a complex challenge. Theadvent of low-volatility ionic liquids as “liquid” support for the formation andstabilization of metal nanoparticles has opened not only a new avenue for thepreparation of soluble “naked” metal nanoparticles but also the possibility toinvestigate the properties of these materials in situ employing techniques oncealmost restricted to solid state such as TEM and XPS. Moreover, ionic liquid isproved to be the ideal medium for multiphase catalytic systems, allowing notonly the preparation and stabilization of transition-metal nanoparticles but alsoeasy catalyst recycling and product separation, thus avoiding the environmentalproblems associated with the related aqueous and organic biphasic regimes.Doubtless ionic liquids are the most versatile liquid platform for the design andpreparation of a new generation of modular soluble metal nanoparticle materialsfor catalytic transformations.

The field defined by Nanocatalysis in Ionic Liquids has had a transformativeeffect upon “soluble” metal nanoparticle catalysts and has given rise to an immenseand exponentially growing field of literature: from fundamental understandingof the transformations occurring in a metal surface to applied advanced cataly-sis such as biomass transformation and water splitting. The editor Dr Prechtl hascaptured the essence of such a fast-moving field and has assembled an outstand-ing team of authors with many pioneering and leading contributions on the field.The end product is not only a state-of-the art collection of reports on the field,but constitutes an instructive guide for both experienced practitioners and new-comers, detailing new ways to approach soluble metal nanoparticle catalysis. Vir-tually all the areas of nanocatalysis are covered in this monograph encompassingthe synthesis (bottom-up and top-down approaches), classical biphasic catalyticreactions (including reductions, oxidations, and coupling), and more advanced

XX Foreword

subjects such as supported ionic liquid phase catalysis and photocatalytic trans-formations.

This monograph provides new information and will certainly inspire and fosternew avenues in the fascinating field of soluble metal nanoparticle catalysis in ionicliquids.

Nottingham, 18 April 2016 Jairton Dupont

XXI

Symbols and Abbreviations

Selected and Common Ionic Liquid Abbreviations

Cations

[Hmim]+ 1-MethylimidazoliumC1, C2, C4, etc. Methyl, ethyl, butyl, and so on[CnCn′ Im]+ 1,3 functionalized imidazolium[CnCn′Cn′′ Im]+ 1,2,3 functionalized imidazolium[C2mim]+/Emim 1-Ethyl-3-methylimidazolium[C3mim]+ 1-Propyl-3-methylimidazolium[C4mim]+/Bmim 1-Butyl-3-methylimidazolium[C4mmim]+ 1,2-Dimethyl-3-butylimidazolium[C5mim]+ 1-Pentyl-3-methylimidazolium[C6mim]+ 1-Hexyl-3-methylimidazolium[(C3CN)C1Im]+ 1-Butyronitrile-3-methylimidazolium[C1C1(EG)Im]+ 1-(2,3-Dihydroxypropyl)-2,3-dimethylimidazolium[C2OHmim]+ 1-(2-hydroxyethyl)-3-methylimidazolium[Cmmim]+ 1-Carboxymethyl-3-methylimidazolium[ammim]+ 1-(3-Aminopropyl)-2,3-dimethylimidazolium[C4mPyr]+/[C4mp]+ 1-Butyl-1-methylpyrrolidinium[C2C6Pip]+ 1-Ethyl-1-hexylpiperidinium[P6,6,6,14]+ Trihexyl(tetradecyl)phosphonium[N6,6,6,14]+ Trihexyl(tetradecyl)ammonium[C4mPy]+ 1-Butyl-3-methylpyridinium[C4CNpy]+ N-Butyronitrile pyridinium[C4mmimDPA]+ 2,3-Dimethyl-1-[3-N ,N-bis(2-

pyridyl)propylamido]imidazolium[TMG]+ 1,1,3,3-Tetramethylguanidinium

Anions

[OAc]− Acetate[TFA]− Trifluoroacetate[DBS]− Dodecylbenzene sulfonate

XXII Symbols and Abbreviations

[OTf]− Trifluoromethanesulfonate[N(Tf)2]− Bis(trifluoromethylsulfonyl)imide[N(CN)2]−/DCA Dicyanamide[EtSO4]− Ethyl sulfate[HCO2]− Formate[PF6]− Hexafluorophosphate[NO3]− Nitrate[BF4]− Tetrafluoroborate[SCN]− Thiocyanate[CF3CO2]− Trifluoroacetate[CF3SO3]− Trifluoromethanesulfonate[FAP]−/[FEP]− Trifluorotris(pentafluoroethyl)phosphatetppts Triphenylphosphine-3,3′,3′′-trisulfonic acid trisodium

salt

1

Part ISynthesis, Characterization, and Evaluation of Nanocatalystsin Ionic Liquids

Nanocatalysis in Ionic Liquids, First Edition. Edited by Martin H.G. Prechtl.© 2017 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2017 by Wiley-VCH Verlag GmbH & Co. KGaA.

3

1Fe, Ru, and Os Nanoparticles

Madhu Kaushik, Yuting Feng, Nathaniel Boyce, and Audrey Moores

1.1Introduction

Although Fe, Ru, and Os are transition metals all belonging to Group 8 of theperiodic table, their prevalence, chemistry, and applications differ greatly. Iron isan earth abundant element, playing a key role in life with implications in someof the most difficult biological processes [1]. Iron is a current topic of interest inthe context of catalysis, both in its homogeneous [2, 3] and heterogeneous forms[4, 5], as a means to replace more toxic and less abundant transition metals.Iron has interesting properties in this context, including magnetic properties, arich redox chemistry, with implications both in molecular and material sciences,an affordable price and nontoxicity. Iron complexes, oxides, and metal-basedmaterials have been applied to a wide array of chemical processes, includingoxidation processes, hydrogenation, C–C coupling, and aromatic substitutions [3,6–9]. Ruthenium belongs to the platinum series and is obtained as a by-productto platinum or nickel mining. Within the platinum series, ruthenium is compa-rably cheaper than its counterparts and thus desirable as a replacement to moreexpensive, catalytically active transition metals. Compared to iron, it is less proneto oxidation when in its reduced form. Ruthenium has established itself as animportant and industrially relevant catalyst, in both its homogeneous and hetero-geneous forms for a number of important processes including the Haber-Boschprocess (dinitrogen to ammonia) [10, 11], the Fischer-Tropsch process (syngasto hydrocarbons) [12, 13], hydrogenation reactions [14], including the partialand selective hydrogenation of benzene and phenol, olefin metathesis [15], CHactivation [16], and organic oxidations just to name a few. Osmium has beencomparatively less explored. Osmium tetroxide and related compounds havedemonstrated early on their ability to catalyze the oxidative cleavage of olefinswith molecular oxygen [17]. Other osmium complexes have now been developedfor a number of reactions including complete and partial hydrogenation, dehydro-genation, and hydroformylation [18, 19]. Nanoparticulate osmium counterparts

Nanocatalysis in Ionic Liquids, First Edition. Edited by Martin H.G. Prechtl.© 2017 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2017 by Wiley-VCH Verlag GmbH & Co. KGaA.

4 1 Fe, Ru, and Os Nanoparticles

have been studied for their catalytic properties toward Fischer–Tropsch reaction,the homologation of alkenes under H2 and the hydrogenolysis of alkanes [20],and electrocatalytic activity useful in fuel cell research [21].

Ionic liquids (ILs) are defined as salts with melting points below 100 ∘C. Overthe last two decades, research on ILs has developed with a focus on liquid onesat or near room temperature [22, 23]. Typically such systems are constituted offlexible organic ion pairs with delocalized charges and tunable lipophilic domains[24]. Because of their liquid nature and specific properties, ILs are used as sol-vents to substitute volatile molecular liquids and specialty materials for a numberof important applications, including synthesis, catalysis and biocatalysis, separa-tion technology, biomass processing and transformation, electrochemical devicesincluding capacitors, fuel cells and solar cells, nanotechnology, sensing, lubricants,hypergolic materials, and pharmaceutics [22, 25–30]. ILs rapidly emerged as aprivileged environment for catalysis because of their unique intrinsic properties.ILs are attractive as potential solvents for a number of reasons: (i) they are non-volatile under ambient conditions; (ii) they are colorless and little viscous; (iii)they possess good solvation properties for a large number of species; (iv) they areimmiscible with many conventional solvents; (v) The properties of ILs can be easilytuned by a careful choice of the cation and anion entities, making them “designersolvents” [31]; and (vi) they are commercially available [30]. The combination ofproperties (i), (iii), (iv), and (v) explain that they are perfectly suited as catalyststabilizers in biphasic systems [32, 33]. ILs have also been developed in supportedversions to afford heterogenized systems of interest in catalysis [27].

Metal nanoparticles (NPs) have been intensely researched in the contextof catalysis [34, 35]. Their high surface-over-volume ratio and unique effectslinked to their nano size (role of defects, photon, and electron-linked properties)explain unique activities at the crossroads of homogeneous and heterogeneouscatalysis [36–38]. They are appealing as highly active catalysts and materialseasily amenable to recovery and recycling strategies [37]. Metal NPs and ILs, asprivileged catalysts and catalysis media respectively, have thus been naturallyexplored in partnership and have opened a unique and rich research field, whichhas already been largely reviewed. Among the papers published over the last10 years, the reader is directed to reviews on ILs in catalysis [25, 39], function-alized ionic liquids (FILs) [40, 41], FILs in catalysis [42], NPs in ILs [36, 43–46],NPs in ILs for catalysis [26, 47–55], and Ru NPs in IL [56]. In this chapter, wefocused on the synthesis, stabilization properties, and catalytic applications of Fe,Ru, and Os NPs in ILs. For Fe, we extended the review to iron oxide NPs as well,as under aerobic condition, reduced iron NPs lead to such species.

1.2Synthesis of Fe, Ru, and Os NPs in ILs

In general, the synthetic methods to access metal and metal oxide NPs in ILshave focused on providing materials with key features relevant for catalysis,

1.2 Synthesis of Fe, Ru, and Os NPs in ILs 5

that is, small sizes, good monodispersity, and high purity [26]. These propertiesare achieved using bottom-up synthetic approaches, either by reduction ofmetal salts, by the direct use of zero-valent molecular species, which can befreed from their ligands via hydrogenation, or simply decomposed (Scheme1.1). The use of additional stabilizers [46] or functional ILs [42] has beenreported to improve the properties of the end product. Top-down approachesare known for the synthesis of Au, Rh, Pd, and Pt NPs in ILs but are not a classicapproach to access NPs of metals of Group 8 [26]. Also, although syntheticroutes via phase transfer [57] from another organic or aqueous medium havebeen reported for other metals such as gold [58] and rhodium [59], Group 8NPs are typically prepared directly in neat ILs. Because of the preorganizedstructure of ILs via electrostatic, hydrogen bonding, and van der Waals interac-tions, especially those with imidazolium and phosphonium functionalities, theIL medium is described as made of polar and nonpolar nanodomains. Thosetunable domains act as nanoreactors and stabilizing chambers via noncovalentinteractions [44, 46]. Thanks to the polarity, thermal stability, and preorganizedsupermolecular structure of ILs, the synthesis of Ru, Fe, and Os NPs could beattained in ambient conditions [44, 60]. In ILs, such strategies have unlockedaccess to metal NPs with precise size control and narrow size distributions [56].Further comments on the stabilization properties of ILs for NPs are provided inSection 1.3.

M0(CO)nM = Fe, Ru, Os

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Scheme 1.1 Summary of the synthetic schemes for accessing Fe, Ru, and Os NPs in ILs.

A complete list of Ru NPs synthesis in ILs was established by Campbell et al. in2013 [56]. In the following sections, we focused on the most distinctive and recentexamples for synthesis of Fe, Ru, and Os NPs. One of the specifics of the synthesisof metal NPs directly within an IL is the difficulty in washing the resulting mate-rial from any salt by-product generated during the reaction. Hence it is importantto select “salt-free” precursors or organometallic precursors decomposing intoeasily washable organic species or volatile [61, 62] ones, such as [Ru(COD)(2-methylallyl)2], [Ru(COD)(COT)], or carbonyl compounds such as (COD= 1,5-cyclooctadiene and COT= 1,3,5-cyclooctatriene) [63], as discussed below.

6 1 Fe, Ru, and Os Nanoparticles

1.2.1Synthesis via Reduction of Metal Precursors or Ligands

Despite the long list of reducers used with this metal, Ru precursors in ILs arereduced by H2 in reported procedures [36, 48, 56, 64]. In a common scheme, a Ruprecursor, such as [Ru(COD)(2-methylallyl)2] or [Ru(COD)(COT)] is dissolvedor suspended into a specific IL under argon and exposed to mild H2 pressureand heating (<90 ∘C) from a few hours to days to obtain a black suspension. Thesize of the resulting Ru NPs – usually between 1.0 and 3.0 nm – and their sizedistribution may be tuned depending on reaction conditions, namely, stirring,temperature, and IL cations/anions (Figure 1.1) [56, 65–70]. From a formal stand-point, [Ru(COD)(2-methylallyl)2] and [Ru(COD)(COT)] precursors differ in thatthe latter is a Ru(0) complex which should not necessitate the use of a reducer.Under H2 pressure, however, the COD and COT ligands are hydrogenated torelease atomic Ru(0) and allow the growth of Ru NPs [61, 62]. RuCl3 and RuO2have also been reported as precursors being easily reduced by H2 to access thedesired NPs. In some ILs, precursor solubility may be a limitation that has beencircumvented via the use of an auxiliary solvent. Our group showed that tetrahy-drofuran (THF) could be successfully used to mix [Ru(COD)(2-methylallyl)2]with phosphonium and imidazolium ILs, before being easily removed in vacuo.Subsequent reduction under H2 pressure afforded small Ru NPs (between 1.5and 2.5 nm) [71]. Although not necessarily required for subsequent catalyticapplications, the separation of the obtained NPs from imidazolium ILs may beperformed and depends on the anion in the IL [65]. Prechtl et al. also showed that

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Figure 1.1 In situ transmission electronmicroscopy (TEM) images of Ru NPs gen-erated from the reduction of [Ru(COD)(2-methylallyl)2] by H2 in (a) [C4C1Im][NTf2],

(b) [C10C1Im][NTf2], (c) [C4C1Im][BF4], and(d) [C10C1Im][BF4]. (Prechtl et al. [65].Reproduced with the permission of AmericanChemical Society.)