ph.d thesis
TRANSCRIPT
Mesoporous Nb and Ta Oxides: Synthesis, Mesoporous Nb and Ta Oxides: Synthesis, Characterization and Applications in Heterogeneous Characterization and Applications in Heterogeneous
CatalysisCatalysis
Yuxiang(Tony) Rao
Department of Chemistry and Biochemistry
University of Windsor
Aug 25,2008
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BackgroundBackground
Mesoporous structure materials
Microporous: pore diameter < 2 nm
Mesoporous: pore diameter 2~50 nm
Macroporous: pore diameter >50 nm
According to the definition of IUPAC:
(International Union of Pure and Applied Chemistry):
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BackgroundBackground
M41S Family (three subgroups): (Mobil Oil Corporation)
a) Hexagonal (MCM-41)
b) Cubic (MCM-48)
c) Lamellar (MCM-50)
Kresge, C.T.; Leonowicz, M.E.; Roth, W.J.; Vartuli, J.C.; Beck, J.S. Nature 1992, 359, 710
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MCM-41MCM-41
MCM-41 (Mobil Composition of Matter No.41)
Ordered mesoporous siliceous materials
High surface area and porosity (up to 1600 m2/g)
Ordered hexagonal array, uniform pore structure (2-50 nm)
Chemically and thermally stable 4
Mesoporous Transition Metal OxidesMesoporous Transition Metal Oxides
The first non-silica mesoporous material has been reported by using ligand-assisted templating approach in 1995. (Ti,Nb,Ta……)
Silica based Mesoporous materials Mesoporous transition metal oxides
Fixed oxidation state
Si (+4)
Variable oxidaion state
Ti(+4,+3,+2,+1)
Ta,Nb(+5,+4,+3,+2,+1)
D.M. Antonelli, J.Y. Ying, Angew Chem Int Edit 1995, 34, 2014-2017
Excellent electron donor and acceptor
Higher surface acidity
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OutlineOutline
• Synthetic method for mesoporous Nb and Ta Oxides
• Characterization techniques Powder-XRD, Nitrogen adsorption/desorption, SEM, TEM, FT-IR,
Amine Titration, TPD, TG-DTA, DSC and Solid-state NMR
• Heterogeneous catalytic applications Benzylation, Alkylation, Isomerization
• Future work Photocatalysis, more NMR experiments
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Ligand-Assisted Templating (LAT) ApproachLigand-Assisted Templating (LAT) Approach
Step 1: bonds are formed between the inorganic species and the surfactant amine headgroups (S–I)
Scheme 1. Synthesis of Mesoporous Nb Oxide Materials with different pore sizes
n-hexylaminen-octadecylamine
niobium ethoxide
Nb5+O-O-
-O-OO-
n-dodecylamine
NH2
+Nb
OEtEtO
H2NOEtOEt
OEt
H2O
HN
Nb
OEt
OEt
NH
Nb
OEt
OEt
NH
Nb
EtO
OEt
NH
Nb
EtOOEt
NH
Nb
EtO OEt
NH
NbEtO
OEtNH
NbEtO
EtO
NH
Nb
EtO
EtO
NH
Nb
OEt
EtO
NH
Nb
OEtEtO
HN
NbOEt
EtOHN
Nb
OEt
OEt
O
HN
NbO
OEtEtO
O
O
OO
O
NH
Nb
EtO
EtO
O
O O
O
O
O
O
O
Et
OEt
OEt
OEtOEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
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Ligand-Assisted Templating (LAT) ApproachLigand-Assisted Templating (LAT) Approach
Step 2: Template Remove and Surface Acidity Enhancement
HN
Nb
OEt
OEt
NH
Nb
OEt
OEt
NH
Nb
EtO
OEt
NH
Nb
EtOOEt
NH
Nb
EtO OEt
NH
NbEtO
OEtNH
NbEtO
EtO
NH
Nb
EtO
EtO
NH
Nb
OEt
EtO
NH
Nb
OEtEtO
HN
NbOEt
EtOHN
Nb
OEt
OEt
O
HN
NbO
OEtEtO
O
O
OO
O
NH
Nb
EtO
EtO
O
O O
O
O
O
O
O
Et
OEt
OEt
OEtOEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
P-toluene sulfonic acid
S
O
O
HO
1M sulfuric/phosphoric acid
Nb
OEt
OEt
Nb
OEt
OEt
Nb
EtO
OEt
Nb
EtOOEt
Nb
EtO OEt
NbEtO
OEt
NbEtO
EtO
Nb
EtO
EtO
Nb
OEt
EtO
Nb
OEtEtO
NbOEt
EtONb
OEt
OEt
O
NbO
OEtEtO
O
O
OO
O
Nb
EtO
EtO
O
O O
O
O
O
O
O
Et
OEt
OEt
OEtOEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
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CharacterizationCharacterization
Powder XRDPowder XRD
The strong (100) reflection at low angle confirmed the retention of mesoporous structure after acid treatment
Figure 1. Powder X-ray diffraction data for Nb-TSM1 and Ta-TSM1 samples. (From Top to Bottom) a) C12 Meso Nb; b) C12 H2SO4 meso Nb; c) C12 Meso Ta; d) C12 H2SO4 Meso Ta
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CharacterizationCharacterization
Type IV Isotherm further confirmed mesoporous structure after acid treatment
BETBET
Figure 2. N2 adsorption/desorption isotherm of a) C12 Meso Nb and C12 H2SO4 Meso Nb;
b) C12 Meso Ta and C12 H2SO4 Meso Ta
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CharacterizationCharacterization
SEMSEM TEMTEM
Figure 3. SEM & TEM of C12 H2SO4 Meso Nb
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CharacterizationCharacterization
FT-IRFT-IR
Figure 4. FT-IR spectra of pyridine adsorbed on C12 Meso Nb, C12 H2SO4 Meso Nb and
Ta, HY Zeolite and H-ZSM5 Zeolite.
Brønsted acid site: 1538cm-1 Lewis acid site: 1443cm-1
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CharacterizationCharacterization
Amine-TitrationAmine-Titration
Sample Ho Acid amount (mmol/g)
C12 Meso Nb -6.6 2.478
C12 H2SO4 Meso Nb -8.2 31.784
C12 Meso Ta -6.6 0.40
C12 H2SO4 Meso Ta -8.2 19.8
HY Zeolite -6.6 1.55
H-ZSM5 -4.4 16.1
Amberlyst 15 N/A N/A
Table 1. Acid strength and acid amount of solid acid catalysts (Measured by Hammett indicators and n-butylamine titration)
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CharacterizationCharacterization
NHNH33 -TPD -TPD
Figure 5. NH3-TPD profiles of sulfated mesoporous Nb and Ta catalysts. Ramp
rate: 10K min-1 B stand for Brønsted acid sites
L stand for Lewis acid sites 14
CharacterizationCharacterization
TGATGA
Figure 6. TGA curves under N2 for sulfated
mesoporous Nb and Ta catalysts
DSCDSC
Figure 7. DSC curves under N2 for sulfated
mesoporous Nb and Ta catalysts
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CharacterizationCharacterization
XRD for Nb samples heated at different temperaturesXRD for Nb samples heated at different temperatures
Amorphous phase transferring to crystalline phase and mesoporous structure collapse during heating process
Figure 8. X-ray diffraction of C12 mesoporous Nb oxides a) at room temperature; b) Heated at
500 ºC for 2 h; c) Heated at 750 ºC for 2 h
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CharacterizationCharacterization
Solid-state NMRSolid-state NMR
Figure 9. 17O MAS NMR spectra of 17O-enriched sol–gel Nb2O5 a) as formed, and after heating to b)
250 °C, c) 500 °C, d) 750 °C, and e) 1000 °C.
Figure 10. 17O MAS NMR spectra of 17O-enriched mesoporous niobia a) as-synthesized, and after heating to b) 250 °C, c) 500 °C, and d) 750 °C.
Skadtchenko, B.O.; Rao, Y.; Kemp. T.F.; Bhattacharya, P.; Thomas, P.A.; Trudeau, M.; Smith, M.E.; Antonelli, D.M. Angew. Chem. Int. Ed. 2007, 46, 2635
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Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications
Reactor and ReactionsReactor and Reactions Benzylation
Alkylation
Isomerization
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Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications
Benzylation: ReactionBenzylation: Reaction
Anisole Benzyl Alcohol 1-benzyl-2-methoxybenzene 1,1'-[oxybis(methylene) ]di
benzene Catalysts: 0.5g
Temperature: Reflux Temperature
Ratio(Anisole/Benzyl Alcohol): 10:1
Rao, Y.; Trudeau, M.L.; Antonelli, D.M. J. Am. Chem. Soc. 2006, 128, 13996. 19
Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications
Benzylation: ActivityBenzylation: Activity
Figure 11. Percent conversion of benzyl alcohol in benzylation of anisole catalyzed by different
mesoporous Nb oxides.
Figure 12. Percent conversion of benzyl alcohol in the benzylation of anisole catalyzed by different bulk
Nb oxides
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Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications
Benzylation: Surface AreaBenzylation: Surface Area
Sample BET surface area(m2/g)
Volume(cm3/g)
BJH Pore size(A)
Nb2O5 3.63 N/A N/A
H2SO4/Nb2O5 5.29 N/A N/A
H3PO4/Nb2O5 2.96 N/A N/A
Meso Nb 612.63 0.3956 22.7
*Meso Nb (Anisole) 587.90 0.3123 20.6
*Meso Nb (Toluene) 386.04 0.2088 20.6
H2SO4/Meso Nb 519.10 0.3408 20.6
*H2SO4/Meso Nb (Anisole) 84.71 0.1409 37.2
*H2SO4/Meso Nb (Toluene) 3.35 0.004 51.1
H3PO4/Meso Nb 502.81 0.3286 20.7
*H3PO4/Meso Nb (Anisole) 76.38 0.0932 39.5
*H3PO4/Meso Nb (Toluene) 6.41 0.0146 47.0
Table 2.The internal structure and surface properties of catalysts before and after reactions
* Denotes surface areas after reaction with substrate in bracket. 21
Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications
Benzylation: Surface AcidityBenzylation: Surface Acidity
Table 3. The amount of acids as mmole g-1 which was calculated from the n-butylamine titration
Indicator Nb2O5 H2SO4/Nb2O5
H3PO4/Nb2O5
Meso Nb
H2SO4/Meso Nb
H3PO4/Meso Nb
Methyl yellow 0.024 0.338 0.317 2.478 31.784 3.086
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Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications
Alkylation: Reaction and ActivityAlkylation: Reaction and Activity
Figure 13. Olefin conversion in the alkylation of benzene with (a) 1-dodecene and (b) 1-tetradecene over sulfated
mesoporous C12-Ta oxide.
Kang, J.; Rao, Y.; Trudeau, M.L; Antonelli, D.M. Angew. Chem. Int. Ed. 2008, 47, 1.
Catalysts: 4.0 wt%
Temperature: Reflux Temperature
Ratio(Benzene/Olefin): 10:1
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Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications
Alkylation: Distribution and Catalyst Loading LevelAlkylation: Distribution and Catalyst Loading Level
Figure 15. 1-Dodecene conversion and 2-phenyldodecane selectivity as a function of catalyst
loading. Reaction conditions: 80 oC, 0.5 h.
Figure 14. Distribution of phenyldodecane isomers over sulfated mesoporous C12-Ta oxide as a function of reaction time. Reaction condition: 80 oC, catalyst loading = 4.0 wt.%. 24
Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications
Alkylation Alkylation
SO42-/C12-Ta 80 1-dodecene 100 41.62
SO42-/C12-Ta[b] 80 1-dodecene 26.8 52.23
SO42-/C12-Ta 80 1-tetradecene 17.5 50.08
SO42-/C12-Ta 150 1-dodecene 100 38.05
SO42-/C6-Ta 80 1-dodecene 46.9 49.93
SO42-/C12-Nb 80 1-dodecene 1.2 100
H-Y zeolite 80 1-dodecene 100 29.48
H-Y zeolite 80 1-tetradecene 73.6 26.53
H-Y zeolite 150 1-dodecene 100 25.83
H-ZSM5 80 1-dodecene 0
0
Catalyst Temp.(oC)
Olefin Conversion(%)
Selectivity(%)
Amberlyst 15 80 1-dodecene 13.5 55.19
Table 4. Catalytic properties of solid acid catalysts in alkylation reactions.[a]
[a] reaction time: 0.5 h. [b] in second run. 25
Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications
Isomerization: ReactionIsomerization: Reaction
Rao, Y.; Kang, J. Antonelli, D.M. J. Am. Chem. Soc. 2008, 130, 394 26
Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications
IsomerizationIsomerization
Table 5. BET surface area, Pore volume and Pore Size measured by N2 adsorption at 77K.
Sample BET (m2/g)
Pore Volume (cm3/g)
BJH Pore Size (Å)
C6 Meso Nb 519.03 0.4858 17.5*
C12 Meso Nb 612.02 0.3199 20.6
C18 Meso Nb 553.72 0.3595 27.2
C6 H2SO4 Meso Nb 160.35 0.293 16.3
C12 H2SO4 Meso Nb 413.97 0.2423 20.5
C18 H2SO4 Meso Nb 282.58 0.2087 25.6
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Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications
IsomerizationIsomerization
Table 5. BET surface area, Pore volume and Pore Size measured by N2 adsorption at 77K.(continue)
Sample BET (m2/g) Pore Volume (cm3/g)
BJH Pore Size (Å)
C6 Meso Ta 253.26 0.1905 17.5*
C12 Meso Ta 582.7 0.3651 18.8
C18 Meso Ta 234.74 0.0538 22.7
C6 H2SO4 Meso Ta 206.4 0.1314 17.0*
C12 H2SO4 Meso Ta 292.19 0.0989 18.2
C18 H2SO4 Meso Ta 188.79 0.0347 22.5
HY Zeolite 779.8 0.116 38.9
H-ZSM5 435.96 0.1076 39
Amberlyst 15 51.86 0.3443 303.1
* The pore size was estimated as 12 Å by using more reliable TEM and XRD on previous work 28
Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications
Isomerization: Confinement EffectsIsomerization: Confinement Effects
Figure 16. 1-hexene isomerization conversion rate and selectivity on different pore size sulfated Nb oxides
(a) activity of different pore size Nb oxides (b) selectivity of different pore size Nb oxides
(a) (b)
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Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications
Isomerization: Confinement EffectsIsomerization: Confinement Effects
(a) (b)
Figure 17. 1-hexene isomerization conversion rate and selectivity on different pore size sulfated Ta oxides
(a) activity of different pore size Ta oxides (b) selectivity of different pore size Ta oxides
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Heterogeneous Catalytic ApplicationsHeterogeneous Catalytic Applications
Isomerization: Catalysts ComparisionIsomerization: Catalysts Comparision
(a) (b)
Figure 18. 1-hexene isomerization conversion rate (A) and selectivity (B) on different catalysts.
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Future Work
Photocatalysis (Mesoporous Ti Oxides:
Amorphous StructureCrystalline Structure)
Research Proposal
Solid-State NMR (17O and 15N Nb and Ta Oxygen Coordination )
Rao, Y.;Kemp, T.F.;Trudeau,M;Smith, M.E.;Antonelli,D.M. submitted to J. Am. Chem. Soc 2008
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Publications(1) Rao, Y., Trudeau, M., Antonelli, D.M. “Sulfated and Phosphated Mesoporous Nb Oxide in the Benzylation of Anisole and Toluene by Benzyl Alcohol.” Journal of the American Chemical Society 2006, 128 (43): 13996
(2) Skadtchenko, B.O., Rao, Y., Kemp, T.F., Bhattacharya, P., Thomas, P.A., Trudeau, M., Smith, M.E., Antonelli, D.M. “A Solid-State 17O NMR Study of Local Order and Crystallinity in Amine-Templated Mesoporous Nb Oxide.” Angewandte Chemie International Edition. 2007, 46:2635
(3) Rao, Y., Kang, J., Antonelli, D.M. “1-Hexene Isomerization Over Sulfated Mesoporous Ta Oxide: The effects of activie site and confinement.” Journal of the American Chemical Society 2008, 130 (2): 394
(4) Kang, J., Rao, Y., Antonelli, D.M. “Sulfated Mesoporous Ta Oxides in the Shape Selective Synthesis of Linear Alkyl Benzene.” Angewandte Chemie International Edition 2008, 47: 4896
(5) Rao, Y., Kang, J., Antonelli, D.M. “Investigation of synthesis and characterization of mesoporous Nb and Ta oxide and application in 1-Hexene isomerization” (Article, submitted to Chemistry of Materials, 2008)
(6) Rao,Y.; Kemp, T.F.; Trudeau, M.; Smith, M.E.; Antonelli, D.M. “17O and 15N Solid State NMR Studies on Ligand-Assisted Templating and Oxygen Coordination in the Walls of Mesoporous Nb, Ta and Ti Oxides” (Article, submitted to Journal of American Chemistry Society, 2008)
(7) Rao,Y.; Antonelli, D.M. “Mesoporous transition metal oxides: characterization and applications in heterogeneous catalysis” (Invited Highlight Paper, submitted to Journal of Materials Chemistry, 2008)
And more coming soon ..…..
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Acknowledgments
Professor David M Antonelli
Antonelli’s Group Members
Dr. Boris O Skadtchenko Dr. Longhui Qiu Dr. Junjie Kang Dr. Xin(Tim) Hu Mr. Ahmad Hamaed Mr. Tuan(Tom) Hoang
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Thank you!
Questions?
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Synthetic Method
Triblock copolymer method
Poly(ethylene oxide)-Poly(propylene oxide)-Poly(ethylene oxide) (PEO-PPO-PEO) as structure-directing agents
• thermally stable (up to 500 ºC)• large pore size (up to 14nm)• thick nanocrystalline pore wall (anatase phase, 4~7nm)
Yang et al. Nature 1998, 396, 152
Modified sol-gel combined with silica-coating pore wall reinforcement method
• high surface area (up to 1000 m2/g)
• small pore size (2~5 nm)
• thin wall thickness (2~3nm)
• crystallized structureKondo et al. Chem. Mater. 2008, 20, 835