Ph.D thesis

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Ph.D thesis

  1. 1. Mesoporous Nb and Ta Oxides: Synthesis, Characterization and Applications in Heterogeneous Catalysis <ul><li>Yuxiang(Tony) Rao </li></ul><ul><li>Department of Chemistry and Biochemistry </li></ul><ul><li>University of Windsor </li></ul><ul><li>Aug 25,2008 </li></ul>
  2. 2. Background Mesoporous structure materials <ul><li>Microporous: pore diameter < 2 nm </li></ul><ul><li>Mesoporous: pore diameter 2~50 nm </li></ul><ul><li>Macroporous: pore diameter >50 nm </li></ul>According to the definition of IUPAC: (International Union of Pure and Applied Chemistry):
  3. 3. Background <ul><li>M41S Family (t hree subgroups ) : </li></ul><ul><li>(Mobil Oil Corporation) </li></ul><ul><li>a) Hexagonal (MCM-41) </li></ul><ul><li>b) Cubic (MCM-48) </li></ul><ul><li>c) Lamellar (MCM-50) </li></ul>Kresge, C.T.; Leonowicz, M.E.; Roth, W.J.; Vartuli, J.C.; Beck, J.S. Nature 1992 , 359 , 710
  4. 4. MCM-41 MCM-41 (Mobil Composition of Matter No.41) <ul><li>Ordered mesoporous siliceous materials </li></ul><ul><li>High surface area and porosity (up to 1600 m 2 /g) </li></ul><ul><li>Ordered hexagonal array, uniform pore structure (2-50 nm) </li></ul><ul><li>Chemically and thermally stable </li></ul>
  5. 5. Mesoporous Transition Metal Oxides <ul><li>The first non-silica mesoporous material has been reported by using ligand-assisted templating approach in 1995. (Ti,Nb,Ta……) </li></ul>D.M. Antonelli, J.Y. Ying, Angew Chem Int Edit 1995 , 34 , 2014-2017 <ul><li>Excellent electron donor and acceptor </li></ul><ul><li>Higher surface acidity </li></ul>Variable oxidaion state Ti(+4,+3,+2,+1) Ta,Nb(+5,+4,+3,+2,+1) Fixed oxidation state Si (+4) Mesoporous transition metal oxides Silica based Mesoporous materials
  6. 6. Outline <ul><li>Synthetic method for mesoporous Nb and Ta Oxides </li></ul><ul><li>Characterization techniques </li></ul><ul><li>Powder-XRD, Nitrogen adsorption/desorption, SEM, TEM, FT-IR, Amine Titration, TPD, TG-DTA, DSC and Solid-state NMR </li></ul><ul><li>Heterogeneous catalytic applications </li></ul><ul><li>Benzylation, Alkylation, Isomerization </li></ul><ul><li>Future work </li></ul><ul><li>Photocatalysis, more NMR experiments </li></ul>
  7. 7. Ligand-Assisted Templating (LAT) Approach <ul><li>Step 1: bonds are formed between the inorganic species and the surfactant amine headgroups (S–I) </li></ul>Scheme 1. Synthesis of Mesoporous Nb Oxide Materials with different pore sizes n-hexylamine n-octadecylamine
  8. 8. Ligand-Assisted Templating (LAT) Approach <ul><li>Step 2: Template Remove and Surface Acidity Enhancement </li></ul>1 M sulfuric/phosphoric acid
  9. 9. Characterization <ul><li>Powder XRD </li></ul>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) C 12 Meso Nb; b) C 12 H 2 SO 4 meso Nb; c) C 12 Meso Ta; d) C 12 H 2 SO 4 Meso Ta
  10. 10. Characterization Type IV Isotherm further confirmed mesoporous structure after acid treatment <ul><li>BET </li></ul>Figure 2. N 2 adsorption/desorption isotherm of a) C 12 Meso Nb and C 12 H 2 SO 4 Meso Nb; b) C 12 Meso Ta and C 12 H 2 SO 4 Meso Ta
  11. 11. Characterization <ul><li>SEM </li></ul><ul><li>TEM </li></ul>Figure 3. SEM & TEM of C 12 H 2 SO 4 Meso Nb
  12. 12. Characterization <ul><li>FT-IR </li></ul>Figure 4. FT-IR spectra of pyridine adsorbed on C 12 Meso Nb, C 12 H 2 SO 4 Meso Nb and Ta, HY Zeolite and H-ZSM5 Zeolite. <ul><li>Brønsted acid site: 1538cm -1 Lewis acid site: 1443cm -1 </li></ul>
  13. 13. Characterization <ul><li>Amine-Titration </li></ul>Table 1. Acid strength and acid amount of solid acid catalysts (Measured by Hammett indicators and n-butylamine titration) Sample Ho Acid amount (mmol/g) C 12 Meso Nb -6.6 2.478 C 12 H 2 SO 4 Meso Nb -8.2 31.784 C 12 Meso Ta -6.6 0.40 C 12 H 2 SO 4 Meso Ta -8.2 19.8 HY Zeolite -6.6 1.55 H-ZSM5 -4.4 16.1 Amberlyst 15 N/A N/A
  14. 14. Characterization <ul><li>NH 3 -TPD </li></ul>Figure 5 . NH 3 -TPD profiles of sulfated mesoporous Nb and Ta catalysts. Ramp rate: 10K min -1 <ul><li>B stand for Brønsted acid sites </li></ul><ul><li>L stand for Lewis acid sites </li></ul>
  15. 15. Characterization <ul><li>TGA </li></ul>Figure 6. TGA curves under N 2 for sulfated mesoporous Nb and Ta catalysts <ul><li>DSC </li></ul>Figure 7. DSC curves under N 2 for sulfated mesoporous Nb and Ta catalysts
  16. 16. Characterization <ul><li>XRD for Nb samples heated at different temperatures </li></ul>Amorphous phase transferring to crystalline phase and mesoporous structure collapse during heating process Figure 8. X-ray diffraction of C 12 mesoporous Nb oxides a) at room temperature; b) Heated at 500 ºC for 2 h; c) Heated at 750 ºC for 2 h
  17. 17. Characterization <ul><li>Solid-state NMR </li></ul>Figure 9. 17 O MAS NMR spectra of 17 O-enriched sol–gel Nb 2 O 5 a) as formed, and after heating to b) 250 °C, c) 500 °C, d) 750 °C, and e) 1000 °C. Figure 10 . 17 O MAS NMR spectra of 17 O-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
  18. 18. Heterogeneous Catalytic Applications <ul><li>Reactor and Reactions </li></ul><ul><li>Benzylation </li></ul><ul><li>Alkylation </li></ul><ul><li>Isomerization </li></ul>
  19. 19. Heterogeneous Catalytic Applications <ul><li>Benzylation: Reaction </li></ul>Anisole Benzyl Alcohol 1-benzyl-2-methoxybenzene 1,1'-[ oxybis ( methylene ) ] dibenzene <ul><li>Catalysts: 0.5g </li></ul><ul><li>Temperature: Reflux Temperature </li></ul><ul><li>Ratio(Anisole/Benzyl Alcohol): 10:1 </li></ul>Rao, Y .; Trudeau, M.L.; Antonelli, D.M. J. Am. Chem. Soc . 2006 , 128 , 13996.
  20. 20. Heterogeneous Catalytic Applications <ul><li>Benzylation: Activity </li></ul>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
  21. 21. Heterogeneous Catalytic Applications <ul><li>Benzylation: Surface Area </li></ul>Table 2. The internal structure and surface properties of catalysts before and after reactions * Denotes surface areas after reaction with substrate in bracket. Sample BET surface area (m 2 /g) Volume (cm 3 /g) BJH Pore size (A) Nb 2 O 5 3.63 N/A N/A H 2 SO 4 /Nb 2 O 5 5.29 N/A N/A H 3 PO 4 /Nb 2 O 5 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 H 2 SO4/Meso Nb 519.10 0.3408 20.6 *H 2 SO4/Meso Nb (Anisole) 84.71 0.1409 37.2 *H 2 SO4/Meso Nb (Toluene) 3.35 0.004 51.1 H 3 PO4/Meso Nb 502.81 0.3286 20.7 *H 3 PO4/Meso Nb (Anisole) 76.38 0.0932 39.5 *H 3 PO4/Meso Nb (Toluene) 6.41 0.0146 47.0
  22. 22. Heterogeneous Catalytic Applications <ul><li>Benzylation: Surface Acidity </li></ul>Table 3. The amount of acids as mmole g -1 which was calculated from the n-butylamine titration Indicator Nb 2 O 5 H 2 SO 4 /Nb 2 O 5 H 3 PO 4 /Nb 2 O 5 Meso Nb H 2 SO 4 /Meso Nb H 3 PO 4 /Meso Nb Methyl yellow 0.024 0.338 0.317 2.478 31.784 3.086
  23. 23. Heterogeneous Catalytic Applications <ul><li>Alkylation: Reaction and Activity </li></ul>Figure 13 . Olefin conversion in the alkylation of benzene with (a) 1-dodecene and (b) 1-tetradecene over sulfated mesoporous C 12 -Ta oxide. Kang, J.; Rao, Y .; Trudeau, M.L; Antonelli, D.M. Angew. Chem. Int. Ed . 2008 , 47 , 1 . <ul><li>Catalysts: 4.0 wt% </li></ul><ul><li>Temperature: Reflux Temperature </li></ul><ul><li>Ratio(Benzene/Olefin): 10:1 </li></ul>
  24. 24. Heterogeneous Catalytic Applications <ul><li>Alkylation: Distribution and Catalyst Loading Level </li></ul>Figure 15 . 1-Dodecene conversion and 2-phenyldodecane selectivity as a function of catalyst loading. Reaction conditions: 80 o C, 0.5 h. Figure 14 . Distribution of phenyldodecane isomers over sulfated mesoporous C 12 -Ta oxide as a function of reaction time. Reaction condition: 80 o C, catalyst loading = 4.0 wt.%.
  25. 25. Heterogeneous Catalytic Applications <ul><li>Alkylation </li></ul>  Table 4. Catalytic properties of solid acid catalysts in alkylation reactions. [a] [a] reaction time: 0.5 h. [b] in second run. SO 4 2- /C 12 -Ta 80 1-dodecene 100 41.62 SO 4 2- /C 12 -Ta [b] 80 1-dodecene 26.8 52.23 SO 4 2- /C 12 -Ta 80 1-tetradecene 17.5 50.08 SO 4 2- /C 12 -Ta 150 1-dodecene 100 38.05 SO 4 2- /C 6 -Ta 80 1-dodecene 46.9 49.93 SO 4 2- /C 12 -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 Ca talyst Temp. ( o C) Olefin Conversion (%) Selectivity (%) Amberlyst 15 80 1-dodecene 13.5 55.19
  26. 26. Heterogeneous Catalytic Applications <ul><li>Isomerization: Reaction </li></ul>  Rao, Y. ; Kang, J. Antonelli, D.M. J. Am. Chem. Soc . 2008 , 130, 394
  27. 27. Heterogeneous Catalytic Applications <ul><li>Isomerization </li></ul>  Table 5 . BET surface area, Pore volume and Pore Size measured by N 2 adsorption at 77K. Sample BET (m 2 /g) Pore Volume (cm 3 /g) BJH Pore Size (Å) C 6 Meso Nb 519.03 0.4858 17.5 * C 12 Meso Nb 612.02 0.3199 20.6 C 18 Meso Nb 553.72 0.3595 27.2 C 6 H 2 SO 4 Meso Nb 160.35 0.293 16.3 C 12 H 2 SO 4 Meso Nb 413.97 0.2423 20.5 C 18 H 2 SO 4 Meso Nb 282.58 0.2087 25.6
  28. 28. Heterogeneous Catalytic Applications <ul><li>Isomerization </li></ul>  Table 5 . BET surface area, Pore volume and Pore Size measured by N 2 adsorption at 77K. (continue) * The pore size was estimated as 12 Å by using more reliable TEM and XRD on previous work Sample BET (m 2 /g) Pore Volume (cm 3 /g) BJH Pore Size (Å) C 6 Meso Ta 253.26 0.1905 17.5 * C 12 Meso Ta 582.7 0.3651 18.8 C 18 Meso Ta 234.74 0.0538 22.7 C 6 H 2 SO 4 Meso Ta 206.4 0.1314 17.0 * C 12 H 2 SO 4 Meso Ta 292.19 0.0989 18.2 C 18 H 2 SO 4 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
  29. 29. Heterogeneous Catalytic Applications <ul><li>Isomerization: Confinement Effects </li></ul>  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)
  30. 30. Heterogeneous Catalytic Applications <ul><li>Isomerization: Confinement Effects </li></ul>  (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
  31. 31. Heterogeneous Catalytic Applications <ul><li>Isomerization: Catalysts Comparision </li></ul>  (a) (b) Figure 18. 1-hexene isomerization conversion rate (A) and selectivity (B) on different catalysts.
  32. 32. Future Work <ul><li>Photocatalysis </li></ul><ul><li>(Mesoporous Ti Oxides: </li></ul><ul><li>Amorphous Structure  Crystalline Structure) </li></ul><ul><li>Research Proposal </li></ul><ul><li>Solid-State NMR </li></ul><ul><li>( 17 O and 15 N  Nb and Ta Oxygen Coordination ) </li></ul>Rao, Y.;Kemp, T.F.;Trudeau,M;Smith, M.E.;Antonelli,D.M. submitted to J. Am. Chem. Soc 2008
  33. 33. 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 17 O 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. “ 17 O and 15 N 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 ..…..
  34. 34. Acknowledgments <ul><li>Professor David M Antonelli </li></ul><ul><li>Antonelli’s Group Members </li></ul><ul><li>Dr. Boris O Skadtchenko </li></ul><ul><li>Dr. Longhui Qiu </li></ul><ul><li>Dr. Junjie Kang </li></ul><ul><li>Dr. Xin(Tim) Hu </li></ul><ul><li>Mr. Ahmad Hamaed </li></ul><ul><li>Mr. Tuan(Tom) Hoang </li></ul>
  35. 35. <ul><li>Thank you! </li></ul><ul><li>Questions? </li></ul>
  36. 36. Synthetic Method <ul><li>Triblock copolymer method </li></ul><ul><li>Poly(ethylene oxide)-Poly(propylene oxide)-Poly(ethylene oxide) (PEO-PPO-PEO) as structure-directing agents </li></ul><ul><li>thermally stable (up to 500 ºC) </li></ul><ul><li>large pore size (up to 14nm) </li></ul><ul><li>thick nanocrystalline pore wall (anatase phase, 4~7nm) </li></ul>Yang et al. Nature 1998 , 396 , 152 <ul><li>Modified sol-gel combined with silica-coating pore wall reinforcement method </li></ul><ul><li>high surface area (up to 1000 m 2 /g) </li></ul><ul><li>small pore size (2~5 nm) </li></ul><ul><li>thin wall thickness (2~3nm) </li></ul><ul><li>crystallized structure </li></ul>Kondo et al. Chem. Mater . 2008 , 20 , 835

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