Dynamic characterization of Co/TiO2Fischer-Tropsch catalysts withinfrared spectroscopy and DFTcalculationsJie Gao, Simon P...
Fischer-Tropsch Synthesis: Syngas to fuels   CO + H2 = hydrocarbons + H2O                                                 ...
Objectives of This Work• Characterization of Co/TiO2• In-situ FTIR spectroscopic measurements for evaluation  of dynamic c...
DRIFTS under Fischer-Tropsch conditions           Full spectrum                              1570              Enlarged CO...
Fischer-Tropsch Co/TiO2 catalysts                                                         Co(NO3)2·6H2O                   ...
IR for CO adsorption on Co/TiO2                                      a. HDP Co/TiO2 300°C                                 ...
Models for Co nanoparticles                            Periodic DFT calculations with MS DMol3                            ...
Characterization of Co/TiO2 F-T catalysts           Co    IWI-Co/TiO2 350°C         HDP-Co/TiO2 350°CEstimates of Co parti...
Characterization of Co/TiO2 F-T catalysts    H2 Temperature Programmed Reduction         Reaction Reduction   H2 consumpti...
Models for Co nanoparticles    2 Co layers on CoO(100)                               1 Co layer on CoO(100)      Correct m...
Models for Co nanoparticles                                                       2048                                    ...
IR for CO adsorption on Co/TiO2 Redux                            2050                                      a. HDP Co/TiO2 ...
CO intensity ratio for Co and CoO                                                                                         ...
F-T reaction mechanisms   CH2*             CH2*                                                Carbide insertion          ...
CH2*             CH2*                       C2H4**                              -36 kJ/mol             +CH2*             C...
CO*              CH3*+H*                     CH3CO**+H*                                 50 kJ/mol             +CO*        ...
Summary• Methodology development for characterization of  dynamic surface changes under reaction  conditions• Cobalt Fisch...
Acknowledgments                                 • Project partially funded by                                 US Congressi...
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IR and DFT analysis of Fischer-Tropsch catalysts

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IR and DFT studies of Co/TiO2 Fischer-Tropsch catalysts. This work was presented at the 22nd North American Catalyst Society meeting on 9 June 2011. It elucitates the structure of Co and CoO Fischer-Tropsch catalysts used in production of synthetic fuels..

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IR and DFT analysis of Fischer-Tropsch catalysts

  1. 1. Dynamic characterization of Co/TiO2Fischer-Tropsch catalysts withinfrared spectroscopy and DFTcalculationsJie Gao, Simon Podkolzin, Adeniyi Lawal Stevens Institute of Technology Hoboken, New Jersey, USAEmiel de Smit, Bert Weckhuysen Utrecht University Utrecht, NetherlandsGeorge Fitzgerald Accelrys San Diego, California, USA
  2. 2. Fischer-Tropsch Synthesis: Syngas to fuels CO + H2 = hydrocarbons + H2O Patents 100 Oil prices, USD per barrel Number of publications 600 $/barrel Research 80 500 60 400 300 40 Prices are unadjusted for inflation. 200 20 100 1920 1940 1960 1980 2000 Embargo 73-74 Chem. Soc. Rev. 37, 2758 (2008) Although F-T technology has been known for more than 80 years, information on the fundamentals of this chemistry is still limited, hindering improvements in catalyst and process development. Page 2
  3. 3. Objectives of This Work• Characterization of Co/TiO2• In-situ FTIR spectroscopic measurements for evaluation of dynamic changes of the surface and surface species• Development of models for reaction mechanism studies Page 3
  4. 4. DRIFTS under Fischer-Tropsch conditions Full spectrum 1570 Enlarged CO range 1996 1448 0.025 a.u. 2056 102 min 0.05 a.u. 1992 1378 102 100 2010 2056 100 Absorbance Absorbance 96 2010 2176 21162060 96 Co type 1 2930 2850 2176 2112 1576 1360 Co type 2 22 2060 22 4 min 4 3000 2500 2000 1500 2200 2100 2000 1900 1800 1700 Wavenumber, cm -1 Wavenumber, cm -1 IWI Co/TiO2-350 catalyst CO + H2 = Hydrocarbons + H2O. Feed GHSV 3010 h-1, CO/H2 mol feed ratio of 0.5, 1 atm, 220°C, CO conversion ~1 mol %. CO is on Co (not support) since the same double peak is observed for other supported Co catalysts: Co/SiO2, Co/Al2O3. J Catal. 211, 422 (2002); Appl. Catal. A 316, 68 (2007) Page 4
  5. 5. Fischer-Tropsch Co/TiO2 catalysts Co(NO3)2·6H2O Degussa P25 TiO2 (45 m2/g, 0.27 cm3/g) 4 Samples: Co IWI-300, IWI-350 IWI-Co/TiO2 350°C HDP-Co/TiO2 350°C HDP-300, HDP-350 Co deposition: IWI HDP Incipient Wetness Impregnation Homogeneous Deposition Precipitation pH adjusted with urea 9.5 wt % 7.8 wt % Drying, calcination at 400°C for 4 h (ramp rate of 5°C/min) Reduction: 300°C 350°C 2 h in 100 ml/min of 50% H2/He flow Page 5
  6. 6. IR for CO adsorption on Co/TiO2 a. HDP Co/TiO2 300°C c. IWI 300°C Spectra evolution as a 2050 0.02 a.u. CO on Co Type 1 CoO 0.02 a.u. 2048 function of He purge 2020 Type 2 2010 1834 10 min duration at room T 10 min • CO at 2050 cm-1Absorbance Absorbance 8 2054 8 6 6 decreases at higher 2052 1942 4 2180 2120 4 reduction T 2020 2020 • CO at 2050 cm-1 is 21782120 1936 1834 2 2 2200 2100 2000 1900 1800 1700 2200 2100 2000 1900 1800 1700 higher for HDP Wavenumber, cm-1 Wavenumber, cm -1 • CO at 2050 cm-1 2048 0.02 a.u. b. HDP350 °C b. HDP 350 0.02 a.u. 2036 2018 d.d. IWI 350°Cmin IWI 350 decreases more rapidly 8 min 10 on He purging 2052 8 • When CO at 2050 cm-1 AbsorbanceAbsorbance 6 6 2174 2120 2046 2172 2116 2020 2020 1936 1876 4 19681944 1830 4 2 dominates, bridged- 2 atop CoO(100) Co(001) bridge 3 fold Co(001) atop bridge 3 fold bonded CO at 1800- CoO(100) Co(001) Co(001) 2042 2020 1852 18021796 2042 2020 18521802 1796 1900 cm-1 is small or Theoretical Theoretical 2200 2100 2000 1900 1800 1700 2200 2100 2000 1900 1800 1700 not detectable Wavenumber, cm-1 Wavenumber, cm-1 Page 6
  7. 7. Models for Co nanoparticles Periodic DFT calculations with MS DMol3 Co(102) Co(001) Co(001) 2 top rows removed Co(001) with 1/6 ML O Co(001) with 1/3 ML O Co(001) with 1/2 ML O Page 7
  8. 8. Characterization of Co/TiO2 F-T catalysts Co IWI-Co/TiO2 350°C HDP-Co/TiO2 350°CEstimates of Co particle sizes (nm) Catalyst EXAFS XPS TEM IWI-Co/TiO2 350°C 2.5 4.0 4.3 HDP-Co/TiO2 350°C 3.2 1.3 3.5 Co particle sizes were similar for different preparation methods and reduction temperatures Page 8
  9. 9. Characterization of Co/TiO2 F-T catalysts H2 Temperature Programmed Reduction Reaction Reduction H2 consumption, au Precipitation XPS spectra Co2p3/2 and Co2p1/2 peaks at 781.1–781.2 eV and 796.5–796.8 eV Impregnation energy separation between the peaks of ~15.5–15.8 eV: Temperature, °C → presence of a CoO-like phase. (A) Co3O4 + H2 → 3CoO + H2O CoO is expected (B) CoO + H2 → Co + H2O at the reaction conditions Page 9
  10. 10. Models for Co nanoparticles 2 Co layers on CoO(100) 1 Co layer on CoO(100) Correct model for CoO(111) catalytic nanoparticles along with Co(001) for metallic Co CoO(100) Page 10
  11. 11. Models for Co nanoparticles 2048 2050 0.02 a.u. IWI 300° C 0.02 a.u. 2010 HDP 300° C 1810 10 min 10 min Absorbance 8 Absorbance 2054 8 2052 6 6 1942 2180 2120 4 2020 4 2020 2178 2120 1936 1834 2 2 2200 2100 2000 1900 1800 1700 2200 2100 2000 1900 1800 1700 CoO(100) atop Wavenumber, cm-1 Wavenumber, cm-1 2048 0.02 a.u. 2036 2018 0.02 a.u. IWI 350° C HDP 350° C bridged 10 min 8 min 2052 8 6 Absorbance Absorbance 2046 6 2020 2174 2120 2172 2116 4 2020 4 1968 1830 1944 1936 1876 3-fold CoO(100) atop bridge 3 fold CoO(100) 2 CoO(100) atop bridge 3 fold CoO(100) 2 Co(001) Co(001) Co(001) Co(001) 2036 2020 1963 1900 1840 2036 2020 1963 1900 1840 Theoretical Theoretical 2200 2100 2000 1900 1800 1700 2200 2100 2000 1900 1800 1700 Wavenumber, cm-1 Wavenumber, cm-1 Calculated heats of adsorption are consistent with peak intensity Co(001) changes on He purging: 143 kJ/mol on Co, 133 kJ/mol on CoO. NO bridged CO on CoO. Page 11
  12. 12. IR for CO adsorption on Co/TiO2 Redux 2050 a. HDP Co/TiO2 300°C 2048 c. IWI 300°C Spectra evolution as a 0.02 a.u. CoO on CoO CO 0.02 a.u. function of He purge 2010 2020 CO on Co 1834 10 min duration at room T 10 minAbsorbance Absorbance 2054 8 8 • CO at 2050 cm-1 6 6 decreases at higher 2052 1942 4 2180 2120 4 reduction T 2020 2020 21782120 2 1936 1834 2 • CO at 2050 cm-1 is higher for HDP samples 2200 2100 2000 1900 1800 1700 2200 2100 2000 1900 1800 1700 Wavenumber, cm-1 Wavenumber, cm-1 • CO at 2050 cm-1 2048 2036 2018 decreases more rapidly 0.02 a.u. b. HDP350 °C b. HDP 350 0.02 a.u. d.d. IWI 350°Cmin IWI 350 10 on He purging 8 min 2052 8 • When CO at 2050 cm-1 AbsorbanceAbsorbance 6 6 2174 2120 2020 4 2172 2116 2046 2020 4 dominates, bridged- 1936 1876 2 19681944 1830 2 bonded CO at 1800-1900 atop CoO(100) Co(001) bridge 3 fold Co(001) atop CoO(100) Co(001) bridge 3 fold Co(001) cm-1 is small or not 2042 2020 1852 18021796 2042 2020 18521802 1796 detectable Theoretical Theoretical 2200 2100 2000 1900 1800 1700 2200 2100 2000 1900 1800 1700 -1 Wavenumber, cm-1 Wavenumber, cm Page 12
  13. 13. CO intensity ratio for Co and CoO Model particle size Intensity ratio for atop CO on Co38 ratio for CoO/Co is 1.4 Co14 Co7 estimated at 1.12 Co and CoO Co26 1.2 Co4 ratio  1.35  1  eCo size /0.16  1.0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Co particle size, nm Ratio of CoO/Co can be estimated based on IR spectra Page 13
  14. 14. F-T reaction mechanisms CH2* CH2* Carbide insertion + CH2*+CH2*C2H4+ 2* CH3*+H* CO* CO insertion + CH3*+CO*COCH3*+ * CH3CO*+H* CHOH* CHOH* CHCOH* H2O Oxygenate + + 2CHOH*CHCOH**+H2O Page 14
  15. 15. CH2* CH2* C2H4** -36 kJ/mol +CH2* CH2* C2H4** -247 kJ/mol + Chain growth through CH2 on Co and CoO Simon Podkolzin Page 15
  16. 16. CO* CH3*+H* CH3CO**+H* 50 kJ/mol +CO* CH3*+H* CH3CO**+H* 12 kJ/mol + Chain growth through CO on Co and CoO. Similar reactions but with different energetics. Simon Podkolzin Page 16
  17. 17. Summary• Methodology development for characterization of dynamic surface changes under reaction conditions• Cobalt Fischer-Tropsch catalysts change dynamically between metallic Co and cobalt oxide CoO• Extent of Co oxidation can be evaluated based on relative IR peak intensities of CO on Co and CoO• Reaction steps are predicted to be similar on Co and CoO, but with different energetics Page 17
  18. 18. Acknowledgments • Project partially funded by US Congressional budget allocation. • Cooperative research license from Accelrys for Materials Studio. • Project partially funded by Dutch government grant NRSC-C 2009-2013. Page 18

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