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..

1. Dynamic characterization of Co/TiO2
Fischer-Tropsch catalysts with
infrared spectroscopy and DFT
calculations
Jie Gao, Simon Podkolzin, Adeniyi Lawal
Stevens Institute of Technology
Hoboken, New Jersey, USA
Emiel de Smit, Bert Weckhuysen
Utrecht University
Utrecht, Netherlands
George Fitzgerald
Accelrys
San Diego, California, USA

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. 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. 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. 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. 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-1
Absorbance
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
Absorbance
Absorbance
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. 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. Characterization of Co/TiO2 F-T catalysts
Co
IWI-Co/TiO2 350°C HDP-Co/TiO2 350°C
Estimates 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. 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. 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. 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. 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 min
Absorbance
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
Absorbance
Absorbance
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. 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. 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. 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. 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. 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. 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