ir and dft analysis of fischer-tropsch catalysts
DESCRIPTION
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..TRANSCRIPT
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
Fischer-Tropsch Synthesis: Syngas to fuels
Page 2
2000 1920 1940 1960 1980
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Prices are unadjusted for inflation.
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on
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Patents
$/barrel Research
Embargo 73-74
CO + H2 = hydrocarbons + H2O
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.
Chem. Soc. Rev. 37, 2758 (2008)
• 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
Objectives of This Work
Page 3
DRIFTS under Fischer-Tropsch conditions
Page 4
170018001900200021002200
Wavenumber, cm-1
Absorb
ance
21162060
2056
2056
102 min
22
4
96
100
0.025 a.u.1996
2176
2010
1500200025003000
Wavenumber, cm-1
Absorb
ance
2850 2112
96
0.05 a.u.
293022
2060
2176 1360
1992
100
102 1378
1570
1448
4 min
2010
1576
170018001900200021002200
Wavenumber, cm-1
Absorb
ance
21162060
2056
2056
102 min
22
4
96
100
0.025 a.u.1996
2176
2010
1500200025003000
Wavenumber, cm-1
Absorb
ance
2850 2112
96
0.05 a.u.
293022
2060
2176 1360
1992
100
102 1378
1570
1448
4 min
2010
1576
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)
Full spectrum Enlarged CO range
Co type 1 Co type 2
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 %.
Fischer-Tropsch Co/TiO2 catalysts
Page 5
IWI-Co/TiO2 350°C HDP-Co/TiO2 350°C
Co
IWI-Co/TiO2 350°C HDP-Co/TiO2 350°C
Co
Co(NO3)2·6H2O Degussa P25 TiO2 (45 m2/g, 0.27 cm3/g)
4 Samples:
IWI-300, IWI-350
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
Spectra evolution as a function of He purge duration at room T
• CO at 2050 cm-1 decreases at higher reduction T
• CO at 2050 cm-1 is higher for HDP
• CO at 2050 cm-1 decreases more rapidly on He purging
• When CO at 2050 cm-1 dominates, bridged-bonded CO at 1800-1900 cm-1 is small or not detectable
IR for CO adsorption on Co/TiO2
Page 6
Wavenumber, cm-1 Wavenumber, cm-1
1700 1800 1900 2000 2100 2200
Ab
so
rba
nce
2
4
6
8
10 min
1942 2020
0.02 a.u.
2050
2054
2178 2120
1700 1800 1900 2000 2100 2200
Ab
so
rba
nce
6
2120 2180
1936
10 min
2
2020
2048
1834
2052
0.02 a.u.
1834 2010
4
8
1700 1800 1900 2000 2100 2200
Wavenumber, cm - 1
Ab
sorb
an
ce
0.02 a.u .
6
8
4
2046 2172
2116
2018
10 min
2
2020
2042 1852 1796
Theoretical
1802
atop
2020
3 fold bridge
Co(001) Co(001) CoO(100)
1944 1968 1830
CoO
d. IWI 350 ° C
1700 1800 1900 2000 2100 2200
Wavenumber, cm - 1
Ab
sorb
an
ce
2048
2052
2120 2174
0.02 a.u .
4
6
8 min
2
1852 1802 1796 2020
Theoretical
2042
atop
CoO(100) Co(001)
3 fold
Co(001)
1876
2020
bridge
1936
b. HDP 350 ° C
2020
1700 1800 1900 2000 2100 2200
Ab
so
rba
nce
2
4
6
8
10 min
1942 2020
0.02 a.u.
2050
2054
2178 2120
1700 1800 1900 2000 2100 2200
Ab
so
rba
nce
6
2120 2180
1936
10 min
2
2020
2048
1834
2052
0.02 a.u.
1834 2010
4
8
1700 1800 1900 2000 2100 2200
Wavenumber, cm - 1
Ab
sorb
an
ce
0.02 a.u .
6
8
4
2046 2172
2116
2018
10 min
2
2020
2042 1852 1796
Theoretical
1802
atop
2020
3 fold bridge
Co(001) Co(001) CoO(100)
1944 1968 1830
1700 1800 1900 2000 2100 2200 1700 1800 1900 2000 2100 2200
Wavenumber, cm - 1
Ab
sorb
an
ce
0.02 a.u .
6
8
4
2046 2172
2116
2018
10 min
2
2020
2042 1852 1796
Theoretical
1802
atop
2020
3 fold bridge
Co(001) Co(001) CoO(100)
1944 1968 1830
0.02 a.u .
6
8
4
2046 2172
2116
2018
10 min
2
2020
1944 1968 1830
a. HDP Co/TiO2 300°C
Type 2
c. IWI 300°C
d. IWI 350
1700 1800 1900 2000 2100 2200
Wavenumber, cm - 1
Ab
sorb
an
ce
2048
2052
2120 2174
0.02 a.u .
4
6
8 min
2
1852 1802 1796 2020
Theoretical
2042
atop
CoO(100) Co(001)
3 fold
Co(001)
1876
2020
bridge
1936
1700 1800 1900 2000 2100 2200 1700 1800 1900 2000 2100 2200
Wavenumber, cm - 1
Ab
sorb
an
ce
2048
2052
2120 2174
0.02 a.u .
4
6
8 min
2 1876
2020 2020
1936
b. HDP 350
2020 2020
2036
CO on Co Type 1
Models for Co nanoparticles
Page 7
Co(001) 2 top rows removed Co(001)
Co(102)
Co(001) with 1/6 ML O
Co(001) with 1/3 ML O Co(001) with 1/2 ML O
Periodic DFT calculations with MS DMol3
Estimates of Co particle sizes (nm)
Characterization of Co/TiO2 F-T catalysts
Page 8
IWI-Co/TiO2 350°C HDP-Co/TiO2 350°C
Co
IWI-Co/TiO2 350°C HDP-Co/TiO2 350°C
Co
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
Characterization of Co/TiO2 F-T catalysts
Page 9
XPS spectra
Co2p3/2 and Co2p1/2 peaks at 781.1–781.2 eV and 796.5–796.8 eV
energy separation between the peaks of ~15.5–15.8 eV:
→ presence of a CoO-like phase.
H2 Temperature Programmed Reduction
Temperature, °C
H2 c
on
sum
pti
on
, au
(A) Co3O4 + H2 → 3CoO + H2O
(B) CoO + H2 → Co + H2O
Reduction Reaction
CoO is expected
at the reaction
conditions
Precipitation
Impregnation
Models for Co nanoparticles
Page 10
CoO(111) 1 Co layer on CoO(100)
2 Co layers on CoO(100)
CoO(100)
Correct model for catalytic
nanoparticles along with Co(001) for
metallic Co
3 fold
8 min
6
4
2
2200 2100 2000 1900 1800 1700
Wavenumber, cm-1
Ab
sorb
ance
2048
2174
2020
2052
1936 1876
2120
0.02 a.u.
atop
CoO(100)Co(001)
2036 2020 19001963 1840
CoO(100)Co(001)
bridge
Theoretical
3 fold
8 min
6
4
2
2200 2100 2000 1900 1800 1700
Wavenumber, cm-1
Ab
sorb
ance
2048
2174
2020
2052
1936 1876
2120
0.02 a.u.
atop
CoO(100)Co(001)
2036 2020 19001963 1840
CoO(100)Co(001)
bridge
Theoretical
3 fold
8 min
6
4
2
2200 2100 2000 1900 1800 1700
Wavenumber, cm-1
Ab
sorb
ance
2048
2174
2020
2052
1936 1876
2120
0.02 a.u.
atop
CoO(100)Co(001)
2036 2020 19001963 1840
CoO(100)Co(001)
bridge
Theoretical
0.02 a.u.2036 2018
20462020
19681944 1830
21722116
2200 2100 2000 1900 1800 1700
10 min
8
6
4
2
Wavenumber, cm-1
Absorb
ance
atopCoO(100)
Co(001)2036 2020 19001963 1840
CoO(100)Co(001)
bridge 3 fold
Theoretical
0.02 a.u.2036 2018
20462020
19681944 1830
21722116
2200 2100 2000 1900 1800 1700
10 min
8
6
4
2
Wavenumber, cm-1
Absorb
ance
atopCoO(100)
Co(001)2036 2020 19001963 1840
CoO(100)Co(001)
bridge 3 fold
Theoretical
HDP 350°C
2200 2100 2000 1900 1800 1700
2048
2180
2010
2020
1810
2052
1936 1834
2120
0.02 a.u.
10 min
8
6
4
2
Wavenumber, cm-1A
bsorb
ance
2200 2100 2000 1900 1800 1700
2048
2180
2010
2020
1810
2052
1936 1834
2120
0.02 a.u.
10 min
8
6
4
2
Wavenumber, cm-1A
bsorb
ance
IWI 300°C
IWI 350°C
10 min
8
6
4
2
2200 2100 2000 1900 1800 1700
Wavenumber, cm-1
Absorb
ance
2050
21782020
2054
1942
2120
0.02 a.u.
10 min
8
6
4
2
2200 2100 2000 1900 1800 1700
Wavenumber, cm-1
Absorb
ance
2050
21782020
2054
1942
2120
0.02 a.u. HDP 300°C
3 fold
8 min
6
4
2
2200 2100 2000 1900 1800 1700
Wavenumber, cm-1
Ab
sorb
ance
2048
2174
2020
2052
1936 1876
2120
0.02 a.u.
atop
CoO(100)Co(001)
2036 2020 19001963 1840
CoO(100)Co(001)
bridge
Theoretical
3 fold
8 min
6
4
2
2200 2100 2000 1900 1800 1700
Wavenumber, cm-1
Ab
sorb
ance
2048
2174
2020
2052
1936 1876
2120
0.02 a.u.
atop
CoO(100)Co(001)
2036 2020 19001963 1840
CoO(100)Co(001)
bridge
Theoretical
3 fold
8 min
6
4
2
2200 2100 2000 1900 1800 1700
Wavenumber, cm-1
Ab
sorb
ance
2048
2174
2020
2052
1936 1876
2120
0.02 a.u.
atop
CoO(100)Co(001)
2036 2020 19001963 1840
CoO(100)Co(001)
bridge
Theoretical
0.02 a.u.2036 2018
20462020
19681944 1830
21722116
2200 2100 2000 1900 1800 1700
10 min
8
6
4
2
Wavenumber, cm-1
Absorb
ance
atopCoO(100)
Co(001)2036 2020 19001963 1840
CoO(100)Co(001)
bridge 3 fold
Theoretical
0.02 a.u.2036 2018
20462020
19681944 1830
21722116
2200 2100 2000 1900 1800 1700
10 min
8
6
4
2
Wavenumber, cm-1
Absorb
ance
atopCoO(100)
Co(001)2036 2020 19001963 1840
CoO(100)Co(001)
bridge 3 fold
Theoretical
HDP 350°C
2200 2100 2000 1900 1800 1700
2048
2180
2010
2020
1810
2052
1936 1834
2120
0.02 a.u.
10 min
8
6
4
2
Wavenumber, cm-1A
bsorb
ance
2200 2100 2000 1900 1800 1700
2048
2180
2010
2020
1810
2052
1936 1834
2120
0.02 a.u.
10 min
8
6
4
2
Wavenumber, cm-1A
bsorb
ance
IWI 300°C
IWI 350°C
10 min
8
6
4
2
2200 2100 2000 1900 1800 1700
Wavenumber, cm-1
Absorb
ance
2050
21782020
2054
1942
2120
0.02 a.u.
10 min
8
6
4
2
2200 2100 2000 1900 1800 1700
Wavenumber, cm-1
Absorb
ance
2050
21782020
2054
1942
2120
0.02 a.u. HDP 300°C
Models for Co nanoparticles
Page 11
CoO(100)
Co(001)
atop
bridged
3-fold
Calculated heats of adsorption are consistent with peak intensity changes on He purging: 143 kJ/mol on Co, 133 kJ/mol on CoO.
NO bridged CO on CoO.
Spectra evolution as a function of He purge duration at room T
• CO at 2050 cm-1 decreases at higher reduction T
• CO at 2050 cm-1 is higher for HDP samples
• CO at 2050 cm-1 decreases more rapidly on He purging
• When CO at 2050 cm-1 dominates, bridged-bonded CO at 1800-1900 cm-1 is small or not detectable
IR for CO adsorption on Co/TiO2 Redux
Page 12
Wavenumber, cm-1 Wavenumber, cm-1
1700 1800 1900 2000 2100 2200
Ab
so
rba
nce
2
4
6
8
10 min
1942 2020
0.02 a.u.
2050
2054
2178 2120
1700 1800 1900 2000 2100 2200
Ab
so
rba
nce
6
2120 2180
1936
10 min
2
2020
2048
1834
2052
0.02 a.u.
1834 2010
4
8
1700 1800 1900 2000 2100 2200
Wavenumber, cm - 1
Ab
sorb
an
ce
0.02 a.u .
6
8
4
2046 2172
2116
2018
10 min
2
2020
2042 1852 1796
Theoretical
1802
atop
2020
3 fold bridge
Co(001) Co(001) CoO(100)
1944 1968 1830
CoO
d. IWI 350 ° C
1700 1800 1900 2000 2100 2200
Wavenumber, cm - 1
Ab
sorb
an
ce
2048
2052
2120 2174
0.02 a.u .
4
6
8 min
2
1852 1802 1796 2020
Theoretical
2042
atop
CoO(100) Co(001)
3 fold
Co(001)
1876
2020
bridge
1936
b. HDP 350 ° C
2020
1700 1800 1900 2000 2100 2200
Ab
so
rba
nce
2
4
6
8
10 min
1942 2020
0.02 a.u.
2050
2054
2178 2120
1700 1800 1900 2000 2100 2200
Ab
so
rba
nce
6
2120 2180
1936
10 min
2
2020
2048
1834
2052
0.02 a.u.
1834 2010
4
8
1700 1800 1900 2000 2100 2200
Wavenumber, cm - 1
Ab
sorb
an
ce
0.02 a.u .
6
8
4
2046 2172
2116
2018
10 min
2
2020
2042 1852 1796
Theoretical
1802
atop
2020
3 fold bridge
Co(001) Co(001) CoO(100)
1944 1968 1830
1700 1800 1900 2000 2100 2200 1700 1800 1900 2000 2100 2200
Wavenumber, cm - 1
Ab
sorb
an
ce
0.02 a.u .
6
8
4
2046 2172
2116
2018
10 min
2
2020
2042 1852 1796
Theoretical
1802
atop
2020
3 fold bridge
Co(001) Co(001) CoO(100)
1944 1968 1830
0.02 a.u .
6
8
4
2046 2172
2116
2018
10 min
2
2020
1944 1968 1830
a. HDP Co/TiO2 300°C
CO on Co
c. IWI 300°C
d. IWI 350
1700 1800 1900 2000 2100 2200
Wavenumber, cm - 1
Ab
sorb
an
ce
2048
2052
2120 2174
0.02 a.u .
4
6
8 min
2
1852 1802 1796 2020
Theoretical
2042
atop
CoO(100) Co(001)
3 fold
Co(001)
1876
2020
bridge
1936
1700 1800 1900 2000 2100 2200 1700 1800 1900 2000 2100 2200
Wavenumber, cm - 1
Ab
sorb
an
ce
2048
2052
2120 2174
0.02 a.u .
4
6
8 min
2 1876
2020 2020
1936
b. HDP 350
2020 2020
2036
CO on CoO
CO intensity ratio for Co and CoO
Page 13
1.0
1.2
1.4
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Inte
nsi
ty r
ati
o f
or
ato
p C
O o
n
Co a
nd
CoO
Co particle size, nm
Co7
Co4
Co14
Co26
Co38
/0.161.35 1 Co sizeratio e
Model particle size
ratio for CoO/Co is
estimated at 1.12
Ratio of CoO/Co can be
estimated based on IR spectra
F-T reaction mechanisms
Page 14
CH2* CH2*
+
CH2*CH2* CH2*CH2*
+CH2*+CH2*C2H4+ 2*
Carbide insertion
CH3*+H* CO*
CH3CO*+H*
+
CH3*+H*CH3*+H* CO*CO*
CH3CO*+H*CH3CO*+H*
+ CH3*+CO*COCH3*+ *
CO insertion
H2OCHOH* CHOH* CHCOH*
+ +
H2OCHOH*CHOH* CHOH*CHOH* CHCOH*CHCOH*
+ +
2CHOH*CHCOH**+H2O
Oxygenate
Simon Podkolzin Page 15
CH2*
+
CH2*
-36 kJ/mol
C2H4**
CH2* C2H4** CH2*
+
Chain growth through CH2 on Co and CoO
-247 kJ/mol
Simon Podkolzin Page 16
50 kJ/mol
12 kJ/mol
Chain growth through CO on Co and CoO.
Similar reactions but with different energetics.
CO*
+
CH3*+H* CH3CO**+H*
CH3CO**+H* CO*
+
CH3*+H*
• 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
Summary
Page 17
Acknowledgments
Page 18
• 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.