high fischer- tropsch performance of cobalt catalyst
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High Fischer- Tropsch Performance of Cobalt Catalyst Supported On Nitrogen-Doped Carbon Nanotubes. Tingjun Fu, Zhenhua Li* School of Chemical Engineering & Technology, Tianjin University, Tianjin 300072, China 2013.11. 6. Outline. - PowerPoint PPT PresentationTRANSCRIPT
Tingjun Fu, Zhenhua Li*School of Chemical Engineering & Technology, Tianjin University,
Tianjin 300072, China2013.11. 6
Effect of carbon porosity on the FT
performance of carbon supported Co
catalysts
FT synthesis over Co catalysts supported
on NCNTs
Outline
Backgrounds
4
Gasifier
SyngasCoal
Gasification
Process
Natural Gas
Biomass
GTL
Coal
Gasification
Process
CTL
Fuel oil
key step
FT process
BTL
Backgrounds
An important supplement way of oil resourcesA kind of strategic reserve technology
Co catalyst and the carbon supports
Metal : Fe, Co, Ru
high productivity, high chain growth probability, high stability, low activity for the WGS reaction, lower price.
SiO2 , ZrO2 , Al2O3 , TiO2 ;
CNTs , CNFs , Cs , AC
Supported Co catalyst
Support
Effect of carbon porosity on the FT performance of carbon supported Co catalysts
contencontentsts
Carbon porosity Cobalt particle size FT perfomance
Carbon with different pore size
SampleBET surface
area (m2/g)
Pore volume
(cm3/g)
Average
pore size
(nm)
AC 1444 0.91 1.0
CNTs-8 306 0.19 3.3
CNTs-20 243 0.65 10.8
CNTs-60 119 0.40 14.8
Table 1 Structural and textual properties of the carbon supports.
Fig.1 XRD patterns of carbon supports .
Incipient wetness impregnation
Co/ACCo/CNTs-8Co/CNTs-20Co/CNTs-60
Carbon with wider pore has a bigger graphitization degree
Co loading : 20 wt %. Calcinated at 200 ℃for5h in Ar.
Pore size effect on the unreduced catalyst
Fig.2 XRD patterns of the unreduced Co catalysts . Fig.3 H2-TPR profiles of the unreduced Co catalysts .
Wider pore resulted in larger Co3O4 particles, higher reduction degree and more stability.
Fig.4. TEM images of prepared unreduced catalysts
Pore size effect on the reduced catalyst
Fig.5. TEM images and Co particle size distributions of the reduced catalysts.
Different carbon porosities resulted in different Co particle location and different particle size distribution.
Catalyst
Particle size (nm) H2 chemisorption
dCo3O4XRD dCo3O4
TEM dCoXRD a dCo
TEM b H2 uptake(μmol/g)
Dispersion(%)d
Co/AC 3.3 3.0 2.5 5.0 321.7 20.3
Co/CNTs-8 4.2 4.3 3.2 7.7 252.0 15.9
Co/CNTs-20 7.3 6.1 5.5 6.9 126.2 8.0
Co/CNTs-60 8.7 7.6 6.5 20.3 69.0 4.4 a d(Co) = 0.75d(Co3O4). b Mean size of Co particle based on TEM analysis
Pore size effect on the reduced catalyst
Table 2 Cobalt particle size and dispersion measured from TEM, XRD and H2 chemisorption.
CatalystsCO
conversion (%)
CO2
selectivity (%)
Hydrocarbon selectivity (%) ( C2-C
4 )
C=/C-
αCH4 C2 C3 C4 C5
+
Co/AC 54 0.6 25.0 0.9 1.9 1.4 70.8 0.24 0.81
Co/CNTs-8 83 1.3 17.7 0.8 1.2 0.9 79.4 0.27 0.84
Co/CNTs-20
85 1.2 12.0 0.5 1.0 0.6 85.9 0.38 0.86
Co/CNTs-60
65 0.9 10.6 0.6 0.9 0.7 87.4 0.50 0.89
Table 3 FT Synthesis results for the different carbon supported Co catalysts
FT performance of the catalysts
Larger carbon pore size resulted in higher C5+ selectivity but too large pore size resulted in lower CO conversion.
Co particle size effect on the FT performance
Fig.6. Relation between TOF and Co particle size.
Fig.7. Relation between C5+ selectivity and Co particle size.
Larger cobalt particles are beneficial for CO conversion and C5+ production as long as the Co particles are larger than 10 nm.
FT synthesis over Co catalysts supported on NCNTs
contencontentsts
N doping Cobalt particle size FT perfomance
Fig. 1 effect of acid treatment on the carbon supports
20 30 40 50 60 70 80
A-CNTs
NCNTs
A-NCNTs
Inte
nsity (
a.u
.)
2-theta(degree)
Fig.2. Raman spectra the supports
Fig.3 XRD patterns of carbon supports .
N doping effect on the CNTs
N content : 2.9 wt%
CNTs A-CNTs
NCNTs A-NCNTs
N doping increased the surface defects and decreased the carbon graphitization degree
Sample BET area (m2/g) Pore volume (cm3/g) Average pore size (nm)
A-CNTs 145 0.35 10.0
A-NCNTs 114 0.32 9.8
Co/A-CNTs 126 0.25 8.3
Co/A-NCNTs 46 0.14 12.5
Table 1 N2 adsorption–desorption results of the supports and cobalt catalysts*.
N doping effect on the Co catalysts
*Incipient wetness impregnation method; Co loading : 20% , Calcinated at 200 ℃ for 5h in Ar.
N doping resulted in more Co particles located inside the tubes
N doping effect on the unreduced catalysts
Fig.4 XRD patterns of the unreduced Co catalysts . Fig.5 H2-TPR profiles of the unreduced Co catalysts .
N doping resulted in better Co dispersion and also increased the interaction between the Co and CNT surface .
Catalyst
Particle size (nm) H2-TPD
dCo3O4XRD dCo
XRD d Co(fresh) TEM dCo(uesd)
TEM H2 uptake
(mol/g)
Dispersion
(%)
Co/A-CNTs 10.1 7.6 16.2 23.0 136 12.3
Co/A-NCNTs 5.5 4.1 5.4 8.9 255 22.9
Table 2 Co particle size and dispersion measured from TEM, XRD and H2 -TPD.
N doping effect on the reduced catalysts
Fig.6. TEM images of the reduced catalysts
Co/A-NCNTs Co/A-CNTs
FT performance of the Co catalysts
Fig. 7. Variation of FT activity with time on stream for different Co catalysts.
Fig.8. The C5+ product distribution for Co/A-CNTs and Co/A-NCNTs catalysts.
N doping improved FT activity Products shifted to lower carbon numbers with most being around C6-C15
N doping effect on the used Co catalysts
Fig.9. TEM images of the used catalysts (after 48h)
Co/A-NCNTs
Co/A-CNTs
Good Co dispersion ability of A-NCNTS during reaction
Conclusion
Carbon porosity strongly impacted the structure, reducibility and FT
performance of the supported Co catalysts.
Cobalt particle size had an impact on the TOF and on the C5+ selectivity.
N doping resulted in more surface defects, lower graphitization degree and
improved the Co dispersion on A-NCNTs .
FT activity for Co/A-NCNTs was enhanced and the C5+ hydrocarbon distribution
was shifted to lower carbon numbers with most being around C6-C15 .
Acknowledgement
NSFC Support
Tutor: Professor Zhenhua Li
Dr. : Jing Lv, Chengdu Huang Master: Suli Bai, Yunhui Jiang, Renjie Liu Our C1 Chemistry and Chemical Technology group
Thank you for your listening! Tianjin. China