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