Study on catalytic performance of cobalt-based catalysts modified with nanodiamonds in Fischer-Tropsch synthesis
Cobalt-based catalysts exhibit excellent reactivity and carbon chain growth capability in the Fischer-Tropsch synthesis reaction,and their catalytic performance is closely related to the reduction degree and size of metal Co particles.Regulating the reduction degree and dispersion degree of metal Co by adding promoters is an important way to enhance their catalytic performance in Fischer-Tropsch synthesis reaction.By using SiC as a support with chemical inertness and good thermal conductivity,and adding a small amount of nanodiamonds(NDs)with rich surface functional groups as structural regulators,the dispersion degree and reduction degree of Co species in the catalyst were effectively improved,and its catalytic performance in Fischer-Tropsch synthesis reaction was enhanced.The results of N2 physical adsorption/desorption show that the addition of NDs has little effect on the parameters such as specific surface areas and pore sizes of the catalysts.The results of CO chemisorption show that the addition of an appropriate amount of NDs promotes the dispersion of active metal Co in the catalysts,increases the surface area of metal Co and provides more active sites for the Fischer-Tropsch synthesis reaction.The results of transmission electron microscopy(TEM)show that after the addition of NDs to Co/SiC(m(NDs)∶m(SiC)=1.0％),the particle sizes of metal Co in the catalysts are reduced,and NDs are uniformly dispersed on the catalyst surface.The results of H2-temperature programmed reduction(H2-TPR)and CO-H2-temperature programmed surface reaction(CO-H2-TPSR)show that the addition of NDs reduces the reduction temperature of Co3O4 to metal Co and promotes the reduction of Co3O4 and the activation of CO.Compared with the Co/SiC catalyst,the NDs-modified Co/1.0NDs-SiC(w(Co)=10％,m(NDs)∶m(SiC)=1.0％)catalyst exhibits an increase of CO conversion rate from 15.6％to 29.0％,and the selectivity of C5+hydrocarbon products still maintains at above 75％,and shows stable operation and no significant deactivation for 70 h.The above results can provide a new research idea for the development of efficient catalysts modified with nanocarbon materials in Fischer-Tropsch synthesis reaction.
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