Study On The Fischer-tropsch Synthesis Performance Of Carbon Supported Co-based Catalyst

The oil resources in china are scarce, and the oil consumption is highlydependent on import. Dependent on the rich coal resource in our country, we candevelop coal-to-liquid technology to get out of the dilemma of overwhelminglydependent on imported oil and then ensure energy security. And the key point inindirect coal-to-liquid process is the development of efficient catalyst forFischer-Tropsch synthesis(FTS).In order to better understand the intrinsic catalytic properties of Co, carbonmaterials were used as Co catalyst support to avoid the interference caused by thestrong interaction between the carrier and the Co metal. The effects of carbon supporttypes and pore structure of carbon nanotubes (CNTs) on catalyst stucture and FTSperformance were studied. The Co particle size effect was obtained and larger Coparticles are formed more easily in larger pores with a decreased Co dispersion.N-doped CNTs (NCNTs) with large diameter was introduced to prepare Co catalyst,and a highly active Co catalyst with high Co dispersion was obtained. Furthermore,we investigated the effect of acid treatment on the N-doped bamboo-like CNTssupported Co catalyst and the enhanced FTS performance was discussed.In this paper, ordered mesoporous carbon-CMK-3was prepared using hardtemplate method. Then CMK-3, AC and CNTs were used as supports for preparing Cocatalyst with similar Co particle size. It was found that CNTs has a better graphitestructure and a better resistance against the carbon gasifying than CMK-3and AC.Catalyst microstructure was closely related to the carbon support. Confinement effectmakes the Co particle size of the Co/CNTs catalyst well kept during reduction andreaction process, correspondingly the Co/CNTs catalyst has the highest reductiondegree and best FT performance.The Co catalysts supported on CNTs with different diameters were studied.CNTs with larger diameter has a higher graphitization degree and was more stableunder a H2atmosphere. CNTs pore structure affects the Co location, the Co dispersionand reduction degree, the number of active sites on the catalyst surface and thencatalytic activity. Large Co particles were more easily formed inside the tubes withlarger diameter, which decreased Co dispersion. There is a relationship between TOF, C5+selectivity and Co particle size that TOF and C5+selectivity increased greatly asthe particle size increases up to about8nm and then it gradually becomes constant atsizes larger than8nm.CNTs pore structure influences the C5+selectivity and productdistribution. Also, the residence time is another factor affecting the productdistribution.N doping reduces the graphitization degree of CNTs but increases the defectdegree. Also, N doping promotes the carbon gasification under H2atmosphere.Compared with CNTs supported Co catalyst, NCNTs supported catalyst has higher Codispersion and better catalytic activity. Highly dispersed Co particles inside largediameter tubes is the main reason for improved FT activity with the hydrocarbonproducts shifting to lower carbon number. Acid treatment significantly influences themorphology and surface properties of the NCNTs. Due to harsh oxidation conditions,over time the segmented structure of the NCNTs begins to deteriorate forming a singlehollow tube. Its graphite degree and the amount of oxygen-containing groups on thesurface are also gradually increased. But the amount of surface N did not change.Acid treatment promotes the location of Co particles inside the tube and also thecarbon gasification but decrease the catalyst reduction ability. Acid treatment for toolong time can destroy the NCNTs structure. The best FTS activity was obtained on thecatalyst supported on NCNTs treated for15h. N doping is an effective method forpreparing highly dispersed Co particles inside the large diameter pipes, which canallow better understanding of the size effect of Co particle located inside CNTs.