title: The effect of the nanofibrous Al2O3aspect ratio on Fischer-Tropsch synthesis over cobalt catalysts.
abstract: A series of nanofibrous alumina materials with diameters of 4-6 nm and with different aspect ratios ranging from 3 to 16 were prepared. Cobalt impregnated catalysts were prepared by means of incipient wetness impregnation on alumina nanofibers while the 'rearranged' catalysts were prepared by using ultrasonication assistance to mix the fibers with the Co3O4nanoparticles. The effects of the alumina nanofiber aspect ratios on the Co catalyst structure and performance for Fischer-Tropsch synthesis were studied. The pore size of the two series of catalysts increased as the aspect ratio of the alumina nanofiber increased. For impregnated catalysts, large Co3O4particles were formed on the external surface of the alumina support when the aspect ratio was 3 and 5, while the crystallite sizes of Co3O4increased from 13.3 nm to 15.6 nm with the increase of the aspect ratio from 7 to 16. The four 'rearranged' catalysts possessed similar and homogeneously dispersed Co3O4crystallites of 9.5 nm. As expected the reduction behavior of the two series of catalysts was primarily influenced by the Co3O4crystallite size and structure. The FT data of the two series of catalysts indicate that dispersed Co catalysts on alumina nanofibers with large aspect ratios having large inter-crystallite pores significantly improve the catalyst activity and C5+selectivity. The FT data of the 'rearranged' catalysts strongly demonstrated that the internal mass transfer of reactants and products increased with a decrease in inter-crystallite pore size, resulting in a decrease of C5+selectivity and C3olefin/paraffin ratio, and an increase of CH4selectively, while the CO consumption rate was little altered. Furthermore, catalytic stability tests showed that the alumina nanofibers with larger aspect ratios inhibited Co migration and coalescence in the matrices of the nanofibrous alumina, and this significantly enhanced the stability of the catalyst. The Cop/Al2O3-16 catalyst possessing uniformly distributed cobalt, improved reducibility and large pores is the preferred choice to generate high catalytic activity, stability and C5+selectivity.
authors.affiliation: Hubei Key Laboratory of Coal Conversion and New Carbon Material, School of Chemical Engineering and Technology, Wuhan University of Science and Technology, Wuhan 430081, China. wghwang@263.net.
authors.forename: Chengchao
authors.initials: C
authors.lastname: Liu
authors.affiliation: Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission & Ministry of Education, South-Central University for Nationalities, Wuhan 430074, China. jinlinli@aliyun.com.
authors.forename: Yuhua
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission & Ministry of Education, South-Central University for Nationalities, Wuhan 430074, China. jinlinli@aliyun.com.
authors.forename: Yanxi
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: College of Chemistry and Material Science, Guangxi Teachers Education University, Nanning 530001, China.
authors.forename: Liang
authors.initials: L
authors.lastname: Wei
authors.affiliation: Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission & Ministry of Education, South-Central University for Nationalities, Wuhan 430074, China. jinlinli@aliyun.com.
authors.forename: Jingping
authors.initials: J
authors.lastname: Hong
authors.affiliation: Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission & Ministry of Education, South-Central University for Nationalities, Wuhan 430074, China. jinlinli@aliyun.com.
authors.forename: Li
authors.initials: L
authors.lastname: Wang
authors.affiliation: Key Laboratory for Green Chemical Process of Ministry of Education, Hubei Key Laboratory of Novel Reactor and Green Chemical Technology, School of Chemical Engineering and Pharmacy, Wuhan Institute of Technology, Wuhan 430073, China.
authors.forename: Sufang
authors.initials: S
authors.lastname: Chen
authors.affiliation: Hubei Key Laboratory of Coal Conversion and New Carbon Material, School of Chemical Engineering and Technology, Wuhan University of Science and Technology, Wuhan 430081, China. wghwang@263.net.
authors.forename: Guanghui
authors.initials: G
authors.lastname: Wang
authors.affiliation: Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission & Ministry of Education, South-Central University for Nationalities, Wuhan 430074, China. jinlinli@aliyun.com.
authors.forename: Jinlin
authors.initials: J
authors.lastname: Li