Silica nanotubes(SNT) have been synthesized using carbon nanotubes(CNT) as a template.Silica-coated carbon nanotubes(SNT-CNT) and SNT were loaded with a cobalt catalyst for use in Fischer-Tropsch synthesis(FTS).The catalysts were prepared by incipient wetness impregnation and characterized by N2 physisorption,X-ray diffraction(XRD),hydrogen temperature programmed reduction(H2-TPR) and transmission electron microscopy(TEM).FTS performance was evaluated in a fixed-bed reactor at 493 K and 1.0 MPa.Co/CNT and Co/SNT catalysts showed higher activity than Co/SNT-CNT in FTS because of the smaller cobalt particle size,higher dispersion and stronger reducibility.The results also showed that structure of the support affects the product selectivity in FTS.The synergistic effects of cobalt particle size,catalytic activity and diffusion limitations as a consequence of its small average pore size lead to medium selectivity to C5+ hydrocarbons and CH4 over Co/SNT-CNT.On the other hand,the Co/CNT showed higher CH4 selectivity and lower C5+ selectivity than Co/SNT,due to its smaller average pore size and cobalt particle size.
This paper studies the impact of structure of cobalt catalysts supported on carbon nanotubes(CNT) on the activity and product selectivity of Fischer-Tropsch synthesis(FTS) reaction.Three types of CNT with average pore sizes of 5,11,and 17 nm were used as the supports.The catalysts were prepared by selectively impregnating cobalt nanoparticles either inside or outside CNT.The TPR results indicated that the catalyst with Co particles inside CNT was easier to be reduced than those outside CNT,and the reducibility of cobalt oxide particles inside the CNT decreased with the cobalt oxide particle size increasing.The activity of the catalyst with Co inside CNT was higher than that of catalysts with Co particles outside CNT.Smaller CNT pore size also appears to enhance the catalyst reduction and FTS activity due to the little interaction between cobalt oxide with carbon and the enhanced electron shift on the non-planar carbon tube surface.
Ru nanoparticles with different sizes confined in the cavities of mesoporous SBA-16 have been successfully synthesized by incipient wetness impregnation method with a Ru loading of 4 wt%. The catalysts were characterized by XRD, N2 adsorption-desorption, H2-TPR, H2-TPD, O2-titration and TEM. The catalytic performance of Fischer-Tropsch synthesis over the catalyst was tested in a fixed-bed reactor. The addition of citric acid in the impregnation procedure shows a significant influence on the size of Ru nanoparticles. The selectivity to C5＋ increases, while the selectivities to methane and C2-C4 light hydrocarbons decrease with Ru average particles size from 2.0 nm to 9.3 nm, . The Ru catalyst confined in the SBA-16 with average nanoparticle size of 5.3 nm gives the best activity.
Jian ChenJinlin LiYanxi ZhaoYuhua ZhangJingping Hong
