摘要
A new hierarchical composite consisted of multi-walled carbon nanotubes （CNTs） layer anchored on macroscopic a-A1203 host matrix was synthesized and used as support for Fischer-Tropsch synthesis （FTS）. The composite constituted by a thin shell of a homogeneous, highly entan-gled and structure-opened carbon nanotubes network and it exhibited a relatively high and fully accessible specific surface area of 76 m2.g-1, compared with that of 5 m2.g-1 of the original a-A1203support. The metal-support interaction between carbon nanotubes surface and cobalt precursor and high effective surface area led to a relatively high dispersion of cobalt nanoparticles. This hierarchically supported cobalt catalyst exhibited a high FTS activity along with an extremely high selectivity towards liquid hydrocarbons compared with the cobalt-based catalyst supported on pristine a-A1203 or on CNTs carriers. This improvement can attribute to the high accessibility of composite surface area com- paring with the macroscopic host structure alone or to the bulk CNTs where the nanoscopic dimension induced a dense packing with low mass transfer which favoured the problem of reactants competitive diffusion towards the cobalt active site. In addition, intrinsic thermal conductivity of decorated CNTs could help the heat dissipating throughout the catalyst body, thus avoiding the formation of local hot spots which appeared in high CO conversion under pure syngas feed in FTS reaction. Cobalt supported on CNTs decorated a-A1203 catalyst also exhibited satisfied high stability during more than 200 h on stream under relatively severe conditions compared with other catalysts reported in the literature. Finally, the macroscopic shape of such composite easily rendered its usage as catalyst support in a fixed-bed configuration without facing problems of transport and pressure drop as encountered with the bulk CNTs.
A new hierarchical composite consisted of multi-walled carbon nanotubes （CNTs） layer anchored on macroscopic a-A1203 host matrix was synthesized and used as support for Fischer-Tropsch synthesis （FTS）. The composite constituted by a thin shell of a homogeneous, highly entan-gled and structure-opened carbon nanotubes network and it exhibited a relatively high and fully accessible specific surface area of 76 m2.g-1, compared with that of 5 m2.g-1 of the original a-A1203support. The metal-support interaction between carbon nanotubes surface and cobalt precursor and high effective surface area led to a relatively high dispersion of cobalt nanoparticles. This hierarchically supported cobalt catalyst exhibited a high FTS activity along with an extremely high selectivity towards liquid hydrocarbons compared with the cobalt-based catalyst supported on pristine a-A1203 or on CNTs carriers. This improvement can attribute to the high accessibility of composite surface area com- paring with the macroscopic host structure alone or to the bulk CNTs where the nanoscopic dimension induced a dense packing with low mass transfer which favoured the problem of reactants competitive diffusion towards the cobalt active site. In addition, intrinsic thermal conductivity of decorated CNTs could help the heat dissipating throughout the catalyst body, thus avoiding the formation of local hot spots which appeared in high CO conversion under pure syngas feed in FTS reaction. Cobalt supported on CNTs decorated a-A1203 catalyst also exhibited satisfied high stability during more than 200 h on stream under relatively severe conditions compared with other catalysts reported in the literature. Finally, the macroscopic shape of such composite easily rendered its usage as catalyst support in a fixed-bed configuration without facing problems of transport and pressure drop as encountered with the bulk CNTs.
基金
the China Scholarship Council (CSC) for the PhD grant during his stay at the LMSPC
