Silicon carbide foam composite containing cobalt as a highly selective and re-usable Fischer-Tropsch synthesis catalyst

摘要

The Fischer-Tropsch synthesis was evaluated on cobalt based catalyst supported on a medium surface area SiC foam ceramic in a fixed-bed configuration. The catalytic results were compared with those obtained on a C0/Al2O3 foam catalyst. At medium conversion (<50%) the two catalysts display similar C_(5+) selectivity indicate that the intrinsic selectivity between the two catalysts is close from each other. However, when the CO conversion was increased to 70%, a significant difference in terms of the C_(5+) selectivity was observed between the two catalysts, i.e. 80% on the Co/SiC and 54% on the Co/Al2O3, which indicate that under severe FTS reaction conditions the SiC seems to be more suitable support than alumina. It is also worth to note that under these reaction conditions the chain length probability, α, obtained on the SiC-based catalyst was 0.91 and wax formation was especially favoured. The improvement of the C_(5+) selectivity observed on the SiC catalyst was attributed to the high efficiency of the support to evacuate heat generated during the course of the reaction owing to it higher thermal conductivity and also to the presence of meso- and macro-porosity of the support. Additional catalytic test conducted on a hybrid support, i.e. Al2O3 coated SiC foam, again confirms the high C_(5+) selectivity under a similar severe reaction conditions in the presence of a SiC structure underneath of the alumina layer which play a role of heat disperser. In addition, the high chemical inertness of the SiC material also allows one to perform an easy recovery of both the active phase and the support by a simple acid washing. The recovered SiC support was further impregnated with a fresh cobalt phase and re-tested in the FTS and the catalytic results are compared with those of the former catalyst. The same product yield was obtained which confirms the potential of SiC to be employed as a re-usable support.