CoAl spinel oxide modified ordered mesoporous alumina supported cobalt-based catalysts for Fischer-Tropsch synthesis

A series of CoAl spinel oxide modified ordered mesoporous alumina with different CoAl2O4 contents were synthesized by a facile one-pot evaporation induced self-assembly (EISA) method. Then they were first investigated as supports for Cobalt-based catalysts for Fischer-Tropsch synthesis (FTS). The results from testing the catalysts clearly showed that the catalysts modified with CoAl2O4 exhibited higher catalytic activity than the common ordered mesoporous alumina catalysts. A volcano-type dependence of the catalytic activity with the contents of CoAl2O4 in the supports was observed. The results from in situ XRD revealed that the cobalt phase of the reduced catalysts modified with CoAl2O4 were more likely to be HCP rather than FCC. As inferred from in situ CO-FTIR and CO-TPD results, the CO dissociation ability was enhanced by increasing the content of the CoAl2O4 modification in the supports. Such a volcano-type dependence of catalytic activity with the contents of CoAl2O4 in the supports was due to the combination of two factors. One was the generation of the HCP cobalt, which exhibited a higher CO dissociation ability. The other was the synergistic effect of lower reducibility and the degree of dispersion. Meanwhile, when the Co/Al ratios was 0.08 and 0.12 in the supports, the catalysts showed higher C5+ selectivity than other catalysts, which was mainly due to their high Co site density on the catalysts surface.