Hydrogen spillover in the Fischer–Tropsch synthesis: an analysis of gold as a promoter for cobalt–alumina catalysts

This study investigated the operation of gold as a potential substitute for the platinum promoter in the Co/Al₂O₃Fischer–Tropsch catalyst. Au–Co/Al₂O₃was tested in conjunction with a model Hybrid Au–Co sample (comprised of a mechanical mixture of Au/Al₂O₃ + Co/Al₂O₃) to investigate hydrogen spillover which has been demonstrated to play a vital role in the reduction promotion mechanism. TPR, TGA and in situ XRD provided evidence to support the improved reducibility of supported cobalt oxide crystallites in Au–Co/Al₂O₃. However, no improvement in the reducibility of the Hybrid Au–Co catalyst was observed, in contrast to previous studies on noble metal reduction promoters. It was hypothesized that even though gold-to-cobalt spillover occurred during reduction in Au–Co/Al₂O₃, the great separation between the gold and cobalt crystallites, combined with gold's much lower affinity for hydrogen activation adversely affected the efficiency of the spillover process in the hybrid sample. Nevertheless, Au–Co/Al₂O₃had an improved mass-based activity, and a turnover frequency comparable to a platinum promoted sample, which highlighted the potential of gold as a reduction promoter for Co/Al₂O₃catalysts.