Modified alumina supports for cobalt Fischer-Tropsch catalysts

The effect of promotion with zirconia on alumina supported cobalt FT-catalysts has been studied. The promoted catalysts show an increase in activity by up to 50 % compared to the unpromoted systems in CO hydrogenation at 5 bar total pressure. The zirconia is introduced as an addition to the support before impregnating with the active metal. For a constant zirconia loading the activity increases with increasing cobalt loading. The increase is asymptotic towards high cobalt loadings as opposed to the unpromoted catalysts which show a linear dependency with cobalt amount. No increase in the cobalt reducibility is observed with TPR-experiments. Neither does hydrogen chemisorption detect any increase in the cobalt dispersion. SSITKA data recorded at low pressure reveals that the overall gain in the catalytic activity is due to an increased coverage with reactive intermediates, and is not caused by an increase of the intrinsic turnover frequency.