Effect of calcination atmosphere and temperature on γ-Al2O3 supported cobalt Fischer-Tropsch catalysts

Abstract

The effect of calcination temperature and atmosphere on the properties of c-Al2O3 supported cobalt Fischer-Tropsch catalysts has been investigated. One common precursor for all the catalysts was prepared by incipient wetness impregnation of c-Al2O3 with an aqueous solution of cobalt nitrate hexahydrate. It was subjected to four different calcination atmospheres (air/50% steam: 30 mL/min, air: 30 mL/min, air: 50 mL/min, N2: 30 mL/min) and eight different calcination temperatures (range: 473–723 K), making the total number of samples 32. Both the post calcination nitrogen content and the cobalt dispersion were measured. The results demonstrated that in order to maximise the cobalt dispersion, it is necessary to use low calcination temperatures and remove the precursor decomposition products (NO, NO2 ,H 2O) efficiently. The Fischer-Tropsch synthesis performance of two catalysts calcined at the same temperature, but at different air flow rates was evaluated. No significant effect of the air flow rate was found on the turnover frequency or C5+ selectivity, but a high flow rate resulted in 30% higher activity per gram catalyst.