Effect of pretreatment on the activity of a Ru-promoted Co/Al2O3 Fischer-Tropsch catalyst

The effect of calcination and reduction temperatures on the activity of a Ru-promoted Co/Al2O3 catalyst for the CO hydrogenation reaction has been studied. The catalyst was prepared by the incipient wetness impregnation method and calcined and reduced at various temperatures. Along with overall steady-state rate analysis, steady-state isotopic transient kinetic analysis was used to investigate the effect of the pretreatment conditions on the intrinsic activity and coverages of surface intermediates. Catalyst characterization techniques such as XRD, TPR, and hydrogen chemisorption were also used. The calcination temperature was found to have a pronounced effect on the overall activity of the catalyst but not on the intrinsic activity of the catalyst sites. On the other hand, the reduction temperature had only a negligible effect on the overall and intrinsic activities. The decrease in rate at high calcination temperatures was caused by a decrease in the number of surface active sites due to a decrease in the reducibility of the catalyst. Neither the reduction nor the calcination conditions had any effect on chain growth probability. Calcination temperature did have, however, a small effect on CH4 selectivity. (C) 1997 Academic Press.