Steady state isotopic transient kinetic analysis (SSITKA) of CO hydrogenation on different Co catalysts

Cobalt Fischer-Tropsch catalysts with different supports, promoters, cobalt loading and surface area have been characterised under methanation conditions (483 K, 1.85 bar, H-2/CO = 10) by steady state isotopic transient kinetic analysis (SSITKA). The catalysts have previously been studied under Fischer-Tropsch conditions and they show large differences in overall activity and selectivity. However, the intrinsic site activity measured from SSITKA is essentially the same for all the catalysts. The catalysts vary in the number of available active surface sites, and the difference in overall activity can be attributed to a change in the number of surface active intermediates, either by a change in coverage or a change in total number of active surface sites. In addition, in situ CO chemisorption at 373 K has been done to confirm the number of surface sites determined by H-2 chemisorption. The CO chemisorption at 373 K gives approximately the same number of surface sites provided that CO adsorbs by covering two adsorption sites, i.e. either dissociatively or by bridge bonding. (c) 2005 Elsevier B.V. All rights reserved.