Effect of support and promoter on the coadsorption of carbon monoxide and hydrogen on Fischer–Tropsch cobalt catalysts

Abstract

Two cobalt Fischer–Tropsch catalysts of composition Co: kieselguhr = 100 : 200 (A) and Co: ThO₂: kieselguhr = 100 : 18 : 200 (B) have been investigated with respect to the adsorption of CO and hydrogen by temperature-programmed desorption (t.p.d.) and infrared (i.r.) techniques. Although CO preadsorption is known to inhibit subsequent hydrogen adsorption, a considerable amount of hydrogen (30 µmol g^–1 on catalyst A and 50 µmol g^–1 on catalyst B) adsorption has been observed on the CO-presaturated surface of these two catalysts, indicating the possibility of adsorption of hydrogen on support materials by a spillover process and/or the formation of surface complex species. T.p.d. and i.r. studies favour the formation of a surface complex between CO and hydrogen, and such complex formation is highly favoured when hydrogen is preadsorbed. The presence of thoria (a promoter) enhances hydrogen adsorption, making complex formation more favourable on catalyst B than on catalyst A.