TEMPERATURE-PROGRAMMED SURFACE-REACTION (TPSR) OF PREADSORBED CARBON CO AND CO H-2 SYNTHESIS OVER RU-CS/AL2O3 CATALYSTS/

A series of silica supported ruthenium-caesium catalysts were prepared by sequential impregnation method, and characterized by total surface area determination, and temperature-programmed surface reaction (TPSR ) of pre-adsorbed CO with H-2 to form mainly methane, The catalytic be haviour of the catalysts prepared was then studied using CO/H-2 synthe sis performed in a continuous flow system operating under differential conditions at atmospheric pressure. TPSR experiments revealed that th e amount of CO adsorbed estimated from methane formed, decreased with the addition of Cs. This was attributed mainly to site blockage, a pur ely geometric effect. The main product of the hydrogenation of the pre -adsorbed CO was methane. Peak temperature of methane shifted to highe r temperatures with Ca doping indicating that methanation proceeds fas ter on Ru/Al2O3 catalyst than on the Cs doped ones. It is suggested th at the addition of Cs lead to a decrease in the rate of CO dissociatio n which is thought to be an essential step in the methanation reaction . Catalytic activity data obtained for the CO/H-2 synthesis indicated that the role of Cs as a catalytic modifier is to limit the methanatio n reaction in preference to hydrocarbon chain growth. It was found tha t the order of reactivity of pre-adsorbed CO towards hydrogenation to methane in TPSR experiments (transient technique) with respect to Cs l oading agreed well with the methanation activity observed in CO/H-2 re action using the continuous flow system ('steady state' activity). Thi s good correlation of relative activities obtained by the two sets of experiments demonstrates the validity of comparing TPSR results with t hose from reaction studies. (C) 1997 Elsevier Science B.V.