Temperature-programmed surface reaction (TPSR) of pre-adsorbed carbon CO and [formula omitted] synthesis over [formula omitted] catalysts

Abstract

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 behaviour of the catalysts prepared was then studied using CO H 2 synthesis performed in a continuous flow system operating under differential conditions at atmospheric pressure. TPSR experiments revealed that the amount of CO adsorbed estimated from methane formed, decreased with the addition of Cs. This was attributed mainly to site blockage, a purely geometric effect. The main product of the hydrogenation of the pre-adsorbed CO was methane. Peak temperature of methane shifted to higher temperatures with Cs doping indicating that methanation proceeds faster on Ru Al 2O 3 catalyst than on the Cs doped ones. It is suggested that the addition of Cs lead to a decrease in the rate of CO dissociation 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 methanation reaction in preference to hydrocarbon chain growth. It was found that the order of reactivity of pre-adsorbed CO towards hydrogenation to methane in TPSR experiments (transient technique) with respect to Cs loading agreed well with the methanation activity observed in CO H 2 reaction using the continuous flow system (‘steady state’ activity). This good correlation of relative activities obtained by the two sets of experiments demonstrates the validity of comparing TPSR results with those from reaction studies.