Catalytic decomposition of methanols over platinum and ruthenium

Abstract

The decomposition kinetics of CH₃OH, CH₃OD and CD₃OH have been studied over platinum and ruthenium catalysts in the temperature range 70–250°C. The reaction over platinum yielded mainly carbon monoxide and hydrogen and the rates showed a marked kinetic isotope effect, whereas ruthenium was much more active giving high yields of methane. The distribution of products from the decomposition of the deuterated methanols on ruthenium suggested that the radical CH₂ may be a surface intermediate with this metal. With platinum, the rate-determining step in the initial stages may involve dissociation of an adsorbed CH₃O intermediate, although chemisorbed CO inhibits the later course of the reaction. At temperatures above about 155°C the addition of ruthenium to a platinum catalyst increased the rate of CO formation from CH₃OH, although the more rapid methanation reaction became dominant with alloy catalysts containing 30 % ruthenium and above. This abrupt change of mechanism may be used to obtain information on the composition of the alloy surface.