Formaldehyde decomposition and oxidation on Pt(110)

Abstract

The decomposition reactions of formaldehyde on clean and oxygen dosed Pt(110) have been studied by LEED, XPS and TPRS. Formaldehyde is adsorbed in two states, a monolayer phase and a multilayer phase which were distinguishable by both TPRS and XPS. The saturated monolayer (corresponding to 8.06 × 10 14 molecules cm −2) desorbed at 134 K and the multilayer phase (which could not be saturated) desorbed at 112 K. The only other reaction products observed at higher temperatures were CO and H 2 produced in desorption limited processes and these reached a maximum upon saturation of the formaldehyde monolayer. The desorption spectrum of hydrogen was found to be perturbed by the presence of CO as reported by Weinberg and coworkers. It is proposed that local lifting of the clean surface (1 × 2) reconstruction is responsible for this behaviour. Analysis of the TPRS and XPS peak areas demonstrated that on the clean surface approximately 50% of the adsorbed monolayer dissociated with the remainder desorbing intact. Reaction of formaldehyde with preadsorbed oxygen resulted in the formation of H 2O (hydroxyl recombination) and CO 2 (decomposition of formate) desorbing at 200 and 262 K, respectively. The CO and H 2 desorption peaks were both smaller relative to formaldehyde decomposition on the clean surface and in particular, H 2 desorbed in a reaction limited process associated with decomposition of the formate species. No evidence was found for methane or hydrocarbon evolution in the present study under any circumstances. The results of this investigation are discussed in the light of our earlier work on the decomposition of methanol on the same platinum surface.