Step effects in the thermal decomposition of methanol on Pt(111)

Abstract

Methanol decomposition to adsorbed CO and hydrogen on Pt(111) was observed using time-resolved high resolution electron energy loss spectroscopy. No reaction was seen at temperatures ≲ 180 K, the molecular methanol desorption temperature. Between 180 and 200 K the decomposition reaction is controlled by the small amount of defects present on our carefully prepared sample. This was principally demonstrated by the fact that only 1–2% of a monolayer of CO was formed regardless of the initial methanol coverage. A steady state reaction run between 200 and 240 K showed only a low rate of CO formation (only a few percent of a monolayer even after many langmuir exposure of methanol). At a 300 K surface temperature, decomposition proceeds much faster, with about 10% of a monolayer of CO being formed. The origin of this temperature dependence is attributed to the ability of the product H and CO to diffuse away from sites where they were initially formed. Using a He seeded methanol beam, there was no apparent incident energy dependence for the methanol decomposition reaction.