The thermal activation of propyl groups on Pt(111)

Abstract

The thermal chemistry of 1‐ and 2‐propyl moieties on Pt(111) was studied by using temperature‐programmed desorption (TPD) and reflection–absorption infrared spectroscopy (RAIRS). The propyl intermediates were prepared via thermal activation of the C–I bond of 1‐ and 2‐iodopropane adsorbed precursors, respectively. It was determined that the subsequent thermal activation of those propyl groups results in a competition between reductive elimination to propane, β‐hydride elimination to propene, and complete decomposition to propylidyne (and eventually to hydrogen and surface carbon). It was found that while the 2‐propyl intermediate favors propene production, 1‐propyl also yields significant amounts of propane. The formation of propene via β‐hydride elimination was identified by isotopic labeling TPD experiments, and directly about 200 K by RAIRS. Coadsorption experiments with hydrogen and deuterium were used to characterize hydrogenation and H–D reactions. All possible propene and propane isotopomers are formed from both 1‐ or 2‐iodopropane on the D/Pt(111) surface, indicating that exchange is likely to occur via a cyclic propyl–propene–propyl mechanism involving the formation of both 1‐ and 2‐propyl intermediates. Relative rates for 1‐ versus 2‐propyl conversion were estimated.