Adsorption of propylene oxide on Pt(111) surfaces and its reactions with gaseous and adsorbed H atoms

Adsorption of propylene oxide (PO) on Pt(111) surfaces and its reactions with gaseous and coadsorbed hydrogen atoms was studied using TDS and HREELS methods. PO adsorbs molecularly and desorbs from the multilayer and monolayer states near 130 and 180 K, respectively. Monolayer PO is bound through the O atom to the Pt surface. Approximately 50% of the monolayer PO molecules dissociate near 180 K leading to desorption of CO and H2 above 250 K. The initial step of the PO dissociation is cleavage of the COC ring. Reactions of gaseous H atoms with PO monolayers on Pt(111) lead to the formation of acetone, n-propanol, and isopropanol. The branching of the reactions toward the products changes with the H atom exposure as the coadsorption of hydrogen weakens the PO/Pt(111) interaction, illustrating the influence of the metallic substrate on the reaction paths in atom/adsorbate reactions. Coadsorbed PO and hydrogen react toward a strongly bound acetone species, probably η2-acetone, with a selectivity of 100%.