Promoted Decomposition of Methanol by Preadsorbed Atomic Oxygen on Ir(100)

The effect of surface atomic oxygen (O*; * denotes adspecies) on decomposition of methanol (CH3OH) on the Ir(100) surface was investigated with varied surface probe techniques and density functional theory (DFT) calculations. Adsorbed methanol on Ir(100) underwent preferentially the initial O–H bond scission to form CH3O* as the major intermediate, and the reaction subsequently proceeded through three competing pathways: hydrogenated to CH3OH* and desorbed, dehydrogenated to CO*, or cleaved the C–O bond to yield CH3*, which dehydrogenated further to C*. The overall decomposition probability attained 60%, with ultimate gaseous products of H2, H2O, and CO. The presence of O* on Ir(100) enhanced the reactivity and altered the reaction pathway. The O*-induced hydrogen bond decreased the dehydrogenation barriers, suppressed the recombinative desorption of CH3OH, and limited the scission of the C–O bond. The decomposition probability was thus promoted, up to nearly 100%, and the major poisoning species C* was significantly reduced. Although the O* promoted the reaction, its site-effect capture of H* shifted the production from H2 to H2O. Consequently, the maximal production of H2 per adsorbed methanol was found to be near the half-saturated O* coverage.