Methanol decomposition on Pt/ZnO(0001)-Zn model catalysts

The relationship between metal particle structure and the reactivity and se lectivity of oxide-supported metal catalysts has been explored here with we ll-defined Pt particles on the Zn-terminated ZnO(0001)-Zn surface, using X- ray photoelectron spectroscopy (XPS), ion scattering spectroscopy (ISS), an d temperature-programmed desorption (TPD). These are model catalysts for th e steam reforming and selective dehydrogenation of methanol. Vapor-deposite d Pt on ZnO(0001) grows in two-dimensional (2D) islands up to similar to0.7 ML. The effect of the 2D island size and 3D island height are studied. Even 0.01 ML of Pt suppresses the dissociative adsorption of methanol to methox y on Zn sites by preferential decoration of defects. Tiny amounts of Pt als o affect the selectivity of methanol conversion at the Zn sites: the dehydr ation pathway of its Zn-bound formate intermediate is suppressed and its de hydrogenation pathway to formaldehyde is eliminated. Even Pt sites on 2D Pt islands catalyze the partial oxidation of methanol to CO and H-2. characte ristic of low-index Pt facets. When the Pt islands are 2-3 layers thick. me thanol decomposition is similar to that on low-index Pt faces.