Methanol partial oxidation on Cu–Zn thin films grown on Ni(1 0 0) surface

Abstract

Methanol partial oxidation on Cu–Zn thin films epitaxially grown on Ni(1 0 0) surface has been investigated in an ultra high vacuum (UHV) system combined with a high-pressure reaction cell. According to temperature programmed reaction (TPR) and temperature programmed desorption (TPD) in UHV, surface reaction between methanol and pre-adsorbed oxygen on epitaxially grown Cu thin films mainly produced H 2 and CO together with HCHO, although addition of Zn greatly suppressed the formation of HCHO. Annealing of the thin films at 420 K prior to admission of methanol and oxygen reactants dramatically accelerated reaction rate of CO 2 product and the maximum formation of H 2 and CO 2 was observed on the surface of 1 ML Cu with 0.25 ML Zn. On the contrary, the rate of methanol partial oxidation in the high-pressure reaction cell monotonously increased with the thickness of Cu films up to 3 ML. The addition of 0.25 ML Zn increased the reaction rate independent of Cu film thicknesses of 1–6 ML. Post-reaction surface analysis showed Cu agglomeration on the Ni substrate. Cu 2p X-ray photoelectron spectroscopy (XPS) and LMM Auger data reveal the presence of Cu + species in addition to metallic Cu atoms abundant in the films corresponding to the higher reactivity. It is proposed that the oxidation number of Cu is controlled by oxided Zn in Cu–Zn alloy.