Methanol oxidation on sputter-coated platinum oxide catalysts

Abstract

Platinum oxide (PtOx) and metallic platinum (Pt) layers deposited by means of radio frequency (rf) magnetron sputtering were examined as potential catalysts for partial oxidation of methanol (POM) reaction (CH3OH + 1/2O2 → 2H2 + CO2) under realistic conditions. Flat Si(100) support and oxygen-plasma etched amorphous carbon films (a-C) were used as substrates for PtOx. Elemental composition and morphology of the catalysts were characterized by x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). XPS analysis of PtOx demonstrates change in its chemical state during the reaction leading to metallic layer with small amounts of stable Pt2+ cations which turns out to be crucial for its catalytic properties, while SEM reveals significant cracking and roughening of the oxide thin films. A reference Pt/Si catalyst, on the contrary, shows no significant differences prior and after the methanol oxidation reaction but lacks to PtOx in both activity (in terms of H2 production rate) and selectivity for POM, generating relatively high amounts of CO which can poison the catalyst surface. PtOx deposited on the porous a-C outperforms the same oxide grown directly on Si, especially in its POM selectivity exceeding 90%. Both oxidic systems, however, require an initial conditioning under real reaction conditions to reach their optimal catalytic capability.