Hydrogen production via methanol oxidation on platinum oxide thin film catalyst: Influence of methanol-to-oxygen ratio

Platinum oxide (PtOx) thin films deposited by means of radio frequency (rf) magnetron sputtering on oxidized Si substrate were investigated under realistic conditions as efficient catalysts promoting oxidation of methanol to produce hydrogen. The main focus was given to the role of reactant mixture (methanol + oxygen) composition at different surface temperatures. Freshly deposited PtOx changes its chemical state and morphology during the initial reaction leading to strongly corrugated metallic Pt layer with small amounts of stable Pt2+ cations providing a crucial ingredient for its specific catalytic properties. With growing temperature or methanol-to-oxygen molar ratio the reaction selectivity of such catalyst generally shifts from pathways producing water to those generating hydrogen. The efficiency for a given reaction route can be thus maximized via independent tuning of the fuel-oxygen ratio and surface temperature. The most intensive hydrogen evolution with the lowest relative amount of CO by-product (but relatively high abundance of methanolic residuals) was achieved with mildly oxygen lean feed above 500 K. The highest selectivity for partial oxidation of methanol pathway (>80%) can be, on the other hand, obtained with stoichiometric or oxygen rich mixture.