Abstract
Thin films of pristine and platinum-doped tungsten oxide were examined as potential catalysts for efficient partial oxidation of methanol. The tungsten oxide layers with different thicknesses were deposited by the means of reactive magnetron sputtering on oxidized silicon wafer and silicon coated with carbon activated via ion etching.
Morphology and chemical analysis were checked before and after the reaction by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). It was found that while pure tungsten oxide layers on silicon exhibit relatively small hydrogen production rates and high ratio of carbon oxides, both etched carbon interlayer (as long as the oxide thickness is low enough) and platinum doping can lead to significant improvement of reactivity, increasing hydrogen yield and decreasing fraction of undesired carbon monoxide in the product mix.
It is suggested that it is due to the strong electronic interaction between WOx and Pt or active C, increasing the acidity of the tungsten oxide reaction sites and thus altering its reactivity preference from methanol dehydration towards dehydrogenation. If both species are present in a very thin oxide, however, the competing electronic interactions lead to partial reduction of their positive effect.
As prepared sputtered thin films are chemically and morphologically unstable under reducing environment of methanol oxidation reaction, but the presence of dispersed Pt in the layer substantially stabilizes its physical structure.