Photoreduction and Reoxidation of Platinum Oxide and Palladium Oxide Surfaces

Article abstract of DOI:10.1021/j100412a082

Powdered samples of PtO and PdO were found to reduce at room temperature under vacuum upon irradiation with 253.7-nm radiation from a mercury lamp.The reduction of the oxide particle surfaces was followed by X-ray photoelectron spectroscopy (XPS or ESCA).The photoreduction proceeded slowly through the first few monolayers and was 75percent completed within the sampling depth (ca. 40 Angstroem) after about 10 h of irradiation.The photoreduced metals, Pt and Pd, were observed to slowly reoxidize upon exposure to the atmosphere.This oxidation of the metals at room temperature is remarkable and suggests a unique nature for the photoreduced metallic crystallites.In contrast, metallic Pt and Pd formed by H2 reduction of the oxides at room temperature were not oxidized when exposed to air.Powdered samples of ZnO were not reduced under identical conditions.A model has been developed to explain and to predict the reduction of metal oxide surfaces by UV irradiation.The model suggests that complete or partial reduction of many oxides can be achieved, depending upon the band gap of the oxide being irradiated and the chemical stability of the photoproducts.