Reduction of supported and unsupported palladium oxide catalysts using methane. Characterization of active oxides

Abstract

Palladium oxide and TiO₂-supported palladium oxide, prepared by the deposition–precipitation technique were reduced using CH₄ at temperatures greater than 300 °C. Other oxides, such as PtO₂, PtO_x/TiO₂, Co₃O₄/TiO₂ and Fe₂O₃ were also used. These oxides showed varying degrees of reduction. During reduction, CH₄ was oxidised and the reaction products (CO, CO₂, H₂O_(g) and H₂) were identified by gas chromatography. The results indicate that CH₄ is capable of causing deep-level redox reactions in the bulk by diffusing through the catalyst surface. Palladium and platinum oxides were found to be suitable materials for such reduction treatments. The most active catalysts were characterized by diffuse reflectance spectroscopy (DRS), elemental analysis, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Formation of Pd with different oxidation states was noted on the surface of the reduced catalyst. Unlike Pd-based catalysts, PtO₂/TiO₂ samples showed a stabilisation of Ti³⁺ on the catalyst surface.