Supported Tantalum Oxide Catalysts: Synthesis, Physical Characterization, and Methanol Oxidation Chemical Probe Reaction

Abstract

Supported tantalum oxide catalysts on Al2O3, TiO2, ZrO2, and SiO2 supports were prepared by the incipient wetness impregnation method. The catalysts were characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and X-ray absorption near edge structure (XANES) under hydrated and dehydrated conditions. The Al2O3-, TiO2-, and ZrO2-supported tantalum oxide catalysts possess similar surface TaOx molecular structures, consisting primarily of polymerized surface TaO5/TaO6 species at high surface coverage. The surface Ta atom density at monolayer coverage are also similar and were found to be 4.5, 6.6, and 6.3 Ta atoms/nm2 on the Al2O3, TiO2, and ZrO2 supports, respectively. The SiO2-supported tantalum oxide catalyst is very different and consists of isolated TaO4 species with a much lower maximum surface Ta density, 0.7 Ta atoms/nm2, due to the lower concentration and reactivity of the silica hydroxyls. The catalytic properties of the surface TaOx species were chemically probed with the metha...