Novel approach to rhenium oxide catalysts for selective oxidation of methanol to DMM

Novel rhenium oxide catalysts have been prepared by impregnation of mesoporous TiO2-anatase support using amounts of homometallic, such as Re4O4(OEt)12, and heterometallic, such as Ta4O2(OEt)14(ReO4)2, rhenium alkoxide solutions with subsequent thermal treatment. The structure of the produced catalytic centers was investigated by X-ray diffraction, XPS, and IR spectroscopy in order to examine the role of Re in enhancing catalytic activity. It has been demonstrated that rhenium is mostly present as perrhenate ligands attached via an oxo-bridge to an oxide surface. The catalytic activity was studied for the selective oxidation of methanol as model reaction, revealing selectivity strongly dependent on the nature of the molecular precursor: in case of ReOx/TiO2, the catalysts are showing selectivity to formaldehyde, and in case of ReOx/Ta2O5/TiO2 to DMM in rich conditions.