Infrared Investigation of the Adsorption and Reactions of Methanol on V₂O₅/TiO₂Catalysts

The oxidation of methanol on a V₂O₅/TiO₂ monolayer catalyst was studied by infrared spectroscopy using transmittance and diffuse-reflectance cells. Methanol was adsorbed on the catalyst surface at room temperature to form methoxy groups. Upon heating to 150 °C, these groups were oxidized to oxymethylene species. The latter species were also formed by adsorption of formaldehyde. When nitrogen saturated with methanol vapor was passed over the catalyst continuously at 150 °C, methoxy, oxymethylene, and formate groups were formed successively. Formaldehyde, methyl formate, dimethoxymethane, and CO were detected simultaneously in the gas phase. When the gas stream was stopped, the formation of these products did not stop immediately; this indicates that the observed surface species are reaction intermediates. On the basis of these results, a mechanism is proposed for the reaction. The results are also compared with those obtained with TiO₂alone; it is concluded that the different oxidation behavior of the support alone is due to different strengths of the C-H bond of the methoxy groups when adsorbed on the support and on the V₂O₅/TiO₂surface.