Methanol oxidation over ZrO2–SiO2 supported phosphomolybdic acid Original Research Article

The physicochemical and catalytic properties of 12-molybdophosphoric acid (HPMo) supported on mixed oxides ZrO2–SiO2 have been investigated. The samples were characterised by X-ray diffraction (XRD), Raman and X-ray photoelectron (XPS) spectroscopic techniques, and temperature programmed reduction (TPR). The effect of both the pre-treatment temperature and the zirconium content on the catalytic behaviour of the samples in methanol oxidation was investigated. A significant decrease in the total activity of HPMo supported on silica was related to the disappearance of the Brönsted acid centres of HPMo and their transformation into MoO3 phases only upon heating. Introduction of ZrO2 into the supports led to a change in the catalytic character from acidic to redox. A correlation between the reducibility of molybdenum oxide species and activity was found; the less reducible catalyst showed higher activity as determined by the redox properties. TPR and XPS data revealed that the dispersion of molybdenum oxide species increases with Zr-loading and the calcination temperature.