Abstract
The physicochemical and catalytic properties of 12-molybdophosphoric acid (HPMo) supported on mixed oxides ZrO 2–SiO 2 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 MoO 3 phases only upon heating. Introduction of ZrO 2 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.
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