Methanol catalytic oxidation over VOx/Al2O3, VOx/ZrO2 and VOx/MgO catalysts has been studied by solid-state nuclear magnetic resonance (NMR) spectroscopy. It was found that stronger acid sites in VOx/Al2O3 result in almostthe same selectivities fordimethoxymethane, paraformaldehyde and formic acid, and weaker acid sites in VOx/ZrO2 favor the formation of paraformaldehyde, while the VOx/MgO catalyst with the base support shows high selectivity for formate. Supporting VOx species on gamma-Al2O3 and ZrO2 leads to the formation of Bronsted acid sites as revealed by the adsorption of probe molecules. The acid strength of Bronsted acid sites on the VOx/Al2O3 catalyst is found to be stronger than that of the VOx/ZrO2 catalyst which has the acid strength similar to zeolite HZSM-5's. The proposed bridging hydroxyl models accounting for the Bronsted acid sites formation were also confirmed by quantum chemical calculation. (c) 2007 Elsevier B.V. All rights reserved.