VPO catalysts supported on ZrO2 and H3PO4-treated ZrO2 were prepared for the first time by means of precipitation-deposition in an organic medium. The physicochemical properties of the catalysts were investigated by the BET, XRD, TEM, Raman, XPS, and H-2-TPR techniques. It was found that the way of H3PO4 treatment conducted on ZrO2 has a significant effect on the nature of the support, as well as on the state and structure of the VPO component loaded on it. The discrepancies in the synergistic interaction between VPO and the different supports induce variation in catalytic performance. The change in VPO loading is found to have an effect on catalyst efficiency. At 673 K, the MA yield is 61 mol% over the 36%VPO/(H3PO4)-p-ZrO2 catalyst, the best performance achieved so far among the supported VPOs. (c) 2006 Elsevier Inc. All rights reserved.