The effects of the nature of silica support and removal of soluble vanadium species by ethanol on the catalytic properties of silica-supported VPO catalysts were investigated. Ethanol preferentially removes V+5 species. For a silica-supported sample of PIV ratio much lower than two, ethanol treatment resulted in a sample of higher PIV ratio and higher selectivity for maleic anhydride in butane oxidation. The crystalline VPO phases formed differed on a hydrophobic vs. hydrophilic silica. (VO)(2)P2O7 could be formed more easily on the former support. interestingly, for all silica-supported catalysts, the maleic anhydride selectivity depended much more strongly on the PIV ratio than on the method of preparation, the nature of the silica, or the crystalline VPO phase present.