Producing metal oxide catalysts with nanometer crystal sizes offers an attractive means of controlling catalytic behavior in selective oxidation reactions. In this work, the catalytic behavior of MgO nanocrystal-supported vanadium was compared to that of vanadium supported on conventionally prepared MgO. It was found that nanocrystals gave higher butene selectivity for weight loadings of 5, 15, and 25%, producing less CO, ethylene, and propylene. Both types of catalysts were characterized using nitrogen adsorption, Raman spectroscopy, XRD, TEM, and XANES to determine the structure of vanadium on the magnesium oxide surface. The catalyst surface structure appears to be similar on both types of catalysts, with a magnesium orthovanadate phase supported on a MgO phase. It is hypothesized that the chemical nature of the support, specifically acid/base properties, was responsible for the differences noted in catalytic behavior, though differences in the domain size of Mg-3(VO4)(2) could also play a role. (C) 2003 Elsevier Inc. All rights reserved.