The molecular designed dispersion (MDD) method was used for the modification of SBA-15 with vanadium oxide. Vanadyl acetylacetonate was grafted on the support surface at different VO(acac)(2) concentrations in a toluene solution, and then converted into the VOx/SBA-15 catalysts at elevated temperatures. The thermal transformation of surface species was studied by FTIR-PAS spectroscopy. The obtained materials were characterized with respect to their texture (BET), metal dispersion (FT-Raman and UV-vis-DR) and reducibility (H-2-TPR). It was found that only isolated V5+ species were present in the samples with a low V loading. The catalyst with the highest V content showed the presence of polymeric V5+ species, which appeared to be easier reducible compared to the isolated form of V. The VOx/SBA-15 samples were tested as catalysts in the oxidative dehydrogenation of ethylbenzene to styrene in the presence of N2O. An increase in the catalytic activity with raising the V content was observed. It was however prove that monomeric V5+ species were considerably more active and selective in the styrene formation than oligomeric ones. (c) 2006 Elsevier B.V. All rights reserved.