The preparation of a series of mobium-based aerogel samples under acidic and basic conditions is reported. The effect of the matrix (SiO2, Al2O3, ZrO2) and of the gelation conditions (acidic or basic) on the surface area, the porosity, and the catalytic activity of the solids in the oxidation of different substrates with hydrogen peroxide is investigated. The amount of niobium is constant in all samples. The oxidation of unsubstituted (cyclooctene) and substituted (geraniol, nerol, and trans-2-pentene-1-ol) olefins is studied. The catalysts are moderately active but produce epoxides in good yields. The latter are influenced by the matrix properties (surface acidity and surface area). The preparation method makes it possible to prepare catalysts that are resistant to leaching and can be recycled several times without appreciable loss of activity. (C) 2004 Elsevier Inc. All rights reserved.