The catalytic properties of palladium and gold nanoparticles deposited on mesoporous TiO2 are investigated in toluene and propene oxidation. The catalysts, containing Pd and Au deposited on mesoporous TiO2 have been prepared by different order of metal deposition (Pd(shell)-Au(core)/TiO2. Pd-Au(alloy)/TiO2 and Au(shell)-Pd(core)/TiO2. For both toluene and propene oxidation reactions, the catalytic activity was found significantly higher when palladium is deposited on already-deposited gold (Pd(shell)-Au(core)/TiO2). This enhanced activity could be explained by the core-shell morphology (Pd-shell and Au-core) observed by UV-vis spectra, TPR profiles and XPS spectra. It was suggested that the oxidation reaction follows a Langmuir-Hinshelwood mechanism where the molecules of oxygen and VOC are in competition for adsorption on the surface of catalyst. Operando DRIFT spectroscopy was carried out to test the catalytic activity in a mixture of volatile organic compounds (toluene and propene). It was demonstrated that there is a competition between the molecules of VOC for adsorption but also the toluene has an inhibition effect for oxidation of propene. (C) 2011 Elsevier B.V. All rights reserved.