Toluene oxidation was catalyzed by NiO/SiO2 and NiO/TiO2/SiO2 under dry and highly humid (relative humidity= 70%) conditions at 250 and 350 degrees C. At 350 degrees C, both catalysts showed nearly complete removal of toluene and conversion of toluene to CO2 under humid as well as dry conditions. Catalytic activity of the NiO/SiO2 was significantly decreased by the increase in the humidity at 250 degrees C, whereas that of NiO/TiO2/SiO2 was much less sensitive to the humidity. A facile adsorption of water on NiO/SiO2 due to the hydrophilic nature of SiO2 surface resulted in a pronounced suppression of toluene adsorption on the surface and lower catalytic activity under humid conditions. On the contrary, a higher affinity of TiO2 towards toluene adsorption even under highly humid conditions can allow more humidity-independent catalytic activity of NiO/TiO2/SiO2. We suggest that the modulation of surface structure of supporting materials of nanoparticle catalysts can be useful for fabrication of more humidity-resistant heterogeneous catalysts. (C) 2015 Elsevier B.V. All rights reserved.