Toluene oxidation catalyzed by NiO/SiO2 and NiO/TiO2/SiO2: Towards development of humidity-resistant catalysts

Abstract Toluene oxidation was catalyzed by NiO/SiO 2 and NiO/TiO 2 /SiO 2 under dry and highly humid (relative humidity = 70%) conditions at 250 and 350 °C. At 350 °C, both catalysts showed nearly complete removal of toluene and conversion of toluene to CO 2 under humid as well as dry conditions. Catalytic activity of the NiO/SiO 2 was significantly decreased by the increase in the humidity at 250 °C, whereas that of NiO/TiO 2 /SiO 2 was much less sensitive to the humidity. A facile adsorption of water on NiO/SiO 2 due to the hydrophilic nature of SiO 2 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 TiO 2 towards toluene adsorption even under highly humid conditions can allow more humidity-independent catalytic activity of NiO/TiO 2 /SiO 2 . 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.