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

Toluene oxidation was catalyzed by NiO/SiO₂ and NiO/TiO₂/SiO₂ 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 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 °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.