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

• NiO/SiO2 and NiO/TiO2/SiO2 catalysts were prepared by ALD process.
• Catalytic activities of each catalyst for toluene oxidation were evaluated under dry and humid conditions.
• Catalytic activity of NiO/SiO2 significantly decreased under humid condition due to competitive adsorption of toluene with water.
• Catalytic activity of NiO/TiO2/SiO2 was maintained even under the presence of water due to strong interaction of toluene with TiO2 surface.
• Humidity-resistance of NiO/TiO2/SiO2 was much pronounced at lower temperature (250 °C).

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.

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