Oxidation of Toluene on Bare and TiO₂-Covered NiO-Ni(OH)₂ Nanoparticles

Abstract

Oxidation of toluene was catalyzed by bare and TiO2-covered NiO-Ni(OH)2 nanoparticles under humid air. For deposition of TiO2, atomic layer deposition was used. Bare NiO-Ni(OH)2 showed a significantly high activity for toluene oxidation. When TiO2 islands were deposited on NiO, formation of CO2 as a result of total oxidation of toluene was completely suppressed at 180 °C, even though the substrate surface was only partially covered by TiO2. We suggest that TiO2 islands preferentially blocked the active sites for total oxidation of toluene under our experimental conditions. On the basis of the X-ray photoelectron spectroscopy data, catalyst surfaces consisted of NiO and Ni(OH)2, and NiO was active for toluene total oxidation, whereas Ni(OH)2 was not. Studies of change in the activity of a heterogeneous catalyst upon preferential decoration of specific surface sites can shed light on the structures and properties of catalytically active sites.