Low-temperature gas-phase toluene catalytic combustion over modified CoCr2O4 spinel catalysts: Effect of Co/Cr content and calcination temperature

Un-supported spinel-type cobalt chromite catalysts were synthetized by propionic acid-mediated sol-gel method and tested for toluene oxidation. The influence of the Co and Cr content and the preparation conditions on physico-chemical, surface and catalytic properties for this reaction has been for the first time evaluated. Co-rich CoCr2O4 was the most active catalyst, likely due to the formation of a single CoCr2O4 spinel phase, a favorable surface composition and higher low-temperature reducibility. Besides, the increase of the calcination temperature, despite worsening textural properties, also has a promoting effect on the catalytic activity by preserving a suitable reducibility and further enhancing the surface properties. Surface Cr6+ ions and adsorbed oxygens (Oads), which are more abundant in the most efficient catalyst (Co-rich catalyst calcined at 685 °C), seem to play an important role on toluene oxidation reaction. These findings may open potential strategies in the development of efficient and economically competitive catalysts for elimination of VOCs like toluene.