Novel CuO-containing catalysts based on ZrO2 hollow spheres for total oxidation of toluene

Abstract

Abstract A bottom-up strategy was used to construct SiO2@ZrO2 core-shell materials with amorphous or tetragonal structure of ZrO2 induced by calcination temperature. After etching of the SiO2 core with NaOH, @ZrO2 hollow spheres were formed as supports for different amounts of CuO (2.5–15.0 wt% of Cu). Significant differences in porosity and distribution of Cu2+ species were identified by X-ray diffraction, low-temperature N2 adsorption, UV-vis-DR and X-ray photoelectron spectroscopy. The Cu-containing catalysts based on tetragonal @ZrO2 exhibited higher surface areas and surface concentrations of finely dispersed Cu2+ compared to the series prepared using amorphous @ZrO2. Moreover, CuO particles deposited on the tetragonal ZrO2 shells appeared to be easier reducible during temperature-programmed reduction (TPR) measurements. Consequently, these catalysts were more active in the total oxidation of toluene, which mainly proceeded by the Mars-van Krevelen mechanism. Nevertheless, an analysis of correlation between the catalytic activity and reducibility for both studied catalyst series revealed that oxygen vacancies present on the surface of tetragonal ZrO2 clearly promote the reaction rate. The developed materials can be considered as useful for commercial application due to high selectivity to the combustion products (CO2 and H2O) and stable work even in a wide range of toluene concentrations and a moisture presence.