Co3O4 Catalysts for Complete Toluene Oxidation: Review including Meta-Analysis of Catalyst Activity Data

Abstract

Designing highly active catalysts for the oxidation of volatile organic compounds (VOCs) involves fine-tuning the catalytic surface and improving its interaction with VOCs. The present review assesses various studies conducted in the last decade on Co3O4 catalysts for the complete oxidation of toluene (C7H8) and provides information on the synthesis and physicochemical characterization of these catalysts. Taking this one step further, data from the literature were carefully chosen for an extensive meta-analysis aiming at elucidating the structure sensitivity of toluene oxidation over Co3O4 catalysts. Specifically, the specific reaction rate was calculated and correlated with the physicochemical properties of the catalysts, namely, the specific surface area, faceting, and Co3+/Co2+ ratio. Based on this analysis, the specific surface area does not exert a significant impact on the specific activity of Co3O4 catalysts for the total oxidation of toluene. Instead, the specific reaction rates are influenced by the morphology, surface concentration, exposed crystallographic planes, and oxidation state of cobalt cations. These factors determine the catalyst’s specific activity by creating defects, oxygen vacancies, or oxygen species with different reactivities. It was also found that a high surface Co3+/Co2+ ratio is necessary for achieving high catalytic performance in the oxidation of VOCs.