Co-Based Bimetallic Oxide Catalysts with Abundant Vacancy Defects for Enhanced Oxidation of Toluene

A series of Co–M (M = Mn, Ce, Cu) bimetallic oxide catalysts were prepared by a modified solvent pyroalcoholysis method, and the performance in the catalytic oxidation of toluene was investigated. The experimental results showed that the conversion rate of the as-prepared Co₁Cu₁ catalyst performed a 50% conversion (T₅₀) and 90% conversion (T₉₀) in toluene oxidation at 211 °C and 241 °C, respectively. A series of the characterization demonstrated that the performance improvement is attributable to the Co₁Cu₁ catalyst owning high Co³⁺ concentration (Co³⁺/Co²⁺ = 1.14), abundant surface adsorbed oxygen (O_ads/O = 67.33%), and excellent low temperature reducibility. Interestingly, these properties promoted the adsorption and deep oxidation of toluene molecules. Concurrently, the XRD and Raman characterizations verified that the spinel structure of Co₃O₄ is altered by Cu doping, producing high-valence surface active Co species and numerous lattice defects that increased the catalyst’s catalytic efficiency. This study showed that creating defect sites by metal doping is a useful strategy for improving Co₃O₄ spinel’s catalytic activity.