The role of cationic defects in boosted lattice oxygen activation during toluene total oxidation over nano-structured CoMnOx spinel

Abstract

Lattice oxygen activation is critical for oxidizing volatile organic compounds (VOCs) on nanometal oxides. Herein, nano-structured cobalt manganese oxides (CoMnO_x) with cationic defects (CMO-Ex, where x represents the acid concentration) were constructed by acid treatment to optimize the lattice oxygen activation of pristine CoMnO_x (CMO-E0) during toluene oxidation. Characterization by positron annihilation spectrometry and HAADF-STEM measurements elucidated that cationic defect (manganese and cobalt defect) content was effectively regulated through acid concentration. Compared with CMO-E0 (T₉₀ = 257 °C), the CMO-E0.05 sample modified by optimum manganese and cobalt defect content delivered the highest toluene catalytic degradation activity (T₉₀ = 238 °C). Moreover, the CMO-E0.05 sample possessed superior catalytic stability (60 h) and water resistance (5 vol% H₂O). Our results showed that manganese and cobalt defects in CoMnO_x could boost the lattice oxygen activation and activity because of the increased cation valance state and shortened metal–oxygen bond, facilitating toluene oxidation. Operando study revealed that the cationic defects accelerated the toluene degradation rate by promoting the key intermediate (maleic anhydride) conversion with highly active lattice oxygen. This work offers insights into the role of cationic defects rather than oxygen defects in developing advanced nano-metallic oxides for VOC oxidation, a critical process to help reduce ozone formation.