Cl‐associated Cu species promote the utilization of surface oxygen during catalytic toluene oxidation over CuO / Al 2 O 3 : Benzaldehyde‐to‐benzoate conversion

This work provides new insights into the role of Cl‐associated Cu species in the catalytic total oxidation of toluene over CuO/Al 2 O 3 catalysts. Anion‐associated Cu species on the catalyst surface significantly influence their catalytic performance for the total oxidation of toluene. In addition, these species appear to influence the reaction pathway by promoting the utilization of surface oxygen. Catalytic performances of four catalysts (Cu‐Cl, Cu‐S, Cu‐N, and Cu‐C)—prepared from copper precursors containing different anionic ligands (chloride, sulfate, nitrate, and acetylacetonate, respectively)—were investigated. The Cl‐ and S‐associated Cu species were formed on the surfaces of the Cu‐Cl and Cu‐S catalysts, respectively. The presence of these anion‐associated surface species explains the observed activity trend of Cu‐Cl > Cu‐N ≈ Cu‐C > Cu‐S. In particular, Cl‐associated Cu species appear to promote the utilization of surface adsorbed oxygen species rather than lattice oxygen, as evidenced by operando DRIFTS, toluene‐TPD, and H 2 ‐TPR analyses. These surface adsorbed oxygen species facilitate the oxidation of benzaldehyde to benzoate, leading to enhanced total oxidation of toluene under isothermal conditions. Moreover, the active surface oxygen species can be readily regenerated in the presence of oxygen gas, resulting in stable catalytic performance for more than 9 h over the Cu‐Cl catalysts.