CoMnxOy nanosheets with molecular-scale homogeneity: an excellent catalyst for toluene combustion

Abstract

The process driven by “redox–precipitation” reactions between Mn⁷⁺, Co²⁺ and Mn²⁺ can yield CoMn_xO_y nanosheet catalysts with (quasi)molecular scaled dispersed compounds which can achieve excellent catalytic activity in toluene combustion with T₅₀ (temperature of 50% toluene conversion) values of 172 °C and 218 °C (GHSV = 67 500 h⁻¹ and 540 000 h⁻¹, respectively). The as-prepared CoMn_xO_y nanosheets demonstrated high specific surface area, and their overall morphology changed when Mn²⁺ was substituted with Mn⁷⁺ during the preparation process. The enhanced catalytic performance in toluene combustion can be ascribed to very high amounts of oxygen electrophilic species (O⁻/O₂⁻), as evidenced by XPS, H₂-TPR and O₂-TPD. In addition to the MnCo₂O_4.5 phase, Co₃O₄ formation can further improve the catalytic properties. According to TEM observations, the Co₃O₄ species were well dispersed on MnCo₂O_4.5 and strongly interacted with MnCo₂O_4.5 by forming an active Co₃O₄–MnCo₂O_4.5 interface. Toluene adsorption and O₂ dissociation could occur at the active interface by creating abundant oxygen vacancies, further providing adequate O₂²⁻ species to take part in toluene oxidation. The influences of water vapor and other VOCs in simulated exhaust were also evaluated. The excellent performance of the catalysts in catalytic toluene combustion demonstrates that they have great potential for practical applications.