Enhanced toluene catalytic oxidation over Ag-Cu co-modified Mn₂O₃: the crucial roles of surface structure...

This study confirms that Ag-Cu bimetallic modification effectively reconstructs the surface microenvironment of Mn₂O₃ and significantly enhances its catalytic performance for toluene oxidation. Ag single modified and Ag-Cu bimetallic modified Mn₂O₃ catalysts were prepared via a hydrothermal-calcination method. It is demonstrated that the synergistic effect between Ag and Cu promotes the partial oxidation of surface Mn³⁺ to Mn⁴⁺, forming a trace MnO₂ thin layer and constructing a heterogeneous valence distribution of "surface Mn⁴⁺/bulk Mn³⁺". Systematic characterizations reveal that the Ag-Cu synergy not only enriches bulk Mn³⁺ active species and generates abundant oxygen vacancies but also establishes dual acid sites comprising weak Lewis and strong Brønsted acids. Furthermore, the cooperation between the MnO₂ thin layer and the Mn₂O₃ bulk phase facilitates the Mn³⁺/Mn⁴⁺ redox cycle, enhances lattice oxygen mobility, and accelerates the oxidation pathway. In-situ DRIFTS studies indicate that, driven by the Ag-Cu synergy and the MnO₂-induced valence cycle, toluene oxidation over the 3Ag3Cu-Mn catalyst follows the conversion path of toluene → benzyl alcohol → benzaldehyde → benzoate → CO₂/H₂O, thereby eliminating the accumulation of refractory intermediates such as maleic anhydride.