Oxygen vacancy-rich K-Mn₃O₄@CeO₂ catalyst for efficient oxidation degradation of formaldehyde at near room...

Synthesis of catalysts with high catalytic degradation activity for formaldehyde (HCHO) at room temperature is highly desirable for indoor air quality control. Herein, a novel K-Mn₃O₄@CeO₂ catalyst with excellent catalytic oxidation activity toward HCHO at near room temperature was reported. In particular, the K addition in K-Mn₃O₄@CeO₂ considerably enhanced the oxidation activity, and importantly, 99.3 % conversion of 10 mL of a 40 mg/L HCHO solution at 30 °C for 14 h was achieved, with simultaneous strong cycling stability. Moreover, the addition of K species considerably influenced the chemical valence state of Mn from +4 (ε-MnO₂) to +8/3 (Mn₃O₄) on the surface of CeO₂, which obviously changed the tunnel structure and the number of oxygen vacancies. One part of K species is uniformly dispersed on K-Mn₃O₄@CeO₂, and the other part exists in the tunnel structure of Mn₃O₄@CeO₂, which is mainly used to balance the negative charge of the tunnel and prevent collapse of the structure, providing enough active sites for the catalytic oxidation of HCHO. We observed a phase transition from tunneled KMnO₂ to Mn₃O₄ to tunneled MnO₂ with the decreasing K⁺ content, in which K-Mn₃O₄@CeO₂ exhibited higher HCHO oxidation activity. In addition, K-Mn₃O₄@CeO₂ exhibited lower oxygen vacancy formation and HCHO adsorption energies in aqueous solution based on density functional theory calculations. This is because the K species provide more active oxygen species and richer oxygen vacancies on the surface of K-Mn₃O₄@CeO₂, promote the mobility of lattice oxygen and the room-temperature reduction properties of oxygen species, and enhance the ability of the catalyst to replenish the consumed oxygen species. Finally, a possible HCHO catalytic oxidation pathway on the surface of K-Mn₃O₄@CeO₂ catalyst is proposed.