Oxygen vacancy-rich K-MnO@CeO catalyst for efficient oxidation degradation of formaldehyde at near room temperature.

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-MnO@CeO catalyst with excellent catalytic oxidation activity toward HCHO at near room temperature was reported. In particular, the K addition in K-MnO@CeO 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-MnO) to +8/3 (MnO) on the surface of CeO, which obviously changed the tunnel structure and the number of oxygen vacancies. One part of K species is uniformly dispersed on K-MnO@CeO, and the other part exists in the tunnel structure of MnO@CeO, 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 KMnO to MnO to tunneled MnO with the decreasing K content, in which K-MnO@CeO exhibited higher HCHO oxidation activity. In addition, K-MnO@CeO 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-MnO@CeO, 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-MnO@CeO catalyst is proposed.