Modulating the formaldehyde oxidation pathway via H2O2 etching on α-MnO2: the role of oxygen vacancies

Engineering oxygen vacancies in α-MnO 2 represents an effective strategy for generating active oxygen species to enhance catalytic performance in HCHO oxidation. In this study, rod-like α-MnO 2 was synthesized via an in situ redox reaction between potassium permanganate (KMnO 4 ) and methanol, followed by modulation of surface oxygen vacancies through the adjustment of H 2 O 2 etching time. Etching duration critically governed catalytic enhancement, with α-MnO 2 -E-2 (2 h etching) exhibiting exceptional activity, robust stability and complete HCHO conversion at 60 °C. Characterization revealed oxygen vacancies on the catalyst surface could be effectively regulated by modifying the H 2 O 2 etching time. Significantly, α-MnO 2 -E-2 demonstrated the highest (Mn 2+ + Mn 3+ )/Mn total ratio and lowest average oxidation state (AOS), directly correlating with maximized oxygen vacancy formation. The introduction of oxygen vacancies facilitated superior oxygen mobility and activation, thereby accelerating HCHO oxidation. In situ DRIFTS analysis further confirmed that only formate species were observed as intermediates on α-MnO 2 -E-2, demonstrating that H 2 O 2 etching simplified the reaction pathway to HCHO → HCOO − → H 2 O + CO 2 .