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

Abstract

Engineering oxygen vacancies in α-MnO₂ represents an effective strategy for generating active oxygen species to enhance catalytic performance in HCHO oxidation. In this study, rod-like α-MnO₂ was synthesized via an in situ redox reaction between potassium permanganate (KMnO₄) and methanol, followed by modulation of surface oxygen vacancies through the adjustment of H₂O₂ etching time. Etching duration critically governed catalytic enhancement, with α-MnO₂-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 H₂O₂ etching time. Significantly, α-MnO₂-E-2 demonstrated the highest (Mn²⁺ + Mn³⁺)/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-MnO₂-E-2, demonstrating that H₂O₂ etching simplified the reaction pathway to HCHO → HCOO⁻ → H₂O + CO₂.