Engineering oxygen vacancies in Au/MnO₂ catalysts for complete formaldehyde removal at near-freezing temperatures

Formaldehyde (HCHO) is a major indoor air pollutant that poses serious risks to human health, making its efficient removal a critical environmental concern. Catalytic oxidation at room and sub-ambient temperatures has attracted significant attention due to its potential to completely decompose HCHO into harmless CO₂ and H₂O. However, practical implementation remains challenging because of low reaction activation energy and limited catalyst performance at reduced temperatures. In this study, Au-loaded manganese oxide nanowire catalysts (x% Au/MnO₂-NWs) were synthesized using a colloidal deposition strategy to achieve efficient HCHO removal under ambient and sub-ambient conditions. The optimized 1% Au/MnO₂-NWs catalyst achieved complete conversion of 280 ppm HCHO at 30 °C and, remarkably, fully oxidized 20 ppm HCHO even at 0 °C, demonstrating outstanding low-temperature activity and practical potential. Comprehensive characterization studies including H₂-TPR, EPR, Raman spectroscopy, and in situ DRIFTS revealed that Au nanoparticles induced abundant oxygen vacancies, which acted as active sites for HCHO adsorption and promoted O₂ activation. The synergistic interaction between Au and MnO₂ significantly enhanced low-temperature catalytic performance, providing mechanistic insights and a solid foundation for the rational design of highly efficient catalysts for indoor formaldehyde removal.