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.