Catalytic Ozonation of Formaldehyde with an Oxygen-Vacancy-Rich MnOx/γ-Al2O3 Catalyst at Room Temperature

Formaldehyde (HCHO) is known as one of the important indoor organic pollutants. How to remove and decompose the low concentration of formaldehyde at room temperature is important for indoor environments. Catalytic ozonation is an efficient method to thoroughly remove HCHO at room temperature, with high efficiency and few byproducts. A series of MnOx/γ-Al2O3 catalysts were prepared in this work via the impregnation method and treated with different reagents (acid, alkali, and H2O2) to evaluate their catalytic activity for HCHO removal. The results showed that MnAl-II (acid treatment) performed well in activity tests, reaching a nearly 100% HCHO conversion at an O3/HCHO of 2.0 and attaining a CO2 selectivity of above 95% at an O3/HCHO of 3.0 at 30 °C, with almost no ozone residual existing. The larger specific surface area, abundant oxygen vacancies, and higher number of acid sites contributed to the excellent performance of MnAl-II. Stability and H2O resistance tests of MnAl-II were also conducted. To reveal the intermediate product formation and further investigate the reaction mechanism of HCHO ozonation, in-situ DRIFTS measurement was carried out combined with DFT calculations.