Mn/HZSM-5 catalyst with high content of Mn4+ and surface hydroxyls for formaldehyde oxidation at room temperature

Catalytic oxidation of gaseous formaldehyde at room temperature over non-noble metal catalysts has wide application prospect. Regulation of catalyst surface active species such as surface hydroxyls, valence state of active metal, oxygen vacancies, etc., is effective in promoting catalytic performance. Herein, we prepared a series of Mn/HZSM-5 catalysts with a facile ball mill strategy. The optimal catalyst 0.4%Mn/HZSM-5 exhibited superior activity of nearly 100% HCHO conversion at 30 °C under 100 ppm gaseous HCHO condition. The characterization results revealed that the catalyst with high specific surface area has a large number of Mn4+ ions and hydroxyls on surface, which facilitates providing more active sites for formaldehyde oxidation. Combining XPS and chemisorption experiments, it was clear that the interaction between Mn4+ and the carriers provided more surface reactive oxygen species. In addition, in situ DRIFTS results revealed that Mn4+ and hydroxyls could jointly activate formaldehyde, and Mn4+ could further activate oxygen to oxidize the reaction intermediate to CO2 and H2O.