Effect of pH on Microstructure and Catalytic Oxidation of Formaldehyde in MnO2 Catalyst

Layered d-MnO2 catalysts were prepared using the one-step redox method in precursor solutions with five different pH values (pH = 7, 9, 11, 13, and 14). The effects of pH on the physical properties and catalytic activity of the catalyst were investigated through XRD, SEM, TEM, BET, XPS, H-2-TPR, and HCHO degradation tests at room temperature. The results showed that the layer spacing, manganese vacancy content, Mn4+/Mn3+ ratio, and surface-reactive oxygen species content of MnO2 increased with the increase in pH value in the alkaline range. When the catalyst was prepared at pH = 13, the above characteristics of the catalyst reached the optimal value which contributed to the high catalytic activity. Combined with the related characterization results, it was proved that changing the pH can affect the degree of oxidation in the catalyst synthesis process, increase the number of active oxygen and the oxygen mobility of the catalyst, and effectively improve the catalytic activity of the manganese dioxide catalyst for HCHO. This work represents a giant step toward the preparation of an effective catalyst for practical applications of HCHO removal at room temperature at a low concentration and high velocity.