Rapid Ultrasound-Assisted Synthesis of Mesoporous Manganese Oxides for Low-Concentration NO Elimination with Superior Water-Resistance

Through a room-temperature ultrasound-assisted redox process, mesoporous manganese oxides were synthesized in short reaction times of 3–9 h. At room temperature, the resultant materials showed superior performance for the elimination of low-concentration NO (10 ppm). Specifically, under humid conditions (50–90 % relative humidity), 97 % NO removal efficiency was obtained over 110 h without deactivation. Synergetic effects between Mn²⁺, Mn³⁺, and Mn⁴⁺ ions were proposed to explain the oxidation of NO to NO₂ on the surface of the catalyst. Density functional theory (DFT) calculations indicated that water molecules strengthen the chemisorption of NO₂ on manganese oxide (001) owing to a much higher adsorption energy. As a result, the probability of the reaction between NO₂ and H₂O increases, and the formation of volatile nitric acid ensures that the catalytically active sites are always available.