Nanodispersed Mn3O4/γ-Al2O3 for NO2 Elimination at Room Temperature

Adsorption is an efficient method for atmospheric NOx abatement under ambient conditions; however, traditional adsorbents suffer from limited adsorption capacity and byproduct formation. Developing a low-cost material with high capacity for atmospheric NO2 elimination remains a challenge. Here, we synthesized a nanodispersed Mn3O4/γ-Al2O3 (Mn/Al) material that exhibits excellent ability to remove NO2. The 10 wt % Mn/Al sample showed the highest removal capacity, with 247.6 mgNO2/gMn/Al, which is superior to that of activated carbon (42.6 mgNO2/g). There were no byproducts produced when Mn/Al was tested with ppb-level NO2. The NO2 abatement mechanism with Mn/Al is different from physisorption or chemisorption. NO2 removal is mainly a catalytic process in air, during which surface hydroxyls and lattice oxygen are involved in the oxidation of NO2 to nitrate. In contrast, a chemical reaction between Mn3+ and NO2 is dominant in N2, where Mn3+ is converted into Mn4+ and NO2 is reduced to nitrite. Washing with deionized water is an effective and convenient method for the regeneration of saturated Mn/Al, and an 86% adsorption capacity was recovered after one washing. The results suggest that this low-cost Mn/Al material with easy preparation and regeneration is a promising candidate material for atmospheric NO2 elimination.