Role of Metallic Ag over Ag/MnO₂ Catalysts for Ozone Decomposition under Humid Conditions

Ag/MnO catalysts have great potential for practical application in ozone (O₃) decomposition due to their superior activity under humid conditions. Metallic Ag nanoparticles (Ag_n⁰) have been identified as the critical active site for O₃ decomposition over Ag/MnO catalysts. However, the role of Ag_n⁰ over Ag/MnO catalysts during the O₃ decomposition remains unclear. In this study, Ag_n⁰ and oxidized Ag nanoparticles (AgO) are constructed on the MnO₂ supports. Under a relative humidity of 65% and a high space velocity of 2800 L·g^-1·h^-1, the conversion of 40 ppm of O₃ over the 4%Ag/γ-MnO₂ catalyst (91%) within 6 h is far superior to that over the 4%Ag/α-MnO₂ (22%) catalyst, which is attributed to the formation of Ag_n⁰ on the 4%Ag/γ-MnO₂ catalyst and AgO on the 4%Ag/α-MnO₂ catalyst. Then, the role of Ag_n⁰ and AgO during O₃ decomposition was determined by in situ Raman spectroscopy and DFT calculations. Compared with AgO, the competitive adsorption of H₂O and O₃ molecules on Ag_n⁰ is weaker, and O₃ molecules can be activated more rapidly on Ag_n⁰; most importantly, peroxide species are more easily desorbed on Ag_n⁰. These advantages of Ag_n⁰ are the key to the superior O₃ decomposition activity of the 4%Ag/γ-MnO₂ catalyst under humid gas. This study provides guidance for understanding the Ag active sites for the decomposition of O₃ and the design of highly efficient Ag/MnO catalysts.