SO<sub>2</sub>-Promoted Molecular Oxygen Activation and NO Oxidation on γ-MnO<sub>2</sub>
Yongcheng Jia, Hao Li, Jun Liu, Tianzeng Chen, Yonghong Wang, Peng Zhang, Biwu Chu, Qingxin Ma, Hong He
Abstract
The activation of molecular oxygen on transition metal oxide surfaces plays a crucial role in atmospheric chemistry and heterogeneous catalysis; however, understanding the intricate mechanisms remains a challenge. In this study, we elucidate for the first time the role of sulfur dioxide (SO 2 ) in enhancing oxygen activation on manganese oxide (γ-MnO 2 ) surface, thereby facilitating the oxidation of nitric oxide (NO) to nitrogen dioxide (NO 2 ). The theoretical calculation results further demonstrate that the adsorbed SO 2 and the formed sulfate can promote the adsorption of O 2 and the reactivity of surface reactive oxygen species toward NO oxidation on γ-MnO 2 (110) surface, respectively. During SO 2 with O 2 reaction, the formation of surface sulfate and surface-active oxygen atoms serves as new active sites to facilitate the oxidation of NO to NO 2 . Comparative analysis of the energy profiles reveals that NO oxidation with SO 2 can release more heat energy than that without SO 2, indicating enhanced thermodynamic accessibility in the presence of SO 2 . Therefore, a novel mechanism for the sulfate-mediated activation of O 2 is proposed, which sheds light on the synergistic effects of multiple pollutants in heterogeneous reactions and is significant for understanding NO oxidation both in the atmosphere and in exhaust treatment.