Synergistic removal of nitrogen oxides and toluene and their interaction mechanism on Cu-MnO2 catalyst

Abstract

Volatile organic compounds (VOCs) and nitrogen oxides (NOx) contribute significantly to the formation of haze and photochemical smog, posing substantial threats to both the environment and human health. Toluene, a typical VOCs, often coexists with NOx in various mobile or stationary flue gases. However, the current understanding of the mutual influence of their synergistic removal remains limited. In this work, the Cu-MnO2 catalyst was prepared using the precipitation method, which demonstrated synergistic removal activity for both NOx and toluene, as well as selectivity towards N2 and CO2. The interaction mechanism was investigated, particularly focusing on the effect of NOx on the adsorption and oxidation performance of toluene. The degree to which NOx inhibits toluene increases with NOx concentration. Furthermore, multiple inhibition ways of NOx on toluene oxidation were discovered, including competitive adsorption of NOx and toluene on the catalyst surface, as evidenced by the breakthrough experiments. TPD and XPS characterization indicated that the addition of NOx reduces oxygen vacancies, thereby weakening toluene oxidation performance. In addition, in-situ DRIFT characterization was conducted, and it was found that the addition of NOx affected the oxidation process of toluene. Apart from benzyl alcohol, benzaldehyde, and benzoic acid, intermediate nitrite species also appeared, and their deposition was also the reason for the decrease in toluene oxidation ability. This work provides new insights into the interaction mechanisms between various components in the collaborative removal of NOx and VOCs.