NO oxidation with H2O2 catalyzed by zeolites in a fixed-bed reactor: Experimental and mechanism

Abstract

In this study, by comparing the NO removal experiments with H2O2 over of β, SAPO-34 and ZSM-5 in a fixed-bed reactor, in which β zeolite showed 91% NO removal efficiency under the optimal experimental conditions (2 mol/L H2O2, 0.3 g catalyst, reaction temperature=140 °C). Through characterization analysis and comparison, the ESR test illustrated ZSM-5 and SAPO-34 produce hydroxyl radicals more efficiently than β, but NO removal efficiency of these two zeolites was lower than β, indicating that the removal of NO was not due to the hydroxyl radicals. NH3-TPD and Py-FTIR analysis revealed that the zeolite catalyzes the oxidation of NO by H2O2 because of the presence of Brønsted acid sites. The highest content of Brønsted acid in β zeolite was the main reason for its highest removal efficiency. Furthermore, through in-situ FTIR analysis, the coordinated NO+ in the framework (Si−O·(NO+)−Al)of zeolites played an important role in catalysis, and a possible reaction path was proposed. Finally, the removal test was carried out for 6 h, and the changes of the catalyst before and after the reaction were studied through XRD and FTIR tests, which showed strong stability.