Simultaneous catalytic ozonation of NO and dichloromethane on Mn/H-ZSM-5 catalysts: Interaction effect and mechanism.

Catalytic ozonation is a promising method for simultaneous removal of NO x and Cl-VOCs, but needs to clarify their interaction mechanism and the influence of catalyst acidity. In this paper, the simultaneous catalytic ozonation of NO and dichloromethane (DCM) on Mn/H-ZSM-5 molecular sieve catalysts were investigated experimentally. Results show that the overall acidity, acid sites type and intensity have a significant impact on the degradation efficiency, the conversion path of Cl element, and the interaction of NO/DCM adsorption-degradation. Nevertheless, regardless of catalysts, NO could be preferentially oxidized by ozone to generate NO 2 in co-ozonation process, which inhibited and even shielded DCM ozonation at O 3 /DCM ratio <1.7. In addition, the highly active oxidizing species such as NO 3 /N 2 O 5 , produced by the deep ozonation of NO 2 , exhibited a synergistic effect on the conversion of DCM and intermediates, which in turn weakened NO 2 deep oxidation. Specifically, NO addition caused a general decrease in the HCl selectivity, and a slight increase in the CHCl 3 selectivity of all samples, while the Cl 2 selectivity was determined by the overall catalyst acidity. The samples with higher overall acidity exhibited lower activity for DCM degradation. In particular, for samples with the weak overall acidity but strong acid sites, the sum selectivity of HCl, Cl 2 , and CHCl 3 was significantly improved under the interplay effect of NO, indicating that strong acidic sites were beneficial to the complete degradation of DCM. In-situ DRIFTS revealed that aldehydes and carboxylates were the key intermediates of DCM ozonation. In the co-ozonation, NO and its oxidation products (such as nitrates) could promote the formation and conversion of these intermediates, and further converted into CO and CO 2 by the active oxidant from ozone. Finally, the interference of H 2 O and SO 2 on the NO/DCM co-ozonation were revealed. [ABSTRACT FROM AUTHOR]