Insight into the promotion effect of H2O for the simultaneous removal of NOx and methanol at low temperature over MnFe2Ox catalyst

Abstract

The research on the simultaneous removal of NO_x and VOCs by NH₃-SCR catalysts has garnered widespread attention. However, the stepwise removal of both gases during the co-removal process is often caused by the inconsistent activity windows. Furthermore, the presence of water vapor in flue gas adversely impacts the catalyst and greatly decreases its catalytic activity. In this study, the low-temperature catalyst MnFe₂O_x was selected to remove NO_x and methanol, with a focus on investigating the influence of H₂O on catalytic reactions. Results show that MnFe₂O_x exhibited nearly 100 % denitrification activity and methanol oxidation performance within 150–240 °C. H₂O in the atmosphere scarcely affected the performance of the synergistic removal and positively influenced N₂ generation. Catalyst characterizations conducted with or without H₂O demonstrated that nitrogen-containing gases were inhibited from adhering to the catalyst surface by the competitive adsorption of H₂O. Furthermore, the dehydrogenation of NH₃ active species to -NH₂/-NH was impeded, which reduced the likelihood of unintended reactions that generate N₂O. The DRIFTs analysis of the simultaneous removal reaction indicates that the presence of H₂O facilitates the formation of significant intermediates like methyl nitrite and isocyanate from methanol, which could hydrolyze to produce NH₃, CO and other reducing gases that would react with NO_x to maintain NO_x removal efficiency. These results offer direction for further research into the influence of water vapor in flue gas on the co-removal of NO_x and VOCs.