Elucidation of the surprising role of NO in N2O decomposition over FeZSM-5

The decomposition of N2O is strongly promoted by NO over steam-activated FeZSM-5. The promoting effect of NO is catalytic, and in addition to NO2, O-2 is formed much more extensively at lower temperatures than in the absence of NO. The promotion effect only requires low NO concentrations in the feed, with no significant improvements at molar NO/N2O feed ratios higher than 0.25. No inhibition by NO was identified even at a molar NO/N2O feed ratio of 10, suggesting different sites for NO adsorption and oxygen deposition by N2O. The latter sites seem to be remote from each other. Transient experiments using in situ FT-IR/MS and Multitrack over FeZSM-5 further elucidate the mechanism of NO promotion. The release of oxygen from the catalyst surface during direct N2O decomposition is a rate-determining step due to the slow oxygen recombination. which is favored by high reaction temperatures. NO addition promotes this oxygen desorption, acting as an oxygen transfer agent, probably via NO2 species. Adsorbed NO may facilitate the migration of atomic oxygen to enhance their recombination. Less than 0.9% of Fe seems to participate in this promotion. A model is proposed to explain the phenomena observed in NO-assisted N2O decomposition, including NO2 decomposition.