Effect of steaming of iron containing AlPO-5 on the structure and activity in N2O decomposition

Iron containing AlPO-5 (FAPO) with variable Fe loading (1, 2, 4, and 9% w/w) was synthesized, characterized, and evaluated in N2O decomposition before and after steaming at 873 K for 5 h. Similar to the observations previously reported for Fe-ZSM-5 catalysts, steam treatment leads to a significant improvement in the activity of FAPO catalysts for N2O decomposition. Characterization by UV–Vis, FT-IR and Mössbauer spectroscopy reveals that migration of Fe from framework to ex-framework positions occurs upon steaming, as well as partial reduction of Fe(III) to Fe(II), explaining the beneficial effect of this procedure on catalyst activity. The relatively low activity of steamed FAPO compared to steamed isomorphously substituted Fe-ZSM-5 is tentatively explained by a negative effect of PO43- groups on the redox properties of the Fe-sites. The implications of our results for a study recently reported by Sankar and coworkers [N.R. Shiju, S. Fiddy, O. Sonntag, M. Stockenhuber, G. Sankar, Chem. Comm. (2006) 4955], demonstrating a high performance of FAPO in N2O mediated oxidation of benzene to phenol, are discussed.