Enhanced Catalytic Performance of an Fe-Substituted La-Hexaaluminate Supported Ir Catalyst for N₂O Decomposition

Fe-substituted hexaaluminates have a high lattice oxygen mobility due to the substitution of Fe ions in Al(5) sites in the mirror planes of hexaaluminates. Herein, an Fe-substituted La-hexaaluminate-supported Ir catalyst was synthesized. It exhibited excellent catalytic activity (T-50 = 284 degrees C) and stability with two cycles at 450 degrees C for nitrous oxide (N2O) decomposition. The characterization of XRD, Fe-57 M & ouml;ssbauer spectroscopy, Raman spectroscopy, and CO-DRIFTS evidenced the origination and formation of oxygen vacancies in the Fe-substituted hexaaluminate after the loading of Ir species, which was related to the lattice oxygen mobility of the hexaaluminate. These oxygen vacancies promoted the preferred formation of Ir-0 species on the Fe-substituted La-hexaaluminate rather than the Ir delta+ ones which were predominant on the Mg-substituted La-hexaaluminates, as revealed by CO-DRIFTS and XPS. Furthermore, in situ XPS and DRIFTS measurements in a N2O atmosphere at different temperatures indicated that oxygen vacancies participated in N2O decomposition, and the ratio of Ir-0 species remained unchanged throughout the experiments. Based on the characterization results, this study concludes that both Ir species and oxygen vacancies act as active sites for N2O decomposition. Compared to Ir delta+, oxygen vacancies and Ir-0 species, enriched with electron density, are more favorable for N2O decomposition and enhance the catalytic activity.