Résumé
The catalytic decomposition of N2O was studied over a series of calcined Mn(Fe)CoAl hydrotalcite-like compounds. The precursors were prepared by coprecipitation and characterized by XRD and TGA. The mixed metal oxides derived after calcination at 600 °C were characterized by XRD, N2 adsorption, H2-TPR and XPS. Moreover, in situ XAFS measurements over selected mixed metal oxides were performed. Such investigations under relevant reaction conditions are rare, while a comprehensive understanding of the involved active species may facilitate a knowledge-based catalyst optimization. The activity of the CoAlOx (Co/Al = 3/1, mol.%) catalyst varied depending on the loading of Mn or Fe (0.0575, 0.0821, 0.1150, 0.1725, 0.2300, mol.%). In the investigated series, Mn0.1725Co3AlOx reached the highest activity with T50 of about 305 and 376 °C under N2O/N2 and N2O,NO,O2/N2 feed, respectively. In situ X-ray absorption experiments over Mn0.1725Co3AlOx suggested that MnxCoyO4 spinels undergo reduction to CoO and MnO upon heating up to 600 °C in He. Under N2O/He conditions, initial reoxidation of cobalt species began at 350 °C. The lower activity obtained for Fe0.1725Co3AlOx is explained by the fact that the majority of Fe was not incorporated into the Co3O4 structure but instead formed less reactive iron oxide clusters.