Understanding the origins of N2O decomposition activity in Mn(Fe)CoAlO hydrotalcite derived mixed metal oxides

Abstract The catalytic decomposition of N 2 O 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, N 2 adsorption, H 2 -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 CoAlO x (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, Mn 0.1725 Co 3 A l O x reached the highest activity with T 50 of about 305 and 376 °C under N 2 O/N 2 and N 2 O,NO,O 2 /N 2 feed, respectively. In situ X-ray absorption experiments over Mn 0.1725 Co 3 A l O x suggested that Mn x Co y O 4 spinels undergo reduction to CoO and MnO upon heating up to 600 °C in He. Under N 2 O/He conditions, initial reoxidation of cobalt species began at 350 °C. The lower activity obtained for Fe 0.1725 Co 3 A l O x is explained by the fact that the majority of Fe was not incorporated into the Co 3 O 4 structure but instead formed less reactive iron oxide clusters.