Applied Catalysis B: Environmental, Vol.243, 66-75, 2019
Understanding the origins of N2O decomposition activity in Mn(Fe)CoAlOx hydrotalcite derived mixed metal oxides
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 degrees 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 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, Mn(0.1725)Co(3)A(1)O(x) reached the highest activity with T50 of about 305 and 376 degrees C under N2O/N-2 and N2O,NO,O-2/N-2 feed, respectively. In situ X-ray absorption experiments over Mn(0.1725)Co(3)A(1)O(x) suggested that MnxCoyO4 spinels undergo reduction to CoO and MnO upon heating up to 600 degrees C in He. Under N2O/He conditions, initial reoxidation of cobalt species began at 350 degrees C. The lower activity obtained for Fe0.1725Co(3)AlO(x) 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.