Effect of preparation method on the solid state properties and the deN(2)O performance of CuO-CeO2 oxides

Abstract

The present work aims at investigating the catalytic decomposition of N2O over CuO-CeO2 single or mixed oxides prepared by different synthesis routes, i.e., impregnation, precipitation and exotemplating. To gain insight into the particular role of CeO2 as well as of CuO-CeO2 interactions, three different types of materials were prepared and tested for N2O decomposition both in the absence and presence of excess O-2: (i) bare CeO2 prepared by precipitation and exotemplating, (ii) CuO/CeO2 oxides synthesized by the impregnation of CeO2 samples prepared in (i) with CuO, and iii) single stage CuO-CeO2 mixed oxides synthesized employing the co-precipitation and exotemplating methods. The corresponding commercial samples were also examined for comparison purposes. All materials were characterized by N-2 adsorption at -196 degrees C, X-ray diffraction (XRD), H-2 temperature-programmed reduction (H-2-TPR), X-ray photoelectron spectroscopy (XPS), micro-Raman spectroscopy (micro-Raman) and scanning electron microscopy (SEM). The results demonstrated the key role of the preparation procedure on the direct catalytic decomposition of N2O. Among the bare CeO2 samples, the best performance was obtained with the samples prepared by the precipitation method, followed by exotemplating, while commercial CeO2 showed the lowest performance. All bare oxides demonstrated low N2O conversion, never exceeding 40% at 600 degrees C. Amongst the CuO-CeO2 oxides, the optimum performance was observed for those prepared by co-precipitation, which achieved complete N2O conversion at 550 degrees C. In the presence of excess oxygen in the feed stream, a slight degradation is observed, with the sequence of deN(2)O performance remaining unchanged. The superiority of the Cu-Ce mixed oxides prepared by precipitation compared to all of the other materials can be mainly ascribed to their excellent redox properties, linked to Ce4+/Ce3+ and Cu2+/Cu+ redox pairs. A redox mechanism for the N2O catalytic decomposition is proposed, involving N2O adsorption on Cu+ sites and their regeneration through Cu-ceria interactions.