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Royal Society of Chemistry, Catalysis Science & Technology, 7(5), p. 3714-3727, 2015

DOI: 10.1039/c5cy00343a

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Effect of preparation method on the solid state properties and the deN2O performance of CuO-CeO2 oxides

This paper is available in a repository.
This paper is available in a repository.

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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 are prepared and tested for N2O decomposition both in the absence and presence of excess O2: (i) bare CeO2 prepared by precipitation and exotemplating, (ii) CuO/CeO2 oxides synthesized by impregnation of CeO2 samples prepared in (i) with CuO and iii) single stage synthesized CuO-CeO2 mixed oxides employing the co-precipitation and exotemplating methods. The corresponding commercial samples were also examined for comparison purposes. All materials were characterized by N2 adsorption at -196 °C, X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS), micro-Raman spectroscopy (micro-Raman) and scanning electron microscopy (SEM). The results demonstrated the key role of 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 °C. Amongst the CuO-CeO2 oxides, the optimum performance was observed for those prepared by co-precipitation, which achieved complete N2O conversion at 550 ºC. In the presence of excess oxygen in the feed stream, a slight degradation is observed, with the sequence of deN2O performance to remain unchanged. The superiority of Cu-Ce mixed oxides prepared by precipitation compared to all other materials can be mainly ascribed to their excellent redox properties, linked to Ce4+/Ce3+ and Cu2+/Cu+ redox pairs. A redox mechanism for N2O catalytic decomposition is proposed involving N2O adsorption on Cu+ sites and their regeneration through Cu-ceria interactions.