CuO on CeO2 (001), a more selective catalyst for CO preferential oxidation: fundamental DFT modeling and experimental data

Trabajo presentado en EUROMAT: European Congress and Exhibition on advanced materials and processes, celebrado en Sevilla (España) del 8 al 13 de septiembre de 2013.For the preferential oxidation of CO in presence of H2 (CO-PrOX), a very important process in fuel cell technology, ceria-supported CuO has shown to be an efficient and selective catalyst [1], less expensive and more convenient than Pt- or Au- based ones. Our recent work [2] shows that its selectivity is improved if one uses as support a specially prepared CeO2 having cubic nanoparticle shape (i.e. exposing mostly the (001) surface, less stable [3]) rather than CeO2 nanoparticles which, like those obtained in typical syntheses of high surface area ceria, expose mainly the most stable (111) surface. An overview of these results will be given, highlighting the importance of understanding the interfacial relationships at the atomic level. We have now carried out quantum calculations within the DFT+U approach on slab models (Fig. 1) of CuOx nanoparticles displaying (111) surfaces (the most stable ones for this oxide) and supported on these two CeO2 surfaces. The results show that the interfacial energy is higher on the CeO2 (001) surface, in agreement with experimental observations suggesting a stronger CuOx-CeO2 interaction on that surface which stabilizes copper against its reduction to the metallic state; differences are found also in the energy needed to create anion vacancies (i.e. to produce reduced species) on the supported CuO phase, in the distribution of the excess electrons generated in such reduction and in the characteristics of CO molecules adsorbed on the reduced Cu centres to form carbonyls. In situ XPS experiments under gas pressure using synchrotron radiation are being undertaken to know more on the role of these different interfaces in the catalytic behaviour.Peer Reviewe