CuOx dispersed on different ceria surfaces: influence on activity and selectivity for the CO-PrOx process

Abstract

Catalytic preferential oxidation of CO in the presence of H2 (CO-PrOx process) is employed for purifying H2 produced from hydrocarbons and fed to low temperature fuel cells in order to avoid CO poisoning of the Pt-based anode employed in such type of fuel cells. Our recent work shows that the selectivity (related to the portion of oxygen used to oxidise CO vs. that employed to oxidise H2, which are basically the two competing reactions in the process) of ceria-supported CuOx in the process is appreciably improved (Fig. 1a) if one uses as support a specially prepared CeO2 having cubic nanoparticle shape (i.e. exposing mostly the (001) surface, less stable) rather than rounded or rod-like CeO2 nanoparticles which, like those obtained in typical syntheses of high surface area ceria, expose mainly other surfaces. Detailed characterization using XRD and TEM along with XPS and EPR evidences that the Cu oxide phase disperses very efficiently on the nanocube-shaped CeO2, suggesting stronger CuO-ceria interaction on the (001) surface of the latter. This could be the reason for the higher stability of surface Cu+ carbonyls during reaction, which apparently could retard the reduction of copper to the non-selective metallic state, as evidenced by DRIFTS data obtained under reaction conditions (Fig. 1b); XPS experiments under gas atmosphere using synchrotron radiation are expected to be completed shortly in order to get further support for this hypothesis. In turn, differences in the catalytic activity of the dispersed CuOx entities as a function of the exposed face present in the underlying CeO2 support are also revealed by such DRIFTS experiments. The experimental results are also complemented by DFT+U calculations on slab models of CuOx nanoparticles supported on different CeO2 surfaces.