We found that a CuO/CeO2 catalyst where the CeO2 carrier is nanocube-shaped, exposing the less stable (001) surface, has better selectivity than others where CeO2 exposes different surfaces in the purification of H2 from CO via preferential oxidation of the latter. Thus we have attempted to understand this phenomenon, which may help to better design the catalyst, using DFT simulations at the PBE+U theory level and periodic CeO2 slab models with CuOx wires lying on them to model the supported catalyst. We find that on CeO2(001) the Cu oxide wires adhere better and deform the CuOx structure more than on CeO2(111) due to the lower stability and higher reactivity of CeO2(001). The deformation and higher wetting effect in the latter case explains that no CuO peaks are seen in XRD for the CeO2 nanocubes-based sample, while they are seen when using a nanosphere-type CeO2 for similar surface Cu coverage. Besides, the progressive reduction of CuO to Cu2O and of the latter to Cu(0) is found to be less favourable on CeO2(001); this agrees with the higher selectivity to CO2 found for the nanocube-supported sample, since H2 activation and oxidation is assumed to require the Cu(0) redox state. In addition, upon anion vacancy formation the fraction of electrons released which goes to form Ce(3+) instead of reducing Cu is larger on CeO2(001) than on CeO2(111), which may have additional consequences for reactivity.

Trabajo presentado en el E-MRS Spring Meeting, celebrado en Lille (Francia) del 26 al 30 de mayo de 2014.

Peer Reviewed