UCL CENTRE FOR MATERIALS RESEARCH

Research Summary

Oxide-supported gold catalysts are known to be very active in the low-temperature water gas shift reaction and in the preferential oxidation of CO in the presence of hydrogen, which are important reactions for the purification of hydrogen feeds in fuel cells.

We have used electronic structure calculations based on the density functional theory to investigate the interaction of gold atoms with the surfaces of cerium and zirconium oxides. We have shown that gold adatoms at the (111) surface of ceria can adopt Au0, Au+ or Au- electronic configurations depending on the adsorption site, thus modifying the redox properties of the ceria surface.

On the other hand, the adsorption of gold at non-defective zirconia surfaces does not lead to any charge transfer behavior, but we have found that the substitution of gold in lattice positions at a zirconia surface induces a dramatic change in the redox properties of the surface, which becomes easily reducible thanks to Au(III) - Au(I) transitions.

Pd atoms can also transfer charge to the Ce atoms at the ceria surface, according to our calculations. Similar conclusions have been reached by an XPS investigation of Pd deposion on ceria ultra-thin films .