Model thin films of Ce(III)-based mixed oxides

Ce(III) sites on cerium oxide-based catalysts are known to be active in many reactions. In order to study the interaction of cerium dioxide with three easily oxidizable elements, aluminum, silicon, and tungsten, and to prepare multicomponent materials of the Ce(III) electronic structure, we followed two inverse approaches: we step-wisely deposited (i) Al, Si, or W onto CeO2(111) and (ii) CeO2 onto Al(111), Si(111), or W(110). We found out that the interaction in all cases was very strong and lead to a formation of mixed oxides of CeAlO3, Ce4.67Si3O13, and Ce6WO12 composition determined by quantitative XPS. The elements were present in Ce(III), Al(III), Si(IV), and W(VI) oxidation states, and the maximum thickness of the films was limited as thicker overlayers prevent the diffusion of the element from the substrate. Above this limit, the deposited aluminum, silicon, or tungsten formed oxides of consequently lower oxidation states on the surface before their purely elemental form was growing, while in the inverse systems, the insufficient diffusion from the Al, Si, and W substrates caused the growth of CeO2 on top of the mixed oxide films. We show that this method permits to prepare model thin films of various thickness and finely tunable Ce(IV) contribution and position (below or above the mixed oxide). Copyright (C) 2014 John Wiley & Sons, Ltd.