Experimental and Theoretical Study on the Electronic Interaction between Rh Adatoms and CeOx Substrate in Dependence on a Degree of Cerium Oxide Reduction

The electronic metal-substrate interaction plays an important role in the surface reactions on supported metal nanoparticles. We study the interaction between rhodium clusters and cerium oxide substrate having various stoichiometries, CeOx (2.00 > x > 1.67), by means of photoelectron spectroscopy. Our results show that rhodium deposited on substrates with stoichiometry of 2.00 > x > 1.93 induces reduction of cerium oxide. On the other hand, cerium oxide with a higher degree of reduction (1.93 > x > 1.67) becomes partially oxidized after the Rh deposition. Density functional theory simulations of Rh adatom adsorbed on the CeO2(111) surface and on an oxygen vacancy at the CeOx(111) surface show that there is a charge transfer between rhodium and cerium oxide substrate. While Rh adsorption on the CeO2(111) surface leads to electron depletion at the Rh adatom and cerium oxide reduction, Rh adsorption on the oxygen vacancy at CeOx(111) leads to electron accumulation about the Rh adatom and partial oxidation of cerium oxide. The results clearly demonstrate that the electronic metal-substrate interaction occurs on Rh/CeOx systems and strongly depends on the stoichiometry of cerium oxide. These findings could be beneficial for designing catalysts with specific properties.