High catalytic activity of Au/CeO x/TiO 2(110) controlled by the nature of the mixed-metal oxide at the nanometer level

Abstract

Mixed-metal oxides play a very important role in many areas of chemistry, physics, materials science, and geochemistry. Recently, there has been a strong interest in understanding phenomena associated with the deposition of oxide nanoparticles on the surface of a second (host) oxide. Here, scanning tunneling microscopy, photoemission, and density-functional calculations are used to study the behavior of ceria nanoparticles deposited on a TiO2(110) surface. The titania substrate imposes nontypical coordination modes on the ceria nanoparticles. In the CeO x/TiO 2(110) systems, the Ce cations adopt an structural geometry and an oxidation state (+3) that are quite different from those seen in bulk ceria or for ceria nanoparticles deposited on metal substrates. The increase in the stability of the Ce 3+ oxidation state leads to an enhancement in the chemical and catalytic activity of the ceria nanoparticles. The codeposition of ceria and gold nanoparticles on a TiO 2(110) substrate generates catalysts with an extremely high activity for the production of hydrogen through the water-gas shift reaction (H 2O + CO → H 2 + CO 2) or for the oxidation of carbon monoxide (2C0 + O 2→2CO 2). The enhanced stability of the Ce 3+ state is an example of structural promotion in catalysis described here on the atomic level. The exploration of mixed-metal oxides at the nanometer level may open avenues for optimizing catalysts through stabilization of unconventional surface structures with special chemical activity.