Chemistry

When Ceria Met Titania

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Science  24 Apr 2009:
Vol. 324, Issue 5926, pp. 441
DOI: 10.1126/science.324_441c

Mixed metal oxides, especially of redox-active metals, can play an important role in catalysis. Both titanium oxide, or titania (TiO2), and cerium oxide (ceria, CeO2) are widely applied individually, often in tandem with lower-oxidation-state transition metals such as platinum, palladium, and gold. It has been largely unclear, however, how these two high-valent metal oxides might behave chemically in tandem with one another. Park et al. sought to answer this question. Specifically, they used a combination of scanning tunneling microscopy (STM), photoemission spectroscopy, and density functional theory (DFT) calculations to examine the structures that form when ceria nanoparticles are grown on the TiO2 (110) surface; growth was induced by deposition of cerium atoms onto the surface, followed by annealing in oxygen. The STM images revealed a structure for the adsorbed ceria nanoparticles that was rather distinct from that seen for adsorption on metal surfaces—dimers run diagonally to the rows and troughs of the titania surface—and photoemission revealed a reduced Ce3+ oxidation state. DFT calculations were consistent with the formation of Ce2O3 dimers. When gold was co-deposited along with the cerium, a highly active catalyst for the water-gas-shift and CO oxidation reactions resulted; much more effective than gold deposited on either metal oxide surface alone.

Proc. Natl. Acad. Sci. U.S.A. 106, 4975 (2009).

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