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Ceria-supported gold catalysts

Ceria-supported gold systems have excellent catalytic activity for the water-gas shift (WGS) reaction, which is a crucial step in many applications such as the production of hydrogen for fuel cells. Despite extensive studies, questions concerning the catalytic roles of gold nanoparticles and the ceria support and the relative importance of different WGS reaction mechanisms remain open. In our recent work, we address a couple of fundamental issues about the nature of reduced ceria surfaces, the gold adsorption and its anchoring site, and the gold nucleation. Answers to these issues would provide insight towards understanding the boundary structure between gold and ceria, which in turn would hold promise to unravel their catalytic roles.

We investigated oxygen vacancy monomer, dimer, trimer and tetramer at ceria surfaces, demonstrating that vacancy growth, involving one subsurface vacancy, could proceed in a linear fashion, although the vacancy clusters are less stable than those containing no subsurface vacancies. Fig.1 shows the spin states of a linear vacancy tetramer, in which the f electrons play a decisive role in stabilizing the structure. On the perfect surface, we also identified a new bridgelike site, which is the most stable gold adsorption site. We also clarified the controversy about the anchoring sites for gold clusters. We showed that the previous suggestion about the cerium vacancy being the anchoring site is incorrect and instead gold would strongly prefer the oxygen vacancy. We also explored the gold nucleation and identified some characteristic cluster structures at the surface. All the calculations were done with the DFT+U method.

Figure 1. The electron densities of the gap states which are localised on the cerium ions neighbouring the vacancy clusters.

Related publications

"Theory of gold on ceria"
C. Zhang, A. Michaelides and S.J. Jenkins
Phys. Chem. Chem. Phys. 13 (2011) 22-33

"Positive charge states and possible polymorphism of gold nanoclusters on reduced ceria"
C. Zhang, A. Michaelides, D.A. King and S.J. Jenkins
J. Am. Chem. Soc. 132 (2010) 2175

"Oxygen vacancy clusters on ceria: Decisive role of cerium f electrons"
C. Zhang, A. Michaelides, D.A. King and S.J. Jenkins
Phys. Rev. B 79 (2009) 075433

"Anchoring sites for gold nanoparticles on ceria: O vacancy versus Ce vacancy"
C. Zhang, A. Michaelides, D.A. King and S.J. Jenkins
J. Phys. Chem. C 113 (2009) 6411

"Structure of gold atoms on stoichiometric and defective ceria surfaces"
C. Zhang, A. Michaelides, D.A. King and S.J. Jenkins
J. Chem. Phys. 129 (2008) 194708

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