Stabilized Gold Nanoparticles on Ceria Nanorods by Strong Interfacial Anchoring Na Ta, † Jingyue (Jimmy) Liu,* ,†,‡ Santhosh Chenna, § Peter A. Crozier, § Yong Li, † Aling Chen, † and Wenjie Shen* ,† † State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China ‡ Department of Physics and § School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, Arizona 85287, United States * S Supporting Information ABSTRACT: Au/CeO 2 catalysts are highly active for low- temperature CO oxidation and water-gas shift reaction, but they deactivate rapidly because of sintering of gold nanoparticles, linked to the collapse or restructuring of the gold-ceria interfacial perimeters. To date, a detailed atomic-level insight into the restructuring of the active gold-ceria interfaces is still lacking. Here, we report that gold particles of 2-4 nm size, strongly anchored onto rod- shaped CeO 2 , are not only highly active but also distinctively stable under realistic reaction conditions. Environmental transmission electron microscopy analyses identified that the gold nanoparticles, in response to alternating oxidizing and reducing atmospheres, changed their shapes but did not sinter at temperatures up to 573 K. This finding offers a new strategy to stabilize gold nanoparticles on ceria by engineering the gold-ceria interfacial structure, which could be extended to other oxide-supported metal nanocatalysts. S ince the discovery that nanosized gold particles, dispersed on metal oxides, are highly active for low-temperature CO oxidation, 1 extensive and intensive studies have been ongoing to understand the chemical nature of the active sites associated with the frequently observed high activities for an increasing number of reactions. 2 It is now generally acknowledged that the gold- oxide interfacial perimeter acts as the active site; the gold particles have to be smaller than 5 nm in order to obtain high activity, while the oxide support, especially reducible oxides, alters the catalytic property significanly. 2b,c,3 In this context, Au/ CeO 2 catalysts have attracted particular attention because of their exceptionally high activities for low-temperature CO oxidation 4 and water-gas shift (WGS) reaction. 3b,5 The key function of ceria is to disperse and stabilize gold nanoparticles through its surface oxygen vacancies that strongly depend on the size and shape of ceria crystallites. For example, CeO 2 of 3-4 nm size with a large number of surface oxygen vacancies increased the CO oxidation rate of gold nanoparticles by 2 orders of magnitude. 4a The use of CeO 2 nanorods that are rich in surface oxygen vacancies has greatly enhanced the activities of gold particles for low-temperature CO oxidation 4b,c and WGS reaction. 5c These highly active Au/CeO 2 catalysts, however, deactivated rapidly under realistic reaction conditions, primarily due to sintering of gold nanoparticles. Such a deactivation behavior is associated with the collapse or restructuring of the active gold-ceria interfaces, induced by the effects of temperature and reactive gases. Changes in the shape and size of gold nanoparticles in Au/ CeO 2 catalysts have been examined both at elevated temper- atures in a vacuum 6 and under reactive gases at ambient temperature. 7 However, changes in the active gold-ceria interface at practical temperatures and under reactive atmos- pheres were not well considered. Herein, we use atomic resolution environmental transmission electron microscopy (ETEM) to directly observe the structural changes of the Au/ CeO 2 catalyst under conditions close to those of the reaction. Gold particles of 2-4 nm size, in response to alternating oxidizing and reducing atmospheres, changed their shapes but did not sinter at temperatures up to 573 K due to the strong interfacial bonding on CeO 2 . The visual evidence was correlated with the prominent stabilities of the Au/CeO 2 catalysts in low- temperature CO oxidation and WGS reaction and raised the possibility of stabilizing gold nanoparticles by engineering the gold-oxide interfacial anchoring pattern. We recently reported that rod-shaped ceria had a much higher activity in CO oxidation than conventional spherical ceria, mainly because of the facile generation of more surface oxygen vacancies. 8 In this work, the CeO 2 nanorods were further calcined at 973 K in air to ensure their stable size and shape during the subsequent loading of gold particles and the reaction tests. Analyses of TEM images showed that the high-temper- ature-treated ceria nanorods were largely enclosed by {111} planes; the average width of the nanorods was ∼8 nm, and their lengths ranged from 50 to 200 nm, with a surface area of 75 m 2 /g (Figure S1 in the Supporting Information (SI)). Gold particles were then dispersed onto the ceria nanorods by a deposition- precipitation method (details in the SI). The size of the gold particles depended strongly on the temperature of calcination. For the Au/CeO 2 catalyst calcined at 573 K, labeled as Au-573, individual Au atoms, subnanometer-sized Au clusters (<1 nm), and faceted Au particles (1-3 nm) were all present, as clearly shown in the aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images (Figures 1a,b and S2a). When the same sample was calcined at 673 K, referred to as Au-673, however, faceted gold particles with a narrow size distribution of 2-4 nm were Received: October 19, 2012 Published: December 11, 2012 Communication pubs.acs.org/JACS © 2012 American Chemical Society 20585 dx.doi.org/10.1021/ja310341j | J. Am. Chem. Soc. 2012, 134, 20585-20588