DOI: 10.1002/cphc.201300537 Structural Characterization of Alumina-Supported Rh Catalysts: Effects of Ceriation and Zirconiation by using Metal–Organic Precursors Anna B. Kroner, [a, d] Mark A. Newton,* [b] Moniek Tromp, [c, d] Andrea E. Russell, [d] Andrew J. Dent, [a] and John Evans* [a, d, e] 1. Introduction Rhodium has long been implemented as a core component in the so-called three-way automotive exhaust catalyst (TWC) as a result of its excellent thermal stability, poison resistance, and superior selectivity for NO x removal. [1–3] A wide range of rhodi- um compounds, for example, single crystal and polycrystalline rhodium surfaces [4–8] as well as supported rhodium parti- cles, [9–12] have been used to build reactivity models of highly dispersed systems. Studies over single crystals have been per- formed with a high degree of control over the surface and mo- lecular/kinetic specificity. However, the behaviour of supported rhodium catalysts has been found to present more complex structures than that of the rhodium single crystal surfaces under equivalent conditions; [13–15] therefore, further study of the structure and catalytic reactivity of dispersed catalysts is re- quired. Owing to the high activity and selectivity of supported rho- dium catalysts, these materials are widely used for reactions such as the hydrogenation of CO, the reduction of NO x to N 2 , the CO–NO reaction, and the water gas shift reaction (WGSR). [11, 16, 17] The overall catalytic performance and catalyst lifetime are significantly improved by doping the catalyst with ceria and/or zirconia. CeO 2 -supported noble-metal catalysts are capable of storing oxygen under oxidizing conditions and re- leasing oxygen under reducing conditions through the facile conversion between the Ce 4 + and Ce 3 +.[18] This feature is strongly related to the creation, healing, and diffusion of oxygen vacancies, especially at the ceria surfaces. [19] The re- peated redox (Lambda) cycling, which TWCs endure under working conditions, [20] places the Rh–Ce interface under signifi- cant stress because of the continuous changes in the lattice The effects of the addition of ceria and zirconia on the struc- tural properties of supported rhodium catalysts (1.6 and 4 wt % Rh/g-Al 2 O 3 ) are studied. Ceria and zirconia are deposited by using two preparation methods. Method I involves the deposi- tion of ceria on g-Al 2 O 3 from Ce(acac) 3 , and the rhodium metal is subsequently added, whereas method II is based on a con- trolled surface reaction technique, that is, the decomposition of metal–organic M(acac) x (in which M = Ce, x = 3 and M = Zr, x = 4) on Rh/g-Al 2 O 3 . The structures of the prepared catalyst materials are characterized ex situ by using N 2 physisorption, transmission electron microscopy, high-angle annular dark-field scanning transmission election microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure spectroscopy (XAFS). All supported rhodium systems readily oxidize in air at room tem- perature. By using ceriated and zirconiated precursors, a larger rhodium-based metallic core fraction is obtained in compari- son to the undoped rhodium catalysts, suggesting that ceria and zirconia protect the rhodium particles against extensive oxidation. XPS results indicate that after the calcination and re- duction treatments, a small amount of chlorine is retained on the support of all rhodium catalysts. EXAFS analysis shows sig- nificant RhCl interactions for Rh/Al 2 O 3 and Rh/CeO x /Al 2 O 3 (method I) catalysts. After reaction with H 2 /He in situ, for series of samples with 1.6 wt % Rh, the EXAFS first shell analysis af- fords a mean size of approximately 30 atoms. A broader spread is evident with a 4 wt % rhodium loading (ca. 30– 110 atoms), with the incorporation of zirconium providing the largest particle sizes. [a] Dr. A. B. Kroner, Prof. A. J. Dent, Prof. J. Evans Diamond Light Source Chilton, Oxfordshire, OX11 0DE (UK) E-mail : john.evans@diamond.ac.uk [b] Dr. M. A. Newton The European Synchrotron Radiation Facility Grenoble, 38043 (France) E-mail : newton@esrf.fr [c] Prof. Dr. M. Tromp Technische Universitat Munchen Lichtenbergstrasse 4, 85748 Garching (Germany) [d] Dr. A. B. Kroner, Prof. Dr. M. Tromp, Prof. A. E. Russell, Prof. J. Evans School of Chemistry, University of Southampton Southampton, SO17 1BJ (UK) E-mail : je@soton.ac.uk [e] Prof. J. Evans Research Complex at Harwell, Rutherford Appleton Laboratory Didcot, OX11 1FA (UK) Supporting Information for this article is available on the WWW under http://dx.doi.org/10.1002/cphc.201300537. # 2013 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. # 2013 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ChemPhysChem 2013, 14, 3606 – 3617 3606 CHEMPHYSCHEM ARTICLES