Supplementary Material (ESI) for Chemical Communications This journal is (c) The Royal Society of Chemistry 2007 Supporting information Genesis of a highly active Cerium Oxide-Supported Gold Catalyst for CO Oxidation Veronica Aguilar-Guerrero and Bruce C. Gates* Experimental A. Sample preparation Samples were synthesized and handled in the absence of moisture and air by using a double manifold Schlenk vacuum line and a dry box purged with Ar that was recirculated through traps containing of supported Cu and zeolites 4A for removal of O 2 and moisture. The sample containing 1 wt% Au on CeO 2 was synthesized from Au(CH 3 ) 2 (C 5 H 7 O 2 ) (Strem 99.9%) and high-surface-area CeO 2 (Daiichi, 99.9%, 173.3 m 2 /g and average particle size 45.7 nm, with this information provided by the supplier). The catalyst was prepared by forming a slurry of Au(CH 3 ) 2 (C 5 H 7 O 2 ) in n-pentane with CeO 2 powder that had been partially dehydroxylated under vacuum at 673 K. The slurry was stirred for 24 h, and the solvent was removed by evacuation for 24 h. B. X-Ray Absorption Spectroscopy (XAS) Data characterizing the as-prepared and treated samples were recorded at 298 K. Approximately 0.2 g of sample was used for this purpose. The XAS experiments were performed at beam line 2-3 of the Stanford Synchrotron radiation Laboratory (SSRL) at the Stanford Linear Accelerator Center, Stanford, CA, and at beam line X-18B of the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory, Upton, NY. The