Active Morphology of Au/γ-Al2O3—A Model by EXAFS

Au/γ-Al2O3 catalysts were prepared by depositing AuCl3 onto low-soda γ-Al2O3 under different pH. EXAFS (extended X-ray absorption fine structure) analysis showed that Au species were mainly in the Au–O bonding environment when dried at 298 K, regardless of the suspension pH during deposition. Au–(O)–Al bonding was also suggested from EXAFS analysis of catalysts prepared at pH ranging from 4.1 to 9.4, indicating a deposition via the coordination of surface hydroxyl groups to Au species. However, Au–(O)–Au was found instead of Au–(O)–Al in the catalyst prepared at an extreme pH of 10.5, indicating a deposition of polymeric Au(OH)3. The catalysts were tested for CO oxidation without further pretreatment. The one prepared at pH 10.5 catalyzed the CO oxidation reaction effectively at 323 K whereas that prepared at pH 4.1 showed negligible activity. This suggested that a specific Au–O morphology, such as the polymeric Au(OH)3, could be responsible for the high CO oxidation activity of supported Au catalysts.