Chlorine Residue in the Au/γ-Al2O3 Prepared by AuCl3 Impregnation—an EXAFS Analysis

From EXAFS (extended X-ray absorption fine structure) analysis, gold was found to have mainly oxygen in its nearest coordination shell in the fresh Au/γ-Al2O3 catalyst prepared by AuCl3 impregnation and vacuum drying at room temperature. After thermal treatment under helium, chlorine appeared within the nearest neighbors of gold and more chlorine showed up as the treatment temperature was increased from 323 to 473 K. No reduced Au species was observed up to 473 K under He. However, the gold became reduced during CO oxidation at 373 K and above. The precursor AuCl3 was found to deposit on γ-Al2O3 via bonding to surface hydroxyl groups. This catalyst showed nearly 100% CO conversion at 573 K, but a very low activity at ≤373 K under the conditions used in this study. Neither the residual chlorine nor the extent of reduction can explain the low activity at lower temperatures.