Au/CeOx/Al2O3 is highly active for CO oxidation at low temperatures and full conversion is already achieved around 60 degrees C. From experimental results, it is concluded that ceria can act as oxygen supplier probably via Mars and van Krevelen mechanism. The H-2-D-2 isotopic exchange reaction is also efficiently catalyzed by Au/Al2O3. The gold particle size is of crucial importance for high activity. Most likely, a gold surface rich in defects activates the H-2 (D-2) molecules.(c) 2005 Elsevier B.V. All rights reserved.