Hydrogenation of 1,3-butadiene over Au/ZrO2 catalysts with different gold loadings and calcination temperatures was reported. The catalysts were characterized in depth to understand their structure-property relationship. Gold oxidation states and surface hydroxyl groups, which were found to be sensitive to the gold loading, calcination temperature, and treatment with water, were shown to play vital roles in the hydrogenation activity of Au/ZrO2. Continued activity decrease was seen when the density of surface hydroxyl groups was lowered by elevating the pre-calcination temperature of ZrO2. Fully dehydroxylated Au/ZrO2 was essentially inactive, but became very active after partial regeneration of the hydroxyl groups by water treatment. Moreover, the activity of Au/ZrO2 increased with increasing Au3+/Au-0 ratio. Isolated Au3+ ions at the support surface showed up to two orders of magnitude higher activity than Au-0 atoms on Au particles. Several models are proposed to address the structural features of active sites for H-2 activation in Au/ZrO2 catalysts. (C) 2011 Elsevier Inc. All rights reserved.