We have investigated the effects of heat treatment in air and H-2/Ar on Au/titania-coated silica aerogel catalysts prepared through adsorption of thiol-capped Au nanoparticles (AuNPs). Sulfur atoms remained on the support surfaces in the form of sulfates upon calcination at temperatures below 773 K. X-ray absorption fine structure and in situ infrared absorption measurements of the catalysts suggested that some of the sulfates affected the catalytic properties of the AuNPs through the interactions between AuNPs and sulfates. The turnover frequency for CO oxidation reaction of the catalysts was enhanced by a factor of 3-5 upon the removal of the sulfates through calcination at 873 K or H-2/Ar treatment at 673 K after calcination at 673 K. These results reveal the importance of the contribution of Au-support interfaces to the CO oxidation efficiency on Au/TiO2 catalyst systems. (C) 2009 Elsevier Inc. All rights reserved.