FTIR absorption spectra of Co. of (CO)-C-12-(CO)-C-13 isotopic mixtures and of CO-O-18(2) interaction on gold catalysts supported on group IV oxides are reported together with CO quantitative chemisorption data. On Au/TiO2 two kinds of metallic gold surface sites, mutually interacting, adsorb CO in spite of the low CO/Au ratio (0.03). On Au/ZrO2, where a CO/Au ratio of 0.30 has been determined, mutually interacting corner sites on non-metallic gold nanoclusters are present. Finally, isolated and negatively charged gold nanoclusters have been evidenced on Au/CeO2. Different absorption coefficients have been found, On all samples, by contacting CO-O-18(2) at 90 K, only (COO)-O-16-O-18 is produced: gold sites are involved in the activation of both molecules. The largest amount of (COO)-O-16-O-18 is produced on the CeO2 supported sample, as a consequence of an easier activation of the oxygen on the anionic gold clusters and on the support. (C) 2009 Elsevier Inc. All rights reserved.