We have characterized a series of Cu ZnO catalysts prepared by several methods, using a combination of adsorbate uptake measurements, temperature-programmed desorption, and FTIR spectroscopy applied to CO, H 2, and O 2 adsorbates. Adsorbed CO is present on the reduced catalysts in several adsorption states which are distinguished by different vibrational frequencies in the range 2104-2067 cm −1, and which desorb with apparent activation energies in the range 10–16 kcal/mol. When CO is adsorbed on oxidized catalysts, the frequencies shift to 2136-2110 cm −1 and the highest desorption energy increases to 19 kcal/mol. For H 2 adsorbed on reduced catalysts, a single desorption state which has an apparent activation energy of 20–21 kcal/mol is observed. When H 2 is adsorbed on oxidized catalysts, the desorption energy of this state increases to 26–27 kcal/mol. For the reduced catalysts, the amounts of reversible CO and H 2 adsorbed are found to correlate linearly with the amount of O 2 chemisorption measured at 98 K, with relative uptakes for CO, H 2, and O 2 in the ratio 9:2:10. These results are interpreted to suggest that Cu is present as metallic clusters which expose a large fraction of high-index surface planes and that the chemical behavior of these planes is significantly different from that of low-index single crystal planes.