Infrared study of CO adsorption and oxidation over Au/Al2O3 catalyst at 150 K

CO adsorption and oxidation over Au/Al2O3 were studied by infrared (IR) spe ctroscopy at 150 K. Two types of CO adsorption were found on the support, A l2O3, With the existence of gaseous CO (266 Pa). An additional band of adso rbed CO at 2110 cm(-1) was found on Au/Al2O3 at 150 K in the presence of ga seous CO and was assigned to CO adsorbed on ultrafine gold particles disper sed on Al2O3 support After evacuation at the same temperature, the band of CO adsorbed on the, ultrafine gold particles decreased in intensity and shi fted to 2118 cm(-1), whereas the CO adsorbed on Al2O3 disappeared. The band at 2118 cm(-1) was assigned to CO irreversibly adsorbed on the ultrafine g old particles at 150 K. CO oxidation by O-2 took place on Au/Al2O3 in the p resence of CO and O-2 gas mixture even at 150 K, whereas CO irreversibility adsorbed on Au/Al2O3 and could not be oxidized by the exposure to O-2 at t he same temperature. Therefore, the reversibly adsorbed CO on the ultrafine gold particles was found to be the active CO species for CO oxidation at 1 50 K. By spectral analysis, the reversibly adsorbed CO was found to show a band at 2108 cm-l. The ultrafine gold particles were oxidized by O-2 treatm ent at 573 K, becoming inert for CO oxidation at 150 K, but were easily rer educed at 573 K by evacuation treatment. The recovered Au/Al2O3 also cataly zed CO oxidation at 150 K.