Infrared Study of CO Adsorption and Oxidation over Au/Al₂O₃ Catalyst at 150 K

CO adsorption and oxidation over Au/Al 2 O 3 were studied by infrared (IR) spectroscopy at 150 K. Two types of CO adsorption were found on the support, Al 2 O 3, with the existence of gaseous CO (266 Pa). An additional band of adsorbed CO at 2110 cm -1 was found on Au/Al 2 O 3 at 150 K in the presence of gaseous CO and was assigned to CO adsorbed on ultrafine gold particles dispersed on Al 2 O 3 support. After evacuation at the same temperature, the band of CO adsorbed on the ultrafine gold particles decreased in intensity and shifted to 2118 cm -1, whereas the CO adsorbed on Al 2 O 3 disappeared. The band at 2118 cm -1 was assigned to CO irreversibly adsorbed on the ultrafine gold particles at 150 K. CO oxidation by O 2 took place on Au/Al 2 O 3 in the presence of CO and O 2 gas mixture even at 150 K, whereas CO irreversibly adsorbed on Au/Al 2 O 3 and could not be oxidized by the exposure to O 2 at the same temperature. Therefore, the reversibly adsorbed CO on the ultrafine gold particles was found to be the active CO species for CO oxidation at 150 K. By spectral analysis, the reversibly adsorbed CO was found to show a band at 2108 cm -1 . The ultrafine gold particles were oxidized by O 2 treatment at 573 K, becoming inert for CO oxidation at 150 K, but were easily rereduced at 573 K by evacuation treatment. The recovered Au/Al 2 O 3 also catalyzed CO oxidation at 150 K.