Comparative study of Au/Al2O3 and Au/CeO2-Al2O3 catalysts

Two gold-containing catalysts, Au/Al2O3 and Au/CeO2-Al2O3, have been prepared by deposition-precipitation and characterized by different techniques (XRD, transmission electron microscopy (TEM), FTIR spectroscopy of adsorbed CO and catalytic test). The Au/CeO2-Al2O3 sample demonstrates a much higher catalytic activity in the CO oxidation reaction than does the Au/Al2O3 sample. IR spectroscopy of adsorbed CO reveals that ceria generally keeps gold in a more oxidized state. Gold is in the form of Au3+ on the as-prepared samples. Low-temperature CO adsorption on the Au/Al2O3 sample evacuated at 473 K leads to the formation of Au+-CO species evidencing reduction of Au3+ to An(+). No gold carbonyls are detected on the Au/CeO2-Al2O3 sample evacuated at the same temperature, this indicating that no auto-reduction has occurred. A carbonyl band at 2143 cm(-1), assigned to Au+-CO species formed with An(+) cations on metal gold particles, is registered after low-temperature CO adsorption on the Au/CeO2-Al2O3 sample evacuated at 673 K, while CO adsorption on the Au/Al2O3 sample treated in the same way leads to the formation of Au-0-CO species (carbonyl band at 2106 cm(-1)). Only metal gold was detected on the hydrogen-reduced Au/Al2O3 sample (carbonyl band at 2101 cm(-1)) while on the Au/CeO2-Al2O3 sample reduced with hydrogen, in addition to the metal gold (carbonyl band at 2108 cm(-1)), Au+ sites were also detected (carbonyl band at 2131 cm(-1)). The role of the cationic gold sites in the CO oxidation reaction is discussed. (c) 2006 Elsevier B.V. All rights reserved.