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 Au+. 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 Au+ 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 Au0–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.

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