Temperature programmed desorption of CO and NO over gold/ceria catalysts for NOx reduction

The present paper reports a study of gold catalysts supported on ceria and ceria-alumina (20 wt.% alumina) by means of temperature programmed desorption (TPD) technique. It was observed that after the CO adsorption, at room temperature, on such samples, pre-treated either in helium or in hydrogen, CO2 is desorbed. Only CO2 was noted in desorption in the case of the pre-treatment in helium sample. In the case of the sample pre-treated in hydrogen a supplementary CO TPD peak was also detected. The formation of CO2 - either during CO adsorption or its desorption - is in agreement with the high oxygen storage and oxidation capacity of this type of catalysts. The reverse water gas shift (RWGS) reaction between CO2 and H2 - incorporated in ceria structure during the pre-treatment - could explain the CO appearance. After NO adsorption on both types of catalysts no trace of N2 was detected in desorption. This means that on these catalysts only a reversible, i.e. a non-dissociative, NO adsorption takes place. This result shows that the adsorption properties of gold/ceria catalysts are completely different, compared to platinum group metals supported on ceria catalysts, fact which could determine a different NO+CO reaction mechanism.