DRIFTS-QMS Study of Room Temperature CO Oxidation on AU/SiO2 Catalyst: Nature and Role of Different Au Species

The nature and role of different Au species on a AU/SiO2 catalyst in room temperature (rt) CO oxidation have been studied by operando diffuse reflectance infrared spectroscopy (DRIFT) coupled with quadruple mass spectrometry (QMS). It has shown that different pretreatments (oxidative and reductive) of Au/SiO2, have a significant effect on the nature of Au species and thus the CO oxidation performance. High temperature (500 degrees C) O-2-treatment leads to cationic Au species which is inactive for rt CO oxidation. Reductive treatment (either H-2 or CO) results in metallic Au species that are immediately active for rt CO oxidation. Furthermore, CO oxidation activity is found in good correlation with the reduction degree of Au species, a clear indication of the essential role of metallic Au species played in rt CO oxidation. The accompanying slight deactivation with the oxidation of metallic Au species on reductively treated Au/SiO2 in CO oxidation suggests that cationic Au species may play a negative role in rt CO oxidation. The effect of water in rt CO oxidation on Au/SiO2 was also investigated. Two positive roles played by water in CO oxidation have been identified: activation of O-2 and assistance the reduction of cationic Au species.