Influence of TiO₂ Bulk Defects on CO Adsorption and CO Oxidation on Au/TiO₂: Electronic Metal–Support Interactions (EMSIs) in Supported Au Catalysts

Electronic metal–support interactions (EMSIs) are demonstrated to severely affect the CO oxidation activity and the CO adsorption properties of Au/TiO 2 catalysts. Bulk oxygen vacancies, generated by a strongly reductive pretreatment of Au/TiO 2 at elevated temperature in 10% CO/N 2, significantly lower the catalytic activity for CO oxidation at 80 °C. With time on stream, the activity slowly increases until reaching the same steady-state value as that obtained for a previously calcined and, hence, defect-poor Au/TiO 2 catalyst (activation period), where the time required for the activation period decreases with reaction temperature but is independent of the oxygen partial pressure. Considering the similar Au particle sizes and Au loadings, we conclude that the different activities originate from the presence of bulk oxygen vacancies generated during pretreatment, which are slowly replenished during reaction. In situ IR spectroscopy measurements reveal that the lower activity in the presence of bulk defects is coupled with and likely results from a strong modification of the CO adsorption strength on the reduced Au/TiO 2 catalysts due to EMSIs. A possible mechanism explaining how these EMSIs may be induced by the presence of bulk defects is discussed.