Investigating the impact of dynamic structural changes of Au/rutile catalysts on the catalytic activity of CO oxidation

The surface properties of oxidic supports and their interaction with the supported metals play critical roles in governing the catalytic activities of oxide-supported metal catalysts. When metals are supported on reducible oxides, dynamic surface reconstruction phenomena, including strong metal-support interaction (SMSI) and oxygen vacancy formation, complicate the determination of the structural-functional relationship at the active sites. Here, we performed a systematic investigation of the dynamic behavior of Au nanocatalysts supported on flame-synthesized TiO2, which takes predominantly a rutile phase, using CO oxidation above room temperature as a probe reaction. Our analysis conclusively elucidated a negative correlation between the catalytic activity of Au/TiO2 and the oxygen vacancy at the Au/TiO2 interface. Although the reversible formation and retracting of SMSI overlayers have been ubiquitously observed on Au/TiO2 samples, the catalytic consequence of SMSI remains inconclusive. Density functional theory suggests that the electron transfer from TiO2 to Au is correlated to the presence of the interfacial oxygen vacancies, retarding the catalytic activation of CO oxidation. We have found that the transfer of electrons from TiO2 to Au, facilitated by interfacial oxygen vacancies (Vo), is the main factor responsible for the low catalytic activity observed in Vo-rich Au/TiO2 catalysts, which consequently leads to the suppression of CO oxidation. Therefore, we recommend that the preparation of Vo-free Au/TiO2 catalysts should be considered to improve both the activity and stability of CO oxidation.image