CO oxidation on Au/FePO4 catalyst: Reaction pathways and nature of Au sites

In situ FTIR spectroscopy coupled with downstream mass spectrometry has been used to clarify the pathways for room temperature (rt) CO oxidation over iron phosphate-supported Au catalyst. The charge state of Au on Au/FePO4 after calcination, reduction, or under reaction conditions was assessed by both FTIR spectroscopy (CO probing) and X-ray absorption near edge spectroscopy (XANES). Results from both approaches show that cationic gold species dominate the surface after pretreatment in O-2 at 200 degrees C. A portion of the cationic gold on Au/FePO4 can be reduced by the initial CO adsorption at rt, and subsequently repeated CO exposures do not reduce the remaining cationic Au. FIR and Raman results from cycled CO reduction and O-2 reoxidation of Au/FePO4 indicate that there are active structural oxygen species on the surface of Au/FePO4 that can be consumed by CO and then replenished by gaseous O-2 at rt. Au activates both CO and O-2 so that the FePO4 Support can undergo reduction (by CO) and reoxidation (by O-2) cycles. The results of CO oxidation with labeled O-18(2) suggest the operation of two parallel reaction pathways at rt: (1) a redox pathway in which FePO4 supplies active oxygen and (2) a direct pathway on metallic Au, via either Langmuir-Hinshelwood or Eley-Rideal mechanism, in which gas phase O-2 provides the active oxygen. (C) 2009 Elsevier Inc. All rights reserved.