Adsorption and reaction of CO on vanadium oxide-Pd(111) "inverse" model catalysts: an HREELS study

The room temperature adsorption and reaction of CO on Pd(111) surfaces deco rated with submonolayer coverages of vanadium oxide - so-called "inverse" m odel catalysts - have been studied by high-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS). The HREEL S surface phonon spectra of the V oxide phases have been measured and used to monitor the changes in the oxide as a result of the interaction with CO. The intramolecular C-O stretching frequency of CO adsorbed on the V-oxide/ Pd(111) surfaces displays two vibrational loss components as a function of CO coverage as it has been observed on the clean Pd(111) surface. The relat ive intensities of the two vibrational features as a function of V oxide co verage however suggest that the balance of CO adsorption sites is modified as compared to clean Pd(111) by the presence of the V oxide-Pd phase bounda ry. Preferential population of high coordination adsorption sites by CO in the vicinity of the oxide-metal interface is proposed. The analysis of the V oxide phonon spectra indicates that adsorbed CO partially reduces the V o xide at the boundaries of the oxide islands to the Pd metal. The reduction of V oxide by CO is dependent on the oxygen content of the V oxide phase. T he reduction of V oxide is confirmed by the XPS V 2p core level shifts.