Interaction of carbon dioxide with Cu overlayers on Pt(111)

Experimental and theoretical studies on the interaction of carbon dioxide with pseudomorphic and rough copper layers deposited on a platinum (111) single crystal are reported. Evidence for carbon dioxide dissociation and carbonate formation is presented and the relevance to methanol synthesis is discussed. Intermediate species on the surfaces were identified using in situ polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) at pressures up to similar to 550 mbar and electron energy loss spectroscopy (EELS) in ultra-high vacuum. Temperature programmed desorption (TPD) reveals a broad high temperature desorption state for CO2 with peak maximum around 450 K. X-ray photoelectron spectroscopy (XPS) shows that approximately one third of the oxygen accumulated on the surface upon CO2 exposure remains after TPD, indicative of carbonate formation via CO2 dissociation supplying O-ads and then facile CO2 + O-ads association, as well as subsequent decomposition at higher temperatures. Density functional theory studies of stepped Cu and Cu/Pt slabs reproduce vibrational frequencies of the carbonate, suggesting a nearly flat tridentate configuration at steps/defect sites.