SPECTROSCOPIC EVIDENCE FOR ADSORPTION SITES LOCATED AT CU/ZNO INTERFACES

FTIR spectra are reported of CO and formic acid adsorption on a series of Cu/ZnO/SiO2 catalysts. Peaks due to linear CO adsorbed on copper diminished in intensity as the loading of ZnO was increased. This behaviour was explained in terms of ZnO island growth on the copper surface. Similarly, reduction of the copper concentration while maintaining a constant ZnO loading also resulted in further attenuation in bands ascribed to CO chemisorbed on copper. Formic acid exposure to a Cu/SiO2 sample produced a formate species displaying a v(as)(COO) mode at 1585 cm(-1). Addition of a small quantity of ZnO to the catalyst resulted in substantial promotion of formate growth, which was accompanied by a shift (and broadening) of the v(as)(COO) vibration to 1660-1600 cm(-1). Since further ZnO incorporation poisoned formate creation it was concluded that formate species bonded to Cu and Zn sites located at interfacial positions had been formed. Tne role of such species in methanol synthesis is discussed.