FTIR STUDY OF CARBON-MONOXIDE OXIDATION AND SCRAMBLING AT ROOM-TEMPERATURE OVER COPPER SUPPORTED ON ZNO AND TIO2 .1.

An FTIR and quadrupole mass spectroscopic study of CO adsorption and o xidation with O-16(2) and O-18(2) on copper supported on ZnO and TiO2 is presented. The experimental results indicate that CO is adsorbed on the metallic particles dispersed on both oxides on two kinds of sites , on the normal terrace sites and on sites at the borderline of the pa rticles. Moreover, on titania, a band at 2126 cm(-1), assigned to CO a dsorbed on isolated Cu atoms and/or on two-dimensional small clusters, is detected. A frequency shift of the bands of CO adsorbed on the met allic particles observed in the CO-O-2 coadsorption experiments and th e occurrence of a scrambling reaction between CO and O-18(2) reveal th at on all these samples, there are metallic sites which are able to ad sorb at the same time oxygen atoms and carbon monoxide. Carbon dioxide and carbonate-like species are formed: the asymmetric stretching freq uencies of CO2 and the quadrupole mass spectroscopic analysis reveal t hat with O-18(2), different isotopic molecular CO2's are formed, while the carbonate-like species have the same frequencies of those produce d in O-16(2). Moreover, these species are completely lacking in the ab sence of oxygen in the gas phase. The experimental results indicate th at there are, on these samples, two independent pathways for the CO ox idation, a direct oxidation of CO at the surface of the metallic parti cles and an induced oxidation with the surface lattice oxygen species of the supports.