FTIR study of carbon monoxide oxidation and scrambling at room temperature over gold supported on ZnO and TiO2 .2.

An FTIR and quadrupole mass spectroscopic study of CO adsorption and oxidation with O-16(2) and O-18(2) is presented together with coadsorption experiments of CO and water on gold supported on ZnO and TiO2. The experimental results are closely related to those presented in the parallel paper on copper catalysts supported on the same oxides. The most important points are as follows: (i) CO is found to be activated on the metallic particles on two kinds of sites, the normal terrace sites and sites at the borderline of the particles; (ii) there is evidence that on the examined samples there are metallic sites which are able to adsorb both oxygen and carbon monoxide molecules at the same time; (iii) carbon dioxide and carbonate-like species are formed; the asymmetric stretching frequencies of CO2, the quadrupole mass spectroscopic analysis, and the IR spectra analysis reveal that with O-18(2), different isotopic molecular CO2 is formed while the carbonate-like species have the same frequencies of those produced in O-16(2); (iv) there are two independent pathways for CO oxidation, a rapid direct oxidation of CO at the surface of the metallic particles and a slow induced oxidation with the surface lattice oxygen species of the supports; (v) evidence is found that CO-H2O coadsorption experiments produce atomic hydrogen on Au/ZnO, not on Au/TiO2.