Effect of pretreatment variables on the reaction of nitric oxide (NO) with Au-TiO₂: DRIFTS studies

The effect of the pretreatment on the interaction between NO and Au-TiO: was examined using DRIFTS as a monitoring tool. For calcined and reduced Au-TiO:, adsorption of NO on the TiO₂ support is not promoted under the conditions employed. Au(NO): is the predominant species on oxidized and reduced Au-TiO₂ with initial bands at 1818 and 1740 cm^-1. Analysis showed that these species are sensitive to the surface coverage, temperature, and the state of the underlying surface, shifting from 1820 cm ^-1 for reduced Au-TiO₂ to 1850 cm^-1 for oxidized Au-TiO: and from 1740 to 1734 cm^-1 with increasing surface temperature. It is proposed that different dinitrosyl components are formed on the surface and are bonded to Au sites in different chemical environments. Small dissociative contributions (N₂O formation) were detected at higher NO pressures and temperatures. Adsorption of NO on oxidized Au-TiO₂ is dominated by bridging NO adsorbates (bands at 1665 and 1641 cm^-1) at low NO exposures, but linearly bound NO (bands at 1873, 1860, 1838, and 1808 cm^-1) were detected with increasing NO coverage. Products of dissociation and associated mainly with the TiO₂ support dominate the spectra for oxidized Au-TiO₂.