Effect of Pretreatment Variables on the Reaction of Nitric Oxide (NO) with Au−TiO₂:  DRIFTS Studies

Abstract

The effect of the pretreatment on the interaction between NO and Au−TiO 2 was examined using DRIFTS as a monitoring tool. For calcined and reduced Au−TiO 2, adsorption of NO on the TiO 2 support is not promoted under the conditions employed. Au(NO) 2 is the predominant species on oxidized and reduced Au−TiO 2 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−TiO 2 to 1850 cm -1 for oxidized Au−TiO 2 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 (N 2 O formation) were detected at higher NO pressures and temperatures. Adsorption of NO on oxidized Au−TiO 2 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 TiO 2 support dominate the spectra for oxidized Au−TiO 2 .