Characterization of Au-Rh/TiO2 bimetallic nanocatalysts by CO and CH3CN adsorption: XPS, TEM and FTIR measurements.

On X-ray photoelectron spectra of the Au-Rh/TiO2 catalysts the position of Au4f peak was practically unaffected by the presence of rhodium, the peak position of Rh3d, however, shifted to lower binding energy with the increase of gold content of the catalysts. Rh enrichment in the outer layers of the bimetallic crystallites was experienced. The bands due to Au0-CO, Rh0-CO and (Rh0)2-CO were observed on the IR spectra of bimetallic samples, no signs for Rh+-(CO)2 were detected on these catalysts. The band due to CH3CN on Lewis acid centers shifted to lower wavenumbers with the increase of Rh content, which shows that the strength of Lewis acid sites weakens with the increase of Rh content of the catalysts. CH3CN, on the other hand, dissociates producing CN(a) species even at this temperature. From the shift to higher wavenumbers of the band due to CN(a) the strengthening of the C-N bond with increasing Rh content has been established. The results were interpreted by electron donation from titania through gold to rhodium and by the higher particle size of bimetallic crystallites. The effects of catalyst composition, reaction temperature and composition of the reacting gas mixtures have been studied on the oxidation of CO in the presence of hydrogen (PROX process). The presence of both O2 and H2 reduced the surface concentration of CO adsorbed on metallic sites. Mass spectroscopic analysis of the gas phase showed that gaseous CO2 formed in the highest amount in CO+O2 mixture, the presence of H2 suppressed the amount of CO2 produced. This negative effect of hydrogen was the lowest on 1% Rh/TiO2, the highest inhibition was observed on Au/TiO2 systems.