Adsorption of acetonitrile and its reaction with oxygen on TiO2-supported Au — Rh bimetallic catalysts

The adsorption of acetonitrile and its surface reactions with oxygen on TiO2-supported Au — Rh bimetallic catalysts were studied by FTIR and mass spectrometry at 300–673 K. The band due to CH3CN on Lewis acid centres shifted to lower wavenumbers with the increase of the Rh content, which shows that the strength of Lewis acid sites weakens with the increase of the Rh content of the catalysts. CH3CN, on the other hand, dissociates producing CN(a) species. From the shift to higher wavenumbers of the band due to CN(a), strengthening of the C — N bond with increasing Rh content has been established. During the heat treatments of the adsorbed CH3CN layer, methylamine (CH3NH2) was detected in the gas phase, the amount of which depended on the composition of the catalysts. Dehydrogenation of the adsorbed acetonitrile also depends on the Rh content: the higher the Rh content of the sample, the lower the temperature of the first appearance of gaseous H2, and the higher the amount of H2 evolved. The presence of gaseous oxygen affects the formation of isocyanate (NCO) surface species only on 1% Au/TiO2 and on 1% (0.75Au–0.25Rh)/TiO2 catalysts.