The adsorption, desorption, and dissociation of CO on supported Rh have been investigated by means of infrared spectroscopy, pulse technique, thermal desorption, and temperature-programmed reaction spectroscopy. The reactivity of surface carbon produced by the disproportionation of CO has been also examined. Special attention has been paid to the effect of supports (TiO2, Al2O3, SiO2, MgO) on these processes. Adsorption of CO on differently supported Rh samples at 300 K produced almost identical infrared spectra; the dominant feature was the appearance of the twin CO band. The desorption temperature of CO, Tmax = 463-473 K, was practically the same for all samples. The efficiency of the supports in promoting the dissociation of CO over Rh decreased in the order TiO2 > Al2O3 > SiO2 > MgO. Temperature-programmed reaction spectroscopy revealed that different kinds of surface carbon are produced by CO dissociation. The ratios of these forms depends on the temperature of their production, as well as on their thermal treatments. The surface carbon reacted with H2 at a lower temperature on Rh TiO2, but the aging of carbon was also fastest on this sample. The activation energy of the hydrogenation of the reactive surface carbon increased in the order Rh TiO2 < Rh Al2O3 < Rh SiO2.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry