INFRARED STUDY OF CARBON-MONOXIDE HYDROGENATION OVER RHODIUM CERIA AND RHODIUM SILICA CATALYSTS

Carbon monoxide hydrogenation over ceria-promoted Rh or Rh/SiO2 catalysts was investigated by means of Fourier transform infrared spectroscopy. In the chemisorption of CO at room temperature, a new absorption band was observed near 1725 or 1696 cm-1 on a reduced 5% Rh-5% CeO2/SiO2 or 5% Rh/CeO2 catalyst, respectively. This new absorption band was attributed to a C- and O-bonded species, located at the metal/support interface. The appearance of this species was related to the shift to lower temperatures of the peak ascribed to CO dissociation in the temperature-programmed desorption spectra after CO adsorption. A flow high-pressure IR cell allowed to study the surface species in situ during CO + H2 reaction and to follow the reactivity of these species toward pure H2. The results suggest that the drop in methane formation may be related to a lower reactivity of surface carbon in the presence of the promoter. The high selectivity to ethanol compared to acetaldehyde on ceria-containing catalysts is explained by a difference of adsorption of acetaldehyde on promoted and unpromoted catalysts. © 1990 American Chemical Society.