ADSORPTION OF CARBON-MONOXIDE ON MANGANESE-PROMOTED RHODIUM SILICA CATALYSTS AS STUDIED BY INFRARED-SPECTROSCOPY

Infrared spectroscopy was used to study the adsorption of carbon monoxide on silica-supported rhodium catalysts promoted with manganese oxide. Addition of the promoter suppressed overall adsorption, weakened the adsorption of the linear CO species, and created a broad new absorption band with a maximum near 1715 cm-1; this new low-frequency band is thought to be due to a tilted Rh-C-O-Mn species. On the promoted catalyst both the new low-frequency species and the linear CO species react with hydrogen much more rapidly than does the linear species on the unpromoted catalyst Additionally the promoted catalyst does not chemisorb CO at 80 K; adsorption on this catalyst is an activated process, and maximum adsorption is observed only when the sample is exposed to CO at 373 K. This increase in adsorption is believed to be caused by a reconstruction of the manganese oxide overlayer. © 1990 American Chemical Society.