INFRARED SPECTROSCOPIC STUDIES OF CO ADSORPTION ON RHODIUM SUPPORTED BY SIO2, AL2O3, AND TIO2

CO adsorption on Rh (0.5 wt%) supported by SiO2, Al2O3, and TiO2 was s tudied by DRIFT spectroscopy at 296 K and atmospheric pressure. A supp ort effect on the particle size distribution was evident by dominant d icarbonyl species on Rh/Al2O3 and Rh/TiO2, characteristic for CO adsor ption on dispersed clusters, while significant proportions of linear- and bridged-bonded CO, ascribed to CO adsorbed on crystalline rhodium, were observed on Rh/SiO2. Adsorption and desorption of CO was nondiss ociative on Rh/SiO2, while on Rh/Al2O3 and Rh/TiO2 CO dissociation occ urred at 296 K. CO desorption at 296 K was reductive, which led to irr eversible agglomeration of rhodium clusters; in thermal CO desorption (up to 500 K), this process was strongly enhanced. (C) 1994 Academic P ress, Inc.