CO adsorption on Rh (0.5 wt%) supported by SiO2, Al2O3, and TiO2 was studied by DRIFT spectroscopy at 296 K and atmospheric pressure. A support effect on the particle size distribution was evident by dominant dicarbonyl species on Rh/Al2O3 and Rh/TiO2, characteristic for CO adsorption 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 nondissociative on Rh/SiO2, while on Rh/Al2O3 and Rh/TiO2 CO dissociation occurred at 296 K. CO desorption at 296 K was reductive, which led to irreversible agglomeration of rhodium clusters; in thermal CO desorption (up to 500 K), this process was strongly enhanced.