Strong interaction between rhodium and ceria

Rh was loaded on various supports including ceria by a colloid deposition method. The average particle size of the starting Rh colloid was about 50 A. When it was deposited on alumina or zinc oxide, Rh particles were clearly observed by a TEM analysis. However, no TEM image of Rh was obtained on ceria which was prepared by calcination at 550°C. ESCA and XRD analyses revealed that Rh penetrated into the ceria and only a small amount remained on the surface. On the other hand Rh was present as metallic particles on the surface of ceria which was calcined at 950°C. The ceria calcined at a low temperature (550°C) had high surface area; thus, this ceria had high surface energy and could dissolve Rh. Although the amount of Rh exposed on the surface of ceria was small, the Rh in this state was highly active in decomposing methanol.