Morphological and structural changes in reducing and steam atmospheres of SiO2-supported Rh catalysts

Reduced centres are formed at the silica surface during the pretreatment of Rh/SiO₂ catalysts at high temperatures (500-900°C). These centres can be titrated with steam according to the reaction: reduced centre + H₂O → oxidized centre + H₂. The selective formation of H₂ when catalysts pretreated in D₂ are reacted with H₂O confirms that steam is decomposed during the titration reaction. XRD, TEM and EDX were used to investigate the morphological and structural changes in the catalysts. Owing to the formation of Rh₂Si alloy, the number of reduced centres formed on SiO₂ is much greater than the number found with Rh/Al₂O₃ reduced under similar conditions. This revised version was published online in July 2006 with corrections to the Cover Date.