MORPHOLOGICAL AND STRUCTURAL-CHANGES IN REDUCING AND STEAM ATMOSPHERES OF SIO2-SUPPORTED RH CATALYSTS

Reduced centres are formed at the silica surface during the pretreatme nt of Rh/SiO2 catalysts at high temperatures (500-900 degrees C). Thes e centres can be titrated with steam according to the reaction: reduce d centre + H2O --> oxidized centre + H-2. The selective formation of H -2 when catalysts pretreated in D-2 are reacted with H2O confirms that steam is decomposed during the titration reaction. XRD, TEM and EDX w ere used to investigate the morphological and structural changes in th e catalysts. Owing to the formation of Rh2Si alloy, the number of redu ced centres formed on SiO2 is much greater than the number found with Rh/Al2O3 reduced under similar conditions.