Rh inclusion in sol-gel SiO2. Effects of Rh precursors on metal dispersionand SiO2-Rh thermal behavior

RhCl3. nH(2)O and [RhCl(C2H4)(2)](2) are used as precursors for the prepara tion of 1%Rh in sol-gel derived SiO2. The gelling process of Si(OEt)(4) is carried out in the absence of solvent and under strong acid catalysis. The thermal behavior of Rh precursors, of SiO2 gel and Rh-SiO2 composites is in dependently studied by analysing organic species released at definite tempe rature intervals and concomitantly collecting infrared, XPS, TEM, XRD and p orosity data. Results indicate that nanometric Rh particles may be obtained from [RhCl(C2H4)(2)](2), their dispersion being homogeneous, dense and sta ble up to 250 degrees C, whereas RhCl3. nH(2)O affords less metallic disper sion with other crystalline Rh-species; in both cases, well-shaped Rh metal crystallites are obtained at 650 degrees C. The different synthetic approa ches used for the preparation of RhCl3- and [RhCl(C2H4)(2)](2)-derived samp les, are invoked to account for the features of Rh dispersion obtained by m ild temperature treatment. Moreover, the particular procedures for sol-gel SiO2 synthesis are related to the high-temperature maintenance of great por osity and elevated specific surface area.