Supported Catalysts: Synthesis and Characterization. Final Report

摘要

The basic steps in the synthesis of supported catalysts are: nucleation, growth and coagulation. The nucleation process is one of polymerization-condensation of the starting inorganic monomer. Silicic acid or hydrated aluminum ions polymerize individually to form long polymeric chains. In the case of metal systems the metal ion and the organic reducing agent form co-polymers which, on reaching a certain size, undergo internal redox reaction to produce the colloidal metal. Using different metal ions, colloidal alloys can be formed. These polymers have been isolated in the case of gold and now are being studied for platinum, palladium and their alloys. Their formation was investigated by the STEM electron microscope at Brookhaven. The growth step is carried out by innoculating a solution containing a potential reducing agent (such as gold chloride or palladium chloride and hydroxyl amine) with nuclei of either platinum, gold, or palladium. In this way by control of the proportion of the nuclei to the ion, the gold and palladium can be grown to the desired size and gold layered on platinum or palladium. Platinum can be grown on platinum by innoculating a hydrogen-platinum chloride system with platinum nuclei. The stability of these colloidal sols is controlled by the electric charge on the particles which counteracts the effect of van der Waals' attraction. The charge is determined by adsorbed ions and can be controlled both in magnitude and in sign. The ionic atmosphere around each particle is controlled by the ionic strength of the solution. The characterization of the materials so prepared can be made both in solution and in the solid phase. The techniques employed are optical absorption, light-scattering, viscosity, ultra-centrifugation, conventional electron microscopy, ultrahigh resolution electron microscopy, laser Raman spectroscopy, electron spin resonance and carbon-13 NMR of absorbed molecules. (ERA citation 06:011312)