Novel Colloid Based Heterogeneous Catalysts

Unprotected, that is to say electrostatically stabilized, colloids of the precious metals can be attached to supports, presumably through electrostatic interactions, and there are numerous examples of heterogeneous catalysts prepared in this manner. Although the use of colloids as heterogeneous catalyst precursors will not be covered in detail here, some results should be mentioned. 

PVP stabilized rhodium or platinum sols (3.5 nm) have been grafted onto mer-capto-derivatized silica. [254] The S-H groups ligate strongly to the metal particles. In this case the grafted catalyts are one to two orders of magnitude more active for the hydrogenation of alkenes than the unsupported colloidal catalysts in the same solvent system, and 300 times more active than commercial Rh/C and Pt/C catalysts. 

2 Liquid Phase Hydrogenation of Unsaturated Organic Moiecules 

Vapor derived colloidal catalysts in nonpolar liquids were investigated as catalysts for the hydrogenation of acenaphthylene (Eqn. 6.6). [133] 

Palladium and cobalt colloids stabilized with iro-butylaluminoxane, (i o-BuAIO) , in methylcyclohexane catalyzed the hydrogenation of the activated double bond of acenaphthylene to acenaphthene at 25 °C, (Eqn. 6.6). In the case of the cobalt catalyst, heating to 80 °C resulted in the further hydrogenation of one of the aromatic rings in acenaphthene, a reaction which was poisoned by the addition of dibenzothiophene. 

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Vorlop et al. suggested a novel strategy for heterogenizing homogeneous and colloidal chiral catalysts based on the three-dimensional entrapment of catalyst by electrostatic attraction between a polyelectrolyte and an active metal in the polymeric matrix. Based on this method, they entrapped chirally stabilized Pt-colloid in alginate (polymannuronate) and conducted twenty-five hydrogenation cycles of EtPy. 

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