Richard Joseph Uriarte

Metal colloid morphology and catalytic activity : further proof of the intermediacy of colloids in the platinum-catalyzed hydrosilylation reaction

Abstract Transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM) were used to analyze the platinum colloids formed during hydrosilylation reactions. Reaction solutions were analyzed for the addition of Et3SiH to either n-hexene or neohexene catalyzed by bis{1,3diviny1,1,1,3,3-tetramethyldisiloxane}Pt0 (Karstedts catalyst) and this analysis showed dramatic differences between the morphology of the Pt colloid formed in each case. The neohexene reaction, which gave 62% conversion to products in 1 h, contained polycrystalline, 2.5-nm-diameter Pt particles, whereas the n-hexene reaction only went to 10% conversion in 1 h and contained 1- to 1.5-nm Pt particles. The reaction of Et3SiH with styrene gave results similar to those with neohexene.

The effect of metal colloid morphology on catalytic activity: Further proof of the intermediacy of colloids in the rhodium-catalyzed hydrosilylation reaction

Abstract The relative activity of different morphological forms of Rh colloids were examined by transmission electron microscopy (TEM) or high resolution electron microscopy (HREM). The degree of agglomeration of the Rh colloid was affected by either its storage history (e.g. refrigerator or bench top) or by the use of a vinyl silicone stabilizer. The smaller particle size (higher surface area) yellow Rh colloid was more active than the larger particle size red Rh colloid. A black Rh colloid, which contained no stabilizer, was more active than both the yellow and red forms. The heterogeneous nature of both Pt and Rh catalyzed reactions was further confirmed by inhibition studies with mercury.