Sintering and impurities of Pt-black catalysts of various treatment has been followed by analtical electron microscopy. Silicon contamination of H2PtCl6 has been incorporated into Pt-black reduced from it in aqueous medium. Sintering in hydrogen between 470 and 750 K produced polydisperse Pt. The silicon content decreased monotonically with increasing sintering temperature. Correlation has been found between specific surface and Si percentage. A mechanism for removal of Si from Pt has been proposed consisting of the Pt catalyzed enhancement of reduction of silicon by hydrogen resulting, ultimately in SiH4. The segregation of carbon above about 670 K was observed leading to a two-dimensional carbonaceous overlayer of graphite character.
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