Silica Particles As an Effective Scavenger for Platinum Catalyst Recovery

Hydrosilylation is the addition reaction between a silicon hydride and an unsaturated bond to form a silicon-oxygen or silicon-carbon bond. Platinum is usually used as a catalyst in hydrosilylation reactions for synthesis of organosilicon products i.e., organosiloxanes (or organosilanes). In general, the homogeneous platinum catalyst is typically not recovered and remains as an impurity in non-volatile products of the reaction. The focus of this study is on recovery of Pt from polymeric siloxanes that have been chemically functionalized through hydrosilylation using Karstedt’s platinum catalyst. The products of this reaction are visibly colored light yellow to dark black due to the platinum metal impurity that results from decomposition of residual catalyst over time. Fixed-bed adsorption technology using thiol-functional silica adsorbent has been shown to be an effective technique for Pt recovery from organosilicon compounds synthesized via hydrosilylation. Here we demonstrate that colloidal thiol-functional silica particles can be used to scavenge residual platinum. The thiol-silica particles (~2 microns in diameter) were synthesized from (3-mercaptopropyl)trimethoxysilane. After washing and drying the product, the resulting colloidal silica particles were in the form of a dry powder that can be dispersed into the product of hydrosilylation. The silica particles are large enough in diameter to easily be separated from the product by centrifugation. This was an effective method for platinum product color removal since the products showed much reduced color and lower platinum metal content.