Poly(hydromethylsiloxane)-derived High Internal Phase Emulsion-Templated Materials (polyhipes) Containing Palladium for Catalytic Applications

Cross-linking of poly(hydromethylsiloxane) (PHMS) with 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane (D4Vi) in water-in-oil high internal phase emulsion (HIPE) whose aqueous phase comprises PdCl2 is developed as a new, one-step route for the fabrication of polysiloxane-based, porous HIPE-templated materials (polyHIPEs) containing palladium. It is shown that the microstructure of the systems depends on the amount of D4Vi with respect to PHMS and is also significantly influenced by the presence of PdCl2 in HIPE. PolyHIPEs thus obtained contain metallic Pd nanoparticles (~ 4–10 nm in size) that strongly interact with the polysiloxane matrix they are dispersed in. The materials catalyse phenylacetylene hydrogenation to styrene yielding this product with fair selectivity. Incorporation of Pd into the pre-formed PHMS-based polyHIPE (the two-step procedure) conducted for comparison results in the material containing nanoclusters of Pd and displaying highly selective hydrogenation of phenylacetylene to styrene, but at a relatively low rate.