Size-Controlled Synthesis of Palladium Nanoparticles on a Silica-Cyclodextrin Substrate: A Novel Palladium Catalyst System for the Heck Reaction in Water

This study offers an example of using a silica-cyclodextrin (SCD) substrate for the capture of metal nanoparticles to prepare a novel nanocatalyst for catalytic organic reactions in water as a green solvent. Also, a simple and efficient method for the size control of palladium nanoparticles (PdNPs) using their immobilization on a SCD substrate was introduced. These new catalyst systems were fully characterized using some different techniques such as XRD, TEM, SEM, TGA, ICP, XPS, and FT-IR. The average size of immobilized PdNPs on silica alpha-, beta-, and gamma-CD substrates were obtained (10, 3, and 5 nm, respectively). The immobilized PdNPs on the silica beta-CD substrate (PdNP-S beta CD) was recognized as the best one for the Heck reaction in aqueous media. It seems that the anchored CD moieties on the silica surface can prevent removal of PdNPs and also their aggregations. Moreover, this substrate can provide appropriate catalytic sites for reactions in aqueous media; therefore, the PdNP-S beta CD catalyst showed high activity in the Heck reaction in aqueous media.