Palladium Nanoparticles Supported on Mesoporous Silica as Efficient and Recyclable Heterogenous Nanocatalysts for the Suzuki C–C Coupling Reaction

Palladium (Pd) nanoparticles were synthesized using the dendrimer-template method and then immobilized on a silica support (SBA-15). The SBA-15 support material was specifically synthesized with a pore size large enough (d = 6.6 nm) to accommodate the dendrimer generation used (G-5 PAMAM-OH; d = 5.4 nm). The morphology of the Pd-supported catalyst (Pd⁰/SBA-15) was characterized by scanning electron microscopy coupled to an energy dispersive X-ray spectrometer which confirmed the elemental composition of the catalyst. Transmission electron microscopy confirmed the ordered array of the mesoporous SBA-15 and showed that the Pd NPs were indeed immobilized inside the pores. The catalyst had a pore size of 5.7 nm, a pore volume of 0.78 cm³/g and a surface area of 493 m²/g as determined by surface adsorption/desorption measurements from BET analysis. The prepared Pd⁰/SBA-15 catalyst was an efficient recyclable heterogeneous catalyst for Suzuki coupling. The catalytic activity was investigated using different experimental conditions such as temperature, catalyst loading, base and solvent variations. The catalyst gave high conversions and turnover frequencies even in aqueous solutions and at fairly low temperatures showing the potential for the green synthesis of important organic molecules through C–C bond formation.