Immobilized Pd nanoparticles on Tris-modified SiO2: Synthesis, characterization, and catalytic activity in Heck cross-coupling reactions

Abstract

The preparation of supported Pd nanoparticles on Tris (tris(hydroxymethyl)aminomethane)-modified SiO2 gel and their catalytic application in Heck coupling are investigated. The catalyst was characterized using a combination of X-ray diffraction, transmission electron microscopy, field-emission scanning electron microscopy, and scanning electron microscopy/energy-dispersive X-ray spectroscopy. The supported Pd nanoparticles were found to be a highly active and reusable catalyst for the Heck reaction at a low Pd loading (0.02 mol%) because of stabilization by the Tris moieties. Several reaction parameters, including the type and amount of solvent, base, and temperature, were evaluated. The heterogeneity of the catalytic system was investigated using different approaches, and showed that slight Pd leaching into the reaction solution occurred under the reaction conditions. Despite this metal leaching, the catalyst can be reused seven times without significant loss of its activity.