Palladium nanoparticles confined in thiol-functionalized ordered mesoporous silica for more stable Heck and Suzuki catalysts

Palladium nanoparticles of similar size of similar to 2 nm were synthesized on different silica-based materials, all functionalized with thiol groups i.e., Aerosil-380, SBA-15, plugged SBA-15 and m-MCF. The resulting materials were used to study the influence of the confinement of Pd nanoparticles in a functionalized silica support on the Heck and the Suzuki reactions. In the case of the Heck reaction, for all catalysts it was proven that leached Pd species were responsible for the activity. However, the catalysts based on ordered mesoporous silica were still able to restrict Pd particle growth, giving rise to an enhanced stability. For the Suzuki reaction, stronger alkaline conditions were required and catalysts based on plugged SBA-15 showed a higher stability than those based on SBA-15 and m-MCF, which both collapsed after the first cycle. At almost identical Pd particle size, ordered mesoporous materials enhance stability and particle growth is slowed down but not fully suppressed.