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

Palladium nanoparticles of similar size of ~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

Modulating the Structure and Properties of Poly(sodium 4-styrenesulfonate)/Poly(diallyldimethylammonium chloride) Multilayers with Concentrated Salt Solutions

Poly(sodium 4-styrenesulfonate) (PSS)/poly(diallyldimethylammonium chloride) (PDADMAC) multilayers were treated with 1–5 M NaCl solutions, resulting in continuous changes in the physicochemical properties of the multilayers. Significant mass loss was observed when the salt concentration was higher than 2 M and reached as high as 72% in a 5 M NaCl solution. The disassembly occurred initially in the superficial layers and then developed in the bulk multilayers. For the multilayers with PDADMAC as the outmost layer, the molar ratio of PSS/PDADMAC was increased and the surface chemistry was changed from PDADMAC domination below 2 M NaCl to PSS domination above 3 M NaCl. Owing to the higher concentrations of uncompensated for polyelectrolytes at both lower and higher salt concentrations, the swelling ratio of the multilayers was decreased until reaching 3 M NaCl and then was increased significantly again. The salt-treated PSS/PDADMAC thin films are expected to show different behaviors in terms of the physical adsorption of various functional substances, cell adhesion and proliferation, and chemical reaction activity

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

Palladium nanoparticles of similar size of ~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