Mesoporous Microcapsules through D-Glucose Promoted Hydrothermal Self-Assembly of Colloidal Silica: Reusable Catalytic Containers for Palladium Catalyzed Hydrogenation Reactions

A facile methodology is reported to fabricate hierarchically ordered silica nanoassemblecl microcapsules (SiO2 NACs) with tailored mesopores by combining polymerization of D-glucose with self-assembly of colloidal silica nanoparticles (SiO2 NPs). This controlled self-assembly of SiO2 NPs during a hydrothermal process enables the formation of core-shell (organic/inorganic) hybrid microspheres of carbon and SiO2, NPs. After removal of carbon, spherical hollow SiO2 NACs are formed having mesopores and their surface area was observed as 248 m(2)/g. The synthesized mesoporous SiO2 NACs can be effectively used to encapsulate palladium nanoparticles (Pd NPs) to act as a heterogeneous catalyst in hydrogenation reactions. The position of Pd NPs in SiO2 NACs (either inside the nanopores or throughout the wall of the capsules) can be dictated by the method of encapsulation which can impart selectivity in hydrogenation of various nitroaromatic compounds, alkyne, and alkenes. The advantages of our catalytic system are greener synthesis of catalyst, that lower Pd content (0.3 mol %) was utilized for the catalytic hydrogenation reaction, heterogeneous nature and reusability.