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 nanoassembled microcapsules (SiO 2 NACs) with tailored mesopores by combining polymerization of d -glucose with self-assembly of colloidal silica nanoparticles (SiO 2 NPs). This controlled self-assembly of SiO 2 NPs during a hydrothermal process enables the formation of core–shell (organic/inorganic) hybrid microspheres of carbon and SiO 2 NPs. After removal of carbon, spherical hollow SiO 2 NACs are formed having mesopores and their surface area was observed as 248 m 2 /g. The synthesized mesoporous SiO 2 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 SiO 2 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.