In Situ Surface Engineering of Mesoporous Silica Generates Interfacial Activity and Catalytic Acceleration Effect

Mesoporous structured catalysts featuring interfacial activity are the most promising candidates for biphasic interface catalysis because their nanopores can concurrently accommodate catalytic active components and provide countless permeable channels for mass transfer between the interior and the exterior of Pickering droplets. However, to date, a convenient and effective strategy for the preparation of an anchor site-containing interfacial active mesoporous catalyst is still lacking. In the present work, we report a novel and efficient interfacial active mesoporous silica (MS) catalyst, which is prepared by a facile cocondensation of two types of organosilanes and subsequent anchoring of Pd NPs onto its surface through the confinement and coordination interactions. The as-prepared catalyst is then applied as emulsifier to stabilize the water-in-oil (W/O) Pickering emulsion and investigated as an interfacial catalyst for the hydrogenation of nitroarenes. An obviously enhanced rate toward the nitrobenzene hydrogenation is observed for the 0.8 mol% Pd/PAP-functionalized mesoporous silica-20 catalyst in the emulsion system (both conversion and selectivity are >99% within 30 min) in comparison to a single aqueous solution. Moreover, the emulsion catalytic system can be easily recycled six times without the separation of the catalyst from the water phase during the recycling process. This finding demonstrates that the incorporation of phenylaminopropyl trimethoxysilane amphiphilic groups during the hydrolysis of tetramethyl orthosilicate not only endows MS with interfacial activity but also improves the catalytic activity and stability.