N-Containing Macromolecule-Coordinated Pd Nanoparticles Confined in Silica Nanoreactors for Selective Hydrogenation of Alkynes

Inhibiting overhydrogenation of alkenes is challenging for alkyne hydrogenations. Especially for those phenyl-activated terminal alkynes, such as phenylacetylene, achieving good alkene selectivity while keeping high catalytic activity is difficult. In this work, we design a templating method to synthesize polymer-covered Pd nanoparticles encapsulated in hollow silica nanoreactors (Pd-polymer@HSNs) as highly efficient semihydrogenation catalysts. Without the sacrifice of templates and by controlling the reduction temperatures, the polymer inside hollow silica nanospheres can be retained. The obtained Pd-polymer@HSNs exhibit enhanced alkene selectivity for a series of alkyne substrates, and high selectivity can be maintained at a prolonged reaction time. Especially Pd-polymer@HSNs demonstrate good styrene selectivity as well as good activity for phenylacetylene substrate and rank as one of the best catalysts with the highest catalytic efficiency among Pd-based catalyst with encapsulated macromolecules. The good performance of Pd-polymer@HSNs can be attributed to the optimum polymer network inside the hollow cavities, which may limit the access of alkene to the active surfaces of Pd NPs to avoid deep-hydrogenation and, in the meantime, favor the access of alkyne to the active surfaces to achieve good activity.