Synthesis of ultrafine Pd nanoparticles encapsulated in imidazolium-based porous polymers for semi-hydrogenation of alkynes

Abstract

Interaction between metal and support can dramatically affect the activity and selectivity of supported metallic nanoparticles. Therefore, the development of novel support is a critical path to achieve advanced catalysis. Here, we report that imidazolium-based porous polymers were prepared through a free-radical cross-linking reaction. These imidazolium-based porous polymers with high specific surface area and abundant imidazonium units were utilized as supports to synthesize ultra-small and narrow dispersed Pd nanoparticles . The optimized catalyst displayed 99% selectivity for styrene at 98% conversion in alkyne semi-hydrogenation under ambient conditions with a general application. Comprehensive characterizations demonstrated that the interaction between cationic imidazolium-based porous polymers and Pd enhanced the alkene selectivity by weakening the adsorption on Pd, as well as stabilized Pd nanoparticles by the anchoring and spatial confining effects. The pivotal roles of the Pd-imidazonium interaction and the mesoporous structure provide valuable guidance for the manufacture of high-performance metallic nanoparticles catalyst for selective hydrogenation.