Dual Microenvironment Modulation of Pd Nanoparticles in Covalent Organic Frameworks for Semihydrogenation of Alkynes.

Abstract

The chemical microenvironment modulation of metal nanoparticles (NPs) holds promise in tackling the long-lasting challenge of trade-off effect between activity and selectivity in catalysis. Herein, ultrafine PdCu2 NPs incorporated into covalent organic frameworks (COFs) with diverse groups on their pore walls have been fabricated for semihydrogenation of alkynes. The Cu species as the primary microenvironment of Pd active sites greatly improves the selectivity. The functional groups as the secondary microenvironment around PdCu2 NPs effectively regulate the activity, in which PdCu2 NPs encapsulated in the COF bearing -CH3 groups exhibit the highest activity with 100% conversion and >96% selectivity. Both experimental and calculation results suggest that the functional group affects the electron-donating ability of the COFs, which successively impacts the charge transfer between COFs and Pd sites, giving rise to modulated Pd electronic state and excellent catalytic performance.