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

The chemical microenvironment modulation of metal nanoparticles (NPs) holds promise for tackling the long‐lasting challenge of the 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 the 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 >99 % conversion and 97 % 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 a modulated Pd electronic state and excellent catalytic performance. The PdCu2 nanoparticles are incorporated into isoreticular COFs, namely, MF−X (X=−CH3, −H, −CF3 and −CN), for the semihydrogenation of alkynes, where PdCu2@MF−CH3 exhibits the best catalytic performance. The dual modulation of the Pd microenvironment turns out to be crucial: the Cu species (primary microenvironment) improves the selectivity, while the engineered pore walls around PdCu2 sites (secondary microenvironment) optimize the activity.