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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. [ABSTRACT FROM AUTHOR]

The exposed facets of supported catalysts play a crucial role in catalysis; however, they are usually ignored and related studies remain rare. Herein, we have fabricated a series of sandwich‐structured metal–organic framework composites, denoted ZIF‐8X@Pd@ZIF‐8 (x represents the morphology of ZIF‐8 core, i.e. ZIF‐8C exposing (100) facet, ZIF‐8RD exposing (110) facet, and ZIF‐8TRD exposing mixed (100) and (110) facets), featuring Pd nanoparticles deposited on the specific crystal facets of ZIF‐8 core, for hydrogenation of p‐chloronitrobenzene. The Pd electronic state is tailored by the ZIF‐8 core, where more electron‐deficient Pd is found in ZIF‐8C@Pd@ZIF‐8 than that in ZIF‐8RD@Pd@ZIF‐8, leading to discriminative adsorption of the −NO2 and −Cl groups of p‐chloronitrobenzene. Consequently, ZIF‐8C@Pd@ZIF‐8 exhibits excellent activity (97.6 %) and selectivity (98.1 %) to p‐chloroaniline. This work highlights crystal facet engineering of supports to modulate the microenvironment and electronic state of supported metal nanoparticles, offering a promising avenue to enhanced catalysis. [ABSTRACT FROM AUTHOR]