Facet Engineering of a Metal–Organic Framework Support Modulates the Microenvironment of Palladium Nanoparticles for Selective Hydrogenation

Abstract

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-8_X @Pd@ZIF-8 (x represents the morphology of ZIF-8 core, i.e., ZIF-8_C exposing (100) facet, ZIF-8_RD exposing (110) facet, and ZIF-8_TRD 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-8_C @Pd@ZIF-8 than that in ZIF-8_RD @Pd@ZIF-8, leading to discriminative adsorption of the -NO₂ and -Cl groups of p-chloronitrobenzene. Consequently, ZIF-8_C @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.