Dynamically modulated synthesis of hollow metal-organic frameworks for selective hydrogenation reactions

Hollow metal-organic frameworks (MOFs) have attracted increasing attention in the field of catalysis in recent years due to their unique cavity structure with fast mass-diffusion rates and easily accessible active sites. Here, we report the use of dynamic modulators, which are formed by the in-situ imine condensation reaction of 4-aminobenzoic acid and 4-formylbenzoic acid, to regulate the growth of MOFs to synthesize well-defined hollow thioether functionalized UiO-67 (denoted as H-UiO-67-S) single crystals. After supporting Pd nanoparticles, the designed catalysts Pd@H-UiO-67-S show excellent conversion (> 99.9%), selectivity (> 99.9%), and stability (10 cycles) in the selective hydrogenation of nitrobenzenes with other reducible groups. Density functional theory calculations and the experimental results reveal that Pd nanoparticles not only selectively adsorb the nitro-groups on nitrobenzene, but also restrict the adsorption of the aniline product, due to the interaction of thioether with Pd in the confined pores of H-UiO-67-S, finally result in a significant increase in selectivity of nitro-hydrogenation.