Synergistic Effects of Hierarchically Porous Structures and Amino Groups in Pd@MOFs for the Selective Hydrogenation of Phenol

Cyclohexanone is a pivotal feedstock for the nylon industry that can be produced via one-step hydrogenation of phenol. Metal organic frameworks (MOFs) have wide applications in heterogeneous catalysis owing to their tuneable porous structures, compositions, and surface properties. Metal nanoparticles (NPs) supported on MOFs (M@MOFs) can effectively catalyze the phenol hydrogenation to cyclohexanone; however, the recyclability of M@MOFs is still not satisfactory, and the influences of the textural properties of M@MOFs are barely investigated. Herein, the surface properties and pore structures of UiO-66 were controllably modified through simply modulating the organic linkers and adjusting the composition of the synthesis solvent, and the synergistic effects of hierarchically porous structures and amino groups in Pd@UiO-66 for the selective hydrogenation of phenol were investigated in detail. Using 2-aminoterephthalic acid as the organic linker and introducing water in the synthesis solvent, Pd@HPUiO-NH₂ with well-developed hierarchically porous structures and amino groups can be fabricated, and then, stable Pd NPs with good dispersion are achieved, resulting in superior catalytic performance in the phenol hydrogenation (97.9% phenol conversion with 93.7% cyclohexanone selectivity after six reaction cycles). Furthermore, the recycled Pd@HPUiO-NH₂ exhibits a high turnover frequency, surpassing most of the reported MOF-based catalysts. These findings can aid the development of high-performance MOF-based catalysts and green cyclohexanone production.