Hierarchical Pd@ZIFs as Efficient Catalysts for p-Nitrophenol Reduction

Hierarchical zeolitic imidazolate frameworks (HZIFs) can achieve highly efficient catalysis due to enhanced molecular diffusion and mass transfer. The development of a simple and low-cost method to prepare HZIFs remains a great challenge. Herein, a novel Pd@HZIF catalyst was synthesized via a facile weak-acid (CuCl2) etching method followed by Pd loading; additionally, the effects of the etching time and the concentration of CuCl2 on the microstructures of HZIFs and Pd@HZIFs and the catalytic performance of Pd@HZIFs in p-nitrophenol reduction were investigated in detail. The results highlighted that hierarchical ZIFs with abundant mesopores could be achieved by adjusting the etching time and the concentration of CuCl2, and the hierarchical structure favored the loading of Pd nanoparticles (NPs) with higher total and surface contents. The as-fabricated Pd@HZIF-30-2 catalyst exhibited superior catalytic performance for p-nitrophenol reduction, with a 100% yield of p-aminophenol and a turnover frequency (TOF) value of 805.3 h–1. More importantly, the crystalline structure could be well retained during the etching process, which endowed Pd@HZIF-30-2 with good reusability during four reaction cycles. This strategy holds good potential in the synthesis of hierarchical ZIF-based composites and their possible utilization in catalysis.