Hierarchical Pd@ZIFs as Efficient Catalysts forp-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 CuCl₂on the microstructures of HZIFs and Pd@HZIFs and the catalytic performance of Pd@HZIFs inp-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 forp-nitrophenol reduction, with a 100% yield ofp-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.