Pd3@ZIF-67-Derived Catalyst with Low Palladium Loading for Efficient Hydrogen Production via Ammonia Borane Hydrolysis

The rapid development of hydrogen storage-related technologies has promoted the commercialization of the hydrogen energy industry. Ammonia borane (AB) has the advantages of good reaction controllability, high hydrogen purity, good hydrogen storage capacity and environmentally friendly by-products. It is one of the most studied hydrogen storage materials at present. In this study, [Pd₃Cl(PPh₂)₂(PPh₃)₃]⁺ (Pd₃) nanoclusters stabilized by triphenylphosphine were successfully deposited into ZIF-67 via an in-situ synthesis approach. A series of Pd₃@ZIF-67 derivatives with low palladium loading were subsequently prepared through heat treatment at varying temperatures (Pd₃@ZIF-67-100, Pd₃@ZIF-67-200, Pd₃@ZIF-67-300, Pd₃@ZIF-67-400, Pd₃@ZIF-67-500, and Pd₃@ZIF-67-600). The influence of varying heat treatment temperatures on the hydrolytic activity of AB catalyzed by the Pd₃@ZIF-67-derived nanocatalyst was systematically investigated. The results show that the Pd₃@ZIF-67 derived catalyst exhibits excellent catalytic activity due to the presence of a synergistic effect of palladium and Co₃O₄. Specifically, the turnover frequency (TOF) based on the active palladium content for the hydrolysis of AB at 298 K were determined as follows: 4431.88 mol_H2·min^-1·mol_Pd^-1 (Pd₃@ZIF-67-200), 4880.65 mol_H2·min^-1·mol_Pd^-1 (Pd₃@ZIF-67-300), 2586.81 mol_H2·min^-1·mol_Pd^-1 (Pd₃@ZIF-67-400), 4160.14 mol_H2·min^-1·mol_Pd^-1 (Pd₃@ZIF-67-500), 3449.82 mol_H2·min^-1·mol_Pd^-1 (Pd₃@ZIF-67-600). As the calcination temperature rises, the structure of the Pd₃@ZIF-67 derived catalyst undergoes a gradual transformation from a complete framework to partial collapse and finally reconstruction. Structural changes led to a distinct "volcanic" tendency in the catalytic activity of Pd₃@ZIF-67 derived catalysts. This hybrid catalyst design strategy optimizes the utilization of noble metal elements and provides a universal platform for the development of efficient metal matrix composite nanocatalysts.