Confined Palladium Nanoparticles within a Robust Hierarchical Porous Zr-Based Metal–Organic Framework for Aromatic Alcohol Oxidation

The development of novel host-guest catalysts with nanoscale active sites provides new opportunities to gain highly efficient catalytic performance for the oxidation of aromatic alcohols into high-value compounds. In this work, we develop a green and facile synthesis method to incorporate Pd nanoparticles (Pd_NP) into a robust hierarchical porous Zr-metal-organic framework (Zr-IPA) through in situ solvent-free synthesis and wet reduction techniques. The optimized Pd_NP/Zr-IPA catalyst exhibits exceptional benzyl alcohol oxidation performance, selectively oxidizing 95.3% of benzyl alcohol to benzaldehyde (yield of 97.7%) at 70 °C within 12 h. Additionally, Pd_NP/Zr-IPA demonstrates superior catalytic activity for the oxidation of various aromatic alcohols using different oxidants. The turnover frequency of Pd_NP/Zr-IPA reaches 82.3 h^-1 at 70 °C, which is 4.2 times larger than that of pre-Pd_NP/Zr-IPA and surpasses most reported MOF-based catalysts in benzyl alcohol oxidation reactions. Quenching and electron paramagnetic resonance tests verified that the exposed (111) faces of the Pd_NP in the Pd_NP/Zr-IPA structure can react with oxidants to generate ^•O₂^- radicals, which play a dominant role in oxidizing benzyl alcohol to benzaldehyde. Our work provides a solvent-free synthesis and a wet reduction strategy for confining nanoparticles within MOFs to enhance catalytic activity in targeted reactions.