Metal-organic frameworks (MOFs) have been used to encapsulate active metal nanoparticles (MNPs) to fabricate MNPs@MOFs composites with high catalytic efficiencies. However, the diffusion of reactants and the accessibility of MNPs located in the center of MOFs may be hindered due to the inherent microporous structures of MOFs, which would affect the catalytic activities of MNPs. Herein, we report a solvent assisted ligand exchange-hydrogen reduction (SALE-HR) strategy to selectively encapsulate ultrafine MNPs (Pd or Pt) within the shallow layers of a MOF, i.e., UiO-67. The particle sizes of the encapsulated MNPs and the thickness of the MNPs-embedded layers can be adjusted easily by controlling the SALE conditions (e.g. time and temperature). Crucially, the LE-Pd@UiO-80-0.5 composite with the thinnest Pd-embedded layers displays remarkable catalytic efficiency with a high turnover frequency (TOF) value of 600 h⁻¹ towards hydrogenation of nitrobenzene under 1 atm H₂ at room temperature. The results indicate that the catalytic efficiency and the utilization of MNPs can be enhanced by compactly encapsulating MNPs within the shallow layers of MOFs as close to their outer surfaces as possible, owing to the short masstransfer distance and enhanced accessibility of overall MNPs.

金属有机骨架（MOF）已用于封装活性金属纳米颗粒（MNP），以制造具有高催化效率的MNPs @ MOFs复合材料。但是，由于MOF固有的微孔结构会影响MNP的催化活性，因此可能会阻碍反应物的扩散和位于MOF中心的MNP的可及性。在这里，我们报告了溶剂辅助的配体交换氢还原（SALE-HR）策略，以选择性地将超细MNP（Pd或Pt）封装在MOF的浅层（即UiO-67）中。封装的MNP的粒径和MNP嵌入层的厚度可以通过控制SALE条件（例如，时间和温度）。至关重要的是，具有最薄的Pd嵌入层的LE-Pd@UiO-80-0.5复合材料显示出显着的催化效率，在室温下于1 atm H ₂下对硝基苯的氢化具有600h ^-1的高周转频率（TOF）值。。结果表明，由于传质距离短和整个MNP的可及性增强，可通过将MNP尽可能紧密地封装在MOF的浅层中并尽可能靠近其外表面来提高MNP的催化效率和利用率。