Size-Tunable Synthesis of Palladium Nanoparticles Confined within Topologically Distinct Metal-Organic Frameworks for Catalytic Dehydrogenation of Methanol

In this study, three topologically distinct zirconium-based metal-organic frameworks (Zr-MOFs), i.e., UiO-66, NU-902, and PCN-222, were synthesized and employed as porous supports to immobilize Pd nanoparticles (NPs) via the solvothermal deposition in MOFs (SIM) technique. Physicochemical characterizations show that the structural, morphological, and textural features of pristine Zr-MOFs are mainly preserved upon the incorporation of Pd NPs. It is shown that the sizes of Pd NPs are controllable by the pore confinement of Zr-MOFs. Reaction testing reveals that Pd@UiO-66 displays significantly higher catalytic activity and lower activation energy as compared to Pd@NU-902 and Pd@PCN-222 for methanol dehydrogenation. The observed enhanced performance of Pd@UiO-66 is attributed to the smaller size of Pd NPs due to the smaller pore size of UiO-66. In situ infrared spectroscopy characterizations suggest that methanol is activated on the surface of UiO-66 to form methoxy adspecies, and the Pd NPs within the framework of UiO-66 aid in the further dehydrogenation of methoxy adspecies, thereby facilitating the overall dehydrogenation of methanol.