Protective Spillover-Hydrogenation Catalyst Based on Pd-Loaded Metal-Organic Frameworks

Metal catalysts are crucial for hydrogenation reactions but suffer from overhydrogenation due to their strong activation capacity. Herein, a protective spillover-hydrogenation catalyst on Pd-loaded metal-organic frameworks (MOFs) is developed, isolating the metal to avoid direct contact with the substrate while ensuring active hydrogen transfer for out-sphere hydrogenation. Specifically, the steric effect was induced by incorporating poly(vinylpyrrolidone) (PVP) on Pd/UiO-66. The barrier formed by PVP's alkane chains prevents the direct contact of aldehydes with Pd, while selectively permeating H₂ molecules for being activated into electrons and protons. In such a process, proton and electron transiently bind with O species and Pd via the hydrogen spillover pathway, respectively, and participate in aldehyde hydrogenation via a consecutive transfer. Meanwhile, the PVP sheath redirects the movement of alcohols away from the metal to inhibit hydrodeoxygenation, thereby achieving the selective hydrogenation of aromatic aldehyde. This noncontact hydrogenation mechanism based on MOF breaks away from conventional substrate-modulation paradigms, providing a new tool for fabricating catalysts with superior chemoselectivity and activity.