Sn/Zr Mixed-Metal Clusters in MOFs as Lewis Acid Catalysts for Biomass-Derived HMF Synthesis

Abstract The depletion of fossil fuels has spurred the search for sustainable routes to platform chemicals, yet the efficient conversion of biomass-derived fructose to 5-(hydroxymethyl)furfural (HMF) remains challenging. While Sn-based Lewis acids are promising catalysts for this dehydration reaction, conventional homogeneous systems suffer from separation and corrosion issues, and heterogeneous supports often fail to stabilize isolated Sn atoms, leading to aggregation into less selective Sn dimers or clusters. Herein, we report a strategy to construct single-atom Sn catalytic sites within a metal–organic framework (MOF). By post-synthetic metalation of the open Zr6 nodes in PCN-224(Co), Sn4+ ions are precisely anchored to form well-defined Sn/Zr mixed-metal clusters without disrupting the parent framework topology. The resulting Sn-PCN-224(Co) catalyst achieves 100% fructose conversion and 72% HMF yield under mild conditions─a dramatic enhancement over the unmodified MOF, which produces negligible HMF. The dispersed Sn centers, spatially isolated by the periodic MOF nodes, effectively suppress deleterious Sn–Sn interactions and stabilize key reaction intermediates, as elucidated by density functional theory (DFT) calculations. This strategy proves general across diverse Zr-MOF platforms (PCN-222, MOF-808, NU-1000), and the catalyst exhibits excellent recyclability. This work demonstrates how precision chemistry in MOFs can address the fundamental challenge of single-atom catalyst stability, offering a robust platform for biomass conversion and sustainable chemical synthesis.