Influence of the Intrinsic Nanocore Environment in a Pd-Metalated Porous Organic Polymer for Catalytic Biomass-Derived Furfural Upgrading

Metalated nanoporous organic polymers (M-POPs) combine covalent bonds and open metal sites to enable structural stability and single-site catalysis. In this work, we constructed two single-site Pd-metalated knitting aromatic polymers (Pd@KAP-1 and Pd@KAP-2) and explored their catalytic activity in lignocellulosic biomass-derived furfural (FFR) upgrading to tetrahydrofurfuryl alcohol (THFAL), a green industrial solvent. Pd@KAP-1 exhibits superior catalytic performance compared to Pd@KAP-2 toward FFR conversion, resulting in 80% conversion with a 95% selectivity toward THFAL. Using in situ DRIFTS analysis, we find that FFR strongly adsorbs on Pd@KAP-1, which is a key determining factor in its higher catalytic efficiency. Our X-ray photoelectron spectroscopic (XPS) measurements show a lower (∼0.3 eV) binding energy displacement of Pd-3d5/2 in Pd@KAP-1 compared to Pd@KAP-2. We attribute this to the presence of a biphenyl ring that enables partial charge transfer between the P and the Pd atoms inside the nanocavity of Pd@KAP-1 to facilitate catalytic hydrogenation. We also carried out a kinetic analysis showing that Pd@KAP-1 has a lower activation barrier than Pd@KAP-2 for the FFR hydrogenation process. Our study demonstrates a novel concept for designing efficient, robust, and sustainable metalated porous organic polymer-based heterogeneous nanocatalysts in biomass refinery industries.