Non-Carbonized Pd Single-Atom Catalyst Supported on Lignin-Functionalized Phenolic Resin for Potent Catalytic Transfer Hydrogenation of Lignin-Derived Aldehydes

Abstract

Single-atom catalysts (SACs) depend significantly on their support properties, and organic polymers have emerged as promising candidates due to their tunable physicochemical properties and diverse functional groups. However, the high-temperature carbonization commonly required for conventional organic polymer-supported SAC fabrication often leads to the loss of these functional groups, thus weakening metal-support interactions and catalytic performance accordingly. Herein, we report a sustainable strategy to synthesize nitrogen-functionalized lignin-based phenolic resin (N-LPR) supports for stabilizing atomically dispersed palladium (Pd) without carbonization. Using ammonia solution (NH₃·H₂O) as both the nitrogen source and catalyst, high molecular weight lignin fractions (L3) were transformed into N-L3PR-50% supports with a unique nano-chain-like structure, high surface area, and abundant amine groups, which can directly anchor Pd sites under room temperature. The resulting Pd@N-L3PR-50% catalyst achieved approximately 100% vanillin conversion and 97.91% selectivity for 2-methoxy-4-methylphenol at 80 °C with excellent cycle stability and adaptability to lignin-derived aldehydes, benefiting from the stable Pd-N coordination and the good adsorption capacity provided by the N-L3PR-50% support. Consequently, this work not only demonstrates a straightforward non-carbonation strategy to prepare lignin-based SACs for potent biomass-derived chemical transformations but also provides a novel avenue for the application of conventional multifunctional organic polymers as support for SACs.