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) are highly dependent on the properties of their supports, and organic polymers have recently 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 Pd without carbonization. Using 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.