Dynamic evolution in stage-evolving Pd catalysis: unlocking efficient and selective hydrogenation of lignin-derived aldehydes

ABSTRACT Selective hydrogenation of lignin-derived aldehydes, particularly achieving high catalyst atomic efficiency under ambient conditions, remains challenging. Here, we developed a stage-evolving Pd catalysis that bridges the functions of distinct Pd states to address this limitation. Operando monitoring reveals a sequential transformation from homogeneous Pd2+ to graphene-confined Pd nanoparticles (∼3.26 nm), with each stage making a specific contribution. In the vanillin hydrogenation at 30°C, this system achieves 99.4% conversion within 30 min with 95.0% yield toward 2-methoxy-4-methylphenol and a remarkable turnover frequency of 673.9 h−1, outperforming conventional static-site Pd catalysts reduced by H2 or NaBH4 (≤42.5% conversion, 12.1% yield). Comprehensive in situ spectroscopic characterizations, combined with kinetic and theoretical investigations, have elucidated the interfacial reaction pathways governing vanillin hydrogenation at distinct Pd active sites and established the correlation between multistage catalysis and product selectivity. Mechanistically, the initial Pd2+ phase facilitates C=O adsorption and subsequent hydrogenation to C–OH (47.47 kJ mol−1), whereas the in-situ-generated Pd/Graphene promotes H2 homolytic dissociation into H* (rather than hydrogen transfer from the isopropanol solvent) and drives the rate-determining hydrodeoxygenation of C–OH (52.44 kJ mol−1). This work paves the way for the rational design of dynamic catalytic systems to achieve atomically efficient hydrogenation of lignin-derived aldehydes.