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

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 sites 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 multi-stage catalysis and product selectivity. Mechanistically, the initial Pd2+ phase facilitates C = O adsorption and subsequent hydrogenation to C-OH (47.47 kJ/mol), 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). This work paves the way for the rational design of dynamic catalytic systems to achieve atomically efficient hydrogenation of lignin-derived aldehydes.