Ni3P featuring electron-rich Niδ+ for aqueous-phase hydrogenation of maleic acid

The aqueous-phase hydrogenation of maleic acid (MAc) represents a sustainable approach to succinic acid (SAc) production, yet its efficiency and stability are hampered by the isomerization of MAc to fumaric acid (FAc) and metal leaching under acidic conditions. Herein, we present a nickel phosphide (Ni 3 P) catalyst for the efficient aqueous hydrogenation of MAc. XPS and XAFS analyses reveal the electronic state of the active Ni δ+ species in Ni 3 P is modulated by the annealing temperature. Coupled with adsorption thermodynamics and in situ DRIFTS studies, we demonstrate that a higher density of active sites, an increased surface Ni/P ratio, and electron-enriched Ni δ+ species collectively enhance the adsorption–desorption kinetics of reactants. As a result, the optimized Ni 3 P-400 catalyst achieves complete conversion to SAc with 100% yield and retains full activity over 15 consecutive cycles. These findings underscore the ability of Ni 3 P to tailor the electronic environment of Ni sites, providing a strategy for the design of acid-resistant and high-performance hydrogenation catalysts.