Defect-Engineered MOF-Derived NiCu@C Catalysts: Cu-induced Ni Particle Size Modulation for Selective Transfer Hydrogenation of HMF

Regulation of the selective hydrogenation of 5-hydroxymethylfurfural (HMF) is crucial for the targeted valorization of biomass resources. Herein, a dual-defect engineering strategy termed “cooperative evolution of ligand and metal-node defects” was adopted to directionally derive carbon-shell-encapsulated NiCu@C catalysts from MOFs by sequentially introducing 3,5-dinitrosalicylic acid (DNS) ligand vacancies and metal-node defects (Cu species), enabling hydrogen-free selective hydrogenation of HMF. Meanwhile, Cu incorporation generates oxygen vacancies, and enables precise tuning of Ni diameter (10.07∼13.75 nm) and carbon-shell thickness (0.81∼2.32 nm), achieving cooperative optimization among defects, particle size, and shell dimensions. Research reveals that Ni particle size serves as the dominant factor in regulating HMF hydrogenation selectivity, which synergizes with secondary factors including defect density and shell thickness to enable efficient HMF conversion. At 0.2 mol/L HMF, a maximum yield of 99% DMF or 70% BHMF can be achieved by regulating the catalyst and reaction system. Kinetic investigations reveal that increasing particle size kinetically favors C=C hydrogenation, steering selectivity toward BHMF, whereas size reduction exclusively drives C=O hydrogenation with high yield and pinpoint DMF formation, thereby establishing a quantitative “size-pathway-product” correlation. Besides, a novel correction function was proposed to refine the kinetic model. Finally, the intrinsic active sites of catalysts with different particle sizes were correlated with DMF yield, and the reaction pathway of HMF hydrogenation over NiCu_0.05@C-1 was verified.