Tuning Ni/Hβ Catalysts via Second-Metal (Zn, Fe, and Cu) Incorporation for Selective Hydrogen-Free Hydrodeoxygenation of 4-Propylguaiacol

The selective upgrading of lignin-derived compounds into high-value chemicals remains a critical challenge. In this study, a series of Ni-based catalysts supported on Hβ zeolite and modified with secondary metals (Zn, Fe, and Cu) were synthesized and systematically evaluated for the catalytic conversion of 4-propylguaiacol in aqueous phase under hydrogen-free conditions. Among the catalysts studied at 220 ° C for 2 h, Ni/Hβ delivered a conversion of 36.1% and a phenolic selectivity of 89.6%. By comparison, NiZn/Hβ exhibited the highest catalytic activity, achieving a conversion of 82.9% with a selectivity of 96.5%, indicating the promotional effect of Zn incorporation. NiFe/Hβ showed a moderate conversion of 45.5% but maintained a high phenolic selectivity of 97.6%. However, NiCu/Hβ showed almost no catalytic activity, with a conversion of only 2.0%. Structural characterization by XRD, XPS, N 2 physisorption, H 2 -TPR, SEM, and TEM revealed that the introduction of Zn significantly improved the dispersion of Ni species and reduced Ni crystallite size, thereby increasing the number of accessible active sites. In contrast, Fe incorporation altered the catalyst structure and reduced catalytic activity, while Cu addition induced metal aggregation and markedly suppressed catalytic performance. The results indicate that appropriate second-metal modification can effectively regulate the metal dispersion, microstructure, and metal–support interactions in Ni/Hβ catalysts, thereby influencing the hydrogen activation ability and the cleavage of Ar–CO 3 bonds.