PtNi/NiAl2O4 Bimetallic Catalyst Enhanced Production of 4-Alkylphenols from Lignin under H2-Free Conditions

As an abundant and renewable biomass resource, lignin has garnered significant interest for its depolymerization and valorization. The production of 4-alkylphenols via lignin hydrogenolysis is particularly promising for chemical and pharmaceutical applications. Herein, we report a PtNi/NiAl₂O₄ bimetallic catalyst enabling efficient, hydrogen-free conversion of lignin to 4-alkylphenols via a self-reforming-driven strategy. A remarkable yield of 27.6 wt % was achieved, including 24.1 wt % 4-ethylphenol, surpassing the performance of previously reported H₂-participated and H₂-free systems. Comprehensive characterizations reveal that electron transfer from Ni to Pt enhances the metallic character of Pt, thereby boosting aqueous-phase reforming (APR) activity to supply active hydrogen species. Concurrently, the chemical state of Ni becomes more oxidized than Ni²⁺, promoting the formation of oxygen vacancies (O_v) which facilitate C_Ar–O bond activation. Kinetic studies demonstrate that the Pt–Ni interaction effectively lowers the activation energies required for both C_Ar–O bond cleavage and the APR step. Furthermore, temperature-programmed surface reaction (TPSR) experiments confirm that the PtNi catalyst significantly enhances C_Ar–O bond cleavage and hydrogen production rates during APR. The catalyst also exhibits excellent scalability and reusability, advancing the high-yield production of 4-alkylphenols from lignin under hydrogen-free conditions.