Role of Ni/Al Molar Ratio in Ni‐Al Mixed Oxide Catalysts for Upgraded Vanillin Hydrodeoxygenation

Ni‐Al mixed oxides were synthesized from layered double hydroxides (LDHs) with varying Ni/Al molar ratios (2, 3, and 4) via a low‐supersaturation coprecipitation method. The mixed oxides, obtained after calcination and reduction, were evaluated as catalysts in the hydrodeoxygenation (HDO) of vanillin, a model compound for lignin‐derived bio‐oil upgrading. The reactions were carried out in a batch reactor at 533 K and 3.92 MPa H2 pressure. Catalyst characterization performed by X‐ray diffraction (XRD), nitrogen physisorption, temperature‐programmed reduction (TPR), and X‐ray photoelectron spectroscopy (XPS) revealed that the electronic interaction between Ni and Al atoms significantly influenced the reducibility of Ni species. The catalyst with a Ni/Al molar ratio of 3 exhibited the highest HDO activity, achieving 79% efficiency with selectivity towards fully deoxygenated products, namely methylcyclohexane (26.8%) and cyclohexane (36.5%). The synergy between Ni0 sites and oxygen vacancies was identified as the key factor in promoting both hydrogenation and deoxygenation pathways.