Engineering nickel-based catalysts for time-efficient cyclohexanol and cyclohexane production under mild conditions: role of loading, support, and oxidation state

Lignin is the largest renewable source of aromatic compounds, representing an attractive feedstock for the sustainable production of renewable fuels and sustainable aviation fuel (SAF) precursors. Hydrodeoxygenation (HDO) of lignin-derived phenolics is a key upgrading strategy; however, the rational design of efficient heterogeneous catalysts capable of selectively controlling hydrogenation and C–O bond cleavage under mild conditions remains challenging. In particular, the interplay between catalyst physicochemical properties, adsorption behavior, and catalytic reaction pathways governing product selectivity is not yet fully understood. Herein, we address this knowledge gap by developing simple, scalable Ni-based heterogeneous catalysts and establishing clear structure–adsorption–reactivity relationships for the selective HDO of guaiacol. Complete guaiacol conversion was achieved under comparatively mild conditions (≤275 °C, ≤20 bar H₂), with product selectivity tuned from partially hydrodeoxygenated products to cyclohexanol and cyclohexane through support engineering. Comprehensive catalyst characterization (ICP-OES, BET, HRTEM, NH 3 -TPD, XRD, XPS, H 2 -TPR, TGA and CHNS analysis), together with adsorption and mechanistic studies, demonstrates that metal dispersion, reducibility, support acidity, and adsorption of oxygenated intermediates synergistically regulate the hydrogenation–deoxygenation pathway. Ni/SiO 2 , despite high Ni dispersion, exhibited limited deoxygenation because of its low acidity. In contrast, Ni/Al 2 O 3 selectively produced cyclohexanol (64% yield) even at only 5 bar H₂, whereas the bifunctional Ni/SiO 2 –Al 2 O 3 catalyst promoted efficient C–O bond activation to achieve 87% cyclohexane through complete hydrodeoxygenation. Mechanistic investigations reveal that adsorption of key intermediates at the metal–support interface governs the competition between hydrogenation and deoxygenation, thereby dictating product selectivity. These findings provide fundamental insight into catalytic mechanisms and reaction pathways in lignin-derived phenolic HDO and establish design principles for scalable heterogeneous catalysts for renewable cyclic alcohols, hydrocarbons, and SAF precursors.