Broadly Substrate-Applicable Efficient Conversion of Lignin-Derived Guaiacol to Cyclohexanol over Co–Ni Alloy Catalyst Supported on MWCNT

The green production of cyclohexanol can be achieved through the hydrogenation of lignin-derived guaiacol. This work demonstrates that a Co–Ni bimetallic catalyst supported on multiwalled carbon nanotubes (Co₅Ni₅/MWCNT) is a promising candidate for this application. Characterization results confirm that the synergistic effects between Co and Ni enhance the reducibility, H₂ adsorption, and binding capability of the catalysts. A response surface model for guaiacol hydrogenation over the Co₅Ni₅/MWCNT was established. Under optimized conditions of 190 °C, 1 MPa initial H₂ pressure, and 60 min, Co₅Ni₅/MWCNT achieved 100% guaiacol conversion and 95.6% cyclohexanol yield. This performance surpasses four commercial catalysts (NiAl, Pd/C, Ru/C, and Pt/C) and most recent literature reports. Furthermore, Co₅Ni₅/MWCNT exhibits exceptional substrate versatility, enabling the efficient conversion of nine lignin derivatives to cyclohexanol-type products under optimized conditions. And the reactivity hierarchy of functional groups during hydrogenation was summarized. Alkoxy group cleavage difficulty correlates with substitution position, from easy to difficult as ortho-position < meta-position < para-position. Functional group cleavage from easy to difficult as alkoxy groups < hydroxyl groups < alkyl groups. After six cycles, the residual activity of Co₅Ni₅/MWCNT remained comparable to that of a fresh monometallic catalyst.