Water-Assisted Selective Hydrodeoxygenation of Guaiacol to Cyclohexanol over Supported Ni and Co Bimetallic Catalysts

Hydrodeoxygenation (HDO) of guaiacol, a typical lignin-derived phenolic compound, at relatively mild conditions was studied over γ-Al2O3 and ZSM-5 supported catalysts with Ni and/or Co as active metal. Among various catalysts, NiCo/γ-Al2O3 catalysts exhibited better guaiacol conversion up to 96.1% with cyclohexanol as the main product in aqueous, due to the proper acidity and interaction between metal particles and support. The effects of process parameters on guaiacol conversion and product distribution were investigated in detail associated with solvent effect. The cleavage of C–O bonds in guaiacol was investigated over NiCo/γ-Al2O3 catalysts in aqueous phase. Phenol was found as the main intermediate with 1-methyl-1,2-cyclohexanediol as another intermediate instead of 2-methoxy-cyclohexanol. The demethoxylation first happened to form phenol, and then, the aromatic ring was hydrogenated to give cyclohexanol after further hydrogenation of cyclohexanone.