Hydrogenation of Lignin-Derived Phenolic Compound Eugenol over Ruthenium-Containing Nickel Hydrotalcite-Type Materials

Sustainable production of fine chemicals and fuels from renewable energy resources is an important process in the current scenario of the energy crisis. In this study, we have reported complete hydrogenation of eugenol, which is an important biomass-derived molecule using ruthenium-containing nickel hydrotalcite (NiRu-HT)-type materials and isopropyl alcohol as a solvent. A series of group VIII metals containing bimetallic Ni-HT-type materials were synthesized, characterized, and demonstrated to participate in eugenol conversion, and among which, Ni-Ru-HT was found to give the highest selectivity toward alkyl cyclohexanol. The reaction conditions, including reaction temperature, hydrogen pressure, and the Ni/Ru ratio, were optimized. Based on the results, it can be concluded that eugenol was first hydrogenated to 4-propyl guaiacol and then underwent simultaneous demethoxylation and aromatic ring hydrogenation to form 4-propylcyclohexanol. Moreover, various lignin-derived phenolic compounds can be efficiently converted into alkyl cyclohexanols and aromatic compounds into alkyl cyclohexane. The in situ formation of metallic ruthenium on the surface of NiRu-HT evident from TPR and TEM analyses is responsible for observed high yields of ring hydrogenated products of eugenol (i.e., 4-propylcyclohexanol).