High stable NiCoAl catalyst prepared by combustion method for the hydrodeoxygenation of lignin-derived phenolic compounds: Effect of calcination temperature

The hydrodeoxygenation of lignin-derived phenolic compounds holds great promise for biomass-derived liquid fuel production. However, achieving a consistently high cyclohexane yield poses a formidable challenge. In this study, NiCoAl catalysts were successfully synthesized using the solution combustion method for the hydrodeoxygenation of lignin-oil. The impact of calcination temperature on the preparation of NiCoAl catalysts was investigated. The results indicate that the selectivity of cyclohexane exhibits an initial increase followed by a decrease as the calcination temperature rises. Notably, the NiCoAl-600 catalyst reached 99.99% guaiacol conversion, with the highest selectivity of cyclohexane (97.96%) achieved. Characterization results demonstrate that the transition of the spinel structure from normal to inverse with rising calcination temperature. Moreover, the catalyst particle size initially decreases and then increases, while the oxygen vacancy concentration in the catalyst increases. It was found that these properties contribute to a better hydrodeoxygenation performances of guaiacol and other phenolic compounds over non-noble NiCoAl catalyst. Possible reaction pathway and mechanism are proposed and discussed. Additionally, the spinel-structured NiCoAl-600 catalyst has good thermal stability, ensuring potential application in the upgrading of lignin-oil.