Bio-phenols production via hydrodeoxygenation of lignin-derived guaiacol and bio-oil over high water-tolerant NiMo/Al2O3-ZrO2 catalysts

Abstract

Transformation of some oxygenated compounds in bio-oil derived from biomass pyrolysis via hydrodeoxygenation (HDO) generally improves its quality and potentially produces bio-based chemicals. Although alumina (Al₂O₃) supported catalysts are normally applied for HDO, they have certain limitations, such as acidity and high susceptibility to water, which need to be improved. In this research, an Al2O3-incorporated zirconia (ZrO2) composite (AZ) was prepared as a support of nickel (Ni)-molybdenum (Mo) catalysts used for HDO of guaiacol (GUA) and real bio-oil derived from pyrolysis of Leucaena leucocephala trunks to produce phenols. In the absence of water, the NiMo catalyst supported on AZ at 1/1 Al2O3/ZrO2 molar ratio [NiMo/AZ(1/1)] having higher reducibility with a greater number of weak-medium acid sites provided >98% GUA conversion with 87% selectivity to phenols. In the presence of water, the NiMo/AZ(1/1) catalyst maintained its catalytic activity, whereas NiMo/Al2O3 catalyst showed its deactivation to obtain the lowering GUA conversion (27.1% reduction). The FESEM and 27Al-NMR analyses revealed that the addition of ZrO2 improved the water tolerance of the catalyst by protecting the Al2O3 structure and preventing the transformation of Lewis acid-related tetrahedral Al to octahedral Al. Moreover, the NiMo/AZ(1/1) catalyst exhibited the highest HDO activity for real bio-oil without solvents, achieving a maximum oil yield of 25.2 wt% with 75.6% selectivity to phenols and the lowest coke formation.

Keywords

• Hydrodeoxygenation
• Al2O3-ZrO2 composite
• Guaiacol
• Bio-oil
• Water tolerance