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

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 Al 2 O 3 -incorporated zirconia (ZrO 2 ) 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 Al 2 O 3 /ZrO 2 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/Al 2 O 3 catalyst showed its deactivation to obtain the lowering GUA conversion (27.1% reduction). The FESEM and 27 Al-NMR analyses revealed that the addition of ZrO 2 improved the water tolerance of the catalyst by protecting the Al 2 O 3 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. • NiMo/Al 2 O 3 -ZrO 2 catalyzed HDO of guaiacol and bio-oil to produce phenols. • The presence of water decreased activity of NiMo/Al 2 O 3 for HDO of guaiacol. • Addition of ZrO 2 to Al 2 O 3 improved water stability of NiMo/AZ(1/1) catalyst during HDO. • Real bio-oil was upgraded to produce bio-phenols using NiMo/AZ(1/1) catalyst.