Ni–MoOx/Nb2O5 catalysts for in situ hydrothermal conversion of guaiacol to catechol

Guaiacol, an important lignin-derived compound, presents a central challenge in the efficient upgrading of biomass into sustainable biofuels. Conventional conversion processes are often limited by dependence on corrosive acids, noble metals, or external hydrogen sources, leading to increased costs and safety concerns. In this study, we developed a hydrothermal conversion method that enables guaiacol to catechol transformation without the need for external hydrogen or inorganic acids. This was accomplished using transition-metal-based n Ni– y MoO x /Nb 2 O 5 catalysts capable of cleaving C–O bonds. The results showed that the Ni/MoO x ratio was critical in governing the formation of the NiMoO 4 spinel phase while inducing a strong metal–support interaction (SMSI) that directly affected the surface acidity and oxygen vacancy concentration. Using the 5Ni-5MoO x /Nb 2 O 5 catalyst (Ni/Mo = 1:1) at 300   °C for 2   h, 26.15% guaiacol conversion was achieved, with catechol selectivity 12.9-fold higher than in the noncatalytic system. This superior performance originated from a synergistic effect between the moderate acid strength and the high concentration of defective oxygen vacancies, which collectively drove the selective cleavage of the O–CH 3 bond. The produced catechol serves as a pivotal platform intermediate for synthesizing renewable fuel additives and advanced biofuel components. This study presents a sustainable catalyst design strategy for converting lignin resources into valuable biofuel precursors.