In-situ hydrogenation of bio-oil/bio-oil phenolic compounds with secondary alcohols over a synthesized mesoporous Ni/CeO₂ catalyst

Mesoporous ceria, which was synthesized under supercritical conditions, was found to be an effective support material of Ni catalyst for the in-situ hydrogenation of m-cresol (a representative compound of bio-oil) using secondary alcohols of 2-propanol (2-PrOH) and 2-butanol (2-BuOH) as a hydrogen source (H-donor) to produce 3-methylcyclohexanol, 3-methylcyclohexene, and methylcyclohexane under a H₂ gas-free atmosphere. The activities of different metal catalysts (Ni, Cu, and Co) for the in-situ hydrogenation of m-cresol were examined using 2-PrOH as a H-donor. Total and effective conversion of m-cresol achieved only over Ni/CeO₂ because of its fair catalytic properties, as determined by N₂ adsorption-desorption, hydrogen temperature-programmed reduction, ammonia temperature-programmed desorption, X-ray diffraction, and transmission electron microscopy. The dependence of Ni/CeO₂ performance on the reaction time (4–6 h) and Ni loading (3–9 wt%) was examined from the in-situ hydrogenation of m-cresol with 2-PrOH. The deactivation test of Ni/CeO₂ was performed by reusing the spent catalyst, which was then regenerated through successive oxidation and reduction, several times in the m-cresol transformation employing 2-PrOH as a H-donor. In addition to m-cresol, other phenolic model compounds of bio-oil, such as anisole, phenol, and guaiacol, were also treated by in-situ hydrogenation with 2-PrOH over Ni/CeO₂. Although this catalyst was effective for phenol and guaiacol transformation, it was relatively ineffective for anisole conversion. The in-situ hydrogenation of crude bio-oil with 2-PrOH and 2-BuOH was accomplished over the Ni/CeO₂ catalyst, resulting in a refined bio-oil with a 37.5–38.9% lower oxygen content and a high heating value (HHV) of up to 25 MJ/kg.