In-situ upgrading of bio-tar over Mg-Ni-Mo catalyst supported by KOH treated activated charcoal in supercritical ethanol

In-situ catalytic hydrodeoxygenation (HDO) of bio-tar in supercritical ethanol for upgraded biofuel was investigated. Highly mesoporous KOH-treated AC (KOH-AC) was synthesized by chemical activation and used as the support for Ni-based catalysts. Among the tested catalysts (AC, KOH-AC, Mg-Ni-Mo/AC, and Mg-Ni-Mo/KOH-AC), Mg-Ni-Mo/KOH-AC with a high surface area of 1310.1 m²/g and a well-developed mesoporous structure exhibited much higher catalytic performance for the HDO of bio-tar. The effects of different reaction temperatures (300–400 °C) and residence time (0–120 min) on the HDO of bio-tar over Mg-Ni-Mo/KOH-AC were also examined. Enhanced properties of liquid fuel with a higher heating value (HHV) of 36.2 MJkg⁻¹, an oxygen content of 11.7 wt%, and a total acid number (TAN) value of 8.6 mgKOHg⁻¹ were obtained from bio-tar over a Mg-Ni-Mo/KOH-AC at 400 °C for 120 min. In these conditions, acids, aldehydes, and oxygenated phenols present in bio-tar (>67 area%) were effectively converted to high value-added species including aromatics, hydrocarbons, and alkyl phenols in upgraded bio-tar (>77 area%) via esterification, hydrogenation, deoxygenation, and ring-alkylation reactions. A series of Mg-Ni-Mo/KOH-AC catalyst recycle test showed the deposition of coke on the catalyst, which became a major reason for the catalyst deactivation.