Hydrodeoxygenation of prairie cordgrass bio-oil over Ni based activated carbon synergistic catalysts combined with different metals

• Inexpensive activated carbon catalysts are used for bio-oil upgrading.
• Effects of catalysts on upgraded bio-oil yield and properties were evaluated.
• Light hydrocarbons and alkyl-phenols from upgraded bio-oil are targeted.
• Mechanisms of producing hydrocarbons, alkyl-phenols and gases were discussed.

Bio-oil can be upgraded through hydrodeoxygenation (HDO). Low-cost and effective catalysts are crucial for the HDO process. In this study, four inexpensive combinations of Ni based activated carbon synergistic catalysts including Ni/AC, Ni-Fe/AC, Ni-Mo/AC and Ni-Cu/AC were evaluated for HDO of prairie cordgrass (PCG) bio-oil. The tests were carried out in the autoclave under mild operating conditions with 500 psig of H2 pressure and 350°C temperature. The catalysts were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) and transmission electron microscope (TEM). The results show that all synergistic catalysts had significant improvements on the physicochemical properties (water content, pH, oxygen content, higher heating value and chemical compositions) of the upgraded PCG bio-oil. The higher heating value of the upgraded bio-oil (ranging from 29.65 MJ/kg to 31.61 MJ/kg) improved significantly in comparison with the raw bio-oil (11.33 MJ/kg), while the oxygen content reduced to only 21.70–25.88% from 68.81% of the raw bio-oil. Compared to raw bio-oil (8.78% hydrocarbons and no alkyl-phenols), the Ni/AC catalysts produced the highest content of gasoline range hydrocarbons (C6–C12) at 32.63% in the upgraded bio-oil, while Ni-Mo/AC generated the upgraded bio-oil with the highest content of gasoline blending alkyl-phenols at 38.41%.