Upgrading of liquid fuel from fast pyrolysis of biomass over modified Ni/CNT catalysts

• NiMo/CNT catalysts possess high catalytic activity for the hydrogenation reaction.
• Upgrading of bio-oil was carried out in mild conditions.
• Synergistic effect was observed in the hydrogenation process of synthetic bio-oil.
• The pH value of bio-oil increased from 2.92 to 3.68 after upgrading.
• The H element content increased from 8.40 wt.% to 11.26 wt.% after upgrading.

A series of non-sulfided nickel-based catalysts with HNO3-pretreated CNTs as support ((x1 + x2) wt.% NiMo/CNTs, xi represents the Ni or Mo loading amount) were synthesized, and evaluated for the hydrogenation of bio-oil model compounds (acetic acid, furfural and hydroxyacetone) and raw bio-oil. Acetic acid was chosen for the initial screening of catalysts. Results showed that reduced (10 + 10) wt.% NiMo/CNT catalyst exhibited the highest activity. Hydrogenation of other model compounds and raw bio-oil was then carried out over reduced (10 + 10) wt.% NiMo/CNT catalyst. A synergistic effect was observed in the hydrogenation process of a model compound mixture, which led to the aldol condensation between furfural and hydroxyacetone to give a C8 compound, which could give most valuable hydrocarbon after deep hydrogenation. After the upgrading process, both the pH and the hydrogen content of bio-oil increased, and the oxygen content decreased, which were all desirable for the further application of upgraded bio-oil.

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