Efficient catalytic transfer hydrogenation of raw bio-oil over various CuO catalysts

A novel method was proposed for biomass fast pyrolysis oil upgrading using catalytic transfer hydrogenation (CTH) based on various CuO catalysts with methanol as the hydrogen donor. The carbonyl compounds in the bio-oil were hydrogenated to synthesize alcohols using a hydrotalcite-like Cu₂Al catalyst at 200℃ for 4 h. The maximum yield of alcohols reached 73.81%. Cu₂Al is well applicable to large-scale application in bio-oil CTH for its excellent CTH performance, treating capacity up to 10 vol%, and stable alcohol production during the 5th reuse process. Given the huge range of molecular size of the complex chemical composition of bio-oil, the CTH of raw bio-oil using three catalysts (i.e., CuO/BC, CuO/Al₂O₃, and Cu₂Al) was compared. The CTH performance (71.56%) of CuO/Al₂O₃ was significantly comparable to that of Cu₂Al, and it is also a good choice. The main reason for this outcome was that the average pore size of the two catalysts was high (>5nm), which reduced the possibility of pore blockage during the reaction and improved stability. The reusability of CuO/BC was markedly lower for its small average pore size (∼2nm). Furthermore, the CTH of raw bio-oil over CuO catalyst was discussed in depth, such that a basis is laid for the upgrading and utilization of bio-oil.