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 biooil were hydrogenated to synthesize alcohols using a hydrotalcite-like Cu2Al catalyst at 200 degrees C 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 (similar to 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.