Catalytic depolymerization of Kraft lignin to produce liquid fuels via Ni–Sn metal oxide catalysts

In this study, Ni–Sn metal oxide catalysts, with strong Lewis acidity, were prepared and applied in lignin depolymerization to produce liquefied fuels. The Ni–Sn metal oxide catalysts could cleave the lignin linkages and stabilize the reaction intermediates due to the high Lewis acidity and the hydrogenation of nickel sites. When the molar ratio of nickel to tin was 1 : 3, a liquid product yield of 90% and a petroleum ether soluble product (mainly monomers and dimer degradation products) yield of 60% were obtained at 310 °C for 24 h. Under these reaction conditions, the petroleum ether soluble product had a higher heating value (HHV) (36.45 MJ kg−1) than Kraft lignin (25.83 MJ kg−1). A meticulous study on Ni–Sn metal oxide catalysts revealed that Lewis acidity and the synergistic effect between Ni and Sn played an important role in lignin depolymerization.