Eco-friendly preparation of ultrathin biomass-derived Ni3S2-doped carbon nanosheets for selective hydrogenolysis of lignin model compounds in the absence of hydrogen

Abstract

Lignin is an abundant source of aromatics, and the depolymerization of lignin provides significant potential for producing high-value chemicals. Selective hydrogenolysis of the C–O ether bond in lignin is an important strategy for the production of fuels and chemical feedstocks. In our study, catalytic hydrogenolysis of lignin model compounds (β-O-4, α-O-4 and 4-O-5 model compounds) over Ni₃S₂-CS catalysts was investigated. Hence, an array of 2D carbon nanostructure Ni₃S₂-CSs-X-Y derived catalysts were produced using different compositions at different temperatures (X = 0 mg, 0.2 mg, 0.4 mg, 0.6 mg, and 0.8 mg; Y = 600 °C, 700 °C, 800 °C, and 900 °C) were prepared and applied for hydrogenolysis of lignin model compounds and depolymerization of alkaline lignin. The highest conversion of lignin model compounds (β-O-4 model compound) was up to 100% and the yield of the obtained corresponding ethylbenzene and phenol could achieve 92% and 86%, respectively, over the optimal Ni₃S₂-CSs-0.4-700 catalyst in iPrOH at 260 °C without external H₂. The 2D carbon nanostructure catalysts performed a good dispersion on the surface of the carbon nanosheets, which facilitated the cleavage of the lignin ether bonds. The physicochemical characterization studies were carried out by means of XRD, SEM, TEM, H₂-TPR, NH₃-TPD, Raman and XPS analyses. Based on the optimal reaction conditions (260 °C, 4 h, 2.0 MPa N₂), various model compounds (β-O-4, α-O-4 and 4-O-5 model compounds) could also be effectively hydrotreated to produce the corresponding aromatic products. Furthermore, the optimal Ni₃S₂-CSs-0.4-700 catalyst could be carried out in the next five consecutive cycle experiments with a slight decrease in the transformation of lignin model compounds.