VS and its doped composition: Catalytic depolymerization of alkali lignin for increased bio-oil production.

VS spheres and VS sheets with doped compositions (Mo, Ag and graphite) were successfully prepared by one-step hydrothermal method and characterized by different techniques including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N adsorption isotherms. Catalysts were applied for the depolymerization of alkali lignin. VS spheres exhibited lower yield of degraded lignin and bio-oil than those with VS sheets and VS flowers heated to 250 °C and held for 1.5 h with 2.0 MPa H. The catalytic depolymerization performance was markedly affected by the dopant in the VS sheets, with the highest degraded lignin yield of 81.22%, achieved over 5 wt% Ag-VS at 290 °C under 2.0 MPa H for 1.5 h, yielding 61.23% bio-oil. The VS-based catalysts show excellent selectivity in the interruption of the lignin structure and target production of bio-oil. The bio-oil showed that the relevant contents of a phenolic-type compound changes significantly according to the dopant in the VS catalyst.