Synthesis Of VS₂ Nanomaterials And Its Application In Catalytic Hydrogenation Of Alkali Lignin

Alkali lignin, produced mainly as a byproduct of the pulp and paper industry and biomass fractionation, has been extensively and intensively investigated because of energy and environmental crisis in the modern society, and it consists of phenylpropane connected by carbon-carbon bond and ether bond. Hydrogen has been considered as a clean, economical and environmentally friendly energy in modern society, and heterogeneous photocatalyst has a promising prospect.In this research, VS2 catalysts, with different morphologies and doping, have been synthesized by hydrothermal method and applied to the hydrogenation of alkali lignin. The effects of reaction temperature, time, pressure of H2 and catalyst have been investigated during the reaction of catalytic hydrogenation. Furthermore, the composition of bio-oil and the mechanism of hydrogenation of VS2 catalyst were also investigated.The result show that different morphologies VS2 catalysts, viz., sheets, nanoflowers and nanoballs were synthesized, and different doping during the process of synthesis have significant effects on the composition of catalysts. When AgNO3 was added in the process of synthesis, the composition of the mixture were Ag2S, VS4 and VS2; when graphite was added, they were graphite, VS4 and VS2; when Ni(NO3)2 was introduced, the final product were Ni2S, S8 and VS2; and when Na2MoO4 was added, the composition of the sample were MoS2 and VS2. The conversion of alkali lignin and yield of bio-oil were 77.02% and 58.75% at optimal condition of 250℃,1.5 h, and 2 MPa H2 with a VS2 sheets catalyst. And the activities of VS2 with different morphologies were sheets> nanoflowers> nanoballs. Although, the activities of catalysts doped with Ni, Mo, Ag and graphite were decreased under above reaction condition, it was enhanced when the temperature increased to 290℃. The conversion of alkali lignin and yield of bio-oil were 78.36%,79.31%,81.22%,80.57% and 60.02%, 58.97%,61.23%,59.35%, respectively. Few compounds using VS2 catalysts have been detected and the content of compounds was relatively high. The major compositions of bio-oil using a VS2 sheets catalyst were aromatics, important chemical reagents, fine chemical, and intermediate of pharmaceutical and materials in organic synthesis.Besides, a novel heterojunction of a MoS2/SrZrO3 photocatalyst was successfully synthesized via a simple hydrothermal process and applied to photocatalytic H2 evolution under UV light irradiation. The rate of H2 evolution for pure SrZrO3 photocatalyst was 1.95 mmol/h, while the rate of H2 evolution of 0.05 wt% MoS2/SrZrO3 was 5.31 mmol/h, nearly 2.7 times of pure samples, which is due to the effect of heterojunction between MoS2 and SrZrO3, which accelerates the transfer of electrons and suppresses the recombination of photogenerated electrons and holes, resulting in the enhancement of H2 evolution.