The catalytic activity and chemical structure of nano MoS2 synthesized in a controlled environment

Abstract

A novel hydrothermal method for the preparation of nano MoS₂ for hydrodesulfurization (HDS) with MoO₃ as a precursor is presented. The redox reaction mechanism is, for the first time, revealed. It is shown to involve the oxidation of S²⁻ to SO₄²⁻ while hexavalent Mo is reduced to quadrivalent Mo to form MoS₂. The HS⁻ group is identified to play a key role in the reduction of MoO₃. The interaction between Na₂S and the HS⁻ group and the yield of the resulting MoS₂ are controlled via the pH of the synthesis solution. Various characterization methods, e.g. XRD, TEM, SEM, BET, TPR, XPS, XANES, EXAFS, etc., are employed for the characterization of the synthesized MoS₂. The results show that high purity MoS₂ is obtained. The ratio of precursors, MoO₃ and Na₂S, influences the crystal structure and catalytic activity. A slightly less amount of sulfur than the stoichiometric ratio of S/Mo produces defect sites, which promote catalyst activities in the hydrodesulfurization of real light cycle oil (LCO).