Constructing a superior Co–Mo HDS catalyst from a crystalline precursor separated from the impregnating solution

Abstract

In this work, a Co tetra-capped Keggin crystalline Co₄Mo₁₂ was separated from the impregnating solution through a self-assembly strategy. The crystalline Co₄Mo₁₂ was structurally characterized and used as a molecular platform to reveal the sulfidation procedure of the precursor in the construction of a superior Co–Mo hydrodesulfurization (HDS) catalyst. The higher HDS reactivity of the sulfide can be attributed to the structure-directing effects of the crystalline Co₄Mo₁₂ precursor. During the sulfidation procedure of the crystalline Co₄Mo₁₂ precursor, it initially decomposes at 100 °C and MoO_xS_y is produced due to the simple O–S exchange. With the temperature increasing to 180 °C, the Keggin-type structure in crystalline Co₄Mo₁₂ begins to collapse and four groups of edge-shared CoMo₂O(S)₁₃ triplets are formed. As the temperature continues to increase, the CoMo₂O(S)₁₃ triplets collapse and MoS₂ is formed due to the deep O–S exchange at 200 °C. In this procedure, the water molecules serving as ligands can retard the sulfidation of Co promoters, which can guarantee Co-promoter interaction and re-dispersion at the edges of MoS₂ nanoparticles to form the type II CoMoS active phase with higher performance. These results suggest that the crystalline Co₄Mo₁₂ precursor can be a superior precursor for the rational design and controllable preparation of HDS active sites.