Preparation of Co–Mo/Al 2O 3 model sulfide catalysts for hydrodesulfurization and their application to the study of the effects of catalyst preparation

Abstract

The preparation conditions of a Co–Mo/Al 2O 3 model sulfide catalyst, in which CoMoS phases are selectively formed, were studied by a CVD technique using Co(CO) 3NO as a precursor. The CVD technique used for the preparation of the Co–Mo/Al 2O 3 model catalyst was applied to reveal the effects of calcination and the addition of a chelating agent (NTA; nitrilotriacetic acid) on the thiophene hydrodesulfurization (HDS) activity of Co–Mo/Al 2O 3 catalysts prepared by impregnation methods. The catalysts were characterized by means of NO adsorption, TEM, FTIR, and XAFS. Al 2O 3-supported Co–Mo model catalysts were prepared by decorating presulfided Mo/Al 2O 3 with Co(CO) 3NO and subsequent sulfiding. It is demonstrated that the model catalyst is prepared, when the Mo content exceeds a monolayer loading and when Mo/Al 2O 3 is calcined prior to the sulfidation. The amount of Co forming CoMoS phases was estimated from the correlation between NO/Mo and Co/Mo ratios. TEM observations have suggested that the NTA addition in the preparation of Mo/Al 2O 3 promotes the lateral growth of MoS 2 slabs. The calcination of Mo/Al 2O 3 increased the dispersion of Mo sulfide phases regardless of NTA addition. It is suggested that the NTA addition to Co–Mo/Al 2O 3 coimpregnation catalysts reduces detrimental effects of Co on the dispersion of Mo species. Furthermore, the calcination increased the Co coverage of the edge sites of MoS 2 particles on simultaneous and double impregnation catalysts. It is suggested that the present preparation technique of the model catalyst predicts the potential maximum activity of a Co–Mo catalyst under study, since the edge sites of MoS 2 particles are fully covered by CoMoS phases. In addition, the CVD technique provides a unique characterization method to evaluate the Co coverage on the edge sites of MoS 2 particles for supported Co–Mo sulfide catalysts.