Effect of sulfiding conditions on the hydrodesulfurization performance of the ex-situ presulfided CoMoS/γ-Al2O3 catalysts

Abstract

The influence of sulfiding conditions in the ex-situ presulfidation process on the morphology and performances of CoMoS/γ-Al2O3 catalysts was studied in details for hydrodesulfurization (HDS) of dibenzothiophene. Surface and bulk characterization using XRD, HRTEM, XPS, TPR and FT-IR confirmed that the sulfiding agent mixture of (NH4)2S and elemental S effectively react with the supported Mo oxide to form intermediate thiosalts from mononuclear ammonium thiomolybdates to polynuclear ammonium thiomolybdates, namely the formed thiosalts from (NH4)2MoS4 to (NH4)2Mo2S12 and (NH4)2Mo3S13,which weaken the strong interaction between the γ-Al2O3 support and Mo oxide, resulting in maximum sulfidation of Mo oxide species. Mo species tend to agglomerate as the number of Mo nuclear increases, which further induces significant changes in the morphology of MoS2 particles. Such observation was further correlated with HDS activity and selectivity. The CoMoS/γ-Al2O3 catalyst with (NH4)2Mo2S12 as intermediate exhibits suitable slab lengths and stacking numbers of MoS2 slabs with optimal compromisebetween the Mo dispersion and ratios of edge sites to rim sites, and show the highest HDS activity. Therefore, a tailor-made catalyst with excellent HDS performance could be developed by adjusting the sulfiding conditions through ex-situ presulfidation method.