Co-promoted MoS2 for hydrodesulfurization: New preparation method of MoS2 at room temperature and observation of massive differences of the selectivity depending on the activation atmosphere

摘要

Co-promoted MoS2 catalysts for hydrodesulfurization (HDS) were prepared from a new amorphous MoS2 precursor and tris-(N,N-dimethyldithiocarbamato)-cobalt(III) as promoter source. The samples were obtained by thermal decomposition in either forming gas atmosphere (H-2/N-2) or nitrogen atmosphere at three different temperatures (350, 380 and 410 degrees C). The catalytic activities and selectivity for the HDS reaction exhibit surprising results. The set of catalysts activated in forming gas show a clear preference for the direct desulfurization (DDS) path, while samples activated in nitrogen are less active for the DDS route. This result indicates a better Co dispersion over the edges of MoS2 nanocrystallites in the catalysts synthesized in H-2/N-2. The activation temperature is shown to be an important factor for the catalytic activity. The most active catalysts prepared in H-2/N-2 and N-2 were treated at 380 and 410 degrees C, respectively. Phase segregation of Co sulfide species could be observed for all catalysts before the HDS, while after the catalytic tests most of the Co species vanished. The most active catalysts exhibit the lowest stacking of MoS2 layers and the shortest slab lengths. The catalysts are intensively characterized by means of chemical analyses, X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) and the reasons for the differences in selectivity and activity during the HDS reaction are revealed and discussed. (C) 2015 Elsevier B.V. All rights reserved.