Understanding the promotion effect: A density functional theory study based on high resolution transmission electron microscopy images for molybdenum disulfide-cobalt promoted interfaces

Many studies had been done in order to understand promotion effect and structure/function in unsupported catalyst. Results indicated that d-electrons play an important role promoting catalytical active sites at the edges of MoS2 catalytically structures. Sulfur removal from crude oil, occurs on the edge of molybdenum di-sulfide (MoS2) nano structures, due to promotion of MoS2 nano structures with nickel or cobalt in sulfur-terminated or molybdenum-terminated (1¯010) edge planes. The promotion leads to formation of so-called CoMoS phase (MoS2/Co9S8 ) first discovered by meaning of Mössbauer spectroscopy, much more CoMoS phase usually called unsupported catalytical particles, have been topic of great interest in scientific community, leading to several intriguing conclusions. Nevertheless atomistic conclusions cannot be concluded by meaning of a single theoretical work, in fact several technical paper were found in an attempt to explain promotion effect on MoS2 nano structures, with no one single conclusion found; meaning key information on about how Cobalt Molybdenum and Sulfur acted together, in terms of atomic position as described by observations made in these nano structures by electron microscopy techniques to create the so-called CoMoS phase. Few technical reports have approached and discussed this intrigue key problem by means of Density Functional Theory methods and are in agreement data obtained by other techniques. As for microstructure characterization, in the literature most of the articles just report the nano structure type indicated as fringes of MoS2 but no further important information like the localization of the promoters. It is also described, in the literature, how one reaction; which is the hydrodesulfurization (HDS) of large molecules usually dibenzothiophene, thiophenes and others contained in crude oil, occurred at edges of MoS2 nano structures when they are Co or Ni promoted, with almost zero activity in the (001) basal planes, as anyone could expect. The meaning could be understood in terms of energetic limits required to nucleate at the MoS2 basal planes. In recent years, in the literature a complete study made by Scanning Tunneling Microscope and DFT calculations for specific herringbone structure on MoS2/Au crystallites, indicating with this the latest results in advance characterization, this research path let catalysis experts to look over new techniques to achieve a complete characterization in nano structured materials. Finally we present here a complete density functional theory and HRTEM study to indicate how two structures MoS2 and Co9S 8 acted together in the formation of the so-called CoMoS phase. In this particular work one can find data based on Density of States and Band Structure calculations of MoS2/Co9S8 interface as well as real time images of high resolution transmission electron microscope (HRTEM), and finally a proposed computational molecular structure to explain the promotion effect in MoS2 nano-structures