A DFT and HRTEM Study on MoS 2 /Co: Locating Promoters in Catalytic Nanostructures
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A DFT and HRTEM Study on MoS2/Co: Locating Promoters in Catalytic Nanostructures Manuel Ramos1), 2), Gilles Berhault3), Jose Rurik Farias1), Jose Trinidad Elizalde1), Domingo Ferrer4), Brenda Torres2) and R. R. Chianelli2) 1
Departamento de Física y Matemáticas, Instituto de Ingeniería y Tecnología-UACJ, Avenida del Charro #610, Cuidad Juárez, MX. CP.32310 2 University of Texas at El Paso, Materials Research and Technology Institute, 303 Burges Hall, El Paso, Texas 79902, U.S.A 3 Institut de Recherches sur la Catalyse et l’Environnement, IRCELYON, CNRS –Université de Lyon, Villeurbanne, 69100, France 4 Microelectronics Research Center, University of Texas at Austin, Austin, TX. 78751, U.S.A.
ABSTRACT Locating cobalt promoters on catalytically MoS2 structures is a challenging task to achieve; this is due to the size on those MoS2 nanostructures. Previous reports in the literature indicate that specific locations for Co in MoS2 slabs are (1010)-plane creating either a sulfur-Co or Molybdenum-Co termination edge, due to lower energy required for the permutation Mo, S and Co to occur. We present results obtained from Density Functional Theory study done on the interface between MoS2 and Co9S8 crystal structures; the interface show an interesting thiocubane cluster and it is suspected to be the responsible for Mo-S-Co bonding to exist, along with HDS reaction. In order to understand electronic properties on thiocubane Density of States and Mulliken Population Analysis calculations were implemented using Cambridge Serial Total Energy Package (CASTEP). Results indicate a strong electron donation from Co to Mo through intermediate sulfur atom bonded to both metals while an enhanced metallic character is also found. INTRODUCTION Because of its uses during hydrodesulphurization reaction, molybdenum sulfide appears to be one of the best candidates to act as a catalyst for sulfur removal from crude oil. Previous studies [1] indicate that when promoted with nickel or cobalt it increased its catalytic activity, fact that makes MoS2 to be studied extensively in the past two decades [2]. The location of promoters (Nickel, Cobalt) has been done by others by conventional characterization techniques X-ray diffraction [3], Field Emission Electron Microscope (TEM and SEM) [4], Mössbauer spectroscopy [5] and lastly with the aid of quantum computational methods [6]. Even though these techniques were implemented to understand the relationship between Mo, S and Co (Ni) atoms, they were unsuccessful to achieved the nature of chemical bonding, that could happen because of scale size, which in most of the cases reports found in the literature reveals solely physical properties like d-spacing, folding, stacking size, surface contact and dislocations. Few are the reports published in the literature as compared with hundreds on conventional techniques
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that provide information about density of states, band structure and Mulliken population analysis [7, 8] for MoS2/Co9S8 structure. The objective of the present study was to address the chem
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