Molecular perspective of MoS 2 /Co unsupported catalyst using computer assisted TEM simulations
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Molecular perspective of MoS2/Co unsupported catalyst using computer assisted TEM simulations Manuel Ramos1,2, Joseph Serrano-Matos5, Eduan Martinez-Soto5, Brenda Torres2, Gilles Berhault4, Domingo Ferrer 3, José Rurik Farias-Mancilla1, Russell R. Chianelli2 1 Departamento de Física y Matemáticas, IIT –UACJ Cuidad Juárez, México, 32310. 2 Materials Research and Technology Institute, UT-El Paso, El Paso TX. 3 Microelectronics Research Laboratory, UT-Austin, Austin TX. 4 IRCELYON, CNRS – University of Lyon, Villeurbanne, 69100, France. 5 Departamento de Química, Universidad Metropolitana, San Juan, PR. *Corresponding author: 450 Ave. Del Charro, Cd. Juárez, Chihuahua. IIT-UACJ, Edificio G Cubículo-A301. E-mail address: [email protected], [email protected] ABSTRACT Understanding the morphology of catalytically active materials has been approached successfully in past decades using field electron microscopy in scanning and transmission modes. In this respect, some simulated TEM measurements for unsupported promoted molybdenum di-sulfide (MoS2/Co) provided some insights about molecular structure in those catalytic layered transition metal sulfides (LTMS). However, due to poor resolution, lack of color enhancement, and other factors, sections of those materials observed under TEM do not resolve the structure by itself; in particular about the localization of cobalt atoms for promoted MoS2 unsupported catalyst. This work concludes an epitaxial growth of MoS2 slabs over (111)-Co9S8 crystallographic plane, with a stacking degree size of 6 slabs. Results presented in here are obtained using experimental HRTEM and TEM simulations using the multi-slice method with a slice thickness of 25 Å and projected potential f (U )
n
¦a e i
( biU 2 )
, where ai and bi are coefficients to be determined.
i 1
Key words: HRTEM, MoS2, Catalytic, Projected Potential INTRODUCTION Transition Metal Sulfides like MoS2 have been used in the past twenty years as catalytic materials for HDS reactions in crude oil [1], the catalytic activity on layered MoS2 can be increased when it is promoted with nickel or cobalt [2] due to the Sabatier principle [3]. In the past decade extensive morphology and chemical activity studies has been conducted with much success using transmission and scanning electron microscopy, powder X-ray diffraction and Mössbauer spectroscopy [4-8]. However, important information has not been brought to literature. It has been applied as a scientific tool to describe two main factors (1) the role of promoters (i.e. Co, Ni) and (2) Structure/Function of physical-chemical properties. Commercial software and open access computational quantum code has made possible to model some of this layered materials, with good success [9, 10]. Here we present a series of images produced by a combination of experimental HRTEM and TEM simulations [11, 12]; this particular study provides particular insights of the layered MoS2/Co nanostructure.
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EXPERIMENT Samples are prepared by mixing ammonium tetrathiomolybdate, (NH4)2MoS4 (ATM) with
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