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Gonzalez G.A.,University of Texas at El Paso | Alvarado M.,University of Texas at El Paso | Ramos M.A.,Institute Ingenieria y Tecnologia | Berhault G.,CNRS Research on Catalysis and Environment in Lyon | Chianelli R.R.,University of Texas at El Paso
Computational Materials Science

Transition state computational studies of the sulfur removal from dibenzothiophene (DBT) molecule have herein been performed considering the Co9S8/MoS2 interface existing on unsupported Co/MoS2 catalysts. The linear synchronous transit (LST) and quadratic synchronous transit (QST) methods integrated in a density functional theory (DFT) program such as Dmol3 were used for the calculations of energy barriers of the transition states. Three different configurations present on the Co9S8/MoS2 interface have been envisaged as possible catalytic sites: sulfur-sulfur (S, S) sites, and molybdenum-sulfur (Mo, S) and molybdenum-molybdenum (Mo, Mo) edge sites. This study revealed that the (Mo, Mo) edge site is the most catalytically active site for the hydrodesulfurization (HDS) reaction followed by the (Mo, S) edge site while the (S, S) site shows almost inertness for the HDS reaction. This information allows us to propose clues to design new catalysts based on bulk Co9S8/MoS2 phases with higher efficiency by increasing the proportion of (Mo, Mo) edge sites. © 2016 Elsevier B.V. Source

Dominguez-Rios C.,CIMAV | Hurtado-Macias A.,CIMAV | Torres-Sanchez R.,CIMAV | Ramos M.A.,Institute Ingenieria y Tecnologia | Gonzalez-Hernandez J.,CIMAV
Industrial and Engineering Chemistry Research

Structure and mechanical properties of electroless nickel-boride (Ni-B) thin film coatings on S7 steel substrate were studied in as-plated and annealed samples. The electroless bath does not contain Pb, Cd, or Ta in the stabilizer agents. The mechanical properties of the Ni-B coatings were obtained from nanoindentation measurements. Models by Korsusky and King were used to obtain hardness and elastic modulus, respectively. The structure of the coatings was observed by atomic force and scanning electron microscopy and XRD. Bath composition, plating time, annealing temperature, and time were considered in order to prepare coatings with optimal mechanical properties. © 2012 American Chemical Society. Source

Ramos M.,Institute Ingenieria y Tecnologia | Ramos M.,University of Texas at El Paso | Ferrer D.,University of Texas at Austin | Martinez-Soto E.,University Metropolitana | And 4 more authors.

Hydrotreatment catalytic operations are commonly performed industrially by layered molybdenum sulfide promoted by cobalt or nickel in order to remove heteroelements (S, N, O) from fossil fuels and biofuels. Indeed, these heteroelements are responsible of the emission of pollutants when these fuels are used in vehicles. In this respect, previous studies made by our research group have shown that the active phase under steady state conditions is partially carbided while strong bending effects of MoS2 slabs were also observed. However, up to now, the morphology of the resulting Co/MoSxCy carbided catalyst has not been fully characterized. In the present study, for the first time, a chemical reaction between the carbon content of a TEM Cu/C grid and a freshly sulfide Co/MoS2 catalyst was in situ observed at 300°C and 450°C by HRTEM experimental techniques at ~10nm of resolution. Results indicate that bending of MoS2 layers occurred due to carbon addition on MoS2 edge sites, as observed in stabilized catalysts after HDS reaction. Using a silicon grid, only cracks of MoS2 slabs were observed without bending effect confirming the role of structural-carbon in this change of morphology. © 2012 Elsevier B.V. Source

Lastra G.,National Autonomous University of Mexico | Carrillo-Castillo A.,Institute Ingenieria y Tecnologia | Quevedo-Lopez M.A.,University of Texas at Dallas | Quevedo-Lopez M.A.,University of Sonora | Olivas A.,National Autonomous University of Mexico
Journal of Electronic Materials

Zinc sulfide (ZnS) thin films have been grown by chemical bath deposition (CBD) using different zinc sources on a silicon nitride (Si3N4) substrate in an alkaline solution. The zinc precursors used were zinc acetate, zinc nitrate, and zinc sulfate. The structural and optical characteristics of the ZnS thin films obtained were analyzed. The morphology of the surface showed that the films were compact and uniform, with some pinholes in the surface depending on the zinc source. The most homogeneous and compact surfaces were those obtained using zinc nitrate as the zinc source with a root-mean-square (RMS) value of 3 nm. The transmission spectra indicated average transmittance of 80% to 85% in the spectral range from 300 nm to 800 nm, and the optical bandgap calculated for the films was around 3.71 eV to 3.74 eV. © 2014 The Minerals, Metals & Materials Society. Source

Vilchis-Nestor A.R.,Autonomous University of Mexico State | Lugo-Medina E.,IT de Los Mochis | Carrillo-Castillo A.,Institute Ingenieria y Tecnologia | Quevedo-Lopez M.A.,University of Texas at Dallas | Olivas A.,National Autonomous University of Mexico

In this work, the influence of substrate on the morphology of ZnS thin films by chemical bath deposition is studied. The materials used were zinc acetate, tri-sodium citrate, thiourea, and ammonium hydroxide/ammonium chloride solution. The growth of ZnS thin films on different substrates showed a large variation on the surface, presenting a poor growth on SiO2 and HfO2 substrates. The thin films on ITO substrate presented a uniform and compact growth without pinholes. The optical properties showed a transmittance of about 85% in the visible range of 300-800 nm with band gap of 3.7 eV. SCANNING 37:389-392, 2015. © 2015 Wiley Periodicals, Inc. Source

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