Sergio Fuentes

Bio: Sergio Fuentes is an academic researcher from National Autonomous University of Mexico. The author has contributed to research in topics: Catalysis & Hydrodesulfurization. The author has an hindex of 35, co-authored 135 publications receiving 3388 citations. Previous affiliations of Sergio Fuentes include Mexican Institute of Petroleum & University of Texas System.

HDS of DBT with Molybdenum Disulfide Catalysts Prepared by In Situ Decomposition of Alkyltrimethylammonium Thiomolybdates

Abstract: Three alkyltrimethylammonium thiomolybdates, [R–N(CH3)3]2MoS4 (where R = lauryl, myristyl or cetyl) were synthesized in aqueous solution, and characterized by 1H-NMR spectroscopy. These alkyltrimethylammonium thiomolybdates were used (the lauryl and myristyl thiomolybdates for the first time) as precursors for in situ prepared MoS2 catalysts, activated during the hydrodesulfurization of dibenzothiophene. The catalysts were analyzed by EDX, showing large voids and a S/Mo ratio around 2. High surface areas up to 443 m2/g and type IV adsorption–desorption nitrogen isotherms were obtained. X-ray diffraction showed that the catalysts are poorly crystalline, with a very weak (002) peak intensity for all samples except the MoS2 catalyst prepared from pure ammonium tetrathiomolybdate precursor. A high dibenzothiophene conversion (74%) was observed with the catalyst obtained from the lauryltrimethylammonium thiomolybdate precursor, attributed mainly to its high specific surface area. Selectivity results showed that all the prepared catalysts strongly favored the hydrogenation pathway.

Highly active Au-CeO2@ZrO2 yolk–shell nanoreactors for the reduction of 4-nitrophenol to 4-aminophenol

Abstract: Highly catalytically active yolk–shell Au-CeO2@ZrO2 nanoreactors (gold core encapsulated into porous zirconia shell and doped by ceria) for the 4-nitrophenol reduction to 4-aminophenol were synthesized. Au cores encapsulated into SiO2 (Au@SiO2) were decorated with ceria via injection of ceria precursor into a void space of silica shell (formed through surface-protected etching of silica by hot water) with its subsequent hydrolysis and thermal treatment (Au-CeO2@SiO2). Au-CeO2@ZrO2 nanoreactors were obtained using Au-CeO2@SiO2 as a template and replacement of SiO2 by ZrO2. The nanoreactors were characterized by STEM-EDS, in situ and ex situ UV–vis spectroscopy, and N2 thermal adsorption. The catalytic activity for decorated Au-CeO2@ZrO2 nanoreactors in the 4-nitrophenol reduction into 4-aminophenol was found to be ∼3 times higher than for non-decorated Au@ZrO2 nanoreactors. The herein proposed route of nanoreactor core decoration may be applied for the synthesis of nanoreactors with cores modified with different materials in order to make them effective for different catalytic reactions.

Preparation of MoS2 and WS2 catalysts by in situ decomposition of ammonium thiosalts

Abstract: The in situ decomposition of ammonium thiometallates during the hydrodesulfurization (HDS) of dibenzothiophene (DBT), to obtain molybdenum disulfide and tungsten disulfide catalysts, was investigated. It was found that very efficient catalysts for the HDS of DBT were obtained by in situ decomposition. Mechanical uniaxial pressing of the precursors (ammonium thiometallates) affected both textural and catalytic properties of the catalysts. Surface areas of molybdenum and tungsten disulfides increased as a function of uniaxial pressing, while catalytic activities went through a maximum. For MoS2, the hydrogenation selectivity was much higher for in situ catalysts than for ex situ ones. For WS2 catalysts, the hydrogenation selectivity was less sensitive to the condition of decomposition (ex situ/in situ). The surface S/M (M = Mo, W) atomic ratio from the Auger signal decreased as a function of uniaxial pressing, while the C/M ratio remained almost constant at 1.6. The best catalyst showed an experimental S/Mo ratio that is slightly higher than the stoichiometric value. The effect of in situ decomposition and mechanical deformation of thiometallate precursors is discussed.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Engineering the surface structure of MoS2 to preferentially expose active edge sites for electrocatalysis

Abstract: Controlling surface structure at the atomic scale is paramount to developing effective catalysts. For example, the edge sites of MoS(2) are highly catalytically active and are thus preferred at the catalyst surface over MoS(2) basal planes, which are inert. However, thermodynamics favours the presence of the basal plane, limiting the number of active sites at the surface. Herein, we engineer the surface structure of MoS(2) to preferentially expose edge sites to effect improved catalysis by successfully synthesizing contiguous large-area thin films of a highly ordered double-gyroid MoS(2) bicontinuous network with nanoscaled pores. The high surface curvature of this catalyst mesostructure exposes a large fraction of edge sites, which, along with its high surface area, leads to excellent activity for electrocatalytic hydrogen evolution. This work elucidates how morphological control of materials at the nanoscale can significantly impact the surface structure at the atomic scale, enabling new opportunities for enhancing surface properties for catalysis and other important technological applications.

Few-Layer MoS2: A Promising Layered Semiconductor

Abstract: Due to the recent expanding interest in two-dimensional layered materials, molybdenum disulfide (MoS2) has been receiving much research attention. Having an ultrathin layered structure and an appreciable direct band gap of 1.9 eV in the monolayer regime, few-layer MoS2 has good potential applications in nanoelectronics, optoelectronics, and flexible devices. In addition, the capability of controlling spin and valley degrees of freedom makes it a promising material for spintronic and valleytronic devices. In this review, we attempt to provide an overview of the research relevant to the structural and physical properties, fabrication methods, and electronic devices of few-layer MoS2. Recent developments and advances in studying the material are highlighted.