Alvaro Mayoral
University of Zaragoza
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Publication
Featured researches published by Alvaro Mayoral.
Nature Chemistry | 2013
Avelino Corma; Patricia Concepción; Mercedes Boronat; María J. Sabater; Javier Navas; Miguel José Yacamán; Eduardo Larios; Alvaro Posadas; M. Arturo López-Quintela; David Buceta; Ernest Mendoza; Gemma Guilera; Alvaro Mayoral
The catalytic activity of gold depends on particle size, with the reactivity increasing as the particle diameter decreases. However, investigations into behaviour in the subnanometre regime (where gold exists as small clusters of a few atoms) began only recently with advances in synthesis and characterization techniques. Here we report an easy method to prepare isolated gold atoms supported on functionalized carbon nanotubes and their performance in the oxidation of thiophenol with O2. We show that single gold atoms are not active, but they aggregate under reaction conditions into gold clusters of low atomicity that exhibit a catalytic activity comparable to that of sulfhydryl oxidase enzymes. When clusters grow into larger nanoparticles, catalyst activity drops to zero. Theoretical calculations show that gold clusters are able to activate thiophenol and O2 simultaneously, and larger nanoparticles are passivated by strongly adsorbed thiolates. The combination of both reactants activation and facile product desorption makes gold clusters excellent catalysts.
Journal of Materials Chemistry | 2015
Javier Sánchez-Laínez; Beatriz Zornoza; Alvaro Mayoral; Ángel Berenguer-Murcia; Diego Cazorla-Amorós; Carlos Téllez; Joaquín Coronas
The synthesis of nano-sized ZIF-11 with an average size of 36 ± 6 nm is reported. This material has been named nano-zeolitic imidazolate framework-11 (nZIF-11). It has the same chemical composition and thermal stability and analogous H2 and CO2 adsorption properties to the conventional microcrystalline ZIF-11 (i.e. 1.9 ± 0.9 μm). nZIF-11 has been obtained following the centrifugation route, typically used for solid separation, as a fast new technique (pioneering for MOFs) for obtaining nanomaterials where the temperature, time and rotation speed can easily be controlled. Compared to the traditional synthesis consisting of stirring + separation, the reaction time was lowered from several hours to a few minutes when using this centrifugation synthesis technique. Employing the same reaction time (2, 5 or 10 min), micro-sized ZIF-11 was obtained using the traditional synthesis while nano-scale ZIF-11 was achieved only by using centrifugation synthesis. The small particle size obtained for nZIF-11 allowed the use of the wet MOF sample as a colloidal suspension stable in chloroform. This helped to prepare mixed matrix membranes (MMMs) by direct addition of the membrane polymer (polyimide Matrimid®) to the colloidal suspension, avoiding particle agglomeration resulting from drying. The MMMs were tested for H2/CO2 separation, improving the pure polymer membrane performance, with permeation values of 95.9 Barrer of H2 and a H2/CO2 separation selectivity of 4.4 at 35 °C. When measured at 200 °C, these values increased to 535 Barrer and 9.1.
Physical Chemistry Chemical Physics | 2010
M. M. Mariscal; Jimena A. Olmos-Asar; C. Gutierrez-Wing; Alvaro Mayoral; Miguel José Yacamán
In the present work new findings on the structure of the S-Au interface are presented. Theoretical calculations using a new semiempirical potential, based on density functional theory and a bond-order Morse potential, are employed to simulate the adsorption process in a more realistic way. The simulation results reveal the formation of gold adatoms on the nanoparticle surface and high surface disorder due to the strong S-Au bond. Experimental data were acquired by aberration (Cs) corrected scanning transmission electron microscopy (STEM) using a high angle annular dark field detector (HAADF) that showed a great similarity with the theory predicted.
Carbon | 2014
Gilberto Casillas; Alvaro Mayoral; Mingjie Liu; Arturo Ponce; Vasilii I. Artyukhov; Boris I. Yakobson; Miguel Jose-Yacaman
Atomic carbon chains have raised interest for their possible applications as graphene interconnectors as the thinnest nanowires; however, they are hard to synthesize and subsequently to study. We present here a reproducible method to synthesize carbon chains in situ TEM. Moreover, we present a direct observation of the bond length alternation in a pure carbon chain by aberration corrected TEM. Also, cross bonding between two carbon chains, 5 nm long, is observed experimentally and confirmed by DFT calculations. Finally, while free standing carbon chains were observed to be straight due to tensile loading, a carbon chain inside the walls of a carbon nanotube showed high flexibility.
Nanoscale | 2010
Alvaro Mayoral; Sergio Mejía-Rosales; Marcelo M. Mariscal; Eduardo Pérez-Tijerina; Miguel Jose-Yacaman
We report the formation of Au/Co nanoparticles and their characterization by aberration (Cs) corrected scanning transmission electron microscopy (STEM). The nanoparticles were synthesized by inert gas condensation, forming initially core-shell and bimetallic crystals. However, after thermal treatment at normal atmospheric conditions, the Co nanoparticles changed their morphology into a fine layer forming a perfect interface with the gold. The ordering of the zone rich in Co presents a fcc arrangement matching the gold lattice. The atomic analysis on the interface and the comparison of the STEM images with numerical simulations corroborated the atomic substitution of gold by cobalt.
Micron | 2011
Isabel Díaz; Alvaro Mayoral
In the present manuscript we have reviewed recent results on transmission electron microscopy of beam sensitive materials such as zeolites and ordered mesoporous materials. The results of the investigation of the fine structure of different zeolite types as MFI, ITQ-7 and the presence of mixture of phases are shown. In addition, the incorporation of metals within the zeolitic framework and their different applications as precursors for metal nanowire growth are also described. The combination of HRTEM together with electron crystallography for solving new ordered mesoporous silica and associated analytical techniques shows the strength of electron microscopy for a full characterization of such materials.
CrystEngComm | 2015
Beatriz Seoane; Alla Dikhtiarenko; Alvaro Mayoral; Carlos Téllez; Joaquín Coronas; Freek Kapteijn; Jorge Gascon
We report the effect of synthesis parameters on the textural properties of Al based MOFs synthesized in the presence CTAB.
Journal of Materials Chemistry | 2011
Alvaro Mayoral; Lawrence F. Allard; Domingo Ferrer; Rodrigo Esparza; Miguel Jose-Yacaman
Single crystal nanowires have been monitored at a wide range of temperatures from room temperature up to 900 °C using an aberration-corrected JEOL 2200FS scanning transmission electron microscope in both, bright field and high angle annular dark field, modes. The in situ measurements allowed heating and cooling the material instantaneously at the desired value making able to analyze the behaviour of silver nanowires at atomic resolution. The nanowires which firstly melted and subsequently vaporized left after the reaction empty carbon nanotubes. In addition, a Chevron-like defect has been also observed for the first time in silver nanowires and a structural analysis has been carried out by aberration corrected scanning transmission electron microscopy using high angle annular dark field imaging.
Chemcatchem | 2013
Alvaro Mayoral; Raul Arenal; Victoria Gascón; Carlos Márquez-Álvarez; Rosa M. Blanco; Isabel Díaz
One of the widely accepted uses of ordered mesoporous materials is as supports of enzymes for biotechnological applications. Enzymes have been trapped, anchored, or encapsulated in organized porous networks of the mesoporous range (2–50 nm). The reactivity of the surface of mesoporous materials has enabled the synthesis of various supports by using different forces for the immobilization process. To design catalysts for specific applications, we have developed functionalized mesoporous materials with tunable hydrophobicity for the immobilization of lipase. More recently, we moved to the immobilization of laccase with amino‐functionalized ordered mesoporous materials. In this case, it is required to use pore expanders along with optimized functionalization techniques. Advanced TEM techniques have been applied to locate not only the functional groups but also the macromolecules inside the silica matrix.
RSC Advances | 2013
Jose L. Hueso; Victor Sebastian; Alvaro Mayoral; Laura Usón; Manuel Arruebo; Jesus Santamaria
The use of tetrakis-(hydroxymethyl)-phosphonium chloride (THPC) as simultaneous reducing agent and stabilizing ligand has been extended to the single-step synthesis at room temperature of a wide variety of monometallic nanoparticles and bi-/tri- metallic nanoalloys containing noble metals with potential application in catalysis. The colloidal suspensions exhibit mean diameters below 4 nm with narrow size distributions and high stability in aqueous solution for long periods of time.