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Nanotecnología en Superficies y Plasma

Unraveling Discharge and Surface Mechanisms in Plasma-Assisted Ammonia Reactions

Navascues, P; Obrero-Perez, JM; Cotrino, J; Gonzalez-Elipe, AR; Gomez-Ramirez, A
ACS Sustainable Chemistry & Engineering, 8 (2020) 14855-14866

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Current studies on ammonia synthesis by means of atmospheric pressure plasmas respond to the urgent need of developing less environmentally aggressive processes than the conventional Haber-Bosch catalytic reaction. Herein, we systematically study the plasma synthesis of ammonia and the much less investigated reverse reaction (decomposition of ammonia into nitrogen and hydrogen). Besides analyzing the efficiency of both processes in a packed-bed plasma reactor, we apply an isotope-exchange approach (using D-2 instead of H-2) to study the reaction mechanisms. Isotope labeling has been rarely applied to investigate atmospheric plasma reactions, and we demonstrate that this methodology may provide unique information about intermediate reactions that, consuming energy and diminishing the process efficiency, do not effectively contribute to the overall synthesis/decomposition of ammonia. In addition, the same methodology has demonstrated the active participation of the interelectrode material surface in the plasma-activated synthesis/decomposition of ammonia. These results about the involvement of surface reactions in packed-bed plasma processes, complemented with data obtained by optical emission spectroscopy analysis of the plasma phase, have evidenced the occurrence of inefficient intermediate reaction mechanisms that limit the efficiency and shown that the rate-limiting step for the ammonia synthesis and decomposition reactions are the formation of NH* species in the plasma phase and the electron impact dissociation of the molecule, respectively.

Octubre, 2020 | DOI: 10.1021/acssuschemeng.0c04461

Materiales de Diseño para la Energía y Medioambiente

Multiple pollutants removal by functionalized heterostructures based on Na-2-Mica

Pazos, MC; Bravo, LR; Ramos, SE; Osuna, FJ; Pavon, E; Alba, MD
Applied Clay Science, 196 (2020) 105749

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Organomica, C8-2-Mica, was obtained from a high charged synthetic mica, Na-2-Mica, by cation exchange reaction with octylammonium cations and these were used to host other bulky guest species such as polyhydroxy aluminium cations, Al(13)20. The hydrolization of 3-mercaptopropyltrimethoxysilane (MPTMS) allowed the covalent attachment with hydroxyl groups of the oligomeric cation, providing thiol groups that create specific adsorption sites, Al(13)20/SH. The structure of the adsorbents was analysed by XRD and Infrared spectroscopy and these were tested as an adsorbent for the removal of zinc and herbicide MCPA from aqueous solutions. C8-2-Mica was the best adsorbent for MCPA and thiol groups favoured the adsorption of Zn2+. Moreover, Al(13)20/SH showed excellent adsorptive properties for the simultaneous adsorption of MCPA and Zn2+.

Octubre, 2020 | DOI: 10.1016/j.clay.2020.105749

Química de Superficies y Catálisis

Bimetallic PdAu catalysts for formic acid dehydrogenation

Santos, JL; Leon, C; Monnier, G; Ivanova, S; Centeno, MA; Odriozola, JA
International Journal of Hydrogen Energy, 45 (2020) 23056-23068

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A series of monometallic and bimetallic palladium gold catalyst were prepared and studied for the formic acid dehydrogenation reaction. Different Pd/Au compositions were employed (PdxAu100-x, where x = 25; 50 and 75) and their impact on alloy structure, particle size and dispersion was evaluated. Active phase composition and reaction parameters such as temperature, formic acid concentration or formate/formic acid ratio were adjusted to obtain active and selective catalyst for hydrogen production. An important particle size effect was observed and related to Pd/Au composition for all bimetallic catalysts. 

Septiembre, 2020 | DOI: 10.1016/j.ijhydene.2020.06.076

Química de Superficies y Catálisis

Free-Carbon Surface for PtCu Nanoparticles: An In Situ Near Ambient Pressure X-ray Photoelectron Spectroscopy Study

Castillo, R; Navarro-Jaen, S; Romero-Sarria, F; Perez-Dieste, V; Escudero, C; Centeno, MA; Daturi, M; Odriozola, JA
Journal of Physical Chemistry C, 124 (2020) 19046-19056

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Usually, nanoparticle synthesis methodologies require the use of organic molecules (capping agent, solvent molecules, etc.), which results in carbon deposits on the nanoparticle surface. These residues modify the surface properties mainly affecting the catalytic behavior. In this work, unsupported poly(vinylpyrrolidone) (PVP)-stabilized PtCu (1:3 molar ratio) bimetallic alloy nanoparticles were synthetized and characterized. An alternative surface cleaning method has been designed, which successfully removes the presence of organic fragments. To address this key issue, we have combined a first nanoparticle washing step with a near ambient pressure X-ray photoelectron spectroscopy (NAPXPS) study in order to obtain a clean active site and the total understanding of the carbon elimination mechanism. The dynamic evolution of the surface organic species composition under different gas mixtures at 750 mTorr and 350 degrees C has been studied, and only under CO2 exposure, NAPXPS analysis revealed a total availability of the active site by the removal of the organic nanoparticle coating.

Septiembre, 2020 | DOI: 10.1021/acs.jpcc.0c04713

Nanotecnología en Superficies y Plasma

The wrinkling concept applied to plasma-deposited polymer-like thin films: A promising method for the fabrication of flexible electrodes

Thiry, Damien; Vinx, Nathan; Damman, Pascal; Aparicio, Francisco F.J.; Tessier, Pierre-Yves; Moerman, David; Leclere, Philippe; Godfroid, Thomas; Deprez, Sylvain; Snyders, Rony
Plasma Processes and Polymers, 17 (2020) e2000119

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In this communication, we report on an innovative solvent-free method that allows for the design of nano-/micropatterns with tuneable dimensions. Our approach is based on the spontaneous wrinkling phenomenon taking place in a bilayer system formed by a mechanically responsive bottom plasma polymer layer and a top aluminum thin film. The dimensions of the wrinkles can be adjusted in a wide range (i.e., from nanometer to micrometer range) by modulating the cross-linking density as well as the thickness of the plasma polymer layer. Finally, it is demonstrated that these wrinkled surfaces could efficiently be used as flexible electrodes. The whole set of our data unambiguously reveals the attractiveness of our method for the fabrication of the micro-/nanopattern with dimensions on demand.

Septiembre, 2020 | DOI: 10.1002/ppap.202000119