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    Hydrogenation-induced superconducting properties of MgB2 investigated using Migdal–Eliashberg formalism: Insights from a first-principles study
    (2024-09-01)
    Tsuppayakorn-aek, Prutthipong
    ;
    Sukmas, Wiwittawin
    ;
    Pluengphon, Prayoonsak
    ;
    Petchsirivej, Sukanya
    ;
    Sakulkalavek, Aparporn
    Theoretical investigation of hydrogenation processes has applied to magnesium diborides under ambient conditions, which identified two structurally stable phases, i.e, Mg<inf>4</inf>B<inf>6</inf>H<inf>2</inf> and Mg<inf>4</inf>B<inf>4</inf>H<inf>4</inf>. These identifications were evaluated through assessments of their lattice dynamics stability using density functional perturbation theory. Both phases exhibit metallic behavior within their electronic band structures. Our findings showcase the significant impact of anisotropic Migdal–Eliashberg calculations, enhancing the superconducting properties within this system and resulting in a notably higher T<inf>c</inf> of 34 K. Mg<inf>4</inf>B<inf>4</inf>H<inf>4</inf> exhibits superconductivity with a T<inf>c</inf> of 17 K under atmospheric conditions, as determined by anisotropic Migdal–Eliashberg calculations. Our study underscores the wide range of structural variations achievable through the hydrogenation of MgB<inf>2</inf> and highlights the crucial importance of hydrogen atom placement within these structures. In addition, the calculation result indicates the influence of band dispersion characteristics on Fermi velocity, a factor attributed to both anharmonicity and harmonicity, which plays a pivotal role in determining the superconducting properties of these materials.
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    Direct Synthesis of Liquefied Petroleum Gas from Carbon Dioxide Using a Copper/Zinc Oxide/Zirconia/Alumina and HY Zeolite Hybrid Catalyst
    (2021-07-27)
    Natakaranakul, Jaru
    ;
    Thongkam, Montree
    ;
    Li, Hangjie
    ;
    Suchamalawong, Phorndranrat
    ;
    Tsubaki, Noritatsu
    Conversion of CO<inf>2</inf> to lower hydrocarbons (HCs) is a high potential process that could reduce and sustainably control this greenhouse gas. In accord with The Sustainable Development Goal from The United Nation Development Program, liquefied petroleum gas (LPG) is viewed as environmentally friendly and is widely used. Small HCs can be directly synthesized from CO<inf>2</inf> hydrogenation over a hybrid catalyst. The main purpose of this study was to investigate the direct synthesis of LPG from CO<inf>2</inf> hydrogenation using a copper/zinc oxide/zirconium/alumina (CZZA) mixed metal and HY zeolite as a hybrid catalyst. The study was conducted in a fixed bed reactor using hydrogen/CO<inf>2</inf>/carbon monoxide as the reactant gas and evaluating four types of production condition, method of catalyst combination, reaction temperature, CZZA/HY zeolite mass ratio, and catalyst weight/volume flow rate. The mixing type between the CZZA and HY zeolite catalysts markedly influenced the HC selectivity with strong suppression of reverse water gas shift reaction. At the optimum condition, a 27.39 % CO<inf>2</inf> conversion level and a high HC (98.70 %) and LPG (66.56 %) selectivity were obtained.
      1
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    Catalytic deoxygenation of benzaldehyde over gallium-modified ZSM-5 zeolite
    (2009-11-15)
    Ausavasukhi, Artit
    ;
    Sooknoi, Tawan
    ;
    Resasco, Daniel E.
    The deoxygenation of benzaldehyde has been investigated over gallium-modified ZSM-5 catalysts. In the absence of H<inf>2</inf>, Ga/HZSM-5 catalyzes benzaldehyde decarbonylation resulting in benzene and CO. The active sites for this reaction are the strong Brønsted acid sites. In the presence of H<inf>2</inf>, the main product is toluene. It is believed that Ga cationic species (Ga<sup>+</sup> / GaH<inf>2</inf><sup>+</sup>) generated during H<inf>2</inf> reduction can promote the hydrogenation/hydrogenolysis reactions that give toluene and water. In the absence of H<inf>2</inf>, toluene can only be observed in transient experiments when the Ga/HZSM-5 catalysts are reduced. It is suggested that the GaH<inf>2</inf><sup>+</sup> species generated under H<inf>2</inf> play an important role in the hydrogenation/hydrogenolysis. However, they readily decompose to Ga<sup>+</sup> in the absence of H<inf>2</inf>. The addition of water to the feed modifies the catalytic activity and selectivity of Ga/HZSM-5 catalysts. On the one hand, water generates additional Brønsted acid sites from the reaction of extra-framework Ga with chemisorbed water (GaO(OH)) and with defect hydroxyls of the zeolite framework (GaOHSi). These additional sites enhance the production of benzene but decrease the production of toluene, due to a decrease in the density of reduced Ga cationic species. © 2009 Elsevier Inc. All rights reserved.
      1