Water Durable Electride Y<sub>5</sub>Si<sub>3</sub>: Electronic Structure and Catalytic Activity for Ammonia Synthesis

Lu, Yangfan; Li, Jiang; Tada, Tomofumi; Yoshitake, T.; Ueda, Shigenori; Yokoyama, Toshiharu; Kitano, Masaaki; Hosono, Hideo

doi:10.1021/jacs.6b00124

Cited by 222 publications

(264 citation statements)

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“…Compared to the strongly reactive layered electrides, such as [Ca 2 N] + :e -and [Y 2 C] 1.8+ :1.8e -, the air stable 1D analogues promise a more friendly system to work on. [18][19][20][21] From a structural perspective, the topology of the cation arrays in our 1D apatite electride [La 8 20, 21 The presence of anionic electrons is associated with the formation of new energy states near the Fermi level with weak electron-phonon interaction, which is indicative of a good source for superconductivity. We are, therefore, motivated to look for possible combined electride and superconducting states by further exploring the chemical variety of Mn 5 Si 3 -type A 5 B 3 phases (A: rare earth or transition metals; B: Ga, Si, Ge, etc).…”

Section: Introductionmentioning

confidence: 99%

Electride and superconductivity behaviors in Mn5Si3-type intermetallics

et al. 2017

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Electrides are unique in the sense that they contain localized anionic electrons in the interstitial regions. Yet they exist with a diversity of chemical compositions, especially under extreme conditions, implying generalized underlying principles for their existence. What is rarely observed is the combination of electride state and superconductivity within the same material, but such behavior would open up a new category of superconductors. Here, we report a hexagonal Nb 5 Ir 3 phase of Mn 5 Si 3 -type structure that falls into this category and extends the electride concept into intermetallics. The confined electrons in the one-dimensional cavities are reflected by the characteristic channel bands in the electronic structure. Filling these free spaces with foreign oxygen atoms serves to engineer the band topology and increase the superconducting transition temperature to 10.5 K in Nb 5 Ir 3 O. Specific heat analysis indicates the appearance of low-lying phonons and two-gap s-wave superconductivity. Strong electron-phonon coupling is revealed to be the pairing glue with an anomalously large ratio between the superconducting gap Δ 0 and T c , 2Δ 0 /k B T c = 6.12. The general rule governing the formation of electrides concerns the structural stability against the cation filling/extraction in the channel site.

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Section: Introductionmentioning

confidence: 99%

Electride and superconductivity behaviors in Mn5Si3-type intermetallics

et al. 2017

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“…

electron donation to adsorbed species, [2a,4,9] enhancing activity. [14] These reactions are challenging environments for any electride or hydride support, as virtually all of these aforementioned electrides (except for Y 5 Si 3 , but only NH 3 synthesis was reported [7] ) or hydrides are not stable in water. [3a,10] The new recent activity concerning NH 3 synthesis, as opposed to other reactions, is doubtlessly related to the stability of the catalysts in these anhydrous and anaerobic environments.

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Hydride‐Enhanced CO₂ Methanation: Water‐Stable BaTiO_2.4H_0.6 as a New Support

Tang

Kobayashi

Tassel

et al. 2018

Advanced Energy Materials

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electron donation to adsorbed species, [2a,4,9] enhancing activity. LiH [3a] and BaH 2 [3b] have also been examined as catalytic supports for NH 3 synthesis, with lattice hydride (H − ) playing a decisive role in the hydrogenation of adsorbed nitrogen. [3a,10] The new recent activity concerning NH 3 synthesis, as opposed to other reactions, is doubtlessly related to the stability of the catalysts in these anhydrous and anaerobic environments. Other than Y 5 Si 3 , all of these materials are not water-stable. [11] However, catalytic reactions involving water as a reactant or byproduct are quite numerous, such as the Fischer-Tropsch process, [12] steam reforming, [13] or the Sabatier reaction (CO 2 methanation). [14] These reactions are challenging environments for any electride or hydride support, as virtually all of these aforementioned electrides (except for Y 5 Si 3 , but only NH 3 synthesis was reported [7] ) or hydrides are not stable in water. However, we note that the oxyhydride BaTiO 2.4 H 0.6 is stable both in air and boiling water, [15] making it a good candidate for testing how hydride-based support materials fare with these other types of reactions. We have previously confirmed that the lattice H − in BaTiO 2.4 H 0.6 can be exchanged with surrounding D 2 gas at 400 °C (based on neuron diffraction). [15a] This H/D exchange involves D 2 bond dissociation and hints that various hydrogenation reactions may be possible. In a more recent study, we found a lattice hydrogen-involved (Mars-van Krevelen mechanism) formation of NH 3 on BaTiO 2.4 H 0.6 under Haber-Bosch conditions, [16] indicating a great potential of oxyhydride for catalysis applications.Hence, in this paper we examine the influence of hydride as it is introduced into a BaTiO 3 support when utilized as a supported metal catalyst for the Sabatier reaction (CO 2 + 4H 2 → CH 4 + 2H 2 O). The activities of Ni/BaTiO 3−x H x and Ru/BaTiO 3−x H x were examined under the identical conditions finding that the activity is enhanced by 2-7 times when compared to Ni, Ru/BaTiO 3 , despite the water-rich environment. We also observe changes in H 2 reaction order when compared to BaTiO 3 -supported catalysts, indicating that activity change is due to the kinetics being influenced by hydride. This work demonstrates that the oxyhydride is an effective support material for CO 2 hydrogenation catalysis, and perhaps other waterinvolved catalytic processes.Three powder samples of BaTiO 3−x H x with x = 0.35, 0.44, and 0.60 were synthesized by reduction with CaH 2 (Supporting Information). [15a] A symmetry change from the Catalytic CO 2 hydrogenation to CH 4 provides a promising approach to producing natural gas, and reducing the emissions of global CO 2 . However, the efficiency of catalytic CO 2 methanation is limited by slow kinetics at low temperatures. This study first demonstrates that an air-and water-stable perovskite oxyhydride BaTiO 2.4 H 0.6 could function as an active support material for Ni-, Ru-based catalysts for CO 2 methanation at 300-350 °C,...

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“…The microscopic model presented here reveals the mechanisms of C12A7 transformation from the crystalline to the amorphous form and explains the dependence of T g on the concentration of electron anions; it also gives insight into the multiple kinetically controlled processes near T m . We propose that use of electrons as highly mobile anions offers a promising method for attenuating the thermal and electronic properties of amorphous materials formed from oxides of nonreducible metals, facilitating the design of structural and functional glasses and building on the recent discoveries of other stable solid electrides (44)(45)(46)(47). Furthermore, the concept of altering network properties via highly mobile weak links, such as electron anions, as opposed to stationary weak links, may have applications in a diverse variety of networks, well beyond the science of noncrystalline materials.…”

Section: Resultsmentioning

confidence: 99%

Electron anions and the glass transition temperature

Johnson

Sushko

Tomota

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Properties of glasses are typically controlled by judicious selection of the glass-forming and glass-modifying constituents. Through an experimental and computational study of the crystalline, molten, and amorphous [Ca 12 Al 14 O 32 ] 2+ · (e -) 2 , we demonstrate that electron anions in this system behave as glass modifiers that strongly affect solidification dynamics, the glass transition temperature, and spectroscopic properties of the resultant amorphous material. The concentration of such electron anions is a consequential control parameter: It invokes materials evolution pathways and properties not available in conventional glasses, which opens a unique avenue in rational materials design.amorphous materials | glass transition | electrides | molecular dynamics | density functional theory O ne of the key challenges in materials design is identification of degrees of freedom that ensure robust control of the properties of interest. Small changes in composition of crystalline materials can lead to large changes in their electronic properties, such as optical absorption and electrical conductivity (1). Similarly, a small concentration of (co)dopants in amorphous materials can be used to control their optical properties (2, 3). Glass properties are typically controlled by varying composition or processing conditions (4). However, delicate control of viscosity and glass transition temperature in multicomponent materials (T g ) has remained elusive due to the collective origin of these properties. Substitution of atomic anions with electron anions in materials to form electrides (5, 6) introduces an additional degree of freedom. Here we demonstrate that electron anions dramatically change dynamics of atoms in an inorganic amorphous material, which strongly affects its T g . Extending the concept of electron anions to other amorphous materials would provide a powerful instrument for the design of glasses with finely tuned characteristics.Calcium aluminates (CA), composed of CaO and Al 2 O 3 , represent a common family of oxide glasses. Whereas pure Al 2 O 3 is a poor glass former, blending it with CaO leads to the formation of stable glasses composed of AlO 4 tetrahedra with strong and directional covalent bonds instead of nondirectional ionic bonds in bulk Al 2 O 3 (7). In contrast, Ca-O bonds retain their ionic character; they are weaker than Al-O bonds and lack a preferred orientation, which enables motion of the AlO 4 tetrahedra relative to each other. Hence, the T g of stoichiometric CA systems decreases by ∼50 K as the CaO content increases from 57 mol% to 70 mol% (Fig. 1). This relatively narrow interval of T g variation with composition is typical of multicomponent glasses (8, 9). The T g for stoichiometric [Ca 12 (5,14,15). In crystalline C12A7:e -, the electrons occupy the cage conduction band (CCB) states associated with the lattice cages (16, 17), leading to polaron-type conduction at x < ∼0.5 and metallic conduction at x > 0.5 (13, 16). The exceptionally low work function of crystalline C12A7:e -...

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Water Durable Electride Y₅Si₃: Electronic Structure and Catalytic Activity for Ammonia Synthesis

Cited by 222 publications

References 26 publications

Electride and superconductivity behaviors in Mn5Si3-type intermetallics

Electride and superconductivity behaviors in Mn5Si3-type intermetallics

Hydride‐Enhanced CO₂ Methanation: Water‐Stable BaTiO_2.4H_0.6 as a New Support

Electron anions and the glass transition temperature

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Water Durable Electride Y5Si3: Electronic Structure and Catalytic Activity for Ammonia Synthesis

Cited by 222 publications

References 26 publications

Electride and superconductivity behaviors in Mn5Si3-type intermetallics

Electride and superconductivity behaviors in Mn5Si3-type intermetallics

Hydride‐Enhanced CO2 Methanation: Water‐Stable BaTiO2.4H0.6 as a New Support

Electron anions and the glass transition temperature

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Product

Resources

About

Water Durable Electride Y₅Si₃: Electronic Structure and Catalytic Activity for Ammonia Synthesis

Hydride‐Enhanced CO₂ Methanation: Water‐Stable BaTiO_2.4H_0.6 as a New Support