Person: Hernando González, María
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First Name
María
Last Name
Hernando González
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Químicas
Department
Química Inorgánica
Area
Química Inorgánica
Identifiers
7 results
Search Results
Now showing 1 - 7 of 7
Item Exceptional Low-Temperature CO Oxidation over Noble-Metal-Free Iron-Doped Hollandites: An In-Depth Analysis of the Influence of the Defect Structure on Catalytic Performance(ACS Catalysis, 2021) Gómez Recio, Isabel; Pan, Huiyan; Azor Lafarga, Alberto Eduardo; Ruiz González, María Luisa; Hernando González, María; Parras Vázquez, Marina Marta; Fernández-Díaz, María Teresa; Delgado, Juan J.; Chen, Xiaowei; Goma Jiménez, Daniel; Portehault, David; Sanchez, Clément; Cabero Piris, Mariona; Martínez-Arias, Arturo; González Calbet, José María; Calvino, José J.A family of iron-doped manganese-related hollandites, KxMn1–yFeyO2−δ (0 ≤ y ≤ 0.15), with high performance in CO oxidation have been prepared. Among them, the most active catalyst, K0.11Mn0.876Fe0.123O1.80(OH)0.09, is able to oxidize more than 50% of CO at room temperature. Detailed compositional and structural characterization studies, using a wide battery of thermogravimetric, spectroscopic, and diffractometric techniques, both at macroscopic and microscopic levels, have provided essential information about this never-reported behavior, which relates to the oxidation state of manganese. Neutron diffraction studies evidence that the above compound stabilizes hydroxyl groups at the midpoints of the tunnel edges as in isostructural β-FeOOH. The presence of oxygen and hydroxyl species at the anion sublattice and Mn3+, confirmed by electron energy loss spectroscopy, appears to play a key role in the catalytic activity of this doped hollandite oxide. The analysis of these detailed structural features has allowed us to point out the key role of both OH groups and Mn3+ content in these materials, which are able to effectively transform CO without involving any critical, noble metal in the catalyst formulation.Item Unambiguous localization of titanium and iron cations in doped manganese hollandite nanowires(Chemical Communications, 2020) Gómez Recio, Isabel; Azor Lafarga, Alberto Eduardo; Ruiz González, María Luisa; Hernando González, María; Parras Vázquez, Marina Marta; Calvino, José Juan; Fernández Díaz, María Teresa; Portehault, David; Sanchez, Clement; González Calbet, José MaríaNew insights into the chemical and structural features of iron or titanium-doped KxMnO2 hollandites are reported. Neutron diffraction and atomically resolved transmission electron microscopy elucidate the localization of the dopant cations that could be one of the key factors governing the functional activity of these nanomaterials.Item Hydroxyapatites as Versatile Inorganic Hosts of Unusual Pentavalent Manganese Cations(Chemistry of Materials, 2020) Varela Losada, María Áurea; Gómez Recio, Isabel; Serrador, Laura; Hernando González, María; Matesanz, Emilio; Torres Pardo, María De La Almudena; Fernández-Díaz, María Teresa; Martínez, Jose ; Gonell, Francisco; Rousse, Gwenaelle; Sanchez, Clément; Laberty-Robert, Christel; Portehault, David; González Calbet, José María; Parras Vázquez, Marina MartaContrary to molecular species, only very few solids are reported to host manganese (V) species. Herein, we report three new compounds with a hydroxyapatite structural backbone built on the MnVO43– anion: Sr5[(Mn1–xSix)O4]3(OH)1–3x (x = 0 and 0.053), Sr5(MnO4)3(OH)1–yFy (y = 0.90), and Sr5[(Mn1–xSix)O4]3F1–3x (x = 0.058). These solids are fully characterized using powder X-ray and neutron powder diffraction, scanning transmission electron microscopy, electron energy loss spectroscopy (EELS), thermogravimetric analysis, and magnetic measurements. Especially, we report for the first time EELS Mn–L2,3 spectra of manganese with the oxidation state (V). Contrary to other Mn(V) oxides, these solids and the nominal compound Sr5(MnO4)3OH do not comprise Ba2+ cations but rely only on Sr2+ cations, showing that barium is not a required element to stabilize Mn(V) species in inorganic solids. We show that by tuning soft chemistry conditions on the one hand and post-treatment topological transformation conditions on the other hand, Mn(V) and hydroxyl groups can be substituted by Si(IV) and fluoride ions, respectively. Hence, we deliver solids with a potentially wide composition range. These compounds show significant oxygen anionic conduction, thus suggesting the emergence of new functional materials built from high-oxidation state manganese cations.Item Characterization of Tunneled Wide Band Gap Mixed Conductors: The Na2O-Ga2O3-TiO2 System(Nanomaterials, 2023) García Fernández, Javier; Hernando González, María; Torres Pardo, María De La Almudena; López García, María Luisa; Fernández-Díaz, María Teresa; Zhang, Qing; Terasaki, Osamu; Ramírez Castellanos, Julio; González Calbet, José MaríaThis article focuses on the Na2O-Ga2O3-TiO2 system, which is barely explored in the study of transparent conductive oxides (TCOs). NaxGa4+xTin−4−xO2n−2 (n = 5, 6, and 7 and x ≈ 0.7–0.8) materials were characterized using neutron powder diffraction and aberration-corrected scanning transmission electron microscopy. Activation energy, as a function of different structures depending on tunnel size, shows a significant improvement in Na+ ion conduction from hexagonal to octagonal tunnels. New insights into the relationship between the crystal structure and the transport properties of TCOs, which are crucial for the design and development of new optoelectronic devices, are provided.Item Quantitative, Spectro-kinetic Analysis of Oxygen in Electron-Beam Sensitive, Multimetallic Oxide Nanostructures(Microscopy and Microanalysis, 2023) López-Haro, Miguel; Gómez Recio, Isabel; Pan, Huiyan; Delgado, Juan ; Chen, Xiaowei; Cauqui, Miguel ; Pérez-Omil, José ; Ruiz González, María Luisa; Hernando González, María; Parras Vázquez, Marina Marta; González Calbet, José María; Calvino, JoséThe oxygen stoichiometry of hollandite, KxMnO2-δ, nanorods has been accurately determined from a quantitative analysis of scanning-transmission electron microscopy (STEM) X-Ray Energy Dispersive Spectroscopy (XEDS) experiments carried out in chrono-spectroscopy mode. A methodology combining 3D reconstructions of high-angle annular dark field electron tomography experiments, using compressed-sensing algorithms, and quantification through the so-called ζ-factors method of XEDS spectra recorded on a high-sensitivity detector has been devised to determine the time evolution of the oxygen content of nanostructures of electron-beam sensitive oxides. Kinetic modeling of O-stoichiometry data provided K0.13MnO1.98 as overall composition for nanorods of the hollandite. The quantitative agreement, within a 1% mol error, observed with results obtained by macroscopic techniques (temperature-programmed reduction and neutron diffraction) validate the proposed methodology for the quantitative analysis, at the nanoscale, of light elements, as it is the case of oxygen, in the presence of heavy ones (K, Mn) in the highly compromised case of nanostructured materials which are prone to electron-beam reduction. Moreover, quantitative comparison of oxygen evolution data measured at macroscopic and nanoscopic levels allowed us to rationalize beam damage effects in structural terms and clarify the exact nature of the different steps involved in the reduction of these oxides with hydrogen.- Project number: PIMCD59/23-24
Item Modelos estructurales 3D de los elementos del bloque p. Del no metal al metal(2024) varela, Aurea; Hernando González, María; Parras Vázquez, Marina Marta; Varela Losada, María Áurea; Matesanz Saez, Emilio; Sánchez Marcos, Jorge; Gutiérrez Martín, Daniel; Hernando González, María Item Exploring reversible redox behavior in the 6H-BaFeO3−δ (0 < δ <0.4) system: impact of Fe3+/Fe4+ ratio on CO oxidation(Inorganic Chemistry, 2024) Gutiérrez Martín, Daniel; Varela, A.; Hernando González, María; Torres Pardo, María De La Almudena; E. Matesanz; I. Gómez-Recio; J. M. González-Calbet; M. T. Fernández-Díaz; J. J. Calvino; M. A. Cauqui; M. P. Yeste; M. ParrasThis work is devoted to evaluating the relationship between the oxygen content and catalytic activity in the CO oxidation process of the 6H-type BaFeO3−δ system. Strong evidence is provided about the improvement of catalytic performance with increasing Fe average oxidation state, thus suggesting the involvement of lattice oxygen in the catalytic process. The compositional and structural changes taking place in both the anionic and cationic sublattices of the catalysts during redox cycles have been determined by temperature-resolved neutron diffraction. The obtained results evidence a structural transition from hexagonal (P63/mmc) to orthorhombic (Cmcm) symmetry. This transition is linked to octahedra distortion when the Fe3+ concentration exceeds 40% (δ values higher than 0.2). The topotactical character of the redox process is maintained in the δ range 0 < δ < 0.4. This suggests that the cationic framework is only subjected to slight structural modifications during the oxygen exchange process occurring during the catalytic cycle.