Artículos (Química Inorgánica)

URI permanente para esta colecciónhttps://hdl.handle.net/11441/10919

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Structure-sensitivity of formic acid dehydrogenation reaction over additive-free Pd NPs supported on activated carbon
(Elsevier, 2021-09-15) Santos, José Luis; Megías Sayago, Cristina; Ivanova, Svetlana; Centeno Gallego, Miguel Ángel; Odriozola Gordón, José Antonio; Universidad de Sevilla. Departamento de Química Inorgánica; Ministerio de Economía y Competitividad (MINECO). España
In this study the size-activity dependence of palladium based catalysts in formic acid dehydrogenation reaction was investigated and evaluated. A wide range of particle sizes was considered and the catalyst series were prepared upon variation of some synthetic parameters, precursor and solvent nature in particular. Synthesis method variations affect significantly Pd particle size and results in diverse activity toward hydrogen production. An optimal size was observed and explained by the diverse proportion of low and high coordinated Pd states available for different samples within the series. The evaluation of particles much bigger than 6 nm changes importantly the fraction of high and low coordination atoms and allows the clear confirmation of the importance of the presence of low coordination atoms on the surface of catalyst.
Overcoming Pd-TiO2Deactivation during H2Production from Photoreforming Using Cu@Pd Nanoparticles Supported on TiO2
(American Chemical Society, 2021-03-01) Platero Moreno, Francisco Jesús; López Martín, Ángeles María; Caballero Martínez, Alfonso; Rojas, T. C.; Nolan, Michael; Colón, G.; Universidad de Sevilla. Departamento de Química Inorgánica; Ministerio de Ciencia e Innovación (MICIN). España; Science Foundation Ireland (SFI). Ireland
Different Cu@Pd-TiO2 systems have been prepared by a two-step synthesis to obtain a bimetallic co-catalyst for the H2 photoreforming reaction. We find that the tailored deposition of Pd covering the Cu nanoclusters by a galvanic replacement process results in the formation of a core@shell structure. The photocatalytic H2 production after 18 h is 350 mmol/g on the Cu@Pd1.0-TiO2 bimetallic system, which is higher than that on the monometallic ones with a H2 production of 250 mmol/g on Pd-supported TiO2. Surface characterization by high-angle annular dark-field scanning transmission electron microscopy, H2-temperature-programed reduction, CO-FTIR spectroscopy, and XPS gives clear evidence of the formation of a core@shell structure. With a Pd loading of 0.2-0.3 at. %, we propose a full coverage of the Cu nanoparticles with Pd. Long-time photoreforming runs show the enhanced performance of supported Cu@Pd with respect to bare palladium leading to a more stable catalyst and ultimately higher H2 production.
IR spectroscopic insights into the coking-resistance effect of potassium on nickel-based catalyst during dry reforming of methane
(Elsevier, 2021-05-15) Azancot Luque, Lola de las Aguas; Bobadilla Baladrón, Luis Francisco; Centeno Gallego, Miguel Ángel; Odriozola Gordón, José Antonio; Universidad de Sevilla. Departamento de Química Inorgánica; Ministerio de Economía y Competitividad (MINECO). España
Dry reforming of methane (DRM) is an effective catalytic route for transforming CO2 and CH4 into valuable syngas and thus potentially attractive for mitigating the emission of environmental harmful gases. Therefore, it is crucial to develop rationally Ni-based catalysts highly resistant to coking and sintering. In this scenario, the addition of small amounts of potassium to nickel catalyst increases their resistance to coking during dry reforming of methane. Nonetheless, the specific role of potassium in these catalysts not have been fully understood and there are still important discrepancies between the different reported studies. This work provides a new approach on the anticoking nature of a K-promoted Ni catalyst by means of a combined IR spectroscopic study of in situ characterization by CO adsorption under static conditions and operando DRIFTS measurements under dynamic conditions of DRM reaction. The involved surface species formed during the reaction were elucidated by transient and steady-state operando DRIFTS studies. It was revealed that the existence of Ni-K interfacial sites favours the gasification of carbonaceous deposits towards reverse Boudouard reaction and reduces the sticking probability of CO2 dissociative adsorption. Moreover, the presence of strongly Mg-O-K basic sites leads to the formation of carbonate intermediates that are subsequently reduced into CO gaseous towards the associative mechanism by RWGS reaction. These results provide a fundamental understanding of the relevant anticoking effect of potassium on Ni-based catalysts.
Guaiacol hydrodeoxygenation in hydrothermal conditions using N-doped reduced graphene oxide (RGO) supported Pt and Ni catalysts: Seeking for economically viable biomass upgrading alternatives
(Elsevier, 2021-02-05) Parrilla-Lahoz, Silvia; Jin, W.; Pastor Pérez, Laura; Carrales-Alvarado, Damarys H.; Odriozola Gordón, José Antonio; Dongil, A. B.; Ramírez Reina, Tomás; Universidad de Sevilla. Departamento de Química Inorgánica; Engineering and Physical Sciences Research Council (EPSRC); The Royal Society. UK.; Ministerio de Ciencia, Innovación y Universidades (MICINN). España
Herein we present an innovative route for model biomass compounds upgrading via “H2-free” hydrodeoxygenation (HDO) reactions. The underlaying idea is to implement a multifunctional catalyst able to activate water and subsequently use in-situ generated hydrogen for the HDO process. In this sense we have developed a series of effective Ni and Pt based catalysts supported on N-promoted graphene decorated with ceria. The catalyst reached commendable conversion levels and selectivity to mono-oxygenated compounds considering the very challenging reaction conditions. Pt outperforms Ni when the samples are tested as-prepared. However, Ni performance is remarkably boosted upon applying a pre-conditioning reductive treatment. Indeed, our NiCeO2/GOr-N present the best activity/selectivity balance and it is deemed as a promising catalyst to conduct the H2-free HDO reaction. Overall, this “proof-concept” showcases an economically appealing route for bio-compounds upgrading evidencing the key role of advanced catalysts for a low carbon future.
Functionalized biochars as supports for Pd/C catalysts for efficient hydrogen production from formic acid
(Elsevier, 2021-03) Santos, José Luis; Megías Sayago, Cristina; Ivanova, Svetlana; Centeno Gallego, Miguel Ángel; Odriozola Gordón, José Antonio; Universidad de Sevilla. Departamento de Química Inorgánica; Ministerio de Economía y Competitividad (MINECO). España
Biomass waste product was used to generate biochars as catalytic supports for selective hydrogen production from formic acid. The supports were obtained after pyrolysis in CO2 atmosphere of non-pretreated and chemically ZnCl2 activated raw materials (vine shoot and crystalline cellulose). The support series includes materials with different textural properties and surface chemistry. The support nature and especially textural properties firstly affects significantly Pd size and dispersion and its interaction with the support and secondly influence in a great extent the catalytic behavior of the final material. The presence of prevailing mesoporous character appeared to be the most important parameter influencing formic acid dehydrogenation and overall hydrogen production.
Effect of potassium loading on basic properties of Ni/MgAl2O4 catalyst for CO2 reforming of methane
(Elsevier, 2021-10) Azancot Luque, Lola de las Aguas; Bobadilla Baladrón, Luis Francisco; Centeno Gallego, Miguel Ángel; Odriozola Gordón, José Antonio; Universidad de Sevilla. Departamento de Química Inorgánica; Ministerio de Economía y Competitividad (MINECO). España; Junta de Andalucía
Coke deposition is one of the key issues in the dry reforming of methane on Ni catalysts. In the present work, we investigate the effect of potassium addition for suppressing carbon deposition in the Dry Reforming of Methane. The results obtained demonstrated that potassium contents above 3 wt% promote carbon gasification, favouring both Reverse Water Gas Shift and Boudouard reaction. Strong basic Mg-O-K sites are responsible for these reactions allowing the suppression of carbon deposits and allowing the stability of the catalyst.
Dehydration of glucose to 5-Hydroxymethlyfurfural on bifunctional carbon catalysts
(Elsevier, 2021-06-05) Bounoukta, Charf Eddine; Megías Sayago, Cristina; Ammari, Fatima; Ivanova, Svetlana; Monzón, Antonio; Centeno Gallego, Miguel Ángel; Odriozola Gordón, José Antonio; Universidad de Sevilla. Departamento de Química Inorgánica; Ministerio de Economía y Competitividad (MINECO). España
The proposed study tries to reply on one important question concerning glucose dehydration: What is the role of bare or tandem Lewis/Brønsted acid sites in the reaction and which are better? A series of mono and bifunctional catalyst are designed and screened for the glucose dehydration reaction. The results clearly reveal that catalyst activity is a function of catalyst composition. The presence of Lewis sites the reaction toward first step isomerization, while the Brønsted acid dehydrate directly glucose to HMF via levoglucosane intermediate. This study proposed also a kinetic modelling of the included reactions and their contrast with the empirical observations.
Tandem catalytic approaches for CO2 enriched Fischer-Tropsch synthesis
(Elsevier B.V., 2024-05-21) Blay Roger, José Rubén; Nawaz, Muhammad Asif; Baena-Moreno, Francisco M.; Bobadilla Baladrón, Luis Francisco; Ramírez Reina, Tomás; Ramírez Reina, Tomás; Universidad de Sevilla. Departamento de Química Inorgánica; Universidad de Sevilla. Departamento de Ingeniería Química y Ambiental
Fischer-Tropsch Synthesis (FTS) allows the conversion of syngas to high-density liquid fuels, playing a key role in the petrochemical and global energy sectors over the last century. However, the current Global Challenges impose the need to recycle CO2 and foster green fuels, opening new opportunities to adapt traditional processes like FTS to become a key player in future bioenergy scenarios. This review discusses the implementation of CO2-rich streams and in tandem catalysis to produce sustainable fuels via the next generation of FTS. Departing from a brief revision of the past, present, and future of FTS, we analyse a disruptive approach coupling FTS to upstream and downstream processes to illustrate the advantages of process intensification in the context of biofuel production via FTS. We showcase a smart tandem catalyst design strategy addressing the challenges to gather mechanistic insights in sequential transformations of reagents in complex reaction schemes, the precise control of structure-activity parameters, catalysts aging-deactivation, optimization of reaction parameters, as well as reaction engineering aspects such as catalytic bed arrangements and non-conventional reactor configurations to enhance the overall performance. Our review analysis includes technoeconomic elements on synthetic aviation fuels as a case of study for FTS applications in the biofuel context discussing the challenges in market penetration and potential profitability of synthetic biofuels. This comprehensive overview provides a fresh angle of FTS and its enormous potential when combined with CO2 upgrading and tandem catalysis to become a front-runner technology in the transition towards a low-carbon future.
Sterically Crowded Gold Germylene Compounds with Methyl and Hydride Substituents
(John Wiley & Sons, 2024-05-02) López Serrano, Joaquín; Bajo Velázquez, Sonia; Campos, Jesús; Universidad de Sevilla. Departamento de Química Inorgánica; European Research Council (ERC); Ministerio de Ciencia, Innovación y Universidades (MICINN). España
This work explores the combination of sterically crowded low-valent germanium compounds bearing one or two terphenyl (C6H3-2,6-Ar2) substituents with gold fragments, the latter stabilized by crowded phosphines also containing a terphenyl moiety. The steric protection of these motifs has allowed to examine a series of unusual gold-germylene compounds featuring small hydride and methyl substituents at the germanium site. A gold-germylene dicationic structure is also reported. The bonding in this series is investigated by computational means, providing understanding for the two-way transfer of electrons from germanium to gold and vice versa.
Monitoring the influence of steam on highly-active rhodium catalyst during the combined reforming of biogas by transient and steady-state operando spectroscopic studies
(Royal Society of Chemistry, 2024-05-21) Garcilaso, Victoria; Blay Roger, José Rubén; González Castaño, Míriam; Bobadilla Baladrón, Luis Francisco; Centeno, Miguel A.; Odriozola Gordón, José Antonio; Universidad de Sevilla. Departamento de Química Inorgánica; Junta de Andalucía; Ministerio de Ciencia, Innovación y Universidades (MICINN). España
The impact derived from incorporating water into CH4/CO2 biogas stream for the generation of syngas was investigated over the Rh/MgAl2O4 catalyst using operando steady-state and transient DRIFT spectroscopy coupled with MS. The incorporation of steam resulted in improved CH4 conversion rates and attained syngas streams with higher H2/CO ratios. It was demonstrated that in the presence of steam, the generation of CHxO species through the reaction of CO* with active *OH species is favored at the metal support surface. Besides, the enhanced resistance delivered by water molecules towards deactivating the coking phenomena was associated with easier carbonaceous decomposition and the exposition of the very active Rh (100) surfaces for methane decomposition. The Rh/MgAl2O4 catalyst was demonstrated to be an effective catalyst for the production of H2-rich syngas streams. More importantly, the insights reported herein provide new evidences regarding the impact of steam on biogas reforming reactions.
Effects of ZrO2 crystalline phase on oxygen vacancy of GaZr oxides and their properties for CO2 hydrogenation to light olefins
(Elsevier B.V., 2024-03-24) Meng, Fanhui; Gong, Zhiyuan; Wang, Qian; Xing, Mingqin; Nawaz, Muhammad Asif; Qiao, Zhipeng; Universidad de Sevilla. Departamento de Química Inorgánica; Chinese Ministry of Science and Technology; National Natural Science Foundation of China (NSFC)
A bifunctional catalyst, comprising GaZr oxide and SAPO-34 zeolite, manifests enhanced catalytic activity in CO2 hydrogenation to light olefins; nonetheless, the comprehensive analysis of the pivotal role played by the underlying structure of ZrO2 in Ga-Zr oxide has not been investigated. Herein, different crystalline structures of ZrO2 were prepared by the co-precipitation method and adopted as a support to deposit Ga to obtain ZrO2 with different ratios of monoclinic ZrO2 (m-ZrO2) to tetragonal ZrO2 (t-ZrO2) in GaZr oxides for CO2 hydrogenation to light olefins. Various characterizations demonstrated that the interface between Ga and the mixed phase of (m-t) ZrO2 produces more oxygen vacancies which favors the adsorption and activation of CO2, and the larger specific surface area and stronger H2 adsorption and dissociation capacity promote CO2 conversion. Interestingly, the GaZr oxide with high m-ZrO2 content exhibits superior catalytic activity than the GaZr oxide with high content of t-ZrO2. The highest light olefins yield (9.0%) and selectivity (77.9%) (CO free) with 27.9% CO2 conversion was achieved. In-situ DRIFT spectra further elaborated that the GaZr oxides with different ZrO2 crystalline phases follow the same reaction pathway to hydrogenate CO2 first to HCOO* and then to CH3O* on GaZr oxide surface. While compared with sole ZrO2, the introduction of Ga significantly promotes the hydrogenation of HCOO* to CH3O*, acting as a crucial reaction intermediate that subsequently diffuses into SAPO-34 pores to enhance the desired light olefins selectivity.
Antimicrobial Activity of Anionic Bis(N-Heterocyclic Carbene) Silver Complexes
(Multidisciplinary Digital Publishing Institute, 2024-09-27) Carrasco Carrasco, Carlos Jesús; Montilla Ramos, Francisco Javier; Villalobo Polo, Eduardo; Angulo, Manuel; Álvarez, Eleuterio; Galindo del Pozo, Agustín; Universidad de Sevilla. Departamento de Microbiología; Ministerio de Ciencia e Innovación (MICIN). España; Universidad de Sevilla
The antimicrobial properties of a series of anionic bis(carbene) silver complexes Na3[Ag(NHCR)2] were investigated (2a–2g and 2c′, where NHCR is a 2,2′-(imidazol-2-ylidene)dicarboxylate-type N-heterocyclic carbene). The complexes were synthesized by the interaction of imidazolium dicarboxylate compounds with silver oxide in the presence of aqueous sodium hydroxide. Complexes 2f,g were characterized analytically and spectroscopically, and the ligand precursor 1f and complexes 2c and 2g were structurally identified by X-ray diffraction methods. The anions of 2c and 2g, [Ag(NHCR)2]3−, showed a typical linear disposition of Ccarbene-Ag-Ccarbene atoms and an uncommonly eclipsed conformation of carbene ligands. The antimicrobial properties of complexes 2a–g, which contains chiral (2b–2e and 2c′) and non-chiral derivatives (2a,f,g), were evaluated against Gram-negative bacteria, Escherichia coli and Pseudomonas aeruginosa, and a Gram-positive bacterium, Staphylococcus aureus. From the observed values of the minimal inhibitory concentration and minimal bactericidal concentration, complexes 2a and 2b showed the best antimicrobial activity against all strains. An interesting chirality–antimicrobial relationship was found, and eutomer 2c′ showed better activity than its enantiomer 2c against the three bacteria. Furthermore, these complexes were investigated experimentally and theoretically by 109Ag nuclear magnetic resonance, and the electronic and steric characteristics of the dianionic carbene ligands were also examined.
Microkinetic Model as a Crucial Tool for Understanding Homogeneous Catalysis
(John Wiley & Sons, 2024-09-09) Jiménez Rama, Raquel; Nova, Ainara; Nicasio Jaramillo, María del Carmen; Universidad de Sevilla. Departamento de Química Inorgánica; Ministerio de Ciencia e Innovación (MICIN). España; European Union (UE); Research Council. Norway
Microkinetic modeling is a computational tool that allows simulating the evolution of the concentration of catalytically relevant species with time, providing a description of the catalytic system closer to the experimental. Microkinetic models have been mainly applied in organometallic catalysis as a means for validating mechanistic proposals by comparing experimental and computed rates and concentrations at a given time. However, this tool becomes very useful when studying complicated reaction mechanisms, aiding in identifying the catalyst resting state, optimizing reaction conditions, or improving the catalyst design. In this Concept, we focus on these applications of microkinetic modeling through the discussion of some selected examples. In addition, we also point out some of the challenges and limitations we may face when building microkinetic models, which may explain why they are still underused.
In situ XRD and operando XRD-XANES study of the regeneration of LaCo0.8Cu0.2O3 perovskite for preferential oxidation of CO
(Elsevier, 2024-09) Pereñíguez Rodríguez, Rosa María; Ferri, Davide; Universidad de Sevilla. Departamento de Química Inorgánica; Ministerio de Ciencia e Innovación (MICIN). España; Swiss National Science Foundation (SNFS)
Combinations of perovskite-type oxides with transition and precious metals exhibit remarkable regenerating properties that can be exploited for catalytic applications. The objective of the present work was to study the structural changes experienced by LaCo0.8Cu0.2O3 under reducing/oxidizing atmosphere (redox) and Preferential Oxidation of CO (PrOx, with high H2 concentration) conditions and their reversibility. LaCo0.8Cu0.2O3 was prepared by ultrasonic spray combustion and was characterized by X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). Structural changes were followed by operando XRD and XAS. Metallic Co and Cu were segregated under both sets of reducing conditions and re-dissolved into the perovskite upon oxidation at 500 °C. Simultaneously, the perovskite-type oxide disappeared under reducing conditions and formed again upon high-temperature oxidation. The effects of this reversible reduction/dissolution of B-site metals on catalyst structure and activity were studied concerning the catalytic process of PrOx. The active phases of cobalt and copper oxides suffer a reduction during the PrOx reaction due to the high H2 concentration; thus, the application of an intermediate oxidation treatment can regenerate the catalytic system and the perovskite can be used for several cycles of reaction and regeneration. In contrast, when this intermediate oxidation treatment is not applied, the catalytic performance decreases in successive activity cycles.
Expanding the scope of multiphase-flash sintering: Multi-dogbone configurations and reactive processes
(Elsevier, 2024-07-15) Manchón Gordón, Alejandro F.; Molina Molina, Sandra; Perejón Pazo, Antonio; Alcalde Conejo, A.; Sánchez Jiménez, Pedro Enrique; Pérez Maqueda, Luis Allan; Universidad de Sevilla. Departamento de Química Inorgánica; Junta de Andalucía; Ministerio de Ciencia e Innovación (MICIN). España
In this work, we have expanded the possibilities of the multiphase-flash sintering (MPFS) technique by investigating several configurations that involve multiple dogbone specimens (ranging from 1 to 3) and multiple phases (also ranging from 1 to 3). Unlike the traditional MPFS approach using complex 3D or cylindrical samples, this new method allows for a direct comparison with the established conventional flash sintering technique. Our experimental results with dense 8-mol% Yttria-stabilized zirconia demonstrate a significant reduction in the onset temperature as the number of phases and dogbones increases. Building on these findings, we achieved the preparation of pure bulk specimens of SrFe12O19 for the first time through reactive multiphase-flash sintering.
Electrophilic Hydrosilylation of Electron-Rich Alkenes Derived from Enamines
(John Wiley & Sons, 2024-04-18) Laglera Gándara, Carlos J.; Fernández de Córdova, Francisco José; Jiménez Pérez, Julián; Ríos Moreno, Pablo; Conejero Iglesias, Salvador; Universidad de Sevilla. Departamento de Química Inorgánica; Ministerio de Ciencia e Innovación (MICIN). España; Junta de Andalucía; Universidad de Oviedo
The low-electron count, air-stable, platinum complexes [Pt(ItBu’)(ItBu)][BArF] (C1) (ItBu=1,3-di-tert-butylimidazol-2-ylidene), [Pt(SiPh)3(ItBuiPr)2][BArF] (C2) (ItBuiPr=1-tert-butyl-3-iso-propylimidazol-2-ylidene), [Pt(SiPh)3(ItBuMe)2][BArF] (C3), [Pt(GePh3)(ItBuiPr)2][BArF] (C4), [Pt(GePh)3(ItBuMe)2][BArF] (C5) and [Pt(GeEt)3(ItBuMe)2][BArF] (C6) (ItBuMe=1-tert-butyl-3-methylimidazol-2-ylidene) are efficient catalysts (particularly the germyl derivatives) in both the silylative dehydrocoupling and hydrosilylation of electron rich alkenes derived from enamines. The steric hindrance exerted by the NHC ligand plays an important role in the selectivity of the reaction. Thus, bulky ligands are selective towards the silylative dehydrocoupling process whereas less sterically hindered promote the selective hydrosilylation reaction. The latter is, in addition, regioselective towards the β-carbon atom of both internal and terminal enamines, leading to β-aminosilanes. Moreover, the syn stereochemistry of the amino and silyl groups implies an anti Si−H bond addition across the double bond. All these facts point to a mechanistic picture that, according to experimental and computational studies, involves a non-classical hydrosilylation process through an outer-sphere mechanism in which a formal nucleophilic addition of the enamine to the silicon atom of a platinum σ-SiH complex is the key step. This is in sharp contrast with the classical Chalk–Harrod mechanism prevalent in platinum chemistry.
Diborane Reductions of CO2 and CS2 Mediated by Dicopper μ-Boryl Complexes of a Robust Bis(phosphino)-1,8-naphthyridine Ligand
(American Chemical Society, 2024-05-03) See, Matthew S.; Ríos Moreno, Pablo; Tilley, T. Don; Universidad de Sevilla. Departamento de Química Inorgánica; Department of Energy. United States
A dinucleating 1,8-naphthyridine ligand featuring fluorene-9,9-diyl-linked phosphino side arms (PNNPFlu) was synthesized and used to obtain the cationic dicopper complexes 2, [(PNNPFlu)Cu2(μ-Ph)][NTf2]; [NTf2] = bis(trifluoromethane)sulfonimide, 6, [(PNNPFlu)Cu2(μ-CCPh)][NTf2], and 3, [(PNNPFlu)Cu2(μ-OtBu)][NTf2]. Complex 3 reacted with diboranes to afford dicopper μ-boryl species (4, with μ-Bcat; cat = catecholate and 5, with μ-Bpin; pin = pinacolate) that are more reactive in C(sp)-H bond activations and toward activations of CO2 and CS2, compared to dicopper μ-boryl complexes supported by a 1,8-naphthyridine-based ligand with di(pyridyl) side arms. The solid-state structures and DFT analysis indicate that the higher reactivities of 4 and 5 relate to changes in the coordination sphere of copper, rather than to perturbations on the Cu-B bonding interactions. Addition of xylyl isocyanide (CNXyl) to 4 gave 7, [(PNNPFlu)Cu2(μ-Bcat)(CNXyl)][NTf2], demonstrating that the lower coordination number at copper is chemically significant. Reactions of 4 and 5 with CO2 yielded the corresponding dicopper borate complexes (8, [(PNNPFlu)Cu2(μ-OBcat)][NTf2]; 9, [(PNNPFlu)Cu2(μ-OBpin)][NTf2]), with 4 demonstrating catalytic reduction in the presence of excess diborane. Related reactions of 4 and 5 with CS2 provided insertion products 10, {[(PNNPFlu)Cu2]2[μ-S2C(Bcat)2]}[NTf2]2, and 11, [(PNNPFlu)Cu2(μ,κ2-S2CBpin)][NTf2], respectively. These products feature Cu-S-C-B linkages analogous to those of proposed CO2 insertion intermediate.
A supervised multiclass framework for mineral classification of Iberian beads
(Public Library of Science, 2024-07-10) Sánchez Gómez, Daniel; Odriozola Lloret, Carlos Patricio; Sousa, Ana Catarina; Garrido Cordero, José Ángel; Romero García, Galo; Martínez Blanes, José María; Edo I. Benaiges, Manel; Villalobos García, Rodrigo; Gonçalves, Victor S.; Universidad de Sevilla. Departamento de Prehistoria y Arqueología; Universidad de Sevilla. Departamento de Química Inorgánica; Fundação para a Ciência e a Tecnologia. Portugal; Ministerio de Ciencia y Tecnología (MCYT). España
Research on personal adornments depends on the reliable characterisation of materials to trace provenance and model complex social networks. However, many analytical techniques require the transfer of materials from the museum to the laboratory, involving high insurance costs and limiting the number of items that can be analysed, making the process of empirical data collection a complicated, expensive and time-consuming routine. In this study, we compiled the largest geochemical dataset of Iberian personal adornments (n = 1243 samples) by coupling X-ray fluorescence compositional data with their respective X-ray diffraction mineral labels. This allowed us to develop a machine learning-based framework for the prediction of bead-forming minerals by training and benchmarking 13 of the most widely used supervised algorithms. As a proof of concept, we developed a multiclass model and evaluated its performance on two assemblages from different Portuguese sites with current mineralogical characterisation: Cova das Lapas (n = 15 samples) and Gruta da Marmota (n = 10 samples). Our results showed that decisión-tres based classifiers outperformed other classification logics given the discriminative importance of some chemical elements in determining the mineral phase, which fits particularly well with the decision-making process of this type of model. The comparison of results between the different validation sets and the proof-of-concept has highlighted the risk of using synthetic data to handle imbalance and the main limitation of the framework: its restrictive class system. We conclude that the presented approach can successfully assist in the mineral classification workflow when specific analyses are not available, saving time and allowing a transparent and straightforward assessment of model predictions. Furthermore, we propose a workflow for the interpretation of predictions using the model outputs as compound responses enabling an uncertainty reduction approach currently used by our team. The Python-based framework is packaged in a public repository and includes all the necessary resources for its reusability without the need for any installation.
Structural, Mössbauer and Magnetic Study of (Mn0.2Co0.2Ni0.2Cu0.2X0.2)Fe2O4 (X=Fe, Mg) Spinel High-entropy Oxides Fabricated via Reactive Flash Sintering
(Elsevier, 2024) Manchón Gordón, Alejandro F.; Almanza Vergara, G. E.; Molina Molina, Sandra; Perejón Pazo, Antonio; Blázquez Gámez, Javier Sebastián; Sánchez Jiménez, Pedro Enrique; Pérez Maqueda, L. A.; Universidad de Sevilla. Departamento de Física de la Materia Condensada; Universidad de Sevilla. Departamento de Química Inorgánica; Junta de Andalucía; Consejo Superior de Investigaciones Científicas (CSIC)
Herein, it is reported the concomitant synthesis and sintering in a single step of (Mn0.2Co0.2Ni0.2Cu0.2X0.2)Fe2O4 (X=Fe, Mg), a spinel-structured high-entropy oxides, by the reactive flash sintering technique. A single phase, identified with a spinel crystal structure ̅, was obtained in just 30 min at a furnace temperature of 1173 K. The structural and magnetic properties of the prepared compounds were assessed by the combined use of various techniques, aiming to understand the correlations between functional properties and crystal structure. Characteristic features of the Mössbauer spectra prove the existence of different nonequivalent Fe environments . Both compositions display soft magnetic behavior, characterized by low coercive fields and saturation magnetization reached at low fields. Thus, the substitution of nonmagnetic Mg2+ for magnetic Fe2+ results in a decrease in magnetic parameters due to the weakening of the super-exchange interaction among the magnetic moments.
Modifying the size of Nickel metallic particles by H2/CO treatment in Ni/ZrO2 methane dry reforming catalysts
(American Chemical Society, 2011-01) González de la Cruz, Víctor Manuel; Pereñíguez Rodríguez, Rosa María; Ternero Fernández, Fátima; Holgado, Juan Pedro; Caballero Martínez, Alfonso; Universidad de Sevilla. Departamento de Química Inorgánica; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; Ministerio de Educación y Ciencia (MEC). España; Junta de Andalucía; Universidad de Sevilla. TEP971: Ingeniería de Materiales Avanzados
The effect of a reduction process with CO or H2 on the size of nickel particles in Ni/ZrO2 dry methane reforming catalysts have been studied by means of in situ X-ray Absorption Spectroscopy (XAS) and Diffuse Reflectance FTIR Spectroscopy (DRIFTS). Our results clearly indicate that a high temperature treatment with CO increases the dispersion of the nickel metallic phase. XAS results have shown a lower coordination number of Ni in the sample treated with CO than that reduced with H2. From the DRIFTS results, it can be established that, under the CO treatment, the formation of Ni(CO)4 complexes corrodes the nickel particles, decreasing their size. The formation of these gas molecules occurs without measurable losses of nickel from the catalyst which maintains the same nickel content after the hydrogen or the CO treatment at high temperature. Therefore, this airborne nickel compound, by colliding with the zirconia surface, must deposit the nickel metal atoms around onto the support. This behavior is evidence of an important interaction between nickel and zirconia surface as unlike other supports there is no losses of nickel during the dispersion process on zirconia. Although different effects of CO on nickel catalysts have been previously described, we have found for the first time several experimental evidences demonstrating the whole redispersion phenomenon.

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