Artículos (Química Inorgánica)

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

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Potentialization of bentonite properties as support in acid catalysts
(2020-03) Amaya, Jahaziel; Bobadilla Baladrón, Luis Francisco; Centeno, Miguel; Moreno, Sonia; Molina, Rafael; Azancot Luque, Lola de las Aguas; Universidad de Sevilla. Departamento de Química Inorgánica
Enhancement of the main physicochemical properties of a natural bentonite was carried out by means of modifications using surfactant, reflux, microwave treatment and, subsequently, the incorporation of AlZr and AlCe species. The evolution of the main changes in each modification stage was evaluated by means of X-ray diffraction, N2 sortometry, scanning microscopy (SEM), NH3-TPD, NH3-DRIFTS and CO adsorption at low temperature. For the evaluation of the catalytic behavior, the dehydration-dehydrogenation reactions of 2-propanol and hydro-conversion of decane were used; both of which generate, in addition, information regarding the acidic properties of the materials. The correlation of the number, type and acid strength with the catalytic behavior, allowed establishing the effect produced by both the delamination method and the nature of the incorporated cation. This generated tools that allow controlling the physicochemical properties, and more specifically, the enhancement of the acidity of new supports based on this type of natural clay mineral.
Clase invertida síncrona en asignaturas STEM
(Ministry Education and Science, 2021-03) Maya Díaz, Celia María; Iglesias Sigüenza, Francisco Javier; Giménez Font, Xavier; Universidad de Sevilla. Departamento de Química Inorgánica; Universidad de Sevilla. Departamento de Química orgánica
Se presenta una metodología de clase invertida, con modificaciones sincrónicas para adaptarse a la dificultad propia de las materias STEM. La clase Invertida Síncrona refuerza la tutoría inicial, para resolver las dudas de los alumnos que les impiden progresar a través del material que trabajan fuera del aula. A continuación, una dinámica de trabajo en grupo, aprendizaje basado en problemas, cuestionarios de integración, y evaluación formativa por pares, dan lugar a una destacable mejora de los resultados académicos, junto a una reducción del tiempo de trabajo y un incremento significativo en el grado de satisfacción del alumnado. Se discute su aplicación a tres asignaturas del Grado en Química de la Universidad de Sevilla, así como una asignatura del Grado de Química de la Universidad de Barcelona.
Atroposelective Transfer Hydrogenation of Biaryl Aminals via Dynamic Kinetic Resolution. Synthesis of Axially Chiral Diamines
(American Chemical Society, 2021-03-18) Carmona, José A.; Rodríguez Franco, Carlos; López Serrano, Joaquín; Ros Lao, Abel; Iglesias Sigüenza, Francisco Javier; Fernández Fernández, Rosario; Lassaletta, José M.; Hornillos, Valentín; Universidad de Sevilla. Departamento de Química Inorgánica; Universidad de Sevilla. Departamento de Química orgánica; Ministerio de Ciencia e Innovación (MICIN). España; Junta de Andalucía
An efficient dynamic kinetic resolution (DKR) approach for the synthesis of axially chiral diamines has been developed on the basis of a ruthenium-catalyzed enantioselective transfer hydrogenation. The strategy relies on the configurational instability of cyclic biaryl aminal precursors in equilibrium with their amino-imine open forms, as supported by DFT calculations. This protocol features a broad substrate scope of aliphatic amines and biaryl scaffolds and proceeds under very mild conditions, allowing the preparation of BINAM homologues in good to high yields and nearly perfect enantioselectivities (up to 99% ee).
A combined experimental and computational study to decipher complexity in the asymmetric hydrogenation of imines with Ru catalysts bearing atropisomerizable ligands
(Royal Society of Chemistry, 2021-01-21) León García, Félix; Comas-Vives, Aleix; Álvarez González, Eleuterio; Pizzano, Antonio; Universidad de Sevilla. Departamento de Química Inorgánica; Ministerio de Ciencia e Innovación (MICIN). España
RuCl2(P-OP)(N-N) complexes (1) containing an atropisomerizable phosphine-phosphite (P-OP) and a chiralC2symmetric diamine (N-N) are readily prepared astransisomers by successive addition of P-OP and N-N ligands to RuCl2(PPh3)3. For these complexes, fast atropisomerization of the biaryl fragment at room temperature has been observed. Compoundtrans-1acleanly isomerizes into a mixture ofcisisomers in EtOH upon heating. DFT calculations reproduce accurately the ratio of isomers observed as well as the greater thermodynamic stability of thecisisomers of1a. Complexes1are efficient catalyst precursors for the asymmetric hydrogenation ofN-aryl imines5in toluene under very mild conditions using KOtBu as a base (4 bar H2, room temperature,5/1/KOtBu = 500/1/10). Among the catalyst precursors,1fprovides good enantioselectivities in the hydrogenation of a wide range ofN-aryl imines (84-96% ee, 16 examples). From DFT calculations, a mechanism consisting in stepwise transfer of a hydride and a proton from the dihydride to the imine has been proposed, with the most favourable paths forRandSproducts involvingcis-dihydridesd1Randd3S, respectively. Among several hydrogen activation pathways examined in thepro-Rroute, the most favorable one consists of hydrogen coordination to a Ru-amido/amine adduct, followed by amine assisted activation of dihydrogen.
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.

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