Artículos (Química Inorgánica)

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

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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.
Study of nanostructured Ni/CeO2 catalysts prepared by combustion synthesis in dry reforming of methane
(Elsevier, 2010-08) González de la Cruz, Víctor M.; Ternero Fernández, Fátima; Pereñíguez Rodríguez, Rosa María; Caballero Martínez, Alfonso; Holgado, Juan Pedro; Universidad de Sevilla. Departamento de Química Inorgánica; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; Ministerio de Ciencia e Innovación (MICIN). España; Junta de Andalucía; Universidad de Sevilla. TEP971: Ingeniería de Materiales Avanzados
This work reports the study of several catalysts of Ni–CeO2 active for dry methane reforming process (CH4 + CO2 → 2CO + 2H2). The use of Ni as active phase is highly preferred, due to its availability, high activity and low cost, although its main lack is the coke formation on the surface of Ni metal particles, resulting in a severe deactivation. Here we report a new synthesis method that allows a simple, effective and fast way to prepare Ni–CeO2 catalysts, in a wide range of metallic loadings, resulting in all the cases in well-formed NiO crystallites with sizes in the range of 12–18 nm. The use of CeO2 as a support has been based on its massive use in TWC catalysts formulations, where it is recognized to activate CH4 and lower hydrocarbon dissociation. Moreover, CeO2 has been reported to have an intrinsic activity in the CH4 reforming reaction. Besides the metallic loading, several factors that control the preparation method of the catalyst have been varied, in order to optimize their performance. Most of the catalysts prepared show activity and selectivity values close to thermodynamic ones, maintaining a good stability on long periods of time and severe conditions. Nevertheless, formation of some carbon nano-fibers has been observed, which could result in a drawback for their application at large scale.
In Situ XAS Study of Synergic Effects on Ni–Co/ZrO2 Methane Reforming Catalysts
(American Chemical Society, 2011-12) González de la Cruz, Víctor Manuel; Ternero Fernández, Fátima; Holgado, Juan Pedro; Pereñíguez Rodríguez, Rosa María; 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
Four different mono and bimetallic Ni–Co/ZrO2 catalysts have been studied by means of in situ XAS, X-ray diffraction, TPR, and measurements of the catalytic activity in the dry reforming reaction of methane (DRM). Even though the cobalt monometallic system has no activity for the methane reforming reaction, both bimetallic catalysts (with 1:1 and 1:2 Ni/Co ratio, respectively), showed a better activity and stability than the nickel monometallic system. The XRD data indicate that a mixed cobalt–nickel spinel is formed by calcination of the precursor solids, leading to the formation of an alloy of both metals after reduction in hydrogen. In situ XAS experiments showed a much better resistance of metals in the bimetallic systems to be oxidized under reaction conditions at temperatures until 750 °C. After these results, we proposed the formation in the bimetallic systems of a more reducible nickel–cobalt alloy phase, which remains completely metallic in contact with the CO2/CH4 reaction mixture at any temperature. The presence of adjacent nickel and cobalt sites seems to avoid the deactivation of cobalt in the DRM reaction. In the case of cobalt sites, the presence of adjacent nickel atoms seems to prevent the deposition of carbon over the cobalt sites, now showing its higher activity in the dry reforming reaction. Simultaneously, this higher activity of the cobalt sites in the bimetallic system produces more hydrogen as a product, maintaining the nickel atoms completely reduced under reaction conditions. This synergic effect accounts for the better performance of the bimetallic systems and points at both, the oxidation state of nickel particles under reaction conditions and the carbon deposition processes, as important factors responsible for differences in catalytic activities and stabilities in this hydrocarbon reaction.
Understanding the thermochemical behavior of La0.6Sr0.4Co0.2Fe0.8O3 and Ce0.9Gd0.1O_Co oxygen transport membranes under real oxy-combustion process conditions
(Elsevier, 2019-11-05) Portillo Estévez, Esmeralda; Ramírez Reina, Tomás; Cano Palacios, Mercedes; Vega Borrero, Fernando; Navarrete Rubia, Benito; Universidad de Sevilla. Departamento de Química Inorgánica; Universidad de Sevilla. Departamento de Ingeniería Química y Ambiental; Engineering and Physical Sciences Research Council (UK); Royal Society (UK)
Oxygen transport membranes (OTM) are a promising alternative to conventional systems of air separation based on cryogenic distillation for oxy-fuel combustion power plants. In this work, a systematic study of the thermochemical stability of La0.6Sr0.4Co0.2Fe0.8O3 (perovskite-type) and cobalt doped Ce0.9Gd0.1O (fluorite-type) is proposed. The experiments were developed in a laboratory scale facility, which is able to mimic realistic oxy-fuel combustion flue gas containing SOx, NOx, H2O and CO2. In order to understand the thermochemical behavior of this type of materials, a full characterization analysis of the tested samples using a wide portfolio of analytical techniques such as X-ray diffraction (XRD), X-ray fluorescence (XRF), infrared spectroscopy (ATR-FTIR), Raman spectroscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) and Brunauer−Emmett−Teller analysis (BET) has been carefully discussed. Our data revealed the superior stability of the CGO samples in comparison with the LSCF at all the test conditions studied in this work. The formation of crystalline and amorphous sulphates and carbonates are evident for the LSCF while for the CGO samples do not react with SOX and barely form carbonates. The presence of silicon species – typically ignored in academic works – has been detected, pointing its relevance for real applications.
Understanding the influence of the alkaline cation K + or Na + in the regeneration efficiency of a biogas upgrading unit
(Wiley, 2019-03-01) Baena-Moreno, Francisco M.; Rodríguez Galán, Mónica; Vega Borrero, Fernando; Ramírez Reina, Tomás; Vilches Arenas, Luis Francisco; Navarrete Rubia, Benito; Universidad de Sevilla. Departamento de Química Inorgánica; Universidad de Sevilla. Departamento de Ingeniería Química y Ambiental; Engineering and Physical Sciences Research Council (UK); Royal Society (UK)
This paper reveals a regeneration method for a carbonate compound after carbon dioxide (CO 2 ) absorption in a biogas upgrading unit run with caustic mixtures, obtaining precipitated calcium carbonate (PCC) as valuable by-product. This process arises as an alternative to physical regeneration, which is highly energy intensive. This work provides novel insights on the regeneration efficiency of carbonates to hydroxides while also studying the influence of K + or Na + in the caustic CO 2 -trapping solution. The compared parameters were the reaction time, temperature, and molar ratio. Moreover, psychochemical characterization of solids was obtained by means of Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray powder diffraction (XRD), and scanning electron microscopy (SEM) images. The results indicate that regeneration efficiencies are slightly lower when potassium is used instead of sodium, but quite acceptable for both of them. The chemical characterization experiments showed the predominance of calcium carbonate. Overall, the results obtained in this study proved that this process is feasible to upgrade biogas through PCC precipitation, which appears to be a promising economically viable process to synergize carbon capture and storage (CCS) and carbon capture and utilization (CCU).
Understanding the effect of Ca and Mg ions from wastes in the solvent regeneration stage of a biogas upgrading unit
(Elsevier, 2019-11-15) Baena-Moreno, Francisco M.; Rodríguez Galán, Mónica; Ramírez Reina, Tomás; Zhang, Zhien; Vilches Arenas, Luis Francisco; Navarrete Rubia, Benito; Universidad de Sevilla. Departamento de Química Inorgánica; Universidad de Sevilla. Departamento de Ingeniería Química y Ambiental; Engineering and Physical Sciences Research Council (UK); Royal Society (UK)
This paper reveals the effect of calcium and magnesium ions in carbonation experiments carried out to regenerate sodium hydroxide from a biogas upgrading unit. This novel study arises as an alternative to standard physical process whose elevated energy consumption imposes economic restrictions. Previous works employed alkaline waste to turn them into value added product. Nevertheless, no attractive economical results were obtained due to the low regeneration efficiencies. Our hypothesis is that both calcium and magnesium waste composition percentages have an impact in the result, hence this work propose an isolated study aiming to determine the of each one in the global performance. To this end, the operational parameters (reaction time, reaction temperature and molar ratio) were tuned as well as physicochemical properties of the final solid samples were analyzed by several techniques. The results indicate that calcium is much more prone than magnesium to reach high efficiencies in aqueous carbonation experiments. Additionally, higher quality products were achieved with calcium. The results of this study suppose an important step for understanding the aqueous carbonation through waste in the path to achieve a more sustainable city and society.
Synergizing Carbon Capture Storage and Utilization in a Biogas Upgrading Lab-scale Plant Based on Calcium Chloride: Influence of Precipitation Parameters
(Elsevier, 2019) Baena-Moreno, Francisco M.; Rodríguez Galán, Mónica; Vega Borrero, Fernando; Ramírez Reina, Tomás; Vilches Arenas, Luis Francisco; Navarrete Rubia, Benito; Universidad de Sevilla. Departamento de Química Inorgánica; Universidad de Sevilla. Departamento de Ingeniería Química y Ambiental; Engineering and Physical Sciences Research Council (UK); Royal Society (UK)
Herein a strategy for biogas upgrading in a continuous flow absorption unit using CaCl 2 as capturing agent is reported. This process is presented as an alternative to the standard physical regeneration processes to capture carbon dioxide (CO 2 ) from biogas effluents with inherent high energy penalties. This work showcases a systematic study of the main parameters (reaction time, reaction temperature, and molar ratio reactant/precipitator) affecting calcium carbonate (CaCO 3 ) precipitation efficiency in a reaction between sodium carbonate (Na 2 CO 3 ) and CaCl 2 . In addition, the purity and main characteristics of the obtained product were carefully analysed via in a combined characterization study using Raman, XRD, and SEM. Our results indicate that acceptable precipitation efficiencies between 62 and 93% can be reached by fine tuning the studied parameters. The characterization techniques evidence pure CaCO 3 in a calcite structure. These results confirmed the technical feasibility of this alternative biogas upgrading process through CaCO 3 production.
Au and Pt Remain Unoxidized on a CeO2-Based Catalyst during the Water-Gas Shift Reaction
(American Chemical Society, 2022-01-12) Ramírez Reina, Tomás; González Castaño, Míriam; López Flores, Víctor; Martínez Tejada, Leidy Marcela; Zitolo, Andrea; Ivanova, Svetlana; Xu, Wenquian; Centeno Gallego, Miguel Ángel; Rodriguez, Jose A.; Odriozola Gordón, José Antonio; Universidad de Sevilla. Departamento de Química Inorgánica; Department of Energy. United States; Ministerio de Ciencia e Innovación (MICIN). España
The active forms of Au and Pt in CeO2-based catalysts for the water-gas shift (WGS) reaction are an issue that remains unclear, although it has been widely studied. On one hand, ionic species might be responsible for weakening the Ce-O bonds, thus increasing the oxygen mobility and WGS activity. On the other hand, the close contact of Au or Pt atoms with CeO2 oxygen vacancies at the metal-CeO2 interface might provide the active sites for an efficient reaction. In this work, using in situ X-ray absorption spectroscopy, we demonstrate that both Au and Pt remain unoxidized during the reaction. Remarkable differences involving the dynamics established by both species under WGS atmospheres were recognized. For the prereduced Pt catalyst, the increase of the conversion coincided with a restructuration of the Pt atoms into cuboctahedrical metallic particles without significant variations on the overall particle size. Contrary to the relatively static behavior of Pt0, Au0 nanoparticles exhibited a sequence of particle splitting and agglomeration while maintaining a zero oxidation state despite not being located in a metallic environment during the process. High WGS activity was obtained when Au atoms were surrounded by oxygen. The fact that Au preserves its unoxidized state indicates that the chemical interaction between Au and oxygen must be necessarily electrostatic and that such an electrostatic interaction is fundamental for a top performance in the WGS process
Ethylene dimerization and oligomerization using Bis(phosphino)boryl supported Ni complexes
(American Chemical Society, 2022-12-21) Kong, Fanji; Ríos Moreno, Pablo; Hauck, Conner; Fernández de Córdova, Francisco José; Dickie, Diane A.; Habgood, Laurel G.; Rodríguez, Amor; Gunnoe, T. Brent; Universidad de Sevilla. Departamento de Química Inorgánica; National Science Foundation (NSF). United States; University of Virginia; Ministerio de Economía y Competitividad (MINECO). España; Junta de Andalucía; Consejo Superior de Investigaciones Científicas (CSIC)
We report the dimerization and oligomerization of ethylene using bis(phosphino)boryl supported Ni(II) complexes as catalyst precursors. By using alkylaluminum(III) compounds or other Lewis acid additives, Ni(II) complexes of the type (RPBP)NiBr (R = tBu or Ph) show activity for the production of butenes and higher olefins. Optimized turnover frequencies of 640 molethylene·molNi–1·s–1 for the formation of butenes with 41(1)% selectivity for 1-butene using (PhPBP)NiBr, and 68 molethylene·molNi–1·s–1 for butenes production with 87.2(3)% selectivity for 1-butene using (tBuPBP)NiBr, have been demonstrated. With methylaluminoxane as a co-catalyst and (tBuPBP)NiBr as the precatalyst, ethylene oligomerization to form C4 through C20 products was achieved, while the use of (PhPBP)NiBr as the pre-catalyst retained selectivity for C4 products. Our studies suggest that the ethylene dimerization is not initiated by Ni hydride or alkyl intermediates. Rather, our studies point to a mechanism that involves a cooperative B/Ni activation of ethylene to form a key 6-membered borametallacycle intermediate. Thus, a cooperative activation of ethylene by the Ni–B unit of the (RPBP)Ni catalysts is proposed as a key element of the Ni catalysis.
Enhanced Dihydrogen Activation by Mononuclear Iridium(II) Compounds: A Mechanistic Study
(Wiley, 2022-08-26) Hidalgo, Nereida; Moreno Díaz, Juan José; García Rubio, Inés; Campos, Jesús; Universidad de Sevilla. Departamento de Química Inorgánica; Ministerio de Ciencia e Innovación (MICIN). España
The organometallic chemistry of 4d and 5d transition metals has been vastly dominated by closed-shell states. The reactivity of their metalloradical species is though remarkable, albeit yet poorly understood and with limited mechanistic investigations available. In this work we report the synthesis and characterization of two mononuclear IrII species, including the first dinitrogen adduct. These compounds activate dihydrogen at a dissimilar rate, in the latter case several orders of magnitude faster than its IrI precursor. A combined experimental/computational investigation to ascertain the mechanism of this transformation in IrII compounds is reported.
σ‑GeH and Germyl Cationic Pt(II) Complexes
(ACS, 2022) Laglera Gándara, Carlos J.; Ríos Moreno, Pablo; Fernández de Córdova, Francisco José; Barturen, Marina; Fernández, Israel; Conejero, 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 Pt(II) complexes [Pt(NHC′)(NHC)]- [BArF] (where NHC is a N-heterocyclic carbene ligand and NHC′ its metalated form) react with tertiary hydrogermanes HGeR3 at room temperature to generate the 14-electron platinum(II) germyl derivatives [Pt(GeR3)(NHC)2][BArF]. Low-temperature NMR studies allowed us to detect and characterize spectroscopically some of the σ-GeH intermediates [Pt(η2-HGeR3)(NHC′)(NHC)][BArF] that evolve into the platinum-germyl species. One of these compounds has been characterized by X-ray diffraction studies, and the interaction of the H−Ge bond with the platinum center has been analyzed in detail by computational methods, which suggest that the main contribution is the donation of the H−Ge to a σ*(Pt−C) orbital, but backdonation from the platinum to the σ*(Ge−H) orbital is significant. Primary and secondary hydrogermanes also produce the corresponding platinum-germyl complexes, a result that contrasts with the reactivity observed with primary silanes, in which carbon−silicon bond-forming reactions have been reported. According to density functional theory calculations, the formation of Pt−Ge/C−H bonds is both kinetically and thermodynamically preferred over the competitive reaction pathway leading to Pt−H/C−Ge bonds.
On the Adsorption Properties and Applications of Mixed-linker MOFs Based on HKUST-1
(Elsevier, 2022) Puerto Rodríguez, Macarena; López Cartes, Carlos; Ayala Espinar, Regla; Universidad de Sevilla. Departamento de Química Inorgánica; Ministerio de Economía y Competitividad (MINECO). España; Junta de Andalucía
Different mixed-linker MOFs based on HKUST-1 have been successfully synthesized using BtTC (1,2,4,5-benzenetetracarboxylate) and BDC (1,4-benzenedicarboxylate) as modulator ligands. These MOFs maintain the HKUST-1 structure up to 25% and 50% of trimesic acid replacing with BtTC and BDC ligands, respectively. A low percentage of modulator ligand provokes an increasing of the MOF surface area keeping its microporosity whereas a higher content of BtTC induces mesoposority in the samples. The adsorption of moisture ambient or vapour iodine reveals that there is a relation between the surface area and the capacity of adsorption of the samples. However, this relation is not found in the experiments of Congo Red removal from aqueous and ethanol solutions. The pH of the solutions has a significant effect on the adsorption capacity of the samples.
Mechanistic Investigations on Hydrogenation, Isomerization and Hydrosilylation Reactions Mediated by a Germyl-Rhodium System
(Wiley, 2022) Bajo Velázquez, Sonia; Theulier, Cyril A.; Campos, Jesús; Universidad de Sevilla. Departamento de Química Inorgánica; European Research Council (ERC); Junta de Andalucía; European Commission (EC)
We recently disclosed a dehydrogenative double C−H bond activation reaction in the unusual pincer-type rhodium-germyl complex [(ArMes)2ClGeRh] (ArMes=C6H3-2,6-(C6H2-2,4,6-Me3)2). Herein we investigate the catalytic applications of this Rh/Ge system in several transformations, namely trans-semihydrogenation of internal alkynes, trans-isomerization of olefins and hydrosilylation of alkynes. We have compared the activity and selectivity of this catalyst against other common rhodium precursors, as well as related sterically hindered rhodium complexes, being the one with the germyl fragment superior in terms of selectivity towards E-isomers. To increase this selectivity, a tandem catalytic protocol that incorporates the use of a heterogeneous catalyst for the trans-semihydrogenation of internal alkynes has been devised. Kinetic mechanistic investigations provide important information regarding the individual catalytic cycles that comprise the overall trans-semihydrogenation of internal alkynes.

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