Caracterización de óxidos mixtos de Ce, Pr y Zr con propiedades redox de interés en catálisis. Estudio del origen de las modificaciones redox producidas por envejecimiento químico-térmico

El empleo en catálisis de óxidos mixtos relacionados con el óxido de cerio esta justificado por una serie de interesantes propiedades, tanto químicas como estructurales. Entre las aplicaciones catalíticas de estos óxidos destacan su uso como componente de los catalizadores de 3 vías usados en automoción. Otras aplicaciones destacadas son su uso en las reacciones de oxidación, por ejemplo, los procesos de oxidación húmeda de contaminantes orgánicos en aguas residuales, o los procesos de combustión catalítica. Además hay otras aplicaciones que en los últimos años han cobrado gran interés, como son los procesos relacionados con la síntesis de hidrógeno con elevados requerimientos de pureza, a partir de hidrocarburos ligeros. En todas las aplicaciones catalíticas de los óxidos mixtos relacionados con el óxido de cerio, las propiedades redox de los mismos juegan un papel clave. Uno de los objetivos de este trabajo ha sido realizar un estudio comparativo de las propiedades redox de los óxidos de Ce/Pr, Ce/Zr y Ce/Pr/Zr. Sobre estos óxidos se han realizado estudios de reducción en distintas atmósferas. Además, se ha medido la OSC, prestando especial atención a los temas relacionados con la rapidez con la que el oxígeno es intercambiable, aspecto muy importante para algunas aplicaciones de estos materiales. También se han tenido en cuenta algunos aspectos relacionados con la estabilidad de la OSC de estas muestras frente a fenómenos de envejecimiento causados por tratamientos térmicos en distintas atmósferas. Los óxidos de Ce/Zr, además de presentar mejores propiedades texturales y redox que el CeO2, presentan unas características redox peculiares, relacionadas con el cambio de reducibilidad que estos materiales sufren dependiendo de su historia químico-térmica, pudiéndose modular el comportamiento redox de estos óxidos dependiendo de los ciclos de reducción y oxidación aplicados. El segundo objetivo de esta Tesis ha sido encontrar una correlación clara entre las modificaciones estructurales que los tratamientos químico/térmicos producen sobre estas muestras y los cambios en las propiedades redox. Este peculiar comportamiento ha sido estudiado por un gran número de grupos de investigación aunque hasta ahora no había habido una explicación satisfactoria. Para estudiar este fenómeno se han preparado dos óxidos de Ce/Zr de muy distinta reducibilidad sobre los cuales se han aplicado una amplia gama de técnicas tanto químicas como estructurales. En esta Tesis se ha creado un modelo para interpretar el comportamiento de estos materiales. Esta Tesis supone un avance importante en la interpretación del comportamiento de los óxidos mixtos de cerio-circonio y contribuye notablemente a una mejor comprensión de la información contenida en la extensa bibliografía existente sobre las propiedades redox de este interesante tipo de materiales

Nanoplastics: From tissue accumulation to cell translocation into Mytilus galloprovincialis hemocytes. resilience of immune cells exposed to nanoplastics and nanoplastics plus Vibrio splendidus combination

Plastic litter is an issue of global concern. In this work Mytilus galloprovincialis was used to study the distribution and effects of polystyrene nanoplastics (PS NPs) of different sizes (50 nm, 100 nm and 1 mu m) on immune cells. Internalization and translocation of NPs to hemolymph were carried out by in vivo experiments, while endocytic routes and effects of PS NPs on hemocytes were studied in vitro. The smallest PS NPs tested were detected in the digestive gland and muscle. A fast and size-dependent translocation of PS NPs to the hemolymph was recorded after 3 h of exposure. The internalization rate of 50 nm PS NPs was lower when caveolae and clathrin endocytosis pathways were inhibited. On the other hand, the internalization of larger particles decreased when phagocytosis was inhibited. The hemocytes exposed to NPs had changes in motility, apoptosis, ROS and phagocytic capacity. However, they showed resilience when were infected with bacteria after PS NP exposure being able to recover their phagocytic capacity although the expression of the antimicrobial peptide Myticin C was reduced. Our findings show for the first time the translocation of PS NPs into hemocytes and how their effects trigger the loss of its functional parameters

Performance of a Direct Methane Solid Oxide Fuel Cell Using Nickel-Ceria-Yttria Stabilized Zirconia as the Anode

A nickel-ceria-yttria stabilized zirconia (Ni-CYSZ) cermet material was synthesized and tested as the anode for the direct oxidation of methane in a solid oxide fuel cell (SOFC) with YSZ as the electrolyte and strontium-doped lanthanum manganite (LSM) as the cathode. Initially, the electrochemical behavior was investigated under several load demands in wet (3% H2O) CH4 at 850 degrees C during 144 h using I-V curves, impedance spectra, and potentiostatic measurements. Long-term tests were subsequently conducted under 180 mAcm(-2) in wet CH4 for 236 h and dry CH4 for 526 h at 850 degrees C in order to assess the cell stability. Material analysis was carried out by SEM-EDS after operation was complete. Similar cell performance was observed with wet (3% H2O) and dry CH4, and this indicates that the presence of water is not relevant under the applied load demand. Impedance spectra of the cell showed that at least three processes govern the direct electrochemical oxidation of methane on the Ni-CYSZ anode and these are related to charge transfer at high frequency, the adsorption/desorption of charged species at medium frequency and the non-charge transfer processes at low frequency. The cell was operated for more than 900 h in CH4 and 806 h under load demand, with a low degradation rate of similar to 0.2 mVh(-1) observed during this period. The low degradation in performance was mainly caused by the increase in charge transfer resistance, which can be attributed to carbon deposition on the anode causing a reduction in the number of active centers. Carbon deposits were detected mostly on the surface of Ni particles but not near the anode/electrolyte interface or the cerium surface. Therefore, the incorporation of cerium in the anode structure could improve the cell lifetime by reducing carbon formatio

Products released from surgical face masks can provoke cytotoxicity in the marine diatom Phaeodactylum tricornutum

Surgical face masks are more present than ever as personal protective equipment due to the COVID-19 pandemic. In this work, we show that the contents of regular surgical masks: i) polypropylene microfibres and ii) some added metals such as: Al, Fe, Cu, Mn, Zn and Ba, may be toxic to some marine life. This work has got two objectives: i) to study the release rate of the products from face masks in marine water and ii) to assess the toxicity in Phaeodactylum tricornutum of these by-products. To achieve these two objectives, we performed release kinetic experiments by adding masks in different stages of fragmentation to marine water (i.e. whole face masks and fragments of them 1.52 ± 0.86 mm). Released microfibres were found after one month in shaking marine water; 0.33 ± 0.24 and 21.13 ± 13.19 fibres·mL−1 were collected from the whole and fragmented face masks, respectively. Significant amounts of dissolved metals such as Mn, Zn and Ni, as well as functional groups only in the water containing the face mask fragments were detected. Water from both treatments was employed to study its toxicity on the marine diatom. Only the water from the face mask fragments showed a significant, dose-dependent, decrease in cell density in P. tricornutum; 53.09 % lower than in the controls. Although the water from the face mask fragments showed greater effects on the microalgae population than the water from the whole face mask, the latter treatment did show significant changes in the photosynthetic apparatus and intrinsic properties of the cells. These results indicate that during fragmentation and degradation face masks a significant chemical print can be observed in the marine environment.Marta Sendra wishes to acknowledge her contract Juan de la Cierva Incorporación (IJC2020-043162-I) funded by MCIN/AEI/10.13039/ 501100011033 and European Union NextGenerationEU/PRTR. Dr. Araceli Rodríguez-Romero is supported by the Spanish grant Juan de la Cierva Incorporación referenced as IJC2018–037545-I

CO Methanation over NiO-CeO2 Mixed-Oxide Catalysts Prepared by a Modified Co-Precipitation Method: Effect of the Preparation pH on the Catalytic Performance

In this study, a series of NiO-CeO2 mixed-oxide catalysts have been prepared by a modified co-precipitation method similar to the one used for the synthesis of hydrotalcites. The syntheses were carried out at different pH values (8, 9 and 10), in order to determine the influence of this synthetic variable on the properties of the obtained materials. These materials were characterized by using different techniques, such as TGA, XRD, ICP, N-2 adsorption-desorption isotherms, H-2 temperature-programmed reduction (H-2-TPR), and electron microscopy, including high-angle annular dark-field transmission electron microscopy (HAADF-TEM) and EDS. The characterization results revealed the influence of the preparation method, in general, and of the pH value, in particular, on the textural properties of the oxides, as well as on the dispersion of the Ni species. The catalyst prepared at a higher pH value (pH = 10) was the one that exhibited better behavior in the CO methanation reaction (almost 100% CO conversion at 235 degrees C), which is attributed to the achievement, under these synthetic conditions, of a combination of properties (metal dispersion, specific surface area, porosity) more suitable for the reaction

Evaluación y Análisis de la Calidad en Prácticas de Laboratorio de Química Inorgánica

Formato artículo para difundir los resultados del proyecto de innovación UCA - AAA_14_059, titulado "EVALUACIÓN Y MEJORA DE LAS PRÁCTICAS DE TALLER Y LABORATORIO DE LAS ÁREAS DE CONOCIMIENTO DE CIENCIA DE LOS MATERIALES E INGENIERÍA METALÚRGICA Y DE QUÍMICA INORGÁNICA".Después de haberse implantado el Grado en Química en la Facultad de Ciencias de la Universidad de Cádiz, el Departamento de Ciencia de los Materiales e Ingeniería Metalúrgica y Química Inorgánica ha llevado a cabo la evaluación de las prácticas de taller y laboratorio de las asignaturas que imparte. Para ello se han desarrollado una serie de cuestionarios dirigidos tanto a los alumnos como a los profesores encargados de impartir las asignaturas. A partir de los resultados ha sido posible realizar un análisis en profundidad de cada asignatura con el fin de contrastar la opinión de alumnos y profesores y evaluar si son necesarias determinadas modificaciones o incluir algunas mejoras que faciliten a los alumnos el normal desarrollo de las prácticas

Reactivity of Vanadium Nanoparticles with Oxygen and Tungsten

A mechanistic study was carried out on the optimal methods of fabrication of products containing higher loads of thermochromic VO2(M1) fabricated by thermal treatments of V nanoparticles in air, that, once achieved, are more stable than other commercial products upon natural aging or reiterated reheating. At the best temperatures for single runs, 55% of VO2 can be attained by the reactions of a limited number of the species initially formed in a process, that, if not stopped, can degrade the product by solid state reactions of oxidations and reductions without O-2 consumption. This fact supports the use of two-step treatments at lower temperatures and faster cooling rates that reach 65% of VO2; such reactions should, ideally, take place in the 550-625 degrees C temperature range. The impregnation of V with a tungstate salt is an ideal and simple doping platform that can decrease the energy of activation of the 2-cycle process, allowing higher yields and enthalpies of transformation (71% of VO2, 26 J/g) than undoped counterparts or trademarks. A good balance is reached for 1% at. of W, with a reduction in T-c of 20 degrees C not significantly resenting the enthalpy of the reversible metal-to-insulator transition. For higher W amounts, the appearance of tetragonal VO2, and W alloyed V3O7 and V2O5, decrease the fractions of increasingly and effectively doped M1-VO2 achieved till 2% of W, a concentration for which T-c attains the stimulating values of 35 degrees C on heating and 25 degrees C on cooling

Unraveling the nature of active sites onto copper/ceria-zirconia catalysts for low temperature CO oxidation

The aim of this research is an attempt to shed some light on the understanding of the nature of the active sites and the generated synergies in the copper/ceria-zirconia formulations for low temperature CO oxidation by means of the creation of copper entities with different physico-chemical nature. For this reason, several CuOx/ceria-zirconia catalysts, with different Cu contents and different methods to incorporate copper species, were synthesized. Focus was specially put in this case trying to link the results of CO oxidation catalytic tests with the CO-temperature programmed reduction profiles/approximate estimations and selected characterization parameters in order to find out correlations among catalysts' properties/reducibility and catalytic behaviors, especially those corresponding to the nature and roles of the different CuOx species in contact with ceria-based support on catalytic activity. Results reveal a significant improvement in CO conversion compared to the ceria-zirconia support by adding a small amount of copper loading (as low as 0.5 %), emphasizing the paramount role of copper incorporated by the method of IWI. From 0.5 up to 2% of copper loading, an interesting increase gradual trend in activity and reducibility can be noted. It should be mentioned that all the catalysts obtained by this procedure are more catalytically active towards CO oxidation than 1%Pt/Al2O3 at low temperatures (T < 130 degrees C). CO-TPR results show that the reducibility of these catalysts is in line with their CO oxidation activity. The method of preparation has been revealed as a critical variable in the catalytic performance, and quite similar catalytic activities can be reached from different synthesis methods and different copper contents, due to the similar nature and type of CuOx species generated over the catalysts' surface, identified by the CO-TPR profiles and the rest of characterization data. Finally, IWI method seems to be the best one among those tested, thus combining superior areas of both alpha and beta contributions assigned on CO-TPR profiles, which seem to be critical in the interpretation of the catalytic behaviors

A Novel Route for the Easy Production of Thermochromic VO₂ Nanoparticles

In this work, a simple, fast and dry method for the fabrication of a thermochromic product with a high load of VO2 (M1) consisting of the controlled heat treatment of pure vanadium nanoparticles in air is presented. After a complete design of experiments, it is concluded that the most direct way to attain the maximum transformation of V into VO2 (M1) consists of one cycle with a fast heating ramp of 42°Cs-1 , followed by keeping 700°C for 530-600 seconds, and a subsequent cooling at 0.05°Cs-1 . Careful examination of these results lead to a second optimum, even more suitable for industrial production (quicker and less energy-intensive because of its lower temperatures and shorter times), consisting of subjecting V to two consecutive cycles of temperatures and times (625°C for 5 minutes) with similar preheating (42°Cs-1 ) but a much faster postcooling ( 8°Cs-1 ). These green reactions only use the power for heating a tube open to atmosphere and a vanadium precursor; without assistance of reactive gases or catalysts, and no special vacuum or pressure requirements. The best products present similar thermochromic properties but higher thermal stability than commercial VO2 particles. These methods can be combined with VO2 doping.A. J. Santos would like to thank the IMEYMAT Institute and the Spanish Ministerio de Educación y Cultura for the concessions of grants (ICARO-173873 and FPU16-04386). University of Cádiz and IMEYMAT are also agreed by financing the mutual facilities available at the UCA R&D Central Services (SC-ICYT), the UCA project references “PUENTE PR2020-003” and “OTRI AT2019/ 032”, and the IMEYMAT projects “PLP2019120-3” and “PLP2021120-1”. Additional support was given by the Spanish State Agency of Research through the “Retos” call (Project No. 1572, Ref. PID2020-114418RB-I00/ AEI / 10.13039/ 501100011033). The regional government of Andalusia with FEDER cofunding also participates through the projects AT-5983 Trewa 1157178 and FEDER-UCA18-10788, and the contract hiring M. Escanciano

Optimization of biogenic sulfur flocculation from an anoxic desulfurization bioreactor using response surface methodology

Elemental sulfur is an interesting byproduct obtained in the anoxic biodesulfurization of biogas. However, the colloidal properties of this biogenic elemental sulfur (S0) make its efficient recovery difficult. The present study investigated the flocculation of S0 produced in an anoxic bioreactor for biogas desulfurization using cationic (Sedifloc 40L4 C, Lizaflock 853 M), anionic (Innoflock 201) and non-ionic flocculants (NI-1009) and a coagulant (polyaluminum chloride). Cationic-type flocculants showed the highest flocculation efficiency, which led to its selection for further evaluation using the response surface methodology of the effects and interactions of its dose, stirring speed and pH on the biogenic sulfur flocculation rate. Optimum S0 flocculation conditions were observed using Lizaflock 853 M at a dose of 0.82 mg L−1, a stirring speed of 30 rpm and a pH of 8.0. A S0 flocculation rate of 97.05% was achieved for an initial concentration of 1730 mg S0 L−1. The Zeta potential of the settled sulfur particles increased after the flocculation process. © 2022 The Author(s