Química y Tecnologías Químicas

Not availableEn esta contribución se hace una sencilla revisión de la química que se realiza en los Institutos del CSIC con la finalidad de obtener una idea general de su estado y de las posibilidades de evolución en un futuro cercano. Para una mejor comprensión de la situación actual, se hace imprescindible un acercamiento a la historia y ala génesis de los Institutos. El estudio comprende, en primer lugar, un examen de la dimensión del potencial de la química, para hacer después un recorrido por cada uno de los Institutos y revisar las actividades de actualidad. Finalmente, se concluye con unas previsiones de futuro y se incide en algunas temáticas que se presentan como especialmente atractivas, dentro del esquema de los programas nacionales y de la UE y de las necesidades o deficiencias del sistema productivo

Quimisorción de CO₂ sobre óxido de escandio

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Químicas, leída en 1976.En esta memoria se recogen los resultados experimentales análisis y discursión de un trabajo sobre la quimisorción de dióxido de carbono sobre oxido de escandio. El trabajo experimental comenzó con un estudio sobre la caracterización estructural y textural del adsorbente la influencia del tratamiento térmico y la desgasificación sobre el grado de hidroxilación de su superficie. Una vez puesto a punto el sistema y estudiadas las condiciones de operación se procedió a la determinación de una serie de isotermas de adsorción en un intervalo entre -78 y 300 c a presiones entre 1 y 500 torr.Fac. de Ciencias QuímicasTRUEProQuestpu

Quimisorción de CO₂ sobre óxido de escandio

En esta memoria se recogen los resultados experimentales análisis y discursión de un trabajo sobre la quimisorción de dióxido de carbono sobre oxido de escandio. El trabajo experimental comenzó con un estudio sobre la caracterización estructural y textural del adsorbente la influencia del tratamiento térmico y la desgasificación sobre el grado de hidroxilación de su superficie. Una vez puesto a punto el sistema y estudiadas las condiciones de operación se procedió a la determinación de una serie de isotermas de adsorción en un intervalo entre -78 y 300 c a presiones entre 1 y 500 torr

Effect of the nature of the support on the enantioselective hydrogenation of 1-phenyl-1,2-propanedione over supported iridium catalysts

The enantioselective hydrogenation of 1-phenyl-1,2-propanedione at 298 K and 40 bar over modified supported iridium catalysts has been studied. Cinchonidine has been used as chiral inducer. The catalysts were obtained by impregnation of Ir(acac)3 on three different supports: SiO2, TiO2 and MoO3, followed by calcination in air and reduction under hydrogen at 773 K. All the solids were characterized by nitrogen adsorption-desorption isotherms at 77 K, H2 chemisorption, XRD, TEM, TPR and XPS. It was found that Ir/SiO2 and Ir/TiO2 catalysts reduced at high temperatures, 773 K, possess similar metal particle size, close to 2.0 nm, eventhough the H/Ir ratio obtained from H2 chemisorption showed larger differences, with the H/Ir ratio being lower for titania- and molybdenum-supported iridium catalysts. In these samples, migration of the partially reduced supports, TiOx and MoOx moieties, on the metal crystals induce the creation of Ird+ species. TPR and XPS results confirmed that the metal component was not completely reduced. The activity was influenced by the nature of the support, being more active those in the SMSI state such as Ir/TiO2 and Ir/MoO3 being more active. This has been attributed to the presence of electron deficient metal species, Ird+, which are responsible for the polarization of the carbonyl bond of the substrates, thus favoring the activity and enantioselectivity of the reaction. The effect of different solvents on the activity and the enantioselectivity of the reaction was also studied. The highest enantiomeric excess (ee) of (R)-1-phenyl-1-hydroxy-2-propanone (20%) was obtained with the Ir/TiO2 catalyst using acetic acid as solvent.The authors thank the support of Núcleo Científico Milenio ICM P99-92, and FONDECYT Grant 1030670.Peer reviewe

Adsorption of nitric oxide and temperature programmed desorption on nonstoichiometric nickel-copper manganites

The interaction of nitric oxide with nonstoichiometric nickel–copper manganites has been investigated by adsorption and temperature programmed desorption (TPD) experiments. Nitric oxide was found to adsorb molecularly at room temperature on such oxides. Reversibly and irreversibly adsorbed NO molecules were evidenced. The amount of reversibly and irreversibly adsorbed NO increased with the nickel content but decreased with the copper one. Moreover, the ratio reversible/irreversible increased with the copper content of the oxides. TPD experiments indicated that adsorbed NO desorbs at low temperature (below 200°C) mainly as NO molecules (70–90%). The balance consists of N2O, a part of which desorbs below 200°C and the rest above 250°C. The area of the peak corresponding to the desorption of nitrous oxide at high temperature is far much larger for copper-free oxides

Equilibrium and kinetics of NO and CO chemisorptions on nonstoichiometric nickel-copper manganites

The equilibrium and kinetics of adsorption of NO and CO on nonstoichiometric nickel-copper manganites have been investigated through volumetric measurements. The adsorption isotherms were satisfactorily fitted to the Freundlich equation. The equilibrium coverages at 298 K were found to depend closely on the chemical composition of the oxide; thus, a decrease in the coverage beyond a maximum copper extent was observed. The adsorption isotherms of NO at various temperatures in the range from 298 to 473 K showed that the equilibrium coverage decreases with increasing temperature. This behavior enabled us to follow the logarithmic decrease of the heat of adsorption of NO on such surfaces. The adsorptions of NO and CO on surfaces preadsorbed with CO and NO, respectively, were also studied. These experiments showed the ability of NO to displace CO preadsorbed molecules whereas the contrary did not hold, suggesting the existence of common adsorption sites as well as some specific CO adsorption sites. Finally, some kinetic data are reported showing that the experimental adsorption results fit the Elovich equation (with t(0) approximate to 0), although two distinct rate processes could be identified

Removal of refractory organosulfur compounds via oxidation with hydrogen peroxide on amorphous Ti/SiO2 catalysts

Efficient removal of benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (DMDBT) has been successfully achieved via oxidation with hydrogen peroxide in liquid phase using an amorphous silica-loaded titanium oxide catalyst. Both BT and DBT are easily oxidized to the corresponding sulfones, however in the case of DMDBT the steric hindrance of the alkyl groups makes the approach of the S-atom to the catalyst active centre (an isolated Ti(IV) species) difficult and therefore its reactivity is inhibited. The concentration of the organosulfur compound, the H2O2 concentration and the nature of the solvent play a key role in the rate of S-removal.Peer reviewe

Complete chemical hydrolysis of cellulose into fermentable sugars via ionic liquids and antisolvent pretreatments

This work describes a relatively simple methodology for efficiently deconstructing cellulose into monomeric glucose, which is more easily transformed into a variety of platform molecules for the production of chemicals and fuels. The approach undertaken here first involves the dissolution of cellulose in an ionic liquid (IL), followed by a second reconstruction step aided by an antisolvent. The regenerated cellulose exhibited strong structural and morphological changes, as revealed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. These changes dramatically affect the hydrolytic reactivity of the cellulose with dilute mineral acids. As a consequence, the glucose yield obtained from the deconstructed-reconstructed cellulose was substantially higher than that achieved via hydrolysis of the starting cellulose. Factors that affect the hydrolysis reaction include the type of cellulose substrate, the type of IL used in the pretreatment and the type of acid used in the hydrolysis step. The best results were obtained by treating the cellulose with IL and using phosphotungstic acid (0.067 mol/L) as a catalyst at 413 K. Under these conditions, the conversion of cellulose was almost complete (> 99 %), with a glucose yield of 87 % after only 5 h of reaction.Comunidad de Madrid (Spain) S2009/ENE-1743CSIC (Spain) 201180E038Peer reviewe

X-ray photoelectron spectroscopic study of non-stoichiometric nickel and nickel-copper spinel manganites

The surface of non-stoichiometric nickel and nickel-copper spinel manganites has been investigated by X-ray Photoelectron Spectroscopy (XPS). The oxidation states of the nickel, copper and manganese cations present on the surface of the samples were determined from the analysis of the M 2p(3/2) core levels (M=Ni, Cu, Mn). In particular both Cu2+ and Cu+ were evidenced in the determined from the analysis of the M 2p(3/2) core levels (M=Ni, Cu, Mn). In particular, both Cu structure whereas only bivalent nickel was observed. The partial substitution of manganese by copper led to a chemical shift towards lower binding energy in the Ni 2p(3/2) region, which was explained by the displacement of some Ni2+ cations from tetrahedral to octahedral sites of the spinel structure. Finally, the surface atomic ratios Ni/Mn for nickel manganites, Ni/(Mn+Cu) and Cu/(Mn+Ni) for nickel-copper manganites, determined from XPS data, were compared to the ratios corresponding to the bulk composition. This study shows in all cases a nickel enrichment at the surface which is not affected by the copper content of the oxide. On the contrary, the ratio Cu/(Mn+Ni) was found to be lower than the corresponding bulk value

Role of the Sulphur Source in the Solvothermal Synthesis of Ag-CdS Photocatalysts: Effects on the Structure and Photoactivity for Hydrogen Production

© 2020 by the authors.The aim of this work is to study the influence of the sulphur source (elemental sulphur, thiourea and L-cysteine) in the solvothermal synthesis of Ag-CdS over its growth, structuration and state of Ag and how these changes influence on its photoactivity. The differences in the generation rate of the S2− from the sulphur sources during the solvothermal synthesis determine the nucleation and growth pathways of CdS affecting to the silver state and its incorporation into the CdS lattice. The hydrogen production on Ag-CdS photocatalysts decreases according the sequence: thiourea > elemental sulphur >> L-cysteine. The changes in the photoactivity of Ag-CdS samples are analysed in terms of the differences in the insertion of Ag+ into the CdS lattice, the formation of composites between CdS and Ag2S and the formation of CdS crystalline domains with strong confinement effect derived from the different sulphur source used in the solvothermal synthesis.The present work was performed within the research program supported by MINECO (Spain) under the projects CTQ2016-76505-C3-1-R and PID2019-1112119RB-100 and CAM within the BIOTRES-CM (S2018/EMT-4344) project. E. Soto would like to acknowledge MINECO for the FPI research grant.Peer reviewe