Academic literature on the topic 'Basic catalysis'

AbstractOrganoselenium catalysis has attracted increasing interest in recent years. This Cluster highlights recent key advances in this area regarding the functionalization of alkenes, alkynes, and arenes by electrophilic selenium catalysis, selenonium salt catalysis, selenium-based chalcogen-bonding catalysis, and Lewis basic selenium catalysis. These achievements might inspire and help future research.1 Introduction2 Electrophilic Selenium Catalysis3 Selenonium Salt Catalysis4 Selenium-Based Chalcogen-Bond Catalysis5 Lewis Basic Selenide Catalysis6 Conclusion

Доля каталитических процессов в нефтехимической промышленности ежегодно возрастает. Более 70% разнообразных химических процессов протекают в присутствии катализаторов, в мировой технологии их доля составляет около 90%. Это связано с расширением функциональных возможностей современных катализаторов. Начиная от повышения эффективности и экологичности производства, расширения номенклатуры товарной продукции, получения продуктов с заданными свойствами, до упрощения технологий в некоторых случаях. Кроме этого использование катализаторов существенно определяет уровень энергетических, капитальных и материальных затрат, новизну технологий и их конкурентоспособность. В связи с этим совершенствование индустрии катализаторов и технологий с их использованием относятся к перспективным задачам развития химического и нефтехимического комплексов мировых промышленных лидеров. В числе приоритетных направлений катализа рассматриваются нанокатализ, катализ в сверхкритических растворителях, катализ ионными жидкостями. Основными инструментами совершенствования катализаторов являются модифицирование состава и дизайн структуры. Это определяет обновление ассортимента и рост рынка катализаторов. Последние годы отличаются интенсивностью научных исследований в сфере разработки и изучения катализаторов различных процессов. С целью обобщения информации по разработкам каталитических систем для основных крупнотоннажных нефтехимических процессов подготовлена данная обзорная статья. Систематизированы сведения исследований состава, структуры, способов приготовления, эффективности новых катализаторов процессов гидрирования, дегидрирования, алкилирования, окисления и полимеризации, которые широко применяются в промышленности органического и нефтехимического синтеза. Для разных процессов проведено сравнение новых и используемых катализаторов по критериям экологичности, регенерируемости, а также по выходу и характеристике целевых продуктов. The share of catalytic processes in the petrochemical industry is growing every year. More than 70% of various chemical processes take place in the presence of catalysts; their share in world technology is about 90%. This is due to the expansion of the functionality of modern catalysts. Starting from increasing the efficiency and environmental friendliness of production, expanding the range of commercial products, obtaining products with desired properties, to simplifying technologies in some cases. In addition, the use of catalysts significantly determines the level of energy, capital and material costs, the novelty of technologies and their competitiveness. In this regard, the improvement of the industry of catalysts and technologies with their use are among the promising tasks of the development of chemical and petrochemical complexes of world industrial leaders. Nanocatalysis, catalysis in supercritical solvents, and ionic liquid catalysis are considered among the priority areas of catalysis. The main tools for improving catalysts are composition modification and structure design. This determines the renewal of the assortment and the growth of the catalyst market. Recent years have been distinguished by the intensity of scientific research in the development and study of catalysts for various processes. In order to generalize information on the development of catalytic systems for the main large-scale petrochemical processes, this review article has been prepared. The data of studies of the composition, structure, preparation methods, efficiency of new catalysts for the processes of hydrogenation, dehydrogenation, alkylation, oxidation and polymerization, which are widely used in the industry of organic and petrochemical synthesis, are systematized. For different processes, a comparison was made between new and used catalysts in terms of environmental friendliness, regenerability, as well as the yield and characteristics of target products.

AbstractThe “Seven Pillars” of oxidation catalysis proposed by Robert K. Grasselli represent an early example of phenomenological descriptors in the field of heterogeneous catalysis. Major advances in the theoretical description of catalytic reactions have been achieved in recent years and new catalysts are predicted today by using computational methods. To tackle the immense complexity of high-performance systems in reactions where selectivity is a major issue, analysis of scientific data by artificial intelligence and data science provides new opportunities for achieving improved understanding. Modern data analytics require data of highest quality and sufficient diversity. Existing data, however, frequently do not comply with these constraints. Therefore, new concepts of data generation and management are needed. Herein we present a basic approach in defining best practice procedures of measuring consistent data sets in heterogeneous catalysis using “handbooks”. Selective oxidation of short-chain alkanes over mixed metal oxide catalysts was selected as an example.

This paper presents a brief history of catalysis, as well as the processes of selective oxidation of hydrocarbons. On the other hand, the basic concepts involved in heterogeneous catalysis are mentioned, emphasizing the role of catalytic materials in chemical oxidation processes and posing a series of guiding questions to be followed when approaching a process catalyzed by solid materials. In the same way, the methods of synthesis of catalysts known in the literature as sol-gel and impregnation are shown, identifying the influence of each stage of preparation with the physical and chemical properties of the materials. Finally, a case study applied to the selective catalytic oxidation of methane and methanol using iron, molybdenum, and vanadium catalytic materials synthesized by the sol-gel method is presented.

This paper presents a brief history of catalysis, as well as of the processes of selective oxidation of hydrocarbons. On the other hand, the basic concepts involved in heterogeneous catalysis are mentioned, emphasizing the role of catalytic materials in chemical oxidation processes and posing a series of guiding questions to be followed when approaching a process catalyzed by solid materials. In the same way, the methods of synthesis of catalysts called in the literature as sol-gel and impregnation are shown, identifying the influence of each stage of preparation with the physical and chemical properties of the materials. Finally, a case study applied to the selective catalytic oxidation of methane and methanol using iron, molybdenum and vanadium catalytic materials synthesized by the sol-gel method is presented.

The production of biodiesel at the industrial level is mainly based on the use of basic catalysts. Otherwise, also acidic catalysis allowed high conversion and yields, as this method is not affected by the percentage of free fatty acids present in the starting sample. This work has been useful in assessing the possible catalytic pathways in the production of fatty acid methyl esters (FAMEs), starting from different cooking waste oil mixtures, exploring particularly acidic catalysis. It was possible to state that the optimal experimental conditions required concentrated sulfuric acid 20% w/w as a catalyst, a reaction time of twelve hours, a temperature of 85 °C and a molar ratio MeOH/oil of 6:1. The role of silica in the purification method was also explored. By evaluating the parameters, type of catalyst, temperature, reaction time and MeOH/oil molar ratios, it has been possible to develop a robust method for the production of biodiesel from real waste mixtures with conversions up to 99%.

En los últimos años, existe un creciente interés en la sustitución de viejas tecnologías por alternativas catalíticas más limpias para el desarrollo de procesos respetuosos con el medio ambiente para la industria química. De esta manera, es un desafío continuo encontrar nuevos catalizadores básicos capaces de realizar, con alta actividad y selectividad, las reacciones para la síntesis de productos de alto valor añadido tanto químicos como farmacéuticos. La investigación descrita en esta Tesis se ha centrado en el estudio de nuevos protocolos de síntesis para catalizadores básicos. Nuevos materiales con basicidad controlada, tipo hidrotalcita, se han sintetizado a lo largo de esta Tesis. Por otra parte, se ha desarrollado un nuevo protocolo de síntesis para líquidos iónicos alifáticos de cadena corta. Además, se presenta un amplio estudio de las propiedades físico-químicas de los líquidos iónicos sintetizados. Las propiedades básicas de los catalizadores desarrollados se han caracterizado por diversas técnicas y así como mediante el empleo de reacciones modelo. Por consiguiente, el trabajo realizado en esta Tesis permite avanzar en el diseño de nuevos sistemas catalíticos más activos y eficientes para su utilización en procesos de química fina.
In the last years, there is an increasing interest in substituting old technologies by cleaner catalytic alternatives to afford more environmental friendly processes in the chemical industry. In this way, it is a continuous challenge to find new base catalysts able to perform, with high activity and selectivity, reactions for the synthesis of pharmaceutical and fine chemicals.
The research described in this thesis has focused on the study of new synthesis protocols for base catalysts. New types of hydrotalcite-like materials with controlled basicity were obtained. Also, a new synthesis protocol for short aliphatic chain ionic liquids and an extensive study of their physico-chemical properties is presented. Their basic properties have been characterized by several techniques and by illustrative test reactions. The work done in this thesis can be regarded as a progress in the design of new catalytic systems, more active and efficient for use in fine chemical processes.

Como consecuencia de una demanda energética creciente, en los últimos años se ha incrementado la producción de biodiesel generándose un exceso de producción de glicerol y provocando que su precio disminuya considerablemente. Por este motivo, durante los últimos años la transformación del glicerol en otros compuestos de valor añadido es uno de los objetivos para la industria química y los grupos de investigación. En esta tesis se han desarrollado diferentes catalizadores basados en hidrotalcitas para la síntesis de glicerol carbonato a partir de la transesterificación del glicerol de una forma eficiente y en condiciones suaves de reacción
The valorisation of glycerol is nowadays an important target of scientific groups due to the great excess of glycerol by-product obtained as consequence of a growing biodiesel production. Catalytic processing of glycerol to more valuable chemicals is demonstrated by the large number of patents and articles reported until now. Glycerol carbonate is one of the most interesting chemicals obtained from catalytic modifications of glycerol. This work describes an approach for obtaining glycerol carbonate in a green and efficient form under soft conditions using layered double hydroxides as solid catalysts.

Transition-metal-catalyzed cross-coupling reactions are reliable tools for forging C–C bonds. The Engle Lab has previously pioneered the intermolecular difunctionalization of unactivated alkenes facilitated by nickel catalysis, where regioselectivity is controlled through the use of a bidentate directing group. A limitation of existing methods is that allyl groups have not yet been successfully incorporated, as the electrophile scope has been limited to alkyl and aryl species. Fundamentally, C–C p-bonds have served as key building blocks for the assembly of complex molecules, and the ability to introduce allyl moieties in a controlled manner enables diverse, downstream functionalization in multi-step synthesis. This work focuses on the use of diverse azaheterocycle directing groups connected to non-conjugated alkenes. Through the use of nickel catalysis, we have been able to successfully introduce and preserve allyl and cinnamyl species at the g-position and alkyl zinc nucleophiles at the b-position with high yield under mild conditions. This novel, 1,2-allylalkylation can accommodate a vast array of substituents with different electronic and steric properties (>20 examples). Our efforts have shifted to exploring different monodentate directing groups and to conduct mechanistic studies to shed light on the catalytic cycle. Interestingly, electron-rich electrophiles provide nearly quantitative NMR and isolated yields, whereas electron-poor electrophiles lead to lower yields. We report a competition experiment to further elucidate this mechanism. While isolated yields were generally higher for electron-rich groups, a competition between p-OMe and p-CF3 electrophiles led to preferential incorporation of the trifluoromethyl-substituted coupling partner, which supports oxidative addition as the product-determining step.

Environmental pollution by polychlorinated chlorinated organic wastes is of great concern. Catalytic hydrodechlorination is considered clean and efficient methodology for safe disposal of chlorinated organic wastes. This work aims at studying the catalytic hydrodechlorination reaction for the removal of environmentally polluting chlorinated organic wastes: 1,2,4-trichlorobenzene (1,2,4-TCB) and Trichloroethylene (TCE). The research has focused on evaluation of the activity, selectivity and stability of newly synthesized Pd based catalysts for hydrodechlorination of 1,2,4-trichlorobenzene and trichloroethylene. The first part, related to the HDC of 1,2,4-TCB, is to obtain active and stable catalyst for the hydrodechlorination of C-Cl bond of aromatic compounds to non chlorinated organic aromatic compound (benzene). While the second part aims at obtaining catalysts that allow high selectivity to ethylene formation during the HDC Trichloroethylene. Pd based hydrotalcite derived mixed oxides with different surface property were explored as catalysts for hydrodechlorination reaction. In addition, bimetallic and monometallic heterogeneous catalytic systems were investigated for selective hydrodechlorination reaction. Detailed characterization of the active centers of the newly synthesized catalysts by different techniques was achieved. This work presents original ideas, which could find a practical application, for the treatment of organo-halogenated pollutants.
La contaminación ambiental mediante compuestos policlorados aromáticos y alifáticos es de gran preocupación. La reacción de hidrodecloración catalítica selectiva (HDC) se presenta como una nueva tecnología eficaz para una eliminación segura de estos tipos de compuestos orgánicos clorados. Es por ello, que este trabajo de investigación se ha enfocado en el estudio de nuevos catalizadores activos, selectivos y estables en diferentes reacciones de hidrodecloración de dos familias de compuestos orgánicos clorados: 1,2,4-triclorobenceno (1,2,4-TCB-compuestos aromáticos clorados) y el tricloroetileno (representativo de un compuesto clorado alifático). La primera parte de la tesis relacionadas con el HDC de 1,2,4-TCB, tiene como objetivo la obtención de catalizadores activos y estables para la hidrogenación del enlace C-Cl en compuestos aromáticos y la obtención final del compuesto aromático orgánico declorado. Mientras que la segunda parte tiene por objeto la obtención de catalizadores que permitan una gran selectividad a etileno y no hacia etano (hidrogenación profunda del tricloroetileno) durante la HDC de tricloroetileno. Por otra parte se ha realizado un estudio profundo en la síntesis de estos nuevos catalizadores, así como en la caracterización de los centros activos de dichos catalizadores, para su correlación con la actividad, selectividad y estabilidad de dichos catalizadores. Presenta ideas originales, lo que podría encontrar una aplicación práctica, para el tratamiento de compuestos órgano-halogenados contaminantes.

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Universidade Federal de Sao Carlos
The investments in the biofuel production have increased a lot in the last years mainly because of smaller damages they cause to the environment in comparison with the derived conventional petroleum fuels. The reaction of biodiesel formation is denominated transesterification and, nowadays that reaction happens in the presence of homogeneous catalyst as the sodium methoxide, sodium hydroxide, (NaOH) or potassium hydroxide (KOH). However, those catalysts create problems such as the possibility of soap formation and they need stages such as the neutralization and washing of the biodiesel. Moreover, the residues of the hydroxides are aggressive to the environment. To eliminate these and other problems, the present work presents a new technology in heterogeneous catalysts with enough basic force to accomplish the transesterification of vegetable oil in tender conditions. For the first time, hybrid catalysts of the type molecular sieves of the family M41S ([CTA]Si-MCM-41, [CTA]Si-MCM-48 and [CTA]Si-MCM-50) were synthesized and used, without modification, in transesterification reactions with monoesters and vegetable oils. The results show that catalysts reach conversions around 96 % in the transesterification of canola oil (1:18) at 79 ºC, however the activity is reduced when the catalyst is reused, due, mainly, to the lixiviation of the CTA+ cation. However, new techniques are being developed in order to increase the catalyst stability.
Os investimentos na produção de biocombustíveis aumentaram significativamente nos últimos anos devido, principalmente, aos menores danos causados ao meio ambiente em comparação aos combustíveis convencionais derivados de petróleo. A reação de formação do biodiesel é denominada transesterificação e, atualmente, essa reação ocorre na presença de catalisador homogêneo como o metóxido de sódio, hidróxido de sódio (NaOH) ou de potássio (KOH). Entretanto, esses catalisadores possuem problemas como possibilidade de formação de sabões e necessitam de etapas como a neutralização e lavagem do biodiesel, além disso, os resíduos dos hidróxidos são agressivos ao meio ambiente. Para eliminar estes e outros problemas o presente trabalho apresenta uma nova tecnologia em catalisadores heterogêneos com força básica suficiente para realizar a transesterificação de óleos vegetais em condições amenas. Pela primeira vez, catalisadores híbridos do tipo peneiras moleculares da família M41s ([CTA]Si-MCM-41, [CTA]Si-MCM-48 e [CTA]Si-MCM-50) foram sintetizados e utilizados, sem modificação, em reações de transesterificação com monoésteres e óleos vegetais. Os resultados mostram que catalisadores atingem conversões em torno de 96 % na transesterificação de óleo de canola (1:18) a 79 ºC, porém a atividade é reduzida no reuso do catalisador, devido, principalmente, à lixiviação do cátion CTA+. Entretanto, novas técnicas estão em desenvolvimento para aumentar a estabilidade dos catalisadores.

Dans la présente étude, la compatibilité de molécules polyfonctionnelles a été évaluée en oxydation catalytique aérobie. L'oxydation du géraniol en citral a été réalisée dans un mélange t-BuOH/eau à 40°C en présence de Pt/C et Pt-Bi/C. A 90°C, l'oxydation sélective du 8-Chloro-1-Octanol en acide 8-Chlorooctanoïque a été réalisée. Par contre, d'autres substrats n'ont pas pu être transformés sélectivement en aldéhyde ou en acide à cause de leur sensibilité vis-À-Vis de l'oxygène (alcool-A) ou de leur réactivité particulière (5-Chloro-1-Pentanol qui est cyclisé en produits non désirés). En conditions anaérobies, le transfert d'H alcool / accepteur a été développé, à partir du géraniol (alcool allylique) comme substrat modèle : il convient de réaliser soit la déshydrogénation sélective de sa fonction alcool, soit son isomérisation lorsque la fonction alcool est déshydrogénée en même temps que la C=C allylique est hydrogénée. Les catalyseurs au Cu supporté ont montré un potentiel beaucoup plus prometteur que les métaux nobles, et de nombreux supports ont été évalués. Le styrène utilisé comme accepteur d'H ne permet pas d'obtenir sélectivement le produit de déshydrogénation du géraniol (citral), par contre l'utilisation d'un accepteur d'H confidentiel permet d'obtenir sélectivement le citral sans former de citronellal (produit d'isomérisation de la fonction alcool allylique) en présence de catalyseur au cuivre sur un support ex-Hydrotalcite. En l'absence d'accepteur, ce catalyseur permet l'isomérisation sélective de différents alcools allyliques avec des sélectivités jusqu'à 90 % en cétones saturées
In this study, we evaluated the compatibility of polyfunctional alcohols with catalytic aerobic oxidation systems. Geraniol dehydrogenation was carried out in mild conditions (t-BuOH / water mixture as solvent, 40°C) in the presence of Pt / C (promoted with Bi to avoid leaching). These catalysts are efficients for the oxidation of 8-Chloro-1-Octanol into corresponding acid at 90°C. However, other reactants were not selectively transformed into aldehyds or acids because of their oxygen sensivity (alcool-A) or their particular reactivity toward cyclization products (5-Chloro-1-Pentanol). In parallel, H transfer dehydrogenation was developed in anaerobic conditions. Geraniol was choosen as a model molecule since it can be selectively dehydrogenated or isomerizd (a reducible function on the substrate is hydrogenated when alcohol function is dehydrogenated). Some noble metals were evaluated for these reactions (Pd in the presence of alkene as H acceptor or Ag for acceptorless dehydrogenation), but performances and selectivities are quite low. Copper catalysts showed better results, and a lot of supports were evaluated. Selectivity toward dehydrogenation product (citral) is not total when styrene is used as hydrogen acceptor, but the use of another H acceptor (confidential) in the presence of copper supported on modified hydrotalcite catalyst allows selective dehydrogenation of geraniol without isomerization intro citronellal. Without H acceptor, this catalyst leads to selective isomerization of secondary allylic alcohols into saturated ketones (90 % selectivity)

Dans le contexte de la valorisation de la biomasse par catalyse hétérogène, la chimie théorique est essentielle pour guider la détermination de la nature des sites actifs en combinaison avec des caractérisations expérimentales. Ensuite, le mécanisme de réaction peut être étudié pour déterminer l’état de transition et intermédiaire déterminant la vitesse et ensuite concevoir de meilleurs catalyseurs in silico. Nous avons mis en œuvre cette approche dans plusieurs réactions impliquant des alcools qui jouent un rôle clé dans le passage du pétrole à la biomasse comme source de matière première pour les produits chimiques de commodités ou spécialités. Tout d'abord, nous nous sommes concentrés sur l'oxydation des alcools en phase liquide par l'oxygène, une réaction qui nécessite généralement un environnement alcalin, ce qui nuit à l'économie d’atomes du processus car il génère le sel carboxylate au lieu de l'acide carboxylique. Nous avons proposé un modèle d'interface métal / eau basique incluant l'adsorption d'anion hydroxyde. Cet anion charge la surface métallique et modifie son activité catalytique. Ce modèle a tout d’abord été validé en comparant l’activité prédite de Au et de Pt en présence et en l’absence de base, puis a été utilisé pour étudier l’oxydation d’éthoxylates d’alcool par des bimétalliques. Ensuite, nous sommes passés à la déshydratation en phase gazeuse d’alcools en C3 et C4 en utilisant des catalyseurs à base de phosphate. La modélisation des surfaces s’est basée sur des caractérisations expérimentales. La couverture moléculaire de l'eau à la surface en fonction de la pression et de la température a été établie à l'aide de la thermodynamique ab initio. Les simulations de spectres infrarouges d'adsorption de CO, NH3 et C2H2 nous ont permis d'identifier les sites acido-basiques qui jouent un rôle important dans l'investigation du mécanisme de réaction qui a suivi
In the context of biomass valorization by heterogeneous catalysis, computational chemistry is key to provide guidance to establish the nature of the active sites in combination with experimental characterizations. Then, the reaction mechanism can be studied to determine the rate determining transition state and intermediate and further design in silico better catalysts. We implemented this approach in several reactions involving alcohols that are key in the shift from a petroleum chemical feedstock to a biomass-based feedstock. Firstly, we focused on liquid phase alcohol oxidation by oxygen, a reaction that generally requires an alkaline environment, which is detrimental to the atom economy of the process since it generates the carboxylate salt instead of the carboxylic acid. We proposed a model of metal/basic water interface that includes the adsorption of hydroxide anion. It charges the metallic surface and modifies its catalytic activity. This model was first validated comparing the predicted activity of Au and Pt in presence and in absence of a base, and then used oxidation of alcohol ethoxylates by bimetals. Then, we switched to gas phase dehydration of C3 and C4 alcohols using phosphate-based catalysts. The modeling of the surfaces was based on experimental characterizations. The molecular coverage of water on the surface in function of the pressure and temperature was established using ab initio thermodynamic. The simulations of infrared spectra of CO, NH3 and C2H2 adsorption allowed us to identify the acido-basic sites which play an important role in the reaction mechanism investigation that followed

2009/2010
Nanosized inorganic particles constitute a field of rapidly growing interest and their tailored synthesis is currently subject of intense study. These particles may show unique properties that are not shared by bulk materials and therefore find a palette of innovative applications, e.g., as diagnostic means, or in drug and even gene delivery, offering the advantage over polymer nanoparticles because they are stable, biologically inert, biocompatible and it is easy to introduce functional groups by modification of the surface hydroxyls. Among various synthetic routes the most explored are the ones carried out in bulk, especially the Stöber synthesis, however the final product are mostly polydisperse particles whose size is difficult to control. On the other hand, w/o microemulsion is providing suitable environment for the control of the particle nucleation and growth kinetics, as the nanodroplets of water are nanoreactors for the synthesis. The main advantage is that the procedure does not require extreme conditions of temperature and pressure and the particle size and shape can be controlled simply by controlling the microemulsion parameters where the most important are the water-to-surfactant molar ratio, R, and water-to-TEOS molar ratio, h. The previous studies focused on the latter synthetic route, in base-catalyzed systems, concerned mainly the evolution of silica nanoparticles and the best results were achieved by SAXS. The volume fraction versus time data gave an insight into nucleation and growth and is in agreement with first order kinetics with respect to TEOS concentration. However, we wanted to understand better the environment in which the synthesis takes place and shed light on the evolution of the soluble species, both of the constituents of the microemulsion and of those taking part to reaction. The soluble species present in the reaction mixture that leads to silica nanoparticle production through the base catalyzed hydrolysis of tetraethyl orthosilicate (TEOS) and the successive condensation were investigated in situ, under the actual synthesis conditions, by means of 1H, 13C, and 29Si NMR spectroscopy. The two former nuclei, owing to higher sensitivity and their presence both in the reacting species and in the constituents of the w/o microemulsion (cyclohexane-Igepal CA520 (5 polyoxyethylene iso-octylphenyl ether)-concentrated ammonia solution) afforded insight into the inverse microemulsion and allowed us to assess the kinetic rate of the hydrolysis step. It was verified that the microemulsion microstructure is maintained during the reaction. Special attention was paid to the reaction medium, and an extended assignment of the 1H and 13C resonances of the surfactant head group was performed. These head group signals undergo some changes due to the environmental modifications induced by transition from cyclohexane solution to w/o microemulsion and further to NH3 containing w/o microemulsion. We followed the quantitative evolution of TEOS and EtOH and assessed their preferential distribution in the various environments provided by this, on the mesoscale heterogeneous, reaction medium. Most authors agree that TEOS is localized mainly in the oil however they argue whether EtOH is preferentially in the water-pools or in oil. The clarification was achieved by means of PGSTE NMR since the diffusion coefficients are commonly exploited to characterize microemulsions, to determine the connectivity of the phase and they can be used to obtain the size of water droplets. It was revealed that NH3 exchanges among the inverse micelles diffusing through cyclohexane and confirmed that the preferred localization for ethanol, a byproduct of the reaction, is the bulk oil. Moreover, it was confirmed that TEOS is localized mainly in the oil. The characterization of the final nanoparticles was carried out by means of transmission electron microscopy (TEM) and it was revealed that the final product were monodispersed particles with radius of 20 nm. The synthesis of SiO2 nanoparticles in an acid-catalyzed system is especially interesting from nanotechnological point of view, owing to the different physical nature of silica synthesized under acidic rather than basic conditions, and from an applicative point of view since intended guest species are not always base resistant. Unfortunately, the application of an acid-catalyzed sol-gel process seems less than straightforward. An inverse microemulsion looks like an optimal reaction medium able to limit the growth of silica particles within the nanometer range. However, relatively few studies have been reported to date, and to the best of our knowledge, only one involves the entire process conducted in an inverse microemulsion with a water core that remains stable throughout the course of the reaction. The cyclohexane-Igepal inverse microemulsion, comprehensively established for the synthesis of silica nanoparticles in NH3-catalyzed sol-gel process, was alternatively studied with an acid-catalyzed sol-gel process. TEOS was used as the silica precursor, while two different aqueous phases containing either HNO3 or HCl at two different concentrations, 0.1 and 0.05 M, were examined in the presence and in the absence of NaF, a catalyst of the condensation step. The evolution of the overall reacting system, specifically hydrolysis and polycondensation of reaction intermediates, was monitored in situ by SAXS. No size variation of the inverse micelles was detected throughout the sol-gel process. Conversely, the density of the micellar core increased after a certain time interval, indicating the presence of the polycondensation product. The IR spectra of the reacting mixture were in agreement with such a hypothesis. 1H and 13C NMR measurements provided information on the soluble species, the surfactant, and TEOS. The TEOS consumption was well fitted by means of an exponential decay, suggesting that a first-order kinetics for TEOS transpires in the various systems examined, with rate constants dependent not only on the acid concentration but also on its nature (anion specific effect), on the presence of NaF, and on the amount of water in the core of the inverse micelle. The self-diffusion coefficients, determined by means of PGSTE NMR, proved that a sizable amount of the byproduct ethanol was partitioned inside the inverse micelles. Moreover, the DOSY spectrum contributed to the assignment of the signals of various oligomeric species present in the commercial mixture of Igepal CA520, since the head group, which is a short polyoxyehtylene chain, is somewhat polydisperse. The embedment of Igepal CA520 in an acid-catalyzed inverse microemulsion led to the separation of 1H signals of the various oligomeric components. This ensued from the differential partitioning between the oil and the surface of the inverse micelles, which depends on the ethyleneoxide number (EON) of the head group and the partition degree, between the two environments, for each individual oligomeric species, and afforded further insight into nonionic inverse microemulsions. It was possible to ascertain that the length distribution of the polyethyleneoxide chains is in good agreement with the Poisson distribution theoretically predicted for the polymerization of ethylene oxide. Characterization of the final product was carried out by means of thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and TEM, which concurrently confirmed that the silica isolated from the inverse nonionic microemulsion is not significantly different from the product of a bulk acid-catalyzed sol-gel synthesis. TEM micrographs illustrated particles with diameters smaller than the diameter of the inverse micelles as determined by SAXS, due to a shrinkage effect, in addition to nanostructured aggregates in the range 20-100 nm. The metal doped silica systems are important for optical applications and if the metal ions are finely dispersed on silica matrix very efficient catalysators can be obtained. The synthesis of silica nanoparticles in HCl-catalyzed inverse microemulsion was carried out in the presence of both Cu2+ and Co2+ ions with the aim to get correspondingly doped nanoparticles. The systems were characterized by means of 1H and 13C NMR and the quantitative evolution of TEOS and EtOH was followed. The introduction of metals in the glass matrix strongly influences their optical visible absorption spectrum so the UV-Vis spectroscopy was applied in the study. The isolated nanoparticles were characterized by means of IR and Raman spectroscopy and their size was determined by TEM. It was demonstrated that inverse micelles can be used to produce Co2+ and Cu2+ doped SiO2 nanoparticles with diameter of about 3 and 4 nm, respectively. Spherical particles smaller than the micellar size and, in the case of Cu2+ doped system, larger, irregularly shaped aggregates with diameter up to 1 μm were observed. Lots of darker zones were observed in the TEM images of some larger particles and aggregates containing Cu and may be assigned to Cu metal particles encapsulated in silica matrix. Therefore, cobalt was successfully doped in silica nanoparticles while copper doping seemed less satisfactory.
Particelle inorganiche di grandezza nanometrica costituiscono un settore di interesse in rapida crescita e la loro sintesi è attualmente oggetto di intenso studio. Queste particelle possono presentare proprietà uniche non condivise da materiali bulk e quindi trovare una vasta gamma di applicazioni innovative, ad esempio, come mezzo diagnostico, o per drug delivery e anche gene delivery, offrendo il vantaggio rispetto nanoparticelle polimeriche di essere stabili, biologicamente inerti, biocompatibili e facilmente funzionalizzabili con gruppi funzionali modificando dei ossidrili superficiali. Tra le varie vie sintetiche più esplorate sono quelle effettuate in bulk, in particolare la sintesi di Stöber, ma il prodotto finale sono particelle per lo più polidisperse la cui dimensione è difficile da controllare. D'altra parte, la microemulsione a/o sta fornendo l'ambiente adatto per il controllo della cinetica di nucleazione e crescita delle particelle, siccome le nanogoccioline d'acqua sono i nanoreattori per la sintesi. Il vantaggio principale è che la procedura non richiede condizioni estreme di temperatura e pressione e la dimensione delle particelle e la forma possono essere controllati semplicemente attraverso il controllo dei parametri di microemulsione tra cui i più importanti sono il rapporto molare acqua-tensioattivo, R, e acqua-TEOS, h. Gli studi precedenti focalizzati su quest'ultima linea sintetica, nei sistemi base-catalizzati, riguardavano principalmente l'evoluzione delle nanoparticelle di silice ed i migliori risultati sono stati raggiunti con SAXS. I dati di frazione di volume in funzione del tempo hanno fornito informazioni sui processi di nucleazione e di crescita e sono in accordo con una cinetica di primo ordine rispetto alla concentrazione di TEOS. Tuttavia, era importante capire meglio l'ambiente in cui la sintesi accade e mettere in luce l'evoluzione della specie solubile, sia dei componenti della microemulsione che di coloro che prendono parte alla reazione. Le specie solubili presenti nella miscela di reazione che porta alla produzione di nanoparticelle di silice attraverso l’idrolisi base-catalizzata di tetraetile ortosilicato (TEOS) e la successiva condensazione sono state studiate in situ, alle condizioni effettive di sintesi, mediante spettroscopia NMR di 1H, 13C, e 29Si. I primi due nuclei, a causa di una maggiore sensibilità e la loro presenza sia nel reagente che nei componenti della microemulsione a/o (cicloesano-Igepal CA520 (5 poliossietilene iso-octilfenil etere)-soluzione di ammoniaca concentrata) hanno offerto una visione della microemulsione inversa e ci hanno permesso di valutare la velocità di idrolisi. È stato verificato che la microstruttura della microemulsione è mantenuta durante la reazione. L’attenzione è stata rivolta particolarmente verso il mezzo di reazione, ed è stata effettuata un’assegnazione estesa delle 1H e 13C risonanze della testa del tensioattivo. Questi segnali della testa subiscono variazioni a causa delle modificazioni ambientali indotte dal passaggio dalla soluzione di cicloesano a microemulsione a/o e in seguito alla microemulsione a/o contenente NH3. Abbiamo seguito l'evoluzione quantitativa del TEOS e EtOH e valutato la loro distribuzione preferenziale nei vari ambienti forniti da questo mezzo di reazione, eterogeneo sulla mesoscala. Molti autori concordano sul fatto che il TEOS è localizzato principalmente in olio. Tuttavia, si dibatte se EtOH si trova preferenzialmente nelle goccioline d'acqua o nell’olio. Il chiarimento è stato realizzato per mezzo di PGSTE NMR in quanto i coefficienti di diffusione sono comunemente sfruttati per caratterizzare le microemulsioni, per determinare la connettività delle fasi e possono essere utilizzati per ottenere le dimensioni delle goccioline d’acqua. È stato rivelato che NH3 scambia tra le micelle inverse diffondendo attraverso il cicloesano ed è stato confermato che la localizzazione preferita per l'etanolo, il sottoprodotto della reazione, è l'olio. Inoltre, è stato confermato che il TEOS è localizzato principalmente nell’olio. La caratterizzazione delle nanoparticelle finali è stata effettuata per mezzo di microscopia elettronica a trasmissione (TEM) ed è stato rivelato che il prodotto finale sono le particelle monodisperse con raggio di 20 nm. La sintesi di nanoparticelle di SiO2 in un sistema con catalisi acida è particolarmente interessante dal punto di vista nanotecnologico, a causa della diversa natura fisica di silice sintetizzata in condizioni acide, piuttosto che in quelle basiche, e da un punto di vista applicativo in quanto le specie ospite previste non sempre sono resistenti alle basi. Purtroppo, l'applicazione di un processo sol-gel catalizzato da acido è meno chiara. Una microemulsione inversa sembra un mezzo di reazione ottimale in grado di limitare la crescita delle particelle di silice alle grandezze nanometriche. Tuttavia, relativamente pochi studi sono stati riportati fino ad oggi, e al meglio delle nostre conoscenze, solo uno riguarda l'intero processo condotto in una microemulsione inversa con un nucleo d’acqua che rimane stabile durante tutto il corso della reazione. La microemulsione inversa cicloesano-Igepal, stabilita per la sintesi di nanoparticelle di silice in processo sol-gel NH3-catalizzato, in alternativa è stata studiata con il processo sol-gel catalizzato da acido. Il TEOS è stato utilizzato come precursore di silice, mentre diverse fasi acquose contenenti HNO3 o HCl a due differenti concentrazioni, 0.1 o 0.05 M, sono state esaminate in presenza ed in assenza di NaF, un catalizzatore della fase di condensazione. L'evoluzione del sistema reagente complessivo, in particolare l’idrolisi e la policondensazione dei intermedi di reazione, è stata monitorata in situ mediante SAXS. Nessuna variazione delle dimensioni delle micelle inverse è stata rilevata durante tutto il processo sol-gel. Al contrario, è aumentata la densità dell’interno micellare dopo un certo intervallo di tempo, indicando la presenza del prodotto di policondensazione. Gli spettri IR della miscela di reazione erano d'accordo con tale ipotesi. Misure NMR 1H e 13C hanno fornito le informazioni sulle specie solubili.. Il consumo di TEOS era in accordo con un decadimento esponenziale, suggerendo una cinetica di primo ordine in TEOS, con costante di velocità dipendente non solo dalla concentrazione di acido, ma anche dalla natura (effetto anione specifico), dalla presenza di NaF, e dalla quantità di acqua nel nucleo della micella inversa. I coefficienti di auto-diffusione, determinati mediante PGSTE NMR, hanno dimostrato che una quantità considerevole del sottoprodotto etanolo è presente all'interno delle micelle inverse. Inoltre, lo spettro DOSY ha contribuito alla assegnazione dei segnali delle varie specie oligomeriche presenti nella miscela commerciale di Igepal CA520, poiché la testa, che è una breve catena di poliossietilene, è un po’ polidispersa. L’inserimento di Igepal CA520 in una microemulsione inversa contenente acido ha portato alla separazione di segnali 1H dei vari componenti oligomerici. Questo risulterebbe dal partizione differenziale tra l'olio e la superficie delle micelle inverse, che dipende dal numero di ossido di etilene (EON) della testa e il grado di partizione, tra i due ambienti, per ogni singola specie oligomerica, offrendo una visione più completa sulle microemulsioni inverse non ioniche. È stato possibile accertare che la distribuzione della lunghezza delle catene poliossietileniche è in buon accordo con la distribuzione di Poisson teoricamente prevista per la polimerizzazione di ossido di etilene. La caratterizzazione del prodotto finale è stata effettuata mediante analisi termogravimetrica (TGA), calorimetria differenziale a scansione (DSC), e TEM, che contemporaneamente hanno confermato che la silice isolata dalla microemulsione inversa non ionica non è significativamente diversa dal prodotto di sintesi sol-gel da catalisi acida in bulk. Le micrografie TEM hanno illustrato, oltre ad aggregati nanostrutturati nel range 20-100 nm, le particelle con diametro inferiore al diametro delle micelle inverse ,determinato da SAXS, a causa di un effetto di contrazione. I sistemi di silice dopati con metalli sono importanti per le applicazioni ottiche, e se gli ioni metallici sono finemente dispersi in matrice di silice possono essere ottenuti catalizzatori molto efficienti. La sintesi di nanoparticelle di silice in microemulsione inversa catalizzata da HCl è stata effettuata in presenza di entrambi ioni, Cu2+ e Co2+, con l'obiettivo di ottenere le nanoparticelle conseguentemente dopate. I sistemi sono stati caratterizzati mediante 1H e 13C NMR ed è stata seguita l'evoluzione quantitativa di TEOS e EtOH. L'introduzione dei metalli nella matrice vetrosa influenza fortemente il loro spettro di assorbimento ottico visibile per cui nello studio è stata applicata la spettroscopia UV-Vis. Le nanoparticelle isolate sono state caratterizzati mediante spettroscopia IR e Raman e la loro dimensione è stata determinata mediante TEM. È stato dimostrato che le micelle inverse possono essere utilizzate per produrre le nanoparticelle di SiO2 dopate di Co2+ e Cu2+ con diametro di circa 3 e 4 nm, rispettivamente. Sono state osservate le particelle sferiche più piccole rispetto alle dimensioni micellari e, nel caso del sistema dopato di Cu2+, aggregati più grandi di forma irregolare con diametro fino a 1 micron. Nei immagini TEM di alcune particelle più grandi e aggregati contenenti Cu sono state osservate molte zone più scure che possono essere assegnate alle particelle di metallo Cu incapsulato in matrice di silice. Pertanto, il cobalto è stato dopato con successo nelle nanoparticelle di silice, mentre il doping con il rame sembrava meno soddisfacente.
XXIII Ciclo
1983

Future limits on emissions for both gasoline and Diesel engines require adequate and advanced systems for the aftertreatment of the exhaust gas. Computer models as a complementary tool to experimental investigations are indispensable to design reliable after-treatment devices such as catalytic converters and Diesel particulate filters. Therefore, the objective of this contribution is to present an integrated 1D to 3D simulation workflow of catalytic converters (Three-Way-Catalyst, Diesel Oxidation Catalyst, Selective Catalytic Reduction Catalyst, ...) and Diesel particulate filters. The parameters or sets of parameters are obtained by a fast and efficient 1D-approach of BOOST. They are readily transferable to the 3D simulation code FIRE to investigate detailed aspects such as spatial distribution of temperatures or heat losses. Thus, identical models predicting flow, energy and conversion of species of the exhaust gas were employed to both the 1D gas exchange/cycle and the 3D CFD simulation code. This approach allows to carry out a basic analysis and to define first layouts for the exhaust system. Characteristic parameters of this first design stage are used for the multi-dimensional simulation to evaluate the overall performance including fine tuning of aftertreatment systems.

Storable hydrocarbon fuels that undergo endothermic reaction provide an attractive heat sink for future high-speed aircraft. An investigation was conducted to explore the endothermic potential of practical fuels, with inexpensive and readily available catalysts, under operating conditions simulative of high-speed flight applications. High heat sink capacities and desirable reaction products have been demonstrated for n-heptane and Norpar 12 fuels using zeolite catalysts in coated-tube reactor configurations. The effects of fuel composition and operating condition on extent of fuel conversion, product composition and the corresponding endotherm have been examined. The results obtained in this study provide a basis for catalytic-reactor/heat-exchanger design and analysis.

A mixing process of catalyst particles into a fluid jet is a key part in a chemical reactor because the efficiency of chemical reaction depends on the particle catalyst distribution. Therefore, a mixing process of polystyrene particles into a water jet was investigated experimentally as a basic study of flow with catalysts in the chemical reactor. The velocity fields of both water and particles were measured by image processing. The main results obtained are as follows. The particle velocity approached to the water velocity at the mixing process, when the particles were entrained into the water jet. Because the particle concentration was very low, the velocity distributions were not changed by the addition of the particles. However, the turbulent intensity of the water increased comparing with the case of the water single phase jet.

Hydrogen production using current fueling facilities is essential for near- term applications of fuel cells. A preliminary process for developing natural gas autothermal reforming (ATR) reactor for solid oxide fuel cell (SOFC) was performed in this study. Catalyst scanning was performed for three catalysts and Pt based catalyst selected for further study. Using Pt catalyst we determined feeding conditions for the thermal neutrality by varying O2/CH4 with selected temperatures and feeding conditions. Temperature profiles of a reactor were observed and reformed gas composition was analyzed to evaluate efficiency, conversion and heat of reaction. O2/CH4 showed strong effects on reactor temperature, efficiency and conversion. Thermal neutral conditions were determined for two cases of ATR system on the basis of yields of products of experimental results. These conditions could be used as a guideline for reformer design and operation parameter for self-sustaining ATR.

The article explores the mechanism of the so-called "support zones" and its use in the Arctic zone of Russia to determine its role as the basis of Russian politics and a catalyst for economic growth in the Arctic regions. The conclusion is drawn on the promotion of the use of “support zones” to strengthen Russian positions in the Arctic at a new qualitative level.