Значение традиционных нравственно-эстетических ценностей в формировании духовного мира ребенка в произведениях Эмиля Амита

Предлагаемый вниманию материал посвящён значению традиционных нравственно-эстетических ценностей в формировании духовного мира подрастающего поколения. Обращение к испокон веков ценимым ценностям под пером автора обретает особое звучание.Пропонований увазі матеріал присвячений проблемі еволюції морального ідеалу в творчості Е.Аміт. Традиційні споконвічні ціності під пером автора набувають особливого звучання.The material which is proposed to you dedicated to a problem of the evolution of the moral ideal in the creation of A Rmit

A DNP-supported solid-state NMR study of carbon species in fluid catalytic cracking catalysts

A combination of solid-state NMR techniques supported by EPR and SEM-EDX experiments was used to localize different carbon species (coke) in commercial fluid catalytic cracking catalysts. Aliphatic coke species formed during the catalytic process and aromatic coke species deposited directly from the feedstock respond differently to dynamic nuclear polarization signal enhancement in integral and crushed FCC particles, indicating that aromatic species are mostly concentrated on the outside of the catalyst particles, whereas aliphatic species are also located on the inside of the FCC particles. The comparison of solid-state NMR data with and without the DNP radical at low and ambient temperature suggests the proximity between aromatic carbon deposits and metals (mostly iron) on the catalyst surface. These findings potentially indicate that coke and iron deposit together, or that iron has a role in the formation of aromatic coke

Lewis Acidity in Cracking and Polymerization Catalysis

The aim of this PhD thesis was to provide insight into the nature and variety of Lewis acidity in solid acid catalysts and to clarify the role of Lewis acid sites in fluid catalytic cracking (FCC) and metallocene-based olefin polymerization catalysis. The definition of an acid site, according to Gilbert Lewis, is an electron pair acceptor.[1–5] A category within the definition of Lewis acidity is the Brønsted acid site (as defined by Johannes Brønsted and Thomas Lowry), which is a molecule capable of donating a proton.[6–8] Cracking and polymerization catalysis by solid acids belong to the pillars of the chemical industry. [9] The fundamental understanding of the chemical nature of their active acid sites is a key parameter for the rational design of these catalysts, which will result in enhanced catalytic performance. An essential part in the investigation into the nature and variety of Lewis acidity in solid catalysts comprised the exploitation of the heterogeneous catalyst characterization toolbox. This PhD thesis has employed a wide range of available state-of-the-art laboratory characterization techniques, including, but not limited to infrared spectroscopy, electronic spectroscopy, optical microscopy, and electron microscopy. A specific category within the characterization toolbox involves the use of probe molecules, whose interaction with acid sites can be studied with spectroscopy. A common thread running throughout this PhD thesis was the necessity to combine multiple characterization techniques at different length-scales, while often pushing the boundaries of what these techniques have to offer in order to achieve insights into the nature and variety of Lewis acidity in solid acid catalysts

Intra- and Interparticle Heterogeneities in Solid Activators for Single-Site Olefin Polymerization Catalysis as Revealed by Micro-Spectroscopy

Transition metal–zeolite composites are versatile catalytic materials for a wide range of industrial and lab-scale processes. Significant advances in fabrication and characterization of well-defined metal centers confined in zeolite matrixes have greatly expanded the library of available materials and, accordingly, their catalytic utility. In this review, we summarize recent developments in the field from the perspective of materials chemistry, focusing on synthesis, postsynthesis modification, (operando) spectroscopy characterization, and computational modeling of transition metal–zeolite catalysts

Insights into the activation of silica-supported metallocene olefin polymerization catalysts by methylaluminoxane

Metallocene-based olefin polymerization catalysts often require large excesses of co-catalyst for optimal catalyst activation. In this work, mechanistic insights into the activation of supported metallocenes by methylaluminoxane as co-catalyst are acquired. UV–vis diffuse reflectance (DR) spectroscopy of five metallocene catalysts with varying co-catalyst loading reveals the presence of different metallocene species on the surface of the catalyst particles. Deconvolution of the obtained spectra, in combination with an extensive TD–DFT study of UV–vis DR spectra of metallocene structures results in a proposed activation mechanism. We find that with increasing MAO loading, more AlMe2 +-bound metallocenes are observed with a shift towards the trimethylaluminum-stabilized cationic methylated metallocene compound. This shift can be directly correlated with a higher activity in the olefin polymerization reaction. Based on this finding, we propose a universal metallocene activation mechanism in which the cationic methylated metallocene is the active species. This species is formed through initial interaction with AlMe2 +, followed by ligand exchange with MAO and stabilized in complex with trimethylaluminum as a dormant species

Nanoparticle Growth in Supported Nickel Catalysts during Methanation Reaction-Larger is Better

A major cause of supported metal catalyst deactivation is particle growth by Ostwald ripening. Nickel catalysts, used in the methanation reaction, may suffer greatly from this through the formation of [Ni(CO)4]. By analyzing catalysts with various particle sizes and spatial distributions, the interparticle distance was found to have little effect on the stability, because formation and decomposition of nickel carbonyl rather than diffusion was rate limiting. Small particles (3–4 nm) were found to grow very large (20–200 nm), involving local destruction of the support, which was detrimental to the catalyst stability. However, medium sized particles (8 nm) remained confined by the pores of the support displaying enhanced stability, and an activity 3 times higher than initially small particles after 150 h. Physical modeling suggests that the higher [Ni(CO)4] supersaturation in catalysts with smaller particles enabled them to overcome the mechanical resistance of the support. Understanding the interplay of particle size and support properties related to the stability of nanoparticles offers the prospect of novel strategies to develop more stable nanostructured materials, also for applications beyond catalysis

Tuning the Redox Chemistry of a Cr/SiO2 Phillips Catalyst for Controlling Activity, Induction Period and Polymer Properties

The Cr/SiO2 Phillips catalyst has taken a central role in ethylene polymerization ever since its discovery in 1953. This catalyst is unique compared to other ethylene polymerization catalysts, since it is active without the addition of a metal-alkyl co-catalyst. However, metal-alkyls can be added for scavenging poisons, enhancing the catalyst activity, reducing the induction period and altering polymer characteristics. Despite extensive research into the working state of the catalyst, still no consensus has been reached. Here, we show that by varying the type of metal-alkyl co-catalyst and its amount, the Cr redox chemistry can be tailored, resulting in distinct catalyst activities, induction periods, and polymer characteristics. We have used in-situ UV-Vis-NIR diffuse reflectance spectroscopy (DRS) for studying the Cr oxidation state during the reduction by tri-ethyl borane (TEB) or tri-ethyl aluminum (TEAl) and during subsequent ethylene polymerization. The results show that TEB primarily acts as a reductant and reduces Cr6+ with subsequent ethylene polymerization resulting in rapid polyethylene formation. TEAl generated two types of Cr2+ sites, inaccessible Cr3+ sites and active Cr4+ sites. Subsequent addition of ethylene also revealed an increased reducibility of residual Cr6+ sites and resulted in rapid polyethylene formation. Our results demonstrate the possibility of controlling the reduction chemistry by adding the proper amount and type of metal-alkyl for obtaining desired catalyst activities and tailored polyethylene characteristics

Influence of acid-base properties on the Lebedev ethanol-to-butadiene process catalyzed by SiO2-MgO materials

The Lebedev ethanol-to-butadiene process entails a complex chain of reactions that require catalysts to possess a subtle balance in the number and strength of acidic and basic sites. SiO2-MgO materials can be excellent Lebedev catalysts if properly prepared, as catalyst performance has been found to depend significantly on the synthesis method. To assess the specific requirements for butadiene production in terms of active sites and to link their presence to the specific preparation method applied, five distinct SiO2-MgO catalysts, prepared by wet-kneading and co-precipitation methods, were thoroughly characterized. The amount and strength of the acidic (pyridine-IR and NH3-TPD) and basic (CDCl3-IR and CO2-TPD) sites of the materials as well as the overall acid/base properties in the liquid phase (Hammett indicators) were determined. The number of acidic and strong basic sites could be correlated with the extent of ethylene and diethyl ether by-product formation. The best performing catalysts are those containing a small amount of strong basic sites, combined with an intermediate amount of acidic sites and weak basic ones. These results thus provide further insight into the relation between the amount and strength of acidic/basic sites, preparation method and catalytic performance

Matrix Effects in a Fluid Catalytic Cracking Catalyst Particle: Influence on Structure, Acidity, and Accessibility

Matrix effects in a fluid catalytic cracking (FCC) catalyst have been studied in terms of structure, accessibility, and acidity. An extensive characterization study into the structural and acidic properties of a FCC catalyst, its individual components (i.e., zeolite H-Y, binder (boehmite/silica) and kaolin clay), and two model FCC catalyst samples containing only two components (i.e., zeolite-binder and binder-clay) was performed at relevant conditions. This allowed the drawing of conclusions about the role of each individual component, describing their mutual physicochemical interactions, establishing structure-acidity relationships, and determining matrix effects in FCC catalyst materials. This has been made possible by using a wide variety of characterization techniques, including temperature-programmed desorption of ammonia, infrared spectroscopy in combination with CO as probe molecule, transmission electron microscopy, X-ray diffraction, Ar physisorption, and advanced nuclear magnetic resonance. By doing so it was, for example, revealed that a freshly prepared spray-dried FCC catalyst appears as a physical mixture of its individual components, but under typical riser reactor conditions, the interaction between zeolite H-Y and binder material is significant and mobile aluminum migrates and inserts from the binder into the defects of the zeolite framework, thereby creating additional Brønsted acid sites and restoring the framework structure