Добірка наукової літератури з теми "Surface Chemistry, Heterogeneous catalysis, nano-catalysis, Gas solid interaction"

AbstractWe report a unique in situ instrument development effort dedicated to studying gas/solid interactions relevant to heterogeneous catalysis and early stages of oxidation of materials via atom probe tomography and microscopy (APM). An in situ reactor cell, similar in concept to other reports, has been developed to expose nanoscale volumes of material to reactive gas environments, in which temperature, pressure, and gas chemistry are well controlled. We demonstrate that the combination of this reactor cell with APM techniques can aid in building a better mechanistic understanding of resultant composition and surface and subsurface structure changes accompanying gas/surface reactions in metal and metal alloy systems through a series of case studies: O2/Rh, O2/Co, and O2/Zircaloy-4. In addition, the basis of a novel operando mode of analysis within an atom probe instrument is also reported. The work presented here supports the implementation of APM techniques dedicated to atomic to near-atomically resolved gas/surface interaction studies of materials broadly relevant to heterogeneous catalysis and oxidation.

Low molecular weight ketones are among the most important products widely used in industry, however, the existing methods for their production are multistage. The significant disadvantages of these methods include the implementation of individual stages at high temperatures and pressures. As a result, the development of more economical and easy-to-implement processes is presented as an actual task for the basic organic synthesis industry. Recently, ethanol has been considered as a possible feedstock for the production of acetone. The prospect of using ethanol as a feedstock is due to the large renewable resources for its production. The growing interest in recent years in the production of ethanol by processing agricultural products and waste from the food and woodworking industries will undoubtedly stimulate further development of the method of producing acetone from ethanol. The catalytic conversion of ethanol to acetone is a relatively new method for producing acetone and, naturally, the number of publications devoted to this process is relatively small. In previously published works, as a rule, the issues of the mechanism of the process, as well as the relationship between the physicochemical and catalytic properties of the proposed active systems in these reactions, are not considered in detail. Active and selective catalysts were selected for the conversion reaction of ethanol to acetone, the mechanism of the process and the relationship between the physicochemical and catalytic properties of the activated sample were studied. The experiments were carried out on an active catalyst with the composition ZnO:CaO=9:1 The main provisions of the electronic theory of catalysis are developed in application to semi¬con-ductors, since, firstly, the theory of semiconductors is now more developed, and secondly, most of the catalysts used in practice belong to semiconductors. The surface of a semiconductor is the protection of two phases: a solid body-gas. The approach to this boundary from the side of the gaseous environment is essential for catalysis. The environment affects the surface and volume of the solid body. The influence of the environment is carried out through adsorption, as a result, the Fermi level shifts, and the electrophysical pro¬pert¬ies of catalysts change in the processes of adsorption and catalysis. Reactions of heterogeneous-catalytic transformation of low molecular weight alcohols are of great practical importance. The relevance of catalytic transformations of ethanol into various valuable products is the most important task of modern catalytic chemistry. To elucidate the mechanism of these reactions, a necessary step is to study the nature of the electronic interaction of reactants with a solid body, since the vast majority of catalysts of heterogeneous-catalytic oxidation - metal oxides, semiconductors, so especially promising is to involve methods for studying the electro physical properties of the surface. Changing these properties and studying the nature of their change in the atmosphere of the reactants, it is possible obtain valuable information about the nature of the electronic interaction of the reactant-catalyst. The works carried out in this direction showed that in most cases the process of chemisorption is accompanied by the appearance of an additional surface potential, indicating the charging of the surface in the presence of a particular reactant. The electrical and catalytic properties of a series of active zinc-calcium oxide catalysts were studied (their activity was also studied in previous experiments). The study of the electrical properties of the catalyst is of the greatest interest for elucidating the mechanism of reactions, since they can provide information about the nature of electronic transitions that limit the course of the reaction. The number of different factors determines the catalytic activity of a solid body. Each of these factors can correlate with certain properties of a solid body. When comparing catalytic and electrophysical properties electrical conductivity is most often measured. Measuring on the same catalyst sample under the same conditions of conductivity change can provide useful information about mechanism of action of the catalyst and the course of the catalytic reaction. Studies of the electrical conductivity of the synthesized catalysts have shown that all the catalysts studied are semiconductors. This article shows the relationship between the electrical and catalytic properties of zinc-calcium oxide catalysts. Keywords: catalyst, electrical conductivity, activation energy, adsorption, ethanol, acetone.

This article briefly reviews the development of surface science and its close relevance to nanoscience and heterogeneous catalysis. The focus of this article is to highlight the importance of nanoscale surface science for understanding heterogeneous catalysis performing at solid–gas and solid–liquid interfaces. Surface science has built a foundation for the understanding of catalysis based on the studies of well-defined single-crystal catalysts in the past several decades. Studies of catalysis on well-defined nanoparticles (NPs) significantly promoted the understanding of catalytic mechanisms to an unprecedented level in the last decade. To understand reactions performed on catalytic active sites at nano or atomic scales and thus reach the goal of catalysis by design, studies of the surface of nanocatalysts are crucial. The challenges in such studies are discussed.

Controlled atmosphere electron microscopy (CAEM) is a form of in situ microscopy in which the sample is exposed to a reactive gas during observation. This instrument essentially combines the nano-structural characterization features of a TEM with a microreactor and is ideal for studying gas/solid reactions in catalysts. Such in situ techniques can provide a link between surface studies performed under UHV conditions and catalytic reactions run in high-pressure reactors. with correctly designed experiments, CAEM is a powerful technique for correlating dynamic changes in microstructure with catalysis and can be used to provide insights on the location of active sites and mechanisms for catalysis. Baker and colleagues have worked for over thirty years on different heterogeneous catalysts using in situ electron microscopy (see [1] for example). Gai has also published many studies on the application of CAEM to oxide catalysts [2].The technique usually relies on detecting a change in the heterogeneous catalyst during a catalytic reaction.

Ion and water transport at the Angstrom/Nano scale has always been one of the focuses of experimental and theoretical research. In particular, the surface properties of the angstrom channel and the solid-liquid interface interaction will play a decisive role in ion and water transport when the channel size is small to molecular or angstrom level. In this paper, the chemical structure and theoretical model of graphene oxide (GO) are reviewed. Moreover, the mechanical mechanism of water molecules and ions transport through the angstrom channel of GO are discussed, including the mechanism of intermolecular force at a solid/liquid/ion interface, the charge asymmetry effect and the dehydration effect. Angstrom channels, which are precisely constructed by two-dimensional (2D) materials such as GO, provide a new platform and idea for angstrom-scale transport. It provides an important reference for the understanding and cognition of fluid transport mechanism at angstrom-scale and its application in filtration, screening, seawater desalination, gas separation and so on.