Mechanisms Of Heterogeneous Catalytic Reactions Research Articles

DEVELOPMENT OF AN ENERGY-SAVING TECHNOLOGY FOR THE PRODUCTION OF SYNTHETIC METHANE FROM CARBON DIOXIDE. 1. RESEARCH OF KINETICS AND MACRO-KINETICS OF THE SABATIER REACTION ON MODIFICATIONS OF THE SERIAL NI/Α-AL2O3 CATALYST GIAP-3-6N

This study presents the results of laboratory research of kinetics and mechanisms of heterogeneous catalytic reactions of hydrogenation of carbon dioxide to carbon monoxide and methane through the Sabatier reaction on modifications of the serial Ni/α-Al2O3 catalyst GIAP-3-6N manufactured in Ukraine. The research was carried out on a laboratory bench using a classic glass gradientless reactor with internal piston stirring, which provides kinetic equations at the level of physicochemical constants of the reactions under consideration. A detailed analysis and review of the literature in the areas of kinetic research of our interest was carried out. A detailed comparison of the kinetic parameters obtained by us for the powder (kinetic) form of contact with a nickel content of 7.5 % (NiO = 7.5 %) with a similar and one of the best foreign analogs containing nickel, Katalco 57-4 (NiO = 15−18 %), produced by the British chemical and metallurgical company Johnson Matthey, was performed. The results of the research confirmed almost equal parameters of the kinetic activity of the compared catalysts in the reactions of hydrogenation of carbon dioxide with hydrogen, including the «Sabatier» reaction, which made it possible to propose a similar mechanism of the processes, calculate the reaction rate constants and their activation energy, propose (determine) kinetic equations for design of reactors and processes, both with the loading of a domestic catalyst and its replacement with a foreign analog. Kinetic equations will be used in the development of multi-ton synthesis gas plants for the production of methanol, ammonia, and synthetic methane, as well as carbon-free e-fuel for internal combustion engines that meet modern climate requirements. Bibl. 28, Fig. 4, Tab. 6.

Recent Developments in Direct C-H Functionalization of Quinoxalin-2(1H)-Ones via Heterogeneous Catalysis Reactions.

In recent years, Web of Science has published nearly one hundred reports per year on quinoxalin-2(1H)-ones, which have attracted great interest due to their wide applications in pharmaceutical and materials fields, especially in recyclable heterogeneous catalytic reactions for direct C-H functionalisation. This review summarises for the first time the methods and reaction mechanisms of heterogeneous catalytic reactions of quinoxalin-2(1H)-ones, including six major types of heterogeneous catalysts involved. The heterogeneous reactions of quinoxalin-2(1H)-ones are summarised by classifying different types of catalytic materials (graphitic phase carbon nitride, MOF, COF, ion exchange resin, piezoelectric materials, and microsphere catalysis). In addition, this review discusses the future development of heterogeneous catalytic reactions of quinoxalin-2(1H)-ones, including the construction of C-B/Si/P/RF/X/Se bonds by heterogeneous catalytic reactions, the enrichment of heterogeneous catalysts such as metal oxides, graphene-based composites, doped metal nanoparticles, and molecular sieve-based porous materials, asymmetric synthesis, and other areas. The aim of this review is to contribute to the development of green and sustainable heterogeneous reaction methods for quinoxalin-2(1H)-ones with applications in materials chemistry and pharmacology.

Communication between active sites regulates heterogeneous catalysis

Understanding the interaction between active sites plays a key role in dictating reaction mechanisms in heterogeneous catalysis. In this issue of <i>Chem</i>, Tang and co-workers find that remote silver atoms can trigger low-temperature carbon monoxide oxidation via electron conduction, demonstrating that communication between active sites can facilitate heterogeneous catalysis.

Chemical kinetics for generalized two-step reaction schemes

Chemical reaction kinetics for steady-state catalytic reactions on heterogeneous catalysts are generally governed by a limited number of elementary steps and the nature of these steps is controlled by the degree of rate control and the surface coverage of reaction intermediates. The generalized two-step reaction scheme, first proposed by Michel Boudart, is used in this paper to drive analytical expressions for the surface coverages by the Most Abundant Reactive Intermediate (MARI); the surface coverage by the Most Abundant Surface Intermediate (MASI); the fraction of the free surface; the degree of rate control for each kinetically significant step; and the overall reaction rate. The two most ubiquitous reaction mechanisms in heterogeneous catalysis, i.e., the associative reaction mechanism and the dissociative reaction mechanism are studied. The applicability of the derived expressions is demonstrated by two case studies: acetone hydrogenation for the associative case and ammonia synthesis for the dissociative case. Scaling relations and BEP correlation are incorporated in the generalized two-step reaction scheme to determine the surface properties of the optimal catalyst. Acetone hydrogenation is used as a case study to demonstrate the applicability of the derived expressions for optimal catalyst. Finally, the application of generalized two-step reaction schemes in understanding the response of a catalyst surface to transient reaction conditions is discussed. Transient reaction kinetics of acetone hydrogenation is used as a case study to demonstrate the applicability of the generalized two-step reaction approach.

Investigations of Hydrocarbon Species on Solid Catalysts by Inelastic Neutron Scattering

The status of surface species on solid catalysts during heterogeneous catalysis is often mysterious. Investigations of these surface species are crucial to deconvolute the reaction network and design more efficient catalysts. Vibrational spectroscopy is a powerful technique to study the interactions between surface species and the catalysts and infrared (IR) and Raman spectroscopies have been widely applied to study reaction mechanisms in heterogeneous catalysis. However, IR/Raman spectra are difficult to model computationally and important vibrational modes may be IR-, Raman- (or both) inactive due to restrictions by optical selection rules. Inelastic neutron scattering (INS) is another form of vibrational spectroscopy and relies on the scattering of neutrons by the atomic nucleus. A consequence of this is that INS is not subject to any optical selection rules and all vibrations are measurable in principle. INS spectroscopy has been used to investigate surface species on catalysts in a wide range of heterogeneous catalytic reactions. In this mini-review, we focus on applications of INS in two important fields: petrochemical reactions and C1 chemistry. We introduce the basic principles of the INS technique, followed by a discussion of its application in investigating two key catalytic systems: (i) the behaviour of hydrocarbons on metal-oxide and zeolite catalysts and (ii) the formation of hydrocarbonaceous species on methane reforming and Fischer–Tropsch catalysts. The power of INS in studying these important catalytic systems is demonstrated.

Kinetic modeling of ZnO‐rGO catalyzed degradation of methylene blue

AbstractPhotodegradation of organic pollutants strongly depends on design of metal oxide semiconductor photocatalysts. Graphene, if composited with ZnO, can effectively enhance its photocatalytic performance for the eradication of pollutants from aqueous medium. Here in, ZnO‐rGO is reported as highly active catalyst for degradation of methylene blue. A 200‐mg/L solution of methylene blue dye was completely degraded within 1 h in comparison to 74% and 56% degradation over ZnO and rGO, respectively. The commonly used mechanisms of heterogeneous catalytic reactions, the Langmuir‐Hinshelwood mechanism, and the Eley‐Rideal mechanisms, were used to describe the reaction kinetics. The Langmuir‐Hinshelwood mechanism was found as more favorable in this study. Apparent activation energy, Eap, true activation energy, ET, entropy, ΔS, and enthalpy, ΔH were calculated as 36.2 kJ/mol, 13.1 kJ/mol, 197.5 J/mol, and 23.1 kJ/mol, respectively.

A Hypersonic Flow Effect on the Melting Rate of a Heat-Protective Surface under Degradation Conditions

The paper presents the results obtained for the distribution of heat flux incident upon a refractory plate of a hypersonic flight vehicle moving at space velocities at various distances from the Earth’s surface. The paper also provides the results of studying phase transitions in the near-wall boundary layer occurring during the hypersonic flow over the ablating surface. The effect of the catalytic wall on heat flux is analyzed. The emphasis is on the analysis of mass loss from the surface of high-velocity flight vehicles based on detailed consideration of the mechanism of heterogeneous catalytic reactions taking place under the surface mass transfer conditions. A temperature distribution is provided across the thickness of the boundary layer at the stagnation point of a blunt-nosed body with a refractory coating for a specific section of the flight path. The mass loss from the surface of crystalline refractory bodies is determined.

Study of heat transfer in the boundary layer in a nitrogen flow past a catalytic graphite wall

The results of investigating the physical and chemical processes in the wall boundary layer on graphite specimens in a nitrogen flow are reported. The effect of the catalytic wall on the heat flux is considered. The emphasis is on analyzing the distribution of the chemical species concentrations across the boundary layer based on a detailed consideration of the mechanism of heterogeneous catalytic reactions under the surface mass flux conditions. The distributions of the chemical species concentrations over the boundary layer thickness at the stagnation point of a blunted graphite body for a particular flight path segment are presented.

On the influence of hypersonic flow at the speed of a reflow heat-proof surface in terms of destruction

The results on the distribution of heat flows coming to the refractory plate of a hypersonic aircraft moving at different distances from the Earth's surface with cosmic velocities are obtained. The results of studies related to the study of phase transitions in the wall boundary layer occurring during the flow of hypersonic flow ablating surface are presented. The influence of the catalytic wall on the heat flow is considered. The main attention is paid to the analysis of the surface entrainment of high-speed aircraft, based on a detailed account of the mechanism of heterogeneous catalytic reactions in the conditions of surface mass transfer. The temperature distribution over the thickness of the boundary layer at the critical point of a blunted body with a refractory coating for a particular section of the flight path is given. Mass entrainment from the surface of crystalline refractory bodies is determined. Ill. 7. Ref. 16.

Quantification of acid site densities on zeolites in the presence of solvents via determination of extinction coefficients of adsorbed pyridine

Fourier transform infrared (FTIR) spectroscopy is frequently used to characterize properties of catalytic sites, identify reaction intermediates, and probe interactions between adsorbates and surfaces, making it a versatile tool for elucidating reaction mechanisms in heterogeneous catalysis. While this technique is typically regarded as qualitative or semiquantitative in nature, quantitative results can be obtained by determining integrated molar extinction coefficients (IMECs), or the amount of signal per mole of adsorbed or bulk species. IMECs for vibrational modes corresponding to pyridine adsorbed onto Brønsted and Lewis acid sites have been determined in the vapor phase; however, the effect of solvents on catalytic sites cannot be captured. Liquid-phase IMECs enable quantification of adsorbates in the presence of solvents, allowing quantitative evaluations of the effect of solvents on catalysts. A method is outlined for determining IMECs of pyridine adsorbed on zeolites in the liquid phase in an attenuated total reflection (ATR) configuration. The method can also be applied to substrates other than pyridine. The IMECs for pyridine adsorbed onto Brønsted and Lewis acid sites in water, acetonitrile, and ethanol are determined. The IMEC values are shown to be dependent on solvent choice, but independent of zeolite framework.

Phase Transitions of Cobalt Oxide Bilayers on Au(111) and Pt(111): The Role of Edge Sites and Substrate Interactions

Well-characterized metal oxides supported on single crystal surfaces serve as valuable model systems to study fundamental chemical properties and reaction mechanisms in heterogeneous catalysis or as new thin film metal oxide catalysts in their own right. Here, we present scanning tunneling microscopy and X-ray photoelectron spectroscopy results for cobalt oxide nanoislands that reveal the detailed atomistic mechanisms leading to transitions between Co-O bilayer and O-Co-O trilayer, induced by oxidation in O2 and reductive vacuum annealing treatments, respectively. By comparing between two different noble metal substrates, Au(111) and Pt(111), we further address the influence of the substrate. Overall, nanoisland edges act to initiate both the oxidation and reduction processes on both substrates. However, important influences of the choice of substrate were found, as the progress of oxidation includes intermediate steps on Au(111) not observed on Pt(111), where the oxidation on the other hand takes place at a significantly higher rate. During reductive treatment of trilayer, the bilayer structure gradually reappears on Pt(111), but not on Au(111) where the reduction rather results in the appearance of a stacked cobalt oxide morphology. These observations point to strong differences in the catalytic behavior between Au and Pt supported cobalt oxides, despite the otherwise strong structural similarities.

Rapid‐Scan Operando Infrared Spectroscopy

AbstractNovel methodology, referred to as rapid‐scan operando, has been demonstrated to be a highly powerful tool for studying reaction mechanisms in heterogeneous catalysis, because it combines rapid scan for IR monitoring in the milliseconds time frame and operando methodology. As proof of concept, the NOx–CO and NOx–H2 reactions were studied as model catalyzed reactions with practical interest for removal of NOx in diesel exhausts. Rapid‐scan operando experiments confirmed state‐of‐the‐art knowledge concerning the reaction mechanisms and, more importantly, allowed us to elucidate, for the first time, the different roles of the surface hydroxy groups depending on the reductant used (CO or H2). Moreover, this new tool was used to distinguish the behavior of carbonates and nitrites under reaction conditions that could not be monitored by conventional IR spectroscopy approaches owing to overlap of their absorbance bands.

Structurally Accurate Model for the “29”-Structure of CuxO/Cu(111): A DFT and STM Study

Copper is a common catalyst for many important chemical reactions including low-temperature water gas shift, selective catalytic reduction of NOx, methanol synthesis, methanol steam reforming, and partial oxidation of methanol. The degree of surface oxidation, or the oxidation state of the active site, during these reactions has been debated and is known to have a large influence on the reaction rates. Therefore, elucidating the atomic-scale structure of copper surface oxides is an important step toward a fuller understanding of reaction mechanisms in heterogeneous catalysis. The so-called “29” monolayer oxide film is a common intermediate in the oxidation of Cu(111). The large size of its unit cell has thus far prevented the development of a definitive model for its structure. Using high-resolution scanning tunneling microscopy (STM) and density functional theory (DFT) calculations, we arrive at a model for the “29” CuxO film on Cu(111). There is very good agreement between experimental and computational...

ChemInform Abstract: Environmental NMR: Fast‐Field‐Cycling Relaxometry

AbstractReview: 69 refs.

Advanced solution methods for microkinetic models of catalytic reactions: A methanol synthesis case study

Microkinetic models, combined with experimentally measured reaction rates and orders, play a key role in elucidating detailed reaction mechanisms in heterogeneous catalysis and have typically been solved as systems of ordinary differential equations. In this work, we demonstrate a new approach to fitting those models to experimental data. For the specific example treated here, by reformulating a typical microkinetic model for a continuous stirred tank reactor to a system of nonlinear equations, we achieved a 1000‐fold increase in solution speed. The reduced computational cost allows a more systematic search of the parameter space, leading to better fits to the available experimental data. We applied this approach to the problem of methanol synthesis by CO/CO2 hydrogenation over a supported‐Cu catalyst, an important catalytic reaction with a large industrial interest and potential for large‐scale CO2 chemical fixation. © 2013 American Institute of Chemical Engineers AIChE J, 60: 1336–1346, 2014

XPS for in situ study of the mechanisms of heterogeneous catalytic reactions

The possibility to use X-ray photoelectron spectroscopy (XPS) for in situ studies of the mechanisms of heterogeneous catalytic reactions over the pressure range from ultrahigh vacuum to 100 mbar is considered. The application of this method to investigation of CO adsorption and hydrogenation as well as kinetics and mechanism of methanol transformation on the palladium surface at pressures of 10−6 mbar to 0.1 mbar is reported.

ChemInform Abstract: Insights into Reaction Mechanisms in Heterogeneous Catalysis Revealed by in situ NMR Spectroscopy

AbstractReview: 58 refs.

Insights into reaction mechanisms in heterogeneous catalysis revealed by in situ NMR spectroscopy

This tutorial review intends to show the possibilities of in situ solid state NMR spectroscopy in the elucidation of reaction mechanisms and the nature of the active sites in heterogeneous catalysis. After a brief overview of the more usual experimental devices used for in situ solid state NMR spectroscopy measurements, some examples of applications taken from the recent literature will be presented. It will be shown that in situ NMR spectroscopy allows: (i) the identification of stable intermediates and transient species using indirect methods, (ii) to prove shape selectivity in zeolites, (iii) the study of reaction kinetics, and (iv) the determination of the nature and the role played by the active sites in a catalytic reaction. The approaches and methodology used to get this information will be illustrated here summarizing the most relevant contributions on the investigation of the mechanisms of a series of reactions of industrial interest: aromatization of alkanes on bifunctional catalysts, carbonylation reaction of methanol with carbon monoxide, ethylbenzene disproportionation, and the Beckmann rearrangement reaction. Special attention is paid to the research carried out on the role played by carbenium ions and alkoxy as intermediate species in the transformation of hydrocarbon molecules on solid acid catalysts.

Catalysis with Small Free Noble Metal Clusters

AbstractFor Abstract see ChemInform Abstract in Full Text.

X-ray photoelectron spectroscopy as a tool for in-situ study of the mechanisms of heterogeneous catalytic reactions

An ESCALAB High Pressure photoelectron spectrometer specially designed by Vacuum Generators Co. (UK) for in-situ measurements at high pressures has been modified for adsorption and catalytic experiments. New construction of a gas cell, which serves to create a high-pressure zone, allows us to measure photoemission spectra in-situ at pressures up to 0.2–0.5 mbar and to use a sample holder with independent heating of a sample. This makes it possible to measure temperature programmed desorption and reaction spectra and, as a consequence, to characterize the catalytic properties simultaneously with the acquisition of X-ray photoelectron spectroscopy (XPS) data. Capabilities of the modified spectrometer are demonstrated by the examples of studies of CO and methanol adsorption on Pd(111) single crystal and methanol oxidation over Cupoly.