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Showing papers on "Reaction rate published in 2001"


Journal ArticleDOI
01 Mar 2001-Polymer
TL;DR: In this paper, a combination of traditional kinetic formal treatments and computer simulation has been made to analyze polydimethylsiloxane (PDMS) thermal degradation, and it was shown that PDMS thermally decomposes to cyclic oligomers through Si-O bond scission in a chain-folded cyclic conformation energetically favored by overlapping of empty silicon d-orbitals with orbitals of oxygen and carbon atoms.

635 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the kinetics of the methane steam reforming, accompanied by the reverse water gas shift reaction over a commercial Ni/α-Al2O3 catalyst in an integral reactor under conditions of no diffusion limitation.

543 citations


Journal ArticleDOI
TL;DR: In this article, the mechanism of nanoparticle formation at supercritical conditions was discussed based on the metal oxide solubility and kinetics of the hydrothermal synthesis reaction using a flow type apparatus over the range of temperature from 523 to 673 K at 30 MPa.
Abstract: Hydrothermal synthesis of CeO2 and AlO(OH) were conducted using a flow type apparatus over the range of temperature from 523 to 673 K at 30 MPa. Nanosize crystals were formed at supercritical conditions. The mechanism of nanoparticle formation at supercritical conditions was discussed based on the metal oxide solubility and kinetics of the hydrothermal synthesis reaction. The reaction rate of Ce(NO3)3 and Al(NO3)3 was evaluated using a flow type reactor. The Arrhenius plot of the first order rate constant fell on a straight line in the subcritical region, while it deviated from the straight line to the higher values above the critical point. The solubility of Ce(OH)3 and AlO(OH) was estimated by using a modified HKF model in a wide range of pH and temperature. In acidic conditions, where hydrothermal synthesis reaction is concerned, solubility gradually decreased with increasing temperature and then drastically dropped above the critical point. The trend of the solubility and the kinetics around the critical point could be explained by taking account of the dielectric constant effect on the reactions. There are two reasons why nanoparticle are formed at supercritical conditions. Larger particles are produced at subcritical conditions due to Ostwald ripening; that could not be observed in supercritical water because of the extremely low solubility. Second reason is the faster nucleation rate in supercritical water because of the lower solubility and the extremely fast reaction rate.

537 citations


Journal ArticleDOI
TL;DR: The results indicate that the dye can be most effectively oxidized in aqueous solution at dye:Fe(2+):H2O2 molar ratio of 1:1.1, which corresponds to about 81% reduction of the initial COD.

445 citations


Journal ArticleDOI
TL;DR: The low-temperature behavior of the selective catalytic reduction (SCR) process with feed gases containing both NO and NO2 was investigated in this article, where the two main reactions are 4NH3 + 2NO + 2 NO2 → 4N2 + 6H2O and 2NH3+ 2NO2 → NH4NO3 + N2 + H2O.
Abstract: The low-temperature behavior of the selective catalytic reduction (SCR) process with feed gases containing both NO and NO2 was investigated. The two main reactions are 4NH3 + 2NO + 2NO2 → 4N2 + 6H2O and 2NH3 + 2NO2 → NH4NO3 + N2 + H2O. The “fast SCR reaction” exhibits a reaction rate at least 10 times higher than that of the well-known standard SCR reaction with pure NO and dominates at temperatures above 200 °C. At lower temperatures, the “ammonium nitrate route” becomes increasingly important. Under extreme conditions, e.g., a powder catalyst at T ≈ 140 °C, the ammonium nitrate route may be responsible for the whole NOx conversion observed. This reaction leads to the formation of ammonium nitrate within the pores of the catalyst and a temporary deactivation. For a typical monolithic sample, the lower threshold temperature at which no degradation of catalyst activity with time is observed is around 180 °C. The ammonium nitrate route is interesting from a standpoint of general DeNOx mechanisms: This reac...

393 citations


Journal ArticleDOI
TL;DR: In this article, the sulfonation reaction is a second-order reaction, which takes place preferentially in the aromatic ring between the two ether links (the first type substitution), and there is only one substituent attached to each repeat unit of the PEEK before the complete substitution of this preferred aromatic ring.
Abstract: Hydrophobic poly(ether ether ketone) (PEEK) were modified by sulfonation at different temperatures (22, 36, 45, and 55°C) and varying period of time with concentrated sulfuric acid used as solvent A kinetic study was carried out based on the assumption that sulfonation reaction is a second-order reaction, which takes place preferentially in the aromatic ring between the two ether (O) links (the first type substitution), and there is only one substituent attached to each repeat unit of the PEEK before the complete substitution of this preferred aromatic ring More than 100% substitution was observed in experiment All the data with substitution degree less than 95% agree fairly well with the kinetic behavior of the second-order reaction The reaction rate coefficient and activation energy for first type substitution were obtained The sulfonated PEEK samples were characterized in terms of ion-exchange capacity (IEC), 1H-NMR, contact angle, and solubility © 2001 John Wiley & Sons, Inc J Appl Polym Sci 82: 2651–2660, 2001

354 citations


Journal ArticleDOI
TL;DR: The study showed that the photo-Fenton process, (a mixture of hydrogen peroxide and ferrous or ferric ion), was the most effective treatment process under acidic conditions and produced a higher rate of degradation of p-chlorophenol at a very short radiation time.

299 citations


Journal ArticleDOI
TL;DR: The mechanism and kinetics of hydroxyapatite precipitation from aqueous solution at the conditions of pH 10-11 and at calcium ion concentrations of more than 0.5 mol/l were investigated and showed that the reaction undergoes the following process: transferring from octacalcium phosphate to amorphous calcium phosphate rapidly, and then from ACP to calcium-deficient hydroxyAPatite (DAP) and HAP.

283 citations


Journal ArticleDOI
TL;DR: In this paper, a correlation was developed for the prediction of the cavitational yield in terms of the cavity collapse pressure, when used with earlier correlations for the pressure amplitude generated during the violent collapse of cavities, will help design engineers to choose particular equipment, operating conditions and geometric parameters to achieve a desired chemical change.
Abstract: Acoustic and hydrodynamic cavitation can be used for a variety of applications ranging from biological applications such as cell disruption to chemical reactions such as oxidation of organic pollutants in aqueous effluents, including biorefractory toxic chemicals. Different equipment used for cavitational effects was compared based on a model reaction (decomposition of potassium iodide resulting into iodine liberation). A correlation was developed for the prediction of the cavitational yield in terms of the cavity collapse pressure. This correlation, when used with earlier correlations for the pressure amplitude generated during the violent collapse of cavities, will help design engineers to choose particular equipment, operating conditions, and geometric parameters to achieve a desired chemical change. The developed equation relating the macroscopic reaction rates with the collapse pressure is the first of its kind reported in the literature. Pilot-plant-scale hydrodynamic cavitation orifice plate setup is most energy-efficient, with significantly higher cavitational yields for the model reaction.

282 citations


Journal ArticleDOI
TL;DR: In this article, the microstructure, physical characteristics, corrosion behavior, and reactivity of zerovalent iron nanoparticles synthesized on a support (primarily a nonporous, hydrophobic polymer resin) were studied.
Abstract: The microstructure, physical characteristics, corrosion behavior, and reactivity of zerovalent iron nanoparticles synthesized on a support (primarily a nonporous, hydrophobic polymer resin) were studied. The remediation of groundwater by zerovalent iron in in situ permeable reactive barriers relies on the redox reaction between metallic iron and a reducible contaminant. Decreasing the size of the iron particles and dispersing them on a support increases the specific surface area of the iron, as well as the ratio of surface to bulk iron atoms, and should thereby increase both the reaction rate and the fraction of iron atoms available for the reaction. Borohydride reduction of aqueous ferrous sulfate gives supported iron nanoparticles, 10−30 nm in diameter, which consist of 85% zerovalent iron by weight. These materials (“ferragels”) are stable in air and have corrosion behavior comparable to iron filings. Interestingly, the presence or absence of a support, as well as the boron remaining from the borohydri...

282 citations


Journal ArticleDOI
TL;DR: Heck reaction proceeds at ambient temperature with considerably enhanced reaction rate through the formation of Pd-biscarbene complexes and stabilized clusters of zero-valent Pd nanoparticles in ionic liquids under ultrasonic irradiation.

Journal ArticleDOI
TL;DR: The reaction kinetics could be interpreted by a three-step mechanism: formation of an inner-sphere chromate-sulfide intermediate complex, intramolecular electron transfer to form Cr(IV) species, and subsequent fast reactions leading to Cr(III).
Abstract: The objective of this work was to investigate the reaction stoichiometry, kinetics, and mechanism for Cr(VI) reduction by hydrogen sulfide in the aqueous phase Batch experiments with excess [Cr(VI)] over [H2S]T indicated that the molar amount of sulfide required for the reduction of 1 M Cr(VI) was 15, suggesting the following stoichiometry: 2CrO4(2-) + 3H2S + 4H+-->2Cr(OH)3(s) + 3S(s) + 2H2O Further study with transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) confirmed that chromium hydroxide and elemental sulfur were the stable products The kinetics of Cr(VI) reduction by hydrogen sulfide was measured under various initial concentrations of Cr(VI) and sulfide as well as pH values controlled by HEPES, phosphate, and borate buffers Results showed that the overall reaction was second-order, ie, first-order with respect to Cr(VI) and first-order to sulfide The reaction rate increased as pH was decreased, and the pH dependence correlated well with the fraction of fully protonated sulfide (H2S) in the pH range of 65-10 The nature of buffers did not influence the reaction rate significantly in the homogeneous system The reaction kinetics could be interpreted by a three-step mechanism: formation of an inner-sphere chromate-sulfide intermediate complex ((H2O4CrVIS)2-), intramolecular electron transfer to form Cr(IV) species, and subsequent fast reactions leading to Cr(III)

Book
01 Jan 2001
TL;DR: In this paper, the RRKM model is used to predict the Mechanisms of Reactions and the relationship between rates and Mechanisms is discussed. But this model is not suitable for the analysis of rate data.
Abstract: Review of Some Elementary Concepts. Analysis of Rate Data. Relationship Between Rates and Mechanisms. Prediction of the Mechanisms of Reactions. Review of Some Thermodynamics and Statistical Mechanics. Introduction to Reaction Rate Theory. Reactions as Collisions. Transition State Theory: The RRKM Model and Related Results. Why Do Reactions Have Activation Barriers? More About Activation Energies. Introduction to Catalysis. Solvents as Catalysts. Catalysis by Metals.

Journal ArticleDOI
TL;DR: In this article, the performance of a CaO-CO 2 chemical heat-pump for upgrading and storing high-temperature thermal energy was studied using the conventional powder method or the metal alkoxide method.

Patent
08 May 2001
TL;DR: In this article, an apparatus and method for carrying out and monitoring the progress and properties of multiple reactions is described, which is especially useful for synthesizing, screening, and characterizing combinatorial libraries.
Abstract: An apparatus and method for carrying out and monitoring the progress and properties of multiple reactions is disclosed. The method and apparatus are especially useful for synthesizing, screening, and characterizing combinatorial libraries, but also offer significant advantages over conventional experimental reactors as well. The apparatus generally includes multiple vessels for containing reaction mixtures, and systems for controlling the stirring rate and temperature of individual reaction mixtures or groups of reaction mixtures. In addition, the apparatus may include provisions for independently controlling pressure in each vessel, and a system for injecting liquids into the vessels at a pressure different than ambient pressure. In situ monitoring of individual reaction mixtures provides feedback for process controllers, and also provides data for determining reaction rates, product yields, and various properties of the reaction products, including viscosity and molecular weight.

Journal ArticleDOI
TL;DR: In this paper, the role of the surface layer in the first-order dissolution rate law was discussed and two alternative ways by which the protective layer concept can be coupled to the saturation concept were proposed.

Book
01 Jan 2001
TL;DR: In this paper, the authors present a detailed look at the physical properties of surface reactions and their relationship with ACT, including the potential energy surface and collision theory of chemical reactions, as well as the free radical reactions.
Abstract: 1 Kinetic Theory of Gases1.1 Introduction1.2 Pressure of an Ideal Gas1.3 Temperature and Energy1.4 Distributions, Mean Values and Distribution Functions1.5 The Maxwell Distribution of Speeds1.6 Energy Distributions1.7 Collisions: Mean Free Path and Collision Number2 The Rates of Chemical Reactions2.1 Introduction2.2 Empirical Observations: Measurement of Reaction Rates2.3 Rates of Reactions: Differential and Integrated Rate Laws2.4 Reaction Mechanisms2.5 Homogeneous Catalysis2.6 Free Radical Reactions: Chains and Branched Chains2.7 Determining Mechanisms from Rate Laws3 Theories of Chemical Reactions3.1 Introduction3.2 Potential Energy Surfaces3.3 Collision Theory3.4 Activated Complex Theory (ACT)3.5 Thermodynamic Interpretation of ACT4 Transport Properties4.1 Introduction4.2 The Functional Form of the Transport Equations4.3 The Microscopic Basis for the Transport Laws4.4 Thermal Conductivity4.5 Viscosity4.6 Diffusion4.7 Time-Dependent Transport5 Reactions in Liquid Solutions5.1 Introduction 5.2 The Cage Effect,Friction, and Diffusion Control5.3 Reactions of Charged Species in Solution: Ionic Strength and Electron Transfer5.4 Experimental Techniques6 Reactions at Solid Surfaces6.1 Introduction6.2 Adsorption and Desorption6.3 Reactions at Surfaces: Catalysis6.4 Surface Diffusion6.5 Advanced Topics in Surface Reactions7 Photochemistry7.1 Introduction7.2 Absorption and Emission of Light7.3 Photophysical Processes7.4 Atmospheric Chemistry7.5 Photodissociation Dynamics8 Molecular Reaction Dynamics8.1 Introduction8.2 A Molecular Dynamics Example8.3 Molecular Collisions:A Detailed Look8.4 Molecular Scattering8.5 Potential Energy Surfaces8.6 Molecular Energy Transfer8.7 Molecular Reaction Dynamics: Some Examples

Journal ArticleDOI
TL;DR: In this paper, the reaction rates of stable and unstable target nuclei in the mass A = 20-40 region have been evaluated and compiled in tabular form on a temperature grid in the range T = 0.01-10.0 GK.
Abstract: Proton-induced reaction rates on 26 stable and 29 unstable target nuclei in the mass A = 20–40 region have been evaluated and compiled. Recommended reaction rates, assuming that all interacting nuclei are in the ground state, are presented in tabular form on a temperature grid in the range T = 0.01–10.0 GK. Most reaction rates involving stable targets were normalized to a set of measured standard resonance strengths in the sd shell. For the majority of reaction rates, experimental information from transfer reaction studies has been used consistently. Our results are compared with recent statistical model (Hauser-Feshbach) calculations. Reaction rate uncertainties are presented and amount to several orders of magnitude for many of the reactions. Several of these reaction rates and/or their corresponding uncertainties deviate from results of previous compilations. In most cases, the deviations are explained by the fact that new experimental information became available recently. Examples are given for calculating reaction rates and reverse reaction rates for thermally excited nuclei from the present results. The survey of literature for this review was concluded in 2000 August.

Journal ArticleDOI
TL;DR: In this paper, a fixed-bed micro-reactor with a K-promoted Fe catalyst was used for CO2 hydrogenation at 1 MPa and with modified residence times in the range of 0.042−21.4 g·s/cm3.
Abstract: CO2 hydrogenation on a K-promoted Fe catalyst was studied in a fixed-bed microreactor between 300 and 400 °C, at 1 MPa, and with modified residence times in the range of 0.042−21.4 g·s/cm3. For temperatures below 360 °C, organic products almost identical with those found in the traditional Fischer−Tropsch reaction with H2/CO were found (paraffins and α-olefins). At 400 °C, formation of carbon deposited on the catalyst became a major reaction. Concerning the mechanism of hydrocarbon formation, the effect of residence time resulted in catalyst particle selectivity values for hydrocarbons always higher than zero. This indicates that, besides the two-step reaction mechanism via CO, a direct hydrocarbon formation from CO2 can occur in principle. With a reaction scheme proposed from these experimental results, a kinetic model was developed using integration and regression features of ASPEN PLUS. Calculated values for CO2 conversion and CO and total hydrocarbon selectivities agree with the experimental data with...

Journal ArticleDOI
TL;DR: In this article, a consensus map was used to identify catalysts that showed high activity for both reactions and good resistance to anodic corrosion in the Pt-Ru-Ir ternary.

Journal ArticleDOI
TL;DR: In this article, stable state enstatite dissolution rates, at far from equilibrium conditions, were measured as a function of aqueous magnesium and silica activity, pH from 1 to 11, and temperature from 28°C to 168°C.

Journal ArticleDOI
TL;DR: Comparison between phosphine- and nonphosphine-based palladacycles suggests that they follow the same reaction mechanism, and the role of water in accelerating the initial formation of the active catalyst species is noted.
Abstract: Experimental kinetic studies of the coupling of p-bromobenzaldehyde (1) with butyl acrylate (2) using the dimeric palladacycles complex (4) with chelating nitrogen ligands were carried out together with kinetic modeling using a reaction rate expression based on the mechanism shown in Scheme 2. The oxidative addition product of 1 was found to be the resting state within the catalytic cycle. The formation of dimeric Pd species external to the catalytic cycle helped to rationalize a non-first-order rate dependence on catalyst concentration. Theoretical modeling showed how the relative concentrations of the different intermediate species within the catalystic cycle can influence the observed rate dependence on Pd concentration. It was shown how conventional kinetic studies may give reaction orders in substrates which differ from those which would be observed under practical synthetic conditions. Comparison between phosphine- and nonphosphine-based palladacycles suggests that they follow the same reaction mechanism. The role of water in accelerating the initial formation of the active catalyst species is noted.

Journal ArticleDOI
TL;DR: In this article, metal-intermetallic (aluminide) laminate (MIL) composites have been fabricated in air using dissimilar metal foils, which exhibit a very high degree of microstructural design and control.
Abstract: Metal-intermetallic (aluminide) laminate (MIL) composites have been fabricated in air using dissimilar metal foils. Foils of varying Al thickness were reacted with foils of Ti-3Al-2.5V resulting in microstructures of well-bonded metal-intermetallic layered composites with either Ti or Al residual metal layers alternating with the Al3Ti intermetallic layers. The MIL composites exhibit a very high degree of microstructural design and control. Microstructure characterization by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffractometry (XRD) has been performed, and basic physical properties of the Ti-Al composites have been determined. The Ti-Al reaction has been studied by interrupting the reaction processing, in steps, to observe the microstructural changes. An oxide layer between the Ti and Al foils initially controls the reaction kinetics. After breakdown of the oxide layer, a two-phase Al+Al3Ti layer (∼10 µm thickness) is formed. After formation of the two-phase layer, liquid phases are continuously present, and Al3Ti spherules (∼10 µm diameter) are formed through interfacial tension, solidify (in times of 2 to 4 µs), and are expelled into the liquid. This mechanism allows for a continuous reaction interface and higher reaction rates. Both reaction regimes, diffusion through the oxide, and, subsequently, the intermetallic phase reaction mechanism result in linear kinetics.

Journal ArticleDOI
TL;DR: In this article, a CO2-expanded solvent medium was proposed for catalytic oxidations in dense CO2 with emphasis on reported homogeneous systems in scCO2, most of which involve transition metal catalysts and dioxygen or organic peroxides as oxidant.

Journal ArticleDOI
TL;DR: In this paper, the performance of the Pt/La 0.5Ce0.5MnO3 catalyst was investigated under lean-burn conditions in the 100-400°C range over 0.1 wt% Pt/γ-Al2O3 and tested under the same reaction conditions.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the kinetics of catalytic hydrogenation of nitrobenzene in acid medium to p-aminophenol in a batch slurry reactor in a temperature range of 323-353 K.

Journal ArticleDOI
TL;DR: The formation of beta-hematin closely parallels many mineralization processes, and this suggests that hemozoin formation may be a unique biomineralization process.
Abstract: Formation of beta-hematin in acidic acetate solution has been investigated using quantitative infrared spectroscopy, X-ray diffraction, and scanning and transmission electron microscopy. The process occurs via rapid precipitation of amorphous (or possibly nanocrystalline) hematin, followed by slow conversion to crystalline beta-hematin. Definitive evidence that the reaction occurs during incubation in acetate medium, rather than during the drying stage, is provided by X-ray diffraction and infrared spectroscopy of the wet material. The reaction follows a sigmoidal function indicative of a process of nucleation and growth and was modeled using the Avrami equation. Reaction rates and the dimensionality of growth (as indicated by the value of the Avrami constant) are strongly influenced by stirring rate. The reaction follows Arrhenius behavior, and there is a strong dependence of both the rate constant and the Avrami constant on acetate concentration. Acetate may act as a phase transfer catalyst, solubilizing hematin and facilitating its redeposition as beta-hematin. The pH dependence of the process indicates that only the monoprotonated species of hematin is active in forming beta-hematin. The formation of beta-hematin closely parallels many mineralization processes, and this suggests that hemozoin formation may be a unique biomineralization process. Inferences are drawn with respect to the formation of hemozoin in vivo.

Journal ArticleDOI
TL;DR: The results indicate that the reaction between NO2 and diesel soot particles does not provide a significant secondary HONO source in the atmosphere, and a Langmuir-Hinshelwood type reaction mechanism was proposed that adequately describes the observed results.
Abstract: Soot particles were collected from a diesel engine using a procedure that realistically mimics exhaust gas conditions in tailpipes and during dilution at room temperature. After being sampled, the particles were exposed to NO2 concentrations and relative humidity in ranges relevant for the troposphere using 13N as tracer. Gas-phase nitrous acid (HONO) and irreversibly bound (i.e., chemisorbed) species were the main reaction products with initial yields of 80−90% and about 10%, respectively. Neither NO nor HNO3 were detectable. The HONO formation increased with increasing engine load (i.e., with a decreasing air to fuel ratio, λ). The reaction rates of HONO and chemisorbed NO2 increased with increasing NO2 concentration and did not depend on relative humidity. At the beginning of reaction, the uptake coefficient averaged over 3 min ranged from 5 × 10-6 to 10-5 for NO2 concentrations between 2 and 40 ppb. The HONO formation rates decreased with time, indicating consumption of reactive surface species, while...

Journal ArticleDOI
TL;DR: In this paper, the authors showed that the major aerosol products formed in gas phase ozonolysis of 1-tetradecene in the presence of excess alcohols, carboxylic acids, water vapor, and aldehydes are α-alkoxytridecyl, α-acyloxy tridecyl and α-hydroxytridecene hydroperoxides.
Abstract: Previous studies in our laboratory have shown that the major aerosol products formed in gas-phase ozonolysis of 1-tetradecene in the presence of excess alcohols, carboxylic acids, water vapor, and aldehydes are α-alkoxytridecyl, α-acyloxytridecyl, α-hydroxytridecyl hydroperoxides, and secondary ozonides. These low volatility compounds are formed from reactions of C13 stabilized Criegee intermediates with the acidic compounds and aldehydes. To obtain a more quantitative understanding of the chemical mechanism and determine the importance of such reactions in the atmosphere, relative rate constant measurements were made using real-time quantitative thermal desorption particle beam mass spectrometry (TDPBMS) for aerosol analysis. The rates of reaction of methanol, 2-propanol, formic acid, water, and formaldehyde with C13 stabilized Criegee intermediates were measured relative to heptanoic acid. The results show that the reactivity of the studied compounds varies over 4 orders of magnitude and increases in th...

Journal ArticleDOI
TL;DR: In this article, 1-decene was converted to 1,2-epoxydecane on UV-irradiated TiO 2 powder using molecular oxygen as the oxygen source.