Showing papers on "Elementary reaction published in 2010"
TL;DR: The surface phase diagram and the volcano describing the catalytic activity are combined and it is found that the reaction mechanism differs depending on catalyst material, which means that the chlorine evolution activity is high for a wide range of oxygen binding energies.
Abstract: Based on density functional theory (DFT) calculations we study the electrochemical chlorine evolution reaction on rutile (110) oxide surfaces. First we construct the Pourbaix surface diagram for IrO2 and RuO2, and from this we find the chlorine evolution reaction intermediates and identify the lowest overpotential at which all elementary reaction steps in the chlorine evolution reaction are downhill in free energy. This condition is then used as a measure for catalytic activity. Linear scaling relations between the binding energies of the intermediates and the oxygen binding energies at cus-sites are established for MO2 (M being Ir, Ru, Pt, Ti). The linear relations form the basis for constructing a generalized surface phase diagram where two parameters, the potential and the binding energy of oxygen, are needed to determine the surface composition. We calculate the catalytic activity as function of the oxygen binding energy, giving rise to a Sabatier volcano. By combining the surface phase diagram and the volcano describing the catalytic activity, we find that the reaction mechanism differs depending on catalyst material. The flexibility in reaction path means that the chlorine evolution activity is high for a wide range of oxygen binding energies. We find that the required overpotential for chlorine evolution is lower than the overpotential necessary for oxygen evolution.
283 citations
TL;DR: In this article, the authors present a systematic study of O2 reduction on the (111) facets of eight transition metals (Rh, Ir, Ni, Pd, Pt, Cu, Ag, and Au) based on periodic density functional theory.
187 citations
TL;DR: URVA can show the mechanism of a reaction expressed in terms of reaction phases, revealing the sequence of chemical processes in the reaction complex and making it possible to determine those electronic factors that control the mechanism and energetics of the reaction.
Abstract: Computational approaches to understanding chemical reaction mechanisms generally begin by establishing the relative energies of the starting materials, transition state, and products, that is, the stationary points on the potential energy surface of the reaction complex. Examining the intervening species via the intrinsic reaction coordinate (IRC) offers further insight into the fate of the reactants by delineating, step-by-step, the energetics involved along the reaction path between the stationary states. For a detailed analysis of the mechanism and dynamics of a chemical reaction, the reaction path Hamiltonian (RPH) and the united reaction valley approach (URVA) are an efficient combination. The chemical conversion of the reaction complex is reflected by the changes in the reaction path direction t(s) and reaction path curvature k(s), both expressed as a function of the path length s. This information can be used to partition the reaction path, and by this the reaction mechanism, of a chemical reaction...
145 citations
TL;DR: In this article, the authors introduce systems of microscopically reversible reactions, including both heterogeneous thermal reactions and electrochemical charge transfer reactions, and evaluate all reaction rates in elementary form, providing a powerful alternative to a Butler-Volmer formalism for the charge-transfer reactions.
106 citations
TL;DR: In this article, a micro-reactor design for steam reforming of methane (SRM) reaction with the integration of a microchannel for Rh-catalyzed endothermic reaction, a micro channel for Pt-catalysed exthermic reaction and a wall in between with Rh or Pt catalysts coated layer is presented.
90 citations
TL;DR: The reaction of urea and formaldehyde, giving monomethylolurea, is reversible in a neutral, acid or alkaline aqueous solution, the forward reaction being bimolecular and the reverse reaction monomolecular as discussed by the authors.
Abstract: The reaction of urea and formaldehyde, giving monomethylolurea, is reversible in a neutral, acid or alkaline aqueous solution, the forward reaction being bimolecular and the reverse reaction monomolecular.
The forward and reverse reactions are catalyzed to the same extent by hydrogen ions as well as by hydroxyl ions. The specific rates are directly proportional to the hydrogen and hydroxyl ion concentrations. There appears to be an influence of the buffer concentration on the reaction rates probably due to a general acid and general base catalysis.
The equilibrium is almost independent of the pH of the solution and of the buffer concentrations.
The activation energies of the forward and the reverse reaction have been determined, giving the heat of reaction. Within experimental error these activation energies may be the same for the non-catalyzed and for the catalyzed system.
The reaction mechanism is discussed.
86 citations
TL;DR: The gas phase reaction between nitric acid and hydroxyl radical, without and with a single water molecule, has been investigated theoretically using the DFT-B3LYP, MP2, QCISD, and CCSD(T) theoretical approaches with the 6-311+G(2df,2p) and aug-cc-pVTZ basis sets.
Abstract: The gas phase reaction between nitric acid and hydroxyl radical, without and with a single water molecule, has been investigated theoretically using the DFT-B3LYP, MP2, QCISD, and CCSD(T) theoretical approaches with the 6-311+G(2df,2p) and aug-cc-pVTZ basis sets. The reaction without water begins with the formation of a prereactive hydrogen-bonded complex and has several elementary reactions processes. They include proton coupled electron transfer, hydrogen atom transfer, and proton transfer mechanisms, and our kinetic study shows a quite good agreement of the behavior of the rate constant with respect to the temperature and to the pressure with the experimental results from the literature. The addition of a single water molecule results in a much more complex potential energy surface although the different elementary reactions found have the same electronic features that the naked reaction. Two transition states are stabilized by the effect of a hydrogen bond interaction originated by the water molecule,...
72 citations
TL;DR: The Fisher information measure results support the concept of a continuum of transient of Zewail and Polanyi for the transition state rather than a single state, which is also in agreement with reaction force analyses.
Abstract: The utility of the Fisher information measure is analyzed to detect the transition state, the stationary points of a chemical reaction, and the bond breaking/forming regions of elementary reactions such as the simplest hydrogen abstraction and the identity SN2 exchange ones. This is performed by following the intrinsic reaction path calculated at the MP2 and QCISD(T) levels of theory with a 6-311++G(3df, 2p) basis set. Selected descriptors of both position and momentum space densities are utilized to support the observations, such as the molecular electrostatic potential (MEP), the hardness, the dipole moment, along with geometrical parameters. Our results support the concept of a continuum of transient of Zewail and Polanyi for the transition state rather than a single state, which is also in agreement with reaction force analyses.
57 citations
TL;DR: In this article, a combination of experimental and quantum mechanical methods were used to elucidate the effect of water solvent on the reaction rate and on the subsequent formation of the primary intermediates.
Abstract: This study has the goal of determining the most probable reaction path and the product distribution for the photo-oxidative degradation of toluene in aqueous media. A combination of experimental and quantum mechanical methods were used to elucidate the effect of water solvent on the reaction rate and on the subsequent formation of the primary intermediates. In the experimental part of the study, the formation yields of hydroxylated intermediates and of benzaldehyde were measured by HPLC, in the presence of nitrate under UVB irradiation as the OH source. Modeling of the reaction paths was performed with density functional theory (DFT) calculations, to investigate the most plausible mechanism for the initial OH attack and to determine the identities of the primary intermediates. Rate coefficients for all the reaction paths were computed by the Transition State Theory (TST) to obtain the product distribution. The effect of solvent water was investigated by using COSMO as the solvation model. The experimental results combined with DFT calculations indicate that ortho -addition to finally give o -cresol is the dominant reaction path for gas and aqueous media. The presence of a dielectric medium such as water has a stabilizing effect that decreases the overall energy for this mechanism. Finally, the significance for surface waters of the reaction between toluene and OH was studied by use of a recently developed photochemical model that foresees the lifetime of a compound upon reaction with OH, as a function of the reaction rate constant, the chemical composition of the surface water layer, and the water column depth.
53 citations
TL;DR: In this paper, an activity relation for the heterogeneous catalytic oxidation of HCl (the Deacon Process) over rutile transition-metal oxide catalysts was established by combining density functional theory calculations (DFT) with microkinetic modeling.
Abstract: We establish an activity relation for the heterogeneous catalytic oxidation of HCl (the Deacon Process) over rutile transition-metal oxide catalysts by combining density functional theory calculations (DFT) with microkinetic modeling. Linear energy relations for the elementary reaction steps are obtained from the DFT calculations and used to establish a one-dimensional descriptor for the catalytic activity. The descriptor employed here is the dissociative chemisorption energy of oxygen. It is found that the commonly employed RuO 2 catalyst is close to optimal, but that there could still be room for improvements. The analysis suggests that oxide surfaces which offer slightly weaker bonding of oxygen should exhibit a superior activity to that of Ru0 2 .
52 citations
TL;DR: In this paper, a detailed one-dimensional transient elementary reaction kinetic model of an anode-supported solid oxide fuel cell (SOFC) operating with syngas based on button cell geometry is developed.
TL;DR: In this article, the intrinsic kinetics of CH4 steam reforming developed over Rh/Ce0.6Zr0.4O2 catalyst in an integral fixed bed reactor with no mass and heat transport limitations and far from equilibrium conditions are guaranteed.
Abstract: This paper presents the intrinsic kinetics of CH4 steam reforming developed over Rh/Ce0.6Zr0.4O2 catalyst in a relatively low temperature range of 475–575 °C and 1.5 bar pressure. The kinetic experiments are conducted in an integral fixed bed reactor with no mass and heat transport limitations and far from equilibrium conditions. Therefore, intrinsic reaction rate measurements are guaranteed. The model is based upon two-site adsorption surface hypothesis, and 14 elementary reaction steps are postulated. CH4 is dissociatively adsorbed onto the Rh active sites, and steam is dissociatively adsorbed on the ceria support active sites as an influential adsorption surface shown in the model. Therefore, no competition between CH4 and steam in adsorbing on the same site surface is observed. The kinetic rate expressions are derived according to the Langmuir–Hinshelwood formalism. The redox surface reactions between the carbon containing species and the lattice oxygen leading to CO and CO2 formation are considered as rate determining steps. The inhibitory effect of gaseous product species is also reflected in the kinetics. The model is found to be statistically accurate and thermodynamically consistent. The estimated activation energies and adsorption enthalpies are in agreement with literature for CH4 steam reforming reaction over Rh. The reaction kinetics is validated by steam reforming experiments at 550 °C and 1.5 bar using 150 mg catalyst in a diluted bed of 5 cm length. The kinetic model is implemented in a one-dimensional pseudo-homogenous plug flow reactor model and thus simulated at identical experimental conditions. The simulation results are in excellent agreement with the experimental values.
TL;DR: In this paper, a review of negative ion reactions with neutral molecules in the gas phase is presented, where rate coefficients and cross-sections for anion-molecule reactions are measured and interpreted to yield information on the underlying dynamics.
Abstract: This review discusses the dynamics of negative ion reactions with neutral molecules in the gas phase. Most anion–molecule reactions proceed via a qualitatively different interaction potential than cationic or neutral reactions. It has been and still is the goal of many experiments to understand these reaction dynamics and the different reaction mechanisms they lead to. We will show how rate coefficients and cross-sections for anion–molecule reactions are measured and interpreted to yield information on the underlying dynamics. We will also present more detailed approaches that study either the transient reaction complex or the energy- and angle-resolved scattering of negative ions with neutral molecules. With the help of these different techniques many aspects of anion–molecule reaction dynamics have been unravelled in the last few years. However, we are still far from a complete understanding of the complex molecular interplay that is at work during a negative ion reaction.
TL;DR: In this article, the detailed reaction mechanism of a C6-C2 dimeric non-phenolic β-O-4 type lignin model compound, 2-(2-methoxyphenoxy)-1-(3,4-dimethylene)ethanol (V′G), was examined under acidolysis conditions (mainly 0.2 mol/l HBr in 82% aqueous 1, 4-dioxane at 85°C), and was suggested to be as follows.
Abstract: The detailed reaction mechanism of a C6-C2 dimeric non-phenolic β-O-4 type lignin model compound, 2-(2-methoxyphenoxy)-1-(3,4-dimethoxyphenyl)ethanol (V′G), was examined under acidolysis conditions (mainly 0.2 mol/l HBr in 82% aqueous 1,4-dioxane at 85°C), and was suggested to be as follows. The initial elementary reaction step is protonation of the α-hydroxyl group, followed by the release of water to afford a benzyl cation intermediate (BC′). The latter step is relatively slow but reversible. The β-proton abstraction from BC′ by the solvents affords an enol ether compound, 1-(2-methoxyphenoxy)-2-(3,4-dimethoxyphenyl)ethene (EE′). This step is practically irreversible, and is the rate-determining step in the disappearance of V′G. The stereoisomers of EE′ are rapidly converted into each other, accompanied by protonation of the double bond. Complete protonation affords a β-oxymethylene cation intermediate (OMC′), which is also formed via hydride transfer from the β- to α-position of BC′ as a minor...
TL;DR: In this paper, the reaction electronic flux, a new descriptor proposed to characterize the electronic activity that takes place during a chemical reaction, is used to elucidate the mechanism of the Schiff's base formation in the Maillard reaction.
Abstract: Within the framework defined by the reaction force analysis, the reaction electronic flux, a new descriptor proposed to characterize the electronic activity that takes place during a chemical reaction, is used to elucidate the mechanism of the Schiff’s base formation in the Maillard reaction The electronic activity is identified as being due to electronic polarization and transfer effects that show up at specific regions along the reaction coordinate It is found that the Schiff base formation step of the Maillard reaction proceeds through consecutive electron polarization and transfer processes, the energy involved at each step of the reaction is quantified through the reaction works obtained from the reaction force profile
TL;DR: In this paper, the authors used density functional theory to investigate the reaction pathway of oxygen reduction/water splitting at a tetrahedral Pt4 cluster, where four extra water molecules were added to account for the effect of water in mediating elementary surface processes.
Abstract: We used density functional theory to investigate the reaction pathway of oxygen reduction/water splitting at a tetrahedral Pt4 cluster. Four extra water molecules were included to account for the effect of water in mediating elementary surface processes. We propose a 6-step reaction sequence that includes a proton transfer between neighbouring active sites. Thermochemical considerations and the nudged elastic band method were employed to calculate reaction and activation energies for the elementary reaction steps. We generated the free energy diagram along the reaction path for various applied potentials. This plot provides vital information on the stability of intermediates and the rate determining processes in oxygen reduction and water splitting. Results suggest that removal of the reaction product, viz. molecular oxygen or water, is an energetically strongly hindered step in either direction.
TL;DR: The chemical reactivity of atomic boron, B(Pj), with inorganic and organic molecules is a fascinating subject of research from the experimental1-35 and theoretical viewpoints and is relevant to material sciences such as borons assisted nanotube growth and the synthesis of novel organo-boron molecules.
Abstract: The chemical reactivity of atomic boron, B(Pj), with inorganic and organic molecules is a fascinating subject of research from the experimental1-35 and theoretical viewpoints.29,30,36-46 Atomic boron resides in the same row as carbon, nitrogen, and oxygen.47 Although the reaction dynamics and kinetics of the latter elements (C, N, O) have been studied in depth,48-53 an investigation of elementary reactions of boron atoms has remained sketchy so far. These studies are of significant interest due to the position of boron between metals and nonmetals. Apart from the fundamental importance of the elementary boron reactions,54,55 bimolecular collisions involving atomic boron are relevant to material sciences56 such as boron assisted nanotube growth57 and the production of boron-doped diamond thin films,58,59 chemical vapor deposition (CVD), high temperature combustion processes,60,61 interstellar chemistry,62 and the synthesis of novel organo-boron molecules.39-41,45,46,63-69
TL;DR: In this article, the authors used temperature-programmed desorption (TPD), molecular beam reactive scattering (MBRS), and Auger electron spectroscopy (AES) to evaluate surface oxide chemistry.
Abstract: Because of gold's resistance to oxidation and corrosion, historically chemists have considered this metal inert. However, decades ago, researchers discovered that highly dispersed gold particles on metal oxides are highly chemically active, particularly in low-temperature CO oxidations. These seminal findings spurred considerable interest in investigations and applications of gold-based materials. Since the discovery of gold's chemical activity at the nanoscale, researchers found that bulk gold also has interesting catalytic properties. Thus, it is important to understand and contrast the intrinsic chemical properties of bulk gold with those of nanoparticle Au. Despite numerous studies, the structure and active site of supported Au nanoclusters and the active oxygen species remain elusive, and model studies under well-controlled conditions could help identify these species. The {111} facet has the lowest surface energy and is the most stable and prevalent configuration of most supported gold nanoparticles. Therefore, a molecular-level understanding of the physical properties and surface chemistry of Au(111) could provide mechanistic details regarding the nature of Au-based catalysts and lead to improved catalytic processes. This Account focuses on our current understanding of oxidative chemistry on well-defined gold single crystals, predominantly from recent investigations on Au(111) that we have performed using modern surface science techniques. Our model system strategy allows us to control reaction conditions, which assists in the identification of reaction intermediates, the determination of the elementary reaction steps, and the evaluation of reaction energetics for rate-limiting steps. We have employed temperature-programmed desorption (TPD), molecular beam reactive scattering (MBRS), and Auger electron spectroscopy (AES) to evaluate surface oxidative chemistry. In some cases, we have combined these results with density functional theory (DFT) calculations. By controlling the reaction parameters that determine product selectivity, we have examined the chemical properties of bulk gold. Based on our investigations, the surface-bound oxygen atoms are metastable at low temperature. We also demonstrate that the oxygen atoms and formed hydroxyls are responsible for some of the distinct chemical behavior of gold and participate in surface reactions either as a Bronsted base or a nucleophilic base. We observe similar reaction patterns on gold surfaces to those on copper and silver surfaces, suggesting that the acid-base reactions that have been observed on copper and silver may also occur on gold. Our model chemical studies on gold surfaces have provided intrinsic fundamental insights into high surface area gold-based catalysts and the origin of the reactive oxygen species.
TL;DR: In this paper, a non-empirical detailed mechanism of the high and low-temperature oxidation and combustion of normal paraffin hydrocarbons is presented. But the mechanism has two specific features: (1) it does not include double oxygen addition (first to the peroxide radical, and then to its isomeric form).
Abstract: Recently, detailed kinetic mechanisms of the oxidation and combustion of higher hydrocarbons, composed of hundreds of components and thousands of elementary reactions, have been proposed. Despite the undoubtful advantages of such detailed mechanisms, their application to simulations of turbulent combustion and gas dynamic phenomena is difficult because of their complexity. At the same time, to some extent limited, they cannot be considered exhaustive. This work applies previously proposed algorithm for constructing an optimal mechanism of the high- and low-temperature oxidation and combustion of normal paraffin hydrocarbons, which takes into account the main processes determining the reaction rate and the formation of key intermediates and final products. The mechanism has the status of a nonempirical detailed mechanism, since all the constituent elementary reactions have a kinetic substantiation. The mechanism has two specific features: (1) it does not include reactions of so-called double oxygen addition (first to the peroxide radical, and then to its isomeric form), i.e., the first addition turns out to be sufficient; (2) it does not include isomeric compounds and their derivatives as intermediates, since this oxidation pathway is slower than the oxidation of molecules and radicals with normal structure. Application of the algorithm makes it possible to compile a compact mechanism, which is important for modeling chemical processes involving paraffin hydrocarbons C n with large n. Previously, based on this algorithm, compact mechanisms of the oxidation and combustion of propane, n-butane, n-pentane, n-hexane, n-heptane, n-octane, n-nonane, and n-decane have been constructed. In this work, we constructed a nonempirical detailed mechanism of the oxidation and combustion of hydrocarbons from n-undecane to n-hexadecane. The most important feature of the new mechanism is its staged nature, which manifests itself through the emergence of cool and blue flames during low-temperature autoignition. The calculation results are compared with experimental data.
TL;DR: In this article, the authors discuss the activation of the catalyst from the following points; activation by restructuring, activation by forming active sites and reactive intermediates, site dependent turnover frequency, and role of promoting materials.
TL;DR: In this paper, density functional theory calculations were carried out in a study of the oxidation of benzene to phenol by N2O on a model (FeO)1+-ZSM-5 cluster: the [(SiH3)4AlO4(FeO)] cluster.
Abstract: Density functional theory calculations were carried out in a study of the oxidation of benzene to phenol by N2O on a model (FeO)1+-ZSM-5 cluster: the [(SiH3)4AlO4(FeO)] cluster. This cluster models the reactivity of Fe3+ oxidic clusters. Results are to be compared with an earlier study (J. Phys. Chem. C 2009, 113, 15307) on a model Fe2+-ZSM-5 cluster. The true activation energies for the elementary reaction step in which phenol is produced appear to be comparable. The major difference between the two systems appears to be the relative stabilities of the intermediate phenolates. On the Fe3+-containing cationic cluster, this appears to be uniquely stable. This result suggests that the experimentally observed preference of Fe2+ sites over (FeO)1+ on ZSM-5 for benzene oxidation to phenol by N2O is due to the reduced formation of adsorbed phenolate, which is possibly an intermediate for deactivation.
TL;DR: In this paper, it was shown that the final states of reaction are not terribly different in energy from the reactants, and that an exoergic reaction can be completely turned off.
Abstract: exoergicreactioncanbecompletelyturnedoff.Thispossibility is afforded by the fact that, for alkali dimers, the final states of reaction are not terribly different in energy from the reactants. Specifically,weconsidercollisionsofapairofKRbmolecules, prepared in their vibrational ground state (ν1 = ν2 = 0) and particular rotational states n1 and n2. These molecules are, in general, subject to two kinds of reactions: the formation of trimers via
TL;DR: Through systematic calculations for the reaction mechanism of methanol decomposition on five different Pt surfaces, it is found that such a reaction shows the same reaction mechanism on these Pt‐based model catalysts, that is, the final products are all H (Hads) and CO (COads) via OH bond breaking in meethanol and CH bond scission in methoxy.
Abstract: The decomposition mechanisms of methanol on five different Pt surfaces, the flat surface of Pt(111), Pt-defect, Pt-step, Pt(110)(1 × 1), and Pt(110)(2 × 1), have been studied with the DFT-GGA method using the repeated slab model. The adsorption energies under the most stable configuration of the possible species and the activation energy barriers of the possible elementary reactions involved are obtained in this work. Through systematic calculations for the reaction mechanism of methanol decomposition on these surfaces, we found that such a reaction shows the same reaction mechanism on these Pt-based model catalysts, that is, the final products are all H (Hads) and CO (COads) via OH bond breaking in methanol and CH bond scission in methoxy. These results are in general agreement with the previous experimental observations. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010.
TL;DR: In this article, the authors investigated the chelotropic addition reaction with different levels of theory (B3LYP, CASSCF, CCSD(T), G2M) and different basis sets.
Abstract: The chelotropic addition reaction (1): singlet vinylidene + acetylene → methylenecyclopropene (MCP), was investigated using different levels of theory (B3LYP, CASSCF, CCSD(T), G2M) and different basis sets (6-31G(d,p), 6-311G(d,p), 6-311++G(3df,3pd), cc-pVTZ). The concerted reaction is spontaneous at room temperature (activation enthalpy of 3 kcal mol−1) and strongly exothermic (ΔE = −64 kcal mol−1; ΔH(298) = −59 kcal mol−1). Analysis of the reaction mechanism with the help of the Unified Reaction Valley approach reveals a complicated sequence of structural and electronic changes, which can be best described by partitioning the mechanism into seven phases: (1) van der Waals, (2) electrophilic attack, (3) biradical, (4) allene, (5) carbene, (6) ring closure, and (7) MCP formation phase. In the transient regions from one phase to the next, structures are located that possess properties of hidden transition states (TSs) or hidden intermediates, i.e. by variation of the electronic nature or the environment of...
TL;DR: In this paper, the chemical absorption rate of carbon dioxide with diisopropanolamine (DIPA) was measured in such non-aqueous solvents as methanol, ethanol, n-propanol and n-butanol, ethylene glycol, propane glycol and propylene carbonate, and aqueous solvent at 298 k and 101.3 kPa.
Abstract: The chemical absorption rate of carbon dioxide with diisopropanolamine (DIPA) was measured in such non-aqueous solvents as methanol, ethanol, n-propanol, n-butanol, ethylene glycol, propylene glycol, and propylene carbonate, and aqueous solvent at 298 K and 101.3 kPa using a semi-batch stirred tank with a planar of gas–liquid interface. The pseudo-first-order reaction rate constant obtained from the measured rate of absorption was used to obtain the elementary reaction rate constants in complicated reactions represented by zwitterion mechanism and the order of overall reaction of CO 2 with amine. The enhancement factor of carbon dioxide at a low concentration of DIPA was obtained using the reaction rate constants obtained under the condition of a pseudo-first-order, fast reaction regime. Correlation between the elementary reaction rate constant and the solubility parameter of the solvent is presented.
TL;DR: In this article, density functional theory calculations were employed to investigate the dissociative adsorption of molecular H2S on a W(111) surface and the energy minimum of the adsorbed H 2S was identified to bind preferentially at the top site.
Abstract: Density functional theory calculations were employed to investigate the dissociative adsorption of molecular H2S on a W(111) surface. The energy minimum of the adsorbed H2S was identified to bind preferentially at the top site. The adsorption sites of other S moieties (SH and S) were also examined, and they were found predominately at the bridge sites between first and second layers and the bridge sites between second and third layers, respectively. The binding of H2S and its S-containing species is stronger on the W(111) surface than on other metal surfaces, such as Pd, Ni, Cu, Au, Ag, and Ir. The elementary reactions of successive abstraction of H from H2S on the surface were examined. We also extend our study to the oxidation reaction of the adsorbed S by adding gaseous oxygen to the surface, which will react with S and eventually form SO2 and then desorb from the surface. Our results show that the above H2S dissociation and sulfur oxidation reactions do not bear high energy barriers and the overall re...
TL;DR: In this paper, a detailed theoretical study of the proton transfer in the HC(O)SH ⇌ HC(S)OH reaction in the gas phase and catalysed by water is presented.
Abstract: A detailed theoretical study of the proton transfer in the HC(O)SH ⇌ HC(S)OH reaction in the gas phase and catalysed by water is presented. The mechanism is analysed within the framework provided by the reaction force; structural parameters and electronic properties are analysed along the reaction path. A complete description of the electronic activity that takes place along the reaction coordinate emerges when analysing the reaction electronic flux, thus allowing one to make a clear distinction between the two reaction mechanisms. Results show that the barrier height of the water-catalysed proton transfer reaction is about a third of that for the intramolecular reaction, thus emphasising the importance of the catalytic effect of H2O.
TL;DR: In this article, the O-atom dynamics behind reflected shock waves in highly argon diluted silane-hydrogen-nitrous oxide mixtures in the temperature range 1606-2528 K and at total pressures from 234 to 584kPa were studied.
TL;DR: The gas‐phase reaction pathways in preparing pyrolytic carbon with propene pyroglysis have been investigated in detail with a total number of 110 transition states and 50 intermediates and found that the most favorable paths are mainly in the radical attacking chain reactions.
Abstract: The gas-phase reaction pathways in preparing pyrolytic carbon with propene pyrolysis have been investigated in detail with a total number of 110 transition states and 50 intermediates. The structure of the species was determined with density functional theory at B3PW91/6-311G(d,p) level. The transition states and their linked intermediates were confirmed with frequency and the intrinsic reaction coordinates analyses. The elementary reactions were explored in the pathways of both direct and the radical attacking decompositions. The energy barriers and the reaction energies were determined with accurate model chemistry method at G3(MP2) level after an examination of the nondynamic electronic correlations. The heat capacities and entropies were obtained with statistical thermodynamics. The Gibbs free energies at 298.15 K for all the reaction steps were reported. Those at any temperature can be developed with classical thermodynamics by using the fitted (as a function of temperature) heat capacities. It was found that the most favorable paths are mainly in the radical attacking chain reactions. The chain was proposed with 26 reaction steps including two steps of the initialization of the chain to produce H and CH(3) radicals. For a typical temperature (1200 K) adopted in the experiments, the highest energy barriers were found in the production of C(3) to be 203.4 and 193.7 kJ/mol. The highest energy barriers for the production of C(2) and C were found 174.1 and 181.4 kJ/mol, respectively. These results are comparable with the most recent experimental observation of the apparent activation energy 201.9 +/- 0.6 or 137 +/- 25 kJ/mol.
TL;DR: The results show that the lifetime of the HSO(5) intermediate under atmospheric conditions is too short for a bimolecular reaction with water to become important, ruling out this reaction pathway as a relevant source for aerosols.
Abstract: A detailed theoretical analysis of the HOSO2 + O2 reaction is performed, paying special attention to the kinetics of the intermediate HSO5 radical. The possible formation of the monohydrated adduct, HSO5·H2O, in the presence of water vapor is examined. For the binding energy of the most stable isomer at T = 0 K, a value of D0(HOSO4–H2O) = 51.7 kJ mol−1 was obtained at the CCSD(T)/CBS level of theory; other energies were adopted from a recently published high-level quantum chemical study of our laboratory. Molecular geometries and vibrational frequencies of the reactants, intermediates, and products were obtained from B3LYP/cc-pVTZ calculations. Rate coefficients and lifetimes of the HSO5 intermediate were calculated by solving a master equation with specific rate coefficients from statistical rate theory. The master equation is extended by a bimolecular sink term, which accounts for the HSO5 + H2O reaction. The relation between thermal and chemical activation in this reaction system is examined. The results show that the lifetime of the HSO5 intermediate under atmospheric conditions is too short for a bimolecular reaction with water to become important. Relative yields of HSO5·H2O well below 1% were obtained, ruling out this reaction pathway as a relevant source for aerosols.