Elementary reaction

About: Elementary reaction is a research topic. Over the lifetime, 2972 publications have been published within this topic receiving 76110 citations.

A Theoretical Investigation of Mixing Effects in the Selective Reduction of Nitric Oxide by Ammonia

Abstract: The macroscopic transport equations governing the axisymmetric flow, mixing, and reaction of NH3 with high temperature combustion products containing NO and O2 have been solved numerically and compared to published experimental data for the same geometry. The elementary chemical kinetic mechanism used was based on an earlier model developed from plug flow experimental data. The results show generally good agreement between the calculations and experimental data. Spatial distributions of the contributions of individual elementary reactions to the overall reaction and of the contribution of diffusion processes and reaction processes to the structure of the reaction zone were evaluated. Additional model calculations were used to evaluate the effect of the rate of mixing of NH3 with combustion products on NO reduction efficiency. Finite rates of mixing were found to have little effect on the temperature dependence of the NO reduction. However, at high temperature the oxidation to form NO was found to...

Unimolecular decomposition of large organic radicals with low reaction thresholds: Decomposition and reversible isomerization of n-pentyl radicals

Abstract: The decomposition kinetics of n-pentyl radicals in the high temperature regime where steady state distributions are not achieved and reversible isomerization to decomposing 2-pentyl radicals is of importance has been analyzed through the solution of the time-dependent master equation. The reactions are characterized by low activation thresholds and lead to large rate constants that vary with time. Particular attention is paid to branching ratios for direct decomposition of the n-pentyl radical and the decomposition that follows reversible isomerization to the 2-pentyl species. The behavior of the system under a variety of conditions is described and the use of branching ratios as a possible means of characterizing the reactions in a manner that is compatible with present methods for employing kinetic data for simulating complex chemical phenomenon is considered. At higher temperatures, rate constants and branching ratios collapse to limiting values. The combination of limiting and the onset of steady state behavior complicates the situation at lower temperatures. The overall behavior of such systems is highly dependent on the magnitude of the barrier to isomerization. The extent of departures from the high pressure-branching ratios are defined.

Addition-Elimination or Nucleophilic Substitution? Understanding the Energy Profiles for the Reaction of Chalcogenolates with Dichalcogenides.

Abstract: We have quantum chemically explored the mechanism of the substitution reaction between CH3X(-) and the homo- and heterodichalcogenides CH3X'X″CH3 (X, X', X″ = S, Se, Te) using relativistic density functional theory at ZORA-OLYP/TZ2P and COSMO for simulating the effect of aqueous solvation. In the gas phase, all substitution reactions proceed via a triple-well addition-elimination mechanism that involves a stable three-center intermediate. Aqueous solvation, in some cases, switches the character of the mechanism to double-well SN2 in which the stable three-center intermediate has become a labile transition state. We rationalize reactivity trends and some puzzling aspects of these elementary reactions, in particular, vanishing activation energies and ghost three-center intermediates, using the activation strain model (ASM).

Influence of coke formation on the conversion of hydrocarbons I. Alkanes on a USY-zeolite.

Abstract: The conversion of n -hexane and 2,2,4 triMe-pentane was studied at 723 K on a USY-zeolite (Si/Al: frame=30; bulk=2.7) in an electrobalance reactor with external recirculation. The influence of the coke content on the reaction paths involved in the conversion of paraffinic model components was evaluated. Coke formation from propylene and i-butene, the main olefinic products formed during the conversion of the two paraffinic model components, was investigated. Under the conditions used, an increase in the molar H/C ratio of the products as a function of coke yield can be observed due to hydride transfer reactions with coke. Coke molecules cannot be considered as being inert with respect to the cracking reactions and their formation leads to the occurrence of reactions that can strongly influence the catalyst performance. In particular, the potential of coke molecules to form highly delocalized carbenium ions and their ability to act as hydride donor towards surface carbenium ions provides reaction paths to paraffinic reaction products. The effect of coke is not identical for all the elementary reactions involved in the conversion of the paraffinic model components.