Elementary reaction

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

Study of Hydrogen Peroxide Reactions on Manganese Oxides as a Tool To Decode the Oxygen Reduction Reaction Mechanism

Abstract: Hydrogen peroxide has been detected as a reaction intermediate in the electrochemical oxygen reduction reaction (ORR) on transition-metal oxides and other electrode materials. In this work, we studied the electrocatalytic and catalytic reactions of hydrogen peroxide on a set of Mn oxides, Mn2O3, MnOOH, LaMnO3, MnO2, and Mn3O4, that adopt different crystal structures to shed light on the mechanism of the ORR on these materials. We then combined experiment with kinetic modeling with the objective to correlate the differences in the ORR activity to the kinetics of the elementary reaction steps, and we uncovered the importance of structural and compositional factors in the catalytic activity of the Mn oxides. We concluded that the exceptional activity of Mn2O3 in the ORR is due to its high catalytic activity both in the reduction of oxygen to hydrogen peroxide and in the decomposition of the latter, and furthermore, we proposed a tentative link between crystal structure and reactivity.

Modelling of the pyrolysis of tert-butylbenzene in supercritical water

Abstract: The thermal decomposition of tert-butylbenzene (TBB) in supercritical water (SCW) was investigated. From experimental data of the overall rate and formation of 30 products (more than 50 experiments; T=500–540°C, p=5–25 MPa, five different environments including SCW) and assuming a free radical mechanism, a high pressure reaction model was developed on the basis of a chemical mechanism. The model, which ultimately consists of 171 elementary reactions (ER), and the chemical mechanism, which identifies the reaction paths for the formation of the main products, were evaluated in an interactive process. For the calculation of the entire set of 342 coefficients of the model, an optimisation method was applied to solve the ‘inverse problem’, using: (1) as initial values all available kinetic data at normal pressure; (2) best estimates for the remaining coefficients, considering limits for the different types of ER; (3) ‘punishment functions’, which force the parameters to vary only within certain limits. Model simulations show reasonable agreement with experimental data. The main difference of the reaction in SCW and at low pressure in an inert environment is the strong inhibition of the overall reaction by a factor of 1000. Simulations indicate that mainly radical decomposition reactions are responsible for this effect. It is assumed that a cage effect of water molecules reduces the reactivity of these species. Also, the pressure dependence of the different types of ER is discussed. The product spectra of the reaction in SCW has a greater variety than at 0.1 MPa and below. Simulations show that this is caused by a promotion of substitution reactions and the suppression of decomposition reactions at SCW conditions. Thus, the difference of the decomposition of TBB in SCW regarding the product spectra to the reaction at normal conditions is mainly a pressure effect. These results seem to be of general significance for free radical reactions. They are in agreement with previous studies of the pyrolysis of ethyl-benzene in SCW as well as in inert conditions at atmospheric pressure.

Non‐Markovian theory of activated rate processes. VI. Unimolecular reactions in condensed phases

Abstract: The non‐Markovian theory of activated rate processes developed by Carmeli and Nitzan is applied to investigate unimolecular reactions in condensed phases with particular emphasis on the molecular size (number of internal degrees of freedom) dependence of the effect of solvent friction on the reaction rate. The model consists of one reaction coordinate coupled to n−1 nonreactive modes. The molecule solvent interaction is treated within the context of the generalized Langevin equation. The reaction dynamics may be roughly described as two consecutive processes: the well (energy diffusion) dynamics where it is assumed that fast intramolecular vibrational relaxation and slower overall molecular energy diffusion dominate the process, and the barrier dynamics where it is assumed that the motion along the reaction coordinate is only weakly coupled to the nonreactive modes. This model leads to a result for the reaction rate which, as in the one‐dimensional case, is obtained as the inverse of the sum of two times:...

Automated derivation of reaction rules for the EROS 6.0 system for reaction prediction

Abstract: The purpose of the EROS 6.0 system is to predict the products of chemical reactions and to model reaction mechanisms. This is accomplished by elementary reaction steps that are selected through the rules that constitute the knowledge base of the EROS 6.0 system. These rules are derived by methods of machine learning. The learning process is based on reaction in data bases. An overview of the EROS 6.0 system is given and the structure of the knowledge as well as the generation of reaction rules are described.

A theoretical study on the insertion of ethylene into the cobalt-hydrogen bond

Abstract: Two of the important elementary reaction steps in the hydroformylation process catalyzed by HCo(CO) 3 have been investigated by theoretical calculations based on the density functional theory. The first step involved the formation of the π complex HCo(CO) 3 (η 2 -C 2 H 4 (I) from HCo(CO) 3 and C 2 H 4 . A total of three stable conformations of I were considered. All had a trigonal-bipyramidal structure