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Jean-michel Savéant - One of the best experts on this subject based on the ideXlab platform.

  • Reorganization energy and pre-Exponential Factor from temperature-dependent experiments in electron transfer reactions. A typical example: the reduction of tert-nitrobutane
    Physical chemistry chemical physics : PCCP, 2011
    Co-Authors: Cyrille Costentin, Cyril Louault, Marc Robert, Vincent Rogé, Jean-michel Savéant
    Abstract:

    The electrochemical one-electron reduction of tert-nitrobutane in N,N′-dimethylformamide is a typical reaction, which has been shown to follow the quadratic model of outersphere electron transfer. The variation of the standard rate constant with temperature allows a separate determination of the reorganization energy and of the pre-Exponential Factor. The value found for the former is in agreement with independent estimates of the solvent and intramolecular reorganization energies. The value of the latter, significantly larger than the collision frequency, implies that the reaction starts to take place before close contact with the electrode surface.

  • h bond relays in proton coupled electron transfers oxidation of a phenol concerted with proton transport to a distal base through an oh relay
    Physical Chemistry Chemical Physics, 2011
    Co-Authors: Cyrille Costentin, Marc Robert, Jean-michel Savéant, Cedric Tard
    Abstract:

    Four molecules comprising a phenol moiety and a distal pyridine base connected by an intermediary H-bonding and an H-bonded alcohol group have been synthesized and their electrochemistry has been investigated by means of cyclic voltammetry. The molecules differ by the substituent at the alcohol functional carbon and by methyl groups on the pyridine. The reaction follows a concerted proton–electron transfer pathway as confirmed by the observation of a significant H/D kinetic isotope effect in all four cases. The standard rate constants characterizing each of the four compounds are analyzed in terms of reorganization energy and pre-Exponential Factor. Intramolecular and solvent reorganization energies appear as practically constant in the series, in which a previously investigated aminophenol is included, whereas significantly different pre-Exponential Factors are observed. That the latter, which is a measure of the efficiency of proton tunneling concerted with electron transfer, be substantially smaller with the H-bond relay molecules than with the aminophenol is related to the fact that two protons are moved in the first case instead of one in the second. Within the H-bond relay molecules, the pre-Exponential Factor varies with the substituent present at the alcohol functional carbon in the order CF3 > H > CH3, presumably as the result of a fine tuning of the balance between the H-bond accepting and H-bond donating properties of the central OH group. The kinetic H/D kinetic isotope effect increases accordingly in the same order.

N. S. Saxena - One of the best experts on this subject based on the ideXlab platform.

Thallada Bhaskar - One of the best experts on this subject based on the ideXlab platform.

  • thermal decomposition kinetics of sorghum straw via thermogravimetric analysis
    Bioresource Technology, 2017
    Co-Authors: Vaibhav Dhyani, Jitendra Kumar, Thallada Bhaskar
    Abstract:

    Abstract The thermal decomposition of sorghum straw was investigated by non-isothermal thermogravimetric analysis, where the determination of kinetic triplet (activation energy, pre-Exponential Factor, and reaction model), was the key objective. The activation energy was determined using different isoconversional methods: Friedman, Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), Starink, Iterative method of Chai & Chen, Vyazovkin AIC method, and Li & Tang equation. The pre-Exponential Factor was calculated using Kissinger’s equation; while the reaction model was predicted by comparison of z-master plot obtained from experimental values with the theoretical plots. The values of activation energy obtained from isoconversional methods were further used for evaluation of thermodynamic parameters, enthalpy, entropy and Gibbs free energy. Results showed three zones of pyrolysis having average activation energy values of 151.21 kJ/mol, 116.15 kJ/mol, and 136.65 kJ/mol respectively. The data was well fitting with two-dimension ‘Valensi’ model for conversion values from 0 to 0.4 with a coefficient of determination (R 2 ) value of 0.988, and with third order reaction model for values from 0.4 to 0.9 with an R 2 value of 0.843.

Behrooz Vahidi - One of the best experts on this subject based on the ideXlab platform.

  • Estimation of power transformer remaining life from activation energy and pre-Exponential Factor in the Arrhenius equation
    Cellulose, 2019
    Co-Authors: Ashkan Teymouri, Behrooz Vahidi
    Abstract:

    In 1936, Ekenstam derived an equation for cellulose ageing kinetic that linked DP to life and reaction rate. Later, Arrhenius obtained an equation that linked reaction rate to temperature, activation energy and coefficient A. Then, using these equations, the transformer life estimation has become possible. Activation energy is usually considered a constant value, but coefficient A depends on moisture and oxygen concentrations inside the transformer. So far, constant values for these Factors have been used, but the transformer condition is constantly changing. In this paper, a new method is proposed for calculating activation energy and coefficient A for any transformer at any time according to the transformer condition for precise life estimation. Finally, for ten transformers with available data, life estimation is performed using the proposed method at the startup time of the transformers. Then, calculation results are compared with the transformer actual life to ensure the accuracy of the proposed method.Graphic abstract

A Simone - One of the best experts on this subject based on the ideXlab platform.

  • effect of water content on the thermal degradation of amorphous polyamide 6 6 a collective variable driven hyperdynamics study
    Polymer Degradation and Stability, 2017
    Co-Authors: Behrouz Arash, Barend J Thijsse, Alessandro Pecenko, A Simone
    Abstract:

    Abstract Thermal degradation under wet conditions is considered as an important aging mechanism in polyamide 6,6 (PA 6,6). The effect of water on thermal degradation of amorphous PA 6,6 is investigated at relatively low temperatures, varying from 1000 to 2000 K, using reactive force field molecular dynamics (MD) and collective variable-driven hyperdynamics simulations. The simulation of the related long-term chemical reactions is made possible thanks to the self-learning accelerated MD concept of hyperdynamics in combination with the corresponding accurate reproduction of the correct dynamics, consistent with unbiased MD simulations. The kinetics of cleavage reactions of the amide bonds in the backbone of the polymer chains, responsible for the thermal degradation of the polymer, is studied, and the influence of water content on the activation energy and pre-Exponential Factor of the cleavage reactions is explored. The results show that activation energy and pre-Exponential Factor are in agreement with experimental data. The proposed simulation framework not only estimates kinetic properties of thermal degradation that are consistent with experimental observations but also provides a predictive tool for studying long-term thermal degradation of PA 6,6.