Complexes of Li, Na and Mg with 2D Allotropies of Second and Third Period. A Theoretical Study

Complexes of Li, Na and Mg with graphene, silicene, phosphorene nanoflakes (NFs) and their 2D allotropies have been studied at dispersion corrected TPSS/def-TZVP level of theory. The energy partition analysis of the complexes revealed that for most of the complexes exchange and correlation energies represent dominant contributions to the binding with strong charge transfer from metal atom to a NF. The exceptions are Mg complexes of graphene and phosphorene NFs where binding is due to dispersion and correlation terms. This difference is also reflected in large Mg-NF distances suggesting weak intermolecular interactions in these complexes. The calculated activation energies for metal hopping are easily achievable at room temperatures for carbon and silicon allotropies. However, they are significantly higher for phosphorus allotropies reaching almost 18 kcal/mol. There is a reasonably good correlation between the activation energies for hopping and binding energies for graphene, silicene and phosphorene NFs. Such correlation is not observed however for graphene, silicene and phosphorene 2D allotropies

Studying on the Addition Reaction Mechanism of Ethylene and Butadiene Based on Density Functional Theory

According to the first principle calculation, the addition reaction mechanism of ethylene and butadiene is determined. The reactant, transition state (TS) and product of this addition reaction are confirmed by optimization calculation and frequency analysis. To verify the correctness of the reaction process, we also calculated the reaction path. Result demonstrates that the addition reaction of ethylene and butadiene is an exothermic reaction. Charge transfer is used to explain this novel reaction. The activation energy of the addition reaction of ethylene and butadiene is 0.83 eV, and the heat release of the whole reaction is 2.01 eV. The molecular structure, charge distribution and energy of butadiene and ethylene are investigated at the molecular level. The calculated activation energy is helpful for understanding the cyclic addition reaction of butadiene and ethylene, providing theoretical guidance for experiments and deepening people's understanding of this reaction.

Calculations of activation energy and frequency factors for corn leafs pyrolysis using excel solver: new concept

Thermal degradations of biomass corn leaves were studied for kinetic modeling. Thermogravimetric-differential analyzer runs at 5, 10, 20, and 30 °C min−1 heating rates were employed. Apparent activation energy and frequency factor values were calculated for first-order kinetics using several procedures. The procedure of Coats and Redfern showed 28.89 to 31.78 kJ mol−1 apparent activation energy and 15.5 to 157.12 min−1 frequency factor, respectively. Calculation of the apparent activation energy and frequency factor using Kissinger–Akahira–Sunose procedure gave 229.9–364.2 kJ/mol and 8.567 × 1023 and 1.13 × 1031 (min−1), respectively as the conversion increased from 0.1 to 0.9. The newly introduced excel solver procedure indicates a distribution activation energy over the entire range of conversion. For first-order reaction kinetics, the calculated apparent activation energy magnitudes ranged between 5.0 kJ mol−1 with frequency factor equals to 0.239 and 196.2 kJ mol−1 with frequency factor 2.89 × 1012 in the studied range. The low or high magnitudes of the calculated activation energy are not associated with a particular value of the conversion. The calculated apparent activation energies are related to the direct solution of the simultaneous equations that constitute the basis of the excel solver.

Thermal and Mechanical Characteristics of Okra (Abelmoschus esculentus) Fibers Obtained via Water- and Dew-Retting

In this research, fibers were extracted from different parts of the okra plant (Abelmoschus esculentus) via water- and dew-retting methods. The fibers were subjected to physical and thermal analyses. The fibers obtained from the upper part of the okra plant showed higher breaking strength and lower linear density. Fibers obtained via water-retting exhibited higher breaking strength, higher elongation at break rates, and lower linear density values. The paper also presents the results of thermogravimetric analysis of the okra fibers. Tests were carried out in oxygen and inert gas atmospheres. Slight differences were found in the thermal resistance of the tested fibers, which was confirmed by an analysis using the αs-αr methodology. The calculated activation energy showed a widespread range of values.

Thermal Characteristics of Okra (Abelmoschus Esculentus) Fibers Obtained via Water- and Dew-Retting

In this study, fibers were extracted from different parts of the okra plant (Abelmoschus esculentus) via water- and dew-retting methods. The fibers were subjected to physical and thermal analyses. The fibers obtained from the upper part of the okra plant show higher breaking strength and lower linear density. Fibers obtained via water-retting exhibited higher breaking strength, elongation at break rates, and lower linear density values. The paper also presents the results of thermogravimetric analysis of the okra fibers. Tests were carried out in oxygen and inert gas atmospheres. The temperature range of the main thermal decomposition stage was in the 275–400°C for range thermo-oxidation and 300–425°C for pyrolysis investigation. Slight differences were found in the thermal resistances of the tested fibers, which was confirmed by an analysis using the alpha s- alpha r methodology. The calculated activation energy values show a large-spread range.

Study of the Oxygen Evolution Reaction at Strontium Palladium Perovskite Electrocatalyst in Acidic Medium

The catalytic activity of Sr2PdO3, prepared through the sol-gel citrate-combustion method for the oxygen evolution reaction (OER) in a 0.1 M HClO4 solution, was investigated. The electrocatalytic activity of Sr2PdO3 toward OER was assessed via the anodic potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The glassy carbon modified Sr2PdO3 (GC/Sr2PdO3) electrode exhibited a higher electrocatalytic activity, by about 50 times, in comparison to the unmodified electrode. The order of the reaction was close to unity, which indicates that the adsorption of the hydroxyl groups is a fast step. The calculated activation energy was 21.6 kJ.mol−1, which can be considered a low value in evaluation with those of the reported OER electrocatalysts. The Sr2PdO3 perovskite portrayed a high catalyst stability without any probability of catalyst poisoning. These results encourage the use of Sr2PdO3 as a candidate electrocatalyst for water splitting reactions.

Calculation of Activation Energy of Commercial Grade H2O2 from DSC for Using Evaluation Thermal Hazard

Hydrogen peroxide is a strong oxidizing agent containing a peroxide functional group that easily decomposes. In this research, a commercial grade of 35 % w/w hydrogen peroxide was evaluated for thermal hazard and reactivity by differential scanning calorimetry (DSC). It was found that the calculated activation energy was 70.03 kJ/mol. The risk assessment of thermal hazard evaluated in terms of the adiabatic decomposition temperature rise at heating rate 2, 4 and 8 °C/min, were 236.5, 159.2 and 217.5 K, respectively. While the time-to-maximum rate were 79.1, 52.6 and 28.3 second, respectively. Therefore, the storage, transportation and usage, proper care must be highly careful by trained and qualified person or the chemist knowledgeable personnel.

Defects and Dopants in CaFeSi2O6: Classical and DFT Simulations

Calcium (Ca)-bearing minerals are of interest for the design of electrode materials required for rechargeable Ca-ion batteries. Here we use classical simulations to examine defect, dopant and transport properties of CaFeSi2O6. The formation of Ca-iron (Fe) anti-site defects is found to be the lowest energy process (0.42 eV/defect). The Oxygen and Calcium Frenkel energies are 2.87 eV/defect and 4.96 eV/defect respectively suggesting that these defects are not significant especially the Ca Frenkel. Reaction energy for the loss of CaO via CaO Schottky is 2.97 eV/defect suggesting that this process requires moderate temperature. Calculated activation energy of Ca-ion migration in this material is high (>4 eV), inferring very slow ionic conductivity. However, we suggest a strategy to introduce additional Ca2+ ions in the lattice by doping trivalent dopants on the Si site in order to enhance the capacity and ion diffusion and it is calculated that Al3+ is the favourable dopant for this process. Formation of Ca vacancies required for the CaO Schottky can be facilitated by doping of gallium (Ga) on the Fe site. The electronic structures of favourable dopants were calculated using density functional theory (DFT).

EFFECT OF CONCENTRATION AND NATURE OF LITHIUM SALT ON CHARACTERISTICS OF GEL ELECTROLYTES DMSO-PVDF-LiAn

The results of the study of electrolytes based on gel solutions of DMSO-PVDF-lithium salt with concentrations up to 0.05 m.f. and above 0.1 m.f. are presented. It is shown that the conductivity of electrolytes is close to the conductivity of lithium salt solutions in pure DMSO and obeys the Arrhenius equation in the studied range of temperatures and concentrations. The calculated activation energies for electrolytes with a salt concentration of up to 0.05 m.f. are 14–15.4 KJ/Mol, and for electrolytes with a salt concentration above 0.1 m.f. - 16.9–20.6 KJ/Mol indicate a fast ion transfer, which in more concentrated solutions is inhibited by an increase in their crystallinity. The analysis of the equivalent circuit models of the Li-Li systems electrochemical impedance spectra showed the tendency of electrolytes to form capacitive elements at the lithium electrode-electrolyte interface. It was recognized the presence of semi-infinite diffusion in LiClO4 and LiIm with salt concentration of 0.05 m.f., due to the imperfection of the film formed on the electrode surface. The efficiency of using DMSO-PVDF-lithium gel electrolytes on steel and platinum electrodes was analyzed by voltammograms.

Thermogravimetric study of nickel-containing zeolites deactivated in glucose conversion

Heterogeneous catalytic conversion of carbohydrates in order to obtain platform- substances over acid catalysts is an important modern area of research. However, today the problem of deactivation of solid catalysts in these processes is poorly understood. The aim of the work was thermogravimetric study of nickel-containing (5% wt.) hydrogen forms of zeolites Y, ZSM-5 and M deactivated in glucose dehydration. The peculiarities of two processes, including endothermic process of dehydration and the exothermic process of carbonaceous deposits combustion, were investigated by the method of ther-mogravimetry. The latter on the DTA curves is represented by two (three) exothermic maxima in the temperature range of 325-450 oC. Among the studied samples only for zeolite Y there is a phase transi-tion without mass change in the range of 900-1000 oC. The mass loss of the samples due to dehydra-tion and combustion of coke is 30, 20 and 15% for NiHY, NiHM and NiHZSM-5, respectively, of which carbonaceous deposits account for 18, 10 and 10% of the mass. A similar rate of dehydration and burnout of deposits was observed in the case of catalysts based on wide-porous zeolites, as well as a lower rate of burnout in the case of medium-porous zeolite ZSM-5. The calculated activation energy of deposition combustion, which is 25-50 kJ/mol, is caused by the proceeding of low-temperature oxi-dation catalyzed by nickel-containing zeolites. It was found that the bulk of coke deposits burns up to 450 oC, which indicates the formation of only coke precursors, which, apparently, are humin com-pounds. They do not undergo further processes of transformation and compaction.