scholarly journals A theoretical study on Ir(III)-catalyzed intermolecular branch-selective allylic C−H amidation

2021 ◽  
Author(s):  
Liang-Cheng Xu ◽  
Xiang-Biao Zhang ◽  
Ying-Gang Zhang
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Theoretical Study ◽  
Coupling Reaction ◽  
Energy Difference ◽  
Reaction Yield ◽  
Theoretical Support ◽  
Amidation Reaction ◽  
Effect On Yield ◽  
Electron Donating Groups

Herein, we report the mechanism of Ir(III)-catalyzed intermolecular branch-selective allylic C−H amidation, including the influence of substituent effect on yield and regioselectivity. The sequence of amidation reaction is alkene coordination, allylic C−H activation, oxidative addition of methyl dioxazolone, reductive elimination of allyl-Ir-nitrenoid complex, amine protonation and proto-demetallation. The apparent activation energy of amidation between hexene and methyl dioxazolone is 17.8 kcal/mol, and the energy difference between two transition state for formation amide is only 2.8 kcal/mol. The introduction of more electron-deficient groups at the allyl terminal increases the apparent activation energy, conversely, the introduction of electron-donating groups significantly reduces the apparent activation energy. Among them, the apparent activation energy of the reaction between aniline group substituted allyl and methyl dioxazolone is only 13.8 kcal/mol, which further improves the reaction yield. In addition, the introduction of more electron-withdrawing groups on dioxazolone can significantly improve the regioselectivity. When 3,4,5,-trifluorophenyl substituted dioxazolone and hexene occur C−N bond coupling reaction, the energy difference of the two transition states is as high as 9.0 kcal/mol, indicating that the regioselectivity is greatly improved. The mechanism explanation of allylic C−H amidation will provide strong theoretical support for streamlined synthesis of allyl branched amides.

scholarly journals The Hydrothermal Stability and the Properties of Non- and Strongly-Interacting Rh Species over Rh/γ, θ-Al2O3 Catalysts

Catalysts ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 99
Author(s):  
Guanghao Cheng ◽  
Gurong Shen ◽  
Jun Wang ◽  
Yunhao Wang ◽  
Weibo Zhang ◽  
...  
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Aging Time ◽  
Reaction Path ◽  
Aging Treatment ◽  
Hydrothermal Stability ◽  
Hydrothermal Aging ◽  
Strongly Interacting

The present work reports the effects of γ-, θ-phase of alumina on the hydrothermal stability and the properties of non- and strongly-interacting Rh species of the Rh/Al2O3 catalysts. Comparing to γ-Al2O3, θ-Al2O3 can not only reduce the amount of occluded Rh but also better stabilize Rh during hydrothermal aging treatment. When the aging time was prolonged to 70 h, all the non-interacting Rh was transformed into strongly-interacting Rh and occluded Rh. The XPS results indicated that non- and strongly-interacting Rh might exist in the form of Rh/Rh3+ and Rh4+, respectively. CO-NO reaction was chosen as a probe reaction to research more information about non- and strongly-interacting Rh. The two Rh species had similar apparent activation energy (Eapp) of 170 kJ/mol, which indicated that non- and strongly-interacting Rh follow the same reaction path. The non-interacting Rh was removed from aged samples by the acid-treated method, and obtained results showed that only 2.5% and 4.0% non-interacting Rh was maintained in aged Rh/γ-Al2O3 and Rh/θ-Al2O3.

The activation energy U(T,B) in high temperature superconductor

2020 ◽  
Vol 92 (2) ◽  
pp. 20601
Author(s):  
Abdelaziz Labrag ◽  
Mustapha Bghour ◽  
Ahmed Abou El Hassan ◽  
Habiba El Hamidi ◽  
Ahmed Taoufik ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Activation Energy ◽  
Phase Diagram ◽  
High Temperature ◽  
Apparent Activation Energy ◽  
High Temperature Superconductor ◽  
Flux Flow ◽  
Resistivity Measurements ◽  
Vortex Phase ◽  
The Magnetic Field

It is reported in this paper on the thermally assisted flux flow in epitaxial YBa2Cu3O7-δ deposited by Laser ablation method on the SrTiO3 substrate. The resistivity measurements ρ (T, B) of the sample under various values of the magnetic field up to 14T in directions B∥ab-plane and B∥c-axis with a dc weak transport current density were investigated in order to determine the activation energy and then understand the vortex dynamic phenomena and therefore deduce the vortex phase diagram of this material. The apparent activation energy U0 (B) calculated using an Arrhenius relation. The measured results of the resistivity were then adjusted to the modified thermally assisted flux flow model in order to account for the temperature-field dependence of the activation energy U (T, B). The obtained values from the thermally assisted activation energy, exhibit a behavior similar to the one showed with the Arrhenius model, albeit larger than the apparent activation energy with ∼1.5 order on magnitude for both cases of the magnetic field directions. The vortex glass model was also used to obtain the vortex-glass transition temperature from the linear fitting of [d ln ρ/dT ] −1 plots. In the course of this work thanks to the resistivity measurements the upper critical magnetic field Hc2 (T), the irreversibility line Hirr (T) and the crossover field HCrossOver (T) were located. These three parameters allowed us to establish a phase diagram of the studied material where limits of each vortex phase are sketched in order to optimize its applicability as a practical high temperature superconductor used for diverse purposes.

scholarly journals Effect of CaO on catalytic combustion of semi-coke

2021 ◽  
Vol 10 (1) ◽  
pp. 011-020
Author(s):  
Luyao Kou ◽  
Junjing Tang ◽  
Tu Hu ◽  
Baocheng Zhou ◽  
Li Yang
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Combustion Rate ◽  
Activation Energies ◽  
Combustion Reaction ◽  
Tg Analysis ◽  
Conversion Rates ◽  
Apparent Activation Energies ◽  
Ozawa Integral Method ◽  
Addition Amount

Abstract Generally, adding a certain amount of an additive to pulverized coal can promote its combustion performance. In this paper, the effect of CaO on the combustion characteristics and kinetic behavior of semi-coke was studied by thermogravimetric (TG) analysis. The results show that adding proper amount of CaO can reduce the ignition temperature of semi-coke and increase the combustion rate of semi-coke; with the increase in CaO content, the combustion rate of semi-coke increases first and then decreases, and the results of TG analysis showed that optimal addition amount of CaO is 2 wt%. The apparent activation energy of CaO with different addition amounts of CaO was calculated by Coats–Redfern integration method. The apparent activation energy of semi-coke in the combustion reaction increases first and then decreases with the increase in CaO addition. The apparent activation energies of different samples at different conversion rates were calculated by Flynn–Wall–Ozawa integral method. It was found that the apparent activation energies of semi-coke during combustion reaction decreased with the increase in conversion.

Effect of orienting coatings on the apparent activation energy of boundary film destruction

2007 ◽  
Vol 28 (1) ◽  
pp. 12-18 ◽  
Author(s):  
I. A. Buyanovskii ◽  
Yu. N. Drozdov ◽  
Z. V. Ignatieva ◽  
T. M. Savinova ◽  
V. A. Levchenko ◽  
...  
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Boundary Film

scholarly journals Influence of dimensionality on phase transition in VO2 nanocrystals

2013 ◽  
Vol 45 (3) ◽  
pp. 305-311 ◽  
Author(s):  
V.A. Blagojevic ◽  
N. Obradovic ◽  
N. Cvjeticanin ◽  
D.M. Minic
Keyword(s):  
Phase Transition ◽  
Activation Energy ◽  
Transition Temperature ◽  
Apparent Activation Energy ◽  
Phase Transition Temperature ◽  
Bulk Material ◽  
Two Dimensional ◽  
Lower Phase ◽  
One Dimensional ◽  
Simultaneous Movement

Hydrothermally synthesized one-dimensional and two-dimensional nanocrystals of VO2 undergo phase transition around 65?C, where temperature and mechanism of phase transition are dependent on dimensionality of nanocrystals. Both nanocrystalline samples exhibit depression of phase transition temperature compared to the bulk material, the magnitude of which depends on the dimensionality of the nanocrystal. One-dimensional nanoribbons exhibit lower phase transition temperature and higher values of apparent activation energy than two-dimensional nanosheets. The phase transition exhibits as a complex process with somewhat lower value of enthalpy than the phase transition in the bulk, probably due to higher proportion of surface atoms in the nanocrystals. High values of apparent activation energy indicate that individual steps of the phase transition involve simultaneous movement of large groups of atoms, as expected for single-domain nanocrystalline materials.

scholarly journals Apparent Activation Energy in Electrochemical Multistep Reactions: A Description via Degrees of Rate Control

2020 ◽  
Author(s):  
Alfredo Calderón-Cárdenas ◽  
Enrique A. Paredes-Salazar ◽  
Hamilton Varela
Keyword(s):  
Activation Energy ◽  
Catalytic Activity ◽  
Apparent Activation Energy ◽  
Chemical Kinetics ◽  
Rate Control ◽  
Rate Coefficients ◽  
Intrinsic Activity ◽  
Empirical Parameter ◽  
Heterogenous Catalysis ◽  
Multistep Reactions

<div> <div> <div> <p>Activation energy is a well-known empirical parameter in chemical kinetics that characterises the dependence of the chemical rate coefficients on the temperature and provides information to compare the intrinsic activity of the catalysts. However, the determination and interpretation of the apparent activation energy in multistep reactions is not an easy task. For this purpose, the concept of degree of rate control is convenient, which comprises a mathematical approach for analyzing reaction mechanisms and chemical kinetics. Although this concept has been used in catalysis, it has not yet been applied in electrocatalytic systems, whose ability to control the potential across the solid/liquid interface is the main difference with heterogenous catalysis, and the electrical current is commonly used as a measure of the reaction rate. Herein we use the definition of ‘degree of rate control for elementary step’ to address some of the drawbacks that frequently arise with interpreting apparent activation energy as a measure of intrinsic electrocatalytic activity of electrode. For this, an electrokinetic model Langmuir-Hinshelwood-like is used for making numerical experiments and verifying the proposed ideas. The results show that to improve the catalytic activity of an electrode material, it must act upon the reaction steps with the highest normalised absolute values of degree of rate control. On the other hand, experiments at different applied voltages showed that if the electroactive surface poisoning process take place, changes in 𝐸𝑎𝑝𝑝 can not be used to compare the catalytic activity of the electrodes. Finally, the importance of making measurements at steady-state to avoid large errors in the calculations of apparent activation energy is also discussed. </p> </div> </div> </div>

Downstream Plasma Activated Etching of IIIV Compound Semiconductorsa

1988 ◽  
Vol 144 ◽  
Author(s):  
R. Iyer ◽  
D.L. Lile
Keyword(s):  
Activation Energy ◽  
Apparent Activation Energy ◽  
Mass Spectrometer ◽  
Vapor Phase ◽  
Compound Semiconductors ◽  
Power Input ◽  
Reaction Process ◽  
Rf Power ◽  
Carrier Gas ◽  
Etch Rates

ABSTRACTWe have demonstrated a novel downstream plasma activated vapor phase etching of III-V compound semiconductors using ethylene di bromide as the etchant. Highly reproducible surfaces and etch rates were obtained by monitoring the reaction process with a mass spectrometer. Etch rates on InP of up to 4500Å/min, at temperatures as low as 160°C, at an rf power input of 25 watts were achieved with no evident damage to the surface as indicated by PL measurements. Apparent activation energy measurements seem to suggest that the etch products might be organometallic in nature, in contrast to inorganic etch products seen in most etching studies. Etching is partially anisotropic and resulted in smoother surfaces when H2 was used as the carrier gas for the etchant instead of N2.

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