DFT modeling of the post-titanocene catalytic system LTiCl2-Bu2Mg-Et2AlCl for alkene polymerization: The role of alkyl bridge Mg–C–Ti and β-agostic C–H–Ti bonds in the formation of active centers

2017 ◽  
Vol 426 ◽  
pp. 600-609 ◽  
Author(s):  
Leila Y. Ustynyuk
Keyword(s):  
Catalytic System ◽  
Active Centers ◽  
Alkene Polymerization ◽  
Dft Modeling

Effect of grain size on the vapour phase hydration of monoclinic and triclinic modifications of tricalcium silicate; role of high temperature activation

1991 ◽  
Vol 56 (10) ◽  
pp. 1993-2008
Author(s):  
S. Hanafi ◽  
G. M. S. El-Shafei ◽  
B. Abd El-Hamid
Keyword(s):  
Particle Size ◽  
Vapour Phase ◽  
Tricalcium Silicate ◽  
Active Centers ◽  
Thermally Activated ◽  
Grain Sizes ◽  
Intermediate Size ◽  
Surface Active ◽  
Temperature Activation

The hydration of tricalcium silicate (C3S) with three grain sizes of monoclinic (M) and triclinic (T) modifications and on their thermally activated samples were investigated by exposure to water vapour at 80°C for 60 days. The products were investigated by XRD, TG and N2 adsorption. The smaller the particle size the greater was the hydration for both dried and activated samples from (M). In the activated samples a hydrate with 2θ values of 38.4°, 44.6° and 48.6° could be identified. Hydration increased with particle size for the unactivated (T) samples but after activation the intermediate size exhibited enhanced hydration. Thermal treatment at 950°C of (T) samples increased the surface active centers on the expense of those in the bulk. Changes produced in surface texture upon activation and/or hydration are discussed.

scholarly journals Zirconocene-Catalyzed Dimerization of α-Olefins: DFT Modeling of the Zr-Al Binuclear Reaction Mechanism

Molecules ◽  
2019 ◽  
Vol 24 (19) ◽  
pp. 3565 ◽  
Author(s):  
Ilya Nifant’ev ◽  
Alexander Vinogradov ◽  
Alexey Vinogradov ◽  
Stanislav Karchevsky ◽  
Pavel Ivchenko
Keyword(s):  
Density Functional Theory ◽  
Reaction Mechanism ◽  
Molecular Hydrogen ◽  
Density Functional ◽  
Effective Agent ◽  
Functional Theory ◽  
Dft Simulation ◽  
Dft Modeling ◽  
Dft Simulations

Zirconocene-mediated selective dimerization of α-olefins usually occurs when precatalyst (η5-C5H5)2ZrCl2 is activated by minimal excess of methylalumoxane (MAO). In this paper, we present the results of density functional theory (DFT) simulation of the initiation, propagation, and termination stages of dimerization and oligomerization of propylene within the framework of Zr-Al binuclear mechanism at M-06x/DGDZVP level of theory. The results of the analysis of the reaction profiles allow to explain experimental facts such as oligomerization of α-olefins at high MAO/(η5-C5H5)2ZrCl2 ratios and increase of the selectivity of dimerization in the presence of R2AlCl. The results of DFT simulations confirm the crucial role of the presence of chloride in the selectivity of dimerization. The molecular hydrogen was found in silico and proven experimentally as an effective agent that increases the rate and selectivity of dimerization.

scholarly journals DFT Modeling of Organocatalytic Ring-Opening Polymerization of Cyclic Esters: A Crucial Role of Proton Exchange and Hydrogen Bonding

Polymers ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 2078 ◽  
Author(s):  
Ilya Nifant’ev ◽  
Pavel Ivchenko
Keyword(s):  
Ring Opening ◽  
Density Functional ◽  
Comparative Modeling ◽  
Ring Opening Polymerization ◽  
Proton Exchange ◽  
Dft Methods ◽  
Experimental Proof ◽  
Cyclic Esters ◽  
Dft Modeling

Organocatalysis is highly efficient in the ring-opening polymerization (ROP) of cyclic esters. A variety of initiators broaden the areas of organocatalysis in polymerization of different monomers, such as lactones, cyclic carbonates, lactides or gycolides, ethylene phosphates and phosphonates, and others. The mechanisms of organocatalytic ROP are at least as diverse as the mechanisms of coordination ROP; the study of these mechanisms is critical in ensuring the polymer compositions and architectures. The use of density functional theory (DFT) methods for comparative modeling and visualization of organocatalytic ROP pathways, in line with experimental proof of the structures of the reaction intermediates, make it possible to establish these mechanisms. In the present review, which continues and complements our recent manuscript that focused on DFT modeling of coordination ROP, we summarized the results of DFT modeling of organocatalytic ROP of cyclic esters and some related organocatalytic processes, such as polyester transesterification.

The role of proton-donors in cyclotrimerization of isocyanates by the action of an amine-epoxide catalytic system

1982 ◽  
Vol 24 (11) ◽  
pp. 2768-2778 ◽  
Author(s):  
N.A. Shibanova ◽  
A.K. Zhitinkina ◽  
L.V. Turetskii ◽  
N.V. Varentsova
Keyword(s):  
Catalytic System ◽  
Proton Donors

scholarly journals The effect of the components of the PdCl2/Fe/I2/Py catalytic system on nitrobenzene carbonylation to ethyl N-phenylcarbamate

2005 ◽  
Vol 3 (1) ◽  
pp. 28-39 ◽  
Author(s):  
Jadwiga Skupińska ◽  
Monika Karpińska ◽  
Maria Ołówek ◽  
Teresa Kasprzycka-Guttman
Keyword(s):  
Catalytic System ◽  
Considerable Increase ◽  
Constant Level ◽  
The Other ◽  
Reaction Products ◽  
Highly Active

AbstractThe PdCl2/Fe/I2/Py catalytic system (Py-pyridine), reported to be highly active in the reaction of nitrobenzene carbonylation to ethyl phenylcarbamate was studied. The present paper describes the role of catalyst components and its effect on the activity and selectivity of the catalyst. The increase in the amount of PdCl2 in the system while retaining a constant level of the other catalyst components, results in the increase of both carbamate and aniline yields. The increase in the amount of iron while retaining the other components constant, initially causes an increase in the carbamate yield; however, at Fe: Pd ratios higher than 36, the carbamate yield remains constant. The change in the amount of iron has no effect on the amount of aniline formed in the system. An increase in the amount of iodine in the system while retaining the other components constant, results in a decrease in carbamate yield and a considerable increase in the aniline yield of the reaction products.

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