scholarly journals Theoretical Study on Ethylene Polymerization Catalyzed by Half-Titanocenes Bearing Different Ancillary Groups

Catalysts ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1392
Author(s):  
Yang Li ◽  
Xiaoling Lai ◽  
Xiaowei Xu ◽  
Yat-Ming So ◽  
Yijing Du ◽  
...  
Keyword(s):  
Ethylene Polymerization ◽  
Density Functional ◽  
Dft Method ◽  
Catalytic Performance ◽  
Deformation Energy ◽  
Active Species ◽  
Chain Termination ◽  
Free Energy Barrier ◽  
Back Side ◽  
Ancillary Ligands

Half-titanocenes are well known to show high activity for ethylene polymerization and good capability for copolymerization of ethylene with other olefins, and the ancillary ligands can crucially affect the catalytic performance. In this paper, the mechanisms of ethylene polymerization catalyzed by three half-metallocenes, (η5-C5Me5)TiCl2(O-2,6-iPr2C6H3) (1), (η5-C5Me5)TiCl2(N=CtBu2) (2) and [Me2Si(η5-C5Me4)(NtBu)]TiCl2 (3), have been investigated by density functional theory (DFT) method. At the initiation stage, a higher free energy barrier was determined for complex 1, probably due to the presence of electronegative O atom in phenoxy ligand. At the propagation stage, front-side insertion of the second ethylene is kinetically more favorable than back-side insertion for complexes 1 and 2, while both side insertion orientations are comparable for complex 3. The energy decomposition showed that the bridged cyclopentadienyl amide ligand could enhance the rigidity of the active species as suggested by the lowest deformation energy derived from 3. At the chain termination stage, β-H transfer was calculated to be a dominant chain termination route over β-H elimination, presumably owing to the thermodynamic perspective.

scholarly journals System Theoretical Study on the Effect of Variable Nonmetallic Doping on Improving Catalytic Activity of 2D-Ti3C2O2 for Hydrogen Evolution Reaction

Nanomaterials ◽  
2021 ◽  
Vol 11 (10) ◽  
pp. 2497
Author(s):  
Ye Su ◽  
Minhui Song ◽  
Xiaoxu Wang ◽  
Jihang Jiang ◽  
Xiaolong Si ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Hydrogen Evolution ◽  
Hydrogen Evolution Reaction ◽  
Hydrogen Absorption ◽  
Density Functional ◽  
Electronic Conductivity ◽  
Dft Method ◽  
Catalytic Performance ◽  
P Element ◽  
Element Doping

2D MXenes have been found to be one of the most promising catalysts for hydrogen evolution reaction (HER) due to their excellent electronic conductivity, hydrophilic nature, porosity and stability. Nonmetallic (NM) element doping is an effective approach to enhance the HER catalytic performance. By using the density functional theory (DFT) method, we researched the effect of nonmetallic doping (different element types, variable doping concentrations) and optimal hydrogen absorption concentration on the surface of NM-Ti3C2O2 for HER catalytic activity and stability. The calculation results show that doping nonmetallic elements can improve their HER catalytic properties; the P element dopants catalyst especially exhibits remarkable HER performance (∆GH = 0.008 eV when the P element doping concentration is 100% and the hydrogen absorption is 75%). The origin mechanism of the regulation of doping on stability and catalytic activity was analyzed by electronic structures. The results of this work proved that by controlling the doping elements and their concentrations we can tune the catalytic activity, which will accelerate the further research of HER catalysts.

scholarly journals Comparison of the Reactivity and Structures for the Neutral and Cationic Bis(imino)pyridyl Iron and Cobalt Species by DFT Calculations

Catalysts ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1396
Author(s):  
Zilong Li ◽  
Yanping Ma ◽  
Wen-Hua Sun
Keyword(s):  
Ethylene Polymerization ◽  
Density Functional ◽  
Natural Bond Orbital ◽  
Dft Method ◽  
Metal Center ◽  
Polymerization Catalysts ◽  
Functional Theory ◽  
Fundamental Information ◽  
Calculation Results ◽  
Cobalt Species

Density Functional Theory (DFT) method was adopted to investigate and compare the reaction mechanisms of ethylene polymerization catalyzed by neutral, cationic bis(imino)pyridyl (PDI) iron and cobalt derivatives. The electronic structure and the oxidation states of the metal center and the PDI ligand were analyzed by taking spin states, natural bond orbital (NBO) charge distribution, etc. into consideration, revealing that the reactivity is closely related to the valence electron numbers instead of the charge numbers. The neutral Co(0) had the lowest reactivity as it possessed the most electrons. During the formation of the cationic Co(+)/Fe(+), one electron was mainly lost from PDI ligand rather than the metal center while the metal center maintained +II valence state through the process. Moreover, a special unsymmetrically bidentate N^N coordination manner was found to provide the deficient metal surroundings with 14e, which may initiate the reactivity of some unsymmetrical species with rich electrons. Finally, an anion [AlMe4]− participating process was proposed to explain the presence of the experimentally observed LCo(+)B(C2H4). A special intermediate, Co(+)B(C2H4) [AlMe4]− with Co in +I and absence of Co–C σ bond, was obtained. These calculation results may provide fundamental information for further understanding and designing the ethylene polymerization catalysts.

scholarly journals Synthesis of HZSM-5 Rich in Paired Al and Its Catalytic Performance for Propane Aromatization

Catalysts ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 622
Author(s):  
Dezhi Shi ◽  
Sen Wang ◽  
Hao Wang ◽  
Pengfei Wang ◽  
Li Zhang ◽  
...  
Keyword(s):  
Density Functional ◽  
Catalytic Performance ◽  
Molar Ratio ◽  
Propane Conversion ◽  
Free Energy Barrier ◽  
Functional Theory ◽  
Molar Ratios ◽  
Propane Aromatization ◽  
Vis Spectroscopy ◽  
Stabilization Effect

A series of HZSM-5 catalysts with similar Si/AlF mole ratio, textual properties and morphology, but different contents of AlF pairs, were synthesized by controlling the Na/Al molar ratios in the precursor gel and used for propane aromatization. It is shown that the catalyst with a Na/Al molar ratio of 0.8 in the synthetic gel possesses the highest paired AlF concentration (64.4%) and shows higher propane conversion (38.2%) and aromatics selectivity (19.7 wt.%). Propane pulse experiments, micro reactor activity estimation, Operando diffuse reflectance ultraviolet-visible (DR UV-vis) spectroscopy and Fourier Transform Infrared Spectroscopy (FTIR) analysis of coke species deposited on the catalysts provide evidence that AlF pairs in the ZSM-5 framework promote oligomerization and cyclization reactions of olefins, and then produce more aromatics. Density Functional Theory (DFT) calculations demonstrate that the cyclization of olefins and hydride transfer reaction occurring on AlF pairs in HZSM-5 zeolite show a lower free energy barrier and a higher rate constant than those on single AlF, indicating that the structure of AlF pairs in the HZSM-5 zeolite has a stronger electrostatic stabilization effect on the transition states than that of single AlF.

scholarly journals Hole Doping to Enhance the Photocatalytic Activity of Bi4NbO8Cl

Catalysts ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1425 ◽  
Author(s):  
Jingbang Sun ◽  
Ni Han ◽  
Yan Gu ◽  
Xiaowang Lu ◽  
Liang Si ◽  
...  
Keyword(s):  
Photocatalytic Activity ◽  
Trypan Blue ◽  
Density Functional ◽  
Degradation Mechanism ◽  
Density Functional Theory Calculations ◽  
Solid State Reaction Method ◽  
Catalytic Performance ◽  
Active Species ◽  
Hole Doping ◽  
X Ray

An increase of carrier concentration is one of the most important routes for enhancing the catalytic performance of semiconductor photocatalysts. In this study, the Sillén–Aurivillius oxychloride Bi4NbO8Cl with hole doping was successfully prepared by a solid-state reaction method. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible diffuse reflectance spectra (UV–vis DRS), X-ray photoelectron spectrometry (XPS) and photoluminescence spectra (PL) were used to characterize and analyze the prepared samples. The experimental results and density functional theory calculations demonstrate that hole doping can be formed in Bi4NbO8Cl by inserting zinc into the niobium site, and the photocatalytic activity can be improved by introducing additional holes into Bi4NbO8Cl. The photogenerated hole (h+) is considered to be the main active species to degrade trypan blue (TB) through trapping experiments. The optimal photocatalyst of Bi4Nb0.8Zn0.2O8Cl exhibits excellent photocatalytic activity in degradation of trypan blue under visible light irritation. Moreover, a possible photocatalytic degradation mechanism is discussed according the experimental and analytical results.

Field Effect Modulation of Electrocatalytic Hydrogen Evolution at Back-Gated Two-Dimensional MoS2 Electrodes

2019 ◽  
Author(s):  
Yan Wang ◽  
Sagar Udyavara ◽  
Matthew Neurock ◽  
C. Daniel Frisbie
Keyword(s):  
Electric Field ◽  
Hydrogen Evolution ◽  
Active Sites ◽  
Density Functional ◽  
Electrode Materials ◽  
Density Functional Theory Calculations ◽  
Electronic Charge ◽  
Back Side ◽  
Gate Electrode ◽  
Conventional Manner

<div> <div> <div> <p> </p><div> <div> <div> <p>Electrocatalytic activity for hydrogen evolution at monolayer MoS2 electrodes can be enhanced by the application of an electric field normal to the electrode plane. The electric field is produced by a gate electrode lying underneath the MoS2 and separated from it by a dielectric. Application of a voltage to the back-side gate electrode while sweeping the MoS2 electrochemical potential in a conventional manner in 0.5 M H2SO4 results in up to a 140-mV reduction in overpotential for hydrogen evolution at current densities of 50 mA/cm2. Tafel analysis indicates that the exchange current density is correspondingly improved by a factor of 4 to 0.1 mA/cm2 as gate voltage is increased. Density functional theory calculations support a mechanism in which the higher hydrogen evolution activity is caused by gate-induced electronic charge on Mo metal centers adjacent the S vacancies (the active sites), leading to enhanced Mo-H bond strengths. Overall, our findings indicate that the back-gated working electrode architecture is a convenient and versatile platform for investigating the connection between tunable electronic charge at active sites and overpotential for electrocatalytic processes on ultrathin electrode materials.</p></div></div></div><br><p></p></div></div></div>

uMBD: A Materials-Ready Dispersion Correction that Uniformly Treats Metallic, Ionic, Covalent, and van der Waals Bonding

2019 ◽  
Author(s):  
Minho Kim ◽  
won june kim ◽  
Tim Gould ◽  
Eok Kyun Lee ◽  
Sébastien Lebègue ◽  
...  
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Electrode Materials ◽  
Full Range ◽  
Van Der Waals ◽  
Dft Method ◽  
Dispersion Correction ◽  
Computational Overhead ◽  
System A ◽  
Battery Design

<p>Materials design increasingly relies on first-principles calculations for screening important candidates and for understanding quantum mechanisms. Density functional theory (DFT) is by far the most popular first-principles approach due to its efficiency and accuracy. However, to accurately predict structures and thermodynamics, DFT must be paired with a van der Waals (vdW) dispersion correction. Therefore, such corrections have been the subject of intense scrutiny in recent years. Despite significant successes in organic molecules, no existing model can adequately cover the full range of common materials, from metals to ionic solids, hampering the applications of DFT for modern problems such as battery design. Here, we introduce a universally optimized vdW-corrected DFT method that demonstrates an unbiased reliability for predicting molecular, layered, ionic, metallic, and hybrid materials without incurring a large computational overhead. We use our method to accurately predict the intercalation potentials of layered electrode materials of a Li-ion battery system – a problem for which the existing state-of-the-art methods fail. Thus, we envisage broad use of our method in the design of chemo-physical processes of new materials.</p>

DFT study on the hydrolysis of metsulfuron-methyl: A sulfonylurea herbicide

2018 ◽  
Vol 17 (08) ◽  
pp. 1850050 ◽  
Author(s):  
Qiuhan Luo ◽  
Gang Li ◽  
Junping Xiao ◽  
Chunhui Yin ◽  
Yahui He ◽  
...  
Keyword(s):  
Free Energy ◽  
Water Molecule ◽  
Carbonyl Group ◽  
Energy Barrier ◽  
Density Functional ◽  
Free Energy Barrier ◽  
Functional Theory ◽  
Metsulfuron Methyl ◽  
Catalytic Role ◽  
Hydrolysis Of

Sulfonylureas are an important group of herbicides widely used for a range of weeds and grasses control particularly in cereals. However, some of them tend to persist for years in environments. Hydrolysis is the primary pathway for their degradation. To understand the hydrolysis behavior of sulfonylurea herbicides, the hydrolysis mechanism of metsulfuron-methyl, a typical sulfonylurea, was investigated using density functional theory (DFT) at the B3LYP/6-31[Formula: see text]G(d,p) level. The hydrolysis of metsulfuron-methyl resembles nucleophilic substitution by a water molecule attacking the carbonyl group from aryl side (pathway a) or from heterocycle side (pathway b). In the direct hydrolysis, the carbonyl group is directly attacked by one water molecule to form benzene sulfonamide or heterocyclic amine; the free energy barrier is about 52–58[Formula: see text]kcal[Formula: see text]mol[Formula: see text]. In the autocatalytic hydrolysis, with the second water molecule acting as a catalyst, the free energy barrier, which is about 43–45[Formula: see text]kcal[Formula: see text]mol[Formula: see text], is remarkably reduced by about 11[Formula: see text]kcal[Formula: see text]mol[Formula: see text]. It is obvious that water molecules play a significant catalytic role during the hydrolysis of sulfonylureas.

scholarly journals First Attempts of the Use of 195Pt NMR of Phenylbenzothiazole Complexes as Spectroscopic Technique for the Cancer Diagnosis

Molecules ◽  
2019 ◽  
Vol 24 (21) ◽  
pp. 3970 ◽  
Author(s):  
Bruna T. L. Pereira ◽  
Mateus A. Gonçalves ◽  
Daiana T. Mancini ◽  
Kamil Kuca ◽  
Teodorico C. Ramalho
Keyword(s):  
Cancer Treatment ◽  
Cancer Diagnosis ◽  
Density Functional ◽  
Chemical Shifts ◽  
Chloride Ion ◽  
Platinum Complexes ◽  
Dft Method ◽  
Ion Concentration ◽  
Implicit Solvent ◽  
Early Cancer Diagnosis

Platinum complexes have been studied for cancer treatment for several decades. Furthermore, another important platinum characteristic is related to its chemical shifts, in which some studies have shown that the 195Pt chemical shifts are very sensitive to the environment, coordination sphere, and oxidation state. Based on this relevant feature, Pt complexes can be proposed as potential probes for NMR spectroscopy, as the chemical shifts values will be different in different tissues (healthy and damaged) Therefore, in this paper, the main goal was to investigate the behavior of Pt chemical shifts in the different environments. Calculations were carried out in vacuum, implicit solvent, and inside the active site of P13K enzyme, which is related with breast cancer, using the density functional theory (DFT) method. Moreover, the investigation of platinum complexes with a selective moiety can contribute to early cancer diagnosis. Accordingly, the Pt complexes selected for this study presented a selective moiety, the 2-(4′aminophenyl)benzothiazole derivative. More specifically, two Pt complexes were used herein: One containing chlorine ligands and one containing water in place of chlorine. Some studies have shown that platinum complexes coordinated to chlorine atoms may suffer hydrolyses inside the cell due to the low chloride ion concentration. Thus, the same calculations were performed for both complexes. The results showed that both complexes presented different chemical shift values in the different proposed environments. Therefore, this paper shows that platinum complexes can be a potential probe in biological systems, and they should be studied not only for cancer treatment, but also for diagnosis.

Understanding the molecular mechanism of the stereoselective conversion of N-trialkylsilyloxy nitronates into bicyclic isoxazoline derivatives

2021 ◽  
Author(s):  
Agnieszka Kącka-Zych ◽  
Radomir Jasinski
Keyword(s):  
Density Functional Theory ◽  
Molecular Mechanism ◽  
Electron Density ◽  
Density Functional ◽  
Dft Method ◽  
Functional Theory ◽  
Molecular Electron ◽  
Molecular Electron Density Theory

Conversion of N-trialkylsilyloxy nitronates into bicyclic isoxazoline derivatives has been explored using Density Functional Theory (DFT) method within the context of the Molecular Electron Density Theory (MEDT) at the B97XD(PCM)/6-311G(d,p)...

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