scholarly journals ZnFe<sub>2</sub>O<sub>4</sub>@dimethylglyoxime: preparation and catalyst application in the synthesis of 2-amino-tetrahydro-4H-chromene-3-carbonitrile derivatives

2020 ◽  
Author(s):  
Ali Maleki ◽  
Haniyeh Dogari ◽  
Fereshte Hassanzadeh-Afruzi
Keyword(s):  
Active Sites ◽  
Dibasic Acid ◽  
Simple Procedure ◽  
Chelating Agent ◽  
Aromatic Aldehydes ◽  
Lewis Base ◽  
Hydroxyl Groups ◽  
Hybrid Catalyst ◽  
Divalent Metal Ions ◽  
Acid Substance

An efficient CoS2/CoSe2 hybrid catalyst for electrocatalytic hydrogen evolution

2017 ◽  
Vol 5 (6) ◽  
pp. 2504-2507 ◽  
Author(s):  
Yaxiao Guo ◽  
Changshuai Shang ◽  
Erkang Wang
Keyword(s):  
Hydrogen Evolution ◽  
Electrocatalytic Activity ◽  
Active Sites ◽  
High Dispersion ◽  
Hybrid Catalyst

The CoS2/CoSe2 hybrid catalyst exhibits superior HER electrocatalytic activity as well as excellent electrochemical durability. CoSe2/DETA nanobelts not only afford an interconnected conducting network, but also demonstrate superior HER electrocatalytic activity. High dispersion and smaller CoS2 nanoparticles on the surface can provide abundant active sites for the HER.

The structure and activity of potassium supported on SBA-15 molecular sieve: Density functional theory study

2014 ◽  
Vol 13 (01) ◽  
pp. 1350076 ◽  
Author(s):  
Bing Liu ◽  
Daxi Wang ◽  
Zhongxue Wang ◽  
Zhen Zhao ◽  
Yu Chen ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Lewis Acid ◽  
Molecular Sieve ◽  
Active Sites ◽  
Density Functional ◽  
Structural Model ◽  
Vibrational Frequencies ◽  
Oxygen Molecule ◽  
Lewis Base ◽  
Functional Theory

The geometries, vibrational frequencies, electronic properties and reactivity of potassium supported on SBA-15 have been theoretically investigated by the density functional theory (DFT) method. The structural model of the potassium supported on SBA-15 was constructed based on our previous work [Wang ZX, Wang DX, Zhao Z, Chen Y, Lan J, A DFT study of the structural units in SBA-15 mesoporous molecular sieve, Comput. Theor. Chem.963, 403, 2011]. This paper is the extension of our previous work. The most favored location of potassium atom was obtained by the calculation of substitution energy. The calculated vibrational frequencies of K /SBA-15 are in good agreement with the experimental results. By analyzing the properties of electronic structure, we found that the O atom of Si - O (2)- K group acts as the Lewis base center and the K atom acts as the Lewis acid center. The reactivity of K /SBA-15 was investigated by calculating the activation of oxygen molecule. The oxygen molecule can be activated by K /SBA-15 with an energy barrier of 103.2 kJ/mol. In the final state, the activated oxygen atoms become new Lewis acid centers, which are predicted to act as the active sites in the catalytic reactions. This study provides a deep insight into the properties of supported potassium catalysts and offers fundamental information for further research.

scholarly journals Heterogeneous Catalytic Synthesis of 2-Methylbenzimidazole from 2-Nitroaniline and Ethanol Over Mg Modified Cu-Pd/γ-Al2O3

Catalysts ◽  
2018 ◽  
Vol 9 (1) ◽  
pp. 8 ◽  
Author(s):  
Feng Feng ◽  
Yaqin Deng ◽  
Zheng Cheng ◽  
Xiaoliang Xu ◽  
Qunfeng Zhang ◽  
...  
Keyword(s):  
Active Sites ◽  
Hydrogen Transfer ◽  
High Efficiency ◽  
Simple Procedure ◽  
Direct Synthesis ◽  
Reaction System ◽  
Simple Method ◽  
Heterogeneous Catalytic ◽  
Coupled Reaction ◽  
Al2o3 Catalyst

The direct synthesis of benzimidazoles from 2-nitroaniline and ethanol over Cu-Pd/γ-Al2O3 catalysts has the advantages of requiring easily available starting materials, having high efficiency, and a simple procedure. The modification by Mg of the Cu-Pd/γ-Al2O3 catalyst could improve the catalytic activity significantly. The addition of Mg to the Cu-Pd/γ-Al2O3 catalyst could maintain and promote the formation of CuPd alloy active sites. Meanwhile, the basicity of the support was enhanced appropriately by Mg, which generated more basic sites (Al-Oδ−) to accelerate the dehydrogenation of alcohol and increased the rate of the whole coupled reaction. The 2-nitroaniline was completely converted over Cu-Pd/(Mg)γ-Al2O3 after reacting for six hours, and the yield of 2-methylbenzimidazole was 98.8%. The results of this work provide a simple method to develop a more efficient catalyst for the “alcohol-dehydrogenation, hydrogen transfer and hydrogenation” coupled reaction system.

Divalent Metal Ions at the Active Sites of the EcoRV and EcoRI Restriction Endonucleases

Biochemistry ◽  
1995 ◽  
Vol 34 (2) ◽  
pp. 697-704 ◽  
Author(s):  
I. Barry Vipond ◽  
Geoffrey S. Baldwin ◽  
Stephen E. Halford
Keyword(s):  
Metal Ions ◽  
Active Sites ◽  
Divalent Metal ◽  
Restriction Endonucleases ◽  
Divalent Metal Ions ◽  
Ecori Restriction

scholarly journals THERMODINAMIC PARAMETERS ON THE SORPTION OF PHOSPHATE IONS BY MONTMORILLONITE

2016 ◽  
Vol 4 (1) ◽  
Author(s):  
Ikhsan Jaslin ◽  
Wijayanti Endang ◽  
Sunarto Sunarto
Keyword(s):  
Active Sites ◽  
Surface Complexation ◽  
Outer Sphere ◽  
Hydroxyl Groups ◽  
Process Data ◽  
Surface Complexes ◽  
Surface Complexation Model ◽  
Surface Hydroxyl ◽  
Phosphate Ions ◽  
Sorbate Concentration

The sorption of phosphate by montmorillonite at 10, 30, and 50 oC were investigated aiming to mainly determine thermodynamic parameters for the formation of surface complexes in the adsorption of phosphate ions by montmorillonite. Data were collected by adsorption edge experiments investigating the effect of pH, adsorption isotherms enabling the effect of sorbate concentration, and acid-base titration calculating protons released or taken up by adsorption process. Data analysis was carried out using surface complexation model to fit the data collected in this study using the parameters obtained from previous study, as well as to calculate the values of ΔH and ΔS. Previous study reported that phosphate ions formed two outer-sphere surface complexes with active sites of montmorillonite through hydrogen bonding. In the first complex,  [(XH)0– H2L─]─, the phosphate was held to permanent-charge X─ sites on the tetrahedral siloxane faces, and the second complex, [[(SO─)(SOH)]– – [H2L]─] 2─ was formed through the interaction between the phosphate and variable charge surface hydroxyl groups at the edges of montmorillonite crystals and on the octahedral alumina faces. The values of ΔH for the first and second reactions are 39.756 and 3.765x10-7 kJ mol‒1 respectively. Since both reactions have positive enthalpy values, it can be concluded that the reactions are endothermic. Large energy for the first reaction is needed by X─  sites (permanent negatively charge sites of montmorillonite) to be partially desolvated, on which K+ or other surface cations are replaced by H+ ions in the surface protonated process, and are then ready to interact phosphate ions in the solution. Small values of ΔH for the second reactions indicates that hydrogen bonds formed by phosphate and SOH sites in the second reaction are easily broken out, and the phosphate can easily desorbed from the surface. The values of ΔS for the first and second reactions are 122.523 and 2.393 x10-2  J K‒1 mol‒1, which are greater than -10 kJ mol‒1 and indicates that the surface reactions occurs through dissociative mechanisms.Keywords:   montmorillonite, adsorption edge, extended constant capacitance, surface complexation model, enthalpy, reaction mechanisms

scholarly journals Modeling of neotame and fructose thermochemistry: Comparison with mono and divalent metal ions by Computational and experimental approach

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Deepali Sharma ◽  
Suvardhan Kanchi ◽  
Ayyappa Bathinapatla ◽  
Inamuddin ◽  
Abdullah M. Asiri
Keyword(s):  
Metal Ions ◽  
Metal Ion ◽  
Density Functional ◽  
Divalent Metal ◽  
Basis Set ◽  
Hydroxyl Groups ◽  
Specific Cell ◽  
Water Medium ◽  
Artificial Sweetener ◽  
Divalent Metal Ions

AbstractThe metal complexes can demonstrate various interesting biological activities in the human body. However, the role of certain metal ions for specific cell activities is still subject to debate. This study is aimed at comparing the thermochemical properties of neotame (artificial sweetener) and α, β-fructose in gas phase and water medium. The interaction of α and β-fructose, neotame with monovalent and divalent metal ions was studied and comprehended by density functional theory (DFT) using B3LYP functional, 6–311 + G (d, p) and D3 basis set. Metal ion affinities (MIA) values depicted that ionic radius of metal ions played an important role in the interaction of α, β-fructose and neotame. The ∆G parameter was calculated to predict and understand the interaction of metal ions with α and β-fructose, neotame. The results suggested that the presence of hydroxyl groups and oxygen atoms in sugar molecules acted as preferred sites for the binding and interaction of mono and divalent ions. For the first time computational study has been introduced in the present study to review the progress in the application of metal binding with sugar molecules especially with neotame. Moreover, voltammetric behaviour of neotame-Zn2+ was studied using cyclic and differential pulse voltammetry. The obtained results suggest that the peak at −1.13 V is due to the reduction of Zn2+ in 0.1 M phosphate buffer medium at pH 5.5. Whereas, addition of 6-fold higher concentration of neotame to the ZnCl2.2H2O resulted in a new irreversible cathodic peak at −0.83, due to the reduction of neotame-Zn2+ complex. The Fourier transform infrared spectroscopy (FTIR) results indicates that the β-amino group (-NH) and carboxyl carbonyl (-C = O) groups of neotame is participating in the chelation process, which is further supported by DFT studies. The findings of this study identify the efficient chelation factors as major contributors into metal ion affinities, with promising possibilities to determine important biological processes in cell wall and glucose transmembrane transport.

scholarly journals Nanocomposites SnO2/SiO2:SiO2 Impact on the Active Centers and Conductivity Mechanism

Materials ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 3618 ◽  
Author(s):  
Dayana Gulevich ◽  
Marina Rumyantseva ◽  
Artem Marikutsa ◽  
Tatyana Shatalova ◽  
Elizaveta Konstantinova ◽  
...  
Keyword(s):  
Active Sites ◽  
Nitrogen Adsorption ◽  
Hydroxyl Groups ◽  
Pure Sno2 ◽  
Active Centers ◽  
Paramagnetic Resonance ◽  
Surface Hydroxyl ◽  
Chemisorbed Oxygen ◽  
Temperature Dependences ◽  
Sio2 Nanocomposites

This paper is focused on the effect of the stabilizing component SiO2 on the type and concentration of active sites in SnO2/SiO2 nanocomposites compared with nanocrystalline SnO2. Previously, we found that SnO2/SiO2 nanocomposites show better sensor characteristics in CO detection (lower detection limit, higher sensor response, and shorter response time) compared to pure SnO2 in humid air conditions. Nanocomposites SnO2/SiO2 synthesized using the hydrothermal method were characterized by low temperature nitrogen adsorption, XRD, energy dispersive X-ray spectroscopy (EDX), thermo-programmed reduction with hydrogen (TPR-H2), IR-, and electron-paramagnetic resonance (EPR)-spectroscopy methods. The electrophysical properties of SnO2 and SnO2/SiO2 nanocomposites were studied depending on the oxygen partial pressure in the temperature range of 200–400 °C. The introduction of SiO2 results in an increase in the concentration of paramagnetic centers Sn3+ and the amount of surface hydroxyl groups and chemisorbed oxygen and leads to a decrease in the negative charge on chemisorbed oxygen species. The temperature dependences of the conductivity of SnO2 and SnO2/SiO2 nanocomposites are linearized in Mott coordinates, which may indicate the contribution of the hopping mechanism with a variable hopping distance over local states.

Modified xanthan gum for crystal violet uptake: kinetic, isotherm, and thermodynamic behaviors

2019 ◽  
Vol 79 (1) ◽  
pp. 165-174 ◽  
Author(s):  
Meixia Zheng ◽  
Fengli Lian ◽  
Yujing Zhu ◽  
Bo Liu ◽  
Zheng Chen ◽  
...  
Keyword(s):  
Crystal Violet ◽  
Active Sites ◽  
Xanthan Gum ◽  
Maximum Adsorption Capacity ◽  
Hydroxyl Groups ◽  
X Ray Diffraction ◽  
Uptake Kinetic ◽  
Freundlich Isotherms ◽  
Pseudo Second Order ◽  
Kinetics Of

Abstract Modified xanthan gum (XG-AM-TTE) was employed as an adsorbent to study the adsorption behavior, thermodynamics and kinetics of crystal violet (CV) from an aqueous solution. Fourier transform infrared spectroscopy analysis indicates that the functional groups present in the adsorbent, such as carboxyl, ester and hydroxyl groups, are included on the external surface of the material, and these groups are potential active sites for interaction with CV. According to X-ray diffraction results, the structure of XG-AM-TTE after CV adsorption became more disordered, and the microstructure change is an indication of effective adsorption of CV to the surface, with CV becoming remarkably dispersed in the adsorbent according to the scanning electron microscopy observations. The adsorption kinetics and adsorption equilibrium were best described by the pseudo-second-order model and Freundlich isotherms, respectively. The thermodynamic parameters, as the Gibbs-free energy (ΔG), enthalpy (ΔH) and entropy (ΔS), indicated that the adsorption is a spontaneous, endothermic and entropy increase process. The maximum adsorption capacity of XG-AM-TTE was 183 ± 12 mg/g, suggesting that XG-AM-TTE is an efficient adsorbent.

scholarly journals Phosphonium-Based Porous Ionic Polymer with Hydroxyl Groups: A Bifunctional and Robust Catalyst for Cycloaddition of CO2 into Cyclic Carbonates

Polymers ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 596
Author(s):  
Yizhu Lei ◽  
Yali Wan ◽  
Wei Zhong ◽  
Dingfu Liu ◽  
Zhou Yang
Keyword(s):  
Ring Opening ◽  
Active Sites ◽  
Active Catalyst ◽  
Hydroxyl Groups ◽  
Cyclic Carbonates ◽  
Initial Activity ◽  
Ionic Polymer ◽  
Hierarchical Pore Structure ◽  
Ring Opening Of Epoxide ◽  
Hierarchical Pore

The integration of synergic hydrogen bond donors and nucleophilic anions that facilitates the ring-opening of epoxide is an effective way to develop an active catalyst for the cycloaddition of CO2 with epoxides. In this work, a new heterogeneous catalyst for the cycloaddition of epoxides and CO2 into cyclic carbonates based on dual hydroxyls-functionalized polymeric phosphonium bromide (PQPBr-2OH) was presented. Physicochemical characterizations suggested that PQPBr-2OH possessed large surface area, hierarchical pore structure, functional hydroxyl groups, and high density of active sites. Consequently, it behaved as an efficient, recyclable, and metal-free catalyst for the additive and solvent free cycloaddition of epoxides with CO2. Comparing the activity of PQPBr-2OH with that of the reference catalysts based on mono and non-hydroxyl functionalized polymeric phosphonium bromides suggested that hydroxyl functionalities in PQPBr-2OH showed a critical promotion effect on its catalytic activity for CO2 conversion. Moreover, PQPBr-2OH proved to be quite robust and recyclable. It could be reused at least ten times with only a slight decrease of its initial activity.

Sign in / Sign up

Export Citation Format

Share Document