scholarly journals Fenton reaction mechanism generating no OH radicals in Nafion membrane decomposition

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Takao Tsuneda
Keyword(s):  
Reaction Mechanism ◽  
Sulfonic Acid ◽  
Fenton Reaction ◽  
Density Functional ◽  
Carbonic Acid ◽  
Membrane Surface ◽  
Decomposition Reaction ◽  
Nafion Membrane ◽  
Oh Radicals ◽  
Cation Hydration

Abstract Mechanism of Fenton reaction, which is a most widely-used degradation test for organic materials using hydrogen peroxide (H$$_2$$ 2 O$$_2$$ 2 ) and iron (Fe) cations, is revealed for the decomposition of hydrated Nafion membrane. This reaction mechanism has been assumed to generate OH radicals. For a doubly-hydrated Nafion membrane model, Fenton reaction with divalent and monovalent Fe (Fe$$^{2+}$$ 2 + and Fe$$^+$$ + ) cation hydration complexes is explored for experimentally-supported hydration numbers using long-range correction for density functional theory. As a result, it is found that H$$_2$$ 2 O$$_2$$ 2 coordinating to the Fe$$^{2+}$$ 2 + hydration complexes first approaches Nafion side chains in high humidity, then leads to the C–S bond dissociation of the side chain to produce carbonic acid group and sulfonic acid ion. On the other hand, once electron transfer proceeds between iron ions, the O–O bond of the coordinating H$$_2$$ 2 O$$_2$$ 2 is extended, then the C–S bond is dissociated to produce trihydroxymethyl group and sulfur trioxide, which are rapidly transformed to carboxyl group and sulfonic acid ion in aquo. This mechanism is confirmed by the vibrational spectrum analysis of the decomposed product. Collective Nafion decomposition mechanisms also suggest that the decomposition reaction uses the recycle of generated Fe cation hydration complexes under acidic condition near membrane surface.

Oxidation reaction mechanism and kinetics between OH radicals and alkyl-substituted aliphatic thiols: H-abstraction pathways

2019 ◽  
Vol 45 ◽  
pp. 146867831988612
Author(s):  
Arezoo Tahan ◽  
Abolfazl Shiroudi
Keyword(s):  
Reaction Mechanism ◽  
Rate Constants ◽  
Oxidation Reaction ◽  
Density Functional ◽  
Effective Rate ◽  
Bimolecular Reaction ◽  
State Theory ◽  
Oh Radicals ◽  
Step Model ◽  
Kinetic Rate Constants

Kinetic rate constants for the oxidation reaction of the hydroxyl radical with CH3SH, C2H5SH, n-C3H7SH, and iso-C3H7SH under inert (Ar) conditions over the temperature range 252–430 K have been studied theoretically using density functional theory along with various exchange–correlation functionals as well as the benchmark CBS-QB3 quantum chemical approach. Bimolecular rate constants were estimated using transition state theory and the statistical Rice–Ramsperger–Kassel–Marcus theory. Comparison with experiment confirms that in the OH addition reaction pathways leading to the related products, the first bimolecular reaction steps have effective negative activation energy barriers. Effective rate constants have been calculated according to a steady-state analysis of a two-step model reaction mechanism. As a consequence of the negative activation energies, pressures higher than 104 bar are required to reach the high-pressure limit. Both from thermodynamic and kinetic viewpoints, the most favorable process here is the oxidation reaction of hydroxyl radicals with n-C3H7SH.

scholarly journals A computational study for the reaction mechanism of metal-free cyanomethylation of aryl alkynoates with acetonitrile

RSC Advances ◽  
2021 ◽  
Vol 11 (30) ◽  
pp. 18246-18251
Author(s):  
Selçuk Eşsiz
Keyword(s):  
Density Functional Theory ◽  
Reaction Mechanism ◽  
Density Functional ◽  
Computational Study ◽  
Coupled Cluster ◽  
Functional Theory ◽  
Metal Free ◽  
Coupled Cluster Methods ◽  
High Level ◽  
Cluster Methods

A computational study of metal-free cyanomethylation and cyclization of aryl alkynoates with acetonitrile is carried out employing density functional theory and high-level coupled-cluster methods, such as [CCSD(T)].

scholarly journals Catalyzed Ethanol Chemical Looping Gasification Mechanism on the Perfect and Reduced Fe2O3 Surfaces

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1663
Author(s):  
Laixing Luo ◽  
Xing Zheng ◽  
Jianye Wang ◽  
Wu Qin ◽  
Xianbin Xiao ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Reaction Mechanism ◽  
Density Functional ◽  
Oxygen Carrier ◽  
Catalytic Decomposition ◽  
Density Functional Theory Calculations ◽  
Chemical Looping ◽  
Functional Theory ◽  
Barrier Energy ◽  
Gasification Technology

Biomass chemical looping gasification (CLG) is a novel gasification technology for hydrogen production, where the oxygen carrier (OC) transfers lattice oxygen to catalytically oxidize fuel into syngas. However, the OC is gradually reduced, showing different reaction activities in the CLG process. Fully understanding the CLG reaction mechanism of fuel molecules on perfect and reduced OC surfaces is necessary, for which the CLG of ethanol using Fe2O3 as the OC was introduced as the probe reaction to perform density functional theory calculations to reveal the decomposition mechanism of ethanol into the synthesis gas (including H2, CH4, ethylene, formaldehyde, acetaldehyde, and CO) on perfect and reduced Fe2O3(001) surfaces. When Fe2O3(001) is reduced to FeO0.375(001), the calculated barrier energy decreases and then increases again, suggesting that the reduction state around FeO(001) favors the catalytic decomposition of ethanol to produce hydrogen, which proves that the degree of reduction has an important effect on the CLG reaction.

scholarly journals Molecular simulation on mechanism of thiophene hydrodesulfurization on surface of Ni2P

2021 ◽  
pp. 014459872199495
Author(s):  
Songjian Du ◽  
Tingting Li ◽  
Xinwei Wang ◽  
Liqiang Zhang ◽  
Zhengda Yang ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Reaction Mechanism ◽  
Heavy Oil ◽  
Density Functional ◽  
Reaction Path ◽  
Functional Theory ◽  
Thiophene Hydrodesulfurization ◽  
Cracking Reaction ◽  
Materials Studio ◽  
Optimal Reaction

Hydrodesulfurization reaction, as the last step of hydrothermal cracking reaction, is of great significance for the reduction of viscosity and desulfurization of heavy oil. Based on Density Functional Theory and using Dmol3 module of Materials Studio, this research simulated the adsorption and hydrodesulfurization of thiophene on Ni2P (001) surface, and discussed the hydrodesulfurization reaction mechanism of thiophene on Ni2P (001) surface. It was found that the direct hydrodesulfurization of thiophene had more advantages than the indirect hydrodesulfurization of thiophene. Finally, the optimal reaction path was determined: C4H4S+H2→C4H6.

scholarly journals Bi-Functional Composting the Sulfonic Acid Based Proton Exchange Membrane for High Temperature Fuel Cell Application

Polymers ◽  
2020 ◽  
Vol 12 (5) ◽  
pp. 1000
Author(s):  
Guoxiao Xu ◽  
Juan Zou ◽  
Zhu Guo ◽  
Jing Li ◽  
Liying Ma ◽  
...  
Keyword(s):  
High Temperature ◽  
Fuel Cell ◽  
Composite Membrane ◽  
Sulfonic Acid ◽  
Elevated Temperatures ◽  
Mechanical Stability ◽  
Strong Dependence ◽  
Proton Exchange ◽  
Nafion Membrane ◽  
Silica Nanofiber

Although sulfonic acid (SA)-based proton-exchange membranes (PEMs) dominate fuel cell applications at low temperature, while sulfonation on polymers would strongly decay the mechanical stability limit the applicable at elevated temperatures due to the strong dependence of proton conduction of SA on water. For the purpose of bifunctionally improving mechanical property and high-temperature performance, Nafion membrane, which is a commercial SA-based PEM, is composited with fabricated silica nanofibers with a three-dimensional network structure via electrospinning by considering the excellent water retention capacity of silica. The proton conductivity of the silica nanofiber–Nafion composite membrane at 110 °C is therefore almost doubled compared with that of a pristine Nafion membrane, while the mechanical stability of the composite Nafion membrane is enhanced by 44%. As a result, the fuel cell performance of the silica nanofiber-Nafion composite membrane measured at high temperature and low humidity is improved by 38%.

scholarly journals DFT Study of the Electronic Structure of Cubic-SiC Nanopores with a C-Terminated Surface

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
M. Calvino ◽  
A. Trejo ◽  
M. I. Iturrios ◽  
M. C. Crisóstomo ◽  
Eliel Carvajal ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Band Gap ◽  
Density Functional ◽  
Surface Passivation ◽  
Phase Changes ◽  
Surface Relaxation ◽  
Oh Radicals ◽  
Functional Theory ◽  
Band Gap Engineering ◽  
Chemical Surface

A study of the dependence of the electronic structure and energetic stability on the chemical surface passivation of cubic porous silicon carbide (pSiC) was performed using density functional theory (DFT) and the supercell technique. The pores were modeled by removing atoms in the [001] direction to produce a surface chemistry composed of only carbon atoms (C-phase). Changes in the electronic states of the porous structures were studied by using different passivation schemes: one with hydrogen (H) atoms and the others gradually replacing pairs of H atoms with oxygen (O) atoms, fluorine (F) atoms, and hydroxide (OH) radicals. The results indicate that the band gap behavior of the C-phase pSiC depends on the number of passivation agents (other than H) per supercell. The band gap decreased with an increasing number of F, O, or OH radical groups. Furthermore, the influence of the passivation of the pSiC on its surface relaxation and the differences in such parameters as bond lengths, bond angles, and cell volume are compared between all surfaces. The results indicate the possibility of nanostructure band gap engineering based on SiC via surface passivation agents.

Density Functional Theory Study of Thiophene Desulfurization and Conversion of Desulfurization Product on Ni(111) Surface and Ni55 Cluster: Implication for the Mechanism of Reactive Adsorption Desulfurization over Ni/ZnO Catalysts

2021 ◽  
Author(s):  
Houyu Zhu ◽  
Xin Li ◽  
Naiyou Shi ◽  
Xuefei Ding ◽  
Zehua Yu ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Reaction Mechanism ◽  
Active Center ◽  
Density Functional ◽  
Density Functional Theory Study ◽  
Functional Theory ◽  
Reactive Adsorption ◽  
Adsorption Desulfurization

Ni/ZnO catalysts have been well recognized by industry and academia for exhibiting excellent desulfurization activities. However, intrinsic reaction mechanism on Ni active center is still obscure. Herein, we performed periodic...

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