The Experts below are selected from a list of 192 Experts worldwide ranked by ideXlab platform
Alexis T. Bell - One of the best experts on this subject based on the ideXlab platform.
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The influence of substrate composition on the kinetics of olefin epoxidation by hydrogen peroxide catalyzed by Iron(III) [tetrakis(pentafluorophenyl)] porphyrin
Journal of Molecular Catalysis A-chemical, 2006Co-Authors: Ned A. Stephenson, Alexis T. BellAbstract:Abstract We have recently proposed a mechanism for the epoxidation of cyclooctene by hydrogen peroxide catalyzed by Iron(III) [tetrakis(pentafluorophenyl)] porphyrin chloride. The expressions for the rate of hydrogen peroxide consumption and the yield of epoxide derived from this mechanism are in excellent agreement with experimental observations for a wide range of reaction conditions. An interesting feature of the expressions for the apparent rate coefficient and the yield of epoxide relative to peroxide consumed is that they are independent of the properties of the olefin. The present work was undertaken with the aim of determining whether this is a general result applicable to the epoxidation of other olefins. To this end, the rates of epoxidation of cyclooctene, styrene, cis-stilbene, cyclohexene, and norbornene were measured under identical conditions. For cyclooctene, styrene, and cis-stilbene, the observed kinetics and yield of epoxide were independent of the substrate, and no evidence was found by either UV–visible or 1H NMR spectroscopy for olefin coordination to the Iron Cation of the porphyrin. By contrast, the rates of cyclohexene and norbornene epoxidation and the corresponding epoxide yields were significantly lower than those of the other three olefins. The lower catalyst activity and lower epoxide yield correlated with both UV–visible and 1H NMR evidence for olefin coordination to the Iron Cation of the porphyrin. Olefin coordination increases the electron density on the Iron Cation and promotes homolytic cleavage relative to heterolytic cleavage of the oxygen-oxygen bond of coordinated hydrogen peroxide. This has the effect of reducing both the apparent rate coefficient for hydrogen peroxide consumption and the epoxide yield.
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Short communiCation The influence of substrate composition on the kinetics of olefin epoxidation by hydrogen peroxide catalyzed by Iron(III) (tetrakis(pentafluorophenyl)) porphyrin
2006Co-Authors: Ned A. Stephenson, Alexis T. BellAbstract:We have recently proposed a mechanism for the epoxidation of cyclooctene by hydrogen peroxide catalyzed by Iron(III) [tetrakis(pentafluorophenyl)] porphyrin chloride. The expressions for the rate of hydrogen peroxide consumption and the yield of epoxide derived from this mechanism are in excellent agreement with experimental observations for a wide range of reaction conditions. An interesting feature of the expressions for the apparent rate coefficient and the yield of epoxide relative to peroxide consumed is that they are independent of the properties of the olefin. The present work was undertaken with the aim of determining whether this is a general result applicable to the epoxidation of other olefins. To this end, the rates of epoxidation of cyclooctene, styrene, cis-stilbene, cyclohexene, and norbornene were measured under identical conditions. For cyclooctene, styrene, and cis-stilbene, the observed kinetics and yield of epoxide were independent of the substrate, and no evidence was found by either UV–visible or 1 H NMR spectroscopy for olefin coordination to the Iron Cation of the porphyrin. By contrast, the rates of cyclohexene and norbornene epoxidation and the corresponding epoxide yields were significantly lower than those of the other three olefins. The lower catalyst activity and lower epoxide yield correlated with both UV–visible and 1 H NMR evidence for olefin coordination to the Iron Cation of the porphyrin. Olefin coordination increases the electron density on the Iron Cation and promotes homolytic cleavage relative to heterolytic cleavage of the oxygen-oxygen bond of coordinated hydrogen peroxide. This has the effect of reducing both the apparent rate coefficient for hydrogen peroxide consumption and the epoxide yield. © 2006 Elsevier B.V. All rights reserved.
Liancheng Wang - One of the best experts on this subject based on the ideXlab platform.
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Iron Cation induced biphase symbiosis of h wo3 o wo3 0 33h2o and their crystal phase transition
CrystEngComm, 2017Co-Authors: H Wang, Ruimin Ding, Conghui Wang, Xiaobo Ren, Liancheng WangAbstract:Herein, tungsten oxide hexagonal prisms with a biphase of h-WO3 and o-WO3·0.33H2O were prepared by a facile hydrothermal method using Fe3+ Cations. The combination of instrumental characterization and software simulation proved that two phases coexisted in one nanoparticle with same morphology. The ratio of two phases could be changed by adjusting the concentration of Fe3+ Cations. On the basis of controlled experiments, a mechanism was proposed to illustrate the formation of this biphase WO3 structure, and it was also proved that the self-growth of Fe species was unfavorable for the coexistence of two phases.
Fernando Vicente - One of the best experts on this subject based on the ideXlab platform.
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Chemical oxidation of 2,4-dimethylphenol in soil by heterogeneous Fenton process.
Journal of hazardous materials, 2008Co-Authors: Arturo Romero, Aurora Santos, Fernando VicenteAbstract:Hydrogen peroxide has been used to oxidize a sorbed aromatic contaminant in a loamy sand with 195.9 g kg(-1) of organic carbon by using Iron as catalyst at 20 degrees C. The 2,4-dimethylphenol (2,4-DMP) was chosen as pollutant. Because of this soil generates a slightly basic pH in contact to an aqueous phase the solubility of the Iron Cation was determined in absence and presence of a chelating agent (l-ascorbic acid, l-Asc) and with and without soil. From results, it was found that in presence of soil the Iron Cation was always adsorbed or precipitaed onto the soil. Therefore, the procedure selected for soil remediation was to add firstly the Iron solution used as catalyst and following the hydrogen peroxide solution used as oxidant. As Iron Cation is sorbed onto the soil before the oxidant reagent is provided a heterogeneous catalytic system results. This modified Fenton runs have been carried out using 0.11 mg(2,4-DMP) g(-1)(soil) and 2.1 mg(Fe) g(-1)(soil). The H(2)O(2)/pollutant weight ratios used were 182 and 364. The results show that H(2)O(2) oxidizes 2,4-DMP producing CO(2) and acetic acid. After 20 min of reaction time a pollutant conversion of 75% and 86% was found, depending on the H(2)O(2) dosage. Moreover, it was found that hydrogen peroxide was heterogeneously decomposed by the soil (due to its organic and/or inorganic components) and its decomposition rate decreases when the Iron was previously precipitated-impregnated into the soil.
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Chemical oxidation of 2,4-dimethylphenol in soil by heterogeneous Fenton process.
Journal of Hazardous Materials, 2008Co-Authors: Arturo Romero, Aurora Santos, Fernando VicenteAbstract:Abstract Hydrogen peroxide has been used to oxidize a sorbed aromatic contaminant in a loamy sand with 195.9 g kg −1 of organic carbon by using Iron as catalyst at 20 °C. The 2,4-dimethylphenol (2,4-DMP) was chosen as pollutant. Because of this soil generates a slightly basic pH in contact to an aqueous phase the solubility of the Iron Cation was determined in absence and presence of a chelating agent ( l -ascorbic acid, l -Asc) and with and without soil. From results, it was found that in presence of soil the Iron Cation was always adsorbed or precipitaed onto the soil. Therefore, the procedure selected for soil remediation was to add firstly the Iron solution used as catalyst and following the hydrogen peroxide solution used as oxidant. As Iron Cation is sorbed onto the soil before the oxidant reagent is provided a heterogeneous catalytic system results. This modified Fenton runs have been carried out using 0.11 mg 2,4-DMP g −1 soil and 2.1 mg Fe g −1 soil . The H 2 O 2 /pollutant weight ratios used were 182 and 364. The results show that H 2 O 2 oxidizes 2,4-DMP producing CO 2 and acetic acid. After 20 min of reaction time a pollutant conversion of 75% and 86% was found, depending on the H 2 O 2 dosage. Moreover, it was found that hydrogen peroxide was heterogeneously decomposed by the soil (due to its organic and/or inorganic components) and its decomposition rate decreases when the Iron was previously precipitated–impregnated into the soil.
Wenjun Zhang - One of the best experts on this subject based on the ideXlab platform.
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Iron vacancies induced bifunctionality in ultrathin feroxyhyte nanosheets for overall water splitting
Advanced Materials, 2018Co-Authors: Bin Liu, Yun Wang, Huiqing Peng, Ruoou Yang, Zheng Jiang, Xingtai Zhou, Chunsing Lee, Huijun Zhao, Wenjun ZhangAbstract:Exploring of new catalyst activation principle holds a key to unlock catalytic powers of cheap and earth-abundant materials for large-scale appliCations. In this regard, the vacancy defects have been proven to be effective to initiate catalytic active sites and endow high electrocatalytic activities. However, such electrocatalytically active defects reported to date have been mostly formed by anion vacancies. Herein, it is demonstrated for the first time that Iron Cation vacancies induce superb water splitting bifunctionality in alkaline media. A simple wet-chemistry method is developed to grow ultrathin feroxyhyte (δ-FeOOH) nanosheets with rich Fe vacancies on Ni foam substrate. The theoretical and experimental results confirm that, in contrast to anion vacan-cies, the formation of rich second neighboring Fe to Fe vacancies in δ-FeOOH nanosheets can create catalytic active centers for both hydrogen and oxygen evolution reactions. The atomic level insight into the new catalyst activation principle based on metal vacancies is adaptable for developing other transi-tion metal electrocatalysts, including Fe-based ones.
Ned A. Stephenson - One of the best experts on this subject based on the ideXlab platform.
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The influence of substrate composition on the kinetics of olefin epoxidation by hydrogen peroxide catalyzed by Iron(III) [tetrakis(pentafluorophenyl)] porphyrin
Journal of Molecular Catalysis A-chemical, 2006Co-Authors: Ned A. Stephenson, Alexis T. BellAbstract:Abstract We have recently proposed a mechanism for the epoxidation of cyclooctene by hydrogen peroxide catalyzed by Iron(III) [tetrakis(pentafluorophenyl)] porphyrin chloride. The expressions for the rate of hydrogen peroxide consumption and the yield of epoxide derived from this mechanism are in excellent agreement with experimental observations for a wide range of reaction conditions. An interesting feature of the expressions for the apparent rate coefficient and the yield of epoxide relative to peroxide consumed is that they are independent of the properties of the olefin. The present work was undertaken with the aim of determining whether this is a general result applicable to the epoxidation of other olefins. To this end, the rates of epoxidation of cyclooctene, styrene, cis-stilbene, cyclohexene, and norbornene were measured under identical conditions. For cyclooctene, styrene, and cis-stilbene, the observed kinetics and yield of epoxide were independent of the substrate, and no evidence was found by either UV–visible or 1H NMR spectroscopy for olefin coordination to the Iron Cation of the porphyrin. By contrast, the rates of cyclohexene and norbornene epoxidation and the corresponding epoxide yields were significantly lower than those of the other three olefins. The lower catalyst activity and lower epoxide yield correlated with both UV–visible and 1H NMR evidence for olefin coordination to the Iron Cation of the porphyrin. Olefin coordination increases the electron density on the Iron Cation and promotes homolytic cleavage relative to heterolytic cleavage of the oxygen-oxygen bond of coordinated hydrogen peroxide. This has the effect of reducing both the apparent rate coefficient for hydrogen peroxide consumption and the epoxide yield.
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Short communiCation The influence of substrate composition on the kinetics of olefin epoxidation by hydrogen peroxide catalyzed by Iron(III) (tetrakis(pentafluorophenyl)) porphyrin
2006Co-Authors: Ned A. Stephenson, Alexis T. BellAbstract:We have recently proposed a mechanism for the epoxidation of cyclooctene by hydrogen peroxide catalyzed by Iron(III) [tetrakis(pentafluorophenyl)] porphyrin chloride. The expressions for the rate of hydrogen peroxide consumption and the yield of epoxide derived from this mechanism are in excellent agreement with experimental observations for a wide range of reaction conditions. An interesting feature of the expressions for the apparent rate coefficient and the yield of epoxide relative to peroxide consumed is that they are independent of the properties of the olefin. The present work was undertaken with the aim of determining whether this is a general result applicable to the epoxidation of other olefins. To this end, the rates of epoxidation of cyclooctene, styrene, cis-stilbene, cyclohexene, and norbornene were measured under identical conditions. For cyclooctene, styrene, and cis-stilbene, the observed kinetics and yield of epoxide were independent of the substrate, and no evidence was found by either UV–visible or 1 H NMR spectroscopy for olefin coordination to the Iron Cation of the porphyrin. By contrast, the rates of cyclohexene and norbornene epoxidation and the corresponding epoxide yields were significantly lower than those of the other three olefins. The lower catalyst activity and lower epoxide yield correlated with both UV–visible and 1 H NMR evidence for olefin coordination to the Iron Cation of the porphyrin. Olefin coordination increases the electron density on the Iron Cation and promotes homolytic cleavage relative to heterolytic cleavage of the oxygen-oxygen bond of coordinated hydrogen peroxide. This has the effect of reducing both the apparent rate coefficient for hydrogen peroxide consumption and the epoxide yield. © 2006 Elsevier B.V. All rights reserved.
