The Experts below are selected from a list of 8502 Experts worldwide ranked by ideXlab platform
Pierre A Jacobs - One of the best experts on this subject based on the ideXlab platform.
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transition metal anion exchanged layered double hydroxides as a bioinspired model of vanadium bromoperoxidase
Journal of Catalysis, 2003Co-Authors: Bert F Sels, Mieke Buntinx, Pierre A JacobsAbstract:Abstract Tungstate-exchanged layered double hydroxides (LDHs) and V-bromoperoxidase enzymes perform oxidative Brominations in a highly similar way: first H 2 O 2 binds on the metal to form a peroxometal complex; next the peroxometal oxidizes Br − to “Br + ”; this electrophilic “Br + ” halogenates an organic compound, or oxidizes a second H 2 O 2 molecule to form excited state singlet oxygen. Full evidence for this similarity is given, based on spectroscopic observation of peroxotungstate and 1 O 2 and on identification of the organic Bromination products. In comparison with the homogeneous oxometallates, or with heterogeneous Ti-catalysts, the bioinspired LDH–WO 4 2− catalyst displays much higher rates of Br − oxidation; this rate enhancement is explained. The activity of LDH–WO 4 2− can be enhanced by changing the elemental composition of the octahedral layer of the LDH structure. Since LDH–WO 4 2− is stable toward leaching and high H 2 O 2 concentrations, it is a practical catalyst for oxidative Bromination.
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layered double hydroxides exchanged with tungstate as biomimetic catalysts for mild oxidative Bromination
Nature, 1999Co-Authors: Bert F Sels, Mieke Buntinx, Dirk De Vos, Frederic Pierard, Kirschde A Mesmaeker, Pierre A JacobsAbstract:The manufacture of a range of bulk and fine chemicals, including flame retardants, disinfectants and antibacterial and antiviral drugs, involves Bromination1. Conventional Bromination methods typically use elemental bromine, a pollutant and a safety and health hazard. Attempts to develop alternative and more benign strategies have been inspired by haloperoxidase enzymes, which achieve selective halogenation at room temperature and nearly neutral pH by oxidizing inorganic halides with hydrogen peroxide2,3. The enzyme vanadium bromoperoxidase has attracted particular interest4,5 in this regard, and several homogeneous inorganic catalysts mimicking its activity are available6,7,8,9,10,11, although they are limited by the requirement for strongly acidic reaction media. A heterogenous mimic operating at neutral pH has also been reported12, but shows only modest catalytic activity. Here we describe a tungstate-exchanged layered double hydroxide that catalyses oxidative Bromination and bromide-assisted epoxidation reactions in a selective manner. We find that the catalyst is over 100 times more active than its homogeneous analogue. The low cost and heterogeneous character of this system, together with its ability to operate efficiently under mild conditions using bromides rather than elemental bromine, raise the prospect of being able to develop a clean and efficient industrial route to brominated chemicals and drugs and epoxide intermediates.
Jinchang Liu - One of the best experts on this subject based on the ideXlab platform.
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effects of Bromination dehydroBromination on the microstructure of isotropic pitch precursors for carbon fibers
Polymers, 2020Co-Authors: Dingcheng Liang, Qiang Xie, Deqian Liu, Shuai Yang, Jinchang LiuAbstract:In this work, isotropic pitch precursors are synthesized by the Bromination-deBromination method with ethylene bottom oil (EO) as the raw material and bromine as the initiator for pitch formation and condensation reactions. The aggregation structure, molecular weight distribution, and molecular structure of isotropic pitch precursors are characterized by thermal mechanical analyzer (TMA), MALDI TOF-MS, and 13C NMR, respectively, for revealing the mechanism of synthesis of isotropic pitch precursors. The results show that at low bromine concentrations, polycyclic aromatic hydrocarbons (PAHs) were mainly ordered in cross-linked structures by Bromination-deBromination through substitution reactions of side chains. The condensed reactivity can be improved by the effect of bromine, meaning that condensation reaction was aggravated by the method of Bromination-dehydroBromination. In the presence of excess bromine, the cross-linked stereo structure of PAHs changed to the planar structure of condensed PAHs, which was not conducive to the subsequent spinning and preparation of carbon fibers.
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controllable synthesis of isotropic pitch precursor for general purpose carbon fiber using waste ethylene tar via Bromination dehydroBromination
Journal of Cleaner Production, 2020Co-Authors: Jinchang Liu, Xujun Chen, Qiang Xie, Dingcheng LiangAbstract:Abstract Nowadays, the substantial amount of waste ethylene tar (ET) lacks a clean and efficient route for utilization. In this work, a feasible approach was developed to fabricate general purpose carbon fiber (GPCF) using ET as a raw material. The method of Bromination–dehydroBromination was used to synthesize controllably isotropic pitch precursor for GPCF. The results show that Bromination–dehydroBromination reaction promotes the cyclization and aromatization of small molecules and relatively low molecular weight components and also prevents excess condensation during thermal treatment. The molecular structure of pitch precursor generated from Bromination–dehydroBromination reaction has more linear and cross-linked structures as more naphthenic groups and the side chain of aromatic rings. The spinnability of pitch precursors and the mechanical performance of GPCFs are optimized when 10 wt% of bromine is introduced in synthetic reaction. The tensile strength, Young’s modulus, and elongation property of the final GPCF are 1072 ± 66 MPa, 47 ± 7 GPa, and 2.3%, respectively, with the diameter of 10.3 ± 0.5 μm.
Bert F Sels - One of the best experts on this subject based on the ideXlab platform.
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transition metal anion exchanged layered double hydroxides as a bioinspired model of vanadium bromoperoxidase
Journal of Catalysis, 2003Co-Authors: Bert F Sels, Mieke Buntinx, Pierre A JacobsAbstract:Abstract Tungstate-exchanged layered double hydroxides (LDHs) and V-bromoperoxidase enzymes perform oxidative Brominations in a highly similar way: first H 2 O 2 binds on the metal to form a peroxometal complex; next the peroxometal oxidizes Br − to “Br + ”; this electrophilic “Br + ” halogenates an organic compound, or oxidizes a second H 2 O 2 molecule to form excited state singlet oxygen. Full evidence for this similarity is given, based on spectroscopic observation of peroxotungstate and 1 O 2 and on identification of the organic Bromination products. In comparison with the homogeneous oxometallates, or with heterogeneous Ti-catalysts, the bioinspired LDH–WO 4 2− catalyst displays much higher rates of Br − oxidation; this rate enhancement is explained. The activity of LDH–WO 4 2− can be enhanced by changing the elemental composition of the octahedral layer of the LDH structure. Since LDH–WO 4 2− is stable toward leaching and high H 2 O 2 concentrations, it is a practical catalyst for oxidative Bromination.
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layered double hydroxides exchanged with tungstate as biomimetic catalysts for mild oxidative Bromination
Nature, 1999Co-Authors: Bert F Sels, Mieke Buntinx, Dirk De Vos, Frederic Pierard, Kirschde A Mesmaeker, Pierre A JacobsAbstract:The manufacture of a range of bulk and fine chemicals, including flame retardants, disinfectants and antibacterial and antiviral drugs, involves Bromination1. Conventional Bromination methods typically use elemental bromine, a pollutant and a safety and health hazard. Attempts to develop alternative and more benign strategies have been inspired by haloperoxidase enzymes, which achieve selective halogenation at room temperature and nearly neutral pH by oxidizing inorganic halides with hydrogen peroxide2,3. The enzyme vanadium bromoperoxidase has attracted particular interest4,5 in this regard, and several homogeneous inorganic catalysts mimicking its activity are available6,7,8,9,10,11, although they are limited by the requirement for strongly acidic reaction media. A heterogenous mimic operating at neutral pH has also been reported12, but shows only modest catalytic activity. Here we describe a tungstate-exchanged layered double hydroxide that catalyses oxidative Bromination and bromide-assisted epoxidation reactions in a selective manner. We find that the catalyst is over 100 times more active than its homogeneous analogue. The low cost and heterogeneous character of this system, together with its ability to operate efficiently under mild conditions using bromides rather than elemental bromine, raise the prospect of being able to develop a clean and efficient industrial route to brominated chemicals and drugs and epoxide intermediates.
Dingcheng Liang - One of the best experts on this subject based on the ideXlab platform.
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effects of Bromination dehydroBromination on the microstructure of isotropic pitch precursors for carbon fibers
Polymers, 2020Co-Authors: Dingcheng Liang, Qiang Xie, Deqian Liu, Shuai Yang, Jinchang LiuAbstract:In this work, isotropic pitch precursors are synthesized by the Bromination-deBromination method with ethylene bottom oil (EO) as the raw material and bromine as the initiator for pitch formation and condensation reactions. The aggregation structure, molecular weight distribution, and molecular structure of isotropic pitch precursors are characterized by thermal mechanical analyzer (TMA), MALDI TOF-MS, and 13C NMR, respectively, for revealing the mechanism of synthesis of isotropic pitch precursors. The results show that at low bromine concentrations, polycyclic aromatic hydrocarbons (PAHs) were mainly ordered in cross-linked structures by Bromination-deBromination through substitution reactions of side chains. The condensed reactivity can be improved by the effect of bromine, meaning that condensation reaction was aggravated by the method of Bromination-dehydroBromination. In the presence of excess bromine, the cross-linked stereo structure of PAHs changed to the planar structure of condensed PAHs, which was not conducive to the subsequent spinning and preparation of carbon fibers.
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controllable synthesis of isotropic pitch precursor for general purpose carbon fiber using waste ethylene tar via Bromination dehydroBromination
Journal of Cleaner Production, 2020Co-Authors: Jinchang Liu, Xujun Chen, Qiang Xie, Dingcheng LiangAbstract:Abstract Nowadays, the substantial amount of waste ethylene tar (ET) lacks a clean and efficient route for utilization. In this work, a feasible approach was developed to fabricate general purpose carbon fiber (GPCF) using ET as a raw material. The method of Bromination–dehydroBromination was used to synthesize controllably isotropic pitch precursor for GPCF. The results show that Bromination–dehydroBromination reaction promotes the cyclization and aromatization of small molecules and relatively low molecular weight components and also prevents excess condensation during thermal treatment. The molecular structure of pitch precursor generated from Bromination–dehydroBromination reaction has more linear and cross-linked structures as more naphthenic groups and the side chain of aromatic rings. The spinnability of pitch precursors and the mechanical performance of GPCFs are optimized when 10 wt% of bromine is introduced in synthetic reaction. The tensile strength, Young’s modulus, and elongation property of the final GPCF are 1072 ± 66 MPa, 47 ± 7 GPa, and 2.3%, respectively, with the diameter of 10.3 ± 0.5 μm.
Weihua Yang - One of the best experts on this subject based on the ideXlab platform.
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fundamental studies on a novel series of bipolar membranes prepared from poly 2 6 dimethyl 1 4 phenylene oxide ppo i effect of anion exchange layers on i v curves of bipolar membranes
Journal of Membrane Science, 2004Co-Authors: Tongwen Xu, Weihua YangAbstract:Abstract In this paper, a new preparation route for a series of bipolar membranes is proposed. The bipolar membranes are initiated directly from same base polymer poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), in which the anion exchange layer is prepared by Bromination with bromine and then quaternary amination instead of chloromethylation with chloromethyl methyl ether and then quaternary amination and the cation exchange layer prepared by conventional sulfonation. The fundamental characteristics of bipolar membranes, current–voltage curves, are fully discussed based on the properties of anion exchange layers which can be controlled by Bromination position and content as well as the amination time. The results show that the prepared bipolar membranes can exhibit lower voltage drop over 100 mA/cm 2 and possess excellent industrial application potentials if the Bromination process and amination process of anion exchange layers are properly controlled.
