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21.
Haobing Wang Xia Wu Yang Yang Masayoshi Nishiura Zhaomin Hou 《Angewandte Chemie (International ed. in English)》2020,59(18):7173-7177
The precise control of monomer sequence and stereochemistry in copolymerization is of much interest and importance for the synthesis of functional polymers, but studies toward this goal have met with only limited success to date. Now, the co‐syndiospecific alternating copolymerization of methoxyphenyl‐ and N,N‐dimethylaminophenyl‐functionalized propylenes with styrene by half‐sandwich rare‐earth catalysts is reported. This reaction efficiently afforded the corresponding functionalized propylene‐alt‐styrene copolymers with a perfect alternating sequence and excellent co‐syndiotacticity (rrrr >99 %), thus constituting the first example of co‐stereospecific alternating copolymerization of polar and non‐polar olefins. 相似文献
22.
Understanding water reduction towards H2 generation is crucial to overcome today's renewable energy obstacles. Previous studies have shown the superior H2 production performances of Cobalt based penta-pyridyl (CoaPPy) and tetra-pyridyl (CoaTPy) complexes in solution. We investigate H2 production cycles of CoaPPy and CoaTPy complexes immersed in water solution by means of Ab-initio Molecular Dynamics and Density Functional Theory. We monitor dynamic properties of the systems, solvent response and structural changes occurring in the catalysts, by simulating all intermediate steps of the H2 production cycle. Reduction free energies and reorganization energies are calculated. Our results show that, following the first electron injection, H2 production proceeds with the singlet spin state. Following the first electron insertion, we observe a significant rearrangement of the hydrogen bonding network in the first solvation shell. The cobalt center turns out to be more accessible for the surrounding water molecules in the case of CoaTPy at all the intermediate steps, which explains its higher catalytic performance over CoaPPy. Following the first reduction reaction, a larger gain in reduction free energy is estimated for CoaTPy with respect to CoaPPy, with a difference of 0.14 eV, in line with the experiments. For the second reduction, instead, CoaPPy shows more negative reduction potential, by 0.41 eV. 相似文献
23.
《Mendeleev Communications》2022,32(4):510-513
The influence of textural characteristics on the catalytic performance of supported KCoMoS2 catalysts was explored to provide essential information for the design of better catalysts for the synthesis of higher alcohols (C1–C5) from syngas. Syngas conversion was carried out over KCoMoS2 catalysts supported on various mesoporous (alumina and carbon-coated alumina) and microporous (two types of powdered activated carbons) materials. The experimental results show that catalysts supported over microporous materials exhibit higher catalytic activity in HAS from syngas than catalysts based on mesoporous materials. 相似文献
24.
Asymmetric synthesis is one of the most important and valuable research fields in modern organic chemistry. Since the use of electricity as a traceless oxidant or reductant under electrochemical conditions, highly reactive intermediates can selectively generate under mild reaction conditions through more environmentally benign conditions compared with the reactions using common chemical oxidants or reductants. Thus, the merging electrochemistry with asymmetric catalysis would provide a unique and powerful approach for the synthesis of optically active compounds under oxidative or reductive conditions. Selected recent (2018–2020) examples of enantioselective electro-organic synthesis using transition metal catalysts or organocatalysts are summarized in this short review. These examples are divided to oxidative and reductive transformations and described together with brief reaction mechanisms. 相似文献
25.
Hydrogen Spillover Enhanced Hydroxyl Formation and Catalytic Activity Toward CO Oxidation at the Metal/Oxide Interface 下载免费PDF全文
Yuekang Jin Guanghui Sun Feng Xiong Liangbing Ding Prof. Dr. Weixin Huang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(11):4252-4256
H2‐promoted catalytic activity of oxide‐supported metal catalysts in low‐temperature CO oxidation is of great interest but its origin remains unknown. Employing an FeO(111)/Pt(111) inverse model catalyst, we herewith report direct experimental evidence for the spillover of H(a) adatoms on the Pt surface formed by H2 dissociation to the Pt?FeO interface to form hydroxyl groups that facilely oxidize CO(a) on the neighboring Pt surface to produce CO2. Hydroxyl groups and coadsorbed water play a crucial role in the occurrence of hydrogen spillover. These results unambiguously identify the occurrence of hydrogen spillover from the metal surface to the noble metal/metal oxide interface and the resultant enhanced catalytic activity of the metal/oxide interface in low‐temperature CO oxidation, which provides a molecular‐level understanding of both H2‐promoted catalytic activity of metal/oxide ensembles in low‐temperature CO oxidation and hydrogen spillover. 相似文献
26.
The effect of amide solvent structure on the direct arylation polymerization (DArP) of 2‐Bromo‐3‐hexylthiophene 下载免费PDF全文
Andrey E. Rudenko Barry C. Thompson 《Journal of polymer science. Part A, Polymer chemistry》2015,53(21):2494-2500
In this work, we investigate the influence of the amide solvent chemical structure on the properties of poly(3‐hexylthiophene) (P3HT) prepared via direct arylation polymerization (DArP). Our findings indicate that for successful polymerization the amide must possess an acyclic aliphatic structure since cyclization of an amide results in a complete shutdown of DArP reactivity as evidenced by failed polymerization in N‐methylpyrrolidone, whereas the presence of an aromatic motif renders the amide solvent susceptible to C? H activation and leads to incorporation of the solvent structure into the P3HT backbone, as demonstrated on the example of N,N‐diethylbenzamide. Additionally, we observed that the steric bulk of alkyl substituents on both the nitrogen atom and the carbonyl group within the amide structure has to be delicately balanced for optimal DArP reactivity. In the optimal cases, P3HT is obtained in high yield, with high molecular weight and contains a minimal amount of structural defects. The obtained polymer samples were comprehensively studied in terms of their chemical structure, optical, thermal and solid‐state properties in thin films using GPC analysis, 1H NMR, MALDI, UV–vis, GIXRD spectroscopy, and DSC. We additionally note a drastic difference of the amide solvent effect between DArP and Stille polymerization. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2494–2500 相似文献
27.
Claudio De Rosa Finizia Auriemma Rocco Di Girolamo Odda Ruiz de Ballesteros 《Journal of Polymer Science.Polymer Physics》2014,52(10):677-699
The combination of the control of the concentration of stereodefects in isotactic polypropylene using metallocene catalysts and the crystallization via the mesophase is a strategy to tailor the mechanical properties. Stiff materials, flexible materials, and thermoplastic elastomers can be produced depending only on the concentration of rr stereodefects. Modulus, ductility, and strength can be modulated through the crystallization of α and γ forms or of the mesophase. Different morphologies are observed depending on the stereoregularity and conditions of crystallization. Crystals of the mesomorphic form always exhibit a nodular morphology, accounting for the similar good deformability of all quenched samples, whatever the concentration of stereodefects. The mesophase transforms by thermal treatments into the α form preserving the nodular morphology, with increase of strength while maintaining the ductility typical of the mesophase. Annealing of the mesophase permits a precise adjustment of crystallinity and size of nodular crystals offering additional options to modify the mechanical properties. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 677–699 相似文献
28.
29.
Chunhui Bao Jonathan M. Horton Zhifeng Bai Dejin Li Timothy P. Lodge Bin Zhao 《Journal of polymer science. Part A, Polymer chemistry》2014,52(24):1600-1619
Polymer brush-grafted particles (i.e., hairy particles) capable of undergoing direct, especially reversible, phase transfer from one liquid phase to another immiscible liquid phase in response to environmental changes have received growing interest due to their great potential in a wide variety of applications. This article is intended to review recent exciting advances in stimuli-triggered phase transfer of hairy particles in liquid-liquid biphasic systems. We start with a discussion of the mechanism of particle transfer across a liquid-liquid interface and progress to the synthesis of polymer brushes grafted on particles and the transfer of hairy particles between two immiscible liquid phases induced by various external stimuli, including temperature, pH, ionic strength, light, and solvents. The applications of thermally triggered phase transfer of hairy particles in catalysis (thermoregulated phase transfer catalysis) are discussed, followed by a summary and our perspective on future development. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1600–1619 相似文献
30.
Fe K‐Edge X‐ray Absorption Fine Structure Determination of γ‐Al2O3‐Supported Iron‐Oxide Species 下载免费PDF全文
Dr. Atsuko Tomita Dr. Takeshi Miki Takeru Tango Tatsuro Murakami Hideyuki Nakagawa Dr. Yutaka Tai 《Chemphyschem》2015,16(9):2015-2020
The structure of FeOx species supported on γ‐Al2O3 was investigated by using Fe K‐edge X‐ray absorption fine structure (XAFS) and X‐ray diffraction (XRD) measurements. The samples were prepared through the impregnation of iron nitrate on Al2O3 and co‐gelation of aluminum and iron sulfates. The dependence of the XRD patterns on Fe loading revealed the formation of α‐Fe2O3 particles at an Fe loading of above 10 wt %, whereas the formation of iron‐oxide crystals was not observed at Fe loadings of less than 9.0 wt %. The Fe K‐edge XAFS was characterized by a clear pre‐edge peak, which indicated that the Fe?O coordination structure deviates from central symmetry and that the degree of Fe?O?Fe bond formation is significantly lower than that in bulk samples at low Fe loading (<9.0 wt %). Fe K‐edge extended XAFS oscillations of the samples with low Fe loadings were explained by assuming an isolated iron‐oxide monomer on the γ‐Al2O3 surface. 相似文献