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相关概念视频

Catalysis02:50

Catalysis

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The presence of a catalyst affects the rate of a chemical reaction. A catalyst is a substance that can increase the reaction rate without being consumed during the process. A basic comprehension of a catalysts’ role during chemical reactions can be understood from the concept of reaction mechanisms and energy diagrams.
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Reduction of Alkenes: Asymmetric Catalytic Hydrogenation02:17

Reduction of Alkenes: Asymmetric Catalytic Hydrogenation

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Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
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Radical Substitution: Halogenation of Alkanes and Alkyl Substituents01:27

Radical Substitution: Halogenation of Alkanes and Alkyl Substituents

8.7K
In the presence of heat or light, alkanes react with molecular halogens to form alkyl halides by a substitution reaction called radical halogenation. This reaction has three steps: initiation, propagation, and termination, as seen in the radical chlorination of methane to produce methyl chloride.
In the initiation step of the reaction, the chlorine molecule undergoes homolytic cleavage in the presence of light or heat, forming two highly reactive chlorine radicals. Propagation occurs in two...
8.7K
Radical Substitution: Allylic Chlorination01:31

Radical Substitution: Allylic Chlorination

2.6K
Typically, when alkenes react with halogens at low temperatures, an addition reaction occurs. However, upon increasing the temperature or under reaction conditions that form radicals, providing a low but steady concentration of halogen radicals, allylic substitution reaction is favored. This is because allylic hydrogens are very reactive as the formed intermediate is resonance stabilized. For example, when propene is treated with chlorine in the gas phase at 400 °C, it undergoes allylic...
2.6K
Halogenation of Alkenes02:46

Halogenation of Alkenes

16.5K
Halogenation is the addition of chlorine or bromine across the double bond in an alkene to yield a vicinal dihalide. The reaction occurs in the presence of inert and non-nucleophilic solvents, such as methylene chloride, chloroform, or carbon tetrachloride.
Consider the bromination of cyclopentene. Molecular bromine is polarized in the proximity of the π electrons of cyclopentene. An electrophilic bromine atom adds across the double bond, forming a cyclic bromonium ion intermediate.
16.5K
Radical Halogenation: Thermodynamics01:34

Radical Halogenation: Thermodynamics

4.0K
The thermodynamic favorability of a reaction is determined by the change in Gibbs free energy (ΔG). ΔG has two components- enthalpy (ΔH) and entropy (ΔS). The entropy component is negligible for alkane halogenation because the number of reactants and product molecules are equal. In this case, the ΔG is governed only by the enthalpy component. The most crucial factor that determines ΔH is the strength of the bonds. ΔH can be determined by comparing the energy...
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Application of Elemental Lanthanides in the Selective C-F Activation of Trifluoromethylated Benzofulvenes Providing Access to Various Difluoroalkenes
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基于兰的催化剂中的动态活性站点进化决定了乙化途径.

Yuting Li1,2, Haifeng Qi3, Zihan Zhu1,2

  • 1State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, 116023, China.

Angewandte Chemie (International ed. in English)
|June 20, 2025
PubMed
概括

兰氧化 (LaOCl) 在乙烯化过程中转化为LaCl3,导致过度化. 稳定LaOCl和管理基是选择性聚乙烯 (PVC) 前体合成的关键.

关键词:
乙烯化以乙为.兰氧化的使用方法天然气是一种天然气.过度化过度化聚乙烯化物 聚乙烯化物结构演变的结构演变.

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科学领域:

  • 催化剂是一种催化剂.
  • 材料科学 材料科学 材料科学
  • 化学工程是化学工程的重要组成部分.

背景情况:

  • 乙的极端化是一种低碳的途径,可产生聚乙烯 (PVC) 前体.
  • 乙化中的选择性问题与过度化有关,而氧化 (LaOCl) 是一个有前途的催化剂.
  • 在富含的条件下LaOCl的结构行为及其在选择性丧失中的作用尚不清楚.

研究的目的:

  • 为了研究LaOCl在乙化过程中的结构动态.
  • 阐明LaOCl催化化过程中选择性丧失背后的机制.
  • 了解表面基和催化剂结构在控制选择性的作用.

主要方法:

  • 集成先进的光谱技术.
  • 理论计算的应用.
  • 合成和表征支持Al2O3的LaCl3模型催化剂.

主要成果:

  • 观察到从LaOCl到LaCl3的连续转化,与产品分布向三乙烯的转变相关.
  • 在化过程中形成的表面基团促进了1,2-二乙烯的吸附和随后的过度化.
  • 在Al2O3上单层分散的LaCl3表现出大小依赖的性,与界面氧稳定Cl基进行选择性乙转化为1,2-二乙.
  • 聚合的LaCl3纳米粒子由于无法稳定Cl基而没有活动.

结论:

  • 催化剂结构显著影响兰他催化化中的选择性.
  • 稳定转移性LaOClx物种和控制表面基化学是提高选择性的关键.
  • 这些发现为设计用于选择性乙化改进的催化剂提供了指导原则.