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Reduction of Alkenes: Asymmetric Catalytic Hydrogenation02:17

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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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Ladder diagrams are useful tools for understanding redox equilibrium reactions, especially the effects of concentration changes on the electrochemical potential of the reaction. The vertical axis in the redox ladder diagrams represents the electrochemical potential, E. The area of predominance is demarcated using the Nernst equation.
Consider the Fe3+/Fe2+ half-reaction, which has a standard-state potential of +0.771 V. At potentials more positive than +0.771 V, Fe3+ predominates, whereas Fe2+...
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Alkenes undergo reduction by the addition of molecular hydrogen to give alkanes. Because the process generally occurs in the presence of a transition-metal catalyst, the reaction is called catalytic hydrogenation.
Metals like palladium, platinum, and nickel are commonly used in their solid forms — fine powder on an inert surface. As these catalysts remain insoluble in the reaction mixture, they are referred to as heterogeneous catalysts.
The hydrogenation process takes place on the...
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Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
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Unlike the easy catalytic hydrogenation of an alkene double bond, hydrogenation of a benzene double bond under similar reaction conditions does not take place easily. For example, in the reduction of stilbene, the benzene ring remains unaffected while the alkene bond gets reduced. Hydrogenation of an alkene double bond is exothermic and a favorable process. In contrast, to hydrogenate the first unsaturated bond of benzene, an energy input is needed; that is, the process is endothermic. This is...
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The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
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通过调整铜催化剂的协调数来调节CO2的反应路径

Jiapeng Jiao1,2, Xinchen Kang3,4, Jiahao Yang3,4

  • 1Shanghai Key Laboratory of Green Chemistry and Chemical Processes, State Key Laboratory of Petroleum Molecular and Process Engineering, School of Chemistry and Molecular Engineering, East China Normal University, Shanghai 200062, China.

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概括

具有不同协调号码 (CN) 的铜催化剂控制二氧化碳电减产品的分布. 高CN有利于C2+碳化合物,而低CN产生甲,提供调整催化剂性能的途径.

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科学领域:

  • 电化学
  • 催化剂
  • 材料科学

背景情况:

  • 基于铜的催化剂有效地将二氧化碳 (CO2) 电降解为有价值的碳化合物产品.
  • 控制二氧化碳电还原的选择性仍然是催化研究的一个重大挑战.

研究的目的:

  • 研究铜的协调数 (CN) 对二氧化碳的电减的影响.
  • 要将催化剂结构,特别是Cu CN,与产品分布 (CH4与C2+碳化合物) 相对应.

主要方法:

  • 通过使用循环电量计,电静电解和脉冲电解来减少 CuO 前体,制造具有不同协调数 (高CN和低CN) 的铜催化剂.
  • 使用现场X射线吸收光谱和拉曼光谱对催化剂和*CO中间吸附的描述.
  • 电化学评估二氧化碳电减性能,包括法拉第效率和部分电流密度.

主要成果:

  • 高CNCu催化剂,如Pot-Cu,主要产生C2+碳化合物,法拉达效率 (FE) 为82.5%,部分电流密度 (j) 为514.3mA cm-2.
  • 低CNCu催化剂,如Pul(3)-Cu,有利于甲 (CH4) 生产,达到最高的FECH4为56.7%,jCH4为234.4mA cm-2.
  • 光谱研究证实,Cu CN决定了*CO吸附,从而指导了CO2减少反应 (CO2RR) 路径.

结论:

  • 的协调数是控制二氧化碳电还原产品选择性的关键因素.
  • 从二氧化碳中选择性地产生甲或更高碳化合物.
  • 这项工作为CO2RR催化剂的结构性能关系提供了基本的见解.