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Heterogeneous Catalysis01:22

Heterogeneous Catalysis

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Heterogeneous catalysis involves a catalyst in a different phase from the reactants. It is a process where the catalyst and the reactants are in distinct phases, typically solid and gas or liquid.Most heterogeneous catalysts are metals, metal oxides, or acids. The list includes transition metals like iron (Fe), cobalt (Co), nickel (Ni), palladium (Pd), platinum (Pt), chromium (Cr), manganese (Mn), tungsten (W), silver (Ag), and copper (Cu). These metals possess partially vacant d orbitals that...
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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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Reduction of Alkenes: Catalytic Hydrogenation02:13

Reduction of Alkenes: Catalytic Hydrogenation

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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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Catalysis02:50

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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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ortho–para-Directing Deactivators: Halogens01:24

ortho–para-Directing Deactivators: Halogens

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Halogens are ortho–para directors. They are more electronegative than carbon. Therefore, as ring substituents, they can withdraw electrons through the inductive effect and deactivate the aromatic ring towards electrophilic substitution. Halogens also have an electron-donating resonance effect on the ring, which influences the orientation of the incoming electrophile. If an electrophile attacks at the ortho or the para position, the halogen donates electrons and stabilizes the intermediate...
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Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation02:24

Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation

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Introduction
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
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探索基于表面电场梯度的Ortho-Para转化催化剂.

Hiroshi Mizoguchi1, Yuichi Shirako2, Shusaku Shoji2

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新的氧化物催化剂,包括有过渡金属的SiO2和CeO2,有效地促进了正向转换. 这些催化剂对准的生产表现出卓越的活性,这对于诸如量子计算之类的应用至关重要.

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科学领域:

  • 材料科学 材料科学 材料科学
  • 催化剂是一种催化剂.
  • 物理化学 物理化学

背景情况:

  • 在需要偏的应用中,将转化为转化 (OP) 是必不可少的.
  • 现有的催化剂缺乏足够的效率和稳定性,无法广泛使用.
  • 表面电场在OP转换中的作用尚未完全理解.

研究的目的:

  • 调查假设,在高离子性氧化物表面上的不均电场促进OP转化.
  • 发现新的氧化物基催化剂,以实现高效的OP转化.
  • 在这些新催化剂上阐明OP转换的机制.

主要方法:

  • 选氧化物材料使用格子能量作为电离性的指标.
  • 合成和表征新的氧化物催化剂与3d后期过渡金属共催化剂.
  • 在冷温度下测量分数和转换率.
  • 分析催化剂表面上的吸附和解离行为.

主要成果:

  • 确定了SiO2,γ-Al2O3和CeO2与过渡金属相结合,作为有效的OP转化催化剂.
  • 在20分钟内使用5%的Fe载荷SiO2.2,达到50%的H2分数 (在77K处平衡).
  • 与Mn3O4.4等基准催化剂相比,其活性显著更高.
  • 观察到小 (1-12nm) 协催化剂纳米颗粒吸附H2没有解离.

结论:

  • 具有不均质电场的高离子性氧化物有效催化OP转化.
  • 发现的催化剂为 Παρα生产提供了卓越的性能.
  • 核四极相互作用和旋转放松在提高OP转换率方面发挥着关键作用.