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相关概念视频

Reduction of Alkenes: Catalytic Hydrogenation02:13

Reduction of Alkenes: Catalytic Hydrogenation

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 surface of...
Distillation: Vapor–Liquid Equilibria01:01

Distillation: Vapor–Liquid Equilibria

Distillation is a separation technique that takes advantage of the boiling point properties of disparate elements in a mixture. To perform distillation, we begin by heating a miscible mixture of two liquids with a significant difference in boiling points (at least 20°C). As the solution heats up and reaches the bubble point of the more volatile component, some molecules of the more volatile component transition into the gas phase and travel upward into the condenser, which is a glass tube with...
¹H NMR: Complex Splitting01:13

¹H NMR: Complex Splitting

A proton M that is coupled to a proton X results in doublet signals for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When M is coupled to a second proton A, such as in styrene oxide, each peak in the doublet is split into another doublet.
Splitting diagrams or splitting tree diagrams are routinely used to depict such complex couplings. While drawing splitting diagrams, the splitting with the larger coupling constant is usually applied first.
¹H NMR of Labile Protons: Deuterium (²H) Substitution00:48

¹H NMR of Labile Protons: Deuterium (²H) Substitution

This lesson illustrates the role of deuterium substitution in simplifying the NMR spectrum of compounds comprising labile protons. One method employed is the use of deuterium. Amongst the three isotopes of hydrogen, deuterium (2H) has a nucleus composed of one proton and one neutron. When the D2O solvent is added to a pure dry ethanol solution, its labile proton is substituted with deuterium.
IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations01:08

IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations

Identical bonds within a polyatomic group can stretch symmetrically (in-phase) or asymmetrically (out-of-phase). Similar to hydrogen bonding, these vibrations also influence the shape of the IR peak. Generally, asymmetric stretching frequencies are higher than symmetric stretching frequencies. For example, primary amines exhibit two distinct IR peaks between 3300–3500 cm−1 corresponding to the symmetric and asymmetric N-H stretching, while secondary amines exhibit a single stretching vibration...
Gas Chromatography: Types of Columns and Stationary Phases01:17

Gas Chromatography: Types of Columns and Stationary Phases

Gas chromatography (GC) relies on stationary phases to separate and analyze components in a sample. There are two main types of stationary phases: liquid and solid. Liquid stationary phases are non-volatile, thermally stable, and chemically inert liquids coated onto the column. Solid stationary phases are particles of adsorbent material, such as silica gel or molecular sieves.
For an analyte to remain on the column for a sufficient amount of time, it must exhibit some level of compatibility (or...

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Original Experimental Approach for Assessing Transport Fuel Stability
09:48

Original Experimental Approach for Assessing Transport Fuel Stability

Published on: October 21, 2016

在甲基蒸发过程中催化剂颗粒中的液相分布的NMR成像,伴随着其蒸汽相化.

Igor V Koptyug1, Alexander V Kulikov, Anna A Lysova

  • 1International Tomography Center, 3A Institutskaya St., Novosibirsk 630090, Russia. koptyug@tomo.nsc.ru

Journal of the American Chemical Society
|August 15, 2002
PubMed
概括

核磁共振 (NMR) 图像被用来监测alpha-methylstyrene (AMS) 的化在现场. 这种技术在催化反应过程中揭示了液相度梯度,即使温度增加.

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科学领域:

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

背景情况:

  • 在现场研究多相异质催化反应对于理解反应机制和优化过程至关重要.
  • 传统方法往往缺乏空间和时间分辨率,以捕捉催化剂颗粒中的动态变化.
  • 核磁共振 (NMR) 成像为探测复杂反应环境提供了一种非侵入性的方法.

研究的目的:

  • 报告NMR成像的首次应用,用于在现场监测多相异质催化反应.
  • 在对 (Pt/gamma-Al2O3) 催化剂上的上对α-甲基 (AMS) 化进行各种静止模式的研究.
  • 在反应过程中可视化和量化催化剂颗粒内的液相分布和度梯度.

主要方法:

  • 利用核磁共振成像,在单个Pt/gamma-Al2O3催化剂颗粒中获得液相分布的二维地图.
  • 在高达185摄氏度的温度下进行了α-甲基烯 (AMS) 化反应.
  • 分析了NMR光谱数据,以量化AMS及其产物的相对量,具有空间分辨率.

主要成果:

  • 在化反应期间,成功可视化了催化剂颗粒内的液相分布.
  • 在涉及AMS蒸发和蒸汽相化条件下观察到显著的液相度梯度.
  • 证明了在多孔介质中量化AMS和烯度的可行性,尽管NMR线在多孔介质中扩大.

结论:

  • 核磁共振成像是一种强大的工具,用于现场调查多相异质催化反应.
  • 该研究强调了影响反应路径的复杂度梯度的存在.
  • 核磁共振成像能够在动态催化系统中空间分辨率量化反应物和产物.