空间限制的催化效应和单分子基激活在化石上的酸位点位置
Rajamani Gounder1, Enrique Iglesia
1Department of Chemical Engineering, University of California at Berkeley, Berkeley, California 94720, USA.
Journal of the American Chemical Society
|January 17, 2009
概括
焦石中的酸位点的位置决定了基激活催化. 在H-MOR热石中较小的口袋增加了裂变和脱率,这是由于对过渡状态的有利热效应造成的.
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
- 物理化学 物理化学
背景情况:
- 石中的布伦斯特酸位点对于基激活催化是至关重要的.
- 反应性受到这些位点在热带石通道内的空间限制的影响.
- 了解这些空间效应是设计高效催化剂的关键.
研究的目的:
- 为了研究布伦斯特德酸位点在热带石通道中的位置如何影响基激活催化.
- 阐明空间约束和性因素对催化速率和选择性的作用.
- 探索基于酸位点定位的合理催化剂设计的机会.
主要方法:
- 在H-MFI,H-FER和H-MOR热质中研究了和n-butan单分子裂变和脱.
- 八个环 (8-MR) 侧口袋中的酸位点的活性与H-MOR.中12个环 (12-MR) 主通道中的酸位点的活性进行比较.
- 通过Born-Haber热化学循环分析了激活障碍物,并通过红外光谱解量化了现场群体.
主要成果:
- 基激活的营业额在热带石结构之间以及H-MOR内的地点之间有很大的差异.
- 在较小的8MR H-MOR口袋中的酸位显示出比12MR通道中的酸位更高的活性.
- 由于在8-MR口袋中被部分封闭而获得的度增长,使过渡状态的自由能量降低,增强反应性,特别是脱.
结论:
- 布伦斯特德酸位点在石微孔中的精确位置对催化性能产生了深刻的影响.
- 与空间限制相关的热效应在基激活中起着关键的,以前未知的作用.
- 这项工作可以通过控制酸位位置来合理设计具有量身定制的催化活性和选择性的热利石.
相关概念视频
01:22Heterogeneous Catalysis
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...
02:34Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration
The rate of acid-catalyzed hydration of alkenes depends on the alkene's structure, as the presence of alkyl substituents at the double bond can significantly influence the rate.
02:13Reduction 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...
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...
02:24Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation
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.
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.
02:50Catalysis
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.
01:27Catalysis
Catalysis influences the rate of chemical reactions by providing an alternative reaction pathway with lower activation energy. A catalyst speeds up a reaction, but it is not consumed during the process. The fundamental principle of catalysis is the ability of a catalyst to alter the reaction mechanism, often introducing a more efficient pathway than the uncatalyzed process.In a catalyzed reaction, the catalyst participates directly in the reaction mechanism. It interacts with reactants to form...