In chemistry, a catalytic cycle is a multistep reaction mechanism that involves a catalyst. The catalytic cycle is the main method for describing the role of catalysts in biochemistry, organometallic chemistry, bioinorganic chemistry, materials science, etc.
Since catalysts are regenerated, catalytic cycles are usually written as a sequence of chemical reactions in the form of a loop. In such loops, the initial step entails binding of one or more reactants by the catalyst, and the final step is the release of the product and regeneration of the catalyst. Articles on the Monsanto process, the Wacker process, and the Heck reaction show catalytic cycles.
A catalytic cycle is not necessarily a full reaction mechanism. For example, it may be that the intermediates have been detected, but it is not known by which mechanisms the actual elementary reactions occur.
Precatalysts are not catalysts but are precursors to catalysts. Precatalysts are converted in the reactor to the actual catalytic species. The identification of catalysts vs precatalysts is an important theme in catalysis research.
The conversion of a precatalyst to a catalyst is often called catalyst activation. Many metal halides are precatalysts for alkene polymerization, see Kaminsky catalyst and Ziegler-Natta catalysis. The precatalysts, e.g. titanium trichloride, are activated by organoaluminium compounds, which function as catalyst activators. Metal oxides are often classified as catalysts, but in fact are almost always precatalysts. Applications include olefin metathesis and hydrogenation. The metal oxides require some activating reagent, usually a reducing agent, to enter the catalytic cycle.
Often catalytic cycles show the conversion of a precatalyst to the catalyst.
Often a so-called sacrificial catalyst is also part of the reaction system with the purpose of regenerating the true catalyst in each cycle. As the name implies, the sacrificial catalyst is not regenerated and is irreversibly consumed, thereby not a catalyst at all.
This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.
This course on homogeneous catalysis provide a detailed understanding of how these catalysts work at a mechanistic level and give examples of catalyst design for important reactions (hydrogenation, ol
The theoretical background and practical aspects of heterogeneous reactions including the basic knowledge of heterogeneous catalysis are introduced. The fundamentals are given to allow the design of m
In organometallic chemistry, a migratory insertion is a type of reaction wherein two ligands on a metal complex combine. It is a subset of reactions that very closely resembles the insertion reactions, and both are differentiated by the mechanism that leads to the resulting stereochemistry of the products. However, often the two are used interchangeably because the mechanism is sometimes unknown.
Oxidative addition and reductive elimination are two important and related classes of reactions in organometallic chemistry. Oxidative addition is a process that increases both the oxidation state and coordination number of a metal centre. Oxidative addition is often a step in catalytic cycles, in conjunction with its reverse reaction, reductive elimination. For transition metals, oxidative reaction results in the decrease in the dn to a configuration with fewer electrons, often 2e fewer.
Organometallic chemistry is the study of organometallic compounds, chemical compounds containing at least one chemical bond between a carbon atom of an organic molecule and a metal, including alkali, alkaline earth, and transition metals, and sometimes broadened to include metalloids like boron, silicon, and selenium, as well. Aside from bonds to organyl fragments or molecules, bonds to 'inorganic' carbon, like carbon monoxide (metal carbonyls), cyanide, or carbide, are generally considered to be organometallic as well.
The spatially resolved identification of active sites on the heterogeneous catalyst surface is an essential step toward directly visualizing a catalytic reaction with atomic scale. To date, ferrous centers on platinum group metals have shown promising pote ...
The constant urge to construct new molecules in an economical and sustainable fashion led to the development of numerous metal-catalyzed transformations. Organocatalysts consisting of abundant and more sustainable elements offer an elegant solution to over ...
Treatment of Ziegler-Natta (ZN) catalysts with BCl3 improves their activity by increasing the number of active sites. Here we show how Ti-47/49 solid-state nuclear magnetic resonance (NMR) spectroscopy enables us to understand the electronic structure of t ...