Related topics: catalyst

Scientists uncover secret to gold's catalytic powers

Settling a decades-long debate, new research conclusively shows that a hierarchy of active species exists in gold on iron oxide catalysis designed for low temperature carbon monoxide oxidation; Nanoparticles, sub-nanometer ...

Cheap hydrogen fuel from seawater may be a step closer

( -- A new catalyst has been developed to generate hydrogen from water cheaply, but the research was originally intended to make molecules that behaved like magnets. Hydrogen is a clean power source currently ...

3D graphene: Solar cells' new platinum?

One of the most promising types of solar cells has a few drawbacks. A scientist at Michigan Technological University may have overcome one of them.

Carbon dots dash toward 'green' recycling role

Graphene quantum dots may offer a simple way to recycle waste carbon dioxide into valuable fuel rather than release it into the atmosphere or bury it underground, according to Rice University scientists.

page 1 from 14


Catalysis is the process in which the rate of a chemical reaction is either increased or decreased by means of a chemical substance known as a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. The catalyst may participate in multiple chemical transformations. Catalysts that speed the reaction are called positive catalysts. Catalysts that slow down the reaction are called negative catalysts or inhibitors. Substances that increase the activity of catalysts are called promoters and substances that deactivate catalysts are called catalytic poisons. For instance, in the reduction of ethyne to ethene, the catalyst is palladium (Pd) partly "poisoned" with lead(II) acetate (Pb(CH3COO)2). Without the deactivation of the catalyst, the ethene produced will be further reduced to ethane.

The general feature of catalysis is that the catalytic reaction has a lower rate-limiting free energy change to the transition state than the corresponding uncatalyzed reaction, resulting in a larger reaction rate at the same temperature. However, the mechanistic origin of catalysis is complex. Catalysts may affect the reaction environment favorably, e.g. acid catalysts for reactions of carbonyl compounds, form specific intermediates that are not produced naturally, such as osmate esters in osmium tetroxide-catalyzed dihydroxylation of alkenes, or cause lysis of reagents to reactive forms, such as atomic hydrogen in catalytic hydrogenation.

Kinetically, catalytic reactions behave like typical chemical reactions, i.e. the reaction rate depends on the frequency of contact of the reactants in the rate-determining step. Usually, the catalyst participates in this slow step, and rates are limited by amount of catalyst. In heterogeneous catalysis, the diffusion of reagents to the surface and diffusion of products from the surface can be rate determining. Analogous events associated with substrate binding and product dissociation apply to homogeneous catalysts.

Although catalysts are not consumed by the reaction itself, they may be inhibited, deactivated or destroyed by secondary processes. In heterogeneous catalysis, typical secondary processes include coking where the catalyst becomes covered by polymeric side products. Additionally, heterogeneous catalysts can dissolve into the solution in a solid-liquid system or evaporate in a solid-gas system.

This text uses material from Wikipedia, licensed under CC BY-SA