Related topics: catalyst

Single-atom nanozymes

Nanozymes are catalytic nanomaterials with enzyme-like characteristics that have attracted enormous recent research interest. The catalytic nanomaterials offer unique advantages of low cost, high stability, tunable catalytic ...

Scientists discover a new class of single-atom nanozymes

Nanozymes—catalytic nanomaterials with enzyme-like characteristics—offer the advantage of low cost, high stability, tunable catalytic activity and ease of mass production. For these reasons, they have been widely applied ...

Monitoring the lifecycle of tiny catalyst nanoparticles

Nanoparticles can be used in many ways as catalysts. To be able to tailor them in such a way that they can catalyse certain reactions selectively and efficiently, researchers need to determine the properties of single particles ...

Design principles for peroxidase-mimicking nanozymes

Nanozymes, enzyme-like catalytic nanomaterials, are considered to be the next generation of enzyme mimics because they not only overcome natural enzymes' intrinsic limitations, but also possess unique properties in comparison ...

Chemist develops a new catalyst for oxidation and amidation

A RUDN chemist has obtained a compound with a new structural type containing atoms of metals (copper and sodium) in a carcass structure and that is shaped like a bicycle helmet. The compound shows catalytic activity in two ...

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Catalysis

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.

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