Scientists use catalysts to destroy cancerous cells from within

Using "Trojan horses" to combat cancer from within the tumour cells themselves without damaging healthy tissues is the aim of this new tool created by researchers from the University of Granada (UGR), the Institute of Nanoscience ...

Economizing on iridium

Iridium is an ideal catalyst for the electrolytic production of hydrogen from water—but it is extremely expensive. But now a new kind of electrode made of highly porous material does an excellent job with just a hint of ...

Breaking carbon dioxide faster, cheaper, and more efficiently

A new catalyst breaks carbon dioxide into useful chemicals faster, cheaper, and more efficiently than the standard method, reports a team of researchers in this week's issue of PNAS. The discovery could make it possible to ...

Light at the end of the nanotunnel for future catalysts

Using a new type of nanoreactor, researchers at Chalmers University of Technology, Sweden, have mapped catalytic reactions on individual metallic nanoparticles. Their work could improve chemical processes, and lead to better ...

New catalyst efficiently produces hydrogen from seawater

Seawater is one of the most abundant resources on earth, offering promise both as a source of hydrogen—desirable as a source of clean energy—and of drinking water in arid climates. But even as water-splitting technologies ...

Scientists take strides towards entirely renewable energy

Scientists from Trinity College Dublin have taken a giant stride towards solving a riddle that would provide the world with entirely renewable, clean energy from which water would be the only waste product.

page 1 from 23

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.

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