A superior, low-cost catalyst for water-splitting

In a significant step toward large-scale hydrogen production, researchers at the Indian Institute of Science (IISc) have developed a low-cost catalyst that can speed up the splitting of water to produce hydrogen gas.

New class of catalysts for energy conversion

Many chemical reactions relevant for new energy sources are highly complex and result in considerable energy loss. Thus, energy conversion and storage systems or fuel cells are not yet widely used in commercial applications. ...

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 ...

Seeking disorder as a catalyst for change

Green chemists dream of replicating the reactions of photosynthesis. Of the possible outcomes, one of the most talked about is the ability to make affordable hydrogen fuels from water. In theory, the only by-product of burning ...

Heterogeneous catalyst goes enzymatic

What if there were no tunnels in the Swiss Alps? Anyone trying to travel through them would have to go up and down hills and zigzag around the ranges. A lot more energy and time is saved by passing through a tunnel than climbing ...

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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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