Thursday, 28 February 2013

Catalysis



Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations. Catalysts that speed the reaction are called positive catalysts. Substances that slow a catalyst's effect in a chemical reaction are called inhibitors. Substances that increase the activity of catalysts are called promoters, and substances that deactivate catalysts are called catalytic poisons.

Catalytic reactions have a lower rate-limiting free energy of activation than the corresponding uncatalyzed reaction, resulting in higher reaction rate at the same temperature. However, the mechanistic explanation of catalysis is complex. Catalysts may affect the reaction environment favorably, or bind to the reagents to polarize bonds, e.g. acid catalysts for reactions of carbonyl compounds, or form specific intermediates that are not produced naturally, such as osmate esters in osmium tetroxide-catalyzed dihydroxylation of alkenes, or cause dissociation of reagents to reactive forms, such as atomic hydrogen in catalytic hydrogenation.

Kinetically, catalytic reactions are 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 slowest step, and rates are limited by amount of catalyst and its "activity". In heterogeneous catalysis, the diffusion of reagents to the surface and diffusion of products from the surface can be rate determining. A Nanomaterial-based catalyst is an example of a heterogeneous catalyst. 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.

Tuesday, 17 July 2012

Magazine

Magazines, periodicals, glossies or serials are publications that are printed with ink on paper, generally published on a regular schedule and contain a variety of content. They are generally financed by advertising, by a purchase price, by pre-paid magazine subscriptions, or all three. At its root the word magazine refers to a collection or storage location. In the case of written publication it is a collection of written articles.

Monday, 5 September 2011

Catalyst


"The Catalyst" is a song by American rock band Linkin Park. Released on August 2, 2010, it is the first single from their fourth studio album, A Thousand Suns, which was released on September 8, 2010. The music video for the song, directed by the band's turntablist Joe Hahn, was released on August 26, 2010.

"The Catalyst" is used in the trailer and credits of the video game Medal of Honor and also the opening song of Namco-Bandai's Arcade game, Mobile Suit Gundam: Extreme Vs.. It was also used in select commercials of the Discovery Channel series, Surviving the Cut. The song was also featured in the video game Linkin Park Revenge for the iPhone, iPad, and iPod Touch. "The Catalyst" has also been used in the advertisement for the 2011 movie The Lincoln Lawyer with Matthew McConaughey.

"The Catalyst", along with five other songs from A Thousand Suns, are featured in the "Linkin Park Track Pack" as downloadable content for the rhythm video game Guitar Hero: Warriors of Rock. The track pack was released on October 19, 2010.