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Révisi nurutkeun 1 Nopémber 2004 05.51

Katalis nyaéta hiji zat nu ngaronjatkeun laju hiji réaksi kimiawi, dina suhu nu tangtu, tanpa teu kabawa robah atawa kahakan ku réaksina (tempo ogé katalisis). Katalis aub na réaksi, tapi lain mangrupa réaktan atawa produk kimia.

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Gambar 1 Profil éntalpi pikeun réaksi nu maké jeung teu maké katalis. AU mangrupa énergi aktivasi pikeun réaksi tanpa katalis, AC mangrupa énergi aktivasi nu dikurangan pikeun réaksi nu sarua nalika dikatalisan. I salaku titik nalika chemical intermediate kabentuk, nu salajengna meta jadi produk.

Katalis ngajadikeun réaksi bisa lumangsung leuwih gancang atawa bisa lumangsung dina suhu nu leuwih handap alatan parobahan nu dipicuna dina réaktan. Katalis nyadiakeun jalur séjén nu énergi aktivasina leuwih handap pikeun lumangsungna réaksi. Molekul nu teu mibanda énergi pikeun meta atawa énergina handap teuing sahingga réaksina bakal lila pisan jadi bisa meta ku ayana katalis. Katalis ngurangan énergi nu dipikabutuh pikeun lumangsungna réaksi.

Dua kategori utama katalis nyaéta katalis homogén jeung hétérogén. Katalis hétérogén aya dina fase nu béda ti réaktan dina réaksi nu dikatalisanana, sedengkeun katalis homogén aya dina fase nu sarua. A simple model for heterogeneous catalysis involves the catalyst providing a surface on which the reactants (or substrates) temporarily become adsorbed. Bonds in the substrate become weakened sufficiently for new products to be created. The bonds between the products and the catalyst are weaker, so the products are released.

Homogenous catalysts generally react with one or more reactants to form a chemical intermediate that subsequently reacts to form the final reaction product, in the process regenerating the catalyst. The following is a typical catalytic reaction scheme, where C represents the catalyst:

A + C → AC (1)
B + AC → AB + C (2)

Although the catalyst (C) is consumed by reaction 1, it is subsequently produced by reaction 2, so for the overall reaction:

A + B + C → AB + C

the catalyst is neither consumed nor produced. Enzymes are biocatalysts. Use of "catalyst" in a broader cultural sense is in rough analogy to the sense described here.

Some of the most famous catalysts ever developed are the Ziegler-Natta catalysts used to mass produce polyethylene and polypropylene. Probably the best-known catalytic reaction is the Haber process for ammonia synthesis, where ordinary iron is used as a catalyst. Catalytic converters break down some of the nastier byproducts of automobile exhaust. They are made from platinum and rhodium.

Tempo ogé