Catalysis

Some substances can dramatically change the speed of a reaction without being consumed. Heating potassium chlorate decomposes it only slowly, over 653–873 K:

Add a little manganese dioxide and the same decomposition runs much faster and at a lower temperature (473–633 K) — yet the $MnO_2$ comes out unchanged in mass and composition.

The systematic study of such effects was begun by Berzelius in 1835, who coined the term catalyst.

• A catalyst is a substance that accelerates a chemical reaction while itself remaining chemically and quantitatively unchanged afterwards; the phenomenon is catalysis.

Promoters and poisons

• Promoters enhance a catalyst's activity.
• Poisons reduce a catalyst's activity. …