In simple terms
A catalyst makes a chemical reaction go faster. It takes part in the reaction, then comes out unchanged and ready to work again.
It does not force a reaction that could not happen anyway. It shortens the route to one that was already possible.
How it works
IUPAC defines a catalyst as a substance that increases the rate of a reaction without modifying the overall standard Gibbs energy change in that reaction. The catalyst is both a reactant and a product, so it is not consumed.
That second point carries weight. Because the energy balance is untouched, a catalyst cannot change where a reaction ends up. It changes only how fast it gets there.
Catalysts fall into two families. Homogeneous catalysts sit in the same phase as the reactants, usually dissolved in the same liquid. Heterogeneous catalysts work at or near the boundary between phases, which is why so many industrial catalysts are solids that gases flow across.
Until 2000, chemists recognized two kinds: metals and enzymes. Benjamin List and David MacMillan independently built a third from small organic molecules, asymmetric organocatalysis, and shared the 2021 Nobel Prize in Chemistry for it.
Why it matters
Catalysts decide whether a chemical process is affordable. A reaction that needs weeks and fierce heat without one may take minutes under mild conditions with it.
They are also how societies clean up. Emissions control, water treatment and cleaner fuel production all lean on catalysts.
Where you’ll see it
- Catalytic converters in car exhaust systems
- Enzymes in digestion, brewing and laundry detergent
- Fertilizer, fuel and plastics manufacturing
- Drug synthesis, where the shape of the product matters
Example
Catalytic converters were fitted to most US passenger cars from the 1975 model year, using platinum and palladium. Three way versions, from about 1980, added rhodium and began cutting nitrogen oxides as well.
Often confused with
A catalyst is not a reagent. A reagent is used up and ends up inside the product. A catalyst is recovered.
Key facts
- IUPAC defines a catalyst as a substance that increases the rate of a reaction without modifying the overall standard Gibbs energy change in the reaction.1
- A catalyst is both a reactant and a product of the reaction, so it is not consumed overall.1
- Catalysts are classed as homogeneous, acting within a single phase, or heterogeneous, acting at or near a phase boundary.1
- Before 2000 only two types of catalyst were recognized, metals and enzymes; asymmetric organocatalysis became a third and won the 2021 Nobel Prize in Chemistry.2
- Catalytic converters were installed on most 1975 and newer US passenger cars, using platinum and palladium, with rhodium added in three way converters from about 1980.3
Related concepts
Quick checkWhy can a catalyst speed up a reaction without being used up?Show answer
It is both a reactant and a product, so it is regenerated by the end of the cycle.
Sources
- International Union of Pure and Applied Chemistry. Compendium of Chemical Terminology (Gold Book), entry C00876: catalyst, from IUPAC Recommendations 1996. Undated (accessed 16 September 2026)
- The Nobel Foundation. Press release: The Nobel Prize in Chemistry 2021. 6 October 2021 (accessed 16 September 2026)
- U.S. Environmental Protection Agency, Region 2. Catalytic converters fact sheet. September 2000 (accessed 16 September 2026)
Editorially reviewed by Specialty Digest Editorial TeamLast reviewed September 16, 2026Researched and drafted with AI assistanceReport an issue