The word catalyst is used very broadly, and is used to describe substances, mixtures, articles and commercial products. The term catalyst can be used to describe a mixture, but also the active substance increasing the rate of reaction
To help understand catalyst manufacture and use, Catalysts Europe use the following definitions:


Catalysts often require an activation step in order to produce the active catalyst. They can be prepared ex-situ (prior to loading) or in-situ (after loading); in the latter case a catalyst precursor is loaded into the reactor and is then activated.

Active catalyst

A substance that increases the rate of reaction. During reaction the catalyst species reacts with a substrate and then returns to the original species.

Catalyst precursor

A substance that requires further activation or reaction to produce the active catalyst.

Fresh catalyst

New or regenerated catalyst or in some cases catalyst precursor that has not been put into operation or use.


The substance resulting from a chemical reaction.


A substance that is reacted further into another species.


The recovery of constituent components from the spent catalyst that can be re-used for catalyst or other applications.


A process to restore the catalytic activity of a spent catalyst. It normally involves thermal treatment to remove surface coatings and/or adsorbed species.

Spent catalyst

A catalytic substance that has reduced activity and no longer meets performance requirements.


An inert substance that acts as a carrier for catalytically active substances such as silica and aluminium oxide. The support is normally inert and does not take part in the reactions.

Self-heating catalyst

These are typically mixtures which in large quantities and after a prolonged duration (several hours or days) are liable to self-heat in contact with air and without an energy supply. This may include some fresh and spent catalysts. Special requirements are required for self-heating catalysts.


ECMA Logo300


© Catalysts Europe 2022         Disclaimer

SG logo descriptor full color RGB october2017 HReurometaux

EU Transparency Register n°64879142323-90