Promoter
A substance that has little catalytic activity itself but greatly increases the effectiveness of a catalyst.
Unit
Dimensionless
In depth
Promoters work by stabilising the catalyst's structure against sintering, by increasing its surface area, or by modifying the electronic properties of the active sites. They are added in small amounts and are essential to the commercial viability of many industrial catalysts.
Examples in the real world
Potassium and aluminium oxides promoting the iron catalyst in ammonia synthesis; molybdenum promoting iron in some processes.