Precious metal catalysts consist of highly dispersed nano-scale precious metal particles on supports with high surface area such as carbon, silica, and alumina.
The nano scale metal particles easily adsorb hydrogen and oxygen in the atmosphere. The hydrogen or oxygen is very active due to its dissociative adsorption through d-electron of out of shell of precious metal atoms.
Precious metals are stable. They do not easily form oxides by oxidation. The oxides of precious metals are, on the other hand, relatively not stable. Precious metals do not easily dissolve in acid or alkaline solution. Because of high thermal stability, precious metal catalyst has been used as automotive exhaust gas purification catalysts.