Precious metals, such as platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), iridium (Ir), silver (Ag), and gold (Au), are chemically very stable and do not react with their environment under normal conditions. They are generally resistant to oxidation and corrosion, even in contact with most acids.

Precious metals often have a high affinity for adsorption of reactants on their surface, which facilitates reactions by stabilizing transition states and lowering the activation energy, which is why they are frequently found in catalysis.

The most well-known example is the three-way catalytic converter in automobiles. In this system, platinum, palladium, and rhodium reduce harmful gases such as carbon monoxide (CO), unburned carbon monoxide (VOCs), and nitrogen oxides (NOx) to less harmful substances like carbon dioxide, water, and nitrogen. Beyond this, precious metal catalysts play a significant role in industry. For example, some platinum-based catalysts are used for the total oxidation of pollutants, while palladium plays a crucial role in hydrogenation reactions, such as the hydrogenation of oils.

Since precious metals have not only chemical but also economic value, it is worthwhile to recover even the smallest quantities from products, which is why precious metal-containing catalysts are usually recycled.