The metals commonly used in catalytic converters are platinum, palladium, and rhodium. These metals are used as catalysts to help break down pollutants in vehicle exhaust systems. The catalysts are in the form of nanoparticles, coated on a substrate or "brick". The chemistry of catalytic converters depends on whether the engine is gasoline or diesel, as each requires different catalyst systems. For example, most gasoline car engines these days are fitted with a Three-way catalyst (TWC), which undertakes three reactions at the same time: carbon monoxide (CO) + hydrocarbons (HC) + nitrogen oxides (NOx) → carbon dioxide (CO2) + water (H2O) + nitrogen (N2) .

The amount of precious metals used in catalytic converters is significant. Each year, about 90 tonnes of platinum, 300 tonnes of palladium, and 30 tonnes of rhodium are used globally for catalytic converters, both diesel and gasoline. However, 30-50% of this comes from recycling. The value of these metals in the PGM (platinum-group metals) market is even higher than that of gold.

Gold can also be used in catalytic converters, but it is not as commonly used as platinum, palladium, and rhodium. Researchers are working to reduce the amount of precious metals needed in catalytic converters while still maximizing their effectiveness.

In summary, the metals commonly used in catalytic converters are platinum, palladium, and rhodium. These metals are used as catalysts to help break down pollutants in vehicle exhaust systems. The amount of precious metals used in catalytic converters is significant, and their value in the PGM market is higher than that of gold.