Catalytic Converter
Also: Automotive catalyst, Three-way catalyst, Exhaust catalyst, Cat
A catalytic converter is an exhaust-gas cleaning system in a vehicle that uses platinum group metals (platinum, palladium, rhodium) to convert harmful combustion residues into non-toxic compounds.
The catalytic converter is one of the most significant industrial applications of platinum and palladium. Since its introduction in Europe in the 1980s, it has drastically reduced pollutant emissions from motor vehicles and is today legally mandated in almost every new car worldwide.
Operating Principle: Heterogeneous Catalysis
A catalyst accelerates chemical reactions without being consumed itself. In the catalytic converter these reactions take place on the surface of precious metal particles applied to a ceramic or metallic support (monolith). The support is coated with a washcoat of aluminium oxide (Al₂O₃) and cerium oxide (CeO₂), which creates an enormously large active surface of several thousand square metres per litre.
The so-called three-way catalyst (TWC) for petrol engines simultaneously converts three groups of pollutants:
CO + ½ O₂ → CO₂ (oxidation of carbon monoxide)
HC + O₂ → CO₂ + H₂O (oxidation of unburnt hydrocarbons)
2 NO + 2 CO → N₂ + 2 CO₂ (reduction of nitrogen oxides)
Palladium and platinum are chiefly responsible for the oxidation reactions (CO, HC), while rhodium plays the key role in the reduction of nitrogen oxides (NOₓ).
The Three Most Important Platinum Group Metals Compared
| Metal | Main function in the cat | Engine type | Cat share of total demand |
|---|---|---|---|
| Palladium | Oxidation CO/HC, cold start | Petrol | ~80-85 % of global demand |
| Platinum | NOₓ reduction, oxidation | Diesel | ~35-40 % of global demand |
| Rhodium | NOₓ reduction (highly efficient) | Both | ~80-90 % of global demand |
Demand from the automotive industry is structurally defining for all three metals and explains a large part of their historical price volatility.
Precious Metal Quantities and Recovery
The exact composition of a converter depends on vehicle type, engine displacement and emission class (Euro 1-7). Modern diesel cars typically contain more platinum, petrol cars more palladium.
At the end of a vehicle's life, converters are processed by specialised refineries. The process comprises:
- Removal and sorting of the converter from the vehicle
- Grinding and homogenising the ceramic monolith
- Smelting or wet-chemical dissolution (aqua regia)
- Refining stages to separate Pt, Pd and Rh
- Reintroduction into primary and secondary production
The melt value calculator gives an orientation, but for converters it can only serve as a rough guide, since the actual content varies widely and can only be determined by laboratory analysis.
Market Relevance and Price Drivers
The automotive catalyst sector is by far the largest single buyer of palladium and rhodium. Shifts in vehicle production - such as the decline of diesel vehicles after the 2015 diesel scandal - led to significant price movements: palladium temporarily exceeded the gold price in 2019/2020, as petrol engines (palladium-intensive) gained market share.
The growth of electric mobility could dampen cat demand in the long term, yet the combustion engine remains globally dominant for the foreseeable future, and hybrid vehicles also require converters. New emission regulations (Euro 7, China 7) tend to increase the PGM loading per vehicle.
In Brief
Catalytic converters are the most important industrial demand source for platinum and palladium and absorb a considerable part of the global annual production of these metals. Their recovery from end-of-life vehicles is an established, economically relevant secondary market.