Catalytic Converter
Also: Car catalyst, Three-way catalyst, Exhaust catalyst, Cat
A catalytic converter is a vehicle exhaust-cleaning system 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 important 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 now legally required 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 carrier (monolith). The carrier is coated with a washcoat of aluminium oxide (Al₂O₃) and cerium oxide (CeO₂), creating an enormous active surface area of several thousand square metres per litre.
The so-called three-way catalyst (TWC) for petrol engines converts three pollutant groups simultaneously:
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 reducing nitrogen oxides (NOₓ).
The three most important platinum-group metals compared
| Metal | Main function in cat | Engine type | 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 |
Automotive-industry demand is structurally decisive for all three metals and explains much 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
- Reintegration into primary and secondary production
The melt-value calculator gives an orientation, but for converters it can serve only as a rough guide, as the actual content varies widely and is determined only by laboratory analysis.
Market relevance and price drivers
The catalytic-converter 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.
Increasing electromobility could dampen catalyst demand in the long term, but 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 PGM loading per vehicle.
In brief
Catalytic converters are the most important industrial demand source for platinum and palladium and tie up a considerable share of the global annual production of these metals. Their recovery from end-of-life vehicles is an established, economically relevant secondary market.