Catalytic Converter
Also: Car catalyst, Three-way catalyst, Exhaust catalyst, Cat
A catalytic converter is a vehicle exhaust-treatment system that uses platinum-group metals (platinum, palladium, rhodium) to turn harmful combustion residues into non-toxic compounds.
The catalytic converter is among the most important applications of platinum and palladium in industry. Since its introduction in Europe during the 1980s it has slashed the pollutant emissions of motor vehicles and is today legally required in almost every new car worldwide.
Operating principle: heterogeneous catalysis
A catalyst speeds up chemical reactions without being consumed itself. Inside the catalytic converter these reactions take place on the surface of precious-metal particles applied to a ceramic or metallic support (the 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 spark-ignition engines simultaneously converts three groups of pollutants:
CO + 1/2 O2 -> CO2 (oxidation of carbon monoxide)
HC + O2 -> CO2 + H2O (oxidation of unburned hydrocarbons)
2 NO + 2 CO -> N2 + 2 CO2 (reduction of nitrogen oxides)
The oxidation reactions (CO, HC) are driven mainly by palladium and platinum, while rhodium plays the key role in reducing nitrogen oxides (NOx).
The three main 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 world demand |
| Platinum | NOx reduction, oxidation | Diesel | ~35-40% of world demand |
| Rhodium | NOx reduction (highly efficient) | Both | ~80-90% of world demand |
Demand from the automotive industry shapes the structure of all three metals and explains much of their historical price volatility.
Precious-metal quantities and recovery
The exact make-up of a converter depends on vehicle type, engine displacement and emissions class (Euro 1-7). Modern diesel cars typically contain more platinum, petrol cars more palladium.
Once a vehicle reaches the end of its life, converters are processed by specialised refiners. 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
- Re-injection into primary and secondary production
The melt value calculator gives a rough guide but, for converters, can serve only as a very approximate benchmark, since 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 cars after the 2015 diesel scandal, produced pronounced price movements: palladium temporarily overtook the gold price in 2019/2020, as petrol engines (which are palladium-intensive) gained market share.
The rise of e-mobility could dampen catalyst demand over the long term, yet the internal-combustion engine remains globally dominant for the foreseeable future, and hybrid vehicles need converters too. New emissions rules (Euro 7, China 7) tend to raise the PGM loading per vehicle.
Key takeaway
Catalytic converters are the single most important source of industrial demand for platinum and palladium, tying up a substantial part of these metals' global annual output. Their recovery from end-of-life vehicles is an established, economically significant secondary market.