Catalytic Converter
Also: Automotive Catalyst, Three-Way Catalyst, Exhaust Catalyst, Cat
A catalytic converter is an exhaust emission control system in a vehicle that uses platinum group metals (platinum, palladium, rhodium) to convert harmful combustion by-products 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 virtually every new car worldwide.
Operating Principle: Heterogeneous Catalysis
A catalyst accelerates chemical reactions without itself being consumed. In a catalytic converter, these reactions take place on the surface of precious metal particles deposited on a ceramic or metallic substrate (monolith). The substrate is coated with a washcoat of aluminium oxide (Al₂O₃) and cerium oxide (CeO₂), which creates an enormously large active surface area 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 unburned hydrocarbons)
2 NO + 2 CO → N₂ + 2 CO₂ (reduction of nitrogen oxides)
Palladium and platinum are primarily 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 | Primary 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 dominant for all three metals and explains a large share of their historical price volatility.
Precious Metal Quantities and Recovery
The exact composition of a catalytic converter depends on vehicle type, engine displacement, and emission standard (Euro 1–7). Modern diesel cars typically contain more platinum, while petrol cars contain more palladium.
When a vehicle reaches the end of its service life, catalytic converters are processed by specialised refineries. The process involves:
- 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-feeding into primary and secondary production
The melt value calculator provides guidance, but can only serve as a rough benchmark for catalytic converters, since the actual metal content varies considerably and can only be determined by laboratory analysis.
Market Relevance and Price Drivers
The automotive catalyst sector is by far the single largest consumer of palladium and rhodium. Shifts in vehicle production — such as the decline in diesel vehicles following the dieselgate scandal in 2015 — triggered significant price movements: palladium temporarily surpassed the gold price in 2019/2020 as petrol engines (palladium-intensive) gained market share.
The growth of electric mobility could dampen catalytic converter demand in the long term; however, the internal combustion engine remains globally dominant for the foreseeable future, and hybrid vehicles also require catalytic 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 account for a substantial share of the global annual production of these metals. Their recovery from end-of-life vehicles is an established, economically significant secondary market.