Nowadays, most people are aware that catalytic converters contain precious metals (hence the high theft rate) but not many know exactly what these metals are and what their purpose in the “cat” is actually for.

What do they do and what do they contain?

The catalytic converter is now a crucial component of modern car and truck exhaust systems and is designed to reduce harmful emissions from all modern internal combustion engines. Aside from the less valuable stuff like nickel, iron and copper, they also contain 3 main precious metals – platinum (Pt), palladium (Pd) and rhodium (Rh) which are known collectively as platinum group metals (or PGMs for short). In this post, we’ll look at the roles these metals play in catalytic converters, why they’re essential and the economic and environmental implications of their use.

Catalytic converter chemistry

OK, so now we need to get a little bit nerdy to explain the more technical aspects of the chemistry – A catalytic converter works by creating chemical reactions that convert toxic gases from engine exhaust fumes into less harmful substances. The key reactions include the oxidation of carbon monoxide (CO) and hydrocarbons (HC) into carbon dioxide (CO2) and water (H2O), and the reduction of nitrogen oxides (NOx) into nitrogen (N2) and oxygen (O2).

Platinum

A platinum nugget

A platinum nugget by Alchemist-hp (talk) (www.pse-mendelejew.de) – Own work, FAL, Link

 

Platinum’s role: Platinum primarily catalyses the oxidation reactions. In other words, it helps convert the really bad stuff like carbon monoxide and hydrocarbons into CO2 and H2O, with the process being particularly effective under oxygen-rich conditions.

Platinum’s applications: Platinum is widely used in catalytic converters for both petrol and diesel engines, with its ability to oxidize pollutants being especially useful in diesel engines due to the oxygen-excess environment.

Palladium

Palladium

A small amount of palladium Hi-Res Images ofChemical Elements, CC BY 3.0, via Wikimedia Commons

 

Palladium’s role: Palladium facilitates oxidation reactions and is more reactive than platinum. It efficiently converts hydrocarbons and carbon monoxide (CO) into less harmful emissions.

Palladium’s applications: Palladium is used in petrol engines and is increasingly used in diesel engines due to its lower cost compared to platinum. As a case in point, modern cats often combine palladium with platinum or rhodium to balance performance and cost.

Rhodium

Rhodium block

A 78-gram block of rhodium – Image by Alchemist-hp (talk) www.pse-mendelejew.deOwn work – Creative Commons, FAL, Link

 

Rhodium’s role: Rhodium is essential for the reduction of nitrogen oxides (NOx) into nitrogen and oxygen. This is a critical reaction in petrol engines that operate under stoichiometric conditions (i.e. balanced oxygen and fuel).

Rhodium’s applications: Due to its high effectiveness and resistance to poisoning, rhodium is used in three-way catalysts (TWCs) in petrol engines and it’s the most expensive (by far) of the 3 metals due to its rarity and effectiveness.

Economic and Environmental Impact

Economic Value – The high cost of PGMs significantly impacts the value of catalytic converters. For example, at the time of writing this article in mid 2024, the market prices for these metals are:

It may surprise many of you to know that rhodium is by far the most valuable; much more so than gold, which makes catalytic converters a tempting target for theft. The precious metal content drives the cost of manufacturing and repairing catalytic converters and is a big influence in the vehicle recycling industry because the recyclers extract these metals from used converters, mainly because recycling is a lot more economical than mining new material.

Catalytic converter

Environmental Significance – It’s fair to say that catalytic converters have been instrumental in reducing vehicle emissions and improving air quality. By converting over 90% of harmful emissions into less harmful gases, they help mitigate the environmental impact of vehicle engines and the PGMs in them are a critical part of this due to their stability and effectiveness at high temperatures as well as their ability to withstand the harsh conditions of exhaust systems.

Johnson Matthey, a leading producer of emission control technologies, emphasizes that about 90 tonnes of platinum, 300 tonnes of palladium, and 30 tonnes of rhodium are used annually in catalytic converters worldwide, with around 30-50% of these metals coming from recycling, which underscores the importance of sustainability in this industry.

Challenges and Future Prospects

Supply and Demand – The global demand for PGMs is influenced by various factors, including automotive industry trends, emission regulations, and the shift towards cleaner energy sources. The transition to battery powered electric vehicles (EVs) may reduce the demand for PGMs in the long term, but in the short to medium term, hybrid and hydrogen vehicles will continue to drive demand. Hydrogen-powered vehicles, for instance, use platinum as a catalyst in fuel cells, suggesting a continued need for PGMs.

Price Fluctuations – The prices of PGMs are subject to significant fluctuations due to supply constraints, geopolitical factors, and changes in demand. For example, the price of palladium surged from £800 to £2,400 per ounce within a year due to increased demand and limited supply. Rhodium’s rarity and specific use in catalytic converters also contribute to its high and volatile price.

Recycling and Sustainability – As mentioned earlier, recycling catalytic converters is more efficient than mining new PGMs, with the extraction process from ores being very labour-intensive and environmentally harmful due to the high energy and resources needed. By contrast, recycling PGMs from used cats reduces environmental impact and supports a circular economy.

In summary

Catalytic converters are vital for reducing emissions, and the use of platinum, palladium, and rhodium is crucial to their effectiveness. These metals’ unique properties make them indispensable for the chemical reactions that clean exhaust gases. While their high cost and market volatility pose challenges, the benefits they provide in terms of environmental protection and sustainability are significant. As the automotive industry evolves, the role of PGMs in emission control will continue to be essential, underscoring the need for efficient recycling and innovative solutions to meet future demands.

About us

We’re Kent and SE London’s leading vehicle recycler and we also pay top prices for unwanted catalytic converters.

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