Finding out and learning about the different types of catalytic converters out there and their value in terms of PGM (Platinum Group Metals) loading can be daunting. So, to make things much easier for you, we have gathered all the relevant information into this article for you.
What is a catalytic converter?
According to Wikipedia, a catalytic converter is “an exhaust emission control device that reduces toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants by catalyzing a redox reaction (an oxidation and a reduction reaction). Catalytic converters are usually used with internal combustion engines fueled by either gasoline or diesel.”
This diagram might help explain better the basic composition and function of a catalytic converter:
These are the different types of catalytic converters.
1. Petrol-based catalytic converters
Three-way Catalytic Converter
It is called three-way because of three reactions happening in it to break down carbon monoxide, unburnt hydrocarbons and nitrogen oxides. The ceramic core contains a rhodium coating that can break down harmful nitrogen oxide emissions into nitrogen and oxygen. The rhodium coating is what sets it apart from the two-way catalytic converter.
Two-way Catalytic Converter
This catalytic converter type has two oxidation processes happening in it: Oxidation of Carbon Monoxide and oxidation of Hydrocarbons. They were used on gasoline engines in American- and Canadian-market automobiles. However, from 1981, due to is ineffectiveness to convert nitrogen oxides into less harmful emissions, automakers began to replace two-way catalytic converters with three-way catalytic converters to meet increasingly stringent environmental regulations. The 2-way converters have been superseded by the three-way version in newer car models.
Metallic Core versus Ceramic Core:
Ceramic core catalytic converters are more common in the market than metallic core ones. An advantage of a metallic core is that they have lower resistance to air flow and require less heat to warm up. Metallic converters are usually found in high-end performance vehicles but they are difficult to process so not many buyers accept them.
2. Diesel-based catalytic converters
Also known as a diesel oxidation catalyst (DOC), the diesel-based catalytic converter is primarily a two-way catalytic converter. Diesel-based catalytic converters contain palladium, platinum, and aluminium oxide, all of which oxidize the Particulate Matter (PM), hydrocarbons, and carbon monoxide.
There is no rhodium in DOC. Unlike the petrol-based catalytic converters, this catalytic converter has a diesel particulate filter (DPF) attached to it to remove the PM.
There is a recent modification to DOCs to reduce nitrogen oxides (NOx) emissions: Selective Catalytic Reduction (SCR).
Selective Catalytic Reduction (SCR)
Under the more recent stricter NOx emission legislations such as Euro 6 regulation, a new technology called Selective Catalytic Reduction (SCR) technology is used in DOCs. This technology involves adding a clear and non-toxic urea solution that hydrolyses and then reduces on the harmful NOx.
However, even with the addition of the SCR technology, PGM loading is still required albeit in smaller quantities in these diesel-based catalytic converters to covert the other pollutants like carbon monoxides and unburnt hydrocarbons and adhere to the ever-progressing emissions regulations
PGM Loading in Catalytic Converters
Now, here’s the topic that is close to everyone’s heart: the amount of PGM loading found in different types of catalytic converter. For both the two-way and the three-way catalytic converters, generally the amount of PGM in catalytic converters ranges from 80 g/ft3 to 90 g/ft3 or about 3,000 parts per million (ppm).
In terms of overall mass, PGM loading weighs 6g to 8g usually in older models for both petrol and diesel vehicles. There are also PGM loading in motorcycles’ converters but it is lower quantity of around 2g. Whereas for in trucks, especially those that run on natural gas, the PPM can go up to 15g or around 6,000ppm.
We hope you would find this article useful. If you have any questions about catalytic converters or would like to find out how to get the best value out of your catalytic converters recycling lot, feel free to email us at firstname.lastname@example.org or https://www.brmetalsltd.com/contact-us/