Catalytic Converters

For this technical article, I will discuss one feature of every modern car – the catalytic converter, standard equipment on every car due to Government regulations across the world.

The “cat” as it is commonly called was first developed in the 1950s after a similar process was developed to split oil into component parts. The inventor, Eugene Houdry, saw that smog in the US was a killer and developed a prototype to help reduce car emissions – a forward thinking concept for its time. Early cats didn’t work too well because the lead added to fuels would poison the converter and clog it up. When lead was removed from fuel, it opened the door for new types of cats to be developed.

The converter is fitted in the exhaust system to process the gases as they pass down the car and out into the big wide world. They consist of a core that is typically ceramic or stainless steel and this has a washcoat added to increase the surface area and then the catalyst is typically a precious metal. Regulations in different countries require different catalysts due to pollution or poison issues.

There are several types of converters. Firstly, there is a two-way version that oxidises carbon monoxide into carbon dioxide and at the same time oxidises unburnt fuel to CO² and water. These have mostly been superseded by three-way converters due to the increased amounts of nitrous oxide produced. Three-way converters are the same as two-way however the split the nitrous oxide into nitrogen and oxygen. The oxygen is used in the other stages of oxidisation and on some versions, excess oxygen is stored to be used if required when needed.

Quite often the converters get too hot due to operating conditions and they have sensors that dictate when they are not functioning properly and have warning lights that advise the driver to stop the engine. Two other oddities come with these converters.

First, if the converter is splitting nitric oxide and people use nitrous oxide to improve performance, then why can’t the converter convert this gas for use with the ignition process? The pollutants are typically NO², i.e nitrogen dioxide – could they be converted to N²O? As you can see – I’m no chemist!

Secondly, because the converters have precious metals in, there have been cases where they have been removed from parked cars so that the crims can extract those metals and sell them.

On the whole though, converters are a very important way for the internal combustion engine to keep itself clean and help reduce sky clogging emissions. With the move to hybrids and electricity we may be in danger of moving the emissions to centralised facilities unless the scientists can figure out how to make carbon capture work or we move to more nuclear sourced electricity – which causes other environmental issues! What a choice.