Catalytic converters cleaning car exhausts

One of the most commonly recognised applications of catalysts are catalytic converters found in your cars to help reduce pollution. Tamsin Bell used her’s on a little road trip to visit Chris Morgan, Technology Director at Johnson Matthey...

Tamsin - Have you ever thought about what comes out of your car? We often hear about the nasty effect car pollution has on the environment, but is there anything we can do to reduce it?

I went to Johnson Matthey, a company that makes devices called catalytic converters that do just that…

Chris - Hello. My names Chris Morgan and I’m the Technology Director for Johnson Matthey where we develop catalytic converters.

Tamsin - How much of an issue is air pollution?

Chris - Particularly in cities where there are high concentrations of particulate matter, soot and oxides of nitrogen in the air, that can cause problems with people with respiratory diseases and asthma, so it’s important that we try to clean those emissions up to improve people’s health.

Tamsin - So what comes out of our cars?

Chris - You inject a mixture of fuel and air into the engine. And that doesn’t burn completely cleanly so you get unburnt hydrocarbons from the fuel, you get carbon monoxide, and with any high temperature combustion process you get oxides of nitrogen formed as well as soot from both gasoline and diesel vehicles. The catalytic converter is important in terms of reducing that pollution to lower levels and improving the health of everyone in those urban environments.

Tamsin - And how can you test for these things?

Chris - We make development catalysts and we fit them onto vehicles, onto engines, and we measure how effective they are.

Tamsin - And can we go and see this?

Chris - Yes, I’ll take you to the lab now.

Tamsin - Johnson Matthey are pioneers in developing chemical technologies to make our air cleaner, using a device called a catalytic converter to transform the polluting particles from our cars. But what would our cars release without these devices? I went to the lab to find out. Chris showed me a control room at Johnson Matthey Technology Centre. A room stacked with analysing machines that overlooked the testing lab…

Chris - Yes, so if you look through the window here we’ve got a passenger car sitting on a rolling road. So there are big metal rollers underneath the ground that the vehicle sits on, and when the test starts those rollers will turn round and that will simulate the vehicle driving along the road. We have a big fan that sits in front of the car to help keep it cool while it’s running the test, otherwise it would overheat. And then at the rear of the car we’re collecting all of the exhaust and taking it through to these analysers behind us where we can measure the concentrations of the pollutants that are being generated.

Tamsin - As the test started an array of numbers flooded onto the screen.

Chris - We are measuring what’s coming out of the engine and you can see different gases. We’re measuring hydrocarbon, carbon monoxide, oxides of nitrogen, and quite high levels. You can see coming out of the engine we have thousands of parts per million hydrocarbons.

Tamsin - Essentially, there are thousands of polluting molecules coming out of our car all the time, but could a catalytic converter change all that?

Chris - This catalytic converter is based around a ceramic honeycomb which sits within the exhaust of the vehicle and has thousands of small channels running through it. And what we do at Johnson Matthey is we apply coatings onto these channels that help to reduce the pollutants that are passing through the unit.

Tamsin - So you’re holding one of the catalytic converters now. So this is like a cylinder and it’s about 15 centimetres in diameter and about 20 centimetres long. It looks quite big. Is this the normal size?

Chris - For a passenger car, yes. Typically, the size of the catalyst relates to the displacement of the engine. Wherever possible, we get it as close to the engine as we can, so if you look in the engine compartment they are often located just downstream of the exhaust manifold that comes out of the engine.

Tamsin - So we're looking at the screen here and we can see lots of horrible things coming out without a catalytic converter. But what happens when we do have the catalytic converter?

Chris - Yes. So if you look at these two sets of numbers, what’s coming out of the engine, we’ve got hundreds or thousand parts per million of these pollutants - the hydrocarbon. And then we measure at the end of the exhaust system, behind  the catalyst, then that number is down into single figures. So we’re converting a very high proportion of the pollutants over the catalyst.

Tamsin - You heard right. A catalytic converter can take over a thousand molecules that are harmful to the environment and reduce them to just one or two. But how?

Chris - Within this honeycomb, the coating we put on contains precious metals, so typically platinum, palladium and rhodium. And those form millions of tiny islands within the coating and when the pollutants land on those precious metals, that helps to react them with oxygen and convert them to carbon dioxide and water.

Tamsin - And why do you use this honeycomb structure?

Chris - Because you need to have the maximum interaction between the gas and the active component. So by having these thousands of channels, and coating applied in those channels, there’s a much shorter distance for the gas to travel to hit the active part of the catalyst and for the reaction to take place. If you just coated the outside of the pipe, a lot of the gas would just go down the middle and never touch the catalyst.

Tamsin - How would you know if you need to get your catalytic converter changed?

Chris - Hopefully you should never need to get it changed. They’re designed to last for the lifetime of the vehicle. The legislation says they should last at least ten years or 160,000 kilometres of driving. But all modern vehicles have a diagnosis system that monitors how well the catalyst is working and if it detects a problem then you get a warning light on the dashboard, and you need to go to the garage and get it checked.

Tamsin - And what next? What can we improve on?

Chris - The big change that’s happening at the moment is not just testing the catalysts in the laboratory under defined test cycles, but making sure that they work under a much wider range of conditions out in the real world. So we’re now not just testing catalysts on vehicles in the laboratory, we’re fitting them to cars with a portable analyser system strapped onto the back of the car. And we’re driving out in the real world, in winter, in summer, seeing real traffic conditions and making sure the catalysts work well under all of those driving styles.