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Other Improvements
Getting Catalysts to Start Working Faster.


If catalysts are made more durable at high temperatures they can be sited closer to the engine. These "close-coupled" and "starter" catalysts reach operating temperature five times faster than conventional catalysts and significantly reduce the pollution arising from the critical first few minutes of a car journey. The time taken for catalysts to start working can be cut from as long as one to two minutes to less than 20 seconds

Other options include:

Use a small catalyst ahead of the main system. The catalyst support is metal so that, when an electric current is passed, it heats up quickly reaching its full operating temperature in just a few seconds.


Use "traps", which act as a chemical store until the
catalyst is at the correct temperature to convert the
gases

image: electrically heated catalyst systems

Diesel cars

Sales of diesel cars have gone up, and since 1997 all those manufactured in Europe have been fitted with catalytic converters. Heavy -duty vehicles last longer on the road and older buses and trucks contribute most of the pollution, including fine particulates.

A possible solution: the Continuously Regenerating Trap (CRT)

This effectively cleans up diesel exhaust. The gases first flow through platinum catalyst, which oxidises carbon monoxide and hydrocarbons to carbon dioxide and water, and at the same time partly converts nitrogen oxides (present as NO) to NO2

The gases then pass through a filter, where sooty particles are trapped. The temperature of the exhaust gas is not hot enough to make the soot burn, and it would soon clog up the filter.

However, in the CRT a chemical reaction between soot and the nitrogen dioxide formed over the catalyst begins to take place at less than 250°C. In this way the filter is continuously self- cleaning during normal vehicle operation. Ultra-low-sulphur diesel fuel has to be used with the CRT.

image: the continuously regenerating trap, used to clean up diesel emissions
Johnson Matthey's patented continuously Regenerating Trap reduces emissions of CO, HC and particulate from heavy duty vehicle exhaust by up to 90%

This has been
successfully employed
in Scandinavia on new
and old trucks and buses.

Catalytic converters are now being fitted to motorcycles, which in some countries are a major form of transport.
image: a scooter in traffic
So why is there still such a problem?
Better engine design, and improved catalysts have reduced pollutants in exhaust gases. But vehicle numbers and distances travelled continue to rise. We need further cuts in pollution per vehicle to get cleaner air

One solution would be to develop transport that does not rely on combustion. And platinum can help here too, as it is the catalyst on which fuel cells depend

barchart: prediction of distances driven in the uk

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