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
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.
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.
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
