@ prads - The theory of reduction oxydation is fine. However in practical terms there is much more to it. The world's cars with their cats do not produce clean air. 2 bye products of the car are cyanide and H2SO3 or sulphurous acid.
The sulphurous acid has sent many mechanics in the US into early retirement because of serious lung damage. These mechanics were specialised in cat changing.
The cyanides of the world's car population accumulating in a year's is enough to instantly kill the entire population of Maharashtra.
Calling the cat environmentally friendly is a load of rubbish. NOX is loved by the plants. Or has any one seen dead plants along the highway express? CO oxydises completely within 4 hours to CO2 without our help.
CO2 has a much bigger bearing on our environment than anything else the car might exhaust.
The DPF is not needed when engines are maintained properly.
The DPF is increasing fuel consumption (and takes away power), which increases CO2 output.
The cat increases fuel consumption too and can't deal with full throttle application. The cat will work adversly in the running hot phase and when reaching temperatures above the temperature window. When the cat is 'dead' as they say, it is by no means dead. It just works adversly. Cats go in from about 8,000kms.
New cars are not better than old cars. In a recent test the Alfo Mito with the 1.3 M-Jet engine the real COs out put per km was about 85 grams above the 99 grams claimed. The Mito was new.
To keep pollution down (and most applies to keeping safety up) it is necessary to maintain cars properly and buy them with brains rather than as a status symbol. Check tyre pressure and make sure that unnecessary weight is not transported due to our laziness.
Car manufacturers just waking up to reality as governments in Europe put a ;ot
of pressure on them. All of a sudden it is possible to slash off the new Peugeot 208 110kg compared to the less roomy 207. The new Mazda MX5 is 200kg lighter than the old one. Even Alfa Romeo can build a light car now after hving realised that even car enthusiast do not buy overweight barges.
Safety and environmental friendliness are not a question of the age of the car rather than the right attitude of the ones owning them.