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Four-way Catalitic Converter
We already know that nitrogen oxides (NOX), carbon monoxide (CO) and hydrocarbons (HC) are balanced in the so-called three-way catalytic converter. Now, a filter effect is added which, in the case of
modern
petrol direct-injection engines, stops and burns increasingly soot particles.
For this purpose, particulate filters, whose separate housing can be saved by the four-way catalytic converter, are also required with increasing exhaust gas norm (for example euro 6), even in gasoline direct injection
systems. It is precisely at the moment the important discussion on the emission of particulate matter (City ban on older diesel), which is important at the time of the diesel, that the modern petrol engine could finally
meet, too.
In the upper picture you see the blue palladium and the red rhodium-containing layers in 120-fold magnification. These two act as catalysts, not only having to be present, but also, according to recent research, do react for
a
very short time.
This has not been noticed for a long time because they are rapidly returning to their initial state. By means of rhodium, NOX (nitrogen oxides) become nitrogen
and oxygen, palladium then ensures the separation of CH (hydrocarbons), CO to CO2 and H2O (water).
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