BASF explains how diesel catalysts work
Catalytic converters are quite common for gasoline engines but diesel catalysts are less known, in part because they face greater challenges. Still, diesel catalysts have not disappeared because they are efficient and, when you start your car, they don't produce heaps of CO2. Their main problem is the large amount of carbon particulates (soot) and nitrogen oxides in the exhaust gas. Standard three-way converters are not effective because of the high oxygen content of these gases. BASF is on the case, though. BASF's catalyst researcher Bob Farrauto said, "To solve this problem, we have developed special diesel oxidation catalysts combined with particulate filters which trap the soot and periodically oxidize it using a combination of catalysts and engine controls."
What about nitrogen oxides, which are the main source of acid rain? NOx storage devices or traps are incorporated into the catalyst to first store the nitrogen oxides which are then converted to nitrogen. The storage catalyst is regenerated afterwards. Alternatively an ammonia-carrying liquid (i.e. urea) can be injected into the exhaust and passed over a highly selective catalyst which converts the NOx into N2.
Gallery: BASF's catalyst research center
[Source: BASF]
Reader Comments (Page 1 of 1)
wxman 2:27PM (4/11/2008)
Just a nitpick, but the correlation between acid rain (i.e., low rainwater pH) and oxides of nitrogen (as nitrate - NO3) is marginal at best (see http://nadp.sws.uiuc.edu/isopleths/maps2006/phlab.gif - rainwater pH, and http://nadp.sws.uiuc.edu/isopleths/maps2006/no3.gif - NO3 concentration in rainwater).
Correlation between acid rain and sulfate is much better (see http://nadp.sws.uiuc.edu/isopleths/maps2006/so4.pdf - SO4 concentration in rainwater).
Certainly it's a good thing that NOx emissions are being controlled better and better, but to say NOx is the main source of acid rain is a bit misleading.
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Xavier Navarro 2:28PM (4/11/2008)
To wxman,
The source stated clearly it was the source for acid rain. Hum... Thanks for pointing this out!
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