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Treatment of diesel exhaust gases
| Details |
Inventors: Cooper, Barry J.; Jung, Hyun J.; Thoss, James E.;
Assignee: Johnson Matthey, Inc. (Valley Forge, PA)
Primary Examiner: Russel; Jeffrey E.
Assistant Examiner:
Attorney, Agent or Firm: Cushman, Darby & Cushman
In a process wherein diesel exhaust gas is passed through a filter to remove particulate therefrom before discharge and particulate deposited on the filter is combusted, the improvement which comprises combusting the particulate with a gas containing NO.sub.2, which may be catalytically generated in the exhaust system. |
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DETAILED DESCRIPTION OF THE INVENTION The NO.
sub.
2 oxidant gas used to combust particulate on the filter may be catalytically generated in a variety of ways.
However, this is preferably accomplished by initially passing the diesel exhaust gas through a catalytic converter position upstream of the filter.
The exhaust gas usually includes a significant amount of NO, O.
sub.
2, CO, CO.
sub.
2, H.
sub.
2 O and SO.
sub.
2 as well as unburnt hydrocarbons and carbonaceous particulate.
The important component, however, is the NO which, according to the invention, is converted to the NO.
sub.
2 oxidant necessary to combust particulate on the filter.
Preferably, the amount of N0.
sub.
2 in the gas as it is fed to the filter will be in the range 100-2000 ppm although it will be appreciated that the NO.
sub.
2 content can be widely varied within and outside this range.
The essential point is that there is enough NO.
sub.
2 in the gas fed to the filter to effectively combust the deposited carbon soots and like particulates.
In a preferred embodiment, the diesel exhaust gas is passed through a low pressure drop monolith catalyst (e.
g.
, a ceramic honeycomb) coated with platinum (Pt) or other platinum group metal (PGM) whereby NO in the exhaust gas is catalytically converted to NO.
sub.
2 by reaction with oxygen.
The thus treated gas is then passed downstream through a wire mesh particulate filter which, if desired, contains a catalyst.
This catalyst may simply comprise a conventional alumina washcoat.
Alternatively, base metal catalysts may be used.
Particularly useful results are obtained if the filter includes a high temperature particulate combustion catalyst, typically a catalyst comprising lanthanum, cesium and vanadium pentoxide (La/Cs/V.
sub.
2 O.
sub.
5) or the like, to combust particulate collected on the filter.
It is to be understood that the catalytically generated oxidant is no necessarily all NO.
sub.
2.
It may be, in whole part N.
sub.
2 O.
sub.
5, N.
sub.
2 O or equivalent oxidant derived from NO in the diesel exhaust
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Manufacturing Materials 
