Staged reductant injection for improved NO.sub.x reduction

  • US 6,125,629 A
  • Filed: 11/13/1998
  • Issued: 10/03/2000
  • Est. Priority Date: 11/13/1998
  • Status: Expired due to Fees
First Claim
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1. A method for converting NOx emissions in the exhaust gases of a vehicle powered by a diesel engine comprising the steps of:

  • a) providing a first SCR catalyst catalytically active when its catalyst bed temperature is within a temperature range of a first low temperature to a first high temperature;

    b) providing a second SCR catalyst chemically different from the first SCR catalyst and catalytically active when its catalyst bed temperature is within a temperature range of a second low temperature to a second high temperature, the second low temperature being less than the first low temperature;

    c) sequentially passing the exhaust gas in any order from one of the SCR catalysts to the other SCR catalysts;

    d) metering a reductant selected from the group consisting of ammonia and an ammonia precursor(s) during warm-up of the engine to the second SCR catalyst until the first SCR catalyst bed is heated from ambient temperature to a temperature whereat it ceases to function as a heat sink; and

    ,e) thereafter and during warm-up, metering the reductant to any one of the SCR catalysts having a catalytically active bed whereby oxidation of reductant and substantial retention of reductant on the catalyst bed is avoided.

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