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Staged three-way conversion catalyst and method of using the same

  • US 5,531,972 A
  • Filed: 01/30/1991
  • Issued: 07/02/1996
  • Est. Priority Date: 11/08/1989
  • Status: Expired due to Fees
First Claim
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1. A method of substantially simultaneously converting HC, CO and NOx pollutants contained in a gaseous stream, the method comprising:

  • (a) flowing the gaseous stream through a first catalyst zone and therein contacting the gaseous stream with a first catalyst member comprising a first catalytic material having an ignition temperature for substantially simultaneous conversion of HC, CO and NOx, when the gaseous stream is a substantially stoichiometric exhaust gas mixture, which is lower than the corresponding ignition temperature of a second catalytic material defined below, the gaseous stream being introduced into the first catalyst zone at a temperature at or above the ignition temperature of the first catalytic material but below an operating temperature range, defined below, to convert within said first catalyst zone some, but less than all, of each of the HC, CO and NOx content of the gaseous stream to innocuous substances and thereby increase the temperature of the gaseous stream, and(b) flowing the gaseous stream from the first catalyst zone to a second catalyst zone and wherein contacting the gaseous stream with a second catalyst member comprising a second catalytic material having a higher conversion efficiency for substantially simultaneous conversion of HC, CO and nox at temperature within the operating temperature range than does the first catalytic material, the gaseous stream being contacted with the second catalytic material at a temperature within the operating temperature range to substantially simultaneously convert at least some of the remaining HC, CO and NOx to innocuous substances.

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