Patent ID: 7803338

Claim:
An apparatus for catalytically processing a gas stream passing therethrough to reduce the presence of NOx therein, said apparatus comprising: a first catalyst positioned in a relatively upstream portion of said gas stream, said first catalyst, comprising silver containing γ-alumina for catalytically processing the gas stream, said first catalyst having a first temperature at which peak NOx reducing catalytic activity occurs, said first catalyst being adapted for both converting a portion of the NOx directly to N 2 , another portion to nitrogen-containing intermediates, with a portion of NOx remaining; and a second catalyst positioned in a relatively downstream portion of said gas stream from said first catalyst, said second catalyst comprising copper containing ZSM-5 having a crystal size in the range of from about 0.5 μm to 2.0 μm and a silicon to aluminum ratio of about 50, and a copper content of about 3% by weight based on the total weight of the second catalyst, for catalytically processing the gas stream downstream from the first catalyst, said second catalyst having a second temperature at which peak NOx reducing catalytic activity occurs, said second catalyst being adapted to facilitate the reaction of the remaining NOx and intermediates for further reduction into N 2 , wherein the value of the second temperature is lower than the value of the first temperature.