Method and apparatus for NOx abatement in lean gaseous streams

A method for the reduction of NOx in a lean NOx-containing gaseous stream comprises:

• (a) passing the lean gaseous stream through a catalyzed NOx trap member comprising an intimate combination of a catalyst material effective for promoting the oxidation of a combustible component in the gaseous stream, and a NOx sorbent material, the gaseous stream being passed through the trap member within a sorbing temperature range to sorb NOx in the trap member whereby to establish a trapping period and provide a NOx-depleted gaseous stream exiting the trap member during the trapping period;
• (b) passing the gaseous stream exiting the trap member through a lean NOx reduction catalyst member;
• (c) introducing the combustible component into the gaseous stream at a location upstream of the trap member under conditions to combust the combustible component on the trap member, the combustible component being introduced in an amount which is limited in order to maintain the bulk composition of the gaseous stream lean but which is enough to heat at least a portion of the trap member to a release temperature sufficient to release trapped NOx from the trap member into the gaseous stream exiting the trap member thence through the catalyst member, whereby to establish a desorbing period;
• (d) maintaining lean NOx-reduction conditions in the catalyst member at least during the desorbing period;
• and
• (e) alternating the establishment of the trapping period of step (a) and the desorbing period of step (c).