26 spaced about inlet face diameter 46 after a period of for example a few seconds during which the reductant flow brings about the removal of nox from the covered segment and its reduction to n 2 of the lnt drive 40 rotates distributor 32 so that distributor outlet 36 covers a different diametrical segment about diameter 52 for example after each brief regeneration period the reductant distributor 32 is moved to successively regenerate each section of the lnt 20 in this example six such regeneration periods are required to complete one regeneration cycle of the entire lnt while about one sixth of the lnt is being stripped of stored nox the remaining five sixths of the inlet face area is receiving exhaust and continuing to trap nox it is now apparent that the distributor outlet portion 36 of the reductant gas distributor 32 is shaped to treat a predetermined relatively small portion of the inlet face 26 of lnt 20 in general it is preferred but not required that the lnt be round in cross section at its inlet so that the distributor 32 can be rotated over a circular area however other lnt inlet face profiles can be accommodated by appropriated sizing shaping and movement of the distributor outlet portion 36 since this invention permits.