An apparatus for regenerating a catalyst absorber after contact with a combustion exhaust which consist of a pair of cooperating louvered doors one on each side of a bed of catalyst absorber, there being at least two beds such that closing a cooperating pair of louvers, isolates the bed contained between the louvers from the exhaust gases while the other bed is left with the louvers open to continue treating the exhaust gas. Between each pair of louvers and associated with the catalyst absorber bed between the respective pair of louvers, there are positioned a regeneration inlet nozzle and a used regeneration gas outlet. By selectively closing various pairs of the louvers, a portion of the bed can be regenerated while the remainder of the bed continues to treat the exhaust gases. In this way an equivalent amount of active or regenerated catalyst absorber is in contact with the combustion exhaust gases to maintain a specified outlet pollution concentration limit.