The disclosure involves a method for reducing the content of NO.sub.x and N.sub.2O in gases. The method includes the conduction of a gas containing N.sub.2O and NO.sub.X over a series of two catalyst beds containing of one or more zeolites charged with iron followed by the: addition of a reduction agent for NO.sub.X between the catalyst beds. The first catalyst bed reaction zone is used to degrade the N.sub.2O and the catalyst bed second reaction zone reduces the NO.sub.X and breaks down at least part of the remaining N.sub.2O. The inventive device comprises at least one radially traversed catalyst bed.