An apparatus for decontaminating exhaust gases, such as in motor vehicles, a rigid metallic housing, a catalyzer body of the monolithic type placed in the housing which serves simultaneously as the outer wall of an exhaust gas conduit, a pair of annular pockets or chambers formed at the end portions of the housing, a resilient and corrugated or accordion-like compensating device placed in the pockets and a shell or sleeve surrounding the catalyzer body and having conical flange end portions cooperating with the resilient and corrugated compensating device for supporting the catalyzer body and the shell within the housing.