a manifold converter comprises a housing constructed of two metal shells welded at their mating edges ; a catalyzer carrier unit installed in the housing in a manner to define therein upstream and downstream portions with respect to the catalyzer carrier unit ; and a sealing mat disposed between the catalyzer carrier unit and the housing to achieve a hermetical sealing therebetween . a binding structure is further employed for binding a given portion of the housing where the sealing mat is located . with this binding structure , undesired permanent expansion of the housing caused by the inevitable thermal expansion is suppressed or at least minimized .