Abstract: A catalytic converter comprises an annular monolithic catalyst element in a cylindrical can having one closed axial end and a central inlet opening and peripheral outlet openings at the other axial end. The catalyst element has an inner cylindrical surface defining a central axial opening therethrough aligned with the inlet opening. A conduit extends from the inlet opening through the central axial opening of the catalyst element to conduct exhaust gases from the inlet opening to the closed end of the casing for return flow through the catalyst element to the outlet openings. The portion of the exhaust conduit within the central opening of the catalyst element is cylindrical and is spaced slightly away from the inner surface of the catalyst element to define an annular space therebetween, the annular space being so thin as to force exhaust gases leaking therethrough into contact with the inner surface of the catalyst element.