Abstract: In an internal combustion engine exhaust system, a catalytic converter mounted on the exhaust manifold has a cylindrical catalyst bed which is disposed on a substantially vertical axis. The exhaust gases flow downwardly into and through a louvered inner tube and then radially through the bed. A frusto-conical baffle is supported from the inner tube and extends outwardly and downwardly into the bed to separate an upper catalyst reservoir portion of the bed from a lower gas flow portion of the bed. During thermal expansion of the bed or upon attrition of the catalyst in the gas flow portion, catalyst beads are discharged from the reservoir portion around the conical baffle and into the gas flow portion.