An internal combustion engine exhaust gas catalytic converter has a simplified basic construction--using only vertically disposed inner and outer louvered tubes defining a radial flow bead catalyst bed, and a pair of shell members embracing the upper and lower ends of the inner and outer tubes to retain the tubes and close the upper and lower ends of the catalyst bed. The shell members have an enlarged waist defining an outlet chamber surrounding the outer tube, and abut along radially-outwardly-directed axially-extending flanges which seal the outlet chamber and close the lower end of the inner tube to direct exhaust gases through the catalyst bed.