A catalytic converter exhaust section comprises a first mounting plate, a second mounting plate, a hollow cylindrically shaped metallic tube and a plurality of substantially identical metallic catalytic converter substrates arranged in a honeycomb pattern. Each of the catalytic converter substrates has a regular hexagonal cross section and an inlet end separated from an outlet end by six planer walls. The metallic substrates are attached in parallel to form a compound honeycomb cross section with an inlet side, an outlet side, and an outer border defined by a portion of the planer walls. The compound honeycomb cross section is affixed within the tube between the first mounting plate and the second mounting plate. The individual substrates are coated with an appropriate catalyst for treatment of a particular exhaust component. The present invention finds particular applicability to treating exhaust from relatively large internal combustion engines that require a catalytic converter cross section larger than that currently possible with monolithic catalytic converter substrates.