Catalytic performance can be improved by reducing heat capacity and increasing geometric surface area (GSA). The effects of the catalyst layout and the substrate cell structure were investigated on the catalytic performance. The catalyst layout covers an under-floor catalyst only, a close-coupled catalyst with an under-floor catalyst and a close-coupled catalyst only, and a dual-bed close-coupled catalyst only. The substrate cell structure covers from conventional 6 mil/ 400 cpsi substrate to the ultra thin-wall and high cell-density substrate of 2 mil/ 900 cpsi. Significant reduction of emissions can be achieved by moving the catalyst location upstream of the exhaust gas and combined with using the ultra thin-wall and high cell-density substrates. Furthermore, dual-bed design demonstrated further improvement of catalytic performance at close-coupled location. NMHC and CO emissions comparable to Ultra Low Emission Vehicle (ULEV) emission limits were achieved by dual-bed close-coupled 2 mil/ 900 cpsi and 3mil/ 600 cpsi catalysts with secondary air injection on Transitional Low Emission Vehicle (TLEV). Optimization of catalyst layout and substrate cell structure was also investigated to make emission performance compatible with pressure drop. Increasing total catalyst volume, NMHC, CO, and NOx emissions comparable to ULEV emission limits were demonstrated by the combination of 2 mil/ 900 cpsi close-coupled and 4 mil/ 400 cpsi oval-shape under-floor catalyst with reduced pressure drop.