Simultaneous conversion of NO, CO and C3H6 under stoichiometric conditions was carried out on washcoated monoliths containing oxygen storage material (OSM)-promoted mixed Platinum group metals (PGM: Pt(95 %)/Pd(5 %)), to evaluate OSM promotion and to identify the best architecture. The studied OSMs include ceriazirconia (Ce0.3Zr0.7O2; CZO) and mixed metal oxide spinel (Mn0.5Fe2.5O4; MFO). PGM supported directly on the OSM was found to be the best design for CZO, leading to a similar to 70 degrees C simultaneous decrease in the light-off temperature (T80; feed temperature giving 80 % conversion) for NO, CO and C3H6 conversion compared to the alumina-supported PGM. Close coupling between the PGM and CZO is responsible for the activity promotion. In contrast, a dual-layer architecture (top PGM layer, bottom MFO layer) outperformed the MFO-supported PGM catalyst. The dual-layer PGM-MFO catalyst decreased the T80 by similar to 50 degrees C for NO, CO and C3H6 conversion compared to the PGM-only catalyst. Enhancement obtained with the dual-layer PGM-MFO architecture relies on a direct catalytic contribution from the spinel. During lean/rich modulation the addition of CZO or spinel helps to mitigate the detrimental impact of modulation on NO, CO and C3H6 conversion above 400 degrees C. The data suggest that both CZO and MFO can buffer lean/rich modulation but exhibit preference to different reductants; CZO-supported PGM and dual-layer PGM-MFO show no conversion decrease during modulation for CO or C3H6 modulation, respectively. Dynamic oxygen storage capacity (DOSC) measurements show that the spinel exhibits similar to 10 times higher DOSC than CZO for both CO and C3H6 reductants. Both CO and C3H6 are equally effective reductants for the MFO but CO is better for CZO and PGM-deposited CZO. The study provides useful insight into benefits of OSM and provides guidance for optimization of the multi-component PGM + OSM catalyst composition and architecture.