A low-oxygen content exhaust flow produced by an engine that is combusting, on average, a stoichiometric mixture of air and fuel generally contains various unwanted gaseous emissions. The exhaust flow is treated by an exhaust aftertreatment system that includes a three-way-catalyst (TWC) and an ammonia-selective catalytic reduction (ammonia-SCR) catalyst positioned downstream from the TWC in a flow direction of the exhaust flow. The ammonia-SCR catalyst includes (1) a base metal ion-substituted zeolite and/or a base metal ion-substituted silicoaluminophosphate and (2) an oxygen storage material selected from the group consisting of a metal oxide or a mixed metal oxide that exhibits oxygen storage and release capacity. The serial arrangement of the TWC and the ammonia-SCR catalyst enhances the conversion of NOX to N2 in the low oxygen-content exhaust flow produced by the engine and helps prevent ammonia slip to the atmosphere.