The differences in hydrocarbons (HCs) emitted by gasoline (E0) and ethanol (EtOH) blend fuels from flex-fuel capable engines can lead to differences in the performance of aftertreatment devices. Vehicle emission results have shown either better performance on E0 compared to E85 or vice versa, dependent on the vehicle calibration. In order to separate the impact of the vehicle and the catalyst, a laboratory study was conducted to evaluate performance on a pulse-flame (pulsator) reactor and compare reactivity towards E0 and E85 (85% EtOH-15% E0) exhaust. The catalysts evaluated were substrate-only, washcoat-only and fully formulated catalysts that had been aged either on a pulsator reactor or dynamometer engine. Catalyst performance was evaluated with light-off tests utilizing both slow and fast temperature ramp rates. During the slow temperature ramp, the feedgas temperature to the catalyst was slowly increased in order to obtain details of catalyst activity versus catalyst temperature. Surface area measurements were obtained to compare aging protocols and performance. The results show that gas phase reactions can occur even on a blank substrate at high temperatures (catalyst temperature greater than 450°C). On the laboratory reactor, the temperature for 50% THC conversion (T50) is lower for E85 exhaust compared to E0 exhaust. The results also elucidate the effect of surface area and water condensation on catalyst performance.