A method for testing the performance of catalysts used for conversion of FCC regenerator gases comprises subjecting the catalyst simultaneously to a mixture of gases including an oxidizing gas and a reducing gas in more than one cycle in which the ratio of the oxidizing gas to the reducing gas varies over the time of the cycle. Test gases comprising O.sub.2, CO, CO.sub.2, steam, nitrogen-containing gases and sulfur-containing gases in which the ratio of O.sub.2 to CO varies over time for each cycle and in which the products of combustion formed during each cycle can be measured periodically over the cycle yields important data on the usefulness of the catalysts for treatment of regenerator flue gas.