NOVELTY - Operating a fuel cell system, comprises: e.g. providing a catalyst containing of essentially of platinum and ruthenium as catalytically active materials, where catalyst is configured for self cleaning of sulfur compounds when performing steam reforming using a low-sulfur-content hydrocarbon fuel; providing a catalytic reactor having surfaces having catalyst disposed on it and configured to expose catalyst to at least a hydrocarbon fuel and steam; reforming a high-sulfur content hydrocarbon fuel with steam for first period of time; and reforming low-sulfur-content hydrocarbon fuel with steam.    USE - The method is useful for operating a fuel cell system which is useful for steam reforming a hydrocarbon fuel (claimed).    ADVANTAGE - The method utilizes minimum platinum content (since the platinum is more expensive than ruthenium) to achieve a desired catalyst regeneration (self-cleaning) time, thus the method is cost effective.    DETAILED DESCRIPTION - Operating a fuel cell system, comprises: providing a catalyst containing of essentially of platinum and ruthenium as catalytically active materials, where the platinum content is selected based on a desired level of sulfur resistance, and the catalyst is configured for self cleaning of sulfur compounds when performing steam reforming using a low-sulfur-content hydrocarbon fuel; providing a catalytic reactor having surfaces having the catalyst disposed on it and configured to expose the catalyst to at least a hydrocarbon fuel and steam; reforming a high-sulfur content hydrocarbon fuel with at least steam for a first period of time; reforming the low-sulfur-content hydrocarbon fuel with at least steam for a second period of time; and providing reformed hydrocarbon fuel to a fuel cell stack. INDEPENDENT CLAIMS are also included for:    (1) a system for steam reforming a hydrocarbon fuel, comprising: a catalytic reactor having surfaces configured for exposure to the hydrocarbon fuel and steam; and the catalyst, where the system is configured to steam reform a hydrocarbon fuel; and    (2) a fuel cell system (10), comprising: a fuel cell stack (12); and a reformer (14) in fluid communication with the fuel cell stack, where the reformer includes the catalytic reactor; and the catalyst, where the reformer is configured to steam reform a hydrocarbon fuel and output reformed fuel to the fuel cell stack.    DESCRIPTION OF DRAWING(S) - The figure schematically illustrates a fuel cell system.    Fuel cell system (10)    Fuel cell stack (12)    Reformer (14)    Desulfurization system (16)    Electrical power lines (20)