Method of improving the operational capacity of three-way catalysts

摘要

A method is disclosed for widening the range of air-fuel ratios over which three-way catalysts having an oxygen storage capacity are operative. Three-way catalysts are operative when new both in oxidizing at least 80% of the unburned hydrocarbons and carbon monoxide and in reducing 80% of the oxides of nitrogen contained in an exhaust gas stream delivered to the catalysts from an engine. In general, the method is conducted by supplying to the engine to be burned therein an air-fuel mixture in which the fuel to air ratio is varied from a rich condition in which more fuel is present than air to burn it to a lean condition in which less fuel is present than air to burn it. The air-fuel ratio is displaced equal amounts to the rich and to the lean sides from a stoichiometric condition. The displacement to each side is generally of an identical nature and the overall frequency of displacement is such that the oxygen storage capacity of the particular three-way catalyst is not exhausted during the lean portion of the cycle.