Patent ID: 8215101

Claim:
A method of purifying exhaust from an internal combustion engine comprising: providing an NO x purification catalyst in an engine exhaust passage; providing an intermediate product producing catalyst in the engine exhaust passage upstream of the NO x purification catalyst, the intermediate product producing catalyst having a smaller cross-section than a cross-section of the engine exhaust passage around the intermediate product producing catalyst such that some exhaust can flow from upstream of the intermediate product producing catalyst to the NO x purification catalyst without passing through the intermediate product producing catalyst and the intermediate product producing catalyst being capable of producing intermediate products, wherein the intermediate products are bonded molecules of an NO x and hydrocarbon produced from the NO x stored in the intermediate product producing catalyst or the NO x contained in the exhaust gas and the hydrocarbon contained in a fed fuel, providing a fuel feed valve in the engine exhaust passage upstream of the intermediate product producing catalyst to feed a mist fuel from the fuel feed valve to the intermediate product producing catalyst, storing NO x in the intermediate product producing catalyst when an air-fuel ratio of the exhaust gas is lean, controlling release of the intermediate products from the intermediate product producing catalyst by feeding the mist fuel from the fuel feed valve to the intermediate product producing catalyst before the intermediate product catalyst becomes saturated with NO x to make the exhaust gas rich or have a stoichiometric air-fuel ratio, passing the intermediate products into the NO x purification catalyst, and purifying the intermediate products in the NO x purification catalyst.