Patent ID: 7146800

Claim:
An exhaust purification method of an internal combustion engine comprising: using a NO x storing catalyst comprised of a precious metal catalyst and a NO x absorbent as a catalyst for purifying NO x in exhaust gas; increasing a ratio of nitrogen dioxide NO 2 with respect to nitrogen monoxide NO produced when burning fuel under a lean air-fuel ratio when said NO x storing catalyst is not activated compared with when said NO x storing catalyst is activated under the same engine operating conditions; storing said nitrogen dioxide NO 2 contained in the exhaust gas in said NO x absorbent at that time; changing nitrogen dioxide NO 2 stored in said NO x absorbent to nitric acid ions NO 3 − when the temperature of said NO x storing catalyst rises; cyclically temporarily switching the air-fuel ratio of the exhaust gas flowing into the NO x storing catalyst from lean to the stoichiometric air-fuel ratio or rich when said NO x storing catalyst is activated; and thereby releasing nitrogen oxides NO x stored in the NO x absorbent in the form of nitric acid ions NO 3 − from the NO x absorbent.