Method of purifying exhaust gas of internal combustion engine and apparatus thereof

A method of purifying an exhaust gas of an internal combustion engine comprising an NOx purifying catalyst arranged in an exhaust gas passage, wherein

• said NOx purifying catalyst is made of a composition consisting of at least one kind of element selected from the group consisting of rare earth metals, at least one kind of element selected from the group consisting of alkaline metals and alkaline earth metals, at least one kind of element selected from the group consisting of platinoid metals (so-called noble metals), and titanium (Ti), said NOx purifying catalyst adsorbing NOx in the exhaust gas onto a surface thereof when the exhaust gas is lean, and reducing the adsorbed NOx to N2 when the exhaust gas is not leaner than stoichiometric, and wherein
• the exhaust gas is purified by adsorbing NOx in the exhaust gas onto said NOx purifying catalyst when the internal combustion engine is being operated under a lean condition, and by setting, after the adsorption, the exhaust gas to an air-fuel ratio state not leaner than stoichiometric for 0.5 second to 4.5 seconds to reduce the NOx adsorbed on said NOx purifying catalyst to N2 through catalytical reaction with a reducing agent.