| abstract |
A process for efficiently reducing nitrogen oxides in exhaust gases including excess oxygen. The process includes intermittently introducing a reducing agent, such as hydrogen and carbon monoxide, for reducing nitrogen oxides to a reducing catalyst, such as platinum, disposed in an exhaust gas passage while maintaining an oxygen excess condition. The reducing agent is intermittently introduced in a manner to satisfy the following equation: [NOx]<[H2]+[CO], wherein [H2], [CO] and [NOx] are molar concentrations of hydrogen, carbon monoxide and nitrogen oxides, respectively. The reducing catalyst may include a transition metal, an alkaline metal and/or an alkaline earth metal. |