Process for reducing nitrogen oxides
AssigneeKabushiki Kaisha Toyota Chuo Kenkyusho
InventorsKoji Yokota, Masayuki Fukui, Toshiyuki Tanaka
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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: [NO.sub.x ]<[H.sub.2 ]+[CO], wherein [H.sub.2 ], [CO] and [NO.sub.x ] 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.
Claims13
A process for reducing nitrogen oxides in exhaust gases including excess oxygen, the amount of which is larger than a stoichiometric amount of oxygen required to oxidize components to be oxidized in said exhaust gases, comprising the steps of:
- i) bringing said exhaust gases into contact with a catalyst for reducing nitrogen oxides;
- and
- ii) reducing said nitrogen oxides by intermittently introducing a reducing agent for reducing nitrogen oxides to said reducing catalyst,
- wherein
- said reducing catalyst comprises a porous carrier of at least one material selected from the group consisting of silica, zeolite and alumina, and platinum loaded thereon,
- said reducing agent is selected from the group consisting of hydrogen (H.sub.2) and carbon monoxide (CO), and
- said reducing agent is intermittently introduced in a manner to satisfy the following equation:
- [NO.sub.x ]<[H.sub.2 ]+[CO],
- wherein [H.sub.2 ], [CO] and [NO.sub.x ] are molar concentrations in said exhaust gases of hydrogen, carbon monoxide and nitrogen oxides, respectively.
Dependencies are inferred from the claim text.