Exhaust gas purifying method
View Patent ↗A method of purifying an exhaust gas, includes: disposing a NOx trapping catalyst in an exhaust pipe of an internal combustion engine, the NOx trapping catalyst including: a metal substrate including cells, a corner portion of each of cells having an acute angle; and a catalyst layer supported in the metal substrate and including a noble metal, a heat-resistant inorganic oxide and a NOx trapping material, the catalyst layer having pores formed by addition of a pore formation promoting material, and the NOx trapping catalyst: adsorbing NOx in the exhaust gas when an exhaust air-fuel ratio is in a lean state; and desorbing and reducing the adsorbed NOx when the exhaust air-fuel ratio is in a stoichiometric state or a rich state; and removing the NOx by the exhaust air-fuel ratio being shifted between the lean state and the rich state.
1. A method of purifying an exhaust gas, the method comprising:
disposing a NOx trapping catalyst in an exhaust pipe of an internal combustion engine,
the NOx trapping catalyst comprising:
a metal substrate including cells, a corner portion of each of cells having an acute angle; and
a catalyst layer supported in the metal substrate, including a noble metal, a heat-resistant inorganic oxide, an NOx trapping material, a pore formation promoting material which includes particles of said pore formation promoting material, and pores having a diameter ranging from 1 μm to 10 μm, with each pore containing therein a particle of said pore formation promoting material, wherein said pores are defined by the noble metal, the heat-resistant inorganic oxide, and the NOx trapping material in the catalyst layer,
wherein said pores are formed by a calcination process by shrinking said pore formation promoting material from pre-calcination particle sizes with diameters ranging from 0.1 μm to 3.0 μm, and
the NOx trapping catalyst:
adsorbing NOx in the exhaust gas when an exhaust air-fuel ratio is in a lean state; and
desorbing and reducing the adsorbed NOx when the exhaust air-fuel ratio is in a stoichiometric state or a rich state; and
removing the NOx by the exhaust air-fuel ratio being shifted between the lean state and the rich state.
2. The method according to claim 1 , wherein
the pore formation promoting material is magnesia (MgO).
3. The method according to claim 1 , wherein
the NOx trapping material is an alkaline metal or an alkaline earth metal.
4. The method according to claim 3 , wherein
the alkaline metal or the alkaline earth metal is potassium (K).
5. The method according to claim 4 , wherein
the catalyst layer includes zeolite which stabilizes the potassium (K).
6. The method according to claim 1 , wherein
the noble metal is platinum (Pt), and
the catalyst layer includes ceria (CeO2).
7. The method according to claim 1 , wherein
the catalyst layer includes titania which suppresses poisoning by sulfur (S).
8. The method according to claim 1 , wherein
the internal combustion engine is a direct injection type internal combustion engine in which fuel is injected directly in a combustion chamber for lean burning,
a three-way catalyst is disposed downstream of the NOx trapping catalyst, and
a catalyst layer of the three-way catalyst includes a trapping material for trapping NOx.
9. An exhaust purifying catalyst which is disposed in an exhaust pipe of an internal combustion engine, the exhaust purifying catalyst comprising:
a metal substrate including cells, a corner portion of each of cells having an acute angle; and
a catalyst layer supported in the metal substrate, including a noble metal, a heat-resistant inorganic oxide, an NOx trapping material, a pore formation promoting material which includes particles of said pore formation promoting material, and pores having a diameter ranging from 1 μm to 10 μm, with each pore containing therein a particle of said pore formation promoting material, wherein said pores are defined by the noble metal, the heat-resistant inorganic oxide, and the NOx trapping material in the catalyst layer,
wherein said pores are formed by a calcination process by shrinking said pore formation promoting material from pre-calcination particle sizes with diameters ranging from 0.1 μm to 3.0 μm, and
wherein the exhaust purifying catalyst adsorbs NOx in an exhaust gas when an exhaust air-fuel ratio is in a lean state, and desorbs and reduces the adsorbed NOx when the exhaust air-fuel ratio is in a stoichiometric state or a rich state.