JP2015047543A - Nox occlusion emission material, exhaust gas purifying system and exhaust gas purifying method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new NOx occlusion emission material which is excellent in NOx occlusion emission performance even in high-temperature environment, a gas purifying system provided with the NOx occlusion emission material and an exhaust gas purifying method using the exhaust gas purifying system.SOLUTION: An NOx occlusion emission material is configured such that copper is deposited onto a heat-resistant oxide; the content proportion of copper is 6 to 12 mass% with respect to the net amount of the heat-resistant oxide; and copper and NOx is occluded and emitted. Further, an exhaust gas purifying system 1 includes an internal combustion engine 2 which exhausts gas, an NOx occlusion emission part 5 which is arranged on the gas flow direction downstream side with respect to the internal combustion engine 2 and is provided with the NOx occlusion emission material and an exhaust gas purification part 6 which is arranged on the gas flow direction downstream side with respect to the NOx occlusion emission part 5 in order to purify a gas containing NOx. Therein, by using the exhaust gas purifying system 1, the exhaust gas is purified.

Description

  The present invention relates to a NOx occlusion / release material, an exhaust gas purification system, and an exhaust gas purification method. More specifically, the present invention relates to a NOx occlusion / release material for storing and releasing NOx contained in exhaust gas discharged from an internal combustion engine, and the NOx occlusion / release. The present invention relates to an exhaust gas purification system including a material, and further relates to an exhaust gas purification method using the exhaust gas purification system.

  Exhaust gas discharged from an internal combustion engine such as an automobile contains hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NOx), etc., and an exhaust gas purifying apparatus for purifying these contains Are known.

  As an exhaust gas purification device, for example, a purification device using a NOx storage / release material is known. In such a device, for example, when the air-fuel ratio (A / F) of the air-fuel mixture supplied to the internal combustion engine is in a lean state, NOx is occluded by the NOx storage / release material, while the air-fuel ratio of the air-fuel mixture is When (A / F) is in a stoichiometric state or a rich state, NOx is released from the NOx storage / release material and purified by a catalyst or the like disposed downstream thereof.

  More specifically, for example, an exhaust gas purification device for purifying nitrogen oxides, carbon monoxide and hydrocarbons contained in exhaust gas of an internal combustion engine, comprising at least an alkali metal element and / or an alkali metal salt Is contained or mixed with a noble metal in a porous carrier, and a nitrogen oxide storage part for storing nitrogen oxides in the exhaust gas temperature range in the vicinity of the internal combustion engine, and nitrogen released from the nitrogen oxide storage part There has been proposed an exhaust gas purification device including a three-way catalyst unit for reducing (purifying) an oxide by reacting with carbon monoxide, hydrocarbons and hydrogen contained in exhaust gas (for example, Patent Document 1). reference.).

  According to such an exhaust gas purification apparatus, in a lean state where the exhaust gas purification performance of the three-way catalyst is not sufficient, NOx is occluded in the nitrogen oxide storage part, and the three-way catalyst can sufficiently exhibit the exhaust gas purification performance. In the region and the rich region, NOx is released from the nitrogen oxide storage part and purified by the three-way catalyst, so that the exhaust gas can be purified efficiently.

Japanese Patent Laid-Open No. 10-80620

  On the other hand, the nitrogen oxide storage part described in the cited document 1 may not have sufficient NOx storage / release performance under a high temperature environment such as 400 ° C. or higher, for example. There is a demand for a novel NOx occlusion / release material that excels in performance.

  An object of the present invention is to provide a novel NOx occlusion / release material excellent in NOx occlusion / release performance even in a high temperature environment, an exhaust gas purification system including the NOx occlusion / release material, and an exhaust gas purification method using the exhaust gas purification system. There is.

  In order to achieve the above object, in the NOx occlusion / release material of the present invention, copper is supported on a heat-resistant oxide, and the content ratio of copper is 6 mass relative to the total amount of the heat-resistant oxide and copper. % To 12% by mass and is characterized by being configured to occlude and release NOx.

  In addition, an exhaust gas purification system of the present invention includes an internal combustion engine that discharges gas, a NOx storage / release portion that is disposed downstream of the internal combustion engine in the gas flow direction and includes the NOx storage / release material, and the NOx storage The exhaust gas purification unit is disposed downstream of the discharge unit in the gas flow direction and purifies the gas containing NOx.

  The exhaust gas purification method of the present invention is an exhaust gas purification method using the above exhaust gas purification system, wherein the air-fuel ratio (A / F) of the air-fuel mixture supplied to the internal combustion engine is 14.5 or more. When NOx contained in the gas discharged from the internal combustion engine is occluded in the NOx occlusion / release section, and the air-fuel ratio (A / F) of the air-fuel mixture supplied to the internal combustion engine is less than 14.5 Further, the temperature of the NOx occlusion / release material is set to 400 ° C. or higher, NOx occluded in the NOx occlusion / release part is released, and the gas containing the released NOx is purified in the exhaust gas purification part. .

  The NOx occlusion / release material of the present invention can exhibit excellent NOx occlusion / release performance under a high temperature environment.

  In addition, in the exhaust gas purification system and the exhaust gas purification method of the present invention, the NOx storage / release material of the present invention is used, so that the NOx storage / release performance is excellent and the exhaust gas can be purified efficiently.

FIG. 1 is a schematic configuration diagram showing an embodiment of an exhaust gas purification system of the present invention. FIG. 2 is a graph showing the NOx concentration before and after the NOx storage / release part. FIG. 3 is a graph showing the relationship between the air-fuel ratio and the NOx release amount in Examples 2-3 and Comparative Example 1. FIG. 4 is a graph showing the relationship between the NOx storage / release material and the NOx release amount in Examples 4 to 8 and Comparative Example 2.

  In the NOx occlusion / release material of the present invention, copper (Cu) is supported on the heat-resistant oxide.

  Although it does not restrict | limit especially as a heat resistant oxide, For example, a zirconia-ceria type oxide, an alumina, etc. are mentioned.

  Examples of the zirconia-ceria based oxide include a zirconia-ceria based composite oxide represented by the following general formula (1).

Zr _{1- (a + b)} Ce _a R _b O _2-c (1)
(Wherein R represents a rare earth element (excluding Ce) and / or alkaline earth metal, a represents the atomic ratio of Ce, b represents the atomic ratio of R, and 1- ( a + b) indicates the atomic ratio of Zr, and c indicates the amount of oxygen defects.)
In the general formula (1), examples of the rare earth element represented by R include Sc (scandium), Y (yttrium), La (lanthanum), Pr (praseodymium), Nd (neodymium), Pm (promethium), and Sm (promethium). Samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), Lu (lutetium) and the like It is done.

  Examples of the alkaline earth metal represented by R include Be (beryllium), Mg (magnesium), Ca (calcium), Sr (strontium), Ba (barium), and Ra (radium).

  These rare earth elements and alkaline earth metals can be used alone or in combination of two or more.

  Moreover, the atomic ratio of Ce shown by a is in the range of 0.1 to 0.65, and preferably in the range of 0.1 to 0.5.

  In addition, the atomic ratio of R represented by b is in the range of 0 to 0.55 (that is, R is an optional component that is optionally included, not an essential component, and if included, 0.55 or less) Atomic ratio). If it exceeds 0.55, phase separation or other complex oxide phases may be generated.

  In addition, the atomic ratio of Zr represented by 1- (a + b) is in the range of 0.35 to 0.9, and preferably in the range of 0.5 to 0.9.

  Further, c represents the amount of oxygen defects, which means the ratio of vacancies formed in the crystal lattice of the fluorite-type crystal lattice normally formed by the oxides of Zr, Ce and R.

  Such a zirconia-ceria-based composite oxide is not particularly limited, and for example, a composite oxide is prepared according to the description of paragraph numbers [0090] to [0102] of JP-A-2004-243305. For example, it can be produced by a production method such as a coprecipitation method, a citric acid complex method, or an alkoxide method.

  Examples of alumina include α-alumina, θ-alumina, and γ-alumina, and preferably θ-alumina.

  α-alumina has an α-phase as a crystal phase, and examples thereof include AKP-53 (trade name, high-purity alumina, manufactured by Sumitomo Chemical Co., Ltd.). Such α-alumina can be obtained by a method such as an alkoxide method, a sol-gel method, or a coprecipitation method.

  θ-alumina is a kind of intermediate (transition) alumina that has a θ-phase as a crystal phase and transitions to α-alumina, and includes, for example, SPHERALITE 531P (trade name, γ-alumina, manufactured by Procatalyze). . Such θ-alumina can be obtained, for example, by subjecting commercially available activated alumina (γ-alumina) to heat treatment at 900 to 1100 ° C. for 1 to 10 hours in the air.

  γ-alumina has a γ-phase as a crystal phase and is not particularly limited, and examples thereof include known ones.

  In addition, alumina containing La and / or Ba can also be used. Alumina containing La and / or Ba can be produced according to the description in paragraph [0073] of JP-A No. 2004-243305.

  These heat-resistant oxides can be used alone or in combination of two or more.

  As the heat-resistant oxide, preferably, alumina is used.

  In the NOx occlusion / release material, the content ratio of copper is 6% by mass or more and 12% by mass or less based on the total amount of the heat-resistant oxide and copper.

  When the content ratio of copper is in the above range, excellent NOx occlusion / release performance can be exhibited.

  In order to obtain the NOx occlusion / release material, for example, copper is supported simultaneously or sequentially on the same heat-resistant oxide. For example, in accordance with the description of paragraph numbers [0122] to [0127] of JP-A No. 2004-243305, copper is supported on the heat-resistant oxide at the above-described ratio.

  Specifically, for example, a salt solution containing copper may be prepared, and the salt-containing solution may be impregnated with a heat-resistant oxide and then fired.

  Examples of the salt-containing solution include nitrate aqueous solution, chloride aqueous solution, hexaammine chloride aqueous solution, dinitrodiammine nitric acid aqueous solution, hexachloro acid hydrate, and practically, nitrate aqueous solution, dinitrodiammine nitric acid solution, Examples include aqueous chloride solutions.

  After impregnating the heat-resistant oxide with a salt solution containing copper, for example, baking is performed at 350 to 1000 ° C. for 1 to 12 hours.

  Further, as another method for supporting copper on the heat-resistant oxide, for example, when the heat-resistant oxide is a zirconia-based composite oxide or a ceria-based composite oxide, zirconium, cerium, an alkaline earth metal, and When coprecipitating or hydrolyzing salt solutions and / or mixed alkoxide solutions containing rare earth elements, add copper salt solution to coprecipitate copper with each component of zirconia complex oxide and ceria complex oxide Then, a method of firing is exemplified.

  Further, when the heat-resistant oxide is θ alumina, α alumina, or γ alumina, copper is precipitated when it is precipitated from an aqueous aluminum salt solution using ammonia or the like in the production process of θ alumina, α alumina, or γ alumina. An example is a method in which a salt solution is added to coprecipitate copper together with θ alumina, α alumina, or γ alumina, and then fired.

  Further, copper may be supported at a time, or may be supported sequentially in a plurality of times.

  Thereby, copper can be carry | supported by a heat resistant oxide, and a NOx occlusion / release material can be obtained as a heat resistant oxide carrying copper.

  In this method, if necessary, the heat-resistant oxide supporting copper can be heat-treated in a reducing atmosphere (for example, a hydrogen-nitrogen mixed gas atmosphere).

  As heat treatment conditions, the heating temperature is, for example, 500 ° C. or higher, preferably 600 ° C. or higher, for example, 1000 ° C. or lower, preferably 900 ° C. or lower. The heating time is, for example, 0.5 hours or more, preferably 1.0 hours or more, for example, 10.0 hours or less, preferably 5.0 hours or less.

  Further, for example, without using heat treatment in a reducing atmosphere as described above, a heat-resistant oxide supporting copper can be used as a NOx occlusion / release material and exposed to high-temperature exhaust gas to be heat-treated simultaneously with use. .

  The NOx occlusion / release material is not particularly limited, and may be used, for example, as the above powder. For example, the NOx occlusion / release material may be formed into an arbitrary predetermined shape by a known method.

  Further, the NOx occlusion / release material of the present invention can be used as it is, but for example, it can be formed as a coating layer on a carrier. The carrier is not particularly limited, and examples thereof include known carriers such as a honeycomb monolith carrier made of cordierite.

  In order to form a coating layer on the carrier, for example, first, the NOx occlusion / release material described above, and other heat-resistant oxides mixed if necessary, are made into a slurry by adding water, and then on the catalyst carrier. In the air, for example, it is dried at 50 to 200 ° C. for 1 to 48 hours, and further fired at 250 to 1000 ° C. for 1 to 12 hours.

  In addition, as another heat resistant oxide mix | blended with NOx occlusion / release material, the heat resistant oxide similar to the heat resistant oxide used for the above-mentioned NOx occlusion / release material, etc. are mentioned, for example.

  And according to said NOx occlusion-release material, since it can express the outstanding NOx occlusion-release performance in a high temperature environment (for example, 400 degreeC or more), and since it does not contain a noble metal etc., it is low-cost. Excellent in properties.

  Next, an exhaust gas purification system using the NOx occlusion / release material will be described in detail with reference to FIG.

  In FIG. 1, an exhaust gas purification system 1 includes an internal combustion engine 2 that discharges gas, an exhaust pipe 3 that discharges gas from the internal combustion engine 2, and a gas flow direction (see arrows) downstream of the internal combustion engine 2. The exhaust gas processing unit 4 is disposed so as to be interposed in the exhaust pipe 3.

  Examples of the internal combustion engine 2 include known engines (E / G) that use gasoline as fuel, such as reciprocating engines and rotary engines.

  Such an internal combustion engine 2 is supplied with an air-fuel mixture in which air and fuel are mixed, and the air-fuel mixture is explosively burned inside the internal combustion engine 2. Thereby, the internal combustion engine 2 generates energy.

  As the exhaust pipe 3, for example, when the internal combustion engine 2 is a multi-cylinder engine, an exhaust manifold (exhaust manifold) that guides and converges gas discharged from each cylinder of the engine can be used. Although not shown, the exhaust manifold includes a branch pipe connected to each cylinder and an air collection pipe that integrates the branch pipes on the downstream side in the gas flow direction.

  In addition, when the exhaust pipe 3 is an exhaust manifold, the exhaust gas treatment unit 4 is preferably interposed in the air collection pipe.

  The exhaust gas treatment unit 4 includes a NOx storage / release unit 5 for storing and releasing NOx, and an exhaust gas purification unit 6 for purifying gas containing NOx.

  The NOx occlusion / release part 5 includes the NOx occlusion / release material, and is disposed downstream of the internal combustion engine 2 and upstream of the exhaust gas purification unit 6 in the gas flow direction.

  More specifically, the NOx occlusion / release part 5 includes, for example, a honeycomb-shaped monolith carrier (not shown) and a NOx occlusion / release material carried as a coat layer (not shown) on the surface of the monolith carrier. I have.

  The amount of the NOx occlusion / release material supported on the monolith carrier is not particularly limited, and is appropriately set according to the purpose and application.

  The exhaust gas purification unit 6 includes, for example, an exhaust gas purification catalyst, and is disposed on the downstream side of the NOx storage / release unit 5 in the gas flow direction.

  More specifically, the exhaust gas purification unit 6 includes, for example, a honeycomb-shaped monolith support (not shown) and an exhaust gas purification catalyst supported as a coat layer (not shown) on the surface of the monolith support. ing.

  As the exhaust gas purification catalyst, for example, a platinum group element (for example, Ru (ruthenium), Rh (rhodium), Pd (palladium), Os (osmium), Ir (iridium), Pt (platinum), etc.) is supported. Known exhaust gas purification catalysts such as heat-resistant oxides can be mentioned.

  The amount of the exhaust gas-purifying catalyst supported on the monolith support is not particularly limited, and is appropriately set according to the purpose and application.

  The exhaust gas treatment unit 4 can further include a preliminary exhaust gas purification unit 7 for preliminarily purifying the gas discharged from the internal combustion engine 2 before reaching the NOx storage / release unit 5. .

  The preliminary exhaust gas purification unit 7 includes, for example, an exhaust gas purification catalyst, and is disposed on the upstream side of the NOx storage / release unit 5 in the gas flow direction.

  More specifically, the preliminary exhaust gas purification unit 7 includes, for example, a honeycomb monolith carrier (not shown) and the exhaust gas purification catalyst supported on the surface of the monolith carrier as a coat layer (not shown). And.

  The amount of the exhaust gas-purifying catalyst supported on the monolith support is not particularly limited, and is appropriately set according to the purpose and application.

  Hereinafter, an exhaust gas purification method using the exhaust gas purification system 1 will be described in detail.

  In this method, first, an air-fuel mixture having a predetermined air-fuel ratio (A / F) is supplied to the internal combustion engine 2 and burned in the internal combustion engine 2.

  The air-fuel ratio (A / F) of the air-fuel mixture varies depending on the driving state of the internal combustion engine 2 so as to cross, for example, 14.5 to 14.7 (stoichiometry region). Normally, a state where the air-fuel ratio (A / F) is 14.5 to 14.7 (stoichiometry region) is a stoichiometric burn state, and a case where the air-fuel ratio (A / F) is less than 14.5 is rich. The burn state and the case where the air-fuel ratio (A / F) exceeds 14.7 is referred to as a lean burn state.

  Such an air-fuel mixture is burned in the internal combustion engine 2 to generate energy, and a gas containing hydrocarbon (HC), carbon monoxide (CO), nitrogen oxide (NOx), etc. It is discharged from the engine 2.

  The gas discharged from the internal combustion engine 2 is supplied to the preliminary exhaust gas purification unit 7, and a part thereof is purified, and then supplied to the NOx occlusion / release unit 5.

  In the NOx occlusion / release section 5, NOx contained in the gas is occluded or released by the NOx occlusion / release material according to the air-fuel ratio (A / F) of the air-fuel mixture supplied to the internal combustion engine 2.

  More specifically, in this method, when the air-fuel ratio (A / F) of the air-fuel mixture supplied to the internal combustion engine 2 is 14.5 or more, part or all of the NOx contained in the gas is reduced to NOx. It is occluded by the occlusion / release material.

  The temperature of the NOx occlusion / release material during NOx occlusion is, for example, 400 ° C. or higher, preferably 450 ° C. or higher, more preferably 500 ° C. or higher, and usually 1000 ° C. or lower.

  Note that the temperature of the NOx occlusion / release material can be determined by adjusting the operating conditions of the internal combustion engine 2, adjusting the distance from the internal combustion engine 2 to the NOx occlusion / release part 5, or heating the exhaust pipe 3 (for example, It can be controlled by heating with an electric heater, etc., cooling the exhaust pipe 3 with a cooling device (for example, a spot cooler, etc.), and the temperature of the gas is regarded as the temperature of the NOx storage / release material Can do.

  The NOx occlusion amount in the NOx occlusion / release material is not particularly limited, and is appropriately set according to the purpose and application.

  Further, the gas (including HC and CO) remaining without being stored in the NOx storage / release material is supplied to the exhaust gas purification unit 6 and purified.

  On the other hand, in the exhaust gas purification system 1 described above, when the air-fuel ratio (A / F) of the air-fuel mixture is less than 14.5, if the temperature of the NOx occlusion / release material is 400 ° C. or higher, the NOx occlusion / release material occludes. The NOx that has been released is released.

  Therefore, in this method, when the air-fuel ratio (A / F) of the air-fuel mixture supplied to the internal combustion engine 2 is less than 14.5, the temperature of the NOx storage / release material is set to 400 ° C. or higher to release NOx.

  The temperature of the NOx occlusion / release material during NOx release is 400 ° C. or higher, preferably 450 ° C. or higher, more preferably 500 ° C. or higher, and usually 800 ° C. or lower.

  If the temperature of the NOx occlusion / release material is within the above range, NOx can be released more favorably.

  When the temperature of the NOx storage / release material is less than 400 ° C., the NOx storage / release material does not release NOx even if the air-fuel ratio (A / F) of the air-fuel mixture is less than 14.5.

  In this method, the NOx released from the NOx occlusion / release material as described above is supplied to the exhaust gas purification unit 6 and purified together with other gases (including HC and CO) discharged from the internal combustion engine 2. The The gas purified in this way is discharged from the exhaust gas purification system 1 to the outside air.

  In the exhaust gas purification system 1 and the exhaust gas purification method, since the above-described NOx storage / release material is used, the NOx storage / release performance is excellent and the exhaust gas can be purified efficiently.

  That is, depending on the type of exhaust gas purification catalyst disposed in the exhaust gas purification unit 6, when the air-fuel ratio (A / F) of the air-fuel mixture supplied to the internal combustion engine 2 is less than 14.5, the NOx purification performance is sufficient. On the other hand, when the air-fuel ratio (A / F) is 14.5 or more, the NOx purification performance may not be sufficiently exhibited.

  On the other hand, according to the exhaust gas purification system 1 and the exhaust gas purification method, when the air-fuel ratio (A / F) is 14.5 or more, the NOx storage / release part 5 stores NOx, while the air-fuel ratio When (A / F) is less than 14.5, NOx is released from the NOx occlusion / release section 5 and purified by the exhaust gas purification section 6. Therefore, exhaust gas can be purified efficiently.

  In the above description, the exhaust gas treatment unit 4 is configured by the preliminary exhaust gas purification unit 7, the NOx occlusion / release unit 5, and the exhaust gas purification unit 6. However, for example, the NOx occlusion / release is not provided without the preliminary exhaust gas purification unit 7. The exhaust gas treatment unit 4 can also be configured from the unit 5 and the exhaust gas purification unit 6. The exhaust gas purification system 1 preferably includes a preliminary exhaust gas purification unit 7 from the viewpoint of reducing the load of exhaust gas treatment in the NOx occlusion / release unit 5 and the exhaust gas purification unit 6.

  Further, the above-mentioned NOx occlusion / release material in which copper is supported on a heat-resistant oxide can also serve as an exhaust gas purification catalyst particularly in a rich burn state.

  That is, the NOx storage / release material described above contains NOx contained in the gas discharged from the internal combustion engine 2 when the air-fuel ratio (A / F) of the air-fuel mixture supplied to the internal combustion engine 2 is 14.5 or more. On the other hand, when the air-fuel ratio (A / F) of the air-fuel mixture supplied to the internal combustion engine 2 is less than 14.5, NOx is released and the released NOx is further purified.

  Therefore, for example, the exhaust gas treatment unit 4 can be configured only from the NOx storage / release unit 5, and the NOx storage / release unit 5 can also be used as the exhaust gas purification unit 6.

  Next, although this invention is demonstrated based on an Example and a comparative example, this invention is not limited by the following Example. The numerical values of the examples shown below can be substituted for the numerical values (that is, the upper limit value or the lower limit value) described in the embodiment.

Example 1
θ alumina was impregnated with an aqueous copper nitrate solution, dried, and then heat-treated (fired) at 650 ° C. for 1 hour in an electric furnace to obtain a NOx occlusion / release material as Cu-supported θ-alumina powder.

The Cu content ratio of this powder was 6% by mass with respect to the total amount of Cu-supported θ-alumina.
<A/F>
Example 2
The NOx occlusion / release material obtained in Example 1 is disposed in the NOx occlusion / release part 5 of the exhaust gas purification system 1 shown in FIG. 1, and an exhaust gas purification catalyst is provided in the exhaust gas purification part 6 and the preliminary exhaust gas purification part 7. As described above, a three-way catalyst containing Pd and Rh was arranged.

  Next, the gasoline engine as the internal combustion engine 2 was driven in a lean burn state with an air-fuel ratio (A / F) of 15.1, and after a predetermined time, switched to a rich burn state with an air-fuel ratio (A / F) of 14.3. .

  In the exhaust gas purification system 1, the operating conditions of the internal combustion engine 2 are adjusted, the distance from the preliminary exhaust gas purification unit 7 to the NOx occlusion / release unit 5 is adjusted, and the exhaust pipe 3 is further connected using a spot cooler. By cooling from the outside, the gas temperature supplied to the NOx occlusion / release part 5 was adjusted to 570 ° C. in both the lean burn state and the rich burn state. This gas temperature was regarded as the temperature of the NOx storage / release material.

  Then, the exhaust gas discharged from the internal combustion engine 2 is processed in the exhaust gas processing unit 4, and the NOx concentration of the gas between the preliminary exhaust gas purification unit 7 and the NOx storage / release unit 5 (hereinafter, the NOx concentration before the storage / release unit). Was measured, and the NOx concentration of the gas between the NOx occlusion / release unit 5 and the exhaust gas purification unit 6 (hereinafter, the NOx concentration after the occlusion / release unit) was measured. The result is shown in FIG.

  In FIG. 2, in the lean burn state, the NOx concentration before the occlusion / release portion and the NOx concentration after the occlusion / release portion are substantially the same, but after switching to the rich burn state, it is higher than the NOx concentration before the occlusion / release portion. The NOx concentration after the occlusion / release part is increased.

  From this, NOx occlusion and release in the NOx occlusion / release part 5 was confirmed.

  Further, after switching from the lean burn state to the rich burn state, the amount of NOx released from the NOx occlusion / release unit 5 in 50 seconds was integrated. The results are shown in Table 1 and FIG.

Example 3
Except that the air-fuel ratio (A / F) in the rich burn state was changed from 14.3 to 14.4, the exhaust gas was treated in the same manner as in Example 2 to store and release NOx in the NOx storage and release part 5 confirmed.

  Further, after switching from the lean burn state to the rich burn state, the amount of NOx released from the NOx occlusion / release unit 5 in 50 seconds was integrated. The results are shown in Table 1 and FIG.

Comparative Example 1
Exhaust gas was treated in the same manner as in Example 2 except that the air-fuel ratio (A / F) in the rich burn state was changed from 14.3 to 14.5. Was not confirmed.

  Further, after switching from the lean burn state to the rich burn state, the amount of NOx released from the NOx occlusion / release unit 5 in 50 seconds was integrated. The results are shown in Table 1 and FIG.

<Temperature conditions>
Example 4
The operating conditions of the internal combustion engine 2 are adjusted, the distance from the preliminary exhaust gas purification unit 7 to the NOx storage / release unit 5 is adjusted, and further, the exhaust pipe 3 is cooled from the outside by using a spot cooler, thereby storing NOx. Exhaust gas was treated in the same manner as in Example 2 except that the temperature of the gas supplied to the discharge unit 5 was adjusted to 454 ° C., and NOx storage and release in the NOx storage / release unit 5 were confirmed.

  Further, after switching from the lean burn state to the rich burn state, the amount of NOx released from the NOx occlusion / release unit 5 in 50 seconds was integrated. The results are shown in Table 2 and FIG.

Example 5
The operating conditions of the internal combustion engine 2 are adjusted, the distance from the preliminary exhaust gas purification unit 7 to the NOx storage / release unit 5 is adjusted, and further, the exhaust pipe 3 is cooled from the outside by using a spot cooler, thereby storing NOx. Exhaust gas was treated in the same manner as in Example 2 except that the temperature of the gas supplied to the discharge unit 5 was adjusted to 509 ° C., and NOx storage and release in the NOx storage / release unit 5 were confirmed.

  Further, after switching from the lean burn state to the rich burn state, the amount of NOx released from the NOx occlusion / release unit 5 in 50 seconds was integrated. The results are shown in Table 2 and FIG.

Example 6
The operating conditions of the internal combustion engine 2 are adjusted, the distance from the preliminary exhaust gas purification unit 7 to the NOx storage / release unit 5 is adjusted, and further, the exhaust pipe 3 is cooled from the outside by using a spot cooler, thereby storing NOx. Exhaust gas was treated in the same manner as in Example 2 except that the temperature of the gas supplied to the discharge unit 5 was adjusted to 551 ° C., and NOx storage and release in the NOx storage / release unit 5 were confirmed.

  Further, after switching from the lean burn state to the rich burn state, the amount of NOx released from the NOx occlusion / release unit 5 in 50 seconds was integrated. The results are shown in Table 2 and FIG.

Example 7
The operating conditions of the internal combustion engine 2 are adjusted, the distance from the preliminary exhaust gas purification unit 7 to the NOx storage / release unit 5 is adjusted, and further, the exhaust pipe 3 is cooled from the outside by using a spot cooler, thereby storing NOx. Exhaust gas was treated in the same manner as in Example 2 except that the gas temperature supplied to the discharge unit 5 was adjusted to 573 ° C., and NOx storage and release in the NOx storage / release unit 5 were confirmed.

  Further, after switching from the lean burn state to the rich burn state, the amount of NOx released from the NOx occlusion / release unit 5 in 50 seconds was integrated. The results are shown in Table 2 and FIG.

Example 8
The operating conditions of the internal combustion engine 2 are adjusted, the distance from the preliminary exhaust gas purification unit 7 to the NOx storage / release unit 5 is adjusted, and further, the exhaust pipe 3 is cooled from the outside by using a spot cooler, thereby storing NOx. Exhaust gas was treated in the same manner as in Example 2 except that the temperature of the gas supplied to the discharge unit 5 was adjusted to 651 ° C., and NOx storage and release in the NOx storage / release unit 5 were confirmed.

  Further, after switching from the lean burn state to the rich burn state, the amount of NOx released from the NOx occlusion / release unit 5 in 50 seconds was integrated. The results are shown in Table 2 and FIG.

Comparative Example 2
The operating conditions of the internal combustion engine 2 are adjusted, the distance from the preliminary exhaust gas purification unit 7 to the NOx storage / release unit 5 is adjusted, and further, the exhaust pipe 3 is cooled from the outside by using a spot cooler, thereby storing NOx. Exhaust gas was treated in the same manner as in Example 2 except that the gas temperature supplied to the discharge part 5 was adjusted to 369 ° C., and NOx storage and release in the NOx storage / release part 5 were not confirmed. .

  Further, after switching from the lean burn state to the rich burn state, the amount of NOx released from the NOx occlusion / release unit 5 in 50 seconds was integrated. The results are shown in Table 2 and FIG.

<Copper loading ratio>
Example 9
A NOx occlusion / release material was obtained as Cu-supported θ-alumina powder in the same manner as in Example 1 except that the amount of the copper nitrate aqueous solution was changed.

  The Cu content ratio of this powder was 12% by mass with respect to the total amount of Cu-supported θ-alumina.

Example 10
Exhaust gas was treated in the same manner as in Example 2 except that the Cu-supported θ-alumina (Cu content: 12% by mass) obtained in Example 9 was used, and NOx occlusion and release in the NOx occlusion / release part 5 were confirmed. did.

  Further, after switching from the lean burn state to the rich burn state, the amount of NOx released from the NOx occlusion / release unit 5 in 50 seconds was integrated. The results are shown in Table 3.

Claims (3)

Copper is supported on the heat-resistant oxide,
The NOx occlusion / release material is characterized in that the content ratio of copper is 6% by mass or more and 12% by mass or less with respect to the total amount of the heat-resistant oxide and copper, and is configured to occlude and release NOx. . An internal combustion engine that discharges gas;
The NOx occlusion / release part, which is disposed downstream of the internal combustion engine in the gas flow direction and includes the NOx occlusion / release material according to claim 1,
An exhaust gas purification system comprising: an exhaust gas purification unit for purifying a gas containing NOx, which is disposed downstream of the NOx storage / release unit in the gas flow direction. An exhaust gas purification method using the exhaust gas purification system according to claim 2,
When the air-fuel ratio (A / F) of the air-fuel mixture supplied to the internal combustion engine is 14.5 or more, NOx contained in the gas discharged from the internal combustion engine is stored in the NOx storage / release section,
When the air-fuel ratio (A / F) of the air-fuel mixture supplied to the internal combustion engine is less than 14.5, the temperature of the NOx storage / release material is set to 400 ° C. or higher, and the NOx stored in the NOx storage / release section Release
An exhaust gas purification method comprising purifying a gas containing released NOx in the exhaust gas purification unit.