JP5081672B2 - Exhaust gas purification device - Google Patents

Description

  The present invention relates to an exhaust gas purification device, and more particularly to an exhaust gas purification device capable of efficiently performing NOx purification and PM purification over a wide temperature range.

The exhaust gas discharged from the lean burn engine contains harmful substances such as carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), and particulate matter (PM). Of these, CO and HC are converted to harmless carbon dioxide (CO ₂ ) and water (H ₂ O) by reacting with oxygen (O ₂ ) in the exhaust gas by installing an oxidation catalyst in the exhaust gas passage. It is possible to purify and remove. On the other hand, NOx needs to be reacted with reducing components such as CO and HC in the exhaust gas and converted to nitrogen (N ₂ ). However, in an oxygen-excess state such as exhaust gas discharged from a lean burn engine, it is reduced. Since the component reacts preferentially with O ₂ , the NOx reduction efficiency is greatly reduced.

  Therefore, a NOx adsorption / reduction catalyst is installed in the exhaust gas passage, and during normal lean burn operation, NOx in the exhaust gas is adsorbed by the NOx adsorption / reduction catalyst, and the exhaust gas atmosphere is periodically made rich with a reducing agent ( There is known a method of efficiently purifying NOx by repeating a cycle of reducing NOx adsorbed on the catalyst by rich spike).

  For example, using an alkali metal, an alkaline earth metal or the like, using a NOx absorbent that absorbs NOx when the air-fuel ratio of the exhaust gas is lean and reduces the oxygen concentration in the exhaust gas, and releases the absorbed NOx, An exhaust gas purification device is disclosed in which NOx absorbed when the exhaust gas is lean is released from the NOx absorbent when the oxygen concentration in the exhaust gas is reduced (see Patent Document 1).

  However, since the NOx absorbent used in the exhaust gas purification apparatus uses an alkali metal, an alkaline earth metal, and a noble metal that is an active species, the activity of the noble metal is likely to decrease, and the NOx purification performance particularly at a low temperature. There was a problem that decreased. For this reason, the realistic purification temperature window of the catalyst using an alkali metal or an alkaline earth metal is 250 ° C. to 500 ° C., and sufficient performance cannot be obtained in an operation region below 250 ° C.

Therefore, the present applicants have proposed a catalyst that uses a cerium-based NOx adsorbent without using an alkali metal or an alkaline earth metal, and at the same time combined with a material having an NH ₃ adsorption function (see Patent Document 2). ). According to this catalyst, NOx adsorbed by lean is converted to NH ₃ when rich, immediately adsorbed to the NH ₃ adsorbent, and NOx is selectively reduced by NH ₃ at the next lean, so that NOx at low temperature is reduced. The purification performance can be dramatically improved.

  However, the cerium-based adsorbent has a NOx adsorption temperature window of 150 ° C. to 400 ° C. and functions sufficiently under normal diesel vehicle operating conditions, but in an operating region where exhaust gas is 400 ° C. or higher. There was a tendency for the performance to decrease slightly.

On the other hand, regarding the removal of PM, it is removed by filtering with a filter called a diesel particulate filter (DPF) made of porous ceramics in which the inlet and outlet are alternately plugged in a wall flow honeycomb shape. Is common.
Japanese Patent No. 2600492 JP 2008-30003 A

  By the way, in a diesel engine, the exhaust gas temperature range of the LA4 mode, which is an American driving mode modeled on normal operating conditions, is 150 ° C. to 350 ° C. However, in the US06 mode modeled on high-load operation, the exhaust gas temperature range is 300 ° C to 500 ° C. Therefore, in a diesel engine, NOx must be purified over a wide temperature range of 150 ° C to 500 ° C.

  Thus, in order to clear exhaust gas regulations that are becoming more severe in recent years, an exhaust gas purification device that can exhibit both high NOx purification ability and high PM purification ability over a wide temperature range is required. However, the present situation is that no such exhaust gas purification device has been found so far.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an exhaust gas purification device capable of efficiently purifying NOx and purifying PM over a wide temperature range. It is in.

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, the above problem is solved by adopting a configuration in which a high-temperature lean NOx catalyst, a filter capable of collecting PM, and a low-temperature lean NOx catalyst are sequentially arranged in series in the exhaust gas passage of the internal combustion engine. The present inventors have found that this can be done and have completed the present invention. More specifically, the present invention provides the following.

  An exhaust gas purification device according to claim 1 is provided in an exhaust gas passage of an internal combustion engine in which lean or rich control is performed, and is an exhaust gas purification device for purifying exhaust gas discharged from the internal combustion engine, A first purification unit having a high-temperature lean NOx catalyst provided in the exhaust gas passage and including at least one selected from the group consisting of alkali metals and alkaline earth metals; and the exhaust gas passage downstream of the first purification unit. A second purification unit that has a filter that collects PM contained in the exhaust gas, and a low-temperature lean NOx catalyst that is provided in the exhaust gas passage downstream of the second purification unit and contains a cerium-based material. A third purification unit.

  The exhaust gas purification device according to claim 2 is the exhaust gas purification device according to claim 1, wherein the high temperature type lean NOx catalyst includes at least one kind of noble metal selected from the group consisting of Pt, Pd, and Rh. And

  The exhaust gas purifying apparatus according to claim 3 is the exhaust gas purifying apparatus according to claim 1 or 2, wherein the high temperature type lean NOx catalyst is selected from the group consisting of alumina, silica, titania, and zirconia. It is characterized by including.

  The exhaust gas purifying apparatus according to claim 4 is the exhaust gas purifying apparatus according to any one of claims 1 to 3, wherein the high-temperature lean NOx catalyst includes an oxygen storage / release material composed of a ceria-zirconia composite oxide. To do.

  The exhaust gas purifying apparatus according to claim 5 is the exhaust gas purifying apparatus according to any one of claims 1 to 4, characterized in that it includes a metal or cordierite carrier.

  The exhaust gas purifying apparatus according to claim 6 is the exhaust gas purifying apparatus according to any one of claims 1 to 5, wherein the filter is made of cordierite, SiC, alumina, or titania.

  The exhaust gas purifying apparatus according to claim 7 is the exhaust gas purifying apparatus according to any one of claims 1 to 6, wherein a central pore diameter of the filter is 10 μm to 30 μm and a porosity is 40% to 60%. Features.

  The exhaust gas purification apparatus according to claim 8 is the exhaust gas purification apparatus according to any one of claims 1 to 7, wherein the second purification unit is supported on the filter surface and is made of a group consisting of Pt, Pd, Rh, and Ag. It further comprises a PM combustion catalyst comprising at least one selected noble metal and at least one support selected from the group consisting of alumina, ceria, zirconia, and titania.

  The exhaust gas purifying apparatus according to claim 9 is the exhaust gas purifying apparatus according to any one of claims 1 to 8, wherein the low-temperature lean NOx catalyst is supported on a carrier and includes a noble metal, the cerium-based material, and a lanthanum-based material. When it is in a lean state, NOx in the exhaust gas is oxidized and adsorbed on the first catalyst layer, and in a rich state, it is oxidized and adsorbed on the first catalyst layer in a lean state. The NOx is converted into nitrogen and water by the reducing component present in the vicinity of the first catalyst layer.

  The exhaust gas purifying device according to claim 10 is the exhaust gas purifying device according to claim 9, wherein the content of the lanthanum-based material contained in the first catalyst layer is 1 g / L to 100 g / L per unit volume. Features.

  The exhaust gas purifying apparatus according to claim 11 is the exhaust gas purifying apparatus according to claim 9 or 10, wherein the noble metal contained in the first catalyst layer is mainly composed of platinum and rhodium as an auxiliary component. To do.

  The exhaust gas purifying apparatus according to claim 12 is the exhaust gas purifying apparatus according to claim 11, wherein the total content of the noble metals is 0.1 g / L to 20 g / L per unit volume.

  The exhaust gas purifying apparatus according to claim 13 is the exhaust gas purifying apparatus according to any one of claims 9 to 12, wherein the low-temperature type lean NOx catalyst is laminated on an upper layer of the first catalyst layer and is made of iron, cerium, and lanthanum. A second catalyst layer containing β zeolite containing at least one element selected from the group consisting of NOx in the exhaust gas is oxidized and adsorbed on the first catalyst layer, In this case, NOx oxidized and adsorbed on the first catalyst layer in the lean state is converted into nitrogen, water, and ammonia by the reducing components present in the vicinity of the first catalyst layer, and ammonia is then added to the second catalyst layer. When ammonia is adsorbed and made lean again, the ammonia adsorbed on the second catalyst layer in the rich state reacts with NOx in the exhaust gas and is converted to nitrogen and water. And features.

  The exhaust gas purification apparatus according to claim 14 is the exhaust gas purification apparatus according to any one of claims 9 to 13, wherein the reducing component is at least one selected from the group consisting of carbon monoxide, hydrocarbons, and hydrogen. It is characterized by.

  The exhaust gas purification device according to claim 15 is the exhaust gas purification device according to any one of claims 9 to 14, wherein the first catalyst layer is made of a zirconium oxide-based material, an alumina-based material, a zeolite-based material, and a silica-based material. It further comprises at least one heat-resistant inorganic oxide selected from the group.

  The exhaust gas purifying apparatus according to claim 16 is the exhaust gas purifying apparatus according to any one of claims 9 to 15, wherein the lanthanum-based material is lanthanum metal, lanthanum oxide, lanthanum-based composite oxide, and a composite of lanthanum and a rare earth element. It is at least one selected from the group consisting of oxides.

  The exhaust gas purifying apparatus according to claim 17 is the exhaust gas purifying apparatus according to any one of claims 9 to 16, wherein the cerium-based material is cerium metal, cerium oxide, a cerium-based composite oxide, and a composite of cerium and a rare earth element. It is at least one selected from the group consisting of oxides.

  The exhaust gas purifying apparatus according to claim 18 is the exhaust gas purifying apparatus according to any one of claims 9 to 17, wherein the first catalyst layer is composed of a plurality of layers.

  The exhaust gas purifying apparatus according to claim 19 is the exhaust gas purifying apparatus according to any one of claims 1 to 18, further comprising an oxidation catalyst section provided in the exhaust gas passage upstream of the first purification section and having an oxidation catalyst. It is characterized by that.

  The exhaust gas purification device according to claim 20 is the exhaust gas purification device according to any one of claims 1 to 19, wherein the high-temperature lean NOx catalyst of the first purification unit is heated to a predetermined temperature or more and the exhaust gas atmosphere is controlled to be rich. By removing the sulfur component adsorbed on the high temperature type lean NOx catalyst, the sulfur component adsorbed on the filter of the second purification unit and the low temperature type lean NOx catalyst of the third purification unit are adsorbed. It is further characterized by further comprising a regeneration means for removing the sulfur component.

  According to the present invention, in particular, exhaust gas that can efficiently purify NOx and PM contained in exhaust gas over a wide temperature range by performing lean or rich control in a lean burn engine such as a diesel engine. A purification device can be provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<First Embodiment>
FIG. 1 shows a schematic configuration of an exhaust gas purification apparatus 10 according to the present embodiment. As shown in FIG. 1, the exhaust gas purification device 10 is provided in the exhaust gas passage 2 of the internal combustion engine 1 where lean or rich control is performed, and is used to purify the exhaust gas discharged from the internal combustion engine 1. In the present embodiment, it is preferable to apply a lean burn engine as the internal combustion engine 1, and it is more preferable to apply a diesel engine.

  The exhaust gas purification device 10 is provided in the exhaust gas passage 2 on the downstream side of the internal combustion engine 1, and is provided in the exhaust gas passage 2 on the downstream side of the first purification unit 11 and the first purification unit 11 having a high temperature type lean NOx catalyst. And a second purification unit 12 having a DPF as a filter for collecting PM contained in the exhaust gas, and a third purification unit having a low-temperature lean NOx catalyst provided in the exhaust gas passage 2 downstream from the second purification unit 12 Unit 13.

  Here, the high temperature type lean NOx catalyst means a catalyst having a high NOx purification performance at 250 ° C. to 500 ° C., and the low temperature type lean NOx catalyst means a catalyst having a high purification performance at 150 ° C. to 400 ° C. To do. Lean means a state where the air-fuel ratio is large (fuel concentration is lean) with respect to stoichiometry, which is the stoichiometric ratio in the complete combustion reaction, and rich means that the air-fuel ratio is small (fuel concentration is high). Means state.

  As in this embodiment, the most important matter in the exhaust gas purification using the NOx adsorption / reduction function is the temperature management of the catalyst. It is known that the lean NOx catalyst has a NOx adsorption temperature range limited by the material. In a lean NOx catalyst using an alkali metal or an alkaline earth metal, the NOx adsorption temperature range is 250 ° C. to 500 ° C., and the NOx adsorption capacity is low at 250 ° C. or less. On the other hand, in a lean NOx catalyst using a cerium-based material, the NOx adsorption temperature range is 150 ° C. to 400 ° C., and if it exceeds 400 ° C., the NOx adsorption capacity is lowered. In the present embodiment, two types of lean NOx catalysts of different materials are combined to enable efficient purification of NOx in a wider temperature range than in the past.

[First purification section]
The first purification unit 11 is provided in the exhaust gas passage 2 on the downstream side of the internal combustion engine 1, and is preferably provided directly below the internal combustion engine 1. The first purification unit 11 has a high temperature type lean NOx catalyst containing at least one selected from the group consisting of alkali metals and alkaline earth metals. For this reason, the 1st purification | cleaning part 11 exhibits high NOx purification performance at 250 to 500 degreeC by the effect | action of a high temperature type | mold lean NOx catalyst. In the first purification unit 11, NOx is occluded in the lean state, and the occluded NOx is released in the rich state, whereby NOx purification is achieved by the action of the coexisting reducing agent.

  The high-temperature type lean NOx catalyst of the first purification unit 11 includes an alkali metal such as Na, K, and Cs and an alkaline earth metal such as Mg, Sr, and Ba. High NOx purification performance is exhibited by the high NOx adsorption ability in the high temperature region of these alkali metals and alkaline earth metals.

  The high temperature type lean NOx catalyst preferably contains at least one noble metal selected from the group consisting of Pt, Pd, and Rh. High purification performance is exhibited by the catalytic action of these noble metals.

  The high-temperature lean NOx catalyst preferably includes at least one support material selected from the group consisting of alumina, silica, titania, and zirconia. According to these support materials, it is possible to carry the above-mentioned noble metal and to obtain a catalyst having high heat resistance.

  The high-temperature lean NOx catalyst preferably includes an oxygen storage / release material composed of a ceria-zirconia composite oxide. By including the oxygen storage / release material, it is possible to purify NOx more efficiently.

  Further, the high-temperature lean NOx catalyst is preferably one in which the above-described components are supported on a metal or cordierite carrier. According to the carrier made of these materials, a catalyst having high heat resistance can be obtained. In particular, from the viewpoint of thermal conductivity, a metal honeycomb carrier is preferably used.

  The method for preparing the high temperature type lean NOx catalyst is not particularly limited, and is prepared by a conventionally known method. Specifically, a slurry containing the above materials constituting the high-temperature lean NOx catalyst is prepared, and the slurry is coated on the support so as to have a desired loading amount by a wash coat method, and then dried and fired. Is done.

[Second purification section]
The second purification unit 12 includes a filter that is provided in the exhaust gas passage 2 on the downstream side of the first purification unit 11 and collects PM contained in the exhaust gas. The filter is not particularly limited as long as it can collect PM, and a conventionally known DPF can be used.

  Nearly 100% of PM is collected by the filter provided in the second purification unit 12. The PM collected and deposited must be removed by combustion by raising the temperature of the exhaust gas. The filter capable of collecting PM has a feature that the temperature is difficult to rise due to its heat capacity because the volume is set large in order to increase the filtration area. For this reason, it is preferable to arrange the filter on the upstream side where the exhaust gas temperature is high as much as possible.

  However, since it is necessary to ensure the temperature rise performance of the upstream high-temperature lean NOx catalyst at the time of start-up, it may be disposed between the upstream high-temperature lean NOx catalyst and the downstream low-temperature lean NOx catalyst. preferable. Further, since the heat capacity is large, even if the operating conditions fluctuate drastically and the exhaust gas temperature changes greatly, there is an effect of maintaining the temperature of the low-temperature lean NOx catalyst on the downstream side appropriately.

  The filter of the second purification unit 12 is preferably a three-dimensional structure made of porous ceramics such as cordierite, SiC, alumina, or titania. Among these, a wall flow type or foam type structure is preferable. According to such a filter, it is possible to efficiently collect PM and obtain a filter having high heat resistance.

  Moreover, it is preferable that the center pore diameter of the filter is 1 μm to 100 μm and the porosity is 20% to 80%. When the central pore diameter of the filter is smaller than the above range, the collection efficiency increases, but the pressure loss increases. When the filter is larger than the above range, the pressure loss is small, but the collection efficiency becomes low. More preferably, the central pore diameter is 10 μm to 30 μm, and the porosity is 40% to 60%.

[Third purification section]
The third purification unit 13 is provided in the exhaust gas passage 2 on the downstream side of the second purification unit 12 and is preferably installed under the floor in the case of an automobile. The third purification unit 13 has a low-temperature lean NOx catalyst containing a cerium-based material. For this reason, the 3rd purification | cleaning part 13 exhibits high NOx purification ability in 150 to 400 degreeC by the effect | action of a low temperature type | mold lean NOx catalyst.

  The low-temperature type lean NOx catalyst of the third purification unit 13 preferably has a first catalyst layer supported on a carrier and containing a noble metal, the cerium-based material, and a lanthanum-based material. In the low temperature type lean NOx catalyst having such a configuration, NOx in the exhaust gas is oxidatively adsorbed on the first catalyst layer when in the lean state. When the rich state is established, the NOx oxidized and adsorbed on the first catalyst layer in the lean state is converted into nitrogen and water by the reducing components present in the vicinity of the first catalyst layer, so that efficient NOx purification is achieved. Done.

(First catalyst layer)
A precious metal such as platinum, a cerium-based material, and a lanthanum-based material are added to the first catalyst layer. For this reason, it has excellent NOx purification performance due to the synergistic effect of noble metals such as platinum, cerium-based materials and lanthanum-based materials.

  Examples of the cerium-based material include cerium metal, cerium oxide, and cerium-based composite oxides, and those obtained by adding various auxiliary materials to these oxides can also be used. Examples of the cerium-based composite oxide include cerium-zirconium composite oxide. When the cerium-zirconium composite oxide is used, 10% by mass or more of cerium oxide in terms of oxide is included in the composite oxide. It is preferable that it is contained, more preferably 30% by mass or more, and most preferably 50% by mass or more.

  Among cerium-based composite oxides, composite oxides of cerium and rare earth elements prepared by adding rare earth elements such as praseodymium, neodymium, and samarium as additives to cerium are preferably used. Such an additive is preferably incorporated in the crystal structure of the cerium-based material and is stably present in a metal or oxide state. By existing in this way, the heat resistance and durability of the cerium-based material can be improved.

  The cerium-based material is effective for NOx adsorption during lean operation, and is particularly effective for NOx adsorption in the temperature range of 150 ° C to 350 ° C. The cerium-based material used in the present embodiment may be a commercially available cerium-based material, or can be obtained by a conventionally known production method.

  Examples of the lanthanum-based material include lanthanum elements, lanthanum oxide, and lanthanum-based composite oxides, and those obtained by adding various auxiliary materials to these oxides can also be used. Examples of the lanthanum-based composite oxide include lanthanum-cerium composite oxide. When the lanthanum-cerium composite oxide is used, 10% by mass or more of lanthanum oxide in terms of oxide is included in the composite oxide. It is preferable that it is contained, more preferably 30% by mass or more, and most preferably 50% by mass or more.

  Among lanthanum-based composite oxides, composite oxides of lanthanum and rare earth elements prepared by adding rare earth elements such as cerium, praseodymium, neodymium, samarium, etc., as additives to lanthanum are preferably used. Such an additive is preferably incorporated in the crystal structure of the lanthanum-based material and stably exists in a metal or oxide state. By existing in this way, the heat resistance and durability of the lanthanum-based material can be improved.

  Lanthanum-based materials are effective for NOx adsorption during lean operation, and are particularly effective for NOx adsorption in the temperature range of 350 ° C to 450 ° C. When the cerium-based material exceeds 350 ° C., the NOx adsorption ability decreases, but the lanthanum-based material can supplement the NOx adsorption ability at a temperature of 350 ° C. or higher. The lanthanum-based material used in the present embodiment may be a commercially available lanthanum-based material, or can be obtained by a conventionally known production method.

  It is preferable that a heat-resistant inorganic oxide other than a cerium-based material or a lanthanum-based material is added to the first catalyst layer. Examples of the heat-resistant inorganic oxide include zirconium oxide materials, alumina materials, zeolite materials, and silica materials. Examples of the zirconium oxide-based material include zirconium oxide and zirconium-based composite oxide. Among them, a composite oxide of zirconium and rare earth is preferably used, and more preferably a composite oxide such as Zr—Nd—Ox. is there.

  The first catalyst layer includes a noble metal as a catalytically active species, a cerium-based material, and a lanthanum-based material, but preferably includes a cerium-based material supporting a noble metal and a lanthanum-based material supporting a noble metal, More preferably, a zirconium-based material supporting a noble metal is included. As the noble metal, platinum is the main component, and gold, palladium, or rhodium can be used as necessary. From the viewpoint of high activity, it is preferable to use platinum as a main component and rhodium as a subcomponent.

The reason why NOx purification in exhaust gas is promoted by using platinum is that NO occupying most of the exhaust gas is oxidized to NO ₂ by the action of platinum, and this NO ₂ is contained in the first catalyst layer. It is thought that this is because the reaction with the reducing component is promoted by the adsorption to the cerium and lanthanum components contained therein.

  In addition, by using rhodium as an auxiliary component, when the air-fuel ratio of exhaust gas is made rich, the reaction between NOx and reducing components such as carbon monoxide, hydrocarbons, hydrogen, etc. is facilitated, and NOx purification performance Will improve. This is presumably because the amount of ammonia produced is improved as a result of the water gas shift reaction being promoted when the air-fuel ratio of the exhaust gas is made rich to facilitate the production of hydrogen.

  Regarding the loading of these noble metals, in addition to the cerium-based material and the lanthanum-based material constituting the first catalyst layer, they can be supported on the entire heat-resistant inorganic oxide, but may be supported on a specific inorganic oxide. . As the specific amorphous oxide, those having a high specific surface area value and excellent heat resistance are preferable, for example, γ-alumina is preferably used.

  The total content of the noble metal that is a catalytically active species contained in the first catalyst layer is preferably 0.1 g / L to 20 g / L per unit volume of the entire first catalyst layer, and preferably 1 g / L to 10 g / L. It is more preferable that If the total content of noble metals is 0.1 g / L or more, the NOx purification ability can be exhibited, and further improvement of the effect cannot be expected even if it exceeds 20 g / L.

  Here, when a noble metal other than platinum is used in combination as the catalytically active species, the amount of platinum is preferably 50% by mass or more, and more preferably 70% by mass or more based on the total amount of noble metals.

  The first catalyst layer may be composed of a single uniform layer or a plurality of layers having different compositions. When forming multiple layers, the arrangement of noble metals, cerium-based materials, lanthanum-based materials, heat-resistant inorganic oxides, and the like can be variously changed. For example, the first layer counted from the carrier side is made of only Pt as the noble metal, and a large proportion of the NOx adsorbent is disposed, and the layer that mainly plays the role of NOx adsorption during lean is set as the second layer, Variations are conceivable in which Pt and Rh are used in combination as the noble metal, and the remaining ratio of the NOx adsorbent is arranged to serve as a layer that mainly plays a role of NOx reduction and ammonia generation during lean.

  The total amount of the cerium-based material, the lanthanum-based material, and the heat-resistant sulfur-free oxide contained in the first catalyst layer is preferably 10 g / L to 300 g / L per unit volume of the entire first catalyst layer. If the total amount is 10 g / L or more, an amount of noble metal capable of exhibiting NOx purification ability can be supported, and if it is 300 g / L or less, the breathability of exhaust gas can be sufficiently maintained.

  The content of the cerium-based material is preferably 1 g / L to 300 g / L per unit volume of the entire first catalyst layer, and more preferably 10 g / L to 200 g / L. If the content of the cerium-based material is 1 g / L or more, the NOx purification performance can be sufficiently exhibited, and if it is 300 g / L or less, the exhaust gas permeability can be sufficiently maintained. In addition, when using together cerium oxide and a cerium-type complex oxide, it is preferable that the ratio shall be the range of 0-50 mass parts of cerium-type complex oxide with respect to 100-50 mass parts of cerium oxides.

  The content of the lanthanum-based material is preferably 1 g / L to 300 g / L per unit volume of the entire first catalyst layer, and more preferably 10 g / L to 200 g / L. If the content of the lanthanum-based material is 1 g / L or more, the NOx purification performance can be sufficiently exhibited, and if it is 300 g / L or less, the exhaust gas breathability can be sufficiently maintained. In addition, when using together a lanthanum oxide and a lanthanum type complex oxide, it is preferable that the ratio makes the range of a lanthanum type complex oxide 0-50 mass parts with respect to 100-50 mass parts of lanthanum oxides.

  The content of the zirconium oxide-based material is preferably 1 g / L to 300 g / L per unit volume of the entire first catalyst layer, and more preferably 10 g / L to 200 g / L. If the content of the zirconium oxide-based material is 1 g / L or more, the NOx purification performance can be sufficiently exerted, and if it is 300 g / L or less, the breathability of the exhaust gas can be sufficiently maintained. In addition, when using together a zirconium oxide and a zirconium type complex oxide, it is preferable that the ratio makes the zirconium type complex oxide the range of 0-50 mass parts with respect to 100-50 mass parts of zirconium oxide.

  As long as the effects of the present invention are not impaired, the first catalyst layer is blended with other components such as a heat resistance improving component such as alumina and silica, a strength improving component, and an adhesion improving component such as a binder. It may be. Preferred examples of the binder include zirconia compounds, alumina compounds, and silica compounds. In addition, as heat resistance improving component and strength improving component, potassium, rubidium, cesium, magnesium, calcium, strontium, barium, antimony, hafnium, tantalum, rhenium, bismuth, gadolinium, holmium, thulium, ytterbium, germanium, selenium, cadmium Preferable examples include alkali metals such as indium, scandium, titanium, niobium, chromium and silver, and alkaline earth metal components.

  In addition, it does not specifically limit as a support | carrier, A conventionally well-known support | carrier is used. For example, a cordierite honeycomb structure is preferably used. Moreover, the preparation method of a low temperature type lean NOx catalyst is not specifically limited, It prepares by a conventionally well-known method. Specifically, it is prepared by preparing a slurry containing the material constituting the low temperature type lean NOx catalyst, coating the slurry on the support so as to obtain a desired loading amount by a wash coat method, and then drying and firing. The

(Operation in a low temperature region below 350 ° C.)
First, when the air-fuel ratio of the exhaust gas is set to a lean state (a normal operation state in a diesel engine), NOx is oxidized in the first catalyst layer (for example, from NO to NO ₂₎ by the action of Pt contained in the first catalyst layer. Oxidized) adsorbed and temporarily stored. At this time, Pt functions as a NO oxidation catalyst, and the cerium-based material and the lanthanum-based material function as a NOx adsorbent.

Next, when the air-fuel ratio of the exhaust gas is made rich, NOx adsorbed on the first catalyst layer in the lean state is reduced by the reducing gas contained in the exhaust gas in the rich state (the following formulas (1) to ( 3)). By repeating the above lean state and rich state, NOx is purified.

(Action in the middle temperature range of 350 ° C to 450 ° C)
First, when the air-fuel ratio of the exhaust gas is set to a lean state (a normal operation state in a diesel engine), NOx is oxidized in the first catalyst layer (for example, from NO to NO ₂₎ by the action of Pt contained in the first catalyst layer. Oxidized) adsorbed and temporarily stored. At this time, Pt functions as a NO oxidation catalyst, and the lanthanum-based material functions as a NOx adsorbent. Unlike the low-temperature region, the cerium-based material has a slightly reduced NOx adsorption capacity.

  Next, when the exhaust gas air-fuel ratio is made rich, the NOx adsorbed on the first catalyst layer in the lean state is reduced by the reducing gas contained in the rich exhaust gas (the above formulas (1) to ( 3)). By repeating the above lean state and rich state, NOx is purified.

  By the way, as the low-temperature type lean NOx catalyst of the third purification unit 13, β zeolite containing at least one element selected from the group consisting of iron, cerium, and lanthanum, which is laminated on the upper layer of the first catalyst layer. What has further the 2nd catalyst layer to contain is more preferable. In the low temperature type lean NOx catalyst having such a configuration, NOx in the exhaust gas is oxidized and adsorbed on the first catalyst layer when it is in the lean state, and is oxidized on the first catalyst layer in the lean state when it is in the rich state. The adsorbed NOx is converted into nitrogen, water, and ammonia by the reducing component present in the vicinity of the first catalyst layer, and ammonia is adsorbed on the second catalyst layer. When the lean state is set again, the ammonia adsorbed on the second catalyst layer in the rich state reacts with NOx in the exhaust gas and is converted into nitrogen and water, so that more efficient NOx purification is achieved. Done.

(Second catalyst layer)
The second catalyst layer is preferably used as the outermost surface layer in direct contact with the exhaust gas. Moreover, it is preferable that a 2nd catalyst layer does not contain a platinum component substantially, and it is more preferable that a noble metal component is not included.

  The second catalyst layer contains β zeolite as a solid acid catalyst having ammonia adsorption ability. Further, the β zeolite used in the present embodiment contains at least one element selected from the group consisting of iron, cerium, and lanthanum.

  By adding at least one element selected from the group consisting of iron, cerium, and lanthanum to β zeolite, the exhaust gas purification performance, particularly NOx purification performance, is improved. This is probably because the iron element promotes adsorption of NOx and reducing components. Further, regarding cerium element and lanthanum element, it is considered that NOx adsorption is promoted by the oxygen storage / release ability of these elements and catalyst poisoning by the reducing component is suppressed by the oxygen storage / release ability. Thus, by using β zeolite containing these three elements, a more excellent effect as a NOx purification catalyst is exhibited due to a synergistic effect.

  The β zeolite used in the present embodiment generally has a relatively complicated three-dimensional pore structure composed of linear pores arranged in one direction having a relatively large diameter and curved pores intersecting the linear pores. For this reason, it has properties such as easy diffusion of cations during ion exchange and diffusion of hydrocarbon molecules during reduction. This can be said to be a specific structure, whereas mordenite, faujasite, etc. have only linear vacancies aligned in one direction. Further, because of such structural features, β-zeolite has high thermal durability, and therefore, by using it as a constituent component of the catalyst, excellent heat resistance can be imparted to the catalyst.

  As the beta zeolite used in the present embodiment, commercially available beta zeolite to which iron element, cerium element, and lanthanum element have been added may be used. It can also be prepared by adding a salt solution of iron, cerium and lanthanum to β zeolite. By preparing in this way, an iron element, a cerium element, and a lanthanum element can be ion-exchanged to the cation site of β zeolite, and the NOx purification performance can be improved. This is probably due to the stabilization of the framework structure of β zeolite by ion exchange.

  The content of β zeolite contained in the second catalyst layer can be appropriately set and is not particularly limited, but is preferably 5 g / L to 300 g / L per unit volume of the entire second catalyst layer, and 15 g / L. More preferably, it is -100 g / L. If the content of β zeolite is 5 g / L or more, the exhaust gas purification ability can be sufficiently exhibited, and if it is 300 g / L or less, the breathability of the exhaust gas can be sufficiently maintained.

  The content of iron element added to β zeolite is preferably 0.1% by mass to 10% by mass in terms of oxide with respect to β zeolite, and preferably 0.5% by mass to 5% by mass. More preferred. When the content exceeds 10% by mass, the active solid acid point cannot be secured, and the activity may be lowered or the heat resistance may be lowered. If the content is 0.1% by mass or more, sufficient NOx purification performance can be obtained.

  In addition, when a cerium element is added, the content of the cerium element added to the β zeolite is preferably 0.05% by mass to 5% by mass in terms of oxide with respect to the β zeolite. More preferably, it is 1 mass%-3 mass%. If content is 0.05 mass% or more, catalyst poisoning by the reducing component in exhaust gas can be prevented. When the content exceeds 5% by mass, the active solid acid point cannot be secured, and the activity may be lowered or the heat resistance may be lowered.

  In addition, when a lanthanum element is added, the content of the lanthanum element added to the β zeolite is preferably 0.05% by mass to 5% by mass in terms of oxide with respect to the β zeolite. More preferably, it is 1 mass%-3 mass%. If it is 0.05 mass% or more, the catalyst poisoning by the reducing component in exhaust gas can be prevented. When the content exceeds 5% by mass, the active solid acid point cannot be secured, and the activity may be lowered or the heat resistance may be lowered.

(Operation in a low temperature region below 350 ° C.)
First, when the air-fuel ratio of the exhaust gas is set to a lean state (normal operation state in a diesel engine), NOx in the exhaust gas passes through the upper layer (second catalyst layer) and reaches the lower layer (first catalyst layer). Next, NOx that reaches the lower layer (first catalyst layer) is oxidized (for example, oxidized from NO to NO ₂ ) by the action of Pt, and is temporarily adsorbed and temporarily stored in the lower layer (first catalyst layer). At this time, Pt functions as a NO oxidation catalyst, and the cerium-based material and the lanthanum-based material function as a NOx adsorbent.

Next, when the air-fuel ratio of the exhaust gas is made rich, NOx adsorbed to the lower layer (first catalyst layer) in the lean state is converted into ammonia by the action of hydrogen generated by the water gas shift reaction (see the following formula (4)). While being converted (see the following formula (5)), this ammonia moves to the upper layer (second catalyst layer) and is adsorbed and stored again. At this time, the zirconium-based material functions as a water gas shift catalyst, Pt functions as an ammonia generation catalyst, and Fe, Ce, and La ion-exchanged β zeolite function as an ammonia adsorbing material. Further, NOx is also reduced simultaneously by the reducing gas contained in the exhaust gas in the rich state (see the above formulas (1) to (3)).

When the air-fuel ratio of the exhaust gas is made lean again, the ammonia stored again in the upper layer (second catalyst layer) reacts with NOx contained in the exhaust gas by the ammonia selective catalytic reduction method (NH ₃ -SCR). The nitrogen is converted into nitrogen (see the following formula (6)), and nitrogen can be released from the surface of the upper layer (second catalyst layer). At this time, Fe, Cg, and La ion exchange β zeolite function as an NH ₃ -SCR catalyst. By repeating the above lean state and rich state, NOx is purified.

(Action in the middle temperature range of 350 ° C to 450 ° C)
First, when the air-fuel ratio of the exhaust gas is set to a lean state (normal operation state in a diesel engine), NOx in the exhaust gas passes through the upper layer (second catalyst layer) and reaches the lower layer (first catalyst layer). Next, NOx that reaches the lower layer (first catalyst layer) is oxidized (for example, oxidized from NO to NO ₂ ) by the action of Pt, and is temporarily adsorbed and temporarily stored in the lower layer (first catalyst layer). At this time, Pt functions as a NO oxidation catalyst, and the lanthanum-based material functions as a NOx adsorbent. Unlike the low-temperature region, the cerium-based material has a slightly reduced NOx adsorption capacity.

  Next, when the air-fuel ratio of the exhaust gas is made rich, the above-described reaction for generating ammonia to purify NOx and the direct NOx reduction reaction with reducing gas proceed simultaneously, but in the temperature range of 350 ° C. or higher, ammonia is generated. Since the efficiency is greatly reduced, the contribution of direct NOx reduction by the reducing gas is greater.

[Function and effect]
Hereinafter, the operation and effect of the exhaust gas purifying apparatus 10 according to the present embodiment will be described separately when the exhaust gas temperature is high, when it is intermediate, and when it is low.

  When the temperature of the exhaust gas is as low as about 150 ° C., the high-temperature lean NOx catalyst of the first purification unit 11 cannot obtain sufficient purification performance. Also in the low temperature type lean NOx catalyst of the third purification unit 13, 150 ° C. is the lower limit region of the temperature window. However, according to the layout adopted in the exhaust gas purification apparatus 10 according to the present embodiment, the high-temperature lean NOx catalyst of the first purification unit 11 provided on the upstream side contains a noble metal with high oxidation activity. The precious metal promotes the combustion reaction of HC and CO in the exhaust gas. For this reason, the temperature of the low temperature type lean NOx catalyst of the 3rd purification | cleaning part 13 provided in the downstream rises with the combustion heat which arose by combustion reaction. Therefore, the temperature of the low-temperature lean NOx catalyst can be increased to a temperature range where high NOx adsorption ability can be exhibited, and as a result, efficient purification of NOx is achieved with the low-temperature lean NOx catalyst.

  When the temperature of the exhaust gas is a medium temperature of about 200 ° C. to 400 ° C., it overlaps with the purification temperature window of either the high temperature type lean NOx catalyst or the low temperature type lean NOx catalyst, so that high NOx purification performance can be exhibited.

  When the temperature of the exhaust gas is as high as about 500 ° C., the low-temperature lean NOx catalyst of the third purification unit 13 cannot obtain sufficient purification performance. Further, even in the high-temperature lean NOx catalyst of the first purification unit 11, the temperature is such that the NOx adsorption capacity is lowered. However, according to the layout adopted in the exhaust gas purification apparatus 10 according to the present embodiment, due to the heat capacity of the filter of the second purification unit 12, the low temperature type lean NOx of the third purification unit 13 provided on the downstream side. The temperature of the catalyst decreases to about 400 ° C. For this reason, the temperature of the low-temperature lean NOx catalyst can be lowered to a temperature range where the NOx adsorption ability is high, and as a result, efficient purification of NOx is achieved with the low-temperature lean NOx catalyst.

  Thus, according to the layout adopted in the exhaust gas purification apparatus 10 according to the present embodiment, when the exhaust gas temperature is low, the temperature of the low-temperature lean NOx catalyst can be increased, while the exhaust gas temperature is high. In this case, the temperature of the low temperature type lean NOx catalyst can be lowered. That is, the temperature of the low-temperature lean NOx catalyst of the third purification unit 13 provided on the downstream side can be shifted within the range of the purification temperature window, so that efficient NOx purification is achieved.

Second Embodiment
A schematic configuration of the exhaust gas purification apparatus 20 according to the present embodiment is shown in FIG. As shown in FIG. 2, the exhaust gas purification apparatus 20 according to the present embodiment is characterized by further including an oxidation catalyst unit (DOC) 24 in the exhaust gas passage 2 upstream of the first purification unit 21. Other configurations are the same as those of the exhaust gas purifying apparatus 10 according to the first embodiment.

[Oxidation catalyst part]
The oxidation catalyst unit 24 only needs to include an oxidation catalyst, and a conventionally known oxidation catalyst is used as the oxidation catalyst. For example, an oxidation catalyst composed of PGM (platinum group metal), alumina material, Ce material, zeolite or the like can be used. Pt, Pd, Rh etc. are mentioned as PGM which is a catalyst metal. The alumina-based material is used for increasing the specific surface area and improving the heat resistance, and examples thereof include alumina and silica alumina. Examples of Ce-based materials include ceria-zirconia composite oxides stabilized with ceria or zirconia. Zeolite acts as an HC adsorbent, and examples thereof include β-type zeolite and MFI-type zeolite.

In the present embodiment, by installing the oxidation catalyst unit 24 including the oxidation catalyst, the HC combustibility in the exhaust gas is improved, and the temperature rising rate during regeneration such as sulfur purge can be improved. In addition, since the efficiency of converting NO into NO ₂ is improved, the NOx adsorption capability of the high-temperature lean NOx catalyst is improved in the downstream first purification unit 21, and as a result, higher NOx purification performance is obtained.

<Third Embodiment>
FIG. 3 shows a schematic configuration of the exhaust gas purifying apparatus 30 according to the present embodiment. As shown in FIG. 3, the exhaust gas purification device 30 according to the present embodiment is a filter (catalyzed) in which a PM combustion catalyst is supported on the filter surface of the second purification unit 12 of the exhaust gas purification device 10 according to the first embodiment. A second purification unit 32 having a soot filter (CSF) is provided. Other configurations are the same as those of the exhaust gas purifying apparatus 10 according to the first embodiment.

[Second purification section]
The PM combustion catalyst included in the second purification unit 32 is not particularly limited, and a conventionally known PM combustion catalyst is used. For example, it is preferable to include at least one noble metal selected from the group consisting of Pt, Pd, Rh, and Ag, and at least one support material selected from the group consisting of alumina, ceria, zirconia, and titania. Used.

  The method for preparing the PM combustion catalyst is not particularly limited, and is prepared by a conventionally known method. Specifically, it is prepared by preparing a slurry containing the above materials constituting the PM combustion catalyst, coating the slurry with a filter so as to obtain a desired loading amount by a wash coat method, and then drying and firing. .

  When the accumulated amount of PM exceeds a certain amount, pressure loss due to clogging occurs and fuel consumption deteriorates. Therefore, regeneration that periodically removes accumulated PM is necessary. In this regard, in this embodiment having a PM combustion catalyst, PM can be easily removed by combustion, and regeneration at a lower temperature is possible. Moreover, since PM regeneration can be performed at a lower temperature, the risk of abnormal temperature rise during filter regeneration is reduced, and abnormal heat deterioration of the low-temperature lean NOx catalyst can be suppressed in the downstream third purification unit 33.

<Fourth embodiment>
FIG. 4 shows a schematic configuration of the exhaust gas purification apparatus 40 according to the present embodiment. The exhaust gas purification apparatus 40 according to the present embodiment adsorbs the high temperature lean NOx catalyst by heating the high temperature lean NOx catalyst of the first purification unit 41 to a predetermined temperature or more and controlling the exhaust gas atmosphere to be rich. And a regenerating unit 45 for removing the sulfur component adsorbed on the filter of the second purification unit 42 and the sulfur component adsorbed on the low-temperature lean NOx catalyst of the third purification unit 43. It is characterized by that. Other configurations are the same as those of the exhaust gas purifying apparatus 10 according to the first embodiment. The reproducing unit 45 can be applied not only to the first embodiment but also to the second embodiment and the third embodiment.

[Reproduction means]
As the regeneration means 45, the high temperature lean NOx catalyst of the first purification unit 41 is heated to a predetermined temperature or higher and the exhaust gas atmosphere is controlled to be rich, so that the high temperature lean NOx catalyst and the low temperature lean NOx catalyst are adsorbed. What is necessary is just a thing which can remove the sulfur component which was adsorb | sucking to the sulfur component which had been adsorb | sucked to the filter of the 2nd purification | cleaning part 42, for example, forced regeneration by post injection is mentioned. Further, sulfur poisoning detection means such as a temperature sensor, PM accumulation amount detection means, regeneration time determination means for judging the regeneration time based on information detected by the sulfur poisoning detection means and the PM accumulation amount detection means, It is preferable to further include a regeneration control means for driving the regeneration means 45 when the regeneration time determination means determines that the regeneration time is reached.

  In general, it is said that the lean NOx catalyst needs to be periodically purged with sulfur in order to avoid deterioration in purification performance due to adsorption of sulfur components. Specifically, purging at about 700 ° C. is required for a high-temperature lean NOx catalyst containing an alkali metal or alkaline earth metal, and about 600 ° C. is required for a low-temperature lean NOx catalyst containing a cerium-based material. In this regard, when the high-temperature lean NOx catalyst and the low-temperature lean NOx catalyst are used in combination as in the exhaust gas purification apparatus 40 according to the present embodiment, almost all of the sulfur components in the exhaust gas are the high-temperature lean NOx. Trapped with catalyst. For this reason, the sulfur component hardly flows into the low temperature type lean NOx catalyst, and the purification performance is hardly lowered by the adsorption of the sulfur component. Further, when the high temperature type lean NOx catalyst is purged with sulfur, the temperature of the low temperature type lean NOx catalyst is also increased and the atmosphere is rich, so that the sulfur component is not re-adsorbed on the low temperature type lean NOx catalyst. Therefore, the sulfur purge is almost unnecessary for the low temperature type lean NOx catalyst.

  On the other hand, DPF has a function of collecting PM, but if the amount of accumulated PM increases, there is a problem that the pores on the filter surface are blocked and the pressure loss increases. Therefore, DPE regeneration that burns and regenerates PM is necessary. Specifically, the DPF requires a lean process of about 650 ° C. In this regard, in the exhaust gas purification apparatus 40 according to the present embodiment, if the sulfur purge of the high temperature type lean NOx catalyst is set to 700 ° C., the filter temperature becomes about 650 ° C., and the low temperature type lean NOx catalyst temperature becomes about 600 ° C. For this reason, the sulfur purge of the lean NOx catalyst and the DPF regeneration can be performed at the same time. As a result, the time required for the regeneration of the lean NOx catalyst and the DPF can be shortened, which is very efficient.

  EXAMPLES Hereinafter, although this invention is demonstrated based on an Example, this invention is not limited to these Examples.

<Example 1>
The following high-temperature type lean NOx catalyst, CSF, and low-temperature type lean NOx catalyst were applied to the exhaust gas purification apparatus 10 according to the first embodiment, and a test was performed according to the evaluation method shown below.

[High-temperature lean NOx catalyst]
Carrier: 400 cell / 25 μm (wall thickness) Metal honeycomb noble metal: Pt, Rh (Pt / Rh = 5/1 (mass ratio))
Alkali metal or alkaline earth metal: K, Ba
Oxygen storage / release material: Ce-Zr composite oxide support material: TiO ₂
Capacity: 0.8L
Placement: Directly under the diesel engine

[CSF]
Material: Wall flow type SiC
Pore diameter: 23 μm
Porosity: 52%
Catalyst: PtPd / Al ₂ O ₃ (PGM 5 g / L, Pt / Pd = 2/1 (mass ratio)),
Catalyst loading: 35 g / L
Capacity: 2.6L

[Low-temperature lean NOx catalyst]
Carrier: 400 cell / 3.5 mil cordierite honeycomb catalyst, catalyst loading: see Table 1 Capacity: 2.0 L
Placement: Below the floor

<Comparative Example 1>
Except that no low-temperature type lean NOx catalyst was installed, a test similar to that in Example 1 was performed on an exhaust gas purification apparatus 50 (see FIG. 5) having the same apparatus configuration as that in Example 1.

<Comparative example 2>
Except that the high-temperature lean NOx catalyst was not installed, a test similar to that in Example 1 was performed on an exhaust gas purification device 60 (see FIG. 6) having the same device configuration as that in Example 1.

<Evaluation method>
Evaluation engine: 2.0 L diesel engine exhaust gas lean / rich ratio: 55 seconds / 5 seconds SV (space velocity): 75,000 h ⁻¹
Exhaust gas temperature: 150 ° C, 170 ° C, 200 ° C, 250 ° C, 300 ° C, 400 ° C, 450 ° C, 500 ° C, 8 points in total

<Evaluation results>
The relationship between the exhaust gas temperature and the NOx purification rate in Examples and Comparative Examples is shown in FIG. Further, FIG. 8 shows the results of examining the gas temperature flowing into the low-temperature lean NOx catalyst at a total of eight exhaust gas temperatures. As shown in FIG. 7, according to this example in which the high temperature type lean NOx catalyst and the low temperature type lean NOx catalyst are used in combination, it is confirmed that a high NOx purification rate can be obtained in a wide temperature range of 150 ° C. to 500 ° C. It was. In particular, the NOx purification rate in the vicinity of 150 ° C. and the NOx purification rate in the vicinity of 500 ° C. were more than simple additions. As shown in FIG. 8, when the exhaust gas temperature is 150 ° C., the temperature of the gas flowing into the low temperature type lean NOx catalyst is slightly raised to about 170 ° C., and the range of the purification window of the low temperature type lean NOx catalyst It is because it has moved in. On the other hand, when the exhaust gas temperature is 500 ° C., the temperature of the gas flowing into the low temperature type lean NOx catalyst is as low as about 420 ° C., which is also within the range of the purification window of the low temperature type lean NOx catalyst. .

It is a schematic block diagram of the exhaust gas purification apparatus which concerns on 1st Embodiment. It is a schematic block diagram of the exhaust gas purification apparatus which concerns on 2nd Embodiment. It is a schematic block diagram of the exhaust gas purification apparatus which concerns on 3rd Embodiment. It is a schematic block diagram of the exhaust gas purification apparatus which concerns on 4th Embodiment. It is a schematic block diagram of the exhaust gas purification apparatus used in Comparative Example 1. It is a schematic block diagram of the exhaust gas purification apparatus used in Comparative Example 2. It is a figure which shows the relationship between exhaust gas temperature and NOx purification rate. It is a figure which shows the relationship between exhaust gas temperature and the gas temperature which flows in into a low temperature type | mold lean NOx catalyst.

Explanation of symbols

10, 20, 30, 40 Exhaust gas purification device 11, 21, 31, 41 First purification unit 12, 22, 32, 42 Second purification unit 13, 23, 33, 43 Third purification unit 24 Oxidation catalyst unit 45 Regeneration means 1 Internal combustion engine 2 Exhaust gas passage

Claims (17)

An exhaust gas purification device for purifying exhaust gas discharged from the internal combustion engine, provided in an exhaust gas passage of an internal combustion engine in which lean or rich control is performed,
A first purification unit having a high-temperature lean NOx catalyst provided in the exhaust gas passage of the internal combustion engine and including at least one selected from the group consisting of alkali metals and alkaline earth metals;
A second purification unit having a filter that is provided in the exhaust gas passage downstream from the first purification unit and that collects PM contained in the exhaust gas;
A third purification unit that is provided in the exhaust gas passage downstream of the second purification unit and has a low-temperature lean NOx catalyst containing a cerium-based material ,
The low-temperature-type lean NOx catalyst is supported on a carrier and includes a first catalyst layer including a noble metal, the cerium-based material, and a lanthanum-based material, and is laminated on the upper layer of the first catalyst layer and is iron, cerium, and lanthanum. A second catalyst layer containing β zeolite containing at least one element selected from the group consisting of:
The first catalyst layer is disposed on the second catalyst layer side and includes platinum and rhodium as noble metals; the first catalyst layer is disposed on the support side and includes only platinum as noble metals; and is more precious than the second layer. A first layer having a high content of
In the low temperature type lean NOx catalyst,
When in the lean state, NOx in the exhaust gas is oxidized and adsorbed on the first catalyst layer,
When in the rich state, NOx oxidized and adsorbed on the first catalyst layer in the lean state is converted into nitrogen, water, and ammonia by the reducing component present in the vicinity of the first catalyst layer, and the second catalyst. Ammonia is adsorbed on the bed,
When the lean condition again, ammonia adsorbed to the second catalyst layer in a rich state, is converted by reaction with NOx in the exhaust gas to nitrogen and water exhaust gas purifying apparatus according to claim Rukoto.   The exhaust gas purification apparatus according to claim 1, wherein the high-temperature lean NOx catalyst contains at least one kind of noble metal selected from the group consisting of Pt, Pd, and Rh.   The exhaust gas purification apparatus according to claim 1 or 2, wherein the high-temperature lean NOx catalyst includes at least one support material selected from the group consisting of alumina, silica, titania, and zirconia.   The exhaust gas purification apparatus according to any one of claims 1 to 3, wherein the high-temperature lean NOx catalyst includes an oxygen storage / release material made of a ceria-zirconia composite oxide.   The exhaust gas purification apparatus according to any one of claims 1 to 4, wherein the high-temperature lean NOx catalyst includes a metal or cordierite carrier.   The exhaust gas purifying apparatus according to any one of claims 1 to 5, wherein the filter is made of cordierite, SiC, alumina, or titania.   The exhaust gas purifying apparatus according to any one of claims 1 to 6, wherein the filter has a central pore diameter of 10 µm to 30 µm and a porosity of 40% to 60%.   The second purification part is supported on the filter surface and at least one kind of noble metal selected from the group consisting of Pt, Pd, Rh, and Ag, and at least selected from the group consisting of alumina, ceria, zirconia, and titania. The exhaust gas purification apparatus according to any one of claims 1 to 7, further comprising a PM combustion catalyst containing one type of support material. The content of lanthanum-based material contained in the first catalyst layer, the exhaust gas purifying apparatus according to any one of claims 1, wherein 8 to be a unit volume per 1g / L~100g / L. The exhaust gas purifier according to any one of claims 1 to 9, wherein the noble metal contained in the first catalyst layer contains platinum as a main component and rhodium as a subcomponent. The exhaust gas purification device according to any one of claims 1 to 10, wherein the total content of the noble metals contained in the first catalyst layer is 0.1 g / L to 20 g / L per unit volume. The exhaust gas purification apparatus according to any one of claims 1 to 11 , wherein the reducing component is at least one selected from the group consisting of carbon monoxide, hydrocarbons, and hydrogen. Wherein the first catalyst layer, claim wherein the zirconium oxide-based material, alumina-based materials, zeolite-based materials, and further comprising at least one refractory inorganic oxide selected from the group consisting of silica-based material 1 To 12. The exhaust gas purifying apparatus according to any one of 12 to 12 . Wherein the lanthanum-based material, lanthanum metal, lanthanum oxide, lanthanum composite oxide, and that one of claims 1 to 13, characterized in that at least one member selected from composite oxides group consisting of lanthanum and rare earth elements Or an exhaust gas purifying apparatus as described above. The cerium-based material, cerium metal, either cerium oxide, cerium complex oxide, and the preceding claims, characterized in that at least one selected from the group consisting of composite oxide of cerium and rare earth elements 14 Or an exhaust gas purifying apparatus as described above. Wherein from the first purification member provided in the exhaust gas passage upstream of the exhaust gas purifying apparatus according to any one of claims 1 to 1 5, characterized by further comprising an oxidation catalyst unit having an oxidation catalyst. The high temperature lean NOx catalyst of the first purification unit is heated to a predetermined temperature or higher and the exhaust gas atmosphere is controlled to be rich, thereby removing sulfur components adsorbed on the high temperature lean NOx catalyst, and further comprising a reproducing means for removing adsorbed have sulfur components and said the two purifier filter third sulfur component adsorbed on the low temperature lean NOx catalyst purifying section from claim 1, wherein 1 6 Any exhaust gas purification apparatus.

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