JP2021014803A - Exhaust emission control device - Google Patents

Abstract

To provide an exhaust emission control device capable of controlling an exhaust emission control system to release NOx adsorbed to an adsorptive layer without the need for adjusting the temperature of the adsorptive layer and an air-fuel ratio.SOLUTION: An exhaust emission control device 50 controls an exhaust emission control system 10 which includes an adsorptive layer 35 including adsorbent installed in an exhaust pipe 12 of an internal combustion engine 20 for adsorbing nitrogen oxide from exhaust gas from the internal combustion engine 20 and for supplying predetermined additive to release the adsorbed nitrogen oxide, an emission control catalyst layer 41 including an emission control catalyst installed in the exhaust pipe 12 for eliminating the nitrogen oxide from the exhaust gas with reductive reaction, and an additive supply device 60 for supplying the additive to the adsorptive layer 35, thereby eliminating predetermined components from the exhaust gas from the internal combustion engine 20. It includes an additive control part 55 for controlling the supply of the additive to the adsorptive layer 35 by the additive supply device, on the basis of the state of the emission control catalyst layer.SELECTED DRAWING: Figure 1

Description

The present invention relates to an exhaust gas purification control device that controls an exhaust gas purification system that purifies the exhaust gas of an internal combustion engine.

As typical catalysts used for purifying nitrogen oxides (NOx) contained in the exhaust of internal combustion engines, NOx storage reduction catalysts such as LNT (Lean NOx Trap) catalysts and NSR (NOx Strage Reduction) catalysts, selective reduction (Selective Catalytic Reduction: SCR) Catalysts and the like are known.

According to Patent Document 1, in an exhaust purification system in which an NSR catalyst and an SCR catalyst are connected in series, the air-fuel ratio of the exhaust gas flowing into the NSR catalyst is controlled on the lean side to release NOx adsorbed on the NSR catalyst, and this release is performed. A technique for reducing the produced NOx with an SCR catalyst is described. Specifically, when both the temperature of the NSR catalyst and the temperature of the SCR catalyst belong to the temperature range in which NOx reduction is possible, ammonia is supplied to the SCR catalyst as a reducing agent and the exhaust gas flows into the NSR catalyst. The air-fuel ratio is alternately changed between the first lean air-fuel ratio that releases NOx adsorbed on the NSR catalyst and the second lean air-fuel ratio that is leaner than the first lean air-fuel ratio. If the control of the first lean air-fuel ratio is continued, the NOx reduction ability of the SCR catalyst may decrease. Therefore, for the purpose of recovering the SCR catalyst, the control of the second lean air-fuel ratio is alternately switched.

JP-A-2018-53882

As a method for desorbing NOx adsorbed on a NOx storage reduction catalyst such as an NSR catalyst, it is known to raise the catalyst temperature and control the air-fuel ratio to the rich side. It takes a certain amount of time to change the catalyst temperature and air-fuel ratio, and the change may affect the characteristics of the internal combustion engine and the exhaust gas purification system, so it is difficult to change it arbitrarily. For example, as described in Patent Document 1, if the control of the first lean air-fuel ratio is continued in order to release the NOx adsorbed on the NSR catalyst, the NOx reduction ability of the SCR catalyst may decrease.

In view of the above, the present invention provides an exhaust gas purification control device capable of controlling the release of NOx adsorbed on the adsorption layer without the need to adjust the temperature and air-fuel ratio of the adsorption layer in the exhaust purification system. The purpose.

The present invention is an adsorbent that is installed in the exhaust pipe of an internal combustion engine, adsorbs nitrogen oxides in the exhaust gas from the internal combustion engine, and releases the adsorbed nitrogen oxides by supplying a predetermined additive. An adsorption layer containing the above, a purification catalyst layer containing a purification catalyst installed in the exhaust pipe and purifying nitrogen oxides in the exhaust by a reduction reaction, and an additive supply device for supplying the additive to the adsorption layer. Provided is an exhaust gas purification control device for controlling an exhaust gas purification system for purifying a predetermined component in exhaust gas from the internal combustion engine. The exhaust gas purification control device includes an additive control unit that controls the supply of the additive to the adsorption layer by the additive supply device based on the state of the purification catalyst layer.

According to the present invention, in the exhaust purification system, the adsorption layer includes an adsorbent that adsorbs nitrogen oxides in the exhaust gas and releases the adsorbed nitrogen oxides by supplying a predetermined additive. The exhaust gas purification control device that controls the exhaust gas purification system includes an additive control unit that controls the supply of the additive to the adsorption layer by the additive supply device based on the state of the purification catalyst layer. Since NOx adsorbed on the adsorption layer can be released by supplying the additive according to the state of the purification catalyst layer by the additive control unit, it is necessary to adjust the temperature and air-fuel ratio of the adsorption layer. Instead, NOx can be released from the adsorption layer at a more appropriate timing according to the state of the purification catalyst layer. For example, when the purification catalyst layer is in a state where NOx released from the adsorption layer can be sufficiently purified, NOx can be released at an appropriate timing by supplying an additive to the adsorption layer, so that purification is possible. In the catalyst layer, NOx released from the adsorption layer can be more reliably purified.

The schematic diagram of the exhaust gas purification system which concerns on 1st Embodiment. The schematic diagram of the crystal structure of the composite oxide which concerns on embodiment. The figure which shows the adsorption characteristic of the adsorbent. The figure explaining the adsorption / reduction / temperature rise desorption test of an adsorbent. The figure which shows the balance of the nitrogen-containing component in an adsorbent. The figure which shows the relationship between a catalyst activity and a catalyst temperature. The flowchart of the exhaust gas purification process which concerns on 1st Embodiment. The flowchart of the exhaust gas purification process which concerns on 2nd Embodiment. The flowchart of the exhaust gas purification process which concerns on 3rd Embodiment. The flowchart of the exhaust gas purification process which concerns on 4th Embodiment.

(First Embodiment)
As shown in FIG. 1, the vehicle exhaust purification system 10 is mounted on the vehicle and includes a first catalyst layer 30, an adsorption layer 35, a second catalyst layer 40, an ECU 50, and a reducing agent supply device 60. ing. The exhaust gas purification system 10 is a system capable of purifying a predetermined component contained in the exhaust gas by circulating the exhaust gas discharged from the internal combustion engine 20 to the first catalyst layer 30, the adsorption layer 35, and the second catalyst layer 40. It is configured as.

The internal combustion engine 20 is a diesel engine, and the air sucked from the intake pipe 11 is compressed by the supercharging device 13 and sucked into the combustion chamber of the internal combustion engine 20, and the fuel injected from the fuel injection valve in this combustion chamber. It is used for combustion together.

The supercharging device 13 includes an intake compressor 14 arranged in the intake pipe 11, an exhaust turbine 15 arranged in the exhaust pipe 12, and a rotating shaft 16 connecting the intake compressor 14 and the exhaust turbine 15. When the exhaust turbine 15 is rotated by the exhaust from the internal combustion engine 20, the intake compressor 14 is rotated along with the rotation, and the intake air is supercharged.

In the exhaust pipe 12, the first catalyst layer 30, the adsorption layer 35, and the second catalyst layer 40 are arranged in this order from the upstream side to the downstream side. The exhaust gas from the internal combustion engine 20 is purified by passing through the first catalyst layer 30, the adsorption layer 35, and the second catalyst layer 40 arranged in the exhaust pipe 12. Mixing members 37 and 38 are installed on the inlet side of the adsorption layer 35 and the inlet side of the second catalyst layer 40, respectively.

The reducing agent supply device 60 includes injectors 61 and 62, reducing agent supply pipes 63 and 64, a pump 65, and a tank 66. The injector 61 is connected to the exhaust pipe 12 at a position on the upstream side of the mixing member 37. The injector 62 is connected to the exhaust pipe 12 at a position on the downstream side of the inlet NOx sensor 23 and on the upstream side of the mixing member 38. A liquid containing a reducing agent is stored in the tank 66. The reducing agent supply pipe 63 connects the injector 61 and the tank 66, and the reducing agent supply pipe 64 connects the injector 62 and the tank 66. The pump 65 is installed between the tank 66 and the reducing agent supply pipes 63 and 64, and distributes and supplies the reducing agent stored in the tank 66 to the reducing agent supply pipes 63 and 64.

By driving the pump 65, the liquid containing the reducing agent stored in the tank 66 is supplied to the injectors 61 and 62 through the reducing agent supply pipes 63 and 64, and is supplied from the injectors 61 and 62 into the exhaust pipe 12. Be jetted. The liquid supplied into the exhaust pipe 12 is agitated by the mixing members 37 and 38, and is supplied as a reducing agent to the adsorption layer 35 and the second catalyst layer 40 located downstream thereof. The injector 61, the reducing agent supply pipe 63, the pump 65, and the tank 66 have a function as an additive supply mechanism for supplying the reducing agent as an additive to the inlet side of the adsorption layer 35. The injector 62, the reducing agent supply pipe 64, the pump 65, and the tank 66 are a reducing agent supply mechanism that supplies the reducing agent to the inlet side of the second catalyst layer 40 (more specifically, the inlet side of the NOx purification catalyst layer 41). It has the function as.

The exhaust pipe 12 is further provided with an inlet NOx sensor 23 and an outlet NOx sensor 24 near the inlet and outlet of the second catalyst layer 40. The inlet NOx sensor 23 detects the amount of NOx in the exhaust gas flowing into the second catalyst layer 40 as a concentration. Further, the outlet NOx sensor 24 detects the amount of NOx in the exhaust gas after being purified by the second catalyst layer 40 as a concentration.

The first catalyst layer 30 is a non-NOx purification catalyst layer provided with a purification catalyst having a function of mainly purifying components other than nitrogen oxides (NOx) in the exhaust gas. For example, a catalyst having a function of purifying unreacted fuel and particle components in the exhaust gas can be used for the first catalyst layer 30. Specific examples of the catalyst used in the first catalyst layer 30 include an oxidation catalyst layer (DOC layer) containing a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), and the like. Can be mentioned.

DOC is a catalyst that oxidizes soluble organic components (SOF) in particulate matter (PM) contained in exhaust gas, and CO and HC in exhaust gas. As the DOC, for example, a catalyst containing a carrier such as a metal oxide and an active species of a noble metal or a base metal is used. As a typical example of DOC, a catalyst in which a noble metal catalyst such as Pt or Pd is supported on alumina or zeolite can be exemplified. When arranged in the exhaust pipe 12, it is often used in the form of supporting Pt and Pd on an alumina carrier having a honeycomb structure.

The DPF is a particulate filter equipped with a catalyst for purifying particulate components in exhaust gas. As the DPF, for example, a catalyst containing a carrier such as a metal oxide and an active species of a noble metal or a base metal is used. As a typical example of the DPF, a catalyst in which a noble metal catalyst such as Pt or Pd is supported on alumina having a honeycomb structure can be exemplified. The DPF filters and collects particulate matter (PM) in the exhaust.

As another name for DPF, DPR (Diesel Particulate Assistation System), DPD (Diesel Particulate Defecter), CRT (Continuary Particulate Defuser), CRT (Continuously Regenerating Trap, etc.), and Control In the present specification, the term DPF is used in the sense of including each catalyst referred to by the above alternative names.

According to DOC, hydrocarbons (HC), CO, and NO in the exhaust gas are oxidized by the catalytic reactions represented by the following formulas (1) to (3).

HC + O ₂ → H ₂ O + CO ₂ … (1)
2CO + O ₂ → 2CO ₂ … (2)
2NO + O ₂ → 2NO ₂ ... (3)

According to the DPF, the carbon (C) in the exhaust gas is oxidized by the catalytic reaction represented by the following formula (4). Further, as the DPF, a catalyst having activity in the catalytic reaction represented by the above formula (3) may be used. By promoting the reaction of the above formula (3) to generate NO ₂ , the catalytic reaction represented by the following formula (4) can be promoted.

C + 2NO ₂ → CO ₂ + 2NO… (4)

Instead of DOC or DPF, a NOx adsorption (Passive NOx Addition: PNA) catalyst may be placed. As the PNA catalyst, for example, a catalyst containing a carrier such as a metal oxide and a NOx-adsorbed species is used. As a specific example of the PNA catalyst, a catalyst having a structure that does not contain Rh, which is a reducing agent, can be exemplified with respect to the LNT catalyst.

The first catalyst layer 30 may contain one or more non-NOx purification catalysts having a function of purifying components other than NOx mainly in the exhaust such as DOC and DPF. For example, only the DOC layer and only the DPF layer may be installed as the first catalyst layer 30. Further, for example, as shown in FIG. 1, the first catalyst layer 30 may be composed of the DOC layer 31 arranged on the upstream side and the DPF layer 32 arranged on the downstream side. The DOC layer 31 corresponds to an oxidation catalyst layer provided with an oxidation catalyst that oxidizes unburned components in the exhaust, and the DPF layer 32 corresponds to a particulate filter that purifies the particulate components in the exhaust.

The adsorption layer 35 contains an adsorbent that adsorbs NOx in the exhaust gas and releases the adsorbed NOx by supplying a predetermined additive. As a specific example of the adsorbent having such a function, the adsorbent Q containing the first composite oxide described in JP-A-2019-34299 can be exemplified. JP-A-2019-34299 is cited by reference and the entire description thereof is incorporated herein by reference. In addition, in this specification, the term "adsorption" includes both physical adsorption and chemical adsorption, and further includes the concept of "occlusal" which means a phenomenon in which a gas or liquid is taken into a solid. Used.

This first composite oxide is represented by the general formula I: A _a B _b C _c O _8.5-δ . In the general formula I, A is at least one selected from the group consisting of rare earth elements, Ca, and In. A is preferably at least one selected from the group consisting of Y, Pr, Dy, Ho, Er, Tm, Yb, Lu, Ca, and In, and more preferably at least one of Y and Ca (that is,). , Y and / or Ca), and particularly preferably at least Y. In this case, the adsorption performance of the adsorbent Q with respect to NOx can be further improved.

For the first composite oxide, for example, the A element source, the B element source, and the C element source constituting this compound are mixed at a desired compounding ratio so that a compound represented by the general formula I can be obtained. Obtained by heating. In the general formula I, a is 0 <a ≦ 1. When a = 0, elements B and C are surplus with respect to the compound represented by the general formula I, and an oxide phase other than the compound represented by the general formula I may be formed. The oxide phase may degrade the adsorption performance for NOx. On the other hand, when a> 1, the surplus element A may form an oxide phase other than the compound represented by the general formula I, and this oxide phase may deteriorate the adsorption performance for NOx. is there. From the viewpoint of forming the compound phase represented by the general formula I as a single phase, 0.5 ≦ a ≦ 1 is more preferable, and 0.9 ≦ a ≦ 1 is further preferable.

B is at least one selected from the group consisting of alkaline earth metal elements. B is preferably at least one of Ba and Sr (that is, Ba and / or Sr). In this case, the adsorption performance of the adsorbent Q with respect to NOx can be further improved. Further, it is particularly preferable that B contains at least Ba from the viewpoint that the crystal structure of the compound represented by the general formula I can be stabilized.

In the general formula I, b is 0 <b ≦ 1. When b = 0, elements A and C are surplus with respect to the compound represented by the general formula I, and an oxide phase other than the compound represented by the general formula I may be formed. The oxide phase may degrade the adsorption performance for NOx. On the other hand, when b> 1, the surplus element B may form an oxide phase other than the compound represented by the general formula I, and this oxide phase may deteriorate the adsorption performance for NOx. is there. From the viewpoint of forming the compound phase represented by the general formula I as a single phase, 0.5 ≦ b ≦ 1 is more preferable, and 0.9 ≦ b ≦ 1 is even more preferable.

In the general formula I, C is an element consisting of at least one selected from the group consisting of transition metals, Al, Zn, and Ga, and having four coordinations of oxygen. C is preferably at least one selected from the group consisting of Fe, Co, Mn, Ni, Al, and Ga, and more preferably at least selected from the group consisting of Fe, Co, and Ga. It is good to be one kind. C may more preferably contain at least Co, and particularly preferably contain Co and Ga and / or Fe (that is, at least one of Ga and Fe). By selecting C in this way, the adsorption performance of the adsorbent Q with respect to NOx can be further improved.

In the general formula I, c is 0 <c ≦ 4. When c = 0, elements A and B are surplus with respect to the compound represented by the general formula I, and an oxide phase other than the compound represented by the general formula I may be formed. The oxide phase may degrade the adsorption performance for NOx. On the other hand, when c> 4, the surplus C element may form an oxide phase other than the compound represented by the general formula I, and this oxide phase may deteriorate the adsorption performance for NOx. is there. From the viewpoint of forming the compound phase represented by the general formula I as a single phase, 3.5 ≦ c ≦ 4 is more preferable, and 3.9 ≦ c ≦ 4 is further preferable.

The first composite oxide has an oxygen-deficient structure as represented by the oxygen-deficient amount δ in the general formula I. δ satisfies 0 <δ ≦ 1.5. When δ> 1.5, the crystal structure may change and the adsorption performance for NOx may decrease.

FIG. 2 shows the crystal structure of the first composite oxide 2 when A is Y, B is Ba, and C is Co in the general formula I. As illustrated in FIG. 2, the first composite oxide 2 has a crystal structure represented by the general formula I, and the crystal structure is formed from Y, Ba, Co and O. Oxygen deficiency 3 is present in the crystal structure.

In FIG. 2, the oxygen deficiency 3 is indicated by a small circle with a broken line. The broken line circle bonded to the oxygen atom O indicates a C element such as Co. Since element C exists inside the bond surface between oxygen atoms, it is shown by a broken line in FIG. As illustrated in FIG. 2, in the crystal structure of the first composite oxide, C in the general formula I has four coordinations of oxygen. In the first composite oxide 2, the oxygen atom exists as an anion.

In the first composite oxide 2, for example, it is considered that the oxygen deficiency 3 is the starting point to generate an adsorption site for NOx in the crystal structure, or the oxygen deficiency 3 itself becomes an adsorption site. When the oxygen deficiency 3 is the starting point, it is considered that the crystal structure is changed by, for example, the oxygen deficiency 3, and as a result, an adsorption site is generated in the crystal structure. That is, the oxygen deficiency 3 is the starting point for the generation of the adsorption site. Then, it is considered that NOx is adsorbed on the adsorption site in the form of nitrate ion, nitric oxide, and nitrogen dioxide.

The first complex oxide having an adsorption site can be represented by the general formula II: A _a B _b C _c O _8.5-δ (NO _x ) _θ . A, B, C, a, b, c, and δ in the general formula II are the same as those in the general formula I. NO _x is a nitrogen oxide. The general formula II indicates that the first composite oxide 2 represented by the general formula I has an adsorption site for NOx, indicating that the first composite oxide 2 can adsorb NOx. ..

In the general formula II, 0 ≦ θ ≦ 1.5. When θ = 0, NOx is not adsorbed, which is the same as the general formula I. When θ> 0, it indicates a state in which NOx is adsorbed on the adsorption site. Θ ≦ 1.5 because NOx is adsorbed on the adsorption site.

The oxygen deficiency 3 can be identified by measuring the thermogravimetric analysis of the adsorbent Q. That is, δ in the general formulas I and II can be determined by thermogravimetric analysis. Specifically, it is as follows. Using a thermogravimetric analyzer STA449 F3 manufactured by NETZSCH, powdered adsorbent Q; 100 mg is first heated in a reducing atmosphere. As a result, the adsorbent Q having an oxygen deficiency amount δ = 0 is produced. For heating in a reducing atmosphere, a reducing atmosphere gas consisting of hydrogen: 5% by volume and nitrogen: the balance is circulated through the adsorbent Q at a flow rate of 100 mL / min, and heated to 500 ° C. at a heating rate of 10 ° C./min. Do it by. Next, the adsorbent Q with δ = 0 is heated in an oxygen atmosphere. The oxygen deficiency amount δ can be obtained as the weight increase at this time. The heating in an oxygen atmosphere is performed by heating the adsorbent Q to 500 ° C. at a heating rate of 2 ° C./min while circulating 100% by volume of oxygen gas through the adsorbent Q at a flow rate of 100 mL / min.

The adsorbent Q can contain a second compound different from the first composite oxide. The second compound is preferably a compound containing at least one selected from the group consisting of transition metal elements, alkaline earth metal elements, aluminum (Al), and zinc (Zn). In this case, the thermal durability of the adsorbent Q is improved. The second compound may be one kind, but may be two or more kinds of compounds.

The second compound is preferably a compound containing at least one element selected from the elements A, B, and C in the general formula I. In this case, the adsorbent Q containing the first composite oxide and the second compound can be obtained by adjusting the blending ratio of the raw materials without increasing the raw material species at the time of producing the first composite oxide. Can be manufactured.

The second compound preferably contains at least one of an oxide and a salt, and more preferably contains at least a carbonate of an alkaline earth metal element. In this case, the thermal durability of the adsorbent Q can be further improved.

The adsorbent Q preferably contains a main phase composed of the first composite oxide and a subphase composed of the second compound. The main phase is the main component phase, and the sub-phase is the sub-component phase. In this case, the thermal durability of the adsorbent Q can be further improved. The main phase and the sub-phase are confirmed by, for example, X-ray diffraction (XRD).

As illustrated in FIGS. 1 and 2, the adsorbent Q contains the specific first composite oxide 2. The first composite oxide 2 has an oxygen-deficient structure as represented by the general formula I: A _a B _b C _c O _8.5-δ . This oxygen-deficient structure can be the starting point for the formation of adsorption sites for NOx or the adsorption sites. That is, the first composite oxide 2 has an adsorption site. Therefore, the adsorbent Q can adsorb NOx even at a high temperature, but can sufficiently adsorb NOx even at a low temperature of, for example, 250 ° C. or lower. This is because NOx can be adsorbed on the adsorption site.

The method for producing the adsorbent Q is not particularly limited, and the adsorbent Q can be produced by a solid phase reaction method, a complex polymerization method, or the like. For example, in the solid-phase reaction method, first, the A source, the B source, and the C source are mixed in a solid state by the stoichiometric ratio produced by the compound represented by the above general formula. Mixing can be performed in a ball mill, a mortar or the like. The mixture is then fired. As a result, the adsorbent Q can be obtained. As the A source, B source, and C source in the solid phase reaction method, oxides, salts, and other compounds containing elements A, B, and C, respectively, can be used.

Further, in the complex polymerization method, a salt containing element A (that is, salt A), a salt containing element B (that is, salt B), and a salt containing element C (that is, salt C) are used. These salts are used to form metal complexes of element A, element B, and element C in water, and then the aqueous solution is gelled with a gelling agent. Next, the gelled metal complex is calcined and fired to obtain the adsorbent Q as an oxide. As the gelling agent, a polyhydric alcohol such as ethylene glycol or propylene glycol can be used.

Further, although the adsorbent Q can be used in combination with the noble metal, NOx can be adsorbed even if the adsorbent Q is prepared by reducing the noble metal content and further setting the noble metal content to 0. .. It is considered that this is because the first composite oxide 2 has the above-mentioned adsorption site, so that the adsorbent Q can adsorb NOx in any form of NO, NO ₂ , or nitric acid. That is, the adsorbent Q can adsorb NO as it is, can be adsorbed as NO ₂ obtained by oxidizing NO with a noble metal, or can adsorb NO ₂ as nitrate ion. The adsorbent Q and the noble metal may be combined. In this case, for example, Pt, Pd, Rh and the like can be used as the precious metal.

Further, conventionally, as a NOx adsorbing material, for example, an alkaline earth metal such as barium (Ba), calcium (Ca), magnesium (Mg), strontium (Sr), or an alkali such as barium oxide (BaO). Earth metal oxides were used. These adsorbents are used by supporting them on a porous carrier, but alkaline earth metals are chemically unstable because they easily react with other members such as carriers when heated. As a result, the adsorption performance for NOx may deteriorate. On the other hand, the first composite oxide 2 contains an alkaline earth metal element B inside the crystal structure as represented by the general formula I. Therefore, the adsorbent Q of this embodiment is chemically stable. That is, even if the adsorbent Q is heated, it is possible to prevent the alkaline earth metal B from reacting with other members such as a carrier. Therefore, the adsorbent Q can suppress the deterioration of the adsorption performance due to heating.

Further, the adsorbent Q preferably contains a compound containing at least one of Mg and Sr. In this case, sulfur poisoning of the adsorbent Q can be suppressed. Examples of the compound containing at least one of Mg and Sr include MgAl ₂ O ₄ and SrCO ₃ .

As described above, according to the present embodiment, it is possible to provide the adsorbent Q having excellent adsorption performance for NOx at low temperature. The adsorbent Q exhibits excellent adsorption performance for NOx even at a low temperature of 250 ° C. or lower. Further, the adsorbent Q can also be used at a high temperature exceeding 250 ° C. Even in this case, it exhibits excellent adsorption performance for NOx.

When the exhaust gas discharged from the internal combustion engine 20 is passed through the adsorbent Q, NOx in the exhaust gas is adsorbed by the adsorbent Q and captured in a lean atmosphere or the like. On the other hand, in a rich atmosphere or the like, the adsorbed NOx is released.

Furthermore, as a result of diligent research, the present inventor has found that the adsorbed NOx can be released by supplying a predetermined additive to the above-mentioned adsorbent Q. It is presumed that the adsorption of NOx on the adsorbent Q is due to an acid-base bond using the adsorption site of the adsorbent Q as a base and NOx as an acid. Therefore, as the additive, a material capable of promoting the cleavage of the acid-base bond of the adsorbent Q can be preferably used.

FIGS. 3 and 5 show an adsorbent Q1 (hereinafter abbreviated as adsorbent Q1) containing YBaCo ₄ O ₇ , which is an example of the composite oxide represented by the above general formula I, and its adsorption performance and desorption. The result of experimentally evaluating the release performance is shown.

FIG. 3 is a diagram showing the adsorption characteristics of the adsorbent Q1 obtained by the NOx adsorption / temperature desorption (TPD) test. The vertical axis of FIG. 3 shows the adsorption rate (%) of NOx supplied to the adsorbent Q1, and the horizontal axis shows the adsorption amount of NOx accumulated in the adsorbent Q1. The NOx adsorption rate Yr can be calculated by the following formula (5), where Xin is the amount of NOx in the exhaust gas flowing into the adsorption layer 35 and Xout is the amount of NOx in the exhaust gas flowing out of the adsorption layer 35.

Yr (%) = 100 × (Xin-Xout) / Xin… (5)

When NOx is adsorbed, the sample temperature is set to a predetermined adsorption temperature, and an N ₂ balanced supply gas containing NO; 100 ppm, H ₂ O; 3 vol%, O ₂ ; 10 vol%, CO ₂ ; 3 vol% as components is used as a space. Feed at a rate SV; 47,000 (1 / h) for 20 minutes. At the time of desorption by raising the temperature of NOx, an N ₂ balanced supply gas containing 10 vol% of O ₂ as a component was supplied with a space velocity SV; 47,000 (1 / h), and the temperature was raised from 100 ° C. to 550 ° C. in 20 minutes. Reference numbers 4 to 7 shown in FIG. 3 show different data in the adsorption temperature at the time of adsorption of NOx. Reference numbers 4, 5, 6 and 7 indicate the cases where the adsorption temperatures are 100 ° C., 150 ° C., 200 ° C. and 250 ° C., respectively.

As shown in FIG. 3, in the adsorbent Q1, when the amount of NOx adsorbed is small, NOx in the supplied exhaust can be adsorbed with a high probability of about 100%, but when the amount of NOx adsorbed is larger than a certain level, The NOx adsorption rate began to decline. That is, it was found that the NOx adsorption rate decreases as the NOx adsorption amount increases. Further, it was clarified that the higher the temperature of the adsorbent Q1, the larger the NOx adsorption amount at which the NOx adsorption rate begins to decrease.

FIG. 4 shows the sample temperature in the NOx adsorption / reduction / thermal desorption (TPD) test, the NOx concentration of the inlet gas (reference number 8), the NOx concentration of the outlet gas (reference number 9), and the NH _{3 of the} inlet gas. It is the figure which showed each time change about the concentration on the same time axis. Specifically, this test was carried out by supplying a predetermined inlet gas to the sample chamber in which the adsorbent Q1 was installed as a sample, and detecting the components in the outlet gas after passing through the sample chamber. 4, during the time 0~t1 the NOx adsorption stroke, heating process during the t1 to t2, during t2~t3 is NH ₃ addition step, during the t3~t4 shows a purge step.

First, in the NOx adsorption process, as shown in FIG. 4 (a), the sample temperature is maintained at a predetermined adsorption temperature Tm1 (150 ° C. in this test), and as shown in Reference No. 8 of FIG. 4 (b), It was supplied as an inlet gas containing NOx having a predetermined concentration. As the inlet gas, an N ₂ balanced adsorption stroke gas containing NO; 100 ppm, H ₂ O; 3 vol%, O ₂ ; 10 vol%, CO ₂ ; 3 vol% was used, and the space velocity was SV; 47,000 (1 / h). Supplied for 20 minutes. As shown in reference number 9 in FIG. 4 (b), NOx was detected in the outlet gas. Reference number 101 indicates an area obtained by integrating the difference between the NOx concentration of the inlet gas (reference number 8) and the NOx concentration in the outlet gas (reference number 9) between 0 and t1. By calculating the area of the reference number 101, the amount of NOx adsorbed on the adsorbent Q1 in the NOx adsorption process can be obtained.

Next, in the heating step, as shown in FIG. 4 (a), the inlet gas switched to N ₂ purge gas from the adsorption process gas, the sample temperature, at a predetermined reduction temperature Tm2 (this test from the adsorption temperature Tm1 is The temperature was raised to 400 ° C.). As the N ₂ purge gas, an N ₂ balanced gas containing 10 vol% of O ₂ as a component was used and supplied at a space velocity SV; 47,000 (1 / h). As the sample temperature rises, a part of NOx adsorbed on the adsorbent Q1 is released in the adsorption process, and NOx is detected in the outlet gas as shown in Reference No. 9 of FIG. 4 (b). Reference numeral 102 indicates the area obtained by integrating the NOx concentration in the outlet gas between t1 and t2 in time. By calculating the area of the reference number 102, the amount of NOx thermally desorbed from the adsorbent Q1 in the heating process can be obtained.

Then, the NH ₃ addition step, as shown in FIG. 4 (a), the temperature of the adsorbent Q1 maintains the reduction temperature Tm2, as shown in FIG. 4 (c), an inlet including additives having a predetermined concentration Supplyed gas. As the inlet gas, an N ₂ balanced addition stroke gas containing NH ₃ ; 50 ppm, H ₂ O; 3 vol%, O ₂ ; 10 vol%, CO ₂ ; 3 vol% was used, and the space velocity SV; 47000 (1 / h). Was supplied for 100 seconds. As shown in FIG. 4B, NOx was detected in the outlet gas by supplying NH ₃ as an additive to the adsorbent Q1 even when the reduction temperature was kept at a constant Tm2.

Moreover, the purging process, as shown in FIG. 4 (a), while maintaining the temperature of the adsorbent Q1 to reduction temperature Tm2, the inlet gas was switched to N ₂ purge gas from the adsorption process gas. The purging process continued until NOx was no longer detected in the outlet gas. Reference numeral 103 indicates the area obtained by integrating the NOx concentration in the outlet gas between t2 and t4 in time. By calculating the area of the reference number 103, the NH ₃ addition step and purge step, additives can be determined amount of NOx desorbed from the adsorbent Q1 resulted from the supply.

Further, the later time t4, and continues the supply of the N ₂ purge gas as an inlet gas, until NOx is not detected in the outlet gas was heated to sample temperature. Reference numeral 104 indicates the area where the NOx concentration in the outlet gas is integrated after the time t4. By calculating the area of the reference number 104, it is possible to obtain the amount of NOx remaining adsorbed on the adsorbent Q1 at the end of the purging process.

FIG. 5 is a diagram showing the balance (in / out) of the nitrogen-containing component in the adsorbent Q1. The "NOx-derived" component, the "thermal desorption" component, the "additive desorption" component, and the "residual" component shown in FIG. 5 are obtained from the areas of reference numbers 101 to 104 in FIG. 4, respectively. As shown in FIG. 5, the breakdown of the nitrogen-containing component (in component) adsorbed on the adsorbent Q1 at the time of NOx adsorption is the "NOx-derived" component derived from the NOx component contained in the adsorption stroke gas and the addition stroke gas. It was an "additive-derived" component derived from NH ₃ contained in. Further, the breakdown of the nitrogen-containing component (out component) released after being adsorbed on the adsorbent Q1 is the "residual" component remaining adsorbed on the adsorbent Q at the end of the purging process and the adsorption temperature Tm1 (adsorption temperature Tm1). The "heat desorption" component that was thermally desorbed from the adsorbent Q when the temperature was raised from 150 ° C.) to the reduction temperature Tm2 (400 ° C.), and the "additive desorption" that was desorbed from the adsorbent Q by supplying the additive. It was an ingredient.

As shown in FIG. 5, the nitrogen-containing component supplied to and adsorbed on the adsorbent Q1 is also released from the adsorbent Q1 by raising the temperature of the adsorbent Q1, but ammonia (NH ₃ ) is added as an additive. It was revealed that the adsorbent Q1 was released from the adsorbent Q1. One of the factors that cause the phenomenon that NOx adsorbed by the adsorbent Q1 is released by supplying the additive is that NO ₂ and nitric acid adsorbed on the adsorbent Q1 supply NH ₃ as an additive. Therefore, it can be presumed that this is because it was reduced to NO, which is less likely to be adsorbed. Based on this estimation, it can be inferred that a material that promotes the reduction of NOx adsorbed on the adsorbent Q can be suitably used as an additive. For example, ammonia (NH ₃ ), hydrocarbon (HC), hydrogen (H ₂ ), aldehydes (RCHO), nitrogen monoxide (CO), etc., which are used as reducing agents for SCR catalysts and LNT catalysts, are additives. Can be suitably used as.

The adsorption layer 35 is an adsorption layer in which the above-mentioned adsorption material Q is supported on the honeycomb structure. The adsorption layer 35 is provided with an adsorption layer temperature sensor 25 that detects the temperature of the adsorption layer 35.

In addition to the honeycomb structure, the adsorbent Q may be supported on a general structure that can be used as a catalyst carrier such as a porous body. Further, it may be supported on a structure installed in the exhaust pipe 12 for a main purpose other than supporting the catalyst, such as the mixing member 37 shown in FIG.

Furthermore, the above-mentioned adsorbent Q may be supported on a carrier together with a noble metal. When a noble metal is supported on the carrier together with the above-mentioned adsorbent Q, the adsorption performance for NOx is improved. It is considered that this is because the noble metal can oxidize NO to NO ₂ and nitric acid, and the above-mentioned adsorbent Q is more likely to adsorb NO ₂ and nitric acid than NO.

Further, the adsorbent Q may be supported on the carrier together with an inorganic binder consisting of at least one selected from the group consisting of alumina, silica, and titania.

Further, the adsorbent Q may be supported on the carrier together with a co-catalyst consisting of at least one selected from the group consisting of ceria, zirconia, and ceria-zirconia solid solution.

When a co-catalyst is further supported on the carrier, the oxidation performance of the noble metal with respect to nitric oxide is improved. As a result, the adsorption performance of nitrogen oxides on the adsorbent Q is improved.

The method for supporting the adsorbent Q on the carrier is not particularly limited. For example, it can be supported by an impregnation method or an ion exchange method. Examples of the impregnation method include an evaporative drying method, a parallel adsorption method, and a pore filling method. The evaporation dry method is preferable from the viewpoint that the catalyst can be adjusted relatively easily.

When a noble metal is used, for example, by supporting the adsorbent Q on which the noble metal is supported on the carrier, the adsorbent Q can be supported on the carrier together with the noble metal.

The co-catalyst and the inorganic binder can be supported on the carrier together with the adsorbent Q. For example, in the evaporation-drying method, the carrier can be supported together by impregnating the carrier with a slurry containing the adsorbent Q, the co-catalyst, and the inorganic binder.

The material of the carrier is not particularly limited, but a material having excellent heat resistance is preferable, and more specifically, a metal oxide material or a ceramic material having excellent heat resistance as exemplified by cordierite, SiC, etc. Is preferable.

Since the above-mentioned adsorbent Q has high adsorption performance for NOx at low temperature and does not easily react chemically with the carrier even when heated, it can stably exhibit high adsorption performance.

The second catalyst layer 40 includes a NOx purification catalyst layer 41 containing a NOx purification catalyst that purifies NOx in exhaust gas by a reduction reaction. The second catalyst layer 40 can be configured to include a reducing agent removing layer 42 on the downstream side of the NOx purification catalyst layer 41, if necessary. A second catalyst temperature sensor 21 for detecting the temperature of the NOx purification catalyst layer 41 is installed in the NOx purification catalyst layer 41.

The NOx purification catalyst layer 41 includes at least a catalyst layer containing a NOx purification catalyst that purifies NOx. Examples of the NOx purification catalyst include a selective reduction catalyst (SCR catalyst), an LNT catalyst, and a three-way catalyst (TWC). The SCR catalyst and the three-way catalyst are NOx purification catalysts that are not NOx storage reduction type, and are generally not prepared so as to have high NOx adsorption. Therefore, the amount of NOx adsorbed is generally lower than that of a NOx storage reduction type catalyst called an LNT catalyst or the like.

The SCR catalyst is a catalyst that selectively reduces NOx by a reducing agent supplied to the exhaust pipe 12. Representative examples of substances used as reducing agents in SCR catalysts include NH ₃ , hydrocarbons (HC), H ₂ , and aldehydes (RCHO). In the SCR catalyst, NOx (NO, NO ₂ ) is reduced to N ₂ by a reducing agent. The reducing agent is oxidized to produce water (H ₂ O), carbon dioxide (CO ₂ ), N _{2 and the} like depending on the type of reducing agent. When NH ₃ is used as a reducing agent, it is supplied to the exhaust pipe 12 as urea water or the like, and NH ₃ is generated in the exhaust pipe 12.

As the SCR catalyst, for example, a catalyst containing a carrier such as a metal oxide or a ceramic and an active species of a noble metal or a base metal is known. More specifically, as a specific example of an SCR catalyst using NH ₃ as a reducing agent, a zeolite catalyst such as ZSM5 containing copper (Cu), iron (Fe) or the like as a cation species can be exemplified. Further, as a specific example of the SCR catalyst using HC, H ₂ , and RCHO as a reducing agent, a catalyst in which silver (Ag) or platinum (Pt) is supported on alumina (Al ₂ O ₃ ) can be exemplified.

The LNT catalyst adsorbs NOx on the catalyst during normal operation of the internal combustion engine 20, and occasionally reduces oxygen (O ₂ ) in the exhaust gas by rich spikes (injecting a large amount of fuel), and also Increases carbon monoxide (CO), hydrocarbons (HC), etc. Then, it reacts with the adsorbed NOx and is reduced to nitrogen. As the LNT catalyst, for example, a catalyst containing a carrier such as a metal oxide or a ceramic, an active species of a noble metal or a base metal, and a NOx-adsorbed species is used. More specifically, as a specific example of the LNT catalyst, a catalyst containing noble metal species such as Pt, Pd, Rh and barium (Ba) and cerium (Ce) as NOx adsorbing species can be exemplified.

Examples of the LNT catalyst include NSR (NOx Strage Reduction) catalyst, NAC (NOx Absorption Catalyst), DPNR (Diesel Particulate-NOx Reduction) catalyst and the like. In the present specification, the term LNT catalyst is used to include each catalyst referred to by the above alternative names.

The three-way catalyst is a catalyst that reduces NOx using CO or hydrocarbon (HC) in the exhaust as a reducing agent. According to the three-way catalyst, for example, by the catalytic reaction represented by the following formulas (6) to (8), CO is oxidized to CO ₂ , hydrocarbon (HC) is oxidized to H ₂ O or CO ₂ , and NOx is converted to CO ₂ . It is reduced to N ₂ .

2CO + 2NO → 2CO ₂ + N ₂ ... (6)
2H ₂ + 2NO → 2H ₂ O + N ₂ ... (7)
[HC] + NO → N ₂ + CO ₂ + H ₂ O ... (8)

As the three-way catalyst, for example, a catalyst containing a carrier such as a metal oxide or a ceramic and an active species of a noble metal is known. More specifically, as shown in FIG. 2, as a specific example of the three-way catalyst, a noble metal catalyst such as platinum (Pt), palladium (Pd), rhodium (Rh) is used as alumina, ceria / zirconia (CeO ₂ / ZrO). _The catalyst carried in ₂ ) and the like can be exemplified. The three-way catalyst may further contain, as a co-catalyst, ceria (CeO ₂ ), zirconia (ZrO ₂ ), lanthania (La ₂ O ₃ ), etc., which have an oxygen storage capacity.

As the reducing agent removing layer 42, a catalyst layer provided with a catalyst for removing components not purified by the NOx purification catalyst layer 41 is arranged. For example, when an SCR catalyst using NH ₃ as a reducing agent is used as the NOx purification catalyst layer 41, it is preferable to use an ammonia slip catalyst (ASC) or the like as a catalyst for the reducing agent removing layer 42. ASC is an oxidation catalyst, mainly for the purpose of suppressing NH ₃ from slipping (passing through) the SCR catalyst and being released into the outside air when the exhaust gas temperature is low (for example, less than 200 ° C.). Will be installed. In ASC, NH ₃ is converted to N ₂ , H ₂ O, and NOx.

In the present embodiment, the DOC layer 31 and the DPF layer 32 are used as the first catalyst layer 30, and the adsorption layer 35 in which the adsorbent Q is supported on the honeycomb is used as the adsorption layer 35, and the NOx of the second catalyst layer 40 is used. A case where an SCR catalyst using NH ₃ as a reducing agent is used as the purification catalyst layer 41 and ASC is used as the reducing agent removing layer 42 will be described as an example. When the SCR catalyst is used as the NOx purification catalyst layer 41, the reducing agent for supplying the NOx purification catalyst layer 41 can be used as an additive for supplying the adsorption layer 35. Therefore, the reducing agent supply device 60 can be configured to also serve as the additive supply device, and the adsorption layer 35 can be mounted without complicating the exhaust gas purification system using the conventional SCR catalyst.

Urea water (urea aqueous solution) is stored in the tank 66 of the reducing agent supply device 60 as a liquid containing the reducing agent. By driving the pump 65, the urea water stored in the tank 66 passes through the reducing agent supply pipes 63 and 64 and is supplied to the injectors 61 and 62, and the urea water is injected from the injectors 61 and 62 into the exhaust pipe 12. can do.

The urea water droplets ejected from the injectors 61 and 62 collide with the mixing members 37 and 38 and the inner wall surface of the exhaust pipe 12 to become finer, or adhere to the wall surface and evaporate, and then the following formula (9) ), And the hydrolysis represented by the following formula (10), changes from urea (CO (NH ₂ ) ₂ ) to NH ₃ , and is supplied to the adsorption layer 35 and the second catalyst layer 40, respectively. To.

CO (NH ₂ ) ₂ → NH ₃ + HNCO… (9)
HNCO + H ₂ O → NH ₃ + CO ₂ … (10)

In the second catalyst layer 40, the catalytic reaction represented by the following formulas (11) to (13) occurs due to the SCR catalyst. As a result, NOx is reduced using NH ₃ as a reducing agent and changed to N ₂ and H ₂ O. The following formula (11) is called a Fast reaction, the formula (12) is called a Standard reaction, and the formula (13) is called a Slow reaction.

NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O… (11)
4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O… (12)
6NO ₂ + 8NH ₃ → 7N ₂ + 12H ₂ O… (13)

The detected values of the second catalyst temperature sensor 21, the inlet NOx sensor 23, the outlet NOx sensor 24, and the adsorption layer temperature sensor 25 are output to the ECU 50. The ECU 50 is an electronic control unit mainly composed of a microcomputer including a CPU, ROM, RAM, etc., and by executing various control programs stored in the ROM, based on the detection signals of the various sensors described above. , Performs various controls of the internal combustion engine 20 and the exhaust purification system 10. The ECU 50 has a function of executing combustion control of the internal combustion engine 20, and also has a function of a control device for executing control of the amount of reducing agent supplied from the reducing agent supply device 60.

The ECU 50 includes a temperature information acquisition unit 51, a component amount acquisition unit 52, an adsorbent state acquisition unit 53, a catalyst state acquisition unit 54, a reducing agent control unit 55, and a combustion control unit 56.

The temperature information acquisition unit 51 acquires temperature information of each catalyst layer constituting the first catalyst layer 30, the adsorption layer 35, and the second catalyst layer 40, respectively. The temperature information acquired by the temperature information acquisition unit 51 may be stored in the ECU 50. The temperature information of each catalyst layer may be a detected value of the temperature detected by a temperature sensor (for example, the second catalyst temperature sensor 21) installed in each catalyst layer, or may be an estimated value.

The temperature information acquisition unit 51 may acquire other parameters related to the temperature of the NOx purification catalyst layer 41 as temperature information. The temperature information of each catalyst layer means the temperature of each catalyst layer and other parameters related to the temperature. For example, the elapsed time from the start of temperature rise of each catalyst layer and the warm-up of the internal combustion engine 20. The completion of the above, the temperature of the cooling return water of the internal combustion engine 20, the fuel consumption amount from the start of the internal combustion engine 20, the elapsed time, the mileage, and the like can be mentioned.

In addition to the temperature information of the NOx purification catalyst layer 41, the temperature information acquisition unit 51 further provides temperature information of the adsorption layer 35, temperature information of the DOC layer 31 and the DPF layer 32 constituting the first catalyst layer 30, and a reducing agent. It may be configured so that the temperature information of the removal layer 42 can be acquired.

The component amount acquisition unit 52 acquires a detected value or an estimated value of the component amount of each component contained in the exhaust gas. The component amount of each component may be a detected value detected by various sensors, or may be an estimated value estimated based on other parameters related to the component amount or the like. For example, the component amount acquisition unit 52 acquires an estimated value of the NOx amount discharged from the internal combustion engine 20 as the NOx component amount, and the NOx component amount in the exhaust detected by the inlet NOx sensor 23 and the outlet NOx sensor 24. To get. The amount of NOx discharged from the internal combustion engine 20 can be estimated based on, for example, the combustion state (engine speed, fuel injection amount, etc.) of the internal combustion engine 20. The data acquired by the component amount acquisition unit 52 may be stored in the ECU 50.

The adsorbent state acquisition unit 53 acquires information indicating the state of the adsorbent layer 35. As the information indicating the state of the adsorption layer 35, for example, the temperature information of the adsorption layer 35 and the information on the amount of NOx adsorbed on the adsorption layer 35 and the amount of the additive can be exemplified. The temperature information of the adsorption layer 35 means the temperature of the adsorption layer 35 and other parameters related to the temperature. Similarly, the information regarding the amount of NOx and the amount of the additive adsorbed on the adsorption layer 35 means the amount of NOx and the amount of the additive, and other parameters related thereto.

The higher the temperature of the adsorption layer 35, the easier it is for NOx adsorbed on the adsorption layer 35 to be released. Further, the larger the amount of NOx adsorbed on the adsorption layer 35 and the amount of additives, the easier it is for the NOx adsorbed on the adsorption layer 35 to be released. Therefore, the adsorption performance of the adsorption layer 35 can be obtained based on the temperature information of the adsorption layer 35 and the information on the amount of NOx adsorbed on the adsorption layer 35 and the amount of the additive. The temperature information of the adsorption layer 35 may be estimated from, for example, the detection value of the adsorption layer temperature sensor 25 or from other parameters related to the temperature of the adsorption layer 35. The amount of NOx adsorbed on the adsorption layer 35 can be calculated, for example, from the estimated value of the amount of NOx discharged from the internal combustion engine 20 and the difference from the amount of NOx in the exhaust gas detected by the inlet NOx sensor 23. ..

The catalyst state acquisition unit 54 detects the activated state of the catalyst in the first catalyst layer 30 and the second catalyst layer 40. The activated state of the catalyst is the degree of activity of the catalytic reaction, and can be obtained based on the temperature information of the catalyst, the adsorbed substance information on the substance adsorbed on the catalyst, and the like.

The activated state of the NOx purification catalyst layer 41 means the activity of the catalytic reaction of the reduction reaction that purifies NOx. The reduction reaction for purifying NOx is more likely to occur when the activated state of the NOx purification catalyst layer 41 is higher, and less likely to occur when the activated state of the NOx purification catalyst layer 41 is lower. The activated state of the NOx purification catalyst layer 41 changes depending on the temperature of the NOx purification catalyst layer 41, the amount of catalytic reaction product (for example, NOx, reducing agent, etc.) adsorbed on the NOx purification catalyst layer 41, and the like. For example, when the NOx purification catalyst layer 41 is an SCR catalyst, its activation state is based on the temperature information of the NOx purification catalyst layer 41 and the amount of the reducing agent adsorbed on the NOx purification catalyst layer 41. , Can be sought. As the temperature information of the NOx purification catalyst layer 41, the detected value of the second catalyst temperature sensor 21 may be used, or may be estimated from other parameters related to the temperature of the NOx purification catalyst layer 41.

As the adsorbed substance information of the NOx purification catalyst layer 41, for example, the adsorbed amount of the reducing agent adsorbed on the NOx purification catalyst layer 41 can be used. Specifically, the total amount of the reducing agent supplied from the injectors 61 and 62 was Lt, the amount of the reducing agent consumed in the adsorption layer 35 was Lq, and the amount of the reducing agent consumed in the NOx purification catalyst layer 41 was Lc. In this case, the adsorption amount La of the reducing agent adsorbed on the NOx purification catalyst layer 41 can be calculated based on the following formula (14).

La = Lt-Lq-Lc ... (14)

In the above formula (14), Lt can be obtained from the amount of reducing agent supplied from the injectors 61 and 62 to the exhaust pipe 12. Further, for Lq, a map or a mathematical formula showing the relationship between the amount of NOx released from the adsorption layer 35 and the amount of the reducing agent required to release NOx is stored in the ECU 50 in advance, and the Lq is released from the adsorption layer 35. It can be obtained by acquiring the obtained NOx amount and referring to a map or the like based on this. Further, in the Lc, a map or a mathematical formula showing the relationship between the amount of NOx purified by the purification catalyst layer 41 and the amount of the reducing agent required to purify NOx is stored in the ECU 50 in advance, and the NOx purification catalyst layer 41 is stored. It can be obtained by acquiring the amount of NOx purified by and referring to a map or the like based on this. The relationship shown in the above map or mathematical formula may be a relationship obtained based on the result measured in advance by an experiment, a chemical reaction formula of a NOx release reaction by a reducing agent in the adsorption layer 35, or a NOx purification catalyst layer. The relationship may be derived from the stoichiometric ratio based on the chemical reaction formula of the NOx purification reaction by the reducing agent in 41. The amount of NOx discharged from the adsorption layer 35 is determined by, for example, acquiring the amount of NOx discharged from the internal combustion engine 20 and the amount of NOx detected by the inlet NOx sensor 23 and calculating the difference between them. Can be done. Further, the amount of NOx purified by the purification catalyst layer 41 can be obtained, for example, by acquiring the amount of NOx detected by the inlet NOx sensor 23 and the amount of NOx detected by the outlet NOx sensor 24 and calculating the difference between them. it can. Alternatively, instead of the NOx amount detected by the inlet NOx sensor 23, the NOx amount discharged from the internal combustion engine 20 and the NOx amount released from the adsorption layer 35 are acquired, and the NOx amount detected by the outlet NOx sensor 24 is used. By calculating the difference between the above, the amount of NOx purified by the purification catalyst layer 41 can also be obtained.

The amount of the reducing agent may be determined by installing a reducing agent sensor or the like that can detect the amount of the reducing agent in the exhaust gas. For example, when an NH ₃ sensor is installed as a reducing agent sensor between the NOx purification catalyst layer 41 and the reducing agent removing layer 42, the amount of NH ₃ at the outlet of the purification catalyst layer 41 is obtained from the detected value. Can be done. The reducing agent sensor may be set on the outlet side of the reducing agent removing layer 42. In this case, the amount of the reducing agent at the outlet of the purification catalyst layer 41 is calculated based on the detected value of the reducing agent sensor and the amount of the reducing agent removed in the reducing agent removing layer 42. When the reducing agent sensor is installed on the outlet side of the reducing agent removing layer 42, the amount of the reducing agent contained in the exhaust discharged from the exhaust purification system 10 can be monitored, and an on-board diagnostic device (OBD) can be monitored. ) Is preferable in that it can be used as a part of the function.

The reducing agent control unit 55 controls the supply amount, supply timing, and the like of the reducing agent supplied from the reducing agent supply device 60 to the exhaust pipe 12. For example, the supply amount and supply timing of the reducing agent supplied from the injector 61 to the inlet side of the adsorption layer 35 based on the amount of NOx contained in the exhaust on the inlet side and the outlet side of the adsorption layer 35 acquired by the component amount acquisition unit 52. Etc. are controlled. The reducing agent control unit 55 has a function as an additive control unit that controls the reducing agent supply device 60 as an additive supply device based on the amount of NOx acquired by the component amount acquisition unit 52. The reducing agent control unit 55 uses information indicating the state of the adsorbent layer 35 acquired by the adsorbent state acquisition unit 53 when controlling the reducing agent supplied as an additive from the injector 61. For example, the supply amount and supply timing of the reducing agent are controlled according to the adsorption performance of the adsorption layer 35. Further, the reducing agent control unit 55 controls the reducing agent supplied as an additive from the injector 61 with reference to the information indicating the state of the second catalyst layer 40 acquired by the catalyst state acquisition unit 54. Thereby, the NOx released from the adsorption layer 35 by the additive can be controlled so as to be sufficiently purified by the NOx purification catalyst layer 41 of the second catalyst layer 40.

Further, the reducing agent control unit 55 supplies the NOx purification catalyst layer 41 from the reducing agent supply device 60 to the exhaust pipe 12 in response to the NOx purification request when the NOx reduction reaction activity is sufficiently obtained. For example, the amount of reducing agent supplied from the injector 62, which is a reducing agent supply mechanism, to the exhaust pipe 12 is controlled based on the temperature information of the NOx purification catalyst layer 41 and the amount of NOx to be reduced. The reducing agent control unit 55 uses information indicating the state of the second catalyst layer 40 acquired by the catalyst state acquisition unit 54 when controlling the reducing agent supplied from the injector 62. For example, the supply amount and supply timing of the reducing agent are controlled according to the activated state of the NOx purification catalyst layer 41.

When the activated state of the NOx purification catalyst layer 41 is sufficiently high, the reduction reaction activity of NOx can be sufficiently obtained in the NOx purification catalyst layer 41, so that an additive or a reducing agent is controlled to be supplied. .. Specifically, for example, when the temperature information of the NOx purification catalyst layer 41 is in a state indicating that it exceeds a predetermined temperature threshold Tc, the activated state of the NOx purification catalyst layer 41 is sufficiently high. Since it can be determined, the injector 61 may supply the additive to the adsorption layer 35, and the injector 62 may control the NOx purification catalyst layer 41 to supply the reducing agent. Further, when the reducing agent control unit 55 indicates that the temperature information of the NOx purification catalyst layer 41 is equal to or less than the temperature threshold Tc, the reducing agent control unit 55 raises the temperature of the NOx purification catalyst layer 41 so as to exceed the temperature threshold Tc. It may be configured in. The temperature threshold can be set, for example, to the active temperature TA of a predetermined catalyst contained in the second catalyst layer 40. More specifically, the activity temperature TA of the LNT catalyst, the SCR catalyst, or the three-way catalyst arranged in the NOx purification catalyst layer 41 may be set.

The active temperature TA is a temperature at which the NOx purification capacity of the catalyst (an index in which the maximum purification capacity of the catalyst is 100%) has a high probability (for example, about 90%). As shown in FIG. 6, in NOx purification catalysts such as SCR catalysts, LNT catalysts, and three-way catalysts, when the catalyst temperature rises from a low temperature range where the catalyst temperature is up to about T2 and there is almost no catalytic activity, the catalyst temperature T1 to 1 In the medium temperature range shown in T2, the catalytic activity increases remarkably and reaches a high probability. Then, in the high temperature region after the catalyst temperature reaches T2, the catalytic activity becomes substantially constant. For example, the catalyst temperature T2 at which the significant increase in catalytic activity is completed can be used as the active temperature TA.

The reducing agent control unit 55 may control the amount of the additive supplied to the adsorption layer 35 based on the amount of NOx adsorbed on the adsorption layer 35. Specifically, as a condition for starting the supply of the reducing agent as an additive to the adsorption layer 35, a condition (Na> A1) is set in which the NOx adsorption amount Na in the adsorption layer 35 is larger than the predetermined adsorption amount threshold value A1. You may.

The adsorption amount threshold value A1 may be set to a value calculated by the following formula (15) using, for example, Pa1 (%) in which the ratio of NOx in the adsorption layer 35 to the maximum adsorption amount Amax is expressed as a percentage. It is preferable to set a margin with respect to the maximum adsorption amount Amax and set Pa1 to, for example, about 80%.

A1 = Amax x Pa1 / 100 ... (15)

Alternatively, the adsorption amount threshold value A1 may be set based on the adsorption rate Yr of the amount of NOx in the exhaust gas that has passed through the adsorption layer 35. As shown in FIG. 3, the adsorption rate of NOx in the exhaust gas by the adsorption layer 35 decreases when the amount of NOx adsorbed on the adsorption layer 35 increases to a certain extent or more. In consideration of this characteristic, the adsorption amount threshold A1 is, for example, the upper limit value of the adsorption amount (first adsorption upper limit value) at which the adsorption rate Yr of the amount of NOx in the exhaust passing through the adsorption layer 35 is equal to or higher than the target adsorption rate Yo. It may be set to the following values, or may be set to a value lower than the adsorption upper limit value with a margin.

Further, when the reducing agent control unit 55 supplies the additive to the adsorption layer 35, the NOx adsorption amount Na in the adsorption layer 35 is smaller than the predetermined adsorption amount threshold value B1 as a condition for stopping the supply. The condition (Na <B1) may be set. The adsorption amount threshold value B1 is preferably set to a value lower than the adsorption amount threshold value A1 (B1 <A1).

The adsorption amount threshold value B1 may be set, for example, based on the adsorption rate Yr of the amount of NOx in the exhaust gas that has passed through the adsorption layer 35. As shown in FIG. 3, within the range where the amount of NOx adsorbed on the adsorption layer 35 is low, the adsorption rate of NOx in the exhaust gas by the adsorption layer 35 is maintained in a high state. In consideration of this characteristic, the adsorption amount threshold value B1 is preferably set to, for example, a value of the adsorption amount at which the adsorption capacity of the adsorption layer 35 is sufficiently recovered. For example, the adsorption rate Yr of the amount of NOx in the exhaust gas that has passed through the adsorption layer 35 is equal to or less than the upper limit value (second adsorption upper limit value) of the adsorption amount at which the predetermined adsorption rate Yh (for example, 99%) is higher than the target adsorption rate Yo. It may be set to the value of.

Alternatively, the adsorption amount threshold value B1 may be set to a value of the adsorption amount so that the NOx amount is not sufficiently released even if the additive is supplied to the adsorption layer 35. Specifically, for example, the sum of the amount of NOx contained in the exhaust discharged from the adsorption layer 35 and the amount of the additive is the same as the amount of the additive contained in the exhaust flowing into the adsorption layer 35. The NOx adsorption amount of the adsorption layer 35 may be set to the adsorption amount threshold B1. Further, for example, in the adsorption amount threshold value B1, S2 / S1 which is the ratio of the amount of NOx L2 released to the amount L1 of the additive supplied to the adsorption layer 35 is a predetermined value (for example, about 0.5) or less. It may be set to the adsorption amount.

In the reducing agent control unit 55, the amount of NOx adsorbed on the adsorption layer 35 is larger than the adsorption amount threshold A1, and the temperature information of the NOx purification catalyst layer 41 is such that the temperature Ts of the NOx purification catalyst layer 41 is a predetermined temperature threshold Tc. The reducing agent supply device 60 may be controlled to start supplying the additive to the adsorption layer 35 when it indicates that it is higher than.

Further, when the reducing agent control unit 55 indicates that the temperature information of the NOx purification catalyst layer 41 is equal to or less than the temperature threshold Tc, the reducing agent control unit 55 raises the temperature of the NOx purification catalyst layer 41 so as to exceed the temperature threshold Tc. It may be configured as follows. In this case, the adsorption amount threshold value A1 is preferably set to a value including a margin considering the time until the NOx purification catalyst layer 41 exceeds the temperature threshold value Tc. The temperature rise of the NOx purification catalyst layer 41 may be heated by controlling the combustion state of the internal combustion engine 20 by increasing the fuel injection amount in the internal combustion engine 20 or the like to increase the heat amount of the exhaust gas. A heating device that heats the NOx purification catalyst layer 41 such as a heater or a burner that heats by energization may be used.

The reducing agent control unit 55 further indicates that the temperature information of the adsorption layer 35 indicates that the temperature Tk of the adsorption layer 35 is higher than the predetermined adsorption layer temperature threshold Tq1 (Tk> Tq1), and the additive to the adsorption layer 35. May be added as a condition to start the supply of. Further, when this condition is not satisfied, the temperature information of the adsorption layer 35 is such that the temperature of the adsorption layer 35 is raised so as to indicate that the temperature Tk of the adsorption layer 35 is higher than the adsorption layer temperature threshold value Tq1. It may be configured. The supply amount of the additive is increased by suppressing the supply of the additive when the temperature of the adsorption layer 35 is too low and supplying the additive after appropriately raising the temperature of the adsorption layer 35. You can save. Similarly, the temperature of the adsorption layer 35 can be raised by increasing the amount of heat of the exhaust gas or by using a heating device.

The reducing agent control unit 55 is preferably configured to change the supply amount of the reducing agent supplied to the NOx purification catalyst layer 41 according to the amount of the additive supplied to the adsorption layer 35. Specifically, when the additive is supplied to the adsorption layer 35, the reducing agent supplied to the NOx purification catalyst layer 41 according to the amount of NOx released from the adsorption layer 35 by supplying the additive. Increase the amount. For example, the amount of the reducing agent is increased by the amount required to purify the amount of NOx released from the adsorption layer 35 to the target adsorption rate Yo in the NOx purification catalyst layer 41. When the supply of the additive to the adsorption layer 35 is stopped, the amount of the reducing agent supplied to the NOx purification catalyst layer 41 is reduced according to the decrease in the amount of NOx released from the adsorption layer 35. The amount of NOx released from the adsorption layer 35 may be obtained from the detected value of the inlet NOx sensor 23, or may be estimated from the temperature of the adsorption layer 35, the rotation speed of the internal combustion engine 20, and the like.

In the reducing agent control unit 55, when the amount La of the reducing agent adsorbed on the NOx purification catalyst layer 41 is larger than a predetermined adsorption amount threshold (reducing agent adsorption amount threshold) D1 for the amount of the reducing agent (La> D1). May be configured to carry out the supply of additives to the adsorption layer 35. The larger the amount La of the reducing agent adsorbed on the NOx purification catalyst layer 41, the faster the reaction rate of the reduction reaction in the NOx purification catalyst layer 41. The adsorption amount threshold D1 may be set as the adsorption amount of the reducing agent so that the reaction rate of the reduction reaction in the NOx purification catalyst layer 41 becomes faster than a predetermined value. Alternatively, the adsorption amount threshold value D1 may be set based on the maximum adsorption amount Dmax, which is the maximum value of the amount of the reducing agent that can be adsorbed by the NOx purification catalyst. For example, the ratio to the maximum adsorption amount Dmax may be set to a value calculated by the following formula (16) using Pd1 (%) expressed as a percentage. Since the maximum adsorption amount Dmax increases as the temperature decreases, the adsorption amount threshold value D1 calculated from the following equation (16) increases as the temperature decreases when Pd1 is set constant. It is preferable that Pd1 has a margin with respect to the maximum adsorption amount Dmax and is set to, for example, about 80%.

D1 = Dmax x Pd1 / 100 ... (16)

When the condition La> D1 is added as a condition for executing the supply of the additive to the adsorption layer 35, it is preferable to use the adsorption amount threshold value A2 instead of the adsorption amount threshold value A1 described above. .. The adsorption amount threshold value A2 is further set as a value including a margin considering the time until the amount La of the reducing agent adsorbed on the NOx purification catalyst layer 41 exceeds the adsorption amount threshold value D1 and is set from the adsorption amount threshold value A1. It is set to a small value (A2 <A1). In the above formula (15), A1 can be replaced with A2 and Pa1 can be replaced with Pa2 to calculate the adsorption amount threshold value A2. For example, when Pa1 is set to about 80%, Pa2 is preferably set to about 70%.

The reducing agent control unit 55 may be configured to adjust the amount of the additive and the amount of the reducing agent according to the characteristics of the adsorbent contained in the adsorbent layer 35.

For example, an adsorbent in which the C element in the general formulas I and II is a transition metal element such as cobalt (Co) and copper (Cu) has an oxidizing power because the positive valence of the transition metal element changes. Is relatively high. Therefore, when NH ₃ is supplied as an additive, excess NH ₃ may be oxidized to generate NOx. Therefore, in order to avoid the generation of NOx from the excess NH ₃ in the adsorption layer 35, the adsorption layer 35 is supplied with the amount of NH ₃ required for releasing NOx from the adsorption layer 35 as an additive. , It is preferable not to supply NH ₃ excessively. That is, it is preferable to supply urea water corresponding to the amount of NH ₃ required for releasing NOx from the adsorption layer 35 from the injector 61.

On the other hand, the adsorbent in which the C elements in the general formulas I and II are aluminum (Al), gallium (Ga), and zinc (Zn) do not change in positive valence unlike the transition metal, and therefore are oxidized. The power is relatively low. Therefore, supplying NH ₃ as an additive, even if NH ₃ excess, is unlikely that NOx is generated. The excess NH ₃ in the adsorption layer 35 reaches the NOx purification catalyst layer 41 on the downstream side of the NH ₃ as it is, and functions as a reducing agent. Therefore, the adsorption layer 35 may be supplied with an excess amount of NH ₃ that exceeds the amount required for releasing NOx from the adsorption layer 35. That is, the injector 61 may supply urea water that is excessive with respect to the amount of NH ₃ required for releasing NOx from the adsorption layer 35.

For example, the reducing agent control unit 55 supplies an excess amount of urea water from the injector 61, considers the amount of urea water supplied from the injector 61 and reaches the NOx purification catalyst layer 41, and considers the insufficient amount of the injector 62. Urea water may be supplied from. Further, the reducing agent control unit 55 supplies the amount of urea water required for the adsorption layer 35 and the urea water required for the NOx purification catalyst layer 41 together from the injector 61, and does not supply urea water from the injector 62. It may be controlled as follows. By supplying urea water from the injector 61 on the upstream side, the reactions represented by the above formulas (9) and (10) can proceed before passing through the exhaust pipe 12 and reaching the NOx purification catalyst layer 41. , The reduction reaction of the SCR catalyst in the NOx purification catalyst layer 41 can be facilitated.

The reducing agent control unit 55 may change the conditions for supplying the additive and the reducing agent according to the operating state of the internal combustion engine 20. For example, when the internal combustion engine 20 continues to operate, the condition that Na> A1 is set as described above is set as a condition for executing the control of supplying the additive to the adsorption layer 35, while the condition is set. When the internal combustion engine 20 shifts from the operating state to the stopped state, the condition that Na> A1 may not be set may not be set.

When the internal combustion engine 20 shifts from the operating state to the stopped state, the NOx purification catalyst layer 41 may be in the activated state. Therefore, when the internal combustion engine 20 shifts from the operating state to the stopped state, the reducing agent control unit 55 determines that the activated state of the reduction reaction of the NOx purification catalyst layer 41 is higher than a predetermined value, the adsorption layer 35 Regardless of the amount of NOx adsorbed on the surface, it is preferable to perform control to release the adsorbed NOx to restore the adsorption performance of the adsorption layer 35.

By controlling in this way, when the internal combustion engine 20 subsequently shifts from the stopped state to the operating state, the suction performance of the suction layer 35 can be made high. When the internal combustion engine 20 shifts from the stopped state to the operating state, the temperatures of the adsorption layer 35 and the NOx purification catalyst layer 41 may be in a low state. Even in such a low temperature state, if the adsorption performance of the adsorption layer 35 is restored, the adsorption layer 35 can surely purify the NOx discharged from the internal combustion engine 20. That is, NOx in the exhaust gas at the time of cold start can be reliably purified.

The supply amount of the reducing agent can be set based on the amount of NOx in the exhaust gas supplied to the NOx purification catalyst layer 41. More specifically, the injection rate and the injection time in the injector 62, which is the reducing agent supply mechanism, can be set according to the supply amount of the reducing agent.

The combustion control unit 56 controls the combustion state of the internal combustion engine 20. The combustion control unit 56 may be configured to be able to control the amount of each component in the exhaust gas by controlling the amount or timing of the fuel and air supplied to the internal combustion engine 20.

FIG. 7 shows a flowchart of the exhaust gas purification process executed by the ECU 50. The process according to FIG. 7 is repeatedly executed at regular intervals.

In step S101, it is determined whether or not the reducing agent is being supplied to the adsorption layer (abbreviated as AD layer in the figure) 35. If it is not supplied, the process proceeds to step S102. If the supply is in progress, the process proceeds to step S121.

When the reducing agent is not supplied to the adsorption layer 35, it is determined by the treatments of steps S102 and S104 whether or not to start the supply of the reducing agent. On the other hand, when the reducing agent is supplied to the adsorption layer 35, it is determined by the treatment of step S121 whether or not to stop the supply of the reducing agent.

In step S102, it is determined whether or not the NOx adsorption amount Na in the adsorption layer 35 is larger than the predetermined adsorption amount threshold value A1. For the NOx adsorption amount Na, for example, the time-dependent change between the estimated value of the NOx amount discharged from the internal combustion engine 20 and the detected value of the inlet NOx sensor 23 is acquired, and the difference obtained by subtracting the latter from the former is integrated over the elapsed time. The calculated value can be used. If Na> A1, the process proceeds to step S104. When Na ≦ A1, the process ends. The adsorption amount threshold value A1 is set to a value calculated by the above formula (15) using the maximum adsorption amount Amax of NOx in the adsorption layer 35 and the ratio Pa1 (%). It is preferable to set a margin with respect to the maximum adsorption amount Amax and set Pa1 to, for example, about 80%.

In step S104, it is determined whether or not the temperature Ts of the NOx purification catalyst layer 41 is higher than the predetermined temperature threshold value Tc1. As the temperature Ts, for example, the detected value of the second catalyst temperature sensor 21 can be used. If Ts> Tc1, the process proceeds to step S106. If Ts ≦ Tc1, the process proceeds to step S108. In step S108, the temperature of the NOx purification catalyst layer 41 is raised to end the process. The temperature threshold Tc1 is preferably set to a value equal to or higher than the active temperature TA of the NOx purification catalyst layer 41. More specifically, for example, the temperature at which 99% of NOx in the exhaust gas is purified by passing through the NOx purification catalyst layer 41 may be set as the temperature threshold value Tc1.

In step S106, the supply of the reducing agent to the adsorption layer 35 is started. The reducing agent is supplied to the adsorption layer 35 as an additive. More specifically, the supply of the reducing agent from the injector 61 is started. Then, the process proceeds to step S107.

In step S107, the amount of the reducing agent supplied to the NOx purification catalyst layer (abbreviated as NCA layer in the figure) 41 is changed. When a reducing agent as an additive is supplied to the adsorption layer 35, NOx adsorbed on the adsorption layer 35 is released by the reducing agent. The amount of reducing agent supplied to the NOx purification catalyst layer 41 is increased according to the amount of NOx released from the adsorption layer 35 into the exhaust gas. More specifically, the amount of the reducing agent supplied from the injector 62 is increased by the amount required to reduce the amount of NOx released from the adsorption layer 35 into the exhaust gas in the NOx purification catalyst layer 41. After that, the process ends.

On the other hand, when the reducing agent is supplied to the adsorption layer 35, in step S121, it is determined whether or not the NOx adsorption amount Na in the adsorption layer 35 is less than the predetermined adsorption amount threshold value B1. If Na <B1, the process proceeds to step S122. When Na ≧ B1, the process is terminated.

The adsorption amount threshold value B1 is a value lower than the adsorption amount threshold value A1 (B1 <A1). The adsorption amount threshold value B1 is set to a value of the adsorption amount at which the adsorption capacity of the adsorption layer 35 is sufficiently recovered. Specifically, the adsorption amount threshold B1 is the upper limit of the adsorption amount at which the adsorption rate Yr of the amount of NOx in the exhaust passing through the adsorption layer 35 becomes a predetermined adsorption rate Yh (for example, 99%) higher than the target adsorption rate Yo. It can be set to a value (second adsorption upper limit value) value.

In step S122, the supply of the reducing agent to the adsorption layer 35 is stopped. More specifically, the supply of the reducing agent from the injector 61 is stopped. After that, the process proceeds to step S123.

In step S123, the amount of the reducing agent supplied to the NOx purification catalyst layer 41 is changed. When the supply of the reducing agent to the adsorption layer 35 is stopped by the treatment in step S122, the release of NOx from the adsorption layer 35 is reduced, and the process is stopped. The amount of reducing agent supplied from the injector 62 to the NOx purification catalyst layer 41 is reduced in accordance with the reduction in the amount of NOx released from the adsorption layer 35 into the exhaust gas. After that, the process ends.

As described above, according to the first embodiment, as shown in steps S102, S104, S106, and S107, the temperature Ts of the NOx purification catalyst layer 41 is higher than the predetermined temperature threshold Tc1, and NOx adsorption in the adsorption layer 35. When the amount Na is larger than the predetermined adsorption amount threshold A1, the supply of the reducing agent as an additive to the adsorption layer 35 is started, and the amount of the reducing agent supplied to the NOx purification catalyst layer 41 is increased. Therefore, when the amount of NOx adsorbed in the adsorption layer 35 is sufficiently large, the reducing agent can be supplied to the adsorption layer 35 to release NOx, and the released NOx is reliably purified by the NOx purification catalyst layer 41. can do.

Further, even if the condition of Na> A1 is satisfied in step S102, if the condition of Ts> Tc1 shown in step S104 is not satisfied, the temperature of the NOx purification catalyst layer 41 is raised as shown in step S108. Executes the process to be performed, and ends the process once. Then, the temperature Ts of the NOx purification catalyst layer 41 rises due to the treatment in step S108, and the temperature of the NOx purification catalyst layer 41 is raised until it is determined that the condition of Ts> Tc1 shown in step S104 is satisfied in the next and subsequent cycles. To do. Therefore, after raising the temperature of the NOx purification catalyst layer 41 until the condition of step S104 is satisfied, a reducing agent can be supplied to the adsorption layer 35 to release NOx.

Further, in the situation where the reducing agent is supplied to the adsorption layer 35, the supply of the reducing agent can be stopped when the NOx adsorption amount Na in the adsorption layer 35 is less than the predetermined adsorption amount threshold value B1. Therefore, it is possible to suppress the excessive supply of the reducing agent to the adsorption layer 35. Further, when the supply of the reducing agent to the adsorption layer 35 is stopped, the amount of the reducing agent supplied to the NOx purification catalyst layer 41 is reduced in accordance with the reduction in the amount of NOx released from the adsorption layer 35. Therefore, it is possible to prevent the excess reducing agent from flowing from the NOx purification catalyst layer 41 into the reducing agent removing layer 42.

(Second Embodiment)
FIG. 8 shows a flowchart of the exhaust gas purification process executed by the ECU 50. The process according to FIG. 8 is repeatedly executed at regular intervals. The second embodiment is different from the flowchart of the first embodiment shown in FIG. 7 in that, as shown in step S203, a determination process relating to the temperature of the adsorption layer 35 is included.

In step S201, similarly to step S101, it is determined whether or not the reducing agent is being supplied to the adsorption layer 35. If not, the process proceeds to step S202. If it is being supplied, the process proceeds to step S221. Since the processing of steps S221 to S223 is the same as the processing of steps S121 to S123 shown in FIG. 6, the description thereof will be omitted.

In step S202, it is determined whether or not the NOx adsorption amount Na in the adsorption layer 35 is larger than the predetermined adsorption amount threshold value A2. If Na> A2, the process proceeds to step S203. When Na ≦ A2, the process is terminated. The adsorption amount threshold value A2 is set to a value larger than the adsorption amount threshold value B1 shown in FIG. 7 and smaller than the adsorption amount threshold value A1 (B1 <A2 <A1). The adsorption amount threshold A2 prevents the adsorption performance of the adsorption layer 35 from being excessively lowered while increasing the amount La of the reducing agent adsorbed on the NOx purification catalyst layer 41 by the treatment of steps S211 to S213 described later. It is a value with a margin to the extent that it can be formed, and the value is smaller than the adsorption amount threshold A1 by that amount.

In step S203, it is determined whether or not the amount La of the reducing agent adsorbed on the NOx purification catalyst layer 41 is larger than the predetermined adsorption amount threshold value D1. The larger the amount of the reducing agent adsorbed on the NOx purification catalyst layer 41, the faster the reaction rate of the reduction reaction in the NOx purification catalyst layer 41. The adsorption amount threshold value D1 is set as an adsorption amount such that the reaction rate of the reduction reaction in the NOx purification catalyst layer 41 becomes faster than a predetermined value.

If La> D1, the process proceeds to step S204. Since the processes of steps S204 and S206 to S208 are the same as the processes of steps S104 and S106 to S108 shown in FIG. 6, the description thereof will be omitted. If La ≦ D2, the process proceeds to step S211.

In step S211 it is determined whether or not the temperature Ts of the NOx purification catalyst layer 41 is higher than the predetermined temperature threshold Tc2. The temperature threshold value Tc2 may be set to the same value as the temperature threshold value Tc1 or may be set to a different value. If Tc2 = Tc1 is set, a positive determination can be obtained in step S204 in the next and subsequent cycles, which is preferable. If Ts> Tc2, the process proceeds to step S212. If Ts ≦ Tc2, the process proceeds to step S213. In step S213, the temperature of the NOx purification catalyst layer 41 is raised to end the treatment.

In step S212, the amount of the reducing agent supplied to the NOx purification catalyst layer 41 is changed. In order to increase the amount of the reducing agent adsorbed on the NOx purification catalyst layer 41, the amount of the reducing agent supplied to the NOx purification catalyst layer 41 is increased. More specifically, the amount of the reducing agent supplied from the injector 62 is increased. After that, the process ends.

As described above, according to the second embodiment, as a condition for starting the supply of the reducing agent as an additive to the adsorption layer 35 and increasing the amount of the reducing agent supplied to the NOx purification catalyst layer 41, further. , As shown in step S203, the condition La> D1 is set. Therefore, since the reaction rate of the reduction reaction in the NOx purification catalyst layer 41 can be increased more than a predetermined value, NOx released from the adsorption layer 35 can be purified more reliably.

When the condition of La> D1 shown in step S203 is not satisfied, the amount of the reducing agent supplied to the NOx purification catalyst layer 41 is increased as shown in steps S211 and S212. Thereby, the adsorption amount La of the reducing agent in the NOx purification catalyst layer 41 can be increased until the condition of La> D1 is satisfied. Further, the adsorption amount threshold value A2 in step S202 is set to a value with a margin sufficient to prevent the adsorption performance of the adsorption layer 35 from being excessively deteriorated while increasing La by the treatment of steps S211 to S213. It is set. Therefore, it is possible to prevent the amount of NOx in the exhaust gas discharged from the exhaust gas purification system 10 from increasing while increasing the amount La of the reducing agent adsorbed on the NOx purification catalyst layer 41.

(Third Embodiment)
FIG. 9 shows a flowchart of the exhaust gas purification process executed by the ECU 50. The flowchart according to FIG. 9 is repeatedly executed at regular intervals. As shown in step S305, the third embodiment is different from the flowchart of the first embodiment shown in FIG. 7 in that it includes a determination process regarding the temperature of the adsorption layer 35.

In step S301, similarly to step S101, it is determined whether or not the reducing agent is being supplied to the adsorption layer 35. If not, the process proceeds to step S302. If it is being supplied, the process proceeds to step S321. Since the processing of steps S321 to S323 is the same as the processing of steps S121 to S123 shown in FIG. 6, the description thereof will be omitted.

In step S302, similarly to step S102, it is determined whether or not the NOx adsorption amount Na in the adsorption layer 35 is larger than the predetermined adsorption amount threshold value A1. If Na> A1, the process proceeds to step S304. When Na ≦ A1, the process ends.

In step S304, similarly to step S104, it is determined whether or not the temperature Ts of the NOx purification catalyst layer 41 is higher than the predetermined temperature threshold value Tc1. If Ts> Tc1, the process proceeds to step S305. If Ts ≦ Tc1, the process proceeds to step S308. In step S308, the temperature of the NOx purification catalyst layer 41 is raised to end the process in the same manner as in step S108.

In step S305, it is determined whether or not the temperature Tk of the adsorption layer 35 is higher than the predetermined adsorption layer temperature threshold value Tq1. If Tk> Tq1, the process proceeds to step S306 and step S307, and then the process ends. Since the processes of steps S306 and S307 are the same as the processes of steps S106 and S107, the description thereof will be omitted. If Ts ≦ Tc1, the process proceeds to step S309. In step S309, the temperature of the adsorption layer 35 is raised to end the process.

As described above, according to the third embodiment, the condition Ts> Tc1 and the condition Na> A1 shown in the first embodiment are further added with the condition Tk> Tq1 shown in step S305, and these three conditions are added. When the conditions are satisfied, the supply of the reducing agent as an additive to the adsorption layer 35 is started, and the amount of the reducing agent supplied to the NOx purification catalyst layer 41 is increased. If the temperature of the adsorption layer 35 is too low, the amount of NOx released with respect to the supplied additive tends to be small. The treatment of step S305 suppresses the supply of additives when the temperature of the adsorption layer 35 is too low, and the treatment of step S309 appropriately raises the temperature of the adsorption layer 35 to supply the additives. You can save the amount.

(Fourth Embodiment)
FIG. 10 shows a flowchart of the exhaust gas purification process executed by the ECU 50. The process according to FIG. 9 is repeatedly executed at regular intervals. As shown in step S400, the fourth embodiment is different from the flowchart according to the first embodiment shown in FIG. 7 in that it includes a process of determining that the internal combustion engine 20 shifts from the operating state to the stopped state. ing.

First, in step S400, it is determined whether or not the ignition off (IG off) has been executed in the vehicle equipped with the exhaust gas purification system 10. Ignition-off has been executed When the ignition-off is executed, the process proceeds to step S401. If it has not been executed, the process ends.

In step S401, similarly to step S101, it is determined whether or not the reducing agent is being supplied to the adsorption layer 35. If it is not supplied, the process proceeds to step S404. If it is being supplied, the process proceeds to step S421. Since the processing of steps S421 to S423 is the same as the processing of steps S121 to S123 shown in FIG. 7, the description thereof will be omitted.

In step S404, similarly to step S104, it is determined whether or not the temperature Ts of the NOx purification catalyst layer 41 is higher than the predetermined temperature threshold value Tc1. If Ts> Tc1, the process proceeds to step S406 and step S407, and then the process ends. Since the processes of steps S406 and S407 are the same as the processes of steps S106 and S107, the description thereof will be omitted. If Ts ≦ Tc1, the process ends.

According to the fourth embodiment, when the ignition off is executed in step S400, that is, when the internal combustion engine 20 shifts from the operating state to the stopped state, the suction layer 35 as shown in step S102 or the like. The process proceeds to step S404 without executing the determination regarding the NOx adsorption amount Na, and the additive is supplied to the adsorption layer 35 and the reducing agent is supplied to the NOx purification catalyst layer 41 on condition that Ts> Tc1. As a result, the adsorbed NOx can be released and the adsorption performance of the adsorption layer 35 can be restored. As a result, when the vehicle is switched from the ignition off state to the ignition on state again, the internal combustion engine 20 can be started with the suction performance of the suction layer 35 being high. Therefore, even when the temperature of the adsorption layer 35 and the NOx purification catalyst layer 41 constituting the exhaust gas purification system 10 is low, such as during a cold start, the adsorption layer 35 in a state where the adsorption performance is restored causes the internal combustion engine. The NOx discharged from 20 can be reliably purified.

According to each of the above embodiments, the following effects can be obtained.

The exhaust purification system 10 that purifies a predetermined component in the exhaust gas from the internal combustion engine 20 includes an adsorption layer 35 and a NOx purification catalyst layer 41 installed in the exhaust pipe of the internal combustion engine 20, and a reducing agent supply device that supplies a reducing agent. 60 and. The adsorption layer 35 contains an adsorbent that adsorbs NOx in the exhaust gas and releases the adsorbed NOx by supplying a predetermined additive. The NOx purification catalyst layer 41 contains a NOx purification catalyst that purifies nitrogen oxides in the exhaust gas by a reduction reaction. The reducing agent supply device 60 has a function as an additive supply device for supplying the additive to the adsorption layer 35.

According to the exhaust gas purification system 10, NOx adsorbed on the adsorbent can be released by supplying the additive to the adsorbent layer 35 by the reducing agent supply device 60, so that the adsorption layer and the NOx purification catalyst layer 41 can be released. It is possible to arbitrarily release NOx without raising the temperature or controlling the air-fuel ratio of the internal combustion engine to the rich side.

The ECU 50 functions as an exhaust gas purification control device that controls the exhaust gas purification system 10. The ECU 50 has a function as an additive control unit that controls the supply of the additive to the adsorption layer 35 by the additive supply device (reducing agent supply device 60) based on the state of the NOx purification catalyst layer 41. A control unit 55 is provided.

The reducing agent control unit 55 as an additive control unit controls the supply of the additive to the adsorption layer 35 based on the activated state of the reduction reaction in which the NOx purification catalyst layer 41 purifies NOx in the exhaust. ..

The reducing agent control unit 55 as the additive control unit is preferably configured to control the supply of the additive to the adsorption layer 35 based on the temperature information of the NOx purification catalyst layer 41. Further, it is preferable that the reducing agent control unit 55 as the additive control unit is configured to control the supply of the additive to the adsorption layer 35 based on the state of the adsorption layer 35.

In the reducing agent control unit 55 as an additive control unit, the amount of NOx adsorbed on the adsorption layer 35 is larger than a predetermined adsorption amount threshold (for example, A1 and A2), and the temperature information of the NOx purification catalyst layer 41 is obtained. The reducing agent supply device 60 is configured to control the reducing agent supply device 60 so as to supply the additive to the adsorption layer 35 when it indicates that the temperature Ts of the NOx purification catalyst layer 41 exceeds a predetermined temperature threshold (for example, Tc1). May be good.

More specifically, in the reducing agent control unit 55 as the additive control unit, the amount of NOx adsorbed on the adsorption layer 35 is larger than the predetermined adsorption amount thresholds (for example, A1 and A2), and the NOx purification catalyst layer When the temperature information of 41 indicates that the temperature Tk of the NOx purification catalyst layer 41 is equal to or lower than a predetermined temperature threshold (for example, Tc1), the temperature Tk of the NOx purification catalyst layer 41 is raised so as to exceed the temperature threshold. It may be configured as follows.

When the reducing agent control unit 55 controls the reducing agent supply device 60 so as to supply the reducing agent as an additive to the adsorption layer 35, the reducing agent control unit 55 increases the supply amount of the reducing agent to the NOx purification catalyst layer 41. It is preferably configured.

The reducing agent control unit 55 as an additive control unit determines an activated state for a reduction reaction in which the NOx purification catalyst layer 41 purifies NOx in the exhaust when the internal combustion engine 20 shifts from the operating state to the stopped state. The reducing agent supply device 60 may be controlled so as to supply the additive to the adsorption layer 35 when the activation state is higher than the activated state of.

The adsorbent used for the adsorption layer 35 of the exhaust purification system 10 to adsorb NOx in the exhaust and release the adsorbed NOx by supplying a predetermined additive is not limited, but is limited to the general formula I: An adsorbent Q represented by A _a B _b C _c O _8.5-δ and containing a composite oxide having an adsorption site for NOx (first composite oxide) can be exemplified. In the general formula I, A is composed of at least one selected from the group consisting of rare earth elements, Ca, and In, B is composed of at least one selected from the group consisting of alkaline earth metal elements, and C is a transition. It consists of at least one selected from the group consisting of metal elements, Al, Zn, and Ga, and a, b, c, and δ are 0 <a≤1, 0 <b≤1, 0 <c≤4, respectively. Satisfy 0 <δ ≦ 1.5.

The first composite oxide is represented by the general formula II: A _a B _b C _c O _8.5-δ (NOx) _θ , and in the above general formula II, A is composed of a rare earth element, Ca, and In. At least one selected from the group, B is composed of at least one selected from the group consisting of alkaline earth metal elements, and C is at least one selected from the group consisting of transition metal elements, Al, Zn, and Ga. A, b, c, δ, and θ are 0 <a ≦ 1, 0 <b ≦ 1, 0 <c ≦ 4, 0 <δ ≦ 1.5, and 0 ≦ θ ≦ 1.5, respectively. It may be a satisfactory composite oxide.

Further, the adsorbent Q may contain a second compound different from the first composite oxide. Further, the adsorbent Q may have a main phase composed of the first composite oxide and a subphase composed of the second compound. Further, the above-mentioned second compound may contain at least one selected from the group consisting of transition metal elements, alkaline earth metal elements, Al, and Zn. In addition, the above-mentioned second compound may contain at least one of an oxide and a salt. In addition, the above-mentioned second compound may contain at least a carbonate of an alkaline earth metal element.

The above-mentioned adsorbent Q may be supported on a carrier. The carrier may be, for example, a structure used as a catalyst carrier such as a honeycomb structure or a porous body, or in the exhaust pipe 12 for a main purpose other than supporting the catalyst, such as a mixing member 38. It may be a structure installed in. Furthermore, the above-mentioned adsorbent Q may be supported on a carrier together with a noble metal. When a noble metal is supported on the carrier together with the above-mentioned adsorbent Q, the adsorption performance for NOx is improved.

Further, the adsorbent Q may be supported on the carrier together with an inorganic binder consisting of at least one selected from the group consisting of alumina, silica, and titania. Further, the adsorbent Q may be supported on the carrier together with a co-catalyst consisting of at least one selected from the group consisting of ceria, zirconia, and ceria-zirconia solid solution. When a co-catalyst is supported, the oxidation performance of the noble metal with respect to nitric oxide is improved. As a result, the adsorption performance of nitrogen oxides on the adsorbent Q is improved.

As the NOx purification catalyst provided in the NOx purification catalyst layer 41, a conventionally known NOx reduction catalyst that reduces and purifies NOx can be used. Specifically, NOx reduction catalysts called LNT catalysts, SCR catalysts, three-way catalysts and the like can be used.

When an SCR catalyst that selectively reduces and purifies NOx by supplying a reducing agent is used as the NOx purification catalyst, the additive may be a substance common to the reducing agent or another substance. It may be. When the additive and the reducing agent are common substances, a reduction having both a function as a reducing agent supply device for supplying the reducing agent to the SCR catalyst and a function as an additive supply device like the exhaust purification system 10. It may be configured to include the agent supply device 60. When the additive and the reducing agent are different, the additive supply device and the reducing agent supply device are configured as separate devices, but even if they are common substances, they are configured as separate devices. You may.

Like the exhaust purification system 10, the exhaust pipe 12 further has at least one of a DOC layer 31 provided with an oxidation catalyst that oxidizes unburned components in the exhaust and a DPF layer 32 that purifies the particulate components in the exhaust. It is preferable to have it inside.

Like the exhaust gas purification system 10, the injector 61 as an additive supply mechanism for supplying an additive to the inlet side of the adsorption layer 35 and the reducing agent supply mechanism for supplying a reducing agent to the inlet side of the NOx purification catalyst layer 41. It may be configured so that the injector 62 and the injector 62 are separately provided. When the additive and the reducing agent are common substances, the amount of the reducing agent (reducing agent as an additive) supplied to the adsorption layer 35 and the NOx purification catalyst layer 41 arranged on the downstream side of the adsorption layer 35. The sum of the amount of the reducing agent to be supplied to the adsorbent may be supplied from the position of the injector 61 to the inlet of the adsorption layer. In this case, the injector 61 has a function as a common reducing agent supply mechanism that injects both the additive and the reducing agent from one place.

Examples of the reducing agent supplied to the SCR catalyst include, but are not limited to, ammonia, hydrocarbons, and carbon monoxide. These reducing agents can also be used as additives to be supplied to the adsorbent to release NOx.

The adsorbent may be configured as an adsorption layer for the purpose of NOx adsorption, such as the adsorption layer 35 according to the exhaust purification system 10, or may be arranged in the exhaust pipe 12 for a purpose other than NOx adsorption. The adsorbent may be supported on another structure. For example, a mixing member that mixes exhaust gas or a particle collecting filter that purifies particulate components in exhaust gas may be used as an adsorbent layer on which an adsorbent is adsorbed.

In the exhaust gas purification system 10, one DOC layer 31, one DPF layer 32, one adsorption layer 35, and one NOx purification catalyst layer 41 are provided, and they are arranged from the internal combustion engine 20 side in this order. Not limited to this. The number of each layer may be singular or plural, and the arrangement of each layer may be appropriately changed.

For example, when one layer each of the DOC layer, the DPF layer, and the adsorption layer is provided, and two NOx purification catalyst layers are provided, the upstream NOx purification catalyst arranged on the upstream side in order from the internal combustion engine 20 side. The layer, the DOC layer, the DPF layer, the adsorption layer, and the downstream NOx purification catalyst layer arranged on the downstream side may be arranged in the exhaust pipe 12 in this order.

Further, when the DOC layer and the DPF layer are provided one by one, and the adsorption layer and the NOx purification catalyst layer are provided by two layers each, the upstream side arranged on the upstream side in order from the internal combustion engine 20 side. The adsorption layer, the upstream NOx purification catalyst layer, the DOC layer, the DPF layer, the downstream adsorption layer arranged on the downstream side, and the downstream NOx purification catalyst layer may be arranged in the exhaust pipe 12 in this order.

In each of the above embodiments, an adsorbent that releases adsorbed NOx by supplying a reducing agent such as ammonia, hydrocarbon, and carbon monoxide, which is supplied to the SCR catalyst, as an additive is exemplified. However, it is not limited to this. Since the adsorbent Q tends to adsorb NO ₂ and nitric acid more easily than NO, a material that reduces NO ₂ and nitric acid adsorbed on the adsorbent to NO, which is less likely to be adsorbed, is preferably used as an additive. Can be done.

The controls and methods thereof described in the present disclosure are realized by a dedicated computer provided by configuring a processor and memory programmed to perform one or more functions embodied by a computer program. May be done. Alternatively, the controls and methods thereof described in the present disclosure may be implemented by a dedicated computer provided by configuring the processor with one or more dedicated hardware logic circuits. Alternatively, the control unit and method thereof described in the present disclosure may be a combination of a processor and memory programmed to perform one or more functions and a processor composed of one or more hardware logic circuits. It may be realized by one or more dedicated computers configured. Further, the computer program may be stored in a computer-readable non-transitional tangible recording medium as an instruction executed by the computer.

10 ... Exhaust purification system, 12 ... Exhaust pipe, 20 ... Internal combustion engine, 35 ... Adsorption layer, 41 ... NOx purification catalyst layer, 50 ... ECU, 55 ... Reducing agent control unit, 60 ... Reducing agent supply device

Claims (9)

It is installed in the exhaust pipe (12) of the internal combustion engine (20), adsorbs the nitrogen oxides in the exhaust from the internal combustion engine, and releases the adsorbed nitrogen oxides by supplying a predetermined additive. And the adsorption layer (35) containing the adsorbent
A purification catalyst layer (41) installed in the exhaust pipe and containing a purification catalyst that purifies nitrogen oxides in the exhaust gas by a reduction reaction.
An exhaust purification control device (50) comprising an additive supply device (60) for supplying the additive to the adsorption layer and controlling an exhaust purification system (10) for purifying a predetermined component in exhaust gas from the internal combustion engine. ) And
An exhaust gas purification control device including an additive control unit (55) that controls the supply of the additive to the adsorption layer by the additive supply device based on the state of the purification catalyst layer. The adsorbent contains a composite oxide (2) represented by the general formula I: A _a B _b C _c O _8.5-δ .
The composite oxide has an adsorption site for the nitrogen oxide and
In the general formula I, A is composed of at least one selected from the group consisting of rare earth elements, Ca, and In, B is composed of at least one selected from the group consisting of alkaline earth metal elements, and C is a transition metal. It consists of at least one selected from the group consisting of elements, Al, Zn, and Ga, and a, b, c, and δ are 0 <a≤1, 0 <b≤1, 0 <c≤4,0, respectively. The exhaust purification control device according to claim 1, which satisfies <δ ≦ 1.5. The additive control unit supplies the additive to the adsorption layer by the additive supply device based on the activated state of the reduction reaction in which the purification catalyst layer purifies the nitrogen oxides in the exhaust gas. The exhaust gas purification control device according to claim 1 or 2 to be controlled. The exhaust purification according to any one of claims 1 to 3, wherein the additive control unit controls the supply of the additive to the adsorption layer by the additive supply device based on the temperature information of the purification catalyst layer. Control device. The exhaust purification control device according to any one of claims 1 to 4, wherein the additive control unit controls the supply of the additive to the adsorption layer by the additive supply device based on the state of the adsorption layer. .. In the additive control unit, the amount of the nitrogen oxide adsorbed on the adsorption layer is larger than the predetermined adsorption amount threshold, and the temperature information of the purification catalyst layer is such that the temperature of the purification catalyst layer has a predetermined temperature threshold. The exhaust purification control device according to claim 5, wherein the additive supply device is controlled so as to supply the additive to the adsorption layer when the amount exceeds the limit. In the additive control unit, the amount of nitrogen oxide adsorbed on the adsorption layer is larger than the predetermined adsorption amount threshold, and the temperature information of the purification catalyst layer is such that the temperature of the purification catalyst layer is equal to or less than the predetermined temperature threshold. The exhaust purification control device according to claim 6, wherein the temperature of the purification catalyst layer is raised so that the temperature of the purification catalyst layer exceeds the temperature threshold. The purification catalyst is a selective reduction catalyst that selectively reduces and purifies the nitrogen oxides by supplying a reducing agent.
The exhaust gas purification system includes a reducing agent supply device (60) that supplies the reducing agent to the purification catalyst layer.
The exhaust gas purification control device includes a reducing agent control unit that controls the supply of the reducing agent by the reducing agent supply device.
The reducing agent control unit increases the supply amount of the reducing agent when the additive control unit controls the additive supply device so as to supply the additive to the adsorption layer. 7. The exhaust purification control device according to any one of 7. In the additive control unit, when the internal combustion engine shifts from the operating state to the stopped state, the activated state for the reduction reaction in which the purifying catalyst layer purifies the nitrogen oxides in the exhaust gas is a predetermined activated state. The exhaust gas purification control device according to any one of claims 1 to 8, wherein the additive supply device is controlled so as to supply the additive to the adsorption layer when the value is higher than that of the above.

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