JP2021080876A - Exhaust emission control device - Google Patents

Abstract

To provide an exhaust emission control device capable of improving NOx elimination efficiency.SOLUTION: An exhaust emission control device 1 includes: an SCR 11 disposed in an exhaust passage 5 in which exhaust gas G flows and reducing NOx included in the exhaust gas G; a DOC 13 disposed downstream of the SCR 11 in the exhaust passage 5 and oxidizing at least NO of NOx; a DPF 14 disposed downstream of the DOC 13 in the exhaust passage 5 and collecting particulate matters included in the exhaust gas G; an SCR 15 disposed downstream of the DPF 14 in the exhaust passage 5 and reducing NOx included in the exhaust gas G; and an urea water injection section 21 disposed upstream of the SCR 11 in the exhaust passage 5 and configured to enable injection of urea water to the exhaust gas G. The SCR 11 includes copper (Cu). An upstream side portion 15a of the SCR 15 includes iron (Fe), and a downstream side portion 15b of the SCR 15 includes copper (Cu).SELECTED DRAWING: Figure 1

Description

The present invention relates to an exhaust gas purification device.

Conventionally, as an exhaust gas purification device for purifying exhaust gas discharged from an engine, for example, the device described in Patent Document 1 is known. This exhaust gas purification device purifies the first reduction catalyst that purifies NOx in the exhaust gas, CO and HC in the exhaust gas, and oxidizes NO in the NOx in order from the upstream side of the exhaust passage through which the exhaust gas flows. It is provided with an oxidation catalyst for collecting exhaust gas, a filter for collecting granular substances in the exhaust gas, and a second reduction catalyst for purifying NOx in the exhaust gas.

JP-A-2018-159334

In the exhaust gas purification device described above, the first reduction catalyst is arranged on the upstream side of the oxidation catalyst, the filter, and the second reduction catalyst. With such an arrangement, the high-temperature exhaust gas immediately after being discharged from the engine flows to the first reduction catalyst, and the first reduction catalyst can be activated at an early stage. Therefore, NOx in the exhaust gas can be activated. It is suitable for improving the purification efficiency of the gas. However, in the above-mentioned exhaust purification device, it cannot be said that the catalyst is configured after fully considering the component ratio in the exhaust gas flowing into the catalyst, and the catalyst is purified depending on the component ratio in the inflowing exhaust gas. Performance may not be fully exhibited. Therefore, there is room for further improvement in terms of improving the purification efficiency of NOx.

An object of the present invention is to provide an exhaust gas purification device capable of improving the purification efficiency of NOx.

The exhaust purification device according to one aspect of the present invention is an exhaust purification device that purifies the exhaust gas discharged from the engine, is arranged in an exhaust passage through which the exhaust gas flows, and reduces NOx contained in the exhaust gas. And the oxidation catalyst which is arranged on the downstream side of the first reduction catalyst in the exhaust passage and oxidizes NO of at least NOx, and the particles which are arranged on the downstream side of the oxidation catalyst in the exhaust passage and contained in the exhaust gas. It is arranged on the downstream side of the filter in the exhaust passage and the filter that collects the state substances, and is arranged on the upstream side of the second reduction catalyst that reduces NOx contained in the exhaust gas and the first reduction catalyst in the exhaust passage. The exhaust gas is provided with a reducing agent injection unit configured to inject a reducing agent, the first reduction catalyst contains copper (Cu), and the upstream portion of the second reduction catalyst is iron ( Fe) is contained, and the downstream portion of the second reduction catalyst contains copper (Cu).

In this exhaust purification device, since the first reduction catalyst is arranged on the upstream side of the oxidation catalyst, the filter, and the second reduction catalyst, the high-temperature exhaust gas immediately after being discharged from the engine is reduced to the first reduction. It can be flushed to the catalyst. As a result, the first reduction catalyst can be activated at an early stage, and the NOx purification efficiency can be improved. Further, the first reduction catalyst is a Cu-based reduction catalyst containing Cu. Since the exhaust gas discharged from the engine contains a large amount of NO, the exhaust gas in a state in which the proportion of NO is high flows into the first reduction catalyst. In such an environment where a large amount of NO is present (or only NO is present), it is possible to use a Cu-based reduction catalyst rather than using another reduction catalyst from the viewpoint of fully exerting the purification performance of NOx. Suitable. Therefore, by using the Cu-based reduction catalyst as the first reduction catalyst, the NOx reduction reaction can be sufficiently proceeded in the first reduction catalyst arranged immediately after the engine, and NOx is efficiently purified. be able to. Further, the upstream portion of the second reduction catalyst is an Fe-based reduction catalyst containing Fe, and the downstream portion of the second reduction catalyst is a Cu-based reduction catalyst containing Cu. There is. Since NO in the exhaust gas that has passed through the first reduction catalyst is _{oxidized to NO 2 by the oxidation catalyst, the proportion of NO 2} is increased in the upstream portion of the second reduction catalyst (for example, NO). Exhaust gas with the same ratio of _{NO 2} and NO 2) flows in. In such an environment where NO and NO ₂ coexist, it is preferable to use an Fe-based reduction catalyst rather than another reduction catalyst from the viewpoint of sufficiently exerting the purification performance of NOx. Therefore, by using the upstream portion of the second reduction catalyst as an Fe-based reduction catalyst, the reduction reaction of NOx can be sufficiently proceeded in the upstream portion, and NOx can be efficiently purified. it can. By NO and NO ₂ or the like is purified in the upstream portion of the second reduction catalyst, the downstream portion NO and NO ₂ and the like in the exhaust gas flowing into the (Cu-based reducing catalyst) of the second reduction catalyst Decreases. _{By reducing NO 2} flowing into the Cu-based reduction catalyst in this way, it is possible to suppress a situation in which a large amount of _{N 2} O, which is difficult to purify and is highly harmful, is generated in the Cu-based reduction catalyst. Since the Cu-based reduction catalyst can sufficiently proceed the NOx reduction reaction even in an environment where only NO is present due to the decrease of _{NO 2, the Cu-based reduction catalyst is contained in the exhaust gas that has passed through the Fe-based reduction catalyst.} NOx can be efficiently purified. Therefore, according to the exhaust gas purification device described above, the purification efficiency of NOx in the exhaust gas can be improved.

The exhaust purification device described above may further include a first ammonia slip catalyst arranged between the first reduction catalyst and the oxidation catalyst in the exhaust passage. When the reducing agent is injected into the exhaust gas on the upstream side of the first reduction catalyst, NH ₃ is generated from the reducing agent. Since the first reduction catalyst containing Cu (Cu-based reduction catalyst) has a property of adsorbing a large amount of _{NH 3 , most of the produced NH 3} is the first when passing through the first reduction catalyst. Adsorbs to the reduction catalyst of 1. The NH ₃ adsorbed on the first reduction catalyst leaks from the first reduction catalyst due to a rapid temperature rise due to the exhaust gas immediately after being discharged from the engine. In the above configuration, since the first ammonia slip catalyst is arranged between the first reduction catalyst and the oxidation catalyst, the leaked NH ₃ is converted into NOx such as _{NO and NO 2} by the first ammonia slip catalyst. After being converted, it flows into the oxidation catalyst. In this way, the leaked NH _{3 is converted into NOx such as NO and NO 2} before flowing into the oxidation catalyst. Therefore, in the oxidation catalyst, the leaked NH ₃ is difficult to purify and is highly harmful N _2. It is possible to suppress the situation where it is oxidized to O. Thereby, the purification efficiency of NOx can be further improved.

The exhaust purification device described above may further include a second ammonia slip catalyst arranged on the downstream side of the second reduction catalyst in the exhaust passage. In this case, NH _{3 in the exhaust gas is oxidized to NO x such as NO and NO 2} by the second ammonia slip catalyst, and then discharged to the outside of the exhaust purification device. Therefore, NH ₃ which is a harmful substance is discharged to the atmosphere. It is possible to suppress the situation where it is released inside.

According to the present invention, the purification efficiency of NOx can be improved.

FIG. 1 is a schematic configuration diagram showing an exhaust gas purification device according to an embodiment. FIG. 2 is a schematic view showing the catalyst configurations of the first reduction catalyst and the first ammonia slip catalyst of FIG. FIG. 3 is a schematic view showing the catalyst configuration of the second reduction catalyst of FIG. FIG. 4 is a schematic configuration diagram showing an exhaust gas purification device according to a comparative example.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the drawings, the same or equivalent elements are designated by the same reference numerals, and duplicate description will be omitted as appropriate.

FIG. 1 is a schematic configuration diagram showing an exhaust gas purification device 1 according to the present embodiment. The exhaust gas purification device 1 is mounted on a vehicle such as a truck and purifies the exhaust gas G discharged from the engine 2 which is an internal combustion engine. The engine 2 is, for example, a diesel engine. The vehicle on which the exhaust gas purification device 1 is mounted may be a large vehicle such as a tractor or a bus, a medium-sized vehicle, a small vehicle, or a light vehicle, in addition to a truck. In the following description, the "upstream side" means the upstream side in the flow direction of the exhaust gas G, and the "downstream side" means the downstream side in the flow direction of the exhaust gas G.

The exhaust purification device 1 is mounted in the exhaust passage 5 through which the exhaust gas G flows. The exhaust gas purification device 1 includes SCR11 (first reduction catalyst), ASC12 (first ammonia slip catalyst), DOC13 (oxidation catalyst), and DPF14 (in order from the upstream side to the downstream side of the exhaust passage 5). A filter), SCR15 (second reduction catalyst), and ASC16 (second ammonia slip catalyst). Further, the exhaust purification device 1 injects urea water into the urea water injection unit 21 (reducing agent injection unit) that injects urea water into the exhaust gas G flowing on the upstream side of the SCR 11 and the exhaust gas G flowing on the upstream side of the SCR 15. The urea water injection unit 22, the control unit 23 that controls the urea water injection unit 21 and the urea water injection unit 22, the sensor 31 that detects the temperature of the exhaust gas G flowing on the upstream side of the SCR11, and the upstream side of the SCR15. It includes a sensor 32 that detects the temperature of the flowing exhaust gas G.

The SCR (Selective Catalytic Reduction) 11 is a selective reduction catalyst that selectively reduces and purifies NOx (nitride oxide) in the exhaust gas G. For example, it is directly under the engine 2 in which the temperature of the exhaust gas G becomes high. Is located in. Immediately below the engine 2 is a position on the downstream side of the outlet of the engine 2 and close to the outlet. The position directly below the engine 2 may be a position within a range in which the cooling of the exhaust gas G flowing out of the engine 2 can be substantially ignored. _{The SCR11 uses NH 3} (ammonia) generated from the urea water injected by the urea water injection unit 21 as a reducing agent to reduce NOx in the exhaust gas G to N ₂ (nitrogen) and H ₂ O (water). ) And other harmless substances.

ASC (Ammonia Slip Catalyst) 12 is a catalyst that reduces _{NH 3 leaked from SCR 11.} When NH ₃ leaked from SCR 11 flows into DOC 13, NH ₃ is oxidized to _{N 2} O in DOC 13. Since N ₂ O is difficult to purify and highly harmful, it is desirable to suppress the production of _{N 2 O as much as possible.} Therefore, by arranging the ASC 12 between the SCR 11 and the DOC 13, it is possible to suppress a situation in which a large _{amount of N 2 O is generated in the DOC 13.}

DOC (Diesel Oxidation Catalyst) 13 is an oxidation catalyst that oxidizes NO (nitric oxide), HC (hydrocarbon), CO (carbon monoxide) and the like in the exhaust gas G. The DOC 13 is composed of, for example, a carrier such as zeolite on which a metal or a metal oxide is supported. The DPF (Diesel Particulate Filter) 14 is a filter that collects and removes particulate matter (PM: Particulate Matter) in the exhaust gas G that has passed through the DOC 13. The DPF 14 is composed of, for example, a ceramic or a metal porous body. A light oil supply unit for supplying light oil to the DOC 13 may be provided on the upstream side of the DOC 13.

SCR15 is a selective reduction catalyst that selectively reduces and purifies NOx in the exhaust gas G. The SCR15 converts NOx in the exhaust gas G into harmless substances such _{as N 2} and H _{2 O by a reduction reaction using NH 3} generated from the urea water injected from the urea water injection unit 22 as a reducing agent. To do. ASC16 is an oxidation catalyst which oxidizes NH ₃ leaked from SCR 15. As ASC16, for example, one in which a noble metal such as Pt is supported on a carrier such as zeolite may be used.

The urea water injection unit 21 is arranged between the engine 2 and the SCR 11 in the exhaust passage 5. The urea water injection unit 21 is configured to be able to inject urea water into the exhaust gas G flowing between the engine 2 and the SCR 11. The urea water injection unit 22 is arranged between the DPF 14 and the SCR 15 in the exhaust passage 5. The urea water injection unit 22 is configured to be able to inject urea water into the exhaust gas G flowing between the DPF 14 and the SCR 15. The urea water injection unit 21 and the urea water injection unit 22 inject urea water according to the control of the control unit 23. When urea water is injected into the exhaust gas G when the exhaust gas G is at a predetermined temperature (for example, 180 ° C.) or higher, NH ₃ is generated by a thermal decomposition reaction and a hydrolysis reaction.

The sensor 31 is located between the engine 2 and the SCR 11 in the exhaust passage 5 and on the upstream side of the urea water injection unit 21. The sensor 31 detects the temperature of the exhaust gas G flowing between the engine 2 and the SCR 11, and outputs the detected temperature to the control unit 23. The sensor 32 is located between the DPF 14 and the SCR 15 in the exhaust passage 5 and on the upstream side of the urea water injection unit 22. The sensor 32 detects the temperature of the exhaust gas G flowing between the DPF 14 and the SCR 15, and outputs the detected temperature to the control unit 23.

The control unit 23 is, for example, a computer configured to include a CPU, RAM, ROM, an input / output interface, etc., and takes in various sensor information and the like from an input interface circuit according to a control program stored in the ROM, and outputs an interface. Outputs command signals required for various controls from the circuit. The control unit 23 is electrically connected to the urea water injection unit 21, the urea water injection unit 22, the sensor 31, and the sensor 32. The control unit 23 may be, for example, an ECU (Electronic Control Unit) of a vehicle.

The control unit 23 controls the urea water injection unit 21 based on the temperature of the exhaust gas G detected by the sensor 31. Specifically, the control unit 23 controls the urea water injection unit 21 so as to inject urea water from the urea water injection unit 21 when the temperature of the exhaust gas G becomes a predetermined temperature (for example, 180 ° C.) or higher. To do. Similarly, the control unit 23 controls the urea water injection unit 22 based on the temperature of the exhaust gas G detected by the sensor 32. Specifically, the control unit 23 controls the urea water injection unit 22 so as to inject urea water from the urea water injection unit 22 when the temperature of the exhaust gas G becomes a predetermined temperature (for example, 180 ° C.) or higher. To do. The above-mentioned "predetermined temperature" means, for example, a temperature at which SCR11 and SCR15 start to activate, which is a temperature required for producing _{NH 3 from urea water.}

Here, the catalyst configurations of SCR11 and ASC12 will be described with reference to FIG. FIG. 2 is a schematic view showing the catalyst configurations of SCR11 and ASC12. As shown in FIG. 2, SCR11 is an SCR containing Cu (copper). Hereinafter, the SCR containing Cu will be referred to as "Cu-based SCR". Examples of the Cu-based SCR include those in which copper zeolite is supported on a carrier such as ceramic. The Cu-based SCR can sufficiently proceed with the reduction reaction of NOx in an environment in which a large amount of NO is present. An environment in which a large amount of NO is present means an environment in which the proportion of NO in NOx is higher than the proportion _{of NO 2 (nitrogen dioxide) in NOx.}

The Cu-based SCR has the property of adsorbing a large amount of _{NH 3. Therefore, most of NH 3} generated from urea water on the upstream side of SCR 11 is adsorbed on SCR 11 when passing through SCR 11. _{The NH 3} adsorbed on the SCR 11 leaks from the SCR 11 due to a rapid temperature rise due to the exhaust gas G immediately after being discharged from the engine 2. In the example shown in FIG. 2, the entire SCR 11 is a Cu-based SCR, but only a part of the SCR 11 may be a Cu-based SCR.

ASC12 is a catalyst having a function as an SCR in addition to a function as an oxidation catalyst. The ASC 12 has an oxidizing unit 12a that functions as an oxidation catalyst and a reducing unit 12b that functions as an SCR. The oxidized portion 12a is arranged on the upstream side of the ASC12. The oxidized portion 12a contains a noble metal such as Pt (platinum), Pd (palladium), or Ru (ruthenium). Examples of the oxidized portion 12a include those in which Pt is supported on a carrier such as zeolite.

The oxidizing unit 12a oxidizes NH ₃ leaked from SCR 11 to NOx such as NO and NO ₂ , and also oxidizes NO in the exhaust gas G that has passed through SCR 11 to NO ₂ . If the oxidizing power of the oxidizing part 12a with respect to _{NH 3 is too high, the oxidizing part 12a oxidizes NH 3} to N ₂ O. Therefore, the oxidizing power of the oxidizing part 12a with respect to _{NH 3 oxidizes NH 3} to N ₂ O. It is set to the extent that _{NH 3} can be oxidized to NO, NO _2, etc. without it.

The reduction unit 12b is arranged on the downstream side of the ASC 12. The reducing portion 12b is an SCR containing a metal such as Fe (iron) or Cu (copper), for example. In this embodiment, the case where the reducing unit 12b is an SCR containing Fe is illustrated. Hereinafter, the SCR containing Fe will be referred to as "Fe-based SCR". Examples of the Fe-based SCR include those in which iron zeolite is supported on a carrier such as ceramic. The reducing unit 12b selectively reduces and purifies NOx in the exhaust gas G that has passed through the oxidizing unit 12a. Specifically, the reducing unit 12b reduces NOx that could not be completely reduced in SCR11, and also reduces NOx produced by the oxidation _{of NH 3 in the oxidizing unit 12a.}

NH ₃ in the exhaust gas G that has flowed into the ASC12 is oxidized to NOx of ₂ such as NO and NO in the oxidation unit 12a, since it is consumed for the reduction reaction of NOx in the reduction unit 12b, of NH ₃ from ASC12 Leakage is suppressed. Further, the NOx reduction reaction in the reduction unit 12b purifies the NOx in the exhaust gas G flowing out of the ASC 12. The oxidized portion 12a and the reduced portion 12b are formed on the upstream side portion and the downstream side portion of the ASC 12, respectively, by, for example, a two-layer coating or a zone coating.

Next, the catalyst configuration of SCR15 will be described with reference to FIG. FIG. 3 is a schematic view showing the catalyst configuration of SCR15. As shown in FIG. 3, the upstream portion 15a of the SCR 15 is an Fe-based SCR, and the downstream portion 15b of the SCR 15 is a Cu-based SCR. The Fe-based SCR can sufficiently proceed with the reduction reaction of NOx in an environment in _{which NO and NO 2 coexist in the exhaust gas G.} The environment in which NO and NO ₂ coexist is an environment in which _{both NO and NO 2} are present to some extent, for example, the ratio of NO in NOx (the ratio of NO) and the ratio of NO _{2 in NOx.} It _{means an environment where (ratio of NO 2} ) is about the same. On the other hand, as described above, the Cu-based SCR can sufficiently proceed with the reduction reaction of NOx in an environment in which a large amount of NO is present (or only NO is present). The NOx of the exhaust gas G flowing into the SCR 15 is purified by the Fe-based SCR and then further purified by the Cu-based SCR.

In the example shown in FIG. 3, the ratio of Fe-based SCR in SCR15 (ratio of Fe-based SCR) and the ratio of Cu-based SCR in SCR15 (ratio of Cu-based SCR) are both about 1/2. However, the present invention is not limited to this example, and the ratio of Fe-based SCR and the ratio of Cu-based SCR can be changed as appropriate. The ratio of Fe-based SCR may be determined, for example, according to the magnitude of the ratio _{of NO 2 and the ratio of NO in DOC13.}

In the exhaust gas purification device 1 having the above configuration, when the temperature of the exhaust gas G acquired by the sensor 31 becomes equal to or higher than a predetermined temperature, urea water is discharged from the urea water injection unit 21 with respect to the exhaust gas G flowing on the upstream side of the SCR 11. Be jetted. _{At this time, NH 3} is produced from urea water by a thermal decomposition reaction and a hydrolysis reaction. When the produced NH ₃ flows into the SCR 11, the reduction reaction of NOx using _{NH 3 as a reducing agent proceeds in the SCR 11.} As a result, NOx is purified in SCR11. The exhaust gas G that has passed through the SCR 11 flows into the ASC 12. At this time, NH ₃ leaked from SCR 11 is reduced in ASC 12.

HC, CO, etc. in the exhaust gas G that have passed through the ASC 12 are purified by the oxidation catalyst, and NO in the exhaust gas G is oxidized to _{NO 2.} Particulate matter in the exhaust gas G is collected and removed in the DPF14. Then, before the exhaust gas G flows into the SCR 15, the temperature of the exhaust gas G is detected by the sensor 32. When the temperature of the exhaust gas G acquired by the sensor 32 becomes equal to or higher than a predetermined temperature, urea water is injected from the urea water injection unit 22 to the exhaust gas G flowing on the upstream side of the SCR 15. _{At this time, NH 3} is produced from urea water by a thermal decomposition reaction and a hydrolysis reaction. When the generated NH ₃ flows into the SCR 15, the reduction reaction of NOx using _{NH 3} as a reducing agent proceeds in each of the upstream portion 15a and the downstream portion 15b of the SCR 15. As a result, NOx is purified in SCR15. Then, since NH ₃ leaked from SCR 15 is oxidized in ASC 16, the _{situation where NH 3} is released into the atmosphere is suppressed.

Next, the operation and effect of the exhaust gas purification device 1 according to the present embodiment will be described together with the problems of the comparative example.

FIG. 4 is a schematic configuration diagram showing an exhaust gas purification device 100 according to a comparative example. As shown in FIG. 4, the exhaust gas purification device 100 purifies CO and HC in the exhaust gas G and oxidizes NO among NOx in this order from the upstream side of the exhaust gas G, and granules in the exhaust gas G. It includes a DPF 114 that collects substances, an SCR 115 that purifies NOx in the exhaust gas G, and an ASC 116 _{that oxidizes NH 3} leaked from the SCR 115. In the exhaust purification device 100, the sensor 132 arranged on the upstream side of the SCR 115 detects the temperature of the exhaust gas G, and when the temperature of the exhaust gas G becomes equal to or higher than a predetermined temperature, the control unit 123 causes the urea water injection unit 122. Urea water is sprayed from. On the other hand, when the temperature of the exhaust gas G is lower than the predetermined temperature, NH ₃ cannot be generated from the urea water even if the urea water is injected from the urea water injection unit 122, and the NOx reduction reaction occurs in the SCR 115. Is not promoted.

In the exhaust gas purification device 100, as shown in FIG. 4, since the SCR 115 is arranged on the downstream side of the DOC 113 and the DPF 114, the distance from the engine 2 to the SCR 115 is long. Therefore, when the engine 2 is started or the like, it takes time for the temperature of the exhaust gas G on the upstream side of the SCR 115 to reach a predetermined temperature. Therefore, the reduction reaction of NOx is not promoted in SCR115 until the temperature of the exhaust gas G reaches a predetermined temperature. Therefore, it is difficult for the exhaust gas purification device 100 to improve the NOx purification efficiency.

On the other hand, in the exhaust gas purification device 1 according to the present embodiment, as shown in FIG. 1, since the SCR 11 is arranged on the upstream side of the DOC 13 and the DPF 14, the high temperature exhaust gas G immediately after being discharged from the engine 2 Can be sent to SCR11. As a result, SCR11 can be activated at an early stage, and NOx purification efficiency can be improved. Further, the SCR 11 is a Cu-based SCR. Since the exhaust gas G discharged from the engine 2 contains a large amount of NO, the exhaust gas G in a state in which the proportion of NO is high flows into the SCR 11. In such an environment where a large amount of NO is present (or only NO is present), it is preferable to use a Cu-based SCR rather than another SCR from the viewpoint of sufficiently exerting the purification performance of NOx. .. Therefore, by using the Cu-based SCR as the SCR11, the reduction reaction of NOx can be sufficiently proceeded in the SCR11 arranged immediately after the engine 2, and the NOx can be efficiently purified.

Further, the upstream portion 15a of the SCR 15 is an Fe-based SCR, and the downstream portion 15b of the SCR 15 is a Cu-based SCR. Since NO in the exhaust gas G that has passed through _{the SCR 11 is oxidized to NO 2 by the DOC 13, the proportion of NO 2} is increased in the upstream portion 15a of the SCR 15 (for example, _{the proportions of NO and NO 2} are the same). Exhaust gas G (in a state of degree) flows in. In such an environment where NO and NO ₂ coexist, it is preferable to use Fe-based SCR rather than other SCR from the viewpoint of sufficiently exerting the purification performance of NOx. Therefore, by making the upstream side portion 15a of the SCR 15 an Fe-based SCR, the reduction reaction of NOx can be sufficiently proceeded in the upstream side portion 15a, and NOx can be efficiently purified.

On the other hand, the Fe-based SCR cannot sufficiently proceed with the reduction reaction of NOx in an environment in which only NO is present (or the proportion of NO is high). Therefore, if the exhaust gas G in a state where the ratio of NO is _{relatively high with respect to the ratio of NO 2} flows into the upstream portion 15a, NO is reduced during the NOx reduction reaction in the Fe-based SCR. It is assumed that NO cannot be completely removed and remains in the exhaust gas G. On the other hand, as described above, the Cu-based SCR can sufficiently proceed with the reduction reaction of NOx in an environment in which only NO is present (or the proportion of NO is high). Therefore, by making the downstream portion 15b of the SCR 15 a Cu-based SCR, NOx in the exhaust gas G that has passed through the Fe-based SCR can be efficiently purified. Furthermore, by NO and NO ₂ or the like in the upstream portion 15a of the SCR15 is purified, NO and NO ₂ and the like in the exhaust gas G flowing into the downstream portion 15b (Cu-based SCR) of SCR15 is reduced. _{By reducing NO 2} flowing into the Cu-based SCR in this way, it is possible to suppress a situation in which a large amount of _{N 2} O, which is difficult to purify and is highly harmful, is generated in the Cu-based SCR. Therefore, according to the exhaust purification device 1 according to the present embodiment, it is possible to improve the purification efficiency of NOx in the exhaust gas G.

The exhaust purification device 1 according to the present embodiment includes an ASC 12 arranged between the SCR 11 and the DOC 13 in the exhaust passage 5. As described above, SCR11 a Cu-based SCR is because it has a property of adsorbing a large amount of NH _3, the number of NH ₃ generated from the urea water adsorbed on SCR11, NH ₃ adsorbed in SCR11, the engine 2 Due to a sudden temperature rise due to the exhaust gas G immediately after being discharged from the SCR11, the SCR11 leaks. When the ASC 12 is placed between the SCR 11 and the DOC 13, the leaked NH ₃ flows into the DOC 13 after being reduced by the ASC 12. As a result, it is possible to prevent the leaked NH ₃ from being oxidized to _{N 2} O, which is difficult to purify and has high toxicity, in DOC13. As a result, the purification efficiency of NOx can be further improved.

The exhaust gas purification device 1 according to the present embodiment includes an ASC 16 arranged on the downstream side of the SCR 15 in the exhaust passage 5. As a result, NH ₃ in the exhaust gas G is oxidized to NOx such as NO and NO ₂ by ASC16 and then discharged to the outside of the exhaust purification device 1, so that NH ₃ which is a harmful substance is released into the atmosphere. It is possible to suppress the situation where it is done.

The present invention is not limited to the above-described embodiments. The configuration of the exhaust gas purification device is not limited to the above-described embodiment, and can be appropriately changed without departing from the gist of the description of the claims. For example, the exhaust gas purification device may not be provided with ASC12 and ASC16, or may be provided with only one of ASC12 and ASC16. The ASC 12 may have the same configuration as the ASC 16. That is, the ASC 12 may have only the oxidized portion 12a. Conversely, the ASC 16 may have an oxidizing portion 12a and a reducing portion 12b, similarly to the ASC 12. The arrangement of the urea water injection unit 21, the urea water injection unit 22, the sensor 31, and the sensor 32 can be changed as appropriate. For example, the sensor 31 may be arranged on the downstream side of the urea water injection unit 21, or the sensor 32 may be arranged on the downstream side of the urea water injection unit 22.

1 ... Exhaust purification device, 2 ... Engine, 5 ... Exhaust passage, 11 ... SCR (first reducing catalyst), 12 ... ASC (first ammonia slip catalyst), 13 ... DOC (oxidation catalyst), 14 ... DPF ( Filter), 15 ... SCR (second reduction catalyst), 15a ... upstream side portion, 15b ... downstream side portion, 16 ... ASC (second ammonia slip catalyst), 21 ... urea water injection unit (reducing agent injection unit) , G ... Exhaust gas.

Claims (3)

An exhaust purification device that purifies the exhaust gas emitted from the engine.
A first reduction catalyst, which is arranged in an exhaust passage through which the exhaust gas flows and reduces NOx contained in the exhaust gas, and
An oxidation catalyst that is arranged downstream of the first reduction catalyst in the exhaust passage and oxidizes at least NO of the NOx.
A filter arranged on the downstream side of the oxidation catalyst in the exhaust passage and collecting particulate matter contained in the exhaust gas,
A second reduction catalyst, which is arranged on the downstream side of the filter in the exhaust passage and reduces NOx contained in the exhaust gas,
A reducing agent injection unit arranged on the upstream side of the first reduction catalyst in the exhaust passage and capable of injecting a reducing agent into the exhaust gas.
With
The first reduction catalyst contains copper (Cu) and contains copper (Cu).
The upstream portion of the second reduction catalyst contains iron (Fe) and contains iron (Fe).
An exhaust gas purification device containing copper (Cu) on the downstream side of the second reduction catalyst. The exhaust purification apparatus according to claim 1, further comprising a first ammonia slip catalyst arranged between the first reduction catalyst and the oxidation catalyst in the exhaust passage. The exhaust purification apparatus according to claim 1 or 2, further comprising a second ammonia slip catalyst arranged on the downstream side of the second reduction catalyst in the exhaust passage.

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