Exhaust emission control system

Abstract

To appropriately eliminate nitrogen oxide in exhaust gas generated by burning synthetic fuel.SOLUTION: An exhaust emission control system S includes: an exhaust passage 15 in which exhaust gas of an engine 10 flows; and an SCR catalyst 40 that is provided in the exhaust passage 15 and reduces and eliminates nitrogen oxide in the exhaust gas. The SCR catalyst 40 includes: a first catalyst part 42 having a surface on which platinum particles with a first grain size adhere; and a second catalyst part 43 having a surface on which platinum particles with a second grain size smaller than the first grain size adhere.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an exhaust gas purification system that purifies exhaust gas from an internal combustion engine. [Background technology]

[0002] The exhaust purification system has a selective catalytic reduction (SCR) catalyst for reducing and purifying nitrogen oxides (NOx) contained in the exhaust gas of the internal combustion engine. The selective catalytic reduction catalyst uses ammonia as a reducing agent to reduce and purify the nitrogen oxides in the exhaust gas. Platinum particles of a specified particle size are attached to the surface of the selective catalytic reduction catalyst as metal particles. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-169095 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, synthetic fuels have been considered as fuels to be injected into internal combustion engines instead of conventional fossil fuels such as petroleum. When synthetic fuels are injected into internal combustion engines and burned, there is a risk that conventional reduction catalysts will not be able to adequately reduce and purify nitrogen oxides in the exhaust gas.

[0005] The present invention has been made in view of these points, and has an object to appropriately purify nitrogen oxides in exhaust gases produced when synthetic fuels are combusted. [Means for solving the problem]

[0006] In one aspect of the present invention, there is provided an exhaust purification system comprising an exhaust passage through which exhaust gas from an internal combustion engine flows, and a reduction catalyst provided in the exhaust passage for reducing and purifying nitrogen oxides in the exhaust gas, the reduction catalyst having a first catalyst portion having platinum particles of a first particle size attached to its surface, and a second catalyst portion having platinum particles of a second particle size smaller than the first particle size attached to its surface.

[0007] Moreover, the first catalyst portion and the second catalyst portion may be cylindrical, and the second catalyst portion may be located downstream of the exhaust passage as viewed from the first catalyst portion.

[0008] Moreover, the first catalyst portion and the second catalyst portion may be adjacent to each other in the exhaust passage.

[0009] In addition, the first catalyst portion may be provided along the axial direction on a central side of the reduction catalyst having a cylindrical shape, and the second catalyst portion may be provided along the axial direction on the outer side of the first catalyst portion.

[0010] The first particle size may be equal to or greater than 30 nm and less than 50 nm, and the second particle size may be equal to or greater than 10 nm and less than 30 nm.

[0011] Further, the exhaust gas may flow through the exhaust passage from the internal combustion engine into which a fuel injection unit injects fuel containing an alkane and an alkene, which are hydrocarbons.

[0012] The exhaust gas purification system may further include a urea water injection unit that injects urea water into the exhaust passage to reduce the nitrogen oxides, and an agitation unit that is provided in the exhaust passage between the urea water injection unit and the reduction catalyst and that agitates the urea water. Effect of the Invention

[0013] The present invention has an effect of being able to appropriately purify nitrogen oxides in exhaust gas produced by burning synthetic fuel. [Brief description of the drawings]

[0014] [Figure 1] 1 is a schematic diagram showing a configuration of an exhaust gas purification system S according to one embodiment. [Diagram 2] FIG. 4 is a schematic diagram for explaining an SCR catalyst 140 according to a modified example. [Diagram 3] 2 is a schematic diagram showing the internal configuration of an SCR catalyst 140. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] <Exhaust gas purification system configuration> Fig. 1 is a schematic diagram showing the configuration of an exhaust purification system S according to one embodiment. As shown in Fig. 1, the exhaust purification system S has an engine 10, an exhaust passage 15, an oxidation catalyst 20, a DPF (Diesel Particulate Filter) 25, a urea water injection unit 30, an agitation unit 35, a SCR (Selective Catalytic Reduction) catalyst 40, an ASC (Ammonia Slip Catalyst) 45, an ozone generation unit 50, an ozone injection unit 55, and a control device 100. The exhaust purification system S is mounted on a vehicle such as a truck, and purifies the exhaust gas of the engine 10.

[0016] The engine 10 is an internal combustion engine that generates power by burning and expanding a mixture of fuel and intake air. The engine 10 is, for example, a diesel engine. The engine 10 is provided with an injector, which is a fuel injection unit that injects fuel into a combustion chamber. The exhaust passage 15 is an exhaust pipe connected to the engine 10. Exhaust gas from the engine 10 flows through the exhaust passage 15.

[0017] In this embodiment, the injector of the engine 10 injects synthetic fuel, which is a carbon-neutral fuel produced from CO2 and H2, as fuel. Therefore, exhaust gas combusted in the engine 10 into which the injector injects the synthetic fuel flows into the exhaust passage 15. Carbon-neutral fuel is fuel that does not increase the CO2 concentration in the atmosphere throughout the entire process from production to use.

[0018] The synthetic fuel is a gaseous synthetic fuel such as methane, or a liquid synthetic fuel such as methanol, but the synthetic fuel of this embodiment is a fuel containing alkanes and alkenes, which are hydrocarbons (HC). Therefore, alkanes and alkenes are also contained in the exhaust gas flowing through the exhaust passage 15. Alkenes are chain hydrocarbons that contain one double bond in the molecule, such as ethylene, and the rest are all single bonds. Alkanes are also called paraffins and are widely used as fuel for diesel engines. Alkanes are chain saturated hydrocarbons such as methane. Research on synthetic fuels generated from hydrogen refined with renewable energy and CO2 is being conducted not only in Japan but also around the world. The synthetic fuel of this embodiment contains more alkanes than alkenes. However, the synthetic fuel is not limited to the above, and may contain fuels other than alkenes as long as they contain at least alkenes.

[0019] The oxidation catalyst 20 is provided in the exhaust passage 15 and oxidizes soot contained in the exhaust gas. For example, the oxidation catalyst 20 oxidizes HC to convert it into carbon dioxide (hereinafter referred to as CO2) and water. The oxidation catalyst 20 also oxidizes NO to NO2. The oxidation catalyst 20 is configured, for example, such that catalytic components and the like are supported on the surface of a ceramic support.

[0020] The DPF 25 is a filter that collects particulate matter (PM) contained in exhaust gas. The DPF 25 is provided downstream of the oxidation catalyst 20. The DPF 25 is made of a honeycomb body made of, for example, metal oxide or ceramics, and collects PM by the pores and surfaces of the partition walls.

[0021] The urea water injection unit 30 injects urea water into the exhaust passage 15. The urea water injection unit 30 is provided between the DPF 25 and the SCR catalyst 40. The urea water injected by the urea water injection unit 30 is hydrolyzed by the heat of the exhaust gas flowing through the exhaust passage 15, producing ammonia. The ammonia can reduce NOx (NO and NO2) in the exhaust gas, converting it into nitrogen and water.

[0022] The stirring unit 35 stirs the urea water injected by the urea water injection unit 30. The ammonia is easily diffused by providing the stirring unit 35. The stirring unit 35 is provided between the urea water injection unit 30 and the SCR catalyst 40 in the exhaust passage 15.

[0023] The SCR catalyst 40 is a catalyst that reduces and purifies nitrogen oxides in the exhaust gas flowing through the exhaust passage 15. The SCR catalyst 40 promotes a reduction reaction with NOx (mainly NO2) in the exhaust gas. Ammonia generated from the urea water is adsorbed onto the SCR catalyst 40. The SCR catalyst 40 reduces NOx to harmless nitrogen and water using the adsorbed ammonia, thereby reducing the emission of NOx. In order to appropriately purify NOx in exhaust gas obtained by burning synthetic fuel, the SCR catalyst 40 has a first catalyst portion 42 and a second catalyst portion 43. The first catalyst portion 42 and the second catalyst portion 43 will be described in detail later.

[0024] The ASC 45 is a catalyst that decomposes excess ammonia desorbed from the SCR catalyst 40. The ASC 45 converts ammonia into nitrogen or water, for example, thereby making it possible to suppress the emission of ammonia.

[0025] The ozone generating unit 50 generates ozone. As an example, the ozone generating unit 50 generates ozone by a silent discharge method. In the silent discharge method, an AC voltage is applied to parallel electrodes with a dielectric between them to generate ozone from oxygen. The ozone generating unit 50 supplies the generated ozone to the ozone spraying unit 55 via a supply path 52 by a pump or the like.

[0026] The ozone injection unit 55 injects ozone into the exhaust passage 15. The ozone injection unit 55 injects the ozone generated by the ozone generation unit 50. The injected ozone oxidizes the soot in the exhaust gas. In the present embodiment, the ozone injection unit 55 injects ozone to oxidize the soot when the oxidation performance of the oxidation catalyst 20 deteriorates. Also, by injecting ozone, NO is oxidized to NO2.

[0027] The concentration detection units 60 and 61 are sensors provided in the exhaust passage 15 for detecting the concentration of CO2 in the exhaust gas. The concentration detection unit 60 is located upstream of the oxidation catalyst 20 in the exhaust passage 15, and the concentration detection unit 61 is located downstream of the oxidation catalyst 20 in the exhaust passage. Since the oxidation catalyst 20 oxidizes CO, the second concentration detected by the concentration detection unit 61 located downstream of the oxidation catalyst 20 is higher than the first concentration detected by the concentration detection unit 60 located upstream of the oxidation catalyst 20.

[0028] The control device 100 controls the operation of the exhaust purification system S. For example, after the engine 10 is started, the control device 100 controls the detection of the CO2 concentration by the concentration detection units 60 and 61 and the injection of ozone by the ozone injection unit 55. When the concentration difference between the first concentration detected by the concentration detection unit 60 and the second concentration detected by the concentration detection unit 61 is lower than a predetermined value (that is, the oxidation performance of the oxidation catalyst 20 has deteriorated), the control device 100 causes the ozone injection unit 55 to inject ozone.

[0029] <Detailed Configuration of SCR Catalyst> As shown in FIG. 1, the SCR catalyst 40 has a first catalyst part 42 and a second catalyst part 43. The first catalyst part 42 and the second catalyst part 43, together with the ASC 45, are arranged in a row in the case 41.

[0030] The first catalyst part 42 has a cylindrical shape, specifically a honeycomb structure. The first catalyst part 42 has a structure in which a catalyst coat layer is formed on a carrier as a base material. As the carrier, for example, zeolite, SiO2, aluminum oxide, etc. are used. The catalyst coat layer supports noble metals and the like.

[0031] The precious metal used in the catalyst coating layer is a platinum group element, and here platinum and rhodium are given as examples. However, the precious metal is not limited to the above, and other platinum group elements (e.g., palladium and iridium) may be used as the catalyst precious metal.

[0032] Platinum particles of a first particle size are attached to the catalyst coating layer, which is the surface of the first catalyst section 42. Here, the first particle size is 30 nm or more and less than 50 nm. Preferably, the first particle size is 35 nm or more and less than 45 nm. The platinum particles of the first particle size are uniformly dispersed in the catalyst coating layer. Note that the "first particle size" does not require that all the platinum particles attached to the catalyst coating layer of the first catalyst section 42 have the same particle size. For example, a statistical value such as a median or average value in the distribution of platinum particles attached to the catalyst coating layer may be included in the range shown above. Or, for example, the maximum value and the minimum value in the distribution of platinum particles attached to the catalyst coating layer may be included in the above-mentioned range. In the case where the distribution of platinum particles attached to the catalyst coating layer is a normal distribution, the range of the average value ±3σ (σ: standard deviation) may be included in the above-mentioned range.

[0033] The second catalyst section 43 has a shape similar to that of the first catalyst section 42, and is cylindrical. The size of the second catalyst section 43 is the same as that of the first catalyst section 42. The second catalyst section 43 is located downstream of the exhaust passage 15 as viewed from the first catalyst section 42. That is, the exhaust gas passes through the second catalyst section 43 after passing through the first catalyst section 42. Here, the second catalyst section 43 is adjacent to the first catalyst section 42 in the exhaust passage 15 (specifically, in the case 41). Also, in the case 41, the distance between the second catalyst section 43 and the first catalyst section 42 is smaller than the distance between the second catalyst section 43 and the ASC 45. However, this is not limited to the above, and the second catalyst section 43 may be separated from the first catalyst section 42 in the case 41.

[0034] The second catalyst section 43, like the first catalyst section 42, has a configuration in which a catalyst coating layer is formed on the surface of a carrier, which is a base material. The configurations of the carrier and catalyst coating layer of the second catalyst section 43 are similar to the configurations of the carrier and catalyst coating layer of the first catalyst section 42. Therefore, detailed explanations of the carrier and catalyst coating layer of the second catalyst section 43 will be omitted. The difference between the second catalyst section 43 and the first catalyst section 42 is the particle size of the platinum particles supported on the catalyst coating layer.

[0035] Platinum particles having a second particle size smaller than the first particle size are attached to the catalyst coating layer, which is the surface of the second catalyst section 43. Here, the second particle size is 10 nm or more and less than 30 nm. Preferably, the second particle size is 15 nm or more and less than 25 nm. The platinum particles having the first particle size are attached to the catalyst coating layer at a higher density than the platinum particles having the second particle size. Note that the "second particle size" does not require that all the platinum particles attached to the catalyst coating layer of the second catalyst section 43 have the same particle size. For example, a statistical value such as a median or average value in the distribution of platinum particles attached to the catalyst coating layer may be included in the range shown above. Or, for example, the maximum value and the minimum value in the distribution of platinum particles attached to the catalyst coating layer may be included in the above-mentioned range. In the case where the distribution of platinum particles attached to the catalyst coating layer is a normal distribution, the range of the average value ±3σ (σ: standard deviation) may be included in the above-mentioned range.

[0036] By providing the first catalytic section 42 and the second catalytic section 43, it is possible to appropriately purify NOx in the exhaust gas resulting from the combustion of the synthetic fuel, as described below. In the following description, it is assumed that the synthetic fuel contains an alkene and an alkane.

[0037] Alkanes are less likely to be adsorbed by platinum particles having a smaller particle size than alkenes, and therefore the efficiency of NOx purification by the second catalytic section 43 is low. In contrast, when the first catalytic section 42 is provided, even if alkanes are contained in the exhaust gas, the alkanes are more likely to be adsorbed by platinum particles having a larger particle size, and therefore the first catalytic section 42 is more likely to reduce and purify NOx.

[0038] Alkenes contain double bonds in their molecules and are therefore easily adsorbed by platinum particles. In the second catalytic section 43, platinum particles with small particle diameters are highly dispersed, so that alkenes are easily adsorbed by the platinum particles of the second catalytic section 43 and are activated and oxidized, thereby improving the purification efficiency of NOx in the exhaust gas. When only the first catalytic section 42 is provided, the amount of alkenes adsorbed by the first catalytic section 42 is less than the amount of alkenes adsorbed by the second catalytic section 43, and the purification efficiency of NOx in the exhaust gas decreases.

[0039] In this embodiment, since the first catalytic section 42 is located upstream of the second catalytic section 43, alkanes contained in large amounts in the exhaust gas are more likely to be adsorbed by the platinum particles of the first catalytic section 42, thereby accelerating the purification of NOx in the exhaust gas.

[0040] In the above, the first catalyst portion 42 is located upstream of the exhaust passage 15, and the second catalyst portion 43 is located downstream of the exhaust passage 15. However, this is not limited to this. For example, the first catalyst portion 42 may be located downstream of the exhaust passage 15, and the second catalyst portion 43 may be located upstream of the exhaust passage 15.

[0041] (Modification) Fig. 2 is a schematic diagram for explaining the SCR catalyst 140 according to a modified example. Fig. 3 is a schematic diagram showing the internal configuration of the SCR catalyst 140.

[0042] In the SCR catalyst 40 of the above-described embodiment, the first catalyst section 42 and the second catalyst section 43 are arranged in a row as shown in FIG. 1. However, in the SCR catalyst 140 of the modified example, the first catalyst section 142 and the second catalyst section 143 are configured in a double layer.

[0043] 2 and 3, the first catalyst portion 142 is provided along the axial direction on the center side of the cylindrical SCR catalyst 140. The first catalyst portion 142 has a similar configuration to the first catalyst portion 42 of the SCR catalyst 40, and platinum particles having a first particle size are attached to the catalyst coating layer of the first catalyst portion 142. The first particle size is equal to or greater than 30 nm and less than 50 nm. Preferably, the first particle size is equal to or greater than 35 nm and less than 45 nm.

[0044] The second catalytic portion 143 is provided on the outside of the first catalytic portion 142 along the axial direction. The axial length of the second catalytic portion 143 is the same as the axial length of the first catalytic portion 142. The second catalytic portion 143 covers the first catalytic portion 142. The second catalytic portion 143 has a configuration similar to that of the second catalytic portion 43 of the SCR catalyst 40, and platinum particles having a second particle size smaller than the first particle size are attached to the catalyst coating layer of the second catalytic portion 143. The second particle size is 10 nm or more and less than 30 nm. Preferably, the second particle size is 15 nm or more and less than 25 nm.

[0045] Even in the modified example, the first catalytic portion 142 makes it easier for alkanes in the synthetic fuel to be adsorbed by platinum particles with a large particle size, making it easier to reduce NOx. Moreover, the second catalytic portion 143 makes it easier for alkenes in the synthetic fuel to be adsorbed by platinum particles with a small particle size, making it easier to reduce NOx. Furthermore, exhaust gas containing alkanes is more likely to pass through the center side of the SCR catalyst 140 than the outside, so by positioning the first catalytic portion 142 on the center side of the SCR catalyst 140, alkanes are more likely to adhere to the first catalytic portion 142, improving the purification efficiency of NOx.

[0046] <Effects of this embodiment> In the above-described embodiment, the SCR catalyst 40 provided in the exhaust passage 15 has a first catalyst portion 42 having platinum particles of a first particle size attached to its surface, and a second catalyst portion 43 having platinum particles of a second particle size smaller than the first particle size attached to its surface. This allows the first catalyst portion 42 and the second catalyst portion 43 to appropriately purify NOx in the exhaust gas obtained by burning a synthetic fuel (for example, a synthetic fuel containing an alkane and an alkene).

[0047] Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. For example, all or part of the device can be configured by distributing or integrating functionally or physically in any unit. In addition, new embodiments resulting from any combination of multiple embodiments are also included in the embodiments of the present invention. The effect of the new embodiment resulting from the combination combines the effect of the original embodiment. [Explanation of symbols]

[0048] 10 Engine 15 Exhaust passage 30 Urea water injection part 35 Stirring section 40 SCR catalyst 42 1st catalyst section 43 Second catalyst section 140 SCR catalyst 142 1st catalyst section 143 Second catalyst section S Exhaust purification system

Claims

1. an exhaust passage through which exhaust gas from the internal combustion engine flows; a reduction catalyst provided in the exhaust passage for reducing and purifying nitrogen oxides in the exhaust gas; Equipped with The reduction catalyst is a first catalyst portion having platinum particles of a first particle size attached to a surface thereof; A second catalyst portion having platinum particles attached to a surface thereof, the platinum particles having a second particle size smaller than the first particle size; An exhaust purification system comprising:

2. The first catalyst portion and the second catalyst portion have a cylindrical shape, The second catalyst portion is located downstream of the exhaust passage as viewed from the first catalyst portion.

2. The exhaust gas purification system according to claim 1.

3. The first catalyst portion and the second catalyst portion are adjacent to each other in the exhaust passage.

3. The exhaust gas purification system according to claim 2.

4. The first catalyst portion is provided along the axial direction of a center side of the cylindrical reduction catalyst, The second catalyst portion is provided on the outside of the first catalyst portion along the axial direction.

2. The exhaust gas purification system according to claim 1.

5. The first particle size is equal to or greater than 30 nm and less than 50 nm, The second particle size is equal to or greater than 10 nm and less than 30 nm.

2. The exhaust gas purification system according to claim 1.

6. In the exhaust passage, the exhaust gas flows from the internal combustion engine into which a fuel injection unit injects fuel containing an alkane and an alkene, which are hydrocarbons.

2. The exhaust gas purification system according to claim 1.

7. a urea water injection unit that injects urea water into the exhaust passage to reduce the nitrogen oxides; a stirring unit that is provided in the exhaust passage between the urea water injection unit and the reduction catalyst and stirs the urea water.

2. The exhaust gas purification system according to claim 1.

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