Exhaust gas purification device

Abstract

The present invention relates to an exhaust gas purification device and aims to improve the purification rate of hydrocarbons. The exhaust gas purification device (200) is provided with a three-way catalyst (220), which includes: a downstream catalyst layer (240) arranged in an exhaust pipe, including a precious metal material containing any one or more of Pd, Rh and Pt and an OSC material containing at least cerium dioxide; an upstream catalyst layer (230) arranged in the exhaust pipe on the engine side than the downstream catalyst layer (240), including a precious metal material and an OSC material, and the content of cerium dioxide is less than that of the downstream catalyst layer (240).

Description

Technical Field

[0001] The present invention relates to an exhaust gas purification device equipped with a three-way catalyst. Background Art

[0002] In order to remove hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx) contained in exhaust gas, a three-way catalyst is provided in the exhaust pipe of a vehicle (e.g., Patent Document 1). The three-way catalyst oxidizes hydrocarbons into water and carbon dioxide (CO2), oxidizes carbon monoxide into carbon dioxide, and reduces nitrogen oxides into nitrogen (N2).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2010-253447 Summary of the invention

[0006] Problems to be solved by the invention

[0007] It is desired to develop a technology capable of improving the purification rate of hydrocarbons among the hydrocarbons, carbon monoxide and nitrogen oxides.

[0008] The present invention has been made in view of such a problem, and an object of the present invention is to propose an exhaust gas purification device capable of improving the purification rate of hydrocarbons.

[0009] Technical solutions to solve problems

[0010] In order to solve the above-mentioned problems, the exhaust gas purification device of the present invention is equipped with a three-way catalyst, which includes: a downstream catalyst layer, which is arranged in the exhaust pipe, including a precious metal material containing any one or more of Pd, Rh and Pt and an OSC material containing at least cerium dioxide; an upstream catalyst layer, which is arranged in the exhaust pipe on the engine side than the downstream catalyst layer, including precious metal materials and OSC materials, and the content of cerium dioxide is less than that of the downstream catalyst layer.

[0011] In addition, the ceria content in the upstream catalyst layer may be 0.33 times or more and 0.67 times or less of that in the downstream catalyst layer.

[0012] Furthermore, the exhaust gas purification device may include a NOx storage reduction catalyst provided on the muffler side of the downstream catalyst layer in the exhaust pipe, and a content of cerium oxide in the three-way catalyst may exceed 0 g / L and be 10 g / L or less.

[0013] Furthermore, the upstream catalyst layer may have a higher loading density of the precious metal material than the downstream catalyst layer.

[0014] In addition, the upstream catalyst layer may include: an upstream lower layer, which is stacked on the carrier and contains at least Rh; an upstream upper layer, which is stacked on the upstream lower layer and contains at least Pd, and the downstream catalyst layer may include: a downstream lower layer, which is stacked on the carrier and contains at least Rh; and a downstream upper layer, which is stacked on the downstream lower layer and contains at least Pd.

[0015] Alternatively, the Pd loading density of the upstream upper layer may be more than 1 times and less than 3 times that of the downstream upper layer.

[0016] In addition, the loading density of Rh in the upstream lower layer may be more than 1 times and less than 3 times that of the downstream lower layer.

[0017] Effects of the Invention

[0018] According to the present invention, the purification rate of hydrocarbons can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a diagram for explaining an engine system according to an embodiment.

[0020] 2(a)-(b) are diagrams for explaining the structure of the exhaust gas purification device according to the embodiment.

[0021] 3(a)-(b) are diagrams illustrating the content ratio of cerium dioxide.

[0022] Figure 4 It is a diagram for explaining an exhaust gas purification device according to a modified example.

[0023] Figure 5 This is a diagram for explaining the amount of ceria contained in the three-way catalyst and the carbon monoxide passing rate.

[0024] Explanation of symbols

[0025] 200: Exhaust gas purification device

[0026] 220: Three-way catalyst

[0027] 230: Upstream catalyst layer

[0028] 232: Upstream Lower Layer

[0029] 234: Upstream

[0030] 240: Downstream catalyst layer

[0031] 242: Downstream lower layer

[0032] 244: Downstream upper layer

[0033] 300: Exhaust gas purification device

[0034] 320: NOx storage reduction catalyst DETAILED DESCRIPTION

[0035] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific values ​​shown in the embodiments are only examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In addition, in this specification and the accompanying drawings, elements having substantially the same functions and structures are marked with the same symbols to omit repeated descriptions, and elements that are not directly related to the present invention are omitted from the drawings.

[0036] [Engine system 100]

[0037] Figure 1 2 is a diagram for explaining the engine system 100 of the present embodiment. Figure 1 In the figure, the dashed arrows indicate the flow of signals.

[0038] like Figure 1 As shown, a microcomputer, namely, an ECU (Engine Control Unit) 10, is provided in an engine system 100 mounted on a vehicle. The microcomputer includes a central processing unit (CPU), a ROM storing programs, a RAM as a work area, etc. The entire engine E is uniformly controlled by the ECU 10. However, the following describes in detail the structure or processing related to the present embodiment, and the description of the structure or processing not related to the present embodiment is omitted.

[0039] The engine E constituting the engine system 100 includes a cylinder block 102, a crankcase 104, a cylinder head 106, and an oil pan 110. The crankcase 104 is formed integrally with the cylinder block 102. The cylinder head 106 is joined to the cylinder block 102 on the side opposite to the crankcase 104. The oil pan 110 is joined to the crankcase 104 on the side opposite to the cylinder block 102.

[0040] A plurality of cylinder barrels 112 are formed in the cylinder block 102. In the plurality of cylinder barrels 112, pistons 114 are slidably supported by connecting rods 116. In the engine E, a space surrounded by the cylinder barrels 112, the cylinder head 106, and the top surface of the piston 114 forms a combustion chamber 118.

[0041] In the engine E, a space surrounded by the crankcase 104 and the oil pan 110 forms a crank chamber 120 . A crankshaft 122 is rotatably supported in the crank chamber 120 , and a piston 114 is connected to the crankshaft 122 via a connecting rod 116 .

[0042] Intake port 124 and exhaust port 126 are provided in cylinder head 106 so as to communicate with combustion chamber 118. The front end (beam portion) of intake valve 128 is located between intake port 124 and combustion chamber 118, and the front end (beam portion) of exhaust valve 130 is located between exhaust port 126 and combustion chamber 118.

[0043] In addition, an intake cam 134a, a rocker arm 134b, an exhaust cam 136a, and a rocker arm 136b are provided in a space surrounded by the cylinder head 106 and a cylinder head cover (not shown). The intake cam 134a fixed to the intake camshaft contacts the intake valve 128 via the rocker arm 134b. The intake valve 128 moves axially with the rotation of the intake camshaft to open and close the intake port 124 and the combustion chamber 118. The exhaust cam 136a fixed to the exhaust camshaft contacts the exhaust valve 130 via the rocker arm 136b. The exhaust valve 130 moves axially with the rotation of the exhaust camshaft to open and close the exhaust port 126 and the combustion chamber 118.

[0044] An intake pipe 140 including an intake manifold is connected to the upstream side of the intake port 124. A throttle valve 142 and an air filter 144 are provided in the intake pipe 140. The throttle valve 142 is opened and closed by an actuator according to the opening of an accelerator (not shown). The air purified by the air filter 144 is sucked into the combustion chamber 118 through the intake pipe 140 and the intake port 124.

[0045] In the cylinder head 106, an injector 150 (fuel injection unit) is provided so that the fuel injection port opens to the combustion chamber 118, and a spark plug 152 is provided so that the tip is located in the combustion chamber 118. The fuel injected from the injector 150 into the combustion chamber 118 is mixed with the air supplied to the combustion chamber 118 from the intake port 124 to form a mixed gas. Then, the spark plug 152 is ignited at a predetermined timing, and the mixed gas generated in the combustion chamber 118 is combusted. Due to this combustion, the piston 114 reciprocates, and this reciprocating motion is converted into the rotational motion of the crankshaft 122 through the connecting rod 116.

[0046] An exhaust pipe 160 including an exhaust manifold is connected to the downstream side of the exhaust port 126. An exhaust gas purification device 200 is provided in the exhaust pipe 160. The exhaust gas purification device 200 purifies the exhaust gas discharged from the exhaust port 126. The specific structure of the exhaust gas purification device 200 will be described in detail later. The exhaust gas purified by the exhaust gas purification device 200 is discharged to the outside through the muffler 164.

[0047] Furthermore, the engine system 100 is provided with an intake air amount sensor 180 , a throttle opening sensor 182 , a crank angle sensor 184 , and an accelerator opening sensor 186 .

[0048] The intake air amount sensor 180 detects the amount of intake air flowing into the engine E. The throttle opening sensor 182 detects the opening of the throttle valve 142. The crank angle sensor 184 detects the crank angle of the crankshaft 122. The accelerator opening sensor 186 detects the opening of an accelerator (not shown).

[0049] The intake air amount sensor 180 , the throttle opening sensor 182 , the crank angle sensor 184 , and the accelerator opening sensor 186 are connected to the ECU 10 , and output signals indicating detection values ​​to the ECU 10 .

[0050] The ECU 10 acquires signals output from the intake air amount sensor 180 , the throttle opening sensor 182 , the crank angle sensor 184 , and the accelerator opening sensor 186 , and controls the engine E. When controlling the engine E, the ECU 10 functions as a signal acquisition unit 12 and a drive control unit 14 .

[0051] The signal acquisition unit 12 acquires signals indicating values ​​detected by the intake air amount sensor 180, the throttle opening sensor 182, the crank angle sensor 184, and the accelerator opening sensor 186. In addition, the signal acquisition unit 12 derives the rotation speed of the engine E (rotation speed of the crankshaft) based on the signal indicating the crank angle obtained from the crank angle sensor 184. In addition, the signal acquisition unit 12 derives the load of the engine E (engine load) based on the signal indicating the intake air amount obtained from the intake air amount sensor 180. As a technique for obtaining the engine load from the intake air amount, various existing techniques can be used, and thus the description thereof is omitted here.

[0052] The drive control unit 14 controls a throttle valve actuator (not shown), the injector 150 , and the spark plug 152 based on the signal acquired by the signal acquisition unit 12 .

[0053] [Exhaust gas purification device 200]

[0054] Fig. 2 (a)-(b) is a diagram illustrating the structure of the exhaust gas purification device 200 of the present embodiment. Fig. 2 (a) is a stereoscopic view of the exhaust gas purification device 200. Fig. 2 (b) is a diagram illustrating the concept of the three-way catalyst 220 in the exhaust gas purification device 200. In addition, in Fig. 2 (a) and Fig. 2 (b), the hollow arrows represent the flow of the exhaust gas. In addition, in Fig. 2 (a) and Fig. 2 (b) of the present embodiment, the X-axis, Y-axis (flow direction of the exhaust gas, extension direction of the exhaust pipe 160) and Z-axis that intersect vertically are defined as shown in the figure.

[0055] As shown in Fig. 2(a), the exhaust gas purification device 200 includes a carrier 210 having a honeycomb structure having a plurality of cells 212 and a three-way catalyst 220 mounted on the carrier 210. The three-way catalyst 220 purifies (removes) hydrocarbons, carbon monoxide, and nitrogen oxides contained in the exhaust gas.

[0056] As shown in FIG. 2( b ), the three-way catalyst 220 includes an upstream catalyst layer 230 and a downstream catalyst layer 240 .

[0057] The upstream catalyst layer 230 includes a noble metal material, an OSC material, and alumina (Al2O3). The noble metal material includes palladium (Pd) and rhodium (Rh). The OSC material includes a cerium oxide (cerium oxide (IV), CeO2)-zirconia (zirconium oxide, ZrO2) composite (Ceria (ceryum (IV), CeO2)-zirconia (zirconia dioxide, ZrO2)). Ceria has oxygen storage capacity (OSC: Oxygen Storage Capacity).

[0058] In the present embodiment, the upstream catalyst layer 230 includes an upstream lower layer 232 and an upstream upper layer 234. The upstream lower layer 232 is stacked on the support 210. The upstream lower layer 232 contains at least Rh. The upstream upper layer 234 is stacked on the upstream lower layer 232. The upstream upper layer 234 contains at least Pd.

[0059] The downstream catalyst layer 240 is disposed on the downstream side of the exhaust gas flow direction in the exhaust pipe 160 relative to the upstream catalyst layer 230. In other words, the downstream catalyst layer 240 is disposed on the muffler 164 side relative to the upstream catalyst layer 230, or the upstream catalyst layer 230 is disposed on the engine E side relative to the downstream catalyst layer 240. The downstream catalyst layer 240 includes a precious metal material, an OSC material, and alumina.

[0060] In the present embodiment, the downstream catalyst layer 240 includes a downstream lower layer 242 and a downstream upper layer 244. The downstream lower layer 242 is stacked on the support 210. The downstream lower layer 242 contains at least Rh. The downstream upper layer 244 is stacked on the downstream lower layer 242. The downstream upper layer 244 contains at least Pd.

[0061] As described above, in the three-way catalyst 220, Pd is contained in the upstream upper layer 234 and the downstream upper layer 244. Pd is more superior to Rh in purifying hydrocarbons. Therefore, Pd is configured in the upstream upper layer 234 and the downstream upper layer 244, which are first contacted by the exhaust gas. As a result, the oxidation reaction of hydrocarbons can be started with the upstream upper layer 234 and the downstream upper layer 244 as the starting point. Moreover, the oxidation reaction started in the upstream upper layer 234 and the downstream upper layer 244 can be chained to the upstream lower layer 232 and the downstream lower layer 242. Therefore, the three-way catalyst 220 can efficiently purify the hydrocarbons contained in the exhaust gas.

[0062] In addition, the upstream lower layer 232 and the downstream lower layer 242 contain Rh. As a result, the three-way catalyst 220 can efficiently purify nitrogen oxides contained in the exhaust gas. In addition, since Rh has a higher melting point than Pd, it is not easy to be thermally aged. Therefore, since Rh is included in the three-way catalyst 220, the thermal aging of the three-way catalyst 220 can be suppressed.

[0063] The length La of the upstream catalyst layer 230 is not less than 30% and not more than 70% of the total length L of the carrier 210. The length La of the upstream catalyst layer 230 is the length starting from the upstream end 210a of the carrier 210. The length Lb of the downstream catalyst layer 240 is not less than 30% and not more than 70% of the total length L of the carrier 210. The length Lb of the downstream catalyst layer 240 is the length starting from the downstream end 210b of the carrier 210. The length La of the upstream catalyst layer 230 and the length Lb of the downstream catalyst layer 240 are, for example, 50% of the total length L.

[0064] If the length La of the upstream catalyst layer 230 and the length Lb of the downstream catalyst layer 240 are less than 30% of the total length L, the portion where the upstream catalyst layer 230 and the downstream catalyst layer 240 are not stacked in the center of the carrier 210 becomes longer. As a result, the exhaust gas purification rate achieved by the three-way catalyst 220 decreases. On the other hand, if the length La of the upstream catalyst layer 230 and the length Lb of the downstream catalyst layer 240 exceed 70% of the total length L, the portion where the upstream catalyst layer 230 and the downstream catalyst layer 240 overlap, that is, the portion where the thickness of the three-way catalyst 220 increases in the center of the carrier 210, becomes longer. In the portion where the thickness of the three-way catalyst 220 increases, the exhaust gas is difficult to flow because the flow path is narrow, and the output of the engine E may decrease.

[0065] Therefore, the length La of the upstream catalyst layer 230 is set to be greater than 30% and less than 70% of the total length L of the carrier 210, and the length Lb of the downstream catalyst layer 240 is set to be greater than 30% and less than 70% of the total length L of the carrier 210. Thus, the exhaust gas purification device 200 can improve the purification rate of the exhaust gas while preventing the output of the engine E from being reduced.

[0066] Next, the relationship between the loading density of the precious metal material and the content of ceria in the upstream catalyst layer 230 and the downstream catalyst layer 240 will be described.

[0067] [Precious metal material loading density]

[0068] The upstream catalyst layer 230 has a higher loading density (g / L) of the precious metal material than the downstream catalyst layer 240. Thus, the exhaust gas purification device 200 can purify the exhaust gas at a lower temperature.

[0069] In this embodiment, the Pd loading density of the upstream upper layer 234 is more than 1 time and less than 3 times that of the downstream upper layer 244. In addition, the Rh loading density of the upstream lower layer 232 is more than 1 time and less than 3 times that of the downstream lower layer 242.

[0070] If the Pd loading density of the upstream upper layer 234 is three times or more than that of the downstream upper layer 244, the upstream upper layer 234 is easily sintered and thermally aged. Therefore, as described above, by setting the Pd loading density of the upstream upper layer 234 to less than three times that of the downstream upper layer 244, the hydrocarbon purification rate can be improved while suppressing thermal aging of the three-way catalyst 220.

[0071] Similarly, if the loading density of Rh in the upstream lower layer 232 is three times or more than that in the downstream lower layer 242, the upstream lower layer 232 is easily sintered and thermally aged. Therefore, as described above, by setting the loading density of Rh in the upstream lower layer 232 to less than three times that in the downstream lower layer 242, the hydrocarbon purification rate can be improved while suppressing thermal aging of the three-way catalyst 220.

[0072] [Content of cerium dioxide]

[0073] The downstream catalyst layer 240 has a higher content of ceria than the upstream catalyst layer 230. In the three-way catalyst 220, hydrocarbons and carbon monoxide are oxidized, but if ceria is included in the three-way catalyst 220, carbon monoxide is selectively oxidized compared to hydrocarbons. Therefore, the content of ceria in the upstream catalyst layer 230, which mainly performs the oxidation reaction of hydrocarbons, can be made smaller than that in the downstream catalyst layer 240. As a result, the exhaust gas purification device 200 can improve the purification rate of hydrocarbons while maintaining the purification rate of carbon monoxide.

[0074] In the present embodiment, the cerium dioxide content of the upstream catalyst layer 230 is greater than 0.33 times and less than 0.67 times that of the downstream catalyst layer 240. Figures 3(a)-(b) are diagrams illustrating the cerium dioxide content ratio. Figure 3(a) is a diagram illustrating the purification window W. Figure 3(b) is a diagram illustrating the purification rate of hydrocarbons and the purification window W for the cerium dioxide content ratio. In addition, in Figure 3(a), the solid line represents the purification rate of nitrogen oxides, and the dotted line represents the purification rate of hydrocarbons. In addition, in Figure 3(b), the white squares represent the purification rate of hydrocarbons, and the black circles represent the width of the purification window W.

[0075] As shown in FIG. 3( a ), the nitrogen oxide purification rate [%] is constant up to a predetermined air-fuel ratio (A / F), but if the predetermined air-fuel ratio is exceeded, the nitrogen oxide purification rate [%] decreases as the air-fuel ratio increases. On the other hand, the hydrocarbon purification rate [%] increases as the air-fuel ratio increases up to a predetermined air-fuel ratio, and becomes constant when the predetermined air-fuel ratio is reached or exceeded. The purification window W is the range of air-fuel ratios in which the nitrogen oxide purification rate and the hydrocarbon purification rate become equal to or higher than the predetermined purification rate PR.

[0076] As shown in FIG. 3( b), when the ratio of ceria in the upstream catalyst layer 230 to the downstream catalyst layer 240 (the content of ceria in the upstream catalyst layer 230 / the content of ceria in the downstream catalyst layer 240) is greater than 0 and less than 0.33, the width (range) of the purification window W increases as the ceria ratio increases. In addition, if the ceria ratio is greater than 0.33, the width of the purification window W is constant regardless of the ceria ratio. That is, if the ceria ratio is less than 0.33, the purification window W becomes narrower, and therefore, in the case of fluctuations in the air-fuel ratio, the purification rate of hydrocarbons decreases, or the purification rate of nitrogen oxides decreases.

[0077] On the other hand, when the ceria ratio is greater than 0 and less than 0.67, the hydrocarbon purification rate is constant regardless of the ceria ratio. In addition, when the ceria ratio exceeds 0.67, the hydrocarbon purification rate decreases as the ceria ratio increases.

[0078] Therefore, by setting the ratio of ceria to 0.33 or more and 0.67 or less, three-way catalyst 220 can improve the purification rate of hydrocarbons and expand the width of purification window W. Thus, even if the air-fuel ratio fluctuates, three-way catalyst 220 can improve the purification rate of hydrocarbons and the purification rate of nitrogen oxides.

[0079] As described above, the exhaust gas purification device 200 of the present embodiment can improve the purification rate of hydrocarbons. In other words, even if the temperature of the exhaust gas drops, the exhaust gas purification device 200 can maintain the purification rate of hydrocarbons at the same level as before.

[0080] [Modifications]

[0081] In the above-mentioned embodiment, the exhaust gas purification device 200 does not include a NOx storage reduction catalyst. However, the exhaust gas purification device may include a NOx storage reduction catalyst.

[0082] Figure 4 2 is a diagram for explaining an exhaust gas purification device 300 according to a modified example. Figure 4 As shown, the exhaust gas purification device 300 includes a three-way catalyst 220 and a NOx storage reduction catalyst 320. In addition, the same reference numerals are attached to the components substantially identical to those of the above-mentioned exhaust gas purification device 200, and the description thereof is omitted.

[0083] The NOx storage reduction catalyst 320 is disposed in the exhaust pipe 160 on the muffler 164 side relative to the three-way catalyst 220 (downstream catalyst layer 240). That is, the NOx storage reduction catalyst 320 is disposed on the downstream side of the three-way catalyst 220 in the exhaust pipe 160. In the case of lean air-fuel ratio greater than the theoretical air-fuel ratio, the NOx storage reduction catalyst 320 oxidizes nitrogen monoxide (NO) into nitrogen dioxide (NO2) and stores nitrogen dioxide. In the case of rich air-fuel ratio less than the theoretical air-fuel ratio, the NOx storage reduction catalyst 320 decomposes the stored nitrogen dioxide and reduces it into nitrogen monoxide, causing the nitrogen monoxide to react with hydrocarbons and carbon monoxide, thereby decomposing and removing hydrocarbons, carbon monoxide, and nitrogen monoxide.

[0084] That is, in rich conditions, the NOx storage reduction catalyst 320 uses carbon monoxide to purify nitrogen monoxide (nitrogen oxides). Here, if the amount of ceria contained in the three-way catalyst 220 is large, the purification rate of carbon monoxide increases, and the amount of carbon monoxide introduced into the NOx storage reduction catalyst 320 decreases. Therefore, in rich conditions, the purification rate of nitrogen oxides in the NOx storage reduction catalyst 320 decreases.

[0085] Figure 5 This is a diagram for explaining the amount of ceria contained in the three-way catalyst 220 and the rate of passage of carbon monoxide. Figure 5 In FIG. 1 , the vertical axis represents the ratio of carbon monoxide passing through (slipping through) the three-way catalyst 220 (the passing rate of carbon monoxide). Figure 5 In FIG. 1 , the horizontal axis represents the content [g / L] of ceria contained in the three-way catalyst 220 per unit volume.

[0086] like Figure 5As shown, if the content of ceria contained in the three-way catalyst 220 exceeds 0 g / L and is 10 g / L or less, the carbon monoxide passing rate is almost unchanged. However, if the content of ceria contained in the three-way catalyst 220 exceeds 10 g / L, the carbon monoxide passing rate decreases as the amount of ceria increases.

[0087] Therefore, the content of ceria in the three-way catalyst 220 of the modified example is set to be more than 0 g / L and less than 10 g / L. Thus, the three-way catalyst 220 can introduce a predetermined amount of carbon monoxide into the NOx storage reduction catalyst 320. Therefore, the exhaust gas purification device 300 can improve the purification performance of the NOx storage reduction catalyst 320.

[0088] The preferred embodiment of the present invention is described above with reference to the accompanying drawings, but it is needless to say that the present invention is not limited to this embodiment. Those skilled in the art understand that various changes or modifications can be thought of within the scope of the claims, which naturally belong to the technical scope of the present invention.

[0089] In addition, in the above-mentioned embodiment and modification, the case where the noble metal material includes Pd and Rh is given as an example. However, the noble metal material may include any one or more of Pd, Rh and Pt (platinum).

[0090] In addition, in the above-mentioned embodiment and modification, the case where the upstream lower layer 232 contains Rh and the upstream upper layer 234 contains Pd is given as an example. However, the upstream lower layer 232 may contain Pd and the upstream upper layer 234 may contain Rh. Similarly, the downstream lower layer 242 may contain Pd and the downstream upper layer 244 may contain Rh.

[0091] In addition, in the above-mentioned embodiment and modification, the case where the OSC material includes the ceria-zirconia composite is given as an example. However, the OSC material may include at least ceria.

[0092] Industrial Applicability

[0093] The present invention can be used in an exhaust gas purification device equipped with a three-way catalyst.

Claims

1. An exhaust gas purification device comprising a three-way catalyst and a NOx storage reduction catalyst, The three-way catalyst comprises: A downstream catalyst layer, which is disposed in the exhaust pipe, comprises a noble metal material and an OSC material, wherein the noble metal material comprises Pd and Rh, and the OSC material comprises at least ceria; and an upstream catalyst layer disposed in the exhaust pipe on the engine side relative to the downstream catalyst layer, the upstream catalyst layer comprising the noble metal material and the OSC material and having a lower content of cerium dioxide than the downstream catalyst layer, in, The NOx storage reduction catalyst is disposed on the muffler side of the downstream catalyst layer in the exhaust pipe. The cerium oxide content of the upstream catalyst layer is 0.33 times or more and 0.67 times or less of that of the downstream catalyst layer, and The content of cerium dioxide in the three-way catalyst exceeds 0 g / L and is 10 g / L or less, The upstream catalyst layer comprises: an upstream lower layer, which is stacked on the carrier and contains at least Rh; and an upstream upper layer, which is stacked on the upstream lower layer and contains at least Pd, and the upstream catalyst layer has a length of not less than 30% and not more than 70% of the total length of the carrier, starting from the upstream end of the carrier, The downstream catalyst layer comprises: a downstream lower layer, which is stacked on the carrier and contains at least Rh; and a downstream upper layer, which is stacked on the downstream lower layer and contains at least Pd, and the downstream catalyst layer has a length of not less than 30% and not more than 70% of the total length of the carrier, starting from the downstream end of the carrier. The Pd loading density of the upstream upper layer is more than 1 times and less than 3 times of that of the downstream upper layer, The loading density of the Rh in the upstream lower layer is more than 1 times and less than 3 times that of the downstream lower layer.

2. The exhaust gas purification device according to claim 1, wherein: The upstream catalyst layer has a higher loading density of the precious metal material than the downstream catalyst layer.

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