Catalytic converter

Abstract

The present invention provides a catalytic converter capable of effectively utilizing the amount of noble metal used in a catalyst and improving the effect of reducing emissions. A catalytic converter (1) is provided with an electrically heated catalyst (2) disposed on the upstream side in the flow direction of exhaust gas, and a non-electrically heated catalyst (3) disposed on the downstream side with respect to the electrically heated catalyst (2). The electrically heated catalyst (2) has, as a catalyst coating layer, only an Rh catalyst coating layer (22) formed on the upstream-side substrate (21). The non-electrically heated catalyst (3) has, as catalyst coating layers, a second Pd catalyst coating layer (322) and an Rh catalyst coating layer (33) that are formed over the entire length of the downstream base material (31), and first and third Pd catalyst coating layers (321, 323) that are disposed in a range of 35% or less from the upstream end surface (31a) of the non-electrically heated catalyst (3) in the flow direction of the exhaust gas. The content of the Pd catalyst in the second Pd catalyst coating layer 322 is less than the content of the Pd catalyst in the first and third Pd catalyst coating layers 321, 323.

Description

Technical Field

[0001] This invention relates to a catalytic converter, and more particularly to a catalytic converter having an electrically heated catalyst. Background Technology

[0002] Conventionally, the technology described in Patent Document 1 is an example of such a technical field. The electrically heated catalyst described in Patent Document 1 includes an exhaust gas purification catalyst disposed upstream of the exhaust gas flow direction and a microwave generator for heating the exhaust gas purification catalyst. Furthermore, the exhaust gas purification catalyst has a catalyst coating layer containing noble metals such as Pd (palladium) and Rh (rhodium) as catalyst metals. Additionally, a downstream catalyst, different from the exhaust gas purification catalyst, is disposed downstream of the exhaust gas purification catalyst in the exhaust gas flow direction.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2022-073203 Summary of the Invention

[0006] However, in electrically heated catalysts with both Pd and Rh catalyst coatings, the performance of the Pd catalyst cannot be fully utilized, resulting in some Pd catalysts failing to contribute to emission reduction. Therefore, there are problems with the ineffective utilization of the amount of precious metals used in the catalyst and the difficulty in improving emission reduction efficiency.

[0007] The present invention was made in view of the following circumstances, and aims to provide a catalytic converter that can effectively utilize the amount of precious metals used in the catalyst and improve the effect of emission reduction.

[0008] The catalytic converter of the present invention is characterized by comprising an electrically heated catalyst disposed on the upstream side along the exhaust flow direction, and a non-electrically heated catalyst disposed on the downstream side relative to the electrically heated catalyst. The electrically heated catalyst has only an Rh catalyst coating layer as a catalyst coating layer formed on the upstream substrate. The non-electrically heated catalyst has an integral Pd catalyst coating layer and an integral Rh catalyst coating layer stacked over the entire length of the exhaust flow direction, and a partial Pd catalyst coating layer disposed along the exhaust flow direction within a range of up to 35% from the upstream end face of the non-electrically heated catalyst as a catalyst coating layer formed on the downstream substrate. The content of Pd catalyst per unit volume of the non-electrically heated catalyst in the integral Pd catalyst coating layer is less than the content of Pd catalyst per unit volume of the non-electrically heated catalyst in the partial Pd catalyst coating layer.

[0009] In the catalytic converter of the present invention, the electrically heated catalyst disposed on the upstream side has only an Rh catalyst coating layer as the catalyst coating layer formed on the upstream substrate. Therefore, even if there is an Rh catalyst with an activity temperature higher than that of a Pd catalyst, the Rh catalyst can be activated earlier by electric heating during engine start-up, etc. This allows for exhaust purification, and a certain level of purification performance can be maintained using only the Rh catalyst coating layer. Furthermore, by eliminating the Pd catalyst required by conventional electrically heated catalysts, the problem of insufficient performance of Pd catalysts, as was previously encountered, can be avoided. In addition, by eliminating the Pd catalyst required by conventional electrically heated catalysts, the amount of Pd catalyst saved can be added to the amount of Pd catalyst in the downstream non-electrically heated catalyst. Therefore, the emission reduction effect can be improved without increasing the amount of precious metals in the catalytic converter.

[0010] Furthermore, the non-electro-heated catalyst positioned downstream has a Pd catalyst coating layer (both a monolithic Pd catalyst coating layer and a partial Pd catalyst coating layer) and an Rh catalyst coating layer (a monolithic Rh catalyst coating layer) formed on the downstream substrate. Therefore, the heat from the high-temperature gas passing through the electro-heated catalyst preheats both the Pd and Rh catalysts to their respective activity temperatures. Additionally, by ensuring that the Pd catalyst content per unit volume of the non-electro-heated catalyst with the monolithic Pd catalyst coating is less than that of the non-electro-heated catalyst with the partial Pd catalyst coating, alloying of the downstream Pd and Rh catalysts is suppressed, maximizing the purification performance of each metal catalyst layer and improving emission reduction. Moreover, by positioning the partial Pd catalyst coating layer within 35% of the exhaust gas flow direction from the upstream end face of the non-electro-heated catalyst in the non-electro-heated catalyst, the exhaust gas can be purified and simultaneously heated using the Pd catalyst with a lower activity temperature, and then purified using the Rh catalyst with a higher activity temperature. As a result, the amount of precious metals used in the catalyst can be effectively utilized, and the preheating time can be shortened, the purification performance can be improved, and the emission reduction effect can be enhanced.

[0011] According to the present invention, the amount of precious metals used in the catalyst can be effectively utilized to improve the emission reduction effect. Attached Figure Description

[0012] Figure 1 This is a cross-sectional schematic diagram of a catalytic converter according to an embodiment.

[0013] Figure 2 This is a three-dimensional schematic diagram showing an electrically heated catalyst.

[0014] Figure 3This is a three-dimensional schematic diagram showing a non-electrically heated catalyst.

[0015] Figure 4 (a) is a cross-sectional schematic diagram showing an electrically heated catalyst, and (b) is a cross-sectional schematic diagram showing a non-electrically heated catalyst.

[0016] Figure 5 (a) is a cross-sectional schematic diagram showing the electrically heated catalyst of Comparative Example 1, and (b) is a cross-sectional schematic diagram showing the non-electrically heated catalysts of Examples 1, 2 and Comparative Examples 1 to 3.

[0017] Symbol Explanation

[0018] 1: Catalytic converter, 2: Electrically heated catalyst, 3: Non-electrically heated catalyst, 4: Housing, 5: Gasket, 6: Insulating material, 7: Exhaust path, 8: Electrode, 21: Upstream side substrate, 21a: Upstream side end face, 21b: Downstream side end face, 22: Rh catalyst coating, 31: Downstream side substrate, 31a: Upstream side end face, 31b: Downstream side end face, 32: Pd catalyst coating, 33: Rh catalyst coating, 41: Upstream connecting pipe, 4 2: Downstream connecting pipe; 43: Inner pipe; 71: Upstream exhaust pipe; 72: Downstream exhaust pipe; 81: Positive electrode; 82: Negative electrode; 211, 311: Outer frame; 212, 312: Partition wall; 213, 313: Hole; 321: First Pd catalyst coating layer; 322: Second Pd catalyst coating layer; 323: Third Pd catalyst coating layer; 811: Positive electrode layer; 812: Positive electrode terminal; 821: Negative electrode layer; 822: Negative electrode terminal. Detailed Implementation

[0019] Hereinafter, embodiments of the catalytic converter of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements are labeled with the same symbols, and repeated descriptions are omitted.

[0020] Figure 1 This is a cross-sectional schematic diagram showing the catalytic converter of the embodiment. The catalytic converter 1 of this embodiment is, for example, a device disposed within the exhaust path 7 of an internal combustion engine in a vehicle, used to purify the exhaust gas discharged from the internal combustion engine. Figure 1 As shown, the catalytic converter 1 is a series catalytic converter having an electrically heated catalyst 2 disposed on the upstream side along the exhaust flow direction and a non-electrically heated catalyst 3 disposed on the downstream side relative to the electrically heated catalyst 2.

[0021] The catalytic converter 1 further comprises a housing 4 having an upstream connecting pipe 41, a cylindrical inner pipe 43, and a downstream connecting pipe 42, a gasket 5, and an insulating material 6. The upstream connecting pipe 41, the inner pipe 43, and the downstream connecting pipe 42 of the housing 4 are made of metal such as stainless steel. The upstream connecting pipe 41 is covered from the outside and fixed to the exhaust inlet side of the inner pipe 43, with its diameter decreasing towards the exhaust inlet side. The downstream connecting pipe 42 is covered from the outside and fixed to the exhaust outlet side of the inner pipe 43, with its diameter decreasing towards the exhaust outlet side. It should be noted that the housing 4 forms part of the exhaust path 7.

[0022] The electrically heated catalyst 2 and the non-electrically heated catalyst 3 are housed in the same housing 4. More specifically, both the electrically heated catalyst 2 and the non-electrically heated catalyst 3 are installed within the inner tube 43 of the housing 4. Inside the inner tube 43, a gasket 5 is sandwiched between the electrically heated catalyst 2 and the non-electrically heated catalyst 3 and the inner circumferential surface of the inner tube 43. This gasket 5 is an insulator, for example, formed of inorganic fibers with alumina as the main component.

[0023] The upstream connecting pipe 41 connects the upstream exhaust pipe 71, whose diameter is smaller than that of the inner pipe 43, to the inner pipe 43. The downstream connecting pipe 42 connects the downstream exhaust pipe 72, whose diameter is smaller than that of the inner pipe 43, to the inner pipe 43. The upstream exhaust pipe 71 and the downstream exhaust pipe 72 constitute part of the exhaust path 7.

[0024] The electrically heated catalyst 2 is, for example, a direct-flow three-way catalyst, having an upstream substrate 21 on which an Rh catalyst coating layer 22 is formed (see reference). Figure 4 (a)). The upstream substrate 21 is a component supporting the Rh catalyst coating 22, for example, formed of a Si-SiC composite material.

[0025] Figure 2 This is a three-dimensional schematic diagram showing an electrically heated catalyst. (Example) Figure 2 As shown, the upstream substrate 21 is a substrate integrally formed by a cylindrical outer frame 211 and a grid-like partition 212 that divides the inner space of the outer frame 211. The partition 212 is a porous body that divides the upstream substrate 21 from the upstream end face 21a to the downstream end face 21b into multiple holes 213. The partition 212 has multiple horizontal wall portions 212A that are separated from each other and arranged in parallel, and multiple vertical wall portions 212B that are orthogonal to the horizontal wall portions 212A and separated from each other and arranged in parallel, in such a way that the divided holes 213 form a rectangular cross-section.

[0026] In this embodiment, the upstream end face 21a of the upstream substrate 21 constitutes the upstream end face of the electrically heated catalyst 2, and the downstream end face 21b constitutes the downstream end face of the electrically heated catalyst 2. Furthermore, the partition wall 212 can be triangular, hexagonal, octagonal, or other shapes besides a lattice structure.

[0027] The Rh catalyst coating layer 22 contains Rh, a catalyst component, and a support comprising a composite oxide (hereinafter referred to as OSC material) mainly composed of CeO2 and ZrO2, and oxides other than the OSC material. It is a layer containing only Rh as a metal catalyst. The catalyst component Rh is supported on a support comprising the OSC material and oxides other than the OSC material. Examples of OSC materials include, for example, cerium oxide (cerium dioxide: CeO2) and composite oxides containing this cerium dioxide. Figure 2 and Figure 4 As shown in (a), the Rh catalyst coating layer 22 is formed on the entire wall surface of the pore 213, covering the entire length of the upstream substrate 21. That is, the Rh catalyst coating layer 22 is formed on the surface of each transverse wall portion 212A and the surface of each longitudinal wall portion 212B.

[0028] The electrically heated catalyst 2 is electrically connected to a pair of electrodes 8 (positive electrode 81 and negative electrode 82) to enable it to be heated by electricity. Although not specifically illustrated, the positive electrode 81 and negative electrode 82 are comb-shaped electrodes mounted on the outer peripheral surface of the outer frame 211 of the upstream substrate 21. The positive electrode 81 has a positive electrode layer 811 disposed on the outer peripheral surface of the outer frame 211 and a positive electrode terminal 812 connected to the positive electrode layer 811. The negative electrode 82 has a negative electrode layer 821 disposed on the outer peripheral surface of the outer frame 211 of the upstream substrate 21 and a negative electrode terminal 822 connected to the negative electrode layer 821.

[0029] The positive electrode layer 811 and the negative electrode layer 821 are formed in an arc shape along the outer periphery of the outer frame 211 in a manner that allows for uniform heating of the entire upstream substrate 21. Preferably, the positive electrode layer 811 and the negative electrode layer 821 are arranged along the entire length of the upstream substrate 21 in the axial direction (i.e., the direction of exhaust flow) of the upstream substrate 21.

[0030] Positive electrode terminal 812 and negative electrode terminal 822 penetrate the wall of the inner tube 43. Insulating material 6 is embedded between the positive electrode terminal 812 and the negative electrode terminal 822 and the inner tube 43. The insulating material 6 is made of an insulating material such as alumina. Thus, the electrically heated catalyst 2 is electrically insulated from the shell 4. Therefore, if a voltage is applied between the positive electrode 81 and the negative electrode 82, current flows through the upstream substrate 21, causing the upstream substrate 21 to heat up due to resistance.

[0031] The non-electro-heated catalyst 3 is, for example, a direct-flow three-way catalyst, having a downstream substrate 31 on which a Pd catalyst coating layer 32 and an Rh catalyst coating layer 33 are formed (see reference). Figure 4 (b)). The downstream substrate 31 is a component supporting the Pd catalyst coating layer 32 and the Rh catalyst coating layer 33, for example, formed of cordierite.

[0032] Figure 3 This is a three-dimensional schematic diagram illustrating a non-electrically heated catalyst. (Example) Figure 3 As shown, the downstream substrate 31 is a substrate integrally formed by a cylindrical outer frame 311 and a grid-like partition wall 312 that divides the inner space of the outer frame 311. The partition wall 312 is a porous body extending from the upstream end face 31a to the downstream end face 31b of the downstream substrate 31, dividing it into multiple holes 313. The partition wall 312 has multiple horizontal wall portions 312A arranged in parallel and separated from each other, and multiple vertical wall portions 312B arranged in parallel and separated from each other, with the divided holes 313 forming a rectangular cross-section.

[0033] In this embodiment, the upstream end face 31a of the downstream substrate 31 constitutes the upstream end face of the non-electro-heated catalyst 3, and the downstream end face 31b constitutes the downstream end face of the non-electro-heated catalyst 3. Furthermore, the partition wall 312 can be triangular, hexagonal, octagonal, or other shapes besides a lattice structure.

[0034] The Pd catalyst coating layer 32 and the Rh catalyst coating layer 33 are formed along the axial direction of the downstream substrate 31 within a specified range on the entire wall surface of the pore 313. That is, the Pd catalyst coating layer 32 and the Rh catalyst coating layer 33 are formed on the surface of each transverse wall portion 312A and the surface of each longitudinal wall portion 312B, respectively, but their formation ranges are different.

[0035] Furthermore, in this embodiment, there are multiple Pd catalyst coating layers 32 (here, three layers). Among the multiple Pd catalyst coating layers, the layer furthest from the downstream substrate 31 in the layer thickness direction has the highest content of non-electrothermal catalyst per unit volume. Hereinafter, based on... Figure 4 (b) will be explained in detail.

[0036] Specifically, such as Figure 4As shown in (b), the non-electro-heated catalyst 3 comprises: a downstream substrate 31, a first Pd catalyst coating layer 321 sequentially stacked on the downstream substrate 31, the aforementioned Rh catalyst coating layer 33, a second Pd catalyst coating layer 322, and a third Pd catalyst coating layer 323. The first Pd catalyst coating layer 321, the second Pd catalyst coating layer 322, and the third Pd catalyst coating layer 323 constitute the aforementioned Pd catalyst coating layer 32. Furthermore, the Rh catalyst coating layer 33 corresponds to the entire Rh catalyst coating layer, the second Pd catalyst coating layer 322 corresponds to the entire Pd catalyst coating layer, and the first Pd catalyst coating layer 321 and the third Pd catalyst coating layer 323 correspond to partial Pd catalyst coating layers.

[0037] Compared to either the first Pd catalyst coating layer 321 or the third Pd catalyst coating layer 323, the second Pd catalyst coating layer 322 has a lower content of Pd catalyst per unit volume of non-electro-heated catalyst (see Examples 1, 2 and Comparative Example 3 described below). Furthermore, among the first Pd catalyst coating layer 321, the second Pd catalyst coating layer 322, and the third Pd catalyst coating layer 323, the third Pd catalyst coating layer 323, which is furthest from the downstream substrate 31, has the highest content of Pd catalyst per unit volume of non-electro-heated catalyst (see Examples 1 and 2 described below).

[0038] The first Pd catalyst coating layer 321, the second Pd catalyst coating layer 322, and the third Pd catalyst coating layer 323 respectively contain Pd as a catalyst component, a support comprising a composite oxide (OSC) material mainly composed of CeO2 and ZrO2 and oxides other than OSC material, and a Ba compound (e.g., BaSO4). The Pd and Ba compound as catalyst components are supported on the support comprising OSC material and oxides other than OSC material.

[0039] The second Pd catalyst coating layer 322 is disposed along the entire length of the downstream substrate 31 along the exhaust flow direction. The first Pd catalyst coating layer 321 and the third Pd catalyst coating layer 323 are each disposed along the exhaust flow direction within a range of 35% or less from the upstream end face 31a on the downstream substrate 31. Moreover, of the first Pd catalyst coating layer 321 and the third Pd catalyst coating layer 323, the first Pd catalyst coating layer 321 is larger than the third Pd catalyst coating layer 323 in terms of the arrangement range (in other words, the formation range) along the exhaust flow direction on the downstream substrate 31 from the upstream end face 31a. It should be noted that the arrangement range of the first Pd catalyst coating layer 321 and the third Pd catalyst coating layer 323 is preferably within 30% of the upstream end face 31a, and more preferably within 20% or more of the upstream end face 31a.

[0040] On the other hand, the Rh catalyst coating layer 33, like the Rh catalyst coating layer 22 of the electrically heated catalyst 2, contains the catalyst component Rh, and a support containing OSC material and oxides other than OSC material. Figure 4 As shown in (b), the Rh catalyst coating 33 is disposed along the entire length of the downstream substrate 31.

[0041] In the catalytic converter 1 configured as described above, before the internal combustion engine starts operating, a voltage is applied between the positive electrode 81 and the negative electrode 82, causing current to flow through the upstream substrate 21, thereby heating the upstream substrate 21 due to resistance. Therefore, even when the exhaust temperature is low after the internal combustion engine starts operating, the temperature of the Rh catalyst in the electrically heated catalyst 2 can be raised to activate the Rh catalyst. Furthermore, the heat from the exhaust gas heated by the electrically heated catalyst 2 can be used to raise the temperature of the Pd catalyst and the Rh catalyst in the non-electrically heated catalyst 3, thereby activating these catalysts.

[0042] In the catalytic converter 1 of this embodiment, the electrically heated catalyst 2, located upstream of the exhaust flow direction, has only an Rh catalyst coating layer 22 as the catalyst coating layer formed on the upstream substrate 21. Therefore, even if it has an Rh catalyst with an activity temperature higher than that of the Pd catalyst, it can be activated earlier by electric heating during engine start-up, etc. As a result, exhaust gas can be purified, and a certain level of purification performance can be maintained even with only the Rh catalyst coating layer 22. Moreover, by eliminating the Pd catalyst required by conventional electrically heated catalysts, the problem of not being able to fully utilize the performance of Pd catalysts, as in the past, can be avoided. Furthermore, by eliminating the Pd catalyst required by conventional electrically heated catalysts, the amount of Pd catalyst saved can be added to the amount of Pd catalyst in the downstream non-electrically heated catalyst 3, thereby improving the emission reduction effect without increasing the amount of precious metals (i.e., Pd and Rh) in the catalytic converter 1.

[0043] Furthermore, the non-electro-heated catalyst 3, positioned downstream of the exhaust flow direction, has a Pd catalyst coating layer 32 and an Rh catalyst coating layer 33 as catalyst coating layers formed on the downstream substrate 31. Therefore, the heat from the high-temperature gas passing through the electrically heated catalyst preheats the Pd and Rh catalysts to their respective activity temperatures. Additionally, by ensuring that the content of Pd catalyst per unit volume of the non-electro-heated catalyst in the overall Pd catalyst coating layer (second Pd catalyst coating layer 322) is less than that in the partial Pd catalyst coating layers (first Pd catalyst coating layer 321, third Pd catalyst coating layer 323), alloying of the Pd and Rh catalysts downstream of the non-electro-heated catalyst 3 is suppressed, thereby maximizing the purification performance of each layer's metal catalyst and improving emission reduction. Furthermore, in the non-electro-heated catalyst 3, by arranging the first Pd catalyst coating layer 321 and the third Pd catalyst coating layer 323 within 35% of the upstream end face 31a along the exhaust flow direction of the non-electro-heated catalyst 3, the exhaust gas can be purified and simultaneously heated using a Pd catalyst with a low activity temperature, and the heated exhaust gas can then be purified using a Rh catalyst with a high activity temperature. As a result, the amount of precious metals (i.e., Pd and Rh) used in the catalyst can be effectively utilized, and the purification performance can be improved while shortening the preheating time, thereby enhancing the emission reduction effect.

[0044] Furthermore, in the non-electro-heated catalyst 3, since the third Pd catalyst coating layer 323 is the layer furthest from the downstream substrate 31 in the layer thickness direction (i.e., the stacking direction of the Pd catalyst coating layer 32 and the Rh catalyst coating layer 33), preheating performance can be improved. Therefore, the purification performance of the Pd catalyst can be brought into play earlier, and the emission reduction effect can be further improved.

[0045] Furthermore, among the first Pd catalyst coating layer 321 and the third Pd catalyst coating layer 323, the third Pd catalyst coating layer 323, which is furthest from the downstream substrate 31, has the highest content of Pd catalyst per unit volume of non-electro-heated catalyst. A higher Pd catalyst content results in better preheating performance; therefore, by increasing the Pd catalyst content in the third Pd catalyst coating layer 323, which is furthest from the downstream substrate 31, the preheating performance can be improved. Consequently, the purification performance of the Pd catalyst can be utilized earlier.

[0046] Furthermore, the electrically heated catalyst 2 and the non-electrically heated catalyst 3 are housed in the same shell 4. In this case, the high-temperature gas after the electrically heated catalyst has passed through can be directly introduced into the non-electrically heated catalyst 3 through the shell 4, thus efficiently utilizing the heat of the high-temperature gas for the activation of the Pd and Rh catalysts, thereby enabling the purification performance of the Pd and Rh catalysts to be realized earlier.

[0047] In this embodiment, although an example of a Pd catalyst coating layer consisting of two layers has been described, the Pd catalyst coating layer may also consist of one layer, three layers, or more. Furthermore, the electrically heated catalyst 2 may further have a coating layer without a catalyst, in addition to the Rh catalyst coating layer 22. For example, a coating layer without a catalyst may be provided between the upstream substrate 21 and the Rh catalyst coating layer 22.

[0048] [Examples 1, 2 and Comparative Examples 1-3]

[0049] The catalytic converter of the embodiments is described in more detail below with comparative examples and examples. It should be noted that, as Figure 5 As shown in (a), Comparative Example 1 differs from the catalytic converter 1 described above in the configuration of the electrically heated catalyst 2 and the non-electrically heated catalyst 3.

[0050] like Figure 5 As shown in (a), the electrically heated catalyst 2 of Comparative Example 1 has an upstream substrate 21, and an A catalyst coating layer (hereinafter referred to as "A layer") and a B catalyst coating layer (hereinafter referred to as "B layer") formed on the upstream substrate 21. The A layer is a Pd catalyst coating layer, and the B layer is an Rh catalyst coating layer. The A layer is formed on the upstream substrate 21 and is disposed over a range of 75% from the upstream end face 21a to the downstream end face 21b. On the other hand, the B layer is disposed over a range of 75% from the downstream end face 21b to the upstream end face 21a, covering both the upstream substrate 21 and the A layer. On the other hand, in the electrically heated catalyst 2 of Comparative Example 2, the A layer is disposed only along the entire length of the upstream substrate 21, and in the electrically heated catalysts 2 of Examples 1, 2 and Comparative Example 3, the B layer is disposed only along the entire length of the upstream substrate 21.

[0051] In addition, such as Figure 5 As shown in (b), the non-electrothermal catalyst 3 of Examples 1, 2 and Comparative Examples 1-3 has a downstream substrate 31, and catalyst coating layers A (hereinafter referred to as "A layer"), B (hereinafter referred to as "B layer"), C (hereinafter referred to as "C layer") and D (hereinafter referred to as "D layer") are sequentially formed on the downstream substrate 31. Layers A, C and D are Pd catalyst coating layers, and layer B is an Rh catalyst coating layer.

[0052] Layer A, equivalent to the first Pd catalyst coating layer described above, is formed on the downstream substrate 31 and is disposed over a 30% area from the upstream end face 31a toward the downstream end face 31b. Layer B is formed on top of Layer A and the downstream substrate 31 in such a way that it covers the entire surface from the upstream end face 31a to the downstream end face 31b.

[0053] Layer C is equivalent to the second Pd catalyst coating layer described above, formed to cover layer B, and disposed on the entire surface from the upstream end face 31a to the downstream end face 31b. Layer D is equivalent to the third Pd catalyst coating layer described above, formed on layer C, and disposed in a range of 21% from the upstream end face 31a to the downstream end face 31b.

[0054] Comparative Examples 1-3 differ in the composition and PGM content of each layer as shown in Table 1 below. The unit of PGM content in Table 1 is g / unit, i.e., the content of Pd or Rh catalyst per electrically heated catalyst (327 ml) or per non-electrically heated catalyst (478 ml). It should be noted that the unit of PGM content can be converted from "g / unit" to "g / l" depending on the volume of the electrically heated or non-electrically heated catalyst (see the lower brackets in Table 1).

[0055] The samples of Examples 1, 2 and Comparative Examples 1-3 were prepared as follows. First, the electrically heated catalyst 2 of each comparative example was prepared. Specifically, a monolithic Si-SiC substrate was used as the upstream substrate 21 with an outer diameter of 80 mm and a length (axial length) of 65 mm (327 ml).

[0056] Next, the aforementioned A layer of the electrically heated catalyst 2 is formed. Specifically, a slurry (containing Pd) for the A layer is prepared by mixing palladium nitrate solution, cerium dioxide-zirconia composite oxide powder, Al2O3 powder, BaSO4 with an average particle size of 100 nm, a binder, and deionized water. At this time, the formulation of the above-mentioned solution, powder, binder, etc., is adjusted so that the PGM amount of the Pd catalyst in the formed A layer (more specifically, the PGM amount of the Pd catalyst after sintering) is the value shown in Table 1.

[0057] Next, in Comparative Examples 1 and 2, the A-layer slurry was poured from the upstream end face 21a of the upstream substrate 21, thereby coating the A-layer slurry over 75% of the total length of the upstream substrate 21 (Comparative Example 1) or the entire length (Comparative Example 2). The upstream substrate 21 coated with the slurry was then placed in a dryer and dried at 120°C for 2 hours, followed by calcination in an electric furnace at 500°C for 2 hours. This formed the A-layer.

[0058] Next, the aforementioned B layer of the electrically heated catalyst 2 is formed. In Examples 1 and 2 and Comparative Examples 1 and 3, specifically, a slurry (containing Rh) for the B layer is prepared by mixing rhodium nitrate solution, cerium dioxide-zirconia composite oxide powder, alumina-zirconia composite oxide powder, Al2O3 powder, binder, and deionized water. At this time, the formulation of the above-mentioned solution, powder, binder, etc., is adjusted so that the PGM amount of the Rh catalyst in the formed B layer (more specifically, the PGM amount of the Rh catalyst after sintering) is the value listed in Table 1.

[0059] Next, the B-layer slurry is poured into the downstream end face 21b of the upstream substrate 21, thereby coating the B-layer slurry over 75% of the total length of the upstream substrate 21 (Comparative Example 1) or the entire length (Examples 1, 2, Comparative Example 3). The upstream substrate 21 coated with the slurry is then placed in a dryer and dried at 120°C for 2 hours, followed by calcination in an electric furnace at 500°C for 2 hours. This forms the B-layer.

[0060] Next, non-electro-heated catalysts 3 for each embodiment and comparative example were prepared. Specifically, firstly, a downstream substrate 31 with an outer diameter of 80 mm and a length (axial length) of 95 mm (478 ml) was prepared using a monolithic cordierite substrate.

[0061] Next, the aforementioned A layer (first Pd catalyst coating layer) of the non-electrothermal catalyst 3 is formed. Specifically, a slurry (containing Pd) for the A layer is prepared by mixing palladium nitrate solution, cerium dioxide-zirconia composite oxide powder, Al2O3 powder, BaSO4 with an average particle size of 100 nm, a binder, and deionized water. At this time, the formulation of the above-mentioned solution, powder, binder, etc. is adjusted so that the PGM amount of the Pd catalyst in the formed A layer (more specifically, the PGM amount of the Pd catalyst after sintering) is the value listed in Table 1.

[0062] Next, the A-layer slurry is poured into the upstream end face 31a of the downstream substrate 31, thereby coating the downstream substrate 31 with the A-layer slurry over 30% of its total length. Then, the downstream substrate 31 coated with the slurry is placed in a dryer and dried at 120°C for 2 hours, followed by calcination in an electric furnace at 500°C for 2 hours. This forms the A-layer.

[0063] Next, the aforementioned B layer of the non-electrothermal catalyst 3 is formed. Specifically, a slurry (containing Rh) for the B layer is prepared by mixing rhodium nitrate solution, cerium dioxide-zirconia composite oxide powder, alumina-zirconia composite oxide powder, Al2O3 powder, binder, and deionized water. At this time, the formulation of the above-mentioned solution, powder, binder, etc., is adjusted so that the PGM amount of the Rh catalyst in the formed B layer (more specifically, the PGM amount of the Rh catalyst after sintering) is the value listed in Table 1.

[0064] Next, the B-layer slurry is poured into the downstream end face 31b of the downstream substrate 31, thereby coating the downstream substrate 31 with the B-layer slurry over 100% of its entire length (i.e., covering the entire length of the downstream substrate 31). Then, the downstream substrate 31 coated with the slurry is placed in a dryer and dried at 120°C for 2 hours, followed by calcination in an electric furnace at 500°C for 2 hours. This forms the B-layer.

[0065] Next, the aforementioned C layer (second Pd catalyst coating layer) of the non-electrothermal catalyst 3 is formed. Specifically, a slurry (containing Pd) for the C layer is prepared by mixing a palladium nitrate solution, a specified organic compound, and ion-exchanged water. At this time, the combination of the above-mentioned solution and organic compound is adjusted so that the PGM amount of the Pd catalyst in the formed C layer (more specifically, the PGM amount of the Pd catalyst after sintering) is the value shown in Table 1.

[0066] Next, the C-layer slurry is poured into the upstream end face 31a of the downstream substrate 31, thereby coating the downstream substrate 31 with the C-layer slurry over 100% of its entire length (i.e., covering the entire length of the downstream substrate 31). The downstream substrate 31 coated with the slurry is then placed in a dryer and dried at 120°C for 2 hours, followed by calcination in an electric furnace at 500°C for 2 hours. This forms the C-layer.

[0067] Next, the aforementioned D layer (third Pd catalyst coating layer) of the non-electrothermal catalyst 3 is formed. Specifically, a slurry (containing Pd) for the D layer is prepared by mixing a palladium nitrate solution, a specified organic compound, and ion-exchanged water. At this time, the combination of the above-mentioned solution and organic compound is adjusted so that the PGM amount of the Pd catalyst in the formed D layer (more specifically, the PGM amount of the Pd catalyst after sintering) is the value shown in Table 1.

[0068] Next, the D-layer slurry is poured into the upstream end face 31a of the downstream substrate 31, thereby coating the downstream substrate 31 with the D-layer slurry over 21% of its total length. Then, the downstream substrate 31 coated with the slurry is placed in a dryer and dried at 120°C for 2 hours, followed by calcination in an electric furnace at 500°C for 2 hours. This forms the D-layer.

[0069] [Table 1]

[0070]

[0071] [Durability Testing]

[0072] Next, the samples from Comparative Examples 1-3 and Examples 1 and 2 were subjected to durability tests under the same conditions. In the durability tests, a Toyota Motor Corporation 1GR-FE engine was used, and a degradation test was conducted at 950°C for 80 hours (equivalent to 200,000 km). Furthermore, in the durability tests, for the exhaust composition, degradation was accelerated by repeatedly cycling rich → stoichiometric → lean exhaust gases by adjusting the throttle valve opening and engine load.

[0073] [Evaluation Method]

[0074] The HC purification rate of the electrically heated catalyst at 500℃ and 450℃ and the HC purification rate of the non-electrically heated catalyst at 500℃ were evaluated for each sample after the durability test, as well as the preheating time of the non-electrically heated catalyst.

[0075] In evaluating the HC purification rates of electrically heated catalysts at 500℃ and 450℃, and the HC purification rates of non-electrically heated catalysts at 500℃, firstly, electrically heated and non-electrically heated catalysts were removed from each sample after durability testing, and then individually reinstalled into the catalytic converter. Next, using a Toyota Motor Corporation A25A engine, the throttle opening and engine load were adjusted with an upstream A / F ratio of 14.4 and temperatures of 500℃ or 450℃ to ensure exhaust flow into the catalyst while maintaining a constant catalyst bed temperature.

[0076] Next, the HC concentration at the upstream end face of the electrically heated catalyst was measured as the inlet HC concentration, and the HC concentration at the downstream end face was measured as the outlet HC concentration. The HC purification rate at 500℃ and 450℃ was calculated according to the following formula (1). The calculation results are summarized in Table 2.

[0077] HC purification rate (%) = (HC concentration at the inlet - HC concentration at the outlet) / HC concentration at the inlet × 100% (1)

[0078] In addition, the HC concentration at the upstream end face of the non-electro-heated catalyst was measured as the inlet HC concentration, and the HC concentration at the downstream end face was measured as the outlet HC concentration. The HC purification rate of the non-electro-heated catalyst at 500°C was calculated according to the above formula (1). The calculation results are summarized in Table 2.

[0079] On the other hand, in evaluating the preheating time of the non-electrically heated catalyst, firstly, both the electrically heated and non-electrically heated catalysts were removed from each sample after the durability test, and the removed non-electrically heated catalyst was reinstalled in the catalytic converter. Next, using an A25A engine manufactured by Toyota Motor Corporation, the throttle valve opening and engine load were adjusted to a current upstream A / F ratio of 14.6 and a temperature of 450°C, so that exhaust gas flowed into the non-electrically heated catalyst at room temperature.

[0080] Next, the inlet and outlet HC concentrations of the non-electrically heated catalyst were measured respectively, and the HC purification rate was calculated using the above formula (1). The time from when the exhaust gas flowed in until the HC purification rate reached 50% was also measured. The measurement results are summarized in Table 2 below.

[0081] [Table 2]

[0082]

[0083] [Inspection]

[0084] Table 2 shows that the HC purification rates of the electrically heated catalyst at 500°C and 450°C were the same as those of the comparative example. Therefore, by using an electrically heated catalyst having only an upstream substrate and a B layer (Rh catalyst coating layer) formed on the upstream substrate, the Rh catalyst is activated by heating to purify the exhaust gas, demonstrating that a certain level of purification performance can be maintained even with only the Rh catalyst coating layer. Furthermore, in Comparative Example 2, which has an electrically heated catalyst having only an A layer (Pd catalyst coating layer), the HC purification rates at 500°C and 450°C were found to be the lowest.

[0085] Furthermore, as shown in Table 2, compared with Comparative Examples 1-3, Examples 1 and 2 had shorter preheating times and better HC purification rates at 500°C for both the preheating time and the HC purification rate of the non-electrically heated catalyst. This demonstrates the ability to improve preheating performance and enable the Pd catalyst to exhibit its purification capabilities earlier.

[0086] Furthermore, in Examples 1 and 2, it is evident that Example 1 has the shortest preheating time. In the case of Example 1, the non-electrothermal catalyst content per unit volume of the third Pd catalyst coating layer (D layer), which is furthest from the downstream substrate 31, is the highest. Since a higher amount of Pd catalyst results in better preheating performance, the preheating time can be shortened by increasing the amount of Pd catalyst contained in this third Pd catalyst coating layer. It should be noted that in Examples 1 and 2, although layers A and D were formed at ranges of 30% and 21% from the upstream end face of the non-electrothermal catalyst, respectively, it has been confirmed that the same effect can be expected as long as they are formed within a range of 35%.

[0087] Furthermore, comparing Comparative Example 3 with Examples 1 and 2 reveals that although Comparative Example 3 also possesses an electrically heated catalyst with only a B layer (Rh catalyst coating layer) and a non-electrically heated catalyst with three Pd catalyst coating layers, the preheating time and HC purification rate of the non-electrically heated catalyst at 500°C are worse than those of Examples 1 and 2. This is believed to be because the PGM content of the C layer (second Pd catalyst coating layer) of the non-electrically heated catalyst in Comparative Example 3 is greater than the PCM content of the A and B layers, resulting in the Pd catalyst in the downstream C layer of the downstream substrate 31 reacting with the Rh catalyst in the B layer to alloy.

Claims

1. A catalytic converter, characterized in that, It comprises: an electrically heated catalyst disposed upstream along the exhaust flow direction, and a non-electrically heated catalyst disposed downstream relative to the electrically heated catalyst. The electrically heated catalyst has only an Rh catalyst coating layer as the catalyst coating layer formed on the upstream substrate. The non-electro-heated catalyst has an integral Pd catalyst coating layer and an integral Rh catalyst coating layer stacked along the entire length of the exhaust flow direction, and a partial Pd catalyst coating layer disposed along the exhaust flow direction within a range of up to 35% from the upstream end face of the non-electro-heated catalyst as a catalyst coating layer formed on the downstream substrate. The content of Pd catalyst per unit volume of the non-electro-heated catalyst in the integral Pd catalyst coating is less than the content of Pd catalyst per unit volume of the non-electro-heated catalyst in the partial Pd catalyst coating.

2. The catalytic converter according to claim 1, wherein, The portion of the Pd catalyst coating is the layer furthest from the downstream substrate in the thickness direction.

3. The catalytic converter according to claim 2, wherein, The Pd catalyst coating consists of multiple layers. The portion of the Pd catalyst coating furthest from the downstream substrate among the multiple portions of the Pd catalyst coating has the highest content of Pd catalyst per unit volume of the non-electrothermal catalyst.

4. The catalytic converter according to claim 1, wherein, The electrically heated catalyst and the non-electrically heated catalyst are housed in the same shell.

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