CATALYTIC CONVERTER

Abstract

Catalytic converter, comprehensive: a substrate with a cellular structure through which exhaust gas flows; and a catalyst layer formed on a cell wall surface of the substrate, wherein the catalyst layer comprises a lower catalyst layer and an upper catalyst layer, wherein the lower catalyst layer is formed on a surface of the substrate and the upper catalyst layer is formed on a surface of the lower catalyst layer. the upper catalyst layer includes: a zirconia compound support with rhodium supported thereon, wherein the zirconia compound support contains zirconia, lanthanum oxide and yttrium oxide, an aluminum oxide compound without rhodium carried on it, wherein the aluminum oxide compound contains aluminum oxide and lanthanum oxide, and a cerium oxide-zirconium oxide-based composite oxide containing cerium oxide, zirconium oxide, lanthanum oxide and neodymium oxide, and the lower catalyst layer includes: an aluminum oxide compound support with platinum supported thereon, wherein the aluminum oxide compound support contains aluminum oxide and lanthanum oxide, which are the same materials as those of the aluminum oxide compound of the upper catalyst layer, and a cerium oxide-zirconium oxide-based composite oxide without platinum supported thereon, wherein the cerium oxide-zirconium oxide-based composite oxide contains cerium oxide, zirconia, lanthanum oxide and neodymium oxide, which are the same materials as those of the cerium oxide-zirconium oxide-based composite oxide of the upper catalyst layer.

Description

PRIORITY CLAIM

[0001] The present application claims priority from the Japanese patent application JP 2015-058620 filed on March 20, 2015, the contents of which are incorporated into this application by reference. BACKGROUND Technical area

[0002] The present invention relates to a catalytic converter which is firmly mounted in a pipe of an exhaust system for exhaust gas. Current state of the art

[0003] A wide range of industries worldwide have undertaken diverse efforts to reduce environmental impacts and burdens. In the automotive industry, in particular, development has been driven daily to promote not only the widespread adoption of fuel-efficient gasoline-powered vehicles, but also of so-called environmentally friendly vehicles, such as hybrid and electric vehicles, as well as to further improve the performance of such vehicles. Alongside the development of these environmentally friendly vehicles, active research has also been conducted on exhaust gas purification catalysts for cleaning exhaust gases emitted from engines. An exhaust gas purification catalyst includes an oxidation catalyst, a three-way catalyst, a NOx storage / reduction catalyst, and similar components.A precious metal catalyst, such as platinum (Pt), palladium (Pd), or rhodium (Rh), exhibits catalytic activity in the exhaust gas purification catalyst. The precious metal catalyst is typically used while supported on a substrate made of a porous oxide, such as aluminum oxide (Al₂O₃).

[0004] A catalytic converter for cleaning exhaust gases is typically located in an exhaust system that connects a vehicle engine and a muffler. The engine can sometimes remove environmentally harmful substances such as CO and NO. xand emit unburned HC and VOCs. To convert such harmful substances into environmentally friendly substances, exhaust gas is passed through a catalytic converter in which a catalyst layer with a precious metal catalyst, such as Rh, Pd or Pt, supported on a substrate, is arranged on the cell wall surface of a substrate, so that CO is converted into CO2 and NO x is converted into N2 and O2, while HC and VOC are burned to produce CO2 and H2O.

[0005] A cerium oxide-zirconium oxide-based composite oxide (also known as a CeO₂-ZrO₂ solid solution, a CZ material, and the like) can be used as a support for a precious metal catalyst. This is also referred to as a promoter and is an essential component of the aforementioned three-way catalyst for the simultaneous removal of CO and NO₂. xand HC, which are harmful components in the exhaust gas. Examples of the essential component of the propellant include CeO2. CeO2 has the property that its oxidation number varies depending on the partial pressure of oxygen in the exhaust gas to which the CeO2 is exposed, for example to Ce 3+ or Ce 4+ CeO2 alters the electrical charge and exhibits a function of absorbing and releasing oxygen as well as a function of storing oxygen (OSC: oxygen storage capacity) to compensate for the deficiency and excess of electrical charges. Furthermore, CeO2 can buffer and mitigate fluctuations in the exhaust atmosphere and maintain the air / fuel ratio approximately at the level of the theoretical air / fuel ratio, thus preserving a cleaning window for the three-way catalytic converter.

[0006] Incidentally, the question of how to reduce the amount of precious metal catalyst used in the aforementioned three-way catalyst is an important factor to consider from the perspective of cost competitiveness. However, if the amount of precious metal catalyst in a three-way catalyst is significantly reduced, the catalytic activity also decreases significantly. This leads to significantly reduced OSC performance and low-temperature activity, as well as significantly reduced NO. x -Cleaning performance in a high-temperature environment and the like. This is because a significantly reduced amount of a precious metal catalyst leads to a significantly reduced number of active sites, and a significantly reduced number of catalytic reaction sites leads to a significantly reduced cleaning performance.

[0007] Of the precious metal catalysts such as Pt, Pd and Rh, which are used especially for a three-way catalyst, Rh possesses the most outstanding NO x -purification performance, but is traded at the highest market price per unit weight. It is known that higher OSC performance is achieved when Rh is supported on a support containing cerium oxide (ceria). However, it is also known that increasing the amount of cerium oxide in the support reduces the NO x The purification performance, which is a characteristic property of rhronic acid, is reduced. Therefore, when rhronic acid is used as a precious metal catalyst for a three-way catalyst, the production of a catalyst that is superior in terms of both OSC performance and NO reduction is significantly impaired. x -The cleaning performance of an optimal three-way catalyst is an urgent task to be solved in the technical field.

[0008] In this regard, patent document 1 discloses an exhaust gas purification catalyst comprising a first oxygen storage material on which no precious metal is supported and which has a regular arrangement structure of the pyrochlore phase type; and a second oxygen storage material which has a higher oxygen storage rate and a lower oxygen storage capacity than the first oxygen storage material, wherein a precious metal from the platinum group is supported on the second oxygen storage material. According to such an exhaust gas purification catalyst, it is possible to provide an exhaust gas purification catalyst that achieves a high NO reduction. x -Provides cleaning performance after continuous use.

[0009] Meanwhile, patent document 2 discloses an exhaust gas purification catalyst with a first catalyst layer and a second catalyst layer formed successively on a support substrate, wherein the first catalyst layer comprises rhodium supported thereon and the second catalyst layer comprises platinum and palladium supported thereon, wherein the ratio of the supported amount of palladium (y) to the supported amount of platinum (x) (y / x; molar ratio) satisfies 0 < y / x ≤ 1.0. According to such an exhaust gas purification catalyst, it is possible to design an exhaust gas purification catalyst for an NOₓ x -storage / reduction type, which has a more outstanding NO x -cleaning performance.

[0010] Furthermore, patent document 3 discloses an exhaust gas purification catalyst comprising a catalyst coating layer with a two-layer structure consisting of a lower layer and an upper layer formed on the surface of the lower layer, wherein at least one of Pt and Pd is supported on at least the upper layer and 60 wt% or more of the total mass of Rh is supported on the lower layer. According to such an exhaust gas purification catalyst, NO is efficiently oxidized by Pt in the upper layer in a lean atmosphere, so that the NO x Storage efficiency is improved, while hydrogen produced in the lower layer passes through the upper layer in a stoichiometric to rich atmosphere, so that the NO x -Reduction efficiency is increased, thus resolving sulfur poisoning.

[0011] Furthermore, when rhodium is supported on cerium oxide, metallization of the rhodium is prevented, thus reducing the NO₂ levels. x -Cleaning performance is reduced, as described above. However, if the amount of cerium oxide is increased to increase the oxygen storage capacity, the pressure drop is amplified.

[0012] This means that even when using the exhaust gas purification catalysts disclosed in patent documents 1 to 3, it is unclear whether a [missing word] will be achieved in terms of both OSC performance and NO [missing word]. x -Cleaning performance of excellent catalytic converters can be provided or not.

[0013] Patent document 4, however, describes composite oxides which are used in a multilayer catalyst. RELATED STATE OF TECHNOLOGY PATENT DOCUMENTS Patent Document 1: JP 2012-024701 A Patent Document 2: JP 2010-201284 A Patent Document 3: JP 2009-285604 A Patent document 4: EP 1 174 174 A1 SUMMARY

[0014] The present invention was made in consideration of the above problems, and one object of the present invention is to provide a catalytic converter with excellent OSC performance and NO x -Cleaning service.

[0015] To solve the aforementioned problem, a catalytic converter according to the present invention comprises a substrate with a cell structure through which exhaust gas flows, and a catalyst layer formed on a cell wall surface of the substrate. The catalyst layer comprises a lower catalyst layer and an upper catalyst layer, wherein the lower catalyst layer is formed on a surface of the substrate and the upper catalyst layer is formed on a surface of the lower catalyst layer. The upper catalyst layer comprises a zirconia compound support with rhodium supported thereon, wherein the zirconia compound support contains zirconia, lanthanum oxide, and yttrium oxide; an aluminum oxide compound without rhodium supported thereon, wherein the aluminum oxide compound contains aluminum oxide and lanthanum oxide; and a cerium oxide-zirconium oxide-based composite oxide containing cerium oxide, zirconia, lanthanum oxide, and neodymium oxide.The lower catalyst layer comprises an aluminum oxide compound support with platinum supported thereon, wherein the aluminum oxide compound support contains aluminum oxide and lanthanum oxide, which are the same materials as those of the aluminum oxide compound of the upper catalyst layer; and a cerium oxide-zirconium oxide-based composite oxide without platinum supported thereon, wherein the cerium oxide-zirconium oxide-based composite oxide contains cerium oxide, zirconium oxide, lanthanum oxide and neodymium oxide, which are the same materials as those of the cerium oxide-zirconium oxide-based composite oxide of the upper catalyst layer.

[0016] The catalytic converter of the present invention is characterized in that the catalyst layer has a two-layer structure consisting of a lower catalyst layer formed on the surface of a substrate and an upper catalyst layer formed thereon, and in that each of the upper catalyst layer and the lower catalyst layer contains a promoter made of the same materials as a promoter without rhodium or platinum, which is a noble metal catalyst, being supported thereon; specifically, the upper and lower catalyst layers each contain an aluminum oxide compound (which contains aluminum oxide and lanthanum oxide) and a cerium oxide-zirconium oxide-based composite oxide (a compound of cerium oxide, zirconium oxide, lanthanum oxide and neodymium oxide).

[0017] According to the inventors, it was found that when rhodium is supported on a substrate that does not contain cerium oxide, the activity of rhodium is increased, which in turn increases NO. x -Cleaning rate increased.

[0018] Furthermore, if each of the upper and lower catalyst layers contains a promoter made of the same materials, it is possible to obtain a good affinity at the interface between the upper and lower catalyst layers and thus increase the bond strength of the two layers.

[0019] Furthermore, if the packed structure in each of the upper and lower catalyst layers is optimized, a catalytic converter with excellent OSC performance is provided.

[0020] In this process, the substrate can be made from a cellular structure, including materials other than ceramics, such as metals, in addition to cordierite, which is made from a composite oxide of magnesium oxide, aluminum oxide, and silicon dioxide, or ceramic materials such as silicon carbide. Furthermore, the substrate can have a so-called honeycomb structure with a series of cells whose grid contour is a square, hexagon, octagon, or the like.

[0021] The lower catalyst layer, formed on the cell wall surface of the substrate, contains aluminum oxide (Al₂O₃) as a support and platinum (Pt) supported on it, and further contains a cerium oxide-zirconium oxide-based composite oxide (CeO₂-ZrO₂ composite oxide). The aluminum oxide supporting the platinum is an aluminum oxide compound containing aluminum oxide (Al₂O₃) and lanthanum oxide (La₂O₃). Furthermore, the cerium oxide-zirconium oxide-based composite oxide (CeO₂-ZrO₂ composite oxide) is a compound containing cerium oxide (CeO₂), zirconium oxide (ZrO₂), lanthanum oxide (La₂O₃), and neodymium oxide (Nd₂O₃).

[0022] The upper catalyst layer, as described above, contains zirconium oxide, which is a support, and rhodium (Rh) supported thereon. It also contains a compound of cerium oxide (CeO2), zirconium oxide (ZrO2), lanthanum oxide (La2O3), and neodymium oxide (Nd2O3), which are the same materials as those of the lower catalyst layer. Furthermore, it contains an aluminum oxide compound comprising aluminum oxide (Al2O3) and lanthanum oxide (La2O3). The zirconium oxide on which the rhodium is supported is a zirconium oxide compound containing zirconium oxide (ZrO2), lanthanum oxide (La2O3), and yttrium oxide (Y2O3).

[0023] Furthermore, in another embodiment of the catalytic converter according to the present invention, the upper catalyst layer is formed in the region of 80% of the total length of the substrate from one end of the substrate on the downstream side of the exhaust gas flow direction, while the lower catalyst layer is formed in the region of 80% of the total length of the substrate from one end of the substrate on the upstream side of the exhaust gas flow direction. In particular, each of the upper catalyst layer and the lower catalyst layer is preferably formed in the region of 65 to 95% of the total length of the substrate.

[0024] The catalytic converter of the present invention preferably comprises a cordierite honeycomb support with excellent thermal shock resistance. Alternatively, the catalytic converter can be an electrically heated converter (EHC). The electrically heated catalytic converter of this type comprises a honeycomb catalyst and a pair of electrodes attached thereto. When current is supplied to the pair of electrodes to heat the honeycomb catalyst, the activity of the honeycomb catalyst is increased, thus purifying exhaust gas flowing through the honeycomb catalyst. When such a converter is applied to an exhaust system connecting a vehicle engine and a muffler, it is possible to purify exhaust gas at room temperature and also at cold temperatures by activating the catalyst through electrical heating.

[0025] As described above, the catalytic converter of the present invention has a catalyst layer with a two-layer structure consisting of a lower catalyst layer formed on the surface of a substrate and an upper catalyst layer formed thereon. The upper catalyst layer comprises a zirconia support with rhodium, an aluminum oxide compound, and a cerium oxide-zirconium oxide-based composite oxide. The lower catalyst layer comprises an aluminum oxide support with platinum, the aluminum oxide support containing the same materials as the upper catalyst layer, and also includes a cerium oxide-zirconium oxide-based composite oxide containing the same materials as the upper catalyst layer. Thus, a catalytic converter with excellent OSC performance and NOₓ is achieved. x Cleaning services provided. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic view of a catalytic converter of the present invention. Fig. 2 is a partially enlarged view of a cell. Fig. Figure 3 is a longitudinal sectional view illustrating one embodiment of a catalyst layer. Fig. Figure 4 is a graph showing the experimental results for a verification of NO. x -Cleaning performance is demonstrated. Fig. Figure 5 is a graph showing the experimental results for a review of OSC performance. DETAILED DESCRIPTION OF THE FORM(S)

[0026] Embodiments of a catalytic converter according to the present invention are described below with reference to the drawings. The catalytic converter shown in the drawings has an upper catalyst layer formed over a region of 80% of the total length of the substrate from one end of the substrate on the downstream side of the exhaust gas flow direction, and also has a lower catalyst layer formed over a region of 80% of the total length of the substrate from one end of the substrate on the upstream side of the exhaust gas flow direction. It should be noted that the length over which each of the upper and lower catalyst layers is formed is preferably in the range of 65 to 95% of the total length of the substrate. (Exhaust system for exhaust gas)

[0027] First, an exhaust system for exhaust gases, in which the catalytic converter of the present invention is provided, is briefly described. An exhaust system for exhaust gases, to which the catalytic converter of the present invention is applied, has a configuration in which a machine, a catalytic converter, a catalytic three-way converter, a secondary silencer, and a main silencer are arranged and connected to one another by means of system pipes, so that exhaust gas generated in the machine flows through each component via the system pipe and is then expelled. Next, an embodiment of the catalytic converter is described. (Design form of the catalytic converter)

[0028] Fig. Figure 1 is a schematic view of the catalytic converter of the present invention. Fig. 2 is a partially enlarged view of a cell. Fig.Figure 3 is a longitudinal sectional view illustrating one embodiment of a catalyst layer.

[0029] A in Fig. The catalytic converter 10 shown generally comprises a cylindrical substrate 1 with a series of cells and a catalyst layer 3 formed on the surface of a cell wall 2 of each cell, as shown in Fig. 2 shown.

[0030] Examples of substrate 1 cordierite, which is made from a composite oxide of magnesium oxide, aluminum oxide and silicon dioxide, include ceramic materials such as silicon carbide, and materials other than ceramic materials such as metallic materials.

[0031] Substrate 1 has a honeycomb structure with a series of cells whose grid contour is a square, a hexagon, an octagon, or the like. Exhaust gas that enters a cell at one end of substrate 1 on the upstream side (Fr side) of the exhaust gas flow direction flows through the substrate 1 and is cleaned in the process, and then the cleaned exhaust gas flows out of one end of substrate 1 on the downstream side (Rr side) of the exhaust gas flow direction (x direction).

[0032] Next, an embodiment of the catalyst layer will be described with reference to Fig. 2 and Fig. 3 described.

[0033] The in Fig. 2 and Fig. The catalyst layer 3 shown includes a lower catalyst layer 4 formed on the surface of a cell wall 2 and an upper catalyst layer 5 formed on the surface of the lower catalyst layer 4.

[0034] The lower catalyst layer 4 is formed in the area of ​​80% of the total length of the substrate 1 from the end of the substrate 1 on the upstream side Fr of the exhaust gas flow direction, while the upper catalyst layer 5 is formed in the area of ​​80% of the total length of the substrate 1 from the end of the substrate 1 on the downstream side Rr of the exhaust gas flow direction.

[0035] The lower catalyst layer 4 contains an aluminum oxide compound support (a compound of aluminum oxide (Al2O3) and lanthanum oxide (La2O3)) with platinum (Pt) supported on it and also contains a cerium oxide-zirconium oxide-based composite oxide (a compound of cerium oxide (CeO2), zirconium oxide (ZrO2), lanthanum oxide (La2O3) and neodymium oxide (Nd2O3)).

[0036] Meanwhile, the upper catalyst layer 5 contains a zirconia compound support (a compound of zirconia (ZrO2), lanthanum oxide (La2O3) and yttrium oxide (Y2O3)) with rhodium (Rh) supported on it and also contains a cerium oxide-zirconia-based composite oxide (a compound of cerium oxide (CeO2), zirconia (ZrO2), lanthanum oxide (La2O3) and neodymium oxide (Nd2O3)), which are the same materials as those of the lower catalyst layer 4, and further contains an aluminum oxide compound (a compound of aluminum oxide (Al2O3) and lanthanum oxide (La2O3)), which are the same materials as those of the lower catalyst layer 4.

[0037] In the upper catalyst layer 5, rhodium (Rh) is supported only on the zirconium oxide compound support, which contains no cerium oxide. Such a structure can inhibit NO x -Improve cleaning rate.

[0038] Since each of the upper and lower catalyst layers 5 and 4 contains a promoter made of the same materials (a cerium oxide-zirconium oxide-based composite oxide and an aluminum oxide compound), the upper and lower catalyst layers 5 and 4 exhibit good affinity at the interface and thus high bond strength. Furthermore, since the packed structure in each of the upper and lower catalyst layers 5 and 4 is optimized, OSC performance is improved.

[0039] By having a two-layer structure with high bond strength in the catalyst layer 3, the catalytic converter 10 shown in the drawing, with the upper and lower catalyst layers 5, 4, becomes a catalytic converter with excellent OSC performance and NOₓ. x -Cleaning service. (Experiments to check the NO x -Cleaning performance and OSC performance, as well as the results thereof)

[0040] The inventors conducted experiments to determine the NO x -To verify the cleaning performance and OSC performance of catalytic converters. Example 1 and Comparative Examples 1-4 were prepared using the procedures described below. <Vergleichsbeispiel 1>

[0041] In comparative example 1, the lower catalyst layer contains Pt as a catalyst (Pt(0.2) / Al₂O₃(25) + CZ(30)), and the upper catalyst layer contains Rh as a catalyst (Rh(0.12) / CeO₂-ZrO₂ composite oxide(40) + Al₂O₃(20)). The unit of the numerical values ​​in parentheses is g / L. Using nitric acid-Pt, Pt / Al₂O₃ (i.e., Material 1) was first prepared, in which Pt is supported on Al₂O₃. Impregnation was used as a method to cause Pt to be supported on Al₂O₃. Next, a slurry 1 was prepared by pouring Material 1, a CZ material, and an Al₂O₃-based binder into distilled water while stirring. Furthermore, the prepared slurry 1 was poured into a substrate, and unneeded portions were removed with a blower, so that the wall surface of the substrate was coated with the slurry 1.This time, the coating material for the Pt layer was prepared such that the Pt content, the content of material 1, and the content of the CZ material, based on the volume of the substrate, were 0.2 g / l, 25 g / l, and 30 g / l, respectively. Finally, the moisture content was removed for two hours using a dryer maintained at 120°C, and firing was carried out for two hours in an electric furnace at 500°C. Similarly, a Rh / CZ material (i.e., material 2) was prepared using nitric acid-based Rh, in which Rh is supported on a CZ material. Here, the CeO₂-ZrO₂ composite oxide contains 20–70 wt% ZrO₂, 20–70 wt% CeO₂, and 10–15 wt% La₂O₃, Y₂O₃, and Pr₆O. 11and Nd₂O₃. Next, a slurry 2 was prepared by pouring material 2, Al₂O₃, and an Al₂O₃-based binder into distilled water while stirring until the materials were suspended in the distilled water. The prepared slurry 2 was poured onto the substrate to be coated, and any excess was removed with a blower, so that the surface of the substrate was coated with slurry 2. This time, the coating material for the Rh layer was prepared such that the Rh content, the material 2 content, and the Al₂O₃ content, based on the volume of the substrate, were 0.12 g / l, 40 g / l, and 20 g / l, respectively. Finally, the moisture was removed for two hours using a dryer maintained at 120°C, and firing was carried out for two hours in an electric kiln at 500°C. <Vergleichsbeispiel 2>

[0042] In Comparative Example 2, the lower catalyst layer contains Pt as a catalyst (Pt(0.2) / Al₂O₃(25) + CZ(30)), and the upper catalyst layer contains Rh as a catalyst (Rh(0.12) / ZrO₂(40) + Al₂O₃(20)). A slurry was prepared by modifying the specifications of the Rh support (Material 2) used in Comparative Example 1 for slurry 2, and then coating, drying, and firing were carried out. Here, ZrO₂ contains 80–90 wt% ZrO₂ and also contains 10–20 wt% La₂O₃, Y₂O₃, and Pr₆O₆. 11 and Nd2O3 as stabilizers. <Vergleichsbeispiel 3>

[0043] In Comparative Example 3, the lower catalyst layer contains Pt as a catalyst (Pt(0.2) / Al₂O₃(25) + CZ(30)), and the upper catalyst layer contains Rh as a catalyst (Rh layer Rh(0.12) / CeO₂(40) + Al₂O₃(20)). A slurry was prepared by modifying the specifications of the Rh support (Material 2) used in Comparative Example 1 for slurry 2, and then coating, drying, and firing were carried out. With respect to the catalyst, the process was not changed, except that the composition of Material 2 in Comparative Example 1 was modified. Here, CeO₂ greater than or equal to 99 wt% was used as CeO₂. <Beispiel 1>

[0044] In Example 1, the lower catalyst layer contains Pt as a catalyst (Pt(0.2) / Al₂O₃(25) + CZ(30)), and the upper catalyst layer contains Rh as a catalyst (Rh(0.12) / ZrO₂(40) + CZ(15) + Al₂O₃(20)). A slurry 2 was prepared by modifying the specifications of the Rh support (material 2) used in Comparative Example 1 for slurry 2, and then coating, drying, and firing were carried out. With respect to the catalyst, the process was not changed, except for the composition of material 2 in Comparative Example 1. Here, ZrO₂ contains 80–90 wt% ZrO₂ and also contains 10–20 wt% La₂O₃, Y₂O₃, and Pr₆O₆. 11 and Nd₂O₃ as stabilizers. Furthermore, the CZ material contains 20–70 wt% ZrO₂, 20–70 wt% CeO₂, and 10–15 wt% La₂O₃, Y₂O₃, and Pr₆O₃. 11 and Nd2O3. <Vergleichsbeispiel 4>

[0045] In Comparative Example 4, the lower catalyst layer contains Pt as a catalyst (Pt(0.2) / Al₂O₃(25) + CZ(30)), and the upper catalyst layer contains Rh as a catalyst (Rh(0.12) / CeO₂(40) + Al₂O₃(20)). A slurry 2 was prepared by modifying the specifications of the Rh support (material 2) used for slurry 2 in Comparative Example 1, and then coating, drying, and firing were performed. With respect to the catalyst, the process was not changed, except that the composition of material 2 in Comparative Example 1 was modified. Here, CeO₂ greater than or equal to 99 wt% was used as CeO₂. Furthermore, the CZ material contains 20–70 wt% ZrO₂, 20–70 wt% CeO₂, and 10–15 wt% La₂O₃, Y₂O₃, and Pr₆O₃. 11 and Nd2O3. <beurteilungsmethode>

[0046] A 4.3-liter 8-cylinder V gasoline engine was used, and the bed temperature of a catalyst on the downstream side was set to 950°C, so that a cycle which includes recirculation, fuel cut-off, rich and lean per minute as one condition was performed for 50 hours.

[0047] An aged catalytic converter was installed, and the purification rate was measured when the incoming gas atmosphere was periodically switched between the rich and lean sides of the air-fuel ratio. Additionally, an aged catalytic converter was installed, and the purification rate was also measured when the incoming gas atmosphere was continuously maintained on the rich side of the air-fuel ratio.

[0048] Table 1 below shows the materials used. [Table 1] Area Material designation Manufacturer composition Upper catalyst layer (Rh layer) ZrO2 DAIICHI KIGENSOKAGAKU KOGYOCo., LTD. ZrO2 (84 Ma%),La2O3 (6 Ma%),Y2O3 (10 Ma%) CeO2-ZrO2 DAIICHI KIGENSOKAGAKU KOGYOCo., LTD. CeO2 (21 Ma%), ZrO2 (72 Ma%), La2O3 (1.7 Ma%),Nd2O3 (5.3 Ma%) Al2O3 Sasol Al2O3 (99 wt%), La2O3 (1 wt%) Lower catalyst layer (Pt layer) CeO2-ZrO2 DAIICHI KIGENSOKAGAKU KOGYOCo., LTD. CeO2 (21 Ma%), ZrO2 (72 Ma%), La2O3 (1.7 Ma%),Nd2O3 (5.3 Ma%) Al2O3 Sasol Al2O3 (99 wt%), La2O3 (1 wt%) <Ergebnisse des Experiments>

[0049] Fig. 4 and Fig. Figure 5 shows the experimental results. Fig. 4 a graph showing the experimental results for a verification of NO x -Cleaning performance is demonstrated. Fig. Figure 5 is a graph showing the experimental results for a review of OSC performance. Both in Fig. 4 as well as in Fig. 5 is the result of comparison example 1 shown as a reference, and the results of other comparison examples and one example are shown in relation to the result of comparison example 1.

[0050] Fig. 4 can confirm that comparative example 2 and example 1 show excellent results for NO. x -purification rate, while the other samples show low NO x -Show cleaning rates.

[0051] However, Fig. 5 confirm that all samples, with the exception of comparison example 2, have a high OSC performance at essentially the same level.

[0052] From the results of Fig. 4 and Fig. 5 confirms that only example 1 shows excellent results for both NO x -purification performance as well as OSC performance. It is assumed that this is due to the composition of the upper catalyst layer and the lower catalyst layer of Example 1. This shows that the catalytic converter of the present invention has excellent NOₓ performance. x -It possesses cleaning performance and OSC performance. DESCRIPTION OF SYMBOLS 1 substrate 2 cell wall 3 catalyst layer 4 Lower catalyst layer 5 Upper catalyst layer 10 Catalytic converter Upstream side of the exhaust flow direction Rr Downstream side of the exhaust flow direction< / beurteilungsmethode>

Claims

[1] Catalytic converter, comprising: a substrate with a cellular structure through which exhaust gas flows; and a catalyst layer formed on a cell wall surface of the substrate, wherein the catalyst layer comprises a lower catalyst layer and an upper catalyst layer, wherein the lower catalyst layer is formed on a surface of the substrate and the upper catalyst layer is formed on a surface of the lower catalyst layer. the upper catalyst layer includes: a zirconia compound support with rhodium supported thereon, wherein the zirconia compound support contains zirconia, lanthanum oxide and yttrium oxide, an aluminum oxide compound without rhodium carried on it, wherein the aluminum oxide compound contains aluminum oxide and lanthanum oxide, and a cerium oxide-zirconium oxide-based composite oxide containing cerium oxide, zirconium oxide, lanthanum oxide and neodymium oxide, and the lower catalyst layer includes: an aluminum oxide compound support with platinum supported thereon, wherein the aluminum oxide compound support contains aluminum oxide and lanthanum oxide, which are the same materials as those of the aluminum oxide compound of the upper catalyst layer, and a cerium oxide-zirconium oxide-based composite oxide without platinum supported thereon, wherein the cerium oxide-zirconium oxide-based composite oxide contains cerium oxide, zirconia, lanthanum oxide and neodymium oxide, which are the same materials as those of the cerium oxide-zirconium oxide-based composite oxide of the upper catalyst layer.

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