CATALYTIC CONVERTER

Abstract

A catalytic converter with excellent OSC performance and No.sub.x purification performance. The catalytic converter includes a substrate with a cell structure and a catalyst layer formed on a cell wall surface of the substrate. The catalyst layer has a catalyst layer arranged on the upstream side and a catalyst layer arranged on the downstream side in an exhaust gas flow direction on the substrate. The catalyst layer on the upstream side includes a support containing an Al.sub.2O.sub.3—CeO.sub.2—ZrO.sub.2 ternary composite oxide (ACZ material) and an Al.sub.2O.sub.3—ZrO.sub.2 binary composite oxide (AZ material), and at least Rh that is a noble metal catalyst carried on the support, and the catalyst layer on the downstream side includes a support and Pd or Pt that is a noble metal catalyst carried on the support. In the support in the catalyst layer on the upstream side, the mass proportion of ACZ material/(ACZ material+AZ material) is in the range of 0.33 to 0.5, and greater than or equal to 75% mass Rh is carried on the Al.sub.2O.sub.3—ZrO.sub.2 binary composite oxide of the support.

Claims

1. A catalytic converter comprising: a substrate with a cell structure through which exhaust gas flows; and a catalyst layer formed on a cell wall surface of the substrate, wherein: the catalyst layer has a catalyst layer on an upstream side arranged on the upstream side in an exhaust gas flow direction on the substrate, and a catalyst layer on a downstream side arranged on the downstream side in the exhaust gas flow direction on the substrate, the catalyst layer on the upstream side includes a support containing an Al.sub.2O.sub.3—CeO.sub.2—ZrO.sub.2 ternary composite oxide and an Al.sub.2O.sub.3—ZrO.sub.2 binary composite oxide, and at least Rh that is a noble metal catalyst carried on the support, the catalyst layer on the downstream side includes a support, and Pd or Pt that is a noble metal catalyst carried on the support, in the support in the catalyst layer on the upstream side, a mass proportion of the Al.sub.2O.sub.3—CeO.sub.2—ZrO.sub.2 ternary composite oxide/(the Al.sub.2O.sub.3—CeO.sub.2—ZrO.sub.2 ternary composite oxide+the Al.sub.2O.sub.3—ZrO.sub.2 binary composite oxide) is in a range of 0.33 to 0.5, and in the catalyst layer on the upstream side, greater than or equal to 75 mass % Rh is carried on the Al.sub.2O.sub.3—ZrO.sub.2 binary composite oxide of the support.

2. The catalytic converter according to claim 1, wherein: the catalyst layer on the upstream side and the catalyst layer on the downstream side partially overlap with each other, and in a portion where the catalyst layer on the upstream side and the catalyst layer on the downstream side partially overlap with each other, the catalyst layer on the downstream side is arranged on a surface of the substrate, and the catalyst layer on the upstream side is arranged on a surface of the catalyst layer on the downstream side.

3. A catalytic converter comprising: a substrate with a cell structure through which exhaust gas flows; and a catalyst layer formed on a cell wall surface of the substrate, wherein: the catalyst layer has a lower catalyst layer arranged on a surface of the substrate, and an upper catalyst layer arranged on a surface of the lower catalyst layer, the upper catalyst layer includes a support containing an Al.sub.2O.sub.3—CeO.sub.2—ZrO.sub.2 ternary composite oxide and an Al.sub.2O.sub.3—ZrO.sub.2 binary composite oxide, and at least Rh that is a noble metal catalyst carried on the support, the lower catalyst layer includes a support, and Pd or Pt that is a noble metal catalyst carried on the support, in the support in the upper catalyst layer, a mass proportion of the Al.sub.2O.sub.3—CeO.sub.2—ZrO.sub.2 ternary composite oxide/(the Al.sub.2O.sub.3—CeO.sub.2—ZrO.sub.2 ternary composite oxide+the Al.sub.2O.sub.3—ZrO.sub.2 binary composite oxide) is in a range of 0.33 to 0.5, and in the upper catalyst layer, greater than or equal to 75 mass % Rh is carried on the Al.sub.2O.sub.3—ZrO.sub.2 binary composite oxide of the support.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 is a schematic view of a catalytic converter of the present disclosure.

[0031] FIG. 2 is a partially enlarged view of a cell.

[0032] FIG. 3 is a longitudinal sectional view illustrating Embodiment 1 of a catalyst layer.

[0033] FIG. 4 is a longitudinal sectional view illustrating Embodiment 2 of a catalyst layer.

[0034] FIG. 5 is a longitudinal sectional view illustrating Embodiment 3 of a catalyst layer.

[0035] FIG. 6 is a graph showing the experimental results of verification of OSC performance and low-temperature activity performance in relation to the ACZ ratio in a support in an upper catalyst layer.

[0036] FIG. 7 is a graph showing the experimental results of verification of the OSC performance and the NO.sub.x purification performance in relation to the Rh rate in an AZ material in the upper catalyst layer.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

[0037] Hereinafter, embodiments of a catalytic converter of the present disclosure will be described with reference to the drawings.

(Exhaust System for Exhaust Gas)

[0038] First, an exhaust system for exhaust gas in which the catalytic converter of the present disclosure is provided will be briefly described. An exhaust system for exhaust gas to which the catalytic converter of the present disclosure is applied has a configuration in which an engine, a catalytic converter, a three-way catalytic converter, a sub-muffler, and a main muffler are arranged and are mutually connected with system pipes so that exhaust gas generated in the engine flows through each part via the system pipe and is then discharged. Next, an embodiment of the catalytic converter will be described.

(Embodiment of Catalytic Converter)

[0039] FIG. 1 is a schematic view of the catalytic converter of the present disclosure. FIG. 2 is a partially enlarged view of a cell. Each of FIGS. 3 to 5 is a longitudinal sectional view illustrating an embodiment of a catalyst layer.

[0040] A catalytic converter 10 shown in FIG. 1 generally includes a cylindrical substrate 1 with a number of cells and a catalyst layer 3 (see FIG. 2) formed on the surface of a cell wall 2 of each cell.

[0041] Herein, examples of the substrate 1 include cordierite made of a composite oxide of magnesium oxide, aluminum oxide, and silicon dioxide, ceramic materials, such as silicon carbide, and materials other than ceramic materials, such as metal materials.

[0042] The substrate 1 has a honeycomb structure with a number of cells whose lattice contour is a quadrangle, a hexagon, an octagon, or the like. Exhaust gas, which has entered a cell at an end of the substrate 1 on the upstream side (Fr side) in the exhaust gas flow direction, flows through the substrate 1, and is purified in the circulation process, and then, the purified exhaust gas flows out from an end of the substrate 1 on the downstream side (Rr side) in the exhaust gas flow direction (X-direction).

[0043] Next, embodiments of a catalyst layer will be described with reference to FIGS. 3 to 5.

[0044] The catalyst layer 3 shown in FIG. 3 is a zone-coated catalyst layer that has a catalyst layer 4 on the upstream side arranged on the upstream side in the exhaust gas flow direction on the substrate 1 and a catalyst layer 5 on the downstream side arranged on the downstream side in the exhaust gas flow direction on the substrate 1.

[0045] The lengths of the catalyst layer 4 on the upstream side and the catalyst layer 5 on the downstream side are both 50% of the total length of the substrate 1 as 100%. It should be noted that other than the embodiment shown in the drawing, it is also possible to adopt an embodiment in which, for example, the lengths of the catalyst layer 4 on the upstream side and the catalyst layer 5 on the downstream side are 60% and 40% of the total length of the substrate 1, respectively.

[0046] The catalyst layer 4 on the upstream side includes a support that contains an Al.sub.2O.sub.3—CeO.sub.2—ZrO.sub.2 ternary composite oxide (ACZ material) and an Al.sub.2O.sub.3—ZrO.sub.2 binary composite oxide (AZ material), and at least Rh that is a noble metal catalyst carried on the support.

[0047] Examples of the embodiment in which at least Rh is contained as a noble metal catalyst include one or more of Rh, Rh/Pd, Rh/Pt, and Rh/Pt/Pd.

[0048] Meanwhile, the catalyst layer 5 on the downstream side includes a support that contains Al.sub.2O.sub.3, CeO.sub.2—ZrO.sub.2 (CZ material), and the like, and Pd or Pt that is a noble metal catalyst carried on the support. It should be noted that the type of support in the catalyst layer 5 on the downstream side is not particularly limited, and any type of support commonly used for exhaust gas catalysts may be adopted.

[0049] Examples of the embodiment in which Pd or Pt is contained as a noble metal catalyst include one or more of Pd, Pt, and Pd/Pt.

[0050] In the support containing the Al.sub.2O.sub.3—CeO.sub.2—ZrO.sub.2 ternary composite oxide (ACZ material) and the Al.sub.2O.sub.3—ZrO.sub.2 binary composite oxide (AZ material) in the catalyst layer 4 on the upstream side, the mass proportion of ACZ material/(ACZ material+AZ material) is in the range of 0.33 to 0.5. Further, in the catalyst layer 4 on the upstream side, greater than or equal to 75 mass % Rh is carried on the AZ material of the support.

[0051] The experimental results, which will be described later, have verified that with the mass proportion of ACZ material/(ACZ material+AZ material) in the range of 0.33 to 0.5, the catalytic converter 10 that is excellent in both the OSC performance and the low-temperature activity performance (NO.sub.x purification performance) is realized.

[0052] Further, it has been also verified that with greater than or equal to 75 mass % Rh being carried on the AZ material of the support, the catalytic converter 10 that is excellent in both the OSC performance and the NO.sub.x purification performance is realized. Such a converter was realized because in order to deal with the problem that with a greater content of CeO.sub.2 in the support in the catalyst layer 4 on the upstream side, the NO.sub.x purification performance, which is a characteristic of Rh, would degrade, greater than or equal to 75 mass % Rh was carried on the AZ material that does not contain CeO.sub.2 in the support, so that the degradation of the NO.sub.x purification performance was suppressed.

[0053] Meanwhile, in a catalyst layer 3A shown in FIG. 4, the lengths of a catalyst layer 4A on the upstream side and a catalyst layer 5A on the downstream side are both 60% of the total length of the substrate 1, and thus 20% of the catalyst layer 4A and 20% of the catalyst layer 5A in length overlap with each other and in the portion where the catalyst layers overlap with each other, the catalyst layer 5A on the downstream side is arranged on the surface of the substrate 1 and the catalyst layer 4A on the upstream side is arranged on the surface of the catalyst layer 5A on the downstream side.

[0054] In addition, a catalyst layer 3B shown in FIG. 5 has a lower catalyst layer 5B arranged on the surface of the substrate 1 and an upper catalyst layer 4B arranged on the surface of the lower catalyst layer 5B.

[0055] Moreover, the upper catalyst layer 4B and the lower catalyst layer 5B are configured similarly to the aforementioned catalyst layers 4 and 4A on the upstream side and catalyst layers 5 and 5A on the downstream side, respectively.

[0056] As the upper catalyst layer 4B is configured similarly to the aforementioned catalyst layers 4 and 4A on the upstream side, a catalytic converter that is excellent in both the OSC performance and the NO.sub.x purification performance is realized.

(Experiments for Verifying OSC Performance and Low-Temperature Activity Performance in Relation to the ACZ Proportion in a Support in an Upper Catalyst Layer and Verifying OSC Performance and NO.sub.x Purification Performance in Relation to the Rh Rate in an AZ Material in an Upper Catalyst Layer, and the Results Thereof)

[0057] The inventors evaluated the performance of catalytic converters by producing catalyst slurry and catalytic converters using methods described below and by conducting endurance tests thereon, so that the optimal ranges of the ACZ proportion in a support in an upper catalyst layer and the Rh rate in an AZ material in the upper catalyst layer were defined. Five types of catalyst layers of Examples 1 and 2 and Comparative Examples 1 to 3 shown in Table 1 below and five types of catalyst layers of Examples 3 and 4 and Comparative Examples 4 to 6 shown in Table 2 below were produced, so that a catalytic converter having each of the catalyst layers was produced to conduct the endurance test thereon.

(Regarding Methods for Producing Catalyst Layers)

[0058] First, using nitric acid Pd, Pd/Al.sub.2O.sub.3 (Material 1) in which Pd is carried on Al.sub.2O.sub.3 was prepared. Impregnation was used as a method for causing Pt to be carried on Al.sub.2O.sub.3. Next, Slurry 1 was prepared by pouring Material 1, a CeO.sub.2—ZrO.sub.2 binary composite oxide (CZ material), sulfuric acid Ba, and an Al.sub.2O.sub.3-based binder into distilled water while agitating them such that the materials were suspended in the distilled water. Further, the prepared Slurry 1 was poured onto a substrate, and unnecessary portions were blown away with a blower, so that the wall surface of the substrate was coated with the materials. At that time, the coating materials for the Pd layer were prepared such that the content of Pd, the content of Material 1, the content of the CZ material, and the content of sulfuric acid Ba with respect to the volume of the substrate were 0.2 g/L, 25 g/L, 30 g/L, and 2.5g/L, respectively. Finally, moisture was dried with a dryer kept at 120° C. for two hours, and baking was performed with an electric furnace at 500° C. for two hours.

[0059] Likewise, using nitric acid Rh, a Rh/AZ material (Material 2) in which Rh is carried on the AZ material was prepared. Next, Slurry 2 was prepared by pouring Material 2, an ACZ material, Al.sub.2O.sub.3, and an Al.sub.2O.sub.3-based binder into distilled water while agitating them such that the materials were suspended in the distilled water. The prepared Slurry 2 was poured onto a substrate, and unnecessary portions were blown away with a blower, so that the wall surface of the substrate was coated with the materials. At that time, the coating materials for the Rh layer were prepared such that the content of Rh, the content of Material 2 and ACZ material, and the content of Al.sub.2O.sub.3 with respect to the volume of the substrate were 0.12 g/L, the proportion shown in Table 1, and 20 g/L, respectively. Finally, moisture was dried with a dryer kept at 120° C. for two hours, and baking was performed with an electric furnace at 500° C. for two hours.

[0060] In summary, in each of the catalyst layers with a two-layer structure of Comparative Examples 1 to 3 and Examples 1 and 2 shown in Table 1, the lower catalyst layer (Pd layer) contains Pd (0.2 g/L)/Al.sub.2O.sub.3 (25 g/L)+CZ material (30 g/L)+sulfuric acid Ba (2.5 g/L), and the upper catalyst layer (Rh layer) contains Rh (0.12 g/L)/AZ material (X g/L)+ACZ material (Y g/L)+Al.sub.2O.sub.3 (20 g/L). The content of the AZ material (X g/L) and the content of the ACZ material (Y g/L) in the Rh layer in each of Examples and Comparative Examples are shown in Table 1.

TABLE-US-00001 TABLE 1 AZ ACZ Proportion of ACZ material material material (g/L) (g/L) (ACZ/(ACZ + AZ)) Comparative 105 0 0 Example 1 Comparative 87.5 17.5 0.17 Example 2 Example 1 70 35 0.33 Example 2 52.5 52.5 0.50 Comparative 0 105 1.00 Example 3

[0061] Meanwhile, in the production of Examples 3 and 4 and Comparative Examples 4 to 6, the lower catalyst layers (Pd layers) were produced using the same production methods as those used for Examples 1 and 2 and Comparative Examples 1 to 3.

[0062] Next, using nitric acid Rh, a Rh/AZ material (Material 2) in which Rh is carried on the AZ material and a Rh/ACZ material (Material 3) in which Rh is carried on the ACZ material were prepared. It should be noted that the percentage of Rh carried in each of Examples 3 and 4 and Comparative Examples 4 to 6 is shown in Table 2.

[0063] Next, Slurry 3 was prepared by pouring Material 2, Material 3, Al.sub.2O.sub.3, and an Al.sub.2O.sub.3-based binder into distilled water while agitating them such that the materials were suspended in the distilled water. The prepared Slurry 3 was poured onto a substrate, and unnecessary portions were blown away with a blower, so that the wall surface of the substrate was coated with the materials. At that time, the coating materials for the Rh layer were prepared such that the content of Rh, the content of Material 2, the content of Material 3, and the content of Al.sub.2O.sub.3 with respect to the volume of the substrate were 0.12 g/L, 52.5 g/L, 52.5 g/L, and 20 g/L, respectively. Finally, moisture was dried with a dryer kept at 120° C. for two hours, and baking was performed with an electric furnace at 500° C. for two hours.

[0064] In summary, in each of the catalyst layers with a two-layer structure of Comparative Examples 4 to 6 and Examples 3 and 4 shown in Table 2, the lower catalyst layer (Pd layer) contains Pd (0.2 g/L)/Al.sub.2O.sub.3 (25 g/L)+CZ material (30 g/L)+sulfuric acid Ba (2.5 g/L), and the upper catalyst layer (Rh layer) contains Rh (X g/L)/AZ material (52.5 g/L)+Rh (0.12-X g/L)/ACZ material (52.5 g/L)+Al.sub.2O.sub.3 (20 g/L). The percentage of Rh (X g/L) carried on the AZ material and the percentage of Rh (0.12-X g/L) carried on the ACZ material in the Rh layer in each of Examples and Comparative Examples are shown in Table 2.

TABLE-US-00002 TABLE 2 Percentage of Rh carried (%) AZ material ACZ material Comparative 0 100 Example 4 Comparative 25 75 Example 5 Comparative 50 50 Example 6 Example 3 75 25 Example 4 100 0

(Regarding Endurance Test)

[0065] Each of the catalytic converters was mounted on the exhaust system of a 4.3 L V8 cylinder gasoline engine, and an endurance test was conducted thereon for 50 hours at a floor temperature of 1000° C. on condition that feedback, fuel cut, rich, and lean were included per minute.

(Regarding Evaluation Method)

[0066] A catalyst converter that had degraded was mounted on the exhaust system and the entering gas temperature was increased by 20° C. per minute, so that the low-temperature activity was evaluated at a temperature at which the purification rate reached 50%. Further, a catalytic converter that had degraded was mounted on the exhaust system, so that the NO.sub.x purification performance in a steady rich state was evaluated with the amount of NO.sub.x exhausted when the entering gas atmosphere was continuously maintained on the rich side of the A/F ratio. Furthermore, a catalytic converter that had degraded was mounted on the exhaust system and the entering gas atmosphere was switched between the rich and lean sides of the A/F ratio, so that the OSC performance was evaluated through the calculation of the OSC from the behavior of a sensor provided on the downstream side of the catalyst in response to the switching.

[0067] FIG. 6 shows the experimental results of the verification of the OSC performance and low-temperature activity performance in relation to the ACZ proportion in the support in the upper catalyst layer, and FIG. 7 shows the experimental results of the verification of the OSC performance and NO.sub.x purification performance in relation to the Rh percentage in the AZ material in the upper catalyst layer.

[0068] FIG. 6 can confirm that with the mass proportion of ACZ material/(ACZ material+AZ material) in the range of 0.33 to 0.5, which is in the range between the mass proportions of Example 1 and Example 2, excellent OSC performance and low-temperature activity performance are both obtained. In accordance with the experimental results, the mass proportion of ACZ material/(ACZ material+AZ material) in the support in the upper catalyst layer was defined to be in the range of 0.33 to 0.5.

[0069] Meanwhile, FIG. 7 can confirm that with greater than or equal to 75 mass % (and less than or equal to 100 mass %) Rh, which is in the range between the mass percentages of Example 3 and Example 4, excellent OSC performance and NO.sub.x purification performance are both obtained. In accordance with the experimental results, the ratio of Rh carried on the AZ material in the support in the upper catalyst layer was defined to be greater than or equal to 75 mass %.

[0070] Although the embodiments of the present disclosure have been described in detail with reference to the drawings, specific structures are not limited thereto, and any design changes that may occur within the spirit and scope of the present disclosure are all included in the present disclosure.

DESCRIPTION OF SYMBOLS

[0071] 1 Substrate [0072] 2 Cell wall [0073] 3, 3A, 3B Catalyst layers [0074] 4, 4A Catalyst layers on the upstream side [0075] 5, 5A Catalyst layers on the downstream side [0076] 4B Upper catalyst layer [0077] 5B Lower catalyst layer [0078] 10 Catalytic converter [0079] Fr Upstream side in the exhaust gas flow direction [0080] Rr Downstream side in the exhaust gas flow direction