Exhaust gas purification system and exhaust gas purification catalyst for gasoline engines

Abstract

To provide an exhaust gas purification system for a gasoline engine that has high NH3 purification performance after endurance.SOLUTION: An exhaust gas purification system for a gasoline engine disclosed herein is disposed in an exhaust path of a gasoline engine. The exhaust gas purification system comprises an upstream catalytic converter including a first catalyst, and a downstream catalytic converter including a second catalyst. The first catalyst contains a catalytic precious metal. The second catalyst has a structure in which an NH3 adsorption layer and a catalyst layer are stacked on a base material. The NH3 adsorption layer of the second catalyst contains zeolite as the NH3 adsorption material. The catalyst layer of the second catalyst contains a catalytic precious metal and an OSC material.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an exhaust gas purification system for a gasoline engine. The present invention also relates to a catalyst for exhaust gas purification suitable for the exhaust gas purification system for a gasoline engine.

Background Art

[0002] Exhaust gas discharged from a gasoline engine of an automobile or the like contains harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). In order to efficiently react and remove these harmful components from the exhaust gas, a catalyst for exhaust gas purification has been conventionally used.

[0003] In order to further reduce the emission of NOx, an exhaust gas purification system for a gasoline engine that combines a start catalyst (S / C) and an underfloor catalyst (UF / C) is known (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, exhaust gas regulations have been increasingly strengthened, and it is desired to reduce the amount of NH3 emissions from gasoline engine vehicles. NH3 is a component that can be generated by over-reduction of NOx by an exhaust gas purification catalyst. In an exhaust gas purification system that combines a start catalyst (S / C) and an underfloor catalyst (UF / C), the higher the NOx purification performance, the greater the amount of NH3 emissions. Patent Document 1 describes that the NH3 purification performance is improved by introducing zeolite having NH3 adsorption ability into an exhaust gas purification system for a gasoline engine.

[0006] However, after diligent research by the inventors, it was found that conventional exhaust gas purification systems for gasoline engines using zeolite with NH3 adsorption capacity have a problem in that the NH3 purification performance deteriorates after extended use.

[0007] This invention has been made in view of the above circumstances, and its purpose is to provide an exhaust gas purification system for gasoline engines that has high NH3 purification performance after durability. [Means for solving the problem]

[0008] The exhaust gas purification system for a gasoline engine disclosed herein is configured to be placed in the exhaust path of a gasoline engine, and the exhaust gas purification system includes an upstream catalytic converter including a first catalyst and a downstream catalytic converter including a second catalyst. The first catalyst contains a catalytic noble metal. The second catalyst has a structure in which an NH3 adsorption layer and a catalyst layer are laminated on a substrate. The NH3 adsorption layer of the second catalyst contains zeolite as an NH3 adsorbent. The catalyst layer of the second catalyst contains a catalytic noble metal and an OSC material.

[0009] In completing the exhaust gas purification system for gasoline engines disclosed herein, the inventors have found the following: In gasoline engine exhaust gas purification systems, the operating environment temperature range is high, and the atmosphere fluctuates between a rich atmosphere and a lean atmosphere. In the region of the air-fuel ratio from rich to stoichiometric, the oxygen concentration is low, so at high temperatures, the structure of the zeolite having NH3 adsorption capacity deteriorates, which reduces the NH3 purification performance after durability.

[0010] Therefore, in the exhaust gas purification system for gasoline engines disclosed herein, a catalyst layer containing an OSC material is laminated onto an NH3 adsorption layer containing a zeolite. This allows oxygen to be supplied from the OSC material to the NH3 adsorption layer even in the rich to stoichiometric regions where the oxygen concentration is low, thereby suppressing structural degradation of the zeolite. Consequently, the exhaust gas purification system disclosed herein provides an exhaust gas purification system with high NH3 purification performance even after extended use.

[0011] In a preferred embodiment of the exhaust gas purification system for a gasoline engine disclosed herein, the NH3 adsorption layer is laminated below the catalyst layer in the second catalyst. This configuration provides an exhaust gas purification system with higher NH3 purification performance after durability.

[0012] In one preferred embodiment of the exhaust gas purification system for a gasoline engine disclosed herein, the zeolite is a CHA-type zeolite supporting Cu. With such a configuration, it is possible to provide an exhaust gas purification system that exhibits particularly high NH3 purification performance after durability.

[0013] The exhaust gas purification system for gasoline engines disclosed herein may take the following forms. In the exhaust gas flow direction of the exhaust path, a gasoline particulate filter is further provided between the upstream catalytic converter and the downstream catalytic converter. • In the exhaust gas flow direction of the exhaust path, a gasoline particulate filter is further provided downstream of the downstream catalytic converter. The first catalyst of the upstream catalytic converter is a tandem-type catalyst comprising an upstream catalyst and a downstream catalyst. In this case, a gasoline particulate filter may be further provided between the upstream catalytic converter and the downstream catalytic converter, or downstream of the downstream catalytic converter. Alternatively, the downstream catalyst of the first catalyst may function as a gasoline particulate filter. · The first catalyst body of the upstream catalyst converter has a function as a gasoline particulate filter.

[0014] From another aspect, the exhaust gas purification catalyst body for a gasoline engine disclosed herein includes a base material, an NH3 adsorption layer laminated on the base material, and a catalyst layer laminated on the NH3 adsorption layer. The NH3 adsorption layer contains zeolite as an NH3 adsorbent and an OSC material. The catalyst layer contains a noble metal catalyst and an OSC material. The exhaust gas purification catalyst body for a gasoline engine is suitable for the above exhaust gas purification system for a gasoline engine. Here, the NH3 adsorption layer may further contain a noble metal catalyst.

Brief Description of the Drawings

[0015] [Figure 1] It is a schematic diagram showing an exhaust gas purification system according to the first embodiment. [Figure 2] It is a perspective view schematically showing a second catalyst body used in the exhaust gas purification system according to the first embodiment. [Figure 3] It is a partial cross-sectional view of an example of the second catalyst body in FIG. 2 cut in the cylinder axis direction. [Figure 4] It is a partial cross-sectional view of another example of the second catalyst body in FIG. 2 cut in the cylinder axis direction. [Figure 5] It is a partial cross-sectional view of still another example of the second catalyst body in FIG. 2 cut in the cylinder axis direction. [Figure 6] It is a partial cross-sectional view schematically showing the laminated structure of the first catalyst body used in the exhaust gas purification system according to the first embodiment. [Figure 7] It is a schematic diagram showing an exhaust gas purification system according to the second embodiment. [Figure 8] It is a schematic diagram showing an exhaust gas purification system according to the third embodiment. [Figure 9] It is a schematic diagram showing an exhaust gas purification system according to the fourth embodiment. [Figure 10] It is a schematic diagram showing an exhaust gas purification system according to the fifth embodiment. [Figure 11]It is a schematic diagram showing an exhaust gas purification system according to the sixth embodiment. [Figure 12] It is a schematic diagram showing an exhaust gas purification system according to the seventh embodiment. [Figure 13] It is a schematic diagram showing an exhaust gas purification system according to the eighth embodiment. [Figure 14] (A) to (F) are each schematic diagrams showing the layer structure of the second catalyst body of the exhaust gas purification systems of each example and each comparative example. [Figure 15] It is a graph showing the NH3 emission amounts after durability of the exhaust gas purification systems of each example and each comparative example.

Mode for Carrying Out the Invention

[0016] Hereinafter, preferred embodiments of the present invention will be described while referring to the drawings. In addition, matters other than those specifically mentioned in this specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in the relevant field. The present invention can be implemented based on the content disclosed in this specification and the common technical knowledge in the relevant field. Further, in the following drawings, members and parts having the same function are denoted by the same reference numerals, and duplicate explanations may be omitted or simplified. The dimensional relationships (length, width, thickness, etc.) in each figure do not necessarily reflect the actual dimensional relationships. In addition, in this specification, the notation "A to B" (A and B are arbitrary numerical values) indicating a range includes the meaning of "not less than A and not more than B", as well as the meaning of "preferably greater than A" and "preferably less than B".

[0017] 〔First Embodiment〕 Figure 1 is a schematic diagram of an exhaust gas purification system 100 according to a first embodiment, which is an example of an exhaust gas purification system disclosed herein. The exhaust gas purification system 100 is configured to be placed in the exhaust path of a gasoline engine 1 and is connected to the gasoline engine 1. The arrow F shown in Figure 1 indicates the direction of exhaust gas flow. The exhaust gas purification system 100 includes an upstream catalytic converter 10 and a downstream catalytic converter 50. The terms "upstream" and "downstream" of the catalytic converters indicate their positional relationship in the direction of exhaust gas flow. Therefore, the downstream catalytic converter 50 is located downstream of the upstream catalytic converter 10 in the exhaust gas flow direction F of the exhaust path of the gasoline engine 1.

[0018] The upstream catalytic converter 10 comprises a first catalyst and a first housing that houses it. The downstream catalytic converter 50 comprises a second catalyst and a second housing that houses it. The first catalyst is located upstream of the second catalyst in the exhaust gas flow direction F. The first catalyst is typically a startup catalyst (S / C), but is not limited thereto. The second catalyst is located downstream of the first catalyst 20 in the exhaust gas flow direction F. The first catalyst is typically an underfloor catalyst (UF / C), but is not limited thereto. The configuration of the first and second housings may be the same as or similar to the housings used in conventional startup catalysts and underfloor catalysts.

[0019] The first and second catalysts will be described in detail below. The first catalyst may have the same or similar configuration as conventionally known catalysts. Therefore, the second catalyst will be described first.

[0020] <Second catalyst body> Examples of the configuration of the second catalyst are shown in Figures 2 to 5. As shown in Figures 3 to 5, the second catalyst 60 has a structure in which an NH3 adsorption layer 80 and a second catalyst layer 90 are laminated on a second substrate 70. Therefore, the second catalyst 60 includes the second substrate 70, the NH3 adsorption layer 80, and the second catalyst layer 90.

[0021] The second substrate 70 constitutes the framework of the second catalyst 60. The second substrate 70 is not particularly limited, and various materials and forms conventionally used in this type of application can be used. The second substrate 70 may be a ceramic support composed of ceramics such as cordierite, aluminum titanate, or silicon carbide, or a metal support composed of stainless steel (SUS), Fe-Cr-Al alloy, Ni-Cr-Al alloy, etc. As shown in Figure 2, the second substrate 70 here has a honeycomb structure. The second substrate 70 in the illustrated example is a straight-flow type substrate, but it may also be a wall-follow type substrate.

[0022] In the drawing, direction X indicates the cylindrical axis direction of the second base material 70, X1 indicates the upstream side in the exhaust gas flow direction F, and X2 indicates the downstream side in the exhaust gas flow direction. The second base material 70 comprises a plurality of cells (cavities) 72 arranged regularly in the cylindrical axis direction X, and partition walls (ribs) 74 that separate the plurality of cells 72. Although not particularly limited, the volume of the second base material 70 (apparent volume including the volume of the cells 72) may be approximately 0.1 to 10 L, for example 0.5 to 5 L. Also, the average length (total length) L of the second base material 70 along the cylindrical axis direction X may be approximately 10 to 500 mm, for example 50 to 300 mm.

[0023] Cell 72 serves as a flow path for exhaust gas. Cell 72 extends in the direction of the cylindrical axis X. Cell 72 is a through-hole that penetrates the second base material 70 in the direction of the cylindrical axis X. The shape, size, number, etc. of cell 72 may be designed considering, for example, the flow rate and composition of the exhaust gas flowing through the second catalyst 60. The shape of the cross-section of cell 72 perpendicular to the cylindrical axis X is not particularly limited. The cross-sectional shape of cell 72 may be a quadrilateral such as a square, parallelogram, rectangle, trapezoid, or other polygons (e.g., triangle, hexagon, octagon), corrugated, circular, or various other geometric shapes. The partition wall 74 faces the cell 72 and separates adjacent cells 72. While not particularly limited, the average thickness of the partition wall 74 (dimension perpendicular to the surface; the same applies hereinafter) may be approximately 0.1 to 10 mil (1 mil is approximately 25.4 μm), for example, 0.2 to 5 mil, from the viewpoint of improving mechanical strength and reducing pressure loss. The partition wall 74 may be porous so that exhaust gas can pass through.

[0024] An NH3 adsorption layer 80 and a second catalyst layer 90 are laminated on the second substrate 70. The lamination order of the NH3 adsorption layer 80 and the second catalyst layer 90 is not particularly limited. As shown in Figure 3, in the second catalyst 60, the NH3 adsorption layer 80 may be located below the second catalyst layer 90 (i.e., on the second substrate 70 side). As shown in Figure 4, the NH3 adsorption layer 80 may be located above the second catalyst layer 90 (i.e., on the exposed surface side of the second catalyst layer 90). As shown in Figure 3, it is preferable that the NH3 adsorption layer 80 is laminated below the second catalyst layer 90. By having the second catalyst layer 90 above the NH3 adsorption layer 80, the oxygen-deficient atmosphere can be further mitigated, resulting in higher NH3 purification performance after durability.

[0025] The NH3 adsorption layer 80 contains zeolite as an NH3 adsorbent. Therefore, the zeolite contained in the NH3 adsorption layer 80 is a zeolite that has NH3 adsorption capacity. An example of such zeolite is a zeolite supported with a transition metal.

[0026] The transition metal supported on the zeolite is, for example, at least one transition metal selected from the group consisting of V, Mn, Fe, Co, Ni, Cu, La, Ce, and Ag, preferably at least one transition metal selected from the group consisting of Fe, Cu, and Ag, more preferably Cu and / or Fe, and most preferably Cu. In this specification, the expression "A and / or B" refers to either A and B, or both A and B.

[0027] The zeolite forming the basic framework is typically an aluminosilicate, but may also be a silicoaluminophosphate (SAPO). The zeolite is preferably one that has pores of a size suitable for adsorbing NH3. Examples of zeolite structures according to the codes defined by the International Zeolite Association (IZA) include AEI, AFX, AFT, AST, BEA, BEC, CHA, EAB, ETR, GME, ITE, KFI, LEV, PAU, SAS, SAT, SAV, THO, UFI, ATT, DDR, ERI, IFY, JST, LOV, LTA, OWE, RHO, RSN, SFW, TSC, UEI, and VSV. Among these, AEI, AFX, AFT, AST, BEA, BEC, CHA, EAB, ETR, GME, ITE, KFI, LEV, PAU, SAS, SAT, SAV, THO, and UFI are listed, with CHA (chabasite) being preferred. The skeletal structure of the zeolite can be confirmed, for example, by X-ray diffraction (XRD). From the viewpoint of NH3 adsorption capacity, a CHA-type zeolite supporting Cu is particularly preferred as the zeolite.

[0028] The amount of zeolite in the NH3 adsorption layer 80 is not particularly limited. From the viewpoint of higher NH3 purification performance after durability, the amount of zeolite in the NH3 adsorption layer 80 is preferably 10% by mass or more. Furthermore, when the fluctuations in the exhaust gas atmosphere are small, increasing the amount of zeolite in the NH3 adsorption layer 80 is advantageous in terms of higher NH3 purification performance after durability. Therefore, the amount of zeolite in the NH3 adsorption layer 80 may be 50% by mass or more, or 80% by mass or more.

[0029] The NH3 adsorption layer 80 may contain components other than those mentioned above as optional components. Examples of optional components include oxygen absorption and release materials (so-called OSC materials) that have oxygen absorption and release capabilities. As the OSC material, known compounds that have oxygen absorption and release capabilities may be used, and specific examples include metal oxides containing ceria (CeO2) (Ce-containing oxides). The Ce-containing oxide may be ceria, or a composite oxide of ceria and a metal oxide other than ceria. From the viewpoint of improving heat resistance and durability, the Ce-containing oxide may be a composite oxide containing at least one of Zr and Al, for example, a ceria (CeO2)-zirconia (ZrO2) composite oxide (CZ composite oxide). From the viewpoint of improving heat resistance, the CZ composite oxide may be, for example, Nd2O3, La2O3, Y2O3, Pr6O 10 It may further contain rare earth metal oxides such as the following.

[0030] When the OSC material is a composite oxide containing cerium oxide, the cerium oxide content is preferably 15% by mass or more, and more preferably 20% by mass or more, from the viewpoint of fully exhibiting its oxygen storage capacity. On the other hand, if the cerium oxide content is too high, the basicity of the OSC material may become too high. Therefore, the cerium oxide content is preferably 60% by mass or less, and more preferably 50% by mass or less.

[0031] The amount of OSC material in the NH3 adsorption layer 80 is not particularly limited. The amount of OSC material in the NH3 adsorption layer 80 is, for example, 10% by mass or more, preferably 20% by mass or more. On the other hand, the amount of OSC material is, for example, 60% by mass or less, preferably 40% by mass or less.

[0032] Another example of an optional component of the NH3 adsorption layer 80 is a catalytic precious metal. By containing a catalytic precious metal in the NH3 adsorption layer 80, exhaust gas can also be purified in the NH3 adsorption layer 80.

[0033] Examples of catalytic precious metals include the platinum group elements: rhodium (Rh), palladium (Pd), platinum (Pt), ruthenium (Ru), osmium (Os), iridium (Ir), gold (Au), and silver (Ag). These can be used individually or in combination of two or more. In particular, from the viewpoint of catalytic performance, at least one selected from the group consisting of Pt, Rh, Pd, Ir, and Ru is preferred, and at least one selected from the group consisting of Pt, Rh, and Pd is more preferred. When two or more of these are used, the catalytic precious metal may be an alloy of the two or more metal species.

[0034] The catalyst noble metal may be supported on the above-mentioned OSC material, or it may be supported on a non-OSC material (e.g., alumina (Al2O3), titania (TiO2), zirconia (ZrO2), silica (SiO2), etc.).

[0035] Further examples of optional components of the NH3 adsorption layer 80 include binders such as alumina sol and silica sol, and various additives.

[0036] The amount of coating (i.e., molding amount) of the NH3 adsorption layer 80 is not particularly limited. The amount of coating is, for example, 10 to 200 g / L per liter of volume of the portion of the substrate in which the NH3 adsorption layer 80 is formed along the cylindrical axis X, and may also be 100 to 200 g / L. By satisfying the above range, it is possible to achieve a high level of both improved purification performance of harmful components and reduced pressure loss. Furthermore, durability and peel resistance can be improved.

[0037] The thickness of the NH3 adsorption layer 80 is not particularly limited and should be designed appropriately considering durability, peel resistance, etc. The thickness of the NH3 adsorption layer 80 may be, for example, 1 to 100 μm, or 5 to 100 μm.

[0038] The coating width (average dimension in the cylindrical axis direction X) of the NH3 adsorption layer 80 is not particularly limited and can be appropriately designed considering the size of the second substrate 70, the flow rate of exhaust gas flowing through the second catalyst 60, etc. The coating width is, for example, 10% to 100% of the total length of the substrate in the cylindrical axis direction X, preferably 20% to 100%, and more preferably 30% to 100%.

[0039] The second catalyst layer 90 contains a catalytic noble metal. This catalytic noble metal is usually supported on a carrier, and therefore the second catalyst layer 90 usually contains a ternary catalyst. The second catalyst layer 90 can be constructed in the same manner as known catalyst layers containing a ternary catalyst.

[0040] Catalyst precious metals are catalytic metal components that purify harmful components in exhaust gas. Examples of catalyst precious metals include those used in the NH3 adsorption layer 80. Catalyst precious metals may be used individually, but it is preferable to use a combination of two or more. From the viewpoint of catalytic performance, at least two catalyst precious metals selected from the group consisting of Pt, Rh, Pd, Ir, and Ru are preferred, with a combination of Rh, which has high reducing activity, and Pd and / or Pt, which has high oxidizing activity, being more preferable.

[0041] It is preferable to use the catalyst precious metal as fine particles with a sufficiently small particle size. The average particle size of the catalyst precious metal particles (specifically, the average value of the particle sizes of 20 or more precious metal particles determined based on a cross-sectional image of the catalyst layer obtained by transmission electron microscopy) is usually around 1 to 15 nm, preferably 10 nm or less, more preferably 7 nm or less, and even more preferably 5 nm or less. This increases the contact area of ​​the catalyst precious metal with the exhaust gas, thereby further improving the purification performance.

[0042] The amount of catalytic precious metal in the second catalyst 60 (the total amount of catalytic precious metal in the NH3 adsorption layer 80 and the second catalyst layer 90) is not particularly limited and can be appropriately determined depending on the type of catalytic precious metal. From the viewpoint of particularly high exhaust gas purification performance, the amount of catalytic precious metal per 1 L of volume of the second substrate 70 may be, for example, 0.01 g / L or more, 0.03 g / L or more, 0.05 g / L or more, 0.08 g / L or more, or 0.10 g / L or more. From the viewpoint of balancing exhaust gas purification performance and cost, the amount may be, for example, 5.00 g / L or less, 3.00 g / L or less, 2.00 g / L or less, 1.50 g / L or less, 1.00 g / L or less, 0.80 g / L or less, or 0.50 g / L or less.

[0043] In this specification, "per 1 L of base material volume" refers to the total bulk volume per 1 L, including the volume of the cell passages in addition to the net volume of the base material. In the following explanation, (g / L) indicates the amount contained in 1 L of base material volume.

[0044] The second catalyst layer 90 contains an OSC material. An example of the OSC material contained in the second catalyst layer 90 is the OSC material that can be used in the NH3 adsorption layer 80.

[0045] The OSC material may or may not have a catalyst precious metal supported on it. It is also possible for some of the OSC material to have a catalyst precious metal supported on it, while other OSC material does not.

[0046] The second catalyst layer 90 further contains a non-OSC material (i.e., a material that does not have oxygen absorption / desorption capabilities), and the catalyst noble metal may be supported on the non-OSC material. Examples of non-OSC materials include alumina (Al2O3), titania (TiO2), zirconia (ZrO2), and silica (SiO2).

[0047] Therefore, in the second catalyst layer 90, either an OSC material or a non-OSC material, or both, are usually used as the support. The support preferably has a large specific surface area, and therefore porous support particles are preferably used. The support particles have a specific surface area of ​​50 to 500 m² as determined by the BET method. 2 / g (especially 200-400m) 2 It is preferable that the particle size is ( / g) from the viewpoint of heat resistance and structural stability. Furthermore, it is preferable that the average particle diameter of the support particles (specifically, the average value of the particle diameters of 20 or more support particles determined based on the cross-sectional image of the catalyst layer obtained by transmission electron microscopy) is between 1 nm and 500 nm (particularly between 10 nm and 200 nm).

[0048] The amount of OSC material in the second catalyst layer 90 is, for example, 10% by mass or more, preferably 30% by mass or more, and more preferably 40% by mass or more. Alternatively, the amount of OSC material in the second catalyst layer 90 is, for example, less than 90% by mass, preferably less than 60% by mass, and more preferably 50% by mass or less.

[0049] The amount of non-OSC material in the second catalyst layer 90 is, for example, 10% by mass or more, preferably 30% by mass or more, and more preferably 40% by mass or more. Alternatively, the amount of non-OSC material in the second catalyst layer 90 is, for example, less than 90% by mass, preferably less than 70% by mass, and more preferably less than 60% by mass.

[0050] The second catalyst layer 90 may further contain components other than those mentioned above. For example, the second catalyst layer 90 may contain metal species such as alkali metal elements, alkaline earth metal elements, transition metal elements, and rare earth elements. These elements (especially alkaline earth elements) may be contained in the form of oxides, hydroxides, carbonates, nitrates, sulfates, phosphates, acetates, formates, oxalates, halides, etc. It is preferable to have alkaline earth metal elements (especially Ba) and Pt and / or Pd coexist in the second catalyst layer 90.

[0051] Other optional components of the second catalyst layer 90 include binders such as alumina sol and silica sol; NOx adsorbents with NOx storage capacity; and various additives such as stabilizers.

[0052] The second catalyst layer 90 may be a single layer or a multi-layer structure. In the examples shown in Figures 3 and 4, the second catalyst layer 90 is a single layer. When the second catalyst layer 90 is a single layer, it may be composed of multiple regions with different compositions, properties, etc. For example, the second catalyst layer 90 has a front portion located upstream X1 in the cylindrical axis direction X and a rear portion located downstream X2 of the front portion, and the composition and / or properties of the front portion and the rear portion may differ. Specifically, for example, the front portion and the rear portion may contain different catalyst precious metals.

[0053] When the second catalyst layer 90 has a multilayer structure, the number of layers is not particularly limited. The second catalyst layer 90 may have a two-layer structure having a substrate-side layer (lower layer) and a surface-side layer (upper layer), or it may have a three-layer or more structure having a substrate-side layer (lower layer), a surface-side layer (upper layer), and one or more intermediate layers located between them. In this multilayer structure, each layer may contain a different catalyst precious metal.

[0054] Figure 5 shows an example where the second catalyst layer 90 has a multilayer structure. In Figure 5, an NH3 adsorption layer 80 is provided on the second substrate 70, and the second catalyst layer 90 is provided on the NH3 adsorption layer 80.

[0055] The second catalyst layer 90 has a lower layer 92 which is the substrate-side layer, and an upper layer 94 provided on top of the lower layer 92. In the illustrated example, the upper layer 94 is also the exposed surface layer of the second catalyst layer 90. The lower layer 92 and the upper layer 94 of the second catalyst layer 90 each contain a catalyst noble metal. The lower layer 92 contains Pd as the catalyst noble metal. On the other hand, the upper layer 94 contains Rh as the catalyst noble metal. In this case, by separating and supporting the oxidation catalyst and the reduction catalyst in the stacking direction, the degradation of the catalyst metal (e.g., sintering due to grain growth) can be suppressed, and the durability of the second catalyst 60 can be further improved.

[0056] The coating amount (i.e., molding amount) of the second catalyst layer 90 is not particularly limited. The coating amount is, for example, 10 to 500 g / L per liter of volume of the substrate portion in which the catalyst layer 20 is formed along the cylindrical axis X, and may also be 100 to 200 g / L. By satisfying the above range, it is possible to achieve a high level of both improved purification performance of harmful components and reduced pressure loss. Furthermore, durability and peel resistance can be improved.

[0057] The thickness of the second catalyst layer 90 is not particularly limited and should be designed appropriately considering durability, peel resistance, etc. The thickness of the second catalyst layer 90 may be, for example, 1 to 100 μm, or 5 to 100 μm.

[0058] The coating width (average dimension in the cylindrical axis direction X) of the second catalyst layer 90 is not particularly limited and can be appropriately designed considering the size of the second substrate 70, the flow rate of exhaust gas circulating through the second catalyst 60, etc. The coating width is, for example, 10% to 100% of the total length of the substrate in the cylindrical axis direction X, preferably 20% to 100%, and more preferably 30% to 100%.

[0059] The second catalyst 60 may have layers other than the NH3 adsorption layer 80 and the second catalyst layer 90.

[0060] The second catalyst 60 can be prepared according to known methods. For example, a slurry for forming an NH3 adsorption layer is prepared containing a zeolite that functions as an NH3 adsorbent, a solvent, and optional components (e.g., OSC material, catalyst noble metal source, binder, etc.). Alternatively, a slurry can be prepared containing a catalyst noble metal source, an OSC material, a non-OSC material if necessary, a solvent, and other optional components. Of these slurries, the lower layer is coated onto the second substrate 70 according to a known method, dried if necessary, and then fired to form the lower layer. Subsequently, the upper layer slurry is coated onto the lower layer formed on the second substrate 70 according to a known method, dried if necessary, and then fired to form the upper layer. This allows the second catalyst 60 to be obtained.

[0061] <First catalyst body> The first catalyst 20 may have the same or similar configuration as the startup catalyst in a known exhaust gas purification system for a gasoline engine, which includes a startup catalyst (S / C) and an underfloor catalyst (UF / C).

[0062] An example of the first catalyst 20 is shown in Figure 6. For example, the first catalyst 20 includes a first substrate 30 and a first catalyst layer 40. The first catalyst 20 is typically positioned in the exhaust path of a gasoline engine 1 near the exhaust manifold and engine compartment (closed couple (CC) position).

[0063] In the first embodiment, a straight-flow type substrate is used for the first substrate 30. However, the first substrate 30 is not limited to this and may be a wall-flow type substrate. For example, as in the embodiment described later, it is also possible to use a wall-flow type substrate as the first substrate 30 and configure the first catalyst 20 as a catalyst-coated type gasoline particulate filter (GPF).

[0064] The first substrate 30 may be a ceramic carrier composed of ceramics such as cordierite, aluminum titanate, or silicon carbide, or it may be a metal carrier composed of stainless steel (SUS), Fe-Cr-Al alloy, Ni-Cr-Al alloy, or the like.

[0065] In the first embodiment, the first catalyst 20 has one first substrate 30, but is not limited thereto. For example, as in the embodiment described later, the first catalyst 20 may be a tandem type catalyst comprising a plurality of first substrates 30, each of which is provided with a first catalyst layer 40. In the tandem type catalyst, the plurality of first substrates 30 may be the same or different. Also, the compositions of the plurality of first catalyst layers 40 may be the same or different.

[0066] The first catalyst layer 40 contains a catalytic noble metal. The catalytic noble metal contained in the first catalyst layer 40 may be the same as the noble metal catalyst contained in the second catalyst layer 90 of the second catalyst 60. The first catalyst layer 40 usually contains a support for the catalytic noble metal. The support contained in the first catalyst layer 40 may be the same as the support contained in the second catalyst layer 90 of the second catalyst 60. Other components contained in the first catalyst layer 40 may also be the same as those in the second catalyst layer 90 of the second catalyst 60.

[0067] The first catalyst layer 40 may have a single-layer structure or a multi-layer structure. If the first catalyst layer 40 has a single-layer structure, it may be composed of multiple regions with different compositions, properties, etc. For example, the first catalyst layer 40 may have a front portion located on the upstream side Y1 and a rear portion located on the downstream side Y2 in the cylindrical axis direction Y, and the composition and / or properties of the front portion and the rear portion may differ. Specifically, for example, the front portion and the rear portion may contain different precious metals.

[0068] When the first catalyst layer 40 has a multilayer structure, the number of layers is not particularly limited. The first catalyst layer 40 may have a two-layer structure having a substrate-side layer (lower layer) and a surface-side layer (upper layer), or it may have a three-layer or more structure having a substrate-side layer (lower layer), a surface-side layer (upper layer), and one or more intermediate layers located between them. In this multilayer structure, each layer may contain a different precious metal.

[0069] In the example shown in Figure 6, the first catalyst layer 40 has a multilayer structure and includes a lower layer 42 on the substrate side and an upper layer 44 on the exposed surface side. The lower layer 42 and the upper layer 44 of the first catalyst layer 40 each contain a catalytic noble metal. The lower layer 42 contains Pd as the catalytic noble metal. On the other hand, the upper layer 44 contains Rh as the catalytic noble metal. In this case, by separating and supporting the oxidation catalyst and the reduction catalyst in the stacking direction, the degradation of the catalytic metal (e.g., sintering due to grain growth) can be suppressed, and the durability of the first catalyst 20 can be further improved.

[0070] The first catalyst 20 can be prepared according to a known method. For example, a slurry containing a catalyst noble metal source, an OSC material, a non-OSC material, a solvent, and an optional component is prepared. This slurry is coated onto the second substrate 70 according to a known method, dried as necessary, and then fired to form the first catalyst layer 40. This allows the first catalyst 20 to be obtained.

[0071] ≪Exhaust Gas Purification System 100≫ In gasoline engine 1, a fuel mixture with air-fuel ratios ranging from the rich region, including the stoichiometric air-fuel ratio, to the lean region is burned. As shown in Figure 1, the exhaust gas generated in gasoline engine 1 is first purified by the first catalyst 20 of the upstream catalytic converter 10. The first catalyst 20 contains catalytic precious metals of a three-way catalyst, and when NOx is purified, NH3 is generated, and exhaust gas containing NH3 flows out of the upstream catalytic converter 10.

[0072] The exhaust gas flowing out of the upstream catalytic converter 10 flows into the downstream catalytic converter 50. Here, if the temperature inside the downstream catalytic converter 50 is low and has not reached the catalytic activation temperature, NH3 cannot be purified. In contrast, the exhaust gas purification system 100 has a second catalyst 60 equipped with an NH3 adsorption layer 80. As a result, the NH3 contained in the exhaust gas is adsorbed by the NH3 adsorption layer 80 of the second catalyst 60 of the downstream catalytic converter 50, and its discharge outside the exhaust gas purification system 100 is suppressed. The NH3 adsorbed on the NH3 adsorption layer 80 is purified in the second catalyst layer 90, for example at the timing of fuel cut (F / C).

[0073] Unlike diesel and lean-burn engines, gasoline engines operate at high temperatures, and the atmosphere fluctuates between rich and lean. Through diligent research, the inventors discovered that when the atmosphere is in the rich to stoichiometric range at high temperatures, oxygen becomes insufficient, leading to structural degradation of the zeolite used as an NH3 adsorbent in the NH3 adsorption layer, resulting in reduced NH3 purification performance.

[0074] Based on this finding, in the second catalyst 60 of the downstream catalytic converter 50 of the exhaust gas purification system 100 according to this embodiment, a second catalyst layer 90 containing OSC material is laminated on the NH3 adsorption layer 80. This allows oxygen to be released from the OSC material so that the atmosphere does not become oxygen-deficient. At this time, since the second catalyst layer 90 exists in a form laminated on the NH3 adsorption layer 80, it has a particularly high effect in mitigating the atmosphere. Therefore, structural deterioration of the zeolite due to oxygen deficiency at high temperatures can be effectively suppressed, and the decrease in NH3 purification performance after durability can be significantly suppressed.

[0075] <<Other Embodiments>> Figures 7-13 show other embodiments. Note that for the following embodiments, the same parts as in the first embodiment are omitted from the explanation.

[0076] The exhaust gas purification system 200 for a gasoline engine, illustrated in Figure 7, according to the second embodiment, is configured to be placed in the exhaust path of a gasoline engine 1 and is connected to the gasoline engine 1. The exhaust gas purification system 200 includes an upstream catalytic converter 10, a downstream catalytic converter 50, and a gasoline particulate filter (GPF) 110. The GPF 110 is located downstream of the upstream catalytic converter 10 and upstream of the downstream catalytic converter 50 in the exhaust gas flow direction F. In other words, the exhaust gas purification system 200 for a gasoline engine according to the second embodiment is the exhaust gas purification system 100 for a gasoline engine according to the first embodiment with a GPF 110 added between the upstream catalytic converter 10 and the downstream catalytic converter 50. As the GPF 110, a known GPF used in a known gasoline engine exhaust gas purification system can be used.

[0077] With this configuration, particulate matter (PM) in the exhaust gas can be captured by the GPF. Therefore, with this configuration, it is possible to provide an exhaust gas purification system for gasoline engines that has high NH3 purification performance after durability and reduced PM emissions.

[0078] The exhaust gas purification system 300 for a gasoline engine, illustrated in Figure 8, according to the third embodiment, includes a gasoline particulate filter (GPF) 110, similar to the second embodiment. However, the GPF 110 is positioned downstream of the downstream catalytic converter 50 in the exhaust gas flow direction F. In other words, the exhaust gas purification system 300 for a gasoline engine according to the third embodiment is the same as the exhaust gas purification system 100 for a gasoline engine according to the first embodiment, with the GPF 110 added downstream of the downstream catalytic converter 50.

[0079] With this configuration, PM in the exhaust gas can be captured by the GPF. Therefore, with this configuration, it is possible to provide an exhaust gas purification system for gasoline engines that has high NH3 purification performance after durability and reduced PM emissions.

[0080] In the exhaust gas purification system 400 for a gasoline engine according to the fourth embodiment illustrated in Figure 9, the first catalyst 20 of the upstream catalytic converter 10 is a tandem type catalyst including an upstream catalyst 22 and a downstream catalyst 24, which differs from the exhaust gas purification system 100 for a gasoline engine according to the first embodiment. With this configuration, the purification performance of the first catalyst 20 can be further improved.

[0081] In the exhaust gas purification system 500 for a gasoline engine according to the fifth embodiment illustrated in Figure 10, the first catalyst 20 of the upstream catalytic converter 10 is a tandem type catalyst including an upstream catalyst 22 and a downstream catalyst 24, and the GPF 110 is positioned downstream of the upstream catalytic converter 10 and upstream of the downstream catalytic converter 50 in the exhaust gas flow direction F. In other words, the exhaust gas purification system 500 for a gasoline engine according to the fifth embodiment is the exhaust gas purification system 400 for a gasoline engine according to the fourth embodiment with the addition of a GPF 110 between the upstream catalytic converter 10 and the downstream catalytic converter 50. With this configuration, the purification performance of the first catalyst 20 can be further enhanced while efficiently capturing PM in the exhaust gas.

[0082] In the exhaust gas purification system 600 for a gasoline engine according to the sixth embodiment shown in Figure 11, the first catalyst 20 of the upstream catalytic converter 10 is a tandem type catalyst including an upstream catalyst 22 and a downstream catalyst 24, and the GPF 110 is positioned downstream of the downstream catalytic converter 50 in the exhaust gas flow direction F. In other words, the exhaust gas purification system 600 for a gasoline engine according to the sixth embodiment is the exhaust gas purification system 400 for a gasoline engine according to the fourth embodiment with the addition of the GPF 110 downstream of the downstream catalytic converter 50. With this configuration, the purification performance of the first catalyst 20 can be further enhanced while efficiently capturing PM in the exhaust gas.

[0083] In the exhaust gas purification system 700 for a gasoline engine according to the seventh embodiment shown in Figure 12, a wall-flow type substrate is used for the substrate of the first catalyst 26 of the upstream catalytic converter 10, and the substrate of the first catalyst 26 has the function of a GPF. With this configuration, PM in the exhaust gas can be captured by the GPF. Therefore, with this configuration, it is possible to provide an exhaust gas purification system for a gasoline engine with high NH3 purification performance after durability and reduced PM emissions.

[0084] In the exhaust gas purification system 800 for a gasoline engine according to the eighth embodiment shown in Figure 13, the first catalyst 20 of the upstream catalytic converter 10 is a tandem type catalyst including an upstream catalyst 22 and a downstream catalyst 26. A wall-flow type substrate is used for the substrate of the downstream catalyst 26, and the substrate of the downstream catalyst 26 has the function of a GPF (Ground Permeable Filter). With this configuration, the purification performance of the first catalyst 20 can be further enhanced while efficiently capturing PM in the exhaust gas.

[0085] Applications of the 100 Gasoline Engine Exhaust Gas Purification System The gasoline engine exhaust gas purification system 100 can be suitably used to purify exhaust gases emitted from gasoline engines of vehicles such as automobiles, trucks, and motorcycles, as well as from ships and other vessels. In particular, it can be suitably used for vehicles such as automobiles and trucks equipped with gasoline engines.

[0086] The following describes test examples relating to the present invention, but it is not intended to limit the present invention to those shown in the following test examples.

[0087] Example 1 As the first substrate, a honeycomb substrate (made of cordierite, diameter: 117 mm, total length: 100 mm, number of cells per square inch: 600 cpsi) was prepared. Palladium nitrate, CeO2-ZrO2 composite oxide powder (OSC material), Al2O3 powder, barium sulfate, a binder, and deionized water were mixed to prepare a Pd-containing slurry. This Pd-containing slurry was poured onto the first substrate as a slurry for forming the lower layer, and the surface of the first substrate was coated with the lower layer forming material by blowing away the excess with a blower. By firing this in an electric furnace, a lower layer containing a Pd catalyst was formed on the first substrate.

[0088] A rhodium-containing slurry was prepared by mixing rhodium nitrate, CeO2-ZrO2 composite oxide powder (OSC material), Al2O3 powder, a binder, and deionized water. This rhodium-containing slurry was poured onto a first substrate with a lower layer formed on top as a slurry for forming the upper layer, and the excess was blown away with a blower to coat the surface of the lower layer formed on the substrate with the material for forming the upper layer. This was then fired in an electric furnace to form an upper layer containing the rhodium catalyst on top of the lower layer. In this way, the first catalyst was produced.

[0089] Next, a honeycomb substrate identical to the first substrate was prepared as the second substrate. A zeolite-containing slurry was prepared by mixing Cu-supported CHA-type zeolite (Cu-CHA), a binder, and deionized water. This zeolite-containing slurry was poured onto the second substrate as a slurry for forming the lower layer, and the excess was blown away with a blower, thereby coating the surface of the second substrate with the lower layer-forming material. By firing this in an electric furnace, a zeolite-containing lower layer was formed on the second substrate.

[0090] The Pd-containing slurry prepared above was poured onto a second substrate with a lower layer formed as an intermediate layer forming slurry, and the excess was blown away with a blower, thereby coating the surface of the lower layer formed on the second substrate with the intermediate layer forming material. This was then fired in an electric furnace to form an intermediate layer containing an Rh catalyst on top of the lower layer.

[0091] The Rh-containing slurry prepared above was poured onto a second substrate, which had an intermediate layer formed on it, as a slurry for forming the upper layer. Unwanted portions were blown away with a blower, thereby coating the surface of the intermediate layer formed on the second substrate with the material for forming the upper layer. This was then fired in an electric furnace to form an upper layer containing the Rh catalyst on the intermediate layer. In this way, the second catalyst was prepared. The exhaust gas purification system of Example 1 was constructed by combining the prepared first and second catalysts. The layer structure of the second catalyst is schematically shown in Figure 14(A).

[0092] Example 2 A first catalyst was prepared in the same manner as in Example 1. Next, a zeolite-containing slurry was prepared by mixing Cu-supported CHA-type zeolite, CeO2-ZrO2-based composite oxide powder (OSC material), a binder, and deionized water. This zeolite-containing slurry was used as a slurry for forming the lower layer, and a second catalyst was prepared in the same manner as in Example 1, except that the amount of OSC material in the Pd-containing slurry and Rh-containing slurry was reduced so that the total amount of OSC material in the second catalyst was the same as the amount of OSC material in the second catalyst of Example 1. The exhaust gas purification system of Example 2 was constructed by combining the prepared first and second catalysts. The layer structure of the second catalyst is schematically shown in Figure 14(B).

[0093] Example 3 A first catalyst was prepared in the same manner as in Example 1. Next, a zeolite-containing slurry was prepared by mixing Cu-supported CHA-type zeolite, palladium nitrate, CeO2-ZrO2-based composite oxide powder (OSC material), a binder, and deionized water. This zeolite-containing slurry was used as a slurry for forming the lower layer, and a second catalyst was prepared in the same manner as in Example 1, except that the amount of Pd in ​​the Pd-containing slurry was reduced so that the total amount of Pd in ​​the second catalyst was the same as the amount of Pd in ​​the second catalyst of Example 1, and the amount of OSC material in the Pd-containing slurry and Rh-containing slurry was reduced so that the total amount of OSC material in the second catalyst was the same as the amount of OSC material in the second catalyst of Example 1. The exhaust gas purification system of Example 3 was constructed by combining the prepared first and second catalysts. The layer structure of the second catalyst is schematically shown in Figure 14(C).

[0094] Example 4 A first catalyst was prepared in the same manner as in Example 1. A second substrate, the same as in Example 1, was prepared. The Pd-containing slurry prepared in Example 1 was poured onto the second substrate as a slurry for forming the lower layer, and the excess was blown away with a blower, thereby coating the surface of the second substrate with the material for forming the lower layer. By firing this in an electric furnace, a Pd-containing lower layer was formed on the second substrate.

[0095] The Rh-containing slurry prepared in Example 1 was poured onto a second substrate with a lower layer formed as an intermediate layer forming slurry, and the excess was blown away with a blower, thereby coating the surface of the lower layer formed on the second substrate with the intermediate layer forming material. This was then fired in an electric furnace to form an intermediate layer containing the Rh catalyst on top of the lower layer.

[0096] The zeolite-containing slurry prepared in Example 1 was poured onto a second substrate with an intermediate layer formed as a slurry for forming the upper layer, and the excess was blown away with a blower, thereby coating the surface of the intermediate layer formed on the second substrate with the material for forming the upper layer. This was then fired in an electric furnace to form a zeolite-containing upper layer on the intermediate layer. In this way, the second catalyst was prepared. The exhaust gas purification system of Example 4 was constructed by combining the prepared first and second catalysts. The layer structure of the second catalyst is schematically shown in Figure 14(D).

[0097] Comparative Example 1 A first catalyst was prepared in the same manner as in Example 1. A second substrate, the same as in Example 1, was prepared. The zeolite-containing slurry prepared in Example 1 was poured into the second substrate from the front portion up to 50% of the total length of the substrate, and the excess was blown away with a blower, thereby coating the surface of the front portion of the second substrate with the material for forming the front portion. By firing this in an electric furnace, a front layer containing zeolite was formed on the front portion of the substrate.

[0098] The Pd-containing slurry prepared in Example 1 was poured from the rear of the second substrate up to 50% of the total length of the substrate, and the excess was blown away with a blower, thereby coating the surface of the rear of the second substrate with the material for forming the rear lower layer. By firing this in an electric furnace, a Pd-containing lower layer was formed on the rear of the second substrate.

[0099] The Rh-containing slurry prepared in Example 1 was poured from the rear of the second substrate up to 50% of the total length of the substrate, and the excess was blown away with a blower, thereby coating the lower surface of the rear of the second substrate with the material for forming the upper layer of the rear section. By firing this in an electric furnace, a Pd-containing upper layer was formed on the lower layer of the rear of the second substrate. In this way, the second catalyst was prepared. The exhaust gas purification system of Comparative Example 1 was constructed by combining the prepared first catalyst and the second catalyst. The layer structure of the second catalyst is schematically shown in Figure 14(E). The amount of Pd and Rh in the substrate was adjusted to be the same as in Example 1.

[0100] Comparative Example 2 A first catalyst was prepared in the same manner as in Example 1. A second catalyst was prepared by swapping the front and rear sections of the second catalyst of Comparative Example 1. The exhaust gas purification system of Comparative Example 2 was constructed by combining the prepared first and second catalysts. The layer structure of the second catalyst is schematically shown in Figure 14(F). The amount of Pd and Rh in the substrate was adjusted to be the same as in Example 1.

[0101] [Durability treatment] The exhaust gas purification systems of each embodiment and comparative example were installed in the exhaust system of a V8 gasoline engine. At this time, the first catalytic converter was positioned upstream in the direction of exhaust gas flow within the exhaust system. With an inlet gas temperature of 950°C, exhaust gases in rich, stoichiometric, and lean atmospheres were repeatedly passed through the exhaust gas purification system for predetermined periods of time over a period of 50 hours. This subjected the first catalytic converter to a 1000°C endurance treatment and the second catalytic converter to a 700°C endurance treatment.

[0102] [Measurement of NH3 emissions] The exhaust gas purification systems of each embodiment and comparative example, which underwent the above-described durability treatment, were installed in a vehicle equipped with a gasoline engine. At this time, the first catalyst was housed in a casing and installed at the startup catalyst position, and the second catalyst was housed in a casing and installed at the underfloor position. An FT-IR analyzer was installed downstream of the second catalyst. The vehicle was operated on a chassis dynamometer according to the WLTC mode, and the ammonium concentration in the exhaust gas was measured to determine the NH3 emission amount. The results are shown in Figure 15.

[0103] As shown in Figure 15, the exhaust gas purification systems of Examples 1 to 4, in which a Cu-CHA-containing NH3 adsorption layer and an OSC material-containing catalyst layer were laminated in the second catalyst, produced significantly lower NH3 emissions after durability than Comparative Examples 1 and 2, in which these layers were arranged in parallel in the direction of exhaust gas flow. Therefore, it can be seen that the exhaust gas purification systems for gasoline engines disclosed herein have high NH3 purification performance after durability.

[0104] A comparison of Examples 1-3 shows that when the OSC material and precious metal catalyst are not placed in the NH3 adsorption layer, the amount of NH3 emitted after durability is smaller than when they are placed. Furthermore, a comparison of Example 1 and Example 4 shows that when the NH3 adsorption layer is placed below the catalyst layer, the amount of NH3 emitted after durability is smaller.

[0105] Although several embodiments of the present invention have been described above, these embodiments are merely examples. The present invention can be implemented in various other forms. The present invention can be implemented based on the contents disclosed herein and common technical knowledge in the art. The technologies described in the claims include various modifications and changes to the embodiments illustrated above. For example, it is possible to replace parts of the above embodiments with other variations, and it is also possible to add other variations to the above embodiments. Furthermore, if a technical feature is not described as essential, it may be deleted as appropriate. [Explanation of symbols]

[0106] 1. Gasoline engine 10 Upstream catalytic converter 20 First catalyst body 30 First base material 40 1st catalyst layer 50 Downstream Catalytic Converters 60 Second catalyst body 70 Second base material 80 NH3 adsorption layer 90 Second catalyst layer

Claims

1. A gasoline engine exhaust gas purification system configured to be placed in the exhaust path of a gasoline engine, The exhaust gas purification system includes an upstream catalytic converter containing a first catalyst and a downstream catalytic converter containing a second catalyst. The first catalyst contains a catalytic noble metal, The second catalyst is provided on a substrate with NH ３ It has a structure in which an adsorption layer and a catalyst layer are stacked, The NH of the second catalyst ３ The adsorption layer is NH ３ It contains zeolite as an adsorbent, The catalyst layer of the second catalyst contains a catalytic noble metal and an OSC material. In the second catalyst, the NH3 adsorption layer is laminated below the catalyst layer. The zeolite is a CHA-type zeolite supporting Cu, The amount of zeolite in the NH3 adsorption layer is 80% by mass or more. Exhaust gas purification system for gasoline engines.

2. The exhaust gas purification system for a gasoline engine according to claim 1, further comprising a gasoline particulate filter between the upstream catalytic converter and the downstream catalytic converter in the exhaust gas flow direction of the exhaust path.

3. The exhaust gas purification system for a gasoline engine according to claim 1, further comprising a gasoline particulate filter downstream of the downstream catalytic converter in the exhaust gas flow direction of the exhaust path.

4. The exhaust gas purification system for a gasoline engine according to claim 1, wherein the first catalyst of the upstream catalytic converter is a tandem type catalyst comprising an upstream catalyst and a downstream catalyst.

5. The exhaust gas purification system for a gasoline engine according to claim 4, further comprising a gasoline particulate filter between the upstream catalytic converter and the downstream catalytic converter in the exhaust gas flow direction of the exhaust path.

6. The exhaust gas purification system for a gasoline engine according to claim 4, further comprising a gasoline particulate filter downstream of the downstream catalytic converter in the exhaust gas flow direction of the exhaust path.

7. The exhaust gas purification system for a gasoline engine according to claim 4, wherein the downstream catalyst of the first catalyst functions as a gasoline particulate filter.

8. The exhaust gas purification system for a gasoline engine according to claim 1, wherein the first catalyst of the upstream catalytic converter functions as a gasoline particulate filter.

9. Substrate and NH laminated on the substrate ３ Adsorption layer and Said NH ３ A catalyst layer stacked on an adsorption layer, A catalytic converter for purifying exhaust gases in a gasoline engine, comprising: Said NH ３ The adsorption layer is NH ３ It contains zeolite and OSC material as adsorbents. The catalyst layer contains a catalyst noble metal and an OSC material. The zeolite is a CHA-type zeolite supporting Cu, The amount of zeolite in the NH3 adsorption layer is 80% by mass or more. A catalytic converter for purifying exhaust gases in gasoline engines.

10. Said NH ３ The adsorption layer further contains a noble metal catalyst, as described in claim 9, for exhaust gas purification catalyst for gasoline engines.

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