Exhaust purification system for gasoline engine and catalyst body for exhaust purification

Abstract

Provided is an exhaust gas purification system for a gasoline engine, which has high NH3 purification performance even after long-term use. The exhaust gas purification system for a gasoline engine disclosed herein is configured to be disposed in an exhaust passage of a gasoline engine. The exhaust gas purification system includes an upstream catalytic converter including a first catalyst body and a downstream catalytic converter including a second catalyst body. The first catalyst body contains a catalyst noble metal. The second catalyst body has a structure in which an NH3 adsorption layer and a catalyst layer are layered on a substrate. The NH3 adsorption layer of the second catalyst body contains a zeolite as an NH3 adsorption material. The catalyst layer of the second catalyst body contains a catalyst noble metal and an OSC material.

Description

Technical Field

[0001] This invention relates to an exhaust gas purification system for gasoline engines. The invention also relates to a catalyst body suitable for exhaust gas purification in this gasoline engine exhaust gas purification system. Furthermore, this application claims priority based on Japanese Patent Application No. 2021-163182, filed on October 4, 2021, the entire contents of which are incorporated herein by reference. Background Technology

[0002] Exhaust gases from gasoline engines in automobiles and other vehicles contain hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). x Harmful components such as ) are present. In order to efficiently react with and remove these harmful components from exhaust gases, catalysts for exhaust gas purification have been used for a long time.

[0003] To further reduce NO x Regarding the exhaust emissions, there are known exhaust gas purification systems for gasoline engines that combine a starter catalyst (S / C) and an underfloor catalyst (UF / C) (for example, see Patent Document 1).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2020-34001 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] In recent years, exhaust emission restrictions have become increasingly stringent, with the aim of reducing NH3 emissions from gasoline engine vehicles. NH3 can be purified by exhaust gas catalysts to reduce NO emissions. x The components produced by over-reduction. In exhaust gas purification systems that combine a start-up catalyst (S / C) and an underfloor catalyst (UF / C), NO... x The higher the purification performance, the greater the amount of NH3 emitted. Patent Document 1 describes how the NH3 purification performance is improved by introducing zeolite with NH3 adsorption capacity into the exhaust gas purification system for gasoline engines.

[0009] However, the inventors conducted in-depth research and found that in existing exhaust gas purification systems for gasoline engines that use zeolites with NH3 adsorption capacity, there is a problem that the NH3 purification performance decreases after durability.

[0010] The present invention was made in view of the above circumstances, and its object is to provide a gasoline engine exhaust gas purification system with high NH3 purification performance after durability.

[0011] Methods for solving problems

[0012] The exhaust gas purification system for a gasoline engine disclosed herein is configured in the exhaust path of a gasoline engine. The system includes an upstream catalytic converter containing a first catalyst body and a downstream catalytic converter containing a second catalyst body. The first catalyst body contains a noble metal catalyst. The second catalyst body has a structure in which an NH3 adsorption layer and a catalyst layer are stacked on a substrate. The NH3 adsorption layer of the second catalyst body contains zeolite as an NH3 adsorption material. The catalyst layer of the second catalyst body contains a noble metal catalyst and an OSC material.

[0013] In completing the exhaust gas purification system for gasoline engines disclosed herein, the inventors discovered the following: In the exhaust gas purification system for gasoline engines, the operating ambient temperature range is high, and the atmosphere varies between rich and lean conditions. In the region where the air-fuel ratio ranges from rich to stoichiometric, the oxygen concentration is low, causing the structure of the zeolite with NH3 adsorption capacity to deteriorate at high temperatures, thereby reducing its durable NH3 purification performance.

[0014] Therefore, in the exhaust gas purification system for gasoline engines disclosed herein, a catalyst layer containing OSC material is stacked on top of an NH3 adsorption layer containing zeolite. Thus, even in regions with low oxygen concentrations (up to stoichiometric levels), oxygen can be supplied to the NH3 adsorption layer from the OSC material, suppressing structural degradation of the zeolite. Therefore, the exhaust gas purification system disclosed herein provides a durable exhaust gas purification system with high NH3 purification performance.

[0015] In a preferred embodiment of the exhaust gas purification system for gasoline engines disclosed herein, the NH3 adsorption layer is stacked in the second catalyst body at a position lower than the catalyst layer. This structure provides an exhaust gas purification system with higher NH3 purification performance over time.

[0016] In a preferred embodiment of the exhaust gas purification system for gasoline engines disclosed herein, the zeolite is a Cu-supported CHA-type zeolite. This structure enables an exhaust gas purification system with particularly high NH3 purification performance over long-term use.

[0017] The exhaust gas purification system for gasoline engines disclosed herein can be implemented in the following manner.

[0018] • A gasoline particulate filter is also provided between the upstream catalytic converter and the downstream catalytic converter in the direction of exhaust gas flow in the exhaust path.

[0019] • In the direction of exhaust gas flow in the exhaust path, a gasoline particulate filter is also provided on the downstream side of the downstream catalytic converter.

[0020] The first catalyst body of the upstream catalytic converter is a catalyst body in series, comprising an upstream catalyst body and a downstream catalyst body. In this case, a gasoline particulate filter may also be provided between the upstream and downstream catalytic converters, or at a position downstream of the downstream catalytic converter. Alternatively, the downstream catalyst body of the first catalyst body may also function as a gasoline particulate filter.

[0021] The first catalyst body of the upstream catalytic converter functions as a gasoline particulate filter.

[0022] From another perspective, the catalyst body for exhaust gas purification of gasoline engines disclosed herein includes a substrate, an NH3 adsorption layer laminated on the substrate, and a catalyst layer laminated on the NH3 adsorption layer. The NH3 adsorption layer contains zeolite and OSC material as NH3 adsorption materials. The catalyst layer contains a catalyst noble metal and OSC material. This catalyst body for exhaust gas purification of gasoline engines is suitable for the aforementioned exhaust gas purification system for gasoline engines. Here, the NH3 adsorption layer may also contain a catalyst noble metal. Attached Figure Description

[0023] Figure 1 This is a schematic diagram illustrating the exhaust gas purification system of the first embodiment.

[0024] Figure 2 This is a perspective view schematically showing the second catalyst body used in the exhaust gas purification system of the first embodiment.

[0025] Figure 3 It is Figure 2 A partial cross-sectional view of the second catalyst body cut along the cylinder axis.

[0026] Figure 4 It is Figure 2 Another example of the second catalyst body is a partial cross-sectional view cut along the cylinder axis.

[0027] Figure 5 It is Figure 2 Another example of the second catalyst body, a partial cross-sectional view cut along the cylinder axis.

[0028] Figure 6 This is a partial cross-sectional view schematically showing the stacked structure of the first catalyst body used in the exhaust gas purification system of the first embodiment.

[0029] Figure 7 This is a schematic diagram illustrating the exhaust gas purification system of the second embodiment.

[0030] Figure 8 This is a schematic diagram illustrating the exhaust gas purification system of the third embodiment.

[0031] Figure 9 This is a schematic diagram illustrating the exhaust gas purification system of the fourth embodiment.

[0032] Figure 10 This is a schematic diagram illustrating the exhaust gas purification system of the fifth embodiment.

[0033] Figure 11 This is a schematic diagram illustrating the exhaust gas purification system of the sixth embodiment.

[0034] Figure 12 This is a schematic diagram illustrating the exhaust gas purification system of the seventh embodiment.

[0035] Figure 13 This is a schematic diagram illustrating the exhaust gas purification system of the eighth embodiment.

[0036] Figures 14(A) to (F) are schematic diagrams showing the layer structure of the second catalyst body of the exhaust gas purification system of each embodiment and each comparative example.

[0037] Figure 15 This is a graph showing the NH3 emissions after durability of the exhaust gas purification systems of each embodiment and each comparative example. Detailed Implementation

[0038] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Matters necessary for implementing the present invention, other than those specifically mentioned in this specification, can be understood by those skilled in the art based on prior art. The present invention can be implemented based on the content disclosed in this specification and common technical knowledge in the field. Furthermore, in the following drawings, components and parts that perform the same function are labeled with the same reference numerals, and sometimes repeated descriptions are omitted or simplified. The dimensional relationships (length, width, thickness, etc.) in the drawings may not reflect actual dimensional relationships. Additionally, the expression "A~B" (A and B are arbitrary values) indicating a range in this specification includes the meaning of A and below B, and includes the meanings of "preferably greater than A" and "preferably less than B".

[0039] [First Embodiment]

[0040] Figure 1 This is a schematic diagram of an exhaust gas purification system 100, which is an example of the exhaust gas purification system disclosed herein, according to a first embodiment. The exhaust gas purification system 100 is configured to be disposed in the exhaust path of the gasoline engine 1 and connected to the gasoline engine 1. Figure 1Arrow F 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" in catalytic converter refer to their positional relationship in the direction of exhaust gas flow. Therefore, the downstream catalytic converter 50 is positioned downstream of the upstream catalytic converter 10 in the exhaust gas flow direction F of the gasoline engine 1. Furthermore, in this specification, "gasoline engine" refers to an engine that uses gasoline as fuel and burns an air-fuel mixture with a stoichiometric air-fuel ratio (air:gasoline = 14.7:1) ranging from a rich to a lean region, excluding lean-burn engines.

[0041] The upstream catalytic converter 10 includes a first catalyst body and a first housing housing the first catalyst body. The downstream catalytic converter 50 includes a second catalyst body and a second housing housing the second catalyst body. The first catalyst body is located upstream of the second catalyst body in the exhaust gas flow direction F. The first catalyst body is typically a start-up catalyst (S / C), but is not limited thereto. The second catalyst body is located downstream of the first catalyst body 20 in the exhaust gas flow direction F. The second catalyst body is typically an underfloor catalyst (UF / C), but is not limited thereto. The structures of the first and second housings can be the same as or similar to those used for existing start-up catalysts and underfloor catalysts.

[0042] The first catalyst and the second catalyst will now be described in detail. The first catalyst may have the same or similar structure as existing known catalysts. Therefore, the second catalyst will be described first.

[0043] <Second Catalyst>

[0044] The composition of the second catalyst is illustrated in... Figures 2-5 .like Figures 3-5 As shown, the second catalyst body 60 has a structure in which an NH3 adsorption layer 80 and a second catalyst layer 90 are stacked on a second substrate 70. Therefore, the second catalyst body 60 includes a second substrate 70, an NH3 adsorption layer 80, and a second catalyst layer 90.

[0045] The second substrate 70 constitutes the framework of the second catalyst body 60. There are no particular limitations on the second substrate 70; various raw materials and forms of substrates used in this application can be used. For example, the second substrate 70 can be a ceramic support made of cordierite, aluminum titanate, silicon carbide, etc., or a metal support made of stainless steel (SUS), Fe-Cr-Al alloys, Ni-Cr-Al alloys, etc. Figure 2 As shown, the second substrate 70 has a honeycomb structure. The second substrate 70 in the example figure is a DC-type substrate, but it can also be a wall-following type substrate.

[0046] In the accompanying drawings, direction X indicates the axial direction of the second substrate 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 substrate 70 includes a plurality of compartments (cavities / units) 72 regularly arranged in the axial direction X and partition walls (ribs) 74 separating the plurality of compartments 72. Although not particularly limited, the volume of the second substrate 70 (the apparent volume including the volume of the compartments 72) can be approximately 0.1 to 10 L, for example 0.5 to 5 L. In addition, the average length (total length) L of the second substrate 70 along the axial direction X can also be approximately 10 mm to 500 mm, for example 50 mm to 300 mm.

[0047] The compartment 72 serves as a flow path for the exhaust gas. The unit 72 extends along the cylindrical axis direction X. The compartment 72 is a through-hole penetrating the second substrate 70 along the cylindrical axis direction X. The shape, size, and number of compartments 72 can be designed, for example, taking into account the flow rate and composition of the exhaust gas flowing in the second catalyst body 60. The shape of the cross-section of the compartment 72 orthogonal to the cylindrical axis direction X is not particularly limited. The cross-sectional shape of the compartment 72 can be, for example, a square, parallelogram, rectangle, trapezoid, or other quadrilaterals, other polygons (e.g., triangles, hexagons, octagons), wavy, circular, or various other geometric shapes. A partition wall 74 faces the compartment 72, separating adjacent compartments 72. Although not particularly limited, the average thickness of the partition wall 74 (the dimension in the direction orthogonal to the surface is the same below) can 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 can also be porous to allow exhaust gas to pass through.

[0048] An NH3 adsorption layer 80 and a second catalyst layer 90 are stacked on the second substrate 70. The stacking order of the NH3 adsorption layer 80 and the second catalyst layer 90 is not particularly limited. Figure 3 As shown, in the second catalyst body 60, the NH3 adsorption layer 80 can also be located below the second catalyst layer 90 (i.e., the layer on the side of the second substrate 70). Figure 4 As shown, the NH3 adsorption layer 80 can also be located above the second catalyst layer 90 (i.e., on the exposed surface side of the second catalyst layer 90). Figure 3 As shown, the NH3 adsorption layer 80 is preferably stacked on a lower side than the second catalyst layer 90. By placing the second catalyst layer 90 on the upper side of the NH3 adsorption layer 80, the oxygen-deficient atmosphere can be further mitigated, and the NH3 purification performance can be further improved after durability.

[0049] The NH3 adsorption layer 80 contains zeolite as an NH3 adsorption material. Therefore, the zeolite contained in the NH3 adsorption layer 80 is a zeolite with NH3 adsorption capacity. As an example of such zeolite, zeolites that support transition metals can be cited.

[0050] The transition metal supported on the zeolite is, for example, at least one transition metal selected from V, Mn, Fe, Co, Ni, Cu, La, Ce, and Ag, preferably at least one transition metal selected from 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 or B, or both A and B.

[0051] Zeolites forming the basic framework are typically aluminosilicates, but can also be aluminosilicate phosphates (SAPO). Zeolites preferably have fine pores of a size suitable for adsorbing NH3. If the structure of zeolites is exemplified using the codes defined by the International Zeolite Association (IZA), examples 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 particularly noteworthy, with CHA (Chevasite) being the most preferred. The framework structure of zeolites can be confirmed, for example, by X-ray diffraction (XRD). From the viewpoint of NH3 adsorption capacity, Cu-supported CHA-type zeolites are particularly preferred as zeolites.

[0052] The amount of the zeolite in the NH3 adsorption layer 80 is not particularly limited. However, from the viewpoint of achieving higher NH3 purification performance over time, the amount of the zeolite in the NH3 adsorption layer 80 is preferably 10% by mass or more. Furthermore, when the atmospheric variation of the exhaust gas is small, increasing the amount of zeolite in the NH3 adsorption layer 80 is advantageous for achieving higher NH3 purification performance over time. Therefore, the amount of the zeolite in the NH3 adsorption layer 80 can be 50% by mass or more, or 80% by mass or more.

[0053] The NH3 adsorption layer 80 may contain any components other than those mentioned above. Examples of arbitrary components include oxygen absorption and release materials (so-called OSC materials) with oxygen absorption and release capabilities. As OSC materials, known compounds with oxygen storage capabilities can be used; specific examples include metal oxides containing cerium oxide (CeO2). The Ce-containing oxide can be cerium oxide or a composite oxide of cerium oxide and other metal oxides. From the viewpoint of improving heat resistance and durability, the Ce-containing oxide can be a composite oxide containing at least one of Zr and Al, such as a cerium oxide (CeO2)-zirconia oxide (ZrO2) composite oxide (CZ composite oxide). From the viewpoint of improving heat resistance, the CZ composite oxide may further contain, for example, Nd2O3, La2O3, Y2O3, and Pr6O3. 10 Rare earth metal oxides, etc.

[0054] When the OSC material is a composite oxide containing cerium oxide, from the viewpoint of fully utilizing its oxygen adsorption capacity, the cerium oxide content is preferably 15% by mass or more, more preferably 20% by mass or more. 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, more preferably 50% by mass or less.

[0055] The amount of the OSC material in the NH3 adsorption layer 80 is not particularly limited. The amount of the 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 the OSC material is, for example, 60% by mass or less, preferably 40% by mass or less.

[0056] As another example of any component of the NH3 adsorption layer 80, a catalyst noble metal can be cited. By containing a catalyst noble metal in the NH3 adsorption layer 80, waste gas can also be purified.

[0057] Examples of noble metals for catalysts include rhodium (Rh), palladium (Pd), platinum (Pt), ruthenium (Ru), osmium (Os), iridium (Ir), gold (Au), and silver (Ag), which are platinum group elements. These can be used alone or in combination of two or more. From the viewpoint of catalytic performance, it is preferable to select at least one from Pt, Rh, Pd, Ir, and Ru, and more preferably at least one from Pt, Rh, and Pd. When using two or more of these, the noble metal for catalysts can be a metal alloyed from two or more of these metals.

[0058] The catalyst noble metal can be supported on the above-mentioned OSC material, or it can be supported on non-OSC materials (such as alumina (Al2O3), titanium dioxide (TiO2), zirconium oxide (ZrO2), silicon dioxide (SiO2), etc.).

[0059] Another example of any component of the NH3 adsorption layer 80 includes binders such as alumina sol and silica sol; and various additives.

[0060] The amount of NH3 adsorption layer 80 coated (i.e., the amount formed) is not particularly limited. This coating amount, relative to the volume of the substrate where the NH3 adsorption layer 80 is formed along the cylinder axis X, is, for example, 10 to 200 g / L, or possibly 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.

[0061] There is no particular limitation on the thickness of the NH3 adsorption layer 80; it can be designed appropriately to consider durability, peel resistance, and other factors. The thickness of the NH3 adsorption layer 80 can be, for example, 1 μm to 100 μm, or 5 μm to 100 μm.

[0062] The coating width (average dimension in the cylindrical axis X) of the NH3 adsorption layer 80 is not particularly limited, and can be appropriately designed taking into account the size of the second substrate 70, the flow rate of the waste gas flowing into the second catalyst body 60, etc. This coating width is, for example, 10% to 100% of the total length of the substrate in the cylindrical axis X, preferably 20% to 100%, and more preferably 30% to 100%.

[0063] The second catalyst layer 90 contains a catalyst noble metal. This catalyst noble metal is typically supported on a carrier, so the second catalyst layer 90 typically contains a three-way catalyst. The second catalyst layer 90 can be constructed in the same manner as a known catalyst layer containing a three-way catalyst.

[0064] Catalyst noble metals are catalytic metal components used to purify harmful components in waste gas. Examples of catalyst noble metals include those used as the NH3 adsorption layer 80. A single catalyst noble metal can be used, but a combination of two or more is preferred. From the viewpoint of catalytic performance, at least two catalyst noble metals selected from Pt, Rh, Pd, Ir, and Ru are preferred, and a combination of Rh (high reducing activity) and Pd and / or Pt (high oxidizing activity) is more preferred.

[0065] The catalyst noble metal is preferably used as particles with a sufficiently small particle size. The average particle size of the catalyst noble metal particles (specifically, the average particle size of more than 20 noble metal particles obtained from a cross-sectional image of the catalyst layer obtained by transmission electron microscopy) is typically around 1 nm to 15 nm, preferably less than 10 nm, more preferably less than 7 nm, and even more preferably less than 5 nm. This increases the contact area between the catalyst noble metal and the waste gas, thereby further improving the purification performance.

[0066] The amount of catalyst noble metal in the second catalyst body 60 (the total amount of catalyst noble metal in the NH3 adsorption layer 80 and the second catalyst layer 90) is not particularly limited and can be appropriately determined according to the type of catalyst noble metal. From the viewpoint of particularly high exhaust gas purification performance, the amount of catalyst noble metal per 1L volume of the second substrate 70 can 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 can 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.

[0067] In this specification, "per 1L volume of substrate" refers to the total volume of the substrate, including the volume of the unit channels. In the following description, (g / L) indicates the amount contained in 1L of substrate volume.

[0068] The second catalyst layer 90 contains an OSC material. As an example of an OSC material contained in the second catalyst layer 90, an OSC material that can be used in the NH3 adsorption layer 80 can be cited.

[0069] The OSC material can support precious metal catalysts or not. It can also be configured such that some OSC materials support precious metal catalysts while others do not.

[0070] The second catalyst layer 90 also includes a non-OSC material (i.e., a material that does not have the ability to absorb and release oxygen), and the catalyst noble metal can be supported on the non-OSC material. Examples of non-OSC materials include alumina (Al2O3), titanium dioxide (TiO2), zirconium oxide (ZrO2), and silicon dioxide (SiO2).

[0071] Therefore, in the second catalyst layer 90, either or both of OSC materials and non-OSC materials are typically used as the support. The support preferably has a large specific surface area, and more preferably, porous support particles are used. From the viewpoint of heat resistance and structural stability, the support particles preferably have a specific surface area of ​​50–500 m² as determined by the BET method. 2 / g (especially 200-400m) 2 / g). In addition, the average particle size of the support particles (specifically, the average particle size of 20 or more support particles obtained from a cross-sectional image of the catalyst layer obtained by transmission electron microscopy) is preferably 1 nm or more and 500 nm or less (especially 10 nm or more and 200 nm or less).

[0072] 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 less than 50% by mass.

[0073] 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. Furthermore, 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.

[0074] The second catalyst layer 90 may also contain components other than those mentioned above. For example, the second catalyst layer 90 may also contain metals such as alkali metals, alkaline earth metals, transition metals, and rare earth elements. These elements (especially alkaline earth metals) may be contained in the form of oxides, hydroxides, carbonates, nitrates, sulfates, phosphates, acetates, formates, oxalates, halides, etc. In the second catalyst layer 90, it is preferable that alkaline earth metals (especially Ba) coexist with Pt and / or Pd.

[0075] Other possible components of the second catalyst layer 90 include binders such as alumina sol and silica sol; [the following text appears to be incomplete and requires further context: "having NO"] x NO of absorption capacity x Adsorbent materials; stabilizers and various additives, etc.

[0076] The second catalyst layer 90 can be a single-layer structure or a multi-layer structure. Figure 3 and Figure 4In the example shown, the second catalyst layer 90 is a single layer. When the second catalyst layer 90 has a single-layer structure, it can be composed of multiple regions with different compositions and properties. For example, the second catalyst layer 90 may also have a front portion located upstream on the X1 side and a rear portion located downstream on the X2 side in the axial direction of the cylinder, with different compositions and / or properties in the front and rear portions. Specifically, for example, different noble catalyst metals may be contained in the front and rear portions.

[0077] When the second catalyst layer 90 has a multilayer structure, the number of layers is not particularly limited. The second catalyst layer 90 can be a two-layer structure having a substrate-side layer (lower layer) and a surface-side layer (upper layer), or it can be 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 can contain different catalyst noble metals.

[0078] An example of a case where the second catalyst layer 90 is a multilayer structure is shown below. Figure 5 .exist Figure 5 In the process, an NH3 adsorption layer 80 is disposed on the second substrate 70, and a second catalyst layer 90 is disposed on the NH3 adsorption layer 80.

[0079] The second catalyst layer 90 has a lower layer portion 92 that serves as a substrate side layer and an upper layer portion 94 disposed above the lower layer portion 92. In the illustrated example, the upper layer portion 94 is also the layer on the exposed surface side of the second catalyst layer 90. The lower layer portion 92 and the upper layer portion 94 of the second catalyst layer 90 each contain a catalyst noble metal. The lower layer portion 92 contains Pd as the catalyst noble metal. On the other hand, the upper layer portion 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 noble metal (e.g., sintering accompanying grain growth) can be suppressed, further improving the durability of the second catalyst body 60.

[0080] The amount of the second catalyst layer 90 coated (i.e., the amount formed) is not particularly limited. This coating amount, relative to the volume of the substrate where the catalyst layer 20 is formed along the cylinder axis X, is, for example, 10 to 500 g / L, or possibly 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.

[0081] The thickness of the second catalyst layer 90 is not particularly limited; it can be appropriately designed considering durability, peel resistance, etc. For example, the thickness of the second catalyst layer 90 can be 1 μm to 100 μm, or it can be 5 μm to 100 μm.

[0082] The coating width (average dimension in the cylindrical axis X) of the second catalyst layer 90 is not particularly limited, and can be appropriately designed taking into account the size of the second substrate 70, the flow rate of the exhaust gas flowing into the second catalyst body 60, etc. The coating width is, for example, 10% to 100% of the total length of the substrate in the cylindrical axis X, preferably 20% to 100%, and more preferably 30% to 100%.

[0083] The second catalyst body 60 may also have layers other than the NH3 adsorption layer 80 and the second catalyst layer 90.

[0084] The second catalyst body 60 can be manufactured according to known methods. For example, a slurry for forming an NH3 adsorption layer is prepared, containing zeolite that functions as an NH3 adsorption material, a solvent, and any components (e.g., OSC material, catalyst noble metal source, binder, etc.). Alternatively, a slurry containing a catalyst noble metal source, OSC material, a non-OSC material as needed, a solvent, and other arbitrary components is prepared. The lower layer side of these slurries is applied to a second substrate 70 according to known methods, dried as needed, and then fired to form a lower layer. Next, the upper layer side slurry is applied to the lower layer formed on the second substrate 70 according to known methods, dried as needed, and then fired to form an upper layer. Thus, the second catalyst body 60 can be obtained.

[0085] <Catalyst 1>

[0086] The first catalyst body 20 may have the same or similar structure as the starting catalyst of a known gasoline engine exhaust gas purification system, which includes a starting catalyst (S / C) and an underfloor catalyst (UF / C).

[0087] An example of the first catalyst 20 is shown in Figure 6 For example, the first catalyst body 20 includes a first substrate 30 and a first catalyst layer 40. Typically, the first catalyst body 20 is disposed in the exhaust path of the gasoline engine 1 at a location near the exhaust manifold and the engine compartment (closed coupling (CC) location).

[0088] In the first embodiment, the first substrate 30 uses a direct-flow substrate. However, the first substrate 30 is not limited to this and may also be a wall-flow substrate. For example, as in the embodiments described later, a wall-flow substrate can be used as the first substrate 30 to configure the first catalyst body 20 as a catalyst-coated gasoline particulate filter (GPF).

[0089] The first substrate 30 can be a ceramic carrier made of ceramics such as cordierite, aluminum titanate, and silicon carbide, or a metal carrier made of stainless steel (SUS), Fe-Cr-Al alloys, Ni-Cr-Al alloys, etc.

[0090] In the first embodiment, the first catalyst body 20 has a first substrate 30, but is not limited thereto. For example, as described in the embodiments below, the first catalyst body 20 may be a series-type catalyst body comprising a plurality of first substrates 30 and wherein a first catalyst layer 40 is provided on each of the first substrates 30. In a series-type catalyst body, the plurality of first substrates 30 may be of the same or different types. In addition, the composition of the plurality of first catalyst layers 40 may be the same or different.

[0091] The first catalyst layer 40 contains a catalyst noble metal. The catalyst noble metal contained in the first catalyst layer 40 may be the same as the catalyst noble metal contained in the second catalyst layer 90 of the second catalyst body 60. The first catalyst layer 40 typically contains a support for carrying the catalyst 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 body 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 body 60.

[0092] The first catalyst layer 40 can be a single-layer structure or a multi-layer structure. When the first catalyst layer 40 is a single-layer structure, it can be composed of multiple regions with different compositions and properties. 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 axial direction Y, with different compositions and / or properties in the front and rear portions. Specifically, for example, different noble metals may be contained in the front and rear portions.

[0093] When the first catalyst layer 40 has a multilayer structure, the number of layers is not particularly limited. The first catalyst layer 40 can be a two-layer structure having a substrate-side layer (lower layer) and a surface-side layer (upper layer), or it can be 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 can contain different noble metals.

[0094] exist Figure 6 In the example shown, the first catalyst layer 40 has a multilayer structure, having a lower layer 42 on the substrate side and an upper layer 44 on the exposed surface side. Both the lower layer 42 and the upper layer 44 of the first catalyst layer 40 contain catalyst noble metals. The lower layer 42 contains Pd as the catalyst noble metal. On the other hand, the upper layer 44 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 noble metal (e.g., sintering accompanying grain growth) can be suppressed, further improving the durability of the first catalyst body 20.

[0095] The first catalyst body 20 can be manufactured according to known methods. For example, a slurry containing a catalyst noble metal source, OSC material, non-OSC material, solvent, and arbitrary components is prepared. The slurry is coated onto a second substrate 70 according to known methods, dried as needed, and then fired to form a first catalyst layer 40. Thus, the first catalyst body 20 can be obtained.

[0096] Exhaust Gas Purification System 100

[0097] In a gasoline engine 1, combustion occurs between a rich region (containing the stoichiometric air-fuel ratio) and a lean region (containing the stoichiometric air-fuel ratio). For example... Figure 1 As shown, the exhaust gas generated in the gasoline engine 1 is first purified in the first catalyst body 20 of the upstream catalytic converter 10. The first catalyst body 20 contains a precious metal catalyst, similar to that of a three-way catalytic converter, for purifying NO. x NH3 is generated during the process, and the exhaust gas containing NH3 flows out from the upstream catalytic converter 10.

[0098] The exhaust gas flowing from the upstream catalytic converter 10 flows into the downstream catalytic converter 50. Here, the temperature within the downstream catalytic converter 50 is low and has not reached the catalyst activation temperature, making it impossible to purify NH3. In contrast, in the exhaust gas purification system 100, the second catalyst body 60 includes an NH3 adsorption layer 80. Thus, the NH3 contained in the exhaust gas is adsorbed by the NH3 adsorption layer 80 of the second catalyst body 60 of the downstream catalytic converter 50, suppressing its emission outside the exhaust gas purification system 100. The NH3 adsorbed in the NH3 adsorption layer 80 is purified in the second catalyst layer 90, for example, during fuel cut-off (F / C).

[0099] Unlike diesel and lean-burn engines, gasoline engines operate at high temperatures, and the atmosphere fluctuates between rich and lean. The inventors conducted in-depth research and concluded that when the atmosphere is concentrated to stoichiometric levels at high temperatures, oxygen deficiency causes structural degradation of the zeolite used as the NH3 adsorption material in the NH3 adsorption layer, thereby reducing NH3 purification performance.

[0100] Based on this understanding, in the second catalyst body 60 of the downstream catalytic converter 50 of the exhaust gas purification system 100 of this embodiment, a second catalyst layer 90 containing OSC material is stacked on the NH3 adsorption layer 80. This allows oxygen to be released from the OSC material, preventing an oxygen-deficient atmosphere. Since the second catalyst layer 90 exists in a form stacked on the NH3 adsorption layer 80, its atmosphere-moderating effect is particularly high. Therefore, it is possible to effectively suppress the structural degradation of zeolite caused by oxygen deficiency at high temperatures, and to significantly suppress the decrease in NH3 purification performance over time.

[0101] Other Implementation Methods

[0102] Figures 7-13 Other implementation methods are indicated. Furthermore, in the following implementation methods, descriptions of parts identical to those in the first implementation method are omitted.

[0103] Figure 7 The exhaust gas purification system 200 for a gasoline engine illustrated in the second embodiment is configured to be disposed in the exhaust path of the gasoline engine 1 and 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 disposed downstream of the upstream catalytic converter 10 and upstream of the downstream catalytic converter 50 in the exhaust gas flow direction F. That is, the exhaust gas purification system 200 for a gasoline engine in the second embodiment is a system in the exhaust gas purification system 100 for a gasoline engine in the first embodiment with the GPF 110 added between the upstream catalytic converter 10 and the downstream catalytic converter 50. As the GPF 110, a known GPF used in known gasoline engine exhaust gas purification systems can be used.

[0104] Based on this structure, particulate matter (PM) in exhaust gas can be captured by the GPF. Therefore, based on this structure, an exhaust gas purification system for gasoline engines with high NH3 purification performance and reduced PM emissions after long-term durability can be provided.

[0105] Figure 8 The exhaust gas purification system 300 for a gasoline engine illustrated in the third embodiment includes a gasoline particulate filter (GPF) 110, similar to that in 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 in the third embodiment is a system in which the GPF 110 is added downstream of the downstream catalytic converter 50 in the exhaust gas purification system 100 for a gasoline engine in the first embodiment.

[0106] Based on this structure, PM in the exhaust gas can be captured by the GPF. Therefore, based on this structure, a gasoline engine exhaust gas purification system with high NH3 purification performance and reduced PM emissions after long-term durability can be provided.

[0107] exist Figure 9 In the gasoline engine exhaust gas purification system 400 of the fourth embodiment, the first catalyst body 20 of the upstream catalytic converter 10 is a series-connected catalyst body including an upstream catalyst body 22 and a downstream catalyst body 24, which differs from the gasoline engine exhaust gas purification system 100 of the first embodiment. With this structure, the purification performance of the first catalyst body 20 can be further improved.

[0108] exist Figure 10 In the gasoline engine exhaust gas purification system 500 of the fifth embodiment, the first catalyst body 20 of the upstream catalytic converter 10 is a series-connected catalyst body including an upstream catalyst body 22 and a downstream catalyst body 24. The GPF 110 is disposed downstream of the upstream catalytic converter 10 and upstream of the downstream catalytic converter 50 in the exhaust gas flow direction F. That is, the gasoline engine exhaust gas purification system 500 of the fifth embodiment is a system in the gasoline engine exhaust gas purification system 400 of the fourth embodiment in which a GPF 110 is added between the upstream catalytic converter 10 and the downstream catalytic converter 50. With this structure, the purification performance of the first catalyst body 20 can be further improved, and PM in the exhaust gas can be captured efficiently.

[0109] exist Figure 11 In the gasoline engine exhaust gas purification system 600 of the sixth embodiment shown, the first catalyst body 20 of the upstream catalytic converter 10 is a series-connected catalyst body including an upstream catalyst body 22 and a downstream catalyst body 24, and the GPF 110 is disposed downstream of the downstream catalytic converter 50 in the exhaust gas flow direction F. That is, the gasoline engine exhaust gas purification system 600 of the sixth embodiment is formed by adding GPF 110 downstream of the downstream catalytic converter 50 in the gasoline engine exhaust gas purification system 400 of the fourth embodiment. With this structure, the purification performance of the first catalyst body 20 can be further improved, and PM in the exhaust gas can be captured efficiently.

[0110] exist Figure 12 In the exhaust gas purification system 700 for a gasoline engine shown in the seventh embodiment, the substrate of the first catalyst body 26 of the upstream catalytic converter 10 is a wall-flow type substrate, and the substrate of the first catalyst body 26 has the function of a gas purification powder (GPF). With this structure, PM in the exhaust gas can be captured by the GPF. Therefore, with this structure, a gasoline engine exhaust gas purification system with high NH3 purification performance and reduced PM emissions after durability can be provided.

[0111] exist Figure 13 In the gasoline engine exhaust gas purification system 800 of the eighth embodiment shown, the first catalyst body 20 of the upstream catalytic converter 10 is a series-connected catalyst body including an upstream catalyst body 22 and a downstream catalyst body 26. The substrate of the downstream catalyst body 26 is a wall-flow type substrate, and the substrate of the downstream catalyst body 26 has the function of a gas permeable powder (GPF). With this structure, the purification performance of the first catalyst body 20 can be further improved, and PM in the exhaust gas can be captured efficiently.

[0112] Applications of Exhaust Gas Purification System 100 for Gasoline Engines

[0113] The exhaust gas purification system 100 for gasoline engines is applicable not only to vehicles such as cars, trucks, and motorcycles, but also to the purification of exhaust gases emitted from gasoline engines in ships and other applications. Specifically, it is suitable for use in vehicles including cars and trucks with gasoline engines.

[0114] The following describes experimental examples related to the present invention, but it is not intended to limit the present invention to the contents shown in the following experimental examples.

[0115] (Example 1)

[0116] 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, binder, and deionized water were mixed to prepare a Pd-containing slurry. This Pd-containing slurry was poured into the first substrate as a substrate for lower layer formation, and unwanted portions were blown away with a blower, thereby coating the surface of the first substrate with the lower layer formation material. By firing it in an electric furnace, a lower layer containing a Pd catalyst was formed on the first substrate.

[0117] Rhodium nitrate, CeO2-ZrO2 composite oxide powder (OSC material), Al2O3 powder, binder, and deionized water were mixed to prepare an Rh-containing slurry. This Rh-containing slurry was then used as a top-layer forming slurry and poured into a first substrate on which a bottom layer had been formed. Unwanted portions were blown away using a blower, and the top-layer forming material was then applied to the surface of the bottom layer of the substrate. By firing this material in an electric furnace, a top layer containing the Rh catalyst was formed on the bottom layer. Thus, the first catalyst body was produced.

[0118] Next, a honeycomb substrate identical to the first substrate is prepared as the second substrate. A zeolite-containing slurry is prepared by mixing Cu-supported CHA-type zeolite (Cu-CHA), a binder, and deionized water. This zeolite-containing slurry is then poured into the second substrate as a base layer forming slurry, and unwanted portions are blown away with a blower, thereby coating the surface of the second substrate with the base layer forming material. By firing it in an electric furnace, a zeolite-containing base layer is formed on the second substrate.

[0119] The Pd-containing slurry prepared above is used as a slurry for forming an intermediate layer and is poured into a second substrate on which a lower layer has been formed. Unwanted portions are blown away with a blower, thereby applying the material for forming the intermediate layer to the surface of the lower layer of the second substrate. By firing it in an electric furnace, an intermediate layer containing an Rh catalyst is formed on the lower layer.

[0120] The Rh-containing slurry prepared above is used as a slurry for upper layer formation and flows into the second substrate on which the intermediate layer is formed. Unwanted portions are blown away with a blower, and the material for upper layer formation is then applied to the surface of the intermediate layer formed on the second substrate. By firing it in an electric furnace, an upper layer containing the Rh catalyst is formed on the intermediate layer. Thus, the second catalyst body is produced. The first and second catalyst bodies are combined to construct the exhaust gas purification system of Example 1. The layer structure of the second catalyst body is schematically shown in Figure 14(A).

[0121] (Example 2)

[0122] The first catalyst body 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 composite oxide powder (OSC material), binder, and deionized water. This zeolite-containing slurry was used as the lower layer forming slurry. The amount of OSC material in the Pd-containing and Rh-containing slurries was reduced so that the total amount of OSC material in the second catalyst body was the same as that in the second catalyst body of Example 1. Otherwise, the second catalyst body was prepared in the same manner as in Example 1. The prepared first and second catalyst bodies were combined to construct the exhaust gas purification system of Example 2. The layer structure of the second catalyst body is schematically shown in Figure 14(B).

[0123] (Example 3)

[0124] The first catalyst body 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 composite oxide powder (OSC material), binder, and deionized water. This zeolite-containing slurry was used as the lower layer forming slurry. The Pd content in the Pd-containing slurry was reduced in a manner consistent with the Pd content in the second catalyst body as in Example 1. The OSC material content in both the Pd-containing and Rh-containing slurries was reduced in a manner consistent with the OSC material content in the second catalyst body as in Example 1. Otherwise, the second catalyst body was prepared in the same manner as in Example 1. The prepared first and second catalyst bodies were combined to construct the exhaust gas purification system of Example 3. The layer structure of the second catalyst body is schematically shown in Figure 14(C).

[0125] (Example 4)

[0126] The first catalyst body was prepared in the same manner as in Example 1. A second substrate identical to that in Example 1 was prepared. The Pd-containing slurry prepared in Example 1 was fed into the second substrate as a slurry for lower layer formation. Unwanted portions were blown away using a blower, thereby coating the surface of the second substrate with the material for lower layer formation. A Pd-containing lower layer was formed on the second substrate by firing it in an electric furnace.

[0127] The Rh-containing slurry prepared in Example 1 was flowed into the slurry used to form the intermediate layer, thus forming the second substrate as the lower layer. The unwanted parts were blown away with a blower, and the material for forming the intermediate layer was then applied to the surface of the lower layer of the second substrate. By firing it in an electric furnace, an intermediate layer containing an Rh catalyst was formed on the lower layer.

[0128] The zeolite-containing slurry prepared in Example 1 was used as a top layer forming slurry and flowed into the second substrate on which the intermediate layer was formed. Unwanted portions were blown away using a blower, and the top layer forming material was then applied to the surface of the intermediate layer formed on the second substrate. By firing it in an electric furnace, a zeolite-containing top layer was formed on the intermediate layer. Thus, the second catalyst body was produced. The first and second catalyst bodies were combined to construct the exhaust gas purification system of Example 4. The layer structure of the second catalyst body is schematically shown in Figure 14(D).

[0129] Comparative Example 1

[0130] The first catalyst body was prepared in the same manner as in Example 1. A second substrate identical to that in Example 1 was prepared. The zeolite-containing slurry prepared in Example 1 was allowed to flow from the front side of the second substrate to a position 50% of the total length of the substrate. Unwanted portions were blown away with a blower, thereby coating the surface of the front side of the second substrate with a material for forming the front side. By firing it in an electric furnace, a zeolite-containing front layer was formed on the front side of the substrate.

[0131] The Pd-containing slurry prepared in Example 1 was allowed to flow from the rear of the second substrate to a position 50% of the total length of the substrate. Unwanted portions were blown away with a blower, thereby coating the rear surface of the second substrate with a material for forming a rear underlayer. By firing it in an electric furnace, a Pd-containing underlayer was formed on the rear of the second substrate.

[0132] The Rh-containing slurry prepared in Example 1 was allowed to flow from the rear of the second substrate to a position 50% of the total length of the substrate. Unwanted portions were blown away with a blower, and the lower surface of the rear of the second substrate was coated with a material for forming the upper layer. By firing it in an electric furnace, a Pd-containing upper layer was formed on the lower layer of the rear of the second substrate. Thus, the second catalyst body was fabricated. The fabricated first and second catalyst bodies were combined to construct the exhaust gas purification system of Comparative Example 1. The layer structure of this second catalyst body is schematically shown in Figure 14(E). The amounts of Pd and Rh in the substrate were adjusted to be the same as in Example 1.

[0133] Comparative Example 2

[0134] The first catalyst body was prepared in the same manner as in Example 1. A second catalyst body was prepared by swapping the front and rear portions of the second catalyst body from Comparative Example 1. The prepared first and second catalyst bodies were combined to construct the exhaust gas purification system of Comparative Example 2. The layer structure of the second catalyst body is schematically shown in FIG14(F). The amounts of Pd and Rh in the substrate were adjusted to be the same as in Example 1.

[0135] [Durability Treatment]

[0136] The exhaust gas purification systems of each embodiment and comparative example were installed in the exhaust system of a V8 gasoline engine. In this case, the first catalyst body was positioned upstream of the exhaust gas flow direction in the exhaust system. The inflow gas temperature was set to 950°C, and after 50 hours, exhaust gases of rich, stoichiometric, and lean atmospheres were repeatedly introduced into the exhaust gas purification system at predetermined intervals. The first catalyst body was then exposed to a durability treatment at 1000°C, and the second catalyst body was exposed to a durability treatment at 700°C.

[0137] [Measurement of NH3 emissions]

[0138] The exhaust gas purification systems of the embodiments and comparative examples that underwent the aforementioned durability treatment were installed in a vehicle including a gasoline engine. In this case, the first catalyst body was housed in the housing and installed in the catalyst start-up position, and the second catalyst body was housed in the housing and installed in the base plate position. An FT-IR analyzer was installed downstream of the second catalyst body. The vehicle was operated on a chassis dynamometer in WLTC mode to measure the ammonium concentration in the exhaust gas and determine the NH3 emission amount. The results are presented as follows: Figure 15 .

[0139] like Figure 15The results show that, in the second catalyst body, the exhaust gas purification systems of Examples 1-4, which have a Cu-CHA-containing NH3 adsorption layer and an OSC-containing catalyst layer stacked in the second catalyst body, have a significantly lower NH3 emission after durability compared to Comparative Examples 1-2, which have these layers arranged side by side in the exhaust gas flow direction. Therefore, it can be concluded that the exhaust gas purification system for gasoline engines disclosed herein has high NH3 purification performance after durability.

[0140] A comparison of Examples 1 to 3 shows that the amount of NH3 emitted after durability is lower when the OSC material and catalyst noble metal are not disposed in the NH3 adsorption layer compared to when they are disposed in the NH3 adsorption layer. Furthermore, a comparison of Examples 1 and 4 shows that the amount of NH3 emitted after durability is lower when the NH3 adsorption layer is disposed below the catalyst layer.

[0141] The present invention has been described above with reference to several embodiments, but these embodiments are merely examples. The present invention can also be implemented in various other ways. The present invention can be implemented based on the content disclosed in this specification and common technical knowledge in the field. The technology described in the claims includes technology obtained by various modifications and alterations to the embodiments illustrated above. For example, a portion of the above embodiments can be replaced with other modifications, and other modifications can be added to the above embodiments. Furthermore, if a technical feature is not described as an essential feature, it can be appropriately omitted.

Claims

1. An exhaust gas purification system for a gasoline engine, configured in the exhaust path of the gasoline engine, characterized in that: 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 noble catalyst metal. The second catalyst has a structure in which an NH3 adsorption layer and a catalyst layer are stacked on a substrate. The NH3 adsorption layer of the second catalyst contains zeolite as an NH3 adsorption material. The catalyst layer of the second catalyst body contains a noble catalyst metal and OSC material. In the second catalyst body, the NH3 adsorption layer is stacked at a position lower than the catalyst layer. The zeolite is a Cu-supported CHA-type zeolite. The amount of zeolite in the NH3 adsorption layer is 80% or more by mass.

2. The exhaust gas purification system for gasoline engines as described in claim 1, characterized in that: In the direction of exhaust gas flow in the exhaust path, a gasoline particulate filter is also provided between the upstream catalytic converter and the downstream catalytic converter.

3. The exhaust gas purification system for gasoline engines as described in claim 1, characterized in that: In the direction of exhaust gas flow in the exhaust path, a gasoline particulate filter is also provided at a position downstream of the downstream catalytic converter.

4. The exhaust gas purification system for gasoline engines as described in claim 1, characterized in that: The first catalyst body of the upstream catalytic converter is a catalyst body in series, comprising an upstream catalyst body and a downstream catalyst body.

5. The exhaust gas purification system for gasoline engines as described in claim 4, characterized in that: In the direction of exhaust gas flow in the exhaust path, a gasoline particulate filter is also provided between the upstream catalytic converter and the downstream catalytic converter.

6. The exhaust gas purification system for a gasoline engine as described in claim 4, characterized in that: In the direction of exhaust gas flow in the exhaust path, a gasoline particulate filter is also provided at a position downstream of the downstream catalytic converter.

7. The exhaust gas purification system for a gasoline engine as described in claim 4, characterized in that: The downstream catalyst of the first catalyst body functions as a gasoline particulate filter.

8. The exhaust gas purification system for a gasoline engine as described in claim 1, characterized in that: The first catalyst body of the upstream catalytic converter functions as a gasoline particulate filter.

9. A catalyst for exhaust gas purification in a gasoline engine, the gasoline engine comprising: Substrate; An NH3 adsorption layer laminated on the substrate; The catalyst body for purifying exhaust gas in gasoline engines, characterized by a catalyst layer stacked on the NH3 adsorption layer, is further characterized by: The NH3 adsorption layer contains zeolite and OSC material as NH3 adsorption materials. The catalyst layer contains a catalyst noble metal and OSC material. The zeolite is a Cu-supported CHA-type zeolite. The amount of zeolite in the NH3 adsorption layer is 80% or more by mass.

10. The catalyst body for exhaust gas purification of gasoline engines as described in claim 9, characterized in that: The NH3 adsorption layer also contains a catalyst, a noble metal.

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