Exhaust gas purification catalyst

Abstract

Provided is an exhaust gas purification catalyst having high HC purification performance during cold start after persistent hydrothermal treatment. The exhaust gas purification catalyst disclosed herein has a substrate, a hydrocarbon adsorption layer, and a catalyst layer. The hydrocarbon adsorption layer is laminated with the catalyst layer such that the hydrocarbon adsorption layer is positioned on one side of the substrate. The catalyst layer contains a catalyst metal. The hydrocarbon adsorption layer includes a molecular sieve that does not substantially contain Si from one end portion of the hydrocarbon adsorption layer to the other end portion of the hydrocarbon adsorption layer in the direction of flow of the exhaust gas. The content of the molecular sieve that does not substantially contain Si in the hydrocarbon adsorption layer is 80 mass% or more. The substantially Si-free molecular sieve is an aluminum phosphate molecular sieve having a 12-membered ring.

Description

Technical Field

[0001] The present invention relates to a catalyst for purifying exhaust gas. This application claims priority based on Japanese Patent Application No. 2022-206103 filed on December 23, 2022, the entire contents of which are incorporated herein by reference. Background Art

[0002] The exhaust gas emitted by internal combustion engines such as automobile engines contains hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NO x ) and other harmful components. Exhaust gas purification catalysts have long been used to efficiently react and remove these harmful components from exhaust gas. Typical exhaust gas purification catalysts include those with a catalyst layer containing a catalytic metal such as Pt (platinum), Pd (palladium), or Rh (rhodium) formed on a highly heat-resistant substrate such as ceramic.

[0003] Immediately after engine startup, when the exhaust gas purification catalyst has not yet been fully heated (a so-called cold start), the exhaust gas purification catalyst has a low temperature, making it difficult to achieve sufficient catalytic activity for hydrocarbon (HC) treatment. Consequently, HC adsorption-type exhaust gas purification catalysts have been developed, in which a catalyst layer containing a catalytic metal is layered on an HC adsorption layer containing an HC adsorbent (see, for example, Patent Documents 1 to 4). Molecular sieves such as zeolites described in Patent Documents 1 to 4 are known as HC adsorbents.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 7-256114

[0007] Patent Document 2: Japanese Patent Application Publication No. 2009-167973

[0008] Patent Document 3: Japanese Patent Application Publication No. 2004-116331

[0009] Patent Document 4: Japanese Patent Publication No. 2020-510519 Summary of the Invention

[0010] Problems to be solved by the invention

[0011] In recent years, due to more stringent exhaust gas restrictions, the catalysts for exhaust gas purification are required to have higher performance in removing harmful components contained in the exhaust gas. For example, higher exhaust gas purification performance during cold start is needed. As a result of in-depth research by the inventors of the present invention, it has been found that in the exhaust gas purification catalysts of the above-mentioned prior art, there is a problem that the HC purification performance during cold start drops significantly after being exposed to high-temperature exhaust gas containing water for a long time (hereinafter referred to as "prolonged hydrothermal treatment").

[0012] The present invention has been completed in view of the above circumstances, and its object is to provide an exhaust gas purification catalyst with high HC purification performance during cold start after prolonged hydrothermal treatment.

[0013] Technical means for solving the problem

[0014] The inventors of the present invention have conducted in-depth research and found that the reason for the significant drop in purification performance after prolonged hydrothermal treatment in the exhaust gas purification catalysts of the above-mentioned prior art using zeolite is that Si contained in the zeolite (aluminosilicate) migrates during prolonged hydrothermal treatment, which has an adverse effect on the noble metal as the catalyst metal. It has also been found that by using a molecular sieve substantially free of Si in a proportion of 80% by mass or more as the HC adsorption material, the HC purification performance of the exhaust gas purification catalyst during cold start after prolonged hydrothermal treatment is suddenly improved. The inventors of the present invention have further conducted in-depth research and found that in a molecular sieve substantially free of Si, by using an aluminophosphate molecular sieve with a 12-membered ring, the HC purification performance of the exhaust gas purification catalyst during cold start after prolonged hydrothermal treatment is significantly improved.

[0015] That is, the exhaust gas purification catalyst [1] disclosed herein has a substrate, a hydrocarbon adsorption layer, and a catalyst layer. The hydrocarbon adsorption layer is laminated with the catalyst layer in such a manner that the hydrocarbon adsorption layer is located on one side of the substrate. The catalyst layer contains a catalyst metal. The hydrocarbon adsorption layer contains a molecular sieve substantially free of Si from one end portion of the hydrocarbon adsorption layer along the exhaust gas flow direction to the other end portion. The content of the molecular sieve substantially free of Si in the hydrocarbon adsorption layer is 80% by mass or more. The molecular sieve substantially free of Si is an aluminophosphate molecular sieve with a 12-membered ring. According to such a configuration, an exhaust gas purification catalyst with high HC purification performance during cold start after prolonged hydrothermal treatment can be provided.

[0016] The exhaust gas purification catalyst [2] disclosed herein is a catalyst in which the hydrocarbon adsorption material in the exhaust gas purification catalyst [1] contains 90% by mass or more of a molecular sieve substantially free of Si. According to such a configuration, an exhaust gas purification catalyst with even higher HC purification performance during cold start after prolonged hydrothermal treatment can be provided.

[0017] The catalyst for purifying exhaust gas disclosed herein [3] is a catalyst in which, among the above-mentioned catalysts for purifying exhaust gas [1] or [2], the framework structure of the above-mentioned aluminophosphate molecular sieve is of the AFI type. With such a configuration, it is beneficial to the HC purification performance during cold start after long-term hydrothermal treatment.

[0018] The catalyst for purifying exhaust gas disclosed herein [4] is a catalyst in which, among any one of the above-mentioned catalysts for purifying exhaust gas [1] to [3], the coating width of the above-mentioned hydrocarbon adsorption layer along the exhaust gas flow direction is 80% or more of the total length of the above-mentioned substrate. With such a configuration, the purification performance of HC is further improved.

[0019] The catalyst for purifying exhaust gas disclosed herein [5] is a catalyst in which, among any one of the above-mentioned catalysts for purifying exhaust gas [1] to [4], a first partial catalyst layer and a second partial catalyst layer are laminated in the above-mentioned catalyst layer. The above-mentioned first partial catalyst layer is located closer to the above-mentioned substrate than the above-mentioned second partial catalyst layer. The above-mentioned first partial catalyst layer and the above-mentioned second partial catalyst layer each contain the above-mentioned catalyst metal. The above-mentioned first partial catalyst layer contains an oxidation catalyst as the above-mentioned catalyst metal. The above-mentioned second partial catalyst layer contains a reduction catalyst as the above-mentioned catalyst metal. With such a configuration, a catalyst for purifying exhaust gas with particularly excellent exhaust gas purification performance can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic diagram showing the exhaust gas purification system according to the first embodiment.

[0021] Figure 2 schematically shows Figure 1 a three-dimensional view of the exhaust gas purification catalyst.

[0022] Figure 3 is a partial cross-sectional view obtained by cutting the exhaust gas purification catalyst of Figure 1 along the cylinder axis direction.

[0023] Figure 4 shows Figure 1 a partial cross-sectional view of the structure of a modified example of the exhaust gas purification catalyst.

[0024] Figure 5 is a graph showing the HC 50% purification temperature after long-term hydrothermal treatment of Examples 1 to 4 and Comparative Examples 1 to 5.

[0025] Figure 6 is a graph showing the HC emission amount after long-term hydrothermal treatment of Example 5 and Comparative Example 6. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] [First Embodiment]

[0027] Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. In addition, matters required for implementing the present invention other than those specifically mentioned in this specification can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be implemented based on the content described in this specification and the common general knowledge in this field. In addition, in the following drawings, components and parts that perform the same function are denoted by the same reference numerals, and redundant descriptions may sometimes be omitted or simplified. The dimensional relationships (length, width, thickness, etc.) in each drawing do not always reflect the actual dimensional relationships. In addition, the expression "A to B" (where A and B are arbitrary values) indicating a range in this specification not only includes the meaning of A or more and B or less, but also includes the meanings of "preferably greater than A" and "preferably less than B".

[0028] "Exhaust Gas Purification System"

[0029] Figure 1 is a schematic diagram of an exhaust gas purification system 1. The exhaust gas purification system 1 includes an internal combustion engine (engine) 2, an exhaust gas purification device 3, and an engine control unit (ECU) 7. The exhaust gas purification system 1 is configured to purify harmful components contained in the exhaust gas discharged from the internal combustion engine 2, such as HC, CO, NO x and the like. Among them, Figure 1 the arrows in the figure indicate the flow direction of the exhaust gas. In addition, in the following description, the side closer to the internal combustion engine 2 along the exhaust gas flow is referred to as the upstream side, and the side farther from the internal combustion engine 2 is referred to as the downstream side.

[0030] The internal combustion engine 2 is configured here with a gasoline engine of a gasoline vehicle as the main body. However, the internal combustion engine 2 may also be an engine other than a gasoline engine, such as a diesel engine or an engine equipped in a hybrid vehicle. The internal combustion engine 2 has a combustion chamber (not shown). The combustion chamber is connected to a fuel tank (not shown). Here, gasoline is stored in the fuel tank. However, the fuel stored in the fuel tank may also be diesel fuel (gas oil) or the like. The fuel supplied from the fuel tank is mixed with oxygen in the combustion chamber and burned. Thereby, the combustion energy is converted into mechanical energy. The combustion chamber communicates with an exhaust port 2a. The exhaust port 2a communicates with the exhaust gas purification device 3. The fuel gas after combustion becomes exhaust gas and is discharged to the exhaust gas purification device 3.

[0031] The exhaust gas purification device 3 has an exhaust passage 4 connected to the internal combustion engine 2, a pressure sensor 8, a first catalyst 9 and a second catalyst 10. The exhaust passage 4 is an exhaust gas flow passage through which the exhaust gas flows. Here, the exhaust passage 4 has an exhaust manifold 5 and an exhaust pipe 6. The upstream end of the exhaust manifold 5 is connected to the exhaust port 2a of the internal combustion engine 2. The downstream end of the exhaust manifold 5 is connected to the exhaust pipe 6. In the middle of the exhaust pipe 6, the first catalyst 9 and the second catalyst 10 are arranged in sequence from the upstream side. However, the arrangement of the first catalyst 9 and the second catalyst 10 can be changed arbitrarily. In addition, the number of the first catalyst 9 and the second catalyst 10 is not particularly limited, and a plurality of each can be provided. In addition, a third catalyst can also be arranged on the downstream side of the second catalyst 10.

[0032] The first catalyst 9 is not particularly limited and can be the same as in the past. For example, the first catalyst 9 can be a diesel particulate filter (DPF) that removes PM contained in the exhaust gas; a diesel oxidation catalyst (DOC) that purifies HC and CO contained in the exhaust gas; or a diesel oxidation catalyst (DOC) that converts HC, CO and NO contained in the exhaust gas into x Three-way catalyst for simultaneous purification; during normal operation (lean burn conditions) it absorbs and stores NO x When a large amount of fuel has been injected (under rich combustion conditions), HC and CO are used as reducing agents to reduce NO x Purified NO x Adsorption reduction (NSR: NO x Storage-Reduction) catalyst, etc. The first catalyst 9 may have a function of increasing the temperature of the exhaust gas flowing into the second catalyst 10, for example. However, the first catalyst 9 is not necessarily a component and may be omitted in other embodiments.

[0033] The second catalyst 10 has the function of purifying harmful components (e.g., HC) in the exhaust gas. Here, the second catalyst 10 is a three-way catalyst. The second catalyst 10 is an example of the exhaust gas purification catalyst disclosed herein. In the following text, the second catalyst 10 may sometimes be referred to as an "exhaust gas purification catalyst." The structure of the second catalyst (exhaust gas purification catalyst) 10 will be described in detail later.

[0034] ECU 7 controls the internal combustion engine 2 and the exhaust gas purification device 3. ECU 7 is electrically connected to the internal combustion engine 2 and sensors (e.g., pressure sensor 8, temperature sensor, oxygen sensor, etc.) installed at various locations of the exhaust gas purification device 3. The configuration of ECU 7 is not particularly limited and can be the same as in the past. ECU 7 is, for example, a processor or an integrated circuit. ECU 7 has an input port (not shown) and an output port (not shown). ECU 7 receives information such as the operating status of the vehicle or the amount, temperature, and pressure of exhaust gas discharged from the internal combustion engine 2. ECU 7 receives information detected by sensors (e.g., pressure measured by pressure sensor 8) through the input port. Based on the received information, ECU 7 sends a control signal through the output port. ECU 7 controls operations such as fuel injection control or ignition control, and intake air volume adjustment control of the internal combustion engine 2. ECU 7 controls the driving and stopping of the exhaust gas purification device 3 based on, for example, the operating status of the internal combustion engine 2 or the amount of exhaust gas discharged from the internal combustion engine 2.

[0035] Catalysts for exhaust gas purification

[0036] Figure 2 : is a perspective view schematically showing the exhaust gas purifying catalyst 10. Figure 2 The arrows in the figure indicate the exhaust gas flow. Figure 2 In FIG. 4 , the left side indicates the upstream side of the exhaust passage 4 relatively close to the internal combustion engine 2, and the right side indicates the downstream side of the exhaust passage relatively far from the internal combustion engine 2. Figure 2 In the figure, the symbol X represents the axial direction of the exhaust gas-purifying catalyst 10. The exhaust gas-purifying catalyst 10 is arranged in the exhaust passage 4 so that the axial direction X is along the flow direction of the exhaust gas. The axial direction X is the flow direction of the exhaust gas. Hereinafter, one of the axial directions X, X1, is sometimes referred to as the upstream side (also referred to as the exhaust gas inflow side or the front side), and the other direction X2 is sometimes referred to as the downstream side (also referred to as the exhaust gas outflow side or the rear side). However, these directions are merely defined for ease of explanation and do not limit the arrangement of the exhaust gas-purifying catalyst 10.

[0037] like Figure 3 As shown, the exhaust gas-purifying catalyst 10 comprises a substrate 11 with a direct current structure, a hydrocarbon (HC) adsorption layer 20, and a catalyst layer 30. The end of the exhaust gas-purifying catalyst 10 in one direction X1 serves as an exhaust gas inlet 10a, and the end in the other direction X2 serves as an exhaust gas outlet 10b. The exhaust gas-purifying catalyst 10 is cylindrical in shape. However, the shape of the exhaust gas-purifying catalyst 10 is not particularly limited and may also take the form of an elliptical cylinder, a polygonal cylinder, a tube, a foam material, a granular material, or a fiber.

[0038] The substrate 11 constitutes the skeleton of the exhaust gas purifying catalyst 10. There is no particular limitation on the substrate 11, and various materials and forms currently used for this purpose can be used. The substrate 11 can be a ceramic carrier composed of ceramics such as cordierite, aluminum titanate, and silicon carbide, or a metal carrier composed of stainless steel (SUS), Fe-Cr-Al alloy, Ni-Cr-Al alloy, etc. Figure 2 As shown, the substrate 11 has a honeycomb structure. The substrate 11 has a plurality of cavities (holes) 12 regularly arranged along the cylindrical axis direction X and a plurality of partition walls (ribs) 14 that separate the cavities 12. The volume of the substrate 11 (apparent volume including the capacity of the cavities 12) can be approximately 0.1 to 10 L, for example, 0.5 to 5 L, but is not particularly limited. Furthermore, the average length (total length) L of the substrate 11 along the cylindrical axis direction X can be approximately 10 to 500 mm, for example, 50 to 300 mm.

[0039] The chamber 12 serves as a flow path for the exhaust gas. The chamber 12 extends along the cylindrical axis direction X. The chamber 12 is a through-hole that penetrates the substrate 11 in the cylindrical axis direction X. The shape, size, and number of the chambers 12 can be designed based on, for example, the flow rate and composition of the exhaust gas flowing through the exhaust gas-purifying catalyst 10. The shape of the cross section of the chamber 12 perpendicular to the cylindrical axis direction X is not particularly limited. The cross-sectional shape of the chamber 12 can be a quadrilateral such as a square, parallelogram, rectangle, trapezoid, or other polygonal shape (such as a triangle, hexagon, or octagon), a wavy shape, or a circle, among other geometric shapes. The partition wall 14 faces the chamber 12 and separates adjacent chambers 12. The average thickness of the partition wall 14 (the dimension perpendicular to the surface, the same below) is not particularly limited, but from the perspective of improving mechanical strength and reducing pressure loss, it can be approximately 0.1 to 10 mils (1 mil is approximately 25.4 μm), for example, 0.2 to 5 mils. The partition wall 14 can be made of a porous material through which the exhaust gas can pass.

[0040] Figure 3 1 is a partial cross-sectional view schematically showing a partial cross section of the exhaust gas purifying catalyst 10 cut along the cylinder axis direction X. Figure 3 As shown, the HC adsorption layer 20 and the catalyst layer 30 are stacked on the substrate 11. The HC adsorption layer 20 is arranged closer to the substrate 11 (i.e., on the lower side) than the catalyst layer 30. With this arrangement, the catalyst layer 30 can efficiently remove HC adsorbed by the HC adsorption layer 20.

[0041] The HC adsorption layer 20 contains a molecular sieve substantially free of Si as an HC adsorption material. The region containing the molecular sieve substantially free of Si extends from one end portion 20a of the HC adsorption layer 20 to the other end portion 20b. Typically, the entire HC adsorption layer 20 contains a molecular sieve substantially free of Si. By providing the HC adsorption layer 20 containing the HC adsorption material, the amount of the HC adsorption material can be increased compared to the case where the HC adsorption material is mixed in the catalyst layer, thereby improving the HC purification performance.

[0042] In this specification, "the molecular sieve is substantially free of Si" means that the ratio of Si atoms to all atoms constituting the molecular sieve is 6 atomic% or less (preferably 3 atomic% or less, more preferably 1 atomic% or less, and further preferably 0 atomic%). Therefore, for example, it is allowed that the molecular sieve contains Si due to the movement of Si, inevitable impurities, etc. Among them, the ratio of Si atoms to all atoms constituting the molecular sieve can be determined by X-ray fluorescence analysis (XRF).

[0043] Moreover, in the present embodiment, as the molecular sieve substantially free of Si, an aluminophosphate (ALPO) molecular sieve having a 12-membered ring is used. The ALPO molecular sieve may be an aluminophosphate (AlPO4) having the same, similar or different framework structure as zeolite. The ALPO molecular sieve is substantially free of Si, and the SiO2 / Al2O3 ratio (molar ratio) of the ALPO molecular sieve is preferably less than 1, more preferably 0.5 or less, further preferably 0.1 or less, and most preferably 0. Since the ALPO molecular sieve used here is substantially free of Si, it is different from aluminophosphate-based zeolites in which the content ratio of Al2O3 relative to SiO2 is increased (although it is a low-silica zeolite, the SiO2 / Al2O3 ratio is usually 1 or more). Among them, the SiO2 / Al2O3 ratio can be determined by X-ray fluorescence analysis (XRF).

[0044] The framework structure of the ALPO molecular sieve used only needs to have a 12-membered ring and is not particularly limited. As examples of the framework structure having a 12-membered ring, AFI, AFR, ATO, ATS, EZT, OSI, SAF, SFO, etc., which are the framework structure codes defined by the International Zeolite Association (IZA: International Zeolite Association), can be cited. The maximum ring member number of the ALPO molecular sieve having a 12-membered ring is typically 12.

[0045] In the present embodiment, the HC adsorption material contained in the HC adsorption layer 20 contains 80 mass% or more of the ALPO molecular sieve having a 12-membered ring. That is, the mass ratio of the ALPO molecular sieve having a 12-membered ring to the total mass of the HC adsorption material contained in the HC adsorption layer 20 is 80 mass% or more.

[0046] In the prior art, molecular sieves such as zeolite are used as HC adsorption materials. Zeolite is a crystalline aluminosilicate that acts as a molecular sieve, and therefore contains Si and Al. According to the research of the inventors of the present invention, once the catalyst layer containing zeolite is subjected to a long-term hydrothermal treatment, the Si contained in the zeolite will move, thereby causing adverse effects on the precious metals that serve as catalyst metals, which will lead to a decrease in exhaust gas purification performance during cold start. It is believed that this is because the SiO2 contained in the zeolite is reduced to SiO in a high-temperature reducing environment, causing SiO x The interfacial migration and evaporation under the morphology are also considered to be caused by the interaction between Si and noble metals leading to catalyst poisoning.

[0047] Therefore, in the present embodiment, by containing 80% by mass or more of a molecular sieve containing substantially no Si as the HC adsorbent, the HC purification performance during cold start is improved even after prolonged hydrothermal treatment.

[0048] ALPO molecular sieves are also known to be useful as HC adsorbents. In this embodiment, an ALPO molecular sieve with a 12-membered ring structure is used. Due to its 12-membered ring structure, the ALPO molecular sieve is highly efficient in adsorbing HC, significantly improving HC purification performance after prolonged hydrothermal treatment.

[0049] Meanwhile, exhaust gas regulations have become increasingly stringent in recent years, leading to a desire to reduce NH3 emissions from gasoline-powered vehicles. ALPO molecular sieves with 12-membered rings can also function as NH3 adsorbents. Therefore, the exhaust gas-purifying catalyst 10 of this embodiment can efficiently purify NH3 from exhaust gas, maintaining high NH3 purification performance even after prolonged hydrothermal treatment.

[0050] From the perspective of achieving improved HC purification performance during cold start after prolonged hydrothermal treatment, the HC adsorbent material contained in the HC adsorption layer 20 preferably contains 90% by mass or more, more preferably 95% by mass or more, further preferably 97% by mass or more, and most preferably 100% by mass of a molecular sieve that is substantially free of Si.

[0051] When the HC adsorbent contains 80% or more by mass and less than 100% by mass of a molecular sieve that is substantially free of Si, the HC adsorbent includes an adsorbent material other than an ALPO molecular sieve having a 12-membered ring (hereinafter referred to as "another HC adsorbent"). The other HC adsorbent may be a zeolite, an ALPO molecular sieve not having a 12-membered ring, or the like. The other HC adsorbent may also be a conventionally known material used as a HC adsorbent for an exhaust gas purification catalyst.

[0052] The amount of the HC adsorbent in the exhaust gas-purifying catalyst 10 is not particularly limited and can be appropriately designed in consideration of the dimensions of the cavity 12 of the substrate 11 and the flow rate of the exhaust gas flowing through the exhaust gas-purifying catalyst 10. The amount of the HC adsorbent per liter of the substrate 11 can be, for example, 1 g / L or more, 5 g / L or more, 10 g / L or more, 15 g / L or more, or 20 g / L or more, and can be, for example, 200 g / L or less, 150 g / L or less, 100 g / L or less, 80 g / L or less, 60 g / L or less, 50 g / L or less, or 40 g / L or less.

[0053] The HC adsorption layer 20 may contain components other than the HC adsorption material as optional components. Examples of the optional components of the HC adsorption layer 20 include binders such as alumina sol and silica sol, and various additives.

[0054] The HC adsorption layer 20 may contain, as other optional components, an oxygen absorbing / releasing material having oxygen absorbing / releasing capabilities (so-called OSC material) and a non-oxygen absorbing / releasing material without oxygen absorbing / releasing capabilities (so-called non-OSC material). Examples of OSC and non-OSC materials are the same as those included in the catalyst layer 30, described later.

[0055] The contents of the OSC material and non-OSC material in the HC adsorption layer 20 are not particularly limited. The greater the amount of HC adsorption material in the HC adsorption layer 20, the greater the ability to adsorb HC. Therefore, the contents of the OSC material and non-OSC material in the HC adsorption layer 20 are each preferably 40% by mass or less, and more preferably 20% by mass or less.

[0056] On the other hand, the HC adsorption layer 20 generally does not contain catalyst metal.

[0057] In a preferred embodiment, the HC adsorption layer 20 is composed only of an ALPO molecular sieve having a 12-membered ring and a binder component.

[0058] A substantially single HC adsorption layer 20 is provided on the substrate 11. Specifically, there is essentially only one HC adsorption layer 20 provided on the substrate 11. Because the HC adsorption layer 20 is a single layer and comprises an ALPO molecular sieve having a 12-membered ring from one end 20a to the other end 20b of the HC adsorption layer 20, HC purification performance during cold start after prolonged hydrothermal treatment is significantly improved. However, additional HC adsorption layers may be provided within a range that does not impair the effects of the present invention (specifically, a length of no more than 10% of the length of the HC adsorption layer 20 in the cylinder axial direction X).

[0059] A part of the HC adsorption layer 20 may have a composition different from that of other parts of the HC adsorption layer 20. For example, the upstream side X1 part (front part) and the downstream side X2 part (rear part) in the cylinder axis direction X of the HC adsorption layer 20 may have different compositions. Specifically, for example, the upstream side X1 part (front part) and the downstream side X2 part (rear part) in the cylinder axis direction X of the HC adsorption layer 20 may contain ALPO molecular sieves with 12-membered rings and different framework structures.

[0060] Therefore, in this specification, when two regions containing HC adsorption materials with different compositions are in contact, they are regarded as a single HC adsorption layer 20.

[0061] The coating amount (i.e., the forming amount) of the HC adsorption layer 20 is not particularly limited. With respect to each 1 L volume of the substrate portion on which the HC adsorption layer 20 is formed along the cylinder axis direction X, this coating amount is, for example, 3 to 200 g / L, and may also be 10 to 100 g / L. By satisfying the above range, it is possible to simultaneously achieve an improvement in the purification performance of harmful components and a reduction in the pressure loss at a high level. Durability and peel resistance can also be improved.

[0062] The thickness of the HC adsorption layer 20 is not particularly limited, and can be appropriately designed considering durability and peel resistance, etc. The thickness of the HC adsorption layer 20 is, for example, 1 to 100 μm, and may be 5 to 100 μm.

[0063] The coating width (average length) in the cylinder axis direction X of the HC adsorption layer 20 is not particularly limited. The larger this coating width, the better the HC purification performance. Therefore, this coating width is, for example, 20% or more, preferably 50% or more, more preferably 80% or more, and further preferably 90% or more of the total length L of the substrate 11, and may also be a length equal to the total length L of the substrate 11.

[0064] The catalyst layer 30 is the reaction site for purifying harmful components in the exhaust gas. The catalyst layer 30 is a porous body having a large number of fine pores (pores). The exhaust gas flowing into the exhaust gas purification catalyst 10 contacts the catalyst layer 30 during the process of flowing in the flow path (chamber 12) of the exhaust gas purification catalyst 10. Thereby, the harmful components in the exhaust gas can be purified. For example, HC and CO contained in the exhaust gas are oxidized by the catalyst layer 30 and converted (purified) into water, carbon dioxide, etc. For example, NO x contained in the exhaust gas is reduced by the catalyst layer 30 and converted (purified) into nitrogen.

[0065] The catalyst layer 30 contains at least a catalyst metal as an essential component. As the catalyst metal, various metal species capable of acting as an oxidation catalyst or a reduction catalyst in the purification of harmful components can be used. As typical examples of the catalyst metal, platinum group elements, namely rhodium (Rh), palladium (Pd), platinum (Pt), ruthenium (Ru), osmium (Os), and iridium (Ir), can be cited. In addition, other metal species can be used in place of the platinum group elements, or other metal species can be used in addition to the platinum group elements. For example, metal species such as iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), silver (Ag), and gold (Au) can be used. In addition, alloys of two or more of these metals can also be used. As the catalyst metal, an oxidation catalyst with high oxidation activity (for example, at least one of Pd and Pt) and a reduction catalyst with high reduction activity (for example, Rh) are preferred, and it is particularly preferred to combine two or more of them. The oxidation catalyst and the reduction catalyst can be present in the same (single) catalyst layer or in respective catalyst layers.

[0066] From the perspective of increasing the contact area with the exhaust gas, the catalyst metal is preferably used in the form of fine particles with a sufficiently small particle size. The average particle size of the catalyst metal (specifically, the average value of the particle sizes of 50 or more catalyst metals obtained by observation with a transmission electron microscope (TEM)) is approximately 1 to 15 nm, for example, 10 nm or less, and can also be 5 nm or less.

[0067] The amount of the catalyst metal in the exhaust gas purification catalyst 10 is not particularly limited and can be appropriately determined according to the type of the catalyst metal and the like. Especially from the perspective of high exhaust gas purification performance, the amount of the catalyst metal per 1 L volume of the substrate 11 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 perspective of the balance between exhaust gas purification performance and cost, it can be, for example, 15.00 g / L or less, 10.00 g / L or less, 5.00 g / L or less, 3.00 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.

[0068] Herein, in this specification, "per 1 L volume of the substrate" refers to the total volume per 1 L including the volume of the chamber passage in addition to the net volume of the substrate. In the following description, the physical quantity recorded as (g / L) represents the amount contained per 1 L volume of the substrate.

[0069] The catalyst metal is usually supported by a carrier. Therefore, the catalyst layer 30 can further contain a carrier that supports the catalyst metal.

[0070] As a carrier for supporting a catalyst metal, materials known as carriers for catalyst metals used in exhaust gas purification catalysts can be used. The carrier is typically an inorganic porous body. Examples of the carrier include materials without oxygen storage capacity (non-OSC materials) such as alumina (Al2O3, Alumina), titanium oxide (TiO2, Titania), zirconium oxide (ZrO2, Zirconia), silica (SiO2, Silica), etc., and materials with oxygen storage capacity (OSC materials) such as cerium oxide (CeO2), cerium-containing composite oxides, etc. The carrier can be either a non-OSC material or an OSC material, or both.

[0071] In order to improve heat resistance, etc., a small amount (for example, 1% by mass or more and 10% by mass or less) of rare earth element oxides such as Pr2O3, Nd2O3, La2O3, Y2O3, etc. can also be added to the oxide used as a non-OSC material. Due to particularly good heat resistance and durability, the non-OSC material is preferably Al2O3, and more preferably Al2O3 composite with La2O3 (La2O3 - Al2O3 composite oxide, LA composite oxide).

[0072] Regarding OSC materials, as cerium-containing composite oxides, cerium-zirconium composite oxides (so-called CZ composite oxides or ZC composite oxides) can be cited. When zirconium oxide is contained in the OSC material, thermal deterioration of cerium oxide can be suppressed. Therefore, cerium-zirconium composite oxides are preferably used as OSC materials.

[0073] In order to improve performance (especially heat resistance and oxygen absorption and release performance, etc.), the OSC material can contain rare earth element oxides. Examples of rare earth elements include Sc, Y, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc. As rare earth element oxides, Pr2O3, Nd2O3, La2O3, and Y2O3 are preferred.

[0074] In the case where the OSC material is a cerium-containing composite oxide, from the perspective of fully exerting its oxygen storage capacity, the content of cerium oxide in the composite oxide is preferably 15% by mass or more, more preferably 20% by mass or more. On the other hand, when the content of cerium oxide is too high, the basicity of the OSC material may become too high. Therefore, the content of cerium oxide is preferably 40% by mass or less, more preferably 30% by mass or less.

[0075] As an example, the catalyst layer 30 contains an OSC material and a non-OSC material, and the catalyst metal is supported by both the OSC material and the non-OSC material.

[0076] The catalyst layer 30 may also contain the above OSC material and / or the above non-OSC material in a state not supporting a catalyst metal. The OSC material and non-OSC material used as a carrier and the OSC material and non-OSC material not used as a carrier preferably do not contain Si.

[0077] The amounts of the OSC material and non-OSC material in the exhaust gas purification catalyst 10 are not particularly limited, and can be appropriately designed in consideration of the size of the chamber 12 of the substrate 11 and the flow rate of the exhaust gas flowing through the exhaust gas purification catalyst 10, etc. As the total amount of the OSC material and non-OSC material per 1 L volume of the substrate 11 (including the total amount of the OSC material and non-OSC material of both the carrier and non-carrier), it can be, for example, 50 g / L or more, 70 g / L or more, 80 g / L or more, 90 g / L or more, or 100 g / L or more, and can be, for example, 500 g / L or less, 400 g / L or less, 300 g / L or less, 250 g / L or less, 200 g / L or less, 180 g / L or less, or 160 g / L or less.

[0078] The catalyst layer 30 preferably contains an OSC material in a form that supports a catalyst metal or does not support a catalyst metal. At this time, excellent purification performance can be stably exhibited even when, for example, the air-fuel ratio of the exhaust gas changes due to vehicle driving conditions, etc.

[0079] The catalyst layer 30 may also contain alkaline earth elements such as calcium (Ca) and barium (Ba). By using alkaline earth elements, poisoning of the catalyst metal (especially oxidation catalyst) can be suppressed. In addition, by using alkaline earth elements, the dispersibility of the catalyst metal can be improved, and caking caused by grain growth of the catalyst metal can be suppressed. In addition, when the catalyst layer 30 contains an OSC material and an alkaline earth element, the oxygen absorption amount of the OSC material can be further increased in a lean combustion environment (oxygen-excess environment) where the fuel ratio is leaner than the theoretical air-fuel ratio. The alkaline earth element can be contained in the form of an oxide, hydroxide, carbonate, nitrate, sulfate, phosphate, acetate, formate, oxalate, halide, etc.

[0080] In addition, the catalyst layer 30 may also contain NO x storage capacity NO x adsorbent materials, stabilizers, etc. As stabilizers, for example, rare earth elements such as yttrium (Y), lanthanum (La), and neodymium (Nd) can be cited. And the rare earth element can exist in the catalyst layer 30 in the form of an oxide.

[0081] As other optional components of the catalyst layer 30, binder materials such as alumina sol and silica sol, various additives, etc. can be cited. The binder is preferably a binder that does not contain Si, and thus alumina sol is preferred.

[0082] The catalyst layer 30 may contain a HC adsorbent. However, since the exhaust gas purifying catalyst 10 according to the present embodiment includes the HC adsorbent layer 20 , it is preferable that the catalyst layer 30 does not contain a HC adsorbent.

[0083] The coating amount (molding amount) of the catalyst layer 30 is not particularly limited, but is generally 30 g / L or more, typically 50 g / L or more, and preferably 70 g / L or more, and can be, for example, 100 g / L or more, and generally 500 g / L or less, typically 400 g / L or less, and for example, 300 g / L or less, per 1 L volume of the exhaust gas-purifying catalyst 10 (the volume of the substrate 11). By meeting the above range, it is possible to achieve both improved purification performance and reduced pressure drop at a high level. In this specification, "coating amount" refers to the mass of the solid components contained in the exhaust gas-purifying catalyst 10 per unit volume.

[0084] The length and thickness of the catalyst layer 30 can be appropriately designed, for example, taking into account the size of the cavity 12 of the substrate 11 and the flow rate of the exhaust gas flowing through the exhaust gas-purifying catalyst 10. The catalyst layer 30 can be provided continuously or intermittently on the partition wall 14 of the substrate 11. For example, the catalyst layer 30 can be provided along the cylinder axis direction X from the exhaust gas inlet 10a or from the exhaust gas outlet 10b.

[0085] The overall coating width (average length) of the catalyst layer 30 in the cylindrical axial direction X is not particularly limited and can be approximately 20% or more, preferably 50% or more, typically 80% or more, for example 90% or more, of the total length L of the substrate 11. Alternatively, the coating thickness (average thickness) of the catalyst layer 30 is not particularly limited and is approximately 1 to 300 μm, typically 5 to 200 μm, for example 10 to 100 μm. This allows for both improved purification performance and reduced pressure drop at a high level.

[0086] A portion of the catalyst layer 30 may have a different composition than other portions of the catalyst layer 30. For example, the upstream side X1 portion (front portion) and the downstream side X2 portion (rear portion) of the catalyst layer 30 in the cylinder axis direction X may have different compositions. Specifically, for example, the upstream side X1 portion (front portion) and the downstream side X2 portion (rear portion) of the catalyst layer 30 in the cylinder axis direction X may contain different catalyst metals.

[0087] Figure 3The exemplified exhaust gas purification catalyst 10 only has an HC adsorption layer 20 and a catalyst layer 30. However, the exhaust gas purification catalyst 10 may also have layers other than them. For example, the exhaust gas purification catalyst 10 may have an additional layer (also referred to as an intermediate layer) between the HC adsorption layer 20 and the catalyst layer 30, may have an additional layer (also referred to as a base layer) between the substrate 11 and the HC adsorption layer 20, and may also have an additional layer above the catalyst layer 30.

[0088] Figure 3 The catalyst layer 30 of the exemplified exhaust gas purification catalyst 10 has a single-layer structure. However, the catalyst layer 30 may also have a multi-layer structure in which each layer contains a catalyst metal. An example of the exhaust gas purification catalyst when the catalyst layer 30 is a multi-layer structure will be described below.

[0089] 《Modified Example of Exhaust Gas Purification Catalyst 10》

[0090] Figure 4 It is a partial cross-sectional view schematically showing a partial cross-section of the exhaust gas purification catalyst 10' as a modified example of the exhaust gas purification catalyst 10 after being cut along the cylinder axis direction X. The exhaust gas purification catalyst 10' has a substrate 11, an HC adsorption layer 20 provided on the substrate 11, and a catalyst layer 30' having a multi-layer structure. The HC adsorption layer 20 and the catalyst layer 30' are laminated in such a way that the HC adsorption layer 20 is closer to the substrate 11 side than the catalyst layer 30'. Since the catalyst layer 30' has a multi-layer structure, the exhaust gas purification performance can be further improved.

[0091] The substrate 11 and the HC adsorption layer 20 are the same as above. The catalyst layer 30' is Figure 3 different from the example shown, and has a multi-layer structure. Specifically, the catalyst layer 30' has a laminated structure in which a first partial catalyst layer (lower layer) 31 and a second partial catalyst layer (upper layer) 32 are laminated along the thickness direction. Therefore, the lower layer 31 is disposed on the substrate 11 side. In the illustrated example, the lower layer 31 is provided in contact with the surface of the HC adsorption layer 20, and the upper layer 32 is provided in contact with the upper surface of the lower layer 31. In the illustrated example, the catalyst layer 30' has a double-layer structure, but the catalyst layer 30' may also have a laminated structure of three or more layers. For example, the catalyst layer 30' may have an intermediate layer between the lower layer 31 and the upper layer 32, and the catalyst layer 30' may also have an additional layer above the upper layer 32.

[0092] The lower layer 31 and the upper layer 32 each contain a catalyst metal. Here, the lower layer 31 and the upper layer 32 may contain the same catalyst metal or different catalyst metals, and preferably contain different catalyst metals.

[0093] Specifically, for example, in the lower layer 31, an oxidation catalyst (e.g., at least one of Pd and Pt) is included as the catalyst metal; in the upper layer 32, a reduction catalyst (e.g., Rh) is included as the catalyst metal. In this case, the exhaust gas purification performance of the exhaust gas purification catalyst 10' is particularly excellent. From the perspective of higher exhaust gas purification performance, it is more advantageous that the catalyst metal in the lower layer 31 is Pt and the catalyst metal in the upper layer 32 is Rh. In this case, it is particularly beneficial for the purification of alkanes. Or, from the perspective of even higher exhaust gas purification performance, it is more advantageous that the catalyst metal in the lower layer 31 is Pd and the catalyst metal in the upper layer 32 is Rh. In this case, it is particularly beneficial for the purification of olefins.

[0094] Among them, when Pt is contained in the lower layer 31, it is preferred that 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, and most preferably 100% of the catalyst metal contained in the lower layer 31 is Pt. When Pd is contained in the lower layer 31, it is preferred that 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, and most preferably 100% of the catalyst metal contained in the lower layer 31 is Pd. When Rh is contained in the upper layer 32, it is preferred that 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, and most preferably 100% of the catalyst metal contained in the upper layer 32 is Rh.

[0095] The lower layer 31 and the upper layer 32 may contain the same optional components as the above-mentioned catalyst layer 30. [Manufacturing Method of Exhaust Gas Purification Catalyst 10]

[0096] The exhaust gas purification catalyst 10 can be manufactured, for example, by the following method. First, a substrate 11, an HC adsorption layer forming slurry for forming the HC adsorption layer 20, and a catalyst layer forming slurry for forming the catalyst layer 30 are prepared.

[0097] The HC adsorption layer forming slurry can be prepared, for example, by mixing an HC adsorption material containing 80% by mass or more of 12-ring ALPO molecular sieve with other optional components (e.g., non-OSC materials, OSC materials, binders, various additives, etc.) in a dispersion medium. The catalyst layer forming slurry can be prepared, for example, by mixing a catalyst metal source (e.g., a solution containing the catalyst metal in ionic form) with other optional components (e.g., non-OSC materials, OSC materials, binders, various additives, etc.) in a dispersion medium. As the dispersion medium, for example, water, a mixture of water and a water-soluble organic solvent, etc. can be used. The properties (e.g., viscosity, solid content fraction, etc.) of these slurries can be appropriately determined according to the size of the substrate 11 used, the shape of the chamber 12 (partition wall 14), the performance requirements for the HC adsorption layer 20 and the catalyst layer 30, etc.

[0098] Next, the HC adsorption layer 20 is formed on the substrate 11 using the slurry for forming the HC adsorption layer. The HC adsorption layer 20 can be formed using conventionally known methods (e.g., impregnation, washcoat, etc.). Specifically, the HC adsorption layer slurry is flowed into the chamber 12 from the end of the substrate 11 and supplied along the cylindrical axis X until a predetermined length is reached. The slurry can be introduced from either the inlet 10a or the outlet 10b. At this point, excess slurry can be suctioned from the opposite end. Furthermore, excess slurry can be discharged from the chamber 12 by, for example, supplying air from the opposite end.

[0099] Next, the substrate 11 to which the slurry has been applied is fired at a predetermined temperature and for a predetermined time. The firing method can be the same as conventional methods. Furthermore, drying can be performed before firing to remove the dispersion medium. This allows the HC adsorption layer 20 to be formed on the substrate 11.

[0100] The catalyst layer 30 is then formed using the catalyst layer forming slurry. The catalyst layer 30 can be formed using conventionally known methods (e.g., impregnation, washcoat, etc.). For example, in the same manner as described above, the catalyst layer forming slurry is flowed from the end of the substrate 11 into the chamber 12 and supplied along the cylindrical axis direction X until a predetermined length is reached. The catalyst layer forming slurry is then applied to the HC adsorption layer 20 formed on the substrate 11.

[0101] The catalyst is then fired at a predetermined temperature and for a predetermined time. The firing method can be the same as conventional methods. Furthermore, drying can be performed before firing to remove the dispersion medium. This allows the catalyst layer 30 to be formed on the HC adsorption layer 20 formed on the substrate 11. The exhaust gas-purifying catalyst 10 can be obtained in this manner.

[0102] Application of Exhaust Gas Purifying Catalyst 10

[0103] The exhaust gas purification catalyst 10 can be applied to purify exhaust gas emitted by internal combustion engines in vehicles such as automobiles and trucks, ships (e.g., electric motorcycles and motorized bicycles), marine products such as tankers, jet skis, personal watercraft, and outboard motors, gardening products such as lawn mowers, chainsaws, and trimmers, leisure products such as golf carts and four-wheeled vehicles, power generation equipment such as cogeneration systems, and waste incinerators. It is particularly suitable for use in vehicles such as automobiles, and is particularly suitable for vehicles equipped with gasoline engines.

[0104] Hereinafter, test examples related to the present invention will be described, but the present invention is not intended to be limited to the embodiments shown in the following test examples.

[0105] [Example 1]

[0106] A honeycomb substrate (cordierite, volume: 0.0175 L, total substrate length: 24 mm, number of cells: 400, cell shape: quadrilateral, partition wall thickness: 6 mil) was prepared as the substrate. AFI-type ALPO-5 (maximum ring number: 12) was prepared as the HC adsorbent. Furthermore, the following materials were prepared as catalyst layer raw materials.

[0107] Non-OSC material: La2O3 composite Al2O3, La2O3 content is 1-10% by mass

[0108] OSC material: CeO2-ZrO2 composite oxide, CeO2 content is 15-40% by mass, with trace amounts of Pd2O3, Nd2O3, La2O3, and Y2O3 added, and high heat resistance treatment implemented

[0109] A slurry for forming an HC adsorption layer was prepared by mixing an HC adsorption material (i.e., AFI type ALPO-5), an Al2O3-based binder, and an aqueous solvent. This slurry was poured onto a substrate, and the excess was blown off with a blower, thereby coating the substrate surface with the HC adsorption layer material. The slurry was then placed in a ventilated dryer set at 120°C for two hours to remove moisture, and then fired in an electric furnace at 500°C for one hour. This formed an HC adsorption layer on the substrate.

[0110] A nitric acid-based Pt aqueous solution, the aforementioned La2O3-complexed Al2O3, the aforementioned CeO2-ZrO2 composite oxide, Ba sulfate, an Al2O3-based binder, and an aqueous solvent were mixed to prepare a slurry for forming the lower catalyst layer. This slurry was poured onto the substrate on which the HC adsorption layer had been formed, and the excess was blown off with a blower, thereby coating the HC adsorption layer with the material for forming the lower catalyst layer. The slurry was placed in a ventilated dryer set at 120°C for two hours to remove moisture, and then calcined in an electric furnace at 500°C for one hour. This formed a lower catalyst layer containing Pt catalyst on the substrate.

[0111] Next, an aqueous Rh nitrate solution, the above La2O3 - composite Al2O3, the above CeO2 - ZrO2 - based composite oxide, an Al2O3 - based binder, and an aqueous solvent were mixed to prepare a slurry for forming the upper catalyst layer. The slurry was made to flow into a substrate on which the lower catalyst layer had been formed, and the excess was blown off with a blower, whereby the surface of the lower catalyst layer was coated with the material for forming the upper catalyst layer. It was placed in a ventilation dryer set at 120°C for 2 hours to remove moisture, and then fired in an electric furnace at 500°C for 1 hour. Thus, an upper catalyst layer containing a Rh catalyst was formed on the lower catalyst layer, and the exhaust gas purification catalyst of Example 1 was obtained. In the obtained exhaust gas purification catalyst, the Pt content per 1 L volume of the substrate was 0.3 g / L, the Rh content was 0.06 g / L, the content of the carrier (non - OSC material + OSC material) was 150 g / L, and the content of the HC adsorption material was 116 g / L.

[0112] [Example 2]

[0113] An exhaust gas purification catalyst of Example 2 was prepared in the same manner as in Example 1, except that a mixture having a mass ratio of 95:5 of AFI - type ALPO - 5 and BEA - type zeolite (SiO2 / Al2O3 ratio = 500) was used as the HC adsorption material.

[0114] [Example 3]

[0115] An exhaust gas purification catalyst of Example 3 was prepared in the same manner as in Example 1, except that a mixture having a mass ratio of 90:10 of AFI - type ALPO - 5 and BEA - type zeolite (SiO2 / Al2O3 ratio = 500) was used as the HC adsorption material.

[0116] [Comparative Example 1]

[0117] An exhaust gas purification catalyst of Comparative Example 1 was prepared in the same manner as in Example 1, except that the HC adsorption layer was not formed because the slurry for forming the HC adsorption layer was not used.

[0118] [Comparative Example 2]

[0119] An exhaust gas purification catalyst of Comparative Example 2 was prepared in the same manner as in Example 1, except that aluminum phosphate was used instead of AFI - type ALPO - 5.

[0120] [Comparative Example 3]

[0121] An exhaust gas purification catalyst of Comparative Example 3 was prepared in the same manner as in Example 1, except that ERI - type ALPO - 17 (the maximum number of elements in the ring is 8) was used instead of AFI - type ALPO - 5.

[0122] [Comparative Example 4]

[0123] Except for using BEA type zeolite (the maximum number of atoms in the ring is 12, SiO2 / Al2O3 ratio = 500) instead of AFI type ALPO-5, the exhaust gas purification catalyst of Comparative Example 4 was prepared in the same manner as in Example 1.

[0124] [Example 4]

[0125] A slurry for forming a lower catalyst layer was prepared by mixing a nitric acid-based Pd aqueous solution, the above La2O3 - compounded Al2O3, the above CeO2 - ZrO2 - based composite oxide, barium sulfate, an Al2O3 - based binder, and an aqueous solvent. Except for using this slurry for forming a lower catalyst layer to form a lower catalyst layer containing a Pd catalyst, the exhaust gas purification catalyst of Example 4 was prepared in the same manner as in Example 1.

[0126] [Comparative Example 5]

[0127] Except for using BEA type zeolite (the maximum number of atoms in the ring is 12, SiO2 / Al2O3 ratio = 500) to form an HC adsorption layer instead of AFI type ALPO-5 and using the slurry for forming a lower catalyst layer prepared in Example 4 to form a lower catalyst layer containing a Pd catalyst, the exhaust gas purification catalyst of Comparative Example 5 was prepared in the same manner as in Example 1.

[0128] [Durable hydrothermal treatment]

[0129] The rich combustion gas and the lean combustion gas were alternately passed through the exhaust gas purification catalysts of each example and each comparative example at 900 °C at a rate of switching every 10 minutes for 10 hours. The composition of the rich combustion gas was CO: 5%, water: 10%, N2: the balance, and the composition of the lean combustion gas was O2: 2.5%, water: 10%, N2: the balance.

[0130] [Catalytic activity evaluation for HC]

[0131] The pretreatment gas A was passed through the exhaust gas purification catalysts of each example and each comparative example that had undergone the above - mentioned durable hydrothermal treatment, and the temperature was raised from 100 °C to 500 °C at a rate of 20 °C / min and held at 500 °C for 5 minutes. Then, an inert gas (N2 gas) was passed through and the temperature was lowered to 100 °C. After the temperature stabilized, the reaction gas A was passed through and the temperature was raised to 550 °C at a rate of 50 °C / min, and the temperature at which the HC purification rate of the reaction gas reached 50% (HC 50% purification temperature: T50) was determined. Among them, the following gases were used as the pretreatment gas A and the reaction gas A. The graphs of the HC 50% purification temperature for each example and each comparative example are shown in Figure 5 .

[0132] Pretreatment gas A

[0133] A / F ratio: 14.6;

[0134] C3H6: 2400 ppmC, C3H8: 600 ppmC, CO: 0.5%, NO: 800 ppm, H2O: 10%, CO2: 10%, O2: 0.6%, N2: balance

[0135] Reaction gas A

[0136] A / F ratio: 14.5;

[0137] C3H6: 1500 ppmC, C 10 H 22 : 1500 ppmC, H2O: 3%, CO2: 10%, O2: 0.3%, N2: balance

[0138] According to Figure 5 the chart, it can be seen that: compared with the waste gas purification catalysts of Comparative Examples 1-5, the waste gas purification catalysts of Examples 1-4 using aluminophosphate molecular sieve with 12-membered rings as the HC adsorption material for the HC adsorption layer have a significantly lower HC 50% purification temperature. It can be known that: the waste gas purification catalysts of Examples 1-4 using aluminophosphate molecular sieve with 12-membered rings, even after long-term hydrothermal treatment, have a significantly increased HC purification performance during cold start. According to this result, it can be known that: by using the waste gas purification catalyst disclosed in the present invention, excellent HC purification performance during cold start after long-term hydrothermal treatment can be obtained.

[0139] [Catalytic activity evaluation for NH3]

[0140] The pretreatment gas A was passed through the waste gas purification catalysts of Example 1 and Comparative Examples 1, 2, and 4 that had undergone the above-mentioned long-term hydrothermal treatment, and the temperature was raised from 100 °C to 500 °C at a rate of 20 °C / min and maintained at 500 °C for 5 minutes. Then, an inert gas (N2 gas) was passed through and the temperature was lowered to 100 °C. After the temperature was stabilized, reaction gas B was passed through and the temperature was raised to 650 °C at a rate of 50 °C / min, and the temperature (NH3 50% purification temperature: T50) at which the NH3 purification rate of the reaction gas reached 50% was determined. Among them, the following gas was used as reaction gas B.

[0141] Reaction gas B

[0142] NH3: 500 ppm, H2O: 3%, CO2: 10%, O2: 0.3%, N2: balance

[0143] The waste gas purification catalyst of Example 1 showed a lower NH3 50% purification temperature than the waste gas purification catalysts of Comparative Examples 1, 2, and 4.

[0144] [Comparative Example 6]

[0145] A honeycomb substrate (cordierite, volume: 0.0175 L, total substrate length: 12.5 mm, number of cells: 400, cell shape: quadrilateral, partition wall thickness: 6 mil) was prepared as the substrate. AFI-type ALPO-5 (maximum ring number: 12) was prepared as the HC adsorbent. Furthermore, the following materials were prepared as catalyst layer raw materials.

[0146] Non-OSC materials: Al2O3

[0147] OSC material: CeO2-ZrO2 composite oxide, CeO2 content 15-40% by mass, with trace amounts of Pr2O3, Nd2O3, La2O3 added, and high heat resistance treatment applied

[0148] A slurry for forming an HC adsorption layer was prepared by mixing an HC adsorption material (i.e., AFI type ALPO-5), a binder, and an aqueous solvent. This slurry was applied to the substrate from the upstream end to 50% of its length using a washcoat method. The front surface of the substrate was then coated with the HC adsorption layer material. The slurry was placed in a ventilated dryer set at 120°C for two hours to remove moisture, and then fired in an electric furnace at 500°C for one hour. This formed an HC adsorption layer containing AFI type ALPO-5 on the front surface of the substrate.

[0149] A nitric acid-based Pd aqueous solution, a nitric acid-based Rh aqueous solution, the aforementioned Al2O3, the aforementioned CeO2-ZrO2 composite oxide, a binder, and an aqueous solvent were mixed to prepare a slurry for forming a catalyst layer. This slurry was applied to the substrate from the upstream end to 50% of its length using a washcoat method. The front HC adsorption layer was then coated with the catalyst layer-forming material. The slurry was placed in a ventilated dryer set at 120°C for two hours to remove moisture, and then fired in an electric furnace at 500°C for one hour. This formed a catalyst layer containing catalytic metal on the front HC adsorption layer of the substrate.

[0150] A slurry for forming an HC adsorption layer was prepared by mixing an HC adsorption material (i.e., ZSM-5), a binder, and an aqueous solvent. This slurry was applied to the substrate from the downstream end to 50% of its length using a washcoat method. The rear surface of the substrate was then coated with the HC adsorption layer material. The slurry was placed in a ventilated dryer set at 120°C for two hours to remove moisture, and then fired in an electric furnace at 500°C for one hour. This formed an HC adsorption layer containing ZSM-5 on the rear surface of the substrate.

[0151] Next, a nitric acid-based Pd aqueous solution, a nitric acid-based Rh aqueous solution, the aforementioned Al2O3, the aforementioned CeO2-ZrO2 composite oxide, a binder, and an aqueous solvent were mixed to prepare a catalyst layer-forming slurry. This slurry was applied to the substrate from the downstream end to 50% of its length using a washcoat method, and the rear HC adsorption layer was coated with the catalyst layer-forming material. The slurry was placed in a ventilated dryer set at 120°C for two hours to remove moisture, and then calcined in an electric furnace at 500°C for one hour. In this way, a catalyst layer containing catalytic metal was formed on the rear HC adsorption layer as well. The exhaust gas-purifying catalyst of Comparative Example 6 was thus obtained. The resulting exhaust gas-purifying catalyst (front and rear) had a Pd content of 8 g / L and a Rh content of 0.7 g / L per liter of substrate volume, a carrier (non-OSC material + OSC material) content of 417 g / L, and a HC adsorption material content of 116 g / L.

[0152] [Example 5]

[0153] A HC adsorbent material (i.e., AFI-type ALPO-5), a binder, and an aqueous solvent were mixed to prepare a slurry for forming an HC adsorbent layer. This slurry was applied to a substrate similar to the one used in Comparative Example 6, from the upstream end to the downstream end, covering 100% of the substrate's length with the HC adsorbent layer material. The slurry was placed in a ventilated dryer set at 120°C for two hours to remove moisture, and then fired in an electric furnace at 500°C for one hour. This formed an HC adsorbent layer containing AFI-type ALPO-5 on the substrate.

[0154] Then, a catalyst layer was formed on the HC adsorption layer in the same manner as in Comparative Example 6, thereby obtaining the exhaust gas-purifying catalyst of Example 5.

[0155] [Permanent hydrothermal treatment and evaluation of catalytic activity for HC]

[0156] The exhaust gas purification catalysts of Example 5 and Comparative Example 6 were subjected to a sustained hydrothermal treatment in the same manner as described above. Then, the pre-treated gas A was introduced and the temperature was raised from 100°C to 500°C at a rate of 20°C / min, and maintained at 500°C for 5 minutes. Then, an inert gas (N2 gas) was introduced and the temperature was lowered to 100°C. After the temperature stabilized, the reaction gas A was introduced and the temperature was raised to 500°C at a rate of 50°C / min, and the HC emission curve at this time was calculated. The results are shown in FIG. Figure 6 .

[0157] exist Figure 6Among them, the blank control indicates the HC emission without the exhaust gas purification catalyst. In Example 5 and Comparative Example 6, significant differences were observed particularly in the temperature range of 230°C to 280°C. From this result, it can be seen that although the HC concentration in the exhaust gas temporarily exceeds 3000 ppmC when HC is released from the HC adsorption layer of the exhaust gas purification catalyst, the HC purification performance of the exhaust gas purification catalyst in Example 5 is much higher than that of the exhaust gas purification catalyst in Comparative Example 6 at this time.

[0158] As described above, several embodiments of the present invention have been described, but the above 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 described in this specification and the common technical knowledge in the art. The technologies described in the scope of claims include the technologies obtained by various deformations and changes of the above-described exemplified embodiments. For example, a part of the above-described embodiment can be replaced with other deformation methods, or other deformation methods can be added to the above-described embodiment. In addition, as long as a certain technical feature is not described as an essential technical feature, it can also be appropriately omitted.

Claims

1. A catalyst for waste gas purification, characterized in that it has a substrate, a hydrocarbon adsorption layer and a catalyst layer, the hydrocarbon adsorption layer is laminated with the catalyst layer in such a manner that the hydrocarbon adsorption layer is located on one side of the substrate, the catalyst layer contains a catalyst metal, the hydrocarbon adsorption layer contains a silicon-free zeolite from one end to the other end of the hydrocarbon adsorption layer along the waste gas flow direction, the content of the silicon-free zeolite in the hydrocarbon adsorption layer is 80% by mass or more, the silicon-free zeolite is an aluminophosphate zeolite having a 12-membered ring.

2. The catalyst for waste gas purification according to claim 1, characterized in that the hydrocarbon adsorption material contains 90% by mass or more of a silicon-free zeolite.

3. The catalyst for waste gas purification according to claim 1, characterized in that the framework structure of the aluminophosphate zeolite is of the AFI type.

4. The catalyst for waste gas purification according to claim 1, characterized in that the coating width of the hydrocarbon adsorption layer along the waste gas flow direction is 80% or more of the total length of the substrate.

5. The catalyst for waste gas purification according to claim 1, characterized in that a first partial catalyst layer and a second partial catalyst layer are laminated in the catalyst layer, the first partial catalyst layer is located closer to the substrate than the second partial catalyst layer, the first partial catalyst layer and the second partial catalyst layer respectively contain the catalyst metal, the first partial catalyst layer contains an oxidation catalyst as the catalyst metal, the second partial catalyst layer contains a reduction catalyst as the catalyst metal.

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