Exhaust gas purifying catalyst

Abstract

According to the present application, a novel exhaust gas purification catalyst having improved HC and CO purification performance in a rich environment can be provided. The exhaust gas purification catalyst according to the present application comprises a substrate, a catalyst layer provided on the substrate, and a reforming reaction layer provided on the substrate. The catalyst layer contains a three-way catalyst. The reforming reaction layer contains a hydrogen production catalyst. The reforming reaction layer is disposed at a position further downstream than the catalyst layer in the exhaust gas flow direction.

Description

Technical Field

[0001] This invention relates to a catalyst for exhaust gas purification. It should be noted that this application claims priority based on Japanese Patent Application No. 2021-118730, filed on July 19, 2021, the entire contents of which are incorporated herein by reference. Background Technology

[0002] Exhaust gases from internal combustion engines such as vehicle engines contain hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). x Harmful components such as exhaust gas are present. To efficiently capture and remove these harmful components from exhaust gas, exhaust gas purification catalysts have been used for a long time.

[0003] Prior art documents concerning catalysts for exhaust gas purification include Patent Document 1. As described in Patent Document 1, a typical catalyst capable of simultaneously and efficiently removing the aforementioned harmful components includes a three-way catalyst. Furthermore, Patent Document 1 also discloses a method in which a catalyst containing nickel and / or palladium is used as a fuel modification catalyst in an exhaust gas treatment system.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Publication No. 2016-513198 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] In recent years, emission regulations, represented by LEVIII and Euro 7, have become increasingly stringent. To meet these regulations, it is necessary to reduce emissions not only during cold starts but also during hot starts (hereinafter referred to as "hot emissions").

[0009] Although exhaust purification using a three-way catalytic converter is achieved through a three-way reaction (i.e., oxidation of HC, oxidation of CO, and oxidation of NO)... x The reduction is carried out, but in an oxygen-deficient combustion environment, NO... xThe reduction of HC is difficult to achieve, therefore, in exhaust gas purification systems, feedback (FB) control can be implemented based on the transition from an ideal fuel ratio to a slightly fuel-rich environment. In response to this control, the environment shifts towards a fuel-rich environment during a momentary fuel oversupply (rich spike) after the fuel ratio (F / C) or during high-load operation. In a fuel-rich environment, oxygen is insufficient, and the oxidation of HC and CO cannot proceed fully, resulting in some HC and CO being emitted unpurified. Furthermore, because a large amount of oxygen is consumed upstream in the exhaust flow direction of the catalyst used for exhaust gas purification, oxygen deficiency is particularly likely to occur downstream in a fuel-rich environment. This also leads to some HC and CO being emitted unpurified. Therefore, to reduce thermal emissions, it is necessary to improve the HC and CO purification performance of the catalyst used for exhaust gas purification in a fuel-rich environment.

[0010] This invention is made in response to the above situation, and its purpose is to provide a novel exhaust gas purification catalyst that improves the purification performance of HC and CO in a fuel-rich environment.

[0011] Technical solutions for solving the problem

[0012] The exhaust gas purification catalyst of the present invention comprises a substrate, a catalyst layer disposed on the substrate, and a reforming reaction layer disposed on the substrate. The catalyst layer contains a three-way catalyst. The reforming reaction layer contains a hydrogen production catalyst. The reforming reaction layer is disposed downstream of the exhaust gas flow direction, closer to the catalyst layer.

[0013] Hydrogen production catalysts utilize water to convert HC and CO into H2 via steam reforming (HC + H2O → CO2 + H2) and CO conversion (CO + H2O → CO2 + H2). Since water is produced during fuel (usually gasoline) combustion and HC oxidation, exhaust gases contain abundant water. Therefore, based on this composition, the reforming reaction layer can use water instead of oxygen to convert HC and CO into carbon dioxide and H2. For this purpose, in exhaust gas purification catalysts, by positioning the reforming reaction layer further downstream than the catalyst layer in the exhaust flow direction, HC and CO can be removed with a high purification rate even under oxygen-deficient conditions. In other words, based on this composition, a novel exhaust gas purification catalyst with improved HC and CO purification performance under fuel-rich environments can be provided.

[0014] In a preferred embodiment of the exhaust gas purification catalyst described in this specification, the hydrogen production catalyst contains an oxide of at least one element selected from Pr, Nd, Co, and Ni. With this composition, the purification performance of the exhaust gas purification catalyst for HC and CO under fuel-rich environments can be further improved.

[0015] In a preferred embodiment of the exhaust gas purification catalyst described in this specification, the hydrogen production catalyst contains nickel oxide. This composition enables the exhaust gas purification catalyst to achieve particularly high purification performance for HC and CO in a fuel-rich environment.

[0016] In a preferred embodiment of the exhaust gas purification catalyst described in this specification, the reforming reaction layer further comprises an OSC material with oxygen absorption and storage capacity. Based on this composition, the OSC material can promote hydrogen production reactions (steam reforming and / or CO conversion reactions) utilizing hydrogen production catalysts, enabling the exhaust gas purification catalyst to achieve particularly high purification performance of HC and CO in a fuel-rich environment.

[0017] In a preferred embodiment of the exhaust gas purification catalyst described in this specification, the hydrogen production catalyst in the reforming reaction layer comprises 5 g / L or more of the substrate portion forming the reforming reaction layer per 1 L volume. With this composition, the exhaust gas purification catalyst exhibits particularly high purification performance for HC and CO in a fuel-rich environment.

[0018] In a preferred embodiment of the exhaust gas purification catalyst described in this specification, the reforming reaction layer further comprises Rh. With this composition, CO, HC, and NO can be removed with a well-balanced and high purification rate. x . Attached Figure Description

[0019] Figure 1 This is a schematic diagram of an exhaust purification system that uses an exhaust purification catalyst.

[0020] Figure 2 for Figure 1 A three-dimensional schematic diagram of a catalyst used for exhaust gas purification.

[0021] Figure 3 To be Figure 2 A cross-sectional view of the structure of the exhaust gas purification catalyst after it has been cut along the cylinder axis.

[0022] Figure 4 This is a cross-sectional view of the structure after the modified exhaust gas purification catalyst is cut along the cylinder axis.

[0023] Figure 5 This is a schematic diagram showing the relationship between the air-fuel ratio (A / F) and the CO purification rate in Experiment Example 1.

[0024] Figure 6 This is a schematic diagram showing the relationship between the air-fuel ratio (A / F) and the THC purification rate in Experiment Example 1.

[0025] Figure 7This is a schematic diagram comparing the CO purification rate and the THC purification rate when the air-fuel ratio (A / F) is 14.2 in Experiment Example 1.

[0026] Figure 8 This is a schematic diagram comparing the CO purification rate and the THC purification rate when the air-fuel ratio (A / F) is 14.2 in Experiment Example 2.

[0027] Figure 9 This is a schematic diagram comparing the CO purification rate and the THC purification rate when the air-fuel ratio (A / F) is 14.2 in Experiment Example 3.

[0028] Figure 10 This is a schematic diagram comparing the CO purification rate and the THC purification rate when the air-fuel ratio (A / F) is 14.2 in Experiment Example 4.

[0029] Figure 11 This is a schematic diagram comparing the CO purification rate and the THC purification rate when the air-fuel ratio (A / F) is 14.2 in Experiment Example 5. Detailed Implementation

[0030] Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be noted that matters necessary for implementing the present invention other than those specifically mentioned in this specification can be considered as design considerations based on prior art by those skilled in the 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 symbols, and repeated descriptions are omitted or simplified. The dimensional relationships (length, width, thickness, etc.) in the figures do not necessarily reflect actual dimensional relationships. Additionally, the symbol "A~B" (A and B are arbitrary values) indicating a range in this specification means above A and below B.

[0031] Exhaust Gas Purification System

[0032] Figure 1 This is a schematic diagram of exhaust gas purification system 1. Exhaust gas purification system 1 includes an internal combustion engine 2, an exhaust gas purification device 3, and an engine control unit (ECU) 7. Exhaust gas purification system 1 utilizes the exhaust gas purification device 3 to remove unburned components—such as HC, CO, and NO—from the exhaust gas discharged from the internal combustion engine 2. x The structure undergoes purification. It should be noted that... Figure 1 The arrows in the diagram indicate the direction of exhaust flow. Furthermore, in the following description, the side closer to the internal combustion engine 2 along the exhaust flow direction is referred to as the upstream side, and the side farther from the internal combustion engine 2 is referred to as the downstream side.

[0033] In this embodiment, the internal combustion engine 2 is primarily a gasoline engine from a gasoline vehicle. However, the internal combustion engine 2 can also be an engine other than a gasoline engine, such as a diesel engine or an engine used 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). The fuel tank stores gasoline. However, the fuel stored in the fuel tank can also be diesel fuel (light oil), etc. The fuel supplied from the fuel tank mixes with oxygen in the combustion chamber and burns. This converts combustion energy into mechanical energy. The combustion chamber is connected to an exhaust port. The exhaust port is connected to an exhaust purification device 3. The combusted fuel gas becomes exhaust gas and is discharged to the exhaust purification device 3. The exhaust gas contains unburned components (harmful components).

[0034] The exhaust purification device 3 includes an exhaust passage 4 connected to the internal combustion engine 2, an oxygen sensor 8, a first catalyst 10, and a second catalyst 9. The exhaust passage 4 is the exhaust flow path through which exhaust gas flows. In this embodiment, the exhaust passage 4 includes an exhaust manifold 5 and an exhaust pipe 6. The upstream end of the exhaust manifold 5 is connected to the exhaust port of the internal combustion engine 2. The downstream end of the exhaust manifold 5 is connected to the exhaust pipe 6. In the middle section of the exhaust pipe 6, the first catalyst 10 and the second catalyst 9 are arranged sequentially from the upstream side. However, the arrangement of the first catalyst 10 and the second catalyst 9 can be arbitrarily changed. Furthermore, the number of the first catalyst 10 and the second catalyst is not particularly limited, and multiple copies of each can be provided. Additionally, the second catalyst 9 is not mandatory and can be omitted in other embodiments.

[0035] In this embodiment, the first catalyst 10 is the catalyst that first comes into contact with the exhaust gas. The first catalyst 10 has the function of purifying HC, CO, and NO, which are harmful components in the exhaust gas. x The function of the first catalyst 10 is detailed below. The first catalyst 10 is an example of the "exhaust gas purification catalyst" disclosed in this embodiment. It should be noted that, in the following text, the first catalyst 10 will sometimes also be referred to as an "exhaust gas purification catalyst". The composition of the first catalyst (exhaust gas purification catalyst) 10 will be described in detail below. The second catalyst 9 can be the same as a conventional catalyst and is not particularly limited. The second catalyst 9 can, for example, simultaneously purify HC, CO, and NO contained in the exhaust gas. x Three-way catalytic converters, or gasoline particulate filters (GPF) that remove PM contained in exhaust gases, etc.

[0036] It should be noted that upstream of the first catalyst 10, a catalyst with a different composition than the first catalyst 10 and the second catalyst 9 can also be configured. Examples include a diesel particulate filter (DPF) to remove PM contained in the exhaust, a diesel oxidation catalyst (DOC) to purify HC, CO, etc., contained in the exhaust, and a catalyst that absorbs NO during normal operation (under lean combustion conditions). x When injecting a large amount of fuel (in a fuel-rich environment), HC and CO are used as reducing agents to purify NO. x NO x Adsorption-reduction (NSR: NO) x Storage-reduction catalysts, etc.

[0037] As described later, hydrogen (H2) is generated during the purification of HC and CO using the first catalyst 10. This hydrogen is typically discharged outside the exhaust purification system 1 and further discharged outside of vehicles such as automobiles. Although the hydrogen can also be recycled, the exhaust containing hydrogen is not returned to the internal combustion engine 2.

[0038] ECU 7 controls the internal combustion engine 2 and the exhaust purification device 3. ECU 7 is electrically connected to the internal combustion engine 2 and sensors (e.g., oxygen sensor 8, temperature sensor (not shown), pressure sensor, etc.) located in various parts of the exhaust purification device 3. It should be noted that the composition of ECU 7 can be the same as existing ones and is not particularly limited. ECU 7 may be, 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 vehicle's operating status, the exhaust volume of the internal combustion engine 2, the exhaust temperature, and the exhaust pressure. ECU 7 receives information detected by sensors (e.g., the oxygen content measured by oxygen sensor 8) through the input port. Based on the received information, ECU 7 sends control signals through the output port. ECU 7 controls the operation of the internal combustion engine 2, including fuel injection control, ignition control, and intake air volume regulation control. ECU 7 controls the operation of the internal combustion engine 2 to achieve, for example, an ideal air-fuel ratio (A / F) in the exhaust. The ECU7 controls the driving and stopping of the exhaust purification device 3 based on, for example, the operating state of the internal combustion engine 2 and the amount of exhaust gas discharged from the internal combustion engine 2.

[0039] Catalysts for Exhaust Gas Purification

[0040] Figure 2 This is a three-dimensional schematic diagram of the exhaust gas purification catalyst 10 of this embodiment. Figure 3 This is a schematic cross-sectional view of the section after the exhaust gas purification catalyst 10 is cut off along the cylinder axis X. It should be noted that... Figure 2 , Figure 3 The arrows in the diagram indicate the direction of exhaust flow. Figure 2 , Figure 3 In the diagram, the left side represents the upstream side of the exhaust passage 4, which is relatively closer to the internal combustion engine 2, and the right side represents the downstream side of the exhaust passage, which is relatively farther away from the internal combustion engine 2. Additionally, the symbol X indicates the cylinder axis direction of the exhaust purification catalyst 10. In the cylinder axis direction X, X1 is the upstream side (also called the exhaust inflow side or front side), and X2 is the downstream side (also called the exhaust outflow side or rear side). The exhaust purification catalyst 10 is arranged in the exhaust passage 4 in a manner that follows the exhaust flow direction along the cylinder axis direction X.

[0041] The exhaust gas purification catalyst 10 has the function of purifying harmful components in exhaust gas. The end of the exhaust gas purification catalyst 10 on the X1 side is the exhaust gas inlet 10a, and the end on the X2 side is the exhaust gas outlet 10b. In this embodiment, the exhaust gas purification catalyst 10 is cylindrical. However, the shape of the exhaust gas purification catalyst 10 is not particularly limited, and it can also be, for example, elliptical cylindrical, polygonal cylindrical, tubular, foamed, granular, fibrous, etc.

[0042] like Figure 3 As shown, the exhaust gas purification catalyst 10 includes a substrate 11, a catalyst layer 20 formed on the substrate 11, and a reforming reaction layer 30 formed on the substrate 11. In the exhaust gas purification catalyst 10, both the catalyst layer 20 and the reforming reaction layer 30 are formed on the same substrate 11, so the exhaust gas purification catalyst 10 can exhibit high purification performance of HC and CO in a fuel-rich environment with high space utilization.

[0043] [Substrate]

[0044] The substrate 11 forms the framework of the catalyst 10 for exhaust gas purification. There are no particular limitations on the substrate 11; various materials and forms already used for this type of application can be used. In the example shown, a direct-flow substrate is used as the substrate 11. The substrate 11 can be a ceramic support made of materials such as cordierite, aluminum titanate, or silicon carbide, or a metal support made of stainless steel (SUS), Fe-Cr-Al alloys, or Ni-Cr-Al alloys. Figure 2As shown, in this embodiment, the substrate 11 has a honeycomb structure. The substrate 11 has a plurality of chambers (cavities) 12 regularly arranged along the cylindrical axis X and partition walls (ribs) 14 separating the plurality of chambers 12. Although not particularly limiting, the length (average length) L of the substrate 11 along the cylindrical axis X can typically be 10 to 500 mm, for example, 50 to 300 mm. In addition, the volume of the substrate 11 can be, for example, 0.1 to 10 L, or 0.5 to 5 L. It should be noted that, in this specification, "volume of the substrate" refers to the apparent volume (bulk volume) including the volume of the internal chambers 12, in addition to the volume of the substrate 11 itself (pure volume).

[0045] Chamber 12 serves as an exhaust flow channel. Chamber 12 extends along the cylindrical axis direction X. Chamber 12 is a through hole penetrating the substrate 11 along the cylindrical axis direction X. The shape, size, and number of chambers 12 can be designed taking into account, for example, the flow rate and composition of the exhaust gas flowing through the exhaust purification catalyst 10. The cross-sectional shape orthogonal to the cylindrical axis direction X of chamber 12 is not particularly limited. The cross-sectional shape of chamber 12 can be various geometric shapes, such as squares, parallelograms, rectangles, trapezoids, and other polygonal shapes (e.g., triangles, hexagons, octagons), wavy shapes, circles, etc. Rib walls 14 face chambers 12 and separate adjacent chambers 12.

[0046] <Catalyst Layer>

[0047] like Figure 3 As shown, the catalyst layer 20 is disposed in the exhaust gas purification catalyst 10 at a position closer to the upstream side of the exhaust gas flow direction than the reforming reaction layer 30. In the example shown, the catalyst layer 20 is configured to be in contact with the reforming reaction layer 30. However, as long as it is located on the substrate 11 on which the reforming reaction layer 30 is formed, the catalyst layer 20 can also be separated from the reforming reaction layer 30.

[0048] In catalyst layer 20, exhaust gas purification is achieved through a three-way reaction. Therefore, catalyst layer 20 contains a three-way catalyst. That is, catalyst layer 20 contains a precious metal and a support for the precious metal. Catalyst layer 20 may also employ the same composition as known catalyst layers containing a three-way catalyst.

[0049] Precious metals are catalytic metals used to purify harmful components in exhaust gas. There are no particular limitations on the type of precious metal used; any known precious metals used in three-way catalytic converters can be used. Specific examples of precious metals include platinum group metals such as rhodium (Rh), palladium (Pd), platinum (Pt), ruthenium (Ru), osmium (Os), iridium (Ir), gold (Au), and silver (Ag). These precious metals can be used alone or in combination of two or more. From the perspective of catalytic performance, at least one selected from Pt, Rh, Pd, Ir, and Ru is preferred, and at least one selected from Pt, Rh, and Pd is more preferred. When two or more of these precious metals are used, the precious metal can also be an alloy formed from two or more of these metals.

[0050] Precious metals are preferably used in combination of two or more of the above-mentioned materials. As a preferred example, a combination of Rh, which has high reducing activity, and Pd and / or Pt, which has high oxidizing activity, can be cited. It should be noted that the expression "A and / or B" used in this specification refers to either A or B, or both A and B.

[0051] Precious metals are preferably used in the form of particles with sufficiently small particle sizes. The average particle size of the precious metal particles (specifically, the average particle size of 20 or more precious metal particles obtained based on a cross-sectional image of the catalyst layer from a transmission electron microscope) is typically in the range of 1 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 precious metal and the exhaust gas, further improving purification performance.

[0052] There is no particular limitation on the content of precious metals. The content of precious metals is, for example, 0.05 to 10 g / L, or 0.1 to 5 g / L, relative to the portion of the substrate in which the catalyst layer 20 is formed along the cylinder axis X per 1 L volume.

[0053] As a support for noble metals, known inorganic compounds used in ternary catalysts can be used, and porous supports with a certain specific surface area are suitable. It should be noted that, unless otherwise specified, "specific surface area" in this specification refers to the specific surface area measured by the BET method. Suitable supports include, for example, alumina (Al₂O₃), cerium oxide (CeO₂), zirconium oxide (ZrO₂), silicon dioxide (SiO₂), titanium dioxide (TiO₂), and their solid solutions (e.g., cerium oxide-zirconia composite oxides (CZ composite oxides), or combinations of these compounds). The support is preferably in particulate form (e.g., alumina powder, CZ powder, etc.). From the perspective of heat resistance and structural stability, a specific surface area of ​​50–500 m² is preferred for the support particles. 2 / g (especially 200-400m) 2 / g). In addition, the average particle size of the support particles (specifically, the average particle size of more than 20 support particles obtained based on cross-sectional images 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).

[0054] The catalyst layer 20 can contain any component other than the three-way catalyst. For example, in addition to noble metals, the catalyst layer 20 can also contain alkali metals, alkaline earth metals, transition metals, rare earth metals, and other metals. These elements (especially alkaline earth metals) can be contained in the form of oxides, hydroxides, carbonates, nitrates, sulfates, phosphates, acetates, formates, oxalates, halides, etc.

[0055] Regarding any component, catalyst layer 20 preferably also contains an oxygen storage and absorbing material (OSC material) with oxygen storage and absorbing capacity, which is not supported by noble metals and serves as a non-support. As the OSC material, known compounds with oxygen storage and absorbing capacity can be used; specific examples include metal oxides containing cerium oxide (CeO2) with high oxygen storage and absorbing capacity (Ce oxides). The Ce oxide can be cerium oxide or a composite oxide of cerium oxide and other metal oxides. From the perspective of improving heat resistance and durability, the Ce 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 perspective of improving heat resistance, the CZ composite oxide can also contain, for example, Nd2O3, La2O3, Y2O3, Pr6O3, etc. 10 Rare earth metal oxides, etc.

[0056] Other components of the catalyst layer 20 may include binders such as alumina sol and silica sol, as well as various additives.

[0057] The catalyst layer 20 can be a single-layer structure or a multi-layer structure. Figure 3 In the example shown, catalyst layer 20 is a single layer. Even when catalyst layer 20 is a single-layer structure, it can still contain regions with different compositions and properties. For example, catalyst 20 may have a upstream front section and a downstream section located closer to the downstream side in the axial direction X, and the front and downstream sections may have different compositions and / or properties. Specifically, for example, the front and downstream sections may contain different precious metals.

[0058] When the catalyst layer 20 has a multilayer structure, the number of layers is not particularly limited. The catalyst layer 20 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 the two layers. In this multilayer structure, each layer can contain different noble metals.

[0059] As a variation of the catalyst 10 for exhaust gas purification, a preferred example of the catalyst layer 20 having a multi-layer structure is shown below. Figure 4 . Figure 4 The meaning of the middle arrow and Figure 3 The arrows in the text are the same. Figure 4 In the modified exhaust gas purification catalyst 10' shown, the catalyst layer 20' has a lower layer 22' serving as a layer on the substrate 11 side, and an upper layer 24' disposed above the lower layer 22'. Both the lower layer 22' and the upper layer 24' contain a three-way catalyst. The lower layer 22' contains Pd as a noble metal in the three-way catalyst. On the other hand, the upper layer 24' contains Rh as a noble metal in the three-way catalyst. In this case, by separately supporting the oxidation catalyst and the reduction catalyst in the stacking direction, deactivation of the catalyst metal (e.g., fusion accompanying grain growth) can be suppressed, and the durability of the exhaust gas purification catalyst can be improved.

[0060] The coating amount (i.e., the forming amount) of catalyst layer 20 (and catalyst layer 20′) is not particularly limited. The coating amount, for example, is 10–500 g / L, or possibly 100–300 g / L, relative to the substrate portion of the catalyst layer 20 formed along the cylinder axis X per 1L volume. By satisfying this range, it is possible to simultaneously improve the purification performance of harmful components and reduce pressure loss at a high level. Furthermore, it also improves durability and peel resistance.

[0061] The thickness of the catalyst layer 20 is not particularly limited and can be appropriately designed considering factors such as durability and peel resistance. The thickness of the catalyst layer 20 can be, for example, 1–100 μm, or 5–100 μm.

[0062] The coating length (average dimension in the cylinder axis direction X) of catalyst layer 20 (and catalyst layer 20′) is not particularly limited and can be appropriately designed taking into account the size of substrate 11, the flow rate of exhaust gas flowing through exhaust purification catalyst 10, etc. This coating length is, for example, 10% to 90% of the total length of substrate in the cylinder axis direction X, preferably 20% to 80%, and more preferably 30% to 70%.

[0063] [Reforming Reaction Layer]

[0064] In the exhaust gas purification catalyst 10, the reforming reaction layer 30 is located closer to the downstream side than the catalyst layer 20 in the exhaust gas flow direction. In the example shown, since the catalyst layer 20 and the reforming reaction layer 30 are disposed in the chamber 12 of the substrate 11 of the exhaust gas purification catalyst 10, the exhaust gas flowing through the catalyst layer 20 can flow into the reforming reaction layer 30.

[0065] The reforming reaction layer 30 contains a hydrogen production catalyst as an essential component. The hydrogen production catalyst is a catalyst that initiates the hydrogen production reaction by converting HC and CO in exhaust gas into carbon dioxide and H2. Specifically, the hydrogen production catalyst is a catalyst that utilizes water and converts HC and CO into H2 through a steam reforming reaction (HC + H2O → CO2 + H2) and a CO conversion reaction (CO + H2O → CO2 + H2).

[0066] As described above, since the oxygen content may be insufficient in a fuel-rich environment, catalyst layer 20 alone may not be sufficient for the oxidation of HC and CO. Furthermore, since a large amount of oxygen is consumed upstream in the exhaust flow direction of the exhaust gas purification catalyst, oxygen deficiency is likely to occur downstream, especially in a fuel-rich environment. On the other hand, water is produced during fuel (typically gasoline) combustion and HC oxidation, resulting in abundant water in the exhaust gas. The reforming reaction layer 30, as described above, uses water instead of oxygen to convert HC and CO into carbon dioxide and H2. Therefore, by positioning the reforming reaction layer 30 further downstream than catalyst layer 20 in the exhaust flow direction of the exhaust gas purification catalyst 10, HC and CO can be removed with a high purification rate even in oxygen-deficient conditions. In other words, by using the exhaust gas purification catalyst 10 of this embodiment, the purification performance of HC and CO in a fuel-rich environment can be improved, thereby reducing thermal emissions.

[0067] The hydrogen production catalyst can be uniformly contained along the cylinder axis X, or it can be contained in a manner in which the content changes in stages from the upstream side to the downstream side. For example, it can be contained in a manner in which the content decreases from the upstream side to the downstream side.

[0068] Hydrogen production catalysts typically contain at least one of rare earth oxides and transition metal oxides (excluding oxides of noble metals other than Rh and Ru). This avoids competition with exhaust gas purification reactions that utilize oxidation reactions, thus promoting hydrogen production.

[0069] Oxides of rare earth elements belonging to Group IIIB of the periodic table can be cited as examples: scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). Among these, oxides of lanthanides are preferred due to their high reactivity and good hydrogen production performance, and from the perspectives of durability and availability, at least one of Pr and Nd is preferred.

[0070] Examples of transition metal oxides (excluding oxides of noble metals other than Rh and Ru) include oxides of elements belonging to the fourth period of the periodic table, such as scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu), and oxides of elements belonging to the fifth period of the periodic table, such as yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), and technetium (Tc). Among these, oxides of metals belonging to the fourth period of the periodic table are preferred due to their high reactivity and good hydrogen production performance; oxides of iron group elements (Fe, Co, Ni) are more preferred, and Ni is particularly preferred. Furthermore, from the perspective of durability, at least one of Co and Ni is preferred. Based on the above, the hydrogen production catalyst preferably contains an oxide selected from at least one element selected from Pr, Nd, Co, and Ni; more preferably, an oxide containing Ni or Pr; and even more preferably, nickel oxide.

[0071] The reforming reaction layer 30 may contain any components other than the hydrogen production catalyst. In this embodiment, the reforming reaction layer 30 contains inorganic oxides as any component, specifically, it contains OSC materials with oxygen uptake and storage capabilities and non-OSC materials without oxygen uptake and storage capabilities.

[0072] In the technology disclosed in this embodiment, the OSC material has the function of promoting hydrogen production reactions (steam reforming and / or CO conversion reactions). The OSC material can also function as a co-catalyst. In the reforming reaction layer 30, it is preferable to arrange the OSC material adjacent to the hydrogen production catalyst. Although not a particularly definitive explanation, according to the inferences of the inventors, the OSC material functions to dissociate H2O in the exhaust gas and provide O atoms to the hydrogen production catalyst, thereby promoting the hydrogen production reaction.

[0073] As an OSC material, an example of a material that can be used in catalyst layer 20 can be cited. The CZ composite oxide can be a Ce-rich oxide or a Zr-rich oxide. The mixing ratio of cerium oxide in the CZ composite oxide is, for example, 10 to 90% by mass, preferably 15 to 70% by mass, when the total CZ composite oxide is 100% by mass. A high cerium oxide mixing ratio can promote the conversion of harmful components to H2; a high zirconium oxide mixing ratio will result in higher heat resistance. When the cerium oxide mixing ratio is within the above range, the technical effects and heat resistance disclosed in this embodiment can be achieved at a high level.

[0074] The OSC material content in the reforming reaction layer 30 is, for example, but not particularly limited, 1 to 100 g / L, preferably 5 to 50 g / L, relative to the portion of the substrate forming the reforming reaction layer 30 along the cylinder axis X per 1L volume. Furthermore, the ratio of the OSC material content to the hydrogen production catalyst content is, for example, 0.1 or more, 0.2 or more, 0.5 or more, 1 or more, 2 or more, or 3 or more, and for example, 30 or less, 20 or less, 10 or less, or 5 or less. This not only promotes the hydrogen production reaction but also allows for control of the coating amount of the reforming reaction layer 30, reducing pressure loss and cost.

[0075] The non-OSC material possesses at least one of the following functions: improving the heat resistance of the reforming reaction layer 30, improving the durability of the reforming reaction layer 30, and inhibiting the peeling of the reforming reaction layer 30 from the substrate 11. Examples of non-OSC materials include metal oxides such as alumina (Al₂O₃), titanium dioxide (TiO₂), zirconium oxide (ZrO₂), and silicon dioxide (SiO₂). Among these, metal oxides containing alumina (Al-containing oxides) are preferred due to their high heat resistance and durability. The Al-containing oxide can be alumina or a composite oxide of alumina and other metal oxides (e.g., rare earth metal oxides). From the perspective of improving heat resistance and durability, the Al-containing oxide is, for example, a La₂O₃-Al₂O₃ composite oxide (LA composite oxide). The LA composite oxide can be a La-rich oxide or an Al-rich oxide. The mixing ratio of metal oxides other than alumina in LA composite oxides, from the perspective of suppressing the deactivation over the years of use, is, for example, less than 50% by mass when the total LA composite oxide is 100% by mass, and can be 0.1 to 20% by mass.

[0076] The content of non-OSC materials in the reforming reaction layer 30 may, but is not specifically limited to, being less than the content of OSC materials. For example, the content of non-OSC materials is 1 to 100 g / L, or 5 to 50 g / L, relative to the portion of the substrate forming the reforming reaction layer 30 along the cylinder axis X per 1L volume.

[0077] Hydrogen production catalysts are typically in particulate form. Particulate hydrogen production catalysts (especially nickel oxide (NiO)) x The hydrogen production catalyst particles are preferably not supported by a support. The support can be made of any component, such as OSC material or non-OSC material. In other words, the hydrogen production catalyst particles are preferably separate from the OSC material or non-OSC material and exist independently. When the hydrogen production catalyst is supported by a support, it is easily subject to interaction with the support (especially cerium oxide in OSC material). Therefore, the metal elements (especially Ni) of the hydrogen production catalyst are difficult to stabilize in the metallic state, making it difficult to initiate steam reforming and CO conversion reactions. Therefore, by using hydrogen production catalyst particles that are not supported by a support, the metal elements (especially Ni) of the hydrogen production catalyst can be easily stabilized in the metallic state, promoting steam reforming and CO conversion reactions.

[0078] The average particle size of the hydrogen production catalyst (specifically, the average particle size of 20 or more particles obtained by electron microscopy) is preferably, but not particularly limited, 1 μm or more. In this case, the metal element (especially Ni) of the hydrogen production catalyst is more easily stabilized in the metallic state, which can further promote the steam reforming reaction and the CO conversion reaction. On the other hand, the average particle size of the hydrogen production catalyst is preferably smaller than the average particle size of OSC materials and / or non-OSC materials. This can maintain stable activity. The average particle size of the hydrogen production catalyst is more preferably 1 μm or more and 9 μm or less, and even more preferably 1 μm or more and 5 μm or less.

[0079] The content of hydrogen production catalyst in the reforming reaction layer 30 is not particularly limited. The higher the content of hydrogen production catalyst, the higher the purification performance of CO and HC is likely to be. Therefore, relative to the portion of the substrate forming the reforming reaction layer 30 along the cylinder axis X per 1L volume, the content of hydrogen production catalyst is preferably 5 g / L or more, more preferably 10 g / L or more, further preferably 20 g / L or more, and most preferably 30 g / L or more.

[0080] On the other hand, it helps to inhibit the excessive reduction of harmful components (e.g., NO). x The substrate, which forms a reforming reaction layer 30 along the cylinder axis direction X for each 1L volume of the substrate (where the excess is reduced to generate ammonia), has a hydrogen production catalyst content of, for example, 100g / L or less, preferably 80g / L or less, and more preferably 60g / L or less.

[0081] The reforming reaction layer 30 can be composed of a hydrogen production catalyst, OSC materials, and non-OSC materials, and may also contain any other components. For example, if the reforming reaction layer 30 contains OSC materials, it can include alkaline earth elements such as calcium (Ca), barium (Ba), and strontium (Sr). This can increase the oxygen uptake and storage capacity of the OSC materials under lean combustion conditions. In addition, it can suppress catalyst poisoning under rich combustion conditions and maintain the activity stability of the hydrogen production catalyst.

[0082] A preferred embodiment of the reforming reaction layer 30 is that it does not contain precious metals. When the reforming reaction layer 30 contains precious metals, the improvement effect of the exhaust gas purification catalyst 10 on CO and HC purification performance is reduced. This is because precious metals adsorb CO and HC, hindering their purification using the hydrogen production catalyst.

[0083] On the other hand, another preferred embodiment of the reforming reaction layer 30 is that the reforming reaction layer 30 contains Rh. Rh is a precious metal, and precious metals can reduce the effect of improving the purification performance of CO and HC of the exhaust gas purification catalyst 10, but the degree to which Rh reduces this effect is very small. On the other hand, Rh can purify NO. x Therefore, when considering the overall harmful components (i.e., CO, HC, and NO) x When the purification performance is good, that is, when CO, HC and NO are removed with a good balance and high purification rate, it can achieve the desired purification performance. x Although Rh is a noble metal, the reforming reaction layer 30 may contain Rh. Therefore, in this embodiment, the reforming reaction layer 30 preferably does not contain any noble metals other than Rh.

[0084] Other components of the reforming reaction layer 30 may include alumina sol, silica sol, and other binders and various additives.

[0085] In the reforming reaction layer 30, the main body may be composed of a hydrogen production catalyst (i.e., a component accounting for 50% or more of the total mass), an OSC material, or a non-OSC material. From the perspective of improving the dispersibility of the hydrogen production catalyst and suppressing fusion, it is preferable that the main body of the reforming reaction layer 30 is composed of OSC material and / or non-OSC material (which can be combined when both are included). Assuming the total reforming reaction layer 30 is 100% by mass, from the perspective of long-term performance of the good technical effects disclosed in this embodiment, the content ratio of the hydrogen production catalyst is, for example, but not particularly limited to, 5-90% by mass, preferably 10-70% by mass. Furthermore, from the perspective of promoting the hydrogen production reaction, the content ratio of the OSC material is, for example, 1-70% by mass, preferably 5-65% by mass. Moreover, from the perspective of improving heat resistance, durability, and peel resistance, the content ratio of the non-OSC material is, for example, 10% by mass or more, preferably 25% by mass or more, and more preferably 30-50% by mass.

[0086] The coating amount (forming amount) of the reforming reaction layer 30 is not particularly limited. For example, the coating amount is 10 to 200 g / L, or 50 to 100 g / L, relative to the portion of the substrate in which the reforming reaction layer 30 is formed along the cylinder axis X per 1L volume. By satisfying the above range, the technical effects disclosed in this embodiment can be stably maintained at a high level over a long period of time.

[0087] The average thickness of the reforming reaction layer 30 is not particularly limited and can be appropriately set considering factors such as durability and peel resistance. For example, the average thickness of the reforming reaction layer 30 can be 1–100 μm, or 5–100 μm.

[0088] The coating length (average dimension in the cylinder axis X) of the reforming reaction layer 30 is not particularly limited, and can be appropriately designed taking into account the size of the substrate 11, the flow rate of the exhaust gas flowing through the exhaust gas purification catalyst 10, etc. The coating length of the reforming reaction layer 30 is, for example, 10% to 90% of the total length of the substrate in the cylinder axis X, preferably 20% to 80%, and more preferably 30% to 70%.

[0089] Method for manufacturing catalyst 10 for exhaust gas purification

[0090] The catalyst for exhaust gas purification can be manufactured, for example, by the following method: First, a substrate 11 is prepared; then, a slurry for forming the catalyst layer 20 is prepared; and finally, a slurry for forming the reforming reaction layer 30 is prepared. The slurry for forming the catalyst layer can be the same as known slurries for forming catalyst layers containing a three-way catalyst. For example, a noble metal source (e.g., a solution containing noble metal ions), a support, and any components (binders, various additives, etc.) can be dispersed in a dispersion medium to prepare the slurry for forming the catalyst layer.

[0091] Regarding the slurry used to form the reforming reaction layer, as a hydrogen production catalyst source, oxides that serve as hydrogen production catalysts or compounds that are converted into oxides of hydrogen production catalysts through calcination (e.g., nitrates, carbonates, oxalates, hydroxides, etc. of rare earth metals and transition metals) can be used. The slurry used to form the catalyst layer can be prepared, for example, by dispersing the hydrogen production catalyst source and any components (OSC materials, non-OSC materials, binders, various additives, etc.) in a dispersion medium. In this embodiment, in particular, when the hydrogen production catalyst is nickel oxide (NiO... x When ), the average particle size is preferably 5 μm or more.

[0092] Next, slurries for forming the catalyst layer and slurries for forming the reforming reaction layer are applied to the substrate 11. These slurries can be applied using conventional methods—such as impregnation or washing. In one embodiment, the slurry for forming the catalyst layer, prepared as described above, is first fed into the chamber 12 from the end of the substrate 11 at the inlet 10a side, along the cylindrical axis X to a predetermined length and then dried. Next, the slurry for forming the reforming reaction layer is fed into the chamber 12 from the end of the substrate 11 at the outlet 10b side, along the cylindrical axis X to a predetermined length and then dried. The substrate 11, after slurry feeding, is then fired at a predetermined temperature and time. The firing method can be the same as in existing methods. This allows the catalyst layer 20 and the reforming reaction layer 30 to be formed on the substrate 11. Thus, the exhaust gas purification catalyst 10 can be formed.

[0093] Applications of Catalyst 10 for Exhaust Gas Purification

[0094] The exhaust purification catalyst 10 is applicable not only to internal combustion engines in vehicles such as cars and trucks, motorized motorcycles, and bicycles with engines, but also to internal combustion engines in marine equipment such as ships, tankers, jet skis, personal water vehicles, and outboard motors; internal combustion engines in gardening equipment such as lawnmowers, chainsaws, and trimmers; internal combustion engines in recreational equipment such as golf carts and ATVs; internal combustion engines in power generation equipment such as combined heat and power systems; and internal combustion engines in waste incinerators. It is particularly well-suited for use in automobiles and other vehicles.

[0095] Example

[0096] The following describes relevant test examples of the present invention, but it is not intended to limit the present invention to the forms shown in the test examples below. It should be noted that in the test examples below, the unit "g / L" refers to the content of the portion of the substrate in which a predetermined layer is formed in the axial direction of the cylinder relative to 1L of volume.

[0097] [Experimental Example 1] Study on reforming reaction layer containing hydrogen production catalyst

[0098] First, a cylindrical honeycomb substrate (made of cordierite, volume: 1.2L, substrate diameter: 118mm, substrate length: 112mm) was prepared. Next, the following three slurries were prepared. It should be noted that the OSC material used a cerium oxide-zirconia composite oxide containing La, Pr, Nd, and Y as additives; the non-OSC material used an alumina composite oxide containing La.

[0099] (A) Slurry for forming the reforming reaction layer: OSC material, non-OSC material, nickel oxide (average particle size 8 μm) as a hydrogen production catalyst, barium sulfate, alumina-based binder, and distilled water are mixed together. The mixture is ground to control the particle size, thus preparing a slurry for forming the reforming reaction layer.

[0100] (B) Pd slurry for forming the catalyst underlayer: OSC material, non-OSC material, Pd nitric acid aqueous solution, barium sulfate, alumina-based binder, and distilled water are mixed together. The mixture is ground to control the particle size, thus preparing a Pd slurry for forming the catalyst underlayer.

[0101] (C) Rh slurry for forming the catalyst top layer: OSC material, non-OSC material, hydrochloric acid Rh aqueous solution, alumina-based binder, and distilled water are mixed together. The mixture is milled to control the particle size, thus preparing an Rh slurry for forming the catalyst top layer.

[0102] [Comparative Example 1]

[0103] The Pd slurry used to form the lower layer of the catalyst was poured into the front side of the substrate (the end side of the exhaust inlet side) and drawn in by a blower, thereby forming a coating on a portion corresponding to 100% of the total length of the substrate in the axial direction. The coating amount of the Pd slurry was set to achieve a Pd content of 0.14 g / L. The coating was then heated and dried in a dryer at 250°C for 1 hour, followed by firing in an electric furnace at 500°C for 1 hour. This formed the lower layer of the catalyst layer.

[0104] Next, the Rh slurry used to form the upper layer was poured in from the front of the substrate and drawn in by a blower, thereby forming a coating on a portion corresponding to 100% of the total length of the substrate in the axial direction. The coating amount of the Rh slurry was set to achieve an Rh content of 0.07 g / L. Then, the coating was heated and dried in a dryer at 250°C for 1 hour, and then fired in an electric furnace at 500°C for 1 hour. This formed the lower layer of the catalyst layer. Thus, the exhaust gas purification catalyst of Comparative Example 1 without a reforming reaction layer was obtained.

[0105] [Comparative Example 2]

[0106] The slurry used to form the reforming reaction layer was poured into the front side of the substrate and drawn in using a blower, forming a coating. The coating length was set to be 50% of the total length of the substrate along the cylindrical axis, and the coating amount was set to ensure that the hydrogen production catalyst content was 48 g / L (calculated as nickel oxide). The coating was then dried in a dryer at 250°C for 1 hour, followed by firing in an electric furnace at 500°C for 1 hour. This resulted in the formation of a reforming reaction layer on the front surface of the substrate.

[0107] Next, a Pd slurry for forming the lower catalyst layer was poured into the substrate from the rear side (the end side of the exhaust outlet) and drawn in using a blower, forming a coating. The coating length was set to be equivalent to 50% of the total length of the substrate along the cylindrical axis, and the coating amount was set to achieve a Pd content of 0.14 g / L. The coating was then dried in a dryer at 250°C for 1 hour, followed by firing in an electric furnace at 500°C for 1 hour. This formed the lower catalyst layer on the rear surface of the substrate.

[0108] Next, the Rh slurry used to form the upper layer was poured in from the rear side of the substrate and drawn in using a blower to form a coating. The coating length was set to be equivalent to 50% of the total length of the substrate along the cylindrical axis. The coating amount was set to achieve an Rh content of 0.07 g / L. Then, the coating was heated and dried in a dryer at 250°C for 1 hour, and then fired in an electric furnace at 500°C for 1 hour. This formed an upper layer of catalyst on top of the lower layer that had already been formed. Thus, the exhaust gas purification catalyst of Comparative Example 2, which has a reforming reaction layer at the front, was obtained.

[0109] [Example 1]

[0110] A Pd slurry for forming the lower catalyst layer was poured into the front of the substrate and drawn in using a blower, forming a coating. The coating length was set to be 50% of the total length of the substrate along the cylindrical axis, and the coating amount was set to achieve a Pd content of 0.14 g / L. The coating was then dried in a dryer at 250°C for 1 hour, followed by firing in an electric furnace at 500°C for 1 hour. This resulted in the formation of the lower catalyst layer on the front surface of the substrate.

[0111] Next, the Rh slurry used to form the upper layer was poured into the front of the substrate and drawn in using a blower, forming a coating. The coating length was set to be 50% of the total length of the substrate along the cylindrical axis. The coating amount was set to achieve an Rh content of 0.07 g / L. The coating was then heated and dried in a dryer at 250°C for 1 hour, followed by firing in an electric furnace at 500°C for 1 hour. This formed an upper catalyst layer on top of the previously formed lower layer.

[0112] Next, the slurry used to form the reforming reaction layer was poured in from the rear side of the substrate and drawn in using a blower, forming a coating. The coating length was set to be 50% of the total length of the substrate along the cylindrical axis, and the coating amount was set to ensure that the hydrogen production catalyst content was 48 g / L (calculated as nickel oxide). Then, the coating was heated and dried in a dryer at 250°C for 1 hour, followed by firing in an electric furnace at 500°C for 1 hour. This formed a reforming reaction layer on the rear surface of the substrate. Thus, the exhaust gas purification catalyst of Example 1 with a reforming reaction layer on the rear was obtained.

[0113] [Evaluation of CO and HC purification performance]

[0114] The CO and HC purification performance of the exhaust gas purification catalyst prepared above was evaluated using a catalyst evaluation device equipped with a gasoline engine (2.5L, naturally aspirated engine). Specifically, the exhaust gas purification catalyst prepared above was placed in the catalyst evaluation device, and simulated exhaust gas with an inflow gas temperature set to 520°C and a modified air-fuel ratio (A / F) was supplied to the engine. The CO purification rate and HC purification rate were calculated based on the ratio of the CO or HC concentration of the gas flowing into the exhaust gas purification catalyst to the CO or HC concentration of the gas flowing out of the exhaust gas purification catalyst. It should be noted that the HC purification rate was obtained as the total hydrocarbon (THC) purification rate. The results are shown below. Figure 5 and Figure 6 Additionally, the curves comparing CO purification rates and THC purification rates under a fuel-rich environment (A / F = 14.2) are shown in the figure below. Figure 7 .

[0115] Depend on Figures 5-7 The results show that, with a catalyst layer at the front and a reforming reaction layer at the rear (Example 1), high CO purification rates and high THC purification rates can be achieved even in a fuel-rich environment. This is because the O2 concentration is low at the rear, allowing the reforming reaction (hydrogen production reaction) to proceed efficiently in the rear reforming reaction layer.

[0116] On the other hand, in the case of a reforming reaction layer at the front and a catalyst layer at the rear (Example 1), there is only a slight increase in CO purification rate and THC purification rate under a fuel-rich environment. This is because the O2 concentration at the front is sufficiently high, and even in the reforming reaction layer at the front, the oxidation reaction is preferentially carried out, so the reforming reaction (hydrogen production reaction) cannot proceed efficiently.

[0117] [Experimental Example 2] Study on Types of Hydrogen Production Catalysts

[0118] [Example 2]

[0119] Except for changing the source of hydrogen production catalyst in the slurry used to form the reforming reaction layer to nitric acid Pr and changing its coating amount to 30 g / L based on praseodymium oxide, the same procedure as in Example 1 was performed to obtain the exhaust gas purification catalyst of Example 2.

[0120] [Example 3]

[0121] Except for changing the source of hydrogen production catalyst in the slurry used to form the reforming reaction layer to Cu nitrate and changing its coating amount to 30 g / L based on copper oxide, the same procedure was performed as in Example 1 to obtain the exhaust gas purification catalyst of Example 3.

[0122] [Example 4]

[0123] Except for changing the source of hydrogen production catalyst in the slurry used to form the reforming reaction layer to Mg nitrate and changing its coating amount to 30 g / L based on magnesium oxide, the same procedure was performed as in Example 1 to obtain the exhaust gas purification catalyst of Example 4.

[0124] [Evaluation of CO and HC purification performance]

[0125] For the exhaust gas purification catalysts of Examples 2-4, CO purification rate and THC purification rate were measured in the same manner as described above. The results are presented in a graph comparing the CO purification rate and THC purification rate under a fuel-rich environment (A / F = 14.2). Figure 8 It should be noted that the results of Comparative Example 1 and Example 1 are shown together in the graph.

[0126] like Figure 8 As shown, when the metals used in the hydrogen production catalyst are Ni and Pr, the CO purification rate and THC purification rate are particularly improved. Among Ni and Pr, Ni has a higher CO purification rate and THC purification rate.

[0127] [Experimental Example 3] Study on the Dosage of Hydrogen Production Catalyst

[0128] [Example 5]

[0129] Except for changing the coating amount of the slurry used to form the reforming reaction layer to 10 g / L based on nickel oxide, the same procedure as in Example 1 was performed to obtain the exhaust gas purification catalyst of Example 5.

[0130] [Example 6]

[0131] Except for changing the coating amount of the slurry used to form the reforming reaction layer to 30 g / L based on nickel oxide, the same procedure as in Example 1 was performed to obtain the exhaust gas purification catalyst of Example 6.

[0132] [Example 7]

[0133] Except for changing the coating amount of the slurry used to form the reforming reaction layer to 50 g / L based on nickel oxide, the same procedure as in Example 1 was performed to obtain the exhaust gas purification catalyst of Example 7.

[0134] [Evaluation of CO and HC purification performance]

[0135] For the exhaust gas purification catalysts of Examples 5-7, CO and HC purification rates were measured in the same manner as described above. The results are presented in a graph comparing CO and THC purification rates under a fuel-rich environment (A / F = 14.2). Figure 9It should be noted that the results of Comparative Example 1 are also shown in the graph.

[0136] Depend on Figure 9 The results show that the greater the coating amount of the hydrogen production catalyst, the higher the CO purification rate and THC purification rate. When the coating amount is above 5 g / L, a fairly high improvement effect on CO purification rate and THC purification rate can be achieved.

[0137] [Experimental Example 4] Study on Hydrogen Production Catalyst Source

[0138] [Example 8]

[0139] Except that nickel oxide was replaced with Ni nitrate as the hydrogen production catalyst source for the slurry used to form the reforming reaction layer, the process was carried out in the same manner as in Example 1, and the exhaust gas purification catalyst of Example 8 was obtained. In Example 8 and Example 1, the coating amount of the hydrogen production catalyst was the same as that calculated from the nickel oxide amount.

[0140] [Evaluation of CO and HC purification performance]

[0141] For the exhaust gas purification catalyst of Example 8, the CO purification rate and THC purification rate were measured in the same manner as described above. The curves comparing the CO purification rate and THC purification rate under a fuel-rich environment (A / F = 14.2) of Example 1, Comparative Example 1, and Comparative Example 8 are shown in the figure. Figure 10 .

[0142] Depend on Figure 10 The results show that, as a hydrogen production catalyst source for forming the reforming reaction layer, the CO purification rate and THC purification rate are higher when nickel oxide particles are used than when Ni nitrate is used. In the case where Ni nitrate is used as the hydrogen production catalyst source (Example 8), the hydrogen production catalyst is highly dispersed on the support. Therefore, the hydrogen production catalyst is prone to interaction with the support (especially cerium oxide in the OSC material). Thus, although the oxidation reaction becomes easier to proceed, Ni becomes difficult to stabilize in the metallic state, making the reforming reaction difficult to carry out. On the other hand, when nickel oxide is used as the hydrogen production catalyst source (Example 1), since there is no interaction with the support, Ni is easily stabilized in the metallic state, facilitating the reforming reaction. Therefore, the CO purification rate and THC purification rate are higher when nickel oxide particles are used as the hydrogen production catalyst source. Furthermore, since larger nickel oxide particles are more easily stabilized in the metallic state, it can be said that a larger median particle size of nickel oxide particles is more preferred (specifically, 1 μm or more, 9 μm or less, especially 1 μm or more, 5 μm or less).

[0143] [Experimental Example 5] Study on the combined use of hydrogen production catalysts and noble metals

[0144] [Example 9]

[0145] Except that Pd nitric acid was added to the slurry used to form the reforming reaction layer at a coating amount of 0.14 g / L, the same procedure as in Example 1 was followed to obtain the exhaust gas purification catalyst of Example 9.

[0146] [Example 10]

[0147] Except for adding dinitrosodiammine platinum to the slurry used to form the reforming reaction layer at a coating amount of 0.14 g / L Pt, the same procedure as in Example 1 was followed to obtain the exhaust gas purification catalyst of Example 9.

[0148] [Example 11]

[0149] Except for adding hydrochloric acid Rh to the slurry used to form the reforming reaction layer at a coating amount of 0.07 g / L, the same procedure as in Example 1 was followed to obtain the exhaust gas purification catalyst of Example 9.

[0150] [Evaluation of CO and HC purification performance]

[0151] For the exhaust gas purification catalysts of Examples 9-11, CO purification rate and THC purification rate were measured in the same manner as described above. The results are presented in a graph comparing the CO purification rate and THC purification rate under a fuel-rich environment (A / F = 14.2). Figure 11 It should be noted that the results of Comparative Example 1 and Example 1 are shown together in the graph.

[0152] like Figure 11 The results show that the improvement in CO and THC purification rates was smaller when Pd and Pt coexisted in the reforming reaction layer (Examples 9 and 10) compared to when they did not coexist (Example 1). This is because a large amount of CO and HC are adsorbed on Pd and Pt, hindering the reforming reaction of the hydrogen production catalyst.

[0153] When Rh coexists in the reforming reaction layer, the decrease in CO and THC purification rates is relatively small. This is because although Rh adsorbs CO and HC, it promotes the reforming reaction in a fuel-rich environment, thus not significantly hindering the reforming reaction overall. Therefore, although the improvement in CO and THC purification rates is small when noble metals coexist, it can be said that Rh can coexist with the hydrogen production catalyst.

[0154] The specific examples of the present invention have been described in detail above, but these are merely illustrative and not intended to limit the scope of protection claimed in this application. The technology described in this invention includes various modifications and alterations to the specific examples described above.

Claims

1. A catalyst for exhaust gas purification, wherein, have Substrate, The catalyst layer disposed on the substrate, and A reforming reaction layer disposed on the substrate. The catalyst layer contains a ternary catalyst. The reforming reaction layer contains a hydrogen production catalyst. The reforming reaction layer is positioned downstream of the exhaust flow direction, closer to the catalyst layer. The hydrogen production catalyst contains nickel oxide, and the catalyst is in particulate form, with none of the catalyst particles being supported by a carrier. When the particle size of more than 20 hydrogen production catalyst particles is observed by electron microscopy and the average value is calculated, and this average value is taken as the average particle size of the hydrogen production catalyst, the average particle size of the hydrogen production catalyst is greater than 1 μm.

2. The catalyst for exhaust gas purification as described in claim 1, characterized in that, The average particle size of the hydrogen production catalyst is less than 9 μm.

3. The catalyst for exhaust gas purification as described in claim 1, characterized in that, The reforming reaction layer also includes an OSC material with oxygen absorption and storage capacity.

4. The catalyst for exhaust gas purification as described in claim 1, characterized in that, The hydrogen production catalyst in the reforming reaction layer has a content of 5 g / L or more in the substrate portion forming the reforming reaction layer per 1 L volume.

5. The catalyst for exhaust gas purification as described in any one of claims 1 to 4, characterized in that, The reforming reaction layer also contains Rh.

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