Method for producing slurry and method for producing exhaust gas purification catalyst

Abstract

The present invention provides a slurry manufacturing method that shortens the grinding time. The disclosed slurry manufacturing method includes: a material preparation step of preparing a slurry manufacturing material containing a first inorganic oxide powder; a first grinding step of grinding the slurry manufacturing material using a first grinding device having a first medium until the average particle diameter of the powder contained in the slurry manufacturing material based on the laser diffraction / scattering method reaches 5 μm or more and 13 μm or less; and a second grinding step of grinding the slurry manufacturing material using a second grinding device having a second medium having an average particle diameter smaller than the first medium after the first grinding step until the average particle diameter of the powder contained in the slurry manufacturing material based on the laser diffraction / scattering method reaches 1 μm or less. Further, the method includes a step of mixing a second inorganic oxide powder in the slurry manufacturing material before the first grinding step or after the first grinding step and before the second grinding step.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a slurry and a method for manufacturing a catalyst for exhaust gas purification. This application claims priority based on Japanese Patent Application No. 2022-048385, filed March 24, 2022, 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 Toxic exhaust components such as toxic gases are present in exhaust gases. Therefore, an exhaust purification catalyst, which has a catalyst metal capable of purifying exhaust components through oxidation or reduction reactions, is placed in the exhaust path from the internal combustion engine.

[0003] A typical exhaust gas purification catalyst comprises: a honeycomb substrate having multiple chambers serving as the flow path for exhaust gas; and a catalyst layer containing a catalyst metal formed within the chambers. Generally, the catalyst layer is formed by coating a slurry containing a catalyst metal and an inorganic oxide carrying the catalyst metal onto the substrate, followed by drying and firing. For example, Patent Document 1 discloses a method for manufacturing an exhaust gas purification catalyst, in which, in the step of manufacturing the wash-coating slurry, catalyst metal powder and γ-Al₂O₃ as a wash-coating material are ground, and during such grinding, a step of adding a mixture (CeO₂ and ZrO₂-CeO₂) is included. Furthermore, Patent Document 2 discloses a technique for preparing a catalyst slurry containing catalyst powder with a specified particle size distribution by wet grinding, dry grinding, or a combination of wet grinding and dry grinding in the process of preparing the catalyst slurry.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. Hei 7-88384

[0007] Patent Document 2: International Publication No. 2018-159214 Summary of the Invention

[0008] However, in the preparation of catalyst slurries, grinding the powder contained in the slurry to below 1 μm requires a long grinding time. Due to the long grinding time, productivity decreases, thus a technique to shorten the grinding time is desired. To shorten the grinding time, methods exist to reduce the diameter of the grinding media (e.g., beads), thereby increasing the contact frequency between the powder and the media. However, according to the inventors' research, the following technical problem has been discovered: due to the presence of coarse particles in the powder, the slits used to separate the grinding media and the powder in the grinding apparatus can sometimes become clogged.

[0009] Therefore, the present invention was made in view of the above-mentioned matters, and one of its objectives is to provide a method for manufacturing a slurry that shortens the grinding time. Another objective is to provide a method for manufacturing an exhaust gas purification catalyst using such a slurry manufacturing method.

[0010] The slurry manufacturing method disclosed in this invention is used to manufacture a slurry containing a first inorganic oxide powder, a second inorganic oxide powder with an average particle size smaller than the first inorganic oxide powder, and a dispersion medium. The method includes: a material preparation step, which prepares a slurry manufacturing material containing the first inorganic oxide powder; a first grinding step, which uses a first grinding apparatus having a first medium to grind the slurry manufacturing material until the average particle size of the powder contained in the slurry manufacturing material, based on laser diffraction / scattering, reaches 5 μm to 13 μm; and a second grinding step, which, after the first grinding step, uses a second grinding apparatus having a second medium with an average particle size smaller than the first medium to grind the slurry manufacturing material until the average particle size of the powder contained in the slurry manufacturing material, based on laser diffraction / scattering, reaches 1 μm or less. Furthermore, it is characterized by including a step of mixing the second inorganic oxide powder into the slurry manufacturing material before the first grinding step or after the first grinding step and before the second grinding step.

[0011] With this configuration, the powder is miniaturized to a size that is unlikely to clog the slit used to separate the media and powder in the second grinding device through the first grinding, and then the second grinding is performed. This improves grinding efficiency and shortens the total grinding time.

[0012] Furthermore, in a preferred embodiment of the slurry manufacturing method disclosed in this invention, the average particle size of the first medium is 1 mm or more and 10 mm or less. With this configuration, the powder contained in the slurry manufacturing material can be efficiently refined to an average particle size of 5 μm or more and 13 μm or less, thus further shortening the grinding time.

[0013] Furthermore, in a preferred embodiment of the slurry manufacturing method disclosed in this invention, the average particle size of the second medium is 0.1 mm or more and 0.5 mm or less. With this configuration, it is easy to refine the average particle size of the powder contained in the slurry manufacturing material to 1 μm or less, thereby further shortening the grinding time.

[0014] Furthermore, in a preferred embodiment of the slurry manufacturing method disclosed in this invention, before mixing the second inorganic oxide powder, the average particle size of the second inorganic oxide powder, based on laser diffraction / scattering, is 5 μm to 13 μm. With this configuration, it is possible to suppress the clogging of the slits in the second grinding device due to the second inorganic oxide powder.

[0015] Furthermore, in a preferred embodiment of the slurry manufacturing method disclosed in this invention, the pulverization method performed in the first grinding step and the second grinding step is wet pulverization. This configuration suppresses powder agglomeration in the slurry manufacturing material, improves powder micronization efficiency, and further shortens the grinding time.

[0016] Furthermore, in a preferred embodiment of the slurry manufacturing method disclosed in this invention, the second inorganic oxide powder is mixed before the first grinding step. With this configuration, the first and second grinding processes can be performed continuously, thus further shortening the grinding time.

[0017] Furthermore, in a preferred embodiment of the slurry manufacturing method disclosed in this invention, a slurry tank is further prepared and connected to the first grinding apparatus in a circulatory manner. The slurry manufacturing material is ground while circulating between the first grinding apparatus and the slurry tank. With this configuration, the first grinding can be performed while monitoring the average particle size of the powder contained in the slurry manufacturing material, thus allowing for a switch from the first grinding to the second grinding at an appropriate time. This further shortens the grinding time.

[0018] Furthermore, in a preferred embodiment of the slurry manufacturing method disclosed in this invention, the slurry tank and the second grinding apparatus are connected in a circulatory manner, and the slurry manufacturing material is ground while circulating between the second grinding apparatus and the slurry tank. With this configuration, grinding can be performed continuously while monitoring the average particle size of the powder contained in the slurry manufacturing material. This prevents over-grinding and thus further shortens the grinding time.

[0019] Furthermore, in one embodiment of the slurry manufacturing method disclosed in this invention, the slurry manufacturing material contains at least one catalyst metal that functions as a catalyst capable of oxidizing or reducing exhaust gas components. Thus, a catalyst layer forming slurry for exhaust gas purification catalysts can be manufactured.

[0020] The present invention also provides a method for manufacturing an exhaust gas purification catalyst. The method for manufacturing an exhaust gas purification catalyst disclosed in this invention is used to manufacture an exhaust gas purification catalyst for purifying exhaust gas discharged from an internal combustion engine. The method includes: a step of preparing a catalyst layer forming slurry using the slurry manufacturing method disclosed in this invention; a step of coating the catalyst layer forming slurry onto a substrate; and a step of firing the substrate coated with the catalyst layer forming slurry. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the general steps of the slurry manufacturing method according to the first embodiment.

[0022] Figure 2 This is a schematic diagram illustrating the configuration of a slurry manufacturing apparatus according to one embodiment.

[0023] Figure 3 This is a flowchart illustrating the general steps of the slurry manufacturing method according to the second embodiment.

[0024] Figure 4 This is a flowchart illustrating the general steps of a method for manufacturing an exhaust gas purification catalyst according to one embodiment.

[0025] Figure 5 This is a perspective view schematically illustrating the structure of an exhaust purification catalyst according to one embodiment.

[0026] Figure 6 This is a schematic diagram showing a cross-section along the cylinder axis of an exhaust gas purification catalyst according to one embodiment.

[0027] Figure 7 This pertains to the average particle size (D) of the powder contained in the slurry manufacturing materials of Examples 1, 2, Comparative Example 1, and Reference Example. 50 A graph showing the relationship between grinding time and grinding time.

[0028] Figure 8 This pertains to the average particle size (D) of the powder contained in the slurry manufacturing materials of Example 3 and Comparative Example 2. 50 A graph showing the relationship between grinding time and grinding time. Detailed Implementation

[0029] The technology disclosed in this invention will now be described with appropriate reference to the accompanying drawings. Matters other than those specifically mentioned in this specification, and matters necessary for implementing this technology, can be grasped by those skilled in the art based on existing technology in the field. This technology can be implemented based on the content disclosed in this specification and technical knowledge in the field. Furthermore, in this specification, when a numerical range is described as "A to B (where A and B are arbitrary values)," it refers not only to "A or more but less than B," but also includes the meanings of "greater than A and less than B," "greater than A and less than B," and "A or more but less than B."

[0030] The slurry manufacturing method disclosed in this invention is a method for manufacturing a slurry containing a first inorganic oxide powder, a second inorganic oxide powder with an average particle size smaller than the first inorganic oxide powder, and a dispersion medium. One embodiment of the slurry manufacturing method disclosed in this invention includes: a material preparation step, which prepares a slurry manufacturing material containing the first inorganic oxide powder; a first grinding step, which uses a first grinding device having a first medium to grind the slurry manufacturing material until the average particle size of the powder contained in the slurry manufacturing material, based on laser diffraction / scattering, reaches 5 μm to 13 μm; and a second grinding step, which, after the first grinding step, uses a second grinding device having a second medium with an average particle size smaller than the first medium to grind the slurry manufacturing material until the average particle size of the powder contained in the slurry manufacturing material, based on laser diffraction / scattering, reaches 1 μm or less. It is further characterized in that the second inorganic oxide powder is mixed into the slurry manufacturing material before the first grinding step or after the first grinding step and before the second grinding step.

[0031] This technology allows for the first grinding process, where the powder is miniaturized to a size that is unlikely to clog the slits used to separate the media and powder in the second grinding apparatus, before the second grinding is performed. This improves grinding efficiency and reduces the total grinding time. Furthermore, by ending the first grinding process when the average particle size of the powder contained in the slurry manufacturing material reaches 5 μm to 13 μm based on laser diffraction / scattering, the process can switch to the second grinding process before the grinding efficiency of the first grinding process significantly decreases, thus further reducing the total grinding time.

[0032] (First Implementation)

[0033] Figure 1 This is a flowchart illustrating the general steps of the slurry manufacturing method according to the first embodiment. Such an embodiment includes a material preparation step S11, a first grinding step S12, and a second grinding step S13.

[0034] In the material preparation step S11, a slurry manufacturing material containing at least a first inorganic oxide powder is prepared. In the first embodiment, a slurry manufacturing material containing a first inorganic oxide powder and a second inorganic oxide powder is prepared. The first and second inorganic oxide powders prepared in this invention are raw materials for the powder components contained in the manufactured slurry.

[0035] The first inorganic oxide powder prepared in this invention (i.e., before grinding) uses a powder with an average particle size larger than the second inorganic oxide powder prepared (before grinding). The average particle size of this first inorganic oxide powder is not particularly limited; for example, it can be 15 μm to 150 μm, 20 μm to 80 μm, or 30 μm to 60 μm. In this specification, unless otherwise specified, "average particle size" refers to the cumulative 50% particle size (Dsize) of the volumetric particle size distribution obtained by measuring particle size distribution using a particle size distribution measuring device based on laser diffraction / scattering. 50 ).

[0036] The type of inorganic oxide powder is not particularly limited and can be appropriately changed according to the intended use of the slurry. For example, in the case of a slurry for forming a catalyst layer for exhaust gas purification catalysts, inorganic oxides capable of supporting catalyst metals or having oxygen storage capacity (OSC) (so-called OSC materials) are suitable. Examples of inorganic oxides capable of supporting catalyst metals include alumina (Al2O3), cerium dioxide (CeO2), zirconium oxide (ZrO2), silicon dioxide (SiO2), and titanium dioxide (TiO2). Rare earth metal oxides such as yttrium oxide (Y2O3), alkali metal oxides, and alkaline earth metal oxides can also be used. Examples of OSC materials include cerium dioxide-zirconia composite oxides (CZ or ZC composite oxides). In addition, OSC materials such as cerium dioxide and cerium dioxide-zirconia composite oxides, which contain trace amounts of oxides of other rare earth elements such as yttrium (Y), lanthanum (La), niobium (Nb), and praseodymium (Pr), are preferred.

[0037] The average particle size of the prepared second inorganic oxide powder (i.e., before grinding) can be smaller than that of the prepared first inorganic oxide powder. The average particle size of such a second inorganic oxide powder is not particularly limited; for example, it can be 1 μm to 50 μm, 3 μm to 30 μm, or 5 μm to 13 μm.

[0038] The type of the second inorganic oxide powder can be appropriately changed depending on the intended use of the slurry. For example, in the case of a slurry for forming a catalyst layer for an exhaust gas purification catalyst, it can be any of the powders exemplified by the first inorganic oxide powder described above. In a preferred example of a slurry for forming a catalyst layer for an exhaust gas purification catalyst, an inorganic oxide (e.g., alumina) capable of supporting catalyst metal can be used as the first inorganic oxide powder, and an OSC material (e.g., CZ composite oxide) can be used as the second inorganic oxide powder.

[0039] Materials for slurry production typically contain a dispersion medium. By including the dispersion medium, wet grinding can be performed as a process. For example, aqueous solvents such as water or deionized water are preferably used as such a dispersion medium. The proportion of the dispersion medium in the overall slurry production material can be, for example, 10 wt% to 90 wt%, preferably 25 wt% to 75 wt%, and more preferably 40 wt% to 60 wt%.

[0040] Furthermore, when the dispersion medium is set to 100 wt%, the proportion of the first inorganic oxide powder is not particularly limited; for example, it can be 10 wt% to 90 wt%, 20 wt% to 70 wt%, or 30 wt% to 50 wt%. Similarly, when the dispersion medium is set to 100 wt%, the proportion of the second inorganic oxide powder is not particularly limited; for example, it can be 10 wt% to 90 wt%, 20 wt% to 70 wt%, or 30 wt% to 50 wt%.

[0041] Materials used for slurry manufacturing may also contain other components. For example, in the case of a slurry for forming a catalyst layer for an exhaust gas purification catalyst, other components may include at least one catalyst metal, co-catalyst, binder, dispersant, thickener, etc., that functions as a catalyst capable of oxidizing or reducing exhaust gas components. Catalyst metals may include, for example, metals belonging to the platinum group elements such as palladium (Pd), rhodium (Rh), and platinum (Pt), or other metals that function as oxidation or reduction catalysts. Pd and Pt have excellent purification performance (oxidation purification capacity) for carbon monoxide and hydrocarbons, and Rh has excellent purification performance (reduction purification capacity) for NOx; therefore, these are particularly preferred catalyst metals for three-way catalysts. Catalyst metals may be mixed in powder form or mixed after calcination in the form of raw material compounds (e.g., water-soluble metal salts such as Pd nitrate and Rh nitrate) that generate catalyst metal particles. Barium sulfate may be an example of a co-catalyst component. Aluminum sol and silica sol may be examples of binders.

[0042] In the first grinding step S12, a first grinding apparatus having a first medium is used to perform grinding until the average particle size of the powder contained in the slurry manufacturing material reaches a predetermined range. This predetermined range is preferably 5 μm or more and 13 μm or less, more preferably 10 μm or more and 13 μm or less. When the average particle size of such powder is 13 μm or less, it is less likely that slit clogging will occur in the second grinding apparatus used in the second grinding step S13. Furthermore, from the viewpoint of shortening the total grinding time by performing grinding at an earlier point in time using a medium with a smaller average particle size, the average particle size of such powder is preferably 5 μm or more, more preferably 10 μm or more.

[0043] Examples of primary grinding devices include ball mills and bead mills, with bead mills being preferred. Compared to ball mills, bead mills have stronger pulverizing power, thus further reducing grinding time.

[0044] The average particle size of the first medium in the first grinding apparatus is preferably 1 mm to 10 mm, more preferably 1 mm to 3 mm, and even more preferably 1 mm to 2 mm. With such an average particle size, the powder contained in the slurry manufacturing material can be efficiently refined to a specified average particle size. The average particle size of the first medium can also be the diameter of a commercially available medium.

[0045] There are no particular limitations on the material used as the primary medium; examples include glass, alumina, zircon, zirconium oxide, and steel.

[0046] The grinding method of the first grinding device is not particularly limited, and examples include dry grinding and wet grinding, with wet grinding being preferred. When wet grinding is used, powder agglomeration can be suppressed, the powder finening efficiency can be improved, and thus the grinding time can be further shortened.

[0047] When the first grinding device is a bead mill, the type of stirring structure (stirring device) of the bead mill is not particularly limited, and examples include disc type, needle type, ring type, etc. In addition, the orientation of the grinding chamber (container) of the bead mill is not particularly limited, for example, it can be vertical or horizontal.

[0048] Examples of operating modes for the first grinding apparatus include cyclic operation, single-path operation, and batch operation, with cyclic operation being preferred. In cyclic operation, the first grinding can be performed while monitoring the average particle size of the powder contained in the slurry manufacturing material, allowing for switching from the first grinding to the second grinding at appropriate times. This further shortens the grinding time.

[0049] In the second grinding step S13, grinding is performed using a second grinding apparatus having a second medium until the average particle size of the powder contained in the slurry manufacturing material reaches 1 μm or less (e.g., 0.1 μm to 0.6 μm). The powder contained in the slurry manufacturing material supplied to the second grinding apparatus is refined to a specified average particle size range through the first grinding. Therefore, clogging of the slits in the second grinding apparatus can be suppressed.

[0050] Examples of second grinding devices include ball mills and bead mills, with bead mills being preferred. Compared to ball mills, bead mills have stronger pulverizing power, thus further reducing grinding time.

[0051] The average particle size of the second medium in the second grinding apparatus is preferably 0.1 mm to 0.5 mm. With such an average particle size, it is easy to refine the average particle size of the powder contained in the slurry manufacturing material to below 1 μm. The average particle size of the second medium can also be the diameter of commercially available media.

[0052] There are no particular limitations on the material used as a second medium; examples include glass, alumina, zircon, zirconia, and steel.

[0053] The grinding method of the second grinding device is not particularly limited, and examples include dry grinding and wet grinding, with wet grinding being preferred. Wet grinding suppresses powder agglomeration and improves powder fineness efficiency, thus further shortening the grinding time. Furthermore, by using wet grinding in both the first and second grinding devices, the first and second grinding processes can be performed continuously, thereby shortening the slurry preparation time.

[0054] When the second grinding device is a bead mill, there is no particular limitation on the type of stirring structure (stirring) of the bead mill, and examples include disc type, needle type, ring type, etc. In addition, there is no particular limitation on the orientation of the grinding chamber (container) of the bead mill, for example, it can be vertical or horizontal.

[0055] Examples of operating modes for the second grinding device include cyclic operation, single-path operation, and batch operation, with cyclic operation being preferred. In cyclic operation, continuous grinding can be performed while monitoring the average particle size of the powder contained in the slurry manufacturing material. This prevents over-grinding and thus further shortens the grinding time.

[0056] The manufacturing method of one embodiment has been described above. The manufacturing method disclosed in this invention may include other steps at any stage. For example, after the second grinding step S13, any component may be mixed into the manufactured slurry. Examples of such components include binders, antioxidants, dispersants, thickeners, etc. Furthermore, in the case of a slurry for forming a catalyst layer for an exhaust gas purification catalyst, a raw material compound that generates catalyst metal particles, a co-catalyst, etc., may be mixed in after firing.

[0057] Figure 2 This is a schematic diagram illustrating the configuration of a slurry manufacturing apparatus according to one embodiment. This technology can be implemented, for example, using the slurry manufacturing apparatus 100 shown. In this embodiment, the slurry manufacturing apparatus 100 includes a slurry tank 110, a pump 120, a first grinding device 140, and a second grinding device 150. The slurry manufacturing apparatus 100 of this embodiment also includes a switching assembly 130. The slurry tank 110 is connected to the pump 120 via a pipe 131. The pump 120 is connected to the switching assembly 130 via a pipe 132. The switching assembly 130 is connected to the first grinding device 140 via a pipe 133, and the first grinding device 140 is connected to the slurry tank 110 via a pipe 134. Thus, the slurry tank 110 and the first grinding device 140 are connected in a cyclical manner, enabling the cyclical operation of the first grinding device 140. Furthermore, as shown in the diagram, the switching assembly 130 is connected to the second grinding device 150 via a pipe 135, and the second grinding device 150 is connected to the slurry tank 110 via a pipe 136. Thus, the slurry tank 110 and the second grinding device 150 are connected in a cyclical manner, enabling the second grinding device 150 to operate cyclically. The switching assembly 130 is configured to switch between the connection to pipe 133 and the connection to pipe 135, allowing switching between the slurry tank 110 and any one of the first grinding device 140 or the second grinding device 150. Figure 2 The arrows in the diagram indicate the direction in which the material 30 for slurry manufacturing can flow.

[0058] The slurry tank 110 is a tank used to store the slurry manufacturing material 30. The slurry tank 110 has a stirring blade 112, which is capable of stirring the slurry manufacturing material in the slurry tank 110.

[0059] Pump 120 functions as a power source to circulate the slurry preparation material 30, enabling the slurry tank 110 to circulate with either the first grinding device 140 or the second grinding device 150. In this embodiment, one pump 120 is provided before the switching assembly 130, but for example, one pump could be provided between the switching assembly 130 and the first grinding device 140, and another pump could be provided between the switching assembly 130 and the second grinding device 150.

[0060] The switching component 130 is an arbitrary element and not a necessary component. By having the switching component 130, the switching between the first grinding and the second grinding becomes smooth, resulting in a shorter grinding time. For example, a switching valve can be used as the switching component 130. Alternatively, the switching component 130 can be replaced by manually changing the pipeline connection, altering the circulation path between the slurry tank 110 and the first grinding device 140 to the circulation path with the second grinding device 150.

[0061] In this embodiment, two grinding devices, a first grinding device 140 and a second grinding device 150, are connected in series. This allows for the continuous execution of the first grinding step S12 and the second grinding step S13, thus helping to shorten the slurry preparation time. The first grinding device 140 is the device used in the first grinding step S12, and can be any device identical to the aforementioned device. Similarly, the second grinding device 150 is the device used in the second grinding step S13, and can be any device identical to the aforementioned device.

[0062] In the slurry manufacturing apparatus 100, the average particle size of the powder contained in the slurry manufacturing material can be monitored while performing the first grinding step S12 or the second grinding step S13. For example, a portion of the slurry manufacturing material in the slurry tank 110 can be collected appropriately, or the particle size can be monitored online.

[0063] (Second Implementation)

[0064] Figure 3 This is a flowchart illustrating the general steps of the slurry manufacturing method according to the second embodiment. The second embodiment includes a material preparation step S21, a first grinding step S22, a second inorganic oxide powder addition step S23, and a second grinding step S24. In the first embodiment described above, in the material preparation step S11 before the first grinding step S12, a slurry manufacturing material containing first inorganic oxide powder and second inorganic oxide powder is prepared. In the second embodiment, in the material preparation step S21, the slurry manufacturing material containing first inorganic oxide powder is prepared, and after the first grinding step S22 and before the second grinding step S24, the second inorganic oxide powder is mixed into the slurry manufacturing material. This prevents the excessive refinement of the second inorganic oxide powder, which has an average particle size smaller than the first inorganic oxide powder. In the second embodiment, matters other than the second inorganic oxide powder in the material preparation step S21 can be the same as in the material preparation step S11 described above. Furthermore, the first grinding step S22 can be the same as the first grinding step S12 described above, and the second grinding step S24 can be the same as the second grinding step S13 described above.

[0065] In the second embodiment, since the second inorganic oxide powder is not subjected to the first grinding, from the viewpoint of preventing the slit of the second grinding device from becoming clogged during the second grinding, the average particle size of the second inorganic oxide powder is preferably 5 μm to 13 μm.

[0066] The slurry manufacturing method disclosed in this invention is suitable for manufacturing a slurry used as a catalyst layer forming slurry for an exhaust gas purification catalyst used to purify exhaust gas discharged from an internal combustion engine. Therefore, this invention provides a method for manufacturing an exhaust gas purification catalyst including the slurry manufacturing method disclosed in this invention.

[0067] Figure 4 This is a flowchart illustrating the general steps of a method for manufacturing an exhaust gas purification catalyst according to one embodiment. The method for manufacturing an exhaust gas purification catalyst disclosed in this invention includes a step of preparing a catalyst layer forming slurry (hereinafter also referred to as "slurry preparation step S31"), a step of coating the catalyst layer forming slurry onto a substrate (hereinafter also referred to as "coating step S32"), and a step of firing the substrate coated with the catalyst layer forming slurry (hereinafter also referred to as "firing step S34"). Furthermore, as... Figure 4 As shown, a drying step S33 may be included, which involves drying the substrate coated with the slurry for forming the catalyst layer. Furthermore, the exhaust gas purification catalyst disclosed in this invention may include other steps at any stage.

[0068] The slurry preparation step S31 only requires preparing a slurry for catalyst layer formation using the slurry manufacturing method disclosed in this invention. The slurry for catalyst layer formation contains powder with an average particle size of less than 1 μm, and is therefore typically suitable for forming a catalyst layer inside a porous partition wall, and can also be used to form a catalyst layer on the surface of a partition wall.

[0069] In the coating process S32, a catalyst layer is coated onto the substrate that forms the skeleton of the catalyst for exhaust gas purification to form a slurry. Figure 5 This is a perspective view schematically illustrating the structure of an exhaust purification catalyst according to one embodiment. Figure 6 This is a schematic diagram showing a cross-section along the cylinder axis of the exhaust gas purification catalyst 1 according to one embodiment. The symbol A in the diagram indicates the exhaust gas flow direction A. The substrate prepared for this invention can be, for example... Figure 5The substrate 10 is a cylindrical material that extends along the exhaust flow direction A, as shown. The substrate 10 may have a honeycomb structure with multiple chambers that form flow paths for fluids (e.g., exhaust). The shape of the substrate is not limited to a cylindrical shape; it can also be an elliptical cylinder, a polygonal cylinder, etc. Furthermore, the overall length and volume of the substrate 10 are not particularly limited and can be appropriately varied according to the performance and size of the internal combustion engine. Additionally, the substrate 10 is not particularly limited and can use existing known raw materials that are applicable to the substrates of exhaust purification catalysts. Examples of such raw materials for the substrate 10 include high heat-resistant materials such as cordierite, silicon carbide (SiC), aluminum titanate ceramics, and stainless steel alloys. For example, cordierite, due to its excellent durability against thermal shock, is particularly suitable as a raw material for the substrate of exhaust purification catalysts for gasoline engines that readily supply high-temperature exhaust.

[0070] Substrate 10 can be, for example, Figure 6 The substrate exhibiting wall flow characteristics is shown below. Specifically, as shown... Figure 5 and 6 As shown, the substrate 10 has an inlet chamber 12 that opens only at its end on the exhaust inflow side, an outlet chamber 14 that opens only at its end on the exhaust outflow side, and a porous partition wall 16 that separates the inlet chamber 12 and the outlet chamber 14. Specifically, the inlet chamber 12 is a gas flow path that opens at its end on the exhaust inflow side and is blocked at its end on the exhaust outflow side by a sealing portion 12a. On the other hand, the outlet chamber 14 is a gas flow path that is blocked at its end on the exhaust inflow side by a sealing portion 14a and opens at its end on the exhaust outflow side. Furthermore, the partition wall 16 is a partition material formed with a plurality of fine holes through which exhaust gas can pass. This partition wall 16 has a plurality of fine holes that connect the inlet chamber 12 and the outlet chamber 14. Wherein, in Figure 5 In the exhaust gas purification catalyst 1 shown, the inlet chamber 12 (outlet chamber 14) of the cross-section perpendicular to the extending direction (cylinder axis direction X) of the partition wall 16 has a square shape. However, the shape of this inlet chamber (outlet chamber) of the cross-section perpendicular to the extending direction is not limited to a square, and various shapes can be adopted. For example, it can be a parallelogram, rectangle, trapezoid or other quadrilaterals, triangle, other polygons (e.g., hexagon, octagon), circle or other geometric shapes.

[0071] The partition wall 16 of the substrate 10 is preferably formed with consideration for the collection performance of particulate matter (PM) and pressure loss suppression performance. For example, the thickness of the partition wall 16 is preferably about 100 μm to 350 μm. In addition, the porosity of the partition wall 16 is preferably about 20 vol% to 70 vol%, more preferably 50 vol% to 70 vol%. Furthermore, from the viewpoint of ensuring sufficient air permeability of the partition wall 16 and suppressing the increase of pressure loss, the average pore diameter is preferably 8 μm or more, more preferably 12 μm or more, and even more preferably 15 μm or more. On the other hand, from the viewpoint of ensuring appropriate PM collection performance, the upper limit of the average pore diameter is preferably 30 μm or less, more preferably 25 μm or less, and even more preferably 20 μm or less. Here, the porosity and average pore diameter of the partition wall 16 refer to values ​​measured using the mercury infiltration method.

[0072] In addition, the substrate is not limited to wall flow type, but can also be a so-called linear flow type substrate composed of multiple through holes.

[0073] The method for coating the catalyst layer forming slurry onto the substrate 10 can be the same as that used in existing coating techniques, such as wash coating and suction coating. In the wash coating method, after immersing the substrate 10 in the catalyst layer forming slurry, the substrate 10 is removed, and excess slurry is removed by blowing air, thereby coating the catalyst layer forming slurry. In the suction coating method, the catalyst layer forming slurry is supplied to one end of the substrate 10 and then drawn in from the other end, introducing the slurry into the interior of the substrate 10, thereby coating the catalyst layer forming slurry. In this case, the configuration of the formed catalyst layer 20 can be adjusted by adjusting the range of immersion in the catalyst layer forming slurry and adjusting the suction time.

[0074] In addition, the thickness of the catalyst layer can be adjusted appropriately according to the viscosity of the slurry used to form the catalyst layer. For example, a commercially available cone-plate viscometer can be used at a rotation speed of 1–100 rpm, room temperature (25°C), and a shear rate of 380 s. -1 Under the given conditions, a viscosity of approximately 10 mPa to 1000 mPa is appropriate.

[0075] The drying process S33 can be carried out under the same conditions as drying using existing technologies, without any particular limitation. For example, drying can be carried out at a temperature of 50°C to 200°C for about 1 to 30 minutes.

[0076] The firing process S34 can be carried out under the same conditions as firing using existing technology, without any particular limitation. For example, it can be fired at a temperature of 400°C to 1000°C for about 30 seconds to 5 hours.

[0077] In this way, it is possible to manufacture, for example Figure 6 Catalyst 1 for exhaust purification, as shown. In Figure 6 In the exhaust gas purification catalyst 1 shown, a catalyst layer 20 is formed inside the partition wall 16, extending along the entire length of the partition wall 16 in the axial direction X and the thickness of the partition wall 16 orthogonal to the axial direction X. However, this is merely an example, and the exhaust gas purification catalyst manufactured is not limited to this. For example, the catalyst layer 20 may also be formed on the surface of the partition wall 16. Furthermore, the catalyst layer 20 may be formed at a predetermined ratio (e.g., 10% to 90%) relative to the entire length of the partition wall 16 in the axial direction X. Moreover, the exhaust gas purification catalyst 1 may also have a second catalyst layer at a different location than the catalyst layer 20, having a different composition.

[0078] The exhaust gas purification catalyst 1 can be used in various applications depending on the composition of the catalyst layer 20, such as as a three-way catalyst, NOx catalyst, oxidation catalyst, reduction (SCR) catalyst, and ammonia slip catalyst (ASC).

[0079] The following describes several embodiments of the technology disclosed in this invention, but it is not intended to limit the technology disclosed in this invention to the technology shown in such embodiments.

[0080] (Experiment 1)

[0081] [Preparation of materials for slurry manufacturing]

[0082] Alumina powder (average particle size: approximately 32 μm), cerium dioxide-zirconia composite oxide (CZ composite oxide) powder (average particle size: approximately 12.8 μm), Pd nitric acid, and water were mixed to prepare a slurry manufacturing material. This slurry manufacturing material was prepared by mass ratio of alumina powder:CZ composite oxide powder:nitric acid Rh:water = 20:23:2:55. The average particle size (D0) of the powder contained in this slurry manufacturing material was determined using a particle size distribution measuring device based on laser diffraction / scattering. 50 The results obtained are shown in Table 1 as the initial particle size. Using this slurry manufacturing material, the grinding processes of Examples 1 and 2, Comparative Example 1, and Reference Example were performed. The slurry manufactured contained an average particle size (D...) 50 A slurry containing powder with a particle size of less than 0.6 μm.

[0083] <Example 1>

[0084] A first bead mill with zirconia beads (first media) of 1 mm diameter is prepared as the first grinding apparatus. A second bead mill with zirconia beads (second media) of 0.5 mm diameter is prepared as the second grinding apparatus. A slurry tank filled with the prepared slurry manufacturing material is then prepared. This slurry tank is connected to the first bead mill in a manner that allows the slurry manufacturing material to circulate. Similarly, the slurry tank is connected to the second bead mill in a manner that allows the slurry manufacturing material to circulate. A switching valve is configured such that the circulation paths between the slurry tank and the first bead mill, and between the slurry tank and the second bead mill, can be switched. First, the slurry manufacturing material is supplied from the slurry tank to the first bead mill, and the first grinding is performed. The first grinding is performed until the average particle size (D) of the powder contained in the slurry manufacturing material reaches a certain value. 50 Once the particle size reaches 12.88 μm, the cycle path is switched to the second bead mill for a second grinding. The second grinding is performed until the average particle size (D) of the powder contained in the material for slurry preparation is reached. 50 The particle size was reduced to 0.6 μm. Thus, a slurry was prepared. A portion of the slurry-making material was recovered during the grinding process, and the average particle size of the powder contained in the slurry-making material was determined using a particle size distribution measuring device based on laser diffraction / scattering. The average particle size (D...) was then... 50 The graph showing the relationship between grinding time and grinding time is shown in [the figure]. Figure 7 For the examples described later, the results will also be presented in the same way. Figure 7 Additionally, the grinding conditions, the particle size based on particle size distribution of the powder contained in the slurry manufacturing material at the end of the first grinding, and the average particle size (D) at the end of the second grinding are considered. 50 The results are shown in Table 1. Similarly, for the examples described later, the grinding conditions and results are also shown in Table 1.

[0085] <Example 2>

[0086] In Example 1, the time point for switching from the first grinding to the second grinding was changed to the average particle size (D) of the powder contained in the slurry manufacturing material. 50 When the thickness reaches 5μm, the same procedure is followed to prepare the slurry.

[0087] <Comparative Example 1>

[0088] In Example 1, the time point for switching from the first grinding to the second grinding was changed to the average particle size (D) of the powder contained in the slurry manufacturing material. 50 When the diameter reached 15.12 μm, the same procedure was followed. However, the second bead mill experienced slit blockage, thus interrupting the second grinding process.

[0089] <Reference Example>

[0090] Using the first bead mill, grinding is carried out until the average particle size (D) of the powder contained in the material for slurry preparation is reached. 50 The slurry was prepared by reaching a diameter of 0.5 μm. That is, in the reference example, the slurry was prepared using a bead mill with zirconia beads having a diameter of 1 mm.

[0091] [Table 1]

[0092]

[0093] like Figure 7 As shown in Table 1, it can be seen that compared to the reference example which uses a single bead mill with 1mm beads to grind until a specified average particle size (here, 0.5mm) is achieved, Examples 1 and 2, which use two bead mills—a first bead mill with 1mm beads and a second bead mill with 0.5mm beads—significantly shorten the total grinding time. However, as in Comparative Example 1, when switching from the first grinding to the second grinding, if the average particle size of the powder in the slurry manufacturing material is too large, the second bead mill experiences slit blockage. Therefore, as shown in Examples 1 and 2, it can be seen that the appropriate time to switch from the first grinding to the second grinding is when grinding is performed using the first grinding mill until the average particle size of the powder in the slurry manufacturing material reaches 5μm to 13μm.

[0094] (Experiment 2)

[0095] [Preparation of materials for slurry manufacturing]

[0096] Alumina powder (average particle size: approximately 32 μm) was mixed with water to prepare a slurry material. This slurry material was prepared by mass ratio of alumina powder to water = 20:55. The average particle size (D) of the powder contained in this slurry material was measured using a particle size distribution measuring device based on laser diffraction / scattering. 50 The results obtained are shown in Table 2 as the initial particle size. Using this slurry manufacturing material, the grinding processes of Example 3 and Comparative Example 2 were performed. The manufactured slurry contained an average particle size (D...) 50 A slurry containing powder with a particle size of less than 0.6 μm.

[0097] <Example 3>

[0098] Prepare a first and second bead mill identical to those in Example 1, and a slurry tank filled with the prepared slurry manufacturing material. Connect the slurry tank to the first bead mill in a manner that allows the slurry manufacturing material to circulate. Similarly, connect the slurry tank to the second bead mill in a manner that allows the filled slurry manufacturing material to circulate. The slurry tank is configured to switch the circulation path with the first bead mill and the circulation path with the second bead mill at desired time points. First, supply the slurry manufacturing material from the slurry tank to the first bead mill and perform a first grinding. Perform the first grinding until the average particle size (D) of the powder contained in the slurry manufacturing material reaches a certain level. 50 The particle size reached 10.40 μm. Then, CZ composite oxide powder (average particle size: approximately 12.8 μm) was added to the first-ground slurry material, resulting in a mass ratio of alumina powder:CZ composite oxide powder:water = 20:25:55. The average particle size (D) of the powder contained in the slurry material after the addition of CZ oxide was... 50 The particle size (D) was 11.76 μm. Next, the cycle path was switched to the second bead mill for a second grinding. The second grinding was performed until the average particle size (D) of the powder contained in the slurry-making material reached the specified value. 50 The particle size was reduced to 0.6 μm. Thus, a slurry was prepared. A portion of the slurry-making material was recovered during the grinding process, and the average particle size of the powder contained in the slurry-making material was determined using a particle size distribution measuring device based on laser diffraction / scattering. The average particle size (D...) was then... 50 The graph showing the relationship between grinding time and grinding time is shown in [the figure]. Figure 8 Additionally, in Figure 8 In the graph, two points are plotted at a grinding time of 34 minutes, indicating the mixing of CZ composite oxides before and after the mixing process. The points after mixing show an increase in average particle size. Additionally, the particle size based on particle size distribution of the powder contained in the slurry material at the end of the first grinding process (before mixing of CZ composite oxides) and the average particle size at the end of the second grinding process (D) are also plotted. 50 The results are shown in Table 2.

[0099] <Comparative Example 2>

[0100] As in the reference example, grinding is performed using only the first bead mill. Grinding continues until the average particle size (D) of the powder contained in the material used to manufacture the slurry is reached. 50 After reaching a particle size of 9.8 μm, CZ composite oxide is added to the slurry preparation material, such that the mass ratio of alumina powder:CZ composite oxide:water is 20:25:55. Then, grinding is continued using a first bead mill until the average particle size (D) of the powder contained in the slurry preparation material is achieved. 50 The thickness reached 0.58 μm. The results are shown below. Figure 8See Table 2. In Comparative Example 2, the grinding process using a first bead mill after mixing the CZ composite oxide powder is referred to as the second grinding process.

[0101] [Table 2]

[0102]

[0103] From Table 2 and Figure 8 It can be seen that even when CZ composite oxides with an average particle size smaller than alumina powder are mixed after the first grinding, the total grinding time is shortened in the second grinding by using beads smaller than those used in the first grinding.

[0104] The above provides a detailed description of specific examples of the technology disclosed in this invention, but these are merely examples and do not limit the scope of protection claimed. The technology described in the scope of protection includes technologies modified or altered from the specific examples illustrated above.

Claims

1. A method for manufacturing a slurry, characterized in that: The slurry contains a first inorganic oxide powder, a second inorganic oxide powder, and a dispersion medium. The manufacturing method includes: The material preparation process involves preparing materials for manufacturing a slurry containing the first inorganic oxide powder. The first grinding step involves using a first grinding apparatus with a first medium to grind the slurry manufacturing material until the average particle size of the powder contained in the slurry manufacturing material, based on laser diffraction / scattering, reaches 5 μm to 13 μm; and The second grinding step, following the first grinding step, involves using a second grinding apparatus with a second medium having an average particle size smaller than the first medium to grind the slurry manufacturing material until the average particle size of the powder contained in the slurry manufacturing material, based on laser diffraction / scattering methods, reaches below 1 μm. The manufacturing method further includes the step of mixing the second inorganic oxide powder into the slurry manufacturing material before the first grinding step or after the first grinding step and before the second grinding step, wherein the average particle size of the second inorganic oxide is smaller than the average particle size of the first inorganic oxide powder before the first grinding step.

2. The manufacturing method as described in claim 1, characterized in that: The average particle size of the first medium is between 1 mm and 10 mm.

3. The manufacturing method as described in claim 1 or 2, characterized in that: The average particle size of the second medium is between 0.1 mm and 0.5 mm.

4. The manufacturing method as described in claim 1 or 2, characterized in that: Before mixing the second inorganic oxide powder, the average particle size of the second inorganic oxide powder based on laser diffraction / scattering method is between 5 μm and 13 μm.

5. The manufacturing method as described in claim 1 or 2, characterized in that: The pulverization method implemented in the first grinding process and the second grinding process is wet pulverization.

6. The manufacturing method as described in claim 1 or 2, characterized in that: The second inorganic oxide powder is mixed before the first grinding process.

7. The manufacturing method as described in claim 1 or 2, characterized in that: Further prepare a slurry tank that can be connected to the first grinding device in a circulating manner, and grind the slurry manufacturing material while circulating it between the first grinding device and the slurry tank.

8. The manufacturing method as described in claim 7, characterized in that: The slurry tank and the second grinding device are connected in a circulatory manner, and the slurry manufacturing material is ground while circulating between the second grinding device and the slurry tank.

9. The manufacturing method as described in claim 1 or 2, characterized in that: The slurry manufacturing material contains at least one catalyst metal that functions as a catalyst capable of oxidizing or reducing exhaust components.

10. A method for manufacturing an exhaust gas purification catalyst, wherein the exhaust gas purification catalyst purifies exhaust gas discharged from an internal combustion engine, the method being characterized by comprising: The step of preparing a slurry for forming a catalyst layer using the manufacturing method of claim 9; The process of forming the catalyst layer by coating a slurry onto a substrate; and The process of firing a substrate coated with the slurry for forming the catalyst layer.

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