Exhaust gas purification catalyst

Abstract

The purpose of the present invention is to provide an exhaust gas purification catalyst capable of improving exhaust gas diffusivity and reactivity with respect to diffused exhaust gas, and to provide an exhaust gas purification catalyst (1) provided with a metal honeycomb substrate (10) and a catalyst layer (20) provided on the metal honeycomb substrate (10), the catalyst layer (20) contains a noble metal element, Ce-based oxide particles, and Ce-Zr-based composite oxide particles, and in a logarithmic differential pore volume distribution curve of the catalyst layer (20) obtained by a mercury intrusion method, a first peak value is present in the range of a pore diameter of 5-15 nm inclusive, a second peak value is present in the range of a pore diameter of 200-3200 nm inclusive, the first peak value is 0.060 mL / g or more, the second peak value is not less than 0.060 mL / g, and the third peak value is not less than 0.060 mL / g. The second peak value is 0.018 mL / g or more.

Description

Technical Field

[0001] This invention relates to catalysts for waste gas purification. Background Technology

[0002] Exhaust gases from internal combustion engines in automobiles, motorcycles, and other vehicles contain harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). To purify these harmful components and render them harmless, catalysts containing precious metals such as Pt, Pd, and Rh are used for exhaust gas purification. Pt and Pd primarily participate in the oxidation purification of HC and CO, while Rh primarily participates in the reduction purification of NOx.

[0003] For exhaust gas purification catalysts, reactions under high SV (Space Velocity) conditions are required. Therefore, improving the exhaust gas diffusion of the catalyst bed is important. In particular, motorized two-wheeled vehicles tend to operate under relatively high SV conditions compared to motorized four-wheeled vehicles, making the reduction of emissions caused by unpurified exhaust gas passing through a key challenge.

[0004] Patent Document 1 discloses a catalyst for purifying waste gas, which improves the diffuseability of waste gas as a catalyst layer. The catalyst layer comprises a substrate and a catalyst layer disposed on the substrate, wherein the catalyst layer satisfies the following conditions:

[0005] (1) In the pore distribution curve measured by mercury porosimeter, there is a peak with the largest pore capacity in the range of pore diameter above 1 μm and below 10 μm.

[0006] (2) In the electron microscope images (1000x magnification) of the surface of the catalyst layer, when calculating the area of ​​the multiple pores contained in the electron microscope images, the standard deviation of the area of ​​the multiple pores is 30 μm. 2 the following.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2021-53604 Summary of the Invention

[0010] The problem the invention aims to solve

[0011] To improve the performance of catalysts used for waste gas purification, catalysts for waste gas purification are required that can improve the diffuseability of waste gas and the reactivity of diffused waste gas.

[0012] The purpose of this invention is to provide a catalyst for purifying waste gas that can improve the diffuseability of waste gas and the reactivity of the diffused waste gas.

[0013] Solution for solving the problem

[0014] The present invention provides the following technical solution.

[0015] [1] A catalyst for purifying waste gas, comprising: a metal honeycomb substrate and a catalyst layer disposed on the metal honeycomb substrate.

[0016] The catalyst layer described above contains noble metal elements, Ce-based oxide particles, and Ce-Zr composite oxide particles.

[0017] In the logarithmic differential pore volume distribution curve of the catalyst layer obtained by mercury intrusion porosimetry, a first peak exists in the range of pore size ≥ 5 nm and ≤ 15 nm, and a second peak exists in the range of pore size ≥ 200 nm and ≤ 3200 nm.

[0018] The first peak value mentioned above is above 0.060 mL / g.

[0019] The second peak value mentioned above is above 0.018 mL / g.

[0020] [2] According to the catalyst for purifying exhaust gas described in [1], the second peak value is present in the range of pore size above 200 nm and below 1600 nm.

[0021] [3] The catalyst for purifying exhaust gas according to [1] or [2], wherein the first peak value is 0.075 mL / g or more and the second peak value is 0.030 mL / g or more.

[0022] [4] The catalyst for purifying exhaust gas according to any one of [1] to [3], wherein the specific surface area of ​​the catalyst layer is 70 m². 2 / g or more and 200m 2 / g or less.

[0023] [5] The catalyst for purifying exhaust gas according to any one of [1] to [4], wherein the mass of the catalyst layer per unit volume of the portion of the metal honeycomb substrate in which the catalyst layer is disposed is 100 g / L or more and 300 g / L or less.

[0024] [6] The catalyst for purifying exhaust gas according to any one of [1] to [5], wherein the catalyst layer comprises Al-based oxide particles.

[0025] [7] According to the catalyst for purifying exhaust gas described in [6], the median particle size of the Al oxide particles is 15 μm or more and 30 μm or less.

[0026] [8] The catalyst for purifying waste gas according to any one of [1] to [5], wherein,

[0027] The catalyst layer described above comprises a first layer disposed on the metal honeycomb substrate and a second layer disposed on the first layer.

[0028] At least a portion of the aforementioned Ce-based oxide particles and at least a portion of the aforementioned Ce-Zr-based composite oxide particles are contained in the aforementioned first layer.

[0029] At least a portion of the aforementioned precious metal elements are contained in the second layer.

[0030] [9] According to the catalyst for purifying exhaust gas described in [8], the content of the Ce-based oxide particles in the first layer is 10% by mass or more and 80% by mass or less, based on the total mass of the Ce-based oxide particles and the Ce-Zr composite oxide particles in the first layer.

[0031]

[10] According to the catalyst for purifying exhaust gas described in [9], the content of the Ce-based oxide particles in the first layer is 20% by mass or more and 70% by mass or less, based on the total mass of the Ce-based oxide particles and the Ce-Zr composite oxide particles in the first layer.

[0032]

[11] The catalyst for purifying waste gas according to any one of [8] to

[10] , wherein,

[0033] The catalyst layer described above contains Al-based oxide particles.

[0034] At least a portion of the aforementioned Al-based oxide particles are contained in the aforementioned first layer.

[0035]

[12] According to the catalyst for purifying exhaust gas described in

[11] , the median particle size of the Al oxide particles is 15 μm or more and 30 μm or less.

[0036]

[13] The catalyst for purifying exhaust gas according to any one of [8] to

[12] , wherein the mass of the first layer per unit volume of the portion of the metal honeycomb substrate in which the first layer is disposed is 100 g / L or more and 180 g / L or less.

[0037] The effects of the invention

[0038] According to the present invention, a catalyst for purifying exhaust gas is provided, which can improve the diffuseability of exhaust gas and the reactivity with diffused exhaust gas. Attached Figure Description

[0039] Figure 1 This is a partial cross-sectional view showing the state of a catalyst for exhaust gas purification disposed in the exhaust path of an internal combustion engine according to one embodiment of the present invention.

[0040] Figure 2 yes Figure 1 AA-line cross-section view.

[0041] Figure 3 yes Figure 2 An enlarged view of the region indicated by the symbol R in the diagram.

[0042] Figure 4 yes Figure 1 BB line cross-section. Detailed Implementation

[0043] The following is based on Figures 1-4 A catalyst 1 for purifying exhaust gas (hereinafter referred to as "catalyst 1") according to one embodiment of the present invention will be described.

[0044] like Figure 1 As shown, catalyst 1 is disposed in the exhaust passage within the exhaust pipe P of an internal combustion engine. The internal combustion engine is, for example, a gasoline engine. Exhaust gas emitted from the internal combustion engine flows from one end of the exhaust pipe P to the other in the exhaust passage within the exhaust pipe P, and is purified by catalyst 1 disposed within the exhaust pipe P. In the accompanying drawings, the direction of exhaust gas flow is indicated by the symbol X. In this specification, the upstream side of the exhaust gas flow direction X is sometimes referred to as the "exhaust gas inflow side" or "upstream side," and the downstream side of the exhaust gas flow direction X is sometimes referred to as the "exhaust gas outflow side" or "downstream side."

[0045] Other exhaust gas purification catalysts can also be configured in the exhaust passage of the exhaust pipe P on the upstream or downstream side of the catalyst 1.

[0046] like Figures 2-4 As shown, the catalyst 1 includes a metal honeycomb substrate 10 (hereinafter referred to as "substrate 10") and a first layer 21 disposed on the substrate 10.

[0047] Substrate

[0048] The substrate 10 will be described below.

[0049] The substrate 10 is a honeycomb structure made of metal material.

[0050] The metallic material constituting the substrate 10 can be appropriately selected from known metallic materials. Examples of materials constituting the substrate 10 include alloys such as stainless steel.

[0051] like Figures 2-4 As shown, the substrate 10 has a cylindrical portion 11, a partition wall portion 12 disposed within the cylindrical portion 11, and a chamber 13 partitioned by the partition wall portion 12.

[0052] like Figure 2As shown, the cylindrical portion 11 defines the shape of the substrate 10, and the axial direction of the cylindrical portion 11 is aligned with the axial direction of the substrate 10. For example... Figure 2 As shown, the cylindrical part 11 is cylindrical, but it can also be other shapes such as elliptical cylindrical or polygonal cylindrical.

[0053] like Figures 2-4 As shown, there is a partition wall 12 between adjacent chambers 13, and the adjacent chambers 13 are separated by the partition wall 12. The thickness of the partition wall 12 is, for example, 20 μm or more and 1500 μm or less.

[0054] like Figure 4 As shown, chamber 13 extends along the exhaust gas flow direction X and has an end on the exhaust gas inflow side and an end on the exhaust gas outflow side.

[0055] like Figure 4 As shown, both the exhaust gas inlet end and the exhaust gas outlet end of chamber 13 are open. Therefore, exhaust gas flowing in from the exhaust gas inlet end (opening) of chamber 13 flows out from the exhaust gas outlet end (opening) of chamber 13. This configuration is called a flow-through type.

[0056] like Figure 2 and Figure 3 As shown, the top view shape of the exhaust gas inflow end (opening) of chamber 13 is quadrilateral, but it can also be hexagonal, octagonal, or other shapes. The top view shape of the exhaust gas outflow end (opening) of chamber 13 is the same.

[0057] The chamber density per square inch of substrate 10 is, for example, more than 100 chambers and less than 1000 chambers. The chamber density per square inch of substrate 10 refers to the total number of chambers 13 per square inch in a cross section obtained by cutting substrate 10 with a plane perpendicular to the exhaust gas flow direction X.

[0058] The volume of the substrate 10 is, for example, 0.1L or more and 20L or less. The volume of the substrate 10 refers to its apparent volume. For example, if the substrate 10 is cylindrical, and the outer diameter of the metal honeycomb substrate 10 is set to 2r, and the length of the substrate 10 is set to L... 10 The volume of substrate 10 is given by the formula: Volume of substrate 10 = π × r 2 ×L 10 express.

[0059] Catalyst Layer

[0060] The catalyst layer 20 will be described below.

[0061] like Figure 3 and Figure 4As shown, the catalyst layer 20 is disposed on the chamber 13 side surface of the partition wall portion 12. "The chamber 13 side surface of the partition wall portion 12" refers to the outer surface of the partition wall portion 12 extending along the exhaust gas flow direction X. The catalyst layer 20 can be disposed directly on the chamber 13 side surface of the partition wall portion 12, or it can be disposed in between other layers, but it is usually disposed directly on the chamber 13 side surface of the partition wall portion 12.

[0062] like Figure 4 As shown, the catalyst layer 20 extends along the exhaust gas flow direction X from the end of the partition wall 12 on the exhaust gas inflow side to the end of the partition wall 12 on the exhaust gas outflow side. The catalyst layer 20 may extend along the exhaust gas flow direction X from the end of the partition wall 12 on the exhaust gas inflow side without reaching the end of the partition wall 12 on the exhaust gas outflow side, or it may extend in a direction opposite to the exhaust gas flow direction X from the end of the partition wall 12 on the exhaust gas outflow side without reaching the end of the partition wall 12 on the exhaust gas inflow side.

[0063] <First peak and second peak>

[0064] In the logarithmic differential pore volume distribution curve of catalyst layer 20, there is a first peak in the range of pore size above 5 nm and below 15 nm, and a second peak in the range of pore size above 200 nm and below 3200 nm.

[0065] In the logarithmic differential pore volume distribution curve of catalyst layer 20, if there is a maximum value in the range of pore size above 5 nm and below 15 nm (that is, if there is a peak in the logarithmic differential pore volume distribution curve of catalyst layer 20 in the range of pore size above 5 nm and below 15 nm), this maximum value is equivalent to the "first peak value".

[0066] In the logarithmic differential pore volume distribution curve of catalyst layer 20, if there are more than two maxima in the range of pore size above 5 nm and below 15 nm (i.e., if there are more than two vertices in the logarithmic differential pore volume distribution curve of catalyst layer 20 in the range of pore size above 5 nm and below 15 nm), the maximum value of these two or more maxima is equivalent to the "first peak value".

[0067] In the logarithmic differential pore volume distribution curve of catalyst layer 20, if there is a maximum value in the range of pore size above 200 nm and below 3200 nm (that is, if there is a peak in the logarithmic differential pore volume distribution curve of catalyst layer 20 in the range of pore size above 200 nm and below 3200 nm), this maximum value is equivalent to the "second peak".

[0068] In the logarithmic differential pore volume distribution curve of catalyst layer 20, if there are more than two maxima in the range of pore size above 200 nm and below 3200 nm (i.e., if there are more than two vertices in the logarithmic differential pore volume distribution curve of catalyst layer 20 in the range of pore size above 200 nm and below 3200 nm), the maximum value among the two or more maxima is equivalent to the "second peak".

[0069] The first peak value is 0.060 mL / g or higher. This first peak value reflects the amount of relatively small pores that contribute to increasing the specific surface area of ​​the catalyst layer 20. With a first peak value of 0.060 mL / g or higher, the specific surface area of ​​the catalyst layer 20 increases, thereby improving its waste gas contact and adsorption properties. By improving the waste gas contact and adsorption properties of the catalyst layer 20, the reactivity of the catalyst layer 20 to diffused waste gas is enhanced.

[0070] The second peak value is above 0.018 mL / g. This second peak value reflects the amount of relatively large pores that contribute to improving the gas diffusivity of the catalyst layer 20. With the second peak value exceeding 0.018 mL / g, the gas diffusivity of the catalyst layer 20 is improved. By improving the gas diffusivity of the catalyst layer 20, unpurified exhaust gas is prevented from passing through the catalyst layer 20 without being purified.

[0071] Smaller pores in the catalyst layer 20 increase its specific surface area but decrease its gas diffusivity. Conversely, larger pores in the catalyst layer 20 improve its gas diffusivity but decrease its specific surface area. Therefore, by controlling the pore size in one way—either decreasing or increasing the pore size—it is impossible to achieve both an increase in the specific surface area and an improvement in the gas diffusivity of the catalyst layer 20. In contrast, the catalyst layer 20 as a whole satisfies the condition that the first peak value corresponding to the amount of relatively small pores is 0.060 mL / g or more, and the second peak value corresponding to the amount of relatively large pores is 0.018 mL / g or more. Thus, by sufficiently ensuring the amount of pores that contribute to increasing the specific surface area and improving the gas diffusivity of the catalyst layer 20, both an increase in the specific surface area and an improvement in the gas diffusivity of the catalyst layer 20 can be achieved. That is, it can improve the gas diffusivity of the catalyst layer 20 and the reactivity of the catalyst layer 20 to diffused waste gas, thereby improving the waste gas purification performance of the catalyst layer 20.

[0072] From the viewpoint of more effectively increasing the specific surface area of ​​the catalyst layer 20, the first peak value is preferably 0.075 mL / g or more, more preferably 0.080 mL / g or more, and even more preferably 0.090 mL / g or more.

[0073] There is no particular upper limit to the first peak value. From the viewpoint of achieving a balance between increasing the specific surface area of ​​the catalyst layer 20 and improving the gas diffusivity of the catalyst layer 20, the first peak value is preferably 0.250 mL / g or less, more preferably 0.240 mL / g or less, and even more preferably 0.230 mL / g or less. These upper limits can be combined with any of the lower limits mentioned above.

[0074] From the viewpoint of more effectively improving the gas diffusivity of the catalyst layer 20, the second peak value is preferably 0.030 mL / g or more, more preferably 0.035 mL / g or more, and even more preferably 0.040 mL / g or more.

[0075] There is no particular upper limit to the second peak value. From the viewpoint of achieving a balance between increasing the specific surface area of ​​the catalyst layer 20 and improving the gas diffusivity of the catalyst layer 20, the second peak value is preferably 0.110 mL / g or less, more preferably 0.080 mL / g or less, and even more preferably 0.070 mL / g or less. These upper limits can be combined with any of the lower limits mentioned above.

[0076] From the viewpoint of more effectively improving the gas diffuseability of the catalyst layer 20, the second peak is preferably located in the range of pore size 200 nm or more and 1600 nm or less, more preferably in the range of pore size 200 nm or more and 950 nm or less, even more preferably in the range of pore size 300 nm or more and 700 nm or less, and most preferably in the range of pore size 400 nm or more and 600 nm or less.

[0077] In this specification, the "logarithmic differential pore volume distribution curve (log differential pore volume distribution curve)" refers to the curve obtained by dividing the increase in pore volume (differential pore volume dV) by the difference between the common logarithm (log) of the upper and lower values ​​of the corresponding pore diameter (difference value d(logD)) and plotting it relative to the midpoint of the increase in pore diameter (the average pore diameter of each interval). It should be noted that "pore diameter" refers to the diameter.

[0078] In the logarithmic differential pore volume distribution curve of catalyst layer 20, the horizontal axis represents the pore size (μm) of catalyst layer 20, and the vertical axis represents the logarithmic differential pore volume (mL / g) per unit mass of catalyst layer 20 for slices M1 or M2 obtained from catalyst 1. Slices M1 and M2 will be described later.

[0079] The logarithmic differential pore volume distribution curve of catalyst layer 20 can be obtained by the following method.

[0080] The catalyst 1 is cut using a plane parallel to the axis of the substrate 10 and a plane perpendicular to the axis of the substrate 10, to cut out... Figure 4 The portion indicated by symbols M1 or M2 is used to obtain slice M1 or M2, which includes a portion of the partition wall portion 12 and a portion of the catalyst layer 20. The length of the portion of the partition wall portion 12 included in slice M1 or M2 is equal to the length of slice M1 or M2. The length of the portion of the catalyst layer 20 included in slice M1 or M2 is equal to the length of slice M1 or M2. Slices M1 and M2 can be obtained from near the exhaust gas inflow end and exhaust gas outflow end of catalyst 1, respectively. For example, a slice M1, containing a portion of the partition wall portion 12 and a portion of the catalyst layer 20, can be obtained by cutting it at two points along the exhaust gas flow direction X, respectively, at distances of 10 mm and 30 mm from the exhaust gas inflow side end of the substrate 10, using a plane perpendicular to the axial direction of the substrate 10. Similarly, a slice M2, containing a portion of the partition wall portion 12 and a portion of the catalyst layer 20, can be obtained by cutting it at two points along the opposite direction of the exhaust gas flow direction X, respectively, at distances of 10 mm and 30 mm from the exhaust gas outflow side end of the substrate 10, using a plane perpendicular to the axial direction of the substrate 10. The dimensions of slice M1 or M2 can be appropriately varied. Slice M1 or M2 is, for example, a cuboid shape with a cross-section of 10 mm long × 10 mm wide and a length of 20 mm.

[0081] By using mercury intrusion porosimetry with slices M1 or M2, the logarithmic differential pore volume distribution curve of catalyst layer 20 can be obtained.

[0082] Mercury intrusion porosimetry can be performed using the "Autopore IV9520" automatic porosity meter manufactured by Shimadzu Corporation, under the following conditions and procedures.

[0083] (Measurement conditions)

[0084] Measurement environment: 25℃

[0085] Measurement chamber: Sample chamber volume 5cm³ 3 The pressed volume is 0.37 cm³. 3

[0086] Measurement range: 0.0048 MPa to 255.1060 MPa

[0087] Measurement points: 54 points within the range of 0.0048 MPa to 0.3447 MPa.

[0088] 77 points within the range of 0.3792 MPa to 255.1060 MPa

[0089] A total of 131 points (points are marked at equal intervals when plotting each pressure using a logarithmic method).

[0090] Press-in volume: Adjusted to be above 25% and below 90%.

[0091] (Low-pressure parameters)

[0092] Exhaust pressure: 50 μmHg

[0093] Exhaust time: 5.0 min

[0094] Mercury injection pressure: 0.0034~0.0036 MPa

[0095] Balance time: 10 seconds

[0096] (High-voltage parameters)

[0097] Balance time: 10 seconds

[0098] (Mercury parameters)

[0099] Forward contact angle: 130.0 degrees

[0100] Retreating contact angle: 130.0 degrees

[0101] Surface tension: 485.0 mN / m (485.0 dyne / cm)

[0102] Mercury density: 13.5335 g / mL

[0103] (Measurement Procedure)

[0104] (a) 54 points were measured in the low-pressure section, ranging from 0.0048 MPa to 0.3447 MPa.

[0105] (b) 77 points were measured in the high-pressure section within the range of 0.3792 MPa to 255.1060 MPa.

[0106] (c) Calculate the logarithmic differential pore volume distribution curve (log differential pore volume distribution curve) from the mercury injection pressure, mercury injection amount and the mass of slice M1 or M2.

[0107] It should be noted that (a), (b), and (c) above can be performed automatically by the software attached to the device. Other conditions can be in accordance with JIS R 1655:2003.

[0108] Slices M1 or M2 contain a portion of the partition wall portion 12 of the substrate 10 and a portion of the catalyst layer 20. However, since the partition wall portion 12 of the substrate 10 does not have pore size, the logarithmic differential pore volume distribution obtained by mercury intrusion porosimetry reflects the logarithmic differential pore volume distribution of the catalyst layer 20.

[0109] The logarithmic differential pore volume distribution curve of the catalyst layer 20 can be obtained by performing mercury intrusion porosimetry using either slice M1 or M2, or by performing mercury intrusion porosimetry using both slices M1 and M2. In the former case, one logarithmic differential pore volume distribution curve is obtained; in the latter case, two logarithmic differential pore volume distribution curves are obtained. When two logarithmic differential pore volume distribution curves are obtained, it is acceptable if at least one curve satisfies the conditions that the first peak value is 0.060 mL / g or higher and the second peak value is 0.018 mL / g or higher; preferably, both curves satisfy these conditions. When two logarithmic differential pore volume distribution curves are obtained, the above description in <first peak value and second peak value> applies to each curve. When two logarithmic differential pore volume distribution curves are obtained, the first peak value in the two curves may be the same or different. When two logarithmic differential pore volume distribution curves are obtained, the second peak value in the two logarithmic differential pore volume distribution curves can be the same or different.

[0110] <Specific surface area of ​​catalyst layer>

[0111] The specific surface area of ​​catalyst layer 20 is preferably 70 m². 2 / g or more and 200m 2 / g or less, preferably 75m 2 / g or more and 145m 2 Below / g, more preferably 80m 2 / g or more and 100m 2 / g or less. The desired specific surface area of ​​the catalyst layer 20 can be achieved by satisfying the condition that the first peak corresponding to the amount of relatively small pores is 0.060 mL / g or more, and the second peak corresponding to the amount of relatively large pores is 0.018 mL / g or more. The specific surface area of ​​the catalyst layer 20 is particularly highly correlated with the first peak. The specific surface area of ​​the catalyst layer 20 can be determined using the QUADRASORB SI (manufactured by Quantachrome) by N2 gas adsorption.

[0112] <Catalyst layer coating amount>

[0113] From the viewpoint of more effectively achieving the desired first peak and second peak, the mass of the catalyst layer 20 per unit volume of the portion of the substrate 10 in which the catalyst layer 20 is disposed is preferably 100 g / L or more and 300 g / L or less, more preferably 110 g / L or more and 250 g / L or less, and even more preferably 120 g / L or more and 200 g / L or less.

[0114] The mass of the catalyst layer 20 per unit volume of the portion of the substrate 10 in which the catalyst layer 20 is disposed is given by the formula: (mass of catalyst layer 20) / (volume of substrate 10) × (average length L of catalyst layer 20) 20 / Length L of substrate 10 10 )) figure it out.

[0115] In this specification, unless otherwise specified, "length" refers to the axial dimension of the substrate 10.

[0116] In this specification, the "mass of catalyst layer 20" refers to the calculated mass obtained by summing the metal-converted mass of noble metal elements and the oxide-converted mass of other metal elements contained in catalyst layer 20. In other words, the "mass of catalyst layer 20" is the calculated mass obtained by summing the metal-converted mass of noble metal elements in catalyst layer 20 and the oxide-converted mass of other metal elements in catalyst layer 20. It should be noted that "metal elements" also include half-metal elements such as Si and B.

[0117] In this specification, "precious metal elements" include Au, Ag, Pt, Pd, Rh, Ir, Ru, and Os.

[0118] In this specification, oxides of rare earth elements other than Ce, Pr, and Tb refer to sesquioxides (Ln₂O₃, where Ln represents rare earth elements other than Ce, Pr, and Tb), oxides of Ce refer to CeO₂, and oxides of Pr refer to Pr₆O₃. 11 The oxides of Tb are Tb4O7, Al is Al2O3, Zr is ZrO2, Si is SiO2, B is B2O3, Cr is Cr2O3, Mg is MgO, Ca is CaO, Sr is SrO, Ba is BaO, Fe is Fe3O4, Mn is Mn3O4, Ni is NiO, Ti is TiO2, Zn is ZnO, and Sn is SnO2.

[0119] The average length L of catalyst layer 20 20 One example of the determination method is as follows.

[0120] A section extending axially along the substrate 10 from the catalyst 1 and having a length L equal to that of the substrate 10. 10Samples of the same length are used. For example, a cylindrical sample with a diameter of 25.4 mm is used. It should be noted that the sample diameter can be changed as needed. The sample is cut at 5 mm intervals using a plane perpendicular to the axis of the substrate 10, obtaining slices 1, 2, ..., n sequentially from the end side of the sample on the exhaust gas inflow side. Each slice is 5 mm long. The composition of the slices is analyzed using X-ray fluorescence (XRF) (e.g., energy-dispersive X-ray (EDX), wavelength-dispersive X-ray (WDX), etc.), inductively coupled plasma atomic emission spectrometry (ICP-AES), scanning electron microscopy-energy-dispersive X-ray analysis (SEM-EDX), etc., to confirm whether the slice contains a portion of the catalyst layer 20.

[0121] For slices that clearly contain a portion of catalyst layer 20, compositional analysis may not be necessary. For example, scanning electron microscopy (SEM) or electron probe microanalysis (EPMA) can be used to observe the cut surface to confirm whether the slice contains a portion of catalyst layer 20. Elemental mapping of the cut surface can also be performed during observation.

[0122] After confirming whether the slice contains a portion of the catalyst layer 20, the length of the catalyst layer 20 contained in the sample is calculated based on the following formula.

[0123] The length of catalyst layer 20 in the sample is 5 mm × (number of slices containing a portion of catalyst layer 20).

[0124] For example, if slices 1 to k contain a portion of catalyst layer 20, but slices (k+1) to n do not contain a portion of catalyst layer 20, the length of catalyst layer 20 contained in the sample is (5×k) mm.

[0125] A more detailed method for determining the length of the catalyst layer 20 contained in the sample is as follows.

[0126] The k-th slice (i.e., the slice obtained from the side of the sample closest to the exhaust gas outlet among the slices containing a portion of the catalyst layer 20) is cut along the axial direction of the substrate 10, and the portion of the catalyst layer 20 present on the cut surface is observed using SEM, EPMA, etc., thereby determining the length of the portion of the catalyst layer 20 in the k-th slice. Then, the length of the catalyst layer 20 contained in the sample is calculated based on the following formula.

[0127] The length of catalyst layer 20 contained in the sample = (5mm × (k-1)) + (the length of a portion of catalyst layer 20 contained in the k-th slice)

[0128] For 8 to 16 samples randomly cut from catalyst 1, the length of the catalyst layer 20 contained in each sample was measured, and their average value was taken as the average length L of the catalyst layer 20. 20 .

[0129] It should be noted that when the catalyst layer 20 extends from the end of the exhaust gas outlet side of the partition wall 12 in a direction opposite to the exhaust gas flow direction X without reaching the end of the exhaust gas inflow side of the partition wall 12, the sample is cut at 5 mm intervals through a plane perpendicular to the axial direction of the substrate 10, and the first slice, the second slice, ..., the nth slice are obtained sequentially from the end of the sample on the exhaust gas outlet side.

[0130] <Precious Metal Elements>

[0131] The catalyst layer 20 contains one or more precious metal elements.

[0132] The precious metal element can be selected from, for example, Au, Ag, Pt, Pd, Rh, Ir, Ru, Os, etc., with Rh, Pt and Pd being preferred.

[0133] The precious metal element is contained in the catalyst layer 20 in the form of a catalytically active component, such as a metal, an alloy containing the precious metal element, or a compound containing the precious metal element (e.g., an oxide of the precious metal element).

[0134] From the perspective of achieving a balance between exhaust gas purification performance and cost, based on the mass of catalyst layer 20, the metal conversion content of precious metal elements in catalyst layer 20 is preferably 0.010% by mass or more and 20% by mass or less, more preferably 0.050% by mass or more and 10% by mass or less, and even more preferably 0.10% by mass or more and 5.0% by mass or less. "Metal conversion content of precious metal elements in catalyst layer 20" refers to the metal conversion content of that single precious metal element when catalyst layer 20 contains one such element, and to the total metal conversion content of the two or more precious metal elements when catalyst layer 20 contains two or more such elements.

[0135] Once the composition of the raw materials used in the manufacture of catalyst layer 20 is determined, the metal conversion content of the precious metal elements in catalyst layer 20 can be calculated from the composition of the raw materials.

[0136] In the absence of a known composition of the raw materials used in the manufacture of catalyst layer 20, the metal conversion content of the noble metal elements in catalyst layer 20 is determined using scanning electron microscopy-energy dispersive X-ray diffraction (SEM-EDX). Specifically, as described below.

[0137] For the specimen obtained from the catalyst layer 20, elemental analysis was performed using SEM-EDX to determine the types of constituent elements in the whole specimen, and the molar % of each determined metal element was obtained. For 10 fields of view of the SEM, the molar % of each metal element was determined separately, and the average value of the molar % of each metal element in the 10 fields of view was taken as the molar % of each metal element in the catalyst layer 20. Based on the molar % of each metal element in the catalyst layer 20, the mass % in terms of metal of the noble metal group elements in the catalyst layer 20 and the mass % in terms of oxide of each metal element other than the noble metal group elements in the catalyst layer 20 were calculated. The mass % in terms of metal of the noble metal group elements in the catalyst layer 20 was calculated by the formula: (mass of noble metal group elements in terms of metal calculated from molar %) / ((mass of noble metal group elements in terms of metal calculated from molar %) + (mass of metal elements other than noble metal group elements in terms of oxide calculated from molar %)) × 100. The mass % in terms of oxide of each metal element other than the noble metal group elements in the catalyst layer 20 was calculated by the formula: (mass of metal elements other than noble metal group elements in terms of oxide calculated from molar %) / ((mass of noble metal group elements in terms of metal calculated from molar %) + (mass of metal elements other than noble metal group elements in terms of oxide calculated from molar %)) × 100.

[0138] At least a part of the catalytic active component containing a noble metal element is preferably supported on one or more carriers selected from Ce-based oxide particles and Ce-Zr-based composite oxide particles. When the catalyst layer 20 contains Al-based oxide particles, at least a part of the catalytic active component containing a noble metal element is preferably supported on one or more carriers selected from Ce-based oxide particles, Ce-Zr-based composite oxide particles, and Al-based oxide particles. The Ce-based oxide particles, Ce-Zr-based composite oxide particles, and Al-based oxide particles will be described later.

[0139] "At least a part of the catalytic active component is supported on the carrier" means that at least a part of the catalytic active component is physically and / or chemically adsorbed and / or held in a state on the outer surface and / or the inner surface of the pores of the carrier. Whether at least a part of the catalytic active component is supported on the carrier can be confirmed, for example, using SEM-EDX. Specifically, in the elemental mapping obtained by performing SEM-EDX analysis on the specimen obtained from the catalyst layer 20, when at least a part of the catalytic active component and the carrier are present in the same region, it can be determined that at least a part of the catalytic active component is supported on the carrier.

[0140] <Ce-based oxide particles>

[0141] The catalyst layer 20 contains Ce-based oxide particles.

[0142] The Ce-based oxide particles contained in the catalyst layer 20 are different from the Ce-based oxide particles used as raw materials for the catalyst layer 20. Hereinafter, the Ce-based oxide particles contained in the catalyst layer 20 will be referred to as "Ce-based oxide particles", and the Ce-based oxide particles used as raw materials for the catalyst layer 20 will be referred to as "Ce-based oxide particles as raw materials".

[0143] Ce-based oxide particles can be used as supports for catalytically active components. From the viewpoint of improving the loading capacity of catalytically active components, Ce-based oxide particles are preferably porous. Ce-based oxide particles differ from cerium dioxide (hereinafter referred to as "cerium dioxide binder") used as a binder. Cerium dioxide binder is derived from cerium dioxide sol used as a raw material for catalyst layer 20, or water-soluble cerium salts such as cerium nitrate and cerium nitrate.

[0144] Ce-based oxide particles are composed of Ce-based oxides. Ce-based oxides refer to oxides containing Ce, specifically oxides in which Ce is the most abundant element (by mass) among the elements excluding O. However, substances belonging to Ce-Zr composite oxide particles are not considered Ce-based oxide particles. It should be noted that the Zr content in Ce-based oxide particles, calculated as ZrO2, is generally lower than that in Ce-Zr composite oxide particles. This difference distinguishes Ce-based oxide particles from Ce-Zr composite oxide particles.

[0145] Ce-based oxide particles may also contain one or more metallic elements other than Ce. These metallic elements may be selected from, for example, rare earth elements other than Ce (e.g., Y, Pr, Sc, La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc.), alkaline earth metals (e.g., Mg, Ca, Sr, Ba, etc.), Fe, Mn, Ni, Zr, Al, etc. These metallic elements may form solid solution phases with Ce and O, or they may form individual phases as crystalline or amorphous phases (e.g., oxide phases of metallic elements other than Ce), or both solid solution phases and individual phases.

[0146] Examples of Ce-based oxide particles include cerium dioxide particles (particles composed of CeO2), particles obtained by modifying the surface of cerium dioxide particles with metal elements other than Ce or their oxides, and particles obtained by dissolving metal elements other than Ce in cerium dioxide particles.

[0147] Ce-based oxide particles are important materials for achieving a first peak value of 0.060 mL / g or higher and a second peak value of 0.018 mL / g or higher. Hereinafter, preferred Ce-based oxide particles for achieving the desired first and second peak values ​​will be described.

[0148] From the viewpoint of more effectively achieving the desired first and second peak values, based on the mass of Ce-based oxide particles, the Ce content in the Ce-based oxide particles, calculated as CeO2, is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more. Theoretically, the upper limit is 100% by mass, but in practice, it can be less than 100% by mass if the presence of unavoidable impurities is taken into account.

[0149] The Ce content in Ce-based oxide particles, calculated as CeO2, can be determined by analyzing the sample obtained from catalyst layer 20 using energy-dispersive X-ray spectroscopy (EDX). The result is obtained from the elemental mapping and EDX elemental analysis of the specified particles. Specifically, Ce-based oxide particles and other particles (e.g., Ce-Zr composite oxide particles, Al-based oxide particles, etc.) are qualitatively identified (color-coded) through elemental mapping. Compositional analysis (elemental analysis) is then performed on the specified particles, allowing the determination of the oxide-converted content of the specified elements within the particles.

[0150] From the viewpoint of more effectively achieving the desired first and second peak values, the median particle size of the Ce-based oxide particles used as raw materials is preferably 0.10 μm or more and 15 μm or less, more preferably 0.50 μm or more and 12 μm or less, even more preferably 1.0 μm or more and 10 μm or less, and even more preferably 2.0 μm or more and 7.0 μm or less. The median particle size is the particle size that constitutes 50% of the cumulative volume in the particle size distribution measured by laser diffraction scattering particle size distribution method. The median particle size is also called D50. During the manufacture of the catalyst layer 20, the median particle size of the Ce-based oxide particles used as raw materials is maintained; therefore, the median particle size of the Ce-based oxide particles is usually the same as the median particle size of the Ce-based oxide particles used as raw materials.

[0151] The median particle size of Ce-based oxide particles used as raw materials can be determined using an automatic sample feeder of a laser diffraction scattering particle size distribution measuring device. The sample is placed in an aqueous dispersion medium, irradiated with ultrasound, and then measured using the laser diffraction scattering particle size distribution measuring device. The specific method for determining the median particle size of Ce-based oxide particles used as raw materials is described below. Using an automatic sample feeder of a laser diffraction scattering particle size distribution measuring device (Microtrac BEL, "Microtrac SDC"), the sample is placed in an aqueous dispersion medium, irradiated with 40W ultrasound for 360 seconds at a flow rate of 32.5 mL / s, and then measured using a laser diffraction scattering particle size distribution measuring device (Microtrac BEL, "Microtrac MT3300EXII"). The determination was performed using pure water as the aqueous dispersion medium. The determination was conducted twice under the following conditions: particle refractive index of 1.5, particle shape of spherical, solvent refractive index of 1.3, zeroing time of 30 seconds, and measurement time of 30 seconds. The average value of the obtained measurements was used as the median particle size of the test sample.

[0152] It should be noted that the median particle size of Ce-based oxide particles can be inferred from the particle size (e.g., directional diameter such as Freret diameter) of the Ce-based oxide particles obtained by observing the sample obtained from the catalyst layer 20 using a scanning electron microscope.

[0153] From the viewpoint of more effectively achieving the desired first and second peak values, the CeO2 crystallite diameter of the Ce-based oxide particles is preferably 6 nm or more, more preferably 10 nm or more, even more preferably 20 nm or more, and even more preferably 30 nm or more. From this viewpoint, the CeO2 crystallite diameter of the Ce-based oxide particles is preferably 200 nm or less, more preferably 100 nm or less, and even more preferably 55 nm or less. These upper limits can be combined with any of the lower limits mentioned above.

[0154] The method for measuring the CeO2 microcrystal diameter of the Ce-based oxide particles is as described below. X-ray diffraction (XRD) is performed using the powder sample obtained from the catalyst layer 20 and a commercially available X-ray diffractometer. In the obtained XRD pattern, the peaks existing at 2θ = 55 - 58° and the peaks existing at 2θ = 46 - 49° among the peaks derived from CeO2 are determined, and the Scherrer formula is applied to the determined peaks to measure the microcrystal diameter. The specific measurement method is as described in the examples. The microcrystal diameter obtained from the peaks existing at 2θ = 55 - 58° is compared with the microcrystal diameter obtained from the peaks existing at 2θ = 46 - 49°, and the larger microcrystal diameter is selected as the CeO2 microcrystal diameter in the Ce-based oxide particles. In the obtained XRD pattern, when neither the peak existing at 2θ = 55 - 58° nor the peak existing at 2θ = 46 - 49° among the peaks derived from CeO2 can be determined due to the peaks derived from components other than CeO2, the microcrystal diameter obtained from the determinable peaks is taken as the CeO2 microcrystal diameter of the Ce-based oxide particles.

[0155] It should be noted that in the above XRD pattern, the peak existing at 2θ = 55 - 58° among the peaks derived from CeO2 is adjacent to the peak existing at 2θ = 58 - 61° among the peaks derived from the Ce-Zr composite oxide, but shows a separated form.

[0156] The CeO2 microcrystal diameter of the Ce-based oxide particles can be adjusted, for example, by adjusting the firing conditions during the production of the Ce-based oxide particles, or by setting a crystallization process (such as exposure to hydrothermal conditions, etc.) at the production stage of the Ce-based oxide particles.

[0157] <Ce-Zr composite oxide particles>

[0158] The catalyst layer 20 contains Ce-Zr composite oxide particles.

[0159] The Ce-Zr composite oxide particles contained in the catalyst layer 20 are different from the Ce-Zr composite oxide particles used as the raw material of the catalyst layer 20. Hereinafter, the Ce-Zr composite oxide particles contained in the catalyst layer 20 will be simply referred to as "Ce-Zr composite oxide particles", and the Ce-Zr composite oxide particles used as the raw material of the catalyst layer 20 will be called "Ce-Zr composite oxide particles as the raw material".

[0160] The Ce-Zr composite oxide particles can be used as the carrier of the catalytic active component. From the viewpoint of improving the loading property of the catalytic active component, the Ce-Zr composite oxide particles are preferably porous.

[0161] Ce-Zr composite oxide particles possess oxygen storage capacity (i.e., the ability to absorb and store oxygen when the oxygen concentration in the exhaust gas is high and release oxygen when the oxygen concentration in the exhaust gas is low), thus mitigating fluctuations in the oxygen concentration in the exhaust gas and expanding the operating window of the catalytically active components. Therefore, by including Ce-Zr composite oxides in the catalyst layer 20, the exhaust gas purification capacity of the catalyst layer 20 is improved.

[0162] Ce-Zr composite oxide particles are composed of Ce-Zr composite oxides. Ce-Zr composite oxides are oxides containing both Ce and Zr.

[0163] Ce-Zr composite oxide particles can also contain one or more metallic elements other than Ce and Zr. The metallic elements other than Ce and Zr can be selected from rare earth elements other than Ce (e.g., Y, Pr, Sc, La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc.), alkaline earth metal elements (e.g., Mg, Ca, Sr, Ba, etc.), Fe, Mn, Ni, Zr, Al, etc. The metallic elements other than Ce and Zr can form solid solution phases together with Ce, Zr, and O, or they can form individual phases as crystalline or amorphous phases (e.g., oxide phases of metallic elements other than Ce), or both solid solution phases and individual phases.

[0164] Examples of Ce-Zr composite oxide particles include particles composed of CeO2-ZrO2 solid solutions, particles obtained by modifying the surface of particles composed of CeO2-ZrO2 solid solutions with metal elements other than Ce and Zr or their oxides, and particles obtained by dissolving metal elements other than Ce and Zr into particles composed of CeO2-ZrO2 solid solutions.

[0165] From the perspective of improving the oxygen storage capacity of Ce-Zr composite oxide particles, based on the mass of the Ce-Zr composite oxide particles, the Ce content in the Ce-Zr composite oxide particles, calculated as CeO2, is preferably 5% by mass or more and 90% by mass or less, more preferably 5% by mass or more and 70% by mass or less, even more preferably 7% by mass or more and 60% by mass or less, and even more preferably 10% by mass or more and 50% by mass or less. The Ce content in the Ce-Zr composite oxide particles, calculated as CeO2, can be calculated in the same way as the Ce content in the Ce oxide particles.

[0166] From the viewpoint of improving the heat resistance of Ce-Zr composite oxide particles, based on the mass of the Ce-Zr composite oxide particles, the ZrO2-converted content rate of Zr in the Ce-Zr composite oxide particles is preferably 10% by mass or more and 95% by mass or less, more preferably 20% by mass or more and 95% by mass or less, still more preferably 40% by mass or more and 95% by mass or less, and still more preferably 50% by mass or more and 90% by mass or less. The ZrO2-converted content rate of Zr in the Ce-Zr composite oxide particles can be determined in the same manner as the CeO2-converted content rate of Ce in the Ce-based oxide particles.

[0167] From the viewpoints of improving the oxygen storage capacity and heat resistance of Ce-Zr composite oxide particles, based on the mass of the Ce-Zr composite oxide particles, the sum of the CeO2-converted content rate of Ce and the ZrO2-converted content rate of Zr in the Ce-Zr composite oxide particles is preferably 70% by mass or more, more preferably 75% by mass or more, still more preferably 80% by mass or more, and still more preferably 85% by mass or more. The upper limit is 100% by mass.

[0168] The median diameter of the Ce-Zr composite oxide particles as a raw material is preferably 0.1 μm or more and 15 μm or less, more preferably 0.5 μm or more and 12 μm or less, and still more preferably 1 μm or more and 10 μm or less. The meaning of the median diameter is as described above. When manufacturing the catalyst layer 20, the median diameter of the Ce-Zr composite oxide particles as a raw material is maintained, and thus generally the median diameter of the Ce-Zr composite oxide particles is the same as that of the Ce-Zr composite oxide particles as a raw material. The median diameter of the Ce-Zr composite oxide particles as a raw material can be measured in the same manner as the median diameter of the Ce-based oxide particles as a raw material. It should be noted that the median diameter of the Ce-Zr composite oxide particles can be estimated based on the particle diameter (e.g., Feret diameter or other directional diameters) of the Ce-Zr composite oxide particles obtained by observing a specimen obtained from the catalyst layer 20 using a scanning electron microscope.

[0169] <Al-based oxide particles>

[0170] The catalyst layer 20 preferably contains Al-based oxide particles in addition to the Ce-based oxide particles and the Ce-Zr composite oxide particles.

[0171] The Al oxide particles contained in the catalyst layer 20 are different from the Al oxide particles used as raw materials for the Al oxide particles contained in the catalyst layer 20. Hereinafter, the Al oxide particles contained in the catalyst layer 20 will be referred to as "Al oxide particles", and the Al oxide particles used as raw materials for the Al oxide particles contained in the catalyst layer 20 will be referred to as "Al oxide particles as raw materials".

[0172] Al-based oxide particles can be used as supports for catalytically active components. From the viewpoint of improving the loading capacity of catalytically active components, porous Al-based oxide particles are preferred. Al-based oxide particles differ from alumina used as a binder (hereinafter referred to as "alumina binder"). Alumina binder is derived from alumina sol used as a raw material for catalyst layer 20.

[0173] By including Al-based oxide particles in the catalyst layer 20, the adhesion between particles (e.g., the adhesion between Ce-based oxide particles and Al-based oxide particles, the adhesion between Ce-Zr composite oxide particles and Al-based oxide particles, etc.) is improved, and the adhesion between the catalyst layer 20 and the substrate 10 is also improved.

[0174] Al-based oxide particles are composed of Al-based oxides. Al-based oxides refer to oxides containing Al, specifically oxides in which Al is the most abundant element by mass among the elements excluding O. However, substances belonging to Ce-Zr composite oxide particles are not considered to be Al-based oxide particles.

[0175] Al-based oxide particles can also contain one or more metallic elements other than Al. These metallic elements can be selected from, for example, rare earth elements other than Ce (e.g., Y, Pr, Sc, La, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc.), alkaline earth metals (e.g., Mg, Ca, Sr, Ba, etc.), B, Si, Zr, Cr, etc. It should be noted that "metallic elements" also includes half-metallic elements such as B and Si. Metallic elements other than Al can form solid solution phases with Al and O, or they can form individual phases as crystalline or amorphous phases (e.g., oxide phases of metallic elements other than Al), or both solid solution phases and individual phases.

[0176] Examples of Al-based oxide particles include alumina particles (particles composed of Al2O3), particles obtained by modifying the surface of alumina particles with metal elements other than Al or their oxides, and particles obtained by dissolving metal elements other than Al into alumina particles.

[0177] From the viewpoint of achieving the desired tightness more effectively, based on the mass of Al-based oxide particles, the amount of Al in the Al-based oxide particles, converted from Al2O3, is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. Theoretically, the upper limit is 100% by mass, but in practice, it can be less than 100% by mass if the presence of unavoidable impurities is taken into account.

[0178] From the viewpoint of more effectively achieving the desired tightness, the median particle size of the Al-based oxide particles used as raw materials is preferably 15 μm or more and 30 μm or less, more preferably 16 μm or more and 25 μm or less, and even more preferably 17 μm or more and 21 μm or less. The significance of the median particle size is as described above. During the manufacture of the catalyst layer 20, the median particle size of the Al-based oxide particles used as raw materials is maintained; therefore, the median particle size of the Al-based oxide particles is usually the same as that of the Al-based oxide particles used as raw materials. The median particle size of the Al-based oxide particles used as raw materials can be measured in the same way as the median particle size of the Ce-based oxide particles used as raw materials. It should be noted that the median particle size of the Al-based oxide particles can be inferred from the particle size (e.g., orientation diameter such as Ferrette diameter) of the Al-based oxide particles obtained by observing the sample obtained from the catalyst layer 20 using a scanning electron microscope.

[0179] The median particle size of the aforementioned Ce-based oxide particles, Ce-Zr-based composite oxide particles, and Al-based oxide particles can be adjusted using known pulverization methods such as ball mills, or by using granulation methods such as spray drying during particle manufacturing.

[0180] <Other Ingredients>

[0181] The catalyst layer 20 may contain one or more inorganic oxide particles other than Ce-based oxide particles, Ce-Zr composite oxide particles, and Al-based oxide particles. The inorganic oxide particles can be used as supports for the catalytically active components. From the viewpoint of improving the loading capacity of the catalytically active components, the inorganic oxide particles are preferably porous. The inorganic oxide particles may or may not have oxygen storage capacity (OSC). Examples of inorganic oxides constituting the inorganic oxide particles include oxides based on rare earth elements other than Ce, zirconium oxide (ZrO2), silicon dioxide (SiO2), titanium dioxide (TiO2), zeolite (aluminosilicate), MgO, ZnO, SnO2, etc.

[0182] The catalyst layer 20 may contain components such as binders and stabilizers. Examples of binders include inorganic oxide-based binders such as alumina sol, cerium dioxide sol, zirconium oxide sol, titanium dioxide sol, and silica sol. Examples of stabilizers include nitrates, carbonates, oxides, and sulfates of alkaline earth metal elements (such as Sr and Ba).

[0183] <Particle content>

[0184] The following describes the content of Ce-based oxide particles, Ce-Zr-based composite oxide particles, and Al-based oxide particles in the catalyst layer 20. In the following description, "Ce-based oxide particles" preferably refers to Ce-based oxide particles that are preferred in terms of achieving the desired first peak value and second peak value described above.

[0185] From the viewpoint of more effectively achieving the desired first and second peak values, based on the total mass of Ce-based oxide particles and Ce-Zr composite oxide particles in catalyst layer 20, the content of Ce-based oxide particles in catalyst layer 20 is preferably 5% by mass or more and 95% by mass or less, more preferably 15% by mass or more and 70% by mass or less, and even more preferably 25% by mass or more and 60% by mass or less.

[0186] From the viewpoint of more effectively achieving the desired oxygen storage capacity, based on the total mass of Ce-based oxide particles and Ce-Zr-based composite oxide particles in the catalyst layer 20, the content of Ce-Zr-based composite oxide particles in the catalyst layer 20 is preferably 5% by mass or more and 95% by mass or less, more preferably 30% by mass or more and 85% by mass or less, and even more preferably 40% by mass or more and 75% by mass or less.

[0187] From the viewpoint of more effectively achieving the desired first and second peak values ​​and the desired oxygen storage capacity, based on the mass of the catalyst layer 20, the total content of Ce-based oxides and Ce-Zr-based composite oxide particles in the catalyst layer 20 is preferably 15% by mass or more and 80% by mass or less, more preferably 25% by mass or more and 70% by mass or less, and even more preferably 35% by mass or more and 65% by mass or less.

[0188] When the catalyst layer 20 contains Al-based composite oxide particles, from the viewpoint of more effectively achieving the desired first peak and second peak, based on the total mass of Ce-based oxide particles, Ce-Zr-based composite oxide particles and Al-based oxide particles in the catalyst layer 20, the content of Ce-based oxide particles in the catalyst layer 20 is preferably 5% by mass or more and 70% by mass or less, more preferably 10% by mass or more and 60% by mass or less, and even more preferably 15% by mass or more and 50% by mass or less.

[0189] When the catalyst layer 20 contains Al-based composite oxide particles, from the viewpoint of more effectively achieving the desired oxygen storage capacity, based on the total mass of Ce-based oxide particles, Ce-Zr-based composite oxide particles and Al-based oxide particles in the catalyst layer 20, the content of Ce-Zr-based composite oxide particles in the catalyst layer 20 is preferably 10% by mass or more and 65% by mass or less, more preferably 20% by mass or more and 60% by mass or less, and even more preferably 30% by mass or more and 55% by mass or less.

[0190] When the catalyst layer 20 contains Al-based composite oxide particles, from the viewpoint of achieving the desired tightness, based on the total mass of Ce-based oxide particles, Ce-Zr-based composite oxide particles and Al-based oxide particles in the catalyst layer 20, the content of Al-based composite oxide particles in the catalyst layer 20 is preferably 10% by mass or more and 60% by mass or less, more preferably 20% by mass or more and 50% by mass or less, and even more preferably 25% by mass or more and 40% by mass or less.

[0191] When the catalyst layer 20 contains Al-based composite oxide particles, from the viewpoint of more effectively achieving the desired first and second peak values, the desired oxygen storage capacity, and the desired tightness, based on the mass of the catalyst layer 20, the total content of Ce-based oxides, Ce-Zr-based composite oxide particles, and Al-based oxide particles in the catalyst layer 20 is preferably 50% by mass or more and 99% by mass or less, more preferably 60% by mass or more and 95% by mass or less, and even more preferably 70% by mass or more and 90% by mass or less.

[0192] Once the composition of the raw materials used in the manufacture of catalyst layer 20 is determined, the content of Ce-based oxide particles, Ce-Zr-based composite oxide particles, and Al-based oxide particles in catalyst layer 20 can be determined from the composition of the raw materials.

[0193] Without determining the composition of the raw materials used in the manufacture of catalyst layer 20, the content of Ce-based oxide particles, Ce-Zr-based composite oxide particles and Al-based oxide particles in catalyst layer 20 is determined by the following steps (A) to (D).

[0194] (A) For the sample obtained from catalyst layer 20, elemental analysis is performed using scanning electron microscopy-energy dispersive X-ray diffraction (SEM-EDX) for any selected number of fields of view (e.g., 30 fields of view) to determine the types of constituent elements in the overall sample and to calculate the oxide equivalent content of the specified elements. The average value of the oxide equivalent content of the specified elements in the multiple fields of view is taken as the oxide equivalent content of the specified elements in the sample.

[0195] (B) For the sample obtained from catalyst layer 20, elemental mapping based on SEM-EDX is performed to determine the types of particles contained in the sample (Ce-based oxide particles, Ce-Zr-based composite oxide particles and Al-based oxide particles, depending on the case).

[0196] (C) For various particles, elemental analysis is performed on any selected number (e.g., 50) particles using SEM-EDX to determine the types of constituent elements in the particles and to calculate the oxide content of the specified elements. The average value of the oxide content of the specified elements in the multiple particles is taken as the oxide content of the specified elements in each type of particle.

[0197] (D) Prepare and solve an equation relating the content of oxides of the specified element in the sample, the content of oxides of the specified element in various particles, and the content of various particles in the sample, thereby calculating the content of various particles in the sample.

[0198] For example, if the Ce source, Zr source, and Al source in the catalyst layer 20 are composed of only three types of particles: Ce-based oxide particles, Ce-Zr-based composite oxide particles, and Al-based oxide particles, the content of Ce-based oxide particles, Ce-Zr-based composite oxide particles, and Al-based oxide particles in the catalyst layer 20 can be determined according to the following steps.

[0199] First, for the sample obtained from catalyst layer 20, elemental analysis was performed using SEM-EDX for 30 randomly selected fields of view to determine the types of constituent elements in the overall sample and to calculate the oxide equivalent content of the specified elements. The average value of the oxide equivalent content of the specified elements in the 30 fields of view was taken as the oxide equivalent content of the specified elements in the sample.

[0200] Next, for the sample obtained from catalyst layer 20, elemental mapping based on SEM-EDX was performed to determine the types of particles contained in the sample (Ce-based oxide particles, Ce-Zr-based composite oxide particles, and Al-based oxide particles).

[0201] Next, for each type of particle, elemental analysis was performed on 50 randomly selected particles using SEM-EDX to determine the types of constituent elements in the 50 particles and to calculate the content of oxides of the specified elements. The average content of oxides of the specified elements in the 50 particles was taken as the content of oxides of the specified elements in each type of particle.

[0202] By following the steps above, the following content rates can be calculated.

[0203] • The Ce content in the whole sample, calculated as CeO2 (hereinafter referred to as "P") T ”)

[0204] • The Ce content in Ce-based oxide particles, calculated as CeO2 (hereinafter referred to as "P1").

[0205] • Ce content in Ce-Zr composite oxide particles, calculated as CeO2 (hereinafter referred to as "P2").

[0206] • Ce content in Al-based oxide particles, calculated as CeO2 (hereinafter referred to as "P3").

[0207] • The Zr content in the whole sample, calculated as ZrO2 (hereinafter referred to as "Q"). T ”)

[0208] • The Zr content in Ce-based oxide particles, calculated as ZrO2 (hereinafter referred to as "Q1").

[0209] • The Zr content in Ce-Zr composite oxide particles, calculated as ZrO2 (hereinafter referred to as "Q2").

[0210] • The Zr content in Al-based oxide particles, calculated as ZrO2 (hereinafter referred to as "Q3").

[0211] • The Al2O3 equivalent content of Al in the whole sample (hereinafter referred to as "R") T ”)

[0212] • The Al content in Ce-based oxide particles, calculated as Al₂O₃ (hereinafter referred to as "R₁").

[0213] • The Al content in Ce-Zr composite oxide particles, calculated as Al2O3 (hereinafter referred to as "R2").

[0214] • The Al content in Al-based oxide particles, calculated as Al₂O₃ (hereinafter referred to as "R₃").

[0215] Next, an equation is constructed and solved to express the relationship between the content of oxides of the specified elements in the sample, the content of oxides of the specified elements in various particles, and the content of various particles in the sample, thereby calculating the content of various particles in the sample.

[0216] Specifically, if the content (mass standard) of Ce-based oxide particles, Ce-Zr-based composite oxide particles and Al-based oxide particles in catalyst layer 20 is set as X, Y and Z, then the following equations (1) to (3) hold true.

[0217] P T =X×P1+Y×P2+Z×P3…(1)

[0218] Q T =X×Q1+Y×Q2+Z×Q3…(2)

[0219] R T =X×R1+Y×R2+Z×R3…(3)

[0220] X, Y and Z are obtained from the above equations (1) to (3). The content of Ce-based oxide particles in catalyst layer 20 is obtained from X (mass basis). The content of Ce-Zr composite oxide particles is obtained from Y (mass basis). The content of Al-based oxide particles is obtained from Z (mass basis).

[0221] <Structure of the catalyst layer>

[0222] The catalyst layer 20 can have a single-layer structure or a stacked structure.

[0223] The following describes an embodiment of the catalyst layer 20 having a layered structure.

[0224] like Figure 3 and Figure 4 As shown, the catalyst layer 20 includes a first layer 21 disposed on the substrate 10 and a second layer 22 disposed on the first layer 21.

[0225] At least a portion of the Ce-based oxide particles in catalyst layer 20 are contained in the first layer 21. This can be a portion or all of the Ce-based oxide particles in catalyst layer 20. The first layer 21 preferably contains Ce-based oxide particles preferred for achieving the desired first and second peak values ​​described above.

[0226] At least a portion of the Ce-Zr composite oxide particles in catalyst layer 20 are contained in the first layer 21. This can be either a portion of the Ce-Zr composite oxide particles in catalyst layer 20 being contained in the first layer 21, or all of the Ce-Zr composite oxide particles in catalyst layer 20 being contained in the first layer 21.

[0227] At least a portion of the noble metal elements in catalyst layer 20 are contained in the second layer 22. This can be either a portion of the noble metal elements in catalyst layer 20 being contained in the second layer 22, or all of the noble metal elements in catalyst layer 20 being contained in the second layer 22.

[0228] When the catalyst layer 20 contains Al-based oxide particles, at least a portion of the Al-based oxide particles in the catalyst layer 20 are contained in the first layer 21. This can be either a portion of the Al-based oxide particles in the catalyst layer 20 being contained in the first layer 21, or all of the Al-based oxide particles in the catalyst layer 20 being contained in the first layer 21.

[0229] Preferably, at least layer 21 of layer 1 21 contributes to the desired first peak and second peak. In addition to layer 1 21, layer 22 may also contribute to the desired first peak and second peak.

[0230] <Level 1>

[0231] The following is an explanation of layer 1, 21.

[0232] like Figure 3 and Figure 4 As shown, the first layer 21 is disposed on the chamber 13 side surface of the partition wall portion 12. The meaning of "chamber 13 side surface of the partition wall portion 12" is as described above. The first layer 21 can be disposed directly on the chamber 13 side surface of the partition wall portion 12, or it can be disposed in between other layers, but it is usually disposed directly on the chamber 13 side surface of the partition wall portion 12.

[0233] like Figure 4 As shown, the first layer 21 extends along the exhaust gas flow direction X from the end of the partition wall 12 on the exhaust gas inflow side to the end of the partition wall 12 on the exhaust gas outflow side. The first layer 21 may extend along the exhaust gas flow direction X from the end of the partition wall 12 on the exhaust gas inflow side without reaching the end of the partition wall 12 on the exhaust gas outflow side, or it may extend in a direction opposite to the exhaust gas flow direction X from the end of the partition wall 12 on the exhaust gas outflow side without reaching the end of the partition wall 12 on the exhaust gas inflow side.

[0234] From the viewpoint of more effectively achieving the desired first peak and second peak, the mass of the first layer 21 per unit volume of the portion of the substrate 10 in which the first layer 21 is disposed is preferably 100 g / L or more and 180 g / L or less, more preferably 110 g / L or more and 160 g / L or less, and even more preferably 120 g / L or more and 150 g / L or less.

[0235] The mass of the first layer 21 per unit volume of the portion of the substrate 10 in which the first layer 21 is disposed is given by the formula: (mass of the first layer 21) / (volume of the substrate 10) × (average length L of the first layer 21) 21 / Length L of substrate 10 10 )) figure it out.

[0236] The above description regarding the quality of catalyst layer 20 also applies to the quality of layer 1 21. In application, "catalyst layer 20" should be replaced with "layer 1 21".

[0237] Regarding the average length L of catalyst layer 20 20 The above description of the measurement method also applies to the average length L of layer 1, 21. 21 The determination method. In application, "catalyst layer 20" is replaced with "layer 1 21", and "average length L" is... 20 Replace “average length L” with “average length L” 21 ".

[0238] It should be noted that when the first layer 21 extends from the end of the exhaust gas outlet side of the partition wall 12 in a direction opposite to the exhaust gas flow direction X without reaching the end of the exhaust gas inflow side of the partition wall 12, the sample is cut at 5mm intervals through a plane perpendicular to the axial direction of the substrate 10, and the first slice, the second slice, ..., the nth slice are obtained sequentially from the end of the exhaust gas outlet side of the sample.

[0239] The following describes the content of Ce-based oxide particles, Ce-Zr-based composite oxide particles, and Al-based oxide particles in the first layer 21. In the following description, "Ce-based oxide particles" preferably refers to Ce-based oxide particles that are preferred in terms of achieving the desired first peak value and second peak value described above.

[0240] From the viewpoint of more effectively achieving the desired first and second peak values, based on the total mass of Ce-based oxide particles and Ce-Zr composite oxide particles in the first layer 21, the content of Ce-based oxide particles in the first layer 21 is preferably 10% by mass or more and 80% by mass or less, more preferably 20% by mass or more and 70% by mass or less, and even more preferably 30% by mass or more and 60% by mass or less.

[0241] From the viewpoint of more effectively achieving the desired oxygen storage capacity, based on the total mass of Ce-based oxide particles and Ce-Zr-based composite oxide particles in the first layer 21, the content of Ce-Zr-based composite oxide particles in the first layer 21 is preferably 20% by mass or more and 90% by mass or less, more preferably 30% by mass or more and 80% by mass or less, and even more preferably 40% by mass or more and 70% by mass or less.

[0242] From the viewpoint of more effectively achieving the desired first and second peak values ​​and the desired oxygen storage capacity, based on the mass of the first layer 21, the total content of Ce-based oxides and Ce-Zr-based composite oxide particles in the first layer 21 is preferably 30% by mass or more and 80% by mass or less, more preferably 40% by mass or more and 70% by mass or less, and even more preferably 45% by mass or more and 65% by mass or less.

[0243] When the first layer 21 contains Al-based composite oxide particles, from the viewpoint of more effectively achieving the desired first peak and second peak, based on the total mass of Ce-based oxide particles, Ce-Zr-based composite oxide particles and Al-based oxide particles in the first layer 21, the content of Ce-based oxide particles in the first layer 21 is preferably 5% by mass or more and 80% by mass or less, more preferably 15% by mass or more and 60% by mass or less, and even more preferably 25% by mass or more and 40% by mass or less.

[0244] When the first layer 21 contains Al-based composite oxide particles, from the viewpoint of more effectively achieving the desired oxygen storage capacity, based on the total mass of Ce-based oxide particles, Ce-Zr-based composite oxide particles and Al-based oxide particles in the first layer 21, the content of Ce-Zr-based composite oxide particles in the first layer 21 is preferably 10% by mass or more and 80% by mass or less, more preferably 20% by mass or more and 70% by mass or less, and even more preferably 30% by mass or more and 60% by mass or less.

[0245] When the first layer 21 contains Al-based composite oxide particles, from the viewpoint of achieving the desired tightness, based on the total mass of Ce-based oxide particles, Ce-Zr-based composite oxide particles and Al-based oxide particles in the first layer 21, the content of Al-based composite oxide particles in the first layer 21 is preferably 10% by mass or more and 60% by mass or less, more preferably 20% by mass or more and 50% by mass or less, and even more preferably 30% by mass or more and 40% by mass or less.

[0246] When the first layer 21 contains Al-based composite oxide particles, from the viewpoint of more effectively achieving the desired first and second peak values, the desired oxygen storage capacity, and the desired tightness, based on the mass of the first layer 21, the total content of Ce-based oxides, Ce-Zr-based composite oxide particles, and Al-based oxide particles in the first layer 21 is preferably 50% by mass or more and 99% by mass or less, more preferably 60% by mass or more and 95% by mass or less, and even more preferably 70% by mass or more and 90% by mass or less.

[0247] <Level 2>

[0248] The following is an explanation of layer 22.

[0249] like Figure 3 and Figure 4 As shown, the second layer 22 is set on the first layer 21.

[0250] "The second layer 22 is disposed on the first layer 21" means that a portion or all of the second layer 22 exists on the main surface opposite to the main surface of the partition wall 12 on one of the two main surfaces of the first layer 21. "The main surface of the first layer 21" refers to the outer surface of the first layer 21 extending along the exhaust gas flow direction X. The second layer 22 can be disposed directly on the main surface of the first layer 21 or disposed in between other layers, but it is usually disposed directly on the main surface of the first layer 21. The second layer 22 can be configured to cover a portion of the main surface of the first layer 21 or to cover the entire main surface of the first layer 21. Both the embodiment in which the second layer 22 is disposed directly on the main surface of the first layer 21 and the embodiment in which the second layer 22 is disposed in between other layers on the main surface of the first layer 21 are included in "the second layer 22 disposed on the first layer 21".

[0251] like Figure 4 As shown, the second layer 22 extends along the exhaust gas flow direction X from the end of the partition wall 12 on the exhaust gas inflow side to the end of the partition wall 12 on the exhaust gas outflow side. The second layer 22 may extend along the exhaust gas flow direction X from the end of the partition wall 12 on the exhaust gas inflow side without reaching the end of the partition wall 12 on the exhaust gas outflow side, or it may extend in the opposite direction to the exhaust gas flow direction X from the end of the partition wall 12 on the exhaust gas outflow side without reaching the end of the partition wall 12 on the exhaust gas inflow side.

[0252] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the mass of the second layer 22 per unit volume of the portion of the substrate 10 in which the second layer 22 is provided is preferably 50 g / L or more and 140 g / L or less, more preferably 55 g / L or more and 120 g / L or less, and even more preferably 60 g / L or more and 100 g / L or less.

[0253] The mass of the second layer 22 per unit volume of the portion of the substrate 10 in which the second layer 22 is disposed is given by the formula: (mass of the second layer 22) / (volume of the substrate 10) × (average length L of the second layer 22) 22 / Length L of substrate 10 10 )) figure it out.

[0254] The above description regarding the quality of catalyst layer 20 also applies to the quality of second layer 22. In application, "catalyst layer 20" should be replaced with "second layer 22".

[0255] Regarding the average length L of catalyst layer 20 20 The above description of the measurement method also applies to the average length L of the second layer 22. 22 The determination method. In application, "catalyst layer 20" is replaced with "second layer 22", and "average length L" is... 20 Replace “average length L” with “average length L” 22 ".

[0256] It should be noted that when the second layer 22 extends from the end of the exhaust gas outlet side of the partition wall 12 in a direction opposite to the exhaust gas flow direction X without reaching the end of the exhaust gas inflow side of the partition wall 12, the sample is cut at 5mm intervals through a plane perpendicular to the axial direction of the substrate 10, and the first slice, the second slice, ..., the nth slice are obtained sequentially from the end of the exhaust gas outlet side of the sample.

[0257] The second layer 22 contains one or more precious metal elements. As mentioned above, the precious metal elements in the second layer 22 are equivalent to at least a portion of the precious metal elements in the catalyst layer 20.

[0258] From the perspective of achieving a balance between exhaust gas purification performance and cost, based on the mass of the second layer 22, the metal conversion content of precious metal elements in the second layer 22 is preferably 0.010% by mass or more and 20% by mass or less, more preferably 0.050% by mass or more and 10% by mass or less, and even more preferably 0.10% by mass or more and 5.0% by mass or less. "Metal conversion content of precious metal elements in the second layer 22" refers to the metal conversion content of that single precious metal element when the second layer 22 contains one such element, and to the total metal conversion content of the two or more precious metal elements when the second layer 22 contains two or more such elements.

[0259] The metal conversion content of the precious metal elements in the second layer 22 can be determined in the same way as the metal conversion content of the precious metal elements in the catalyst layer 20.

[0260] The second layer 22 preferably contains one or more supports, and at least a portion of the catalytically active component containing the noble metal element is loaded on one or more supports. The meaning and confirmation method of "at least a portion of the catalytically active component is loaded on the support" are the same as those described above.

[0261] The support can be selected from, for example, inorganic oxides. Inorganic oxides are, for example, particulate. From the viewpoint of improving the loading capacity of the catalytically active component, porous inorganic oxides are preferred. Inorganic oxides may or may not have oxygen storage capacity (OSC). In this specification, inorganic oxides having OSC are sometimes referred to as "OSC materials." Inorganic oxides used as supports are different from inorganic oxides used as binders (e.g., inorganic oxide-based binders such as alumina binders, zirconium oxide binders, titanium dioxide binders, and silica binders).

[0262] Examples of inorganic oxides include Ce-based oxides, Ce-Zr composite oxides, Al-based oxides, oxides of rare earth elements other than Ce, and oxides based on zirconium oxide (ZrO2), silicon dioxide (SiO2), titanium dioxide (TiO2), zeolite (aluminosilicate), MgO, ZnO, SnO2, etc. The descriptions of Ce-based oxides, Ce-Zr composite oxides, and Al-based oxides are as described above. Ce-based oxide particles may be preferred Ce-based oxide particles for achieving the desired first and second peak values ​​described above, or they may be other Ce-based oxide particles.

[0263] <Catalyst Manufacturing>

[0264] Catalyst 1 can be manufactured by forming a catalyst layer 20 on substrate 10.

[0265] The catalyst layer 20 can be formed as follows: a slurry is prepared by mixing a source of noble metal elements (e.g., a salt of noble metal elements), Ce-based oxide particles as raw materials, Ce-Zr-based composite oxides as raw materials, Al-based oxide particles as raw materials as appropriate, and other components (e.g., binders, solvents, etc.) as appropriate; the slurry is coated on the substrate 10 and dried and fired to form the catalyst layer 20.

[0266] When the catalyst layer 20 has a first layer 21 and a second layer 22, the catalyst 1 can be manufactured by forming the second layer 22 on the upper side of the first layer 21 after forming the first layer 21 on the substrate 10.

[0267] The first layer 21 can be formed as follows: a first slurry is prepared by mixing Ce-based oxide particles as raw materials, Ce-Zr composite oxide as raw materials, Al-based oxide particles as raw materials as appropriate, and other components (such as binders, solvents, etc.) as appropriate; the first slurry is coated on the substrate 10, dried, and fired to form the first layer 21.

[0268] The second layer 22 can be prepared by mixing a source of precious metal elements and other components (such as inorganic oxides, binders, solvents, etc.) as appropriate. The second slurry is then coated onto the first layer 21, dried, and fired to form the second layer 22.

[0269] As sources of precious metal elements, examples include salts of precious metal elements, such as nitrates, ammonium complex salts, acetates, and chlorides. As binders, examples include alumina sol, zirconium oxide sol, titanium dioxide sol, silica sol, and cerium dioxide sol. As solvents, examples include water and organic solvents.

[0270] The drying temperature is, for example, 70°C or higher and 150°C or lower, and the drying time is, for example, 5 minutes or higher and 1 hour or lower. The firing temperature is, for example, 200°C or higher and 700°C or lower, and the firing time is, for example, 0.5 hours or higher and 5 hours or lower. Firing can be carried out, for example, in an atmospheric atmosphere.

[0271] From the viewpoint of adjusting the CeO2 crystallite diameter in Ce-based oxide particles to a desired range, it is preferable to apply a heat load to the Ce-based oxide particles used as raw materials to adjust the CeO2 crystallite diameter. The heat load can be applied, for example, by firing at 1000°C in an atmospheric atmosphere for 1 hour. The CeO2 crystallite diameter in the Ce-based oxide particles used as raw materials is preferably 6 nm or more, more preferably 10 nm or more, even more preferably 20 nm or more, and even more preferably 30 nm or more. The upper limit of the CeO2 crystallite diameter in the Ce-based oxide particles used as raw materials is, for example, 200 nm, preferably 100 nm, and more preferably 55 nm. These upper limits can be combined with any of the lower limits mentioned above. The method for determining the CeO2 crystallite diameter in the Ce-based oxide particles used as raw materials is the same as the method for determining the CeO2 crystallite diameter in Ce-based oxide particles used as raw materials, except that the method is the same as that for determining the CeO2 crystallite diameter in Ce-based oxide particles.

[0272] From the viewpoint of more effectively achieving the desired first and second peak values, the specific surface area of ​​the Ce-based oxide particles used as raw materials is preferably 100 m². 2 / g or more and 200m 2 / g or less, more preferably 120m 2 / g or more and 180m 2 Below / g, more preferably 130m 2 / g or more and 160m 2 / g or less. The specific surface area of ​​Ce-based oxide particles used as raw materials can be determined by N2 gas adsorption using powdered Ce-based oxide particles and Quantachrome QUADRASORB SI.

[0273] From the viewpoint of more effectively achieving the desired first and second peak values, the specific surface area of ​​the Ce-based oxide particles contained in the slurry is preferably 60 m². 2 / g or more and 160m 2 / g or less, preferably 70m 2 / g or more and 140m 2 Below / g, more preferably 80m 2 / g or more and 120m 2 / g or less. The specific surface area of ​​Ce-based oxide particles contained in the slurry can be determined using a slurry containing Ce-based oxide particles and Quantachrome's QUADRASORB SI by N2 gas adsorption. The slurry containing Ce-based oxide particles can be prepared by mixing water and Ce-based oxide particles. The specific surface area of ​​Ce-based oxide particles contained in the slurry is preferably determined when the slurry does not contain Ce-Zr composite oxide particles, Al oxide particles, or binders.

[0274] Example

[0275] The present invention will now be described in further detail based on embodiments, comparative examples, and experimental examples.

[0276] [Example 1]

[0277] (1) Formation and analysis of the first layer

[0278] (1-1) Preparation of Ce-based oxide particles, Ce-Zr-based composite oxide particles and Al-based oxide particles

[0279] Ce-based oxide particles were prepared. The Ce content in the Ce-based oxide particles, calculated from CeO2, was approximately 100% by mass (>99% by mass).

[0280] Ce-Zr composite oxide particles were prepared. In the Ce-Zr composite oxide particles, the content of Ce as CeO2 was 20% by mass, the content of Zr as ZrO2 was 70% by mass, and the content of Nd as Nd2O3 was 10% by mass.

[0281] Al-based oxide particles were prepared. In the Al-based oxide particles, the content of Al as Al2O3 was 99% by mass, and the content of La as La2O3 was 1% by mass.

[0282] (1-2) Determination of the median particle size of Ce-based oxide particles and Al-based oxide particles

[0283] The median particle size of Ce-based oxide particles was determined as follows. An automated sample feeder (Microtrac SDC, MicrotracBEL) was used to measure the particle size distribution. The sample was placed in an aqueous dispersion medium and irradiated with 40W ultrasound for 360 seconds at a flow rate of 32.5 mL / s. The measurement was then performed using a Microtrac MT3300EXII (MicrotracBEL) laser diffraction particle size distribution analyzer. Pure water was used as the aqueous dispersion medium. The measurement was performed twice under the following conditions: particle refractive index of 1.5, spherical particle shape, solvent refractive index of 1.3, zeroing time of 30 seconds, and measurement time of 30 seconds. The average value of the measured values ​​was taken as the median particle size of the sample. The median particle size of the Ce-based oxide particles determined in this way was 5.0 μm.

[0284] The median particle size of Al-based oxide particles was determined under the same conditions as that of Ce-based oxide particles. The median particle size of Al-based oxide particles was 19 μm.

[0285] (1-3) Determination of CeO2 crystallite diameter in Ce-based oxide particles

[0286] The diameter of CeO2 crystallites in Ce-based oxide particles was determined as follows. Ce-based oxide particles and a commercially available powder X-ray diffractometer (MiniFlex 600, Rigaku Corporation) were used. X-ray diffraction (XRD) was performed under the following conditions: X-ray source: CuKα; operating axis: 2θ / θ; measurement method: continuous; counting unit: cps; start angle: 5°; end angle: 90°; sampling width: 0.02°; scan speed: 10° / min; voltage: 40kV; current: 150mA. In the obtained XRD pattern, peaks originating from CeO2 at 2θ = 55–58° and peaks at 2θ = 46–49° were identified. The crystallite diameter was automatically calculated using analytical software (PDXL version 2, Rigaku Corporation) by applying the Scherrer equation to the identified peaks. The crystallite diameter determined from the peak at 2θ = 55~58° was compared with that determined from the peak at 2θ = 46~49°, and the larger crystallite diameter was selected as the CeO2 crystallite diameter in the Ce-based oxide particles. The CeO2 crystallite diameter in the Ce-based oxide particles is 6.6 nm.

[0287] (1-4) Determination of the specific surface area of ​​Ce-based oxide particles

[0288] The specific surface area of ​​powdered Ce-based oxide particles was determined using the N2 gas adsorption method manufactured by Quantachrome (QUADRASORB SI). The specific surface area of ​​the powdered Ce-based oxide particles was 138 m². 2 / g.

[0289] The specific surface area of ​​Ce-based oxide particles in the slurry was determined using the N2 gas adsorption method of QUADRASORB SI (Quantachrome, Inc.). The slurry containing Ce-based oxide particles was prepared by mixing water and Ce-based oxide particles in a mixing container. The specific surface area of ​​the Ce-based oxide particles in the slurry was measured without Ce-Zr composite oxide particles, Al oxide particles, or binders. The specific surface area of ​​the Ce-based oxide particles in the slurry was 84 m². 2 / g.

[0290] (1-5) Preparation of slurry for forming the first layer

[0291] Add water, Ce-based oxide particles (Ce content converted from CeO2: approximately 100% by mass (>99% by mass)), median particle size: 5.0 μm, crystallite diameter: 6.6 nm, specific surface area: 138 m² to a mixing container. 2The following components were mixed and stirred to prepare a slurry for forming the first layer: Ce-Zr composite oxide particles (Ce content converted to CeO2: 20% by mass, Zr content converted to ZrO2: 70% by mass, Nd content converted to Nd2O3: 10% by mass), Al oxide particles (Al content converted to Al2O3: 99% by mass, La content converted to La2O3: 1% by mass, median particle size: 19 μm), and a binder. The amounts of each component in the slurry for forming the first layer were adjusted so that, based on the mass of the first layer after firing (100% by mass), the composition was: Ce oxide particles: 18.5% by mass, Ce-Zr composite oxide particles: 43.1% by mass, Al oxide particles: 26.5% by mass, and the remainder being binder.

[0292] (1-6) Formation of the first layer

[0293] Prepare at 400 chambers / inch on a plane orthogonal to the axis. 2 The density is a flow-through metal honeycomb substrate with axially extending cells divided by partition walls and a volume of 0.075L.

[0294] The metal honeycomb substrate is impregnated in a slurry for forming the first layer. After drying the metal honeycomb substrate coated with the slurry at 80°C for 1 hour, it is fired at 450°C for 1 hour to form the first layer. The mass of the first layer per unit volume of the portion of the metal honeycomb substrate in which the first layer is provided is 120 g / L.

[0295] (2) Formation of the second layer

[0296] (2-1) Preparation of slurry for forming the second layer

[0297] Water, palladium nitrate, Ce-Zr composite oxide particles (Ce content converted to CeO2: 5% by mass, Zr content converted to ZrO2: 88.5% by mass, and oxide content converted to rare earth elements other than Ce: 6.5% by mass) and binder were added to a mixing container and mixed and stirred to prepare a slurry for forming the second layer. The proportions of each component in the slurry for forming the second layer were adjusted so that, based on the mass of the fired second layer (100% by mass), palladium (converted to metal) was 0.2% by mass, Ce-Zr composite oxide particles were 87.8% by mass, and the remainder was binder.

[0298] (2-2) Formation of the second layer

[0299] A metal honeycomb substrate with a first layer disposed thereon is impregnated in a slurry for forming a second layer. The metal honeycomb substrate coated with the slurry for forming a second layer is dried at 80°C for 1 hour and then fired at 450°C for 1 hour to form a second layer on the first layer. The mass of the second layer per unit volume of the portion of the metal honeycomb substrate with the second layer disposed thereon is 60 g / L.

[0300] As described above, a catalyst for purifying exhaust gas is manufactured having a metal honeycomb substrate and a catalyst layer disposed on the metal honeycomb substrate, wherein the catalyst layer has a first layer disposed on the metal honeycomb substrate and a second layer disposed on the first layer.

[0301] [Example 2]

[0302] The amounts of each component in the slurry for forming the first layer were adjusted so that, based on the mass of the first layer after firing (100% by mass), Ce-based oxide particles were 30.8% by mass, Ce-Zr-based composite oxide particles were 30.8% by mass, Al-based oxide particles were 26.5% by mass, and the remainder was binder. Otherwise, the same operation as in Example 1 was performed to manufacture a catalyst for exhaust gas purification.

[0303] [Example 3]

[0304] The amounts of each component in the slurry for forming the first layer were adjusted so that, based on the mass of the first layer after firing (100% by mass), the Ce-based oxide particles were 43.1% by mass, the Ce-Zr-based composite oxide particles were 18.5% by mass, the Al-based oxide particles were 26.5% by mass, and the remainder was binder. Otherwise, the same operation as in Example 1 was performed to manufacture a catalyst for exhaust gas purification.

[0305] [Example 4]

[0306] Prepare Ce-based oxide particles, Ce-Zr-based composite oxide particles, Al-based oxide particles, and metal honeycomb substrates identical to those in Example 1.

[0307] Water, palladium nitrate, platinum nitrate, rhodium nitrate, Ce-based oxide particles, Ce-Zr composite oxide particles, Al-based oxide particles, and a binder were added to a mixing container and mixed and stirred to prepare a slurry for catalyst layer formation. The amounts of each component in the slurry were adjusted so that, based on the mass of the calcined catalyst layer (100% by mass), palladium was 0.2% by mass (metal conversion), platinum was 0.2% by mass (metal conversion), rhodium was 0.1% by mass (metal conversion), Ce-based oxide particles were 18.7% by mass, Ce-Zr composite oxide particles were 45.3% by mass, Al-based oxide particles were 22.7% by mass, and the remainder was binder.

[0308] A metal honeycomb substrate is impregnated in a catalyst layer forming slurry. The metal honeycomb substrate coated with the catalyst layer forming slurry is dried at 80°C for 1 hour and then fired at 450°C for 1 hour to form a catalyst layer. The mass of the catalyst layer per unit volume of the portion of the metal honeycomb substrate in which the catalyst layer is disposed is 140 g / L.

[0309] As described above, a catalyst for purifying exhaust gas is manufactured having a metal honeycomb substrate and a catalyst layer disposed on the metal honeycomb substrate, wherein the catalyst layer is a single layer.

[0310] [Example 5]

[0311] The amounts of each component in the slurry for forming the catalyst layer were adjusted so that, based on the mass of the calcined catalyst layer (100% by mass), platinum was 0% by mass (i.e., no platinum nitrate was added when preparing the slurry for forming the catalyst layer), palladium was 0.05% by mass (by metal conversion), rhodium was 0.08% by mass (by metal conversion), Ce-based oxide particles were 18.7% by mass, Ce-Zr-based composite oxide particles were 45.4% by mass, Al-based oxide particles were 22.7% by mass, and the balance was binder. Otherwise, the same operation as in Example 4 was performed to manufacture the catalyst for exhaust gas purification.

[0312] [Comparative Example 1]

[0313] The amounts of each component in the slurry for forming the first layer were adjusted so that, based on the mass of the first layer after firing (100% by mass), Ce-based oxide particles were 0% by mass (i.e., no Ce-based oxide particles were added when preparing the slurry for forming the first layer), Ce-Zr-based composite oxide particles were 61.5% by mass, Al-based oxide particles were 26.5% by mass, and the remainder was binder. Otherwise, the same operation as in Example 1 was performed to manufacture a catalyst for exhaust gas purification.

[0314] [Comparative Example 2]

[0315] The amounts of each component in the slurry for forming the first layer were adjusted so that, based on the mass of the first layer after firing (100% by mass), Ce-based oxide particles were 61.5% by mass, Ce-Zr-based composite oxide particles were 0% by mass (i.e., no Ce-Zr-based composite oxide particles were added when preparing the slurry for forming the first layer), Al-based oxide particles were 26.5% by mass, and the remainder was binder. Otherwise, the same operation as in Example 1 was performed to manufacture a catalyst for exhaust gas purification.

[0316] [Comparative Example 3]

[0317] The amounts of each component in the slurry for forming the catalyst layer were adjusted so that, based on the mass of the calcined catalyst layer (100% by mass), palladium was 0.2% by mass (metal equivalent), platinum was 0.2% by mass (metal equivalent), rhodium was 0.1% by mass (metal equivalent), Ce oxide particles were 0% by mass (i.e., no Ce oxide particles were added when preparing the slurry for forming the catalyst layer), Ce-Zr composite oxide particles were 45.3% by mass, Al oxide particles were 45.3% by mass, and the balance was binder. Otherwise, the same operation as in Example 4 was performed to manufacture the catalyst for exhaust gas purification.

[0318] [Comparative Example 4]

[0319] The amounts of each component in the slurry for forming the catalyst layer were adjusted so that, based on the mass of the calcined catalyst layer (100% by mass), platinum was 0% by mass (i.e., no platinum nitrate was added when preparing the slurry for forming the catalyst layer), palladium was 0.05% by mass (i.e., 0.08% by mass (i.e., no Ce-based oxide particles were added when preparing the slurry for forming the catalyst layer), Ce-Zr composite oxide particles were 45.4% by mass, Al oxide particles were 45.4% by mass, and the balance was binder. Otherwise, the same operation as in Comparative Example 3 was performed to manufacture a catalyst for exhaust gas purification.

[0320] [Experimental Example]

[0321] (1) Determination of pore volume

[0322] The catalysts for exhaust gas purification in Examples 1-4 and Comparative Examples 1-3 were cut using planes parallel to the axial direction of the substrate and planes perpendicular to the axial direction of the substrate, respectively, to cut out... Figure 4 The portion indicated by symbol M1 is used to obtain slice M1, which includes a portion of the partition wall and a portion of the catalyst layer. The length of the portion of the partition wall included in slice M1 is equal to the length of slice M1. The length of the portion of the catalyst layer included in slice M1 is equal to the length of slice M1. Slice M1 is obtained near the exhaust gas inflow end of the catalyst. Specifically, slice M1 is obtained by cutting along the exhaust gas flow direction X at two points, 10 mm and 30 mm away from the exhaust gas inflow end of the substrate, respectively, with a plane perpendicular to the axis of the substrate. Slice M1 is a cuboid with a cross-section of 10 mm long × 10 mm wide and a length of 20 mm.

[0323] Using slices M1 cut from the catalysts for exhaust gas purification from Examples 1-4 and Comparative Examples 1-3, the logarithmic differential pore volume distribution of the catalyst layer was determined by mercury porosimetry, and the logarithmic differential pore volume distribution curve of the catalyst layer was obtained. The specific measurement conditions are as follows.

[0324] [Determination of Logarithmic Differential Pore Volume Distribution]

[0325] As the measuring device, the logarithmic differential pore volume distribution was measured using the "Autopore IV9520" automatic porosity meter manufactured by Shimadzu Corporation, under the following conditions and steps.

[0326] (Measurement conditions)

[0327] Measurement environment: 25℃

[0328] Measurement chamber: Sample chamber volume 5cm³ 3 The pressed volume is 0.37 cm³. 3

[0329] Measurement range: 0.0048 MPa to 255.106 MPa

[0330] Measurement points: 54 points within the range of 0.0048 MPa to 0.3447 MPa.

[0331] 77 points within the range of 0.3792 MPa to 255.1060 MPa

[0332] A total of 131 points (points are marked at equal intervals when plotting each pressure using a logarithmic method).

[0333] Press-in volume: Adjusted to be above 25% and below 90%.

[0334] (Low-pressure parameters)

[0335] Exhaust pressure: 50 μmHg

[0336] Exhaust time: 5.0 min

[0337] Mercury injection pressure: 0.0034~0.0036 MPa

[0338] Balance time: 10 seconds

[0339] (High-voltage parameters)

[0340] Balance time: 10 seconds

[0341] (Mercury parameters)

[0342] Forward contact angle: 130.0 degrees

[0343] Retreating contact angle: 130.0 degrees

[0344] Surface tension: 485.0 mN / m (485.0 dyne / cm)

[0345] Mercury density: 13.5335 g / mL

[0346] (Measurement Procedure)

[0347] (a) 54 points were measured in the low-pressure section, ranging from 0.0048 MPa to 0.3447 MPa.

[0348] (b) 77 points were measured in the high-pressure section within the range of 0.3792 MPa to 255.1060 MPa.

[0349] (c) The logarithmic differential pore volume distribution curve (log differential pore volume distribution curve) is obtained from the mercury injection pressure, mercury injection amount and the mass of slice M1.

[0350] It should be noted that (a), (b), and (c) above are performed automatically by the software attached to the device. Other conditions are in accordance with JIS R 1655:2003.

[0351] The first peak, existing in the range of pore size greater than 5 nm and less than 15 nm, and the second peak, existing in the range of pore size greater than 200 nm and less than 3200 nm, were determined from the logarithmic differential pore volume distribution curve of the catalyst layer. The results are shown in Table 1.

[0352] [Table 1]

[0353]

[0354] The catalysts for exhaust gas purification in Examples 4 and 5 differ in the content of platinum, palladium, and rhodium based on metal conversions, but are the same in the content of Ce-based oxide particles, Ce-Zr-based composite oxide particles, and Al-based oxide particles. Therefore, it is presumed that the positions of the first peak, the second peak, and the third peak in Example 5 are the same as those in Example 4.

[0355] The catalysts used for exhaust gas purification in Comparative Examples 3 and 4 differ in the content of platinum, palladium, and rhodium based on metal conversions, but are the same in the content of Ce-based oxide particles, Ce-Zr-based composite oxide particles, and Al-based oxide particles. Therefore, it is speculated that the positions of the first peak, the second peak, and the third peak in Comparative Example 4 are the same as those in Comparative Example 3.

[0356] (2) Measurement of specific surface area

[0357] The specific surface area of ​​the catalyst layer in each catalyst of the examples and comparative examples was determined by N2 gas adsorption method using QUADRASORB SI, manufactured by Quantachrome. The results are shown in Table 2.

[0358] [Table 2]

[0359]

[0360] The catalysts for exhaust gas purification in Examples 4 and 5 differ in the content of platinum, palladium, and rhodium based on metal conversions, but are the same in the content of Ce-based oxide particles, Ce-Zr-based composite oxide particles, and Al-based oxide particles. Therefore, it is presumed that the specific surface area of ​​Example 5 is the same as that of Example 4.

[0361] The catalysts for exhaust gas purification in Comparative Examples 3 and 4 differ in the content of platinum, palladium, and rhodium based on metal conversions, but are the same in the content of Ce-based oxide particles, Ce-Zr-based composite oxide particles, and Al-based oxide particles. Therefore, it is presumed that the specific surface area of ​​Comparative Example 4 is the same as that of Comparative Example 3.

[0362] (3) Measurement and evaluation of exhaust gas purification performance

[0363] (3-1) Measurement and evaluation of emissions

[0364] The exhaust gas purification catalysts of Examples 1-3 and Comparative Examples 1-2 were placed in the exhaust passage of the muffler of a motorized two-wheeled vehicle, and the emissions (g / km) of carbon monoxide (CO), hydrocarbons (HC), non-methane hydrocarbons (NMHC), and nitrogen oxides (NOx) were measured under the following conditions. The results are shown in Table 3.

[0365] Vehicle used: 120cc single-cylinder motorized two-wheeler

[0366] Fuel: Unleaded gasoline

[0367] Driving mode: WMTC

[0368] Test method: according to ISO 6460

[0369] [Table 3]

[0370]

[0371] The exhaust gas purification catalyst of Example 4 was placed upstream of the exhaust passage of the muffler of a motorized two-wheeled vehicle, and the exhaust gas purification catalyst of Example 5 was placed downstream. Emissions of carbon monoxide (CO), hydrocarbons (HC), non-methane hydrocarbons (NMHC), and nitrogen oxides (NOx) were measured (g / km). The vehicle was changed to a single-cylinder 100cc motorized two-wheeled vehicle, and measurements were performed under the same conditions as described above. The exhaust gas purification catalyst of Comparative Example 3 was placed upstream of the exhaust passage of the muffler of the motorized two-wheeled vehicle, and the exhaust gas purification catalyst of Comparative Example 4 was placed downstream. Measurements were performed in the same manner as described above. The results are shown in Figure 4.

[0372] The catalysts for purifying exhaust gas in Examples 4 and 5 differ in the content rates in terms of the metal conversion of platinum, palladium, and rhodium, but are the same in the content rates of Ce-based oxide particles, Ce-Zr-based composite oxide particles, and Al-based oxide particles.

[0373] The catalysts for purifying exhaust gas in Comparative Examples 3 and 4 differ in the content rates in terms of the metal conversion of platinum, palladium, and rhodium, but are the same in the content rates of Ce-based oxide particles, Ce-Zr-based composite oxide particles, and Al-based oxide particles.

[0374] The catalysts for purifying exhaust gas in Example 5 and Comparative Example 4 differ in the content rates of Ce-based oxide particles, Ce-Zr-based composite oxide particles, and Al-based oxide particles, but are the same in the content rates in terms of the metal conversion of platinum, palladium, and rhodium.

[0375] [Table 4]

[0376]

[0377] For each of the catalysts for purifying exhaust gas in Examples 1 to 3 and Comparative Examples 1 to 2, the emissions (EM) of CO, HC, NMHC, and NOx were evaluated using the following evaluation criteria. The results are shown in Table 7.

[0378] <Evaluation Criteria for Exhaust Gas Volume of CO>

[0379] A: EM ≤ 0.730 g / km

[0380] B: 0.730 g / km < EM ≤ 0.750 g / km

[0381] C: 0.750 g / km < EM

[0382] <Evaluation Criteria for Exhaust Gas Volume of HC> [[ID=​​​​​​​​​​​​​​​​​​​​​​

[0391] A: EM ≤ 0.056 g / km

[0392] B: 0.056 g / km < EM ≤ 0.057 g / km

[0393] C: 0.057 g / km < EM

[0394] (3 - 2) Measurement and Evaluation of Light-off Temperature

[0395] Configure the waste gas purification catalysts of Examples 1 to 4 and Comparative Examples 1 to 3 in the reaction tube. Under the condition of an air-fuel ratio (A / F) of 14.5, introduce simulated waste gas (containing CO, C3H6, NO, O2, CO2, H2O, N2) into the reaction tube, and measure the amounts of CO, HC, and NOx contained in the simulated waste gas flowing out of the outlet of the reaction tube. The gas temperature at the inlet of the reaction tube when the purification rates of CO, HC, and NOx reach 50% is determined as the light-off temperature T50 (°C). It should be noted that the light-off temperature T50 is determined during the heating process. The results are shown in Tables 5 and 6.

[0396] [Table 5]

[0397]

[0398] [Table 6]

[0399]

[0400] For the waste gas purification catalysts of Examples 1 to 3 and Comparative Examples 1 to 2, evaluate the T50 of CO, HC, and NOx using the following evaluation criteria.

[0401] <Evaluation Criteria for T50 of CO>

[0402] A: T50 ≤ 260 °C

[0403] B: 260 °C < T50 ≤ 270 °C

[0404] C: 270 °C < T50

[0405] <Evaluation Criteria for T50 of HC>

[0406] A: T50 ≤ 330 °C

[0407] B: 330 °C < T50 ≤ 340 °C

[0408] C: 340 °C < T50

[0409] <Evaluation of T50 of NOx>

[0410] A: T50 ≤ 280 °C

[0411] B: 280℃ <T50≤290℃

[0412] C: 290℃ <T50

[0413] The T50 evaluation results for CO, HC, and NOx are as follows: the case with 3 evaluations A (all evaluations A) is set as the comprehensive T50 evaluation A; the case with evaluations B but not evaluation C is set as the comprehensive T50 evaluation B; and the case with 3 evaluations C (all evaluations C) is set as the comprehensive T50 evaluation C. The results are shown in Table 7.

[0414] (3-3) Comprehensive evaluation of exhaust gas purification performance

[0415] The evaluation results of total CO, HC, NMHC and NOx emissions, along with the comprehensive evaluation of T50, are used to determine the overall performance of exhaust gas purification. Cases with three or more ratings of A are designated as comprehensive evaluation A; cases with two or fewer ratings of A, including rating B but excluding rating C, are designated as comprehensive evaluation B; and cases with one or more ratings of C are designated as comprehensive evaluation C. The results are shown in Table 7.

[0416] [Table 7]

[0417]

[0418] Explanation of reference numerals in the attached figures

[0419] 1. Catalysts for exhaust gas purification

[0420] 10. Metal honeycomb substrate

[0421] 11···Tubular part

[0422] 12···Separation wall section

[0423] Room 13

[0424] 20···Catalyst Layer

[0425] 21···First Floor

[0426] 22···Second Floor

Claims

1. A catalyst for purifying waste gas, comprising: a metal honeycomb substrate and a catalyst layer disposed on the metal honeycomb substrate. The catalyst layer comprises noble metal elements, Ce-based oxide particles, and Ce-Zr-based composite oxide particles. In the logarithmic differential pore volume distribution curve of the catalyst layer obtained by mercury intrusion porosimetry, a first peak exists in the range of pore size greater than 5 nm and less than 15 nm, and a second peak exists in the range of pore size greater than 200 nm and less than 3200 nm. The first peak value is above 0.060 mL / g. The second peak value is above 0.018 mL / g.

2. The catalyst for purifying waste gas according to claim 1, wherein, The second peak exists in the range of aperture above 200 nm and below 1600 nm.

3. The catalyst for purifying waste gas according to claim 1, wherein, The first peak value is above 0.075 mL / g, and the second peak value is above 0.030 mL / g.

4. The catalyst for purifying waste gas according to any one of claims 1 to 3, wherein, The catalyst layer has a specific surface area of ​​70 m². 2 / g or more and 200m 2 / g or less.

5. The catalyst for purifying waste gas according to any one of claims 1 to 3, wherein, The mass of the catalyst layer per unit volume of the portion of the metal honeycomb substrate in which the catalyst layer is disposed is more than 100 g / L and less than 300 g / L.

6. The catalyst for purifying waste gas according to any one of claims 1 to 3, wherein, The catalyst layer contains Al-based oxide particles.

7. The catalyst for purifying waste gas according to claim 6, wherein, The median particle size of the Al-based oxide particles is greater than 15 μm and less than 30 μm.

8. The catalyst for purifying waste gas according to any one of claims 1 to 3, wherein, The catalyst layer comprises a first layer disposed on the metal honeycomb substrate and a second layer disposed on the first layer. At least a portion of the Ce-based oxide particles and at least a portion of the Ce-Zr-based composite oxide particles are contained in the first layer. At least a portion of the precious metal element is contained in the second layer.

9. The catalyst for purifying waste gas according to claim 8, wherein, Based on the total mass of the Ce-based oxide particles and the Ce-Zr composite oxide particles in the first layer, the content of the Ce-based oxide particles in the first layer is more than 10% by mass and less than 80% by mass.

10. The catalyst for purifying waste gas according to claim 9, wherein, Based on the total mass of the Ce-based oxide particles and the Ce-Zr composite oxide particles in the first layer, the content of the Ce-based oxide particles in the first layer is more than 20% by mass and less than 70% by mass.

11. The catalyst for purifying waste gas according to claim 8, wherein, The catalyst layer contains Al-based oxide particles. At least a portion of the Al-based oxide particles are contained in the first layer.

12. The catalyst for purifying waste gas according to claim 11, wherein, The median particle size of the Al-based oxide particles is greater than 15 μm and less than 30 μm.

13. The catalyst for purifying waste gas according to claim 8, wherein, The mass of the first layer per unit volume of the portion of the metal honeycomb substrate in which the first layer is disposed is more than 100 g / L and less than 180 g / L.

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