Exhaust gas cleaning catalyst

Abstract

The purpose of the present invention is to provide an exhaust gas cleaning catalyst with which it is possible to realize improved exhaust gas diffusion and improved reactivity with diffused exhaust gas. In order to achieve the foregoing, provided is an exhaust gas cleaning catalyst (1) comprising a metal honeycomb base material (10) and a catalyst layer (20) provided on the metal honeycomb base material (10). The catalyst layer (20) contains a noble metal element, Ce-based oxide particles, and Ce-Zr-based composite oxide particles. A logarithmic differential pore volume distribution curve of the catalyst layer (20) obtained by a mercury intrusion method shows a first peak value in the pore diameter range from 5 nm to 15 nm and a second peak value in the pore diameter range from 200 nm to 3200 nm, the first peak value being 0.060 mL / g or more, and the second peak value being 0.018 mL / g or more.

Description

Exhaust gas purification catalyst

[0001] The present invention relates to a catalyst for purifying exhaust gases.

[0002] Exhaust gases emitted from internal combustion engines of automobiles, motorcycles, etc. contain harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). Exhaust gas purification catalysts containing precious metal elements such as Pt, Pd, and Rh are used to purify and neutralize these harmful components. Pt and Pd are primarily involved in the oxidation purification of HC and CO, while Rh is primarily involved in the reduction purification of NOx.

[0003] Exhaust gas purification catalysts are required to react under high SV (Space Velocity) conditions. Therefore, it is important to improve the exhaust gas diffusion properties of the catalyst layer. In particular, motorcycles are more likely to experience high SV conditions than automobiles, and the reduction of emissions due to unpurified exhaust gas blowing through has become an issue.

[0004] Patent Literature 1 discloses an exhaust gas purifying catalyst having an improved exhaust gas diffusion property of a catalyst layer, which comprises a substrate and a catalyst layer provided on the substrate, wherein the catalyst layer satisfies the following conditions: (1) in a pore distribution curve measured with a mercury porosimeter, the largest peak of pore volume is in the range of pore diameters of 1 μm or more and 10 μm or less; (2) in an electron microscope observation image (observation magnification 1000 times) of the surface of the catalyst layer, when the areas of a plurality of pores included in the electron microscope observation image are calculated, the standard deviation of the areas of the plurality of pores is 30 μm or less. ２ The present invention discloses an exhaust gas purification catalyst that satisfies all of the following:

[0005] Japanese Patent Application Laid-Open No. 2021-53604

[0006] In order to improve the exhaust gas purification performance of exhaust gas purification catalysts, there is a demand for exhaust gas purification catalysts that can realize improved exhaust gas diffusion and improved reactivity to the diffused exhaust gas.

[0007] An object of the present invention is to provide an exhaust gas purification catalyst that can realize improved exhaust gas diffusion and improved reactivity to the diffused exhaust gas.

[0008] The present invention provides the following inventions. [1] An exhaust gas purification catalyst comprising a metal honeycomb substrate and a catalytic layer provided on the metal honeycomb substrate, wherein the catalytic layer contains a precious metal element, Ce-based oxide particles, and Ce—Zr-based composite oxide particles, and wherein a logarithmic differential pore volume distribution curve of the catalytic layer obtained by mercury intrusion porosimetry has a first peak value in a pore diameter range of 5 nm to 15 nm and a second peak value in a pore diameter range of 200 nm to 3200 nm, the first peak value being 0.060 mL / g or more, and the second peak value being 0.018 mL / g or more. [2] The exhaust gas purification catalyst according to [1], wherein the second peak value is in a pore diameter range of 200 nm to 1600 nm. [3] The exhaust gas purification catalyst 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. [4] The specific surface area of ​​the catalyst layer is 70 m ２ / g or more 200m ２[5] The catalyst for purifying exhaust gas according to any one of [1] to [3], wherein the mass of the catalyst layer per unit volume of the portion of the metal honeycomb substrate where the catalyst layer is provided is 100 g / L or more and 300 g / L or less. [6] The catalyst for purifying exhaust gas according to any one of [1] to [5], wherein the catalyst layer contains Al-based oxide particles. [7] The catalyst for purifying exhaust gas according to [6], wherein the median diameter of the Al-based oxide particles is 15 μm or more and 30 μm or less. [8] The catalyst for purifying exhaust gas according to any one of [1] to [5], wherein the catalyst layer comprises a first layer provided on the metal honeycomb substrate and a second layer provided on the first layer, wherein 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, and at least a portion of the precious metal element is contained in the second layer. [9] The exhaust gas purifying catalyst according to [8], wherein 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-based composite oxide particles in the first layer.

[10] The exhaust gas purifying catalyst according to [9], wherein 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-based composite oxide particles in the first layer.

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

[10] , wherein the catalyst layer contains Al-based oxide particles, and at least a part of the Al-based oxide particles are contained in the first layer.

[12] The exhaust gas purifying catalyst according to

[11] , wherein the median diameter of the Al-based oxide particles is 15 μm or more and 30 μm or less.

[13] The mass of the first layer per unit volume of the portion of the metal honeycomb substrate where the first layer is provided is 100 g / L or more and 180 g / L or less. [8] An exhaust gas purification catalyst according to any one of

[12] to

[13] .

[0009] According to the present invention, there is provided an exhaust gas purification catalyst that can realize improved exhaust gas diffusibility and improved reactivity to the diffused exhaust gas.

[0010] Fig. 1 is a partial end view showing a state in which an exhaust gas purification catalyst according to one embodiment of the present invention is arranged in an exhaust path of an internal combustion engine. Fig. 2 is an end view taken along line A-A in Fig. 1. Fig. 3 is an enlarged view of the area indicated by the symbol R in Fig. 2. Fig. 4 is an end view taken along line B-B in Fig. 1.

[0011] An exhaust gas purifying catalyst 1 (hereinafter referred to as "catalyst 1") according to one embodiment of the present invention will be described below with reference to FIGS.

[0012] As shown in Figure 1, a catalyst 1 is disposed in an exhaust passage in an 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 through the exhaust passage in the exhaust pipe P from one end to the other end of the exhaust pipe P and is purified by the catalyst 1 provided in the exhaust pipe P. In the drawing, the exhaust gas flow direction is indicated by the symbol X. In this specification, the upstream side of the exhaust gas flow direction X may be referred to as the "exhaust gas inflow side" or "upstream side," and the downstream side of the exhaust gas flow direction X may be referred to as the "exhaust gas outflow side" or "downstream side."

[0013] In the exhaust passage in the exhaust pipe P, other exhaust gas purifying catalysts may be arranged upstream or downstream of the catalyst 1 .

[0014] As shown in FIGS. 2 to 4, the catalyst 1 includes a metal honeycomb substrate 10 (hereinafter referred to as the “substrate 10 ”) and a first layer 21 provided on the substrate 10 .

[0015] <<Substrate>> The substrate 10 will be described below.

[0016] The substrate 10 is a honeycomb structure made of a metal material.

[0017] The metal material constituting the substrate 10 can be appropriately selected from known metal materials, such as alloys such as stainless steel.

[0018] As shown in FIGS. 2 to 4, the substrate 10 has a cylindrical portion 11 , partition walls 12 provided inside the cylindrical portion 11 , and cells 13 separated by the partition walls 12 .

[0019] As shown in Fig. 2, the tubular portion 11 defines the outer shape of the substrate 10, and the axial direction of the tubular portion 11 coincides with the axial direction of the substrate 10. As shown in Fig. 2, the shape of the tubular portion 11 is cylindrical, but it may be other shapes such as an elliptical cylinder or a polygonal cylinder.

[0020] 2 to 4, the partition wall 12 is present between adjacent cells 13, and the adjacent cells 13 are separated by the partition wall 12. The thickness of the partition wall 12 is, for example, not less than 20 μm and not more than 1500 μm.

[0021] As shown in FIG. 4, the cell 13 extends in the exhaust gas flow direction X, and has an end on the exhaust gas inlet side and an end on the exhaust gas outlet side.

[0022] As shown in Fig. 4, both the end on the exhaust gas inlet side and the end on the exhaust gas outlet side of the cell 13 are open. Therefore, the exhaust gas that flows in from the end (opening) on ​​the exhaust gas inlet side of the cell 13 flows out from the end (opening) on ​​the exhaust gas outlet side of the cell 13. This type of configuration is called a flow-through type.

[0023] 2 and 3, the end (opening) of the cell 13 on the exhaust gas inlet side has a rectangular shape in plan view, but may have other shapes such as a hexagon, an octagon, etc. The end (opening) of the cell 13 on the exhaust gas outlet side also has a similar shape in plan view.

[0024] The cell density per square inch of the substrate 10 is, for example, 100 cells or more and 1000 cells or less. The cell density per square inch of the substrate 10 means the total number of cells 13 per square inch in a cross section obtained by cutting the substrate 10 along a plane perpendicular to the exhaust gas flow direction X.

[0025] The volume of the substrate 10 is, for example, 0.1 L or more and 20 L or less. The volume of the substrate 10 means the apparent volume of the substrate 10. For example, when the substrate 10 is cylindrical, the outer diameter of the metal honeycomb substrate 10 is 2r, and the length of the substrate 10 is L. １０ Then, the volume of the substrate 10 is calculated by the formula: Volume of the substrate 10 = π × r ２ ×L １０ It is expressed as:

[0026] <Catalyst Layer> The catalyst layer 20 will be described below.

[0027] 3 and 4 , the catalyst layer 20 is provided on the cell 13 side surface of the partition wall section 12. The "cell 13 side surface of the partition wall section 12" means the outer surface of the partition wall section 12 extending in the exhaust gas flow direction X. The catalyst layer 20 may be provided directly on the cell 13 side surface of the partition wall section 12 or may be provided via another layer; however, the catalyst layer 20 is usually provided directly on the cell 13 side surface of the partition wall section 12.

[0028] 4 , the catalyst layer 20 extends along the exhaust gas flow direction X from the end of the partition wall 12 on the exhaust gas inlet side to the end of the partition wall 12 on the exhaust gas outlet 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 inlet side so as not to reach the end of the partition wall 12 on the exhaust gas outlet side, or may extend in the direction opposite to the exhaust gas flow direction X from the end of the partition wall 12 on the exhaust gas outlet side so as not to reach the end of the partition wall 12 on the exhaust gas inlet side.

[0029] <First Peak Value and Second Peak Value> In the logarithmic differential pore volume distribution curve of the catalyst layer 20, the first peak value exists in the pore diameter range of 5 nm to 15 nm, and the second peak value exists in the pore diameter range of 200 nm to 3200 nm.

[0030] In the logarithmic differential pore volume distribution curve of the catalytic layer 20, when one maximum value exists in the pore diameter range of 5 nm or more and 15 nm or less (i.e., when one peak exists in the pore diameter range of 5 nm or more and 15 nm or less in the logarithmic differential pore volume distribution curve of the catalytic layer 20), the one maximum value corresponds to the "first peak value."

[0031] In the logarithmic differential pore volume distribution curve of the catalytic layer 20, when two or more maximum values ​​exist in the pore diameter range of 5 nm or more and 15 nm or less (i.e., when two or more peaks exist in the pore diameter range of 5 nm or more and 15 nm or less in the logarithmic differential pore volume distribution curve of the catalytic layer 20), the maximum value of the two or more maximum values ​​corresponds to the "first peak value."

[0032] In the logarithmic differential pore volume distribution curve of the catalytic layer 20, when one maximum value exists in the pore diameter range of 200 nm or more and 3200 nm or less (i.e., when one peak exists in the pore diameter range of 200 nm or more and 3200 nm or less in the logarithmic differential pore volume distribution curve of the catalytic layer 20), the one maximum value corresponds to the "second peak value."

[0033] In the logarithmic differential pore volume distribution curve of the catalytic layer 20, when two or more maximum values ​​exist in the pore diameter range of 200 nm or more and 3200 nm or less (i.e., when two or more peaks exist in the pore diameter range of 200 nm or more and 3200 nm or less in the logarithmic differential pore volume distribution curve of the catalytic layer 20), the maximum value of the two or more maximum values ​​corresponds to the "second peak value."

[0034] The first peak value is 0.060 mL / g or more. The first peak value reflects the amount of relatively small pores that contribute to an increase in the specific surface area of ​​the catalyst layer 20. When the first peak value is 0.060 mL / g or more, the specific surface area of ​​the catalyst layer 20 increases, and the exhaust gas accessibility and exhaust gas adsorption ability of the catalyst layer 20 are improved. The improved exhaust gas accessibility and exhaust gas adsorption ability of the catalyst layer 20 improve the reactivity of the catalyst layer 20 with diffused exhaust gas.

[0035] The second peak value is 0.018 mL / g or more. The second peak value reflects the amount of relatively large pores that contribute to improving the exhaust gas diffusion property of the catalyst layer 20. When the second peak value is 0.018 mL / g or more, the gas diffusion property of the catalyst layer 20 is improved. The improvement in the gas diffusion property of the catalyst layer 20 prevents unpurified exhaust gas from passing through the catalyst layer 20 without being purified.

[0036] As the pores of the catalyst layer 20 become smaller, the specific surface area of ​​the catalyst layer 20 increases, but the gas diffusibility of the catalyst layer 20 decreases. On the other hand, as the pores of the catalyst layer 20 become larger, the gas diffusibility of the catalyst layer 20 improves, but the specific surface area of ​​the catalyst layer 20 decreases. Therefore, a single type of pore size control, that is, by either reducing the pores of the catalyst layer 20 or increasing the pores of the catalyst layer 20, cannot achieve both an increase in the specific surface area and an improvement in the gas diffusibility 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 also satisfies the condition that the second peak value corresponding to the amount of relatively large pores is 0.018 mL / g or more. This makes it possible to ensure a sufficient number of pores that contribute to an increase in the specific surface area of ​​the catalyst layer 20 and an sufficient number of pores that contribute to improving the gas diffusibility of the catalyst layer 20, thereby achieving an increase in the specific surface area of ​​the catalyst layer 20 and an improvement in the gas diffusibility of the catalyst layer 20. In other words, it is possible to improve the gas diffusibility of the catalyst layer 20 and the reactivity of the catalyst layer 20 with diffused exhaust gas, thereby improving the exhaust gas purification performance of the catalyst layer 20.

[0037] From the viewpoint of more effectively realizing an increase in 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.

[0038] The upper limit of the first peak value is not particularly limited. From the viewpoint of achieving a balance between an increase in the specific surface area of ​​the catalyst layer 20 and an improvement in 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. Each of these upper limits may be combined with any of the above-mentioned lower limits.

[0039] From the viewpoint of more effectively improving the gas diffusibility 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.

[0040] The upper limit of the second peak value is not particularly limited. From the viewpoint of achieving a balance between an increase in the specific surface area of ​​the catalyst layer 20 and an improvement in 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. Each of these upper limits may be combined with any of the above-mentioned lower limits.

[0041] From the viewpoint of more effectively improving the gas diffusion properties of the catalyst layer 20, the second peak value is preferably in the pore diameter range of 200 nm or more and 1600 nm or less, more preferably in the pore diameter range of 200 nm or more and 950 nm or less, even more preferably in the pore diameter range of 300 nm or more and 700 nm or less, and most preferably in the pore diameter range of 400 nm or more and 600 nm or less.

[0042] In this specification, the term "logarithmic differential pore volume distribution curve (log differential pore volume distribution curve)" refers to a curve obtained by dividing the pore volume increase (differential pore volume dV) by the difference in common logarithm (log) between the upper and lower pore diameters corresponding thereto (difference value d(logD)), and plotting the resulting value (logarithmic differential pore volume dV / d(logD)) against the midpoint of the pore diameter increase (average pore diameter for each interval). Note that "pore diameter" refers to diameter.

[0043] In the logarithmic differential pore volume distribution curve of the catalyst layer 20, the horizontal axis represents the pore diameter (μm) of the catalyst layer 20, and the vertical axis represents the logarithmic differential pore volume (mL / g) of the catalyst layer 20 per unit mass of the cut pieces M1 or M2 obtained from the catalyst 1. The cut pieces M1 and M2 will be described later.

[0044] The logarithmic differential pore volume distribution curve of the catalyst layer 20 can be obtained by the following method.

[0045] The catalyst 1 is cut along a plane parallel to the axial direction of the substrate 10 and a plane perpendicular to the axial direction of the substrate 10, and the portions indicated by the symbols M1 and M2 in FIG. 4 are cut out to obtain cut pieces M1 and M2 including a part of the partition wall portion 12 and a part of the catalyst layer 20. The length of the part of the partition wall portion 12 included in the cut piece M1 or M2 is equal to the length of the cut piece M1 or M2. The length of the part of the catalyst layer 20 included in the cut piece M1 or M2 is equal to the length of the cut piece M1 or M2. The cut pieces M1 and M2 can be obtained from the vicinity of the exhaust gas inlet end and the vicinity of the exhaust gas outlet end of the catalyst 1, respectively. For example, by cutting the substrate 10 at two locations 10 mm and 30 mm away from the exhaust gas inlet end in the exhaust gas flow direction X along a plane perpendicular to the axial direction of the substrate 10, a 20 mm-long cut piece M1 can be obtained, which includes a portion of the partition wall 12 and a portion of the catalyst layer 20. By cutting the substrate 10 at two locations 10 mm and 30 mm away from the exhaust gas outlet end in the direction opposite to the exhaust gas flow direction X along a plane perpendicular to the axial direction of the substrate 10, a 20 mm-long cut piece M2 can be obtained, which includes a portion of the partition wall 12 and a portion of the catalyst layer 20. The size of the cut piece M1 or M2 can be changed as appropriate. The cut piece M1 or M2 has, for example, a rectangular parallelepiped cross section measuring 10 mm long x 10 mm wide and 20 mm long.

[0046] By performing mercury porosimetry using the cut piece M1 or M2, a logarithmic differential pore volume distribution curve of the catalyst layer 20 can be obtained.

[0047] Mercury intrusion porosimetry can be carried out using an automatic porosimeter "Autopore IV9520" manufactured by Shimadzu Corporation under the following conditions and procedures.

[0048] (Measurement conditions) Measurement environment: 25°C Measurement cell: sample chamber volume 5 cm ３ , indentation volume 0.37 cm ３Measurement range: 0.0048 MPa to 255.1060 MPa Measurement points: 54 points in the range of 0.0048 MPa to 0.3447 MPa 77 points in the range of 0.3792 MPa to 255.1060 MPa A total of 131 points (points are marked so that they are evenly spaced when the pressure is plotted logarithmically) Pressurization volume: Adjusted to be 25% or more and 90% or less. (Low pressure parameters) Exhaust pressure: 50 μmHg Exhaust time: 5.0 min Mercury injection pressure: 0.0034 to 0.0036 MPa Equilibration time: 10 sec (High pressure parameters) Equilibration time: 10 sec (Mercury parameters) Advancing contact angle: 130.0 degrees Receding contact angle: 130.0 degrees Surface tension: 485.0 mN / m (485.0 dyne / cm) Mercury density: 13.5335 g / mL (Measurement procedure) (a) In the low pressure section, measure 54 points in the range of 0.0048 MPa to 0.3447 MPa or less. (b) In the high pressure section, measure 77 points in the range of 0.3792 MPa to 255.1060 MPa or less. (c) A logarithmic differential pore volume distribution curve (log differential pore volume distribution curve) is calculated from the mercury injection pressure, the amount of mercury injected, and the mass of the cut piece M1 or M2. Note that steps (a), (b), and (c) above can be performed automatically using software provided with the apparatus. Other conditions can be in accordance with JIS R 1655:2003.

[0049] The cut piece M1 or M2 includes a part of the partition wall portions 12 of the substrate 10 and a part of the catalytic layer 20. However, since the partition wall portions 12 of the substrate 10 do not have pore diameters, the logarithmic differential pore volume distribution obtained by mercury intrusion porosimetry reflects the logarithmic differential pore volume distribution of the catalytic layer 20.

[0050] A logarithmic differential pore volume distribution curve of the catalytic layer 20 may be obtained by performing mercury porosimetry using either one of the cut pieces M1 or M2, or by performing mercury porosimetry using both the cut pieces M1 and M2. In the former case, one logarithmic differential pore volume distribution curve is obtained, and 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 sufficient that at least one of the logarithmic differential pore volume distribution curves satisfies the conditions that the first peak value is 0.060 mL / g or more and the second peak value is 0.018 mL / g or more. However, it is preferable that both of the two logarithmic differential pore volume distribution curves satisfy these conditions. When two logarithmic differential pore volume distribution curves are obtained, the above description of <First Peak Value and Second Peak Value> applies to each logarithmic differential pore volume distribution curve. When two logarithmic differential pore volume distribution curves are obtained, the first peak values ​​in the two logarithmic differential pore volume distribution curves may be the same or different. When two logarithmic differential pore volume distribution curves are obtained, the second peak values ​​in the two logarithmic differential pore volume distribution curves may be the same or different.

[0051] <Specific surface area of ​​catalyst layer> The specific surface area of ​​the catalyst layer 20 is preferably 70 m ２ / g or more 200m ２ / g or less, more preferably 75m ２ / g or more 145m ２ / g or less, more preferably 80m ２ / g or more 100m ２ / g or less. When 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, the desired specific surface area of ​​the catalyst layer 20 can be realized. The specific surface area of ​​the catalyst layer 20 is particularly highly correlated with the first peak value. The specific surface area of ​​the catalyst layer 20 was measured using a QUADRASORB SI (manufactured by Quantachrome) ２ It can be measured by gas adsorption method.

[0052] <Coating Amount of Catalyst Layer> From the viewpoint of more effectively achieving the desired first peak value and second peak value, the mass of the catalyst layer 20 per unit volume of the portion of the substrate 10 where the catalyst layer 20 is provided 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.

[0053] The mass of the catalyst layer 20 per unit volume of the portion of the substrate 10 where the catalyst layer 20 is provided is calculated by the formula: (mass of the catalyst layer 20) / ((volume of the substrate 10)×(average length L of the catalyst layer 20) ２０ / Length L of the substrate 10 １０ )) is calculated.

[0054] As used herein, "length" refers to the axial dimension of substrate 10 unless otherwise specified.

[0055] In this specification, the "mass of the catalytic layer 20" refers to the sum of the mass of precious metal elements in metal equivalent and the mass of metal elements other than precious metal elements in oxide equivalent, among all the metal elements contained in the catalytic layer 20. In other words, the "mass of the catalytic layer 20" refers to the calculated mass obtained by summing the mass of precious metal elements contained in the catalytic layer 20 in metal equivalent and the mass of metal elements other than precious metal elements contained in the catalytic layer 20 in oxide equivalent. Note that the "metal elements" also include metalloid elements such as Si and B.

[0056] In this specification, the term "noble metal element" includes Au, Ag, Pt, Pd, Rh, Ir, Ru, and Os.

[0057] In this specification, oxides of rare earth elements other than Ce, Pr, and Tb are referred to as sesquioxides (Ln ２ O ３ , Ln represents a rare earth element other than Ce, Pr, and Tb), and the oxide of Ce is CeO ２ Pr oxide is Pr ６ O １１ The oxide of Tb is Tb ４ O ７ The oxide of Al is Al ２ O ３ Zr oxide is ZrO２ The oxide of Si is SiO ２ The oxide of B is B ２ O ３ Cr oxide is Cr ２ O ３ , Mg oxide is MgO, Ca oxide is CaO, Sr oxide is SrO, Ba oxide is BaO, Fe oxide is Fe ３ O ４ Mn oxide is Mn ３ O ４ Ni oxide is NiO, Ti oxide is TiO ２ Zn oxide is ZnO, Sn oxide is SnO ２ means.

[0058] Average length L of the catalyst layer 20 ２０ An example of the measurement method is as follows.

[0059] Extending from the catalyst 1 in the axial direction of the substrate 10, the length L of the substrate 10 １０ A sample having the same length as the sample is cut out. The sample is, for example, cylindrical with a diameter of 25.4 mm. The diameter of the sample can be changed as needed. The sample is cut at 5 mm intervals along a plane perpendicular to the axial direction of the substrate 10, and a first cut piece, a second cut piece, ..., an nth cut piece are obtained in order from the end of the sample on the exhaust gas inlet side. The length of the cut pieces is 5 mm. The composition of the cut pieces is analyzed using an X-ray fluorescence analyzer (XRF) (e.g., an energy dispersive X-ray analyzer (EDX), a wavelength dispersive X-ray analyzer (WDX), etc.), an inductively coupled plasma atomic emission spectrometer (ICP-AES), a scanning electron microscope-energy dispersive X-ray analysis method (SEM-EDX), etc., and it is confirmed based on the composition of the cut pieces whether or not the cut pieces include a part of the catalyst layer 20.

[0060] It is not necessary to perform composition analysis on a cut piece that is clearly containing a part of the catalyst layer 20. For example, the cut surface can be observed using a scanning electron microscope (SEM), an electron probe microanalyzer (EPMA), or the like to confirm whether the cut piece contains a part of the catalyst layer 20. When observing the cut surface, elemental mapping of the cut surface may be performed.

[0061] After confirming whether the cut pieces contain a part of the catalyst layer 20, the length of the catalyst layer 20 contained in the sample is calculated based on the following formula: Length of the catalyst layer 20 contained in the sample = 5 mm x (number of cut pieces containing a part of the catalyst layer 20)

[0062] For example, if the first to kth cut pieces include a portion of the catalyst layer 20, but the (k+1)th to nth cut pieces do not include a portion of the catalyst layer 20, the length of the catalyst layer 20 included in the sample is (5 x k) mm.

[0063] An example of a more detailed method for measuring the length of the catalyst layer 20 included in the sample is as follows. The kth cut piece (i.e., the cut piece obtained from the exhaust gas outflow side of the sample among the cut pieces including a portion of the catalyst layer 20) is cut in the axial direction of the substrate 10, and the portion of the catalyst layer 20 present on the cut surface is observed using an SEM, an EPMA, or the like, to measure the length of the portion of the catalyst layer 20 in the kth cut piece. Then, the length of the portion of the catalyst layer 20 included in the sample is calculated based on the following formula: Length of the catalyst layer 20 included in the sample = (5 mm × (k - 1)) + (length of the portion of the catalyst layer 20 included in the kth cut piece)

[0064] For 8 to 16 samples arbitrarily cut out from the catalyst 1, the length of the catalyst layer 20 included in each sample is measured, and the average value thereof is taken as the average length L of the catalyst layer 20. ２０ Let's say.

[0065] When the catalyst layer 20 extends from the end of the partition wall portion 12 on the exhaust gas outlet side along the direction opposite to the exhaust gas flow direction X so as not to reach the end of the partition wall portion 12 on the exhaust gas inlet side, the sample is cut at 5 mm intervals along a plane perpendicular to the axial direction of the substrate 10, and a first cut piece, a second cut piece, ..., an n-th cut piece are obtained in order from the end of the sample on the exhaust gas outlet side.

[0066] <Noble Metal Element> The catalyst layer 20 contains one or more kinds of noble metal elements.

[0067] The noble metal element can be selected from, for example, Au, Ag, Pt, Pd, Rh, Ir, Ru, Os, etc., and is preferably selected from Rh, Pt, and Pd.

[0068] The precious metal element is contained in the catalyst layer 20 in a form that can function as a catalytically active component, for example, in the form of a catalytically active component containing a precious metal element, such as a metal, an alloy containing a precious metal element, or a compound containing a precious metal element (e.g., an oxide of a precious metal element).

[0069] From the viewpoint of achieving a balance between exhaust gas purification performance and cost, the content of the precious metal element in the catalyst layer 20 in terms of metal conversion is preferably 0.010 mass % or more and 20 mass % or less, more preferably 0.050 mass % or more and 10 mass % or less, and even more preferably 0.10 mass % or more and 5.0 mass % or less, based on the mass of the catalyst layer 20. The "content of the precious metal element in terms of metal conversion in the catalyst layer 20" means the content of one precious metal element in terms of metal when the catalyst layer 20 contains one kind of precious metal element, or means the total content of the two or more precious metal elements in terms of metal when the catalyst layer 20 contains two or more kinds of precious metal elements.

[0070] When the composition of the raw materials used to manufacture the catalyst layer 20 is known, the content of the precious metal elements in the catalyst layer 20 in terms of metal can be determined from the composition of the raw materials.

[0071] When the composition of the raw materials used to manufacture the catalyst layer 20 is unknown, the content of the precious metal elements in the catalyst layer 20 in terms of metal can be determined using scanning electron microscope-energy dispersive X-ray analysis (SEM-EDX). Specifically, this is as follows.

[0072] An elemental analysis is performed on a sample obtained from the catalyst layer 20 using SEM-EDX to identify the type of constituent elements in the entire sample and to determine the mole percentage of each identified metal element. The mole percentage of each metal element is determined for each of 10 SEM fields, and the average mole percentage of each metal element in the 10 fields is taken as the mole percentage of each metal element in the catalyst layer 20. From the mole percentage of each metal element in the catalyst layer 20, the mass percentage of the precious metal group elements in the catalyst layer 20 in terms of metal, and the mass percentage of each metal element other than the precious metal group elements in the catalyst layer 20 in terms of oxide are calculated. The mass percentage of the precious metal group elements in the catalyst layer 20 in terms of metal is calculated using the formula: (mass of the precious metal group elements in terms of metal calculated from mole percentage) / ((mass of the precious metal group elements in terms of metal calculated from mole percentage) + (mass of the metal elements other than the precious metal group elements in terms of oxide calculated from mole percentage)) × 100. The mass % of each metal element other than the precious metal group elements in the catalytic layer 20 in terms of oxide is calculated from the formula: (mass of each metal element other than the precious metal group elements in terms of oxide calculated from mol %) / ((mass of the precious metal group elements in terms of metal calculated from mol %)+(mass of the metal elements other than the precious metal group elements in terms of oxide calculated from mol %))×100.

[0073] At least a portion of the catalytically active component containing a precious metal element is preferably supported on one or more supports selected from Ce-based oxide particles and Ce—Zr-based composite oxide particles. When catalyst layer 20 contains Al-based oxide particles, at least a portion of the catalytically active component containing a precious metal element is preferably supported on one or more supports selected from Ce-based oxide particles, Ce—Zr-based composite oxide particles, and Al-based oxide particles. Ce-based oxide particles, Ce—Zr-based composite oxide particles, and Al-based oxide particles will be described later.

[0074] "At least a portion of the catalytically active component is supported on the support" means that at least a portion of the catalytically active component is physically and / or chemically adsorbed and / or retained on the outer surface and / or the inner surface of the pores of the support. Support of at least a portion of the catalytically active component on the support can be confirmed, for example, using SEM-EDX or the like. Specifically, when elemental mapping obtained by analyzing a sample obtained from the catalyst layer 20 with SEM-EDX shows that at least a portion of the catalytically active component and the support are present in the same region, it can be determined that at least a portion of the catalytically active component is supported on the support.

[0075] <Ce-Based Oxide Particles> The catalyst layer 20 contains Ce-based oxide particles.

[0076] The Ce-based oxide particles contained in the catalytic layer 20 are distinguished from the Ce-based oxide particles used as a raw material for the catalytic layer 20. Hereinafter, the Ce-based oxide particles contained in the catalytic layer 20 will be simply referred to as "Ce-based oxide particles," and the Ce-based oxide particles used as a raw material for the catalytic layer 20 will be referred to as "Ce-based oxide particles as raw material."

[0077] The Ce-based oxide particles can be used as a support for catalytically active components. From the viewpoint of improving the supportability of the catalytically active components, the Ce-based oxide particles are preferably porous. The Ce-based oxide particles are distinguished from ceria used as a binder (hereinafter referred to as "ceria binder"). The ceria binder is derived from ceria sol or a water-soluble cerium salt such as cerium nitrate, which is used as a raw material for the catalyst layer 20.

[0078] The Ce-based oxide particles are composed of a Ce-based oxide. The Ce-based oxide refers to an oxide containing Ce, in which Ce is the element contained in the greatest amount by mass of elements other than O constituting the oxide. However, Ce-Zr-based composite oxide particles are not considered to be Ce-based oxide particles. Note that Zr in Ce-based oxide particles is ZrO ２ The converted content is usually expressed as ZrO of Zr in the Ce-Zr based composite oxide particles. ２The Ce-based oxide particles are distinguished from Ce—Zr-based composite oxide particles in this respect.

[0079] The Ce-based oxide particles may contain one or more metal elements other than Ce. The metal elements other than Ce 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 metal elements (e.g., Mg, Ca, Sr, Ba, etc.), Fe, Mn, Ni, Zr, Al, etc. The metal elements other than Ce may form a solid solution phase together with Ce and O, or may form a single phase that is a crystalline phase or an amorphous phase (e.g., an oxide phase of a metal element other than Ce), or may form both a solid solution phase and a single phase.

[0080] Examples of Ce-based oxide particles include ceria particles (CeO ２ Examples of the ceria particles include particles obtained by modifying the surface of ceria particles with a metal element other than Ce or its oxide, and particles obtained by dissolving a metal element other than Ce in ceria particles.

[0081] Ce-based oxide particles are an important material for achieving a first peak value of 0.060 mL / g or more and a second peak value of 0.018 mL / g or more. Ce-based oxide particles that are preferable for achieving the desired first peak value and second peak value will be described below.

[0082] From the viewpoint of more effectively realizing the desired first peak value and second peak value, CeO of Ce in the Ce-based oxide particles ２ The converted content is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more, based on the mass of the Ce-based oxide particles. The upper limit is theoretically 100% by mass, but considering the presence of unavoidable impurities, it may actually be less than 100% by mass.

[0083] CeO in Ce-based oxide particles ２The converted content can be determined from elemental mapping obtained by analyzing a sample obtained from the catalyst layer 20 by energy dispersive X-ray spectroscopy (EDX) and EDX elemental analysis of the specified particles. Specifically, the Ce-based oxide particles and other particles (e.g., Ce-Zr-based composite oxide particles, Al-based oxide particles, etc.) are qualitatively identified (color-coded) by elemental mapping, and the specified particles are subjected to composition analysis (elemental analysis), thereby determining the oxide-converted content of the specified element in the specified particles.

[0084] From the viewpoint of more effectively achieving the desired first peak value and second peak value, the median diameter of the Ce-based oxide particles used as the raw material is preferably 0.10 μm to 15 μm, more preferably 0.50 μm to 12 μm, even more preferably 1.0 μm to 10 μm, and even more preferably 2.0 μm to 7.0 μm. The median diameter is the particle size at which the cumulative volume is 50% in a volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method. The median diameter is also referred to as D50. When producing the catalyst layer 20, the median diameter of the Ce-based oxide particles used as the raw material is maintained, and therefore the median diameter of the Ce-based oxide particles is usually the same as the median diameter of the Ce-based oxide particles used as the raw material.

[0085] The median diameter of the Ce-based oxide particles used as raw materials can be measured using a laser diffraction scattering particle size distribution analyzer automatic sample feeder, by adding the sample to be measured to an aqueous dispersion medium, irradiating it with ultrasonic waves, and then using the laser diffraction scattering particle size distribution analyzer. A specific method for measuring the median diameter of the Ce-based oxide particles used as raw materials is as follows. Using a laser diffraction scattering particle size distribution analyzer automatic sample feeder (Microtrac SDC, manufactured by Microtrac-Bell), the sample to be measured is added to an aqueous dispersion medium, irradiated with 40 W ultrasonic waves for 360 seconds at a flow rate of 32.5 mL / sec, and then measurement is performed using a laser diffraction scattering particle size distribution analyzer (Microtrac MT3300EXII, manufactured by Microtrac-Bell). The measurement is carried out twice using pure water as the aqueous dispersion medium under the conditions of a particle refractive index of 1.5, particle shape as a sphere, solvent refractive index of 1.3, set zero of 30 seconds, and measurement time of 30 seconds, and the average value of the obtained measured values ​​is adopted as the median diameter of the sample to be measured.

[0086] The median diameter of the Ce-based oxide particles can be estimated from the particle diameter (e.g., a unidirectional diameter such as a Feret diameter) of the Ce-based oxide particles, which is determined by observing a sample obtained from the catalyst layer 20 using a scanning electron microscope.

[0087] From the viewpoint of more effectively realizing the desired first peak value and second peak value, CeO of the Ce-based oxide particles ２ The crystallite diameter 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. ２ The crystallite size is preferably 200 nm or less, more preferably 100 nm or less, and even more preferably 55 nm or less. Each of these upper limits may be combined with any of the above lower limits.

[0088] CeO of Ce-based oxide particles ２ The crystallite size was measured as follows: X-ray diffraction (XRD) was performed using a powder sample obtained from the catalyst layer 20 and a commercially available X-ray diffractometer. ２Among the peaks derived from the above, the peaks present at 2θ=55 to 58° and the peaks present at 2θ=46 to 49° are identified, and the Scherrer equation is applied to the identified peaks to measure the crystallite diameter. Specific measurement methods are as described in the Examples. The crystallite diameter determined from the peaks present at 2θ=55 to 58° and the crystallite diameter determined from the peaks present at 2θ=46 to 49° are compared, and the larger crystallite diameter is determined as the CeO in the Ce-based oxide particles. ２ In the obtained XRD pattern, CeO ２ The peaks derived from components other than CeO ２ When either one of the peaks at 2θ=55 to 58° and the peak at 2θ=46 to 49° cannot be identified, the crystallite diameter calculated from the peak that can be identified is used as the CeO of the Ce-based oxide particles. ２ The crystallite diameter.

[0089] In the above XRD pattern, CeO ２ Among the peaks derived from the Ce—Zr-based composite oxide, the peak at 2θ=55 to 58° and the peak at 2θ=58 to 61° are adjacent to each other but are shown separately.

[0090] CeO of Ce-based oxide particles ２ The crystallite size may be adjusted, for example, by adjusting the firing conditions when producing the Ce-based oxide particles, or by providing a crystallization step (e.g., exposure to hydrothermal conditions) in the production stage of the Ce-based oxide particles.

[0091] <Ce—Zr-based composite oxide particles> The catalyst layer 20 contains Ce—Zr-based composite oxide particles.

[0092] The Ce—Zr-based composite oxide particles contained in the catalytic layer 20 are distinguished from the Ce—Zr-based composite oxide particles used as a raw material for the catalytic layer 20. Hereinafter, the Ce—Zr-based composite oxide particles contained in the catalytic layer 20 will be simply referred to as "Ce—Zr-based composite oxide particles," and the Ce—Zr-based composite oxide particles used as a raw material for the catalytic layer 20 will be referred to as "Ce—Zr-based composite oxide particles as raw material."

[0093] The Ce—Zr-based composite oxide particles can be used as a support for catalytically active components. From the viewpoint of improving the supportability of the catalytically active components, the Ce—Zr-based composite oxide particles are preferably porous.

[0094] The Ce-Zr composite oxide particles have an oxygen storage capacity (i.e., the capacity to store oxygen when the oxygen concentration in the exhaust gas is high and to release oxygen when the oxygen concentration in the exhaust gas is low), which alleviates fluctuations in the oxygen concentration in the exhaust gas and widens the operating window of the catalytically active component. Therefore, by including a Ce-Zr composite oxide in the catalyst layer 20, the exhaust gas purification capacity of the catalyst layer 20 is improved.

[0095] The Ce—Zr-based composite oxide particles are composed of a Ce—Zr-based composite oxide, which is an oxide containing Ce and Zr.

[0096] The Ce—Zr-based composite oxide particles may contain one or more metal elements other than Ce and Zr. The metal 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 metal elements other than Ce and Zr may form a solid solution phase together with Ce, Zr, and O, or may form a single phase that is a crystalline phase or an amorphous phase (e.g., an oxide phase of a metal element other than Ce), or may form both a solid solution phase and a single phase.

[0097] Examples of Ce-Zr based composite oxide particles include CeO ２ -ZrO ２ Particles composed of solid solution, CeO ２ -ZrO ２ Particles obtained by modifying the surface of particles composed of a solid solution with a metal element other than Ce and Zr or its oxide, CeO ２ -ZrO ２ Examples of such particles include particles obtained by dissolving metal elements other than Ce and Zr in solid solution particles.

[0098] From the viewpoint of improving the oxygen storage capacity of the Ce—Zr-based composite oxide particles, the Ce in the Ce—Zr-based composite oxide particles is ２ The content of Ce in terms of CeO in the Ce-Zr based composite oxide particles 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, based on the mass of the Ce-Zr based composite oxide particles. ２ The converted content of Ce in the Ce-based oxide particles is CeO ２ It can be calculated in the same manner as the converted content.

[0099] From the viewpoint of improving the heat resistance of the Ce—Zr-based composite oxide particles, the Zr in the Ce—Zr-based composite oxide particles is changed to ZrO ２ The content of Zr in the Ce-Zr based composite oxide particles in terms of ZrO 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, even more preferably 40% by mass or more and 95% by mass or less, and even more preferably 50% by mass or more and 90% by mass or less, based on the mass of the Ce-Zr based composite oxide particles. ２ The converted content of Ce in the Ce-based oxide particles is CeO ２ It can be calculated in the same manner as the converted content.

[0100] From the viewpoint of improving the oxygen storage capacity and heat resistance of the Ce—Zr-based composite oxide particles, the Ce in the Ce—Zr-based composite oxide particles is ２ Conversion rate and ZrO ２ The total converted content is preferably 70% by mass or more, more preferably 75% by mass or more, even more preferably 80% by mass or more, and even more preferably 85% by mass or more, based on the mass of the Ce—Zr-based composite oxide particles, with the upper limit being 100% by mass.

[0101] The median diameter of the Ce—Zr-based composite oxide particles used as the 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 even more preferably 1 μm or more and 10 μm or less. The significance of the median diameter is as described above. When producing the catalytic layer 20, the median diameter of the Ce—Zr-based composite oxide particles used as the raw material is maintained, and therefore the median diameter of the Ce—Zr-based composite oxide particles is usually the same as the median diameter of the Ce—Zr-based composite oxide particles used as the raw material. The median diameter of the Ce—Zr-based composite oxide particles used as the raw material can be measured in the same manner as the median diameter of the Ce-based oxide particles used as the raw material. The median diameter of the Ce—Zr-based composite oxide particles can be estimated from the particle diameter of the Ce—Zr-based composite oxide particles (e.g., a unidirectional diameter such as a Feret diameter) determined by observing a sample obtained from the catalytic layer 20 using a scanning electron microscope.

[0102] <Al-Based Oxide Particles> The catalyst layer 20 preferably contains Al-based oxide particles in addition to the Ce-based oxide particles and the Ce—Zr-based composite oxide particles.

[0103] The Al-based oxide particles contained in the catalytic layer 20 are distinguished from Al-based oxide particles used as a raw material for the Al-based oxide particles contained in the catalytic layer 20. Hereinafter, the Al-based oxide particles contained in the catalytic layer 20 will be simply referred to as "Al-based oxide particles," and the Al-based oxide particles used as a raw material for the Al-based oxide particles contained in the catalytic layer 20 will be referred to as "Al-based oxide particles as raw material."

[0104] The Al-based oxide particles can be used as a carrier for catalytically active components. From the viewpoint of improving the supportability of the catalytically active components, the Al-based oxide particles are preferably porous. The Al-based oxide particles are distinguished from alumina used as a binder (hereinafter referred to as "alumina binder"). The alumina binder is derived from alumina sol used as a raw material for the catalyst layer 20.

[0105] The inclusion of Al-based oxide particles in the catalyst layer 20 improves the adhesion between particles (for example, the adhesion between Ce-based oxide particles and Al-based oxide particles, the adhesion between Ce-Zr-based composite oxide particles and Al-based oxide particles, etc.), and also improves the adhesion between the catalyst layer 20 and the substrate 10.

[0106] The Al-based oxide particles are composed of Al-based oxides. The Al-based oxide refers to an oxide containing Al, in which the element other than O that constitutes the oxide has the largest content by mass of Al. However, Ce—Zr-based composite oxide particles are not considered to be Al-based oxide particles.

[0107] The Al-based oxide particles may contain one or more metal elements other than Al. The metal elements other than Al 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 metal elements (e.g., Mg, Ca, Sr, Ba, etc.), B, Si, Zr, Cr, etc. The term "metal element" also includes metalloid elements such as B and Si. The metal elements other than Al may form a solid solution phase with Al and O, or may form a single phase that is a crystalline phase or an amorphous phase (e.g., an oxide phase of a metal element other than Al), or may form both a solid solution phase and a single phase.

[0108] Examples of Al-based oxide particles include alumina particles (Al ２ O ３ Examples include particles obtained by modifying the surface of alumina particles with a metal element other than Al or its oxide, and particles obtained by dissolving a metal element other than Al in alumina particles.

[0109] From the viewpoint of more effectively realizing the desired adhesiveness, the Al content of the Al-based oxide particles is ２ O ３The converted amount is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, based on the mass of the Al-based oxide particles. The upper limit is theoretically 100% by mass, but considering the presence of unavoidable impurities, it may actually be less than 100% by mass.

[0110] From the viewpoint of more effectively achieving the desired adhesion, the median diameter of the Al-based oxide particles as raw material 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 diameter is as described above. When producing the catalyst layer 20, the median diameter of the Al-based oxide particles as raw material is maintained, and therefore the median diameter of the Al-based oxide particles is usually the same as the median diameter of the Al-based oxide particles as raw material. The median diameter of the Al-based oxide particles as raw material can be measured in the same manner as the median diameter of the Ce-based oxide particles as raw material. The median diameter of the Al-based oxide particles can be estimated from the particle diameter of the Al-based oxide particles (e.g., a unidirectional diameter such as a Feret diameter) determined by observing a sample obtained from the catalyst layer 20 using a scanning electron microscope.

[0111] The median diameter of the above-mentioned Ce-based oxide particles, Ce—Zr-based composite oxide particles, and Al-based oxide particles may be adjusted using a known pulverization method such as a ball mill, or may be adjusted using a granulation method such as a spray-drying method during the production of the particles.

[0112] <Other Components> The catalyst layer 20 may contain one or more inorganic oxide particles other than Ce-based oxide particles, Ce—Zr-based composite oxide particles, and Al-based oxide particles. The inorganic oxide particles can be used as a carrier for catalytically active components. From the viewpoint of improving the supportability of 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 of rare earth elements other than Ce, zirconia (ZrO ２ ), silica (SiO ２ ), titania (TiO２ ), zeolite (aluminosilicate), MgO, ZnO, SnO ２ and the like.

[0113] The catalyst layer 20 may contain components such as a binder and a stabilizer. Examples of binders include inorganic oxide binders such as alumina sol, ceria sol, zirconia sol, titania sol, and silica sol. Examples of stabilizers include nitrates, carbonates, oxides, and sulfates of alkaline earth metal elements (e.g., Sr, Ba, etc.).

[0114] <Particle Content> The following describes the contents of Ce-based oxide particles, Ce—Zr-based composite oxide particles, and Al-based oxide particles in the catalytic layer 20. In the following description, the term "Ce-based oxide particles" preferably refers to Ce-based oxide particles that are suitable for achieving the desired first peak value and second peak value described above.

[0115] From the viewpoint of more effectively achieving the desired first peak value and second peak value, the content of the Ce-based oxide particles in the catalytic layer 20 is preferably 5 mass % or more and 95 mass % or less, more preferably 15 mass % or more and 70 mass % or less, and even more preferably 25 mass % or more and 60 mass % or less, based on the total mass of the Ce-based oxide particles and the Ce—Zr-based composite oxide particles in the catalytic layer 20.

[0116] From the viewpoint of more effectively realizing the desired oxygen storage capacity, the content of the Ce—Zr-based composite oxide particles in the catalytic layer 20 is preferably 5 mass % or more and 95 mass % or less, more preferably 30 mass % or more and 85 mass % or less, and even more preferably 40 mass % or more and 75 mass % or less, based on the total mass of the Ce-based oxide particles and the Ce—Zr-based composite oxide particles in the catalytic layer 20.

[0117] From the viewpoint of more effectively achieving the desired first peak value and second peak value and the desired oxygen storage capacity, the total content of the Ce-based oxide and Ce—Zr-based composite oxide particles in the catalytic layer 20 is preferably 15 mass % or more and 80 mass % or less, more preferably 25 mass % or more and 70 mass % or less, and even more preferably 35 mass % or more and 65 mass % or less, based on the mass of the catalytic layer 20.

[0118] When the catalytic layer 20 contains Al-based composite oxide particles, from the viewpoint of more effectively achieving the desired first peak value and second peak value, the content of Ce-based oxide particles in the catalytic layer 20 is preferably 5 mass % or more and 70 mass % or less, more preferably 10 mass % or more and 60 mass % or less, and even more preferably 15 mass % or more and 50 mass % or less, based on the total mass of the Ce-based oxide particles, Ce—Zr-based composite oxide particles, and Al-based oxide particles in the catalytic layer 20.

[0119] When the catalytic layer 20 contains Al-based composite oxide particles, from the viewpoint of more effectively realizing the desired oxygen storage capacity, the content of the Ce—Zr-based composite oxide particles in the catalytic layer 20 is preferably 10 mass % or more and 65 mass % or less, more preferably 20 mass % or more and 60 mass % or less, and even more preferably 30 mass % or more and 55 mass % or less, based on the total mass of the Ce-based oxide particles, Ce—Zr-based composite oxide particles, and Al-based oxide particles in the catalytic layer 20.

[0120] When the catalytic layer 20 contains Al-based composite oxide particles, from the viewpoint of achieving desired adhesion, the content of the Al-based composite oxide particles in the catalytic 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, based on the total mass of the Ce-based oxide particles, Ce—Zr-based composite oxide particles, and Al-based oxide particles in the catalytic layer 20.

[0121] When the catalytic layer 20 contains Al-based composite oxide particles, from the viewpoint of more effectively achieving the desired first peak value and second peak value, the desired oxygen storage capacity, and the desired adhesion, the total content of the Ce-based oxide, Ce—Zr-based composite oxide particles, and Al-based oxide particles in the catalytic 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, based on the mass of the catalytic layer 20.

[0122] When the composition of the raw materials used to manufacture the catalytic layer 20 is known, the contents of the Ce-based oxide particles, the Ce—Zr-based composite oxide particles, and the Al-based oxide particles in the catalytic layer 20 can be determined from the composition of the raw materials.

[0123] When the composition of the raw materials used to manufacture the catalyst layer 20 is unknown, the contents of Ce-based oxide particles, Ce—Zr-based composite oxide particles, and Al-based oxide particles in the catalyst layer 20 can be determined by the following procedures (A) to (D). (A) For a sample obtained from the catalyst layer 20, elemental analysis is performed using a scanning electron microscope-energy dispersive X-ray analysis method (SEM-EDX) on multiple arbitrarily selected fields of view (e.g., 30 fields of view) to identify the types of constituent elements in the entire sample and to determine the oxide-equivalent contents of the specified elements. The average of the oxide-equivalent contents of the specified elements in the multiple fields of view is defined as the oxide-equivalent content of the specified element in the sample. (B) For the sample obtained from the catalyst layer 20, elemental mapping is performed using SEM-EDX to identify the types of particles (Ce-based oxide particles, Ce—Zr-based composite oxide particles, and, in some cases, Al-based oxide particles) contained in the sample. (C) For each type of particle, a plurality of arbitrarily selected particles (e.g., 50 particles) are subjected to elemental analysis using SEM-EDX to identify the types of constituent elements in the plurality of particles and to determine the content of the predetermined element in terms of oxide. The average of the contents of the predetermined element in terms of oxide in the plurality of particles is taken as the content of the predetermined element in terms of oxide in each type of particle. (D) The content of each type of particle in the sample is calculated by creating and solving an equation that represents the relationship between the content of the predetermined element in terms of oxide in the sample, the content of the predetermined element in terms of oxide in each type of particle, and the content of each type of particle in the sample.

[0124] For example, when the Ce source, Zr source, and Al source in the catalytic layer 20 are composed of only three types of particles, namely, Ce-based oxide particles, Ce—Zr-based composite oxide particles, and Al-based oxide particles, the contents of the Ce-based oxide particles, Ce—Zr-based composite oxide particles, and Al-based oxide particles in the catalytic layer 20 can be measured by the following procedure.

[0125] First, elemental analysis is performed using SEM-EDX on 30 arbitrarily selected fields of view of the sample obtained from the catalyst layer 20 to identify the types of constituent elements in the entire sample and to determine the oxide-equivalent content of the predetermined element. The average value of the oxide-equivalent content of the predetermined element in the 30 fields of view is taken as the oxide-equivalent content of the predetermined element in the sample.

[0126] Next, elemental mapping is performed by SEM-EDX on the sample obtained from the catalyst layer 20 to identify the types of particles contained in the sample (Ce-based oxide particles, Ce—Zr-based composite oxide particles, and Al-based oxide particles).

[0127] Next, for each type of particle, 50 arbitrarily selected particles are subjected to elemental analysis using SEM-EDX to identify the types of constituent elements in the 50 particles and to determine the content of the predetermined element in terms of oxide. The average value of the content of the predetermined element in terms of oxide in the 50 particles is taken as the content of the predetermined element in terms of oxide in each type of particle.

[0128] By the above procedure, the following contents can be determined: CeO of Ce in the entire sample ２ Converted content rate (hereinafter referred to as “P”) Ｔ ") CeO of Ce in Ce-based oxide particles ２ Converted content rate (hereinafter referred to as “P”) １ ") CeO of Ce in Ce-Zr based composite oxide particles ２ Converted content rate (hereinafter referred to as “P”) ２ ") CeO of Ce in Al-based oxide particles ２ Converted content rate (hereinafter referred to as “P”) ３ ") ZrO in the entire sample ２ Conversion rate (hereinafter referred to as "Q Ｔ ") ZrO of Zr in Ce-based oxide particles ２ Conversion rate (hereinafter referred to as "Q １ ") ZrO in Ce-Zr composite oxide particles ２ Conversion rate (hereinafter referred to as "Q ２ ") ZrO in Al-based oxide particles ２ Conversion rate (hereinafter referred to as "Q ３") Al in the entire sample ２ O ３ Conversion rate (hereinafter referred to as "R Ｔ ") Al in Ce-based oxide particles ２ O ３ Conversion rate (hereinafter referred to as "R １ ") Al in Ce-Zr based composite oxide particles ２ O ３ Conversion rate (hereinafter referred to as "R ２ ") Al in Al-based oxide particles ２ O ３ Conversion rate (hereinafter referred to as "R ３ ")

[0129] Next, an equation is created that expresses the relationship between the oxide-equivalent content of the specified element in the sample, the oxide-equivalent content of the specified element in each type of particle, and the content of each type of particle in the sample, and the content of each type of particle in the sample is then solved to calculate the content of each type of particle in the sample.

[0130] Specifically, when the contents (by mass) of the Ce-based oxide particles, the Ce—Zr-based composite oxide particles, and the Al-based oxide particles in the catalyst layer 20 are X, Y, and Z, the following formulas (1) to (3) are established. Ｔ = X x P １ + Y × P ２ +Z×P ３ ...(1) Q Ｔ = X × Q １ + Y × Q ２ + Z × Q ３ ... (2) R Ｔ = X × R １ + Y × R ２ +Z×R ３ ...(3)

[0131] From the above formulas (1) to (3), X, Y, and Z can be determined, and the content (mass basis) of Ce-based oxide particles in the catalyst layer 20 can be determined from X, the content (mass basis) of Ce—Zr-based composite oxide particles can be determined from Y, and the content (mass basis) of Al-based oxide particles can be determined from Z.

[0132] <Structure of Catalyst Layer> The catalyst layer 20 may have a single-layer structure or a laminated structure.

[0133] Hereinafter, an embodiment of the catalyst layer 20 having a laminated structure will be described.

[0134] As shown in FIGS. 3 and 4, the catalyst layer 20 includes a first layer 21 provided on the substrate 10 and a second layer 22 provided on the first layer 21 .

[0135] At least a portion of the Ce-based oxide particles in the catalytic layer 20 is contained in the first layer 21. A portion of the Ce-based oxide particles in the catalytic layer 20 may be contained in the first layer 21, or all of the Ce-based oxide particles in the catalytic layer 20 may be contained in the first layer 21. The first layer 21 preferably contains Ce-based oxide particles that are suitable for achieving the desired first peak value and second peak value described above.

[0136] At least a portion of the Ce—Zr-based composite oxide particles in the catalytic layer 20 are contained in the first layer 21. A portion of the Ce—Zr-based composite oxide particles in the catalytic layer 20 may be contained in the first layer 21, or all of the Ce—Zr-based composite oxide particles in the catalytic layer 20 may be contained in the first layer 21.

[0137] At least a portion of the precious metal elements in the catalytic layer 20 is contained in the second layer 22. A portion of the precious metal elements in the catalytic layer 20 may be contained in the second layer 22, or all of the precious metal elements in the catalytic layer 20 may be contained in the second layer 22.

[0138] When the catalytic layer 20 contains Al-based oxide particles, at least a portion of the Al-based oxide particles in the catalytic layer 20 is contained in the first layer 21. A portion of the Al-based oxide particles in the catalytic layer 20 may be contained in the first layer 21, or all of the Al-based oxide particles in the catalytic layer 20 may be contained in the first layer 21.

[0139] Of the first layer 21 and the second layer 22, it is preferable that at least the first layer 21 contributes to the desired first peak value and second peak value. In addition to the first layer 21, the second layer 22 may also contribute to the desired first peak value and second peak value.

[0140] <First Layer> The first layer 21 will be described below.

[0141] 3 and 4 , the first layer 21 is provided on the cell 13 side surface of the partition wall portion 12. The meaning of "the cell 13 side surface of the partition wall portion 12" is as described above. The first layer 21 may be provided directly on the cell 13 side surface of the partition wall portion 12 or may be provided via another layer; however, the first layer 21 is usually provided directly on the cell 13 side surface of the partition wall portion 12.

[0142] 4 , the first layer 21 extends along the exhaust gas flow direction X from the end of the partition wall portion 12 on the exhaust gas inlet side to the end of the partition wall portion 12 on the exhaust gas outlet side. The first layer 21 may extend along the exhaust gas flow direction X from the end of the partition wall portion 12 on the exhaust gas inlet side so as not to reach the end of the partition wall portion 12 on the exhaust gas outlet side, or may extend in the direction opposite to the exhaust gas flow direction X from the end of the partition wall portion 12 on the exhaust gas outlet side so as not to reach the end of the partition wall portion 12 on the exhaust gas inlet side.

[0143] From the viewpoint of more effectively achieving the desired first peak value and second peak value, the mass of the first layer 21 per unit volume of the portion of the substrate 10 where the first layer 21 is provided 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.

[0144] The mass of the first layer 21 per unit volume of the portion of the substrate 10 where the first layer 21 is provided is calculated 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 the substrate 10 １０ )) is calculated.

[0145] The above description regarding the mass of the catalyst layer 20 also applies to the mass of the first layer 21. When applying, "catalyst layer 20" should be read as "first layer 21."

[0146] Average length L of the catalyst layer 20 ２０ The above description of the method for measuring the average length L of the first layer 21 ２１ When applying this method, the "catalyst layer 20" is attached to the "first layer 21" and the "average length L２０ " is "average length L ２１ " can be read as ".

[0147] In addition, when the first layer 21 extends from the end of the partition portion 12 on the exhaust gas outlet side along the direction opposite to the exhaust gas flow direction X so as not to reach the end of the partition portion 12 on the exhaust gas inlet side, the sample is cut at 5 mm intervals along a plane perpendicular to the axial direction of the substrate 10, and a first cut piece, a second cut piece, ..., an n-th cut piece are obtained in order from the end of the sample on the exhaust gas outlet side.

[0148] The following describes the contents 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, the term “Ce-based oxide particles” preferably refers to Ce-based oxide particles that are suitable for achieving the desired first and second peak values ​​described above.

[0149] From the viewpoint of more effectively achieving the desired first peak value and second peak value, the content of the Ce-based oxide particles in the first layer 21 is preferably 10 mass % or more and 80 mass % or less, more preferably 20 mass % or more and 70 mass % or less, and even more preferably 30 mass % or more and 60 mass % or less, based on the total mass of the Ce-based oxide particles and the Ce—Zr-based composite oxide particles in the first layer 21.

[0150] From the viewpoint of more effectively realizing the desired oxygen storage capacity, the content of the 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, based on the total mass of the Ce-based oxide particles and the Ce—Zr-based composite oxide particles in the first layer 21.

[0151] From the viewpoint of more effectively achieving the desired first peak value and second peak value and the desired oxygen storage capacity, the total content of the Ce-based oxide and Ce—Zr-based composite oxide particles in the first layer 21 is preferably 30 mass % or more and 80 mass % or less, more preferably 40 mass % or more and 70 mass % or less, and even more preferably 45 mass % or more and 65 mass % or less, based on the mass of the first layer 21.

[0152] When the first layer 21 contains Al-based composite oxide particles, from the viewpoint of more effectively achieving the desired first peak value and second peak value, the content of Ce-based oxide particles in the first layer 21 is preferably 5 mass % or more and 80 mass % or less, more preferably 15 mass % or more and 60 mass % or less, and even more preferably 25 mass % or more and 40 mass % or less, based on the total mass of the Ce-based oxide particles, Ce—Zr-based composite oxide particles, and Al-based oxide particles in the first layer 21.

[0153] When the first layer 21 contains Al-based composite oxide particles, from the viewpoint of more effectively realizing the desired oxygen storage capacity, the content of the Ce—Zr-based composite oxide particles in the first layer 21 is preferably 10 mass % or more and 80 mass % or less, more preferably 20 mass % or more and 70 mass % or less, and even more preferably 30 mass % or more and 60 mass % or less, based on the total mass of the Ce-based oxide particles, Ce—Zr-based composite oxide particles, and Al-based oxide particles in the first layer 21.

[0154] When the first layer 21 contains Al-based composite oxide particles, from the viewpoint of achieving desired adhesion, the content of the 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, based on the total mass of the Ce-based oxide particles, Ce—Zr-based composite oxide particles, and Al-based oxide particles in the first layer 21.

[0155] When the first layer 21 contains Al-based composite oxide particles, from the viewpoint of more effectively achieving the desired first peak value and second peak value, the desired oxygen storage capacity, and the desired adhesion, the total content of the Ce-based oxide, Ce—Zr-based composite oxide particles, and Al-based oxide particles in the first layer 21 is preferably 50 mass % or more and 99 mass % or less, more preferably 60 mass % or more and 95 mass % or less, and even more preferably 70 mass % or more and 90 mass % or less, based on the mass of the first layer 21.

[0156] <Second Layer> The second layer 22 will now be described.

[0157] As shown in FIGS. 3 and 4, the second layer 22 is disposed on the first layer 21 .

[0158] The phrase "the second layer 22 is provided on the first layer 21" means that part or all of the second layer 22 is present on one of the two main surfaces of the first layer 21 opposite the main surface on the partition wall portion 12 side. The "main surface of the first layer 21" means the outer surface of the first layer 21 extending in the exhaust gas flow direction X. The second layer 22 may be provided directly on the main surface of the first layer 21 or may be provided via another layer, but is typically provided directly on the main surface of the first layer 21. The second layer 22 may be provided so as to cover part of the main surface of the first layer 21 or may be provided so as to cover the entire main surface of the first layer 21. The phrase "the second layer 22 provided on the first layer 21" encompasses both an embodiment in which the second layer 22 is provided directly on the main surface of the first layer 21 and an embodiment in which the second layer 22 is provided on the main surface of the first layer 21 via another layer.

[0159] 4 , the second layer 22 extends along the exhaust gas flow direction X from the end of the partition wall portion 12 on the exhaust gas inlet side to the end of the partition wall portion 12 on the exhaust gas outlet side. The second layer 22 may extend along the exhaust gas flow direction X from the end of the partition wall portion 12 on the exhaust gas inlet side so as not to reach the end of the partition wall portion 12 on the exhaust gas outlet side, or may extend in the direction opposite to the exhaust gas flow direction X from the end of the partition wall portion 12 on the exhaust gas outlet side so as not to reach the end of the partition wall portion 12 on the exhaust gas inlet side.

[0160] 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 where 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.

[0161] The mass of the second layer 22 per unit volume of the portion of the substrate 10 where the second layer 22 is provided is calculated 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 the substrate 10 １０ )) is calculated.

[0162] The above description regarding the mass of the catalyst layer 20 also applies to the mass of the second layer 22. When applied, "catalyst layer 20" is read as "second layer 22."

[0163] Average length L of the catalyst layer 20 ２０ The above description of the method for measuring the average length L of the second layer 22 ２２ In this case, the "catalyst layer 20" is attached to the "second layer 22" and the "average length L ２０ " is "average length L ２２ " can be read as ".

[0164] In addition, when the second layer 22 extends from the end of the partition portion 12 on the exhaust gas outlet side along the direction opposite to the exhaust gas flow direction X so as not to reach the end of the partition portion 12 on the exhaust gas inlet side, the sample is cut at 5 mm intervals along a plane perpendicular to the axial direction of the substrate 10, and a first cut piece, a second cut piece, ..., an n-th cut piece are obtained in order from the end of the sample on the exhaust gas outlet side.

[0165] The second layer 22 contains one or more precious metal elements. As described above, the precious metal elements in the second layer 22 correspond to at least a part of the precious metal elements in the catalyst layer 20.

[0166] From the viewpoint of balancing exhaust gas purification performance and cost, the content of the precious metal element in the second layer 22 in terms of metal is preferably 0.010 mass % or more and 20 mass % or less, more preferably 0.050 mass % or more and 10 mass % or less, and even more preferably 0.10 mass % or more and 5.0 mass % or less, based on the mass of the second layer 22. The "content of the precious metal element in terms of metal in the second layer 22" means the content of one precious metal element in terms of metal when the second layer 22 contains one type of precious metal element, or means the total content of the two or more precious metal elements in terms of metal when the second layer 22 contains two or more types of precious metal elements.

[0167] The content of the noble metal element in the second layer 22 in terms of metal can be measured in the same manner as the content of the noble metal element in terms of metal in the catalyst layer 20 .

[0168] The second layer 22 preferably includes one or more carriers, and at least a portion of the catalytically active component containing a precious metal element is supported on the one or more carriers. The meaning of "at least a portion of the catalytically active component is supported on a carrier" and the method for confirming this are the same as those described above.

[0169] The support can be selected from, for example, inorganic oxides. The inorganic oxide is, for example, particulate. From the viewpoint of improving the supportability of the catalytically active component, the inorganic oxide is preferably porous. The inorganic oxide may or may not have oxygen storage capacity (OSC). In this specification, an inorganic oxide having OSC may be referred to as an "OSC material." The inorganic oxide used as a support is distinguished from the inorganic oxide used as a binder (e.g., inorganic oxide-based binders such as alumina binder, zirconia binder, titania binder, and silica binder).

[0170] Examples of inorganic oxides include Ce-based oxides, Ce-Zr-based composite oxides, Al-based oxides, oxides of rare earth elements other than Ce, and zirconia (ZrO ２ ), silica (SiO ２ ), titania (TiO ２ ), zeolite (aluminosilicate), MgO, ZnO, SnO ２ Examples of the Ce-based oxide include oxides based on Ce and Al. The Ce-based oxide, Ce-Zr-based composite oxide, and Al-based oxide have been described above. The Ce-based oxide particles may be Ce-based oxide particles that are preferable for achieving the desired first and second peak values ​​described above, or may be other Ce-based oxide particles.

[0171] <Production of Catalyst> The catalyst 1 can be produced by forming a catalyst layer 20 on a substrate 10 .

[0172] The catalyst layer 20 can be formed by mixing a source of a precious metal element (e.g., a salt of a precious metal element), Ce-based oxide particles as a raw material, Ce-Zr-based composite oxide as a raw material, optionally Al-based oxide particles as a raw material, and optionally other components (e.g., a binder, a solvent, etc.) to prepare a slurry, applying the slurry onto the substrate 10, drying, and firing.

[0173] When the catalyst layer 20 comprises a first layer 21 and a second layer 22, the catalyst 1 can be manufactured by forming the first layer 21 on the substrate 10 and then forming the second layer 22 on the upper side of the first layer 21.

[0174] The first layer 21 can be formed by mixing Ce-based oxide particles as raw materials, Ce-Zr-based composite oxide as raw materials, and optionally Al-based oxide particles as raw materials, and optionally other components (e.g., a binder, a solvent, etc.) to prepare a first slurry, applying the first slurry onto the substrate 10, drying, and firing.

[0175] The second layer 22 can be formed by mixing a source of a precious metal element and, optionally, other components (e.g., inorganic oxides, binders, solvents, etc.) to prepare a second slurry, applying the second slurry onto the first layer 21, drying, and firing.

[0176] Examples of the source of the noble metal element include salts of the noble metal element, such as nitrates, ammine complex salts, acetates, and chlorides. Examples of the binder include alumina sol, zirconia sol, titania sol, silica sol, and ceria sol. Examples of the solvent include water and organic solvents.

[0177] The drying temperature is, for example, 70° C. to 150° C., and the drying time is, for example, 5 minutes to 1 hour. The firing temperature is, for example, 200° C. to 700° C., and the firing time is, for example, 0.5 hours to 5 hours. The firing can be carried out, for example, in the air.

[0178] CeO in Ce-based oxide particles ２From the viewpoint of adjusting the crystallite size to a desired range, a heat load is applied to the Ce-based oxide particles as a raw material, and the CeO ２ It is preferable to adjust the crystallite size. The heat load can be applied by, for example, firing at 1000°C for 1 hour in an air atmosphere. ２ The crystallite size 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. ２ The upper limit of the crystallite size is, for example, 200 nm, preferably 100 nm, and more preferably 55 nm. These upper limits may be combined with any of the lower limits described above. ２ The method for measuring the crystallite size is the same as that for the CeO in the Ce-based oxide particles, except that the measurement is carried out using Ce-based oxide particles as the raw material. ２ The method for measuring the crystallite size is the same as that for measuring the crystallite size.

[0179] From the viewpoint of more effectively realizing the desired first peak value and second peak value, the specific surface area of ​​the Ce-based oxide particles as the raw material is preferably 100 m ２ / g or more 200m ２ / g or less, more preferably 120m ２ / g or more 180m ２ / g or less, more preferably 130m ２ / g or more 160m ２ The specific surface area of ​​the Ce-based oxide particles used as raw materials is determined by measuring the specific surface area of ​​the powdered Ce-based oxide particles and the specific surface area of ​​the Ce-based oxide particles using QUADRASORB SI manufactured by Quantachrome Corporation. ２ It can be measured by gas adsorption method.

[0180] From the viewpoint of more effectively realizing the desired first peak value and second peak value, the specific surface area of ​​the Ce-based oxide particles contained in the slurry is preferably 60 m ２ / g or more 160m ２ / g or less, more preferably 70m ２ / g or more 140m ２ / g or less, more preferably 80m ２ / g or more 120m ２ The specific surface area of ​​the Ce-based oxide particles contained in the slurry is measured by measuring the specific surface area of ​​the Ce-based oxide particles in a slurry containing the Ce-based oxide particles using QUADRASORB SI manufactured by Quantachrome Corporation. ２ It can be measured by a gas adsorption method. A slurry containing Ce-based oxide particles can be prepared by mixing water and Ce-based oxide particles. The specific surface area of ​​the Ce-based oxide particles contained in the slurry is preferably measured in a state where the slurry does not contain Ce—Zr-based composite oxide particles, Al-based oxide particles, or a binder.

[0181] The present invention will be described in further detail below based on examples, comparative examples and test examples.

[0182] Example 1 (1) Formation and Analysis of First Layer (1-1) Preparation of Ce-Based Oxide Particles, Ce—Zr-Based Composite Oxide Particles, and Al-Based Oxide Particles Ce-based oxide particles were prepared. ２ The converted content was nearly 100% by mass (>99% by mass).

[0183] Ce—Zr-based composite oxide particles were prepared. In the Ce—Zr-based composite oxide particles, CeO ２ The converted content is 20 mass%, ZrO ２ The converted content is 70 mass%, Nd ２ O ３ The converted content was 10% by mass.

[0184] Al-based oxide particles were prepared. ２ O ３ The converted content is 99% by mass, and the La content is ２ O ３ The converted content was 1% by mass.

[0185] (1-2) Measurement of Median Diameter of Ce-Based Oxide Particles and Al-Based Oxide Particles The median diameter of Ce-based oxide particles was measured as follows. Using a laser diffraction scattering particle size distribution analyzer automatic sample feeder (Microtrac SDC manufactured by Microtrac-Bell), the sample to be measured was introduced into an aqueous dispersion medium, and irradiated with 40 W ultrasonic waves for 360 seconds at a flow rate of 32.5 mL / sec. After that, measurement was performed using a laser diffraction scattering particle size distribution analyzer (Microtrac MT3300EXII manufactured by Microtrac-Bell). The measurement was performed twice using pure water as the aqueous dispersion medium under the following conditions: particle refractive index of 1.5, particle shape of spherical, solvent refractive index of 1.3, set zero of 30 seconds, and measurement time of 30 seconds. The average of the obtained measured values ​​was adopted as the median diameter of the sample to be measured. The median diameter of the Ce-based oxide particles measured in this manner was 5.0 μm.

[0186] The median diameter of the Al-based oxide particles was measured under the same conditions as those for the Ce-based oxide particles, and was found to be 19 μm.

[0187] (1-3) CeO in Ce-based oxide particles ２ Measurement of crystallite size CeO in Ce-based oxide particles ２ The crystallite size was measured as follows. X-ray diffraction (XRD) was performed using Ce-based oxide particles and a commercially available powder X-ray diffractometer ("MiniFlex600" manufactured by Rigaku Corporation) under the following conditions: X-ray source: CuKα, operation axis: 2θ / θ, measurement method: continuous, counting unit: cps, start angle: 5°, end angle: 90°, sampling width: 0.02°, scan speed: 10° / min, voltage: 40 kV, current: 150 mA. In the obtained XRD pattern, CeO ２ Among the diffraction peaks resulting from the above, the peaks present at 2θ = 55 to 58° and the peaks present at 2θ = 46 to 49° were identified, and the crystallite diameter was automatically calculated by applying the Scherrer equation to the identified peaks using analytical software ("PDXL version 2" manufactured by Rigaku Corporation). The crystallite diameter obtained from the peaks present at 2θ = 55 to 58° and the crystallite diameter obtained from the peaks present at 2θ = 46 to 49° were compared, and the larger crystallite diameter was determined to be CeO in the Ce-based oxide particles.２ The crystallite size was selected as the CeO crystallite size for the Ce-based oxide particles. ２ The crystallite diameter was 6.6 nm.

[0188] (1-4) Measurement of the specific surface area of ​​Ce-based oxide particles ２ The specific surface area of ​​the powdered Ce-based oxide particles was measured by a gas adsorption method. The specific surface area of ​​the powdered Ce-based oxide particles was 138 m ２ / g.

[0189] N using QUADRASORB SI manufactured by Quantachrome ２ The specific surface area of ​​the Ce-based oxide particles contained in the slurry was measured by gas adsorption. The slurry containing Ce-based oxide particles was prepared by adding water and Ce-based oxide particles to a mixing vessel and mixing the water and Ce-based oxide particles. The specific surface area of ​​the Ce-based oxide particles contained in the slurry was measured in a state where the slurry did not contain Ce-Zr composite oxide particles, Al-based oxide particles, or binder. The specific surface area of ​​the Ce-based oxide particles contained in the slurry was 84 m ２ / g.

[0190] (1-5) Preparation of slurry for forming first layer: In a mixing vessel, water, Ce-based oxide particles (CeO ２ Converted content: almost 100% by mass (>99% by mass), median diameter: 5.0 μm, crystallite diameter: 6.6 nm, specific surface area: 138 m ２ / g), Ce-Zr based composite oxide particles (CeO ２ Conversion content: 20 mass% ZrO ２ Conversion content: 70% by mass of Nd ２ O ３ Conversion rate: 10 mass %), Al-based oxide particles (Al ２ O ３ Conversion content: 99% by mass, La ２ O ３The resulting mixture was mixed and stirred to prepare a first layer forming slurry. The amounts of the components in the first layer forming slurry were adjusted so that, based on the mass of the fired first layer (100 mass%), the Ce-based oxide particles were 18.5 mass%, the Ce-Zr-based composite oxide particles were 43.1 mass%, the Al-based oxide particles were 26.5 mass%, and the remainder was the binder.

[0191] (1-6) Formation of the first layer Cells extending in the axial direction and partitioned by partition walls were arranged at 400 cells / inch in the plane perpendicular to the axial direction. ２ A flow-through metal honeycomb substrate having a density of 0.075 L and a volume of 0.075 L was prepared.

[0192] The metal honeycomb substrate was immersed in the first layer forming slurry, and the metal honeycomb substrate coated with the first layer forming slurry was dried at 80° C. for 1 hour and then 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 where the first layer was provided was 120 g / L.

[0193] (2) Formation of Second Layer (2-1) Preparation of Slurry for Forming Second Layer In a mixing vessel, water, palladium nitrate, Ce—Zr-based composite oxide particles (CeO ２ Conversion content: 5 mass% ZrO ２ The amount of each component in the second layer forming slurry was adjusted so that, based on the mass of the second layer after firing (100 mass%), palladium was 0.2 mass% in terms of metal, the Ce-Zr composite oxide particles were 87.8 mass%, and the remainder was the binder.

[0194] (2-2) Formation of the second layer The metal honeycomb substrate on which the first layer was provided was immersed in the second layer forming slurry, and the metal honeycomb substrate coated with the second layer forming slurry was dried at 80°C for 1 hour and then fired at 450°C for 1 hour to form the second layer on the first layer. The mass of the second layer per unit volume of the portion of the metal honeycomb substrate on which the second layer was provided was 60 g / L.

[0195] In this manner, an exhaust gas purification catalyst was produced, which comprises a metal honeycomb substrate and a catalyst layer provided on the metal honeycomb substrate, wherein the catalyst layer comprises a first layer provided on the metal honeycomb substrate and a second layer provided on the first layer.

[0196] Example 2 An exhaust gas purifying catalyst was produced in the same manner as in Example 1, except that the amounts of the components in the first layer-forming slurry were adjusted so that, based on the mass of the fired first layer (100 mass%), the Ce-based oxide particles were 30.8 mass%, the Ce—Zr-based composite oxide particles were 30.8 mass%, the Al-based oxide particles were 26.5 mass%, and the remainder was the binder.

[0197] Example 3 An exhaust gas purifying catalyst was produced in the same manner as in Example 1, except that the amounts of the components in the first layer-forming slurry were adjusted so that, based on the mass of the fired first layer (100 mass%), the Ce-based oxide particles were 43.1 mass%, the Ce—Zr-based composite oxide particles were 18.5 mass%, the Al-based oxide particles were 26.5 mass%, and the remainder was the binder.

[0198] Example 4 The same Ce-based oxide particles, Ce—Zr-based composite oxide particles, Al-based oxide particles, and metal honeycomb substrate as in Example 1 were prepared.

[0199] Water, palladium nitrate, platinum nitrate, rhodium nitrate, Ce-based oxide particles, Ce—Zr-based composite oxide particles, Al-based oxide particles, and a binder were added to a mixing vessel, and the mixture was mixed and stirred to prepare a slurry for forming a catalyst layer. The amounts of each component in the slurry for forming a catalyst layer were adjusted so that, based on the mass of the catalyst layer after firing (100 mass%), palladium was 0.2 mass% in terms of metal, platinum was 0.2 mass% in terms of metal, rhodium was 0.1 mass% in terms of metal, Ce-based oxide particles were 18.7 mass%, Ce—Zr-based composite oxide particles were 45.3 mass%, Al-based oxide particles were 22.7 mass%, and the remainder was the binder.

[0200] A metal honeycomb substrate was immersed in the catalyst layer forming slurry, and the metal honeycomb substrate coated with the catalyst layer forming slurry was 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 where the catalyst layer was provided was 140 g / L.

[0201] In this manner, an exhaust gas purifying catalyst was produced, which included a metal honeycomb substrate and a catalyst layer provided on the metal honeycomb substrate, the catalyst layer being a single layer.

[0202] Example 5 An exhaust gas purification catalyst was produced by the same operation as in Example 4, except that the amount of each component in the catalyst layer-forming slurry was adjusted so that, relative to the mass of the catalyst layer after calcination (100 mass%), platinum was 0 mass% in metal equivalent (i.e., platinum nitrate was not added when preparing the catalyst layer-forming slurry), palladium was 0.05 mass% in metal equivalent, rhodium was 0.08 mass% in metal equivalent, Ce-based oxide particles were 18.7 mass%, Ce—Zr-based composite oxide particles were 45.4 mass%, Al-based oxide particles were 22.7 mass%, and the remainder was binder.

[0203] Comparative Example 1 An exhaust gas purifying catalyst was produced by the same operation as in Example 1, except that the amounts of the respective components in the first layer-forming slurry were adjusted so that, relative to the mass of the fired first layer (100 mass%), the Ce-based oxide particles were 0 mass% (i.e., no Ce-based oxide particles were added when preparing the first layer-forming slurry), the Ce—Zr-based composite oxide particles were 61.5 mass%, the Al-based oxide particles were 26.5 mass%, and the remainder was the binder.

[0204] Comparative Example 2 An exhaust gas purifying catalyst was produced by the same operation as in Example 1, except that the amounts of the respective components in the first layer-forming slurry were adjusted so that, relative to the mass of the fired first layer (100 mass%), the Ce-based oxide particles were 61.5 mass%, the Ce—Zr-based composite oxide particles were 0 mass% (i.e., no Ce—Zr-based composite oxide particles were added when preparing the first layer-forming slurry), the Al-based oxide particles were 26.5 mass%, and the remainder was the binder.

[0205] Comparative Example 3 An exhaust gas purification catalyst was produced by the same operation as in Example 4, except that the amounts of each component in the catalyst layer-forming slurry were adjusted so that, relative to the mass of the catalyst layer after calcination (100 mass%), palladium was 0.2 mass% in terms of metal, platinum was 0.2 mass% in terms of metal, rhodium was 0.1 mass% in terms of metal, Ce-based oxide particles were 0 mass% (i.e., no Ce-based oxide particles were added during the preparation of the catalyst layer-forming slurry), Ce—Zr-based composite oxide particles were 45.3 mass%, Al-based oxide particles were 45.3 mass%, and the remainder was binder.

[0206] Comparative Example 4 An exhaust gas purification catalyst was produced by performing the same operation as in Comparative Example 3, except that the amounts of each component in the catalyst layer-forming slurry were adjusted so that, relative to the mass of the catalyst layer after calcination (100 mass%), platinum was 0 mass% in metal equivalent (i.e., platinum nitrate was not added when preparing the catalyst layer-forming slurry), palladium was 0.05 mass% in metal equivalent, rhodium was 0.08 mass% in metal equivalent, Ce-based oxide particles were 0 mass% (i.e., Ce-based oxide particles were not added when preparing the catalyst layer-forming slurry), Ce—Zr-based composite oxide particles were 45.4 mass%, Al-based oxide particles were 45.4 mass%, and the remainder was binder.

[0207] [Test Example] (1) Measurement of Pore Volume Each of the exhaust gas purification catalysts of Examples 1 to 4 and Comparative Examples 1 to 3 was cut along a plane parallel to the axial direction of the substrate and a plane perpendicular to the axial direction of the substrate, and the portion indicated by symbol M1 in FIG. 4 was cut out to obtain a cut piece M1 including a part of the partition wall portion and a part of the catalyst layer. The length of the part of the partition wall portion included in the cut piece M1 was equal to the length of the cut piece M1. The length of the part of the catalyst layer included in the cut piece M1 was equal to the length of the cut piece M1. The cut piece M1 was obtained from the vicinity of the exhaust gas inlet end of the catalyst. Specifically, the cut piece M1 was obtained by cutting the substrate at two locations 10 mm and 30 mm away from the exhaust gas inlet end in the exhaust gas flow direction X along a plane perpendicular to the axial direction of the substrate. The cut piece M1 had a rectangular parallelepiped cross section measuring 10 mm long x 10 mm wide and 20 mm long.

[0208] The logarithmic differential pore volume distribution of the catalyst layer was measured by mercury intrusion porosimetry using a cut piece M1 cut out from each of the exhaust gas purifying catalysts of Examples 1 to 4 and Comparative Examples 1 to 3, and a logarithmic differential pore volume distribution curve of the catalyst layer was obtained. The specific measurement conditions were as follows:

[0209] [Measurement of Logarithmic Differential Pore Volume Distribution] The logarithmic differential pore volume distribution was measured using an automatic porosimeter "Autopore IV9520" manufactured by Shimadzu Corporation as a measuring device under the following conditions and procedures. (Measurement conditions) Measurement environment: 25°C Measurement cell: sample chamber volume 5 cm ３ , indentation volume 0.37 cm ３ Measurement range: 0.0048 MPa to 255.106 MPa Measurement points: 54 points in the range of 0.0048 MPa to 0.3447 MPa 77 points in the range of 0.3792 MPa to 255.1060 MPa A total of 131 points (points were marked so that they were evenly spaced when the pressure was plotted logarithmically) Indentation volume: adjusted to be 25% or more and 90% or less. (Low pressure parameters) Exhaust pressure: 50 μmHg Exhaust time: 5.0 min Mercury injection pressure: 0.0034 to 0.0036 MPa Equilibration time: 10 sec (High pressure parameters) Equilibration time: 10 sec (Mercury parameters) Advancing contact angle: 130.0 degrees Receding contact angle: 130.0 degrees Surface tension: 485.0 mN / m (485.0 dyne / cm) Mercury density: 13.5335 g / mL (Measurement procedure) (a) 54 points were measured in the low pressure range from 0.0048 MPa to 0.3447 MPa. (b) 77 points were measured in the high pressure range from 0.3792 MPa to 255.1060 MPa. (c) A logarithmic differential pore volume distribution curve (log differential pore volume distribution curve) was calculated from the mercury injection pressure, the mercury injection amount, and the mass of the cut piece M1. Note that steps (a), (b), and (c) above were performed automatically using software attached to the apparatus. Other conditions were in accordance with JIS R 1655:2003.

[0210] From the logarithmic differential pore volume distribution curve of the catalyst layer, the first peak value present in the pore diameter range of 5 nm to 15 nm and the second peak value present in the pore diameter range of 200 nm to 3200 nm were determined. The results are shown in Table 1.

[0211]

[0212] The exhaust gas purification catalysts of Examples 4 and 5 differ in terms of the metal-equivalent contents of platinum, palladium, and rhodium, but are identical in terms of the contents of Ce-based oxide particles, Ce—Zr-based composite oxide particles, and Al-based oxide particles. Therefore, it is presumed that the first peak value, the second peak value, and the position of the second peak value in Example 5 are similar to those in Example 4.

[0213] The exhaust gas purification catalysts of Comparative Examples 3 and 4 differ in terms of the metal-equivalent contents of platinum, palladium, and rhodium, but are identical in terms of the contents of Ce-based oxide particles, Ce—Zr-based composite oxide particles, and Al-based oxide particles. Therefore, it is presumed that the first peak value, the second peak value, and the position of the second peak value in Comparative Example 4 are similar to those in Comparative Example 3.

[0214] (2) Measurement of specific surface area: Quantachrome QUADRASORB SI was used. ２ The specific surface area of ​​the catalyst layer of each of the catalysts of the examples and comparative examples was measured by gas adsorption method. The results are shown in Table 2.

[0215]

[0216] The exhaust gas purification catalysts of Examples 4 and 5 differ in terms of the metal-equivalent contents of platinum, palladium, and rhodium, but are identical in terms of the contents 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 similar to that of Example 4.

[0217] The exhaust gas purification catalysts of Comparative Examples 3 and 4 differ in terms of the metal-equivalent contents of platinum, palladium, and rhodium, but are identical in terms of the contents 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 similar to that of Comparative Example 3.

[0218] (3) Measurement and Evaluation of Exhaust Gas Purification Performance (3-1) Measurement and Evaluation of Emissions Each of the exhaust gas purification catalysts of Examples 1 to 3 and Comparative Examples 1 and 2 was placed in the exhaust passage of a motorcycle muffler, 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. Vehicle used: Single-cylinder 120cc motorcycle Fuel: Unleaded gasoline Driving mode: WMTC Measurement method: Compliant with ISO 6460

[0219]

[0220] The exhaust gas purification catalyst of Example 4 was placed on the upstream side in the exhaust passage of a motorcycle muffler, and the exhaust gas purification catalyst of Example 5 was placed on the downstream side, and the emissions (g / km) of carbon monoxide (CO), hydrocarbons (HC), non-methane hydrocarbons (NMHC), and nitrogen oxides (NOx) were measured. The measurements were carried out under the same conditions as above, except that the vehicle used was changed to a single-cylinder 100cc motorcycle. The exhaust gas purification catalyst of Comparative Example 3 was placed on the upstream side in the exhaust passage of a motorcycle muffler, and the exhaust gas purification catalyst of Comparative Example 4 was placed on the downstream side, and the same measurements were carried out as above. The results are shown in Table 4.

[0221] The exhaust gas purification catalysts of Examples 4 and 5 differ in the metal-equivalent contents of platinum, palladium, and rhodium, but are the same in the contents of Ce-based oxide particles, Ce—Zr-based composite oxide particles, and Al-based oxide particles.

[0222] The exhaust gas purification catalysts of Comparative Examples 3 and 4 differ in terms of the metal-equivalent contents of platinum, palladium, and rhodium, but are identical in terms of the contents of Ce-based oxide particles, Ce—Zr-based composite oxide particles, and Al-based oxide particles.

[0223] The exhaust gas purification catalysts of Example 5 and Comparative Example 4 differ in the contents of Ce-based oxide particles, Ce—Zr-based composite oxide particles, and Al-based oxide particles, but are identical in the contents of platinum, palladium, and rhodium in terms of metal.

[0224]

[0225] The exhaust gas purifying catalysts of Examples 1 to 3 and Comparative Examples 1 and 2 were evaluated for CO, HC, NMHC, and NOx emissions (EM) using the following evaluation criteria. The results are shown in Table 7.

[0226] <Evaluation criteria for CO emissions> A: EM≦0.730 g / km B: 0.730 g / km<EM≦0.750 g / km C: 0.750 g / km<EM

[0227] <Evaluation criteria for HC displacement> A: EM≦0.132 g / km B: 0.132 g / km<EM≦0.135 g / km C: 0.135 g / km<EM

[0228] <NMHC engine displacement evaluation criteria> A: EM≦0.125g / km B: 0.125g / km<EM≦0.128g / km C: 0.128g / km<EM

[0229] <Evaluation criteria for NOx emissions> A: EM≦0.056 g / km B: 0.056 g / km<EM≦0.056 g / km C: 0.057 g / km<EM

[0230] (3-2) Measurement and Evaluation of Light-Off Temperature Each of the exhaust gas purification catalysts of Examples 1 to 4 and Comparative Examples 1 to 3 was placed in a reaction tube, and simulated exhaust gas (CO, C) was measured under the condition of an air-fuel ratio (A / F) of 14.5. ３ H ６ , NO, O ２ , CO ２ , H ２ O, N ２ The simulated exhaust gas (including the above-mentioned components) was introduced into the reaction tube, and the amounts of CO, HC, and NOx contained in the simulated exhaust gas flowing out from the outlet of the reaction tube were measured. The gas temperature at the inlet of the reaction tube when the purification rate of CO, HC, and NOx reached 50% was determined as the light-off temperature T50 (°C). The light-off temperature T50 was determined during temperature rise. The results are shown in Tables 5 and 6.

[0231]

[0232]

[0233] For each of the exhaust gas purifying catalysts of Examples 1 to 3 and Comparative Examples 1 and 2, the T50 values ​​of CO, HC and NOx were evaluated using the following evaluation criteria.

[0234] <Evaluation criteria for CO T50> A: T50≦260°C B: 260°C<T50≦270°C C: 270°C<T50

[0235] <Evaluation criteria for HC T50> A: T50≦330°C B: 330°C<T50≦340°C C: 340°C<T50

[0236] <Evaluation of NOx T50> A: T50≦280°C B: 280°C<T50≦290°C C: 290°C<T50

[0237] As a result of the T50 evaluation of CO, HC, and NOx, if there were three A ratings (all A ratings), the overall T50 rating was A, if there were B ratings but no C ratings, the overall T50 rating was B, and if there were three C ratings (all C ratings), the overall T50 rating was C. The results are shown in Table 7.

[0238] (3-3) Overall Evaluation of Exhaust Gas Purification Performance The evaluation results of CO, HC, NMHC, and NOx emissions and the overall evaluation of T50 were added together, and the overall evaluation of exhaust gas purification performance was given as A when there were three or more evaluations of A, as B when there were two or less evaluations of A and some evaluations of B but no evaluation of C, and as C when there was one or more evaluations of C. The results are shown in Table 7.

[0239]

[0240] DESCRIPTION OF SYMBOLS 1... catalyst for purifying exhaust gas 10... metal honeycomb substrate 11... cylindrical portion 12... partition wall portion 13... cell 20... catalyst layer 21... first layer 22... second layer

Claims

1. A catalyst for purifying exhaust gas comprising a metal honeycomb substrate and a catalyst layer provided on the metal honeycomb substrate, wherein the catalyst layer contains precious metal elements, Ce-based oxide particles, and Ce-Zr-based composite oxide particles, and a logarithmic differential pore volume distribution curve of the catalyst layer obtained by mercury intrusion porosimetry has a first peak value in a pore diameter range of 5 nm to 15 nm and a second peak value in a pore diameter range of 200 nm to 3200 nm, the first peak value being 0.060 mL / g or more, and the second peak value being 0.018 mL / g or more.

2. The exhaust gas purifying catalyst according to claim 1, wherein the second peak value is in a pore diameter range of 200 nm or more and 1600 nm or less.

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

4. The specific surface area of ​​the catalyst layer is 70 m ２ / g or more 200m ２ The exhaust gas purifying catalyst according to any one of claims 1 to 3, wherein the molecular weight of the exhaust gas purifying catalyst is 1000 or less.

5. A catalyst for purifying exhaust 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 on which the catalyst layer is provided is 100 g / L or more and 300 g / L or less.

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

7. The exhaust gas purifying catalyst according to claim 6, wherein the median diameter of the Al-based oxide particles is 15 μm or more and 30 μm or less.

8. A catalyst for purifying exhaust gas according to any one of claims 1 to 3, wherein the catalyst layer comprises a first layer provided on the metal honeycomb substrate and a second layer provided 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, and at least a portion of the precious metal element is contained in the second layer.

9. The exhaust gas purification catalyst according to claim 8, wherein the content of the Ce-based oxide particles in the first layer is 10 mass % or more and 80 mass % or less, based on the total mass of the Ce-based oxide particles and the Ce-Zr-based composite oxide particles in the first layer.

10. An exhaust gas purification catalyst as described in claim 9, wherein the content of the Ce-based oxide particles in the first layer is 20 mass % or more and 70 mass % or less, based on the total mass of the Ce-based oxide particles and the Ce-Zr-based composite oxide particles in the first layer.

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

12. The exhaust gas purifying catalyst according to claim 11, wherein the median diameter of the Al-based oxide particles is 15 μm or more and 30 μm or less.

13. A catalyst for purifying exhaust gas as described in claim 8, wherein the mass of the first layer per unit volume of the portion of the metal honeycomb substrate on which the first layer is provided is 100 g / L or more and 180 g / L or less.

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