Exhaust gas purification catalyst

Abstract

The present disclosure provides an exhaust gas purification catalyst having improved exhaust gas purification performance.SOLUTION: An exhaust gas purification catalyst of the present disclosure includes a substrate and a coating layer laminated on the substrate, wherein the coating layer includes a first catalytic metal and a metal oxide carrier, a pore volume of the coating layer is larger than 0.44 mL / g, the first catalytic metal is at least one selected from the group consisting of platinum and palladium, and the first catalytic metal is dispersed in a depth direction from an outer surface of the coating layer, A ratio (Rb / Rs) of the abundance ratio Rb in the range within 20 μm from the bottom face of the coating layer in the thickness direction to the abundance ratio Rs in the range within 20 μm from the surface of the coating layer in the thickness direction is 0.20 to 1.50.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an exhaust gas purification catalyst. [Background technology]

[0002] Exhaust gas from internal combustion engines is required to comply with various environmental regulations, so the exhaust gas is purified by an exhaust gas purification catalyst before being released into the environment.

[0003] The main focus of exhaust gas purification catalysts is the removal of hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) from exhaust gases. Of these, hydrocarbons (HC) and carbon monoxide (CO) are purified by being converted to water (H2O) and carbon dioxide (CO2) via oxidation reactions, while nitrogen oxides (NOx) are purified by being converted to nitrogen (N2) via reduction reactions.

[0004] Patent Document 1 discloses an exhaust gas purification catalyst for a two-stroke general-purpose engine, which has a substrate and a coating layer on the substrate, the coating layer containing a precious metal and a metal oxide, the precious metal containing palladium and one or more metals selected from platinum and rhodium, the zirconia content of the coating layer being 0.07 mol or less per 100 g of metal oxide contained in the coating layer, and the total content of one or more metal oxides selected from lanthana and alkaline earth metal oxides in the coating layer being 0.05 mol or more per 100 g of metal oxide contained in the coating layer.

[0005] Patent Document 2 discloses an exhaust gas purification catalyst having a catalytic layer containing at least rhodium and palladium, characterized in that the rhodium is supported at least on the surface of partition walls of a carrier, the palladium is supported at least inside the partition walls of the carrier, and the supporting density of the palladium is higher on the upstream side than on the downstream side. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2017 / 200013 [Patent Document 2] International Publication No. 2020 / 071065 Summary of the Invention [Problem to be solved by the invention]

[0007] Provided is an exhaust gas purification catalyst with improved exhaust gas purification performance. [Means for solving the problem]

[0008] The present inventors have found that the above object can be achieved by the following means: <<Aspect 1>> An exhaust gas purification catalyst having a substrate and a coating layer laminated on the substrate, the coating layer has a first catalytic metal and a metal oxide support, and the pore volume of the coating layer is greater than 0.44 mL / g; the first catalytic metal is at least one selected from the group consisting of platinum and palladium, and is present dispersedly in the depth direction from the outer surface of the coating layer, and the ratio (Rb / Rs) of the abundance ratio Rb within 20 μm from the bottom surface of the coating layer in the thickness direction to the abundance ratio Rs within 20 μm from the surface of the coating layer in the thickness direction is 0.20 to 1.50; Exhaust gas purification catalyst.

[0009] <<Aspect 2>> The exhaust gas purification catalyst according to aspect 1, wherein the coating layer further supports a second catalytic metal, the second catalytic metal being rhodium, and the second catalytic metal being dispersed within a range of 20 μm in a depth direction from an outer surface of the coating layer.

[0010] Aspect 3 3. The exhaust gas purifying catalyst according to claim 1, wherein the metal oxide support contains alumina and ceria.

[0011] Aspect 4 4. The exhaust gas purifying catalyst according to aspect 3, wherein in the metal oxide support, the molar ratio of the ceria to the alumina (CeO2 / Al2O3) is 0.90 to 1.10.

[0012] Aspect 5 5. The exhaust gas purifying catalyst according to any one of aspects 1 to 4, wherein the value of the abundance ratio Rb / the abundance ratio Rs is 0.45 to 1.00. [Effects of the Invention]

[0013] According to the present disclosure, it is possible to provide an exhaust gas purification catalyst with improved exhaust gas purification performance. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram of an exhaust gas purification catalyst 1 according to one embodiment of the present disclosure. [Figure 2] FIG. 2 is a diagram showing Rb / Rs of an exhaust gas purification catalyst 1 according to one embodiment of the present disclosure. [Figure 3] FIG. 3 is a schematic diagram showing Rb / Rs of an exhaust gas purification catalyst 2 according to another embodiment of the present disclosure. [Figure 4] FIG. 4 is a schematic diagram showing Rb / Rs of an exhaust gas purifying catalyst 3 different from the embodiment of the present disclosure. [Figure 5] FIG. 5 is a graph showing the relationship between Rb / Rs and temperature characteristics of the samples of Example 1 and Comparative Examples 1 to 11. [Figure 6] FIG. 6 is a graph showing the relationship between Rb / Rs and temperature characteristics for the samples of Example 1 and Comparative Examples 3, 12, and 13. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present disclosure will be described in detail. Note that the present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the present disclosure.

[0016] 1. Exhaust gas purification catalyst The exhaust gas purification catalyst of the present disclosure is an exhaust gas purification catalyst having a substrate and a coating layer laminated on the substrate, wherein the coating layer has a first catalytic metal and a metal oxide support, the pore volume of the coating layer is greater than 0.44 mL / g, the first catalytic metal is at least one selected from the group consisting of platinum and palladium, and is present dispersedly in the depth direction from the outer surface of the coating layer, and the ratio (Rb / Rs) of the abundance ratio Rb within 20 μm from the bottom surface of the coating layer in the thickness direction to the abundance ratio Rs within 20 μm from the surface of the coating layer in the thickness direction is 0.20 to 1.50.

[0017] The exhaust gas purification catalyst of the present disclosure has the above-mentioned configuration and therefore has improved exhaust gas purification performance. Although not limited by the theory, the principle behind the improved exhaust gas purification performance of the exhaust gas purification catalyst of the present disclosure is thought to be as follows.

[0018] Platinum and palladium, catalytic metals used in exhaust gas purification catalysts, are generally susceptible to catalyst poisoning. Furthermore, these metals are more susceptible to thermal sintering than rhodium and other metals. Therefore, there is a need to improve the durability of exhaust gas purification catalysts using platinum and palladium.

[0019] In the exhaust gas purification catalyst of the present disclosure, a first catalytic metal, which is at least one selected from the group consisting of platinum and palladium, is present dispersed in the depth direction from the outer surface of the coating layer, and the ratio (Rb / Rs) of the abundance ratio Rb within a range of 20 μm from the bottom surface of the coating layer in the thickness direction to the abundance ratio Rs within a range of 20 μm from the surface of the coating layer in the thickness direction is 0.20 to 1.50. By dispersing the first catalytic metal in the coating layer in this manner, catalyst poisoning and sintering due to heat are suppressed.

[0020] Furthermore, in the exhaust gas purification catalyst of the present disclosure, the pore volume of the coating layer is greater than 0.44 mL / g, which allows the exhaust gas to penetrate deep into the coating layer, thereby supplying the exhaust gas to the first catalytic metal dispersed deep within.

[0021] Fig. 1 is a schematic diagram of an exhaust gas purification catalyst 1 according to one embodiment of the present disclosure. In Fig. 1, the exhaust gas purification catalyst 1 has a coating layer 20 on a substrate 10. In the coating layer 20, a first catalytic metal 30 is dispersed.

[0022] 2 to 4 are schematic diagrams showing the ratio (Rb / Rs) of the abundance ratio Rb within 20 μm in the thickness direction from the bottom surface of the coating layer to the abundance ratio Rs within 20 μm in the thickness direction from the surface of the coating layer for an exhaust gas purification catalyst 1 according to one embodiment of the present disclosure, an exhaust gas purification catalyst 2 according to another embodiment of the present disclosure, and an exhaust gas purification catalyst 3 different from the embodiment of the present disclosure, respectively. Figures 2 to 4 are not intended to limit the exhaust gas purification catalyst of the present disclosure. Furthermore, Figures 2 to 4 are for illustrative purposes and do not accurately reflect dimensions.

[0023] 1 to 3, exhaust gas purification catalysts 1 to 3 all have a coating layer 20 on a substrate 10. The exhaust gas purification catalysts 1 to 3 differ from each other in the distribution 21 of the first catalytic metal 30 in the coating layer 20. In the exhaust gas purification catalyst 1, the Rb / Rs is 0.20. In the exhaust gas purification catalyst 2, the Rb / Rs is 1.50. In the exhaust gas purification catalyst 3, the Rb / Rs is 0.10.

[0024] In Fig. 2, the distribution of the first catalytic metal 30 in the coating layer 20 decreases slightly from the surface layer to the deeper layers of the coating layer 20. In Fig. 3, the distribution of the first catalytic metal 30 in the coating layer 20 increases from the surface layer to the deeper layers of the coating layer 20. In Fig. 4, the distribution of the first catalytic metal 30 in the coating layer 20 decreases significantly from the surface layer to the deeper layers of the coating layer 20.

[0025] In exhaust gas purification catalysts 1 and 2, Rb / Rs is 0.20 to 1.50, which suppresses catalyst poisoning of the first catalytic metal and sintering due to heat, and allows exhaust gas to penetrate deep into the coating layer, thereby allowing exhaust gas to be supplied to the first catalytic metal dispersed deep inside.

[0026] On the other hand, in the exhaust gas purification catalyst 3, since Rb / Rs is 0.10, the first catalytic metal is distributed in large amounts on the surface of the coating layer, and many of the first catalytic metals are susceptible to catalyst poisoning. In addition, since many of the first catalytic metals are present in close proximity to each other, they are prone to sintering.

[0027] The abundance ratio Rb within 20 μm from the bottom surface of the coating layer in the thickness direction, and the abundance ratio Rs within 20 μm from the surface of the coating layer in the thickness direction, can be measured using the following method. A field emission electron probe microanalyzer (FE-EPMA) is used to measure the distribution of catalytic metals in the coating layer of an exhaust gas purification catalyst, for example, at a position 10 mm from the exhaust gas inlet end of the exhaust gas purification catalyst. Here, the FE-EPMA measures the thickest part of the coating layer of the sample using an accelerating voltage of 20 kV, a probe current of 50 mA, a collection time of 30 seconds, and a magnification of 150x. From the obtained FE-EPMA image, the abundance ratio Rb within 20 μm from the bottom surface of the coating layer in the thickness direction and the abundance ratio Rs within 20 μm from the surface of the coating layer in the thickness direction are calculated using image processing, and Rb / Rs is calculated.

[0028] 1-1. Base material The substrate that can be used in the exhaust gas purification catalyst of the present disclosure is not particularly limited as long as it is a substrate that is generally used in exhaust gas purification catalysts. Examples of such substrates that can be used include honeycomb substrates, more specifically, metal honeycomb substrates.

[0029] 1-2. Coating layer The coating layer of the exhaust gas purification catalyst of the present disclosure includes a first catalytic metal and a metal oxide support. The coating layer may further include a second catalytic metal. The coating layer may optionally include other components, such as a binder, for example, an alumina binder.

[0030] The pore volume of the coating layer is greater than 0.44 mL / g. The pore volume of the coating layer may be greater than 0.44 mL / g, 0.45 mL / g or greater, 0.46 mL / g or greater, 0.47 mL / g or greater, or 0.48 mL / g or greater. The pore volume may be 1.00 mL / g or less, 0.90 mL / g or less, 0.80 mL / g or less, 0.70 mL / g or less, 0.60 mL / g or less, or 0.50 mL / g or less.

[0031] The pore volume of the coating layer can be measured by the BET method. More specifically, the pore volume of the coating layer can be measured by subjecting the coating layer to powder obtained by thoroughly crushing the coating layer.

[0032] The thickness of the coating layer may be, for example, 40 μm to 5000 μm. The thickness of the coating layer may be 40 μm or more, 50 μm or more, 60 μm or more, 70 μm or more, 80 μm or more, 90 μm or more, 100 μm or more, or 200 μm or more. The thickness of the coating layer may be 5000 μm or less, 4000 μm or less, 3000 μm or less, 2000 μm or less, 1000 μm or less, 500 μm or less, 300 μm or less, or 100 μm or less.

[0033] 1-2-1. Metal oxide support The metal oxide support is not particularly limited as long as it is a metal oxide support used in exhaust gas purification catalysts. The metal oxide support may contain, for example, alumina, ceria, zirconia, lanthana, etc.

[0034] The metal oxide support preferably contains alumina and ceria. In this case, the molar ratio of cerium atoms to aluminum atoms (CeO2 / Al2O3) is preferably 0.90 to 1.10. The molar ratio of cerium atoms to aluminum atoms in this range further improves exhaust gas purification performance. CeO2 / Al2O3 may be 0.9 or more, 0.95 or more, or 1.00 or more. CeO2 / Al2O3 may be 1.10 or less, 1.05 or less, or 1.00 or less.

[0035] The metal oxide support can support a first catalytic metal, and when the coating layer further contains a second catalytic metal, the metal oxide support can further support a second catalytic metal.

[0036] 1-2-2. First catalytic metal The first catalytic metal is at least one selected from the group consisting of platinum and palladium. The first catalytic metal is present and dispersed in the depth direction from the outer surface of the coating layer. The ratio (Rb / Rs) of the abundance ratio Rb of the first catalytic metal within 20 μm from the bottom surface of the coating layer in the thickness direction to the abundance ratio Rs of the first catalytic metal within 20 μm from the surface of the coating layer in the thickness direction is 0.20 to 1.50.

[0037] The value of Rb / Rs may be 0.20 or more, 0.25 or more, 0.30 or more, 0.35 or more, 0.40 or more, or 0.45 or more.The value of Rb / Rs may be 1.50 or less, 1.40 or less, 1.30 or less, 1.20 or less, 1.10 or less, 1.00 or less, less than 1.00, 0.90 or less, 0.80 or less, 0.70 or less, or 0.60 or less.

[0038] The value of Rb / Rs is particularly preferably 0.45 to 1.00. When the value of Rb / Rs is within this range, the first catalytic metal is dispersed particularly uniformly in the depth direction of the coating layer, thereby providing the exhaust gas purification catalyst with higher durability.

[0039] Rs may be greater than 0% and less than 50%. Rs may be greater than 0%, 5% or more, 10% or more, 15% or more, 20% or more, 25% or more, or 30% or more. Rs may be less than 50%, 45% or less, 40% or less, or 35% or less.

[0040] In the coating layer, the amount of the first catalytic metal relative to 100 g of the metal oxide support is 1.0 × 10 -3 The amount of the first catalytic metal relative to 100 g of the metal oxide support can be 1.0 × 10 -3 g or more, 2.0×10 -3 g or more, 3.0×10 -3 g or more, 4.0×10 -3 g or more, or 5.0 x 10 -3 g or more, and may be 1.0 g or less, 1.0 x 10 -1 g or less, 1.0×10 -2 g or less, 9.0×10 -3 g or less, 8.0×10 -3 g or less, 7.0×10 -3 g or less, or 6.0 x 10 -3 It may be less than or equal to g.

[0041] 1-2-3. Second catalytic metal When the coating layer contains a second catalytic metal, the second catalytic metal is preferably rhodium, and is dispersed within a range of 20 μm from the outer surface of the coating layer in the depth direction.

[0042] The rhodium as the second catalytic metal is dispersed within a range of 20 μm from the outer surface of the coating layer in the depth direction, which differentiates its distribution from the first catalytic metal, thereby suppressing alloying between the first catalytic metal and the second catalytic metal. Furthermore, the rhodium as the second catalytic metal is less susceptible to catalyst poisoning and heat than the first catalytic metal. Therefore, the second catalytic metal is dispersed within a range of 20 μm from the outer surface of the coating layer in the depth direction, which further improves the exhaust gas purification performance of the exhaust gas purification catalyst of the present disclosure.

[0043] In the coating layer, the amount of the second catalytic metal relative to 100 g of the metal oxide support is 1.0 × 10 -4 The amount of the second catalytic metal relative to 100 g of the metal oxide support can be 1.0 × 10 -4 g or more, 2.0×10 -4 g or more, 3.0×10 -4 g or more, 4.0×10 -4 g or more, or 5.0 x 10 -4 g or more, and may be 1.0 g or less, 1.0 x 10 -1 g or less, 1.0×10 -2 g or less, 1.0×10 -3 g or less, 9.0×10 -4 g or less, 8.0×10 -4 g or less, 7.0×10 -4 g or less, or 6.0 x 10 -4 It may be less than or equal to g.

[0044] 2. Manufacturing method of exhaust gas purification catalyst The manufacturing method of the present disclosure can manufacture the exhaust gas purification catalyst of the present disclosure.

[0045] The manufacturing method of the present disclosure includes: (A) forming a coating layer precursor on a substrate by depositing a slurry containing a metal oxide support and a first catalytic metal on the substrate and drying the slurry; and (B) post-baking the coating layer precursor to form a coating layer on the substrate; Contains:

[0046] Here, the first catalytic metal is at least one selected from the group consisting of platinum and palladium.

[0047] In the manufacturing method of the present disclosure, step (A) is repeated multiple times before step (B) by changing the concentration of the slurry, whereby in the coating layer formed by step (B), the first catalytic metal is present dispersed in the depth direction from the outer surface of the coating layer, and the ratio (Rb / Rs) of the abundance ratio Rb within 20 μm from the bottom surface of the coating layer in the thickness direction to the abundance ratio Rs within 20 μm from the surface of the coating layer in the thickness direction can be made to be 0.20 to 1.50.

[0048] The pore volume of the coating layer is adjusted to be greater than 0.44 mL / g mainly by selecting the metal oxide support.

[0049] The manufacturing method of the present disclosure preferably further includes, after step (B), (C) depositing a slurry containing a second catalytic metal onto the coating layer, whereby the second catalytic metal is supported on the coating layer.

[0050] For the substrate, metal oxide support, first catalytic metal, and second catalytic metal in the production method of the present disclosure, reference can be made to the descriptions in "1. Exhaust gas purification catalyst" above.

[0051] The exhaust gas purification catalyst of the present disclosure can also be produced by a method other than the production method of the present disclosure. For example, to create a state in which the precious metal is dispersed in the coating layer, a slurry containing alumina A is coated on a substrate and calcined to form a coating layer that does not contain a precious metal. Then, the coating layer that does not contain a precious metal is impregnated multiple times with a precious metal solution containing platinum and palladium, thereby producing the exhaust gas purification catalyst of the present invention. [Example]

[0052] 3. Examples 1 to 4 and Comparative Examples 1 to 14 Samples of Examples 1 to 4 and Comparative Examples 1 to 14 were prepared and tested as follows.

[0053] 3-1. Preparation of samples for each example 3-1-1. Examples 1 and 2, and Comparative Examples 1 and 2 (1) Example 1 A metal honeycomb substrate with a diameter of 40 mm, a length of 60 mm, and a volume of 400 cells per square inch (cpsi) was used as the substrate.

[0054] Platinum, palladium, alumina A, CeZr composite oxide, alumina sol, and pure water were mixed to prepare a slurry.

[0055] The slurry was applied to the substrate and dried at 80°C, and a first coating layer precursor was laminated on the substrate. Next, slurries with different platinum and palladium contents were applied to the first coating layer precursor and dried at 80°C, and a second coating layer precursor was laminated on the first coating layer precursor. This operation was repeated multiple times until the total thickness of the first to n-th coating layer precursors reached 100 μm, and finally, the mixture was fired at 500°C for 1 hour to form a coating layer on the substrate.

[0056] Next, a rhodium nitrate solution was applied to the coating layer, dried at 80°C, and then fired at 500°C for 1 hour to prepare a sample.

[0057] The mass ratio of the sample of Example 1 was platinum:palladium:rhodium:alumina:CeZr composite oxide=0.202:0.379:0.113:30:70.

[0058] The abundance ratios Rs of platinum and palladium in the sample of Example 1 within 20 μm from the surface of the coating layer in the thickness direction are as shown in Table 1 below. The ratio (Rb / Rs) of the abundance ratio Rb within 20 μm from the bottom surface of the coating layer in the thickness direction to the abundance ratio Rs within 20 μm from the surface of the coating layer in the thickness direction is as shown in Table 2 below. Rb and Rs were measured by the measurement in "3-4. Measurement of catalytic metal distribution" below.

[0059] (2) Example 2 and Comparative Examples 1 and 2 Samples of Example 2 and Comparative Examples 1 and 2 were prepared in the same manner as Example 1, except that the amounts of platinum and palladium in the slurries used to form the first coating layer precursor to the nth coating layer precursor were varied so that Rs was as shown in Table 1.

[0060] 3-1-2. Comparative Examples 3 to 6 The sample of Comparative Example 3 was prepared in the same manner as in Example 1, except that alumina B having a different pore volume was used instead of alumina A. Furthermore, the samples of Comparative Examples 4 to 6 were prepared in the same manner as in Example 2 and Comparative Examples 1 and 2, respectively, except that alumina B having a different pore volume was used.

[0061] 3-1-3. Comparative Examples 7 to 10 The sample of Comparative Example 7 was prepared in the same manner as in Example 1, except that alumina C having a different pore volume was used instead of alumina A. Furthermore, the samples of Comparative Examples 8 to 10 were prepared in the same manner as in Example 2 and Comparative Examples 1 and 2, respectively, except that alumina C having a different pore volume was used.

[0062] 3-1-4. Comparative Examples 11 and 12 A sample of Comparative Example 11 was prepared in the same manner as in Example 1, except that alumina B was used instead of alumina A and the composition ratio of the sample was platinum:palladium:rhodium:alumina:CeZr composite oxide:lanthanum carbonate = 0.202:0.379:0.113:48:45:4. A sample of Comparative Example 12 was prepared in the same manner as in Comparative Example 2, except that alumina B was used instead of alumina A and the composition ratio of the sample was platinum:palladium:rhodium:alumina:CeZr composite oxide:lanthanum carbonate = 0.202:0.379:0.113:48:45:4.

[0063] 3-1-5. Examples 3 and 4 Samples of Examples 3 and 4 were prepared in the same manner as in Example 1, except that the contents of alumina A and CeZr oxide in Example 1 were varied so that the Ce / Al ratio was as shown in Table 3.

[0064] The composition ratio of the sample of Example 3 was platinum:palladium:rhodium:alumina:CeZr oxide=0.202:0.379:0.113:22:75, and the composition ratio of the sample of Example 4 was platinum:palladium:rhodium:alumina:CeZr oxide=0.202:0.379:0.113:25:83.

[0065] 3-2.Evaluation of temperature characteristics Each sample was attached to a 2000cc gasoline engine, and the average engine speed was controlled at 3000 rpm with a theoretical air-fuel ratio A / F of 14.55. The exhaust gas temperature at the catalyst inlet was varied to determine the temperature (T50) at which 50% of the HC, CO, and NOx in the exhaust gas were purified.

[0066] 3-3. Measurement of catalytic metal distribution A field emission electron probe microanalyzer (FE-EPMA) was used to measure the distribution of the catalytic metal in the coating layer of each sample at a position 10 mm from the exhaust gas inlet end.

[0067] The FE-EPMA was used to measure the thickest part of the coating layer of the sample at an accelerating voltage of 20 kV, an irradiation current of 50 mA, a collection time of 30 seconds, and a magnification of 150 times.

[0068] From the obtained FE-EPMA images, image processing was used to calculate the abundance ratio Rb within a range of 20 μm from the bottom surface of the coating layer in the thickness direction and the abundance ratio Rs within a range of 20 μm from the surface of the coating layer in the thickness direction, and Rb / Rs was obtained.

[0069] 3-4. Measurement of pore volume The total pore volume of the alumina, CeZr composite oxide, and alumina binder used was measured by the BET method. The pore volume of the coating layer was measured by performing the BET method on the powder obtained by thoroughly crushing the coating layer.

[0070] 3-5.Results The results are shown in Figures 5 and 6 and Tables 1 to 3.

[0071] [Table 1]

[0072] As shown in Table 1 and FIG. 5, in Example 1, in which the pore volume was 0.464 mL / g and the Rb / Rs was 0.410, the temperature (°C) at which 50% of HC, CO, and NOx in the exhaust gas were purified (T50) was 327°C, a low value. That is, the exhaust gas purification performance was good. Similarly, in Example 2, in which the pore volume was 0.493 mL / g and the Rb / Rs was 0.310, the T50 was 335°C, and the exhaust gas purification performance was good. On the other hand, in Comparative Examples 1 to 10, in which the pore volume was 0.44 mL / g or less or the Rb / Rs was less than 0.200, the T50 was higher than in Examples 1 and 2.

[0073] [Table 2]

[0074] As shown in Table 2 and FIG. 6, in Example 1, the temperature (° C.) (T50) at which 50% of HC, CO, and NOx in the exhaust gas are purified was a low value of 327° C.

[0075] In contrast, Comparative Example 2, in which the pore volume was 0.488 and the Rb / Rs was 0.005, exhibited a relatively high T50 of 341°C. Similarly, Comparative Example 11, in which the Rb / Rs was 0.420 and the pore volume was 0.397, exhibited a relatively high T50 of 363°C. Comparative Example 12, in which the Rb / Rs was 0.006 and the pore volume was 0.397, exhibited a relatively high T50 of 371°C.

[0076] [Table 3]

[0077] As shown in Table 3, Examples 1, 3, and 4, in which the molar ratio of cerium atoms to aluminum atoms (Ce / Al) was 0.93 to 1.10, had a temperature (°C) (T50) at which 50% of HC, CO, and NOx in the exhaust gas were purified, of 325 to 329, and all of them showed good exhaust gas purification performance. Example 2, in which the Ce / Al was 1.00, showed particularly good exhaust gas purification performance. [Explanation of symbols]

[0078] 1-3 Exhaust gas purification catalyst 10 Base material 20 Coating Layer 21 Distribution of the first catalytic metal in the coating layer 30 Catalytic Metals

Claims

1. An exhaust gas purification catalyst having a substrate and a coating layer laminated on the substrate, the coating layer includes a first catalytic metal and a metal oxide support, and the pore volume of the coating layer is greater than 0.44 mL / g; the first catalytic metal is at least one selected from the group consisting of platinum and palladium, and is present dispersedly in the depth direction from the outer surface of the coating layer, and the ratio (Rb / Rs) of the abundance ratio Rb in a range of 20 μm from the bottom surface of the coating layer in the thickness direction to the abundance ratio Rs in a range of 20 μm from the surface of the coating layer in the thickness direction is 0.20 to 1.50; Exhaust gas purification catalyst.

2. 2. The exhaust gas purification catalyst according to claim 1, wherein the coating layer further supports a second catalytic metal, the second catalytic metal being rhodium, and the second catalytic metal being dispersed within a range of 20 μm from the outer surface of the coating layer in a depth direction.

3. 3. The exhaust gas purifying catalyst according to claim 1, wherein the metal oxide support contains alumina and ceria.

4. In the metal oxide support, the molar ratio of the ceria to the alumina (CeO ２ / Al ２ O ３ 4. The exhaust gas purifying catalyst according to claim 3, wherein the ratio of the total mass of the exhaust gas to the total mass of the catalyst is 0.90 to 1.

10.

5. 3. The exhaust gas purification catalyst according to claim 1, wherein a value of the abundance ratio Rb / the abundance ratio Rs is 0.45 to 1.00.

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