Exhaust gas purification catalyst, method for manufacturing the same, and exhaust gas purification method using the exhaust gas purification catalyst.

Abstract

This disclosure provides a means for improving the exhaust gas purification performance (particularly HC purification performance) of an exhaust gas purification catalyst at low temperatures. The above problem is solved by controlling the ratio of the palladium concentration in the gas inlet region of the lower catalyst layer to the palladium concentration in the gas outlet region of the lower catalyst layer to be within a predetermined range in an exhaust gas purification catalyst comprising a lower catalyst layer and an upper catalyst layer having predetermined compositions.

Description

[Technical Field]

[0001] The present invention relates to an exhaust gas purification catalyst, a method for producing the same, and an exhaust gas purification method using the exhaust gas purification catalyst. [Background technology]

[0002] Many technologies have been proposed for the treatment of exhaust gases produced by internal combustion engines. For example, in the treatment of exhaust gases from gasoline engines, a three-way catalyst has been proposed that simultaneously oxidizes carbon monoxide (CO) and hydrocarbons (HC) to carbon dioxide (CO2) and water (H2O), and reduces nitrogen oxides (NOx) to nitrogen (N2). A three-way catalyst generally has a configuration in which a catalyst layer containing noble metals and refractory inorganic oxides is supported on a refractory three-dimensional structure (e.g., a honeycomb support).

[0003] It is known that at low temperatures, such as during engine startup, three-way catalytic converters have low activity and cannot adequately purify exhaust gases, resulting in the emission of gases containing high levels of pollutants (especially HC). Therefore, development is underway to create three-way catalytic converters that can exhibit sufficient purification performance at even lower temperatures (in a shorter time after engine startup).

[0004] For example, Japanese Patent Publication No. 2019-69402 (corresponding to U.S. Patent Application Publication No. 2019 / 0105637) discloses an exhaust gas purification catalyst having a catalyst coating layer in which an upper layer and a lower layer are sequentially formed on the surface of a substrate; the upper layer contains Rh and Pd and a support; the upper layer includes a Pd outermost layer on the surface in a range of 20 mm or more downstream from the upstream end, where the Pd concentration is relatively higher than in other parts of the upper layer; the lower layer contains Pd and / or Pt and a support; and 60% by mass or more of the Pd contained in the Pd outermost layer is present from the surface of the Pd outermost layer to 50% of the thickness of the upper layer. According to this document, such a configuration makes it possible to provide an exhaust gas purification catalyst with excellent HC purification performance and warm-up performance. [Overview of the project] [Problems that the invention aims to solve]

[0005] However, our own investigations have revealed that even with the technology described in the above-mentioned literature, sufficient exhaust gas purification performance may not be obtained at low temperatures.

[0006] This invention has been made in view of the above circumstances, and aims to provide a means for improving the exhaust gas purification performance (especially HC purification performance) of an exhaust gas purification catalyst at low temperatures (for example, below 400°C). [Means for solving the problem]

[0007] The inventors of the present invention conducted diligent studies to solve the above problems. As a result, they found that the above problems can be solved by controlling the ratio of the palladium concentration in the gas inlet region of the lower catalyst layer to the palladium concentration in the gas outlet region of the lower catalyst layer to be within a predetermined range (i.e., the palladium concentration in the gas inlet region of the lower catalyst layer is higher than the palladium concentration in the gas outlet region of the lower catalyst layer) in an exhaust gas purification catalyst comprising a lower catalyst layer and an upper catalyst layer having a predetermined composition, and thus completed the present invention.

[0008] In other words, an exhaust gas purification catalyst according to one embodiment of the present invention comprises: a fire-resistant three-dimensional structure having partitions that extend along the gas inlet end face to the gas outlet end face and partition a plurality of gas flow paths penetrating from the gas inlet end face to the gas outlet end face; a lower catalyst layer formed in contact with the partitions and containing palladium, alumina, and cerium-zirconium composite oxide; and an upper catalyst layer formed on at least a portion of the lower catalyst layer and constituting the outermost layer, containing rhodium, alumina, and cerium-zirconium composite oxide. The lower catalyst layer in the catalyst is located on the gas inlet side, and the palladium concentration is C L1[g / g] is the gas inlet side region L1, and the gas outlet side is located where the palladium concentration is C L2 It consists of a gas outlet side region L2 having a palladium concentration of [g / g], and the boundary X between the gas inlet side region L1 and the gas outlet side region L2 is located within a range of 8% to 80% from the gas inlet side end face with respect to the length of the partition wall; and the palladium concentration C of the gas outlet side region L2. L2 The palladium concentration C in the gas inlet region L1 is L1 The ratio (C L1 / C L2 ) is characterized by being between 30 and 230. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic front cross-sectional view showing a part of an exhaust gas purification catalyst according to one embodiment of the present invention. [Figure 2] Figure 2 is a schematic front cross-sectional view showing a part of an exhaust gas purification catalyst according to another embodiment of the present invention. [Figure 3] Figure 3 is a schematic front cross-sectional view showing a part of an exhaust gas purification catalyst according to yet another embodiment of the present invention. [Modes for carrying out the invention]

[0010] The embodiments of the present invention will be described below, but the technical scope of the present invention should be determined based on the claims and is not limited to the embodiments described below. In this specification, the numerical range "A to B" means "A or more, B or less". Also, "A and / or B" means "either A or B" or "both A and B".

[0011] <Exhaust gas purification catalyst> The catalyst for purifying exhaust gas according to one embodiment of the present invention (hereinafter, also simply referred to as "catalyst") includes a refractory three-dimensional structure having a partition wall that extends along the gas inflow side end face to the gas outflow side end face and partitions and forms a plurality of gas flow paths penetrating from the gas inflow side end face to the gas outflow side end face; a lower catalyst layer formed to contact the partition wall and containing palladium, alumina, and a cerium-zirconium composite oxide; and an upper catalyst layer formed on at least a part of the upper part of the lower catalyst layer and constituting the outermost layer and containing rhodium, alumina, and a cerium-zirconium composite oxide. And in the catalyst, the lower catalyst layer is located on the gas inflow side and has a gas inflow side region L1 with a palladium concentration of C L1 [g / g], and a gas outflow side region L2 located on the gas outflow side and having a palladium concentration of C L2 [g / g], and is composed of; the boundary X between the gas inflow side region L1 and the gas outflow side region L2 is located within a range of 8% or more and 80% or less from the gas inflow side end face with respect to the length of the partition wall; the ratio (C L2 of the palladium concentration of the gas inflow side region L1 to the palladium concentration C L1 of the gas outflow side region L2 (C L1 / C L2A key feature is that the palladium concentration is between 30 and 230. According to the inventors' research, it has been found that a catalyst having the above configuration improves exhaust gas purification performance (especially HC purification performance) at low temperatures (e.g., below 400°C). The mechanism by which such an effect is achieved is not fully clear, but the following mechanism is hypothesized. That is, during low-temperature starting, the catalyst temperature is higher on the gas inlet side (catalyst inlet side) than on the gas outlet side (catalyst outlet side) (the catalyst reaches its activation temperature in a shorter time). In the lower catalyst layer in contact with the refractory three-dimensional structure, by controlling the ratio of the palladium concentration in the gas inlet side region to the palladium concentration in the gas outlet side region to be within a predetermined range (so that the palladium concentration in the gas inlet side region is higher than that in the gas outlet side region), the amount of palladium that reaches the activation temperature increases, and it is thought that the exhaust gas purification performance is improved. It should be noted that the above mechanism is based solely on speculation, and its accuracy does not affect the technical scope of the present invention.

[0012] The overall structure of the exhaust gas purification catalyst according to this embodiment will be described in more detail below, with reference to the attached drawings. In the description of the drawings, the same elements are denoted by the same reference numeral, and redundant explanations are omitted. Also, the dimensional ratios in the drawings are exaggerated for illustrative purposes and may differ from the actual ratios.

[0013] Figure 1 is a schematic front cross-sectional view showing a part of an exhaust gas purification catalyst according to one embodiment of the present invention. This embodiment corresponds to catalyst A of Example 1 described later. As shown in Figure 1, the exhaust gas purification catalyst 1 has a fire-resistant three-dimensional structure 10, a lower catalyst layer 20, and an upper catalyst layer 30.

[0014] The fire-resistant three-dimensional structure 10 extends from the gas inlet end face 10a to the gas outlet end face 10b and has partition walls that divide and form multiple gas flow paths that penetrate from the gas inlet end face 10a to the gas outlet end face 10b. In the exhaust gas purification catalyst 1 shown in Figure 1, the length of the partition wall from the gas inlet end face 10a to the gas outlet end face 10b is 130 mm.

[0015] The lower catalyst layer 20 is formed so as to be in contact with the partition wall of the fire-resistant three-dimensional structure 10. The lower catalyst layer 20 consists of a gas inlet region L1 and a gas outlet region L2, and the gas inlet region L1 and the gas outlet region L2 are in contact with each other at boundary X. In the exhaust gas purification catalyst 1 shown in Figure 1, boundary X is located 30 mm from the gas inlet end face 10a (23.1% of the length of the partition wall). The lower catalyst layer 20 (gas inlet region L1 and gas outlet region L2) is composed of palladium (Pd), alumina (Al2O3), cerium-zirconium composite oxide (CeO2-ZrO2), lantana (La2O3), and barium sulfate (BaSO4). Palladium concentration C in gas inlet region L1 L1 The palladium concentration is 0.08582 [g / g], indicating that the palladium concentration is substantially uniform throughout the gas inlet region L1. Furthermore, the palladium concentration C in the gas outlet region L2 is... L2 It is 0.0006197 [g / g], and C L2 C for L1 The ratio (C L1 / C L2 ) is 138.

[0016] The upper catalyst layer 30 is formed on the lower catalyst layer 20 and is located on the outermost surface. In the exhaust gas purification catalyst 1 shown in Figure 1, the upper catalyst layer 30 is formed adjacent to the gas outlet side region L2 of the lower catalyst layer 20 and does not exist on the gas inlet side region L1. By adopting such a configuration, the exhaust gas purification performance at low temperatures can be further improved. That is, in the catalyst according to a preferred embodiment, the gas inlet side region L1 of the lower catalyst layer constitutes the outermost surface. The upper catalyst layer 30 is composed of rhodium (Rh), alumina (Al2O3), cerium-zirconium composite oxide (CeO2-ZrO2), and lantana (La2O3).

[0017] Figure 2 is a schematic front cross-sectional view of a part of an exhaust gas purification catalyst according to another embodiment of the present invention. This embodiment corresponds to catalyst B of Example 2 described later. The exhaust gas purification catalyst 2 shown in Figure 2 differs from the exhaust gas purification catalyst 1 shown in Figure 1 in that an upper catalyst layer 30 is also formed on the gas inlet side region L1 (i.e., the upper catalyst layer 30 is formed from the gas inlet side end face 10a to the gas outlet side end face 10b).

[0018] Figure 3 is a schematic front cross-sectional view of a part of an exhaust gas purification catalyst according to yet another embodiment of the present invention. This embodiment corresponds to catalyst C of Example 3 described later. The exhaust gas purification catalyst 3 shown in Figure 3 differs from the exhaust gas purification catalyst 2 shown in Figure 2 in that a predetermined proportion of palladium is present in both the gas inlet-side region L1 of the lower catalyst layer and the region of the upper catalyst layer that is in contact with the gas inlet-side region L1 of the lower catalyst layer (gas inlet-side region U1 of the upper catalyst layer). In the exhaust gas purification catalyst 3 shown in Figure 3, there is no palladium in the region of the upper catalyst layer that is in contact with the gas outlet-side region L2 of the lower catalyst layer (gas outlet-side region U2 of the upper catalyst layer). The boundary Y between the gas inlet-side region U1 and the gas outlet-side region U2 is located at a position 30 mm from the gas inlet-side end face 10a (23.1% of the length of the partition wall), the same as boundary X. Palladium concentration C of the gas inlet-side region L1 L1 The palladium concentration is 0.06031 [g / g], indicating that the palladium concentration is substantially uniform throughout the gas inlet region L1. Furthermore, the palladium concentration C in the gas inlet region U1 is... U1 It is 0.05972 [g / g], and C L1 C for U1 The ratio (C U1 / C L1 ) is 0.990.

[0019] Next, we will describe each component included in the exhaust gas purification catalyst of this embodiment.

[0020] [Fireproof three-dimensional structure] The refractory three-dimensional structure serves as a support for the catalyst layer. The type and size of the refractory three-dimensional structure are not particularly limited, and those known in the field of exhaust gas purification catalysts can be used as appropriate. Honeycomb supports are preferably used as the refractory three-dimensional structure. Examples of honeycomb supports include monolithic honeycomb supports, metal honeycomb supports, and plug honeycomb supports such as particulate filters. The material of the honeycomb support is preferably a heat-resistant metal such as cordierite, silicon carbide, silicon nitride, stainless steel, or Fe-Cr-Al alloy.

[0021] The above honeycomb carrier is manufactured by extrusion molding or by winding sheet-like elements. The shape of the gas passages (cell shape) may be hexagonal, quadrilateral, square, triangular, or corrugated. A cell density (number of cells / unit cross-sectional area) of 100 cells / square inch to 1200 cells / square inch (15.5 cells / square centimeter to 186 cells / square centimeter) is sufficient for use, and preferably 200 cells / square inch to 900 cells / square inch (31 cells / square centimeter to 139.5 cells / square centimeter).

[0022] The length of the fire-resistant three-dimensional structure (length of the partition wall) along the gas flow direction is preferably more than 15 mm and 1000 mm or less, more preferably 30 mm or more and 500 mm or less, and even more preferably 50 mm or more and 300 mm or less.

[0023] [Lower catalyst layer] The lower catalyst layer is formed so as to be in contact with the partition wall of the three-dimensional structure (directly above the partition wall). The lower catalyst layer consists of a gas inlet region L1 (hereinafter also simply referred to as "region L1") located on the gas inlet side and a gas outlet region L2 (hereinafter also simply referred to as "region L2") located on the gas outlet side. Regions L1 and L2 are in contact with each other at boundary X. The lower catalyst layer (regions L1 and L2) contains palladium, alumina, and cerium-zirconium composite oxide.

[0024] Palladium functions as a catalyst for oxidation reactions. The catalyst in this embodiment has a palladium concentration C in region L2. L2 [g / g] Palladium concentration C in region L1 L1 [g / g] ratio (C L1 / C L2 The characteristic feature is that the ratio is between 30 and 230. If the ratio is less than 30, the exhaust gas purification performance (especially HC purification performance) at low temperatures may not be fully realized. If the ratio exceeds 230, the palladium may not be sufficiently dispersed in region L1, and the purification performance commensurate with the amount of palladium may not be obtained. From the viewpoint of further improving the exhaust gas purification performance at low temperatures, the ratio is preferably between 40 and 220, more preferably between 90 and 210, and even more preferably between 100 and 200. Note that the palladium concentration C in region L1 L1 The palladium concentration C in region L2 is not particularly limited, but is preferably 0.01900 g / g or more and 0.15000 g / g or less, more preferably 0.02000 g / g or more and 0.14000 g / g or less, even more preferably 0.06000 g / g or more and 0.13000 g / g or less, and particularly preferably 0.06500 g / g or more and 0.12000 g / g or less. L2 While not particularly limited, it is preferably 0.0001000 g / g or more and 0.001000 g / g or less.

[0025] The palladium concentration in the gas inlet region L1 is preferably substantially uniform throughout the region L1. This configuration allows for highly dispersed palladium support in region L1, thereby further improving exhaust gas purification performance at low temperatures. In this specification, "substantially uniform palladium concentration throughout the gas inlet region L1" means that when the palladium concentration is measured at any 10 points in region L1, and the maximum value among the 10 obtained palladium concentrations is taken as the "maximum concentration" and the minimum value as the "minimum concentration," the value of {(maximum concentration - minimum concentration) / minimum concentration} × 100 is within 10%. This value is preferably within 5%, more preferably within 3%, even more preferably within 1%, and particularly preferably within 0%. The composition of the catalyst layer can be confirmed by inductively coupled plasma (ICP) emission spectroscopy or X-ray fluorescence (XRF) analysis.

[0026] The palladium content per liter of the refractory three-dimensional structure in the lower catalyst layer (regions L1 and L2) is preferably 0.05 g / L or more and 5 g / L or less, more preferably 0.1 g / L or more and 4.5 g / L or less, and even more preferably 1 g / L or more and 4 g / L or less.

[0027] Examples of palladium raw materials (palladium sources) include palladium nitrates, acetates, ammonium salts, amine salts, carbonates, and tetraamminepalladium salts. In one preferred embodiment, the palladium source in region L1 is palladium nitrate and tetraamminepalladium salt, and the palladium source in region L2 is palladium nitrate.

[0028] Alumina functions as a carrier for precious metals (palladium). Specific examples of alumina include γ-alumina, δ-alumina, and θ-alumina, with γ-alumina being preferred.

[0029] Furthermore, alumina may be included in the form of a composite oxide of alumina and an oxide of another element. Examples of other elements in this case include phosphorus, zirconium, silicon, titanium, and lanthanum. Specific examples of composite oxides include Al-P composite oxide, Al-Zr-P composite oxide, Al-Zr composite oxide, Al-Si composite oxide, Al-Si-Zr composite oxide, Al-Ti composite oxide, Al-Ti-Zr composite oxide, Al-Si-Ti-Zr composite oxide, and Al-La composite oxide. The aluminum content in the above composite oxide is preferably more than 50% by mass and less than 100% by mass, more preferably 60% by mass or more and 99% by mass or less, even more preferably 70% by mass or more and 97% by mass or less, and particularly preferably 75% by mass or more and 95% by mass or less, based on Al2O3.

[0030] The alumina content per liter of the refractory three-dimensional structure in the lower catalyst layer (regions L1 and L2) is preferably 10 g / L to 300 g / L, more preferably 20 g / L to 250 g / L, and even more preferably 50 g / L to 200 g / L. If the alumina content is within the above range, the precious metal (palladium) can be sufficiently dispersed and supported.

[0031] Examples of alumina raw materials include powders of alumina (γ-alumina, δ-alumina, θ-alumina, or composite oxides of alumina and oxides of other elements), and aluminum chloride, aluminum nitrate (e.g., aluminum nitrate nonahydrate), aluminum sulfate, aluminum acetate, and aluminum hydroxide, which become alumina when calcined. Furthermore, when alumina is included in the form of a composite oxide of alumina and oxides of other elements, the raw materials for the oxides of other elements are as follows: Examples of phosphorus sources for phosphorus oxide include phosphoric acid, phosphorous acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate. Among these, phosphoric acid is preferred. Examples of zirconium sources for zirconia include zirconium oxynitrate, zirconium oxychloride, zirconium nitrate, basic zirconium sulfate, zirconium carbonate, and zirconium hydroxide. Among these, zirconium nitrate is preferred. Examples of silicon sources for silica include silicon oxide, orthosilicate, metasilicic acid, and silica sol. Examples of raw materials (titanium sources) for titania include inorganic titanium compounds such as titanium tetrachloride and titanium sulfate, titanium oxalate, and tetraisopropyl titanate. Examples of raw materials (lanthanum sources) for lantana include lanthanum oxide, lanthanum nitrate, lanthanum sulfate, lanthanum carbonate, and lanthanum acetate. Among these, the alumina raw material is preferably alumina powder (γ-alumina, δ-alumina, θ-alumina, or composite oxides of alumina and oxides of other elements).

[0032] Cerium-zirconium composite oxide (CeO2-ZrO2) can primarily act as an oxygen storage and release material. Here, the oxygen storage and release material has the function of stably carrying out oxidation-reduction reactions by absorbing oxygen in an oxidizing atmosphere (lean) and releasing oxygen in a reducing atmosphere (rich), in response to fluctuations in the air-fuel ratio (A / F) which changes according to the operating conditions.

[0033] The cerium (Ce) content in the cerium-zirconium composite oxide is preferably 3% to 65% by mass, more preferably 5% to 50% by mass, and even more preferably 10% to 47% by mass, based on the oxide (CeO2) equivalent. The zirconium (Zr) content in the cerium-zirconium composite oxide is preferably 35% to 97% by mass, more preferably 50% to 95% by mass, and even more preferably 53% to 90% by mass, based on the oxide (ZrO2) equivalent. When the cerium (Ce) and zirconium (Zr) content is within the above range, oxygen absorption and desorption can proceed even at low temperatures.

[0034] Cerium-zirconium composite oxides may also be included in the form of a composite oxide of cerium-zirconium composite oxide and an oxide of at least one metal selected from the group consisting of lanthanum (La), yttrium (Y), neodymium (Nd), and praseodymium (Pr). Specific examples of such composite oxides include cerium-zirconium-lanthanum composite oxide and cerium-zirconium-lanthanum-yttrium composite oxide.

[0035] The content of cerium-zirconium composite oxide per liter of the refractory three-dimensional structure in the lower catalyst layer (regions L1 and L2) is preferably 5 g / L to 200 g / L, more preferably 10 g / L to 100 g / L, and even more preferably 20 g / L to 90 g / L. If the content of cerium-zirconium composite oxide is within the above range, the exhaust gas purification performance (especially HC purification performance) at low temperatures can be further improved.

[0036] The lower catalyst layer (regions L1 and L2) optionally contains at least one co-catalyst selected from the group consisting of Group 1 elements, Group 2 elements, and rare earth elements. Specific examples of elements include potassium, magnesium, calcium, strontium, barium, and lanthanum. These elements are incorporated into the catalyst in the form of oxides, sulfates, or carbonates after calcination. In particular, the lower catalyst layer (regions L1 and L2) preferably contains both rare earth elements and Group 2 elements, and more preferably contains lanthanum oxide (La2O3) and barium sulfate (BaSO4). The inclusion of a co-catalyst in the lower catalyst layer (regions L1 and L2) can improve the efficiency of exhaust gas purification performance (especially HC purification performance). When the lower catalyst layer (regions L1 and L2) contains lanthanum oxide (La2O3), the content of lanthanum oxide (La2O3) per liter of the refractory three-dimensional structure is preferably 0.5 g / L or more and 20 g / L or less, more preferably 0.8 g / L or more and 10 g / L or less, and even more preferably 1 g / L or more and 5 g / L or less. When the lower catalyst layer (regions L1 and L2) contains barium sulfate (BaSO4), the content of barium sulfate (BaSO4) per liter of the refractory three-dimensional structure is preferably 1 g / L or more and 30 g / L or less, more preferably 3 g / L or more and 25 g / L or less, and even more preferably 5 g / L or more and 20 g / L or less.

[0037] The lower catalyst layer (region L1 and / or region L2) may contain other precious metals besides palladium, to the extent that it does not significantly impair the effects of the present invention. Examples of other precious metals include platinum (Pt) and rhodium (Rh). However, the content of other precious metals per liter of refractory three-dimensional structure in the lower catalyst layer is preferably 3 g / L or less, more preferably 1 g / L or less, and even more preferably 0 g / L (not included).

[0038] The lower catalyst layer may contain the above-mentioned palladium, alumina, and cerium-zirconium composite oxide, an optional co-catalyst, an optional other noble metal, and other components not listed above, to the extent that they do not significantly impair the effects of the present invention. Examples of other components include manganese, iron, cobalt, nickel, and copper. However, the content of other components per liter of refractory three-dimensional structure in the lower catalyst layer is preferably 10 g / L or less, more preferably 5 g / L or less, even more preferably 3 g / L or less, particularly preferably 1 g / L or less, and most preferably 0 g / L (not included).

[0039] The total amount of catalyst supported in the lower catalyst layer is not particularly limited, but is preferably 50 g / L to 200 g / L, more preferably 80 g / L to 190 g / L, and even more preferably 120 g / L to 180 g / L. If the total amount of catalyst supported is within the above range, the desired exhaust gas purification performance can be achieved while suppressing an excessive increase in pressure loss.

[0040] The catalyst according to this embodiment is also characterized in that the boundary X between region L1 and region L2 is located within a range of 8% to 80% of the length of the partition wall from the gas inlet side end face. If the boundary X is located in a range of less than 8% or more than 80%, sufficient exhaust gas purification performance (especially HC purification performance) at low temperatures may not be obtained. From the viewpoint of further improving exhaust gas purification performance (especially HC purification performance) at low temperatures, the boundary X is preferably located within a range of 8% to 70%, more preferably within a range of 9% to 50%, and even more preferably within a range of 10% to 30% from the gas inlet side end face.

[0041] Furthermore, the composition and boundary locations of each catalyst layer can be confirmed by inductively coupled plasma (ICP) emission spectroscopy or X-ray fluorescence (XRF) analysis.

[0042] [Upper catalyst layer] The upper catalyst layer is formed on the lower catalyst layer and is located at the outermost surface. Other layers may be placed between the lower and upper catalyst layers, but it is preferable that the lower and upper catalyst layers are adjacent to each other. The upper catalyst layer contains rhodium, alumina, and cerium-zirconium composite oxide.

[0043] Rhodium functions as a catalyst for the reduction reaction. The rhodium content per liter of the refractory three-dimensional structure in the upper catalyst layer is preferably 0.01 g / L to 2 g / L, more preferably 0.05 g / L to 1.5 g / L, and even more preferably 0.1 g / L to 1 g / L.

[0044] Examples of rhodium raw materials (rhodium sources) include inorganic salts of rhodium such as nitrates, sulfates, acetates, ammonium salts, amine salts, hexaammine salts, carbonates, bicarbonates, nitrites, and oxalates; carboxylates such as formates; and hydroxides, alkoxides, oxides, etc. According to one preferred embodiment, the rhodium source is at least one selected from the group consisting of rhodium nitrates, ammonium salts, amine salts, and carbonates.

[0045] In addition to the rhodium mentioned above, the upper catalyst layer contains palladium at a concentration C, as shown in Figure 3, in the region of the upper catalyst layer that is in contact with the gas inlet region L1 of the lower catalyst layer (gas inlet region U1 of the upper catalyst layer). L1 It is preferable that it is contained at a high concentration of the same magnitude as C. That is, in a preferred embodiment of the catalyst, the upper catalyst layer is located on the gas inlet side, and the palladium concentration is C U1 It consists of a gas inlet region U1 with a palladium concentration of [g / g] and a gas outlet region U2 located on the gas outlet side that is substantially free of palladium, and the boundary Y between the gas inlet region U1 and the gas outlet region U2 is located at substantially the same position as the boundary X with respect to the length of the partition wall, and the palladium concentration C of the gas inlet region L1 in the lower catalyst layer L1 The palladium concentration C in the gas inlet region U1 of the upper catalyst layer U1 The ratio (C U1 / C L1) is 0.800 or more and less than 1.000. By adopting such a configuration, the amount of palladium in the gas inlet-side region U1 of the upper catalyst layer, which is more likely to come into contact with the gas, is increased, and therefore the exhaust gas purification performance at low temperatures (especially HC purification performance) can be further improved compared to the case in which palladium is not included in the gas inlet-side region U1. In this specification, "substantially palladium-free" means "no palladium (0 g / L)" or "contains palladium, and the palladium content per liter of the refractory three-dimensional structure is greater than 0 g / L and less than or equal to 0.01 g / L". "Substantially the same position" means that the distance between the position of boundary X and the position of boundary Y is within 5 mm. The distance between the position of boundary X and the position of boundary Y is preferably within 3 mm, more preferably within 1 mm, and most preferably 0 mm (boundary X and boundary Y are in the same position).

[0046] The above ratio (C U1 / C L1 From the viewpoint of further improving exhaust gas purification performance (especially HC purification performance) at low temperatures, a ratio (C) that is closer to 1 is preferable. Specifically, the above ratio (C U1 / C L1 The coefficient of the

[0047] The upper catalyst layer (region U1 and / or region U2) may contain platinum (Pt) in addition to rhodium and palladium, to the extent that it does not significantly impair the effects of the present invention. However, the platinum (Pt) content per liter of the refractory three-dimensional structure in the lower catalyst layer is preferably 0.01 g / L or less, and more preferably 0 g / L (not contained).

[0048] The alumina and its raw materials contained in the upper catalyst layer are the same as those described in the section on the lower catalyst layer, so a detailed explanation is omitted here. Note that the alumina contained in the upper catalyst layer may be the same as or different from that contained in the lower catalyst layer. The alumina content per liter of the refractory three-dimensional structure in the upper catalyst layer (regions U1 and U2) is preferably 5 g / L to 70 g / L, more preferably 10 g / L to 60 g / L, and even more preferably 20 g / L to 50 g / L. If the alumina content is within the above range, the precious metal (rhodium, or rhodium and palladium) can be sufficiently dispersed and supported.

[0049] The cerium-zirconium composite oxide (CeO2-ZrO2) and its raw materials contained in the upper catalyst layer are the same as those described in the section on the lower catalyst layer, so a detailed explanation is omitted here. Note that the cerium-zirconium composite oxide contained in the upper catalyst layer may be the same as or different from that contained in the lower catalyst layer. The content of cerium-zirconium composite oxide per liter of refractory three-dimensional structure in the upper catalyst layer (regions U1 and U2) is preferably 5 g / L to 70 g / L, more preferably 10 g / L to 60 g / L, and even more preferably 20 g / L to 50 g / L. If the content of cerium-zirconium composite oxide is within the above range, the exhaust gas purification performance (especially HC purification performance) at low temperatures may be improved.

[0050] The upper catalyst layer (regions U1 and U2) optionally includes at least one co-catalyst selected from the group consisting of Group 1 elements, Group 2 elements, and rare earth elements. Details of the co-catalyst are the same as those described in the section on the lower catalyst layer, so a detailed explanation is omitted here. From the viewpoint of improving the efficiency of exhaust gas purification performance (especially HC purification performance), it is preferable that the upper catalyst layer (regions U1 and U2) contains lanthanum oxide (La2O3). The content of lanthanum oxide (La2O3) per liter of refractory three-dimensional structure in the upper catalyst layer is preferably 0.1 g / L to 10 g / L, more preferably 0.3 g / L to 5 g / L, and even more preferably 0.5 g / L to 3 g / L.

[0051] The upper catalyst layer may contain the rhodium, alumina, and cerium-zirconium composite oxides, as well as optional components such as platinum and co-catalysts, and other components not mentioned above, to the extent that they do not significantly impair the effects of the present invention. Details of the other components are the same as those described in the section on the lower catalyst layer, so a detailed explanation is omitted here. The content of other components per liter of refractory three-dimensional structure in the upper catalyst layer is preferably 10 g / L or less, more preferably 5 g / L or less, even more preferably 3 g / L or less, particularly preferably 1 g / L or less, and most preferably 0 g / L (not included).

[0052] The total amount of material supported in the upper catalyst layer is not particularly limited, but is preferably 50 g / L to 200 g / L, more preferably 60 g / L to 150 g / L, and even more preferably 65 g / L to 120 g / L. If the total amount of material supported is within the above range, the desired exhaust gas purification performance can be achieved while suppressing an excessive increase in pressure loss.

[0053] <Method for manufacturing an exhaust gas purification catalyst> Next, a method for manufacturing the exhaust gas purification catalyst described above will be explained. The method for manufacturing the catalyst is not particularly limited, but the following method is preferred. In other words, a method for manufacturing an exhaust gas purification catalyst according to another embodiment of the present invention comprises: applying, drying, and firing a slurry for a lower catalyst layer containing a palladium source, an alumina raw material, and a cerium-zirconium composite oxide raw material onto the partition wall of the fire-resistant three-dimensional structure to form a lower catalyst layer (hereinafter also referred to as "lower catalyst layer formation step (1)" or "step (1)"); applying, drying, and firing an upper catalyst layer slurry containing a rhodium source, an alumina raw material, and a cerium-zirconium composite oxide raw material onto the lower catalyst layer to form an upper catalyst layer (hereinafter also referred to as "upper catalyst layer formation step (2)" or "step (2)"); and applying, drying, and firing a palladium solution containing a palladium complex salt and a thickener from the gas inlet side end face to a position within a range of 8% to 80% of the length of the partition wall from the gas inlet side end face (hereinafter also referred to as "Pd supporting step (3)" or "step (3)"). The following provides a detailed explanation of each step.

[0054] [Lower catalyst layer formation step (1)] In step (1), a slurry for the lower catalyst layer containing a palladium source, alumina raw material, and cerium-zirconium composite oxide raw material is applied to the partition walls of the refractory three-dimensional structure, dried, and fired to form the lower catalyst layer.

[0055] The slurry for the lower catalyst layer contains a palladium source, alumina raw material, and cerium-zirconium composite oxide raw material. Since the palladium source, alumina raw material, and cerium-zirconium composite oxide raw material are the same as those described in the section on the lower catalyst layer, a detailed explanation is omitted here.

[0056] In this embodiment, the alumina raw material is preferably alumina powder (γ-alumina, δ-alumina, θ-alumina, or a composite oxide of alumina and an oxide of another element), and more preferably alumina with a large pore volume (hyporus alumina) in order to improve the dispersibility of the noble metal (palladium). The pore volume of the alumina raw material (alumina powder) can be measured by nitrogen adsorption. The pore volume of the alumina raw material (pore volume per 1 g of alumina raw material) is preferably 0.4 cm³. 3 / g or more 3.0cm 3 It is less than or equal to / g, and more preferably 0.6cm 3 / g or more 2.5cm 3 It is less than or equal to / g, and more preferably 0.7cm 3 / g or more 1.5cm 3 It is less than / g. The pore volume of the alumina raw material is 0.7 cm³. 3 A concentration of 1.5 cm³ or more is preferable because it results in high dispersion of the noble metal (palladium) supported on the alumina. On the other hand, a pore volume of 1.5 cm³ in the alumina raw material is preferable. 3 A value of less than / g is preferable because it prevents the alumina from becoming excessively bulky and suppresses an increase in pressure loss.

[0057] The specific surface area of ​​alumina raw material (alumina powder) can be measured by the BET multi-point method in accordance with ISO 9277:2010. When the alumina raw material is hypoporous alumina, the BET specific surface area (BET surface area per gram of alumina raw material) is preferably 50 m². 2 / g or more 500m 2 / g or less, more preferably 60m 2 / g or more 300m 2 It is less than or equal to / g, and more preferably 80m 2 / g or more 200m 2 It is less than / g. The BET specific surface area of ​​the alumina raw material is 80m². 2 A BET specific surface area of ​​the alumina raw material of 200 m² is preferable because it results in high dispersion of the noble metal (palladium) supported on the alumina. 2 A value of less than / g is preferable because it prevents the alumina from losing surface area when exposed to high-temperature exhaust gas.

[0058] When the alumina raw material is hypoporous alumina, it is preferable that the cerium-zirconium composite oxide raw material has a small specific surface area from the viewpoint of preferentially supporting the precious metal (palladium) on the hypoporous alumina and improving the dispersibility of the precious metal (palladium). The BET specific surface area of ​​the cerium-zirconium composite oxide raw material is preferably 1.0 m². 2 / g or more 30m 2 It is less than or equal to / g, and more preferably 1.0m 2 / g or more 20m 2 It is less than or equal to / g, and more preferably 1.0m 2 / g or more 10m 2 The BET specific surface area of ​​the cerium-zirconium composite oxide raw material is 1.0 m². 2 A value of 10 / g or higher is preferable because it allows for sufficient oxygen absorption and release performance. On the other hand, a BET specific surface area of ​​the cerium-zirconium composite oxide raw material is 10 m². 2 A value of 0 / g or less is preferable because it allows the precious metal (palladium) to be supported in high dispersion on the hypoporous alumina. That is, in the manufacturing method according to a preferred embodiment, the pore volume measured by the nitrogen adsorption method of the alumina raw material contained in the slurry for the lower catalyst layer is 80 cm³. 3 / g or more 200cm 3 The BET specific surface area of ​​the cerium-zirconium composite oxide raw material contained in the slurry for the lower catalyst layer is 1.0 m² or less. 2 / g or more 10m 2 It is less than / g.

[0059] The slurry for the lower catalyst layer may further contain, if necessary, any optional components other than those contained in the lower catalyst layer (the co-catalysts, other precious metals, and other components described above) and / or their raw materials. Since the co-catalysts, other precious metals, and other components are the same as those described in the section on the lower catalyst layer, a detailed explanation is omitted here.

[0060] The solvent contained in the slurry for the lower catalyst layer is not particularly limited, but examples include water (pure water, ultrapure water, deionized water, distilled water, etc.), ethanol, lower alcohols such as 2-propanol, and organic alkaline aqueous solutions. Among these, water and lower alcohols are preferred, and water is more preferred. The amount of solvent in the slurry for the lower catalyst layer is not particularly limited, but it is an amount such that the proportion of solids in the slurry (solids mass concentration) is preferably 5 to 60% by mass, more preferably 10 to 50% by mass.

[0061] As a method for applying the slurry for the lower catalyst layer onto the partition walls of the fire-resistant three-dimensional structure, known methods such as wash coating can be appropriately employed. The amount of slurry applied is such that the amount of solids in the slurry and the amount of each component in the lower catalyst layer fall within the aforementioned ranges.

[0062] Regarding the method for drying and firing the coating film formed on the partition wall by the above coating, known methods can be appropriately employed. In this specification, "drying" refers to removing the solvent contained in the coating film, and "firing" refers to further high-temperature treatment of the coating film from which the solvent has been removed to adhere each component to the partition wall. The drying conditions are not particularly limited, but are carried out in air; preferably at a temperature of 50°C or higher and less than 300°C, more preferably at a temperature of 80°C or higher and 200°C; preferably for 5 minutes or more and 10 hours or less, more preferably for 30 minutes or more and 8 hours or less. The firing conditions are also not particularly limited, but are carried out in air; preferably at a temperature of 300°C or higher and 1200°C or less, more preferably at a temperature of 400°C or higher and 700°C or less; preferably for 10 minutes or more and 10 hours or less, more preferably for 30 minutes or more and 5 hours or less.

[0063] [Upper catalyst layer formation step (2)] In step (2), an upper catalyst layer is formed by applying, drying, and firing an upper catalyst layer slurry containing a rhodium source, alumina raw material, and cerium-zirconium composite oxide raw material onto the lower catalyst layer.

[0064] The slurry for the upper catalyst layer contains a rhodium source, alumina raw material, and cerium-zirconium composite oxide raw material. Since the rhodium source, alumina raw material, and cerium-zirconium composite oxide raw material are the same as those described in the section on the upper catalyst layer, a detailed explanation is omitted here.

[0065] In this embodiment, the alumina raw material is preferably alumina powder (γ-alumina, δ-alumina, θ-alumina, or a composite oxide of alumina and an oxide of another element). The pore volume of the alumina raw material (pore volume per gram of alumina raw material) is not particularly limited, but is preferably 0.2 cm³. 3 / g or more 1.5cm 3 It is less than or equal to / g, and more preferably 0.3cm 3 / g or more 1.2cm 3 It is less than or equal to / g, and more preferably 0.4cm 3 / g or more 0.7cm 3 It is less than / g. The pore volume of the alumina raw material is 0.4 cm³. 3 A concentration of 0.7 cm³ or more is preferable because it ensures a good dispersion of the precious metal (rhodium). On the other hand, the pore volume of the alumina raw material is 0.7 cm³. 3 A value of less than / g is preferable because it prevents the thickness of the catalyst layer from increasing excessively, which would inhibit gas diffusion to the lower catalyst layer.

[0066] The specific surface area of ​​the alumina raw material (alumina powder) is not particularly limited, but is preferably 50 m². 2 / g or more 500m 2 / g or less, more preferably 60m 2 / g or more 300m 2 It is less than or equal to / g, and more preferably 80m 2 / g or more 200m 2 It is less than / g. The BET specific surface area of ​​the alumina raw material is 80m². 2 A value of 200 m² or more is preferable because it allows for efficient dispersion of precious metals. On the other hand, if the BET specific surface area of ​​the alumina raw material is 200 m² 2 A value of less than / g is preferable because it prevents the alumina from losing surface area when exposed to high-temperature exhaust gas.

[0067] The BET specific surface area of the cerium-zirconium composite oxide raw material is not particularly limited, but is preferably 20 m 2 / g or more and 300 m 2 / g or less, more preferably 30 m 2 / g or more and 200 m 2 / g or less, still more preferably 40 m 2 / g or more and 150 m 2 / g or less. When the BET specific surface area of the cerium-zirconium composite oxide raw material is 40 m 2 / g or more, it is preferable because sufficient oxygen storage and release performance is exhibited. On the other hand, when the BET specific surface area of the cerium-zirconium composite oxide raw material is 150 m 2 / g or less, it is preferable because the surface area is unlikely to decrease when the cerium-zirconium composite oxide is exposed to high-temperature exhaust gas.

[0068] The slurry for the upper catalyst layer may further contain, if necessary, optional components other than those described above (the promoter, "other noble metals", "other components") contained in the upper catalyst layer and / or their raw materials. Since the promoter, "other noble metals", and "other components" are the same as those described in the column of the upper catalyst layer, detailed description thereof is omitted here.

[0069] The solvent contained in the slurry for the upper catalyst layer and its amount are the same as those described in the column of step (1), and thus detailed description thereof is omitted here.

[0070] As a method for applying the slurry for the upper catalyst layer onto the lower catalyst layer, known methods such as wash coating can be appropriately employed. The coating amount of the slurry is an amount such that the amount of the solid content in the slurry and the amounts of the respective components in the upper catalyst layer are within the ranges described above. When a part of the lower catalyst layer (the portion that becomes the gas inflow side region L1) is exposed as in the embodiment shown in FIG. 1, the slurry for the upper catalyst layer may be applied from the gas outflow side end face 10b to a predetermined length.

[0071] The methods for drying and firing are the same as those described in the column of step (1), and thus detailed description thereof is omitted here.

[0072] [Pd loading process (3)] In step (3), a palladium solution containing a palladium complex salt and a thickener is applied, dried, and fired from the gas inlet end face to a position within a range of 8% to 80% of the length of the partition wall from the gas inlet end face to the gas outlet end face.

[0073] The complex salts containing palladium are not particularly limited, but include tetraamminepalladium ions ([Pd(NH3)4] 2+ It is preferable that the complex salt contains ) as a complex ion. The anion of the complex salt is not particularly limited. Examples of tetraamminepalladium salts include tetraamminepalladium(II) acetate ([Pd(NH3)4](CH3COO)2), tetraamminepalladium(II) chloride ([Pd(NH3)4]Cl2), tetraamminepalladium(II) hydroxide ([Pd(NH3)4](OH)2), tetraamminepalladium(II) nitrate ([Pd(NH3)4](NO3)2), and tetraamminepalladium(II) bicarbonate ([Pd(NH3)4](HCO3)2). Among these, tetraamminepalladium(II) acetate and tetraamminepalladium(II) nitrate are preferred from the viewpoint of the stability of the palladium solution, and tetraamminepalladium(II) acetate is more preferred.

[0074] From the viewpoint of supporting a desired amount of palladium, the amount of tetraamminepalladium salt in the palladium solution is preferably 1% to 30% by mass, and more preferably 3% to 20% by mass, based on 100% by mass of the palladium solution.

[0075] Thickening agents are added to control the amount of palladium loaded and the position of the boundary (X, or X and Y) to a desired location. Examples of thickening agents include β-1,3-glucans such as scleroglucan, curdlan, paramylon, patiman, and laminaran; and polysaccharides such as xanthan gum and guar gum. Among these, scleroglucan, xanthan gum, and guar gum are preferred, with scleroglucan being more preferred, from the viewpoint of ease of the above control.

[0076] The amount of thickener in the palladium solution is preferably 0.1% to 10% by mass, and more preferably 0.15% to 5.0% by mass, based on 100% by mass of the palladium solution, from the viewpoint of easily controlling the amount of palladium supported and the position of the boundary.

[0077] The solvent contained in the palladium solution is not particularly limited, but examples include water (pure water, ultrapure water, deionized water, distilled water, etc.), ethanol, lower alcohols such as 2-propanol, and organic alkaline aqueous solutions. Of these, water is preferred.

[0078] The method for applying the palladium solution is not particularly limited, but one example is to immerse the catalyst precursor that has undergone step (2) into a container containing the palladium solution from the gas inlet side end face. In this case, the area to which the palladium solution is applied is controlled so that the boundary (X, or X and Y) is at a desired position. When the gas inlet side end face is used as the starting point for the area to which the palladium solution is applied, the endpoint is within a range of 8% to 80% from the gas inlet side end face relative to the length of the partition wall from the gas inlet side end face to the gas outlet side end face. From the viewpoint of further improving the exhaust gas purification performance at low temperatures, the position of this endpoint is preferably within a range of 8% to 70%, more preferably within a range of 9% to 50%, and even more preferably within a range of 10% to 30%. The area to which the palladium solution is applied becomes the gas inlet side region (L1, or L1 and U1) after subsequent drying and firing.

[0079] The drying and firing methods are the same as those described in section (1), so a detailed explanation is omitted here.

[0080] <Exhaust gas purification methods> According to yet another embodiment of the present invention, an exhaust gas purification method is provided, comprising bringing the above-mentioned exhaust gas purification catalyst into contact with exhaust gas discharged from an internal combustion engine. Examples of internal combustion engines include gasoline engines, gasoline hybrid engines, diesel engines, diesel hybrid engines, and engines that use natural gas, ethanol, dimethyl ether, etc., as fuel. Among these, gasoline engines and gasoline hybrid engines are preferred, and gasoline engines are more preferred.

[0081] One method for bringing exhaust gas into contact with a catalyst is to install an exhaust gas purification catalyst in the exhaust passage of the exhaust port of an internal combustion engine and allow the exhaust gas to flow into the exhaust passage.

[0082] According to the present invention, even after high-temperature durability, the exhaust gas purification performance (particularly HC purification performance) at low temperatures can be improved. Here, high-temperature durability is performed by exposing the catalyst to an atmosphere of 650°C to 1200°C for 5 to 500 hours, more preferably to an atmosphere of 800°C to 1100°C for 10 to 100 hours.

[0083] The exhaust gas temperature is not particularly limited as long as it is within the temperature range of exhaust gas during normal operation of an internal combustion engine (e.g., a gasoline engine), but is preferably 0°C to 800°C, and more preferably 50°C to 700°C. The air-fuel ratio (A / F) of the exhaust gas is usually 10 to 30, and preferably 11 to 14.7.

[0084] In this specification, "exhaust gas temperature" refers to the temperature of the exhaust gas at the catalyst inlet. Here, "catalyst inlet" refers to the portion of the exhaust pipe where the exhaust gas purification catalyst is installed, from the catalyst end face on the exhaust gas inflow side toward the internal combustion engine to 10 cm, and also refers to the central portion in the longitudinal direction (axial direction) of the exhaust pipe.

[0085] Furthermore, in this specification, "catalyst bed" refers to the central portion of the exhaust pipe between the catalytic converter end face on the exhaust gas inlet side and the catalytic converter end face on the exhaust gas outlet side, and also to the central part of the cross-section of the exhaust pipe (or, if the cross-section of the exhaust pipe is not circular, to the centroid of the cross-section of the exhaust pipe).

[0086] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above and can be modified in various ways within the scope of the claims. Furthermore, the embodiments described herein can be combined in any way to form other embodiments.

[0087] The following embodiments are also included in the scope of the present invention: an exhaust gas purification catalyst according to claim 1 having the features of claim 2; an exhaust gas purification catalyst according to claim 1 or 2 having the features of claim 3; an exhaust gas purification catalyst according to any one of claims 1 to 3 having the features of claim 4; a method for manufacturing an exhaust gas purification catalyst according to any one of claims 1 to 4 having the features of claim 5; a manufacturing method according to claim 5 having the features of claim 6; and an exhaust gas purification method using an exhaust gas purification catalyst according to any one of claims 1 to 4 having the features of claim 7. [Examples]

[0088] The present invention will be described in more detail below with reference to examples. However, the technical scope of the present invention is not limited to the following examples. Unless otherwise specified, each operation was carried out under conditions of room temperature (25°C) and relative humidity of 40% RH to 50% RH.

[0089] <Examples of exhaust gas purification catalyst fabrication> [Example 1] (Formation of the lower catalyst layer precursor) Palladium nitrate (Pd(NO3)2), γ-alumina (Al2O3, pore volume 0.9 cm 3 / g, BET specific surface area 150 m 2 / g, average particle diameter (D50) 30 μm), cerium-zirconium composite oxide (CeO2-ZrO2, CeO2 content 44 mass%, BET specific surface area 1.7 m 2 / g), lanthanum acetate (La(CH3COO)3) and barium sulfate (BaSO4) were weighed respectively so that the mass ratio of Pd:Al2O3:CeO2-ZrO2:La2O3:BaSO4 after firing would be 0.1:95:50:3:15. Each weighed raw material was added to deionized water and wet pulverized to prepare slurry a1. Slurry a1 was applied from the gas inlet side end face to the gas outlet side end face of a cordierite honeycomb carrier (diameter 103 mm, length 130 mm, cylindrical shape, 1.083 L, 600 cells per square inch (1 inch = 25.4 mm), cell wall thickness 2.5 mil (1 mil = 0.0254 mm), cell shape square, the same hereinafter) as a refractory three-dimensional structure so that the supported amount after firing would be 163.1 g / L. After drying at 150 °C for 15 minutes, it was fired at 550 °C for 30 minutes to obtain A1 provided with a lower catalyst layer precursor on the refractory three-dimensional structure.

[0090] (Formation of the lower catalyst layer) An aqueous solution of tetraamminepalladium(II) acetate and scleroglucan were added to deionized water so that the Pd concentration (in terms of metal) would be 7.0 mass% and the scleroglucan concentration would be 0.5 mass%, and stirred for 2 hours to prepare palladium solution P1. Palladium solution P1 was applied from the inlet side end face of A1 to a position 30 mm (23.1% of the length of the partition wall) so that the palladium supported amount after firing would be 3.51 g / L. After drying at 150 °C for 15 minutes, it was fired at 550 °C for 30 minutes to obtain A2 provided with a lower catalyst layer (consisting of a gas inlet side region L1 with a palladium concentration C L1 of 0.08582 [g / g] and a gas outlet side region L2 with a palladium concentration C L2 of 0.0006197 [g / g]) on the refractory three-dimensional structure.

[0091] (Formation of the upper catalyst layer) Rhodium nitrate (Rh(NO3)2), γ-alumina (Al2O3, pore volume 0.5 cm³) 3 / g, BET specific surface area 130m 2 / g, average particle size (D50) 50μm), cerium-zirconium composite oxide (CeO2-ZrO2, CeO2 content 25% by mass, BET specific surface area 75m²) 2 The raw materials (Rh / g) and lanthanum oxide (La2O3) were weighed so that the mass ratio of Rh:Al2O3:CeO2-ZrO2:La2O3 after calcination was 0.2:40:35:1. Each weighed raw material was added to deionized water and wet-milled to prepare slurry a3. Slurry a3 was applied to a position 100 mm from the outlet end face of A2 so that the load after calcination was 76.2 g / L, dried at 150°C for 15 minutes, and then calcined at 550°C for 30 minutes to obtain catalyst A, which had a lower catalyst layer and an upper catalyst layer on a refractory three-dimensional structure.

[0092] [Example 2] (Formation of the lower catalytic layer precursor) A1 was obtained using the same method as in Example 1 (formation of the lower catalyst layer precursor).

[0093] (Formation of the lower catalytic layer) A2 was obtained using the same method as in Example 1 (Formation of the lower catalyst layer) described above.

[0094] (Formation of the upper catalyst layer) The slurry a3 from Example 1 (Formation of the upper catalyst layer) was applied to A2 from the gas inlet end face to the gas outlet end face so that the load after firing was 76.2 g / L. After drying at 150°C for 15 minutes, it was fired at 550°C for 30 minutes to obtain catalyst B, which had a lower catalyst layer and an upper catalyst layer on a refractory three-dimensional structure.

[0095] [Example 3] (Formation of the lower catalytic layer precursor) A1 was obtained using the same method as in Example 1 described above.

[0096] (Formation of the upper catalyst layer precursor) The slurry a3 from Example 1 (Formation of the Upper Catalyst Layer) described above was applied to A1 from the gas inlet end face to the gas outlet end face so that the load after firing was 76.2 g / L. After drying at 150°C for 15 minutes, it was fired at 550°C for 30 minutes to obtain C2, in which a lower catalyst layer precursor and an upper catalyst layer precursor were provided on a refractory three-dimensional structure.

[0097] (Formation of the lower catalyst layer and the upper catalyst layer) In Example 1 (Formation of the Lower Catalyst Layer), the palladium solution P1 was applied to a position 30 mm (23.1% of the length of the partition wall) from the inlet end face of C2 so that the palladium load after firing was 3.51 g / L. After drying at 150°C for 15 minutes, it was fired at 550°C for 30 minutes to form a lower catalyst layer (palladium concentration C) on the refractory three-dimensional structure. L1 The gas inlet region L1 and palladium concentration C are 0.06031 [g / g]. L2 (consisting of the gas outlet side region L2 where the concentration is 0.0006197 [g / g]) and the upper catalyst layer (palladium concentration C U1 The gas inlet region U1 and palladium concentration C are 0.05972 [g / g]. U2 A catalyst C was obtained that included a gas outlet side region U2 where the concentration is 0 [g / g].

[0098] [Comparative Example 1] (Formation of the lower catalytic layer precursor) A1 was obtained using the same method as in Example 1 described above.

[0099] (Formation of the upper catalyst layer precursor) The slurry a3 from Example 1 (Formation of the Upper Catalyst Layer) described above was applied to A1 from the gas inlet end face to the gas outlet end face so that the load after firing was 76.2 g / L. After drying at 150°C for 15 minutes, it was fired at 550°C for 30 minutes to obtain C2, in which a lower catalyst layer precursor and an upper catalyst layer precursor were provided on a refractory three-dimensional structure.

[0100] (Formation of the lower catalyst layer and the upper catalyst layer) In Example 1 (Formation of the Lower Catalyst Layer), the palladium solution P1 was applied to a position 10 mm (7.7% of the length of the partition wall) from the inlet end face of C2 so that the palladium load after firing was 3.51 g / L. After drying at 150°C for 15 minutes, it was fired at 550°C for 30 minutes to form a lower catalyst layer (palladium concentration C) on the refractory three-dimensional structure. L1 The gas inlet region L1 and palladium concentration C are 0.1606 [g / g]. L2 (consisting of the gas outlet side region L2 where the concentration is 0.0006197 [g / g]) and the upper catalyst layer (palladium concentration C U1 The gas inlet region U1 and palladium concentration C are 0.1601 [g / g]. U2 A catalyst D was obtained that included a gas outlet side region U2 where the concentration is 0 [g / g].

[0101] [Example 4] (Formation of the lower catalytic layer precursor) A1 was obtained using the same method as in Example 1 described above.

[0102] (Formation of the upper catalyst layer precursor) The slurry a3 from Example 1 (Formation of the Upper Catalyst Layer) described above was applied to A1 from the gas inlet end face to the gas outlet end face so that the load after firing was 76.2 g / L. After drying at 150°C for 15 minutes, it was fired at 550°C for 30 minutes to obtain C2, in which a lower catalyst layer precursor and an upper catalyst layer precursor were provided on a refractory three-dimensional structure.

[0103] (Formation of the lower catalyst layer and the upper catalyst layer) In Example 1 (Formation of the Lower Catalyst Layer), the palladium solution P1 was applied to a position 15 mm (11.5% of the length of the partition wall) from the inlet end face of C2 so that the palladium load after firing was 3.51 g / L. After drying at 150°C for 15 minutes, it was fired at 550°C for 30 minutes to form a lower catalyst layer (palladium concentration C) on the refractory three-dimensional structure. L1 The gas inlet region L1 and palladium concentration C are 0.1133 [g / g]. L2 (consisting of the gas outlet side region L2 where the concentration is 0.0006197 [g / g]) and the upper catalyst layer (palladium concentration C U1The gas inlet region U1 and palladium concentration C are 0.1127 [g / g]. U2 A catalyst E was obtained that included a gas outlet side region U2 where the concentration is 0 [g / g].

[0104] [Example 5] (Formation of the lower catalytic layer precursor) A1 was obtained using the same method as in Example 1 described above.

[0105] (Formation of the upper catalyst layer precursor) The slurry a3 from Example 1 (Formation of the Upper Catalyst Layer) described above was applied to A1 from the gas inlet end face to the gas outlet end face so that the load after firing was 76.2 g / L. After drying at 150°C for 15 minutes, it was fired at 550°C for 30 minutes to obtain C2, in which a lower catalyst layer precursor and an upper catalyst layer precursor were provided on a refractory three-dimensional structure.

[0106] (Formation of the lower catalyst layer and the upper catalyst layer) In Example 1 (Formation of the Lower Catalyst Layer), the palladium solution P1 was applied to a position 65 mm (50.0% of the length of the partition wall) from the inlet end face of C2 so that the palladium load after firing was 3.51 g / L. After drying at 150°C for 15 minutes, it was fired at 550°C for 30 minutes to form a lower catalyst layer (palladium concentration C) on the refractory three-dimensional structure. L1 The gas inlet region L1 and palladium concentration C are 0.02908 [g / g]. L2 (consisting of the gas outlet side region L2 where the concentration is 0.0006197 [g / g]) and the upper catalyst layer (palladium concentration C U1 The gas inlet region U1 and palladium concentration C are 0.02848 [g / g]. U2 A catalyst F was obtained that included a gas outlet side region U2 where the concentration is 0 [g / g].

[0107] [Example 6] (Formation of the lower catalytic layer precursor) A1 was obtained using the same method as in Example 1 described above.

[0108] (Formation of the upper catalyst layer precursor) The slurry a3 from Example 1 (Formation of the Upper Catalyst Layer) described above was applied to A1 from the gas inlet end face to the gas outlet end face so that the load after firing was 76.2 g / L. After drying at 150°C for 15 minutes, it was fired at 550°C for 30 minutes to obtain C2, in which a lower catalyst layer precursor and an upper catalyst layer precursor were provided on a refractory three-dimensional structure.

[0109] (Formation of the lower catalyst layer and the upper catalyst layer) In Example 1 (Formation of the Lower Catalyst Layer), the palladium solution P1 was applied to a position 100 mm (76.9% of the length of the partition wall) from the inlet end face of C2 so that the palladium load after firing was 3.51 g / L. After drying at 150°C for 15 minutes, it was fired at 550°C for 30 minutes to form a lower catalyst layer (palladium concentration C) on the refractory three-dimensional structure. L1 The gas inlet region L1 and palladium concentration C are 0.01931 [g / g]. L2 (consisting of the gas outlet side region L2 where the concentration is 0.0006197 [g / g]) and the upper catalyst layer (palladium concentration C U1 The gas inlet region U1 and palladium concentration C are 0.01870 [g / g]. U2 A catalyst G was obtained that included a gas outlet side region U2 where the concentration is 0 [g / g].

[0110] [Example 7] (Formation of the lower catalytic layer precursor) A1 was obtained using the same method as in Example 1 described above.

[0111] (Formation of the upper catalyst layer precursor) The slurry a3 from Example 1 (Formation of the Upper Catalyst Layer) described above was applied to A1 from the gas inlet end face to the gas outlet end face so that the load after firing was 76.2 g / L. After drying at 150°C for 15 minutes, it was fired at 550°C for 30 minutes to obtain C2, in which a lower catalyst layer precursor and an upper catalyst layer precursor were provided on a refractory three-dimensional structure.

[0112] (Formation of the lower catalyst layer and the upper catalyst layer) In Example 1 (Formation of the Lower Catalyst Layer), the palladium solution P1 was applied to a position 30 mm (23.1% of the length of the partition wall) from the inlet end face of C2 so that the palladium load after firing was 1.75 g / L. After drying at 150°C for 15 minutes, it was fired at 550°C for 30 minutes to form a lower catalyst layer (palladium concentration C) on the refractory three-dimensional structure. L1 The gas inlet region L1 and palladium concentration C are 0.03138 [g / g]. L2 (consisting of the gas outlet side region L2 where the concentration is 0.0006197 [g / g]) and the upper catalyst layer (palladium concentration C U1 The gas inlet region U1 and palladium concentration C are 0.03078 [g / g]. U2 A catalyst H was obtained that included a gas outlet side region U2 where the concentration is 0 [g / g].

[0113] [Example 8] (Formation of the lower catalytic layer precursor) A1 was obtained using the same method as in Example 1 described above.

[0114] (Formation of the upper catalyst layer precursor) The slurry a3 from Example 1 (Formation of the Upper Catalyst Layer) described above was applied to A1 from the gas inlet end face to the gas outlet end face so that the load after firing was 76.2 g / L. After drying at 150°C for 15 minutes, it was fired at 550°C for 30 minutes to obtain C2, in which a lower catalyst layer precursor and an upper catalyst layer precursor were provided on a refractory three-dimensional structure.

[0115] (Formation of the lower catalyst layer and the upper catalyst layer) In Example 1 (Formation of the Lower Catalyst Layer), the palladium solution P1 was applied to a position 30 mm (23.1% of the length of the partition wall) from the inlet end face of C2 so that the palladium load after firing was 2.63 g / L. After drying at 150°C for 15 minutes, it was fired at 550°C for 30 minutes to form a lower catalyst layer (palladium concentration C) on the refractory three-dimensional structure. L1 The gas inlet region L1 and palladium concentration C are 0.04606 [g / g]. L2 (consisting of the gas outlet side region L2 where the concentration is 0.0006197 [g / g]) and the upper catalyst layer (palladium concentration C U1The gas inlet region U1 and palladium concentration C are 0.04547 [g / g]. U2 A catalyst I was obtained that included a gas outlet side region U2 where the concentration is 0 [g / g].

[0116] [Comparative Example 2] (Formation of the lower catalytic layer) Palladium nitrate (Pd(NO3)2), γ-alumina (Al2O3, pore volume 0.9 cm³) 3 / g, BET specific surface area 150m 2 / g, average particle size (D50) 30μm), cerium-zirconium composite oxide (CeO2-ZrO2, CeO2 content 44% by mass, BET specific surface area 1.7m²) 2 Pd (pd / g), lanthanum acetate (La(CH3COO)3), and barium sulfate (BaSO4) were weighed out so that the mass ratio of Pd:Al2O3:CeO2-ZrO2:La2O3:BaSO4 after calcination was 3.6:95:50:3:15. Each weighed raw material was added to deionized water and wet-milled to prepare slurry j1. Slurry j1 was applied to a cordierite support (diameter 103 mm, length 130 mm, cylindrical, 1.083 L, 600 cells per square inch (1 inch = 25.4 mm), cell wall thickness 2.5 mil (1 mil = 0.0254 mm), hereafter the same) as a refractory three-dimensional structure, from the gas inlet end face to the gas outlet end face, so that the load after calcination was 166.6 g / L. After drying at 150°C for 15 minutes, it was calcined at 550°C for 30 minutes to obtain J1, a refractory three-dimensional structure with a lower catalyst layer precursor.

[0117] (Formation of the upper catalyst layer) Using the same method as in Example 1 described above, an upper catalyst layer was formed, and a catalyst J was obtained in which a lower catalyst layer and an upper catalyst layer were provided on a fire-resistant three-dimensional structure.

[0118] [Comparative Example 3] (Formation of the lower catalytic layer) A1 was obtained using the same method as in Example 1 (formation of the lower catalyst layer precursor).

[0119] (Formation of the upper catalyst layer) Palladium nitrate (Pd(NO3)2), rhodium nitrate (Rh(NO3)2), γ-alumina (Al2O3, pore volume 0.5 cm³) 3 / g, BET specific surface area 130m 2 / g, average particle size (D50) 50μm), cerium-zirconium composite oxide (CeO2-ZrO2, CeO2 content 25% by mass, BET specific surface area 75m²) 2 Pd ( / g) and lanthanum oxide (La2O3) were weighed so that the mass ratio of Pd:Rh:Al2O3:CeO2-ZrO2:La2O3 after calcination was 3.5:0.2:40:35:1. Each weighed raw material was added to deionized water and wet-milled to prepare slurry k1. Slurry k1 was applied to A1 up to a position 100 mm from the outlet end face so that the load after calcination was 79.7 g / L, dried at 150°C for 15 minutes, and then calcined at 550°C for 30 minutes to obtain catalyst K, which had a lower catalyst layer and an upper catalyst layer on a refractory three-dimensional structure.

[0120] <Durability Test> A V8, 5.6-liter engine was used, and the engine was operated for 50 seconds to achieve an A / F ratio of 14.6 at the catalytic converter inlet and a catalytic converter bed temperature of 1000°C. This was followed by operation for 5 seconds at an A / F ratio of 12.0, then stopping the fuel supply and operating for 5 seconds. This cycle was repeated for a total of 50 hours to perform the heat treatment.

[0121] <Catalyst performance test> A 2.0-liter inline four-cylinder engine was operated with an A / F ratio of 14.6, and the exhaust gas temperature was raised from 70°C to 400°C at a rate of 1300°C / min. The gas emitted from the catalytic converter outlet was sampled, and the THC (Total Hydrocarbons) purification rate was calculated. The temperature at which each purification rate reached 50% was defined as T50, and the catalytic performance was evaluated based on the time it took to reach T50. The results are shown in Table 1 below. Note that a shorter time to reach T50 indicates higher exhaust gas purification performance.

[0122] [Table 1]

[0123] As shown in Table 1, the present invention makes it possible to improve the exhaust gas purification performance of an exhaust gas purification catalyst at low temperatures. Since the total amount of each component in the lower and upper catalytic layers is the same for catalysts A to G, the difference in purification performance is solely due to the palladium concentration C in the gas inlet region L1 of the lower catalytic layer. L1 And the palladium concentration C in the gas outlet region L2 of the lower catalyst layer L2 The ratio (C L1 / C L2 This is thought to be due to setting the range within a predetermined range.

[0124] Comparing catalysts A to C, it can be seen that catalyst A, in which the gas inlet-side region L1 of the lower catalyst layer constitutes the outermost layer (the gas inlet-side region L1 of the lower catalyst layer is not covered by other catalyst layers), exhibits further improved exhaust gas purification performance at low temperatures.

[0125] A comparison of catalysts C through G reveals that when the boundary X is located approximately 11.5% from the gas inlet end face, the exhaust gas purification performance at low temperatures is further improved.

[0126] This application is based on Japanese Patent Application No. 2024-110282, filed on 9 July 2024, the disclosures of which are referenced and incorporated in whole. [Explanation of Symbols]

[0127] 1, 2, 3 Exhaust gas purification catalysts, 10 Fireproof three-dimensional structure, 10a Gas inlet side end face, 10b Gas outlet side end face, 20 Lower catalyst layer, 30 upper catalyst layer, L1, U1 gas inlet side region, L2, U2 gas outlet side region, X, Y boundaries.

Claims

1. A fire-resistant three-dimensional structure having partition walls that extend from the gas inlet end face along the gas outlet end face and divide a plurality of gas flow paths that penetrate from the gas inlet end face to the gas outlet end face, A lower catalyst layer formed in contact with the partition wall, comprising palladium, alumina, and a cerium-zirconium composite oxide, An upper catalyst layer formed on at least a portion of the lower catalyst layer and constituting the outermost layer, containing rhodium, alumina, and cerium-zirconium composite oxide, It has, The lower catalyst layer is located on the gas inlet side, and the palladium concentration is C Ｌ１ A gas inlet region L1 has a concentration of [g / g], and a gas outlet region located on the gas outlet side has a palladium concentration of C Ｌ２ It consists of a gas outlet side region L2 which is [g / g], The boundary X between the gas inlet region L1 and the gas outlet region L2 is located within a range of 8% to 80% of the length of the partition wall from the gas inlet end face. Palladium concentration C in the gas outlet region L2 Ｌ２ The palladium concentration C in the gas inlet region L1 Ｌ１ The ratio (C Ｌ１ / C Ｌ２ ) is between 30 and 230, The upper catalyst layer is composed of a gas inlet region U1 located on the gas inlet side and having a palladium concentration of C U1 [g / g], and a gas outlet region U2 located on the gas outlet side and substantially free of palladium. The boundary Y between the gas inlet region U1 and the gas outlet region U2 is located at substantially the same position as the boundary X with respect to the length of the partition wall. An exhaust gas purification catalyst wherein the ratio of the palladium concentration C U1 in the gas inlet-side region U1 of the upper catalyst layer to the palladium concentration C L1 in the gas inlet-side region L1 of the lower catalyst layer (C U1 / C L1) is 0.800 or more and less than 1.

000.

2. The exhaust gas purification catalyst according to claim 1, wherein the gas inlet-side region L1 of the lower catalyst layer constitutes the outermost layer.

3. The exhaust gas purification catalyst according to claim 1, wherein the palladium concentration is substantially uniform throughout the entire gas inlet region L1.

4. A slurry for a lower catalyst layer, containing a palladium source, alumina raw material, and cerium-zirconium composite oxide raw material, is applied to the partition wall of the fire-resistant three-dimensional structure, dried, and fired to form a lower catalyst layer. The upper catalyst layer is formed by applying, drying, and firing an upper catalyst layer slurry containing a rhodium source, alumina raw material, and cerium-zirconium composite oxide raw material onto the lower catalyst layer. A palladium solution containing a palladium complex salt and a thickener is applied, dried, and fired from the gas inlet end face to a position within a range of 8% to 80% of the length of the partition wall from the gas inlet end face. A method for producing an exhaust gas purification catalyst according to any one of claims 1 to 3, comprising:

5. The pore volume of the alumina raw material contained in the slurry for the lower catalyst layer, as measured by nitrogen adsorption, is 0.7 cm³. ３ / g or more 1.5cm ３ / g or less, The BET specific surface area of the cerium-zirconium composite oxide raw material contained in the slurry for the lower catalyst layer is 1.0 m ２ / g or more and 10 m ２ / g or less, and the method for producing a catalyst for purifying exhaust gas according to claim 4.

6. A catalyst for purifying exhaust gas according to any one of claims 1 to 3, Exhaust gases emitted from internal combustion engines, A method for purifying exhaust gas, comprising bringing into contact with a substance.

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