Catalyst for exhaust gas purification

Abstract

The present invention relates to a catalyst for purifying exhaust gas that uses Rh and La in combination, and aims to provide a catalyst for purifying exhaust gas that can effectively exert the action of La while preventing a decrease in the exhaust gas purification performance (particularly, NOx purification performance) of Rh due to La. To achieve this object, the exhaust gas purification catalyst (1) includes a substrate (10), a first catalyst layer (20) provided on the upstream side of the substrate (10), and a second catalyst layer (30) provided on the downstream side of the substrate (10). The first catalyst layer (20) includes a lower layer (21) containing Pd and an upper layer (22) containing Rh. The second catalyst layer (30) includes a lower layer (31) containing Pt and an upper layer (32) containing Rh. The content of La in La 2 O 3 in terms of conversion in the first catalyst layer (20) is 5% by mass or more based on the mass of the first catalyst layer (20), and the content of La in La 2 O 3 in terms of conversion in the second catalyst layer (30) is 3% by mass or less based on the mass of the second catalyst layer (30). Provided is the exhaust gas purification catalyst (1).

Description

Technical Field

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

Background Art

[0002] Exhaust gas discharged from internal combustion engines such as automobiles and motorcycles contains harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). For the purpose of purifying and detoxifying these harmful components, a catalyst for purifying exhaust gas containing noble metal elements such as Pt, Pd, and Rh is used. Pt and Pd are mainly involved in the oxidative purification of HC and CO, and Rh is mainly involved in the reduction purification of NOx.

[0003] La is used as a component of the catalyst layer of the exhaust gas purification catalyst (for example, Patent Documents 1 and 2).

[0004] Due to the increasing demand for exhaust gas purification performance in recent years, improvement of the exhaust gas purification performance of exhaust gas purification catalysts has been demanded.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] La has an effect of improving heat resistance. Therefore, by increasing the content rate of La, the heat resistance can be improved.

[0007] Since the exhaust gas purification performance of Rh (especially NOx purification performance) deteriorates due to the oxidation of Rh, Rh is preferably used in a reducing atmosphere. However, La has the effect of promoting the oxidation of noble metal elements. Therefore, in an exhaust gas purification catalyst using Rh and La in combination, if the content of La is increased, there is a concern that Rh is oxidized by La and the exhaust gas purification performance of Rh (especially NOx purification performance) deteriorates.

[0008] The present invention provides an exhaust gas purification catalyst using Rh and La in combination, which can prevent the deterioration of the exhaust gas purification performance of Rh (especially NOx purification performance) by La while effectively exerting the action of La.

[0009] The present invention also provides an exhaust gas purification system using Rh and La in combination, which can prevent the deterioration of the exhaust gas purification performance of Rh (especially NOx purification performance) by La while effectively exerting the action of La.

Means for Solving the Problems

[0010] The present invention provides the following inventions. [1] A substrate, A first catalyst layer provided on the upstream side of the substrate, A second catalyst layer provided on the downstream side of the substrate, An exhaust gas purification catalyst comprising: The first catalyst layer includes a lower layer containing Pd and an upper layer containing Rh, The second catalyst layer includes a lower layer containing Pt and an upper layer containing Rh, The content of La in La 2 O 3 conversion in the first catalyst layer is 5% by mass or more based on the mass of the first catalyst layer, The content of La in La 2 O 3 conversion in the second catalyst layer is 3% by mass or less based on the mass of the second catalyst layer. An exhaust gas purification catalyst. [2] The content rate of noble metal elements other than Pt in the lower layer of the second catalyst layer, in terms of metal, is 1% by mass or less based on the mass of the lower layer of the second catalyst layer. The La of La in the lower layer of the second catalyst layer 2 O 3 The content rate in terms of conversion is 2% by mass or less based on the mass of the lower layer of the second catalyst layer. The exhaust gas purification catalyst according to [1]. [3] The La of La in the upper layer of the first catalyst layer 2 O 3 The content rate in terms of conversion is 5% by mass or more based on the mass of the upper layer of the first catalyst layer. The La of La in the upper layer of the second catalyst layer 2 O 3 The content rate in terms of conversion is 4% by mass or less based on the mass of the upper layer of the second catalyst layer. The exhaust gas purification catalyst according to [1] or [2]. [4] An exhaust passage through which exhaust gas flows, A first exhaust gas purification catalyst provided on the upstream side in the exhaust passage, A second exhaust gas purification catalyst provided on the downstream side in the exhaust passage, An exhaust gas purification system comprising: The first exhaust gas purification catalyst includes a first substrate and a first catalyst layer provided on the first substrate. The second exhaust gas purification catalyst includes a second substrate and a second catalyst layer provided on the second substrate. The first catalyst layer includes a lower layer containing Pd and an upper layer containing Rh. The second catalyst layer includes a lower layer containing Pt and an upper layer containing Rh. The La of La in the first catalyst layer 2 O 3 The content rate in terms of conversion is 5% by mass or more based on the mass of the first catalyst layer. The La of La in the second catalyst layer 2 O 3 The content rate in terms of conversion is 3% by mass or less based on the mass of the second catalyst layer. The exhaust gas purification system. [5] The content rate in terms of metal of noble metal elements other than Pt in the lower layer of the second catalyst layer is 1% by mass or less based on the mass of the lower layer of the second catalyst layer. La in the lower layer in the second catalyst layer 2 O 3 The content rate in terms of LaO conversion in the lower layer in the second catalyst layer is 2% by mass or less based on the mass of the lower layer in the second catalyst layer. The exhaust gas purification system according to [4]. [6] The content rate in terms of LaO conversion of La in the upper layer of the first catalyst layer is 5% by mass or more based on the mass of the upper layer of the first catalyst layer. 2 O 3 The exhaust gas purification system according to [4] or [5], wherein the content rate in terms of LaO conversion of La in the upper layer of the second catalyst layer is 4% by mass or less based on the mass of the upper layer of the second catalyst layer. La in the upper layer in the second catalyst layer 2 O 3 The exhaust gas purification system according to [4] or [5], wherein the content rate in terms of LaO conversion of La in the upper layer of the second catalyst layer is 4% by mass or less based on the mass of the upper layer of the second catalyst layer.

Advantages of the Invention

[0011] According to the exhaust gas purification catalyst and the exhaust gas purification system of the present invention, while effectively exerting the action of La, it is possible to prevent a decrease in the exhaust gas purification performance (particularly, NOx purification performance) of Rh by La. Therefore, according to the exhaust gas purification catalyst and the exhaust gas purification system of the present invention, it is possible to effectively improve the exhaust gas purification performance.

Brief Description of the Drawings

[0012]

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Mode for Carrying Out the Invention

[0013] ≪Explanation of Terms≫ Hereinafter, the terms used in this specification will be explained. The following explanations apply to the entire specification unless otherwise specified. Note that the following explanations regarding the catalyst layer apply to all catalyst layers (for example, the first catalyst layer 20, the second catalyst layer 30, the lower layer 21, the upper layer 22, the lower layer 31, the upper layer 32, etc. described later).

[0014] <Metal element> The "metal element" includes semi-metal elements such as Si and B.

[0015] <Rare earth element> The "rare earth element" includes Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0016] <Noble metal element> The "noble metal element" includes Pt, Pd, Rh, Ru, Os, Ir, Au, and Ag.

[0017] <Oxide> The meaning of the "oxide" of the metal element is as follows. Oxides of rare earth elements excluding Ce, Pr, and Tb are sesquioxides (M 2 O 3 , where M represents a rare earth element other than Ce, Pr, and Tb), the oxide of Ce is CeO 2 , the oxide of Pr is Pr 6 O 11 , the oxide of Tb is Tb 4 O 7 , the oxide of Al is Al 2 O 3For the oxide of Zr, it is ZrO 2 For the oxide of Si, it is SiO 2 For the oxide of B, it is B 2 O 3 For the oxide of Cr, it is Cr 2 O 3 For the oxide of Mg, it is MgO; for the oxide of Ca, it is CaO; for the oxide of Sr, it is SrO; for the oxide of Ba, it is BaO; for the oxide of Fe, it is Fe 3 O 4 For the oxide of Mn, it is Mn 3 O 4 For the oxide of Ni, it is NiO; for the oxide of Ti, it is TiO 2 For the oxide of Zn, it is ZnO; for the oxide of Sn, it is SnO 2 This means.

[0018] <Mass of the catalyst layer> "Mass of the catalyst layer" means classifying all the metal elements contained in the catalyst layer into noble metal elements and metal elements other than noble metal elements, obtaining the mass in terms of metal for noble metal elements and the mass in terms of oxide for metal elements other than noble metal elements, and summing them up. That is, "mass of the catalyst layer" means the calculated mass obtained by summing the mass in terms of metal of the noble metal elements contained in the catalyst layer and the mass in terms of oxide of the metal elements other than noble metal elements contained in the catalyst layer.

[0019] <Content rate in terms of metal of noble metal elements in the catalyst layer and content rate in terms of oxide of metal elements other than noble metal elements in the catalyst layer> "Content rate in terms of metal of noble metal elements in the catalyst layer" (mass%) is obtained from the formula: (mass in terms of metal of the noble metal element in the catalyst layer) / (mass of the catalyst layer) × 100. "Mass in terms of metal of the noble metal element" means the mass of the metal obtained by assuming that the noble metal element exists as the metal composed of the noble metal element. For example, the mass in terms of metal of Pd, the mass in terms of metal of Pt, and the mass in terms of metal of Rh respectively mean the mass of metal Pd, the mass of metal Pt, and the mass of metal Rh. The meaning of "mass of the catalyst layer" is as described above.

[0020] The "content rate in terms of oxide of the metal element in the catalyst layer" (mass %) is obtained from the formula: (mass of the oxide of the metal element in terms of the metal element in the catalyst layer) / (mass of the catalyst layer) × 100. The "mass of the oxide of the metal element other than the noble metal element" means the mass of the oxide obtained by assuming that the metal element other than the noble metal element exists as the oxide of the metal element. The meanings of "oxide" of the metal element and "mass of the catalyst layer" are as described above.

[0021] For example, the "content rate in terms of La₂O₃ of La in the catalyst layer" (mass %) is obtained from the formula: (mass of La in terms of La₂O₃ in the catalyst layer) / (mass of the catalyst layer) × 100. 2 O 3 The "mass of La in terms of La₂O₃" means the mass of La₂O₃ obtained by assuming that La exists as La₂O₃. 2 O 3 For example, the "content rate in terms of La₂O₃ of La in the catalyst layer" (mass %) is obtained from the formula: (mass of La in terms of La₂O₃ in the catalyst layer) / (mass of the catalyst layer) × 100. 2 O 3 The "mass of La in terms of La₂O₃" means the mass of La₂O₃ obtained by assuming that La exists as La₂O₃. 2 O 3 For example, the "content rate in terms of La₂O₃ of La in the catalyst layer" (mass %) is obtained from the formula: (mass of La in terms of La₂O₃ in the catalyst layer) / (mass of the catalyst layer) × 100. 2 O 3 The "mass of La in terms of La₂O₃" means the mass of La₂O₃ obtained by assuming that La exists as La₂O₃.

[0022] When information on the raw materials used for forming the catalyst layer (for example, composition, amount, etc.) is known, the content rate in terms of metal of the noble metal element in the catalyst layer (mass %) and the content rate in terms of oxide of the metal element other than the noble metal element in the catalyst layer (mass %) can be obtained from the information on the raw materials.

[0023] When information on the raw materials used for forming the catalyst layer is not known, the content rate in terms of metal of the noble metal element in the catalyst layer (mass %) and the content rate in terms of oxide of the metal element other than the noble metal element in the catalyst layer (mass %) can be obtained by conventional methods such as scanning electron microscope - energy dispersive X - ray analysis method (SEM - EDX). Specifically, it is as follows.

[0024] Perform elemental analysis of the catalyst layer using conventional methods such as SEM-EDX to identify the types of constituent elements of the catalyst layer and determine the molar percentages of the identified metal elements. For each of the 10 fields of view of the SEM, determine the molar percentage of each metal element, and use the average value of the molar percentages of each metal element in the 10 fields of view as the molar percentage of each metal element in the catalyst layer.

[0025] For each noble metal element in the catalyst layer, calculate the V value from the following formula. V value = (molar percentage of each noble metal element in the catalyst layer) × (molar mass of each noble metal element)

[0026] For each metal element other than the noble metal elements in the catalyst layer, calculate the W value from the following formula. W value = (molar percentage of each metal element other than the noble metal elements in the catalyst layer) × (molar mass of the oxide of each metal element)

[0027] The content rate (mass %) in terms of metal of each noble metal element in the catalyst layer is calculated from the following formula. Content rate (mass %) in terms of metal of each noble metal element in the catalyst layer = (V value for each noble metal element) / {(sum of V values for all noble metal elements) + (sum of W values for all metal elements other than noble metal elements)} × 100

[0028] The content rate (mass %) in terms of oxide of each metal element other than the noble metal elements in the catalyst layer is calculated from the following formula. Content rate (mass %) in terms of oxide of each metal element other than the noble metal elements in the catalyst layer = (W value for each metal element other than the noble metal elements) / {(sum of V values for all noble metal elements) + (sum of W values for all metal elements other than noble metal elements)} × 100

[0029] <Al-based oxide> An Al-based oxide is an oxide containing Al, and among the metal elements constituting the oxide, the oxide in which the metal element with the largest content rate on a mass basis is Al. However, those corresponding to Ce-Zr composite oxides shall not be regarded as Al-based oxides. Ce-Zr composite oxides will be described later. Al-based oxides are distinguished from alumina used as a binder. In this specification, alumina used as a binder may sometimes be referred to as "alumina binder".

[0030] Al-based oxides are, for example, particulate. Al-based oxides are used as a carrier for a catalytic active component. From the viewpoint of improving the supportability of the catalytic active component, it is preferable that the Al-based oxide is porous.

[0031] Al-based oxides generally have higher heat resistance than other inorganic oxides (for example, Ce-based oxides, Ce-Zr composite oxides, etc.). Therefore, when the catalyst layer contains an Al-based oxide, the heat resistance of the catalyst layer is improved, and the exhaust gas purification performance of the catalyst layer is improved.

[0032] Al-based oxides may contain one or more metal elements other than Al (hereinafter referred to as "additional element M1"). The additional element M1 can be selected, for example, from rare earth elements (for example, Ce, Y, Pr, La, Nd, Sm, Eu, Gd, etc.), alkaline earth metal elements (for example, Mg, Ca, Sr, Ba, etc.), B, Si, Zr, Cr, etc.

[0033] In the Al-based oxide, the additional element M1 may form a solid solution phase (for example, a solid solution phase of Al 2 O 3 and the oxide of the additional element M1), or may form a single phase in a crystalline phase or an amorphous phase (for example, the oxide phase of the additional element M1), or may form both a solid solution phase and a single phase, but at least a part of the additional element M1 preferably forms a solid solution phase.

[0034] Examples of methods for preparing an Al-based oxide containing a solid solution phase include a coprecipitation method, a solid-phase method, and the like.

[0035] Examples of the Al-based oxide include alumina (an oxide composed of Al and O), an oxide obtained by modifying the surface of alumina with an additional element M1 or its oxide, an oxide obtained by dissolving an additional element M1 or its oxide in alumina, and the like. Examples of the Al-based oxide containing an additional element M1 include alumina-silica, alumina-zirconia, alumina-chromia, alumina-ceria, alumina-lanthana, and the like.

[0036] From the viewpoint of improving the heat resistance of the Al-based oxide, the content of Al in terms of Al 2 O 3 in the Al-based oxide is preferably 80% by mass or more, more preferably 85% by mass or more, still more preferably 90% by mass or more, based on the mass of the Al-based oxide. The upper limit is 100% by mass.

[0037] From the viewpoint of improving the heat resistance of the Al-based oxide, the Al-based oxide preferably contains La.

[0038] In the Al-based oxide containing La, at least a part of La preferably forms a solid solution phase (for example, a solid solution phase of Al 2 O 3 and La 2 O 3 ). Although the detailed mechanism is not clear, it is considered that when at least a part of La forms a solid solution phase, the crystal strain increases, and the heat resistance of the Al-based oxide is improved.

[0039] From the viewpoint of improving the heat resistance of the Al-based oxide, the content of La in terms of La 2 O 3 in the solid solution phase formed in the Al-based oxide is preferably 0.1% by mass or more and 20% by mass or less, more preferably 0.5% by mass or more and 15% by mass or less, still more preferably 1% by mass or more and 10% by mass or less, based on the mass of the Al-based oxide.

[0040] The content rate in terms of oxide of each metal element in the Al-based oxide is calculated from the formula: (mass of the oxide of each metal element in terms of oxide in the Al-based oxide) / (mass of the Al-based oxide) × 100. The mass of the Al-based oxide means the total mass of the metal element oxides obtained by assuming that the metal elements in the Al-based oxide exist as oxides respectively. The meaning of "oxide" of the metal element is as described above.

[0041] When the composition of the Al-based oxide is known, the content rate in terms of oxide of each element in the Al-based oxide can be determined from the composition of the Al-based oxide.

[0042] When the composition of the Al-based oxide is unknown, the content rate in terms of oxide of each metal element in the Al-based oxide can be determined from the elemental mapping obtained by analyzing a sample containing the Al-based oxide by energy dispersive X-ray spectroscopy (EDX) and the EDX elemental analysis of the specified particles. Specifically, the Al-based oxide particles and other particles can be qualitatively identified (color-coded) by elemental mapping, and the content rate in terms of oxide of each metal element in the specified particles can be determined by performing a composition analysis (elemental analysis) on the specified particles.

[0043] Whether at least a part of La forms a solid solution phase in the Al-based oxide containing La can be determined as follows. First, perform EDX elemental analysis on the target Al-based oxide to confirm the presence of La in the target Al-based oxide. Next, measure the XRD diffraction pattern of the target Al-based oxide using an XRD (X-ray diffractometer). Next, compare the obtained XRD diffraction pattern with the reference data of the crystal structure of the target Al-based oxide (for example, γ-alumina, θ-alumina, δ-alumina, α-alumina, etc.) recorded in the ICSD (International Crystal Structure Database). At this time, paying attention to the maximum peak position of the reference data, if there is a peak shift to the low angle side with respect to the maximum peak position in the XRD diffraction pattern of the target Al-based oxide, it can be determined that at least a part of La in the target Al-based oxide forms a solid solution phase. When all of La in the target Al-based oxide forms a solid solution phase, La 2 O 3 -derived peaks do not appear in the XRD diffraction pattern. Therefore, when determining whether all of La in the target Al-based oxide forms a solid solution phase, it is preferable to confirm whether La 2 O 3 -derived peaks appear in the XRD diffraction pattern.

[0044] Based on the abundance of La by EDX elemental analysis and the degree of the peak shift, the content rate in terms of La 2 O 3 in the target Al-based oxide that forms a solid solution phase can be calculated. Also, perform XPS (X-ray photoelectron spectroscopy) measurement on the target Al-based oxide and analyze the peaks attributed to LaAlO 3 to obtain a semi-quantitative value. In this way, the content rate in terms of La 2 O 3 in the target Al-based oxide that forms a solid solution phase can be obtained by comprehensively considering the analysis results of XRD, EDX, XPS, etc.

[0045] <Ce-based oxide> A Ce-based oxide is an oxide containing Ce, and among the metal elements constituting the oxide, the metal element with the highest content rate on a mass basis is Ce. However, those corresponding to Ce-Zr composite oxides shall not be regarded as Ce-based oxides. Ce-Zr composite oxides will be described later. Ce-based oxides are distinguished from ceria used as a binder. In this specification, ceria used as a binder may be referred to as "ceria binder".

[0046] Ce-based oxides are, for example, particulate. Ce-based oxides are used as a carrier for a catalytic active component. From the viewpoint of improving the supportability of the catalytic active component, it is preferable that the Ce-based oxide is porous.

[0047] Ce-based oxides have oxygen storage capacity and mitigate fluctuations in the oxygen concentration in exhaust gas to expand the operating window of the catalytic active component. Therefore, when the catalyst layer contains a Ce-based oxide, the exhaust gas purification performance of the catalyst layer is improved.

[0048] Ce-based oxides may contain one or more metal elements other than Ce (hereinafter referred to as "additional element M2"). The additional element M2 can be selected, for example, from rare earth elements other than Ce, alkaline earth metal elements (for example, Mg, Ca, Sr, Ba, etc.), Fe, Mn, Ni, Zr, Al, etc.

[0049] In the Ce-based oxide, the additional element M2 may form a solid solution phase (for example, a solid solution phase of CeO 2 and an oxide of the additional element M2), or may form a single phase that is a crystalline phase or an amorphous phase (for example, an oxide phase of the additional element M2), or may form both a solid solution phase and a single phase. However, it is preferable that at least a part of the additional element M2 forms a solid solution phase.

[0050] Examples of methods for preparing a Ce-based oxide containing a solid solution phase include a coprecipitation method, a solid phase method, and the like.

[0051] Examples of the Ce-based oxide include ceria (an oxide composed of Ce and O), an oxide obtained by modifying the surface of ceria with an additional element M2 or its oxide, an oxide obtained by solid-solubilizing an additional element M2 or its oxide in ceria, and the like.

[0052] <Ce-Zr composite oxide> The Ce-Zr composite oxide is a composite oxide containing Ce and Zr, and the content of Ce in the composite oxide in terms of CeO 2 is 5% by mass or more and 95% by mass or less based on the mass of the composite oxide, and the content of Zr in the composite oxide in terms of ZrO 2 is 5% by mass or more and 95% by mass or less based on the mass of the composite oxide.

[0053] The Ce-Zr composite oxide is, for example, particulate. The Ce-Zr composite oxide is used as a carrier for a catalytic active component. From the viewpoint of improving the supportability of the catalytic active component, the Ce-Zr composite oxide is preferably porous.

[0054] The Ce-Zr composite oxide has an oxygen storage capacity, alleviates fluctuations in the oxygen concentration in the exhaust gas, and expands the operating window of the catalytic active component. Therefore, when the catalyst layer contains the Ce-Zr composite oxide, the exhaust gas purification ability of the catalyst layer is improved.

[0055] The Ce-Zr composite oxide may contain one or more metal elements (hereinafter referred to as "additional element M3") other than Ce and Zr. The additional element M3 can be selected, for example, from rare earth elements other than Ce, alkaline earth metal elements (e.g., Mg, Ca, Sr, Ba, etc.), Fe, Mn, Ni, Al, and the like.

[0056] In the Ce-Zr composite oxide, Ce may form a solid solution phase (e.g., a solid solution phase of CeO 2 and ZrO 2 and the like), or a single phase in a crystalline phase or an amorphous phase (e.g., CeO 2It may form a single-phase or may form both a solid solution phase and a single-phase, but at least a part of Ce preferably forms a solid solution phase.

[0057] In the Ce-Zr composite oxide, Zr may form a solid solution phase (e.g., a solid solution phase of CeO 2 and ZrO 2 etc.), or may form a single-phase that is a crystalline phase or an amorphous phase (e.g., ZrO 2 single-phase), or may form both a solid solution phase and a single-phase, but at least a part of Zr preferably forms a solid solution phase.

[0058] When the Ce-Zr composite oxide contains an additional element M3, the additional element M3 may form a solid solution phase (e.g., a solid solution phase of CeO 2 and the oxide of the additional element M3, ZrO 2 and the oxide of the additional element M3, CeO 2 and ZrO 2 and the oxide of the additional element M3, etc.), or may form a single-phase that is a crystalline phase or an amorphous phase (e.g., a single-phase of the oxide of the additional element M3), or may form both a solid solution phase and a single-phase, but at least a part of the additional element M3 preferably forms a solid solution phase.

[0059] Examples of the method for preparing a Ce-Zr composite oxide containing a solid solution phase include a coprecipitation method, a solid-phase method, etc.

[0060] Examples of the Ce-Zr composite oxide include CeO 2 -ZrO 2 solid solution, an oxide obtained by modifying the surface of the CeO 2 -ZrO 2 solid solution with an additional element M3 or its oxide, an oxide obtained by dissolving an additional element M3 or its oxide in the CeO 2 -ZrO 2 solid solution, etc.

[0061] From the viewpoint of improving the oxygen storage capacity of the Ce-Zr composite oxide, the content of Ce in the Ce-Zr composite oxide in terms of CeO 2 is preferably 5% by mass or more and 80% by mass or less, more preferably 10% by mass or more and 60% by mass or less, still more preferably 10% by mass or more and 50% by mass or less, based on the mass of the Ce-Zr composite oxide.

[0062] From the viewpoint of improving the heat resistance of the Ce-Zr composite oxide, the content of Zr in the Ce-Zr composite oxide in terms of ZrO 2 is preferably 10% by mass or more and 95% by mass or less, more preferably 30% by mass or more and 90% by mass or less, still more preferably 40% by mass or more and 90% by mass or less, based on the mass of the Ce-Zr composite oxide.

[0063] From the viewpoint of improving the oxygen storage capacity and heat resistance of the Ce-Zr composite oxide, the total content of Ce in the Ce-Zr composite oxide in terms of CeO 2 and the content of Zr in terms of ZrO 2 is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, based on the mass of the Ce-Zr composite oxide. The upper limit is 100% by mass.

[0064] From the viewpoint of improving the heat resistance and oxygen storage capacity of the Ce-Zr composite oxide, the Ce-Zr composite oxide preferably contains La.

[0065] In the Ce-Zr composite oxide containing La, at least a part of La is in a solid solution phase (for example, a solid solution phase with CeO 2 and La 2 O 3 , a solid solution phase with ZrO 2 and La 2 O 3 , a solid solution phase with CeO 2 and ZrO 2 and La 2 O 3It is preferable that a solid solution phase (such as a solid solution with [metal]) is formed. Although the detailed mechanism is not clear, it is considered that at least a part of La forms a solid solution phase, which increases the crystal strain and improves the heat resistance and oxygen storage capacity of the Ce-Zr composite oxide.

[0066] From the viewpoint of improving the heat resistance and oxygen storage capacity of the Ce-Zr composite oxide, the La of the La that forms a solid solution phase in the Ce-Zr composite oxide 2 O 3 The content in terms of conversion is preferably 0.1% by mass or more and 20% by mass or less, more preferably 0.5% by mass or more and 15% by mass or less, and even more preferably 1% by mass or more and 10% by mass or less, based on the mass of the Ce-Zr composite oxide.

[0067] The content in terms of conversion of each metal element in the Ce-Zr composite oxide is calculated from the formula: (mass of the oxide of each metal element in the Ce-Zr composite oxide) / (mass of the Ce-Zr composite oxide) × 100. The mass of the Ce-Zr composite oxide means the total mass of the metal element oxides obtained by assuming that the metal elements in the Ce-Zr composite oxide exist as oxides respectively. The meaning of "oxide" of the metal element is as described above.

[0068] The content in terms of conversion of each metal element in the Ce-Zr composite oxide can be determined in the same manner as the content in terms of conversion of each metal element in the Al-based oxide.

[0069] Whether at least a part of La forms a solid solution phase in the Ce-Zr composite oxide containing La can be determined in the same manner as whether at least a part of La forms a solid solution phase in the Al-based oxide containing La. When comparing the XRD diffraction pattern of the target Ce-Zr composite oxide with the reference data of the crystal structure of the target Ce-Zr composite oxide, as the reference data of the crystal structure of the target Ce-Zr composite oxide, the fluorite-type CeO 2 -ZrO 2 , pyrochlore-type CeO 2 -ZrO2 It is possible to use data such as. In the Ce-Zr-based composite oxide, La of La that forms a solid solution phase 2 O 3 The conversion content is the same as the La of La that forms a solid solution phase in the Al-based oxide 2 O 3 It can be determined in the same manner as the conversion content.

[0070] ≪Exhaust gas purification catalyst≫ Hereinafter, based on FIGS. 1 to 6, an exhaust gas purification catalyst 1 (hereinafter referred to as "catalyst 1") according to an embodiment of the present invention will be described.

[0071] As shown in FIG. 1, the catalyst 1 is disposed in an exhaust passage in the exhaust pipe P of an internal combustion engine. The internal combustion engine is, for example, a gasoline engine or the like. The exhaust gas discharged from the internal combustion engine flows through the exhaust passage in the exhaust pipe P from one end to the other end of the exhaust pipe P and is purified by the catalyst 1 provided in the exhaust pipe P. In the drawing, the exhaust gas flow direction is indicated by the symbol X. In this specification, the upstream side in the exhaust gas flow direction X may be referred to as the "exhaust gas inflow side" or "upstream side", and the downstream side in the exhaust gas flow direction X may be referred to as the "exhaust gas outflow side" or "downstream side".

[0072] In the exhaust passage in the exhaust pipe P, other exhaust gas purification catalysts may be disposed upstream or downstream of the catalyst 1.

[0073] As shown in FIGS. 2 to 6, the catalyst 1 includes a substrate 10, a first catalyst layer 20 provided upstream of the substrate 10, and a second catalyst layer 30 provided downstream of the substrate 10.

[0074] As shown in FIGS. 4 and 6, the first catalyst layer 20 includes a lower layer 21 provided on the substrate 10 and an upper layer 22 provided on the lower layer 21. The lower layer 21 contains Pd, and the upper layer 22 contains Rh. The entire first catalyst layer 20 may be composed of the lower layer 21 and the upper layer 22, but it is not essential that the entire first catalyst layer 20 be composed of the lower layer 21 and the upper layer 22. A part of the first catalyst layer 20 may be composed of either the lower layer 21 or the upper layer 22. Therefore, in addition to the part composed of the lower layer 21 and the upper layer 22, the part composed of either the lower layer 21 or the upper layer 22 is also a part of the first catalyst layer 20.

[0075] As shown in FIGS. 5 and 6, the second catalyst layer 30 includes a lower layer 31 provided on the substrate 10 and an upper layer 32 provided on the lower layer 31. The lower layer 31 contains Pt, and the upper layer 32 contains Rh. The entire second catalyst layer 30 may be composed of the lower layer 31 and the upper layer 32, but it is not essential that the entire second catalyst layer 30 be composed of the lower layer 31 and the upper layer 32. A part of the second catalyst layer 30 may be composed of either the lower layer 31 or the upper layer 32. Therefore, in addition to the part composed of the lower layer 31 and the upper layer 32, the part composed of either the lower layer 31 or the upper layer 32 is also a part of the second catalyst layer 30.

[0076] In this specification, the lower layer means a layer located closer to the partition portion 12 than the upper layer.

[0077] The catalyst 1 is characterized in that the content of La in La 2 O 3 conversion in the first catalyst layer 20 is 5% by mass or more based on the mass of the first catalyst layer 20, and the content of La in La 2 O 3 conversion in the second catalyst layer 30 is 3% by mass or less based on the mass of the second catalyst layer 30.

[0078] In the catalyst 1, since the first catalyst layer 20 is provided on the upstream side of the substrate 10 and the second catalyst layer 30 is provided on the downstream side of the substrate 10, the exhaust gas contacts the second catalyst layer 30 after contacting the first catalyst layer 20. Therefore, the temperature of the exhaust gas contacting the first catalyst layer 20 is higher than that of the exhaust gas contacting the second catalyst layer 30. Accordingly, the first catalyst layer 20 is required to have higher heat resistance than the second catalyst layer 30.

[0079] La has an effect of improving heat resistance. Therefore, by increasing the content of La in terms of La 2 O 3 in the first catalyst layer 20, the heat resistance of the first catalyst layer 20 can be improved.

[0080] Since the exhaust gas purification performance of Rh (especially, NOx purification performance) deteriorates due to the oxidation of Rh, Rh is preferably used in a reducing atmosphere. On the other hand, La has an effect of promoting the oxidation of noble metal elements. Therefore, if the content of La in terms of La 2 O 3 in the first catalyst layer 20 is increased, there is a concern that Rh in the first catalyst layer 20 is oxidized by La in the first catalyst layer 20, and the exhaust gas purification performance (especially, NOx purification performance) of Rh in the first catalyst layer 20 deteriorates. However, since the first catalyst layer 20 is provided on the upstream side of the substrate 10, the amount of reducing components (for example, hydrocarbons (HC), carbon monoxide (CO), etc.) in the exhaust gas contacting the first catalyst layer 20 varies due to fluctuations in the operating conditions of the internal combustion engine and temporarily increases. Therefore, even if Rh in the first catalyst layer 20 is oxidized by La in the first catalyst layer 20, the oxidized Rh is reduced by the temporarily increased reducing components. Accordingly, even if the content of La in terms of La 2 O 3 in the first catalyst layer 20 is increased, it is possible to prevent the deterioration of the exhaust gas purification performance (especially, NOx purification performance) of Rh in the first catalyst layer 20 due to La in the first catalyst layer 20.

[0081] Since the exhaust gas contacts the second catalyst layer 30 after contacting the first catalyst layer 20, the amount of reducing components in the exhaust gas contacting the second catalyst layer 30 is less likely to vary and is less likely to increase temporarily. Therefore, when Rh in the second catalyst layer 30 is oxidized by La in the second catalyst layer 30, the oxidized Rh is less likely to be reduced. On the other hand, since the exhaust gas contacts the second catalyst layer 30 after contacting the first catalyst layer 20, the temperature of the exhaust gas contacting the second catalyst layer 30 is lower than the temperature of the exhaust gas contacting the first catalyst layer 20. Therefore, the heat resistance of the second catalyst layer 30 may be lower than that of the first catalyst layer 20.

[0082] As described above, in the first catalyst layer 20, from the viewpoint of preventing the reduction of the exhaust gas purification performance (particularly, NOx purification performance) of Rh in the first catalyst layer 20 by La in the first catalyst layer 20, rather than reducing the content of La in terms of La 2 O 3 in the first catalyst layer 20, from the viewpoint of improving the heat resistance of the first catalyst layer 20, it is required to increase the content of La in terms of La 2 O 3 in the first catalyst layer 20. In the second catalyst layer 30, from the viewpoint of improving the heat resistance of the second catalyst layer 30, rather than increasing the content of La in terms of La 2 O 3 in the second catalyst layer 30, from the viewpoint of preventing the reduction of the exhaust gas purification performance (particularly, NOx purification performance) of Rh in the second catalyst layer 30 by La in the second catalyst layer 30, it is required to decrease the content of La in terms of La 2 O 3 in the second catalyst layer 30. Therefore, the catalyst 1 is characterized in that the content of La in terms of La 2 O 3 is 5% by mass or more based on the mass of the first catalyst layer 20, and the content of La in terms of La 2 O 3 is 3% by mass or less based on the mass of the second catalyst layer 30. According to the catalyst 1, while effectively exerting the action of La, it is possible to prevent the reduction of the exhaust gas purification performance (particularly, NOx purification performance) of Rh by La, thereby realizing an improvement in the exhaust gas purification performance.

[0083] In addition to the effect of improving heat resistance, La has the effect of trapping phosphorus components to prevent phosphorus poisoning of noble metal elements. Further, when the Ce-Zr composite oxide contains La, La in the Ce-Zr composite oxide has the effect of improving the oxygen storage capacity of the Ce-Zr composite oxide. These effects of La also contribute to the improvement of the exhaust gas purification performance of Catalyst 1.

[0084] <Substrate> Hereinafter, the substrate 10 will be described.

[0085] The material constituting the substrate 10 can be appropriately selected from known materials. Examples of the material constituting the substrate 10 include ceramic materials and metal materials, and ceramic materials are preferred. Examples of ceramic materials include carbide ceramics such as silicon carbide, titanium carbide, tantalum carbide, and tungsten carbide; nitride ceramics such as aluminum nitride, silicon nitride, boron nitride, and titanium nitride; oxide ceramics such as alumina, zirconia, cordierite, mullite, zircon, aluminum titanate, and magnesium titanate. Examples of metal materials include alloys such as stainless steel.

[0086] As shown in FIG. 1, the catalyst 1 is disposed in the exhaust path of the internal combustion engine such that the axial direction of the substrate 10 coincides with or substantially coincides with the exhaust gas flow direction X.

[0087] As shown in FIGS. 2 to 6, the substrate 10 has a cylindrical portion 11, a partition portion 12 provided in the cylindrical portion 11, and cells 13 partitioned by the partition portion 12. The substrate 10 is preferably a honeycomb structure.

[0088] As shown in FIGS. 2 and 3, the cylindrical portion 11 defines the outer shape of the substrate 10, and the axial direction of the cylindrical portion 11 coincides with the axial direction of the substrate 10. As shown in FIGS. 2 and 3, the shape of the cylindrical portion 11 is cylindrical, but other shapes such as elliptical cylindrical and polygonal cylindrical may also be used.

[0089] As shown in FIGS. 2 and 3, the partition portion 12 is provided inside the cylindrical portion 11. As shown in FIGS. 2 to 6, the partition portion 12 exists between adjacent cells 13, and the adjacent cells 13 are partitioned by the partition portion 12. The partition portion 12 may have a porous structure through which the exhaust gas can pass. The thickness of the partition portion 12 is, for example, 20 μm or more and 1500 μm or less.

[0090] As shown in FIG. 6, the cell 13 extends in the exhaust gas flow direction X and has an end on the exhaust gas inflow side and an end on the exhaust gas outflow side.

[0091] As shown in FIG. 6, both the end on the exhaust gas inflow side and the end on the exhaust gas outflow side of the cell 13 are open. Therefore, the exhaust gas flowing in from the end (opening) on the exhaust gas inflow side of the cell 13 flows out from the end (opening) on the exhaust gas outflow side of the cell 13. Such a mode is called a flow-through type.

[0092] As shown in FIGS. 2 to 5, the planar shape of the end (opening) on the exhaust gas inflow side of the cell 13 is a quadrilateral, but it may be other shapes such as a hexagon or an octagon. The same applies to the planar shape of the end (opening) on the exhaust gas outflow side of the cell 13.

[0093] The cell density per square inch of the substrate 10 is, for example, 100 cells or more and 1000 cells or less. The cell density per square inch of the substrate 10 means the total number of cells 13 per square inch in the cross section obtained by cutting the substrate 10 in a plane perpendicular to the exhaust gas flow direction X.

[0094] The volume of the substrate 10 is, for example, 0.1 L or more and 20 L or less. The volume of the substrate 10 means the apparent volume of the substrate 10. For example, when the substrate 10 is cylindrical, if the outer diameter of the substrate 10 is 2r and the length of the substrate 10 is L, the volume of the substrate 10 is expressed by the formula: volume of the substrate 10 = π × r 2 × L. In this specification, "length" means the dimension in the axial direction of the substrate 10.

[0095] <The first catalyst layer> The first catalyst layer 20 will be described below.

[0096] As shown in FIGS. 4 and 6, the first catalyst layer 20 is provided in the upstream region of the surface of the partition wall portion 12 on the cell 13 side. The "surface of the partition wall portion 12 on the cell 13 side" means the outer surface of the partition wall portion 12 extending in the exhaust gas flow direction X. The "upstream region" means a region extending along the exhaust gas flow direction X from the exhaust gas inflow side end of the partition wall portion 12 so as not to reach the exhaust gas outflow side end of the partition wall portion 12. The first catalyst layer 20 may be provided directly on the surface of the partition wall portion 12 on the cell 13 side, or may be provided via another layer, but is usually provided directly on the surface of the partition wall portion 12 on the cell 13 side.

[0097] As shown in FIG. 6, the first catalyst layer 20 extends along the exhaust gas flow direction X from the exhaust gas inflow side end of the partition wall portion 12 so as not to reach the exhaust gas outflow side end of the partition wall portion 12.

[0098] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the mass (mass after firing) of the first catalyst layer 20 per unit volume of the portion of the base material 10 where the first catalyst layer 20 is formed is preferably 70 g / L or more and 380 g / L or less, more preferably 120 g / L or more and 300 g / L or less, and even more preferably 150 g / L or more and 250 g / L or less.

[0099] The mass of the first catalyst layer 20 per unit volume of the portion of the base material 10 where the first catalyst layer 20 is formed is calculated by the formula: (mass of the first catalyst layer 20) / ((volume of the base material 10)×(average length L of the first catalyst layer 20 20 / length L of the base material 10 10 ).

[0100] An example of the measurement method of the average length L of the first catalyst layer 20 is as follows. 20 is as follows.

[0101] From the catalyst 1, it extends in the axial direction of the base material 10, and the length L of the base material 10 10Cut out a sample having the same length as [the reference]. The sample is, for example, cylindrical with a diameter of 25.4 mm. Note that the value of the diameter of the sample can be changed as needed. Cut the sample at 5 mm intervals by a plane perpendicular to the axial direction of the substrate 10, and obtain a first cut piece, a second cut piece, ···, an nth cut piece in order from the end side on the exhaust gas inflow side of the sample. The length of the cut piece is 5 mm. Analyze the composition of the cut piece using a fluorescent X-ray analyzer (XRF) (for example, an energy dispersive X-ray analyzer (EDX), a wavelength dispersive X-ray analyzer (WDX), etc.), an inductively coupled plasma atomic emission spectrometer (ICP-AES), a scanning electron microscope - energy dispersive X-ray analysis method (SEM-EDX), etc., and confirm whether the cut piece contains a part of the first catalyst layer 20 based on the composition of the cut piece.

[0102] Regarding the cut pieces that are clearly found to contain a part of the first catalyst layer 20, it is not always necessary to perform a composition analysis. For example, the cut surface can be observed using a scanning electron microscope (SEM), an electron probe microanalyzer (EPMA), etc., to confirm whether the cut piece contains a part of the first catalyst layer 20. When observing the cut surface, elemental mapping of the cut surface may be performed.

[0103] After confirming whether the cut piece contains a part of the first catalyst layer 20, calculate the length of the first catalyst layer 20 contained in the sample based on the following formula. Length of the first catalyst layer 20 contained in the sample = 5 mm × (number of cut pieces containing a part of the first catalyst layer 20)

[0104] For example, if the first cut piece to the kth cut piece contain a part of the first catalyst layer 20, but the (k + 1)th to the nth cut pieces do not contain a part of the first catalyst layer 20, the length of the first catalyst layer 20 contained in the sample is (5 × k) mm.

[0105] An example of a more detailed measurement method for the length of the first catalyst layer 20 contained in the sample is as follows. The kth piece (i.e., the piece obtained from the exhaust gas outflow side of the sample among the pieces including a part of the first catalytic layer 20) is cut in the axial direction of the substrate 10, and the part of the first catalytic layer 20 present on the cut surface is observed using an SEM, an EPMA, or the like, to measure the length of the part of the first catalytic layer 20 in the kth piece. Then, the length of the first catalytic layer 20 included in the sample is calculated based on the following formula. Length of the first catalyst layer 20 included in the sample=(5 mm×(k−1))+(length of the part of the first catalyst layer 20 included in the kth cut piece)

[0106] For 8 to 16 samples arbitrarily cut out from the catalyst 1, the length of the first catalyst layer 20 included in each sample was measured, and the average value of the lengths was taken as the average length L of the first catalyst layer 20. 20 Let us assume that.

[0107] Average length L of the first catalyst layer 20 20 The larger the average length L of the first catalyst layer 20, the longer the contact time between the first catalyst layer 20 and the exhaust gas. 20 When the other conditions are the same, the average length L 20 The larger the ratio, the more the reactivity between the first catalytic layer 20 and exhaust gas is improved, and the less reducing exhaust gas reaches the second catalytic layer 30. This creates an environment in which reduction of Rh in the second catalytic layer 30 is less likely to occur, so that the reduction action of Rh can be more effectively exerted in the second catalytic layer 30, which contains less La, which promotes the oxidation of Rh, and a decrease in exhaust gas purification performance (particularly, NOx purification performance) can be prevented.

[0108] Length L of the substrate 10 10 Average length L of the first catalyst layer 20 20 Percentage of (L 20 / L 10×100) is preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. The upper limit can be appropriately adjusted in consideration of the balance between exhaust gas purification performance and cost, etc. The upper limit is preferably 90% or less, more preferably 80% or less, and even more preferably 70% or less. These upper limits may be combined with any of the above-mentioned lower limits respectively.

[0109] The length L of the substrate 10 10 The average length L of the lower layer 21 of the first catalyst layer 20 with respect to 21 The percentage (L 21 / L 10 ×100) and the length L of the substrate 10 10 The average length L of the upper layer 22 of the first catalyst layer 20 with respect to 22 The percentage (L 22 / L 10 ×100) is the same as the percentage (L 10 The average length L of the first catalyst layer 20 with respect to the length L of the substrate 10 20 The percentage (L 20 / L 10 ×100). The length L of the substrate 10 10 The average length L of the lower layer 21 of the first catalyst layer 20 with respect to 21 And the length L of the substrate 10 10 The average length L of the upper layer 22 of the first catalyst layer 20 with respect to 22 May be the same or different.

[0110] The first catalyst layer 20 contains La. Thereby, the heat resistance of the first catalyst layer 20 is improved. Also, phosphorus poisoning of the noble metal element in the first catalyst layer 20 is prevented. Further, through the oxidation of Pd by La, the exhaust gas purification performance of Pd in the first catalyst layer 20 is improved. Also, when the Ce-Zr based composite oxide in the first catalyst layer 20 contains La, the heat resistance and oxygen storage capacity of the Ce-Zr based composite oxide in the first catalyst layer 20 are improved.

[0111] At least one of the lower layer 21 and the upper layer 22 contains La. In one embodiment, one of the lower layer 21 and the upper layer 22 contains La and the other does not contain La. In another embodiment, both the lower layer 21 and the upper layer 22 contain La. From the viewpoint of effectively exerting the action of La, it is preferable that both the lower layer 21 and the upper layer 22 contain La.

[0112] The first catalyst layer 20 contains one or more La sources. The La source is an oxide containing La. The La source can be selected from, for example, Al-based oxides containing La, Ce-based oxides containing La, Ce-Zr-based composite oxides containing La, and the like.

[0113] From the viewpoint of improving the heat resistance and / or oxygen storage capacity of the first catalyst layer 20, the La source is preferably selected from Al-based oxides containing La and Ce-Zr-based composite oxides containing La. In one embodiment, the first catalyst layer 20 contains, as the La source, an Al-based oxide containing La and a Ce-Zr-based composite oxide containing La. The Al-based oxide containing La contributes to the improvement of the heat resistance of the first catalyst layer 20, and the Ce-Zr-based composite oxide containing La contributes to the improvement of the heat resistance and oxygen storage capacity of the first catalyst layer 20.

[0114] From the viewpoint of effectively exerting the action of La, the content of La in La 2 O 3 in the first catalyst layer 20, in terms of conversion, is preferably 5.5% by mass or more, more preferably 6% by mass or more, based on the mass of the first catalyst layer 20. The upper limit can be appropriately adjusted in consideration of the balance between exhaust gas purification performance and cost, the content of other components, etc. The upper limit is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. These upper limits can be combined with any of the above-mentioned lower limits, respectively.

[0115] Regarding a certain catalyst layer, the "content of La in La 2 O 3 in terms of conversion in the catalyst layer" means that when the catalyst layer contains one type of La source, the La in La 2 O 3Means the content in terms of conversion. When the catalyst layer contains two or more La sources, it refers to the total content of La derived from the two or more La sources in terms of La 2 O 3 in terms of conversion. This definition applies to all catalyst layers (e.g., the first catalyst layer 20, the second catalyst layer 30, the lower layer 21, the upper layer 22, the lower layer 31, the upper layer 32, etc.).

[0116] The mass of La in terms of La 2 O 3 in the first catalyst layer 20, among the mass in terms of conversion, the proportion of the mass of La derived from the Al-based oxide containing La and the Ce-Zr-based composite oxide containing La in terms of La 2 O 3 in terms of conversion is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. The upper limit is 100% by mass.

[0117] Regarding a certain catalyst layer, "the mass of La derived from the Al-based oxide containing La and the Ce-Zr-based composite oxide containing La in terms of La 2 O 3 in terms of conversion" means, when the catalyst layer contains the Al-based oxide containing La and does not contain the Ce-Zr-based composite oxide containing La, the mass of La derived from the Al-based oxide containing La in terms of La 2 O 3 in terms of conversion; when the catalyst layer contains the Ce-Zr-based composite oxide containing La and does not contain the Al-based oxide containing La, it means the mass of La derived from the Ce-Zr-based composite oxide containing La in terms of La 2 O 3 in terms of conversion; when the catalyst layer contains both the Al-based oxide containing La and the Ce-Zr-based composite oxide containing La, it means the sum of the mass of La derived from the Al-based oxide containing La in terms of La 2 O 3 in terms of conversion and the mass of La derived from the Ce-Zr-based composite oxide containing La in terms of La 2 O 3 in terms of conversion. This definition applies to all catalyst layers (e.g., the first catalyst layer 20, the second catalyst layer 30, the lower layer 21, the upper layer 22, the lower layer 31, the upper layer 32, etc.).

[0118] <Lower layer of the first catalyst layer> Hereinafter, the lower layer 21 of the first catalyst layer 20 will be described.

[0119] As shown in FIGS. 4 and 6, the lower layer 21 is provided in the upstream region of the cell 13 side surface of the partition portion 12. The meanings of the "cell 13 side surface of the partition portion 12" and the "upstream region" are as described above. The lower layer 21 may be provided directly on the cell 13 side surface of the partition portion 12, or may be provided via another layer, but is usually provided directly on the cell 13 side surface of the partition portion 12.

[0120] The lower layer 21 may be composed of a portion that bulges from the cell 13 side surface of the partition portion 12 toward the cell 13 side (hereinafter referred to as the "bulging portion"), or may be composed of a portion existing inside the partition portion 12 (hereinafter referred to as the "intrinsic portion"), or may have a bulging portion and an intrinsic portion. The present invention includes any of an embodiment in which the lower layer 21 is composed of a bulging portion, an embodiment in which the lower layer 21 is composed of an intrinsic portion, and an embodiment in which the lower layer 21 has a bulging portion and an intrinsic portion.

[0121] As shown in FIGS. 4 and 6, the lower layer 21 preferably has a bulging portion. Thereby, the contact property between the lower layer 21 and the exhaust gas is improved, and the exhaust gas purification performance is improved.

[0122] As shown in FIG. 6, the lower layer 21 extends along the exhaust gas flow direction X from the end portion on the exhaust gas inflow side of the partition portion 12 so as not to reach the end portion on the exhaust gas outflow side of the partition portion 12.

[0123] From the viewpoint of achieving a good balance between the exhaust gas purification performance and the cost, the mass of the lower layer 21 per unit volume of the portion of the base material 10 where the lower layer 21 is formed (the mass after firing) is preferably 50 g / L or more and 230 g / L or less, more preferably 70 g / L or more and 180 g / L or less, and even more preferably 80 g / L or more and 150 g / L or less.

[0124] The mass of the lower layer 21 per unit volume of the portion of the base material 10 where the lower layer 21 is formed is given by the formula: (mass of the lower layer 21) / ((volume of the base material 10) × (average length L of the lower layer 21 21 / length L of the base material 10 10 )) is calculated.

[0125] The average length L of the first catalyst layer 20 20 The above description regarding the average length L of the first catalyst layer 20 21 also applies to the average length L of the lower layer 21. When applying, "the first catalyst layer 20" is read as "the lower layer 21", and "average length L 20 " is read as "average length L 21 ".

[0126] The lower layer 21 contains Pd.

[0127] The lower layer 21 is covered by the upper layer 22. For this reason, the noble metal elements in the lower layer 21 are less likely to be phosphorus-poisoned, while the noble metal elements in the upper layer 22 are likely to be phosphorus-poisoned. On the other hand, Pd is likely to be phosphorus-poisoned, while Rh is less likely to be phosphorus-poisoned. Therefore, Pd is suitable as the noble metal element contained in the lower layer 21, and Rh is suitable as the noble metal element contained in the upper layer 22.

[0128] Since the first catalyst layer 20 is provided on the upstream side of the second catalyst layer 30, the temperature of the exhaust gas in contact with the first catalyst layer 20 is higher than the temperature of the exhaust gas in contact with the second catalyst layer 30. On the other hand, Pd has better heat resistance than Pt. Therefore, Pd is more suitable than Pt as the noble metal element contained in the lower layer 21.

[0129] The content of La in La 2 O 3 in the first catalyst layer 20, in terms of La conversion, is 5% by mass or more based on the mass of the first catalyst layer 20. Therefore, the noble metal elements in the first catalyst layer 20 are easily oxidized by La in the first catalyst layer 20. On the other hand, when Pt is oxidized, the exhaust gas purification performance deteriorates, while when Pd is oxidized, the exhaust gas purification performance improves. Therefore, Pd is more suitable than Pt as the noble metal element contained in the lower layer 21.

[0130] Pd is included in the lower layer 21 in the form of a catalytically active component that can function as a catalytically active component, for example, metallic Pd, an alloy containing Pd, a compound containing Pd (for example, an oxide of Pd), etc. From the viewpoint of improving the exhaust gas purification performance, the catalytically active component containing Pd is preferably in particulate form.

[0131] From the viewpoint of effectively exerting the exhaust gas purification performance of Pd, the content of Pd in terms of metal in the lower layer 21 is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, still more preferably 1% by mass or more, based on the mass of the lower layer 21. The upper limit can be appropriately adjusted in consideration of the balance between the exhaust gas purification performance and the cost, etc. The upper limit is preferably 20% by mass or less, more preferably 15% by mass or less, still more preferably 10% by mass or less. These upper limits may be combined with any of the above-mentioned lower limits, respectively.

[0132] The lower layer 21 may contain one or more noble metal elements other than Pd.

[0133] The noble metal element other than Pd can be selected from, for example, Rh, Pt, Ru, Ir, Os, etc. The noble metal element other than Pd is included in the lower layer 21 in the form of a catalytically active component that can function as a catalytically active component, for example, a metal, an alloy containing the noble metal element, a compound containing the noble metal element (for example, an oxide of the noble metal element), etc. From the viewpoint of enhancing the exhaust gas purification performance, the catalytically active component containing the noble metal element other than Pd is preferably in particulate form.

[0134] When the lower layer 21 contains Pd and a noble metal element other than Pd, Pd and the noble metal element other than Pd may form an alloy, and the active sites of Pd involved in the exhaust gas purification performance may decrease. Therefore, when the lower layer 21 contains Pd, it is preferable that the content rate in terms of metal of the noble metal element other than Pd in the lower layer 21 is small. Specifically, the content rate in terms of metal of the noble metal element other than Pd in the lower layer 21 is preferably 0.05% by mass or less, more preferably 0.01% by mass or less, based on the mass of the lower layer 21. The lower limit is 0% by mass. The "content rate in terms of metal of the noble metal element other than Pd in the lower layer 21" means the content rate in terms of metal of the one noble metal element when the lower layer 21 contains one noble metal element other than Pd, and means the total content rate in terms of metal of the two or more noble metal elements when the lower layer 21 contains two or more noble metal elements other than Pd.

[0135] The lower layer 21 preferably contains one or more carriers, and at least a part of the catalytic active component is supported on one or more carriers.

[0136] "At least a part of the catalytic active component is supported on the carrier" means a state in which at least a part of the catalytic active component is physically or chemically adsorbed or retained on the outer surface and / or the inner surface of the pores of the carrier. This definition applies to all catalyst layers (for example, the lower layer 21, the upper layer 22, the lower layer 31, the upper layer 32, etc.).

[0137] That at least a part of the catalytic active component is supported on the carrier in a certain catalyst layer can be confirmed, for example, by using SEM-EDX or the like. Specifically, in the elemental mapping obtained by analyzing the cross section of the catalyst layer by SEM-EDX, when at least a part of the catalytic active component and the carrier are present in the same region, it can be determined that at least a part of the catalytic active component is supported on the carrier.

[0138] The carrier can be selected from, for example, inorganic oxides. The inorganic oxide is, for example, in particulate form. From the viewpoint of improving the supportability of the catalytic active component, the inorganic oxide is preferably porous. The inorganic oxide may or may not have an oxygen storage capacity (OSC). The inorganic oxide used as the carrier is distinguished from the inorganic oxide used as a binder (for example, inorganic oxide-based binders such as alumina binder, zirconia binder, titania binder, silica binder, etc.).

[0139] Examples of the inorganic oxide include oxides based on Al-based oxides, Ce-based oxides, Ce-Zr composite oxides, oxides of rare earth elements other than Ce, zirconia (ZrO 2 ), silica (SiO 2 ), titania (TiO 2 ), zeolite (aluminosilicate), MgO, ZnO, SnO 2 , etc.

[0140] From the viewpoint of improving the heat resistance and / or oxygen storage capacity of the lower layer 21, the carrier is preferably selected from Al-based oxides, Ce-based oxides, and Ce-Zr composite oxides, and more preferably selected from Al-based oxides and Ce-Zr composite oxides. In one embodiment, the lower layer 21 contains an Al-based oxide and a Ce-Zr composite oxide as the carrier.

[0141] The lower layer 21 preferably contains La. Thereby, the heat resistance of the lower layer 21 is improved. Also, phosphorus poisoning of the noble metal element in the lower layer 21 is prevented. Further, through the oxidation of Pd by La, the exhaust gas purification performance of Pd in the lower layer 21 is improved. Also, when the Ce-Zr composite oxide in the lower layer 21 contains La, the heat resistance and oxygen storage capacity of the Ce-Zr composite oxide in the lower layer 21 are improved.

[0142] When the lower layer 21 contains La, the lower layer 21 contains one or more La sources. The description regarding the La source is the same as above.

[0143] From the perspective of improving the heat resistance and / or oxygen storage capacity of the lower layer 21, the La source is preferably selected from an Al-based oxide containing La and a Ce-Zr-based composite oxide containing La. In one embodiment, the lower layer 21 contains, as the La source, an Al-based oxide containing La and a Ce-Zr-based composite oxide containing La. The Al-based oxide containing La contributes to the improvement of the heat resistance of the lower layer 21, and the Ce-Zr-based composite oxide containing La contributes to the improvement of the heat resistance and oxygen storage capacity of the lower layer 21.

[0144] From the perspective of effectively exerting the action of La, the La of La in the lower layer 21 2 O 3 The content in terms of conversion is preferably 5% by mass or more, more preferably 6% by mass or more, still more preferably 7% by mass or more, based on the mass of the lower layer 21. The upper limit can be appropriately adjusted in consideration of the balance between the exhaust gas purification performance and the cost, the content of other components, etc. The upper limit is preferably 20% by mass or less, more preferably 15% by mass or less, still more preferably 10% by mass or less. These upper limits may be combined with any of the above-mentioned lower limits respectively.

[0145] The La of La in the lower layer 21 2 O 3 Among the mass in terms of conversion of La, the proportion occupied by the La of La derived from the Al-based oxide containing La and the Ce-Zr-based composite oxide containing La 2 O 3 in terms of conversion is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more. The upper limit is 100% by mass.

[0146] From the perspective of improving the heat resistance of the lower layer 21, the lower layer 21 preferably contains Al.

[0147] When the lower layer 21 contains Al, the lower layer 21 contains one or more Al sources. The Al source is an oxide containing Al. The Al source can be selected, for example, from Al-based oxides, Ce-based oxides containing Al, Ce-Zr-based composite oxides containing Al, alumina binders, etc. In one embodiment, the lower layer 21 contains an Al-based oxide and an alumina binder as the Al source.

[0148] From the viewpoint of improving the heat resistance of the lower layer 21, the content of Al in the lower layer 21 in terms of Al 2 O 3 conversion is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, based on the mass of the lower layer 21. The upper limit can be appropriately adjusted in consideration of the balance between the exhaust gas purification performance and the cost, the content of other components, etc. The upper limit is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less. These upper limits can be combined with any of the above-mentioned lower limits respectively.

[0149] Regarding a certain catalyst layer, the "content of Al in terms of Al 2 O 3 conversion in the catalyst layer" means the content of Al in terms of Al 2 O 3 conversion derived from the one Al source when the catalyst layer contains one Al source, and means the total content of Al in terms of Al 2 O 3 conversion derived from the two or more Al sources when the catalyst layer contains two or more Al sources. This definition applies to all catalyst layers (for example, the lower layer 21, the upper layer 22, the lower layer 31, the upper layer 32, etc.).

[0150] From the viewpoint of improving the oxygen storage capacity of the lower layer 21, it is preferable that the lower layer 21 contains Ce.

[0151] When the lower layer 21 contains Ce, the lower layer 21 contains one or more Ce sources. The Ce source is an oxide containing Ce. The Ce source can be selected, for example, from Al-based oxides containing Ce, Ce-based oxides, Ce-Zr-based composite oxides, ceria binders, etc. In one embodiment, the lower layer 21 contains a Ce-Zr-based composite oxide as the Ce source.

[0152] From the viewpoint of improving the heat resistance and oxygen storage capacity of the lower layer 21, it is preferable that the lower layer 21 contains Zr.

[0153] When the lower layer 21 contains Zr, the lower layer 21 contains one or more Zr sources. The description regarding the Zr source is the same as above. In one embodiment, the lower layer 21 contains a Ce-Zr-based composite oxide as the Zr source.

[0154] From the viewpoint of improving the heat resistance and oxygen storage capacity of the lower layer 21, the content of Zr in the lower layer 21 in terms of ZrO 2 is preferably 10% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more based on the mass of the lower layer 21. The upper limit can be appropriately adjusted considering the balance between exhaust gas purification performance and cost, the content of other components, etc. The upper limit is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less. These upper limits can be combined with any of the above-mentioned lower limits respectively.

[0155] Regarding a certain catalyst layer, the "content of Zr in terms of ZrO 2 in the catalyst layer" means the content of Zr in terms of ZrO 2 derived from the one Zr source when the catalyst layer contains one Zr source, and means the total content of Zr in terms of ZrO 2 derived from the two or more Zr sources when the catalyst layer contains two or more Zr sources. This definition applies to all catalyst layers (for example, the lower layer 21, the upper layer 22, the lower layer 31, the upper layer 32, etc.).

[0156] The lower layer 21 may contain components such as a binder and a stabilizer. Examples of the binder include inorganic oxide-based binders such as alumina sol, ceria sol, zirconia sol, titania sol, and silica sol. Examples of the stabilizer include carbonates, oxides, sulfates, etc. of alkaline earth metal elements (e.g., Sr, Ba, etc.).

[0157] <Upper layer of the first catalyst layer> Hereinafter, the upper layer 22 of the first catalyst layer 20 will be described.

[0158] As shown in FIGS. 4 and 6, the upper layer 22 is provided above the lower layer 21.

[0159] "The upper layer 22 is provided above the lower layer 21" means that a part or all of the upper layer 22 exists on the main surface of the lower layer 21 opposite to the main surface on the side of the partition portion 12 among the two main surfaces of the lower layer 21. The "main surface of the lower layer 21" means the outer surface of the lower layer 21 extending in the exhaust gas flow direction X. The upper layer 22 may be directly provided on the main surface of the lower layer 21 or may be provided via another layer, but usually it is directly provided on the main surface of the lower layer 21. The upper layer 22 may be provided so as to cover a part of the main surface of the lower layer 21 or may be provided so as to cover the entire main surface of the lower layer 21. "The upper layer 22 is provided above the lower layer 21" includes both the embodiment in which the upper layer 22 is directly provided on the main surface of the lower layer 21 and the embodiment in which the upper layer 22 is provided on the main surface of the lower layer 21 via another layer.

[0160] As shown in FIG. 6, the upper layer 22 extends along the exhaust gas flow direction X from the exhaust gas inflow side end of the partition portion 12 so as not to reach the exhaust gas outflow side end of the partition portion 12.

[0161] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the mass (mass after firing) of the upper layer 22 per unit volume of the portion of the substrate 10 where the upper layer 22 is formed is preferably 20 g / L or more and 150 g / L or less, more preferably 50 g / L or more and 120 g / L or less, and even more preferably 70 g / L or more and 100 g / L or less.

[0162] The mass per unit volume of the upper layer 22 in the portion of the base material 10 where the upper layer 22 is formed is given by the formula: (mass of the upper layer 22) / ((volume of the base material 10)×(average length L of the upper layer 22 22 / length L of the base material 10 10 )) is calculated.

[0163] The average length L of the first catalyst layer 20 20 The above description regarding the average length L also applies to the average length L of the upper layer 22 22 When applying, "the first catalyst layer 20" is replaced with "the upper layer 22", and "average length L 20 " is replaced with "average length L 22 ".

[0164] The upper layer 22 contains Rh.

[0165] Rh is contained in the upper layer 22 in the form of a catalytically active component containing Rh, such as metallic Rh, an alloy containing Rh, a compound containing Rh (e.g., an oxide of Rh), etc. From the viewpoint of improving the exhaust gas purification performance, the catalytically active component containing Rh is preferably in particulate form.

[0166] From the viewpoint of effectively exerting the exhaust gas purification performance of Rh, the content of Rh in terms of metal in the upper layer 22 is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more, based on the mass of the upper layer 22. The upper limit can be appropriately adjusted in consideration of the balance between exhaust gas purification performance and cost, etc. The upper limit is preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less. These upper limits can be combined with any of the above-mentioned lower limits respectively.

[0167] In addition to Rh, the upper layer 22 may contain one or more noble metal elements other than Rh.

[0168] Noble metal elements other than Rh can be selected from, for example, Pd, Pt, Ru, Ir, Os, etc. Noble metal elements other than Rh are contained in the upper layer 22 in the form of a catalytically active component capable of functioning as a catalytically active component, for example, a metal, an alloy containing a noble metal element, a compound containing a noble metal element (for example, an oxide of a noble metal element), etc. From the viewpoint of enhancing the exhaust gas purification performance, the catalytically active component containing a noble metal element other than Rh is preferably in particulate form.

[0169] When the upper layer 22 contains Rh and a noble metal element other than Rh, there is a possibility that Rh and the noble metal element other than Rh form an alloy and the active sites of Rh involved in the exhaust gas purification performance decrease. Therefore, the content of the noble metal element other than Rh in the upper layer 22 in terms of metal is preferably small. Specifically, the content of the noble metal element other than Rh in the upper layer 22 in terms of metal is preferably 0.05% by mass or less, more preferably 0.01% by mass or less, based on the mass of the upper layer 22. The lower limit is 0% by mass. The "content of the noble metal element other than Rh in the upper layer 22 in terms of metal" means the content of the noble metal element in terms of metal when the upper layer 22 contains one kind of noble metal element other than Rh, and means the total content of the two or more kinds of noble metal elements in terms of metal when the upper layer 22 contains two or more kinds of noble metal elements other than Rh.

[0170] The upper layer 22 preferably contains one or more carriers, and at least a part of the catalytically active component is supported on one or more carriers.

[0171] The carrier can be selected from, for example, inorganic oxides. The description of the inorganic oxides is the same as above.

[0172] From the viewpoint of improving the heat resistance and / or oxygen storage capacity of the upper layer 22, the carrier is preferably selected from Al-based oxides, Ce-based oxides, and Ce-Zr-based composite oxides, and more preferably selected from Al-based oxides and Ce-Zr-based composite oxides. In one embodiment, the upper layer 22 contains an Al-based oxide and a Ce-Zr-based composite oxide as carriers.

[0173] The upper layer 22 preferably contains La. Thereby, the heat resistance of the upper layer 22 is improved. Further, phosphorus poisoning of the noble metal element in the upper layer 22 is prevented. Further, when the Ce-Zr-based composite oxide in the upper layer 22 contains La, the heat resistance and oxygen storage capacity of the Ce-Zr-based composite oxide in the upper layer 22 are improved.

[0174] When the upper layer 22 contains La, the upper layer 22 contains one or more La sources. The description regarding the La source is the same as above.

[0175] From the viewpoint of improving the heat resistance and / or oxygen storage capacity of the upper layer 22, the La source is preferably selected from an Al-based oxide containing La and a Ce-Zr-based composite oxide containing La. In one embodiment, the upper layer 22 contains, as the La source, an Al-based oxide containing La and a Ce-Zr-based composite oxide containing La. The Al-based oxide containing La contributes to the improvement of the heat resistance of the upper layer 22, and the Ce-Zr-based composite oxide containing La contributes to the improvement of the heat resistance and oxygen storage capacity of the upper layer 22.

[0176] From the viewpoint of effectively exerting the action of La, the La of La in the upper layer 22 2 O 3 The content in terms of conversion is preferably 5% by mass or more, more preferably 6% by mass or more, and even more preferably 7% by mass or more, based on the mass of the upper layer 22. The upper limit can be appropriately adjusted in consideration of the balance between exhaust gas purification performance and cost, the content of other components, etc. The upper limit is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. These upper limits may be combined with any of the above-mentioned lower limits respectively.

[0177] The La of La in the upper layer 22 2 O 3 Among the mass in terms of conversion of La, the proportion of the mass of La in terms of conversion derived from the Al-based oxide containing La and the Ce-Zr-based composite oxide containing La 2 O 3 is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. The upper limit is 100% by mass.

[0178] From the viewpoint of improving the heat resistance of the upper layer 22, it is preferable that the upper layer 22 contains Al.

[0179] When the upper layer 22 contains Al, the upper layer 22 contains one or more Al sources. The description regarding the Al source is the same as above. In one embodiment, the upper layer 22 contains an Al-based oxide and an alumina binder as the Al source.

[0180] From the viewpoint of improving the heat resistance of the upper layer 22, the Al of Al in the upper layer 22 2 O 3 The content in terms of conversion is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more, based on the mass of the upper layer 22. The upper limit can be appropriately adjusted in consideration of the balance between the exhaust gas purification performance and the cost, the content of other components, etc. The upper limit is preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less. These upper limits may be combined with any of the above-mentioned lower limits respectively.

[0181] From the viewpoint of improving the oxygen storage capacity of the upper layer 22, it is preferable that the upper layer 22 contains Ce.

[0182] When the upper layer 22 contains Ce, the upper layer 22 contains one or more Ce sources. The description regarding the Ce source is the same as above. In one embodiment, the upper layer 22 contains a Ce-Zr composite oxide as the Ce source.

[0183] From the viewpoint of improving the heat resistance and oxygen storage capacity of the upper layer 22, it is preferable that the upper layer 22 contains Zr.

[0184] When the upper layer 22 contains Zr, the upper layer 22 contains one or more Zr sources. The description regarding the Zr source is the same as above. In one embodiment, the upper layer 22 contains a Ce-Zr composite oxide as the Zr source.

[0185] From the viewpoint of improving the heat resistance and oxygen storage capacity of the upper layer 22, the content of Zr in terms of ZrO in the upper layer 22 is preferably 10% by mass or more, more preferably 15% by mass or more, still more preferably 20% by mass or more, based on the mass of the upper layer 22. The upper limit can be appropriately adjusted in consideration of the balance between the exhaust gas purification performance and the cost, the content of other components, etc. The upper limit is preferably 95% by mass or less, more preferably 90% by mass or less, still more preferably 85% by mass or less. These upper limits may be combined with any of the above-mentioned lower limits respectively. 2

[0186] The upper layer 22 may contain components such as a binder and a stabilizer. The explanations regarding the binder and the stabilizer are the same as above.

[0187] <Second catalyst layer> Hereinafter, the second catalyst layer 30 will be described.

[0188] As shown in FIGS. 5 and 6, the second catalyst layer 30 is provided in the downstream region of the cell 13 side surface of the partition wall portion 12. The meaning of the "cell 13 side surface of the partition wall portion 12" is the same as above. The "downstream region" means a region extending along the direction opposite to the exhaust gas flow direction X from the exhaust gas outflow side end of the partition wall portion 12 so as not to reach the exhaust gas inflow side end of the partition wall portion 12. The second catalyst layer 30 may be provided directly on the cell 13 side surface of the partition wall portion 12, or may be provided via another layer, but usually it is provided directly on the cell 13 side surface of the partition wall portion 12.

[0189] As shown in FIG. 6, the second catalyst layer 30 extends along the direction opposite to the exhaust gas flow direction X from the exhaust gas outflow side end of the partition wall portion 12 so as not to reach the exhaust gas inflow side end of the partition wall portion 12.

[0190] As shown in FIG. 6, the second catalyst layer 30 is provided on the downstream side of the first catalyst layer 20. "The second catalyst layer 30 is provided on the downstream side of the first catalyst layer 20" means that at least a part of the second catalyst layer 30 exists in a region on the downstream side in the exhaust gas flow direction X of the region where the first catalyst layer 20 is provided, among the surfaces of the partition wall portion 12 on the cell 13 side.

[0191] As shown in FIG. 6, the end portion on the exhaust gas inflow side of the second catalyst layer 30 is in contact with the end portion on the exhaust gas outflow side of the first catalyst layer 20 at the boundary surface S. However, the end portion on the exhaust gas inflow side of the second catalyst layer 30 may have a portion that overlaps with the end portion on the exhaust gas outflow side of the first catalyst layer 20 (that is, a portion that is located above the end portion on the exhaust gas outflow side of the first catalyst layer 20 and covers the end portion on the exhaust gas outflow side of the first catalyst layer 20). Also, the end portion on the exhaust gas outflow side of the first catalyst layer 20 may have a portion that overlaps with the end portion on the exhaust gas inflow side of the second catalyst layer 30 (that is, a portion that is located above the end portion on the exhaust gas inflow side of the second catalyst layer 30 and covers the end portion on the exhaust gas inflow side of the second catalyst layer 30). These cases are also included in "the second catalyst layer 30 is provided on the downstream side of the first catalyst layer 20".

[0192] The end portion on the exhaust gas inflow side of the lower layer 31 of the second catalyst layer 30 may have a portion that overlaps with the end portion on the exhaust gas outflow side of the lower layer 21 of the first catalyst layer 20 (that is, a portion that is located above the end portion on the exhaust gas outflow side of the lower layer 21 of the first catalyst layer 20 and covers the end portion on the exhaust gas outflow side of the lower layer 21 of the first catalyst layer 20). Also, the end portion on the exhaust gas outflow side of the lower layer 21 of the first catalyst layer 20 may have a portion that overlaps with the end portion on the exhaust gas inflow side of the lower layer 31 of the second catalyst layer 30 (that is, a portion that is located above the end portion on the exhaust gas inflow side of the lower layer 31 of the second catalyst layer 30 and covers the end portion on the exhaust gas inflow side of the lower layer 31 of the second catalyst layer 30). These cases are also included in "the second catalyst layer 30 is provided on the downstream side of the first catalyst layer 20".

[0193] The end portion on the exhaust gas inflow side of the upper layer 32 of the second catalyst layer 30 may have a portion overlapping with the end portion on the exhaust gas outflow side of the upper layer 22 of the first catalyst layer 20 (i.e., a portion located above the end portion on the exhaust gas outflow side of the upper layer 22 of the first catalyst layer 20 and covering the end portion on the exhaust gas outflow side of the upper layer 22 of the first catalyst layer 20). Also, the end portion on the exhaust gas outflow side of the upper layer 22 of the first catalyst layer 20 may have a portion overlapping with the end portion on the exhaust gas inflow side of the upper layer 32 of the second catalyst layer 30 (i.e., a portion located above the end portion on the exhaust gas inflow side of the upper layer 32 of the second catalyst layer 30 and covering the end portion on the exhaust gas inflow side of the upper layer 32 of the second catalyst layer 30). In these cases as well, it is included in "the second catalyst layer 30 is provided on the downstream side of the first catalyst layer 20".

[0194] From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, the mass (mass after firing) of the second catalyst layer 30 per unit volume of the portion of the substrate 10 where the second catalyst layer 30 is formed is preferably 70 g / L or more and 380 g / L or less, more preferably 150 g / L or more and 300 g / L or less, and even more preferably 200 g / L or more and 260 g / L or less.

[0195] The mass of the second catalyst layer 30 per unit volume of the portion of the substrate 10 where the second catalyst layer 30 is formed is calculated by the formula: (mass of the second catalyst layer 30) / ((volume of the substrate 10) × (average length L 30 of the second catalyst layer 30 / L 10 of the substrate 10)).

[0196] The average length L 20 of the first catalyst layer 20 described above regarding the measurement method is also applicable to the measurement method of the average length L 30 of the second catalyst layer 30. When applying, "the first catalyst layer 20" is read as "the second catalyst layer 30", and "average length L 20 " is read as "average length L 30 ". However, in the measurement method of the average length L 30 of the second catalyst layer 30, the sample is cut at 5 mm intervals by a plane perpendicular to the axial direction of the substrate 10, and the first cut piece, the second cut piece, ···, the nth cut piece are obtained in order from the end portion side on the exhaust gas outflow side of the sample.

[0197] Average length L of the second catalyst layer 30 30 can be appropriately adjusted in consideration of the balance between exhaust gas purification performance and cost, the average length L of the first catalyst layer 20 20 and the like.

[0198] The second catalyst layer 30 may or may not contain La. When the second catalyst layer 30 contains La, the heat resistance of the second catalyst layer 30 is improved. Further, when the Ce-Zr composite oxide in the second catalyst layer 30 contains La, the heat resistance and oxygen storage capacity of the Ce-Zr composite oxide in the second catalyst layer 30 are improved.

[0199] In one embodiment where the second catalyst layer 30 contains La, one of the lower layer 31 and the upper layer 32 contains La and the other does not contain La. In another embodiment where the second catalyst layer 30 contains La, both the lower layer 31 and the upper layer 32 contain La. From the viewpoint of effectively exerting the action of La, it is preferable that both the lower layer 31 and the upper layer 32 contain La.

[0200] When the second catalyst layer 30 contains La, the second catalyst layer 30 contains one or more La sources. The description regarding the La source is the same as above.

[0201] From the viewpoint of improving the heat resistance and / or oxygen storage capacity of the second catalyst layer 30, the La source is preferably selected from an Al-based oxide containing La and a Ce-Zr composite oxide containing La. In one embodiment, the second catalyst layer 30 contains, as the La source, an Al-based oxide containing La and a Ce-Zr composite oxide containing La. The Al-based oxide containing La contributes to the improvement of the heat resistance of the second catalyst layer 30, and the Ce-Zr composite oxide containing La contributes to the improvement of the heat resistance and oxygen storage capacity of the second catalyst layer 30.

[0202] From the viewpoint of preventing the reduction of the exhaust gas purification performance of the noble metal element (especially Rh) in the second catalyst layer 30 by La in the second catalyst layer 30, the La of La in the second catalyst layer 30 2 O 3The content of the conversion is preferably 2.7% by mass or less, more preferably 2.5% by mass or less, based on the mass of the second catalyst layer 30. The lower limit may be 0% by mass or may be more than 0% by mass. When the second catalyst layer 30 contains La, from the viewpoint of effectively exerting the action of La, the lower limit is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.1% by mass or more. Each of these lower limits may be combined with any of the above upper limits.

[0203] La in La of the second catalyst layer 30 2 O 3 Among the masses of the conversion, the proportion of La derived from the Al-based oxide containing La and the Ce-Zr-based composite oxide containing La in the La 2 O 3 The proportion occupied by the mass of the conversion is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. The upper limit is 100% by mass.

[0204] <Lower layer of the second catalyst layer> Hereinafter, the lower layer 31 of the second catalyst layer 30 will be described.

[0205] As shown in FIGS. 5 and 6, the lower layer 31 is provided in the downstream region of the cell 13 side surface of the partition portion 12. The meanings of the "cell 13 side surface of the partition portion 12" and the "downstream region" are as described above. The lower layer 31 may be provided directly on the cell 13 side surface of the partition portion 12 or may be provided via another layer, but usually, it is provided directly on the cell 13 side surface of the partition portion 12.

[0206] The lower layer 31 may be composed of a portion that bulges toward the cell 13 side from the cell 13 side surface of the partition portion 12 (hereinafter referred to as the "bulging portion"), or may be composed of a portion existing inside the partition portion 12 (hereinafter referred to as the "intrinsic portion"), or may have a bulging portion and an intrinsic portion. The present invention includes any of the embodiments in which the lower layer 31 is composed of a bulging portion, the embodiments in which the lower layer 31 is composed of an intrinsic portion, and the embodiments in which the lower layer 31 has a bulging portion and an intrinsic portion.

[0207] As shown in FIGS. 5 and 6, the lower layer 31 preferably has a raised portion. Thereby, the contact property between the lower layer 31 and the exhaust gas is improved, and the exhaust gas purification performance is improved.

[0208] As shown in FIG. 6, the lower layer 31 extends along a direction opposite to the exhaust gas flow direction X from the end portion of the partition portion 12 on the exhaust gas outflow side so as not to reach the end portion of the partition portion 12 on the exhaust gas inflow side.

[0209] From the viewpoint of achieving a good balance between the exhaust gas purification performance and the cost, the mass (mass after firing) of the lower layer 31 per unit volume of the portion of the base material 10 where the lower layer 31 is formed is preferably 50 g / L or more and 230 g / L or less, more preferably 100 g / L or more and 180 g / L or less, and even more preferably 130 g / L or more and 160 g / L or less.

[0210] The mass of the lower layer 31 per unit volume of the portion of the base material 10 where the lower layer 31 is formed is calculated from the formula: (mass of the lower layer 31) / ((volume of the base material 10)×(average length L of the lower layer 31 31 / length L of the base material 10 10 ).

[0211] The average length L of the second catalyst layer 30 30 The above description regarding the average length L of the second catalyst layer 30 31 also applies to the average length L of the lower layer 31. When applying, "the second catalyst layer 30" is read as "the lower layer 31", and "the average length L 30 " is read as "the average length L 31 ".

[0212] The lower layer 31 contains Pt. Since Pt is lower in cost than Rh and Pd, it is used from the viewpoint of cost reduction.

[0213] Since the lower layer 31 is covered by the upper layer 32, the exhaust gas in contact with the lower layer 31 has a more stable atmosphere than the exhaust gas in contact with the upper layer 32. More specifically, the exhaust gas in contact with the lower layer 31 is less likely to be in an atmosphere with a large amount of oxygen or a large amount of reducing substances (CO / HC) instantaneously. Rh has excellent purification performance in an environment with large atmospheric fluctuations, and Pt has excellent purification performance in a stable atmospheric environment. Therefore, Pt is suitable as the noble metal element contained in the lower layer 31, and Rh is suitable as the noble metal element contained in the upper layer 32.

[0214] Since the second catalyst layer 30 is provided on the downstream side of the first catalyst layer 20, the temperature of the exhaust gas in contact with the second catalyst layer 30 is lower than the temperature of the exhaust gas in contact with the first catalyst layer 20. On the other hand, Pt is inferior in heat resistance to Pd. Therefore, Pt is more suitable than Pd as the noble metal element contained in the lower layer 31.

[0215] La of La in the second catalyst layer 30 2 O 3 The content in terms of conversion is 3% by mass or less based on the mass of the second catalyst layer 30. Therefore, the noble metal elements in the second catalyst layer 30 are less likely to be oxidized by La in the second catalyst layer 30. On the other hand, when Pd is oxidized, the exhaust gas purification performance is improved, while when Pt is oxidized, the exhaust gas purification performance is deteriorated. Therefore, Pt is more suitable than Pd as the noble metal element contained in the lower layer 31.

[0216] Pt is contained in the lower layer 31 in the form of a catalyst active component capable of functioning, for example, in the form of a catalyst active component containing Pt such as metallic Pt, an alloy containing Pt, or a compound containing Pt (for example, an oxide of Pt). From the viewpoint of improving the exhaust gas purification performance, the catalyst active component containing Pt is preferably in a particulate form.

[0217] From the viewpoint of effectively exerting the exhaust gas purification performance of Pt, the content of Pt in terms of metal in the lower layer 31 is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.3% by mass or more, based on the mass of the lower layer 31. The upper limit can be appropriately adjusted in consideration of the balance between the exhaust gas purification performance and cost, etc. The upper limit is preferably 5% by mass or less, more preferably 3% by mass or less, still more preferably 1% by mass or less. These upper limits may be combined with any of the above-mentioned lower limits respectively.

[0218] The lower layer 31 may contain one or two or more noble metal elements other than Pt.

[0219] Noble metal elements other than Pt can be selected from, for example, Rh, Pd, Ru, Ir, Os, etc. Noble metal elements other than Pt are contained in the lower layer 31 in the form of a catalytic active component capable of functioning as a catalytic active component, for example, a metal, an alloy containing a noble metal element, a compound containing a noble metal element (for example, an oxide of a noble metal element), etc. From the viewpoint of enhancing the exhaust gas purification performance, the catalytic active component containing a noble metal element other than Pt is preferably in a particulate form.

[0220] When the lower layer 31 contains Pt and a noble metal element other than Pt, there is a possibility that Pt and the noble metal element other than Pt form an alloy and the active sites of Pt involved in the exhaust gas purification performance decrease. Therefore, when the lower layer 31 contains Pt, it is preferable that the content of the noble metal element other than Pt in the lower layer 31 in terms of metal is small. Specifically, the content of the noble metal element other than Pt in the lower layer 31 in terms of metal is preferably 1% by mass or less, more preferably 0.3% by mass or less, still more preferably 0.05% by mass or less, based on the mass of the lower layer 31. The lower limit is 0% by mass. The "content of the noble metal element other than Pt in the lower layer 31 in terms of metal" means the content of the one kind of noble metal element in terms of metal when the lower layer 31 contains one kind of noble metal element other than Pt, and means the total content of the two or more kinds of noble metal elements in terms of metal when the lower layer 31 contains two or more kinds of noble metal elements other than Pt.

[0221] The lower layer 31 preferably contains one or more carriers, and at least a part of the catalytic active component is supported on one or more carriers.

[0222] The carrier can be selected from, for example, inorganic oxides. The description of the inorganic oxides is the same as above.

[0223] From the viewpoint of improving the heat resistance and / or oxygen storage capacity of the lower layer 31, the carrier is preferably selected from Al-based oxides, Ce-based oxides, and Ce-Zr-based composite oxides, and more preferably selected from Al-based oxides and Ce-Zr-based composite oxides. In one embodiment, the lower layer 31 contains an Al-based oxide and a Ce-Zr-based composite oxide as the carrier.

[0224] The lower layer 31 may or may not contain La. When the lower layer 31 contains La, the heat resistance of the lower layer 31 is improved. Also, when the Ce-Zr-based composite oxide in the lower layer 31 contains La, the heat resistance and oxygen storage capacity of the Ce-Zr-based composite oxide in the lower layer 31 are improved.

[0225] When the lower layer 31 contains La, the lower layer 31 contains one or more La sources. The description of the La source is the same as above.

[0226] From the viewpoint of improving the heat resistance and / or oxygen storage capacity of the lower layer 31, the La source is preferably selected from Al-based oxides containing La and Ce-Zr-based composite oxides containing La. In one embodiment, the lower layer 31 contains an Al-based oxide containing La and a Ce-Zr-based composite oxide containing La as the La source.

[0227] From the viewpoint of preventing the decrease in the exhaust gas purification performance of the noble metal element (especially Pt) in the lower layer 31 due to La in the lower layer 31, the La of La in the lower layer 31 2 O 3The content of the conversion is preferably 2% by mass or less, more preferably 1.9% by mass or less, still more preferably 1.8% by mass or less, based on the mass of the lower layer 31. The lower limit may be 0% by mass or may be more than 0% by mass. When the lower layer 31 contains La, from the viewpoint of effectively exerting the action of La, the lower limit is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, still more preferably 0.05% by mass or more. These lower limits may be combined with any of the above upper limits respectively.

[0228] La in La of the lower layer 31 2 O 3 Among the masses of the conversion, the proportion of La derived from the Al-based oxide containing La and the Ce-Zr-based composite oxide containing La in the La 2 O 3 The proportion occupied by the mass of the conversion is preferably 70% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more. The upper limit is 100% by mass.

[0229] When the content of the noble metal element other than Pt in the lower layer 31 in terms of metal conversion is small, the content of Pt in the lower layer 31 in terms of metal conversion becomes relatively large, and the influence of Pt on the exhaust gas purification performance of the lower layer 31 becomes large. In this case, the decrease in the exhaust gas purification performance of the lower layer 31 becomes remarkable due to the oxidation of Pt in the lower layer 31 by La in the lower layer 31 and the resulting decrease in the exhaust gas purification performance of Pt in the lower layer 31. Therefore, when the content of the noble metal element other than Pt in the lower layer 31 in terms of metal conversion is small, the content of La in La of the lower layer 31 2 O 3 The content of the conversion is preferably small. Thereby, a decrease in the exhaust gas purification performance of the lower layer 31 can be effectively prevented. Specifically, from the viewpoint of effectively preventing a decrease in the exhaust gas purification performance of the lower layer 31, the content of the noble metal element other than Pt in the lower layer 31 in terms of metal conversion is preferably 1% by mass or less, more preferably 0.3% by mass or less, still more preferably 0.05% by mass or less, based on the mass of the lower layer 31, and the La in La of the lower layer 31 2 O 3It is preferable to combine with the above embodiment in which the conversion content rate is preferably 2% by mass or less, more preferably 1.9% by mass or less, and still more preferably 1.8% by mass or less based on the mass of the lower layer 31. The descriptions of the former and latter embodiments are as described above.

[0230] From the viewpoint of improving the heat resistance of the lower layer 31, the lower layer 31 preferably contains Al.

[0231] When the lower layer 31 contains Al, the lower layer 31 contains one or more Al sources. The description of the Al source is the same as above. In one embodiment, the lower layer 31 contains an Al-based oxide and an alumina binder as the Al source.

[0232] From the viewpoint of improving the heat resistance of the lower layer 31, the Al of Al in the lower layer 31 2 O 3 The conversion content rate is preferably 20% by mass or more, more preferably 30% by mass or more, and still more preferably 40% by mass or more based on the mass of the lower layer 31. The upper limit can be appropriately adjusted in consideration of the balance between the exhaust gas purification performance and the cost, the content rate of other components, etc. The upper limit is preferably 90% by mass or less, more preferably 80% by mass or less, and still more preferably 70% by mass or less. These upper limits may be combined with any of the above-mentioned lower limits respectively.

[0233] From the viewpoint of improving the oxygen storage capacity of the lower layer 31, the lower layer 31 preferably contains Ce.

[0234] When the lower layer 31 contains Ce, the lower layer 31 contains one or more Ce sources. The description of the Ce source is the same as above. In one embodiment, the lower layer 31 contains a Ce-Zr composite oxide as the Ce source.

[0235] From the viewpoints of improving the heat resistance and oxygen storage capacity of the lower layer 31, the lower layer 31 preferably contains Zr.

[0236] When the lower layer 31 contains Zr, the lower layer 31 contains one or more Zr sources. The description of the Zr source is the same as above. In one embodiment, the lower layer 31 contains a Ce-Zr composite oxide as the Zr source.

[0237] From the viewpoint of improving the heat resistance and oxygen storage capacity of the lower layer 31, the content of Zr in the lower layer 31 in terms of ZrO 2 conversion is preferably 10% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more based on the mass of the lower layer 31. The upper limit can be appropriately adjusted in consideration of the balance between the exhaust gas purification performance and cost, the content of other components, etc. The upper limit is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less. These upper limits may be combined with any of the above-mentioned lower limits respectively.

[0238] The lower layer 31 may contain components such as a binder and a stabilizer. The description of the binder and the stabilizer is the same as above.

[0239] <Upper layer of the second catalyst layer> Hereinafter, the upper layer 32 of the second catalyst layer 30 will be described.

[0240] As shown in FIGS. 5 and 6, the upper layer 32 is provided above the lower layer 31.

[0241] The phrase "the upper layer 32 is provided above the lower layer 31" means that part or all of the upper layer 32 is present on the main surface of the lower layer 31 that is opposite to the main surface on the side of the partition portion 12 among the two main surfaces of the lower layer 31. The "main surface of the lower layer 31" means the outer surface of the lower layer 31 extending in the exhaust gas flow direction X. The upper layer 32 may be provided directly on the main surface of the lower layer 31, or may be provided via another layer, but usually it is provided directly on the main surface of the lower layer 31. The upper layer 32 may be provided so as to cover a part of the main surface of the lower layer 31, or may be provided so as to cover the entire main surface of the lower layer 31. The phrase "the upper layer 32 is provided above the lower layer 31" includes both the embodiment in which the upper layer 32 is provided directly on the main surface of the lower layer 31 and the embodiment in which the upper layer 32 is provided on the main surface of the lower layer 31 via another layer.

[0242] As shown in FIG. 6, the upper layer 32 extends along a direction opposite to the exhaust gas flow direction X from the end portion on the exhaust gas outflow side of the partition portion 12 so as not to reach the end portion on the exhaust gas inflow side of the partition portion 12.

[0243] From the viewpoint of achieving a good balance between the exhaust gas purification performance and the cost, the mass (mass after firing) of the upper layer 32 per unit volume of the portion of the base material 10 where the upper layer 32 is formed is preferably 20 g / L or more and 150 g / L or less, more preferably 50 g / L or more and 120 g / L or less, and even more preferably 70 g / L or more and 100 g / L or less.

[0244] The mass of the upper layer 32 per unit volume of the portion of the base material 10 where the upper layer 32 is formed is calculated by the formula: (mass of the upper layer 32) / ((volume of the base material 10) × (average length L of the upper layer 32 32 / length L of the base material 10 10 ))

[0245] The average length L of the second catalyst layer 30 30 The above description regarding the average length L 32 also applies to the average length L of the upper layer 32. When applying, "the second catalyst layer 30" is read as "the upper layer 32", and "the average length L 30 " is read as "the average length L 32 ".

[0246] The upper layer 32 contains Rh.

[0247] Rh is contained in the upper layer 32 in the form of a catalytically active component capable of functioning as a catalytically active component, for example, metallic Rh, an alloy containing Rh, a compound containing Rh (for example, an oxide of Rh), etc. From the viewpoint of improving the exhaust gas purification performance, the catalytically active component containing Rh is preferably in particulate form.

[0248] From the viewpoint of effectively exerting the exhaust gas purification performance of Rh, the content of Rh in terms of metal in the upper layer 32 is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, still more preferably 0.1% by mass or more, based on the mass of the upper layer 32. The upper limit can be appropriately adjusted in consideration of the balance between the exhaust gas purification performance and the cost, etc. The upper limit is preferably 1% by mass or less, more preferably 0.5% by mass or less, still more preferably 0.3% by mass or less. These upper limits may be combined with any of the above-mentioned lower limits respectively.

[0249] In addition to Rh, the upper layer 32 may contain one or more noble metal elements other than Rh.

[0250] The noble metal element other than Rh can be selected, for example, from Pd, Pt, Ru, Ir, Os, etc. The noble metal element other than Rh is contained in the upper layer 32 in the form of a catalytically active component capable of functioning as a catalytically active component, for example, a metal, an alloy containing the noble metal element, a compound containing the noble metal element (for example, an oxide of the noble metal element), etc. From the viewpoint of enhancing the exhaust gas purification performance, the catalytically active component containing the noble metal element other than Rh is preferably in particulate form.

[0251] When the upper layer 32 contains Rh and a noble metal element other than Rh, Rh and the noble metal element other than Rh may form an alloy, and there is a risk that the active sites of Rh involved in the exhaust gas purification performance will decrease. Therefore, it is preferable that the content rate in terms of metal of the noble metal element other than Rh in the upper layer 32 is small. Specifically, the content rate in terms of metal of the noble metal element other than Rh in the upper layer 32 is preferably 0.05% by mass or less, more preferably 0.01% by mass or less, based on the mass of the upper layer 32. The lower limit is 0% by mass. The "content rate in terms of metal of the noble metal element other than Rh in the upper layer 32" means the content rate in terms of metal of the one kind of noble metal element when the upper layer 32 contains one kind of noble metal element other than Rh, and means the total content rate in terms of metal of the two or more kinds of noble metal elements when the upper layer 32 contains two or more kinds of noble metal elements other than Rh.

[0252] The upper layer 32 preferably contains one or more kinds of carriers, and at least a part of the catalytic active component is supported on one or more kinds of carriers.

[0253] The carrier can be selected from, for example, inorganic oxides. The description of the inorganic oxides is the same as above.

[0254] From the viewpoint of improving the heat resistance and / or oxygen storage capacity of the upper layer 32, the carrier is preferably selected from Al-based oxides, Ce-based oxides, and Ce-Zr-based composite oxides, and more preferably selected from Al-based oxides and Ce-Zr-based composite oxides. In one embodiment, the upper layer 32 contains an Al-based oxide and a Ce-Zr-based composite oxide as the carrier.

[0255] The upper layer 32 may or may not contain La. When the upper layer 32 contains La, the heat resistance of the upper layer 32 is improved. Further, when the Ce-Zr-based composite oxide in the upper layer 32 contains La, the heat resistance and oxygen storage capacity of the Ce-Zr-based composite oxide in the upper layer 32 are improved.

[0256] When the upper layer 32 contains La, the upper layer 32 contains one or more kinds of La sources. The description of the La source is the same as above.

[0257] From the viewpoint of improving the heat resistance and / or oxygen storage capacity of the upper layer 32, the La source is preferably selected from an Al-based oxide containing La and a Ce-Zr-based oxide containing La. In one embodiment, the upper layer 32 contains, as the La source, an Al-based oxide containing La and a Ce-Zr-based composite oxide containing La.

[0258] From the viewpoint of preventing a decrease in the exhaust gas purification performance of the noble metal element (especially Rh) in the upper layer 32 due to La in the upper layer 32, the La of La in the upper layer 32 2 O 3 The content in terms of conversion is preferably 4% by mass or less, more preferably 3.5% by mass or less, and even more preferably 3% by mass or less, based on the mass of the upper layer 32. The lower limit may be 0% by mass or may be more than 0% by mass. When the upper layer 32 contains La, from the viewpoint of effectively exerting the action of La, the lower limit is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, and even more preferably 0.05% by mass or more. These lower limits may be combined with any of the above upper limits respectively.

[0259] The La of La in the upper layer 32 2 O 3 Among the mass in terms of conversion of La, the proportion of La in terms of conversion derived from the Al-based oxide containing La and the Ce-Zr-based oxide containing La 2 O 3 in terms of conversion is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. The upper limit is 100% by mass.

[0260] From the viewpoint of improving the heat resistance of the upper layer 32, the upper layer 32 preferably contains Al.

[0261] When the upper layer 32 contains Al, the upper layer 32 contains one or more Al sources. The description of the Al source is the same as above. In one embodiment, the upper layer 32 contains, as the Al source, an Al-based oxide and an alumina binder.

[0262] From the viewpoint of improving the heat resistance of the upper layer 32, the content of Al in the upper layer 32 in terms of Al 2 O 3 is preferably 15% by mass or more, more preferably 20% by mass or more, still more preferably 25% by mass or more, based on the mass of the upper layer 32. The upper limit can be appropriately adjusted in consideration of the balance between the exhaust gas purification performance and cost, the content of other components, etc. The upper limit is preferably 90% by mass or less, more preferably 80% by mass or less, still more preferably 70% by mass or less. These upper limits may be combined with any of the above-mentioned lower limits respectively.

[0263] From the viewpoint of improving the oxygen storage capacity of the upper layer 32, the upper layer 32 preferably contains Ce.

[0264] When the upper layer 32 contains Ce, the upper layer 32 contains one or more Ce sources. The description of the Ce source is the same as above. In one embodiment, the upper layer 32 contains a Ce-Zr composite oxide as the Ce source.

[0265] From the viewpoint of improving the heat resistance and oxygen storage capacity of the upper layer 32, the upper layer 32 preferably contains Zr.

[0266] When the upper layer 32 contains Zr, the upper layer 32 contains one or more Zr sources. The description of the Zr source is the same as above. In one embodiment, the upper layer 32 contains a Ce-Zr composite oxide as the Zr source.

[0267] From the viewpoint of improving the heat resistance and oxygen storage capacity of the upper layer 32, the content of Zr in the upper layer 32 in terms of ZrO 2 is preferably 10% by mass or more, more preferably 15% by mass or more, still more preferably 20% by mass or more, based on the mass of the upper layer 32. The upper limit can be appropriately adjusted in consideration of the balance between the exhaust gas purification performance and cost, the content of other components, etc. The upper limit is preferably 95% by mass or less, more preferably 90% by mass or less, still more preferably 85% by mass or less. These upper limits may be combined with any of the above-mentioned lower limits respectively.

[0268] The upper layer 32 may contain components such as a binder and a stabilizer. The descriptions of the binder and the stabilizer are the same as above.

[0269] <Manufacture of Catalyst> The catalyst 1 can be manufactured by forming the lower layer 21 on the substrate 10 and then forming the upper layer 22 on the lower layer 21, and by forming the lower layer 31 on the substrate 10 and then forming the upper layer 32 on the lower layer 31. After forming the lower layer 21 and the upper layer 22 on the substrate 10, the lower layer 31 and the upper layer 32 may be formed on the substrate 10, or after forming the lower layer 31 and the upper layer 32 on the substrate 10, the lower layer 21 and the upper layer 22 may be formed on the substrate 10.

[0270] The lower layer 21 is formed by mixing a source of a noble metal element (for example, a salt of a noble metal element such as Pd), optionally a source of La (for example, an Al-based oxide containing La, a Ce-based oxide containing La, a Ce-Zr-based composite oxide containing La, etc.) and optionally other components (for example, an inorganic oxide other than the source of La, a binder such as an alumina binder, a solvent, etc.) to prepare a first slurry, applying the first slurry onto the substrate 10, drying it, and firing it.

[0271] The upper layer 22 is formed by mixing a source of a noble metal element (for example, a salt of a noble metal element such as Rh), optionally a source of La (for example, an Al-based oxide containing La, a Ce-based oxide containing Al, a Ce-Zr-based composite oxide containing Al, etc.) and optionally other components (for example, an inorganic oxide other than the source of La, a binder such as an alumina binder, a solvent, etc.) to prepare a second slurry, applying the second slurry onto the lower layer 21, drying it, and firing it.

[0272] The lower layer 31 can be formed by mixing a source of noble metal element (e.g., a salt of noble metal element such as Pt), optionally a source of La (e.g., an Al-based oxide containing La, a Ce-based oxide containing La, a Ce-Zr-based composite oxide containing La, etc.) and optionally other components (e.g., an inorganic oxide other than the source of La, a binder such as an alumina binder, a solvent, etc.) to prepare a third slurry, applying the third slurry onto the substrate 10, drying it, and firing it.

[0273] The upper layer 32 can be formed by mixing a source of noble metal element (e.g., a salt of noble metal element such as Rh), optionally a source of La (e.g., an Al-based oxide containing La, a Ce-based oxide containing Al, a Ce-Zr-based composite oxide containing Al, etc.) and optionally other components (e.g., an inorganic oxide other than the source of La, a binder such as an alumina binder, a solvent, etc.) to prepare a fourth slurry, applying the fourth slurry onto the lower layer 31, drying it, and firing it.

[0274] Examples of the salt of noble metal element include nitrate, ammine complex salt, acetate, chloride, etc. Examples of the binder include alumina sol, zirconia sol, titania sol, silica sol, ceria sol, etc. Examples of the solvent include water, organic solvent, etc.

[0275] The drying temperature is, for example, 70°C or higher and 150°C or lower, and the drying time is, for example, 5 minutes or longer and 1 hour or shorter. The firing temperature is, for example, 200°C or higher and 700°C or lower, and the firing time is, for example, 0.5 hour or longer and 5 hours or shorter. The firing can be carried out, for example, in an air atmosphere.

[0276] ≪Exhaust gas purification system≫ Hereinafter, the exhaust gas purification system 100 will be described with reference to FIGS. 7 to 9.

[0277] As shown in FIG. 7, the exhaust gas purification system 100 includes an exhaust pipe P, a first exhaust gas purification catalyst 1B (hereinafter referred to as "catalyst 1B") provided upstream in the exhaust passage of the exhaust pipe P, and a second exhaust gas purification catalyst 1C (hereinafter referred to as "catalyst 1C") provided downstream in the exhaust passage of the exhaust pipe P.

[0278] One end P1 of the exhaust pipe P is connected to an internal combustion engine (for example, a gasoline engine or the like), and the exhaust gas discharged from the internal combustion engine flows through the exhaust pipe P from one end P1 to the other end P2. That is, the exhaust pipe P forms an exhaust passage through which the exhaust gas flows. In the drawing, the exhaust gas flow direction is indicated by the symbol X. The exhaust gas flowing through the exhaust pipe P is treated by the catalyst 1B provided upstream in the exhaust passage of the exhaust pipe P, and the exhaust gas that has passed through the catalyst 1B is treated by the catalyst 1C provided downstream in the exhaust passage of the exhaust pipe P.

[0279] Hereinafter, the catalyst 1B will be described with reference to FIG. 8. In the catalyst 1B, the same members as those of the catalyst 1 are indicated by the same reference numerals as those of the catalyst 1. Unless otherwise specified below, the above description regarding the catalyst 1 is also applicable to the catalyst 1B.

[0280] As shown in FIG. 8, the catalyst 1B includes a first substrate 10B and a first catalyst layer 20B provided on the first substrate 10B.

[0281] As shown in FIG. 8, the first catalyst layer 20B includes a lower layer 21B provided on the first substrate 10B and an upper layer 22B provided on the lower layer 21B. The lower layer 21B contains Pd, and the upper layer 22B contains Rh.

[0282] The above description regarding the substrate 10 is also applicable to the first substrate 10B. When applying, "substrate 10" is replaced with "first substrate 10B".

[0283] The above description regarding the first catalyst layer 20 is also applicable to the first catalyst layer 20B unless otherwise specified below. When applying, "first catalyst layer 20" is replaced with "first catalyst layer 20B".

[0284] The above description regarding the lower layer 21 and the upper layer 22 of the first catalyst layer 20 is also applicable to the lower layer 21B and the upper layer 22B of the first catalyst layer 20B, unless otherwise specified below. When applying, "lower layer 21" is read as "lower layer 21B", and "upper layer 22" is read as "upper layer 22B".

[0285] As shown in FIG. 8, the first catalyst layer 20B, the lower layer 21B, and the upper layer 22B extend along the exhaust gas flow direction X from the end of the partition wall portion 12 on the exhaust gas inflow side to the end of the partition wall portion 12 on the exhaust gas outflow side. The first catalyst layer 20B, the lower layer 21B, and the upper layer 22B may extend along the exhaust gas flow direction X from the end of the partition wall portion 12 on the exhaust gas inflow side so as not to reach the end of the partition wall portion 12 on the exhaust gas outflow side, or may extend along the direction opposite to the exhaust gas flow direction X from the end of the partition wall portion 12 on the exhaust gas outflow side so as not to reach the end of the partition wall portion 12 on the exhaust gas inflow side.

[0286] Hereinafter, the catalyst 1C will be described with reference to FIG. 9. In the catalyst 1C, the members identical to those of the catalyst 1 are denoted by the same reference numerals as those of the catalyst 1. The above description regarding the catalyst 1 is also applicable to the catalyst 1C, unless otherwise specified below.

[0287] As shown in FIG. 9, the catalyst 1C includes a second substrate 10C and a second catalyst layer 30C provided on the second substrate 10C.

[0288] As shown in FIG. 9, the second catalyst layer 30C includes a lower layer 31C provided on the second substrate 10C and an upper layer 32C provided on the lower layer 31C. The lower layer 31C contains Pt, and the upper layer 32C contains Rh.

[0289] The above description regarding the substrate 10 is also applicable to the second substrate 10C. When applying, "substrate 10" is read as "second substrate 10C".

[0290] The above description regarding the second catalyst layer 30 applies also to the second catalyst layer 30C, unless otherwise specified below. When applying, "the second catalyst layer 30" shall be read as "the second catalyst layer 30C".

[0291] The above description regarding the lower layer 31 and the upper layer 32 of the second catalyst layer 30 applies also to the lower layer 31C and the upper layer 32C of the second catalyst layer 30C, unless otherwise specified below. When applying, "the lower layer 31" shall be read as "the lower layer 31C", and "the upper layer 32" shall be read as "the upper layer 32C".

[0292] As shown in FIG. 9, the second catalyst layer 30C, the lower layer 31C, and the upper layer 32C extend along the exhaust gas flow direction X from the end on the exhaust gas inflow side of the partition wall portion 12 to the end on the exhaust gas outflow side of the partition wall portion 12. The second catalyst layer 30C, the lower layer 31C, and the upper layer 32C may extend along the exhaust gas flow direction X from the end on the exhaust gas inflow side of the partition wall portion 12 so as not to reach the end on the exhaust gas outflow side of the partition wall portion 12, or may extend along the direction opposite to the exhaust gas flow direction X from the end on the exhaust gas outflow side of the partition wall portion 12 so as not to reach the end on the exhaust gas inflow side of the partition wall portion 12.

[0293] For the same reason as described for the catalyst 1, in the first catalyst layer 20B, from the viewpoint of preventing the deterioration of the exhaust gas purification performance (particularly, NOx purification performance) of Rh in the first catalyst layer 20B by La in the first catalyst layer 20B, rather than decreasing the content of La in terms of La 2 O 3 in the first catalyst layer 20B, from the viewpoint of improving the heat resistance of the first catalyst layer 20B, it is required to increase the content of La in terms of La 2 O 3 in the first catalyst layer 20B. In the second catalyst layer 30C, from the viewpoint of preventing the deterioration of the exhaust gas purification performance (particularly, NOx purification performance) of Rh in the second catalyst layer 30C by La in the second catalyst layer 30C, rather than increasing the content of La in terms of La 2 O 3 in the second catalyst layer 30C, from the viewpoint of improving the heat resistance of the second catalyst layer 30C, it is required to increase the content of La in terms of La 2 O 3It is required to reduce the content rate in terms of conversion. Therefore, in the exhaust gas purification system 100, the content rate of La in terms of La 2 O 3 in terms of conversion in the first catalyst layer 20B is 5% by mass or more based on the mass of the first catalyst layer 20B, and the content rate of La in terms of La 2 O 3 in terms of conversion in the second catalyst layer 30C is 3% by mass or less based on the mass of the second catalyst layer 30C. According to the exhaust gas purification system 100, while effectively exerting the action of La, it is possible to prevent a decrease in the exhaust gas purification performance of Rh by La (particularly, NOx purification performance), and thereby, it is possible to realize an improvement in the exhaust gas purification performance.

[0294] In addition to the action of improving heat resistance, La has an action of trapping the phosphorus component to prevent phosphorus poisoning of the noble metal element. Further, when the Ce-Zr based composite oxide contains La, La in the Ce-Zr based composite oxide has an action of improving the oxygen storage capacity of the Ce-Zr based composite oxide. These actions of La also contribute to the improvement of the exhaust gas purification performance of the exhaust gas purification system 100.

[0295] The larger the average length L 20B of the first catalyst layer 20B, the longer the contact time between the first catalyst layer 20B and the exhaust gas. Therefore, when other conditions except for the average length L 20B of the first catalyst layer 20B are the same, the larger the average length L 20B of the first catalyst layer 20B, the more the reactivity between the first catalyst layer 20B and the exhaust gas is improved, and the less the reducing exhaust gas reaching the second catalyst layer 30C becomes. As a result, since it becomes an environment where reduction of Rh in the second catalyst layer 30C hardly occurs, in the second catalyst layer 30C where there is little La that promotes oxidation of Rh, the reduction action of Rh can be more effectively exerted, and a decrease in the exhaust gas purification performance (particularly, NOx purification performance) can be prevented.

[0296] The length L 10B of the first substrate 10B and the length L 10c of the second substrate 10C, the percentage of the average length L 20B of the first catalyst layer 20B with respect to the total length (L 20B / (L 10B +L 10c )×100) is preferably 30% or more, more preferably 40% or more, and even more preferably 50% or more. The upper limit can be appropriately adjusted in consideration of the balance between the exhaust gas purification performance and the cost, etc. The upper limit is preferably 90% or less, more preferably 80% or less, and even more preferably 70% or less. These upper limits may be combined with any of the above-mentioned lower limits respectively.

[0297] In Catalyst 1, since the first catalyst layer 20 and the second catalyst layer 30 are provided on one substrate, there is a limit to the average length L 20 of the first catalyst layer 20, and it may be difficult to increase the average length L 20 of the first catalyst layer 20. On the other hand, in the exhaust gas purification system 100, since the first catalyst layer 20B and the second catalyst layer 30C are provided on two substrates respectively, there is no such limit, which is advantageous.

Examples

[0298] Hereinafter, the present invention will be described based on examples and comparative examples.

[0299] In the following examples and comparative examples, that all of La in the OSC material forms a solid solution phase was confirmed by the fact that the peak derived from La 2 O 3 does not appear in the XRD diffraction pattern of the OSC material, and by comparing the XRD diffraction pattern of the OSC material with the reference data of the crystal structure (fluorite-type CeO 2 -ZrO 2 ) recorded in the ICSD, and based on the fact that there is a peak shift to the low angle side with respect to the maximum peak position of the reference data in the XRD diffraction pattern of the OSC material. Also, EDX elemental analysis of the OSC material was performed to calculate the content of La 2 O 3 in terms of La forming a solid solution phase in the OSC material.

[0300] In the following examples and comparative examples, La 2 O3 In the modified alumina, the fact that all of La forms a solid solution phase means that La 2 O 3 -derived peaks do not appear in the XRD diffraction pattern of the modified alumina, and, based on the comparison between the XRD diffraction pattern of the La 2 O 3 modified alumina and the reference data of the crystal structure (θ-alumina) of La 2 O 3 modified alumina recorded in the ICSD, it was confirmed that there is a peak shift to the low angle side with respect to the maximum peak position of the reference data. Also, EDX elemental analysis of the La 2 O 3 modified alumina was performed, and the content of La in the La 2 O 3 modified alumina forming a solid solution phase was calculated in terms of La 2 O 3 modified alumina. 2 O 3 modified alumina forming a solid solution phase was calculated in terms of La 2 O 3 modified alumina.

[0301] Example 1 (1) Production of the first exhaust gas purification catalyst The first exhaust gas purification catalyst having a lower layer formed on a flow-through type substrate and an upper layer formed on the lower layer was produced as follows.

[0302] (1-1) Preparation of the lower layer forming slurry An OSC material having the following composition was prepared. Content in terms of Ce of CeO 2 : 40.0 mass% Content in terms of Zr of ZrO 2 : 51.0 mass% Content in terms of La of La 2 O 3 : 9.0 mass% (all of La forms a solid solution phase)

[0303] Into a mixing container, an aqueous palladium nitrate solution, the OSC material, La 2 O 3 modified alumina (La in terms of La2 O 3 Conversion content: 8.0 mass% (all of La forms a solid solution phase), alumina sol and water were added, mixed and stirred to prepare a slurry for forming the lower layer. The amount of each component in the slurry for forming the lower layer was based on the mass of the lower layer after firing (100 mass%), Pd was 5.0 mass% in terms of metal, the OSC material was 40.0 mass%, and La 2 O 3 Modified alumina was adjusted to be 50.0 mass%, and the solid content of the alumina sol was adjusted to be 5.0 mass%.

[0304] (1-2) Formation of the lower layer As a flow-through type substrate, a cell extending in the axial direction partitioned by partition walls with a thickness of 50 to 70 μm was provided with a density of 600 cells / inch 2 in the plane perpendicular to the axial direction, having an axial length of 100 mm and a volume of 1.0 L, and a flow-through type substrate was prepared.

[0305] The flow-through type substrate was immersed in the slurry for forming the lower layer, and the flow-through type substrate coated with the slurry for forming the lower layer was dried at 150 °C for 0.5 hours and then fired at 500 °C for 1 hour to form the lower layer. The mass of the lower layer per unit volume of the portion of the flow-through type substrate where the lower layer was formed was 100 g / L. The length of the lower layer was 100 mm.

[0306] (1-3) Preparation of the slurry for forming the upper layer An OSC material having the following composition was prepared. Ce in CeO 2 Conversion content: 10.0 mass% Zr in ZrO 2 Conversion content: 81.0 mass% La in La 2 O 3 Conversion content: 9.0 mass% (all of La forms a solid solution phase)

[0307] In a mixing container, an aqueous rhodium nitrate solution, an OSC material, La 2 O 3 Modified alumina (La in La 2 O 3Conversion content: 8.0 mass% (all of La forms a solid solution phase), alumina sol and water were added, mixed and stirred to prepare a slurry for upper layer formation. The amount of each component in the slurry for upper layer formation was adjusted so that, based on the mass of the upper layer after firing (100 mass%), Rh was 1.0 mass% in terms of metal, the OSC material was 40.0 mass%, La 2 O 3 modified alumina was 50.0 mass%, and the solid content of the alumina sol was 9.0 mass%.

[0308] (1-4) Formation of the upper layer The flow-through type substrate with the lower layer formed was immersed in the slurry for upper layer formation, and after drying the flow-through type substrate coated with the slurry for upper layer formation at 150 °C for 0.5 hours, it was fired at 500 °C for 1 hour to form an upper layer on the lower layer. The mass of the upper layer per unit volume of the portion of the flow-through type substrate where the upper layer was formed was 80 g / L. The length of the upper layer was 100 mm.

[0309] As described above, a first exhaust gas purification catalyst including a lower layer formed on the flow-through type substrate and an upper layer formed on the lower layer was manufactured.

[0310] (2) Manufacture of the second exhaust gas purification catalyst As described below, a second exhaust gas purification catalyst including a lower layer formed on the flow-through type substrate and an upper layer formed on the lower layer was manufactured.

[0311] (2-1) Preparation of the slurry for lower layer formation An OSC material having the following composition was prepared. Ce in CeO 2 Conversion content: 40.0 mass% Zr in ZrO 2 Conversion content: 58.0 mass% La in La 2 O 3 Conversion content: 2.0 mass% (all of La forms a solid solution phase)

[0312] Into a mixing container, an aqueous solution of platinum nitrate, the OSC material, La 2 O3 Modified alumina (La in La 2 O 3 Conversion content: 2.0 mass% (all of La forms a solid solution phase)), alumina sol and water were added, mixed and stirred to prepare a slurry for forming the lower layer. The amount of each component in the slurry for forming the lower layer was based on the mass of the lower layer after firing (100 mass%), Pt was 1.0 mass% in terms of metal, the OSC material was 60.0 mass%, and La 2 O 3 Modified alumina was adjusted to be 30.0 mass% and the solid content of the alumina sol was adjusted to be 9.0 mass%.

[0313] (2-2) Formation of the lower layer As a flow-through type substrate, a flow-through type substrate having cells extending in the axial direction partitioned by partitions with a thickness of 50 to 70 μm and having a density of 600 cells / inch 2 in the plane perpendicular to the axial direction, an axial length of 100 mm, and a volume of 1.0 L was prepared.

[0314] The flow-through type substrate was immersed in the slurry for forming the lower layer, and the flow-through type substrate coated with the slurry for forming the lower layer was dried at 150 °C for 0.5 hour and then fired at 500 °C for 1 hour to form the lower layer. The mass of the lower layer per unit volume of the portion of the flow-through type substrate where the lower layer was formed was 140 g / L. The length of the lower layer was 100 mm.

[0315] (2-3) Preparation of the slurry for forming the upper layer An OSC material having the following composition was prepared. Ce in CeO 2 Conversion content: 10.0 mass% Zr in ZrO 2 Conversion content: 86.0 mass% La in La 2 O 3 Conversion content: 4.0 mass% (all of La forms a solid solution phase)

[0316] In a mixing container, an aqueous rhodium nitrate solution, an OSC material, La 2 O 3 Modified alumina (La in La2 O 3 Conversion content: 2.0% by mass (all of La forms a solid solution phase), alumina sol and water were added, mixed and stirred to prepare a slurry for upper layer formation. The amount of each component in the slurry for upper layer formation was based on the mass of the upper layer after firing (100% by mass), Rh was 0.2% by mass in terms of metal, the OSC material was 60.0% by mass, and La 2 O 3 Modified alumina was adjusted to be 30.0% by mass, and the solid content of the alumina sol was adjusted to be 9.8% by mass.

[0317] (2 - 4) Formation of the upper layer The flow - through type substrate with the lower layer formed was immersed in the slurry for upper layer formation, and the flow - through type substrate coated with the slurry for upper layer formation was dried at 150 °C for 0.5 hours and then fired at 500 °C for 1 hour to form an upper layer on the lower layer. The mass of the upper layer per unit volume of the part of the flow - through type substrate where the upper layer was formed was 80 g / L. The length of the upper layer was 100 mm.

[0318] In the above - mentioned manner, a second exhaust gas purification catalyst comprising a lower layer formed on a flow - through type substrate and an upper layer formed on the lower layer was manufactured.

[0319] (3) Evaluation of exhaust gas purification performance The manufactured first and second exhaust gas purification catalysts were respectively installed on the upstream side and the downstream side of the exhaust passage of the engine, and as a deterioration treatment assuming a driving of 100,000 - 200,000 km, a durability treatment was carried out under the following durability conditions. <Durability conditions> · Durability engine: Passenger car NA 2L gasoline engine · Gasoline used: Commercially available regular gasoline · Treatment temperature: 900 °C · Treatment time: 100 hours

[0320] The first and second exhaust gas purification catalysts after the durability treatment were installed on the upstream and downstream sides of the exhaust passage of a vehicle (a passenger car equipped with a 1.5L direct injection turbo engine), respectively, and the vehicle was operated according to the driving conditions of the Worldwide Harmonized Light Vehicles Test Cycle (WLTC). During the low-temperature operation from the start of operation to 589 seconds, the medium-speed operation from 589 seconds to 1022 seconds after the start of operation, the high-speed operation from 1022 seconds to 1477 seconds after the start of operation, and the ultra-high-speed operation from 1477 seconds to 1800 seconds after the start of operation, the emissions of non-methane hydrocarbons (NMHC) and nitrogen oxides (NOx) in the exhaust gas passing through the first and second exhaust gas purification catalysts were measured, and the total emissions of NMHC and NOx per unit driving distance were determined. Note that certified test fuel was used as gasoline, and an exhaust gas measuring device manufactured by Horiba, Ltd. was used as the exhaust gas measuring device.

[0321] [Example 2] In the production of the first exhaust gas purification catalyst, the La in the lower layer forming slurry 2 O 3 modification amount of alumina La 2 O 3 The first and second exhaust gas purification catalysts were produced and the exhaust gas purification performance was evaluated in the same manner as in Example 1, except that the modification amount was changed to 2.0 mass%.

[0322] [Example 3] An OSC material having the following composition was prepared. Ce content of CeO 2 in terms of conversion: 10.0 mass% Zr content of ZrO 2 in terms of conversion: 88.0 mass% La content of La 2 O 3 in terms of conversion: 2.0 mass% (all of La forms a solid solution phase)

[0323] Into a mixing container, an aqueous rhodium nitrate solution, the OSC material, La 2 O 3 modified alumina (La of La 2 O 3Conversion content: 2.0 mass% (all of La forms a solid solution phase), alumina sol and water were added, mixed and stirred to prepare a slurry for upper layer formation. The amount of each component in the slurry for upper layer formation was based on the mass of the upper layer after firing (100 mass%), with Rh being 1.0 mass% in terms of metal, the OSC material being 40.0 mass%, and La 2 O 3 Modified alumina was adjusted to be 50.0 mass%, and the solid content of the alumina sol was adjusted to be 9.0 mass%.

[0324] In the production of the first exhaust gas purification catalyst, except for using the slurry for upper layer formation prepared above, the first and second exhaust gas purification catalysts were produced in the same manner as in Example 1, and the exhaust gas purification performance was evaluated.

[0325] 〔Comparative Example 1〕 (A) Preparation of slurry for lower layer formation An OSC material with the following composition was prepared. Ce content in terms of CeO 2 Conversion content: 40.0 mass% Zr content in terms of ZrO 2 Conversion content: 51.0 mass% La content in terms of La 2 O 3 Conversion content: 9.0 mass% (all of La forms a solid solution phase)

[0326] An aqueous solution of platinum nitrate, the OSC material, La 2 O 3 Modified alumina (La content in terms of La 2 O 3 Conversion content: 8.0 mass% (all of La forms a solid solution phase)), alumina sol and water were added, mixed and stirred to prepare a slurry for lower layer formation. The amount of each component in the slurry for lower layer formation was based on the mass of the lower layer after firing (100 mass%), with Pt being 1.0 mass% in terms of metal, the OSC material being 60.0 mass%, and La 2 O 3 Modified alumina was adjusted to be 30.0 mass%, and the solid content of the alumina sol was adjusted to be 9.0 mass%.

[0327] (B) Preparation of the slurry for upper layer formation An OSC material with the following composition was prepared. CeO of Ce 2 Content in terms of conversion: 10.0 mass% ZrO of Zr 2 Content in terms of conversion: 86.0 mass% La of La 2 O 3 Content in terms of conversion: 4.0 mass% (all of La forms a solid solution phase)

[0328] Into a mixing container, an aqueous rhodium nitrate solution, the OSC material, La 2 O 3 Modified alumina (La of La 2 O 3 Content in terms of conversion: 8.0 mass% (all of La forms a solid solution phase)), alumina sol and water were added, mixed and stirred to prepare a slurry for upper layer formation. The amounts of each component in the slurry for upper layer formation were based on the mass of the upper layer after firing (100 mass%), with Rh being 0.2 mass% in terms of metal, the OSC material being 60.0 mass%, La 2 O 3 Modified alumina being 30.0 mass%, and the solid content of the alumina sol being adjusted to 9.8 mass%.

[0329] In the production of the catalyst for purifying the second exhaust gas, except for using the slurry for lower layer formation prepared in the above (A) and the slurry for upper layer formation prepared in the above (B), the catalysts for purifying the first and second exhaust gases were produced in the same manner as in Example 1, and the exhaust gas purification performance was evaluated.

[0330] 〔Comparative Example 2〕 (C) Preparation of the slurry for lower layer formation An OSC material with the following composition was prepared. CeO of Ce 2 Content in terms of conversion: 40.0 mass% ZrO of Zr 2 Content in terms of conversion: 58.0 mass% La of La 2 O 3 Content in terms of conversion: 2.0 mass% (all of La forms a solid solution phase)

[0331] To a mixing container, an aqueous palladium nitrate solution, an OSC material, La 2 O 3 modified alumina (content in terms of La 2 O 3 : 2.0 mass% (all of La forms a solid solution phase)), alumina sol and water were added, mixed and stirred to prepare a slurry for forming the lower layer. The amounts of the respective components in the slurry for forming the lower layer were adjusted such that, based on the mass of the lower layer after firing (100 mass%), Pd was 5.0 mass% in terms of metal, the OSC material was 40.0 mass%, La 2 O 3 modified alumina was 50.0 mass%, and the solid content of the alumina sol was 5.0 mass%.

[0332] (D) Preparation of slurry for forming the upper layer An OSC material having the following composition was prepared. Content in terms of Ce of CeO 2 : 10.0 mass% Content in terms of Zr of ZrO 2 : 88.0 mass% Content in terms of La of La 2 O 3 : 2.0 mass% (all of La forms a solid solution phase)

[0333] To a mixing container, an aqueous rhodium nitrate solution, an OSC material, La 2 O 3 modified alumina (content in terms of La 2 O 3 : 2.0 mass% (all of La forms a solid solution phase)), alumina sol and water were added, mixed and stirred to prepare a slurry for forming the upper layer. The amounts of the respective components in the slurry for forming the upper layer were adjusted such that, based on the mass of the upper layer after firing (100 mass%), Rh was 1.0 mass% in terms of metal, the OSC material was 40.0 mass%, La 2 O 3 modified alumina was 50.0 mass%, and the solid content of the alumina sol was 9.0 mass%.

[0334] (E) Preparation of slurry for forming the lower layer An OSC material having the following composition was prepared. Ce of CeO 2 Content by conversion: 40.0 mass% Zr of ZrO 2 Content by conversion: 58.0 mass% La of La 2 O 3 Content by conversion: 2.0 mass% (all of La forms a solid solution phase)

[0335] Into a mixing container, an aqueous solution of platinum nitrate, an OSC material, La 2 O 3 Modified alumina (La of La 2 O 3 Content by conversion: 2.0 mass% (all of La forms a solid solution phase)), alumina sol and water were added, mixed and stirred to prepare a slurry for forming the lower layer. The amounts of each component in the slurry for forming the lower layer were based on the mass of the lower layer after firing (100 mass%), with Pt being 1.0 mass% in terms of metal, the OSC material being 60.0 mass%, La 2 O 3 Modified alumina being 30.0 mass% and the solid content of the alumina sol being adjusted to 9.0 mass%.

[0336] (F) Preparation of the slurry for forming the upper layer An OSC material with the following composition was prepared. Ce of CeO 2 Content by conversion: 10.0 mass% Zr of ZrO 2 Content by conversion: 88.0 mass% La of La 2 O 3 Content by conversion: 2.0 mass% (all of La forms a solid solution phase)

[0337] Into a mixing container, an aqueous solution of rhodium nitrate, an OSC material, La 2 O 3 Modified alumina (La of La 2 O 3Conversion content: 2.0% by mass (all of La forms a solid solution phase), alumina sol and water were added, mixed and stirred to prepare a slurry for upper layer formation. The amount of each component in the slurry for upper layer formation was based on the mass of the upper layer after firing (100% by mass), with Rh being 0.2% by mass in terms of metal, the OSC material being 60.0% by mass, and La 2 O 3 modified alumina being 30.0% by mass, and the solid content of the alumina sol being adjusted to 9.8% by mass.

[0338] In the production of the first exhaust gas purification catalyst, the slurry for lower layer formation prepared in (C) above and the slurry for upper layer formation prepared in (D) above were used, and in the production of the second exhaust gas purification catalyst, except for using the slurry for lower layer formation prepared in (E) above and the slurry for upper layer formation prepared in (F) above, the first and second exhaust gas purification catalysts were produced in the same manner as in Example 1, and the exhaust gas purification performance was evaluated.

[0339] 〔Comparative Example 3〕 In the production of the first exhaust gas purification catalyst, the slurry for lower layer formation prepared in (C) of Comparative Example 2 and the slurry for upper layer formation prepared in (D) of Comparative Example 2 were used, and in the production of the second exhaust gas purification catalyst, except for using the slurry for lower layer formation prepared in (A) of Comparative Example 1 and the slurry for upper layer formation prepared in (B) of Comparative Example 1, the first and second exhaust gas purification catalysts were produced in the same manner as in Example 1, and the exhaust gas purification performance was evaluated.

[0340] The results are shown in Tables 1 and 2. In Table 2, the total emission amounts of NMHC and NOx are shown as relative values when the value of Comparative Example 3 is taken as 1.

[0341]

Table 1

[0342]

Table 2

[0343] The first exhaust gas purification catalysts of Examples 1 to 3 and Comparative Examples 1 to 3 include a first substrate and a first catalyst layer (lower layer and upper layer) provided on the first substrate, and the first catalyst layer contains Rh. The second exhaust gas purification catalysts of Examples 1 to 3 and Comparative Examples 1 to 3 include a second substrate and a second catalyst layer (lower layer and upper layer) provided on the second substrate, and the second catalyst layer contains Rh.

[0344] The first and second exhaust gas purification catalysts of Examples 1 to 3 satisfy the following conditions. · The content of La in terms of La 2 O 3 in the first catalyst layer is 5% by mass or more based on the mass of the first catalyst layer. · The content of La in terms of La 2 O 3 in the second catalyst layer is 3% by mass or less based on the mass of the second catalyst layer.

[0345] The first and second exhaust gas purification catalysts of Comparative Examples 1 to 3 do not satisfy one or more of the above conditions.

[0346] As shown in Table 2, when the first exhaust gas purification catalyst satisfying the above conditions is installed on the upstream side of the exhaust passage and the second exhaust gas purification catalyst satisfying the above conditions is installed on the downstream side of the exhaust passage (Examples 1 to 3), compared with the case where the first exhaust gas purification catalyst that does not satisfy one or more of the above conditions is installed on the upstream side of the exhaust passage and the second exhaust gas purification catalyst that does not satisfy one or more of the above conditions is installed on the downstream side of the exhaust passage (Comparative Examples 1 to 3), the exhaust gas purification performance was higher.

Explanation of Reference Numerals

[0347] P... Exhaust pipe of internal combustion engine 1, 1B, 1C... Exhaust gas purification catalyst 10, 10B, 10C... Substrate 11... Cylindrical part 12... Partition part 13... Cell 20, 20B... First catalyst layer 21, 21B... Lower layer of the first catalyst layer 22,22B ··· Upper layer of the first catalyst layer 30,30C ··· Second catalyst layer 31,31C ··· Lower layer of the second catalyst layer 32,32C ··· Upper layer of the second catalyst layer 100 ··· Exhaust gas purification system

Claims

1. A substrate; A first catalyst layer provided on the upstream side of the substrate; A second catalyst layer provided downstream of the substrate; An exhaust gas purifying catalyst comprising: the first catalyst layer comprises a lower layer containing Pd and an upper layer containing Rh; the second catalyst layer comprises a lower layer containing Pt and an upper layer containing Rh, La in the first catalyst layer ２ O ３ The converted content is 5% by mass or more based on the mass of the first catalyst layer, La in the second catalyst layer ２ O ３ The exhaust gas purifying catalyst has a converted content of 3 mass% or less based on the mass of the second catalyst layer.

2. a content of precious metal elements other than Pt in the lower layer of the second catalytic layer in terms of metal is 1 mass% or less based on the mass of the lower layer of the second catalytic layer; La in the lower layer of the second catalyst layer ２ O ３ 2. The exhaust gas purifying catalyst according to claim 1, wherein the converted content is 2 mass % or less based on the mass of the lower layer in the second catalyst layer.

3. La in the upper layer of the first catalyst layer ２ O ３ the content in terms of carbon black is 5% by mass or more based on the mass of the upper layer of the first catalytic layer, La in the upper layer of the second catalyst layer ２ O ３ 3. The exhaust gas purifying catalyst according to claim 1, wherein the converted content is 4 mass % or less based on the mass of the upper layer of the second catalyst layer.

4. an exhaust passage through which exhaust gas flows; a first exhaust gas purifying catalyst provided upstream in the exhaust passage; a second exhaust gas purifying catalyst provided downstream in the exhaust passage; An exhaust gas purification system comprising: the first exhaust gas purifying catalyst comprises a first substrate and a first catalyst layer provided on the first substrate, the second exhaust gas purifying catalyst comprises a second substrate and a second catalyst layer provided on the second substrate, the first catalyst layer comprises a lower layer containing Pd and an upper layer containing Rh; the second catalyst layer comprises a lower layer containing Pt and an upper layer containing Rh, La in the first catalyst layer ２ O ３ The converted content is 5% by mass or more based on the mass of the first catalyst layer, La in the second catalyst layer ２ O ３ The converted content is 3 mass% or less based on the mass of the second catalyst layer.

5. a content of precious metal elements other than Pt in the lower layer of the second catalytic layer in terms of metal is 1 mass% or less based on the mass of the lower layer of the second catalytic layer; La in the lower layer of the second catalyst layer ２ O ３ The exhaust gas purification system according to claim 4 , wherein the converted content is 2 mass % or less based on the mass of the lower layer in the second catalyst layer.

6. La in the upper layer of the first catalyst layer ２ O ３ the content in terms of carbon black is 5% by mass or more based on the mass of the upper layer of the first catalytic layer, La in the upper layer of the second catalyst layer ２ O ３ The exhaust gas purification system according to claim 4 or 5, wherein the converted content is 4 mass % or less based on the mass of the upper layer of the second catalyst layer.

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