Exhaust gas purification catalyst

Abstract

A waste gas purification catalyst has a substrate and a catalyst layer disposed on the substrate. The catalyst layer includes layer a, layer b, and layer c. Layer a is disposed upstream of the waste gas flow direction closer to layer b. Layer c is stacked with at least one of layers a and b. In the stacked portion of layer c with at least one of layers a and b, layer c is disposed further away from the substrate than at least one of layers a and b. Layer a contains Pd, layer b contains Pt, and the mass content C of Pd in ​​layer a is C. Pd The mass content C of Pt in layer b Pt The ratio, i.e., C Pd / C Pt The value is greater than 1. Layer c contains Rh, Ce-Zr composite oxide and Zr oxide, and in layer c, at least a portion of Rh is loaded onto Zr oxide.

Description

Technical Field

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

[0002] The exhaust gases (also known as waste gases) emitted from internal combustion engines of automobiles, motorcycles, etc., contain harmful components such as HC (hydrocarbons), CO (carbon monoxide), and NOx (nitrogen oxides). Previously, three-way catalysts were used to purify and neutralize these harmful components. As three-way catalysts, precious metals such as Pt (platinum), Pd (palladium), and Rh (rhodium) are known to be used. Pt and Pd primarily function in the oxidation and purification of HC and CO, while Rh primarily functions in the reduction and purification of NOx. In recent years, due to stricter emissions regulations and increased environmental awareness, attempts have been made to improve the exhaust gas purification performance of the precious metal catalysts mentioned above.

[0003] Patent Document 1 discloses a waste gas purification catalyst having a substrate and a catalyst coating formed on the substrate. The catalyst coating comprises Rh particles and a co-catalyst composed of Ce-Zr composite oxide and Ce-free Zr composite oxide. The Rh particles have a specific range of average particle size and standard deviation of particle size. The Rh particles are respectively loaded on the Ce-Zr composite oxide and the Ce-free Zr composite oxide.

[0004] It should be noted that Patent Documents 2 and 3 disclose an exhaust gas purification catalyst disposed in the exhaust path of an internal combustion engine to purify the exhaust gas discharged from the internal combustion engine. The exhaust gas purification catalyst has a substrate dividing a unit for exhaust gas flow and a catalyst layer disposed on the surface of the substrate. The catalyst layer includes: a palladium layer containing palladium extending from the exhaust gas inflow end (i.e., a first end) of the unit to the exhaust gas outflow end (i.e., a second end); a platinum layer containing platinum extending from the second end to the first end; and a rhodium layer containing rhodium stacked on both the palladium layer and the platinum layer.

[0005] Additionally, Patent Document 4 discloses a trimetallic layered catalyst article comprising: a. an upper layer comprising platinum supported on at least one of an oxygen storage component, a zirconium oxide component, and an alumina component, and rhodium supported on the oxygen storage component; b. a lower layer comprising a front region and a rear region, the front region comprising palladium supported on the oxygen storage component and the alumina component, and the rear region comprising platinum supported on at least one of the alumina component, the cerium dioxide component, and the oxygen storage component; and c. a substrate, wherein the weight ratio of palladium to platinum is in the range of 1.0:0.4 to 1.0:2.0.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2021-104472

[0009] Patent Document 2: Japanese Patent Application Publication No. 2020-157262

[0010] Patent Document 3: Japanese Patent Application Publication No. 2020-157263

[0011] Patent Document 4: International Publication No. 2020 / 190999 Summary of the Invention

[0012] The problem the invention aims to solve

[0013] In recent years, there has been a demand for improved NOx purification performance of exhaust gas purification catalysts, particularly in the immediate period after an internal combustion engine is started.

[0014] Patent document 1 describes how NOx can be purified even at low temperatures by loading Rh particles onto Ce-Zr composite oxides and Zr composite oxides, respectively (improved low-temperature activity).

[0015] However, the inventors have discovered that the exhaust gas purification catalyst described in Patent Document 1 has poor purification performance for non-methane hydrocarbons (NMHC) other than methane.

[0016] Therefore, the purpose of this invention is to provide an exhaust gas purification catalyst that can take into account both the NOx purification performance and the NMHC purification performance of an internal combustion engine immediately after startup.

[0017] Solution for solving the problem

[0018] That is, the main idea of ​​this invention is as follows. [1]

[0020] A waste gas purification catalyst has a substrate and a catalyst layer disposed on the substrate.

[0021] The catalyst layer comprises layer a, layer b, and layer c.

[0022] Layer a is positioned upstream of the flow direction of the exhaust gas, closer to the surface than layer b.

[0023] The layer c is stacked on top of at least one of the layers a and b.

[0024] In the stacked portion of layer c with at least one of layers a and b, layer c is disposed at a position further away from the substrate than at least one of layers a and b.

[0025] Layer a contains Pd.

[0026] Layer b contains Pt.

[0027] The mass content C of Pd contained in layer a Pd The mass content C of Pt contained in layer b Pt The ratio, i.e., C Pd / C Pt Greater than 1,

[0028] Layer c comprises Rh, Ce-Zr composite oxides, and Zr oxides.

[0029] In layer c, at least a portion of the Rh is loaded onto the Zr-based oxide. [2]

[0031] According to the waste gas purification catalyst described in [1], wherein the layer c does not contain Al, or if it contains Al, the content of Al2O3 relative to the mass of the layer c is less than 22% by mass. [3]

[0033] According to the waste gas purification catalyst described in [1] or [2], wherein the mass M of the Zr-based oxide contained in layer c is... ZrO2 The mass M of the Ce-Zr composite oxide contained in layer c CZ The ratio, i.e., M ZrO2 / M CZ It is between 1.5 and 6.0. [4]

[0035] According to any one of the waste gas purification catalysts [1] to [3], wherein the mass content C of Pd contained in layer a is... Pd The mass content C of Zr-based oxides contained in layer c ZrO2 The ratio, i.e., C Pd / C ZrO2 It is above 0.015 and below 0.120. [5]

[0037] According to any one of the waste gas purification catalysts [1] to [4], wherein the mass content C of Pt contained in layer b is... Pt The mass content C of Zr-based oxides contained in layer c ZrO2 The ratio, i.e., C Pt / C ZrO2 It is above 0.001 and below 0.008.

[0038] The effects of the invention

[0039] According to the present invention, an exhaust gas purification catalyst is provided that can take into account both the NOx purification performance and the NMHC purification performance immediately after the internal combustion engine starts. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of one embodiment of the waste gas purification catalyst of the present invention.

[0041] Figure 2 This is a schematic diagram of one embodiment of the waste gas purification catalyst of the present invention.

[0042] Figure 3 This is a schematic diagram of one embodiment of the waste gas purification catalyst of the present invention.

[0043] Figure 4 This is a schematic diagram of one embodiment of the waste gas purification catalyst of the present invention.

[0044] Figure 5 This is a schematic diagram of one embodiment of the waste gas purification catalyst of the present invention.

[0045] Figure 6 This is a schematic diagram of one embodiment of the waste gas purification catalyst of the present invention.

[0046] Figure 7 This is a schematic diagram of one embodiment of the waste gas purification catalyst of the present invention.

[0047] Figure 8 This is a schematic diagram of one embodiment of the waste gas purification catalyst of the present invention.

[0048] Figure 9 This is a schematic diagram of one embodiment of the waste gas purification catalyst of the present invention.

[0049] Figure 10 This is a schematic diagram of one embodiment of the waste gas purification catalyst of the present invention. Detailed Implementation

[0050] The following is a detailed description of the methods for carrying out the present invention.

[0051] The waste gas purification catalyst of the present invention has a substrate and a catalyst layer disposed on the substrate.

[0052] The catalyst layer comprises layer a, layer b, and layer c.

[0053] Layer a is positioned upstream of the flow direction of the exhaust gas, closer to the surface than layer b.

[0054] The layer c is stacked on top of at least one of the layers a and b.

[0055] In the stacked portion of layer c with at least one of layers a and b, layer c is disposed at a position further away from the substrate than at least one of layers a and b.

[0056] Layer a contains Pd.

[0057] Layer b contains Pt.

[0058] The mass content C of Pd contained in layer a Pd The mass content C of Pt contained in layer b Pt The ratio, i.e., C Pd / C Pt Greater than 1,

[0059] Layer c comprises Rh, Ce-Zr composite oxides, and Zr oxides.

[0060] In layer c, at least a portion of the Rh is loaded onto the Zr-based oxide.

[0061] The exhaust gas purification catalyst (also simply referred to as "catalyst") of the present invention, through the above-described configuration, achieves the effect of simultaneously achieving NOx purification performance and NMHC purification performance immediately after the internal combustion engine starts. The mechanism by which the above-described effect is obtained through the present invention is not yet fully understood, but the inventors presume the following. However, the present invention is not limited by any of the following presumed mechanisms.

[0062] Generally, Rh is considered to primarily contribute to NOx purification. To fully utilize Rh's NOx purification performance, oxygen storage components (also known as "OSC materials") with the ability to mitigate fluctuations in oxygen concentration in exhaust gas (OSC capability) are considered effective. In this invention, Ce-Zr composite oxides (also known as "CZ") capable of functioning as OSC materials are used.

[0063] Czar (CeO2) functions not only as an OSC material but also as a support. The CeO2 in Cz has the property of oxidizing Rh, thus reducing its activity. Therefore, it is considered to use not only Cz but also other supports in Rh-containing catalyst layers. The most common support other than Cz is one with Al2O3 as its main component.

[0064] Since the exhaust gas purification reaction is a chemical reaction, the higher the temperature, the faster the reaction proceeds, resulting in a higher purification rate. Immediately after the internal combustion engine starts, the catalyst temperature is low, thus the purification rate is low. To improve NOx purification performance immediately after engine start-up, rapidly heating the catalyst after engine start-up is effective. However, Al2O3 has a high specific heat, resulting in a slow heating process, which is considered detrimental to improving purification performance immediately after engine start-up. Therefore, this invention combines Zr-based oxides (with a lower specific heat than Al2O3 and without the Rh-oxidizing properties of CZ) with CZ in the Rh-containing layer c. It is believed that this can improve NOx purification performance immediately after engine start-up.

[0065] From the viewpoint of suppressing the oxidation and reduced activity of Rh due to CZ, at least a portion of Rh needs to be loaded onto Zr-based oxides.

[0066] Furthermore, it is believed that Rh not only contributes to the purification of NOx but also to the purification of non-methane hydrocarbons (NMHC). However, according to the research of the inventors, the effect of Zr-based oxides in assisting Rh in the purification of NMHC is weaker than that of Al2O3.

[0067] Therefore, it is believed that the NMHC purification performance of the internal combustion engine immediately after startup can be improved by adopting the following configurations (I) and (II) in this invention.

[0068] (I) Layer a containing Pd and layer b containing Pt are arranged such that layer a is closer to the upstream side of the exhaust gas flow direction than layer b.

[0069] (II) Make the mass content C of Pd in ​​layer a Pd The mass content C of Pt in layer b Pt The ratio, i.e., C Pd / C Pt Greater than 1.

[0070] Compared to Pd, Pt is more beneficial for the purification of saturated hydrocarbons in NMHC. Compared to Pd, Pd is more beneficial for the purification of unsaturated hydrocarbons. Therefore, by using both Pd and Pt, the overall emission of NMHC can be reduced more significantly compared to using only one. It should be noted that Pt also helps in the purification of NOx. However, compared to Pd, Pt has the property that its particles tend to move and aggregate when exposed to high-temperature environments, and its active sites are more easily reduced. The temperature of the exhaust gas upstream of the exhaust gas flow direction is high, while the temperature of the exhaust gas downstream of the exhaust gas flow direction is low compared to the upstream side. Therefore, in order to place the Pt-containing layer downstream of the exhaust gas flow direction where the temperature is low, the present invention adopts the above-described configuration (I), in which layer a containing Pd is placed upstream of the exhaust gas flow direction, and layer b containing Pt is placed downstream of the exhaust gas flow direction.

[0071] Furthermore, with the configuration described in (II) above, a greater amount of catalyst active ingredients can be disposed upstream of the exhaust gas flow direction, which is close to the internal combustion engine (e.g., an engine) and where the temperature is prone to rise. Therefore, even with the same total mass of catalyst active ingredients, the NMHC purification performance immediately after the internal combustion engine starts can be improved.

[0072] For the reasons stated above, it is believed that the exhaust gas purification catalyst of the present invention can take into account both the NOx purification performance and the NMHC purification performance immediately after the internal combustion engine starts.

[0073] <Substrate>

[0074] The waste gas purification catalyst of the present invention has a substrate.

[0075] The substrate can be any substrate previously known for its use in exhaust gas purification catalysts. For example, a substrate having a partition wall made of porous material and an exhaust gas flow path (the space between the partition walls) divided by the partition wall is preferred. As for the shape of the substrate, known substrates such as honeycomb, DPF (diesel particulate filter), or GPF (gasoline particulate filter) are preferred. Furthermore, the material of the partition wall can be, for example, ceramic materials such as alumina (Al2O3), mullite (3Al2O3-2SiO2), cordierite (2MgO-2Al2O3-5SiO2), aluminum titanate (Al2TiO5), silicon carbide (SiC), and stainless steel.

[0076] <Catalyst Layer>

[0077] The waste gas purification catalyst of the present invention has a catalyst layer.

[0078] A catalyst layer is disposed on a substrate. The catalyst layer may be disposed directly (in contact with at least a portion of the surface of the substrate) on at least a portion of the surface of the substrate, or it may be disposed on at least a portion of the surface of the substrate in between other layers.

[0079] The catalyst layer consists of layer a, layer b, and layer c.

[0080] [Layer a]

[0081] Layer a contains Pd.

[0082] Pd is the active component of the catalyst.

[0083] The mass content C of Pd in ​​layer a Pd Preferably, it is 0.010% by mass or more, more preferably 0.050% by mass or more, and even more preferably 0.10% by mass or more. Additionally, C PdPreferably, it is 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0084] C Pd It is the ratio (mass%) of the mass of Pd contained in layer a to the mass of layer a.

[0085] The content (concentration rate) of each element, represented by Pd, in layer a can be determined using conventional methods such as scanning electron microscopy-energy dispersive X-ray diffraction (SEM-EDX). Specifically, as described below.

[0086] For the sample obtained from layer a, elemental analysis was performed using conventional methods such as SEM-EDX to determine the types of constituent elements of the sample as a whole and to calculate the content (mass %) of each metal element. The content (mass %) of each metal element was calculated for each of the 10 fields of view of the SEM, and the average content (mass %) of each metal element in the 10 fields of view was taken as the content (mass %) of each metal element in layer a.

[0087] It should be noted that when calculating the content (mass %) using the above method, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au are calculated as metallic elements, while other metallic elements are calculated as oxides. The specific oxide forms of each element are as follows. Oxides of rare earth elements other than Ce, Pr, and Tb are sesquioxides (M₂O₃, where M represents a rare earth element other than Ce, Pr, and Tb). Ce's oxide is CeO₂, and Pr's oxide is Pr₆O. 11 The oxides of Tb are Tb4O7, Al is Al2O3, Zr is ZrO2, Si is SiO2, B is B2O3, Mg is MgO, Ca is CaO, Sr is SrO, Ba is BaO, Fe is Fe3O4, Mn is Mn3O4, Cu is CuO, Ti is TiO2, Zn is ZnO, and Sn is SnO2.

[0088] In addition to Pd, layer a may also contain other catalyst active components. Commonly known catalyst active components other than Pd can be used, such as Rh, Pt, gold (Au), silver (Ag), iridium (Ir), ruthenium (Ru), and osmium (Os).

[0089] Layer a preferably does not contain any catalyst active components other than Pd, or if it does contain catalyst active components other than Pd, the proportion of such components is small. Specifically, based on the total mass of Pd and catalyst active components other than Pd contained in layer a, the mass of catalyst active components other than Pd contained in layer a is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less.

[0090] Layer a may further contain components other than those mentioned above.

[0091] For example, layer a can contain Ce-Zr composite oxides.

[0092] "Ce-Zr composite oxides" refers to composite oxides containing Ce and Zr. Alternatively, it can be defined as composite oxides in which the CeO2 content (calculated as Ce) is 5% to 95% of the total mass of the composite oxide, and the ZrO2 content (calculated as Zr) is 5% to 95% of the total mass of the composite oxide.

[0093] Ce-Zr composite oxides are typically granular. Whether layer a contains Ce-Zr composite oxides can be determined using conventional methods such as SEM-EDX. Specifically, the process is as follows: First, the sample containing layer a is analyzed using SEM-EDX, and the particles containing Ce and Zr are identified through the obtained elemental mapping. Next, compositional analysis (elemental analysis) is performed on the identified particles. If the compositional analysis results are within the aforementioned range, the material can be determined to be a Ce-Zr composite oxide.

[0094] Ce-Zr composite oxides can function as oxygen storage components (OSC materials).

[0095] Furthermore, Ce-Zr composite oxides can function as support components for the aforementioned catalyst active ingredients. It should be noted that supported catalyst active ingredients refer to those physically or chemically adsorbed or retained on the outer surface or inner surface of pores. Specifically, the presence of catalyst active ingredients on the support component can be confirmed, for example, by analyzing the cross-section of the exhaust gas purification catalyst using SEM-EDX to obtain elemental mapping, confirming that the support component and the catalyst active ingredient exist in the same region, thus determining that the support component is "loaded" with catalyst active ingredients.

[0096] The CeO2 content of Ce in the Ce-Zr composite oxide that may be included in layer a is preferably 10% by mass or more and 70% by mass or less relative to the mass of the Ce-Zr composite oxide, more preferably 20% by mass or more and 60% by mass or less, and even more preferably 30% by mass or more and 50% by mass or less.

[0097] The Zr content of Zr in the Ce-Zr composite oxide that may be included in layer a, relative to the mass of the Ce-Zr composite oxide, is preferably 10% by mass or more and 80% by mass or less, more preferably 20% by mass or more and 75% by mass or less, and even more preferably 30% by mass or more and 70% by mass or less.

[0098] Layer a may contain Ce-Zr composite oxides that include rare earth elements other than Ce and / or alkaline earth metals such as barium (Ba), strontium (Sr), and calcium (Ca). Examples of rare earth elements other than Ce include scandium (Sc), yttrium (Y), lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). These rare earth elements may be added as oxides to the Ce-Zr composite oxides. The rare earth elements and / or alkaline earth metals contained in the Ce-Zr composite oxides may be one or more.

[0099] When layer a contains a Ce-Zr composite oxide, the content of the Ce-Zr composite oxide in layer a is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more, relative to the mass of layer a. Furthermore, the content of the Ce-Zr composite oxide in layer a is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less, relative to the mass of layer a.

[0100] The content of Ce-Zr composite oxides in layer a can be determined using conventional methods such as SEM-EDX. Specifically, as described below.

[0101] (1) For the sample obtained from layer a, use conventional methods such as SEM-EDX to perform elemental analysis, determine the types of constituent elements of the whole sample, and calculate the content (mass%) of each element.

[0102] (2) For the sample obtained from layer a, elemental mapping is performed using conventional methods such as SEM-EDX to determine the types of particles contained in the sample (e.g., Ce-Zr composite oxide particles and other particles as appropriate).

[0103] (3) For various particles, elemental analysis was performed on any selected number (e.g., 50) particles using SEM-EDX to determine the types of constituent elements of the particles and to calculate the content (mass%) of each element. For various particles, the average content (mass%) of each element was calculated.

[0104] (4) By creating and solving equations that represent the relationship between the content rate (mass%) of each element in the sample, the content rate (mass%) of each element in each particle and the content rate (mass%) of each particle in the sample, the content rate (mass%) of each particle in the sample is calculated and used as the content rate (mass%) of each particle in layer a.

[0105] Layer a can also contain OSC materials other than Ce-Zr composite oxides. As an OSC material, any metal oxide that produces a change in the valence of its constituent elements and has the ability to store oxygen under the working conditions of the exhaust gas purification catalyst can be used without particular restrictions. Examples include oxides of elements such as manganese (Mn), iron (Fe), and copper (Cu) that easily undergo valence state changes under the working conditions of the catalyst, as well as composite oxides containing these elements.

[0106] Layer a may also contain inorganic oxides other than the oxygen storage component as a carrier. Examples of inorganic oxides other than the oxygen storage component include oxide materials based on the aforementioned metal oxides other than the oxygen storage component, such as rare earth oxides like Al₂O₃, ZrO₂, SiO₂, TiO₂, and La₂O₃, zeolites (aluminosilicates), MgO, ZnO, and SnO₂, and oxide materials formed by combining these materials. Other examples include phosphates and borates of aluminum (Al), zirconium (Zr), silicon (Si), titanium (Ti), rare earth elements, magnesium (Mg), and zinc (Zn). The inorganic oxide other than the oxygen storage component is preferably a porous material. Examples of porous materials include those with a BET specific surface area of ​​30 m². 2 / g or more and 600m 2 Those below / g.

[0107] Furthermore, from the viewpoint of suppressing the decrease in catalyst activity and heat resistance caused by phosphorus poisoning, layer a may contain an alkaline earth metal compound. Preferred alkaline earth metal elements include Sr and Ba. Alkaline earth metal compounds may include oxides and carbonates.

[0108] Layer a may contain an adhesive. The adhesive may be selected from materials such as alumina, zirconium oxide, titanium dioxide, silicon dioxide, and cerium oxide.

[0109] The mass of layer a per unit volume of the portion of the substrate in which layer a is formed is preferably 20 g / L or more and 200 g / L or less, more preferably 50 g / L or more and 180 g / L or less, and even more preferably 70 g / L or more and 160 g / L or less.

[0110] [Layer b]

[0111] Layer b contains Pt.

[0112] Pt is the active component of the catalyst.

[0113] The mass content C of Pt in layer b Pt Preferably, it is 0.010% by mass or more, more preferably 0.050% by mass or more, and even more preferably 0.10% by mass or more. Additionally, C Pt Preferably, it is 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0114] C Pt It is the ratio (mass%) of the mass of Pt contained in layer b to the mass of layer b.

[0115] The Pt content in layer b can be determined using the same method as the Pd content in layer a.

[0116] In addition to Pt, layer b may also contain other catalyst active components. Commonly known catalyst active components other than Pt can be used, such as Rh, Pd, Au, Ag, Ir, Ru, and Os.

[0117] Layer b preferably does not contain any catalyst active components other than Pt, or if it does contain catalyst active components other than Pt, the proportion of such components is small. Specifically, based on the total mass of Pt and catalyst active components other than Pt contained in layer b, the mass of catalyst active components other than Pt contained in layer b is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less.

[0118] Layer b may further contain components other than those mentioned above.

[0119] For example, layer b may contain Ce-Zr composite oxides.

[0120] Ce-Zr composite oxides can function as OSC materials.

[0121] In addition, Ce-Zr composite oxides can function as support components for the above-mentioned catalyst active components.

[0122] Whether layer b contains Ce-Zr composite oxides can be determined in the same way as whether layer a contains Ce-Zr composite oxides.

[0123] The CeO2 content of Ce in the Ce-Zr composite oxide that layer b may contain is preferably 10% by mass or more and 70% by mass or less relative to the mass of the Ce-Zr composite oxide, more preferably 20% by mass or more and 60% by mass or less, and even more preferably 30% by mass or more and 50% by mass or less.

[0124] The Zr content of Zr in the Ce-Zr composite oxide that layer b may contain, converted to ZrO2, is preferably 10% by mass or more and 80% by mass or less relative to the mass of the Ce-Zr composite oxide, more preferably 20% by mass or more and 75% by mass or less, and even more preferably 30% by mass or more and 70% by mass or less.

[0125] Layer b may contain Ce-Zr composite oxides that include rare earth elements other than Ce and / or alkaline earth metal elements such as Ba, Sr, and Ca. Examples of rare earth elements other than Ce that are the same as those described in the description of layer a above can be cited.

[0126] When layer b contains a Ce-Zr composite oxide, the content of the Ce-Zr composite oxide in layer b relative to the mass of layer b is preferably 40% by mass or more, more preferably 50% by mass or more, and even more preferably 60% by mass or more. Furthermore, the content of the Ce-Zr composite oxide in layer b relative to the mass of layer b is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less.

[0127] The content of Ce-Zr composite oxides in layer b can be determined using the same method as the content of Ce-Zr composite oxides in layer a.

[0128] Layer b may also contain OSC materials other than Ce-Zr composite oxides. Examples of OSC materials are those identical to those described in the preceding description of layer a.

[0129] Layer b may also contain inorganic oxides other than oxygen storage components as a carrier. Examples of inorganic oxides other than oxygen storage components are those identical to those described in the previous description of layer a.

[0130] Furthermore, from the viewpoint of suppressing the decrease in catalyst activity and heat resistance caused by phosphorus poisoning, layer b may contain an alkaline earth metal compound. Preferred alkaline earth metal elements include Sr and Ba. Alkaline earth metal compounds may include oxides and carbonates.

[0131] Layer b may contain an adhesive. The adhesive may be selected from materials such as alumina, zirconium oxide, titanium dioxide, silicon dioxide, and cerium oxide.

[0132] The mass of layer b per unit volume of the portion of the substrate in which layer b is formed is preferably 20 g / L or more and 200 g / L or less, more preferably 50 g / L or more and 180 g / L or less, and even more preferably 70 g / L or more and 160 g / L or less.

[0133] [Layer c]

[0134] Layer c contains Rh, Ce-Zr composite oxides and Zr oxides.

[0135] Rh is the active component of the catalyst.

[0136] The mass content of Rh in layer c is C Rh Preferably, it is 0.0010% by mass or more, more preferably 0.0050% by mass or more, and even more preferably 0.010% by mass or more. Additionally, C Rh Preferably, it is 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less.

[0137] C Rh It is the ratio (mass%) of the mass of Rh contained in layer c to the mass of layer c.

[0138] The content of Rh in layer c can be determined using the same method as the content of Pd in ​​layer a.

[0139] In addition to Rh, layer c may also contain other catalyst active components. Commonly known catalyst active components other than Rh can be used, such as Pt, Pd, Au, Ag, Ir, Ru, and Os.

[0140] When layer c contains Pt, the content of Pt in layer c is preferably 10% by mass or more and 60% by mass or less, more preferably 20% by mass or more and 50% by mass or less, and even more preferably 30% by mass or more and 40% by mass or less, relative to the total mass of Rh and Pt contained in layer c.

[0141] Layer c contains Ce-Zr composite oxides.

[0142] Ce-Zr composite oxides can function as OSC materials.

[0143] In addition, Ce-Zr composite oxides can function as support components for the above-mentioned catalyst active components.

[0144] Whether layer c contains Ce-Zr composite oxides can be determined in the same way as whether layer a contains Ce-Zr composite oxides.

[0145] The Ce content of Ce in the Ce-Zr composite oxide contained in layer c, as converted from CeO2, is preferably 5% by mass or more and 40% by mass or less relative to the mass of the Ce-Zr composite oxide, more preferably 8% by mass or more and 30% by mass or less, and even more preferably 10% by mass or more and 20% by mass or less.

[0146] The Zr content of Zr in the Ce-Zr composite oxide contained in layer c, calculated as ZrO2, is preferably 20% by mass or more and 95% by mass or less relative to the mass of the Ce-Zr composite oxide, more preferably 30% by mass or more and 90% by mass or less, and even more preferably 40% by mass or more and 85% by mass or less.

[0147] The Ce-Zr composite oxide contained in layer c may contain rare earth elements other than Ce and / or alkaline earth metal elements such as Ba, Sr, and Ca. Examples of rare earth elements other than Ce that are the same as those described in the description of layer a above can be cited.

[0148] The content of Ce-Zr composite oxides in layer c is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, and particularly preferably 12% by mass or more, relative to the mass of layer c. Furthermore, the content of Ce-Zr composite oxides in layer c is preferably 90% by mass or less, more preferably 50% by mass or less, and even more preferably 20% by mass or less, relative to the mass of layer c.

[0149] The content of Ce-Zr composite oxides in layer c can be determined using the same method as the content of Ce-Zr composite oxides in layer a.

[0150] Layer c may also contain OSC materials other than Ce-Zr composite oxides. Examples of OSC materials include those described in the description of layer a. However, from the viewpoint of suppressing the decrease in activity caused by Rh oxidation, if layer c does not contain OSC materials other than Ce-Zr composite oxides, or if layer c does contain OSC materials other than Ce-Zr composite oxides, the content of OSC materials other than Ce-Zr composite oxides in layer c is preferably 50% by mass or less, more preferably 30% by mass or less, more preferably 20% by mass or less, more preferably 10% by mass or less, further preferably 5% by mass or more, and particularly preferably 1% by mass or less.

[0151] Layer c contains Zr-based oxides.

[0152] "Zr-based oxides" refer to oxides containing Zr, where the Zr content (ZrO2 equivalent) of Zr in the oxide is more than 50% by mass relative to the mass of the oxide, and the Ce content (CeO2 equivalent) of Ce in the oxide is less than 5% by mass relative to the mass of the oxide.

[0153] Zr-based oxides can function as support components for the above-mentioned catalyst active ingredients.

[0154] Whether layer c contains Zr-based oxides can be determined in the same way as whether layer a contains Ce-Zr-based composite oxides.

[0155] The Zr content of Zr in the Zr-based oxide contained in layer c, calculated as ZrO2, is preferably 50% by mass or more and 98% by mass or less relative to the mass of the Zr-based oxide, more preferably 60% by mass or more and 95% by mass or less, and even more preferably 70% by mass or more and 90% by mass or less.

[0156] The Ce content of Ce in the Zr oxide contained in layer c, calculated as CeO2, is preferably less than 3% by mass relative to the mass of the Zr oxide, and more preferably 0% by mass (i.e., Ce is not present).

[0157] The Zr-based oxides contained in layer c may include rare earth elements other than Ce and / or alkaline earth metal elements such as Ba, Sr, and Ca. Examples of rare earth elements other than Ce include Sc, Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0158] The mass content C of Zr-based oxides in layer c ZrO2 Preferably, it is 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, and particularly preferably 70% by mass or more. Additionally, C ZrO2 Preferably, it is 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less.

[0159] C ZrO2 It is the ratio (mass%) of the mass of Zr-based oxides contained in layer c to the mass of layer c.

[0160] The content of Zr-based oxides in layer c can be determined using the same method as the content of Ce-Zr-based composite oxides in the aforementioned layer a.

[0161] From the perspective of improving OSC capability and inhibiting the activity reduction caused by Rh oxidation, the mass M of Zr-based oxides contained in layer c is... ZrO2 The mass M of Ce-Zr composite oxides contained in layer c CZ The ratio, i.e., M ZrO2 / M CZ Preferably, the value is 1.0 or higher and 7.0 or lower, more preferably 1.5 or higher and 6.0 or lower, even more preferably 2.0 or higher and 6.0 or lower, particularly preferably 3.0 or higher and 6.0 or lower, and most preferably 4.0 or higher and 5.5 or lower.

[0162] In particular, M ZrO2 / M CZWhen the value is above 1.5, it can effectively inhibit the decrease in activity caused by the oxidation of Rh, M ZrO2 / M CZ When the value is below 6.0, OSC capabilities can be further improved.

[0163] Layer c may further contain components other than those mentioned above.

[0164] Layer c may also contain inorganic oxides other than oxygen storage components and Zr-based oxides as a support. Examples of inorganic oxides other than oxygen storage components and Zr-based oxides include Al2O3, which is the same as the inorganic oxides other than ZrO2 mentioned in the description of layer a above.

[0165] As mentioned above, Al2O3 has a high specific heat. Therefore, for the purpose of improving the NOx purification performance after the internal combustion engine is started, layer c does not contain Al, or if Al is contained, the content of Al converted to Al2O3 relative to the mass of layer c is preferably less than 30% by mass.

[0166] When layer c contains Al, the Al content converted from Al₂O₃ relative to the mass of layer c is more preferably 22% by mass or less, more preferably 15% by mass or less, and particularly preferably 13% by mass or less. It should be noted that when the binder contained in layer c contains Al, the Al content converted from Al₂O₃ in layer c also includes Al derived from the binder.

[0167] Furthermore, from the viewpoint of suppressing the decrease in catalyst activity and heat resistance caused by phosphorus poisoning, layer c may contain an alkaline earth metal compound. Preferred alkaline earth metal elements include Sr and Ba. Alkaline earth metal compounds include oxides and carbonates.

[0168] Layer c may contain an adhesive. The adhesive may be selected from materials such as alumina, zirconium oxide, titanium dioxide, silicon dioxide, and cerium oxide.

[0169] In layer c, at least a portion of Rh is loaded onto Zr-based oxides.

[0170] If Rh is loaded onto Zr-based oxides, the oxidation and reduced activity caused by Ce-Zr composite oxides can be suppressed. On the other hand, if Rh is loaded onto Ce-Zr composite oxides, the activity of Rh decreases, while the OSC capacity of Ce-Zr composite oxides is improved, thus improving the overall purification performance of the layer.

[0171] As can be seen from the above, the mass percentage of Rh loaded in the Zr oxide in layer c, based on the total mass of Rh contained in layer c, is preferably 50% or more and 90% or less, more preferably 60% or more and 87% or less, and even more preferably 70% or more and 85% or less.

[0172] The mass percentage of Rh loaded in the Ce-Zr composite oxide in layer c, based on the total mass of Rh contained in layer c, is preferably 10% by mass or more and 50% by mass or less, more preferably 13% by mass or more and 40% by mass or less, and even more preferably 15% by mass or more and 30% by mass or less.

[0173] The adjustment of the mass percentage of Rh loaded in the Zr-based oxide or Ce-Zr-based composite oxide in layer c, based on the total mass of Rh contained in layer c, can be achieved, for example, in the preparation of the slurry for forming layer c described later, by adjusting the mass ratio of Ce-Zr-based composite oxide to Zr-based oxide when mixing the Rh supply source, Ce-Zr-based composite oxide, Zr-based oxide, and solvent.

[0174] The mass of layer c per unit volume of the portion of the substrate in which layer c is formed is preferably 40 g / L or more and 160 g / L or less, more preferably 60 g / L or more and 140 g / L or less, and even more preferably 80 g / L or more and 120 g / L or less.

[0175] [C Pd / C Pt ]

[0176] In the waste gas purification catalyst of the present invention, the mass content C of Pd in ​​layer a is... Pd The mass content C of Pt in layer b Pt The ratio, i.e., C Pd / C Pt Greater than 1.

[0177] C Pd / C Pt Preferably, it is 1.5 or higher, more preferably 2.0 or higher, and even more preferably 2.5 or higher. Additionally, C Pd / C Pt It can be below 50.0, below 30.0, below 10.0, or below 5.0.

[0178] [C Pd / C ZrO2 ]

[0179] Pd has excellent purification effect on unsaturated hydrocarbons in NMHC, but from the point of view of cost reduction, it is preferable to use an amount corresponding to that of Zr-based oxides.

[0180] In the waste gas purification catalyst of the present invention, the mass content C of Pd in ​​layer a is... Pd The mass content of Zr-based oxides in layer c is C ZrO2 The ratio, i.e., C Pd / C ZrO2 Preferably, the value is 0.015 or more and 0.120 or less, more preferably 0.015 or more and 0.080 or less, and even more preferably 0.015 or more and 0.050 or less.

[0181] [C Pt / C ZrO2 ]

[0182] Pt exhibits excellent purification effects on saturated hydrocarbons in NMHC. However, Pt tends to aggregate easily when exposed to high temperatures; if excessive Pt is used, the distance between Pt particles decreases, making aggregation even easier. Therefore, it is preferable to use an amount of Pt appropriate for the Zr-based oxides.

[0183] In the waste gas purification catalyst of the present invention, the mass content C of Pt in layer b is... Pt The mass content of Zr-based oxides in layer c is C ZrO2 The ratio, i.e., C Pt / C ZrO2 Preferably, the value is 0.001 or higher and 0.008 or lower, more preferably 0.002 or higher and 0.007 or lower, and even more preferably 0.003 or higher and 0.006 or lower.

[0184] <Layer Composition of Exhaust Gas Purification Catalyst>

[0185] In the exhaust gas purification catalyst of the present invention, layer a is disposed upstream of the exhaust gas flow direction, closer to layer b (hereinafter, "upstream" and "downstream" refer to the upstream and downstream sides of the exhaust gas flow direction, respectively). Here, "layer a is disposed upstream of layer b" means that the upstream end of layer a is upstream of the upstream end of layer b, and the downstream end of layer a is upstream of the downstream end of layer b. Therefore, as described above, by disposing layer b, which contains Pt, downstream of the low-temperature exhaust gas flow direction, it is believed that the aggregation of Pt particles can be suppressed, and the reduction of active sites can be inhibited.

[0186] Furthermore, layer c is stacked with at least one of layers a and b, and in the stacked portion of layer c with at least one of layers a and b, layer c is positioned further away from the substrate than at least one of layers a and b. Therefore, in the stacked portion of layer c with at least one of layers a and b, layer c containing Rh comes into contact with the exhaust gas first. It is believed that by having layer c come into contact with the high-temperature exhaust gas first, layer c can heat up more rapidly, thereby improving the NOx purification performance of the internal combustion engine in this invention immediately after startup.

[0187] A schematic diagram of one embodiment of the waste gas purification catalyst of the present invention is shown in the figure. Figure 1 .

[0188] Figure 1 The exhaust gas purification catalyst 10 has a substrate S1 and a catalyst layer 1 disposed on the substrate S1.

[0189] Catalyst layer 1 comprises layer a (denoted by reference numeral a), layer b (denoted by reference numeral b), and layer c (denoted by reference numeral c).

[0190] Layer a is positioned upstream of layer b, closer to the direction of exhaust gas flow X.

[0191] Layer c is stacked with layers a and b.

[0192] In the stacked portion of layer c with layers a and b, layer c is located further away from the substrate S1 than layers a and b.

[0193] Figure 1 The exhaust gas purification catalyst 10 has layers a and b disposed on a single substrate, but in this invention, layers a and b may also be disposed on different substrates respectively. Figure 2 A schematic diagram illustrating one embodiment of the waste gas purification catalyst of the invention. Figure 2 The exhaust gas purification catalyst 11 has a substrate S1 and a substrate S2 as substrates. Substrate S1 and substrate S2 are different substrates. The exhaust gas purification catalyst 11 has a catalyst layer 2 composed of layer a and layer c1 disposed on substrate S1, and a catalyst layer 3 composed of layer b and layer c2 disposed on substrate S2. Layer c1 and layer c2 are both equivalent to layer c.

[0194] In the exhaust gas purification catalyst of the present invention, one of layer a and layer b can cover at least a portion of the other. Figure 3 A schematic diagram illustrating one embodiment of the waste gas purification catalyst of the present invention. Figure 3 In the exhaust gas purification catalyst 12, layer a covers a portion of layer b. It should be noted that, apart from layer a covering a portion of layer b, the exhaust gas purification catalyst 12 is... Figure 1 The same as the exhaust gas purification catalyst 10.

[0195] in addition, Figure 3 In the exhaust gas purification catalyst 12, layer a covers a portion of layer b, but in the exhaust gas purification catalyst of the present invention, layer b may also cover a portion of layer a.

[0196] Figure 1 In the exhaust gas purification catalyst 10, layer a and layer b are in contact. However, in the exhaust gas purification catalyst of the present invention, layer a and layer b can be in contact (layer a and layer b can be formed without gaps in the direction of exhaust gas flow) or they can be separated. As a technical solution for separating layer a and layer b, as described above... Figure 2 Like the exhaust gas purification catalyst 11, there are technical solutions where layer a and layer b are disposed on different substrates, and technical solutions where layer a and layer b are disposed separately on one substrate, etc. Figure 4 A schematic diagram illustrating one embodiment of the waste gas purification catalyst of the present invention. Figure 4 In the exhaust gas purification catalyst 13, layer a and layer b are disposed separately on a substrate. Layer c exists between layer a and layer b.

[0197] In the exhaust gas purification catalyst 13, there is a layer c between layer a and layer b. However, in the exhaust gas purification catalyst of the present invention, when layer a and layer b are separated, layer c may exist between layer a and layer b, other layers (layers other than layer a, layer b and layer c) may exist, or no layers may exist (vacuum may exist between layer a and layer b).

[0198] It should be noted that the components of the exhaust gas purification catalyst 13 other than those described above are the same as those described above. Figure 1 The same as the exhaust gas purification catalyst 10.

[0199] Figure 1 In the exhaust gas purification catalyst 10, layer c is stacked on the entirety of layer a and layer b. However, in the exhaust gas purification catalyst of the present invention, layer c may be stacked on at least a portion of layer a and layer b. Figures 5-8 These are schematic diagrams illustrating one embodiment of the waste gas purification catalyst of the present invention. Figure 5 In the exhaust gas purification catalyst 14, layer c is stacked in a portion of layer a. Figure 6 In the exhaust gas purification catalyst 15, layer c is stacked in a portion of layer b. Figure 7 In the waste gas purification catalyst 16, layer c is stacked in all of layer a and part of layer b. Figure 8 In the exhaust gas purification catalyst 17, layer c is stacked in all of layer b and a part of layer a.

[0200] It should be noted that the components of the exhaust gas purification catalysts 14-17 other than those described above are... Figure 1 The same as the exhaust gas purification catalyst 10.

[0201] In addition, in the exhaust gas purification catalyst of the present invention, layer c may also be stacked in a portion of layer a and a portion of layer b.

[0202] In the exhaust gas purification catalyst of the present invention, layer c is stacked with at least one of layers a and b. However, in the stacked portion, layer c may or may not be in contact with at least one of layers a and b. In the stacked portion, if layer c is not in contact with at least one of layers a and b, other layers (layers other than layers a, b, and c) may be present between layer c and at least one of layers a and b. Figure 9 A schematic diagram illustrating one embodiment of the waste gas purification catalyst of the present invention. Figure 9 In the exhaust gas purification catalyst 18, in the stacked portion, there is a layer d that serves as another layer between layer c and layers a and b. The exhaust gas purification catalyst 18 has a catalyst layer 4 composed of layers a, b, d, and c. It should be noted that, for example, layer d can be a layer containing Rh, but with a different Rh content than layer c.

[0203] It should be noted that the components of the exhaust gas purification catalyst 18 other than those described above are the same as those described above. Figure 1 The same as the exhaust gas purification catalyst 10.

[0204] In the waste gas purification catalyst of the present invention, the substrate may or may not be in contact with at least one of layer a and layer b. If the substrate is not in contact with at least one of layer a and layer b, other layers (layers other than layer a, layer b and layer c) may exist between the substrate and at least one of layer a and layer b. Figure 10 A schematic diagram illustrating one embodiment of the waste gas purification catalyst of the present invention. Figure 10 In the exhaust gas purification catalyst 19, a layer d is provided between the substrate S1 and the layer b as another layer. The exhaust gas purification catalyst 19 has a catalyst layer 5 composed of layers a and c disposed on the substrate S1, and a catalyst layer 6 composed of layers d and b disposed on the substrate S1. As a layer d, for example, a layer containing Pt with a different Pt content than layer b can be cited.

[0205] It should be noted that the components of the exhaust gas purification catalyst 19 other than those described above are the same as those described above. Figure 1 The same as the exhaust gas purification catalyst 10.

[0206] From the viewpoint of purifying saturated and unsaturated hydrocarbons, in each embodiment, when the length of the substrate is set to 100%, the length of layer a is preferably 10% or more and 60% or less, more preferably 20% or more and 50% or less, and even more preferably 30% or more and 40% or less. From the viewpoint of purifying saturated and unsaturated hydrocarbons, in each embodiment, when the length of the substrate is set to 100%, the length of layer b is preferably 40% or more and 90% or less, more preferably 50% or more and 80% or less, and even more preferably 60% or more and 70% or less. From the viewpoint of NOx purification, in each embodiment, when the length of the substrate is set to 100%, the length of layer c is preferably 60% or more, more preferably 70% or more, and even more preferably 80% or more. The upper limit is 100% or less. It should be noted that the length of the substrate or catalyst layer refers to the dimension of the substrate or catalyst layer along the flow direction X of the exhaust gas. In addition, the above-mentioned substrate length is as follows: Figure 2 When different substrates are shown, it refers to the total length of each substrate.

[0207] The exhaust gas purification catalyst of the present invention, as an exhaust gas purification catalyst for internal combustion engines, can efficiently purify NOx and NMHC. Therefore, it is possible to provide an exhaust gas purification system that introduces exhaust gas from the internal combustion engine into the exhaust gas purification catalyst in the exhaust path connected to the internal combustion engine without passing through other exhaust gas purification catalysts. It should be noted that examples of internal combustion engines that emit NOx and NMHC include gasoline engines, engines fueled by compressed natural gas, and engines fueled by gasoline (flexible fuel) containing any amount of ethanol.

[0208] <Catalyst Manufacturing>

[0209] The exhaust gas catalyst of the present invention can be manufactured by forming layers a and b on a substrate, and forming layer c on at least one of layers a and b. The mass content C of Pd contained in layer a is specified as follows: Pd The mass content C of Pt in layer b Pt The ratio, i.e., C Pd / C Pt Adjust in ways greater than 1.

[0210] Layer a can be formed as follows: a slurry for forming layer a is prepared by mixing a Pd supply source (e.g., Pd nitrate, ammonium complex salt, acetate, chloride, etc.) and other components (e.g., OSC materials such as Ce-Zr composite oxides, inorganic oxides other than OSC materials, binders, solvents, etc.) as appropriate; the slurry for forming layer a is coated on a substrate and then dried and fired.

[0211] Layer b can be formed as follows: a slurry for forming layer b is prepared by mixing a Pt supply source (e.g., Pt nitrate, ammonium complex salt, acetate, chloride, etc.) and other components (e.g., OSC materials such as Ce-Zr composite oxides, inorganic oxides other than OSC materials, binders, solvents, etc.) as appropriate; the slurry for forming layer b is applied to a substrate and then dried and fired.

[0212] Layer c can be formed as follows: a slurry for forming layer c is prepared by mixing a source of Rh (e.g., nitrate, ammonium complex salt, acetate, chloride, etc. of Rh), Ce-Zr composite oxide, Zr oxide, and other components as appropriate (e.g., OSC material other than Ce-Zr composite oxide, inorganic oxide other than OSC material, binder, solvent, etc.), the slurry for forming layer c is applied to at least one of layer a and layer b, and then dried and fired.

[0213] Example

[0214] Next, the embodiments of the present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples.

[0215] [Example 1]

[0216] (1) Preparation of slurry for layer a formation

[0217] Add 1.2 parts by mass of palladium nitrate aqueous solution (based on Pd metal conversion), 70.4 parts by mass of Ce-Zr composite oxide (Ce content of CeO2 conversion: 40% by mass, Zr content of ZrO2 conversion: 50% by mass, and oxide content of one or more rare earth elements other than Ce conversion: 10% by mass) to pure water, 14.2 parts by mass of La2O3 modified alumina (La2O3 content: 1% by mass), 6.1 parts by mass of barium hydroxide (based on oxide conversion), and 8.1 parts by mass of binder containing alumina sol (Al2O3 content in solid component: 50% by mass) to pure water, mix and stir to prepare a slurry for forming layer a.

[0218] (2) Preparation of slurry for layer b formation

[0219] Add 0.4 parts by mass of dinitrosodiammineplatinum solution (based on Pt metal conversion), 70.4 parts by mass of Ce-Zr composite oxide (Ce content of CeO2 conversion: 40% by mass, Zr content of ZrO2 conversion: 50% by mass, and oxide content of one or more rare earth elements other than Ce conversion: 10% by mass) to pure water, 15.0 parts by mass of La2O3 modified alumina (La2O3 content: 1% by mass), 6.1 parts by mass of barium hydroxide (based on oxide conversion), and 8.1 parts by mass of binder containing alumina sol (Al2O3 content in solids conversion: 12.5% ​​by mass) to pure water, mix and stir to prepare a slurry for forming layer b.

[0220] (3) Formation of layer a and layer b

[0221] As a flow-through substrate, a cordierite honeycomb porous substrate (manufactured by NGK Corporation, axial length: 80 mm, outer diameter: 93 mm, volume: 0.54 L, compartment density: 900 compartments / inch) with axially extending compartments divided by partition walls with a thickness of 50-70 µm was prepared. 2 ).

[0222] The portion of the flowable substrate from the end on the upstream side of the exhaust gas flow direction X to a position of 30 mm is impregnated in the slurry for forming layer a, and the slurry for forming layer a is coated on the upstream side of the flowable substrate.

[0223] Next, the portion of the flowable substrate impregnated in the slurry for forming layer b, from the end on the downstream side of the exhaust gas flow direction X to a position of 50 mm, is coated with the slurry for forming layer b on the downstream side of the flowable substrate.

[0224] Next, the flow-through substrate coated with slurry for forming layer a and slurry for forming layer b is dried at 90°C and then fired at 450°C. In this way, layers a and b are formed seamlessly on the flow-through substrate in the direction of exhaust gas flow X. The mass of layer a per unit volume (washcoat) of the portion of the flow-through substrate where layer a is formed is 127.8 g / L. The mass of layer b per unit volume (washcoat) of the portion of the flow-through substrate where layer b is formed is 127.8 g / L. It should be noted that the washcoat refers to the mass of the catalyst layer after firing.

[0225] (4) Preparation of slurry for layer c formation

[0226] Add the following to pure water: 0.1 parts by mass of dinitrosodiammineplatinum solution (based on Pt metal conversion), 0.2 parts by mass of rhodium nitrate aqueous solution (based on Rh metal conversion), 15.0 parts by mass of Ce-Zr composite oxide (Ce content converted to CeO2: 15% by mass, Zr content converted to ZrO2: 70% by mass, and content converted to oxides of one or more rare earth elements other than Ce: 15% by mass), and 74.4 parts by mass of Zr oxide. (Ce content converted to CeO2: 0% by mass, Zr content converted to ZrO2: 83% by mass, content converted to oxides of one or more rare earth elements other than Ce: 17% by mass), 0.3 parts by mass of neodymium nitrate (based on oxide conversion), and 10 parts by mass of a binder containing alumina sol (Al2O3 content in solids: 100% by mass) are mixed and stirred to prepare a slurry for forming layer c. It should be noted that in the slurry for forming layer c, based on the mass of the fired layer c (100% by mass), it contains 10.0% by mass of Al (based on Al2O3 conversion).

[0227] (5) Formation of layer c

[0228] The flowable substrate having layers a and b is impregnated in a slurry for forming layer c, and the slurry for forming layer c is coated on the flowable substrate having layers a and b.

[0229] Next, the flowable substrate coated with the slurry for forming layer c is dried at 90°C and then fired at 450°C. Layer c is formed on layers a and b in this manner. The mass of the upper catalyst layer per unit volume (coating loading) of the portion of the substrate where layer c is formed is 100 g / L. It should be noted that the coating loading refers to the mass of the catalyst layer after firing.

[0230] As described above, the exhaust gas purification catalyst of Example 1 is manufactured having a flowable substrate, a layer a disposed on the upstream side of the flowable substrate, a layer b disposed on the downstream side of the flowable substrate, and a layer c disposed on the upper side of layers a and b.

[0231] Schematic diagram of the exhaust gas purification catalyst in Example 1 and Figure 1 The same as the exhaust gas purification catalyst 10.

[0232] Hereinafter, layer a and the layer located at the position corresponding to layer a in the exhaust gas purification catalysts of the examples and comparative examples will also be referred to as the "lower upstream catalyst layer".

[0233] Layer b and the layer located at the position corresponding to layer b in the exhaust gas purification catalysts of the examples and comparative examples are also referred to as the "lower downstream catalyst layer".

[0234] Layer c and the layer located at the position corresponding to layer c in the exhaust gas purification catalysts of the examples and comparative examples are also referred to as the "upper catalyst layer".

[0235] In addition, the layer disposed between the substrate and the upper catalyst layer (layer c) in the exhaust gas purification catalyst of Comparative Example 1 is also referred to as the "lower catalyst layer".

[0236] In the exhaust gas purification catalyst of Example 1, the mass content C of Pd contained in layer a is... Pd The mass content C of Pt in layer b Pt The ratio, i.e., C Pd / C Pt It is version 3.0.

[0237] The mass M of Zr-based oxides contained in layer c ZrO2 The mass M of Ce-Zr composite oxides contained in layer c CZ The ratio, i.e., M ZrO2 / M CZ It is 5.0.

[0238] The mass content C of Pd in ​​layer a Pd The mass content of Zr-based oxides in layer c is C ZrO2 The ratio, i.e., C Pd / C ZrO2 It is 0.0161.

[0239] The mass content C of Pt in layer b Pt The mass content of Zr-based oxides in layer c is C ZrO2 The ratio, i.e., C Pt / C ZrO2 It is 0.0054.

[0240] Based on the total mass of Rh contained in layer c, the mass percentage of Rh loaded in the Zr-based oxides in layer c is 74.8% by mass.

[0241] The mass percentage of Rh loaded in the Ce-Zr composite oxide in layer c is 15.1% based on the total mass of Rh contained in layer c.

[0242] [Example 2]

[0243] (6) Preparation of slurry for layer c formation

[0244] Add the following to pure water: 0.1 parts by mass of dinitrosodiammineplatinum solution (based on Pt metal conversion), 0.2 parts by mass of rhodium nitrate aqueous solution (based on Rh metal conversion), 45.0 parts by mass of Ce-Zr composite oxide (Ce content converted to CeO2: 15% by mass, Zr content converted to ZrO2: 70% by mass, and content converted to oxides of one or more rare earth elements other than Ce: 15% by mass), and 44.4 parts by mass of Zr-based oxide. A slurry for forming layer c is prepared by mixing and stirring the following: Ce (CeO2 content: 0% by mass, ZrO2 content: 83% by mass, oxide content of one or more rare earth elements other than Ce: 17% by mass); 0.3 parts by mass of neodymium nitrate (oxide content); and 10 parts by mass of a binder containing alumina sol (Al2O3 content in solids: 100% by mass). It should be noted that in the slurry for forming layer c, based on the mass of the fired layer c (100% by mass), it contains 10.0% by mass of Al (Al2O3 content).

[0245] Except for using the slurry for forming layer c as described in (6) above, the exhaust gas purification catalyst of Example 2 was manufactured in the same manner as in Example 1.

[0246] In the exhaust gas purification catalyst of Example 2, the mass content C of Pd contained in layer a is... Pd The mass content C of Pt in layer b Pt The ratio, i.e., C Pd / C Pt It is version 3.0.

[0247] The mass M of Zr-based oxides contained in layer c ZrO2 The mass M of Ce-Zr oxides contained in layer c CZ The ratio, i.e., M ZrO2 / M CZ It is 1.0.

[0248] The mass content C of Pd in ​​layer a Pd The mass content of Zr-based oxides in layer c is C ZrO2 The ratio, i.e., C Pd / C ZrO2 It is 0.0270.

[0249] The mass content C of Pt in layer b Pt The mass content of Zr-based oxides in layer c is C ZrO2 The ratio, i.e., C Pt / C ZrO2 It is 0.0090.

[0250] The mass percentage of Rh loaded in the Zr oxides in layer c is 44.7% based on the total mass of Rh contained in layer c.

[0251] Based on the total mass of Rh contained in layer c, the mass percentage of Rh loaded in the Ce-Zr composite oxide in layer c is 45.3% by mass.

[0252] [Comparative Example 1]

[0253] (7) Preparation of slurry for forming the lower catalyst layer

[0254] Add 0.7 parts by mass of palladium nitrate aqueous solution (based on Pd metal conversion), 70.4 parts by mass of Ce-Zr composite oxide (Ce content of CeO2 conversion: 40% by mass, Zr content of ZrO2 conversion: 50% by mass, and oxide content of one or more rare earth elements other than Ce conversion: 10% by mass) to pure water, 14.7 parts by mass of La2O3 modified alumina (La2O3 content: 1% by mass), 6.1 parts by mass of barium hydroxide (based on oxide conversion), and 8.1 parts by mass of binder containing alumina sol (Al2O3 content in solid component: 50.0% by mass) to pure water, mix and stir to prepare a slurry for forming the lower catalyst layer.

[0255] (8) Formation of the lower catalyst layer

[0256] As a flowable substrate, a cordierite honeycomb porous substrate, the same as that in Example 1, was prepared.

[0257] The entire flow-through substrate was impregnated with a slurry for forming the lower catalyst layer, and then coated with the slurry. Next, the flow-through substrate coated with the slurry was dried at 90°C and then fired at 450°C. In this way, a lower catalyst layer was formed on the flow-through substrate in the direction of exhaust gas flow (X). That is, the lower catalyst layer of Comparative Example 1 consisted of only one layer, instead of two layers as in the Examples and other comparative examples, namely a lower upstream catalyst layer and a lower downstream catalyst layer. The mass of the lower catalyst layer per unit volume (coating loading) in the portion of the flow-through substrate where the lower catalyst layer was formed was 127.8 g / L.

[0258] Except for forming a lower catalyst layer to replace layers a and b as described in (7) and (8) above, the exhaust gas purification catalyst of Comparative Example 1 was manufactured in the same manner as in Example 1.

[0259] [Comparative Example 2]

[0260] (9) Preparation of slurry for forming the lower downstream catalyst layer

[0261] Add 0.4 parts by mass of palladium nitrate aqueous solution (based on Pd metal conversion), 70.4 parts by mass of Ce-Zr composite oxide (Ce content of CeO2 conversion: 40% by mass, Zr content of ZrO2 conversion: 50% by mass, and oxide content of one or more rare earth elements other than Ce conversion: 10% by mass) to pure water, 15.0 parts by mass of La2O3 modified alumina (La2O3 content: 1% by mass), 6.1 parts by mass of barium hydroxide (based on oxide conversion), and 8.1 parts by mass of binder containing alumina sol (Al2O3 content in solids: 12.5% ​​by mass) to pure water, mix and stir to prepare a slurry for forming the lower downstream catalyst layer.

[0262] Except that the slurry for forming the lower downstream catalyst layer manufactured in (9) above is used instead of the slurry for forming layer b, the exhaust gas purification catalyst of Comparative Example 2 is manufactured in the same manner as in Example 1.

[0263] In the exhaust gas purification catalyst of Comparative Example 2, the mass content C of Pd in ​​layer a is... Pd The mass content D of Pd in ​​the downstream catalyst layer below Pd The ratio, i.e., C Pd / D Pd It is version 3.0.

[0264] The mass content C of Pd in ​​layer a Pd The mass content of Zr-based oxides in layer c is C ZrO2 The ratio, i.e., C Pd / C ZrO2 It is 0.0161.

[0265] [Comparative Example 3]

[0266] (10) Preparation of slurry for forming upper catalyst layer

[0267] Add 0.1 parts by mass of dinitrosodiammineplatinum solution (based on Pt metal conversion), 0.2 parts by mass of rhodium nitrate aqueous solution (based on Rh metal conversion), 45.0 parts by mass of Ce-Zr composite oxide (Ce content of CeO2 conversion: 15% by mass, Zr content of ZrO2 conversion: 70% by mass, content of oxides of one or more rare earth elements other than Ce conversion: 15% by mass) to pure water, 44.4 parts by mass of La2O3 modified alumina (La2O3 content: 1% by mass), 0.3 parts by mass of neodymium nitrate (based on oxide conversion), and 10 parts by mass of binder containing alumina sol (Al2O3 content in solid component: 100% by mass) to pure water, mix and stir to prepare a slurry for forming an upper catalyst layer. It should be noted that in the slurry for forming the upper catalyst layer, based on the mass of the calcined upper catalyst layer (100% by mass), it contains 54.0% by mass of Al when converted to Al2O3.

[0268] Except that the slurry for forming the upper catalyst layer was used instead of the slurry for forming layer c, the exhaust gas purification catalyst of Comparative Example 3 was manufactured in the same manner as in Example 1.

[0269] In the exhaust gas purification catalyst of Comparative Example 3, the mass content C of Pd in ​​layer a is... Pd The mass content C of Pt in layer b Pt The ratio, i.e., C Pd / C Pt It is version 3.0.

[0270] The mass percentage of Rh loaded in the Zr oxides of layer c is 0, based on the total mass of Rh contained in layer c.

[0271] Based on the total mass of Rh contained in layer c, the mass percentage of Rh loaded in the Ce-Zr composite oxide in layer c is 45.3% by mass.

[0272] [Comparative Example 4]

[0273] (11) Preparation of slurry for forming upper catalyst layer

[0274] Add 0.1 parts by mass of dinitrosodiammineplatinum solution (based on Pt metal conversion), 0.2 parts by mass of rhodium nitrate aqueous solution (based on Rh metal conversion), 45.0 parts by mass of Zr oxides (Ce O2 content: 0% by mass, Zr O2 content: 83% by mass, oxide content of one or more rare earth elements other than Ce: 17% by mass), 44.4 parts by mass of La2O3 modified alumina (La2O3 content: 1% by mass), 0.3 parts by mass of neodymium nitrate (based on oxide conversion), and 10 parts by mass of binder containing alumina sol (Al2O3 content in solids: 100% by mass) to pure water, mix and stir to prepare a slurry for forming an upper catalyst layer. It should be noted that in the slurry for forming the upper catalyst layer, based on the mass of the calcined upper catalyst layer (100% by mass), it contains 54.0% by mass of Al when converted to Al2O3.

[0275] Except that the slurry for forming the upper catalyst layer was used instead of the slurry for forming layer c as described in (11) above, the exhaust gas purification catalyst of Comparative Example 4 was manufactured in the same manner as in Example 1.

[0276] In the exhaust gas purification catalyst of Comparative Example 4, the mass content C of Pd in ​​layer a is... Pd The mass content C of Pt in layer b Pt The ratio, i.e., C Pd / C Pt It is version 3.0.

[0277] The mass content C of Pd in ​​layer a Pd The mass content D of Zr-based oxides in the upper catalyst layer ZrO2 The ratio, i.e., C Pd / D ZrO2 It is 0.0267.

[0278] The mass content C of Pt in layer b Pt The mass content D of Zr-based oxides in the upper catalyst layer ZrO2 The ratio, i.e., C Pt / D ZrO2 It is 0.0089.

[0279] The mass percentage of Rh loaded in the Zr oxides of layer c is 45.3% based on the total mass of Rh contained in layer c.

[0280] The mass percentage of Rh loaded in the Ce-Zr composite oxide in layer c is 0, based on the total mass of Rh contained in layer c.

[0281] [Comparative Example 5]

[0282] (12) Preparation of slurry for forming upper catalyst layer

[0283] A slurry for forming the upper catalyst layer was prepared by adding 0.1 parts by mass of dinitrosodiammineplatinum solution (based on Pt metal conversion), 0.2 parts by mass of rhodium nitrate aqueous solution (based on Rh metal conversion), 89.4 parts by mass of Ce-Zr composite oxide (Ce O2 content: 15% by mass, Zr O2 content: 70% by mass, oxide content of one or more rare earth elements other than Ce: 15% by mass), 0.3 parts by mass of neodymium nitrate (based on oxide conversion), and 10 parts by mass of binder containing alumina sol (Al2O3 content in solids: 100% by mass) to pure water and mixing and stirring. It should be noted that the slurry for forming the upper catalyst layer contains 10.0% by mass of Al (based on Al2O3 conversion), with the mass of the calcined upper catalyst layer as the base (100% by mass).

[0284] Except that the slurry for forming the upper catalyst layer was used instead of the slurry for forming layer c, the exhaust gas purification catalyst of Comparative Example 5 was manufactured in the same manner as in Example 1.

[0285] In the exhaust gas purification catalyst of Comparative Example 5, the mass content C of Pd in ​​layer a is... Pd The mass content C of Pt in layer b Pt The ratio, i.e., C Pd / C Pt It is version 3.0.

[0286] The mass percentage of Rh loaded in the Zr oxides of layer c is 0, based on the total mass of Rh contained in layer c.

[0287] Based on the total mass of Rh contained in layer c, the mass percentage of Rh loaded in the Ce-Zr composite oxide in layer c is 89.9% by mass.

[0288] [Comparative Example 6]

[0289] (13) Preparation of slurry for forming upper catalyst layer

[0290] A slurry for forming the upper catalyst layer was prepared by adding 0.1 parts by mass of dinitrosodiammineplatinum solution (based on Pt metal conversion), 0.2 parts by mass of rhodium nitrate aqueous solution (based on Rh metal conversion), 89.4 parts by mass of Zr-based oxides (Ce O2 content: 0% by mass, Zr O2 content: 83% by mass, oxide content of one or more rare earth elements other than Ce: 17% by mass), 0.3 parts by mass of neodymium nitrate (based on oxide conversion), and 10 parts by mass of binder containing alumina sol (Al2O3 content in solids: 100% by mass) to pure water and mixing and stirring. It should be noted that the slurry for forming the upper catalyst layer contains 10.0% by mass of Al (based on Al2O3 conversion), based on the mass of the calcined upper catalyst layer (100% by mass).

[0291] Except that the slurry for forming the upper catalyst layer was used instead of the slurry for forming layer c as described in (13) above, the exhaust gas purification catalyst of Comparative Example 6 was manufactured in the same manner as in Example 1.

[0292] In the exhaust gas purification catalyst of Comparative Example 6, the mass content C of Pd in ​​layer a is... Pd The mass content C of Pt in layer b Pt The ratio, i.e., C Pd / C Pt It is version 3.0.

[0293] The mass content C of Pd in ​​layer a Pd The mass content D of Zr-based oxides in the upper catalyst layer ZrO2 The ratio, i.e., C Pd / D ZrO2 It is 0.0134.

[0294] The mass content C of Pt in layer b Pt The mass content D of Zr-based oxides in the upper catalyst layer ZrO2 The ratio, i.e., C Pt / D ZrO2 It is 0.0045.

[0295] The mass percentage of Rh loaded in the Zr oxides in layer c is 89.9% based on the total mass of Rh contained in layer c.

[0296] The mass percentage of Rh loaded in the Ce-Zr composite oxide in layer c is 0, based on the total mass of Rh contained in layer c.

[0297] (Durability treatment)

[0298] The exhaust gas purification catalysts of Examples 1-2 and Comparative Examples 1-6 were respectively mounted on exhaust pipes, and the exhaust pipes were installed in gasoline engines. The engine speed / torque was adjusted so that the catalyst temperature was 950°C, and a durability treatment was carried out for 50 hours.

[0299] (Evaluation of exhaust gas purification performance)

[0300] Vehicles equipped with durable-treated exhaust gas purification catalysts were operated under the operating conditions of the World Harmonized Exhaust Test Mode (WLTC). The emissions (emission values) of non-methane hydrocarbons (NMHC) and nitrogen oxides (NOx) in the exhaust gas after passing through the exhaust gas purification catalyst were measured, and the emissions of NMHC and NOx per unit distance traveled were calculated (g / km).

[0301] The vehicle used was a gasoline vehicle; the gasoline used was the fuel used in the certification test; and the exhaust gas measuring device used was a HORIBA, Ltd. device. Table 1 shows the NMHC emissions (g / km) and NOx emissions (g / km) per unit distance traveled at 100 seconds in the test mode. It should be noted that the NMHC and NOx emissions at 100 seconds in the test mode represent the NMHC and NOx emissions immediately after the internal combustion engine is started, respectively.

[0302] In Table 1, "precious metals contained in the lower downstream catalyst layer" refers to the precious metals that are included as active components of the catalyst in the lower downstream catalyst layer. It should be noted that the exhaust gas purification catalyst of Comparative Example 1 does not have a lower downstream catalyst layer, but for convenience, the precious metals contained in the lower catalyst layer are listed in Table 1.

[0303] In Table 1, “(A)” represents the ratio of the mass content of precious metals in the lower upstream catalyst layer to the mass content of precious metals in the lower downstream catalyst layer. It should be noted that the exhaust gas purification catalyst of Comparative Example 1 does not have a lower upstream catalyst layer and a lower downstream catalyst layer, therefore “(A)” cannot be calculated. However, the exhaust gas purification catalyst of Comparative Example 1 has a lower catalyst layer consisting of only one type of layer; therefore, for convenience, “(A)” for Comparative Example 1 is set to 1.0.

[0304] In Table 1, “(B)” indicates the mass content of Al contained in the upper catalyst layer, calculated based on the mass content of Al2O3 in the upper catalyst layer.

[0305] In Table 1, “(C)” represents the ratio of the mass of Zr-based oxides contained in the upper catalyst layer to the mass of Ce-Zr-based composite oxides contained in the upper catalyst layer.

[0306] In Table 1, “(D)” represents the ratio of the mass content of Pd in ​​the lower upstream catalyst layer to the mass content of Zr-based oxides in the upper catalyst layer.

[0307] The mass content of Zr-based oxides in the upper catalyst layer is the ratio (mass%) of the mass of Zr-based oxides in the upper catalyst layer to the mass of the upper catalyst layer.

[0308] The mass content of Pd in ​​the lower upstream catalyst layer is the ratio (mass%) of the mass of Pd in ​​the lower upstream catalyst layer to the mass of the lower upstream catalyst layer.

[0309] In Table 1, “(E)” represents the ratio of the mass content of Pt in the lower downstream catalyst layer to the mass content of Zr-based oxides in the upper catalyst layer.

[0310] In Table 1, “(F)” represents the NMHC emission per unit distance traveled at 100 seconds in the test mode (g / km).

[0311] In Table 1, “(G)” represents the NOx emission per unit distance traveled (g / km) at 100 seconds in the test mode.

[0312] In Table 1, “(H)” represents the mass percentage of Rh loaded in the Zr-based oxides in the upper catalyst layer, based on the total mass of Rh contained in the above catalyst layers.

[0313] In Table 1, “(I)” represents the mass percentage of Rh loaded in the Ce-Zr composite oxide in the upper catalyst layer, based on the total mass of Rh contained in the above catalyst layers.

[0314] [Table 1]

[0315]

[0316] As shown in Table 1, the exhaust gas purification catalysts of Examples 1 and 2 have small values ​​for both "(F)" and "(G)", which can balance the NOx purification performance and NMHC purification performance immediately after the internal combustion engine starts. In particular, it can be seen that compared with Example 2, Example 1 has even smaller values ​​for "(F)" and "(G)", and its NOx purification performance and NMHC purification performance immediately after the internal combustion engine starts are particularly excellent.

[0317] It can be seen that the exhaust gas purification catalysts of Comparative Examples 1 to 6 have larger values ​​of "(G)" compared to the Examples, resulting in lower NOx purification performance immediately after the internal combustion engine starts. Furthermore, it can be seen that the exhaust gas purification catalysts of Comparative Examples 1, 5, and 6 also have larger values ​​of "(F)" than the Examples, resulting in lower NMHC purification performance immediately after the internal combustion engine starts.

[0318] Industrial availability

[0319] According to the present invention, an exhaust gas purification catalyst is provided that can take into account both the NOx purification performance and the NMHC purification performance immediately after the internal combustion engine starts.

[0320] The present invention has been described in detail with reference to specific embodiments, but it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention.

[0321] This application is based on Japanese Patent Application No. 2023-204822 filed on December 4, 2023, the contents of which are incorporated herein by reference.

[0322] Explanation of reference numerals in the attached figures

[0323] S1 and S2 substrates

[0324] a layer a

[0325] layer b

[0326] c, c1, c2 layers

[0327] d Other layers

[0328] Catalyst layers 1, 2, 3, 4, 5, 6

[0329] 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 Waste gas purification catalysts

[0330] X indicates the direction of exhaust gas flow.

Claims

1. A waste gas purification catalyst, comprising a substrate and a catalyst layer disposed on the substrate, The catalyst layer comprises layer a, layer b, and layer c. Layer a is positioned upstream of the flow direction of the exhaust gas, closer to the surface than layer b. The layer c is stacked on top of at least one of the layers a and b. In the stacked portion of layer c with at least one of layers a and b, layer c is disposed at a position further away from the substrate than at least one of layers a and b. Layer a contains Pd. Layer b contains Pt. The mass content C of Pd contained in layer a Pd The mass content C of Pt contained in layer b Pt The ratio, i.e., C Pd / C Pt Greater than 1, Layer c comprises Rh, Ce-Zr composite oxides, and Zr oxides. In layer c, at least a portion of the Rh is loaded onto the Zr-based oxide.

2. The waste gas purification catalyst according to claim 1, wherein, The layer c does not contain Al, or if it does contain Al, the content of Al in Al2O3 relative to the mass of the layer c is less than 22% by mass.

3. The waste gas purification catalyst according to claim 1 or 2, wherein, The mass M of the Zr-based oxides contained in layer c ZrO2 The mass M of the Ce-Zr composite oxide contained in layer c CZ The ratio, i.e., M ZrO2 / M CZ It is between 1.5 and 6.

0.

4. The waste gas purification catalyst according to claim 1 or 2, wherein, The mass content C of Pd contained in layer a Pd The mass content C of Zr-based oxides contained in layer c ZrO2 The ratio, i.e., C Pd / C ZrO2 It is above 0.015 and below 0.

120.

5. The waste gas purification catalyst according to claim 1 or 2, wherein, The mass content C of Pt in layer b Pt The mass content C of Zr-based oxides contained in layer c ZrO2 The ratio, i.e., C Pt / C ZrO2 It is above 0.001 and below 0.008.

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