Catalyst composition for exhaust gas purification and method for producing the same and method for producing exhaust gas purifying catalyst

Abstract

To provide a catalyst composition for exhaust gas purification using a support-noble metal element composite containing a carrier and a noble metal element supported on the carrier, which can prevent degradation of exhaust gas purification performance after exposure to high temperature environments.SOLUTION: There is provided a catalyst composition for exhaust gas purification which comprises a support-noble metal element composite containing a carrier and a noble metal element supported on the carrier in which the dispersion degree of the noble metal element is 38% or more, wherein when the catalyst composition for exhaust gas purification is subjected to heat treatment at 1000°C for 15 hours under the atmosphere, the dispersion degree of the noble metal element after the heat treatment is 0.87% or more of the dispersion degree of the noble metal element before the heat treatment.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a catalyst composition for purifying exhaust gas, a method for producing the same, and a method for producing 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). In exhaust gas purification catalysts that purify and detoxify these harmful components, a carrier - noble metal element composite containing a carrier (for example, CeO 2 -ZrO 2 solid solution, alumina, etc.) and a noble metal element (for example, Pt, Pd, Rh, etc.) supported on the carrier is used (for example, Patent Document 1).

[0003] On the other hand, the carrier - noble metal element composite is also used in dehydrogenation reactions for converting alkanes to alkenes (for example, Patent Document 2).

[0004] Patent Document 2 discloses a technique for forming an alumina overcoat on a carrier - noble metal element composite using atomic layer deposition (ALD) in order to reduce coke formation during the dehydrogenation reaction for converting alkanes to alkenes.

[0005] The alumina overcoat suppresses the migration of the noble metal element and suppresses the growth of metal particles caused by the migration of the noble metal element. Since large metal particles are more likely to cause coke formation than small metal particles, coke formation can be suppressed by suppressing the growth of metal particles.

[0006] In addition, the alumina overcoat suppresses the arrival of the alkene generated by the dehydrogenation reaction at the noble metal element. Since one of the causes of coke formation is that the alkene reaches and polymerizes at the noble metal element, coke formation can be suppressed by suppressing the arrival of the alkene at the noble metal element.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] When the exhaust gas purification catalyst is exposed to a high-temperature environment, the noble metal elements move, sintering of the noble metal elements occurs, and the exhaust gas purification performance deteriorates.

[0009] Therefore, one aspect of the present invention is an exhaust gas purification catalyst composition using a carrier-noble metal element composite including a carrier and a noble metal element supported on the carrier, and an object thereof is to provide an exhaust gas purification catalyst composition capable of preventing a decrease in exhaust gas purification performance after exposure to a high-temperature environment and a method for producing the same.

[0010] Another aspect of the present invention is an exhaust gas purification catalyst using a carrier-noble metal element composite including a carrier and a noble metal element supported on the carrier, and an object thereof is to provide a method for producing an exhaust gas purification catalyst capable of preventing a decrease in exhaust gas purification performance after exposure to a high-temperature environment.

[0011] In the present invention, “high temperature” preferably means a temperature of 800° C. or higher, more preferably 900° C. or higher, and even more preferably 950° C. or higher.

Means for Solving the Problems

[0012] In order to solve the above problems, the present invention provides the following inventions. [1] An exhaust gas purification catalyst composition including a carrier-noble metal element composite including a carrier and a noble metal element supported on the carrier, wherein the dispersion degree of the noble metal element is 38% or more. When the exhaust gas purification catalyst composition is heat-treated at 1000 °C for 15 hours in air, the dispersion degree of the noble metal element after the heat treatment is 0.87% or more of the dispersion degree of the noble metal element before the heat treatment. The exhaust gas purification catalyst composition. [2] The exhaust gas purification catalyst composition according to [1], wherein the exhaust gas purification catalyst composition includes a coating film that coats the composite. [3] The exhaust gas purification catalyst composition according to [2], wherein the coating film contains an M-O bond (wherein M represents a metal element other than a noble metal element). [4] The exhaust gas purification catalyst composition according to [3], wherein the metal element represented by M is Al. [5] The following steps: (1A) A step of preparing a carrier-noble metal element composite including a carrier and a noble metal element supported on the carrier; and (2A) A step of forming a coating film that coats the composite by using atomic layer deposition, the coating film containing an M-O bond (wherein M represents a metal element other than a noble metal element). A method for producing an exhaust gas purification catalyst composition according to claim 1, including: In the method, the number of single atomic layer formation cycles performed in step 2A is 1 or more and 3 or less. [6] The production method according to [5], wherein the metal element represented by M is Al. [7] The following steps: (1B) A step of preparing a substrate having a gas flow path; (2B) A step of forming a first catalyst layer including a carrier-noble metal element composite including a carrier and a noble metal element supported on the carrier on the wall surface of the gas flow path; and (3B) A step of forming a coating film that coats the composite in the first catalyst layer by using atomic layer deposition, the coating film containing an M-O bond (wherein M represents a metal element other than a noble metal element). A method for producing an exhaust gas purification catalyst, including: In the method, the number of single atomic layer formation cycles performed in step 3B is 1 or more and 3 or less. The production method according to [7], wherein the metal element represented by [8] is Al. [9] After step 3B, the following step: (4B) A step of forming a second catalyst layer on the upper side of the first catalyst layer The production method according to [7] or [8], including this.

Advantages of the Invention

[0013] According to one aspect of the present invention, there is provided an exhaust gas purification catalyst composition using a carrier-noble metal element composite including a carrier and a noble metal element supported on the carrier, which can prevent a decrease in exhaust gas purification performance after being exposed to a high-temperature environment, and a method for producing the same.

[0014] Further, according to another aspect of the present invention, there is provided a method for producing an exhaust gas purification catalyst using a carrier-noble metal element composite including a carrier and a noble metal element supported on the carrier, which can prevent a decrease in exhaust gas purification performance after being exposed to a high-temperature environment.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0016] ≪Explanation of Terms≫ Hereinafter, the terms used in this specification will be explained. The following explanations apply to the whole of this specification unless otherwise specified.

[0017] The term "metal element" includes semi-metal elements such as Si and B.

[0018] <Rare earth element> The term "rare earth element" includes Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0019] <Noble metal element> The term "noble metal element" includes Pt, Pd, Rh, Ru, Os, Ir, Au, and Ag.

[0020] <Oxide> The meaning of the term "oxide" is as follows. Oxides of rare earth elements excluding Ce, Pr, and Tb are sesquioxides (Ln 2 O 3 , where Ln represents rare earth elements 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 3 the oxide of Zr is ZrO 2 the oxide of Si is SiO 2 the oxide of B is B 2 O 3 the oxide of Cr is Cr 2 O 3 the oxide of Mg is MgO, the oxide of Ca is CaO, the oxide of Sr is SrO, the oxide of Ba is BaO, the oxide of Fe is Fe 3 O 4 the oxide of Mn is Mn 3 O 4 the oxide of Ni is NiO, the oxide of Ti is TiO 2 the oxide of Zn is ZnO, the oxide of Sn is SnO 2 the oxide of V is V 2 O 5 the oxide of Co is Co 3 O 4 the oxide of Cu is CuO, the oxide of Ga is Ga 2 O 3For the oxide of Nb, it is Nb 2 O 5 For the oxide of Mo, it is MoO 3 For the oxide of Ru, it is RuO 2 For the oxide of In, it is In 2 O 3 For the oxide of Gd, it is Gd 2 O 3 For the oxide of Hf, it is HfO 2 For the oxide of Ta, it is Ta 2 O 5 For the oxide of W, it is WO 3 It means.

[0021] <Mass of metal element in terms of metal conversion> The term "mass of metal element in terms of metal conversion" means the mass of the metal obtained by assuming that the metal element exists as the metal composed of the metal element.

[0022] <Mass of metal element in terms of oxide conversion> The term "mass of metal element in terms of oxide conversion" means the mass of the oxide obtained by assuming that the metal element exists as the oxide of the metal element. The meaning of "oxide" of the metal element is as described above.

[0023] <Mass of catalyst composition or catalyst layer> The term "mass of catalyst composition or catalyst layer" classifies all metal elements contained in the catalyst composition or catalyst layer into noble metal elements and metal elements other than noble metal elements, determines the mass in terms of metal conversion for noble metal elements and the mass in terms of oxide conversion for metal elements other than noble metal elements, and means the sum of these. That is, the term "mass of catalyst composition or catalyst layer" means the calculated mass obtained by summing the mass of noble metal elements in terms of metal conversion contained in the catalyst composition or catalyst layer and the mass of metal elements other than noble metal elements in terms of oxide conversion contained in the catalyst composition or catalyst layer.

[0024] When information on raw materials (such as composition, amount, etc.) used in the production of the catalyst composition or catalyst layer is known, the mass of the catalyst composition or catalyst layer can be determined from the information on the raw materials used in the production of the catalyst composition or catalyst layer.

[0025] <Al-based oxide> The term "Al-based oxide" means an oxide containing Al, and among the metal elements constituting the oxide, the oxide in which the metal element with the largest content rate based on mass 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.

[0026] Al-based oxides are used as carriers for catalytic active components and are distinguished from alumina (alumina binder) used as a binder. Al-based oxides are, for example, particulate. From the viewpoint of improving the loading property of the catalytic active component, it is preferable that the Al-based oxide is porous.

[0027] It is preferable that the Al-based oxide has a particle size suitable for use as a carrier for the catalytic active component. The average particle size of the Al-based oxide is preferably 2 μm or more and 50 μm or less, more preferably 4 μm or more and 25 μm or less, and even more preferably 6 μm or more and 12 μm or less. The method for measuring the average particle size of the Al-based oxide is as follows. A sample containing the Al-based oxide is observed using a scanning electron microscope, and the defined-direction diameters (Feret diameters) of 100 Al-based oxides arbitrarily selected from the field of view are measured, and the average value is taken as the average particle size of the Al-based oxide.

[0028] Generally, Al-based oxides have higher heat resistance than other inorganic oxides. Therefore, by using an Al-based oxide as a carrier in a catalyst composition or a catalyst layer, the heat resistance of the catalyst composition or the catalyst layer is improved, and the exhaust gas purification performance of the catalyst composition or the catalyst layer is improved.

[0029] The Al-based oxide may contain one or more metal elements other than Al (hereinafter referred to as "additional element M1"). The additional element M1 can be selected from, for example, rare earth elements (e.g., Ce, Y, Pr, La, Nd, Sm, Eu, Gd, etc.), alkaline earth metal elements (e.g., Mg, Ca, Sr, Ba, etc.), B, Si, Zr, Cr, etc.

[0030] As the Al-based oxide, for example, alumina (Al 2 O 3 ), an oxide obtained by modifying the surface of alumina with an additional element M1, an oxide obtained by solid-solubilizing an additional element M1 in alumina, etc. may be mentioned. Examples of the Al-based oxide containing an additional element M1 include alumina-silica, alumina-zirconia, alumina-chromia, alumina-ceria, alumina-lanthana, etc.

[0031] 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 90% by mass or more, more preferably 95% by mass or more, still more preferably 98% by mass or more, based on the mass of the Al-based oxide. The upper limit is 100% by mass.

[0032] The content of Al in terms of Al 2 O 3 in the Al-based oxide is defined by the formula: content of Al in terms of Al 2 O 3 in the Al-based oxide = (mass of Al in terms of Al 2 O 3 in the Al-based oxide) / (mass of the Al-based oxide) × 100. "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.

[0033] From the viewpoint of improving the heat resistance of the Al-based oxide, the Al-based oxide preferably contains one or more rare earth elements. The rare earth element can be selected from, for example, La, Nd, Y, Pr, etc. In one embodiment, the Al-based oxide contains La. The Al-based oxide may contain one or more other rare earth elements in addition to La.

[0034] From the perspective of improving the heat resistance of the Al-based oxide, the content of the rare earth element in terms of oxide in the Al-based oxide is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.5% by mass or more and 5% by mass or less, still more preferably 1% by mass or more and 3% by mass or less, based on the mass of the Al-based oxide. The "content of the rare earth element in terms of oxide in the Al-based oxide" means the content of the oxide of the single rare earth element when the Al-based oxide contains one kind of rare earth element, and means the total content of the oxides of two or more kinds of rare earth elements when the Al-based oxide contains two or more kinds of rare earth elements.

[0035] The content of the rare earth element in terms of oxide in the Al-based oxide is defined by the formula: content of the rare earth element in terms of oxide in the Al-based oxide = (mass of the rare earth element in terms of oxide in the Al-based oxide) / (mass of the Al-based oxide) × 100. The meaning of the "mass of the Al-based oxide" and the meaning of the "oxide" of the metal element are as described above.

[0036] When the composition of the Al-based oxide is known, the content of each metal element in terms of oxide in the Al-based oxide can be determined from the composition of the Al-based oxide.

[0037] When the composition of the Al-based oxide is unknown, the content of each metal element in terms of oxide 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 are qualitatively identified (color-coded) by elemental mapping, and the content of each metal element in terms of oxide in the specified Al-based oxide particles can be determined by performing a composition analysis (elemental analysis) on the specified Al-based oxide particles.

[0038] <Ce-based oxide> The term "Ce-based oxide" refers to an oxide containing Ce, and among the metal elements constituting the oxide, the oxide in which the metal element with the largest content rate based on mass is Ce. However, those corresponding to Ce-Zr composite oxides shall not be regarded as Ce-based oxides. The Ce-Zr composite oxide will be described later.

[0039] Ce-based oxides are used as carriers for catalytic active components and are distinguished from ceria (ceria binder) used as a binder. Ce-based oxides are, for example, particulate. From the viewpoint of improving the supportability of catalytic active components, Ce-based oxides are preferably porous.

[0040] Ce-based oxides preferably have a particle size suitable for use as a carrier for catalytic active components. The average particle size of Ce-based oxides is preferably 1 μm or more and 30 μm or less, more preferably 2 μm or more and 15 μm or less, and even more preferably 3 μm or more and 8 μm or less. The measurement method for the average particle size of Ce-based oxides is the same as that for the average particle size of Al-based oxides.

[0041] Ce-based oxides have oxygen storage capacity (the ability to store oxygen when the oxygen concentration in the exhaust gas is high and release oxygen when the oxygen concentration in the exhaust gas is low), and can mitigate fluctuations in the oxygen concentration in the exhaust gas and expand the operating window of the catalytic active component. Therefore, by using Ce-based oxides as carriers in the catalyst composition or catalyst layer, the exhaust gas purification performance of the catalyst composition or catalyst layer is improved.

[0042] 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 (such as Y, Pr, La, Nd, Sm, Eu, Gd, etc.), alkaline earth metal elements (such as Mg, Ca, Sr, Ba, etc.), Fe, Mn, Ni, Zr, Al, etc.

[0043] Examples of Ce-based oxides include ceria (CeO 2) Examples include oxides obtained by modifying the surface of ceria with additional element M2, oxides obtained by dissolving additional element M2 in solid solution in ceria, and the like.

[0044] From the viewpoint of improving the oxygen storage capacity of the Ce-based oxide, the content of Ce in the Ce-based oxide in terms of CeO 2 is preferably 90% by mass or more, more preferably 95% by mass or more, still more preferably 99% by mass or more, based on the mass of the Ce-based oxide. The upper limit is 100% by mass.

[0045] The content of Ce in the Ce-based oxide in terms of CeO 2 is defined by the formula: content of Ce in terms of CeO in the Ce-based oxide 2 content = (mass of Ce in terms of CeO in the Ce-based oxide 2 in the Ce-based oxide) / (mass of the Ce-based oxide) × 100. "Mass of the Ce-based oxide" means the total mass of the metal element oxides obtained by assuming that the metal elements in the Ce-based oxide exist as oxides respectively. The meaning of "oxide" of the metal element is as described above.

[0046] The content of each metal element in the Ce-based oxide in terms of oxide can be determined in the same manner as the content of each metal element in the Al-based oxide in terms of oxide.

[0047] <Ce-Zr composite oxide> The term "Ce-Zr composite oxide" refers to a composite oxide containing Ce and Zr, wherein 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.

[0048] The content of Ce in the Ce-Zr composite oxide in terms of CeO 2 is defined by the formula: content of Ce in terms of CeO in the Ce-Zr composite oxide 2 content = (mass of Ce in terms of CeO in the Ce-Zr composite oxide 2Defined by (mass of conversion) / (mass of Ce-Zr composite oxide)×100, and the ZrO of Zr in the Ce-Zr composite oxide 2 The content rate of conversion is expressed by the formula: the ZrO of Zr in the Ce-Zr composite oxide 2 Content rate of conversion = (ZrO of Zr in the Ce-Zr composite oxide 2 mass of conversion) / (mass of Ce-Zr composite oxide)×100. "Mass of Ce-Zr composite oxide" means the total mass of 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.

[0049] The Ce-Zr composite oxide is used as a carrier for the catalytic active component. The Ce-Zr composite oxide is, for example, particulate. From the viewpoint of improving the supportability of the catalytic active component, the Ce-Zr composite oxide is preferably porous.

[0050] The Ce-Zr composite oxide preferably has a particle diameter suitable for use as a carrier for the catalytic active component. The average particle diameter of the Ce-Zr composite oxide is preferably 2 μm or more and 20 μm or less, more preferably 4 μm or more and 10 μm or less. The measurement method of the average particle diameter of the Ce-Zr composite oxide is the same as that of the Al-based oxide.

[0051] The Ce-Zr composite oxide has an oxygen storage capacity, which mitigates the fluctuation of the oxygen concentration in the exhaust gas and expands the operating window of the catalytic active component. Therefore, by using the Ce-Zr composite oxide as a carrier in the catalyst composition or the catalyst layer, the exhaust gas purification performance of the catalyst composition or the catalyst layer is improved.

[0052] In the Ce-Zr composite oxide, Ce and Zr may each form a solid solution phase (for example, a solid solution phase of CeO 2 and ZrO 2 etc.), or a single phase in the crystalline phase or the amorphous phase (for example, CeO 2 single phase and ZrO 2It may form a single layer, or may form both a solid solution phase and a single phase. However, at least a part of Ce and at least a part of Zr preferably form a solid solution phase, respectively.

[0053] The Ce-Zr composite oxide may contain one or more metal elements other than Ce and Zr (hereinafter referred to as "additional element M3"). The additional element M3 can be selected from, for example, rare earth elements other than Ce (for example, Y, Pr, La, Nd, Sm, Eu, Gd, etc.), alkaline earth metal elements (for example, Mg, Ca, Sr, Ba, etc.), Fe, Mn, Ni, Al, etc.

[0054] Examples of the Ce-Zr composite oxide include CeO 2 -ZrO 2 solid solution, CeO 2 -ZrO 2 oxide obtained by modifying the surface of the solid solution with additional element M3, CeO 2 -ZrO 2 oxides obtained by dissolving additional element M3 in the solid solution, and the like.

[0055] From the viewpoint of improving the oxygen storage capacity and heat resistance of the Ce-Zr composite oxide, the total content of Ce in terms of CeO 2 and the content of Zr in terms of ZrO 2 is preferably 70% by mass or more, more preferably 75% by mass or more, even more preferably 80% by mass or more, and even more preferably 85% by mass or more, based on the mass of the Ce-Zr composite oxide. The upper limit is 100% by mass.

[0056] The content of each metal element in the Ce-Zr composite oxide in terms of oxide can be determined in the same manner as the content of each metal element in the Al-based oxide in terms of oxide.

[0057] ≪Exhaust gas purification catalyst composition≫ The exhaust gas purification catalyst composition of the present invention (hereinafter referred to as "catalyst composition") contains a carrier-noble metal element composite.

[0058] <Support-noble metal element composite> The support-noble metal element composite includes a support and a noble metal element supported on the support.

[0059] From the viewpoint of improving the loadability of the noble metal element, the support is preferably porous.

[0060] The form of the support is not particularly limited as long as it can support the noble metal element. Examples of the form of the support include particulate, layered, etc. The particles may be primary particles or secondary particles. The secondary particles are agglomerated particles formed by agglomeration of primary particles. Examples of the shape of the primary particles include spherical, flaky, columnar, needle-like, polyhedral, irregular, etc. Spherical includes true spherical, ellipsoidal, etc. Flaky includes scaly, lamellar, flat, etc. Columnar includes cylindrical, elliptical columnar, polygonal columnar, etc., and also includes shapes in which a part of cylindrical, elliptical columnar, polygonal columnar, etc. is missing.

[0061] The support can be selected from, for example, inorganic oxides. The inorganic oxide may or may not have an oxygen storage capacity (OSC). The inorganic oxide used as the support 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.).

[0062] Examples of the inorganic oxide include oxides based on Al-based oxides, Ce-based oxides, Ce-Zr-based 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.

[0063] The noble metal element supported on the support may be composed of one kind of noble metal element or may be composed of two or more kinds of noble metal elements.

[0064] In the present invention, "supported on a carrier" means a state in which a noble metal element is physically or chemically adsorbed or held on the outer surface and / or the inner surface of pores of the carrier.

[0065] The fact that a noble metal element is supported on a carrier can be confirmed, for example, by using SEM-EDX or the like. Specifically, in the element mapping obtained by analyzing the catalyst composition by SEM-EDX, if the noble metal element and the carrier are present in the same region, it can be determined that the noble metal element is supported on the carrier.

[0066] From the viewpoint of enhancing the exhaust gas purification performance, the noble metal element is preferably selected from Pt, Pd, and Rh. The noble metal element exists in the form of a catalyst active component containing a noble metal element, such as 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., which can function as a catalyst active component. From the viewpoint of enhancing the exhaust gas purification performance, the catalyst active component containing a noble metal element is preferably in a particulate form.

[0067] The content of the carrier in the carrier-noble metal element composite can be appropriately adjusted in consideration of the balance between the exhaust gas purification performance and the cost, etc. The content of the carrier in the carrier-noble metal element composite is, based on the mass of the carrier-noble metal element composite, for example, 80% by mass or more and 99.99% by mass or less, preferably 95% by mass or more and 99.95% by mass or less, more preferably 97% by mass or more and 99.90% by mass or less.

[0068] The content of the carrier in the carrier-noble metal element composite is defined by the formula: content of the carrier in the carrier-noble metal element composite = (mass of the carrier in the carrier-noble metal element composite) / (mass of the carrier-noble metal element composite)×100.

[0069] The content rate of the noble metal element in terms of metal in the carrier-noble metal element composite can be appropriately adjusted in consideration of the balance between exhaust gas purification performance and cost, etc. The content rate of the noble metal element in terms of metal in the carrier-noble metal element composite is, based on the mass of the carrier-noble metal element composite, for example, 0.01% by mass or more and 20% by mass or less, preferably 0.05% by mass or more and 5% by mass or less, more preferably 0.10% by mass or more and 3% by mass or less. The "content rate of the noble metal element in terms of metal in the carrier-noble metal element composite" means the content rate of the one kind of noble metal element in terms of metal when one kind of noble metal element is supported on the carrier, and means the total content rate of the two or more kinds of noble metal elements in terms of metal when two or more kinds of noble metal elements are supported on the carrier.

[0070] The content rate of the noble metal element in terms of metal in the carrier-noble metal element composite is defined by the formula: content rate of the noble metal element in terms of metal in the carrier-noble metal element composite = (mass of the noble metal element in terms of metal in the carrier-noble metal element composite) / (mass of the carrier-noble metal element composite) × 100.

[0071] The content rate of the carrier-noble metal element composite in the catalyst composition can be appropriately adjusted in consideration of the balance between exhaust gas purification performance and cost, etc. The content rate of the carrier-noble metal element composite in the catalyst composition is, based on the mass of the catalyst composition, for example, 20% by mass or more, preferably 50% by mass or more, more preferably 80% by mass or more. The upper limit is 100% by mass.

[0072] The content rate of the carrier-noble metal element composite in the catalyst composition is defined by the formula: content rate of the carrier-noble metal element composite in the catalyst composition = (mass of the carrier-noble metal element composite in the catalyst composition) / (mass of the catalyst composition) × 100.

[0073] When information on the raw materials used in the production of the catalyst composition (for example, composition, amount, etc.) is known, the content rate of the carrier in the carrier-noble metal element composite, the content rate of the noble metal element in terms of metal in the carrier-noble metal element composite, and the content rate of the carrier-noble metal element composite in the catalyst composition can be determined from the information on the raw materials used in the production of the catalyst composition.

[0074] When information on the raw materials used in the production of the catalyst composition is unknown, the content rate of the carrier in the catalyst composition and the content rate in terms of metal of the noble metal element in the catalyst composition are determined, and based on these, the content rate of the carrier in the carrier-noble metal element composite, the content rate in terms of metal of the noble metal element in the carrier-noble metal element composite, and the content rate of the carrier-noble metal element composite in the catalyst composition can be determined. Specifically, the content rate of the carrier in the carrier-noble metal element composite is calculated from the formula: (content rate of the carrier in the catalyst composition) / (content rate of the carrier in the catalyst composition + content rate in terms of metal of the noble metal element in the catalyst composition) × 100, the content rate in terms of metal of the noble metal element in the carrier-noble metal element composite is calculated from the formula: (content rate in terms of metal of the noble metal element in the catalyst composition) / (content rate of the carrier in the catalyst composition + content rate in terms of metal of the noble metal element in the catalyst composition) × 100, and the content rate of the carrier-noble metal element composite in the catalyst composition can be determined from the formula: (content rate of the carrier in the catalyst composition) + (content rate in terms of metal of the noble metal element in the catalyst composition).

[0075] The content rate of the carrier in the catalyst composition can be determined by a conventional method such as SEM-EDX. Specifically, it is as follows.

[0076] (1) For a sample obtained from the catalyst composition, elemental analysis is performed using a conventional method such as SEM-EDX to identify the types of constituent elements of the entire sample and to determine the content rate (mass%) in terms of oxide of each identified metal element. (2) For a sample obtained from the catalyst composition, elemental mapping is performed using a conventional method such as SEM-EDX to identify the types of carrier particles contained in the sample (for example, Al-based oxides, Ce-based oxides, Ce-Zr-based composite oxides, etc.). (3) For each type of carrier particle, a plurality of arbitrarily selected (for example, 50) carrier particles are subjected to elemental analysis by SEM-EDX to identify the types of constituent elements of the carrier particles and to determine the content rate (mass%) in terms of oxide of each identified metal element. For each type of carrier particle, the average value of the content rate (mass%) in terms of oxide of each metal element is determined, and this is taken as the content rate (mass%) in terms of oxide of each metal element in each type of particle. (4) By creating and solving an equation representing the relationship between the content rate (mass %) of each metal element in terms of its oxide in the sample, the content rate (mass %) of each metal element in terms of its oxide in each type of carrier particle, and the content rate (mass %) of each type of carrier particle in the sample, the content rate (mass %) of each type of carrier particle in the sample is calculated, and this is taken as the content rate (mass %) of each type of carrier particle in the catalyst composition.

[0077] The content rate of the noble metal element in the catalyst composition in terms of the metal can be calculated from the mass of the noble metal element in terms of the metal in the melt obtained by dissolving the catalyst composition by alkali fusion or the like and measuring it by inductively coupled plasma atomic emission spectrometry (ICP - AES).

[0078] <Dispersion degree of noble metal element> The dispersion degree of the noble metal element in the catalyst composition (the dispersion degree of the noble metal element before heat treatment) is 38% or more. When the catalyst composition is heat - treated at 1000 °C for 15 hours in air, the dispersion degree of the noble metal element after heat treatment is 0.87% or more of the dispersion degree of the noble metal element before heat treatment. The fact that the dispersion degrees of the noble metal element before and after heat treatment are within the above ranges means that the migration and sintering of the noble metal element that may occur due to the exposure of the catalyst composition to a high - temperature environment are prevented. Therefore, according to the catalyst composition in which the dispersion degrees of the noble metal element before and after heat treatment are within the above ranges, it is possible to prevent the deterioration of the exhaust gas purification performance of the catalyst composition after being exposed to a high - temperature environment.

[0079] From the viewpoint of more effectively preventing the deterioration of the exhaust gas purification performance of the catalyst composition after being exposed to a high - temperature environment, the dispersion degree of the noble metal element before heat treatment is preferably 39% or more, more preferably 40% or more, and even more preferably 41% or more. The upper limit is not particularly limited. The upper limit may be 80% or less, or 70% or less, or 60% or less. These upper limits may be combined with any of the above - mentioned lower limits respectively.

[0080] From the perspective of more effectively preventing the degradation of the exhaust gas purification performance of the catalyst composition after exposure to a high-temperature environment, the dispersion degree of the noble metal element after heat treatment is preferably 0.90% or more, more preferably 0.95% or more, and even more preferably 1.0% or more of the dispersion degree of the noble metal element before heat treatment. The upper limit is not particularly limited. The upper limit may be 50% or less, may be 40% or less, or may be 30% or less. These upper limits may be combined with any of the above-mentioned lower limits respectively.

[0081] The dispersion degree of the noble metal element before heat treatment can be measured by the CO pulse method using a sample obtained from the catalyst composition after pretreatment and a commercially available metal dispersion degree measuring device (for example, BELMETAL3 manufactured by Microtrac BEL Co., Ltd.). The dispersion degree of the noble metal element after heat treatment can be measured in the same manner as the dispersion degree of the noble metal element before heat treatment, except that a sample obtained from the catalyst composition is heat-treated at 1000 °C for 15 hours in the atmosphere, then pretreated, and the pretreated sample is used.

[0082] In the pretreatment of the sample, the sample is subjected to an oxidation treatment at 400 °C with a mixed gas of O 2 and He, then subjected to a reduction treatment with H 2 gas, and then cooled to 50 °C. In order to avoid changes in the measured value of the dispersion degree due to substances other than the noble metal element contained in the sample adsorbing CO, after cooling, a masking treatment with CO 2 is carried out. After the masking treatment, measurement by the CO pulse method is performed.

[0083] The CO pulse method is a method of calculating the dispersion degree of the noble metal element in the sample from the total gas consumption by introducing CO gas in a pulsed manner into the sample until saturation is reached. The analysis of the CO pulse adsorption measurement results can be carried out in the automatic analysis mode of the waveform analysis software "ChemMaster" attached to the device. The analysis can be carried out in accordance with the "ChemMaster Waveform Analysis Software Instruction Manual (Ver. 1.3) Microtrac BEL Co., Ltd.".

[0084] The dispersion degree of the noble metal element is the ratio of the number B of noble metal atoms exposed on the surface of the sample (including the inner surface and the outer surface; the same applies hereinafter) to the total number A of noble metal atoms in the sample, and can be calculated from the following formula. Dispersion degree of noble metal element (%) = (B / A) × 100

[0085] The number B of noble metal atoms exposed on the surface of the sample is calculated from the CO adsorption amount measured by the CO pulse method on the premise that the noble metal atoms exposed on the surface of the sample and CO are adsorbed in a 1:1 ratio.

[0086] <Coating film> The catalyst composition preferably includes a coating film that coats the carrier-noble metal element composite. By coating the carrier-noble metal element composite with the coating film, the dispersion degree of the noble metal element before and after the above-described desired heat treatment can be realized. Thereby, the movement and sintering of the noble metal element that may occur due to the exposure of the catalyst composition to a high-temperature environment can be prevented, and the decrease in the exhaust gas purification performance of the catalyst composition after being exposed to a high-temperature environment can be prevented.

[0087] The coating film coats at least a part of the surface of the carrier-noble metal element composite. The "at least a part of the surface of the carrier-noble metal element composite" coated by the coating film includes at least a part of the noble metal element present on the surface of the carrier-noble metal element composite and at least a part of the carrier portion present on the surface of the carrier-noble metal element composite. That is, the coating film coats at least a part of the noble metal element present on the surface of the carrier-noble metal element composite and at least a part of the carrier portion present on the surface of the carrier-noble metal element composite.

[0088] In the present invention, the "surface of the carrier-noble metal element composite" includes the inner surface and the outer surface of the carrier-noble metal element composite. The inner surface of the carrier-noble metal element composite includes the inner surface of the pores existing inside the carrier-noble metal element composite (that is, not exposed on the outer surface of the carrier-noble metal element composite), and the outer surface of the carrier-noble metal element composite includes the inner surface of the pores exposed on the outer surface of the carrier-noble metal element composite.

[0089] The coating film preferably covers at least a part of the outer surface of the carrier-noble metal element composite. The "at least a part of the outer surface of the carrier-noble metal element composite" covered by the coating film includes at least a part of the noble metal element present on the outer surface of the carrier-noble metal element composite and at least a part of the carrier portion present on the outer surface of the carrier-noble metal element composite. That is, the coating film preferably covers at least a part of the noble metal element present on the outer surface of the carrier-noble metal element composite and at least a part of the carrier portion present on the outer surface of the carrier-noble metal element composite.

[0090] In addition to at least a part of the outer surface of the carrier-noble metal element composite, the coating film may cover at least a part of the inner surface of the carrier-noble metal element composite. The "at least a part of the inner surface of the carrier-noble metal element composite" covered by the coating film includes at least a part of the noble metal element present on the inner surface of the carrier-noble metal element composite and at least a part of the carrier portion present on the inner surface of the carrier-noble metal element composite. That is, in addition to at least a part of the noble metal element present on the outer surface of the carrier-noble metal element composite and at least a part of the carrier portion present on the outer surface of the carrier-noble metal element composite, the coating film may cover at least a part of the noble metal element present on the inner surface of the carrier-noble metal element composite and at least a part of the carrier portion present on the inner surface of the carrier-noble metal element composite.

[0091] From the viewpoint of more effectively realizing the dispersion degree of the noble metal element before and after the above-mentioned desired heat treatment, the coating film preferably contains an M-O bond. Examples of the coating film containing an M-O bond include a metal oxide film. The coating film may contain an M-OH bond in addition to the M-O bond. Examples of the coating film containing an M-O bond and an M-OH bond include a metal oxide film having a hydroxyl group.

[0092] M represents a metal element other than a noble metal element. M can be selected from, for example, Mg, Al, Si, Ti, V, Co, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ru, In, Sn, Gd, Hf, Ta, W, etc. In one embodiment, M is Al.

[0093] Examples of the metal oxide film include, for example, MgO film, Al 2 O 3 film, SiO 2 film, TiO 2 film, V 2 O 5 film, Co 3 O 4 film, NiO film, CuO film, ZnO film, Ga 2 O 3 film, ZrO 2 film, Nb 2 O 5 film, MoO 3 film, RuO 2 film, In 2 O 3 film, SnO 2 film, Gd 2 O 3 film, HfO 2 film, Ta 2 O 5 film, WO 3 film, etc.

[0094] Examples of the metal oxide film having a hydroxyl group include, for example, MgO film having a hydroxyl group, Al 2 O 3 film having a hydroxyl group, SiO 2 film having a hydroxyl group, TiO 2 film having a hydroxyl group, V 2 O 5 film having a hydroxyl group, Co 3 O 4 film having a hydroxyl group, NiO film having a hydroxyl group, CuO film having a hydroxyl group, ZnO film having a hydroxyl group, Ga 2 O 3 film having a hydroxyl group, ZrO 2 film having a hydroxyl group, Nb 2 O 5 film having a hydroxyl group, MoO 3 film having a hydroxyl group, RuO2 A film of In having a hydroxyl group 2 O 3 A film of SnO having a hydroxyl group 2 A film of Gd having a hydroxyl group 2 O 3 A film of HfO having a hydroxyl group 2 A film of Ta having a hydroxyl group 2 O 5 A film of WO having a hydroxyl group 3 Examples thereof include films and the like.

[0095] The coating film containing an M - O bond can be formed by atomic layer deposition. The atomic layer deposition method will be described later.

[0096] ≪Method for Producing Exhaust Gas Purification Catalyst Composition≫ The catalyst composition of the present invention comprises the following steps: (1A) A step of preparing a carrier - noble metal element composite containing a carrier and a noble metal element supported on the carrier; and (2A) A step of forming a coating film that coats the carrier - noble metal element composite using atomic layer deposition, the coating film containing an M - O bond (wherein M represents a metal element other than the noble metal element). It can be produced by a method including these steps.

[0097] After step 2A, the following step: (3A) A step of firing the carrier - noble metal element composite on which the coating film is formed may be carried out.

[0098] Substances (such as source gases, oxidants, etc.) used for carrying out atomic layer deposition may remain in the pores of the carrier - noble metal element composite on which the coating film is formed. Firing can surely remove the substances that may remain in the pores. The firing temperature is, for example, 300°C or higher and 700°C or lower, and the firing time is, for example, 1 hour or longer and 10 hours or shorter. Firing can be carried out, for example, in an air atmosphere.

[0099] <Step 1A> In step 1A, a carrier - noble metal element composite is prepared.

[0100] The carrier-noble metal element composite can be prepared, for example, by impregnating a carrier with an aqueous solution containing a salt of a noble metal element and then evaporating to dryness. Examples of the salt of the noble metal element include nitrates, ammine complex salts, acetates, chlorides, and the like. After evaporation to dryness, the obtained dried product may be calcined. The calcination temperature is, for example, 450°C or higher and 550°C or lower, and the calcination time is, for example, 0.5 hour or longer and 3 hours or shorter. The calcination can be carried out, for example, in an air atmosphere.

[0101] <Step 2A> In Step 2A, a coating film that coats the carrier-noble metal element composite and contains an M-O bond (wherein M represents a metal element other than the noble metal element) is formed using an atomic layer deposition method.

[0102] The atomic layer deposition method (ALD: Atomic layer deposition) is a well-known thin film formation technique. In Step 2A, the atomic layer deposition method can be carried out according to a conventional method, except that the number of single atomic layer formation cycles is set to 1 or more and 3 or less. Hereinafter, the single atomic layer formation cycle is referred to as an "ALD cycle".

[0103] If the number of ALD cycles carried out in Step 2A is 4 or more, a thick and dense coating film is formed, which hinders the contact between the exhaust gas and the noble metal element and reduces the exhaust gas purification performance. Therefore, the number of ALD cycles carried out in Step 2A is set to 1 or more and 3 or less. The number of ALD cycles carried out in Step 2A may be 1, but is preferably 2 or 3, and more preferably 3.

[0104] One ALD cycle forms a single atomic layer (i.e., one layer of atomic layer). One ALD cycle includes the following steps a to d: (a) A step of introducing a precursor into the reaction space; (b) A step of purging the reaction space with an inert gas; (c) A step of introducing an oxidizing agent into the reaction space; and (d) Step of purging the reaction space with an inert gas includes.

[0105] Steps a to d are continuously carried out in this order.

[0106] By carrying out the first ALD cycle, the first single atomic layer is formed on the surface of the carrier-noble metal element composite. Therefore, when the number of ALD cycles carried out in Step 2A is 1, a coating film composed of the first single atomic layer is formed.

[0107] After the first ALD cycle, by carrying out the second ALD cycle, the second single atomic layer is formed on the surface of the first single atomic layer. Therefore, when the number of ALD cycles carried out in Step 2A is 2, a coating film composed of the first single atomic layer and the second single atomic layer is formed.

[0108] After the second ALD cycle, by carrying out the third ALD cycle, the third single atomic layer is formed on the surface of the second single atomic layer. Therefore, when the number of ALD cycles carried out in Step 2A is 3, a coating film composed of the first single atomic layer, the second single atomic layer and the third single atomic layer is formed.

[0109] <The first ALD cycle> Hereinafter, the first ALD cycle will be described. The carrier-noble metal element composite is installed in the reaction space of the ALD apparatus before the first ALD cycle is started.

[0110] Process a In Project A, a precursor is introduced into the reaction space, and the surface of the carrier-noble metal element composite is exposed to the precursor. As a result, the precursor reacts with the hydroxyl groups present on the surface of the carrier-noble metal element composite and chemisorbs on the surface of the carrier-noble metal element composite, forming an M-O bond. M is a metal element contained in the precursor. The O in the M-O bond is derived from the hydroxyl groups present on the surface of the carrier-noble metal element composite. The hydroxyl groups present on the surface of the carrier-noble metal element composite can be generated, for example, by the reaction of the noble metal element (e.g., the noble metal element present on the surface of the noble metal element-containing particles present on the surface of the carrier-noble metal element composite) present on the surface of the carrier-noble metal element composite with water, oxygen, etc. in the air, and by the reaction of the carrier portion (e.g., inorganic oxide) present on the surface of the carrier-noble metal element composite with water, oxygen, etc. in the air.

[0111] When all the hydroxyl groups present on the surface of the carrier-noble metal element composite react with the precursor and the reaction is completed (i.e., the chemisorption of the precursor on the surface of the carrier-noble metal element composite is saturated), a first precursor layer is formed.

[0112] When the reaction is completed, the precursor is no longer consumed, and the concentration of the precursor in the gas discharged from the reaction space (hereinafter referred to as "exhaust gas") increases. Therefore, by monitoring the concentration of the precursor in the exhaust gas, the completion of the reaction can be detected. Examples of methods for monitoring the concentration of the precursor in the exhaust gas include mass spectrometry. Note that it is not necessary to monitor the concentration of the precursor in the exhaust gas every time. Once the exposure conditions of the precursor to the surface of the carrier-noble metal element composite sufficient to achieve the completion of the reaction are grasped by the above method, the same exposure conditions may be adopted thereafter.

[0113] The explanation regarding M is as described above.

[0114] When exposing the surface of the carrier-noble metal element composite to the precursor, the temperature of the reaction space is, for example, 50°C or higher and 200°C or lower, preferably 100°C or higher and 150°C or lower.

[0115] When exposing the surface of the carrier-noble metal element composite to the precursor, the pressure in the reaction space is not particularly limited. However, from the perspective of enhancing the efficiency of the precursor introduced into the reaction space to diffuse in the reaction space and adsorb onto the carrier-noble metal element composite, a lower pressure in the reaction space is preferred. The pressure in the reaction space is, for example, 10000 Pa or less, preferably 3000 Pa or less, more preferably 1000 Pa or less. The lower limit is, for example, 100 Pa.

[0116] The precursor introduced into the reaction space is in a gaseous state.

[0117] As the precursor, for example, a compound represented by the formula: M(R) x can be used.

[0118] The description of M is as above.

[0119] x R's each independently represent a halogen atom, an alkyl group, a dialkylamino group or an alkyloxy group.

[0120] The halogen atom can be selected from a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, but is preferably a chlorine atom.

[0121] The number of carbon atoms of the alkyl group is, for example, 1 to 10, preferably 1 to 6, more preferably 1 to 4, and even more preferably 1 to 3. The alkyl group may be linear or branched. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, an isobutyl group, a tert-butyl group, etc.

[0122] The dialkylamino group is a group represented by the formula: -N(-Q 1 )(-Q 2 ) [wherein Q 1 and Q 2 each independently represent an alkyl group.]. The description of the alkyl group is as above.

[0123] The alkyloxy group is a group represented by the formula: -O-alkyl group, and the description of the alkyl group is as described above.

[0124] X is, for example, an integer from 2 to 6, and is appropriately selected according to the type of the metal element represented by M. When M is Mg, x = 2. When M is Al, x = 3. When M is Si, x = 4. When M is Ti, x = 4. When M is V, x = 5. When M is Co, x = 2. When M is Ni, x = 2. When M is Cu, x = 2. When M is Zn, x = 2. When M is Ga, x = 3. When M is Zr, x = 4. When M is Nb, x = 5. When M is Mo, x = 6. When M is Ru, x = 4. When M is In, x = 3. When M is Sn, x = 4. When M is Gd, x = 3. When M is Hf, x = 4. When M is Ta, x = 5. When M is W, x = 6.

[0125] The formula: M(-R) x Specific examples of the compound represented by are WF 6 , TiCl 4 , HfCl 4 , SnCl 4 , Al(CH 3 ) 3 , Zn(CH 2 CH 3 ) 2 , Al(OCH 3 ) 3 , Ta(OCH 2 CH 3 ) 5 , Ti(OCH(CH 3 )) 2 ), Ti(OC(CH 4 )) 3 ), Ti(N(CH 3 )) 4 ), Ti(N(CH 3 )) 2 ), Zr(N(CH 4 )(CH 3 CH 2 CH 3 )) 4, Ta(N(CH 3 ) 2 ) 5 and the like.

[0126] As the precursor, for example, a β-diketonate metal complex may be used.

[0127] Examples of the β-diketonate metal complex include Cu(C 5 HF 6 O 2 ) 2 (Cu(hfac) 2 ), Ni(C 5 H 7 O 2 ) 2 (Ni(acac) 2 ), Zr(OCC(CH 3 ) 3 CHCOC(CH 3 ) 3 ) 4 (Zr(tmhd) 4 ) and the like.

[0128] Hereinafter, taking the case of using Al(CH 3 ) 3 (hereinafter referred to as "TMA") as an example, the process by which the precursor chemisorbs on the surface of the carrier-noble metal element composite will be described.

[0129] When the surface of the carrier-noble metal element composite is exposed to TMA, some of the methyl groups of TMA (one or two of the three methyl groups of TMA) react with H derived from the hydroxyl groups present on the surface of the carrier-noble metal element composite to form methane and desorb from the Al of TMA. Then, the Al from which the methyl group has dissociated reacts with the O present on the surface of the carrier-noble metal element composite to form an Al-O bond. In this way, TMA chemisorbs on the surface of the carrier-noble metal element composite. When all the hydroxyl groups present on the surface of the carrier-noble metal element composite react with TMA and the reaction is completed (the chemisorption of TMA on the surface of the carrier-noble metal element composite is saturated), the first precursor layer is formed.

[0130] Process b In step b, the reaction space is purged with an inert gas. That is, an inert gas is introduced into the reaction space to remove unreacted precursors and by-products (for example, methane generated when using TMA as a precursor) from the reaction space.

[0131] As the inert gas, for example, nitrogen, argon, helium, etc. can be used. One kind of inert gas may be used alone, or two or more kinds of inert gases may be used in combination.

[0132] Process c In step c, an oxidizing agent is introduced into the reaction space to expose the surface of the first precursor layer to the oxidizing agent. Thereby, the functional groups or ligands present on the surface of the first precursor layer (functional groups or ligands bonded to the metal element represented by M) react with the oxidizing agent and are converted into hydroxyl groups, and M-OH bonds are formed.

[0133] When all the functional groups or ligands present on the surface of the first precursor layer react with the oxidizing agent and are converted into hydroxyl groups (that is, when the reaction is completed), the first single atomic layer is formed. The first single atomic layer contains M-O bonds and M-OH. That is, the first single atomic layer is a metal oxide film having hydroxyl groups.

[0134] When the reaction is completed, the oxidizing agent is no longer consumed, and the concentration of the oxidizing agent in the gas discharged from the reaction space (hereinafter referred to as "exhaust gas") increases. Therefore, by monitoring the concentration of the oxidizing agent in the exhaust gas, the completion of the reaction can be detected. As a method for monitoring the concentration of the precursor in the exhaust gas, for example, mass spectrometry can be mentioned. It should be noted that it is not necessary to monitor the concentration of the precursor in the exhaust gas every time. Once the exposure conditions of the oxidizing agent to the surface of the first precursor layer sufficient to achieve the completion of the reaction are grasped by the above method, the same exposure conditions may be adopted thereafter.

[0135] When exposing the surface of the first precursor layer to the oxidizing agent, the temperature of the reaction space is, for example, 50°C or higher and 200°C or lower, preferably 100°C or higher and 150°C or lower.

[0136] When exposing the surface of the first precursor layer to an oxidizing agent, the pressure in the reaction space is not particularly limited. However, from the viewpoint of enhancing the efficiency of the oxidizing agent introduced into the reaction space to diffuse in the reaction space and adsorb onto the entire surface of the first precursor layer, it is preferable that the pressure in the reaction space is low. The pressure in the reaction space is, for example, 10,000 Pa or less, preferably 3,000 Pa or less, more preferably 1,000 Pa or less. The lower limit is, for example, 100 Pa.

[0137] The oxidizing agent introduced into the reaction space is in a gaseous state.

[0138] As the oxidizing agent, for example, water, hydrogen peroxide, nitrous oxide, nitrogen dioxide, oxygen (O 2 ), ozone, etc. can be used.

[0139] Hereinafter, taking the case where TMA is used as the precursor and water is used as the oxidizing agent as an example, the process in which the functional groups present on the surface of the first precursor layer are converted to hydroxyl groups will be described.

[0140] When the surface of the first precursor layer is exposed to water, the methyl groups (methyl groups bonded to Al) present on the surface of the first precursor layer react with H derived from water to form methane and desorb from Al. Then, the Al from which the methyl group has dissociated reacts with OH derived from water, and an Al-OH bond is formed. In this way, the methyl groups present on the surface of the first precursor layer are converted to hydroxyl groups. When all the methyl groups present on the surface of the first precursor layer are converted, the first single atomic layer is formed. The first single atomic layer contains Al-O bonds and Al-OH. That is, the first single atomic layer is an Al 2 O 3 film with hydroxyl groups.

[0141] Process d In step d, the reaction space is purged with an inert gas. That is, an inert gas is introduced into the reaction space to remove unreacted oxidizing agent and by-products (for example, methane generated when TMA is used as the precursor) from the reaction space.

[0142] As the inert gas, for example, nitrogen, argon, helium, etc. can be used. One kind of inert gas may be used alone, or two or more kinds of inert gases may be used in combination.

[0143] <Second ALD cycle> Hereinafter, the second ALD cycle will be described.

[0144] Process a In step a, a precursor is introduced into the reaction space, and the surface of the first single atomic layer is exposed to the precursor. As a result, the precursor chemisorbs on the surface of the first single atomic layer, and a second precursor layer is formed on the surface of the first single atomic layer.

[0145] The above description regarding step a of the first ALD cycle is also applicable to step a of the second ALD cycle. When applying, "the surface of the carrier-noble metal element composite" is read as "the surface of the first single atomic layer", and "the first precursor layer" is read as "the second precursor layer".

[0146] Process b The above description regarding step b of the first ALD cycle is also applicable to step b of the second ALD cycle.

[0147] Process c In step c, an oxidant is introduced into the reaction space, and the surface of the second precursor layer is exposed to the oxidant. As a result, the functional group or ligand (the functional group or ligand bonded to the metal element represented by M) present on the surface of the second precursor layer is converted to a hydroxyl group, and the second single atomic layer is formed.

[0148] The above description regarding step c of the first ALD cycle is also applicable to step c of the second ALD cycle. When applying, "the first precursor layer" is read as "the second precursor layer", and "the first single atomic layer" is read as "the second single atomic layer".

[0149] Process d The above description regarding step d of the first ALD cycle also applies to step d of the second ALD cycle.

[0150] <Third ALD cycle> The third ALD cycle will be described below.

[0151] Process a In step a, a precursor is introduced into the reaction space, and the surface of the second single atomic layer is exposed to the precursor. As a result, the precursor chemisorbs on the surface of the second single atomic layer, and a third precursor layer is formed on the surface of the second single atomic layer.

[0152] The above description regarding step a of the first ALD cycle also applies to step a of the third ALD cycle. When applying, "the surface of the carrier-noble metal element composite" is read as "the surface of the second single atomic layer", and "the second precursor layer" is read as "the third precursor layer".

[0153] Process b The above description regarding step b of the first ALD cycle also applies to step b of the third ALD cycle.

[0154] Process c In step c, an oxidant is introduced into the reaction space, and the surface of the third precursor layer is exposed to the oxidant. As a result, the functional groups or ligands (functional groups or ligands bonded to the metal element represented by M) present on the surface of the third precursor layer are converted to hydroxyl groups, and a third single atomic layer is formed.

[0155] The above description regarding step c of the first ALD cycle also applies to step c of the third ALD cycle. When applying, "the second precursor layer" is read as "the third precursor layer", and "the second single atomic layer" is read as "the third single atomic layer".

[0156] Process d The above description regarding step d of the first ALD cycle also applies to step d of the third ALD cycle.

[0157] <<Method for Producing Catalyst for Exhaust Gas Purification>> The method for producing a catalyst for exhaust gas purification according to the present invention comprises the following steps: (1B) Preparing a substrate having a gas flow path; (2B) Forming a first catalyst layer containing a carrier-noble metal element composite on the wall surface of the gas flow path, the carrier-noble metal element composite containing a carrier and a noble metal element supported on the carrier; and (3B) Using atomic layer deposition to form a coating film that coats the carrier-noble metal element composite in the first catalyst layer, the coating film containing an M-O bond (wherein M represents a metal element other than the noble metal element). It includes.

[0158] The catalyst for exhaust gas purification produced by the above production method (hereinafter referred to as "catalyst") comprises a substrate having a gas flow path, a first catalyst layer provided on the substrate, and a coating film that coats the carrier-noble metal element composite in the first catalyst layer.

[0159] The above production method may, after step 3B, include the following step: (4B) Forming a second catalyst layer on the upper side of the first catalyst layer It may include.

[0160] When the above production method includes step 4B, the catalyst produced by the above production method comprises a substrate having a gas flow path, a first catalyst layer provided on the substrate, a coating film that coats the carrier-noble metal element composite in the first catalyst layer, and a second catalyst layer provided on the upper side of the first catalyst layer.

[0161] <Embodiment of Catalyst> Hereinafter, with reference to FIGS. 1 to 4, embodiments of the catalyst produced by the above production method will be described.

[0162] As shown in FIG. 1, the catalyst 1 is disposed in the exhaust passage within the exhaust pipe P of the 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 of the exhaust pipe P toward the other end, and is purified by the catalyst 1 provided in the exhaust pipe P. In the drawings, the exhaust gas flow direction is indicated by the symbol X. Hereinafter, the upstream side in the exhaust gas flow direction X may be referred to as the "exhaust gas inflow side" or the "upstream side", and the downstream side in the exhaust gas flow direction X may be referred to as the "exhaust gas outflow side" or the "downstream side".

[0163] Other exhaust gas purification catalysts may be disposed on the upstream side and / or the downstream side of the catalyst 1 in the exhaust passage within the exhaust pipe P.

[0164] As shown in FIGS. 2 to 4, the catalyst 1 includes a substrate 10, a first catalyst layer 20 provided on the substrate 10, and a coating film (not shown) that coats the carrier-noble metal element composite in the first catalyst layer 20.

[0165] <Substrate> Hereinafter, the substrate 10 will be described.

[0166] The material constituting the substrate 10 can be appropriately selected from known materials. Examples of the material constituting the substrate 10 include metal materials and ceramic materials. Examples of the 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, and oxide ceramics such as alumina, zirconia, cordierite, mullite, zircon, aluminum titanate, and magnesium titanate. Examples of the metal materials include alloys such as stainless steel.

[0167] As shown in FIGS. 2 to 4, the substrate 10 has a cylindrical portion 11, a partition portion 12 provided within the cylindrical portion 11, and cells 13 partitioned by the partition portion 12. The substrate 10 is preferably a honeycomb structure.

[0168] Cell 13 is an example of a "gas flow path", and the surface of the partition portion 12 on the cell 13 side is an example of a "wall surface of the gas flow path".

[0169] As shown in FIG. 2, the cylindrical portion 11 defines the outer shape of the base material 10, and the axial direction of the cylindrical portion 11 coincides with the axial direction of the base material 10. As shown in FIG. 2, the shape of the cylindrical portion 11 is cylindrical, but it may be other shapes such as an elliptical cylinder or a polygonal cylinder.

[0170] As shown in FIGS. 2 to 4, a 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.

[0171] As shown in FIG. 4, 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.

[0172] As shown in FIG. 4, 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.

[0173] As shown in FIGS. 2 and 3, 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.

[0174] The cell density per square inch of the base material 10 is, for example, 100 cells or more and 1000 cells or less. The cell density per square inch of the base material 10 means the total number of cells 13 per square inch in the cross section obtained by cutting the base material 10 in a plane perpendicular to the exhaust gas flow direction X.

[0175] The substrate 10 has a length L10. In the present invention, unless otherwise specified, "length" means the axial dimension of the substrate 10.

[0176] 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, the volume of the substrate 10 is expressed by the formula: volume of the substrate 10 = π × r 2 × L10.

[0177] <First catalyst layer> Hereinafter, the first catalyst layer 20 will be described.

[0178] As shown in FIGS. 3 and 4, the first catalyst layer 20 is provided on 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 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. Usually, it is provided directly on the surface of the partition wall portion 12 on the cell 13 side. The "first catalyst layer 20 provided on the substrate 10" includes both an embodiment in which the first catalyst layer 20 is provided directly on the surface of the partition wall portion 12 on the cell 13 side and an embodiment in which the first catalyst layer 20 is provided via another layer on the surface of the partition wall portion 12 on the cell 13 side.

[0179] The first catalyst layer 20 may be composed of a portion (hereinafter referred to as the "raised portion") that bulges from the surface of the partition wall portion 12 on the cell 13 side toward the cell 13 side, or may be composed of a portion existing inside the partition wall portion 12 (hereinafter referred to as the "internal portion"), or may have a raised portion and an internal portion. The "first catalyst layer 20 provided on the substrate 10" includes any of an embodiment in which the first catalyst layer 20 is composed of a raised portion, an embodiment in which the first catalyst layer 20 is composed of an internal portion, and an embodiment in which the first catalyst layer 20 has a raised portion and an internal portion.

[0180] As shown in FIG. 4, the first catalyst layer 20 extends 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 20 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.

[0181] The first catalyst layer 20 contains a carrier-noble metal element composite. The description in the column of <carrier-noble metal element composite> above is also applicable to the carrier-noble metal element composite in the first catalyst layer 20, unless otherwise specified. When applying, "catalyst composition" is replaced with "first catalyst layer 20".

[0182] The content of the carrier-noble metal element composite in the first catalyst layer 20 can be appropriately adjusted in consideration of the balance between exhaust gas purification performance and cost. The content of the carrier-noble metal element composite in the first catalyst layer 20 is preferably adjusted so that the mass of the noble metal element in terms of metal in the first catalyst layer 20 per unit volume of the portion of the base material 10 where the first catalyst layer 20 is formed falls within a predetermined range. The mass of the noble metal element in terms of metal in 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, for example, 0.01 g / L or more and 10 g / L or less, preferably 0.01 g / L or more and 5 g / L or less, more preferably 0.01 g / L or more and 3 g / L or less.

[0183] The mass in terms of metal of the noble metal element in the first catalyst layer 20 per unit volume of the portion of the base material 10 where the first catalyst layer 20 is formed can be obtained from the formula: (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) × (the content rate in terms of metal of the noble metal element in the first catalyst layer 20). The "content rate in terms of metal of the noble metal element in the first catalyst layer 20" means the content rate in terms of metal of the one kind of noble metal element when the first catalyst layer 20 contains one kind of noble metal element, and means the total content rate of the two or more kinds of noble metal elements when the first catalyst layer 20 contains two or more kinds of noble metal elements.

[0184] 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 can be obtained from the formula: (the mass of the first catalyst layer 20) / ((the volume of the base material 10) × (the average length L20 of the first catalyst layer 20 / the length L10 of the base material 10)). From the viewpoint of achieving a good balance between exhaust gas purification performance and cost, 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 preferably 10 g / L or more and 200 g / L or less, more preferably 20 g / L or more and 150 g / L or less, and even more preferably 50 g / L or more and 120 g / L or less.

[0185] The content rate in terms of metal of the noble metal element in the first catalyst layer 20 can be obtained in the same manner as the content rate in terms of metal of the noble metal element in the catalyst composition.

[0186] An example of the measurement method of the average length L20 of the first catalyst layer 20 is as follows.

[0187] Cut out a sample that extends in the axial direction of the substrate 10 from the catalyst 1 and has the same length as the length L10 of the substrate 10. The sample is, for example, cylindrical with a diameter of 25.4 mm. The value of the diameter of the sample can be changed as needed. When the first catalyst layer 20 extends along the exhaust gas flow direction X from the end of the partition wall portion 12 on the exhaust gas inflow side, cut the sample at 5 mm intervals by a plane perpendicular to the axial direction of the substrate 10, and in order from the end side of the exhaust gas inflow side of the sample, obtain the first cut piece, the second cut piece, ···, the nth cut piece. When the first catalyst layer 20 extends 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, cut the sample at 5 mm intervals by a plane perpendicular to the axial direction of the substrate 10, and in order from the end side of the exhaust gas outflow side of the sample, obtain the first cut piece, the second cut piece, ···, the nth cut piece. In either case, 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 based on the composition of the cut piece, confirm whether the cut piece contains a part of the first catalyst layer 20.

[0188] For 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.

[0189] 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)

[0190] For example, when the first to kth cut pieces include a part of the first catalyst layer 20, and the (k + 1)th to nth cut pieces do not include a part of the first catalyst layer 20, the length of the first catalyst layer 20 included in the sample is (5 × k) mm.

[0191] An example of a more detailed method for measuring the length of the first catalyst layer 20 included in the sample is as follows.

[0192] When the kth cut piece (when the first catalyst layer 20 extends along the exhaust gas flow direction X from the end of the exhaust gas inflow side of the partition wall portion 12, it is the cut piece obtained from the most exhaust gas outflow side of the sample among the cut pieces including a part of the first catalyst layer 20; when the first catalyst layer 20 extends along the direction opposite to the exhaust gas flow direction X from the end of the exhaust gas outflow side of the partition wall portion 12, it is the cut piece obtained from the most exhaust gas inflow side of the sample among the cut pieces including a part of the first catalyst layer 20) is cut in the axial direction of the base material 10, and a part of the first catalyst layer 20 present on the cut surface is observed using SEM, EPMA, etc., the length of a part of the first catalyst layer 20 in the kth cut piece is measured. Then, based on the following formula, the length of the first catalyst layer 20 included in the sample is calculated. Length of the first catalyst layer 20 included in the sample = (5 mm × (k - 1)) + (Length of a part of the first catalyst layer 20 included in the kth cut piece)

[0193] Regarding 8 to 16 samples arbitrarily cut out from the catalyst 1, the length of the first catalyst layer 20 included in each sample is measured, and their average value is taken as the average length L20 of the first catalyst layer 20.

[0194] The first catalyst layer 20 may contain other components such as a binder and a stabilizer. Examples of the binder include inorganic oxide-based binders such as alumina binder, ceria binder, zirconia binder, titania binder, and silica binder. Examples of the stabilizer include nitrates, carbonates, oxides, sulfates, etc. of alkaline earth metal elements (e.g., Sr, Ba, etc.).

[0195] <Coating film> The description of the <coating film> in the above also applies to the coating film that coats the carrier-noble metal element composite in the first catalyst layer 20, unless otherwise specified below.

[0196] By coating the carrier-noble metal element composite in the first catalyst layer 20 with a coating film, it is possible to prevent the movement and sintering of the noble metal element that may occur due to the exposure of the catalyst 1 to a high-temperature environment, and it is possible to prevent a decrease in the exhaust gas purification performance of the catalyst 1 after being exposed to a high-temperature environment.

[0197] The coating film covers at least a part of the surface of the carrier-noble metal element composite present on the surface of the first catalyst layer 20. The meaning of the "surface of the carrier-noble metal element composite" and the meaning of the "at least a part of the surface of the carrier-noble metal element composite" covered by the coating film are the same as above. The coating film may cover at least a part of the surface of other parts present on the surface of the first catalyst layer 20 in addition to at least a part of the surface of the carrier-noble metal element composite present on the surface of the first catalyst layer 20.

[0198] In the present invention, the "surface of the first catalyst layer 20" includes the inner surface and the outer surface of the first catalyst layer 20. The inner surface of the first catalyst layer 20 includes the inner surface of the pores existing inside the first catalyst layer 20 (that is, not exposed on the outer surface of the first catalyst layer 20), and the outer surface of the first catalyst layer 20 includes the inner surface of the pores exposed on the outer surface of the first catalyst layer 20. Note that the pores of the first catalyst layer 20 are derived from, for example, the voids between the carrier-noble metal composites constituting the first catalyst layer 20.

[0199] The coating film preferably covers at least a part of the surface of the carrier-noble metal element composite present on the inner surface of the first catalyst layer 20. The coating film may cover at least a part of the surface of the carrier-noble metal element composite present on the outer surface of the first catalyst layer 20 in addition to at least a part of the surface of the carrier-noble metal element composite present on the inner surface of the first catalyst layer 20.

[0200] <Second catalyst layer> As shown in FIGS. 2 to 4, the catalyst 1 may include a second catalyst layer 30.

[0201] As shown in FIG. 4, the second catalyst layer 30 is provided above the first catalyst layer 20. The expression "the second catalyst layer 30 is provided above the first catalyst layer 20" means that a part or all of the second catalyst layer 30 exists on the main surface of the first catalyst layer 20 opposite to the main surface on the partition wall portion 12 side among the two main surfaces of the first catalyst layer 20. The "main surface of the first catalyst layer 20" means the outer surface of the first catalyst layer 20 extending in the exhaust gas flow direction X. When at least a part of the coating film exists on the outer surface of the first catalyst layer 20, the at least a part of the coating film constitutes at least a part of the "outer surface of the first catalyst layer 20". The second catalyst layer 30 may be provided directly on the main surface of the first catalyst layer 20, or may be provided via another layer. The second catalyst layer 30 may be provided so as to cover a part of the main surface of the first catalyst layer 20, or may be provided so as to cover the entire main surface of the first catalyst layer 20. The expression "the second catalyst layer 30 is provided above the first catalyst layer 20" includes both an embodiment in which the second catalyst layer 30 is provided directly on the main surface of the first catalyst layer 20 and an embodiment in which the second catalyst layer 30 is provided on the main surface of the first catalyst layer 20 via another layer.

[0202] As shown in FIG. 4, the second catalyst layer 30 extends along the exhaust gas flow direction X from the end portion on the exhaust gas inflow side of the partition wall portion 12 to the end portion on the exhaust gas outflow side of the partition wall portion 12. The second catalyst layer 30 may extend along the exhaust gas flow direction X from the end portion on the exhaust gas inflow side of the partition wall portion 12 so as not to reach the end portion 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 portion on the exhaust gas outflow side of the partition wall portion 12 so as not to reach the end portion on the exhaust gas inflow side of the partition wall portion 12.

[0203] The second catalyst layer 30 contains one or more noble metal elements. The second catalyst layer 30 may contain one or more carriers. When the second catalyst layer 30 contains a carrier, at least a part of the noble metal element is preferably supported on the carrier. The descriptions of the carrier and the noble metal element in the column of <carrier-noble metal element composite> above are applicable to the second catalyst layer 30 as well, unless otherwise specified. When applying, "catalyst composition" is read as "second catalyst layer 30". The content rates of the noble metal element and the carrier in the second catalyst layer 30 can be appropriately adjusted in consideration of the balance between the exhaust gas purification performance and the cost, etc.

[0204] As described above, by coating the carrier-noble metal element composite in the first catalyst layer 20 with a coating film, it is possible to prevent the movement and sintering of the noble metal element that may occur due to the exposure of the catalyst 1 to a high-temperature environment, and it is possible to prevent the deterioration of the exhaust gas purification performance of the catalyst 1 after being exposed to the high-temperature environment. However, when the carrier-noble metal element composite in the first catalyst layer 20 is coated with a coating film, there is a possibility that the exhaust gas purification performance of the catalyst 1 before being exposed to the high-temperature environment may deteriorate. Therefore, it is preferable to provide the second catalyst layer 30. By providing the second catalyst layer 30, it is possible to achieve both prevention of deterioration of the exhaust gas purification performance of the catalyst 1 before being exposed to the high-temperature environment and prevention of deterioration of the exhaust gas purification performance of the catalyst 1 after being exposed to the high-temperature environment.

[0205] <Embodiment of the method for manufacturing a catalyst> Hereinafter, taking the catalyst 1 as an example, an embodiment of the method for manufacturing a catalyst will be described.

[0206] Process 1B In step 1B, the substrate 10 is prepared. The cell 13 is an example of a "gas flow path".

[0207] Process 2B In step 2B, the first catalyst layer 20 is formed on the cell 13 side surface of the partition wall portion 12. The cell 13 side surface of the partition wall portion 12 is an example of a "wall surface of a gas flow path".

[0208] The first catalyst layer 20 can be formed by mixing a carrier-noble metal element composite and other components (e.g., binder, stabilizer, solvent, etc.) to prepare a first slurry, applying the first slurry onto the substrate 10, drying, and firing. The carrier-noble metal element composite can be prepared in the same manner as in Step 1A.

[0209] The drying temperature is, for example, 60°C or higher and 150°C or lower, and the drying time is, for example, 0.1 hour or longer and 1 hour or shorter. The firing temperature is, for example, 300°C or higher and 700°C or lower, and the firing time is, for example, 1 hour or longer and 10 hours or shorter. The firing can be carried out, for example, in an air atmosphere.

[0210] Process 3B In Step 3B, an atomic layer deposition method is used to form a coating film that coats the carrier-noble metal element composite in the first catalyst layer 20. The number of ALD cycles performed in Step 3B is 1 or more and 3 or less. Step 3B can be carried out in the same manner as in Step 2A. The description regarding Step 2A is also applicable to Step 3B. When applying, "carrier-noble metal element composite" is read as "carrier-noble metal element composite in the first catalyst layer 20".

[0211] Process 4B When the catalyst 1 includes the second catalyst layer 30, Step 4B is carried out. In Step 4B, the second catalyst layer 30 is formed on the upper side of the first catalyst layer 20.

[0212] The second catalyst layer 30 can be formed by mixing a salt of a noble metal element (e.g., nitrate, ammine complex salt, acetate, chloride, etc.) and optionally other components (e.g., carrier, binder, stabilizer, solvent, etc.) to prepare a second slurry, applying the second slurry onto the first catalyst layer 20, drying, and firing. The drying and firing can be carried out in the same manner as in Step 2B.

Example

[0213] <Example 1> (1) Pt-supported Al 2 O3 Production of powder La 2 O 3 Modified Al 2 O 3 Powder (content of La in terms of La 2 O 3 : 1% by mass, content of Al in terms of Al 2 O 3 : 99% by mass) was impregnated with an aqueous solution of dinitrodiammineplatinum nitrate for 2 hours, evaporated to dryness, and then calcined at 500 °C for 1 hour in air to obtain Pt-supported Al 2 O 3 powder. The content of Pt in terms of metal in the Pt-supported Al 2 O 3 powder was 1.00% by mass.

[0214] (2) Performance of ALD cycles For 10 g of the Pt-supported Al 2 O 3 powder obtained in the above (1), one ALD cycle was performed.

[0215] "Performing one ALD cycle" means continuously performing the following steps (a1), (b1), (c1), and (d1) in this order on the object to be processed introduced into the reaction space of the ALD apparatus. Step (a1): Introduce TMA (trimethylaluminum) into the reaction space and expose the object to be processed to TMA for 2000 seconds. Step (b1): Purge the reaction space with nitrogen gas for 2000 seconds. Step (c1): Introduce ultrapure water into the reaction space and expose the object to be processed to ultrapure water for 5000 seconds. Step (d1): Purge the reaction space with nitrogen gas for 5000 seconds.

[0216] All of steps (a1) to (d1) were performed at 120 °C. The above exposure conditions of the object to be processed to TMA or water were determined by preliminarily confirming that the reaction was completed by adopting the above exposure conditions and monitoring the concentration of TMA or water in the gas discharged from the reaction space.

[0217] Pt-supported Al subjected to 1 ALD cycle 2 O 3 powder was taken out from the ALD apparatus, calcined at 500 °C for 1 hour under the atmosphere, and Pt-supported Al 2 O 3 powder (hereinafter referred to as "the catalyst composition of Example 1") was obtained.

[0218] <Example 2> Except that the ALD cycle was carried out 2 times, in the same manner as in Example 1, Pt-supported Al coated with a coating film composed of the first single atomic layer and the second single atomic layer 2 O 3 powder (hereinafter referred to as "the catalyst composition of Example 2") was obtained.

[0219] <Example 3> Except that the ALD cycle was carried out 3 times, in the same manner as in Example 1, Pt-supported Al coated with a coating film composed of the first single atomic layer, the second single atomic layer and the third single atomic layer 2 O 3 powder (hereinafter referred to as "the catalyst composition of Example 3") was obtained.

[0220] <Example 4> (1) Preparation of Rh-supported ZrO 2 powder ZrO 2 powder (Zr content in terms of ZrO 2 conversion: approximately 100% by mass (>99.5% by mass)) was impregnated with an aqueous Rh nitrate solution for 2 hours, evaporated to dryness, and then calcined at 500 °C for 1 hour under the atmosphere to obtain Rh-supported ZrO 2 powder. The content of Rh in terms of metal in the Rh-supported ZrO 2 powder was 1.0% by mass.

[0221] (2) Conducting the ALD cycle For 10 g of the Rh-supported ZrO 2 powder obtained in (1) above, the ALD cycle was carried out once in the same manner as in Example 1, and then Rh-supported ZrO 2The powder was taken out from the ALD apparatus and calcined at 500 °C for 1 hour under the atmosphere to obtain Rh-supported ZrO coated with a coating film composed of the first single atomic layer. 2 Powder (hereinafter referred to as "the catalyst composition of Example 4") was obtained.

[0222] <Example 5> Except that the ALD cycle was carried out twice, in the same manner as in Example 4, Rh-supported ZrO coated with a coating film composed of the first single atomic layer and the second single atomic layer was obtained. 2 Powder (hereinafter referred to as "the catalyst composition of Example 5") was obtained.

[0223] <Example 6> Except that the ALD cycle was carried out three times, in the same manner as in Example 4, Rh-supported ZrO coated with a coating film composed of the first single atomic layer, the second single atomic layer, and the third single atomic layer was obtained. 2 Powder (hereinafter referred to as "the catalyst composition of Example 6") was obtained.

[0224] <Comparative Example 1> Without carrying out the ALD cycle, the Pt-supported Al obtained in (1) of Example 1 was used as the catalyst composition of Comparative Example 1. 2 O 3 Powder was used.

[0225] <Comparative Example 2> Except that the ALD cycle was carried out five times, in the same manner as in Example 1, Pt-supported Al coated with a coating film composed of the first single atomic layer, the second single atomic layer, the third single atomic layer, the fourth single atomic layer, and the fifth single atomic layer was obtained. 2 O 3 Powder (hereinafter referred to as "the catalyst composition of Comparative Example 2") was obtained.

[0226] <Measurement of the Dispersion Degree of Noble Metal Elements> The catalyst compositions obtained in Examples 1 to 6 and Comparative Examples 1 and 2 were heat-treated at 1000 °C for 15 hours under the atmosphere. Pretreatment was carried out on each of the heat-treated catalyst compositions and the freshly prepared catalyst compositions before heat treatment. In the pretreatment of the catalyst composition, the catalyst composition was subjected to an oxidation treatment at 400 °C with a mixed gas of O 2 and He, and then H2 It was subjected to a reduction treatment with gas and then cooled to 50 °C. To avoid changes in the measured value of the dispersion degree due to the adsorption of CO by substances other than the noble metal element contained in the catalyst composition, after cooling, CO 2 masking treatment was carried out. After the masking treatment, using the pretreated catalyst composition and a metal dispersion degree measuring device (BELMETAL3 manufactured by Microtrac BEL Co., Ltd.), the amount of CO adsorbed on the noble metal element was measured by the CO pulse method, and the dispersion degree of the noble metal element was calculated. Here, the "dispersion degree of the noble metal element" is the ratio of the number B of noble metal atoms exposed on the surface of the catalyst composition (including the inner surface and the outer surface; the same applies hereinafter) to the total number A of noble metal atoms in the catalyst composition, and the dispersion degree of the noble metal element (%) = (B / A) × 100 was calculated. The number B of noble metal atoms exposed on the surface of the catalyst composition was calculated from the amount of CO adsorption measured by the CO pulse method based on the premise that the noble metal atoms exposed on the surface of the catalyst composition and CO adsorb in a 1:1 ratio.

[0227] The results for Examples 1 to 6 and Comparative Examples 1 to 2 are shown in Table 1. The content of the noble metal element (Pt or Rh) in terms of metal in each catalyst composition was determined by ICP - AES.

[0228]

Table 1

[0229] <Example 7> (1) Preparation of slurry La 2 O 3 modified Al 2 O 3 powder (content of La in terms of La 2 O 3 : 1 mass%, content of Al in terms of Al 2 O 3 : 99 mass%) was dispersed in an aqueous solution of dinitrodiammineplatinum nitrate and impregnated for 2 hours, and then alumina sol was added to prepare a slurry.

[0230] (2) Preparation of catalyst A commercially available cordierite monolith honeycomb substrate (cell density: 400 cells / square inch, diameter: 25.4 mm, length: 40 mm, volume: 20 mL) was immersed in the slurry obtained in the above (1), and then the substrate was pulled up, and the excess slurry was blown off with compressed air. Next, it was dried at 120 °C for 20 minutes until the weight loss due to moisture disappeared, and a catalyst comprising the substrate and the catalyst layer formed on the substrate was formed. The mass of Pt in terms of metal in the catalyst layer was 0.99 g / L based on the volume of the substrate.

[0231] (3) Performance of ALD cycle One ALD cycle was performed on the catalyst obtained in the above (2).

[0232] "Performing one ALD cycle" means continuously performing the following steps (a2), (b2), (c2) and (d2) in this order on the object to be processed introduced into the reaction space of the ALD apparatus. Step (a2): TMA is introduced into the reaction space, and the object to be processed is exposed to TMA for 110 seconds. Step (b2): The reaction space is purged with nitrogen gas for 500 seconds. Step (c2): Ultrapure water is introduced into the reaction space, and the object to be processed is exposed to ultrapure water for 500 seconds. Step (d2): The reaction space is purged with nitrogen gas for 1500 seconds.

[0233] All of steps (a2) to (d2) were performed at 120 °C. The above exposure conditions of the object to be processed to TMA or water were determined by preliminarily confirming that the reaction was completed by adopting the above exposure conditions by monitoring the concentration of TMA or water in the gas discharged from the reaction space.

[0234] The catalyst subjected to one ALD cycle was taken out from the ALD apparatus and calcined at 500 °C for 1 hour in the atmosphere to obtain a catalyst in which the catalyst layer was coated with a coating film composed of the first single atomic layer.

[0235] <Example 8> Except for performing the ALD cycle twice, a catalyst in which the catalyst layer was coated with a coating film composed of the first single atomic layer and the second single atomic layer was obtained in the same manner as in Example 7.

[0236] <Example 9> Except for performing the ALD cycle three times, a catalyst in which the catalyst layer was coated with a coating film composed of the first single atomic layer, the second single atomic layer, and the third single atomic layer was obtained in the same manner as in Example 7.

[0237] <Comparative Example 3> The catalyst obtained in (2) of Example 7 was used as it was without performing the ALD cycle.

[0238] <Comparative Example 4> Except for performing the ALD cycle five times, a catalyst in which the catalyst layer was coated with a coating film composed of the first single atomic layer, the second single atomic layer, the third single atomic layer, the fourth single atomic layer, and the fifth single atomic layer was obtained in the same manner as in Example 7.

[0239] <Exhaust gas purification performance test> The catalysts obtained in Examples 7 to 9 and Comparative Examples 3 to 4 were heat-treated at 1000 °C for 15 hours in the air. The exhaust gas purification performance of the heat-treated catalysts was evaluated as follows.

[0240] A model gas having the following composition with an A / F of 14.6 was passed through the heat-treated catalyst at a flow rate of 25 L / min while adjusting the CO concentration and O 2 concentration so that the A / F varied in the range of 14.4 to 14.8. The temperature of the gas flowing into the exhaust gas purification catalyst was gradually increased from room temperature at a predetermined heating rate, and the amount of CO contained in the exhaust gas passing through the catalyst was determined using the following device, and the CO purification rate (%) was determined based on the following formula. Here, X represents the detected amount when no catalyst was installed, and Y represents the detected amount after the catalyst was installed. CO purification rate (%) = (X - Y) / X × 100

[0241] [Model gas (composition based on volume)] CO: 0.3%, C 3 H 6 : 1000 ppmC, NO: 500 ppm, O 2 : 0.28%, CO2 : 14%, H 2 O: 10%, N 2 : The balance [Heating rate] 10 °C / min [Evaluation device] MOTOR EXHAUST GAS ANALYZER MEXA7100 manufactured by Horiba, Ltd.

[0242] The inlet gas temperature of the catalyst when the CO purification rate reached 10% was determined as the light-off temperature T10 (°C). T10 (°C) was measured during the heating process.

[0243] The results for Examples 7 to 9 and Comparative Examples 3 to 4 are shown in Table 2.

[0244]

Table 2

Explanation of symbols

[0245] 1 ··· Catalyst for exhaust gas purification 10 ··· Substrate 11 ··· Cylindrical part 12 ··· Partition part 13 ··· Cell 20 ··· First catalyst layer 30 ··· Second catalyst layer

Claims

1. A catalyst composition for purifying exhaust gas, comprising a support-precious metal element composite containing a support and a precious metal element supported on the support, the precious metal element having a dispersion degree of 38% or more, The catalyst composition for exhaust gas purification, wherein when the catalyst composition for exhaust gas purification is heat-treated at 1000°C for 15 hours in the atmosphere, the dispersion degree of the precious metal element after the heat treatment is 0.87% or more of the dispersion degree of the precious metal element before the heat treatment.

2. 2. The catalyst composition for purifying exhaust gas according to claim 1, further comprising a coating film that coats the composite.

3. 3. The exhaust gas purifying catalyst composition according to claim 2, wherein the coating film contains an MO bond (wherein M represents a metal element other than a noble metal element).

4. 4. The exhaust gas purifying catalyst composition according to claim 3, wherein the metal element represented by M is Al.

5. The following steps: (1A) preparing a support-precious metal element composite including a support and a precious metal element supported on the support; and (2A) forming a coating film that coats the composite by using an atomic layer deposition method, the coating film including an M-O bond (wherein M represents a metal element other than a noble metal element); A method for producing the exhaust gas purifying catalyst composition according to claim 1, comprising: The aforementioned manufacturing method, wherein the number of monoatomic layer formation cycles carried out in step 2A is 1 to 3.

6. The method according to claim 5 , wherein the metal element represented by M is Al.

7. The following steps: (1B) providing a substrate having a gas flow passage; (2B) forming a first catalyst layer on a wall surface of the gas flow passage, the first catalyst layer including a carrier-precious metal element composite including a carrier and a precious metal element supported on the carrier; and (3B) forming a coating film that coats the complex in the first catalyst layer using an atomic layer deposition method, the coating film including an M-O bond (wherein M represents a metal element other than a noble metal element); A method for producing an exhaust gas purifying catalyst, comprising: The aforementioned manufacturing method, wherein the number of times of the monoatomic layer formation cycle carried out in step 3B is 1 to 3.

8. The method according to claim 7 , wherein the metal element represented by M is Al.

9. After step 3B, the following steps: (4B) forming a second catalyst layer on the upper side of the first catalyst layer The method of claim 7 or 8, comprising:

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