Method for producing nitrous oxide decomposition catalyst

Abstract

This method for producing a nitrous oxide decomposition catalyst for decomposing nitrous oxide in exhaust gas comprises: a preparation step for preparing a slurry including an active ingredient, an inorganic binder, and a dispersant; and a coating step for coating a substrate with the slurry. In addition, the inorganic binder contains a metal oxide and / or a metalloid oxide, and the dispersant contains a carboxylic acid and / or an alcohol.

Description

Method for producing nitrous oxide decomposition catalyst

[0001] The present invention relates to a method for producing a catalyst for decomposing nitrous oxide.

[0002] BACKGROUND ART Conventionally, in order to treat exhaust gas, a technique is known in which an exhaust gas treatment catalyst is disposed in an exhaust passage through which the exhaust gas flows, and harmful substances in the exhaust gas are decomposed.

[0003] As a method for producing various catalysts including such catalysts for exhaust gas treatment, a method has been proposed in which a slurry containing a catalytically active component and an inorganic binder is applied to glass paper and the glass paper is heated to form a catalyst (see, for example, Patent Document 1). Specifically, Example 1 of Patent Document 1 describes preparing a slurry by adding a catalytically active component to a silica sol in which silica as an inorganic binder is dispersed in water.

[0004] Japanese Patent Application Laid-Open No. 2016-190226

[0005] However, the catalyst manufacturing method of Patent Document 1 involves adding an inorganic binder and the active components of the catalyst to water to prepare a slurry, applying this slurry to glass paper, and heating the glass paper after the slurry has been applied to form the catalyst. However, this method has the drawback of resulting in insufficient dispersion of the inorganic binder within the slurry, resulting in insufficient catalyst strength.

[0006] The present invention provides a method for producing a nitrous oxide decomposition catalyst, which can improve the strength of the nitrous oxide decomposition catalyst.

[0007] The present invention [1] provides a method for producing a nitrous oxide decomposition catalyst that decomposes nitrous oxide in exhaust gas, the method comprising: a preparation step of preparing a slurry containing an active component, an inorganic binder, and a dispersant; and a coating step of coating the slurry onto a substrate, wherein the inorganic binder contains a metal oxide and / or a semi-metal oxide, and the dispersant contains a carboxylic acid and / or an alcohol.

[0008] The present invention [2] includes the method for producing a nitrous oxide decomposition catalyst according to [1], wherein the inorganic binder contains at least one selected from the group consisting of alumina, silica, and ceria.

[0009] The present invention [3] includes the method for producing a nitrous oxide decomposition catalyst according to [1], wherein the dispersant contains at least one selected from the group consisting of acetic acid, citric acid, lactic acid, methanol, and isopropanol.

[0010] The present invention [4] includes the method for producing a nitrous oxide decomposition catalyst according to any one of [1] to [3], wherein the active component is a composite metal oxide containing cobalt.

[0011] The present invention [5] includes the method for producing a nitrous oxide decomposition catalyst according to [4], wherein the composite metal oxide is a composite metal oxide represented by the following formula (1) or the following formula (2): Ｘ A １－Ｘ Co ２ O ４ (1) (In formula (1), A is at least one selected from the group consisting of Fe, Mn, Ce, Zr, La, alkali metals, and alkaline earth metals. X is greater than 0 and less than 1.) Mg Ｙ B １－Ｙ Co ２ O ４ (2) (In formula (2), B is at least one metal selected from the group consisting of Fe, Mn, Zn, Ni, Zr, La, alkali metals, and alkaline earth metals (excluding Mg). Also, Y is greater than 0 and less than 1.)

[0012] The present invention [6] includes the method for producing a nitrous oxide decomposition catalyst according to any one of [1] to [3], wherein the substrate is an inorganic fiber sheet.

[0013] The present invention [7] includes the method for producing a nitrous oxide decomposition catalyst according to any one of [1] to [3], further comprising a calcination step of calcining the substrate coated with the slurry after the coating step.

[0014] The method for producing a nitrous oxide decomposition catalyst of the present invention includes a preparation step of preparing a slurry containing an active component, an inorganic binder, and a dispersant, wherein the inorganic binder contains a metal oxide and / or a semi-metal oxide, and the dispersant contains a carboxylic acid and / or an alcohol, so that the inorganic binder is uniformly dispersed in the dispersant, thereby improving the strength of the nitrous oxide decomposition catalyst.

[0015] Fig. 1 is a perspective view showing a nitrous oxide decomposition catalyst produced by the method for producing a nitrous oxide decomposition catalyst of the present invention. Fig. 2 is a perspective view showing a nitrous oxide decomposition catalyst device including a nitrous oxide decomposition catalyst unit filled with the nitrous oxide decomposition catalyst shown in Fig. 1.

[0016] 1. Nitrous Oxide Decomposition Catalyst One embodiment of a nitrous oxide decomposition catalyst 1 will be described with reference to FIG.

[0017] The nitrous oxide decomposition catalyst 1 decomposes nitrous oxide (N ２ O) to nitrogen (N ２ ) and oxygen (O ２ ) and a catalyst for decomposing it into

[0018] The nitrous oxide decomposition catalyst 1 comprises an active component 2, an inorganic binder 3, and a substrate 4. As will be described in detail later, in the nitrous oxide decomposition catalyst 1, the active component 2 and the inorganic binder 3 are supported on the substrate 4.

[0019] The nitrous oxide decomposition catalyst 1 is in the form of a flat plate and / or a corrugated plate.

[0020] If the nitrous oxide decomposition catalyst 1 has a flat and / or corrugated shape, the active component 2 can be efficiently supported on the substrate 4, and a sufficient contact area with the exhaust gas can be secured, thereby enabling efficient decomposition of nitrous oxide.

[0021] [Active ingredient] Active ingredient 2 is N ２ O to N ２ and O ２ , or N ２ and H ２There are no particular limitations on the active ingredient 2 as long as it can be decomposed into O. Specifically, examples of the active ingredient 2 include metals and metal compounds. Preferably, examples include metal compounds.

[0022] Examples of metals include cobalt (Co), nickel (Ni), magnesium (Mg), iron (Fe), manganese (Mn), cerium (Ce), zirconium (Zr), lanthanum (La), zinc (Zn), alkali metals, and alkaline earth metals (excluding Mg). The metals can be used alone or in combination of two or more.

[0023] Examples of metal compounds include metal oxides, such as metal oxides containing at least one metal selected from the group consisting of Co, Ni, Mg, Fe, Mn, Ce, Zr, La, Zn, alkali metals, and alkaline earth metals (excluding Mg).Preferably, composite metal oxides containing Co are used.

[0024] If the active component 2 is a composite metal oxide containing Co, it can decompose nitrous oxide with high efficiency.

[0025] Examples of the composite metal oxide containing cobalt include the composite metal oxide represented by the following formula (1).

[0026] Ni Ｘ A １－Ｘ Co ２ O ４ (1) (In formula (1), A is at least one selected from the group consisting of Fe, Mn, Ce, Zr, La, alkali metals, and alkaline earth metals. X is greater than 0 and less than 1.)

[0027] The composite metal oxide represented by the above formula (1) contains dicobalt tetroxide, Ni, and A, which will be described later.

[0028] A is, for example, at least one selected from the group consisting of Fe, Mn, Ce, Zr, La, alkali metals, and alkaline earth metals. Preferably, A is at least one selected from the group consisting of Fe, Mn, Ce, Zr, La, Cs, Mg, Ca, Sr, and Ba. More preferably, A is at least one selected from the group consisting of Fe, Mn, Ce, Cs, and Sr. Even more preferably, A is at least one selected from the group consisting of Fe, Ce, and Cs. Especially preferably, A is Fe.

[0029] In the above formula (1), X is, for example, more than 0, preferably 0.25 or more, more preferably 0.50 or more, even more preferably 0.75 or more, and for example, less than 1, preferably 0.95 or less.

[0030] In the nitrous oxide decomposition catalyst 1, the composite metal oxide represented by the above formula (1) forms, for example, a spinel structure. The spinel structure is one of the crystal structures found in metal oxides, and for example, tricobalt tetroxide (Co ３ O ４ Specifically, the composite metal oxide represented by the formula (1) is a solid solution of Co, Ni, and A, and is formed into tricobalt tetroxide (Co ３ O ４ ) forms a spinel structure in which a part of Co is substituted with Ni and / or A.

[0031] Furthermore, examples of the composite metal oxide containing cobalt include composite metal oxides represented by the following formula (2).

[0032] Mg Ｙ B １－Ｙ Co ２ O ４ (2) (In formula (2), B is at least one selected from the group consisting of Fe, Mn, Zn, Ni, Zr, La, alkali metals, and alkaline earth metals (excluding Mg). Also, Y is more than 0 and less than 1.)

[0033] The composite metal oxide represented by the above formula (2) contains dicobalt tetroxide, Mg, and B, which will be described later.

[0034] B is, for example, at least one selected from the group consisting of Fe, Mn, Zn, Ni, Zr, La, alkali metals, and alkaline earth metals (excluding Mg). Preferably, B is at least one selected from the group consisting of Fe, Zn, Ni, and Sr. More preferably, B is at least one selected from the group consisting of Zn and Ni. Even more preferably, B is Zn.

[0035] In the above formula (2), Y is, for example, more than 0, preferably 0.25 or more, more preferably 0.50 or more, and even more preferably 0.75 or more, and is, for example, less than 1, preferably 0.95 or less.

[0036] In the nitrous oxide decomposition catalyst 1, the compound of the formula (2) forms, for example, a spinel structure. The spinel structure is one of the crystal structures found in oxides of metal elements, and for example, tricobalt tetroxide (Co ３ O ４ Specifically, the compound of the above formula (2) is a solid solution of Co, Mg, and B, and is formed into tricobalt tetroxide (Co ３ O ４ ) forms a spinel structure in which a part of Co is substituted with Mg and / or B.

[0037] When the active ingredient 2 is a composite metal oxide represented by the above formula (1) or (2), it can decompose nitrous oxide with high efficiency.

[0038] The active component 2 preferably contains a metal oxide. More preferably, it contains a composite metal oxide containing Co. Even more preferably, it contains a composite metal oxide represented by the above formula (1) or (2). Particularly preferably, it is a composite metal oxide represented by the above formula (1) or (2).

[0039] [Inorganic Binder] The inorganic binder 3 increases the strength of the substrate 4. The inorganic binder 3 contains a metal oxide and / or a semi-metal oxide. Preferably, the inorganic binder 3 is a metal oxide and / or a semi-metal oxide.

[0040] If the inorganic binder 3 contains a metal oxide and / or a semi-metal oxide, when a slurry containing the active component 2, the inorganic binder 3, and a dispersant is prepared in the method for producing a nitrous oxide decomposition catalyst described below, the inorganic binder 3 is uniformly dispersed in the dispersant, and the active component 2 and the inorganic binder 3 can be uniformly mixed in the slurry. Therefore, when the slurry is applied to the substrate 4, the inorganic binder 3 is uniformly applied to the substrate 4, and as a result, the strength of the nitrous oxide decomposition catalyst 1 can be improved.

[0041] Metal oxides include, for example, alumina and ceria.

[0042] An example of the semi-metal oxide is silica.

[0043] The inorganic binder 3 can be used alone or in combination of two or more kinds. That is, the inorganic binder 3 includes, for example, at least one selected from the group consisting of alumina, silica, and ceria. Preferably, the inorganic binder 3 includes at least one selected from the group consisting of alumina and silica. More preferably, the inorganic binder 3 includes alumina.

[0044] [Substrate] The substrate 4 may be, for example, an inorganic fiber sheet. Examples of the inorganic fiber sheet include glass paper and ceramic paper. Preferably, glass paper is used.

[0045] The glass paper may be commercially available glass paper containing an organic binder, such as acrylic resin, polyvinyl alcohol (PVA)-polyvinyl acetate copolymer, unsaturated polyester resin, or epoxy resin.

[0046] The shape of the substrate 4 is, for example, a flat plate and / or a corrugated plate. That is, the shape of the substrate 4 corresponds to the shape of the nitrous oxide decomposition catalyst 1. The substrate 4 is preferably flat glass paper and / or corrugated glass paper.

[0047] The dimensions of the substrate 4 are adjusted appropriately depending on the application. Specifically, the length of the substrate 4 in the first direction (exhaust gas flow direction) and the length of the substrate 4 in the second direction (width direction) are not particularly limited.

[0048] The amount of the active ingredient 2 carried per unit area of ​​the substrate 4 is, for example, 40 g / m ２ More than 75 g / m ２ or more, for example, 400 g / m ２ Preferably, 375 g / m or less ２ The amount of active ingredient 2 supported per unit area of ​​the substrate 4 is the amount of active ingredient 2 supported per unit area on the surface of the substrate 4 extending in the planar direction (exhaust gas flow direction and width direction).

[0049] 2. Method for Producing Nitrous Oxide Decomposition Catalyst One embodiment of the method for producing a nitrous oxide decomposition catalyst of the present invention will be described.

[0050] The method for producing a nitrous oxide decomposition catalyst includes, in order, a preparation step of preparing a slurry containing an active component, an inorganic binder, and a dispersant, and a coating step of applying the slurry to a substrate. If necessary, the method for producing a nitrous oxide decomposition catalyst may further include a firing step after the coating step of firing the substrate to which the slurry has been applied.

[0051] (Preparation Step) In the preparation step, a slurry containing an active ingredient, an inorganic binder, and a dispersant is prepared. Specifically, the active ingredient is prepared (preparation step), and the obtained active ingredient and inorganic binder are dispersed in a dispersant to obtain a slurry (dispersion step).

[0052] [Preparation Step] In the preparation step, the active ingredient is prepared. Methods for preparing the active ingredient include, for example, coprecipitation, citric acid complex method, evaporation to dryness method, impregnation method, and alkoxide method. Preferably, the coprecipitation method is used.

[0053] First, the case where the composite metal oxide represented by the above formula (1) as the active ingredient is prepared by the coprecipitation method will be described.

[0054] Specifically, a cobalt salt, a nickel salt, and a salt containing element A are dissolved in a solvent, and a coprecipitant is added to the prepared solution to coprecipitate a precipitate containing the composite metal oxide represented by formula (1) above, and the precipitate is calcined, thereby obtaining the composite metal oxide represented by formula (1) above as the active component.

[0055] Examples of the cobalt salt include inorganic metal salts of cobalt. Examples of the inorganic metal salts of cobalt include cobalt nitrate, cobalt sulfate, and cobalt chloride. Preferably, cobalt nitrate (Co(NO ３ ) ２ ・6H ２ O) can be mentioned.

[0056] Examples of nickel salts include inorganic metal salts of nickel. Examples of nickel inorganic metal salts include nickel nitrate, nickel sulfate, and nickel chloride. Preferably, nickel nitrate (Ni(NO ３ ) ２ ・6H ２ O) can be mentioned.

[0057] Examples of salts containing the element A include inorganic metal salts containing the element A. Examples of inorganic metal salts containing the element A include nitrates, sulfates, and chlorides containing the element A. Preferably, nitrates containing the element A are used.

[0058] Specifically, when A is Fe, examples of the iron salt include inorganic metal salts of iron. Examples of inorganic metal salts of iron include iron nitrate, iron sulfate, and iron chloride. Preferably, iron nitrate (Fe(NO ３ ) ３ ・9H ２ O) can be mentioned.

[0059] Examples of the solvent include ion-exchanged water and ultrapure water, and preferably ion-exchanged water.

[0060] The concentrations of the cobalt salt, nickel salt, and salt containing element A may be added to the solvent so as to satisfy the composition ratio in the composite metal oxide represented by the above formula (1). The cobalt salt is added to the solvent to a concentration of, for example, 0.02 mol / L or more and, for example, 20 mol / L or less. The nickel salt is added to the solvent to a concentration of, for example, 0.01 mol / L or more and, for example, 10 mol / L or less. The salt containing element A is added to the solvent to a concentration of, for example, 0.01 mol / L or more and, for example, 10 mol / L or less.

[0061] In this way, a solution in which a cobalt salt, a nickel salt, and a salt containing element A are dissolved in a solvent can be obtained.

[0062] A coprecipitant is added to the prepared solution to coprecipitate a precipitate containing the composite metal oxide represented by the above formula (1) in the solution, and the precipitate is then washed.

[0063] As the coprecipitant, for example, an alkaline liquid or solid can be used. ２ CO ３ , N.H. ３ Water and NaOH are preferred. ２ CO ３ Examples include:

[0064] The coprecipitant may be added to the extent that a precipitate forms in the solution. Specifically, the coprecipitant may be added dropwise until the pH of the solution reaches 9, at which point a precipitate forms. The coprecipitant may be added dropwise at room temperature.

[0065] The resulting precipitate is then recovered by any method, including, for example, filtration and removal of the solvent using an aspirator.

[0066] The recovered precipitate is washed and dried as necessary.

[0067] The washing method is not particularly limited, and for example, washing with ion-exchanged water repeatedly until the pH reaches 7 can be mentioned.

[0068] The method for drying the washed precipitate is not particularly limited, and examples thereof include evaporation to dryness, etc. This allows the washed precipitate to be obtained as a dry powder.

[0069] The temperature for drying the precipitate is, for example, 70° C. or higher and, for example, 120° C. or lower. The drying time for the precipitate is, for example, 3 hours or higher and, for example, 50 hours or lower.

[0070] In this manner, a precipitate (dry powder) containing the composite metal oxide represented by the above formula (1) can be obtained.

[0071] Next, the precipitate (dry powder) containing the composite metal oxide represented by the above formula (1) is calcined.

[0072] The method for calcining the precipitate (dry powder) is not particularly limited, and any known method can be used as long as the desired active ingredient can be obtained.

[0073] The firing temperature of the precipitate (dry powder) is, for example, 300° C. or higher and, for example, 800° C. or lower. The firing time of the precipitate (dry powder) is, for example, 0.5 hours or higher and, for example, 10 hours or lower.

[0074] If the calcination temperature and calcination time of the precipitate (dry powder) are within the above ranges, the composite oxide represented by the above formula (1) can be obtained without causing a decrease in activity.

[0075] In this manner, the composite metal oxide represented by the above formula (1) can be obtained as the active component.

[0076] Next, the case where the composite metal oxide represented by the above formula (2) as the active ingredient is prepared by the coprecipitation method will be described.

[0077] Specifically, a cobalt salt, a magnesium salt, and a salt containing the element B are dissolved in a solvent, and a coprecipitant is added to the prepared solution to coprecipitate a precipitate containing the composite metal oxide represented by the above formula (2), and the precipitate is calcined, thereby obtaining the composite metal oxide represented by the above formula (2) as the active component.

[0078] In addition, among the methods for preparing the composite metal oxide represented by the above formula (2) as an active component, the same parts as those in the method for preparing the composite metal oxide represented by the above formula (1) as an active component will not be described. Specifically, in the method for preparing the composite metal oxide represented by the above formula (1) as an active component, a cobalt salt, a nickel salt, and a salt containing element A are dissolved in a solvent, whereas in the method for preparing the composite metal oxide represented by the above formula (2) as an active component, a cobalt salt, a magnesium salt, and a salt containing element B are dissolved in a solvent.

[0079] Examples of the cobalt salt include the same cobalt salts as those described in the preparation method of the composite metal oxide represented by the above formula (1) as the active component.

[0080] Examples of magnesium salts include inorganic metal salts of magnesium, such as magnesium nitrate, magnesium sulfate, and magnesium chloride.

[0081] Examples of salts containing the element B include inorganic metal salts containing the element B. Examples of inorganic metal salts containing the element B include nitrates, sulfates, and chlorides containing the element B, and preferably nitrates containing the element B.

[0082] Examples of the solvent include the same solvents as those described in the preparation method of the composite metal oxide represented by the formula (1) as the active component.

[0083] The concentrations of the cobalt salt, magnesium salt, and salt containing B element may be added to the solvent so as to satisfy the composition ratio in the composite metal oxide represented by the above formula (2). The cobalt salt is added to the solvent to a concentration of, for example, 0.02 mol / L or more and, for example, 20 mol / L or less. The magnesium salt is added to the solvent to a concentration of, for example, 0.01 mol / L or more and, for example, 10 mol / L or less. The salt containing B element is added to the solvent to a concentration of, for example, 0.01 mol / L or more and, for example, 10 mol / L or less.

[0084] In this way, a solution can be obtained in which the cobalt salt, the magnesium salt, and the salt containing element B are dissolved in the solvent. Then, the composite metal oxide represented by the above formula (2) as the active component can be obtained by the same procedure as in the method for preparing the composite metal oxide represented by the above formula (1) as the active component.

[0085] [Dispersion step] In the dispersion step, for example, the active ingredient obtained in the preparation step and the inorganic binder described above are weighed, added to a dispersant, and stirred to disperse, thereby obtaining a slurry.Also, for example, the active ingredient obtained in the preparation step may be added to a dispersion liquid of an inorganic binder and a dispersant, and stirred to disperse, thereby obtaining a slurry.

[0086] The dispersant contains a carboxylic acid and / or an alcohol. The dispersant may also contain water. That is, the dispersant may be an aqueous solution of a carboxylic acid and / or an alcohol.

[0087] If the dispersant contains a carboxylic acid and / or an alcohol, the inorganic binder can be dispersed uniformly, thereby improving the strength of the nitrous oxide decomposition catalyst.

[0088] When the dispersant is an aqueous solution of a carboxylic acid and / or an alcohol, the concentration of the carboxylic acid and / or the alcohol in the aqueous solution is, for example, 0.1% or more and, for example, less than 20%.

[0089] Examples of carboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, maleic acid, fumaric acid, phthalic acid, trimellitic acid, hydroxyacetic acid, lactic acid, salicylic acid, malic acid, tartaric acid, citric acid, aspartic acid, and glutamic acid. Preferred are carboxylic acids having 1 to 6 carbon atoms. More preferred are acetic acid, citric acid, and lactic acid.

[0090] The carboxylic acids may be used alone or in combination of two or more kinds.

[0091] Examples of alcohols include methanol, ethanol, n-propanol, isopropanol, n-butyl alcohol, tert-butyl alcohol, n-pentyl alcohol, n-hexyl alcohol, 2-ethylhexanol, phenol, benzyl alcohol, ethylene glycol, propylene glycol, diethylene glycol, ethylene glycol mono-n-propyl ether, propylene glycol monomethyl ether, and glycerin. Preferred are monovalent alcohols having 1 to 4 carbon atoms. More preferred are methanol and isopropanol.

[0092] The dispersant contains a carboxylic acid and / or an alcohol, preferably at least one selected from the group consisting of acetic acid, citric acid, lactic acid, methanol, and isopropanol.

[0093] Examples of combinations of inorganic binders and dispersants include a combination containing alumina and a carboxylic acid, a combination containing silica and an alcohol, and a combination containing ceria and a carboxylic acid. Preferred examples include a combination containing alumina and acetic acid, a combination containing alumina and citric acid, a combination containing alumina and lactic acid, a combination containing silica and methanol, a combination containing silica and isopropanol, and a combination containing ceria and citric acid. More preferred examples include a combination containing alumina and acetic acid, a combination containing alumina and citric acid, a combination containing alumina and lactic acid, a combination containing silica and methanol, and a combination containing silica and isopropanol. More preferred examples include a combination containing alumina and acetic acid, a combination containing alumina and citric acid, and a combination containing alumina and lactic acid.

[0094] Commercially available dispersions containing an inorganic binder and a dispersant may also be used. Examples of commercially available dispersions include AS-200 (trade name: alumina sol containing alumina and acetic acid, manufactured by Nissan Chemical Industries, Ltd.), methanol silica sol (trade name: silica sol containing silica and methanol, manufactured by Nissan Chemical Industries, Ltd.), MA-ST series (trade name: silica sol containing silica and methanol, manufactured by Nissan Chemical Industries, Ltd.), IPA-ST series (trade name: silica sol containing silica and isopropanol, manufactured by Nissan Chemical Industries, Ltd.), PGM-ST series (trade name: silica sol containing silica and propylene glycol monomethyl ether, manufactured by Nissan Chemical Industries, Ltd.), Al-C20 (trade name: alumina sol containing alumina and citric acid, manufactured by Taki Chemical Industries, Ltd.), Al-L7 (trade name: alumina sol containing alumina and lactic acid, manufactured by Taki Chemical Industries, Ltd.), and B-10 (trade name: ceria sol containing ceria and citric acid, manufactured by Taki Chemical Industries, Ltd.).

[0095] The combination of the inorganic binder and dispersant described above allows the inorganic binder to be uniformly dispersed in the dispersant, thereby improving the strength of the nitrous oxide decomposition catalyst.

[0096] The amount of the inorganic binder mixed per 100 parts by mass of the active ingredient is, for example, 0.01 parts by mass or more, preferably 0.1 parts by mass or more, and for example, 50 parts by mass or less, preferably 30 parts by mass or less.

[0097] The amount of the inorganic binder mixed per 100 parts by mass of the active ingredient is, for example, 0.01 to 50 parts by mass, or preferably 0.1 to 30 parts by mass.

[0098] The blending amount of the inorganic binder relative to 100 parts by mass of the active component is the same ratio (blending amount) in the nitrous oxide decomposition catalyst obtained after the firing step described below.

[0099] The amount of the active ingredient mixed per 100 parts by mass of the dispersant is, for example, 30 parts by mass or more, preferably 50 parts by mass or more, and for example, 300 parts by mass or less, preferably 200 parts by mass or less.

[0100] The amount of the active ingredient blended relative to 100 parts by mass of the dispersant is, for example, 30 to 300 parts by mass, or preferably 50 to 200 parts by mass.

[0101] The content of the inorganic binder in the dispersant is, for example, 0.1 mass % or more, preferably 0.5 mass % or more, and for example, 50 mass % or less, preferably 30 mass % or less.

[0102] The content of the inorganic binder in the dispersant is, for example, 0.1% by mass to 50% by mass, or preferably 0.5% by mass to 30% by mass.

[0103] When the content of the inorganic binder in the dispersant is within the above range, the inorganic binder can be reliably dispersed uniformly in the dispersant.

[0104] The method for stirring the active ingredient and / or inorganic binder is not particularly limited, and any known method can be used. The stirring time is, for example, 5 to 30 minutes.

[0105] In this way, a slurry containing the active ingredient, the inorganic binder, and the dispersant can be obtained.

[0106] (Coating Step) In the coating step, the slurry obtained in the preparation step is coated onto a substrate.

[0107] In the coating step, the substrate preferably has a flat plate shape, more preferably a flat glass paper.

[0108] Examples of the coating method include the so-called dipping method, brush coating method, spray coating method, and drop coating method. The brush coating method is preferred.

[0109] When the slurry is applied to the substrate by a brush coating method, specifically, the slurry obtained in the preparation step is dropped onto the substrate and spread over the substrate using a brush.

[0110] In this way, a substrate coated with the slurry can be obtained.

[0111] (Firing Step) In the firing step, the substrate coated with the slurry is fired. More specifically, the substrate coated with the slurry is dried and then fired.

[0112] As a method for drying the substrate coated with the slurry, for example, a method of placing the substrate coated with the slurry in a heated mold and drying the slurry can be mentioned.

[0113] The drying temperature (heating temperature of the mold) of the substrate coated with the slurry is, for example, 70° C. or more and, for example, 120° C. or less. The drying time of the substrate coated with the slurry is, for example, 0.5 hours or more and, for example, 50 hours or less.

[0114] When the shape of the substrate coated with the slurry after drying is to be flat, the substrate coated with the slurry is dried using a flat mold. When the shape of the substrate coated with the slurry after drying is to be corrugated, the substrate coated with the slurry is dried and simultaneously shaped into a corrugated shape. Specifically, the substrate coated with the slurry is placed in a heated corrugated mold and shaped using a jig.

[0115] Next, the substrate coated with the dried slurry is fired.

[0116] The method for firing the substrate coated with the dried slurry is not particularly limited, and a known method can be used. The substrate coated with the dried slurry can be fired in a stacked state of multiple sheets. Specifically, flat substrates coated with the dried slurry and corrugated substrates coated with the dried slurry can be alternately stacked and fired.

[0117] The baking temperature of the substrate coated with the dried slurry is, for example, 300° C. or more and, for example, 800° C. or less. The baking time of the substrate coated with the dried slurry is, for example, 0.5 hours or more and, for example, 10 hours or less.

[0118] In this way, a catalyst for decomposing nitrous oxide can be obtained.

[0119] The nitrous oxide decomposition catalyst obtained by the above-mentioned method for producing a nitrous oxide decomposition catalyst has high strength.

[0120] 3. Nitrous Oxide Decomposition Catalyst Apparatus One embodiment of a nitrous oxide decomposition catalyst apparatus 10 including the above-described nitrous oxide decomposition catalyst 1 will now be described with reference to FIG.

[0121] The nitrous oxide decomposition catalyst device 10 is disposed in an exhaust passage through which exhaust gas flows. ２ The system is equipped with a nitrous oxide decomposition catalyst 1 that decomposes O.

[0122] 2, the nitrous oxide decomposition catalyst device 10 includes, for example, a nitrous oxide decomposition catalyst unit 11. The nitrous oxide decomposition catalyst unit 11 includes a casing 12 and a nitrous oxide decomposition catalyst 1 filled in the casing 12.

[0123] The nitrous oxide decomposition catalyst device 10 includes a plurality of nitrous oxide decomposition catalyst units 11. The number of nitrous oxide decomposition catalyst units 11 in the nitrous oxide decomposition catalyst device 10 is not particularly limited as long as it is two or more, and can be adjusted appropriately depending on the installation space, etc. Furthermore, a plurality of nitrous oxide decomposition catalyst units 11 are arranged in a direction perpendicular to the exhaust gas flow direction. In one embodiment of the nitrous oxide decomposition catalyst device 10 shown in Figure 2, the plurality of nitrous oxide decomposition catalyst units 11 are aligned in a first direction (e.g., width direction) perpendicular to the exhaust gas flow direction, and a second direction (e.g., height direction) perpendicular to the exhaust gas flow direction and the first direction.

[0124] The shape of the casing 12 is not particularly limited, but examples thereof include a rectangular tube shape and a cylindrical shape extending in the exhaust gas flow direction. A rectangular tube shape extending in the exhaust gas flow direction is preferred. Specifically, the casing 12 may be one consisting of a casing main body that is generally U-shaped in cross section and a flat lid that covers the opening of the casing main body, one consisting of only a casing main body that is generally square-shaped in cross section, or one consisting of a casing main body that is generally L-shaped in cross section and a lid that fits onto the casing and has a generally inverted L-shaped in cross section.

[0125] The dimensions of the casing 12 are adjusted as appropriate depending on the application. Specifically, the width of the casing 12 is not particularly limited as long as it can accommodate the nitrous oxide decomposition catalyst 1. Furthermore, the height of the casing 12 is not particularly limited as long as it can ensure an appropriate number of layers of the nitrous oxide decomposition catalyst 1.

[0126] The inorganic fiber blanket 13 may be laid on the entire inner peripheral surface of the casing 12. By laying the inorganic fiber blanket 13 on the inner surface of the casing 12, vibration can be suppressed.

[0127] Examples of inorganic fibers of the inorganic fiber blanket 13 include ceramic fibers, glass fibers, silica sol fibers, alumina fibers, and rock wool. Ceramic fibers are preferred.

[0128] In the nitrous oxide decomposition catalyst unit 11, the nitrous oxide decomposition catalyst 1 is packed in a direction perpendicular to the flow direction of exhaust gas within the casing 12. Specifically, in the nitrous oxide decomposition catalyst unit 11, flat plate-shaped nitrous oxide decomposition catalysts 1 and corrugated plate-shaped nitrous oxide decomposition catalysts 1 are alternately stacked without being bonded within the casing 12. By stacking them in this manner, the nitrous oxide decomposition catalyst 1 forms a cross-sectional network structure (honeycomb structure).

[0129] The number of stacked flat plate-shaped nitrous oxide decomposition catalysts 1 and corrugated plate-shaped nitrous oxide decomposition catalysts 1 is not particularly limited.

[0130] The nitrous oxide decomposition catalyst unit 11 is manufactured by preparing a casing 12 with an inorganic fiber blanket 13 laid on the inner surface, and filling the casing 12 with a stack of nitrous oxide decomposition catalysts 1, in which flat nitrous oxide decomposition catalysts 1 and corrugated nitrous oxide decomposition catalysts 1 are alternately stacked without being bonded together.

[0131] The nitrous oxide decomposition catalyst device 10 is manufactured by arranging the nitrous oxide decomposition catalyst units 11 manufactured as described above in a line in the width direction and height direction as shown in FIG.

[0132] The method for producing a nitrous oxide decomposition catalyst of the present invention includes a preparation step of preparing a slurry containing an active component, an inorganic binder, and a dispersant, wherein the inorganic binder contains a metal oxide and / or a semi-metal oxide, and the dispersant contains a carboxylic acid and / or an alcohol. Therefore, the inorganic binder is uniformly dispersed in the dispersant, thereby improving the strength of the nitrous oxide decomposition catalyst.

[0133] 5. Modifications In the modification, the same components and steps as those in the above-described embodiment of the nitrous oxide decomposition catalyst are designated by the same reference numerals, and detailed descriptions thereof will be omitted. Furthermore, unless otherwise specified, the modification can achieve the same effects as those in the embodiment of the nitrous oxide decomposition catalyst. Furthermore, the above-described embodiment and modification of the nitrous oxide decomposition catalyst can be combined as appropriate.

[0134] In one embodiment of the above-described nitrous oxide decomposition catalyst, a flat and / or corrugated inorganic fiber sheet is used as the substrate 4 supporting the active component 2 and inorganic binder 3 in the nitrous oxide decomposition catalyst 1, but this is not limited thereto. Specifically, the substrate 4 supporting the active component 2 and inorganic binder 3 may be any substrate that is typically used in nitrous oxide decomposition catalysts 1, and examples thereof include monolith substrates having a cross-sectional network structure (honeycomb structure).

[0135] Examples of materials for the monolith substrate include ceramics, cordierite, silicon carbide, silica, alumina, mullite, ceria, zirconia, composite oxides thereof, solid solutions thereof, and mixtures thereof.

[0136] The shape of the monolith substrate is not particularly limited as long as it has a cross-sectional mesh structure, and examples thereof include a columnar body and a block body.

[0137] Furthermore, as the monolith substrate having a cross-sectional mesh structure (honeycomb structure), known ones can be used, and examples thereof include honeycomb filters and high-density honeycombs.

[0138] When a monolith substrate having a cross-sectional mesh structure (honeycomb structure) is used, the nitrous oxide decomposition catalyst can be manufactured by the same manufacturing method as the embodiment of the manufacturing method of the nitrous oxide decomposition catalyst described above. Specifically, like the embodiment of the manufacturing method of the nitrous oxide decomposition catalyst described above, the manufacturing method includes a preparation step, a coating step, and, if necessary, a calcination step.

[0139] More specifically, as in the above-described embodiment of the method for producing a nitrous oxide decomposition catalyst, a slurry containing an active component, an inorganic binder, and a dispersant is first prepared (preparation step). Next, the obtained slurry is applied to a monolith substrate having a cross-sectional network structure (honeycomb structure) by a hot-dip method (coating step). Thereafter, the monolith substrate having a cross-sectional network structure (honeycomb structure) to which the slurry has been applied is fired (firing step).

[0140] More specifically, as in the above-described embodiment of the method for producing a nitrous oxide decomposition catalyst, a slurry containing an active component, an inorganic binder, and a dispersant is first prepared (preparation step). Next, the obtained slurry is applied to a monolith substrate having a cross-sectional network structure (honeycomb structure) by a hot-dip method (coating step). Thereafter, the monolith substrate having a cross-sectional network structure (honeycomb structure) to which the slurry has been applied is fired (firing step).

[0141] In this way, a nitrous oxide decomposition catalyst can be produced using a monolith substrate having a cross-sectional mesh structure (honeycomb structure).

[0142] The present invention will be described in more detail below with reference to examples and comparative examples. It should be noted that the present invention is in no way limited to these examples and comparative examples. The specific numerical values ​​of the blending ratios (content ratios), physical property values, parameters, etc. used in the following description can be replaced with the upper limit (a numerical value defined as "equal to or less than") or lower limit (a numerical value defined as "equal to or more than") of the corresponding blending ratios (content ratios), physical property values, parameters, etc. described in the "Description of the Invention" above.

[0143] Example 1 (Preparation Step) Nickel nitrate (Ni(NO ３ ) ２・6H ２ O), iron nitrate (Fe(NO ３ ) ３ ・9H ２ O), and cobalt nitrate (Co(NO ３ ) ２ ・6H ２ O) in a composition ratio (atomic ratio) of Ni ０．９ Fe ０．１ Co ２ O ４ The solution was then stirred while adding 15 wt % K. ２ CO ３ was added dropwise at 10 mL / min until the pH reached 9, yielding a precipitate. The precipitate was filtered and washed with ion-exchanged water. Filtration and washing were repeated until the pH of the ion-exchanged water used for washing reached 7. The washed precipitate was recovered, dried at 100°C for 12 hours, and calcined at 400°C for 2 hours to yield an active ingredient.

[0144] Next, 224 parts by mass of the active ingredient and 74 parts by mass of ion-exchanged water were added to 100 parts by mass of AS-200 (trade name, alumina sol containing alumina and acetic acid, manufactured by Nissan Chemical Industries, Ltd.) and dispersed to obtain a slurry.

[0145] (Coating process) The slurry obtained in the preparation process was applied to a flat glass paper sheet with a length of 250 mm in the direction of exhaust gas flow, a length of 80 mm in the width direction, and a thickness of 0.8 mm by a brush coating method. Specifically, the slurry obtained in the preparation process was dropped onto the glass paper sheet, and then spread over the glass paper sheet using a brush. In this way, the active component and the inorganic binder were supported on the glass paper sheet.

[0146] At this time, the amount of the active ingredient carried per unit area of ​​the substrate (glass paper) was 270 g / m ２ It was.

[0147] (Firing step) The glass paper carrying the active component and the inorganic binder was dried at 100° C. for 1 hour, and then further dried at 120° C. for 2 hours. After drying, the glass paper was fired at 400° C. for 4 hours to obtain the nitrous oxide decomposition catalyst of Example 1.

[0148] Example 2 A nitrous oxide decomposition catalyst of Example 2 was obtained in the same manner as in Example 1, except that the inorganic binder and dispersant were changed to those shown in Table 1. Specifically, Al-C20 (trade name, alumina sol containing alumina and citric acid, manufactured by Taki Chemical Industry Co., Ltd.) was used as the dispersion containing the inorganic binder and dispersant.

[0149] Example 3 A nitrous oxide decomposition catalyst of Example 3 was obtained in the same manner as in Example 1, except that the inorganic binder and dispersant were changed to those shown in Table 1. Specifically, Al-L7 (trade name, alumina sol containing alumina and lactic acid, manufactured by Taki Chemical Industry Co., Ltd.) was used as the dispersion containing the inorganic binder and dispersant.

[0150] Example 4 A nitrous oxide decomposition catalyst of Example 4 was obtained in the same manner as in Example 1, except that the inorganic binder and dispersant were changed to those shown in Table 1. Specifically, methanol silica sol (trade name: silica sol containing silica and methanol, manufactured by Nissan Chemical Industries, Ltd.) was used as the dispersion containing the inorganic binder and dispersant.

[0151] Example 5 A nitrous oxide decomposition catalyst of Example 5 was obtained in the same manner as in Example 1, except that the inorganic binder and dispersant were changed to those shown in Table 1. Specifically, IPA-ST (trade name, silica sol containing silica and isopropanol, manufactured by Nissan Chemical Industries, Ltd.) was used as the dispersion containing the inorganic binder and dispersant.

[0152] Example 6 A nitrous oxide decomposition catalyst of Example 6 was obtained in the same manner as in Example 1, except that the inorganic binder and dispersant were changed to those shown in Table 1. Specifically, B-10 (trade name, ceria sol containing ceria and citric acid, manufactured by Taki Chemical Industry Co., Ltd.) was used as the dispersion containing the inorganic binder and dispersant.

[0153] Comparative Example 1 A nitrous oxide decomposition catalyst of Comparative Example 1 was obtained in the same manner as in Example 1, except that the inorganic binder and dispersant were changed to those shown in Table 1. Specifically, Aluminasol 520 (trade name, alumina sol containing alumina and nitric acid, manufactured by Nissan Chemical Industries, Ltd.) was used as the dispersion containing the inorganic binder and dispersant.

[0154] Comparative Example 2 A nitrous oxide decomposition catalyst of Comparative Example 2 was obtained in the same manner as in Example 1, except that the inorganic binder and dispersant were changed to those shown in Table 1. Specifically, ZSL-20N (trade name, zirconia sol consisting of zirconia and water, manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd.) was used as the dispersion liquid containing the inorganic binder and dispersant.

[0155] Comparative Example 3 A nitrous oxide decomposition catalyst of Comparative Example 3 was obtained in the same manner as in Example 1, except that the inorganic binder and dispersant were changed to those shown in Table 1. Specifically, Snowtex O (trade name, silica sol consisting of silica and water, manufactured by Nissan Chemical Industries, Ltd.) was used as the dispersion liquid containing the inorganic binder and dispersant.

[0156] <Evaluation> [Strength] The nitrous oxide decomposition catalyst (flat plate) of each Example and Comparative Example was lifted with a finger, and the strength of the nitrous oxide decomposition catalyst was evaluated according to the following criteria. The results are shown in Table 1. {Criteria} A: Maintains flat shape when lifted B: Breaks when lifted

[0157]

[0158] <Discussion> Referring to Table 1, it can be seen that all of the nitrous oxide decomposition catalysts of Examples were able to maintain their flat shape without breaking when lifted, indicating improved strength. In contrast, the nitrous oxide decomposition catalysts of Comparative Examples 1 to 3 broke when lifted, indicating insufficient strength.

[0159] In addition, the nitrous oxide decomposition catalysts of Examples 1 to 6 were subjected to the same conditions as those of Examples 1 to 6, except that air, N ２ , N ２ O and H ２ The gas containing O is contacted with the N ２ From the O concentration, N after contact ２ It was confirmed that the O concentration decreased. In other words, it was confirmed that all of the nitrous oxide decomposition catalysts of Examples 1 to 6 had activity.

[0160] The above invention is provided as an exemplary embodiment of the present invention, but this is merely an example and should not be interpreted as limiting. Modifications of the present invention that are obvious to those skilled in the art are intended to be included in the scope of the following claims.

[0161] The method for producing a nitrous oxide decomposition catalyst of the present invention is suitably used for producing a nitrous oxide decomposition catalyst that decomposes nitrous oxide and is used to treat exhaust gases.

[0162] 1 Nitrous oxide decomposition catalyst 2 Active component 3 Inorganic binder 4 Substrate

Claims

1. A method for producing a nitrous oxide decomposition catalyst that decomposes nitrous oxide in exhaust gas, comprising: a preparation step of preparing a slurry containing an active ingredient, an inorganic binder, and a dispersant; and a coating step of coating the slurry onto a substrate, wherein the inorganic binder contains a metal oxide and / or a semi-metal oxide, and the dispersant contains a carboxylic acid and / or an alcohol.

2. The method for producing a nitrous oxide decomposition catalyst according to claim 1, wherein the inorganic binder comprises at least one selected from the group consisting of alumina, silica, and ceria.

3. The method for producing a catalyst for decomposing nitrous oxide according to claim 1, wherein the dispersant comprises at least one selected from the group consisting of acetic acid, citric acid, lactic acid, methanol, and isopropanol.

4. The method for producing a nitrous oxide decomposition catalyst according to any one of claims 1 to 3, wherein the active component is a composite metal oxide containing cobalt.

5. The method for producing a nitrous oxide decomposition catalyst according to claim 4, wherein the composite metal oxide is a composite metal oxide represented by the following formula (1) or (2): Ｘ A １－Ｘ Co ２ O ４ (1) (In formula (1), A is at least one selected from the group consisting of Fe, Mn, Ce, Zr, La, alkali metals, and alkaline earth metals. X is greater than 0 and less than 1.) Mg Ｙ B １－Ｙ Co ２ O ４ (2) (In formula (2), B is at least one metal selected from the group consisting of Fe, Mn, Zn, Ni, Zr, La, alkali metals, and alkaline earth metals (excluding Mg). Also, Y is greater than 0 and less than 1.) 6. The method for producing a nitrous oxide decomposition catalyst according to any one of claims 1 to 3, wherein the substrate is an inorganic fiber sheet.

7. The method for producing a nitrous oxide decomposition catalyst according to any one of claims 1 to 3, further comprising a calcination step of calcining the substrate coated with the slurry after the coating step.

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