Method for producing nitrous oxide decomposition catalyst, and nitrous oxide decomposition catalyst

Abstract

This method for producing a nitrous oxide decomposition catalyst for decomposing the nitrous oxide in an exhaust gas comprises a preparation step for preparing a product that contains the following: an active component containing the composite metal oxide represented by formula (1); and an impurity component containing an alkali metal element. The product containing the active component and impurity component is prepared in the preparation step by a coprecipitation method using a coprecipitation agent containing an alkali metal element. In the product, the percentage content of alkali metal element with reference to the total main element amount in the active component and impurity component is at least 0.45 mass% and not more than 4.50 mass%.　(1): NiXA1-XCo2O4 (In formula (1), A is at least one selected from the group consisting of Fe, Mn, Ce, Zr, La, and alkaline earth metals. In addition, X is greater than 0 and less than 1.)

Description

Method for producing nitrous oxide decomposition catalyst and nitrous oxide decomposition catalyst

[0001] The present disclosure relates to a method for producing a nitrous oxide decomposition catalyst and a nitrous oxide decomposition catalyst.

[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 a nitrous oxide decomposition catalyst, which is one of such catalysts for treating exhaust gases, a method has been proposed which includes a step of adding a coprecipitant to an aqueous solution prepared by mixing a nickel salt, a cobalt salt, and a copper salt to obtain a precipitate (see, for example, Patent Document 1). Patent Document 1 exemplifies a coprecipitant containing an alkali metal element.

[0004] Japanese Patent Application Laid-Open No. 2022-098865

[0005] In the nitrous oxide decomposition catalyst described in Patent Document 1, the component containing an alkali metal element used as a coprecipitant is an impurity component. Such impurity components are removed by thoroughly washing the resulting precipitate. However, the present inventors have discovered that the nitrous oxide decomposition rate can be improved by leaving a specific content of impurity components containing an alkali metal element in the nitrous oxide decomposition catalyst.

[0006] The present disclosure provides a method for producing a nitrous oxide decomposition catalyst and a nitrous oxide decomposition catalyst that can improve the nitrous oxide decomposition rate.

[0007] The present disclosure [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 product containing an active component containing a composite metal oxide represented by the following formula (1) and an impurity component containing an alkali metal element, wherein in the preparation step, the product containing the active component and the impurity component is prepared by coprecipitation using a coprecipitant containing the alkali metal element, and the content of the alkali metal element relative to the total amount of main elements of the active component and the impurity component is 0.80 mass% or more and 4.20 mass% or less. Ｘ A１－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, and alkaline earth metals. X is greater than 0 and less than 1.)

[0008] The present disclosure [2] includes a method for producing the nitrous oxide decomposition catalyst according to [1], further comprising a preparation step of preparing a slurry containing the product, an inorganic binder, and a dispersant, and a coating step of coating the slurry on a substrate.

[0009] The present disclosure [3] includes the method for producing a nitrous oxide decomposition catalyst according to [2], wherein the inorganic binder contains at least one selected from the group consisting of metal hydroxides and metal oxides.

[0010] The present disclosure [4] includes the method for producing a nitrous oxide decomposition catalyst according to [2] or [3], wherein the dispersant contains at least one selected from the group consisting of a carboxylic acid, an alcohol, and water.

[0011] The present disclosure [5] includes the method for producing a nitrous oxide decomposition catalyst according to any one of [2] to [4], wherein the substrate is an inorganic fiber sheet.

[0012] The present disclosure [6] includes the method for producing a nitrous oxide decomposition catalyst according to any one of [2] to [5], further comprising a calcination step of calcining the substrate coated with the slurry after the coating step.

[0013] The present disclosure [7] includes a nitrous oxide decomposition catalyst comprising an active component containing a composite metal oxide represented by the following formula (1) and an impurity component containing an alkali metal element, wherein the content of the alkali metal element relative to the total amount of main elements of the active component and the impurity component is 0.80 mass% or more and 4.20 mass% or less. 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, and alkaline earth metals. X is greater than 0 and less than 1.)

[0014] The present disclosure [8] includes the nitrous oxide decomposition catalyst according to [7], wherein the alkali metal element is K.

[0015] The present disclosure [9] includes the nitrous oxide decomposition catalyst according to [7] or [8], wherein the content of the alkali metal element relative to the total amount of main elements of the active component and the impurity component is 1.15 mass% or more and 3.80 mass% or less.

[0016] The present disclosure

[10] includes the nitrous oxide decomposition catalyst according to any one of [7] to [9], further comprising an inorganic binder and a substrate that supports the active component, the impurity component, and the inorganic binder.

[0017] The present disclosure

[11] includes the nitrous oxide decomposition catalyst according to

[10] , wherein the inorganic binder includes at least one selected from the group consisting of metal hydroxides and metal oxides.

[0018] The present disclosure

[12] includes the nitrous oxide decomposition catalyst according to

[10] or

[11] , wherein the substrate is an inorganic fiber sheet.

[0019] The method for producing a nitrous oxide decomposition catalyst according to the present disclosure includes a preparation step of preparing a product containing an active component containing the composite metal oxide represented by formula (1) above and an impurity component containing an alkali metal element, wherein the content of the alkali metal element relative to the total amount of main elements in the active component and the impurity component is 0.80 mass% or more and 4.20 mass% or less, thereby improving the nitrous oxide decomposition rate.

[0020] The nitrous oxide decomposition catalyst of the present disclosure comprises an active component containing the composite metal oxide represented by formula (1) above and an impurity component containing an alkali metal element, and the content of the alkali metal element relative to the total amount of main elements of the active component and the impurity component is 0.80 mass% or more and 4.20 mass% or less, thereby enabling an improvement in the nitrous oxide decomposition rate.

[0021] Figure 1 is a perspective view showing the nitrous oxide decomposition catalyst of the present disclosure. Figure 2 is a perspective view showing a nitrous oxide decomposition catalyst device including a nitrous oxide decomposition catalyst unit packed with the nitrous oxide decomposition catalyst shown in Figure 1. Figure 3 is a graph showing the relationship between the nitrous oxide decomposition rate (%) and the content ratio (mass %) of alkali metal elements relative to the total amount of main elements of the active component and impurity components for the nitrous oxide decomposition catalysts of Examples 1 to 8 and Comparative Examples 1 to 7.

[0022] 1. Nitrous Oxide Decomposition Catalyst One embodiment of a nitrous oxide decomposition catalyst 1 will be described with reference to FIG.

[0023] 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

[0024] Nitrous oxide decomposition catalyst 1 comprises active component 2 and impurity components 5. Nitrous oxide decomposition catalyst 1 further comprises inorganic binder 3 and substrate 4, as required. As will be described in detail later, in nitrous oxide decomposition catalyst 1 of this embodiment, active component 2, impurity components 5, and inorganic binder 3 are supported on substrate 4.

[0025] As described above, the nitrous oxide decomposition catalyst 1 contains the active component 2 and the impurity component 5. As will be described in detail later, if the nitrous oxide decomposition catalyst 1 contains the impurity component 5 at a specific content ratio, the nitrous oxide decomposition rate can be improved.

[0026] The nitrous oxide decomposition catalyst 1 is in the form of a flat plate and / or a corrugated plate.

[0027] 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.

[0028] [Active Component] The active component 2 contains a composite metal oxide represented by the following formula (1): The active component 2 preferably comprises a composite metal oxide represented by the following formula (1).

[0029] Ni Ｘ A１－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, and alkaline earth metals. X is greater than 0 and less than 1.)

[0030] The composite metal oxide represented by the above formula (1) contains dicobalt tetroxide, Ni, and A, which will be described later.

[0031] A is, for example, at least one selected from the group consisting of Fe, Mn, Ce, Zr, La, and alkaline earth metals. Preferably, A is at least one selected from the group consisting of Fe, Mn, Ce, Zr, La, Mg, Ca, Sr, and Ba. More preferably, A is at least one selected from the group consisting of Fe, Mn, Ce, and Sr. Even more preferably, A is at least one selected from the group consisting of Fe and Ce. Especially preferably, A is Fe.

[0032] 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.

[0033] 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.

[0034] When the active ingredient 2 is a composite metal oxide represented by the above formula (1), it can decompose nitrous oxide with high efficiency, in other words, it can improve the decomposition rate of nitrous oxide.

[0035] 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). Particularly preferably, it is a composite metal oxide represented by the above formula (1).

[0036] 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).

[0037] [Impurity Components] The impurity components 5 are mixed in during the preparation process described below. Specifically, in the preparation process, a precipitate containing an active component is prepared by a coprecipitation method using a coprecipitant. This coprecipitant contains an alkali metal element. Therefore, the impurity components 5 containing the alkali metal element derived from this coprecipitant are mixed in the precipitate. Typically, the impurity components 5 are removed by washing the precipitate. In the present disclosure, the impurity components 5 containing the alkali metal element derived from the coprecipitant are intentionally left.

[0038] In this embodiment, the impurity components 5 are mixed in during the manufacturing process, but are not limited to this. The impurity components 5 may also be added separately.

[0039] The impurity components 5 contain alkali metal elements. Examples of alkali metal elements include K (potassium element) and Na (sodium element). Preferably, K is used. Note that K and Na as alkali metal elements mean potassium element and sodium element, respectively.

[0040] Specifically, the impurity components 5 include, for example, alkali metals and compounds containing alkali metal elements. Examples of alkali metals include potassium and sodium. Examples of compounds containing alkali metal elements include oxides of alkali metals, hydroxides of alkali metals, and carbonates of alkali metals. Examples of alkali metal oxides include potassium oxide and sodium oxide. Examples of alkali metal hydroxides include potassium hydroxide and sodium hydroxide. Examples of alkali metal carbonates include potassium carbonate, sodium carbonate, potassium bicarbonate, and sodium bicarbonate. Note that potassium and sodium as alkali metals refer to metallic potassium and metallic sodium, respectively.

[0041] That is, the impurity components 5 contain at least one selected from the group consisting of alkali metals and compounds containing alkali metal elements. Preferably, the impurity components 5 contain at least one selected from the group consisting of potassium and compounds containing K (elemental potassium). More preferably, the impurity components 5 contain at least one selected from the group consisting of potassium and potassium oxide.

[0042] The nitrous oxide decomposition rate can be improved if the nitrous oxide decomposition catalyst 1 contains a specific content of impurity components 5 containing an alkali metal element. In particular, the nitrous oxide decomposition rate can be further improved if the nitrous oxide decomposition catalyst 1 contains a specific content of impurity components 5 containing K (potassium) as an alkali metal element.

[0043] The impurity component 5 may contain one alkali metal element or may contain multiple alkali metal elements. Furthermore, the impurity component 5 may be a single alkali metal or a compound containing an alkali metal element, or may be a combination of multiple alkali metals and compounds containing alkali metal elements.

[0044] The amount of impurities 5 carried per unit area of ​​the substrate 4 is, for example, 0.10 g / m ２ More than 0.30 g / m ２ More preferably, 0.45 g / m２ or more, for example, 30 g / m ２ Preferably, 20 g / m or less ２ More preferably, 15 g / m ２ The amount of impurities 5 supported per unit area of ​​the substrate 4 is the amount of impurities 5 supported per unit area on the surface of the substrate 4 extending in the planar direction (flow direction and width direction of the exhaust gas).

[0045] The content ratio of the alkali metal element relative to the total amount of the main elements of the active component 2 and the impurity components 5 is 0.80% by mass or more, preferably 1.00% by mass or more, and more preferably 1.15% by mass or more. The content ratio of the alkali metal element relative to the total amount of the main elements of the active component 2 and the impurity components 5 is 4.20% by mass or less, preferably 4.00% by mass or less, and more preferably 3.80% by mass or less. The content ratio of the alkali metal element relative to the total amount of the main elements of the active component 2 and the impurity components 5 is, for example, 0.80% by mass to 4.20% by mass, preferably 1.00% by mass to 4.00% by mass, and more preferably 1.15% by mass to 3.80% by mass.

[0046] If the content ratio of the alkali metal element relative to the total amount of the main elements of the active component 2 and the impurity component 5 is within the above range, the nitrous oxide decomposition rate can be improved.

[0047] The total amount of the main elements in the active component 2 and the impurity component 5 is the total amount of the main elements contained in the active component 2, namely, Ni, A (A is at least one selected from the group consisting of Fe, Mn, Ce, Zr, La, and alkaline earth metals), Co, and O, and the main elements contained in the impurity component 5, namely, alkali metal elements (specifically, K and Na) and O.

[0048] The content ratio of the alkali metal element relative to the total amount of the main elements in the active component 2 and the impurity component 5 can be measured, for example, by energy dispersive X-ray fluorescence analysis.

[0049] [Inorganic Binder] The inorganic binder 3 increases the strength of the substrate 4. There are no particular limitations on the inorganic binder 3, as long as it is one that is commonly used in nitrous oxide decomposition catalysts. Examples of the inorganic binder 3 include metal hydroxides and metal oxides. The inorganic binder 3 preferably contains at least one selected from the group consisting of metal hydroxides and metal oxides. Note that the inorganic binder 3 does not contain an alkali metal element. Specifically, the inorganic binder 3 excludes alkali metal hydroxides and alkali metal oxides. In other words, the inorganic binder 3 is different from the impurity components 5.

[0050] If inorganic binder 3 contains at least one selected from the group consisting of metal hydroxides and metal oxides, when a slurry containing active component 2, impurity component 5, inorganic binder 3, and a dispersant is prepared in the method for producing a nitrous oxide decomposition catalyst described below, inorganic binder 3 is uniformly dispersed in the dispersant, and active component 2, impurity component 5, and inorganic binder 3 can be uniformly mixed in the slurry. Therefore, when the slurry is applied to substrate 4, inorganic binder 3 is uniformly applied to substrate 4, and as a result, the strength of nitrous oxide decomposition catalyst 1 can be improved.

[0051] Examples of metal hydroxides include iron hydroxide, zirconium hydroxide, aluminum hydroxide, cerium hydroxide, magnesium hydroxide, and aluminum oxide hydroxide.

[0052] The metal hydroxides can be used alone or in combination of two or more. That is, the metal hydroxide includes, for example, at least one selected from the group consisting of iron hydroxide, zinc hydroxide, aluminum hydroxide, cerium hydroxide, magnesium hydroxide, and aluminum hydroxide oxide. Preferably, the metal hydroxide includes at least one selected from the group consisting of iron hydroxide, aluminum hydroxide, and cerium hydroxide. More preferably, the metal hydroxide includes iron hydroxide.

[0053] Examples of metal oxides include alumina, ceria, and silica. Although silica is silicon oxide, it is included in the metal oxides in the present disclosure.

[0054] The metal oxide can be used alone or in combination of two or more kinds. That is, the metal oxide includes, for example, at least one selected from the group consisting of alumina, silica, and ceria. Preferably, the metal oxide includes at least one selected from the group consisting of alumina and silica. More preferably, the metal oxide includes alumina.

[0055] The inorganic binder 3 can be used alone or in combination of two or more kinds. That is, a metal hydroxide and a metal oxide may be used in combination.

[0056] The amount of the inorganic binder 3 carried per unit area of ​​the substrate 4 is, for example, 0.4 g / m ２ More than 1.0 g / m ２ More preferably, 2.0 g / m ２ or more, for example, 320 g / m ２ Preferably, 250 g / m or less ２ More preferably, 200 g / m ２ The amount of inorganic binder 3 supported per unit area of ​​the substrate 4 is the amount of inorganic binder 3 supported per unit area on the surface of the substrate 4 extending in the surface direction (exhaust gas flow direction and width direction).

[0057] [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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 2. Method for Producing Nitrous Oxide Decomposition Catalyst One embodiment of the method for producing a nitrous oxide decomposition catalyst according to the present disclosure will be described. The method for producing a nitrous oxide decomposition catalyst is a method for producing the above-described nitrous oxide decomposition catalyst that decomposes nitrous oxide in exhaust gas.

[0062] The method for producing a nitrous oxide decomposition catalyst includes, in order, a preparation step of preparing a product containing an active component containing the composite metal oxide represented by formula (1) above and an impurity component containing an alkali metal element, a preparation step of preparing a slurry containing the product containing the active component and the impurity component, an inorganic binder, and a dispersant, and a coating step of applying the slurry to a substrate. The method for producing a nitrous oxide decomposition catalyst may further include, as necessary, a calcination step after the coating step of calcining the substrate to which the slurry has been applied.

[0063] (Preparation Step) In the preparation step, a product containing the active ingredient and impurities is prepared. Examples of a method for preparing a product containing the active ingredient and impurities include a coprecipitation method.

[0064] Specifically, a product containing an active component containing the composite metal oxide represented by the above formula (1) and impurity components containing alkali metal elements is prepared by a coprecipitation method using a coprecipitant containing an alkali metal element.

[0065] First, a cobalt salt, a nickel salt, and a salt containing the element A are dissolved in a solvent, and a coprecipitant is added to the prepared solution to coprecipitate a precipitate containing an active component containing the composite metal oxide represented by the above formula (1) and an impurity component containing an alkali metal element. The precipitate is then washed and calcined, thereby obtaining a product containing an active component containing the composite metal oxide represented by the above formula (1) and an impurity component containing an alkali metal element.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] Examples of the solvent include ion-exchanged water and ultrapure water, and preferably ion-exchanged water.

[0071] 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.

[0072] 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.

[0073] A coprecipitating agent is added to the prepared solution, and a precipitate containing the active component containing the composite metal oxide represented by the above formula (1) and impurity components containing alkali metal elements is coprecipitated in the solution, and the precipitate is then washed.

[0074] The co-precipitating agent may be, for example, an alkaline liquid or solid. The co-precipitating agent may also contain an alkali metal element. For example, K ２ CO ３ , and NaOH. Preferably, K ２ CO ３ The alkali metal element contained in the coprecipitant is the same as the alkali metal element contained in the impurity component.

[0075] 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.

[0076] The resulting precipitate is then recovered by any method, including, for example, filtration and removal of the solvent using an aspirator.

[0077] The recovered precipitate is washed and, if necessary, dried.

[0078] An example of a washing method is repeatedly washing with ion-exchanged water until the pH reaches 7. The amount of ion-exchanged water used for washing per 100 g of the recovered precipitate is, for example, 400 mL or more, preferably 500 mL or more, and for example, 1300 mL or less, preferably 1200 mL or less.

[0079] When a coprecipitant is added dropwise until the pH of the solution reaches 9 to obtain a precipitate, if the amount of ion-exchanged water used for washing per 100 g of the recovered precipitate is within the above range, the content ratio of alkali metal elements relative to the total amount of main elements in active component 2 and impure components 5 can be controlled within a specific range, thereby improving the nitrous oxide decomposition rate.

[0080] 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.

[0081] 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.

[0082] In this manner, a precipitate (dry powder) containing an active component containing the composite metal oxide represented by the above formula (1) and impurities containing alkali metal elements can be obtained.

[0083] Next, the precipitate (dried powder) containing the active component containing the composite metal oxide represented by the above formula (1) and impurity components containing alkali metal elements is calcined.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] In this way, a product containing an active component containing the composite metal oxide represented by the above formula (1) and impurities containing alkali metal elements can be obtained.

[0088] (Preparation Step) In the preparation step, a slurry containing the product, an inorganic binder, and a dispersant is prepared. Specifically, the product obtained in the preparation step and the inorganic binder are weighed, added to the dispersant, and dispersed by stirring to obtain a slurry.

[0089] The dispersant contains at least one selected from the group consisting of a carboxylic acid, an alcohol, and water. Preferably, it is at least one selected from the group consisting of a carboxylic acid, an alcohol, and water. When the dispersant contains a carboxylic acid and water, the dispersant is an aqueous solution of the carboxylic acid, and when the dispersant contains an alcohol and water, the dispersant is an aqueous solution of the alcohol.

[0090] When the dispersant contains at least one selected from the group consisting of a carboxylic acid, an alcohol, and water, the inorganic binder can be reliably dispersed uniformly, thereby improving the strength of the nitrous oxide decomposition catalyst.

[0091] 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%.

[0092] 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.

[0093] The carboxylic acids may be used alone or in combination of two or more kinds.

[0094] 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.

[0095] Examples of combinations of inorganic binders and dispersants include a combination containing iron hydroxide and a carboxylic acid, a combination of iron hydroxide and water, a combination of zirconium hydroxide and a carboxylic acid, a combination of aluminum hydroxide and a carboxylic acid, a combination of aluminum hydroxide and water, a combination of cerium hydroxide and a carboxylic acid, a combination of cerium hydroxide and water, a combination of magnesium hydroxide and water, a combination of aluminum hydroxide oxide and water, and a combination of strontium hydroxide and water.Preferably, a combination containing iron hydroxide and a carboxylic acid, a combination of iron hydroxide and water, a combination of aluminum hydroxide and a carboxylic acid, a combination of aluminum hydroxide and water, a combination of cerium hydroxide and a carboxylic acid, and a combination of cerium hydroxide and water are included.More preferably, a combination containing iron hydroxide and a carboxylic acid and a combination of iron hydroxide and water are included.

[0096] 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.

[0097] The combination of the metal hydroxide and dispersant described above allows the inorganic binder to be reliably and uniformly dispersed in the dispersant, thereby improving the strength of the nitrous oxide decomposition catalyst.

[0098] 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, 80 parts by mass or less, preferably 50 parts by mass or less.

[0099] The blending amount of the inorganic binder relative to 100 parts by mass of the active component is the same in the nitrous oxide decomposition catalyst obtained after the firing step described below.

[0100] The amount of the active ingredient mixed per 100 parts by mass of the dispersant is, for example, 5 parts by mass or more, preferably 10 parts by mass or more, and for example, 300 parts by mass or less, preferably 200 parts by mass or less.

[0101] The amount of the inorganic binder mixed relative to 100 parts by mass of the dispersant is, for example, 0.1 parts by mass or more, preferably 0.5 parts by mass or more, and for example, 100 parts by mass or less, preferably 50 parts by mass or less.

[0102] When the blending amount of the inorganic binder relative to 100 parts by mass of the dispersant is within the above range, the inorganic binder can be reliably dispersed uniformly in the dispersant.

[0103] The method for stirring the above product and inorganic binder is not particularly limited, and any known method can be used. The stirring time is, for example, 5 to 30 minutes.

[0104] In this way, a slurry containing the above product, an inorganic binder, and a dispersant can be obtained.

[0105] (Coating Step) In the coating step, the slurry obtained in the preparation step is coated onto a substrate.

[0106] In the coating step, the substrate preferably has a flat plate shape, more preferably a flat glass paper.

[0107] 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.

[0108] 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.

[0109] In this way, a substrate coated with the slurry can be obtained.

[0110] (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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] Next, the substrate coated with the dried slurry is fired.

[0115] 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.

[0116] 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.

[0117] In this way, a catalyst for decomposing nitrous oxide can be obtained.

[0118] The nitrous oxide decomposition catalyst obtained by the above-mentioned method for producing a nitrous oxide decomposition catalyst has high strength.

[0119] 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.

[0120] The nitrous oxide decomposition catalyst device 10 is disposed in an exhaust passage through which exhaust gas flows. ２ The nitrous oxide decomposition catalyst 1 is provided to decompose O.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] 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.

[0127] 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).

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 4. Effects The method for producing a nitrous oxide decomposition catalyst of the present disclosure includes a preparation step of preparing a product containing an active component containing the composite metal oxide represented by formula (1) above and an impurity component containing an alkali metal element, wherein the content of the alkali metal element relative to the total amount of main elements of the active component and the impurity component is 0.80 mass% or more and 4.20 mass% or less, thereby improving the nitrous oxide decomposition rate.

[0132] The nitrous oxide decomposition catalyst of the present disclosure comprises an active component containing the composite metal oxide represented by formula (1) above and an impurity component containing an alkali metal element, and the content of the alkali metal element relative to the total amount of main elements of the active component and the impurity component is 0.80 mass% or more and 4.20 mass% or less, thereby enabling an improvement in the nitrous oxide decomposition rate.

[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 nitrous oxide decomposition catalyst described above, a flat and / or corrugated inorganic fiber sheet is used as the substrate 4 supporting the active component 2, the impurity components 5, and the inorganic binder 3 in the nitrous oxide decomposition catalyst 1, but this is not limited to this. Specifically, the substrate 4 supporting the active component 2, the impurity components 5, and the inorganic binder 3 may be any substrate that is typically used for the nitrous oxide decomposition catalyst 1, such as a monolith substrate 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 preparation step, a coating step, and, if necessary, a calcination step.

[0139] More specifically, first, as in one embodiment of the method for producing a nitrous oxide decomposition catalyst described above, a product containing an active component and impurities is prepared (preparation step). Next, a slurry containing the product containing the active component and impurities, an inorganic binder, and a dispersant is 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] In this way, a nitrous oxide decomposition catalyst can be produced using a monolith substrate having a cross-sectional mesh structure (honeycomb structure).

[0141] The present disclosure will be described in more detail below with reference to examples and comparative examples. It should be noted that the present disclosure is not 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 above-mentioned "Modes for Carrying Out the Invention."

[0142] Example 1 The nitrous oxide decomposition catalyst of Example 1 was obtained by the following procedure.

[0143] 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 ３was 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 collected, dried at 100°C for 12 hours, and calcined at 400°C for 2 hours, yielding the nitrous oxide decomposition catalyst of Example 1 (a product containing an active component and impurities).

[0144] In the nitrous oxide decomposition catalyst of Example 1, the content ratio of alkali metal elements (specifically, K (potassium element)) to the total amount of main elements of the active component and impurities was 0.82 mass%. Note that an energy dispersive X-ray fluorescence analyzer (EA1400, manufactured by Hitachi Corporation) was used to measure the content ratio of alkali metal elements (specifically, K (potassium element)) to the total amount of main elements of the active component and impurities in the nitrous oxide decomposition catalyst of Example 1.

[0145] Examples 2 to 8 Nitrous oxide decomposition catalysts of each Example were obtained in the same manner as in Example 1, except that the content ratio of an alkali metal element (specifically, K (potassium element)) relative to the total amount of main elements of the active component and impurity components was adjusted as shown in Table 1.

[0146] Comparative Examples 1 to 7 Nitrous oxide decomposition catalysts for each Comparative Example were obtained in the same manner as in Example 1, except that the content ratio of an alkali metal element (specifically, K (potassium element)) relative to the total amount of main elements of the active component and impurity components was adjusted as shown in Table 1.

[0147] <Evaluation> [Nitrous oxide decomposition rate] 3.2 g of the nitrous oxide decomposition catalyst (0.5 mm to 1.0 mm pellets) of each Example and Comparative Example was packed into a reactor. ２ , N ２ 0 was mixed and introduced into the evaporator. ２ 0 was introduced into the evaporator. In the evaporator, all gases (H ２ The reactor temperature (gas temperature in the reactor) was heated to 400°C using an electric heater. The ventilation volume SV (ventilation volume per catalyst volume) was 10,811 h－１ At the inlet and outlet of the reactor, N ２ Using a 0 meter, ２ The nitrous oxide decomposition rate was calculated using the following formula. The results are shown in Table 1. The relationship between the nitrous oxide decomposition rate (%) and the content (mass %) of alkali metal elements relative to the total amount of main elements of the active component and impurities for each example and comparative example is shown in Figure 3.

[0148] {Gas composition} N ２ 0:100ppmvd 0 ２ : 12 volume%-dry N ２ :Balance H ２ 0:10% by volume-wet

[0149] {Nitrous oxide decomposition rate} Nitrous oxide decomposition rate (%) = (N at reactor feed port) ２ 0 concentration - N at reactor outlet ２ 0 concentration) / (N at reactor feed port ２ 0 concentration) x 100

[0150]

[0151] <Discussion> Referring to Table 1, the nitrous oxide decomposition catalysts of Examples 1 to 8 have an alkali metal element content of 0.80 mass% or more and 4.20 mass% or less relative to the total amount of main elements of the active component and impurities, and contain impurities at a specific rate. As a result, the nitrous oxide decomposition rate exceeds 60%, thereby improving the nitrous oxide decomposition rate. In particular, the nitrous oxide decomposition catalysts of Examples 3 to 7 have an alkali metal element content of 1.15 mass% or more and 3.80 mass% or less relative to the total amount of main elements of the active component and impurities, and contain impurities at a specific rate. As a result, the nitrous oxide decomposition rate exceeds 85%, thereby further improving the nitrous oxide decomposition rate.

[0152] In contrast, the nitrous oxide decomposition catalysts of Comparative Examples 1 to 3 had an alkali metal element content of less than 0.80% by mass relative to the total amount of main elements of the active component and impurities, resulting in a low impurity content. Consequently, the nitrous oxide decomposition rate was low. Furthermore, the nitrous oxide decomposition catalysts of Comparative Examples 4 to 7 had an alkali metal element content of more than 4.50% by mass relative to the total amount of main elements of the active component and impurities, resulting in a high impurity content. Consequently, the nitrous oxide decomposition rate was low.

[0153] 3, the nitrous oxide decomposition rate increases sharply from Comparative Example 3 (alkali metal element content: 0.68% by mass) to Example 1 (alkali metal element content: 0.82% by mass). Also, the nitrous oxide decomposition rate decreases sharply from Example 8 (alkali metal element content: 4.17% by mass) to Comparative Example 4 (alkali metal element content: 5.46% by mass).

[0154] The above invention is provided as an exemplary embodiment of the present disclosure, but this is merely an example and should not be interpreted as limiting. Modifications of the present disclosure that are obvious to those skilled in the art are intended to be included in the scope of the following claims.

[0155] The method for producing a nitrous oxide decomposition catalyst according to the present disclosure is suitable for producing a nitrous oxide decomposition catalyst with an improved nitrous oxide decomposition rate, which is used to treat exhaust gases. Furthermore, the nitrous oxide decomposition catalyst according to the present disclosure is suitable for treating exhaust gases containing nitrous oxide.

[0156] 1 Nitrous oxide decomposition catalyst 2 Active component 3 Inorganic binder 4 Base material 5 Impurity component

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 product containing an active component containing a composite metal oxide represented by the following formula (1) and an impurity component containing an alkali metal element, wherein in the preparation step, the product containing the active component and the impurity component is prepared by coprecipitation using a coprecipitant containing the alkali metal element, and the content of the alkali metal element relative to the total amount of main elements of the active component and the impurity component is 0.80 mass% or more and 4.20 mass% or less. 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, and alkaline earth metals. X is greater than 0 and less than 1.) 2. The method for producing a nitrous oxide decomposition catalyst according to claim 1, further comprising: a preparation step of preparing a slurry containing the product, an inorganic binder, and a dispersant; and a coating step of coating the slurry onto a substrate.

3. The method for producing a nitrous oxide decomposition catalyst according to claim 2, wherein the inorganic binder comprises at least one selected from the group consisting of metal hydroxides and metal oxides.

4. The method for producing a nitrous oxide decomposition catalyst according to claim 2, wherein the dispersant comprises at least one selected from the group consisting of a carboxylic acid, an alcohol, and water.

5. The method for producing a nitrous oxide decomposition catalyst according to claim 2, wherein the substrate is an inorganic fiber sheet.

6. The method for producing a nitrous oxide decomposition catalyst according to any one of claims 2 to 5, further comprising a calcination step of calcining the substrate coated with the slurry after the coating step.

7. A nitrous oxide decomposition catalyst comprising: an active component containing a composite metal oxide represented by the following formula (1); and an impurity component containing an alkali metal element, wherein the content of the alkali metal element relative to the total amount of main elements of the active component and the impurity component is 0.80 mass% or more and 4.20 mass% or less. 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, and alkaline earth metals. X is greater than 0 and less than 1.) 8. The nitrous oxide decomposition catalyst according to claim 7, wherein the alkali metal element is potassium.

9. The nitrous oxide decomposition catalyst according to claim 7, wherein the content of said alkali metal element relative to the total amount of main elements of said active component and said impurity component is 1.15 mass % or more and 3.80 mass % or less.

10. The nitrous oxide decomposition catalyst according to claim 7, further comprising an inorganic binder; and a substrate that supports the active component, the impurity component, and the inorganic binder.

11. The nitrous oxide decomposition catalyst according to claim 10, wherein the inorganic binder comprises at least one selected from the group consisting of metal hydroxides and metal oxides.

12. The nitrous oxide decomposition catalyst according to claim 10, wherein the substrate is an inorganic fiber sheet.

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