Nitrous oxide decomposition catalyst and method for decomposing nitrous oxide

Abstract

This nitrous oxide decomposition catalyst contains a compound represented by formula (1).　(1): NiXA1-XCo2O4 (In formula (1), A represents at least one element that is selected from the group consisting of Fe, Mn, Ce, Zr, La, alkali metals and alkaline earth metals. In addition, X is more than 0 and less than 1.)

Description

Nitrous oxide decomposition catalyst and method for decomposing nitrous oxide

[0001] The present invention relates to a nitrous oxide decomposition catalyst and a method 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] For example, nitrous oxide (N ２ As a method for decomposing nitrous oxide (NO), a method using a nitrous oxide decomposition catalyst containing cobalt, nickel, and copper has been proposed (see, for example, Patent Document 1).

[0004] The method for decomposing nitrous oxide using the nitrous oxide decomposition catalyst disclosed in Patent Document 1 can decompose nitrous oxide under relatively low temperature conditions.

[0005] Japanese Patent Application Laid-Open No. 2022-098865

[0006] However, the method of decomposing nitrous oxide using the nitrous oxide decomposition catalyst of Patent Document 1 has the drawback that it is unable to sufficiently decompose nitrous oxide under conditions in which the exhaust gas contains moisture that it would normally contain.

[0007] The present invention aims to provide a nitrous oxide decomposition catalyst and a method for decomposing nitrous oxide that can sufficiently decompose nitrous oxide in exhaust gas under relatively low temperature conditions, even when the exhaust gas contains moisture.

[0008] The present invention [1] includes a nitrous oxide decomposition catalyst containing a compound represented by the following formula (1): 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.)

[0009] The present invention [2] includes the nitrous oxide decomposition catalyst according to [1], wherein X in the formula (1) is 0.75 or more.

[0010] The present invention [3] includes the nitrous oxide decomposition catalyst according to [1], wherein A is at least one selected from the group consisting of Fe, Mn, Sr, Cs, and La.

[0011] The present invention [4] includes a catalyst for decomposing nitrous oxide, which contains a compound represented by the following formula (2): Mg Ｙ B １－Ｙ Co ２ O ４ (2) (In formula (1), 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 [5] includes the nitrous oxide decomposition catalyst according to [4], wherein Y in the formula (2) is 0.75 or more.

[0013] The present invention [6] includes the nitrous oxide decomposition catalyst according to [4], wherein B is at least one selected from the group consisting of Zn and Ni.

[0014] The present invention [7] includes a method for decomposing nitrous oxide, comprising a step of decomposing nitrous oxide in exhaust gas using the nitrous oxide decomposition catalyst according to any one of [1] to [6].

[0015] The present invention [8] is a method for producing the exhaust gas containing H ２ [7] The method for decomposing nitrous oxide according to [7], wherein the O concentration is 5% by volume or more, and the decomposition temperature in the step of decomposing nitrous oxide is 450°C or less.

[0016] The nitrous oxide decomposition catalyst of the present invention can sufficiently decompose nitrous oxide in exhaust gases under relatively low temperature conditions, even when the exhaust gases contain moisture.

[0017] The method for decomposing nitrous oxide of the present invention includes a step of decomposing nitrous oxide in exhaust gas using the above-mentioned nitrous oxide decomposition catalyst. Therefore, even if the exhaust gas contains moisture, the nitrous oxide in the exhaust gas can be sufficiently decomposed under relatively low temperature conditions.

[0018] Figure 1 shows a graph of the X-ray diffraction (XRD) patterns of the nitrous oxide decomposition catalysts of Examples 1, 5, 7, 12, and 14. Figure 2 shows a graph of the X-ray diffraction (XRD) patterns of the nitrous oxide decomposition catalysts of Example 1 and Comparative Example 2.

[0019] 1. Nitrous oxide decomposition catalyst Nitrous oxide decomposition catalyst is a catalyst that decomposes nitrous oxide (N) in exhaust gases. ２ O) to nitrogen (N ２ ) and oxygen (O ２ ) and a catalyst for decomposing it into

[0020] First Embodiment A nitrous oxide decomposition catalyst according to a first embodiment contains a compound represented by the following formula (1).

[0021] 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.)

[0022] As described above, the nitrous oxide decomposition catalyst of the first embodiment contains dicobalt tetroxide, Ni, and A, which will be described later.

[0023] A is at least one selected from the group consisting of Fe, Mn, Ce, Zr, La, alkali metals, and alkaline earth metals.

[0024] Examples of alkali metals include Cs, K, Rb, and Na.

[0025] Alkaline earth metals include, for example, Mg, Ca, Sr, and Ba.

[0026] A is preferably at least one selected from the group consisting of Fe, Mn, Ce, Zr, La, Cs, Ca, Sr, and Ba, more preferably at least one selected from the group consisting of Fe, Mn, Ce, Zr, La, Cs, and Sr, even more preferably at least one selected from the group consisting of Fe, Ce, Zr, La, and Cs, and particularly preferably Fe.

[0027] When A includes any of the elements described above, the nitrous oxide decomposition catalyst of the first embodiment can sufficiently decompose nitrous oxide in exhaust gases under relatively low temperature conditions, even when the exhaust gases contain moisture. Specifically, when A includes any of the elements described above, the nitrous oxide decomposition catalyst of the first embodiment can improve the decomposition rate of nitrous oxide in exhaust gases under relatively low temperature conditions when the exhaust gases contain moisture.

[0028] Also, A is sulfur dioxide (SO ２ ) From the viewpoint of durability, it is preferably at least one selected from the group consisting of Fe, Mn, Sr, Cs, and La, and more preferably at least one selected from the group consisting of Fe, Sr, and La.

[0029] Specifically, if A contains the above elements, sulfur dioxide (SO ２ Even when the nitrous oxide decomposition catalyst of the first embodiment is exposed to a sulfur dioxide (SO )-containing gas (described later), the catalyst can sufficiently decompose the nitrous oxide in the exhaust gas under conditions where the exhaust gas contains moisture and the temperature is relatively low. In other words, when A contains the above-mentioned elements, the nitrous oxide decomposition catalyst of the first embodiment can sufficiently decompose the nitrous oxide in the exhaust gas when the exhaust gas contains sulfur dioxide (SO ). ２ ) and moisture, and it is suggested that this improves the decomposition rate of nitrous oxide in exhaust gases under relatively low temperature conditions.

[0030] In the above formula (1), X is more than 0, preferably 0.25 or more, more preferably 0.50 or more, even more preferably 0.75 or more, and particularly preferably 0.90 or more. X is less than 1, preferably 0.95 or less.

[0031] If X is within the above range, the decomposition rate of nitrous oxide can be improved under conditions where the exhaust gas contains moisture and the temperature is relatively low. ２ ) From the viewpoint of durability, it is also preferable that X is within the above range.

[0032] In the above formula (1), when A is Mg, the type of element is the same as in formula (2) described later, but when X is 0.5 or more, it is included in the first embodiment, and when X is less than 0.5, it is included in the second embodiment described later. Also, A preferably does not contain Mg. In such a case, (1) becomes as follows:

[0033] 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 (excluding Mg). X is greater than 0 and less than 1.)

[0034] In the nitrous oxide decomposition catalyst of the first embodiment, the compound of 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 compound of 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.

[0035] Second Embodiment A nitrous oxide decomposition catalyst according to a second embodiment contains a compound represented by the following formula (2).

[0036] 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.)

[0037] As described above, the nitrous oxide decomposition catalyst of the second embodiment contains dicobalt tetroxide, Mg, and B, which will be described later.

[0038] 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).

[0039] Examples of alkali metals include Cs, K, Rb, and Na.

[0040] Alkaline earth metals (excluding Mg) include, for example, Ca, Sr, and Ba.

[0041] B is preferably at least one selected from the group consisting of Fe, Zn, Ni, and Sr, more preferably at least one selected from the group consisting of Zn and Ni, and even more preferably Zn.

[0042] When B contains any of the elements described above, the nitrous oxide decomposition catalyst of the second embodiment can sufficiently decompose nitrous oxide in exhaust gases under relatively low temperature conditions, even when the exhaust gases contain moisture. Specifically, when B contains any of the elements described above, the nitrous oxide decomposition catalyst of the second embodiment can improve the decomposition rate of nitrous oxide in exhaust gases under relatively low temperature conditions when the exhaust gases contain moisture.

[0043] Also, B is sulfur dioxide (SO ２ ) From the viewpoint of durability, it is preferably at least one selected from the group consisting of Zn and Ni.

[0044] In the formula (2), Y is greater than 0, preferably 0.25 or greater, more preferably 0.50 or greater, even more preferably 0.75 or greater, and particularly preferably 0.90 or greater. Y is less than 1, preferably 0.95 or less.

[0045] Specifically, if B contains the above elements, sulfur dioxide (SO ２ Even when the nitrous oxide decomposition catalyst of the second embodiment is exposed to a sulfur dioxide (SO )-containing gas (described later), the catalyst can sufficiently decompose the nitrous oxide in the exhaust gas under conditions where the exhaust gas contains moisture and the temperature is relatively low. In other words, when B contains the above-mentioned elements, the nitrous oxide decomposition catalyst of the second embodiment can sufficiently decompose the nitrous oxide in the exhaust gas when the exhaust gas contains sulfur dioxide (SO ).２ ) and moisture, and it is suggested that this improves the decomposition rate of nitrous oxide in exhaust gases under relatively low temperature conditions.

[0046] If Y is within the above range, the decomposition rate of nitrous oxide can be improved under conditions where the exhaust gas contains moisture and the temperature is relatively low. ２ ) From the viewpoint of durability, it is also preferable that Y is within the above range.

[0047] In the above formula (2), when B is Ni, the type of element is the same as in the above formula (1), but when Y is 0.5 or more, this falls within the second embodiment, and when Y is less than 0.5, this falls within the first embodiment. Even when B is Ni, Y is preferably 0.75 or more, more preferably 0.9 or more, and less than 1, preferably 0.95 or less. In such cases, formula (2) becomes as follows:

[0048] 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). Y is greater than 0 and less than 1. When B is Ni, Y is greater than or equal to 0.5 and less than 1.)

[0049] In the nitrous oxide decomposition catalyst of the second embodiment, 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.

[0050] If necessary, an additive may be added to the nitrous oxide decomposition catalyst.

[0051] Examples of additives include components that accelerate the decomposition reaction of nitrous oxide, components that control the shape of the nitrous oxide decomposition catalyst, and components that bind particles of the nitrous oxide decomposition catalyst together.

[0052] Such additives are not particularly limited as long as they are additives typically used in nitrous oxide decomposition catalysts, and examples of such additives include silicates, titanates, aluminates, and zirconates.

[0053] The amount of additive added is not particularly limited as long as it does not impair the activity of the catalyst. The amount of additive added is, for example, 50 parts by mass or less, preferably 30 parts by mass or less, more preferably 20 parts by mass or less, even more preferably 10 parts by mass or less, particularly preferably 5 parts by mass or less, and most preferably 3 parts by mass or less, per 100 parts by mass of the nitrous oxide decomposition catalyst. When an additive is included, the amount of additive added is, for example, 0.1 parts by mass or more, preferably 0.3 parts by mass or more, more preferably 0.5 parts by mass or more, per 100 parts by mass of the nitrous oxide decomposition catalyst.

[0054] The shape of the nitrous oxide decomposition catalyst is not particularly limited, and examples thereof include powder, granules, spheres, pellets, extrusion moldings, and tablets.

[0055] The nitrous oxide decomposition catalyst can also be used by coating it on a honeycomb carrier or the like.

[0056] Examples of materials for the honeycomb carrier include inorganic fiber sheets (e.g., glass paper (glass nonwoven fabric)), cordierite, silicon carbide, mullite, alumina, zirconia, titania, titanium phosphate, aluminum titanate, betalite, spondumene, aluminosilicate, and magnesium silicate. Examples of methods for coating glass paper (glass nonwoven fabric) as a honeycomb carrier include the method described in Japanese Patent No. 5,909,436.

[0057] Nitrous oxide (N) in the nitrous oxide decomposition catalyst ２The decomposition rate of HCl is, for example, more than 55.0%, preferably 58.0% or more, more preferably 60.0% or more, even more preferably 65.0% or more, particularly preferably 70.0% or more, and most preferably 80.0% or more.

[0058] In addition, in the nitrous oxide decomposition catalyst, nitrous oxide (N ２ The decomposition rate of nitrous oxide (NO) can be calculated by the following formula. As will be described in detail in the Examples below, the exhaust gas is brought into contact with the nitrous oxide decomposition catalyst in the reactor. ２ The O concentration is the N concentration of the exhaust gas before contacting the nitrous oxide decomposition catalyst. ２ O concentration and N ２ The O concentration is the N concentration of the exhaust gas after contact with the nitrous oxide decomposition catalyst. ２ O concentration. ２ Decomposition rate of O (%) = (N at reactor feed port) ２ O concentration - N at reactor outlet ２ O concentration) / (N at reactor feed port ２ O concentration)×100

[0059] Sulfur dioxide (SO ) in nitrous oxide decomposition catalyst ２ Nitrous oxide (N) after durability test ２ The decomposition rate of hydroxybenzoates (O) is, for example, 40.0% or more, preferably 42.0% or more, more preferably 45.0% or more, even more preferably 50.0% or more, and particularly preferably 51.0% or more.

[0060] Sulfur dioxide (SO ) in nitrous oxide decomposition catalyst ２ Nitrous oxide (N) after durability test ２ Since the decomposition rate of sulfur dioxide (SO O) is equal to or higher than the lower limit, the nitrous oxide decomposition catalyst ２ ) durability. ２ Even if the nitrous oxide decomposition catalyst is exposed to a sulfur dioxide (SO )-containing gas (described later), the catalyst can sufficiently decompose the nitrous oxide in the exhaust gas under conditions where the exhaust gas contains moisture and is at a relatively low temperature. ２) and moisture, and it is suggested that this improves the decomposition rate of nitrous oxide in exhaust gases under relatively low temperature conditions.

[0061] In addition, sulfur dioxide (SO ２ Nitrous oxide (N) after durability test ２ The decomposition rate of sulfur dioxide (SO 2 O) can be calculated by the following formula. ２ ) The nitrous oxide decomposition catalyst after the durability test is brought into contact with the exhaust gas. ２ The O concentration is calculated by the sulfur dioxide (SO ２ ) N2O content in exhaust gas before contact with nitrous oxide decomposition catalyst after durability test ２ O concentration and N ２ The O concentration is calculated by the sulfur dioxide (SO ２ ) N2O content in exhaust gas after contact with nitrous oxide decomposition catalyst after durability test ２ O concentration. Sulfur dioxide (SO ２ ) N after durability test ２ Decomposition rate of O (%) = (N at reactor feed port) ２ O concentration - N at reactor outlet ２ O concentration) / (N at reactor feed port ２ O concentration)×100

[0062] In addition, as will be described in detail in the examples below, sulfur dioxide (SO ２ The durability test is performed by subjecting the nitrous oxide decomposition catalyst to sulfur dioxide (SO ２ )-containing gas (N ２ O: 100ppmvd, O ２ : 12% by volume, N ２ : Balance, H ２ O: 10% by volume, SO ２ This test involves exposing the specimen to a gas containing 10 ppm VD for 8 hours.

[0063] 2. Method for Producing Nitrous Oxide Decomposition Catalyst Next, a method for producing a nitrous oxide decomposition catalyst will be described.

[0064] Examples of methods for producing the nitrous oxide decomposition catalyst include the coprecipitation method, the citric acid complex method, the evaporation to dryness method, the impregnation method, and the alkoxide method, and preferably the coprecipitation method.

[0065] <Method for producing nitrous oxide decomposition catalyst of first embodiment> In the case where the method for producing the nitrous oxide decomposition catalyst is a coprecipitation method, in the first embodiment described above, the method includes a preparation step of dissolving a cobalt salt, a nickel salt, and a salt containing an A element in a solvent, a coprecipitation step of adding a coprecipitant to the prepared solution to coprecipitate a precipitate containing the compound represented by formula (1), and a calcination step of calcining the precipitate.

[0066] [Preparation Step] In the preparation step, a cobalt salt, a nickel salt, and a salt containing the element A are dissolved in a solvent.

[0067] 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, and preferably cobalt nitrate (Co(NO ３ ) ２ ・6H ２ O) can be mentioned.

[0068] Examples of nickel salts include inorganic metal salts of nickel. Examples of nickel salts include nickel nitrate, nickel sulfate, and nickel chloride, and preferably nickel nitrate (Ni(NO ３ ) ２ ・6H ２ O) can be mentioned.

[0069] 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, and preferably nitrates containing the element A.

[0070] 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, and preferably iron nitrate (Fe(NO ３ ) ３ ・9H ２ O) can be mentioned.

[0071] Examples of the solvent include ion-exchanged water and ultrapure water, and preferably ion-exchanged water.

[0072] The cobalt salt can be added to the solvent to a concentration of, for example, 0.02 mol / L or more, preferably 0.2 mol / L or more, and for example, 20 mol / L or less, preferably 2 mol / L or less.

[0073] The nickel salt can be added to the solvent to a concentration of, for example, 0.01 mol / L or more, preferably 0.1 mol / L or more, and for example, 10 mol / L or less, preferably 1 mol / L or less.

[0074] The salt containing the element A can be added to the solvent to a concentration of, for example, 0.01 mol / L or more, preferably 0.1 mol / L or more, and for example, 10 mol / L or less, preferably 1 mol / L or less.

[0075] The cobalt salt, nickel salt, and salt containing element A are added to and dissolved in a solvent so as to satisfy the composition ratio in the compound of formula (1).

[0076] 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.

[0077] [Coprecipitation Step] A coprecipitant is added to the prepared solution to coprecipitate a precipitate containing the compound represented by formula (1) in the solution, and the precipitate is washed.

[0078] As the coprecipitant, for example, an alkaline liquid or solid can be used. ２ CO ３ , N.H. ３ Water and NaOH are included, and preferably K ２ CO ３ Examples include:

[0079] The coprecipitant may be added dropwise to the extent that a precipitate forms in the solution, for example, by adding it dropwise until the pH of the solution reaches 9. A precipitate forms as a result of the dropping. The coprecipitant can be added at room temperature.

[0080] The resulting precipitate is then collected.

[0081] The recovery method is not particularly limited, and for example, the compound can be recovered by removing the solvent using filtration and an aspirator.

[0082] The recovered precipitate is washed and dried as necessary.

[0083] The washing method is not particularly limited, and for example, washing with ion-exchanged water repeatedly until the pH reaches 7 can be mentioned.

[0084] 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.

[0085] The drying temperature is, for example, 70° C. or more, preferably 90° C. or more, and for example, 120° C. or less. The drying time is, for example, 6 hours or more, and for example, 100 hours or less, preferably 50 hours or less, and more preferably 24 hours or less.

[0086] In this manner, a precipitate (dry powder) containing the compound represented by formula (1) can be obtained.

[0087] [Caking Step] The precipitate (dry powder) containing the compound represented by formula (1) is calcined.

[0088] The calcination method is not particularly limited, and any known method can be used as long as the desired catalyst can be obtained.

[0089] The firing temperature is, for example, 300° C. or higher, preferably 350° C. or higher, and for example, 800° C. or lower, preferably 700° C. or lower, more preferably 600° C. or lower, and even more preferably 500° C. or lower. The firing time is, for example, 0.5 hours or higher, preferably 1 hour or higher, and for example, 12 hours or lower, preferably 6 hours or lower, more preferably 4 hours or lower, and even more preferably 3 hours or lower.

[0090] If the calcination temperature and time are within the above ranges, the oxide can be obtained without causing a decrease in activity.

[0091] In this manner, a catalyst containing the compound represented by formula (1) can be obtained.

[0092] <Method for producing a nitrous oxide decomposition catalyst according to the second embodiment> When the method for producing a nitrous oxide decomposition catalyst is a coprecipitation method, the second embodiment described above includes a preparation step of dissolving a cobalt salt, a magnesium salt, and a salt containing element B in a solvent, a coprecipitation step of adding a coprecipitant to the prepared solution to coprecipitate a precipitate containing the compound represented by formula (2), and a calcination step of calcining the precipitate.

[0093] In the method for producing the nitrous oxide decomposition catalyst of the second embodiment, the same steps as those in the method for producing the nitrous oxide decomposition catalyst of the first embodiment (coprecipitation step and calcination step) will not be described. In other words, only the preparation step will be described below.

[0094] [Preparation Step] In the preparation step, a cobalt salt, a magnesium salt, and a salt containing the element B are dissolved in a solvent.

[0095] The cobalt salt may be the same as that used in the method for producing the nitrous oxide decomposition catalyst of the first embodiment.

[0096] Examples of magnesium salts include inorganic metal salts of magnesium. Examples of inorganic metal salts of magnesium include magnesium nitrate, magnesium sulfate, and magnesium chloride, and preferably magnesium nitrate (Mg(NO ３ ) ２ ・6H ２ O) can be mentioned.

[0097] 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.

[0098] Specifically, when B is Zn, examples of the zinc salt include inorganic metal salts of zinc. Examples of the inorganic metal salt of zinc include zinc nitrate, zinc sulfate, and zinc chloride, and preferably zinc nitrate (Zn(NO ３ )２ ・6H ２ O) can be mentioned.

[0099] Examples of the solvent include the same solvents as those used in the method for producing the nitrous oxide decomposition catalyst of the first embodiment.

[0100] The cobalt salt can be added to the solvent to a concentration of, for example, 0.02 mol / L or more, preferably 0.2 mol / L or more, and for example, 20 mol / L or less, preferably 2 mol / L or less.

[0101] The magnesium salt can be added to the solvent to a concentration of, for example, 0.01 mol / L or more, preferably 0.1 mol / L or more, and for example, 10 mol / L or less, preferably 1 mol / L or less.

[0102] The salt containing the element B can be added to the solvent to a concentration of, for example, 0.01 mol / L or more, preferably 0.1 mol / L or more, and for example, 10 mol / L or less, preferably 1 mol / L or less.

[0103] The cobalt salt, magnesium salt, and salt containing element B are added to and dissolved in a solvent so as to satisfy the composition ratio in the compound of formula (2).

[0104] In this way, a solution in which the cobalt salt, the magnesium salt, and the salt containing the element B are dissolved in the solvent can be obtained.

[0105] 3. Method for Decomposing Nitrous Oxide (Method for Using Nitrous Oxide Decomposition Catalyst) Next, a method for decomposing nitrous oxide will be described.

[0106] The method for decomposing nitrous oxide includes, for example, a step of decomposing nitrous oxide in exhaust gas using the above-mentioned nitrous oxide decomposition catalyst.

[0107] Specifically, the method for decomposing nitrous oxide involves filling a reactor with the above-described nitrous oxide decomposition catalyst and supplying nitrous oxide (N ２ By supplying exhaust gas containing nitrous oxide (N O), the nitrous oxide in the exhaust gas is brought into contact with the nitrous oxide decomposition catalyst, and the nitrous oxide (N ２ O) to nitrogen (N２ ) and oxygen (O ２ The exhaust gas after decomposition is discharged from the reactor outlet.

[0108] The amount of the nitrous oxide decomposition catalyst to be filled is not particularly limited, and can be adjusted depending on the amount of exhaust gas supplied, the concentration of nitrous oxide contained in the exhaust gas, and the like.

[0109] The exhaust gas may contain, for example, N ２ O and O ２ And, H ２ O. Also, N ２ may also include:

[0110] N in exhaust gas ２ The O concentration is not particularly limited and is, for example, 10 ppmvd or more, preferably 30 ppmvd or more, more preferably 50 ppmvd or more, and even more preferably 80 ppmvd or more, and for example, 50,000 ppmvd or less, preferably 10,000 ppmvd or less, more preferably 5,000 ppmvd or less, and even more preferably 1,000 ppmvd or less. Here, ppmvd indicates parts per million per volume of the dry gas.

[0111] O in exhaust gas ２ The concentration of is, for example, 3 vol% or more, preferably 5 vol% or more, more preferably 8 vol% or more, even more preferably 10 vol% or more, and for example, 30 vol% or less, preferably 25 vol% or less, more preferably 20 vol% or less, even more preferably 15 vol% or less.

[0112] H in exhaust gas ２ The O concentration is, for example, 1 vol% or more, preferably 3 vol% or more, more preferably 5 vol% or more, even more preferably 8 vol% or more, and for example, 30 vol% or less, preferably 25 vol% or less, more preferably 20 vol% or less, even more preferably 15 vol% or less, and particularly preferably 12 vol% or less.

[0113] The above-mentioned nitrous oxide decomposition catalyst can sufficiently decompose nitrous oxide even when the exhaust gas contains moisture within the above range.

[0114] The amount of exhaust gas supplied is not particularly limited.

[0115] The ventilation volume SV (ventilation volume per catalyst volume) is, for example, 1,000 h －１ More than 3,000 hours, preferably －１ More preferably, 5,000 hours －１ More preferably, 8,000 hours or more －１ or more, for example, 50,000 h －１ Preferably, 30,000 hours or less －１ Less than 20,000 hours, more preferably －１ More preferably, 15,000 hours or less －１ The following is the result.

[0116] The decomposition temperature of nitrous oxide is, for example, 200°C or higher, preferably 250°C or higher, more preferably 300°C or higher, even more preferably 350°C or higher, and for example, 700°C or lower, preferably 600°C or lower, more preferably 500°C or lower, even more preferably 450°C or lower, particularly preferably 400°C or lower.

[0117] The above-mentioned nitrous oxide decomposition catalyst is capable of sufficiently decomposing nitrous oxide even under the above-mentioned relatively low temperature conditions. Note that the above-mentioned decomposition temperature of nitrous oxide is the temperature of the exhaust gas in the reactor.

[0118] <Effects> The nitrous oxide decomposition catalyst of the present invention can sufficiently decompose nitrous oxide in exhaust gases under relatively low temperature conditions, even when the exhaust gases contain moisture.

[0119] Furthermore, the method for decomposing nitrous oxide of the present invention uses the nitrous oxide decomposition catalyst of the present invention, and therefore, even if the exhaust gas contains moisture, the nitrous oxide in the exhaust gas can be sufficiently decomposed under relatively low temperature conditions.

[0120] <Applications> The above-mentioned nitrous oxide decomposition catalyst can be used as one of the catalysts for decomposing harmful substances in exhaust gas by being placed in an exhaust passage through which exhaust gas flows. Such a nitrous oxide decomposition catalyst contains the moisture that exhaust gas would normally contain, and can sufficiently decompose nitrous oxide under relatively low temperature conditions. Therefore, it is possible to omit the process of removing moisture from the exhaust gas and the process of adjusting the temperature of the exhaust gas. Such a nitrous oxide decomposition catalyst is useful in a wide range of applications, including chemical plants, NH ３ Marine engines that use LNG fuel, heavy oil fuel, methane fuel, and methanol fuel, and NH ３ It is used to decompose nitrous oxide in exhaust gases emitted from thermal power plants and other facilities that contain a mixture of nitrous oxide and nitrous oxide.

[0121] 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.

[0122] Example 1 <Preparation of nitrous oxide decomposition catalyst> 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% by mass of 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 a nitrous oxide decomposition catalyst of Example 1. The nitrous oxide decomposition catalyst was pulverized and molded into pellets.

[0123] Examples 2 to 19 and Comparative Example 1 Nitrous oxide decomposition catalysts of each Example and Comparative Example 1 were obtained in the same manner as in Example 1, except that each nitrate was weighed so that the nitrous oxide decomposition catalyst had the composition and composition ratio shown in Tables 1 to 3.

[0124] Comparative Example 2 <Preparation of Nitrous Oxide Decomposition Catalyst> Nickel nitrate (Ni(NO ３ ) ２ ・6H ２ O), iron nitrate (Fe(NO ３ ) ３ ・9H ２ O), and cobalt oxide (Co ３ O ４ ) were weighed and mixed so that the composition ratio (atomic ratio) was Ni:Fe:Co = 0.75:0.25:3. The mixture was dried at 120°C for 2 hours and calcined at 400°C for 4 hours to obtain a nitrous oxide decomposition catalyst of Comparative Example 2. The nitrous oxide decomposition catalyst was molded into pellets.

[0125] <Evaluation> [Evaluation of Nitrous Oxide Decomposition] 3.2 g of the nitrous oxide decomposition catalyst (pellet form) of each Example and Comparative Example was packed into a reactor. ２ , N ２ The mixture was mixed with 200 ml of water and introduced into the evaporator. ２ O was introduced into the evaporator. In the evaporator, all gases (H ２ 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, N２ Using an O meter, ２ The O concentration was measured and calculated using the following formula: ２ The decomposition rate of O was calculated. The results are shown in Tables 1 to 3.

[0126] {Gas composition} N ２ O: 100ppmvd O ２ : 12% by volume N ２ :Balance H ２ O: 10% by volume

[0127] {N ２ Decomposition rate of N ２ Decomposition rate of O (%) = (N at reactor feed port) ２ O concentration - N at reactor outlet ２ O concentration) / (N at reactor feed port ２ O concentration)×100

[0128] [SO ２ Evaluation of Nitrous Oxide Decomposition After Durability Test] 3.2 g of the nitrous oxide decomposition catalyst (pellet form) of each Example and Comparative Example was packed into a reactor.

[0129] (SO ２ Durability test) Next, air, N ２ , N ２ O, SO ２ The mixture was mixed and introduced into an evaporator. ２ O was introduced into the evaporator. In the evaporator, all gases (H ２ O) and sulfur dioxide (SO ２ )-containing gas was prepared. ２ 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 In addition, sulfur dioxide (SO ２ In other words, the nitrous oxide decomposition catalysts of each Example and Comparative Example were heated to a temperature of 1000°C for 8 hours. ２ )-containing gas for 8 hours.

[0130] Sulfur dioxide (SO２ ) Containing gas composition} N ２ O: 100ppmvd O ２ : 12% by volume N ２ : Balance SO ２ : 10 ppm vd H ２ O: 10% by volume

[0131] SO ２ After the durability test, the nitrous oxide decomposition rate of each of the nitrous oxide decomposition catalysts of the Examples and Comparative Examples was evaluated in the same manner as above. The results are shown in Table 4.

[0132] [Evaluation of X-ray Diffraction Patterns] X-ray diffraction (XRD) patterns were measured for the nitrous oxide decomposition catalysts of Examples 1, 5, 7, 12, and 14, and Comparative Example 2, using a Uitima IV (manufactured by Rigaku Corporation). The measurement conditions were a tube voltage of 40 kV and a tube current of 40 mA. To align the peak positions, Si was mixed as a standard sample and correction was performed at Si 2θ = 28.44. The results are shown in Figures 1 and 2. Figure 1 shows the XRD patterns for Examples 1, 5, 7, 12, and 14, and Figure 2 shows the XRD patterns for Example 1 and Comparative Example 2.

[0133]

[0134]

[0135]

[0136]

[0137] <Discussion> As shown in FIG. 1, all of the catalysts in the examples ３ O ４ The diffraction peak is shifted to a position where 2θ becomes smaller from the diffraction peak position due to the spinel structure of Ni. Ｘ A １－Ｘ Co ２ O ４ and a nitrous oxide decomposition catalyst containing a compound represented by the formula: Ｙ B １－Ｙ Co ２ O ４ The nitrous oxide decomposition catalyst containing the compound represented by the formula: ３O ４ It was suggested that a portion of the Co in the Co atom is present in a state of being substituted with one of the ions, forming a solid solution. The nitrous oxide decomposition catalysts described in Examples 1 to 19 were able to improve the decomposition rate of nitrous oxide under conditions where the exhaust gas contained moisture and the temperature was relatively low.

[0138] As shown in FIG. 2, Comparative Example 2 is Co ３ O ４ The diffraction peaks are at almost the same positions as those attributable to the spinel structure of Comparative Example 1. This suggests that the nitrous oxide decomposition catalyst of Comparative Example 2 does not form a solid solution. The nitrous oxide decomposition catalyst of Comparative Example 2 had a low nitrous oxide decomposition rate when the exhaust gas contained moisture and the temperature was relatively low. Furthermore, Comparative Example 1 is a nitrous oxide decomposition catalyst containing cobalt, nickel, and copper, and had a relatively low nitrous oxide decomposition rate when the exhaust gas contained moisture and the temperature was relatively low.

[0139] The nitrous oxide decomposition catalysts of Examples 1, 2, 4, 6 to 8, 12, 14, 15, and 18 were also ２ Even after the durability test, the decomposition rate of nitrous oxide was improved under conditions where the exhaust gas contained moisture and the temperature was relatively low. Ｘ A １－Ｘ Co ２ O ４ wherein A is at least one selected from the group consisting of Fe, Mn, Sr, Cs, and La; and a nitrous oxide decomposition catalyst comprising a compound represented by the formula: Ｙ B １－Ｙ Co ２ O ４ The nitrous oxide decomposition catalyst contains a compound represented by the formula: ２ ) and moisture, suggesting that the decomposition rate of nitrous oxide is improved even under relatively low temperature conditions.

[0140] 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.

[0141] The nitrous oxide decomposition catalyst of the present invention is used in chemical plants, NH ３ Marine engines that use LNG fuel, heavy oil fuel, methane fuel, and methanol fuel, and NH ３ It is used to decompose nitrous oxide in exhaust gases emitted from thermal power plants and other facilities that contain a mixture of nitrous oxide and nitrous oxide.

Claims

1. A nitrous oxide decomposition catalyst comprising a compound represented by the following formula (1): 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, an alkali metal, and an alkaline earth metal. Also, X is more than 0 and less than 1.) 2. The nitrous oxide decomposition catalyst according to claim 1, wherein in formula (1), X is 0.75 or more.

3. The nitrous oxide decomposition catalyst according to claim 1, wherein A is at least one selected from the group consisting of Fe, Mn, Sr, Cs, and La.

4. A nitrous oxide decomposition catalyst comprising a compound represented by the following formula (2): 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, an alkali metal, and an alkaline earth metal (excluding Mg). Y is more than 0 and less than 1.) 5. The nitrous oxide decomposition catalyst according to claim 4, wherein in formula (2), Y is 0.75 or more.

6. The nitrous oxide decomposition catalyst according to claim 4, wherein B is at least one selected from the group consisting of Zn and Ni.

7. A method for decomposing nitrous oxide, comprising a step of decomposing nitrous oxide in exhaust gas using the nitrous oxide decomposition catalyst according to any one of claims 1 to 6.

8. H in the exhaust gas ２ 8. The method for decomposing nitrous oxide according to claim 7, wherein the O concentration is 5% by volume or more, and the decomposition temperature in the step of decomposing nitrous oxide is 450° C. or less.