Nitrous oxide decomposition catalyst and nitrous oxide decomposition method

Abstract

This nitrous oxide decomposition catalyst contains a compound represented by formula (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, and X is greater than 0 and less than 1.

Description

Technical Field

[0001] This invention relates to a catalyst for the decomposition of nitrous oxide and a method for the decomposition of nitrous oxide. Background Technology

[0002] Previously, in order to treat exhaust gas, a technique was known to be to place a catalyst for exhaust gas treatment in the exhaust passage through which the exhaust gas flows, so as to decompose harmful substances in the exhaust gas.

[0003] For example, as a method for decomposing nitrous oxide (N2O) contained in exhaust gas, a decomposition method using a nitrous oxide decomposition catalyst containing cobalt, nickel and copper has been proposed (for example, see Patent Document 1).

[0004] Patent Document 1 describes a method for decomposing nitrous oxide using a nitrous oxide decomposition catalyst, which can decompose nitrous oxide under relatively low temperature conditions.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2022-098865 Summary of the Invention

[0008] (a) Technical problems to be solved

[0009] However, the nitrous oxide decomposition method using a nitrous oxide decomposition catalyst in Patent Document 1 has the disadvantage that it cannot fully decompose nitrous oxide under conditions where the exhaust gas may contain moisture.

[0010] This invention provides a nitrous oxide decomposition catalyst and a method for fully decomposing nitrous oxide in exhaust gas even when the exhaust gas contains moisture, under relatively low temperature conditions.

[0011] (II) Technical Solution

[0012] The present invention [1] comprises a nitrous oxide decomposition catalyst comprising a compound represented by the following formula (1).

[0013]

[0014] In formula (1), A is selected from at least one of the group consisting of Fe, Mn, Ce, Zr, La, alkali metals and alkaline earth metals, and X is greater than 0 and less than 1.

[0015] The present invention [2] includes the nitrous oxide decomposition catalyst described in [1], wherein, in the formula (1), X is 0.75 or more.

[0016] The present invention [3] includes the nitrous oxide decomposition catalyst described in [1], wherein A is at least one selected from the group consisting of Fe, Mn, Sr, Cs and La.

[0017] The present invention [4] includes a nitrous oxide decomposition catalyst comprising a compound represented by the following formula (2).

[0018]

[0019] 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), and Y is greater than 0 and less than 1.

[0020] The present invention [5] includes the nitrous oxide decomposition catalyst described in [4], wherein, in the formula (2), Y is 0.75 or more.

[0021] The present invention [6] includes the nitrous oxide decomposition catalyst described in [4], wherein B is at least one selected from the group consisting of Zn and Ni.

[0022] The present invention [7] includes a method for decomposing nitrous oxide, comprising the step of decomposing nitrous oxide in exhaust gas using any one of the nitrous oxide decomposition catalysts described in any one of [1] to [6].

[0023] The present invention [8] includes the method for decomposing nitrous oxide as described in [7], wherein the H2O concentration in the exhaust gas is 5% by volume or more, and the decomposition temperature in the process of decomposing nitrous oxide is below 450°C.

[0024] (III) Beneficial Effects

[0025] The nitrous oxide decomposition catalyst of the present invention can fully decompose nitrous oxide in exhaust gas even when the exhaust gas contains moisture, under relatively low temperature conditions.

[0026] The nitrous oxide decomposition method of the present invention includes a step of decomposing nitrous oxide in exhaust gas using the above-described nitrous oxide decomposition catalyst. Therefore, even when the exhaust gas contains moisture, nitrous oxide in the exhaust gas can be fully decomposed under relatively low temperature conditions. Attached Figure Description

[0027] Figure 1 The graphs show the X-ray diffraction (XRD) patterns of the nitrous oxide decomposition catalysts of Examples 1, 5, 7, 12 and 14.

[0028] Figure 2The graphs show the X-ray diffraction (XRD) patterns of the nitrous oxide decomposition catalysts of Example 1 and Comparative Example 2. Detailed Implementation

[0029] 1. Nitrous oxide decomposition catalyst

[0030] Nitrous oxide decomposition catalyst is a catalyst that decomposes nitrous oxide (N2O) in exhaust gas into nitrogen (N2) and oxygen (O2).

[0031] <First Implementation Plan>

[0032] The nitrous oxide decomposition catalyst of the first embodiment comprises a compound represented by the following formula (1).

[0033]

[0034] In formula (1), A is selected from at least one of the group consisting of Fe, Mn, Ce, Zr, La, alkali metals and alkaline earth metals, and X is greater than 0 and less than 1.

[0035] As described above, the nitrous oxide decomposition catalyst of the first embodiment comprises cobalt tetroxide, Ni and A (described later).

[0036] A is selected from at least one of the group consisting of Fe, Mn, Ce, Zr, La, alkali metals, and alkaline earth metals.

[0037] Examples of alkali metals include Cs, K, Rb, and Na.

[0038] Alkaline earth metals include, for example, Mg, Ca, Sr and Ba.

[0039] 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.

[0040] As long as A contains the aforementioned elements, the nitrous oxide decomposition catalyst of the first embodiment can fully decompose nitrous oxide in the exhaust gas even when the exhaust gas contains moisture, under relatively low temperature conditions. Specifically, as long as A contains the aforementioned elements, the nitrous oxide decomposition catalyst of the first embodiment can improve the decomposition rate of nitrous oxide in the exhaust gas under conditions where the exhaust gas contains moisture and is at a relatively low temperature.

[0041] Furthermore, from the perspective of sulfur dioxide (SO2) durability, A 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.

[0042] Specifically, as long as A contains the aforementioned elements, the nitrous oxide decomposition catalyst of the first embodiment, even when exposed to sulfur dioxide (SO2) gas (described later), can fully decompose nitrous oxide in the exhaust gas under conditions where the exhaust gas contains moisture and is at a relatively low temperature. That is, it implies that as long as A contains the aforementioned elements, the nitrous oxide decomposition catalyst of the first embodiment can improve the decomposition rate of nitrous oxide in the exhaust gas under conditions where the exhaust gas contains sulfur dioxide (SO2) and moisture and is at a relatively low temperature.

[0043] In the above formula (1), X is greater 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. Furthermore, X is less than 1, preferably 0.95 or less.

[0044] As long as X is within the above range, the decomposition rate of nitrous oxide can be improved under conditions where the exhaust gas contains moisture and is at a relatively low temperature. Furthermore, from the perspective of sulfur dioxide (SO2) durability, it is also preferable that X is within the above range.

[0045] Furthermore, in the above formula (1), when A is Mg, the element type becomes the same as in the formula (2) described later. However, 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. In addition, A preferably does not contain Mg. In this case, (1) is as follows.

[0046]

[0047] In formula (1), A is selected from at least one of the group consisting of Fe, Mn, Ce, Zr, La, alkali metals and alkaline earth metals (excluding Mg), and X is greater than 0 and less than 1.

[0048] In the nitrous oxide decomposition catalyst of the first embodiment, the compound of formula (1) forms, for example, a spinel structure. A spinel structure refers to a crystal structure of an oxide considered to be a metal, such as the structure of cobalt tetroxide (Co3O4). Specifically, the compound of formula (1) is a solid solution of Co, Ni, and A, forming a spinel structure in which some of the Co in cobalt tetroxide (Co3O4) is replaced by Ni and / or A.

[0049] <Second Implementation Plan>

[0050] The nitrous oxide decomposition catalyst of the second embodiment comprises a compound represented by the following formula (2).

[0051]

[0052] In formula (2), B is selected from at least one of the group consisting of Fe, Mn, Zn, Ni, Zr, La, alkali metals and alkaline earth metals (excluding Mg), and Y is greater than 0 and less than 1.

[0053] As described above, the nitrous oxide decomposition catalyst of the second embodiment comprises cobalt tetroxide, Mg and B, which will be described later.

[0054] B is selected from at least one of the following groups: Fe, Mn, Zn, Ni, Zr, La, alkali metals, and alkaline earth metals (excluding Mg).

[0055] Examples of alkali metals include Cs, K, Rb, and Na.

[0056] Alkaline earth metals (excluding Mg) include, for example, Ca, Sr and Ba.

[0057] 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.

[0058] As long as B contains the aforementioned elements, the nitrous oxide decomposition catalyst of the second embodiment can fully decompose nitrous oxide in the exhaust gas even when the exhaust gas contains moisture, under relatively low temperature conditions. Specifically, as long as B contains the aforementioned elements, the nitrous oxide decomposition catalyst of the second embodiment can significantly improve the decomposition rate of nitrous oxide in the exhaust gas even when the exhaust gas contains moisture and is at a relatively low temperature.

[0059] Furthermore, from the perspective of sulfur dioxide (SO2) durability, B is preferably selected from at least one of the groups consisting of Zn and Ni.

[0060] Furthermore, in the above formula (2), Y is greater 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. Additionally, Y is less than 1, preferably 0.95 or less.

[0061] Specifically, as long as B contains the aforementioned elements, the nitrous oxide decomposition catalyst of the second embodiment, even when exposed to sulfur dioxide (SO2) gas (described later), can fully decompose nitrous oxide in the exhaust gas under conditions where the exhaust gas contains moisture and is at a relatively low temperature. That is, it implies that as long as B contains the aforementioned elements, the nitrous oxide decomposition catalyst of the second embodiment can improve the decomposition rate of nitrous oxide in the exhaust gas under conditions where the exhaust gas contains sulfur dioxide (SO2) and moisture and is at a relatively low temperature.

[0062] As long as Y is within the above range, the decomposition rate of nitrous oxide can be improved under conditions where the exhaust gas contains moisture and is at a relatively low temperature. Furthermore, from the perspective of sulfur dioxide (SO2) durability, Y being within the above range is also preferred.

[0063] Furthermore, in equation (2) above, when B is Ni, the element types become the same as in equation (1) above. However, when Y is 0.5 or more, it is included in the second embodiment, and when Y is less than 0.5, it is included in the first embodiment. In addition, even when B is Ni, Y is preferably 0.75 or more, more preferably 0.9 or more, and Y is less than 1, preferably 0.95 or less. In this case, equation (2) is as follows.

[0064]

[0065] In formula (2), B is selected from at least one of the group consisting of Fe, Mn, Zn, Ni, Zr, La, alkali metals and alkaline earth metals (excluding Mg), and Y is greater than 0 and less than 1. In addition, when B is Ni, Y is greater than 0.5 and less than 1.

[0066] In the nitrous oxide decomposition catalyst of the second embodiment, the compound of formula (2) above forms, for example, a spinel structure. A spinel structure refers to a crystal structure that is considered an oxide of a metal, such as the structure of cobalt tetroxide (Co3O4). Specifically, the compound of formula (2) above is a solid solution of Co, Mg, and B, forming a spinel structure in which some of the Co in cobalt tetroxide (Co3O4) is replaced by Mg and / or B.

[0067] Additives may also be added to the nitrous oxide decomposition catalyst as needed.

[0068] As additives, examples include components that promote the decomposition reaction of nitrous oxide, components that control the shape of the nitrous oxide decomposition catalyst, and components that bind the nitrous oxide decomposition catalysts together.

[0069] As such additives, there are generally no particular restrictions as long as they can be used in nitrous oxide decomposition catalysts. Examples of such additives include silicates, titanates, aluminates, and zirconates.

[0070] The amount of additive incorporated is not particularly limited as long as it does not impair the catalyst activity. For 100 parts by mass of the nitrous oxide decomposition catalyst, the amount of additive incorporated is, for example, 50 parts by mass or less, preferably 30 parts by mass or less, more preferably 20 parts by mass or less, further preferably 10 parts by mass or less, particularly preferably 5 parts by mass or less, and most preferably 3 parts by mass or less. Furthermore, when the additive is included, 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, for 100 parts by mass of the nitrous oxide decomposition catalyst.

[0071] There are no particular limitations on the shape of nitrous oxide decomposition catalysts; for example, powders, granules, spheres, pellets, extruded parts, and plates can be listed.

[0072] In addition, nitrous oxide decomposition catalysts can also be used, for example, by coating them onto a honeycomb carrier.

[0073] Materials used as cellophane carriers include, for example, inorganic fiber sheets (e.g., cellophane (glass nonwoven fabric)), cordierite, silicon carbide, mullite, alumina, zirconium oxide, titanium dioxide, titanium phosphate, aluminum titanate, petalite, spodumene, aluminum silicate, and magnesium silicate. Methods for coating these materials onto the cellophane (glass nonwoven fabric) used as the cellophane carrier include, for example, the method described in Japanese Patent 5909436.

[0074] The decomposition rate of nitrous oxide (N2O) in the nitrous oxide decomposition catalyst is, for example, greater than 55.0%, preferably 58.0% or more, more preferably 60.0% or more, further preferably 65.0% or more, particularly preferably 70.0% or more, and most preferably 80.0% or more.

[0075] Furthermore, the decomposition rate of nitrous oxide (N2O) in the nitrous oxide decomposition catalyst can be calculated using the following formula. Details will be described in the embodiments described later. In the reactor, the nitrous oxide decomposition catalyst is brought into contact with the exhaust gas. That is, the N2O concentration at the reactor inlet is the N2O concentration of the exhaust gas before contact with the nitrous oxide decomposition catalyst, while the N2O concentration at the reactor outlet is the N2O concentration of the exhaust gas after contact with the nitrous oxide decomposition catalyst.

[0076] N2O decomposition rate (%) = (N2O concentration at reactor inlet - N2O concentration at reactor outlet) / (N2O concentration at reactor inlet) × 100

[0077] The decomposition rate of nitrous oxide (N2O) in the nitrous oxide decomposition catalyst after a durability test of sulfur dioxide (SO2) 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.

[0078] By ensuring that the decomposition rate of nitrous oxide (N2O) in the nitrous oxide decomposition catalyst exceeds the aforementioned lower limit after a durability test for sulfur dioxide (SO2), the nitrous oxide decomposition catalyst exhibits sulfur dioxide (SO2) durability. Specifically, even when exposed to a gas containing sulfur dioxide (SO2) (described later), the nitrous oxide decomposition catalyst can fully decompose nitrous oxide in the exhaust gas under conditions where the exhaust gas contains moisture and is at a relatively low temperature. This implies that the nitrous oxide decomposition catalyst can improve the decomposition rate of nitrous oxide in the exhaust gas under conditions where the exhaust gas contains sulfur dioxide (SO2) and moisture and is at a relatively low temperature.

[0079] Furthermore, the decomposition rate of nitrous oxide (N2O) in the nitrous oxide decomposition catalyst after the sulfur dioxide (SO2) durability test can be calculated using the following formula. Details will be described in the examples described later. In the reactor, the nitrous oxide decomposition catalyst after the sulfur dioxide (SO2) durability test is brought into contact with the exhaust gas. That is, the N2O concentration at the reactor inlet is the N2O concentration of the exhaust gas before contact with the nitrous oxide decomposition catalyst after the sulfur dioxide (SO2) durability test, while the N2O concentration at the reactor outlet is the N2O concentration of the exhaust gas after contact with the nitrous oxide decomposition catalyst after the sulfur dioxide (SO2) durability test.

[0080] The decomposition rate (%) of N2O after the sulfur dioxide (SO2) durability test = (N2O concentration at reactor inlet - N2O concentration at reactor outlet) / (N2O concentration at reactor inlet) × 100

[0081] Furthermore, details will be described in the embodiments described later. The sulfur dioxide (SO2) durability test refers to the test in which the nitrous oxide decomposition catalyst is exposed to a gas containing sulfur dioxide (SO2) (containing N2O: 100 ppmvd, O2: 12 vol%, N2: Balance, H2O: 10 vol%, SO2: 10 ppmvd) for 8 hours.

[0082] 2. Method for manufacturing nitrous oxide decomposition catalyst

[0083] Next, the method for manufacturing the nitrous oxide decomposition catalyst will be explained.

[0084] Methods for manufacturing nitrous oxide decomposition catalysts include, for example, coprecipitation, citric acid complexation, evaporation, impregnation, and alkoxide methods, with coprecipitation being a preferred method.

[0085] <Method for manufacturing nitrous oxide decomposition catalyst according to the first embodiment>

[0086] When the method for manufacturing the nitrous oxide decomposition catalyst is a coprecipitation method, in the first embodiment described above, it includes a conditioning step of dissolving cobalt salt, nickel salt and salt containing element A in a solvent; a coprecipitation step of adding a coprecipitant to the conditioning solution to coprecipitate a precipitate containing a compound represented by formula (1); and a calcination step of calcining the precipitate.

[0087] [Modification Process]

[0088] In the modulation process, cobalt salt, nickel salt, and salt containing element A are dissolved in a solvent.

[0089] Examples of cobalt salts include inorganic metal salts of cobalt. Examples of inorganic metal salts of cobalt include cobalt nitrate, cobalt sulfate, and cobalt chloride, with cobalt nitrate (Co(NO3)2·6H2O) being a preferred example.

[0090] Examples of nickel salts include, for example, inorganic metal salts of nickel. Examples of inorganic metal salts of nickel include, for example, nickel nitrate, nickel sulfate, and nickel chloride, with nickel nitrate (Ni(NO3)2·6H2O) being a preferred example.

[0091] Examples of salts containing element A include inorganic metal salts containing element A. Examples of inorganic metal salts containing element A include nitrates, sulfates, and chlorides, with nitrates containing element A being a preferred example.

[0092] Specifically, if A is Fe, then it is an iron salt, for example, inorganic metal salts of iron can be listed. Inorganic metal salts of iron, for example, ferric nitrate, ferric sulfate and ferric chloride can be listed, with ferric nitrate (Fe(NO3)3·9H2O) being a preferred example.

[0093] Examples of solvents include ion-exchanged water and ultrapure water, with ion-exchanged water being a preferred example.

[0094] Cobalt salts can be added to solvents at concentrations 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.

[0095] Nickel salts can be added to solvents at concentrations of, for example, 0.01 mol / L or higher, preferably 0.1 mol / L or higher, and further, for example, 10 mol / L or lower, preferably 1 mol / L or lower.

[0096] Salts containing element A can be added to solvents at concentrations of, for example, 0.01 mol / L or more, preferably 0.1 mol / L or more, and further, for example, 10 mol / L or less, preferably 1 mol / L or less.

[0097] In addition, cobalt salt, nickel salt and salt containing element A are added to the solvent in such a way that the composition ratio in the compound of formula (1) is satisfied and dissolved.

[0098] Through the above methods, a solution can be obtained by dissolving cobalt salts, nickel salts, and salts containing element A in a solvent.

[0099] [Co-precipitation process]

[0100] Add a coprecipitant to the prepared solution to coprecipitate the precipitate containing the compound of formula (1) in the solution, and wash the precipitate.

[0101] As a coprecipitant, alkaline liquids and solids can be used. Specifically, K2CO3, ammonia, and NaOH can be listed, with K2CO3 being the preferred example.

[0102] The coprecipitant should be added in such a way that it produces a precipitate in the solution; for example, it can be added dropwise until the pH of the solution reaches 9. A precipitate is formed by this dropwise addition. Alternatively, the coprecipitant can be added at room temperature.

[0103] Then, the obtained precipitate is recovered.

[0104] There are no particular limitations on the recovery method; for example, the solvent can be removed by filtration and aspirator for recovery.

[0105] Wash and dry the recovered precipitate as needed.

[0106] There are no particular limitations on the washing method. For example, one method is to repeatedly wash with ion-exchanged water until the pH reaches 7.

[0107] Furthermore, there are no particular limitations on the drying method for the washed precipitate; methods such as evaporation and drying can be listed. Therefore, the washed precipitate can be obtained as a dried powder.

[0108] The drying temperature is, for example, 70°C or higher, preferably 90°C or higher, and also, for example, 120°C or lower. The drying time is, for example, 6 hours or more, and also, for example, 100 hours or less, preferably 50 hours or less, and more preferably 24 hours or less.

[0109] By using the above methods, a precipitate (dry powder) containing the compound shown in formula (1) can be obtained.

[0110] [Firing process]

[0111] The precipitate (dry powder) containing the compound represented by formula (1) is calcined.

[0112] There are no particular limitations on the firing method, as long as the required catalyst can be obtained and a known method can be used.

[0113] The firing temperature is, for example, 300°C or higher, preferably 350°C or higher, and further preferably 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 further preferably 12 hours or lower, preferably 6 hours or lower, more preferably 4 hours or lower, and even more preferably 3 hours or lower.

[0114] As long as the firing temperature and time are within the above range, oxides can be produced without reducing their activity.

[0115] In the above manner, a catalyst containing the compound shown in formula (1) can be obtained.

[0116] <Method for manufacturing nitrous oxide decomposition catalyst according to the second embodiment>

[0117] When the method for manufacturing the nitrous oxide decomposition catalyst is a coprecipitation method, in the second embodiment described above, the process includes a conditioning step of dissolving cobalt salt, magnesium salt and salt containing element B in a solvent; a coprecipitation step of adding a coprecipitant to the conditioning solution to coprecipitate a precipitate containing the compound represented by formula (2); and a calcination step of calcining the precipitate.

[0118] Furthermore, in the manufacturing method of the nitrous oxide decomposition catalyst in the second embodiment, the steps that are the same as those in the manufacturing method of the nitrous oxide decomposition catalyst in the first embodiment (co-precipitation step and calcination step) are omitted. That is, only the preparation step is described below.

[0119] [Modification Process]

[0120] In the modulation process, cobalt salts, magnesium salts, and salts containing element B are dissolved in a solvent.

[0121] As cobalt salts, examples include those produced using the same method as the nitrous oxide decomposition catalyst described in the first embodiment above.

[0122] Examples of magnesium salts include, for example, inorganic metal salts of magnesium. Examples of inorganic metal salts of magnesium include magnesium nitrate, magnesium sulfate, and magnesium chloride, with magnesium nitrate (Mg(NO3)2·6H2O) being a preferred example.

[0123] Examples of salts containing element B include inorganic metal salts containing element B. Examples of inorganic metal salts containing element B include nitrates, sulfates, and chlorides, with nitrates containing element B being a preferred example.

[0124] Specifically, if B is Zn, then as a zinc salt, for example, inorganic metal salts of zinc can be listed. As inorganic metal salts of zinc, for example, zinc nitrate, zinc sulfate and zinc chloride can be listed, with zinc nitrate (Zn(NO3)2·6H2O) being a preferred example.

[0125] As a solvent, solvents that are the same as those used in the manufacturing method of the nitrous oxide decomposition catalyst of the first embodiment described above can be listed.

[0126] Cobalt salts can be added to solvents at concentrations 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.

[0127] Magnesium salts can be added to the solvent at concentrations 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.

[0128] Salts containing element B can be added to solvents at concentrations of, for example, 0.01 mol / L or more, preferably 0.1 mol / L or more, and further, for example, 10 mol / L or less, preferably 1 mol / L or less.

[0129] In addition, cobalt salts, magnesium salts, and salts containing element B are added to the solvent in such a way that the composition ratios in the compound satisfying formula (2) are met, and the mixture is dissolved.

[0130] Through the above methods, a solution can be obtained by dissolving cobalt salts, magnesium salts, and salts containing element B in a solvent.

[0131] 3. Methods for the decomposition of nitrous oxide (methods for using nitrous oxide decomposition catalysts)

[0132] Next, the decomposition method of nitrous oxide will be explained.

[0133] The decomposition method of nitrous oxide includes, for example, a process of decomposing nitrous oxide in exhaust gas using the above-mentioned nitrous oxide decomposition catalyst.

[0134] Specifically, as a method for decomposing nitrous oxide, the aforementioned nitrous oxide decomposition catalyst is filled into a reactor, and exhaust gas containing nitrous oxide (N2O) is supplied from the reactor feed port. This allows the nitrous oxide in the exhaust gas to come into contact with the nitrous oxide decomposition catalyst, thereby decomposing the nitrous oxide (N2O) into nitrogen (N2) and oxygen (O2). The decomposed exhaust gas can be discharged through the reactor outlet.

[0135] There is no particular limit to the amount of nitrous oxide decomposition catalyst that can be filled, and it can be adjusted according to the exhaust supply and the concentration of nitrous oxide in the exhaust.

[0136] The exhaust gas may contain, for example, N2O, O2, and H2O. Additionally, it may contain N2.

[0137] The concentration of N2O in the exhaust gas is not particularly limited, but 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. Furthermore, it is, 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. Additionally, ppmvd refers to parts per million per unit volume of the dry gas.

[0138] The concentration of O2 in the exhaust gas is, for example, 3% by volume or more, preferably 5% by volume or more, more preferably 8% by volume or more, and even more preferably 10% by volume or more. In addition, it is, for example, 30% by volume or less, preferably 25% by volume or less, more preferably 20% by volume or less, and even more preferably 15% by volume or less.

[0139] The concentration of H2O in the exhaust gas is, for example, 1% by volume or more, preferably 3% by volume or more, more preferably 5% by volume or more, even more preferably 8% by volume or more, and in addition, for example, 30% by volume or less, preferably 25% by volume or less, more preferably 20% by volume or less, even more preferably 15% by volume or less, and particularly preferably 12% by volume or less.

[0140] The aforementioned nitrous oxide decomposition catalyst can fully decompose nitrous oxide even when the exhaust gas contains moisture within the range described above.

[0141] There is no particular limit to the amount of exhaust gas supplied.

[0142] Ventilation rate SV (ventilation rate per unit volume of catalyst) is, for example, 1,000 h⁻¹. -1The above is preferably 3,000h. -1 The above, more preferably 5,000h -1 The above is further preferred to be 8,000h. -1 In addition, for example, 50,000h -1 The following is preferred: 30,000h -1 Hereinafter, 20,000h is more preferred. -1 Hereinafter, 15,000h is further preferred. -1 the following.

[0143] The decomposition temperature of nitrous oxide is, for example, 200°C or higher, preferably 250°C or higher, more preferably 300°C or higher, and even more preferably 350°C or higher. In addition, it is, for example, 700°C or lower, preferably 600°C or lower, more preferably 500°C or lower, even more preferably 450°C or lower, and particularly preferably 400°C or lower.

[0144] The aforementioned nitrous oxide decomposition catalyst can fully decompose nitrous oxide even under the relatively low temperature conditions described above. Furthermore, the decomposition temperature of the nitrous oxide is the same as the temperature of the exhaust gas inside the reactor.

[0145] <Technical Effects>

[0146] The nitrous oxide decomposition catalyst of the present invention can fully decompose nitrous oxide in exhaust gas even when the exhaust gas contains moisture, under relatively low temperature conditions.

[0147] Furthermore, the nitrous oxide decomposition method of the present invention employs the nitrous oxide decomposition catalyst of the present invention. Therefore, even when the exhaust gas contains moisture, nitrous oxide in the exhaust gas can be fully decomposed under relatively low temperature conditions.

[0148] <Uses>

[0149] The aforementioned nitrous oxide decomposition catalyst, when placed in the exhaust passage through which the exhaust gas flows, can serve as a catalyst for decomposing harmful substances in exhaust gas. This nitrous oxide decomposition catalyst can fully decompose nitrous oxide even under conditions where exhaust gas may contain moisture and is at relatively low temperatures. Therefore, the processes of removing moisture from the exhaust gas and adjusting the exhaust gas temperature can be omitted. This nitrous oxide decomposition catalyst can be used for the decomposition of nitrous oxide in exhaust gas from chemical plants, marine engines using LNG fuel mixed with NH3, heavy oil fuel, methane fuel, and methanol fuel, and thermal power plants using NH3.

[0150] Example

[0151] The following examples and comparative examples are provided to further illustrate the present invention in more detail. However, the present invention is not limited to any of the examples and comparative examples. Furthermore, the specific values ​​of blending ratios (including proportions), physical property values, parameters, etc., used in the following description can be replaced by the upper limits (defined as "below" or "less than") or lower limits (defined as "above" or "greater than") of the blending ratios (including proportions), physical property values, parameters, etc., recorded in the above-described "Specific Embodiments".

[0152] Example 1

[0153] <Modulation of Nitrous Oxide Decomposition Catalysts>

[0154] To make the composition ratio (atomic ratio) Ni 0.9 Fe 0.1 By using the Co2O4 method, nickel nitrate (Ni(NO3)2·6H2O), ferric nitrate (Fe(NO3)3·9H2O), and cobalt nitrate (Co(NO3)2·6H2O) were weighed and dissolved in ion-exchanged water. Then, while stirring the solution, 15% by mass of K2CO3 was added dropwise at a rate of 10 mL / min until the pH reached 9, resulting in a precipitate. The precipitate was filtered and washed with ion-exchanged water. Filtration and washing were repeated until the pH of the ion-exchanged water used for washing reached 7. The washed precipitate was recovered, dried at 100°C for 12 hours, and calcined at 400°C for 2 hours, thereby obtaining the nitrous oxide decomposition catalyst of Example 1. Furthermore, the nitrous oxide decomposition catalyst was pulverized and granulated.

[0155] Examples 2-19 and Comparative Example 1

[0156] Except for weighing each nitrate in the manner described in Tables 1 to 3 to make the nitrous oxide decomposition catalyst have the composition and composition ratios recorded in Example 1, the nitrous oxide decomposition catalysts of each Example and Comparative Example 1 were obtained in the same manner as in Example 1.

[0157] Comparative Example 2

[0158] <Modulation of Nitrous Oxide Decomposition Catalysts>

[0159] Nickel nitrate (Ni(NO3)2·6H2O), ferric nitrate (Fe(NO3)3·9H2O), and cobalt tetroxide (Co3O4) were weighed and mixed in an atomic ratio of 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 the nitrous oxide decomposition catalyst of Comparative Example 2. Furthermore, the nitrous oxide decomposition catalyst was formed into granules.

[0160] <Evaluation>

[0161] [Decomposition Evaluation of Nitrous Oxide]

[0162] 3.2 g of the nitrous oxide decomposition catalyst (granular) from each of the examples and comparative examples was packed into the reactor. Hypothetically, exhaust gas was mixed with air, N2, and N2O in a manner that resulted in the following gas composition, and this mixture was introduced into the evaporator. Further, H2O was introduced into the evaporator in a manner that achieved the following moisture content. In the evaporator, all gases (including H2O) were mixed and supplied to the reaction vessel at a rate of 2.8 NL / min-wet. The temperature of the reaction vessel (the temperature of the gas inside the reaction vessel) was heated to 400°C using an electric heater. Additionally, the ventilation rate SV (ventilation rate per unit volume of catalyst) was set to 10,811 h. -1 The N2O concentration was measured at the inlet and outlet of the reaction vessel using an N2O meter, and the decomposition rate of N2O was calculated according to the following formula. The results are shown in Tables 1 to 3.

[0163] {Gas Composition}

[0164] N2O: 100ppmvd

[0165] O2: 12% by volume

[0166] N2: Balance

[0167] H2O: 10% by volume

[0168] {Decomposition rate of N2O}

[0169] N2O decomposition rate (%) = (N2O concentration at reactor inlet - N2O concentration at reactor outlet) / (N2O concentration at reactor inlet) × 100

[0170] [Evaluation of nitrous oxide decomposition after SO2 durability test]

[0171] 3.2g of nitrous oxide decomposition catalyst (granular) from each of the examples and comparative examples was packed into the reactor.

[0172] (SO2 durability test)

[0173] Then, air, N2, N2O, and SO2 are mixed in the manner described below and introduced into the evaporator. Further, H2O is introduced into the evaporator in the manner described below regarding its moisture content. In the evaporator, all gases (including H2O) are mixed to prepare a gas containing sulfur dioxide (SO2). The sulfur dioxide (SO2) gas is then supplied to the reactor at a humid condition at a rate of 2.8 NL / min, and the temperature of the reaction vessel (the temperature of the gas inside the reactor) is heated to 400°C using an electric heater. Additionally, the ventilation rate SV (ventilation rate per unit volume of catalyst) is set to 10,811 h. -1 In addition, a gas containing sulfur dioxide (SO2) was supplied for 8 hours. In other words, the nitrous oxide decomposition catalysts of each embodiment and each comparative example were exposed to a gas containing sulfur dioxide (SO2) for 8 hours.

[0174] {Composition of gases containing sulfur dioxide (SO2)}

[0175] N2O: 100ppmvd

[0176] O2: 12% by volume

[0177] N2: Balance

[0178] SO2: 10 ppm vd

[0179] H2O: 10% by volume

[0180] The nitrous oxide decomposition catalysts of each embodiment and comparative example after SO2 durability testing were evaluated for nitrous oxide decomposition rates in the same manner as described above. The results are shown in Table 4.

[0181] [Evaluation of X-ray diffraction patterns]

[0182] X-ray diffraction (XRD) patterns of the nitrous oxide decomposition catalysts in Examples 1, 5, 7, 12, 14, and Comparative Example 2 were measured using a UitimaIV (manufactured by Rigaku Corporation). The measurement conditions were set to a tube voltage of 40 kV and a tube current of 40 mA. Furthermore, to align peak positions, Si was used as a standard for mixing, and correction was performed using 2θ = 28.44 for Si. The results are shown below. Figure 1 and Figure 2 .in addition, Figure 1 The XRD patterns are for Examples 1, 5, 7, 12, and 14. Figure 2 The XRD patterns are those of Example 1 and Comparative Example 2.

[0183] [Table 1]

[0184]

[0185] [Table 2]

[0186]

[0187] [Table 3]

[0188]

[0189] [Table 4]

[0190]

[0191] <Inspection>

[0192] like Figure 1 As shown, all catalysts in the examples exhibit diffraction peaks at positions shifted laterally by 2θ from the diffraction peak positions of the spinel structure derived from Co3O4. That is, this suggests the inclusion of Ni. X A 1-X The nitrous oxide decomposition catalyst represented by Co2O4 and compounds containing Mg Y B 1-Y The nitrous oxide decomposition catalyst represented by Co2O4 exists in a state where some of the Co in Co3O4 is replaced by a certain ion, and forms a solid solution. Furthermore, the nitrous oxide decomposition catalysts described in Examples 1-19 can improve the decomposition rate of nitrous oxide under conditions where the exhaust gas contains moisture and is at a relatively low temperature.

[0193] like Figure 2 As shown, Comparative Example 2 exhibits a diffraction peak at a position almost identical to the diffraction peak of the spinel structure derived from Co3O4. This suggests that the nitrous oxide decomposition catalyst of Comparative Example 2 did not form a solid solution. Furthermore, the nitrous oxide decomposition catalyst of Comparative Example 2 exhibited a lower nitrous oxide decomposition rate under conditions where the exhaust gas contained moisture and the temperature was relatively low. Comparative Example 1, which contained cobalt, nickel, and copper, also showed a relatively low nitrous oxide decomposition rate under similar conditions.

[0194] Furthermore, the nitrous oxide decomposition catalysts in Examples 1, 2, 4, 6-8, 12, 14, 15, and 18, even after the aforementioned SO2 durability test, were able to improve the nitrous oxide decomposition rate under conditions of exhaust gas containing moisture and relatively low temperature. That is, this suggests the inclusion of Ni... X A 1-X The compound represented by Co2O4, wherein A is a nitrous oxide decomposition catalyst selected from at least one of the group consisting of Fe, Mn, Sr, Cs, and La, and contains Mg Y B 1-YThe compound represented by Co2O4, wherein B is at least one selected from the group consisting of Zn and Ni, is a nitrous oxide decomposition catalyst that can improve the decomposition rate of nitrous oxide even under conditions where the exhaust gas contains sulfur dioxide (SO2) and moisture and is at a relatively low temperature.

[0195] Furthermore, the above-described invention is provided as an example embodiment of the present invention and is merely an example, not a limiting interpretation. Modifications that will be apparent to those skilled in the art are also covered within the scope of protection of the present invention.

[0196] Industrial applicability

[0197] The nitrous oxide decomposition catalyst of the present invention can be used for the decomposition treatment of nitrous oxide in exhaust gases from chemical plants, marine engines using LNG fuel mixed with NH3, heavy oil fuel, methane fuel and methanol fuel, and thermal power plants using NH3.

Claims

1. A nitrous oxide decomposition catalyst comprising a compound represented by the following formula (1): In formula (1), A is selected from at least one of the group consisting of Fe, Mn, Ce, Zr, La, alkali metals and alkaline earth metals, and X is greater than 0 and less than 1.

2. The nitrous oxide decomposition catalyst according to claim 1, wherein, In the above formula (1), X is 0.75 or higher.

3. The nitrous oxide decomposition catalyst according to claim 1, wherein, A is selected from at least one of 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): In formula (2), B is selected from at least one of the group consisting of Fe, Mn, Zn, Ni, Zr, La, alkali metals and alkaline earth metals, and Y is greater than 0 and less than 1, wherein the alkaline earth metals do not include Mg.

5. The nitrous oxide decomposition catalyst according to claim 4, wherein, In equation (2), Y is 0.75 or higher.

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

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

8. The method for decomposing nitrous oxide according to claim 7, wherein, The H2O concentration in the exhaust gas is above 5% by volume, and the decomposition temperature in the process of decomposing the nitrous oxide is below 450°C.

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