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

Abstract

Provided are: a nitrous oxide decomposition method capable of decomposing nitrous oxide for a long period of time while maintaining the decomposition rate of nitrous oxide; and a method for producing a nitrous oxide decomposition catalyst suitable for use in the decomposition method. The present invention relates to: a method for decomposing nitrous oxide, which comprises a step for bringing a catalyst into contact with a nitrous oxide-containing gas containing nitrous oxide, water vapor, and oxygen; and a method for producing a nitrous oxide decomposition catalyst suitable for use in the method. The catalyst is a catalyst in which a first component such as a ruthenium compound and a second component such as a zirconium compound are supported on a carrier comprising titanium oxide, or a catalyst in which a first component such as a ruthenium compound is supported on a carrier comprising titanium oxide and silicon oxide.

Description

Technical Field

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

[0002] From the perspective of protecting the global environment and preventing air pollution, nitrogen oxides (NOx) in exhaust gas are a problem, and their emissions are subject to strict regulations. In particular, nitrogen dioxide (NO2), which is harmful to humans and is believed to cause photochemical smog and acid rain, is subject to emission regulations. To reduce its emissions, various denitrification technologies are being researched and put into practical use. However, nitrous oxide (N2O), a nitrogen oxide, is not currently subject to emission regulations and is often released directly into the atmosphere. In practice, while denitrification treatment is used to decompose and remove nitrogen monoxide and nitrogen dioxide from exhaust gases from chemical manufacturing facilities such as nitric acid, ε-caprolactam, and adipic acid plants, there are also cases where the by-product nitrous oxide is not decomposed and removed and is emitted (released) into the atmosphere.

[0003] However, when greenhouse gases like nitrous oxide are released into the atmosphere, the increased concentration of these gases leads to an enhanced greenhouse effect, which is believed to contribute to global warming. Furthermore, nitrous oxide is said to have a global warming effect approximately 300 times greater than that of carbon dioxide. Consequently, in recent years, there has been growing interest in reducing atmospheric emissions of nitrous oxide, not only from carbon dioxide and methane. With growing awareness of environmental sustainability, nitrous oxide is expected to be subject to emission regulations in the near future. Consequently, there is a demand for technologies that can decompose and remove nitrous oxide from exhaust gases, thereby suppressing atmospheric emissions. For example, Patent Document 1 describes a nitrous oxide decomposition method that uses a catalyst to catalytically crack a gas containing nitrous oxide in the presence of a reducing gas. The catalyst is characterized by supporting at least one precious metal selected from the group consisting of ruthenium (Ru), rhodium (Rh), palladium (Pd), rhenium (Re), osmium (Os), iridium (Ir), and platinum (Pt).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 06-218232 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] The nitrous oxide decomposition method described in Patent Document 1 is a method for decomposing nitrous oxide by allowing carbon monoxide, hydrocarbon gas, mineral oil-based hydrocarbon gas, alcohols, etc. to coexist as reducing gases during catalytic cracking of the gas containing nitrous oxide, thereby decomposing the nitrous oxide in the nitrous oxide-containing gas.

[0009] However, the catalyst used in the decomposition of nitrous oxide (nitrous oxide decomposition catalyst) gradually loses its catalytic activity as it is used to decompose nitrous oxide. Therefore, considering the aforementioned situation regarding nitrous oxide, it is desirable to suppress the decrease in the decomposition rate of nitrous oxide and maintain a high decomposition rate even when nitrous oxide decomposition is performed for a long period of time. However, Patent Document 1 does not investigate this point.

[0010] An object of the present invention is to provide a method for decomposing dinitrogen monoxide that can decompose dinitrogen monoxide for a long period of time while maintaining the decomposition rate of dinitrogen monoxide, and a method for producing a dinitrogen monoxide decomposition catalyst suitable for use in the decomposition method.

[0011] Means for solving problems

[0012] That is, the subject of the present invention is achieved by the following means.

[0013] <1> A method for decomposing nitrous oxide, comprising the step of contacting a catalyst with a nitrous oxide-containing gas comprising nitrous oxide, water vapor, and oxygen, wherein the catalyst comprises a first component comprising at least one selected from ruthenium and a ruthenium compound, and a second component comprising at least one selected from antimony, an antimony compound, cerium, a cerium compound, zirconium, a zirconium compound, silicon, and a silicon compound, supported on a carrier comprising titanium oxide.

[0014] <2> The method for decomposing nitrous oxide according to <1>, wherein the second component is an oxide containing at least one selected from antimony oxide, cerium oxide, zirconium oxide, and silicon oxide.

[0015] <3> The method for decomposing nitrous oxide according to <1>, wherein the second component contains at least one selected from zirconium and zirconium compounds.

[0016] <4> The method for decomposing nitrous oxide according to any one of <1> to <3>, wherein the content of the metal element contained in the second component of the catalyst is in a molar ratio of 0.1 to 5 relative to the content of the ruthenium element contained in the first component.

[0017] <5> The method for decomposing nitrous oxide according to any one of <1> to <4>, wherein the first component contains ruthenium oxide.

[0018] <6> The method for decomposing nitrous oxide according to any one of <1> to <5>, wherein the content of ruthenium in the catalyst is 0.5 to 10% by mass.

[0019] <7> The method for decomposing nitrous oxide according to any one of <1> to <6>, wherein the catalyst is located on a substrate having a honeycomb structure.

[0020] <8> A method for decomposing nitrous oxide, comprising the step of contacting a catalyst with a nitrous oxide-containing gas comprising nitrous oxide, water vapor, and oxygen, wherein the catalyst comprises a first component containing at least one selected from ruthenium and a ruthenium compound supported on a carrier comprising titanium oxide and silicon oxide.

[0021] <9> The method for decomposing nitrous oxide according to <8>, wherein the content of the silicon oxide in the support is 1 to 20% by mass.

[0022] <10> The method for decomposing nitrous oxide according to <8> or <9>, wherein the silicon oxide is derived from colloidal silica having a particle size of 5 to 45 nm.

[0023] <11> The method for decomposing nitrous oxide according to any one of <8> to <10>, wherein the support further supports a second component containing at least one selected from antimony, antimony compounds, cerium, cerium compounds, zirconium, zirconium compounds, silicon, and silicon compounds.

[0024] <12> The method for decomposing nitrous oxide according to <11>, wherein the second component is an oxide containing at least one selected from antimony oxide, cerium oxide, zirconium oxide, and silicon oxide.

[0025] <13> The method for decomposing nitrous oxide according to any one of <8> to <10>, wherein the support further supports a second component containing at least one selected from zirconium and a zirconium compound.

[0026] <14> The method for decomposing nitrous oxide according to <11> to <13>, wherein the content of the metal element contained in the second component of the catalyst is 0.1 to 5 in molar ratio relative to the content of the ruthenium element contained in the first component.

[0027] <15> The method for decomposing nitrous oxide according to any one of <8> to <14>, wherein the first component contains ruthenium oxide.

[0028] <16> The method for decomposing nitrous oxide according to any one of <8> to <15>, wherein the content of ruthenium in the catalyst is 0.5 to 10% by mass.

[0029] <17> The method for decomposing nitrous oxide according to any one of <8> to <16>, wherein the catalyst is located on a substrate having a honeycomb structure.

[0030] <18> A method for producing a nitrous oxide decomposition catalyst, comprising:

[0031] A step of calcining a carrier precursor to obtain a carrier, wherein the carrier precursor is obtained by extruding a carrier raw material mixture containing titanium oxide, silicon oxide and water;

[0032] a step of supporting a first component raw material containing a ruthenium compound on a carrier;

[0033] a step of supporting a second component raw material containing at least one selected from antimony compounds, cerium compounds, zirconium compounds, and silicon compounds on a carrier; and

[0034] A step of calcining a catalyst precursor in which the first component raw material and the second component raw material are supported on a carrier.

[0035] <19> The method for producing a nitrous oxide decomposition catalyst according to <18>, wherein the second component raw material is a zirconium compound.

[0036] <20> The method for producing a nitrous oxide decomposition catalyst according to <18> or <19>, wherein the silicon oxide is colloidal silicon dioxide having a particle size of 5 to 45 nm.

[0037] <21> The method for producing a nitrous oxide decomposition catalyst according to any one of <18> to <20>, comprising the step of calcining the catalyst precursor and then disposing the calcined catalyst precursor on a substrate having a honeycomb structure.

[0038] Effects of the Invention

[0039] The present invention can provide a method for decomposing dinitrogen monoxide, which can decompose dinitrogen monoxide for a long period of time while maintaining the decomposition rate of dinitrogen monoxide, and a method for producing a dinitrogen monoxide decomposition catalyst suitable for use in the decomposition method. DETAILED DESCRIPTION

[0040] In the present invention and this specification, a numerical range expressed using “to” means a range including the numerical values ​​described before and after “to” as the lower limit and the upper limit.

[0041] [[Decomposition method of nitrous oxide]]

[0042] The method for decomposing nitrous oxide of the present invention (hereinafter, sometimes simply referred to as the "decomposition method of the present invention") includes a step of contacting a catalyst (sometimes also referred to as a "nitrous oxide decomposition catalyst") described later with a nitrous oxide-containing gas containing nitrous oxide, water vapor, and oxygen (hereinafter, sometimes referred to as the "contact step").

[0043] By the contact step using the catalyst described below, as described below, the dinitrogen monoxide in the dinitrogen monoxide-containing gas can be decomposed into nitrogen molecules (usually nitrogen gas) and oxygen molecules (usually oxygen gas) for a long period of time while maintaining a high decomposition rate.

[0044] [catalyst]

[0045] The catalyst used in the decomposition method of the present invention is a nitrous oxide decomposition catalyst having a function of decomposing nitrous oxide, and is a catalyst in which a component other than the first component such as ruthenium that exhibits catalytic activity (a second component or silicon oxide) is present on the surface, near the surface, or in the pores of the carrier. Preferred catalysts include the following catalysts.

[0046] Catalyst I: A catalyst comprising a support comprising titanium oxide, supported on the support a first component (hereinafter referred to as a first supported component) containing at least one selected from ruthenium and a ruthenium compound, and a second component (hereinafter referred to as a second supported component) containing at least one selected from antimony, an antimony compound, cerium, a cerium compound, zirconium, a zirconium compound, silicon, and a silicon compound;

[0047] Catalyst II: A catalyst in which the first supported component is supported on a carrier composed of titanium oxide and silicon oxide.

[0048] In Catalyst II, the first and second supported components are preferably supported on a carrier comprising titanium oxide and silicon oxide. For convenience, this catalyst is referred to as "Catalyst II (preferred embodiment)." It should be noted that in Catalyst II, silicon oxide is preferably present (dispersed) on or near the surface of the titanium oxide primary particles.

[0049] In the present invention, the term "supported component" generally refers to the components (element, compound, etc.) supported on a support constituting the catalyst. Examples thereof include the first supported component, the second supported component, and the third supported component described below. Furthermore, a "catalyst comprising a supported component supported on a support" refers to a catalyst in which the supported component is attached to the surface and / or pores of the support.

[0050] The catalyst used in the decomposition method of the present invention contains at least one selected from ruthenium and ruthenium compounds as a first supported component supported on the carrier, from the perspective of a balance between catalytic activity and cost.

[0051] <Carried Components>

[0052] Catalyst I includes a first supported component having nitrous oxide decomposition capability (catalytic activity) and a second supported component different from the first supported component as supported components supported on a carrier described below. The supported component supported by Catalyst I may also include a third supported component that is neither the first nor the second supported component.

[0053] On the other hand, Catalyst II includes a first supported component having nitrous oxide decomposition capability as a supported component supported on a carrier described below. The supported component supported by Catalyst II preferably includes a second supported component different from the first supported component, and may also include a third supported component that is neither the first nor the second supported component.

[0054] Hereinafter, each supported component will be described.

[0055] (First supported component)

[0056] The first supported component supported by Catalyst I and Catalyst II includes at least one selected from ruthenium and ruthenium compounds. The number of types of the first supported component supported by each catalyst is not particularly limited as long as it is one or more, and can be, for example, 1 to 4.

[0057] -Ruthenium compounds-

[0058] There are no particular restrictions on ruthenium compounds, and examples thereof include ruthenium oxide, ruthenium hydroxide, ruthenium nitrate, ruthenium chloride, ruthenic acid, chlororuthenate, chlororuthenate hydrate, salts of ruthenic acid, ruthenium oxychloride, salts of ruthenium oxychloride, ruthenium ammonia complex, chlorides of ruthenium ammonia complex, ruthenium bromide, ruthenium carbonyl complex, ruthenium organic acid salts, and ruthenium nitrosyl complexes.

[0059] Examples of ruthenium oxide include RuO2 and the like.

[0060] Examples of ruthenium hydroxide include Ru(OH) 3 .

[0061] Examples of ruthenium nitrate include Ru(NO 3 ) 3 .

[0062] Examples of ruthenium chloride include RuCl 3 and RuCl 3 hydrate.

[0063] Examples of ruthenic acid include H2RuO4.

[0064] As chlororuthenate, K3RuCl6 and [RuCl6] are mentioned. 3- Salts with anions such as K2RuCl6, (NH4)2RuCl6, etc. [RuCl6] 2-Anionic salts.

[0065] As the chlororuthenate hydrate, there is exemplified the hydrate consisting of [RuCl5(H2O)4] 2- As the anion salt hydrate, with [RuCl2 (H2O) 4] ＋ Cationic salt hydrates, etc.

[0066] As a salt of ruthenic acid, containing Ru VI O4 2- (tetraoxoruthenate(VI) ion) salts and Ru VII O4 - (perruthenate ion, tetraoxoruthenate (VII) ion). Examples of cations forming the salt include cations of alkali metal elements, cations of alkaline earth metal elements, Ag ＋ , ammonium cations, etc. Among them, alkali metal salts of ruthenic acid (salts of Li, Na, K, Rb, and Cs) are preferred, and Na salts or K salts of ruthenic acid are more preferred. Specifically, Na2RuO4, K2RuO4, etc. are mentioned.

[0067] Examples of ruthenium oxychloride include Ru2OCl4, Ru2OCl5, and Ru2OCl6.

[0068] Examples of ruthenium oxychloride salts include K2Ru2OCl 10 , Cs2Ru2OCl4, etc.

[0069] Examples of ruthenium ammonia complexes include [Ru(NH3)6] 2＋ 、〔Ru(NH3)6〕 3＋ 、〔Ru(NH3)5H2O〕 2＋ etc. are complexes of complex ions.

[0070] Examples of chlorides of ruthenium ammonia complexes include [Ru(NH3)5Cl] 2＋ It is a complex of complex ions, [Ru(NH3)6]Cl2, [Ru(NH3)6]Cl3, [Ru(NH3)6]Br3, etc.

[0071] Examples of ruthenium bromide include RuBr 3 and RuBr 3 hydrate.

[0072] Examples of ruthenium carbonyl complexes include Ru(CO)5, Ru3(CO) 12 wait.

[0073] Examples of ruthenium organic acid salts include [Ru3O(OCOCH3)6(H2O)3]OCOCH3 hydrate and Ru2(RCOO)4Cl (R = alkyl group having 1 to 3 carbon atoms).

[0074] Examples of the ruthenium nitrosyl complex include K2[RuCl5NO)], [Ru(NH3)5(NO)]Cl3, [Ru(OH)(NH3)4(NO)](NO3)2, and Ru(NO)(NO3)3.

[0075] The ruthenium compound is preferably ruthenium oxide, ruthenium nitrate, ruthenium chloride, ruthenium bromide, a salt of ruthenic acid, or a ruthenium nitrosyl complex, more preferably ruthenium oxide, and even more preferably ruthenium oxide.

[0076] Ruthenium compounds are compounds containing ruthenium as one of their constituent elements, and may also include elements other than ruthenium (metal or non-metal). For example, ruthenium oxide is an oxide containing ruthenium as one of its constituent elements. This includes not only oxides of ruthenium alone (RuO₂), but also composite oxides containing ruthenium and elements other than ruthenium (metal or non-metal).

[0077] It should be noted that (metal) ruthenium also includes not only metal ruthenium but also alloys of ruthenium and metals other than ruthenium.

[0078] The content of the ruthenium element constituting the first supported component in the catalyst (based on 100% of the total mass of the catalyst) is not particularly limited in either Catalyst I or Catalyst II and can be appropriately set, for example, preferably 0.5 to 10% by mass, more preferably 0.5 to 5% by mass, and even more preferably 1 to 3% by mass.

[0079] (Second supported component)

[0080] The second supported component supported by catalyst I and preferably supported by catalyst II contains at least one selected from antimony, antimony compounds, cerium, cerium compounds, zirconium, zirconium compounds, silicon and silicon compounds. The second supported component refers to a component that does not substantially contain ruthenium element as its constituent element. In the present invention, "does not substantially contain" refers to a situation where it is inevitably mixed and contained. If a catalyst supported by the second supported component is used in the decomposition of nitrous oxide, even if the decomposition of nitrous oxide is carried out for a long time, the reduction in the catalytic activity of the catalyst can be suppressed, and nitrous oxide can be decomposed with a high decomposition rate. The second supported component can have the decomposition ability (catalytic activity) of nitrous oxide or may not have the decomposition ability (catalytic activity) of nitrous oxide.

[0081] The number of types of the second supported component supported on Catalyst I is not particularly limited as long as it is one or more, and can be, for example, 1 to 8, preferably 1 to 4. On the other hand, the number of types of the second supported component supported on Catalyst II is not particularly limited, and can be 0 to 8, preferably 1 to 6, and more preferably 1 to 4.

[0082] As each compound of antimony, cerium, zirconium, and silicon, there are no particular limitations as long as it is a compound containing these elements, and any appropriate compound can be used. For example, compounds of the same type as the above-mentioned ruthenium compound (compounds obtained by replacing the ruthenium element in the ruthenium compound with at least one of antimony, cerium, zirconium, and silicon) can be used.

[0083] -Antimony compounds-

[0084] Examples of the antimony compound include antimony oxide, antimony sulfate, antimony chloride, and salts of antimonic acid, with antimony oxide and antimony chloride being preferred.

[0085] Examples of antimony oxide include Sb2O3, Sb2O4, and Sb2O5.

[0086] Examples of antimony sulfate include Sb 2 (SO 4 ) 3 and the like.

[0087] Examples of antimony chloride include SbCl 3 and the like.

[0088] Examples of antimony acid salts include NaSbO3 and the like.

[0089] -Cerium compounds-

[0090] Examples of the cerium compound include cerium oxide, cerium hydroxide, cerium nitrate, cerium chloride, salts of ceric acid, cerium sulfate, and cerium carbonate. Preferred are cerium oxide, cerium nitrate, cerium chloride, and cerium sulfate.

[0091] Examples of cerium oxide include CeO 2 and Ce 2 O 3 .

[0092] Examples of cerium hydroxide include CeO 2 ·2H 2 O and the like.

[0093] Examples of cerium nitrate include Ce(NO 3 ) 3 ·6H 2 O and the like.

[0094] Examples of cerium chloride include CeCl 3 ·7H 2 O and the like.

[0095] Examples of the salt of ceric acid include Ce(NH 4 ) 2 (NO 3 ) 6 hydrate and the like.

[0096] Examples of cerium sulfate include Ce(SO 4 ) 2 ·4H 2 O and the like.

[0097] Examples of cerium carbonate include Ce 2 (CO 3 ) 3 · 8H 2 O and the like.

[0098] -Zirconium compounds-

[0099] Examples of the zirconium compound include zirconium oxide, zirconium hydroxide, zirconium oxynitrate, zirconium chloride, zirconium sulfate, zirconium acetate, and zirconium acetylacetonate. Preferred are zirconium oxide, zirconium oxynitrate, zirconium chloride, and zirconium sulfate.

[0100] Examples of zirconium oxide include ZrO 2 and the like.

[0101] Examples of zirconium hydroxide include Zr(OH) 4 and the like.

[0102] Examples of zirconyl nitrate include ZrO(NO 3 ) 2 · 2H 2 O and the like.

[0103] Examples of zirconium chloride include ZrCl 3 , ZrCl 4 and the like.

[0104] Examples of zirconium sulfate include Zr(SO 4 ) 2 ·4H 2 O and the like.

[0105] Examples of zirconium acetylacetonate include Zr(C5H7O2)4 and the like.

[0106] -Silicon compounds-

[0107] Examples of the silicon compound include silicon oxide, silicon chloride, salts of silicic acid, and silicon alkoxides, and silicon oxide and salts of silicic acid are preferred.

[0108] Examples of silicon oxide include SiO 2 and the like.

[0109] Examples of silicon chloride include SiCl 4 and the like.

[0110] Examples of the salt of silicic acid include salts of orthosilicic acid, pyrosilicic acid, metasilicic acid, and the like. Specific examples include Na2SiO3, Na4SiO4, Na2Si2O5, and Na2Si4O9.

[0111] Examples of silicon alkoxides include Si(OC2H5)4, Si(OC3H7)4, and Si(OC4H9)4.

[0112] A preferred compound as the second supported component is at least one selected from zirconium and zirconium compounds. On the other hand, a preferred compound as the second supported component is preferably an oxide comprising at least one selected from antimony oxide, cerium oxide, zirconium oxide, and silicon oxide, more preferably comprising at least zirconium oxide, and even more preferably zirconium oxide.

[0113] The content (total content) of the metal elements (antimony, cerium, zirconium, and silicon) constituting the second supported component in the catalyst (out of 100% of the total mass of the catalyst) is not particularly limited for either Catalyst I or Catalyst II and can be appropriately set. For example, the content of these metal elements in Catalyst I is preferably 0.003 to 49% by mass, more preferably 0.01 to 14% by mass, and even more preferably 0.4 to 3.7% by mass. On the other hand, the content of these metal elements in Catalyst II is preferably 0 to 49% by mass, more preferably 0 to 14% by mass, and even more preferably 0 to 3.7% by mass.

[0114] In addition, the content of each metal element in the catalyst can be appropriately set in consideration of the above-mentioned total content.

[0115] In either Catalyst I or Catalyst II, from the viewpoint of being able to suppress a decrease in catalytic activity (a decrease in the decomposition rate of nitrous oxide), the content (total content) of the metal element constituting the second supported component relative to the content of the ruthenium element constituting the first supported component is preferably 0.1 to 5, more preferably 0.1 to 3, and even more preferably 0.1 to 2.1 in terms of the molar ratio (content (mole) of the metal element / content (mole) of the ruthenium element).

[0116] (Third supported component)

[0117] The third supported component that can be supported on Catalyst I and Catalyst II is not particularly limited as long as it is not included in either the first or second supported components. Examples include metals such as aluminum, niobium, tin, copper, iron, cobalt, nickel, vanadium, chromium, molybdenum, tungsten, manganese, tellurium, and sodium, and compounds of these metals (preferably oxides or sulfates of these metals). A preferred third supported component is at least one oxide or sulfate selected from the group consisting of aluminum oxide, niobium oxide, manganese oxide, tellurium oxide, tin oxide, sodium oxide, and sodium sulfate.

[0118] The content (total content) of the metal element constituting the third supported component in the catalyst (in 100% of the total mass of the catalyst) is not particularly limited in either Catalyst I or Catalyst II and can be appropriately set.

[0119] <Carrier>

[0120] The support constituting Catalyst I comprises titanium oxide and contains substantially no silicon oxide, but may contain other compounds described below. On the other hand, the support constituting Catalyst II only requires titanium oxide and silicon oxide, but may contain other compounds described below.

[0121] In the present invention, a carrier refers to a material obtained by shaping primary particles of titanium oxide or a compound containing titanium oxide and / or secondary particles formed by agglomeration of primary particles into a desired shape. Furthermore, the surface of the carrier refers to the surface of a formed body, and the pores of the carrier refer to any one or more of the pores of the primary particles, the spaces between primary particles in the secondary particles, and the spaces between secondary particles in an aggregate of secondary particles.

[0122] In the present invention, the crystal form of the titanium oxide constituting the support is not particularly limited and may be any of a rutile crystal form, anatase crystal form, and a brookite crystal form. In the present invention, the titanium oxide constituting the support preferably contains a rutile crystal form of titanium oxide. From the viewpoint of catalytic activity, taking the total amount of titanium oxide contained in the support as 100% by mass, the content of rutile crystal form titanium oxide in the titanium oxide contained in the support is preferably 20% by mass or more, more preferably 30% by mass or more, further preferably 80% by mass or more, and particularly preferably 90% by mass or more.

[0123] In the present invention, titanium oxide containing rutile crystal-type titanium oxide refers to titanium oxide containing rutile crystals, wherein the ratio of rutile crystals to anatase crystals in the titanium oxide is determined by X-ray diffraction analysis. Various radiation sources can be used as X-ray sources. For example, copper Kα rays can be cited. When copper Kα rays are used, the ratio of rutile crystals and the ratio of anatase crystals are determined using the intensity of the diffraction peak at 2θ = 27.5 degrees of the (110) plane and the intensity of the diffraction peak at 2θ = 25.3 degrees of the (101) plane, respectively. The support used in the present invention is a support having the peak intensity of rutile crystals and the peak intensity of anatase crystals, or a support having the peak intensity of rutile crystals. That is, it can be a support having both the diffraction peak of rutile crystals and the diffraction peak of anatase crystals, or it can be a support having only the diffraction peak of rutile crystals.

[0124] The support constituting Catalyst II comprises silicon oxide, preferably on the surface (including the vicinity of the surface) and / or on the inner surfaces (including the vicinity of the inner surfaces) of the pores of the support. When Catalyst II having a support comprising silicon oxide is used in the decomposition of nitrous oxide, a decrease in the catalytic activity of Catalyst II can be suppressed even when the decomposition of nitrous oxide is carried out for a long period of time, enabling the decomposition of nitrous oxide at a high decomposition rate. Silicon oxide is preferably silicon dioxide.

[0125] From the perspective of facilitating the manufacture of the carrier, the silicon oxide contained in the carrier constituting Catalyst II is preferably silicon oxide derived from colloidal silica (for example, a dried product of colloidal silica in the form of particles or granules). The particle size of the silicon oxide in the colloidal silica is not particularly limited. From the perspective of increasing the number of silicon oxide particles, it is preferably 5 to 45 nm, and more preferably 5 to 22 nm. The particle size of silicon oxide is set to the average particle size measured as follows. Average particle size (d) [nm] is the specific surface area (S) [m 2 / g], and calculated using the following formula. Here, ρ is the true density of silicon oxide, using 2.2 [g / cm 3 ]value.

[0126] d = 6000 / (S × ρ)

[0127] It should be noted that the particle size of silicon oxide present in the support of Catalyst II does not need to be maintained at the particle size of silicon oxide in colloidal silica, but it is preferred to maintain it.

[0128] The content of silicon oxide in the support constituting Catalyst II (in 100% of the total mass of the support) is not particularly limited and can be appropriately set. For example, from the perspective of suppressing a decrease in catalytic activity and maintaining it for a long time, it is preferably 1 to 20% by mass, more preferably 1 to 10% by mass, and even more preferably 1 to 5% by mass.

[0129] In the present invention, whether silicon oxide is the second supported component (catalyst I) or whether silicon oxide constitutes the support (catalyst II) can be confirmed by observing the catalyst with a scanning electron microscope or a scanning transmission electron microscope.

[0130] Examples of other compounds that may be contained in the supports constituting Catalyst I and Catalyst II include metal oxides or metal sulfates other than titanium oxide and other than silicon oxide, composite oxides of titanium oxide and other metal oxides, composite oxides of titanium oxide, silicon oxide and other metal oxides, mixtures of titanium oxide and other metal oxides or metal sulfates, and mixtures of titanium oxide, silicon oxide and other metal oxides or metal sulfates. Examples of the metal oxides include aluminum oxide, zirconium oxide, cerium oxide, and sodium oxide. Examples of the metal sulfates include sodium sulfate.

[0131] Titanium oxide produced by a known method may be used, or a commercially available product may be used.

[0132] As a method for producing rutile crystal-type titanium oxide, the following method can be mentioned.

[0133] A method in which titanium tetrachloride is added dropwise to ice-cooled water to dissolve the mixture, then neutralized with an aqueous ammonia solution at a temperature above 20°C to produce titanium hydroxide (orthotitanic acid). The resulting precipitate is then washed with water to remove chloride ions and then calcined at a temperature above 600°C (Catalyst Preparation Chemistry, 1989, p. 211, Kodansha).

[0134] A method in which a reaction gas is prepared by passing an oxygen-nitrogen mixed gas through a titanium tetrachloride evaporator, introduced into a reactor, and reacted at a temperature above 900°C (Catalyst Preparation Chemistry, 1989, p. 89, Kodansha);

[0135] A method in which titanium tetrachloride is hydrolyzed in the presence of ammonium sulfate and then calcined (e.g., Catalyst Engineering Lecture 10 Elements Catalyst Overview (Japanese: Catalyst Engineering Lecture 10 Elements Catalyst Handbook), 1978, p. 254, Chijin Bookstore);

[0136] Methods for calcining anatase-type titanium oxide (e.g., Metal Oxides and Composite Oxides, 1980, p. 107, Kodansha);

[0137] A method for hydrolyzing an aqueous solution of titanium chloride by heating; and

[0138] A method in which an aqueous solution of a titanium compound such as titanium sulfate or titanium chloride is mixed with rutile-type titanium oxide powder, the mixture is subjected to heating hydrolysis or alkali hydrolysis, and then fired at a temperature of about 500°C.

[0139] The support composed of silicon oxide constituting Catalyst II can be produced by the step of obtaining the support described in the method for producing Catalyst II described later.

[0140] The support can be obtained by shaping titanium oxide or the like into a desired shape. When the support contains titanium oxide and a compound other than titanium oxide (eg, silicon oxide), the support can be obtained by shaping a mixture of titanium oxide and the compound other than titanium oxide into a desired shape.

[0141] The shape of the catalyst (support) is not particularly limited and can be appropriately set.

[0142] In a preferred embodiment of the present invention, a honeycomb shape (honeycomb structure) can be used. The honeycomb-shaped catalyst in this preferred embodiment is usually used as is (in a honeycomb structure), but can also be crushed and the crushed product can be classified before use. In this case, the size can be approximately the same as that of the spherical particles described below.

[0143] On the other hand, in another preferred embodiment of the present invention, various shapes can be adopted.As such shape, there is no particular restriction, can enumerate for example granular shape such as sphere, cylinder, annulus, monolithic shape, wavy shape or pulverize the granular shape, particulate etc. of the appropriate size that obtains after shaping classification.The shape of catalyzer is preferably granular shape such as sphere, cylinder, annulus, monolithic shape, wavy shape or granular shape etc., from the viewpoint of the decomposition efficiency of nitrous oxide, more preferably annular granular shape.

[0144] In the present invention, the honeycomb structure refers to a "honeycomb structure" in the general sense, such as a honeycomb catalyst often used as an exhaust gas purification catalyst, and includes a structure in which a plurality of through holes densely arranged in a planar direction are perforated on a base such as a columnar body.

[0145] As a substrate, an appropriate shape is selected according to the shape of the reaction device (such as a reaction tube, etc.) filled with the catalyst, the filling method of the honeycomb structure in the reaction device, etc., and examples include a columnar body, a block, a plate, etc. The opening shape of the through hole is not particularly limited, and examples include polygons such as a quadrilateral and a hexagon, a circle, an ellipse, etc. The arrangement of the through holes is not particularly limited and is appropriately determined considering the shape of the opening, etc. For example, in the planar direction of the substrate (usually a plane perpendicular to the axis), a series (parallel) configuration (Straight arrengement), a staggered arrangement (staggered arrengment), a honeycomb arrangement (honeycomb arrengement), etc. can be mentioned.

[0146] Examples of the honeycomb structure include circular holes arranged in parallel, staggered, and honeycomb arrangements, and polygonal square holes arranged in parallel, staggered, and honeycomb arrangements.

[0147] When the catalyst is in the form of a powder, such as granules or microparticles, it is preferably disposed as a washcoat layer on a honeycomb-structured substrate. The honeycomb-structured substrate can be composed of any material typically used in automotive catalysts, typically consisting of metal or ceramic, such as various stainless steels or cordierite. The substrate typically provides multiple wall surfaces for the application and adhesion of the washcoat layer, thereby functioning as a substrate for the catalyst. The mass of the washcoat layer per unit volume of the honeycomb-structured substrate is preferably 10 to 200 g / L, more preferably 30 to 100 g / L.

[0148] The size of the catalyst (support) is not particularly limited and can be appropriately set.

[0149] When the catalyst is in the form of spherical particles or cylindrical pellets, the catalyst diameter is preferably 10 mm or less from the perspective of catalytic activity. It should be noted that the catalyst diameter referred to herein refers to the diameter of the sphere in the case of spherical particles, the diameter of the cross section in the case of cylindrical pellets, and the maximum diameter of the cross section in the case of other shapes. When the catalyst is in the form of spherical particles or cylindrical pellets, the catalyst is preferably filled in the catalyst-filled area of ​​the reaction device (reaction tube) to form a catalyst-filled layer, and the filling volume ratio is preferably 35 to 74% by volume.

[0150] In the preferred embodiment and another preferred embodiment of the present invention (the substrate in the case of a powdered catalyst), the honeycomb structure (catalyst) preferably has a volume ratio of 35 to 50% by volume, preferably 38 to 50% by volume, in order to further improve the decomposition efficiency of nitrous oxide. The volume ratio of the honeycomb structure (catalyst) refers to the ratio (percentage) of the actual volume of the honeycomb structure to the apparent volume of the honeycomb structure. The apparent volume and actual volume can be calculated using conventional methods based on the dimensions of the honeycomb structure.

[0151] In order to further improve the decomposition efficiency of nitrous oxide, the honeycomb structure (catalyst), when filled in the catalyst-filled region of the reaction device (reaction tube) to form a catalyst-filled layer, preferably has a honeycomb structure filling volume ratio of 35 to 50 volume%, and more preferably has a honeycomb structure filling volume ratio of 38 to 50 volume%. The filling volume ratio refers to the ratio (percentage) of the actual volume of the honeycomb structure to the volume of the catalyst-filled region of the reaction device (reaction tube).

[0152] Taking into account the above-mentioned volume ratio or filling volume ratio, the size of the catalyst can be set, for example, to a size suitable for the catalyst filling area of ​​the reaction device (reaction tube), and can generally be set to an external size that is approximately the same as the internal size (inner diameter and length) of the catalyst filling area.

[0153] The opening diameter (also referred to as the cell size), the distance between the through holes (also referred to as the thickness of the inner wall), the porosity, etc. of the through holes in the above-mentioned honeycomb structure can be appropriately determined and can be determined by taking into account the (filling) volume rate, etc. in the present invention. For example, as the cell size, it can be set to 1 to 3 mm, preferably 1 to 2 mm. As the thickness of the inner wall, it can be set to 0.1 to 2 mm, preferably 0.2 to 1 mm. As the porosity ([(total area of ​​through holes opened on the surface of the honeycomb structure) / (apparent surface area of ​​the honeycomb structure)]×100 (%)), it can be set to 50 to 65%, preferably 50 to 62%. The cell size and the thickness of the inner wall can be determined by observing and measuring the surface of the honeycomb shape. The porosity can be calculated based on the measured total area of ​​the through holes and the calculated apparent surface area.

[0154] In the present invention, the catalyst may be used in combination of a plurality of catalysts (number) or a plurality of catalysts.

[0155] In a preferred embodiment of the present invention, the catalyst includes a honeycomb structure satisfying the aforementioned filling volume ratio by combining multiple catalysts (a configuration in which the multiple catalysts filled in the catalyst-filled region collectively form a honeycomb structure satisfying the aforementioned filling volume ratio). However, it is preferred that the catalyst have a honeycomb structure satisfying the aforementioned filling volume ratio on their own. In this case, the aforementioned filling volume ratio is synonymous with the filling ratio of the catalyst (the catalyst filling ratio of a single catalyst). Furthermore, when combining multiple catalysts, it is preferred that the honeycomb structure of each catalyst satisfy the aforementioned volume ratio.

[0156] In another preferred embodiment of the present invention (when the catalyst is in the form of powder), a plurality of catalysts may be used in combination as the catalyst disposed as the washcoat layer.

[0157] In the decomposition method of the present invention, the catalyst may be used after being diluted with an inactive substance.

[0158] <Method for producing catalyst>

[0159] The catalyst used in the decomposition method of the present invention can be produced by various known methods. For example, it can be produced by immersing a support containing titanium oxide in a solution containing a supported component, allowing the supported component to adhere to the support, and then drying. The solvent in the solution containing the supported component is not particularly limited, and water, ethanol, etc. can be used. After drying, the catalyst can be calcined.

[0160] When the catalyst contains ruthenium oxide, it can be obtained, for example, by a method comprising the following steps: impregnating a support containing titanium oxide in a solution containing ruthenium halide or a ruthenium nitrosyl complex, supporting the ruthenium halide or the ruthenium nitrosyl complex on the support, drying the supported material in which the ruthenium halide or the ruthenium nitrosyl complex is supported on the support, and calcining the dried material.

[0161] When producing catalyst I, as solutions containing supported components, solution A containing a first supported component or a first supported component raw material capable of forming the first supported component (also referred to as a first component raw material) and solution B containing a second supported component or a second supported component raw material capable of forming the second supported component (also referred to as a second component raw material) can be used. Alternatively, a mixed solution of solution A and solution B can be used.

[0162] When producing Catalyst II, Solution A can be used as the solution containing the supported component. It is also preferable to use Solution A and Solution B in combination, and it is also preferable to use a mixed solution of Solution A and Solution B.

[0163] A preferred method for producing Catalyst II will be specifically described below. However, Catalyst I can also be produced by using a carrier raw material mixture that does not contain silica in the step of obtaining a carrier described below.

[0164] A preferred method for producing Catalyst II includes the following steps.

[0165] In a preferred production method, after performing step 1, either step 2 or step 3 may be performed first. Alternatively, step 2A described below may be performed instead of step 2 or step 3.

[0166] Step 1: a step of calcining a carrier precursor to obtain a carrier, wherein the carrier precursor is obtained by extruding a carrier raw material mixture containing titanium oxide, silicon oxide, and water;

[0167] Step 2: a step of supporting the first component raw material containing a ruthenium compound on the support obtained in step 1 or the support on which the second component raw material was supported in step 3;

[0168] Step 3: a step of supporting a second component raw material containing at least one selected from an antimony compound, a cerium compound, a zirconium compound, and a silicon compound on the support obtained in Step 1 or the support on which the first component raw material was supported in Step 2;

[0169] Step 4: a step of calcining the catalyst precursor in which the first component raw material and the second component raw material are supported on the carrier obtained in step 1;

[0170] Step 2A: A step of supporting the support obtained in Step 1 with a first component raw material containing a ruthenium compound and a second component raw material containing at least one selected from an antimony compound, a cerium compound, a zirconium compound, and a silicon compound.

[0171] (Process 1)

[0172] The titanium oxide used in step 1 is not particularly limited, and as described above, titanium oxide produced by various production methods and commercially available products can be used.

[0173] The silicon oxide used in step 1 is not particularly limited. Silicon oxides produced by various methods and commercial products can be used. However, from the perspective of facilitating the production of the carrier, it is preferably used in the form of an aqueous dispersion, and colloidal silica is more preferably used. The particle size of the silicon oxide in the colloidal silica is not particularly limited. From the perspective of increasing the number of silicon oxide particles, it is preferably 5 to 45 nm, and more preferably 5 to 22 nm. The particle size of silicon oxide is set to the average particle size measured by the above method. Examples of commercially available colloidal silica include those used in the examples described below. Known organic binders can also be used in step 1.

[0174] In step 1, titanium oxide, silicon oxide, and water are mixed to prepare a carrier raw material mixture. The form of the carrier raw material mixture is not particularly limited and may be a liquid mixture such as a solution or slurry or a powder mixture, but is preferably a clay mixture such as clay.

[0175] The mixing ratio of titanium oxide, silicon oxide, and water is not particularly limited and can be appropriately set. The mixing ratio of titanium oxide to silicon oxide is preferably set to a ratio that provides the aforementioned content of silicon oxide in the support. The mixing ratio of water is not particularly limited and can be appropriately set. It is preferably set to a ratio that provides a clay-like mixture of the support raw materials. Water may be mixed separately from titanium oxide and silicon oxide, or water in colloidal silica used as silicon oxide may be utilized.

[0176] Titanium oxide, silicon oxide, and water can be mixed using a conventional mixing device or kneading device. The mixing conditions are not particularly limited, but for example, the mixing temperature can be 5 to 40° C., and the mixing time can be 1 to 30 minutes.

[0177] Next, in step 1, the prepared carrier raw material mixture is extruded to obtain a carrier precursor.

[0178] The shape of the support precursor is not particularly limited and can be formed into an appropriate shape, but is preferably formed into the above-mentioned honeycomb structure.

[0179] The carrier raw material mixture can be extruded using a conventional extruder, such as a vacuum kneading extruder or a hydraulic extruder. In particular, when producing a catalyst having a honeycomb structure, a vacuum kneading extruder is preferably used. Extrusion conditions are not particularly limited; for example, the kneading or extrusion temperature can be set to 5 to 40°C.

[0180] In this way, a carrier precursor can be obtained, and the shaped body can be dried as needed to prepare the carrier precursor.

[0181] In step 1, the support precursor is then fired to obtain a support.

[0182] The carrier precursor can be fired by conventional methods, using various heating machines. The firing conditions used for firing titanium oxide or silicon oxide can be applied without particular limitation. For example, the firing temperature can be set to 250°C or higher, preferably 400 to 900°C, and the firing time can be set to 2 to 120 hours.

[0183] (Process 2)

[0184] In step 2, the first component raw material containing the ruthenium compound is supported on a carrier.

[0185] The carrier used in this step differs depending on the order of performing Step 2 and Step 3. Specifically, when Step 2 is performed before Step 3, or when Step 2 is performed simultaneously with Step 3 (Step 2A), the carrier obtained in Step 1 (unsupported carrier) is used. On the other hand, when Step 2 is performed after Step 3, the carrier supported by the second component raw material in Step 3 is used.

[0186] The first component raw material used in step 2 contains a ruthenium compound. The ruthenium compound may be any compound that becomes the first supported component, such as ruthenium or a ruthenium compound, in the produced catalyst. It may be the first supported component itself or a precursor compound for the first supported component. Examples of the ruthenium compound used in step 2 include various known compounds, such as the aforementioned first supported component and precursor compounds of the first supported component, such as Ru(NO₃)₃, RuCl₃, RuCl₃ hydrate, Na₂RuO₄, K₂RuO₄, and Ru(NO)(NO₃)₃.

[0187] The first component raw material is typically used in the form of an aqueous solution. The content (concentration) of the first component raw material in this case is not particularly limited, but is preferably set within the range that satisfies the aforementioned content of ruthenium in the catalyst. For example, based on ruthenium, it is more preferably 1 to 40% by mass, and even more preferably 2 to 10% by mass. The aqueous solution used in step 2 may contain components other than the first supported component and the second supported component. Examples of such components include the aforementioned third supported component and an organic solvent such as an alcohol for achieving a good fusion between the aqueous solution and the support. In addition to aqueous solutions, solutions containing organic solvents such as alcohols may also be used.

[0188] In step 2, the carrier is brought into contact with the first component raw material, so that the first component raw material is supported on the carrier.

[0189] The contact method and conditions are not particularly limited and can be set appropriately. As a contact method, various methods for loading various components onto a carrier can be used as a catalyst production method. Examples include immersing the carrier in the aforementioned aqueous solution, spraying or applying the aqueous solution to the carrier, and the like. The amount of the aqueous solution used is not particularly limited, but is preferably set within the range that satisfies the aforementioned ruthenium content in the catalyst. For example, 0.1 to 10 mL is more preferred, and 0.2 to 2 mL is even more preferred, per gram of the carrier. Examples of contact conditions include contact at 5 to 40°C (preferably 10 to 30°C) for 1 to 300 minutes (preferably 5 to 180 minutes).

[0190] In step 2, the support impregnated with the first component raw material can be dried by a conventional method.

[0191] In this manner, the first component raw material can be supported or adsorbed on the carrier containing titanium oxide and silicon oxide.

[0192] (Process 3)

[0193] In step 3, a second component raw material containing at least one selected from antimony compounds, cerium compounds, zirconium compounds, and silicon compounds is supported on a carrier.

[0194] The carrier used in this step differs depending on the order in which Steps 2 and 3 are performed. Specifically, when Step 3 is performed before Step 2, or when Step 2 is performed simultaneously with Step 3 (Step 2A), the carrier obtained in Step 1 (unsupported carrier) is used. On the other hand, when Step 3 is performed after Step 2, the carrier supporting the first component raw material obtained in Step 2 is used.

[0195] The second component raw material used in step 3 includes an antimony compound, a cerium compound, a zirconium compound, or a silicon compound. These compounds can be any compound that becomes the second supported component, such as the antimony compound, in the produced catalyst. They can be the second supported component itself or a precursor compound for the second supported component. Examples of the compounds used in step 3 include various well-known compounds, such as the aforementioned second supported component and precursor compounds of the second supported component, such as SbCl₃, Ce(NO₃)₃·6H₂O, ZrO(NO₃)₂·2H₂O, and Si(OC₂H₅)₄.

[0196] The second component raw material is typically used in the form of an aqueous solution. The content (concentration) of the second component raw material in this case is not particularly limited, but is preferably set within the range that satisfies the aforementioned content of the second component raw material (element) in the catalyst. For example, based on the element, it is more preferably 0.01 to 20% by mass, and even more preferably 1 to 15% by mass. The aqueous solution used in step 3 may contain components other than the first supported component and the second supported component. Examples of such components include the aforementioned third supported component and the aforementioned organic solvent. In addition to aqueous solutions, solutions containing organic solvents such as alcohols may also be used.

[0197] In step 3, the support is brought into contact with the second component raw material, and the second component raw material is supported on the support.

[0198] The contact method and conditions are not particularly limited and are the same as those described in Step 2 above. In particular, the amount of the aqueous solution containing the second component raw material used is not particularly limited, but is preferably set within the range satisfying the aforementioned content of the second component raw material (element) in the catalyst. For example, the amount is more preferably 0.1 to 10 mL, and even more preferably 0.2 to 2 mL, per 1 g of the support.

[0199] In step 3, the support impregnated with the second component raw material can be dried by a conventional method.

[0200] In this manner, the second component raw material can be supported or adsorbed on the carrier containing titanium oxide and silicon oxide.

[0201] (Process 2A)

[0202] In a preferred method for producing Catalyst II, Step 2 and Step 3 may be performed simultaneously. In this case, Step 2A is performed instead of Step 2 and Step 3 to support the support obtained in Step 1.

[0203] The first component raw material and the second component raw material used in step 2A are the same as those described in steps 2 and 3.

[0204] The first and second raw materials are typically used in the form of aqueous solutions. The content (concentration) of the first and second raw materials is not particularly limited, as described in Steps 2 and 3. The aqueous solution used in Step 2A may contain components other than the first and second supported components. Examples of such components include the third supported component and the organic solvent described above. In addition to aqueous solutions, solutions containing organic solvents such as alcohols may also be used.

[0205] In step 2A, the support is contacted with the first and second component raw materials to support the support. The contact method and conditions are not particularly limited and are the same as those described in step 2 above. In step 2A, the support impregnated with the first and second component raw materials can be dried by conventional methods.

[0206] In this manner, the first component raw material and the second component raw material can be supported or adsorbed on the carrier containing titanium oxide and silicon oxide.

[0207] (Process 4)

[0208] In step 4, the catalyst precursor obtained in steps 2 and 3, or step 2A, in which the first component raw material and the second component raw material are supported on a carrier, is calcined.

[0209] The catalyst precursor can be calcined by conventional methods, using various heating machines. The calcination conditions are not particularly limited, and depending on the component being supported, suitable calcination conditions for the component can be applied without particular limitation. For example, the calcination temperature can be 100 to 600°C, preferably 200 to 400°C, and the calcination time can be 1 to 30 hours, preferably 1 to 10 hours.

[0210] (Other processes)

[0211] In the preferred production method of Catalyst II, steps other than Steps 1 to 4 described above may be performed. For example, in Steps 2, 3, and 2A, steps such as drying the support after contact with the aqueous solution, crushing or pulverizing the catalyst obtained in Step 4, and adjusting the shape or size of the catalyst obtained in Step 4 (e.g., classifying the crushed or pulverized catalyst) may be included.

[0212] The production method of the present invention comprising the above steps can produce a nitrous oxide decomposition catalyst suitable for use in the decomposition method of the present invention in a simple process. Specifically, by carrying out steps 1 to 4 above, a catalyst II (preferably a preferred embodiment) can be produced, wherein a first supported component and a second supported component are supported or adsorbed on a support composed of titanium oxide and silicon oxide.

[0213] It should be noted that, if the above-mentioned step 3 or step 2A is not performed, a catalyst II in which the first supported component is supported or adsorbed on a carrier composed of titanium oxide and silicon oxide can be produced.

[0214] In the above step 1, if the support raw material mixture is prepared without mixing silica with titanium oxide, it is possible to produce a catalyst I in which the first supported component and the second supported component are supported or adsorbed on a support composed of titanium oxide.

[0215] (Formation of Carrier Coat)

[0216] In the preferred embodiment in which the catalyst is disposed on a substrate having a honeycomb structure as a carrier coating, the catalyst can be manufactured by crushing, pulverizing, etc. the catalyst produced by the above method into powder, and then preferably disposing it as a carrier coating on a substrate having a honeycomb structure. The carrier coating of the catalyst can be applied and bonded to the surface of the substrate by any method known in the art. For example, the carrier coating is formed by applying a slurry containing the catalyst to the substrate using a method such as spraying or dipping and drying it. The catalyst is prepared in a liquid such as water or alcohol so as to have a specific solid content (for example, about 30 to about 90% by mass). It should be noted that the catalyst used in the preparation of the slurry can be a catalyst obtained by crushing, pulverizing, etc. the catalyst produced by the above method.

[0217] [Containing nitrous oxide gas]

[0218] The decomposition method of the present invention uses a nitrous oxide-containing gas comprising nitrous oxide, water vapor and oxygen.

[0219] The nitrous oxide-containing gas is a gas containing nitrous oxide, water vapor (water) and oxygen. The nitrous oxide-containing gas may contain one or more gases other than these three gases of nitrous oxide, water vapor and oxygen. Examples of such gases include ammonia, nitrogen, carbon dioxide, nitric oxide, nitrogen dioxide, various gases such as inert gases (helium, argon) as diluent gases, and reducing gases. The nitrous oxide-containing gas may contain a liquid. In the decomposition method of the present invention, the nitrous oxide-containing gas may be a gas at least during contact with the above-mentioned catalyst (under the reaction conditions). Before contact, it may be a liquid or a mixture of a gas and a liquid.

[0220] The content (concentration) and content ratio of each component in the nitrous oxide-containing gas are not particularly limited and can be appropriately set. Except for components with special effects, it is usually efficient to use it directly relative to the value unique to the factory that discharges the nitrous oxide-containing gas. Therefore, for example, the molar concentration of nitrous oxide in the nitrous oxide-containing gas is usually preferably 0.002 to 10 mol%. The molar concentration of water vapor is usually preferably 0.1 to 10 mol%. The molar concentration of oxygen in the nitrous oxide-containing gas is preferably 0.1 to 21 mol%. It should be noted that the nitrous oxide-containing gas can also be obtained by mixing multiple gases containing one or more of nitrous oxide, water vapor or oxygen-containing gas. As the oxygen-containing gas, air can be mentioned.

[0221] From the perspective of further improving the decomposition rate of nitrous oxide, the nitrous oxide-containing gas may also contain ammonia. From the perspective of the decomposition rate of nitrous oxide, the molar concentration of ammonia in the nitrous oxide-containing gas at this time is preferably 0.0002 mol% or more, preferably 1 mol% or less. The molar concentration of ammonia is more preferably 0.0002 to 0.5 mol%, and further preferably 0.0002 to 0.2 mol%.

[0222] The ratio of ammonia to water vapor in the nitrous oxide-containing gas (ammonia / water vapor) is not particularly limited and can be appropriately set. From the perspective of the nitrous oxide decomposition rate, it is preferably 0.0010 or greater as a molar ratio. It is more preferably 0.0010 to 0.050 as a molar ratio. From the perspective of suppressing or avoiding problems with residual ammonia (emission to the atmosphere, removal), it is more preferably 0.0010 to 0.030, and even more preferably 0.0010 to 0.010. Furthermore, the ratio of ammonia to nitrous oxide in the nitrous oxide-containing gas (ammonia / nitrous oxide) is not particularly limited and can be appropriately set. It is preferably 0.005 to 10 as a molar ratio. Furthermore, within the above range, the oxygen content in the nitrous oxide-containing gas is preferably 0.01 to 10,000 times the molar content of ammonia.

[0223] In the decomposition method of the present invention, which can suppress the decrease in the decomposition rate for a long time, the nitrous oxide-containing gas does not need to contain a reducing gas that increases the decomposition rate of nitrous oxide. In the present invention, the nitrous oxide-containing gas does not contain a reducing gas, and includes an embodiment in which the nitrous oxide-containing gas contains a reducing gas at a molar ratio of less than 0.005 relative to the nitrous oxide, in addition to an embodiment in which the content of the reducing gas is 0 mol%.

[0224] On the other hand, in order to further improve the decomposition rate of nitrous oxide, the nitrous oxide-containing gas may also contain a reducing gas. In addition, similarly, from the aspect of further improving the decomposition rate of nitrous oxide, the saturated hydrocarbon gas contained in the nitrous oxide-containing gas or the saturated hydrocarbon gas as a raw material for reacting with the oxygen produced in the reactor to produce reducing gases such as carbon monoxide gas may also be contained. With regard to the decomposition rate of nitrous oxide, it is preferred to make the nitrous oxide-containing gas contain a reducing gas. As the reducing gas, any reducing gas other than ammonia may be used, and the reducing gas used in the conventional catalytic reduction method may be used without particular limitation. For example, gases of alcohol compounds such as unsaturated hydrocarbon gases such as ethylene, propylene, α-butene, β-butene, carbon monoxide gas, hydrogen, and methanol, ethanol, propanol, butanol, etc. may be enumerated. Among them, at least one of the carbon monoxide gas, unsaturated hydrocarbon gas, and hydrogen is preferred. In addition, as the saturated hydrocarbon gas that becomes the raw material for producing reducing gases such as carbon monoxide gas, methane, ethane, propane, n-butane, etc. may be enumerated. Preferred saturated hydrocarbon gases include ethane, propane, and n-butane. In order to contain the saturated hydrocarbon gas, for example, a mixture such as natural gas, liquefied natural gas, or liquefied petroleum gas can be used.

[0225] The content of the reducing gas or saturated hydrocarbon gas in the nitrous oxide-containing gas is not particularly limited and can be appropriately set. For example, the molar concentration of the reducing gas or saturated hydrocarbon gas in the nitrous oxide-containing gas is 0.001 to 1 mol%. The molar ratio of the reducing gas or saturated hydrocarbon gas in the nitrous oxide-containing gas to water vapor [reducing gas or saturated hydrocarbon gas / water vapor] is preferably 0.0003 to 0.03. In addition, the content ratio of the reducing gas or saturated hydrocarbon gas contained in the nitrous oxide-containing gas to nitrous oxide [reducing gas or saturated hydrocarbon gas / nitrous oxide] is preferably 0.01 to 100 in terms of molar ratio.

[0226] In the present invention, the nitrous oxide-containing gas can be prepared by appropriately mixing nitrous oxide, water vapor, oxygen, and ammonia, the above-mentioned gases other than these. In addition, various waste gases discharged from chemical manufacturing equipment, as well as waste gases discharged from automobiles, power plants using ammonia fuel, and ships, can also be used. For example, the gases discharged from chemical manufacturing equipment such as nitric acid manufacturing plants, ε-caprolactam manufacturing plants, and adipic acid manufacturing plants, in addition to nitrous oxide, mostly also contain water vapor, oxygen, and ammonia, and can be effectively used in the decomposition method of the present invention. In particular, when the waste gas meets the content, content ratio, etc. within the above-mentioned range, it can be directly applied to the decomposition method of the present invention without adjusting the content, etc., which is preferred from this point of view.

[0227] [Contact process]

[0228] The decomposition method of the present invention includes a step of bringing the above-mentioned catalyst into contact with the above-mentioned nitrous oxide-containing gas (contact step).

[0229] The contact process is the process of contacting a catalyst with a gas containing nitrous oxide, and the contact process in the decomposition method of known nitrous oxide can be applied. As the contact process in the decomposition method of known nitrous oxide, the method (process) of putting down in writing in the patent documentation 1, that a catalyst is contacted with nitrous oxide under the coexistence of a reducing gas can be enumerated. In addition, both can be contacted by the process of circulating in the reaction tube that is filled with nitrous oxide-containing gas. The method of contacting a gas containing nitrous oxide with a catalyst can be batch-type, or can be a continuous type, and from the aspect of reaction efficiency, further from the aspect of being able to effectively utilize the effect of the present invention that can maintain catalytic activity for a long time, a preferred continuous type. As a continuous type, for example, a fixed bed form, a fluidized bed form can be enumerated.

[0230] In the contact step, as the dinitrogen monoxide in the dinitrogen monoxide-containing gas contacts the catalyst, a decomposition reaction of dinitrogen monoxide represented by the following formula occurs even in the presence of water vapor, and the dinitrogen monoxide is efficiently decomposed into nitrogen molecules and oxygen molecules.

[0231] Decomposition reaction of nitrous oxide: N2O→N2+1 / 2O2

[0232] When nitrous oxide-containing gas contains ammonia, ammonia further promotes the decomposition reaction of nitrous oxide. The details of its mechanism of action are not yet clear, but it is considered as described below. For example, it is speculated that in the presence of a catalyst that shows a reducing action as a catalyst loaded with ruthenium, ammonia reacts with nitrous oxide on the catalyst surface, thereby nitrous oxide can be decomposed into nitrogen molecules and water molecules, thereby further promoting the decomposition reaction of nitrous oxide. On the other hand, it is speculated that in the presence of a catalyst that does not show a reducing action as a catalyst loaded with ruthenium oxide, by reacting with the oxygen atoms remaining in the catalyst surface and removing the oxygen atoms from the catalyst surface, catalytic activity is continued (inactivation of the catalyst is suppressed), and the above-mentioned decomposition reaction can be promoted.

[0233] When a known process is applied as the contact process, the contact method and contact conditions can be appropriately adopted from those that can be adopted in each process, and examples thereof include the following conditions.

[0234] The contact temperature (reaction temperature) can be appropriately determined, but is preferably 500°C or lower from the viewpoint of catalytic activity degradation and preferably 100°C or higher from the viewpoint of reaction rate. The contact temperature is preferably 200-450°C, more preferably 250-400°C.

[0235] The supply rate of the nitrous oxide-containing gas relative to the mass of the catalyst in the continuous contact method is not particularly limited and can be appropriately determined. For example, as a flow rate relative to 1 g of the catalyst at 0°C and 0.1013 MPa (absolute), it is preferably 10 to 10,000 cm 3 / min, more preferably 50 to 5000 cm 3 / minute.

[0236] The contact time is appropriately determined according to the nitrous oxide concentration in the nitrous oxide-containing gas, the supply rate, the contact temperature, etc. In the decomposition method of the present invention, since the catalytic activity can be maintained for a long time, the contact time can be set to be longer, for example, 0.3 seconds or more.

[0237] The reaction pressure varies depending on the contact temperature, the supply rate of the nitrous oxide-containing gas, the pressure of the external air around the reactor, etc., but is preferably higher than the pressure of the external air, preferably 0.08 to 1 MPa (absolute) in absolute pressure, and more preferably 0.09 to 0.7 MPa (absolute) in absolute pressure.

[0238] [Other processes]

[0239] The decomposition method of the present invention may include steps other than the contact step, for example, a step of adjusting the component content of the nitrous oxide-containing gas, a step of introducing ammonia gas or a reducing gas into the nitrous oxide-containing gas, and the like.

[0240] The decomposition method of the present invention can decompose nitrous oxide over a long period of time while maintaining the decomposition rate of nitrous oxide, and can decompose nitrous oxide efficiently (at a high decomposition rate) over a long period of time. In particular, in a continuous process that effectively utilizes the effect of the present invention, namely, the ability to maintain catalytic activity over a long period of time, the simple process of passing the nitrous oxide-containing gas through the catalyst enables efficient and long-term decomposition of nitrous oxide.

[0241] The decomposition method of the present invention can be used in a variety of fields and applications to decompose and remove nitrous oxide, such as in chemical manufacturing facilities, automobiles, ammonia-fueled power plants, and ship exhaust gas treatment. In particular, it is suitable for use in chemical manufacturing facilities such as nitric acid manufacturers, ε-caprolactam manufacturers, and adipic acid manufacturers, which emit nitrous oxide-containing gas containing nitrous oxide, water vapor, and oxygen.

[0242] When the decomposition method of the present invention is applied to existing manufacturing equipment, the location of the apparatus performing the decomposition method is not particularly limited. Typically, the apparatus is installed at the final stage of the exhaust gas flow direction, such as the front end of the exhaust tower. Specifically, in nitric acid manufacturing equipment, the apparatus is installed at the rear end of the denitration reactor. This allows the apparatus performing the decomposition method of the present invention to be easily integrated into existing manufacturing equipment, effectively utilizing existing manufacturing equipment.

[0243] [Example]

[0244] Hereinafter, examples of the present invention will be described, but the present invention is not limited to these examples.

[0245] [Example 1]

[0246] Nitrous oxide decomposition catalysts corresponding to Catalyst I were produced as follows. These catalysts were subjected to a forced deterioration treatment and then used in a nitrous oxide decomposition reaction to evaluate the nitrous oxide decomposition rate.

[0247] <Calculation of the Decomposition Rate of Nitrous Oxide Concentration>

[0248] The decomposition rate of nitrous oxide concentration was calculated using a gas chromatograph (GC-2014 (detector: TCD, column: SHINCARBON-ST50 / 80 4m, manufactured by Shimadzu Corporation) to measure the content of nitrous oxide in the nitrous oxide-containing gas (used for decomposition of nitrous oxide). B and the content of nitrous oxide C in the reaction outlet gas (reaction gas) AThe analysis (measurement) is performed, and based on the analyzed nitrous oxide concentration, the decomposition rate of the nitrous oxide concentration (sometimes simply referred to as "nitrous oxide decomposition rate") is calculated using the following formula.

[0249] Decomposition rate of nitrous oxide concentration X (%) = [(C B -C A ) / C B ]×100

[0250] <Experimental Example 1>

[0251] (Catalyst 1: Preparation of ZrO2-RuO2 / TiO2 Catalyst)

[0252] 100 parts by mass of titanium oxide powder (manufactured by Showa Denko K.K.) and 2 parts by mass of an organic binder (YB-152A (trade name) manufactured by Yuken Industry Co., Ltd.) were mixed. Subsequently, 29 parts by mass of pure water and 12.5 parts by mass of titanium oxide sol (CSB (trade name) manufactured by Sakai Chemical Industry Co., Ltd., titanium oxide sol containing 40% by mass, 100% anatase crystal) were added and kneaded. The mixture was extruded into strips with a diameter of 3.0 mm, dried at 60°C for 2 hours, and then crushed to a length of approximately 3-5 mm. The resulting carrier precursor 1 was heated from room temperature to 600°C in air over 1.7 hours and then calcined at 600°C for 3 hours, yielding a white titanium oxide carrier 1 (rutile TiO₂ ratio of 90% or greater) (Step 1: Silica was not used in the preparation of the carrier raw material mixture).

[0253] 0.2 g of ruthenium chloride hydrate (manufactured by FURUYA METAL, RuCl₃·nH₂O, Ru content 40%) and 0.1 g of zirconyl nitrate dihydrate (manufactured by KISHIDA CHEMICAL, ZrO(NO₃)₂·2H₂O, Zr content 34%) were dissolved in 2.3 g of ion-exchanged water. The resulting aqueous solution was impregnated into 10.0 g of titanium oxide support 1 at 25°C using the incipient wetness method. The support was then air-dried overnight at room temperature (25°C) in an air atmosphere to obtain catalyst precursor 1 supporting ruthenium chloride hydrate and zirconyl nitrate dihydrate (Step 2A).

[0254] The catalyst precursor 1 (10 g) was filled in a quartz glass tube (inner diameter 27 mm) equipped with a jacket for measuring the internal temperature, and then heated at 200 cm in a tubular electric furnace. 3Under a flow of air at 0°C, 0.1013 MPa (absolute) / minute, the furnace temperature was raised to 250°C and then held at the same temperature for 2 hours for firing. The temperature inside the quartz glass tube of the tubular electric furnace at 250°C was 300°C. This firing yielded a ZrO2-RuO2 / TiO2 catalyst containing 1.3% by mass of ruthenium oxide (1.0% by mass as ruthenium element) and 0.6% by mass of zirconium oxide (molar ratio of zirconium element content to ruthenium element content = 0.5) (Step 4). The resulting cylindrical pellets of ZrO2-RuO2 / TiO2 were pulverized and sieved into particles of 0.7 to 1.0 mm, yielding Catalyst 1.

[0255] (Forced degradation treatment)

[0256] 0.9 g (1.0 cm) of the obtained catalyst 1 was 3 ) was filled into a stainless steel reaction tube (8 mm inner diameter) equipped with a thermocouple for measuring the internal temperature. The reaction tube was placed in an electric furnace and flowed with 3.0 mol% oxygen, 0.7 mol% water vapor, and the balance nitrogen (flow rate: 435 cm) at atmospheric pressure (0.1 MPa (absolute)). 3 The temperature of the stainless steel reaction tube was raised to 340°C by a mixed gas (0°C, 0.1013 MPa (absolute) / min). The reaction tube was then maintained at the same temperature for 24 hours, thereby performing a forced degradation treatment at 340°C. This resulted in a forced degradation-treated catalyst 1.

[0257] (Decomposition reaction of nitrous oxide using catalyst 1 after forced degradation treatment)

[0258] The mixed gas flowing through the stainless steel reaction tube filled with the catalyst 1 after the forced degradation treatment was switched to 0.18 mol% of nitrous oxide, 3.0 mol% of oxygen, 0.7 mol% of water vapor, and the balance of nitrogen (flow rate: 435 cm 3 A mixed gas (0°C, 0.1013 MPa (absolute) / minute) was added to the stainless steel reaction tube, and the temperature was adjusted to 320°C. After maintaining the temperature at 320°C for 0.5 hours, the post-reaction gas emitted from the stainless steel reaction tube was collected into a gas sampling bag. The collected post-reaction gas was analyzed using a gas chromatograph as described above, and the decomposition rate of the nitrous oxide concentration (nitrous oxide decomposition rate) was calculated. The results are shown in Table 1.

[0259] <Experimental Example 2>

[0260] (Catalyst 2: Preparation of CeO2-RuO2 / TiO2 Catalyst)

[0261] A CeO₂-RuO₂ / TiO₂ catalyst containing 1.3 mass% of ruthenium oxide (1.0 mass% as ruthenium element) and 0.8 mass% of cerium oxide (molar ratio of cerium element content to ruthenium element content = 0.5) was obtained by the same procedure as in Experimental Example 1, except that the zirconyl nitrate in the aqueous solution used in Step 2A was replaced with 0.3 g of cerium nitrate hexahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., Ce(NO₃)₃·6H₂O, Ce content 32 mass%). The catalyst was crushed and sieved into particles of 0.7 to 1.0 mm to obtain Catalyst 2.

[0262] (Decomposition reaction of nitrous oxide using catalyst 2 after forced degradation treatment)

[0263] Using this catalyst 2, the same operation as in Experimental Example 1 was carried out to perform forced degradation treatment and decomposition reaction of dinitrogen monoxide, and the decomposition rate of dinitrogen monoxide concentration after the forced degradation treatment was calculated. The results are shown in Table 1.

[0264] <Experimental Example 3>

[0265] (Catalyst 3: Preparation of Sb2O3-RuO2 / TiO2 Catalyst 3)

[0266] A Sb2O3-RuO2 / TiO2 catalyst containing 1.3% by mass of ruthenium oxide (1.0% by mass as ruthenium element) and 0.7% by mass of antimony trioxide (molar ratio of antimony element content to ruthenium element content = 0.5) was obtained by the same procedure as in Experimental Example 1, except that 0.1 g of antimony chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., SbCl3, Sb content 53% by mass) was used in place of zirconyl nitrate in the aqueous solution used in Step 2A. The catalyst was crushed into cylindrical pellets and sieved to obtain particles of 0.7 to 1.0 mm, thereby obtaining Catalyst 3.

[0267] (Decomposition reaction of nitrous oxide using catalyst 3 after forced degradation treatment)

[0268] Using this catalyst 3, the same operation as in Experimental Example 1 was carried out to perform forced degradation treatment and decomposition reaction of dinitrogen monoxide, and the decomposition rate of dinitrogen monoxide concentration after the forced degradation treatment was calculated. The results are shown in Table 1.

[0269] <Experimental Example 4>

[0270] (Catalyst 4: Preparation of SiO2-RuO2 / TiO2 Catalyst)

[0271] 60.0 g of the titanium oxide support 1 obtained in Experimental Example 1 was placed in a 200 mL eggplant flask. The flask was then placed in a rotary impregnation-drying apparatus. While the flask was tilted 60 degrees from vertical and rotated at 80 rpm, a solution prepared by dissolving 2.13 g of tetraethoxysilane (Wako Pure Chemical Industries, Ltd., Si(OC2H5)4) in 9.22 g of ethanol was added dropwise to the flask at 25°C over 20 minutes, thereby impregnating the titanium oxide support with the solution. Next, while the impregnated support 1 was rotated at 80 rpm to stir the support 1, the temperature within the flask was maintained at 30°C. A mixed gas of water vapor and nitrogen (water vapor concentration: 2.0 vol%) was continuously supplied to the flask at a flow rate of 277 mL / min (0°C, 0.1 MPa equivalent) for 4 hours and 20 minutes, thereby drying the impregnated support 1. 62.3 g of the obtained dried product was heated from room temperature to 300° C. over 1.2 hours under air flow and then calcined at the same temperature for 2 hours to obtain 60.6 g of a solid in which silica was supported on a titania support (silica-supported titania support) (Step 3).

[0272] 30.1 g of the obtained silica-supported titanium oxide support was added to a 200 mL eggplant-shaped flask, which was placed in a rotary impregnation-drying apparatus. At a temperature of 25°C, the eggplant-shaped flask was tilted 60 degrees from the vertical direction and rotated at 80 rpm. An aqueous solution prepared by dissolving 0.71 g of ruthenium chloride hydrate (manufactured by FURUYA METAL, RuCl3·nH2O, Ru content 40%) in 6.89 g of pure water was added dropwise to the eggplant-shaped flask over 30 minutes, thereby impregnating the flask with the aqueous solution to obtain 37.70 g of a ruthenium chloride support. Next, while the ruthenium chloride support was added to the eggplant-shaped flask and the ruthenium chloride support was stirred by rotating the eggplant-shaped flask at 80 rpm, the temperature in the eggplant-shaped flask was maintained at 35° C., and air was continuously supplied to the eggplant-shaped flask at a flow rate of 692 mL / min (0° C., 0.1 MPa conversion) for 3 hours and 40 minutes to allow the air to circulate, thereby drying the flask to obtain 32.21 g of catalyst precursor 4 (step 2).

[0273] 32.21 g of catalyst precursor 4 was placed in a sealed container and maintained at 20°C in a thermostatic bath for 120 hours. The mass of catalyst precursor 4 after the maintenance period was 32.21 g. The water content, based on the mass of the silica-supported titanium oxide support contained in catalyst precursor 4 after the maintenance period, remained unchanged compared to before the maintenance period, and the amount of water evaporated was 0 g. 21.48 g of catalyst precursor 4 after the maintenance period was heated from room temperature to 280°C over 1.2 hours under air circulation and then calcined at the same temperature for 2 hours. This yielded a SiO2-RuO2 / TiO2 catalyst containing 1.3 mass% ruthenium oxide (1.0 mass% as ruthenium element) and 0.8 mass% silica (molar ratio of silicon element content to ruthenium element content = 1.3) (Step 4). The obtained cylindrical pellet-shaped SiO2-RuO2 / TiO2 catalyst was crushed and sieved into particles of 0.7 to 1.0 mm, thereby obtaining Catalyst 4.

[0274] (Decomposition reaction of nitrous oxide using catalyst 4 after forced degradation treatment)

[0275] Using this catalyst 4, the same operation as in Experimental Example 1 was carried out to perform forced degradation treatment and decomposition reaction of dinitrogen monoxide, and the decomposition rate of dinitrogen monoxide concentration after the forced degradation treatment was calculated. The results are shown in Table 1.

[0276] Comparative Example 1

[0277] (Catalyst 5: Preparation of RuO2 / TiO2 Catalyst)

[0278] In step 2, a RuO2 / TiO2 catalyst containing 1.3% by mass of ruthenium oxide (1.0% by mass as ruthenium element) was obtained by the same procedure as in Experimental Example 1, except that an aqueous solution containing only 0.2 g of ruthenium chloride hydrate (manufactured by FURUYA METAL Co., Ltd., RuCl3·nH2O, Ru content 40%) was used to support the support 1 obtained in Experimental Example 1. The resulting cylindrical pellets of RuO2 / TiO2 catalyst were pulverized and sieved into particles of 0.7 to 1.0 mm, thereby obtaining Catalyst 5.

[0279] (Decomposition reaction of nitrous oxide using catalyst 5 after forced degradation treatment)

[0280] Using this catalyst 5, forced degradation treatment and nitrous oxide decomposition reaction were carried out in the same manner as in Experimental Example 1, and the decomposition rate of nitrous oxide concentration after the forced degradation treatment was calculated. The results are shown in Table 1.

[0281]

Table 1

[0282]

[0283] Experimental Examples 1 to 4 correspond to examples of the decomposition method of the present invention using Catalyst I.

[0284] The "molar ratio in the catalyst" in Table 1 represents the molar ratio of the content of the metal element (zirconium, cerium, antimony or silicon) contained in the second supported component to the content of the ruthenium element contained in the first supported component in the catalyst [content of the metal element (molar) / content of the ruthenium element (molar)].

[0285] <Experimental Example 5>

[0286] (Catalyst 6: Preparation of ZrO2-RuO2 / TiO2 Catalyst)

[0287] To 100 parts by mass of titanium oxide powder (manufactured by Showa Denko Ceramics Co., Ltd.) were added 12 parts by mass of an organic binder and 35 parts by mass of water, respectively, and the mixture was mixed and kneaded to produce a molded clay. Metolose (manufactured by Shin-Etsu Chemical Co., Ltd.) and UNILUBE (manufactured by NOF Corporation) were used as organic binders. The resulting molded clay was formed using a vacuum extruder to produce a honeycomb formed body (cubic shape, 20 mm in length, 20 mm in width, and 20 mm in height, with through-holes arranged in parallel in the vertical and horizontal directions, a volume fraction of 36%, a quadrilateral opening shape of the through-holes, a cell size of 1.4 mm, an inner wall thickness of 0.35 mm, an open porosity of 64%, and 100% rutile TiO2). The resulting honeycomb formed body was air-dried at room temperature for 2 days to produce a carrier precursor 2. The support precursor 2 was fired at 600° C. for 2 hours in an electric furnace to obtain a support 2 with a honeycomb structure (the honeycomb structure maintained the shape and size of the honeycomb formed body) (Step 1: However, silicon oxide was not used in the preparation of the support raw material mixture).

[0288] Next, Support 2 (7 g) was immersed in an aqueous solution (approximately 40 mL) containing 4.2 g of ruthenium chloride hydrate (Furuya Metal, RuCl₃·nH₂O, 40% Ru content) and 1.0 g of zirconium oxynitrate dihydrate (Kishida Chemical, ZrO(NO₃)₂·2H₂O, 34% Zr content) at 25°C. After 10 minutes, Support 2 was removed from the aqueous solution, and excess liquid was blown off with air. The resulting Support 2 was left on a laboratory bench at room temperature (approximately 20°C) and air-dried until no further weight loss occurred, yielding Catalyst Precursor 6 (Step 2A).

[0289] Catalyst precursor 6 was calcined at 290°C for 2 hours in an electric furnace to obtain a ZrO2-RuO2 / TiO2 catalyst containing 2.6% by mass of ruthenium oxide (2.0% by mass as ruthenium element) and 0.6% by mass of zirconium oxide (molar ratio of zirconium element content to ruthenium element content = 0.2) (Step 4). The resulting honeycomb-shaped ZrO2-RuO2 / TiO2 catalyst was pulverized and sieved into particles of 0.7 to 1.0 mm to obtain Catalyst 6.

[0290] (Decomposition reaction of nitrous oxide using catalyst 6 after forced degradation)

[0291] Using this catalyst 6, the same operation as in Experimental Example 1 was carried out to perform forced degradation treatment and decomposition reaction of dinitrogen monoxide, and the decomposition rate of dinitrogen monoxide concentration after the forced degradation treatment was calculated. The results are shown in Table 2.

[0292] <Experimental Example 6>

[0293] (Catalyst 7: Preparation of ZrO2-RuO2 / TiO2 Catalyst)

[0294] A ZrO₂-RuO₂ / TiO₂ catalyst containing 2.6 mass% of ruthenium oxide (2.0 mass% as ruthenium element) and 1.1 mass% of zirconium oxide (molar ratio of zirconium element content to ruthenium element content = 0.5) was obtained by the same procedure as in Experimental Example 5, except that the mass of zirconium oxynitrate dihydrate (manufactured by Kishida Chemical, ZrO(NO₃)₂·2H₂O, Zr content 34%) was changed to 2.1 g in the aqueous solution used in Step 2A. The catalyst was crushed and sieved into particles of 0.7 to 1.0 mm to obtain Catalyst 7.

[0295] (Decomposition reaction of nitrous oxide using catalyst 7 after forced degradation)

[0296] Using this catalyst 7, the same operation as in Experimental Example 1 was carried out to perform forced degradation treatment and decomposition reaction of dinitrogen monoxide, and the decomposition rate of dinitrogen monoxide concentration after the forced degradation treatment was calculated. The results are shown in Table 2.

[0297] <Experimental Example 7>

[0298] (Catalyst 8: Preparation of ZrO2-RuO2 / TiO2 Catalyst)

[0299] A ZrO₂-RuO₂ / TiO₂ catalyst containing 2.6 mass% of ruthenium oxide (2.0 mass% as ruthenium element) and 2.2 mass% of zirconium oxide (molar ratio of zirconium element content to ruthenium element content = 0.9) was obtained by the same procedure as in Experimental Example 5, except that the mass of zirconium oxynitrate dihydrate (manufactured by Kishida Chemical, ZrO(NO₃)₂·2H₂O, Zr content 34%) was changed to 4.5 g in the aqueous solution used in Step 2A. The catalyst was crushed and sieved into particles of 0.7 to 1.0 mm to obtain Catalyst 8.

[0300] (Decomposition reaction of nitrous oxide using catalyst 8 after forced degradation treatment)

[0301] Using this catalyst 8, the same operation as in Experimental Example 1 was carried out to perform forced degradation treatment and decomposition reaction of dinitrogen monoxide, and the decomposition rate of dinitrogen monoxide concentration after the forced degradation treatment was calculated. The results are shown in Table 2.

[0302] <Experimental Example 8>

[0303] (Catalyst 9: Preparation of ZrO2-RuO2 / TiO2 Catalyst)

[0304] A ZrO₂-RuO₂ / TiO₂ catalyst containing 2.6 mass% of ruthenium oxide (2.0 mass% as ruthenium element) and 3.3 mass% of zirconium oxide (molar ratio of zirconium element content to ruthenium element content = 1.4) was obtained by the same procedure as in Experimental Example 5, except that the mass of zirconium oxynitrate dihydrate (manufactured by Kishida Chemical, ZrO(NO₃)₂·2H₂O, Zr content 34%) was changed to 7.3 g in the aqueous solution used in Step 2A. The catalyst was crushed and sieved into particles of 0.7 to 1.0 mm to obtain Catalyst 9.

[0305] (Decomposition reaction of nitrous oxide using catalyst 9 after forced degradation treatment)

[0306] Using this catalyst 9, the same operation as in Experimental Example 1 was carried out to perform forced degradation treatment and decomposition reaction of dinitrogen monoxide, and the decomposition rate of dinitrogen monoxide concentration after the forced degradation treatment was calculated. The results are shown in Table 2.

[0307] <Experimental Example 9>

[0308] (Catalyst 10: Preparation of ZrO2-RuO2 / TiO2 Catalyst)

[0309] A ZrO₂—RuO₂ / TiO₂ catalyst containing 2.6 mass% of ruthenium oxide (2.0 mass% as ruthenium element) and 5.0 mass% of zirconium oxide (molar ratio of zirconium element content to ruthenium element content = 2.1) was obtained by the same procedure as in Experimental Example 5, except that the mass of zirconium oxynitrate dihydrate (manufactured by Kishida Chemical, ZrO(NO₃)₂·2H₂O, Zr content 34%) was changed to 8.3 g in the aqueous solution used in Step 2A. The catalyst was crushed and sieved into particles of 0.7 to 1.0 mm to obtain Catalyst 10.

[0310] (Decomposition Reaction of Nitrous Oxide Using Catalyst 10 After Forced Degradation Treatment)

[0311] Using this catalyst 10, the same operation as in Experimental Example 1 was carried out to perform forced degradation treatment and a decomposition reaction of dinitrogen monoxide, and the decomposition rate of dinitrogen monoxide concentration after the forced degradation treatment was calculated. The results are shown in Table 2.

[0312] Comparative Example 2

[0313] (Catalyst 11: Preparation of RuO2 / TiO2 Catalyst)

[0314] In step 2, the same procedures as in Experimental Example 5 were followed, except that an aqueous solution containing only 4.2 g of ruthenium chloride hydrate (manufactured by FURUYA METAL Co., Ltd., RuCl₃·nH₂O, 40% Ru content) was used to obtain a RuO₂ / TiO₂ catalyst containing 2.6% by mass of ruthenium oxide (2.0% by mass as ruthenium element). The resulting honeycomb-shaped RuO₂ / TiO₂ catalyst was pulverized and sieved into particles of 0.7 to 1.0 mm, thereby obtaining Catalyst 11.

[0315] (Decomposition reaction of nitrous oxide using catalyst 11 after forced degradation treatment)

[0316] Using this catalyst 11, the same operation as in Experimental Example 1 was carried out to perform forced degradation treatment and decomposition reaction of dinitrogen monoxide, and the decomposition rate of dinitrogen monoxide concentration after the forced degradation treatment was calculated. The results are shown in Table 2.

[0317]

Table 2

[0318]

[0319] Experimental Examples 5 to 9 correspond to examples of the decomposition method of the present invention using Catalyst I.

[0320] The “molar ratio in the catalyst” in Table 2 represents the molar ratio of the content of the metal element (zirconium element) contained in the second supported component to the content of the ruthenium element contained in the first supported component in the catalyst [content of the metal element (mole) / content of the ruthenium element (mole)].

[0321] <Experimental Example 10>

[0322] (Catalyst 12: Preparation of ZrO2-RuO2 / TiO2 Catalyst)

[0323] A ZrO₂-RuO₂ / TiO₂ catalyst containing 1.8 mass% of ruthenium oxide (1.4 mass% as ruthenium element) and 0.6 mass% of zirconium oxide (molar ratio of zirconium element content to ruthenium element content = 0.4) was obtained by the same procedure as in Experimental Example 5, except that the mass of ruthenium chloride hydrate (manufactured by FURUYA METAL Co., Ltd., RuCl₃·nH₂O, Ru content 40%) was changed to 2.9 g in the aqueous solution used in Step 2A. The catalyst was crushed and sieved into particles of 0.7 to 1.0 mm to obtain Catalyst 12.

[0324] (Decomposition reaction of nitrous oxide using catalyst 12 after forced degradation treatment)

[0325] Using this catalyst 12, the same operation as in Experimental Example 1 was carried out to perform forced degradation treatment and decomposition reaction of dinitrogen monoxide, and the decomposition rate of dinitrogen monoxide concentration after the forced degradation treatment was calculated. The results are shown in Table 3.

[0326] <Experimental Example 11>

[0327] (Catalyst 13: Preparation of ZrO2-RuO2 / TiO2 Catalyst)

[0328] The same procedures as in Experimental Example 5 were followed, except that the mass of ruthenium chloride hydrate (manufactured by FURUYA METAL Co., Ltd., RuCl₃·nH₂O, Ru content 40%) was changed to 6.3 g in the aqueous solution used in Step 2A. A ZrO₂-RuO₂ / TiO₂ catalyst containing 3.9 mass% of ruthenium oxide (3.0 mass% as ruthenium element) and 0.6 mass% of zirconium oxide (molar ratio of zirconium element content to ruthenium element content = 0.2) was obtained. The resulting honeycomb-shaped ZrO₂-RuO₂ / TiO₂ catalyst was pulverized and sieved into particles of 0.7 to 1.0 mm, thereby obtaining Catalyst 13.

[0329] (Decomposition reaction of nitrous oxide using catalyst 13 after forced degradation treatment)

[0330] Using this catalyst 13, the same operation as in Experimental Example 1 was carried out to perform forced degradation treatment and decomposition reaction of dinitrogen monoxide, and the decomposition rate of dinitrogen monoxide concentration after the forced degradation treatment was calculated. The results are shown in Table 3.

[0331] <Experimental Example 12>

[0332] (Catalyst 14: Preparation of ZrO2-RuO2 / TiO2 Catalyst)

[0333] The same procedures as in Experimental Example 5 were followed, except that the mass of ruthenium chloride hydrate (manufactured by FURUYA METAL Co., Ltd., RuCl₃·nH₂O, Ru content 40%) was changed to 11.4 g in the aqueous solution used in Step 2A. A ZrO₂-RuO₂ / TiO₂ catalyst containing 7.0 mass% of ruthenium oxide (5.3 mass% as ruthenium element) and 0.6 mass% of zirconium oxide (molar ratio of zirconium element content to ruthenium element content = 0.1) was obtained. The resulting honeycomb-shaped ZrO₂-RuO₂ / TiO₂ catalyst was pulverized and sieved into particles of 0.7 to 1.0 mm, thereby obtaining Catalyst 14.

[0334] (Decomposition reaction of nitrous oxide using catalyst 14 after forced degradation treatment)

[0335] Using this catalyst 14, the same operation as in Experimental Example 1 was carried out to perform forced degradation treatment and a decomposition reaction of dinitrogen monoxide, and the decomposition rate of dinitrogen monoxide concentration after the forced degradation treatment was calculated. The results are shown in Table 3.

[0336] Table 3 also shows the results of Experimental Example 1, Experimental Example 5, Comparative Example 1, and Comparative Example 2.

[0337]

Table 3

[0338]

[0339] Experimental Examples 10 to 12 correspond to examples of the decomposition method of the present invention using Catalyst I.

[0340] The “molar ratio in the catalyst” in Table 3 represents the molar ratio of the content of the metal element (zirconium element) contained in the second supported component to the content of the ruthenium element contained in the first supported component in the catalyst [content of the metal element (mole) / content of the ruthenium element (mole)].

[0341] [Example 2]

[0342] A nitrous oxide decomposition catalyst corresponding to Catalyst II was produced as follows. These catalysts were used in a nitrous oxide decomposition reaction, and the nitrous oxide decomposition rate was evaluated.

[0343] <Calculation of the Decomposition Rate of Nitrous Oxide Concentration>

[0344] The decomposition rate of nitrous oxide concentration was calculated by using a gas chromatograph (Varian Micro GC (detector: Micro TCD, column: CP-PoraPLOT Q 10m)) to measure the nitrous oxide content C in the nitrous oxide-containing gas (used for decomposition of nitrous oxide). B and the content of nitrous oxide C in the reaction outlet gas (reaction gas) A Analysis (measurement) was performed, and the decomposition rate of the nitrous oxide concentration (nitrous oxide decomposition rate) was calculated from the analyzed nitrous oxide concentration using the following formula.

[0345] Decomposition rate of nitrous oxide concentration (%) = [(C B -C A ) / C B ]×100

[0346] <Experimental Example 13>

[0347] (Catalyst 15: Preparation of RuO2 / SiO2-containing TiO2 Catalyst)

[0348] To 100 parts by mass of titanium oxide powder (manufactured by Showa Denko Ceramics Co., Ltd.) were added 12 parts by mass of an organic binder, 24.6 parts by mass of water, and 17.5 parts by mass of silica sol, respectively, and the mixture was mixed and kneaded to produce a molded clay. Metolose (manufactured by Shin-Etsu Chemical Co., Ltd.) and UNILUBE (manufactured by NOF Corporation) were used as the organic binders. Snowtex ST-CM (manufactured by Nissan Chemical Co., Ltd., particle size 22 nm, solid content 30% by mass) was used as the silica sol. The resulting molded clay was formed using a vacuum extruder to produce a honeycomb formed body (cubic shape, 20 mm in length, 20 mm in width, and 20 mm in height, with through-holes arranged in parallel in the vertical and horizontal directions, a volume fraction of 36%, a quadrilateral opening shape of the through-holes, a cell size of 1.4 mm, an inner wall thickness of 0.35 mm, and an open porosity of 64%). The resulting honeycomb formed body was air-dried at room temperature for two days to produce a carrier precursor 3 (the honeycomb structure retained the shape and dimensions of the honeycomb formed body). The support precursor 3 was fired at 600° C. for 2 hours in an electric furnace to obtain a support 3 (the SiO 2 content in the support was 5% by mass, and the honeycomb structure maintained the shape and size of the honeycomb formed body) (step 1).

[0349] Next, Support 3 (6 g) was immersed in approximately 50 mL of a ruthenium chloride aqueous solution prepared to a Ru content of 2.9 mass % at 25°C. After 10 minutes, Support 3 was removed from the aqueous solution, and excess liquid was blown off with air. The support was then allowed to stand at room temperature and air-dried until no further mass loss occurred, yielding Catalyst Precursor 15 (Step 2).

[0350] The catalyst precursor 15 was calcined at 300°C for 2 hours in an electric furnace to obtain a RuO2 / SiO2-containing TiO2 catalyst containing 1.3% by mass of ruthenium oxide (1.0% by mass as ruthenium element) (Step 4). The resulting honeycomb-shaped RuO2 / SiO2-containing TiO2 catalyst was pulverized in a magnetic mortar to obtain a powdered catalyst 15.

[0351] (Decomposition reaction of nitrous oxide using catalyst 15)

[0352] The decomposition reaction of dinitrogen monoxide was carried out using BELLCAT II (manufactured by Microtrac BEL). A reaction tube (inner diameter 8 mm) was filled with 0.1 g of catalyst 15. The reaction tube was placed in an electric furnace and heated at atmospheric pressure (0.1 MPa (absolute)) and 100 cm 3 The temperature was raised to 380°C under a helium flow rate of 0.1013 MPa (absolute) / min (0°C). Then, at the same pressure and temperature, the gas in contact with the catalyst 15 was switched from helium to a gas containing 0.1 mol% of nitrous oxide, 3.0 mol% of oxygen, and 0.5 mol% of water (flow rate: 100 cm 3 The nitrous oxide decomposition reaction was carried out at 0°C, 0.1013 MPa (absolute) / minute. The remainder of the nitrous oxide-containing gas was helium. The nitrous oxide decomposition reaction was carried out for 5 hours. After the 5-hour reaction, the reaction outlet gas (reacted gas) was analyzed as described above, and the nitrous oxide decomposition rate was calculated. The results are shown in Table 4.

[0353] <Experimental Example 14>

[0354] (Catalyst 16: Preparation of TiO2 Catalyst Containing RuO2 / SiO2)

[0355] In step 1, the same procedures as in Experimental Example 13 were followed, except that the amounts of water and silica sol mixed with the titanium oxide powder were changed to 13 parts by mass of water and 37 parts by mass of silica sol. A RuO2 / SiO2-containing TiO2 catalyst comprising Support 4 (the SiO2 content in the support was 10.0% by mass) and 1.3% by mass of ruthenium oxide (1.0% by mass as ruthenium element) was obtained. The resulting honeycomb-shaped RuO2 / SiO2-containing TiO2 catalyst was pulverized in a magnetic mortar to obtain a powdered Catalyst 16.

[0356] (Decomposition reaction of nitrous oxide using catalyst 16)

[0357] Using this catalyst 16, the same operation as in Experimental Example 13 was carried out to carry out a decomposition reaction of dinitrogen monoxide, and the decomposition rate of dinitrogen monoxide concentration was calculated. The results are shown in Table 4.

[0358] <Experimental Example 15>

[0359] (Catalyst 17: Preparation of RuO2 / SiO2-containing TiO2 Catalyst)

[0360] In step 1, the same procedures as in Experimental Example 13 were followed, except that the silica sol mixed with the titanium oxide powder was replaced with Snowtex ST-S (manufactured by Nissan Chemical Co., Ltd., particle size 9 nm, solid content 30% by mass). A RuO2 / SiO2-containing TiO2 catalyst comprising Support 5 (the SiO2 content in the support was 5.0% by mass) and 1.3% by mass of ruthenium oxide (1.0% by mass as ruthenium element) was obtained. The resulting honeycomb-shaped RuO2 / SiO2-containing TiO2 catalyst was pulverized in a magnetic mortar to obtain a powdered Catalyst 17.

[0361] (Decomposition reaction of nitrous oxide using catalyst 17)

[0362] Using this catalyst 17, the same operation as in Experimental Example 13 was carried out to carry out a decomposition reaction of dinitrogen monoxide, and the decomposition rate of dinitrogen monoxide concentration was calculated. The results are shown in Table 4.

[0363] <Experimental Example 16>

[0364] (Catalyst 18: Preparation of TiO2 Catalyst Containing RuO2 / SiO2)

[0365] In step 1, the same procedures as in Experimental Example 13 were followed, except that the silica sol mixed with the titanium oxide powder was replaced with Snowtex ST-30L (manufactured by Nissan Chemical Co., Ltd., particle size 45 nm, solid content 30% by mass). A RuO2 / SiO2-containing TiO2 catalyst comprising Support 6 (the SiO2 content in the support was 5.0% by mass) and 1.3% by mass of ruthenium oxide (1.0% by mass as ruthenium element) was obtained. The resulting honeycomb-shaped RuO2 / SiO2-containing TiO2 catalyst was pulverized in a magnetic mortar to obtain a powdered Catalyst 18.

[0366] (Decomposition reaction of nitrous oxide using catalyst 18)

[0367] Using this catalyst 18, the same operation as in Experimental Example 13 was carried out to carry out a decomposition reaction of dinitrogen monoxide, and the decomposition rate of dinitrogen monoxide concentration was calculated. The results are shown in Table 4.

[0368] Comparative Example 3

[0369] (Catalyst 19: Preparation of RuO2 / TiO2 Catalyst)

[0370] In step 2, the same procedures as in Experimental Example 13 were followed, except that the carrier 2 produced in Experimental Example 5 (the SiO content in the carrier was 0 mass%) was used to obtain a RuO / TiO catalyst containing 1.3 mass% of ruthenium oxide (1.0 mass% as ruthenium element). The resulting honeycomb-shaped RuO / TiO catalyst was pulverized in a magnetic mortar to obtain a powdered catalyst 19.

[0371] (Decomposition reaction of nitrous oxide using catalyst 19)

[0372] Using this catalyst 19, the same operation as in Experimental Example 13 was carried out to carry out a decomposition reaction of dinitrogen monoxide, and the decomposition rate of dinitrogen monoxide concentration was calculated. The results are shown in Table 4.

[0373]

Table 4

[0374]

[0375] Experimental Examples 13 to 16 correspond to examples of the decomposition method of the present invention using Catalyst II.

[0376] In Table 4, “particle size of silica sol” refers to the average particle size of silicon oxide in colloidal silica used as a raw material of silicon oxide, and this particle size is also maintained in the catalyst (support).

[0377] [Example 3]

[0378] The following operation was performed to produce a nitrous oxide decomposition catalyst equivalent to Catalyst II (preferred embodiment). The same operation as in Example 1 was followed, and the produced catalyst was subjected to a forced degradation treatment. The nitrous oxide decomposition reaction was then performed, and the nitrous oxide decomposition rate was evaluated. It should be noted that the decomposition rate of the nitrous oxide concentration was calculated in the same manner as in Example 1.

[0379] <Experimental Example 17>

[0380] The catalyst 6 produced in Experimental Example 5 was used, and the forced degradation treatment and nitrous oxide decomposition reaction were carried out in the same manner as in Experimental Example 5, except that the forced degradation treatment temperature was set to 380°C. The nitrous oxide concentration decomposition rate after the forced degradation treatment was calculated. The results are shown in Table 5.

[0381] <Experimental Example 18>

[0382] (Catalyst 20: Preparation of TiO2 Catalyst Containing ZrO2-RuO2 / SiO2)

[0383] At 25°C, support 3 (7 g) produced in Experimental Example 13 was immersed in an aqueous solution (approximately 40 mL) containing 4.2 g of ruthenium chloride hydrate (Furuyamel Corporation, RuCl₃·nH₂O, 40% Ru content) and 1.0 g of zirconium oxynitrate dihydrate (Kishida Chemical, ZrO(NO₃)₂·2H₂O, 34% Zr content). After 10 minutes, support 3 was removed from the aqueous solution, and excess liquid was blown off with air. The resulting support 3 was left on a laboratory bench at room temperature (approximately 20°C) and air-dried until no further weight loss occurred, yielding catalyst precursor 20 (Step 2A).

[0384] The resulting catalyst precursor 20 was calcined in an electric furnace at 290°C for 2 hours to obtain a ZrO2-RuO2 / SiO2-containing TiO2 catalyst containing 2.6% by mass of ruthenium oxide (2.0% by mass as ruthenium element) and 0.6% by mass of zirconium oxide (molar ratio of zirconium element content to ruthenium element content = 0.2) (Step 4). The resulting honeycomb-shaped ZrO2-RuO2 / SiO2-containing TiO2 catalyst was pulverized and sieved into particles of 0.7 to 1.0 mm, thereby obtaining Catalyst 20.

[0385] (Decomposition reaction of nitrous oxide using catalyst 20 after forced degradation treatment)

[0386] Using this catalyst 20, the same operation as in Experimental Example 17 was carried out to perform forced degradation treatment and decomposition reaction of dinitrogen monoxide, and the decomposition rate of dinitrogen monoxide concentration after the forced degradation treatment was calculated. The results are shown in Table 5.

[0387] Comparative Example 4

[0388] Using the catalyst 11 produced in Comparative Example 2, the same procedures as in Experimental Example 17 were followed to perform forced degradation and nitrous oxide decomposition reactions, and the decomposition rate of nitrous oxide concentration after the forced degradation was calculated.

[0389]

Table 5

[0390]

[0391] Experimental Examples 17 and 18 correspond to examples of the decomposition method of the present invention using Catalyst II (preferred embodiment).

[0392] The “molar ratio in the catalyst” in Table 5 represents the molar ratio of the content of the metal element (zirconium element) contained in the second supported component to the content of the ruthenium element contained in the first supported component in the catalyst [content of the metal element (mole) / content of the ruthenium element (mole)].

[0393] The results shown in Tables 1 to 5 clearly show that when Catalysts 5, 11, or 19 whose supports do not contain silica and do not support the second supported component are used, although nitrous oxide can be decomposed, the decomposition rate is low, and nitrous oxide cannot be decomposed efficiently for a long period of time (Comparative Examples 1 to 4).

[0394] In contrast, when using Catalyst I, which is formed by supporting a first supported component and a second supported component on a carrier, or Catalyst II, which is formed by supporting a first supported component and a second supported component on a carrier having titanium oxide and silicon oxide (preferred embodiment) (each experimental example of Example 1 and Example 3), nitrous oxide can be decomposed at a high decomposition rate even after forced degradation treatment. Furthermore, when using Catalyst II, which is formed by supporting a first supported component on a carrier having titanium oxide and silicon oxide (each experimental example of Example 2), a high decomposition rate is exhibited even after a 5-hour nitrous oxide decomposition reaction. These results indicate that the decomposition method of the present invention using Catalysts I and II can efficiently decompose nitrous oxide over a long period of time.

Claims

1. A method for decomposing nitrous oxide, comprising bringing a catalyst into contact with a nitrous oxide-containing gas comprising nitrous oxide, water vapor and oxygen, wherein the catalyst is composed of a carrier comprising titanium oxide and comprising a first component comprising at least one selected from ruthenium and a ruthenium compound and a second component comprising at least one selected from antimony, an antimony compound, cerium, a cerium compound, zirconium, a zirconium compound, silicon and a silicon compound.

2. The method for decomposing nitrous oxide according to claim 1, wherein: The second component is an oxide containing at least one selected from antimony oxide, cerium oxide, zirconium oxide, and silicon oxide.

3. The method for decomposing nitrous oxide according to claim 1, wherein: The second component contains at least one selected from zirconium and zirconium compounds.

4. The method for decomposing nitrous oxide according to claim 1, wherein: The content of the metal element contained in the second component of the catalyst is 0.1 to 5 in terms of molar ratio relative to the content of the ruthenium element contained in the first component.

5. The method for decomposing nitrous oxide according to claim 1, wherein: The first component contains ruthenium oxide.

6. The method for decomposing nitrous oxide according to claim 1, wherein: The content of ruthenium element in the catalyst is 0.5% by mass to 10% by mass.

7. The method for decomposing nitrous oxide according to claim 1, wherein: The catalyst is located on a substrate having a honeycomb structure.

8. A method for decomposing nitrous oxide, comprising the step of contacting a catalyst with a nitrous oxide-containing gas comprising nitrous oxide, water vapor and oxygen, wherein the catalyst is a first component containing at least one selected from ruthenium and a ruthenium compound supported on a carrier comprising titanium oxide and silicon oxide.

9. The method for decomposing nitrous oxide according to claim 8, wherein: The content of the silicon oxide in the carrier is 1% by mass to 20% by mass.

10. The method for decomposing nitrous oxide according to claim 8, wherein: The silicon oxide is derived from colloidal silicon dioxide with a particle size of 5 nm to 45 nm.

11. The method for decomposing nitrous oxide according to claim 8, wherein: The support further supports a second component including at least one selected from the group consisting of antimony, antimony compounds, cerium, cerium compounds, zirconium, zirconium compounds, silicon, and silicon compounds.

12. The method for decomposing nitrous oxide according to claim 11, wherein: The second component is an oxide containing at least one selected from the group consisting of antimony oxide, cerium oxide, zirconium oxide, and silicon oxide.

13. The method for decomposing nitrous oxide according to claim 8, wherein: The support further supports a second component containing at least one selected from zirconium and a zirconium compound.

14. The method for decomposing nitrous oxide according to claim 11, wherein: The content of the metal element contained in the second component of the catalyst is 0.1 to 5 in terms of molar ratio relative to the content of the ruthenium element contained in the first component.

15. The method for decomposing nitrous oxide according to claim 8, wherein: The first component contains ruthenium oxide.

16. The method for decomposing nitrous oxide according to claim 8, wherein: The content of ruthenium element in the catalyst is 0.5% by mass to 10% by mass.

17. The method for decomposing nitrous oxide according to claim 8, wherein: The catalyst is located on a substrate having a honeycomb structure.

18. A method for producing a nitrous oxide decomposition catalyst, comprising: A step of calcining a carrier precursor to obtain a carrier, wherein the carrier precursor is obtained by extruding a carrier raw material mixture containing titanium oxide, silicon oxide and water; a step of supporting a first component raw material containing a ruthenium compound on a carrier; a step of supporting a second component raw material containing at least one selected from antimony compounds, cerium compounds, zirconium compounds, and silicon compounds on a carrier; and A step of calcining a catalyst precursor in which the first component raw material and the second component raw material are supported on a carrier.

19. The method for producing a nitrous oxide decomposition catalyst according to claim 18, wherein: The second component raw material is a zirconium compound.

20. The method for producing a nitrous oxide decomposition catalyst according to claim 18, wherein: The silicon oxide is colloidal silicon dioxide with a particle size of 5nm to 45nm. 21 . The method for producing a nitrous oxide decomposition catalyst according to claim 18 , comprising the step of arranging the catalyst precursor on a substrate having a honeycomb structure after firing.

Images