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• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
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  • Y02C20/00—Capture or disposal of greenhouse gases
  • Y02C20/10—Capture or disposal of greenhouse gases of nitrous oxide (N2O)

Definitions

• the present invention relates to a method for decomposing nitrous oxide and a method for producing a nitrous oxide decomposition catalyst.
• nitrogen oxides (NOx) in exhaust gases are considered to be a problem, and their emissions are strictly regulated.
• the nitrogen oxides that are particularly subject to emission regulations are nitrogen dioxide (NO 2 ), which is harmful to the human body and is considered to be the cause of photochemical smog and acid rain, and various denitrification technologies have been studied and put into practical use to reduce emissions.
• NO 2 O nitrogen dioxide
• N 2 O nitrous oxide
• gases emitted from chemical manufacturing plants such as nitric acid manufacturing plants, ⁇ -caprolactam manufacturing plants, and adipic acid manufacturing plants have nitric oxide and nitrogen dioxide decomposed and removed by denitrification treatment, but by-product nitrous oxide is often not decomposed and removed and is emitted (released) into the atmosphere.
• Nitrous oxide is said to have a global warming effect about 300 times that of carbon dioxide. For this reason, in recent years, interest in reducing the emission of nitrous oxide into the atmosphere, along with carbon dioxide and methane, has been growing. With the rise in awareness of sustainable environments, it is expected that nitrous oxide will be subject to emission control gases in the near future, and therefore a technology is required to decompose and remove nitrous oxide in exhaust gases and suppress emissions into the atmosphere.
• Patent Document 1 describes a nitrous oxide decomposition method in which a gas containing nitrous oxide is catalytically decomposed in the presence of a reducing gas using a catalyst characterized by supporting at least one or more precious metals selected from ruthenium (Ru), rhodium (Rh), palladium (Pd), rhenium (Re), osmium (Os), iridium (Ir), and platinum (Pt).
• Ru ruthenium
• Rh palladium
• Pr palladium
• Re rhenium
• Os osmium
• Ir iridium
• platinum platinum
• the nitrous oxide decomposition method described in Patent Document 1 is said to be capable of decomposing nitrous oxide in a nitrous oxide-containing gas by catalytically decomposing the gas containing nitrous oxide in the presence of a reducing gas such as carbon monoxide, a hydrocarbon gas, a mineral oil-based hydrocarbon gas, or an alcohol.
• a reducing gas such as carbon monoxide, a hydrocarbon gas, a mineral oil-based hydrocarbon gas, or an alcohol.
• the catalyst used for decomposing nitrous oxide also gradually loses catalytic activity when used to decompose nitrous oxide.
• Patent Document 1 does not consider this point.
• the objective of the present invention is to provide a method for decomposing nitrous oxide that can decompose 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 that is suitable for use in this decomposition method.
• a catalyst comprising a titanium oxide-containing carrier, a first component containing at least one selected from the group consisting of ruthenium and ruthenium compounds, and a second component containing at least one selected from the group consisting of antimony, antimony compounds, cerium, cerium compounds, zirconium, zirconium compounds, silicon, and silicon compounds, and A method for decomposing nitrous oxide, comprising the step of contacting nitrous oxide with a nitrous oxide-containing gas comprising water vapor and oxygen.
• ⁇ 2> The method for decomposing nitrous oxide according to ⁇ 1>, 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.
• ⁇ 3> The method for decomposing nitrous oxide according to ⁇ 1>, wherein the second component contains at least one selected from the group consisting of zirconium and zirconium compounds.
• ⁇ 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 in the catalyst is 0.1 to 5 in terms of a molar ratio relative to the content of the ruthenium element contained in the first component.
• ⁇ 5> The method for decomposing nitrous oxide according to any one of ⁇ 1> to ⁇ 4>, wherein the first component contains ruthenium oxide.
• ⁇ 6> The method for decomposing nitrous oxide according to any one of ⁇ 1> to ⁇ 5>, wherein the catalyst has a ruthenium content of 0.5 to 10 mass%.
• ⁇ 7> The method for decomposing nitrous oxide according to any one of ⁇ 1> to ⁇ 6>, wherein the catalyst is on a substrate having a honeycomb structure.
• a catalyst comprising a support containing titanium oxide and silicon oxide and a first component containing at least one selected from the group consisting of ruthenium and ruthenium compounds supported on the support;
• a method for decomposing nitrous oxide comprising the step of contacting nitrous oxide with a nitrous oxide-containing gas comprising water vapor and oxygen.
• the method for decomposing nitrous oxide according to ⁇ 8> wherein the content of the silicon oxide in the carrier is 1 to 20 mass %.
• ⁇ 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 the group consisting of antimony, antimony compounds, cerium, cerium compounds, zirconium, zirconium compounds, silicon, and silicon compounds.
• 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 any one of ⁇ 8> to ⁇ 10>, wherein the support further supports a second component containing at least one selected from the group consisting of zirconium and zirconium compounds.
• ⁇ 14> The method for decomposing nitrous oxide according to any one of ⁇ 11> to ⁇ 13>, wherein the content of the metal element contained in the second component in the catalyst is 0.1 to 5 in terms of a molar ratio relative to the content of the ruthenium element contained in the first component.
• ⁇ 15> The method for decomposing nitrous oxide according to any one of ⁇ 8> to ⁇ 14>, wherein the first component contains ruthenium oxide.
• ⁇ 16> The method for decomposing nitrous oxide according to any one of ⁇ 8> to ⁇ 15>, wherein the catalyst has a ruthenium element content of 0.5 to 10 mass%.
• ⁇ 17> The method for decomposing nitrous oxide according to any one of ⁇ 8> to ⁇ 16>, wherein the catalyst is on a substrate having a honeycomb structure.
• a method for producing a nitrous oxide decomposition catalyst comprising: ⁇ 19> The method for producing a nitrous oxide decomposition catalyst according to ⁇ 18>, wherein the second component raw material is a zirconium compound.
• ⁇ 20> The method for producing a nitrous oxide decomposition catalyst according to ⁇ 18> or ⁇ 19>, wherein the silicon oxide is colloidal silica having a particle size of 5 to 45 nm.
• ⁇ 21> The method for producing the nitrous oxide decomposition catalyst according to any one of ⁇ 18> to ⁇ 20>, comprising a step of calcining the catalyst precursor and then disposing the catalyst precursor on a substrate having a honeycomb structure.
• the present invention provides a method for decomposing nitrous oxide that can decompose nitrous oxide over a long period of time while maintaining the decomposition rate of nitrous oxide, and a method for producing a nitrous oxide decomposition catalyst that is suitable for use in this decomposition method.
• a numerical range expressed using “ ⁇ ” means a range that includes the numerical values written before and after " ⁇ " as the lower and upper limits.
• the nitrous oxide decomposition method of the present invention includes a step of contacting a catalyst described below (sometimes referred to as the "nitrous oxide decomposition catalyst") with a nitrous oxide-containing gas containing nitrous oxide, water vapor, and oxygen (hereinafter sometimes referred to as the "contact step").
• a catalyst described below sometimes referred to as the "nitrous oxide decomposition catalyst”
• a nitrous oxide-containing gas containing nitrous oxide, water vapor, and oxygen hereinafter sometimes referred to as the "contact step”
• the nitrous oxide in the nitrous oxide-containing gas can be decomposed into nitrogen molecules (usually nitrogen gas) and oxygen molecules (usually oxygen gas) over a long period of time while maintaining a high decomposition rate.
• 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 a first component such as ruthenium exhibiting catalytic activity (a second component or silicon oxide) is present on the surface, near the surface, or within the pores of a support.
• a component other than a first component such as ruthenium exhibiting catalytic activity (a second component or silicon oxide) is present on the surface, near the surface, or within the pores of a support.
• a second component or silicon oxide a second component or silicon oxide
• Catalyst I A first component (hereinafter also referred to as the first supported component) containing at least one selected from the group consisting of ruthenium and ruthenium compounds on a support containing titanium oxide.
• Catalyst II A catalyst comprising the first supported component supported on a carrier containing titanium oxide and silicon oxide.
• the first supported component and the second supported component are preferably supported on a carrier containing titanium oxide and silicon oxide, and for convenience, this catalyst is referred to as "catalyst II (preferred embodiment).”
• silicon oxide is preferably present (dispersed) on or in the vicinity of the surface of the primary particles of titanium oxide.
• the supported component is a general term for components (such as elements and compounds) supported on a carrier constituting a catalyst, and examples thereof include a first supported component, a second supported component, and a third supported component, which will be described later.
• the term "catalyst in which a supported component is supported on a carrier” refers to a catalyst in which the supported component is attached to the surface and/or inside the pores of the carrier.
• the first supported component supported on the carrier contains at least one selected from the group consisting of ruthenium and ruthenium compounds, from the viewpoint of the balance between catalytic activity and cost.
• Catalyst I includes, as supported components supported on a carrier described below, a first supported component having a nitrous oxide decomposing ability (catalytic activity) and a second supported component different from the first supported component.
• the supported components supported by catalyst I may include a third supported component which does not fall into either the first supported component or the second supported component.
• catalyst II contains a first supported component having a nitrous oxide decomposition ability as a supported component supported on a carrier described later.
• the supported component supported by catalyst II preferably contains a second supported component different from the first supported component, and may contain a third supported component that does not fall into either the first supported component or the second supported component.
• Each supported component will be described below.
• the first supported component supported by catalyst I and catalyst II contains at least one selected from the group consisting of 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.
• the ruthenium compound is not particularly limited, and examples thereof include ruthenium oxide, ruthenium hydroxide, ruthenium nitrate, ruthenium chloride, ruthenic acid, chlororuthenium salts, chlororuthenium salt hydrates, salts of ruthenium acid, ruthenium oxychloride, salts of ruthenium oxychloride, ruthenium ammine complexes, chlorides of ruthenium ammine complexes, ruthenium bromide, ruthenium carbonyl complexes, ruthenium organic acid salts, and ruthenium nitrosyl complexes.
• Ruthenium oxide includes RuO2 .
• Ruthenium hydroxide includes Ru(OH) 3 .
• Ruthenium nitrate includes Ru( NO3 ) 3 .
• Ruthenium chloride includes RuCl 3 , RuCl 3 hydrate, and the like.
• Ruthenic acids include H2RuO4 .
• chlororuthenium salts include salts with [RuCl 6 ] 3- as the anion, such as K 3 RuCl 6 , and salts with [RuCl 6 ] 2- as the anion, such as K 2 RuCl 6 and (NH 4 ) 2 RuCl 6 .
• chlororuthenium salt hydrates include salt hydrates with [RuCl 5 (H 2 O) 4 ] 2- as the anion and salt hydrates with [RuCl 2 (H 2 O) 4 ] + as the cation.
• Ruthenic acid salts include salts of Ru VI O 4 2- (tetraoxoruthenic acid (VI) acid ion) and salts of Ru VIIO 4 - (perruthenic acid ion, tetraoxoruthenic acid (VII) acid ion).
• Examples of cations that form salts include cations of alkali metal elements, cations of alkaline earth metal elements, Ag + , and ammonium cation.
• alkali metal salts of ruthenic acid salts of Li, Na, K, Rb, and Cs
• Na or K salts of ruthenic acid are more preferred. Specific examples include Na 2 RuO 4 and K 2 RuO 4 .
• Ruthenium oxychlorides include Ru2OCl4 , Ru2OCl5 , Ru2OCl6 , and the like.
• Ruthenium oxychloride salts include K2Ru2OCl10 , Cs2Ru2OCl4 , and the like .
• Examples of ruthenium ammine complexes include complexes having complex ions such as [Ru(NH 3 ) 6 ] 2+ , [Ru(NH 3 ) 6 ] 3+ , and [Ru(NH 3 ) 5 H 2 O] 2+ .
• chlorides of ruthenium ammine complexes include complexes with [Ru(NH 3 ) 5 Cl] 2+ as the complex ion, [Ru(NH 3 ) 6 ]Cl 2 , [Ru(NH 3 ) 6 ]Cl 3 , and [Ru(NH 3 ) 6 ]Br 3 .
• Ruthenium bromide includes RuBr 3 , RuBr trihydrate , and the like.
• Ruthenium carbonyl complexes include Ru(CO) 5 and Ru 3 (CO) 12 .
• Examples of ruthenium nitrosyl complexes include K2 [ RuCl5NO )], [Ru( NH3 ) 5 (NO)] Cl3 , [Ru(OH)( NH3 ) 4 (NO)]( NO3 ) 2 , Ru(NO)( NO3 ) 3 , and the like.
• 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 contains ruthenium oxide, and further preferably is ruthenium oxide.
• the ruthenium compound may be a compound containing ruthenium as one of its constituent elements, or may be a compound containing an element (metal or nonmetal) other than ruthenium.
• ruthenium oxide may be an oxide containing ruthenium as one of its constituent elements, and may include a composite oxide containing ruthenium and an element (metal or nonmetal) other than ruthenium, in addition to an oxide (RuO 2 ) of ruthenium alone.
• (metallic) ruthenium and includes, in addition to metallic ruthenium, alloys of ruthenium with metals other than ruthenium.
• the content of the ruthenium element constituting the first supported component in the catalyst (100% of the total mass of the catalyst) is not particularly limited in either catalyst I or catalyst II and may be set appropriately, but is preferably 0.5 to 10 mass%, more preferably 0.5 to 5 mass%, and even more preferably 1 to 3 mass%.
• the second supported component which is supported by catalyst I and preferably supported by catalyst II, contains at least one selected from the group consisting of 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, “substantially does not contain” means that it is inevitably mixed and contains ruthenium.
• This second supported component may have a decomposition ability (catalytic activity) of nitrous oxide, or may not have a decomposition ability (catalytic activity) of nitrous oxide.
• the number of types of the second supported component supported by catalyst I is not particularly limited as long as it is one or more, and can be, for example, 1 to 8 types, and preferably 1 to 4 types.
• the number of types of the second supported component supported by catalyst II is not particularly limited, and can be 0 to 8 types, and preferably 1 to 6 types, and more preferably 1 to 4 types.
• the compounds of antimony, cerium, zirconium and silicon are not particularly limited as long as they contain these elements, and any appropriate compound can be used.
• compounds of the same type as the above-mentioned ruthenium compounds compounds in which the ruthenium element in the ruthenium compound is replaced with at least one of antimony element, cerium element, zirconium element and silicon element can be mentioned.
• Antimony compounds examples include antimony oxide, antimony sulfate, antimony chloride, and salts of antimonic acid, with antimony oxide and antimony chloride being preferred.
• antimony oxide examples include Sb 2 O 3 , Sb 2 O 4 , and Sb 2 O 5 .
• antimony sulfate examples include Sb2 ( SO4 ) 3 .
• Antimony chlorides include SbCl3 and the like. Salts of antimonic acid include NaSbO3 , etc.
• cerium compound examples include cerium oxide, cerium hydroxide, cerium nitrate, cerium chloride, salts of ceric acid, cerium sulfate, and cerium carbonate, with cerium oxide, cerium nitrate, cerium chloride, and cerium sulfate being preferred.
• cerium oxide examples include CeO2 and Ce2O3 .
• cerium hydroxide examples include CeO2.2H2O .
• An example of the cerium nitrate is Ce(NO 3 ) 3.6H 2 O.
• cerium chloride examples include CeCl 3 .7H 2 O.
• An example of a salt of ceric acid is Ce(NH 4 ) 2 (NO 3 ) hexahydrate .
• cerium sulfate examples include Ce(SO 4 ) 2.4H 2 O.
• cerium carbonate examples include Ce 2 (CO 3 ) 3.8H 2 O.
• zirconium compounds examples include zirconium oxide, zirconium hydroxide, zirconium oxynitrate, zirconium chloride, zirconium sulfate, zirconium acetate, and zirconium acetylacetonate, with zirconium oxide, zirconium oxynitrate, zirconium chloride, and zirconium sulfate being preferred.
• zirconium oxide includes ZrO2 and the like.
• Zirconium hydroxide includes Zr(OH) 4 and the like.
• zirconium oxynitrate examples include ZrO(NO 3 ) 2.2H 2 O.
• Zirconium chloride includes ZrCl3 , ZrCl4 , and the like.
• zirconium sulfate include Zr(SO 4 ) 2.4H 2 O.
• Zirconium acetylacetonate includes Zr( C5H7O2 ) 4 and the like.
• silicon compounds include silicon oxide, silicon chloride, salts of silicic acid, and silicon alkoxides, with silicon oxide and salts of silicic acid being preferred. Silicon oxides include SiO2 and the like. Silicon chlorides include SiCl4 and the like. Examples of the silicic acid salt include salts of orthosilicic acid, pyrosilicic acid, metasilicic acid, and the like, and specific examples thereof include Na 2 SiO 3 , Na 4 SiO 4 , Na 2 Si 2 O 5 , and Na 2 Si 4 O 9 . Examples of silicon alkoxides include Si( OC2H5 ) 4 , Si( OC3H7 ) 4 , and Si( OC4H9 ) 4 .
• a preferred compound among the second supported components is at least one selected from zirconium and zirconium compounds.
• a preferred type of compound among the second supported components is preferably an oxide containing at least one selected from the group consisting of antimony oxide, cerium oxide, zirconium oxide, and silicon oxide, more preferably containing at least zirconium oxide, and even more preferably being zirconium oxide.
• the content (total content) of the metal elements 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 a molar ratio (metal element content (mol)/ruthenium element content (mol)).
• the third supported component that may be supported by catalyst I and catalyst II is not particularly limited as long as it is a component that does not fall under either the first supported component or the second supported component, and examples thereof 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 the above 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.
• the content (total content) of the metal elements constituting the third supported component in the catalyst is not particularly limited in either Catalyst I or Catalyst II, and may be set appropriately.
• the support constituting catalyst I contains titanium oxide and is substantially free of silicon oxide, but may contain other compounds as described below.
• the support constituting catalyst II may contain titanium oxide and silicon oxide, and may contain other compounds as described below.
• the support refers to primary particles of titanium oxide or a compound containing titanium oxide and/or secondary particles formed by aggregation of the primary particles molded into a desired shape.
• the surface of the support refers to the surface of the molded body, and the pores of the support refer to one or more of the pores of the primary particles, the gaps between the primary particles in the secondary particles, and the gaps between the secondary particles in the aggregate of the secondary particles.
• the crystal form of the titanium oxide constituting the carrier is not particularly limited, and may be any of rutile crystal form, anatase crystal form, and brookite crystal form.
• the titanium oxide constituting the carrier preferably contains titanium oxide of rutile crystal form. From the viewpoint of catalytic activity, the content of titanium oxide of rutile crystal form in the titanium oxide contained in the carrier is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more, based on the total amount of titanium oxide contained in the carrier being 100% by mass.
• titanium oxide containing titanium oxide in the rutile crystal form refers to titanium oxide that contains rutile crystals, as determined by measuring the ratio of rutile crystals to anatase crystals in the titanium oxide using X-ray diffraction analysis.
• Various sources of X-rays are used.
• copper K ⁇ rays can be used.
• the carrier used in the present invention is a carrier that has a peak intensity of rutile crystals and a peak intensity of anatase crystals, or a carrier that has a peak intensity of rutile crystals.
• the carrier may have both a diffraction peak of rutile crystals and a diffraction peak of anatase crystals, or it may have only a diffraction peak of rutile crystals.
• the carrier constituting catalyst II contains silicon oxide, and preferably contains silicon oxide on the surface (including the surface vicinity) of the carrier and/or on the inner surface (including the inner surface vicinity) of the pores.
• catalyst II the carrier of which contains silicon oxide
• the decrease in catalytic activity of catalyst II can be suppressed even if the decomposition of nitrous oxide is performed for a long period of time, and nitrous oxide can be decomposed at a high decomposition rate.
• Silicon dioxide is preferable as the silicon oxide.
• the silicon oxide contained in the carrier constituting the catalyst II is preferably silicon oxide derived from colloidal silica (e.g., a dried product of colloidal silica in a particulate or granular form) in terms of facilitating the production of the carrier.
• the particle size of silicon oxide in the colloidal silica is not particularly limited, but is preferably 5 to 45 nm, more preferably 5 to 22 nm, in terms of increasing the number of silicon oxide particles.
• the particle size of silicon oxide is the average particle size measured as follows. The average particle size (d) [nm] is calculated from the specific surface area (S) [m 2 /g] obtained by evaporating the water contained in the colloidal silica to dryness, using the following formula.
• ⁇ is a value of 2.2 [g/cm 3 ] as the true density of silicon oxide.
• d 6000/(S ⁇ )
• the particle size of the silicon oxide present in the carrier of Catalyst II does not necessarily have to maintain the same particle size as that of the silicon oxide in the colloidal silica, but it is preferable that it does.
• the content of silicon oxide in the carrier constituting catalyst II (100% of the total mass of the carrier) is not particularly limited and may be set as appropriate, but for example, in order to suppress a decrease in catalytic activity and maintain it for a long period of 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.
• silicon oxide is the second supported component (catalyst I) or whether silicon oxide constitutes the carrier (catalyst II) can be confirmed by observing the catalyst with a scanning electron microscope or a scanning transmission electron microscope.
• each carrier constituting catalyst I and catalyst II include, for example, 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, mixtures of titanium oxide, silicon oxide and other metal oxides or metal sulfates, etc.
• metal oxides include aluminum oxide, zirconium oxide, cerium oxide, sodium oxide, etc.
• the metal sulfates include sodium sulfate, etc.
• Titanium oxide prepared by a known method can be used, and commercially available products can also be used.
• the rutile crystal form of titanium oxide can be prepared by the following method. A method in which titanium tetrachloride is dissolved dropwise in ice-cooled water, neutralized with an aqueous ammonia solution at a temperature of 20° C. or higher to produce titanium hydroxide (orthotitanic acid), and the resulting precipitate is washed with water to remove chlorine ions and then calcined at a temperature of 600° C. or higher (Catalyst Preparation Chemistry, 1989, p.
• the silicon oxide-containing carrier that constitutes catalyst II can be manufactured by a process for obtaining the carrier, which is described in the method for manufacturing catalyst II below.
• the carrier can be obtained by forming titanium oxide or the like into the desired shape.
• the carrier contains titanium oxide and other compounds (e.g., silicon oxide), it can be obtained by forming a mixture of titanium oxide and other compounds into the desired shape.
• the shape of the catalyst (support) is not particularly limited and can be set appropriately.
• the catalyst may be in a honeycomb shape (honeycomb structure).
• the honeycomb-shaped catalyst in a preferred embodiment is usually used as is (in a honeycomb structure), but it may also be crushed and the crushed product may be classified before use.
• the size may be approximately the same as that of the spherical granules described below.
• various shapes can be adopted. Such shapes are not particularly limited, and examples thereof include pellet shapes such as spherical, cylindrical, and ring shapes, monolithic and corrugated shapes, and granular and fine particles of a suitable size obtained by crushing and classifying after molding.
• the shape of the catalyst is preferably a pellet shape such as spherical, cylindrical, and ring shapes, a monolithic shape, a corrugated shape, or a granular shape, but from the viewpoint of the decomposition efficiency of nitrous oxide, a ring-shaped pellet shape is more preferable.
• the honeycomb structure refers to a "honeycomb structure" that is generally meant as a honeycomb catalyst that is widely used, for example, as an exhaust gas purification catalyst, and includes, for example, a structure in which a substrate such as a columnar body is perforated with a plurality of through holes that are densely arranged in the planar direction.
• the substrate may have an appropriate shape selected according to the shape of the reactor (e.g., reaction tube) in which the catalyst is filled, the state of filling the honeycomb structure in the reactor, and the like, and may have a columnar shape, a block shape, a plate shape, and the like.
• the shape of the through-holes is not particularly limited, and may be, for example, a polygonal shape such as a square or a hexagon, a circle, an ellipse, and the like.
• the arrangement of the through-holes is not particularly limited, and may be appropriately determined in consideration of the shape of the openings, and the like. For example, in the planar direction of the substrate (usually a plane perpendicular to the axis), a series (parallel) arrangement, a staggered arrangement, a honeycomb arrangement, and the like may be mentioned.
• honeycomb structure examples include a round hole parallel arrangement, a round hole staggered arrangement, and a round hole honeycomb arrangement, all of which have a circular opening shape of the through holes; a square hole parallel arrangement, a square hole staggered arrangement, and a square hole honeycomb arrangement, all of which have a polygonal opening shape of the through holes.
• the catalyst When the catalyst is in the form of a powder such as granules or fine particles, the catalyst is preferably disposed as a washcoat layer on a substrate having a honeycomb structure.
• the substrate having a honeycomb structure may be made of any material typically used to prepare automotive catalysts, and is typically made of metal or ceramic, for example, various stainless steels or cordierite.
• the substrate typically provides a number of walls to which the washcoat layer is applied and adhered, thereby functioning as a substrate for the catalyst.
• the mass of the washcoat layer is preferably 10 to 200 [g/L] per unit volume of the substrate having a honeycomb structure, and more preferably 30 to 100 [g/L].
• the size of the catalyst (carrier) is not particularly limited and can be set appropriately.
• the catalyst diameter is preferably 10 mm or less from the viewpoint of catalytic activity.
• the catalyst diameter here means the diameter of a sphere in the case of a spherical granule, the diameter of a cross section in the case of a cylindrical pellet, and the maximum diameter of a cross section in the case of other shapes.
• the filling volume ratio is preferably 35 to 74 volume % when the catalyst is filled in the catalyst filling region of a reactor (reaction tube) to form a catalyst filling layer.
• the dimensions of the honeycomb structure preferably have a volume fraction of 35 to 50 volume %, and more preferably 38 to 50 volume %, in order to further increase the efficiency of decomposing nitrous oxide.
• the volume fraction of the honeycomb structure 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 by ordinary methods from the dimensions of the honeycomb structure.
• the honeycomb structure can further increase the decomposition efficiency of nitrous oxide
• the honeycomb structure has a filling volume ratio of 35 to 50 volume %, and more preferably a honeycomb structure with a filling volume ratio of 38 to 50 volume %, when the honeycomb structure (catalyst) is filled in the catalyst filling region of the reactor (reaction tube) to form a catalyst filling layer.
• the filling volume ratio refers to the ratio (percentage) of the actual volume of the honeycomb structure to the volume of the catalyst filling region of the reactor (reaction tube).
• the dimensions of the catalyst can be set, for example, to dimensions that fit the catalyst filling area of the reaction apparatus (reaction tube), usually to outer dimensions that are approximately the same as the inner dimensions (inner diameter and length) of the catalyst filling area, taking into account the volume ratio or filling volume ratio.
• the opening diameter of the through holes (also called cell size), the distance between the through holes (also called inner wall thickness), the opening ratio, etc. are appropriately determined, and in the present invention, they are determined taking into consideration the (filling) volume ratio, etc.
• the cell size can be 1 to 3 mm, and is preferably 1 to 2 mm.
• the thickness of the inner wall can be 0.1 to 2 mm, and is preferably 0.2 to 1 mm.
• the opening ratio ([(total area of through holes opening on the surface of the honeycomb structure)/(apparent surface area of the honeycomb structure)] ⁇ 100(%)) can be 50 to 65%, and is preferably 50 to 62%.
• the cell size and the thickness of the inner wall can be measured by observing and measuring the surface of the honeycomb shape. The opening ratio can be calculated from the measured total area of the through holes and the calculated apparent surface area.
• the catalyst includes a honeycomb structure that satisfies the above-mentioned filling volume ratio by combining multiple catalysts (a honeycomb structure in which multiple catalysts filled in the catalyst filling region form a honeycomb structure that satisfies the above-mentioned filling volume ratio as a whole), but it is preferable that the catalyst alone has a honeycomb structure that satisfies the above-mentioned filling volume ratio.
• the above-mentioned filling volume ratio is synonymous with the catalyst filling rate (catalyst filling rate of the catalyst alone).
• the honeycomb structure of each catalyst satisfies the above-mentioned volume ratio.
• the catalyst disposed as the washcoat layer may be a combination of a plurality of catalysts.
• the catalyst can also be used after diluting it with an inert substance.
• the catalyst used in the decomposition method of the present invention can be produced by various known production methods, for example, by impregnating a support containing titanium oxide with a solution containing the 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, but water, ethanol, etc. can be used. After drying, the catalyst may be calcined.
• the catalyst contains ruthenium oxide
• it can be obtained, for example, by a method including a step of impregnating a support containing titanium oxide with a solution containing a ruthenium halide or a ruthenium nitrosyl complex to support the ruthenium halide or ruthenium nitrosyl complex on the support, a step of drying the support in which the ruthenium halide or ruthenium nitrosyl complex is supported on the support, and a step of calcining the dried product.
• the solutions containing the supported components can be solution A containing a first supported component or a first supported component raw material (also referred to as a first component raw material) capable of forming the first supported component, and solution B containing a second supported component or a second supported component raw material (also referred to as a second component raw material) capable of forming the second supported component, or a mixed solution of solution A and solution B can also be used.
• the above-mentioned solution A can be used as the solution containing the components to be supported. It is also preferable to use solution A and solution B in combination, or to use a mixed solution of solution A and solution B.
• 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 not containing silicon oxide in the step of obtaining the carrier described below.
• a preferred method for preparing Catalyst II includes the following steps. In a preferred production method, after step 1, either step 2 or step 3 may be carried out first, and step 2A described below may be carried out instead of steps 2 and 3.
• Step 1 A step of calcining a carrier precursor obtained by extruding a carrier raw material mixture containing titanium oxide, silicon oxide and water to obtain a carrier.
• Step 2 A step of supporting a first component raw material containing a ruthenium compound on the carrier obtained in step 1 or on the carrier on which a second component raw material is supported in step 3.
• Step 3 A step of supporting a second component raw material containing at least one selected from the group consisting of an antimony compound, a cerium compound, a zirconium compound and a silicon compound on the carrier obtained in step 1 or on which a first component raw material is supported in step 2.
• Step 4 A step of calcining a catalyst precursor in which the first component raw material and the second component raw material are supported on the carrier obtained in step 1.
• Step 2A A step of supporting, on the support obtained in step 1, a first component raw material containing a ruthenium compound and a second component raw material containing at least one compound selected from the group consisting of an antimony compound, a cerium compound, a zirconium compound and a silicon compound.
• the titanium oxide used in step 1 is not particularly limited, and as described above, those produced by various methods or commercially available products can be used.
• the silicon oxide used in step 1 is not particularly limited, and may be one produced by various methods or a commercially available product. However, it is preferable to use it as an aqueous dispersion, and more preferable to use colloidal silica, in terms of facilitating the production of the carrier.
• the particle size of silicon oxide in colloidal silica is not particularly limited, but is preferably 5 to 45 nm, more preferably 5 to 22 nm, in terms of increasing the number of silicon oxide particles.
• the particle size of silicon oxide is the average particle size measured by the above-mentioned method. Examples of commercially available colloidal silica include those used in the examples described below.
• a known organic binder may also be used in step 1.
• step 1 titanium oxide, silicon oxide, and water are mixed to prepare a carrier raw material mixture.
• the form of this carrier raw material mixture is not particularly limited, and it can be a liquid mixture such as a solution or a slurry, or a powder mixture, but it is preferable to prepare a clay-like mixture such as a clay.
• the mixing ratio of titanium oxide, silicon oxide and water is not particularly limited and is set appropriately, but it is preferable that the mixing ratio of titanium oxide and silicon oxide is set to a ratio that results in the above-mentioned content of silicon oxide in the carrier.
• the mixing ratio of water is not particularly limited and is set appropriately and is preferably set to a ratio that results in the carrier raw material mixture becoming a clay-like mixture.
• water may be mixed separately from titanium oxide and silicon oxide, or the water in the colloidal silica used as silicon oxide may be used.
• the titanium oxide, silicon oxide and water can be mixed using a normal mixer or kneader.
• 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.
• the prepared carrier raw material mixture is then extruded to obtain a carrier precursor.
• the shape of the carrier precursor is not particularly limited and can be formed into an appropriate shape, and it is preferable to form it into the above-mentioned honeycomb structure.
• the extrusion of the carrier raw material mixture can be carried out using a conventional extruder, for example, a vacuum kneading extrusion molding machine, a hydraulic extrusion molding machine, etc. In particular, when producing a catalyst having a honeycomb structure, it is preferable to use a vacuum kneading extrusion molding machine.
• the extrusion conditions are not particularly limited, but for example, the kneading or extrusion temperature can be 5 to 40°C. In this manner, a carrier precursor can be obtained, and if necessary, the formed body can be dried to obtain a carrier precursor.
• the support precursor is then calcined to obtain the support.
• the calcination of the carrier precursor can be carried out by a conventional method, and various heaters can be used.
• the calcination conditions are not particularly limited and may be the same as those for calcining titanium oxide or silicon oxide.
• the calcination temperature may be 250° C. or higher, preferably 400 to 900° C., and the calcination time may be 2 to 120 hours.
• Step 2 a first component raw material containing a ruthenium compound is supported on a support.
• the carrier used in this step differs depending on the order of steps 2 and 3. That is, when step 2 is performed prior to 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 with the second component raw material in step 3 is used.
• the first component raw material used in step 2 contains a ruthenium compound.
• This ruthenium compound may be a compound that becomes the first supported component such as ruthenium or a ruthenium compound in the catalyst after production, and may be the first supported component itself or a precursor compound leading to the first supported component.
• the ruthenium compound used in step 2 may be various known compounds, such as the above-mentioned first supported component, and further, Ru(NO 3 ) 3 , RuCl 3 , RuCl 3 hydrate, Na 2 RuO 4 , K 2 RuO 4 , Ru(NO)(NO 3 ) 3 , which are also precursor compounds of the first supported component.
• the first component raw material is usually used in the form of an aqueous solution.
• the content (concentration) of the first component raw material at this time is not particularly limited, but is preferably set to a range that satisfies the above content of the ruthenium element in the catalyst, for example, more preferably 1 to 40 mass%, and even more preferably 2 to 10 mass%, based on the ruthenium element.
• the aqueous solution used in step 2 may contain a component other than the first supported component and the second supported component, and such components include, for example, the above-mentioned third supported component, and further an organic solvent such as alcohol for making the aqueous solution well compatible with the carrier.
• an organic solvent such as alcohol
• a solution of an organic solvent such as alcohol can also be used.
• step 2 the support is contacted with the first component raw material to support the first component raw material on the support.
• the contact method and conditions are not particularly limited and can be set appropriately.
• various methods for supporting various components on a carrier can be applied as a method for producing a catalyst, and examples thereof include a method of immersing a carrier in the above aqueous solution, and a coating method of spraying or applying the above aqueous solution to a carrier.
• the amount of the aqueous solution used at this time is not particularly limited, but is preferably set within a range that satisfies the above content of ruthenium element in the catalyst, and is, for example, more preferably 0.1 to 10 mL, and even more preferably 0.2 to 2 mL per 1 g of carrier.
• Examples of the contact conditions include a condition of contacting at 5 to 40° C. (preferably 10 to 30° C.) for 1 to 300 minutes (preferably 5 to 180 minutes).
• the support impregnated with the first component raw material can be dried by conventional methods. In this manner, the first component raw material can be supported or adsorbed on the carrier containing titanium oxide and silicon oxide.
• Step 3 a second component raw material containing at least one compound selected from the group consisting of antimony compounds, cerium compounds, zirconium compounds and silicon compounds is supported on the support.
• the carrier used in this step differs depending on the order of steps 2 and 3. That is, when step 3 is performed prior to step 2, or when step 2 and step 3 are performed simultaneously (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 supported with the first component raw material obtained in step 2 is used.
• the second component raw material used in step 3 contains an antimony compound, a cerium compound, a zirconium compound, or a silicon compound.
• These compounds may be compounds that become the second supported component such as an antimony compound in the catalyst after production, and may be the second supported component itself or a precursor compound leading to the second supported component.
• the above compounds used in step 3 include various known compounds, such as the above-mentioned second supported component, and also SbCl 3 , Ce(NO 3 ) 3.6H 2 O, ZrO(NO 3 ) 2.2H 2 O, Si(OC 2 H 5 ) 4 , which are precursor compounds of the second supported component.
• the second component raw material is usually used in the form of an aqueous solution.
• the content (concentration) of the second component raw material at this time is not particularly limited, but is preferably set to a range that satisfies the above content of the second component raw material (element) in the catalyst, for example, more preferably 0.01 to 20 mass%, and even more preferably 1 to 15 mass% on an elemental basis.
• the aqueous solution used in step 3 may contain components other than the first supported component and the second supported component, and examples of such components include the above-mentioned third supported component and further the above-mentioned organic solvent.
• a solution of an organic solvent such as alcohol can also be used.
• step 3 the support is contacted with the second component feedstock to support the second component feedstock on the support.
• the contact method and conditions are not particularly limited and are the same as the contact method and conditions described in the above step 2.
• the amount of the aqueous solution containing the second component raw material used is not particularly limited, but is preferably set within a range that satisfies the above content of the second component raw material (element) in the catalyst, and is, for example, more preferably 0.1 to 10 mL, and even more preferably 0.2 to 2 mL, per gram of carrier.
• the support impregnated with the second component source can be dried by conventional methods. In this manner, the second component raw material can be supported or adsorbed on the carrier containing titanium oxide and silicon oxide.
• Step 2A In a preferred method for producing catalyst II, steps 2 and 3 can be carried out simultaneously.
• step 2A is carried out in which the first component raw material and the second component raw material are supported on the support obtained in step 1, instead of steps 2 and 3.
• the first and second component raw materials used in step 2A are as described in steps 2 and 3.
• the first component raw material and the second component raw material are usually used in the form of an aqueous solution.
• the content (concentration) of the first component raw material and the second component raw material at this time is not particularly limited, and is as described in step 2 and step 3.
• the aqueous solution used in step 2A may contain a component other than the first supported component and the second supported component, and such components include, for example, the above-mentioned third supported component and further the above-mentioned organic solvent.
• a solution of an organic solvent such as an alcohol can also be used.
• the carrier is contacted with the first component raw material and the second component raw material to support the first component raw material and the second component raw material on the carrier.
• the contact method and conditions are not particularly limited and are the same as the contact method and conditions described in step 2.
• the carrier impregnated with the first component raw material and the second component raw material can be dried by a conventional method. 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.
• Step 4 the catalyst precursor obtained in step 2 and step 3 or step 2A, in which the first component raw material and the second component raw material are supported on a carrier, is calcined.
• the calcination of the catalyst precursor can be carried out by a conventional method, and various heaters can be used.
• the calcination conditions are not particularly limited, and the calcination conditions applied to the calcination of the supported component can be applied without any particular limitation.
• the calcination temperature can be 100 to 600°C, preferably 200 to 400°C
• the calcination time can be 1 to 30 hours, preferably 1 to 10 hours.
• steps other than the above steps 1 to 4 may also be performed.
• steps 2, 3, and 2A there may be mentioned a step of drying the support that has been contacted with the aqueous solution, a step of crushing or disintegrating the catalyst obtained in step 4, and a step of adjusting the shape or size of the catalyst obtained in step 4 (for example, a step of classifying the crushed or disintegrated catalyst).
• the production method of the present invention having the above steps can easily produce a nitrous oxide decomposition catalyst suitable for use in the decomposition method of the present invention.
• catalyst II (preferred embodiment) in which the first supported component and the second supported component are supported or adsorbed on a carrier containing titanium oxide and silicon oxide.
• the above step 3 or step 2A it is possible to produce catalyst II in which the first supported component is supported or adsorbed on a carrier containing titanium oxide and silicon oxide.
• catalyst I can be produced in which the first supported component and the second supported component are supported or adsorbed on a carrier containing titanium oxide.
• the catalyst produced by the above method can be powdered by crushing, disintegration, etc., and then disposed on a substrate having a honeycomb structure, preferably as a washcoat layer, to produce the catalyst.
• the washcoat layer of the catalyst can be applied and adhered to the substrate surface by any known means in the art.
• the washcoat layer is formed by coating a substrate with a slurry containing a catalyst prepared to have a specific solid content (e.g., about 30 to about 90% by mass) in a liquid such as water or alcohol by means of spraying, immersion, or the like, and drying the slurry.
• the catalyst used to prepare the slurry can be a catalyst produced by the above method that has been powdered by crushing, disintegration, or the like.
• the decomposition method of the present invention uses a nitrous oxide-containing gas that includes nitrous oxide, water vapor, and oxygen.
• the nitrous oxide-containing gas may be any gas containing nitrous oxide, water vapor (water) and oxygen, and may contain one or more gases other than the three gases of nitrous oxide, water vapor and oxygen. Examples of such gases include various gases such as ammonia, nitrogen, carbon dioxide, nitric oxide, nitrogen dioxide, inert gases (helium, argon) as dilution gases, and further reducing gases.
• the nitrous oxide-containing gas may contain a liquid.
• the nitrous oxide-containing gas may be in a gaseous state at least while in contact with the catalyst (under reaction conditions), and may be in a liquid state or a mixture of gas and liquid before contact.
• the content (concentration) and content ratio of each component in the nitrous oxide-containing gas are not particularly limited and can be set as appropriate, but except for components with special effects, it is usually efficient to use the values specific to the factory from which the nitrous oxide-containing gas is discharged almost as is. Therefore, for example, the molar concentration of nitrous oxide in the nitrous oxide-containing gas is generally and preferably 0.002 to 10 mol %. The molar concentration of water vapor is generally and preferably 0.1 to 10 mol %. The molar concentration of oxygen gas in the nitrous oxide-containing gas is preferably 0.1 to 21 mol %.
• the nitrous oxide-containing gas can also be obtained by mixing multiple gases containing at least one of nitrous oxide, water vapor, or oxygen-containing gas. An example of an oxygen-containing gas is air.
• the nitrous oxide-containing gas may contain ammonia gas in order to further increase the decomposition rate of nitrous oxide.
• the molar concentration of ammonia in the nitrous oxide-containing gas is preferably 0.0002 mol% or more and preferably 1 mol% or less in terms of the decomposition rate of nitrous oxide.
• the molar concentration of ammonia is more preferably 0.0002 to 0.5 mol%, and even more preferably 0.0002 to 0.2 mol%.
• the content ratio of ammonia to water vapor contained in the nitrous oxide-containing gas [ammonia/water vapor] is not particularly limited and can be set appropriately, but from the viewpoint of the decomposition rate of nitrous oxide, it is preferable that the molar ratio is 0.0010 or more.
• the molar ratio is more preferably 0.0010 to 0.050, and from the viewpoint of suppressing or avoiding the problem of remaining ammonia (discharge into the atmosphere, implementation of removal work), it is more preferably 0.0010 to 0.030, and even more preferably 0.0010 to 0.010.
• the content ratio of ammonia to nitrous oxide contained in the nitrous oxide-containing gas is not particularly limited and can be set appropriately, but it is preferable that the molar ratio is 0.005 to 10.
• the content of oxygen gas in the nitrous oxide-containing gas is preferably 0.01 to 10,000 times the molar content of ammonia within the above-mentioned range.
• the nitrous oxide-containing gas does not need to contain a reducing gas that improves the decomposition rate of nitrous oxide.
• the nitrous oxide-containing gas not containing a reducing gas includes an embodiment in which the content of the reducing gas is 0 mol %, as well as an embodiment in which the reducing gas is contained in a molar ratio to nitrous oxide of less than 0.005.
• the nitrous oxide-containing gas may contain a reducing gas in order to further increase the decomposition rate of nitrous oxide.
• a saturated hydrocarbon gas that serves as a raw material for generating a reducing gas such as carbon monoxide gas by reacting with oxygen contained in the nitrous oxide-containing gas or generated in the reactor may be contained.
• a method in which a reducing gas is contained in the nitrous oxide-containing gas is preferred.
• the reducing gas may be any reducing gas other than ammonia, and any gas used in a general catalytic reduction method may be used without any particular limitation.
• unsaturated hydrocarbon gases such as ethylene, propylene, ⁇ -butylene, ⁇ -butylene, carbon monoxide gas, hydrogen gas, and gases of alcohol compounds such as methanol, ethanol, propanol, and butanol may be used.
• unsaturated hydrocarbon gases such as ethylene, propylene, ⁇ -butylene, ⁇ -butylene, carbon monoxide gas, hydrogen gas, and gases of alcohol compounds such as methanol, ethanol, propanol, and butanol
• saturated hydrocarbon gases that serve as a raw material for generating a reducing gas
• saturated hydrocarbon gases include methane, ethane, propane, and n-butane.
• Preferred saturated hydrocarbon gases include ethane, propane, and n-butane.
• the saturated hydrocarbon gas may be a mixture of natural gas, liquefied natural gas, and liquefied petroleum gas.
• the content of the reducing gas or saturated hydrocarbon gas in the nitrous oxide-containing gas is not particularly limited and can be set appropriately.
• 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 to the water vapor in the nitrous oxide-containing gas [reducing gas or saturated hydrocarbon gas/water vapor] is preferably 0.0003 to 0.03.
• the content ratio of the reducing gas or saturated hydrocarbon gas to the nitrous oxide contained in the nitrous oxide-containing gas [reducing gas or saturated hydrocarbon gas/nitrous oxide] is preferably 0.01 to 100 in molar ratio.
• the nitrous oxide-containing gas can be prepared by appropriately mixing nitrous oxide, water vapor, oxygen, ammonia, and other gases other than these.
• various exhaust gases discharged from chemical manufacturing plants, and even exhaust gases discharged from automobiles, power plants that use ammonia fuel, and ships can also be used.
• gases discharged from chemical manufacturing plants such as nitric acid manufacturing plants, ⁇ -caprolactam manufacturing plants, and adipic acid manufacturing plants often contain water vapor, oxygen gas, and even ammonia gas in addition to nitrous oxide, and can be effectively used in the decomposition method of the present invention.
• the exhaust gas satisfies the above-mentioned ranges of content, content ratio, etc., it is preferable in that it can be applied directly to the decomposition method of the present invention without adjusting the content, etc.
• the decomposition method of the present invention includes contacting the above catalyst with the nitrous oxide-containing gas (contact step).
• the contact step may be any step of contacting a catalyst with a nitrous oxide-containing gas, and may be any contact step in a known method for decomposing nitrous oxide.
• Examples of contact steps in known methods for decomposing nitrous oxide include the method (step) of contacting a catalyst with nitrous oxide in the presence of a reducing gas, as described in Patent Document 1. The two may also be contacted by passing the nitrous oxide-containing gas through a reaction tube filled with the catalyst.
• the method for contacting the nitrous oxide-containing gas with the catalyst may be a batch method or a continuous method, and a continuous method is preferred in terms of reaction efficiency and in that the effect of the present invention, which is that catalytic activity can be maintained for a long period of time, can be effectively utilized.
• continuous methods include a fixed bed method and a fluidized bed method.
• nitrous oxide in the nitrous oxide-containing gas comes into contact with the catalyst, and a decomposition reaction of nitrous oxide shown in the following formula occurs, even in the presence of water vapor, and nitrous oxide is efficiently decomposed into nitrogen molecules and oxygen molecules.
• Decomposition reaction of nitrous oxide N2O ⁇ N2 + 1/ 2O2
• the ammonia When the nitrous oxide-containing gas contains ammonia, the ammonia further promotes the decomposition reaction of nitrous oxide.
• the details of the mechanism of action are not yet clear, it is thought to be as follows. For example, in the presence of a catalyst that exhibits a reducing action, such as a catalyst supported by ruthenium, it is presumed that the ammonia reacts with nitrous oxide on the catalyst surface, decomposing nitrous oxide into nitrogen molecules and water molecules, thereby further promoting the decomposition reaction of nitrous oxide.
• the contact method and contact conditions can be appropriately selected from the methods and conditions that can be used in each step, and examples of the conditions include the following conditions.
• the contact temperature (reaction temperature) is appropriately determined, but is preferably 500° C. or less from the viewpoint of catalyst activity deterioration, and is preferably 100° C. or more from the viewpoint of reaction rate.
• the contact temperature is preferably 200 to 450° C., more preferably 250 to 400° C.
• the supply rate of the nitrous oxide-containing gas relative to the mass of the catalyst is not particularly limited and may be determined as appropriate. For example, the flow rate per 1 g of catalyst at 0° C.
• the contact time is appropriately determined depending on the nitrous oxide concentration or supply rate in the nitrous oxide-containing gas, the contact temperature, etc. In the decomposition method of the present invention, since the catalytic activity can be maintained for a long period of time, the contact time can be set long, for example, to 0.3 seconds or more.
• the reaction pressure varies depending on the contact temperature, the supply rate of the nitrous oxide-containing gas, the pressure of the outside air around the reactor, etc., but is preferably a pressure higher than the outside air, preferably an absolute pressure of 0.08 to 1 MPa (absolute), more preferably an absolute pressure of 0.09 to 0.7 MPa (absolute).
• the decomposition method of the present invention may include a step other than the contact step, such as a step of adjusting the component contents of the nitrous oxide-containing gas, or a step of introducing ammonia gas or a reducing gas into the nitrous oxide-containing gas.
• the decomposition method of the present invention can decompose nitrous oxide for a long period of time while maintaining the decomposition rate of nitrous oxide, and can decompose nitrous oxide efficiently (at a high decomposition rate) for a long period of time.
• nitrous oxide can be decomposed efficiently for a long period of time by the simple process of circulating (passing) nitrous oxide-containing gas through the catalyst.
• the decomposition method of the present invention can be used in various fields and applications for decomposing and removing nitrous oxide, such as exhaust gas treatment from chemical manufacturing plants, automobiles, power plants using ammonia fuel, and ships.
• the method can be suitably used in chemical manufacturing plants such as nitric acid manufacturing plants, ⁇ -caprolactam manufacturing plants, and adipic acid manufacturing plants that emit nitrous oxide-containing gas containing nitrous oxide, water vapor, and oxygen.
• the installation position of the device for carrying out the decomposition method of the present invention is not particularly limited, but it is usually installed at the last stage in the flow direction of the exhaust gas, for example, at the front stage of the exhaust tower.
• the device for carrying out the decomposition method of the present invention can be easily installed alongside an existing production plant, allowing the existing production plant to be effectively utilized.
• Nitrous oxide decomposition catalysts corresponding to catalyst I were produced as follows, and after subjecting these catalysts to forced aging treatment, they were used in a nitrous oxide decomposition reaction to evaluate the nitrous oxide decomposition rate.
• the decomposition rate of the nitrous oxide concentration was calculated by analyzing (measuring) the nitrous oxide content C B in the nitrous oxide-containing gas (used for decomposing nitrous oxide) and the nitrous oxide content C A in the reaction outlet gas (post-reaction gas) using gas chromatography (Shimadzu Corporation, GC-2014 (detector: TCD, column: SHINCARBON-ST50/80 4m)), and calculating the decomposition rate of the nitrous oxide concentration (sometimes simply referred to as the "nitrous oxide decomposition rate") from the analyzed nitrous oxide concentration according to the following formula.
• Nitrous oxide concentration decomposition rate X (%) [(C B -C A )/C B ] x 100
• This mixture was extruded into a noodle shape with a diameter of 3.0 mm, dried at 60°C for 2 hours, and then crushed to a length of about 3 to 5 mm.
• the carrier precursor 1 thus obtained was heated in air from room temperature to 600°C over 1.7 hours, and then calcined by holding at 600°C for 3 hours to obtain a carrier 1 formed of white titanium oxide (rutile crystal form TiO2 ratio 90% or more) (Step 1: However, silicon oxide was not used in the preparation of the carrier raw material mixture).
• ruthenium chloride hydrate Fluya Metal Co., Ltd., RuCl3.nH2O , Ru content 40%
• zirconium oxynitrate dihydrate Kishida Chemical Co., Ltd., ZrO( NO3 ) 2.2H2O , Zr content 34%) were dissolved in 2.3 g of ion-exchanged water.
• the obtained aqueous solution was impregnated into 10.0 g of support 1 made of titanium oxide at a temperature of 25°C by the incipient wetness method, and then air-dried overnight at room temperature (25°C) in an air atmosphere to obtain a catalyst precursor 1 supporting ruthenium chloride hydrate and zirconium oxynitrate dihydrate (Step 2A).
• This catalyst precursor 1 (10 g) was packed into a quartz glass tube (inner diameter 27 mm) equipped with a sheath tube for measuring the internal temperature, and then fired in an electric tubular furnace by raising the furnace temperature to 250° C. under an air flow of 200 cm 3 (0° C., 0.1013 MPa (absolute))/min, and then maintaining the same temperature for 2 hours.
• the internal temperature of the quartz glass tube at an electric tubular furnace temperature of 250° C. was 300° C.
• the obtained cylindrical pellet-shaped ZrO 2 —RuO 2 /TiO 2 catalyst was crushed and sieved into granules of 0.7 to 1.0 mm to obtain catalyst 1.
• the eggplant-shaped flask containing the impregnated carrier 1 was rotated at 80 rpm to stir the carrier 1, and the temperature in the eggplant-shaped flask was set to 30 ° C.
• a mixed gas of water vapor and nitrogen (water vapor concentration: 2.0 volume %) was continuously supplied into the eggplant-shaped flask at a flow rate of 277 mL / min (0 ° C, 0.1 MPa conversion) for 4 hours and 20 minutes, and the carrier 1 after impregnation was dried by circulating it.
• the obtained dried product (62.3 g) was heated from room temperature to 300°C over 1.2 hours under air flow, and then calcined by maintaining at the same temperature for 2 hours to obtain 60.6 g of a solid in which silicon oxide was supported on a titanium oxide support (silicon oxide-supported titanium oxide support) (Step 3).
• 30.1 g of the obtained silicon oxide-supported titanium oxide carrier was placed in a 200 mL eggplant-shaped flask and set in a rotary impregnation-drying apparatus.
• an aqueous solution prepared by dissolving 0.71 g of ruthenium chloride hydrate (manufactured by Furuya Metal Co., Ltd., RuCl 3 ⁇ nH 2 O, Ru content 40%) in 6.89 g of pure water was added dropwise into the eggplant-shaped flask over a period of 30 minutes to impregnate the flask with the aqueous solution, thereby obtaining 37.70 g of a ruthenium chloride-supported material.
• step 2 while stirring the ruthenium chloride-supported material by rotating the eggplant-shaped flask containing the ruthenium chloride-supported material at 80 rpm, the temperature inside the eggplant-shaped flask was raised to 35° C., and air was continuously supplied into the eggplant-shaped flask at a flow rate of 692 mL/min (0° C., 0.1 MPa equivalent) for 3 hours and 40 minutes to circulate the air, thereby drying the material, and 32.21 g of catalyst precursor 4 was obtained (step 2). 32.21 g of catalyst precursor 4 was placed in a sealed container and held in a thermostatic bath at 20° C. for 120 hours. The mass of catalyst precursor 4 after holding was 32.21 g.
• step 2 an RuO 2 /TiO 2 catalyst containing 1.3 mass % of ruthenium oxide (1.0 mass % as ruthenium element) was obtained in the same manner as in Experimental Example 1, except that an aqueous solution containing only 0.2 g of ruthenium chloride hydrate (Furuya Metal Co., Ltd., RuCl 3 ⁇ nH 2 O, Ru content 40%) was used to support ruthenium chloride hydrate on support 1 obtained in Experimental Example 1. The obtained cylindrical pellet-shaped RuO 2 / TiO 2 catalyst was crushed and sieved into granules of 0.7 to 1.0 mm, to obtain catalyst 5.
• Experimental Examples 1 to 4 correspond to examples of the decomposition method of the present invention using Catalyst I.
• the "molar ratio in catalyst” 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 metal element (moles)/content of ruthenium element (moles)].
• Example 5 (Preparation of catalyst 6: ZrO2 - RuO2 / TiO2 catalyst) 100 parts by mass of titanium oxide powder (manufactured by Showa Denko Ceramics Co., Ltd.) was mixed and kneaded to obtain a clay.
• As the organic binder Metolose (manufactured by Shin-Etsu Chemical Co., Ltd.) and Unilube (manufactured by NOF Corp.) were used.
• the obtained clay was molded using a vacuum extrusion molding machine to obtain a honeycomb molded body (cubic shape of 20 mm in length, 20 mm in width, and 20 mm in height, through holes arranged in parallel in the vertical and horizontal directions, volume ratio 36%, through hole opening shape of square with cell size of 1.4 mm, inner wall thickness 0.35 mm, opening ratio 64%, 100% rutile crystal type TiO 2 ).
• the obtained honeycomb molded body was air-dried at room temperature for 2 days to obtain a carrier precursor 2.
• the carrier precursor 2 was fired in an electric furnace at 600° C.
• a honeycomb-structured carrier 2 (the honeycomb structure retains the shape and dimensions of the honeycomb molded body) (Step 1: However, no silicon oxide was used in preparing the carrier raw material mixture).
• the carrier 2 (7 g ) was immersed at 25° C. in an aqueous solution (about 40 mL) containing 4.2 g of ruthenium chloride hydrate (manufactured by Furuya Metal Co., Ltd., RuCl3.nH2O , Ru content 40%) and 1.0 g of zirconium oxynitrate dihydrate (manufactured by Kishida Chemical Co., Ltd., ZrO( NO3 ) 2.2H2O , Zr content 34%).
• the obtained honeycomb-shaped ZrO2 - RuO2 / TiO2 catalyst was crushed and sieved into granules of 0.7 to 1.0 mm to obtain catalyst 6.
• Decomposition reaction of nitrous oxide using catalyst 6 after forced deterioration treatment Using this catalyst 6, forced degradation treatment and a 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 2.
• the obtained honeycomb - shaped ZrO2 - RuO2 / TiO2 catalyst was crushed and sieved into granules of 0.7 to 1.0 mm, to obtain catalyst 7.
• Decomposition reaction of nitrous oxide using catalyst 7 after forced deterioration treatment Using this catalyst 7, forced degradation treatment and a 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 2.
• Example 7 (Preparation of catalyst 8: ZrO2 - RuO2 / TiO2 catalyst)
• the obtained honeycomb-shaped ZrO2 - RuO2 / TiO2 catalyst was crushed and sieved into granules of 0.7 to 1.0 mm, to obtain catalyst 8.
• Decomposition reaction of nitrous oxide using catalyst 8 after forced deterioration treatment Using this catalyst 8, forced degradation treatment and a 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 2.
• the obtained honeycomb - shaped ZrO2 - RuO2 / TiO2 catalyst was crushed and sieved into granules of 0.7 to 1.0 mm, to obtain catalyst 9.
• Decomposition reaction of nitrous oxide using catalyst 9 after forced deterioration treatment Using this catalyst 9, forced degradation treatment and a 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 2.
• the obtained honeycomb -shaped ZrO2 - RuO2 / TiO2 catalyst was crushed and sieved into granules of 0.7 to 1.0 mm to obtain catalyst 10.
• Decomposition reaction of nitrous oxide using catalyst 10 after forced deterioration treatment Using this catalyst 10, forced degradation treatment and a nitrous oxide decomposition reaction were carried out in the same manner as in Experimental Example 1, and the decomposition rate of the nitrous oxide concentration after the forced degradation treatment was calculated. The results are shown in Table 2.
• Experimental Examples 5 to 9 correspond to examples of the decomposition method of the present invention using Catalyst I.
• the "molar ratio in catalyst” 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 metal element (moles)/content of ruthenium element (moles)].
• the obtained honeycomb-shaped ZrO2-RuO2 / TiO2 catalyst was crushed and sieved into granules of 0.7 to 1.0 mm to obtain catalyst 12.
• Decomposition reaction of nitrous oxide using catalyst 12 after forced deterioration treatment Using this catalyst 12, forced degradation treatment and a nitrous oxide decomposition reaction were carried out in the same manner as in Experimental Example 1, and the decomposition rate of the nitrous oxide concentration after the forced degradation treatment was calculated. The results are shown in Table 3.
• the obtained honeycomb-shaped ZrO2-RuO2 / TiO2 catalyst was crushed and sieved into granules of 0.7 to 1.0 mm to obtain catalyst 13. (Decomposition reaction of nitrous oxide using catalyst 13 after forced deterioration treatment) Using this catalyst 13, forced degradation treatment and a 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 3.
• Example 12 (Preparation of catalyst 14: ZrO2 - RuO2 / TiO2 catalyst)
• the obtained honeycomb-shaped ZrO2-RuO2 / TiO2 catalyst was crushed and sieved into granules of 0.7 to 1.0 mm to obtain catalyst 14.
• Decomposition reaction of nitrous oxide using catalyst 14 after forced deterioration treatment Using this catalyst 14, forced degradation treatment and a nitrous oxide decomposition reaction were carried out in the same manner as in Experimental Example 1, and the decomposition rate of the nitrous oxide concentration after the forced degradation treatment was calculated. The results are shown in Table 3.
• Table 3 also lists the results of Experimental Example 1, Experimental Example 5, Comparative Example 1, and Comparative Example 2.
• Experimental Examples 10 to 12 correspond to examples of the decomposition method of the present invention using Catalyst I.
• the "molar ratio in catalyst” 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 metal element (moles)/content of ruthenium element (moles)].
• Nitrous oxide decomposition catalysts corresponding to Catalyst II were produced as follows, and these catalysts were used in a nitrous oxide decomposition reaction to evaluate the decomposition rate of nitrous oxide.
• the decomposition rate of the nitrous oxide concentration was calculated by analyzing (measuring) the nitrous oxide content C B in the nitrous oxide-containing gas (used for decomposing nitrous oxide) and the nitrous oxide content C A in the reaction outlet gas (post-reaction gas) using gas chromatography (VARIAN, micro GC (detector: micro TCD, column: CP-PoraPLOT Q 10m)), and calculating the decomposition rate of the nitrous oxide concentration (nitrous oxide decomposition rate) from the analyzed nitrous oxide concentration using the following formula.
• Decomposition rate of nitrous oxide concentration (%) [(C B -C A )/C B ] x 100
• Example 13> (Catalyst 15: Preparation of RuO2 / SiO2- containing TiO2 catalyst) 100 parts by mass of titanium oxide powder (manufactured by Showa Denko Ceramics Co., Ltd.) was mixed and kneaded with 12 parts by mass of organic binder, 24.6 parts by mass of water, and 17.5 parts by mass of silica sol to obtain a clay.
• organic binder Metolose (manufactured by Shin-Etsu Chemical Co., Ltd.) and Unilube (manufactured by NOF Corporation) were used.
• silica sol Snowtex ST-CM (manufactured by Nissan Chemical Co., Ltd., particle size 22 nm, solid content 30% by mass) was used.
• the obtained clay was molded using a vacuum extrusion molding machine to obtain a honeycomb molded body (cubic shape of 20 mm in length, 20 mm in width, and 20 mm in height, through holes arranged in parallel in the vertical and horizontal directions, volume ratio 36%, through hole opening shape is rectangular with cell size 1.4 mm, inner wall thickness 0.35 mm, opening ratio 64%).
• the obtained honeycomb molded body was air-dried at room temperature for 2 days to obtain a carrier precursor 3 (the honeycomb structure retains the shape and dimensions of the honeycomb molded body).
• the carrier precursor 3 was fired at 600°C for 2 hours using an electric furnace to obtain a carrier 3 ( SiO2 content in the carrier: 5 mass%, honeycomb structure retains the shape and dimensions of the honeycomb molded body) (Step 1).
• the support 3 (6 g) was immersed in about 50 mL of an aqueous ruthenium chloride solution prepared so that the Ru content was 2.9 mass %, at 25° C.
• the support 3 was pulled out of the aqueous solution, and excess liquid was blown off with an air blower, and the support 3 was left to stand at room temperature and air-dried until no mass loss was observed, thereby obtaining a catalyst precursor 15 (step 2).
• the catalyst precursor 15 was calcined in an electric furnace at 300° C.
• step 4 The obtained honeycomb-shaped RuO 2 /SiO 2 -containing TiO 2 catalyst was pulverized in a magnetic mortar to obtain a powder catalyst 15.
• the decomposition reaction of nitrous oxide was carried out using a BELLCAT II (manufactured by Microtrack Bell). 0.1 g of catalyst 15 was packed into a reaction tube (inner diameter 8 mm). The reaction tube was placed in an electric furnace, and the temperature was raised to 380° C. under normal pressure (0.1 MPa (absolute)) and a flow of helium at 100 cm 3 (0° C., 0.1013 MPa (absolute))/min.
• the gas to be contacted 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 (0° C., 0.1013 MPa (absolute))/min), and the decomposition reaction of nitrous oxide was carried out.
• the remainder of the nitrous oxide-containing gas was helium.
• the decomposition reaction of nitrous oxide was carried out for 5 hours. After 5 hours of reaction, the reaction outlet gas (post-reaction gas) was analyzed as described above, and the decomposition rate of nitrous oxide was calculated. The results are shown in Table 4.
• step 1 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, and the same procedure as in Experimental Example 13 was repeated to obtain a RuO2 / SiO2 -containing TiO2 catalyst containing carrier 4 ( SiO2 content in carrier: 10.0% by mass) and 1.3% by mass of ruthenium oxide (1.0% by mass as ruthenium element).
• the obtained honeycomb-shaped RuO2 / SiO2 -containing TiO2 catalyst was pulverized in a magnetic mortar to obtain a powdered catalyst 16.
• This catalyst 16 Using this catalyst 16, a decomposition reaction of nitrous oxide was carried out in the same manner as in Experimental Example 13, and the decomposition rate of nitrous oxide was calculated. The results are shown in Table 4.
• Example 3 A nitrous oxide decomposition catalyst corresponding to catalyst II (preferred embodiment) was manufactured as described below, and the manufactured catalyst was subjected to forced aging treatment in the same manner as in Example 1, and then a nitrous oxide decomposition reaction was carried out to evaluate the nitrous oxide decomposition rate. The decomposition rate of nitrous oxide concentration was calculated in the same manner as in Example 1.
• the obtained honeycomb-shaped ZrO2 - RuO2 / SiO2 -containing TiO2 catalyst was crushed and sieved into granules of 0.7 to 1.0 mm to obtain a catalyst 20.
• Decomposition reaction of nitrous oxide using catalyst 20 after forced deterioration treatment Using this catalyst 20, forced degradation treatment and a nitrous oxide decomposition reaction were carried out in the same manner as in Experimental Example 17, and the decomposition rate of the nitrous oxide concentration after the forced degradation treatment was calculated. The results are shown in Table 5.
• Examples 17 and 18 represent examples of the cracking process of the present invention using Catalyst II (preferred embodiment).
• the "molar ratio in catalyst” 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 metal element (moles)/content of ruthenium element (moles)].

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