JPWO2008081799A1 - Nitrous oxide decomposition catalyst and treatment method of nitrous oxide-containing gas - Google Patents

Abstract

A novel nitrous oxide decomposition catalyst capable of efficiently decomposing and removing nitrous oxide without containing expensive components such as noble metals and a method for treating a nitrous oxide-containing gas using the catalyst are provided. The nitrous oxide decomposition catalyst of the present invention includes an A component (for example, CaCO3) containing at least one selected from Group 2 elements and a B component containing at least one selected from Group 3, 4 and 14 elements (For example, CeO2) and a C component (NiO) containing a nickel element contain a catalyst component.

Description

  The present invention relates to a nitrous oxide decomposition catalyst and a method for treating a nitrous oxide-containing gas.

Nitrous oxide (N ₂ O) contained in various industrial exhaust gas discharged from combustion exhaust gas and chemical plants decomposes in the stratosphere to produce nitric oxide and shows high greenhouse effect. Development of an efficient decomposition and removal method is desired. For example, it is known that nitrous oxide is by-produced in the nitric acid production process by catalytic oxidation of ammonia, and if it can decompose and remove nitrous oxide generated from nitric acid plants in various parts of the world, it will promote prevention of global warming. Is possible.

Therefore, as a method for decomposing and removing nitrous oxide by contacting it with a catalyst, a method using a catalyst in which palladium, nickel, cobalt or the like is supported on a carrier such as aluminum oxide or zirconium oxide (Patent Document 1), or hydrophobic alumina. A method using a catalyst supporting ruthenium and / or rhodium and zirconium oxide or the like (Patent Document 2), or a catalyst containing rhodium oxide or cobalt oxide, a manganese compound, and an alkali or alkaline earth metal compound. A method (Patent Document 3) and the like have been proposed.
JP-A-63-7826 JP-A-6-142517 JP-A-6-106027

  An object of the present invention is to provide a novel nitrous oxide decomposition catalyst capable of efficiently decomposing and removing nitrous oxide, and nitrous oxide for efficiently decomposing and removing nitrous oxide by contacting the catalyst with a gas containing nitrous oxide. It is providing the processing method of nitrogen-containing gas.

As a result of diligent research to achieve the above object, the present inventors have found that the above object can be achieved by using a nitrous oxide decomposition catalyst containing the following A component, B component and C component. The present invention has been completed.
A component: at least one element selected from group 2 elements B component: at least one element selected from group 3, 4 and 14 elements C component: nickel element That is, nitrous oxide decomposition according to the present invention The catalyst for use comprises an A component containing at least one selected from Group 2 elements, a B component containing at least one selected from Group 3, 4 and 14 elements, and a C component consisting of nickel elements. It is contained as a catalyst component.

  The method for treating a nitrous oxide-containing gas according to the present invention comprises treating the nitrous oxide-containing gas using the above nitrous oxide decomposition catalyst.

  The nitrous oxide decomposition catalyst according to the present invention (hereinafter sometimes simply referred to as “catalyst”) is composed of an A component containing at least one selected from Group 2 elements and Group 3, Group 4 and Group 14 elements. A B component containing at least one kind selected and a C component made of nickel element are contained as catalyst components.

  Thus, the nitrous oxide decomposition catalyst of the present invention has high performance and can decompose and remove nitrous oxide with a high removal rate. Therefore, the nitrous oxide-containing gas can be efficiently purified by using the nitrous oxide decomposition catalyst of the present invention.

  Further, the nitrous oxide decomposition catalyst of the present invention exhibits high nitrous oxide decomposition performance comparable to conventional nitrous oxide decomposition catalysts using expensive metal components such as noble metals. Therefore, the nitrous oxide decomposition catalyst of the present invention is inexpensive because it does not use expensive metal components such as noble metals.

  The component A constituting the nitrous oxide decomposition catalyst of the present invention is at least one selected from group 2 elements, preferably at least one selected from Mg, Ca, Sr and Ba, more preferably selected from Mg and Ca. At least one kind.

  Further, the component A containing at least one selected from the group 2 elements of the present invention may be contained in the catalyst of the present invention as a simple substance or a compound containing at least one of the elements. An embodiment in which at least one selected from these Group 2 elements is included in the catalyst according to the present invention, that is, the component A is not particularly limited, but is included in the catalyst of the present invention as an oxide, carbonate, sulfate or the like. More preferably it is included. As one of the effects of the A component, it has a function of improving the heat resistance of the catalyst.

  Specific examples of the component A include magnesium oxide, magnesium carbonate, magnesium sulfate, calcium oxide, calcium carbonate, calcium sulfate, strontium oxide, strontium carbonate, strontium sulfate, barium oxide, barium carbonate, and barium sulfate. Of these, magnesium oxide, calcium oxide and calcium carbonate are more preferred, magnesium oxide and carbon calcium are even more preferred, and calcium carbonate is particularly preferred because it is highly effective in improving the heat resistance of the catalyst. Calcium carbonate is relatively stable to heat and is used in the form of calcium carbonate in the catalyst component when used under reaction conditions at a relatively low temperature of about 600 ° C.

  The content of the component A in the catalyst of the present invention is 10 to 89.9% by mass, preferably 50%, based on the oxide of each element, with respect to the total mass (100% by mass) of the nitrous oxide decomposition catalyst. -79.5 mass%. If it is less than 10% by mass, the effect of improving the heat resistance is not sufficient. On the other hand, if it exceeds 89.9% by mass, the content of nickel oxide as the C component is lowered and it is difficult to obtain high nitrous oxide decomposition efficiency. .

  In addition, the “oxide standard” in this specification is an oxide conversion including a monovalent oxide and a divalent oxide, and the same applies to the oxide standards of the B component and the C component described below. is there.

  The B component according to the present invention is at least one selected from Group 3, Group 4 and Group 14 elements, preferably lanthanoid elements (Group 3) such as Y, La, Ce and Nd, Ti, Zr (Group 4), In addition, at least one selected from Si and Sn (group 14), more preferably at least one selected from Y, Ce, La, Zr and Si.

  Further, the B component containing at least one element selected from Group 3, Group 4 and Group 14 elements of the present invention may be included in the catalyst of the present invention as a simple substance or compound containing at least one of the elements. Although the aspect containing at least 1 sort (s) chosen from these 3 group, 4 group, and 14 group elements, ie, B component, is not specifically limited, It is preferable that it is an oxide. The B component has a function of suppressing particle growth of nickel oxide, which is the C component, as one of its effects.

  Specific examples of the component B include yttrium oxide, cerium oxide, lanthanum oxide, zirconium oxide, and silicon oxide.

  Content of B component in the catalyst of this invention is 0.1-30 mass% with respect to the total mass (100 mass%) of the nitrous oxide decomposition catalyst on the oxide basis of each element, preferably 0. .5 to 20% by mass. When the content is less than 0.1% by mass, the particle growth suppressing effect of nickel oxide cannot be obtained sufficiently. Moreover, even if it exceeds 30 mass%, the effect by addition will not be acquired any more.

The C component containing the nickel element of the present invention may be contained in the catalyst of the present invention as nickel alone or as a nickel compound. Specifically, the C component containing the nickel element of the present invention preferably contains nickel oxide (NiO) as a main component, and more preferably nickel oxide. Nickel oxide is NiO, but Ni ₃ O ₄ , NiO ₂ and other nickel oxides may be included as long as the function of NiO is not impaired. Furthermore, nickel oxide may exist as a mixture with other metal oxides, or may form a solid solution or composite oxide with other metals.

  In the present invention, “the main component contains nickel oxide (NiO)” means that nickel oxide (NiO) is included as the main component, and is substantially composed of nickel oxide (NiO). This is a concept including both of NiO). In some cases, an element other than nickel oxide (NiO) may be included in order to improve the characteristics of the catalyst. In addition, being substantially made of nickel oxide (NiO) means that mixing of impurities of about 0.1 to 5% by mass or less is allowed. For example, nickel raw materials for battery materials to which several percent of cobalt, zinc or the like is added are sold, and these can also be used.

  Content of C component in the catalyst of this invention is 10-89.9 mass% with respect to the whole mass (100 mass%) of the catalyst for nitrous oxide decomposition | disassembly as nickel oxide, Preferably it is 20-50 mass% It is. If it is less than 10% by mass, the performance per unit volume of the catalyst will be low, and in order to obtain the prescribed treatment performance, the amount of catalyst used will be undesirably large. Moreover, when it exceeds 89.9 mass%, content of A component will decrease and the effect of heat resistance improvement will no longer be acquired sufficiently.

  Content of A component, B component, and C component in the catalyst of this invention is A component: B component (oxide conversion): C component (oxide conversion) = 10-89.9%: 0 as above-mentioned. 0.1-30%: 10-89.9% (mass) (100% in total).

  The shape of the catalyst of the present invention is not particularly limited and is not particularly limited as long as it is a known shape, and examples thereof include a pellet shape, a powder shape, and a tablet shape.

  The total pore volume of the catalyst according to the present invention is preferably 0.1 to 0.5 cc / g, more preferably 0.15 to 0.4 cc / g, and particularly preferably 0.2 to 0.35 cc / g.

BET specific surface area of the catalyst according to the present invention is preferably 3~200m ² / g, more preferably ^{5~150m 2 / g, 7~50m 2 /} g is particularly preferred.

  Among the catalysts of the present invention containing the A component, B component, and C component, nickel oxide (NiO), which is the C component, even after undergoing a thermal history in the temperature range when treating the nitrous oxide-containing gas. From the standpoints of nitrous oxide decomposition performance and the like, it is preferable that the crystal particles have a small agglomeration, that is, a crystallite diameter of nickel oxide (NiO) is small. Specifically, it is preferable that the crystallite diameter of nickel oxide (NiO) in the component C in the catalyst after thermal aging treatment at 550 to 650 ° C. for 40 to 60 hours is 1 to 50 nm or less, 550 to 600 ° C. More preferably, the crystallite diameter of nickel oxide (NiO) in component C in the catalyst after thermal aging treatment for 40 to 48 hours is from 15 nm to 45 nm.

  The above-mentioned “thermal aging treatment at 600 ° C. for 48 hours” means that the catalyst sample is placed in an electric furnace and subjected to an aging treatment at 600 ° C. for 48 hours in an air atmosphere. After the aging treatment, a sample is taken out, powder X-ray diffraction analysis is performed, and the crystallite diameter of nickel oxide (NiO) is obtained from the diffraction pattern in accordance with Scherrer's formula.

  The catalyst in which the crystallite diameter of nickel oxide after the heat aging treatment is 50 nm or less is obtained, for example, by setting the ratio of the B component and the C component (mass basis of oxide) to 1/99 to 50/50. It is done. Therefore, in the catalyst of the present invention, the mass ratio of B component / C component (as oxide) is preferably 1/99 to 50/50, more preferably 10/90 to 30/70. When the ratio of the B component is small, nickel oxide particle growth is caused under the use conditions, and as a result, the catalyst performance tends to deteriorate. On the other hand, when the proportion of the B component is large, the content ratio of the A component and the C component is reduced, so that the effect of the present invention is hardly obtained.

  Although the preparation process of the catalyst of the present invention is shown below, it is not limited to the following preparation method unless it is contrary to the gist of the present invention.

  A raw material compound (for example, a powdery raw material compound) of component A, component B and component C according to the present invention is mixed with an appropriate amount of water and, if necessary, a molding aid, etc., and molded into a desired shape. Thereafter, drying is performed at 30 to 150 ° C. for 0.1 to 50 hours, and baking is performed in air or in an oxygen atmosphere at 300 to 900 ° C., preferably 400 to 700 ° C. for 1 to 10 hours. At this time, a predetermined amount of water is added to a part of the raw material compounds, for example, the raw material compounds of the B component and the C component (further, if necessary, a molding aid or the like), and after molding into a desired shape, the same as above After preparing a composite containing each element of the B component and the C component by drying and firing under the conditions described above, a predetermined amount of the raw material compound of component A and water is added to the composite, and if necessary, molding aid is added. The catalyst of the present invention may be prepared by adding an agent or the like to form a desired shape and then drying and calcining under the same conditions as described above.

  As described above, since the B component has an effect of suppressing particle growth of nickel oxide, which is an example of the C component, the B component is preferably present in the vicinity of the nickel oxide. Therefore, the raw material compound of component B and the raw material compound of component C are mixed substantially uniformly, or after both solid solutions are prepared, they are mixed with the raw material of component A, and the same method as described above. It is preferably prepared by molding into a desired shape, drying, and firing in the range of 300 to 700 ° C, preferably 400 to 600 ° C.

As described above, it is preferable to combine the raw material compound of the B component and the raw material compound of the C component in advance as a homogeneous mixture or a solid solution. However, in the preparation method of such a composite (for example, composite powder) There is no particular limitation, and generally used physical mixing method, impregnation support method, spray pyrolysis method, coprecipitation method, uniform precipitation method, surface precipitation method, sol-gel method, solid phase reaction method, etc. Can do. Specifically, the following method is exemplified.
(1) Both the raw material compound of component B and the raw material compound of component C are sufficiently mixed in powder form and fired at 700 to 1000 ° C. to prepare a composite (Method 1).
(2) Either a raw material compound of component B or a raw material compound of component C is mixed as a solution and fired at 400 to 800 ° C. to prepare a composite (Method 2).
(3) Both the raw material compound of component B and the raw material compound of component C are mixed as a solution, adjusted to pH 5-9 by addition of alkali or acid, and coprecipitated by hydrolysis reaction. After filtration and washing, the composite is prepared by firing at 400 to 800 ° C. (Method 3).

  The “substantially uniformly mixing” in the present specification is for forming a complex oxide, a dense mixed oxide, or a solid solution, specifically, at least one of the above (Method 1) to (Method 3). One method or a method capable of shear kneading each of the above components, for example, kneading using an extruder, a Banbury mixer, a roller, a kneader, or the like, or a method of firing after the shear kneading, an apparatus for kneading is As long as the above components can be shear kneaded, there is no particular limitation without being limited to the above examples.

  Among these, the method (2) and the method (3) are preferably used. As a raw material for the B component, a water-soluble salt such as chloride, nitrate, acetate, or a sol is used instead of adding as a solid powder such as an oxide, hydroxide, or carbonate of each element. It is preferable to form a uniform mixture, a complex oxide, or a solid solution by compounding.

  In the said method (2) and method (3), 400-800 degreeC is preferable and baking temperature is 500-700 degreeC more preferably. When the firing temperature is less than 400 ° C., it is difficult to obtain the effect of suppressing particle growth. On the other hand, when the firing temperature exceeds 800 ° C., the specific surface area of the resulting composite is undesirably reduced.

  The alkali is not particularly limited, and for example, ammonia or the like can be dissolved in water and used.

  The molding aid according to the present invention is not particularly limited and known ones can be used, and examples thereof include organic binders such as polyvinyl alcohol, polyethylene glycol, methyl cellulose, glycerin, and starch.

  The raw material compound of component A according to the present invention forms nitrates, chlorides, hydroxides, and acetates of each element (that is, at least one element selected from group 2 elements) in the catalyst preparation step. Any of these can be used, and nitrates, chlorides, hydroxides, acetates, and the like of the respective elements can be used. For example, nitrates and chlorides may be hydrolyzed to form hydroxides, or added as they are and converted to oxides by heat treatment in the catalyst component preparation step. Further, a compound that is present as a precursor at the time of preparation of the catalyst component and becomes an oxide in the environment in which the catalyst component is used, for example, can also be used as a raw material compound of the component A. Specific examples include magnesium oxide, magnesium carbonate, magnesium sulfate, calcium oxide, calcium carbonate, calcium sulfate, strontium oxide, strontium carbonate, strontium sulfate, barium oxide, barium carbonate, and barium sulfate. May be used. Further, the compound of the raw material of the component A according to the present invention is preferably added in an amount of 10 to 89.9% by weight, assuming that the total of the raw material compounds of the component A, the component B and the component C is 100% by weight. It is more preferable to add ~ 79.5 mass%.

  In the catalyst preparation step, the compound of the raw material of the component B according to the present invention is carbonate, water, in addition to the oxide of each element (at least one element selected from group 3, group 4 and group 14 elements). Any of oxides, chlorides, nitrates, sulfates, acetates, and precursors of oxides such as sols can be used as long as they can become oxides in the catalyst preparation step. Specifically, yttrium oxide, cerium oxide, lanthanum oxide, zirconium oxide and silicon oxide, lanthanum nitrate hexahydrate, zirconium oxynitrate dihydrate, silica sol (Nissan Chemical Industry Co., Ltd. Snowtex S), cerium nitrate Hexahydrate may be mentioned, and a commercially available product may be used. Moreover, the compound of the raw material of B component which concerns on this invention shall add 0.1-30 mass% in conversion of an oxide, when the sum total of the compound of the raw material of A component, B component, and C component shall be 100 mass%. It is more preferable to add 0.5 to 20% by mass.

  In addition to nickel oxide, any compound that can be converted to nickel oxide in the catalyst preparation step can be used as the raw material compound of component C according to the present invention. For example, nickel carbonate, nickel nitrate, nickel chloride, nickel hydroxide, nickel acetate, etc. can be used, and commercially available ones may be synthesized and used.

  Moreover, the compound of the raw material of C component which concerns on this invention shall add 10-89.9 mass% in conversion of an oxide, when the sum total of the compound of the raw material of A component, B component, and C component is 100 mass%. It is preferable to add 20 to 50% by mass.

  In addition, the shape of the raw material compounds of the A component, B component, and C component according to the present invention is not particularly limited, and it is possible to use known materials such as powder, particles, pellets, and tablets. it can.

  The nitrous oxide decomposition catalyst used in the present invention contains an A component, a B component, and a C component as catalyst components, and the catalyst components are extruded into pellets and honeycombs as they are to form a tertiary. An original structure may be used, and the catalyst component may be applied and supported on a fire-resistant three-dimensional structure. That is, the catalyst according to the present invention contains the catalyst component composed of the A component, the B component, and the C component according to the present invention, and includes a refractory three-dimensional structure and a refractory inorganic oxide. But you can.

  The shapes of the catalyst and the fire-resistant three-dimensional structure of the present invention are not particularly limited, and can be appropriately selected from a cylindrical shape, a ring shape, a spherical shape, a plate shape, a honeycomb shape, and other integrally formed shapes. The catalyst and the fire-resistant three-dimensional structure can be molded by a general molding method such as a tableting molding method or an extrusion molding method. In the case of a spherical catalyst, the average particle diameter is usually 1 to 10 mm. In the case of a honeycomb-shaped catalyst, it is the same as a so-called monolith structure, and is manufactured by an extrusion molding method or a method of winding up a sheet-like element. The shape of the gas passage port (cell shape) may be hexagonal, quadrangular, triangular or corrugated. The cell density (number of cells / unit cross section) is usually 25 to 800 cells / in 2 (× 2.5 cm).

  Further, the catalyst of the present invention may be used by being supported on a refractory inorganic oxide having a predetermined shape appropriately selected from the above shapes. As this refractory inorganic oxide, it is generally used for the preparation of this type of catalyst. For example, in addition to silica, alumina, zirconia, titania, etc., a composite oxidation composed of two or more of Si, Ti, Zr, etc. Things can be used.

  Examples of the fire-resistant three-dimensional structure covering the catalyst component include a heat-resistant three-dimensional structure such as a honeycomb structure, but an integrally formed honeycomb structure is preferable. For example, a monolith honeycomb structure, a metal honeycomb structure In addition, a plug honeycomb structure and the like, and a pellet structure and the like can also be used instead of a three-dimensional integrated structure.

  As the monolith structure, what is usually referred to as a ceramic honeycomb structure may be used. A honeycomb structure made of magnesium silicate or the like is preferable, and cordierite is particularly preferable. In addition, an integrated structure using an oxidation-resistant heat-resistant metal such as stainless steel or Fe—Cr—Al alloy is used.

  The catalyst of the present invention is suitable for use at a reaction temperature in the range of 250-900 ° C, preferably 350-700 ° C, more preferably 400-600 ° C. That is, the nitrous oxide decomposition catalyst of the present invention exhibits high nitrous oxide decomposition performance in a relatively low temperature range of 250 to 900 ° C. By using the catalyst of the present invention, nitrous oxide can be effectively decomposed even at a relatively low temperature of 500 ° C. or less without using an expensive platinum group metal. In addition, a normal nickel oxide catalyst has a problem in heat resistance, and under the use conditions as described above, particle growth occurs and causes significant thermal degradation. In the catalyst of the present invention, such particles Growth can be effectively suppressed.

  The “48 ° C. thermal aging treatment at 600 ° C.” of the present invention takes into account accelerated endurance conditions assuming a tail gas treatment of a nitric acid plant, particularly at a reaction temperature of 350 to 500 ° C. If the crystallite diameter of nickel oxide (NiO) after the aging treatment is 50 nm or less, excellent low-temperature activity comparable to that of a platinum-based catalyst can be maintained.

  The method for treating a nitrous oxide-containing gas of the present invention is to decompose and remove nitrous oxide in the nitrous oxide-containing gas using the nitrous oxide decomposition catalyst of the present invention described above.

  As the nitrous oxide-containing gas according to the present invention, from a fixed combustion apparatus such as a fluidized bed boiler, a sewage sludge incinerator, a transportation vehicle such as a passenger car or a truck, and a chemical plant that produces adipic acid, glyoxal, nitric acid, etc. Examples include nitrous oxide-containing gas that is discharged.

The gas concentration of nitrous oxide in the nitrous oxide-containing gas according to the present invention is usually 0.01 to 10% by volume, preferably 0.02 to 0.5% by volume. The nitrous oxide-containing gas, as a component other than nitrous oxide, nitrogen, oxygen, carbon dioxide, carbon monoxide, water, hydrogen, _{ammonia, NOx (NO, NO 2)} , also include such SOx Good.

The method for treating a nitrous oxide-containing gas according to the present invention directly decomposes nitrous oxide into nitrogen and oxygen without adding a reducing agent such as hydrocarbon, carbon monoxide, hydrogen or ammonia. A nitrous oxide-containing gas can be treated. The reaction temperature is 250 to 900 ° C, preferably 350 to 700 ° C, more preferably 400 to 600 ° C. The space velocity (SV) is 1,000 to 50,000 hr ⁻¹ , preferably 2,000 to 20,000 hr ⁻¹ . Furthermore, the reaction pressure is 1 to 40 bar, preferably 1 to 20 bar.

The nitrous oxide decomposition catalyst of the present invention exhibits excellent nitrous oxide decomposition performance even in the presence of NOx (NO, NO ₂ ). Therefore, according to the treatment method of the present invention, nitrous oxide in a gas containing NOx (NO, NO ₂ ) together with nitrous oxide can be efficiently decomposed and removed. Conventional nitrous oxide decomposition catalysts are known to degrade nitrous oxide decomposition performance when NOx coexists, and usually a method of treating nitrous oxide after removing NOx in the pretreatment is selected. It was. Although the cause of the degradation of nitrous oxide decomposition performance in the presence of NOx is not clear, reaction inhibition due to the difference in adsorption / desorption rate, nitrous oxide byproduct derived from NOx, and the like are considered.

  In general, the higher the temperature of the nitrous oxide decomposition reaction is, the more the reaction is promoted. On the other hand, the selective denitration reaction of NOx with ammonia becomes disadvantageous as the temperature increases, and therefore, the treatment is performed at 400 ° C. or lower, preferably 300 ° C. or lower. . Therefore, the conventional method of treating nitrous oxide after removing NOx in the previous stage is not preferable in terms of heat efficiency. For example, when applied to tail gas of a nitric acid plant, the temperature of the exhaust gas at 500 ° C. is cooled to a temperature suitable for the denitration reaction and then raised again to a temperature suitable for the nitrous oxide decomposition reaction. It is a typical processing method. On the other hand, when the catalyst of the present invention is used, NOx can be removed after nitrous oxide is decomposed, so that exhaust gas containing nitrous oxide and NOx can be treated efficiently and efficiently.

Accordingly, one of the methods for treating a nitrous oxide-containing gas of the present invention is to bring exhaust gas containing nitrous oxide and NOx (NO, NO ₂ ) into contact with the catalyst component or catalyst of the present invention, It is preferable to include a step of decomposing nitrous oxide, and then a step of adding ammonia or urea to the treated gas to decompose and remove remaining NOx (NO, NO ₂ ) (denitration treatment). The temperature in the nitrous oxide decomposition step is 250 to 900 ° C, preferably 350 to 700 ° C, more preferably 400 to 600 ° C, and the temperature of the denitration treatment step is 150 to 500 ° C, preferably 200 to 450 ° C. More preferably, it is 250-350 degreeC.

The concentration ratio between NO and NO ₂ in the exhaust gas is not particularly limited, and is a NOx concentration of 0.0001 to 0.5% by volume, preferably 0.3% by volume or less.

  The denitration treatment step can be performed under conditions generally used for denitration treatment. The amount of ammonia to be added can be appropriately selected within a molar ratio of ammonia / NOx of 0.3 / 1 to 3/1, preferably 0.5 / 1 to 1.5 / 1. The amount of urea added is preferably ½ of the number of moles of ammonia. As the denitration catalyst, a combination of a carrier component such as titania, alumina, silica, or zeolite and an oxide such as V, Cu, W, Mo, or Fe can be used.

The method for treating a nitrous oxide-containing gas of the present invention is suitable for treating tail gas of a nitric acid production plant, for example. In the production of nitric acid, a process is known in which the raw material ammonia is contact oxidized at a high temperature of 850 ° C. or more to form NO, and further oxidized and converted to NO ₂ , and then absorbed into water by an absorption tower to produce nitric acid. Yes. The tail gas of the nitric acid plant is a gas after the nitric acid is absorbed, and the tail gas is discharged to the outside air through the expansion turbine. Nitrous oxide is by-produced when ammonia is oxidized at high temperatures. The typical composition of the tail gas of the nitric acid plant is 0.03 to 0.35% by volume of nitrous oxide, 0.01 to 0.35% by volume of NOx, 1 to 4% by volume of oxygen, and 0% of water. 3 to 2% by volume. The tail gas has a gas temperature of 350 to 500 ° C. and a pressure of 4 to 11 bar by process heat exchange before the expansion turbine.

The invention is further illustrated by the following examples, which illustrate advantageous embodiments of the invention.
Example 1
A solution obtained by dissolving 64 g of lanthanum nitrate hexahydrate in 150 g of water was added to and mixed with 400 g of nickel carbonate, dried at 150 ° C. for 10 hours, and then calcined at 600 ° C. for 5 hours in an air atmosphere to prepare B component / C A powdery composite (a) having a component mass ratio (as oxide) of 10/90 was obtained. 200 g of the obtained composite (a) and 800 g of magnesium oxide were mixed with a kneader while adding an appropriate amount of water and a molding aid (starch), and then pellets having a diameter of 5 mm and a length of 5 mm by an extruder. And then dried at 150 ° C. for 3 hours and then calcined at 500 ° C. for 2 hours in an air atmosphere to obtain a catalyst (1). The composition of the pellet-shaped catalyst (1) was A component / B component / C component (MgO / La ₂ O ₃ / NiO) = 80: 2: 18 (mass%).
(Example 2)
A solution obtained by dissolving 297 g of cerium nitrate hexahydrate in 300 g of water was added to and mixed with 600 g of nickel hydroxide, dried at 150 ° C. for 10 hours, and then calcined at 600 ° C. for 5 hours in an air atmosphere. A powdery composite (b) having a component mass ratio (as oxide) of 20/80 was obtained. 500 g of the obtained composite (b) and 500 g of calcium carbonate were mixed with an appropriate amount of water and a molding aid (starch) and mixed for ○ to ○ hours with a kneader, and then 5 mm in diameter and long with an extruder. The catalyst was molded into a 5 mm thick pellet, dried at 150 ° C. for 3 hours, and calcined at 500 ° C. for 2 hours in an air atmosphere to obtain a catalyst (2). The composition of the pellet-shaped catalyst (2) was A component / B component / C component (CaCO ₃ / CeO ₂ / NiO) = 50: 10: 40 (mass%).
(Examples 3 to 5)
In Example 2, catalysts (3) to (5) having the compositions shown in Table 1 were obtained in the same manner as in Example 2 except that the mixing ratio of each component was changed.
(Examples 6 and 7)
In Example 2, catalysts (6) and (7) having the compositions shown in Table 1 were obtained in the same manner as in Example 2 except that the firing temperature of the composite (b) was changed to 400 ° C and 700 ° C. .
(Example 8)
In Example 4, a catalyst (8) having the composition shown in Table 1 was prepared in the same manner as in Example 4 except that silica sol (Snowtex S manufactured by Nissan Chemical Industries, Ltd.) was used instead of cerium nitrate hexahydrate. Obtained.
Example 9
In Example 2, a catalyst (9) having the composition shown in Table 1 was obtained in the same manner as in Example 2, except that zirconium oxynitrate dihydrate was used instead of cerium nitrate hexahydrate.
(Example 10)
800 g of nickel nitrate hexahydrate and 58 g of cerium nitrate hexahydrate were dissolved in 2000 g of water and ammonia water was gradually added dropwise with stirring to adjust pH = 8 and left as it was overnight. Next, the precipitate is filtered and washed, dried at 150 ° C. for 10 hours, and calcined at 700 ° C. for 5 hours to obtain a powdery composite (c) having a B component / C component mass ratio (as oxide) of 10/90. Obtained. Thereafter, a catalyst (10) having the composition shown in Table 1 was obtained in the same manner as in Example 4.
(Examples 11 and 12)
A catalyst (11) and a catalyst (12) having the compositions shown in Table 1 were obtained in the same manner as in Example 10 except that the composite was prepared by changing the mass ratio of the B component / C component in Example 10. .
(Comparative Example 1)
A mixture of nickel nitrate hexahydrate dissolved in water and aluminum oxide (α-Al ₂ O ₃ ) was mixed well with a kneader while adding an appropriate amount of molding aid (starch), and then an extruder. Were formed into pellets having a diameter of 5 mm and a length of 5 mm, dried at 150 ° C. for 3 hours, and then calcined at 500 ° C. for 2 hours in an air atmosphere to obtain a comparative catalyst (1). The composition of this comparative catalyst (1) was Al ₂ O ₃ / NiO = 80: 20 (mass%).
(Comparative Example 2)
In Comparative Example 1, a comparative catalyst (2) having the composition shown in Table 1 was prepared in the same manner as in Comparative Example 1 except that powder obtained by firing nickel carbonate at 450 ° C. was used instead of nickel nitrate hexahydrate. Obtained.
(Comparative Example 3)
In Comparative Example 2, a comparative catalyst (3) having the composition shown in Table 1 was obtained in the same manner as in Comparative Example 2 except that calcium carbonate was used instead of aluminum oxide. This comparative catalyst (3) consists of an A component and a C component, and lacks a B component.
(Comparative Examples 4 and 5)
In Comparative Example 1, comparative catalysts (4) and (5) having the compositions shown in Table 1 were prepared in the same manner as in Comparative Example 2, except that an aqueous rhodium nitrate solution or an aqueous palladium chloride solution was used instead of nickel nitrate hexahydrate. Obtained.
(Measurement of crystallite diameter)
The catalysts (1) to (12) and the comparative catalysts (1) to (3) were subjected to thermal aging treatment in an electric furnace at 600 ° C. for 48 hours in an air atmosphere, and then nickel oxide crystals were obtained by X-ray diffraction. The child diameter was measured. The crystallite size of the new catalyst before heat aging was measured in the same manner and the results are shown in Table 1.
(Performance evaluation method)
120 ml of the catalysts (1) to (12) were filled in a glass reaction tube having an inner diameter of 30 mm. A synthesis gas having the following composition was introduced into the catalyst layer under the following conditions.
<Syngas composition>
Nitrous oxide (N ₂ O): 1000 ppm, oxygen (O ₂ ): 3% by volume, water (H ₂ O): 1% by volume, remaining: nitrogen (N ₂ )
<Reaction conditions>
Treatment temperature: 500 ° C., reaction pressure: 5 bar, space velocity (SV): 2500 hr ⁻¹
One hour after the synthesis gas was introduced, the concentration of nitrous oxide (N ₂ O) in the synthesis gas at the inlet and outlet of the catalyst layer was measured using a non-dispersive infrared N ₂ O meter (Nippon Thermo Electron Co., Ltd.). Manufactured, Model 46C-HL), and the N ₂ O removal rate was calculated according to the following formula. The results are shown in Table 1.

  Similarly, for a catalyst heat-treated at 600 ° C. for 48 hours in an electric furnace, the treatment performance was measured under the above reaction conditions, and the results are shown in Table 1.

  The catalysts (1) to (12) of the present invention have superior performance after a new product and after heat treatment accelerated aging, as compared with the comparative catalysts (1) to (3). In addition, the performance is comparable to the comparative catalysts (4) and (5), which are expensive platinum group catalysts.

  Next, the catalysts (2) to (4) and the comparative catalysts (4) and (5) coexist in the same manner except that 500 ppm of nitrogen oxide (NO) was added to the synthesis gas under the above reaction conditions. The lower nitrous oxide decomposition performance was measured and the results are shown in Table 2. The catalysts (2) to (4) of the present invention have better nitrous oxide decomposition performance even in the presence of NOx as compared with the comparative catalysts (4) and (5).

  Note that this application is based on Japanese Patent Application No. 2006-349135 filed on Dec. 26, 2006, the disclosure of which is incorporated by reference in its entirety.

  The catalyst for decomposing nitrous oxide and the method for treating a nitrous oxide-containing gas of the present invention can be used to remove nitrous oxide discharged from a combustion plant such as a sludge incinerator or a chemical plant such as a nitric acid production process. it can.

Claims (7)

  A catalyst component comprising an A component containing at least one selected from Group 2 elements, a B component containing at least one selected from Group 3, 4 and 14 elements, and a C component containing nickel elements Containing nitrous oxide decomposition catalyst.   The crystallite diameter of nickel oxide (NiO) in the component C in the catalyst after the nitrous oxide decomposition catalyst is thermally aged at 550 to 650 ° C. for 40 to 60 hours is 1 nm to 50 nm. Item 2. The catalyst for nitrous oxide decomposition according to Item 1.   3. The nitrous oxide decomposition catalyst according to claim 1, wherein a mass ratio (based on oxide) of the B component / the C component is 1/99 to 50/50.   The sub-component according to claim 1, 2 or 3, wherein the B component raw material compound and the C component raw material compound are mixed substantially uniformly and then added to the A component raw material compound. Nitrogen oxide decomposition catalyst.   A method for treating a nitrous oxide-containing gas, wherein the nitrous oxide-containing gas is treated using the nitrous oxide decomposition catalyst according to claim 1. The method for treating a nitrous oxide-containing gas according to claim 5, wherein the nitrous oxide-containing gas is a gas containing NO and NO ₂ in addition to N ₂ O.   In treating the nitrous oxide-containing gas, the gas is treated with the nitrous oxide decomposition catalyst according to any one of claims 1 to 4, and then ammonia or urea is added to the treated gas. The method for treating a nitrous oxide-containing gas according to claim 5 or 6, wherein a denitration treatment is performed.