WO2013047484A1 - Catalyst for decomposition of nitrous oxide, method for producing catalyst for decomposition of nitrous oxide, and method for processing nitrous oxide-containing gas - Google Patents

Abstract

Provided is a catalyst for decomposition of nitrous oxide, which is highly active at low temperatures and is capable of efficiently decomposing and removing nitrous oxide without being affected by nitrogen oxide or carbon dioxide even in cases where the nitrogen oxide or the carbon dioxide is contained in a gas to be processed. A catalyst for decomposition of nitrous oxide of the present invention contains a cobalt oxide as a catalyst component A and a compound of at least one metal element as a catalyst component B. This catalyst for decomposition of nitrous oxide is characterized in that: the atomic ratio of the catalyst component B to the catalyst component A is from 0.0005 to 0.15; and the melting point of an oxide of the metal element is within the range from 200˚C to 1,000˚C and/or the ionic radius of the metal element of the catalyst component B is within the range from 0.90Å to 1.88Å.

Description

Nitrous oxide decomposition catalyst, method for producing nitrous oxide decomposition catalyst, and method for treating nitrous oxide-containing gas

The present invention provides a catalyst for nitrous oxide decomposition that exhibits high activity even at low temperatures and is less susceptible to the influence of NO and NO ₂ contained in a nitrous oxide-containing gas, and the production of the nitrous oxide decomposition catalyst The present invention relates to a method and a method for treating a nitrous oxide-containing gas.

Nitrous oxide (N ₂ O) contained in various combustion exhaust gases discharged from power generation gas turbines, boilers, waste incinerators, etc. and various industrial exhaust gases discharged from chemical plants, etc. is about 310 times that of carbon dioxide. Since the greenhouse effect is exhibited, the development of an efficient decomposition and removal method is desired.

As a method for decomposing and removing nitrous oxide by contacting it with a catalyst, a method using a catalyst in which ruthenium and / or rhodium and zirconium oxide are supported on hydrophobic alumina (Patent Document 1), rhodium oxide, cobalt trioxide (Co) _A method using a catalyst containing ₂ O ₃ ), a manganese compound, and an alkali or alkaline earth metal compound (Patent Document 2) has been proposed. In these conventional techniques, nitrous oxide is treated at a low temperature. Therefore, it was necessary to use an expensive noble metal such as rhodium.

On the other hand, Patent Document 3 proposes a catalyst containing tribasic cobalt oxide (Co ₃ O ₄ ) as a main component and containing an alkali metal and / or an alkaline earth metal. The catalyst disclosed in Patent Document 3 can decompose and remove nitrous oxide at a relatively low temperature without supporting an expensive noble metal. However, it has been found that the catalyst of Patent Document 3 has a problem in practicality because it may cause a rapid deterioration in performance due to poisoning substances contained in the processing gas.

JP-A-6-142517 Japanese Patent Laid-Open No. 6-106027 JP 2007-54717 A

An object of the present invention is to efficiently decompose and remove nitrous oxide at a low temperature without supporting an expensive noble metal, to have a highly durable nitrous oxide decomposition catalyst, a method for producing the catalyst, and nitrous oxide to the catalyst. An object of the present invention is to provide a method for treating a nitrous oxide-containing gas, which efficiently decomposes and removes nitrous oxide by contacting a gas containing nitrous acid.

As a result of diligent research to achieve the above-mentioned object, the present inventors have determined that suboxidation in which cesium and / or rubidium are blended at a specific molar ratio with cobalt oxide as a catalyst with almost no performance degradation in the presence of carbon dioxide. A nitrogen decomposition catalyst has already been filed (Japanese Patent Application No. 2010-198073). However, this catalyst easily deteriorates in performance when NO or NO ₂ coexists in the nitrous oxide-containing gas, and there is still a problem in using it for a long period of time. As a result of further investigation, the activity of the nitrous oxide decomposition catalyst containing cobalt oxide as the main component has a high correlation with the melting point of the oxide of the metal element added as the second component, and the composition should be further optimized. It has been found that the durability is remarkably improved.

That is, a catalyst for decomposing nitrous oxide containing a cobalt oxide as the catalyst A component and at least one metal element compound selected from the group consisting of groups 5 to 15 as the catalyst B component (hereinafter referred to as the first nitrous oxide decomposition). The atomic ratio of the catalyst B component to the catalyst A component is 0.0005 to 0.15, and the melting point of the oxide of the metal element that is the catalyst B component is 200 to 1000 ° C. A catalyst for nitrous oxide decomposition was found.

Further, the first nitrous oxide decomposition catalyst is a metal salt containing cobalt carbonate as a raw material for the catalyst A component cobalt oxide and at least one metal element selected from the group consisting of groups 5 to 15 as the catalyst B component. It is preferable to manufacture by mixing aqueous solution, drying, and baking.

In addition, the inventors of the present invention have a high correlation between the activity of the nitrous oxide decomposition catalyst mainly composed of cobalt oxide and the ionic radius of the metal element added as the second component, and further by optimizing the composition. It was also found that the durability was remarkably improved. *

That is, a catalyst for decomposing nitrous oxide containing a compound of cobalt oxide as the catalyst A component and a compound of at least one metal element selected from the group consisting of groups 2 to 3 and 11 to 15 as the catalyst C component (hereinafter referred to as second catalyst). The atomic ratio of the catalyst C component to the catalyst A component is 0.0005 to 0.15, and the ionic radius of the metal element of the catalyst C component is 0.90 to A nitrous oxide decomposition catalyst characterized by being in the range of 1.88 kg was also found.

Further, the second nitrous oxide decomposition catalyst is at least one metal element selected from the group consisting of cobalt carbonate as a raw material for catalyst A component cobalt oxide and catalyst C component from groups 2 to 3 and 11 to 15 It is preferable to manufacture by mixing a metal salt aqueous solution containing, drying and firing.

Further, the method for treating a nitrous oxide-containing gas of the present invention treats the nitrous oxide-containing gas using the first or second nitrous oxide decomposition catalyst, and the treatment gas is NO and / or NO. ₂ (hereinafter may be referred to as nitrogen oxide or NOx) and carbon dioxide are also applicable.

The first and second nitrous oxide decomposition catalysts in the present invention exhibit high activity at low temperatures, and even when nitrogen oxides or carbon dioxide are contained in the processing gas, they are not affected by the nitrous oxide. Can be efficiently decomposed and removed. Therefore, by using the first and second nitrous oxide decomposition catalysts in the present invention, nitrous oxide contained in various exhaust gases can be efficiently and stably treated over a long period of time.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and various modifications can be made without departing from the scope of the present invention. .

First, the first nitrous oxide decomposition catalyst will be described.

The first nitrous oxide decomposition catalyst contains a cobalt oxide as the catalyst A component and a compound of at least one metal element selected from the group consisting of Groups 5 to 15 as the catalyst B component. A catalyst for nitrous oxide decomposition, wherein the atomic ratio of the components is 0.0005 to 0.15, and the melting point of the oxide of the metal element that is the catalyst B component is in the range of 200 to 1000 ° C. is there.

The atomic ratio of the catalyst B component to the catalyst A component is 0.0005 to 0.15, preferably 0.005 to 0.10, more preferably 0.01 to 0.05. The cobalt oxide as the catalyst A component is a main component, and good low-temperature activity can be exhibited by firing at a temperature close to the oxide melting point of the metal element added as the catalyst B component. When the atomic ratio exceeds 0.15, the content of cobalt oxide in the catalyst decreases, so that the initial activity and long-term durability may not be sufficiently obtained. On the other hand, when the atomic ratio is less than 0.0005, the effect of adding the catalyst B component is weakened, and the reaction rate at a low temperature is remarkably reduced. Details of the catalyst A component will be described later.

The catalyst B component is a compound of at least one metal element selected from the group consisting of groups 5 to 15, and the oxide melting point of the metal element is in the range of 200 to 1000 ° C. A more preferable oxide melting point is in the range of 300 to 800 ° C., and further preferably in the range of 350 to 700 ° C. When the melting point of the oxide is less than 200 ° C., it is easy to sinter by heat load, and there is a problem in heat resistance. When the melting point of the oxide exceeds 1000 ° C., the effect of the present invention by adding the catalyst B component cannot be obtained.

In the group 5-15 metal element compound as the catalyst B component, the oxides whose melting point is in the above range are the group 5 vanadium oxide (V ₂ O ₅ ), the group 6 molybdenum oxide (MoO ₃ ). , Group 7 manganese oxide (MnO ₂ ), Group 10 palladium oxide (PdO), Group 11 silver oxide (Ag ₂ O), Group 12 cadmium oxide (CdO), Group 14 lead oxide (PbO), 15 Group antimony oxide (Sb ₂ O ₃ ), bismuth oxide (Bi ₂ O ₃ ), and the like. Further, since the melting point of the oxide varies depending on the valence of the oxide, an optimum raw material having the melting point of the oxide within the above range is selected and used.

Note that oxides of alkali metals belonging to Group 1 such as cesium oxide (Cs ₂ O), potassium oxide (K ₂ O), rubidium oxide (Rb ₂ O) also have an oxide melting point within the above range. Although the improvement in low-temperature activity can be obtained also for a catalyst obtained by adding a group III metal element compound as a catalyst B component, if nitrogen oxides or carbon dioxide coexists in the processing gas, the catalyst B component of the present invention is rapidly deteriorated. Group 1 alkali metals are excluded. On the other hand, a catalyst in which a compound of a metal element of Group 5 to 15 is added as a catalyst B component has little influence even when nitrogen oxides or carbon dioxide coexists, and good durability can be obtained. As a more preferable catalyst B component, it is preferable to use a compound of a metal element such as group 14 Pb, group 15 Sb, or Bi having a relatively high oxide melting point. In particular, Bi and Pb are metal elements preferable as the catalyst B component because they have high low temperature activity and excellent durability.

Next, the second nitrous oxide decomposition catalyst will be described.

The second nitrous oxide decomposition catalyst contains a cobalt oxide as the catalyst A component and a suboxide containing at least one compound of a metal element selected from the group consisting of groups 2 to 3 and 11 to 15 as the catalyst C component. A catalyst for nitrogen decomposition, wherein the atomic ratio of the catalyst C component to the catalyst A component is 0.0005 to 0.15, and the ionic radius of the metal element of the catalyst C component is 0.90 to 1.88% It is a catalyst for nitrous oxide decomposition characterized by the above.

The atomic ratio of the catalyst C component to the catalyst A component is 0.0005 to 0.15, preferably 0.005 to 0.10, more preferably 0.01 to 0.05. The cobalt oxide which is the catalyst A component is a main component, and the better low temperature activity can be expressed as the ionic radius of the metal element added as the catalyst C component increases. When the atomic ratio exceeds 0.15, the content of cobalt oxide in the catalyst decreases, so that the initial activity and long-term durability may not be sufficiently obtained. On the other hand, when the atomic ratio is less than 0.0005, the effect of adding the catalyst C component is weakened and the reaction rate at a low temperature is remarkably reduced. Details of the catalyst A component will be described later.

The catalyst C component is a compound of at least one metal element selected from the group consisting of groups 2 to 3 and groups 11 to 15 in the periodic table, and has an ionic radius in the range of 0.90 to 1.88%. A more preferable ionic radius is in the range of 0.95 to 1.65 Å, and still more preferably in the range of 1.00 to 1.50 Å. There is no metal element having an ionic radius exceeding 1.88%, and when it is less than 0.90%, the effect of addition is rapidly weakened, and the low-temperature activity improvement is insufficient.

As the metal element of the catalyst C component in the range of the ionic radius, lanthanoids such as Group 2 Ca, Sr, Ba, Group 3 La, Ce, Nd, Y, Group 11 Ag, Group 12 Cd, Group 13 Tl, Group 14 Pb, Group 15 Bi, and the like are preferable.

Cs and Rb are typical metal elements having a large ion radius. Although improvement in low-temperature activity is also obtained for a catalyst obtained by adding a group 1 alkali metal having K and Na to these two elements and having an ionic radius within the scope of the present invention as a catalyst C component, nitrogen oxides are contained in the process gas. Since coexistence of carbon dioxide and carbon dioxide causes a rapid decrease in performance, group 1 alkali metals are excluded from the catalyst component C of the present invention. On the other hand, a catalyst to which a compound containing a metal element other than an alkali metal is added as a catalyst C component has little influence even when nitrogen oxides or carbon dioxide coexists, and good durability can be obtained. As a more preferable metal element of the catalyst C component, it is preferable to use a metal element such as Ag, Pb, or Bi of Group 11 to Group 15, which is lower in basicity than Group 2 and Group 3 metal elements. In particular, Group 14 Pb and Group 15 Bi have high low-temperature activity and excellent durability, and are preferred metal elements for the catalyst C component.

Hereinafter, common items in the first nitrous oxide decomposition catalyst and the second nitrous oxide decomposition catalyst will be described.

The cobalt oxide as the catalyst A component is preferably cobalt trioxide (Co ₃ O ₄ ), but may contain CoO or Co ₂ O ₃ depending on the cobalt raw material and the catalyst preparation method. . In addition to the above-mentioned cobalt oxides that are commercially available, cobalt nitrate, cobalt chloride, cobalt acetate, cobalt carbonate, basic cobalt carbonate (xCoCO ₃ · yCo (OH) ₂ ), cobalt hydroxide and the like are calcined. What forms a cobalt oxide by this can be used. A particularly preferable cobalt raw material is cobalt carbonate (including basic cobalt carbonate).

As raw materials for the catalyst B component or the catalyst C component, oxides, nitrates, sulfates, chlorides, acetates, carbonates, hydroxides, and the like of each metal element can be used. Depending on the raw material of the catalyst, the production method, the production conditions such as the calcination temperature, the form of the compound of the metal element that is the catalyst B component or the catalyst C component after catalysis is different and may be an oxide of the metal element. Although it is particularly preferable, a part or most of it may be present as the starting compound. Note that since the oxide melting point varies depending on the valence of the oxide, an optimal raw material having an oxide melting point within the above range is selected and used as the catalyst B component. In addition, since the ionic radius also varies depending on the valence and coordination number of the metal salt used as the raw material, an optimal raw material having an ionic radius within the above range is selected and used as the catalyst C component.

Further, in the first and second nitrous oxide decomposition catalysts in the present invention, in the diffraction pattern measured by the powder X-ray diffraction method, the oxide of cobalt as the catalyst A component is cobalt trioxide (Co ₃ O _4). It is preferable that a diffraction peak derived from a single oxide of the catalyst B component or the catalyst C component is not detected. Thus, the diffraction peak derived from the single oxide of the catalyst B component or the catalyst C component is not detected because the catalyst B component or the catalyst C component is located in the vicinity of the main component cobalt oxide (that is, cobalt tetroxide). The oxide may exist as amorphous fine particles, or may form a solid solution by dissolving with cobalt oxide. In particular, it is preferable that the catalyst A component and the catalyst B component or the catalyst C component form a solid solution. In the diffraction pattern measured by the powder X-ray diffraction method, the formation of a solid solution can be confirmed by the peak being shifted to the low angle side or the high angle side from the diffraction peak position of cobalt tetroxide. The diffraction peak position is preferably 0.01 to 0.10 degree in 2θ, more preferably 0.02 to 0.06 degree, and is shifted to the low angle side or the high angle side. When the ionic radius of the catalyst B component or the catalyst C component is larger than the ionic radius of cobalt which is the catalyst A component, the diffraction peak of the solid solution shifts to the low angle side, and when the ionic radius is smaller than cobalt, it shifts to the high angle side. .

The shape of the first and second nitrous oxide decomposition catalysts in the present invention is not particularly limited, and may be appropriately selected from a cylindrical shape, a ring shape, a spherical shape, a plate shape, a honeycomb shape, and other integrally formed ones. Can do. The catalyst can be molded by a general molding method such as a tableting method or an extrusion method. In the case of a spherical shape, the average particle diameter is usually 1 to 10 mm. In the case of a honeycomb shape, it is manufactured by an extrusion molding method or a method of winding a sheet-like element, and the shape of the gas passage port (cell shape) may be any of a hexagon, a tetragon, a triangle, or a corrugation. . The cell density (number of cells / unit cross section) is usually 25 to 800 cells / in 2. The catalyst component may be extruded or supported on a ceramic carrier such as cordierite having a predetermined shape or a metal carrier.

Next, a typical production method of the first and second nitrous oxide decomposition catalysts in the present invention will be described below, but the present invention is not limited to the following production methods unless contrary to the gist of the present invention.

First, a method for producing the first nitrous oxide decomposition catalyst will be described below.

The first method for producing a nitrous oxide decomposition catalyst is selected from the group consisting of cobalt carbonate (including basic cobalt carbonate) as a raw material for catalyst A component cobalt oxide and group 5 to 15 as a raw material for catalyst B component. It is manufactured by thoroughly mixing an aqueous metal salt solution of at least one metal element, drying it, and firing it. By using this production method, it is possible to form a solid solution relatively easily without using complicated production processes such as a coprecipitation method and using simple production equipment.

The drying conditions are not particularly limited, but it is preferable that the drying temperature is 80 to 200 ° C. and the drying time is 1 to 20 hours in consideration of productivity. If the drying temperature is less than 80 ° C. or the drying time is less than 1 hour, drying may be insufficient and the catalyst performance may be adversely affected. Moreover, it is not preferable from a viewpoint of energy efficiency or production efficiency to make a drying temperature higher than 200 degreeC, or to make drying time longer than 20 hours.

The firing conditions can be appropriately changed depending on the method for producing the catalyst, and are not particularly limited. However, firing is preferably performed at 200 to 1000 ° C. for 1 to 10 hours in an air atmosphere. When the firing temperature is less than 200 ° C. or the firing time is less than 1 hour, the raw material cobalt carbonate is not sufficiently converted to cobalt oxide, or the formation of solid solution is insufficient and the predetermined performance is obtained. There may not be. Further, if the calcination temperature exceeds 1000 ° C. or the calcination time exceeds 10 hours, it is not preferable because the specific surface area of the catalyst may decrease or the performance may be deteriorated by sintering due to heat load. The raw material of the catalyst B component is preferably a nitrate or acetate that is water-soluble and has low anion persistence, and easily forms an oxide upon firing.

Furthermore, in the first method for producing a nitrous oxide decomposition catalyst, the calcination is preferably carried out at a temperature not higher than 200 ° C. added to the oxide melting point of the metal element as the catalyst B component. For example, when Mn is selected as the catalyst B component, firing is preferably performed at a temperature lower than 735 ° C. obtained by adding 200 ° C. to the melting point (535 ° C.) of MnO ₂ that is the oxide. More preferably, firing is performed at a temperature lower than the melting point of the oxide, more preferably 200 ° C. or more lower than the melting point of the oxide. If the firing temperature is higher than the temperature obtained by adding 200 ° C. to the melting point of the oxide of the metal element, performance is deteriorated by sintering, which is not preferable.

Next, a method for producing the second nitrous oxide decomposition catalyst will be described below.

The second method for producing a catalyst for nitrous oxide decomposition is cobalt carbonate (including basic cobalt carbonate) as a raw material for catalyst A component cobalt oxide, and group 2 to 3 as catalyst C component raw material. And a metal salt aqueous solution containing at least one metal element selected from the group consisting of 11 to 15 groups, thoroughly mixed, dried and then fired. By using this production method, it is possible to form a solid solution relatively easily without using complicated production processes such as a coprecipitation method and using simple production equipment.

Suitable drying conditions are the same as those for the first nitrous oxide decomposition catalyst.

The calcining conditions can be appropriately changed depending on the method for producing the catalyst, and is not particularly limited. However, it is preferable to calcine at 300 to 700 ° C. for 1 to 10 hours in an air atmosphere. When the firing temperature is less than 300 ° C. or the firing time is less than 1 hour, the raw material cobalt carbonate is not sufficiently converted to cobalt oxide, or the formation of a solid solution is insufficient and the predetermined performance is obtained. There may not be. Further, when the calcination temperature exceeds 700 ° C. or the calcination time exceeds 10 hours, it is not preferable because the specific surface area of the catalyst may be reduced or the performance may be deteriorated by sintering due to heat load. In addition, it is preferable to use a nitrate or acetate of the metal element which is water-soluble, has low anion persistence, and easily forms an oxide upon firing.

Further, in both the first nitrous oxide decomposition catalyst and the second nitrous oxide decomposition catalyst, the raw material compound containing the catalyst A component and the catalyst B component or the catalyst C component, and an appropriate amount of water, After sufficiently kneading the molding aid and the like, it can be formed into a desired catalyst shape by extrusion molding, drying and firing. The raw material compound containing the catalyst A component and the catalyst B component or the catalyst C component is wet pulverized by adding an appropriate amount of water and a binder to form an aqueous slurry, which is then coated on a ceramic carrier or metal carrier, dried, and calcined. It may be manufactured.

Next, the processing method of the nitrous oxide-containing gas of the present invention uses the first nitrous oxide decomposition catalyst or the second nitrous oxide decomposition catalyst, and NO and / or NO is used as the nitrous oxide-containing gas. Nitrous oxide can be efficiently decomposed even if ₂ is contained. In this treatment method, nitrous oxide is directly decomposed into nitrogen and oxygen by a catalyst, and a nitrous oxide-containing gas is treated without adding a reducing agent such as hydrocarbon, carbon monoxide, hydrogen or ammonia. be able to. In addition, it is known that when NO or NO ₂ coexists with a conventional catalyst for decomposing nitrous oxide, the performance of nitrous oxide treatment is lowered. Usually, a method of treating nitrous oxide after removing NOx in the previous stage It was chosen.

The nitrous oxide concentration of the nitrous oxide-containing gas is 1 to 50000 ppm, and preferably 5 to 5000 ppm. When the nitrous oxide concentration is less than 1 ppm, efficient treatment is difficult, and when it exceeds 50,000 ppm, it is preferable to treat by a method other than the catalytic method. In the treatment method, the reaction temperature is 200 to 700 ° C., preferably 250 to 450 ° C., more preferably 300 to 400 ° C. If the reaction temperature is less than 200 ° C, nitrogen oxides coexisting in the treatment gas may accumulate in the catalyst, and it is difficult to stably treat for a long time. If it exceeds 700 ° C, the exhaust gas is heated. In addition, a large amount of fuel is required, resulting in a problem of economy. The space velocity (SV) is 1,000 to 50,000 hr ⁻¹ , preferably 2,000 to 20,000 hr ⁻¹ . Furthermore, the reaction pressure in the treatment method of the present invention is 0.1 to 2 MPa, preferably 0.1 to 1 MPa.

Such nitrous oxide-containing gases include various combustion exhaust gases such as gas turbines for power generation, boilers, waste incinerators, sewage sludge incinerators, and industrial exhaust gases emitted from chemical plants that produce adipic acid, nitric acid, etc. Is mentioned. The nitrous oxide-containing gas often contains nitrogen oxides such as NO and NO _2, and a specific NOx concentration (NO concentration + NO ₂ concentration) to which the present invention can be applied is 0.1 to 1000 ppm. More preferably, it is 1 to 500 ppm. This is because when the NOx concentration exceeds 1000 ppm, it is necessary to design the exhaust gas treatment system in total including measures against NOx, and when it is less than 0.1 ppm, the negative influence is reduced. The nitrous oxide-containing gas may contain nitrogen, oxygen, carbon dioxide, carbon monoxide, water, hydrogen, ammonia, SOx, etc. in addition to NOx.

This application claims the benefit of priority based on Japanese Patent Application No. 2011-212734 and Japanese Patent Application No. 2011-212735 filed on September 28, 2011. The entire contents of the specifications of Japanese Patent Application No. 2011-212734 and Japanese Patent Application No. 2011-121735 filed on September 28, 2011 are incorporated herein by reference.

The present invention will be described in more detail with reference to the following examples showing advantageous embodiments of the present invention. Examples 1 to 7 are examples of the first nitrous oxide decomposition catalyst, and Examples 8 to 14 are examples of the second nitrous oxide decomposition catalyst.

Example 1
After adding an aqueous solution containing 6.4 g of silver nitrate to 40 g of commercially available cobalt carbonate (manufactured by Nacalai Tesque, basic cobalt carbonate), the mixture is thoroughly mixed as a paste, dried in a 120 ° C. drier for 5 hours, and then air atmosphere The catalyst was calcined at 250 ° C. for 2 hours to obtain a catalyst having an Ag / Co ratio of 0.10.

(Examples 2 to 3)
A catalyst was obtained in the same manner as in Example 1 except that the calcination temperature of the catalyst in Example 1 was changed as shown in Table 1.

(Examples 4 to 7)
A catalyst was obtained in the same manner as in Example 1 except that the raw materials shown in Table 1 were added in each atomic ratio instead of silver nitrate in Example 1, and the calcination temperature was 500 ° C.

(Comparative Example 1)
A catalyst having the composition shown in Table 1 was obtained in the same manner as in Example 1 except that potassium nitrate was added instead of silver nitrate in Example 1.

(Comparative Example 2)
A catalyst having the composition shown in Table 1 was obtained in the same manner as in Example 1 except that cesium nitrate was added instead of silver nitrate in Example 1.

(Comparative Example 3)
A catalyst was obtained in the same manner as in Example 1 except that silver nitrate was not added in Example 1.

<Measurement of X-ray diffraction>
The position of the main diffraction peak of Co ₃ O ₄ where 2θ is detected at around 36.9 degrees from the diffraction patterns of the catalysts of Examples 1 to 7 and Comparative Examples 1 to 3 measured by powder X-ray diffraction (XRD). The results are shown in Table 1. X-ray source is Cu K _alpha, tube voltage 45 kV, tube current was measured range 2θ of 5 to 90 degrees 40mA at 25 ° C..

<Catalytic activity test>
Activity tests of the catalysts of Examples 1 to 7 and Comparative Examples 1 to 3 were carried out by the following evaluation methods. Each catalyst powder was compacted into granules after being pressure-molded and classified at 0.6 to 1.18 mm, and 1 ml of the catalyst was charged into a SUS reaction tube having an inner diameter of 10 mm. The reaction gas having the following gas composition was adjusted to a space velocity of 10,000 hr ⁻¹ and the nitrous oxide decomposition activity was measured at a reaction temperature of 350 ° C.

<Syngas composition>
N ₂ O: 300 ppm, NO: 50 ppm, CO ₂ : 300 ppm, O ₂ : 16%, H ₂ O: 10%, N ₂ : Nitrous oxide concentration in the synthesis gas on the inlet side and outlet side of the balance catalyst layer Measurement was performed with a gas chromatograph (manufactured by Shimadzu Corporation, GC8A, column: porapakQ), and the N ₂ O decomposition rate was calculated by the following equation.
N ₂ O decomposition rate (%) = 100 × (inlet side N ₂ O concentration−outlet side N ₂ O concentration) / inlet side N ₂ O concentration 1 hour and 20 hours after the introduction of the synthesis gas Table 1 shows the nitrous oxide decomposition performance.

　実施例１～７の亜酸化窒素分解用触媒は比較例３の触媒と比較して酸化物融点が２００～１０００℃の触媒Ｂ成分を配合することにより１時間後の初期低温活性が大幅に向上されている。次にＮＯが存在する同試験条件において１０時間程度反応を継続すると亜酸化窒素分解性能はほぼ安定する。そこで２０時間経過後の触媒性能をＮＯｘ耐性の評価として示したが比較例１及び２の触媒がほとんど処理性能が消失するのに対し、実施例１～７の各触媒は良好な耐久性を有している。これら結果より触媒性能は触媒Ｂ成分の酸化物融点と触媒の焼成温度に密接に関連していると推定される。

The catalysts for decomposing nitrous oxide of Examples 1 to 7 significantly improve the initial low-temperature activity after 1 hour by adding the catalyst B component having an oxide melting point of 200 to 1000 ° C. as compared with the catalyst of Comparative Example 3. Has been. Next, when the reaction is continued for about 10 hours under the same test conditions where NO is present, the nitrous oxide decomposition performance is almost stabilized. Thus, the catalyst performance after 20 hours was shown as an evaluation of NOx resistance, but the catalysts of Comparative Examples 1 and 2 almost lost their treatment performance, whereas the catalysts of Examples 1 to 7 had good durability. is doing. From these results, it is estimated that the catalyst performance is closely related to the oxide melting point of the catalyst B component and the calcination temperature of the catalyst.

Examples 8 to 14 are described below. In addition, Comparative Examples 1 to 3 are catalysts obtained by the same production method as described above.

(Example 8)
An aqueous solution containing 6.4 g of lead nitrate is added to 40 g of commercially available cobalt carbonate (manufactured by Nacalai Tesque, basic cobalt carbonate) and thoroughly mixed as a paste, dried for 5 hours in a 120 ° C. drier, then air Calcination was performed in an atmosphere at 400 ° C. for 2 hours to obtain a catalyst having a Pb / Co ratio of 0.05.

(Examples 9 to 11)
A catalyst was obtained in the same manner as in Example 8 except that the amount of lead nitrate added was changed to the atomic ratio shown in Table 2.

(Examples 12 to 14)
A catalyst was obtained in the same manner as in Example 8 except that the raw materials shown in Table 2 were added in each atomic ratio instead of lead nitrate in Example 8.

X-ray diffraction measurement, catalytic activity test, and synthesis gas composition are the same as those in Examples 1 to 7 and Comparative Examples 1 to 3 described above. Table 2 shows the nitrous oxide decomposition performance of Examples 8 to 14 and Comparative Examples 1 to 3 after 1 hour and 20 hours from the introduction of the synthesis gas.

　実施例８～１４の亜酸化窒素分解用触媒は比較例３の触媒と比較してイオン半径の大きい触媒Ｃ成分を配合することにより１時間後の初期性能が大幅に向上されている。これら結果はＸ線回折の測定結果から固溶体が形成していることによると推定される。次にＮＯが存在する同試験条件において１０時間程度反応を継続すると亜酸化窒素分解性能はほぼ安定する。そこで２０時間経過後の触媒性能をＮＯｘ耐性の評価として示したが比較例１及び２の触媒はほとんど処理性能が消失するのに対し、実施例８～１４の各触媒は良好な耐久性を有している。

In the catalysts for decomposing nitrous oxide of Examples 8 to 14, the initial performance after 1 hour is greatly improved by blending the catalyst C component having a large ionic radius as compared with the catalyst of Comparative Example 3. These results are presumed to be due to the formation of a solid solution from the measurement results of X-ray diffraction. Next, when the reaction is continued for about 10 hours under the same test conditions where NO is present, the nitrous oxide decomposition performance is almost stabilized. Therefore, the catalyst performance after 20 hours was shown as an evaluation of NOx resistance, but the catalysts of Comparative Examples 1 and 2 almost lost the treatment performance, whereas the catalysts of Examples 8 to 14 had good durability. is doing.

According to the present invention, it is possible to provide a nitrous oxide decomposition catalyst having high activity at a low temperature without using an expensive noble metal. Even if nitrogen oxide (NOx) is contained in the nitrous oxide-containing gas, it can be treated stably and can be expected to be used for various industrial applications.

Claims (6)

A catalyst for nitrous oxide decomposition containing a cobalt oxide as a catalyst A component and at least one compound of a metal element selected from the group consisting of groups 5 to 15 as a catalyst B component, the catalyst for the catalyst A component For the decomposition of nitrous oxide, wherein the atomic ratio of the B component is 0.0005 to 0.15, and the melting point of the metal element oxide as the catalyst B component is in the range of 200 to 1000 ° C. catalyst. A catalyst for nitrous oxide decomposition containing a cobalt oxide as the catalyst A component and at least one metal element compound selected from the group consisting of groups 2 to 3 and 11 to 15 as the catalyst C component, The atomic ratio of the catalyst C component to the A component is 0.0005 to 0.15, and the ionic radius of the metal element of the catalyst C component is in the range of 0.90 to 1.88%. Catalyst for nitrous oxide decomposition. A catalyst for nitrous oxide decomposition according to claim 1 or 2,
In the diffraction pattern measured by a powder X-ray diffraction method, the oxide of cobalt as the catalyst A component has a crystal structure of cobalt trioxide (Co ₃ O ₄ ), and the catalyst B component or the A diffraction peak derived from a single oxide of the catalyst C component is not detected. A catalyst for nitrous oxide decomposition. A method for producing a nitrous oxide decomposition catalyst according to claim 1 or 3,
The metal salt aqueous solution of at least one metal element selected from the group consisting of cobalt carbonate (including basic cobalt carbonate) as a raw material of the catalyst A component cobalt oxide and the catalyst B component as a raw material of the catalyst B component A method for producing a catalyst for nitrous oxide decomposition, which is obtained by mixing and drying and calcining. A method for producing a nitrous oxide decomposition catalyst according to claim 2 or 3,
At least one metal element selected from the group consisting of cobalt carbonate (including basic cobalt carbonate) as a raw material for the cobalt oxide of the catalyst A component, and groups 2-3 and 5-15 as the raw material for the catalyst C component A method for producing a catalyst for nitrous oxide decomposition, which is obtained by mixing the aqueous metal salt solution and drying and then firing. A nitrous oxide-containing gas characterized by treating a nitrous oxide-containing gas containing NO and / or NO ₂ with the nitrous oxide decomposition catalyst according to any one of claims 1 to 3. Processing method.