Composite material, nitrogen oxide adsorbent, nitrogen oxide adsorption method, and nitrogen oxide removal device

Abstract

To provide a composite material having high adsorptivity of nitrogen oxide even at low temperature and in a gas atmosphere containing water.SOLUTION: A composite material has noble metal and zeolite. The zeolite includes lta in its skeleton, with the molar ratio of SiO2 / Al2O3 being 11 or more. Preferably the zeolite has a maximum ring size of 3.6Åor less and is of RHO type.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a composite material used for a nitrogen oxide adsorbent or the like, and is applied, for example, to the purification of various exhaust gases, particularly exhaust gases discharged from internal combustion engines such as automobiles.

Background Art

[0002] In the purification of exhaust gas containing nitrogen oxides discharged from internal combustion engines such as automobiles, a method has been put into practical use in which ammonia generated by the decomposition reaction of urea is used as a reducing agent using urea, and the exhaust gas is brought into contact with an SCR (Selective Catalytic Reduction) catalyst. However, at the time of engine startup, since the SCR catalyst has not reached the operating temperature, there is a problem that nitrogen oxides are not purified and are directly discharged. For example, the exhaust gas temperature of a diesel engine is as low as 100 to 200°C for about 800 seconds from engine startup, and nitrogen oxides that could not be detoxified during this period are contained in the exhaust gas (Non-Patent Document 1).

[0003] In the current urea-SCR method installed in diesel engines, since urea decomposes into ammonia and the SCR catalyst is activated, generally, the temperature at the urea dosing position needs to be approximately 150°C or higher. At temperatures below 150°C, the temperature at which the catalyst is activated has not been reached, and there is a problem that nitrogen oxides are not purified and are discharged in the low-temperature region such as at startup. By the way, in California starting from 2023, strict regulations are planned to reduce the emission amount of nitrogen oxides contained in exhaust gas to about 10% of the current level, and a method for further reducing the nitrogen oxides contained in the exhaust gas discharged at the time of engine startup is required.

[0004] As a method for reducing nitrogen oxides discharged during engine startup, as described in Non-Patent Document 2, an adsorbent such as zeolite is disposed upstream of the exhaust gas purification catalyst, nitrogen oxides are adsorbed in the low-temperature range during engine startup, and after the temperature reaches or exceeds the temperature at which the exhaust gas purification catalyst is activated, nitrogen oxides are desorbed from the adsorbent and purified by the exhaust gas purification catalyst on the downstream side. A system has been proposed.

[0005] Further, Patent Document 1 describes an exhaust gas purification catalyst in which a pre-stage catalyst carrying rhodium on zeolite is disposed upstream of the exhaust gas, and a post-stage catalyst carrying platinum or palladium is disposed downstream thereof. According to this exhaust gas purification catalyst, a method has been proposed in which nitrogen oxides are adsorbed by the pre-stage catalyst in the low-temperature range and the nitrogen oxides desorbed from the pre-stage catalyst are reduced and purified by the post-stage catalyst in the high-temperature range.

[0006] Patent Document 2 discloses a system in which nitrogen oxides from lean exhaust gas are adsorbed at a temperature below 200 °C and subsequently thermally released at a temperature above 200 °C. It is taught that the nitrogen oxide adsorbent comprises palladium, and cerium oxide or mixed oxide, or a composite oxide containing cerium and at least one other group 4 transition metal.

[0007] In Patent Document 3, it has been reported that an adsorbent (Passive NOx Adsorber; PNA) in which palladium is supported on small-pore zeolite whose maximum pore diameter in the zeolite crystal structure is composed of an 8-membered oxygen ring releases the nitrogen oxides adsorbed at low temperature at a higher temperature. Furthermore, it is taught that an adsorbent composed of zeolite has higher resistance to S components than an adsorbent using ceria oxide as a carrier. Non-Patent Document 3 also reports that CHA-type zeolite carrying palladium can hold nitrogen oxides up to a high temperature because nitrogen oxides are desorbed at a temperature of 150 °C or higher.

Prior Art Documents

Non-Patent Documents

[0008]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Patent Document

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0010] In the adsorbent for low-temperature nitrogen oxides using zeolite such as the pre-stage catalyst described in Patent Document 1, there was a phenomenon that the adsorption amount of nitrogen oxides decreased due to the influence of moisture contained in the exhaust gas. Therefore, although the cause was not clear, there was a problem that zeolite loaded with rhodium had low stability.

[0011] Depending on the type of metal supported on the zeolite, the interaction with water was strong. When water coexisted as in automobile exhaust gas, it was considered that water was preferentially adsorbed and the adsorption performance of nitrogen oxides decreased. For example, Patent Document 3 states that a nitrogen oxide adsorbent in which palladium is supported on an 8-membered ring zeolite with a small pore diameter (ring size), such as CHA-type zeolite supporting palladium, is effective. Further, as a result of comparing the adsorption characteristics of Pd / ZSM-5 and Pd / CHA in Non-Patent Document 4, it is reported that Pd / CHA with a small ring size is less affected by water in NO adsorption at 120°C. However, this is only the result of comparing the adsorption performance in a high-temperature region where the water adsorption capacity is weak, and water is more likely to be adsorbed on zeolite in a temperature region lower than 120°C, at which nitrogen oxides are discharged from the exhaust gas since engine startup. Despite the importance of the adsorption characteristics in a gas atmosphere containing water, the adsorption characteristics in the competitive adsorption of water and nitrogen oxides in that temperature region have not been clearly elucidated. Actually, as described in Reference Examples 1 and 2 of this patent, it can be seen that when the adsorption temperature is lowered from 120°C to 80°C in an atmosphere where water coexists, the adsorption amount of nitrogen oxides decreases.

[0012] In this patent, the influence of water concentration on the adsorption of nitrogen oxides at 80°C was evaluated using Pd / CHA for adsorption performance. As a result, it was clarified that the nitrogen oxide adsorption amount tended to decrease as the water concentration increased (see Comparative Example 2). Therefore, Pd / CHA is considered to be a more effective adsorbent than Pd / ZSM-5 in the high-temperature region, but the problem of being affected by water was confirmed in the low-temperature region.

[0013] The present invention has been made to solve the above problems, and an object thereof is to provide a composite material having high nitrogen oxide adsorption performance even at low temperatures and in a gas atmosphere containing water.

Means for Solving the Problems

[0014] The inventors of the present invention included lta defined by the International Zeolite Association (IZA) as a composite building unit (CBU) in the framework, SiO 2 / Al 2 O 3The inventors have successfully developed a nitrogen oxide adsorbent in which a composite material obtained by supporting a noble metal such as palladium on a zeolite having a specific molar ratio in a range of 11 or more has a surprising effect that the adsorption performance of nitrogen oxides does not decrease even in the presence of water, but rather the amount of nitrogen oxides adsorbed is increased in the presence of water, and thus have reached the present invention. That is, the present invention provides the following [1] to [9]. [1] A composite material containing a noble metal and a zeolite, wherein the zeolite contains lta defined by the International Zeolite Association (IZA) as a composite building unit in its framework, and SiO 2 / Al 2 O 3 The composite material is characterized in that the molar ratio is 11 or more. [2] The composite material according to [1] above, wherein the maximum ring size of the zeolite is 3.6 Å or less. [3] The composite material according to [1] or [2] above, wherein the zeolite is an RHO-type zeolite. [4] The composite material according to any one of [1] to [3] above, wherein the noble metal is palladium and its content is 0.1% by mass or more. [5] When the nitrogen oxide adsorption amount when a gas containing 200 volume ppm of nitrogen oxides and 5 volume% of oxygen and having a water vapor content of 0 volume% is passed through the composite material at 80 ° C. is A1, and the nitrogen oxide adsorption amount when a gas containing 200 volume ppm of nitrogen oxides and 5 volume% of oxygen and having a water vapor content of 5 volume% is passed through the composite material at 80 ° C. is A2, the nitrogen oxide adsorption amount change rate represented by the ratio (A2 / A1) is 0.6 or more and 2.0 or less. The composite material according to any one of [1] to [4] above. [6] A composite material containing a noble metal and a zeolite, wherein when a gas containing 200 volume ppm of nitrogen oxides, 5 volume % of oxygen, and having a water vapor content of 0 volume % is passed through the composite material at 80°C, the nitrogen oxide adsorption amount is denoted as A1, and when a gas containing 200 volume ppm of nitrogen oxides, 5 volume % of oxygen, and having a water vapor content of 5 volume % is passed through the composite material at 80°C, the nitrogen oxide adsorption amount is denoted as A2, the composite material having a nitrogen oxide adsorption amount change rate represented by the ratio (A2 / A1) of 0.6 or more and 2.0 or less. [7] A nitrogen oxide adsorbent comprising the composite material according to any one of the above items [1] to [6]. [8] A method for adsorbing nitrogen oxides in a gas containing water and nitrogen oxides using the composite material according to any one of the above items [1] to [6]. [9] A nitrogen oxide removal device comprising the composite material according to any one of the above items [1] to [6], the removal device removing nitrogen oxides in a gas containing water and nitrogen oxides by adsorbing the nitrogen oxides with the composite material. [Effect of the Invention]

[0015] According to the present invention, it is possible to provide a composite material having high nitrogen oxide adsorption performance without being affected by water even at low temperatures such as at engine startup and in a gas atmosphere containing water. [Brief Description of the Drawings]

[0016]

Figure 1

Figure 2

[0017] Hereinafter, embodiments of the present invention will be described in detail. However, the following description is an example (representative example) of embodiments of the present invention, and the present invention is not limited to these contents at all.

[0018] [Composite Material] The composite material according to an embodiment of the present invention is a composite material containing a noble metal and zeolite, and contains lta defined as a composite building unit by the International Zeolite Association (IZA) in its framework, and SiO 2 / Al 2 O 3 has a molar ratio of 11 or more. Hereinafter, the composite material according to an embodiment of the present invention will be described in detail.

[0019] Since the above zeolite has an lta framework, it is easy to support a noble metal effective for adsorbing nitrogen oxides. In addition, zeolite contains at least oxygen, aluminum (Al), and silicon (Si) as atoms constituting the framework structure, and some of these atoms may be substituted with other atoms (Me). Aluminosilicate zeolite is more preferable than AlPO-based or SAPO-based zeolite. Among aluminosilicate zeolites having lta, zeolites having an 8-membered oxygen ring structure in the framework are preferable. Further, zeolites having an RHO structure (hereinafter referred to as RHO-type zeolites) in the code defining the framework structure of zeolites defined by the International Zeolite Association (IZA) are more preferable.

[0020] The structure of zeolite is characterized by X-ray diffraction data. However, when measuring the actually produced zeolite, it is affected by the growth direction of the zeolite, the ratio of the constituent elements, the adsorbed substances, the presence of defects, the drying state, the alkali cation species, etc., and there is a slight shift in the intensity ratio and peak position of each peak. Therefore, the same numerical values as all the parameters of the RHO structure described in the IZA regulations are not necessarily obtained, and a width of about 20% is allowed. The main peaks of RHO-type zeolite, when using CuKα radiation, are, for example, the peak of the 110 plane at 2θ = 9.1° ± 0.2°, the peak of the 211 plane at 2θ = 15.8° ± 0.2°, the peak of the 301 or 310 plane at 2θ = 20.4° ± 0.2°, the peak of the 312 or 321 plane at 2θ = 24.2° ± 0.2°, the peak of the 330 or 411 plane at 2θ = 27.5° ± 0.2°, and so on.

[0021] As described above, the composite material of the present invention contains a noble metal and zeolite. It is preferable that the noble metal is supported on the zeolite in the composite material of the present invention. The noble metal used in the composite material is selected from the group consisting of, for example, platinum, palladium, rhodium, gold, silver, iridium, ruthenium, osmium, and mixtures thereof. Among these, palladium is preferable because of its excellent affinity for nitrogen oxides. The valence of the noble metal is not particularly limited and may be either monovalent or divalent. Also, in the composite material of the present invention, the noble metal is usually not included in the skeletal structure of the zeolite in terms of its state of existence.

[0022] Since the noble metal serves as an adsorption site for nitrogen oxides in the adsorbent, a large amount of noble metal is preferably present to adsorb a large amount of nitrogen oxides. From such a viewpoint, the content of the noble metal contained in the composite material is usually 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.7% by mass or more, particularly preferably 0.8% by mass, and most preferably 1.0% by mass or more. Since a large amount of the noble metal is fixed to the zeolite and the gas to be treated can easily penetrate into the pores without the pores being blocked by the noble metal, the content of the noble metal contained in the composite material is usually 10% by mass or less, preferably 8% by mass or less, more preferably 6.0% by mass or less, still more preferably 5.0% by mass or less, particularly preferably 4.0% by mass or less, and especially preferably 3.0% by mass or less.

[0023] The SiO 2 / Al 2 O 3 The molar ratio is 11 or more. SiO 2 / Al2 O 3 Due to a high molar ratio, even in a low-temperature gas atmosphere containing water, it is easy to maintain high nitrogen oxide adsorption performance without being affected by water. When used as a catalyst or adsorbent, since it is preferable to have more active sites and adsorption sites, SiO 2 / Al 2 O 3 The molar ratio is preferably small, specifically, 100 or less is preferable, more preferably 50 or less, still more preferably 30 or less, particularly preferably 25 or less, especially preferably 22 or less, and most preferably 20 or less. On the other hand, zeolite with a small amount of Al in the framework is less likely to cause structural destruction due to the desorption of Al in the framework even when exposed to a gas containing water vapor. Therefore, SiO 2 / Al 2 O 3 The molar ratio is preferably large. That is, SiO 2 / Al 2 O 3 A higher molar ratio can maintain high nitrogen oxide adsorption performance without being affected by water. From these viewpoints, SiO 2 / Al 2 O 3 The molar ratio is usually 11 or more, preferably 12 or more, more preferably 13 or more, and particularly preferably 14 or more.

[0024] Note that zeolite containing lta as CBU in the zeolite structure usually has a low SAR (hereinafter sometimes referred to as "SAR"). For example, as described in Microporous Materials Volume 4, Issues 2-3, June 1995, Pages 231-238, SiO 2 / Al 2 O 3 The molar ratio is at most 10 even if it is high. In contrast, the composite material according to the present embodiment contains lta in the framework, but SiO 2 / Al 2 O 3The molar ratio is 11 or more, whereby high nitrogen oxide adsorption performance can be exhibited without being affected by water even in a gas atmosphere containing water and at a low temperature.

[0025] The zeolite containing lta as CBU in the zeolite structure in the composite material is not particularly limited. For example, CLO, KFI, LTA, LTN, PAU, RHO, TSC, UFI, and MWF are preferable, KFI, LTA, LTN, PAU, RHO, and MWF are more preferable, MWF, LTA, PAU, and RHO are particularly preferable, MWF, PAU, and RHO are especially preferable, and RHO is most preferable. The preferable point that lta is contained as CBU in the zeolite structure is that the gas diffuses through the d8r of lta. Since d8r is larger in size than d6r, it has pores large enough for the gas to diffuse even when water is adsorbed, so it is less affected by the adsorbed water. In addition, since these zeolites have a small ring size for gas intrusion, there is an effect that it is difficult to cause pore blockage by large-sized hydrocarbons contained in automotive exhaust gas.

[0026] In the composite material, the smaller the maximum ring size of the zeolite, the easier it is to prevent the intrusion of water and hydrocarbons into the pores. Therefore, the maximum ring size in the crystal structure of the zeolite is preferably 3.7 Å or less, and most preferably 3.6 Å or less. On the other hand, the lower limit value of the maximum ring size needs to be a size that does not affect the loading of the noble metal serving as the adsorption point and the intrusion of the gas. Usually, it is 2.0 Å or more, preferably 2.5 Å or more, more preferably 3.0 Å or more, particularly preferably 3.2 Å or more, especially preferably 3.4 Å or more, and most preferably 3.5 Å or more. The maximum ring size in the crystal structure of the zeolite is the value described in ATLAS OF ZEOLITE FRAME WORK TYPES (Sixth Revised Edition, 2007, ELSEVIER) by Ch. Baerlocher et al.

[0027] The framework density of the zeolite in the present invention (hereinafter sometimes abbreviated as "FD") is not particularly limited, but is usually 12.0 T / nm 3 or more, preferably 12.5 T / nm 3 or more, more preferably 13.0 T / nm 3 or more. On the other hand, it is usually 14.4 T / nm 3 or less, preferably 14.3 T / nm 3 or less, particularly preferably 14.2 T / nm 3 or less, most preferably 14.1 T / nm 3 or less. The framework density (T / nm 3 ) means the number of T atoms (atoms of elements other than oxygen that make up the zeolite framework) present per unit volume nm 3 of the zeolite, and this value is determined by the structure of the zeolite. When the FD is high, the structure is stable and sufficient durability tends to be obtained. On the other hand, when the FD is low, a sufficient adsorption amount can be obtained, making it suitable for use as an adsorbent. The above framework density is the value described in ATLAS OF ZEOLITE FRAME WORK TYPES (Sixth Revised Edition, 2007, ELSEVIER) by Ch. Baerlocher et al.

[0028] The particle size of the zeolite is not particularly limited. However, since the diffusibility of the gas is likely to be high when used as an adsorbent, 0.01 μm or more is preferable, 0.1 μm or more is more preferable, 1.0 μm or more is particularly preferable, and 2.0 μm or more is most preferable. On the other hand, 10 μm or less is preferable, 8 μm or less is more preferable, 6 μm or less is particularly preferable, 5.5 μm or less is especially preferable, and 5.0 μm or less is most preferable. The particle size is the average particle size, and specifically, it is measured by the method described in the section of Examples below. The specific surface area of the zeolite is not particularly limited. However, since there are many active sites present on the inner surface of the pores, it is preferably in the following range. That is, 200 m 2 / g or more is preferable, more preferably 300 m 2 / g or more, still more preferably 400 m2 is 1000 m / g or more. On the other hand, it is preferably 1000 m / g or less, more preferably 800 m / g or less, still more preferably 700 m / g or less. The specific surface area of the zeolite is measured by the BET method described in the Examples section below. 2 is preferably 1000 m / g or less, more preferably 800 m / g or less, still more preferably 700 m / g or less. The specific surface area of the zeolite is measured by the BET method described in the Examples section below. 2 is preferably 1000 m / g or less, more preferably 800 m / g or less, still more preferably 700 m / g or less. The specific surface area of the zeolite is measured by the BET method described in the Examples section below. 2 is preferably 1000 m / g or less, more preferably 800 m / g or less, still more preferably 700 m / g or less. The specific surface area of the zeolite is measured by the BET method described in the Examples section below. The acid amount of the zeolite is preferably 0.5 mmol / g or more, more preferably 0.7 mmol / g or more, still more preferably 0.9 mmol / g or more, and particularly preferably 1.2 mmol / g or more. On the other hand, it is preferably 3.0 mmol / g or less, more preferably 2.5 mmol / g or less. The acid amount of the zeolite is measured by the method described in the Examples section below.

[0029] The composite material of the present invention may contain alkali metal atoms mainly derived from raw materials, such as sodium, potassium, cesium, etc. The content is preferably 0.001 or more and 1.0 or less as the molar ratio to aluminum in the composite material. When the content is small, it is difficult for the structure of the zeolite to be destroyed by alkali metal atoms in a steam atmosphere. Also, if the alkali metal atoms are forcibly removed from the composite material, it may damage the zeolite skeleton, etc. Therefore, the molar ratio of alkali metal atoms to aluminum in the catalyst is preferably at least the above lower limit value.

[0030] The composite material of the present invention contains nitrogen oxides (NO) at 200 volume ppm and oxygen at 5 volume %, and when a gas with a water vapor content of 0 volume % is passed through the composite material at 80°C, the nitrogen oxide adsorption amount is defined as A1. When a gas containing nitrogen oxides (NO) at 200 volume ppm, oxygen at 5 volume %, and a water vapor content of 5 volume % is passed through the composite material at 80°C, the nitrogen oxide adsorption amount is defined as A2. The change rate of the nitrogen oxide adsorption amount represented by the ratio (A2 / A1) is preferably 0.6 or more and 2.0 or less. The change rate of the nitrogen oxide adsorption amount is more preferably 0.7 or more, further preferably 0.8 or more, particularly preferably 0.9 or more, and most preferably 1.0 or more. On the other hand, 1.5 or less is more preferable, 1.3 or less is further preferable, 1.25 or less is particularly preferable, and 1.20 or less is most preferable. By setting the change rate of the nitrogen oxide adsorption amount within the above range, the nitrogen oxide adsorption performance of the composite material can be maintained well even in a low-temperature water vapor atmosphere. Note that the change rate of the nitrogen oxide adsorption amount is specifically measured by the method described in the examples section below.

[0031] In another embodiment of the present invention, the composite material contains a noble metal and zeolite, and the change rate of the nitrogen oxide adsorption amount represented by the above-mentioned ratio (A2 / A1) is 0.6 or more and 2.0 or less. The composite material according to another embodiment can have high nitrogen oxide adsorption performance even in a gas atmosphere containing water at low temperature by setting the change rate of the nitrogen oxide adsorption amount within the above range. The composite material according to another embodiment is SiO 2 / Al 2 O 3 The molar ratio does not necessarily have to be 11 or more, and lta does not necessarily have to be included as CBU in the zeolite structure. However, the SiO 2 / Al 2 O 3 The molar ratio may be 11 or more, and lta may be included as CBU in the zeolite structure. The details of the composite material according to another embodiment are as described for the composite material according to the above-mentioned one embodiment, and the description thereof is omitted.

[0032] [Manufacturing method of composite material] As a method for producing the composite material according to each of the above embodiments, there is no particular limitation. For example, a method of synthesizing zeolite and then supporting a predetermined amount of noble metal through a metal supporting step can be mentioned. That is, a zeolite containing Al and Si in its framework structure and having a SiO 2 / Al 2 O 3 molar ratio of 11 or more is produced, and a method of supporting a desired amount of noble metal on this based on the mass of the zeolite can be mentioned, etc. Hereinafter, as an example of the production of zeolite used in the production of the composite material, aluminosilicate zeolite will be described as an example. In the description of the following production method, aluminosilicate zeolite may be simply referred to as "zeolite".

[0033] <Method for Producing Zeolite> Zeolite is usually obtained by mixing each raw material to obtain a pre-reaction mixture and then performing hydrothermal synthesis. As raw materials for zeolite, usually, an aluminum atom raw material, a silicon atom raw material, an alkali metal atom raw material, and water are used. Further, an organic structure-directing agent or seed crystals may also be used.

[0034] <Aluminum Atom Raw Material> The aluminum atom raw material used for producing zeolite is not particularly limited, and amorphous aluminum hydroxide, aluminum hydroxide having a gibbsite structure, aluminum hydroxide having a boehmite structure, aluminum nitrate, aluminum sulfate, aluminum oxide, sodium aluminate, boehmite, pseudo-boehmite, aluminum alkoxide, and further, a compound containing silica such as zeolite can be used as the aluminum atom raw material. As the aluminum atom raw material used for producing zeolite, aluminosilicate zeolite having a building unit common to RHO-type zeolite, such as FAU-type zeolite, is particularly preferable. In this case, the Si content contained in FAU-type zeolite is preferably higher from the viewpoint that more building units can be added to the pre-reaction mixture as zeolite raw materials. Specifically, SiO 2 / Al 2 O 3 The molar ratio is preferably 5 or more, more preferably 7 or more, still more preferably 10 or more, particularly preferably 20 or more, especially preferably 25 or more, and most preferably 30 or more. The aluminum atomic raw material may be used alone or in combination of two or more kinds at any ratio.

[0035] The amount of the aluminum atomic raw material used is, from the viewpoints of the ease of preparing the pre-reaction mixture or the aqueous gel obtained by aging this and the production efficiency, SiO contained in the pre-reaction mixture other than the seed crystal 2 / Al 2 O 3 in terms of molar ratio, is usually 100 or less, preferably 50 or less, more preferably 40 or less, still more preferably 30 or less. The lower limit is not particularly limited, but from the viewpoint of uniformly dissolving the aluminum atomic raw material in the aqueous gel, it is usually 10 or more, preferably 15 or more, more preferably 18 or more, still more preferably 20 or more. Note that, in the SiO 2 / Al 2 O 3 molar ratio shown as the amount of the aluminum atomic raw material used, SiO 2 is the molar amount of SiO 2 when all the silicon (Si) contained in the pre-reaction mixture is SiO 2 , and Al 2 O 3 is the molar amount of Al 2 O 3 when all the aluminum (Al) contained in the pre-reaction mixture is Al 2 O 3 .

[0036] <Silicon atomic raw material> The silicon atom raw material used for producing the zeolite used in the present invention is not particularly limited, and various known substances can be used. For example, zeolite may be used, or colloidal silica, amorphous silica, sodium silicate, trimethylethoxysilane, tetraethyl orthosilicate, aluminosilicate gel, etc. can be used. These may be used alone or in combination of two or more in any ratio. In particular, an aluminosilicate zeolite having a building unit common to the RHO type zeolite, such as the FAU type zeolite, is preferable. The silicon atom raw material is used such that the usage amounts of other raw materials with respect to the silicon atom raw material are within the preferable ranges described above or below.

[0037] <Alkali metal atom raw material> The alkali metal atoms contained in the alkali metal atom raw material used for producing zeolite are not particularly limited, and known ones used in the synthesis of zeolite can be used. It is preferable to cause the presence of alkali metal ions for crystallization by using one or two or more selected from the group consisting of lithium, sodium, potassium, rubidium, and cesium. Among these, it is particularly preferable to contain both sodium atoms and cesium atoms. As the alkali metal atom raw material, hydroxides, oxides, sulfates, nitrates, phosphates, chlorides, bromides, etc. of inorganic acid salts such as the above alkali metal atoms, and organic acid salts such as acetates, oxalates, citrates, etc. can be used. The alkali metal atom raw material may contain one or two or more.

[0038] By using an appropriate amount of the alkali metal atom raw material, the organic structure directing agent described below can be easily coordinated with aluminum in a suitable state, facilitating the formation of a crystal structure. The molar ratio (R / Si) of the alkali metal atom raw material (R) to silicon (Si) contained in the reaction mixture before reaction other than the seed crystal is usually 0.1 or more, preferably 0.2 or more, more preferably 0.25 or more, still more preferably 0.3 or more, and is usually 2.0 or less, preferably 1.5 or less, more preferably 1.0 or less, still more preferably 0.8 or less, particularly preferably 0.6 or less, and most preferably 0.4 or less. When using an alkali metal atom raw material containing an alkali metal atom component as an aluminum atom raw material or a silicon atom raw material, it is preferable to use it so that the total with the alkali metal atom component in these raw materials falls within the above R / Si range.

[0039] <Organic structure directing agent> In the production of zeolite, it is preferable to use an organic structure directing agent (also referred to as a "template". Hereinafter, the organic structure directing agent may be referred to as "OSDA"). As the organic structure directing agent, a macrocyclic compound typified by crown ether is preferably used. The template is not particularly limited, but a macrocyclic compound having a heteroatom such as oxygen, nitrogen, or sulfur as an electron-donating (donor) atom is preferable. From the viewpoint of ease of formation of zeolite crystals, in particular, 12-crown-4-ether, 15-crown-5-ether, 18-crown-6-ether, 24-crown-8-ether, dibenzo-18-crown-6-ether, cryptand [2.2], and cryptand [2.2.2] are preferable. Only one kind of template may be used, or two or more kinds may be used in combination at an arbitrary ratio. Among these, 18-crown-6-ether is particularly preferable.

[0040] In addition, as the template, a polymer such as polydiallyldimethylammonium chloride (hereinafter referred to as PDADMAC) may be used. In this case, as described in Microporous and Mesoporous Materials 132 (2010) 352-356 of non-patent literature, RHO-type zeolite can be synthesized without using cesium as the alkali metal. When using these organic structure-directing agents, one kind may be used alone, or two or more kinds may be used in any ratio combination.

[0041] When using an organic structure-directing agent, the amount used is, from the viewpoint of the ease of crystal formation, a molar ratio to silicon (Si) contained in the raw material mixture other than the seed crystal, usually 0.01 or more, preferably 0.03 or more, more preferably 0.05 or more, still more preferably 0.08 or more, particularly preferably 0.10 or more. Also, in order to sufficiently obtain the effect of cost reduction, it is usually 1 or less, preferably 0.8 or less, more preferably 0.5 or less, still more preferably 0.3 or less, particularly preferably 0.2 or less. Note that RHO-type zeolite can be obtained without using an organic structure-directing agent as described on page 106 of Molecular Sieves, Adv. Chem. Ser., 121 (1973).

[0042] <Water> The amount of water used is, from the viewpoints of the kneadability of the raw material gel and the ease of crystal formation, a molar ratio to silicon (Si) contained in the raw material mixture other than the zeolite added as the seed crystal, usually 1 or more, preferably 3 or more, more preferably 5 or more, still more preferably 7 or more, particularly preferably 10 or more. When within this range, crystals are more likely to form, which is preferable. Also, in order to sufficiently obtain the effect of cost reduction for waste liquid treatment, it is usually 100 moles or less, preferably 80 or less, more preferably 50 or less, still more preferably 25 or less, particularly preferably 15 or less.

[0043] <Seed crystal> Seeds may be used to produce the zeolite used in the present invention. The zeolite used as a seed in the present invention may be used alone as one type, or two or more types may be used in any ratio combination. When using seeds, a large amount is preferably used in terms of accelerating the reaction rate and suppressing the generation of impurities. Therefore, when all the silicon (Si) contained in the raw material mixture other than the zeolite added as a seed is SiO 2 Assuming it is 2 For SiO

[0044] The zeolite used as a seed is not particularly limited as long as it is a zeolite. Zeolites containing at least one of d8r and lta in the building unit constituting the crystal structure are preferred, zeolites containing at least lta are more preferred, and zeolites containing both are even more preferred. Also, zeolites of the building unit constituting the crystal structure are preferred, and when producing RHO-type zeolite, the RHO type is most preferred. Zeolites containing d8r include MER type, SBE type, PAU type, RHO type, TSC type, etc. Zeolites containing lta include KFI type, LTA type, LTN type, UFI type, MWF type, PAU type, RHO type, TSC type, etc. And zeolites containing both include PAU type, RHO type, TSC type, etc.

[0045] The zeolite used as a seed crystal may be an uncalcined product that has not been calcined after hydrothermal synthesis or a calcined product that has been calcined after hydrothermal synthesis. However, in order to make it easier for the zeolite to exhibit its function as a crystal nucleus, it is preferably less soluble in alkali, so an uncalcined product is preferred. However, depending on the composition or temperature conditions in the raw material mixture, uncalcined zeolite may be difficult to dissolve and may be difficult to exhibit its function as a crystal nucleus. In such a case, in order to increase the solubility, it is preferable to use a zeolite from which OSDA has been removed by calcination.

[0046] <Mixing of raw materials> In the method for producing zeolite, usually, after mixing each raw material, hydrothermal synthesis is carried out. The order of mixing the raw materials is not particularly limited. However, it is preferable to add the silicon atom raw material and the aluminum atom raw material after preparing the alkali solution, from the viewpoint that the raw materials are more easily dissolved uniformly. Specifically, water and the alkali metal atom raw material are mixed, or when an organic structure-directing agent is used, water, the alkali metal atom raw material, and the organic structure-directing agent are mixed to prepare an aqueous alkali metal solution, and then the aluminum atom raw material and the silicon atom raw material are added thereto, or it is preferable to mix by adding the aluminum atom raw material and the silicon atom raw material in this order. Further, when using a seed crystal, it is preferable to add the seed crystal after adding the aluminum atom raw material and the silicon atom raw material.

[0047] <Preparation of crown ether-alkali aqueous solution> When using a crown ether as the organic structure-directing agent, as described above, it is advisable to mix water, an alkali metal atom raw material, and a crown ether as the organic structure-directing agent to prepare a crown ether-alkali aqueous solution. At this time, there is no restriction on the mixing order of each raw material, and it may be appropriately selected according to the conditions used. Usually, first, the alkali metal atom raw material is dissolved in water, and then the crown ether is added and mixed. At this time, mixing may be carried out at room temperature, but in order to facilitate the dissolution of the raw materials, the mixing temperature is usually 50 °C or higher, preferably 60 °C or higher, more preferably 80 °C or higher. Also, regarding the upper limit, there is no particular limitation, but usually 200 °C or lower, preferably 150 °C or lower, particularly preferably 100 °C or lower. Note that room temperature is the temperature when placed in a state without strict temperature control in the laboratory.

[0048] From the viewpoint of the ease of forming zeolite crystals, the concentration of the crown ether in the crown ether-alkali aqueous solution is preferably 3.0% by mass or more, more preferably 5.0% by mass or more. On the other hand, it is preferably 80% by mass or less, more preferably 60% by mass or less.

[0049] The crown ether-alkali aqueous solution preferably does not substantially contain an aluminum atom raw material and a silicon atom raw material. Here, "does not substantially contain" preferably means that the content in the crown ether-alkali aqueous solution is 0.1% by mass or less, and more preferably does not contain at all.

[0050] In the production of zeolite, in addition to the above substances, additives such as auxiliary agents that are components for assisting the synthesis of zeolite, for example, acid components that accelerate the reaction, stabilizers for metals such as polyamines, may be added and mixed in an arbitrary step as needed to prepare a pre-reaction mixture.

[0051] <Aging> The reaction mixture prepared as described above may be hydrothermally synthesized immediately after preparation. However, in order to obtain RHO-type zeolite with less impurities or high crystallinity, it is preferably aged for a certain period of time under predetermined temperature conditions. The aging temperature is usually 100 °C or lower, preferably 80 °C or lower, more preferably 50 °C or lower. The lower limit is not particularly provided, but it is usually 0 °C or higher, preferably 10 °C or higher. The aging temperature may be constant during aging, or may be changed stepwise or continuously. The aging time is not particularly limited, but it is usually 2 hours or longer, preferably 3 hours or longer, more preferably 5 hours or longer, still more preferably 10 hours or longer, particularly preferably 12 hours or longer. On the other hand, it is usually 10 days or shorter, preferably 5 days or shorter, more preferably 2 days or shorter, still more preferably 1 day or shorter.

[0052] <Hydrothermal synthesis> Hydrothermal synthesis is usually carried out by putting the reaction mixture obtained as described above into a pressure-resistant container and maintaining a predetermined temperature under self-generated pressure or gas pressurization to such an extent that crystallization is not inhibited, with stirring, or while rotating or rocking the container, or in a static state. The temperature of hydrothermal synthesis is usually 110 °C or higher and 200 °C or lower, preferably 190 °C or lower, more preferably 180 °C or lower, still more preferably 170 °C or lower. The reaction time is not particularly limited, but it is usually 5 hours or longer, preferably 10 hours or longer, more preferably 12 hours or longer, still more preferably 1 day or longer. On the other hand, it is usually 10 days or shorter, preferably 6 days or shorter, more preferably 5 days or shorter, still more preferably 4 days or shorter, particularly preferably 3 days or shorter. The reaction temperature may be constant during the reaction, or may be changed stepwise or continuously. The method for producing zeolite described above is preferable because the yield of the target zeolite is improved and it is difficult to generate different types of zeolites.

[0053] <Recovery of zeolite> After hydrothermal synthesis, the produced zeolite is separated from the reaction solution. The obtained zeolite (hereinafter sometimes referred to as "zeolite containing OSDA, etc.") usually contains alkali metal atoms in its pores. Also, when an organic structure-directing agent is used, this is also contained in the pores. The method for separating the zeolite containing OSDA, etc. from the reaction solution is not particularly limited, but usually methods such as filtration, decantation, or direct drying can be mentioned. The zeolite containing OSDA, etc. separated from the reaction solution can be washed with water and dried as necessary, and then calcined, etc. in order to remove the organic structure-directing agent, etc., so as to obtain a zeolite that does not contain the organic structure-directing agent, etc. Note that as the adsorbent described later, it is preferable to use the zeolite after removing these.

[0054] <Removal of Organic Structure-Directing Agent, etc. from Zeolite Containing OSDA, etc.> As a method for removing the organic structure-directing agent, etc. from the zeolite containing OSDA, removal by calcination is preferable in terms of productivity. The calcination temperature is preferably 300 °C or higher, more preferably 400 °C or higher, still more preferably 450 °C or higher, and particularly preferably 500 °C or higher. On the other hand, it is preferably 800 °C or lower, more preferably 700 °C or lower, still more preferably 600 °C or lower. The atmosphere is preferably a gas containing oxygen, but carbonization may be carried out using an inert gas such as nitrogen. In the method for producing zeolite, by selecting the raw materials and adjusting their ratios, etc., zeolite having a desired crystal form and a molar ratio such as SiO 2 / Al 2 O 3 can be produced.

[0055] (Counter Cation Species of Zeolite) The counter cations possessed by the zeolite before the noble metal loading treatment are not particularly limited, but preferably are alkali cations such as sodium cations, ammonium cations, and protons. The ion exchange reaction proceeds more easily with cations having a smaller ionic radius. On the other hand, since protons may destabilize the zeolite structure when present as an acid in the liquid after ion exchange, sodium cations and ammonium cations are more preferred, and ammonium cations are particularly preferred.

[0056] By performing an ion exchange treatment on the zeolite before loading the noble metal, the type of counter cation possessed by the zeolite can be changed. For example, an alkali metal atom raw material, an aluminum atom raw material, a silicon atom raw material, an organic structure directing agent, and the alkali metal moiety derived from the alkali metal atoms contained in the zeolite added in the present invention can be converted into a proton type or an ammonium type and used, and known techniques can be employed for the method. For example, it can be carried out by a method such as treating with an ammonium salt such as NH 4 NO 3 , NaNO 3 or an acid such as hydrochloric acid at room temperature to 100 °C and then washing with water.

[0057] <Method for Loading Noble Metal> The aluminosilicate zeolite produced as described above may contain a noble metal by loading the noble metal. Examples of the noble metal raw material used when loading the noble metal include oxides, hydroxides, sulfates, nitrates, chlorides, bromides, and other inorganic acid salts containing noble metals, and organic acid salts such as acetates. Specific examples of the method for loading a noble metal onto the zeolite include an impregnation loading method, a liquid phase ion exchange method, a solid phase ion exchange method, a precipitation loading method, a CVD method, a spray drying method, and the like. Further, after loading by the liquid phase ion exchange method or the solid phase ion exchange method, a loading by the impregnation method may be combined. Among the above, preferably, the noble metal is loaded onto the zeolite by the solid phase ion exchange method, the impregnation loading method, or the spray drying method, and particularly preferably by the impregnation loading method.

[0058] (Impregnation and support method) The solvent used in the impregnation and support method may be water or an organic solvent as long as the noble metal raw material can be dissolved, but usually water is preferred. The amount of the solvent used in the impregnation and support treatment may be determined by the mass ratio to the zeolite. Generally, since a smaller amount of water results in a smaller amount of waste liquid after the ion exchange treatment, the mass ratio to the zeolite is preferably 100 or less, more preferably 50 or less, still more preferably 25 or less, particularly preferably 20 or less, especially preferably 15 or less, and most preferably 10 or less. On the other hand, since it is easy to stir and perform uniform impregnation and support, usually, the mass ratio to the zeolite is 1 or more, preferably 3 or more, more preferably 5 or more, still more preferably 7 or more, and particularly preferably 9 or more.

[0059] The impregnation and support treatment is usually carried out by dissolving the noble metal raw material in a solvent to prepare a slurry liquid containing zeolite, and then removing the organic solvent by performing a reduced-pressure heat treatment on this. The heating temperature may be any condition under which the solvent vaporizes, and it also varies depending on the pressure, but usually, it is carried out at 100°C or lower, preferably 80°C or lower, more preferably 70°C or lower, and still more preferably 60°C or lower. On the other hand, since the solvent vaporizes easily, usually, it is carried out at 0°C or higher, preferably 10°C or higher, more preferably 15°C or higher, still more preferably 20°C or higher, and particularly preferably 30°C or higher.

[0060] After removing the solvent in the impregnation and support treatment, by repeating the step of adding the solvent again and removing it again, the noble metal can be supported on the zeolite surface more uniformly. Therefore, the number of times of the steps of adding and removing the solvent is not particularly limited, and the treatment may be repeated until the desired effect is obtained.

[0061] (Steam treatment) Noble metals impregnated and supported on the surface are usually mostly supported as oxides near the zeolite surface. Therefore, in order to support them as noble metal cations in the pores of the zeolite, it is preferable to perform steam treatment. The steam treatment temperature is preferably 500 °C or higher, more preferably 600 °C or higher, still more preferably 650 °C or higher, particularly preferably 700 °C or higher, and most preferably 750 °C or higher, because a higher temperature can more effectively disperse noble metal cations in the pores. On the other hand, a lower temperature is preferable in that structural destruction due to the desorption of Al from the acid sites of the zeolite is less likely to occur, preferably 900 °C or lower, more preferably 875 °C or lower, still more preferably 850 °C or lower, particularly preferably 825 °C or lower, and most preferably 800 °C or lower.

[0062] In the steam treatment, the concentration of water contained in the treatment gas is preferably 1% by volume or higher, more preferably 5% by volume or higher, still more preferably 8% by volume or higher, particularly preferably 10% by volume or higher, and most preferably 20% by volume or higher, because a higher concentration can more effectively disperse noble metal cations in the pores. On the other hand, from the viewpoint that structural destruction due to the desorption of Al from the acid sites of the zeolite is less likely to occur, a lower concentration is preferable, so the water concentration is preferably 100% by volume or lower, more preferably 90% by volume or lower, still more preferably 80% by volume or lower, particularly preferably 70% by volume or lower, especially preferably 60% by volume or lower, and most preferably 50% by volume or lower. The contact conditions of the steam treatment gas are not particularly limited, but are usually 100 / h or higher, preferably 1000 / h or higher in terms of space velocity (SV). On the other hand, they are usually 500000 / h or lower, preferably 300000 / h or lower, and more preferably 100000 / h or lower. The time of the steam treatment varies depending on factors such as temperature, steam concentration, and SV, so the optimal time may vary depending on the conditions. Usually, it is 1 hour or longer, more preferably 3 hours or longer, and still more preferably 5 hours or longer. Also, the upper limit of the steam treatment time is not particularly limited, but is, for example, 24 hours.

[0063] Further, the zeolite may be calcined after impregnating and supporting the noble metal. Specifically, the zeolite is preferably calcined at 300°C to 900°C, more preferably 350°C to 850°C, still more preferably 400°C to 800°C for 1 second to 24 hours, preferably 10 seconds to 8 hours, and still more preferably about 30 minutes to 5 hours. This calcination is not necessarily required, but by performing the calcination, the dispersibility of the noble metal supported on the skeletal structure of the zeolite can be enhanced, which is effective for improving the adsorption capacity. The calcination may be performed, for example, before the above-mentioned steam treatment.

[0064] However, the method of incorporating the noble metal into the zeolite is not limited to the method of supporting the noble metal after synthesizing the aluminosilicate zeolite, and other methods may be used. For example, by adding a noble metal (either in elemental form or as a compound) before the aforementioned hydrothermal synthesis, zeolite containing the noble metal may be directly synthesized.

[0065] [Use] The use of the composite material of the present invention is not particularly limited, and it is preferably used as a catalyst, an adsorbent, a separation material, etc. The composite material of the present invention is more preferably used as an adsorbent for nitrogen oxides.

[0066] [Nitrogen Oxide Adsorbent] The nitrogen oxide adsorbent includes the above-mentioned composite material. The nitrogen oxide adsorbent may consist of the above-mentioned composite material alone, but may also contain, in addition to the composite material, a binder such as silica, alumina, clay minerals, etc. For example, the nitrogen oxide adsorbent may be obtained by mixing a binder with the above-mentioned composite material as needed, granulating it, and molding it into a predetermined shape. Preferably, it is molded into a honeycomb shape and used.

[0067] When obtaining the nitrogen oxide adsorbent of the present invention by molding, usually, a composite material containing a noble metal and zeolite is kneaded with an inorganic binder such as silica or alumina, or an inorganic fiber such as alumina fiber or glass fiber, and molded by an extrusion method, a compression method, etc., and then fired to obtain it. Preferably, at this time, by molding it into a honeycomb shape, a honeycomb-shaped adsorbent can be obtained.

[0068] Also, the nitrogen oxide adsorbent may be obtained by a coating method. When obtaining the nitrogen oxide adsorbent by the coating method, usually, the composite material containing the noble metal and zeolite of the present invention and an inorganic binder such as silica or alumina are mixed to prepare a slurry, which is applied to the surface of a molded body made of an inorganic material such as cordierite and fired. Preferably, at this time, by applying it to a honeycomb-shaped molded body, a honeycomb-shaped adsorbent can be obtained. Here, since the adsorbent for exhaust gas treatment described later is taken as an example, an inorganic binder is used, but an organic binder may be used depending on the application and usage conditions.

[0069] When using the composite material of the present invention as a nitrogen oxide adsorbent, usually, the adsorbed nitrogen oxides are rendered harmless after adsorption. When used in an engine system, the composite material of the present invention may be installed upstream of the SCR catalyst, upstream of the particulate filter, or upstream of the oxidation catalyst. Also, the nitrogen oxide adsorbent of the present invention may be mixed with the oxidation catalyst and installed.

[0070] When using the composite material of the present invention as an adsorbent for nitrogen oxides, usually, the composite material of the present invention is brought into contact with a gas containing nitrogen oxides to adsorb the nitrogen oxides contained in the gas. The gas to be treated may contain components other than nitrogen oxides, for example, hydrocarbons, carbon monoxide, carbon dioxide, hydrogen, nitrogen, oxygen, sulfur oxides, water, etc. The adsorbent of the present invention exhibits excellent nitrogen oxide adsorption ability when treating a gas containing water. The adsorption of nitrogen oxides using the composite material of the present invention can be specifically applied to the adsorption of nitrogen oxides contained in various exhaust gases discharged from diesel vehicles, gasoline vehicles, various diesel engines for stationary power generation, ships, agricultural machinery, construction machinery, motorcycles, aircraft, boilers, gas turbines, etc.

[0071] In addition, the adsorbent of the present invention exhibits particularly excellent nitrogen oxide adsorption ability when treating a gas containing water in a low-temperature environment. Therefore, the adsorbent can be used, for example, to treat a gas at 20 to 110°C, and it is preferable to adsorb nitrogen oxides in these low-temperature ranges. Further, the adsorbent may be placed in an environment at a temperature higher than the low-temperature range (for example, a temperature higher than 110°C) after adsorption, thereby releasing the adsorbed nitrogen oxides.

[0072] <Nitrogen Oxide Removal Device> The composite material (nitrogen oxide adsorbent) of the present invention can be used as a device (nitrogen oxide removal device) for removing nitrogen oxides. The nitrogen oxide removal device includes at least the above composite material, and the composite material adsorbs nitrogen oxides from a gas that circulates in the device and contains water and nitrogen oxides. The gas may contain components other than water and nitrogen oxides, and the details are as described above. The nitrogen oxide removal device can be used, for example, as a system for purifying automotive exhaust gas.

[0073] In addition to the composite material, the nitrogen oxide removal device includes a nitrogen oxide reduction catalyst, and in the gas flow path, it is preferable that the composite material is arranged in front of the nitrogen oxide reduction catalyst. The nitrogen oxide reduction catalyst is preferably a selective reduction type catalyst (SCR catalyst) that reduces nitrogen oxides with a reducing agent. Examples of the reducing agent include ammonia. The reducing agent may be supplied from a reducing agent supply unit to the SCR catalyst, and the supplied reducing agent may be ammonia itself or a compound capable of generating ammonia. An example of a compound capable of generating ammonia is urea. The SCR catalyst is not particularly limited, and a known SCR catalyst can be used.

[0074] In the nitrogen oxide removal device having the above-described SCR catalyst, when the temperature of the flowing gas (e.g., exhaust gas) is in the low temperature range (e.g., 20 to 110°C), nitrogen oxides in the exhaust gas are adsorbed by the composite material. Further, when the temperature of the exhaust gas is in the high temperature range (e.g., a temperature higher than 110°C), usually, the nitrogen oxides adsorbed on the adsorbent are desorbed by the high-temperature exhaust gas. On the other hand, the SCR catalyst is a catalyst that can reduce nitrogen oxides with a reducing agent at a high temperature range (e.g., a temperature higher than 110°C). Generally, the exhaust gas is at a low temperature at the initial stage of operation, but becomes high temperature after a certain period of time from the start of operation.

[0075] Therefore, in the nitrogen oxide removal device having the SCR catalyst, for example, when low-temperature exhaust gas is discharged and passes through the nitrogen oxide adsorbent, the nitrogen oxides contained in the exhaust gas are adsorbed by the nitrogen oxide adsorbent, thereby reducing the amount of nitrogen oxides in the exhaust gas. On the other hand, when high-temperature exhaust gas is discharged and passes through the composite material, nitrogen oxides are not adsorbed by the composite material, and furthermore, the adsorbed nitrogen oxides are desorbed. Therefore, the exhaust gas containing the desorbed nitrogen oxides is sent from the composite material to the SCR catalyst. In the SCR catalyst, the nitrogen oxides contained in the exhaust gas are reduced to nitrogen etc. by the reducing agent. Thereby, the nitrogen oxide removal device can reduce the nitrogen oxides contained in the exhaust gas even when the exhaust gas is at a high temperature. Further, the nitrogen oxide removal device may appropriately include a particulate filter, an oxidation catalyst, etc., and the composite material may be used, for example, by mixing it with an oxidation catalyst.

Example

[0076] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

[0077] 〔Analysis and Evaluation〕 In the following examples and comparative examples, the analysis and performance evaluation of the obtained zeolite were carried out by the following methods.

[0078] [Measurement of Powder XRD] [Sample Preparation] 100 mg of zeolite pulverized using an agate mortar was held in a sample holder. [Apparatus Specifications and Measurement Conditions] The specifications and measurement conditions of the powder XRD measuring apparatus are as shown in Tables 1 and 2 below.

[0079] [Table 1] [Table 2]

[0080] [Measurement of Average Particle Size of Zeolite] In the present invention, the particle size was measured as the average value of the particle sizes of 30 or more arbitrarily selected particles in particle observation using a scanning electron microscope. The particle size was defined as the diameter of a circle (equivalent circular diameter) having an area equal to the projected area of the particle.

[0081] [Composition Analysis of Zeolite] The contents of silicon atoms and aluminum atoms in the zeolite of the standard sample were determined as follows. After heating and dissolving the zeolite of the standard sample in an aqueous hydrochloric acid solution, the contents (mass %) of silicon atoms and aluminum atoms were determined by ICP analysis. Then, fluorescence X-ray analysis of this standard sample was performed to create a calibration curve between the fluorescence X-ray intensity and the elemental concentration by ICP analysis. Using this calibration curve, the contents (mass %) of silicon atoms and aluminum atoms in the zeolite sample were determined by fluorescence X-ray (XRF) analysis. ICP analysis was performed using an apparatus named ULTIMA 2C manufactured by Horiba, Ltd. XRF analysis was performed using an apparatus named EDX-700 manufactured by Shimadzu Corporation.

[0082] [Measurement of Specific Surface Area of Zeolite] 20 mg of the composite material containing noble metal and zeolite was placed in a quartz cell, and after subjecting it to heat treatment under reduced pressure at 400 °C for 2 hours, the adsorption isotherm (adsorbed gas: nitrogen) was measured at liquid nitrogen temperature using BELSORP-miniII manufactured by MicrotracBEL Corp. The specific surface area was calculated by the BET multipoint method from the nitrogen adsorption isotherm. The calculation was performed at p / p0 = 0.01 to 0.10 where good linearity was obtained in the BET plot. Pretreatment temperature: 400 °C, pretreatment time: 2 hours, pretreatment atmosphere: vacuum, adsorbed gas: nitrogen, BET analysis range: p / p0 = 0.01 to 0.10

[0083] [Measurement of Acid Amount of Zeolite] The maximum peak intensity by the ammonia temperature-programmed desorption method (NH 3 -TPD) of the composite material containing noble metal and zeolite is determined as follows. The composite material containing noble metal and zeolite was spread in a glass petri dish and stored in a desiccator with a relative humidity of 50% using a saturated aqueous magnesium nitrate solution for 12 hours to be hygroscopic. The hygroscopic composite material was measured for the thermogravimetric change from room temperature to 800 °C under air flow, and the weight change was taken as the moisture content. 50 mg of the hygroscopic composite material was filled in a quartz glass cell, and the measurement was carried out under the following conditions. Measuring device: BELCAT-II (manufactured by MicrotracBEL Corp) Pretreatment temperature: 450 °C, pretreatment time: 1 hour, ammonia adsorption temperature: 160 °C, ammonia adsorption time: 15 minutes, desorption temperature range: 160 °C to 800 °C

[0084] [Measurement of Nitrogen Oxide Adsorption Amount] The amount of nitrogen oxides adsorbed on the nitrogen oxide adsorbent (adsorbed NO amount) was determined as follows. A gas with a water vapor content of 0% by volume and a gas with a water vapor content of 5% by volume were each passed through, and the adsorbed NO amount was measured for each case. (Pretreatment Conditions) Gas composition: nitrogen Temperature rising rate: 10 K / min Drying time: 500 °C Holding time: 0.5 hour (NO adsorption conditions) Adsorption temperature: 80 °C, 120 °C Gas composition: NO = 200 volume ppm, O 2 = 5 volume %, water = 0 volume % or 5 volume %, balance N 2 Space velocity (SV): 70,000 / h NO adsorption time: 30 minutes After NO adsorption, the supply of only NO was stopped and the gas was passed for 30 minutes. Then, the temperature was raised under the following conditions to desorb the gas adsorbed on NO, and the amount of nitrogen oxide adsorbed on the adsorbent was measured based on the amount of desorbed NO. (NO desorption conditions) Heating rate: 10 K / min Desorption temperature range: 80 °C to 600 °C (Measuring equipment) NOx meter: ECL-88A Lite manufactured by Yanaco Technical Science Co., Ltd.

[0085] [Example 1] [Manufacture of RHO-type zeolite] RHO-type zeolite was synthesized as follows. 22.8 g of 18-crown-6-ether (manufactured by Tokyo Chemical Industry Co., Ltd.), 5.8 g of NaOH (manufactured by Kishida Chemical Co., Ltd.), and 4.7 g of CsOH·H 2 O (manufactured by Mitsuwa Chemical Co., Ltd.) were dissolved in 84.1 g of water, and the resulting solution was stirred at 80 °C for 3 hours to obtain a crown ether-alkali aqueous solution.

[0086] 29.8 g of FAU-type zeolite (SiO 2 / Al 2 O 3 molar ratio = 30, CBV720 manufactured by Zeolyst), the above crown ether-alkali aqueous solution was added dropwise, and 0.6 g of RHO-type zeolite synthesized according to Microporous Materials 4 (1995) 231-238 was added as a seed crystal (assuming that all Si in the raw material mixture was SiO 2 when it became 2To this, 2.0 mass% was added, and the mixture was stirred at room temperature for 2 hours to prepare a pre-reaction mixture. The composition of this mixture (molar ratio excluding seed crystals) is as follows. SiO 2 / Al 2 O 3 / NaOH / CsOH / H 2 O / 18-crown-6-ether = 1 / 0.033 / 0.30 / 0.06 / 10 / 0.18

[0087] After aging this pre-reaction mixture at room temperature for 24 hours, it was placed in a pressure-resistant container and left in an oven at 160 °C for 72 hours of hydrothermal synthesis. After this hydrothermal synthesis reaction, the reaction solution was cooled and filtered to recover the formed crystals. When the recovered crystals were dried at 100 °C for 12 hours and the obtained powder was subjected to XRD measurement, it was confirmed that RHO-type zeolite having peaks and relative intensities at the positions shown in Fig. 1 was obtained. By XRF analysis, the SiO 2 / Al 2 O 3 ratio was 15 and the average particle size was 5.0 μm.

[0088] 〔OSDA Removal Treatment〕 To remove the organic matter in the zeolite, the RHO-type zeolite synthesized as described above was calcined in an air stream at 500 °C for 5 hours.

[0089] 〔Ion Exchange Treatment to Ammonium Type〕 Next, to remove the alkali cations (sodium cation, cesium cation) contained in the calcined RHO-type zeolite, it was dispersed in a 1 mol / L NH 4 NO 3 aqueous solution and subjected to an ion exchange treatment at 80 °C for 2 hours. After the treatment for a predetermined time, the zeolite was recovered by filtration and washed three times with ion-exchanged water. Thereafter, the ion exchange treatment using the NH 4 NO 3 aqueous solution, filtration recovery, and three washes were repeated five times. By drying the obtained zeolite powder at 100 °C for 12 hours, ammonium-type RHO-type zeolite was obtained.

[0090] [Palladium Loading Treatment] The impregnation treatment of palladium on zeolite was carried out under the following conditions. After dissolving 0.075 g of palladium nitrate (manufactured by Aldrich) in 10 g of ion-exchanged water as a solvent so that 3% by mass of palladium was loaded on the ammonium-type RHO zeolite, 1 g of the ammonium-type RHO zeolite was added to prepare a mixed slurry. While distilling the mixed slurry under reduced pressure at 50 °C using an evaporator, water as the solvent was removed. Then, the step of adding 10 g of ion-exchanged water again to form a slurry and then distilling it under reduced pressure using an evaporator was repeated 3 times in total to obtain RHO zeolite impregnated with palladium.

[0091] [Steam Treatment] The RHO zeolite loaded with palladium was subjected to steam treatment at 750 °C with 10% by volume of steam at a space velocity SV = 3000 / h for 5 hours to obtain palladium-loaded RHO zeolite. The specific surface area of the RHO zeolite loaded with palladium after the steam treatment was 560 m 2 / g.

[0092] [Example 2] Palladium-loaded RHO zeolite was obtained in the same manner as in Example 1, except that the steam concentration during the steam treatment of the palladium-loaded RHO zeolite was changed to 20% by volume.

[0093] [Comparative Example 1] (Manufacture of RHO zeolite by a general method) RHO zeolite was synthesized by the method described in Microporous Materials 4 (1995) 231-238. Its XRD pattern is shown in Figure 2. Also, the SiO 2 / Al 2 O 3 ratio was 10 and the average particle size was 1.9 μm. The above RHO-type zeolite was subjected to an OSDA removal treatment, an ion exchange treatment to an ammonium type, a palladium loading treatment, and a steam treatment under the same conditions as in Example 1 to obtain a palladium-loaded RHO-type zeolite.

[0094] [Comparative Example 2] (Production of CHA-type zeolite) First, a CHA-type zeolite as a seed crystal was synthesized. After preparing a reaction mixture having the following composition, hydrothermal synthesis was carried out at 160 °C for 2 days, and then the reaction solution was cooled and filtered to recover the crystals formed. The recovered crystals were dried at 100 °C for 12 hours to obtain a CHA-type zeolite for seed crystals. Al 2 O 3 / SiO 2 / NaOH / KOH / OSDA / H 2 O = 0.033 / 1 / 0.1 / 0.06 / 0.07 / 20

[0095] The raw materials for the seed crystal are as follows. Al source: Al(OH) 3 (Al 2 O 3 : 53.5% by mass, manufactured by Aldrich) Na source: NaOH (manufactured by Wako Pure Chemical Industries, Ltd.) K source: KOH (manufactured by Wako Pure Chemical Industries, Ltd.) OSDA: Aqueous solution of N,N,N-trimethyl-1-adamantanammonium hydroxide (TMADAOH) (containing 25% by mass of TMADAOH, manufactured by Seikem Co., Ltd.) Si source: Colloidal silica (silica concentration: 30% by mass, Cataloid Si-30, manufactured by Nippon Shokubai Catalysts & Chemicals, Ltd.)

[0096] Next, a raw material mixture for hydrothermal synthesis having the following composition was prepared, and the above-mentioned CHA-type zeolite for seed crystals was added thereto so that all the Si in the raw material mixture was SiO 2 assuming that it had become 2It was added to be 2.0 mass%. After hydrothermal synthesis was carried out at 160 °C for 2 days, the reaction solution was cooled and the crystals formed were recovered by filtration. The recovered crystals were dried at 100 °C for 12 hours to obtain CHA-type zeolite. Also, the SiO 2 / Al 2 O 3 molar ratio was 25. Al 2 O 3 / SiO 2 / NaOH / KOH / OSDA / H 2 O = 0.033 / 1 / 0.1 / 0.06 / 0.07 / 20

[0097] The raw materials are as follows. Al source: Al(OH) 3 (Al 2 O 3 : 53.5 mass%, manufactured by Aldrich) Na source: NaOH (manufactured by Wako Pure Chemical Industries, Ltd.) K source: KOH (manufactured by Wako Pure Chemical Industries, Ltd.) OSDA: Aqueous solution of N,N,N-trimethyl-1-adamantanammonium hydroxide (TMADAOH) (containing 25 mass% of TMADAOH, manufactured by Seikem Co., Ltd.) Si source: Colloidal silica (silica concentration: 30 mass%, Cataloid Si-30, manufactured by Nippon Shokubai Catalysts & Chemicals, Ltd.)

[0098] 〔OSDA removal treatment〕 To remove the organic matter in the zeolite, the CHA-type zeolite was calcined in an air stream at 600 °C for 5 hours.

[0099] 〔Ion exchange treatment to ammonium form〕 Next, to remove the alkali cations (sodium cation, potassium cation) contained in the calcined CHA-type zeolite, it was dispersed in a 1 mol / L NH 4 NO 3 aqueous solution, and an ion exchange treatment was carried out at 80 °C for 2 hours. After the treatment for a predetermined time was completed, the zeolite was recovered by filtration and washed 3 times with ion-exchanged water. Then, once again, it was dispersed in a 1 mol / L NH 4 NO3 Ion exchange treatment and washing were performed twice using an aqueous solution. The obtained zeolite powder was dried at 100 °C for 12 hours to obtain ammonium-type CHA zeolite.

[0100] 〔Palladium loading treatment〕 The impregnation treatment for loading palladium was carried out under the following conditions. After dissolving 0.075 g of palladium nitrate (manufactured by Aldrich) in 10 g of ion-exchanged water as a solvent so that 3 mass% of palladium was loaded on the ammonium-type CHA zeolite, 1 g of the ammonium-type CHA zeolite was added to prepare a mixed slurry. While distilling the mixed slurry under reduced pressure using an evaporator, water as the solvent was removed. Thereafter, the process of adding 10 g of ion-exchanged water again to form a slurry and distilling it under reduced pressure using an evaporator was repeated 3 times in total to obtain CHA zeolite loaded with palladium by impregnation.

[0101] 〔Steam treatment〕 Steam treatment was performed on the CHA zeolite loaded with palladium by passing 10 vol% of steam at 750 °C through it at a space velocity SV = 3000 / h for 15 hours to obtain palladium-loaded CHA zeolite.

[0102] [Comparative Example 3] (Production of AEI-type zeolite 1) A raw material mixture for hydrothermal synthesis having the following composition was prepared, and the CHA zeolite (unfired product) with SAR = 25 synthesized in Comparative Example 2 was added thereto so that it became 5.0 mass% with respect to SiO when all the Si in the raw material mixture was SiO. 2 When it became 2 Hydrothermal synthesis was carried out at 180 °C for 1 day, and then the reaction solution was cooled and filtered to recover the crystals formed. The recovered crystals were dried at 100 °C for 12 hours to obtain AEI-type zeolite 1. Also, the SiO / AlO molar ratio by XRF analysis was 11. 2 / Al 2 O 3 Al 2 O 3 / SiO 2 ​ / NaOH / OSDA / H 2 O = 0.054 / 1 / 0.22 / 0.43 / 22

[0103] The raw materials are as follows. Al source: Al(OH) 3 (Al 2 O 3 : 53.5 mass%, manufactured by Aldrich) Na source: NaOH (manufactured by Wako Pure Chemical Industries, Ltd.) OSDA: N,N-dimethyl-3,5-dimethylpiperidinium hydroxide (containing 35 mass%, manufactured by Seikem Co., Ltd.) Si source: Colloidal silica (silica concentration: 40 mass%, ST-40, manufactured by Nissan Chemical Industries, Ltd.)

[0104] 〔OSDA removal treatment〕 In order to remove the organic substances in the zeolite, AEI-type zeolite 1 was calcined at 600 °C under an air stream for 5 hours.

[0105] 〔Ion exchange treatment to ammonium form〕 Next, in order to remove the alkali cations (sodium cations) contained in the calcined AEI-type zeolite, it was dispersed in a 1 mol / L NH 4 NO 3 aqueous solution, and an ion exchange treatment was carried out at 80 °C for 2 hours. After the treatment for a predetermined time, the zeolite was recovered by filtration and washed 3 times with ion-exchanged water. Then, once again, an ion exchange treatment and washing using a 1 mol / L NH 4 NO 3 aqueous solution were carried out a total of 2 times. The obtained zeolite powder was dried at 100 °C for 12 hours to obtain ammonium-form AEI-type zeolite 1.

[0106] 〔Palladium loading treatment〕 The impregnation treatment for supporting palladium was carried out under the following conditions. In order to support 3% by mass of palladium on the ammonium-type AEI zeolite 1, 0.075 g of palladium nitrate (manufactured by Aldrich) was dissolved in 10 g of ion-exchanged water as a solvent, and then 1 g of the ammonium-type AEI zeolite 1 was added to prepare a mixed slurry. While distilling the mixed slurry under reduced pressure using an evaporator, the water as the solvent was removed. Thereafter, the step of adding 10 g of ion-exchanged water again to form a slurry and distilling it under reduced pressure using an evaporator was repeated three times in total to obtain the AEI zeolite 1 impregnated with palladium.

[0107] [Steam treatment] The AEI zeolite 1 impregnated with palladium was subjected to steam treatment by passing 10% by volume of steam at 750 °C at a space velocity SV = 3000 / h for 5 hours to obtain the palladium-supported AEI zeolite 1.

[0108] [Comparative Example 4] [Palladium loading treatment] The impregnation treatment for supporting palladium was carried out under the following conditions. The AEI zeolite 2 impregnated with palladium was obtained by using the same method as in Comparative Example 3 except that 0.025 g of palladium nitrate (manufactured by Aldrich) was used so that 1% by mass of palladium was supported on the ammonium-type AEI zeolite 1.

[0109] [Steam treatment] The AEI zeolite 2 impregnated with palladium was subjected to steam treatment by passing 10% by volume of steam at 750 °C at a space velocity SV = 3000 / h for 5 hours to obtain the palladium-supported AEI zeolite 2.

[0110] [Comparative Example 5] (Production of AEI zeolite 2) The AEI zeolite 2 was obtained by the method described in Example 2 of U.S. Patent 5,958,370. The details are as follows. 1.9 g of water, 5.5 g of N,N-dimethyl-3,5-dimethylpiperidinium hydroxide (manufactured by Seikem), and 20.5 g of 1 M (mol / L) NaOH aqueous solution (manufactured by Wako Pure Chemical Industries) were mixed, and 2.4 g of Y-type zeolite (USY30 CBV720, manufactured by Zeolyst) (framework density: 12.7 T / 1000 Å 3 ) was added and stirred to dissolve to obtain a transparent solution. 1.9 g of Snowtex 40 (silica concentration: 40% by mass, manufactured by Nissan Chemical Industries) was added thereto, and the mixture was stirred at room temperature for 2 hours to obtain a pre-reaction mixture. This pre-reaction mixture was placed in a pressure-resistant container and hydrothermally synthesized for 7 days while rotating in an oven at 135 °C (15 rpm). After this hydrothermal synthesis reaction, the reaction solution was cooled, and the crystals formed were collected by filtration. The collected crystals were dried at 100 °C for 12 hours to obtain AEI-type zeolite 2. Also, the SiO 2 / Al 2 O 3 molar ratio was 15.

[0111] 〔OSDA removal treatment〕 To remove the organic matter in the zeolite, AEI-type zeolite 2 was calcined in a stream of air at 600 °C for 5 hours.

[0112] 〔Ion exchange treatment to ammonium form〕 Next, to remove the alkali cations (sodium cations) contained in the calcined AEI-type zeolite, it was dispersed in a 1 mol / L NH 4 NO 3 aqueous solution, and an ion exchange treatment was carried out at 80 °C for 2 hours. After the treatment for a predetermined time was completed, the zeolite was collected by filtration and washed 3 times with ion-exchanged water. Then, once again, an ion exchange treatment and washing using a 1 mol / L NH 4 NO 3 aqueous solution were carried out a total of 2 times. The obtained zeolite powder was dried at 100 °C for 12 hours to obtain ammonium-type AEI-type zeolite 2.

[0113] 〔Palladium loading treatment〕 The impregnation treatment for supporting palladium was carried out under the following conditions. In order to support 1% by mass of palladium on the ammonium-type AEI zeolite 2, 0.025 g of palladium nitrate (manufactured by Aldrich) was dissolved in 10 g of ion-exchanged water as a solvent, and then 1 g of the ammonium-type AEI zeolite 2 was added to prepare a mixed slurry. While distilling the mixed slurry under reduced pressure using an evaporator, water as the solvent was removed. Thereafter, the step of adding 10 g of ion-exchanged water again to form a slurry and distilling it under reduced pressure using an evaporator was repeated three times in total to obtain the AEI zeolite 3 impregnated with palladium.

[0114] 〔Steam treatment〕 The AEI zeolite 3 impregnated with palladium was subjected to steam treatment by passing 10% by volume of steam at 750 °C at a space velocity SV = 3000 / h for 5 hours to obtain the palladium-supported AEI zeolite 3.

[0115] 〔Evaluation of nitrogen oxide adsorption performance〕 For the composite materials of each example and comparative example, the nitrogen oxide adsorption amounts (A1, A2) were measured when the moisture content in the gas was 0% by volume and 5% by volume, respectively, and the nitrogen oxide adsorption amount change rate was obtained from the ratio (A2 / A1) and shown in Table 3. In addition, in Reference Example 1, the CHA zeolite supporting palladium described in Comparative Example 2 was used, and in Reference Example 2, the AEI zeolite supporting palladium described in Comparative Example 3 was used. The results with the adsorption temperature changed to 120 °C are also shown in Table 3.

[0116]

Table 3

[0117] It has been clarified that the specific RHO zeolite supporting the noble metal of the present invention exhibits the characteristic that the nitrogen oxide adsorption amount is not decreased but rather higher when water is included even in a gas atmosphere close to the water concentration actually contained in automobile exhaust gas. Even among nitrogen oxide adsorbents of the present invention having the same RHO-type structure, those with a higher SAR exhibit the characteristic of expressing a high nitrogen oxide adsorption capacity without being affected by water. Generally, it is known that as the SAR increases, the acid sites of the zeolite, which serve as water adsorption sites, decrease, making it difficult for water to penetrate into the zeolite pores. However, as described above, since the zeolite of the example of the present application is less affected by water than Comparative Examples 2 and 5 with an equivalent or higher SAR, it is not simply the case that increasing the SAR makes it less susceptible to the influence of water. It is presumed that this supports the importance of a specific structure and a specific SAR in the coexistence of nitrogen oxides and water.

[0118] On the other hand, when palladium is supported on a high-SAR CHA-type zeolite as in Comparative Example 2, it was clarified that it is affected by water. This is presumably because the CHA-type zeolite has a small-sized d6r in its structure, and when the gas diffuses, the water adsorbed on the d6r reduces the diffusibility of the gas and thus the adsorption performance of nitrogen oxides. In contrast, the nitrogen oxide adsorbent of the present invention contains lta as a CBU in the zeolite structure, and the gas diffuses through the d8r of lta. Since the d8r is larger in size than the d6r, it is presumed that even when water is adsorbed, the pores are large enough for the gas to diffuse, making it less susceptible to the influence of the adsorbed water. Moreover, since water has a smaller kinetic diameter than nitrogen oxides, preferably coordinating water creates a state where the gas diffuses more easily than when only nitrogen oxides coordinate to the adsorption sites. It is considered that the nitrogen oxide adsorbent of the present invention adsorbs a larger amount of nitrogen oxides from a gas containing water. As described above, in the present invention, as a nitrogen oxide adsorbent that exhibits high nitrogen oxide adsorption performance even in the presence of water, a composite material in which a noble metal is supported on a zeolite having a specific CBU and a SiO 2 / Al 2 O 3 molar ratio can be provided.

Claims

1. A nitrogen oxide adsorbent comprising a composite material containing a noble metal and a zeolite, wherein the zeolite contains lta defined by the International Zeolite Association (IZA) as a composite building unit in the framework, and the SiO ２ / Al ２ O ３ molar ratio is 11 or more. The nitrogen oxide adsorbent is characterized by this.

2. The nitrogen oxide adsorbent according to claim 1, wherein the maximum ring size of the zeolite is 3.6 Å or less.

3. The nitrogen oxide adsorbent according to claim 1 or 2, wherein the zeolite is an RHO-type zeolite.

4. The nitrogen oxide adsorbent according to any one of claims 1 to 3, wherein the noble metal is palladium and its content is 0.1% by mass or more.

5. When a gas containing 200 volume ppm of nitrogen oxides and 5 volume% of oxygen and having a water vapor content of 0 volume% is passed through the composite material at 80°C, the nitrogen oxide adsorption amount is designated as A1, and when a gas containing 200 volume ppm of nitrogen oxides and 5 volume% of oxygen and having a water vapor content of 5 volume% is passed through the composite material at 80°C, the nitrogen oxide adsorption amount is designated as A2, the change rate of nitrogen oxide adsorption amount represented by the ratio (A2 / A1) is 0.6 or more and 2.0 or less. The nitrogen oxide adsorbent according to any one of claims 1 to 4.

6. A nitrogen oxide adsorbent comprising a composite material containing a noble metal and a zeolite, when a gas containing 200 volume ppm of nitrogen oxides and 5 volume% of oxygen and having a water vapor content of 0 volume% is passed through the composite material at 80°C, the nitrogen oxide adsorption amount is designated as A1, and when a gas containing 200 volume ppm of nitrogen oxides and 5 volume% of oxygen and having a water vapor content of 5 volume% is passed through the composite material at 80°C, the nitrogen oxide adsorption amount is designated as A2, the change rate of nitrogen oxide adsorption amount represented by the ratio (A2 / A1) is 0.6 or more and 2.0 or less. The nitrogen oxide adsorbent.

7. The nitrogen oxide adsorbent according to any one of claims 1 to 6 for adsorbing nitrogen oxides from a gas containing water.

8. A method for adsorbing nitrogen oxides in a gas containing water and nitrogen oxides by using the nitrogen oxide adsorbent according to any one of claims 1 to 7.

9. A nitrogen oxide removal device comprising the nitrogen oxide adsorbent according to any one of claims 1 to 7, wherein the nitrogen oxides in the gas are removed by adsorbing the nitrogen oxides from the gas containing water and nitrogen oxides by the composite material.

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