JP2003024777A - Nitrogen oxide adsorber and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitrogen oxide adsorber with the capability of removing excess water droplets generated by condensation or the like and adsorbing a nitrogen oxide. SOLUTION: This nitrogen oxide adsorber contains an adsorbing substance 1 with a nitrogen oxide adsorbing power, a water repelling substance with water repellency, and an binding substance which binds these substances. In addition, the water-repelling substance and the binding substance are the same and water-repellent integrating substances 2. Further, the method for manufacturing the nitrogen oxide adsorber comprises the step to disperse particles of the adsorbing substance into a solvent, then add the water repelling substance and the binding substance or the water reppelent binding substance and mix/ grind the mixture to adjust the slurry and the step to bake the dried slurry and the step to grind the baked slurry.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a relatively dilute nitrogen oxide discharged into the atmosphere from an internal combustion engine used in automobiles and small power generators, heaters such as fan heaters and stoves, and incinerators. The present invention relates to a nitrogen oxide adsorbent that adsorbs substances and a method for producing the same.

[0002]

2. Description of the Related Art Nitrogen oxides emitted from a conventional gasoline engine automobile are reduced and purified by a three-way catalyst or the like and then released into the atmosphere. On the other hand, since it is difficult for catalysts to completely reduce and purify nitrogen oxides emitted from lean-burn engines and automobiles equipped with diesel engines, trace amounts of diluted nitrogen oxides are emitted to the atmosphere. In particular, since retention of nitrogen oxides easily occurs in closed spaces such as underground parking lots and road tunnels, a method for removing dilute nitrogen oxides is required. As one of the methods,
A method of capturing nitrogen oxides using an adsorbent and then decomposing and removing the nitrogen oxides by various methods has been put into practical use.

For example, Japanese Unexamined Patent Publication No. 5-253444 discloses a method of removing dilute nitrogen oxides by a rotary adsorption type denitration device. In this conventional technique, nitrogen oxides are once adsorbed on a rotary nitrogen oxide adsorbent, and then,
Ammonia is used to reduce and purify the adsorbed nitrogen oxides. In this prior art, a ruthenium halide is supported on a ceramic paper carrier that holds anatase-type titania as a nitrogen oxide adsorbent.

In Japanese Patent Laid-Open No. 2001-120951, a gas containing nitrogen oxides is mixed with ozone,
A method of removing nitrogen oxides by adsorbing it onto zeolite terminated with hydrogen ions is disclosed. According to this conventional technique, ozone is used to oxidize nitric oxide, which is a main component of nitrogen oxides in the atmosphere, to nitrogen dioxide or dinitrogen pentoxide, thereby enabling efficient adsorption to a hydrogen-terminated zeolite. .

[0005]

However, in the nitrogen oxide adsorbent disclosed in Japanese Unexamined Patent Publication No. 5-253444, since water acts as an adsorption interfering substance, the treatment gas is provided in the preceding stage of the nitrogen oxide adsorbent. A device for dehumidifying is required, and since the energy consumed by this dehumidifying device is large, a large amount of energy is required for adsorbing nitrogen oxides.

Further, in the nitrogen oxide adsorbent disclosed in Japanese Unexamined Patent Publication No. 2001-120951, it is not necessary to dehumidify the processing gas, but under the high humidity condition where dew condensation occurs on the nitrogen oxide adsorbent. However, there is a problem that the adsorption efficiency is extremely reduced.

The present invention has been made to solve the above-mentioned problems of the conventional ones, and nitrogen oxidation capable of retaining the ability to adsorb nitrogen oxides by eliminating excessive water droplets caused by dew condensation or the like. The object is to provide a substance adsorbent.

[0008]

SUMMARY OF THE INVENTION The present invention has been made as a result of the inventors' earnest research on the structure of a nitrogen oxide adsorbent in view of the above problems.

The nitrogen oxide adsorbent according to the present invention comprises an adsorbing substance having a nitrogen oxide adsorbing ability, a water repellent substance having water repellency, and a binding substance binding these substances. is there.

Further, the water-repellent substance and the binder substance are the same, and they are water-repellent binder substances.

Further, the water repellent substance contains a fluorine atom or a silicon atom.

Further, the water-repellent binding substance is a polymer having a tetrafluoroethylene structure.

The adsorbing material is a composite oxide of silicon and aluminum.

The composite oxide of silicon and aluminum contains a metal or ion having a positive charge.

Further, the noble metal is supported on the adsorbent.

The noble metal is platinum, palladium, ruthenium or rhodium.

Further, in the method for producing a nitrogen oxide adsorbent according to the present invention, the particles of the adsorbent are dispersed in a solvent, the water repellent substance and the binder substance are added, or the water repellent binder substance is added, and the mixture is pulverized. The step of adjusting the slurry, the step of drying the slurry, the step of firing the dried slurry,
And a step of crushing the calcined slurry.

Further, the particles of the adsorbing substance are dispersed in a solvent,
A step of adding a water-repellent substance and a binder substance or a water-repellent binder substance, mixing and pulverizing to prepare a slurry, a step of applying the slurry to a substrate and then drying, and a dried slurry. It has a step of firing.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1. 1 is a cross-sectional view schematically showing the structure of a nitrogen oxide adsorbent according to Embodiment 1 of the present invention. In FIG. 1, 1 is an adsorbent (particles) having a nitrogen oxide adsorbing ability, and 2 is a repellent material. It is a water-soluble binding substance, that is, a water-repellent binding substance. In the thus configured device, nitrogen dioxide among the nitrogen oxides contained in the processing gas (for example, air) reacts with the water molecules captured by the adsorbent 1 to become nitric acid. Adsorption due to the electrical action of the negative charge of the nitrate ion (NO ₃ ⁻ ) generated at this time and the positive charge of the adsorbent 1 causes the nitrate ion to be captured by the adsorbent 1, resulting in the nitrogen oxidation. The substance is adsorbed on the adsorbent substance 1. On the other hand, the binding substance 2 binds the adsorbing substances (particles) 1 to each other or binds the adsorbing substance 1 to the base material, but if the binding substance 2 is water repellent, dew condensation will occur. Water that inhibits adsorption of nitrogen oxides (especially liquid water) even when used under high humidity conditions
It is possible to suppress the contact of the adsorbent 1 with the adsorbent 1 and prevent the surface of the adsorbent 1 from being covered with water. As a result, the nitrate ions easily come close to the adsorption site of the adsorbent 1, so that the trapping amount increases and the nitrogen oxide adsorption amount increases.

Embodiment 2. FIG. 2 is a sectional view schematically showing the structure of the nitrogen oxide adsorbent according to the second embodiment of the present invention. In FIG. 2, 3 is a noble metal (particle), which is carried by the adsorbent 1. In such a structure, when nitric oxide, which is the main component of nitrogen oxides contained in the processing gas (for example, air), comes into contact with the noble metal 3, catalytic reaction causes dissociation to become reactive. At that time, it is oxidized by oxygen in the vicinity and converted into nitrogen dioxide or dinitrogen pentoxide. This nitrogen dioxide or dinitrogen pentoxide reacts with the water molecules trapped in the adsorbent 1 to become nitric acid. After that, as in the case of the first embodiment, nitrate ions are captured by the adsorbent 1, and as a result, nitrogen oxides are adsorbed by the adsorbent 1. Thus, not only nitrogen dioxide contained in the process gas but also nitric oxide can be adsorbed by the oxidation, so that the adsorption amount of nitrogen oxides can be increased. Note that, since the binding substance 2 is water repellent, the adsorption amount of nitrogen oxides is increased, as in the case of the first embodiment.

1 and 2, the case where the water-repellent binding substance 2 is used is shown. Thus, when the water-repellent substance and the binder substance are the same, it is possible to reduce the number of constituent materials, improve economic efficiency, and increase the adsorbable surface area of the adsorbent substance 1. Become. However, the water repellent substance and the binding substance may be different substances.

The water-repellent substance has a contact angle with water of 10
Any substance having a temperature of 0 degree or higher may be used. Specifically, those having a silicon atom or a fluorine atom, such as a silicon oxide skeleton substituted with a methoxy group or an ethoxy group and a carbon skeleton substituted with fluorine, are preferable from the viewpoint of heat resistance and the like.

As the water-repellent binding substance 2, the binding temperature is below the maximum heat resistant temperature of the adsorbing substance 1, and the melting temperature or decomposition temperature of the water-repellent binding substance 2 is the desorption of the adsorbed nitrogen oxides. Any material having a temperature higher than the separation temperature can be used. Specifically, a resin compound containing fluorine, such as polytetrafluoroethylene, which is a polymer having a tetrafluoroethylene structure, or polyvinylidene fluoride, which is a polymer having a vinylidene fluoride structure, has high heat resistance,
It is also preferable because it has high water repellency. In particular, polytetrafluoroethylene is more preferable because it has a high contact angle of 113 degrees and thus has high water repellency, and when it is heated to about 350 ° C., it exhibits binding properties.

As the adsorbing substance 1, a composite oxide of silicon and aluminum is preferable because it has high thermal stability and can adsorb a large amount of nitrogen oxide by the positively charged portion appearing near the aluminum atom. . Among them, zeolite itself has a strong molecular structure because it is crystalline, has a large specific surface area compared to other adsorbents such as activated carbon, and since it is easy to introduce a metal element, nitrogen oxides It is more preferable because a large amount can be adsorbed.

When the composite oxide further contains a metal or ion having a positive charge other than aluminum, it becomes possible to increase the amount of positive charges on the composite oxide and to adsorb a larger amount of nitrogen oxide. It will be possible. The metal or ion contained in the composite oxide, that is, the element to be substituted may be any one having a positive charge, and specifically, an alkali metal such as Na or K or Ca, Sr or Ba.
Alkaline earth metals such as, Group 1B groups such as Cu and Ag, and hydrogen are preferable because they can be in a positive charge state suitable for nitrogen oxide adsorption.

The noble metal supported on the adsorbent 1 is
Any material having an oxidation catalytic activity may be used. Specifically, any element belonging to Group 8 of the periodic table may be used, among which Pt and P
Noble metal elements such as d, Rh, Ru, Ir, and Os are preferable because they have appropriate oxidation activity. Especially Pt, Pd, R
u and Rh are preferable from the viewpoint of being able to dissociate and adsorb oxygen and nitrogen oxides on the surface of these noble metals with high efficiency, and from the viewpoint of economy.

[0027]

EXAMPLES The present invention will be described below with reference to specific examples, but of course the present invention is not limited thereto.

Preparation of metal element-substituted zeolite: 200 g of zeolite containing Na as an adsorbent (Tosoh Corporation, model number HSZ-320NAA) was dispersed in 1500 mL of an aqueous strontium nitrate solution (concentration 0.13M),
The mixture was stirred at 95 ° C for 24 hours in a reaction vessel equipped with a reflux tower. After the stirring was stopped, the temperature was lowered to room temperature to take out the zeolite, followed by filtration and washing with purified water, and then at 150 ° C. for 3 hours.
Sr in which Na was replaced with Sr
A substituted zeolite was obtained.

In the same manner, various metal-substituted zeolites in which Na was replaced with K, Ba, Ca, Cu, and Ag respectively using aqueous solutions of potassium nitrate, barium nitrate, calcium nitrate, copper nitrate, and silver nitrate were obtained. In addition, after substituting NH ₄ for NH ₄ with ammonia water, it was replaced with 5 under a hydrogen stream.
The mixture was heated at 00 ° C. for 1 hour to obtain a zeolite substituted with H.

Noble metal loading: Zeolite containing Na and K, Ba, Ca, Cu, Ag and H obtained above
Various zeolites containing (hereinafter, these Na, K, Ba,
The respective zeolites containing Ca, Cu, Ag and H are collectively referred to as various zeolites. ) 80 g of dinitroammine platinum nitric acid aqueous solution (platinum weight fraction: 0.7% by weight)
Dispersed in 200 mL, heated to 50 ° C. and stirred for 4 hours. Then, the dispersion solution is heated at 150 ° C for 3 hours at 300 ° C.
At room temperature for 2 hours to load the platinum compound, which is a precursor of the noble metal, on various zeolites, and then at 500 ° C for 2 hours in a mixed gas of hydrogen and nitrogen (volume ratio 1: 4). Then, reduction treatment was performed and metallization was performed to obtain various zeolites carrying platinum.

In the same manner as above, various zeolites carrying noble metals palladium, ruthenium and rhodium were obtained by using dinitroammine palladium nitric acid aqueous solution, ruthenium nitrate aqueous solution and rhodium nitrate aqueous solution.

Example 1. After dispersing 50 g of each kind of zeolite supporting the noble metal obtained in water, 10 g of a silicone water repellent (GE Toshiba Silicone Co., Ltd., trade name Tospearl 105) which is a water repellent substance and a binding substance are dispersed. 33 g of colloidal alumina (Catalyst Kasei Co., Ltd., trade name: Cataloid AP-3) was added, and pulverized, dispersed and mixed by a ball mill to obtain a slurry. This slurry was placed in an alumina container and kept at 120 ° C for 2 hours and at 400 ° C for 1 hour.
It was heated for a period of time, dried and calcined to obtain a lump in which the zeolite particles and the water repellent were bound. This agglomerate was crushed to an appropriate size using a mortar, and the crushed product was placed in an evaluation container to obtain a sample A for adsorption performance evaluation.

Example 2. A slurry obtained by the same method as in Example 1 was used, and the slurry was used to form a cordierite honeycomb that is a honeycomb-shaped porous ceramics base material (manufactured by NGK Insulators Ltd .: 400 cells / square inch, wall thickness 6 mils). ) Was impregnated into the interior of the cord, and then the excess slurry was removed by air blow to apply the slurry to the inner wall surface of the cordierite honeycomb. This slurry-coated honeycomb was heated at 120 ° C. for 2 hours and at 400 ° C. for 1 hour to be dried and fired, the zeolite and the water repellent were bound to the inner wall surface of the honeycomb, and the honeycomb-supported honeycomb was evaluated for adsorption performance. Sample B for use.

Example 3. After dispersing 50 g of various zeolites carrying a noble metal in water, 15 g of tetrafluoroethylene dispersion emulsion (trade name D-1 manufactured by Daikin Industries, Ltd.), which is a water-repellent binding substance, is added, and pulverized and dispersed by a ball mill. -Mixed to obtain a slurry. Place this slurry in an alumina container at 120 ° C for 2 hours and at 400 ° C for 3 hours.
It was heated for 0 minutes, dried and calcined to obtain a lump in which the zeolite particles and the water repellent were bound. This agglomerate was crushed into an appropriate size using a mortar, and the crushed product was put in an evaluation container to obtain an adsorption performance evaluation sample C.

Example 4. A slurry obtained by the same method as in Example 3 was used, and the slurry was made of cordierite honeycomb which is a honeycomb-shaped porous ceramic substrate (manufactured by NGK Insulators, Ltd .: 400 cells / square inch, wall thickness 6 mils). ) Was impregnated into the interior of the cord, and then the excess slurry was removed by air blow to apply the slurry to the inner wall surface of the cordierite honeycomb. This slurry-coated honeycomb was heated at 120 ° C. for 2 hours and at 400 ° C. for 30 minutes to be dried and fired to bond zeolite and a water repellent to the inner wall surface of the honeycomb, and the honeycomb-supported honeycomb was evaluated for adsorption performance. Sample D for.

Comparative Example 1. After dispersing 50 g of various zeolites carrying a noble metal in water, 33 g of colloidal alumina (catalyst Kasei Co., Ltd., trade name: Cataloid AP-3), which is a binding substance, is added, and pulverized and dispersed by a ball mill.
A slurry was obtained by mixing. This slurry was placed in an alumina container, heated at 120 ° C. for 2 hours and at 400 ° C. for 1 hour, dried and fired to obtain a lump in which zeolite particles were bound. This agglomerate was crushed into an appropriate size using a mortar, and the crushed product was placed in an evaluation container to obtain a sample E for adsorption performance evaluation.

Comparative Example 2. A slurry obtained by the same method as in Comparative Example 1 was used, and the slurry was made of cordierite honeycomb which is a honeycomb-shaped porous ceramic substrate (manufactured by NGK Insulators Ltd .: number of cells 400 cells / inch 2; wall thickness 6 mils). ) Was impregnated into the interior of the cord, and then the excess slurry was removed by air blow to apply the slurry to the inner wall surface of the cordierite honeycomb. This slurry-coated honeycomb was heated at 120 ° C. for 2 hours and at 400 ° C. for 1 hour to be dried and fired to bind zeolite to the inner wall surface of the honeycomb, and the one carried on the honeycomb was designated as adsorption performance evaluation sample F. did.

Evaluation 1. Using the adsorption performance evaluation samples A to F obtained in Examples 1 to 4 and Comparative Examples 1 and 2, an evaluation gas was passed to perform a nitric oxide adsorption performance evaluation test.
The test conditions are as follows. Nitric oxide concentration of evaluation gas: 10 ppm (air carrier) Space velocity of evaluation gas: 5600 / hour Adsorption temperature (temperature of adsorption performance evaluation samples A to F and evaluation gas): 20 ° C Moisture content in evaluation gas: 0 .46% (volume ratio, humidity 20
% Equivalent) Distribution time of evaluation gas: 50 minutes

Evaluation 2. Using the adsorption performance evaluation samples A to F obtained in Examples 1 to 4 and Comparative Examples 1 and 2, an evaluation gas was passed to perform a nitric oxide adsorption performance evaluation test.
The test conditions are as follows. Nitric oxide concentration of evaluation gas: 10 ppm (air carrier) Space velocity of evaluation gas: 5600 / hour Adsorption temperature (temperatures of samples A to F for evaluation of adsorption performance and evaluation gas): 20 ° C. Moisture content in evaluation gas: 2 0.2% (volume ratio, humidity 95%
Equivalent) Distribution time of evaluation gas: 50 minutes

Results. The results evaluated for each sample are summarized in Tables 1-6 below. The numbers in each table represent the amount (mg) of NO adsorbed per 1 g of zeolite.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

[Table 3]

[0044]

[Table 4]

[0045]

[Table 5]

[0046]

[Table 6]

From the above, the nitrogen oxide adsorbents (adsorption performance evaluation samples A to D) obtained according to the present invention are nitrogen oxide adsorbents (adsorption performance evaluation samples E and F) containing no water-repellent substance. Compared with the above, it was clear that the adsorption performance did not deteriorate even under high humidity conditions, and a nitrogen oxide adsorbent having good adsorption ability could be obtained.

[0048]

INDUSTRIAL APPLICABILITY As described above, the nitrogen oxide adsorbent according to the present invention comprises an adsorbent substance having a nitrogen oxide adsorbing ability, a water repellent substance having water repellency, and a binder substance binding these substances. Since it is equipped with, it is possible to obtain a nitrogen oxide adsorbent capable of retaining the ability to adsorb nitrogen oxides by removing excess water droplets caused by dew condensation or the like.

Further, since the water-repellent substance and the binder substance are the same and are water-repellent binder substances, it is possible to reduce the number of constituent materials, improve the economical efficiency, and increase the adsorbable surface area of the adsorbent substance. It becomes possible.

Further, since the water-repellent substance contains a fluorine atom or a silicon atom, heat resistance can be improved.

Further, since the water-repellent binding substance is a polymer having a tetrafluoroethylene structure, the water-repellent binding substance is excellent in water repellency, and the binding property is exhibited at a relatively low temperature of about 350 ° C., so that the adsorption substance is heated at a high temperature. Can be bound without heating.

Further, since the adsorbing substance is a composite oxide of silicon and aluminum, it has a high thermal stability, and moreover it is possible to adsorb a large amount of nitrogen oxides by the positively charged portions appearing in the vicinity of aluminum atoms. .

Since the composite oxide of silicon and aluminum contains a metal or ion having a positive charge, it becomes possible to increase the amount of positive charge on the composite oxide and to adsorb a larger amount of nitrogen oxide. It becomes possible.

Since the noble metal is supported on the adsorbent, the oxidation of nitric oxide, which is the main nitrogen oxide, can be promoted, and as a result, the adsorption amount of nitrogen oxide can be increased.

Further, since the noble metal is platinum, palladium, ruthenium, or rhodium, it is possible to dissociate and adsorb oxygen and nitrogen oxides on the surface of these noble metals with high efficiency. The amount can be increased and the economy is excellent.

Further, in the method for producing a nitrogen oxide adsorbent according to the present invention, the particles of the adsorbent are dispersed in a solvent, the water repellent substance and the binder substance are added, or the water repellent binder substance is added, and the mixture is pulverized. A step of adjusting the slurry, a step of drying the slurry, a step of firing the dried slurry,
And a step of pulverizing the calcined slurry, it is possible to obtain the nitrogen oxide adsorbent that can retain the ability to adsorb nitrogen oxides by removing excess water droplets caused by dew condensation, etc. be able to.

Further, the particles of the adsorbing substance are dispersed in a solvent,
A step of adding a water-repellent substance and a binder substance or a water-repellent binder substance, mixing and pulverizing to prepare a slurry, a step of applying the slurry to a substrate and then drying, and a dried slurry. Since it has a step of baking, it is possible to obtain a nitrogen oxide adsorbent that can retain the ability to adsorb nitrogen oxides by removing excess water droplets caused by dew condensation, etc. it can.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing a structure of a nitrogen oxide adsorbent according to a first embodiment of the present invention.

FIG. 2 is a sectional view schematically showing a structure of a nitrogen oxide adsorbent according to a second embodiment of the present invention.

[Explanation of symbols]

1 adsorbed substance (particle), 2 water-repellent binding substance, 3 noble metal (particle).

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroaki Nakamune             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. (72) Inventor Minoru Sato             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. (72) Inventor Norio Mitsuda             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. (72) Inventor Masato Kurahashi             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. (72) Inventor Koji Ota             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. F-term (reference) 3G091 AA02 AA05 AA06 AA07 AB09                       BA14 GA01 GA06 GA16 GB01X                       GB01Y GB05Y GB06Y GB07Y                       GB09Y GB10X GB10Y GB17X                 4G066 AA13D AA15D AA16D AA28D                       AA52D AA53D AA62B AA62C                       AC15D AC28D CA28 DA02                       FA03 FA12 FA15 FA22 FA28

Claims (10)

[Claims] 1. An adsorbent having nitrogen oxide adsorption capacity,
A nitrogen oxide adsorbent comprising a water-repellent substance having water repellency and a binding substance binding these substances. 2. The nitrogen oxide adsorbent according to claim 1, wherein the water-repellent substance and the binder substance are the same and are water-repellent binder substances. 3. The nitrogen oxide adsorbent according to claim 1 or 2, wherein the water repellent substance contains a fluorine atom or a silicon atom. 4. The nitrogen oxide adsorbent according to claim 2, wherein the water-repellent binding substance is a polymer having a tetrafluoroethylene structure. 5. The nitrogen oxide adsorbent according to claim 1 or 2, wherein the adsorbing substance is a composite oxide of silicon and aluminum. 6. The nitrogen oxide adsorbent according to claim 5, wherein the composite oxide of silicon and aluminum contains a metal or ion having a positive charge. 7. The nitrogen oxide adsorbent according to claim 1, wherein a noble metal is supported on the adsorbent. 8. The nitrogen oxide adsorbent according to claim 7, wherein the noble metal is platinum, palladium, ruthenium, or rhodium. 9. A step of dispersing particles of an adsorbent substance in a solvent, adding a water-repellent substance and a binder substance or adding a water-repellent binder substance, mixing and pulverizing the mixture to prepare a slurry, and drying the slurry. A method for producing a nitrogen oxide adsorbent, comprising: a step of firing the dried slurry, and a step of pulverizing the fired slurry. 10. A step of dispersing particles of an adsorbent substance in a solvent, adding a water-repellent substance and a binder substance or adding a water-repellent binder substance and mixing and pulverizing the mixture to prepare a slurry, wherein the slurry is used as a base material. A method for producing a nitrogen oxide adsorbent, comprising: a step of drying after coating and a step of firing the dried slurry.