JP2001259416A - Nitrogen oxides adsorption material and exhaust gas cleaning method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently adsorb NOx in exhaust gas from the low temperature region and to improve NOx cleaning performance at the low temperature region. SOLUTION: A nitrogen oxides adsorption material is constituted of a basic carrier and a noble metal deposited on the basic carrier by using a noble metal colloidal liquid chemicals. Since the particle size of the deposited noble metal is large (1-5 nm) and uniform and deposite state is more metal-like, the electron transfer between NO ad the noble metal is activated and the oxidation activity of NO is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitrogen oxide adsorbent for adsorbing nitrogen oxides efficiently and a method for purifying exhaust gas using the nitrogen oxide adsorbent.

[0002]

2. Description of the Related Art HC and CO contained in exhaust gas from automobiles
A three-way catalyst is widely used as an exhaust gas purifying catalyst for purifying nitrogen oxides (NO _x ). This three-way catalyst is composed of a porous oxide carrier such as alumina (Al ₂ O ₃ ), silica (SiO ₂ ), zirconia (ZrO ₂ ), titania (TiO ₂ ), platinum (Pt), rhodium (Rh), It carries a noble metal such as palladium (Pd). This three-way catalyst oxidizes and purifies HC and CO in exhaust gas,
It purifies by reducing NO _x , and can most effectively purify exhaust gas in a stoichiometric atmosphere burned in a stoichiometric atmosphere near the stoichiometric air-fuel ratio.

[0003] In recent years, lean-burn engines that burn in an oxygen-excess atmosphere have been used for the purpose of reducing carbon dioxide (CO ₂ ). The lean burn engine is normally burned in oxygen excess lean conditions, and is driven by a system that reduces and purifies NO _x exhaust gas as a reducing atmosphere by temporarily stoichiometric-rich condition. And as the best catalysts for this system, occludes NO _x in lean atmosphere, _the NO _x storage-reduction type exhaust gas purifying catalyst development with _the NO _x storage element that releases NO _x occluded in the stoichiometric-rich atmosphere Have been.

[0004] This NO_x If an occlusion reduction type catalyst is used,
The ratio changes from lean to pulsating from stoichiometric to rich
Control on the lean side_x Is NO_x Sucking
Occluded by storage elements, which are released on the stoichiometric or rich side
Is purified by reacting with reducing components such as HC and CO
NO even if exhaust gas from lean burn engine _x 
Can be efficiently purified. Like this
Control the air-fuel ratio so that it is on the stoichiometric to rich side.
Is described as "hitting a rich spike."

[0007] in JP-A-7-163871 is, NO _x adsorption material made of CeO ₂ is disclosed to increase the _the NO _x purification activity by combining with such _the NO _x reduction catalyst is described.

[0006] However in the conventional three-way catalyst, the engine start at low temperatures range of the catalyst activation temperature or less of the precious metal, such as for purification becomes difficult, there is a problem that HC and NO _x in the low temperature range is discharged.

Further, the NO _x storage reduction catalyst has a problem that the NO _x storage capacity is insufficient in a low temperature range where the exhaust gas temperature is particularly lower than 300 ° C., and the NO _x storage capacity decreases as the temperature decreases. Therefore if the exhaust gas, such as at between starting and cold is in the low temperature range, there is a problem that _the NO _x purification ability is lower than the high temperature region.

[0008] Then JP-A-7-163871, although it is described that improves _the NO _x purification performance by _the NO _x adsorption material, there is no description about the purification of the NO _x in low-temperature region of less than 300 ° C..

[0009]

The present inventors have found 0005] As a result of intensive studies on the purification behavior of the catalyst, the exhaust gas NO _x is removed by contacting the catalyst for exhaust gas purification, HC
And that CO is efficiently purified from the low temperature range. It has been found that by arranging the nitrogen oxide adsorbent upstream of the exhaust gas purifying catalyst, HC and CO can be purified from a low temperature range, and the purification temperature window is widened. The cause of this is not clear, but NO _x
It is conceivable that the absence of NO improves the reactivity of HC and CO with O _2, and that the noble metal surface is hardly poisoned by NO _x .

[0010] That is the nitrogen oxide adsorbing material is easy to adsorb NO _x, it adsorbs NO _x in low-temperature region. Therefore, a nitrogen oxide adsorbent is arranged upstream of the exhaust gas flow, and NO
_{x If a} storage-reduction catalyst is placed,
Since the exhaust gas containing almost no NO _x is supplied to the NO _x storage-and-reduction type catalyst, is in the exhaust gas discharged from the NO _x storage-and-reduction type catalyst NO _x are hardly contained. When the exhaust gas temperature rises, NO _x, which has been adsorbed is supplied to the NO _x storage-and-reduction type catalyst desorbed from the nitrogen oxide adsorbing material, are reduced and purified by the NO _x storage-and-reduction type catalyst.

Examples of the nitrogen oxide adsorbent include alkali metal oxides, alkaline earth metal oxides, rare earth element oxides, Co ₃ O ₄ , NiO ₂ , MnO ₂ , Fe ₂ O ₃ , and ZrO _2. Transition metal oxides, zeolites and the like. These can be used alone or in combination of two or more to provide a nitrogen oxide adsorbent. Al ₂ O ₃ , SiO ₂ , SiO ₂ -Al ₂ O ₃ ,
A porous oxide carrier such as ZrO ₂ , TiO ₂ , zeolite or the like, which supports a metal element selected from an alkali metal, an alkaline earth metal and a rare earth element, can also be used.

[0012] ZrO ₂ to which an alkali metal or an alkaline earth metal is added exhibits superior NO _x adsorbing ability as compared with other nitrogen oxide adsorbing materials. When a noble metal such as Pt, Rh, and Pd, or a transition metal oxide such as Co ₃ O ₄ , NiO ₂ , MnO ₂ , and Fe ₂ O ₃ is supported on ZrO ₂ to which an alkali metal or an alkaline earth metal is added. , NO _x adsorbing capability is further improved. This is because Pt, Co ₃ O ₄ , NiO ₂ , MnO ₂ , Fe ₂ O _3, etc., exhibit oxidizing activity, and NO in the exhaust gas is oxidized to NO ₂ , resulting in an increase in NO _x adsorption. It is considered.

[0013] However, according to a further study of the present inventors, the nitrogen oxide adsorbent as described above, although low temperature adsorption is high, it is clear that the adsorption rate of the NO _x is smaller adsorption amount of late NO _x Was.

[0014] The present invention has been made in view of such circumstances, the NO _x in the exhaust gas so as to efficiently adsorbed from the low temperature region, and an object thereof to improve _the NO _x purification performance at low temperature range .

[0015]

A feature of the nitrogen oxide adsorbent of the present invention that solves the above-mentioned problems is that it comprises a basic carrier and a noble metal supported on the basic carrier by using a noble metal colloid drug solution. It is in.

Preferably, the basic carrier is ZrO ₂ ,
More preferably, ZrO ₂ contains at least one element selected from La, K and Ca. Preferably, the noble metal is Pt.

The characteristics of the exhaust gas purifying method of the present invention are as follows.
By arranging the nitrogen oxide adsorbing material according to the oxygen excess exhaust gas to claim 1 adsorbs NO _x in the exhaust gas, the NO _x from the nitrogen oxide adsorbent temporarily reduce the oxygen concentration in the exhaust gas It is to release and reduce and purify.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS NO in exhaust gas is oxidized to NO ₂
Is considered to be absorbed by the basic carrier. Therefore to improve the adsorption rate of the NO _x nitrogen oxide adsorbent, and in order to increase the adsorption amount of the NO _x, it is effective to promote the oxidation of NO.

That is, the nitrogen oxide adsorbent of the present invention comprises a basic carrier and a noble metal supported on the basic carrier by using a noble metal colloid solution. This nitrogen oxide adsorbent is not clear why showing high _the NO _x adsorption rate and high _the NO _x adsorption amount, more metal is supported state the particle size of the noble metal supported is a large uniform and 1~5nm It is considered that the oxidation activity of NO was further increased due to the more active electron transfer between NO and the noble metal because it was like.

As the basic carrier, ZrO ₂ , Al ₂ O ₃ , MgA
Examples include l ₂ O ₄ and MgO. Above all, it is highly basic and NO _x
ZrO _2, which has excellent adsorption characteristics and easily releases adsorbed NO _x during a rich spike, is particularly preferable. La, K and
If ZrO ₂ containing at least one element selected from Ca is used, thermal stability is improved and durability is improved, and NO
_{The x} adsorption speed and the NO _x adsorption amount are further improved.

The reason why the addition of such an element is effective is not clear, but this element is dissolved in the ZrO ₂ lattice to form a complex, whereby the ZrO ₂ surface is modified and NO _x is newly added.
It is likely that adsorption sites are created.

The content of at least one element selected from La, K and Ca is preferably in the range of 1 to 10 mol%. If the content is less than this range, it is difficult to maintain thermal stability, and if the content is more than this range, the NO of ZrO ₂
Hydroxyl groups, which are _x adsorption sites, cannot be used effectively, so that the NO _x adsorption ability and the NO _x purification ability also decrease.

The noble metal supported on the basic carrier is Pt, P
Although it can be selected from d, Rh, Ir and the like, it is particularly desirable to use Pt which is particularly excellent in oxidation activity. The noble metal is supported using a noble metal colloid drug solution.

The noble metal colloid drug solution is prepared by mixing a water-soluble noble metal salt and an alcohol in an aqueous solution of a water-soluble polymer such as polyvinylpyrrolidone and polyvinyl alcohol, and heating the mixture.
It can be prepared by forming a polymer protective noble metal colloid. This method is called a polymer protection method.
Then, the above-mentioned basic carrier powder is dispersed in the aqueous solution of the polymer-protected noble metal colloid, and the noble metal can be supported by drying and firing. Further, the carrier may be supported by using a method utilizing an electrostatic effect, a method utilizing adsorption of a polymer chain to a carrier, or the like.

The noble metal supported by using a general noble metal salt aqueous solution or the like is supported as fine atoms.
Therefore, it is easily oxidized to PtO ₂ or the like. However, the noble metal supported using the noble metal colloid drug solution is 10 to several tens.
It is carried as relatively large noble metal particles in which 00 atoms are collected. Therefore, it is considered that it is difficult to be oxidized and the metal state is easily maintained.

The particle size of the noble metal supported by using a noble metal salt aqueous solution or the like is preferably in the range of 1 to 5 nm. Theoretically, if the particle size is 1 to 5 nm, the number of constituent atoms is 10 to 3000. If the particle size of the noble metal is smaller than 1 nm, it approaches the atomic state, and the NO _x adsorption activity decreases. If the particle size is larger than 5 nm, the surface area decreases, so that the number of active sites decreases and the NO _x adsorption activity decreases.

The amount of the noble metal supported is 120 g of the basic carrier.
The range is preferably 1 to 5 g per unit. If the supported amount is less than this, the NO _x adsorption activity is low, and even if the supported amount is larger, the effect is saturated and the cost is increased.

[0028] Then the exhaust gas purifying method of the present invention adsorbs NO _x in the exhaust gas arranged in the exhaust gas during the first oxygen-excess lean atmosphere nitrogen oxide adsorbent as described above. NO in the exhaust gas by the catalytic action of the metal-like noble metal supported on the nitrogen oxide adsorbing material is efficiently oxidized NO _x becomes, is efficiently adsorbed on basic supports. Therefore also well adsorb NO _x in low-temperature region, is large adsorption often adsorption rate. The lean atmosphere is not particularly limited, but an atmosphere of exhaust gas burned with an air-fuel ratio (A / F) of 15 to 50 is suitable.

[0029] Then when temporarily stoichiometric-rich atmosphere to reduce the oxygen concentration in the exhaust gas, nitrogen oxides NO _x which had been adsorbed by the adsorbent is released, released NO _x nitrogen oxide adsorbent It is reduced and purified by reacting with CO, HC, etc. in the exhaust gas by the catalytic action of the metal-like noble metal supported on. The stoichiometric to rich atmosphere is not particularly limited, but an atmosphere of exhaust gas burned with an air-fuel ratio (A / F) of about 10 to 14 is suitable. The time or frequency of the rich spike for temporarily lowering the oxygen concentration can be set variously according to the purpose.

As mentioned above, the nitrogen oxide adsorption of the present invention
No material alone, NO_x Can be absorbed and reduced
You. But NO_x For more efficient reduction and purification
Is located in the exhaust gas flow path on the downstream side of the nitrogen oxide adsorbent of the present invention.
Three-way catalyst or NO_x It is desirable to arrange a storage reduction catalyst
New This releases nitrogen from the nitrogen oxide adsorbent
NO that could not be reduced by oxide adsorbent_x The downstream touch
It can be reduced and purified with a medium, stoichiometric to rich atmosphere
NO in_x Can be further reduced. Ma
NO on the downstream catalyst_x If the storage reduction catalyst is used,
NO in stoichiometric to rich atmosphere_x Emissions
Can be further reduced, and NO in exhaust gas_x 
NO that was not absorbed by the nitrogen oxide adsorbent
_x NO_x Since it can be stored in the storage reduction catalyst,
NO in a lean atmosphere with excess oxygen _x Emissions are even lower
Can be reduced.

[0031]

The present invention will be specifically described below with reference to examples and comparative examples.

(Example 1) 200 g of water and 0.65 of PtCl ₄ (5H ₂ O)
An aqueous solution obtained by mixing 66 g with 200 g of water and a number average molecular weight of 2
An aqueous solution prepared by mixing 0.89 g of 5,000 polyvinylpyrrolidone was prepared, and both aqueous solutions were mixed and stirred to prepare a uniform aqueous solution. 100 g of ethanol was added to this aqueous solution, and refluxed at 90 ° C. for 4 hours to obtain a Pt colloid drug solution.

The ZrO ₂ powder was put into the Pt colloid solution, stirred at 200 ° C. for about 2 hours and evaporated to dryness. this
After drying at 110 ° C for 2 hours, it was calcined at 450 ° C for 2 hours to obtain a nitrogen oxide adsorbent powder. In this nitrogen oxide adsorbent powder,
₂ g of Pt is supported on 120 g of ZrO ₂ . This powder was subjected to CIP molding under the conditions of 65 MPa × 2 minutes, and the resultant was pulverized into pellets having a size of 0.5 to 0.8 mm.

[0034] (Example 2) ZrO ₂ except that the powder lanthanum oxide instead of using the ZrO ₂ powder containing 2 mol% in the same manner as in Example 1, pellets of the nitrogen oxide adsorbent of Example 2 Was prepared.

[0035] (Example 3) except that the instead of the ZrO ₂ powder with ZrO ₂ powder containing potassium oxide 2 mol% in the same manner as in Example 1, pellets of nitrogen oxide of Example 3 adsorbed Materials were prepared.

[0036] (Example 4) except that calcium oxide in place of ZrO ₂ powder with ZrO ₂ powder containing 2 mol% in the same manner as in Example 1, pellets of the nitrogen oxide adsorbent of Example 4 Was prepared.

Comparative Example 1 ZrO ₂ powder was put into an aqueous solution of dinitrodiammineplatinic acid in nitric acid, stirred at 200 ° C. for about 2 hours, and evaporated to dryness. After drying it at 110 ° C for 2 hours, 450
The mixture was calcined at 2 ° C. for 2 hours to obtain a nitrogen oxide adsorbent powder. In this nitrogen oxide adsorbent powder, ₂ g of Pt is supported for 120 g of ZrO ₂ . This powder was subjected to CIP molding under the conditions of 65 MPa × 2 minutes, and the resultant was pulverized into pellets having a size of 0.5 to 0.8 mm.

[0038] (Comparative Example 2) ZrO ₂ except that the powder lanthanum oxide instead of using the ZrO ₂ powder containing 2 mol% in the same manner as in Comparative Example 1, pellets of the nitrogen oxide adsorbent of Comparative Example 2 Was prepared.

[0039] (Comparative Example 3) except that the potassium oxide instead of ZrO ₂ powder with ZrO ₂ powder containing 2 mol% in the same manner as in Comparative Example 1, pellets of the nitrogen oxide adsorbent of Comparative Example 3 Was prepared.

[0040] (Comparative Example 4) except that calcium oxide in place of ZrO ₂ powder with ZrO ₂ powder containing 2 mol% in the same manner as in Comparative Example 1, pellets of the nitrogen oxide adsorbent of Comparative Example 4 Was prepared.

[0041] <Test-Evaluation> Each of the nitrogen oxide adsorbing material disposed on the evaluation unit, and _the NO _x adsorption amount under the conditions shown in FIG. 1
NO _x adsorption rate were measured. First, heat from room temperature to 450 ° C at a heating rate of 17.5 ° C / min in a N ₂ gas atmosphere.
Hold at 50 ° C. for 10 minutes. Then cool to 100 ℃
By flowing a model gas shown in adsorbing 30 minutes NO _x at 100 ° C.. The flow rate of the model gas is 7 L / min. Then, heat to 450 ° C at a heating rate of 17.5 ° C / min and hold at 450 ° C for 10 minutes. Then the concentration of NO _x in the gas continuously measured out,
And _the NO _x adsorption amount was determined and _the NO _x adsorption rate of the initial 1 minute from _the NO _x adsorption start. The respective results are shown in FIG. 2 and FIG.

[0042]

[Table 1]

[0043] When the nitrogen oxide adsorbent NO _x is saturated adsorption, then NO is pass through without play adsorption after a NO _{x (x>} 1) on Pt. Therefore, the incoming gas (N
The NO oxidation activity can be determined from the difference between O) and the outgassing (NO + NO _x ). FIG. 4 shows the results of Example 1 and Comparative Example 1.

From FIGS. 2 and 3, the nitrogen oxides of the respective embodiments are shown.
The adsorbent is NO compared to the corresponding comparative example _x High adsorption, NO
_x It can be seen that the adsorption speed is also high. This is a Pt colloid drug
It is clear that this is the effect of supporting Pt using the liquid.
You.

FIG. 4 shows that the NO conversion rate of Example 1 was higher in the entire temperature range from 100 ° C. to 400 ° C., and that the nitrogen oxide adsorbent of Example 1 had higher NO oxidation activity than Comparative Example 1. . A similar tendency was shown in comparison of the nitrogen oxide adsorbents of the other examples and comparative examples. Therefore, the improvement of the NO _x adsorption amount and _the NO _x adsorption rate in the nitrogen oxide adsorbent of Example believed this high NO oxidation activity greatly contributes to support Pt with Pt colloid chemical It believed improved NO oxidation activity and _the NO _x adsorption amount and _the NO _x adsorption rate is improved by.

Example 5 A pellet-like nitrogen oxide adsorbent of Example 5 was prepared in the same manner as in Example 1 except that Al ₂ O ₃ powder was used instead of ZrO ₂ powder.

Comparative Example 5 A pellet-shaped nitrogen oxide adsorbent of Comparative Example 5 was prepared in the same manner as in Comparative Example 1 except that Al ₂ O ₃ powder was used instead of ZrO ₂ powder.

[0048] The nitrogen oxide adsorbing material <Test-Evaluation> Example 5 and Comparative Example 5 were the same manner as described above under the conditions shown in FIG. 1 NO _x adsorption amount and NO _x adsorption rate were measured. The results are shown in FIGS.

5 and 6, the nitrogen oxide adsorbent of Example 5 has a larger NO _x adsorption amount than the corresponding Comparative Example 5,
_The NO _x adsorption rate seen that also large. It is clear that this is the effect of supporting Pt using a Pt colloidal drug solution, and the same effect as that of ZrO ₂ is achieved even when Al ₂ O ₃ is used as a carrier.

Example 6 A slurry was prepared by dispersing 7 parts by weight of ZrO ₂ powder and 13 parts by weight of ZrO ₂ sol in water, and was allowed to adhere to the surface of a cordierite honeycomb substrate, followed by drying and drying.
By firing, a ZrO ₂ coat layer was formed. The ZrO ₂ coating layer was formed in an amount of 240 g per liter of the honeycomb substrate.

Next, the honeycomb substrate having the ZrO ₂ coating layer was immersed in the same Pt colloid solution as in Example 1 to absorb water,
After being pulled up, it was dried and fired to carry Pt. The supported amount of Pt is 2 g per liter of the honeycomb substrate.

Comparative Example 6 A honeycomb substrate having a ZrO ₂ coating layer similar to that of Example 6 was prepared in the same manner as in Example 6, except that a nitric acid aqueous solution of dinitrodiammine platinum was used instead of the Pt colloid chemical solution. The same amount of Pt was loaded.

Comparative Example 7 100 parts by weight of Al ₂ O ₃ powder and TiO
₂ powder 100 parts by weight, ZrO ₂ powder 50 parts by weight, CeO ₂ -ZrO ₂
A slurry containing 20 parts by weight of the composite oxide powder was prepared, attached to the surface of a cordierite honeycomb substrate, dried and fired to form a coat layer. The coating layer was formed in an amount of 270 g per liter of the honeycomb substrate.

Next, the honeycomb substrate having the above-mentioned coating layer was immersed in a dinitrodiamineplatinum nitric acid solution to carry out ion exchange, and then dried and fired to carry Pt. The supported amount of Pt is 2 g per liter of the honeycomb substrate. Further, Ba, Li and K were successively carried in the same manner using a barium acetate aqueous solution, a lithium nitrate aqueous solution and a potassium nitrate aqueous solution. 0.2 mol of Ba, 0.1 mol of Li per 1 L of honeycomb substrate
0.1 mol of K is supported.

The nitrogen oxide adsorbent of Comparative Example 7 corresponds to a conventional NO _x storage reduction catalyst.

<Test / Evaluation> The nitrogen oxide adsorbents of Example 6, Comparative Examples 6 and 7 were placed in the exhaust system of a 1.8 L lean burn engine, respectively, and tested and evaluated.

[0057] engine speed and 2000rpm constant, adsorbed to saturation NO _x in lean atmosphere, hit once rich spike to 0.3 seconds rich atmosphere, required to adsorb to saturation as lean atmosphere again NO _{The x} adsorption amount was measured at four levels of 150 ° C, 200 ° C, 250 ° C and 300 ° C. The measured NO _x adsorption amount corresponds to the hatched portion shown in FIG. 7, and corresponds to the NO _x amount that can be purified by one rich spike. FIG. 8 shows the results.

FIG. 8 shows that the nitrogen oxide adsorbents of Example 6 and Comparative Example 6 showed NO _x even in a low temperature region as compared with Comparative Example 7.
It can be seen that in the low-temperature region around 200 ° C., the NO _x purifying ability is superior to that of the conventional NO _x storage reduction catalyst. And Example 6 is more excellent in NO _x purification ability than Comparative Example 6, and it is clear that this is the effect of supporting Pt using a Pt colloidal chemical solution.

As described above, the nitrogen of Example 6 and Comparative Example 6
NOx adsorbent at low temperature _x Occupation reduction catalyst
Higher NO_x It is not clear why it shows the ability to purify, but
It is thought to be. That is, the nitrogen of Example 6 and Comparative Example 6
NOx adsorbent is NO_x Alkali metal element as occlusion material
NO adsorbed because it contains no elemental or alkaline earth metal elements
_x Weak interaction with adsorbed NO_x Is acceptable even at low temperatures
It is considered that it is easily released and reduced and purified. Also implemented
Carrying Pt using Pt colloid drug solution as in Example 6
Pt became metal-like, and the activity of Pt itself improved
NO in low temperature range_x It is thought that purification activity was further improved
It is.

[0060]

That is, according to the nitrogen oxide adsorbent of the present invention, the amount of adsorbed NO _x in a low temperature range is large and the adsorbing speed of NO _x is also large. Therefore, according to the exhaust gas purifying method of the present invention, it is possible to further suppress the emission of the NO _x in the low temperature range, thereby improving _the NO _x purification rate.

[Brief description of the drawings]

FIG. 1 is a time chart showing temperature conditions used in a test in an example.

2 is a graph showing the _the NO _x adsorption amount of the nitrogen oxide adsorbent of Examples and Comparative Examples.

FIG. 3 shows the initial NO of nitrogen oxide adsorbents of Examples and Comparative Examples.
6 is a graph showing an adsorption speed.

FIG. 4 is a graph showing the relationship between the temperature of the nitrogen oxide adsorbent of Example 1 and Comparative Example 1 and the NO conversion.

FIG. 5: NO of nitrogen oxide adsorbent of Example 5 and Comparative Example 5
₆ is a graph showing the amount of _x adsorption.

FIG. 6 is a graph showing the initial NO _x adsorption rates of the nitrogen oxide adsorbents of Example 5 and Comparative Example 5.

FIG. 7 is an explanatory diagram showing the definition of the NO _x amount that can be purified by one rich spike.

FIG. 8 is a graph showing the amount of NO _x that the nitrogen oxide adsorbents of Examples and Comparative Examples can purify by one rich spike.

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Claims (5)

[Claims] 1. A nitrogen oxide adsorbing material comprising: a basic carrier; and a noble metal supported on the basic carrier by using a noble metal colloid drug solution. 2. The nitrogen oxide adsorbent according to claim 1, wherein the basic carrier is ZrO ₂ . 3. The nitrogen oxide adsorbent according to claim 2, wherein the ZrO ₂ contains at least one element selected from La, K and Ca. 4. The nitrogen oxide adsorbent according to claim 1, wherein the noble metal is Pt. 5. adsorbs NO _x in exhaust gas by placing the nitrogen oxide adsorbing material according to the oxygen excess exhaust gas to claim 1, wherein the nitrogen oxide temporarily reduce the oxygen concentration in the exhaust gas exhaust gas purification method which comprises reducing purified by releasing NO _x from the object adsorbent.