JP2006175299A - Nox occlusion material, its carrying method and nox occlusion reduction type catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an NOx occlusion material capable of suppressing a reaction of cordierite or the like with a substrate and suppressing sulfur poisoning. <P>SOLUTION: The NOx occlusion material comprises a composite body in which an alkaline element comprising at least one kind selected from alkaline metal and alkaline earth metal and combinable with titanium and a titanium element are made composite in the fine state. Because of the fine shape, it has a large reactable area with NOx and movement of the alkaline element is suppressed by combination. Further, since movement of the alkaline element is suppressed, movement of carried noble metal is also suppressed and grain growth of the noble metal is suppressed. Further, approaching of a sulfur oxide is suppressed by a titanium element having high acidity and the sulfur poisoning is suppressed. Since grain grotwh of a sulfate produced by a reaction of the alkaline element and the sulfur oxide is suppressed and dispersibility is enhanced, restoration property from the sulfur poisoning is enhanced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention, oxygen excess occludes NO _x in lean atmosphere, _the NO _x storage material and how bearing that releases NO _x at a rich atmosphere of the stoichiometric or oxygen-deficient, and _the NO _x storage carrying the _the NO _x storage material The present invention relates to a reduced catalyst.

Conventionally, as a catalyst for exhaust gas purification of automobiles, a three-way catalyst that purifies by performing CO and HC oxidation and NO _x reduction simultaneously in exhaust gas at a stoichiometric air-fuel ratio (stoichiometric) has been used. As such a three-way catalyst, for example, a porous carrier layer made of γ-alumina is formed on a heat-resistant substrate made of cordierite or the like, and platinum (Pt), rhodium (Rh) or the like is formed on the porous carrier layer. Those carrying a noble metal are widely known.

On the other hand, in recent years, from the viewpoint of protecting the global environment, carbon dioxide (CO ₂ ) in exhaust gas discharged from internal combustion engines such as automobiles has become a problem. Is being viewed. In this lean burn, since the amount of fuel used is reduced, CO ₂ emissions can be reduced.

In contrast, conventional three-way catalysts are those that simultaneously oxidize, reduce, and purify CO, HC, and NO _x in exhaust gas when the air-fuel ratio is the stoichiometric air-fuel ratio (stoichiometric). In an excess atmosphere, it does not show sufficient purification performance for NO _x reduction and removal. Therefore, it has been desired to develop a catalyst and a purification system that can efficiently purify NO _x even in an oxygen-excess atmosphere.

Therefore, in lean burn, a system for reducing and purifying NO _x using exhaust gas as a reducing atmosphere has been developed by always burning under lean conditions with excess oxygen and intermittently changing from stoichiometric to rich conditions. And as the best catalysts for this system, occludes NO _x in lean atmosphere, stoichiometric ~ _the NO _x storage-reduction type exhaust purifying catalyst is developing with _the NO _x storage material that releases occluded NO _x in a rich atmosphere And is available for use.

As _the NO _x storage material with absorbing and releasing action of the NO _x, the alkaline earth metals, known alkali metal and rare earth elements, for example, JP-A-05-317652, and alkaline earth metals such as Ba Pt was supported on a porous carrier such as alumina NO _x storage-and-reduction type catalyst has been proposed. Japanese Laid-Open Patent Publication No. 06-031139 proposes a NO _x storage reduction catalyst in which an alkali metal such as K and Pt are supported on a porous carrier such as alumina. Furthermore, Japanese Patent Laid-Open No. 05-168860 proposes a NO _x storage reduction catalyst in which a rare earth element such as La and Pt are supported on a porous carrier such as alumina.

With these NO _x storage-and-reduction type catalyst, by controlling so that the stoichiometric-rich side air-fuel ratio from the lean side in a pulsed manner, the exhaust gas becomes stoichiometric-rich atmosphere from a lean atmosphere in pulses. Therefore, on the lean side, NO _x is occluded in the NO _x occlusion material, and it is released on the stoichiometric or rich side and reacts with reducing components such as HC and CO to be purified, so the exhaust gas from the lean burn engine Even if it exists, NO _x can be purified efficiently. Further, HC and CO in the exhaust gas are oxidized by the noble metal and consumed for the reduction of NO _x , so that HC and CO are also efficiently purified.

By the way, due to stricter exhaust gas regulations and higher engine performance, the average temperature and maximum temperature of the gas entering the exhaust gas purification catalyst have been increasing in recent years, and the exhaust gas purification catalyst has further improved heat resistance. Is desired. In addition, as the incoming gas temperature rises, it is desired to improve the NO _x purification performance in a high temperature range.

However, in the conventional NO _x storage-and-reduction type catalyst, there is a problem that reaction with _the NO _x storage material and carrier in a high temperature region is _the NO _x storage ability is decreased occurs. Further, the conventional exhaust gas purifying catalyst has a narrow temperature range (temperature window) showing the maximum purifying ability, and it has been difficult to ensure the NO _x purifying ability in a high temperature range.

Furthermore, in the NO _x storage-reduction catalyst, sulfur poisoning of the NO _x storage material due to SO _x caused by a small amount of sulfur contained in the fuel (decrease in NO _x storage capacity due to sulfate formation) occurs, and as a result Durability will be reduced.

Therefore, JP-A 09-201532 discloses an amorphous material comprising at least one NO _x storage element selected from the group consisting of alkali metals, alkaline earth metals and rare earth elements, a porous oxide carrier, and a noble metal. complex oxides constitutes the substrate from, the noble metal NO _x storage-and-reduction type catalyst comprising a uniformly high dispersion to a substrate has been proposed.

According to this NO _x storage-reduction catalyst, the porous carrier, the NO _x storage material, and the noble metal constitute an amorphous composite oxide, so that the movement of the NO _x storage material is suppressed and the NO _x storage material. Reaction with the substrate. Further, since scattering and elution of the NO _x storage material are suppressed, noble metal grain growth at high temperatures can be prevented, and performance degradation can be suppressed even after a high temperature durability test.

Japanese Patent Application Laid-Open No. 10-128114 discloses NO _x storage comprising a composite compound containing a first element selected from alkali metals and a second element selected from at least one of alkaline earth metals, rare earth elements and transition metals. The materials are listed. According to this NO _x storage material, the elution of the first element at the time of supporting the noble metal is suppressed, and the transpiration of the first element at a high temperature is suppressed. Thus after the high temperature durability is also maintained higher _the NO _x storage ability of the alkali metal is first element, _the NO _x storage ability is improved durability as well as stabilized. In addition, since highly dispersed support of alkali metal is maintained even when high heat is applied, the growth of sulfate crystals produced by sulfur poisoning is suppressed, and as a result, the detachment of sulfate is facilitated and durability is improved. improves.

However, in the catalyst described in Japanese Patent Application Laid-Open No. 09-201532, both the noble metal and the NO _x storage material are taken into the substrate, so that there is a problem in contact with exhaust gas and the reaction efficiency is low. . In addition, the NO _x storage material described in JP-A-10-128114 has a problem that the reaction efficiency is low because the composite compound is not fine, and there is no description of titanium contained in the category of the second element. Absent.
JP 06-031139 JP 09-201532 A JP-A-10-128114

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a NO _x storage material capable of suppressing a reaction with a base material such as cordierite and suppressing sulfur poisoning and a method for supporting the same. To do. Moreover, the _the NO _x storage material by carrying, and to provide a NO _x storage-and-reduction type catalysts having after the durability is high _the NO _x purification activity.

The feature of the NO _x storage material of the present invention that solves the above problems is that the alkaline element that can be combined with titanium and composed of at least one selected from alkali metals and alkaline earth metals, and the titanium element are combined in a fine state. It consists of a complex.

Further, the feature of the method for supporting the NO _x storage material of the present invention is the first compound comprising an alkaline element which is composed of at least one selected from alkali metals and alkaline earth metals and can be combined with titanium,
A fourth compound produced from a second compound comprising a titanium alkoxide and a third compound having a polydentate ligand;
The purpose is to impregnate a support made of a porous oxide in which hydrogen peroxide having a molar ratio of 1/2 or more with respect to titanium coexists, and then firing.

The feature of the NO _x storage reduction catalyst of the present invention is that it comprises a support made of a porous oxide, a noble metal supported on the support, and the NO _x storage material of the present invention supported on the support. . In this catalyst, it is preferable to further support an independent NO _x storage material which is composed of at least one selected from alkali metals and alkaline earth metals and which is not complexed with titanium. It is also preferable that the NO _x storage material of the present invention is supported on the exhaust gas upstream side and the independent NO _x storage material is supported on the exhaust gas downstream side.

According to the NO _x storage material of the present invention, since the alkaline element and the titanium element are complexed in a fine state, the area capable of reacting with NO _x is large. Therefore, the NO _x storage ability by the alkaline element is expressed well. Moreover, since it is compounded with the titanium element, the movement of the alkaline element is suppressed, and the reaction with the base material such as cordierite is suppressed. Since the movement of the alkaline element is suppressed, the movement of the supported noble metal is also suppressed, and the noble metal grain growth is suppressed. In addition, the titanium element with high acidity suppresses the proximity of sulfur oxides to suppress sulfur poisoning, and also suppresses the grain growth of sulfate produced by the reaction between alkaline elements and sulfur oxides. And the recovery from sulfur poisoning is improved. Therefore, according to _the NO _x storage-reduction catalyst of the present invention, the high _the NO _x storage capacity and high sulfur leaving due to miniaturization, it becomes possible to achieve both a moving suppression by compounding, after durability High NO _x storage capacity is maintained and the durability of NO _x purification performance is excellent.

Further, if an independent NO _x storage material that is not combined with titanium is further supported, the NO _x storage capacity in a high temperature region is improved. However, in carrying the independent _the NO _x storage material NO _x storage-and-reduction type catalyst, the activity is lowered by grain growth of a noble metal in a high temperature range, after endurance has the disadvantage of not exhibit independence _the NO _x storage material original characteristics. Therefore, if the NO _x storage material of the present invention is supported on the exhaust gas upstream side, and the independent NO _x storage material is supported on the exhaust gas downstream side where the low temperature exhaust gas flows compared to the upstream side, the NO _x storage reduction catalyst is downstream. The grain growth of the noble metal on the side can be suppressed, and the original high NO _x storage capacity of the independent NO _x storage material can be expressed.

Further, according to the method for supporting the NO _x storage material of the present invention, it is possible to stably support a complex in which an alkaline element and a titanium element are combined in a fine state. Therefore, the original characteristics of the NO _x storage material of the present invention are expressed, and an NO _x storage reduction type catalyst having excellent characteristics can be manufactured.

The NO _x storage material of the present invention is composed of a composite in which an alkaline element that can be combined with titanium and at least one selected from alkali metals and alkaline earth metals and a titanium element are combined in a fine state. It is not clear at this time how alkaline elements and titanium elements are complexed, but from the results of observation by X-ray diffraction, this complex has a fine particle size of several nanometers or less. It is clear that it exists stably.

The alkaline element is at least one selected from alkali metals and alkaline earth metals and can be combined with titanium. As may be complexed with titanium, K, Na, Li, Cs , Ba, Sr, Ca, although such as Mg is exemplified, easily react with a substrate such as cordierite having a high _the NO _x storage capacity K The present invention is particularly useful when A single species may be used, or a plurality of species may be mixed.

  The composition ratio of the alkaline element and the titanium element is not particularly limited, but the molar ratio of the alkaline element: titanium element is preferably in the range of 1: 1 to 3: 1.

In producing the NO _x storage material of the present invention, it is difficult to form a complex in a fine state even if a complex can be formed only by mixing and heating an alkaline element compound and a titanium compound. . Therefore, for example, a molar ratio with respect to titanium, a fourth compound produced from a first compound containing an alkaline element, a second compound containing a titanium alkoxide, and a third compound having a polydentate ligand. There is a method in which a solution in which ½ or more hydrogen peroxide coexists is prepared and baked. Alternatively, the precursor may be precipitated by hydrolysis or pH adjustment using this solution, and may be fired.

  In the solution containing the first compound, the fourth compound and hydrogen peroxide, a complex in which an alkaline element and a titanium element are coordinated to the fourth compound is formed, and a complex is formed by firing the complex. can do. Immediately after firing, the composite is considered to be a simple substance or a mixture of a composite oxide, titanate or the like in which an oxide of an alkaline element and a titanium oxide are combined.

However, in the above production method, there is a high possibility that the composite becomes coarse particles due to sintering during firing, and a catalyst obtained by supporting the composite is not practical. Therefore, the method for supporting the NO _x storage material of the present invention employs a method in which the above solution is impregnated into a carrier made of a porous oxide and then fired. Or the support | carrier which consists of porous oxides in the said solution may be mixed, and a precursor may be deposited by carrying out hydrolysis or pH adjustment after that, and you may bake it.

According to this method, the precursor deposited by concentration during firing or the precursor deposited by hydrolysis or pH adjustment is deposited and supported on the surface of the carrier, so that the particles during firing are interacted with the carrier. Growth is suppressed. Therefore, the formed composite can be supported on the carrier in a fine state, and the NO _x storage material can be supported in a fine state.

  The first compound is a compound containing an alkaline element that is composed of at least one selected from alkali metals and alkaline earth metals and can be complexed with titanium, and is dissolved in a solution. If the solution is an aqueous solution, a water-soluble alkaline element nitrate, an alkaline element acetate, or the like can be used. It may contain a water-soluble alcohol.

The second compound is a compound containing titanium alkoxide, and examples thereof include titanium methoxide, titanium ethoxide, titanium propoxide, and titanium butoxide. These may be used alone or in combination. Further, at least titanium alkoxide may be included, and other metal alkoxides may coexist as long as the characteristics as the NO _x storage material are not impaired.

  The third compound is a compound having a polydentate ligand (chelate ligand), and citric acid, oxalic acid, ethylenediamine, ethyl acetoacetate, glycol, pinacol and the like are exemplified. Citric acid having an acidic ligand is particularly preferable because an alkaline element is coordinate-bonded. A fourth compound in which a multidentate ligand is coordinated to titanium can be produced by mixing the second compound and the third compound and heating as necessary.

The addition amount of the first to third compounds may be selected according to the characteristics of the target NO _x storage material.

  The solution further contains hydrogen peroxide having a molar ratio of 1/2 or more with respect to titanium. Hydrogen peroxide reacts with titanium to form a beloxo complex, thereby suppressing gelation in the presence of the first compound. Therefore, when the addition amount is less than 1/2 in terms of molar ratio with respect to titanium, the stability of the aqueous solution is lowered and it becomes difficult to carry highly dispersed on the carrier.

As the support made of a porous oxide, porous oxides used in conventional NO _x storage reduction catalysts such as alumina, ceria, zirconia, titania, and complex oxides selected from these are used. be able to. The solution is impregnated into the carrier, by being heated in this state, it evaporated to dryness, calcined, and the alkaline element and titanium element carrying _the NO _x storage material comprising a composite of the complex in a fine state be able to.

The NO _x storage-reduction catalyst of the present invention comprises a support made of a porous oxide, a noble metal supported on the support, and the NO _x storage material of the present invention supported on the support. The above-described porous oxide is used for the support. The precious metal serves to promote the occlusion to _the NO _x storage material by oxidizing the NO in the exhaust gas in a lean atmosphere, by reducing the NO _x released from _the NO _x storage material in a rich atmosphere from the stoichiometric to the N ₂ purification To do. At the same time, CO and HC in the exhaust gas are oxidized and purified. As such a noble metal, at least one selected from Pt, Rh, Pd, Ir and the like can be used, and the supported amount can be in the range of 0.1 to 10% by weight with respect to the support.

Further, the supported amount of the NO _x storage material of the present invention is practically in the range of 0.01 mol to 5 mol per liter of the catalyst as the concentration of the alkaline element in the composite.

In order to carry the NO _x storage material of the present invention on the carrier, it is desirable to use the loading method of the present invention. In order to support the noble metal on the carrier, a conventionally used adsorption supporting method, water absorbing supporting method, or the like can be used.

NO _x storage-and-reduction type catalyst of the present invention, by forming the catalyst powder carrying a noble metal and NO _x storage material in the support powder may be used as the catalyst pellets, the carrier coating layer cordierite or honeycomb substrate made of metal It is also preferable to form a honeycomb catalyst by supporting the noble metal and NO _x storage material on the coating layer. In the latter case, the solution prepared by the carrying method of the present invention is impregnated into the coat layer and fired to form a NO _x composed of a composite in which an alkaline element and a titanium element are complexed in a fine state. An occlusion material can be carried.

The NO _x storage-reduction catalyst of the present invention preferably further supports an independent NO _x storage material that is made of at least one selected from alkali metals and alkaline earth metals and is not complexed with titanium. By supporting the independent NO _x storage material, the NO _x storage capacity in the high temperature region is improved. The independent NO _x storage material is at least one selected from alkali metals and alkaline earth metals, and may be the same as or different from the alkaline element of the NO _x storage material of the present invention. Further, the supported amount of the independent NO _x storage material may be in the range of 0.01 mol to 5 mol per liter of the catalyst.

However, in carrying the independent _the NO _x storage material NO _x storage-and-reduction type catalyst, activity decreases by an independent _the NO _x storage moving grain growth of the noble metal associated with the material in the high temperature region, after the durability is independently _the NO _x storage material inherent characteristics May not be possible. Therefore, it is desirable to use an NO _x storage reduction catalyst in which the NO _x storage material of the present invention is supported on the exhaust gas upstream side and the independent NO _x storage material is supported on the exhaust gas downstream side. Since the exhaust gas flows at a lower temperature on the downstream side than the upstream side, it is possible to suppress the noble metal grain growth on the downstream side and to suppress the reaction between the independent NO _x storage material and the base material, which is inherently high in the independent NO _x storage material. Can express NO _x storage capacity.

  Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples.

Example 1
1.5 mol of citric acid as a third compound having a polydentate ligand was dissolved in ion-exchanged water and heated to 75 ° C. To this solution was added 0.3 mol of titanium isopropoxide as the second compound, and after dissolution, the mixture was cooled to room temperature to prepare an aqueous solution of titanium citrate complex (concentration 0.57 mol / L) as the fourth compound.

  To 6.15 ml of the obtained aqueous solution of titanium citrate complex, 0.6 ml of 30% aqueous hydrogen peroxide solution is added, and further 1.64 ml of aqueous potassium acetate solution (concentration 4.26 mol / L) as the first compound is added and stirred, and K-Ti A composite precursor aqueous solution was prepared. The molar ratio Ti / K of each component in the solution is 1/2, and K and Ti are compounded in a fine state.

On the other hand, 100 g of γ-alumina powder, 100 g of TiO ₂ —ZrO ₂ composite oxide powder (weight ratio TiO ₂ / ZrO ₂ = 30/70), 50 g of Rh / ZrO ₂ powder in which 1% by weight of Rh is supported on zirconia, CeO ₂ -An aqueous slurry containing 20 g of ZrO ₂ composite oxide powder (molar ratio Ce / Zr = 7/3) and an inorganic binder, and a honeycomb substrate made of cordierite with hexagonal cells (diameter 30 mm, length 50 mm) A coat layer was formed by wash coating. The amount of coat layer formed is 270 g per liter of honeycomb substrate. Pt was selectively adsorbed and supported on this coat layer using a dinitrodiammine platinum nitric acid solution, and calcined in the atmosphere at 300 ° C. for 3 hours to prepare a Pt-supported catalyst. The amount of Pt supported is 2 g per 1 L of honeycomb substrate.

To the Pt supported catalyst, a predetermined amount of the K-Ti composite precursor solution imbibed impregnated, and calcined 3 hours at 300 ° C. in air, _the NO _x storage to _the NO _x storage material is supported in the present invention A reduced catalyst was prepared. The amount of the supported K-Ti composite is such that K is 0.4 mol and Ti is 0.2 mol per liter of the honeycomb substrate.

  As a result of observation by X-ray diffraction, the K-Ti composite was in the form of fine particles having a particle size of several nm or less and was highly dispersed and supported.

(Comparative Example 1)
K was supported in the same manner as in Example 1 except that a potassium acetate aqueous solution was used instead of the K-Ti complex precursor aqueous solution on the Pt-supported catalyst prepared in the same manner as in Example 1. The amount of K supported is 0.4 mol per liter of honeycomb substrate.

(Example 2)
As the catalyst NO _x storage-and-reduction type catalyst the length of Example 1 was cut into half so that the exhaust-gas upstream side, and _the NO _x storage reduction catalyst a length of Comparative Example 1 is halved cut catalyst so that the exhaust gas downstream side, and by connecting the two in series and _the NO _x storage reduction catalyst of example 2.

<Test and evaluation>
Durability tests were conducted on the NO _x storage reduction type catalysts of Examples and Comparative Examples, in which air heated to 750 ° C. was circulated at a flow rate of 1 L / min for 5 hours.

  Next, each model gas shown in Table 1 simulating exhaust gas on the downstream side of the start catalyst (oxidation catalyst) of the direct injection gasoline engine was used and distributed to each catalyst after the durability test in the pattern shown in FIG. Processing, S poisoning processing, and S regeneration processing were performed. That is, after pretreatment rich gas was circulated at 650 ° C. for 5 minutes, S poisoning treatment was conducted in which S poison lean gas / S poison rich gas was circulated at 400 ° C. for 41 minutes while fluctuating at 120 seconds / 3 seconds. At this time, the supply amount of S per 2 L of each catalyst was 3 g. Thereafter, an S regeneration treatment was performed in which an S regeneration lean gas was treated at 600 ° C. for 5 minutes, and then an S regeneration rich gas was treated at 600 ° C. for 10 minutes.

  The S concentration in the outgas from each catalyst during the S regeneration rich gas flow was measured over time, and the results are shown in FIG. From FIG. 2, it can be seen that the catalyst of Example 1 has significantly improved S-elimination compared to the catalyst of Comparative Example 1, and this is due to the fact that K is supported in a fine state combined with Ti. It is clear that this is a special effect.

Next, for each catalyst after the S regeneration treatment, the evaluation lean gas / evaluation rich gas shown in Table 2 was circulated at SV = 51400 h ⁻¹ while fluctuating at 120 seconds / 3 seconds, at 300 ° C., 400 ° C. and 500 ° C. The high temperature NO _x purification rate was measured respectively. Further, the evaluation lean gas / evaluation rich gas shown in Table 3 was circulated at SV = 25700 h ⁻¹ while fluctuating at 60 seconds / 3 seconds, and the low temperature NO _x purification rates at 270 ° C., 300 ° C. and 330 ° C. were measured. Each result is shown in Table 4.

From Table 4, it can be seen that the catalysts of Example 1 and Example 2 are superior in NO _x purification performance at high and low temperatures as compared with the catalyst of Comparative Example 1 even after the high temperature durability test. This is considered to be due to the fact that the reaction between K and the substrate was suppressed, the growth of Pt grains was suppressed, and the sulfur detachment property was improved. In addition, it can be seen that the catalyst of Example 2 is particularly excellent in NO _x purification performance in a high temperature range as compared with the catalyst of Example 1, and it is clear that it is desirable to carry an independent NO _x storage material on the exhaust gas downstream side. It is.

It is a time chart which shows the evaluation pattern in an Example. It is a graph which shows the relationship between the time at the time of S reproduction | regeneration processing, and desorption S concentration.

Claims (7)

A NO _x storage material comprising a composite of at least one element selected from alkali metals and alkaline earth metals, an alkaline element that can be combined with titanium, and a titanium element in a fine state. The NO _x storage material according to claim 1, wherein the alkaline element is potassium. A first compound comprising an alkaline element which is composed of at least one selected from alkali metals and alkaline earth metals and can be combined with titanium;
A fourth compound produced from a second compound comprising a titanium alkoxide and a third compound having a polydentate ligand;
_The NO _x storage material according to claim 1 or claim 2 and a half or more of hydrogen peroxide in a molar ratio, were prepared from solutions coexist against titanium. A first compound comprising an alkaline element which is composed of at least one selected from alkali metals and alkaline earth metals and can be combined with titanium;
A fourth compound synthesized from a second compound containing a titanium alkoxide and a third compound having a polydentate ligand;
A method for supporting an NO _x storage material, comprising impregnating a porous oxide carrier with a solution in which hydrogen peroxide having a molar ratio of 1/2 or more with respect to titanium coexists, and then firing the support. NO _x to a carrier made of a porous oxide, characterized the noble metal supported on the carrier, and _the NO _x storage material according to claim 1 supported on the carrier, in that it consists of Occlusion reduction type catalyst. The carrier, _the NO _x storage-reduction type catalyst according to claim 5 which further carries the titanium comprises at least one uncomplexed independently _the NO _x storage material selected from alkali metals and alkaline earth metals. The _the NO _x storage material according to any one of claims 1 to 3 supported on the exhaust-gas upstream side, _the NO _x storage-reduction type catalyst according to the independent _the NO _x storage material in claim 6 comprising supported on the exhaust gas downstream side .

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