JP2000350934A - Catalyst for cleaning exhaust gas and method for cleaning exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit the deterioration of hydrogen generating reaction properties and further enhance the NOx cleaning power after an endurance life. SOLUTION: A desulfurization catalyst such as a Co-Mo/Al2O3 catalyst or Ni-Mo/Al2O3 is added to a catalyst-carrying layer. It is considered that SOx contained in an exahust gas is mainly desulfurized by hydrogenation by the help of the desulfurization catalyst and thereby the adsorption of SOx into the catalyst-carrying layer and the chemical reaction of SOx with an NOx occluding material are inhibited. In addition, the sulfur poisoning of the desulfurization catalyst itself is inhibited, so that the deterioration of a hydrogen generating reaction is inhibited and the NOx cleaning power after the endurance life is further enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the, NO _x in the exhaust gas contains excess oxygen than the amount required to oxidize the carbon monoxide contained in the exhaust gas (CO) and hydrocarbons (HC) a NO _x storage-and-reduction type catalyst for purifying an exhaust gas which can efficiently purify, an exhaust gas purification method using the catalyst.

[0002]

BACKGROUND ART In a lean-burn engine, normally is burned with oxygen excess fuel lean condition, the system reduces and purifies NO _x exhaust gas as a reducing atmosphere is developed by the intermittent fuel stoichiometric-rich condition, Has been put to practical use. And as the best catalysts for this system, occludes NO _x in lean atmosphere, with _the NO _x storage element that emits occluded NO _x at stoichiometric-rich atmosphere
NO _x storage-and-reduction type exhaust gas purifying catalyst has been developed.

For example, JP-A-5-317652 proposes an exhaust gas purifying catalyst in which an alkaline earth metal such as Ba and Pt are supported on a porous oxide carrier such as γ-Al ₂ O ₃ . Also, JP-A-6-31139 discloses that an alkali metal such as K is used.
An exhaust gas purifying catalyst in which Pt is supported on a porous oxide carrier such as γ-Al ₂ O ₃ has been proposed. Further, Japanese Patent Application Laid-Open No. 5-168860 proposes an exhaust gas purifying catalyst in which a rare earth element such as La and Pt are supported on a porous oxide carrier such as γ-Al ₂ O ₃ .

[0004] By using this NO _x storage-and-reduction type catalyst, by controlling so that the stoichiometric-rich side in a pulsed manner the air-fuel ratio from the lean side, the stoichiometric-rich atmosphere exhaust gas from a lean atmosphere in pulses . Thus, NO _x is occluded in _the NO _x storage element is in the lean side, because it is purified by reacting with reducing components, such as being released in the stoichiometric or rich side HC and CO, in exhaust gases from lean-burn engines can efficiently purify NO _x even. Further, HC and CO in the exhaust gas are oxidized by the noble metal and consumed in the reduction of NO _x , so that HC and CO are also efficiently purified.

However, exhaust gas contains fuel.
SO produced by burning sulfur_TwoIncludes a lean atmosphere
SO oxidized by precious metals in the exhaust gas of the atmosphere_ThreeBecomes
And it is also caused by the water vapor contained in the exhaust gas.
It easily becomes sulfuric acid, and these are NO _xSulfur reacts with storage elements
Salts and sulfates are produced,_xThe occlusion element is poisoned
It became clear that it deteriorated.

[0006] When thus _the NO _x storage element is deteriorated poisoning become sulfites and sulfates, it becomes impossible to occlude NO _x longer, with the result the catalyst after the durability test (hereinafter, durable purification performance of the NO _x in) that after there has been a problem of a decrease. This phenomenon is called sulfur poisoning of the NO _x storage material. Therefore, Japanese Unexamined Patent Publication No. 10-33984, with the noble metal and NO _x storage material, Co, catalyst carrying at least one element selected from Fe and Ni is disclosed. Co, Fe and Ni have a function of promoting a steam reforming reaction or a water gas shift reaction, and generate hydrogen. Hydrogen as well as reducing the NO _x by its strong reducing power, for the reduction of sulfite and sulfate of _the NO _x storage material, NO
_x Sulfur poisoning of the storage material is suppressed. Therefore, with this catalyst, the NO _x purification performance is improved, and a high NO _x purification performance is ensured even after durability.

[0007]

[Problems to be solved by the invention]
Even in the catalyst disclosed in JP 84, there is a problem that larger than _the NO _x purification intolerance degree after the durability is expected. It is considered that this is because at least one element selected from Co, Fe and Ni itself causes sulfur poisoning and deteriorates the hydrogen generation reactivity.

The present invention has been made in view of such circumstances, and an object of the present invention is to further improve the NO _x purification capability after durability by suppressing deterioration of the hydrogen generation reactivity.

[0009]

The exhaust gas purifying catalyst of the present invention which solves the above-mentioned problems is characterized by a base material, a catalyst support layer formed on the surface of the base material, and a noble metal supported on the catalyst support layer. At least one kind of NO selected from alkali metals, alkaline earth metals and rare earth elements supported on the catalyst supporting layer;
and _x storage element, the more it becomes _the NO _x storage-reduction type exhaust gas purifying catalyst, the catalyst supporting layer is to containing desulfurization catalyst.

[0010] desulfurization catalyst, Co and Mo are selected and Co-Mo / Al ₂ O ₃ catalyst comprising supported on alumina, the Ni-Mo / Al ₂ O ₃ catalyst Ni and Mo is supported on alumina Desirably, at least one kind is used. The molar ratio of Co or Ni to Mo is particularly preferably from 5 to 90%. The desulfurization catalyst is desirably contained in the catalyst support layer in an amount of 5 to 50% by weight.

The features of the exhaust gas purifying method of the present invention are as follows.
The above-described exhaust gas purifying catalyst, the air-fuel ratio (A / F) operated at 18 or higher in contact with the exhaust gas from the intermittent lean-burn engines with fuel stoichiometric-rich atmosphere, the NO _x contained in the exhaust gas occluded _the NO _x storage element in the fuel-lean atmosphere is to reduce the released NO _x from _the NO _x storage element in the fuel stoichiometric-rich atmosphere.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the exhaust gas purifying catalyst of the present invention,
It contains desulfurization catalyst in the catalyst-carrying layer of the conventional NO _x storage-and-reduction type catalyst. Thus the sulfur components in the exhaust gas (SO _x) are considered to be primarily hydrodesulfurization by desulfurization catalyst, since the reaction between the adsorption and _the NO _x storage material to the catalyst-carrying layer is suppressed, NO _x purification after the durability test Performance is improved.

As desulfurization catalysts, Co-Mo, Ni-Mo, Co-
A binary system in which two metals such as W and Ni-W are supported on alumina is recommended. Although a monolithic system in which Co or Ni alone or both are supported on alumina has a certain degree of desulfurization catalytic action, there is a problem that the hydrogen production reactivity is liable to deteriorate due to sulfur poisoning of the desulfurization catalyst itself. However, by the binary, for sulfur poisoning of the desulfurization catalyst itself is suppressed, NO _x purifying ability after durability is suppressed deterioration of the hydrogen generation reaction is further improved. In addition, among the binary desulfurization catalysts exemplified above, Mo-based Co-Mo or Ni-
A material in which Mo is supported on alumina is particularly preferable.

In a desulfurization catalyst in which Co-Mo or Ni-Mo is supported on alumina, the molar ratio of Co or Ni to Mo (Co / M
o, Ni / Mo) is preferably 5 to 90%. Co or N
When i is out of this range, the desulfurization action is reduced, so that the effect contained in the catalyst supporting layer cannot be obtained. The desulfurization catalyst is
It is desirable that the catalyst supporting layer contains 5 to 50% by weight. If the content of the desulfurization catalyst is less than 5% by weight, the effect of the content cannot be obtained. If the content exceeds 50% by weight, the effect is saturated and the purification activity is reduced due to the decrease in the amount of other components.

Examples of the substrate include a honeycomb monolith substrate formed from cordierite or metal foil, or a pellet substrate. Catalyst supporting layer is formed from a porous oxide support, such as mainly _{Al 2 O 3, SiO 2,} ZrO 2, TiO 2, SiO 2 -Al 2 O 3. Among them, γ-Al ₂ O ₃ having a high specific surface area and excellent heat resistance is preferably used as a main component. Further, by containing TiO ₂ , sulfur poisoning can be further prevented. In this case, the molar ratio of Al ₂ O ₃ / TiO ₂ = 4 /
It is desirable to set the range of 1 to 1/3. Within this range, both purification performance and sulfur poisoning resistance can be achieved. If the amount of Al ₂ O ₃ is less than this, the purification performance is low, and sintering of the noble metal is likely to occur. If the amount of TiO ₂ is less than this, the sulfur poisoning resistance decreases.

The catalyst-supporting layer further comprises Rh-supported ZrO ₂
Is preferable. By containing Rh / ZrO ₂ , the aqueous shift reaction is further promoted, so that sulfur poisoning can be further suppressed. It is also preferable to include CeO ₂ . Purification performance is further improved by the oxygen storage / release capability of CeO ₂ . CeO ₂ -ZrO ₂ stabilized with ZrO ₂ (ceria-
Use of a zirconia composite oxide) further improves the durability.

To form the catalyst supporting layer, Al_TwoO_ThreeWhat
Slurry is prepared from any oxide carrier powder and honeycomb
After applying slurry to the base material in the shape of a pellet or pellet
It can be formed by firing. Desulfurization catalyst
To be included in the catalyst support layer, use Al_TwoO_ThreeOxide carriers such as
Powder and desulfurization catalyst powder to form a catalyst-supporting layer.
I just need. In addition, Al_TwoO_ThreeWhen containing Co-
By supporting Mo or Ni-Mo on the catalyst support layer, the desulfurization catalyst
It can also be formed. The desulfurization catalyst is used for the catalyst support layer.
It is particularly preferred to include it in the surface layer. This allows the catalyst
SO to holding layer_xAdsorption can be effectively suppressed, and NO
_xSulfur poisoning of the storage material can be further suppressed.

As the noble metal, Pt, Rh, Pd, Ir or
One or more types of Ru can be used. The amount of the carrier per 1 liter of the carrier volume is Pt and Pd.
0.1 to 20 g is preferable, and 0.5 to 10 g is particularly preferable. In the case of Rh, the amount is preferably 0.01 to 10 g, particularly preferably 0.05 to 5 g. As the NO _x storage material, at least one selected from alkali metals, alkaline earth metals, and rare earth elements can be used. Above all, high alkalinity and NO
_It is preferable to use at least one of an alkali metal and an alkaline earth metal having high _x storage capacity.

Examples of the alkali metal include lithium, sodium, potassium and cesium. The alkaline earth metal refers to a Group 2A element in the periodic table, and examples thereof include barium, beryllium, magnesium, calcium, strontium, and the like. In addition, scandium,
Examples include yttrium, lanthanum, cerium, praseodymium, neodymium, dysprosium, ytterbium and the like.

[0020] The noble metal and NO _x storage material to carry the catalyst supporting layer may be formed catalyst supporting layer in advance a noble metal and _the NO _x storage material from carrying the oxide support powder, adsorption, evaporation to dryness The catalyst can be supported on the catalyst supporting layer by a known method such as a solid method. Loading amount of _the NO _x storage material is 0.05 to 1.0 mols is preferable with respect to the support volume of 1 liter. Loading amount is 0.0
If the amount is less than 5 moles, the NO _x storage capacity is small, and the NO _x purification performance is reduced.

In the exhaust gas purification method of the present invention, the air-fuel ratio (A / A
F) is operated at 18 or more to intermittently come into contact with exhaust gas from a lean burn engine which is in a fuel stoichiometric to rich atmosphere. Then the fuel-lean atmosphere, NO _x is NO contained in exhaust gas is oxidized on the catalyst, it is NO _x
It is stored in the storage material. When the fuel stoichiometric-rich atmosphere is set intermittently, NO _x is released from the NO _x occluding material, and the NO _x is reduced by reacting with HC and CO in the exhaust gas on the catalyst.

At this time, SO ₂ in the exhaust gas is oxidized to SO _x in a lean atmosphere, but it is considered that the SO ₂ is mainly hydrodesulfurized by a desulfurization catalyst in a stoichiometric to rich atmosphere, and is discharged again as SO _2. . Therefore, adsorption of SO _x on the catalyst support layer is suppressed and NO
is sulfur poisoning suppression of _x storage material, _the NO _x storage material expresses after the durability is high _the NO _x storage capacity.

When the desulfurization catalyst is a binary system such as Co—Mo / Al ₂ O ₃ , sulfur poisoning of the desulfurization catalyst itself is suppressed, so that deterioration of the hydrogen generation reaction is suppressed and NO after endurance is reduced. _x Purification ability is further improved.

[0024]

The present invention will be specifically described below with reference to examples and comparative examples. Embodiment 1 FIG. 1 schematically shows the structure of an exhaust gas purifying catalyst according to this embodiment. This exhaust gas purifying catalyst includes a honeycomb-shaped substrate 1 formed of cordierite, and a catalyst supporting layer 2 formed on the surface of the substrate 1, and the catalyst supporting layer 2 includes Pt and Rh. and a noble metal, Ba, and _the NO _x storage material consisting of K and Li, and desulfurization catalyst 3 consisting of Co-Mo / Al ₂ O ₃ are supported. Hereinafter, the method for producing the exhaust gas purifying catalyst will be described, and the detailed description of the configuration will be substituted.

First, ZrO ₂ powder was impregnated with a predetermined amount of an aqueous solution of rhodium nitrate having a predetermined concentration, dried and fired to carry Rh. The Rh carrying amount of the obtained Rh / ZrO ₂ powder was 1.0% by weight. On the other _{hand, (NH 4) 6 Mo 7} O 24 · 4H 2 O aqueous solution and _{Co (NO 3) 2 · 6H} 2 O
A mixed aqueous solution having a predetermined concentration is prepared by mixing the aqueous solutions at a molar ratio of Mo: Co = 2: 1, and a predetermined amount of the mixed aqueous solution is impregnated into a predetermined amount of γ-Al ₂ O ₃ powder and evaporated. After drying 5
Baking at 00 ° C. for 3 hours, co-supporting Co and Mo, Co-Mo / Al ₂
O ₃ powder were prepared. In this Co—Mo / Al ₂ O ₃ powder, 2% by weight of Co is supported and 4% by weight of Mo is supported.

Next, the Rh / ZrO ₂ powder and the Co—Mo / A
l ₂ O ₃ powder, γ-Al ₂ O ₃ powder, TiO ₂ powder and CeO ₂ -ZrO ₂
The powder was mixed to prepare a mixed powder. The mixing ratio of each powder in the mixed powder is Al ₂ O ₃ powder: TiO ₂ powder = 1: 1, and the ratio of Rh / ZrO ₂ powder is １ ／ of the total weight of Al ₂ O ₃ powder and TiO ₂ powder. , Co-Mo / Al ₂ O ₃ powder is composed of Al ₂ O ₃ powder and TiO ₂
1/10 of the total weight of the powder, and CeO ₂ -ZrO ₂ powder is Al ₂
This is 1/10 of the total weight of the O ₃ powder and the TiO ₂ powder.

After this mixed powder is mixed well, it is mixed with a predetermined amount of water to form a slurry, and has a diameter of 30 mm, a length of 50 mm and a volume of 35 mm.
Immerse the base material 1 of cc in the slurry and pull it up at 250 ° C
The catalyst support layer 2 was formed by drying for 15 minutes. The catalyst supporting layer was formed in an amount of 280 g per liter of the substrate 1. The base material 1 having the catalyst supporting layer 2 is impregnated with a predetermined amount of a barium acetate aqueous solution having a predetermined concentration, and dried at 250 ° C. for 15 minutes.
Baking was carried out at 30 ° C. for 30 minutes to carry Ba. The amount of Ba supported is
Is 0.2 mol per liter. The concentration is 15g /
L for 15 minutes at 250 ° C
For 15 minutes.

This is immersed in an aqueous solution of dinitrodiammineplatinic nitric acid of a predetermined concentration, pulled up and baked at 300 ° C. for 15 minutes.
Pt was loaded. The supported amount of Pt is 2 g per liter of the base material 1. This is impregnated with a predetermined amount of a mixed aqueous solution of potassium nitrate and lithium nitrate at a predetermined concentration.
After drying for minutes, it was baked at 500 ° C. for 30 minutes to carry K and Li. K and
The supported amount of Li was 0.1
Is a mole. Thus, the catalyst of Example 1 was prepared.

Example 2 An aqueous solution of Ni (NO ₃ ) ₂ .6H ₂ O was used in place of the aqueous solution of Co (NO ₃ ) ₂ .6H ₂ O, and the molar ratio of Mo: Ni =
2: 1 and formed by using a mixed aqueous solution of a predetermined concentration mixed at a ratio, to prepare a Ni-Mo / Al ₂ O ₃ powder. This Ni-Mo / A
In the l ₂ O ₃ powder, 2% by weight of Ni is supported and 4% by weight of Mo is supported.

Then, instead of the Co-Mo / Al ₂ O ₃ powder, this Ni
Except for using -mo / Al ₂ O ₃ powder in the same manner as in Example 1 to prepare a catalyst of Example 2. Mo (Example 3) molar ratio: Co = 19: was prepared Co-Mo / Al ₂ O ₃ powder with a mixed aqueous solution of a predetermined concentration mixed with 1 become ratio. In this Co—Mo / Al ₂ O ₃ powder, 0.5% by weight of Co is supported, and 9.5% by weight of Mo is supported.

Then, a catalyst of Example 3 was prepared in the same manner as in Example 1 except that this Co—Mo / Al ₂ O ₃ powder was used. (Example _{4) Co (NO 3) 2} · 6H 2 instead of Ni O solution (NO _{3) 2}
Using a 6H ₂ O aqueous solution and a mixed aqueous solution of a predetermined concentration mixed at a molar ratio of Mo: Ni = 19: 1, Ni-Mo /
Al ₂ O ₃ powder was prepared. In this Ni-Mo / Al ₂ O ₃ powder,
Ni is loaded at 0.5% by weight and Mo is loaded at 9.5% by weight.

Then, instead of the Co-Mo / Al ₂ O ₃ powder, this Ni
Except for using -Mo / Al ₂ O ₃ powder in the same manner as in Example 1 to prepare a catalyst of Example 4. Example 5 A Co—Mo / Al ₂ O ₃ powder was prepared using a mixed aqueous solution having a predetermined concentration mixed at a molar ratio of Mo: Co = 1: 9. In this Co—Mo / Al ₂ O ₃ powder, 1% by weight of Co is supported, and 9% by weight of Mo is supported.

A catalyst of Example 5 was prepared in the same manner as in Example 1 except that this Co-Mo / Al ₂ O ₃ powder was used. (Example 6) Ni (NO ₃ ) ₂ instead of Co (NO ₃ ) ₂ .6H ₂ O aqueous solution
Using a 6H ₂ O aqueous solution and a mixed aqueous solution of a predetermined concentration mixed at a molar ratio of Mo: Ni = 1: 9, Ni-Mo /
Al ₂ O ₃ powder was prepared. In this Ni-Mo / Al ₂ O ₃ powder,
Ni is loaded at 1% by weight and Mo is loaded at 9% by weight.

Then, instead of the Co—Mo / Al ₂ O ₃ powder, this Ni
Except for using -Mo / Al ₂ O ₃ powder in the same manner as in Example 1 to prepare a catalyst of Example 6. Except that the (Example _{7) Co-Mo / Al 2} O 3 1/20 the amount of the powder of the total weight of Al ₂ O ₃ powder and TiO ₂ powder in the same manner as in Example 1, Example 7 Was prepared.

Example 8 The procedure of Example 1 was repeated except that the amount of the Co—Mo / Al ₂ O ₃ powder was １ ／ of the total weight of the Al ₂ O ₃ powder and the TiO ₂ powder. The catalyst of Example 8 was prepared. (Example _{9) (NH 4) 6 Mo} 7 O 24 · 4H 2 O aqueous solution without using, Co (N
O ₃₎ using only ₂ · 6H ₂ O aqueous solution were prepared Co / Al ₂ O ₃ powder. In this Co / Al ₂ O ₃ powder, 1% by weight of Co is supported.

This Co-Mo / Al ₂ O ₃ powder is replaced with this Co
/ A catalyst of Example 9 was prepared in the same manner as in Example 1 except that Al ₂ O ₃ powder was used. Example 10 Ni (N ₄ ) ₆ Mo ₇ O ₂₄ · 4H ₂ O
O ₃ ) Ni / Al ₂ O ₃ powder was prepared using only the aqueous solution of ₂ · 6H ₂ O. In this Ni / Al ₂ O ₃ powder, 1% by weight of Ni is supported.

Then, instead of the Co—Mo / Al ₂ O ₃ powder, this Ni
/ A catalyst of Example 10 was prepared in the same manner as in Example 1, except that Al ₂ O ₃ powder was used. (Comparative Example _{1) Co-Mo / Al 2} O 3 except that the powder was not used in the same manner as in Example 1 to prepare a catalyst of Comparative Example 1.

<Test / Evaluation> Each of the above catalysts was placed in a laboratory reactor, and using the model gas shown in Table 1, at a catalyst bed temperature of 400 ° C. and a total flow rate of 4.7 L / min. A cycle of lean gas 55 seconds-rich gas 5 seconds was repeatedly introduced for one hour, and each was subjected to a sulfur poisoning durability test.

[0039]

[Table 1] For each new and durable catalyst, using the model gas shown in Table 2, the catalyst bed temperature was 600 ° C and the total flow rate was 30L.
At a rate of / min, CO and HC purification rates were measured by repeatedly flowing lean gas for 5 minutes and rich gas for 10 seconds. Table 2
The CO and HC purification rates were measured in the same manner using a gas obtained by adding 10% of H ₂ O to the model gas shown in FIG. The respective results are shown in FIG. 2 and FIG.

[0040]

[Table 2] 2 and 3, when the of H ₂ O adding H ₂ O in comparison with the catalyst after the catalyst durability test in Comparative Example 1 after the durability test of each Example
The difference between the purification rate and the case without the addition is large, and the purification rate is greatly improved by the addition of H ₂ O. The large consumption of HC and CO due to the addition of H ₂ O means that hydrogen was generated by a water gas shift reaction or a steam reforming reaction. Means that

[0041] However, in the catalyst of Example 9 and Example 10, the difference in the purification rate of the cases of adding H ₂ O after the durability and H ₂ O was not added as compared with the catalysts of Examples 1-8 is small The degree of deterioration of the hydrogen generation reaction in the durability test is large. That is, it can be seen that by using a binary desulfurization catalyst like the catalysts of Examples 1 to 8, deterioration of the hydrogen generation reaction in the durability test is suppressed.

That is, like the catalysts of Examples 1 to 8,
By the -Mo / Al ₂ O ₃ powder or Ni-Mo / Al ₂ O ₃ powder comprising the catalyst-carrying layer, the deterioration of the hydrogen generation reaction is suppressed, NO _x storage material by hydrogen also occurs after endurance Sulfur poisoning deterioration can be suppressed.

[0043]

Effects of the Invention] That is, according to the catalyst and the exhaust gas purifying method for purifying an exhaust gas of the present invention, since a stable hydrogen generation reaction from the initial to after the durability test results, NO _x storage material that sulfur poisoning by hydrogen generated is reduced As a result, the NO _x storage capacity is restored and NO _x is reduced by hydrogen. Thus after the running is also obtained higher _the NO _x purification performance, durability is remarkably improved.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a configuration of an exhaust gas purifying catalyst according to one embodiment of the present invention.

FIG. 2 is a graph showing a CO purification rate of each catalyst of an example and a comparative example.

FIG. 3 is a graph showing HC purification rates of respective catalysts of an example and a comparative example.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/08 F01N 3/28 301C 3/10 B01D 53/36 D 3/28 301 102B F-term (reference) 3G091 AA12 AA13 AA17 AB06 AB09 AB11 BA11 BA14 BA20 BA33 BA39 CB02 EA30 FB10 FB11 FB12 FC02 GA01 GA07 GA20 GB01W GB01X GB02W GB03W GB04W GB05W GB10X GB16X GB17X HA08 HA18 4A048 BA26X BA26Y BA30X BA30Y BA31Y BA32Y BA33X BA33Y BA37X BA37Y BA38X BA38Y CC46 CC50 EA04 4G069 AA03 AA08 BA01A BA01B BA04A BA04B BA05A BA05B BA13A BA13B BC01A BC03B CA04B BC13B BC BC BC BC BC BC BC BC BC BC BC BC BC BC BC BC BC BC BC

Claims (5)

[Claims] 1. A substrate, a catalyst supporting layer formed on the surface of the substrate, a noble metal supported on the catalyst supporting layer, an alkali metal, an alkaline earth metal and a rare earth supported on the catalyst supporting layer. at least one NO _x storage element selected from the elements in a more becomes NO _x storage-and-reduction type exhaust gas purifying catalyst, the exhaust gas purifying catalyst, characterized in that the said catalyst supporting layer comprising a desulfurization catalyst. Wherein said desulfurization catalyst, Co and Mo and Co-Mo / Al ₂ O ₃ catalyst comprising supported on _{alumina, Ni-Mo / Al 2 O} 3 catalyst Ni and Mo is supported on alumina The exhaust gas purifying catalyst according to claim 1, wherein the catalyst is at least one member selected from the group consisting of: 3. The Co—Mo / Al ₂ O ₃ catalyst and the Ni—Mo catalyst
/ In Al ₂ O ₃ catalyst, the exhaust gas purifying catalyst according to claim 2, wherein the molar ratio of Mo Co or Ni is 5 to 90%. 4. The method according to claim 1, wherein the desulfurization catalyst is contained in the catalyst support layer.
The exhaust gas purifying catalyst according to claim 1, wherein the catalyst is contained in an amount of 50% by weight. 5. The exhaust gas according to any one of claims 1 to 4,
When the purification catalyst is operated at an air-fuel ratio (A / F) of 18 or more,
Lean bar that is sometimes fuel stoichiometric ~ rich atmosphere
Contact with the exhaust gas from the engine
NO_xThe fuel in a lean atmosphere_xOccluded in the storage element
NO in fuel stoichiometric to rich atmosphere _xFrom occlusion elements
NO released_xExhaust gas purification characterized by reduction of wastewater
Method.