JP2002011347A - SOx absorber, exhaust gas purifying catalyst using the same, and exhaust gas purifying method - Google Patents

Abstract

(57) Abstract: enables regeneration process at a low temperature, is a SO _x absorber be possible to play also treated in the exhaust gas. The present invention includes a composite oxide composed of a rare earth element M and an aluminum oxide, the molar ratio M / Al is 0.01 to 0.5, and M is present in the aluminum oxide in a highly-dispersed state substantially substantially. Of a porous body containing no aluminate. Since a large number of basic sites (M) required for SO _x absorption exist in a highly dispersed state, they were absorbed.
SO _x is easily decomposed, it can be reproduced at a low temperature of 450 to 600 ° C..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates includes a SO _x absorbent absorbs SO _x contained in the exhaust gas, a catalyst and an exhaust gas purifying method for purifying exhaust gas using the SO _x absorbent.

[0002]

_2. Description of the Related Art For the purpose of suppressing CO ₂ emissions by reducing fuel consumption, automobile engines and the like are burnt in a fuel-lean atmosphere with an excess of oxygen. And as a catalyst for purifying an exhaust gas to efficiently reduce and purify of the NO _x even under fuel-lean atmosphere, NO _x storage reduction catalysts, it has been developed _the NO _x selective reduction catalyst, have been put to practical use. Further, HC oxidation catalysts are widely used in order to more efficiently oxidize and purify HC in exhaust gas.

The NO _x storage-reduction catalyst is a NO _x storage material which is selected from a porous carrier, a noble metal supported on the porous carrier, an alkali metal, an alkaline earth metal and a rare earth element, and which is supported on the porous carrier. The combustion system is used in an exhaust system of a combustion system in which a mixture is constantly burned in an oxygen-excess lean atmosphere and the ratio of the air-fuel mixture is intermittently controlled to a stoichiometric to rich atmosphere.

[0004] As _the NO _x selective reduction catalyst used in the fuel-lean atmosphere, that carries a Cu zeolite carrier, such as those supporting the noble metal is known to alumina. As the HC oxidation catalyst, a catalyst in which Pt having high oxidation activity is supported on a carrier such as alumina is known.

However, the exhaust gas in the fuel-lean atmosphere contains SO _x such as SO ₂ . Therefore, when such exhaust gas comes into contact with the NO _x storage reduction catalyst, the NO _x storage material and SO _x react with each other to generate stable sulfate, and the NO _x storage capacity of the NO _x storage material decreases. There is.

In a NO _x selective reduction catalyst or an HC oxidation catalyst, the supported catalytic metal having catalytic activity is SO _x
Covered with caused the problem that activity is reduced, also there is a problem that trouble the order sulfur component on the catalyst metal is further oxidized SO _x occurring is increasingly promoted. Moreover, there is a problem that the amount of sulfate discharged increases.

[0007] SO_x Hands to suppress the above-mentioned problems due to
SO as one of the steps_x The use of absorbents is being considered.
SO like this_x As the absorbent, for example, JP-A-57-1626
No. 45 discloses that a single layer is dispersed on the surface of alumina.
One in which a lanthanum oxide layer is formed is disclosed. Ma
JP-A-5-146675 discloses silica, lantana, and the like.
Contains active ingredients such as alumina stabilizer and alkali metal
SO composed of alumina _x An adsorbent is disclosed.

[0008] Such SO_x Exhaust gas purification as described above
If it is located upstream of the catalyst for_x Is SO_x 
Because it is absorbed by the absorbent, SO_x Exhaust gas with reduced concentration
Is NO _x Storage reduction catalyst, NO_x Selective reduction catalyst or HC
Suppresses sulfur poisoning described above due to contact with oxidation catalyst
be able to.

[0009]

In the way SO _x absorber [SUMMARY OF THE INVENTION], absorption of the SO _x becomes difficult absorption to the higher of the SO _x saturated. Then, the absorbed SO _x is decomposed to SO
_{x It} is necessary to perform a regeneration process to regenerate the absorption capacity.

However, in the case of the conventional SO _x absorbent, it is necessary to perform a heating treatment at a high temperature of 600 to 700 ° C. in a gas in a reducing atmosphere, and it is difficult to actually perform a regeneration treatment in an exhaust gas. Therefore, there is a problem that the regeneration process has to be performed separately, and the number of steps and costs are large.

[0011] The present invention has been made in view of such circumstances, it is possible to playback processing at a low temperature, and an object thereof is to the SO _x absorber be possible to play also treated in the exhaust gas.

[0012]

Features of the SO _x absorber of the present invention to solve the above problems SUMMARY OF THE INVENTION, in SO _x absorber comprising a composite oxide consisting of rare earth elements M and aluminum oxide,
The molar ratio M / Al is in the range of 0.01 to 0.5, M is present in the aluminum oxide uniformly and in a highly dispersed state, and the porous material substantially does not contain the aluminate of M.

The exhaust gas purifying catalyst of the present invention has the following features:
It is characterized by comprising the SO _x absorbent and at least one catalyst selected from a NO _x storage reduction catalyst, a NO _x selective reduction catalyst, and an HC oxidation catalyst.

The characteristics of the exhaust gas purifying method of the present invention are as follows.
An exhaust gas purifying catalyst comprising the SO _x absorbent and the NO _x selective reduction catalyst is supplied from a lean burn engine which is operated at an air-fuel ratio (A / F) of 15 or more and has an intermittent fuel stoichiometric to rich atmosphere. SO with contacting with the exhaust gas, the NO _x contained in the exhaust gas is occluded in the NO _x storage-and-reduction type catalyst in fuel-lean atmosphere, reducing the released NO _x fuel stoichiometric ~ rich atmosphere from the NO _x storage-and-reduction type catalyst _x Absorbent SO
_x To regenerate absorption capacity.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The SO _x absorber of the present invention has a molar ratio M / Al of the rare earth element M to Al of 0.01 to 0.5, and the rare earth element M is uniformly dispersed in the aluminum oxide in a highly dispersed state. It is present and is composed of a porous body substantially free of M aluminate. That is, since the basic site (M) necessary for SO _x absorption is present in a large amount in a highly dispersed state, the absorbed SO _x is easily decomposed, and 450 to 6
Regeneration at a low temperature of 00 ° C. becomes possible.

If the molar ratio M / Al is less than 0.01, a sufficient amount of SO _x cannot be obtained because the amount of M is insufficient.
If it exceeds 0.5, the specific surface area is reduced, so that sufficient SO _x absorption capacity cannot be obtained. The molar ratio M / Al is particularly preferably in the range of 0.02 to 0.1, and if M is not present in a highly dispersed state, the absorbed SO _x becomes difficult to decompose. In addition, when M aluminate is present, SO _x becomes difficult to be decomposed due to a reduction in lattice defects in the composite oxide. Therefore, there arises a disadvantage that the temperature required for the regeneration process becomes high.

The specific surface area of the composite oxide is 100 to 300 m ² / g
It is desirable that With such a porous body, M can be contained in a more highly dispersed state.

It is particularly desirable that the composite oxide has mesopores and at least a part of the mesopores communicates in a three-dimensional network to form a communication path. The mesopore pore diameter means a pore in the meso range (range 1 to 50 nm), a SO _x absorbent material of the present invention M is included in a highly dispersed state in such mesopores It is thought that it is exposed. Therefore, the exhaust gas easily enters the communication path composed of the mesopores and is absorbed by the basic site M.
And improves contact probability between the exhaust gas, in order to improve the absorption amount per unit amount of M, the absorption capacity of the SO _x is remarkably improved.

The composite oxide is preferably a composite oxide of only M and Al, but may contain other metals such as Si, Zr, and Ti.

In order to prepare such a composite oxide, it can be easily produced by a coprecipitation method, an alkoxide method or the like. It is preferable to use a coprecipitation method in which the raw material cost is low.

As the rare earth element M, Sc, Y, La, Pr,
Nd, the like Sm is preferably exemplified, it is particularly desirable to use a stabilizing effect is greater SO _x absorption capability of aluminum oxide is high La.

The SO _x absorbent of the present invention preferably contains at least one noble metal selected from Pt, Rh, Pd and Ir. By containing such a noble metal, SO ₂ is oxidized to generate SO ₃ or SO ₄ ions, and the reactivity with M is increased, so that the SO _x absorption ability is further improved. The noble metal may be contained in the composite oxide or may be supported on the composite oxide. The amount of the noble metal supported is preferably in the range of 0.1 to 10% by weight based on the composite oxide. If the amount is less than this range, the above-mentioned effects of the noble metal will not be exhibited, and if the amount exceeds this range, the effect will be saturated and the cost will rise.

One exhaust gas purifying catalyst of the present invention is the present invention.
Ming SO_x Alkali metals, alkaline earth metals and
Selected from rare earth elements_x At least one kind of occlusion material
Is carried. With such a configuration, a lean atmosphere
SO in gas exhaust gas_x Prefers M to suck
Collected, NO_x NO poisoning of the storage material is prevented, so NO _x 
It can be used effectively as an occlusion catalyst. This NO_x 
The loading amount of the occluding material is 0.05 to 1 with respect to 100 g of the composite oxide.
A molar range is preferred. NO_x 0.05 mol of occlusion material carried
If the amount is less, the carried effect is not exhibited, and
NO and noble metals are NO_x SO covered with occlusion material_x Sucking
Yield decreases.

A second exhaust gas purifying catalyst of the present invention comprises the SO _x absorbent of the present invention and a NO _x storage reduction catalyst. As a result, the sulfur poisoning of the NO _x storage material of the NO _x storage reduction catalyst can be prevented in the same manner as the action of the exhaust gas purifying catalyst, and high NO _x purification performance is exhibited even after durability.

The SO _x absorbent and the NO _x storage-reduction catalyst may be used in the form of a mixture of powders or pellets, or may be formed of a honeycomb monolith. They can also be used in series in the exhaust gas stream. In the latter case, it is desirable to arrange the SO _x absorbent upstream of the NO _x storage reduction catalyst. It is also possible to use the upper layer of the NO _x storage reduction catalyst coated on a monolith substrate by coating the SO _x absorbent.

In the case of the exhaust gas purifying catalyst comprising the SO _x absorbent of the present invention and the NO _x storage reduction catalyst, the air-fuel ratio (A
/ F) is desirably used in exhaust gas from a lean burn engine which is operated at 15 or more and has an intermittent fuel stoichiometric to rich atmosphere. In this way, with the NO _x contained in the exhaust gas is occluded in the NO _x storage-and-reduction type catalyst in fuel-lean atmosphere, can reduce the released NO _x fuel stoichiometric ~ rich atmosphere from the NO _x storage-and-reduction type catalyst the SO _x absorbed in the SO _x absorbent in fuel-lean atmosphere can be decomposed in the fuel stoichiometric-rich atmosphere. That SO _x absorbent material of the present invention, it is possible to decompose SO _x are absorbed at a low temperature of 600 ° C. or less, playing a SO _x absorption capability of the SO _x absorber can be disassembled SO _x in the exhaust gas temperature region can do.

The third exhaust gas purifying catalyst of the present invention comprises the SO _x absorbent of the present invention and the NO _x selective reduction catalyst, and another exhaust gas purifying catalyst of the present invention comprises the SO _x absorbent of the present invention. _It consists of an _x absorbent and an HC oxidation catalyst. In these exhaust gas purifying catalysts, SO _{x in} the exhaust gas
_{Since x} is preferentially absorbed by the absorbent, it is possible to prevent such a problem that the catalytic metal of the NO _x selective reduction catalyst or the HC oxidation catalyst is covered with SO _x and the activity is reduced, and NO _x
The durability of the selective reduction catalyst or the HC oxidation catalyst is improved.

In these exhaust gas purifying catalysts, the SO _x absorbent and the NO _x selective reduction catalyst or the HC oxidation catalyst may be used in the form of a mixture in the form of powder or pellets. However, those formed in a honeycomb monolith shape can be used in series in the exhaust gas flow. In the latter case, it is desirable that the SO _x absorbent is disposed upstream of the exhaust gas flow. It is also possible to use the upper layer of the NO _x storage reduction catalyst coated on a monolith substrate by coating the SO _x absorbent.

As the NO _x storage-reduction type catalyst, a carrier such as alumina, titania, silica, zirconia, etc.
Rh, can be used with catalytic metals such as Pd, alkali metal, a known carrying _the NO _x storage material selected from alkaline earth metals and rare earth elements.

As the NO _x selective reduction type catalyst, a catalyst in which Cu, Co, Ni, Fe or the like is supported on a zeolite support, or a catalyst metal such as Pt, Rh, Pd or the like is supported on a support such as alumina, titania, silica or zirconia. Can be used.

Further, as the HC oxidation catalyst, a known catalyst in which a catalyst metal having excellent oxidation activity such as Pt is supported on a carrier such as alumina, titania, silica, and zirconia can be used.

[0032]

The present invention will be described below in detail with reference to examples.

Example 1 A raw material aqueous solution was prepared by dissolving 0.4 mol of aluminum nitrate and 0.02 mol of lanthanum nitrate in 1 liter of water. 56.4 g of 25% aqueous ammonia was added to this raw material aqueous solution to co-precipitate it at pH = 8.8,
After aging at 120 ° C. for 2 hours, the mixture was filtered and washed, dried, and calcined in air at 800 ° C. for 5 hours to obtain a La-Al ₂ O ₃ composite oxide powder. The molar ratio of the La-Al ₂ O ₃ composite oxide powder was La / Al = 0.05, the specific surface area was 133 m ² / g, and LaAlO ₃ was not confirmed in the crystal structure by XRD, and γ- It had only an Al ₂ O ₃ structure.

Next, using a dinitrodiammineplatinum nitrate solution of a predetermined concentration, the obtained La-Al ₂ O ₃ composite oxide powder was
Impregnating carrying Pt, was prepared Pt / La-Al ₂ O ₃ powder carrying Pt on La-Al ₂ O ₃ and then calcined 3 hours at 300 ° C. in a drying after the atmosphere. The supported amount of Pt in the Pt / La-Al ₂ O ₃ powder was La-Al ₂ O ₃
Pt is 2 g for 120 g of After compacting the Pt / La-Al ₂ O ₃ powder, and the SO _x absorbent pellet shape of crushed and 0.3 to 0.7 mm was prepared.

(Example 2) Pt / La-Al ₂ O ₃ powder prepared in the same manner as in Example 1 was impregnated with K using an aqueous solution of potassium acetate having a predetermined concentration, dried, and dried at 300 ° C. in air. in 3 hours fired to _{Pt / La-Al 2 O K} / carrying K in _{3 Pt / La-Al 2 O} 3
A powder was prepared. Loading amount of K in _{K / Pt / La-Al 2} O 3 powder, K is 0.2 mol per 120g of _{Pt / La-Al 2 O 3} . After compacting the _{K / Pt / La-Al 2} O 3 powder was used to prepare the 0.3 to 0.7 mm pellet catalyst was crushed.

Comparative Example 1 20 g of a commercially available γ-Al ₂ O ₃ powder (specific surface area: 200 m ² / g) was impregnated with Pt using a dinitrodiammineplatinum nitrate solution of a predetermined concentration, dried, and dried. Pt / A supporting Pt on Al ₂ O ₃ by firing at 300 ° C. for 3 hours
l ₂ O ₃ powder was prepared. The supported amount is ₂ g of Pt with respect to 120 g of Al ₂ O ₃ . After compacting this Pt / Al ₂ O ₃ powder,
Crushed and was prepared SO _x absorbent pellet shape 0.3 to 0.7 mm.

Comparative Example 2 20 g of a commercially available γ-Al ₂ O ₃ powder (specific surface area: 200 m ² / g) was coated with
The impregnated carrier at dried in air and then calcined 5 hours at 800 ° C. to prepare a La / Al ₂ O ₃ powder carrying the La to Al ₂ O _3. The obtained La / Al ₂ O ₃ powder had a molar ratio La / Al = 0.05,
It has a specific surface area of 140 m ² / g and has a γ-Al ₂ O ₃
It was noted that LaAlO ₃ was present.

[0038] The La / Al ₂ O ₃ powder 20g, was impregnated support Pt with dinitrodiammine platinum nitrate solution having a predetermined concentration, and calcined 3 hours at 300 ° C. in a drying after the atmosphere La / Al ₂
Was prepared Pt / La / Al ₂ O ₃ powder carrying Pt on O _3. The loading amount is ₂ g of Pt for 120 g of La / Al ₂ O ₃ . After compacting this Pt / La / Al ₂ O ₃ powder, it is crushed to 0.3-
A 0.7 mm pellet-shaped SO _x absorbent was prepared.

Comparative Example 3 A raw material aqueous solution was prepared by dissolving 107 g of magnesium acetate and 379 g of aluminum nitrate in 1800 ml of ion-exchanged water. 650 g of 25% aqueous ammonia was added to the aqueous solution of the raw material, and the mixture was coprecipitated, aged at 120 ° C. under 2 atm for 2 hours, filtered, washed, dried, and dried in air.
The powder was fired at 50 ° C. for 5 hours to obtain MgAl ₂ O ₄ powder. This MgAl ₂
The molar ratio of the O ₄ powder was Mg / Al = 0.05, and the specific surface area was 102 m ² / g.

20 g of this MgAl ₂ O ₄ powder was impregnated with Pt using a dinitrodiammine platinum nitrate solution of a predetermined concentration,
After drying, baking in air at 300 ° C for 3 hours, Pt to MgAl ₂ O ₄
To support Pt / MgAl ₂ O ₄ powder. Loading amount is MgA
Pt is 2 g for 120 g of l ₂ O ₄ . This Pt / MgAl ₂ O
₄ after compacting the powder to prepare a SO _x absorbent pellet shape of 0.3 to 0.7 mm are crushed.

(Comparative Example 4) Kt was added to the Pt / Al ₂ O ₃ powder prepared in Comparative Example 1 using an aqueous solution of potassium acetate having a predetermined concentration.
Impregnated carrier to prepare a K / Pt / Al ₂ O ₃ powder carrying the K in at dried in air and then calcined 3 hours at _{300 ℃ Pt / Al 2 O 3} . The amount of K carried in the K / Pt / Al ₂ O ₃ powder is Pt /
K is 0.2 mol per 120 g of Al ₂ O ₃ powder. This K / Pt / Al ₂ O ₃ powder is compacted and then crushed to 0.3 to 0.7.
mm pellet catalyst was prepared.

<Test / Evaluation> The SO _x absorbent of Example 1
For SO _x absorbing material of Comparative Examples 1 to 3, carried out SO _x absorption test were respectively measured SO _x absorption amount and SO _x absorption rate.

In the SO _x absorption test, a predetermined amount of each SO _x absorbent was placed in an evaluation device, and the mixture was treated at 600 ° C. for 1 hour while flowing a lean model gas shown in Table 1 at a rate of 500 cc / min. The amount of SO _x passed through the SO _x absorbent is 1.39 mmol. Then, the amount of absorption was calculated from the quantitative value of S in the treated SO _x absorbent, and the ratio of the amount of S absorbed to the amount of S in the total gas flow was defined as the SO _x absorption rate. Table 2 shows the results.

[0044]

[Table 1]

[0045]

[Table 2]

From Table 2, it is clear that the SO _x absorbing material of Example 1 shows superior values of the S absorption amount and SO _x absorption ratio to Comparative Example 1. However, the specific surface area of γ-Al ₂ O ₃ of Comparative Example 1 is larger than that of La-Al ₂ O _{3 of} Example 1, and there is a contradiction with the SO _x absorption capacity simply assumed from the specific surface area.

Therefore, the pore size distribution of the La-Al ₂ O ₃ composite oxide used in Example 1 and the pore size distribution of γ-Al ₂ O ₃ used in Comparative Example 1 were measured, and the results were shown in FIG. Shown in From FIG.
The La-Al ₂ O ₃ composite oxide has a narrower pore size distribution than that of γ-Al ₂ O ₃ and is concentrated around 10 nm, which is a mesopore.

That is, in the La—Al ₂ O ₃ composite oxide used in Example 1, at least a part of the mesopores communicates in a three-dimensional network to form a communication path, thereby forming contact with the gas. High probability. Furthermore, the La-Al ₂ O ₃ composite oxide used in Example 1 had a base amount obtained from the CO ₂ adsorption amount of 1.7 times as large as that of γ-Al ₂ O ₃ used in Comparative Example 1, and was large. Base point. For these reasons, it is considered that the SO _x absorption amount was higher than that of Comparative Example 1.

Next, the above of the SO _x is absorbed SO _x absorbent was placed in each evaluation device, while the He gas containing H ₂ 5% was passed through at a flow rate of 120 cc / min, 20 ° C. / min The temperature was raised from room temperature to 800 ° C. at a heating rate of, and the mass spectrum intensity of the generated H ₂ S was continuously measured. The results are shown in FIG.

As is apparent from FIG. 2, the SO _{x of} Example 1 was used.
In the absorbent, H ₂ S was generated at around 450 ° C., and the peak intensity became maximum at around 560 ° C.
In this case, both the formation start temperature and the temperature at which the peak intensity becomes maximum are higher than those in Example 1. In Comparative Example 1, the peak area is extremely small.

That is, SO of Comparative Examples 1 to 3_x With absorbent material,
SO being collected_x Is finally decomposed in the high temperature range and H_TwoS
In contrast, the SO of Example 1_x With absorbent material,
SO _x Begins to decompose at temperatures as low as 450 ° C, around 560 ° C
Has the highest decomposition rate. That is, SO of Example 1
x The absorbent material must be renewable at a low temperature
It is clear. The SO of Comparative Example 1_x Peak at absorber
The area is small, SO _x Because the absorption of
SO_x It can be seen that the absorption capacity is insufficient.

Although the SO _x absorbents of Example 1 and Comparative Example 2 similarly contain La and Pt, Example 1 has a lower H ₂ S generation temperature than Comparative Example 2. Low. This is due to the fact that LaAlO ₃ does not exist in the SO _x absorbent of Example 1 and LaAlO ₃ exists in the SO _x absorbent of Comparative Example 2.

Next, the catalyst for Comparative Example 4 and the catalyst of Example 2 was measured _the NO _x storage amount after the durability test.

In the durability test, each catalyst was placed in an evaluation device, and the model gas shown in Table 1 was alternately flowed for 30 seconds each for rich gas and lean gas. Catalyst bed temperature is 600
° C, and the flow rate was adjusted so that the total amount of S was 2.25 in molar ratio to the amount of supported potassium.

After the endurance test, each catalyst was placed in the evaluation device, and a cycle shown in Table 3 in which a lean model gas was flowed for 10 minutes, then a rich spike model gas was flowed for 3 seconds, and then a rich model gas was flowed for 6 minutes was repeated. Meanwhile, the amount of NO _x stored when a lean model gas was flowed after the rich spike was measured. Space velocity is SV =
180,000 and the temperature of the gas containing the catalyst is 250 ℃, 300 ℃, 400 ℃
The measurement was performed at five levels of ℃, 500 ℃ and 600 ℃. Fig. 3 shows the results.
Shown in

[0056]

[Table 3]

[0057] From FIG. 3, the catalyst of Example 2 showed high _the NO _x storage amount after the durability test compared to the catalyst of Comparative Example 4, NO _x
It can be seen that sulfur poisoning of the storage material is suppressed. It is clear that this is the effect of supporting the NO _x storage material on the SO _x absorption material of Example 1.

[0058]

According to the SO _x absorbent of the present invention,
The absorption amount of SO _x increases as compared with the conventional case. Since the regeneration treatment at a low temperature of 600 ° C. or less is possible, the regeneration in the exhaust gas becomes possible. Therefore, the exhaust gas purifying catalyst can be used in combination with various exhaust gas purifying catalysts, and by suppressing the sulfur poisoning of the exhaust gas purifying catalyst, the purification rate after durability is remarkably improved.

[Brief description of the drawings]

FIG. 1 is a graph showing the pore size distribution of La-Al ₂ O ₃ used in Example 1 and γ-Al ₂ O ₃ used in Comparative Example 1.

FIG. 2 is a graph showing the relationship between the mass spectrum intensity of H ₂ S generated by decomposition of SO _x adsorbed on the SO _x absorbents of Examples and Comparative Examples and temperature.

FIG. 3 is a graph showing the NO _x storage amount after rich spike of the catalysts of Example 2 and Comparative Example 4 at each temperature.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/24 F01N 3/28 301C 3/28 301 301P F02D 41/04 305A F02D 41/04 305 B01D 53 / 36 104A (72) Inventor Akihiko Suda 41st, Chukumi Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside Toyota Central Research Institute, Inc. 3G091 AA12 AB02 AB05 AB06 AB08 BA11 BA14 BA15 BA20 BA32 BA39 CB02 DA01 DA02 DB10 FB02 FB10 FB11 FB12 FC02 FC07 GA01 GA06 GA16 GB01W GB01X GB01Y GB02Y GB03Y GB04 GB05 GBY GB05 GBY GB09X GB10X GB10Y GB16X GB17X HA07 HA18 HA20 3G301 HA15 JA25 MA01 NE13 NE14 4D048 AA02 AA06 AA18 AB02 AB03 AB07 BA03X BA14X BA15Y BA18X BA30X BA31Y BA33Y BA42X 4G066 AA12B AA13B AA16B AA20B AA53A AB07A AB23A BA24 BA26 BA32 BA36 CA23 CA28 BC02 BC02 BC02A01 BC03A01 BC CA08 CA12 CA13 CA15 DA06 EA02Y EB11 EC03X EC03Y FA02 FB09 FB14

Claims (8)

[Claims] 1. An SO _x absorbent comprising a composite oxide comprising a rare earth element M and an aluminum oxide, wherein a molar ratio M /
An SO _x absorbent, wherein Al is 0.01 to 0.5, M is uniformly present in a highly dispersed state in the aluminum oxide, and the porous material is substantially free of aluminate of M. 2. The composite oxide has a specific surface area of 100 to 300.
SO _x absorbing material according to claim 1, characterized in that the m ² / g. 3. The composite oxide has mesopores, and at least a part of the mesopores communicates in a three-dimensional network to form a communication path. And the SO _x absorbent according to claim 2. 4. The SO _x absorbent according to claim 1, wherein said M is La. 5. The SO _x absorbent according to claim 1, wherein the SO _x absorbent contains at least one noble metal selected from Pt, Rh, Pd and Ir. 6. The method according to claim 1, wherein
An exhaust gas purifying catalyst, characterized in that an SO _x absorbent carries at least one NO _x occluding material selected from an alkali metal, an alkaline earth metal and a rare earth element. 7. A method according to claim 1, wherein
An exhaust gas purifying catalyst comprising: a SO _x absorbent; and at least one catalyst selected from a NO _x storage reduction catalyst and an HC oxidation catalyst. 8. The method according to claim 1, wherein
An exhaust gas purifying catalyst composed of an SO _x absorbent and a NO _x storage-reduction catalyst is operated at an air-fuel ratio (A / F) of 15 or more and is intermittently set to a fuel stoichiometric-rich atmosphere from a lean burn engine. And contained in the exhaust gas
The NO _x occluded in the NO _x storage-and-reduction type catalyst in fuel-lean atmosphere, SO _x absorption of the SO _x absorbent with fuel stoichiometric-rich atmosphere to reduce the released NO _x from the NO _x storage-and-reduction type catalyst An exhaust gas purification method characterized by regenerating the function.