JP2000246107A - Catalyst for cleaning exhaust gas, its production and method for cleaning exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit the sulfur poisoning of an NOx occlusion material and to enhance durability. SOLUTION: This catalyst for cleaning exhaust gas has a support containing at least titania particles and another porous oxide. The titania particles in the support are ultrafine particles having <50 nm particle diameter. Since the ultrafine particulate titania particles are used, interfaces with the another porous oxide are extremely increased, and since SOx is hardly adsorbed on the porous oxide such as alumina at the interfaces, the sulfur poisoning of an NOx occlusion material present on the interfaces is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the 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), NO _x TECHNICAL FIELD The present invention relates to a catalyst capable of efficiently purifying exhaust gas, a production method thereof, and 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 material that releases occluded NO _x at stoichiometric ~ rich atmosphere NO
_x Oxidation reduction type exhaust gas purifying catalysts have been developed.

For example, Japanese Patent Application Laid-Open No. 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 alumina. 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 alumina has been proposed. Further, Japanese Patent Application Laid-Open No. H5-168860 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 alumina.

[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 material 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. The HC and CO in the exhaust gas, since it is consumed in the reduction of the NO _x while being oxidized by the noble metal, HC and
CO is also purified efficiently.

[0005] However in the exhaust gas, contains SO _x to sulfur contained in the fuel (S) is generated by the combustion, it becomes that it SO ₃ is oxidized by the noble metal in the exhaust gas of a lean atmosphere. And it will be readily sulfate by water vapor also contained in the exhaust gas, these sulfites and sulfates are produced by the reaction with _the NO _x storage material, thereby _the NO _x storage material it would degrade poisoned became. The porous oxide support such as alumina from the the property that easily adsorbs SO _x, there is a problem that the sulfur poisoning is facilitated.

[0006] When thus _the NO _x storage material 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. Moreover, since titania does not adsorb SO _x , an experiment was conducted with the supposition of using a titania carrier. As a result, SO _x flows downstream as it is not adsorbed on titania, only SO _x in direct contact with the noble metal is revealed that since only the degree of poisoning is small is oxidized. However, it has also been found that the titania carrier has a problem that the initial activity is low and the NO _x purification performance after durability remains low.

Therefore, the applicant of the present application has proposed in Japanese Patent Application Laid-Open No. Hei 8-099034 to use a composite carrier composed of TiO ₂ —Al ₂ O ₃ . By using a carrier in which alumina and titania are mixed or a composite oxide is used, Al
The advantages of ₂ O ₃ increase the initial NO _x purification rate. Also TiO
₂ is less likely to adsorb SO _x than Al ₂ O ₃ , and the adsorbed SO _x is easier to desorb at lower temperatures than when it is occluded by the NO _x storage material, thus preventing sulfur poisoning. . Therefore, when the above composite carrier is used, the adsorption of SO _x is prevented and the NO _x purification rate after endurance is improved while securing a high initial NO _x purification rate.

[0008]

However, the above-mentioned Japanese Patent Application Laid-Open
Also in the exhaust gas purifying catalyst using the carrier of a mixture of alumina and titania, as disclosed in 8-099034 JP, NO _x purifying Considering the after endurance strengthening the current and emission control in recent years air pollution capacity is insufficient, early development of an exhaust gas purifying catalyst exhibiting high _the NO _x purification performance from the initial to after the durability is desired.

The present invention has been made in view of such circumstances, and an object of the present invention is to further suppress the sulfur poisoning of the NO _x occluding material and further improve the durability.

[0010]

The exhaust gas purifying catalyst of the present invention which solves the above-mentioned problems is characterized by a carrier made of a porous oxide, a noble metal carried on the carrier, an alkali metal carried on the carrier, and an alkali metal. at least one of the NO _x storage material selected from alkaline earth metals and rare earth elements, a more becomes NO _x storage-and-reduction type exhaust gas purifying catalyst, the support comprises at least titania particles and other porous oxide And the titania particles are ultrafine particles.

The method of the present invention for producing an exhaust gas purifying catalyst is characterized in that the catalyst comprises a porous oxide carrier, a noble metal supported on the carrier, and an alkali metal, an alkaline earth metal and a rare earth element supported on the carrier. At least one selected
And _the NO _x storage material, a more becomes NO _x production method of storage-reduction type exhaust gas purifying catalyst, slurry the finely divided titania powder were mixed with the porous oxide and water in the presence of a surfactant And forming a carrier from the slurry.

The characteristics of the exhaust gas purifying method of the present invention are as follows.
A carrier comprising a porous oxide, a noble metal supported on a carrier, an alkali metal supported on a carrier, more be at least one of the NO _x storage material selected from alkaline earth metals and rare earth elements, at least the carrier A NO _x storage-reduction type exhaust gas purifying catalyst containing ultrafine titania particles and other porous oxides is operated at an air-fuel ratio (A / F) of 18 or more and intermittently switches to a fuel stoichiometric to rich atmosphere. is contacted with the exhaust gas from lean-burn engines, the NO _x contained in the exhaust gas is occluded in _the NO _x storage material in the fuel lean atmosphere, reducing the NO _x released from _the NO _x storage material in the fuel stoichiometric-rich atmosphere Is to do.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In the exhaust gas purifying catalyst of the present invention,
The carrier contains ultrafine titania particles and other porous oxides. By using the carrier having such a configuration, the sulfur poisoning of the NO _x storage material carried can be effectively suppressed, and a high NO _x purification ability is exhibited even after durability. The reason for this is not clear, but by using ultrafine titania particles, the number of interfaces with other porous oxides becomes extremely large, and SO _x is adsorbed on other porous oxides such as alumina at the interface. Because it is difficult to
It is considered that sulfur poisoning of the NO _x storage material present at the interface is prevented.

The particle size of the ultrafine titania particles is 50 nm.
Is preferably less than 20 nm, and more preferably less than 20 nm. When the particle diameter is more than 50 nm, NO _x storage material is likely to be sulfur poisoning, NO _x purifying ability after durability is lowered. As the porous oxide of the fine titania particles, alumina, silica, zirconia, titania, silica-alumina and the like can be used. Among them, γ-alumina having high activity and excellent heat resistance is particularly desirable. The particle size of the porous oxide is not particularly limited.

The mixing ratio of the particulate titania particles and the other porous oxide can be appropriately designed according to the type of the porous oxide while maintaining a balance between the purification performance and the sulfur poisoning resistance. . For example, when the other porous oxide is alumina, the molar ratio is preferably in the range of Al ₂ O ₃ / TiO ₂ = 4/1 to 1/3. Within this range, both purification performance and sulfur poisoning resistance can be achieved. If the amount of alumina is less than this, the purification performance is low and sintering of the noble metal is likely to occur. If the amount of titania is less than this, the sulfur poisoning resistance is reduced.

Further, the carrier preferably contains ceria. Purification performance is further improved by the oxygen storage / release capability of ceria. The use of ceria stabilized with zirconia (ceria-zirconia composite oxide) further improves the durability. Noble metals include 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.

[0017] In addition, as _the NO _x storage material, alkali metal,
At least one selected from alkaline earth metals and rare earth elements can be used. Above all, alkalinity is high
It is preferable to use at least one of an alkali metal and an alkaline earth metal having high NOx storage capacity. Examples of the alkali metal include lithium, sodium, potassium, rubidium, cesium, and francium. 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.

The loading amount of the NO _x occluding material is desirably in the range of 0.05 to 1.0 mol per liter of the carrier. Loading amount
If the amount is less than 0.05 mol, the NO _x storage capacity is small and the NO _x purification performance is reduced. Even if the amount exceeds 1.0 mol, the effect is saturated and a problem occurs due to a decrease in the amount of other components. Now, in order to produce the carrier used in the exhaust gas purifying catalyst of the present invention described above, it is only necessary to dry-mix a powder composed of fine titania particles and another porous oxide powder, It is desirable to form a carrier from a slurry formed by mixing the titania powder of Example 1 with a porous oxide and water in the presence of a surfactant. Since the aggregation of the particulate titania powder is suppressed by the presence of the surfactant, the titania powder is mixed with the porous oxide powder in a state of primary particles, so that the number of interfaces can be further increased.

A surfactant may be added to the dispersion in which the two powders are mixed, or an ultrafine titania powder may be mixed in a dispersion of another porous oxide powder containing the surfactant. It is preferable to mix another porous oxide powder with a dispersion liquid of ultrafine titania powder which has been highly dispersed in advance with a surfactant. As a result, a slurry in which almost all of the ultrafine titania powder is highly dispersed in the form of primary particles is obtained, and a carrier having many interfaces can be formed.

Examples of the surfactant include anionic, cationic and nonionic surfactants, metal soaps such as sodium stearate, and polymer surfactants such as polyvinyl alcohol, polyvinylpyrrolidone, polyacrylamide and polyacrylic acid. Agents and the like can be used. The addition amount is at least the amount in which the ultrafine titania powder is dispersed, and is not less than the critical micelle concentration.

In order to form a catalyst from the slurry obtained as described above, a slurry is coated on a honeycomb-shaped carrier substrate, dried and fired to form a carrier layer, and a noble metal and NO _{The x-} occluding material may be supported by a standard method. Further, for example, by cutting after extrusion of the slurry was formed into pellets, it may be dried and calcined by supporting the noble metal and _the NO _x storage material after producing the catalyst pellets. Further, when preparing the slurry, a noble metal-supported powder in which a noble metal is previously supported on a part or all of another porous oxide powder may be used.

In the exhaust gas purifying 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, at the interface between the titania particles and the other porous oxide powder,
Since the adsorption of SO _x is suppressed and the titania particles are in the form of fine particles, the number of interfaces is extremely large. Therefore, adsorption of SO _{x on} the surface of another porous oxide can be extremely suppressed, and sulfur poisoning of the NO _x storage material by the adsorbed SO _x can be effectively suppressed. Thereby, the durability is remarkably improved, and a high NO _x purification ability can be maintained for a long period of time.

[0024]

The present invention will be specifically described below with reference to examples and comparative examples. (Example 1) Ultrafine TiO ₂ powder having an average particle diameter of 20 nm,
Γ-Al ₂ O ₃ powder having a particle size of 300 to 400 nm was mixed at a weight ratio of 1: 1 and milled in a ball mill for 24 hours to be sufficiently mixed. 40 g of this mixed powder was dispersed in 200 g of water, and 17.03 g of barium acetate was added and dissolved by stirring well, then concentrated and dried, and calcined at 550 ° C. for 2 hours.

Next, ammonium bicarbonate (NH_FourHCO_Three)
 4.3 g in a solution of 300 g of water
The whole amount of the Ba acetate-supported powder was mixed and stirred for 15 minutes, followed by suction
It was filtered and dried to obtain Ba carbonate-supported powder. This Ba carbonate support
Disperse the entire amount of powder in 300 g of water,
Predetermined amount of aqueous solution of nitrodiammine platinum complex (3.
42 × 10^-3Mol), stirred for 30 minutes, filtered and
And bake at 450 ° C for 2 hours to carry Pt
Was. The supported amount of Pt was 8.54 × 10 ^-FiveMole
And the supported amount of Ba is 1.67 × 10^-3Mo
It is.

The catalyst powder obtained has a particle size of 1 by a conventional method.
It was a pellet catalyst of ３3 mm, which was used in the tests described below. (Comparative Example 1) The pellet catalyst of Comparative Example 1 was prepared in the same manner as in Example 1 except that the fine particle TiO ₂ powder having an average particle diameter of 50 nm was used instead of the ultrafine TiO ₂ powder having an average particle diameter of 20 nm. Was prepared.

<Test Example 1> The pellets of Example 1 and Comparative Example 1
Each catalyst was placed in a laboratory reactor and shown in Table 1.
A model exhaust gas with a gas space velocity of 100,000h^-1Condition
Introduced in. Rich in catalyst bed temperature range of 250 to 450 ° C
Switching gas from gas steady state to lean gas steady state
NO of exhaust gas_xUntil the concentration becomes steady,
NO occluded by the medium_xAmount (NO_x(Saturated occlusion amount) was measured. Ma
Spike rich gas for 10 seconds from steady state
After switching to lean gas again
NO _xStorage amount (NO after rich spike)_xOcclusion amount)
Was. The results are shown in FIGS. 1 and 2, respectively.

[0028]

[Table 1] Further, the pellet catalysts of Example 1 and Comparative Example 1 were respectively disposed in a laboratory reactor, and a model exhaust gas having a composition shown in Table 2 was subjected to a catalyst bed temperature of 600 ° C. and a gas space velocity of 100,000 h ⁻¹ ,
A cycle of lean gas 55 seconds-rich gas 5 seconds was repeatedly introduced for 4 hours, and each was subjected to a sulfur poisoning endurance test. And for each of the catalyst after sulfur poisoning durability test, in the same manner as described above to measure the NO _x saturation occlusion amount and the rich spike after _the NO _x storage amount, and the results are shown in Figures 3 and 4.

[0029]

[Table 2] As can be seen from FIGS. 1-4, the initial NO of the catalyst of Example 1 was
_{The x} storage capacity is equivalent to that of Comparative Example 1, but the NO _x saturated storage amount after the sulfur poisoning durability test is about twice that of Comparative Example 1, and the NO _x storage amount after the rich spike is about 1.2 times. Also, from the comparison between FIGS. 1 and 3 and the comparison between FIG. 2 and FIG.
The degree of decrease in the NO _x storage amount is smaller for the catalyst of Example 1, and the catalyst of Example 1 is superior in durability to the catalyst of Comparative Example 1. It is clear that this is the effect of using the ultrafine TiO ₂ powder having an average particle diameter of 20 nm in Example 1. In the case of using the fine TiO ₂ powder having an average particle diameter of 50 nm as in Comparative Example 1, Means that the effect of suppressing sulfur poisoning is small. That is, it is clear that the particle diameter of the ultrafine TiO ₂ powder is desirably less than 50 nm.

Example 2 A predetermined amount of ZrO ₂ powder was put into a rhodium nitrate aqueous solution containing a predetermined amount of Rh, and after stirring, evaporated and dried to carry Rh. Rh was loaded at 0.42% by weight. This Rh / ZrO ₂ powder and ultrafine particles Ti having an average particle diameter of 20 nm
O ₂ powder and γ-Al ₂ O ₃ powder were mixed. The mixing ratio (weight ratio) is TiO ₂ : Al ₂ O ₃ = 1: 1, and the Rh / ZrO ₂ powder is TiO ₂
The amount was 1/20 of the total weight of Al ₂ O ₃ . Furthermore, CeO ₂ −Zr
The O ₂ composite oxide powder was added to 1/10 of the total weight of TiO ₂ and Al ₂ O ₃ and mixed well.

The obtained mixed powder was slurried with water and coated on a ceramic monolith carrier substrate having a capacity of 1.3 L. The coating amount is 270 g per liter of the monolith carrier substrate. After drying at 250 ° C. for 15 minutes, a predetermined concentration of barium acetate aqueous solution is absorbed, and dried at 250 ° C. for 15 minutes, and then 500 ° C.
For 30 minutes. This was immersed in an aqueous solution of ammonium bicarbonate having a concentration of 15 g / L for 15 minutes, and dried at 250 ° C. for 15 minutes to carry Ba. The amount of Ba supported is per liter of the monolithic carrier substrate.
0.2 mol.

Further, a nitric acid solution of a dinitrodiammineplatinum complex having a predetermined concentration is absorbed by the carrier on which Ba is supported.
Drying and baking at 00 ° C. for 15 minutes carried Pt. The supported amount of Pt is 2.0 g per liter of the monolithic carrier substrate. Further, an aqueous solution containing potassium nitrate and lithium nitrate at a predetermined concentration was absorbed, dried at 250 ° C., and baked at 500 ° C. for 30 minutes to carry K and Li. The loading amounts of K and Li are each 0.1 mol per 1 L of the monolithic carrier substrate.

(Comparative Example 2) Ultrafine particles having an average particle diameter of 20 nm
Instead of TiO ₂ powder, except that the average particle diameter was used fine TiO ₂ powder 50nm in the same manner as in Example 2, Comparative Example 2
Was prepared. The catalyst of Comparative Example 2 <Test Example 2> Example 2, mounted in an exhaust system of a lean burn engine of 1.8L, under the same conditions as in Test Example 1, the initial of the NO _x saturation occlusion amount and the rich spike after NO _x
The amount of occlusion was measured. The results are shown in FIGS.

Further, the sulfur concentration is adjusted so that the sulfur concentration becomes 500 ppm.
Simulates urban driving using fuel with yellow additive
An accelerated endurance test for 50 hours was performed with the pattern. After endurance test
NO _xNO after saturated storage and rich spike_xSame amount of storage
7 and FIG. 8 show the results. 5-8
Thus, the catalyst of Example 2 was compared to the catalyst of Comparative Example 2.
Initial and endurance NO_xLarge storage capacity, especially after endurance_x
The storage amount of the catalyst of Example 2 is much higher and the durability is excellent.
ing. This is because in Example 2, the average particle diameter was more than 20 nm.
Fine particle TiO_TwoIt is clear that this is the effect of using powder.
Fine particles having an average particle diameter of 50 nm as in Comparative Example 2.
Child TiO_TwoIt means that powder has little effect on sulfur poisoning.
ing.

<Test Example 3> Ultrafine particles Ti having an average particle diameter of 20 nm
And O ₂ powder, an electron micrograph of the fine TiO ₂ powder having an average particle diameter of 50nm shown in FIGS. Furthermore, the average particle size is 20
nm ultrafine TiO ₂ powder and γ-Al ₂ O ₃ powder in a weight ratio of 1: 1
Fig. 11 shows an electron micrograph of the mixed powder obtained by milling with a ball mill for 24 hours.
FIG. 12 shows electron micrographs of the mixed powder obtained by mixing TiO ₂ powder and γ-Al ₂ O ₃ powder at a weight ratio of 1: 1 and milling the mixture by a ball mill for 24 hours.

9 to 12, it can be seen that the TiO ₂ powder is in a state of adhering to the surface of the Al ₂ O ₃ particles in the mixed powder, and FIGS. 13 and 14 show the adhering state in FIGS. 11 and 12, respectively.
Is determined. That is, the average particle diameter
20 nm ultra-fine TiO ₂ powder is 50 nm average particle diameter TiO ₂
It is clear that it is in a highly dispersed state as compared to powder, and the interface between ultrafine TiO ₂ and Al ₂ O ₃ with an average particle diameter of 20 nm is
It is more than the interface between the fine particles of TiO ₂ and Al ₂ O ₃ having an average particle diameter of 50 nm, which is considered to have contributed to the improvement of the NO _x storage ability described above.

(Example 3) When the primary particle diameter is 300 to 500 mm
After preparing TiO ₂ powder and treating the surface with stearic acid, a polyether-modified silicone oil as a surfactant was mixed at a predetermined ratio, and the mixture was thoroughly stirred. On the other hand, a predetermined amount of ZrO ₂ is contained in an aqueous rhodium nitrate solution containing a predetermined amount of Rh.
The powder was charged, and after stirring, evaporated and dried to carry Rh. Rh
Was carried by 0.5% by weight. Also, γ-Al ₂ O ₃ powder and CeO ₂ −
A ZrO ₂ composite oxide powder was prepared.

These powders were mixed at a predetermined ratio, and water was added to form a slurry. The composition in the slurry is Ti by weight.
O ₂ : Al ₂ O ₃ = 1: 1, Rh / ZrO ₂ powder is ４ of the total weight of TiO ₂ and Al ₂ O ₃ , CeO ₂ -ZrO ₂ composite oxide powder is TiO ₂
It is 1/10 of the total weight of Al ₂ O ₃ . Using this slurry, a monolithic carrier substrate was prepared in the same manner as in Example 2.

Using this monolithic carrier substrate, Ba, Pt, K and Li were carried in the same manner as in Example 2. The amount of each carried is the same as in Example 2. (Example 4) primary particle diameter instead of the TiO ₂ powder 300 to 500 Å, the surface primary particle diameter using a TiO ₂ powder 100 to 300 Å was treated stearate, polyether-modified silicone oil as a surfactant Was added to a predetermined amount of water and stirred. And the same Rh / ZrO ₂ powder as in Example 3,
The γ-Al ₂ O ₃ powder and the CeO ₂ -ZrO ₂ composite oxide powder were further mixed to prepare a slurry having the same composition as in Example 3. Then, a monolith carrier substrate was coated in the same manner as in Example 3, and a monolith catalyst was prepared in the same manner.

Example 5 A monolith catalyst of this example was prepared in the same manner as in Example 3 except that no surfactant was used. Example 6 A monolith catalyst of this example was prepared in the same manner as in Example 4 except that no surfactant was used.

(Comparative Example 3) A primary particle diameter of 300 to 500 mm
Instead of the TiO ₂ powder, a primary particle diameter except for using TiO ₂ powder 50nm in the same manner as in Example 3, was prepared monolithic catalyst of this comparative example. <Test Example 4> Each monolith catalyst was attached to the exhaust system of a 1.8 L lean burn engine. A 50-hour accelerated durability test was performed in a pattern simulating running. Then, using the same engine, after the rich spike _the NO _x storage amount were measured under the same conditions as in Test Example 1. The rich spike was measured at two levels, 0.5 seconds and 1 second.
℃ and 400 ℃. The catalyst after the durability test was subjected to destructive analysis, and the sulfur poisoning amount was measured. Figure the result
15-17.

[0042] than 15-17, less than each of the examples is _the NO _x storage amount after the rich spike is the catalyst of Comparative Example 3, which revealed to be due to sulfur poisoning amount is larger than each of the embodiments It is. And in each embodiment, NO _x occlusion amount after the durability test compared to Comparative Example 3 is much, NO _x occlusion amount after the durability test as the primary particle diameter of the TiO ₂ is small is increased. When compared to Examples 3 and 4 and Examples 5, 6, and decreases the _the NO _x storage amount towards the Examples 5 and 6, are increasingly also sulfur poisoning amount. This difference is caused by the presence or absence of the surfactant, and it is clear that the effect is obtained by further improving the dispersibility of TiO ₂ by using the surfactant.

[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, stably high _the NO _x purification performance from the initial to after the durability test was obtained, the durability is remarkably improved. Further, according to the method for manufacturing an exhaust gas purifying catalyst of the present invention, an exhaust gas purifying catalyst having improved durability can be stably and easily manufactured.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a temperature and an initial NO _x saturation storage amount.

2 is a graph showing the relationship between the temperature and the initial rich spike after _the NO _x storage amount.

FIG. 3 is a graph showing a relationship between a temperature and a NO _x saturation storage amount after a sulfur poisoning durability test.

FIG. 4. Temperature and after rich spike after sulfur poisoning endurance test
4 is a graph showing a relationship with an NO _x storage amount.

FIG. 5 is a graph showing a relationship between a temperature and an initial NO _x saturation storage amount.

6 is a graph showing the relationship between the temperature and the initial rich spike after _the NO _x storage amount.

FIG. 7 is a graph showing the relationship between the temperature and the NO _x saturation storage amount after the sulfur poisoning durability test.

FIG. 8 After temperature and after rich spike after sulfur poisoning endurance test
4 is a graph showing a relationship with an NO _x storage amount.

FIG. 9 is an electron micrograph showing the particle structure of ultrafine TiO ₂ powder having an average particle diameter of 20 nm.

FIG. 10 is an electron micrograph showing the particle structure of fine TiO ₂ powder having an average particle diameter of 50 nm.

FIG. 11 Ultrafine TiO ₂ powder with an average particle diameter of 20 nm and γ-Al ₂ O ₃
5 is an electron micrograph showing the particle structure of a powder mixture with a powder.

FIG. 12 is an electron micrograph showing a particle structure of a mixed powder of fine TiO ₂ powder having an average particle diameter of 50 nm and γ-Al ₂ O ₃ powder.

FIG. 13 Ultrafine TiO ₂ powder with an average particle diameter of 20 nm and γ-Al ₂ O ₃
It is explanatory drawing which shows the particle structure of the mixed powder with powder.

FIG. 14 is an explanatory diagram showing a particle structure of a mixed powder of a fine particle TiO ₂ powder having an average particle diameter of 50 nm and a γ-Al ₂ O ₃ powder.

FIG. 15 is a graph showing the NO _x storage amount after a 0.5-second rich spike.

FIG. 16 is a graph showing the NO _x storage amount after a one-second rich spike.

FIG. 17 is a graph showing the amount of sulfur poisoning.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Ichiro Hachisuka 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Yasuo Ikeda 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation ( 72) Inventor Hiroshi Hirayama 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Co., Ltd. (72) Inventor Kiyotaka Hayashi 7800 Chihama, Oto-cho, Ogasa-gun, Shizuoka Prefecture Cataler Co., Ltd. 7800 Chihama, Oto-cho, Ogasa-gun F-term in Cataler Co., Ltd. (reference) BC75B CA02 CA13 EA01Y EA02Y EA19 EB18X ED07 FA02 FB30

Claims (5)

[Claims] 1. A carrier comprising a porous oxide, a noble metal carried on the carrier, an alkali metal carried on the carrier,
At least one of the NO _x storage material selected from alkaline earth metals and rare earth elements, a more becomes NO _x storage-and-reduction type exhaust gas purifying catalyst, the carrier least titania particles and other porous oxides Wherein the titania particles are ultrafine particles. 2. The exhaust gas purifying catalyst according to claim 1, wherein the titania particles have a particle size of less than 50 nm. 3. The exhaust gas purifying catalyst according to claim 1, wherein the titania particles have a particle size of less than 20 nm. 4. A carrier comprising a porous oxide, a noble metal carried on the carrier, an alkali metal carried on the carrier,
By weight of at least one NO and _x storage material, become more NO _x production method of storage-reduction type exhaust gas purifying catalyst selected from alkaline earth metals and rare earth elements, the finely divided titania powder detergent A method for producing an exhaust gas purifying catalyst, comprising: forming a slurry by mixing with a porous oxide and water in the presence thereof; and forming the carrier from the slurry. 5. A carrier comprising a porous oxide, a noble metal carried on the carrier, an alkali metal carried on the carrier,
Becomes more and at least one NO _x storage material selected from alkaline earth metals and rare earth elements, _the NO _x storage reduction type exhaust gas to the carrier comprising a porous oxide of otherwise at least finely divided titania particles The purification catalyst is used at the air-fuel ratio (A
/ F) was is operated at 18 or higher in contact with the exhaust gas from a lean burn engine which is intermittently fuel stoichiometric-rich atmosphere, occluding NO _x contained in the exhaust gas to the _the NO _x storage material in the fuel lean atmosphere exhaust gas purification method, characterized in that, and reducing the NO _x released from the _the NO _x storage material in the fuel stoichiometric-rich atmosphere.