JP2000202243A - Method for purifying exhaust gas of internal combustion engine, purification catalyst and apparatus for purifying exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the SOx resistance and NOx removing performance of an NOx adsorption reduction type catalyst. SOLUTION: When a catalyst which contains at least one selected from alkali metals and alkaline earth metals, Rh and Pt, chemically adsorbs NOx in a higher air-fuel ratio than a theoretical air-fuel ratio and reduces and removes the chemically adsorbed NOx in the theoretical air-fuel ratio or below is disposed in the exhaust gas passage of an internal combustion engine, Zr is incorporated into the catalyst and at least one selected from Pd, Ir and Ru is further incorporated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying exhaust gas from an internal combustion engine of an automobile or the like, an exhaust gas purifying apparatus and an exhaust gas purifying catalyst, and more particularly to a lean fuel combustion.
TECHNICAL FIELD The present invention relates to an internal combustion engine capable of exhaustion, a method for purifying exhaust gas emitted from an automobile equipped with the internal combustion engine, an exhaust gas purification device, and an exhaust gas purification catalyst.

[0002]

2. Description of the Related Art An exhaust gas purifying catalyst is disposed in an exhaust gas passage of an internal combustion engine, and an exhaust gas having an air-fuel ratio higher than a stoichiometric air-fuel ratio (hereinafter referred to as an oxidizing atmosphere) and an exhaust gas having a stoichiometric air-fuel ratio or less (hereinafter referred to as a reducing atmosphere). JP-A-10-212933 discloses a method for purifying nitrogen oxides in exhaust gas by alternately contacting exhaust gas with a fuel ratio.
No., published in Japanese Unexamined Patent Publication No. This publication describes that as an exhaust gas purifying catalyst, a function of chemically adsorbing NOx in so-called lean exhaust gas having an air-fuel ratio higher than the stoichiometric air-fuel ratio, and a function of adsorbing NO
It is disclosed that an adsorption reduction catalyst having a function of reducing and purifying x is used.

Japanese Patent Application Laid-Open No. 9-327617 discloses a catalyst containing an alkaline earth metal and titanium and containing titanium in an amorphous form. JP-A-10-1009032 discloses a catalyst having an alkaline earth metal and titania, and containing a part of the alkaline earth metal and titania in the form of a composite oxide. According to the study of the present inventors, these catalysts correspond to NOx adsorption reduction catalysts. Further, these catalysts can maintain high NOx purification performance while suppressing SOx poisoning, in which SOx contained in exhaust gas is captured by alkaline earth metals.

[0004]

In the NOx adsorption reduction catalyst described in the above prior art, SOx conversion to alkaline earth metal
The amount of capture increases with time. SOx poisoning easily proceeds in an oxidizing atmosphere. Therefore, if the operation in the oxidizing atmosphere is continued for a long time, the NOx purification performance is significantly deteriorated.

[0005] In view of the above-mentioned problems of the prior art, it has been studied to remove SOx trapped in a catalyst component in a reducing atmosphere.

[0006] It is an object of the present invention to provide a method in which S
An object of the present invention is to provide a NOx adsorption-reduction type exhaust gas purifying catalyst, an exhaust gas purifying method, and an exhaust gas purifying apparatus that can remove Ox by changing the atmosphere of the exhaust gas to a reducing atmosphere.

[0007]

Means for Solving the Problems The present inventors have arranged a NOx adsorption reduction catalyst for chemically adsorbing NOx in an oxidizing atmosphere and reducing and purifying the chemically adsorbed NOx in a reducing atmosphere in an exhaust gas passage of an internal combustion engine. In an exhaust gas purification method for purifying nitrogen oxides in exhaust gas by alternately repeating operation in an oxidizing atmosphere and a reducing atmosphere, an excellent SOx resistance
A catalyst having high NOx purification performance while maintaining poisoning was studied.

As a result, a NOx adsorption-reduction type catalyst containing at least one of an alkali metal and an alkaline earth metal, Rh and Pt, containing zirconium (Zr), has excellent resistance to SOx poisoning and high poisoning. It has been found that NOx purification performance can be provided. In addition, Pd
It has been found that this effect can be further enhanced by containing at least one selected from Ir and Ru.

The present invention provides an exhaust gas purifying method described below,
The present invention relates to an exhaust gas purification device and an exhaust gas purification catalyst.

(1) At least one selected from alkali metals and alkaline earth metals and R
h and Pt, a NOx adsorption reduction catalyst is provided for chemically adsorbing NOx when the air-fuel ratio in the exhaust gas is higher than the stoichiometric air-fuel ratio and for reducing and purifying the chemically adsorbed NOx when the air-fuel ratio is lower than the stoichiometric air-fuel ratio. An exhaust gas purification method in which exhaust gas having an air-fuel ratio higher than the stoichiometric air-fuel ratio and exhaust gas having an air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio are alternately brought into contact with the catalyst, wherein Zr is contained in the catalyst. A method for purifying exhaust gas of an internal combustion engine (claim 1).

(2) In the exhaust gas passage of the internal combustion engine, at least one kind selected from alkali metals and alkaline earth metals and R
h and Pt, a NOx adsorption reduction catalyst is provided for chemically adsorbing NOx when the air-fuel ratio in the exhaust gas is higher than the stoichiometric air-fuel ratio and for reducing and purifying the chemically adsorbed NOx when the air-fuel ratio is lower than the stoichiometric air-fuel ratio. An exhaust gas purification method in which exhaust gas having an air-fuel ratio higher than the stoichiometric air-fuel ratio and exhaust gas having an air-fuel ratio lower than the stoichiometric air-fuel ratio are alternately brought into contact with the catalyst, wherein Zr, Pd, Ir, and Ru are contained in the catalyst. A method for purifying exhaust gas of an internal combustion engine comprising at least one selected from the group consisting of:

(3) The method for purifying exhaust gas of an internal combustion engine according to claim 1 or 2, wherein the catalyst further contains at least one of Ti and Si.

(4) The method according to claim 3, wherein:
An exhaust gas purifying method for an internal combustion engine, comprising a composite oxide of at least one selected from an alkali metal and an alkaline earth metal and at least one selected from Zr, Ti and Si. ).

(5) The method for purifying exhaust gas of an internal combustion engine according to claim 3, wherein the catalyst further contains a rare earth metal.

(6) NOx is chemically adsorbed in the exhaust gas passage of the internal combustion engine when the air-fuel ratio in the exhaust gas is higher than the stoichiometric air-fuel ratio, and when the air-fuel ratio is lower than the stoichiometric air-fuel ratio, the chemically adsorbed NOx is reduced and purified. An exhaust gas purification method in which an adsorption-reduction catalyst is disposed, and the exhaust gas having an air-fuel ratio higher than the stoichiometric air-fuel ratio and the exhaust gas having an air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio are alternately brought into contact with the catalyst. S on the surface of the porous carrier
A method for purifying exhaust gas of an internal combustion engine, characterized by comprising r, Mg, Ti, Zr, Rh, Pt, Pd and Ce.

(7) NOx is chemically adsorbed in the exhaust gas passage of the internal combustion engine when the air-fuel ratio in the exhaust gas is higher than the stoichiometric air-fuel ratio, and when the air-fuel ratio is equal to or lower than the stoichiometric air-fuel ratio, the chemically adsorbed NOx is reduced and purified. An exhaust gas purification method in which an adsorption-reduction catalyst is disposed, and the exhaust gas having an air-fuel ratio higher than the stoichiometric air-fuel ratio and the exhaust gas having an air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio are alternately brought into contact with the catalyst. N on the surface of the porous carrier
A method for purifying exhaust gas of an internal combustion engine, characterized by comprising a material carrying a, Mg, Ti, Zr, Rh, Pt, Pd and Ce.

(8) NOx is chemically adsorbed in the exhaust gas passage of the internal combustion engine when the air-fuel ratio in the exhaust gas is higher than the stoichiometric air-fuel ratio, and when the air-fuel ratio is lower than the stoichiometric air-fuel ratio, the chemically adsorbed NOx is reduced and purified. An exhaust gas purification method in which an adsorption-reduction catalyst is disposed, and the exhaust gas having an air-fuel ratio higher than the stoichiometric air-fuel ratio and the exhaust gas having an air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio are alternately brought into contact with the catalyst. On the surface of the porous carrier,
At least one kind of alkali metal or alkaline earth metal selected from Na, Mg, K, Li, Cs, Sr and Ca, at least one kind selected from Ti and Si, Rh, Pt, and Zr; A material carrying at least one selected from Pd, Ir and Ru and a rare earth metal,
With respect to 100 parts by weight of the porous carrier, at least one kind of alkali metal or alkaline earth metal is 5 to 30 parts by weight in total, 8-35 parts by weight of Ti, 3-25 parts by weight of Si,
3-25 parts by weight of Zr, 0.05-0.5 parts by weight of Rh,
1.5-5 parts by weight of Pt, 0.25-3 parts by weight of at least one of Pd, Ir, and Ru, and 5-5-part weight of rare earth metal
An exhaust gas purifying method comprising 50 parts by weight (claim 8).

(9) disposed in an exhaust gas passage of the internal combustion engine,
NOx is chemically adsorbed when the air-fuel ratio of the exhaust gas is higher than the stoichiometric air-fuel ratio and contains at least one selected from alkali metals and alkaline-earth metals, and Pt and Rh. An exhaust gas purifying catalyst for an internal combustion engine, wherein the exhaust gas purifying catalyst for reducing and purifying NOx contains Zr (claim 9).

(10) When the air-fuel ratio of the exhaust gas is higher than the stoichiometric air-fuel ratio, the air-fuel ratio is at least one selected from the group consisting of alkali metals and alkaline earth metals, Pt, and Rh. An exhaust gas purifying catalyst for chemically adsorbing NOx and reducing and purifying the chemically adsorbed NOx when the stoichiometric air-fuel ratio is equal to or less than a stoichiometric air-fuel ratio, characterized in that it contains Zr and at least one selected from Pd, Ir and Ru. An exhaust gas purifying catalyst for an internal combustion engine, comprising:

(11) The exhaust gas purifying catalyst for an internal combustion engine according to claim 9 or 10, further comprising at least one of Ti and Si.

(12) In the eleventh aspect, the alkali metal or alkaline earth metal is Na, Mg, K, Li,
An exhaust gas purifying catalyst for an internal combustion engine, comprising at least one selected from the group consisting of Cs, Sr, and Ca, and a composite oxide of Zs, Ti, and at least one of Si (Claim 12).

(13) The exhaust gas purifying catalyst for an internal combustion engine according to claim 11, further comprising a rare earth metal (claim 13).

(14) Sr and Mg on the surface of the porous carrier
An exhaust gas purifying catalyst for an internal combustion engine, wherein the catalyst carries titanium, Ti, Zr, Rh, Pt, Pd and Ce.
4).

(15) Na and Mg on the surface of the porous carrier
An exhaust gas purifying catalyst for an internal combustion engine, wherein the catalyst carries titanium, Ti, Zr, Rh, Pt, Pd and Ce.
5).

(16) Na, M on the surface of the porous carrier
g, K, Li, Cs, Sr, Ca, at least one of alkali metals or alkaline earth metals, at least one of Ti and Si, Rh and Pt, P
at least one selected from d, Ir and Ru, and Zr
And a rare earth metal, and 5 to 30 parts by weight of alkali metal or alkaline earth metal, 8 to 35 parts by weight of Ti and 3 to 3 parts by weight of Si based on 100 parts by weight of the porous carrier. −25 parts by weight, 3-25 parts by weight of Zr, R
h at 0.05-0.5 parts by weight, Pt at 1.5-5 parts by weight,
An exhaust gas purifying catalyst for an internal combustion engine, comprising 0.25-3 parts by weight of at least one selected from Pd, Ir, and Ru and 5-50 parts by weight of a rare earth metal (Claim 16).

(17) When the exhaust gas flow path of the internal combustion engine contains at least one selected from alkali metals and alkaline earth metals, Rh and Pt, and the air-fuel ratio of the exhaust gas is higher than the stoichiometric air-fuel ratio, NOx And a NOx adsorption reduction catalyst for reducing and purifying the chemically adsorbed NOx when the stoichiometric air-fuel ratio is lower than the stoichiometric air-fuel ratio. An exhaust gas having an air-fuel ratio higher than the stoichiometric air-fuel ratio and an air-fuel ratio lower than the stoichiometric air-fuel ratio are disposed on the catalyst. An exhaust gas purifying apparatus for an internal combustion engine, wherein the catalyst contains Zr, wherein the exhaust gas purifying apparatus alternately contacts the exhaust gas.

(18) When the exhaust gas passage of the internal combustion engine contains at least one selected from alkali metals and alkaline earth metals, Rh and Pt, and the air-fuel ratio of the exhaust gas is higher than the stoichiometric air-fuel ratio, NOx And a NOx adsorption reduction catalyst for reducing and purifying the chemically adsorbed NOx when the stoichiometric air-fuel ratio is lower than the stoichiometric air-fuel ratio. An exhaust gas having an air-fuel ratio higher than the stoichiometric air-fuel ratio and an air-fuel ratio lower than the stoichiometric air-fuel ratio are disposed on the catalyst. An exhaust gas purifying apparatus for an internal combustion engine, wherein the catalyst contains Zr and at least one selected from Pd, Ir, and Ru. Claim 18).

(19) An exhaust gas purifying apparatus for an internal combustion engine according to claim 17 or 18, wherein the catalyst further comprises at least one of Ti and Si.
9).

(20) The exhaust gas purifying catalyst for an internal combustion engine according to claim 19, wherein the catalyst further comprises a rare earth metal (claim 20).

(21) NOx is chemisorbed into the exhaust gas passage of the internal combustion engine when the air-fuel ratio of the exhaust gas is higher than the stoichiometric air-fuel ratio, and NOx is reduced and purified when the air-fuel ratio is lower than the stoichiometric air-fuel ratio. In an exhaust gas purifying apparatus in which an adsorption reduction catalyst is arranged so that exhaust gas having an air-fuel ratio higher than the stoichiometric air-fuel ratio and exhaust gas having an air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio are alternately brought into contact with the catalyst, the catalyst may be porous. S on the surface of the carrier
An exhaust gas purifying apparatus for an internal combustion engine carrying r, Mg, Ti, Zr, Rh, Pt, Pd, and Ce (claim 21).

(22) NOx is chemically adsorbed to the exhaust gas passage of the internal combustion engine when the air-fuel ratio of the exhaust gas is higher than the stoichiometric air-fuel ratio, and when the air-fuel ratio is lower than the stoichiometric air-fuel ratio, the NOx that is chemically adsorbed is reduced and purified. An exhaust gas purifying apparatus in which an adsorption reduction catalyst is disposed so that exhaust gas having an air-fuel ratio higher than the stoichiometric air-fuel ratio and exhaust gas having an air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio are alternately brought into contact with the catalyst. N on the surface of the carrier
An exhaust gas purifying apparatus for an internal combustion engine, comprising: a, Mg, Ti, Zr, Rh, Pt, Pd, and Ce.

(23) NOx is chemically adsorbed to the exhaust gas passage of the internal combustion engine when the air-fuel ratio of the exhaust gas is higher than the stoichiometric air-fuel ratio, and when the air-fuel ratio is lower than the stoichiometric air-fuel ratio, the chemically adsorbed NOx is reduced and purified. In an exhaust gas purifying apparatus in which an adsorption reduction catalyst is arranged so that exhaust gas having an air-fuel ratio higher than the stoichiometric air-fuel ratio and exhaust gas having an air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio are alternately brought into contact with the catalyst, the catalyst may be porous. On the surface of the carrier,
At least one alkali metal or alkaline earth metal selected from Na, Mg, K, Li, Cs, Sr, and Ca; at least one selected from Ti and Si; Rh and Pt; Pd and Ir And at least one selected from the group consisting of Ru and Zr and a rare earth metal. The total amount of alkali metal or alkaline earth metal is 5 to 30 parts by weight based on 100 parts by weight of the porous carrier. , Ti 8-
35 parts by weight, 3-25 parts by weight of Si, 3-25 parts by weight of Zr, 0.05-0.5 parts by weight of Rh, 1.5-5 parts by weight of Pt
An exhaust gas purifying apparatus for an internal combustion engine, comprising 0.25-3 parts by weight of at least one kind selected from Pd, Ir and Ru, and 5-50 parts by weight of a rare earth metal. ).

The SOx poisoning in the exhaust gas purifying catalyst of the present invention is caused by the following equations (1) to (3). First, SO ₃ is generated by oxidation of SO ₂ (formula (1)). The generated SO ₃ reacts with a component that chemically adsorbs NOx (M: NOx adsorbent) to generate a sulfite compound (formula (2)) or a sulfate compound (formula (3)). Since the sulfurous acid compound and the sulfuric acid compound show strong acidity, it becomes difficult for Nox which is an acidic molecule to be adsorbed (formula (4)).

SO ₂ + 1 / 2O ₂ → SO ₃ (1) M + SO ₃ → M-SO ₃ (2) M-SO ₃ + 1 / 2O ₂ → M-SO ₄ (3) M + NOx → M-NOx (4) Conventional Japanese Patent Application Laid-Open Nos. 9-327617 and 10
In the catalyst described in JP-A-1009032, SOx trapping (Equations (2) and (3)) is suppressed by supporting Ti on the alkaline earth metal.

However, simply suppressing the capture of SOx by the NOx adsorbed component causes a decrease in NOx purification performance with the progress of SOx poisoning.

The present inventors have proposed that NOx in an oxidizing atmosphere
As SOx trapping on adsorbed components is inevitable,
An exhaust gas purifying catalyst capable of removing trapped SOx in a reducing atmosphere was studied.

It is considered that the removal reaction of trapped SOx roughly follows the equations (5) to (8). HC, CO, H ₂ coexisting in the reducing atmosphere exhaust gas is converted to HC, CO, H ₂
Captured on adsorbed components (PM). This adsorbed HC, C
_{O, H 2 (PM-HC} , CO, H 2) and sulfite compound reacts capture SOx is reduced and removed from the NOx adsorption component (formula (6)). In addition, SOx removal by the reaction of reducing the sulfate compound to the sulfite compound (Formula (7)) and the reduction reaction of the sulfate compound (Formula (8)) also occur.

PM + HC, CO, H ₂ → PM-HC, CO, H ₂ (5) M-SO ₃ + PM-HC, CO, H ₂ → PM + M + H ₂ S + SO ₂ + CO ₂ + H ₂ O (6) M-SO ₄ + PM-HC, CO, H ₂ → PM + M-SO ₃ + CO ₂ + H ₂ O (7) M-SO ₄ + PM-HC, CO, H ₂ → PM + M + H ₂ S + SO ₂ + CO ₂ + H ₂ O (8) In order to proceed with (5), HC, CO, H ₂
HC adsorbing, CO, H ₂ adsorbate is required. N
As a result of examining the removal reaction of trapped SOx in a reducing atmosphere in which O and oxygen coexist, CO among HC, CO, and H ₂ most contributed to the removal of trapped SOx.

Accordingly, the removal of the trapped SOx requires the removal of HC, C
It is preferable to include a regeneration-promoting component that selectively adsorbs CO among O and H ₂ .

The reaction temperature is also an important factor in the removal reaction of trapped SOx. Supplying a reducing atmosphere exhaust gas of 600 ° C. or more in an automobile leads to deterioration of fuel efficiency. Therefore, considering practicality, the reaction temperature is desirably about 500 ° C.

According to the exhaust gas purifying catalyst of the present invention, 500
In a reducing atmosphere of about ° C. HC, CO, it can be removed trapped SOx in a reducing agent such as H _2.

Here, one of the indices of the CO adsorption capacity of the regeneration promoting component is the absolute value of the CO enthalpy of adsorption (ΔH). A material having a larger absolute value of the enthalpy of adsorption of CO has an ability to attract CO more strongly. In the following, a metal having CO adsorption ability is replaced with a metal single crystal (11
1) Absolute value (ΔH) of the enthalpy of adsorption of CO on the surface (Source: Chemical Society of Japan, Basic Handbook of Chemical Chemistry (Revised 4th Edition), 1993).

Ru (ΔH: 160 kJ / mol)> Pd (14
2), Ir (142)> Pt (138)> Rh (132)> C
o (128)> Ni (125)> Fe (105)> Cu (50)
> Ag (27) From the above ranking, Ru, Pd, and Ir are desirable as the regeneration promoting components that strongly attract CO. Since Ru easily evaporates at a high temperature and Ir is rare, Pd, which is relatively inexpensive and stably present, is preferable as a regeneration promoting component in consideration of practicality. The CO adsorbing power varies depending on the supported state in addition to the metal species of the regeneration promoting component. CO as a regeneration promoting component
The characteristics of the adsorptive power can be determined by the thermal desorption method of CO.
The measuring method is as follows. After CO is saturatedly adsorbed on the exhaust gas purifying catalyst at 100 ° C., the temperature is raised at 5-10 ° C./min in a He gas stream. The amount of CO desorbed at the catalyst outlet with respect to the temperature is measured. C
In the case of a catalyst having a high O adsorbing power, the temperature at which the amount of CO desorbed becomes maximum shifts to the high temperature side.

Capture S in a reducing atmosphere of about 500 ° C.
In the case of an exhaust gas purifying catalyst capable of removing Ox, 200-
At 220 ° C., the amount of CO desorption reached a maximum. On the other hand, the captured SO
175 ° C in the case of an exhaust gas purification catalyst that cannot remove x
In the vicinity, the amount of CO desorption became maximum.

From the above, the regeneration promoting component is represented by the absolute value (ΔΔ) of the CO adsorption enthalpy of the metal single crystal (111) plane.
Pd, Ru, and Ir having H) of 140 kJ / mol or more are preferable. Considering practicality, Pd that is difficult to evaporate at high temperatures is preferable. Furthermore, the maximum value of the CO desorption temperature is 200-220 ° C. in the temperature rise desorption of CO.
It is preferable to have the following characteristics.

Here, focusing on the NOx adsorption component, the removal of the trapped SOx in the reducing atmosphere can be completed more quickly when the amount of SOx trapped by the NOx adsorption component is smaller. Further, sulfite compounds are more easily reduced than sulfate compounds.

The NOx adsorbing component is at least one selected from alkali metals and alkaline earth metals, Zr,
By using at least one kind selected from i and Si, T
The capture of SOx is more suppressed than that having only i.
By having Zr, N that captures SOx in a short time
It is considered that SOx can be removed from the Ox adsorption component.

It is desirable that at least one selected from alkali metals and alkaline earth metals and at least one of Zr, Ti and Si form a composite oxide.

The alkali metal and the alkaline earth metal are N
At least one selected from a, Sr, K, Li, Ca, Cs, and Mg is desirable, and Na and Sr are particularly preferable.

As the composite oxide of Sr and Ti, Sr
TiO ₃ , Sr ₂ TiO ₄ , Sr ₃ Ti ₂ O ₇ , Sr ₄ Ti ₃ O ₁₀ ,
SrTi ₁₂ O ₁₉ , SrTi ₂₁ O ₃₈ and the like. Sr and S
As a composite oxide with i, SrSiO ₃ , Sr ₃ Si
O ₅ , Sr ₂ SiO ₄ and the like. Examples of composite oxides of Sr and Zr include SrZrO ₃ , Sr ₂ ZrO ₄ , Sr ₃ Zr ₂ O ₇ ,
Sr ₄ Zr ₃ O ₁₀ and the like. Examples of the composite oxide of Sr, Ti, and Zr include Sr ₂ (Ti _0.25 Zr _0.75 ) O ₄ . As a composite oxide of Sr, Ti and Si, SrT
iSi ₂ O ₈ and the like.

As the composite oxide of Na and Ti, Na
₂ TiO ₃ , Na ₂ Ti ₃ O ₇ , Na ₂ Ti ₄ O ₉ , Na
₂ Ti ₆ O ₁₃ , Na ₄ , Ti ₅ O ₁₂ , Na _0.23 TiO ₂ , N
_{a 2 TiO 19, Na 4 Ti} 3 O 8, Na 4 Ti 3 O 8, Na 4 T
iO ₄ , Na ₈ Ti ₅ O ₁₄ , γ-Na ₂ TiO ₃ , β-Na ₂
There are TiO ₃ , NaTiO ₂ , Na _0.46 TiO _{2 and the} like. N
As a composite oxide of a and Si, Na ₄ SiO ₄ , β-
Na ₂ Si ₂ O ₅ , Na ₂ Si ₂ O ₅ , Na ₂ Si ₄ O ₉ , γ-
Na ₂ Si ₂ O ₅ , Na ₆ Si ₂ O ₇ , α-Na ₂ Si ₂ O ₅ ,
δ-Na ₂ Si ₂ O ₅ , Na ₂ Si ₃ O ₇ , α-Na ₂ Si ₂ O
₅ , Na ₆ Si ₈ O ₁₉ , Na ₂ Si ₃ O ₇ , α-Na ₂ Si ₂ O
₅ , Na ₂ SiO ₃ , Na ₄ SiO ₄ , Na ₂ SiO ₃ , Na ₄ Si
O _4, and the like _{Oα-Na 2 Si 2 O 5} , Na 2 Si 2 O 5, Na 2 Si 4 O 9. As a composite oxide of Na and Zr, NaZ
rO ₃ , α-NaZrO ₃ , Na ₂ ZrO ₃ and the like. Further, as a composite oxide of Na, Zr and Si, Na ₂ Z
_{rSiO 5, Na 2 Zr 2 Si} 10 O 31, Na 14 Zr 2 Si 4 O 11,
And the like _{Na 2 ZrSi 4 O 11, Na} 14 Zr 2 Si 10 O 31. As a composite oxide of Na, Ti and Si, Na ₂
Examples include TiSi ₂ O ₇ , NaTiSi ₂ O ₆ , and Na ₂ TiSiO ₅ .

The structure of the composite oxide can be confirmed by a powder X-ray diffraction method. In order to obtain the composite oxide, 6
It is desirable to perform a heat treatment at a temperature of 00 ° C. or higher. Firing temperature is
Desirably 700 ° C.

The NOx reduction components are preferably Rh and Pt. When the three-way catalyst function in a reducing atmosphere is enhanced, it is desirable to add an oxygen storage function to the exhaust gas purifying catalyst. Cerium (Ce) is preferably contained as a material having an oxygen storage function.

In order to increase the heat resistance of the exhaust gas purifying catalyst, it is effective to add La or Y as a rare earth metal in addition to Ce.

The catalyst composition of the NOx purification catalyst according to the present invention is such that the total amount of alkali metal or alkaline earth metal is 5 to 30 parts by weight and Ti is 3 parts by weight with respect to 100 parts by weight of the porous carrier.
-35 parts by weight, 3-25 parts by weight of Si, 3-25 parts by weight of Zr
Parts by weight, Rh 0.05-0.5 parts by weight, Pt 1.5-
It is preferable that the total amount of Pd, Ir and Ru is 0.25-3 parts by weight, and the rare earth metal is 5-40 parts by weight.

A particularly preferable ratio is that the total amount of at least one alkali metal or alkaline earth metal is 8 to 15 parts by weight and Ti is 4-1 to 100 parts by weight of the porous carrier.
5 parts by weight, 5-10 parts by weight of Si, 5-10 parts by weight of Zr, 0.10-0.20 parts by weight of Rh, and 1.0-3.
0 parts by weight, Pd is 0.25-0.8 parts by weight, and rare earth metal is 10-30 parts by weight.

The NOx purification catalyst according to the present invention can be used in various shapes depending on the application. It can be applied as a pellet, plate, granule, powder, etc., including a honeycomb shape obtained by coating a honeycomb structure made of various materials such as cordierite or stainless steel with a catalyst component supported on a porous carrier. it can. When it is arranged in an exhaust gas passage of an automobile, a honeycomb shape is preferable.

As a method for preparing the NOx purification catalyst, any of a physical preparation method such as an impregnation method, a kneading method, a coprecipitation method, a sol-gel method, an ion exchange method, a vapor deposition method, and a preparation method utilizing a chemical reaction can be applied. is there.

When the regeneration accelerating component and the NOx adsorbing component are close to each other, the removal reaction of the trapped SOx of the formulas (5) to (8) tends to proceed. Therefore, in the case of preparing a catalyst by the impregnation method, it is preferable to use a mixed solution of a raw material containing a regeneration promoting component and a NOx adsorption component and simultaneously impregnate the carrier with the regeneration promotion component and the NOx adsorption component.

As starting materials for the NOx purification catalyst, various compounds such as nitric acid compounds, acetic acid compounds, complex compounds, hydroxides, carbonate compounds, organic compounds, dinitrodiamine complexes, metals and metal oxides can be used. .

When Pd is used as a regeneration promoting component, it is preferably prepared using a dinitrodiamine Pd solution. When a dinitrodiamine Pd solution is used, NO
The proximity effect with the x-adsorbed component is increased. As a result, the reduction and removal of the trapped SOx from the NOx adsorption component are promoted.

In the above method, a metal oxide or a composite oxide such as titania, silica, silica-alumina, magnesia and the like can be used as the porous carrier in addition to alumina. Alumina is preferred because it has heat resistance.

The exhaust gas purifying catalyst of the present invention is preferably mounted on a stratified or homogeneous lean burn vehicle that can be operated in an oxidizing atmosphere. Further, the exhaust gas purifying apparatus having the exhaust gas purifying catalyst of the present invention preferably includes the following exhaust gas control device.

It has an operating state determining means and an air-fuel ratio (A / F) control unit. The operating state determining means includes NOx adsorption amount estimating means, NOx removal amount estimating means, SOx absorption amount estimating means, and SOx absorbing amount estimating means.
It has x emission amount estimation means. The NOx adsorption amount at an air-fuel ratio higher than the stoichiometric air-fuel ratio is estimated by the NOx adsorption amount estimation means, and the SOx absorption amount is estimated by the SOx absorption amount estimation means. When the NOx adsorption amount estimating means or the SOx absorption amount estimating means determines that the predetermined NOx adsorption amount or the SOx absorption amount is exceeded, the NOx removal amount estimating means and the SOx release amount estimating means instruct the A / F control unit. And the operation is performed below the stoichiometric air-fuel ratio.

As a method for detecting the NOx adsorption amount and the SOx trapping amount, for example, a NOx sensor, an oxygen sensor, an exhaust gas temperature sensor, an air flow sensor, a boost pressure gauge and an engine speed meter can be used.

[0066]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described with reference to specific examples, but the present invention is not limited to these examples.

Example 1 A slurry composed of alumina powder and an alumina precursor and adjusted to be nitric acid was coated on a cordierite honeycomb (400 cells / inc 2), dried and fired to obtain an apparent volume 1 of the honeycomb. An alumina-coated honeycomb coated with 190 g of alumina per liter was obtained. After impregnating the alumina-coated honeycomb with a mixed solution of Ce nitrate and Zr nitrate,
Drying at 0 ° C. followed by firing at 600 ° C.

Next, a dinitrothodiamine Pt nitric acid solution, Rh nitrate, dinitrodiamine Pd, Sr nitrate and M nitrate M
g and a mixed solution of titania sol and dried at 200 ° C.
Subsequently, firing was performed at 600 ° C.

Finally, a titania sol was impregnated, dried at 200 ° C., and subsequently calcined at 700 ° C.

As described above, for 100 g of alumina,
Pd 0.26g, Sr11g, Ti4g, Ti
6 g, Ti 4 g, Mg 0.9 g, Rh 0.11 g, Pt 1.
Example catalyst 1 containing 4 g, Ce 14 g, and Zr 6 g was obtained. Further, Example Catalyst 2 not supporting Zr was obtained. Note that the first component and the second component in the table indicate the order of loading, with the smaller number being loaded first. In addition, the supported amount per 100 g of alumina is described before the supported component. For example, 14 Ce indicates that Ce is supported at a ratio of 14 g in terms of metal to 100 g of alumina.

[0071]

[Table 1]

Test Example 1 Examples Catalysts 1 and 2 were examined for the amount of trapped SOx.

The gas used in the test was an SOx poisoning model gas for SOx poisoning in an oxidizing atmosphere. In order to accelerate the SOx poisoning of the catalyst with the SOx poisoning model gas, the SOx concentration in the gas was set to 150 ppm.

The composition of the accelerated SOx poisoning model gas is SO
₂ : 150 ppm, NOx: 600 ppm, C ₃ H ₆ : 500 ppm
, CO: 0.1%, CO ₂ : 10%, O ₂ : 5%, H
₂ O: 10%, N ₂ : balance.

The test procedure followed the following procedure.

The SOx poisoning treatment is performed at 300 ° C.
x Poisoned model gas was circulated for 1 h. At this time, the catalyst volume was 6 cc, and the SV was 30,000 / h.

The amount of SOx trapped is determined by measuring the amount of S in the catalyst after the flow of the accelerated SOx poisoning model gas with an S concentration analyzer (Horiba Seisakusho E
MIA-120).

(Test Results) Table 2 shows that the catalysts of Example Catalysts 1 and 2
The amount of captured Ox was shown. SO of Example Catalyst 1 with Zr
It is clear that x capture is suppressed.

[0079]

[Table 2]

Test Example 2 SOx Resistance of Catalysts 1 and 2 of the Examples
In order to examine the poisoning, the NOx purification rates before and after SOx poisoning and the recovery of the catalyst performance by the catalyst regeneration treatment were examined.
The gas used in the test was an oxidizing atmosphere model gas simulating lean burn exhaust gas, a reducing atmosphere model gas simulating stoichiometric air-fuel ratio combustion, and an SOx poisoning model gas for SOx poisoning in an oxidizing atmosphere. In order to accelerate the SOx poisoning of the catalyst with the SOx poisoning model gas, the SOx concentration in the gas was set to 150 ppm.

The composition of the oxidizing atmosphere model gas is NOx:
_{600ppm, C 3 H 6: 500ppm} , CO: 0.1%, C
O ₂ : 10%, O ₂ : 5%, H ₂ O: 10%, N ₂ : balance.

The composition of the reducing atmosphere model gas is NOx:
1000 ppm, C ₃ H ₆ : 600 ppm, CO: 0.5%, C
O ₂ : 5%, O ₂ : 0.5%, H ₂ : 0.3%, H ₂ O: 10
%, N ₂ : balance.

The composition of the accelerated SOx poisoning model gas is SO
₂ : 150 ppm, NOx: 600 ppm, C ₃ H ₆ : 500 ppm
, CO: 0.1%, CO ₂ : 10%, O ₂ : 5%, H
₂ O: 10%, N ₂ : balance.

The test method followed the following procedure.

First, a NOx purification rate was measured by performing a test in which a reducing atmosphere model gas and an oxidizing atmosphere model gas were alternately passed through the catalyst layer every three minutes (hereinafter referred to as a repeated test). The catalyst volume was 6 cc and the SV was 30,000 / h.

Next, after the accelerated SOx poisoning model gas was passed through the catalyst layer, a repeated test was performed to measure the NOx purification rate after SOx poisoning. As poisoning conditions, the poisoning temperature
The poisoning time was 300 ° C., the poisoning time was 1 hour, and the SV was 30,000 / h.

Finally, the reducing atmosphere model gas was changed to SV: 3
After flowing through the catalyst layer at 000 / h at 500 ° C. for 10 minutes (hereinafter referred to as regeneration treatment), a repeated test was performed to measure the NOx purification rate after the regeneration treatment.

Unless otherwise specified hereafter, the repetitive test conditions are a temperature of 400 ° C. and an SV of 30,000 / h. Also,
The NOx purification rate was defined as a decrease rate of the NOx concentration before and after the catalyst layer flow after one minute of the switching of the oxidizing atmosphere model gas of the equation (1). The definition formula is shown in Formula 1.

[0089]

(Equation 1)

(Test Results) Table 3 shows the measurement results of the NOx purification rate at 400 ° C. Example catalyst 1 having Zr
Is excellent in the recovery of the NOx purification performance by the regeneration treatment.

[0091]

[Table 3]

Test Example 3 The structures of the NOx adsorbents of the catalysts of Examples 1 and 2 were examined by a powder X-ray diffraction method. Example catalyst 1
And 2 are composite oxides of Sr and Ti, SrTiO ₃
was gotten. Further, for the example catalyst 1, Sr and Z
Thus, a composite oxide SrZrO ₃ with r was obtained.

"Example 2" Based on Example 1, Example 3 in which the amount of Pd was increased and Example Catalyst 4-6 supporting Si and Zr were produced. Table 4 shows the catalyst composition.

Example 1 According to Test Example 2, the resistance to SOx poisoning was evaluated. Table 5 shows the test results. Example catalyst 3-6
In any case, the NOx purification performance was recovered by the regeneration treatment. N
When comparing the Ox purification rate with the regeneration rate, the Pd carrying amount was 0.7.
Example catalyst 3 with 5 g was good. Regeneration promoter and Z
This is considered to be a synergistic effect of supporting r.

The effect of adding Si and Tii to Zr is obtained from the catalyst 4-6 of the embodiment. The catalyst of Example 5 containing Zr, Ti and Si had the best recoverability of the NOx purification performance by the regeneration treatment. In addition, the regeneration rate of the NOx purification rate was defined as Expression 2.

[0096]

(Equation 2)

[0097]

[Table 4]

[0098]

[Table 5]

Example 3 The amount of Zr supported on the catalyst of Example 1 was 2-30 g per 100 g of the carrier, and the resistance to SOx poisoning was examined in accordance with Test Example 2 of Example 1. The results are shown in Table 6. When the amount of supported Zr was 2 g or less, the NOx purification rate was not restored by the regeneration treatment. When the amount of supported Zr was increased, the initial NOx purification rate was reduced. In order to make the initial NOx purification rate 60% or more, the Zr carrying amount is preferably 3 to 10 g. Further, in order to set the initial NOx purification rate to 50% or more, the amount of Zr carried must be 10%.
The ratio is preferably 3 to 25 g with respect to 0 g.

[0100]

[Table 6]

Example 4 Example catalyst 250-3 was added.
The reducing atmosphere model gas is circulated in the range of 0 ° C.
The purification rate and hydrocarbon purification rate were measured.

The NOx purification rate was defined as the reduction rate of the NOx concentration before and after circulation of the catalyst layer one minute after the switching of the reducing atmosphere model gas.

The definition of the hydrocarbon purification rate was defined as the reduction rate of the hydrocarbon concentration before and after the catalyst layer flow one minute after the switching of the reducing atmosphere model gas.

As a result of measurement, it was found that NO
The x purification rate was almost 100%. The hydrocarbon purification rate is 80% or more at 300 ° C or more, and almost 1 at 400 ° C or more.
00%.

Example 5 Example 1 According to Test Example 1, Example Catalysts 7-16 were produced. Table 7 shows Example Catalyst 7-1.
6 was indicated. Further, the SOx resistance was examined according to Test Example 2 of Example 1. Table 8 shows the results. Comparing the regeneration rates of the NOx purification rates, the catalyst of the embodiment 8-11 carrying Zr was superior to the catalyst of the embodiment 7 in the recovery performance. Also, Z
The catalyst of Example 11 supporting r, Si and Ti had the best recovery performance. The same was true for the example catalysts 12-16. That is, the example catalyst 13-1 supporting Zr
No. 6 was excellent in recovery of NOx purification rate.

[0106]

[Table 7]

[0107]

[Table 8]

[0108]

According to the exhaust gas purifying method, the exhaust gas purifying catalyst and the exhaust gas purifying apparatus of the present invention, S-resistant in an oxidizing atmosphere.
High NOx purification performance could be enhanced while maintaining Ox poisoning.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) F01N 3/20 F01N 3/20 B 3/24 3/24 R 3/28 301 3/28 301C (72) Inventor Masato Kaneda 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Kazunari Nagayama 7-1-1, Omika-machi, Hitachi City, Ibaraki Prefecture Inside the research institute (72) Inventor Toshio Yamashita 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd.Hitachi Research Laboratory (72) Inventor Osamu Kuroda Hitachi, Ltd. In-vehicle equipment division (72) Inventor Yuichi Kitahara 2520 No. Odaiba, Hitachinaka-shi, Ibaraki Prefecture F-ter in Hitachi, Ltd. automotive equipment division (Ref.) BA15X BA18X BA19X BA30X BA31X BA32X BA33X BA41X BA42X BB02 4G069 AA04 AA08 AA09 BA01A BA01B BA01C BA02A BA02B BA02C BA04A BA04B BA04C BA05A BA05B BA05C BA06A BA06B BA06C BA13A BA13B BA13C BB04A BB04B BB04C BB06A BB06B BB06C BC01A BC08A BC12A BC12B BC12C BC38A BC43A BC43B BC43C BC69A BC71A BC71B BC71C BC72A BC72B BC72C BC75A BC75B BC75C CA03 CA08 CA13 DA06 EA18 FA03 FA06 FB14

Claims (23)

[Claims] 1. An exhaust gas flow path for an internal combustion engine, wherein at least one selected from alkali metals and alkaline earth metals and Rh and P
and a NOx adsorption reduction catalyst for reducing and purifying NOx when the air-fuel ratio in the exhaust gas is higher than the stoichiometric air-fuel ratio, and reducing and purifying the chemically adsorbed NOx when the air-fuel ratio in the exhaust gas is lower than the stoichiometric air-fuel ratio. An exhaust gas purification method in which an exhaust gas having an air-fuel ratio higher than the stoichiometric air-fuel ratio and an exhaust gas having an air-fuel ratio lower than the stoichiometric air-fuel ratio are alternately brought into contact with the catalyst, wherein the catalyst contains Zr. Engine exhaust gas purification method. 2. An exhaust gas flow path for an internal combustion engine, wherein at least one selected from alkali metals and alkaline earth metals and Rh and P
and a NOx adsorption reduction catalyst for reducing and purifying NOx when the air-fuel ratio in the exhaust gas is higher than the stoichiometric air-fuel ratio, and reducing and purifying the chemically adsorbed NOx when the air-fuel ratio in the exhaust gas is lower than the stoichiometric air-fuel ratio. In an exhaust gas purification method in which an exhaust gas having an air-fuel ratio higher than the stoichiometric air-fuel ratio and an exhaust gas having an air-fuel ratio lower than the stoichiometric air-fuel ratio are alternately brought into contact with the catalyst, the catalyst is selected from Zr, Pd, Ir, and Ru. An exhaust gas purifying method for an internal combustion engine, comprising: at least one selected from the group consisting of: 3. The method for purifying exhaust gas of an internal combustion engine according to claim 1, wherein said catalyst further contains at least one of Ti and Si. 4. The catalyst according to claim 3, wherein at least one selected from an alkali metal and an alkaline earth metal in said catalyst is used.
An exhaust gas purification method for an internal combustion engine, wherein r, at least one selected from Ti and Si forms a composite oxide. 5. The exhaust gas purifying method for an internal combustion engine according to claim 3, wherein said catalyst further contains a rare earth metal. 6. An NOx adsorber for chemically adsorbing NOx in an exhaust gas passage of an internal combustion engine when the air-fuel ratio in the exhaust gas is higher than a stoichiometric air-fuel ratio, and reducing and purifying the chemically adsorbed NOx when the air-fuel ratio is lower than the stoichiometric air-fuel ratio. In an exhaust gas purification method in which a reduction catalyst is disposed and exhaust gas having an air-fuel ratio higher than the stoichiometric air-fuel ratio and exhaust gas having an air-fuel ratio equal to or less than the stoichiometric air-fuel ratio are alternately contacted with the catalyst, Sr and Mg on the surface of the carrier
An exhaust gas purifying method for an internal combustion engine, comprising: a carrier that carries Pt, Ti, Zr, Rh, Pt, Pd, and Ce. 7. A NOx adsorber for chemically adsorbing NOx in an exhaust gas passage of an internal combustion engine when the air-fuel ratio in the exhaust gas is higher than a stoichiometric air-fuel ratio, and reducing and purifying the chemically adsorbed NOx when the air-fuel ratio in the exhaust gas is lower than the stoichiometric air-fuel ratio. In an exhaust gas purification method in which a reduction catalyst is disposed and exhaust gas having an air-fuel ratio higher than the stoichiometric air-fuel ratio and exhaust gas having an air-fuel ratio equal to or less than the stoichiometric air-fuel ratio are alternately contacted with the catalyst, Na and Mg on the surface of the carrier
An exhaust gas purifying method for an internal combustion engine, comprising: a carrier that carries Pt, Ti, Zr, Rh, Pt, Pd, and Ce. 8. A NOx adsorber for chemically adsorbing NOx in an exhaust gas passage of an internal combustion engine when the air-fuel ratio in the exhaust gas is higher than a stoichiometric air-fuel ratio, and reducing and purifying the chemically adsorbed NOx when the air-fuel ratio is lower than the stoichiometric air-fuel ratio. In an exhaust gas purification method in which a reduction catalyst is disposed and exhaust gas having an air-fuel ratio higher than the stoichiometric air-fuel ratio and exhaust gas having an air-fuel ratio equal to or less than the stoichiometric air-fuel ratio are alternately contacted with the catalyst, Na, M on the surface of the carrier
g, K, Li, Cs, Sr and Ca, at least one of alkali metals or alkaline earth metals, and Ti
And at least one selected from Si, Rh and Pt,
Zr, at least one selected from Pd, Ir, and Ru, and a rare earth metal are supported, and at least one alkali metal or alkaline earth metal is added to 100 parts by weight of the porous carrier. 5-30 parts by weight in total, T
i is 8-35 parts by weight, Si is 3-25 parts by weight, Zr is 3 parts by weight.
-25 parts by weight, 0.05 to 0.5 parts by weight of Rh, 1.5 to 5 parts by weight of Pt, 0.25 to 3 parts by weight of at least one of Pd, Ir, and Ru, and rare earth metal. An exhaust gas purifying method characterized by comprising 5 to 50 parts by weight. 9. When the air-fuel ratio of the exhaust gas is higher than the stoichiometric air-fuel ratio, wherein the air-fuel ratio is at least one selected from the group consisting of alkali metals and alkaline earth metals, Pt, and Rh. An exhaust gas purifying catalyst for an internal combustion engine, which chemically adsorbs Zr and reduces and purifies the chemically adsorbed NOx when the air-fuel ratio is equal to or lower than a stoichiometric air-fuel ratio, wherein the exhaust gas purifying catalyst contains Zr. 10. At least one selected from an alkali metal and an alkaline earth metal is disposed in an exhaust gas passage of an internal combustion engine.
An exhaust gas purifying catalyst containing a seed, Pt, and Rh, which chemically adsorbs NOx when the air-fuel ratio of the exhaust gas is higher than the stoichiometric air-fuel ratio and reduces and purifies the chemically adsorbed NOx when the air-fuel ratio is lower than the stoichiometric air-fuel ratio; And an at least one selected from the group consisting of Pd, Ir and Ru. 11. The method according to claim 9 or 10, further comprising:
An exhaust gas purifying catalyst for an internal combustion engine, comprising at least one of Si and Si. 12. The method according to claim 11, wherein said alkali metal or alkaline earth metal is Na, Mg, K, Li, Cs,
An exhaust gas purifying catalyst for an internal combustion engine, comprising at least one selected from the group consisting of Sr and Ca, and comprising a composite oxide of these and at least one of Zr, Ti and Si. 13. The exhaust gas purifying catalyst for an internal combustion engine according to claim 11, further comprising a rare earth metal. 14. A porous carrier comprising Sr, Mg and Ti on the surface thereof.
An exhaust gas purifying catalyst for an internal combustion engine, which carries Zr, Rh, Pt, Pd and Ce. 15. The method according to claim 15, wherein Na, Mg and Ti are formed on the surface of the porous carrier.
An exhaust gas purifying catalyst for an internal combustion engine, which carries Zr, Rh, Pt, Pd and Ce. 16. The method according to claim 16, wherein Na, Mg, K,
At least one of an alkali metal or an alkaline earth metal selected from Li, Cs, Sr, and Ca, at least one selected from Ti and Si, Rh and Pt, Pd and Ir
And at least one selected from Ru, Zr, and a rare earth metal, and 5-30 parts by weight of alkali metal or alkaline earth metal in total with respect to 100 parts by weight of the porous carrier. , Ti at 8-35 parts by weight, Si at 3-25 parts by weight, Zr at 3-25 parts by weight, and Rh at 0.0.
5-0.5 parts by weight, Pt 1.5-5 parts by weight, Pd and I
at least one selected from r and Ru in a total amount of 0.25
An exhaust gas purifying catalyst for an internal combustion engine, comprising -3 parts by weight and 5 to 50 parts by weight of a rare earth metal. 17. An exhaust gas passage of an internal combustion engine, wherein at least one selected from alkali metals and alkaline earth metals is added to Rh.
And a Pt, and a NOx adsorption reduction catalyst is provided for chemically adsorbing NOx when the air-fuel ratio of the exhaust gas is higher than the stoichiometric air-fuel ratio and for reducing and purifying the chemically adsorbed NOx when the air-fuel ratio is lower than the stoichiometric air-fuel ratio. An exhaust gas purifying apparatus wherein an exhaust gas having an air-fuel ratio higher than the stoichiometric air-fuel ratio and an exhaust gas having an air-fuel ratio lower than the stoichiometric air-fuel ratio are alternately brought into contact with the catalyst, wherein the catalyst contains Zr. Exhaust gas purification equipment. 18. At least one selected from alkali metals and alkaline earth metals and Rh in an exhaust gas flow path of an internal combustion engine.
And a Pt, and a NOx adsorption reduction catalyst is provided for chemically adsorbing NOx when the air-fuel ratio of the exhaust gas is higher than the stoichiometric air-fuel ratio and for reducing and purifying the chemically adsorbed NOx when the air-fuel ratio is lower than the stoichiometric air-fuel ratio. In the exhaust gas purifying apparatus, the catalyst is made to alternately contact an exhaust gas having an air-fuel ratio higher than the stoichiometric air-fuel ratio and an exhaust gas having an air-fuel ratio lower than the stoichiometric air-fuel ratio, wherein the catalyst is selected from Zr, Pd, Ir, and Ru. An exhaust gas purifying apparatus for an internal combustion engine, comprising at least one of the following. 19. An exhaust gas purifying apparatus for an internal combustion engine according to claim 17, wherein said catalyst further comprises at least one of Ti and Si. 20. The exhaust gas purifying apparatus for an internal combustion engine according to claim 19, wherein said catalyst further comprises a rare earth metal. 21. A NOx adsorber for chemically adsorbing NOx in an exhaust gas passage of an internal combustion engine when the air-fuel ratio of the exhaust gas is higher than a stoichiometric air-fuel ratio, and reducing and purifying the chemically adsorbed NOx when the air-fuel ratio is lower than the stoichiometric air-fuel ratio. In an exhaust gas purifying apparatus in which a reduction catalyst is arranged so that exhaust gas having an air-fuel ratio higher than the stoichiometric air-fuel ratio and exhaust gas having an air-fuel ratio lower than the stoichiometric air-fuel ratio are alternately contacted with the catalyst, the catalyst comprises a porous carrier. Sr and Mg on the surface of
An exhaust gas purifying apparatus for an internal combustion engine, which carries Ti, Zr, Rh, Pt, Pd, and Ce. 22. A NOx adsorbent for chemically adsorbing NOx in an exhaust gas passage of an internal combustion engine when the air-fuel ratio of the exhaust gas is higher than a stoichiometric air-fuel ratio, and reducing and purifying the chemically adsorbed NOx when the air-fuel ratio is lower than the stoichiometric air-fuel ratio. In an exhaust gas purifying apparatus in which a reduction catalyst is arranged so that exhaust gas having an air-fuel ratio higher than the stoichiometric air-fuel ratio and exhaust gas having an air-fuel ratio lower than the stoichiometric air-fuel ratio are alternately contacted with the catalyst, the catalyst comprises a porous carrier. Na and Mg on the surface of
An exhaust gas purifying apparatus for an internal combustion engine, which carries Ti, Zr, Rh, Pt, Pd, and Ce. 23. A NOx adsorber for chemically adsorbing NOx in an exhaust gas passage of an internal combustion engine when the air-fuel ratio of the exhaust gas is higher than a stoichiometric air-fuel ratio, and reducing and purifying the chemically adsorbed NOx when the air-fuel ratio is lower than the stoichiometric air-fuel ratio. In an exhaust gas purifying apparatus in which a reduction catalyst is arranged so that exhaust gas having an air-fuel ratio higher than the stoichiometric air-fuel ratio and exhaust gas having an air-fuel ratio lower than the stoichiometric air-fuel ratio are alternately contacted with the catalyst, the catalyst comprises a porous carrier. Na, M on the surface of
g, K, Li, Cs, Sr, Ca, at least one of alkali metals or alkaline earth metals, at least one of Ti and Si, Rh and Pt, P
at least one selected from d, Ir and Ru, and Zr
And a rare earth metal, and 5 to 30 parts by weight of alkali metal or alkaline earth metal, 8 to 35 parts by weight of Ti and 3 to 3 parts by weight of Si based on 100 parts by weight of the porous carrier. −25 parts by weight, 3-25 parts by weight of Zr, R
h at 0.05-0.5 parts by weight, Pt at 1.5-5 parts by weight,
An exhaust gas purifying apparatus for an internal combustion engine, comprising 0.25-3 parts by weight of at least one selected from Pd, Ir, and Ru and 5-50 parts by weight of a rare earth metal.