KR101673331B1 - Catalyst, method for manufacturing the same, and exhaust gas purifying catalyst system using the same - Google Patents

Abstract

A catalyst, a method for producing the same, and a catalyst system for purification of exhaust gas containing the same are disclosed. An embodiment of the present invention provides a catalyst of the following general formula (1).
[Chemical Formula 1]
_{AB 1 - y B 'y O} 3
(Wherein A, B, B ', and y are as defined in the specification).

Description

TECHNICAL FIELD The present invention relates to a catalyst, a method for producing the catalyst, and a catalyst system for purification of exhaust gas containing the same. DESCRIPTION OF THE RELATED ART [0002]

One embodiment of the present invention relates to a catalyst, a method for producing the same, and a catalyst system for purification of exhaust gas containing the same.

The harmful components contained in the vehicle exhaust gas are unburned hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) produced by high temperature combustion.

All cars powered by gasoline engines and diesel engines emit exhausts containing these harmful components. As the number of cars increases year by year, governments around the world are tightly regulating emissions and fuel efficiency standards are also being strengthened have. Therefore, it is essential that devices for suppressing or purifying these harmful substances occur in all automobiles.

Automotive catalysts are called three-way catalysts because they convert CO and HC into carbon dioxide and water while reducing NOx to harmless nitrogen and oxygen. BACKGROUND ART [0002] A post-treatment catalyst for purification of exhaust gas of automobiles is formed by coating a porous honeycomb with oxides and noble metals as catalyst components, and a wash coating method is a typical method for manufacturing such a coating layer.

One embodiment of the present invention is a catalyst capable of simultaneously removing hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) present under gasoline exhaust gas conditions and having high temperature stability, And a catalyst system for purifying exhaust gases.

An embodiment of the present invention provides a catalyst of the following general formula (1).

[Chemical Formula 1]

_{AB 1 - y B 'y O} 3

(Where A is a rare earth element, B is Al, Ga, In, or a combination thereof, B 'is Pd, Pt, Rh, or a combination thereof, and the range of y is 0.005? Y? 0.05. )

The catalyst may be represented by the following formula (2).

(2)

LaAl _{1 - y} Pd _y O ₃

(Here, the range of y is 0.005? Y? 0.05.)

Another embodiment of the present invention is directed to a method of fabricating a semiconductor device, comprising: preparing a metal precursor solution; Adding a carboxylic acid to the metal precursor solution to prepare a mixed metal salt solution; And drying and calcining the mixed metal salt solution.

The step of preparing the metal precursor solution may include dissolving the rare earth precursor, the aluminum precursor, and the palladium precursor in distilled water.

The molar ratio of the rare earth precursor: aluminum precursor: palladium precursor may be 1: 0.95 to 0.995: 0.05 to 0.005.

The rare earth precursor is _{La (NO 3) 3 · 6H} 2 O, Pr (NO 3) 3 · 6H 2 O, Nd (NO 3) 3 · 6H 2 O, Er (NO 3) 3 · 5H 2 O, or both . ≪ / RTI >

The aluminum precursor may be Al (NO ₃ ) ₃ .9H ₂ O, AlCl ₃ .6H ₂ O, or a combination thereof.

The palladium precursor may be palladium nitrate, palladium chloride, or a combination thereof.

In the step of preparing a mixed metal salt solution by adding carboxylic acid to the metal precursor solution, the content of the carboxylic acid may be 1 to 20% by weight more than the content of the metal precursor solution.

The carboxylic acid may include citric acid, acetic acid, oxalic acid, malonic acid, latic acid, malic acid, or a combination thereof.

In the step of drying and firing the mixed metal salt solution, the firing may be performed at 500 to 800 ° C for 3 to 7 hours.

Drying and firing the mixed metal salt solution; Thereafter, stabilizing the calcined catalyst may be further included.

The stabilization may be carried out at 500 to 700 ° C for 10 to 20 hours.

The stabilization may be performed in an atmosphere of oxygen and a carbon monoxide atmosphere.

The stabilization may include injecting a background gas for 40 to 50 seconds; 3% oxygen gas for 3 to 6 seconds to form an oxidizing atmosphere; Injecting the background gas for 100 to 130 seconds; And 3% carbon monoxide gas for 3 to 6 seconds to form a reducing atmosphere, wherein the background gas is at least one selected from the group consisting of 10% H ₂ O, 10% CO ₂ , and the remainder N ₂ .

Yet another embodiment of the present invention is a catalyst comprising the above-described catalyst; Oxygen Storage Capacity (OSC); And an alumina-based material.

The catalyst may be a combination of Pd and Al ₂ O ₃ , or a combination of Rh and an oxygen storage material (OSC).

The oxygen storage material may be Ce, Zr, Pr, Nd, La, Y, or a combination thereof.

The alumina-based material may include Al ₂ O ₃ , La doped Al ₂ O ₃ , MgAl ₂ O ₄ , or a combination thereof.

According to an embodiment of the present invention, there is provided a catalyst capable of simultaneously removing hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) present under gasoline exhaust gas conditions and having high temperature stability, And a catalyst system for purification of exhaust gas containing the same can be provided.

1 is a graph showing the amount of CO purification according to the temperature of the d-catalyst.
2 is a graph showing the amount of C ₃ H ₆ purified according to the temperature of the d-catalyst.
3 is a graph showing the amount of H ₂ purification according to the temperature of the d-catalyst.
4 is a graph showing the amount of NO purification according to the temperature of the d-catalyst.
5 is a graph showing the amount of CO purification according to the temperature of the a-catalyst (I).
6 is a graph showing a purification amount of C ₃ H ₆ according to the temperature of the a-catalyst (I).
7 is a graph showing the amount of purification of H ₂ according to the temperature of the a-catalyst (I).
8 is a graph showing the amount of NO purification according to the temperature of the a-catalyst (I).
9 is a graph showing the amount of CO purification according to the temperature of the a-catalyst (II).
10 is a graph showing the amount of C ₃ H ₆ purified according to the temperature of a-catalyst (II).
11 is a graph showing the amount of purification of H ₂ according to the temperature of a-catalyst (II).
12 is a graph showing the amount of NO purification according to the temperature of the a-catalyst (II).
13 is a configuration diagram showing an exhaust gas purifying apparatus including a catalyst system according to an embodiment of the present invention.
14 is a configuration diagram showing an exhaust gas purifying apparatus including a catalyst system according to another embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

Throughout the specification, when an element is referred to as " comprising ", it means that it can include other elements as well, without excluding other elements unless specifically stated otherwise.

An embodiment of the present invention provides a catalyst of the following general formula (1).

[Chemical Formula 1]

_{AB 1 - y B 'y O} 3

At this time, A is a rare earth element and may be at least one selected from the group consisting of lanthanum, La, praseodymium, erbium, Er, neodymium and the like.

B is aluminum, Al, gallium, indium, In, or a combination thereof. B 'is palladium (Pd), platinum (Pt), rhodium rhodium, Rh), or a combination thereof, and the range of y is preferably 0.005? y? 0.05. The range of y is for the synthesis of perovskite catalysts in a range similar to the structural stability and the noble metal content of commercial three-way catalysts.

More specifically, the catalyst according to one embodiment of the present invention may be represented by the following formula (2).

(2)

LaAl _{1 - y} Pd _y O ₃

Here, the range of y is preferably 0.005? Y? 0.05.

According to an embodiment of the present invention, it is possible to simultaneously remove hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) present under gasoline exhaust gas conditions.

Another embodiment of the present invention provides a method of manufacturing a semiconductor device, comprising: (S1) preparing a metal precursor solution; (S2) adding a carboxylic acid to the metal precursor solution to prepare a mixed metal salt solution; And a step (S3) of drying and calcining the mixed metal salt solution.

First, in another embodiment of the present invention, in the above-described method for producing a catalyst, step (S1) of preparing a metal precursor solution may include dissolving a rare earth precursor, an aluminum precursor, and a palladium precursor in distilled water.

At this time, the content of the rare earth precursor, the aluminum precursor, and the palladium precursor is preferably in a molar ratio of 1: 0.95 to 0.995: 0.05 to 0.005. At this time, when the content of the rare earth precursor, the aluminum precursor, and the palladium precursor is within the above range, there is an advantage that a perovskite structure is formed.

More specifically, the rare earth precursor is, for _{example, La (NO 3) 3 ·} 6H 2 O, Pr (NO 3) 3 · 6H 2 O, Nd (NO 3) 3 · 6H 2 O, Er (NO 3) 3 · 5H ₂ O, or a combination thereof.

The aluminum precursor may be, for example, Al (NO ₃ ) ₃ .9H ₂ O, AlCl ₃ .6H ₂ O, or a combination thereof, but is not limited thereto.

The palladium precursor may be, for example, palladium nitrate, palladium chloride, or a combination thereof, but is not limited thereto.

In another embodiment of the present invention, the step (S2) of adding a carboxylic acid to the metal precursor solution to prepare a mixed metal salt solution is carried out by stirring for about 1 hour.

In this case, the content of the carboxylic acid is preferably in the range of 1 to 20% by weight, more than the content of the metal precursor solution. At this time, when the content of the carboxylic acid is more than 1 wt% or more than 20 wt% of the metal precursor solution, formation of complex compounds between the precursor metals becomes uneven have.

Wherein the carboxylic acid is selected from the group consisting of citric acid, acetic acid, oxalic acid, malonic acid, latic acid, malic acid, Lt; / RTI >

In another embodiment of the present invention, the step (S3) of forming a catalyst precursor by drying and calcining the mixed metal salt solution may include heating the mixed metal salt solution to a predetermined temperature, Slowly drying the distilled water over a certain portion first, and then completely drying the second portion.

Further, the dried mixed metal salt is baked. At this time, the firing may be performed at 500 to 800 ° C for 3 to 7 hours, more specifically at 600 to 700 ° C for 4 to 6 hours. When the temperature and time at the time of firing are equal to the above range, there is an advantage that the state of the catalyst is stabilized.

According to another embodiment of the present invention, there is provided a method of manufacturing a mixed metal salt, comprising: drying and firing the mixed metal salt solution; Thereafter, stabilizing the fired catalyst (S4) may be carried out.

At this time, the stabilization is performed in an atmosphere of oxygen and carbon monoxide, and may be performed at 500 to 700 ° C for 10 to 20 hours, more preferably at 550 to 600 ° C for 15 to 20 hours. When the temperature and time at the stabilization are equal to the above range, the stabilization is advantageously performed more efficiently.

More specifically, the stabilization may include injecting a background gas for 40 to 50 seconds (S41); 3% oxygen gas for 3 to 6 seconds to form an oxidizing atmosphere (S42); Injecting the background gas for 100 to 130 seconds (S43); And 3% carbon monoxide gas for 3 to 6 seconds to form a reducing atmosphere (S44).

At this time, the background gas contains 10% of H ₂ O, 10% of CO ₂ , and the remaining N ₂ .

Yet another embodiment of the present invention is a catalyst comprising the above-described catalyst; Oxygen Storage Capacity (OSC); And an alumina-based material.

In another embodiment of the present invention, the catalyst may be a combination of Pd and Al ₂ O ₃ , or may be a combination of Rh and an oxygen storage capacity (OSC).

In another embodiment of the present invention, the oxygen storage material can be Ce, Zr, Pr, Nd, La, Y, or a combination thereof.

Further, in another embodiment of the present invention, the alumina-based material may include Al ₂ O ₃ , La doped Al ₂ O ₃ , MgAl ₂ O ₄ , or a combination thereof.

More specifically, the catalyst system for purifying exhaust gases according to another embodiment of the present invention can be applied to a gasoline exhaust gas purifying apparatus.

13 is a configuration diagram showing an exhaust gas purifying apparatus including a catalyst system according to an embodiment of the present invention. 14 is a configuration diagram showing an exhaust gas purifying apparatus including a catalyst system according to another embodiment of the present invention.

13 and 14, the gasoline exhaust gas purifying apparatus is composed of a catalytic converter located at the rear end of a gasoline internal combustion engine operated in lambda (lambda) 1 and composed of two bricks, The devices are mounted in series.

More specifically, the WCC (Warming-up Catalytic Converter) is composed of a front brick and a rear brick.

First, the front brick is a redox catalyst composed of a palladium or palladium / rhodium catalyst. More specifically, the palladium catalyst is a combination of LaAl _{1 - y} Pd _y O ₃ , or LaAl _{1 - y} Pd _y O ₃ and Pd / alumina; Oxygen storage material; Alumina, wherein the palladium / rhodium catalyst comprises a combination of LaAl _{1 - y} Pd _y O ₃ , or LaAl _{1 - y} Pd _y O ₃ and Pd / alumina; Rhodium / oxygen storage material (OSC); Alumina. ≪ / RTI >

Rear brick, on the other hand, is a redox catalyst composed only of palladium / rhodium catalyst. More specifically, the palladium / rhodium catalyst comprises a combination of LaAl _{1 - y} Pd _y O ₃ , or LaAl _{1 - y} Pd _y O ₃ and Pd / alumina; Rhodium / oxygen storage material (OSC); Alumina. ≪ / RTI >

Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are only illustrative of the present invention and are not intended to limit the scope of the present invention.

Example

Example  One

(La: Al: Pd = 1: 0.984: 0.016) of the metal precursors La (NO ₃ ) ₃ .6H ₂ O, Al (NO ₃ ) ₃ .9H ₂ O and palladium nitrate solution, And dissolved in distilled water to prepare a metal precursor solution.

An additional 10 wt% excess (La: citric acid = 1: 1.1) of citric acid was added to the solution in the same molar amount of the metal precursor, and the mixture was stirred for 1 hour. Thereafter, the temperature was raised to 80 DEG C, and the distilled water was slowly evaporated while continuously maintaining the temperature for 8 hours with continuous stirring.

The catalyst precursor in a gel state in which a certain amount or more of distilled water was removed was dried in an oven at 110 ° C.

Finally, the dried catalyst precursor was calcined at 270 ° C pre-combustion and in an air atmosphere at 700 ° C for 5 hours to obtain LaAlO ₃ And a LaAl _{1 - y} Pd _y O ₃ (y = 0.016) perovskite catalyst were synthesized.

Example  2

Pd was carried on the LaAlO ₃ support prepared in Example 1 by impregnation, followed by drying in an oven at 110 ° C and firing in an air atmosphere at 500 ° C for 5 hours to complete a Pd / LaAlO ₃ catalyst preparation Respectively. The Pd content was set to 0.8 wt%.

Comparative Example  One

Pd was supported on the prepared Al ₂ O ₃ (γ-Al ₂ O ₃ , Alfa Aesar) support by impregnation, followed by drying in an oven at 110 ° C. and calcination in an air atmosphere at 500 ° C. for 5 hours Pd / Al ₂ O ₃ catalyst. The Pd content was set to 0.8 wt%.

evaluation

Activity evaluation ( light - off test , LOT )

(Activity evaluation condition)

The LOT of the catalyst was measured in a steady state using a fixed bed continuous flow reactor system and 0.5 g of powder sample was measured at 20/30 mesh size Of pellet powder.

The prepared catalyst was mixed with 0.7 cc of glass beads (size of 0.56-0.85 mm (20/30 mesh size)), mounted in a U-type stainless steel tube reactor, maintained in an isothermal state (Molten-salt bath furnace) was used. The concentration of the injected reaction gas was calculated as CO 1 vol%, C ₃ H ₆ 500 ppm, O ₂ 1 vol%, NO 500 ppm, H ₂ 0.3% by volume, 10% by volume of H ₂ O, and CO ₂ 10% by volume, and the remaining amount was Ar. The concentration of the reaction gas before and after the reaction was analyzed by GC (Gas Chromatography) (HP 6890, Agilent) in the case of H ₂ , O ₂ , CO, and C ₃ H _{6 and in} the case of NO, N ₂ O and NH ₃ FT-IR (Fourier Transform Infrared Spectroscopy) (Nicolet 6700, Thermo Electron Co.). All of the catalyst prior to the activity evaluation was pretreated in the region λ (lambda) = 1 (A / F = 14.7), activity evaluation is the stoichiometric air-fuel ratio than the O ₂ is a slightly excess λ = 1.01 (A / F = 14.8) in the region . During the activity evaluation, the gas hourly space velocity (GHSV) of the reactor was maintained at 100,000 h ^-1 .

(Evaluation results)

1. Initial activity evaluation

Before the catalytic activity evaluation, the catalysts prepared in Example 1, Example 2, and Comparative Example 1 were stabilized in oxygen and carbon monoxide atmosphere at 600 ° C for 16 hours, and initial activity was measured. At this time, the catalyst after stabilization is represented by 'd-catalyst'.

FIGS. 1 to 4 are graphs showing the purities of CO, C ₃ H ₆ , H ₂ , and NO according to the temperature of the d-catalyst.

In addition, Table 1 below shows the 50% purification temperature and the 20% purification temperature of the NO of CO, C ₃ H _6, and H ₂ obtained from the temperature increase of the activity evaluation d- catalyst.

Catalyst T ₅₀ (캜) T ₂₀ (캜) CO C ₃ H ₆ H ₂ NO Example 1
(d-LaAlPdO ₃ ) 231 251 209 151 Example 2
(d-Pd / LaAlO ₃₎ 217 235 208 184 Comparative Example 1
_{(d-Pd / Al 2 O} 3) 242 262 222 231

The catalyst of Example 1 (d-LaAlPdO ₃ ) and Example 2 (d-Pd / LaAlO ₃ ) were compared with those of Comparative Example 1 _{(d-Pd / Al 2 O} 3) superior purification performance of the catalyst and, in particular, the purifying performance of CO and C ₃ H ₆ in examples _{2 (d-Pd / LaAlO 3} ) catalyst, purification performance of NO in examples 1 (d-LaAlPdO ₃ ) The catalyst was found to be better.

2. Evaluation of thermal durability

Before evaluating the catalyst activity, the catalyst prepared in Example 1 was stabilized in oxygen and carbon monoxide atmosphere at 600 ° C for 16 hours, and then thermally treated at 1000 ° C for 6 hours and 24 hours for thermal durability evaluation. At this time, the catalyst after heat treatment for 6 hours is denoted by a-catalyst (I), and the catalyst after heat treatment for 24 hours is denoted by a-catalyst (II).

5 to 8 are graphs showing the amounts of purification of CO, C ₃ H ₆ , H ₂ , and NO according to the temperature of the a-catalyst (I).

In addition, Table 2 below shows the 50% purification temperature and the 20% purification temperature of the NO of CO, C ₃ H _6, and H ₂ obtained from the temperature rising Activity of the a- catalyst (I).

Catalyst T ₅₀ (캜) T ₂₀ (캜) CO C ₃ H ₆ H ₂ NO Example 1
(a-LaAlPdO ₃ (I)) 242 259 231 189 Example 2
_{(a-Pd / LaAlO 3 (} I)) 239 256 235 259 Comparative Example 1
_{(a-Pd / Al 2 O} 3 (I)) 259 282 250 293

Referring to Table 2, Example 1 (a-LaAlPdO ₃ (I)) It can be seen that the purification performance of CO, C ₃ H ₆ and H _{2 of the} catalyst is similar to that of the catalyst of Example 2 (a-Pd / LaAlO ₃ (I)), and the NO purification performance is similar to that of the above- Example 1 (a-LaAlPdO ₃ (I)) It can be seen that the catalyst is excellent. In addition, the cleaning performance of the catalyst of Comparative Example 1 (a-Pd / Al ₂ O ₃ (I)) is lowest regardless of the deterioration before and after the deterioration.

Thus, LaAlO ₃ Fe LaAlPdO ₃ is replaced with palladium in the B-site of the perovskite The catalyst can be seen that after six hours at 1000 ℃ than Pd / LaAlO ₃ catalyst heat treated, similar to the thermal stability.

9 to 12 are graphs showing the amounts of purification of CO, C ₃ H ₆ , H ₂ , and NO according to the temperature of the a-catalyst (II).

In addition, Table 3 below shows the 50% purification temperature and the 20% purification temperature of the NO of CO, C ₃ H _6, and H ₂ obtained from the temperature rising Activity of the a- catalyst (II).

Catalyst T ₅₀ (캜) T ₂₀ (캜) CO C ₃ H ₆ H ₂ NO Example 1
(a-LaAlPdO ₃ (II)) 245 267 235 204 Example 2
_{(a-Pd / LaAlO 3 (} II)) 253 281 244 283 Comparative Example 1
(a-Pd / Al ₂ O ₃ (II)) 285 316 277 355

Referring to Table 3, Example 1 (a-LaAlPdO ₃ (II)) (A-Pd / LaAlO ₃ (II)) catalyst in the same manner as in the above-described d-catalyst, a-catalyst (I) -LaAlPdO ₃ (II) It can be seen that the catalyst is excellent.

Thus, LaAlO ₃ Fe LaAlPdO ₃ is replaced with palladium in the B-site of the perovskite The catalyst can be seen that in 1000 ℃ 24 hours after the heat treatment, the thermal stability superior to Pd / LaAlO ₃ catalyst.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. As will be understood by those skilled in the art. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (19)

A catalyst of the following formula 1,
Oxygen Storage Capacity (OSC); And
Alumina based materials;
And an exhaust gas purifying catalyst system.
[Chemical Formula 1]
_{AB 1-y B 'y O} 3
(Where A is a rare earth element, B is Al, Ga, In, or a combination thereof, B 'is Pd, Pt, Rh, or a combination thereof, and the range of y is 0.005? Y? 0.05. )
The method according to claim 1,
Wherein the catalyst is a catalyst system for purification of exhaust gas having the following formula (2).
(2)
LaAl _1-y Pd _y O ₃
(Here, the range of y is 0.005? Y? 0.05.)
The method according to claim 1,
The catalyst
Preparing a metal precursor solution;
Adding a carboxylic acid to the metal precursor solution to prepare a mixed metal salt solution; And
Drying and firing the mixed metal salt solution;
Wherein the exhaust gas purifying catalyst system is produced by a method comprising the steps of:
The method of claim 3,
Preparing the metal precursor solution,
Wherein the rare earth precursor, the aluminum precursor, the palladium precursor, or a combination thereof is dissolved in distilled water.
5. The method of claim 4,
Wherein the molar ratio of the rare earth precursor: aluminum precursor: palladium precursor is 1: 0.95 to 0.995: 0.05 to 0.005.
5. The method of claim 4,
The rare earth precursor is _{La (NO 3) 3 · 6H} 2 O, Pr (NO 3) 3 · 6H 2 O, Nd (NO 3) 3 · 6H 2 O, Er (NO 3) 3 · 5H 2 O, or both Wherein the exhaust gas purifying catalyst system comprises:
5. The method of claim 4,
Wherein the aluminum precursor is Al (NO ₃ ) ₃ .9H ₂ O, AlCl ₃ .6H ₂ O, or a combination thereof.
5. The method of claim 4,
Wherein the palladium precursor is palladium nitrate, palladium chloride, or a combination thereof.
The method of claim 3,
Adding a carboxylic acid to the metal precursor solution to prepare a mixed metal salt solution,
Wherein the content of the carboxylic acid is 1 to 20% by weight more than the content of the metal precursor solution.
10. The method of claim 9,
The carboxylic acid may be used for purification of exhaust gas containing citric acid, acetic acid, oxalic acid, malonic acid, latic acid, malic acid, Catalyst system.
The method of claim 3,
Drying and firing the mixed metal salt solution,
Wherein the calcination is performed at 500 to 800 DEG C for 3 to 7 hours.
The method of claim 3,
Drying and firing the mixed metal salt solution; Since the,
And stabilizing the calcined catalyst. ≪ Desc / Clms Page number 19 >
13. The method of claim 12,
Wherein the stabilization is performed at 500 to 700 占 폚 for 10 to 20 hours.
14. The method of claim 13,
Wherein the stabilization is performed in an atmosphere of oxygen and a carbon monoxide atmosphere.
15. The method of claim 14,
The stabilization may include,
Injecting a background gas for 40 to 50 seconds;
Injecting 3 vol% oxygen gas for 3 to 6 seconds to form an oxidizing atmosphere;
Injecting the background gas for 100 to 130 seconds; And
3 vol% carbon monoxide gas is injected for 3 to 6 seconds to form a reducing atmosphere;
And a second step of,
The background gas of the exhaust gas purifying catalyst system comprises 10% by volume of H ₂ 0, 10% by volume of CO _2, and the balance denied N _2.
A gasoline exhaust gas purifying apparatus, which is located at the rear end of a gasoline internal combustion engine and comprises the catalyst system of claim 1.
delete The method according to claim 1,
Wherein the oxygen storage material is Ce, Zr, Pr, Nd, La, Y, or combinations thereof.
The method according to claim 1,
Wherein the alumina-based material comprises Al ₂ O ₃ , La-doped Al ₂ O ₃ , MgAl ₂ O ₄ , or a combination thereof.

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