JP2002079053A - Exhaust gas cleaning catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas cleaning catalyst having heat resistance higher than that of a conventional catalyst corresponding to the recent strengthing of the regulation on the exhaust gas. SOLUTION: The exhaust gas cleaning catalyst obtained by coating a refractory three-dimensional structure with a catalytically active component containing at least one of noble metals, a refractory inorganic oxide and zirconium oxide containing cerium and lanthanum. In this catalyst, the crystal structure of zirconium oxide containing cerium and lanthanum is a single structure of tetragonal zirconium oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NO), which are harmful components contained in exhaust gas from internal combustion engines such as automobiles.
The present invention relates to an exhaust gas purifying catalyst for simultaneously removing x).

[0002]

2. Description of the Related Art Various proposals have been made on an exhaust gas purifying catalyst for removing harmful components in exhaust gas discharged from an internal combustion engine (Japanese Patent Application Laid-Open No. 7-60117).

[0003] In recent years, various studies have been made, including improvement of engines, in order to respond to stricter exhaust gas regulations worldwide. As one of the most influential means, a method of increasing the temperature of the catalyst bed immediately after the start of the engine more quickly by making the position of the catalyst closer to the engine side to accelerate the ignition of the catalyst has been studied. Such a method of using a catalyst has excellent purification performance of exhaust gas immediately after the start of the engine, but since it is used near the engine, it is exposed to a higher temperature than in the past, so a catalyst having higher heat resistance is required. It will be.

[0004] Further, for the purpose of parts assurance, fuel cooling has been used to keep the temperature of members such as catalysts below a certain level. However, in order to respond to recent demands for low fuel consumption, fuel cooling must be performed. Therefore, the demand for heat resistance of the catalyst is increasing. Under such circumstances, it has not always been possible to say that the conventional catalysts meet the demand for heat resistance.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide an exhaust gas purifying catalyst having higher heat resistance than conventional ones in order to cope with the recent tightening of exhaust gas regulations.

[0006]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problem, and have found that one of the most important components in a three-way catalyst for a gasoline vehicle is the adsorption and desorption of oxygen. Attention was paid to an oxygen storage material having an action. To date, various types of cerium oxide have been used as oxygen storage materials. To date, zirconium oxide has been added, oxides of rare earth elements have been added, and cerium oxide has been dissolved in zirconium oxide in order to improve the heat resistance of the oxygen storage capacity of cerium oxide. A disclosed technique is disclosed (Japanese Patent No. 2659796).
Among these technologies, the reaction temperature zone is relatively low,
At 500 ° C., when cerium oxide is dissolved in zirconium oxide, the oxygen storage capacity per unit cerium oxide is highest.

Furthermore, it is found that the oxygen storage capacity and heat resistance can be further improved by dissolving other rare earth oxides, especially lanthanum oxide, together with zirconium oxide rather than dissolving only cerium oxide. know. However, in a conventional oxygen storage material, when cerium oxide or lanthanum oxide is dissolved in zirconium oxide, some components cannot be completely dissolved in zirconium oxide and independent cerium oxide or the like is formed. And the crystal structure was non-uniform.

Accordingly, in the present invention, as described below, a catalyst having higher heat resistance has been successfully developed by using an oxygen storage material having higher heat resistance. In other words, as an oxygen storage material having higher heat resistance, cerium oxide and lanthanum oxide are dissolved in zirconium oxide as a solid solution, and a uniform tetragonal oxide is formed without forming independent cerium oxide or the like. This is a catalyst using a composite oxide having a zirconium crystal structure. In addition, it was also confirmed that this composite oxide has a higher oxygen storage capacity at 400 to 500 ° C. than that of the conventional oxygen storage material after durability at 900 ° C. or more.

Accordingly, an object of the present invention is to provide a catalyst comprising a three-dimensional structure coated with a catalytically active component containing at least one noble metal, a refractory inorganic oxide, and a zirconium oxide containing cerium and lanthanum. The exhaust gas purifying catalyst is characterized in that the zirconium oxide containing cerium and lanthanum has a single crystal structure of tetragonal zirconium oxide.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The noble metal used in the present invention includes at least one selected from the group consisting of palladium, platinum and rhodium. The form of the noble metal is not particularly limited as long as it has catalytic activity. The amount of precious metal used is usually 0.0
It is 5 to 30 g, preferably 0.15 to 20 g. 0.
If the amount is less than 05 g, the catalytic activity at the initial stage and after the endurance is insufficient, while if it exceeds 30 g, the catalytic activity cannot be obtained in proportion to the amount used, which is not preferable. Here, the amount of the catalyst component such as a noble metal used per liter of the integrated structure refers to the apparent volume of the molded product itself when the catalyst component itself is molded, and the amount of the refractory three-dimensional structural component. Is displayed based on the apparent volume of the three-dimensional structure.

The refractory inorganic oxide (excluding zirconium oxide containing cerium and lanthanum and alkaline earth metal oxide) used in the present invention may be any one which is usually used as a catalyst carrier. For example, α-alumina, or activated alumina such as γ, δ, η, θ, titania, or zirconia, titania, silicon oxide or a composite oxide thereof, for example, alumina-titania, alumina-zirconia, titania-zirconia, etc. Activated alumina powder is preferred. The amount of refractory inorganic oxide used is
Usually, 10 to 300 g per liter of the integrated structure,
Preferably it is 50-250 g. If the amount is less than 10 g, the noble metal cannot be sufficiently dispersed and the durability is not sufficient. On the other hand, if the amount exceeds 300 g, the pressure loss of exhaust gas increases, which is not preferable.

The zirconium oxide containing cerium and lanthanum used in the present invention has a single crystal structure of tetragonal zirconium oxide.
This crystal structure can be confirmed by the X-ray diffraction method. In contrast to the conventional zirconium oxide containing cerium and lanthanum, which has various independent oxide peaks including cerium oxide, it is used in the present invention. In the resulting oxide, only the peak of tetragonal zirconium oxide appears. That is, it shows a tetragonal uniform crystal structure.

[0013] The zirconium oxide containing cerium and lanthanum usually has a mass ratio of (a) cerium to zirconium of 1: 8 to 1 in terms of CeO ₂ : ZrO _2.
1: 1, preferably 1: 5 to 1: 1; (b) the mass ratio of lanthanum to zirconium is calculated as La ₂ O ₃ ;
In O ₂ terms, 1: 1.5 to 1: 60, preferably 1:
1.5 to 1:40.

With respect to the method for producing zirconium oxide containing cerium and lanthanum, for example, the following two types can be mentioned as typical examples, but are limited to these methods unless they violate the gist of the present invention. is not.

(1) A zirconium solution such as zirconium oxychloride is hydrolyzed to obtain zirconium hydroxide, and a solution of a compound of cerium and lanthanum is added and mixed, neutralized by adding an alkali, washed, dried, Bake.

(2) A zirconium solution such as zirconium nitrate, a cerium solution such as cerium nitrate, and a lanthanum solution such as lanthanum nitrate are mixed, neutralized by adding an alkali, washed, dried and fired.

The supported amount of each catalyst component is, per liter of the three-dimensional structure, a precious metal amount of 0.05 to 30 g, a cerium amount of 10 to 100 g in terms of CeO ₂ , a zirconium amount of 10 to 100 g in terms of ZrO ₂ , The amount of lanthanum is La ₂ O ₃
0.1 to 50 g in conversion and 10 to 10
Preferably, it is 300 g. In addition, each amount of cerium, lanthanum, and zirconium is an amount contained in the zirconium oxide containing cerium and lanthanum.

Further, it is preferable to use an alkaline earth metal oxide, which is used in an amount of usually 0.1 to 50 g, preferably 1 to 30 g per liter of the integrated structure.
It is. If the amount is less than 0.1 g, particularly the heat resistance of the Pd-containing catalyst is insufficient, while if it exceeds 50 g, a result proportional to the amount used is not obtained, which is not preferable.

The amount of zirconium oxide containing cerium and lanthanum used is as follows:
Usually, it is 5-250 g, preferably 10-200 g. If it is less than 5 g, the durability and OSC performance are insufficient, while if it exceeds 250 g, the pressure loss of exhaust gas increases, which is not preferable.

Further, the catalyst containing Pd as a noble metal preferably contains an alkaline earth metal oxide from the viewpoint of durability and NOx purification ability, in addition to the above catalyst components. Examples of the alkaline earth metal oxide include oxides of barium, magnesium, calcium, and strontium, with barium being preferred.

The loading amount of each catalyst component is as follows: per liter of the three-dimensional structure, the amount of noble metal is 0.05 to 30 g, the amount of cerium is 10 to 100 g in terms of CeO ₂ , and the amount of zirconium is 10 to 100 g in terms of ZrO _2. , The amount of lantern is L
a ₂ O ₃ in terms of in 0.1 to 50 g, the refractory inorganic oxide content 1
0 to 300 g and the amount of alkaline earth metal oxide is 0.1
Preferably, it is ５０50 g. In addition, each amount of cerium, lanthanum, and zirconium is an amount contained in the zirconium oxide containing cerium and lanthanum.

Examples of the refractory three-dimensional structure covering the above-mentioned catalyst component include a honeycomb carrier and the like, but a monolithic honeycomb structure is preferable. Examples thereof include a monolith honeycomb carrier, a metal honeycomb carrier, and a plug honeycomb carrier. be able to.

The monolithic carrier may be any one usually referred to as a ceramic honeycomb carrier. In particular, cordierite, mullite, α-alumina, zirconia, titania, titanium phosphate, aluminum titanate, betalite, spongemen, alumino A honeycomb carrier made of silicate, magnesium silicate, or the like is preferable, and cordierite is particularly preferable.
In addition, an integrated structure using an oxidation-resistant heat-resistant metal such as stainless steel or an Fe—Cr—Al alloy is used.

These monolith carriers are manufactured by an extrusion molding method, a method of winding a sheet-like element, or the like. The shape of the gas passage port (cell shape) may be any of a hexagon, a square, a triangle, and a corrugation. The cell density (the number of cells per unit square area of 6.45 cm ² (1 square inch)) is sufficient if it is 100 to 1500 cells, and preferably 200 to 900 cells.

In the present invention, the method of coating the catalyst component is not particularly limited, but usually, the impregnation method is suitably used.

The catalyst according to the present invention can be prepared, for example, by the following method. First, into a predetermined amount of an aqueous solution of a nitrate of a noble metal such as platinum, a powder of a refractory inorganic oxide such as alumina and a powder of a zirconium oxide containing cerium and lanthanum are thoroughly mixed and impregnated. After that, 80-250 ° C, preferably 100
Drying at a temperature of ~ 150C, then 300-850C,
Preferably at a temperature of 400 to 700 ° C. for 0.5 to 5 hours,
Preferably, firing is performed for 1 to 2 hours. When Pd is contained as a noble metal, it is preferable to use an alkaline earth metal oxide. Such an alkaline earth metal oxide or a salt thereof such as a nitrate or an acetate is added at this stage. When all oxide powders are used except for the noble metal, the next wet pulverization step may be performed without passing through the drying and baking steps.

Next, the obtained powder is wet-pulverized using a ball mill or the like to form a slurry, and the thus obtained slurry of the catalyst composition is impregnated with a refractory ternary structure made of cordierite or the like. , After removing excess slurry, 80
To 250 ° C, preferably 100 to 150 ° C, and if necessary, 300 to 850 ° C, preferably 400 to
Firing at 700 ° C. for 0.5 to 3 hours, preferably 1 to 2 hours. The amount of the catalytically active component carried is not particularly limited, and is usually in the range of 30 to 400 g per liter of the catalyst.

It is also possible to prepare a slurry having the same or different composition by the same method as described above and impregnate it to form a multilayer coating. Furthermore, it is also possible to impregnate the noble metal salt later in the form of an aqueous solution or the like.

The catalyst of the present invention is excellent in simultaneously purifying carbon monoxide, hydrocarbons and nitrogen oxides contained in exhaust gas from an internal combustion engine, particularly a gasoline engine. Further, the catalyst is preferably installed at a position close to the engine from the viewpoint of efficient hydrocarbon purification.

[0030]

The present invention will be described below in more detail with reference to Examples, but it should not be construed that the invention is limited thereto unless it departs from the gist of the present invention.

(Reference Example) First, X of the cerium and lanthanum-containing zirconium oxide used in the present invention was used.
FIG. 1 shows a spectrum chart by a line diffraction method, and FIG. 2 shows a spectrum chart by a conventional X-ray diffraction method of a zirconium oxide containing cerium and lanthanum. From FIG. 2, the conventional oxide has various independent oxide peaks including cerium oxide, while from FIG. 1, the oxide used in the present invention is a tetragonal zirconium oxide. There was only a peak of a uniform crystal structure. FIG.
Shows the case of Example 1 as a representative example. This evaluation was performed after aging for 10 hours at 1000 ° C. in air.

Next, a comparison of the oxygen storage amounts showing the ability of the zirconium oxide containing cerium and lanthanum used in the present invention and the conventional zirconium oxide containing cerium and lanthanum to desorb and desorb oxygen is shown. It is shown in FIG.

[0033]

[Table 1]

Measurement method: After reduction in H ₂ at 450 ° C. for 30 minutes, O ₂ was pulsed to measure O ₂ consumption.

As is clear from Table 1, the oxide used in the present invention has about three times the oxygen storage capacity as compared with the conventional oxide. This evaluation was performed after aging at 1000 ° C. in air for 10 hours.

(Example 1) Zirconium oxide 4 in mass ratio
0 g, cerium oxide 20 g, lanthanum oxide 15 g
After hydrolyzing the zirconium oxychloride solution to obtain zirconium hydroxide, an aqueous nitric acid solution of cerium and lanthanum is added and mixed, neutralized by adding an alkali, and then washed and dried (at 120 ° C. for 2 hours). ), Firing (70
(0 ° C. for 1 hour) to obtain a zirconium-cerium-lanthanum composite oxide (A1).

40 g of the obtained (A1) was mixed with 2 g of palladium.
In an aqueous solution of palladium nitrate. afterwards,
After sufficiently drying at 150 ° C., the mixture was calcined at 500 ° C. for 1 hour to obtain a palladium-containing zirconium-cerium-lanthanum composite oxide (B1).

Next, 30 g of alumina (γ-Al ₂ O ₃ ) having a specific surface area of 150 m ² / g is impregnated with an aqueous palladium nitrate solution containing 2 g of palladium, dried sufficiently at 150 ° C., and calcined at 500 ° C. for 1 hour. Thus, palladium-containing alumina was obtained.

32 g of the obtained palladium-containing alumina
(A1) 35 g, (B1) 42 g, specific surface area 150
45 g of m ² / g alumina (γ-Al ₂ O ₃ ), 30 g of barium hydroxide as an oxide, 5 g of acetic acid,
150 g of ion-exchanged water was put into a ball mill pot together with media balls, and wet-pulverized for 15 hours to obtain an aqueous slurry.

The obtained aqueous slurry was applied to a cordierite monolith carrier (manufactured by Nippon Insulator: cell density: 400 cells /
After being immersed in 6.45 cm ² (1 square inch), outer diameter 33 mm × length 76 mm), taken out, excess slurry was blown with compressed air, then dried (150 ° C. for 2 hours), and calcined (500 ° C. For 1 hour) to obtain Catalyst 1.

(Example 2) The amounts of zirconium oxychloride, cerium and lanthanum were changed so that the mass ratio was 12.5 g of cerium oxide and 9.5 g of lanthanum oxide with respect to 25 g of zirconium oxide. Example 1
In the same manner as in the above, a zirconium-cerium-lanthanum composite oxide (A2) was obtained.

Next, instead of (A1) 40 g, (A2) 47
g2, except that g was used, in the same manner as in Example 1, palladium-containing zirconium-cerium-lanthanum composite oxide (B2)
I got

49 g of the obtained (B2) and a specific surface area of 15
0m^Two/ G of alumina (γ-Al_TwoO _Three) 103 g, and
Barium hydroxide equivalent to 10 g as oxide and acetic acid 5
g, 150 g of ion-exchanged water in a ball mill for 15 hours
After pulverizing to obtain an aqueous slurry, the same as in Example 1,
Catalyst 2 was obtained by coating on a Norris carrier.

Example 3 In the same manner as in Example 1, zirconium-cerium-lanthanum composite oxide (A1) 47
g was impregnated with an aqueous palladium nitrate solution containing 2 g of palladium to obtain a palladium-containing zirconium-cerium-lanthanum composite oxide (B3) in the same manner as in Example 1.

Separately, 10 g of alumina (γ-Al ₂ O ₃ ) having a specific surface area of 150 m ² / g was impregnated with an aqueous rhodium nitrate solution containing 0.2 g of rhodium. Then, after sufficiently drying at 150 ° C., it was baked at 500 ° C. for 1 hour to obtain rhodium-containing alumina.

10.2 g of the obtained rhodium-containing alumina
28 g of (A1), 49 g of (B3) and a specific surface area of 15
65 g of alumina (γ-Al ₂ O ₃ ) of 0 m ² / g, barium hydroxide equivalent to 10 g as an oxide, and acetic acid 5
g and 150 g of ion-exchanged water were wet-pulverized with a ball mill for 15 hours to obtain an aqueous slurry, and then coated on a monolithic carrier in the same manner as in Example 1 to obtain Catalyst 3.

Example 4 A zirconium-cerium-lanthanum composite oxide (A1) was prepared in the same manner as in Example 1, and then a palladium-containing zirconium-cerium-lanthanum composite oxide was prepared in the same manner as in Example 3. A product (B3) was obtained.

49 g of the obtained (B3) and a specific surface area of 15
43 g of 0 m ² / g alumina (γ-Al ₂ O ₃ ), 10 g of barium hydroxide as an oxide, and acetic acid 4 g
g and 150 g of ion-exchanged water were wet-ground with a ball mill for 15 hours to obtain an aqueous slurry. The obtained aqueous slurry was used to coat a monolithic carrier in the same manner as in Example 1, and
d A catalyst coating (C4) layer was obtained.

Separately, 10.2 g of rhodium-containing alumina obtained in the same manner as in Example 3, 13 g of (A1), and alumina (γ-Al ₂ O ₃ ) 47 having a specific surface area of 150 m ² / g were used.
g, 5 g of acetic acid, and 126 g of ion-exchanged water were wet-ground with a ball mill for 15 hours to obtain an aqueous slurry.

The obtained aqueous slurry was used to coat the Pd catalyst coating layer (C4) to obtain a catalyst 4.

Example 5 A mass ratio of 40 g of zirconium oxide to 10 g of cerium oxide and 10 g of lanthanum oxide
g in the same manner as in Example 1 except that the amounts of zirconium oxychloride, cerium and lanthanum were changed so as to obtain g.
5) was prepared.

47 g of the obtained (A5) was mixed with 2 g of palladium.
In the same manner as in Example 1, a palladium-containing zirconium-cerium-lanthanum composite oxide (B5) was obtained.

10.2 g of rhodium-containing alumina obtained in the same manner as in Example 3, 13 g of (A5) and (B5) 4
9 g of alumina (γ-Al ₂₎ having a specific surface area of 150 m ² / g.
80 g of O ₃ ), barium hydroxide equivalent to 10 g as an oxide, 5 g of acetic acid, and 150 g of ion-exchanged water were wet-pulverized with a ball mill for 15 hours to obtain an aqueous slurry. Using the obtained aqueous slurry, a catalyst 5 was obtained by coating a monolithic carrier in the same manner as in Example 1.

Example 6 In the same manner as in Example 5, a zirconium-cerium-lanthanum composite oxide (A5) and a palladium-containing zirconium-cerium-lanthanum composite oxide (B5) were prepared.

49 g of the obtained (B5) and a specific surface area of 15
0m^Two/ G of alumina (γ-Al_TwoO _Three) 43 g, and
Barium hydroxide equivalent to 10 g as oxide and acetic acid 5
g, 150 g of ion-exchanged water in a ball mill for 15 hours
Pulverize to an aqueous slurry and use the obtained aqueous slurry
Then, in the same manner as in Example 4, a Pd catalyst coating layer (C6) was obtained.
Was.

Separately, 10.2 g of rhodium-containing alumina obtained in the same manner as in Example 3, 13 g of (A5), and alumina (γ-Al ₂ O ₃ ) 47 having a specific surface area of 150 m ² / g were used.
g, 4 g of acetic acid, and 126 g of ion-exchanged water were wet-ground with a ball mill for 15 hours to obtain an aqueous slurry.

The obtained aqueous slurry was coated on a Pd catalyst coating layer (C6) to obtain a catalyst 6.

(Example 7) In Example 6, rhodium was added.
Specific surface area 150m in place of alumina containing 10.2g ^Two/ G
Alumina (γ-Al_TwoO_Three) 10 g of rhodium 0.2 g
Contains rhodium nitrate aqueous solution containing platinum and 0.2 g of platinum
Impregnated with an aqueous solution of platinum nitrate, and obtained in the same manner as in Example 3.
Other than using 10.4 g of platinum-rhodium-containing alumina
In the same manner as in Example 6, catalyst 7 was obtained.

(Comparative Examples 1 to 7) In preparing a zirconium-cerium-lanthanum composite oxide, zirconium hydroxide obtained by hydrolysis of zirconium oxychloride using zirconium as a raw material was replaced with a corresponding amount of zirconium oxide. Catalysts were prepared in the same manner as in Examples 1 to 7, except that oxides having a crystal structure other than tetragonal were prepared. FIG. 2 shows the crystal structure of Comparative Example 1 as a representative example.

Comparative Examples 8 to 9 Instead of the zirconium-cerium-lanthanum composite oxide, zirconium oxide 4
An aqueous cerium nitrate solution was added to zirconium oxide and mixed so that the amount of cerium oxide became 20 g with respect to 0 g, and the mixture was dried.
Catalysts were prepared in the same manner as in Examples 1 and 3, except that a zirconium-cerium composite oxide having a crystal structure other than the tetragonal system obtained by firing was used.

Comparative Example 10 Zirconium-Cerium-
Instead of lanthanum composite oxide, zirconium oxide 25
g of zirconium oxide was added to and mixed with zirconium oxide so as to obtain 12.5 g of cerium oxide, and the mixture was dried and calcined to obtain a zirconium-cerium composite oxide having a crystal structure other than tetragonal. Prepared a catalyst in the same manner as in Example 7.

[0062]

[Table 2]

The obtained catalyst had the catalyst components shown in Table 2 per liter of the integrated structure.

(Evaluation) Examples 1 to 7 and Comparative Examples 1 to 10
The catalyst obtained in the above was evaluated for catalytic activity after engine durability.

Using a commercially available electronically controlled engine,
A multi-converter filled with each catalyst was installed in the exhaust system of the engine, and a durability test was performed.

The engine is operated in a mode operation in which steady operation is performed for 60 seconds and deceleration is performed for 6 seconds (the fuel is cut during deceleration, and the catalyst is exposed to a high-temperature oxidizing atmosphere). The catalyst was durable for 50 hours under the condition of ℃. The evaluation of the catalyst performance after the endurance was carried out by using a commercially available engine of an electronic control system and installing a multi-converter filled with each catalyst in the exhaust system of the engine. The three-way performance of the catalyst was such that the catalyst inlet temperature was 400 ° C and the space velocity was 25.
Evaluation was performed under the condition of 000 hr ^-1 . At this time, a 1 Hz sine wave type signal is introduced from an external oscillator into the control unit of the engine, and the air-fuel ratio (A / F) is set to ± 1.0.
A / F, the average air-fuel ratio was continuously changed while oscillating at 1 Hz, and the catalyst inlet and outlet gas compositions at this time were simultaneously analyzed to find that the average air-fuel ratio A / F was from 15.1 to 14.1. The purification rates of CO, HC and NOx were determined.

The thus obtained CO, HC and N
A ternary characteristic curve is created by plotting the purification rate of Ox versus the inlet air-fuel ratio on a graph, and the purification rate at the intersection (crossover point) of the CO and NOx purification curves and the HC purification rate at the A / F value at the intersection. Are shown in Table 3.

The purifying performance of the catalyst at a low temperature is determined by fixing the average air-fuel ratio A / F = 14.6 while vibrating the gas under the condition of the air-fuel ratio of ± 0.5 A / F (1 Hz). And a heat exchanger was installed in front of the catalytic converter of the engine exhaust system, and the temperature of the catalyst inlet gas was set to 200 to 50.
The temperature was changed at a constant heating rate (20 ° C./min) to 0 ° C., and the composition of the gas at the inlet and outlet of the catalyst was analyzed.
And the NOx purification rate was determined. The temperature (light-off temperature) at which the purification rates of CO, HC and NOx thus obtained reached 50% was measured, and Table 3 was obtained.
Shown in

[0069]

[Table 3]

Table 3 shows that the catalyst of the present invention can efficiently remove the three components of CO, HC and NOx simultaneously. Further, it can be seen that the heat resistance is improved as compared with the conventional catalyst.

[0071]

According to the present invention, it is possible to simultaneously remove carbon monoxide, hydrocarbons and nitrogen oxides contained in exhaust gas from an internal combustion engine such as an automobile. further,
Since the catalyst of the present invention contains a zirconium oxide containing cerium and lanthanum, it has excellent heat resistance and durability.

[Brief description of the drawings]

FIG. 1 is a chart of a zirconium oxide containing cerium and lanthanum used in the present invention by an X-ray diffraction method.

FIG. 2 is a chart of a conventional zirconium oxide containing cerium and lanthanum by an X-ray diffraction method.

Continuation of front page (71) Applicant 395016659 65 CHALLENGER ROAD R IDGEFIELD PARK, NEW JERSEY 07660 U.S.A. S. A. (72) Inventor Shigera Taniguchi 992, Nishioki, Okihama-shi, Abashiri-ku, Himeji-shi, Hyogo Pref. (Ref.) BC72B CA03 CA07 CA08 CA09 DA06 EA19 EC03Y EC25 ED06 EE09 FA02 FA03 FB14 FB23

Claims (2)

[Claims] 1. A catalyst in which a refractory three-dimensional structure is coated with a catalytically active component containing at least one noble metal, a refractory inorganic oxide, and a zirconium oxide containing cerium and lanthanum. An exhaust gas purifying catalyst, characterized in that the zirconium oxide containing carbon has a single structure of tetragonal zirconium oxide. 2. The catalyst according to claim 1, further comprising an alkaline earth metal oxide.