JPH0523599A - Catalyst for decontaminating exhaust gas - Google Patents

Abstract

PURPOSE:To simultaneously remove hydrocarbon(HC), carbon monoxide(CO) and nitrogen oxide (NOx) which are harmful components discharged from an internal combustion engine such as an automobile. CONSTITUTION:A catalyst for decontaminating exhaust gas is obtained by coating a honeycomb carrier having an integral structure with the catalytic composition which incorporates barium sulfate carried with platinum group metal wherein platinum group metal is carried on barium sulfate, refractory inorganic oxide and rare earth oxide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying catalyst. More specifically, the present invention relates to an exhaust gas purifying catalyst that simultaneously removes harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) emitted from internal combustion engines of automobiles, In particular, the present invention relates to an exhaust gas purifying catalyst that has excellent durability even when used under severe conditions such as a high temperature oxidizing atmosphere, and that has high purification performance at low temperatures against the above harmful components.

[0002]

2. Description of the Related Art Conventionally, in a catalyst for purifying exhaust gas discharged from an internal combustion engine of an automobile or the like, a platinum group metal is supported in a high dispersion on a high surface area refractory inorganic oxide such as activated alumina. Although the activity is high, platinum group metal particles grow when exposed to severe conditions such as high temperature oxidizing atmosphere, and a large decrease in performance was observed due to unfavorable interaction with carrier materials such as alumina and cocatalyst components such as ceria. . In particular, when activated alumina is used as the platinum group metal carrier material, there is a phase transition to α-alumina at a high temperature of 900 ° C. or higher, and the deterioration of the catalytic performance is unavoidable.

For the above problems, for example, US Pat. No. 423
3189 and U.S. Pat. No. 4,172,047 propose the use of zirconia or α-alumina as a carrier material that does not interact with the platinum group metal, but does not suppress the particle growth of the platinum group metal and has sufficient performance. Absent. Further, when a platinum group metal is supported on activated alumina, it has been confirmed that activated alumina, which is a carrier substance, elutes when an acidic slurry is prepared, which is one of the causes of deterioration of catalytic performance.

On the other hand, in JP-A-61-234931 and JP-A-62-149343, rare earth elements such as La and Nd and B are added to activated alumina which is a platinum group metal carrier material.
Although a method of suppressing the phase transition to α-alumina by adding an alkaline earth metal element such as a or Sr is disclosed, the effect is not sufficient, and conversely, the above-mentioned additive is a platinum group metal or a cocatalyst. However, there is a problem that the cerium oxide, which is the above, is adversely affected and the catalyst performance is deteriorated, and the slurry properties are deteriorated.

[0005]

Therefore, an object of the present invention is to provide a novel exhaust gas that effectively utilizes platinum group metals and does not cause a significant deterioration in catalyst performance even when used under high temperature conditions such as engine exhaust gas. It is to provide a purification catalyst.

[0006]

Means for Solving the Problems As a result of earnest studies by the present inventors, a catalyst containing platinum group metal-supported barium sulfate in which a platinum group metal is supported on barium sulfate has a temperature of 900 ° C. or higher, particularly 1000 ° C. or higher. The inventors have found that they maintain excellent catalyst performance even when used at high temperatures, and have completed the present invention.

According to the present invention, there is provided an integrated structure of a catalyst composition comprising a platinum group metal supported on barium sulfate, a refractory inorganic oxide such as activated alumina, and a rare earth oxide such as cerium oxide. The present invention is achieved by an exhaust gas purifying catalyst, which is obtained by coating the honeycomb carrier of the present invention.

The barium sulfate used is not particularly limited, and may be a commercially available product, or a product obtained by filtering and washing a white precipitate obtained by adding dilute sulfuric acid to an aqueous barium salt solution. It is known that the specific surface area of barium sulfate is usually about 0.1 to 10 m ² / g and is stable up to 1200 ° C. or higher. This barium sulfate can be used in an amount of 1 to 50 g per liter of exhaust gas purifying catalyst.

As the platinum group metal according to the present invention, platinum group metals such as platinum, palladium and rhodium are used alone or in combination, and 0.1 to 5.0 g can be used per 1 liter of exhaust gas purifying catalyst.

These platinum group metals can be supported on the above barium sulfate by an ordinary method. For example, in the impregnation method, barium sulfate supporting platinum group metal is obtained by impregnating barium sulfate with a salt solution of a platinum group metal, followed by drying and firing. The supported concentration of the platinum group metal on barium sulfate is 0.5 to 30% by weight, preferably 1 to
It is supported in the range of 20% by weight. When two or more platinum group metals are contained in the catalyst composition, all of them are supported on the same barium sulfate, separately supported on barium sulfate, or partially supported on barium sulfate and the rest is refractory. A method of loading on an inorganic oxide or a rare earth oxide can be used.

The refractory inorganic oxide may be an oxide of alumina, silica, titania, or zirconia, or a complex oxide or mixture thereof, preferably activated alumina. This refractory inorganic oxide is 30 to 30 per liter of exhaust gas purifying catalyst.
0 g can be used.

Next, as a method of adding the rare earth oxide to the catalyst composition, a precursor compound which is in the form of an oxide upon firing or in use, is prepared from a compound such as an oxide, a carbonate or a hydroxide. Or a method of supporting the precursor compound on a refractory inorganic oxide such as activated alumina. In this case, in the range of 0.1 to 50% by weight with respect to the refractory inorganic oxide. It is preferable to carry.
Examples of the rare earth oxide include cerium, lanthanum, neodymium, and the like, but it is particularly preferable to use cerium oxide, and 5 to 100 g can be used per liter of exhaust gas purifying catalyst.

The thus obtained catalyst composition containing barium sulfate supporting platinum group metal, refractory inorganic oxide and rare earth oxide is made into an aqueous slurry by a usual method using a ball mill or the like to form a monolith structure. The resulting honeycomb carrier is coated with it, then dried and fired if necessary to obtain a finished catalyst.

Examples of the monolith carrier used in the present invention include ceramic monolith carriers such as cordierite and mullite, and metal monolith carriers such as stainless steel and Fe—Cr—Al alloy.

[0015]

[Effect] The catalyst for purifying exhaust gas of the present invention is characterized in that the platinum group metal is supported on barium sulfate. Barium sulphate is insoluble in water, hardly elutes during slurry preparation, and barium sulphate is a thermally stable substance that hardly changes even when exposed to high temperatures, so the platinum group metal is sufficiently fixed. .

Although the details are not clear, it is considered that vanium sulfate has a preferable interaction with the platinum group metal and has an effect of suppressing particle growth of the platinum group metal, for example. As a result, the platinum group metal can be effectively used without significant deterioration in catalytic performance even when exposed to high temperature conditions of 900 ° C. or higher.

Specific examples will be described below, but the examples are not limited to these examples as long as the object of the present invention is not impaired.

[0018]

Example 1 20 g of barium sulfate having a specific surface area of 5 m ² / g was impregnated with a mixed aqueous solution of dinitrodiaminoplatinum containing 2.0 g of platinum and rhodium nitrate containing 0.4 g of rhodium and dried at 150 ° C., and then 500 The barium sulfate carrying platinum group metal was prepared by firing at ℃ for 1 hour. A monolithic carrier made of cordierite was obtained by pulverizing the barium sulfate supporting platinum group metal thus obtained, 80 g of commercially available cerium oxide, and 200 g of activated alumina having a specific surface area of 150 m ² / g in a ball mill for 15 hours. (40
0 cell / square inch) was dipped, the excess slurry was blown off with compressed air, and then dried at 150 ° C. for 2 hours to obtain a finished catalyst (1).

[0019]

Comparative Example 1 Platinum was prepared by impregnating 200 g of activated alumina with a mixed aqueous solution of dinitrodiamino platinum containing 2.0 g of platinum and rhodium nitrate containing 0.4 g of rhodium, drying at 150 ° C., and then firing at 500 ° C. for 1 hour. A group metal-supported alumina was prepared. The platinum group metal-supported alumina thus obtained, 80 g of commercially available cerium oxide, and 20 g of barium sulfate were pulverized with a ball mill to obtain an aqueous slurry. Thereafter, a comparative catalyst (A) was obtained in the same manner as in Example 1.

[0020]

Comparative Example 2 A comparative catalyst (B) was obtained in the same manner as in Comparative Example 1 except that 22 g of barium nitrate was used instead of barium sulfate.

[0021]

Example 2 40 g of barium sulfate was impregnated with a mixed aqueous solution of dinitrodiaminoplatinum containing 2.0 g of platinum and rhodium nitrate containing 0.4 g of rhodium, dried at 150 ° C., and then calcined at 500 ° C. for 1 hour to obtain platinum. A group metal-supported barium sulfate was prepared. Next, 320 g of a cerium nitrate aqueous solution (25% by weight) was impregnated into 180 g of activated alumina to obtain 150 °
After drying in, the mixture was baked at 500 ° C. for 1 hour to prepare cerium oxide-supported alumina. The two types of powder thus obtained were crushed with a ball mill to obtain an aqueous slurry. Thereafter, a completed catalyst (2) was obtained in the same manner as in Example 1.

[0022]

Example 3 A finished catalyst (3) was obtained in the same manner as in Example 2 except that 2.0 g of platinum and 0.4 g of rhodium were respectively supported on 20 g of barium sulfate.

[0023]

Comparative Example 3 A comparative catalyst (C) was obtained in the same manner as in Example 2 except that 40 g of α-alumina having a specific surface area of 3 m ² / g was used in place of barium sulfate.

[0024]

Example 4 30 g of barium sulfate having a specific surface area of 5 m ² / g was impregnated with a mixed aqueous solution of palladium nitrate containing 2.0 g of palladium and rhodium nitrate containing 0.4 g of rhodium, dried at 150 ° C., and then 500 ° C. Then, it was baked for 1 hour to prepare barium sulfate carrying platinum group metal. The platinum group metal-supported barium sulfate, 80 g of commercially available cerium oxide, and 190 g of activated alumina having a specific surface area of 150 m ² / g were wet-ground for 15 hours with a ball mill to obtain an aqueous slurry.
Thereafter, a completed catalyst (4) was obtained in the same manner as in Example 1.

[0025]

Comparative Example 4 Activated alumina having a specific surface area of 150 m ² / g was wet pulverized with a ball mill to prepare an aqueous slurry, the activated alumina was coated on the monolith carrier, and the monolith carrier was immersed in an aqueous cerium nitrate solution and dried. 1 at ℃
After calcination for a period of time to support cerium, it is then immersed in an aqueous solution of palladium nitrate and rhodium nitrate and dried, then 50
The platinum group metal was supported by firing at 0 ° C. for 1 hour. The monolithic carrier thus obtained was immersed in an aqueous barium acetate solution, dried and then calcined at 500 ° C. for 1 hour to obtain a comparative catalyst (D).

[0026]

Test Example Catalysts 1 to 4 obtained from the examples and catalysts A to D obtained from the comparative examples were tested for catalyst performance after engine running. The endurance engine uses an electronically controlled engine (8 cylinders 4400cc) and carries out a mode operation of 60 seconds of steady operation and 6 seconds of deceleration (fuel is cut and the catalyst is exposed to a high-temperature oxidizing atmosphere during deceleration), and the catalyst temperature is increased in steady operation. The catalyst was aged for 50 hours under the condition of 1000 ° C. The catalyst was evaluated using an 1800 cc electronically controlled engine, CO at a catalyst inlet temperature of 450 ° C.,
The results of measuring the purification rates of HC and NOx are shown in Table 1.

[0027]

[Table 1]

From the results shown in Table 1, it is clear that the exhaust gas purifying catalyst disclosed in the present invention is an excellent catalyst with little deterioration in performance even when used under severe conditions such as a high temperature oxidizing atmosphere.

Continued front page    (72) Inventor Tomohisa Ohata             Hyogo prefecture Himeji city             1 Inside Japan Catalyst Research Institute

Claims (2)

[Claims] 1. A honeycomb carrier having an integral structure is coated with a catalyst composition containing a platinum group metal-supported barium sulfate in which a platinum group metal is supported on barium sulfate, a refractory inorganic oxide and a rare earth oxide. An exhaust gas purifying catalyst characterized by being made at the most. 2. At least one platinum group metal selected from the group consisting of platinum, palladium and rhodium is supported on barium sulfate so as to have a supported concentration of 0.5 to 30% by weight with respect to barium sulfate. The catalyst according to item 1.