JPH05237390A - Catalyst for purification of exhaust gas - Google Patents

Abstract

PURPOSE:To obtain a production method of catalyst for purification of exhaust gas which can simultaneously remove hydrocarbons, carbon monoxide and nitrogen oxides exhausted from an internal combustion engine such as an automobile even at a low temp. and has excellent durability even when used under severe conditions such as an oxidizing, atmosphere at high temp. CONSTITUTION:This catalyst for purification of exhaust gas consists of a one- body structure coated with a catalyst component. This catalyst component contains a refractory inorg. oxide to which barium is fixed, platinum metals, and cerium compds. The inorg. oxide with barium fixed is obtd. by impregnating a refractory inorg. oxide with a barium salt soln. and treating the impregnated material with sulfuric acid. Or, the refractory inorg. oxide may be added.

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 hydrocarbons (H 2) which are harmful components emitted from internal combustion engines such as automobiles.
C), an exhaust gas purifying catalyst that simultaneously removes carbon monoxide (CO) and nitrogen oxides (NOx) has excellent durability even when used under severe conditions such as a high temperature oxidizing atmosphere, In addition, the present invention relates to an exhaust gas purifying catalyst having a high purification performance at low temperatures against the above-mentioned harmful components.

[0002]

2. Description of the Related Art Conventionally, in a catalyst for purifying exhaust gas emitted from an internal combustion engine of an automobile or the like, a platinum group metal is supported on a high surface area refractory inorganic oxide such as activated alumina in a highly dispersed manner, so that the initial activation However, when exposed to harsh conditions such as a high temperature oxidizing atmosphere, the platinum group metal particles grow, and a large decrease in performance is observed due to unfavorable interactions with carrier materials such as alumina and cocatalyst components such as ceria. In particular, when activated alumina is used as a carrier material for platinum group metals, at a high temperature of 900 ° C. or higher, a part of it undergoes a phase transition to α-alumina, and a decrease in catalytic performance is unavoidable. To solve the above problems, Japanese Patent Laid-Open No. 61-2
No. 34931 and JP-A-62-149343, a phase transition to α-alumina by adding a rare earth element such as lanthanum and neodymium or an alkaline earth metal element such as barium and strontium to activated alumina which is a carrier material of a platinum group metal. A method of suppressing is disclosed. However, the above-mentioned additives are easily eluted when preparing an acidic slurry in the catalyst production to deteriorate the slurry property, or lanthanum, barium, etc., which are additional components when dried after being coated on a monolith carrier, are unevenly distributed in the catalyst layer. The desired effect was not obtained. Particularly for barium, it has been found by the present inventors that although barium has an effect of stabilizing activated alumina, it unfavorably interacts with cerium which is a co-catalyst component. was there.

[0003]

Therefore, an object of the present invention is to utilize a platinum group metal effectively and to purify a novel exhaust gas which does not deteriorate the catalytic performance even when used under high temperature conditions such as engine exhaust gas. It is to provide a catalyst for use.

[0004]

As a result of earnest efforts, the present inventors have made a catalyst composition a refractory inorganic oxide obtained by immobilizing barium with sulfuric acid on a refractory inorganic oxide. The inventors have found that the above problems can be solved by using them, and have completed the present invention. The details will be described below.

In a first aspect of the present invention, a refractory inorganic oxide (a), a platinum group metal and a cerium compound having a fixed barium obtained by impregnating a refractory inorganic oxide with an aqueous barium salt solution and then treating with sulfuric acid is provided. An exhaust gas purifying catalyst, which is obtained by coating the contained catalyst composition on an integral structure.

The platinum group metal is contained in an amount of 0.5 to 30% by weight based on the refractory inorganic oxide (a) on which barium is fixed.
It is preferable that the refractory inorganic oxide is supported at a concentration of.

As a second invention, a refractory inorganic oxide (a) fixed with barium obtained by impregnating a refractory inorganic oxide with a barium salt aqueous solution and then treating with sulfuric acid, a platinum group metal, a cerium compound, and Refractory inorganic oxide (b)
An exhaust gas purifying catalyst, which is obtained by coating a catalyst composition containing C on an integral structure.

The platinum group metal is contained in an amount of 0.5 to 30% by weight based on the refractory inorganic oxide (a) on which barium is fixed.
It is preferable that the refractory inorganic oxide is supported at a concentration of.

The refractory inorganic oxide used as the source of the refractory inorganic oxide (a) or (b) used is alumina,
Silica, titania, zirconia, etc., or a complex oxide or mixture thereof can be used, and preferably,
It is activated alumina. The amount of the refractory inorganic oxide (a) used is 30 g to 300 g, preferably 80 g to 200 g, per liter of the catalyst.

A water-soluble salt is used as the barium source, and examples thereof include barium nitrate, barium acetate, barium chloride, and barium hydroxide. Upon use, a salt obtained by dissolving the salt in pure water or an acidic aqueous solution such as nitric acid is used, and the amount used is 0.1 to 30 mol%, preferably 0.5 to the refractory inorganic oxide (a). Is about 20 mol%. If it is less than 0.1 mol%, the effect of addition of barium is small, and if it exceeds 30 mol%, no performance improvement commensurate with the addition is observed.

As a method for fixing barium to the refractory inorganic oxide (a) according to the present invention, a slurry composition obtained by impregnating the refractory inorganic oxide (a) with the above barium salt aqueous solution is used. Barium salt is added to the refractory inorganic oxide (a) by adding dropwise sulfuric acid water diluted with concentrated sulfuric acid or pure water little by little with sufficient stirring so as to be 1 to 1.2 times the molar amount of barium salt. It forms and fixes barium sulfate.

When the amount is less than 1 mol times, the fixation of barium becomes insufficient, the slurry properties are deteriorated, and the cerium is adversely affected. When it exceeds 1.2 mol times, excess sulfuric acid is used. The presence of the roots causes problems such as elution of the refractory inorganic oxide (a) and corrosion of the production equipment during catalyst production.

By subjecting the refractory inorganic oxide (a) impregnated with barium salt to sulfuric acid treatment, barium forms and fixes barium sulfate on the refractory inorganic oxide (a), and thus the ball mill etc. Can be used as a slurry composition. Depending on the catalyst production conditions, barium may be used after being treated with sulfuric acid and, if necessary, dried or calcined. The firing temperature is not particularly limited, but is 300 to 800.
C is preferred.

The refractory inorganic oxide of barium (a)
In the case of supporting barium alone on the refractory inorganic oxide (a) as described above, but when supporting a platinum group metal and barium on the refractory inorganic oxide (a), The procedure described in can be used. That is,
(1) A method of directly supporting a refractory inorganic oxide and then a platinum group metal, (2) A method of previously supporting a platinum group metal on a refractory inorganic oxide, and then fixing barium, (3)
There is a method of impregnating a refractory inorganic oxide with a mixed solution of an aqueous solution of a platinum group metal and an aqueous solution of barium salt, and then treating with sulfuric acid. The method (2) is preferable.

As the platinum group metal supported on the refractory inorganic oxide (a), at least one platinum group metal is selected from the group consisting of platinum, palladium and rhodium.
Preferably, platinum, palladium, or a combination of platinum and palladium in a concentration of 0.1 to 10% by weight, and / or rhodium in a concentration of 0.02 to 2.0% by weight, etc. are used with respect to the catalyst composition. It

As a method of supporting the platinum group metal, 0.5 to 30% by weight based on the refractory inorganic oxide (a) to be supported,
By supporting the refractory inorganic oxide (a) at a high concentration of preferably 1 to 20% by weight, the interaction between the platinum group metal and the refractory inorganic oxide (a) is suppressed and the durability of the catalyst and The purification ability can be improved.

As the cerium source, it is possible to use an oxide, a carbonate, a hydroxide or the like in the form of an oxide of cerium at the time of firing or during use. Also,
When a water-soluble salt is used, the refractory inorganic oxide (a), the noble metal-supported refractory inorganic oxide (a) or the refractory inorganic oxide (b) is impregnated with the salt and baked. It can also be used by supporting it on the refractory inorganic oxide (a) or the refractory inorganic oxide (b).

The amount of cerium used is calculated as oxide.
5 to 100 g can be used per liter of catalyst. Further, in the case where the refractory inorganic oxide (a) is supported and used, a method in which it is impregnated and supported in the range of 0.1 to 50% by weight in terms of cerium oxide is also considered.

The integral structure according to the present invention is made of a ceramic such as cordierite or mullite, or a metal monolith such as stainless steel or Fe--Cr--Al alloy, and its shape is a so-called honeycomb type or corrugated type. There are things.

Next, a second invention is the same as the first invention.
Further, it is a catalyst to which a refractory inorganic oxide (B) is added separately. In this case, the amount of the refractory inorganic oxide (b) used is 45 g to 359 g, preferably 9 g per liter of the catalyst.
It is 5 g to 295 g. In this case, the total of the refractory inorganic oxides (a) and (b) is 50 g to 400 g, preferably 100 g to 300 g. If it is less than 50 g, good catalyst performance cannot be obtained, and 400 g
If it exceeds, it becomes difficult to coat the catalyst composition on the monolithic structure, and further, the back pressure of the catalyst itself becomes high, which is not preferable, and the catalyst performance commensurate with the increased amount is not observed. is there. The catalyst according to the first invention,
The catalyst according to the second invention obtained by adding the refractory inorganic oxide (b) has an effect of improving heat resistance as compared with the first catalyst.

[0021]

(Effects) (1) Immobilized barium obtained by using the catalyst according to the present invention improves the thermal stability of the refractory inorganic oxide or the like that is a platinum-group metal supporting substrate, and at the same time improves the platinum group metal content. It acts as a co-catalyst and can improve NOx performance. (2) In addition, in the conventional production method of adding barium to the catalyst composition, the adverse effect of barium on cerium was unavoidable, but in the catalyst according to the present invention, barium is water-insoluble and is not produced during slurry preparation. There is no elution, and there is no concern about adverse effects on the slurry properties and cerium. (3) As a result, even if exposed to a high temperature condition of 900 ° C. or higher, the catalytic performance is not significantly reduced, and the platinum group metal can be effectively used.

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.

[0023]

【Example】

Example 1 A mixed aqueous solution of dinitrodiaminoplatinum containing 2.0 g of platinum and rhodium nitrate containing 0.4 g of rhodium was treated with activated alumina 20 having a specific surface area of 150 m ² / g.
After impregnating it with 0 g and drying it at 150 ° C., it was baked at 500 ° C. for 1 hour to support the platinum group metal on the activated alumina. Next, an aqueous solution of 22 g of barium acetate dissolved in 200 g of pure water was impregnated into a platinum group metal-supported alumina, and 100 cc of dilute sulfuric acid (2N) was added little by little with a dropping funnel with sufficient stirring to obtain a slurry composition. The product was dried and calcined at 500 ° C. for 1 hour to obtain a platinum group metal-supported alumina having barium immobilized thereon. The catalyst composition thus obtained and 80 g of commercially available cerium oxide were pulverized with nitric acid water in a ball mill for 15 hours, and a monolithic carrier made of cordierite (400 cells / square inch) was dipped in the resulting aqueous slurry to obtain an excess. The slurry was blown off with compressed air and then dried at 150 ° C. for 2 hours to obtain a finished catalyst (1).

Comparative Example 1 220 g of activated alumina 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. Then, a platinum group metal-supported alumina was prepared. The platinum group metal-supported alumina thus obtained and 80 g of commercially available cerium oxide were pulverized with a ball mill to prepare an aqueous slurry, and Comparative catalyst (A) was obtained in the same manner as in Example 1 below.

Comparative Example 2 A comparative catalyst (B) was obtained in the same manner as in Example 1 except that the step of fixing barium by sulfuric acid treatment was not carried out.

Comparative Example 3 200 g of activated alumina 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. Then, a platinum group metal-supported alumina was prepared. The platinum group metal-supported alumina thus obtained, and 80 g of commercially available cerium oxide and 20 g of barium sulfate were pulverized with a ball mill to prepare an aqueous slurry, and Comparative catalyst (C) was obtained in the same manner as in Example 1 below. ..

Example 2 A mixed aqueous solution of dinitrodiamino platinum containing 2.0 g of platinum and rhodium nitrate containing 0.4 g of rhodium was impregnated in 20 g of activated alumina having a specific surface area of 150 m ² / g and dried at 150 ° C. After doing 500
The platinum group metal was supported on activated alumina by firing at 1 ° C. for 1 hour. Next, an aqueous solution prepared by dissolving 6.6 g of barium acetate in 30 g of pure water was impregnated into the platinum group metal-supported alumina, and 1.5 g of concentrated sulfuric acid was dropped little by little with sufficient stirring to obtain a slurry composition. The slurry composition thus obtained, 80 g of commercially available cerium oxide, and activated alumina 20
0 g was crushed with a ball mill, and a completed catalyst (2) was obtained in the same manner as in Example 1 below.

Example 3 A mixed aqueous solution containing dinitrodiamino platinum containing 2.0 g of platinum, rhodium nitrate containing 0.4 g of rhodium and 6.7 g of barium nitrate was added to 20 g of zirconia having a specific surface area of 90 m ² / g. 1.5 g of concentrated sulfuric acid was added little by little with sufficient stirring of the slurry composition obtained by impregnation, then dried at 150 ° C. and calcined at 500 ° C. for 1 hour to carry out barium-fixed platinum group metal-supported zirconia. Got The catalyst composition thus obtained, and 80 g of commercially available cerium oxide and 200 g of activated alumina were pulverized with a ball mill, and a completed catalyst (3) was obtained in the same manner as in Example 1. Example 4 Palladium nitrate containing 2.0 g of palladium and 0.4 g of rhodium
Rhodium nitrate containing aqueous solution containing a specific surface area of 150
It was impregnated with 20 g of m ² / g of activated alumina, dried at 150 ° C., and calcined at 500 ° C. for 1 hour to support the platinum group metal on the activated alumina. Next, 10.9 g of barium acetate was added to pure water 3
A platinum group metal-supported alumina was impregnated with an aqueous solution dissolved in 0 g, and 2.5 g of concentrated sulfuric acid was dropped little by little with sufficient stirring to obtain a slurry composition, which was dried and calcined at 500 ° C. for 1 hour to obtain barium. Thus, a platinum group metal-supported alumina in which was fixed was obtained. Next, cerium nitrate aqueous solution (25% by weight) 32
200 g of activated alumina was impregnated with 0 g of the alumina, dried at 150 ° C., and calcined at 500 ° C. for 1 hour to prepare cerium oxide-supported alumina. The two types of catalyst compositions thus obtained were pulverized with a ball mill, and the completed catalyst (4) was obtained in the same manner as in Example 1 below.

Comparative Example 4 Activated alumina having a specific surface area of 150 m ² / g was crushed with a ball mill to prepare an aqueous slurry, and the monolith carrier was coated with alumina. The monolith carrier is immersed in an aqueous cerium nitrate solution, dried and then calcined at 500 ° C. for 1 hour to carry cerium, and then immersed in an aqueous solution of palladium nitrate and rhodium nitrate and dried to 500
The platinum group metal was supported by firing at ℃ for 1 hour. The catalyst thus obtained was immersed in an aqueous barium acetate solution and dried,
Comparative catalyst (D) was obtained by calcining at 500 ° C. for 1 hour.

(Test Example) Catalysts 1 to 4 obtained from the examples
Also, the catalyst performance of the catalysts A to D obtained from the comparative examples was tested after running the engine for a long time. The endurance engine uses an electronically controlled engine (8 cylinders, 4400 cc), and the steady operation 6
The catalyst was aged for 50 hours under the condition that the catalyst temperature was 1000 ° C. in the steady operation by carrying out a mode operation of 0 seconds and 6 seconds of deceleration (fuel is cut during deceleration and the catalyst is exposed to a high temperature oxidizing atmosphere). The catalyst was evaluated using an 1800 cc electronically controlled engine, and the results of measuring the purification rates of CO, HC and NOx at a catalyst inlet temperature of 450 ° C. are shown in Table 1.

[0031]

[Table 1]

From the results shown in Table 1, it is clear that the exhaust gas purifying catalyst according to the manufacturing method disclosed in the present invention is an excellent catalyst that does not deteriorate in performance even when used under severe conditions such as a high temperature oxidizing atmosphere. is there.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomohisa Ohata 1 992 Nishikioki, Kamahama, Aboshi-ku, Himeji-shi, Hyogo 1

Claims (5)

[Claims] 1. A catalyst composition containing a barium-immobilized refractory inorganic oxide (a) obtained by impregnating a refractory inorganic oxide with a barium salt aqueous solution and then treating with sulfuric acid, a platinum group metal and a cerium compound. An exhaust gas purifying catalyst in which a monolithic structure is covered. 2. A platinum group metal is supported on the refractory inorganic oxide (a) in a concentration of 0.5 to 30% by weight based on the refractory inorganic oxide (a) on which barium is immobilized. The catalyst according to claim 1. 3. A refractory inorganic oxide (a) fixed with barium, which is obtained by impregnating a refractory inorganic oxide with a barium salt aqueous solution and then treating with sulfuric acid, a platinum group metal, a cerium compound and a refractory inorganic oxide. An exhaust gas purifying catalyst comprising an integral structure coated with a catalyst composition containing (b). 4. The refractory inorganic oxide (a) is supported by a platinum group metal at a concentration of 0.5 to 30% by weight based on the refractory inorganic oxide (a) on which barium is immobilized. The catalyst according to claim 3. 5. The refractory inorganic oxide (a) is obtained by supporting a platinum group metal on a refractory inorganic oxide, impregnating a barium salt aqueous solution, and then treating with sulfuric acid. The described catalyst.