JPS5933019B2 - Method for producing platinum supported catalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a platinum-supported catalyst for exhaust gas purification.

More specifically, platinum is characterized by using a solution in which a platinum ammine complex compound and a compound having three or more carboxyl groups in one molecule coexist when supporting platinum on a carrier mainly composed of alumina. The present invention relates to a method for producing a supported catalyst.

Platinum (Pt), palladium (Pd), rhodium (
Although it is a very expensive metal along with the platinum group metals of the periodic table such as Rh) and iridium (Ir), it has long been known to have extremely high activity as a catalytic material.

In particular, recently, platinum alone or a composite or mixed catalyst with other platinum group elements has been used for automobile exhaust gas purification and general industrial exhaust gas purification. It is attracting particular attention because there is no concern about secondary pollution caused by the pollution.

However, since platinum is a very expensive metal, it is necessary to keep the amount of platinum supported on the catalyst to an extremely small amount from an economical and resource standpoint, and at the same time, it is required to exhibit high catalytic activity.

For example, platinum-supported catalysts can be used to absorb unburned hydrocarbons (HC) and carbon monoxide (C) contained in exhaust gas from automobile internal combustion engines.
When used for the oxidation of O) or the reduction of nitrogen oxides, the operating temperature range of the catalyst ranges from room temperature to over 800℃, and the air-fuel ratio (A/F), space velocity (SV), etc. fluctuate from moment to moment. lead (lead) contained in exhaust gas.
It must also be able to withstand poisonous components that are harmful to the catalyst, such as Pb), phosphorus (P), and sulfur (S).

In addition, in particular, automobiles are subject to conditions where catalysts are likely to wear out due to collisions between the catalysts due to vibrations.

As a result, the catalytic metal such as platinum attached to the surface of the catalyst gradually peels off, resulting in loss of catalytic activity.

In the past, many attempts have been made to support platinum group metals only on the outer surface of the carrier and to obtain high catalytic performance with the aim of reducing the amount supported.

Among these proposals, various compounds are used as starting materials for depositing platinum.

Common examples include chloroplatinic acid or a salt thereof, or a platinum chloride.

However, catalysts produced using these chlorine-containing compounds have the drawback of particularly poor initial performance, as will be described later.

This seems to be because chlorine cannot be removed sufficiently during thermal decomposition.

Therefore, as a starting material, it is preferable to use a compound that does not contain chlorine or a compound that easily eliminates chlorine by thermal decomposition even if it contains chlorine.

The present inventors have found that it is advantageous to use a compound containing ammine, that is, a platinum ammine complex compound (hereinafter abbreviated as APF) as a starting material.

However, as APF, dinitrodiammine platinum (hereinafter referred to as
As a catalyst using P-5alt as a starting material, Revue de Simy Mineral (Rev
1
, (1970), pages 1101-1112, and patent applications such as Japanese Patent Application Laid-Open No. 123491/1983 are also known.

However, when platinum is supported on a carrier according to these known methods, pt adheres only to the outermost surface of the carrier,
Therefore, as mentioned above, when these catalysts were used to purify automobile exhaust gas, the PT gradually peeled off due to wear, resulting in a significant deterioration in performance and a major drawback in terms of durability.

As a result of further intensive research by the present inventors, we found that when a compound having three or more carboxyl groups in one molecule coexists in an immersion liquid containing APF, it is found that not only the surface of the catalyst carrier (catalyst carrier) It was discovered that platinum could be supported even inside the material, and the present invention was completed.

An object of the present invention is to provide a method by which a catalyst with improved initial catalyst performance and improved durability can be obtained.

The method for producing a platinum-supported catalyst of the present invention is characterized in that platinum is supported on an inorganic porous catalyst carrier using a solution in which APF and a compound having three or more carboxyl groups in one molecule coexist. It is something to do.

Since the catalyst obtained by the method of the present invention does not use a chlorine-containing platinum compound as a starting material, it is not affected by chlorine (
, so it has the advantage of improved initial performance.

In addition, since a solution containing APF and a compound having three or more carboxyl groups in one molecule is used, when the carrier is immersed in this solution, the solution is sufficiently immersed into the pores of the catalyst carrier. In the resulting catalyst, platinum is supported not only on the surface of the carrier but also inside the pores of the carrier, so even if the platinum on the surface of the carrier peels off or the catalytic performance deteriorates after long-term use, the pores of the carrier will remain intact. It has the advantage of improved durability because the catalyst activity is maintained well by the platinum supported inside.

The APF used in the present invention has NI (
3. N2H4, NH2OH, pyridine or CH3N
They contain amines such as H2, (CH3)2NH, etc. Among them, those containing NH3 are particularly desirable because they are inexpensive.

Therefore, the present invention uses dinitrodiammine platinum (P-salt), which is a typical APF and is generally easily available.
).

Here, examples of compounds having three or more carboxyl groups in one molecule include hydroxytricarboxylic acids such as citric acid and dexarlic acid, tricarboxylic acids such as tricarballylic acid and camphoronic acid, hemimellitic acid, trimellidic acid, pyromellitic acid, and benzenepentameric acid. Examples include aromatic carboxylic acids such as carboxylic acid and benzenehexacarboxylic acid.

In the present invention, one or more of these carboxyl group-containing compounds can coexist with APF.

The aforementioned carboxylic acid during dipping can be included in the dipping solution, preferably in a proportion of 0.1 to 30 grams per 11 of the carrier.

Here, if the amount of carboxylic acid added is increased, the thickness of the PT support layer becomes thicker (if the amount of added carboxylic acid exceeds 3M'/l carrier,
4-ball alumina granules can support up to the center of the granules.

Therefore, the thickness of the PT support layer can be changed by appropriately selecting the amount of carboxylic acid added.

As the solvent for the immersion liquid, water, ammonia water, nitric acid aqueous solution, or an organic solvent such as alcohol can be used.

Furthermore, if necessary, other catalyst components, such as platinum group metals such as Pd and PH, or transition elements such as Cu, Ni, and Co, may be coexisting in the immersion liquid.

In the present invention, an inorganic porous carrier containing 50 mol % or more of AI among the metal components constituting the carrier is used as the carrier.

Among these inorganic carriers, transitional alumina or a carrier containing them as a main component is preferred.

In carrying out the present invention, if necessary, the carrier may be supported with other catalyst components or may be subjected to treatments commonly used in catalyst production before contacting the carrier with the above-mentioned immersion liquid. good.

The supporting treatment is carried out by bringing the immersion liquid containing the APF of the present invention into contact with the carrier or a suitably treated carrier, thereby impregnating the carrier with the immersion liquid.

The impregnation process can be followed, if necessary, by any other suitable treatment commonly practiced in the art.

What is particularly important in the supporting treatment is to decompose APF before it is completed as a catalyst, and the simplest method is heat treatment.

For example, 300℃ or higher in air, preferably 400 to 60℃
This is done by firing at 0°C.

Hereinafter, the present invention will be explained according to examples.

Example 1 In this example, commercially available activated alumina carrier A was used.

Support A mainly consists of γ-alumina and δ-alumina, and has an average specific surface area of 70-120i and an average bulk density of 0.64-
0.70? /cc 2-4mm ball.

Pt1. OP, 340 ml of nitric acidic P-salt aqueous solution containing pyromellitic anhydride 42
was sprayed onto the carrier and left to stand for about 15 minutes while stirring.

Then, after drying at 120°C for 2 hours, drying at 500°C in air
The catalyst was calcined for 1 hour to obtain the desired catalyst 1A.

Reference Example 1 Catalyst 1a as a control was obtained in the same manner as in Example 1 except that a nitric acidic P-salt aqueous solution containing Pt1'iI (but not containing pyromellitic acid) was used.

Reference Example 2 Example 1 except that a chloroplatinic acid aqueous solution containing PtlP was used
Catalyst 2a as a control was obtained in the same manner as above.

Example 2 Using an X-ray microanalyzer (EPMA), the pt loading distribution from the catalyst surface to the inside was measured for the catalyst 1A of the present invention and the control catalysts 1a and 2a.

The results are shown in FIGS. 1 to 3. As is clear from FIG. 1, in the catalyst 1A of the present invention, PT is supported not only on the surface of the catalyst carrier but also within a distance of 130 μm from the surface of the carrier, whereas in the control catalyst 1A, PT is supported only in a concentrated manner on the surface of the carrier. In addition, the control catalyst 2a has a small amount of catalyst supported on the surface of the carrier, and furthermore, PT is supported deep inside the carrier, making it uneconomical.

Example 3 A 600-hour durability test was conducted on the present catalyst 1A and the control catalysts 1a and 2a.

The durability test is shown in Table 1.

A catalyst activity evaluation test was conducted on the catalysts before and after the durability test under the conditions shown in Table 2.

The results obtained are shown in Table 3.

From the results shown in Table 3, catalyst 1 obtained by the present invention
It can be seen that catalyst A has superior performance compared to the control catalysts 1a and 1b.

That is, in comparison with Catalyst 1a using P-salt that does not contain pyromellitic acid, in terms of durability performance, and
In comparison with Catalyst 2a using a chlorine-containing platinum compound as a starting material, it can be seen that it is superior, particularly in initial performance and HC purification rate after durability.

Example 4 After immersing the carrier A11 in a 0.2 molar cerium nitrate solution 11 for 10 minutes, the excess solution was removed.

Next, after drying at 120° C. for 5 minutes, carrier C was obtained by baking at 800° C. for 2 hours.

Next, the same operation as in Example 1 was performed except that carrier C was used.

After that, Rh0. Rhodium chloride aqueous solution containing IP o, s
, g for 30 minutes and excess liquid was removed.

Next, it was dried at 120°C for 2 hours and then calcined at 600°C for 1 hour to obtain the target catalyst 4A.

Reference Example 3 Example 4 except that 340 ml of a nitric acidic P-8alt aqueous solution (not containing pyromellitic acid) containing 1.0 g of Pt was used.
A control catalyst 3a was obtained in the same manner as above.

Example 5 Mainly composed of γ-alumina, alumina purity 99% or more, average specific surface area 130-15o, 4, average bulk density 0
．． 2-41n7 IL sphere of 32-0.40.

The carrier BIJ was PtO, 5g, Pd1. Immerse in an aqueous solution of nitric acid acidic P-salt and palladium nitrate containing 5 g of Og and 5 g of dexaric acid, and add about 4 g of water while stirring occasionally.
After standing for 0 minutes, excess liquid was removed.

Next, after drying at 120°C for 2 hours, it was calcined in air at 600°C for 1 hour to obtain the target catalyst 5A.

Reference example 4 Pt0.5g, Pd1. Nitric acidic P-sal containing Og
Catalyst 4a as a control was obtained by carrying out the same operation as in Example 5, except that t, palladium nitrate mixed aqueous solution (not containing dexaric acid), o, s, and g were used.

Example 6 Catalysts 4A, 5A according to the invention and control catalyst 3a
, 4a was subjected to the same durability test and catalytic activity test as in Example 3.

The results obtained are shown in Table 4.

From the results shown in Table 4, it can be seen that the catalyst according to the present invention is superior to the control catalyst in terms of durability.

[Brief explanation of drawings]

Figures 1 to 3 show catalyst IA, respectively. A chart showing the pt distribution based on EPMA analysis for 1a and 2a is shown.

Claims (1)

[Claims] 1. A method for producing a platinum-supported catalyst, which comprises supporting platinum on an inorganic porous catalyst carrier using a dinitrodiammine platinum solution containing a compound having three or more carboxyl groups in each molecule.