JPS61197042A - Production of monolithic catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To obtain the titled catalyst having the concn. difference in an easy method by immersing a monolithic carrier in the inside of a prescribed vessel filled with an aq. soln. contg. a catalytic component and inserting a catwhisker into the monolithic carrier to impress DC voltage. CONSTITUTION:In a monolithic catalyst for purifying an exhaust gas, an aq. soln. 4 contg. a catalytic component is filled in a nearly closed-end cylindrical vessel 1 wherein the bottom part is made of an insulator and the side part is electrically-conductive and a monolithic carrier 5 provided with a catalytic deposition layer is immersed in the aq. soln. 4. A catwhisker 6 is inserted into a cell of the central part in the radius direction of the monolithic carrier in the range between one end of the monolithic carrier and the other end thereof and DC voltage is impressed between the catwhisker 6 and the side part of the vessel 1. By such a simple method, the titled catalyst can be produced in a method capable of the mass production and also the concn. difference of the catalytic component can be continuously imparted and the weight to be deposited with the catalytic component can be made to a shape suitable for the distribution of flow velocity of the exhaust gas.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing a monolithic catalyst for exhaust gas purification, and more specifically, the amount of catalyst components supported on the monolithic catalyst is varied from the center in the radial direction of the monolithic catalyst. The present invention relates to a method of manufacturing a monolithic catalyst for exhaust gas purification in which the amount decreases gradually toward the periphery.

[Conventional technology]

Monolithic catalysts are used to remove harmful substances such as hydrocarbons (HC), -carbon oxides (CO), and nitrogen oxides (NOX) contained in automobile exhaust gas.

This monolithic catalyst is a monolithic structure with a large number of cells (pores) arranged along the flow of exhaust gas, coated with activated alumina, and then coated with an active component (usually a precious metal) that has a catalytic effect. It carries the following. This monolithic catalyst has a smaller heat capacity than a granular catalyst.
It has the advantage of excellent warm-up properties and low back pressure, and is therefore widely used for purifying automobile exhaust gas.

By the way, each cell of a monolithic catalyst has the same size, so when it is installed in a catalytic converter, the flow velocity of exhaust gas is high in the central part of the monolithic catalyst, which corresponds to the inlet diameter of the catalytic converter, and the flow rate of exhaust gas is high in the peripheral part. The flow becomes slower. As a result, the catalyst component supported in the central portion is more likely to deteriorate than the catalyst component supported in the peripheral portion, and the catalyst component in the peripheral portion is not fully utilized. Therefore, it becomes difficult to maintain the purification performance of the monolith catalyst in a good state for a long period of time.

As a countermeasure to this problem, a monolithic catalyst and a method for manufacturing the same have been proposed in which more catalyst components are supported in the central part where the exhaust gas flow velocity is higher than in the peripheral part where the exhaust gas flow velocity is lower (Japanese Unexamined Patent Publication No. 54-99090). ).

By the way, the method for producing a monolithic catalyst disclosed in JP-A-54-99090 utilizes masking or the use of a monolithic carrier in order to change the concentration of catalyst components in the central part and peripheral part of the monolithic catalyst. Methods such as double immersion in an aqueous solution containing catalyst components are used.

[Problem that the invention seeks to solve]

However, the above method requires a very complicated process of supporting the catalyst components, and is therefore unsuitable for mass production.

Further, in the above method, although it is possible to change the supported concentration of the catalyst component in stages, there is a problem in that it is not possible to provide a continuous concentration difference.

Means for Solving Problem c] The above problem is solved by the method for manufacturing a monolithic catalyst for exhaust gas purification of the present invention, which will be described below.

That is, in the method of manufacturing a monolithic catalyst for exhaust gas purification according to the present invention, a catalyst supporting layer is formed on a monolithic carrier having a columnar shape and having a large number of cells disposed therein from the exhaust gas inlet side to the outlet side. , a method for manufacturing a monolithic catalyst for exhaust gas purification, in which a catalytic acid content is supported on the catalyst support layer with the concentration decreasing gradually from the center to the periphery in the radial direction, and the bottom part is made of an insulating material. A substantially cylindrical container with a bottom made of a conductive material was prepared, the container was filled with an aqueous solution containing a catalyst component, and a monolithic carrier provided with a catalyst support layer was immersed in this aqueous solution. Later, a needle electrode is inserted into the central cell in the radial direction of this monolithic carrier from one end of the monolithic carrier to the other, and a DC voltage is applied between this needle electrode and the side of the container. There is.

In the present invention, as the catalyst component, platinum group elements such as platinum and palladium can be used alone or in combination of two or more.

In the present invention, the catalyst components are usually used in the form of salts.

Any water-soluble material may be used, such as PdC1, KtPdCz4, KtRhCβ, PtC1, Pt (NHa) *(Not)g
etc. can be used.

[Effect]

The catalyst component is ionized into positive or negative ions in an aqueous solution. For this reason, when a DC voltage is applied between the needle electrode inserted into the center of the monolithic carrier and the side of the container,
A potential difference is created in the radial direction between the needle electrode and the side of the container.

Therefore, when the catalyst component is a positive ion, the needle electrode is the negative electrode,
If the side of the container is used as a positive electrode, positive ions migrate to the center due to the potential gradient. At this time, while the pores in the inner wall surface of the cell are 3 to 5 μm in size, the ions of the catalyst component are one or two orders of magnitude smaller, so that they can sufficiently pass through the pores of the cell. However, since some of the catalyst component ions are captured on the inner wall surface of the cell during migration, only some of them reach the center. As a result, a monolithic catalyst is obtained in which the concentration of supported catalyst components gradually decreases from the center toward the periphery in the radial direction of the monolithic catalyst.

Note that when the catalyst component is ionized to become negative ions, similar results can be obtained by using the needle electrode as the positive electrode.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

Here, FIG. 1 is a schematic configuration diagram showing one step of the manufacturing method of the monolithic catalyst for exhaust gas purification according to the embodiment of the present invention, and FIG. A graph showing the concentration distribution of the monolithic catalyst obtained by the manufacturing method, and FIG. 3 is a graph showing the purification rate of the monolithic catalyst obtained in the example of the present invention and the monolithic catalyst obtained in the comparative example.

It has a columnar shape with a diameter of 93m and an axial length of 100m, with a cell density of 30.
An alumina slurry prepared by stirring and mixing 100 parts by weight of activated alumina powder, 60 parts by weight of alumina sol, and 45 parts by weight of water is charged into the entire flow path direction of a cordierite monolith carrier of 0 parts/square inch. After removing excess slurry, it is dried and fired. As a result, a total of 60 g of activated alumina layer was coated on the inner wall surface of the cell of the monolithic carrier.

Next, this monolithic carrier was immersed in a metal container 1 as shown in FIG. This metal container 1 has an inner diameter of 95 f.
It has the shape of a cylindrical body with a bottom.The bottom part 2 is made of rubber, and the cylindrical side part 3 is made of metal. Note that the inner surface of the side portion 3 is coated with Teflon so as not to react with the aqueous solution in which the catalyst component is dissolved. In this metal container l, there is a platinum concentration of 2 g/It [P t
(NH3) 6] Filled with an aqueous solution 4 of C1m. A monolithic carrier 5 coated with an activated alumina layer is immersed into this metal container 1 . Next, in the center of this monolithic carrier 5, a diameter 0 piece whose surface was coated with Teflon
．． A needle electrode 6 of 5 tm was inserted to the bottom and connected to a DC power source 7 such that the needle electrode 6 was a negative electrode and the side 3 of the metal container 1 was a positive electrode. Then, apply 4v DC voltage and
It was left for 0 minutes.

After 30 minutes, the monolithic carrier 5 is taken out from the metal container 1 and washed with water. Then, the rhodium concentration is 0.2 g
/ Rh Cj of l! The sample was immersed again in another metal container (not shown) filled with an aqueous hydrochloric acid solution of x, a DC voltage of 4 V was applied in the same manner as above, and the sample was left for 30 minutes.

At this time, the wires were wired so that the needle electrode was the positive electrode and the side portion was the cathode.

Thereafter, the monolithic carrier on which platinum and rhodium were supported was taken out from the metal container and dried to obtain a monolithic catalyst on which platinum and rhodium were supported.

The monolithic catalyst obtained as a result has an average supported amount of platinum and rhodium of all I! 1.0g per
, 0.1g, but in the center as shown in Figure 2,
They are 3.0 g and 0.3 g, respectively, per 11 catalyst volumes, and 0.2 g and 0.02 g, respectively, at the periphery, and the supported amount gradually decreases from the center to the periphery.

(Comparative Example) A monolithic carrier on which an activated alumina layer was formed in the same manner as in the example was coated with a layer of 46.5 M in the central area that was twice as large as that in the peripheral area by a method using the masking method described in JP-A-54-99090. Supported platinum and rhodium.

In the monolithic catalyst obtained as a result, the average amount of platinum and rhodium supported was the same as in the example, and these platinum and rhodium were 0.4g and 0.04g in the center, 0.6g and 0.6g in the peripheral area, respectively. 0.06 g was supported.

(Evaluation Test) The monolithic catalysts obtained in Examples and Comparative Examples were subjected to the following tests and compared.

First, the monolithic catalysts obtained in Examples and Comparative Examples were held in metal containers, attached to the engine exhaust system of a vehicle, and run for 200 hours in a pattern simulating city driving to conduct a durability test. . Subsequently, the sample after the durability test was mounted on an engine with a displacement of 2.81. This engine is 20
It was operated under the conditions of 0 Orpm and -360 uHH, and the obtained exhaust gas was brought to a constant temperature with a cooler and then introduced into a sample to measure the purification rate of hydrocarbons (HC). This result is the third
As shown in the figure.

As is clear from FIG. 3, it can be seen that the monolithic catalyst obtained in this example has a superior hydrocarbon purification rate compared to the conventional catalyst. Note that similar results were obtained for other carbon monoxide and nitrogen oxides.

Although specific embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, but includes various embodiments within the scope of the claims.

〔Effect of the invention〕

As described above, the method for manufacturing a monolithic catalyst for exhaust gas purification according to the present invention provides the following effects.

(b) After immersing the monolith carrier in a predetermined container, it is only necessary to insert a needle electrode into the monolith carrier and apply a DC voltage.
There is no need for dipping.

Therefore, it is easy to operate, increases work efficiency, and is suitable for mass production.

(b) Differences in the concentration of catalyst components can be made continuously instead of stepwise as in the conventional method. Therefore, the supported amount of the catalyst component can be adapted to the flow velocity distribution of the exhaust gas more than before, and the purification performance is improved.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing one step of a method for manufacturing a monolithic catalyst for exhaust gas purification according to an embodiment of the present invention, and FIG. A graph showing the concentration distribution of the obtained monolithic catalyst. FIG. 3 is a graph showing the purification rate of the monolithic catalyst obtained in the example of the present invention and the monolithic catalyst obtained in the comparative example. Preparation container 2---Bottom 3---One side (electrode) 4---Aqueous solution 5---Monolith carrier 6---One needle electrode 7------ --- DC Power Supply Applicant: Toyota Motor Corporation Figure 1 Figure 2 Figure 3 Input "Temperature/i ("C)

Claims (1)

[Claims] (1) A catalyst support layer is formed on a columnar monolithic carrier in which a large number of cells are arranged from the exhaust gas inlet side to the exhaust gas outlet side. A method for manufacturing a monolithic catalyst for exhaust gas purification in which the monolithic catalyst is supported with a concentration gradually decreasing from the center to the periphery, the bottom being made of an insulating material and the sides being made of a conductive material. After preparing a shaped container, filling this container with an aqueous solution containing a catalyst component, and immersing a monolithic carrier provided with a catalyst supporting layer in this aqueous solution, the monolithic carrier is radially injected into the center cell of the monolithic carrier. A method for manufacturing a monolithic catalyst for exhaust gas purification, which comprises inserting a needle electrode from one end of a monolithic carrier to the other end, and applying a DC voltage between the needle electrode and the side of a container.