JPH04110045A - Catalyst body for purification of exhaust gas and its production - Google Patents

Abstract

PURPOSE:To improve the adhesion of the catalyst to a catalytic body for purification of exhaust gas as well as to obtain high catalytic activity by forming the skeleton of the catalytic body with ceramic fibers. CONSTITUTION:At least one kind of noble metal 4 such as Pt, Pd or Rh is supported on the surface of activated alumina 3 having a large surface area to form fine catalyst powder 5. This powder 5 is adhered to the surfaces of ceramic fibers 2 with an inorg. binder 6 so as to fill the gaps among the fibers 2 and through holes 7 are pierced in the resulting catalytic plate 1 consisting of the ceramic fibers 2, the fine catalyst powder 5 and the inorg. binder 6 so that exhaust gas can be passed through the holes 7. High catalytic activity is obtd. and the adhesion of the catalyst can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to the use of unburned hydrocarbons and carbon oxides discharged from various combustors, automobiles, or cooking appliances such as gas ovens and oven ranges that use oil or gas as fuel. The present invention relates to an exhaust gas purification catalyst that completely burns carbon dioxide and decomposes it into carbon dioxide and water, and a method for producing the same.

Conventional technologyUnburned hydrocarbons emitted from combustion equipment, etc.
-The exhaust gas purification catalyst body, which oxidizes and decomposes carbon oxide into carbon dioxide gas and water vapor in the coexistence of air, is a ceramic honeycomb structure obtained by molding and firing raw materials such as silica-5-alumina, and contains fine powder such as activated alumina and inorganic materials on the surface. coated with binder, and then coated with platinum, palladium,
Those that support a catalyst made of a noble metal such as rhodium are common.

Recently, there are also products that use belovskite-type composite oxides instead of precious metals as catalysts, but these also have a structure in which a perovskite-type composite oxide catalyst is supported on the surface of a ceramic honeycomb structure along with an inorganic binder. .

In all of these, a catalyst is later supported on the surface of a ceramic honeycomb structure that has already been molded.

Problems to be Solved by the Invention Conventional exhaust gas purification catalyst bodies are mainly made of cordierite containing alumina, silica, and magnesia as main components from the viewpoint of heat resistance and durability. This cordierite has a small surface area (approximately 0.2/nf/g) and is not necessarily suitable as a catalyst carrier as it is. Therefore, in order to increase the surface area, it is common to coat the surface of cordierite with fine particles such as activated alumina, which have a large surface area, and to support a catalyst thereon.

However, in such a conventional configuration, only the surface layer of the ceramic honeycomb structure functions as a catalyst body. Therefore, when a large amount of exhaust gas is to be processed, there is a problem in that sufficient catalytic activity cannot be obtained unless the size of the exhaust gas purification catalyst is increased to reduce the load, or the temperature of the exhaust gas catalyst is raised. .

In addition, since the ceramic honeycomb structure used as a support does not have a porous structure, the coating layer and catalyst that are placed on top of it to increase the surface area have poor adhesion, and they fall off during use, resulting in a decrease in catalytic performance. There was a problem. In addition, the excessive use of inorganic binders for adhesion has the problem of reducing the catalyst performance due to the following: ■reducing the surface area of the coating layer, ■covering the catalyst surface, and ■reacting with the catalyst. I don't like doing that.

Therefore, the present invention aims to improve the composition and structure of the materials constituting the exhaust gas purification catalyst body, thereby preventing the deterioration in the performance of the catalyst, which is the problem mentioned above, and improving the adhesion of the exhaust gas purification catalyst. The first purpose is to obtain a catalyst body.

The second purpose is to provide an effective manufacturing method for obtaining an exhaust gas purification catalyst body.

Means for Solving the Problems In order to solve the first problem, the present invention provides an exhaust gas purification catalyst body comprising: ceramic fibers; noble metal-supported activated alumina fine powder held on the surface and in the voids of the ceramic fibers;
It is composed of an inorganic binder that binds the ceramic fibers and the noble metal-supported activated alumina fine powder, and is provided with ventilation holes so that exhaust gas can pass through the exhaust gas purification catalyst body.

Moreover, in order to achieve the second object, the present invention is used by the following method.

■ A raw ceramic sheet is made from a mixed slurry of ceramic fibers and an organic binder using a papermaking method.
The green ceramic sheet is provided with vents through which exhaust gas passes, and the green ceramic sheet having the vents is fired at a temperature at which the organic binder decomposes to produce a calcined/metal-supported activated alumina fine powder. A mixed slurry made of an inorganic binder is held between the surfaces and between the ceramic fibers constituting the calcined sheet and fired.

■ A raw ceramic sheet is made from a mixed slurry of ceramic fibers and an organic binder using a papermaking method.
After producing a calcined sheet by firing the ceramic raw sheet at a temperature at which the organic binder decomposes, a mixed slurry consisting of noble metal-supported activated alumina fine powder and an inorganic binder is applied to the surfaces of the ceramic fibers constituting the calcined sheet and The ceramic fibers are held in the gaps between the ceramic fibers, and the corrugated and non-wavy ones are bonded together using an inorganic binder, and the bonded fibers are laminated or rolled and fired.

■ Instead of the noble metal-supported activated alumina fine powder described in (■) and (■) above, activated alumina fine powder that does not support noble metals is used, and after firing a calcined sheet, it is impregnated with a salt solution containing noble metals, and heated and fired in air. do.

The exhaust gas purification catalyst body of the present invention placed in an exhaust gas stream containing unburned gas and carbon monoxide is heated to a temperature at which it functions as a catalyst. Unburned gas and carbon monoxide in the exhaust gas passing through the heated exhaust gas purification catalyst come into contact with oxygen on the catalyst surface and are converted into carbon dioxide and water vapor through an oxidation reaction.

At this time, the catalyst exists not only on the surface of the exhaust gas purification catalyst body, but also in the voids between the ceramic fibers that form the framework of the exhaust gas purification catalyst body, and since the exhaust gas purification catalyst body is porous, the exhaust gas can diffuse into the interior, and the catalyst present not only on the surface but also within the interior functions. That is, the exhaust gas purification catalyst body of the present invention can be used as a catalyst. This increases the surface area where catalysts can act, resulting in high catalytic activity.

In addition, in the method for producing an exhaust gas purification catalyst, the oxidation catalyst can be supported not only on the surface of the exhaust gas purification catalyst but also inside the body, and an exhaust gas purification catalyst with excellent catalytic performance and adhesion can be efficiently manufactured. can do.

Embodiment Hereinafter, one embodiment of the present invention will be described based on the accompanying drawings. In FIG. 1, reference numeral 1 denotes a catalyst plate serving as an exhaust gas purification catalyst body, and this catalyst plate 1 consists of ceramic fibers 2, catalyst fine powder 5 in which platinum metal 4 is supported on the surface of activated alumina 3, and an inorganic binder 6. The catalyst plate 1 is provided with ventilation holes 7 through which exhaust gas passes.

Catalyst plate) 1 is manufactured by the following manufacturing method. First, thoroughly mix ceramic fiber 2 and organic binder.
Then, a solvent is added to prepare a slurry having an appropriate viscosity. Create ceramic raw sheets from this slurry using the papermaking method! (paper making) and drying. Ventilation holes 7 through which exhaust gas passes are opened in the dried ceramic raw sheet by a method such as punching. Thereafter, the raw ceramic sheet having the ventilation holes 7 is fired at a temperature at which the organic binder decomposes to produce a calcined sheet. Next, the catalyst fine powder 5 carrying platinum on the surface and the a'it-free binder 6 are thoroughly mixed, and water is added to prepare a mixed slurry having an appropriate viscosity. This mixed slurry is applied to the surfaces of the ceramic fibers 2 constituting the calcined sheet and to the gaps between the ceramic fibers 2 by a method such as brushing or roller dipping, and then dried.

Further, by firing this, the catalyst plate 1 can be obtained.

In the above, the size of the vent hole 7 through which exhaust gas passes varies depending on the usage conditions such as the flow rate, pressure drop, temperature, and size of the exhaust gas purification catalyst body of the exhaust gas, and is not limited to the size of the vent hole 7. After producing the calcined sheet, the holes may be formed in any step after supporting the fine catalyst powder 5 and inorganic binder 6 on the calcined sheet or after the final firing, but the holes may be formed from the viewpoints of ease of processing and dimensional accuracy. It is better to open the raw ceramic sheet after it has dried.

Since the calcined sheet is fired at a temperature at which the organic binder decomposes, the organic binder disappears after firing and the sheet has a porous structure consisting only of ceramic fibers.

On the other hand, since the catalyst fine powder 5 and the inorganic binder 6 are supported on the calcined sheet having the above-mentioned porous structure, they are present not only on the apparent surface of the calcined sheet but also inside the calcined sheet. That is, the catalyst plate 1 is made of ceramic fibers 2
forms the skeleton, and the catalyst fine powder 5 and the inorganic binder 6 exist around it. Furthermore, by controlling the amount of catalyst fine powder 5 supported, a porous structure in which exhaust gas can diffuse can also be obtained inside the catalyst plate 1.

When the content of the fine catalyst powder 5 is reduced, the catalyst performance deteriorates, and when the content is increased, the adhesion of the fine catalyst powder 5 increases, and the exhaust gas purification catalyst body becomes dense, so the surface area that functions as a catalyst decreases. Catalyst performance deteriorates. Therefore, the content of catalyst fine powder 5 in catalyst plate l is 20~
A range of 50% by weight is preferable. In addition, the inorganic binder 6 is used for the purpose of adhering the fine catalyst powder 5 and the ceramic fiber 2, and it is better to have as little as possible from the point of view of catalyst performance. A range of 5 to 10% by weight is suitable for the content of .

From the viewpoint of heat resistance and workability, the material of the ceramic fiber 1112 is preferably at least one of alumina, silica, or a composite of the two, such as mullite, or a fiber thereof having a fiber diameter of 1 to 5 μm.

The catalyst fine powder 5 consists of activated alumina 4 and platinum 3, and the activated alumina 4 is mainly r-AItOl, but depending on the intended use, ceria, zirconia, etc. may be added to increase the heat resistance temperature. , and palladium, rhodium, or a mixture thereof may be used instead of platinum 3.

From the viewpoint of heat resistance, silica, alumina, and zirconia made of colloidal particles are suitable for the material of the inorganic binder 6.

The material for the inorganic binder is not limited to any material as long as it decomposes and scatters at low temperatures.

Next, the operation of the configuration of this embodiment will be explained. A catalyst plate 1, which is an exhaust gas purification catalyst body, is disposed in an exhaust gas stream containing unburned gas and carbon monoxide discharged from automobiles, combustion equipment, medical equipment, etc., and is heated to a temperature at which it functions as a catalyst. The hydrocarbons and carbon oxides in the exhaust gas that encounter the heated catalyst spray 1 come into contact with the oxygen in the exhaust gas on the surface of the fine catalyst powder 5, and are converted into carbon dioxide and water vapor through an oxidation reaction, and are then released through the vent hole 7. be discharged.

The fine catalyst powder 5 present in the catalyst plate 1 is present not only on the surface of the catalyst plate 1 but also in the voids between the ceramic fibers 2 forming the skeleton of the catalyst plate 1. Further, since the catalyst plate 1 is porous, the exhaust gas diffuses into the interior thereof, and the fine catalyst powder 5 present not only on the surface but also inside can function as a catalyst. That is, the exhaust gas purification catalyst body made of the catalyst plate 1 of the present invention has a large surface area that functions as a catalyst, and high catalytic activity can be obtained.

Furthermore, since the exhaust gas purification catalyst body is porous, its heat capacity is small and the time required to reach a temperature at which it functions as a catalyst is shortened.

Furthermore, in the method for manufacturing an exhaust gas purification catalyst body comprising the catalyst plate 1 of the present invention, the catalyst fine powder 5 can be supported not only on the surface of the exhaust gas catalyst body but also inside the exhaust gas catalyst body, and the exhaust gas has excellent catalytic performance and adhesion. A purification catalyst body can be effectively produced.

Next, another example manufactured by the same method as above will be described using FIG. 2.

In FIG. 2, reference numeral 8 denotes a corrugated catalyst plate, and since this corrugated catalyst plate 8 is made of the same material as the catalyst plate 1 of the above-described embodiment, a description of its composition will be omitted. The exhaust gas vents 9 are obtained by bonding the catalyst plate 1 and the corrugated nib 8 together. Further, the honeycomb-shaped exhaust gas purification catalyst body is formed by laminating a plurality of pairs of the above-mentioned bonded catalyst plates 1 and corrugated nib plates 8 as shown in FIG.

Next, a specific method for manufacturing the honeycomb-shaped exhaust gas purification catalyst body will be described. First, the ceramic fibers 2 are thoroughly mixed with an organic binder, and a solvent is further added to prepare a slurry having an appropriate viscosity. A ceramic green sheet is produced from this mixed slurry by a papermaking method and dried. dried cerami.

The raw sort is fired at a temperature that decomposes the organic binder to produce a calcined sheet.

Next, the fine catalyst powder 5 and the inorganic binder 6 are thoroughly mixed,
Add water to prepare a mixed slurry with an appropriate viscosity. This mixed slurry is applied to the surfaces of the ceramic fibers 2 constituting the calcined sheet and to the gaps between the ceramic fibers 2 by using a brush, a roller, dipping, or the like, and then dried. Then, the calcined sheet carrying the fine catalyst powder 5 is corrugated using a corrugate, and the corrugated calcined sheet and the uncorrugated calcined sheet (supporting the fine catalyst powder) are bonded together with an inorganic binder. . Next, a honeycomb-shaped exhaust gas purification catalyst body can be obtained by laminating a plurality of bonded pairs and firing them.

Note that an inorganic binder is used for adhesion during the above-mentioned lamination process. The inorganic binder 1' and the adhesion between the corrugated calcined sheet and the uncorrugated calcined sheet may be the same as the inorganic binder 6 used to support the catalyst fine powder 5.

Further, the size of the vent hole 7, which is the number of laminated sheets described above, is determined as appropriate depending on the exhaust gas treatment conditions. Note that in all of the above production methods, examples were shown in which a fine catalyst powder was used in which platinum metal was first supported on activated alumina, but a plate or a honeycomb structure was first produced using activated alumina powder. A method may also be adopted in which the catalyst plate or exhaust gas purification catalyst body is then impregnated with a platinum metal salt solution.

Further, the functions and effects of each material 1 of the honeycomb-shaped exhaust gas purification catalyst body of this example are the same as those of the previous example.

EXPERIMENTAL EXAMPLE An exhaust gas purification catalyst body was manufactured using the configuration and manufacturing method shown in FIG. Specifications such as the composition and shape of the material 1 used in the production of this exhaust gas purification catalyst are as follows.

(1) Constituent materials and composition of catalyst plate 1 ■ Ceramic fiber alumina/silica fiber 50% by weight ■ Catalyst fine powder activated alumina 45% by weight (contains 1% palladium) ■ Inorganic binder silica sol (solid content) 5% by weight (2) Thickness of catalyst plate 1: 0.7 mm, diameter: 200 pieces/1 nch"Acrylic resin was used as the organic binder.

Exhaust gas purification catalyst body (catalyst plate l) prepared as in 2.
), the conversion rate (purification rate) was evaluated by gas crostography under the conditions of a fixed flow type with a carbon monoxide concentration of 0.1% (air balance) and a space velocity of 2000 hours, and it was found that the conversion rate (purification rate) was 90% or more at 150°C. Conversion Experiment Example 2 An exhaust gas purification catalyst body was manufactured using the configuration and manufacturing method shown in FIG. Specifications such as the composition and shape of the material 1 applied to the production of this exhaust gas purification catalyst body are as follows.

(1) Constituent materials and composition of exhaust gas purification catalyst body (catalyst plate, corrugated catalyst plate) ■ Ceramic fiber alumina/silica fiber 50% by weight ■ Catalyst fine powder activated alumina 45% by weight (platinum 1%)
(Contains) ■ Inorganic binder alumina sol (solid content) 5% by weight (2) Thickness of catalyst plate corrugated niblate 0.3 body (3) Number of ventilation holes 200 pieces/1 nch" Acrylic resin was used as the organic binder. .

Regarding the exhaust gas purification catalyst body prepared in this way, a space velocity of 10.0OOhr-' was obtained using two types of gases with a carbon monoxide concentration of 0.1% (air balance) and a methane concentration of 1% (air balance) in a fixed flow type. When the conversion rate (purification rate) was evaluated by gas chromatography under the following conditions, -carbon oxide conversion rate was 90% or more at 120'C, and methane conversion rate was 90% or more at 450C.

Experimental Example 3 An exhaust gas purification catalyst body was produced using the manufacturing method shown in Experimental Example 2. Specifications such as the composition and shape of the material 9 applied to the production of this exhaust gas purification catalyst body are as follows.

(1) Constituent materials and composition of exhaust gas purification catalyst body (catalyst plate corrugated niblate) ■ Ceramic fiber alumina/silica fiber 60% by weight ■ Catalyst fine powder activated alumina cerium oxide 36% by weight (900°
C, fired for 5 hours) (Contains 0.5% platinum, 0.5% rhodium) ■ Inorganic binder zirconia (solid content) 4% by weight (2) Catalyst plate, thickness of wavy niblate 0.3 m (3) Thickness Number of pores: 300/1 nch" Note that an acrylic resin was used as the organic binder.

Regarding the exhaust gas purification catalyst body prepared in this way, the space velocity was 10.000 hr using two types of gases, 0.1% concentration of carbon monoxide (air balance) and 1% concentration of propylene (air balance), in a fixed flow type. When the conversion rate (purification rate) was evaluated by gas chromatography under the conditions of -', a conversion rate of 90% or more was obtained for -carbon oxide at 100''C, and a conversion rate of 90% or more for propylene at 150°C.

Effects of the Invention As described above, in the present invention, since the ceramic fibers constitute the skeleton of the exhaust gas purification catalyst body, the fine catalyst powder supported is not only on the surface of the exhaust gas purification catalyst body but also in the voids between the ceramic fibers. The exhaust gas purification catalyst body can have a porous structure as a whole. Therefore, the exhaust gas to be purified can also diffuse into the interior.
The catalyst fine powder present not only on the surface but also inside can function as a catalyst. That is, the exhaust gas purification catalyst of the present invention can increase the surface area that functions as a catalyst, and can obtain high catalytic activity.

Furthermore, since the exhaust gas purification catalyst body of the present invention is porous, it has a small heat capacity, and can be heated to a temperature that functions as a catalyst in a short time, and the energy required for heating can be reduced.

Furthermore, in the method for producing an exhaust gas purification catalyst body of the present invention, the catalyst fine powder can be supported not only on the surface of the exhaust gas purification catalyst body but also inside the body. Since the catalyst is present in between, it is possible to prevent the catalyst from falling off, and it is possible to effectively produce an exhaust gas purifying catalyst body with excellent adhesion.

FIG. 3 shows the difference between this exhaust gas purification catalyst and a conventional exhaust gas purification catalyst (using cordierite honeycomb). Even though the quality and quantity of supported fine catalyst powder were exactly the same, there was a large difference in performance.
This demonstrates the magnitude of the diffusion effect of the carrier.

[Brief explanation of drawings]

A sectional view and an enlarged sectional view of an exhaust gas purification catalyst according to an embodiment of the present invention are shown, and FIG. 3 is a performance comparison characteristic diagram of an exhaust gas purification catalyst according to an embodiment of the present invention and a conventional exhaust gas purification catalyst. 1... Catalyst plate, 2... Ceramic fiber, 3... Activated alumina, 4... White metal, 5 Catalyst fine powder, 6... Inorganic binder, Vent hole , Shaka Epres

Claims (6)

[Claims] (1) Ceramic fibers, a fine catalyst powder in which at least one kind of noble metal such as platinum, palladium, and rhodium is supported on the surface of activated alumina having a large surface area in the voids between the ceramic fibers, and the ceramic fibers and the fine catalyst powder. An exhaust gas purification catalyst body that is composed of an inorganic binder that adheres the organic matter and is equipped with ventilation holes to allow exhaust gas to pass through. (2) The exhaust gas purification catalyst body according to claim 1, wherein the ceramic fibers are made of at least one of alumina, silica, or a composite of both, such as mullite. (3) Claim 1 in which the inorganic binder is mainly composed of at least one of alumina, silica, and zirconia.
Exhaust gas purification catalyst body described in . (4) A green ceramic sheet is produced from a mixed slurry consisting of ceramic fibers and an organic binder by a papermaking method, vent holes are provided in the green ceramic sheet through which exhaust gas passes, and the green ceramic sheet having the vent holes is After producing a calcined sheet by firing at a temperature at which it decomposes, a mixed slurry consisting of a fine catalyst powder in which at least one kind of noble metal such as platinum, palladium, or rhodium is supported on the surface of activated alumina having a large surface area and an inorganic binder is added to the slurry as described above. A method for producing an exhaust gas purification catalyst body, in which the catalyst is supported on the surface of ceramic fibers constituting a calcined sheet and in the gaps between the ceramic fibers and then fired. (5) A ceramic raw sheet is produced from a mixed slurry consisting of ceramic fibers and an organic binder by a papermaking method, and the ceramic raw sheet is fired at a temperature at which the organic binder decomposes to produce a calcined sheet. A mixed slurry consisting of fine catalyst powder and an inorganic binder in which at least one kind of noble metal such as platinum, palladium, or rhodium is supported on the surface of alumina is supported on the surface of the ceramic fibers constituting the calcined sheet and in the voids between the ceramic fibers. A method for producing an exhaust gas purification catalyst body, in which a corrugated and non-wavy structure is bonded with an inorganic binder, and the bonded structure is laminated or rolled up to form a honeycomb structure, which is then fired. (6) A mixed slurry consisting of activated alumina and an organic binder instead of fine catalyst powder is supported on the surface of the ceramic fibers constituting the calcined sheet and in the voids between the ceramic fibers, and after firing, precious metals such as platinum, palladium, rhodium, etc. 6. The method for producing an exhaust gas purification catalyst according to claim 4 or 5, which comprises impregnating the catalyst in a salt solution containing at least one of the above, blowing off the excess salt solution with compressed air, and then firing.