JPH04145946A - Catalyst for purification of exhaust gas - Google Patents

Abstract

PURPOSE:To obtain a catalyst having high performance and durability and usable in a wide temp. range by carrying fine ceramic powder on the surfaces of ceramic fibers and in the gaps and bonding an oxidation catalyst on the surfaces of the ceramic fibers and the ceramic powder and in the gaps with an inorg. binder. CONSTITUTION:Fine ceramic powder 5 is carried on the surfaces of ceramic fibers 4 and in the gaps. An oxidation catalyst 6 consisting of a perovskite type multiple oxide represented by a formula ABO3 and particles of a noble metal such as Pt or Pd are fixed on the surfaces of the fibers 4 and the powder 5 and in the gaps with an inorg. binder 7. The resulting catalyst has improved performance and durability and can be used in a wide temp. range.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to oil smoke and unburned hydrocarbons discharged from various combustion appliances that use oil or gas as fuel, automobiles, gas ovens, microwave ovens, and other cooking appliances. - This relates to an exhaust gas purification catalyst that completely burns carbon oxide and decomposes it into carbon dioxide gas and water.

Conventional technology Conventionally, silica, alumina, etc. have been used as exhaust gas purification catalysts that oxidize and decompose oil smoke, unburned hydrocarbons, and carbon oxides discharged from combustion equipment and cooking appliances into carbon dioxide and water vapor in the presence of air. There is a ceramic honeycomb structure obtained by molding and firing ceramic powder, the surface of which is coated with fine powder such as alumina, and a catalyst made of a noble metal such as platinum, rhodium, palladium, etc. is supported on the surface.

The ceramic honeycomb structure used in this exhaust gas purification catalyst body is mainly made of cordierite, which has alumina, silica, and magnesia as its main components, from the viewpoint of durability.

This cordierite has a high density and a small surface area, making it unsuitable as a catalyst carrier. Therefore, in order to increase the surface area, it is common to coat the surface of cordierite with fine particles such as alumina, which have a large surface area, and then support a catalyst on the surface of the cordierite.

Recently, there are also products that use perovskite-type composite oxides instead of noble 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. .

Problems to be Solved by the Invention However, in such a conventional structure, since the ceramic honeycomb structure is not porous, the adhesion of the coating layer applied thereon is poor, and the coating layer falls off during use, resulting in poor catalytic performance. There was a problem with a significant drop in the performance. The above-mentioned decrease in adhesion can be improved by using a large amount of inorganic binder, but using a large amount of inorganic binder will reduce the surface area of the coating layer.
■There was a problem that the catalyst performance deteriorated due to reaction with the catalyst.

Catalysts using perovskite-type composite oxides as oxidation catalysts have excellent catalytic performance and durability at high temperatures, but they have poor catalytic performance at low temperatures and have a particle size compared to noble metal catalysts such as platinum. is large, so the number of active sites that function as catalysts is small. Therefore, when a large amount of exhaust gas is to be processed, sufficient catalytic performance cannot be obtained unless the size of the exhaust gas purification catalyst is increased to reduce the load on the catalyst, or the temperature of the exhaust gas purification catalyst is increased. was there.

On the other hand, a catalyst body in which a noble metal catalyst such as platinum is supported as an oxidation catalyst on a coating layer of fine particles such as alumina with a large surface area has excellent catalytic performance at low temperatures, but at high temperatures the particles of the noble metal catalyst There was a problem that sintering and migration from the surface of the catalyst body to the inside occurred, resulting in a significant deterioration of catalyst performance.

In addition, the above-mentioned catalysts are poisoned by sulfur and phosphorus contained in exhaust gases emitted from automobiles, cookers, etc., and the catalyst performance is significantly deteriorated after short-term use.

Therefore, the present invention aims to improve the catalyst performance and durability, which are the problems mentioned above, by improving the type, composition, and structure of the materials constituting the exhaust gas purification catalyst, and to purify exhaust gas so that it can be used in a wide temperature range. The purpose is to obtain a catalyst body.

Means for Solving the Problems And, in order to achieve the above object, the present invention provides ceramic fibers, ceramic fine powders supported on the surfaces and voids of the ceramic fibers, and ceramic fibers and ceramic fine powders supported on the surfaces and voids of the ceramic fibers. Basic structural formula A supported in voids
An oxidation catalyst composed of a fine powder of a perovskite-type composite oxide represented by B O3 and particles of at least one noble metal of platinum, palladium, and rhodium, and the ceramic fiber, the ceramic fine powder, and the oxidation catalyst are bonded. It is composed of an inorganic binder and has vents, such as a honeycomb structure, to allow exhaust gas to pass through.

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. Oil smoke, unburned gas, and carbon oxide 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.

The oxidation catalyst used in the exhaust gas purification catalyst body is composed of fine powder of perovskite-type composite oxide and noble metal particles such as platinum. In this configuration, noble metal particles such as platinum function to purify exhaust gas at low temperatures, and fine powder of perovskite type composite oxide functions to purify exhaust gas at high temperatures.

Perovskite-type composite oxide has excellent heat resistance, so its performance as a catalyst does not deteriorate, and most of the precious metal powder-r is fixed in the voids of ceramic fibers, ceramic fine powder, and perovskite-type composite oxide, as mentioned above. sontaring and migration are prevented.

In addition, the oxidation catalyst is not on the surface of the exhaust gas purification catalyst body.
It also exists in the voids between the ceramic fibers that form the framework of the exhaust gas purification catalyst, and since the exhaust gas purification catalyst is porous, exhaust residue can also diffuse into its interior, leaving only the surface inside. The oxidation catalyst present also functions as a catalyst.

Furthermore, since not only the oxidation catalyst but also fine ceramic powder is present on the surface of the catalyst layer, the oxidation catalyst is prevented from being poisoned by sulfur and phosphorus contained in the exhaust gas.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the accompanying drawings. FIGS. 1 and 2 show an exhaust gas purification catalyst body having a honeycomb J structure, where 1 is a catalyst plate and 2 is a corrugated catalyst plate. This honeycomb-shaped exhaust gas purification catalyst body is produced by laminating a plurality of pairs of the above-mentioned bonded catalyst plates 1 and corrugated catalyst plates 2 as shown in FIG. The vent hole 3 is obtained by rolling the catalyst plate 1 and the corrugated catalyst plate 2, and the vent hole 3 is formed at the same time as the exhaust gas purifying catalyst body is produced by adhering the catalyst plate 1 and the corrugated catalyst plate 2.

As shown in FIG. 3, the catalyst plate 1 and the corrugated catalyst plate 2 are made of ceramic fibers 4, ceramic fine powder 5,
The oxidation catalyst 6 is composed of an oxidation catalyst 6 and an inorganic binder 7, and the oxidation catalyst 6 is composed of fine powder 6a of a perovskite-type composite oxide and particles 6b of at least one noble metal selected from platinum, palladium, and rhodium.

Next, a specific method for manufacturing the honeycomb-shaped exhaust gas purification catalyst body will be described. First, the ceramic fibers 4 and the organic binder are thoroughly mixed, 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. The dried ceramic green sheet 1- is fired at a temperature at which the organic binder decomposes to produce a calcined sheet. Next, the ceramic fine powder 5, the oxidation catalyst 6 (perovskie I type composite oxide fine powder 6a, noble metal particles 6b), and the inorganic binder 7 are thoroughly mixed, and water is added to adjust the viscosity to a suitable mixed slurry. do. This mixed slurry is supported on the surfaces of the ceramic fibers 4 constituting the calcined sheet and in the gaps between the ceramic fibers 4 by a method such as brushing, rollers, dipping, etc., and is dried to produce a catalyst plate. Then, the catalyst plate 1 is corrugated using a corcator to produce a corrugated catalyst plate 2, and then the catalyst plate 1 and the corrugated catalyst plate 2 are bonded together using an inorganic binder. Next, a honeycomb-shaped exhaust gas purification catalyst body can be obtained by stacking a plurality of bonded pairs, or by rolling and firing each time.

Note that an inorganic binder is used as the adhesive material during the above-mentioned lamination and winding processes. This inorganic binder may be the same as the inorganic binder 7 used to support the oxidation catalyst 6 and the like. Further, the number of times of lamination or winding and the size of the ventilation L13 are determined as appropriate depending on the exhaust gas treatment conditions.

Since the calcined sheet is fired at a temperature at which the organic binder decomposes, after firing, the organic binder is removed and the sheet has a porous structure consisting only of ceramic fibers 4.

On the other hand, the ceramic fine powder 5, the oxidation catalyst 6, and the inorganic binder 7 are supported on the calcined sheet with the above-mentioned porous structure, so they exist not only on the surface of the calcined sheet but also inside it. It turns out. That is, the catalyst plate 1-1 and the corrugated catalyst plate +-2 have a structure in which ceramic fibers 4 form the skeleton, and ceramic fine powder 5, oxidation catalyst 6, and inorganic binder 7 are present around the skeleton. Further, by controlling the amounts of the ceramic fine powder 5 and the oxidation catalyst 6 to be supported, it is possible to obtain a porous structure in which the exhaust gas can diffuse inside the catalyst plate 1 and the corrugated catalyst plate 2 as well.

When the content of the ceramic fine powder 5 and the perovskite type composite oxide fine powder 6a decreases, the catalyst performance deteriorates and the mechanical strength as an exhaust gas purification catalyst body becomes weak. On the other hand, if the amount increases, the adhesion of the ceramic fine powder 5 etc. will deteriorate and the exhaust gas purification catalyst will become denser, so the surface area that functions as a catalyst will decrease and the catalyst performance will deteriorate. Therefore, the content of the ceramic fine powder 5 and the perovskite type composite oxide fine powder 6a in the catalyst plate 1 and the corrugated catalyst plate 2 is preferably in the range of 20 to 50% by weight. In addition, since the fine powder 6a of perovskite type composite oxide is easily poisoned by sulfur and phosphorus contained in exhaust gas, it is better to increase the amount of fine ceramic powder 5. The blending ratio of the fine powder 6a is preferably in the range of 1=1 to 9:1 by weight. Note that the amount of the noble metal particles 6b is not particularly limited, and an appropriate amount is determined depending on the performance and cost required for the catalyst.

The inorganic binder 7 is used for the purpose of bonding the ceramic fibers 4, the ceramic fine powder 5, and the oxidation catalyst 6, and from the viewpoint of catalyst performance, it is better to have as little as possible, and the solid content of the inorganic binder 7 is 5 to 10. A weight percent range is suitable.

From the viewpoint of heat resistance and cost, the ceramic fiber 4 is preferably made of at least one of alumina, silica, and zirconia, and has a fiber diameter of 1 to 5 μm.

The material of the ceramic fine powder 5 is preferably made of at least one of alumina, ceria, zirconia, and barium oxide in terms of heat resistance and cost.

In order to achieve excellent catalytic performance over a wide range of temperatures, the material for oxidation catalyst 6 is a fine powder of perovskite-type composite oxide, which has excellent heat resistance and catalytic performance at high temperatures and is low cost, and catalytic performance at low temperatures. It is preferable to use a combination of noble metal particles consisting of at least one of platinum, palladium, and rhodium, which have excellent properties.

As the material for the inorganic binder 7, silica, alumina, and zirconia made of colloidal particles are suitable for the purpose from the viewpoint of heat resistance.

The material for the organic 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.

The exhaust gas purification catalyst body is placed in an exhaust gas stream containing unburned gas and carbon monoxide discharged from automobiles, combustion equipment, cooking appliances, etc., and is heated to a temperature at which it functions as a catalyst. Oil smoke in exhaust gas that passes through a heated exhaust gas purification catalyst body,
Hydrocarbons and carbon oxides come into contact with oxygen in the exhaust gas on the surface of the oxidation catalyst 6, and are converted into carbon dioxide and water vapor through an oxidation reaction, which are then discharged from the vent 3.

The oxidation catalyst 6 used in the catalyst plate 1 and the corrugated catalyst plate 2 constituting the exhaust gas purification catalyst body of the present invention is made of fine powder 6a of perovskite type composite oxide and particles 6b of at least one noble metal selected from platinum, palladium, and rhodium. It consists of

In this configuration, noble metal particles 6b such as platinum, which has excellent catalytic performance at low temperatures, function to purify exhaust gas under low temperatures, and fine powder of perovskite composite oxide 6b functions under high temperatures.
Since a functions to purify exhaust gas, excellent catalytic performance can be achieved in a wide temperature range from low to high temperatures.

Further, the exhaust gas purification catalyst body of the present invention has a skeleton made of ceramic fibers 4, surrounded by fine ceramic powder 5, an oxidation catalyst 6, and an inorganic binder 7, and has a porous structure that allows exhaust gas to diffuse inside. ing. Therefore, the exhaust gas is diffused into the interior thereof, and the oxidation catalyst 6 present not only on the surface but also inside can function as a catalyst. Further, by using the ceramic fine powder 5, the dispersibility of the oxidation catalyst 6 can be further improved. As a result, the exhaust gas purification catalyst body of the present invention can have a large surface area that functions as a catalyst, and can increase the number of active sites that function as a catalyst.

Furthermore, the fine powder 6a of perovskite type composite oxide has a stable crystal structure even at high temperatures, so it maintains its function as a catalyst, and most of the noble metal particles 6b, such as platinum, palladium, and rhodium, are made of ceramic fibers 4, Since it is fixed in the voids between the ceramic fine powder 5 and the Pelola Sky 1~ type composite oxide fine powder 6a, sontaring and migration are prevented.

In addition, due to the presence of the ceramic fine powder 5, sulfur contained in exhaust gas emitted from automobiles and cookers,
Poisoning of the oxidation catalyst 6 by phosphorus is prevented, and deterioration of the catalyst is suppressed.

In addition, since the exhaust gas purification catalyst body is a porous body whose skeleton is made of ceramic fibers 4, its heat capacity is small.
The time required to reach a temperature that functions as a catalyst can be shortened.

Hereinafter, specific experimental examples of the present invention will be described.

Experimental Example 1 An exhaust gas purification catalyst body was manufactured using the configuration shown in FIG. 1 and the manufacturing method described above. The specifications of the materials, composition, shape, etc. 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) 1, corrugated catalyst plate 2) ■Ceramic fiber 4 Alumina/silica 50% by weight ■Ceramic fine powder 5 T-alumina 22% by weight ■Oxidation catalyst 6 Perovskite Type composite oxide fine powder 6aLao, q
Ceo, l Coo: l 21% by weight Noble metal particles 6b Palladium 2% by weight ■Inorganic binder 7 Alumina sol (solid content) 5% by weight (2) Catalyst plate l, thickness of corrugated catalyst plate 2 0°3nvn (3) Vent hole Number of 3: 200/1hch2 Note that an acrylic resin was used as the organic binder.

Using the exhaust gas purification catalyst t fabricated in this way, two types of gases, 0.1% concentration of carbon monoxide (air balance) and 0.1% concentration of propane (air balance), were used in a fixed flow type. When the conversion rate (purification rate) was evaluated by gas chromatography under the condition of a space velocity of 15,000 hr', a conversion rate of over 90% was obtained for -carbon oxide at 160'C, and a conversion rate of over 90% at 370°C for propane was obtained. .

Furthermore, when ceria was used instead of T-alumina in ceramic fine powder 5, almost the same results as above were obtained.

Experimental Example 2 An exhaust gas purification catalyst body was manufactured using the configuration shown in FIG. 1 and the manufacturing method described above. The specifications of the materials, composition, shape, etc. 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 1, corrugated catalyst plate 2) Ceramic fiber 4 Alumina 58% by weight b ■Ceramic fine powder 5 Alumina/silica 15% by weight ■Oxidation catalyst 6 Perovskite type Complex oxide fine powder 6aLao, q
Ceo, I Coo: l 5% by weight Noble metal particles 6b Palladium 2% by weight ■Inorganic binder 7 Alumina sol (solid content) 10% by weight (2) Catalyst flake) L Wave-shaped catalyst plate 2 thickness 0.3 mm (3) Ventilation Number of ports 3: 200/1hch2 Note that acrylic resin was used as the organic binder.

The exhaust gas purification catalyst body produced in this way was subjected to a fixed flow system using two types of gases, one with a concentration of 0.1% carbon monoxide (air balance) and the other with a concentration of 0.1% hyflopane (air balance), at a space velocity of 15,000 hr- When the conversion rate (purification rate) was evaluated by gas chromatography under the conditions of
A conversion of more than 90% was obtained at 90°C.

Experimental Example 3 An exhaust gas purification catalyst was manufactured using the configuration shown in FIG. 1 and the manufacturing method described above. The specifications of the materials, composition, shape, etc. applied to the production of the scum purification catalyst body during this period are as follows.

(1) Constituent materials and composition of exhaust gas purification catalyst body (catalyst plate 1, corrugated catalyst plate 1-2) ■ Ceramic fiber 4 Zirconia 59% by weight ■ Ceramic fine powder 5 Zirconia/Harium oxide J. 24% by weight ■ Oxidation catalyst 6 Fine powder of perovskite type composite oxide 6aLao, a
Sro, 2 Coo, q Mno, + 0y1
0% by weight Precious metal particles 6b Platinum 2% by weight ■Inorganic binder 7 Zirconia sol (solid content) 5% by weight (2) Thickness of catalyst plate 1 and corrugated catalyst plate 2: 0.3 mm (3) Number of vents 3: 200 /1hch" In addition, an acrylic resin was used as the organic binder.

The exhaust gas purification catalyst body produced in this manner was subjected to a fixed flow system using two types of gases, one with a concentration of 0.1% carbon monoxide (air balance) and the other with a concentration of 0.1% hyfluorane (air balance), at a space velocity of 15,000 hr- When the conversion rate (purification rate) was evaluated by gas chromatography under the conditions of
More than 90% conversion was obtained at 40°C.

Furthermore, when rhodium was used instead of the noble metal particles 6b, almost the same results as above were obtained.

Experimental Example 4 The exhaust gas purification catalyst body produced in Experimental Examples 1 to 3 was placed at the exhaust port of a gas staple, and a cooking experiment using swordfish and mackerel containing large amounts of sulfur and phosphorus was conducted 100 times. Thereafter, when the conversion rate (purification rate) was evaluated using the same method as in Experimental Examples 1 to 3, no deterioration in performance was observed and good results were obtained.

Effects of the Invention As described above, the exhaust gas purification catalyst of the present invention provides the following effects.

(1) By using an oxidation catalyst consisting of fine powder of a perovskite-type composite oxide and particles of at least one noble metal of platinum, palladium, and rhodium,
At low temperatures, noble metal particles such as platinum, which has excellent catalytic performance at low temperatures, function to purify exhaust gas, while at high temperatures, perovskite-type composite oxides function to purify exhaust gas, so it can be used in a wide temperature range from low to high temperatures. Excellent catalytic performance can be achieved.

(2) By using ceramic fibers, it is possible to create a porous structure that allows exhaust gas to diffuse into the interior, so that not only the apparent surface of the catalyst body but also the oxidation catalyst present inside the catalyst body can function as a catalyst. As well as being able to
By using ceramic fine powder, the dispersibility of the oxidation catalyst can be increased, so the surface area that functions as a catalyst can be increased, and the number of active sites that can function as a catalyst can be increased. As a result, better catalyst performance can be achieved.

(3) The fine powder of perovskite-type composite oxide used as an oxidation catalyst has excellent heat resistance, so it can prevent performance deterioration as a catalyst even when used at high temperatures.On the other hand, platinum, palladium, rhodium, etc. Since most of the precious metal particles are fixed in the gaps between the ceramic fibers, fine ceramic powder, and fine perovskite composite oxide powder, sintering and migration can be prevented.

(4) Poisoning of the oxidation catalyst by sulfur and phosphorus is suppressed by the presence of fine ceramic powder on the surface of the catalyst layer. As a result, excellent catalytic performance can be maintained during long-term use.

(5) Since the exhaust gas purification catalyst body of the present invention has a structure in which the oxidation catalyst and the ceramic fine powder are intertwined with the ceramic fibers, the oxidation catalyst and the ceramic fine powder do not fall off, and a product with excellent adhesion can be obtained.

(6) Since the exhaust gas purification catalyst body of the present invention is porous, its heat capacity is small, and it can be heated to a temperature that functions as a catalyst in a short time, and the energy required for heating can be reduced. Ru.

[Brief explanation of the drawing]

Figures 1 and 2 are perspective views of an exhaust gas purification catalyst body which is an embodiment of the present invention, and Figure 3 is a perspective view of catalyst plates 1 to 1 and corrugated catalyst plates constituting the gas purification catalyst body. FIG. 1... Catalyst plate, 2... Corrugated catalyst plate 1~. 3... Ventilation 1'', 4... Ceramic fiber, 5... Ceramic fine powder, 6...
Oxidation catalyst, 6a...Fine powder of perovskite type composite oxide, 6b...Precious metal particles, 7...Inorganic Hink Agent's name: Patent attorney Akira Kokaji and 2 others i<C'J (TsC(

Claims (5)

[Claims] (1) Ceramic fibers, ceramic fine powder supported on the surfaces and voids of the ceramic fibers, oxidation catalyst supported on the surfaces and voids of the ceramic fibers and the ceramic fine powder, and the ceramic fibers and the ceramic fine powder supported on the surfaces and voids of the ceramic fibers. An exhaust gas purification catalyst body comprising a powder and an inorganic binder that adheres the oxidation catalyst, and is provided with a vent so that exhaust gas can pass through. (2) The exhaust gas purification catalyst body according to claim 1, wherein the exhaust gas purification catalyst body has a honeycomb-like structure. (3) Claim 1, wherein the oxidation catalyst comprises fine powder of a perovskite-type composite oxide represented by the basic structural formula ABO_3, and particles of at least one noble metal selected from platinum, palladium, and rhodium. Exhaust gas purification catalyst. (4) The exhaust gas purification catalyst body according to claim 1, wherein the ceramic fiber contains at least one of alumina, ceria, and zirconia as a main component. (5) The exhaust gas purification catalyst body according to claim 1, wherein the ceramic fine powder contains at least one of alumina, ceria, zirconia, and barium oxide as a main component.