JPH04104838A - Waste gas purifying catalytic body - Google Patents

Abstract

PURPOSE:To obtain a purifying catalyst having high performance in a wide range from a low temp. to a high temp. by providing the surface of a ceramic structural body with a catalytic layer constituted of a mixture of ceramic fine powder, an oxidation catalyst and an inorganic binder. CONSTITUTION:A catalytic layer 2 is formed on the surface of a ceramic structural body essentially consisting of alumina and silica and having a vent hole 6. The above catalytic layer 2 is constituted of ceramic fine powder 3, an oxidation catalyst 4 composed of Perovskite type compound oxides 4a and noble metal particles 4b such as platinum and palladium and an inorganic binder 5. The waste gas purifying catalyst obtd. by the above-mentioned manner can be applied in the range from a low temp. to a high temp. is furthermore excellent in productivity and is low-cost as well.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to various combustion equipment using oil, gas, etc. as fuel,
The present invention relates to an exhaust gas purification catalyst having excellent catalytic performance that completely burns oil smoke, unburned hydrocarbons, and carbon oxides discharged from cooking appliances such as automobiles, gas ovens, and oven ranges, and decomposes them 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 emitted from combustion equipment into carbon dioxide and water shavings in the coexistence 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, or palladium is supported on the surface.

The ceramic honeycomb structure used in this exhaust gas purification catalyst body is mainly made of cordierite whose main components are alumina, silica, and mag-2-shear from the viewpoint of durability.

Since this cordierite has a high density, its surface area is small and it is not suitable as a catalyst carrier. Therefore, in order to increase the surface area, the cordierite surface is coated with fine particles such as alumina with a large surface area, and the catalyst is placed on top of it. It is common to carry

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, although catalyst bodies using perovskite-type composite oxides as oxidation catalysts have excellent catalytic performance and durability at high temperatures, they have poor catalytic performance at low temperatures, and they do not contain metals such as platinum. Because the particle size is larger than that of noble metal catalysts, the number of active sites that function as a catalyst is small. Therefore, if 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. There was an issue.

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.

Furthermore, since noble metal catalysts are expensive and have limited resources, there is a strong demand for alternative catalysts.

Therefore, the present invention improves the type, composition, and structure of the materials constituting the exhaust gas purification catalyst, thereby improving the catalytic performance of the above-mentioned problem, and achieving exhaust gas purification with excellent productivity and low cost. The purpose is to provide a catalyst body.

Means for Solving the Problems In order to achieve the above objects, the exhaust gas purification catalyst body of the present invention has a ceramic structure having three components: alumina and glue, which is equipped with a vent through which exhaust gas passes, and has a ceramic microstructure. A catalyst layer made of a mixture of powder, an oxidation catalyst, and an inorganic binder is provided.

Therefore, according to the present invention, by providing a catalyst layer made of a mixture of ceramic fine powder, an oxidation catalyst, and an inorganic binder on the surface of a ceramic structure, the exhaust gas purification catalyst body is heated to a temperature at which it functions as a catalyst. The oil smoke, unburned gas, and carbon monoxide in the exhaust gas that passes through the exhaust gas purification catalyst body come into contact with the catalyst surface together with oxygen, and are converted into carbon dioxide gas and water vapor by an oxidation reaction.

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

Perovskite-type composite oxides have excellent heat resistance, so there is no deterioration in their performance as catalysts, and most of the precious metal catalysts are fixed in the voids between the ceramic fine powder, perovskite-type composite oxides, and inorganic binder, so the above-mentioned Nontalling and migration are prevented.

In addition, since the catalyst layer of the exhaust gas purification catalyst body in the present invention contains fine ceramic powder, the dispersibility of the oxidation catalyst is improved, and the number of active sites that function as a catalyst is increased, resulting in an increase in catalytic performance. .

Embodiments Hereinafter, embodiments of the present invention will be described based on the accompanying drawings. In FIG. 1, reference numeral 1 denotes a ceramic structure having a vent 6 through which exhaust gas passes, serving as the skeleton of an exhaust gas purification catalyst, and a catalyst layer 2 is formed on the surface of this ceramic structure 1. As shown in FIG. 2, this catalyst layer 2 is composed of a fine ceramic powder 3, an oxidation catalyst 4, and an inorganic binder 5. It is composed of rhodium and at least one noble metal particle 4h.

The catalyst layer 2 is manufactured by the following method.

First, ceramic fine powder 3, oxidation catalyst 4, and nothing! A mixed slurry is prepared by thoroughly mixing the binder 5 and adjusting the viscosity to an appropriate level by adding water.Next, this mixed slurry is applied to the surface of the ceramic structure 1 by spraying, dipping, etc., and dried. . Then, by firing this, the catalyst layer 2 can be obtained.

At this time, the oxidation catalyst 4 exists not only on the surface of the catalyst layer 20 but also inside the catalyst layer 2, but the catalyst layer 2 is made porous by the ceramic fine powder 3 and the perovskite type composite oxide fine powder 4a in the oxidation catalyst 4. Therefore, the exhaust gas can also diffuse into the interior of the catalyst layer 2. That is, the catalyst layer 2 has a structure such that the oxidation catalyst 4 present therein can also function as a catalyst.

If the amounts of the ceramic powder 3 and the oxidation catalyst 4 are too small, the catalytic performance will be poor, and if they are too large, the adhesion of the catalyst layer 2 will be poor. In order to achieve both the above-described catalyst performance and adhesion, the thickness of the catalyst layer 2 is preferably in the range of 10 to 200 μm. In addition, the inorganic binder 5 is used for the purpose of bonding the ceramic structure 1 and the catalyst layer 2 and the ceramic fine powder 3 and the oxidation catalyst 4, and the solid content of the inorganic binder 5 is preferably as small as possible from the viewpoint of catalyst performance. The content ranges from 5 to 10% by weight based on the contents of the ceramic fine powder 3 and the oxidation catalyst 4.

The material for the ceramic fine powder 3 is preferably one made of at least one of alumina, cerium oxide, zirconia, and baryta 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 4 is a perovskite-type composite oxide that has excellent heat resistance and catalytic performance at high temperatures and is low cost, and a perovskite-type composite oxide that has excellent catalytic performance at low temperatures. It is preferable to use a combination of noble metal particles containing only one type of platinum, palladium, and rhodium.

From the viewpoint of heat resistance, silica, alumina, zirconia, etc. made of colloidal particles are suitable as the material for the inorganic binder 5 for this purpose.

The size of the vent 6 through which the exhaust gas passes varies depending on usage conditions such as the flow rate, pressure, temperature, and size of the exhaust gas purification catalyst, and is not limited.

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, carbon oxides, etc. come into contact with the surface of the oxidation catalyst 4 together with oxygen in the exhaust gas, are converted into carbon dioxide gas and water vapor by an oxidation reaction, and are discharged from the vent 6.

The oxidation catalyst 4 used in the exhaust gas purification catalyst body is composed of fine powder 4a of perovskite-type composite oxide and noble metal particles 4b of at least 11a of platinum, para7'' and rhodium. Then, noble metal particles such as platinum 4b, which have excellent catalytic performance at low temperatures.
The perovskite type composite oxide 4a functions to purify exhaust gas at high temperatures, so excellent catalytic performance can be achieved in a wide temperature range from low to high temperatures.

The oxidation catalyst 4 present in the catalyst layer 2 exists not only on the outer surface of the catalyst layer 2 but also inside the catalyst layer 2, and as the catalyst layer 2 is porous as described above, exhaust gas is The oxidation catalyst 4 that diffuses into the interior and exists not only on the surface but also inside can function as a catalyst, and by using the ceraminol fine powder 3, the dispersibility of the oxidation catalyst 4 can be increased. 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 catalysts that function as a catalyst, thereby achieving better catalytic performance.

Since the perovskite-type composite oxide 4a has a stable crystal structure even at high temperatures, it maintains its function as a catalyst.
Most of the noble metal particles 4b such as platinum, para, rhum, and rhodium are fixed in the voids between the ceramic fine powder 3, the perovskite composite oxide 4a, and the inorganic binder 5, so that the above-mentioned sintering and migration silane are prevented. As a result, deterioration of catalyst performance can be prevented during long-term use.

Next, 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 FIGS. 1 and 2 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) Honeycomb-shaped ceramic structure 1 ■Material: Cordierite whose main components are alumina, silica, and magnesia ■Number of vents 6: 200 pieces/1 nch" (2) Constituent materials and composition of catalyst layer 2■ Ceramic fine powder 3 ・T-alumina 75% by weight ■Oxidation catalyst 4 ・Perovskite type composite oxide 4a La,. Alumina sol (solid content) 5% by weight Regarding the exhaust gas purification catalyst body prepared in this way, carbon monoxide concentration of 0.1% (air balance) and propane concentration of 0.1% were obtained using a fixed flow system.
When the conversion rate (purification rate) was evaluated by gas chromatography under the condition of space velocity 15,000 hr-' using two types of gases with a concentration of is 9 at 350°C
A conversion rate of more than 0% was obtained.

Furthermore, when a mixed fine powder of zirconia and barida was used instead of T-alumina in the ceramic fine powder 3, almost the same results as above were obtained.

Experimental Example 2 An exhaust gas purification catalyst body was manufactured using the configuration shown in FIGS. 1 and 2 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) Honeycomb-shaped ceramic structure 1 ■Material Cordierite whose main components are alumina, silica, and magnesia ■Number of vents 6: 200/1 nch" (2) Constituent materials and composition of catalyst layer 2 ■Ceramic Fine powder 3 - Cerium oxide 50% by weight ■ Oxidation catalyst 4 - Perovskite type composite oxide 4a Lao, * Sro, t Coo, q Mno,
l Os 44% by weight ・Precious metal particles 4b Platinum 1.0% by weight ■Inorganic binder 5 ・Zirconia sol (solid content) 5% by weight Regarding the exhaust gas purification catalyst body prepared in this way, carbon monoxide 0.1% in a fixed flow type. Concentration (air balance) and propylene 0.
When the conversion rate (purification rate) was evaluated by gas chromatography using two types of gases with a concentration of 1% (air balance) and a space velocity of 15,000 hr-', -carbon oxide was more than 90% at 180°C, Propylene is 400°C
A conversion rate of over 90% was obtained.

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

Thus, according to the above embodiment, the ceramic fine powder 3, the perovskite type composite oxide 4a, and the noble metal particles 4b
Since the oxidation catalyst 4 consisting of the following was provided on the surface of the ceramic structure 1 together with the inorganic binder 5, an extremely high conversion rate was obtained.

Effects of the Invention As is clear from the examples, the exhaust gas purification catalyst of the present invention has a catalyst layer made of a mixture of fine ceramic powder, an oxidation catalyst, and an inorganic binder on the surface of the ceramic structure constituting the exhaust gas purification catalyst. Due to this formation, the oxidation catalyst functions to purify exhaust gas in a wide temperature range from low to high temperatures even at high temperatures, and can exhibit excellent catalytic performance.

In addition, since the catalyst layer has a porous structure so that exhaust gas can diffuse into the inside, not only the oxidation catalyst present on the surface of the catalyst layer but also the oxidation catalyst inside can function as a catalyst, and it is possible to use fine ceramic powder. Since the dispersibility of the oxidation catalyst can be increased, 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.

Furthermore, the 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,
Most of the precious metal particles such as palladium and rhodium are fixed in the voids between the ceramic fine powder, the perovskite complex oxide, and the inorganic binder, so sintering and migration can be prevented. As a result, excellent catalytic performance can be maintained during long-term use.

The catalyst layer is formed by attaching a mixed slurry consisting of fine ceramic powder, an oxidation catalyst, and an inorganic binder to the surface of the ceramic structure by spraying or dipping, so it can be produced through a simple manufacturing process. .

[Brief explanation of the drawing]

FIG. 1 is an enlarged sectional view of a main part of an exhaust gas purification catalyst body according to an embodiment of the present invention, and FIG. 2 is an enlarged sectional view of a main part of a catalyst layer. 1...Ceramic structure, 2...Catalyst layer, 3...Ceramink fine powder, 4...
Oxidation catalyst, 5... Inorganic binder, 6...
···vent.

Claims (3)

[Claims] (1) Exhaust gas purification catalyst body in which a catalyst layer made of a mixture of fine ceramic powder, oxidation catalyst, and inorganic binder is formed on the surface of a ceramic structure mainly composed of alumina and silica, which is equipped with vents through which exhaust gas passes. . (2) The exhaust gas purification catalyst body according to claim 1, wherein the oxidation catalyst comprises 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. (3) The exhaust gas purification catalyst body according to claim 1, wherein the ceramic fine powder comprises at least one of alumina, cerium oxide, zirconia, and baryta.