JPH07328442A - Filter for purifying waste gas and its production - Google Patents

Abstract

PURPOSE:To produce a filter reducing the combustion temp. of a fine particle- shaped substance and preventing the deterioration of a catalyst by preventing a chemical reaction of a filter part with the catalyst during the combustion of the substance. CONSTITUTION:This filter consists of a filter part 1, a coating layer 2 contg. lithium oxide, chromium oxide, vanadium oxide, potassium vanadate, lithium aluminate, chromium aluminate or a multiple oxide consisting of an alkali metal or a rare earth metal and alumina disposed on the surface of the filter part 1 and a catalyst 3 carried on the coating layer 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying filter carrying a catalyst for oxidizing and removing hydrocarbons and combustible carbon fine particles contained in exhaust gas discharged from a combustion engine such as a diesel engine, and a filter therefor. The present invention relates to a manufacturing method.

[0002]

2. Description of the Related Art In recent years, most of fine particles (solid carbon fine particles, liquid or solid high molecular weight hydrocarbon fine particles) in exhaust gas of diesel engine have a particle diameter of 1 μm.
Since it is less than m, it easily floats in the atmosphere and is easily taken into the human body during breathing. Moreover, since the particulate matter contains a carcinogenic substance, the regulation of emission of the particulate matter will be further strengthened in the future.

Conventionally, as a method of removing the particulate matter, a method of capturing the particulate matter in the exhaust gas using a heat-resistant ceramics filter and then burning the particulate matter with a burner or a heater, or
A method of adding a substance that promotes combustion of particulate matter during combustion (fuel additive method) has been proposed and is being studied for practical use, but each method has advantages and disadvantages,
It is desired to develop a better system.

A catalyst is used to remove particulate matter from exhaust gas.
If it can be burnt and removed at the temperature, it does not require a special device,
This is the most effective method for purifying exhaust gas. The catalyst
As for heat resistance, cost, and high activity, ABO₃ 
Type (A is rare earth metal or part of rare earth metal is alkali gold
Substitute with a genus or alkaline earth metal. B is Cr, Mn,
Placed with transition metal such as Co or partially alkali metal or noble metal
Replace. ) Composite oxide is used to support the catalyst.
As a filter part, the cost, physical or chemical
The cordy light (2M
gO ・ 5SiO ₂ ・ 2Al₂ O₃ ), Mullite (2Al
₂ O₃ ・ 3 SiO₂ ) Heat-resistant ceramics containing alumina such as
A mix is used. In addition, the catalyst and the filter
Between the catalyst and the filter part to prevent reaction during combustion
Alkaline earth metal, rare earth metal, cobalt, nickel
It has been carried out to provide an intermediate layer containing an oxide such as
It

[0005]

However, in the conventional exhaust gas purifying filter described above, when burned and used for a long time in a high temperature atmosphere (900 ° C. or higher), alumina in the filter portion and ABO ₃ used for the catalyst are used. -Type complex oxide forms a spinel compound (BAl ₂ O ₃ ) with the transition metal (B) contained therein, destroys the ABO ₃ -type complex oxide, and deteriorates the reactivity of the catalyst with the particulate matter. Then
There is a problem that the activity of the catalyst itself deteriorates, and the temperature at which the particulate matter is burned rises due to the deterioration of the activity of the catalyst, and the filter is destroyed. The intermediate layer containing an oxide of an alkaline earth metal, a rare earth metal, cobalt, nickel or the like is provided to solve the above-mentioned problems, but the spinel compound (BAl ₂ O
It is not enough to prevent the formation reaction of ₃ ), and the problem that the catalyst deteriorates, the temperature at which the particulate matter is burned rises, and the filter breaks has not been sufficiently solved.

The present invention solves the above-mentioned problems of the prior art. Even when exposed to a high temperature atmosphere during combustion, a spinel compound is not formed between the filter part and the catalyst, and the reaction with the particulate matter of the catalyst. It is an object of the present invention to provide an exhaust gas purifying filter that does not deteriorate in properties, does not raise the temperature for burning particulate matter due to deterioration of a catalyst, and does not cause destruction of the filter during combustion. Further, the present invention provides a method for producing an exhaust gas purifying filter, wherein a sufficiently stable coating layer that does not cause a chemical reaction between the filter part and the catalyst is easily formed with a high yield between the filter part and the catalyst. The purpose is to provide.

[0007]

In order to achieve this object, the exhaust gas purifying filter according to claim 1 of the present invention comprises a filter portion, a coating layer provided on the surface of the filter portion, and the coating layer. And a catalyst supported on. The exhaust gas purifying filter according to claim 2 is the filter according to claim 1, wherein the coating layer is lithium oxide, chromium oxide, vanadium oxide, potassium vanadate, lithium aluminate, chromium oxide, and an alkaline earth metal or rare earth. It has a structure which is one of the composite oxides of metal and alumina. The exhaust gas purifying filter according to claim 3 has the structure according to claim 1 or 2, wherein the filter portion is made of heat-resistant ceramics. The exhaust gas purifying filter according to claim 4 is the filter according to any one of claims 1 to 3, wherein the coating layer is
1 to 50% by weight of the weight of the filter part, preferably 1
It has a composition of 0 to 20% by weight. The exhaust gas purifying filter according to claim 5 is the filter for purifying exhaust gas according to any one of claims 1 to 4, wherein the catalyst is an ABO ₃ type (A is a rare earth metal, or a part of the rare earth metal is an alkali metal, or Substitute with alkaline earth metal, B is Cr, Mn, C
Substitution with a transition metal such as o or a part of alkali metal or noble metal. ), Or a composition having the composition of the ABO ₃ type composite oxide and the A oxide and / or the B oxide. The method for producing an exhaust gas purifying filter according to claim 6, wherein an impregnation step of impregnating the filter portion with an aqueous solution of a metal salt, a drying step of impregnating in the impregnation step and then drying, and a drying step of drying are performed. The temperature of the filter is 800 ° C or higher, preferably 900 ° C.
The coating layer forming step of firing the above to form the coating layer is provided. The method for manufacturing an exhaust gas purifying filter according to claim 7, wherein the metal salt according to claim 6 is any one of a nitrate, an acetate, a sulfate, and a chloride of a metal element forming a coating layer. It has a composition that is a seed. The method for manufacturing an exhaust gas purifying filter according to claim 8 is the method according to claim 6 or 7, wherein the aqueous solution of the metal salt is aluminum nitrate or aluminum acetate added to an aqueous solution of a lithium or chromium salt. is doing. The method for manufacturing an exhaust gas purifying filter according to claim 9, wherein a coating layer is formed on a ceramic sheet, and a catalyst is carried on the coating layer, and then the sheet is adhered to form the filter portion. Have a configuration.

[0008]

With this exhaust gas purifying filter of the present invention, when the particulate matter is burned, the filter and the catalyst are completely separated by the coating layer, so atoms are diffused between the filter and the catalyst. Without being
ABO contained in the filter part does not react with the transition metal contained in the ABO ₃ type composite oxide,
_{The 3} type complex oxide is not destroyed, the reactivity during combustion with the particulate matter is not deteriorated, the combustion temperature of the particulate matter is not increased, and the filter may be destroyed. Absent. Further, by the method for producing an exhaust gas purifying filter of the present invention, a coating layer in which the filter and the catalyst do not react between the filter portion and the catalyst is formed sufficiently uniformly, with good productivity, easily, and with high yield. You can

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

(Example 1, Comparative Example 1) FIG. 1 is a sectional view of an exhaust gas purifying filter according to an example of the present invention. Figure 1
In the above, 1 is a filter part, 2 is a coating layer separating the filter part 1 from the catalyst, and 3 is a catalyst that burns particulate matter. 2 is a perspective view of an exhaust gas purifying filter according to an embodiment of the present invention, and FIG. 3 is an enlarged view of a main part of a portion A of FIG. 2 and 3, 4 is a tubular honeycomb structure, 5 is a flat sheet, and 6 is a corrugated sheet. FIG. 4 is a cross-sectional view showing the flow of exhaust gas of the exhaust gas purifying filter according to one embodiment of the present invention.

Here, mullite, cordierite, silicon carbide, silica or the like is used for the filter portion 1.

Here, the coating layer 2 becomes insufficient as the coating layer 2 becomes less than 10% by weight, and there is a problem in adhesiveness as the coating layer 2 exceeds 20% by weight.
Neither is preferable. As an alkaline earth metal,
Examples include beryllium, magnesium, calcium, strontium, barium, and radium. Rare earth metals include scandium, yttrium, lanthanum,
Cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, yttetrium, lutetium and the like can be mentioned.

Here, strontium, lanthanum, lithium, chromium and the like are used as the catalyst. Examples of the alkali metal include lithium, sodium, potassium and rubidium. Examples of the transition metal include iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, platinum and the like. Examples of the noble metal include gold, silver, copper, mercury, palladium and platinum.

The manufacturing method of the first embodiment will be described below. 30% by weight of lithium acetate and 30% of chromium nitrate
A commercially available mullite filter part was impregnated with an aqueous solution containing any one of 5% by weight of potassium metavanadate and 5% by weight of potassium metavanadate, and then dried in air using a dryer. By repeating the impregnation and drying steps, the filter part 1 was coated with the content of the aqueous solution of 1 to 150% by weight based on the filter part. This filter part 1 was fired in air at 900 ° C. for 3 hours using an electric furnace,
A 10 to 20 wt% oxide coating layer was formed on.

Here, as the firing temperature becomes lower than 900 ° C., the heat resistance becomes poor, which is not preferable.

Furthermore, lanthanum acetate, chromium nitrate, lithium acetate, and platinum chloride are mixed with warm water of about 20 ° C. to 60 ° C. so that the metal molar ratio is 1: 0.5: 0.4: 0.1. An aqueous solution was prepared by dissolving each in 5 ml. The filter part 1 on which the coating layer is formed is impregnated with this aqueous solution, then dried in air using a dryer, and further baked in air at 800 ° C. for 5 hours using an electric furnace,
An exhaust gas purifying filter was prepared in which 30% by weight of the catalyst was supported on the filter part 1. Carbon particles were burned with this exhaust gas purifying filter, and the burning temperature at this time was measured using a thermal analyzer, and the results are shown in FIG.

The exhaust gas purifying filter of the first comparative example was prepared in the same manner as in the first embodiment except that the coating layer forming step of the first embodiment was omitted, and the same procedure as in the first embodiment was performed. The combustion temperature was measured and the results are shown in FIG.

FIG. 5 is a graph showing the relationship between the coating amount of oxide and the combustion temperature of the coating layer 2 of the first and third embodiments of the present invention and the first and second comparative examples.

Example 1 having a coating layer containing lithium oxide and Comparative Example 1 having no coating layer were prepared.
As the reheat treatment, an electric furnace was used and the temperature was kept at 800 ° C. for up to 1200 hours, and the deterioration with time of the combustion temperature at the time of carbon particle combustion was measured. FIG. 7 shows the first of the present invention.
FIG. 5 is a relationship diagram between the reheat treatment time and the combustion temperature of the example and the first comparative example.

As is apparent from FIG. 5, the exhaust gas purifying filter according to the first embodiment of the present invention is excellent in that the combustion temperature at the time of burning carbon particles is lower than that in the first comparative example. The effect is obtained.

As is apparent from FIG. 7, the exhaust gas purifying filter according to the first embodiment of the present invention does not raise the combustion temperature during carbon combustion so much even if it is kept at a high temperature, and the exhaust gas purifying filter An excellent effect can be obtained in that the activity of is not deteriorated.

As described above, according to the first embodiment of the present invention, a coating layer of lithium or chromium oxide and potassium vanadate is provided between the filter portion and the catalyst, so that when carbon particles are burned. The combustion temperature can be lowered, damage to the exhaust gas purification filter can be reduced, and the life of the exhaust gas purification filter can be extended.

Example 2 An aqueous solution containing lithium acetate and aluminum nitrate in a molar ratio of 1: 1 or chromium nitrate and aluminum nitrate in a molar ratio of 1: 1 was used as an aqueous solution for forming a coating layer. Except for the above, an exhaust gas purifying filter was prepared in the same manner as in Example 1, and the combustion temperature during carbon particle combustion was measured. The results are shown in FIG. Figure 6
FIG. 4 is a relationship diagram between the coating amount of oxide and the combustion temperature of the coating layers of the second example of the present invention and the first comparative example.

As is apparent from FIG. 6, the exhaust gas purifying filter according to the second embodiment of the present invention is a comparative example 1.
Compared with the above, an excellent effect is obtained in that the combustion temperature at the time of burning carbon particles is lowered by 50 ° C. or more.

As described above, according to the second embodiment of the present invention, by providing the coating layer containing lithium aluminate or chromium aluminate between the filter part and the catalyst, the combustion temperature at the time of burning carbon particles is improved. Can be reduced, damage to the exhaust gas purification filter can be reduced, and the life of the exhaust gas purification filter can be made extremely long.

(Example 3, Comparative Example 2) As a second comparative example, 5 to 13% by weight of lanthanum acetate and 1% of cobalt acetate were used.
Using 6% by weight and an aqueous solution containing 1% of nickel acetate of 16% by weight and the aqueous solution used in Example 1 as Example 3, a coating layer was applied to a commercially available filter part in the same manner as in Example 1. Formed. Next, lanthanum acetate, chromium acetate, lithium acetate, and platinum chloride are used in a metal molar ratio of 1
An aqueous solution was prepared by dissolving in warm water such that the ratio was 0.5: 0.4: 0.1. After concentrating the water content of this aqueous solution with stirring on a hot plate, it is dried and solidified on the hot plate, and then calcined at 400 ° C to 500 ° C for 30 minutes in an electric furnace to remove the nitric acid component and coagulate. It was a collection. This aggregate was crushed in a mortar and baked at 800 ° C. for about 5 hours to prepare a composite oxide as a catalyst. About 5 g of this composite oxide was dissolved in 200 ml of distilled water, and the filter portion having the coating layer was impregnated while stirring on a stirrer. This filter 100 in the air
After drying at ℃, it was fired at 800 ℃ for 1 hour in an electric furnace to produce an exhaust gas purifying filter. This exhaust gas purifying filter was measured for combustion temperature during carbon particle combustion in the same manner as in Example 1, and the results are shown in FIG.

As is apparent from FIG. 5, in the exhaust gas purifying filter according to the third embodiment of the present invention, as the coating amount of oxide in the coating layer increases,
An excellent effect is obtained in that the combustion temperature is lowered.

As described above, according to the third embodiment of the present invention, by providing the coating layer containing the oxide of lithium or chromium and the potassium vanadate between the filter portion and the catalyst, the carbon particles are burned. The combustion temperature at the time can be lowered, and damage to the filter can be reduced.

[0029]

As described above, the present invention is based on lithium oxide,
Chromium oxide, vanadium oxide, potassium vanadate,
By providing a coating layer containing lithium aluminate, chromium aluminate, and a composite oxide of alkaline earth metal or rare earth metal and alumina between the filter part and the catalyst, Since no chemical reaction occurs between the filter and the catalyst during combustion, and the catalyst does not deteriorate, the combustion temperature during combustion of the particulate matter can be lowered, and the exhaust gas purification filter must be kept at a high temperature. It is possible to realize an excellent exhaust gas purifying filter that can prevent the exhaust gas purifying filter from being damaged and the like and that can prolong the life of the exhaust gas purifying filter extremely. Further, the method for producing an exhaust gas purifying filter of the present invention is an excellent exhaust gas purifying that the coating layer that can completely prevent the chemical reaction between the filter portion and the catalyst can be produced very easily, stably, and with high yield. A method for manufacturing a filter for use can be realized.

[Brief description of drawings]

FIG. 1 is a sectional view of an exhaust gas purifying filter according to an embodiment of the present invention.

FIG. 2 is a perspective view of an exhaust gas purifying filter according to an embodiment of the present invention.

FIG. 3 is an enlarged view of a main part of an exhaust gas purifying filter according to an embodiment of the present invention.

FIG. 4 is a cross-sectional view showing a flow of exhaust gas of an exhaust gas purifying filter according to an embodiment of the present invention.

FIG. 5 is a relational diagram between the coating amount of oxide and the combustion temperature of the coating layers of the first and third examples of the present invention and the first and second comparative examples.

FIG. 6 is a graph showing the relationship between the coating amount of oxide and the combustion temperature of the coating layers of the second example and the first comparative example of the present invention.

FIG. 7 is a graph showing the relationship between reheat treatment time and combustion temperature in the first embodiment of the present invention and the first comparative example.

[Explanation of symbols]

 1 Filter Part 2 Coating Layer 3 Catalyst 4 Honeycomb Structure 5 Flat Sheet 6 Corrugated Sheet

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B01J 35/04 321 A

Claims (9)

[Claims] 1. An exhaust gas purifying filter comprising a filter portion, a coating layer provided on the surface of the filter portion, and a catalyst supported on the coating layer. 2. The coating layer is any one of lithium oxide, chromium oxide, vanadium oxide, potassium vanadate, lithium aluminate, chromium oxide, and a complex oxide of alkaline earth metal or rare earth metal and alumina. The exhaust gas purifying filter according to claim 1, wherein the exhaust gas purifying filter is one type. 3. The exhaust gas purifying filter according to claim 1 or 2, wherein the filter portion is made of heat resistant ceramics. 4. The coating layer according to claim 1, wherein the coating layer is 1 to 50% by weight, preferably 10 to 20% by weight of the weight of the filter portion. Exhaust gas purification filter. 5. The catalyst replaces an ABO ₃ type (A is a rare earth metal or a part of the rare earth metal with an alkali metal or an alkaline earth metal. B is a transition of Cr, Mn, Co, etc.). A metal, or a part thereof is replaced with an alkali metal or a noble metal), or a composition of an ABO ₃ type composite oxide and an A oxide and / or a B oxide. The exhaust gas purifying filter according to any one of claims 1 to 4, characterized in that. 6. An impregnating step of impregnating the filter portion with an aqueous solution of a metal salt, a drying step of impregnating in the impregnating step and then drying, and a temperature of the filter portion dried in the drying step is 800 ° C. or higher, preferably. And a coating layer forming step of molding the coating layer by firing at 900 ° C. or higher. 7. The exhaust gas according to claim 6, wherein the metal salt is any one of nitrates, acetates, sulfates and chlorides of metal elements forming the coating layer. Manufacturing method of purification filter. 8. The exhaust gas purifying filter according to claim 6 or 7, wherein the aqueous solution of the metal salt is obtained by adding aluminum nitrate or aluminum acetate to an aqueous solution of a salt of lithium or chromium. Production method. 9. An exhaust gas purifying filter, comprising: forming a coating layer on a ceramic sheet; further supporting a catalyst on the coating layer; and adhering the sheet to form the filter portion. Production method.