JPS62171749A - Production of carrier of catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To obtain the titled carrier having excellent resistance to thermal shock and high surface area by using a material obtained by burning a mixture of alumina sol, an alkali titanate, molten silica, and a rare earth element substance as the carrier of a catalyst for purifying exhaust gas. CONSTITUTION:A mixture consisting of alumina sol such as a colloidal soln. of alumina hydrate in water, the titanates of lithium, sodium, etc., molten silica, and rare earth elements such as Ce, La, etc., is calcined at 1,000-1,300 deg.C to form a carrier of the catalyst for purifying exhaust gas from automobiles and industrial and public-welfare waste combustion gases. Consequently, a catalyst having large surface area, high catalytic activity, a low thermal expansion coefficient, and excellent resistance to thermal shock can be obtained at a low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing a catalyst carrier for use in a catalyst for purifying automobile exhaust gas or various combustion exhaust gases for industrial and consumer use.

Conventional technology Conventional exhaust gas purification catalysts are made of refractory ceramics such as
A T-washcoat is applied to the honeycomb base material of cordierite, alumina, mullite, and spodenimene.
A coating layer such as 9205 is applied, and the specific surface area is usually 10 to 3.
0 rtt'/g, to which a catalytic active material,
For example, even if the catalyst is prepared by supporting platinum, rhodium, palladium, ruthenium, etc., the problems that the invention attempts to solve. Alumina has the disadvantage that under high temperature atmosphere (800'C to 1000'G), the crystals transform to α-1203 and the specific surface area is extremely reduced.

In addition, the supported catalyst active material is also buried inside,
The catalytic ability will be deactivated. In order to solve this problem, there is a proposal (Japanese Unexamined Patent Publication No. 85791/1983) to mix ceria (CeO2) into the alumina coating layer. Although the above-mentioned problems were slightly improved by this, there were also problems such as peeling of the washcoat layer from the base material and destruction of the crystal structure of the base material. The physical properties had expired. Furthermore, in terms of the catalyst manufacturing process, there is a heat treatment process to create ceramic as a base material, and a 7. It was very complicated, including the steps of applying r-t and heat treatment, and supporting the catalyst and activating it by heat treatment.

The present invention aims to solve the above-mentioned disadvantages, and has a sufficiently large specific surface area without a wash coat.
The present invention provides a low-cost carrier for an exhaust gas purifying catalyst that has excellent high-temperature stability, thermal shock resistance, and mechanical strength.

Means for Solving the Problems The catalyst carrier for exhaust gas purification of the present invention is obtained by burning a mixture consisting of at least alumina sol, an alkali titanate, fused silica, and a rare earth substance.

Function: By the method of the present invention, a catalyst carrier having excellent thermal shock resistance and a high specific surface area can be obtained.

The alumina sol used in the present invention is a colloidal liquid of alumina hydrate (boehmite type) using water as a dispersion medium, and Cl -, CH, GO07NOi, etc. are generally used as stabilizers. The particle shape means feather-like, granular or rod-like, amorphous or crystalline form of precipitated boehmite. Alumina sol has a small particle size,
The ceramic carrier obtained by using alumina sol as a starting material also has a high specific surface area. However, it also has contradictory properties that are undesirable as catalyst carriers, such as poor high-temperature stability, extremely reduced mechanical strength, and increased thermal expansion coefficient. The three components described below are necessary to resolve this contradiction, although the reason is not clear.

Alkali titanate has the general formula M20-nTio□ (where M is lithium, sodium, potassium, rubidium,
It represents an alkali metal atom selected from senlum, barium, strontium, and calcium, and n is an integer of 1 or more. ).

Fused silica has a thermal expansion coefficient of 0.5 Xl 0-6/d
eg (room temperature to 1000'C), the smallest of all substances,
It is generally known as a material that reduces thermal expansion. However, fused silica is also a glass-forming oxide, and when heat treated at temperatures above 100°C in the coexistence of other substances, it becomes vitrified and forms crystals such as cristobalite and trichimanite, which can be used as a catalyst support. was considered an undesirable material.

Rare earth substances are usually used in automobile catalysts, and include oxides of rare earth elements such as Oe, La, Pr, Nd, and Sm, such as CeO7, La2O3, etc., and salts thereof, such as chlorides, Salts of rare earth elements, such as nitrates, acetates, hydroxides, and sulfates, form stable oxides when subjected to simulated firing. It is thought that the rare earth element oxide, when added together with alumina, suppresses the decrease in the specific surface area of alumina and improves the catalytic performance through the reaction shown in the example below.

2C602+11mu120s=20eh105+11
202 Although it is an interesting substance when viewed as a catalyst, adding it to the raw material that becomes the ceramic catalyst carrier is
Strict and difficult. For example, it is generally said that these rare earth materials are alkaline components and easily form network structure compositions (vitrification) with silica etc., making it difficult to obtain materials with large specific surface areas and excellent thermal shock resistance. This is my opinion.

According to the present invention, by firing the composition consisting of at least the four components described above, it was possible to obtain a catalyst carrier having excellent thermal shock resistance and a large specific surface area, although the reason is not clear.

In addition to the above-mentioned essential components, shaping aids such as carboxymethylcellulose, methylcellulose or plasticizers such as glycerin, petrolatum, etc. can also be added.

Example The present invention will be explained in detail below.

Example 1 50 parts by weight of alumina sol containing 20% by weight of alumina, 5 parts by weight of potassium titanate (K2O.6Ti02),
80 parts by weight of fused silica, cerium nitrate (Go(NO3)
26120), further mixed with 4.0 parts by weight of methylcellulose as a molding aid and 2.0 parts by weight of glycerin as a plasticizer, and mixed with 1.5 parts by weight using a screw kneader.
After kneading for 5 minutes, feed it to a screw extruder,
It is cylindrical with a diameter of 100mm and a length of 1oOIII11.
It was formed into a honeycomb shape having square cells with a wall thickness of 0.3 mm and a negative side of 1.0 mm. This molded body was heated to 1000°C at a heating rate of 1oo'C/hour, and at 1000°C
Time ■ Baked. The honeycomb-shaped ceramic thus obtained was used as a catalyst carrier, and platinum and rhodium were each added in an amount of 1.0% per 11 catalyst carriers. A catalyst was prepared by supporting Of and 200 mg. Note that chloroplatinic acid was used for the platinum, and rhodium nitrate was used for the rhodium. A mixed solution of both was impregnated, dried, and then heat-treated at 600'C in a hydrogen atmosphere containing nitrogen to produce an exhaust gas purification catalyst.

Also, for comparison, a product without cerium nitrate additive (Comparative Example 1)
Exhaust gas purification catalysts were prepared and compared in the same manner as in the example using a product without the addition of alumina sol (Comparative Example 2) and a product without the addition of potassium titanate (Comparative Example 3).

Note that when cerium nitrate and the like were removed, the amount of fused silica was increased accordingly.

The above four types of exhaust gas purification catalysts were evaluated using the following two evaluation methods.

(1) Using the above exhaust gas purification catalyst, the catalyst temperature is 2oo
°C, space velocity 40.0OOhr-', co inlet concentration 5o
The initial CO purification rate and the CO purification rate after heat treatment of the catalyst at 1000° C. for 100 hours in an electric furnace were measured under OP (in air) conditions.

(2) Each of the above exhaust gas purification catalysts is installed in the exhaust gas path of a vehicle equipped with a 2800 cc engine, and the air-fuel ratio is set to 1.
C
The purification rate of O1 hydrocarbons (HC) and nitrogen oxides (NOx) was measured at the initial stage and after 100 hours of bench durability. The evaluation is based on NOx in the basic ternary characteristic diagram shown in Figure 1.
Evaluation was made based on the purification rate at the intersection of the curve and the 00 curve for black people and the purification rate at the intersection B between the NOx curve and the HC curve.

The results of evaluation method (1) are shown in Table 1, and the results of evaluation method (2) are shown in Table 2.

As is clear from Table 1, Table 2, and Table 1, the catalysts of the comparative examples showed extremely greater thermal deterioration than the catalysts of the examples.

Similarly, in the bench durability test results shown in Table 2, the catalysts of Comparative Examples 1 and 2 showed significant deterioration from the initial stage for Go, He, and NOx component gases. In addition, 10 of Comparative Example 3
In the 0-hour durability test, the catalyst was destroyed due to insufficient strength and could not be measured. By the way, the specific surface area of the catalyst in the example is 2
It was 1 rrl/9' and a dog.

Example 2 A honeycomb molded body having the same composition and the same shape as in Example 1 was obtained,
950℃, 1000'C, 1200℃11300℃,
Samples were prepared by increasing the temperature to 1350'C (7) at a heating rate of 100'C/hour and baking for an additional hour. Table 3 shows the results of measuring the compressive strength, thermal shock temperature, and specific surface area of these samples.

(Left below) Table 3 As is clear from Table 3, the combustion temperature is 100°C ~
The range of 1300℃ is excellent, and outside this range, the pressure resistance,
It was unsuitable as a catalyst carrier in terms of physical properties such as thermal shock resistance and specific surface area.

Example 3 Four components were mixed so that the solid content composition range shown in Table 4 was obtained, and a forming aid and a plasticizer were added in the same manner as in Example 1 to obtain a honeycomb-shaped molded body. The combustion was completed and a honeycomb-shaped catalyst carrier was manufactured. Platinum and rhodium were similarly supported on this to prepare an exhaust gas purifying catalyst. Each of these catalysts was evaluated in three items: durability characteristics (evaluation method (2) of Example 1), compressive strength, and thermal shock characteristics. As is clear from Table 4, the solid content composition is such that the alumina contained in the alumina sol is 5 to 25% by weight, and the alkali titanate is 1 to 25% by weight.
9 parts by weight, 66-85 parts by weight of fused silica, 1 part by weight of rare earth material
~9% by weight is good as a catalyst carrier for exhaust gas purification,
Outside this range, the durability, compressive strength, and thermal shock properties were poor.

(Margin below) Evaluation O: Good ×: Unsuitable Example 4 50 parts by weight of alumina sol containing 20% by weight of alumina, 5 parts by weight of alkali titanate using various alkalis, 80 parts by weight of fused silica, 6 parts by weight of cerium nitrate. A honeycomb-shaped ceramic was produced in the same manner as in Example 1 using a mixture of 4.0 parts by weight, 4.0 parts by weight of methylcellulose, and 2.0 parts by weight of Grise IJ as raw materials, and platinum and rhodium were supported in the same manner as in Example 1. The GO purification rate was measured by the evaluation method (1) above. The results are shown in Table 6.

Table 6 1 Titanic acid Initial After heat treatment:
Alkali salt lithium titanate 100% 88 Sodium titanate 100 89 Potassium titanate 100 96 Rubidium titanate 100 8. Cesium titanate 100 88 Barium titanate 1oO9° Strontium titanate 100 891 Calcium titanate
10n QQ As is clear from Table 6, the compositions consisting of alumina sol, each alkali titanate salt, fused silica, and rare earth material were excellent with little deterioration due to heat treatment. Among them, those using potassium titanate showed extremely little thermal deterioration.

Example 6 6 parts by weight of alumina sol containing 20 parts by weight of alumina, 6 parts by weight of potassium titanate, 80 parts by weight of fused silica,
5 parts by weight of various rare earth substances (lanthanum nitrate (La (No.
5) s・6H20), cerium nitrate (06 (NO5)
2*sH2o) lSamarium nitrate (Sm(NOs)
s)-praseodymium nitrate (Pr(NO5)3.6H2
0), neodymium nitrate (Nd(Nos)s・6H
Example 1 using a mixture of 6 types of each of 20), 4.0 parts by weight of methylcellulose, and 2.0 parts of glycerin.
Honeycomb-shaped ceramics are manufactured in the same manner as above, and platinum,
Rhodium was supported in the same manner as in Example 1, and the GO purification rate was measured by evaluation method (1). The results are shown in Table 6.

Table 6 As is clear from Table 6, the compositions consisting of alumina sol, alkali titanate, fused silica, and each rare earth substance exhibited little deterioration in purification ability due to heat treatment and were excellent as catalysts. Among them, those using salts consisting of lanthanum and cerium had extremely low thermal deterioration. In the examples, comparisons were made using nitrates, but good results were obtained when used in the form of hydrates, chlorides, etc. Additions in the form of oxides were also effective. The thermal shock resistance was also excellent, with a coefficient of thermal expansion as small as 1.3 x 10-'/'C. Also, regarding mechanical strength, there were no particular problems in practical use.

Effects of the Invention As described above, according to the present invention, a catalyst having a small specific surface area, excellent catalytic performance, and furthermore a small coefficient of thermal expansion and excellent thermal shock resistance can be obtained at low cost.

[Brief explanation of drawings]

The figure is a diagram showing the relationship between the purification rate and the air-fuel ratio of an exhaust gas purification catalyst according to an embodiment of the present invention. Name of agent: Patent attorney Toshio Nakao and 1 other person t4
．． o t4. s tso
ts, s air fuel ratio

Claims (4)

[Claims] (1) A mixture consisting of at least alumina sol, alkali titanate, fused silica and rare earth material
A method for producing a catalyst carrier for exhaust gas purification, characterized by baking at a temperature of 1300°C to 1300°C. (2) The solid content in the mixture is 5 to 25% by weight of alumina, 1 to 9% by weight of alkali titanate, 65 to 85% by weight of fused silica, and 1 to 9% by weight of rare earth material contained in the alumina sol. A method for producing a catalyst carrier for exhaust gas purification according to claim 1. (3) The method for producing a catalyst carrier for exhaust gas purification according to claim 1 or 2, wherein the alkali titanate salt is potassium titanate. (4) The method for producing a catalyst carrier for exhaust gas purification according to claim 1 or 2, wherein the rare earth substance is an oxide or salt of cerium or lanthanum.