JPS633653B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a liquid composition for alumina coating on refractory materials such as honeycomb catalysts. Generally, catalysts are made by impregnating a carrier made of a refractory material such as alumina, silica, alumina-silica, cordierite, mullite, zirconia, etc. with a catalytic active ingredient made of metals such as copper, nickel, cobalt, platinum, palladium, or their oxides. , produced by supporting. At that time, it is not possible to obtain a catalyst with sufficient catalytic activity simply by impregnating and supporting the catalytic active component on the carrier, so these carriers are usually coated with activated alumina to make the carrier surface catalytically active. After making it into a state, impregnating it with catalytic active ingredients,
Generally, it is carried. Therefore, since the quality of the activated alumina coating has a very significant effect on catalyst performance, this active alumina coating layer must have a large specific surface area, as is required for general catalysts, and must be resistant to vibration and reaction gas flow. It also requires strong adhesion so that it will not peel off due to thermal shock or the like. A method for producing a transparent alumina solution from an organoaluminum compound is already known, but the conventional method can only produce a transparent alumina solution with an alumina content of about 2 to 3% by weight. The alumina content is too low to be used as an alumina liquid composition for activated alumina coating (wash coating), which requires more than 10% of active alumina, and when trying to prepare a highly concentrated transparent alumina solution, a diluted transparent alumina solution is evaporated as it is. Even when concentrated, when the alumina concentration reached 5 to 6% by weight, it gelled and turned into a pudding-like solid when left to stand, making it completely unusable for wash coating. In addition, as a method of combining rare earth elements in the alumina coating layer, for example, US Patent No.
Although it is proposed in No. 3951860, if an attempt is made to improve the thermal properties of alumina by adding rare earth elements into the alumina coating layer using the conventional method, a considerably large amount of rare earth elements is required; Rather, the disadvantage was that the properties of activated alumina were lost. Additionally, if a rare earth salt is directly added to a liquid composition of alumina produced from boehmite, the liquid composition will gel in a very short time and will not maintain a liquid state in which alumina is evenly dispersed, resulting in poor wash coating. It was possible. Therefore, the conventional method for adding rare earth salts into an alumina coating layer is to first perform alumina coating, then impregnate the alumina coating layer with a water-soluble rare earth salt, and calcinate to convert the rare earth salts into rare earth oxides. The alumina coating layer was formed by the method described in the previous paper. In such a method, the rare earth addition process becomes complicated, and it is extremely difficult to effectively disperse the rare earth into the alumina coating layer. An object of the present invention is to provide an alumina liquid composition for coating a catalyst carrier that fully satisfies these requirements. In line with the above objectives, the present inventors investigated a method for producing a highly concentrated transparent alumina liquid composition and a method for directly adding a rare earth salt to the transparent liquid composition. After hydrolyzing aluminum alkoxide in hot water, if you leave it in a hot water bath, the hydrolyzate will coagulate and precipitate, separating into a liquid part and a precipitate part.The supernatant liquid can be easily separated, and the precipitate part It is obtained by mixing inorganic or organic acids, steaming or drying to form a translucent solid, and peptizing it with water. This method produces highly concentrated transparent alumina, which is completely impossible with conventional methods. It has been found that a liquid composition can be obtained. In addition, as a method for dispersing rare earth elements in the alumina coating layer, it has not been possible to directly liquefy rare earth oxides, but in the transparent alumina liquid composition produced from the above aluminum alkoxide, rare earth oxides remain as they are. It can be dissolved to form a solid solution. Furthermore, a colloidal alumina liquid composition (Japanese Unexamined Patent Publication No. 53-45314) which the present inventors previously invented for active alumina coating and the above-mentioned transparent alumina liquid composition or the above-mentioned transparent alumina liquid composition obtained by making a rare earth oxide into a solid solution. It has been found that an excellent alumina liquid composition for coating a catalyst support can be prepared without gelation when mixed with alumina. A preferred example of the method for producing an alumina liquid composition for coating a catalyst carrier according to the present invention will be described in detail below. (1) Transparent alumina liquid composition: 1 mol of aluminum alkoxide to 20 ~
Add 30 mol and stir at a temperature of 70℃ or higher for 10 to 30 minutes to hydrolyze.If the container is left in a hot water bath of 80℃ or higher for 30 minutes or more, the liquid part and precipitate will separate, so decannize the supernatant liquid. Remove by tachion. Even if it is attempted to directly separate the hydrolyzate, it is extremely difficult to separate it, and even if it takes a long time to separate, the hydrolyzate thus obtained will not become transparent upon peptization. Furthermore, even if a centrifugal dehydrator is used to separate the hydrolyzate and the liquid part, the dehydration effect is not much different from the method using decantation, and the method is easier to handle. Another disadvantage of using a centrifugal dehydrator is that if the cake after separation is exposed to air for a long time, it will not become transparent. During hydrolysis separated by the above decantation, 1 mol of the aluminum alkoxide was added to an inorganic acid such as hydrochloric acid or nitric acid or an organic acid such as acetic acid or glycolic acid.
Add an amount equivalent to 0.1 to 0.5 mol to the solution and mix until thoroughly distributed. The mixture is directly placed in a steam generator and subjected to steam treatment at a temperature of 90°C or higher for 3 hours or more, or dried at a temperature of 200°C or lower for 3 hours or more to obtain a translucent solid.
12-20 mol of the solid thus prepared
When the mixture is stirred with water at room temperature for 2 hours or more, the solid material is peptized and a highly concentrated transparent alumina liquid composition is obtained. In addition, one or more of yttrium oxide, lanthanum oxide, neodymium oxide, samarium oxide, europium oxide, dysprosium oxide, ytterbium oxide, etc. are contained in the obtained transparent alumina liquid composition (hereinafter referred to as transparent liquid composition). Add 0.1 to 1 part by weight of rare earth oxide of 70
When heated and stirred at a temperature of 0.degree. C. or higher, the rare earth oxide is completely dissolved in the transparent liquid composition. The clear liquid composition for dissolving rare earth oxides may be of dilute concentration. Furthermore, the rare earth oxide used here may be a single oxide of a rare earth element or a mixed oxide, but if it is added as a soluble salt, it will form a colloidal alumina liquid composition. Since gelation occurs when mixed with rare earth oxides, it is necessary to add rare earth oxides. The amount of rare earth oxide added is 0.05 to 5% by weight based on the alumina content in the transparent liquid composition.
Preferably it is 0.2 to 2% by weight; if the concentration is lower than this, there is no effect of rare earth addition, and if the amount added is greater than this, it will not dissolve and become a solid solution. When adding rare earth elements, it is also possible to prepare a transparent alumina liquid composition with a low concentration and concentrate it as necessary. The dissolution temperature of the rare earth oxide is preferably 70°C or higher, and the higher the temperature, the faster the dissolution rate. However, transparent liquid compositions without the addition of rare earth oxides can also be used as liquid compositions for coating catalyst supports in the present invention. (2) Colloidal alumina liquid composition: On the other hand, a colloidal alumina liquid composition (hereinafter referred to as colloidal liquid composition) was produced as follows. 20 to 50 parts by weight of an acidic aqueous solution is added to 80 to 50 parts by weight of boehmite or pseudoboehmite, and the mixture is kneaded with a kneader or the like for 10 to 30 minutes with a total of 100 parts by weight. The acidic aqueous solution used here is acetic acid,
Organic acids such as glycolic acid and formic acid or inorganic acids such as hydrochloric acid and nitric acid are dissolved in water to form an acidic aqueous solution,
The amount of acidic substances present in the acidic aqueous solution is alumina 1
For organic acids, 0.5 to gram molecule
0.06 gram equivalent, and 0.4 to 0.04 gram equivalent for inorganic acids. Next, this kneaded product is cured in a closed container at room temperature for 2 hours or more, and then heat-treated at a temperature of 200°C or less. Add water to the material to be heat treated prepared in this way, and add it for 5 to 50 minutes while stirring occasionally.
After curing for 6 hours, the solid matter is peptized and a colloidal liquid composition in which alumina is uniformly suspended is obtained. The alumina liquid composition for coating a catalyst carrier according to the present invention can also be obtained by mixing this colloidal liquid composition with the transparent liquid composition or the transparent liquid composition to which the rare earth oxide is added. The content of rare earth oxide in the alumina liquid composition for catalyst carrier coating can be determined depending on the purpose of use, but for example, when coating is applied, the alumina content in the alumina liquid composition for catalyst carrier coating On the other hand, 5% by weight or less is sufficient, preferably 0.5 to 3% by weight, so the mixing ratio of the liquid compositions of both aluminas may be determined so as to have such a rare earth oxide content. In the present invention, the alumina liquid composition for coating a catalyst carrier is a general term for a transparent alumina liquid composition, a rare earth-added transparent alumina liquid composition, and a mixture of these with a colloidal alumina liquid composition, and hereinafter simply referred to as a coating alumina liquid composition. It is called an alumina liquid composition. The alumina liquid composition for coating thus prepared is coated onto a carrier made of a refractory material such as alumina, silica, cordierite, mullite, zirconia, etc. to support a catalyst active component such as platinum, palladium, or rhodium. It was found that the catalyst obtained by this method had better carbon monoxide and hydrocarbon purification performance and durability than a catalyst similarly obtained by applying conventional alumina coating. Furthermore, it is also effective as an alumina coating for three-way catalysts that simultaneously remove carbon monoxide, hydrocarbons, and nitrogen oxides for automobile exhaust gas. In this way, this coating alumina liquid composition is suitable for alumina coating of catalysts used in the purification of carbon monoxide, hydrocarbons, and nitrogen oxides in automobile exhaust gas, industrial waste gas, household fuel waste gas, various deodorizing devices, etc. It can be applied to a very wide range. EXAMPLES The present invention will be explained in more detail below with reference to Examples, but the present invention is not limited thereto. Example 1 75 parts by weight of 204 parts by weight of aluminum isopropoxide
It was added to 450 parts by weight of water heated to ℃ and stirred for 30 minutes. After stirring, place the entire container in a hot water bath at 80-90℃.
After soaking for 30 minutes, the hydrolyzate precipitated and coagulated and was separated from the supernatant, so the supernatant was removed. 18 parts by weight of acetic acid was added to the hydrolyzate thus obtained, and mixed by gentle stirring so that the acetic acid was distributed throughout. The dried product obtained was a translucent solid. 30 parts by weight of water was added to this solid and stirred for 3 hours to obtain a transparent liquid composition. The alumina concentration was about 15% by weight. This transparent liquid composition contains 0 dysprosium oxide.
~2.5 parts by weight were added to prepare alumina liquid composition solutions Nos. 1 to 5 for coating. Comparative Example 1 40 parts by weight of a 1N acetic acid solution was added to 50 parts by weight of alumina manufactured by Condeia, and the mixture was kneaded for 10 minutes using a ribbon kneader. The kneaded product was then taken out from the kneader, placed in a sealed plastic container, cured at room temperature for 6 hours, and then dried for 16 hours in a dryer adjusted to 110°C. After cooling this dried product to room temperature, it was gradually peptized in 117 parts by weight of water and cured for 5 hours with stirring to obtain a colloidal liquid composition. The alumina concentration was about 25% by weight. This was designated as alumina liquid composition No. 12 as a comparative example. Example 2 10 parts by weight of a transparent liquid composition prepared in the same manner as in Example 1 using ytterbium oxide and 10 parts by weight of the colloidal liquid composition prepared in Comparative Example 1 were mixed to prepare an alumina liquid for coating. Composition solution No.
6 to 8 were prepared. The alumina concentration was 20% by weight, and the dysprosium oxide concentration was 0.1 to 0.4% by weight. Example 3 14 parts by weight of aluminum butoxide was added to 100 parts by weight of water heated to 80°C, and 0.3 parts by weight of neodymium oxide and 0.3 parts by weight of samarium oxide were added to this.
Stir for 60 minutes. After stirring, a hydrolyzate was obtained in the same manner as in Example 1. Add 1 part by weight of hydrochloric acid to the hydrolyzate thus obtained, mix to the extent that the hydrochloric acid is distributed throughout, and then place the mixture in a sealed container.
Steam treatment was carried out for 5 hours in steam at 95-100°C. The dried product obtained was a translucent solid.
30 parts by weight of water was added to this solid and stirred for 2 hours to obtain a transparent liquid composition. The alumina concentration was about 15% by weight and the rare earth oxide concentration was about 2% by weight. An alumina liquid composition solution for coating containing a rare earth oxide is obtained by mixing 10 parts by weight of this transparent liquid composition with 10 parts by weight and 20 parts by weight of colloidal liquid compositions produced in the same manner as in Comparative Example 1. No.9
~10 were prepared. The alumina concentration is 20% by weight and 22% by weight, the rare earth oxide concentration is 1% by weight and
It was 0.7% by weight. Example 4 1 part by weight of a lanthanide group mixed oxide obtained from a nitric acid extract of a rare earth raw material was added to a transparent liquid composition obtained in the same manner as in Example 1, and the rare earth mixed oxide was dissolved in the same manner. Alumina liquid composition solution No. 11 for coating containing rare earth oxides was prepared by mixing 30 parts by weight of this transparent liquid composition and 20 parts by weight of a colloidal liquid composition obtained in the same manner as in Comparative Example 1. did. The alumina concentration was 18% by weight and the rare earth oxide concentration was 0.6% by weight. Test Example Using the coating alumina liquid compositions prepared in Examples 1 to 4, Solutions No. 1 to 11 and the alumina liquid composition solution No. 12 prepared in Comparative Example, a cordierite honeycomb carrier (cell density: 300 cell/in ² )
was coated with approximately 12% by weight alumina. After alumina coating, it was calcined at 700°C for 3 hours. 2g of this honeycomb carrier 1 as palladium
Solution No. 1 was prepared by immersing it in an aqueous solution of a complex of palladium chloride and 1 part by weight of palladium and 2 parts by weight of azodicarbonamide, and reducing it with hydrogen at 500°C.
~11 and a catalyst using solution No.12 was prepared.
For catalyst performance, a catalyst activity determination test was conducted under the following conditions. The judgment test was conducted using a new catalyst in air at 850℃ for 100℃.
Catalytic activity was evaluated for the catalyst that had been heat treated for a period of time. [Catalytic activity determination test] Gas composition (volume basis) CO: 1.05% O ₂ : 3.0% H ₂ : 0.35% CO ₂ : 10% C ₃ H ₆ : 500 ppm H ₂ O: 10% NO: 500 ppm N ₂ : Balance Space velocity: 75000Hr ^-1 The test results are shown in Table 1.

[Table] 1) Rare earth oxide concentration relative to alumina content

Claims (1)

[Claims] 1. Alumina hydrate using aluminum alkoxide as a starting material is mixed with an acidic substance and heated at 90 to 200°C.
A transparent alumina liquid composition for coating a catalyst carrier obtained by heat treating with water and peptizing with water. 2 Mix alumina hydrate using aluminum alkoxide as a starting material with an acidic substance and heat at 90 to 200℃.
A transparent alumina liquid composition obtained by heat treatment with water and peptization with water and boehmite or pseudoboehmite are kneaded with an acidic aqueous solution, cured at room temperature in a closed container, and then heat treated at a temperature of 200℃ or less. , and a colloidal alumina liquid composition obtained by further adding water and curing. 3. The alumina liquid composition according to claim 1 or 2, further comprising a rare earth oxide as a solution. 4. The alumina liquid composition according to claim 3, wherein the content of the rare earth oxide is 5% by weight or less based on the alumina in the alumina liquid composition.