JPH051057B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a thermally stable catalyst carrier composition. Specifically, the present invention improves the heat resistance of conventional activated alumina and stabilized alumina so that they can continue to have a high surface area even when exposed to high temperatures exceeding 1000°C for long periods of time, particularly at 1200°C for 200 hours. The present invention relates to a method for producing a stabilized alumina composition, that is, an alumina-silica composite oxide, which has a specific surface area of at least 20 m ² /g even after the calcination treatment. [Prior art] Activated alumina is a substance with a high surface area and excellent heat resistance. Taking advantage of its properties, it can be used in various catalysts such as automobile exhaust gas purification catalysts, industrial exhaust gas treatment catalysts, and catalytic combustion catalysts. It is used as a carrier, etc. However, activated alumina has the disadvantage that when exposed to high temperatures of around 1000℃ or higher, its crystal structure changes and it eventually becomes α-alumina, resulting in a decrease in specific surface area.To prevent this, the above-mentioned In such fields of application, silica, alkaline earth elements, rare earth elements, and the like are usually added as stabilizers to activated alumina in the form of oxides, hydroxides, or various compounds. In this case, the activated alumina and the above-mentioned stabilizer essentially coexist as a mixture;
At temperatures below 1000℃ or 1100-1400
Although the stabilizing effect can be seen when exposed to high temperatures for a very short period of several hours, even at high temperatures of
When exposed to high temperatures exceeding 1000℃ for a long period of time, for several tens of hours or more, oxides of α-alumina and stabilizers, and even low-surface-area composite oxides of alumina and stabilizers with spinel or perovskite structures, are destroyed. It is known that the specific surface area decreases rapidly. For example, silicon dioxide (SiO ₂
5 to 10% by weight of silica sol is added and immersed,
The product calcined at 1000° C. after drying has a specific surface area of about 90 m ² /g and is stabilized, but it is a mixture of activated alumina and amorphous silica. Further, when this was fired at 1200° C. for 5 hours, although some α-alumina formation was observed, the specific surface area was 28 m ² /g, and it was still quite stable. However, when exposed for an additional 100 hours at 1200°C, it eventually changed to an α-alumina and cristobalite structure.
It becomes SiO ₂ and the specific surface area decreases to 3 to 5 m ² /g. On the other hand, the heat resistance temperature required of the above-mentioned catalysts is increasing year by year, and heat resistance of 1000° C. or higher is becoming required. In particular, in water-capacity boilers and gas turbines where the application of catalytic combustion methods has been considered in recent years, the catalyst temperature is 1000 to 1200℃, and depending on the conditions, 1300 to 1300℃.
As these catalysts reach temperatures as high as 1500°C, if stabilized alumina manufactured by conventional methods is used as a support for these catalysts, the catalysts undergo a large thermal history and their specific surface area rapidly decreases over time. This has the disadvantage that the catalyst activity decreases as a result. Furthermore, there is a risk that cracks may occur in the catalyst layer and the catalytic active sites may peel off. [Objective of the Invention] The object of the present invention is to overcome the above-mentioned problems in heat resistance of activated alumina or alumina stabilized by conventional methods, and to maintain α-alumina even when exposed to high temperatures exceeding 1000°C for a long time. It is an object of the present invention to provide a method for producing a carrier composition for a catalyst that has little change in crystal structure, has heat resistance that allows it to maintain a high surface area, and as a result has little deterioration in catalytic performance. [Structure of the Invention] That is, the present invention provides for adding magnesium (Mg), strontium (Sr), and ythtrium to a mixed aqueous solution of alumina hydrate and colloidal silica.
At least one element selected from the group consisting of (Y), lanthanum (La), cerium (Ce), neodymium (Nd), titanium (Ti), zirconium (Zr), chromium (Cr), and tin (Sn). by adding a compound of
This is a method for producing a heat-resistant catalyst carrier composition, which is characterized in that the mixed aqueous solution is thickened into a gel, and the resulting gel is dried and fired. Moreover, the catalyst carrier composition obtained by the present invention shows a 20
It exhibits unprecedented heat resistance with a specific surface area of m ² /g or more. Normally, methods for producing composite oxides include precipitation methods, impregnation methods, mixing methods, coprecipitation methods, etc., and most of the solid industrial catalysts currently in use are composites of each composition using these methods. It is used. However, in the precipitation method, due to the difference in the solubility product of each composition, in the impregnation method, due to the movement of each composition when the slurry obtained by impregnation or immersion is dried and fired, and in the mixing method, due to the solid phase reaction. It is difficult to mix each composition uniformly, and because the particle size of each composition is uneven, it is difficult to uniformly disperse the stabilizer into alumina, and free alumina and stabilizer exist. I can't avoid it. When exposed to high temperatures for a long time, these eventually become oxides or aluminates of α-alumina and the stabilizer, causing a decrease in the specific surface area. In addition, in the coprecipitation method, the difference in the solubility product of the hydroxides of alkaline earth elements and rare earth elements as carrier carriers and aluminum is small, and precipitation occurs almost simultaneously, but metal ions in a soluble state due to the difference in solubility products Precipitation due to adsorption and inclusion does not occur completely and co-precipitation is difficult to occur, so the operation is highly influenced by conditions such as precipitating agent, temperature, and pH, and strict operation is required. When preparing a large amount for industrial use, preparation with a high concentration solution is unlikely to result in coprecipitation and only produces a homogeneous precipitate, so it must be prepared multiple times with a low concentration solution. It is difficult to control the particle size of the product, and operations such as filtration and washing are complicated, making it impractical. On the other hand, the catalyst carrier composition of the present invention is thickened and gelled by adding a compound of the element specified by the present invention to a homogeneous mixed aqueous solution of alumina hydrate and colloidal silica. will be uniformly dispersed, and by drying and aging it, it will have a high surface area even after long-term high-temperature firing. The reason for this is not well understood, but when a compound of the element specified by the present invention is added to the stable existence region of alumina hydrate and colloidal silica, a pH change and a cation concentration change occur, causing repulsion between particles. Under conditions where the electric double layer does not function sufficiently, the particles come together and bonds with silica as the crosslinking source occur, forming a composite with highly dispersed silica as the core and aluminum surrounding it. It is expected that this will prevent alumina from becoming pregelatinized, resulting in a thermally stable catalyst carrier composition. Compounds of elements specified by the present invention, namely:
Mg, Sr, Y, La, Ce, Nd, Ti, Zr, Cr, Sn compounds include nitrate, carbonate, acetate, oxalate,
Any water-soluble compound such as chloride may be used. A mixed aqueous solution of alumina hydrate and colloidal silica is thickened into a gel by a compound of at least one element selected from the group of Mg, Sr, Y, La, Ce, Nd, Ti, Zr, Cr and Sn. 10-150 when converting
It is appropriate to maintain the temperature in the temperature range of 20°C to 80°C, more preferably in the range of 20 to 80°C, and gradually add the compound of the above elements while sufficiently stirring the mixed aqueous solution. If the temperature during thickening gelation exceeds 150°C, the gel produced during gelation will simultaneously dry, and the drying rate will be too fast, causing the solids in the alumina gel to move to the surface layer and cause silica formation. or
Undesirable uneven distribution of Mg, Sr, Y, La, Ce, Nd, Ti, Zr, Cr, and Sn occurs. Furthermore, at temperatures below 10°C, it is difficult to form a gel in which these solids are uniformly dispersed, and therefore it is necessary to stir and mix for a long time, which is not practical. In addition, when a homogeneous mixed aqueous solution of alumina hydrate and colloidal silica is thickened and gelled, basic compounds such as ammonia, ammonia carbonate, aliphatic amines such as trimethylamine, as well as compounds of the elements specified by the present invention are used. It is also possible to use compounds in combination. Further, during or after gelation, it is appropriate to sufficiently knead and stir the mixture while maintaining the temperature in the range of 10 to 150°C for at least 20 minutes, preferably 30 minutes or more. As a result, it is possible to uniformly disperse the silica in a form in which the aluminum is almost completely surrounded by the silica as the core. In drying the solid material after gelation, aging is not necessary and may be carried out immediately after sufficient stirring and kneading. When drying, rapid high-temperature drying is undesirable as it will migrate to the surface layer of stabilizers such as silica, so the temperature should be gradually raised in a dryer with a small temperature distribution, such as a hot air circulation dryer, and the final 10 at 150-200℃
It is preferable to dry for at least an hour. Calcination may be carried out after the dry solid is roughly pulverized to about 500 microns or, if necessary, after pulverized to about 20 to 30 microns. The dried powder is then calcined in the presence of air at a temperature range of 500 to 1100°C, preferably 600 to 1000°C for at least 3 hours to obtain a finished catalyst carrier composition. The heat-resistant catalyst carrier composition obtained as described above contains alumina in a range of 70 to 99.4% by weight and silica in a range of 0.5 to 20% by weight, preferably 0.8% by weight.
~12% by weight range and Mg, Sr, Y, La, Ce,
It is preferable that the oxide of at least one element selected from the group consisting of Nd, Ti, Zr, Cr and Sn has a composition in the range of 0.1 to 10% by weight, preferably in the range of 1 to 6% by weight. As the alumina raw material, an amorphous alumina hydrate having a boehmite structure or a precipitated boehmite structure that is partially soluble in inorganic or organic acids is suitable, and alumina hydrates such as gibbsite or diaspore are not preferred. When silica is less than 0.5% by weight, silica has almost no effect as a stabilizer, and
When the amount exceeds 20% by weight, the effect as a stabilizer is recognized, but when fired for a long time, mullite, which is a composite oxide with alumina, begins to be produced, and its effect decreases. As colloidal silica, any type of hydrogen ion concentration such as acidic, neutral, or basic can be used, but acidic silica is particularly preferable, and the particle size may be 50 millimicrons or less, especially 10 to 10 mm. 20
Millimicron ones are preferred. If sodium present as a silica sol stabilizer is contained in an amount of 0.1% or more as sodium oxide, the effect of silica as an alumina stabilizer will be weakened, so sodium oxide is preferably 0.05% or less. Next, the present invention will be specifically explained using examples. However, the composition, manufacturing method, etc. are not limited to these. Example 1 Boehmite (manufactured by Conoco, trade name: SB Alumina) was added to an acetic acid solution prepared by adding 230 ml of acetic acid to 2070 ml of water.
270 g was added and stirred for 2 hours using a homomixer to obtain an alumina sol. This sol was placed in a kneader heated to 60°C, 13.9 g of colloidal silica (manufactured by Nissan Chemical Industries, Ltd., trade name: Snowtex) was added, and while stirring, 200 ml of an aqueous solution containing 56.3 g of chromium nitrate was added. The mixture was kneaded and stirred for 1 hour. The pH of the kneaded product at this time was 7.5. Thereafter, the gelled solid was placed in a hot air circulation dryer and dried at 150°C for 12 hours. Next, the dry solid was pulverized with an atomizer to form a powder of 10 to 20 microns, and then calcined at 800°C for 5 hours to produce 1.3 silica.
A composite oxide containing 5% by weight of chromia and 93.7% by weight of alumina was obtained. Example 2 662 g of boehmite (manufactured by Condeia, trade name: Dispural) with a specific surface area of 150 m ² /g
was added to 1,830 ml of water containing 19.6 ml of 60% nitric acid, and stirred for 1 hour using a homomixer to partially dissolve the mixture to obtain an alumina sol. Next, this sol was transferred to a kneader heated to 80° C., and while stirring, 126 g of colloidal silica (manufactured by Nissan Chemical Industries, Ltd., trade name: Snowtex) was added to obtain a uniform mixed solution. Next, while stirring the solution, 200 ml of an aqueous solution containing 81.2 g of lanthanum nitrate was gradually added to obtain a kneaded product. The pH of the kneaded product at this time was 8.4. Then, it was dried and calcined in the same manner as in Example 1 to give 4.5% by weight of silica, 5.5% by weight of lantana,
A composite oxide containing 90% by weight of alumina was obtained. Comparative Example 1 Colloidal silica (manufactured by Nissan Chemical Industries ^, Ltd., trade name:
It was immersed in a mixed solution of 470 g of water in which 126 g of SnowText and 81.2 g of lanthanum nitrate were dissolved, and evaporated to dryness while thoroughly mixing and stirring. Then, pulverization was carried out in the same manner as in Example 1,
After firing, a composite oxide containing 4.5% by weight of silica, 5.5% by weight of lanthana, and 90% by weight of alumina was obtained. Example 3 Same as Example 1 except that magnesium nitrate was used instead of chromium nitrate in Example 1, 1.3% by weight of silica, 1.7% by weight of magnesia,
A composite oxide containing 97.0% by weight of alumina was obtained. Example 4 1.3% by weight of silica and 1.3% by weight of neodymia were prepared in the same manner as in Example 1 except that neodymium nitrate and titanium oxalate were used instead of chromium nitrate in Example 1.
A composite oxide containing 0.4% by weight, 1.7% by weight as titania, and 96.6% by weight as alumina was obtained. Example 5 Example 1 except that zirconium nitrate and yttrium nitrate were used instead of chromium nitrate in Example 1.
In the same manner as above, a composite oxide containing 1.3% by weight of silica, 1.5% by weight of zirconia, 0.2% by weight of itria, and 97.0% by weight of alumina was obtained. Example 6 A composite oxide containing 4.5% by weight of silica, 0.5% by weight of ceria, and 95.0% by weight of alumina was prepared in the same manner as in Example 2 except that cerium acetate was used instead of lanthanum nitrate in Example 2. Obtained. Example 7 Example 2 except that strontium nitrate and stannous chloride were used instead of lanthanum nitrate in Example 2.
In the same manner as above, a composite oxide containing 4.5% by weight of silica, 0.5% by weight of strontium oxide, 1.8% by weight of stannous oxide, and 93.2% by weight of alumina was obtained. Example 8 The composite oxides obtained in Examples 1 to 7 and Comparative Example 1 were heated at 1200°C for 20 hours and 50 hours, respectively.
After firing in air atmosphere for 100 hours, 200 hours, and 300 hours, the surface area was filled with nitrogen gas as an adsorption gas.
Measured with a BET type specific surface meter. Table 1 shows the surface area measurement results. As shown in Table 1, the composite oxides obtained in Examples 1 to 7 have a specific surface area of 20 m ² /g or more even after calcination at 1200°C for 200 hours, and are thermally stable catalyst carrier compositions. I understand that. On the other hand, the composite oxide produced by the immersion method in Comparative Example 1 was 20
It was stabilized up to the time of firing, but after 50 hours of firing the surface area changed significantly over time and the stabilizing effect disappeared. 【table】

Claims (1)

[Claims] 1. At least one member selected from the group consisting of magnesium, strontium, yttrium, lanthanum, cerium, neodymium, titanium, zirconium, chromium, and tin is added to the mixed aqueous solution of alumina hydrate and colloidal silica. A method for producing a heat-resistant catalyst carrier composition, which comprises adding a compound of the above elements to thicken and gel the mixed aqueous solution, and drying and calcining the resulting gel. 2. The heat-resistant catalyst carrier composition is 70% as alumina.
-99.4% by weight, 0.5-20% by weight as silica and oxidation of at least one element selected from the group consisting of magnesium, strontium, yttrium, lanthanum, cerium, neodymium, titanium, zirconium, chromium and tin. Thing is
A method according to claim 1, characterized in that it has a composition ranging from 0.1 to 10% by weight. 3. The method according to claim 1 or 2, wherein the alumina hydrate is amorphous, has a boehmite structure, or a solidified boehmite structure, and is partially soluble in acids. 4 Claims 1 and 2 characterized in that the thickening and gelling of the mixed aqueous solution of alumina hydrate and colloidal silica is carried out at a temperature range of 10 to 150°C.
Or the method described in 3.