JPH0333644B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an alumina composite oxide useful as a heat-resistant functional material, and particularly to an alumina composite oxide used as a support for catalysts, sensors, etc. used at high temperatures. (Prior Art) Flame combustion, which has the great advantage of being simple and easy to use, has been widely used in human life since prehistoric times, for cooking, heating, internal combustion engines, etc. However, flame combustion (1) generates harmful substances such as nitrogen oxides and carbon monoxide, (2) produces unburned substances with soot and bad odor, and (3) has low energy efficiency. ,
(4) There are constraints and drawbacks such as the fuel-air ratio having to fall within a specific narrow range, and these have become major social problems in recent years from the perspective of preserving the living environment and efficient use of energy resources. I'm getting used to it. In order to improve the above-mentioned drawbacks of flame combustion, a catalytic combustion method that uses a catalyst during combustion is considered to be effective, and various catalysts have been prepared and studied. However, no satisfactory catalyst has been found for combustion in automobile engines, jet engines, kerosene stoves, gas turbines, boilers, etc., which emit most of the air pollutants, except in the case of some passenger cars. This means that combustion in these devices
One of the major reasons is that there are no catalysts that can sufficiently withstand this high temperature, which is extremely high at 800 to 1500°C. Therefore, there is a need to develop highly heat-resistant materials that can be used as carriers for catalysts and sensors that can be used at such high temperatures. Generally, from the viewpoint of specific surface area and heat resistance, activated carbon, silica, alumina, titania,
Zirconia, zeolite, etc. are frequently used. However, both have poor thermal stability at high temperatures of 1000℃ or higher, and even alumina, which is said to have excellent heat resistance, rapidly changes to α-alumina with a corundum structure with a small surface area at temperatures above 1000℃. , it is impossible to play a role as a carrier for catalysts, sensors, etc. at high temperatures. For this reason, various attempts have been made to improve heat resistance by mixing different metal oxides into alumina.
La ₂ O ₃ −Al ₂ O ₃ based materials (Japanese Patent Application Laid-open No. 60-226414) and
BaO−Al ₂ O ₃ based materials (Chemistry Letters, 1985
Year P151-154; Surface 1986, Vol 24, No. 11658)
Products with unprecedented heat resistance have been discovered, such as: Both the La ₂ O ₃ −Al ₂ O ₃ type material and the BaO−Al ₂ O ₃ type material mentioned above are prepared by a coprecipitation method in the presence of a large amount of water, and the La ₂ O ₃ −Al ₂ O ₃ type material The system material is 1000
The specific surface area is 85 m ² /g when fired at 1200°C or higher, and 37m ² /g when fired at 1200°C, and BaO ₂ O ₃ material has a specific surface area of 100 m ² /g when fired at 1100°C and 50 m ² /g when fired at 1200°C. It has been reported that (Problem to be solved by the invention) However, when considering gases emitted at extremely high speeds from automobiles and aircraft, and fuels that tend to cause coking on the catalyst surface, such as aromatic compounds, the specific surface area of is necessary, and the existing ones are insufficient. In addition, in general, in practical combustion catalysts, first a heat-resistant support (hamnica structure such as mullite or codierite) is placed on a heat-resistant support.
Next, a step-by-step preparation method is used in which the active ingredient is loaded, so those obtained as powder by the coprecipitation method, such as the two types of carriers mentioned above, have a big problem because they do not adhere easily to the support. I understand. Therefore, it is an object of the present invention to overcome the problems of the prior art and to provide a method for producing a heat-resistant carrier material that maintains a high specific surface area even at high temperatures. (Means for Solving the Problems) In order to achieve the above-mentioned object, the present inventors have conducted intensive research on a method for compounding alumina and different metal oxides and on improving heat resistance. When aluminum alkoxide and a different type of alkoxide are hydrolyzed in the presence of a polyfunctional oxygen-containing organic compound, the hydrolysis and dehydration condensation reaction of the alkoxide are controlled by the organic compound, resulting in high homogeneity and a high specific surface area. The present inventors have discovered that a complex oxide exhibiting the following properties can be obtained, and based on this knowledge, the present invention has been completed. That is, the present invention mixes aluminum alkoxide and at least one selected from strontium alkoxide, barium alkoxide, lanthanium alkoxide, and zirconium alkoxide in the presence of at least one oxygen-containing organic compound having a plurality of functional groups. To provide a method for producing a heat-resistant alumina composite oxide, which comprises: preparing a homogeneous solution by hydrolyzing the solution, forming a sol, gelling the solution, drying the gel, and then heat-treating the gel at 1000°C or higher. It is something. The oxygen-containing organic compound having a plurality of functional groups (hereinafter simply referred to as a polyfunctional oxygen-containing compound) used in the present invention has a hydroxyl group as one of the functional groups, and at least one of the hydroxyl groups is bonded to a tertiary carbon. Preferably. As such, for example, hexylene glycol (2-methyl-2,4
-pentanediol), pinacol (2,3-dimethyl-2,3-butanediol), diacetone alcohol, etc., and such polyfunctional oxygen-containing compounds cause complex-forming reactions with metal alkoxides. It forms a complex with a metal alkoxide by causing a ligand exchange reaction. The resulting complex behaves differently from the original alkoxide in hydrolysis reactions and dehydration condensation reactions. Therefore, by utilizing such properties, it is possible to control the hydrolysis/condensation reaction between metal alkoxides. In other words, the hydrolysis and polycondensation reactions of metal alkoxides are controlled and regulated by the polyfunctional oxygen-containing organic compound, so solization and gelation are controlled, resulting in a homogeneous, well-mixed product with excellent heat resistance. Thus, an alumina composite oxide can be obtained. In the present invention, it is also possible to use a mixture of two or more types of polyfunctional oxygen-containing compounds, depending on the alkoxide raw material used.
This will be done as appropriate. The alkoxide used in the present invention can be any alkoxide of aluminum, strontium, barium, lanthanium, or zirconium, regardless of the type of alkyl group. Mention may be made of methoxide, ethoxide, iso- or n-propoxide, n-, sec- or tert-butoxide, which have the advantage of being cheaper than longer chain alkoxides. aluminum alkoxide and strontium,
Regarding the mixing ratio of barium, zirconium, and lanthanum oxide with each alkoxide, each of strontium oxide, barium oxide, zirconium oxide, and lanthanum oxide is mixed in the range of 3 to 25% by weight of the total weight in the final composite oxide. It's good. The content of the above four metal oxides is 3
When it is less than 25% by weight, α-alumina tends to be generated by firing at high temperature, resulting in a small specific surface area, and when it is more than 25% by weight, the crystal growth of the four metal oxides becomes significant, In this case as well, the specific surface area is significantly reduced. In the present invention, aluminum alkoxide and the above four various alkoxides are first mixed in the presence of a polyfunctional oxygen-containing compound to form an organic solution, but a solvent is used to prepare the solution. Basically, any one that can dissolve the five types of alkoxides mentioned above can be used. For example, all kinds of alcohols such as methanol, ethanol, propanol, and butanol, ketones such as acetone and methyl ethyl ketone, ethers such as ethyl ether, tetrahydrofuran, and dioxane, and aromatic compounds such as benzene and toluene can be used. However, the polyfunctional oxygen-containing compound itself can also be used as a solvent. The mixing temperature of this alkoxide is usually 10-200℃
is within the range of When creating a sol by hydrolysis, it is generally enough to drop water, but sometimes water is added depending on the raw material alkoxide used to prevent rapid precipitation of metal hydroxides and oxides. We need to devise a method. Such methods include adding water after diluting it with an organic solvent or an organic compound unrelated to hydrolysis/condensation reactions, bubbling a gas containing moisture, or adding water to a solution in a humid atmosphere. A method of leaving the mixture while stirring is used, and these methods may be used in combination as appropriate depending on the speed and progress of hydrolysis. In the present invention, the solution becomes a sol in the hydrolysis stage and finally becomes a gel, but for gelation, the sol may be directly gelled and dried;
The sol may be impregnated and applied to other substances, turned into a gel, and dried. The drying method is not particularly specified, and any method can be applied. Regarding the heat treatment, although the present invention is characterized in that the treatment is performed at a temperature of 1000°C or higher, a pretreatment may be performed at a temperature of 1000°C or lower before the heat treatment is performed at a temperature of 1000°C or higher. There are no particular restrictions on the temperature and atmosphere in the pretreatment, and various commonly used gas atmospheres such as air, oxygen, nitrogen, hydrogen, argon, and helium can be used at various temperatures, and a combination of these can be used in the pretreatment. can be processed. Similarly to the pretreatment, heat treatment at a high temperature of 1000°C is not particularly limited, and can be performed at various temperatures exceeding 1000°C, in various atmospheres, and by various methods. Further, there is no particular restriction on the heat treatment time, and the heat treatment can be performed at an appropriate temperature and atmosphere for a predetermined time. (Effect of the invention) According to the method of the present invention as described above,
SrO-Al ₂ O _3- based material, Ba-Al ₂ O ₃ as an alumina composite oxide that maintains a high specific surface area even at high temperatures
based materials, La ₂ O ₃ - Al ₂ O ₃ based materials and ZrO ₂ -
Al ₂ O ₃ based materials are obtained, which have a higher specific surface area than those produced by coprecipitation. Furthermore, the alumina composite oxide obtained by the method of the present invention has high heat resistance, and even when heated at a high temperature of 1000° C. or higher, the degree of decrease in specific surface area is much smaller than that of the conventional method. Furthermore, since this method has the characteristic of passing through a sol state, it has an advantage over conventional methods in that it can be impregnated onto a support or coated in a sol state. That is, the present invention solves at once the high surface area and the ease of attachment to a support, which are essential for catalyst carriers and sensor carriers used at high temperatures. As described above, the present invention has the following advantages: (1) There are many types of composite oxides that are heat resistant and provide a high specific surface area, and (2) They can be used in either powder or sol state. This method has a wider range of applications and greater economic effects than conventional methods. (Examples) Hereinafter, the present invention will be explained in more detail based on Examples. Example 1 72.1g of aluminum iso-
Propoxide (Al(Oiso-Pr) ₃ ) was added, 100 g of ethanol and 50 g of hexylene glycol were added thereto, and the mixture was stirred for 30 minutes while heating in an oil bath at 120°C. 4.0 g of strontium iso-propoxide (Sr(Oiso-Pr) ₂ ) was added to this solution, and the mixture was further heated and stirred at the same temperature for 2 hours. Next, add water to this solution.
A solution prepared by diluting 8.0 g with 50 g of ethanol was added dropwise through a dropping funnel. 30 minutes after the completion of the dropwise addition, 20 g of an ethanol solution containing 8 g of water was added at the same temperature to cause gelation.
It was aged by leaving it for a while. The gel was dried under reduced pressure using a rotary evaporator and then incubated in air at 300°C for 3 hours and at 550°C for 3 hours.
Firing was performed in stages at 800°C for 3 hours and at 1000°C _for 3 hours to obtain 10wt% SrO- _Al2O3 . This material showed no diffraction lines in powder X-ray diffraction (XRD), indicating that it was amorphous. The specific surface area was also measured using the BET method. The results are shown in Table 1. Example 2 72.2 g of Al(Oiso-Pr) ₃ was placed in a 300 ml beaker, 100 g of ethanol and 100 g of hexylene glycol were added, and the mixture was heated in an oil bath at 120°C.
Stir for 30 minutes. 3.0 g of barium ethoxide (Ba(OC ₂ H ₅ ) ₂ ) was added to this solution, and the mixture was further heated and stirred at the same temperature for 2 hours. Next, 60 g of an ethanol solution containing 8 g of water was added dropwise to this solution using a dropping funnel. After the dropwise addition was completed, 66 g of an ethanol solution containing 16.5 g of water was added over 30 minutes. After heating and stirring in an oil bath at 120° C. for 30 minutes, 10.3 g of water was further added to form a gel. The subsequent operations were performed in exactly the same manner as in Example 1 to obtain 10 wt% BaO-Al ₂ O ₃ . This was found to be amorphous by XRD. The specific surface area of this material was measured. The results are shown in Table 1. Example 3 10 wt% BaO-Al ₂ was prepared in the same manner as in Example 2 except that 3.7 g of barium n-butoxide (Ba(On-Bu) ₂ ) was used instead of Ba(OC ₂ H ₅ ) _2. Got _O3 . This material was found to be amorphous by XRD. The non-surface area of this sample is shown in Table 1. Example 4 Put 72.1 g of Al(Oiso-Pr) ₃ in a 300 ml beaker, add 3.9 g of lanthanium iso-propoxide (La(Oiso-Pr) ₃ ) and hexylene glycol.
100 g was added, and the mixture was heated and stirred in a 180°C oil bath for 2 hours. 50 g of ethanol solution containing 19 g of water in this solution
was added to form a gel. The subsequent operations were performed in exactly _{the same} manner as in Example 1 to obtain 10 wt% _La2O3 - _Al2O3 . This material was found to be amorphous by XRD. Table 1 shows the non-surface area of this product. Example 5 62.5g of Al(Oiso-Pr) ₃ in a 300ml beaker,
103 g of hexylene glycol and 30 g of ethanol were added, and the mixture was heated and stirred in a 120° C. oil bath for 30 minutes. To this were added 5.45 g of zirconium n-propoxide (Zr(On-Pr) ₄ ) and 1.1 g of acetic acid, and the mixture was heated and stirred at the same temperature for 2 hours. Next, add 20g to this solution.
80 g of an ethanol solution containing water was added dropwise in 4 portions of 20 g over 30 minutes to form a gel. 10wt% by performing the subsequent operations in exactly the same manner as in Example 1.
_{Zr2O3 - Al2O3 was} obtained. This material was found to be amorphous by XRD. Table 1 shows the specific surface area of this product. Example 6 The sample of Example 10 was further baked at 1200°C for 3 hours. In XRD, slightly broad diffraction lines based on the crystal structure of SrO.6Al ₂ O ₃ were observed. Table 1 shows the specific surface area of this product. As shown in Table 1, the specific surface area was 43 m ² /g, which is superior to the product baked under the same conditions obtained in the comparative example described below. Examples 7 and 8 Each sample of Examples 2 and 3 was fired at 1200° C. for 3 hours to obtain samples of Examples 7 and 8, respectively.
In XRD, both samples showed no diffraction lines and were found to be amorphous. Table 1 shows the specific surface area of each. Example 9 Al(Oiso-Pr) 87.2g of aluminum instead of _3
10wt % SrO-
_{Obtained Al2O3} . No obvious diffraction lines were observed in XRD, indicating that it was amorphous. Table 1 shows the specific surface area of this product. Example 10, 11 Al(Oiso-Pr) 87.2g of aluminum instead of ₃
The procedure was exactly the same as in Examples 2 and 3, respectively, except that sec-butoxide (Al(Osec-Bu) ₃ ) was used.
10wt _% BaO- _Al2O3 was obtained. Both samples
XRD showed no diffraction lines and it was found to be amorphous. Table 1 shows the specific surface area of each sample. Example 12 Instead of Al(Oiso-Pr) ₃ , 87.2 g of Al(Osec-
Bu) 10wt% in the same manner as in Example 4 except that ₃ was used.
La ₂ O ₃ −Al ₂ O ₃ was obtained. No diffraction lines were observed in XRD, indicating that it was amorphous. Table 1 shows the specific surface area.
It was shown to. Example 13 Al(Oiso-Pr) _87.2g of Al(Osec-
Bu) 10wt in the same manner as in Example 5 except that ₃ was used.
% _ZrO2 - _{Al2O3 was} obtained. No diffraction lines were observed in XRD, indicating that it was amorphous. Table 1 shows the specific surface area. Example 14 The sample obtained in Example 12 was further heated at 1200°C for 3 hours.
It was fired in Only 3 to 5 broad diffraction lines were observed in XRD, and it was estimated that this material had a structure close to amorphous. Table 1 shows the specific surface area. Example 15 In a 300ml beaker, 75.4g of Al(Osec-Bu) ₃ and
Add 50g of isopropanol, add 80g of pinacol, and stir in an oil bath at 60℃ for 30 minutes. 5.5 g of Zr(On-Pr) ₄ was added and dissolved in this solution, and 1.1 g of acetic acid was further added and stirred at the same temperature for 2 hours.
The subsequent operations were carried out in exactly the same manner as in Example 5,
10wt _{% ZrO2} - _Al2O3 was obtained. XRD revealed that this material was amorphous. Table 1 shows the specific surface area of this product. Comparative Example 1 87.6g of Al(Osec-Bu) ₃ was placed in a 300ml beaker, 50g of isopropanol was added, and 120g of
The mixture was warmed and stirred in an oil bath at ℃ for 30 minutes. to this
After adding 4.0 g of Sr (Oiso-Pr) ₂ and completely dissolving it,
The mixture was further stirred at the same temperature for 1 hour. Next, the temperature in the oil bath was lowered to 80°C and stirred for 1 hour. A precipitate was formed by adding this solution into 320 g of water previously heated to 80°C. This solution was allowed to stand overnight, filtered and dried, and then the same calcination procedure as in Example 1 was followed to obtain 10 wt% SrO-Al ₂ O ₃ . Table 1 shows the specific surface area. Comparative Examples 2 to 5 In Comparative Examples 2 to 5, Sr(Oiso-Pr) ₂ was
3.0g Ba _{( OC2H5} ) ₂ , 3.7g Ba(On-Bu) ₂ , 3.9
_Comparative Examples ₂ ~
Five samples were obtained. Table 1 shows the specific surface area of each sample.
Shown below. Comparative Example 6 Put 72.1g of Al(Oiso-Pr) ₃ in a 300ml beaker, add 100g of hexylene glycol,
Warm in a 120°C oil bath and stir. Add to this solution 12.7g of magnesium nitrate in 20g of ethanol.
The hexahydrate was dissolved and stirred at the same temperature for 2 hours. The subsequent operations were performed in the same manner as in Example 1, and 10wt%MgO−
_{Obtained Al2O3} . Table 1 shows the specific surface area of this product. Comparative Examples 7 to 11 Instead of magnesium nitrate hexahydrate, 8.4 g calcium nitrate tetrahydrate, 4.1 g strontium nitrate, 3.4 g barium nitrate, 5.3 g lanthanum nitrate hexahydrate and 6.4 g Using cerium ammonium nitrate (Ce(NH ₄ ) ₂ (NO ₃ ) ₆ ),
An alumina composite oxide was obtained in the same manner as in Comparative Example 6. These were designated as Comparative Examples 7 to 11. However, strontium nitrate and barium nitrate are difficult to dissolve in ethanol, so when adding these two,
It was dissolved in 8.5g of water and added. Table 1 shows the specific surface area of each composite oxide. Comparative Examples 12, 13 Two types of alumina composite oxides were obtained in the same manner as in Comparative Example 1, except that strontium n-propoxide or barium ethoxide was used instead of strontium isopropoxide, and these were further prepared in Example 6, It was baked at 1200°C for 3 hours in the same manner as in 7 and 8. The specific surface area of this sample is shown in Table 1 as Comparative Examples 12 and 13. Examples 16-19 The amounts of Al(Oiso-Pr) ₃ and Ba(On-Bu) ₂ used were changed, and the weight of barium oxide in the final composite compound was 5wt%, 15wt%, 20wt%, and 25wt%, respectively. Alumina composite oxides having the respective compositions were obtained in exactly the same manner as in Example 3, except that the composition was adjusted to be as follows. In XRD, BaO− of any composition
Neither Al ₂ O ₃ nor Al 2 O 3 showed any obvious diffraction lines, indicating that it was amorphous. Table 2 shows the specific surface area of each. Comparative Examples 14, 15 Example 16 except that Ba(On-Bu) ₂ was not used at all.
An alumina composite oxide was prepared in exactly the same manner as Comparative Example 14. The specific surface area of this product is shown in Table 2. Furthermore, this sample was fired at 1000℃ for 100 hours,
This was designated as Comparative Example 15, and the specific surface area is shown in Table 2. Example 20 The sample obtained in Example 17 was heated at 1200°C for 3 hours.
It was further fired. In XRD, broad diffraction peaks based on the magnetoplumbite of BaO.6Al ₂ O ₃ and the corundum structure of α-Al ₂ O ₃ were observed. The specific surface area is shown in Table 2. Example 21 The sample obtained in Example 18 was fired at 1200°C for 3 hours, and further fired at 1450°C for 3 hours. From XRD
It was found that it has a magnetoplumbite structure of BaO・Al ₂ O ₃ . The specific surface area is shown in Table 2. Example 22 The sample obtained in Example 3 was fired for an additional 97 hours at 1000°C for a total firing time of 100 hours, and the influence thereof was investigated. No diffraction lines were observed in XRD, indicating that it was amorphous. The specific surface area is shown in Table 2.

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Claims (1)

[Claims] 1. Oxygen-containing organic compound having multiple functional groups
Aluminum alkoxide and at least one selected from strontium alkoxide, barium alkoxide, lanthanium alkoxide, and zirconium alkoxide are mixed in the presence of one or more species to form a homogeneous solution, and then this solution is hydrolyzed. A method for producing a heat-resistant alumina composite oxide, which comprises forming a sol, turning it into a gel, drying the gel, and then heat-treating the gel at 1000°C or higher. 2. The method for producing a heat-resistant alumina composite oxide according to claim 1, wherein the oxygen-containing organic compound having a plurality of functional groups has a hydroxyl group bonded to a tertiary carbon as a functional group. 3. The heat-resistant alumina composite oxide according to claim 1, wherein the content of at least one selected from strontium oxide, barium oxide, lanthania, and zirconia in the produced alumina composite oxide is 3 to 25% by weight. How things are manufactured.