JPH0553542B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing a heat-resistant catalyst carrier, and particularly to a method for producing a heat-resistant catalyst carrier by impregnating and kneading β-alumina. (Prior Art) In recent years, research and development efforts have been underway to apply the so-called catalytic combustion method, which uses a catalyst to promote combustion, to make it more efficient and compact by applying it to various types of combustors, including gas turbines. ing. Since the catalysts used in these combustors are usually used at high temperatures of 1000°C or higher, they require heat-resistant carriers that are difficult to sinter and do not crack even when subjected to thermal shock. Conventionally, a La-β-Al ₂ O ₃ carrier produced by a coprecipitation method has been known as a carrier with excellent heat resistance (Japanese Patent Laid-Open No. 59-080752). This La−β−Al ₂ O ₃
The reason why the carrier has excellent heat resistance is that the β-alumina structure is composed of _three Al ₂ O layers and La
- It has a laminate structure in which the spinel layer of Al ₂ O ₃ is repeated every four layers, and therefore the La-
This is thought to be because the AlO ₃ layer inhibits the crystal growth of the Al ₂ O ₃ layer. On the other hand, regarding the thermal changes and reactivity of alumina hydrate and lanthanum compounds, gibbsite (Al ₂ O ₃ 3H ₂ O), a type of alumina hydrate, has a
It changes to γ- _Al2O3 or χ- _Al2O3 at 400℃, further changes to γ- _Al2O3 at 900~ _{1000 ℃} , _and then from 1100~
Sintering progresses at 1200°C while undergoing a phase transition to α-Al ₂ O ₃ . On the other hand, in the case of lanthanum nitrate (La( _{NO 3} ) 3.6H ₂ O), which is an example of a lanthanum compound, the temperature is 700℃.
It decomposes into lanthanum oxide (La ₂ O ₃ ). Furthermore, this reaction between La ₂ O ₃ and Al ₂ O ₃ is carried out at 1300°C.
It happens above. For this reason, aluminum hydroxide supports or γ-
In the case of the so-called impregnation method, in which an Al ₂ O ₃ carrier is impregnated with lanthanum nitrate to form an alumina hydrate and then fired to obtain β-Al ₂ O ₃ , the firing process is as shown in Figure 5. with γ-Al ₂ O ₃ or χ- Al ₂ O ₃ and La ₂ O ₃
At temperatures above 1000℃, most of the γ-Al ₂ O ₃ grows into large particles of α-Al ₂ O ₃ .
Good β-Al ₂ O ₃ cannot be obtained. Therefore, the above
A laminate structure, which is the ideal structure of La-β-Al ₂ O _3, cannot be obtained. Similarly, when attempting to obtain alumina hydrate or γ-Al ₂ O ₃ and a lanthanum compound by a kneading method, the same phenomenon as described above occurs. That is, before β-alumina is formed, γ-
A support with a high specific surface area cannot be obtained by sintering accompanied by a transition from Al ₂ O ₃ to α-Al ₂ O ₃ , and it cannot be used in a method for producing a highly active, heat-resistant support for a combustion catalyst. Therefore, in order to mix lanthanum oxide and alumina at the molecular level, a method has been proposed in which an alkali is added to a mixed solution of lanthanum nitrate and aluminum nitrate to cause coprecipitation. (Unexamined Japanese Patent Publication 1983)
−080752). (Problems to be Solved by the Invention) However, when the present inventors conducted further research on the carrier produced by this coprecipitation method, it was found that the carrier did not have sufficiently excellent heat resistance. That's what I found out. The reason for this is the 6th
As shown in the figure, when the pH changes due to the addition of alkali (NH ₃ aqueous solution), aluminum hydroxide (Al
(OH) ₃ ) and lanthanum hydroxide (La(OH) ₃ ) have different precipitate formation regions, and as alkali is added,
It was found that first a precipitate of aluminum hydroxide was formed, and then a precipitate of lanthanum hydroxide was formed. As a result, it was found that aluminum hydroxide and lanthanum hydroxide were not mixed at the molecular level, which was insufficient to obtain a support having a β-alumina structure with excellent heat resistance. Therefore, there has been a desire for a method for producing a catalyst carrier that allows mixing of lanthanum and aluminum at the molecular level. An object of the present invention is to solve the problems of the prior art described above and to provide a method for manufacturing a carrier having a β-alumina structure with excellent heat resistance. (Means for Solving the Problems) In short, the present invention provides rehydratable alumina with
Barium (Ba) and/or Lanthanum (La)
It is characterized by adding a solution containing the compound by impregnation or kneading, and then firing. The catalyst carrier of the present invention further supports an oxidation catalyst such as palladium, and is used as a combustion catalyst in various combustors such as gas turbines. First, the principle of the present invention will be explained. Gibbsite, a type of alumina hydrate
When Al ₂ O ₃ 3H ₂ O is dehydrated by heating it in a vacuum at 250°C or rapidly, for example at about 1000°C for several seconds, it becomes ρ-alumina (Al ₂ O ₃ 0.4H ₂ O).
is obtained. Since this ρ-alumina was rapidly dehydrated, it can be considered that it was dehydrated while retaining the gibbsite structure, and the Al ₂ O ₃ molecules remained in the same position as they were in the gibbsite structure. Therefore, the Al ₂ O ₃ molecules are separated from each other and have a structure with voids through which water molecules have escaped. Therefore, ρ−
Alumina is extremely fine particles, and Al ₂ O ₃ exists as particles close to the molecular level, and has a specific surface area so high that it cannot be measured by N ₂ adsorption. This ρ-alumina undergoes rehydration by adding water and turns into baryrite (Al ₂ O ₃ .3H ₂ O). This rehydration occurs even at room temperature and is not very fast. Therefore, when this unrehydrated ρ-alumina and an aqueous solution of a lanthanum compound are mixed, the lanthanum compound is incorporated into the pores of ρ-alumina before the ρ-alumina is rehydrated, and the lanthanum and alumina are bonded at the molecular level. Uniform mixing is possible. As mentioned above, the rehydration rate of ρ-alumina is not very high at room temperature, and alumina is acidic and easily adsorbs lanthanum ions (La ³⁺ ) in the solution. The feature of the present invention is that it makes it possible to do this. By firing this mixture, a support with excellent heat resistance and a β-alumina structure in which _three layers of Al ₂ O and _three layers of LaAlO are repeated every four layers can be obtained. Specifically, the catalyst support of the present invention can be prepared by simply adding a solution containing a barium and/or lanthanum compound to a rehydratable alumina such as ρ-alumina by impregnation or kneading, and then calcination. It can be manufactured by any method. Here, the rehydratable alumina refers to ρ-alumina or alumina obtained by making an alumina hydrate rehydrated by rapid thermal dehydration. In addition, barium and/or lanthanum compounds include:
Any material may be used as long as it produces an oxide or carbonate upon firing. Since the carbonates mentioned above produce oxides through partial decomposition, they have the same effects as those of oxides. The composition of the catalyst carrier is such that the element barium or lanthanum is more than 0 relative to aluminum.
It is preferably selected within 15 atomic %, preferably 2 to 7 atomic %. The firing temperature is generally preferably 700°C or higher. Hereinafter, the present invention will be explained in detail using Examples. Example 1 50 g of ρ-alumina powder obtained by vacuum degassing gibbsite (Al ₂ O ₃ 3H ₂ O) at 250°C and 22.4 g of lanthanum nitrate (La(NO ₃ ) ₃ 6H ₂ O). 30ml of distilled water
was added and kneaded, and the resulting paste was dried at 180°C and further calcined at 700°C. After crushing this using a hammer mill, 5φ×
It was molded to 5L (unit: mm) and fired at 700℃ to form a catalyst carrier. These steps are shown in FIG. 1A. Example 2 In place of lanthanum nitrate in Example 1, 13.2 g of barium acetate (Ba(CH ₃ COO) ₂ ) was added and a catalyst carrier was obtained in the same manner. Example 3 25 ml of lanthanum nitrate aqueous solution (La concentration 0.29 g/ml) was added to 50 g of the ρ-alumina molded product obtained by molding the ρ-alumina powder of Example 1 into a size of 5φ x 5 L using a hydraulic press.
It was impregnated and calcined at 700°C to form a catalyst carrier. These steps are shown in FIG. 1B. Example 4 In place of the ρ-alumina in Example 1, commercially available rehydratable alumina (BK- manufactured by Sumitomo Aluminum Refining Co., Ltd.) was used.
103), a catalyst support was obtained in the same manner. Examples 5 to 8 The amount of lanthanum nitrate in Example 1 was changed from 22.4 g to 4.5 g (Example 5), 13.4 g (Example 6), and 44.7 g, respectively.
g (Example 7), 67.1 g (Example 8),
A catalyst carrier was obtained using the same procedure. Comparative Example 1 A catalyst carrier was obtained in the same manner as in Example 1 except that hydrated alumina was used in place of the rehydratable alumina. Comparative example 2 Aluminum nitrate (Al(NO ₃ ) ₃・9H ₂ O) 350g
and 21 g of lanthanum nitrate (La(NO ₃ ) ₃ 6H ₂ O) were dissolved in 3.7 g of distilled water and stirred at room temperature. To the resulting solution, 5M ammonia water was added while stirring.
The mixture was gradually added over an hour or more until the pH reached 7, and a coprecipitate was obtained. The precipitate was washed by decanting three to five times with 500 ml of distilled water each time. The obtained precipitate was suction filtered, dried at 180°C, and further calcined at 700°C. These steps are shown in FIG. Comparative Example 3 A catalyst carrier was obtained in the same manner as in Example 1 except that the addition of lanthanum nitrate was omitted. Test Example 1 The carriers obtained in Examples 1 to 4 and Comparative Examples 1 to 2 were
Heat treatment was performed at 1300°C for 2 hours. The specific surface area of this material was measured by the BET method. Table 1 shows the results for the carriers of Examples 1 to 4 and Comparative Examples 1 and 2.

[Table] From the results in Table 1, the catalyst carrier of the present invention is
It can be seen that a high specific surface area can be obtained even at a high temperature of 1300°C compared to the comparative example. Further, the results of Examples 1 and 5 to 8 and Comparative Example 3 are plotted against the amount of lanthanum added, and the results are shown in FIG. From this figure, the amount of lanthanum added in the present invention is more than 0 and less than 15 at%, especially 2 to 15 at%.
It can be seen that a range of 7 atomic % is appropriate. Test 2 The carriers obtained in Examples 1 and 2 and Comparative Example 2 were
They were heat treated at 1300°C for 2 hours and subjected to X-ray diffraction. Figure 3 shows the results. As can be seen from this figure, clear peaks of LaAlO ₃ and α-Al ₂ O ₃ are seen in the comparative example carrier, indicating crystal growth, but no sharp peaks are observed in the catalyst carrier of the present invention. , it can be seen that no crystal growth occurs. Examples 9 and 10 and Comparative Examples 4 and 5 Examples 1 and 2 and Comparative Examples 1 and 2
Add 0.5wt of palladium nitrate to the catalyst carrier obtained in
% and calcined at 1000°C and 1300°C for 2 hours. A combustion test of the obtained catalyst was conducted under the following conditions, and the methane combustion rate was measured when the combustion start temperature and gas preheating temperature were constant at 500°C. Conditions SV: 30000h ^-1 CH ₄ : 3% O ₂ : 8% H ₂ : Balance The results obtained are shown in Table 2.

[Table] From this table, it can be seen that the carrier of the present invention maintains a high specific surface area and is excellent as a carrier for a catalyst used at high temperatures. (Effects of the Invention) According to the present invention, it is possible to mix a lanthanum or barium compound and alumina at the molecular level, and a catalyst carrier with excellent heat resistance having a β-alumina structure, that is, a catalyst that allows combustion to occur at high temperatures. It is possible to obtain a heat-resistant catalyst carrier for high temperatures using a simple process. In addition, in production using the conventional coprecipitation method, the production flow was complicated and required a lot of equipment such as precipitation layers and filtration equipment, but the production method of the present invention does not require much of such equipment, and the flow It has become easy to put the manufacturing technology into practical use.

[Brief explanation of the drawing]

FIGS. 1A and 1B are block diagrams showing the manufacturing process of a heat-resistant catalyst carrier of the present invention, FIG. 2 is a diagram showing the results of an example of the present invention, and FIG.
Figures 4A and 4B, which show the results of X-ray diffraction in the example of the present invention, are obtained by the conventional coprecipitation method.
A schematic diagram and a cross-sectional view of the molecular structure of the La-β-Al ₂ O ₃ carrier, Figure 5 shows the Al ₂ O ₃ −
Figure 6 is a diagram schematically explaining the formation of La ₂ O ₃ carrier, Figure 6 is a diagram explaining the difference in the precipitate formation region of Al(OH) ₃ and La(OH) ₃ , Figure 7 is a diagram schematically explaining the formation of La 2 O 3 carrier. FIG.

Claims (1)

[Claims] 1. Rehydratable alumina containing barium and/or
Or, a method for producing a heat-resistant catalyst carrier, which comprises adding an aqueous solution containing a lanthanum compound in an amount of more than 0 and less than 15 atomic % based on aluminum by impregnation or kneading, and then firing. 2. The rehydratable alumina according to claim 1 is ρ-alumina (Al ₂ O ₃・0.4H ₂ O) and/or alumina made rehydrated by rapid dehydration treatment at high temperature. A method for producing a heat-resistant catalyst carrier, characterized by the following.