JPH0771633B2 - Method for producing large surface area alumina for high temperature catalytic combustion - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing alumina , which is a carrier material for high temperature catalytic combustion, and has a large surface area.
The present invention relates to a method for producing alumina for high temperature catalytic combustion .

[0002]

2. Description of the Related Art Currently, the energy required to operate a boiler, a gas turbine, etc. is provided by flame combustion in which oil, coal, natural gas, etc. are burned by air in the absence of a catalyst. In flame combustion, the combustion temperature reaches 2000 ° C., so that nitrogen in the air is oxidized to form nitrogen oxides (referred to as thermal NOx), which are released into the atmosphere together with the combustion exhaust gas, which adversely affects the global environment. On the other hand, in catalytic combustion, a fuel such as natural gas diluted with a large excess of air is ignited and burned in the catalyst layer, so the temperature does not become as high as in flame combustion and the generation of nitrogen oxides is extremely small. can do. Furthermore, even a lean fuel that cannot be combusted in the absence of a catalyst can continue stable combustion by catalytic combustion, so it can be said that it is an extremely convenient combustion system from the viewpoint of resource saving.

[0003] As support material for high temperature catalytic combustion, although conventional lanthanum · beta-alumina _{(La · β-Al 2 O} 3) or barium hexaaluminate (BaAl ₁₂ O ₁₉₎ or the like are known, which are crystal structures It is a different kind of upper alumina. Alumina easily undergoes a phase transition when heated above 1100 ° C to become α-alumina with a stable crystal structure, and has a surface area of 5 m ² / g.
Decrease to the following. There is known a method of coating the alumina surface with silica to suppress the phase transition and increase the surface area, but there is no example where the surface area of the product after high temperature firing at 1300 ° C. or higher was examined. As shown in the reference example, in the case of η-alumina whose surface is coated with silica (alumina referenced by the Catalysis Society, ALO-4), 1300-300
The surface area after firing at 1400 ° C is far below 20 m ² / g,
The silica coating method on ALO-4 cannot increase the surface area.

As a result of intensive studies, the inventors of the present invention selected needle-shaped crystal ammonium carboxyaluminum hydroxide as an alumina source, coated the surface with silica, and baked it at 1300 ° C. for 35 m ² / g
As described above, the alumina having a large surface area of 20 m ² / g or more after firing at 1400 ° C. has been successfully manufactured.

[0005]

An object of the present invention is [0005] to be Solved, severe temperature conditions smell that 1400 ℃
Be fired Te still greater than ^{20 m} 2 / g larger surface area
Aluminum for high temperature catalytic combustion with excellent thermal stability that can be maintained
To provide a manufacturing method for the

[0006]

[Means for Solving the Problems] And the above problems
In order to solve the above, the present invention provides an aluminum ammonium carboxyhydroxide [Al (NH ₄ ) CO ₃ (O
H) ₂ ] needle-like crystals are used as a source of alumina, and the surface thereof is coated with silica, followed by firing to obtain a high
Characterized by producing large surface area alumina for warm catalytic combustion
To do. In addition, according to such a preferred embodiment of the method of the present invention,
If the silica coating is
Runs are used, and even considering application to high temperature catalytic combustion
For example, the firing should be performed at 1300 to 1400 ° C.
Becomes

More specifically, the preparation of alumina according to the present invention is as follows. First, needle-like crystals of ammonium aluminum carboxyhydroxide as a starting material are synthesized by the method already established (JP-A-2-62485). That is, an aqueous solution of ammonium alum is added to an aqueous solution of ammonium hydrogen carbonate with stirring at room temperature, and the generated precipitate is transferred to a sealed container and aged at 100 ° C. for 24 hours. The obtained contents are suction filtered and washed with water, and then ethanol washing is repeated to replace water with ethanol, and an ethanol solution of tetraethoxysilane is added and dried. After that, the product of the present invention is obtained by firing at 1300 to 1400 ° C in an electric furnace.

[0008]

The large surface area for high temperature catalytic combustion according to the present invention
According to the method of manufacturing Lumina, the
Aluminum ammonium hydroxide [Al (NH ₄ ) C
O ₃ (OH) ₂ ] needle-like crystals are used, and the surface thereof is silica.
From the place of baking after coating, make the target
Even when alumina is fired at high temperature
Transfer can be advantageously suppressed and thus has a higher surface area for high temperature catalytic combustion than any of the previously reported examples.
Lumina is obtained in an advantageous manner. Hereinafter, the present invention will be described in detail with reference to Examples.

[0009]

EXAMPLES First, needle-shaped crystals of ammonium carboxyaluminum hydroxide as a starting material were synthesized by an already established method (JP-A-2-62485). That is, an aqueous solution of ammonium hydrogen carbonate having a concentration of 1.2 mol / l and an aqueous solution of ammonium alum having a concentration of 0.1 mol / l were added with stirring at room temperature, and the formed precipitate was transferred to a Teflon-sealed container to obtain 100 Aging at 24 ° C for 24 hours. The obtained content is suction filtered and washed with water, and then ethanol washing is repeated to replace water with ethanol, an ethanol solution of tetraethoxysilane is added, and the mixture is dried at 80 ° C. The obtained dry powder was fired in an electric furnace at 1300 to 1400 ° C. for 5 hours to obtain a product of the present invention. The temperature rising rate was 10 ° C./minute, and the temperature was left to cool naturally. The amount of tetraethoxysilane used for the surface coating is 0.046 to 0.173 g per unit weight of alumina.

Table 1 summarizes the surface area measurement results of alumina surface-coated with varying amounts of silica. The table also shows the surface area of alumina without silica coating.

[0011]

[Table 1]

[0012]

[Reference Example] Catalysis Society Reference Alumina (ALO-4) powder was used as an alumina source, and this was dispersed in ethanol as it was, and tetraethoxysilane was added at 0.1, 0.2 and 0.5 CC, and the mixture was kept at 80 ° C overnight. After being dried and calcined at each temperature for 5 hours, reference silica-coated alumina was used, and the surface area measurement results are summarized in Table 2. The table also shows the surface area of ALO-4 without silica coating.

[0013]

[Table 2]

Claims (3)

[Claims] 1. Ammoni of aluminum carboxyhydroxide
Needle crystals of um [Al (NH ₄ ) CO ₃ (OH) ₂ ]
Alumina source, whose surface was coated with silica
Large surface area for high temperature catalytic combustion characterized by subsequent firing
Alumina manufacturing method. 2. The silica coating is tetraeth
The high temperature catalyst according to claim 1, which is carried out using xylsilane.
A method for producing large surface area alumina for combustion. 3. The firing is performed at a temperature of 1300 to 1400 ° C.
High temperature catalytic combustion according to claim 1 or 2
Manufacturing method of large surface area alumina for baking.