JP2021159861A - Manufacturing method of catalyst - Google Patents

Abstract

To provide a manufacturing method of a catalyst excellent in catalytic activity, by immobilizing efficiently 12CaO-7Al2O3 compound on a ceramic support.SOLUTION: A manufacturing method of a catalyst includes steps of: (A) producing aqueous slurry containing calcium aluminate and a transition metal; (B) coating a ceramic support surface with the aqueous slurry; and (C) generating and immobilizing 12CaO-7Al2O3 compound particles on a ceramic support by heat-treating the ceramic support at the temperature of 400-600°C.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a catalyst containing _{a 12CaO / 7Al 2} O _{3 compound.}

Calcium aluminate having a 12CaO / 7Al ₂ O ₃ compound structure has free oxygen in the lattice, and is known to be useful as an oxidation catalyst, an ionic conductor, and a co-catalyst (Patent Documents 1 and 2). .. Further, in this 12CaO / 7Al ₂ O ₃ compound, by supporting a transition metal such as Ni or Pt on the surface thereof, a catalyst for purifying engine exhaust gas, a catalyst for hydrogen production, etc. can be obtained from a hydrocarbon gas such as methane. Is also known (Patent Documents 3, 4, 5).

JP-A-2002-3128 Japanese Unexamined Patent Publication No. 2006-96571 JP-A-2018-143940 Japanese Unexamined Patent Publication No. 2018-143941 Japanese Unexamined Patent Publication No. 2003-190787

However, most of the catalysts currently in practical use in the industrial world, including those for environmental purification and automobiles, are not used as powders, but are supported and used on various supports. The reason is that powder causes clogging, which makes it difficult to distribute gas, and there is a concern about the environmental impact of scattering. Therefore, it is desired that the catalyst of the present invention is also supported on a support for use. However, a method for supporting a 12CaO / 7Al ₂ O ₃ compound on a support has not been sufficiently studied. Further, it is effective to support a transition metal on the surface of the 12CaO / 7Al ₂ O ₃ compound particles in order to impart high catalytic activity, but the method has not been sufficiently studied. Therefore, an object of the present invention is _{to provide a method for efficiently immobilizing a 12CaO / 7Al 2} O ₃ compound on a ceramic support and producing a catalyst having excellent catalytic activity.

_{As a result of diligent studies on the production method of the catalyst using the 12CaO / 7Al 2} O ₃ compound, the present inventors used an aqueous slurry containing calcium aluminate and a transition metal and immobilized the catalyst on the ceramic support. , And found that a catalyst having excellent catalytic activity can be obtained, and completed the present invention.

That is, the present invention provides the following [1] to [4].
[1] (A) A step of preparing an aqueous slurry containing calcium aluminate and a transition metal, (B) a step of coating the aqueous slurry on the surface of a ceramic support, and (C) 400 to 600 of the ceramic support. A method for producing a catalyst, which comprises a step of heat-treating at a temperature of ° C. _{to generate and immobilize 12CaO / 7Al 2} O _{3 compound particles on the ceramic support.}
[2] Further, (D) the method for producing a catalyst according to [1], which comprises a step of reducing the transition metal to impart catalytic activity.
[3] The method for producing a catalyst according to [1] or [2], wherein the ceramic support is a ceramic support having a honeycomb structure.
_{[4] A transition metal having a ceramic support and a calcium aluminate layer containing 12CaO / 7Al 2} O ₃ compound particles on the surface of the ceramic support, and having catalytic activity is widely dispersed in the entire calcium aluminate layer. A catalyst characterized in that it contains a gap through which gas can flow inside the calcium aluminate layer.

According to the method of the present invention, a catalyst _{containing a 12CaO / 7Al 2} O ₃ compound having excellent catalytic activity can be obtained. This catalyst can be used as an industrially useful oxidation catalyst and reduction catalyst, and is particularly useful as a catalyst for hydrogen production by direct decomposition of hydrocarbons.

A scanning electron microscope image of the catalyst cross section is shown. The observation direction of the catalyst cross section at the time of observation with a scanning electron microscope is shown. The element mapping image of calcium of the catalyst cross section is shown. The element mapping image of nickel of the catalyst cross section is shown.

The method for producing a catalyst of the present invention includes (A) a step of producing an aqueous slurry containing calcium aluminate and a transition metal, (B) a step of coating the aqueous slurry on the surface of a ceramic support, and (C) the ceramics. The process includes a step of heat-treating the support at a temperature of 400 to 600 ° C. _{to generate and immobilize 12CaO / 7Al 2} O ₃ compound particles on the ceramic support. The details will be described below.

<Process (A)>
Examples of the calcium aluminate used in the step (A) include various calcium aluminate compounds, amorphous calcium aluminate, and calcium aluminate hydrate, and one or more of these may be used. Examples of the calcium aluminate compound include 3CaO / Al ₂ O ₃ , 12 CaO / 7 Al ₂ O ₃ , CaO / Al ₂ O _{3 and the} like. As the calcium aluminate _{hydrate, 3CaO · Al 2 O 3 ·} xH 2 O, 2CaO · Al 2 O 3 · xH 2 O, etc. _{4CaO · Al 2 O 3 · xH} 2 O and the like. These may be one or a mixture of two or more, but after the heat treatment, it is preferred to include as much as possible 12CaO · 7Al ₂ O ₃ compound. From that point, the calcium aluminate, with CaO / Al ₂ O ₃ molar ratio is preferably from 1.4 to 2.0, more preferably 1.5 to 1.9, 1.6 to 1.8 and more preferable.

Although the calcium aluminate in the present invention is used in the ^{form of a powder, it is desirable that the calcium aluminate is a fine powder having a BET specific surface area of 1 m 2} / g or more in terms of dispersion in an aqueous slurry.

Here, by dispersing the powder particles of calcium aluminate in water to form an aqueous slurry, calcium aluminate hydrate is formed on the surface of the calcium aluminate particles. When a calcium aluminate hydrate layer is formed on the surface of the calcium aluminate particles, the hydration of the calcium aluminate particles does not proceed any further. The calcium aluminate particles exist in a state of being dispersed in an aqueous slurry with a calcium aluminate hydrate layer on the surface. The hydrate has a good affinity with the surface of the ceramic support, and by arranging the calcium aluminate hydrate on the surface of the calcium aluminate particles, a good coating layer can be formed on the surface of the ceramic support.

The content of calcium aluminate in the aqueous slurry is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 20 parts by mass, still more preferably 1 to 10 parts by mass with respect to 100 parts by mass of water.

Examples of the transition metal used in the step (A) include one or more elements selected from Group 8, Group 9, and Group 10 such as Ni, Pt, Pd, Ru, Rh, and Co. For example, a heterogeneous catalyst such as a binary system or a ternary system may be used. These transition metals can be selected according to the desired catalytic activity. For example, in the case of a catalyst for hydrogen production, Ni, Pt, Pd, Ru, Rh are more preferable, and Ni is particularly preferable.

The form of the transition metal is not particularly limited as long as it is dispersed in the aqueous slurry, but in order to secure a stable dispersed state, and to support the transition metal having a smaller particle size on the 12CaO / 7Al ₂ O ₃ compound. Therefore, it is preferable to use a water-soluble salt. Examples thereof include nitrates, acetates, sulfates, carbonates and chromates, and nitrates and acetates, which are often highly soluble in water, are particularly preferable. Specifically, nickel nitrate hexahydrate or nickel acetate tetrahydrate is preferable.

When the transition metal is added as a transition metal salt, it is preferably added with a saturated solubility in water. The content of the transition metal in the aqueous slurry is not particularly limited because it varies depending on the compound type, but is preferably 0.1 to 30 parts by mass, more preferably 1 to 20 parts by mass with respect to 100 parts by mass of water. ..

Here, since it is necessary for the aqueous slurry containing calcium aluminate and the transition metal to maintain a stable dispersed state, it is effective to add a small amount of a dispersant or a retarding agent. The dispersant is not particularly limited as long as it is generally used, and examples thereof include a water reducing agent for cement used in a cement composition. Further, as the retarder, oxycarboxylic acid such as citric acid and tartaric acid can be used.

As a method for producing an aqueous slurry, it is preferable to add calcium aluminate and a transition metal (transition metal salt) to water, and then slowly stir with a weak force using a stirrer using a stirring blade, a stirrer or the like. Since it is sufficient that the surface of the calcium aluminate particles is hydrated to form a layer of calcium aluminate hydrate on the particle surface, it is not necessary to stir and mix with an unnecessarily strong force. The stirring time is not particularly limited, but is preferably 1 to 120 minutes, more preferably 5 to 90 minutes. Here, the preparation temperature of the aqueous slurry may be 0.1 to 30 ° C., which is the temperature after the addition of calcium aluminate and the transition metal salt.

<Process (B)>
The aqueous slurry is coated on the surface of the ceramic support. Here, examples of the ceramic support include ceramic pellets, ceramic foam, ceramic honeycomb, and a sealing type ceramic honeycomb, and a ceramic support having a honeycomb structure is more preferable because a large amount of calcium aluminate particles can be coated. .. Here, examples of the ceramics include silicon carbide, cordierite, mullite, alumina, zirconia, titania, titanium phosphate, aluminum titanate, aluminosilicate and the like. Further, the ceramic support in the present invention includes a ceramic support whose surface has properties as ceramics. For example, a metal having a passivation of ceramics such as a metal oxide on the surface of iron, aluminum, chromium, titanium or an alloy thereof can also be used.

Examples of the method of coating the aqueous slurry on the surface of the ceramic support include a method of coating or spraying on the surface of the ceramic support, and a method of immersing the ceramic support in the aqueous slurry. The immersion time of about 10 seconds is sufficient, but the immersion temperature is preferably 0.1 to 30 ° C.

After coating the aqueous slurry, it is dried in the air atmosphere. It is preferable to dry at 100 ° C. for about 1 hour. Further, if necessary, coating and drying can be repeated a plurality of times to thicken the coating layer. In the method of the present invention, since the transition metal is coated in a state of being dispersed in calcium aluminate, the catalytic activity can be efficiently exhibited even if the coating layer becomes thick. The thickness of the coating layer is not particularly limited, but is preferably 1 to 200 μm, more preferably 5 to 150 μm, and even more preferably 10 to 100 μm.

<Process (C)>
Next, the ceramic support whose surface is coated with the aqueous slurry is heat-treated at a temperature of 400 to 600 ° C. As a result, the calcium aluminate hydrate on the surface of the calcium aluminate particles is decomposed to produce calcium aluminate such _{as a 12CaO / 7Al 2} O _{3 compound.} As a result, the coating layer of the calcium aluminate particles containing the transition metal is firmly immobilized on the ceramic support. It is also preferable that the decomposition of the hydrate creates a gap through which gas can flow in the calcium aluminate layer containing the _{12CaO / 7Al 2} O _{3 compound.}

The heat treatment of the ceramic support is preferably 400 to 600 ° C. from the viewpoint of changing the calcium aluminate hydrate into a 12CaO / 7Al ₂ O _{3 compound and preventing excessive agglutination of the transition metal.} 500 ° C. is more preferable. The heat treatment time of about 60 minutes is sufficient in consideration of the above factors.

<Process (D)>
The atmosphere of the heat treatment is not particularly limited, but it can usually be carried out in the atmosphere. By creating a hydrogen atmosphere, the transition metal activation treatment can be performed at the same time. When the heat treatment is performed in the atmosphere, it is preferable to separately activate the transition metal in a hydrogen atmosphere.

<Catalyst>
According to the production method of the present invention, a ceramic support and a _{calcium aluminate layer containing 12CaO / 7Al 2} O ₃ compound particles are provided on the surface of the ceramic support, and the entire calcium aluminate layer has catalytic activity. A catalyst in which the transition metal is widely dispersed and contains a gap through which gas can flow is obtained inside the calcium aluminate layer. In this catalyst, when the transition metal and the reaction target (hydrocarbon, etc.) come into contact with each other during the catalytic reaction, the reaction target easily comes into contact with not only the surface of the coating layer but also the transition metal inside the layer, and has high catalytic activity. ..

Next, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

<Example 1>
(Preparation of 12CaO / 7Al ₂ O ₃ compound particles)
A mixed powder having a molar ratio of calcium oxide and α-type aluminum oxide [(CaO) / (Al ₂ O ₃ )] = 1.63 was melted in a melting furnace. The maximum surface temperature at the time of melting was 1800 ° C., and after 40 minutes had passed, it was confirmed that the entire amount had melted, and the mixture was poured into a mold. Then, it was naturally cooled to obtain a 12CaO · 7Al ₂ O ₃ compound. For the crushing treatment, after crushing with a pin mill, crushing was performed using a single track jet mill (manufactured by Seishin Enterprise Co., Ltd.). The specific surface area of the 12CaO / 7Al ₂ O ₃ ^{compound powder obtained at this time was 1.8 m 2} / g. The specific surface area was calculated as the BET specific surface area using a nitrogen gas adsorption measuring device (BELsorb MAX manufactured by Microtrac Bell Co., Ltd.).

(Catalyst preparation)
2 parts by mass and 100 parts by mass of the obtained 12CaO / 7Al ₂ O ₃ compound powder and nickel nitrate hexahydrate (Fuji Film Wako Pure Chemical Industries, Ltd.) were added to 100 parts by mass of distilled water, respectively, and stirred for 1 hour. To obtain an aqueous slurry. As a support, a honeycomb type cordierite having a number of stitches per square inch of 400 was used, and the honeycomb surface was cut into 3 cm × 3 cm × in the vertical direction and 5 cm in the horizontal direction. The honeycomb support was immersed in an aqueous slurry for 10 seconds and dried in an air atmosphere at 100 ° C. for 1 hour. The same dipping and drying treatments were repeated a total of 4 times. Then, heat treatment was performed at 400 ° C. for 1 hour in an atmospheric atmosphere to obtain a catalyst.

(Evaluation of catalyst performance by direct decomposition reaction of methane)
After the catalyst was placed in a flow-type reaction tube and reduced at 400 ° C. for 1 hour in a hydrogen atmosphere, methane gas was circulated at 700 ° C. at 4.5 L / hr, and the hydrogen production characteristics at that time were subjected to gas chromatography. Was measured. As a result, the methane conversion rate at the initial stage of methane distribution was 56.1%, and the hydrogen concentration was 70.8%.

<Example 2>
(Catalyst preparation)
_{The 12CaO / 7Al 2} O ₃ compound powder, nickel nitrate hexahydrate, and citric acid powder obtained in the same procedure as in Example 1 were added to 100 parts by mass of distilled water, 2 parts by mass, 100 parts by mass, and 0. 01 parts by mass was added and stirred for 1 hour to obtain an aqueous slurry. Using the same honeycomb support as in Example 1, the mixture was immersed in an aqueous slurry for 10 seconds and dried at 100 ° C. for 1 hour in an air atmosphere. The same dipping and drying treatments were repeated a total of 4 times. Then, heat treatment was performed at 400 ° C. for 1 hour in an atmospheric atmosphere to obtain a catalyst.

(Evaluation of catalyst performance by direct decomposition reaction of methane)
After the catalyst was placed in a flow-type reaction tube and reduced at 400 ° C. for 1 hour in a hydrogen atmosphere, methane gas was circulated at 700 ° C. at 4.5 L / hr, and the hydrogen production characteristics at that time were subjected to gas chromatography. Was measured. As a result, the methane conversion rate at the initial stage of methane distribution was 69.4%, and the hydrogen concentration was 81.6%.

<Comparative example 1>
(Catalyst preparation)
Example 1 Each 2 parts by mass of against distilled water 100 parts by weight of 12CaO · 7Al ₂ O ₃ compound powder obtained by the same procedure as to give an aqueous slurry was stirred for 1 hour. Using the same honeycomb support as in Example 1, the mixture was immersed in an aqueous slurry for 10 seconds and dried at 100 ° C. for 1 hour in an air atmosphere. The same dipping and drying treatments were repeated a total of 4 times. Then, 100 parts by mass of nickel nitrate hexahydrate was added to 100 parts by mass of distilled water, the honeycomb support was immersed in the aqueous solution obtained by stirring for 1 hour for 10 seconds, and heat-treated at 400 ° C. for 1 hour in an air atmosphere. To obtain a catalyst.

(Evaluation of catalyst performance by direct decomposition reaction of methane)
After the catalyst was placed in a flow-type reaction tube and reduced at 400 ° C. for 1 hour in a hydrogen atmosphere, methane gas was circulated at 700 ° C. at 4.5 L / hr, and the hydrogen production characteristics at that time were subjected to gas chromatography. Was measured. As a result, the methane conversion rate at the initial stage of methane distribution was 36.2%, and the hydrogen concentration was 52.3%.

<Comparative example 2>
(Catalyst preparation)
Example 1 Each 2 parts by mass of against distilled water 100 parts by weight of 12CaO · 7Al ₂ O ₃ compound powder obtained by the same procedure as to give an aqueous slurry was stirred for 1 hour. Using the same honeycomb support as in Example 1, the mixture was immersed in an aqueous slurry for 10 seconds and dried at 100 ° C. for 1 hour in an air atmosphere. The same dipping and drying treatments were repeated a total of 4 times. Then, 100 parts by mass of nickel nitrate hexahydrate was added to 100 parts by mass of distilled water, and the honeycomb support was immersed in an aqueous solution obtained by stirring for 1 hour for 10 seconds and dried at 100 ° C. for 1 hour in an air atmosphere. .. The same dipping and drying treatments were repeated a total of 4 times. Then, the heat treatment was performed at 400 ° C. for 1 hour in the atmospheric atmosphere to obtain a catalyst.

(Evaluation of catalyst performance by direct decomposition reaction of methane)
After the catalyst was placed in a flow-type reaction tube and reduced at 400 ° C. for 1 hour in a hydrogen atmosphere, methane gas was circulated at 700 ° C. at 4.5 L / hr, and the hydrogen production characteristics at that time were subjected to gas chromatography. Was measured. As a result, the methane conversion rate at the initial stage of methane distribution was 43.8%, and the hydrogen concentration was 60.6%.

Claims (4)

(A) A step of preparing an aqueous slurry containing calcium aluminate and a transition metal, and
(B) A step of coating the surface of the ceramic support with the aqueous slurry and
(C) A method for producing a catalyst, which comprises a step of heat-treating the ceramic support at a temperature of 400 to 600 ° C. _{to generate and immobilize 12CaO / 7Al 2} O _{3 compound particles on the ceramic support.} The method for producing a catalyst according to claim 1, further comprising (D) a step of reducing the transition metal to impart catalytic activity. The method for producing a catalyst according to claim 1 or 2, wherein the ceramic support is a ceramic support having a honeycomb structure. _{A transition metal having a ceramic support and a calcium aluminate layer containing 12CaO / 7Al 2} O ₃ compound particles on the surface of the ceramic support and having catalytic activity is widely dispersed throughout the calcium aluminate layer. Moreover, the catalyst is characterized by including a gap through which gas can flow inside the calcium aluminate layer.

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