JPH09285729A - Catalytic combustion catalyst for use at high temperature - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a catalytic combustion catalyst having catalytic activity in a temp. range from a relatively low temp. and capable of maintaining the activity for a long time by using a compsn. represented by a specified formula as a base. SOLUTION: This catalytic combustion catalyst is based on a compsn. represented by the formula BaMnXAl12-x O19-a [where X is >1 to 2, preferably about 1.5, (a) is a number determined by X and the valences of Ba, Mn and Al, and when the valance of Ba is 2, the valence of Mn is represented by (z) and the valence of Al is 3, the equation a=X×(3-z)/2 is satisfied]. The compsn. is obtd. by regulating the amt. X for Mn substd. in a compd. having a magnetoplumbite structure. This catalyst is generally produced by an alkoxide method and it is, e.g. produced by adding an aq. soln. of Mn nitrate to alkoxides of Ba and Al so that the objective compsn. is obtd., hydrolyzing the alkoxides and carrying out aging, evaporation to dryness and firing.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a high temperature catalytic combustion catalyst applied to a catalytic combustor.

[0002]

2. Description of the Related Art Conventionally, noble metal-supported catalysts and transition metal oxide catalysts have been known as catalysts for catalytic combustion, but noble metal components and transition metals which become active components under conditions where the catalyst temperature exceeds 1000 ° C. The catalyst performance deteriorates due to volatilization of metal components and sintering, which makes it difficult to use for a long period of time. In addition, BaMn _1.0 Al ₁₁ O _19-a, which is known as a catalyst material having excellent heat resistance, is unlikely to deteriorate in catalytic performance, but has a problem that catalytic performance is low under initial conditions (“chemical device”). February 1987 issue 134-1
Page 37, Hiromichi Arai, "High-temperature catalytic combustion" support and catalyst "").

Particularly, as a conventional example, Japanese Patent Laid-Open No. 1-200303
There is a catalyst disclosed in Japanese Patent Publication No. 1, which is A _1-z C _z
B _x Al _12-x O _19-a [wherein A is one or more elements selected from the group consisting of Ca, Ba and Sr, C is a rare earth element, B is Mn, etc., and z is 0.4 or less. Number, x is about 0.1
Is a number within the range of 4 to 4, a is determined by the number of valences X, Y and Z of the elements A, C and B, and a = 1-1 / 2
A heat-resistant catalyst comprising a composition represented by {Xz (X-Y) + xZ-3y} as a main component. However, this catalyst does not satisfy both conditions of having a catalytic activity from a very low temperature and maintaining the catalytic activity for a long time.

[0004]

A catalyst for catalytic combustion is required to have a performance satisfying both conditions of having a catalytic activity from a relatively low temperature and maintaining the catalytic activity for a long time. However, the above-mentioned catalyst described as the prior art has a problem in heat resistance and thus is difficult to use for a long period of time, and has a low catalytic activity and a problem in catalytic activity from a low temperature. I was not completely satisfied.

In view of the above-mentioned state of the art, the present invention intends to solve the drawbacks of conventional catalysts and to provide a high temperature catalytic combustion catalyst which has catalytic activity from a relatively low temperature and which can maintain the catalytic activity for a long time. is there.

[0006]

The present invention provides (1) composition formula B
aMn _x Al _12-x O _19-a (where 1 <x ≦ 2, a is determined by the valences of X and Ba, Mn, Al, and Ba is 2
If the valence and the valence of Mn are Z and the valence of Al is trivalent, a = X ×
(3-Z) / 2 catalytic combustion catalyst and high temperature, characterized in that a main component represented by the composition by number) represented by (2) the composition formula _{BaMn x Al 12-x O 19} -a X is 1.
5 is the high temperature catalytic combustion catalyst according to (1) above.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION It is known that a compound having a magnetoplumbite structure represented by BaAl ₁₂ O ₁₉ has a large specific surface area even under a high temperature of 1400 ° C. and is a material having excellent heat resistance. BaMn _1.0 Al ₁₁ O _19-a is conventionally known as a catalyst material that takes advantage of this heat resistance. However, it is known that this catalyst does not deteriorate in catalytic performance even when used at 1000 ° C. or higher, and it becomes a catalyst excellent in heat resistance. However, since the catalytic performance is low and the activity expression temperature is high, it can be used. It was difficult.

In the present invention, attention was paid to the amount of Mn substitution in the magnetoplumbite structure, and a detailed study was conducted.
The higher the Mn substitution amount, the lower the heat resistance and the smaller the specific surface area. When the catalyst pretreatment temperature is low, the higher the Mn substitution amount, the higher the catalyst activity. I found that there is a tendency. According to the present invention, based on this finding, when the Mn substitution amount x in BaMn _x Al _12-x O _19-a is 1 <x ≦ 2, a is determined by X and the valence of Ba, Mn, and Al, and Ba is Divalent, Mn valence is Z, Al
Is a number represented by a = X × (3-Z) / 2, and has high heat resistance under a use condition of about 1200 ° C., thereby maintaining stable catalyst performance for a long period of time and M
This is the completion of a catalyst that exhibits activity from a low temperature as compared with a catalyst having an n substitution amount x = 1.

The high temperature catalytic combustion catalyst of the present invention is generally produced by the alkoxide method. Specifically, Ba, A
It can be produced by adding an aqueous solution of nitric acid of Mn to 1 alkoxide so as to have a desired composition, hydrolyzing the alkoxide, aging, evaporating to dryness, and baking.

[0010]

EXAMPLE FIG. 1 shows the test results of the ignition performance when the Mn substitution amount was changed. Mn substitution amount (x) up to 1.5 Mn
As the amount of substitution increases, it becomes possible to start combustion from a low temperature. However, when the Mn substitution amount x> 1.5, the combustion start temperature rises as the Mn substitution amount increases. That is, Mn
It has an excellent catalytic activity when the substitution amount is 1 <x ≦ 2, especially around x = 1.5. The conventional example of BaMn _1.0 Al ₁₁ O _19-a has an ignition temperature of 620 ° C., while the BaMn _1.5 Al _10.5 O _{19-a of} the present invention has an ignition temperature of 585 ° C. It can be seen that the combustion starting ability from low temperature is excellent.

FIG. 2 shows the test results concerning the heat resistance when the Mn substitution amount was changed. The heat resistance was evaluated by determining the reaction rate constant of the catalyst exposed to the atmospheric condition of 1200 ° C. for a certain period of time and comparing it with the initial state. As the Mn substitution amount increases, the degree of activity decrease with respect to the use time tends to increase, but especially when the Mn substitution amount is 2 or less, the activity decrease with use time is small, and the catalyst can be used for a long time. In FIG. 2, K ₀ is the reaction rate constant under the initial conditions, and K is the reaction rate constant of the catalyst after the time corresponding to the horizontal axis has elapsed.

From the results shown in FIGS. 1 and 2, the Mn substitution amount x is set to 1 <
It will be understood that by adjusting x ≦ 2, especially around x = 1.5, the combustion starting ability from a low temperature is excellent and the catalyst can be used for a long period of time.

[0013]

The high temperature catalytic combustion catalyst of the present invention, as compared with the conventional BaMn _1.0 Al ₁₁ O _19-a catalyst having a composition of having the same degree of catalyst durability, and the combustion start capacity from a low temperature There is an effect that can provide an improved catalyst.

[Brief description of drawings]

FIG. 1 is a chart showing the change in ignition performance depending on the amount of Mn substitution in a high temperature catalytic combustion catalyst of the present invention.

FIG. 2 is a chart showing the evaluation results of heat resistance according to the Mn substitution amount in the high temperature catalytic combustion catalyst of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigemi Bandai 1-1-1, Niihama, Arai-cho, Takasago-shi, Hyogo Prefecture Takasago Research Institute, Mitsubishi Heavy Industries, Ltd. (72) Kuniaki Aoyama 2-1-1, Niihama, Arai-cho, Takasago, Hyogo Prefecture No. 1 Mitsubishi Heavy Industries, Ltd. Takasago Works (72) Inventor Koichi Nishida 1-1-1, Niihama, Arai-cho, Takasago, Hyogo Prefecture Mitsubishi Heavy Industries Takasago Works

Claims (2)

[Claims] 1. A composition formula BaMn _x Al _12-x O _19-a (where 1 <x ≦ 2, a is determined by the valences of X and Ba, Mn, and Al, and Ba is divalent and Mn is valence Z, Al 3
A high temperature catalytic combustion catalyst comprising a composition represented by a = X × (3-Z) / 2) as a main component. 2. The high temperature catalytic combustion catalyst according to claim 1, wherein _{x in the} composition formula BaMn _x Al _12-x O _19-a is 1.5.