JPH08309184A - High temperature combustion catalyst and method for producing the same - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a high-temperature combustion catalyst that has high activity and has little decrease and fluctuation in oxidation activity even in the temperature range of 600 to 1000 ° C. A catalyst for high temperature combustion comprising palladium oxide supported on a heat-resistant inorganic support containing zirconia, which contains 5 mol% or more of non-reducing palladium oxide with respect to total palladium oxide. A heat-resistant inorganic carrier containing mechanochemically activated zirconia is impregnated with a palladium compound that produces palladium oxide by firing, dried, and then fired at a temperature of 400 to 1200 ° C. in the atmosphere. [Effect] During the firing process, the zirconia in the mechanochemically activated carrier interacts with the palladium raw material to form the non-reducible palladium oxide. The presence of this reduction-resistant palladium oxide maintains a high oxidation activity even in the catalytic combustion reaction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high temperature combustion catalyst and a method for producing the same, and particularly to a gas turbine,
The present invention relates to a high-temperature combustion catalyst that can be used in a high-temperature combustor such as a boiler and has a small decrease and fluctuation in oxidation activity and high oxidation activity, and a method for producing the same.

[0002]

2. Description of the Related Art The catalytic combustion method is a method of premixing a fuel such as methane or propane with air and then performing flameless combustion in a catalyst layer, and has an advantage that the amount of nitrogen oxides generated is extremely small. As a combustion catalyst used in this catalytic combustion method, a catalyst in which palladium oxide is supported on a heat-resistant carrier such as alumina, zirconia, magnesia, or silica has been widely studied because of its high activity.

However, the supported palladium oxide catalyst has a low activity due to the particle growth of palladium oxide at high temperature.
Palladium oxide dissociates into palladium at temperatures above ℃ and the oxidation activity decreases significantly (Appl. Catal., A81,227 (1992)).
There are problems such as.

Conventionally, as a method for suppressing the grain growth of palladium oxide, an intermediate layer is provided between the palladium oxide and the carrier (JP-A-63-72345), and the oxide is dispersed on the palladium oxide ( JP-A-3-186347
Method) has been proposed. On the other hand, as a method of suppressing the dissociation of palladium oxide, a method of adding a lanthanum component (JP-A-4-27432) is proposed.

[0005]

However, even when the above-mentioned conventional improved supported palladium oxide catalyst is used, the amount of 600 to
There is a problem that it is not possible to sufficiently prevent the decrease and fluctuation of the oxidation activity in the temperature range of 1000 ° C.

The present invention solves the above-mentioned conventional problems, and provides a high temperature combustion catalyst and a method for producing the same, which is highly active and has a small decrease and fluctuation in oxidation activity even in the temperature range of 600 to 1000 ° C. To aim.

[0007]

A combustion catalyst for high temperature according to claim 1 is a catalyst in which palladium oxide is supported on a heat-resistant inorganic carrier containing zirconia, and a non-reducing palladium oxide is used with respect to total palladium oxide. It is used in the temperature range of 600 to 1000 ° C., characterized by containing 5 mol% or more.

A method for producing a high temperature combustion catalyst according to claim 2 is
The method for producing a high temperature combustion catalyst according to claim 1, wherein a mechanochemically activated heat-resistant inorganic carrier containing zirconia is impregnated with a palladium compound which produces palladium oxide by firing. After drying, it is characterized in that it is fired at a temperature of 400 to 1200 ° C. in the atmosphere.

That is, the inventors of the present invention have conducted extensive studies on a high temperature combustion catalyst in order to solve the above-mentioned problems, and as a result,
The non-reducing palladium oxide is present in the palladium oxide supported on the zirconia (ZrO ₂ ) type carrier, and the catalyst containing such non-reducing palladium oxide is mechanochemically activated zirconia. The present invention has been completed by finding that it can be obtained by firing at 400 to 1200 ° C. using a system carrier.

The present invention will be described in detail below according to the procedure for producing the high temperature combustion catalyst according to the present invention.

In the present invention, the heat-resistant inorganic carrier supporting palladium oxide is a zirconia carrier, and
A carrier containing zirconia and another inorganic substance is used.
In the case of a carrier containing zirconia and another inorganic substance, the type of the other inorganic substance is not particularly limited, but those having less decrease in specific surface area when heated to 1000 ° C. are preferable, such as alumina, magnesia and silica. It is possible to use the ceramic powder of No. 3, or a powder obtained by stabilizing these ceramic powders with various additives. In this case, if the content of zirconia in the carrier is too small, the effect of the present invention cannot be sufficiently obtained. Therefore, the amount of zirconia contained in the carrier is preferably 3 mol% or more, particularly preferably 5 mol% or more, with respect to the inorganic substance other than zirconia in the carrier.

When a carrier containing an inorganic substance other than zirconia such as alumina as a main component is used, a zirconium salt such as zirconium nitrate, zirconium propoxide, zirconium acetylacetonate or the like is used in the production of the carrier. It is preferable to produce a carrier containing zirconium with good dispersibility using the organozirconium compound of. For example, zirconium acetylacetonate is impregnated into an alumina powder using a solvent such as water or ethanol, dried, and then baked in the atmosphere at a temperature of 500 to 1300 ° C. to coat the surface of the alumina particle with zirconia. It is possible to obtain a highly dispersed zirconia-containing carrier.

In order to support palladium oxide on such a zirconia-containing heat-resistant inorganic carrier, a solution containing a palladium compound which produces palladium oxide by calcination is impregnated into the heat-resistant inorganic carrier and dried, followed by calcination. In this case, during and / or before the impregnation, the carrier surface is mechanically and chemically activated by grinding it with a ball mill, a sand mill or the like. By carrying out such activation, it is possible to generate the non-reducible palladium oxide by the interaction between the carrier and the palladium compound by the firing in the subsequent step.

Specifically, a heat-resistant inorganic carrier containing zirconia, a palladium raw material such as palladium salt such as palladium acetylacetonate, palladium nitrate and palladium acetate, a solvent such as ethanol, acetone and water, and the carrier are activated. Mixing and grinding media such as zirconia balls and nylon balls for solidification are put in a container and ball-milled. A longer ball mill time is preferable for activating the surface of the carrier as pulverization progresses, but impurities are mixed in at the same time, so that it is usually preferably about 5 to 100 hours. Also,
In order to prevent evaporation of the organic solvent and decomposition of the palladium raw material, the temperature during the ball mill treatment is preferably about room temperature.

Mechanochemical activation means are as follows:
Not limited to the ball mill, a sand mill, a medium stirring mill, or the like can be used.

In the present invention, the heat-resistant inorganic carrier containing zirconia thus impregnated with the palladium raw material and dried is fired in the atmosphere at a firing temperature of 400 to 1200 ° C., preferably 500. ˜900 ° C. If the calcination temperature is lower than 400 ° C, the decomposition of the palladium raw material is insufficient, and since the calcination temperature is low, it is difficult to form the non-reducing palladium. Further, the dissociated palladium grows and the activity decreases.

If the amount of palladium oxide supported on the thus-supported palladium oxide catalyst is less than 0.05% by weight in terms of palladium, the activity is greatly affected by volatilization of palladium due to long-term use at high temperature. Becomes
If it exceeds 5% by weight, the proportion of crystalline palladium oxide increases, and the activity fluctuation becomes large. Therefore, the supported amount of palladium oxide is preferably about 0.05 to 5% by weight in terms of palladium.

According to such a method, the non-reducing palladium oxide is contained in an amount of 5 mol% or more based on the total palladium oxide.
Usually, 10 to 50 mol% is contained and 600 to 100
It is possible to obtain a supported palladium oxide catalyst with little activity variation with respect to temperature change at 0 ° C.

In the present invention, the hardly-reducing palladium oxide is a reduction-resistant oxidation that is not reduced in a hydrogen atmosphere near room temperature but is reduced in a high-temperature hydrogen atmosphere at 180 to 330 ° C. It is palladium.

[0020]

[Function] In the supported palladium oxide catalyst of the present invention,
During the calcination process in the atmosphere, the zirconia in the mechanochemically activated carrier interacts with the palladium raw material to form the non-reducible palladium oxide. This was clarified by the temperature-programmed reduction measurement using hydrogen. That is, when palladium oxide is supported on zirconia, which has poor reactivity, or on a carrier such as alumina containing no zirconia, the palladium oxide is reduced by hydrogen at around room temperature. On the other hand, in the catalyst of the present invention, 5 mol% or more of the supported palladium oxide is not reduced at room temperature and
It is a reduction-resistant palladium oxide that is reduced at a high temperature of 80 to 330 ° C. Due to the presence of this reduction-resistant palladium oxide, the high temperature combustion catalyst of the present invention is
It becomes possible to maintain a high oxidation activity even in the catalytic combustion reaction at 00 to 1000 ° C.

[0021]

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples unless it exceeds the gist.

Example 1 Zirconia powder, palladium acetylacetonate, nylon balls and ethanol were placed in a resin container and activated and impregnated while being ball-milled at room temperature for 12 hours. Then, it is dried at 70 ° C., and the obtained dry mixture is calcined in the air at 500 ° C. for 4 hours to obtain 100 g of a catalyst.
A high temperature combustion catalyst of a supported palladium oxide catalyst supporting 0.5 g of palladium oxide per palladium was obtained.

Examples 2 to 4 High temperature combustion catalysts were prepared in the same manner as in Example 1 except that the temperature for calcining the supported palladium oxide catalyst was set to the temperature shown in Table 1.

Example 5 δ-alumina powder was impregnated with zirconium acetylacetonate in an amount of 10 mol% with respect to alumina, and was impregnated with ethanol as a solvent. After drying, 11
The support was prepared by baking the surface of δ-alumina particles with zirconia by firing in air at 00 ° C. for 2 hours.
Palladium oxide was loaded on this carrier in the same manner as in Example 1 to prepare a high temperature combustion catalyst.

Comparative Example 1 Zirconia powder was impregnated with an ethanol solution containing palladium acetylacetonate, dried at 70 ° C., and the obtained dry mixture was calcined at 1300 ° C. for 4 hours in the atmosphere to obtain a catalyst. 0.5 per 100g converted to palladium
A combustion catalyst of a supported palladium oxide catalyst supporting g of palladium oxide was obtained.

Comparative Example 2 The temperature for calcining the supported palladium oxide catalyst was 500 ° C.
A combustion catalyst was prepared in the same manner as in Comparative Example 1 except that

Comparative Example 3 δ-alumina powder was impregnated with an ethanol solution containing palladium acetylacetonate and dried at 70 ° C. The obtained dry mixture was calcined in the air at 1100 ° C. for 4 hours to obtain a combustion catalyst of a supported palladium oxide catalyst carrying 0.5 g of palladium oxide per 100 g of the catalyst.

Comparative Examples 4 and 5 Combustion catalysts were prepared in the same manner as in Example 1 except that the temperature for calcining the supported palladium oxide catalyst was set to the temperature shown in Table 1.

Comparative Example 6 A combustion catalyst was prepared in the same manner as in Example 4 except that δ-alumina powder was used instead of zirconia powder.

[Measurement of Characteristics of Each Combustion Catalyst] Measurement of Change in Methane Oxidation Activity with Change in Reaction Temperature The methane oxidation activity of the catalysts produced in Examples 1 to 5 and Comparative Examples 1 to 3 was examined. First, 0.4 g of each prepared combustion catalyst was filled in a fixed bed flow reactor, and 1.6 liters of a mixed gas of 0.5% methane-99.5% air was flowed per minute.

Next, the methane conversion rate during the temperature rising process was measured while the reaction temperature was sequentially raised to a predetermined temperature, and subsequently, the methane conversion ratio during the temperature lowering process was measured while the reaction temperature was sequentially lowered to the predetermined temperature.

The methane conversions of the high temperature combustion catalysts of Examples 1, 2 and 3 are shown in FIGS. 1, 2 and 3, respectively.
Shown in It is understood from FIGS. 1 to 3 that in the high temperature combustion catalysts of Examples 1 to 3, the methane conversion rate only gradually decreases as the temperature decreases, and the activity drop at around 700 to 750 ° C. is not seen. .

The methane conversions of the high temperature combustion catalysts of Examples 4 and 5 are shown in FIGS. 4 and 5, respectively. From FIGS. 4 and 5, the high temperature combustion catalysts of Examples 4 and 5 have 700
A decrease in methane conversion was observed at ℃, but Comparative Example 1 below.
It can be seen that it is smaller than the decrease in the methane conversion rate in the vicinity of 700 to 750 ° C.

The methane conversion rates of the combustion catalysts of Comparative Example 1, Comparative Example 2 and Comparative Example 3 are shown in FIGS. 6, 7 and 8, respectively. As is clear from FIGS. 6 to 8, in the combustion catalysts of Comparative Examples 1 to 3, the methane conversion rate drastically decreased as the temperature decreased, and the methane conversion rate at 750 ° C. greatly decreased from 40% to 13%. .

Measurement of Ratio of Hardly Reducible Palladium Oxide to Total Supported Palladium Oxide For the combustion catalysts produced in Examples 1 to 5 and Comparative Examples 1 to 6, total supported palladium oxide was determined by temperature programmed reduction using hydrogen. Table 1 shows the ratio of the non-reducible palladium oxide with respect to. The measurement by the temperature-elevated reduction was performed by using a mixed gas of 10% hydrogen-90% argon, flowing this gas at room temperature for 15 minutes, and then raising the temperature to 500 ° C at 10 ° C / minute. As is clear from Table 1,
In all of Examples 1 to 5, although hardly reducible palladium oxide was generated, this could not be detected by the catalysts of Comparative Examples 1 to 6.

Measurement of Palladium Dispersity With respect to the combustion catalysts produced in Examples 1 to 5 and Comparative Examples 1 to 6, the polydispersity of palladium determined by CO adsorption measurement (assuming that CO is adsorbed on Pd in a one-to-one relationship) And adsorption C
Table 1 shows the molar ratio of O and Pd. In Comparative Examples 2 and 4, the non-reducing Pd cannot be detected even though the degree of dispersion is relatively good, because the activity of the carrier is poor and the calcination temperature is low. It is presumed that the reaction has not progressed.

Measurement of Temperature Rise Reduction Profile of Combustion Catalyst The temperature rise reduction profiles of the combustion catalysts of Example 1, Example 4 and Comparative Example 1 were measured as typical examples, and are shown in FIGS.
It is shown in 0 and 11.

[0038]

[Table 1]

[0039]

As described above in detail, according to the combustion catalyst for high temperature and the method for producing the same of the present invention, the oxidation activity is high, and the oxidation activity is reduced and fluctuated even in the high temperature range of 600 to 1000 ° C. A few high-performance high temperature combustion catalysts are provided.

[Brief description of drawings]

1 is a diagram showing a methane conversion rate of a high temperature combustion catalyst prepared in Example 1. FIG.

2 is a diagram showing a methane conversion rate of a high temperature combustion catalyst prepared in Example 2. FIG.

3 is a diagram showing a methane conversion rate of a high temperature combustion catalyst prepared in Example 3. FIG.

FIG. 4 is a diagram showing a methane conversion rate of a high temperature combustion catalyst prepared in Example 4.

5 is a diagram showing a methane conversion rate of a high temperature combustion catalyst prepared in Example 5. FIG.

FIG. 6 is a diagram showing a methane conversion rate of a combustion catalyst prepared in Comparative Example 1.

FIG. 7 is a diagram showing a methane conversion rate of a combustion catalyst prepared in Comparative Example 2.

8 is a diagram showing a methane conversion rate of a combustion catalyst prepared in Comparative Example 3. FIG.

FIG. 9 is a graph showing a temperature reduction profile of the high temperature combustion catalyst prepared in Example 1.

FIG. 10 is a diagram showing a temperature reduction profile of the high temperature combustion catalyst prepared in Example 4.

FIG. 11 is a diagram showing a temperature reduction profile of the high temperature combustion catalyst prepared in Comparative Example 1.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Narui 5 1978, Kozugushi, Ube City, Ube Yamaguchi Prefecture Ube Kosan Co., Ltd. Ube Laboratory

Claims (2)

[Claims] 1. A catalyst in which palladium oxide is supported on a heat-resistant inorganic carrier containing zirconia, wherein the non-reducing palladium oxide is contained in an amount of 5 mol% or more based on the total palladium oxide. High temperature combustion catalyst used in the temperature range of ℃. 2. A mechanochemically activated, heat-resistant inorganic carrier containing zirconia is impregnated with a palladium compound which produces palladium oxide by firing, and dried, and then at 400 to 1200 ° C. in the atmosphere. The method for producing a high temperature combustion catalyst according to claim 1, wherein the method is for calcination at a temperature.