JP2516797B2 - Combustion catalyst - Google Patents

Description

TECHNICAL FIELD The present invention relates to a combustion catalyst excellent in high temperature heat resistance.

[Prior Art and Its Deficiencies] Combustion catalysts used at high temperatures, such as gas turbines, kerosene and gas heaters, oil and gas refueling equipment, heavy oil combustion equipment, fuel cell reformer combustion catalysts, etc. As a carrier for high temperature combustion catalyst, cordierite (2MgO.2Al ₂
O ₃・ 5SiO ₂ ), mullite (3Al ₂ O ₃ -2SiO ₂ ), zirconia, etc. are used, but since these are not porous,
A porous material such as activated alumina is coated on these for use. A catalytically active metal such as platinum or palladium is supported on the coating material and used as a catalyst. However, these catalysts are usually
In the above cases, the crystal structure of porous materials such as alumina changes and the specific surface area decreases with crystal growth, which causes a decrease in active sites due to aggregation of active metals, resulting in loss of catalytic activity. There was a drawback that

In addition, lanthanum beta alumina (La ₂ O ₃ · 11Al ₂ O ₃ ) and barium alumina (BaO · 6Al ₂ O ₃ ) have been reported to have high heat resistance, but both have a specific surface area that is satisfactory after high temperature firing. It is not very large and costly for commercial use.

[Problems to be Solved by the Invention] An object of the present invention is to provide thermal deterioration when used under high temperature,
In particular, it is an object of the present invention to provide a combustion catalyst excellent in heat resistance, in which an increase in the combustion start temperature is small and the activity does not decrease during steady combustion after long-time use at high temperature.

[Means for Solving the Problems] As a result of earnest studies, the inventors of the present application have found that by adding silica in a certain range of content to alumina, 1000 ° C. or
The inventors have found that the specific surface area after calcining at 1200 ° C can be kept high, and by using this as a carrier and carrying a specific metal catalyst thereon, a combustion catalyst with excellent heat resistance can be obtained, thus completing the present invention. did.

That is, the present invention is composed of silica and alumina, the content of silica is 2.5% by weight to 25% by weight, and the specific surface area after firing at 1200 ° C in air is 50 m ² / g or more. Provided is a combustion catalyst in which palladium or palladium and at least one selected from the group consisting of titanium, magnesium and manganese are supported on an inorganic porous carrier.

[Advantages of the Invention] According to the present invention, thermal deterioration when used under high temperature,
In particular, there is provided a combustion catalyst which has a small increase in the combustion start temperature and which does not cause a decrease in activity during steady combustion after long-time use at high temperature and which has excellent heat resistance. The catalyst carrier used for the combustion catalyst of the present invention has a large specific surface area at high temperature,
Because of its porosity, the catalyst metal can be supported in a well-dispersed state, so that the catalytic ability is increased. further,
Since it retains a large specific surface area even when it is used at a high temperature for a long time, it maintains good dispersibility of the catalyst and does not cause deterioration of the catalytic ability.

[Detailed Description of the Invention] As described above, the porous catalyst carrier used in the combustion catalyst of the present invention is composed of silica and Al ₂ O _3, and the ratio of SiO _{2 to} the whole is 2.5 to 25% by weight, preferably Is 5% to 20% by weight.

The porous catalyst carrier used for the combustion catalyst of the present invention is characterized by having a very large specific surface area at a high temperature, and has a specific surface area after calcination at 1200 ° C of 50 ² m / g or more, preferably 60 m. ² / g or more. 1200 ° C when Al ₂ O _{3 is used} alone
In the firing whereas all becomes α-Al ₂ O _3, the heat-resistant porous material of the present invention, there when fired at the same temperature and mullite (3Al ₂ O ₃ -2SiO ₂₎ and θ-Al ₂ O ₃ is And SiO ₂
It has been found that suppresses the alpha conversion of Al ₂ O ₃ and maintains a high surface area. This catalyst carrier is described in Japanese Patent Application No. 61-310791 previously filed by the applicant of the present application.

In the combustion catalyst of the present invention, palladium is supported alone or together with titanium, manganese, or magnesium on the above-mentioned porous catalyst carrier. The amount of palladium supported is preferably 0.1% to 5%, more preferably 0.5% to 2%, based on the weight of the catalyst carrier. The amount of titanium, manganese, or magnesium supported is preferably 0.05% to 0.8%, more preferably 0.1% to 0.3%, based on the weight of the catalyst carrier. In a particularly preferred embodiment, the metals supported are palladium and titanium, and the ratio of titanium to palladium is 5% by weight to
30% by weight.

The porous catalyst carrier used for the combustion catalyst of the present invention can be produced by mixing the aluminum hydrate and the silicic acid compound and drying the heat-resistant porous material. The aluminum hydrate can be prepared, for example, by dissolving an aluminum salt in water and adding aqueous ammonia. As the aluminum salt, aluminum sulfate, aluminum chloride, aluminum nitrate and aluminum acetate are preferable, and the concentration when dissolved in water is 0.05 mol to
0.4 mol, particularly 0.13 to 0.15 mol, is preferred. Also,
The concentration of aqueous ammonia is not particularly important, for example 0.05
It is about 1 to 2 regulations. Addition of aqueous ammonia to the aluminum salt solution causes aluminum hydrate to precipitate.
Water glass is preferable as the silicic acid compound. Water glass is added dropwise to the aluminum hydrate. The addition amount of water glass is selected so that the amount of SiO ₂ is within the above range. After the addition of water glass, the pH of the mixture is adjusted to about 7 to 8 to precipitate the porous material that constitutes the catalyst carrier. Next, this precipitate is collected by filtration and molded into an appropriate form. This porous material can be formed into a honeycomb type, a columnar type, a spherical type or any other shape in the same manner as a conventional catalyst carrier. It can also be used as a catalyst carrier by coating the surface of a non-porous substance such as cordierite or mullite.

Next, palladium or palladium and titanium, manganese, or magnesium are supported on the catalyst carrier thus obtained. This is to prepare a solution of a salt of these metals, for example, a nitrate or a hydrochloride or an acid salt or ester containing these metals, and immerse the catalyst support obtained as described above therein, and then dry it. Can be done by doing. In this case, the concentration of metal ions in the metal salt solution is usually about 0.05% by weight to 0.5% by weight.

The combustion catalyst of the present invention has a large specific surface area at high temperature and maintains that the catalyst metal is supported in a highly dispersed state, and thus is particularly suitable as a combustion catalyst used at high temperature. Examples of such catalysts include high temperature combustion catalysts such as gas turbines, kerosene and gas heaters, oil and gas refueling equipment, heavy oil combustion equipment, fuel cell reformer combustion catalysts, etc. Examples of the substance combusted using the combustion catalyst include gaseous fuels containing hydrocarbon as a main component, liquid fuels such as petroleum-based ones, coal-based ones, and synthetic fuels such as oxygen-containing compounds. When burned, these substances produce carbon dioxide, water, and in some cases nitrogen oxides and sulfur oxides.

[Examples and Comparative Examples] Next, the effects of the present invention will be specifically described by showing Examples and Comparative Examples of the present invention.

Examples 1 to 3 and Comparative Example 1 Deionized water prepared by the ion exchange method was heated to about 30 ° C., and 633 g of aluminum sulfate was dissolved to a concentration of 0.13 to 0.15M. While stirring this, 1N aqueous ammonia was gradually added dropwise until the pH reached 8, to precipitate aluminum hydrate.

Next, water glass No. 3 was treated with 4 times the amount of deionized water so that the silica content was 5% by weight (Example 1), 10% by weight (Example 2) or 20% by weight (Example 3). After adding the diluted aqueous solution to this, it was heated to 60 ° C. and aged for 3 hours with stirring to obtain a silica-alumina hydrate.

The precipitate was washed by filtration, dried at 120 ° C. for 20 hours, and then pulverized with a ball mill. After adding an appropriate amount of water to this and kneading to make a clay, it is extruded by an extruder having a large number of dies with holes having a diameter of 1.5 mm, made into a columnar shape, dried at 120 ° C, and dried at 500 ° C for 3 hours. It was calcined to obtain a catalyst carrier.

On the other hand, a catalyst carrier (Comparative Example 1) made of alumina alone was obtained in the same manner as above except that water glass was not added.

After calcining the obtained carrier in air at 1200 ° C. for 15 hours,
The specific surface area was measured by the BET method using N ₂ adsorption. The results are shown in Table 1 below.

Commercially available primary nitric acid was added to deionized water to prepare a 0.1N aqueous nitric acid solution, and commercially available palladium chloride powder was added to this solution 1.
5.0 g was added and dissolved by heating to prepare a palladium solution.
60 g of each cylindrical catalyst carrier pellet obtained as described above was dipped in 200 ml of this solution and dipped for about 2 hours while slowly stirring. 120 after washing with deionized water
It was dried at ℃ for 12 hours. Further, it was calcined at 500 ° C. for 3 hours to obtain the catalysts of Examples 1 to 3 and Comparative Example 1.

Examples 4-9 89 mg (Example 4), 178 mg (Example 5), 285 mg (Example 6), 534 mg (Example 7), 890 mg of isopropyl orthotitanate were added to 120 ml of isopropyl alcohol.
30 g of the palladium-supported pellet obtained in Example 1 was immersed in a solution obtained by dissolving (Example 8) or 1.42 g (Example 9) for 60 minutes. After impregnation, it was dried at 120 ° C. for 3 hours. Further, it is fired at 500 ° C. for 3 hours to give Examples 4-9.
The catalyst was obtained.

Example 10 20 g of the palladium-supported solvent obtained in Example 1 was immersed in 80 ml of a solution prepared by dissolving 1.27 g of magnesium nitrate in 240 ml of a 0.1 N aqueous nitric acid solution for 60 minutes. Then this is 500
The catalyst of Example 10 was obtained by calcination for 3 hours.

Example 11 30 g of the palladium-supported catalyst obtained in Example 1 was immersed in 120 ml of a solution prepared by dissolving 4.28 g of manganese nitrate in 600 ml of a 0.1N aqueous nitric acid solution for 60 minutes. Then this is 500 ℃
Calcination was performed for 3 hours to obtain the catalyst of Example 11.

Comparative Example 2 The catalyst carrier composed of only alumina obtained in Comparative Example 1 was treated in the same manner as in Example 6 to obtain the catalyst of Comparative Example 2.

Test Example In order to evaluate the heat resistance of the catalysts of Examples 1 to 11 and Comparative Examples 1 and 2, the catalyst was first heat-treated in air at 1000 ° C. for 16 hours, then 1200 ° C. for 16 hours, and further 1300 ° C. for 16 hours. . A methane combustion experiment was conducted on the catalyst that had been subjected to heat treatment at each temperature. The composition of the gas used in the methane combustion experiment was 2% by volume of methane, 4% by volume of oxygen and 94% by volume of nitrogen, the space velocity was 11,000 H ^-1 , and the gas preheating temperature was 300.
It was ℃ -650 ℃.

The combustion start temperature and the combustion rate of methane at 550 ° C for each example were obtained. The methane combustion start temperature means the temperature at which the combustion rate of methane reaches 10%. The results are shown in the table. The results shown in the table are the results when the catalyst after the heat treatment at 1300 ° C. was used.

As is apparent from the table, in the case of using the combustion catalyst of the present invention, the combustion rate of methane at 550 ° C. is as high as 2 to 4 times that in the case of using the catalyst of Comparative Example, and the combustion start temperature is Is also significantly lower. From this, it is understood that the combustion catalyst of the present invention has extremely excellent heat resistance.

1 and 2 show the combustion rates of methane at various temperatures when the catalysts of Example 1 and Comparative Example 1 that were heat-treated as described above were used. 1 and 2, curves A and B are fresh catalysts which are not heat-treated for heat resistance test, and A1 and B1 are 1000 ° C and 16 ° C, respectively.
Catalyst after heat treatment for 2 hours, A2 and B2 are 1000 ℃, 16 hours +1200
The catalysts after heat treatment at 16 ° C. for 16 hours, A3 and B3 show the results when the catalysts after heat treatment at 1000 ° C., 16 hours + 1200 ° C., 16 hours + 1300 ° C., 16 hours were used. 1 and 2, in the case of using the catalyst of Example 1, as compared with the case of using the catalyst of Comparative Example 1, when the same heat treatment was applied, the combustion rate of methane at the same temperature was It is significantly high, and the difference in the burning rate becomes larger as the heat treatment time becomes longer, showing that the catalyst of the present invention has excellent heat resistance.

Further, when the catalysts of Examples 1, 6, 10 and 11 and Comparative Example 1 were subjected to the above heat treatments,
Figure 3 shows the combustion rate of methane at 550 ° C. In FIG. 3, ◯ indicates the result of Example 1, Indicates the results for Example 6, Δ indicates the results for Example 10, ▽ indicates the results for Example 11, and □ indicates Comparative Example 1.
The results are shown below. It can be seen from FIG. 3 that the catalyst of the example has a significantly smaller decrease in the methane combustion rate than the catalyst of the comparative example even if the heat treatment time is long and the temperature is high.

[Brief description of drawings]

FIG. 1 is a diagram showing the burning rate of methane at various temperatures when the catalyst of Example 1 that has been subjected to various heat treatments is used. FIG. 2 shows the catalyst of Comparative Example 1 that has been subjected to various heat treatments. Fig. 3 is a graph showing the combustion rate of methane at various temperatures in the case where the heat treatment was performed. Fig. 3 shows the case where the catalysts of Examples 1, 6, 10 and 11 and Comparative Example 1 were used and the above heat treatments were performed.
It is a figure which shows the combustion rate of methane in 0 degreeC.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B01J 35/10 301 B01D 53/36 104Z

Claims (4)

(57) [Claims] 1. A heat-resistant inorganic porous carrier comprising silica and alumina, having a silica content of 2.5 to 25% by weight and having a specific surface area of 50 m ² / g or more after firing at 1200 ° C. in air. At least one selected from the group consisting of palladium or palladium and titanium, magnesium and manganese above
Combustion catalyst carrying seeds. 2. The combustion catalyst according to claim 1, wherein the supported amount of palladium is 0.1% to 5% with respect to the weight of the catalyst carrier. 3. The combustion catalyst according to claim 1, wherein the amount of at least one selected from the group consisting of titanium, magnesium and manganese is 0.08% to 1% with respect to the weight of the catalyst carrier. 4. Palladium and titanium are supported on the catalyst carrier, and the supported amount of titanium is 5% by weight of the supported amount of palladium.
The combustion catalyst according to any one of claims 1 to 3, wherein the combustion catalyst is from 30 to 30% by weight.