JPH06218282A - Heat resistant catalyst carrier and production thereof - Google Patents

Abstract

PURPOSE:To provide a catalyst carrier for waste gas purification and catalytic combustion shoving high activity and long service life even at a high temp. of >=1200 deg.C. CONSTITUTION:The catalyst carrier is composed practically of alumina, has a crystal layer having one of gamma, delta, theta, alpha phase, has >=30m<2>/g specific surface area after heat treating at 1200 deg.C or >=5m<2>/g specific surface area (by BET method) after heat treating at 1400 deg.C and is improved in heat resistance by applying alumina and further SiO2, CaO, SrO, BaO, La2O3 and the producing method is provided. The alumina source is obtained by a method by hydrolyzing a solution of aluminum salt, aluminum alkoxide or aluminum alkoxide derivative to obtain an alumina gel and after steam or hydrothermal treating the alumina gel at 250-400 deg.C, then heat-treating at >=450 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant catalyst carrier and a method for producing the same, and more specifically to 1200 ° C.
The present invention relates to a catalyst carrier for exhaust gas purification having high activity and long life, which is used near a catalyst combustor used at high temperatures and an internal combustion engine, and a method for producing the same.

[0002]

2. Description of the Related Art As a catalyst currently in practical use, a catalytic converter for purifying exhaust gas of an automobile engine is controlled at about 850.degree. In petrochemical processes, it is usually 2
The temperature is from 00 to 600 ° C., and is about 750 ° C. in the steam reforming process.

For high temperature use, attempts have been made to improve heat resistance (hereinafter, heat resistance means to maintain a high specific surface area even after heat treatment) by adding a second component. For example, according to Japanese Examined Patent Publication No. 4-17910, BaO, Ca
It is disclosed that the heat resistance is improved by adding 3 to 25 mol of O and SrO with respect to 100 mol of alumina. In particular, the powder prepared by the alkoxide method has excellent heat resistance at a temperature of 1200 ° C. or higher.

Further, Japanese Examined Patent Publication No. 4-35219 is La ↓
It is disclosed that by containing β-alumina composed of 2O ↓ 3 · 11-14Al ↓ 2O ↓ 3, it is effective as a catalyst carrier used at a high temperature of 600 ° C or higher.

Similarly, Japanese Examined Patent Publication No. 4-35220 discloses that 1 to 20 mol% of the total amount of lanthanum, neodymium, praseodymium oxide and alumina composite oxide have excellent heat resistance. . In these disclosures, β-alumina, a compound having a similar structure to β-alumina, and a mixture thereof with alumina contributed to the improvement of heat resistance, and the heat resistance of alumina itself was not improved. Moreover, the state of existence of β-alumina is not mentioned at all.

As a method for improving the heat resistance of alumina itself, an application of alumina aerogel prepared by sol-gel method and dried by supercritical drying method as a heat resistant catalyst carrier is disclosed in JP-A-3-1991.
No. 20 is shown. Alumina obtained by this method has a large specific surface area and excellent heat resistance in a high temperature range around 1200 ° C. This is because heat resistance at 1200 ° C. was achieved by delaying the α-forming temperature of the transition alumina, and the heat resistance after α-forming was not disclosed. In addition, since the supercritical drying method requires high temperature and high pressure,
Since the devices used are expensive and it is difficult to increase the size of the device, they are not suitable for mass production.

Another method for preparing a catalyst carrier is disclosed in Japanese Patent Laid-Open No.
No. 8-252 discloses heat treatment of two or more kinds of oxides under steam, and JP-A No. 58-216740 discloses a method for preparing a boehmite sol having a controlled pore system by a hydrothermal treatment method. There is. However, these methods focus on the control of the pore structure, and the effect of these methods on the heat resistance of the catalyst carrier is not shown at all.

[0008]

At present, a catalyst for purifying exhaust gas of automobile engines, which has been treated with one layer of an oxidation catalyst, is now in the direction of a two-stage catalyst of oxidation-reduction due to the tightening of regulations on NO ↓ X. It's going on. Therefore, the catalytic converter tends to approach the engine side where the temperature becomes higher. Therefore, stable heat resistance at a higher temperature of around 1000 ° C. is required.

Further, in order to use energy resources efficiently, it is desired to burn fuel at a temperature as high as possible, for example, in a gas turbine. However, in the conventional method, a mixture of fuel and air is ignited and combusted by using a spark plug or the like, so that a high temperature part exceeding 2000 ° C. partially exists in the combustor. It is known that a large amount of nitrogen oxide (NO ↓ X) is generated in this high temperature portion, which causes problems such as environmental pollution. In order to solve such a problem, a catalytic combustion method (catalytic combustion method) in which a reaction of fuel and oxygen is promoted using a catalyst has been attracting attention in recent years.
According to this method, (1) complete combustion at low temperature is possible,
(2) Complete combustion is possible with a wide range of fuel / air ratios, (3)
It is characterized by less generation of thermal knocks. However, in order to establish this technique, it is necessary to develop a catalyst carrier having stable heat resistance in a high temperature range of 1000 ° C. or higher, and more preferably up to about 1500 ° C., which is the lower limit temperature of thermal knox formation. Conventionally, γ-alumina, which has a high specific surface area and excellent heat resistance, has been used as a catalyst carrier, but it is converted to α-alumina by heat treatment at 1000 to 1100 ° C, and the specific surface area is drastically reduced, resulting in reaction activity. Since the area is reduced, it cannot be used as a catalyst carrier in a high temperature range (> 1000 ° C.).

The present invention has been made in view of the above situation, and provides an alumina heat-resistant catalyst carrier having excellent heat resistance in a high temperature range of 1200 ° C. or higher, which cannot be achieved by a conventional alumina carrier, and the same. An object of the present invention is to provide a manufacturing method having excellent productivity.

[0011]

According to the present invention, the crystal phase is γ,
δ, θ or α phase and consisting essentially of alumina,
Provided is a catalyst carrier having a specific surface area of 30 m ↑ 2 / g or 5 m ↑ 2 / g or more after heat treatment at 1200 ° C. or 1400 ° C. and excellent heat resistance at high temperatures. Furthermore, on this alumina carrier, SiO ↓ 2, CaO, Sr
It has been found that a catalyst carrier having a coating layer of one or more oxides selected from O, BaO or La ↓ 2O ↓ 3 has superior heat resistance.

The present invention further provides a method for producing the above catalyst carrier. An alumina precursor gel is prepared by hydrolyzing an aluminum salt, an aluminum alkoxide or an aluminum alkoxide derivative solution, and the obtained alumina precursor gel is subjected to steam or hydrothermal treatment at a temperature of 250 to 400 ° C or higher, and further 450 ° C or higher. By heat treatment at the temperature of 1, the alumina-based heat-resistant catalyst carrier is manufactured. Further, after the alumina is dispersed in a metal salt solution of Si, Ca, Sr, Ba, or La, the metal salt is hydrolyzed to obtain SiO ↓ 2, CaO, S on the alumina.
A heat resistant catalyst support coated with rO, BaO or La ↓ 2O ↓ 3 is produced.

The present invention is used as a catalyst carrier used in catalytic combustion or the like by improving the heat resistance of alumina, and has a well-known β-value having heat resistance.
A catalyst carrier or catalyst using a compound having an alumina structure (JP-B-4-17910, JP-B-4-35219,
It is essentially different from Japanese Examined Patent Publication No. 4-35220). The alumina provided by the present invention has excellent heat resistance even at a high temperature exceeding 1200 ° C. Especially 1400 ° C
5m ↑ 2 / g or more even after high temperature treatment of 1
It has a specific surface area of 0 m ↑ 2 / g or more and has excellent heat resistance that cannot be achieved with known alumina. Further, control of pore distribution by hydrothermal treatment (Japanese Patent Laid-Open No. 58-21670).
No.) and improvement of mechanical properties (Japanese Patent Laid-Open No. 3-5316), but the findings of the previous report relate to structural control by hydrothermal treatment, and no disclosure regarding improvement of heat resistance is made. In the present invention, it is newly found that an alumina porous body having excellent heat resistance can be easily obtained by using the sol-gel method and hydrothermal or steam treatment in combination.

Further, as compared with the production of alumina airgel under supercritical conditions (Japanese Patent Laid-Open No. 3-5316), a high temperature and high pressure vessel is not required, so that the apparatus can be simplified and the size can be easily increased, which is advantageous in terms of cost. It is also highly productive.

[0015]

In the heat-resistant catalyst carrier of the present invention, the alumina precursor gel obtained by the sol-gel method and the hydrothermal or steam treatment method inhibit the sintering of alumina,
As a result, the heat resistance is improved to 1200 ° C or 1400 ° C.
A larger specific surface area can be maintained even in a temperature range exceeding ℃. By coating the surface of the alumina with an oxide having a sintering suppressing action as necessary, a coating film of β-alumina or a compound having a similar structure is formed after the heat treatment at a high temperature, and as a result, the alumina is calcined. The binding is inhibited and the heat resistance is further improved. At this time, it is possible to reduce the addition amount of the sintering inhibitor as compared with the conventional method. or,
By supporting a metal or oxide having catalytic activity on this alumina carrier, a catalyst having heat resistance at high temperature can be obtained.

Further, the present invention will be described in detail.
The catalyst carrier of the present invention has a crystalline phase composed of a γ, δ, θ or α phase, is substantially composed of alumina without other additives, and is 30 m ↑ 2 // after heat treatment at 1200 ° C.
It is a catalyst carrier having excellent heat resistance at high temperatures, characterized by having a specific surface area of 5 m ↑ 2 / g or more after heat treatment at g or 1400 ° C. As used herein, γ-alumina refers to transitional alumina excluding δ and θ-alumina. Also,
The heat treatment at 1200 ° C and 1400 ° C means 1 in the air.
An operation of heating to a predetermined temperature at a heating rate of 00 ° C./min and holding for 5 hours is shown. As necessary, SiO ↓ 2, CaO, SrO, BaO or La on the above-mentioned alumina.
It is effective to coat one or more kinds of oxides selected from ↓ 2O ↓ 3 to improve the heat resistance of the catalyst carrier. The coating is sufficient to completely cover the alumina, and therefore SiO ↓ 2, CaO, SrO,
The addition amount of BaO or La ↓ 2O ↓ 3 is not more than the stoichiometric amount required to produce a compound having a β-alumina structure, which has been conventionally reported. The addition amount depends on the specific surface area of the coated alumina.

Next, the method for producing the catalyst carrier according to the present invention will be described starting from the starting materials. A metal salt, an alkoxide, or an alkoxide derivative is used as the aluminum and the coating metal raw material. The metal salt is not particularly limited as long as it is soluble in the solvent used, acetate,
Nitrate, chloride, etc. are used. For aluminum, it is more preferable to use an alkoxide or an alkoxide derivative because of the ease of producing a gel by hydrolysis.

The alkoxide or alkoxide derivative is
It is represented by the chemical formula M (OR) ↓ n. R represents an alkyl group or a substituent by an organic compound capable of multidentate coordination via oxygen or nitrogen, and is selected depending on the solubility in a solvent. As the polydentate organic compound, not only a compound in which an anion such as carboxylate binds to aluminum through carbonyl oxygen, but also a compound in which a neutral compound is coordinated as it is can be used. The alkyl group is not particularly limited, but one having 1 to 6 carbon atoms is preferable in view of price and metal concentration. The polydentate organic compound is preferably β-diketone, β-ketoester, alkanolamine and the like, but is not particularly limited as long as it is a compound that reduces the hydrolysis rate of alkoxide. Further, not only as a substituent but also as a mixed addition of these polydentate organic compounds to the alkoxide solution is similarly effective.

The solution is not particularly limited as long as it is an organic solvent in which the above aluminum salt, aluminum alkoxide or aluminum alkoxide derivative is soluble, but alcohols are particularly preferably used. Preferred are monohydric alcohols such as methanol, ethanol and propanol, dihydric alcohols such as ethylene glycol, and alkoxy alcohols such as methoxyethanol and ethoxyethanol. Next, a method for producing the alumina precursor gel will be described. The alumina precursor gel is obtained by hydrolyzing an aluminum salt, an aluminum alkoxide or an aluminum alkoxide derivative.

When the hydrolysis is carried out using an aluminum alkoxide or an aluminum alkoxide derivative, it is preferable to use water in a molar amount of 0.5 to 4 times the number of alkoxy groups contained in the aluminum alkoxide or aluminum alkoxide derivative. If the amount of water is small, gelation does not occur, while if it is large, precipitation occurs and gel cannot be obtained.
At this time, it is possible to use an acid or a base as a catalyst. It is more preferable to use a mineral acid such as hydrochloric acid or nitric acid or an organic acid such as acetic acid as the acid, and ammonia or amine containing no metal as an impurity as the base. The actual amount of water used is determined by the aluminum concentration, the type of solvent, the presence or absence and type of catalyst, and the concentration.

In the present invention, it is preferable to use an alumina precursor gel. In an aqueous system, it is possible to use an alumina-based sol, but in this case, it is difficult to increase the concentration, and it is generally necessary to use an acid to stabilize the sol. Therefore, the mixed acid corrodes the inside of the processing tank used for steam or hydrothermal treatment. Therefore, a special treatment such as expensive Teflon is required for the treatment tank, and such treatment of the reaction tank limits the reaction temperature. On the other hand, it is difficult to obtain a stable alumina sol in a non-aqueous system. Thus, in order to obtain precursors with a wide range of heat treatment conditions and various metal concentrations, it is necessary to use gel.

Steam or hydrothermal treatment is 250 ° C. to 400 ° C.
Performed at the temperature of. By this treatment, the crystal grains of boehmite in the precursor grow. A treatment temperature of 250 ° C. to 400 ° C. is preferable because sufficient boehmite crystal growth is required to obtain excellent heat resistance against heat treatment at 1200 ° C. or higher. Steam or hydrothermal treatment in a temperature range of 250 ° C to 350 ° C is more preferable.

The precursor gel obtained is calcined at a predetermined temperature. A temperature of 450 ° C. or higher is necessary to burn out the residual organic matter in the pores. The firing temperature is set according to the target specific surface area value, pore size distribution, crystal phase and the like. When used as a catalyst, the catalyst metal may be supported and then heat-treated at a predetermined temperature.

The coating of the second component on the alumina of the present invention comprises:
The obtained heat-resistant alumina is dispersed in a metal salt solution of the coating component, and then reprecipitation or hydrolysis of the metal salt on alumina is performed. The metal salt of the second component is preferably hydrolyzed by shifting the pH to the basic side. Ammonia and amines are used as catalysts,
Hydrolysis with urea is more preferred for a more homogeneous coating.

[0025]

The present invention will be described in more detail based on the following examples, but the present invention is not limited to these examples.

(Preparation of Alumina Catalyst Support) Example 1 Ethyl Acetate Aluminum Diisopropylate 27
4 g was dissolved in 500 ml of ethanol and then hydrolyzed with 72 ml of 1N aqueous ammonia to obtain a gel. The obtained gel was hydrothermally treated at 270 ° C. for 10 hours in an autoclave. After drying, it was calcined at 600, 1000 and 1200 ° C. for 5 hours to obtain the desired alumina carrier. Alumina calcined at each temperature has a specific surface area of 162, 127, 51 m ↑.
The crystal phase was γ, δ, θ and α phase.

Comparative Example 1 An alumina precursor gel obtained in the same manner as in Example 1 was
It was dried at 270 ° C. under a supercritical condition of 250 kg / cm ↑ 2. Furthermore, 5 at 600, 1000, 1200 ℃
It was calcined for a time to obtain an alumina carrier. Alumina calcined at each temperature has a specific surface area of 320.4, 141.5, 6 respectively.
It was 5.8 m ↑ 2 / g, and the crystal phase was γ, δ and θ, α phase.

Comparative Example 2 An alumina precursor gel obtained in the same manner as in Example 1 was
It was hydrothermally treated at 200 ° C. for 10 hours in an autoclave.
After drying, it was calcined at 600, 1000 and 1200 ° C. for 5 hours to obtain an alumina carrier. Alumina calcined at each temperature is
Specific surface area is 167.2, 97.3, 6.5m ↑ 2 /
The crystal phase was γ, δ and θ, α phase.

Comparative Example 3 Further, commercially available boehmite (Catapal D, Disp) was used.
al11N7-80, Dispal23N4-80; V
istaChemical) and γ-alumina (PU
RLOXSBa-230; manufactured by Condea) was measured for changes in specific surface area before and after heat treatment.

(Evaluation of heat resistance of alumina catalyst carrier) The alumina obtained in Example 1 and Comparative Examples 1, 2 and 3 was used as 120%.
The heat resistance was evaluated by heat treatment at 0 ° C., 1400 ° C. and 1500 ° C. for 5 hours each. The results are summarized in Table 1. The alumina obtained according to this example has a heat resistance of 30 m ↑ 2 / g at 1200 ° C. regardless of the calcination temperature.
It showed excellent heat resistance of 5 m ↑ 2 / g or more at 00 ° C. 1
Even after heat treatment at 500 ° C., it shows a high heat resistance of 5 m ↑ 2 / g, which cannot be achieved by the alumina known so far. Alumina by supercritical drying method (Comparative Example 1)
Also showed heat resistance equal to or higher than that of the alumina of the present invention up to 1200 ° C., but at 1400 ° C., 4 m ↑ 2 / g or less, 150
At 0 ° C, the specific surface area was less than half, about 2m ↑ 2 / g. Alumina precursor gel hydrothermally treated at low temperature (Comparative Example 2), commercially available γ-alumina and boehmite (Comparative Example 3)
Had a specific surface area of 100m ↑ 2 / g up to about 1000 ° C, but about 5m ↑ by heat treatment at 1200 ° C.
It can be seen that the heat resistance in the high temperature range of 2 / g is low. The alumina carrier prepared this time is 1200, 1400, 15
After heat treatment at 00 ° C. for 5 hours, heat resistance was evaluated by measuring the change in specific surface area before and after the heat treatment by the BET method.

[0031]

[Table 1]

(Preparation of Second Component-Coated Alumina Catalyst Carrier) Example 2 The alumina obtained by calcining at 1000 ° C. in Example 1 was dispersed in silica sol (HAS6: ethanol solution manufactured by Colcoat). After removing the solvent, heat treatment was performed at 500 ° C. to obtain silica-coated alumina.

Example 3 The alumina obtained by calcining at 1000 ° C. in Example 1 was dispersed in an aqueous barium nitrate solution, urea was added, and the mixture was stirred for 2 hours. After removing the solvent by filtration, heat treatment was performed at 1000 ° C. to obtain barium oxide-coated alumina.

Example 4 The alumina obtained by calcining at 1000 ° C. in Example 1 was dispersed in an aqueous lanthanum nitrate solution, urea was added, and the mixture was stirred for 2 hours. After removing the solvent by filtration, heat treatment was performed at 500 ° C. to obtain lanthanum oxide-coated alumina.

(Evaluation of Heat Resistance of Alumina Catalyst Carrier Coated with Second Component) Table 2 shows the relationship between the heat resistance of the prepared coated alumina at 1400 ° C. and the addition amount of the coating oxide. The coated alumina according to the present invention showed improved heat resistance as compared with the alumina of Example 1 by adding the optimum amount of the second component. Si
The O ↓ 2-coated alumina (Example 2) showed the highest specific surface area when the addition amount to alumina was around 4 mol%. B
The aO-coated alumina (Example 3) had the highest specific surface area around 4 mol% similarly to SiO ↓ 2. Also, La ↓
The 2O ↓ 3 coated alumina (Example 4) showed the highest heat resistance at 1.5 mol%. The addition amount of these is the optimum amount reported in the past, in other words, the amount of 1/3 to 1/4 of the stoichiometric ratio required for producing the compound having the β-alumina structure. As described above, by using the alumina of the present invention, it becomes possible to obtain a catalyst carrier having excellent heat resistance by adding a smaller amount of the sintering inhibitor.

[0036]

[Table 2]

Further, since the alumina according to the above embodiment is a bulk body, when it is used as a catalyst carrier for a fixed bed,
Dehydration and molding required for the preparation of alumina carrier by the conventional method,
There is no need to perform a granulation molding step by drying. further,
It goes without saying that it is possible to provide a catalyst having excellent heat resistance at high temperature by supporting a metal or metal oxide having catalytic activity on the catalyst carrier obtained in the present invention.

[0038]

As described above, according to the present invention, an alumina-based catalyst carrier having excellent heat resistance at high temperatures can be obtained. Therefore, it can be suitably used as a carrier for catalytic catalytic combustion for automobiles and gas turbines having severe heat resistance.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location B01J 23/02 ZAB A 8017-4G 23/10 ZAB A 8017-4G 35/10 ZAB 8017-4G 301 J 8017-4G 37/02 ZAB 8017-4G 101 E 8017-4G

Claims (4)

[Claims] 1. A material which is substantially composed of alumina and has a crystal phase of any one of γ, δ, θ and α phases and has a specific surface area of 30 m ↑ 2 / g or more or 140 after heat treatment at 1200 ° C.
A heat-resistant catalyst carrier having a specific surface area of 5 m ↑ 2 / g or more after heat treatment at 0 ° C. 2. SiO ↓ 2, CaO, SrO, BaO, L
The heat-resistant catalyst carrier according to claim 1, which has a coating layer of at least one oxide selected from a ↓ 2O ↓ 3. 3. An alumina precursor gel is prepared by hydrolyzing an aluminum salt, aluminum alkoxide or aluminum alkoxide derivative solution, and the obtained alumina precursor gel is subjected to steam or hydrothermal treatment at a temperature of 250 ° C. to 400 ° C. The method for producing a heat-resistant catalyst carrier, further comprising heat treatment at a temperature of 450 ° C. or higher. 4. Dispersing in a solution of one or more kinds of metal salts of Si, Ca, Sr, Ba or La, and then hydrolyzing the metal salts to obtain SiO.sub.2 ↓, CaO, Sr on alumina.
The method for producing a heat-resistant catalyst carrier according to claim 3, wherein O, BaO or La ↓ 2O ↓ 3 is coated.