JPH0829931B2 - Heat-resistant inorganic porous composition and catalyst carrier comprising the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat-resistant inorganic porous composition, and a catalyst carrier comprising the same, which is suitable for use under high temperature conditions, and will be described in more detail. For example, the present invention relates to a heat-resistant inorganic porous composition having a controlled pore distribution, and a catalyst carrier comprising the same.

[Conventional technology]

Catalysts used under high temperature conditions, such as gas turbines, kerosene and gas heaters, oil and gas refueling equipment, heavy oil combustion equipment, high temperature combustion catalysts such as combustion catalysts for fuel cell reformers, steam reformers, etc. As a carrier for catalysts for odor and purification of odors and exhaust gas, cordierite (2MgO ・ 2Al ₂ O ₃・ 5SiO ₂ ) and mullite (3Al
₂ O ₃ −2 SiO ₂ ) and the like are used, but since they are not porous, they are used by coating the surface with a porous substance. Alumina is generally used as the porous substance, and it is used as a catalyst by supporting a catalytically active metal. However, alumina is converted to α-alumina under a high temperature use condition, its specific surface area becomes small, the dispersed state of active metal is lowered, and it is rapidly deactivated.

There is also a report that lanthanum β-alumina (LaO ₃ · 11Al ₂ O ₃ ) and barium alumina (BaO · 6Al ₂ O ₃ ) have high heat resistance (Japanese Patent Laid-Open No. 62-153158). There is a problem that the subsequent specific surface area is not sufficiently large and the cost is high for commercial use.

Furthermore, a basic compound is added to a mixed aqueous solution of alumina hydrate and colloidal silica to thicken the mixed aqueous solution, and the resulting gel is dried and calcined to obtain a heat-resistant catalyst carrier composition. It has been reported (Japanese Patent Laid-Open No. 61-287446) and has a structure layer of a sintered ceramic material and a high surface area carrier layer of a porous oxide integrated with the structure layer. A monolithic catalyst carrier having a carrier layer of 50 to 93% by weight of alumina and 7 to 50% by weight of silica as a main component has been reported (JP-A-61-242639). There is a problem that the specific surface area decreases rapidly when used at a high temperature of ° C for a long time.

The present inventor has previously made a heat-resistant inorganic porous composition composed of silica and alumina, having a silica content of 2 to 30% by weight, and having a specific surface area of 20 m ² / g or more after firing in air. This composition uses aluminum salt and water glass as raw materials, first, ammonia water is added to an aqueous solution of the aluminum salt to precipitate an aluminum hydrate, and then water glass is dropped to the aluminum hydrate. A heat-resistant inorganic porous composition prepared by precipitating a substance having the above composition by adjusting pH, and calcining the precipitate at 1200 ° C., which retains a specific surface area of 20 m ² / g or more even for a long calcining time. (Japanese Patent Application No. 61-310791 and Japanese Patent Laid-Open No. 63-295484).

[Problems to be Solved by the Invention]

The present invention is an improvement on the invention related to the above-mentioned application, and has a large specific surface area (20 m ²
/ g) or more) and a heat-resistant porous composition that maintains the pore volume.

Another object of the present invention is to provide a catalyst carrier composed of a heat-resistant porous composition capable of retaining a large catalytic activity even if it is kept at a high temperature for a long time.

[Means for solving the problem]

The present invention comprises silica and alumina, the content of silica is in the range of 2% by weight to 30% by weight, the total pore volume is 0.3 ml / g or more in the pore distribution measurement by the oxygen adsorption method, and A heat-resistant inorganic porous composition having a pore volume of 100 Å or more, 60% or more of the total pore volume, and a specific surface area of 20 m ² / g or more after firing at 1200 ° C. in air. In particular, in the pore distribution, the volume of the pores in the pore diameter range of 100 to 400Å is 0.20.
The present invention is characterized by providing a heat-resistant inorganic porous composition having a content of ml / g or more.

The present invention is also characterized by providing a combustion catalyst carrier comprising the heat-resistant inorganic porous composition.

The content of silica in the heat-resistant inorganic porous composition of the present invention is in the range of 2% by weight to 30% by weight, preferably 2.5 to 25% by weight. Silica content is 2% by weight
If it is less than the above, the heat-resistant inorganic porous composition of the present invention cannot be obtained, the number of pores having a small pore diameter increases, and these fine pores are destroyed by high temperature firing, and the total pore volume decreases. .
On the other hand, when the content of silica exceeds 30% by weight, the component ratio of mullite increases due to high temperature firing, the total pore volume decreases, and the reaction activity decreases.

Suitable total pore volume is 0.4 ml / g or more, and 1.5 ml / g
It is preferably 1.3 ml / g or less. When the total pore volume is 0.3 ml / g or less, sufficient diffusion rate of the reaction reagent and reaction product cannot be obtained as described later, while 1.5 ml / g
If it exceeds, the strength cannot be maintained, and there is a problem that the filling amount in the reaction container decreases with the decrease in bulk density. The volume of pores having a pore diameter of 100 to 400 L is more preferably 0.26 ml / g or more.

The composition of the present invention has a specific surface area of 20 m ² / g or more after firing in air at 1200 ° C., preferably 50 m ² / g,
Particularly, 70 m ² / g or more is preferable.

Next, a method for producing the heat resistant inorganic porous composition of the present invention will be described.

In general, in the production of this type of catalyst carrier, for example, a colloidal gel of each component of the catalyst carrier is prepared, and this is aged, dried, molded or fired, then impregnated with a metal component, and finished through the steps of firing. In the process of preparation, the aging operation has a significant effect on the physical properties of the product, that is, the pore structure.

 The method for producing the silica-alumina composition of the present invention comprises: an alumina hydrogel forming step, a silica coating step, and an alumina-silica crystal aging step.

First, as a starting material in the step of forming alumina and hydrogel, inorganic salts such as aluminum sulfate, nitrate and chloride, and soluble aluminum salts such as alkali metal aluminate are used.

This alumina source is used in the form of an aqueous solution, and the concentration of the soluble salt may be in the range of about 0.1 to 4.0 mol, preferably about 0.3 to 2.0 mol, and a basic compound such as aqueous ammonia is added to the salt aqueous solution. Form an alumina hydrogel.

In this alumina hydrogel production process, it is important to produce as small an alumina hydrogel as possible. When a large alumina hydrogel is produced, the alumina in the central portion is converted into α-alumina during firing at high temperature, resulting in a decrease in specific surface area. To do this, the pH in this production process
Is important, and it is recommended to adjust the pH to 8 or above, or 6 or below. In the pH range of 6 to 8, the solubility of alumina hydrogel is small and large crystals are formed.

The alumina hydrogel is then subjected to a silica coating process.

In this coating process, alkali metal silicate (Na
₂ O: SiO ₂ = 1: 2 to 1: 4 is preferred) Aqueous solution (the concentration of the soluble salt is about 0.1 to 10 mol, preferably about 0.3 to
It is preferable to use a concentration in the range of 5.0 mol), and the solution is dropped onto the alumina hydrogel formed in the above-mentioned alumina hydrogel formation step and well dispersed to perform coating. In the method of coprecipitating alumina and silica, silica becomes a nucleus, and alumina may be generated and grown on it.
In this case, alumina grows in the aging step described later, and α-alumina is formed in the firing process, which is not preferable.

The silica-alumina crystals thus formed are subjected to an aging step.

This aging step is intended to dissolve small crystals and grow the crystals to produce crystals of uniform size.
The silica-alumina crystal produced in the coating step is allowed to grow as it is. However, if this aging step is carried out at a pH of around 8, rearrangement of silica-alumina crystals will occur, and silica-alumina having an alumina coating layer-
It may become an alumina crystal. In order to grow the silica-alumina crystal as it is, it was found that the pH should be lowered to 6.0 in this aging step.
This suppresses the rearrangement of silica-alumina crystals, and the silica-alumina having a small crystallite diameter is used as it is,
It is possible to grow while expanding the pore volume. The aging step is 40 to 90 ° C, preferably 50 to 80 ° C,
It is carried out for 1 to 5 hours, preferably 1.5 to 3 hours.

If this aging step is not carried out and the silica-alumina having a small crystal diameter is fired, the pore size of the alumina is small and calcination causes crystallization to lower the heat resistance. Therefore, a composition having a large pore size can be obtained by increasing the crystallite size in the aging step.

The silica-alumina crystals grown in this aging step are
After filtration, it is washed with an aqueous solution of ammonium carbonate, ammonium chloride or ammonium nitrate and dried in air at 80 to 200 ° C, preferably 90 to 150 ° C.

The silica-alumina composition after drying is 400 to 1200 ° C.,
The heat-resistant inorganic porous composition of the present invention can be produced by preferably firing in air at 500 to 1000 ° C.

Next, the shape of the catalyst carrier of the present invention will be described. That is, the silica-alumina precipitate collected by filtration is dried,
If necessary, the powder obtained by crushing is calcined, or without being calcined, water is added to this and mixed under humidity control. Alternatively, the precipitate (hydrogel) may be mixed. This mixture is extruded to obtain an extruded product, a honeycomb-shaped product, a granular product, or the like, which is fired in the air at 400 to 1200 ° C, preferably 500 to 1000 ° C.

On the other hand, when a catalyst such as mullite, silica-alumina, cordierite, or honeycomb is wash-coated and used as a combustion catalyst, the above powder is used as an acid (acetic acid, nitric acid, hydrochloric acid, etc.) or a base (ammonium hydroxide, etc.). ) And / or a hydrogel-added suspension of the support. Excessive deposits are purged with an inert gas (such as nitrogen), and then dried and baked. Drying in air 80-200 ℃, preferably 90-150
The firing temperature is 400 ° C to 1200 ° C, preferably 500 to 1000 ° C in the air.

Further, when the catalyst carrier of the present invention is used as a catalyst carrier for purifying automobile exhaust gas, the active metal component of the periodic table
At least one metal component selected from the group of Group VIII metals, such as iron, nickel, iron group metal components such as cobalt,
A noble metal such as platinum, palladium, iridium, rhodium, ruthenium or osmium is supported. The preferred active metal component is at least one selected from the group of platinum, palladium, rhodium, and iridium. These active metal components can be supported on the carrier as oxides in catalytically effective amounts. The preferred loading amount is 1% to 10% by weight,
Particularly, it is in the range of 2% by weight to 5% by weight.

Further, in the composition of the present invention, an alkaline earth metal such as barium, calcium, strontium, zirconium, and magnesium, an element periodic table such as boron, scandium, and yttrium Group III metal, titanium, zirconium, hafnium 1% to 30% by weight, preferably 1% by weight, of one or more oxides of Group IV metals, rare earth elements such as lanthanum, cerium and thorium
It can be used by adding in the range of 10 to 10% by weight.
The method of addition is not limited, but it is preferable to coprecipitate alumina or silica at the same time.

[Action]

Generally, in the catalytic reaction, the quality of the catalyst carrier significantly affects the activity, life, selectivity or economy of the catalyst, and it is desired that the catalyst carrier has an appropriate pore volume. That is, it is considered that the increase in the pore size causes an increase in the diffusion rate of the reaction reagent and the reaction product into and out of the catalyst particles, and as a result, the catalytic activity is improved.
Further, since the reaction proceeds on the surface of the catalyst, the surface area should not be extremely reduced, and the mutual relationship between these physical properties is required to exist within a specific range.

The present inventors have found that alumina-silica having small pores is easier to sinter than the large pores during firing and easily loses the pores. That is, when an alumina-silica carrier having small pores is fired at a low temperature to support a catalyst metal and used at a high temperature, a part of the metal is sintered in the carrier, and the proportion of the metal that acts effectively is reduced. On the other hand, even when the carrier is used at a high temperature by firing the carrier at a high temperature to support the catalyst metal, the carrier is already low in specific surface area, and thus the metal easily aggregates. Decrease. When used in an oxidation reaction accompanied by diffusion control, it is necessary to improve the free diffusion effect of reaction molecules, and for this purpose, it is desirable to use a carrier having a relatively large pore and a large pore volume. .

From this point of view, the present inventors have studied the alumina-silica composition, the total pore volume is 0.3 ml / g or more, and the pore volume of 100 Å or more pore diameter 60 of the total pore volume. % Or more, the specific surface area after firing at 1200 ° C. in air is 20 m ² / g or more, and in the pore distribution, the volume of pores in the pore diameter range of 100 to 400 Å is 0.20 ml / g or more. It has been found that by using the silica-alumina composition which is, it is possible to maintain the pore volume and the specific surface area even at high temperature calcination and high temperature reaction, and when this composition is used as a catalyst carrier, The inventors have found that it is a desirable carrier for a catalyst that exhibits reaction activity.

Then, by preparing this silica-alumina composition by the above-mentioned manufacturing method, it is possible to obtain a heat-resistant inorganic porous composition having the structure as described above. By coating the alumina hydrogel with silica, the porous θ −
It seems that the alumina is stabilized and the conversion to α-alumina is suppressed. On the other hand, addition of silica produces mullite, which is a composite with alumina, and a decrease in specific surface area occurs, but by optimizing the addition amount of the silica and controlling the growth of the silica-alumina crystal, α
-It is thought that it is possible to realize the suppression of aluminization, the securing of pores by the stabilization of θ-alumina, and the securing of the specific surface area at high temperatures.

Hereinafter, examples of the heat-resistant inorganic porous composition of the present invention will be described in comparison with comparative examples.

[Example 1] A 0.15 mol aluminum sulfate aqueous solution was prepared, 1N aqueous ammonia was added to the solution to adjust the pH to 8, and then the silica glass content in the product was adjusted to 10% by weight. (JIS K-1408) aqueous solution was added to form a silica-alumina precipitate.

The precipitate formed is aged at 60 ° C for 3 hours, and the final pH is adjusted to 6.2.
Lowered. After aging, the precipitate was filtered, washed with water, dried in air at 120 ° C for 12 hours, and then calcined in air at 500 ° C for 3 hours, calcined at 1000 ° C for 15 hours, calcined at 1200 ° C for 15 hours. An alumina composition was obtained.

[Example 2] A silica-alumina composition was obtained in the same manner as in Example 1 except that the final pH during aging was lowered to 7.5.

[Example 3] No. 3 water glass aqueous solution was used, and the silica content in the product was 5
Added so that it would be wt%, and final at the time of aging
A silica-alumina composition was obtained in the same manner as in Example 1 except that the pH was lowered to 6.0.

[Example 4] No. 3 water glass aqueous solution was used, and the silica content in the product was 5
Added so that it would be wt%, and final at the time of aging
A silica-alumina composition was obtained in the same manner as in Example 1 except that the pH was lowered to 7.7.

[Comparative Example 1] An aqueous solution of aluminum sulfate and No. 3 water glass (JIS K-140 so that the silica content in the product would be 10% by weight).
8) Mix the aqueous solution and add aqueous ammonia to adjust the pH to 8,
Silica-alumina was simultaneously precipitated. The precipitate is filtered without aging, separated from the aqueous solution, washed with water, and then at 120 ° C.
Dried in air for 12 hours and calcined in air at 500 ° C. for 3 hours.

[Comparative Example 2] Ammonia water was added to an aqueous solution of aluminum sulfate to adjust the pH.
8 and then the silica content in the product is 5% by weight
No. 3 water glass (JIS K-1408) aqueous solution was added thereto to form a silica-alumina precipitate, and the mixture was fired in the same manner as in Comparative Example 1 without aging.

[Comparative Example 3] Alumina powder was obtained and calcined in the same manner as Comparative Example 1 in the same manner as Comparative Example 1 except that only aluminum sulfate was used as a raw material and silica was not used.

[Comparative Example 4] The alumina powder prepared in Comparative Example 3 as a raw material and a commercially available silica gel powder were mixed and fired in the same manner as in Comparative Example 1.

The fired products prepared in these Examples and Comparative Examples were fired at 500 ° C. for 3 hours, 1000 ° C. for 15 hours, and
After calcination at 200 ℃ for 15 hours, specific surface area (m ² / g), pore volume (ml / g), pore distribution (%), 100Å relative to total pore volume
The ratio of the pores having the above diameters and the volume (ml / g) of the pores having the pore diameters of 100Å to 400Å were measured, and the results are shown in Tables 1 to 3 below.

Incidentally, among the above-mentioned physical properties, the specific surface area (m ² / g) is measured by a BET type specific surface area meter using nitrogen gas as an adsorption gas, and the pore distribution is determined by an isothermal adsorption line by a Sorptomatic 1800 manufactured by Carlo Erba, Using relative pressure, Kelvin formula, Dollimore & Hea
Calculated using the method of L (J.Appl.Chem.14, March, 1964).

Next, for each of the above compositions, the specific surface area during firing at 1200 ° C. in air, the firing time is 15 hours, 100 hours, 300
The heat resistance was evaluated as time. The results are shown in Table 4 below.

Table 4 shows the results of firing at 1200 ° C. in air, but the same tendency of deterioration is estimated even at a low temperature of 1200 ° C. or lower.

[Example 5] (Method for preparing catalyst) The precipitate prepared in Example 1 was filtered and washed to obtain 120
After drying at ℃ for 20 hours, it was crushed by a ball mill. After adding water to this and kneading to make it into a clay shape, it is extruded by an extruder equipped with a die having many holes with a diameter of 1/16 inch,
After forming into a cylindrical shape, it is dried in air at 120 ° C and then 500 ° C.
It was calcined in air for 3 hours to obtain a catalyst carrier.

Commercially available primary nitric acid was added to deionized water to prepare a 0.1N nitric acid aqueous solution, and 1.6 g of commercially available palladium chloride powder was added to this aqueous solution 1 and dissolved by heating to prepare a palladium solution.

20 ml of the above cylindrical catalyst carrier was immersed in 25 ml of this solution, and 0.024 g of palladium was added while slowly stirring for about 2 hours.
/ 20 ml (carrier) was supported. After washing with deionized water, it was dried in air at 120 ° C. for 12 hours and calcined in air at 500 ° C. for 3 hours.

Similarly to the above, Examples 2, 3, 4 and Comparative Examples 1, 2,
Using the compositions obtained in 3 and 4 as a carrier, palladium was supported to prepare a catalyst.

(Activity test) A mixture of CO; 1%, O ₂ ; 4%, and the balance; N ₂ was used as a reaction gas, and the space velocity was 30000 V / H / V, the inter-reaction heating furnace temperature was 250 ° C. The silica glass tube having an inner diameter of 12.7 mm (volume: 1.9 cm ³ ) was passed through a reactor filled with each catalyst shown in Table 5. After the reactor inlet temperature rose to 250 ° C and became stable, the reactor outlet gas was analyzed by gas chromatography. The catalyst used was 500 ° C / 3 hours calcined product, 1
It is a product baked at 000 ° C / 100 hours and a product baked at 1200 ° C / 100 hours. The results of measuring the CD conversion rate are shown in Table 5 below.

Table 5 shows that the catalyst using the carrier of the present invention has a reaction activity similar to that of the comparative example in the low temperature treatment of 500 ° C. for 3 hours, but the high temperature of 1000 ° C. and 1200 ° C. It can be seen that even if treated, it still shows a high CO conversion rate.

An accelerated durability test is also conducted to check the durability of the catalyst.
The test was performed on the products baked at 1000 ° C and 1200 ° C. In the accelerated durability test, the catalyst was placed in an electric furnace, heated to 1000 ° C., and steam was injected into the furnace at a water / air mole fraction of 0.0082.
After holding for 200 to 500 hours, the specific surface area of the catalyst (ml /
g) is measured. The compositions of Examples 1 and 3 of the present invention and Comparative Examples 2 and 3 of Comparative Example were used as a carrier to prepare a catalyst. The results are shown in Table 6 below. Further, the composition of the present invention showed almost no change in pore distribution. This also shows that it withstands long-term operation under high temperature conditions.

[Advantages of the Invention] The present invention comprises silica and alumina, the content of silica is in the range of 2% by weight to 30% by weight, and the total pore volume in the pore distribution measurement by the nitrogen adsorption method is 0.3 ml / g or more, and the pore volume with a pore diameter of 100 Å or more is 60% or more of the total pore volume, and the specific surface area after firing at 1200 ° C in air is 20 m ² / g or more. The present invention provides a heat-resistant inorganic porous composition having a pore volume of 0.20 ml / g or more in the pore size distribution range of 100 to 400 Å, and a catalyst carrier comprising the heat-resistant inorganic porous composition. To do. Since the heat-resistant inorganic porous composition of the present invention has the above-mentioned pore distribution and specific surface area, in particular when used as a catalyst carrier, not only use under low temperature conditions but also deactivation of the catalyst under high temperature conditions. The amount can be reduced and high reaction activity can be maintained.

Claims (4)

[Claims] 1. Silica and alumina, the content of silica is in the range of 2 to 30% by weight, and the total pore volume is 0.3 ml / g or more in the pore distribution measurement by the nitrogen adsorption method. A heat-resistant inorganic porous composition having a pore volume of 100 Å or more, 60% or more of the total pore volume, and a specific surface area of 20 m ² / g or more after firing in air at 1200 ° C. 2. The heat-resistant inorganic porous composition according to claim 1, wherein the pore volume in the pore size distribution in the range of 100 to 400 Å is 0.20 ml / g or more. 3. Silica and alumina, the content of silica is in the range of 2% to 30% by weight, and the total pore volume is 0.3 ml / g or more in the pore distribution measurement by the nitrogen adsorption method. From a heat-resistant inorganic porous composition having a pore volume of 100 Å or more and 60% or more of the total pore volume and a specific surface area of 20 m ² / g or more after firing at 1200 ° C in air A catalyst carrier. 4. The catalyst carrier according to claim 3, wherein the pore volume in the pore size distribution in the range of 100 to 400 Å is 0.26 ml / g or more.