JP2000026108A - Production of heat resistant inorganic oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a heat resistant inorg. oxide that undergoes a slight change in the shape even at a high temp. by bringing a silane coupling agent into contact with an inorg. oxide and firing the inorg. oxide at the thermal decomposition temp. of the silane coupling agent or above. SOLUTION: An inorg. oxide is immersed in a soln. of a silane coupling agent, mixed and stirred to stick the silane coupling agent to the surface of the inorg. oxide. The silane coupling agent is, e.g. N-β-(aminoethyl)-γ- aminopropyltrimethoxysilane or γ-aminopropyltriethoxysilane. The inorg. oxide is, e.g. Al oxide, Mg oxide or Ti oxide. The inorg. oxide is then fired at the thermal decomposition temp. of the silane coupling agent or above (about 400-800 deg.C) to form a very thin layer of silica on the surface of the inorg. oxide in about 0.1-10 wt.% coating weight based on the amt. of the inorg. oxide. The reduction of the large specific surface area of the inorg. oxide and the growth of oxide grains are inhibited and the objective heat resistant inorg. oxide useful as a catalyst carrier for use at a high temp. is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a heat-resistant inorganic oxide having a small morphological change even at a high temperature, and is particularly suitable for a catalyst carrier or the like which needs to maintain a low-temperature phase even at a high temperature. The present invention relates to a method for producing a heat-resistant inorganic oxide used in a method.

[0002]

2. Description of the Related Art When an inorganic oxide powder is used in an environment exposed to heat, the oxide particles grow due to the heat, the specific surface area decreases, and depending on the material, the crystal of the material may be reduced. It is known that a phase transition occurs. Specifically, there is a problem that the refractory material and the container of the firing furnace are deformed or broken, or when used as a catalyst, the specific surface area is reduced and the activity is reduced.

In order to improve the heat resistance of the inorganic oxide,
The entire powder or powder surface is treated with oxide or composite oxide
It is known to For example, C for alumina
elements such as a, Sr, Ba, Y, and La are added.
You. However, even with these methods, the specific surface
Product is not sufficiently suppressed, for example, a specific surface area of 160 m ^Two
/ G of γ-alumina and the above elements are added
However, the specific surface area after degradation at 1100 ° C. for 20 hours is 50
m^Two/ G.

[0004] Since an exhaust gas purifying catalyst for automobiles is required to have a high contact probability with gas, 100 m ² / g is required.
Activated alumina having the above specific surface area is widely used. However, it is inevitable that a catalyst used for purifying exhaust gas of an internal combustion engine, particularly for purifying exhaust gas of an automobile is exposed to a high temperature by a combustion gas.
It is known that the temperature rises to as high as ° C. These supports also have the drawback that they have high surface activity due to their high specific surface area and are easily sintered. For example, specific surface area 160
Even if γ-alumina of m ² / g is used as a carrier, the specific surface area after deterioration is finally reduced to about 10 m ² / g.

It is also known to add silica to the surface of an inorganic oxide to improve heat resistance. For example, a method in which an alumina powder is impregnated with an ethanol solution of silicon alkoxide and then fired at 1300 ° C. or more to cover the surface (for example, J. MATER. CHEM., 1992.2)
(5), p. 577-578, Mori et al.) And a method of subjecting silicon alkoxide to powder surface treatment by a CVD method (for example, Coloring Material 65 (3), p. 170-).
175, Fukui et al.). However, these methods have problems such as complicated handling such as evaporation and flammability of the alkoxide, calcination at a high temperature, and necessity of a vacuum device, and the like, and the steps and devices are complicated.

Accordingly, an object of the present invention is to suppress a decrease in the high specific surface area of an inorganic oxide even when used at a high temperature, to suppress the growth of oxide particles, or to reduce the phase transition temperature of the crystal structure. It is an object of the present invention to provide a method for producing a heat-resistant inorganic oxide, which can be used as a catalyst carrier for high temperature, in particular, can be used to increase the temperature.

[0007]

Means for Solving the Problems As a result of diligent studies on the above-mentioned problems, the present inventors have found that a silane coupling agent is attached to the surface of an inorganic oxide and is decomposed by thermal decomposition of the silane coupling agent or more. It has been found that an inorganic oxide having extremely high heat resistance can be produced by coating an extremely thin layer of silica.

[0008] The present invention has been made based on the above findings, and comprises a step of bringing a silane coupling agent into contact with an inorganic oxide and firing at a temperature not lower than the thermal decomposition temperature of the silane coupling agent. Is provided.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the present invention, the silane coupling agent is brought into contact with the inorganic oxide. Specifically, a silane coupling agent is attached to the surface of the inorganic oxide. As a method of attaching the silane coupling agent to the surface of the inorganic oxide, for example, the inorganic oxide is immersed in a silane coupling agent solution, mixed, and stirred.

The silane coupling agent used here is a general-purpose silane coupling agent such as N-β (aminoethyl) -γ-aminopropyltrimethoxysilane, γ
-Aminopropyltriethoxysilane, γ- (2-aminoethyl) aminopropylmethyldimethoxysilane, γ
-Anilinopropyltrimethoxysilane and the like, but are not particularly limited as long as a solvent is selected. Further, in order to assist the dissolution of the silane coupling agent in the solvent, an acid, a base, an inorganic salt, an organic substance, or the like may be optionally added to the silane coupling agent.

Further, as the inorganic oxide, aluminum oxide, magnesium oxide, titanium oxide, cerium oxide,
Examples thereof include zirconium oxide and iron oxide.

Next, sintering is performed at a temperature not lower than the thermal decomposition temperature of the silane coupling agent, and silica is attached to the surface of the inorganic oxide.
The thermal decomposition temperature of the silane coupling agent is appropriately selected depending on the type of the selected silane coupling agent, the heat treatment atmosphere, and the like. Generally, 400 to 800 ° C., preferably 650 ° C., at which organic matter is burned and decomposed to generate silica. It is about.

It has been widely practiced to attach a silane coupling agent to the surface of an inorganic oxide. For example, Japanese Unexamined Patent Publication (Kokai) No. 61-91232 discloses that magnesium oxide fired at a high temperature in advance is subjected to a silane coupling treatment to provide a powder which can be easily filled into a resin and has a small moisture absorption. Also, JP-A-2-5520
No. 6, JP-A-3-93605, JP-A-2-2-2
No. 96717 discloses that addition of a silicon compound to an oxide is effective for improving fluidity. Alternatively, JP-A-5-139726, JP-A-6-80405, JP-A-6-80406 and the like disclose that a silane compound is treated on an oxide in order to improve hydrophobicity.

As described above, it is known that a silane coupling agent is attached to the surface of an inorganic oxide. However, these methods use the fact that the silane coupling agent has both a hydrophilic group and a hydrophobic group to make use of the inorganic oxidizing agent. It has been used to hydrophobize the surface of an object or to improve fluidity.

In the present invention, unlike these viewpoints, it is noted that the use of a silane coupling agent makes it possible to attach a silicon compound extremely thinly to the surface of an inorganic oxide. It has been found that an extremely thin layer of silica can be easily formed on the surface of the inorganic oxide.

The use of a silane coupling agent to deposit a silicon compound on the surface of an inorganic oxide and form a thin layer of silica obtained by thermally decomposing the silicon compound, thereby improving the heat resistance of the inorganic oxide has been known. Not reported. In particular, this inorganic oxide is effective for heat-resistant materials such as refractories and catalyst carriers.

It has been reported in a paper that the highest specific surface area is maintained when a single layer of silica is supported on the surface of an inorganic oxide (for example, "Ceramics", Vol. 29, No. 9, pp. 823-830). ). According to this, when the silica is carried on the inorganic oxide surface in a single layer, a large amount of the carried silica forms a multilayer of the silica, and in this case, a high specific surface area is maintained even after firing at a high temperature. However, it has been reported that the specific surface area is rather reduced when the surface coverage is multi-layered by increasing the amount of supported silica. However, in the case of this paper, a method of supporting alkoxide silane in a gas phase by a CVD method is used to form a single layer.

When the production method of the present invention is used, basically, only a single layer of the silicon compound is formed on the surface of the inorganic oxide.
Therefore, even when the inorganic oxide is impregnated in the silane coupling agent solution, a particularly complicated process is not required, and a single layer of silica can be formed very easily by firing the inorganic oxide.

The reason that the excess amount of silica coating on the inorganic oxide lowers the specific surface area is considered to be because silica tends to be vitreous. However, it is considered that when silica is thinly coated on the surface of the inorganic oxide, it acts on the grain boundaries between the particles of the inorganic oxide at a high temperature, and sintering hardly occurs to suppress neck growth, thereby improving heat resistance. . This improvement in heat resistance not only prevents sintering due to high temperature, but also suppresses the change from low-temperature phase to high-temperature phase for oxides with phase transformation. is there. Therefore, the coating amount of silica with respect to the inorganic oxide is 0.1 to 10% by weight, preferably about 0.1 to 5% by weight.

In addition, the silica covering the surface of the inorganic oxide fixes the activity of oxygen, so that the movement of oxygen vacancies on the surface of the inorganic oxide, which triggers crystal growth during sintering, is improved, so that the heat resistance is improved. I do.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments and the like.

Example 1 and Comparative Example 1 To 100 g of a silane coupling agent (γ-aminopropyltriethoxysilane, KBE903 manufactured by Shin-Etsu Silicone Co., Ltd.) was added 900 g of water, followed by mixing and stirring for 1 hour. 100 g of TiO ₂ (anatase) is immersed in this silane coupling aqueous solution,
The mixture was mixed and stirred with a stirrer for 20 hours. Subsequently, suction filtration was performed to collect the silane-coupled TiO ₂ .

The recovered powder was washed with a sufficient amount of water, and suction-filtered again to recover the powder. After drying the recovered powder, the powder was heated at 650 ° C. for 5 hours to burn off the organic components of the silane coupling agent, and the T coated with silica was removed.
An iO ₂ powder was obtained (Example 1). The silica coating amount of this powder was analyzed by fluorescent X-ray to find that it was 2.05% by weight.

The TiO ₂ (Example 1) produced in this way was fired at 600 to 1000 ° C. for 2 hours.
A chart of the line diffraction is shown in FIG. For comparison, untreated TiO ₂ (Comparative Example 1) was heated to 700 to 1000 ° C.
FIG. 1 shows an X-ray diffraction chart of the sample fired for 2 hours in FIG.
(B). In addition, in FIG. 1, A shows anatase and R shows rutile, respectively.

From the results shown in FIGS. 1A and 1B, the embodiment
1 TiO_TwoIs the TiO of Comparative Example 1. _TwoCompared to the peak
It is recognized that the length is small and sintering is suppressed.
The peak of the rutile phase, which is a high-temperature phase, reaches up to 1000 ° C.
Did not appear.

Further, the state of change of crystallites determined by the Scherrer method from the peak of X-ray diffraction was evaluated. The crystallite size at 900 ° C. was 438 ° in Example 1 and 1260 ° in Comparative Example 1. It can be seen that the silane coupling treatment keeps the crystallite diameter small and suppresses sintering.

Example 2 and Comparative Example 2 To 100 g of a silane coupling agent (γ-aminopropyltriethoxysilane, KBE903 manufactured by Shin-Etsu Silicone Co., Ltd.) was added 900 g of water, followed by mixing and stirring for 1 hour. This silane coupling aqueous solution was impregnated with 100 g of cerium oxide (CeO ₂ ) and mixed and stirred with a stirrer for 20 hours. Next, suction filtration was performed to collect the silane-coupled CeO ₂ .

The recovered powder was washed with a sufficient amount of water, and suction-filtered again to recover the powder. After drying the recovered powder, it is heated at 650 ° C. for 5 hours to burn off the organic components of the silane coupling agent and to remove the silica-coated C.
eO ₂ powder was obtained (Example 2). The silica coating amount of this powder was analyzed by fluorescent X-ray and found to be 1.96% by weight.

A sample obtained by firing CeO ₂ (Example 2) thus manufactured at 700 to 1100 ° C. for 2 hours,
For comparison, untreated CeO ₂ (Comparative Example 2) was
The state of the change in crystallites determined by the Schaller method from the peak of X-ray diffraction of the sample fired at 100 ° C. for 2 hours was evaluated. The results are shown in Table 1.

[0030]

[Table 1]

From these results, it can be seen that the silane coupling treatment keeps the crystallite diameter small and suppresses sintering. The sample obtained by calcining the CeO ₂ of Example 2 at 1000 ° C. for 2 hours is the same as the sample of CeO _{2 of} Comparative Example ₂ at 1000 ° C.
The yellow color derived from oxygen deficiency was stronger than that of the sample fired for 2 hours. This indicates that the present invention can suppress the disappearance of oxygen vacancies.

Example 3 and Comparative Example 3 To 100 g of a silane coupling agent (γ-aminopropyltriethoxysilane, KBE903 manufactured by Shin-Etsu Silicone Co., Ltd.) was added 900 g of water, followed by mixing and stirring for 1 hour. Activated alumina (γ-alumina, specific surface area 16
(0 m ² / g) was immersed, and mixed and stirred with a stirrer for 20 hours. Next, suction filtration was performed to collect silane-coupled γ-Al ₂ O ₃ .

The recovered powder was washed with a sufficient amount of water, and suction-filtered again to recover the powder. After drying the recovered powder, the powder was heated at 650 ° C. for 5 hours to burn off the organic component of the silane coupling agent, and the silica-coated γ
-Al ₂ O ₃ to obtain a powder (Example 3). When the silica coating amount of this powder was analyzed by fluorescent X-ray, it was 2.25% by weight.
Met.

The thus obtained γ-Al ₂ O
₃ and the sample was baked for 20 hours (Example 3) and 1100 ° C., X-ray diffraction of untreated gamma-Al ₂ O ₃ for comparison (Comparative Example 3), a gamma-Al ₂ O ₃ of Comparative Example 3 2 at 1100 ° C
X-ray diffraction of the sample fired for 0 hours is shown in FIG.

As a result, the γ-Al ₂ O ₃ of Comparative Example 3 was changed into α-alumina, which is a high-temperature phase, by the heat treatment, and the specific surface area at this time was 8 m ² / g. In the alumina of Example 3, the peak of the α phase which is a high temperature phase was not observed. The specific surface area of Example 3 was 107 m ^2.
/ G, confirming that the decrease in specific surface area due to thermal degradation and the phase change to α phase, which is a high temperature phase, could be suppressed.

Example 4 and Comparative Example 4 The γ-Al ₂ O ₃ powder obtained in Example 3 after the silane coupling treatment was calcined at 1100 ° C. for 20 hours with γ-Al ₂ O ₃ . The aqueous boehmite sol was mixed in water at a ratio of 8: 2, and this was mixed with a cordierite honeycomb (76 mm in diameter, 50 m in length).
m) to absorb water and carry alumina. The honeycomb was fired at 500 ° C. Amount of alumina carried is about 36 g
It was calculated. This honeycomb was put into 1 liter of palladium nitrate solution (0.35 / liter), and was impregnated with palladium, calcined at 500 ° C., and reduced with a reducing agent.
A palladium-supported catalyst honeycomb was prepared. The carried amount of palladium was calculated to be about 0.2 g.

On the other hand, for comparison, a palladium-supported catalyst honeycomb was produced using the γ-alumina of Comparative Example 3 with the same other composition and conditions (Comparative Example 4).

The two honeycombs were fired at 1000 ° C. for 20 hours to be thermally degraded. Each of the honeycombs was mounted on a mini vehicle, and the exhaust gas purification rate was measured in the 10-15 mode. Table 2 shows the results.

[0039]

[Table 2]

As is clear from the results in Table 2, Example 4
Showed a higher purification rate than Comparative Example 4.

[0041]

As described above, the production method of the present invention suppresses a decrease in the high specific surface area of the inorganic oxide even when used at a high temperature, suppresses the growth of oxide particles, Alternatively, a heat-resistant inorganic oxide which can raise the phase transition temperature of the crystal structure and is particularly used as a high-temperature catalyst carrier is obtained.

[Brief description of the drawings]

1 (a) and 1 (b) show X-rays after silane coupling treatment of TiO ₂ according to Example 1 and Comparative Example 1 and untreated at 600 to 1000 ° C. for 2 hours in air. It is a diffraction chart.

FIG. 2 shows γ-Al according to Example 3 and Comparative Example 3.
_{2 is} an X-ray diffraction chart of a silane coupling treatment of ₂ O ₃ (after calcination at 1100 ° C. for 20 hours) and a non-treatment (after sintering at 1100 ° C. for 20 hours).

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] August 10, 1998 (1998.8.1)
0)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0024

[Correction method] Change

[Correction contents]

The TiO ₂ (Example 1) thus produced was fired at 700 to 1000 ° C. for 2 hours.
A chart of the line diffraction is shown in FIG. For comparison, untreated TiO ₂ (Comparative Example 1) was heated to 700 to 1000 ° C.
X-ray diffraction chart of the sample fired for 2 hours
(B). In addition, in FIG. 1, A shows anatase and R shows rutile, respectively.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0029

[Correction method] Change

[Correction contents]

A sample obtained by firing CeO ₂ (Example 2) thus manufactured at 700 to 1100 ° C. for 2 hours,
For comparison, untreated CeO ₂ (Comparative Example 2) was
From the X-ray diffraction peak of the sample fired at 100 ° C for 2 hours
The state of change of crystallites determined by the Scherrer method was evaluated. The results are shown in Table 1.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] Fig. 1

[Correction method] Change

[Correction contents]

1 (a) and 1 (b) show silane coupling treatment of TiO ₂ and untreated TiO ₂ according to Example 1 and Comparative Example 1. FIG.
700 to 1000 ° C., is X-ray diffraction chart after firing for 2 hours in air.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) B01J 23/745 C01B 33/12 C 4G072 C01B 33/12 C01F 5/02 4G076 C01F 5/02 7/02 D 7/02 17/00 G 17/00 C01G 23/04 Z C01G 23/04 25/02 25/02 49/00 A 49/00 B01J 23/74 301Z F term (reference) 4G002 AA02 AB05 AE05 4G042 DA01 DB27 DC03 DE03 DE12 4G047 CA02 CA07 CA08 CB08 CB09 CC03 4G048 AA05 AB04 AC08 AE05 4G069 AA01 AA08 BA01A BA01B BA01C BA03A BA03B BA03C BA04A BA04B BA04C BA06A BC06C BC43A BC43B BC43C BD02ABC023 BD02B02A UU15 4G076 AA02 AB02 AB11 AB13 BA39 BF02 DA01

Claims (5)

[Claims] 1. A method for producing a heat-resistant inorganic oxide, comprising: bringing a silane coupling agent into contact with an inorganic oxide; and baking at a temperature not lower than the thermal decomposition temperature of the silane coupling agent. 2. The heat-resistant inorganic oxide according to claim 1, wherein the silane coupling agent is adhered to the surface of the inorganic oxide, and then the silica is coated on the surface of the inorganic oxide by thermally decomposing the silane coupling agent. Production method. 3. The method for producing a heat-resistant inorganic oxide according to claim 2, wherein the coating amount of the silica is 0.1 to 10% by weight. 4. The method according to claim 1, wherein the inorganic oxide is aluminum oxide,
4. The method according to claim 1, wherein the material is selected from magnesium oxide, titanium oxide, cerium oxide, zirconium oxide and iron oxide.
3. The method for producing an inorganic oxide according to item 1. 5. A catalyst or catalyst carrier using the heat-resistant inorganic oxide obtained by the production method according to claim 1.