JPH08257399A - Production of titania catalyst - Google Patents

Abstract

PURPOSE: To produce a titania catalyst capable of increasing photocatalytic activity even if a noble metal cocatalyst is not supported. CONSTITUTION: A hydrolyxed sol prepared by mixing titanium alkoxide and silicon alkoxide so as to become a mol. ratio of (1-x)TiO2 .xSiO2 (x=0-0.5) is gelled and baked at heat treatment temp. of 350-1200 deg.C to produce a titanium type catalyst which is, in turn, treated with alkali to obtain a titania catalyst.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a titania catalyst, and more particularly to a method for easily producing a titania catalyst having excellent photocatalytic activity.

[0002]

2. Description of the Related Art Titania is widely known as a material having excellent catalytic activity, and various photocatalytic reactions have been studied.

The photocatalytic reaction is carried out by (1) the reaction molecules are brought close to the catalyst surface, and (2) electrons and holes excited by light irradiation inside the catalyst reduce or oxidize the reaction molecules on the catalyst surface. It is thought to accelerate the chemical reaction.

As means for improving the catalytic activity, the catalyst powder is made finer, which leads to an increase in the specific surface area of the catalyst (increase in the catalytic activity points), or even if it is polycrystalline, the crystal grain size (single It can be expected that reducing the diameter of the crystal), that is, refining the crystal, is an effective means. Then, as a method of refining crystals, a sol-gel method, a vapor phase method, etc. are known.

Further, in the research paper “Preparation and Photocatalytic Activity of TiO ₂ —SiO ₂ Catalyst Supporting Platinum and Ruthenium” published in “Science and Industry Vol. 66”, issued in January 1992, titania was prepared by the sol-gel method. It has been reported that the crystal grain size becomes smaller when silica (SiO ₂ ) is doped (added) when preparing the system catalyst powder.

[0006]

However, in the case of the titania-based catalyst, it is premised that platinum and ruthenium are supported as the co-catalyst to increase the photocatalytic activity.
It is presumed that O ₂ / SiO ₂ plays a role as a carrier that hardly expects catalytic activity.

Since these supporting operations are carried out in the form of an aqueous chloride solution of the noble metal, it is troublesome and the cost tends to be high.

Further, as a result of examination and examination by the present inventors, it was found that it is difficult to obtain a high catalytic activity only with TiO ₂ / SiO ₂ .

In view of the above, the present invention is directed to TiO ₂ or TiO ₂ without supporting a precious metal co-catalyst or the like.
_An object of the present invention is to provide a method for producing a titania-based catalyst that can increase the catalytic activity only with ₂ / SiO ₂ .

[0010]

The present invention has been made in order to achieve the above object, and has the following constitution to solve the above problems.

(1-x) TiO ₂ · xSiO ₂ (x = 0
Is a method of producing a titania-based catalyst by gelling a hydrolyzed sol in which titanium alkoxide and silicon alkoxide are mixed so as to have a molar ratio of 0.5 to 0.5) and then firing the gelled product at 350 to 1200 ° C. Then, the calcined titania-based catalyst is surface-treated with an acid or an alkali.

[0012]

Detailed Description of Means The method for producing a titania-based catalyst of the present invention will be described below with reference to FIGS.

(1) In the method for producing the titania-based catalyst of the present invention, a hydrolyzed sol (colloidal solution) in which titanium alkoxide and silicon alkoxide are mixed in a predetermined ratio is gelled, and the gelled product is then baked (crystallized). It is assumed that the manufacturing is performed by

Here, the molar ratio of titania and silica is shown as follows.
Property (1-x) TiO₂ ・ XSiO ₂ X = 0 to 0.
5, preferably x = 0.02-0.25
It

Although only titania may be used, it is desirable to dope (add) a small amount of silica so that the crystal grain size becomes small as described above. And the range is x = 0.0
It is set to 2 to 0.25. When x is less than 0.02, it is difficult to obtain the effect of silica addition (crystal refinement: increase in specific surface area),
If the amount of silica added is too large, the refinement of crystals is not promoted so much, and the ratio of titania is relatively reduced, which rather reduces the catalytic activity. (Refer to FIG. 1, which is a graph showing the relationship between the amount of silica added and the specific surface area.) The firing conditions are usually 350 to 1200 ° C. × 0.3 to 2 h, preferably, though the firing conditions vary depending on the ratio of silica.
It is preferably 450 to 600 ° C. × 0.5 to 1.5 hours. It is desirable that the temperature is relatively low because the crystal can be made finer (the specific surface area can be increased). However, if it is too low, firing becomes difficult and the firing time becomes relatively long,
Productivity decreases.

The titania-based catalyst (titania-silica composite fine particle crystal) used in the present invention is, for example, JP-A-5-5.
It is prepared by the method described in Japanese Patent No. 8649.

It is not a mixture of silica fine particles and titania fine particles, but is prepared by gelling a hydrolyzed sol solution of silicon alkoxide and titanium alkoxide in a predetermined ratio, followed by firing and, if necessary, pulverization.

When the hydrolyzed sol solution is prepared, titanium alkoxide and silicon alkoxide are mixed and then hydrolyzed at the same time, or one of them is partially hydrolyzed (hereinafter referred to as preliminary hydrolysis) and the other is added. And further hydrolyze (hereinafter referred to as final hydrolysis)
There are ways. The latter method is used especially when the hydrolysis rates of the silicon alkoxide and the titanium alkoxide used are significantly different and precipitation is likely to occur during hydrolysis.

The titanium alkoxide is a compound represented by the general formula Ti (OR) ₄ (where R is an alkyl group or an alkoxyalkyl group), or one or two alkoxide groups (OR) in the above general formula. A compound in which is substituted with a carboxyl group or a β-dicarbonyl group, or a mixture thereof is preferable. Specific examples of the above titanium _{alkoxide, Ti (O-isoC 3 H} 7) 4, Ti
(O-nC ₄ H ₉ ) ₄ , Ti (O-CH ₂ CH (C ₂ H ₅ ) C ₄ H ₉ ) ₄ , Ti (OC ₁₇ H ₃₅ ) ₄ , Ti
_{(O-isoC 3 H 7)} 2 [CO (CH 3) CHCOCH 3] 2, Ti (O-nC 4 H 9) 2 [OC 2 H 4 N
(C ₂ H ₄ OH) ₂ ] ₂ , Ti (OH) ₂ [OCH (CH ₃ ) COOH] ₂ , Ti (OCH ₂ CH (C ₂ H ₅ )
Compounds such as CH (OH) C ₃ H ₇ ) ₄ and Ti (O-nC ₄ H ₉ ) ₂ (OCOC ₁₇ H ₃₅ ).

There are various kinds of the above-mentioned silicon alkoxides, and those which are industrially easily available include, for example, compounds represented by the general formula Si (OR ¹ ) ₄ (wherein R ¹ is an alkyl group or an alkoxyalkyl group), or One or two alkoxide groups (OR ¹ ) in the above general formula
A compound in which is substituted with a carboxyl group or a β-dicarbonyl group, a low condensate obtained by partially hydrolyzing them, or a mixture thereof is used without particular limitation. As the alkyl group, a methyl group,
Preferable examples include lower alkyl groups such as ethyl group, isopropyl group, butyl group, and examples of alkoxyalkyl groups include methoxymethyl group, ethoxymethyl group, methoxyethyl group, ethoxyethyl group, methoxypropyl group and the like. . These silicon alkoxides may be commercially available products as they are, or may be purified by distillation before use.

The hydrolysis is carried out with stirring in the presence of a solvent such as alcohol, an acid or a base catalyst, if necessary, in addition to water. At this time, it is desirable to carry out the hydrolysis in a water bath or a hot water bath. A catalyst and a solvent such as alcohol are not always necessary, but a catalyst has an effect of accelerating the rate of hydrolysis and polycondensation, and a solvent such as alcohol has an effect of suppressing the generation of precipitates and preparing a more uniform sol solution. There is.

As the catalyst, an acid or basic compound as it is or in a state of being dissolved in a solvent such as water or alcohol (hereinafter referred to as an acidic catalyst or a basic catalyst) is used. The concentration at that time is not particularly limited, but when the concentration is high, the hydrolysis and polycondensation rates tend to be high. However, if a basic catalyst with a high concentration is used, a precipitate may be generated in the sol solution,
The concentration of the basic catalyst is preferably 1N (converted to a concentration in an aqueous solution) or less.

The type of acidic catalyst or basic catalyst is not particularly limited, but when it is necessary to use a catalyst with a high concentration, a catalyst composed of elements that hardly remain in the catalyst crystal grains after sintering is used. Good. Specifically, as the acidic catalyst, hydrogen halide such as hydrochloric acid, nitric acid, sulfuric acid, sulfurous acid, hydrogen sulfide, perchloric acid, hydrogen peroxide, carbonic acid,
Carboxylic acids such as formic acid and acetic acid, substituted carboxylic acids in which R of the structural formula RCOOH is substituted with another element or a substituent,
Examples of the basic catalyst such as sulfonic acid such as benzenesulfonic acid include ammoniacal bases such as aqueous ammonia and amines such as ethylamine and aniline.

(2) The present invention is characterized in that the titania catalyst obtained by the above method is surface-treated with an alkali or an acid.

Here, an aqueous solution of sodium / potassium hydroxide (usually 1 to 17 N) or the like can be suitably used as the alkali, and hydrofluoric acid (usually 0.1 to 10 N) or the like can be suitably used as the acid. It is presumed that this surface treatment removes the amorphous silica (which is considered to adversely affect the catalytic activity) remaining on the surface of the titania-based catalyst powder. At this time, it is washed with water after each surface treatment. When the surface treatment is performed with an alkali, it is desirable to neutralize the surface with an inorganic acid such as dilute hydrochloric acid after washing with water.

The alkali / neutralization method is usually carried out by a method such as dipping / spraying.

(3) The fired product prepared as described above is
Although it may be used as it is as a catalyst (photoactive), it is usually pulverized before use. As a pulverization method, a fine pulverizer or an ultrafine pulverizer such as a ball / rod mill or a micronizer is usually used.

[0028]

The operation and effect of the present invention has the following operation and effects due to the above-mentioned constitution.

(1) By surface-treating a silica-doped or dopeless titania-based calcined product with an alkali or an acid, the photocatalytic properties are increased, as will be supported in the examples described later. It is presumed that this is because the titania-silica amorphous remaining in the titania-based fired body is removed.

(2) When silica is doped in a predetermined amount or more,
Furthermore, by lowering the calcination temperature as much as possible, the photocatalytic properties are also increased. It is presumed that the particle size of the single crystal becomes smaller (relatively increases the specific surface area) and the catalytically active surface increases.

As described above, according to the method for producing a titania-based catalyst of the present invention, the photocatalytic activity can be easily increased without supporting the noble metal promoter.

[0032]

[Test Example] A test example conducted to confirm the effects of the present invention will be described below.

(1) Relationship between the amount of silica added and the specific surface area The composition is (1-x) TiO ₂ · xSiO ₂ (x = 0,
0.05, 0.1) commercially available isobutoxysilane and tetraethoxysilane are dissolved in ethanol and water to a sol solution, diluted hydrochloric acid is added as a hydrolysis catalyst, and the mixture is left to stand after hydrolysis. Gelled. (Refer to the process chart of FIG. 4) Each gel is heat-treated at a temperature of 500/600/700 ° C. for 2 hours and baked,
The fired product was crushed in an agate mortar and finely powdered (particle size <3
The specific surface area of each titania catalyst prepared by preparing a 20 mesh titania catalyst was measured based on the BET method. The results are shown in FIG. 1, and it can be seen that the specific surface area increases as the amount of silica added increases. Further, it can be seen that the specific surface area decreases as the firing temperature (crystallization temperature) increases.

(2) Relationship between calcination temperature and catalytic activity The catalytic activity of each of the catalysts obtained above with a silica addition amount of 0.05 mol% and a crystallization temperature of 500/600/700 ° C. was measured by the optical Kolbe method. It was measured by. The results are shown in FIG. 2, and it can be seen that the lower the crystallization temperature is (the larger the specific surface area is), the higher the crystallization temperature is.

(3) Relationship between alkali treatment and catalytic activity: Alkali surface treated products and non-treated products prepared at a calcining temperature of 600 ° C. with a silica addition amount of 0.1 or 0.2 mol%, respectively, are subjected to the optical Kolbe method. The catalytic activity was measured by. The results are shown in FIG. 3, and it can be seen that the alkaline surface-treated product has significantly higher catalytic activity than the untreated product.

The surface treatment is NaOHaq (17
N) soaked in alkali (room temperature 5 hours), washed with water,
Completed with acid wash with aq (0.1 N).

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of silica added and the specific surface area.

FIG. 2 is a graph showing the relationship between calcination temperature and catalytic activity.

FIG. 3 is a graph showing the relationship between the presence or absence of alkali treatment and the catalytic activity.

FIG. 4 is a process diagram of the sol-gel method in the above test example.

Claims (3)

[Claims] 1. A (1-x) TiO ₂ .xSiO ₂ (x =
A method for producing a titania-based catalyst by gelling a hydrolyzed sol in which titanium alkoxide and silicon alkoxide are mixed so as to have a molar ratio of 0 to 0.5) and then calcining at a heat treatment temperature of 350 to 1200 ° C. A method for producing a titania-based catalyst, characterized in that the calcined titania-based catalyst is surface-treated with an alkali or an acid. 2. The method according to claim 1, wherein x = 0.02-0.
25 is a method for producing a titania-based catalyst. 3. The method for producing a titania-based catalyst according to claim 1, wherein the heat treatment temperature is 450 to 600 ° C.