JPH0397623A - Production of titanium oxide for fixing gold superfine grains - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a method for producing ultrafine gold particle-immobilized titanium oxide,
Specifically, ultrafine gold particles are supported on titanium oxide in a highly dispersed manner, and are used as low-temperature oxidation catalysts and low-temperature reduction catalysts. This invention relates to a method for producing titanium oxide fixed with ultrafine gold particles, which can be effectively used for gas sensors, B materials, etc.

[Problems to be solved by conventional techniques and inventions] Conventionally,
Gold has been considered to be a representative metal with poor chemical activity, but when it is made into ultrafine particles with a particle size of 10 nm or less and dispersed and supported on metal oxides such as iron, cobalt, and nickel, it becomes extremely effective. The present inventors have reported that it acts as a catalyst (Chemistry Letters
, pp. 405-408 (1987). Surface chemistry 8. 4
07-414 (1987). Chemistry Ex
press 3, 159-162 (1988), J.
Catalysis Yui5.301-309 (1989
)).

Examples of methods for preparing such ultrafine gold particle-immobilized metal oxides include: ■ Co-precipitation method (Japanese Patent Application Laid-open No. 60-238148) ■ Homogeneous precipitation precipitation method (Japanese Patent Application Laid-open No. 62-155937), ■ Drop neutralization Precipitation method (Japanese Unexamined Patent Publication No. 63-252908),■
Reducing agent addition method (Japanese Unexamined Patent Publication No. 63-252908),■
Methods such as pH-controlled neutralization precipitation method (Japanese Unexamined Patent Publication No. 63-252908) have been developed by the present inventors.

However, each of these methods has its advantages and disadvantages, and there are restrictions on the weight of gold that can be supported in the form of ultrafine particles and the type of carrier, making it virtually impossible to use it in cosmetics, gas sensors, etc. .

In order to solve these conventional problems, the present inventors first neutralized an aqueous solution in which a gold compound and a water-soluble metal salt were dissolved with an alkaline aqueous solution when preparing an oxide with immobilized ultrafine gold particles. When obtaining a coprecipitate by or after the production of a coprecipitate, adding a carboxylic acid or a salt thereof to form P, and then heating to suppress aggregation of ultrafine gold particles,
It has been discovered that extremely fine ultrafine gold particles can be supported uniformly and firmly, and an application has been filed based on this knowledge (Japanese Patent Application No. 3,603).

In this invention, titanium sulfate,
Ultrafine gold particles immobilized oxide (titanium oxide) is prepared by co-precipitating titanium trichloride with a gold compound.

Although the gold ultrafine particle-immobilized oxide thus obtained has excellent properties as an oxidation catalyst, reduction catalyst, gas sensor, pigment, etc., the carbon monoxide oxidation catalytic activity is
C was also IOOX, but the hydrogen oxidation catalyst activity (temperature at which the conversion rate is 502) is an indicator of high dispersion of ultrafine gold particles.
The temperature was still high at 45-76°C.

[Means for Solving the Problems] As a result of further research to solve the above conventional problems, the present inventors found that, instead of using the coprecipitation method as described above, titanium oxide having specific properties prepared in advance was used. We have discovered a method to directly support gold in the form of ultrafine particles in a highly dispersed manner on ultrafine particles of hydrated titanium oxide or wash-coated ceramic bodies (beads, honeycombs, etc.) with these particles. Based on this, the present invention has been completed.

That is, the present invention uses titanium oxide and/or hydrated titanium oxide, which has an amorphous or anatase crystalline system and an average particle size of 500 or less, in the presence of a carboxylic acid or a salt thereof, and a gold compound. A method for producing ultrafine gold particles-immobilized titanium oxide, which comprises supporting a gold precipitate on titanium oxide and/or hydrated titanium oxide by adding it to a neutral aqueous solution, and then heating this support. It provides:

In the present invention, titanium oxide, Eiwa titanium oxide, or a mixture thereof is used as a carrier.

As the titanium oxide or hydrated titanium oxide, those whose crystal system is amorphous or anatase type are used. It is not preferable if other crystal systems are mixed, since the catalyst activity will be reduced.

Furthermore, as titanium oxide or Eiwa titanium oxide, those having an average particle diameter of 500 particles or less, preferably 50 to 400 particles are used. If the average particle diameter exceeds 500 particles, the specific surface area as a carrier becomes low, resulting in a decrease in catalytic activity, which is not preferable.

In the present invention, as the carrier, a ceramic body such as beads or honeycomb may be wash-coated with titanium oxide, Eiwa titanium oxide, or a mixture thereof as described above. When such a solid body is coated with ultrafine titanium oxide particles as a carrier, the exposed portion of the surface of the ultrafine titanium oxide particles increases, so it can be used efficiently as a catalyst for exhaust gas purification.

Further, as titanium oxide or Eiwa titanium oxide, the specific surface area is 50 m2/g or more, preferably 100 n'f/g.
The above are used. If the specific surface area is less than 50 m2/g, the number of sites capable of supporting gold in a highly dispersed manner decreases, resulting in a decrease in catalytic activity, which is not preferable.

Such ultrafine particulate titanium oxide or Eiwa titanium oxide can be obtained, for example, by the method described in JP-A-61-201604.

In the present invention, first, an aqueous solution in which a gold compound is dissolved is adjusted to pH 5 to 9, preferably 6 to 8, with stirring to prepare a neutral aqueous solution of a gold compound. As shown in FIG. 1, when the pH is within this range, the carbon monoxide oxidation catalytic activity and the hydrogen oxidation catalytic activity become high.

This is believed to be because gold particles precipitate in fine particles only within this pH range.

Specifically, the gold compound here includes, for example, chloroauric acid (I
IAuCln), sodium chloraurate (NaAuCl
4) Gold cyanide (^uCN), potassium gold cyanide (K
[Au(CN)zl), diethylamine trichloride auric acid ((
Examples include water-soluble gold salts such as Cdls) 2NIl・AUC1,].

Further, as the alkaline aqueous solution used for neutralizing the aqueous solution, an aqueous solution containing sodium carbonate, sodium hydroxide, potassium carbonate 9-ammonium, etc. can be used.

Furthermore, the gold compound aqueous solution has a concentration of the gold compound of I
The temperature of the gold compound aqueous solution is preferably 20 to 90''C.

Next, the titanium oxide and/or hydrated titanium oxide are added to the thus obtained neutral aqueous solution of the gold compound in the presence of a carboxylic acid or a salt thereof.

More specifically, the titanium oxide and/or metal are added to the neutral aqueous solution of the gold compound thus obtained. After or before adding Eiwa titanium oxide under stirring, carboxylic acid or its salt is added.

In this case, the pH immediately after addition is 5-i, preferably 6-8.
Adjust the type and amount of carboxylic acid or its salt so that When the pH is within this range, carbon monoxide oxidation catalytic activity and hydrogen oxidation catalytic activity become high. This is thought to be because gold particles precipitate as fine particles only within this pH range. The hydrogen ion of carboxylic acid p
Adjust H within this range.

Here, as the carboxylic acid or its salt, glycolic acid (HOOC-CH20H), oxalic acid (HOOC-CH20H),
COOH), lactic acid [C11,・CI1(Of{)・C
OOI{] , malonic acid (HOOC-CH'z・COO
}I), maleic acid {}i00c - CI=C}I
- COOI+), succinic acid (HOOC - CI
1■・CH2・+1,001+), malic acid [HOOC
- CI(OH)・CHz・COOI+), tartaric acid [HOOC − CI(011)・Coo}I],
Citric acid (HOOC・CJIZ・C(OH”)
OH)・Cl2COO and their potassium. Sodium, magnesium. Examples include salts of strontium, barium, manganese, cobalt, nickel, etc. The amount of carboxylic acid or its salt added may vary depending on the type of compound used, the addition method, etc., but usually it is sufficient to be at least 1 times the number of moles of gold to be supported, and it is difficult to dissociate. In the case of a compound, it can be added up to about 30 times the molar amount.

Furthermore, when using a carboxylate salt that is easily dissociated, for example, trisodium citrate, the pH of the aqueous solution should be kept within a range that does not change significantly due to the addition of Na'' ions.

In addition, when adding carboxylic acid or its salt after adding titanium oxide and/or hydrated titanium oxide to a neutral aqueous solution of a gold compound, add titanium oxide and/or hydrated titanium oxide to a neutral aqueous solution of a gold compound. The carboxylic acid or its salt is preferably added within about 1 hour, preferably within about 30 minutes.

The specific addition method and amount of the carboxylic acid or its salt may be determined by considering the pH of the aqueous solution, the dissociation equilibrium of the carboxylic acid or its salt, etc. is 0. OO01
It is preferable that the amount is in the range of mol/1 to 0.01 mol/l. Carboxylic acid ion amount is 0.01
mol/], the amount of carboxylic acid ions will be adsorbed almost entirely on the surface of titanium oxide and/or hydrated titanium oxide, and the adsorption of gold complex ions remaining in the liquid phase will be inhibited. In addition, since gold complex ions are reduced in the liquid phase and colloidal gold particles are removed, the amount of gold that can be effectively supported on titanium oxide and/or hydrated titanium oxide is reduced. arise. On the other hand, when the concentration of carboxylic acid ions is less than 0.0001 mol/1, the amount of carboxylic acid ions adsorbed to titanium oxide and/or hydrated titanium oxide is small, and the effect of preventing aggregation of gold hydroxide is insufficient. unable to perform.

As a carboxylic acid salt, for example, sodium citrate temporarily exceeds 0.01 mol/l, so it is preferable to add it gradually.

However, in the case of magnesium citrate, it is difficult to dissociate, so even if the entire amount is added at once, only a part of it will dissociate as citrate ions, making it extremely easy to handle. For example, at pH=9.6, the ratio of citrate ions to magnesium citrate is 1:17, and only 1/18 of the added magnesium citrate dissociates into citrate ions. When this citrate ion is adsorbed onto the precipitate and disappears from the liquid phase, dissociation occurs and citrate ion is replenished. In this way, considering the dissociation equilibrium and pH, the concentration of citrate ion is always 0.0001 mo.
It may be controlled to fall within the range of l/1 to 0.01 mol/l.

In the method of the present invention, after the above-described operation is completed, it is preferable to stir the obtained solution for about 30 minutes or more to ripen it. P
It is more preferable that the pH of the solution at the end of the heating is about 6 to 9.

In the present invention, the addition operation of the aqueous solution of the gold compound and the carboxylic acid or its salt is preferably carried out at a liquid temperature of about 20 to 90°C.

The amount of gold compound used is determined by the amount of ultrafine gold particles supported on titanium oxide and/or hydrated titanium oxide. The upper limit of supported fireflies depends on the type and shape of titanium oxide and/or hydrated titanium oxide used. Although it varies depending on the specific surface area etc., it is usually 0.5 to 0.5 atomic percent of gold in the total metal.
IO! (1 to 40% by weight).

In this way, a gold precipitate is supported on titanium oxide and/or hydrated titanium oxide.

Next, the gold compound obtained by the method described above! ? By heating the A-supported titanium oxide and/or hydrated titanium oxide after washing thoroughly with water, the raw gold hydroxide is decomposed into gold, and gold is deposited on the titanium oxide and/or hydrated titanium oxide. are uniformly precipitated as ultrafine particles and are strongly fixed. In addition, the heating temperature at this time is 100 to 800
The temperature is preferably about 'C, and the heating time may be about 1 to 24 hours.

In the ultrafine gold particle-immobilized titanium oxide and/or hydrated titanium oxide obtained by the method of the present invention as described above, the ultrafine gold particles have a small particle size and ? The diameter distribution becomes narrower,
Ultrafine gold particles are uniformly supported on titanium oxide and/or hydrated titanium oxide.

Figure 1 shows the effect on the oxidation catalytic activity of the obtained ultrafine gold particle-immobilized titanium oxide and/or hydrated titanium oxide with respect to the pH during ripening of an aqueous solution of a gold compound adjusted with a carboxylic acid or its salt. This is a graph showing the influence. In the figure, TI/2[H21 and TI/■[C01] on the vertical axis indicate the temperature at which the conversion rate of hydrogen or carbon monoxide is 50χ, respectively. In addition, in the pH range of 6 to 9 for T+zz [CO], the conversion rate is 100χ at O''C, indicating that the activity is extremely high.The hydrogen conversion temperature is also lowest in the pH range of 6 to 8, and in this range It can be seen that the activity is the highest.

Furthermore, FIG. 2 is a graph showing the relationship between the amount of magnesium citrate added and the catalyst activity. In the figure, p of the aqueous solution
When H is 8.5, the amount of magnesium citrate added is H
When the pH is 6 times or more the number of moles of AuCl4, the catalyst activity is saturated at a high level, and when the pH is 7 times or more, the catalytic activity is saturated at a high level.

From FIG. 2, it can be seen that when the amount of carboxylic acid or its salt added is about 5 times the mole number of gold to be supported,
It can be seen that the hydrogen oxidation catalyst activity remains constant at a high level.

Further, FIG. 3 is a graph showing the influence of the gold content in the carrier on the oxidation catalytic activity of ultrafine gold particle-immobilized titanium oxide and/or hydrated titanium oxide. The gold content in the carrier is 1 atm! If it is above, it can be seen that both the carbon monoxide oxidation catalytic activity and the hydrogen catalytic activity are saturated at a high level. In addition, in the figure, the number attached to the shoulder of the graph showing the catalytic activity of hydrogen (H2) shows the number of moles of magnesium citrate added to gold.

Titanium oxide and/or hydrated titanium oxide on which gold is supported in a highly dispersed manner obtained by the method of the present invention can be used in various applications such as low-temperature oxidation catalysts, low-temperature reduction catalysts, gas sensors, and pigments.

For example, the ultrafine gold particle-immobilized titanium oxide and/or
Alternatively, hydrated titanium oxide can generate hydrogen at a relatively low temperature of 300'C or less. Carbon monoxide, methanol. Since fuels such as propane can be burned in a wide range of concentrations, gold can be directly supported in the form of ultrafine particles in a highly dispersed manner, either in fine particle form, or directly onto ceramic bodies such as beads or honeycombs that have been wash-coated. It can be used as an oxidation catalyst for various catalytic combustion type heaters and kitchen heaters. It can also be used as an exhaust gas purification catalyst for oil stoves, oil fan heaters, gas fan heaters, and as air purification filters for air conditioners. In addition, it can be used as a catalyst for solvent oxidation treatment in the paint industry, etc., and as a catalyst for factory exhaust gas. When used as an oxidation catalyst here, gold is added at 0.5 to 1
Ultrafine gold particles immobilized titanium oxide containing about 0 atomic % and/
Or hydrated titanium oxide is preferred. Especially carbon monoxide
In the case of oxidation at a temperature of 200°C or lower, it is preferable to heat a precursor supporting gold hydroxide at a temperature of about 200 to 500°C.

Furthermore, the ultrafine gold particle-immobilized titanium oxide and/or Eiwa titanium oxide of the present invention is also useful as a catalyst for reducing nitrogen oxides such as No and Not with hydrogen, carbon monoxide, and the like.

Furthermore, the ultrafine gold particle-immobilized titanium oxide and/or
Alternatively, hydrated titanium oxide has extremely high oxidation catalytic activity even at relatively low temperatures around room temperature.
It can also be used as a sensor element for flammable gases such as carbon monoxide, methanol, and hydrocarbons. For use as a combustible gas sensor element, for example, a coiled platinum wire or the like can be coated with ultrafine gold particles immobilized titanium oxide and/or
Alternatively, it may be coated with a sintered body of hydrated titanium oxide, or a thick layer of ultrafine gold particle-immobilized titanium oxide and/or hydrated titanium oxide may be formed on the plate-shaped thermistor. When these sensor elements come into contact with air containing flammable gas, the flammable gas burns on the surface of the sensor element, generating combustion heat. Therefore, in a platinum wire coated with particulate matter, the temperature of the platinum wire increases and the electrical resistance increases, so that combustible gas can be detected.

Furthermore, when a thick film is formed on the thermistor, the temperature rise after combustion can be directly detected by the thermistor.

Further, the ultrafine gold particle-immobilized titanium oxide and/or hydrated titanium oxide of the present invention has a particle size of the ultrafine gold particles. Unique reddish-purple and bluish-purple colors depending on shape etc. Because it has a dark blue color, it is used in cosmetics,
paints. It can also be used as a pigment in glazes, etc.

〔Example〕

Next, the present invention will be explained in detail with reference to examples.

Production example (Production of ultrafine titanium oxide) Raw material titanium tetraisopropoxide (Ti (OicJt) 41
at 189 g/hr, nitrogen gas I. The raw material was introduced into a vaporizer heated to 130° C. with a flow rate of 0.5 Nm 2 /hr to completely vaporize the raw material.

On the other hand, 1200g/hr of water was mixed with nitrogen gas at 2.26Nrr.
r/hr and introduced into a vaporizer heated to 450°C to prepare heated steam. This heated steam was introduced into a reactor with an inner diameter of 30 mtn at the same time as the vaporized raw material, and a hydrolysis reaction was carried out at 260°C to obtain ultrafine titanium oxide particles. When the ultrafine particles were observed using an electron microscope, the primary particle diameter (average particle diameter) was 200.

Also, the X-ray diffraction pattern shows that these ultrafine particles are amorphous! It has been certified. Furthermore, when the specific surface area was examined by the BET method using nitrogen gas, it was found to be 130 bo/g.

Example 1 Chloroauric acid (HAuC1a-4HzO) 0.273g
(0.00066 mol) was dissolved in water at 120'C, an aqueous solution of sodium carbonate (Na2CO,,) was added dropwise to adjust the pH to 6.9. Subsequently, titanium oxide ultrafine particles 1, Og obtained by vacuum drying the ultrafine titanium oxide particles obtained in the above production example, were added, and after 5 minutes, a saturated aqueous solution of magnesium citrate (Mgz(CJsOt)z) (6.
0g/I! ．． ) to 100d (citrate ion 0.00
066 x 6 mol) was added and aged with continued stirring for 1 hour. The pH of the aqueous solution at the end of ripening was 7.8.
The resulting slurry was filtered, thoroughly washed with water, vacuum dried, and further calcined in air at 400°C for 5 hours to obtain Au-supported Tilt (atomic ratio: Au/Ti).
=1/19) A catalyst was obtained.

Using 0.20g of this catalyst sieved to 70-120 mesh, 1% by volume of carbon monoxide or hydrogen.
Flowing the air mixed gas containing air at a rate of 6 7 ml/min,
The oxidation catalytic activity towards carbon monoxide or hydrogen was investigated.

The result is calculated as the temperature at which the oxidation reaction rate becomes 502 (T+zz
[CO], T+/z[lhl] shown in Table 1.

Example 2 In Example 1, the same operation as in Example 1 was carried out, except that the ultrafine titanium oxide obtained in the production example was dried at 120°C for 1 hour as the ultrafine titanium oxide particles. I did it. The results are shown in Table 1.

Example 3 In Example 1, the same operation as in Example 1 was carried out, except that the ultrafine titanium oxide obtained in the production example was calcined at 550°C for 1 hour as the ultrafine titanium oxide particles. I did it. The crystal system of these ultrafine titanium oxide particles was anatase type. The results are shown in Table 1.

Comparative Example 1 The same procedure as in Example 1 was carried out, except that in Example 1, the ultrafine titanium oxide particles obtained in the Production Example were burned at 1200°C for 1 hour. I did this. The crystal system of the ultrafine titanium oxide particles was rutile type. The results are shown in Table 1.

Comparative Example 2 Example 1 was repeated except that ultrafine titanium oxide particles (P-25, thread monocrystalline system: anatase + rutile type) manufactured by West German Degussa were used as the ultrafine titanium oxide particles in Example 1.
The same operation was performed. The results are shown in Table 1.

Comparative Example 3 The same operation as in Example 1 was carried out, except that high-purity titanium oxide ultrafine particles (crystal system: anatase + rutile type) made by Daiku Trial were used as the titanium oxide ultrafine particles. The results are shown in Table 1.

Comparative Example 4 In Example 1, ultrafine titanium oxide particles obtained in the production example were heated to lO at 1200°C.
The same operation as in Example 1 was performed except that the time-calcined product was used. The crystal system of the titanium oxide ultrafine particles was rutile type, and as sintering progressed, the particle size became 800 particles. The results are shown in Table 1.

Table XI [Effects of the Invention] According to the production method of the present invention, ultrafine gold particles are supported on titanium oxide and/or hydrated titanium oxide in a very highly dispersed manner.

This ultrafine gold particle-immobilized titanium oxide and/or hydrated titanium oxide can burn fuels such as hydrogen, carbon monoxide, methanol, and propane in a wide range of concentrations at low temperatures.
It is useful as an oxidation catalyst for various catalytic combustion type heaters and kitchen heaters, and can also be used as a reduction catalyst in addition to being used in exhaust gas purification catalysts and gas sensor elements.

In particular, when immobilized titanium oxide and/or hydrated titanium oxide having a specific surface area of 50rd/g or more is used, the catalyst has excellent catalytic activity.

Furthermore, since the ultrafine gold particle-immobilized titanium oxide and/or hydrated titanium oxide have a unique color tone, they are also useful as pigments for cosmetics, paints, glazes, and the like.

[Brief explanation of drawings]

Figure 1 shows the effect on the oxidation catalytic activity of the obtained ultrafine gold particle-immobilized titanium oxide and/or hydrated titanium oxide with respect to the pH of an aqueous solution of a gold compound adjusted with a carboxylic acid or its salt. This is a graph showing the influence. Furthermore, FIG. 2 is a graph showing the relationship between the amount of magnesium citrate added and the catalyst activity. Further, FIG. 3 is a graph showing the influence of the gold content in the carrier on the oxidation catalytic activity of ultrafine gold particle-immobilized titanium oxide and/or hydrated titanium oxide.

Claims (2)

[Claims] (1) Titanium oxide and/or hydrated titanium oxide with an amorphous or anatase crystal system and an average particle size of 500 Å or less are added to a neutral aqueous solution of a gold compound in the presence of a carboxylic acid or a salt thereof. 1. A method for producing ultrafine gold particles-immobilized titanium oxide, which comprises supporting a gold precipitate on titanium oxide and/or hydrated titanium oxide by adding hydrated titanium oxide to titanium oxide, and then heating the supported material. (2) Titanium oxide and/or hydrated titanium oxide is 5
The method for producing ultrafine gold particle-immobilized titanium oxide according to claim 1, wherein the titanium oxide has a specific surface area of 0 m^2/g or more.