JPH0738945B2 - Gold-oxide composite, flammable gas oxidation catalyst, flammable gas sensor and pigment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gold-oxide composite, a combustible gas oxidation catalyst, a combustible gas sensor and a pigment using the gold-oxide composite.

[0002]

2. Description of the Related Art Conventionally, catalysts having a structure in which a noble metal such as platinum or palladium is dispersed and carried on the surface of an oxide carrier are known. Such a catalyst utilizes the principle that highly reactive noble metal is highly dispersed to increase the efficiency of the reaction, and that the active site on the oxide and the active site of the metal cooperate to make the catalyst highly active. Is. However, in a catalyst having gold as an active species, it has been difficult to make gold highly dispersed by an ordinary preparation method, and gold has been considered to be a metal having poor catalytic activity.

On the other hand, the present inventors have found that gold has a grain size of 1
We have developed a method of supporting ultrafine particles of 0 nm or less on oxides of iron, cobalt, nickel, etc., and reported that such a supported gold catalyst can be an extremely highly active oxidation catalyst (J. Catalysis, 115, 301-3
09 (1989)). As a method for preparing such a gold catalyst, a coprecipitation method (Japanese Patent Publication No. 3-12934), a uniform precipitation method (Japanese Unexamined Patent Publication No. 62-155937), a drop neutralization precipitation method (Japanese Unexamined Patent Publication No. 63-252908). , Reducing agent addition method
3-252908), pH-controlled neutralization precipitation method (Japanese Patent Laid-Open No. Sho 6-62).
3-252908), carboxylic acid metal salt addition method (JP-A-2-252610), and precipitation method (JP-A-3-97).
No. 623) and the like. However, it is necessary to properly use these preparation methods depending on the type of carrier oxide, and it is necessary to strictly control the preparation conditions in order to obtain a high degree of dispersion. In addition, no matter which preparation method is used, it is impossible to obtain a highly active catalyst unless gold is supported in an ultrafine particle state of 10 nm or less.

[0004]

In view of the above-mentioned prior art, the present inventor obtains a highly active catalyst without requiring a complicated operation of forming ultrafine particles even when gold is used as an active species. I have been diligently conducting research. as a result,
When a conventional catalyst supporting structure is reversed to form a gold-oxide composite having a structure in which a metal oxide is dispersed and supported on the surface of gold, the gold and the metal are not converted into ultrafine particles. It has been found that the interface portion with the oxide can be made very large, resulting in a catalyst with high activity due to the metal-oxide interaction. Further, since this gold-oxide complex exhibits excellent activity in oxidation reaction, it can be used as a sensor element for combustible gas, and further, it is highly useful as a pigment by utilizing a unique color tone. Found.

That is, the present invention uses a support or gold fine particles coated with gold as a carrier, and has a structure in which a transition metal oxide is dispersed and carried on the surface, and a gold-oxide composite. The present invention relates to a flammable gas oxidation catalyst, a flammable gas sensor, and a pigment, which are composed of such a gold-oxide complex.

In the gold-oxide composite of the present invention, a support coated with fine gold particles or gold is used as a carrier for supporting a metal oxide.

The size of the fine gold particles, which is the carrier of the gold-oxide composite of the present invention, is not particularly limited and a wide range of particle diameters of about 5 nm to 50 μm can be obtained depending on the production conditions. It may be appropriately selected depending on the application.

When a support coated with gold is used as a carrier, the type of support is not particularly limited,
A support of any material, shape and size can be used, and a support coated with gold by a method such as electroless plating or vacuum deposition may be used. In particular, for the purpose of obtaining a highly active catalyst, it is preferable to use a porous support in order to increase the surface area of gold. Examples of such a porous support include ceramic molded bodies such as beads and honeycombs.

In the gold-oxide composite of the present invention, a transition metal oxide is used as the metal oxide dispersed and carried on the surface of gold. As such a transition metal oxide, preferably, iron oxide, cobalt oxide, nickel oxide, vanadium oxide, chromium oxide, manganese oxide, copper oxide, titanium oxide, zinc oxide, tin oxide and the like can be exemplified. Alternatively, two or more kinds may be used. The particle size of these metal oxides is not particularly limited, can be adjusted in a wide range according to the production conditions, and can be usually a particle size of about 1 nm to 5 μm, and can be appropriately selected according to the purpose. Good.

The ratio of gold to the transition metal oxide is not particularly limited, and can be adjusted by the raw material ratio at the time of production, and the transition metal / gold atomic ratio is in the range of about 1/2 to 1/1000. A gold-oxide composite in which a metal oxide is uniformly dispersed can be obtained.

The gold-oxide composite of the present invention can be obtained, for example, by the following method.

First, as a gold precursor, a soluble or insoluble compound of gold is dissolved or dispersed in water, and a soluble salt of a transition metal component supported in this aqueous solution or aqueous dispersion is added. Examples of soluble compounds of gold include chloroauric acid (HAuCl ₄ ), sodium chloroaurate (NaAuCl ₄ ).
₄ ), gold cyanide (AuCN), potassium gold cyanide (K [Au (CN) ₂ ]), diethylamine trichloroaurate ((C ₂ H ₅ ) ₂ NH.AuCl ₃ ) and the like.
Examples of the insoluble gold compound include gold hydroxide and carbonate. Examples of the supported soluble salt of the transition metal component include nitrates and acetates of transition metals such as iron, cobalt, nickel, vanadium, chromium, manganese, copper, titanium, zinc and tin. 1 x 10 soluble gold salt
It may be added at a concentration of about ⁻⁵ to 1 × 10 ⁻² mol / l. The gold insoluble salt may be dispersed in water at a concentration of about 0.001 to 10% by weight.

The soluble salt of the transition metal component may be added in such an amount that the atomic ratio of gold to the transition metal component becomes a predetermined value of the desired gold-oxide composite. In order to obtain a gold-oxide composite in which a transition metal oxide is uniformly dispersed and supported,
The transition metal / gold atomic ratio is preferably about 1/2 to 1/1000, and more preferably about 1/5 to 1/100.

Next, after evaporating the water content from the aqueous solution or the aqueous dispersion containing the soluble compound or insoluble compound of gold and the soluble salt of the transition metal component, it is fired in the air. By this operation, the soluble compound or insoluble compound of gold changes to a more stable metal state, and the hydroxide or water-soluble salt of the transition metal component dispersed and supported on this surface changes to the oxide form. . The method for evaporating the water content from the aqueous solution or the aqueous dispersion may be any method, but it is usually preferable to heat to about 40 to 90 ° C. The firing temperature is 200 to 500 ° C
The degree is appropriate.

After preparing an aqueous solution or dispersion containing a soluble compound or insoluble compound of gold and a soluble salt of a transition metal component in the same manner as described above, an equimolar amount to 100 of the transition metal component is prepared. The transition metal component is precipitated in the form of a hydroxide on the precursor of the gold carrier by adding a basic substance in an amount about twice the molar amount, and the precipitate is also calcined. You can get the body. As the basic substance, for example, sodium carbonate, sodium hydroxide, potassium carbonate, ammonia or the like can be used. The temperature of the aqueous solution or the aqueous dispersion when adding the basic substance is preferably about 20 to 90 ° C. Further, instead of directly adding the basic substance, after adding urea, the solution is heated to about 70 to 100 ° C., preferably about 90 to 100 ° C., and ammonia generated by decomposition of urea can be used as a base. . The amount of urea used may be about equimolar to 100 times the molar amount of the transition metal component.

After the precipitation is generated, it is filtered by a method such as
The gold-oxide composite of the present invention can be obtained by separating the precipitate, drying the precipitate, and calcining the precipitate. The firing temperature is
As in the above method, about 200 to 500 ° C is suitable.

According to the above-described method of drying and removing water from an aqueous solution or dispersion containing a soluble compound or insoluble compound of gold and a soluble salt of a transition metal component, or a method of forming a precipitate by adding a basic substance. , Particle size 50 nm to 5
It is possible to obtain a gold-oxide composite in which a transition metal oxide having a particle diameter of about 1 nm to 50 nm is supported on the surface of gold fine particles of about μm. These particle diameters differ depending on the production conditions such as the amount of oxide with respect to gold and the firing temperature.

The gold-oxide composite of the present invention can be obtained by using gold in a metallic state instead of the soluble compound or the insoluble compound of gold. In this method, a gold colloidal solution (diameter 5
nm-500 nm gold fine spherical particles are dispersed in water) or gold fine powder is dispersed in water, and other methods are the method of drying and removing water described above, or addition of a basic substance to form a precipitate. The gold-oxide composite of the present invention can be obtained by performing the operation under the same conditions as in the above method. The amount of gold dispersed in the gold dispersion is 0.001 to 1
It may be about 0% by weight. In the case of using gold in the metallic state, a carrier in which the particle size of the gold that is usually used is almost maintained is obtained, so the gold fine powder or gold colloid solution used as a raw material should have the required carrier particle size. It may be selected and used as appropriate. Fine gold powder has a particle size of 100n
It is suitable to use the one having a thickness of about m to 50 μm. By this method, a gold-oxide composite in which a transition metal oxide having a particle diameter of about 1 nm to 50 nm is supported on gold fine particles can be obtained.

In the above various manufacturing methods,
Gold may agglomerate during firing, so in order to prevent this, the mixture before firing should have an equivalent weight to 100 to gold.
It is preferable to calcine after adding and mixing about twice the weight of quartz powder. Quartz powder has a particle size of 20 μm to 5 μm.
It is preferable to use one having a diameter of about 00 μm. When a gold colloid solution is used, the gold colloid is likely to agglomerate when removing water, but quartz powder is added to the liquid before water removal and mixed, and then water is removed. It is possible to prevent the aggregation of gold.

When a support whose surface is coated with gold is used as a carrier, the transition metal component is about 1/2 to 1/100 times the molar number of the gold atoms exposed on the surface of the carrier. Method of immersing the carrier in an aqueous solution containing a soluble salt of, and then evaporating the water under the same conditions as those described above and then calcining, or adding a basic substance to obtain a precipitate and then calcining According to the method described above, a gold-oxide composite in which oxide fine particles of about 1 nm to 5 μm are dispersed and carried on the gold surface of the support can be obtained. The number of gold atoms exposed on the surface of the support whose surface is coated with gold is
It can be estimated from the weight of gold used for coating and the coating thickness.

The gold-oxide composite of the present invention has the ability to oxidize carbon monoxide, hydrogen, hydrocarbons, etc. at low temperatures, and has the unique catalytic property of further promoting the reaction in the presence of moisture. They are extremely useful as catalysts for oxidation reactions.

Further, since the gold-oxide composite of the present invention exhibits an excellent activity for the oxidation reaction of carbon monoxide, hydrogen, hydrocarbons and the like existing in the air, it is a sensor element for these flammable gases. It also functions as a gas sensor by electrically detecting the temperature rise of the element due to the combustion heat generated when combustible gas burns on the element surface.

Further, when the particle size of gold as a carrier in the obtained gold-oxide composite is about 5 nm to 500 nm, for example, when gold colloid is used as a carrier raw material, the particle size of the gold causes a peculiarity. It is also used as a pigment for cosmetics, paints, glazes, etc., because it shows color development such as red, magenta, blue violet, and changes in color tone such as becoming closer to gray as the amount of oxide carried increases. be able to.

[0024]

The gold-oxide composite of the present invention has a structure in which a transition metal oxide is supported on the surface of gold as a carrier with good dispersibility. The gold-oxide composite is obtained without the complicated operation of forming gold into ultrafine particles, has a high catalytic activity, and has a carbon monoxide content.
It is extremely useful as a catalyst for the oxidation reaction of hydrogen, hydrocarbons and the like. Further, since the gold-oxide complex exhibits excellent activity for oxidation reaction, it can be used as a sensor element for combustible gas, and is also useful as a pigment by utilizing a unique color tone. .

[0025]

The present invention will be described in more detail below with reference to examples.

[0026]

Example 1 0.2 g of gold hydroxide powder (obtained by neutralizing an aqueous solution of chloroauric acid with sodium carbonate) was dispersed in 20 ml of an aqueous solution in which 0.042 mmol of cobalt nitrate was dissolved (atom). Ratio Co / Au = 1/1
9). This dispersion was heated to 70 ° C. to evaporate excess water to remove it, and thereby to be dried to obtain a powder. 2g of quartz powder, which is sieved to 120-250 mesh
, And after mixing well, 40 more in air
It was calcined at 0 ° C. for 4 hours. After firing, with distilled water, then washed repeatedly and dried to gold cobalt oxide supported on the powder metal carrier - to obtain an oxide complex _{(Co 3 O 4 / Au)} .

When the gold-oxide composite was observed with an electron microscope, it was found that the structure was such that oxides of about 10 nm size were dispersed and carried on the surface of gold fine particles of about 100 to 500 nm.

Using 0.2 g of this gold-oxide composite, an air mixed gas containing 1% by volume of carbon monoxide (dry CO gas) or air containing 1% by volume of carbon monoxide was bubbled into water at 0 ° C. The moist CO gas thus produced was circulated at 67 ml / min to examine the oxidation catalytic activity for carbon monoxide or hydrogen.

[0029]

Comparative Example 1 Cobalt nitrate 0.042 in the same amount as in Example 1
120-250 in 20 ml of an aqueous solution in which mmol is dissolved.
2 g of sieved quartz powder was added to the mesh. This was heated to 70 ° C. to evaporate and remove excess water to dry it to a powder state. Furthermore, by baking in air at 400 ° C. for 4 hours, a cobalt oxide catalyst (Co ₃ O ₄ ) was obtained. Using this catalyst, the oxidation catalytic activity was examined in the same manner as in Example 1.

[0030]

Comparative Example 2 To 0.2 g of gold hydroxide was added 2 g of quartz powder which had been sieved to 120-250 mesh, and they were mixed well and then calcined in air at 400 ° C. for 4 hours. After firing, the gold catalyst was obtained by repeatedly washing with distilled water and then drying. Using this catalyst, the oxidation catalytic activity was examined in the same manner as in Example 1.

The results of Example 1, Comparative Example 1 and Comparative Example 2 are shown in FIG. 1 as a graph of the relationship between the oxidation temperature and the oxidation reaction rate. Table 1 shows the temperature (T1 / 2) at which the oxidation reaction rate becomes 50%.

Table 1Catalyst composition Oxidation catalytic activity (℃) T1 / 2  Dry CO gas Wet CO gas  Example 1 Co₃O_Four/ Au 80 43 Comparative Example 1 Co₃O_Four151 237 Comparative Example 2 Au 450 or more 450 or more From FIG. 1, the gold-oxide composite of the present invention is cobalt oxide.
The reaction proceeds at a lower temperature than that of the pure catalyst, resulting in higher catalytic activity.
It turns out that it has sex. Also, with gold-only catalysts, 45
The reaction hardly proceeded even at a high temperature of 0 ° C. Also, monoacid
Cobalt oxide only when carbon dioxide reaction gas contains moisture
With the catalyst, the reaction is hotter than with dry gas.
In contrast to the suppression effect of being required, the present invention
In the case of gold-oxide complex, the reaction is accelerated by moisture.
It can be seen that the catalytic action also changed qualitatively.

[0033]

[Example 2] 300 m of gold colloid solution containing 25 mg of gold
Iron chloride aqueous solution was added to 1 (atomic ratio Fe / Au = 1/1
9), and 30 times more urea was added to iron. At this point, the solution retains the gold colloidal red color and pH
Was 3.7. When this solution was continuously boiled at 100 ° C. for 2 hours, a black fine precipitate was generated and the pH was increased to 7.9. After washing this precipitate with water, 2 g of sieving quartz powder was added to a 120-250 mesh, and by heating, the excess water was evaporated and removed to dryness to obtain a powder. Further, by firing in air at 400 ° C. for 4 hours, a gold-oxide composite (Fe ₂ O ₃ / Au) having iron oxide supported on a gold colloid carrier was obtained.

When the gold-oxide composite was observed with an electron microscope, iron oxide was carried only on the surface of the gold colloid particles having a diameter of about 40 nm, and oxides released from the gold colloid particles were hardly observed. It was

Using 0.2 g of this composite, an air mixed gas containing 1% by volume of carbon monoxide (dry CO gas) or air containing 1% by volume of carbon monoxide was bubbled through water at 0 ° C. to obtain wet CO. The gas was passed at 67 ml / min to examine the oxidation catalytic activity for carbon monoxide. The result is 350 ℃
Table 2 shows the reaction rate in.

[0036]

Comparative Example 3 In Example 2, the colloidal gold was not included,
An iron oxide catalyst was obtained in the same manner as in Example 2, except that an aqueous solution containing the same amount of iron chloride was used. Table 2 shows the results of examining the oxidation catalytic activity of this catalyst for carbon monoxide in the same manner as in Example 2.

Table 2Catalyst composition Oxidation catalytic activity (%)  Dry CO gas Wet CO gas  Example 2 Fe₂O₃/ Au 18.5 78.8 Comparative Example 3 Fe₂O₃2.5 From the results above 2.5, the gold-oxide composite of the present invention shows that iron oxide
It can be seen that it has a higher catalytic activity than the pure catalyst.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between an oxidation temperature and an oxidation reaction rate when various catalysts are used.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location G01N 25/22 6928-2J 27/16 B 9115-2J

Claims (4)

[Claims] 1. A gold-oxide composite having a structure in which a support or gold fine particles coated with gold is used as a carrier, and a transition metal oxide is dispersed and carried on the surface thereof. 2. A flammable gas oxidation catalyst comprising a gold-oxide composite having a structure in which a support or gold fine particles coated with gold is used as a carrier, and a transition metal oxide is dispersed and carried on the surface thereof. 3. A flammable gas sensor comprising a gold-oxide composite having a structure in which a support or gold fine particles coated with gold is used as a carrier, and a transition metal oxide is dispersed and carried on the surface thereof. 4. A pigment comprising a gold-oxide complex having a structure in which a support or gold fine particles coated with gold is used as a carrier, and a transition metal oxide is dispersed and carried on the surface thereof.