JP2003320250A - Catalyst and production of the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst having an excellent catalyst activity by depositing a noble metal such as palladium, platinum, or the like on a photocatalyst particle of titanium oxide or the surface of a substrate of a ceramic carrier in a highly dispersed state. <P>SOLUTION: A noble metal is deposited on the substrate surface by reducing a noble metal compounds to the noble metal at a relatively low temperature using at least one compound selected from hypophosphorous acid, phosphorous acid and their salts as a reducing agent in a solvent containing a photocatalyst particle, the substrate such as of a ceramic carrier. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a catalyst having a precious metal supported on its surface and a method for producing the same.

[0002]

2. Description of the Related Art In the field of catalysts, a catalyst in which a noble metal is supported on the surface of a substrate is used for various reactions. For example, when a noble metal is supported on the surface of the photocatalyst particles, the photocatalytic activity is further increased, and thus a composite photocatalyst in which palladium or the like is supported on photocatalyst particles such as titanium oxide is known (for example, see Patent Document 1). . The photocatalyst has a different activity expression mechanism from that of a normal thermocatalyst, and is excited by irradiation with light having a wavelength having an energy equal to or more than the band gap peculiar to the photocatalyst, and exhibits strong catalytic activity. Utilizing its photocatalytic activity, it is possible to oxidize and decompose chemical substances, especially organic substances, and to oxidize and remove some inorganic substances such as nitrogen oxides and carbon monoxide, and at a low cost as an energy source. Since it is possible to use light having a very low environmental load, application to environmental purification, deodorization, antifouling, sterilization, etc. has been promoted in recent years. As the photocatalyst, metal compounds such as oxides and sulfides, particularly titanium oxide and zinc oxide having high photocatalytic activity are generally used. Further, a so-called CO shift reaction in which carbon monoxide is reacted with water vapor to generate hydrogen and carbon dioxide is applied to removal of carbon monoxide, production of hydrogen, reforming reaction of a fuel cell, and the like.
As a catalyst used for the O shift reaction, there is known a catalyst carrier made of titanium oxide, zirconium oxide, cerium oxide or the like, on which a noble metal such as platinum or palladium is carried (see, for example, Patent Document 2).

[0003]

[Patent Document 1] Japanese Unexamined Patent Publication No. 10-296082

[Patent Document 2] Japanese Patent Laid-Open No. 2001-347166

[0004]

Such a noble metal-supported catalyst is obtained by irradiating a noble metal compound such as chloride with ultraviolet light in a medium liquid in which a substrate such as photocatalyst particles or a ceramic carrier is dispersed to irradiate the surface of the substrate. A so-called photodeposition method for depositing a noble metal is known. However, this method is not industrially applicable because the reaction requires a long time and the amount that can be treated at one time is limited. Also known is a method of reacting a noble metal compound with a reducing agent such as formic acid, hydrazine, sodium borohydride, etc. However, this method cannot obtain a sufficient effect as compared with the amount of the noble metal supported. Also,
There is also known a method of impregnating a substrate with a solution of a noble metal salt, followed by heating and reducing with a reducing gas, but similarly, the obtained effect was insufficient as compared with the amount of the noble metal supported.

Therefore, the present invention overcomes the above-mentioned problems of the prior art, and a noble metal-supported catalyst having a high catalytic activity, particularly a photocatalyst having a high catalytic activity, a catalyst for a CO shift reaction, and an industrial use thereof. A method of manufacturing is provided.

[0006]

As a result of intensive studies to solve these problems, the present inventor has found that at least one selected from hypophosphorous acid, phosphorous acid and salts thereof as a reducing agent. The present invention has been completed by finding that it can be used and reacted with a noble metal compound.

That is, the present invention is characterized in that a noble metal produced by reducing a noble metal compound with at least one selected from hypophosphorous acid, phosphorous acid and salts thereof is carried on the surface of a substrate. A catalyst, a photocatalyst in which the substrate is photocatalyst particles, or a CO shift reaction catalyst in which the substrate is a ceramic carrier. Further, the present invention is characterized in that, in a liquid medium containing a substrate, a noble metal compound is reduced with at least one selected from hypophosphorous acid, phosphorous acid and salts thereof to produce a noble metal surface. And a photocatalyst using photocatalyst particles as the substrate, and a CO shift reaction catalyst using a ceramic carrier as the substrate.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a noble metal-supported catalyst, in which a noble metal compound is reduced with at least one selected from hypophosphorous acid, phosphorous acid and salts thereof, and a noble metal produced is supported on the surface of a substrate. It was made. In the present invention, hypophosphite (phosphinic acid), hypophosphite such as sodium salt, potassium salt, ammonium salt, phosphorous acid (phosphonic acid), diphosphite (diphosphonic acid) is used as a reducing agent for a noble metal compound. It is important to use at least one of phosphorous acid such as acid) and its phosphite such as sodium salt, potassium salt and ammonium salt, and among these reducing agents, those capable of reducing the compound of the precious metal to be carried. May be selected appropriately. In particular, hypophosphorous acid is preferable because it has a relatively strong reducing power and can reduce all noble metal compounds. The catalyst of the present invention is superior in catalytic activity to a catalyst in which a noble metal is supported by a conventional reduction reaction using formic acid, hydrazine, sodium borohydride or the like, or a catalyst which is heated and reduced with a reducing gas. Although the reason for this is not well understood, it is likely that the reduction reaction using at least one selected from hypophosphorous acid, phosphorous acid, and salts thereof proceeds even at a relatively low temperature, so that finer precious metals are It is presumed that the noble metal is likely to exhibit the effect of the noble metal because it is easily generated and is supported on the surface of the substrate in a highly dispersed state. Further, unlike the plating method, there is no need for a treatment step with an activator such as palladium or tin, which is industrially advantageous.

The noble metal referred to in the present invention means platinum group such as platinum, palladium, rhodium and ruthenium, and gold and silver, and these may be used alone or in combination of two or more. Palladium is preferable because it is relatively inexpensive and highly effective. The amount of the noble metal supported can be appropriately adjusted depending on the use of the catalyst such as the photocatalyst and the catalyst for the CO shift reaction, and is preferably in the range of 0.01 to 5% by weight, and 0.1 to 0. More preferably, it is in the range of 5% by weight. If the supported amount of the noble metal is less than 0.01% by weight, it is difficult to obtain the desired catalytic activity, and even if it exceeds 5% by weight, it is difficult to obtain a further effect, which is not economical.

The substrate supporting the noble metal may be of any type, for example, spherical or needle-shaped, rod-shaped or plate-shaped particles or fine particles, or a honeycomb-shaped, sheet-shaped, corrugated or spherical-shaped substrate. Various shapes and sizes can be used as the substrate. The material of the substrate may be one normally used in the field of catalysts, such as titanium oxide,
Inorganic compounds such as aluminum oxide, silicon oxide, zirconium oxide and the like, a mixture thereof, a ceramic carrier made of a composite oxide thereof such as zeolite, or an organic carrier such as activated carbon or a porous polymer, of a known material Any thing can be used. Among the carriers, titanium oxide, particularly rutile titanium oxide, is preferable because it has excellent thermal stability, and the average primary particle size is 0.005 to 0.1 μm.
Fine particles in the range of m are more preferable because they have a large specific surface area and excellent catalyst performance.

One of the preferred embodiments of the present invention is a photocatalyst using photocatalyst particles as a substrate in the above catalyst. The photocatalyst particles used in the present invention are not particularly limited as long as they exhibit catalytic activity by irradiation with light having a wavelength having an energy of a band gap or more, and examples thereof include titanium oxide, zinc oxide, tungsten oxide, and iron oxide. Alternatively, known compounds such as a composite of two or more of them can be used. The photocatalyst particles are vanadium,
One or more elements such as iron, cobalt, nickel, copper, and zinc may be contained. Among the photocatalyst particles, titanium oxide, particularly, the average primary particle size is 0.005 to 0.
Fine particles having a size in the range of 1 μm are preferable because of high photocatalytic activity. The type of titanium oxide that can be used is not particularly limited, and any of anhydrous titanium oxide, hydrous titanium oxide, titanium hydroxide, titanic acid, etc. may be used, and crystalline ones such as rutile type and anatase type and amorphous ones may be used. You can have
A mixture of these may be used.

In the photocatalyst of the present invention, since the noble metal is supported on the surface of the photocatalyst particles in a highly dispersed state, the effect of the noble metal is easily exhibited, and it is suitable for various uses such as environmental purification, deodorization, antifouling and sterilization. It is useful. This photocatalyst can be fixed to the surface of a base material such as metal, tile, enamel, cement, concrete, glass, fiber, wood, paper or plastic, and used for the photocatalytic reaction. As a fixing means, a conventional method such as a method of sintering a photocatalyst or a method of using a binder can be used. If necessary, a binder may be mixed with the photocatalyst, and the mixture may be molded into a flat plate shape, a corrugated plate shape, a honeycomb shape, a spherical shape, a curved surface shape or the like, and used for the photocatalytic reaction.

Another preferred embodiment of the present invention is a CO shift reaction catalyst in which a ceramic carrier is used as a substrate in the above catalyst. The ceramic support used in the present invention, titanium oxide, aluminum oxide, silicon oxide, inorganic compounds such as zirconium oxide,
Known materials such as a mixture thereof or a complex oxide can be used. Among the ceramic carriers, titanium oxide is preferable, and rutile type titanium oxide is more preferable because it has excellent thermal stability, and the average primary particle size is 0.005 to 0.005.
Fine particles in the range of 0.1 μm are more preferable because they have a large specific surface area and excellent catalyst performance.

Since the precious metal is supported on the surface of the catalyst for CO shift reaction in a highly dispersed state in the catalyst of the present invention, its catalytic effect is easily exhibited, and carbon monoxide is removed, hydrogen is produced, and fuel cells are reformed. It is useful for reactions. This noble metal-supported CO shift reaction catalyst can be used, for example, by further supporting it on a porous material such as zeolite or a honeycomb plate.

Further, the present invention is a catalyst used for removing carbon monoxide. In the above catalyst, when platinum group is supported as a noble metal, preferably palladium is carried, the removal capacity of carbon monoxide becomes high. Therefore, a carbon monoxide remover for indoor use, carbon monoxide contained in exhaust gas of a factory, etc. It is useful as a scavenger. It is known that a platinum group metal, particularly palladium, strongly adsorbs carbon monoxide, and a catalyst supporting a platinum group metal is adsorbed with, for example, the photocatalytic action of the photocatalyst or the catalytic action of the CO shift reaction catalyst. It is considered that the carbon monoxide removing ability is excellent due to the synergistic effect with the action.

Next, the present invention is a method for producing a noble metal-supported catalyst, wherein the noble metal compound is directly reduced with at least one selected from hypophosphorous acid, phosphorous acid and salts thereof in a medium containing a substrate. Then, it is a method for producing a catalyst in which a precious metal is supported on the surface of a substrate. The noble metal produced by the reduction can be deposited on the surface of the substrate, or the noble metal compound adsorbed on the substrate can be reduced on the surface to support the noble metal on the surface of the substrate. In the present invention, hypophosphite (phosphinic acid), hypophosphite such as sodium salt, potassium salt, ammonium salt, phosphorous acid (phosphonic acid), diphosphite (diphosphonic acid) is used as a reducing agent for a noble metal compound. Acid) and at least one kind of phosphite such as sodium salt, potassium salt and ammonium salt thereof, and hypophosphorous acid is particularly preferable. As a specific method, for example, a solution of a noble metal compound such as water and the above-mentioned reducing agent may be added to a suspension prepared by dispersing a substrate in a medium such as water. After the substrate is dispersed in the above solution, the reducing agent may be added. In the present invention, a method of adding a noble metal compound to a medium containing a substrate and then adding the reducing agent to reduce the noble metal compound is preferable because finer noble metals are highly dispersed and easily supported. . The reducing agent may be added in an amount necessary for reducing the noble metal compound, and is preferably 0.5 to 5.0 times the amount of the noble metal compound. The slurry temperature during the reduction reaction can be appropriately set, but in order to facilitate the reaction, a range of about 0 to 100 ° C. is preferable,
The range of 0 to 50 ° C is more preferable, and the range of 5 to 40 ° C is further preferable. In the liquid medium containing the substrate, the noble metal compound is easily adsorbed on the surface of the substrate, or the reduction reaction is prevented from abruptly occurring, or the generated noble metal is easily deposited on the surface. In addition, the pH of the liquid medium may be adjusted by optionally adding an acid or an alkali. After supporting the noble metal, operations such as pH adjustment, filtration / washing, drying, and pulverization are appropriately performed as necessary.

The noble metal compound used in the present invention is not particularly limited, such as a noble metal chloride, nitrate, sulfate or complex compound, but it is preferable to use a chloride which is easily reduced. The noble metal referred to in the present invention means platinum group such as platinum, palladium, rhodium, ruthenium, and gold and silver, and these may be used alone or in combination of two or more, but palladium is particularly preferable. It is inexpensive and highly effective, which is preferable.
The amount of the noble metal supported can be appropriately adjusted by adjusting the amount of the noble metal compound added, and the amount is 0.01 to
The range of 5% by weight is preferable, and the range of 0.1 to 0.5% by weight is more preferable.

As the substrate used in the present invention, the above-mentioned ones can be used. In particular, a photocatalyst can be produced by using photocatalyst particles such as titanium oxide, zinc oxide, tungsten oxide, iron oxide, or a composite of two or more kinds thereof as a substrate, and titanium oxide, aluminum oxide, silicon oxide, oxide The use of an inorganic compound such as zirconium, a mixture thereof, or a ceramic support such as a complex oxide as a substrate is a preferred embodiment because a CO shift reaction catalyst can be produced.

As described above, after reducing the noble metal compound, in the present invention, if the substrate used is fine particles, filtration and washing may be difficult or it may take time. In such a case, when activated carbon is added to the liquid medium after the reduction reaction as a filter aid, and filtration and washing are carried out, the filtration rate and the washing rate are increased, and the noble metal-supported catalyst, particularly the noble metal-supported photocatalyst and CO shift reaction A catalyst and the like can be obtained relatively easily, which is preferable. The amount of activated carbon added is preferably in the range of 0.5 to 10% by weight with respect to the substrate,
The range of 5 to 5% by weight is more preferable.

[0020]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited thereto.

Example 1 Photocatalytic titanium oxide (ST-01: manufactured by Ishihara Sangyo Co., Ltd., average particle size 0.01 μm) was dispersed in pure water, and 750 liters of a slurry having a concentration of 200 g / liter was placed in a reaction vessel. , Bubbling nitrogen gas. Nitrogen gas was continuously supplied until it was filtered and washed as described below. While stirring this slurry, at room temperature, 15 liters of a 50 g / liter aqueous solution of palladium chloride in hydrochloric acid was added, and further, 15 liters of a 50% aqueous solution of hypophosphorous acid were added to react palladium chloride with hypophosphorous acid. Let After the reaction, 4.5 liters of 17% sodium hydroxide aqueous solution was added, and the slurry p
H was adjusted to 5. Next, 1500 g of activated carbon (WHC2C: manufactured by Takeda Pharmaceutical Co., Ltd.) was put into the slurry, and after mixing, the specific resistance of the filtrate was 100 using a filter press.
Filtration and washing were performed until it became 00 Ω · cm or more. The time required for filtration and washing was about 16 hours. After filtration and washing, it was dried at 110 ° C. overnight and pulverized with a pin mill to obtain a palladium-supported photocatalyst (Sample A). When this sample A was observed with an electron microscope, it was confirmed that palladium was supported on the surface of the photocatalytic titanium oxide particles.

Comparative Example 1 A photocatalytic titanium oxide (ST-01: manufactured by Ishihara Sangyo Co., Ltd., average particle size 0.01 μm) was dispersed in pure water. The pH of the slurry was adjusted to 10 by adding 10 liters of the aqueous sodium carbonate solution. While stirring the slurry, 30 liters of an aqueous hydrochloric acid solution of 50 g / liter of palladium chloride was added while maintaining the pH at 10.
Add over time and stir for an additional 15 minutes. Then 1
After 83.5 kg of 7% aqueous sodium hydroxide solution was added to adjust the pH of the slurry to 13.5, 10.95 kg of 88% aqueous formic acid solution was added and stirred to react palladium chloride with formic acid. After the reaction, pure water was added to adjust the slurry concentration to 100 g / liter, and then 60 ° C. at 80 ° C.
Aged for a minute. After aging, cool the slurry to 60 ° C or lower, and then use a filter press to reduce the filtrate resistivity to 1
Filtration and washing were performed until it reached 0000 Ω · cm or more.
The time required for filtration and washing was about 40 hours. filtration·
After washing, it was dried and pulverized in the same manner as in Example 1 to obtain a palladium-supported photocatalyst (Sample B). When this sample B was observed with an electron microscope, it was confirmed that palladium was supported on the surface of the photocatalytic titanium oxide particles.

Evaluation 1 Palladium loading amount The palladium loading amount of Samples A and B obtained in Example 1 and Comparative Example 1 was measured by a fluorescent X-ray analyzer (RIX-3000).
Type: manufactured by Rigaku Denki Co., Ltd.).

Evaluation 2 Carbon Monoxide Removal Amount The carbon monoxide removal amount of Samples A and B obtained in Example 1 and Comparative Example 1 was measured. A sample amount of 0.1 g was placed in a closed circulation type reaction vessel, carbon monoxide gas was introduced into the vessel so that the initial concentration was 15 ppm, and then the carbon monoxide gas was circulated at 6 liters / minute, and the illuminance was changed. 1 mW / cm
^The sample was exposed to a black light of 90 for 90 minutes. Then, the sample gas is sampled from the container, and the concentration of carbon monoxide in the sample gas is measured by a methanizer (MTN
-1 type: Gas chromatograph equipped with Shimadzu Corporation (GC-14A type: Shimadzu Corporation, column: 3 mm)
φ × 2m, filling material: Porapak T, Waters
(Manufactured by Mfg. Co., Ltd.) and the amount of reduction in concentration was taken as the amount of removal.

Table 1 shows the results of the amount of palladium carried and the amount of carbon monoxide removed. The sample A has a larger amount of carbon monoxide removed per unit weight of palladium than the sample B, and it can be seen that the palladium carrying effect of the sample A is advantageous. Since it is considered that this is due to the difference in the supported state of palladium, the experimental results in Table 1 not only show that the photocatalyst of the present invention is highly active, but also are used as a catalyst, particularly for removing carbon monoxide. It shows that it is also effective as a catalyst and a catalyst for CO shift reaction.

[0026]

[Table 1]

[0027]

INDUSTRIAL APPLICABILITY The present invention provides a catalyst, particularly a photocatalyst, in which a noble metal produced by reducing a noble metal compound with at least one selected from hypophosphorous acid, phosphorous acid and salts thereof is supported on the surface of a substrate. Since it is a catalyst for CO shift reaction and has excellent catalytic activity and photocatalytic activity, it has various uses in the fields of catalysts and photocatalysts, removal of carbon monoxide, C
It can be used for O shift reaction. Further, the present invention is
A noble metal-supported catalyst, particularly a noble metal-supported photocatalyst or CO shift, is produced by reducing a noble metal compound with at least one selected from hypophosphorous acid, phosphorous acid and salts thereof in a medium containing a substrate. A method for producing a catalyst for reaction, which is economically and industrially advantageous and provides a highly active catalyst.

Claims (12)

[Claims] 1. A catalyst comprising a noble metal formed by reducing a noble metal compound with at least one selected from hypophosphorous acid, phosphorous acid and salts thereof on the surface of a substrate. 2. The catalyst according to claim 1, which is a photocatalyst using photocatalyst particles as a substrate. 3. The catalyst according to claim 1, which is a catalyst for CO shift reaction using a ceramic carrier as a substrate. 4. The catalyst according to claim 1, which is used for removing carbon monoxide. 5. The catalyst according to claim 1, wherein the base is titanium oxide. 6. The catalyst according to any one of claims 1 to 4, wherein a noble metal is supported on the substrate in a range of 0.01 to 5% by weight. 7. The catalyst according to claim 1, wherein the noble metal is palladium. 8. A noble metal compound is produced by reducing a noble metal compound with at least one selected from hypophosphorous acid, phosphorous acid and salts thereof in a medium containing the substrate. A method for producing a catalyst carrying a noble metal. 9. The method for producing a catalyst according to claim 8, wherein the photocatalyst particles are used as the substrate to obtain a photocatalyst in which a noble metal is supported on the surface of the photocatalyst particles. 10. The method for producing a catalyst according to claim 8, wherein a ceramic carrier is used as a substrate, and a CO shift reaction catalyst in which a precious metal is supported on the surface of the ceramic carrier is obtained. 11. The method according to claim 8, wherein activated carbon is added to the medium liquid after forming the noble metal, and the medium is filtered and washed.
10. The method for producing the catalyst according to any one of 10. 12. Activated carbon in an amount of 0.5 to 10% by weight based on the substrate.
The method for producing the catalyst according to claim 11, wherein the catalyst is added in the range of.