JP5237616B2 - Method for producing a titanium oxide carrier comprising a platinum group metal or an alloy of a platinum group metal and another metal supported thereon - Google Patents

Description

  The present invention relates to a method for producing a titanium oxide support comprising a platinum group metal or an alloy of a platinum group metal and another metal supported in a finely and uniformly highly dispersed state.

  Active research is being conducted to purify the environment by decomposing exhaust gases discharged from factories and various volatile organic compounds generated at home using catalysts.

  In these studies, catalysts in which a platinum group metal is supported on various carriers, for example, platinum-supported titanium oxide, palladium-supported titanium oxide, rhodium-supported alumina, platinum-supported carbon and the like are used.

  The performance of these platinum group metal supported catalysts varies greatly depending on the supported state of the platinum group metal on the support, and various studies have been made to improve the performance. For example, Patent Documents 1 and 2 propose a method in which a fine platinum group metal is supported on a carbon support having a large support surface area. However, according to this method, a fine titanium oxide support is difficult to increase. It is difficult to uniformly support platinum group metal or platinum group metal alloy particles with high dispersion.

  Patent Document 3 discloses that platinum is supported on a photocatalyst by applying a photodeposition method in which platinum acid is supported on a photocatalyst and then reduced by ultraviolet rays. However, this photodeposition method requires a long time and is difficult to process in large quantities.

  Further, Patent Documents 4 and 5 disclose a method in which a photocatalyst is immersed in an aqueous solution of palladium chloride or palladium nitrate and reduced with a reducing agent such as formic acid, hydrazine, or sodium borohydride to obtain a composite photocatalyst. However, with this method, it is difficult to agglomerate the metal particles and to support the metal particles on the titanium oxide support in a highly dispersed state.

JP-A-9-153366 JP 11-47595 A JP 2000-157874 A JP 2003-210984 A Japanese Patent Laid-Open No. 10-296082

  The method described in the above patent document is not optimal as a method for supporting a platinum group metal on a titanium oxide carrier, and has a high activity in which platinum group metal particles are supported finely and uniformly in a highly dispersed state on a titanium oxide carrier. A new catalyst cannot be obtained.

  On the other hand, in the method of using an inorganic metal compound such as palladium chloride or palladium nitrate as a raw material and heat-treating it under an atmospheric gas, chlorine, hydrogen chloride, nitrogen oxide gas, etc. are generated, which is safe for the human body. The influence on the environment and the influence on the environment becomes a problem, and it is necessary to provide the manufacturing equipment with a gas processing facility for processing the gas generated by the reduction, resulting in an increase in equipment costs.

An object of the present invention is to support a platinum group metal or an alloy of a platinum group metal and other metal finely and uniformly on a titanium oxide carrier in a highly dispersed state, and also in terms of safety and environment. It is an object of the present invention to provide a highly active method for producing a highly active titanium oxide support that supports a platinum group metal or an alloy of a platinum group metal and other metals.

  As a result of various studies, the present inventors have achieved the above object by adsorbing a platinum group metal to a titanium oxide support in the form of a salt of a specific organic carboxylic acid and then reducing it to a platinum group metal. As a result, the present invention has been completed.

  Thus, the present invention provides a salt of an organic carboxylic acid selected from the group consisting of formic acid, acetic acid, propionic acid, lactic acid, oxalic acid, malonic acid and maleic acid and a platinum group metal (a), and optionally further, the organic carboxylic acid. A solution containing a salt of an acid and a metal (b) other than the platinum group metal (a) is brought into contact with the titanium oxide carrier, and after the metal salt is adsorbed on the titanium oxide carrier, the reduction treatment is performed, A method for producing a titanium oxide support comprising a platinum group metal (a) or an alloy of a platinum group metal (a) and another metal (b) supported by converting a metal salt into a metal Is to provide.

  A titanium oxide carrier that carries a platinum group metal (a) or an alloy of a platinum group metal (a) and another metal (b) produced by the method of the present invention is produced by a conventional method. Platinum group metal (a) or platinum group metal (a) or platinum group metal (a) or platinum group metal (a) ) And other metal (b) other than that are supported in a highly dispersed state, and therefore, high catalytic activity can be exhibited.

  Moreover, according to the method of the present invention, unlike the conventional method, there is no generation of harmful gas such as chlorine gas, hydrogen chloride gas, NOx, and the production cost of the catalyst can be reduced. Is also possible.

  Hereinafter, the method of the present invention will be described in more detail.

BEST MODE FOR CARRYING OUT THE INVENTION

  The present invention provides formic acid for supporting a platinum group metal (a) or an alloy of a platinum group metal (a) and another metal (b) on a titanium oxide support in a finely and uniformly highly dispersed state. A salt (A) of an organic carboxylic acid and a platinum group metal (a) selected from the group consisting of acetic acid, propionic acid, lactic acid, oxalic acid, malonic acid and maleic acid, and optionally further, the organic carboxylic acid and the platinum group It has an essential feature in that a solution containing a salt (B) with a metal (b) other than the metal (a) (hereinafter referred to as “supporting solution”) is used.

  Salt (A) of the above organic carboxylic acid and platinum group metal (a) used in the present invention and salt (B) of the organic carboxylic acid and other metal (b) other than platinum group metal (a) (These are collectively referred to as “organic carboxylic acid metal salts” hereinafter) are decomposed at a lower temperature than inorganic metal compounds such as palladium chloride and palladium nitrate. In addition, since only carbon dioxide and water are generated during reductive decomposition, there is no need for an exhaust treatment facility such as when chlorine, hydrogen chloride, or nitrogen oxide is generated. It is extremely useful as a material for supporting a titanium oxide carrier.

In the present invention, the platinum group metal (a) for forming the salt (A) with the organic carboxylic acid in the present invention is an oxidative decomposition of various organic substances or inorganic substances (for example, volatile organic substances, odor components, nitrogen oxides, etc.). Those exhibiting a high catalytic action for the reaction are used, and in the present invention, platinum (Pt), palladium (Pd) and ruthenium (Ru) are particularly mentioned, and these may be used alone or in combination. Or it can be used in combination. Of these, platinum is particularly preferred as the platinum group metal (a).

  In the present invention, a salt (A) of an organic carboxylic acid and a platinum group metal (a) may be a salt of another metal (b) other than the organic carboxylic acid and the platinum group metal (a), if necessary. It can be used in combination with B), whereby an alloy of platinum group metal (a) and other metal (b) can be supported on the titanium oxide support. As the metal (b) other than the platinum group metal (a) for forming the salt (B), a metal having a catalytic action on the oxidative decomposition reaction of various organic substances or inorganic substances, or a platinum group metal By using in combination with (a), one that improves the catalytic action of platinum group metal (a) for the oxidative decomposition reaction of various organic or inorganic substances can be used, and salt (A) is formed. Platinum group metals other than the three types of platinum (Pt), palladium (Pd) and ruthenium (Ru) used for the purpose are also included. Specific examples include rhodium (Rh), iridium (Ir), gold (Au), silver (Ag), iron (Fe), cobalt (Co), nickel (Ni), and the like. Or in combination of two or more. As the metal (b) other than the platinum group metal (a), silver (Ag), cobalt (Co) and nickel (Ni) are particularly suitable.

  Use of both when a salt (A) of an organic carboxylic acid and a platinum group metal (a) is used in combination with a salt (B) of another metal (b) other than the organic carboxylic acid and the platinum group metal (a) The ratio is not strictly limited and can be appropriately changed depending on the use of the finally obtained supported titanium oxide carrier, but a metal other than the platinum group metal (a) and the platinum group metal (a). It is preferred that the platinum group metal (a) is generally at least 40 mol%, in particular 50 to 90 mol%, more particularly 50 to 70 mol%, based on the total amount with (b).

  The organic carboxylic acid metal salt is dissolved or dispersed in an aqueous medium, particularly deionized water or distilled water, to prepare a supported solution. The concentration of the organic carboxylic acid metal salt in the supporting solution is usually preferably in the range of 1% by weight to the saturation concentration, particularly in the range of 4 to 10% by weight. Further, the supporting solution may contain free organic carboxylic acid, but if the amount increases, metal ions may aggregate and precipitate, so the concentration of free organic carboxylic acid in the supporting solution is usually It is desirable to keep it at 10% by weight or less, particularly 5% by weight or less.

  In addition, a surfactant can be added to the supporting solution as necessary. Examples of the surfactant that can be added include nonionic surfactants such as polyoxyethylene tridecyl ether, ethylene glycol, and N, N-dimethylethanolamine; cationic surfactants such as alkyltrimethylammonium salts; Anionic surfactants such as alkylbenzenesulfonic acid ammonium salts; amphoteric surfactants such as alkylbenzylammonium salts.

  On the other hand, the titanium oxide carrier may be substantially composed of titanium oxide, or may be one in which the surface of a base material such as conductive carbon or metal oxide is coated with titanium oxide. Examples of the metal oxide include alumina, zirconia, silica, iridium oxide, and ruthenium oxide. The titanium oxide carrier can take any shape depending on the application, and can be, for example, a powder, a granular shape, a pellet shape, a honeycomb shape, a pleated shape, or a corrugated plate shape.

The support of the platinum group metal (a) or the alloy of the platinum group metal (a) and other metal (b) on these titanium oxide supports is obtained by bringing the titanium oxide support into contact with the support solution as described above. After the metal salts (A) and (B) are adsorbed on the titanium oxide support, reduction treatment is performed to convert the metal salt into a metal. The contact between the titanium oxide support and the support solution can be performed by, for example, a method of immersing in the support solution or spraying the support solution onto the titanium oxide support, thereby sufficiently supporting the support solution on the titanium oxide support. Adsorb.

  The titanium oxide carrier is brought into contact with the supporting solution, and then the excess supporting solution is removed and dried as necessary. Drying can usually be carried out by leaving it in the atmosphere at room temperature or heating it to a temperature up to about 80 ° C. As a result, a titanium oxide carrier on which a metal salt is adsorbed is obtained.

  Next, by reducing the titanium oxide carrier on which the metal salts (A) and (B) are adsorbed, the platinum group metal (a) or the platinum group metal (a) and other metal (b) A titanium oxide support in which the alloy is finely and uniformly supported in a highly dispersed state can be obtained. The reduction treatment is performed, for example, by heating to a temperature of about 40 to about 400 ° C., preferably about 40 to about 300 ° C. in a reducing gas (such as hydrogen) atmosphere, or in an inert gas (such as nitrogen) atmosphere. It can be carried out by heating to a temperature of about 300 to about 800 ° C., preferably about 300 to about 400 ° C., and decomposing the supported metal salts (A) and (B) into metals. In particular, titanium oxide carrying both a salt (A) of an organic carboxylic acid and a platinum group metal (a) and a salt (B) of the organic carboxylic acid and a metal (b) other than the platinum group metal (a). In the case of the carrier, it is supported in an alloy state in which the platinum group metal (a) and the other metal (b) are in solid solution with each other by heat treatment at a temperature of 400 to 800 ° C. in an inert atmosphere such as nitrogen. The obtained titanium oxide support can be obtained.

  The above reduction treatment also includes alcohols such as methanol and ethanol; aldehydes such as formaldehyde (formalin); ketones such as acetone; carboxylic acids such as formic acid; ethers such as methyl ethyl ether; hydrazine, It can also be performed using a reducing agent such as sodium borohydride.

  The titanium oxide carrier formed by supporting the platinum group metal (a) or the alloy of the platinum group metal (a) and the other metal (b) obtained in this way is a photocatalytic action of titanium oxide and the platinum group metal (a It has a high catalytic action synergistically with the oxidizing action of), and can be advantageously used, for example, for decomposing volatile organic substances such as acetaldehyde and formaldehyde and deodorizing odorous substances such as ammonia.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

Example 1
Platinum oxalate containing 12 g of platinum in terms of platinum was dissolved in 1000 mL of deionized water to obtain a platinum carrying solution with a platinum concentration of 12 g / L. After 990 g of pelleted titanium oxide was immersed in 1000 mL of this platinum-supported solution at 25 ° C. for 49 hours, it was filtered and dried at 100 ° C. to obtain platinum oxalate-supported titanium oxide. This platinum oxalate-supported titanium oxide was heated at 300 ° C. for 2.5 hours in a nitrogen atmosphere and then further reduced at 40 ° C. for 2.5 hours in a hydrogen atmosphere to obtain 1 mass% platinum-supported titanium oxide.

Example 2
The platinum oxalate-supported titanium oxide obtained in Example 1 is immersed in ethanol as a reducing agent, heated to the boiling point of ethanol, and refluxed for 18 hours to reduce platinum oxalate to platinum and to support 1 mass% platinum. Titanium oxide was obtained.

Example 3
Palladium maleate containing 12 g of palladium in terms of palladium is dissolved in 1000 mL of deionized water, 0.1 g of nonionic surfactant (polyoxyethylene tridecyl ether) is added to the resulting aqueous solution, and the palladium concentration is 12 g / A solution for supporting palladium of L was obtained. After 999 g of powdered titanium oxide was immersed in 100 mL of this palladium-supported solution at 25 ° C. for 49 hours, it was filtered and dried at 100 ° C. to obtain palladium maleate-supported titanium oxide. This palladium maleate-supported titanium oxide was reduced in a hydrogen atmosphere at 300 ° C. for 2.5 hours to obtain 0.1 mass% palladium-supported titanium oxide.

Example 4
Platinum oxalate containing 12 g of platinum in terms of platinum and ruthenium oxalate containing 6.2 g of ruthenium in terms of ruthenium are dissolved in 1000 mL of deionized water, the platinum concentration is 12 g / L, and the platinum concentration relative to all metals in the solution As a result, a platinum-ruthenium alloy-supported solution having a concentration of 50 mol% was obtained. 992.4 g of powdered titanium oxide was immersed in 500 mL of the platinum-ruthenium alloy supporting solution at 25 ° C. for 49 hours, filtered, and dried at 100 ° C. to obtain platinum oxalate and ruthenium oxalate-supported titanium oxide. . This platinum oxalate and ruthenium oxalate-supported titanium oxide were reduced at 800 ° C. for 2.5 hours in a nitrogen atmosphere to obtain 1 mass% platinum-0.52 mass% ruthenium alloy-supported titanium oxide.

Example 5
Platinum oxalate containing 12 g of platinum in terms of platinum and cobalt acetate containing 3.6 g of cobalt in terms of cobalt are dissolved in 1000 mL of deionized water, the platinum concentration is 12 g / L, and the platinum concentration relative to all metals in the solution is A 50 mol% platinum-cobalt alloy supporting solution was obtained. After 987 g of powdered titanium oxide was immersed in 1000 mL of this platinum-cobalt alloy supporting solution at 25 ° C. for 49 hours, it was filtered and dried at 100 ° C. to obtain platinum oxalate and cobalt acetate supporting titanium oxide. The platinum oxalate and cobalt acetate-supported titanium oxide were reduced at 800 ° C. for 2.5 hours in a nitrogen atmosphere to obtain 1 mass% platinum-0.3 mass% cobalt alloy-supported titanium oxide.

Example 6
Platinum oxalate containing 12 g of platinum in terms of platinum, gold oxalate containing 12.1 g of gold in terms of gold and silver oxalate containing 6.1 g of silver in terms of silver are dissolved in 1000 mL of deionized water, A platinum-gold-silver alloy-supported solution having a platinum concentration of 12 g / L and a platinum concentration of 50 mol% with respect to all metals in the solution and a concentration of 25 mol% with respect to all metals in the gold and silver solution was obtained. . The platinum-gold-silver alloy supporting solution was treated in the same manner as in Example 4 to obtain 1 mass% platinum-1.01 mass% gold-0.51 mass% silver alloy-supporting titanium oxide.

Example 7
890 g of powdered aluminum oxide was dispersed in 1000 mL of ethanol, and titanium alkoxide containing 100 g of titanium in terms of titanium oxide was added and hydrolyzed to obtain titanium hydroxide-coated aluminum oxide. This titanium hydroxide-coated aluminum oxide was heat-treated at 800 ° C. for 2.5 hours in the air to obtain titanium oxide-coated aluminum oxide. This titanium oxide-coated aluminum oxide was treated in the same manner as in Example 1 using titanium oxide instead of titanium oxide to obtain 1 mass% platinum-supported titanium oxide-coated aluminum oxide.

Comparative Example 1
Chloroplatinic acid containing 10 g of platinum in terms of platinum was dissolved in 1000 mL of deionized water to obtain a platinum carrying solution with a platinum concentration of 10 g / L. 990 g of pellet-shaped titanium oxide was immersed in 1000 mL of this platinum-supported solution and dried at 100 ° C. to obtain platinum chloride-supported titanium oxide. This platinum chloride-supported titanium oxide was heated at 500 ° C. for 2.5 hours in a nitrogen atmosphere to obtain 1 mass% platinum-supported titanium oxide.

Comparative Example 2
To 1000 mL of the platinum-supported solution obtained in Comparative Example 1, cobalt nitrate containing 3 g of cobalt in terms of cobalt was added and dissolved by stirring at room temperature to obtain a platinum-cobalt alloy-supported solution. 987 g of pelleted titanium oxide was immersed in 1000 mL of this platinum-cobalt alloy supporting solution, and dried at 100 ° C. to obtain platinum chloride and cobalt nitrate supporting titanium oxide. The platinum chloride and cobalt nitrate-supported titanium oxide were heated at 800 ° C. for 2.5 hours in a nitrogen atmosphere to obtain 1 mass% platinum-0.3 mass% cobalt alloy-supported titanium oxide.

Comparative Example 3
1000 mass of dinitrodiammine platinum ethanol solution containing 10 g of platinum in terms of platinum and having a platinum concentration of 10 g / L was treated in the same manner as in Comparative Example 1 to obtain 1 mass% platinum-supported titanium oxide.

  For the metal specific surface area of the metal-supported titanium oxide supports obtained in Examples 1 to 7 and Comparative Examples 1 to 3, a highly accurate fully automatic gas adsorption measuring device “BELSORP28SA” (trade name, manufactured by Nippon Bell Co., Ltd.) is used. And obtained from the amount of irreversible adsorption of carbon monoxide. The results are shown in Table 1 below. It can be seen that the metal-supported titanium oxide supports of Examples 1 to 7 clearly have a larger metal surface area than the metal-supported titanium oxide supports of Comparative Examples 1 to 3.

  FIG. 1 is a TEM photograph of platinum-supported titanium oxide prepared by pulverizing the pellet-shaped platinum-supported titanium oxide prepared in Example 1 with a mortar. Giant particles of 50 nm are titanium oxide particles, and particles of about 1 nm on the surface of titanium oxide are platinum particles. As is clear from this photograph, it can be seen that very fine platinum particles are supported in a highly dispersed state on the titanium oxide surface.

FIG. 2 is a cross-sectional photograph of platinum-supported titanium oxide produced in Example 1 and Comparative Example 3. From this photograph, it can be confirmed that the platinum-supported titanium oxide of Example 1 changed to black-gray to the inside of the pellet, and platinum was supported to the inside of the titanium oxide pellet. On the other hand, the platinum-supported titanium oxide pellet of Comparative Example 3 has a black-gray outer peripheral portion and platinum is supported, but the inside is the same white as titanium oxide and it can be confirmed that platinum is not supported. Therefore, when the platinum-supported titanium oxide pellet of Comparative Example 3 is used for, for example, decomposition of a volatile organic substance, the volatile organic substance may be adsorbed on the titanium oxide inside the pellet and remain without being decomposed.

FIG. 3 is a graph showing the decomposition characteristics of acetaldehyde of platinum-supported titanium oxide and non-supported titanium oxide support of Example 1. The plate-supported titanium oxide or titanium oxide support of Example 1 is used in the NOx removal performance test of the photocatalyst material (JISR 1701 “Testing method for air purification performance of photocatalyst material Part 1 Nitrogen oxide”). Acid glass and others are installed in a transparent continuous gas flow type apparatus made of acrylic resin, and air containing 5 ppm acetaldehyde is circulated at 1 L / min for 90 minutes under dark conditions (no UV irradiation) where no light is applied. The concentration of acetaldehyde at the outlet of the measuring vessel for 90 minutes was measured under bright conditions with subsequent ultraviolet irradiation (irradiation with ultraviolet light having an irradiance of 10 W / m ² using a black light (TOSHIBA FL20SBLB)). As can be seen from FIG. 3, the platinum-supported titanium oxide of Example 1 has undergone acetaldehyde decomposition even under dark conditions, and further proceeds under light conditions. On the other hand, the adsorption of acetaldehyde progresses at first in the dark condition in the titanium oxide carrier, so although the outlet acetaldehyde concentration is low, the adsorption approaches saturation as time passes. Rises. Therefore, it is considered that the titanium oxide carrier has no ability to decompose acetaldehyde under dark conditions. Therefore, it is clear that the platinum-supported titanium oxide of Example 1 is more active as an acetaldehyde removal catalyst than the titanium oxide support.

These are TEM photographs of platinum-supported titanium oxide prepared by pulverizing the pellet-shaped platinum-supported titanium oxide prepared in Example 1 with a mortar. These are cross-sectional photographs of platinum-supported titanium oxide produced in Example 1 and Comparative Example 3. These are the graphs which show the decomposition characteristics of acetaldehyde of platinum-supported titanium oxide and non-supported titanium oxide support of Example 1.

Claims (3)

A salt (A) of an organic carboxylic acid selected from the group consisting of oxalic acid, malonic acid and maleic acid and at least one platinum group metal (a) selected from platinum and ruthenium, or salt (A) and cobalt acetate A platinum group metal (a) or a platinum group metal (a), wherein the solution containing the catalyst is brought into contact with a titanium oxide support, a metal salt is adsorbed on the titanium oxide support and then reduced to convert the metal salt into a metal. A method for producing a titanium oxide carrier carrying an alloy of a platinum group metal (a) and cobalt. The method according to claim 1, wherein the titanium oxide support is a conductive carbon or metal oxide coated with titanium oxide or titanium oxide. A method according to claim 1 or 2 carried out by heat treatment to a reduction treatment at a temperature of 300 ° C. to 800 ° C. under an inert atmosphere.