JP2006346645A - Metal filter and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-temperature oxidation catalyst capable of removing carbon monoxide at low temperatures such as room temperature for long periods, and further, maintain firmly the catalyst inside a ventilation flue while suppressing a pressure loss by increasing an opening rate to prevent a dust generation. <P>SOLUTION: A great number of ventilation flues (3) are defined in a thickness direction of a metal substrate (2). A catalyst layer (5) which keeps the low-temperature oxidation catalyst fixed to a substrate wall surface (4) with a binding component is formed inside the ventilation flue (3). The low-temperature oxidation catalyst comprises fine particles of titanium oxide, the surface of which is supported by an oxide of a transition metal such as nickel and a small gold particle as a coprecipitate. The low-temperature oxidation catalyst and the binding component are heated to 250°C or more when being fixed to the substrate wall surface (4). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a metal filter. More specifically, the present invention includes a low-temperature oxidation catalyst that can efficiently remove carbon monoxide at low temperatures such as room temperature over a long period of time, while increasing the aperture ratio and suppressing pressure loss. The present invention relates to a metal filter that securely holds a catalyst on the inner surface of a ventilation passage to prevent the occurrence of powder falling and a method for manufacturing the same.

  In recent years, awareness of health and a comfortable living environment have been aimed at, and there is a demand for removal of carbon monoxide generated from cigarette smoking and heating appliances. One method for removing carbon monoxide is to convert carbon monoxide to carbon dioxide using a catalyst.

  The oxidation catalyst is carried on a filter incorporated in an apparatus such as an air purifier, for example, and air in the room or the like passes through the filter to remove carbon monoxide discharged to the living environment. This filter not only requires excellent catalytic performance such as being able to oxidize carbon monoxide satisfactorily at low temperatures such as room temperature, and low performance deterioration due to moisture, dust and gas in the air. There is a demand for the air permeability of the base material such that there is no generation of fine powder due to falling off, and the filter has a low pressure loss and excellent ventilation performance.

  Conventionally, as a catalyst capable of removing carbon monoxide at a low temperature such as room temperature, a catalyst in which noble metal fine particles such as gold are supported on the surface of a metal oxide such as titanium oxide or nickel oxide has been proposed (Patent Document 1). reference). However, when the performance of this catalyst was measured, the catalytic action at a low temperature such as room temperature was not sufficiently high, and it was not easy to efficiently remove carbon monoxide in the living environment.

  The above-mentioned low-temperature oxidation catalyst is conventionally supported on a porous substrate by impregnation or coating. For example, the above-mentioned catalyst is supported on a porous adsorbent, and the nonwoven fabric is impregnated with fine particles of the porous adsorbent. Thereafter, a nonwoven fabric processed into a honeycomb shape or the like (see Patent Document 2), a ceramic honeycomb impregnated with a low-temperature oxidation catalyst (see Patent Document 3), and the like are known.

However, those using the above nonwoven fabric as the base material, the fine particles carrying the low-temperature oxidation catalyst are held between the fibers of the base material. Produce. For this reason, not only the catalyst performance deteriorates early, but also the problem that the detached powder may contaminate the living environment, and a powder removing device is required downstream of the filter to prevent this, and it cannot be implemented at low cost. There is also.
It is conceivable to fix the above fine particles to the nonwoven fabric with a binder, but this binder may reduce the breathability of the nonwoven fabric, and stabilizers, surfactants, organic polymers, etc. are catalyst fine particles. There is a problem of hindering the catalytic action to conceal and poison. In order to protect the catalyst from the inhibitory components contained in the binder, it has been proposed that the catalyst fine particles contain an alkali metal (see Patent Document 2 above), but in this method, the catalyst activity is maintained sufficiently high. I can't do it.

  On the other hand, when the above ceramic honeycomb is used, the walls constituting the honeycomb are impregnated with noble metal ions exhibiting a catalytic function and reduced or fired to carry the oxidation catalyst. The catalytic function is the air flow state in the honeycomb. Depends greatly on A ceramic honeycomb is manufactured by molding ceramic fine particles with a binder and firing the ceramic honeycomb. However, if the thickness of the wall defining the pores of the honeycomb is reduced, the ceramic honeycomb is easily broken or damaged during firing. For this reason, it is not easy to reduce the wall thickness and increase the aperture ratio, and the pressure loss increases. In addition, the firing must be held at a high temperature of 1000 ° C. or higher for a long time, which is expensive and a honeycomb having a thin depth cannot be manufactured. Furthermore, since it is fragile, handling is necessary, and there is a problem that it is not easy to incorporate into an air purifier or the like.

Japanese Patent Laid-Open No. 11-114419 JP 2003-88759 A JP 2000-345175 A

  The technical problem of the present invention is to solve the above-mentioned problems, and includes a low-temperature oxidation catalyst that can efficiently remove carbon monoxide over a long period of time at a low temperature such as room temperature, and suppresses pressure loss by increasing the aperture ratio. However, another object of the present invention is to provide a metal filter and a method for manufacturing the same that are securely held on the inner surface of the air passage to prevent the occurrence of powder falling.

In order to solve the above-described problems, the present invention is configured as follows, for example, based on FIGS. 1 to 3 showing an embodiment of the present invention.
That is, the present invention relates to a metal filter, which is a metal filter in which a large number of ventilation paths (3) are provided in the thickness direction of the metal substrate (2), and the low-temperature oxidation catalyst is a base material with a caking component. A catalyst layer (5) fixed to the wall surface (4) is formed on the inner surface of the ventilation path (3).

  The present invention 2 also relates to a method for producing a metal filter, wherein a coating liquid is prepared by mixing fine particles of a low-temperature oxidation catalyst and a binder, and a large number of ventilation paths (3) provided in the thickness direction are provided. After applying the above-mentioned coating liquid to the inner surface of each ventilation path (3) of the metal substrate (2) provided, the substrate wall surface ( It is fixed to 4).

  The present invention 3 also relates to a method for producing a metal filter, comprising preparing precursor fine particles in which fine particles of noble metal hydroxide and fine particles of transition metal hydroxide are supported on the surface of oxide fine particles, The body fine particles and the binder are mixed to prepare a coating liquid, and each of the ventilation paths (3) of the metal substrate (2) having a large number of ventilation paths (3) provided in the thickness direction is provided. After applying the above coating solution on the inner surface, heat treatment is performed at 250 ° C. or higher, and the above precursor fine particles are oxidized at a low temperature by supporting noble metal fine particles and transition metal oxide fine particles on the surface of the oxide fine particles. While making it a catalyst, this low-temperature oxidation catalyst is fixed to a base-material wall surface (4) with a caking component.

The low-temperature oxidation catalyst and the caking component are heated to 250 ° C. or higher, preferably 300 ° C. or higher when being fixed to the wall surface. The above caking components are used as caking agents in the form of sols, gels, emulsions, etc. The organic components that inhibit the catalytic action, such as stabilizers and surfactants contained in this caking agent, Decomposes on heating.
The heating temperature is set within a range that does not adversely affect the metal substrate. For example, when an adhesive is used to form the metal substrate, the heating temperature is lower than the decomposition temperature of the adhesive. For example, it is set to 500 ° C. or lower.

  The coating solution to be applied to the metal base material may be prepared by pulverizing a pre-fired low-temperature oxidation catalyst and mixing it with a binder. It is not easy to do. Therefore, as in the above-described Invention 3, precursor fine particles in which noble metal hydroxide fine particles and transition metal hydroxide fine particles are supported on the surface of the oxide fine particles are prepared, and the precursor fine particles are prepared. It is preferable to prepare a coating solution by mixing with a binder before baking, apply the coating solution to the inner surface of the air passage, and heat-treat. In this case, the precursor is fired by this heat treatment to become a low-temperature oxidation catalyst, and the catalytic action inhibiting component contained in the binder is decomposed.

  The caking component is not limited to a specific material as long as it can fix the low-temperature oxidation catalyst to the surface of the metal substrate. For example, a metal oxide such as alumina, silica, or a fluorine-based polymer is used. In particular, in the case of a fluorine-based polymer, since it softens during the heating, the low-temperature oxidation catalyst can be more reliably fixed to the substrate surface, which is preferable.

  The low-temperature oxidation catalyst is not particularly limited as long as it oxidizes carbon monoxide to carbon dioxide at a low temperature, but coprecipitates precious metal fine particles and transition metal oxide fine particles. By using oxide fine particles supported on the surface, carbon monoxide is efficiently oxidized and removed to carbon dioxide over a long period of time in a low-temperature state without external heating such as room temperature due to the synergistic action of the three. Can be preferred.

  Specifically, examples of the oxide fine particles include titanium oxide, aluminum oxide, and silica. Examples of the transition metal include atoms such as nickel, copper, cobalt, iron, and manganese, and compounds thereof. Examples of the noble metal fine particles include platinum, gold, palladium, and compounds thereof.

  The catalyst layer only needs to be firmly fixed to the substrate surface in such an amount that it can sufficiently exhibit the catalyst performance. Specifically, the thickness is set to about 2 to 40 μm. This is because if it is too thin, carbon monoxide cannot be oxidized sufficiently, and if it is excessively thick, the low-temperature oxidation catalyst is peeled off from the surface of the metal substrate to cause powder falling.

  Said metal base material is not limited to a specific metal material, Metal materials, such as aluminum, copper, and stainless steel, can be used. In particular, aluminum is preferred because it is lightweight and easy to handle, and is excellent in terms of ease of application of the coating liquid, durability of the catalyst, cost, and the like.

Moreover, many ventilation paths formed in the thickness direction of said metal base material are not limited to a specific shape. Specifically, the opening shape may be a hexagonal, quadrangular or circular honeycomb, or a corrugated shape in which single-stage cardboards are stacked.
The opening area of this ventilation path is preferably set to an inner diameter of about 1 mm to 6 mm, more preferably 2 to 4 mm in terms of a circle, from the relationship between pressure loss and the amount of catalyst attached.
Moreover, the wall thickness of the wall defining the ventilation path only needs to be thick enough not to be deformed or broken during handling, but if it is thickened, pressure loss increases and it becomes heavy and difficult to handle. For this reason, the opening ratio of this ventilation path, that is, the ratio of the opening area of the entire ventilation path to one side of the metal filter is usually set to 90% or more, and more preferably set to 98% or more.

  Since this invention is comprised as mentioned above, there exists the following effect.

  (1) Since the base material is made of metal, the inner surface of the air passage can be formed smoothly, the wall thickness defining the air passage can be reduced, and the aperture ratio can be increased to suppress pressure loss. . In addition, since the low-temperature oxidation catalyst is firmly held on the inner surface of the ventilation path by the caking component, it is possible to prevent the occurrence of powder falling even when the metal filter is subjected to vibration or the like, and there is no possibility of deteriorating the living environment. Furthermore, since the above air passage has little pressure loss, air and exhaust from the heating appliance can pass well through this air passage, and the catalyst layer is securely held on the inner surface of the air passage, so that the catalyst layer is oxidized. Carbon can be efficiently removed over a long period of time.

  (2) After applying the coating liquid in which the fine particles of the low-temperature oxidation catalyst and the binder are mixed to the inner surface of the air passage, heat treatment is performed at 250 ° C. or higher to make the low-temperature oxidation catalyst a wall surface with a binder component. When it is fixed on the surface, organic components that inhibit the catalytic action, such as stabilizers and surfactants contained in the binder, are decomposed by the above heat treatment, so that the catalyst performance of the low-temperature oxidation catalyst is demonstrated well. And carbon monoxide can be efficiently removed over a long period of time.

  (3) After applying the coating liquid in which the precursor fine particles and the binder are mixed to the inner surface of the ventilation path, the precursor fine particles are converted into oxide fine particles by heat treatment at 250 ° C. or higher. Necessary for the production of a low-temperature oxidation catalyst when a low-temperature oxidation catalyst with precious metal fine particles and transition metal oxide fine particles supported on the surface is fixed to the substrate wall surface with a caking component. Can be processed at once, and the decomposition treatment of the catalytic action inhibiting component contained in the binder can be performed at a time, so that the heating efficiency is excellent and the cost can be reduced. In addition, in this case, it is not necessary to pulverize the low-temperature oxidation catalyst after calcination, and the fine granular low-temperature oxidation catalyst can be efficiently fixed to the inner surface of the air passage.

  (4) Further, in this case, since the low-temperature oxidation catalyst is composed of oxide fine particles having noble metal fine particles and transition metal oxide fine particles supported on the surface, It is possible to efficiently oxidize and remove carbon monoxide to carbon dioxide over a long period in a low temperature state without external heating.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 and 2 show an embodiment of the present invention, FIG. 1 is a schematic perspective view of a metal filter, and FIG. 2 is a partially broken perspective view in which a main part of the metal filter is enlarged.

As shown in FIG. 1, the metal filter (1) is composed of a honeycomb-shaped metal substrate (2) formed of a metal material such as aluminum, and a large number of ventilation paths (3) are permeable in the thickness direction. It is set up.
The cross-sectional shape of the ventilation path (3) is formed in a hexagonal shape having an opening corresponding to a circular area with a diameter of 4 mm, for example. Moreover, the thickness of the base-material wall surface (4) which divides this ventilation path (3) is formed in the thickness of about 0.025 mm, for example. Therefore, the aperture ratio of the metal filter (1) is about 98%.

As shown in FIG. 2, the catalyst layer (5) which fixed the low-temperature oxidation catalyst to the base-material wall surface (4) with the caking component is formed in the inner surface of said ventilation path (3). The thickness of this catalyst layer (5) is, for example, 4 to 20 μm.
In addition, said low-temperature oxidation catalyst and caking component are heated at 250-500 degreeC, Preferably it is 300-400 degreeC, when fixing to said base-material wall surface (4). The above-mentioned binder component is mixed with a low-temperature oxidation catalyst and applied to the substrate wall surface, so it is formed into a binder such as a sol, gel, emulsion, etc. The surfactant contained in this binder is Since it decomposes | disassembles by said heat processing, the catalytic activity of a low-temperature oxidation catalyst is maintained highly.

The low-temperature oxidation catalyst contained in the above catalyst layer has fine oxide particles of transition metal such as nickel and iron and fine noble metal particles such as gold on the surface of oxide fine particles such as titanium oxide, aluminum oxide and silica. It is supported as a coprecipitate.
The oxide fine particles are solid particles, and it is preferable to reduce the particle size and increase the specific surface area so that transition metal oxides and noble metal fine particles are efficiently supported. Specifically, those having an X-ray particle diameter of 7 to 20 nm and a specific surface area of 50 to 350 m ² / g are used.

  The particle diameter of the noble metal fine particles may be in a range in which the catalytic action is effectively exhibited, and is set, for example, in a range of about 5 nm from the noble metal atomic size. However, the particle diameter is preferably small, and is set to 3 nm or less, preferably 2 nm or less, more preferably 1 nm or less. If the amount of the noble metal fine particles supported is too small, the catalytic action is not sufficiently exerted, and if the amount supported is too large, the corresponding catalytic action cannot be improved, which is not economical. For this reason, the amount of the precious metal fine particles supported is preferably 0.1 to 3% by weight, more preferably 0.5 to 2% by weight, based on the oxide fine particles.

  As the transition metal oxide, nickel oxide, iron oxide or the like may be used alone, or a plurality of types may be used in combination. The loading amount of these transition metal oxide fine particles is not particularly limited, but if set to the same level as the noble metal fine particle loading amount, the three including oxide fine particles such as titanium oxide act synergistically and are good It is preferable because it can exhibit a good catalytic action. Specifically, the supported amount of the transition metal oxide fine particles is set to 0.25 to 5% by weight, more preferably 0.5 to 3% by weight with respect to the supported amount of the noble metal fine particles. Is set. For example, when nickel oxide and iron oxide are used in combination, the blending amount of nickel with respect to iron is set to 1/3 to 3 weight ratio, more preferably 0.5 to 2 weight ratio.

  The caking component is made of a metal oxide such as alumina, silica, or a fluorine-based polymer, and may be a mixture of a plurality of these. Examples of the fluorine polymer include polymers and copolymers such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), and PTFE-hexafluoropropylene copolymer. Is used. These fluoropolymers preferably melt at 300 to 400 ° C.

  Next, a method for forming a catalyst layer including the low temperature oxidation catalyst will be described. In this embodiment, in order to simplify the description, gold is used as the noble metal and titanium oxide fine particles are used as the oxide fine particles. However, in the present invention, other noble metals such as platinum may be used. Or fine particles such as silica.

  First, an aqueous solution of chloroauric acid and transition metal nitrate is adjusted to pH 6 to 9 with sodium hydroxide, sodium carbonate or the like to generate a hydroxide. Next, fine particles of titanium oxide are added to this hydroxide aqueous solution and treated at 50 to 80 ° C. for a predetermined time. The solid components are washed with water and separated into solid and liquid, and gold hydroxide and titanium oxide are deposited on the surface of the fine particles of titanium oxide. Precursor fine particles co-precipitated with the transition metal hydroxide are obtained. The aqueous solution of chloroauric acid and transition metal nitrate may be adjusted in pH after adding titanium oxide particles.

The precursor fine particles can be prepared by the following method instead of the above method.
First, the titanium oxide is suspended and dispersed in water so that it is sufficiently acclimated to water. After adding an aqueous solution of chloroauric acid and transition metal nitrate to this titanium oxide suspension dispersion, the metal component is adsorbed on titanium oxide, adjusted to pH 6-9 with sodium hydroxide, sodium carbonate, etc. After processing at 80 ° C. for a predetermined time, the solid component is washed with water and separated into solid and liquid.

  Next, the precursor fine particles prepared by the above procedure are mixed with a binder containing a binder component at a predetermined ratio to prepare a coating solution. As the binder, a metal oxide such as alumina, a silica sol or gel, or a fluorine polymer emulsion may be used, and both may be used together.

When using the above sol or gel of alumina or silica, the amount of addition is 5 to 20% by weight, preferably 10 to 15% by weight of caking components such as alumina and silica, based on the total solid content after the addition. To be adjusted.
Moreover, when using said fluoropolymer emulsion, the addition amount is 5-20 weight% with respect to the total solid before addition.

The metallic substrate (2) formed in a honeycomb shape is immersed in the coating solution and removed, and the excess solution is removed so that the coating solution is applied almost uniformly on the inner surface of each ventilation passage (3). To do. After drying this at room temperature, it is fired by heating at 250 ° C. or higher, preferably 300 ° C. or higher.
By this firing, the precursor fine particles become a low-temperature oxidation catalyst in which coprecipitates of gold fine particles and transition metal oxide fine particles are supported on the surfaces of titanium oxide fine particles. In addition, organic components that inhibit the catalytic action, such as stabilizers and surfactants contained in the binder, are decomposed. As a result, a metal filter (1) in which a low-temperature oxidation catalyst that exhibits excellent catalytic performance even at a low temperature such as room temperature is firmly fixed as the catalyst layer (5) to the inner surface of the ventilation path (3) is obtained. .

  In this embodiment, the above-mentioned precursor fine particles were mixed with a binder to prepare a coating solution. However, in the present invention, it is also possible to prepare fine particles of a low-temperature oxidation catalyst in advance and mix this with a binder to prepare a coating solution. Also in this case, in order to decompose the catalytic action inhibiting component contained in the binder, it is heated to 250 ° C. or higher, preferably 300 ° C. or higher after being applied to the metal substrate.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.

(Example 1)
After adding 72.0 g of titanium oxide to 960 ml of deionized water and stirring for 1 hour at 60 ° C. to adjust to water, 144 ml of chloroauric acid tetrahydrate (2.26 g / 100 ml) was added at 62 ° C. Stir for 15 minutes. Next, 360 ml of nickel nitrate hexahydrate (2.817 g / 100 ml) was added and stirred for 20 minutes. To this suspension was added 390 ml of a 0.2N aqueous sodium hydroxide solution and kept at 60-62 ° C. for 2 hours with stirring. Then, precursor fine particles were prepared. The resulting microparticles were colored light greenish gray.

  Next, after the stirring was stopped and the reaction product was allowed to stand, the supernatant was removed, and the solid content was washed with 5000 ml of deionized water to remove unreacted chloroauric acid and nickel nitrate. Washing with water was repeated until no chlorine ions were detected in the supernatant. After washing with water, the supernatant was removed and the solid and liquid were separated by centrifugation.

Next, the recovery rate of the precursor fine particles is set to 85%, and silica sol (manufactured by Nissan Chemical Industries, Ltd., product name Snow) is added to the precursor fine particles so that the caking component silica is 15% by weight of the total solid content. Tex 20) was added as a binder, and deionized water was further added to prepare a coating solution having a solid concentration of 23%.
An aluminum honeycomb substrate was dipped in this coating solution for 2 minutes and then gently removed to remove excess liquid adhering to the substrate and dried at room temperature. Next, the dried honeycomb substrate was heated at 120 ° C. for 20 minutes and then heat-treated (fired) at 400 ° C. for 1 hour to obtain an aluminum filter.

(Example 2)
Add 108.0 g of titanium oxide to 1440 ml of deionized water, stir for 50 minutes at 62 ° C. to adjust to water, then add 111 ml of chloroauric acid tetrahydrate (2.26 g / 100 ml) at 62 ° C. Stir for 20 minutes. Next, 270 ml of nickel nitrate hexahydrate (2.817 g / 100 ml) was added and stirred for 30 minutes. To this suspension was added 288 ml of 0.2N aqueous sodium hydroxide solution, and the mixture was kept at 60 to 61 ° C. for 2 hours with stirring. Thus, precursor fine particles were prepared. The resulting microparticles were colored light greenish gray. Thereafter, the reaction product was washed with water in the same manner as in Example 1, and then the solid and liquid were separated by centrifugation.

Next, the recovery rate of the precursor fine particles is set to 85%, and the same silica sol as that of Example 1 is caking to the precursor fine particles so that the caking component silica becomes 17.5% by weight of the total solid content. In addition to the above, deionized water was further added to prepare a coating solution having a solid content concentration of 22%.
Next, as in Example 1 above, an aluminum honeycomb substrate was immersed in this coating solution for 2 minutes, taken out gently, dried at room temperature, heated at 120 ° C. for 20 minutes, and then at 400 ° C. An aluminum filter was obtained by heat treatment (firing) for 1 hour.

Example 3
After adding 72.0 g of titanium oxide to 960 ml of deionized water and stirring for 1 hour at 60 ° C. to adjust to water, 144 ml of chloroauric acid tetrahydrate (2.26 g / 100 ml) was added at 62 ° C. Stir for 15 minutes. Next, 360 ml of nickel nitrate hexahydrate (2.817 g / 100 ml) was added and stirred for 20 minutes. To this suspension was added 400 ml of a 0.2N aqueous sodium hydroxide solution and kept at 60 to 62 ° C. for 2 hours with stirring. Then, precursor fine particles were prepared. The resulting microparticles were colored light greenish gray. Thereafter, the reaction product was washed with water in the same manner as in Example 1, and then the solid and liquid were separated by centrifugation.

Next, the recovery rate of the precursor fine particles is set to 85%, and 5% by weight of polytetrafluoroethylene (manufactured by Daikin Industries, Ltd., PTFE emulsion) is used as a binder with respect to the total solid content of the precursor fine particles. In addition, deionized water was further added to prepare a coating solution having a solid content of 20%.
Next, as in Example 1 above, an aluminum honeycomb substrate was immersed in this coating solution for 2 minutes, taken out gently, dried at room temperature, heated at 120 ° C. for 20 minutes, and then at 400 ° C. An aluminum filter was obtained by heat treatment (firing) for 1 hour.

Example 4
Precursor fine particles were prepared in the same procedure as in Example 3 above, the recovery rate of the precursor fine particles was set to 85%, and 10% by weight based on the total solid content of the precursor fine particles in Example 3 above. The used polytetrafluoroethylene was added as a binder, and deionized water was further added to prepare a coating solution having a solid content concentration of 20%.
Next, as in Example 1 above, an aluminum honeycomb substrate was immersed in this coating solution for 2 minutes, taken out gently, dried at room temperature, heated at 120 ° C. for 20 minutes, and then at 400 ° C. An aluminum filter was obtained by heat treatment (firing) for 1 hour.

(Example 5)
Add 72.0 g of titanium oxide to 960 ml of deionized water, stir at 60 ° C. for 45 minutes to adjust to water, then add 74 ml of chloroauric acid tetrahydrate (2.26 g / 100 ml) at 62 ° C. Stir for 5 minutes. Next, 180 ml of nickel nitrate hexahydrate (2.817 g / 100 ml) was added and stirred for 30 minutes. To this suspension was added 192 ml of a 0.2N aqueous sodium hydroxide solution and held at 60 to 61 ° C. for 105 minutes with stirring. Thus, precursor fine particles were prepared. The resulting microparticles were colored light greenish gray. Thereafter, the reaction product was washed with 3000 ml of deionized water in the same manner as in Example 1, and then the solid and liquid were separated by centrifugation.

Next, the recovery rate of the precursor fine particles is set to 85%, and the same silica sol as that of Example 1 is used as a binder so that the precursor fine particles have 15% by weight of the solid component silica. After the addition, 5% by weight of the total solid content of the same polytetrafluoroethylene as in Example 3 was added as a binder, deionized water was added thereto, and the solid content concentration was 21%. A liquid was prepared.
Next, as in Example 1 above, an aluminum honeycomb substrate was immersed in this coating solution for 2 minutes, taken out gently, dried at room temperature, heated at 120 ° C. for 20 minutes, and then at 400 ° C. An aluminum filter was obtained by heat treatment (firing) for 1 hour.

Example 6
Precursor fine particles are prepared in the same procedure as in Example 1 above, and the recovery rate of the precursor fine particles is set to 85%, and the caking component silica is 15% by weight of the total solid content in the precursor fine particles. After adding the same silica sol as in Example 1 as a binder, 10% by weight of the same polytetrafluoroethylene as in Example 3 was added as a binder to the total solid content, and deionized water was added thereto. Was added to prepare a coating solution having a solid concentration of 23%.
Next, as in Example 1 above, an aluminum honeycomb substrate was immersed in this coating solution for 2 minutes, taken out gently, dried at room temperature, heated at 120 ° C. for 20 minutes, and then at 400 ° C. An aluminum filter was obtained by heat treatment (firing) for 1 hour.

(Comparative Example 1)
Precursor fine particles were prepared by the same procedure as in Example 1 above, the recovery rate of the precursor fine particles was set to 85%, deionized water was added to the precursor fine particles, and a coating solution having a solid content concentration of 23% was obtained. Prepared.
Next, as in Example 1 above, an aluminum honeycomb substrate was immersed in this coating solution for 2 minutes, taken out gently, dried at room temperature, heated at 120 ° C. for 20 minutes, and then at 400 ° C. An aluminum filter was obtained by heat treatment (firing) for 1 hour.

  For each of the above Examples and Comparative Examples, the amount of catalyst supported relative to the weight of the honeycomb substrate was measured. Moreover, each particle peeling rate when each obtained aluminum filter was dropped 10 times from a height of 25 cm was measured. The particle peeling rate was determined as a percentage obtained by dividing the peeled particle amount by the original catalyst carrying amount. These measurement results are shown in the peelability comparison table of FIG.

From the measurement results, the following became clear.
(1) In the case of Comparative Example 1 in which no binder is used, since the particle peeling rate is high, the low temperature oxidation catalyst is not firmly fixed to the wall surface of the base material, and when the filter is subjected to vibration or the like, the fine particles are formed. Since it keeps detaching continuously, there is a risk of polluting the living environment downstream of the filter due to powder falling. On the other hand, in each of the embodiments of the present invention, the particle peeling rate is low, and even if the filter is subjected to vibration or the like, occurrence of powder falling due to separation of fine particles is prevented.

  (2) As a binder, a low temperature oxidation catalyst is more securely fixed to the wall surface of the base material when a fluoropolymer alone is used than when a silica sol is used alone. When both molecules are used, the low temperature oxidation catalyst is more reliably fixed to the wall surface of the substrate.

  The metal filters described in the above embodiments and examples are examples for embodying the technical idea of the present invention. The material and shape of the metal substrate, the low-temperature oxidation catalyst, and the adhesive The components, blending amounts, and the like are not limited to those of the above-described embodiments and examples, and various modifications can be made within the scope of the claims of the present invention. For example, in the above-described embodiments and examples, the coating solution is applied to the surface of the metal substrate by dipping, but the coating solution can be applied by other means such as spraying.

  The metal filter of the present invention includes a low-temperature oxidation catalyst that can efficiently remove carbon monoxide over a long period of time at a low temperature such as room temperature, while increasing the aperture ratio and suppressing pressure loss, and also ventilating the catalyst. Since it can be securely held on the inner surface of the glass and the occurrence of powder falling can be prevented, it is suitably used for removing carbon monoxide generated from cigarette smoking and heating appliances in the living environment, but for other uses, It is also suitably used as a metal filter provided with a low temperature oxidation catalyst.

It is a schematic perspective view of a metal filter showing an embodiment of the present invention. It is the partially broken perspective view which expanded the principal part of metal filters of an embodiment. It is a measurement result comparison table | surface of each particle peeling rate of each Example and comparative example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Metal filter 2 ... Metal base material 3 ... Ventilation path 4 ... Base material wall surface 5 ... Catalyst layer

Claims (12)

  A metal filter in which a large number of ventilation paths (3) are permeated in the thickness direction of the metal substrate (2), and a catalyst layer in which a low-temperature oxidation catalyst is fixed to the substrate wall surface (4) with a caking component ( 5) is formed on the inner surface of the ventilation path (3), a metal filter.   2. The metal filter according to claim 1, wherein the low-temperature oxidation catalyst and the caking component are heated to 250 ° C. or higher when being fixed to the substrate wall surface (4).   The metal filter according to claim 1 or 2, wherein the caking component includes at least one of a metal oxide, silica, and a fluorine-based polymer.   The metal filter according to any one of claims 1 to 3, wherein the low-temperature oxidation catalyst comprises oxide fine particles having precious metal fine particles and transition metal oxide fine particles supported on a surface thereof.   The metal filter according to claim 4, wherein the oxide fine particles include fine particles of at least one of titanium oxide, aluminum oxide, and silica.   The metal filter according to claim 4 or 5, wherein the transition metal includes at least one of nickel, copper, cobalt, iron, manganese, and a compound thereof.   The metal filter according to any one of claims 4 to 6, wherein the noble metal fine particles include at least one of platinum, gold, palladium, and a compound thereof.   The metal filter according to any one of claims 1 to 7, wherein the catalyst layer (5) has a thickness of 2 to 40 µm.   The metal filter according to any one of claims 1 to 8, wherein the ventilation path (3) has an opening ratio of 90% or more. Mix the fine particles of the low-temperature oxidation catalyst and the binder to prepare a coating solution,
After applying the above coating liquid to the inner surface of each ventilation path (3) of a metal base (2) having a large number of ventilation paths (3) provided in the thickness direction, heat treatment is performed at 250 ° C. or higher. Then, the low-temperature oxidation catalyst is fixed to the substrate wall surface (4) with a caking component. Prepare precursor fine particles in which fine particles of noble metal hydroxide and fine particles of transition metal hydroxide are supported on the surface of oxide fine particles,
Prepare the coating solution by mixing the precursor fine particles and the binder,
After applying the above coating liquid to the inner surface of each ventilation path (3) of a metal base (2) having a large number of ventilation paths (3) provided in the thickness direction, heat treatment is performed at 250 ° C. or higher. Then, the precursor fine particles are converted into a low-temperature oxidation catalyst in which noble metal fine particles and transition metal oxide fine particles are supported on the surface of the oxide fine particles, and the low-temperature oxidation catalyst is bonded to the substrate wall surface with a caking component. (4) It fixes to (4), The manufacturing method of a metal filter characterized by the above-mentioned.   The method for producing a metal filter according to claim 10 or 11, wherein the binder contains at least one of a metal oxide or silica sol or gel and a fluoropolymer emulsion.

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