Platinum-supported catalyst, air purification system and air purification method

Abstract

To provide a novel platinum-supported catalyst, and an air cleaning system and an air cleaning method using the platinum-supported catalyst.SOLUTION: Provided are: a platinum-supported catalyst in which platinum nanoparticles with a particle size of 10 nm or less are uniformly supported on the surface of a porous carrier with an apparent volume of 5 mm3 or more; an air cleaning system that has a first cleaning unit including a platinum-supported catalyst that converts chemical substance in the air into intermediate product, and a second cleaning unit including a photocatalyst that decomposes the intermediate product into a final product containing carbon dioxide and water; and an air cleaning method comprising a step of converting chemical substance in the air into another compound using a platinum-supported catalyst.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a platinum-supported catalyst, and an air purification system and an air purification method that utilize the platinum-supported catalyst. [Background technology]

[0002] Semiconductor devices, displays, micromachines, thin coating films, etc. are manufactured in clean rooms where the number of particles in the gas, temperature, humidity, etc. are controlled during manufacturing and inspection. These products are processed with nano-level control, and in order to prevent adverse effects during processing, it is sometimes necessary to reduce the concentration of chemical substances in the atmosphere. For example, in the semiconductor manufacturing process, if a wafer is contaminated with chemical substances, it can affect the coatability of the resist, causing changes in the film thickness of the resist and the adhesion between the resist and the wafer, making it impossible to achieve the desired processing accuracy and resulting in a decrease in yield.

[0003] When it is necessary to control the concentration of chemical substances in the atmosphere, chemical filters based on activated carbon are usually used. Because chemical filters adsorb chemical substances, they need to be replaced before they break through (the amount of adsorption is saturated), which requires time and cost to maintain, and there is also a risk of dust being generated during replacement.

[0004] The present inventors have reported that isopropyl alcohol is oxidized to produce acetone as a secondary product without UV irradiation using a hybrid catalyst in which platinum is supported on titanium dioxide pellets by impregnation (Non-Patent Documents 1 and 2). [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Maki Ichihara, Hirofumi Horada, Yoshihide Wakayama, Hironori Taki, Yuji Saito, "Possibility study of VOC decomposition using hybrid catalysts", Taisei Corporation Technology Center Report, No. 52 (2019) [Non-Patent Document 2] Maki Ichihara, Hirofumi Horada, Yoshihide Wakayama, Hironori Taki, Yuji Saito, "Examination of the possibility of VOC decomposition in a lightless environment using hybrid catalysts", Proceedings of the Architectural Institute of Japan, University Academic Lecture Series, 2019, p919-920 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a novel platinum-supported catalyst, and an air purification system and an air purification method that utilize this platinum-supported catalyst. [Means for solving the problem]

[0007] The means for solving the problems of the present invention are as follows. 1. Apparent volume 5mm 3 A platinum supported catalyst, characterized in that platinum nanoparticles having a particle size of 10 nm or less are uniformly supported on the surface of the above-mentioned porous support. 2. The platinum supported catalyst according to 1, wherein the amount of platinum supported is 0.005% by weight or more and 1.2% by weight or less. 3. The BET specific surface area of ​​the porous carrier as determined by nitrogen adsorption is 20 m 2 3. The supported platinum catalyst according to 1 or 2, wherein the supported platinum content is 1 / g or more. 4. The platinum-supported catalyst according to any one of 1. to 3., wherein the porous carrier is titanium dioxide having photocatalytic activity. 5. An air purification system comprising a purification device equipped with the platinum supported catalyst according to any one of 1. to 4. above, which converts chemical substances in the air into intermediate products. 6. The air purification system according to claim 5, wherein the purification device processes isopropyl alcohol or propylene glycol monomethyl ether acetate. 7. The air purification system according to claim 5 or 6, further comprising a second purification device equipped with a photocatalyst that decomposes the intermediate product into a final product containing carbon dioxide and water. 8. An air purification method comprising a step of converting chemical substances in the air into other chemical substances using the platinum-supported catalyst according to any one of 1. to 4. Effect of the Invention

[0008] In the impregnation method, platinum is precipitated by heat treatment, but it precipitates first on the outside where heat is transmitted, and then on the inside as heat is transmitted, resulting in an uneven distribution of platinum particles. In addition, platinum precipitated on the outside may aggregate and block the pores. In contrast, the platinum-supported catalyst of the present invention has excellent reactivity because active sites are uniformly present on its surface and the pores are not blocked by platinum. Furthermore, the platinum-supported catalyst of the present invention adsorbs and concentrates chemical substances in the pores of the porous carrier, and the platinum supported in the pores reacts with the chemical substances concentrated in the pores, so that even low-concentration chemical substances can be efficiently treated. The platinum-supported catalyst of the present invention has excellent handleability because the carrier is not powdery, and it is easy to incorporate into air conditioning units and the like, and to recover after use. In addition, hybrid catalysts produced by the impregnation method require approximately 2 to 5% by weight of platinum, making them expensive, but the platinum-supported catalyst of the present invention supports platinum nanoparticles with a particle size of 10 nm or less, so that even a small amount of support can provide sufficient catalytic performance, making it low cost.

[0009] The air purification system of the present invention using this platinum-supported catalyst can decompose chemical substances in the air into intermediate products, and further decompose them into final products containing carbon dioxide and water by combining with a photocatalyst. The air purification system of the present invention can convert chemical substances into intermediate products that are easily decomposed by the platinum-supported catalyst, so that the amount of catalyst can be reduced compared to the case where only a photocatalyst is used, and a low volume and low cost can be achieved. The air purification system of the present invention can be installed in the piping of an existing air conditioner. Since the air purification system of the present invention can decompose various chemical substances, it can be suitably used for air purification in clean rooms for semiconductor devices, displays, etc. It can also be suitably used for treating exhaust gas containing chemical substances generated from chemical plants, printing plants, etc. [Brief description of the drawings]

[0010] [Figure 1] 1 is a schematic diagram of an embodiment of an air purification system. [Diagram 2] SEM image of platinum-supported catalyst 1. [Diagram 3] Graph showing the change in isopropyl alcohol and acetone concentration over time when isopropyl alcohol is decomposed by platinum-supported catalyst 1. [Figure 4] Graph showing the change in isopropyl alcohol and acetone concentration over time when isopropyl alcohol is decomposed by platinum-supported catalyst 2. [Diagram 5] 1 is a graph showing the change in the concentration of isopropyl alcohol and acetone over time when isopropyl alcohol is decomposed using a multi-platinum supported catalyst 3. [Figure 6] Spectrum of PGMEA decomposition using platinum-supported catalyst 1. [Figure 7] Graph showing the change in isopropyl alcohol and acetone concentration over time when isopropyl alcohol is decomposed by platinum-supported catalyst 1. [Figure 8] 1 is a graph showing the change in the concentration of isopropyl alcohol and acetone over time when isopropyl alcohol is decomposed by a platinum-supported catalyst 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Platinum supported catalyst The platinum-supported catalyst has an apparent volume of 5 mm 3 Platinum nanoparticles with a particle size of 10 nm or less are uniformly supported on the surface of the porous carrier. The apparent volume means the volume including the porous part of the porous carrier. 3 The above porous carriers are not as fine as powders, making them easy to handle, and they can be easily incorporated into air conditioning units and collected after use. 3 If the volume is more than 5 mm, dust is unlikely to be generated, and the device can be suitably used to supply clean air to clean rooms.3 There is no particular limitation as long as it is more than 10 mm 3 If the apparent volume is too large, the gaps between the carriers become large, and it becomes difficult for the gas to reach the inside of the porous carrier. Therefore, the apparent volume of the porous carrier is preferably 8000 mm or more. 3 It is preferable that the length is less than 4000 mm. 3 It is more preferable that:

[0012] The BET specific surface area of ​​the porous carrier used in the present invention by nitrogen adsorption is 20 m 2 / g or more, and 2 / g or more is more preferable. The larger the BET specific surface area, the higher the reactivity, but the lower the strength and the more brittle the material becomes, and the more likely it is to break and generate dust. Therefore, when the material is used to supply clean air to a clean room where it is required to suppress the generation of dust, the BET specific surface area should be 200 m 2 / g or less, and 2 It is more preferable that the molecular weight is not more than 1 / g. The material of the porous carrier is not particularly limited, and examples thereof include metal oxides such as titanium oxide, aluminum oxide, silicon oxide, and iron oxide, carbon, etc. By using titanium dioxide having photocatalytic activity, it is possible to exhibit photocatalytic activity in addition to the catalytic activity with platinum as the active site.

[0013] The particle size of platinum nanoparticles can be obtained by calculating the equivalent circle diameter from an electron microscope image obtained by imaging the surface. Of 100 or more platinum nanoparticles obtained by screen processing of the electron microscope image, those with a particle size (equivalent circle diameter) of 10 nm or less are preferably 90% or more, more preferably 95% or more, even more preferably 99% or more, and most preferably 100%. In addition, it can be confirmed from this electron microscope image whether the platinum nanoparticles are uniformly supported on the surface. In the present invention, the number of platinum nanoparticles present in any three or more regions of 200 nm x 200 nm or more in the electron microscope image is preferably within ±20% of the average value, more preferably within ±10%, and even more preferably within ±5%. Furthermore, the platinum supported catalyst can be crushed and the pores exposed on the cross section observed with an electron microscope image to confirm the platinum nanoparticles supported on the pore surface.

[0014] The platinum-supported catalyst of the present invention can be used in various reactions without any particular limitation as long as the reaction is promoted by this catalyst. For example, hydrogenation reactions, dehydrogenation reactions, oxidation reactions of chemical substances such as ethanol, isopropyl alcohol, ethyl acetate, propylene glycol monomethyl ether (PGME), propylene glycol monomethyl ether acetate (PGMEA), toluene, and ammonia, and oxidation reactions of inorganic compounds such as CO can be mentioned. In the platinum-supported catalyst of the present invention, chemical substances are adsorbed in the pores of the porous support, so that the chemical substances are concentrated in the pores. In the platinum-supported catalyst of the present invention, platinum nanoparticles are supported not only on the surface but also in the pores, and the platinum nanoparticles supported in the pores act on the chemical substances concentrated in the pores, so that the catalyst can efficiently react with low-concentration chemical substances.

[0015] - Manufacturing method of platinum supported catalyst In the platinum-supported catalyst of the present invention, platinum nanoparticles having a particle size of 10 nm or less are uniformly supported on the surface of a porous support. Such a platinum-supported catalyst can be produced, for example, by a radiation method. The radiation method is a method in which an aqueous metal ion solution (an aqueous platinum ion solution in the present invention) in which a support is dispersed is irradiated with radiation, the metal ions are reduced by reducing species generated by radiolysis of water, nanoparticles are precipitated, and the precipitated nanoparticles are supported on the support. The nanoparticles are uniformly precipitated by the radiation method, and the precipitated nanoparticles are uniformly supported on the surface of the support.

[0016] The radiation used is not particularly limited, but in view of transparency and safety, it is preferable to use gamma rays, X-rays, or electron beams. Radiation can be irradiated under conditions of an absorbed dose of 1 J / kg or more, preferably 1 J / kg or more and 1,000,000 J / kg or less. In particular, when gamma rays are used as the ionizing radiation, it is preferable to irradiate with gamma rays under conditions of a dose of 1 Gy or more. A specific example of a preferable gamma ray irradiation is one in which a cobalt-60 gamma ray source (energy of gamma ray photon: 1.25 MeV) is used as the radiation source, and the irradiation is carried out under conditions of a dose rate of about 3 kGy / h and an irradiation time of 1 to 18 hours.

[0017] In the platinum-supported catalyst of the present invention, the amount of platinum supported on the porous carrier can be adjusted by the platinum concentration in the platinum ion aqueous solution, radiation intensity, radiation exposure time, etc. The platinum-supported catalyst of the present invention can uniformly support platinum nanoparticles, so that the amount of platinum is high. The amount of platinum in the platinum-supported catalyst of the present invention is preferably 1.2 wt% or less, more preferably 1.0 wt% or less, and even more preferably 0.8 wt% or less. The lower limit of the amount of platinum is not particularly limited as long as it exhibits catalytic activity, but is preferably 0.005 wt% or more, and preferably 0.01 wt% or more.

[0018] Air Purification System The air purification system of the present invention has a purification device equipped with a platinum-supported catalyst that converts chemical substances in the air into intermediate products. The air purification system of the present invention can have a second purification device downstream of the purification device equipped with the platinum-supported catalyst, the second purification device equipped with a photocatalyst that decomposes the intermediate products generated in the purification device into final products containing carbon dioxide and water. The photocatalyst used in the second purification device can be any known photocatalyst without any particular restrictions, but is preferably a porous titanium dioxide body. The porous body can adsorb and concentrate the intermediate product in the pores, allowing for efficient decomposition. The porous titanium dioxide body has an apparent volume of 5 mm, similar to the porous carrier of the platinum-supported catalyst. 3 The upper limit is preferably 8000 mm or more. 3 It is preferable that the length is less than 4000 mm. 3 It is more preferable that the BET specific surface area by nitrogen adsorption is 20 m or less. 2 / g or more, and 2 / g or more is more preferable, and 200m 2 / g or less, and 2 / g or less is more preferable. In addition, by using titanium dioxide having photocatalytic activity as a porous carrier for the platinum-supported catalyst, the air purification system of the present invention can integrate a purification device using platinum as an active site and a second purification device using a photocatalyst.

[0019] FIG. 1 shows a schematic diagram of one embodiment of an air purification system of the present invention. An air purification system 1 according to one embodiment is installed in an air conditioning system of a clean room. Air containing isopropyl alcohol (IPA) in the clean room is taken in through a ventilation duct (RA), some of it is exhausted, and the rest is mixed with outside air in an air handling unit (AHU) where the temperature, humidity, etc. are adjusted, and then purified in an air purification system 1. The air purification system 1 has a first purification device 11 equipped with a platinum supported catalyst, and a second purification device 12 equipped with a photocatalyst. IPA is converted into acetone (ACT) in the first purification device 11, and the acetone is decomposed into carbon dioxide and water in the second purification device 12. The air from which IPA has been removed in the air purification system 1 is returned to the clean room through a return air duct (SA) after foreign matter has been removed by a HEPA filter.

[0020] The air purification system of the present invention is equipped with a first purification device equipped with a platinum-supported catalyst upstream of a second purification device equipped with a photocatalyst, and since the first purification device converts chemical substances into intermediate products in advance, it has superior purification performance compared to air purification systems that decompose chemical substances into final products using only photocatalysts.The air purification system of the present invention requires a small amount of catalyst per unit time of the flow rate of the gas to be purified, so the purification system can be made smaller in capacity and at lower cost. EXAMPLES

[0021] "Example 1" A porous support made of titanium dioxide (Evonik, Aerolyst 7711, apparent volume 11.3 mm 3 (φ1.7mm×5mm cylinder), BET specific surface area 35~55m 2 2.0 g of the catalyst (100 mL) was dispersed in 100 mL of an aqueous solution containing platinum ions (HPtCl: 1 mM, isopropyl alcohol: 1 vol%), and argon gas was bubbled through the catalyst for 15 minutes, after which the catalyst was evacuated to fill the pores with the aqueous solution. The catalyst was then irradiated with gamma rays from a cobalt-60 gamma ray source (25 kGy, 2.5 hours → 15 kGy, 1.5 hours) while stirring, yielding platinum-supported catalyst 1. The amount of platinum supported was approximately 0.2% by weight.

[0022] "Comparative Example 1" 10 g of a porous support made of titanium oxide (Evonik, Aerolyst7711) was dispersed in 100 mL of an aqueous solution containing platinum ions (H2PtCl6:1 mM), and after bubbling with argon gas for 15 minutes, the solution was filled into the pores by vacuuming. After removing excess aqueous solution by filtration, the catalyst was calcined at 500°C for 2 hours in a 5% hydrogen gas atmosphere to obtain platinum-supported catalyst 2. The amount of platinum supported was about 0.2% by weight.

[0023] "Comparative Example 2" A support made of titanium dioxide powder (CIK Nano Tek Co., Ltd., Nano Tek TiO2, spherical particles with an average particle size of approximately 50 nm and a bulk density of 0.33 g / cm 3 , BET specific surface area 50m 2 %. The platinum-supported catalyst 3 was obtained in the same manner as in Example 1, except that 100% by weight of platinum was used instead of 100% by weight of 100% by weight of the catalyst.

[0024] SEM observation The surface of the produced platinum-supported catalyst 1 was observed by SEM. Figure 2 shows the SEM image. It was confirmed that platinum nanoparticles with a particle size of 10 nm or less are uniformly supported on the surface of the porous support in platinum-supported catalyst 1. Note that platinum-supported catalyst 3 was produced by the same radiation method as platinum-supported catalyst 1, and therefore it is presumed that platinum nanoparticles with a particle size of 10 nm or less are uniformly supported on the support surface.

[0025] Experiment 1: IPA decomposition 0.1 g of each of the platinum-supported catalysts 1 to 3 was placed in a 100 mL vial, and isopropyl alcohol (IPA) was added to the vial to give a concentration of 65.8 μmol / L. After 90 minutes had passed since the addition, the vial was irradiated with UV (253.7 nm) for 30 minutes. After 30 minutes, 60 minutes, 90 minutes, 3 hours, and 24 hours had passed since the injection, the gas in the vial was extracted with a syringe, and the concentrations of isopropyl alcohol (IPA) and acetone (ACT) were measured using a gas chromatograph (Shimadzu Corporation, GC-2014, detector FID). The results are shown in Figures 3 to 5.

[0026] For platinum-supported catalyst 3, the IPA concentration decreased for 60 minutes after injection, but there was almost no change thereafter, and IPA was still detected at a high concentration 24 hours after injection. Acetone was only detected after UV irradiation, and its concentration did not change without UV irradiation. This confirmed that platinum-supported catalyst 3 only adsorbs IPA, and that decomposition of IPA does not proceed without UV irradiation.

[0027] In the case of the platinum supported catalyst 1 of the present invention, 30 minutes after injection, IPA was not detected, but a high concentration of acetone was detected. In the case of the platinum-supported catalyst 2, IPA was no longer detected 3 hours after injection. Acetone was detected 30 minutes after injection, but the acetone concentration was lower than that in Example 1 and gradually increased over time, but did not reach that of Example 1.

[0028] Experiment 2: PGMEA decomposition 0.1 g of platinum-supported catalyst 1 was placed in a 100 ml vial, and propylene glycol monomethyl ether acetate (PGMEA) was injected to a concentration of 367 μmol / L. 48 hours after injection, the gas in the vial was extracted with a syringe and analyzed using a gas chromatograph (Shimadzu Corporation, GC-2014, detector FID). The results are shown in Figure 6. Low molecular weight compounds other than PGMEA were detected, which confirmed that platinum-supported catalyst 1 was able to decompose PGMEA and produce some chemical substances.

[0029] 0.02 g of platinum-supported catalyst 1 was placed in a 20 mL vial, and propylene glycol monomethyl ether acetate (PGMEA) was injected to a concentration of 184 μmol / L. Seven hours after injection, the mixture was analyzed using a gas chromatograph mass spectrometer (Shimadzu Corporation, GCMS-QP2010) to detect propylene glycol monomethyl ether (PGME). 0.1 g of platinum supported catalyst 1 was placed in a 100 ml vial, and propylene glycol monomethyl ether acetate (PGMEA) was added to make the concentration 367 μmol / L. 48 hours after the injection, 3 ml of ultrapure water was added, and after 4 hours, acetic acid was detected when the mixture was analyzed by high performance liquid chromatography (Waters 2965, etc.).

[0030] From this, it was confirmed that the platinum-supported catalyst 1 decomposed PGMEA to produce PGME and acetic acid as intermediate products.

[0031] "Example 2" Except for changing the platinum ion concentration in the platinum ion-containing aqueous solution to 1 / 10 of that in Example 1 (HPtCl: 0.1 mM) and not performing argon gas bubbling or evacuation, gamma rays were irradiated in the same manner as in Example 1 to obtain platinum-supported catalyst 4. The amount of platinum supported was about 0.02% by weight.

[0032] Experiment 3: IPA decomposition 0.1 g of each of the platinum-supported catalysts 1 and 4 was placed in a 100 mL vial, and isopropyl alcohol (IPA) was added to the vial to give a concentration of 24.4 μmol / L. Immediately after the addition, the vial was irradiated with UV (253.7 nm). The gas in the vial was extracted with a syringe at 8-minute intervals from 2 minutes after injection until 58 minutes, and then at 90 minutes, 120 minutes, 150 minutes, and 180 minutes, and the concentrations of isopropyl alcohol (IPA) and acetone (ACT) were measured using a gas chromatograph (Shimadzu Corporation, GC-2014, detector FID). The results are shown in Figures 6 and 7.

[0033] The platinum-supported catalyst 4 prepared in Example 2 had catalytic activity equivalent to that of the platinum-supported catalyst 1, even though it was not subjected to argon gas replacement or vacuum drawing during production and the amount of platinum supported was only 0.02 wt %. [Explanation of symbols]

[0034] 1. Air Purification System 11 First Purification Device 12 Second Purification Device

Claims

1. Apparent volume 5mm ３ The surface of the porous carrier is supported with platinum nanoparticles having a particle size of 10 nm or less, The porous support is composed only of a metal oxide, The platinum nanoparticles are characterized in that the number of platinum nanoparticles present in any three or more regions of 200 nm x 200 nm or more in an electron microscope image is within ±20% of the average value.

2. 2. The platinum supported catalyst according to claim 1, wherein the amount of platinum supported is 0.005% by weight or more and 1.2% by weight or less.

3. The porous carrier has a BET specific surface area of ​​20 m2 as determined by nitrogen adsorption. ２ 3. The platinum supported catalyst according to claim 1, wherein the platinum supported catalyst has a molecular weight of 1 / g or more.

4. 4. The platinum supported catalyst according to claim 1, wherein the porous carrier is titanium dioxide having photocatalytic activity.

5. 5. An air purification system comprising a purification device comprising the platinum supported catalyst according to any one of claims 1 to 4, which converts chemical substances in the air into intermediate products.

6. 6. The air purification system of claim 5, wherein the purification device processes isopropyl alcohol or propylene glycol monomethyl ether acetate.

7. 7. The air purification system according to claim 5, further comprising a second purification device equipped with a photocatalyst for decomposing the intermediate products into final products including carbon dioxide and water.

8. 5. An air purification method comprising a step of converting chemical substances in the air into other chemical substances by using the platinum supported catalyst according to claim 1.

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