JP7615436B2 - Platinum-supported catalyst, air purification system and air purification method - Google Patents

Description

The present invention relates to a platinum-supported catalyst, and an air purification system and air purification method that utilize this platinum-supported catalyst.

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.

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 becomes saturated), which requires time and money to maintain, and there is also a risk of dust being generated when replacing them.

The inventors have reported that a hybrid catalyst in which platinum is supported on titanium dioxide pellets by impregnation oxidizes isopropyl alcohol without UV irradiation to produce acetone as a secondary product (Non-Patent Documents 1 and 2).

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) Maki Ichihara, Hirofumi Horada, Yoshihide Wakayama, Hironori Taki, Yuji Saito, "Examination of the possibility of VOC decomposition in a lightless environment using hybrid catalysts", Abstracts of the Architectural Institute of Japan University Academic Lectures, 2019, pp. 919-920

The objective of the present invention is to provide a novel platinum-supported catalyst and an air purification system and air purification method that utilize this platinum-supported catalyst.

The means for solving the problems of the present invention are as follows.
1. 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 a porous support having an apparent volume of 5 mm3 or ^more .
2. The platinum supported catalyst according to 1., characterized in that the amount of platinum supported is 0.005% by weight or more and 1.2% by weight or less.
3. The platinum supported catalyst according to 1. or 2., wherein the porous carrier has a BET specific surface area determined by nitrogen adsorption of 20 m ² /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 5., wherein the purification device processes isopropyl alcohol or propylene glycol monomethyl ether acetate.
7. The air purification system according to 5. or 6., further comprising a second purification device equipped with a photocatalyst that decomposes the intermediate product into an end 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.

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, etc., and to recover after use. In addition, hybrid catalysts produced by the impregnation method require about 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 it can exert sufficient catalytic activity even with a small amount of support, making it low cost.

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 the amount of catalyst can be reduced compared to when only a photocatalyst is used, achieving low volume and low cost. 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 purifying air 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.

1 is a schematic diagram of an embodiment of an air purification system. SEM image of platinum supported catalyst 1. Graph showing the change in isopropyl alcohol and acetone concentration over time when isopropyl alcohol is decomposed by platinum supported catalyst 1. Graph showing the change in isopropyl alcohol and acetone concentration over time when isopropyl alcohol is decomposed by platinum supported catalyst 2. Graph showing the change in isopropyl alcohol and acetone concentration over time when isopropyl alcohol is decomposed by a multiplatinum supported catalyst 3. Spectrum of PGMEA decomposition using platinum supported catalyst 1. Graph showing the change in isopropyl alcohol and acetone concentration over time when isopropyl alcohol is decomposed by platinum supported catalyst 1. Graph showing the change in isopropyl alcohol and acetone concentration over time when isopropyl alcohol is decomposed by a platinum supported catalyst 4.

Platinum-supported catalyst The platinum-supported catalyst is a catalyst in which platinum nanoparticles having a particle size of 10 nm or less are uniformly supported on the surface of a porous carrier having an apparent volume of 5 mm ³ or more. The apparent volume means the volume including the porous part of the porous carrier. A porous carrier having an apparent volume of 5 mm ³ or more is not as fine as a powder, so it is easy to handle and can be easily incorporated into an air conditioning unit or collected after use. In addition, if the apparent volume is 5 mm ³ or more, dust is unlikely to be generated, so it can be suitably used to supply clean air to a clean room. The apparent volume is not particularly limited as long as it is 5 mm ³ or more, but it is preferably 10 mm ³ or more. If the apparent volume is too large, the gap between the carriers will become large, and it will be difficult for the gas to reach the inside of the porous carrier. Therefore, the apparent volume of the porous carrier is preferably 8000 mm ³ or less, and more preferably 4000 mm ³ or less.

The BET specific surface area by nitrogen adsorption of the porous carrier used in the present invention is preferably 20 m ² /g or more, more preferably 30 m ² /g or more, from the viewpoint of reactivity. The larger the BET specific surface area, the higher the reactivity, but the lower the strength and the more brittle the carrier becomes, so that it is more likely to break and generate dust. Therefore, when used to supply clean air to a clean room where it is required to suppress the generation of dust, the BET specific surface area is preferably 200 m ² /g or less, more preferably 100 m ² /g or less.
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.

The particle size of platinum nanoparticles can be determined by calculating the equivalent circle diameter from an electron microscope image obtained by imaging the surface. Of the 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 nanoparticles supported on the pore surface can be confirmed by crushing the platinum-supported catalyst and observing the pores exposed on the cross section with an electron microscope image.

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 the catalyst, for example, hydrogenation reaction, dehydrogenation reaction, oxidation reaction 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 reaction of inorganic compounds such as CO, etc.
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.

- 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 manufactured, for example, by a radiation method. The radiation method is a method in which a metal ion aqueous solution (a platinum ion aqueous 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. Nanoparticles are uniformly precipitated by the radiation method, and the precipitated nanoparticles are uniformly supported on the surface of the support.

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 a gamma ray 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.

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, the radiation intensity, the radiation exposure time, etc. The platinum-supported catalyst of the present invention can support platinum nanoparticles uniformly, so that it has high activity even with a small amount of platinum. 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. In addition, 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.

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 a 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 purifier can be any conventionally known photocatalyst without any particular limitations, but is preferably a titanium dioxide porous body. The porous body can adsorb and concentrate the intermediate product in the pores, so that it can be decomposed efficiently. The titanium dioxide porous body preferably has an apparent volume of 5 mm ³ or more, and the upper limit is preferably 8000 mm ³ or less, and more preferably 4000 mm ³ or less, like the porous carrier of the platinum-supported catalyst. In addition, the BET specific surface area by nitrogen adsorption is preferably 20 m ² /g or more, more preferably 30 m ² /g or more, preferably 200 m ² /g or less, and more preferably 100 m ² /g or less. In addition, the air purification system of the present invention can also integrate the purification device using platinum as an active site and the second purification device using a photocatalyst by using titanium dioxide having photocatalytic ability as the porous carrier of the platinum-supported catalyst.

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), a portion of it is exhausted, and the remainder is mixed with outside air in an air conditioner (AHU) to adjust the temperature, humidity, etc., and then purified by 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 by the air purification system 1 is returned to the clean room through a return air duct (SA) after foreign matter is removed by a HEPA filter.

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, making it possible to reduce the capacity and cost of the purification system.

"Example 1"
2.0 g of a porous support made of titanium dioxide (Evonik, Aerolyst 7711, apparent volume 11.3 mm ³ (φ1.7 mm × 5 mm cylinder), BET specific surface area 35-55 m ² /g) was dispersed in 100 mL of an aqueous solution containing platinum ions (H ₂ PtCl ₆ : 1 mM, isopropyl alcohol: 1 vol%), and after bubbling with argon gas for 15 minutes, the solution was filled into the pores by evacuation. Thereafter, the mixture was irradiated with gamma rays from a cobalt 60 gamma ray source (25 kGy, 2.5 hours → 15 kGy, 1.5 hours) while stirring, to obtain platinum-supported catalyst 1. The amount of platinum supported was about 0.2 wt%.

"Comparative Example 1"
10 g of a porous support made of titanium oxide (Evonik, Aerolyst 7711) was dispersed in 100 mL of an aqueous solution containing platinum ions (H ₂ PtCl ₆ : 1 mM), and argon gas was bubbled for 15 minutes, after which the solution was evacuated to fill the pores. After filtering to remove excess aqueous solution, 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.

"Comparative Example 2"
A platinum-supported catalyst 3 was obtained in the same manner as in Example 1, except that a carrier made of titanium dioxide powder (CIK Nano Tek Co., Ltd., Nano Tek TiO ₂ , spherical particles with an average particle diameter of about 50 nm, bulk density of 0.33 g/cm ³ , BET specific surface area of 50 m ² /g) was used. The amount of platinum supported was about 1 wt %.

SEM Observation The surface of the produced platinum-supported catalyst 1 was observed by SEM. FIG. 2 shows an SEM image.
It was confirmed that platinum nanoparticles with a particle size of 10 nm or less were uniformly supported on the surface of the porous carrier 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 were uniformly supported on the carrier surface.

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 poured in to give a concentration of 65.8 μmol/L. After 90 minutes had passed since the pouring, the mixture was irradiated with UV (253.7 nm) for 30 minutes.
30 minutes, 60 minutes, 90 minutes, 3 hours, and 24 hours after 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.

Platinum-supported catalyst 3 showed a decrease in IPA concentration for 60 minutes after injection, but there was little 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.

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.

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. After 48 hours had passed since the 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 FIG. 6.
Low molecular weight compounds other than PGMEA were detected. This confirmed that the platinum supported catalyst 1 was able to decompose PGMEA and generate some chemical substances.

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 the 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 poured in to give a concentration of 367 μmol/L. 48 hours after the pouring, 3 ml of ultrapure water was added, and after 4 hours, analysis was performed by high performance liquid chromatography (Waters 2965 or the like), whereby acetic acid was detected.

From this, it was confirmed that platinum-supported catalyst 1 decomposed PGMEA, producing PGME and acetic acid as intermediate products.

"Example 2"
Except for changing the platinum ion concentration in the platinum ion-containing aqueous solution to 1/10 of that in Example 1 (H ₂ PtCl ₆ : 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 wt %.

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 poured therein to a concentration of 24.4 μmol/L. Immediately after the pouring, the mixture 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.

The platinum-supported catalyst 4 produced in Example 2 had catalytic activity equivalent to that of platinum-supported catalyst 1, even though argon gas replacement and vacuum drawing were not performed during production and the amount of platinum supported was only 0.02% by weight.

1 Air purification system 11 First purification device 12 Second purification device

Claims (8)

A porous carrier having an apparent volume of 5 mm3 or ^more has platinum nanoparticles with a particle size of 10 nm or less supported on its surface ,
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 . The platinum-supported catalyst according to claim 1, characterized in that the amount of platinum supported is 0.005% by weight or more and 1.2% by weight or less. 3. The platinum supported catalyst according to claim 1, wherein the porous carrier has a BET specific surface area determined by nitrogen adsorption of 20 m ² /g or more. The platinum-supported catalyst according to any one of claims 1 to 3, characterized in that the porous carrier is titanium dioxide having photocatalytic properties. An air purification system having a purification device equipped with a platinum-supported catalyst according to any one of claims 1 to 4, which converts chemical substances in the air into intermediate products. The air purification system of claim 5, characterized in that the purification device processes isopropyl alcohol or propylene glycol monomethyl ether acetate. The air purification system according to claim 5 or 6, characterized in that it has a second purification device equipped with a photocatalyst that decomposes the intermediate product into a final product containing carbon dioxide and water. 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 claims 1 to 4.