JP2003220341A - Method for treating photocatalyst body and nitrogen oxide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photocatalyst body which has a higher photocatalytic action than that of conventional ones. <P>SOLUTION: In order to improve the photocatalytic ability of the photocatalyst body, this photocatalyst body has a structure where a photocatalyst is carried in pores formed in a transparent base material so as to be oriented in a prescribed direction and fluid to be treated passes through the pores. By having the structure where the fluid to be treated passes through the pores carrying photocatalytic fine particles, the oxidation and decomposition reaction of adsorbed components to be treated proceeds also in the pores. As the photocatalyst body has the structure where the fluid to be treated passes through the pores sequentially, the desorption of intermediate reactants in the middle of the oxidation and decomposition reaction can be inhibited, so that the reaction can proceed more completely. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photocatalyst body, and more particularly to a photocatalyst body for chemically decomposing and removing odorous components, exhaust gas components, impurities and the like in the air or water. The present invention also relates to a method of treating nitrogen oxide with the photocatalyst.

[0002]

2. Description of the Related Art A photocatalyst is a substance which absorbs light and gives its energy to a reaction product which does not absorb light to cause a reaction, and by utilizing this principle, for example, oxidation of an organic compound or an unsaturated compound. Attempts have been made to produce photocatalysts having various applications such as organic synthesis such as hydrogenation of methane, removal and decomposition of harmful chemical substances in waste liquid and exhaust gas. Further, by utilizing the same action, application to a bactericidal action or an antifouling action for decomposing stains has been attempted.

As the photocatalyst, a photocatalyst such as titanium oxide is used in a thin film so that it can receive ultraviolet rays well, or as disclosed in JP-A-10-151355, pores having a pore diameter of 2 to 50 nm. Coating or carrying a photocatalyst on a porous body made of silica having a silane, or a photocatalyst sheet carrying a light catalyst on a mesh or on a perforated support substrate as disclosed in JP-A-2000-51334. As disclosed in Japanese Patent Application Laid-Open No. 2000-157864, titania is coated on the surfaces of silica fibers and reinforcing fibers. In addition, there are some which use an adsorbent in combination with a photocatalyst.

By using these photocatalysts, relatively low concentrations of environmental pollutants such as nitrogen oxides diffused in the environment can be decomposed and removed at low cost by the photocatalyst using light energy as a main driving force. it can.

[0005]

However, it has been difficult to say that the conventional photocatalyst has a sufficient photocatalytic action.

Therefore, it is an object of the present invention to provide a photocatalyst having a higher photocatalytic action than the conventional one.

Another object of the present invention is to provide a method for treating nitrogen oxides using the photocatalyst.

[0008]

In order to solve the above problems, the inventors of the present invention have conducted diligent research on the reason why conventional photocatalysts cannot exhibit sufficient photocatalytic activity. Mainly used, surface roughness,
There is a limit to the unevenness and shape of the device, and because activated carbon is used as the adsorbent, the activated carbon does not transmit light, so the photocatalytic activity is reduced by that amount, and the activated carbon is consumed by being oxidatively decomposed and transparent. Regarding the use of the body, it is limited to the treatment on the surface, the use of glass beads, the use of the porous body is used as a simple carrier of a photocatalyst such as titanium oxide, the use of the pores is silica gel, Although a zeolite mixture has been used, it has been found that it is difficult to secure sufficient continuous reaction time (contact time) and reaction field due to constant adsorption of reactants.

Therefore, based on these findings, the present inventors support the photocatalyst in the pores formed in the transparent substrate and oriented in a predetermined direction in order to improve the photocatalytic activity of the photocatalyst. The inventor has invented a photocatalyst having a structure that allows a fluid to be processed to pass through the pores.

That is, by adopting a structure in which the fluid to be treated passes through the pores carrying the photocatalyst fine particles, the oxidation and decomposition reaction of the adsorbed components to be treated can proceed even in the pores. Further, since the fluid to be treated has a structure in which it sequentially passes through the pores, the separation of the intermediate reactant during the oxidation and decomposition reaction can be suppressed, and the oxidation and decomposition can proceed more completely.

For example, when NO is oxidized to NO ₃ ⁻ by a photocatalyst, N which is not preferable as an intermediate product.
O ₂ is produced, but it was observed that some of the intermediate NO ₂ was leaked in the conventional photocatalyst that is oxidized and decomposed only by the reaction on the surface. In the photocatalyst of the present invention which causes a reaction, leakage of intermediate products can be suppressed to a minimum.

Further, it can be expected that an effect of adsorbing an oxidation product to some extent can be expected in the vicinity of the latter stage of the pores, and that a final oxidation product can be retained without being discharged to the outside of the system.

By the way, the conventional removal of nitrogen oxides by a photocatalyst using titanium oxide or the like is applied in a room temperature environment, and the oxidation reaction of nitrogen oxides to nitric acid is dominant. Further, when the reducing agent was not added, even if the fluid to be treated was heated, the treatment reaction of the nitrogen oxide was not promoted by heat, and the photocatalytic reaction by light such as ultraviolet rays was dominant.

Therefore, as a result of intensive studies on the method for treating nitrogen oxides with a photocatalyst, the present inventors have obtained the following findings for the purpose of solving the above problems.

That is, the present inventors have studied various additives for the purpose of promoting the decomposition of nitrogen oxides, and as a result, by adding a reducing agent to the fluid to be treated, decomposition of nitrogen oxides at room temperature is promoted. I was found to be done. It was also found that when a reducing agent is added to the fluid to be treated, the decomposition and removal of nitrogen oxides can be promoted by raising the temperature of the fluid to be treated. The following inventions have been completed based on the above findings.

The method for treating nitrogen oxides of the present invention is a method for treating nitrogen oxides, in which a fluid to be treated containing nitrogen oxides is introduced and treated from the one side of the photocatalyst. In the present invention, in the method for treating nitrogen oxide, the reducing agent is added to the fluid to be treated before being introduced into the photocatalyst.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION [Photocatalyst] The photocatalyst of the present invention comprises a transparent substrate and photocatalyst fine particles.

The transparent substrate is made of a material which is transparent to light having a wavelength capable of exerting the photocatalytic action of the photocatalyst which constitutes the photocatalyst fine particles. For example, when a photocatalyst that absorbs ultraviolet rays is used, a material containing silicon dioxide as a main component such as quartz glass, Vycor glass, and silica can be exemplified. It should be noted that even if it is transparent, it does not have to completely transmit all the light of the required wavelength, and an appropriate amount (ratio)
Any light can be used as long as it can transmit the light. Needless to say, there is no limitation on the transmittance of light having a wavelength not related to the photocatalytic reaction. Here, it is preferable to dispose a light source such as an ultraviolet lamp in the vicinity of the transparent base material so that a light beam from the light source can be irradiated as necessary.

The transparent substrate has pores which can pass the fluid to be processed from one surface side to the other surface side and are oriented in a predetermined direction. That is, the fluid to be processed permeates through the pores and reaches from the one surface side to the other surface side. Here, the one surface side of the transparent substrate is the surface on the side to which the fluid to be processed to be processed by the present photocatalyst is supplied, and the other surface side is the fluid to be processed passing through the pores from the one surface side. This is the surface on the outflow side. The supply of the fluid to be treated to the present photocatalyst does not cause any particular problem in the present invention and can be performed by any method. The shape of the transparent base material is a plate-like body, the front and back surfaces of which correspond to the one surface side and the other surface side, respectively, and the tubular body whose inner and outer surfaces correspond to the one surface side and the other surface side, respectively. Any shape such as a shape can be adopted.

By orienting the pores in a predetermined direction, the pores can be efficiently formed in the transparent substrate. The predetermined direction may be any direction, but a direction in which one surface side of the transparent substrate is connected to the other surface side is preferable.

The average pore diameter of the fine pores is preferably 0.1 to 50 μm, more preferably 1 to 50 μm.
Within this range, the ventilation resistance is not so large that the fluid to be treated can sufficiently pass through the pores, and at the same time, the contact area between the fluid to be treated and the pores (that is, photocatalyst fine particles) can be sufficiently secured. Further, in order to secure a sufficient contact time between the fluid to be treated and the photocatalyst fine particles in the pores, the average length is preferably 10 times or more, more preferably 50 times or more the pore diameter. The volume of pores is preferably 35% or more of the apparent volume of the transparent substrate from the viewpoint of photocatalytic activity.

The method for producing the transparent substrate having pores is not particularly limited, and a known method can be applied. For example, as the transparent base material having pores, a porous body that appears as an intermediate product in the above-mentioned Vycor glass manufacturing process can be used. That is, Na ₂ O—B ₂ O ₃ —SiO ₂ -based glass is prepared from silica sand, boric acid, and soda ash by a normal melting process, and after molding this, heat treatment is performed at several hundreds of degrees Celsius so that the inside of the glass is SiO ₂ rich phase and Na ₂ O-B ₂
Phase separation by spinodal decomposition occurs on the O ₃ rich phase on a scale of several nm. This phase separation can be controlled by heat treatment conditions, composition conditions and the like. For example, if the heat treatment temperature is high and the heat treatment time is long, the pore size can be increased, and conversely, if the heat treatment temperature is low and the heat treatment time is shortened, the pore size can be reduced. When this phase-separated glass is immersed in an acid solution,
Only Na ₂ O-B ₂ O ₃ phase is eluted with acid porous glass with SiO ₂ skeleton is obtained.

Further, the transparent substrate can be formed by bundling a plurality of capillaries. The plurality of capillaries are oriented from one surface side through which the fluid to be processed passes toward the other surface side. The size of the pores of these capillaries becomes almost the same as the pore diameter of the transparent substrate. Further, in addition to the holes of the capillaries, the gap between the outer walls of the capillaries can be made into pores to carry the photocatalyst.

By forming the transparent substrate by bundling a plurality of capillaries, there is an effect that an arbitrary length can be selected in the longitudinal direction. As a result, the area for supporting the photocatalyst fine particles necessary for the photocatalytic action can be significantly expanded.

The method of bundling a plurality of capillaries into a transparent substrate is not particularly limited. For example, the capillaries may be used as a photocatalyst while they are bundled, the capillaries may be fused by heating appropriately, or the capillaries may be bonded with an appropriate adhesive.

The material of the photocatalyst fine particles is not limited. Examples thereof include metal oxide semiconductors such as titanium oxide and zinc oxide, and compound semiconductors. Titanium oxide is preferably used. The particle diameter of the photocatalyst fine particles is 7 to 20 n
m, and more preferably 7 to 10 nm. The amount of the photocatalyst fine particles carried on the transparent substrate is preferably 0.2 mg / mL or more based on the apparent volume of the transparent substrate.

As a method for supporting or coating the fine particles of the photocatalyst in the pores of the transparent substrate, for example, a suspension of the fine particles of the photocatalyst is prepared, and the suspension is sucked into the fine pores having a vacuum inside. There are methods such as a method of pressing and a method of press-fitting from one side of the pores.

[Method for Treating Nitrogen Oxide]
This is a method in which the above-mentioned photocatalyst is used and the fluid to be treated is introduced from one surface side to the other surface side of the transparent substrate supporting the photocatalyst fine particles of the photocatalyst. The fluid to be treated introduced into the photocatalyst is decomposed and removed on the photocatalyst fine particles in the pores of the transparent base material of the photocatalyst. The photocatalyst is irradiated with light having a wavelength at which the photocatalyst acts.

The fluid to be treated introduced into the photocatalyst contains nitrogen oxides, and the reducing agent is added before introduction. The type of reducing agent to be added is not particularly limited, but it is preferable to use a gas or a substance having high volatility because it is excellent in the mixing property with the fluid to be treated. Examples of the reducing agent include hydrocarbon compounds such as propane. The addition amount of the reducing agent is not particularly limited, but can be appropriately selected according to the amount of nitrogen oxide in the fluid to be treated. For example, the reducing agent can be added to about 240 to the nitrogen oxide 40 contained in the fluid to be treated.

The fluid to be treated is preferably heated before being introduced into the photocatalyst. Decomposition of nitrogen oxides can be accelerated by heating the fluid to be treated. The temperature of the fluid to be treated is preferably room temperature to 300 ° C, more preferably 200 ° C to 250 ° C.

[0031]

Example (Test 1) (Example 1) Production of photocatalyst body Commercially available anatase-type titania sol (particle diameter 7 nm) as photocatalyst fine particles and a transparent substrate (pore diameter 10 μm, porosity 40%, outer diameter 10 mm) , Thickness 0.5mm and length 50m
and a cylindrical translucent Vycor glass of m) were placed in a stainless steel vacuum container and then held under reduced pressure. The stainless steel vacuum container was returned to normal pressure, and the titania sol was sucked into the pores by the pressure. The transparent substrate sucked with the titania sol was dried at 110 ° C. for 1 hour. Do this operation 3
When the amount of the titanium oxide fine particles carried was calculated from the value of the mass increase repeatedly, it was found that 0.35 mass% was carried on the transparent substrate. Further, from the observation result of the pores of the prepared photocatalyst, it was revealed that the titanium oxide fine particles were uniformly dispersed in the pores.

Measurement of Photocatalyst Property The photocatalyst 1 of Example 1 was evaluated at room temperature using the apparatus shown in FIG. One end of the photocatalyst 1 of this example was sealed with a shield rubber 5, and an inner cylindrical tube 2 for gas discharge (made of quartz glass, outer diameter 9.6 mm, thickness 1.0 mm) was connected to the other end. . The photocatalyst 1 and the inner tube 2 were covered with a reaction column 3 (made of quartz glass, inner diameter 10.5 mm). A gas to be processed as a fluid to be processed flows in from one end of the reaction column 3 (A), and the inflowing gas to be processed passes through the pores of the photocatalyst body 1 and flows into the inner cylindrical tube 2 to enter the inner cylindrical tube 2. It is discharged from the end to the outside (B).

The gas to be treated contains 40 ppm of NO. The flow rate of the gas to be processed was set to 200 mL / min. Ultraviolet rays were irradiated from the outside of the reaction column 3 with a commercially available black light (100 W). As a result, as shown in FIG.
The NO concentration in the gas to be treated flowing out from B decreased to 22 ppm 8 minutes after the irradiation with ultraviolet rays, and then the NO concentration in the permeated gas increased and became steady at about 27 ppm. Examination of the photocatalyst 1 that passed the gas to be treated revealed that nitric acid (HNO ₃ ) generated by the catalytic reaction was retained in the pores. The NO concentration was measured by a Horiba general-purpose gas analyzer CLA-510SS, which measures chemiluminescence by mixing ozone gas.

(Examples 2 and 3) The photocatalyst 1 described in Example 1 was evaluated using the apparatus shown in FIG. Example 1
One end of the photocatalyst body 1 was sealed with a shield ceramic 5, and an inner cylindrical tube 2 for gas discharge (made of quartz glass, outer diameter 9.6 mm, thickness 1.0 mm) was connected to the other end. The photocatalyst 1 and the inner tube 2 are a reaction column 3 (made of quartz glass, inner diameter 1
0.5 mm) was wrapped around it. A gas to be treated as a fluid to be treated is introduced from one end of the reaction column 3 (A),
The gas to be processed that has flowed in passes through the pores of the photocatalyst 1 and flows into the inner cylindrical tube 2, and is discharged to the outside from the end portion of the inner cylindrical tube 2 (B).

The gas to be treated contains 40 ppm of NO and 240 ppm of propane as a reducing agent. The flow rate of the gas to be processed was set to 200 mL / min. Ultraviolet rays were irradiated from the outside of the reaction column 3 with a commercially available black light (100 W). A test in which the temperature of the gas to be treated was room temperature (Example 2) and a test in which the temperature of the gas to be treated was heated to 250 ° C. (Example 3) were performed.

As a result, as shown in FIG. 2, in the test of Example 2, the NO concentration in the gas to be treated flowing out from B was reduced to 19 ppm in 8 minutes after the irradiation with ultraviolet rays, and then, in the permeated gas. The NO concentration increased and became steady at about 25 ppm. In addition, in the test of Example 3, 16 minutes after irradiation with ultraviolet rays,
After decreasing to ppm, the NO concentration in the permeated gas was 15
It was stabilized at about ppm.

When the photocatalysts 1 of Examples 2 and 3 through which the gas to be treated was passed were examined, it was found that the state of retention of nitric acid produced by the catalytic reaction in the pores was not much different from that of Example 1. became.

That is, in Example 2 in which the reducing agent is added to the gas to be treated in advance at a room temperature in which the concentration of nitrogen oxides is the same, the NO concentration is 2 p with respect to the result of Example 1.
pm decreased. Further, in Example 3 in which the gas to be treated was heated to 250 ° C., the NO concentration was further 10 compared to Example 2.
ppm decreased. This decrease is due to NO in the gas to be treated being N
_This is because it was reduced to ₂ . Although details are not shown in the test of Example 1 above, no significant difference in NO concentration was observed even when the gas to be treated was heated under the test conditions described in Example 1, and the effect of heat was not found. It was

(Embodiment 4) 6300 capillary tubes (made of transparent glass, hole diameter 50 μm, outer diameter 60 μm, length 50 mm) are bundled and inserted into a transparent quartz glass tube having an inner diameter of 10 mm and an outer diameter of 12 mm, and are fixed by adhesion to be transparent. Base material (porosity 35%)
And

This transparent substrate and a commercially available anatase type titania sol (particle size 7 nm) as photocatalyst fine particles were placed in a stainless steel vacuum container and then held under reduced pressure.
The stainless steel vacuum container was returned to normal pressure, and the titania sol was sucked into the pores by the pressure. The transparent substrate sucked with the titania sol was dried at 110 ° C. for 1 hour. This operation was repeated 3 times to obtain the photocatalyst of Example 4. When the amount of the titanium oxide fine particles carried was calculated from the value of the mass increase, it was found that 0.06 mass% was carried on the transparent substrate. Further, from the observation result of the pores of the prepared photocatalyst, it was revealed that the titanium oxide fine particles were uniformly dispersed in the pores.

The photocatalyst of Example 4 was subjected to the test shown in Example 2. The results are also shown in FIG. In the test of Example 2, the NO concentration in the gas to be treated flowing out from B dropped to 14 ppm 8 minutes after the irradiation with ultraviolet rays, and then the NO concentration in the permeated gas rose to a steady state at about 22 ppm. When the photocatalyst body 1 of Example 4 in which the gas to be treated was passed was examined, it was revealed that nitric acid generated by the catalytic reaction was retained in the pores.

The NO concentration in the gas to be treated treated with the photocatalyst of Example 4 was lower than the NO concentration in the gas to be treated with the photocatalysts of Examples 1 and 2 by using the capillary tube. It is considered that the area for supporting the photocatalyst fine particles could be increased.

Comparative Example 1 Commercially available titania sol (particle size 7 nm) as photocatalyst fine particles and an alumina base material (pore diameter 12 μm, porosity 40%, outer diameter 10 m) were used.
m, thickness 1.6 mm, length 50 mm), and titanium oxide fine particles were loaded in the pores of the alumina substrate in the same manner as in Example 1. The amount of titanium oxide fine particles supported as photocatalyst fine particles was 0.1% by mass based on the alumina base material.

The photocatalytic activity of this photocatalyst was evaluated by the same apparatus and method as in Example 1. Under the same conditions for supplying the target gas as in Example 1, the flow rate of the target gas was 220 mL /
It became a minute. The results are also shown in FIG. N in the passing gas
The O concentration once dropped to 30 ppm in 8 minutes after the irradiation with ultraviolet rays, and then became steady at 35 ppm.

Comparative Example 2 The transparent substrate used in Example 1 was directly subjected to the test shown in Example 1 without supporting the titanium oxide fine particles. The results are also shown in FIG. The NO concentration in the passing gas was constant regardless of the irradiation of ultraviolet rays.

(Test 2) (Samples 1 to 4) As the photocatalyst for the test, the pore diameter was 10 μm, and the substrate thickness (corresponding to the length of the pore) / pore diameter was the value shown in Table 1. Is Example 1
Samples 1 to 4 were manufactured by the same method as that for the photocatalyst.

A test similar to the test shown in Example 1 was conducted for each sample, and the NO removal rate from the NO concentration in the passing gas {(NO concentration in the gas to be treated-NO concentration in the passing gas)
/ NO concentration in the gas to be treated x 100 (%)}, and N
The O ₂ concentration was measured and the residual rate with respect to theoretically generated NO ₂ was determined. The results are also shown in Table 1. Note that NO ₂
The concentration was measured by a Horiba general-purpose gas analyzer CLA-510SS, which measures chemiluminescence by mixing ozone gas.

[0048]

[Table 1]

As is clear from Table 1, when the value of the substrate thickness / pore size is 10 or more, the NO removal rate is 30 or more, and the substrate thickness / pore size is increased if the NO removal rate is more than 30. Also N
There was no significant change in the O removal rate. In addition, Sample 1 having a substrate thickness / pore diameter value of 5 also shows a relatively high NO ₂ remaining amount of 6%, and the substrate thickness / pore diameter is also shown by the value of the NO ₂ remaining amount. It has been clarified that the value of is preferably 10 or more.

As a result of the above-mentioned test in which the pore diameter is kept constant and the value of substrate thickness / pore diameter is controlled, in order to efficiently carry out the photochemical reaction with respect to the gas to be treated containing the component to be decomposed, In addition to increasing the area of the pores to increase the area for supporting the photocatalyst fine particles, the length of the pores should be sufficiently long to secure a sufficient time for the gas to be passed and the photocatalyst fine particles to come into contact with each other. It seems that it is necessary.

(Test 3) (Samples 5 to 10) A photocatalyst similar to that of Example 1 was prepared except that the value of substrate thickness / pore diameter was fixed at 50 and the average pore diameter was set to the value shown in Table 2. Manufactured. Then, the same evaluation as in Test 2 was performed on each sample.

[0052]

[Table 2]

As is clear from Table 2, the NO 5 removal rate of sample 5 (pore diameter 0.05 μm) having a small pore diameter was as low as 8%, and sample 6 (pore diameter 0.1 μm) to sample 10 (pore diameter 60 μm). ), The NO removal rate was 15% or higher, which is relatively high. In particular, in samples 7 to 9 having pore diameters of 1 to 50 μm, the NO removal rate was 30% or more, which was a more excellent value. In addition, considering the value of the NO ₂ residual rate together, samples 6 to 9
It is considered that the pore size of 0.1 to 50 μm is preferable.

When the pore diameter is too small, it is considered that the titanium oxide fine particles cannot be sufficiently supported in the pores, and the air resistance value increases, so that the photocatalytic activity cannot be sufficiently exhibited. Further, it is considered that when the pore size is too large, the contact between the gas to be treated and the titanium oxide fine particles becomes insufficient and the values of the NO removal rate and the NO ₂ remaining amount deteriorate.

(Test 3) The volume density of the pores formed in the transparent substrate was adjusted by adjusting the ratio of the raw material component SiO _2.
Photocatalysts of Samples 11 to 15 were manufactured so that the porosity values shown in Table 1 were obtained. Regarding the manufactured samples 11 to 15, N
The O removal rate and the value of ventilation resistance were measured. The value of the ventilation resistance was determined by measuring the differential pressure in the fluid flow path at the inlet of the reaction column 3 and the outlet end of the inner cylindrical tube 2 with a water column manometer.

[0056]

[Table 3]

As is clear from Table 3, the porosity is 35%.
It was revealed that the above-mentioned samples 12 to 15 have a high NO removal rate of 15% or more, a low ventilation resistance of 10 mmAq or less, and a porosity of 35% or more. .

The pore density of the transparent substrate is related to the porosity. When the porosity is small, the pore density is low and the catalyst area is also low. Therefore, it is considered that when the porosity is 35% or more, the photocatalytic activity of the titanium oxide fine particles can be sufficiently exhibited. Further, the ventilation resistance is proportional to the square of the porosity. Therefore, in view of the value of ventilation resistance, the porosity is preferably 35% or more and ventilation resistance of 10 mmAq or less. Further, as the porosity increases, the surface area capable of supporting the titanium oxide fine particles also increases, which is also preferable in that respect.

(Test 4) Regarding titanium oxide fine particles as photocatalyst fine particles, the value of the potential induced by light irradiation, which is a characteristic relating to the photocatalytic ability, is defined by setting the average particle diameter of the titanium oxide fine particles to 7, 20, 30, 180 nm. Was measured. The electric potential was measured by measuring the electromotive force at the time of ultraviolet irradiation between the KCl solution arranged via the semipermeable membrane and the KCl solution in which the titanium oxide fine particles of each particle size were suspended. The results are shown in Table 4.

[0060]

[Table 4]

As is clear from Table 4, when the particle size of titanium oxide fine particles is 7 to 20 nm, the potential is -16.
It was found that while the excellent value was 0 to −150 mV, when the particle size exceeded 20 nm, the potential decreased to about −50 mV. Therefore, it is appropriate that the particle diameter of the titanium oxide fine particles is 7 to 20 nm.

The photocatalytic ability of anatase type titanium oxide is a surface photochemical reaction that receives ultraviolet rays. Therefore, the smaller the particle size of the titanium oxide fine particles, the larger the surface area per unit area. Further, as the surface area increases, the number of defects that become active sites for photocatalytic activity also increases. Therefore, it is considered preferable that the titanium oxide fine particles have a small particle size (20 nm or less). However, if it is made too small, it is difficult to process. Therefore, including the cost factor, it is considered that 7 nm or more is preferable for practical use.

(Test 5) Samples 16 to 18 were manufactured in substantially the same manner as the photocatalyst of Example 1 except that the supported amount of titanium oxide fine particles was changed. The change in the carried amount was adjusted by changing the number of times of sucking titania sol. Table 5 shows the measurement results of the NO removal rate of each sample.

[0064]

[Table 5]

As is clear from Table 5, the NO removal rate is improved as the amount of titanium oxide fine particles carried is increased. Sample 1 with a carried amount of 0.20 mg / mL or more
Nos. 7 and 18 are preferable because the NO removal rate is 15% or more. Furthermore, when the supported amount is 0.35 mg / mL or more, N
The O removal rate is 32%, which is an excellent value.

[0066]

As described above, the photocatalyst body of the present invention comprises a transparent base material having pores that can pass a fluid to be treated and is oriented in a predetermined direction, and photocatalyst fine particles carried in the pores. By having it, it becomes possible to sufficiently secure the contact time between the fluid to be treated and the photocatalyst fine particles, and it is possible to exhibit a high photocatalytic ability.

Furthermore, according to the method for treating nitrogen oxides of the present invention, the nitrogen oxides can be decomposed and removed more efficiently by adding the reducing agent to the gas to be treated.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a test apparatus used in Examples.

FIG. 2 is a graph showing the results of test 1.

[Explanation of symbols]

1 ... Photocatalyst 2 ... Inner tube 3 ... Reaction column 4 ... Black light 5 ... Shield rubber

Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B01D 53/86 ZAB B01J 21/06 A 53/94 35/10 301F B01J 21/06 C03C 17/25 A 35/10 301 B01D 53/36 ZABJ C03C 17/25 102D (71) Applicant 000116655 Aichi Steel Co., Ltd. 1 Wanowari, Arao-cho, Tokai-shi, Aichi (72) Inventor Takenobu Sakai 1 Toyota-cho, Toyota-shi, Aichi Toyota Motor Co., Ltd. (72) Inventor Katsuhiro Onda 2-4-1 Rokuno, Atsuta-ku, Nagoya, Aichi Prefecture Fine Ceramics Center Foundation (72) Inventor Yuji Iwamoto 2-4-1 Rono, Atsuta-ku, Nagoya City, Aichi Foundation Corporate Fine Ceramics Center (72) Inventor Hisashi Shiraki 2-chome Toyota-cho, Kariya city, Aichi Stock company Toyota automatic loom F-term (reference) 4C080 AA07 AA10 BB02 BB05 CC07 HH05 JJ03 KK02 KK08 LL03 LL10 MM02 NN02 NN06 NN12 QQ03 QQ11 QQ12 4D048 AA06 AA22 AB03 AC02 AC10 BA07X BA41X BB03 BB05 BB15 BB17 CC52 EA01 4G059 AA16 AA17 AB01 AB09 AB11 AC22 EA04 EB07 4G069 AA03 AA08 BA18CA18 CA18 CA17 CA17 CA17 CA17 CA17 CA17 CA17 CA17 CA17 CA17 CA17 CA17 CA17 CA17 CA17 CA11

Claims (11)

[Claims] 1. A transparent base material having pores capable of passing a fluid to be treated from one surface side to the other surface side and oriented in a predetermined direction, and photocatalyst fine particles carried in the pores. And photocatalyst. 2. The photocatalyst body according to claim 1, wherein the predetermined direction is a direction connecting the one surface side and the other surface side. 3. The pores have an average pore diameter of 0.1 to 50 μm.
The photocatalyst body according to claim 1 or 2, wherein m is m and the average length is 10 times or more the pore size. 4. The photocatalyst body according to claim 1, wherein the volume of the pores is 35% or more with respect to the apparent volume of the transparent substrate. 5. The average particle diameter of the photocatalyst fine particles is 7 to 2.
It is 0 nm, The photocatalyst body in any one of Claims 1-4. 6. The photocatalyst body according to claim 1, wherein the amount of the photocatalyst fine particles carried is 0.2 mg / mL or more based on the apparent volume of the transparent substrate. 7. The transparent substrate is a plate-shaped body, and the one surface side and the other surface side are front and back surfaces of the plate-shaped body.
6. The photocatalyst body according to any one of 6. 8. The transparent substrate is a tubular body, and the one surface side and the other surface side are front and back surfaces of the tubular body.
7. The photocatalyst body according to any one of 7. 9. The transparent base material is configured by bundling a plurality of capillaries, and the capillaries are oriented from the one surface side to the other surface side, respectively. Photocatalyst. 10. A method for treating nitrogen oxides, which comprises introducing a treatment target fluid containing nitrogen oxides from the one surface side of the photocatalyst body according to claim 1 to treat the nitrogen oxides. A method for treating nitrogen oxides, which comprises adding a reducing agent to the fluid to be treated before being introduced into. 11. The fluid to be processed is heated.
The method for treating nitrogen oxide according to 0.