JP2015048351A - Method for reducing carbon dioxide using photocatalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To mass-produce an organic compound such as methanol and formaldehyde from steam and carbon dioxide for effectively utilizing carbon dioxide in the air and carbon dioxide in a flue gas as resources in an amount larger than the conventional proposal.SOLUTION: A structural body obtained by scattering an integrated matter (C) made of an integrated matter (A) of titanium oxide, zirconium oxide and cobalt oxide and a photocatalyst (B) having excellent reduction capacity onto an electroconductive substance is arranged into a mixed gas including steam and carbon dioxide, and the integrated matter (C) is irradiated with ultraviolet light. The photocatalyst having excellent reduction capacity is a platinum-carried titanium dioxide.

Description

  The present invention relates to a technique for producing useful organic compounds such as methanol and formaldehyde at room temperature from water vapor and carbon dioxide under ultraviolet irradiation by using a special photocatalyst.

  In recent years, the warming of the atmosphere has progressed due to an increase in the concentration of carbon dioxide in the atmosphere, and abnormal weather frequently occurs, which has become a big social problem on a global scale. Therefore, research for recovering and processing carbon dioxide in exhaust gas has been conducted. In addition, research on converting carbon dioxide into a useful organic compound as a resource has been conducted, and the importance of these research has been increasing.

In those studies, as an attempt to convert the carbon constituting the carbon dioxide molecule into a low molecular weight organic substance using a photocatalyst, the reaction product was analyzed after irradiating high energy ultraviolet rays in the latter half of the 1970s. However, there is a report showing the possibility, but it is an analysis level to the last, and the production amount is extremely small and is not practically used. Since then, atmospheric warming has been observed, and in association with the increase in atmospheric carbon dioxide molecules, research aimed at reducing carbon dioxide molecules to prevent atmospheric warming has become active, but it is still in practical use. Not in. In addition, a method of synthesizing a novel organic compound for the purpose of reducing carbon dioxide with reference to plant photosynthesis has been actively studied, but has not been put into practical use.
Most of the carbon dioxide immobilization experiments using photocatalysts are a form in which titanium dioxide particles or crystals are immersed or dispersed in water and irradiated with simulated sunlight or high-energy ultraviolet light. The sacrificial reagent is easily added to enhance the reduction action, and the amount of the reduced organic compound is very small. The aim of the present invention is “practical use of carbon dioxide in the air without sacrificial reagent in the gas phase” There are no reports aimed at “reduction by quantity”.

  In recent years, proposals have been made to combine a photocatalyst and a carbon dioxide reduction catalyst to produce a low molecular weight organic compound containing methanol under the irradiation of sunlight using carbon dioxide and water as raw materials. (See Patent Documents 1 and 2)

  However, both Patent Documents 1 and 2 are technologies that generate hydrogen ions from water with a photocatalyst, supply carbon dioxide, and generate an organic compound such as methanol by the action of a carbon dioxide reduction catalyst. Carbon dioxide is reduced by a catalyst rather than a photocatalyst. Further, in order for the carbon dioxide reduction catalyst to function effectively, it is necessary to make the vicinity of the carbon dioxide reduction catalyst a relatively high temperature environment.

  JP 2003-275599 A (pages 1 to 6)   JP 2004-59507 A (pages 1-7)

  The present invention provides a method for producing useful organic compounds such as methanol and formaldehyde (C1 compounds mainly consisting of one molecule of carbon) at room temperature from water vapor and carbon dioxide in the atmosphere and exhaust gas using a photocatalyst. It is intended to provide.

  When a photocatalyst receives light having a wavelength shorter (higher energy) than the wavelength corresponding to the band gap energy peculiar to the substance, electrons in the valence band are excited to the conduction band, and electrons having a reducing ability are generated. Holes with high oxidizing ability are generated in the band. Usually, most of the electrons and holes generated by light irradiation are recombined and deactivated as heat, but some of them diffuse and reach the surface to cause an oxidation reaction or a reduction reaction. As typical photocatalysts, titanium dioxide, zinc oxide and the like are known.

When a useful low-molecular-weight organic compound such as methanol or formaldehyde is produced from water vapor and carbon dioxide using a photocatalyst, the photocatalyst first acts on water molecules to generate hydrogen ions (H ⁺ ) and {hydroxide ions ( OH ⁻ ) or an oxidation product of oxygen}, and then the generated hydrogen ions are bound to carbon dioxide to form low molecular organic compounds such as formaldehyde and methanol. The -valent oxygen constituting the hydroxide ion is expected to easily generate oxygen molecules (O ₂ ) due to the strong oxidizing action of holes, but in the case of the gas phase, oxygen molecules cannot be easily generated. Therefore, decomposition of new water molecules does not proceed because hydroxide ions remain. In addition, among the electrons and holes generated by photocatalysis, there is no step of electrically erasing the remaining holes after the electrons are consumed by the reduction reaction, so there is an excess of holes, which are generated by the subsequent photocatalysis. The recombined electrons are recombined with the remaining holes and disappear, and the supply (reduction action) of the electrons is significantly reduced.

  In green plants, as soon as the complex of dye and protein absorbs visible light and generates excited electrons and holes, the electrons are transferred and charge separation is performed. At the same time, hydroxide ions are oxidized by the catalytic action of manganese compounds. By releasing both hydroxide ions and holes by releasing them as oxygen molecules, the dye-protein complex can continuously absorb visible light and generate excited electrons and holes. ing. Furthermore, the electrons are excited again by light energy to give a higher reducing ability and produce a reducing compound with a moderate reducing ability (light reaction), which is used for the next step, carbon dioxide fixation (dark reaction). ing.

  The present inventor has previously proposed a photocatalyst excellent in oxidation ability among an integrated product consisting of a photocatalyst excellent in oxidation ability and a photocatalyst excellent in reduction ability, {cerium oxide supporting titanium dioxide, iron (III) oxide and platinum ( IV) integrated product}, {integrated product of titanium dioxide and aluminum metal} and {integrated product of titanium dioxide and zirconium oxide} have been proposed. Although they are materials suitable for practical use, it is more preferable if a photocatalytic material capable of producing more low molecular weight organic compounds when irradiated with ultraviolet rays or sunlight can be found.

  Therefore, the present inventor has eagerly searched for a photocatalyst excellent in carbon dioxide reduction ability, and has {reduced ability in which titanium dioxide, zirconium oxide, and cobalt oxide are integrated (A)} and {reduction ability in which platinum is supported on titanium dioxide. It has been found that a further integrated photocatalyst (B)} is excellent in the reduction of carbon dioxide, and has devised a composite structure that is dispersed on a plate having high electrical conductivity. The content of the photocatalyst (B) is that the hydroxide ions generated by the decomposition of water vapor are oxidized by an integrated product (A) of titanium dioxide, zirconium oxide and manganese oxide and consumed as oxygen molecules, and at the same time have excellent reducing ability. It seems to have affinity with carbon dioxide and zirconium oxide in the vicinity, and by supplying electrons to carbon dioxide in the vicinity of zirconium oxide and reducing it, hydrogen ions are combined to produce methanol and formaldehyde . Therefore, the amount of methanol and formaldehyde produced was measured to confirm that it was produced in a larger amount than the previous proposal, and the present invention was completed.

  Here, the integrated product refers to a powder in a state where two or more kinds of particles are bonded by pressure bonding. That is, two or more kinds of solid particles are rubbed together by mechanical force, and are bonded and joined together.

Conventionally, the name of a complex or a complex is generally used, and the term “composite” means that two or more kinds of substances are attached, or are in a state of being mixed inhomogeneously, or It was unclear whether the mixture was uniformly mixed.
The mixture of the present invention refers to a state in which two or more kinds of substances are simply rubbed together, that is, a combination of pressure bonding and joining while maintaining an interface with each other.

  Further, in the case of the present invention, since the particle diameter of titanium dioxide or titanium dioxide carrying platinum is nanometer, it has a long interface with the rubbing partner. In addition, once the nanometer order particles are attached, the attached state is maintained by van der Waals force, so that they are not separated from the adherend. Thus, since it is a completely new composite having properties different from those of conventionally used pressure-bonded products, the name of an integrated product is used.

That is, the gist of the present invention is as follows.
(1) In a mixed gas containing water vapor and carbon dioxide,
Integrated material consisting of titanium dioxide, zirconium oxide and cobalt oxide (A) and titanium dioxide carrying platinum (B)
The structure (D) in which the object (C) integrated with the material is dispersed on the electrically conductive material,
Irradiate the integrated product (C) with ultraviolet light,
The method for reducing carbon dioxide characterized by producing an organic compound (2) The method for reducing carbon dioxide according to claim 1, wherein the electrically conductive substance is a copper plate.

  By using the carbon dioxide reduction method of the present invention, it becomes possible to produce useful low-molecular-weight organic compounds such as methanol and formaldehyde from water vapor and carbon dioxide as raw materials by irradiation with ultraviolet light or sunlight. . Methanol is a useful organic compound by itself, and formaldehyde is a raw material for organic compounds with higher added value.

  When carbon dioxide is selected as the reductant, carbon dioxide contained in a minute amount in the air or combustion exhaust gas containing more carbon dioxide may be used. It becomes.

In the present invention, first, an integrated product (A) composed of titanium dioxide, zirconium oxide and cobalt oxide and a product (B) in which platinum is supported on titanium dioxide (B) are further dispersed on an electrically conductive material. The thing (D) is cooled, and then the cooled (D) is placed in a mixed gas containing water vapor and carbon dioxide, and the integrated product (C) is irradiated with light containing ultraviolet light. By adopting such a form, moisture in the atmosphere is condensed on the cooled surface of (C) to form a thin film of water, thereby preventing generation of a multilayer physical adsorption layer of nitrogen on the surface of the integrated product. As a result, the original action of the photocatalyst is exhibited, and carbon dioxide is reduced to produce a low molecular weight organic compound.

In (C), nitrogen is normally adsorbed on the surface, and when it is cooled in a refrigerator, nitrogen is desorbed to become a clean surface. Water condensed there condenses to form a thin film of water, prevents the adsorption of nitrogen on the surface of (C) due to ultraviolet light irradiation in the next step, and develops the original properties (photocatalytic activity) of the photocatalyst. When the surface of the fine particle titanium dioxide is in contact with the atmosphere, when it is irradiated with ultraviolet light, nitrogen adsorption precedes and the activity as a photocatalyst such as water decomposition is significantly inhibited.

  In the present invention, when (A) and (B) integrated (C) are dispersed on an electrically conductive material (D) are placed in a dish-like container such as a petri dish, the experiment is easy.

  Hereinafter, a sample in which (A) and (B) integrated (C) are dispersed on an electrically conductive material (D) in a dish-like container such as a petri dish is referred to as a test specimen.

  Here, titanium dioxide constituting (A), zirconium oxide, cobalt oxide and titanium dioxide constituting (B) may be powder, lump, plate or foil, but powder is preferred, and the particle size is The smaller the surface area, the larger the surface area.

Here, the case where a carbon dioxide molecule is used as a reductant will be described.
First, an integrated product (C) composed of (A) and (B) is sprayed on an electrically conductive plate or foil, (D) a sample placed in a petri dish (test body) is cooled, and then, for example, light A cooled specimen (D) is placed in a bag-like, box-like or tubular container that allows the gas to pass through, a mixed gas containing carbon dioxide gas and water vapor is introduced into the container, and ultraviolet light is contained from above. What is necessary is just to irradiate light. The light source may be outside or inside the container. The mixed gas may be air, an artificial gas containing water vapor and carbon dioxide, or combustion exhaust gas having a high carbon dioxide concentration.

  When the ultraviolet light is irradiated, water vapor and carbon dioxide in the mixed gas are consumed by the action of the photocatalyst and a low molecular weight organic compound is generated, so that the composition of the mixed gas changes. Therefore, the mixed gas may be exchanged for a certain amount of the initial mixed gas every certain time, or the initial mixed gas may be recovered while recovering the reduction product of carbon dioxide (that is, a low molecular weight organic compound). May be supplied continuously. In the following description, the case where the mixed gas to be supplied is the atmosphere will be described.

  It is considered that the thickness of the condensed water condensed on the surface of the integrated object is almost determined by the volume and temperature of the atmosphere supplied to the container, the humidity, and the surface quality of the integrated object (C). Appropriate values for the temperature and humidity of the atmosphere supplied to the container vary depending on the volume of the atmosphere supplied, the weight of the integrated product (C), and the dispersion state of the integrated product. It is preferable to measure the concentration of the low-molecular-weight organic product to be generated and maintain the temperature and humidity at the highest concentration, but when 0.1 g of the integrated product is dispersed almost uniformly in a circle with a diameter of 60 mm. When the temperature is 22 to 26 ° C. and the humidity is 65 to 75%, good results are obtained. When 0.2 g of the integrated product is dispersed almost uniformly in a circle with a diameter of 60 mm, the temperature is 28 to 32 ° C., Good results were obtained at a humidity of 60-70%. However, these conditions are only a guideline, and it is preferable to obtain an optimum value each time under actual operating conditions with an actual device.

  As other factors, water decomposition by photocatalysis occurs during irradiation with ultraviolet light, but if the temperature and humidity around the integrated object are low, the dew condensation on the surface of the integrated object (C) disappears and nitrogen molecules are adsorbed. On the other hand, if the temperature or humidity is too high, the amount of condensation is too much and the liquid film of water on the surface of the photocatalyst becomes thick, so that hydrogen ions generated on the surface of the integrated product (C) and carbon dioxide molecules in the atmosphere Is difficult to contact, and the affinity between zirconium oxide and carbon dioxide is hindered, making it difficult for carbon dioxide to be reduced in the vicinity of zirconium oxide, and the production of low-molecular organic compounds is extremely reduced, which is not preferable. .

Moreover, in the reduction | restoration of the carbon dioxide of this invention, when the integrated object (C) contacts air | atmosphere, it is necessary to maintain the temperature at which the surface of the integrated object (C) dew condensation. Furthermore, it is preferable that the surface of the integrated product (C) is kept at a temperature below the dew point even during the reduction. That is, the surface temperature of the integrated object (C) is 1 ° C. to dew point so that the gas (room air) surrounding the integrated object (C) does not freeze on the surface of the integrated object (C) and forms a liquid film without gaps. It is preferable to maintain the temperature, and it is preferable to maintain a low temperature of about 1 to 10 ° C, more preferably about 1 to 5 ° C.

  As described in paragraphs [0026], [0027] and [0028], the thickness of the condensed liquid film depends on the temperature and humidity of the supplied air, the amount of the integrated material (C), and the size of the surface area depending on the state of dispersion. It is important to maintain a preferable thickness of the liquid film because the amount of carbon dioxide reduction varies depending on the thickness of the liquid film that has changed slightly and has condensed.

Two forms of implementing the present invention are possible:
(1) When the amount of low-molecular-weight organic matter generated from the integrated product (C) decreases, replace the separately prepared integrated product (C) with one that has been cooled, and supply the atmosphere containing water vapor and carbon dioxide. Repeat the operation.
(2) By contacting ice or a cold insulation agent directly under the test specimen in the container and continuously cooling, the surface of (C) is constantly brought into a dew-condensed state with an appropriate liquid film thickness, and water vapor and carbon dioxide. Reducing carbon dioxide continuously by supplying air containing or continuously or intermittently. As a method of constantly maintaining the surface of the integrated object in the dew condensation state, the surface temperature of the integrated object may be kept below the dew point of the atmosphere, and the integrated object is cooled indirectly by cooling the metal plate on which the integrated object is placed. May be.

The two forms have the following characteristics.
(1) The supplied air only needs to satisfy the conditions necessary for dew condensation, but another test body in which the test body including the integrated product (C) composed of (A) and (B) is cooled is used. It is necessary to replace it regularly.
In (2), although it is possible to perform continuous reduction, it is necessary to stably maintain the dew condensation state with an appropriate liquid film thickness. Therefore, it is necessary to constantly control the temperature and humidity of the supplied air. Management is required.

The integrated product (C) composed of (A) and (B) used in the present invention may be adjusted in the air, but is preferably performed in the air dehumidified at low temperature or in the air dried under reduced pressure. Although it may be in the atmosphere, it is preferable to keep it at a low temperature under reduced pressure. It is optimal if storage can be realized in a state in which the integrated product is not brought into contact with nitrogen after removing the nitrogen physically adsorbed on the integrated product surface after adjustment.
It is preferable to store the raw materials used for the adjustment in a state where the surface is clean.

  As a method for treating the specimen before introducing the mixed gas, it may be stored in the refrigerator for a certain period of time, but more preferably, the specimen is first decompressed and the integrated body (C) composed of (A) and (B). Nitrogen physically adsorbed on the surface is removed, and then (C) is cooled. Or you may perform pressure reduction and cooling simultaneously.

  Furthermore, other points of the configuration of the present invention will be described.

  The photocatalyst particles have an oxidation site and a reduction site on the same particle surface. Since (A) and (B) which are constituents of the present invention have not only an oxidation site but also a reduction site, carbon dioxide can be reduced using only (A) or (B). ) And (B) are preferably used in the form of an integrated product (C) because of its high ability to reduce carbon dioxide.

  Further, carbon dioxide is reduced even if (C) is not particularly sprayed on the electrically conductive material, but the amount of carbon dioxide reduction increases when sprayed on the electrically conductive material.

  Zirconium oxide can be used as a high purity reagent, a standard purity reagent, or an industrial material, and partially stabilized zirconia and stabilized zirconia can also be used. Partially stabilized zirconia and stabilized zirconia have oxygen ion permeation performance, so that the effect of preventing recombination with hydrogen ions by moving oxygen ions generated by photocatalysis from the catalytic active point can be expected. Expensive. In addition, a zirconium oxide is so preferable that a particle size is small.

As the cobalt oxide, a high purity reagent, a standard purity reagent, or an industrial material can be used.
There are multiple types depending on the valence of cobalt, but the type is not particularly specified. Ones can be used to present the structure of forty-three cobalt oxide _(Co 3 _{O 4),} but can also be used cobalt (II) oxide and cobalt oxide (IV).

  Furthermore, as the photocatalyst (B) excellent in reducing ability of the present invention, titanium dioxide carrying platinum is preferable.

  As a method for supporting platinum, a photodeposition method in which titanium dioxide is dispersed in an aqueous solution in which a water-soluble platinum compound is dissolved, and platinum is precipitated on the surface of titanium dioxide by irradiation with ultraviolet light is suitable.

  As titanium dioxide used in the present invention, a smaller particle size is preferable because it has a larger surface area, but a commercially available material may be used as long as it is granular. When titanium dioxide is used, anatase type, rutile type and brookite type can be used, but anatase type is particularly preferable. The smaller the particle size, the larger the surface area per unit weight, so 100 nm or less is preferable, and 10 nm or less is particularly preferable.

  The reduction of carbon dioxide according to the present invention cools the integrated product (C) to about 1 to 8 ° C., and when (C) is a small amount of about 0.2 g, the mixed gas such as the introduced air is about the room humidity in summer. However, the temperature and humidity of the introduced mixed gas must be such that the moisture of the mixed gas can be condensed on the surface of the integrated object with an appropriate liquid film thickness.

  In other words, a liquid film with an appropriate film thickness may be generated on the surface of the integrated product, so if the gas mixture contains a proper amount of water vapor even at high temperatures such as combustion exhaust gas, If the surface temperature is below the dew point, dew condensation will occur and the photocatalytic effect will appear, so carbon dioxide can be reduced.

  Next, a method for preparing (A) and (B), which are constituent components of the present invention, will be described.

  First, the preparation method of (A) may be carried out by pressing titanium dioxide, zirconium oxide and cobalt oxide into a mortar at room temperature and mixing them uniformly with a spatula or the like, followed by strong rubbing and pressure bonding. Usually, it can be used at room temperature, but may further be fired and pulverized at 700 ° C. or lower after pressure bonding. When the temperature is raised to 700 ° C. or higher, titanium dioxide tends to change from anatase type to rutile type, which is not preferable. Moreover, when crimping, you may grind and join with various ball mills.

  The blending ratio (weight ratio) of (A) depends on the particle size of each component, but titanium dioxide is 10 to 50% of the whole, zirconium oxide is 30 to 70% of the whole, and cobalt oxide is 5 to 40% of the whole. The ratio of 100% can be selected as a whole.

  In the present invention, the blending ratio is a weight ratio, and so on.

  The ratio of (A) and (B) is preferably (A) / (B) = 20/80 to 80/20. A suitable ratio is selected depending on the particle size of the particles to be used.

  As the photocatalyst (B) excellent in reducing ability, fine particle anatase type titanium dioxide may be used as it is, but it is preferable to use a fine particle anatase type titanium dioxide carrying platinum by a photodeposition method. Further, titanium dioxide impregnated with a water-soluble alkali compound, dried, fired and pulverized (titanium dioxide / alkali compound composite) may be used, or platinum is added to the titanium dioxide / alkali compound composite by a photodeposition method. You may use what was carry | supported.

  In the present invention, (A) and (B) are used in an integrated manner. However, the integration is only required to be almost uniformly mixed and joined, and it is sufficient to lightly grind them with a mortar. Industrially, it can be pressed by a ball mill or the like.

  Next, the integrated product (C) of the above (A) and (B) is spread on an electrically conductive material (for example, a copper plate). It is possible to drop the liquid into a metal plate, or after the film is dropped, it may be lightly rubbed with a metal plate or a plastic plate and distributed more uniformly.

  Next, the specimen (C) dispersed on the electrically conductive material and placed in a petri dish or the like is stored in a refrigerator. The storage time depends on the amount of the integrated product and the surface quality of the raw material fine particles. However, when the weight of the integrated product used in the examples is 0.2 g, the storage time in the refrigerator is preferably 24 hours or more, and 48 hours or more. Further preferred.

Furthermore, other components of the present invention will be described.

    The water vapor used in the present invention may be water vapor existing in the atmosphere, or may be humidified by evaporating ground water or tap water when the air is dry. In the experiments at the time of the present invention, it was recognized that ethanol and formaldehyde generation tended to be high at high temperatures and high humidity in midsummer. Moreover, the water for humidification should have few impurities, and pure water is suitable.

  Carbon dioxide in the atmosphere, carbon dioxide in combustion exhaust gas, or the like can be used as the carbon dioxide that is a reduction target. Since the carbon dioxide concentration in the combustion exhaust gas is much higher than the carbon dioxide concentration in the atmosphere, the contact frequency with the integrated substance is increased, which is advantageous for the production of useful organic substances. When using combustion exhaust gas, it is better to remove particulates in the exhaust gas with an air filter or the like and remove gas components other than water vapor and carbon dioxide. Moreover, you may concentrate the carbon dioxide in air | atmosphere.

  The type of the electrically conductive material used in the present invention is not limited as long as it is a material having high electrical conductivity, but a metal plate or foil such as copper or aluminum is preferable, and a copper plate is particularly preferable.

  The light source containing ultraviolet rays used in the present invention may be a light source containing ultraviolet rays such as an ultraviolet lamp or black light, or may be sunlight. Since the present invention reduces carbon dioxide gas to produce low-molecular organic compounds that are effective as industrial raw materials such as chemistry, it seems that it is often implemented in factory buildings, and there is no need to be particular about natural light. It is preferable to use an inexpensive ultraviolet light source. If an LED having the same wavelength as that of the black light is available, it is most preferable because it has a long life, is highly efficient with respect to the power used, and can be used without waste as a wavelength.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited to the Example shown below. In the examples, “%” and “parts” are based on weight unless otherwise noted.

1.1 Preparation of integrated product (C) composed of (A) and (B) 1.1.1 Preparation of (A) White titanium dioxide AMT-100 having anatase type crystal structure manufactured by Teika Co., Ltd. in a mortar ( 0.3 g of particle size 6 nm, specific surface area 260 m ² / g), 0.5 g of high purity zirconium oxide 3N (particle size 30-50 microns) manufactured by Kanto Chemical Co., Ltd., and grade 1 reagent manufactured by Kanto Chemical (A) was prepared by taking 0.2 g of cobalt oxide (Co ₃ O ₄ ) and stirring it uniformly, followed by stirring with strong rubbing.
1.1.2 Preparation of (B) Take 1.0 g of white titanium dioxide AMT-100 having an anatase type crystal structure manufactured by Teika Co., Ltd. into a glass petri dish with an inner diameter of 93 mm, add 30 ml of pure water and stir. Add 0.3 g of 1% aqueous solution of chloroplatinic acid and stir, add 0.1 g of reagent grade ethanol and stir, place under 10 cm of 20 W black light and irradiate with black light for 20 hours, then dry at 120 ° C. for 1 hour, Platinum-supported titanium dioxide was prepared.
1.1.3 Preparation of integrated product (C) A total of 1.0 g of (A) obtained in 1.1.1 and (B) obtained in 1.1.2 at a ratio of 1: 1 in a mortar. It was lightly stirred to prepare an integrated product of the present invention (titanium dioxide: zirconium oxide: cobalt oxide: platinum-supported titanium dioxide = 1.5: 2.5: 1.0: 5).

1.2 Carbon dioxide reduction experiment A test specimen in which 0.2 g of the integrated product obtained in 1.1.3 was uniformly sprayed on a copper plate on a glass petri dish with an inner diameter of 68 mm and a copper plate was placed in a refrigerator ( In order to prevent condensation in the refrigerator, cool it for 3 days in a household dehumidifier dry pet (component calcium chloride) manufactured by Este Co., Ltd., and then take it out. ), Put in a gas barrier bag (OE-4, OE-4) and heat seal the entrance. A 1cm square urethane tape is attached to the gas barrier bag, and air is injected with a syringe so that the air in the bag becomes about 1000 ml. Just under the black light (black light fluorescent lamp FL20S-BLB-A (20W) manufactured by Toshiba Lighting & Technology Corp.) Set. The integrated product in the test body was at a position 10 cm immediately below the black light. Then, the black light is irradiated for 30 minutes, and after irradiation, the methanol gas concentration in the bag is measured using the Kitagawa gas detector tube No119U and the formaldehyde gas concentration is measured using the Kitagawa gas detector tube No171SA. The number of μmoles of methanol gas and formaldehyde gas was calculated (gas concentration (ppm) × residual air volume (ml) / {irradiation time (0.5 Hr) × photocatalyst weight (0.2 g) × 22400}). The temperature of the injected air was 30.6 ° C. and the humidity was 66%, and the measurement results were as shown in Table 1.
The gas remaining in the barrier bag after irradiation with black light was 1000 ml including 200 ml sucked in the measurement of two types of gas detector tubes.

2.1 Preparation of integrated product (C) composed of (A) and (B) 2.1.1 Preparation of (A) White titanium dioxide AMT-100 having anatase type crystal structure manufactured by Teika Co., Ltd. in a mortar ( Uniformly take 0.5 g of particle size 6 nm, specific surface area 260 m ² / g), 0.5 g of high-purity zirconium oxide 3N of high-purity reagent manufactured by Kanto Chemical Co., Ltd. and 0.5 g of reagent primary cobalt oxide manufactured by Kanto Chemical Co., Ltd. After stirring, (A) was prepared by mixing with strong rubbing.

2.1.2 Preparation of (B) (B) was prepared according to 1.1.2.
2.1.3 Preparation of integrated product (C) A total of 1.0 g of (A) obtained in 2.1.1 and (B) obtained in 1.1.2 at a ratio of 1: 1 in a mortar. The mixture was lightly stirred to prepare an integrated product of the present invention (titanium dioxide: zirconium oxide: cobalt oxide: platinum-supported titanium dioxide = 0.166: 0.166: 0.166: 0.5).
2.2. Carbon dioxide reduction experiment A test specimen in which 0.2 g of an integrated product obtained in 1.1.3 was uniformly spread on a copper plate on a glass petri dish with an inner diameter of 68 mm was placed in a refrigerator (in the refrigerator). In order to prevent condensation, cool it for 3 days in a domestic dehumidifier dry pet (component calcium chloride) made by Este Co., Ltd. and take it out (temperature and humidity in the refrigerator at the time of removal is 2 ° C, 15%), gas barrier Put in a bag (OE-4, OE-4) and heat seal the entrance. A 1cm square urethane tape is attached to the gas barrier bag, and air is injected with a syringe so that the air in the bag becomes about 1000 ml. Just under the black light (black light fluorescent lamp FL20S-BLB-A (20W) manufactured by Toshiba Lighting & Technology Corp.) Set. The integrated product in the test body was at a position 10 cm immediately below the black light. Then, the black light is irradiated for 30 minutes, and after irradiation, the methanol gas concentration in the bag is measured using the Kitagawa gas detector tube No119U and the formaldehyde gas concentration is measured using the Kitagawa gas detector tube No171SA. The number of μmoles of methanol gas and formaldehyde gas was calculated (gas concentration (ppm) × residual air volume (ml) / {irradiation time (0.5 Hr) × photocatalyst weight (0.2 g) × 22400}). The temperature of the injected air was 32.5 ° C. and the humidity was 67%, and the measurement results were as shown in Table 1.
The gas remaining in the barrier bag after irradiation with black light was 1000 ml including 200 ml sucked in the measurement of two types of gas detector tubes.

Examples outside the scope of claims.
3.1.1 Preparation of (A) After taking 0.5 g of high purity zirconium oxide 3N of high purity reagent manufactured by Kanto Chemical Co., Ltd. and 0.5 g of reagent grade 1 cobalt oxide manufactured by Kanto Chemical Co. Stirring with strong rubbing, an integrated product having a composition close to that of (A) containing no titanium dioxide was prepared.
2.1.2 Preparation of (B) (B) was prepared according to 1.1.2.
3.1.3 Preparation of integrated product (C) A total of 1.0 g of (A) obtained in 3.1.1 and (B) obtained in 1.1.2 at a ratio of 1: 1 in a mortar. It was lightly stirred to prepare an integrated product of the present invention (titanium dioxide: zirconium oxide: cobalt oxide: platinum-supported titanium dioxide = 0: 0, 25: 0.25: 0.5).

3.2. Carbon dioxide reduction experiment A test specimen in which 0.2 g of an integrated product obtained in 1.1.3 was uniformly spread on a copper plate on a glass petri dish with an inner diameter of 68 mm was placed in a refrigerator (in the refrigerator). In order to prevent condensation, cool it for 2 days in a domestic dehumidifier dry pet (component calcium chloride) manufactured by Este Co., Ltd. and take it out (temperature and humidity in the refrigerator at the time of removal is 4 ° C, 24%), gas barrier Put in a bag (OE-4, OE-4) and heat seal the entrance. A 1cm square urethane tape is attached to the gas barrier bag, and air is injected with a syringe so that the air in the bag becomes about 1000 ml. Just under the black light (black light fluorescent lamp FL20S-BLB-A (20W) manufactured by Toshiba Lighting & Technology Corp.) Set. The integrated product in the test body was at a position 10 cm immediately below the black light. Then, the black light is irradiated for 30 minutes, and after irradiation, the methanol gas concentration in the bag is measured using the Kitagawa gas detector tube No119U and the formaldehyde gas concentration is measured using the Kitagawa gas detector tube No171SA. The number of μmoles of methanol gas and formaldehyde gas was calculated (gas concentration (ppm) × residual air volume (ml) / {irradiation time (0.5 Hr) × photocatalyst weight (0.2 g) × 22400}). The temperature of the injected air was 31.6 ° C. and the humidity was 60%, and the measurement results were as shown in Table 1.
The gas remaining in the barrier bag after irradiation with black light was 1000 ml including 200 ml sucked in the measurement of two types of gas detector tubes.

  In Table 1, Examples 1 and 2 are examples included in the claims, and Example 3 is an example outside the claims.

  In addition, it was found that the barrier bag used in this experiment does not transmit oxygen molecules or nitrogen molecules, but carbon dioxide molecules are relatively easily transmitted. Therefore, when the carbon dioxide molecules in the bag are consumed, a concentration gradient is generated, and carbon dioxide molecules outside the bag (that is, in the atmosphere) enter the bag and are also reduced. It is highly possible that the concentration of formaldehyde and methanol, which are reduction products, has become large. If so, it can be said that the result of the example showed the true value of the carbon dioxide reducing ability of the integrated product of the present invention regardless of the amount of carbon dioxide in the barrier bag before the reduction.

  By using the method of the present invention, it is useful to use steam, carbon dioxide, methanol, formaldehyde, etc. under irradiation of ultraviolet rays having a relatively large wavelength (that is, relatively small energy) such as black light or sunlight including ultraviolet rays. Since a large amount of organic compounds are produced at room temperature, carbon dioxide in the atmosphere or combustion exhaust gas can be a chemical industry resource.

Titanium dioxide generates electrons and holes by photocatalytic action in response to irradiated ultraviolet rays, but if there are hydrogen ions generated by the dissociation of water near the surface of the photocatalyst and further carbon dioxide, It is considered that hydrogen ions are bonded to carbon dioxide by a reducing action to produce low molecular weight organic compounds such as formaldehyde and methanol. In addition, hydroxide ions generated by dissociation of water are considered to exist, and the -valent oxygen constituting the hydroxide ions easily consumes holes due to the strong oxidation action of the holes and easily generates oxygen molecules (O ₂ ) is expected to generate. However, especially in the case of the gas phase, oxygen molecules are not easily generated, and among the electrons and holes generated by the photocatalytic action, a step of electrically erasing holes remaining after the electrons are consumed by the reduction reaction Therefore, the number of holes becomes excessive, and electrons generated by the subsequent photocatalytic action recombine with the remaining holes and disappear, and the supply (reduction action) of electrons is remarkably reduced. Alternatively, when the photocatalyst is in the atmosphere, it is considered that the photocatalytic action itself is hindered by the adsorption of nitrogen on the surface of the photocatalyst, as pointed out by the present inventor in JP2013-6180A.

  As a method for treating the specimen before introducing the mixed gas, it may be stored in the refrigerator for a certain period of time, but more preferably, the specimen is first decompressed and the integrated body (C) composed of (A) and (B). Nitrogen physically adsorbed on the surface is removed, and then (C) is cooled. Or you may perform pressure reduction and cooling simultaneously. Note that the decompression process described in the paragraph [0032] and this paragraph is an idea at present, and the effects such as the increase of the reduced product have not been confirmed by experiments.

1.1 Preparation of integrated product (C) composed of (A) and (B) 1.1.1 Preparation of (A) White titanium dioxide AMT-100 having anatase type crystal structure manufactured by Teika Co., Ltd. in a mortar ( 0.3 g of particle size 6 nm, specific surface area 260 m ² / g), 0.5 g of high purity zirconium oxide 3N (particle size 10-15 microns) manufactured by Kanto Chemical Co., Ltd., and grade 1 reagent manufactured by Kanto Chemical (A) was prepared by taking 0.2 g of cobalt oxide (Co ₃ O ₄ ) and stirring it uniformly, followed by stirring with strong rubbing.
1.1.2 Preparation of (B) Take 1.0 g of white titanium dioxide AMT-100 having an anatase type crystal structure manufactured by Teika Co., Ltd. into a glass petri dish with an inner diameter of 93 mm, add 30 ml of pure water and stir. Add 0.3 g of 1% aqueous solution of chloroplatinic acid and stir, add 0.1 g of reagent grade ethanol and stir, place under 10 cm of 20 W black light and irradiate with black light for 20 hours, then dry at 120 ° C. for 1 hour, Platinum-supported titanium dioxide was prepared.
1.1.3 Preparation of integrated product (C) A total of 1.0 g of (A) obtained in 1.1.1 and (B) obtained in 1.1.2 at a ratio of 1: 1 in a mortar. It was lightly stirred to prepare an integrated product of the present invention (titanium dioxide: zirconium oxide: cobalt oxide: platinum-supported titanium dioxide = 1.5: 2.5: 1.0: 5).

Claims (2)

In a mixed gas containing water vapor and carbon dioxide,
Integrated material consisting of titanium dioxide, zirconium oxide and cobalt oxide (A) and titanium dioxide carrying platinum (B)
The structure (D) in which the object (C) integrated with the material is dispersed on the electrically conductive material,
Irradiate the integrated product (C) with ultraviolet light,
Method for reducing carbon dioxide characterized by producing organic compound The method for reducing carbon dioxide according to claim 1, wherein the electrically conductive substance is a copper plate.