Photocatalyst, method for producing photocatalyst, method for producing hydrogen, method for producing carbon monoxide, and method for producing methane

Abstract

To provide a photocatalyst capable of efficiently producing methane.SOLUTION: At least one kind of metal ion d0 in which an electron configuration of an outermost d orbital is Md0 and at least one kind of metal ion d10 in which an electron configuration of an outermost d orbital is Md10, a total of the number of kinds of Md0 and the number of kinds of Md10 being 5 or more, in an X-ray diffraction pattern measured by an X-ray diffractometer using a CuK α ray, a half-width of a diffraction peak having the highest intensity among diffraction peaks observed at 2 θ: 29.0 ° to 31.0 ° is 0.20 ° or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a photocatalyst, a method for producing a photocatalyst, a method for producing hydrogen, a method for producing carbon monoxide, and a method for producing methane. [Background technology]

[0002] BACKGROUND ART Various techniques have been proposed for synthesizing methane by reacting carbon dioxide with hydrogen for the purpose of immobilizing carbon dioxide or the like. For example, Patent Document 1 discloses a method for synthesizing methane from carbon dioxide and hydrogen, which is characterized by including a first reaction step in which carbon dioxide and hydrogen are reacted to obtain carbon monoxide, and a second reaction step in which the carbon monoxide produced in the first reaction step is reacted with hydrogen to obtain methane.

[0003] On the other hand, high entropy alloys (HEAs) have been proposed as new alloys that are distinct from the technical concepts of conventional alloys (for example, alloys in which one to three main metal elements are added in small amounts of multiple sub-elements). HEAs are defined as alloys composed of five or more main metal elements (i.e., metal elements each accounting for 5 atomic % to 35 atomic % of the total alloy). For example, Non-Patent Document 1 describes TiHfZrNbTaO, an HEA. 10 The alloy is used as a photocatalyst. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-140382 [Non-patent literature]

[0005] [Non-Patent Document 1] Interim evaluation report for the FY2020 Grant-in-Aid for Scientific Research on Innovative Areas (Research Area Proposal Type), "High-Entropy Alloys: A New Material Theory Based on Elemental Diversity and Heterogeneity", Area Number: 6006, Area Abbreviation: High-Entropy Alloys, June 2020 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in Patent Document 1, the process for producing carbon monoxide and hydrogen and the process for producing methane are separated, which poses a problem of increased production costs. Furthermore, as a result of investigations by the inventors of the present disclosure, the HEA disclosed in Non-Patent Document 1 was found to have poor performance as a photocatalyst.

[0007] The present disclosure has been made in light of these circumstances, One embodiment of the present disclosure relates to providing a photocatalyst that can efficiently produce methane. One embodiment of the present disclosure relates to a method for producing a photocatalyst that can efficiently produce methane. One embodiment of the present disclosure relates to providing a method for efficiently producing hydrogen from water. One embodiment of the present disclosure relates to providing a method for efficiently producing carbon monoxide from carbon dioxide. One embodiment of the present disclosure provides a method for producing methane from carbon dioxide and water in one step. [Means for solving the problem]

[0008] The present disclosure includes the following aspects. <1> A photocatalyst comprising a metal oxide, The metal oxide is The electron configuration of the outermost d orbital is d 0 at least one metal ion M d0 and, The electron configuration of the outermost d orbital is d 10 at least one metal ion M d10 and, Said M d0 The number of types and the M d10 The total number of types is 5 or more, In an X-ray diffraction pattern measured by an X-ray diffractometer using CuKα radiation, the half-width of the diffraction peak with the highest intensity among the diffraction peaks observed at 2θ: 29.0° to 31.0° is 0.20° or less. Photocatalyst. <2> Said M d0 But Ti 4+ , V 5+ , Zr 4+ , Nb 5+ , Hf 4+ , Ta 5+ , and W 6+ At least one selected from the group consisting of Said M d10 However, Cu + , Zn 2+ , Ga 3+ , Cd 2+ , In 3+ , Sn 4+ , Pb 4+ , and Bi 5+ At least one selected from the group consisting of <1> The photocatalyst described in <3> Said M d0 But Ti 4+ , Zr 4+ , Nb 5+ , and Ta 5+ Including, Said M d10 However, Zn 2+ or Ga 3+ Including, <1> or <2> The photocatalyst described in <4> The half width is 0.17° or less. <1> ~ <3> The photocatalyst according to any one of the above items. <5> a promoter is attached to the surface of the metal oxide; <1> ~ <4> The photocatalyst according to any one of the above items. <6> Said M d0 and the oxide of M d10A mixture containing the oxide is subjected to a twisting operation under a pressure of 5 GPa or more; Annealing the mixture that has been subjected to the twisting operation at 900°C to 1300°C. <1> ~ <5> 10. A method for producing the photocatalyst according to any one of the above. <7> depositing a promoter on the surface of the metal oxide contained in the annealed mixture; <6> A method for producing the photocatalyst described in <8> mixing the annealed mixture with a sacrificial agent; <6> or <7> A method for producing the photocatalyst described in <9> <1> ~ <5> Using the photocatalyst described in any one of obtaining hydrogen from water, Methods for producing hydrogen. <10> <1> ~ <5> Using the photocatalyst described in any one of obtaining carbon monoxide from carbon dioxide, Carbon monoxide production method. <11> <1> ~ <5> Using the photocatalyst described in any one of further reacting carbon monoxide and hydrogen obtained from carbon dioxide and water to obtain methane; Methods for producing methane. [Effects of the Invention]

[0009] According to one embodiment of the present disclosure, a photocatalyst capable of efficiently producing methane is provided. According to one embodiment of the present disclosure, a method for producing a photocatalyst capable of efficiently producing methane is provided. According to one embodiment of the present disclosure, there is provided a method for efficiently producing hydrogen from water. According to one embodiment of the present disclosure, there is provided a method for efficiently producing carbon monoxide from carbon dioxide. According to one embodiment of the present disclosure, there is provided a method for producing methane in one step from carbon dioxide and water. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of methane production when a photocatalyst according to an embodiment of the present disclosure is used. [Figure 2] FIG. 2 is a diagram schematically showing the configuration of an apparatus for performing HPT (High-Pressure Torsion) treatment. [Figure 3] FIG. 3 shows X-ray diffraction (XRD) patterns of the metal oxide (2-2) and the metal oxide (2-3) obtained in Production Example 2. [Figure 4] FIG. 4 is a graph showing carbon monoxide (CO) production from metal oxides (1-1), (1-2) and (1-3). [Figure 5] FIG. 5 is a graph showing hydrogen (H2) production from metal oxides (1-1), (1-2) and (1-3). [Figure 6] FIG. 6 is a graph showing carbon monoxide (CO) production from metal oxides (2-2) and (2-3). [Figure 7] FIG. 7 is a graph showing hydrogen (H2) production from metal oxides (2-2) and (2-3). [Figure 8] FIG. 8 is a graph showing methane (CH4) production from metal oxides (2-2) and (2-3). [Figure 9] FIG. 9 is a graph showing methane (CH4) production from metal oxides (1-3), (2-3), (3-3), (4-3) and (5-3). [Figure 10] FIG. 10 is a graph showing the production of hydrogen (H2) from water using metal oxides (1-3) and (2-3). DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of the present disclosure will be described in detail below. However, the present disclosure is not limited to the following embodiment. In the following disclosure, components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present disclosure. In the present disclosure, combinations of preferred aspects are more preferred aspects. In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the lower and upper limits, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. In the present disclosure, when the composition contains multiple substances corresponding to each component, the amount of each component in the composition means the total amount of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, "contains mainly" means that the target substance is contained in the largest amount relative to the whole. For example, this means that the content of the target substance is 50% by mass or more relative to the whole. In this disclosure, "mass%" and "wt%" are synonymous, and "parts by mass" and "parts by weight" are synonymous. In this disclosure, "%" indicating the amount of a component is based on mass unless otherwise specified. In the present disclosure, when multiple elements are listed using "or" or "or," unless otherwise expressly stated, it does not exclude the selection of a combination of the multiple elements unless a technical contradiction arises. In the present disclosure, even if an element is referred to in the singular, unless expressly stated otherwise, it does not exclude the presence of a plurality insofar as it does not create a technical contradiction. When embodiments of the present disclosure are described with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. Furthermore, the sizes of the components in each drawing are conceptual, and the relative size relationships between the components are not limited to these.

[0012] ≪Photocatalyst≫ The photocatalyst of the present disclosure is A photocatalyst comprising a metal oxide, The metal oxide is The electron configuration of the outermost d orbital is d 0 at least one metal ion M d0 and, The electron configuration of the outermost d orbital is d 10 at least one metal ion M d10 and, Said M d0 The number of types and the M d10 The total number of types is 5 or more, In an X-ray diffraction pattern measured by an X-ray diffractometer using CuKα radiation, the half-width of the diffraction peak with the highest intensity among the diffraction peaks observed at 2θ: 29.0° to 31.0° is 0.20° or less.

[0013] According to the photocatalyst of the present disclosure, a photocatalyst capable of efficiently producing methane is provided. The action of the photocatalyst of the present disclosure is presumed to be as follows. Located on the left side of the periodic table, when an ion is formed, the electron configuration of the outermost d orbital is d 0 On the other hand, atoms on the right side of the periodic table have an electron configuration of d orbitals in the outermost shell when they become ions. 10 The atom with d has high electronegativity. 0 The metal ion M d0 and d 10 The metal ion M d10Metal oxides containing these compounds are high-entropy oxides due to lattice distortion caused by the presence of various elements with different atomic radii and the coexistence of atoms with high and low electronegativity, which facilitate charge separation, and are excellent active sites for photocatalytic reactions. Furthermore, the inventors speculate that the photocatalyst disclosed herein exhibits a high conversion rate of carbon dioxide and water to carbon monoxide and hydrogen, and also a high conversion rate of carbon monoxide and hydrogen to methane, because it has a homogeneous and high proportion of interstitial oxygen defects in its crystal structure.

[0014] The principle of the photocatalyst of the present disclosure will be explained using Fig. 1. Note that Fig. 1 is a diagram for explanation by way of example, and does not limit the embodiments of the present disclosure. Specifically, as shown in Figure 1, the metal oxide is M, such as TiO2. d0 and M, such as ZnO d10 By including both of these, when the metal oxide is irradiated with light, M d0 and M d10 The transfer of electrons in the conduction band (CB) and holes in the valence band (VB) between the two regions is efficient. d10 The oxidation of water on M to produce oxygen and hydrogen ions, d0 The inventors speculate that the generation of carbon monoxide and hydrogen by the reduction of carbon dioxide and hydrogen ions as described above is carried out efficiently, and that the production of methane from carbon monoxide and hydrogen is also carried out efficiently.

[0015] And M d0 The number of types and M d10 The inventors speculate that when the total number of types is five or more, the metal oxide becomes the high-entropy oxide described above.

[0016] Furthermore, in the X-ray diffraction pattern of the photocatalyst of the present disclosure measured by an X-ray diffractometer using CuKα radiation, the half-value width of the diffraction peak with the highest intensity among the diffraction peaks observed at 2θ=29.0° to 31.0° is 0.20° or less. In the present disclosure, the half width refers to the full width at half maximum (FWHM), which is the half width of the diffraction peak with the highest intensity among the diffraction peaks observed at 2θ=29.0° to 31.0° in an X-ray diffraction pattern measured by an X-ray diffraction (XRD) device using CuKα radiation. Although the reason for this is not clear, the inventors speculate that if the half-width is 0.20° or less, the photocatalyst of the present disclosure will have a homogeneous and high proportion of oxygen vacancies that are effective in the photocatalytic reaction. It should be noted that the present disclosure is in no way limited to the above-mentioned presumed mechanism.

[0017] <Metal oxides> The photocatalyst of the present disclosure comprises a metal oxide.

[0018] From the viewpoint of efficiently producing methane, the total content of the metal oxides is preferably 90% by mass to 100% by mass, more preferably 95% by mass to 100% by mass, even more preferably 98% by mass to 100% by mass, and particularly preferably 100% by mass, relative to the total amount of the photocatalyst.

[0019] [M d0 ] Metal oxides have an electron configuration of the outermost d orbital of d 0 at least one metal ion M d0 Includes: From the viewpoint of efficient methane production, M d0 is Ti 4+ , V 5+ , Zr 4+ , Nb 5+ , Hf 4+ , Ta 5+ , and W 6+ Preferably, the material contains at least one selected from the group consisting of Ti 4+ , V 5+ , Zr 4+ , Nb 5+ , Hf 4+ , Ta 5+ , and W 6+ More preferably, the material contains at least two selected from the group consisting of Ti 4+ , V5+ , Zr 4+ , Nb 5+ , Hf 4+ , Ta 5+ , and W 6+ It is more preferable that the composition contains at least four kinds selected from the group consisting of Ti 4+ , V 5+ , Zr 4+ , Nb 5+ , Hf 4+ , Ta 5+ , and W 6+ More preferably, the composition contains four selected from the group consisting of Ti 4+ , Zr 4+ , Nb 5+ , and Ta 5+ It is particularly preferred that the composition contains:

[0020] From the viewpoint of efficient methane production, M d0 The total content of the metal oxides including the above is preferably 10% by mass to 70% by mass, more preferably 20% by mass to 60% by mass, and even more preferably 30% by mass to 50% by mass, based on the total amount of the metal oxides.

[0021] [M d10 ] Metal oxides have an electron configuration of the outermost d orbital of d 10 at least one metal ion M d10 Includes: From the viewpoint of efficient methane production, M d10 is Cu + , Zn 2+ , Ga 3+ , Cd 2+ , In 3+ , Sn 4+ , Pb 4+ , and Bi 5+ Preferably, the material contains at least one selected from the group consisting of Cu + , Zn 2+ , Ga 3+ , Cd 2+ , In 3+ , Sn 4+ , Pb 4+ , and Bi 5+More preferably, the compound contains one selected from the group consisting of Zn 2+ , Ga 3+ , In 3+ , and Bi 5+ It is more preferable that the compound contains one selected from the group consisting of Zn 2+ and Ga 3+ It is more preferable that the compound contains at least one of the following: Zn 2+ or Ga 3+ More preferably, the compound contains Zn. 2+ or Ga 3+ It is particularly preferred that:

[0022] From the viewpoint of efficient methane production, M d10 The total content of the metal oxides including the above is preferably 1 mass % to 15 mass %, more preferably 2 mass % to 12 mass %, and even more preferably 3 mass % to 8 mass %, based on the total amount of the metal oxides.

[0023] [M d0 and M d10 combination of From the viewpoint of efficient methane production, M contained in metal oxides d0 and M d10 As a combination of M d0 But Ti 4+ , V 5+ , Zr 4+ , Nb 5+ , Hf 4+ , Ta 5+ , and W 6+ and M d10 However, Cu + , Zn 2+ , Ga 3+ , Cd 2+ , In 3+ , Sn 4+ , Pb 4+ , and Bi 5+ It is preferable that the composition contains at least one selected from the group consisting of: M d0 But Ti 4+ , V 5+ , Zr 4+, Nb 5+ , Hf 4+ , Ta 5+ , and W 6+ M d10 However, Cu + , Zn 2+ , Ga 3+ , Cd 2+ , In 3+ , Sn 4+ , Pb 4+ , and Bi 5+ It is more preferable that the composition contains one selected from the group consisting of: M d0 But Ti 4+ , V 5+ , Zr 4+ , Nb 5+ , Hf 4+ , Ta 5+ , and W 6+ M d10 However, Zn 2+ , Ga 3+ , In 3+ , and Bi 5+ It is more preferable that the composition contains one selected from the group consisting of: M d0 But Ti 4+ , Zr 4+ , Nb 5+ , Ta 5+ Including M d10 However, Zn 2+ or Ga 3+ More preferably, it comprises M d0 But Ti 4+ , Zr 4+ , Nb 5+ , Ta 5+ and M d10 However, Zn 2+ or Ga 3+ It is particularly preferred that:

[0024] From the viewpoint of efficient methane production, M d0 M relative to the total content of metal oxides including d10The total content of the metal oxides including the above is preferably 5% by mass to 30% by mass, more preferably 8% by mass to 25% by mass, and even more preferably 12% by mass to 20% by mass.

[0025] [M d0 and M d10 Number of types] In metal oxides, M d0 The number of types and M d10 The total number of types is 5 or more. d0 and M d10 There is no particular upper limit on the total number of types of M. For example, it may be 10 or less, or 7 or less. d0 and M d10 The total number of types is preferably five.

[0026] <Components other than metal oxides> The photocatalyst of the present disclosure may contain components other than metal oxides as needed. Examples of components other than metal oxides include promoters and the like.

[0027] The total content of components other than metal oxides may be 0% by mass to 3% by mass, 0% by mass to 2% by mass, or 0% by mass to 1% by mass relative to the total amount of the photocatalyst.

[0028] [Cocatalyst] Specific examples of the promoter include platinum, gold, palladium, ruthenium, rhodium, silver, copper, and iridium. The promoter may be attached to the surface of the metal oxide (i.e., supported), or may not be attached (i.e., not supported). The promoter may be used alone or in combination of two or more types, but preferably contains platinum.

[0029] The total content of the co-catalysts is preferably 1% by mass to 50% by mass, more preferably 2% by mass to 40% by mass, and even more preferably 3% by mass to 30% by mass, based on the total amount of the photocatalyst.

[0030] <FWHM of diffraction peak> In the photocatalyst of the present disclosure, in an X-ray diffraction pattern measured with an X-ray diffractometer using CuKα radiation, the half-width of the diffraction peak with the highest intensity among the diffraction peaks observed at 2θ: 29.0° to 31.0° is 0.20° or less.

[0031] The half width is preferably 0.18° or less, and more preferably 0.17° or less. The lower limit of the half width is not particularly limited, and may be, for example, 0.05° or more.

[0032] When a graph obtained by X-ray diffraction under the conditions described in the Examples is fitted by the least squares method and baseline corrected, the maximum peak intensity at 2θ=29.0° to 31.0° is preferably 5000 [intensity [counts]] or more, more preferably 6000 [intensity [counts]] or more, even more preferably 10000 [intensity [counts]] or more, and particularly preferably 12000 [intensity [counts]] or more. The upper limit of the half-width is not particularly limited, and may be, for example, 500000 [intensity [counts]] or less.

[0033] <Photocatalyst manufacturing method> The method for producing a photocatalyst according to the present disclosure includes: Said M d0 and the oxide of M d10 A mixture containing the oxide is subjected to a twisting operation under a pressure of 5 GPa or more; and annealing the mixture that has been subjected to the twisting treatment at 900°C to 1300°C.

[0034] According to the method for producing a photocatalyst of the present disclosure, a photocatalyst capable of efficiently producing methane is produced. The action of the photocatalyst manufacturing method of the present disclosure is presumed to be as follows. The electron configuration of the outermost d orbital is d0 at least one metal ion M d0 The oxides and the electron configuration of the outermost d orbital are d 10 at least one metal ion M d10 When a mixture containing oxides of metals is subjected to a twisting process under a pressure of 5 GPa or more, the metal oxides in the mixture undergo plastic deformation. 0 The metal ion M d0 and d 10 The metal ion M d10 Metal oxides containing these compounds are high-entropy oxides due to lattice distortion caused by the presence of various elements with different atomic radii and the coexistence of atoms with high and low electronegativity, which facilitate charge separation, and are excellent active sites for photocatalytic reactions. Furthermore, the inventors speculate that the photocatalyst disclosed herein exhibits a high conversion rate of carbon dioxide and water to carbon monoxide and hydrogen, and also a high conversion rate of carbon monoxide and hydrogen to methane, because it has a homogeneous and high proportion of interstitial oxygen defects in its crystal structure.

[0035] In the photocatalyst manufacturing method of the present disclosure, the mixture that has been subjected to the twisting treatment is annealed at 900°C to 1300°C. This is because simply subjecting the mixture to the twisting treatment under high pressure does not allow the elements to mix on an atomic scale. By annealing the mixture that has been subjected to the twisting treatment at 900°C to 1300°C, the elements can be mixed on an atomic scale, and a single-phase or two-phase high-entropy oxide can be effectively formed. It should be noted that the present disclosure is in no way limited to the above-mentioned presumed mechanism.

[0036] <Processing that involves twisting under high pressure> The method for producing the photocatalyst of the present disclosure comprises: d0 oxides and M d10 The method includes subjecting a mixture containing the oxide of the present invention to a twisting operation under a pressure of 5 GPa or more.

[0037] [M d0 oxides and M d10 mixtures containing oxides of From the viewpoint of atomic-scale mixing of elements, the M d0 and the oxide of M d10 The mixture containing the oxide of M d0 and the oxide of M d10 It is preferable that the mixed powder contains oxides of the above.

[0038] From the viewpoint of obtaining a photocatalyst that can efficiently produce methane, d0 Specific examples of the oxide include TiO2, V2O5, ZrO2, Nb2O5, HfO2, Ta2O5, and WO3, and the oxide preferably contains at least one selected from the group consisting of TiO2, V2O5, ZrO2, Nb2O5, HfO2, Ta2O5, and WO3, and more preferably contains at least two selected from the group consisting of TiO2, V2O5, ZrO2, Nb2O5, HfO2, Ta2O5, and WO3. It is more preferable that the composition contains at least four selected from the group consisting of TiO2, V2O5, ZrO2, Nb2O5, HfO2, Ta2O5, and WO3, it is even more preferable that the composition contains four selected from the group consisting of TiO2, V2O5, ZrO2, Nb2O5, HfO2, Ta2O5, and WO3, it is particularly preferable that the composition contains TiO2, ZrO2, Nb2O5, and Ta2O5.

[0039] From the viewpoint of obtaining a photocatalyst that can efficiently produce methane, d10 Specific examples of the oxide include Cu2O, ZnO, Ga2O3, CdO, In2O3, SnO2, PbO2, and Bi2O5. Preferably, the oxide contains at least one selected from the group consisting of Cu2O, ZnO, Ga2O3, CdO, In2O3, SnO2, PbO2, and Bi2O5, more preferably, it contains one selected from the group consisting of Cu2O, ZnO, Ga2O3, CdO, In2O3, SnO2, PbO2, and Bi2O5, even more preferably, it contains one selected from the group consisting of ZnO, Ga2O3, In2O3, and Bi2O5, still more preferably, it contains at least one of ZnO and Ga2O3, even more preferably, it contains ZnO or Ga2O3, and ZnO or Ga2O3 is particularly preferred.

[0040] From the viewpoint of obtaining a photocatalyst that can efficiently produce methane, d0 oxides and M d10 In a mixture containing oxides of M d0 M relative to the total content of oxides d10 The total content of these oxides is preferably 1% by mass to 20% by mass, more preferably 3% by mass to 15% by mass, and even more preferably 6% by mass to 12% by mass.

[0041] [High-pressure twisting process] In the present disclosure, the process of performing a twisting operation under an applied pressure of 5 GPa or more is also referred to as HPT (High-Pressure Torsion) process. The details of the method for carrying out the HPT treatment are not particularly limited. For example, the HPT treatment may be carried out according to the following procedure using an HPT apparatus having the configuration shown in FIG. The HPT apparatus shown in Fig. 2 is equipped with a pair of anvils (upper anvil and lower anvil) for applying pressure to a sample. At least one of the anvils (for example, the lower anvil in Fig. 2) is rotatable in a direction perpendicular to the direction of pressure applied to the sample.

[0042] When performing HPT treatment using the HPT apparatus shown in Figure 2, first, a metal oxide mixture as a sample is placed between a pair of anvils. Next, the anvils are closed to apply pressure to the mixture (pressure application). Next, while pressure is being applied to the sample, one of the anvils is rotated in a direction perpendicular to the direction of pressure being applied to the sample (twisting operation). The state of the resulting metal oxide can be controlled by changing the conditions of the HPT treatment (pressure, rotation speed of the device in the twisting operation, temperature, etc.).

[0043] The pressure applied to the sample in the HPT treatment is not particularly limited as long as it is 5 GPa or more, and can be selected depending on the type of sample and the desired physical properties as a photocatalyst. From the viewpoint of increasing the absorbance of the metal oxide in the visible region, the pressure applied to the sample is preferably 5 GPa or more, more preferably 6 GPa or more, and may be 10 GPa or less, 9 GPa or less, or 8 GPa or less.

[0044] The conditions for the twisting operation applied to the sample are not particularly limited, and can be selected depending on the type of sample and the desired physical properties as a photocatalyst. From the viewpoint of increasing the absorbance of the metal oxide in the visible range, the rotation number of the device in the twisting operation is preferably 0.5 rotations or more, more preferably 1 rotation or more, and even more preferably 2 rotations or more. The rotation number of the device in the twisting operation may be 20 rotations or less.

[0045] The temperature of the sample during the HPT treatment is not particularly limited and can be selected depending on the type of sample and the desired physical properties as a photocatalyst, for example, it may be selected from the range of 273 K (0° C.) to 523 K (250° C.).

[0046] Whether or not a metal oxide has been subjected to HPT treatment can be confirmed by a known method, for example, by comparing the physical properties, such as color, particle structure, or crystal structure, between the raw metal oxide and the metal oxide after HPT treatment.

[0047] <Annealing at 900℃~1300℃> The method for producing a photocatalyst according to the present disclosure includes annealing the mixture that has been subjected to the twisting treatment at 900°C to 1300°C.

[0048] The temperature at which the annealing treatment is carried out is 900°C to 1300°C, preferably 950°C to 1250°C, more preferably 900°C to 1200°C, further preferably 950°C to 1150°C, and particularly preferably 1000°C to 1150°C. The annealing time is preferably 0.5 to 70 hours.

[0049] <Other processing> The method for producing a photocatalyst according to the present disclosure may include treatments other than the HPT treatment and annealing treatment, such as vapor deposition of a promoter and mixing with a sacrificial agent.

[0050] [Vapor deposition of promoter] The method of making the photocatalyst of the present disclosure preferably includes vapor-depositing a promoter onto the surface of the metal oxide contained in the annealed mixture. Specific examples of the co-catalyst include platinum, gold, palladium, ruthenium, rhodium, silver, copper, and iridium. The co-catalyst may be attached to the surface of the metal oxide used as the photocatalyst (i.e., supported), or may not be attached to the surface (i.e., unsupported). A single co-catalyst may be used, or two or more may be used in combination, but platinum is preferred. Platinum may be vapor-deposited, for example, as HPtCl6·6H2O.

[0051] The method for depositing the co-catalyst on the surface of the metal oxide contained in the annealed mixture is not particularly limited. For example, the co-catalyst is deposited on the surface of the metal oxide contained in the annealed mixture by dispersing the annealed mixture in a liquid containing the co-catalyst.

[0052] [Mixing with sacrificial agents] The method of manufacturing the photocatalyst of the present disclosure preferably includes mixing the annealed mixture with a sacrificial agent, which promotes hydrogen production by preventing the recombination of electron-hole pairs generated by excitation of the photocatalyst (specifically, by injecting electrons donated by the sacrificial agent into the holes). Specific examples of sacrificial agents include monohydric alcohols such as methanol and ethanol; dihydric alcohols such as ethylene glycol and propylene glycol; trihydric alcohols such as glycerin; carboxylic acids such as formic acid, acetic acid, and oxalic acid; amines such as ethylenediaminetetraacetic acid (EDTA) and triethanolamine (TEA); sugars; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; and polyolefin resins such as polyethylene and polypropylene. Although only one type of sacrificial agent may be used, or two or more types may be used in combination, it is preferable that the sacrificial agent contains a monohydric alcohol.

[0053] The method for mixing the annealed mixture with the sacrificial agent is not particularly limited. For example, the annealed mixture and the sacrificial agent are mixed by dispersing the annealed mixture in a liquid containing the sacrificial agent.

[0054] <Hydrogen production method> The method for producing hydrogen of the present disclosure includes obtaining hydrogen from water using the photocatalyst of the present disclosure. The photocatalyst of the present disclosure can decompose water into hydrogen and oxygen. The method for producing hydrogen of the present disclosure may obtain hydrogen from water and carbon dioxide using the photocatalyst of the present disclosure.

[0055] In the photocatalyst disclosed herein, the metal oxide contained in the photocatalyst itself exhibits excellent light utilization efficiency. Therefore, for example, the hydrogen production efficiency can be improved without supporting a metal as a promoter on the metal oxide or doping the metal oxide with a different element. In other words, the hydrogen production method disclosed herein can achieve high hydrogen production efficiency using a photocatalyst without increasing production costs due to metal support or doping, or generating waste liquid due to chemical treatment.

[0056] The method for producing hydrogen disclosed herein simply requires reacting water with the photocatalyst disclosed herein, and other detailed production conditions are not particularly limited, and the method can be carried out under conditions similar to those for reaction with known photocatalysts. For example, the light used in the photocatalytic reaction may be visible light, ultraviolet light, or infrared light, or may be sunlight or xenon light. The wavelength of the light may be, for example, 400 nm to 800 nm.

[0057] <Method for producing carbon monoxide> The method for producing carbon monoxide of the present disclosure includes obtaining carbon monoxide from carbon dioxide using the photocatalyst of the present disclosure. The photocatalyst of the present disclosure can reduce carbon dioxide and efficiently produce carbon monoxide. The method for producing carbon monoxide of the present disclosure may obtain carbon monoxide from water and carbon dioxide using the photocatalyst of the present disclosure.

[0058] In the photocatalyst disclosed herein, the metal oxide contained in the photocatalyst itself exhibits excellent light utilization efficiency. Therefore, for example, the carbon monoxide production efficiency can be improved without supporting a metal as a promoter on the metal oxide or doping the metal oxide with a different element. In other words, the carbon monoxide production method disclosed herein can achieve high carbon monoxide production efficiency using a photocatalyst without increasing production costs due to metal support or doping, or generating waste liquid due to chemical treatment.

[0059] An embodiment of the carbon monoxide production method of the present disclosure also includes a synthesis gas production method. This synthesis gas production method includes producing both hydrogen and carbon monoxide by the above-mentioned hydrogen production method and carbon monoxide production method to produce synthesis gas. The obtained synthesis gas can be produced by the Fischer-Tropsch synthesis (2nH2 + nCO → -(CH2) n - + nH2O) can be used in the process of producing hydrocarbons.

[0060] The method for producing carbon monoxide of the present disclosure simply requires reacting carbon dioxide with the photocatalyst of the present disclosure, and other detailed production conditions are not particularly limited, and the method can be carried out under conditions similar to the reaction conditions for known photocatalysts. For example, the light used in the photocatalytic reaction may be visible light, ultraviolet light, or infrared light, or may be sunlight or xenon light. The wavelength of the light may be, for example, 400 nm to 800 nm.

[0061] <Methane production method> The method for producing methane of the present disclosure includes using the photocatalyst of the present disclosure to further react carbon monoxide and hydrogen obtained from carbon dioxide and water to obtain methane. The method for producing methane according to the present disclosure may include obtaining carbon monoxide and hydrogen from carbon dioxide and water using the photocatalyst according to the present disclosure, and further obtaining methane from the obtained carbon monoxide and hydrogen. The photocatalyst according to the present disclosure can efficiently produce carbon monoxide and hydrogen from carbon dioxide and water, and can also efficiently produce methane by reacting the carbon monoxide and hydrogen. In other words, according to the method for producing methane according to the present disclosure, methane can be produced in one step from carbon dioxide and water.

[0062] Methane synthesized by the methane production method of the present disclosure is applicable not only to city gas supply applications, but also to a wide range of applications and fields that require a supply of high-purity methane, such as fuel for power generation and NGV (natural gas vehicle). The carbon dioxide generated during the combustion of methane for the above-mentioned purposes can be used as a raw material for methane production by using the photocatalyst of the present disclosure together with water. Therefore, the embodiment of the methane production method of the present disclosure can contribute to the realization of a carbon-neutral cycle.

[0063] The methane production method of the present disclosure simply requires reacting carbon dioxide and water using the photocatalyst of the present disclosure, and other detailed production conditions are not particularly limited, and can be carried out under conditions similar to the reaction conditions for known photocatalysts. For example, the light used in the photocatalytic reaction may be visible light, ultraviolet light, or infrared light, or may be sunlight or xenon light. The wavelength of the light may be, for example, 400 nm to 800 nm. [Example]

[0064] The present disclosure will be explained in more detail below with reference to examples, but the present disclosure is not limited to the following examples as long as it does not deviate from the gist of the disclosure. The materials, amounts used, proportions, and processing procedures shown in the following examples can be changed as appropriate as long as they do not deviate from the gist of the present disclosure.

[0065] [1] Measurement and evaluation methods Various physical properties were measured and evaluated by the following methods.

[0066] [1.1] Full width at half maximum (FWHM) of the diffraction peak with the highest intensity The metal oxides obtained by the method described below were ground in an agate mortar to prepare a mixed powder. This mixed powder was evenly placed in the recesses of a silicon plate (Rigaku Corporation) for wide-angle X-ray diffraction profile measurement. The mixed powder was compressed using a glass plate to form a flat surface. The silicon plate containing the metal oxide was attached to a wide-angle X-ray diffractometer (device: SmartLab, Rigaku Corporation, measurement software: PDXL). Specifically, the silicon plate was attached to the standard sample stage in the sample chamber of the wide-angle X-ray diffractometer. The wide-angle X-ray diffractometer and measurement conditions are described below. Next, wide-angle X-ray diffraction profile measurement was performed using CuKα radiation and X-ray diffraction at a wavelength λ of 0.1542 nm under the following <Optical Conditions>. Next, a diffraction profile was obtained under the following measurement conditions, and the resulting graph was fitted by the least squares method and baseline corrected. From the baseline-corrected graph, the full width at half maximum (FWHM) of the diffraction peak with the highest intensity among the diffraction peaks observed at 2θ = 29.0 to 31.0° was calculated.

[0067] <Optical conditions> Slit system: Variable + fixed slit system Solar / PSC: 5° IS:2 / 3° ISL: 10mm RS1:2 / 3° Solar: 5° RS2: 0.3 mm IS: 2.211mm RS1: 1.315mm RS2: 0.3 mm

[0068] <Measurement conditions> Scan axis: 2θ / θ Scan mode: 1D (scan) Energy Mode: Standard Start: 10° End: 80 End: 100° (scan angle) Step: 0.05° (0.01°) Speed: 2° / min Tube voltage: 45kV Tube current: 200mA

[0069] [2] Examples and comparative examples of photocatalysts and their manufacturing methods [2.1] Manufacturing Example 1 The powder raw materials TiO2 (55 mg), ZrO2 (85 mg), Nb2O5 (92 mg), Ta2O5 (154 mg), and ZnO (57 mg) were mixed and pressed under a pressure of 380 MPa to obtain a pellet-shaped metal oxide (1-1). Metal oxide (1-1) was then twisted (1 rpm, 6 turns) at 300 K (27 °C) under a pressure of 6 GPa using the high-pressure twisting apparatus shown in Figure 2 to obtain metal oxide (1-2). Metal oxide (1-2) was then annealed at 1100 °C for 48 hours, and finally metal oxide (1-3) (TiZrNbTaZnO 10 ) was obtained.

[0070] [2.2] Manufacturing Example 2 Metal oxide (2-2) was obtained by twisting under pressure in the same manner as in Production Example 1, except that Ga2O3 (65 mg) was used instead of ZnO (57 mg) as a raw material. Furthermore, metal oxide (2-2) that had been twisted in the same manner as in Production Example 1 was annealed to obtain metal oxide (2-3) (TiZrNbTaGaO 10.5 ) was obtained.

[0071] [2.3] Manufacturing Example 3 The metal oxide (3-3) (TiZrNbTaBiO) was obtained by twisting under pressure in the same manner as in Production Example 1, except that BiO (147 mg) was used instead of ZnO (57 mg). 11.5 ) was obtained.

[0072] [2.4] Manufacturing Example 4 The metal oxide (4-3) (TiZrNbTaInO 10.5 ) was obtained.

[0073] [2.5] Manufacturing Example 5 The metal oxide (5-3) (TiZrNbTaHfO) was obtained by the same method as in Production Example 1, except that TiO (52 mg), ZrO (81 mg), HfO (138 mg), NbO (87 mg), and TaO (145 mg) were used as raw materials. The metal oxide (5-3) was obtained by twisting under pressure and then annealing. 11 ) was obtained.

[0074] For the metal oxides obtained in Production Examples 1 to 5, the diffraction peaks observed at 2θ=29.0° to 31.0° had the highest intensity, and the 2θ [°], maximum intensity [counts], and full width at half maximum (FWHM) [°] were as shown in Table 1. In Table 1, [-] indicates that no diffraction peak was observed.

[0075] [Table 1]

[0076] FIG. 3 shows the X-ray diffraction (XRD) patterns observed at 2θ=10° to 80° for the metal oxide (2-2) and metal oxide (2-3) obtained in Production Example 2.

[0077] [3] Examples and comparative examples of reactions using photocatalysts [3.1] Carbon dioxide and water produce carbon monoxide, hydrogen, and methane Using the obtained metal oxide, a test was carried out to produce carbon monoxide, hydrogen, and methane from carbon dioxide and water by the method described below. The reactor used a continuous quartz reactor, and the reaction medium was methanol, a sacrificial agent, at 8 cm 3 100 mg of the obtained metal oxide was dispersed in 500 ml of 1 M NaHCO3 aqueous solution (buffer solution). Carbon dioxide gas was bubbled through a hole at the top of the reactor at a flow rate of 30 mL / min and passed through the reaction medium. The photocatalytic reaction was carried out using a high-pressure mercury lamp (Cenlite, HL400BH-8, 400 W) installed in the reactor at a 14 W / cm 2 The experiment was carried out at an intensity of 1000 kJ / s. Before starting the light irradiation, a blank test was carried out without irradiation for 2 hours. The reaction temperature was kept constant at 298 K using a water chiller. The gas generated during the reaction was allowed to flow into a gas chromatograph (Shimadzu Corporation, GC-8A) through a hole at the top of the reactor. To prevent gas accumulation, a separate gas outlet served as a vent. The gas chromatograph was equipped with a flame ionization detector with a methane converter (Shimadzu Corporation, MTN-1) and a thermal conductivity detector to measure the production rates of carbon monoxide, hydrogen, and methane. The production rate data for carbon monoxide (CO), hydrogen (H2), and methane (CH4) from 0 hours (start of the test) to 8 hours when using each metal oxide are shown in Figures 4 to 9. The production rates of CO, H2, and CH4 5 hours after the start of the test are as shown in Table 2. In Table 2, [-] indicates that the data was not measured.

[0078] [Table 2]

[0079] [3.2] Hydrogen production from water For the metal oxide (1-3) and the metal oxide (2-3), a test for reducing water to produce hydrogen was carried out by the method described below. The photocatalytic reaction took place in a volume of 193 cm 3A cylindrical batch reactor was placed in the reactor, and xenon light (Cenlite, HL400BH-8, 300W) was irradiated at 15 W / cm 2 The water-splitting reactor was connected to a circulation pump that could easily circulate the gas in the circuit. The water-splitting reaction may generate oxygen, so it was necessary to confirm that there was no oxygen in the system. Therefore, a vacuum pump and argon gas were used to evacuate the gas in the system for a sufficient time until all oxygen gas had been removed. To start the reaction, 50 mg of each metal oxide sample was placed on a 27 cm 3 of H2O, 8cm 3 of methanol (sacrificial agent), and optionally 0.25 cm 3 The catalyst was dispersed in a mixture of 0.01M H3PtCl6·6H2O (promoter, for depositing Pt), and . Sampling from the reactor was performed every hour using a gas sampling valve consisting of two four-way valves. Finally, the hydrogen production rate was measured using a gas chromatograph (Shimadzu, GC-8A, Ar carrier) equipped with a molecular sieve column and a thermal conductivity detector (TCD-GC). Details are shown in Figure 10.

[0080] As a result, the metal oxide (2-3) (cocatalyst (0.25 cm 3 When 0.01M H3PtCl6·6H2O was used as a photocatalyst, the hydrogen production rate after 180 minutes from the start of the test was 22.0 mmol / m 2 (Note: "m 2 " indicates the surface area of ​​the photocatalyst used.) Under the same conditions, the hydrogen production rate of metal oxide (1-3) (with co-catalyst) was 18.5 mmol / m 2 It was. In addition, the promoter (0.25 cm 3 The hydrogen evolution rate of metal oxide (2-3) without 0.01M H3PtCl6·6H2O was 21.0 mmol / m 2 It was.

[0081] From the above, it was concluded that the metal oxides (1-3), (2-3), (3-3), and (4-3) were photocatalysts capable of efficiently producing methane. Furthermore, the metal oxides (1-3), (2-3), (3-3), and (4-3) enabled efficient production of hydrogen from water, efficient production of carbon monoxide from carbon dioxide, and one-step production of methane from carbon dioxide and water.

Claims

1. A photocatalyst comprising a metal oxide, The metal oxide is The electron configuration of the outermost d orbital is d ０ At least one metal ion M ｄ０ and, The electron configuration of the outermost d orbital is d １０ At least one metal ion M ｄ１０ and, Said M ｄ０ and the number of types of M ｄ１０ The total number of types is 5 or more, In an X-ray diffraction pattern measured by an X-ray diffractometer using CuKα radiation, the half-value width of the diffraction peak having the highest intensity among the diffraction peaks observed at 2θ: 29.0° to 31.0° is 0.20° or less. Photocatalyst.

2. Said M ｄ０ But Ti ４＋ , V ５＋ , Zr ４＋ , Nb ５＋ , Hf ４＋ , Ta ５＋ , and W ６＋ At least one selected from the group consisting of Said M ｄ１０ But Cu ＋ , Zn ２＋ , Ga ３＋ , Cd ２＋ , In ３＋ , Sn ４＋ , Pb ４＋ , and Bi ５＋ At least one selected from the group consisting of The photocatalyst according to claim 1.

3. Said M ｄ０ But Ti ４＋ , Zr ４＋ , Nb ５＋ , and Ta ５＋ Including, Said M ｄ１０ But Zn ２＋ or Ga ３＋ Including, The photocatalyst according to claim 1.

4. The half width is 0.17° or less. The photocatalyst according to claim 1.

5. a promoter is attached to the surface of the metal oxide; The photocatalyst according to claim 1.

6. Said M ｄ０ and the oxides of M ｄ１０ A treatment is performed to twist the mixture containing the oxide of the present invention while applying a pressure of 5 GPa or more to the mixture. Annealing the mixture that has been subjected to the twisting operation at 900°C to 1300°C. A method for producing the photocatalyst according to any one of claims 1 to 5.

7. depositing a promoter on the surface of the metal oxide contained in the annealed mixture; A method for producing the photocatalyst according to claim 6.

8. mixing the annealed mixture with a sacrificial agent; A method for producing the photocatalyst according to claim 6.

9. Using the photocatalyst according to any one of claims 1 to 5, obtaining hydrogen from water, Methods for producing hydrogen.

10. Using the photocatalyst according to any one of claims 1 to 5, obtaining carbon monoxide from carbon dioxide, Carbon monoxide production method.

11. Using the photocatalyst according to any one of claims 1 to 5, further reacting carbon monoxide and hydrogen obtained from carbon dioxide and water to obtain methane; Methods for producing methane.

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