JP4859217B2 - Metal oxide catalyst - Google Patents

Description

The present invention relates to a metal oxide catalyst that decomposes a water molecule H—O—H in contact with a surface or a Q—O—H type organic molecule having a hydroxyl group (Q is an arbitrary group), and more specifically, is stable at room temperature. The present invention relates to a metal oxide catalyst made of an oxide having a structure (MOx) in which metal ions (M ^{n +} ) are surrounded by oxygen ions in a crystal structure in a state.

  Conventionally, when a metal oxide is used as a chemical decomposition catalyst or as a photocatalyst, it has been a conventional means to increase the catalyst surface area in order to increase the reaction efficiency. This is because even if the details of the catalytic reaction mechanism are not clear, it is clear that the larger the surface area than the smaller the surface area, the greater the action even if the amount of catalyst used is small. However, there has been almost no attempt to obtain a highly efficient catalyst by actively controlling the coordination number of oxygen to metal ions in metal oxides, whether it is a catalyst for decomposition reaction of chemical substances or a photocatalyst. .

References for understanding the present invention are exemplified below.
J. et al. A. Baglio, G.G. . Gashurov, Acta Cryst. B24, 292 (1968). P. M.M. Touboul and P.M. Toledano, Acta Cryst. B36, 240 (1980). S. Tokunaga, H.M. Kato, A.A. Kudo, Chem. Mater. 13 (2001) 4624-4628 A. W. Sleight, H.M. -y. Chen, A.M. Ferretti, D.H. E. Cox, Mater. Res. Bull. 14 (1979) 1571-1581

  The inventor tackled this problem and found that the target molecule is surely and rapidly adsorbed on the catalyst surface in the initial reaction process, which is an important condition for increasing the efficiency of the catalytic reaction. The problem was to obtain a highly efficient catalyst.

Invention 1 of the metal oxide catalyst (where ^Si 4+, ^{B 3+} also a category of metal ion ^{(M n +).)} Is at room temperature a metal ion in the crystal structure in the stable state ^{(M n +)} is x number of oxygen ions Metal oxide consisting of an oxide having an enclosed structure (MOx) and decomposing water molecules H—O—H contacting the surface or Q—O—H type organic molecules having a hydroxyl group (Q is an arbitrary group) a catalyst, Ri tare removing a portion of the metal ion (M n ⁺⁾ and oxygen ions average distance of oxygen ions is 2.2 angstroms or less in the structure (MOx) in its surface, the metal ions are ^{, In 3+, Ga 3+, Al} 3+, B 3+, Si 4+, Ge 4+, Sn 4+, Ti 4+, Zr 4+, Hf 4+, V 5+, Nb 5+, Ta 5+, Sb 5+, Bi 5+, W 6+, o ^6+, and in one or more of ^{Cr 6+} ions, x of the A octahedral x is 6 (MOx), or oxygen ions to be removed is 5 or less, or, wherein (MOx) there a tetrahedron is 4, was adopted a structure in which oxygen ions to be removed is 3 or less, wherein the der Rukoto.

Invention 2 of the metal oxide catalyst employed the configuration wherein the Oite the invention 1, a semiconductor which does not exhibit metallic electric conductivity.

Invention 3 of the metal oxide catalyst, in the first or second aspect, and characterized therein matrix crystals, (wherein, R Y elemental) vanadium-containing composite oxide represented by a composition RVO ₄ that is The configuration to adopt was adopted.

The metal oxide catalyst of the invention 4 employs a configuration characterized in that in the invention 3 , the inside of the host crystal has a zircon type crystal structure belonging to the I41 / amd space group.

The metal oxide catalyst according to the invention 5 is characterized in that, in the invention 1 or 2, the inside of the base crystal is a vanadium-containing composite oxide (wherein T is In) represented by the composition TVO _4. It was adopted.

The metal oxide catalyst according to the invention 6 employs a configuration characterized in that, in the invention 1 or 2 , the inside of the host crystal has a crystal structure represented by the composition InVO ₄ and belonging to the Cmcm space group.

Invention 7 is a chemical substance or a hazardous chemical substance characterized by irradiating a chemical substance or a hazardous chemical substance with light or heating in the presence of the metal oxide catalyst according to any one of the inventions 1 to 6. Disassembly method.

  The above invention has found that the target molecule is surely and rapidly adsorbed on the catalyst surface is an important factor in the catalytic reaction, and has been found to be achieved by the above configuration. It was made.

A molecule such as a water molecule H—O—H or a Q—O—H type organic molecule is stable when an H ⁺ ion or a Q ⁺ ion is bonded to an oxygen ion of O ²⁻ . Therefore, when other cations (M ^{n +} ) that do not belong to the oxygen ions in the vicinity of O ²⁻ such as water molecules H—O—H or Q—O—H type organic molecules approach, the electrical balance is maintained. Therefore, there may be a phenomenon in which H ⁺ or Q ⁺ leaves O ²⁻ instead. In particular, when H ⁺ or Q ⁺ is attracted to an anion (such as L ⁿ⁻ ) such as an oxygen ion other than the molecule to which the molecule belongs, it becomes more unstable with respect to the approach of M ^{n +} .

For example, when water molecules are adsorbed on the metal oxide, H ⁺ is attracted to the oxygen ions constituting the metal oxide surface, and at the same time, the oxygen ions belonging to the water molecule also appear on the metal ions constituting the surface of the metal oxide. Be attracted. Accordingly, the water molecule H—O—H or the Q—O—H type organic molecule becomes more or less unstable. However, it is not obvious whether these molecules deviate.

As a result of intensive studies based on the first principle theory, when the metal oxide adsorbs water molecules H—O—H or Q—O—H type organic molecules, the distance between oxygen ions and M ^{n +} is approximately 2.2 angstroms or less. Then, it became clear that the molecules were easily separated.

Theoretically, when M ^{n +} and n is 3, the distance between oxygen ions belonging to the adsorbed molecule and M ^{n +} is approximately 2.2 angstroms or less, and dissociative adsorption is likely to occur even at room temperature. It is clear that if the distance is the same, if n is larger than 3 in M ^{n +} , it is easier to deviate. Even if n is 1 or 2, if the size of the M ^{n +} ion is sufficiently small, the adsorbed molecule approaches the M ^{n +} ion, so that the effect of attracting the H ⁺ ion to the surrounding oxygen ion can be expected. A state of being easily separated can occur.

On the other hand, when a stable structure (MOx) in which a metal ion (M ^{n +} ) is surrounded by x oxygen ions covers the crystal surface, oxygen in the target molecule is present in the metal oxide crystal structure. The probability that ions break into the MOx structure covering the surface at a temperature as low as room temperature is very low, and even if the ions are adsorbed around the structure, the distance between oxygen ions and M ^{n +} ions in the adsorbed molecules is large. The molecules do not diverge.

However, for example, when the surface of a metal oxide in which oxygen ion tetracoordination is stable inside the crystal is tricoordinated, or the surface of a metal oxide in which hexacoordination is stable inside the crystal is constituted by tetracoordination, etc. These surfaces have the property of adsorbing water molecules H—O—H and Q—O—H type organic molecules as if they were trying to maintain the crystal structure inside the metal oxide. This is considered to be a kind of self-organizing action. In other words, the distance between the oxygen ion in the adsorbed molecule and the metal ion on the surface of the metal oxide has a property that is substantially equal to the distance between the metal ion inside the crystal and the oxygen ion. Therefore, when the distance between oxygen ions O ²⁻ and M ^{n +} in the (MOx) structure inside the crystal is 2.2 angstroms or less, it is adsorbed to the structure in which some of the (MOx) structure oxygen ions formed on the surface are removed. The distance between oxygen ions and M ^{n +} ions of the molecules to be reduced is approximately 2.2 angstroms or less.

  As a result, most of the surface having a structure obtained by removing a part of the (MOx) structure oxygen ions on the catalyst surface exhibits a catalytic action due to dissociative adsorption, and can be a highly efficient catalyst.

When the oxygen coordination number is large, the distance between the oxygen ions O ²⁻ and M ^{n +} in the (MOx) structure inside the crystal tends to increase, and even if the number of adsorbed molecules per M ^{n +} can be increased, there is a difference. It is difficult to obtain adsorption. By this invention 2, it becomes easy to obtain dissociative adsorption. The range of materials selection is also widened.

In the present invention 1, the crystal inside (MO _4, or, MO ₆₎ because many things distance ⁺ oxygen ions ^{O 2-} and ^{M n} is short in the structure, further enhanced the ability to deviate the adsorbed molecules.

The present invention ^{1, In 3+, Ga 3+,} Al 3+, B 3+, Si 4+, Ge 4+, Sn 4+, Ti 4+, Zr 4+, Hf 4+, V 5+, Nb 5+, Ta 5+, Sb 5+, Bi 5+, In a metal oxide catalyst having W ⁶⁺ , Mo ⁶⁺ and Cr ⁶⁺ ions as adsorption sites, the ability to dissociate adsorbed molecules is enhanced.

According to the present invention 2 , the metal oxide can be used as a photocatalyst.

The present invention 3-6, further vanadium-containing composite oxide represented by a composition RVO ₄ (wherein, R Y elemental), or vanadium-containing composite oxide represented by a composition TVO ₄ (in the formula, T can increase its efficiency when In) is used as a photocatalyst.

According to the present invention 7 , the target molecule can be further easily decomposed.

A molecule such as a water molecule H—O—H or a Q—O—H type organic molecule is stable when an H ⁺ ion or a Q ⁺ ion is bonded to an oxygen ion of O ²⁻ . Therefore, when other cations (M ^{n +} ) that do not belong to the oxygen ions in the vicinity of O ²⁻ such as water molecules H—O—H or Q—O—H type organic molecules approach, the electrical balance is maintained. Therefore, there may be a phenomenon in which H ⁺ or Q ⁺ leaves O ²⁻ instead. In particular, when H ⁺ or Q ⁺ is attracted to an anion (such as L ⁿ⁻ ) such as an oxygen ion other than the molecule to which the molecule belongs, it becomes more unstable with respect to the approach of M ^{n +} .

For example, when water molecules are adsorbed on the metal oxide, H ⁺ is attracted to the oxygen ions constituting the metal oxide surface, and at the same time, the oxygen ions belonging to the water molecule also appear on the metal ions constituting the surface of the metal oxide. Be attracted. Accordingly, the water molecule H—O—H or the Q—O—H type organic molecule becomes more or less unstable. However, it is not obvious whether these molecules deviate.

As a result of intensive studies based on the first principle theory, when the metal oxide adsorbs water molecules H—O—H or Q—O—H type organic molecules, the distance between oxygen ions and M ^{n +} is approximately 2.2 angstroms or less. Then, it became clear that the molecules were easily separated.

Theoretically, when M ^{n +} and n is 3, the distance between oxygen ions belonging to the adsorbed molecule and M ^{n +} is approximately 2.2 angstroms or less, and dissociative adsorption is likely to occur even at room temperature. It is clear that if the distance is the same, if n is larger than 3 in M ^{n +} , it is easier to deviate. Even if n is 1 or 2, if the size of the M ^{n +} ion is sufficiently small, the adsorbed molecule approaches the M ^{n +} ion, so that the effect of attracting the H ⁺ ion to the surrounding oxygen ion can be expected. A state of being easily separated can occur.

On the other hand, when a stable structure (MOx) in which a metal ion (M ^{n +} ) is surrounded by x oxygen ions covers the crystal surface, oxygen in the target molecule is present in the metal oxide crystal structure. The probability that ions break into the MOx structure covering the surface at a temperature as low as room temperature is very low, and even if the ions are adsorbed around the structure, the distance between oxygen ions and M ^{n +} ions in the adsorbed molecules is large. The molecules do not diverge.

However, for example, when the surface of a metal oxide in which oxygen ion tetracoordination is stable inside the crystal is tricoordinated, or the surface of a metal oxide in which hexacoordination is stable inside the crystal is constituted by tetracoordination, etc. These surfaces have the property of adsorbing water molecules H—O—H and Q—O—H type organic molecules as if they were trying to maintain the crystal structure inside the metal oxide. This is considered to be a kind of self-organizing action. That is, the distance between the oxygen ion in the adsorbed molecule and the metal ion on the surface of the metal oxide has a property that is substantially equal to the distance between the metal ion and the oxygen ion inside the crystal. Therefore, when the distance between oxygen ions O ²⁻ and M ^{n +} in the (MOx) structure inside the crystal is 2.2 angstroms or less, it is adsorbed to the structure in which some of the (MOx) structure oxygen ions formed on the surface are removed. The distance between oxygen ions and M ^{n +} ions of the molecules to be reduced is approximately 2.2 angstroms or less.

  As a result, most of the surface having a structure obtained by removing a part of the (MOx) structure oxygen ions on the catalyst surface exhibits a catalytic action due to dissociative adsorption, and can be a highly efficient catalyst.

An oxide containing an MO ₆ octahedron is used as a base crystal, the MO ₆ octahedron is exposed on the surface, and a structure in which some O ²⁻ ions are removed from the MO ₆ octahedron is formed. For example, if M is In ³⁺ , Nb ⁵⁺ , Ta ⁵⁺ , or W ⁶⁺ , it has an InTaO ₄ or InNbO ₄ crystal structure belonging to the P2 / a space group, or a crystal structure belonging to the P2 ₁ / n space group. WO ₃ is manufactured and the surface is subjected to reduction treatment.

A metal oxide containing an MO ₄ tetrahedron is used as a base crystal, the MO ₄ tetrahedron is exposed on the surface, and one or two O ²⁻ ions are removed from the MO ₄ tetrahedron to form a structure. For example, if M is V ⁵⁺ , YVO ₄ having a crystal structure belonging to the I4 ₁ / amd space group, InVO ₄ having a crystal structure belonging to the Cmcm space group, and the like are manufactured, and the surface is reduced.

An oxide containing Bi often contains Bi as Bi ³⁺ ions. However, Bi ³⁺ ions are exposed on the surface, and the Bi ³⁺ ions on the surface are oxidized to Bi ⁵⁺ ions using an oxidizing agent. May be formed on the surface. Of course, good catalytic action can also be obtained, for example, by reducing the surface of ZnBi ₂ O ₆ having a trirutile structure having an MO ₆ octahedron having the characteristics of claim 1 .

  The reduction treatment can be performed by heat treatment in a reducing atmosphere. For example, surface oxygen atoms may be stripped off by heating in a hydrogen gas atmosphere. There is also a method of stripping surface oxygen by a plasma method. In many cases, production is possible with a non-equilibrium film forming apparatus such as an electron beam evaporation apparatus.

  If the MO bond distance is relatively large, the rate of dissociative adsorption may be reduced, but this can be overcome by raising the reaction temperature to some extent. The MO bond distance and reaction temperature in the catalyst may be adjusted in accordance with the properties of the target molecule to be decomposed.

When used as a photocatalyst, for the purpose of spatially separating excited electrons from the semiconductor oxide of the present invention, a noble metal such as Pt, a transition metal such as Ni, NiO, IrO ₂ , NiO _x , RuO _2, etc. It is also possible to modify the catalyst surface by supporting an oxide as a promoter. The supporting method can be performed by an impregnation method or a photo-deposition method. In addition, the reaction solution used for the water decomposition reaction is not limited to pure water, and usually carbonates, hydrogen carbonates, iodine salts, bromine salts, etc. You may use the water which mixed salt. The photocatalyst of the present invention is added to the aqueous solution. The amount of catalyst added is basically selected so that incident light can be efficiently absorbed. The wavelength of the light to be irradiated needs to include light having a wavelength in a region where the semiconductor is absorbed.

Some of the catalysts incorporating the present invention can be applied to many photocatalytic reactions. For example, in the case of decomposing organic substances, alcohol, agricultural chemicals, malodorous substances, etc. generally act as electron donors and are oxidatively decomposed by holes. In particular, the invention according to claim 7 can be expected to have high oxidation efficiency. As a reaction form, the catalyst may be suspended in an aqueous solution containing an organic substance and irradiated with light, or the catalyst may be fixed to a substrate. A gas phase reaction may be used, such as decomposition of malodorous substances.

Hereinafter, the present invention will be described in detail. In the following examples, the present invention will be described by taking metal oxides, InVO ₄ , YVO ₄ , and BiVO ₄ as examples. The explanation is based on first-principles quantum molecular dynamics theory.

The crystal structure of the composite metal oxide YVO ₄ is shown in FIG. The space group to which it belongs is I41 / amd. In the crystal structure, Y ³⁺ is surrounded by 8 oxygens (V ⁵⁺ is surrounded by 4 oxygens), and the average distance of Y—O is 2.37. (2.30 to 2.44) angstrom (Non-patent Document 1). For example, when the (010) plane is cut out at the cleavage position indicated by reference numeral 3 in the drawing and one oxygen ion is taken out from a part of the VO ₄ tetrahedron exposed on the surface, as shown in FIG. The VO ₃ structure can be exposed. This structure satisfies the conditions described in claims 1, 3 or 6. FIG. 3 shows the result of a simulation based on quantum molecular dynamics in which water molecules are arranged in the vicinity of the surface and the temperature is controlled at 300 K. It can be seen that water molecules are adsorbed by being separated from -OH and -H. This is because the H ⁺ of the oxygen ions of water molecules bearing a positive to attract the V ions to oxygen ions H ⁺ are attracted existing around the same time V ions when repel V ions, water molecules in the O-H This is because the bond is easily broken. This is true not only for water molecules but also for bonding of O—H groups and O—R groups, and it is considered that other molecules having these groups are often decomposed. As can be seen from comparison with Comparative Example 1 below, it can be seen how important the formation of the VO ₃ structure is in promoting dissociative adsorption.

Comparative Example 1

When the (010) plane of YVO ₄ in FIG. 1 in Example 1 is simply cut out at the cleavage position indicated by reference numeral 3 in the drawing, the surface is formed of a VO ₄ tetrahedron and a YO ₇ oxygen seven-coordinate structure. be able to. This is shown in FIG. FIG. 5 shows the result of a simulation by quantum molecular dynamics in which water molecules are arranged in the vicinity of the surface and the temperature is controlled at 300 K. It was found that water molecules adsorb in the form of water molecules, and dissociative adsorption hardly occurs.

The crystal structure of the composite metal oxide InVO ₄ is shown in FIG. The space group to which it belongs is Cmcm, and in the crystal structure, V ⁵⁺ is surrounded by 4 oxygens (In ³⁺ is surrounded by 6 oxygens), and its V—O average distance is about 1.7 angstroms. (Non-Patent Document 2). When the crystal is cut out in the (001) plane, the surface can be formed of a VO ₃ structure in which one oxygen is removed from the VO ₄ tetrahedron, and the condition described in claim 1 or 3 is satisfied. it can. This is shown in FIG. FIG. 8 shows the result of a simulation based on quantum molecular dynamics in which water molecules are arranged in the vicinity of the surface and the temperature is controlled at 300K. It can be seen that water molecules are adsorbed to -OH and -H.

In the crystal structure of InVO ₄ in Example 2, In ³⁺ has an InO ₆ octahedron surrounded by _six oxygen ions. The In—O distance is about 2.16 angstrom (Non-patent Document 2). For example, when the (100) plane is cut out as shown by a broken line in FIG. 9, the surface can be formed of a VO ₄ tetrahedron and an InO ₄ coordination structure obtained by removing two oxygen atoms from an InO ₆ octahedron, The conditions described in claim 2 can be satisfied. FIG. 10 shows the result of a simulation based on quantum molecular dynamics in which water molecules are arranged in the vicinity of the surface and the temperature is controlled at 300K. It can be seen that water molecules are adsorbed to -OH and -H. This is because the In ion attracts oxygen ions of water molecules, and the positive H ⁺ repels the In cation, and at the same time, H ⁺ is attracted to oxygen ions existing around the In ions. This is because it becomes easier to break the bond. This is true not only for water molecules but also for bonding of O—H groups and O—R groups, and it is considered that other molecules having these groups are often decomposed.

Comparative Example 2

The crystal structure of the composite metal oxide BiVO ₄ is shown in FIG. In the crystal structure, Bi ³⁺ is surrounded by eight oxygen ions, and the Bi—O distance of the BiO ₈ polyhedron averages about 2.47 angstroms (2.354 to 2.628) (Non-patent Documents 3 and 4). It is. For example, when the (100) plane is cut out as indicated by a broken line in FIG. 11, a BiO ₅ oxygen pentacoordinate structure in which three oxygen atoms are removed from the VO ₄ tetrahedron and the BiO ₈ polyhedron can be formed. FIG. 12 shows the result of simulation by quantum molecular dynamics in which water molecules are arranged in the vicinity of the surface and the temperature is controlled at 300K. It was found that water molecules adsorb in the form of water molecules, and dissociative adsorption hardly occurs. Although the number of adsorbed molecules per ion is large, the molecular decomposition power itself was found to be weak.

According to the present invention, it is possible to increase the decomposition efficiency of the target molecule in the metal oxide catalyst. A function as a catalyst can be imparted to a metal oxide that has not been conventionally recognized as a catalyst. If it is used for the thermal decomposition reaction of various organic substances, the reaction temperature can be lowered and it is economical. It can be used for decomposing harmful organic substances, and can greatly contribute to environmental purification. Considering the decomposition mechanism of harmful organic substances by the photocatalyst and the initial reaction process in the hydrogen and oxygen generation mechanism, in the metal oxide photocatalyst (including oxides of Si ⁴⁺ and B ³⁺ ), In ³⁺ , Ga ³⁺ , Al ^{3+ , B 3+, Si 4+, Ge} 4+, Sn 4+, Ti 4+, Zr 4+, Hf 4+, V 5+, Nb 5+, Ta 5+, Sb 5+, Bi 5+, W 6+, Mo 6+, at least one of Cr ⁶⁺ ions It can also be used to increase the efficiency of metal oxide photocatalysts that contain as a main raw material. The application range of the present invention is extremely wide.

An example of a cleavage position (dashed line portion) in the case where oxygen 7-coordinated Y ions are exposed on the surface of a complex oxide YVO ₄ crystal containing Y ³⁺ ions. (010) surface of YVO ₄ exposing the YO ₇ polyhedron, VO ₄ tetrahedron and VO ₃ structure. A state in which water molecules are dissociated and adsorbed at a temperature of 300 K on the surface where the oxygen tricoordinate V ions are exposed. The (010) surface of YVO ₄ exposing the YO ₇ polyhedron and the VO ₄ tetrahedron. A state in which water molecules are adsorbed at a temperature of 300K on the surface where oxygen 7-coordinated Y ions are exposed. An example of a cleavage position (dashed line portion) in the case of exposing oxygen 3-coordinated V ions to the surface in a complex oxide InVO ₄ crystal containing V ⁵⁺ ions. The (001) plane of InVO ₄ with the VO ₃ structure exposed on the surface. A state in which water molecules are dissociated and adsorbed at a temperature of 300 K on the surface where the oxygen tricoordinate V ions are exposed. An example of a cleavage position (dashed line portion) in the case where an oxygen 4-coordinate In ion is exposed on the surface of a complex oxide InVO ₄ crystal containing In ³⁺ ions. A state in which water molecules are dissociated and adsorbed at a temperature of 300 K on the surface where In ions with 4-coordinate oxygen are exposed. An example of a cleavage position (dashed line portion) in the case where an oxygen 5-coordinate Bi ion is exposed on the surface in a complex oxide BiVO ₄ crystal containing Bi ³⁺ ions. A state in which water molecules are adsorbed at a temperature of 300K on the surface where oxygen-coordinated Bi ions are exposed.

Explanation of symbols

1. VO ₄ tetrahedron2. YO ₈ polyhedron 3. Cleave position 4. 4. Oxygen ions 5. Vanadium ion Yttrium ion7. 7. A structure in which three oxygen ions are coordinated to vanadium ions. 8. Hydrogen ion The part where the water molecule -OH is dissociated and adsorbed on the vanadium ion with three coordinated oxygen ions (in circle)
10. 10. A structure in which oxygen ions are coordinated to yttrium ions. Water molecule 12. The portion where water molecules are adsorbed on yttrium ions with seven coordinated oxygen ions (in circle)
13. InO ₆ octahedron 14. Indium ions 15. The part where the -OH of water molecule is dissociated and adsorbed on the indium ion with four coordinated oxygen ions (in circle)
16. BiO ₈ polyhedron 17. Bismuth ion 18. The portion where water molecules are adsorbed on bismuth ions with five coordinated oxygen ions (in circle)

Claims (7)

It consists of an oxide having a structure (MO _x ) in which a metal ion (M ^{n +} ) is surrounded by x oxygen ions in the crystal structure in a room temperature stable state, and has water molecules H—O—H or hydroxyl groups in contact with the surface. A metal oxide catalyst (wherein Si ⁴⁺ and B ³⁺ are also in the category of metal ions (M ^{n +} )) that decomposes a Q—O—H type organic molecule (Q is an arbitrary group), and has a metal ion (M ^{n +} ) category. A part of oxygen ions in which an average distance between metal ions and oxygen ions in a structure (MO _x ) is 2.2 angstroms or less is removed, and the metal ions are In ³⁺ , Ga ³⁺ , Al ³⁺ , B ^3+. , Si ⁴⁺ , Ge ⁴⁺ , Sn ⁴⁺ , Ti ⁴⁺ , Zr ⁴⁺ , Hf ⁴⁺ , V ⁵⁺ , Nb ⁵⁺ , Ta ⁵⁺ , Sb ⁵⁺ , Bi ⁵⁺ , W ⁶⁺ , Mo ⁶⁺ , Cr ⁶⁺ A tetrahedron that is more than that and _{x of} (MO _x ) is 6 and has 5 or less oxygen ions to be removed, or x of 4 of (MO _x ) is 4 A metal oxide catalyst, wherein three or less oxygen ions are removed. The metal oxide catalyst according to claim 1, wherein the metal oxide catalyst is a semiconductor that does not exhibit metallic electrical conduction. In the metal oxide catalyst according to claim 1 or 2, metal therein matrix crystals, vanadium-containing composite oxide represented by a composition RVO ₄ (wherein, R Y elemental) characterized in that it is a Oxide catalyst. 4. The metal oxide catalyst according to claim 3, wherein the inside of the base crystal has a zircon type crystal structure belonging to the I41 / amd space group. The metal oxide catalyst according to claim 1 or 2, wherein the inside of the base crystal is a vanadium-containing composite oxide (wherein T is In) represented by the composition TVO ₄ . catalyst. 3. The metal oxide catalyst according to claim 1, wherein the inside of the base crystal has a crystal structure represented by the composition InVO ₄ and belonging to the Cmcm space group. In the presence of the metal oxide catalyst according to any one of claims 1 to 6 , a chemical substance or a hazardous chemical substance is irradiated with light or heated. Disassembly method.