Semiconductor junction-type catalyst and method for hydrogenating oxygen-containing compound using the same

Abstract

To provide a catalyst for selectively producing methanol by hydrogenating carbon dioxide, and a method for efficiently producing methanol using the catalyst.SOLUTION: A catalyst comprising an n-type semiconductor oxide represented by the following formula (1) and / or a joint substance of a metal component M and an n-type semiconductor oxide represented by the following formula (2): InDbOnXx(1)MaInDbOnXx(2) SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a semiconductor junction catalyst and a method for hydrogenating oxygen-containing compounds using the catalyst, and in particular to a catalyst for efficiently hydrogenating carbon dioxide to produce methanol and a method for producing the catalyst. Specifically, the present invention relates to a technology for hydrogenating carbon dioxide to produce methanol by using a solid catalyst in which an electrically conductive metallic substance is junctioned with an n-type semiconductor oxide having a high carrier electron concentration, and bringing the carbon dioxide and hydrogen into contact with each other via the catalyst. [Background technology]

[0002] The chemical conversion of carbon dioxide, a stable compound, requires the use of energy and hydrogen, but with the aid of catalysts, heat, pressure, etc., there is potential for rapid conversion in a limited space. When hydrogenating carbon dioxide using a catalyst, the possible products are carbon monoxide, formic acid, formalin, methanol, and methane, and suitable reaction technologies and catalysts for each have been proposed. However, the reaction mechanisms for each have not been fully elucidated, and efficiency is still insufficient.

[0003] Of these target products, methanol is the most attractive. Because methanol is a liquid at room temperature and has low corrosiveness, it can play a role in immobilizing carbon dioxide gas, which causes global warming, as a liquid. Furthermore, because methanol is chemically reactive, useful chemical products can be produced by chemical conversion using methanol as a raw material. In other words, methanol can be used not only as a fuel but also as a resource for chemical production.

[0004] The presence of a catalyst is essential for the synthesis of methanol from carbon dioxide, and in addition to the widely known copper-zinc oxides (Patent Documents 1 and 2), various catalysts have been reported in recent years, such as a catalyst in which palladium is supported on indium oxide (Non-Patent Document 1) and a catalyst in which indium oxide is supported on zirconium oxide (Non-Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 45-016682 [Patent Document 2] Japanese Patent Application Publication No. 49-017391 [Non-patent literature]

[0006] [Non-Patent Document 1] APPLIED CATALYSIS B: ENVIRONMENTAL, 218, 2017, 488-497 [Non-patent document 2] Angew.Chem.Int.Ed.2016, 55, 6261-6265 Summary of the Invention [Problem to be solved by the invention]

[0007] However, from an economic perspective, it is clear that methods for synthesizing methanol from carbon dioxide still have issues in terms of efficiency. To efficiently obtain methanol from carbon dioxide, a catalyst is needed that can directly produce methanol from carbon dioxide during hydrogenation, that is, a catalyst that selectively converts carbon dioxide to methanol without producing carbon monoxide or methane as by-products. Even if the conversion rate is low, if the methanol selectivity is high, efficiency can be improved by increasing the amount of catalyst or raising the reaction temperature to increase the rate. Copper-zinc oxide catalysts are believed to be active in this reaction, and it may be thought that there are no problems with the catalyst, but conventional copper-zinc oxide catalysts were developed specifically for the synthesis of methanol by hydrogenating carbon monoxide, and when carbon dioxide is hydrogenated, the selectivity to methanol is not high. The reason for the low methanol selectivity with copper-zinc oxide catalysts is that the reverse water-gas shift reaction of carbon dioxide to carbon monoxide occurs, and the reaction of methanol to carbon monoxide and hydrogen occurs. However, if the large amount of carbon monoxide produced as a by-product is to be recycled rather than incinerated, the process becomes more complex and the reactor must be enlarged.

[0008] Furthermore, when the present inventors performed a carbon dioxide hydrogenation reaction using known catalysts other than copper-zinc-based oxide catalysts, the carbon dioxide conversion rate and methanol selectivity were low and unsatisfactory. In order to efficiently obtain methanol from carbon dioxide, there has been a need for a catalyst that directly produces methanol from carbon dioxide in the hydrogenation of carbon dioxide, that is, a catalyst that selectively converts carbon dioxide to methanol without by-producing carbon monoxide or methane, and further a method for synthesizing methanol more selectively at low temperatures that are favorable in thermodynamic equilibrium. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a catalyst for selectively producing methanol by hydrogenating an oxygen-containing compound, and an efficient method for producing methanol using the same. [Means for solving the problem]

[0009] The inventors of the present invention considered the reaction mechanism of the reduction of carbon dioxide by hydrogen, and as elements required for a catalyst for converting carbon dioxide to methanol, it is necessary to be able to夺取 one oxygen atom from carbon dioxide, and to promote the supply of electrons obtained from hydrogen in order to reduce the remaining carbon while reducing the oxygen to water, and they obtained the view that it is important that they exist in the same particles of the catalyst. And, by arranging the hydrogen activation ability, oxygen deprivation ability, electron supply ability, and electrical conductivity, while separating the oxidation site that夺取 electrons from hydrogen and the reduction site that supplies electrons to carbon dioxide, they came to the recognition that a structure that maintains the electrical conductivity between the two is important. Focusing on these, when exploring the relationship between the complexation of each component and the catalyst performance, surprisingly, they found that a form in which an n-type semiconductor oxide having specific elements and molar ratios, and further, a metallic substance having electrical conductivity and an n-type semiconductor oxide having a high carrier electron concentration are joined is excellent as a catalyst, and thus the present invention was achieved.

[0010] That is, the present invention has the following gists [1] to

[13] . [1] A catalyst containing an n-type semiconductor oxide represented by the following formula (1). InD b O n X x (1) (In the above formula (1), the constituent component D represents at least one element selected from the group consisting of Fe, Cr, Zr, Ti, Sn, Al, Ga, and Zn, b and n each represent the molar ratio of D and O to In, and are numbers satisfying 0 < b ≦ 3 and 0 < n ≦ 6, the constituent component X represents at least one element selected from the group consisting of P, S, Se, Te, Sb, Bi, Pb, Cl, I, F, H, C, Si, and Ge, x represents the molar ratio of X to In, and is a number satisfying 0 ≦ x ≦ 1.) [2] The catalyst according to [1], wherein in the X-ray diffraction measurement XRD (CuKα) of the n-type semiconductor oxide, a halo due to an amorphous structure is observed in the range of diffraction angle (2θ) from 10° to 50°. [3] The BET specific surface area of the n-type semiconductor oxide is 5m2 The catalyst according to [1] or [2], wherein the amount is / g or more. [4] The electrical conductivity of the n-type semiconductor oxide is 1.0×10 -8 The catalyst according to any one of [1] to [3], wherein the electrical conductivity is S / cm or more. [5] The n-type semiconductor oxide has a carrier electron concentration measured by the four-terminal method Hall measurement of 1.0×10 15 / cm 3 The catalyst according to any one of [1] to [4], wherein the carrier electron concentration is / cm or more. [6] The catalyst according to any one of [1] to [5], wherein the constituent component D consists of at least two kinds of elements. [7] The catalyst according to any one of [1] to [6], comprising a conjugate substance represented by the following formula (2), in which a metal component M is joined to the n-type semiconductor oxide. M a InD b O n X x (2) (In the above formula (2), the metal component M is a component containing at least one element selected from the group consisting of Ni, Cu, Pd, Pt, Rh, Ru, Ir, Au, and Ag, a represents the molar ratio of M to In, and is a number satisfying 0 < a ≦ 5.) [8] The catalyst according to [7], wherein the specific surface area of the conjugate substance by the BET method is 1 m 2 / g or more. [9] The catalyst according to [7] or [8], wherein the electrical conductivity of the metal component M is 1.0×10 -6 S / cm or more.

[10] The catalyst according to any one of [1] to [9], which is obtained through heat treatment at 100°C or higher and 1200°C or lower.

[11] The catalyst according to any one of [1] to

[10] , which is used for the hydrogenation of oxygen-containing compounds.

[12] The catalyst according to

[11] , wherein the oxygen-containing compound is carbon dioxide.

[13] A method for producing methanol, which comprises performing a hydrogenation reaction of an oxygen-containing compound using the catalyst according to any one of [1] to

[12] to produce methanol. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a catalyst for selectively producing methanol by hydrogenating an oxygen-containing compound, and an efficient method for producing methanol using the catalyst. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is an XRD chart of the catalyst obtained in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0013] The following describes in detail the embodiments of the present invention. Note that the following description is an example (typical example) of the embodiment of the present invention, and the present invention is not limited to the contents thereof as long as it does not depart from the gist of the present invention.

[0014] [catalyst] The catalyst of the present invention is an n-type semiconductor oxide InD represented by the following formula (1): b O n X x and / or a metal component M represented by the following formula (2) and an n-type semiconductor oxide InD b O n X x The use of this catalyst makes it possible to hydrogenate oxygen-containing compounds such as carbon dioxide under mild conditions.

[0015] InD b O n X x (1) (In the formula (1), Component D represents at least one element selected from the group consisting of Fe, Cr, Zr, Ti, Sn, Al, Ga, and Zn; Component X represents at least one element selected from the group consisting of P, S, Se, Te, Sb, Bi, Pb, Cl, I, F, H, C, Si, and Ge; b, n, and x each represent the molar ratios of D, O, and X to In, and are numbers that satisfy 0 < b ≤ 3, 0 < n ≤ 6, and 0 ≤ x ≤ 1.

[0016] M a InD b O n X x (2) (In the above formula (2), The metal component M is a component containing at least one element selected from the group consisting of Ni, Cu, Pd, Pt, Rh, Ru, Ir, Au, and Ag. a represents the molar ratio of M to In, and is a number that satisfies 0 < a ≤ 5. The constituent component D represents at least one element selected from the group consisting of Fe, Cr, Zr, Ti, Sn, Al, Ga, and Zn. The constituent component X represents at least one element selected from the group consisting of P, S, Se, Te, Sb, Bi, Pb, Cl, I, F, H, C, Si, and Ge. b, n, and x each represent the molar ratios of D, O, and X to In, and are numbers that satisfy 0 < b ≤ 3, 0 < n ≤ 6, and 0 ≤ x ≤ 1.

[0017] InD of formula (1) b O n X x The reason why it is effective as a hydrogenation catalyst is that it has sufficient carrier electrons in the conduction band as an n-type semiconductor and has a surface that can adsorb carbon dioxide. The carrier electrons in the conduction band play their role in the reduction reaction. While activating hydrogen, it reduces the adsorbed carbon dioxide.

[0018] Also, in formula (2), the metal component M further provides functions such as dissociative adsorption of hydrogen, and by supplying the activated hydrogen to the n-type semiconductor oxide of formula (1), the reduction reaction of carbon dioxide is promoted. One of the reasons why formula (2) is effective is that the activation of hydrogen and the function of stealing charges from hydrogen occur on the metal component M, and the activation of stealing oxygen from carbon dioxide and the function of reducing carbon dioxide occur on InD b O n X xThe suppression of side reactions occurring on the n-type semiconductor oxide is also considered to be a factor in the efficient progress of the reaction. Furthermore, the smooth and rectified transfer of charge and hydrogen between the two is achieved by the metal / semiconductor junction, and the high electrical conductivity within the two is also thought to contribute to the efficient progress of the reaction. In particular, n-type semiconductor oxide InD b O n X x In materials containing In (indium) such as the above, the spatially extended s orbital of In constitutes part of the conduction band, so even in an amorphous structure with poor crystallinity (atoms not regularly arranged), a bus of conduction band through which electrons flow is formed, and as a result, the supply of electrons obtained from hydrogen is promoted, and the reduction reaction is thought to proceed efficiently.

[0019] The catalyst of the present invention is an n-type semiconductor oxide InD b O n X x The bonding material is not particularly limited as long as it contains a bonding material in which the metal component M of the formula (2) and an n-type semiconductor oxide are bonded together, and may contain other components of the molded body such as a support, carrier, binder, etc. Specifically, the bonding material may be supported on the carrier described below, or may be physically mixed with the carrier described below.

[0020] The type of carrier is not particularly limited, but typically, SiO2, GeO2, Al2O3, Re2O7, Cr2O3, ZnO, MgO, CaO, BaO, ZrO2, TiO2, CeO2, SnO2, ITO, STO, BTO, SiC, activated carbon, graphite, carbon, etc. Preferred are SiO2, GeO2, Cr2O3, ZnO, ZrO2, TiO2, CeO2, SnO2, ITO, STO, BTO, and SiC, and more preferred are ZnO, Cr2O3, ZrO2, and TiO 2、 The support may be in the form of powder or pellets, or in the form of paper or a substrate. The support may be mixed with the bonding material and used as a compact.

[0021] The proportion of the n-type semiconductor oxide and / or bonding material in the catalyst is not particularly limited as long as it does not impair the effects of the present invention, but the amount of the bonding material relative to the total catalyst is usually 5 mass% or more, preferably 10 mass% or more, and particularly preferably 20 mass% or more. There is no particular upper limit, and it may be 100 mass%.

[0022] <Joining material> M a InD b O n X x (2) The bonding material represented by the above formula (2) is a material in which a metal component M is bonded to an n-type semiconductor oxide represented by formula (1). InD in Eq. (1) b O n X x The reason why is effective as a hydrogenation catalyst is that, as an n-type semiconductor, it has sufficient carrier electrons in the conduction band and can provide a surface that can adsorb carbon dioxide. The carrier electrons in the conduction band play a role in the reduction reaction, activating hydrogen and simultaneously reducing the adsorbed carbon dioxide. In addition, in formula (2), M also provides functions such as dissociative adsorption of hydrogen, and the activated hydrogen is provided to the n-type semiconductor oxide of formula (1), which promotes the reduction reaction of carbon dioxide. Another reason for its effectiveness is that the functions of hydrogen activation and depriving charge from hydrogen occur on the metal component M, while the functions of activation to deprive oxygen from carbon dioxide and reduction of carbon dioxide occur on the InD b O n X x The suppression of side reactions occurring on the n-type semiconductor oxide is also considered to be a factor in the efficient progress of the reaction. Furthermore, the smooth and rectified transfer of charge and hydrogen between the two is achieved by the metal / semiconductor junction, and the high electrical conductivity within the two is also thought to contribute to the efficient progress of the reaction.

[0023] In particular, n-type semiconductor oxide InD b O n X xIn materials containing In (indium) such as the above, the spatially extended s orbital of In constitutes part of the conduction band, so even in an amorphous structure with poor crystallinity (atoms not regularly arranged), a conduction band bus through which electrons flow is formed, and as a result, the supply of electrons obtained from hydrogen is promoted, and the reduction reaction is thought to proceed efficiently. InD b O n X x The amount of is not particularly limited, but is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 5% by mass or more, particularly preferably 10% by mass or more, in terms of mass % relative to the total mass of the bonding material, and is preferably 99% by mass or less, more preferably 98% by mass or less, even more preferably 95% by mass or less, particularly preferably 90% by mass or less. Within these ranges, a favorable balance is achieved between the supply of electrons obtained by activation of hydrogen in the hydrogenation reaction and the generation of water by oxidation of hydrogen.

[0024] InD, an n-type semiconductor oxide of formula (1) b O n X x There are no restrictions on the form of InD b O n X x It can be crystalline like In2O3 or ZnO, or non-crystalline (amorphous structure), but non-crystalline (amorphous structure) is preferable to maintain a high surface area. Usually, their presence can be confirmed by XRD (X-ray diffraction). In the case of a non-crystalline (amorphous structure), a raised baseline called a halo due to the amorphous structure is observed between diffraction angles (2θ) of 10-50° in XRD measured with a CuKα radiation source. The maximum intensity count number (X1) of the halo is compared with the X-ray count number (X2) of the baseline at 2θ of 70°, and the ratio X1 / X2 is usually 1.2 or more and 6 or less, preferably 1.3 or more and 5 or less, more preferably 1.4 or more and 4.5 or less, even more preferably 1.5 or more and 4 or less, and particularly preferably 1.6 or more and 3.5 or less.

[0025] The n-type semiconductor oxide of formula (1) of the present invention preferably has a high surface area. When expressed as a specific surface area measured by the BET method, it is preferably 5 m 2 / g or more, more preferably 10m 2 / g or more, more preferably 20m 2 / g or more, particularly preferably 30m 2 / g or more, preferably 400m 2 / g or less, more preferably 300m 2 / g or less, more preferably 250m 2 / g or less, particularly preferably 200m 2 / g or less. If the surface area is large enough, sufficient contact with gas-phase molecules is ensured, allowing the catalytic reaction to proceed efficiently. Furthermore, if the surface area is within a certain range (not too large), the electrons required for the reduction of carbon dioxide adsorption are sufficient. As a result, the reduction reaction to methanol, which requires many reduction electrons, is promoted, and high selectivity to methanol is maintained. Furthermore, if the surface area is within a certain range (not too large), the number of surface defects is suppressed, preventing the loss of electrical conductivity due to phenomena such as conduction electrons being trapped by defects, and as a result, the reduction reaction is maintained.

[0026] The carrier electron concentration of the n-type semiconductor oxide in formula (1) is usually 1.0 × 10 15 / cm 3 or more, preferably 1.0 × 10 16 / cm 3 More preferably, 1.0 × 10 17 / cm 3 More preferably, 1.0 x 10 18 / cm 3 or more, usually 1.0 × 10 21 / cm 3 The following is InD b O m X x The carrier electron concentration can be determined by Hall measurement using the four-probe method. For example, InD b O n X xAfter pressing the powder, electrodes (Pt, etc.) are vapor-deposited to form four terminals, and evaluation can be performed by performing Hall measurements, etc. It is also possible to roughly estimate the free electron absorption observed in diffuse reflectance UV-Vis absorption spectra, etc. Specifically, it is possible to roughly estimate the free electron absorption from the rising position of the absorption corresponding to the plasma frequency to the low energy side by fitting it with the Drude equation. Also, InD b O n X x It is preferable that the InD has high electrical conductivity. b O n X x The electrical conductivity of is usually 1.0×10 -8 S / cm or more, preferably 1.0×10 -6 S / cm or more, preferably 1.0×10 -4 S / cm or more, more preferably 1.0 × 10 -2 S / cm or more, particularly preferably 1.0 × 10 -1 S / cm or more, usually 1.0 × 10 2 The electrical conductivity can be measured by the four-terminal method described above or the two-terminal method such as Hiresta or Loresta.

[0027] (Component D) InD b O n X x The component D in the InD of the present invention constitutes an n-type semiconductor oxide and plays a role in reducing carbon dioxide to methanol by utilizing the charge obtained by the oxidation of hydrogen. b O n X xThe constituent D is at least one element selected from the group consisting of Fe, Cr, Zr, Ti, Sn, B, Al, Ga and Zn, preferably at least one element selected from the group consisting of Sn, Zr, Al, Ga and Zn, more preferably at least one element selected from the group consisting of Ga and Zn, and particularly preferably Zn. It is preferable to use two or more types of D. This is because using multiple types of D makes it easier to form an amorphous structure, resulting in a high specific surface area, and also makes it possible to control the band structure, which is an important characteristic of n-type semiconductors. In fact, InD b O n X x As D, oxides or composite oxides of Sn, B, Al, Ga, and Zn have excellent performance as n-type semiconductor oxides. On the other hand, from the viewpoint of catalytic reaction, if an element with high deoxidation ability (Fe, Cr, Zr) is selected as component D, there is a tendency for the element to act as an active site, and excessive reduction reaction to methane tends to be promoted, resulting in a decrease in methanol selectivity. Therefore, embodiments containing large amounts of these elements are not preferred. A small amount (for example, 0.4 moles or less per mole of In) can provide an adequate number of active sites, suppressing the promotion of excessive reduction reaction, and thereby increasing methanol selectivity.

[0028] InD b O n X x The valence of In and D in InD can be evaluated by, for example, X-ray photoelectron spectroscopy or X-ray absorption spectroscopy (XANES). b O n X x The proportion of trivalent In in the total In is usually 30 mol % or more, preferably 40 mol % or more, more preferably 50 mol % or more, and even more preferably 60 mol % or more.

[0029] The molar ratio b of component D to In is greater than 0, preferably 0.01 or greater, more preferably 0.02 or greater, even more preferably 0.05 or greater, even more preferably 0.1 or greater, particularly preferably 0.2 or greater, and is 3.0 or less, preferably 2.7 or less, more preferably 2.4 or less, even more preferably 2.1 or less, and particularly preferably 1.8 or less. If the value of b is greater than 3.0, there is a concern that the methanol selectivity may decrease. Furthermore, by keeping the value within these ranges, a large surface area is ensured, resulting in a high-performance catalyst.

[0030] (n) n represents the number of oxygen atoms (molar ratio relative to indium) required to satisfy the valence of In and D in formula (1). Although not particularly limited, n of a catalyst that exhibits excellent performance is preferably slightly less than the total number of oxygen atoms that satisfy the oxidation states of In and D, and has oxygen deficiencies. Typically, n in the molar ratio relative to In is greater than 0, preferably 0.5 or more, more preferably 0.8 or more, even more preferably 0.9 or more, and particularly preferably 1.0 or more, and is typically 6 or less, preferably 5 or less, and even more preferably 4 or less.

[0031] (Component X) The catalyst of the present invention may contain X for the purpose of stabilizing the structure, removing impurities, or improving semiconductor properties as a donor that generates carrier electrons, depending on the types of D and M in formulas (1) and (2). X is at least one element selected from the group consisting of P, S, Se, Te, Sb, Bi, Pb, Cl, I, F, H, C, Si, and Ge, and is preferably H. Multiple types of X may also be used. The amount of X is not particularly limited. Depending on the types of M and D, X may not be necessary. It is preferable that the molar ratio of X is the same as or smaller than that of D. In terms of mass % relative to the total bonding material, the amount is preferably 0.1 mass % or more, more preferably 0.2 mass % or more, even more preferably 0.3 mass % or more, still more preferably 0.5 mass % or more, particularly preferably 1 mass % or more, and is preferably 80 mass % or less, more preferably 75 mass % or less, even more preferably 70 mass % or less, still more preferably 65 mass % or less, particularly preferably 50 mass % or less, and most preferably 30 mass % or less. The amount of X can be measured by elemental analysis such as ICP (inductively coupled plasma), LECO analysis, OHN meter, or H2-TPD (programmed temperature programmed desorption) analysis.

[0032] The molar ratio x of X to In is preferably 1 or less, more preferably 0.5 or less, even more preferably 0.2 or less, and particularly preferably 0.1 or less. It may also be 0, but is preferably 0.01 or more, more preferably 0.02 or more, even more preferably 0.03 or more, and particularly preferably 0.04 or more. Within these ranges, a favorable balance is achieved between the supply of electrons by activation of hydrogen and the generation of water by oxidation of hydrogen in the hydrogenation reaction. When X is H (hydrogen), its content (amount of hydrogen adsorbed / absorbed) can be measured by measuring the amount of adsorption using a constant volume method (pressure reduction) or by analyzing hydrogen adsorbed / absorbed under certain conditions by increasing the temperature and desorbing it. The saturated amount of hydrogen adsorbed / absorbed at 200°C is usually 0.02 mol H atoms / g or more, preferably 0.04 mol H atoms / g or more, more preferably 0.06 mol H atoms / g or more, and particularly preferably 0.08 mol H atoms / g or more. By adsorbing and absorbing a large amount of hydrogen into an n-type semiconductor oxide, it is possible to provide a sufficient hydrogen source for the hydrogenation reaction. At the same time, hydrogen acts as a donor, increasing the number of carrier electrons and participating in the reduction reaction, thereby accelerating the reaction of carbon dioxide to methanol.

[0033] A portion of X may be introduced as a compound. While there are no particular limitations on the type or structure, compounds such as delafossite-type sulfides and perovskite-type sulfides, carbonates, and antimony oxides are preferably used. Chalcogenides such as selenides and tellurides, and chalcopyrite-type compounds can also be used. When X is hydrogen (H), it can be introduced by treating the catalyst with hydrogen gas after synthesis.

[0034] [Metal component M] M in equation (2) a InD b O n X x The metal component M of the bonding material plays a role in activating molecular hydrogen in the hydrogenation reaction and supplying dissociated hydrogen and electrons obtained from the hydrogen to the n-type semiconductor oxide. The metal component M is at least one element selected from the group consisting of V, Nb, Ni, Cu, Pd, Pt, Rh, Ru, Ir, Au, and Ag, preferably at least one element selected from Cu, Pd, Pt, Rh, Ir, Au, and Ag, more preferably at least one element selected from Cu, Pd, and Ag, and particularly preferably Pd. Multiple types of M may be used, or alloys such as PdAg, PdAu, and PdCu, and / or alloys and IMCs (intermetallic compounds) containing M as a metal component may be used. The molar ratio a of the metal component M to In is greater than 0, preferably 0.001 or greater, more preferably 0.005 or greater, even more preferably 0.01 or greater, still more preferably 0.02 or greater, and particularly preferably 0.04 or greater, and although there are no upper limits, it is usually 5 or less, preferably 4 or less, more preferably 3 or less, even more preferably 2 or less, and particularly preferably 1 or less. By keeping it within these ranges, the balance between the supply of electrons by activation of hydrogen in the hydrogenation reaction and the production of water by oxidation of hydrogen is in a preferred range, and it is possible to avoid the generation of undesirable by-products due to insufficient reverse reaction (oxidation reaction of the product with water).

[0035] Furthermore, as long as M fulfills its role as a metal component (activating hydrogen and conducting electricity), its form is not limited, and conductive oxides and hydrides containing M can also be used. In addition, p-type semiconductors such as those with a delafossite structure can also be used. The proportion of the metal component M in the entire joining material is usually 1 wt% or more and 99 wt% or less, preferably 2 wt% or more and 98 wt% or less, more preferably 5 wt% or more and 95 wt% or less, and particularly preferably 10 wt% or more and 90 wt% or less. The work function of the metal component M is an important index that influences the flow of electrons within the junction material. To supply electrons to the n-type semiconductor oxide, a low work function of the metal component M is preferable. The work function can be determined, for example, by Kelvin probe (contact potential difference) method, by comparison with a standard material (e.g., an Au thin film). The value measured by this method is usually 5.5 eV or less, preferably 5 eV or less, more preferably 4.8 eV or less, and particularly preferably 4.5 eV or less. If the work function is lower than that of the n-type semiconductor oxide, the metal / semiconductor junction will be an ohmic contact, and the barrier to the flow of electrons between the metal / semiconductor junction will be small. The work function can be measured by several methods, such as photoelectron spectroscopy and photoelectron yield method.

[0036] The metal component M preferably has a high surface area, preferably 5 m 2 or more, expressed as a specific surface area measured by the BET method. 2 / g or more, more preferably 10m 2 / g or more, more preferably 20m 2 / g or more, particularly preferably 30m 2 / g or more, preferably 400m 2 / g or less, more preferably 300m 2 / g or less, more preferably 250m 2 / g or less, particularly preferably 200m 2 / g or less. Furthermore, it is preferable that the metal component M has high electrical conductivity. The electrical conductivity of the metal component M is usually 1.0×10 -6 S / cm or more, preferably 1.0×10 -4 S / cm or more, preferably 1.0×10-2 S / cm or more, more preferably 1.0 S / cm or more, and particularly preferably 1.0×10 1 S / cm or more, usually 1.0 × 10 6 Electrical conductivity can be measured by the four-terminal method mentioned above, two-terminal methods such as Hiresta and Loresta, as well as by a current-voltage meter, a potentiometer, or an impedance measuring instrument.

[0037] [Catalyst Preparation] The raw materials used in preparing the catalyst of the present invention are usually water-soluble salts such as halides and nitrates of M, In, D, and X, or acidic solutions thereof. Water-soluble raw materials not containing halogen elements, such as carbonates, formates, acetates, oxalates, nitrates, and sulfates, as well as ammine nitrates, ethylenediamine nitrates, and ammine nitro compounds, may also be used.

[0038] The catalyst may be prepared by any suitable method, including impregnation, coprecipitation, etc. For example, a basic solution such as ammonia water, sodium carbonate aqueous solution, sodium hydroxide aqueous solution, or ethanolamine is added dropwise to a mixed aqueous solution of nitrates of the constituent elements to precipitate a mixed hydroxide, which is then aged or hydrothermally treated as necessary, filtered, washed with water, and recovered as a hydroxide gel-like precursor, which is then dried and heat-treated to obtain a bonding material.

[0039] In the catalyst of the present invention, the important factors are the bonding strength between the metal component M and the semiconductor and / or the control of impurities that affect the semiconductor properties. These can be controlled by the method of producing the catalyst. The catalyst can be produced in the following manner: (1) The metal component M, In, component D, and component X, which are raw materials for the catalyst, are dissolved in a solution, and M is produced in one pot. a InD b O n X x (2) a method for synthesizing InD from In, component D, and component X b O n X x (3) a method of synthesizing InD from In and component D b On After synthesizing InD, the metal component M and the component X are introduced. For example, when producing by the method (3), an InD is synthesized by the above-mentioned procedure using a mixed aqueous solution of metal salts that does not contain the metal component M or the component X. b O n After obtaining a substance mainly composed of M or X, M or X may be introduced later by, for example, impregnating the obtained substance with an aqueous solution or alcohol solution of a salt of metal component M or component X.

[0040] Furthermore, it is also preferable to add a reducing agent to adjust the mixed state of the constituent elements and the degree of oxidation-reduction, specifically hydrogen, ethanol, ethylene glycol, glycerin, sorbitol, glucose, citric acid, ascorbic acid, ethanolamine, oxalic acid, acetol, acetoin, hydroxylamine, hydrazine, or a salt thereof.

[0041] Furthermore, it is preferable to subject the obtained catalyst to a heat treatment such as calcination for dehydration, decarboxylation, decomposition of remaining salts, development of the crystal structure, and improvement of bonding strength. The temperature during heat treatment such as calcination is preferably 100°C or higher, preferably 150°C or higher, more preferably 200°C or higher, even more preferably 250°C or higher, and particularly preferably 300°C or higher. The temperature is also preferably 1200°C or lower, more preferably 1100°C or lower, even more preferably 1000°C or lower, and particularly preferably 900°C or lower. The catalyst of the present invention is preferably obtained through the above-mentioned heat treatment. The atmosphere during the heat treatment is not particularly limited, but the heat treatment is carried out in a vacuum, inert gas, air, or carbon dioxide atmosphere. In order to adjust the mixed state of the constituent elements and the degree of oxidation-reduction, the heat treatment in a vacuum or inert gas atmosphere is also preferably used. In particular, M a InD b O n X xIn the synthesis of M, for example, in order to adjust the redox degree of M, a suitable method is to first heat-treat a precursor containing the reducing agent at a temperature of 350°C or less in an air stream to decompose and remove excess reducing agent, and then calcinate at a higher temperature in a nitrogen stream. This stepwise calcination method in which the redox atmosphere is controlled makes it possible to lower the calcination temperature while adjusting the redox degree and structure of M, and an oxide with a higher surface area can be obtained. M synthesized by these methods a InD b O n X x The surface area of ​​a material is usually expressed as a specific surface area measured by the BET method. 2 / g or more, preferably 5m 2 / g or more, more preferably 10m 2 / g or more, more preferably 20m 2 / g or more, particularly preferably 30m 2 / g or more, usually 400m 2 / g or less, preferably 300m 2 / g or less, more preferably 250m 2 / g or less, more preferably 200m 2 / g or less, particularly preferably 150m 2 / g or less.

[0042] In preparing the catalyst, it is also suitable to partially reduce the catalyst by subjecting it to high-temperature treatment in a hydrogen atmosphere or a mixed gas atmosphere of hydrogen and carbon dioxide, or by mixing it with a reducing agent such as NaBH4, before the target hydrogenation reaction. The reduction temperature is not particularly limited, but is preferably 100°C or higher, more preferably 125°C or higher, even more preferably 150°C or higher, and particularly preferably 200°C or higher, and is preferably 800°C or lower, more preferably 700°C or lower, even more preferably 600°C or lower, and particularly preferably 500°C or lower.

[0043] Other methods that can be used include physical mixing, flux deposition, sol-gel (dipping), electron deposition, photoelectrodeposition, sputtering, ALD (atomic layer deposition), and PLD (pulsed laser deposition). These methods are promising because they can produce high-quality materials with few defects at low temperatures. On the other hand, solid-phase synthesis and hydrothermal synthesis can also be used. The former uses oxides or salts as raw materials, grinds and mixes them using a ball mill or similar, and then fires them in air or an inert gas stream at temperatures typically between 200°C and 1200°C. After preparation by these methods, a method of adding further constituent elements is also preferably used. For example, M a InD b O n X x After obtaining InD by solid-phase synthesis or hydrothermal synthesis, it is possible to introduce additional metal components M later by immersing it in an aqueous salt solution containing an element M different from the metal component M previously introduced, and then performing heat treatment or reduction treatment. b O n X x After synthesizing, a part of the surface is masked with a silylating agent or the like, and then the metal component M is introduced by a sputtering method or the like, and then the masking agent is removed. b O n X x The catalyst of the present invention can also be prepared by physically mixing the oxide of the metal component M with the oxide of the metal component M.

[0044] The calcined or reduced catalyst prepared by the above method is preferably pulverized and mixed to further increase the interparticle bonding and improve electrical conductivity. A wet pulverizer or a dry pulverizer is used for pulverization. Furthermore, methods such as pressing the obtained catalyst to form a shape or mixing it with a conductive material such as carbon black are also preferably used. This ensures a route for supplying electrons to the carbon dioxide activation sites, thereby promoting methanol production.

[0045] [Evaluation of the semiconducting properties of catalysts] There is no particular method for measuring the electrical conductivity of a catalyst, but resistivity measuring instruments such as the Hiresta and Loresta can be used. Electrical conductivity can be calculated as the reciprocal of the volume resistivity measured using a low-efficiency measuring instrument. For example, when a catalyst is measured at 25°C under a pressure of 20 kN using the Mitsubishi Chemical Analytech MCP-PD-51 powder resistivity measuring system equipped with a low-resistance or high-resistance powder probe unit, the volume resistivity is usually 1.0 x 10 10 Ω·cm or less, preferably 1.0×10 9 Ω·cm or less, more preferably 1.0×10 8 The volume resistivity is 1.0×10 Ω·cm or less. 8 If the resistance is Ω·cm or less, the catalyst exhibits semiconducting properties and has good electrical conductivity. At that time, InD b O n X x In the situation where the metal component M is bonded to the powder, it is difficult to measure the electrical conductivity of the powder. b O n X x The electrical conductivity of the catalyst can be evaluated by synthesizing the metal component M and the InD that constitutes the catalyst. b O n X x When the electrical conductivity of a powder is evaluated at room temperature, for example, using a powder resistivity measurement system MCP-PD-51 equipped with a low-resistance or high-resistance probe unit for powders manufactured by Mitsubishi Chemical Analytech, the volume resistivity at room temperature under a pressure of 20 kN is typically 1.0 × 10 10 Ω·cm or less, preferably 1.0×10 9 Ω·cm or less, more preferably 1.0×10 8 The volume resistivity is 1.0×10 Ω·cm or less. 8 If the resistance is Ω·cm or less, the carrier exhibits semiconducting properties and has good electrical conductivity.

[0046] In addition, the semiconductor carrier concentration and electrical conductivity can be determined by Hall measurements. b O n X xand metal component M are formed into disks or plates with a thickness of 1 mm or less, and then Pt or other materials are vapor-deposited as terminals. When these are measured at room temperature under vacuum using a Toyo Technica Hall measurement device using the four-terminal method, the carrier concentration is usually 1.0 × 10 15 / cm 3 Over 1.0 x 10 22 / cm 3 Less than or equal to 1.0 × 10 16 / cm 3 Over 1.0 x 10 21 / cm 3 or less, more preferably 1.0 × 10 17 / cm 3 Over 1.0 x 10 20 / cm 3 or less, more preferably 1.0 × 10 18 / cm 3 Over 1.0 x 10 19 / cm 3 If the carrier concentration is equal to or higher than the lower limit, electrical conductivity is obtained, and the charge obtained from hydrogen can be effectively supplied to the carbon dioxide reduction site. On the other hand, if the carrier concentration is equal to or lower than the upper limit, mobility can be ensured, and side reactions such as over-reduction and reduction to CO can be prevented from occurring, which reduces the selectivity of the reaction to methanol. The electrical conductivity evaluated by four-probe Hall measurement at room temperature under vacuum is usually 1.0 × 10 -8 S / cm or more, preferably 1.0×10 -6 S / cm or more, preferably 1.0×10 -4 S / cm or more, more preferably 1.0 × 10 -2 S / cm or more.

[0047] Furthermore, InD b O n X x The electrical conductivity of InD and the supply of electrons to carbon dioxide are mainly related to electrons in the conduction band, but the proportion of electrons in the conduction band can be predicted not only from electrical conductivity and resistivity but also from the band gap. The band gap can be determined from various absorption and emission spectra and the temperature dependence (slope) of electrical conductivity. Formula (1) InD b O n X xThe band gap of the organic compound is usually 1 eV or more and 7 eV or less, preferably 1.5 eV or more and 6 eV or less, and more preferably 2 eV or more and 5 eV or less.

[0048] In addition, the metal components M and InD, which are necessary for the efficient reaction of carbon dioxide to methanol, b O n X x The smooth electron transfer to the metal component M and InD b O n X x In some cases, the work function of InD, which reduces carbon dioxide, is also a factor. b O n X x The work function of the metal component M and InD of the present invention is preferably large. b O n X x The powder of a sample prepared independently can be formed into a disk shape and measured by the Kelvin probe method using, for example, a Riken Keiki FAC-2. The work function of the metal component M is usually 2.0 eV or more and 6.0 eV or less, preferably 2.5 eV or more and 5.5 eV or less, more preferably 3.0 eV or more and 5.0 eV or less, when corrected by assuming that the measured value of the pure Au plate is 5.11 eV. b O n X x The work function of the organic compound is usually 3.0 eV or more and 7.0 eV or less, preferably 3.5 eV or more and 6.5 eV or less, and more preferably 4.0 eV or more and 6.0 eV or less.

[0049] [Evaluation of hydrogen adsorption and absorption of catalysts] In relation to and containing component X, InD b O n X x InD can adsorb and absorb hydrogen more effectively. When it is bonded to a metal component M, the hydrogen molecule activation ability of the metal component M or the hydride of the metal component M contributes to the formation of a hydrogen molecule. b O n X xThe amount of hydrogen adsorption and absorption can be measured by measuring the amount of adsorption using a constant volume method (pressure reduction) or by heating hydrogen adsorbed and absorbed under certain conditions and then analyzing the change in conductivity using a mass spectrometer or gas chromatography. To give an example of the latter, it can be carried out as follows by the so-called TPD (programmed temperature desorption) analysis method using a flow-type tubular reactor or a vacuum cell connected to a quadrupole mass spectrometer.

[0050] InD reactors and cells b O n X x and M a InD b O n X x Then, an inert gas is passed through the column at a temperature higher than the adsorption temperature, or the column is evacuated to remove the hydrogen, water, CO2, etc. that have already been adsorbed. b O n X x and M a InD b O n X x While the temperature is maintained at the adsorption temperature, molecular hydrogen gas at a predetermined pressure is introduced into the reactor or cell, and the adsorption temperature is maintained for a certain period of time. After that, the temperature is lowered to room temperature, and the reactor or cell is evacuated or an inert gas is passed through, thereby removing the unadsorbed molecular hydrogen gas from the system (at this time, some of the adsorbed hydrogen becomes hydrogen gas and is removed by vacuum evacuation). b O n X x and M a InD b O n X x (Then, the reactor or cell is heated at a constant rate of, for example, 10°C / min from room temperature to a temperature above the adsorption temperature, during which InD b O n X x and M a InD b O n X xThe amount of hydrogen gas desorbed from the sample is detected and recorded as the amount of hydrogen gas, and the amount of hydrogen gas is calculated by comparing it with a calibration curve that has been obtained in advance by introducing hydrogen gas at a constant pressure and volume.

[0051] InD measured in this way b O n X x and M a InD b O n X x The amount of hydrogen adsorption / absorption when maintained at normal pressure, 200°C, and for 30 minutes is usually 0.02 mol H atom / g or more, preferably 0.04 mol H atom / g or more, more preferably 0.06 mol H atom / g or more, and particularly preferably 0.08 mol H atom / g or more. By adsorbing / absorbing a large amount of hydrogen, the n-type semiconductor oxide can provide a sufficient hydrogen source for the hydrogenation reaction, and at the same time, the hydrogen acts as a donor, increasing the number of carrier electrons and participating in the reduction reaction, thereby accelerating the reaction of carbon dioxide to methanol.

[0052] [Hydrogenation of oxygen-containing compounds using hydrogenation catalysts] The catalyst (hydrogenation catalyst) of the present invention is preferably used for hydrogenating oxygen-containing compounds. When carrying out a hydrogenation reaction of an oxygen-containing compound using the catalyst of the present invention, the raw material can be carbon dioxide, carbon monoxide, or an organic or inorganic compound having one or more carbonyl groups such as a formyl group, a ketone group, a carboxylic acid group, an ester group, or an amide group. In particular, the catalyst of the present invention is particularly useful when carbon dioxide is used as the raw material, which is abundant on Earth, inexpensive, and requires a large number of electrons for its physical conversion. The hydrogenation of carbon dioxide may be carried out in either the gas phase or the liquid phase. In the gas phase, the catalyst of the present invention is loaded into a tubular reactor, and a mixed gas of carbon dioxide and hydrogen is passed through the reactor. Inert gases, water, carbon monoxide, or a trace amount of oxygen may also be present.

[0053] The reaction of synthesizing methanol from carbon dioxide and hydrogen (carbon dioxide hydrogenation reaction) is in thermodynamic equilibrium, and the equilibrium conversion rate decreases at high temperatures. Therefore, the synthesis reaction temperature is preferably 50°C or higher, more preferably 100°C or higher, and even more preferably 125°C or higher, and is preferably 400°C or lower, more preferably 300°C or lower, and even more preferably 275°C or lower.

[0054] In addition, increasing the pressure is advantageous because it also increases the equilibrium conversion rate, and the synthesis reaction pressure is preferably 0.2 MPa or more, more preferably 0.5 MPa or more, even more preferably 1.0 MPa or more, particularly preferably 2.0 MPa or more, preferably 10 MPa or less, more preferably 8 MPa or less, and even more preferably 6 MPa or less. When the pressure is above the lower limit, the reaction rate does not slow down and productivity is good. When the pressure is below the upper limit, it is possible to prevent the reaction rate from slowing down due to catalyst poisoning by water.

[0055] A higher hydrogen / carbon dioxide molar ratio is advantageous in terms of equilibrium. It is preferably 0.2 or more, more preferably 0.5 or more, more preferably 1.0 or more, and even more preferably 2.0 or more, and is preferably 10 or less, more preferably 6.0 or less, more preferably 4.0 or less, and even more preferably 3.0 or less. By keeping the ratio at or above the lower limit, reverse reactions can be suppressed, and by keeping the ratio at or below the upper limit, the equipment for separating, recovering, and circulating unreacted hydrogen can be made smaller. It is also suitable to separate carbon monoxide and the like produced as a by-product from methanol, and then convert the carbon monoxide into methanol or the like in a separate reactor, or to pass the carbon monoxide together with unreacted carbon dioxide through the reactor again.

[0056] In the catalyst of the present invention and the method for hydrogenating an oxygen-containing compound using the catalyst, InD b O n X x n-type semiconductor oxide and / or M a InD b O n X xBy using a catalyst made of a bonding material represented by the formula (1), carbon dioxide can be selectively converted into methanol under milder conditions. By proceeding with the reaction at a low temperature, which is favorable for equilibrium, it is possible to reduce the burden of separating by-products and recycling unreacted raw materials, and carbon dioxide can be converted efficiently. Therefore, this method is industrially advantageous for synthesizing methanol from carbon dioxide.

[0057] Furthermore, the catalyst of the present invention, which selectively converts carbon dioxide into methanol in the hydrogenation of carbon dioxide, also exhibits high performance in the reverse reaction, i.e., the steam reforming of methanol to produce hydrogen, selectively giving hydrogen and carbon dioxide. This reaction is a reduction reaction of water with methanol, and is useful as a method for producing hydrogen gas for fuel cells. In addition, because it is active in the reduction reaction of water, it can also be an effective catalyst for water decomposition and electrolytic hydrogen generation reactions. b O n X x n-type semiconductor oxide and / or M a InD b O n X x By applying light or voltage to the bonding material represented by the formula (1), it is possible to increase the carrier electron concentration, which promotes the reduction reaction that generates hydrogen from water. [Example]

[0058] The present invention will be described in more detail below, but the present invention is not limited to these examples. The catalyst of the present invention was loaded into a reaction tube made of glass or SUS, and while a gas was passed through the reaction tube, the catalyst loading section was heated in a tubular furnace. Further, at a predetermined reaction temperature, a raw material gas containing carbon dioxide, hydrogen, and internal standard nitrogen was passed through. The products and unreacted raw materials were sent to two TCD gas chromatographs (GC-14B manufactured by Shimadzu Corporation (for CO2 and methanol, etc.), GC-8A manufactured by Shimadzu Corporation (for hydrogen, CO, methane)) installed in series from a gas sampling cock provided at the reaction tube outlet, and quantified from the relative chromatographic area ratio with the internal standard gas nitrogen. The operating conditions of the gas chromatograph, etc. are as follows.

[0059] <Method for measuring organic substances> Apparatus: TCD-GC GC-14B manufactured by Shimadzu Corporation (medium-polarity column, 3 m) Measurement conditions: Using a programmed temperature rise in the column section <Method for measuring inorganic gases> Apparatus: TCD-GC GC-8A manufactured by Shimadzu Corporation (molecular sieve, 3 m) Measurement conditions: Column section at 70 °C

[0060] After correcting the obtained chromatographic areas by respective factors, the ratio was determined, and the selectivity was determined as follows. Methanol selectivity (%) = methanol (mmol) / (methanol + carbon monoxide + methane) × 100 Also, the methanol production rate was calculated from the chromatographic area. The methanol production rate (mmol / h / g) means the amount of methanol produced per 1 g of catalyst per hour.

[0061] Also, the X-ray diffraction measurement and conductivity measurement of the prepared catalyst were carried out as follows. <Powder X-ray diffraction measurement method> After finely pulverizing the sample in a mortar, it was evaluated using X’PertProMPD manufactured by PANalytical with an X-ray source of CuKα and a scanning range (2θ) of 5° - 90°.

[0062] <Measurement of specific surface area by BET method> The specific surface area was measured using a MicrotrackBell BELSORP II nitrogen adsorption apparatus. Approximately 0.2 g of sample was placed in a dedicated cell and degassed at 400°C, after which the specific surface area was calculated by the BET method.

[0063] <Volume resistivity measurement method> The samples were finely ground in a mortar and then evaluated using a powder resistivity measurement device. When using Loresta, the volume resistivity of the sample powder was evaluated using a Mitsubishi Chemical Analytech Loresta GP powder resistivity measurement system or MCP-PD-51. The system consisted of 1.0 g of powder, a four-point probe, 3.0 mm electrode spacing, 0.7 mm electrode radius, 10.0 mm sample radius, and an applied voltage limiter of 90 V, under a pressure of 20 kN. When using Hiresta, the system consisted of a Mitsubishi Chemical Analytech Hiresta UX powder resistivity measurement system or MCP-PD-51. The sample radius was 10.0 mm, and 1.0 g of powder was measured under a pressure of 20 kN with a double ring electrode method. The powder density was calculated from the thickness at a pressure of 20 kN and the weight of the sample.

[0064] <Carrier electron concentration measurement method> The sample was finely crushed in a mortar and then pressed using a tablet press and a hydraulic press to form circular disks with a diameter of 7 mm and a thickness of less than 1 mm. The disks were sintered in air at 500°C and then hydrogen-reduced at 200°C under atmospheric hydrogen flow, after which they were removed into the atmosphere at room temperature. After masking the disks with a perforated plate, they were placed in the vacuum chamber of a sputtering deposition system. Pt was deposited on one side to a thickness of approximately 200 nm, and electrode terminals were attached to the four corners of each side. The electrode-attached disks were placed in a Toyo Technica Hall measurement device, and Hall measurements and electrical conductivity measurements were performed using the x-probe method under vacuum.

[0065] <Method for measuring hydrogen adsorption and absorption> The amount of hydrogen adsorption and absorption was measured using H2-TPD (programmed temperature-programmed desorption spectrometry) as follows. A 200 mg sample was used. After removing adsorbed species at 400 °C under a helium stream, it was hydrogen-treated at 250 °C. The chamber was again evacuated at 400 °C to remove the water generated during the hydrogen treatment, and then hydrogen was adsorbed at 200 °C. The sample was cooled to room temperature under a hydrogen stream without contact with the atmosphere, and then switched to a helium stream. The temperature was raised to 500 °C at a rate of 10 °C / min. The desorbed gas was scanned at 2-second intervals using a QMS to create a profile. The amount of hydrogen adsorbed and absorbed by the sample was calculated as the amount of H2 gas per g of sample from the m / e = 2 area obtained from the profile to the area of ​​the previously calculated known volume of hydrogen. The contribution of the HO (m / e = 18) fragment from the m / e = 2 area was subtracted from the m / e = 2 area.

[0066] <Work function measurement method using the Kelvin probe method> The sample was finely crushed in a mortar and then pressed into a circular disk with a diameter of 10 mm and a thickness of less than 1 mm using a tablet press and a hydraulic press. The disk was air-sintered at 500 °C and then hydrogen-reduced at 200 °C under atmospheric hydrogen gas pressure. It was then removed to the atmosphere at room temperature and immediately sealed in a sample bottle. The work function (value) was measured using a Riken Keiki Fermi level measurement system (FAC-2) in a nitrogen box at room temperature using the Kelvin probe (contact potential difference) method. Before each measurement, a gold (Au) plate was measured to confirm that the work function value was 5.11 eV before measuring the sample disk to ensure the reliability of the measurements.

[0067] <Elemental analysis, oxygen content analysis> The elements constituting the samples and the content of Na derived from the sodium carbonate used during sample preparation were quantitatively analyzed as follows. After dissolving the samples in aqua regia, the content was quantified using an inductively coupled plasma optical emission spectrometer (ICP-OES, Thermo Fisher Scientific iCAP7600DuO) with an acid matrix matching calibration curve method. Furthermore, the oxygen content of the samples was quantitatively analyzed using an ONH analyzer (Horiba, Ltd. EMGA-930) with an impulse furnace heating extraction and IR detection (O) / TCD detection (N, H) under an inert gas atmosphere using Sn as the solvent.

[0068] Example 1 In 1.2 Ga 1.0 Zn 1.0 O x was prepared by the coprecipitation method. Indium nitrate (5N), gallium nitrate (4N), and zinc nitrate (3N) manufactured by Kojundo Chemical Laboratory Co., Ltd. were dissolved in approximately 400 cc of deionized water on a 0.05 molar scale. The mixture was heated to 70°C and stirred while a 10% aqueous solution of sodium carbonate was added dropwise, resulting in a precipitate. The dropwise addition was continued, and the pH was adjusted to 8. The mixture was heated and stirred for 1 hour, then allowed to cool to room temperature and left overnight. The resulting precipitate was collected by suction filtration, thoroughly washed with deionized water, and then evaporated to dryness at below 100°C while stirring to obtain a mixed hydroxide gel. The mixture was loaded into a quartz firing tube and dried at 120°C for 8 hours while circulating air. It was then heated to 500°C and held there for 4 hours for firing. After cooling, the mixture was removed and the pale cream-colored In 1.2 Ga 1.0 Zn 1.0 O x obtained.

[0069] The results of powder X-ray diffraction measurement of the obtained oxide are shown in Figure 1. As shown in Figure 1, no diffraction lines were present between diffraction angles 2θ 20° and 70°, and a halo was observed between 2θ 30° and 40°, where the maximum intensity count number (X1) was compared with the baseline X-ray count number (X2) at 2θ 70°, with X1 / X2 = 2.5, indicating an amorphous structure. The BET specific surface area was measured and found to be 130 m 2The powder was molded into a disk, and a sample was calcined in air at 500°C, and a sample was then reduced with hydrogen at 200°C. Hall measurements were performed on both samples, and both showed n-type semiconductivity, with the carrier electron concentration of the former being 1.0 × 10 18 / cm 3 , the latter is 1.2 × 10 19 / cm 3 The electrical conductivity of the former was 0.01 S / cm and that of the latter was 0.08 S / cm. Furthermore, the work functions of a sample formed into a 10 mm diameter disk and then calcined in air at 500°C and a sample subsequently reduced with hydrogen at 200°C were measured, and the former was 5.5 eV and the latter was 5.43 eV.

[0070] Using this oxide powder as a catalyst, the hydrogenation reaction of carbon dioxide was carried out as follows. 1.0 g of the oxide powder was loaded into a reaction tube with an inner diameter of 8 mm and installed in a reactor equipped with an electric furnace. The tube was heated in the electric furnace while flowing a carbon dioxide / hydrogen / nitrogen (8 / 48 / 6) feed gas at a total flow rate of 60 Nml / min. The temperature was raised to 300°C in approximately 30 minutes and maintained at this temperature for 30 minutes as a pretreatment for the reaction. The reaction temperature was then lowered to 190°C without changing the gas composition. The pressure was 0.9 MPa. Approximately 25 minutes after the predetermined reaction temperature was reached, a portion of the outlet gas was introduced into a gas chromatograph via a sampling valve directly connected to the reaction tube outlet, and the methanol, carbon dioxide, nitrogen, carbon monoxide, methane, and other products were analyzed. Furthermore, the reaction temperature was changed by adjusting the electric furnace without changing the feed gas composition or pressure. Analysis was performed in the same manner approximately 25 minutes after the predetermined reaction temperature was reached. This procedure was repeated while changing the reaction temperature in increments of approximately 10 to 15°C, and catalytic performance was evaluated at reaction temperatures up to 300°C. The results are shown in Table 1. After the reaction evaluation, the sample was allowed to cool and then removed into the air for powder X-ray diffraction measurement. No diffraction lines were observed between 2θ 20° and 70°, but a halo was observed between 2θ 30° and 40°, where the maximum intensity count number (X1) was X1 / X2 = 2.4 compared to the baseline X-ray count number (X2) at 2θ 70°, indicating an amorphous structure.

[0071] Furthermore, the amount of hydrogen adsorption and absorption of the above oxide powder was evaluated by the amount of hydrogen desorbed in H2-TPD analysis of a sample exposed to hydrogen gas at 200°C for 30 minutes, and was found to be 0.17H2 mol / g. Furthermore, the above oxide powder was treated under a hydrogen stream at 200°C under normal pressure for 2 hours, then removed from the sample under argon at room temperature. Elemental analysis was performed using an ICP optical emission spectrometer and an OHN analyzer. The composition was found to be almost the same as the feed ratio. Na was less than 0.1 mol% for 1.2 mol of In, and oxygen was 0.1 mol% for 1.2 mol of In. 1.2 Ga 1.0 Zn 1.0 The amount was 4.45 moles, which was greater than the stoichiometric amount of 4.3 moles, and it was found that some of the oxygen existed as carbonate groups and hydroxyl groups.

[0072] Example 2 In obtained by the same preparation as in Example 1 1.2 Ga 1.0 Zn 1.0 O x The material was impregnated with a deionized aqueous solution of tetraammine Pd(II) nitrate. After removing water by evaporation and drying at 100°C or less while stirring, the dried product was loaded into a quartz calcination tube and dried at 120°C for 8 hours while circulating air. The temperature was then raised to 500°C and maintained at this temperature for 4 hours. After cooling, the product was removed and a light brown Pd (5 mass%) / In solution was obtained. 1.2 Ga 1.0 Zn 1.0 O x obtained. Powder X-ray diffraction measurement of the resulting bonded material powder revealed no diffraction lines between 2θ 20° and 70°, and a halo was observed between 2θ 30° and 40°, where the maximum intensity count (X1) was compared with the baseline X-ray count (X2) at 2θ 70°, with X1 / X2 = 3.0, indicating an amorphous structure. BET specific surface area was measured and found to be 107 m 2 / g.

[0073] Using the resulting powder of bonding material as a catalyst, a carbon dioxide hydrogenation reaction was carried out in the same manner as in Example 1. The results are shown in Table 1. After the reaction evaluation, the sample was allowed to cool and then taken out into the air for powder X-ray diffraction measurement. A halo was observed between 2θ 30° and 40°, where the maximum intensity count number (X1) was X1 / X2 = 2.8 compared with the baseline X-ray count number (X2) at 2θ 70°, indicating an amorphous structure.

[0074] Furthermore, the above Pd (5 mass%) / In 1.2 Ga 1.0 Zn 1.0 O x The amount of hydrogen adsorption and absorption of the sample was evaluated by the amount of hydrogen desorbed in H2-TPD analysis of a sample exposed to hydrogen gas at 200°C for 30 minutes, and was found to be 0.28H2 mol / g. Furthermore, the oxide powder was treated under a hydrogen stream at 200°C under normal pressure for 2 hours, then removed from the stream at room temperature under argon. Elemental analysis was performed using an ICP optical emission spectrometer and an OHN analyzer. The composition was found to be almost the same as the starting material ratio. Furthermore, Na was 0.2 mol% or less relative to 1.2 mol of In, and oxygen was 0.2 mol% or less. 1.2 Ga 1.0 Zn 1.0 The amount was 4.41 moles, which was greater than the stoichiometric amount of 4.3 moles, and it was found that some of the oxygen existed as carbonate groups and hydroxyl groups.

[0075] Example 3 In 1.0 Zn 1.0 O xwas prepared by the coprecipitation method. Indium nitrate (4N) and zinc nitrate (3N) manufactured by Kojundo Chemical Laboratory Co., Ltd. were dissolved in approximately 400 cc of deionized water on a 0.05 molar scale. The mixture was heated to 70°C and stirred while adding sodium carbonate solution dropwise, resulting in a precipitate. The dropwise addition was continued and the pH was adjusted to 8. The mixture was heated and stirred for 1 hour, then allowed to cool to room temperature and left overnight. The resulting precipitate was collected by suction filtration, thoroughly washed with deionized water, and then evaporated to dryness at 100°C or below while stirring to obtain a mixed hydroxide gel. The mixture was loaded into a quartz firing tube and dried at 120°C for 8 hours while circulating air. It was then heated to 500°C and held there for 4 hours for firing. After cooling, the mixture was removed and a pale yellow In 1.0 Zn 1.0 Got Ox.

[0076] Powder X-ray diffraction measurement of the obtained oxide showed no diffraction lines between 2θ 20° and 70°, and a halo was observed between 2θ 30° and 40°, where the maximum intensity count (X1) was compared with the baseline X-ray count (X2) at 2θ 70°, with X1 / X2 = 3.2, indicating an amorphous structure. BET specific surface area was measured and found to be 71 m 2 The powder was molded into a disk, and a sample was calcined in air at 500°C, and a sample was then reduced with hydrogen at 200°C. Hall measurements were performed on both samples, and both showed n-type semiconductivity, with the carrier electron concentration of the former being 3.0 × 10 17 / cm 3 , the latter is 1.2 × 10 19 / cm 3 The electrical conductivity of the former was 0.02 S / cm and that of the latter was 0.02 S / cm. Furthermore, the work functions of a sample formed into a 10 mm diameter disk and then calcined in air at 500°C and a sample subsequently reduced with hydrogen at 200°C were measured, and the former was 5.57 eV and the latter was 5.38 eV.

[0077] Using this oxide powder as a catalyst, a carbon dioxide hydrogenation reaction was carried out in the same manner as in Example 1. The results are shown in Table 1. After the reaction evaluation, the sample was allowed to cool and then taken out into the air for powder X-ray diffraction measurement. No diffraction lines were observed between diffraction angles 2θ 20° and 70°, but a halo was observed between 2θ 30° and 40°, where the maximum intensity count number (X1) was X1 / X2 = 2.5 compared with the baseline X-ray count number (X2) at 2θ 70°, indicating an amorphous structure.

[0078] Example 4 In obtained by the same preparation as in Example 3 1.0 Zn 1.0 O x The material was impregnated with a deionized aqueous solution of tetraammine Pd(II) nitrate. After removing water by evaporation and drying at 100°C or less while stirring, the dried product was loaded into a quartz calcination tube and dried at 120°C for 8 hours while circulating air. The temperature was then raised to 500°C and maintained at this temperature for 4 hours. After cooling, the product was removed and a light brown Pd (5 mass%) / In solution was obtained. 1.0 Zn 1.0 O x obtained. Powder X-ray diffraction measurement of the resulting bonded material powder revealed no diffraction lines between diffraction angles 2θ 20° and 70°, and a halo was observed between 2θ 30° and 40°, where the maximum intensity count (X1) was compared with the baseline X-ray count (X2) at 2θ 70°, with X1 / X2 = 2.5, indicating an amorphous structure. BET specific surface area measurement revealed a value of 65 m 2 / g.

[0079] Using the powder of the resulting bonding material as a catalyst, a carbon dioxide hydrogenation reaction was carried out in the same manner as in Example 1. The results are shown in Table 1. After the reaction evaluation, the sample was allowed to cool and then taken out into the air for powder X-ray diffraction measurement. A halo was observed between 2θ 30° and 40°, where the maximum intensity count number (X1) was compared with the baseline X-ray count number (X2) at 2θ 70°, with X1 / X2 = 2.4, indicating an amorphous structure.

[0080] Example 5 In 1.0 Ga 0.3 O x was prepared by the coprecipitation method. Indium nitrate (4N) and gallium nitrate (5N) manufactured by Kojundo Chemical Laboratory Co., Ltd. were dissolved in approximately 250 cc of water on a 0.05 molar scale. The mixture was heated to 70°C and stirred while adding sodium carbonate solution dropwise, resulting in a precipitate. The dropwise addition was continued and the pH was adjusted to 8. The mixture was heated and stirred for 1 hour, then allowed to cool to room temperature and left overnight. The resulting precipitate was collected by suction filtration, thoroughly washed with deionized water, and then evaporated to dryness at below 100°C while stirring to obtain a mixed hydroxide gel. The mixture was loaded into a quartz firing tube and dried at 120°C for 8 hours while circulating air. It was then heated to 500°C and held there for 4 hours for firing. After cooling, the mixture was removed and the pale cream-colored In 1.0 Ga 0.3 O x obtained.

[0081] Powder X-ray diffraction measurement of the obtained oxide showed no diffraction lines between 2θ 20° and 70°, and a halo was observed between 2θ 30° and 40°, where the maximum intensity count (X1) was compared with the baseline X-ray count (X2) at 2θ 70°, with X1 / X2 = 2.8, indicating an amorphous structure. BET specific surface area was measured and found to be 90 m 2 The powder was molded into a 10 mm diameter disk, and the work function of a sample that was calcined in air at 500°C and then reduced with hydrogen at 200°C was measured. The former was 5.54 eV, and the latter was 5.30 eV. Using this oxide powder as a catalyst, a carbon dioxide hydrogenation reaction was carried out in the same manner as in Example 1. The results are shown in Table 1. After the reaction evaluation, the sample was allowed to cool and then taken out into the air for powder X-ray diffraction measurement. A halo was observed between 2θ 30° and 40°, where the maximum intensity count number (X1) was compared with the baseline X-ray count number (X2) at 2θ 70°, with X1 / X2 = 2.4, indicating an amorphous structure.

[0082] Example 6 In obtained by the same preparation as in Example 5 1.0 Ga 0.3 O x The material was impregnated with a deionized aqueous solution of tetraammine Pd(II) nitrate. After removing water by evaporation and drying at 100°C or less while stirring, the dried product was loaded into a quartz calcination tube and dried at 120°C for 8 hours while circulating air. The temperature was then raised to 500°C and maintained at this temperature for 4 hours. After cooling, the product was removed and a light brown Pd (5 mass%) / In solution was obtained. 1.0 Ga 0.3 O x obtained. Powder X-ray diffraction measurement of the resulting bonded material powder revealed that no diffraction lines were present between diffraction angles 2θ 20° and 70°, and a halo was observed between 2θ 30° and 40°, where the maximum intensity count (X1) was compared with the baseline X-ray count (X2) at 2θ 70°, with X1 / X2 = 3.0, indicating an amorphous structure. BET specific surface area measurement revealed a value of 55 m 2 / g. Using the powder of the resulting bonding material as a catalyst, a carbon dioxide hydrogenation reaction was carried out in the same manner as in Example 1. The results are shown in Table 1. After the reaction evaluation, the sample was allowed to cool and then taken out into the air for powder X-ray diffraction measurement. A halo was observed between 2θ 30° and 40°, where the maximum intensity count number (X1) was compared with the baseline X-ray count number (X2) at 2θ 70°, with X1 / X2 = 2.6, indicating an amorphous structure.

[0083] (Comparative Example 1) In the same manner as in Example 1, InO was grown using only indium nitrate. xwas prepared. Indium nitrate (4N) manufactured by Kojundo Chemical Laboratory Co., Ltd. was dissolved in approximately 150 cc of deionized water on a 0.04 mol scale. The mixture was heated to 70°C and an aqueous sodium carbonate solution was added dropwise while stirring, resulting in the formation of a precipitate. The dropwise addition was continued, and the pH was adjusted to 8. The mixture was heated and stirred for 1 hour, then allowed to cool to room temperature and left overnight. The resulting precipitate was collected by suction filtration, thoroughly washed with deionized water, and then evaporated to dryness at 100°C or below while stirring, yielding a mixed hydroxide gel. The mixture was loaded into a quartz firing tube and dried at 120°C for 8 hours while circulating air, after which it was heated to 500°C and held there for 4 hours for firing. After cooling, the mixture was removed and a pale cream-colored InO x obtained.

[0084] Powder X-ray diffraction measurement of the obtained oxide showed that diffraction lines were present between the diffraction angles 2θ 20° and 70°, which matched with cubic-In2O3 (JCPDS03-065-3170), indicating that the obtained oxide was crystalline In2O3. Furthermore, no halo was observed, indicating that it was not an amorphous structure. BET specific surface area measurement revealed a value of 70m 2 The powder was molded into a disk, and a sample was calcined in air at 500°C, and a sample was then reduced with hydrogen at 200°C. Hall measurements were performed on both samples, and both showed n-type semiconductivity, with the carrier electron concentration of the former being 9.8 × 10 16 / cm 3 , the latter is 4.9 × 10 18 / cm 3 The electrical conductivity of the former was 0.03 S / cm and that of the latter was 0.94 S / cm. Furthermore, the work functions of a sample formed into a 10 mm diameter disk and then calcined in air at 500°C and a sample subsequently reduced with hydrogen at 200°C were measured; the former was 5.66 eV and the latter was 5.34 eV.

[0085] Using this oxide powder as a catalyst, the hydrogenation reaction of carbon dioxide was carried out in the same manner as in Example 1. The results are shown in Table 2. After the reaction evaluation, the sample was allowed to cool and then taken out into the air for powder X-ray diffraction measurement. Diffraction lines were found to be present between diffraction angles 2θ of 20° and 70°, which matched those of cubic In2O3 (JCPDS03-065-3170), demonstrating that crystalline In2O3 was maintained even after the reaction evaluation. Furthermore, no halo was observed between diffraction angles 2θ of 20° and 70°, indicating that the sample did not have an amorphous structure. Furthermore, the hydrogen adsorption / absorption capacity of the above oxide powder was evaluated by the amount of hydrogen desorbed in H2-TPD analysis of a sample exposed to hydrogen gas at 200°C for 30 minutes, and was found to be 0.11 H2 mol / g.

[0086] (Comparative Example 2) InO prepared in the same manner as in Comparative Example 1 x The material was impregnated with a deionized aqueous solution of tetraammine Pd(II) nitrate. After removing water by evaporation and drying at 100°C or less while stirring, the dried product was loaded into a quartz calcination tube and dried at 120°C for 8 hours while circulating air. The temperature was then raised to 500°C and maintained at this temperature for 4 hours. After cooling, the product was removed and a light brown Pd (5 mass%) / InO x obtained. Powder X-ray diffraction measurement of the resulting bonding material powder showed that diffraction lines were present between the diffraction angles 2θ 20° and 70°, which matched with cubic-In2O3 (JCPDS03-065-3170), indicating that the resulting oxide was crystalline In2O3. Furthermore, no halo was observed, indicating that it was not an amorphous structure. BET specific surface area measurement revealed a value of 62 m 2 / g.

[0087] The carbon dioxide hydrogenation reaction was carried out in the same manner as in Example 1 using the powder of the resulting bonding material as a catalyst. The results are shown in Table 2. After the reaction evaluation, the sample was allowed to cool and then removed into the air for powder X-ray diffraction measurement. Diffraction lines were observed between diffraction angles 2θ of 20° and 70°, which matched those of cubic In2O3 (JCPDS03-065-3170), demonstrating that crystalline In2O3 was maintained even after the reaction evaluation. Furthermore, no halo was observed between diffraction angles 2θ of 20° and 70°, indicating that the sample did not have an amorphous structure. Furthermore, the above Pd (5 mass%) / InO x The hydrogen adsorption / absorption amount of the sample was evaluated by the amount of hydrogen desorbed in H2-TPD analysis of the sample exposed to hydrogen gas at 200°C for 30 minutes, and was found to be 0.17 H2 mol / g.

[0088] (Comparative Example 3) For comparison, we tested In2O3 from Wako Pure Chemical Industries. The In2O3 powder was loaded into a quartz calcination tube and dried at 120°C for 8 hours while circulating air. The temperature was then raised to 500°C and held there for 4 hours. After cooling, the product was removed and cream-colored In2O3 was obtained. Powder X-ray diffraction measurement of the obtained oxide showed that diffraction lines were present between the diffraction angles 2θ 20° and 70°, which matched with cubic-In2O3 (JCPDS04-012-5550), indicating that the obtained oxide was crystalline In2O3. Furthermore, no halo was observed, indicating that it was not an amorphous structure. BET specific surface area measurement revealed a value of 2m 2 The powder was molded into a disk, and a sample was calcined in air at 500°C, and a sample was then reduced with hydrogen at 200°C. Hall measurements were performed on both samples, and both showed n-type semiconductivity, with the carrier electron concentration of the former being 6.2 × 10 16 / cm 3 , the latter is 9.9 × 10 18 / cm 3The electrical conductivity of the former was 0.02 S / cm and that of the latter was 12 S / cm. Furthermore, the work functions of a sample formed into a 10 mm diameter disk and then calcined in air at 500°C and a sample subsequently reduced with hydrogen at 200°C were measured, and the former was 5.55 eV and the latter was 5.42 eV.

[0089] Using the In2O3 powder calcined in air at 500°C as a catalyst, a carbon dioxide hydrogenation reaction was carried out in the same manner as in Example 1. The results are shown in Table 2. After the reaction evaluation, the sample was allowed to cool and then removed into the air for powder X-ray diffraction measurement. Diffraction lines were observed between diffraction angles 2θ of 20° and 70°, which matched those of cubic In2O3 (JCPDS04-012-5550), demonstrating that crystalline In2O3 was maintained even after the reaction evaluation. Furthermore, no halo was observed between diffraction angles 2θ of 20° and 70°, indicating that the sample did not have an amorphous structure. Furthermore, the hydrogen adsorption / absorption capacity of the above oxide powder was evaluated by the amount of hydrogen desorbed in H2-TPD analysis of a sample exposed to hydrogen gas at 200°C for 30 minutes, and was found to be 0.011 H2 mol / g.

[0090] Comparative Example 4 The Wako Pure Chemical In2O3 used in Comparative Example 3 was impregnated with a deionized aqueous solution of tetraammine Pd(II) nitrate. After evaporating and drying the mixture at 100°C or below while stirring, the dried product was loaded into a quartz calcination tube and dried at 120°C for 8 hours while circulating air. The temperature was then raised to 500°C and maintained there for 4 hours for calcination. After cooling, the product was removed to obtain light brown Pd (5% by mass) / In2O3. Powder X-ray diffraction measurement of the resulting bonding material powder showed that diffraction lines were present between the diffraction angles 2θ 20° and 70°, which matched with cubic-In2O3 (JCPDS04-012-5550), indicating that the resulting oxide was crystalline In2O3. Furthermore, no halo was observed, indicating that it was not an amorphous structure. BET specific surface area measurement revealed a value of 4 m 2 / g.

[0091] The carbon dioxide hydrogenation reaction was carried out in the same manner as in Example 1 using the powder of the resulting bonding material as a catalyst. The results are shown in Table 2. After the reaction evaluation, the sample was allowed to cool and then removed into the air for powder X-ray diffraction measurement. Diffraction lines were observed between diffraction angles 2θ of 20° and 70°, which matched those of cubic In2O3 (JCPDS04-012-5550), demonstrating that crystalline In2O3 was maintained even after the reaction evaluation. Furthermore, no halo was observed between diffraction angles 2θ of 20° and 70°, indicating that the sample did not have an amorphous structure. Furthermore, the hydrogen adsorption / absorption capacity of the above Pd (5 mass%) / In2O3 was evaluated by the amount of hydrogen desorbed in H2-TPD analysis of a sample exposed to hydrogen gas at 200°C for 30 minutes, and was found to be 0.018 H2 mol / g.

[0092] (Comparative Example 5) ZnO was prepared using only zinc nitrate in the same manner as in Example 1. Zinc nitrate (3N) manufactured by Kojundo Chemical Laboratory Co., Ltd. was dissolved in approximately 150 cc of deionized water at a 0.04 mol scale. The mixture was heated to 70°C and stirred while adding sodium carbonate solution dropwise, resulting in a precipitate. The dropwise addition was continued, and the pH was adjusted to 8. Stirring was continued for 1 hour while heating, then allowed to cool to room temperature and left overnight. The resulting precipitate was collected by suction filtration, thoroughly washed with deionized water, and then evaporated to dryness at 100°C or below while stirring, yielding a mixed hydroxide gel. The mixture was loaded into a quartz calcination tube and dried at 120°C for 8 hours while circulating air. It was then heated to 500°C and held there for 4 hours for calcination. After cooling, the mixture was removed and a pale cream-colored ZnO was obtained. Powder X-ray diffraction measurement of the obtained oxide showed that diffraction lines existed between the diffraction angles 2θ 20° and 70°, which matched with hexagonal ZnO (JCPDS01-070-8070), indicating that the obtained oxide was crystalline ZnO. Furthermore, no halo was observed, indicating that it was not an amorphous structure. BET specific surface area measurement was found to be 17m 2The powder was molded into a disk, and a sample was calcined in air at 500°C, and a sample was then reduced with hydrogen at 200°C. Hall measurements were performed on both samples, and both showed n-type semiconductivity, with the carrier electron concentration of the former being 1.0 × 10 13 / cm 3 , the latter is 1.5 × 10 14 / cm 3 The electrical conductivity of the former is 2.5×10 -6 S / cm, the latter is 4.3 × 10 -6 Furthermore, the work functions of a sample formed into a 10 mm diameter disk and then calcined in air at 500°C and a sample subsequently reduced with hydrogen at 200°C were measured; the former was 5.26 eV and the latter was 5.15 eV.

[0093] Using this oxide powder as a catalyst, the hydrogenation reaction of carbon dioxide was carried out in the same manner as in Example 1. The hydrogenation of carbon dioxide did not proceed within the temperature range of 200°C to 300°C, and neither methanol nor CO was produced. After the reaction evaluation, the sample was allowed to cool and then removed into the atmosphere. Powder X-ray diffraction measurements were performed. Diffraction lines were observed between diffraction angles 2θ 20° and 70°, which matched those of hexagonal ZnO (JCPDS01-070-8070). This indicated that crystalline ZnO was maintained even after the reaction evaluation. Furthermore, no halo was observed between diffraction angles 2θ 20° and 70°, indicating that the sample did not have an amorphous structure. Furthermore, the hydrogen adsorption / absorption capacity of the above oxide powder was evaluated by the amount of hydrogen desorbed in H2-TPD analysis of a sample exposed to hydrogen gas at 200°C for 30 minutes, and was found to be 0.01 H2 mol / g.

[0094] (Comparative Example 6) ZnO prepared in the same manner as in Comparative Example 5 was impregnated with a deionized aqueous solution of tetraammine Pd(II) nitrate. After evaporating and drying the mixture at 100°C or below while stirring, the dried product was loaded into a quartz firing tube and dried at 120°C for 8 hours while circulating air. The temperature was then raised to 500°C and maintained there for 4 hours for firing. After cooling, the product was removed to obtain light brown Pd (5% by mass) / ZnO. Powder X-ray diffraction measurement of the resulting bonding material powder showed that diffraction lines existed between the diffraction angles 2θ 20° and 70°, which matched with hexagonal ZnO (JCPDS01-070-8070), indicating that the resulting oxide was crystalline ZnO. Furthermore, no halo was observed, indicating that it was not an amorphous structure. BET specific surface area measurement revealed a value of 11 m 2 / g.

[0095] The carbon dioxide hydrogenation reaction was carried out in the same manner as in Example 1 using the powder of the resulting bonding material as a catalyst. The results are shown in Table 2. After the reaction evaluation, the sample was allowed to cool and then removed into the air for powder X-ray diffraction measurement. Diffraction lines were observed between diffraction angles 2θ of 20° and 70°, which matched those of hexagonal ZnO (JCPDS01-070-8070) and PdZn (JCPDS01-080-3086). This indicated that crystalline ZnO was maintained even after the reaction evaluation, and that PdZn had also been produced. Furthermore, no halo was observed between diffraction angles 2θ of 20° and 70°, indicating that the sample did not have an amorphous structure. Furthermore, the hydrogen adsorption / absorption capacity of the above Pd (5 mass%) / ZnO was evaluated by the amount of hydrogen desorbed in H2-TPD analysis of a sample exposed to hydrogen gas at 200°C for 30 minutes, and was found to be 0.31 H2 mol / g.

[0096] Example 7 In obtained by the same preparation as in Example 1 1.0 Ga 1.0 Zn 1.0 O x The powder was impregnated with a deionized aqueous solution of rhodium (III) nitrate in the same manner as in Example 2. After removing water by evaporation and drying at 100°C or less while stirring, the dried product was loaded into a quartz firing tube and dried at 120°C for 8 hours while circulating air. The temperature was then raised to 500°C and maintained at this temperature for 4 hours. After cooling, the powder was taken out and a light brown Rh (5 mass%) / In 1.0 Ga 1.0 Zn 1.0 O x obtained. When the powder of the obtained bonding material was subjected to powder X-ray diffraction measurement, no diffraction lines were present between diffraction angles 2θ 20° and 70°, and a halo was observed between 2θ 30° and 40°, where the maximum intensity count number (X1) was X1 / X2 = 2.2 compared to the baseline X-ray count number (X2) at 2θ 70°, indicating an amorphous structure. The resulting powder of bonding material was used as a catalyst to carry out the hydrogenation reaction of carbon dioxide in the same manner as in Example 1. The results are shown in Table 3.

[0097] Example 8 In obtained by the same preparation as in Example 1 1.0 Ga 1.0 Zn 1.0 O x The product was impregnated with a deionized aqueous solution of tetraammine Pt(IV) nitrate in the same manner as in Example 2. After removing water by evaporation and drying at 100°C or less while stirring, the dried product was loaded into a quartz firing tube and dried at 120°C for 8 hours while circulating air. The temperature was then raised to 500°C and maintained at this temperature for 4 hours. After cooling, the product was taken out and a light brown Pt (2.5 mass%) / In powder was obtained. 1.0 Ga 1.0 Zn 1.0 O x obtained. When the powder of the resulting bonded material was subjected to powder X-ray diffraction measurement, no diffraction lines were present between diffraction angles 2θ 20° and 70°, and a halo was observed between 2θ 30° and 40°, where the maximum intensity count number (X1) was X1 / X2 = 2.5 compared to the baseline X-ray count number (X2) at 2θ 70°, indicating an amorphous structure. The resulting powder of bonding material was used as a catalyst to carry out the hydrogenation reaction of carbon dioxide in the same manner as in Example 1. The results are shown in Table 3.

[0098] Example 9 In obtained by the same preparation as in Example 1 1.0 Ga 1.0 Zn 1.0 O xThe powder was impregnated with a deionized aqueous solution of iridium (IV) nitrate in the same manner as in Example 2. After removing water by evaporation and drying at 100°C or less while stirring, the dried product was loaded into a quartz firing tube and dried at 120°C for 8 hours while circulating air. The temperature was then raised to 500°C and maintained at this temperature for 4 hours. After cooling, the powder was taken out and a light brown Ir (2.5 mass%) / In 1.0 Ga 1.0 Zn 1.0 O x obtained. When the powder of the resulting bonded material was subjected to powder X-ray diffraction measurement, no diffraction lines were present between diffraction angles 2θ 20° and 70°, and a halo was observed between 2θ 30° and 40°, where the maximum intensity count number (X1) was X1 / X2 = 2.4 compared to the baseline X-ray count number (X2) at 2θ 70°, indicating an amorphous structure. The resulting powder of bonding material was used as a catalyst to carry out the hydrogenation reaction of carbon dioxide in the same manner as in Example 1. The results are shown in Table 3.

[0099] Example 10 Ethylenediamine gold chloride was prepared from chloroauric acid and ethylenediamine, and then ethylenediamine gold nitrate was prepared by ion exchange. 1.0 Ga 1.0 Zn 1.0 O x The powder was impregnated with a deionized aqueous solution of ethylenediamine gold nitrate in the same manner as in Example 2. After removing water by evaporation and drying at 100°C or less while stirring, the dried product was loaded into a quartz firing tube and dried at 120°C for 8 hours while circulating air. The temperature was then raised to 500°C and maintained at this temperature for 4 hours. After cooling, the powder was removed and a light brown Au (2.5 mass%) / In powder was obtained. 1.0 Ga 1.0 Zn 1.0 O x obtained. When the powder of the resulting bonded material was subjected to powder X-ray diffraction measurement, no diffraction lines were present between diffraction angles 2θ 20° and 70°, and a halo was observed between 2θ 30° and 40°, where the maximum intensity count number (X1) was X1 / X2 = 1.8 compared to the baseline X-ray count number (X2) at 2θ 70°, indicating an amorphous structure. The resulting powder of bonding material was used as a catalyst to carry out the hydrogenation reaction of carbon dioxide in the same manner as in Example 1. The results are shown in Table 3.

[0100] Example 11 In 1.0 Al 1.0 O x was prepared by the coprecipitation method. Indium nitrate (4N) and aluminum nitrate (3N) manufactured by Kojundo Chemical Laboratory Co., Ltd. were dissolved in approximately 150 cc of water on a 0.04 molar scale. The mixture was heated to 70°C and stirred while adding sodium carbonate solution dropwise, resulting in a precipitate. The dropwise addition was continued and the pH was adjusted to 8. The mixture was heated and stirred for 1 hour, then cooled to room temperature and left overnight. The resulting precipitate was collected by suction filtration, thoroughly washed with deionized water, and evaporated to dryness at 100°C or below while stirring to obtain a mixed hydroxide gel. The mixture was loaded into a quartz firing tube and dried at 120°C for 8 hours while circulating air. It was then heated to 500°C and held there for 4 hours for firing. After cooling, the mixture was removed and a pale yellow In 1.0 Al 1.0 O x obtained. The obtained oxide powder was formed into a 10 mm diameter disk, and the work functions of a sample that was air-sintered at 500°C and then hydrogen-reduced at 200°C were measured. The former was 5.48 V, and the latter was 5.31 eV. This In 1.0 Al 1.0 O x The material was impregnated with a deionized aqueous solution of tetraammine Pd(II) nitrate. After removing water by evaporation and drying at 100°C or less while stirring, the dried product was loaded into a quartz calcination tube and dried at 120°C for 8 hours while circulating air. The temperature was then raised to 500°C and maintained at this temperature for 4 hours. After cooling, the product was removed and a light brown Pd (5 mass%) / In solution was obtained.1.0 Al 1.0 O x obtained. Powder X-ray diffraction measurement of the resulting bonded material powder revealed no diffraction lines between diffraction angles 2θ 20° and 70°, and a halo was observed between 2θ 30° and 40°, where the maximum intensity count (X1) was X1 / X2 = 1.8 compared to the baseline X-ray count (X2) at 2θ 70°, indicating an amorphous structure. BET specific surface area was measured and found to be 91 m 2 / g. Using the powder of the resulting bonding material as a catalyst, a carbon dioxide hydrogenation reaction was carried out in the same manner as in Example 1. The results are shown in Table 3. After the reaction evaluation, the sample was allowed to cool and then taken out into the air for powder X-ray diffraction measurement. A halo was observed between 2θ 30° and 40°, where the maximum intensity count number (X1) was compared with the baseline X-ray count number (X2) at 2θ 70°, with X1 / X2 = 1.6, indicating an amorphous structure.

[0101] Example 12 In 1.2 Al 1.0 Zn 1.0 O x was prepared by the coprecipitation method. Indium nitrate (4N), aluminum nitrate (3N), and zinc nitrate (3N) manufactured by Kojundo Chemical Laboratory Co., Ltd. were dissolved in approximately 150 cc of water on a 0.04 molar scale. The mixture was heated to 70°C and stirred while adding sodium carbonate solution dropwise, resulting in a precipitate. The dropwise addition was continued and the pH was adjusted to 8. The mixture was heated and stirred for 1 hour, then allowed to cool to room temperature and left overnight. The resulting precipitate was collected by suction filtration, thoroughly washed with deionized water, and then evaporated to dryness at below 100°C while stirring to obtain a mixed hydroxide gel. The mixture was loaded into a quartz firing tube and dried at 120°C for 8 hours while circulating air. It was then heated to 500°C and held there for 4 hours for firing. After cooling, the mixture was removed and a pale yellow In 1.2 Al 1.0 Zn 1.0 O x obtained. The obtained oxide powder was molded into a disk of 10 mm diameter and then calcined in air at 500°C. The work function of the sample was measured and found to be 5.41 eV. This In 1.2 Al 1.0 Zn 1.0 O x The material was impregnated with a deionized aqueous solution of tetraammine Pd(II) nitrate. After removing water by evaporation and drying at 100°C or less while stirring, the dried product was loaded into a quartz calcination tube and dried at 120°C for 8 hours while circulating air. The temperature was then raised to 500°C and maintained at this temperature for 4 hours. After cooling, the product was removed and a light brown Pd (5 mass%) / In solution was obtained. 1.2 Al 1.0 Zn 1.0 O x obtained.

[0102] Powder X-ray diffraction measurement of the resulting bonded material powder revealed no diffraction lines between diffraction angles 2θ 20° and 70°, and a halo was observed between 2θ 30° and 40°, where the maximum intensity count (X1) was X1 / X2 = 2.5 compared to the baseline X-ray count (X2) at 2θ 70°, indicating an amorphous structure. The BET specific surface area was measured and found to be 103 m 2 / g. Using the resulting powder of bonding material as a catalyst, a carbon dioxide hydrogenation reaction was carried out in the same manner as in Example 1. The results are shown in Table 3. After the reaction evaluation, the sample was allowed to cool and then taken out into the air for powder X-ray diffraction measurement. A halo was observed between 2θ 30° and 40°, where the maximum intensity count number (X1) was compared with the baseline X-ray count number (X2) at 2θ 70°, with X1 / X2 = 2.2, indicating an amorphous structure.

[0103] (Comparative Example 7) GaOn was prepared using only gallium nitrate in the same manner as in Example 1. Gallium nitrate (5N) manufactured by Kojundo Chemical Laboratory Co., Ltd. was dissolved in approximately 150 cc of deionized water at a 0.04 mol scale. The mixture was heated to 70°C, and aqueous sodium carbonate solution was added dropwise with stirring, resulting in a precipitate. The dropwise addition was continued, and the pH was adjusted to 8. Stirring was continued for 1 hour while heating, then allowed to cool to room temperature and left overnight. The resulting precipitate was collected by suction filtration, thoroughly washed with deionized water, and then evaporated to dryness at below 100°C while stirring, yielding a mixed hydroxide gel. The mixture was loaded into a quartz firing tube and dried at 120°C for 8 hours while circulating air. It was then heated to 500°C and held there for 4 hours for calcination. After cooling, the mixture was removed and white GaOn was obtained. Powder X-ray diffraction measurement of the obtained oxide showed that diffraction lines existed between the diffraction angles 2θ 20° and 70°, which matched with hexagonal α-Ga2O3 (JCPDS01-074-1610), indicating that the obtained oxide was crystalline Ga2O3. Furthermore, no halo was observed, indicating that it was not an amorphous structure. The BET specific surface area was measured and found to be 77 m 2 / g. Using this oxide powder as a catalyst, the hydrogenation reaction of carbon dioxide was carried out in the same manner as in Example 1. The results are shown in Table 3. After the reaction evaluation, the sample was allowed to cool and then removed into the air for powder X-ray diffraction measurement. Diffraction lines were observed between diffraction angles 2θ of 20° and 70°, which matched those of α-Ga2O3 (JCPDS01-074-1610), demonstrating that crystalline Ga2O3 was maintained even after the reaction evaluation. Furthermore, no halo was observed between diffraction angles 2θ of 20° and 70°, indicating that the sample did not have an amorphous structure.

[0104] (Comparative Example 8) GaOn prepared in the same manner as in Comparative Example 7 was impregnated with a deionized aqueous solution of tetraammine Pd(II) nitrate. The mixture was stirred and evaporated to dryness at temperatures below 100°C. The dried product was then loaded into a quartz calcination tube and dried at 120°C for 8 hours under air circulation. The temperature was then raised to 500°C and maintained there for 4 hours for calcination. The product was allowed to cool and then removed to obtain a light brown Pd (5% by mass) / GaOn. Powder X-ray diffraction measurement of the resulting bonding material powder revealed that diffraction lines existed between the diffraction angles 2θ of 20° and 70°, which matched with hexagonal α-Ga2O3 (JCPDS01-074-1610), indicating that the resulting oxide was crystalline Ga2O3. Furthermore, no halo was observed, indicating that it was not an amorphous structure. The BET specific surface area was measured to be 42 m 2 / g. The carbon dioxide hydrogenation reaction was carried out in the same manner as in Example 1 using the powder of the resulting bonding material as a catalyst. The results are shown in Table 3. After the reaction evaluation, the sample was allowed to cool and then removed into the air for powder X-ray diffraction measurement. Diffraction lines were observed between diffraction angles 2θ of 20° and 70°, which matched those of hexagonal α-Ga2O3 (JCPDS01-074-1610), indicating that crystalline Ga2O3 was maintained even after the reaction evaluation. Furthermore, no halo was observed between diffraction angles 2θ of 20° and 70°, indicating that the sample did not have an amorphous structure.

[0105] [Table 1]

[0106] [Table 2]

[0107] [Table 3]

[0108] From the comparison of Examples 1, 3, and 5 with Comparative Examples 1, 3, 5, and 7, it is clear that InD containing the element D in addition to In (indium) b O n X x It can be seen that the catalyst containing the n-type semiconductor oxide produces methanol more efficiently in the carbon dioxide hydrogenation reaction. Furthermore, from a comparison of Examples 2, 4, 6, 11, and 12 with Comparative Examples 2, 4, 6, and 8, it was found that the bonding material M of the metal component M and the n-type semiconductor oxide containing the element D in addition to In (indium) a InD b O n X x It can be seen that the catalyst containing α-methyl-2-propanol is more efficient in producing methanol in the hydrogenation reaction of carbon dioxide. From the comparison of Example 1 with Comparative Examples 1, 3, and 5, it is clear that InD containing the element D in addition to In (indium) b O n X x The catalyst containing the n-type semiconductor oxide has an amorphous structure, a high specific surface area, a high carrier electron concentration, and a high amount of hydrogen adsorption and absorption, and is therefore able to efficiently produce methanol in the carbon dioxide hydrogenation reaction. Furthermore, from the comparison of Example 2 with Comparative Examples 2, 4, and 6, it is clear that the bonding material M of the metal component M and the n-type semiconductor oxide containing the element D in addition to In (indium) a InD b O n X x The catalyst containing α-methyl-2-propanol has an amorphous structure, a high specific surface area, and a large amount of hydrogen adsorption and absorption, and is therefore able to efficiently produce methanol in the carbon dioxide hydrogenation reaction. Furthermore, from Examples 7 to 10, a bonding material M of a metal component M and an n-type semiconductor oxide containing an element D in addition to In (indium) was obtained. a InD b O n X x It can be seen that amorphous catalysts can be obtained using a variety of M's, and that they serve as catalysts that efficiently produce methanol in the hydrogenation reaction of carbon dioxide.

Claims

1. A catalyst comprising an n-type semiconductor oxide represented by the following formula (1): InD ｂ O ｎ X ｘ (1) (In the formula (1), Component D represents at least one element selected from the group consisting of Fe, Cr, Zr, Ti, Sn, Al, Ga, and Zn; b and n represent the molar ratios of D and O to In, respectively, and are numbers satisfying 0<b≦3 and 0<n≦6; Component X represents at least one element selected from the group consisting of P, S, Se, Te, Sb, Bi, Pb, Cl, I, F, H, C, Si, and Ge; x represents the molar ratio of X to In, and is a number satisfying 0≦x≦1.

2. 2. The catalyst according to claim 1, wherein a halo resulting from an amorphous structure is observed in the n-type semiconductor oxide in X-ray diffraction measurement XRD (CuKα) in the diffraction angle (2θ) range of 10° to 50°.

3. The specific surface area of ​​the n-type semiconductor oxide measured by the BET method is 5 m ２ The catalyst according to claim 1 or 2, wherein the Mo content is 1 / g or more.

4. The electrical conductivity of the n-type semiconductor oxide is 1.0×10 －８ 3. The catalyst according to claim 1, wherein the surface area of ​​the catalyst is 100 nm.

5. The n-type semiconductor oxide has a carrier electron concentration of 1.0×10 as measured by a four-probe Hall measurement. １５ / cm ３ The catalyst according to claim 1 or 2, wherein

6. 3. The catalyst according to claim 1, wherein said component D consists of at least two elements.

7. The catalyst according to claim 1 or 2, comprising a bonding material represented by the following formula (2) in which a metal component M is bonded to the n-type semiconductor oxide: M ａ InD ｂ O ｎ X ｘ (2) (In the formula (2), the metal component M is a component containing at least one element selected from the group consisting of Ni, Cu, Pd, Pt, Rh, Ru, Ir, Au, and Ag; a represents the molar ratio of M to In, and is a number that satisfies 0<a≦5.

8. The specific surface area of ​​the bonding material measured by the BET method is 1 m ２ The catalyst according to claim 7, wherein the Cr content is 1 / g or more.

9. The electrical conductivity of the metal component M is 1.0×10 －６ 8. The catalyst according to claim 7, wherein the solubility is 100 S / cm or more.

10. The catalyst according to claim 1 or 2, which is obtained through a heat treatment at 100°C or higher and 1200°C or lower.

11. 3. The catalyst according to claim 1, which is used for hydrogenating oxygen-containing compounds.

12. 12. The catalyst of claim 11, wherein the oxygen-containing compound is carbon dioxide.

13. A method for producing methanol, comprising carrying out a hydrogenation reaction of an oxygen-containing compound using the catalyst according to claim 11 to produce methanol.

Images