Composite, hydrogen generation catalyst, catalyst ink, electrode, and method for producing composite

Abstract

A composite according to the present invention contains a molybdenum compound, a first metal (PM), and a second metal (M). The first metal (PM) is platinum or a combination of platinum and palladium, and the second metal (M) is one or more selected from the group consisting of metals.

Description

Composite, hydrogen generation catalyst, catalyst ink, electrode, and method for manufacturing the composite.

[0001] The present invention relates to a composite, a hydrogen generation catalyst, a catalyst ink, an electrode, and a method for producing the composite. This application claims priority under Japanese Patent Application No. 2024-185157, filed in Japan on October 21, 2024, the contents of which are incorporated herein by reference.

[0002] Water electrolysis technology is attracting attention as a technology that can produce hydrogen from water using renewable energy, aiming to solve environmental and energy resource problems. ２ Layered transition metal chalcogen compounds, such as those represented by ), are expected to be materials that are inexpensive, abundant in resources, and possess high catalytic activity.

[0003] Patent Document 1 describes a method for producing molybdenum disulfide doped with metal ions. It also states that the metal cations of the doped metal are uniformly dispersed between each layer of molybdenum disulfide, and that this material maintains a two-dimensional sheet-type structure of molybdenum disulfide in its crystalline structure.

[0004] Chinese Patent Application Publication No. 106608652 Specification

[0005] However, there is still room for further investigation regarding the provision of novel catalyst materials containing molybdenum compounds such as molybdenum disulfide. The present invention aims to provide a composite material, a hydrogen generation catalyst, a catalyst ink, an electrode, and a method for producing the composite material, which possess excellent catalytic activity despite a low platinum content, by forming a composite material with a molybdenum compound, a first metal (PM) containing platinum, and a second metal (M).

[0006] The present invention encompasses the following embodiments: [1] A composite comprising a molybdenum compound, a first metal (PM), and a second metal (M), wherein the first metal (PM) is platinum, or a combination of platinum and palladium, and the second metal (M) is one or more metals other than platinum and palladium. [2] The composite according to [1], wherein the second metal (M) is one or more selected from the group consisting of Ni, Cu, Ag, Co, Ru, Fe, and Al. [3] The composite according to [1] or [2], wherein the first metal (PM) is a combination of platinum and palladium. [4] The composite according to any one of [1] to [3], wherein the ratio of the total content of the first metal (PM) to the total mass of the composite, as determined by XRF analysis, is 0.5% by mass or more and 15% by mass or less. [5] The composite according to any one of [1] to [5], wherein the ratio of the total content of the second metal (M) to the total mass of the composite, as determined by XRF analysis, is 0.1% by mass or more and 8% by mass or less. [6] The composite according to any one of [1] to [5], wherein the ratio of the total content of the first metal (PM) and the second metal (M) to the total mass of the composite, as determined by XRF analysis, is 0.6% by mass or more and 20% by mass or less. [7] The composite according to any one of [1] to [6], wherein the molybdenum compound contains molybdenum sulfide, and the molybdenum sulfide contains molybdenum disulfide having a 3R structure. [8] The molybdenum compound contains a composite of molybdenum carbide and carbon, and the molybdenum carbide is Mo ２ A composite according to any one of [1] to [7], having a C crystalline structure and having a carbon content of 6% or more relative to the total mass (100% by mass) of the composite. [9] The median diameter D of the composite as determined by dynamic light scattering. ５０ However, the composite according to any one of [1] to [8], wherein the specific surface area of ​​the composite, as measured by the BET method, is 10 m ２[1] to

[10] a composite according to any one of [1] to [9], wherein the composite is greater than or equal to / g.

[11] A composite according to any one of [1] to

[10] , wherein metal particles are supported on the molybdenum compound, the metal of the metal particles is at least one selected from the group consisting of the first metal (PM) and the second metal (M), and the average particle size of the metal particles is 20 nm or less.

[12] A hydrogen generation catalyst comprising the composite according to any one of [1] to

[11] .

[13] A hydrogen generation catalyst according to

[12] , further comprising a conductive material.

[14] A catalyst ink comprising the composite according to any one of [1] to

[11] and a solvent.

[15] An electrode coated with the catalyst ink according to

[14] .

[16] A method for producing a composite containing a molybdenum compound, a first metal (PM), and a second metal (M), wherein the molybdenum compound is at least one compound selected from the group consisting of molybdenum sulfide, molybdenum carbide, and a composite of molybdenum carbide and carbon, the first metal (PM) is platinum, or a combination of platinum and palladium, the second metal (M) is one or more metals other than platinum and palladium, and the method for producing a composite comprises a mixing step of mixing the molybdenum compound with a metal-containing solution containing the first metal (PM) and the second metal (M) such that the total mass of the first metal (PM) and the second metal (M) is 50 parts by mass or less with respect to the total mass (100 parts by mass) of the molybdenum compound.

[17] The method for producing a composite according to

[16] , further comprising a reduction step of adding a reducing agent to the mixture obtained in the mixing step.

[18] The method for producing the composite according to

[16] or

[17] , wherein the molybdenum compound comprises a composite of molybdenum carbide and carbon, and the composite is obtained by calcining molybdenum trioxide and carbon in the presence of at least one inorganic compound selected from the group consisting of inorganic salts and inorganic hydroxides.

[0007] According to the present invention, by forming a composite with a molybdenum compound, a first metal (PM) containing platinum, and a second metal (M), it is possible to provide a composite that exhibits excellent catalytic activity despite a low platinum content, a hydrogen generation catalyst, a catalytic ink, an electrode, and a method for producing the composite.

[0008] This is a schematic diagram showing an example of an apparatus used for producing molybdenum trioxide particles. This is an image obtained by transmission electron microscopy of the particles obtained in Example 5. This is an image obtained by transmission electron microscopy of the particles obtained in Example 8. This is an image obtained by transmission electron microscopy of the particles obtained in Example 14. This is an image obtained by transmission electron microscopy of the particles obtained in Example 18. This is an image obtained by transmission electron microscopy of the particles obtained in Example 19. This is an image obtained by transmission electron microscopy of the particles obtained in Example 20. This is an image obtained by elemental mapping using high-resolution electron microscopy of the particles obtained in Example 5.

[0009] (Composite) The composite of one embodiment of the present invention comprises a molybdenum compound, a first metal (PM), and a second metal (M). The first metal (PM) is platinum, or a combination of platinum and palladium. The second metal (M) is one or more metals other than platinum and palladium.

[0010] The composite of this embodiment has a structure in which the molybdenum compound is combined with a first metal (PM) and a second metal (M).

[0011] In this specification, the term "composite" may refer to a state in which a molybdenum compound, a first metal (PM), and a second metal (M) are integrated through any interaction. The interaction is not particularly limited, but examples include physical interactions between the surface of the molybdenum compound particles (for example, if the shape of the molybdenum compound particles is sheet-like or ribbon-like as described later, the depressions and wrinkles on the surface) and the surface of each metal particle, as well as chemical bonds such as coordination bonds, ionic bonds, and intermolecular forces. Examples of chemical bonds include S-Pd, S-Pt, C-Pd, C-Pt, S-M, or C-M bonds, depending on the type of molybdenum compound and each metal.

[0012] The composite of this embodiment may have a structure in which metal particles are supported on and combined with the molybdenum compound. The metal of the metal particles may be at least one selected from the group consisting of the first metal (PM) and the second metal (M). The average particle diameter of the metal particles is preferably 20 nm or less. The metal particles may contain the first metal (PM) and one or more of the second metal (M). Examples of the mixed form of the composite metal of the first metal (PM) and one or more of the second metal (M) include an alloy structure, a core-shell structure, and a hetero structure, etc.

[0013] The composite of this embodiment may be a particulate structure (composite particles). The median diameter D of the composite of this embodiment determined by the dynamic light scattering method ５０ is preferably 1000 nm or less, more preferably 600 nm or less, and still more preferably 500 nm or less. A composite in which the median diameter D ５０ is below the above upper limit value can exhibit catalytic activity more effectively.

[0014] The median diameter D of the composite of this embodiment determined by the dynamic light scattering method ５０ may, as an example, be 20 nm or more, may be 40 nm or more, may be 100 nm or more, or may be 300 nm or more.

[0015] The median diameter D of the composite of this embodiment determined by the dynamic light scattering method ５０ As an example of the numerical range of the above numerical values, it may be 20 nm or more and 1000 nm or less, may be 40 nm or more and 600 nm or less, may be 100 nm or more and 500 nm or less, or may be 300 nm or more and 500 nm or less.

[0016] The median diameter D of the composite of this embodiment calculated by the dynamic light scattering method ５０ can be determined as the particle diameter at which the ratio of volume integration % is 50% in the particle diameter distribution measured wet using ethanol as the medium using a dynamic light scattering type particle size distribution measuring device (for example, Nanotrac WaveII manufactured by Microtrac Bell).

[0017] The specific surface area of ​​the composite of this embodiment, as measured by the BET method, is 10 m². ２ It is preferable that it be 30m or more per gram. ２ It is more preferable that it be 40m or more per g. ２ It is even more preferable that the specific surface area is greater than or equal to the lower limit. Composites having a specific surface area greater than or equal to the lower limit have a larger specific surface area, which increases the number of catalytically active sites and facilitates mass transfer in the reaction system, thereby more effectively improving catalytic activity.

[0018] The specific surface area of ​​the composite of this embodiment, as measured by the BET method, is, for example, 1000 m². ２ It may be less than / g, and 500m ２ It may be less than / g, and 300m ２ It may be less than / g, and 200m ２ It may be less than / g.

[0019] An example of the numerical range for the specific surface area of ​​the composite of this embodiment, as measured by the BET method, is 10 m. ２ / g or more 1000m ２ It may be less than / g, and 20m ２ / g or more 500m ２ It may be less than / g, and 30m ２ / g or more 300m ２ It may be less than / g, and 40m ２ / g or more 200m ２ It may be less than / g.

[0020] The specific surface area mentioned above is measured using a specific surface area meter (e.g., BELSORP-mini from Microtrac-Bel), and the surface area per gram of sample, measured from the amount of nitrogen gas adsorbed by the BRETA method (Brunauer-Emmett-Teller method), is defined as the specific surface area (m²). ２ It is calculated as ( / g).

[0021] The ratio of the total content of the first metal (PM) to the total mass of the composite, as determined by XRF analysis, is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1% by mass or more, most preferably 2% by mass or more, and particularly preferably 3% by mass or more, from the viewpoint of exhibiting catalytic activity. A composite in which the content of the first metal (PM) is equal to or greater than the above lower limit can more effectively exhibit catalytic activity derived from the first metal (PM). Furthermore, from the viewpoint of balancing cost and catalytic activity, the total content of the first metal (PM) is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. An example of the numerical range for the above value of the ratio of the total content of the first metal (PM) to the total mass (100% by mass) of the composite of this embodiment, as determined by XRF analysis, may be 0.1% by mass or more and 50% by mass or less, 0.5% by mass or more and 15% by mass or less, or 1% by mass or more and 10% by mass or less.

[0022] The ratio of the total content of the second metal (M) to the total mass of the composite, as determined by XRF analysis, is preferably 0.1% by mass or more, and more preferably 0.4% by mass or more, from the viewpoint of exhibiting catalytic activity. Furthermore, the ratio of the total content of the second metal (M) to the total mass of the composite is preferably 8% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0023] As determined by XRF analysis, the ratio of the total content of the first metal (PM) and the second metal (M) (hereinafter, "the first metal (PM) and the second metal (M)" are referred to as "essential contained metals") to the total mass of the composite is preferably 0.6% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more, from the viewpoint of exhibiting catalytic activity. Furthermore, the total content of the first metal (PM) and the second metal (M) is preferably 20% by mass or less, and more preferably 15% by mass or less.

[0024] In the composite of this embodiment, the first metal (PM) is preferably a combination of platinum and palladium. In this case, the molar ratio (Pt:Pd:M) of platinum, palladium, and the second metal (M) is preferably 1:0.1:0.1 to 1:10:10, more preferably 1:0.1:0.1 to 1:10:5, even more preferably 1:0.3:0.2 to 1:3:5, and particularly preferably 1:0.5:0.3 to 1:2:3, from the viewpoint of catalytic activity.

[0025] The ratio of molybdenum content to the total mass (100% by mass) of the composite of this embodiment, as determined by X-ray fluorescence (XRF) analysis, may be 30% by mass or more, 40% by mass or more, or 50% by mass or more.

[0026] The ratio of molybdenum content to the total mass (100% by mass) of the composite of this embodiment, as determined by XRF analysis, may be, for example, 80% by mass or less, 75% by mass or less, or 70% by mass or less.

[0027] An example of the numerical range for the ratio of molybdenum content to the total mass (100% by mass) of the composite of this embodiment, as determined by XRF analysis, is that it may be 30% by mass or more and 80% by mass or less, 40% by mass or more and 75% by mass or less, or 50% by mass or more and 70% by mass or less.

[0028] The molybdenum compound according to this embodiment is preferably at least one compound selected from the group consisting of molybdenum sulfide, molybdenum carbide, and composites of molybdenum carbide and carbon. The molybdenum compound may be molybdenum sulfide or a composite of molybdenum carbide and carbon. The molybdenum sulfide is preferably molybdenum disulfide.

[0029] If the molybdenum compound in the composite of this embodiment is molybdenum sulfide, the ratio of sulfur content to the total mass (100% by mass) of the composite of this embodiment, as determined by X-ray fluorescence (XRF) analysis, may be 15% by mass or more, 20% by mass or more, or 25% by mass or more.

[0030] The ratio of sulfur content to the total mass (100% by mass) of the composite of this embodiment, as determined by XRF analysis, may be, for example, 50% by mass or less, 45% by mass or less, or 40% by mass or less.

[0031] An example of the numerical range for the ratio of sulfur content to the total mass (100% by mass) of the composite of this embodiment, as determined by XRF analysis, is that it may be 15% by mass or more and 50% by mass or less, 20% by mass or more and 45% by mass or less, or 25% by mass or more and 40% by mass or less.

[0032] The following provides details about molybdenum disulfide, molybdenum carbide, metalloid (PM), and metalloid (M).

[0033] <Molybdenum disulfide> In the composite of this embodiment, it is preferable that the molybdenum disulfide has a 3R structure. The molybdenum disulfide is compounded with the first metal (PM) to form the composite.

[0034] The molybdenum disulfide is preferably in the form of molybdenum disulfide particles. The shape of the primary particles in the molybdenum disulfide particle portion in the two-dimensional image obtained by photographing the molybdenum disulfide particles with a transmission electron microscope (TEM) may be any shape, but it is preferably particulate, spherical, plate-shaped, needle-shaped, string-shaped, ribbon-shaped, or sheet-shaped, and more preferably string-shaped, ribbon-shaped, or sheet-shaped. The molybdenum disulfide particles may contain a combination of these shapes. Here, ribbon-shaped or sheet-shaped means a thin layer shape, and ribbon-shaped means a long thin layer shape.

[0035] When the primary particles of the molybdenum disulfide particle portion are in the shape of a string, ribbon, or sheet, the average thickness of 50 primary particles of the molybdenum disulfide particle portion is preferably 100 nm or less, more preferably 50 nm or less, even more preferably 30 nm or less, and particularly preferably 15 nm or less.

[0036] As an example of the numerical range of the above thickness, when the shape of the primary particles of the molybdenum disulfide particle portion is string-shaped, ribbon-shaped, or sheet-shaped, the average thickness of 50 primary particles of the molybdenum disulfide particle portion may be 1 to 100 nm, 3 to 50 nm, 5 to 30 nm, or 5 to 15 nm.

[0037] The shape of the molybdenum disulfide particle portion is preferably string-shaped, ribbon-shaped, or sheet-shaped, and the shape of the 50 primary particles of the molybdenum disulfide particle portion preferably has an average size in the range of length (vertical) × width (horizontal) × thickness (height) = 50 to 1000 nm × 50 to 1000 nm × 3 to 100 nm, more preferably in the range of 100 to 500 nm × 100 to 500 nm × 5 to 50 nm, and particularly preferably in the range of 50 to 200 nm × 50 to 200 nm × 5 to 20 nm. The string-shaped, ribbon-shaped, or sheet-shaped shape allows for a large specific surface area of ​​the molybdenum disulfide particle portion. The aspect ratio of the primary particles in the molybdenum disulfide particle portion, i.e., the value of (length (width and height)) / thickness (height)), is preferably 1.2 to 1200, more preferably 2 to 800, even more preferably 5 to 400, and particularly preferably 10 to 200, on average over 50 particles.

[0038] The length, width, and thickness of the molybdenum disulfide particle portion can be measured using an atomic force microscope (AFM).

[0039] The primary particle shape of the molybdenum disulfide particles is not a simple sphere, but rather a string-like, ribbon-like, or sheet-like shape with a large aspect ratio, thereby increasing the specific surface area and effectively improving catalytic activity.

[0040] Molybdenum disulfide particles are molybdenum disulfide (MoS ２ The composite of this embodiment contains molybdenum disulfide (MoS) relative to the total mass (100% by mass) of the composite. ２ It is preferable that the composite contains 50% by mass or more of the above-mentioned molybdenum disulfide, more preferably 80% by mass or more, and even more preferably 85% by mass or more. A composite in which the proportion of molybdenum disulfide is equal to or greater than the above-mentioned lower limit can more effectively exhibit catalytic activity derived from molybdenum disulfide.

[0041] Molybdenum disulfide (MoS) relative to the total mass (100% by mass) of the composite ２ The upper limit of the content of ) should be set so as not to exceed the total mass (100% by mass) of the composite of this embodiment. For example, it may be 99.9% by mass or less, 99.5% by mass or less, or 99.0% by mass or less.

[0042] Furthermore, the above molybdenum disulfide (MoS ２ The content of ) may be a value determined by XRF analysis, and can be calculated as the sum of the molybdenum content and sulfur content determined by XRF analysis of the composite of this embodiment as exemplified above.

[0043] In this embodiment, the ratio of the content of essential metals contained in the composite to the total mass (100 mass%) of the composite, as determined by XRF analysis, is 0.1% by mass or more and 20% by mass or less, and molybdenum disulfide (MoS ２ Examples of composites include one in which the content of ) is 80% by mass or more and 99.9% by mass or less, and in which the content of the essential metals is 0.5% by mass or more and 15% by mass or less, and molybdenum disulfide (MoS ２ Examples of composites include one in which the content of ) is 85% by mass or more and 99.5% by mass or less, and the content of essential metals is 1% by mass or more and 12% by mass or less, and molybdenum disulfide (MoS ２ Examples of composites include those in which the content of ) is between 88% by mass and 99% by mass.

[0044] Furthermore, the composite of this embodiment can be provided as an aggregate of composite particles (e.g., powder), and the aggregate contains molybdenum disulfide (MoS ２ If it contains MoS ｘ The product may contain molybdenum sulfide particles, which include one or more types of molybdenum sulfide represented by (X = 1 to 3).

[0045] Also, the above D ５０ For specific surface area and XRF analysis, values ​​measured using an aggregate of composite particles (e.g., powder) as a sample can be used.

[0046] Molybdenum disulfide may have a 3R crystal structure, or it may have both a 2H crystal structure and a 3R crystal structure. Molybdenum disulfide particles having such 2H and 3R crystal structures are products uniquely developed by the applicant, and their crystal structure has not only 2H but also the unusual 3R (rhombohedral) structure. The 3R structure tends to have a distorted crystal structure and has more catalytically active sites, so the presence of a 3R crystal structure in molybdenum disulfide contributes to improved catalytic activity.

[0047] The molybdenum disulfide particles having a 3R crystal structure can be produced, for example, by the <Method for Producing Molybdenum Disulfide Particles> described later. This method makes it possible to synthesize molybdenum disulfide particles that have a 3R structure, are on an nm scale, and are advantageous for achieving a large specific surface area, which is difficult to achieve by crushing mined materials or synthesis from general-purpose molybdenum trioxide.

[0048] The relative abundance of the 3R crystal structure in the crystalline phase of molybdenum disulfide may be 5% to 90%, 10% to 80%, 20% to 70%, or 20% to 50%.

[0049] The presence of 2H and 3R crystal structures in molybdenum disulfide particles can be confirmed, for example, using an extended Rietveld analysis software that can consider crystallite size (HighScorePlus, manufactured by Malvern Panalytical). This Rietveld analysis software simulates the entire XRD diffraction profile using a crystal structure model that includes crystallite size, compares it with the XRD diffraction profile obtained experimentally, and optimizes the crystal structure factors such as crystal lattice constants, atomic coordinates, and weight fraction (abundance) of the crystal structure model using the least squares method so that the residual between the experimentally obtained diffraction profile and the calculated diffraction profile is minimized. By accurately identifying and quantifying each phase of the 2H and 3R crystal structures, it is possible to calculate the crystallite size in addition to the crystal structure type and its ratio calculated by normal Rietveld analysis. Hereinafter, in this specification, the analysis method using HighScorePlus described above will be referred to as "extended Rietveld analysis".

[0050] Furthermore, in the case of molybdenum disulfide particles, the crystallite size of the 3R crystal structure obtained by extended Rietveld analysis using the profile obtained from the above XRD may be 1 nm to 150 nm, and it is preferable that the crystal phase consists of crystallites of 5 nm to 50 nm, and it is more preferable that the crystallite size is 10 nm to 40 nm.

[0051] Furthermore, in the molybdenum disulfide particles of this embodiment, it is preferable that the crystallite size of the 2H crystal structure obtained by extended Rietveld analysis using the profile obtained from the above XRD is 1 nm to 150 nm, and more preferably that the crystal phase is composed of crystallites of 1 nm to 150 nm, and more preferably that the crystallite size is 5 nm to 150 nm.

[0052] The 2H crystal structure obtained by extended Rietveld analysis preferably consists of a single crystalline phase composed of crystallites having a predetermined crystallite size. In this case, the crystallite size of the 2H crystal structure is more preferably 1 nm to 20 nm, and more preferably 5 nm to 15 nm.

[0053] The crystallite sizes of the 2H crystal structure and the 3R crystal structure can also be calculated, for example, using the peak full width at half maximum of the XRD diffraction profile.

[0054] The ratio of the 2H crystal structure and the 3R crystal structure in the crystalline phase obtained by extended Rietveld analysis using the profile obtained from the above XRD is preferably 10:90 to 90:10.

[0055] From the viewpoint of the above-mentioned effects, the relative abundance of the 2H crystal structure and the 3R crystal structure in the crystalline phase obtained by extended Rietveld analysis using the profile obtained from the above-mentioned XRD (2H:3R) is more preferably 10:90 to 80:20, and even more preferably 40:60 to 80:20.

[0056] Furthermore, the 2H crystal structure obtained by the extended Rietveld analysis may consist of a first crystal phase composed of crystallites having a predetermined crystallite size, and a second crystal phase having a smaller crystallite size than the first crystal phase. The crystallite size of the first crystal phase of the 2H crystal structure is, for example, greater than 20 nm and 150 nm or less, and may be between 50 nm and 150 nm, or between 100 nm and 150 nm. However, it is preferable that the first crystal phase is not present in the crystal phase of the 2H crystal structure, or that its abundance is small. Furthermore, the crystallite size of the second crystal phase of the 2H crystal structure is preferably between 1 nm and 20 nm, and may be between 1 nm and 15 nm, or between 5 nm and 15 nm.

[0057] The crystallite size of the first crystal phase of the 2H crystal structure, the crystallite size of the 3R crystal structure, and the crystallite size of the second crystal phase of the 2H crystal structure can also be calculated, for example, using the peak full width at half maximum of the XRD diffraction profile, as described above.

[0058] The relative abundance of the first crystal phase of the 2H crystal structure, the 3R crystal structure, and the second crystal phase of the 2H crystal structure in the crystal phase (2H (first crystal phase): 3R: 2H (second crystal phase)) obtained by extended Rietveld analysis using the profile obtained from the above XRD is preferably 30 to 0:10 to 70:80 to 15, and more preferably 25 to 0:20 to 60:75 to 20.

[0059] In the profile obtained from powder X-ray diffraction (XRD) of the molybdenum disulfide particles using Cu-Kα rays as the X-ray source, it is preferable that the peaks around 2θ = 39.5° and 49.5° originate from the 2H crystal structure, the peaks around 2θ = 32.5°, 39.5°, and 49.5° originate from the 3R crystal structure, and the full width at half maximum of the peaks around 2θ = 39.5° and 49.5° is 1° or more. Furthermore, the molybdenum disulfide particles may have crystal structures other than the 2H and 3R crystal structures of molybdenum disulfide, such as a 1H crystal structure.

[0060] The fact that the molybdenum disulfide particles have a metastable 3R crystal structure can be distinguished by the fact that, in the profile obtained from powder X-ray diffraction (XRD) using Cu-Kα rays as the X-ray source, the peaks around 2θ = 39.5° and the peaks around 2θ = 49.5° both consist of composite peaks of the 2H crystal structure and the 3R crystal structure.

[0061] In practice, the relative abundance of the 2H crystal structure is determined by the profile obtained from the powder X-ray diffraction (XRD) described above, based on the peak around 2θ = 39.5° and the broad peak around 2θ = 49.5°. Furthermore, the relative abundance of the 3R crystal structure is determined by optimizing the difference between the peak around 2θ = 39.5° and the broad peak around 2θ = 49.5° using two peaks around 2θ = 32.5° and two peaks around 2θ = 39.5°. In other words, both the peak around 2θ = 39.5° and the peak around 2θ = 49.5° are composite waves originating from the 2H and 3R crystal structures, and the relative abundance of the 2H and 3R crystal structures in molybdenum disulfide particles can be calculated using these composite waves.

[0062] Furthermore, the molybdenum disulfide particles may also contain an amorphous phase. The relative abundance of the amorphous phase of the molybdenum disulfide particles is expressed as 100 (%) - (degree of crystallinity (%)), and is preferably 5% or more, more preferably 15% or more, and even more preferably 20% or more.

[0063] Whether the crystal structure of molybdenum disulfide is a 2H crystal structure or a 3R crystal structure, the distance between Mo and S atoms is almost the same due to covalent bonding. Therefore, in the broad-field X-ray absorption fine structure (EXAFS) profile of molybdenum at the K absorption edge, the intensity of the peak caused by Mo and S atoms is the same. On the other hand, because the 2H crystal structure of molybdenum disulfide is hexagonal, another hexagon is located directly below the Mo atom at a 90° angle. As a result, the distance between Mo and Mo atoms is shorter, and the peak intensity II caused by Mo and Mo atoms is stronger. Conversely, because the 3R crystal structure of molybdenum disulfide is rhombohedral, the hexagons are not directly below the Mo atom at a 90° angle, but rather shifted by half an angle. As a result, the distance between Mo and Mo atoms is longer, and the peak intensity II caused by Mo and Mo atoms is weaker. In the pure 2H crystal structure of molybdenum disulfide, the ratio (I / II) decreases, but as the 3R crystal structure is acquired, the ratio (I / II) increases.

[0064] <Molybdenum Carbide> It is preferable that the molybdenum compound included in the composite of this embodiment is a composite of molybdenum carbide and carbon. Molybdenum carbide has a crystal structure of Mo ２ It is preferable that the composite has a C crystal structure and that the carbon content is 6% or more relative to the total mass (100% by mass) of the composite. The carbon content is the amount of carbon element obtained by elemental analysis, and is the total content of free carbon and carbon derived from molybdenum carbide.

[0065] Furthermore, the composite material according to this embodiment is crystalline Mo ２ A hybrid structure of C and carbon is preferred. Crystalline Mo ２ The state of existence of C and carbon is not particularly limited; for example, Mo ２ A state in which carbon exists on the surface of C, Mo ２ Examples include a state in which carbon domains are scattered within a C matrix.

[0066] In this embodiment, Mo ２ The presence of the crystalline structure of C can be detected by the diffraction profile obtained from XRD analysis using molybdenum carbide as a sample. In this embodiment, Mo ２ The C crystal structure may be either an α crystal or a β crystal, but an α crystal is preferred.

[0067] In this embodiment, the carbon content of the composite material relative to the total mass (100% by mass) of the composite material is 6% or more, preferably 8% or more, more preferably 10% or more, and even more preferably 15% or more. When the carbon content is above the lower limit of the above range, the specific surface area of ​​the composite material can be increased.

[0068] In the composite according to this embodiment, there is no particular upper limit to the carbon content relative to the total mass (100% by mass) of the composite, but it is preferably 90% or less, more preferably 80% or less, and even more preferably 60% or less. When the carbon content is below the upper limit within the above range, the conductivity and catalytic activity of the composite are easily improved.

[0069] In this embodiment, it is preferable that the composite material contains a carbon-derived graphite band G and a disorder band D, as measured by Raman spectroscopy.

[0070] In this embodiment, the composite preferably has a ratio (G / D) of the graphite band G to the disorder band D of 0.75 or higher, more preferably 0.78 or higher, and even more preferably 0.80 or higher. When G / D is above the lower limit of the above range, the number of defects originating from the disorder band D is reduced, and the conductivity and catalytic activity of the composite are easily improved.

[0071] In this embodiment, the upper limit of the G / D ratio is not particularly limited, but it is preferably 2.0 or less, more preferably 1.5 or less, and even more preferably 1.0 or less. When the G / D ratio is below the upper limit of the above range, the synergistic effect with the composite material is more easily exhibited, and the catalytic activity is more easily improved. The measurement by Raman spectroscopy is performed according to the following procedure.

[0072] [Analysis by Raman Spectroscopy] For Raman spectroscopy, for example, a powder sample is placed on a glass slide and measured using a laser Raman spectrophotometer (NRS-5500, manufactured by JASCO Corporation) under the following measurement conditions: excitation laser 532 nm, laser intensity 0.6 mW, exposure time 30 sec, objective lens 100x, and point measurement. After measurement, the baseline-corrected XPS spectrum can be analyzed using the Spectra Manager software to calculate the above G / D ratio.

[0073] In this embodiment, the composite material has a specific surface area of ​​10 to 2000 m² as measured by the BET method. ２ Preferably, it is 20 to 1500 m / g. ２ It is more preferable that the amount is / g, and 50 to 1500m ２ It is even more preferable that the value is / g. When the specific surface area measured by the BET method is within the above preferred range, for example, when a composite material is used as a catalyst, the number of catalytically active sites can be increased and mass transfer in the reaction system can be facilitated, thereby improving catalytic activity even more effectively.

[0074] The specific surface area mentioned above is measured using a specific surface area meter (e.g., BELSORP-mini from Microtrac-Bel), and the surface area per gram of sample, measured from the amount of nitrogen gas adsorbed by the BRETA method (Brunauer-Emmett-Teller method), is defined as the specific surface area (m²). ２ It is calculated as ( / g).

[0075] In this embodiment, the composite material has a median diameter D calculated by dynamic light scattering. ５０ However, it is preferably 1500 nm or less, more preferably 1000 nm or less, and even more preferably 500 nm or less. Median diameter D ５０ If the value is below the upper limit of the preferred range mentioned above, for example, when the composite material is used as a catalyst, it is easier to exhibit catalytic activity more effectively.

[0076] The median diameter D of the composite material of this embodiment, determined by dynamic light scattering. ５０ For example, it may be 20 nm or more, or 40 nm or more.

[0077] The median diameter D of the composite material of this embodiment, determined by dynamic light scattering. ５０ Examples of the numerical range for the above values ​​include 20 nm to 1500 nm, 40 nm to 1000 nm, or 40 nm to 500 nm.

[0078] The median diameter D of the composite material of this embodiment, calculated by dynamic light scattering. ５０ This can be determined as the particle size at which the volume integrated percentage accounts for 50% in the particle size distribution measured wet using a dynamic light scattering particle size analyzer (for example, Nanotrac Wave II manufactured by Microtrac-Bell).

[0079] In this embodiment, the molybdenum carbide contained in the composite preferably has an average crystallite size of 50 nm or less, more preferably 45 nm or less, and even more preferably 40 nm or less, determined from the peak at 2θ = 39.4 ± 0.5° of the profile obtained by X-ray diffraction measurement. The above average crystallite size is considered to reflect the particle size and shape of the molybdenum carbide, and is preferable because a smaller crystallite size tends to increase the number of catalytically active sites such as interfaces and defects. The lower limit of the average crystallite size may be, for example, 1 nm or more, 3 nm or more, 4 nm or more, or 5 nm or more.

[0080] [Measurement of Molybdenum Carbide Crystallite Size] The crystallite size of the above-mentioned molybdenum carbide is measured using, for example, an X-ray diffractometer (e.g., Rigaku Corporation, SmartLab 9kW), a scintillation counter as the detector, and PDXL2 as the analysis software. The measurement method is the 2θ / θ method, and the average crystallite size is calculated using the Scherrer formula from the full width at half maximum of the peak appearing at 2θ = 39.4 ± 0.5°. The measurement conditions are as follows: scan speed (2θ) is 2.0° / min, scan range (2θ) is 10 to 70°, step (2θ) is 0.02°, and there is no standard instrument width.

[0081] <First Metal (PM)> The first metal (PM) may be platinum, or a combination of platinum and palladium. It is preferable that the first metal (PM) includes a combination of platinum and palladium.

[0082] <<Platinum>> The platinum contained in the composite of this embodiment is preferably platinum particles. The platinum particles may also be granular structures containing platinum. The platinum contained in the composite of this embodiment is compounded with the molybdenum compound contained in the composite of this embodiment to form a composite. Furthermore, if the composite of this embodiment also contains the above-mentioned palladium, the platinum contained in the composite of this embodiment is compounded with the above-mentioned palladium, and the compounded first metal (PM) is compounded with the molybdenum compound to form a composite. Furthermore, the platinum contained in the composite of this embodiment is compounded with the molybdenum compound independently of the palladium to form a composite.

[0083] The shape of the platinum particles is not particularly limited and may include spherical, hemispherical, wire-like structures connecting multiple platinum particles, or aggregates of these shapes.

[0084] The form in which the platinum particles are contained in the composite of this embodiment is not particularly limited, but the platinum particles may be present on the surface of the molybdenum compound particles, or they may be attached to or bonded to the surface of the molybdenum compound particles.

[0085] The number of platinum particles present per 100 nm × 100 nm surface area of ​​the molybdenum compound particles, as confirmed on a two-dimensional image obtained by imaging the composite with a transmission electron microscope (TEM), may be, for example, 5 to 5,000 or 10 to 1,000.

[0086] The average particle diameter of the platinum particles may be 20 nm or less, 15 nm or less, or 13 nm or less.

[0087] As an example, the lower limit of the average particle diameter of the platinum particles may be 0.5 nm or more, 0.7 nm or more, or 1 nm or more.

[0088] Examples of the numerical range for the average particle diameter of the platinum particles mentioned above include 0.5 nm to 20 nm, 0.7 nm to 15 nm, or 1 nm to 13 nm.

[0089] The average particle diameter of platinum particles is determined by taking a transmission electron microscope (TEM) image of the composite and using the average of the maximum distance between two points on the contour line of 50 randomly selected platinum particles (excluding those formed by the aggregation of multiple platinum particles) that are visible in the two-dimensional image.

[0090] The platinum particles contain platinum. The form in which the platinum is contained in the composite of this embodiment is not particularly limited, and for example, it may be contained in the platinum particles as a platinum compound. Examples of the platinum compound include platinum oxide.

[0091] The platinum particles may include platinum that does not have a crystalline structure. The platinum particles may include platinum that does not have the crystalline structure of a platinum metal crystal. The platinum particles may include platinum that is not in a form in which a portion of the molybdenum in the crystalline structure of the molybdenum compound contained in the composite of this embodiment is substituted. The platinum particles may include zero-valent platinum.

[0092] Regarding the platinum content in the above-described forms, the platinum particles may contain, on a molar basis, 50% or more of platinum that does not have a crystalline structure relative to the platinum contained in the platinum particles. The platinum particles may contain, on a molar basis, 50% or more of platinum that does not have a crystalline structure of platinum metal crystals relative to the platinum contained in the platinum particles. The platinum particles may contain, on a molar basis, 50% or more of platinum that is not in a form where it is substituted for a portion of the molybdenum in the crystalline structure of a molybdenum compound, relative to the platinum contained in the platinum particles. The platinum particles may contain, on a molar basis, 50% or more of zero-valent platinum relative to the platinum contained in the platinum particles.

[0093] The platinum particles may include aggregates of platinum atoms, or aggregates of platinum atoms that do not have a crystalline structure. The platinum particles may include aggregates of platinum atoms that do not have a crystalline structure of a platinum metal crystal. The platinum particles may include aggregates of platinum atoms that are not in a form where they are substituted for a portion of the molybdenum in the crystalline structure of a molybdenum compound. The platinum particles may include aggregates of zero-valent platinum atoms.

[0094] The platinum contained in the platinum particles preferably does not have a crystalline structure, and more preferably does not have a crystalline structure of platinum metal crystals.

[0095] Similarly, the composite of this embodiment may contain platinum that does not have a crystalline structure. The composite of this embodiment may contain platinum that does not have the crystalline structure of a platinum metal crystal. The composite of this embodiment may contain platinum that is not in a form in which some of the molybdenum in the crystalline structure of a molybdenum compound is substituted. The composite of this embodiment may contain platinum with a valence of 0.

[0096] Regarding the platinum content in the above-described forms, the composite of this embodiment may contain, on a molar basis, 50% or more of platinum that does not have a crystalline structure relative to the platinum contained in the composite. The composite of this embodiment may contain, on a molar basis, 50% or more of platinum that does not have a crystalline structure of platinum metal crystals relative to the platinum contained in the composite. The composite of this embodiment may contain, on a molar basis, 50% or more of platinum that is not in a form where it is substituted for a portion of the molybdenum in the crystalline structure of a molybdenum compound, relative to the platinum contained in the composite. The composite of this embodiment may contain, on a molar basis, 50% or more of platinum with a valence of 0 relative to the platinum contained in the composite.

[0097] Similarly, the composite of this embodiment may include aggregates of platinum atoms that do not have a crystalline structure. The composite of this embodiment may include aggregates of platinum atoms that do not have a crystalline structure of platinum metal crystal. The composite of this embodiment may include aggregates of platinum atoms that are not in a form where they are substituted for a portion of the molybdenum in the crystalline structure of a molybdenum compound. The composite of this embodiment may include aggregates of platinum atoms with a valence of 0.

[0098] The platinum contained in the composite of this embodiment preferably does not have a crystalline structure, and more preferably does not have a crystalline structure of platinum metal crystals.

[0099] In the composite of this embodiment, the platinum may form platinum clusters. Furthermore, the platinum in the platinum particles may also form platinum clusters.

[0100] The presence of a platinum-containing crystalline structure can be detected based on the diffraction profile obtained from X-ray diffraction analysis using the composite of this embodiment as a sample. It can also be detected based on the analysis of the crystalline structure by electron diffraction.

[0101] As described above, the composite of molybdenum compound particles and platinum particles is combined to enable superior catalytic performance.

[0102] Furthermore, if the platinum in the above-mentioned platinum particles does not constitute the crystalline structure of a platinum metal crystal, but rather exists as an aggregate of platinum atoms in the particles of the molybdenum compound included in the composite of this embodiment, even better catalytic performance can be achieved.

[0103] The composite of this embodiment is suitably usable as a constituent material for a catalyst ink capable of forming a catalyst layer. Furthermore, the composite of this embodiment is suitably usable as an electrode material used as a constituent material for an electrode catalyst layer.

[0104] <<Palladium>> The palladium contained in the composite of this embodiment is preferably palladium particles. The palladium particles may also be granular structures containing palladium. The palladium contained in the composite of this embodiment is compounded with the molybdenum compound contained in the composite of this embodiment to form the composite. Furthermore, if the composite of this embodiment contains palladium and platinum, the palladium contained in the composite of this embodiment may be compounded with the platinum, and the compounded first metal may be compounded with the molybdenum compound to form the composite. Furthermore, the palladium contained in the composite of this embodiment may be compounded with the molybdenum compound independently of the platinum to form the composite. In the case of a composite formed by the compounding of palladium and platinum, it is preferably in the form of particles. The composite formed by the compounding of palladium and platinum may be an alloy of palladium and platinum, a composite particle having a core-shell structure, or a heteroparticle containing palladium primary particles containing palladium and platinum primary particles containing platinum particles. A composite particle having a core-shell structure is a structure in which one type of material acts as a core, and layers of other types of materials exist on the surface of the core. For example, a composite made by compounding palladium and platinum is said to have a core-shell structure if, for example, a composite particle in which a platinum layer exists on the surface of a palladium-containing core, or a composite particle in which a palladium layer exists on the surface of a platinum-containing core.

[0105] The shape of the palladium particles is not particularly limited and may include spherical, hemispherical, wire-like structures connecting multiple palladium particles, or aggregates of these shapes.

[0106] The form in which palladium particles are contained in the composite of this embodiment is not particularly limited, but the palladium particles may be present on the surface of the molybdenum compound particles, or they may be attached to or bonded to the surface of the molybdenum compound particles.

[0107] The number of palladium particles present per 100 nm × 100 nm surface area of ​​the molybdenum compound particles, as confirmed on a two-dimensional image obtained by imaging the composite with a transmission electron microscope (TEM), may be, for example, 5 to 5,000 or 10 to 1,000.

[0108] The average particle size of the palladium particles may be 20 nm or less, 15 nm or less, or 13 nm or less.

[0109] As an example, the lower limit of the average particle diameter of the palladium particles may be 0.5 nm or more, 0.7 nm or more, or 1 nm or more.

[0110] Examples of the numerical range for the average particle diameter of the palladium particles mentioned above include 0.5 nm to 20 nm, 0.7 nm to 15 nm, or 1 nm to 13 nm.

[0111] The average particle diameter of palladium particles is determined by taking a transmission electron microscope (TEM) image of the composite and using the average of the maximum distance between two points on the contour line of 50 randomly selected palladium particles (excluding aggregates of multiple palladium particles) that are visible in the two-dimensional image.

[0112] The palladium particles contain palladium. The form in which palladium is contained in the composite of this embodiment is not particularly limited, and for example, it may be contained in the palladium particles as a palladium compound. Examples of the palladium compound include palladium oxide.

[0113] The palladium particles may include palladium that does not have a crystalline structure. The palladium particles may include palladium that does not have the crystalline structure of a palladium metal crystal. The palladium particles may include palladium that is not in a form in which a portion of the molybdenum in the crystalline structure of the molybdenum compound contained in the composite of this embodiment is substituted. The palladium particles may include palladium with a valence of 0.

[0114] Regarding the content ratio of palladium in the above-described forms, the palladium particles may contain 50% or more, on a molar basis, palladium that does not have a crystalline structure, relative to the palladium contained in the palladium particles. The palladium particles may contain 50% or more, on a molar basis, palladium that does not have a crystalline structure of palladium metal crystals, relative to the palladium contained in the palladium particles. The palladium particles may contain 50% or more, on a molar basis, palladium that is not in a form where it is substituted for a portion of the molybdenum in the crystalline structure of a molybdenum compound, relative to the palladium contained in the palladium particles. The palladium particles may contain 50% or more, on a molar basis, zero-valent palladium, relative to the palladium contained in the palladium particles.

[0115] The palladium particles may contain aggregates of palladium atoms, or aggregates of palladium atoms that do not have a crystalline structure. The palladium particles may contain aggregates of palladium atoms that do not have a crystalline structure of palladium metal crystals. The palladium particles may contain aggregates of palladium atoms that are not in a form where they are substituted for a portion of the molybdenum in the crystalline structure of a molybdenum compound. The palladium particles may contain aggregates of 0-valent palladium atoms.

[0116] The palladium contained in the palladium particles preferably does not have a crystalline structure, and more preferably does not have a crystalline structure of palladium metal crystals.

[0117] Similarly, the composite of this embodiment may contain palladium that does not have a crystalline structure. The composite of this embodiment may contain palladium that does not have the crystalline structure of a palladium metal crystal. The composite of this embodiment may contain palladium that is not in a form in which a portion of the molybdenum in the crystalline structure of a molybdenum compound is substituted. The composite of this embodiment may contain palladium with a valence of 0.

[0118] Regarding the content ratio of palladium in the above-mentioned forms, the composite of this embodiment may contain 50% or more, on a molar basis, palladium that does not have a crystalline structure, relative to the palladium contained in the composite. The composite of this embodiment may contain 50% or more, on a molar basis, palladium that does not have a crystalline structure of palladium metal crystals, relative to the palladium contained in the composite. The composite of this embodiment may contain 50% or more, on a molar basis, palladium that is not in a form where it is substituted for a portion of the molybdenum in the crystalline structure of a molybdenum compound, relative to the palladium contained in the composite. The composite of this embodiment may contain 50% or more, on a molar basis, palladium with a valence of 0, relative to the palladium contained in the composite.

[0119] Similarly, the composite of this embodiment may include aggregates of palladium atoms that do not have a crystalline structure. The composite of this embodiment may include aggregates of palladium atoms that do not have a crystalline structure of palladium metal crystals. The composite of this embodiment may include aggregates of palladium atoms that are not in a form where they are substituted for a portion of the molybdenum in the crystalline structure of a molybdenum compound. The composite of this embodiment may include aggregates of palladium atoms that have a valence of 0.

[0120] The palladium contained in the composite of this embodiment preferably does not have a crystalline structure, and more preferably does not have a crystalline structure of palladium metal crystals.

[0121] In the composite of this embodiment, palladium may form palladium clusters. Furthermore, palladium in the palladium particles may also form palladium clusters.

[0122] The presence of palladium-containing crystal structures can be detected based on the diffraction profile obtained from X-ray diffraction analysis of the composite of this embodiment as a sample. It can also be detected based on the analysis of the crystal structure by electron diffraction.

[0123] Furthermore, if the palladium in the palladium particles does not constitute the crystalline structure of a palladium metal crystal, but rather exists as an aggregate of palladium atoms in the particles of the molybdenum compound included in the composite of this embodiment, even better catalytic performance can be achieved.

[0124] As described above, the composite of molybdenum compound particles, platinum particles, and palladium particles allows for superior catalytic performance.

[0125] <Second Metal (M)> The second metal (M) included in the composite of this embodiment is one or more metals other than platinum and palladium, and may be one or more transition metals other than platinum and palladium. Examples of the transition metals include elements located between Group 3 and Group 11 of the periodic table. Specific examples of the transition metals include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Ru, Rh, Ag, Ta, W, Au, etc. The second metal (M) is preferably one or more selected from the group consisting of Ni, Cu, Ag, Co, Ru, Fe, and Al, more preferably one or more selected from the group consisting of Ni, Cu, Ag, Co, Ru, and even more preferably one or more selected from the group consisting of Ni, Co, Cu. The second metal (M) may consist of two types containing Ni, or it may consist of Ni alone. If the second metal (M) consists of two or more types containing Ni, the Ni content relative to the total number of moles of the second metal (M) may be 5 mol% or more, 15 mol% or more, or 30 mol% or more.

[0126] The secondary metal (M) included in the composite of this embodiment is preferably secondary metal (M) particles. The secondary metal (M) particles are granular structures containing secondary metal (M). The secondary metal (M) included in the composite of this embodiment is compounded with the molybdenum compound included in the composite of this embodiment to form the composite. Alternatively, the secondary metal (M) included in the composite of this embodiment may be compounded with the palladium or platinum mentioned above, and further compounded with the molybdenum compound to form the composite. Alternatively, the secondary metal (M) included in the composite of this embodiment may be compounded with the molybdenum compound independently of the palladium or platinum to form the composite of this embodiment.

[0127] If the second metal (M) includes two or more types, they may exist in the same form or in different forms depending on the properties of each metal.

[0128] The shape of the second metal (M) particles is not particularly limited and may include spherical, hemispherical, wire-like structures connecting multiple second metal (M) particles, or aggregates of these shapes.

[0129] The form in which the second metal (M) particles are contained in the composite of this embodiment is not particularly limited, but the second metal (M) particles may be present on the surface of the molybdenum compound particles, or they may be attached to or bonded to the surface of the molybdenum compound particles.

[0130] The number of second metal (M) particles present per 100 nm × 100 nm surface area of ​​the molybdenum compound, as confirmed on a two-dimensional image obtained by imaging the composite with a transmission electron microscope (TEM), may be, for example, 5 to 5,000 or 10 to 1,000.

[0131] The average particle size of the second metal (M) particles may be 20 nm or less, 15 nm or less, or 13 nm or less.

[0132] As an example, the lower limit of the average particle diameter of the second metal (M) particles may be 0.5 nm or more, 0.7 nm or more, or 1 nm or more.

[0133] Examples of the numerical range for the average particle diameter of the second metal (M) particles include 0.5 nm to 20 nm, 0.7 nm to 15 nm, and 1 nm to 13 nm.

[0134] The average particle diameter of the secondary metal (M) particles is determined by taking a transmission electron microscope (TEM) image of the composite and using the average of the maximum distance between two points on the contour line of 50 randomly selected secondary metal (M) particles (excluding those formed by the aggregation of multiple secondary metal (M) particles) that are observed in the two-dimensional image.

[0135] The second metal (M) particles contain the second metal (M). The form in which the second metal (M) is contained in the composite of this embodiment is not particularly limited, and for example, it may be contained in the second metal (M) particles as a second metal (M) compound. Examples of the second metal (M) compound include oxides of the second metal (M). For example, if the second metal (M) is nickel, examples of oxides of the second metal (M) include nickel oxide.

[0136] The second metal (M) particles may include a second metal (M) that does not have a crystalline structure. The second metal (M) particles may include a second metal (M) that does not have the crystalline structure of a second metal (M) metal crystal. The second metal (M) particles may include a second metal (M) that is not in a form in which a portion of the molybdenum in the crystalline structure of the molybdenum compound contained in the composite of this embodiment is substituted. The second metal (M) particles may include a second metal (M) with zero valence.

[0137] Regarding the content ratio of the second metal (M) in the above-described form, the second metal (M) particles may contain 50% or more of second metal (M) that does not have a crystalline structure, on a molar basis, relative to the second metal (M) contained in the second metal (M) particles. The second metal (M) particles may contain 50% or more of second metal (M) that does not have a crystalline structure of a second metal (M) metal crystal, on a molar basis, relative to the second metal (M) contained in the second metal (M) particles. The second metal (M) particles may contain 50% or more of second metal (M) that is not in a form where it is substituted for a part of the molybdenum in the crystalline structure of a molybdenum compound, on a molar basis, relative to the second metal (M) contained in the second metal (M) particles. The second metal (M) particles may contain 50% or more of zero-valent second metal (M) on a molar basis, relative to the second metal (M) contained in the second metal (M) particles.

[0138] The second metal (M) particles may include aggregates of second metal (M) atoms, and may include aggregates of second metal (M) atoms that do not have a crystalline structure. The second metal (M) particles may include aggregates of second metal (M) atoms that do not have a crystalline structure of a second metal (M) metal crystal. The second metal (M) particles may include aggregates of second metal (M) atoms that are not in a form in which a portion of the molybdenum in the crystalline structure of a molybdenum compound is substituted. The second metal (M) particles may include aggregates of zero-valent second metal (M) atoms.

[0139] In the composite of this embodiment, the second metal (M) may form second metal (M) clusters. Furthermore, the second metal (M) in the second metal (M) particles may form second metal (M) clusters.

[0140] Furthermore, if the second metal (M) in the second metal (M) particles does not constitute a crystalline structure of a second metal (M) metal crystal, but rather exists as an aggregate of second metal (M) atoms in the particles of the molybdenum compound included in the composite of this embodiment, even better catalytic performance can be achieved.

[0141] As described above, the composite of molybdenum compound particles, first metal (PM) particles, and second metal (M) particles is combined, enabling it to exhibit superior catalytic performance.

[0142] (Method for producing the composite) The method for producing the composite of this embodiment includes a mixing step of mixing a molybdenum compound and an essential metal-containing solution. The "essential metal-containing solution" is a metal-containing solution containing the first metal (PM) and the second metal (M). In the mixing step, the molybdenum compound is mixed such that the total mass of the first metal (PM) and the second metal (M) is 50 parts by mass or less relative to the total mass (100 parts by mass) of the molybdenum compound. Preferably, the molybdenum compound is at least one compound selected from the group consisting of molybdenum sulfide, molybdenum carbide, and composites of molybdenum carbide and carbon. The terms molybdenum sulfide, molybdenum carbide, composite, first metal (PM), and second metal (M) have the same meanings as the terms molybdenum sulfide, molybdenum carbide, composite, first metal (PM), and second metal (M) described in the composite of this embodiment above. The molybdenum compound may be molybdenum compound particles, and the essential metal-containing particles may be essential metal-containing particles.

[0143] Preferably, the process further includes a reduction step in which a reducing agent is added to the mixture obtained in the mixing step. The reducing agent is not particularly limited as long as it can promote the reduction of the second metal (M) source, and known reducing agents can be used. Specific examples of the reducing agent include sodium phosphinate monohydrate, ascorbic acid, trisodium citrate dihydrate, and sodium borohydride. The reducing agent may also be added during the mixing step.

[0144] The composite manufacturing method of this embodiment makes it possible to manufacture the composite of this embodiment as described above.

[0145] The aforementioned essential metal-containing solution can be obtained by dissolving any of the aforementioned essential metal-containing sources in a solvent.

[0146] When the essential metal component is palladium, the palladium source can be any palladium compound that can produce a palladium solution, such as palladium acetate, palladium nitrate, palladium nitrite, palladium sulfate, palladium carbonate, palladium chloride, sodium palladium(II) chloride, palladium hydroxide, and palladium oxide.

[0147] When the essential metal component is platinum, the platinum source can be any platinum compound capable of producing a platinum solution, such as hexachloroplatin(IV) acid hexahydrate, potassium hexachloroplatinate, ammonium hexachloroplatinate, sodium hexachloroplatinate, ammonium tetrachloroplatinate, and potassium tetrachloroplatinate.

[0148] When the essential metal component is the second metal (M), the source of the second metal (M) can be any metal compound capable of producing a solution of the second metal (M), such as an organic acid salt, an inorganic acid salt, a chloride, or a bromide. Examples of organic acids in the organic acid salt include carboxylic acids such as acetic acid. Examples of inorganic acids in the inorganic acid salt include sulfuric acid, hydrochloric acid, and nitric acid. A specific example of the source of the second metal (M) is, for example, CH ３ COOAg, Ni(CH ３ COO) ２ 4H ２ O, Coso ４ ・5H ２ O, CuSO ４ AgNO ３ RuCl ３ 3H ２ O, CoCl ２ 6H ２ O, FeCl ３ 6H ２ O, FeCl ２ 4H ２ O, NiBr ２ 3H ２ Examples include O.

[0149] Any solvent capable of dissolving the above-mentioned essential metal source is acceptable, and examples include alcohols such as methanol and ethanol, water, benzene, dichloromethane, acetone, and chloroform.

[0150] The method of mixing described above is not particularly limited, but it is preferable to mix the essential metal-containing solution with the dispersion of molybdenum compound particles.

[0151] The essential metal components mentioned above are the first metal (PM) and the second metal (M). Alternatively, a solution of the first metal (PM) and a solution of the second metal (M) may be prepared separately and then mixed to prepare an essential metal component solution containing both the first metal (PM) and the second metal (M). Alternatively, a source of the first metal (PM) and a source of the second metal (M) may be dissolved in the solvent to prepare an essential metal component solution containing both the first metal (PM) and the second metal (M). The method of mixing the essential metal component solution is not particularly limited, but it is preferable to mix the essential metal component solution with a dispersion of molybdenum compound particles.

[0152] If the first metal (PM) is a combination of platinum and palladium, a platinum solution, a palladium solution, and a second metal (M) solution may be prepared separately and then mixed to prepare an essential metal-containing solution containing platinum, palladium, and the second metal (M). Alternatively, the platinum source, palladium source, and second metal (M) source may be dissolved in the solvent to prepare an essential metal-containing solution containing platinum, palladium, and the second metal (M). The method of mixing the essential metal-containing solution is not particularly limited, but it is preferable to mix the essential metal-containing solution with a dispersion of molybdenum compound particles.

[0153] As a method for preparing the above-mentioned essential metal-containing solution, it is preferable to add a compound that promotes solvent dispersion (dispersant) from the viewpoint of improving dispersibility. Examples of dispersants include polyvinylpyrrolidone (PVP), sodium citrate, and polyacrylic acid. In the solvent after the addition of the dispersant, the amount of the dispersion promoter used, in the molar ratio of dispersant to essential metal-containing material, may be 1:1 or more, or 100:1 or less.

[0154] A dispersion of molybdenum compound particles can be obtained by mixing the solvent exemplified in the above-mentioned essential metal-containing solution with the molybdenum compound particles.

[0155] By mixing an essential metal-containing solution with molybdenum compound particles to obtain a mixture, and then contacting the molybdenum compound particles with the essential metal-containing solution, it is possible to form a composite of molybdenum compound particles and essential metal-containing particles.

[0156] From the viewpoint of preventing aggregation of molybdenum compound particles, it is preferable to stir the mixture of the essential metal solution and the molybdenum compound particles. The degree of stirring can be exemplified by 50 to 1000 rpm.

[0157] The concentration of the essential metal in the essential metal solution may be, for example, 0.00001 to 0.1 mol / L, or 0.0001 to 0.01 mol / L.

[0158] The temperature of the mixture of molybdenum compound particles and essential metal solution should be such that a composite can be formed, and for example, it may be 10 to 100°C or 20 to 80°C.

[0159] The holding time for the mixture of molybdenum compound particles and essential metal solution should be such that a composite can be formed. For example, it may be between 10 minutes and 48 hours, or between 30 minutes and 12 hours.

[0160] In the method for producing the composite of this embodiment, the mixture of molybdenum compound particles and the essential metal solution may be irradiated with light to promote the reduction of essential metals. The light irradiation can be carried out by appropriately selecting the amount of light and wavelength to the extent that photoreduction of the essential metals occurs. The light irradiation may be carried out by setting up a light source and controlling the amount of light, or it may be carried out by irradiation with light from a normal indoor environment (such as fluorescent lamps or LEDs) or by irradiation with natural light.

[0161] In the method for producing the composite of this embodiment, the composite can be produced without heat treatment. For example, the obtained composite, or the mixture of the essential metal solution and molybdenum compound particles, is preferably not heated above 200°C, more preferably above 100°C, and even more preferably above 80°C.

[0162] After a complex is formed from the above mixture, the complex can be easily obtained by separating it through processes such as centrifugation or drying.

[0163] The method for producing the composite according to this embodiment may further include a molybdenum compound particle production step for producing the molybdenum compound particles.

[0164] The following describes an example of a method for producing molybdenum disulfide particles, assuming that the molybdenum compound is molybdenum disulfide.

[0165] <Method for producing molybdenum disulfide particles> The molybdenum disulfide particles can be produced, for example, by a molybdenum disulfide particle production process that includes heating molybdenum trioxide particles, in which the average particle diameter of the primary particles is 2 nm or more and 1000 nm or less, at a temperature of 200 to 1000°C in the presence of a sulfur source.

[0166] In another respect, the molybdenum disulfide particles can be produced, for example, by a molybdenum disulfide particle production process that includes heating molybdenum trioxide particles obtained by the molybdenum trioxide particle production process described later at a temperature of 200 to 1000°C in the presence of a sulfur source.

[0167] The average particle diameter of primary molybdenum trioxide particles is defined as the average of the primary particle diameters of 50 randomly selected primary particles. This is achieved by photographing molybdenum trioxide particles with a scanning electron microscope (SEM) or transmission electron microscope (TEM), measuring the major axis (the longest observed Ferret diameter) and minor axis (the shortest Ferret diameter perpendicular to the longest Ferret diameter) of the smallest unit particles constituting the aggregate on the two-dimensional image (i.e., primary particles), and taking the average of these values ​​as the primary particle diameter.

[0168] In the method for producing the molybdenum disulfide particles, the average particle diameter of the primary particles of the molybdenum trioxide particles is preferably 1 μm or less. From the viewpoint of reactivity with sulfur, it is more preferably 600 nm or less, even more preferably 400 nm or less, and particularly preferably 200 nm or less. The average particle diameter of the primary particles of the molybdenum trioxide particles may be 2 nm or more, 5 nm or more, or 10 nm or more.

[0169] The molybdenum trioxide particles used in the production of the aforementioned molybdenum disulfide particles preferably consist of an aggregate of primary particles having a β-crystalline structure of molybdenum trioxide. Compared to conventional molybdenum trioxide particles consisting only of α-crystals as their crystalline structure, these molybdenum trioxide particles have better reactivity with sulfur and possess a β-crystalline structure of molybdenum trioxide, thus improving the conversion rate R to molybdenum disulfide in the reaction with a sulfur source. Ｃ It can be made larger.

[0170] The β-crystal structure of molybdenum trioxide is shown in the profile obtained from powder X-ray diffraction (XRD) using Cu-Kα rays as the X-ray source, MoO ３ This can be confirmed by the presence of a peak (around 2θ: 23.01°, No. 86426 (Inorganic Crystal Structure Database (ICSD))) which is attributed to the (011) plane of the β crystal. The α crystal structure of molybdenum trioxide is MoO ３ This can be confirmed by the presence of a peak on the (021) plane of the α crystal (around 2θ: 27.32° - No. 166363 (Inorganic Crystal Structure Database (ICSD))).

[0171] In the profile obtained from powder X-ray diffraction (XRD) using Cu-Kα rays as the X-ray source, the molybdenum trioxide particles showed MoO ３ The peak intensity attributable to the (011) plane of the β crystal of MoO ３ It is preferable that the ratio (β(011) / α(021)) to the peak intensity attributed to the (021) plane of the α crystal (around 2θ: 27.32° - No. 166363 (Inorganic Crystal Structure Database (ICSD))) is 0.1 or greater.

[0172] MoO ３ The peak intensity attributable to the (011) plane of the β crystal, and MoO ３ For the peak intensities attributed to the (021) plane of the α crystal, the maximum peak intensity is read, and the ratio (β(011) / α(021)) is determined.

[0173] In the molybdenum trioxide particles, the ratio (β(011) / α(021)) is preferably 0.1 to 10.0, more preferably 0.2 to 10.0, and particularly preferably 0.4 to 10.0.

[0174] The β-crystal structure of molybdenum trioxide is observed in the Raman spectrum obtained from Raman spectroscopy at wavenumbers 773 and 848 cm⁻¹. －１ and 905 cm －１ This can also be confirmed by the presence of a peak at wavenumber 663, 816 cm⁻¹. The α-crystal structure of molybdenum trioxide is at wavenumber 663, 816 cm⁻¹. －１ and 991 cm －１ This can be confirmed by the presence of a peak at that point.

[0175] The average particle diameter of the primary particles of the molybdenum trioxide particles may be between 5 nm and 2000 nm.

[0176] Examples of sulfur sources include sulfur and hydrogen sulfide, which may be used individually or in combination.

[0177] The method for producing the molybdenum disulfide particles may include heating molybdenum trioxide particles, which consist of an aggregate of primary particles having a β-crystalline structure of molybdenum trioxide, at a temperature of 100 to 800°C in the absence of a sulfur source, and then heating them at a temperature of 200 to 1000°C in the presence of a sulfur source.

[0178] The heating time in the presence of a sulfur source may be any amount of time required for the sulfidation reaction to proceed sufficiently, and may be 1 to 20 hours, 2 to 15 hours, or 3 to 10 hours.

[0179] In the method for producing the molybdenum disulfide particles, the MoO ３ The ratio of the amount of sulfur in the sulfur source to the total amount of other materials is preferably such that the sulfidation reaction proceeds sufficiently. ３ The amount of sulfur in the sulfur source is preferably 450 mol% or more, more preferably 600 mol% or more, and even more preferably 700 mol% or more, per 100 mol% of the total amount. ３The amount of sulfur in the sulfur source may be 3000 mol% or less, 2000 mol% or less, or 1500 mol% or less per 100 mol% of the total amount.

[0180] In the method for producing the molybdenum disulfide particles, the heating temperature in the presence of the sulfur source should be a temperature at which the sulfurization reaction proceeds sufficiently, preferably 320°C or higher, more preferably 340°C or higher, and even more preferably 360°C or higher. The heating temperature may also be 320 to 1000°C, 340 to 1000°C, or 360 to 500°C. By lowering the heating temperature, the degree of crystallinity of the molybdenum disulfide particles is reduced, and the proportion of the amorphous phase can be increased.

[0181] In the method for producing molybdenum disulfide particles described above, as a post-treatment, the obtained molybdenum disulfide particles may be cooled and then heated as needed. In this heat treatment, it is preferable to calcine the molybdenum disulfide particles in an inert atmosphere, for example. By heating and calcining the obtained molybdenum disulfide particles, the crystallization of the amorphous phase is promoted, and the degree of crystallinity is improved. As the degree of crystallinity improves, new 2H crystal structures and 3R crystal structures are formed, and the ratio of the 2H crystal structures to the 3R crystal structures changes. By performing reheating as a post-treatment in this way, the ratio of the 3R crystal structures can be improved. Furthermore, by changing the temperature when heating the obtained molybdenum disulfide particles, the ratio of the 2H crystal structures to the 3R crystal structures can be adjusted.

[0182] When the obtained molybdenum disulfide particles are heated and calcined at a predetermined temperature or higher, the amorphous phase changes to a 2H crystal structure, and a second crystal phase is newly formed, consisting of crystallites with a crystallite size of 20 nm or less, preferably 10 nm or less. At this time, if there were crystallites with a crystallite size of 10 nm or less in the 2H crystal structure before heating the molybdenum disulfide particles, after heating the molybdenum disulfide particles, these crystallites grow to a crystallite size of 100 nm or more, and a first crystal phase is formed, consisting of these grown crystallites.

[0183] From the viewpoint of increasing the abundance ratio of the crystal phase of the 3R crystal structure and minimizing the abundance ratio of the first crystal phase of the 2H crystal structure as much as possible, the heating temperature of the molybdenum disulfide particles in the post-treatment is preferably 500 to 900 °C, more preferably 500 to 800 °C.

[0184] Also, the heating rate of the molybdenum disulfide particles in the post-treatment is preferably 1 °C / min or more and 50 °C / min or less, more preferably 2 °C / min or more and 10 °C / min or less.

[0185] In the method for producing the molybdenum disulfide particles, the molybdenum trioxide particles have a MoO ３ content ratio measured by fluorescent X-ray (XRF) of preferably 99.5% or more. Thereby, the conversion rate R Ｃ to molybdenum sulfide can be increased, and high-purity molybdenum disulfide with no risk of generating disulfide derived from impurities and good storage stability can be obtained.

[0186] The molybdenum trioxide particles preferably have a specific surface area measured by the BET method of 10 m ２ / g to 100 m ２ / g.

[0187] In the molybdenum trioxide particles, the specific surface area is preferably 10 m ２ / g or more because the reactivity with sulfur is good, more preferably 20 m ２ / g or more, and even more preferably 30 m ２ / g or more. In the molybdenum trioxide particles, since the production becomes easy, it is preferably 100 m ２ / g or less, may be 90 m ２ / g or less, or may be 80 m ２ / g or less.

[0188] In the molybdenum trioxide particles, in the radial distribution function obtained from the extended X-ray absorption fine structure (EXAFS) profile at the K absorption edge of molybdenum, the ratio (I Ｏ of the peak intensity I due to Mo-O to the peak intensity II due to Mo-Mo Ｏ / IIＯ It is preferably greater than 1.1.

[0189] The intensity I of the peak due to Mo - O Ｏ , and the peak intensity II due to Mo - Mo Ｏ respectively read the maximum intensity of the peak, and the ratio (I Ｏ / II Ｏ ) is determined. The ratio (I Ｏ / II Ｏ ) is considered to be an indication that the β crystal structure of MoO is obtained in the molybdenum trioxide particles. The larger the ratio (I ３ / II Ｏ ), the better the reactivity with sulfur. Ｏ

[0190] In the molybdenum trioxide particles, the ratio (I Ｏ / II Ｏ ) is preferably 1.1 to 5.0, may be 1.2 to 4.0, or may be 1.2 to 3.0.

[0191] <<Method for producing molybdenum trioxide particles>> As the molybdenum trioxide particles, commercially available molybdenum trioxide may be used, or those produced by a molybdenum trioxide production process including vaporizing a molybdenum oxide precursor compound to form molybdenum trioxide vapor and cooling the molybdenum trioxide vapor may be used.

[0192] The method for producing the molybdenum trioxide particles includes firing a raw material mixture containing a molybdenum oxide precursor compound and a metal compound other than the molybdenum oxide precursor compound, and vaporizing the molybdenum oxide precursor compound to form molybdenum trioxide vapor. The ratio of the metal compound to 100% by mass of the raw material mixture is preferably 70% by mass or less in terms of oxide.

[0193] The method for producing the molybdenum trioxide particles can be preferably carried out using the production apparatus 1 shown in FIG. 1.

[0194] Figure 1 is a schematic diagram showing an example of an apparatus used for manufacturing molybdenum trioxide particles. As shown in Figure 1, the manufacturing apparatus 1 includes a calcination furnace 2 that calcines a molybdenum trioxide precursor compound or the raw material mixture to vaporize the molybdenum trioxide precursor compound, a cross-shaped cooling pipe 3 connected to the calcination furnace 2 to atomize the molybdenum trioxide vapor vaporized by the calcination, and a recovery machine 4 which is a recovery means for recovering the molybdenum trioxide particles atomized in the cooling pipe 3. In this case, the calcination furnace 2 and the cooling pipe 3 are connected via an exhaust port 5. The cooling pipe 3 has an opening adjustment damper 6 at the left end of an outside air intake port (not shown) and an observation window 7 at the upper end. The recovery machine 4 is connected to an exhaust device 8, which is a first blowing means. When the exhaust device 8 exhausts air, the internal gas of the recovery machine 4 and the cooling pipe 3 is drawn in, and outside air is blown into the cooling pipe 3 from the opening adjustment damper 6 of the cooling pipe 3. In other words, the exhaust device 8 performs a suction function, passively generating airflow into the cooling pipe 3. The manufacturing apparatus 1 may also have an external cooling device 9, which makes it possible to arbitrarily control the cooling conditions of the molybdenum trioxide vapor generated from the firing furnace 2.

[0195] By opening the opening adjustment damper 6, air is drawn in from the outside air intake, and the molybdenum trioxide vapor vaporized in the firing furnace 2 is cooled in an air atmosphere to form molybdenum trioxide particles, thereby achieving the ratio (I Ｏ / II Ｏ ) can be made larger than 1.1, and in molybdenum trioxide particles, MoO ３ The β crystal structure is easily obtained. Cooling molybdenum trioxide vapor in a nitrogen atmosphere with a low oxygen concentration, such as when molybdenum trioxide vapor is cooled using liquid nitrogen, increases the oxygen vacancy density, and the ratio (I Ｏ / II Ｏ It is easy to lower )

[0196] The aforementioned molybdenum oxide precursor compound is not particularly limited as long as it forms molybdenum trioxide vapor when calcined, but includes metallic molybdenum, molybdenum trioxide, molybdenum dioxide, molybdenum sulfide, ammonium molybdate, and phosphomolybdic acid (H ３ PMo １２ O ４０ ), silicic acid (H ４ SiMo １２ O ４０ ), aluminum molybdate, silicon molybdate, magnesium molybdate (MgMo ｎ O ３ｎ＋１ (n=1-3), sodium molybdate (Na ２ Mo ｎ O ３ｎ＋１ (n=1-3), titanium molybdate, iron molybdate, potassium molybdate (K ２ Mo ｎ O ３ｎ＋１ (n=1-3), zinc molybdate, boron molybdate, lithium molybdate (Li ２ Mo ｎ O ３ｎ＋１ Examples include (n=1-3), cobalt molybdate, nickel molybdate, manganese molybdate, chromium molybdate, cesium molybdate, barium molybdate, strontium molybdate, yttrium molybdate, zirconium molybdate, and copper molybdate. These molybdenum oxide precursor compounds may be used individually or in combination of two or more. The form of the molybdenum oxide precursor compound is not particularly limited; for example, it may be in powder form such as molybdenum trioxide, or in liquid form such as an aqueous solution of ammonium molybdate, but it is preferably in powder form, which is easy to handle and energy efficient.

[0197] It is particularly preferable to use commercially available α-crystalline molybdenum trioxide as the molybdenum trioxide precursor compound. Furthermore, when ammonium molybdate is used as the molybdenum oxide precursor compound, it is converted to thermodynamically stable molybdenum trioxide by calcination, so the vaporized molybdenum oxide precursor compound is the aforementioned molybdenum trioxide.

[0198] Molybdenum trioxide vapor can also be formed by calcining a raw material mixture containing a molybdenum oxide precursor compound and a metal compound other than the said molybdenum oxide precursor compound.

[0199] Of these, the molybdenum oxide precursor compound is preferable because it allows for easier control of the purity of the resulting molybdenum trioxide particles, the average particle size of the primary particles, and the crystal structure.

[0200] In some cases, an intermediate may be formed between the molybdenum oxide precursor compound and a metal compound other than the molybdenum oxide precursor compound. However, even in this case, the intermediate can be decomposed by calcination, allowing molybdenum trioxide to be vaporized in a thermodynamically stable form.

[0201] As for metal compounds other than the molybdenum oxide precursor compound, it is preferable to use an aluminum compound to prevent damage to the firing furnace, and it is also possible to omit metal compounds other than the molybdenum oxide precursor compound in order to improve the purity of the molybdenum trioxide particles.

[0202] The metal compounds other than the molybdenum oxide precursor compound are not particularly limited, and examples include aluminum compounds, silicon compounds, titanium compounds, magnesium compounds, sodium compounds, potassium compounds, zirconium compounds, yttrium compounds, zinc compounds, copper compounds, iron compounds, and the like. Of these, it is preferable to use the aluminum compound, silicon compound, titanium compound, or magnesium compound as the metal compound.

[0203] In some cases, an intermediate may be formed between the molybdenum oxide precursor compound and a metal compound other than the molybdenum oxide precursor compound. However, even in this case, the intermediate can be decomposed by calcination, allowing molybdenum trioxide to be vaporized in a thermodynamically stable form.

[0204] As a metal compound other than the molybdenum oxide precursor compound, it is preferable to use an aluminum compound to prevent damage to the firing furnace. In the above manufacturing method, it is not necessary to use a metal compound other than the molybdenum oxide precursor compound in order to improve the purity of the molybdenum trioxide particles.

[0205] Examples of aluminum compounds include aluminum chloride, aluminum sulfate, basic aluminum acetate, aluminum hydroxide, boehmite, pseudoboehmite, transition aluminum oxides (such as γ-aluminum oxide, δ-aluminum oxide, and θ-aluminum oxide), α-aluminum oxide, and mixed aluminum oxides having two or more crystalline phases.

[0206] When calcining a raw material mixture containing a molybdenum oxide precursor compound and a metal compound other than the molybdenum oxide precursor compound, the content ratio of the molybdenum oxide precursor compound to 100% by mass of the raw material mixture is preferably 40% by mass or more and 100% by mass or less, and may also be 45% by mass or more and 100% by mass or less, or 50% by mass or more and 100% by mass or less.

[0207] The firing temperature varies depending on the molybdenum oxide precursor compound, metal compound, and desired molybdenum trioxide particles used, but it is generally preferable to set the temperature at which the intermediate can decompose. For example, when a molybdenum compound is used as the molybdenum oxide precursor compound and an aluminum compound is used as the metal compound, aluminum molybdate may be formed as an intermediate, so the firing temperature is preferably 500 to 1500°C, more preferably 600 to 1550°C, and even more preferably 700 to 1600°C.

[0208] There are no specific restrictions on the firing time, but for example, it can be between 1 minute and 30 hours, between 10 minutes and 25 hours, or between 100 minutes and 20 hours.

[0209] The heating rate varies depending on the molybdenum oxide precursor compound used, the metal compound, and the properties of the desired molybdenum trioxide particles, but from the viewpoint of manufacturing efficiency, it is preferably 0.1°C / min to 100°C / min, more preferably 1°C / min to 50°C / min, and even more preferably 2°C / min to 10°C / min.

[0210] The internal pressure inside the firing furnace is not particularly limited and may be positive or reduced pressure, but from the viewpoint of suitably discharging the molybdenum oxide precursor compound from the firing furnace to the cooling pipe, firing is preferably carried out under reduced pressure. Specifically, the degree of reduced pressure is preferably -5000 Pa to -10 Pa, more preferably -2000 Pa to -20 Pa, and even more preferably -1000 Pa to -50 Pa. A reduced pressure of -5000 Pa or higher is preferable because it does not require excessive airtightness or mechanical strength of the firing furnace, thus reducing manufacturing costs. On the other hand, a reduced pressure of -10 Pa or lower is preferable because it prevents clogging of the molybdenum oxide precursor compound at the exhaust port of the firing furnace.

[0211] Furthermore, when gas is blown into the firing furnace during firing, the temperature of the blown gas is preferably 5 to 500°C, and more preferably 10 to 100°C.

[0212] Furthermore, the gas blowing speed is preferably 1 L / min or more and 500 L / min or less, and more preferably 10 L / min or more and 200 L / min or less, per 100 L of the effective volume of the firing furnace.

[0213] The temperature of the vaporized molybdenum trioxide vapor varies depending on the type of molybdenum oxide precursor compound used, but is preferably 200 to 2000°C, and more preferably 400 to 1500°C. When the temperature of the vaporized molybdenum trioxide vapor is 2000°C or lower, it tends to be easily atomized in the cooling pipe by blowing in outside air (0 to 100°C).

[0214] The discharge rate of molybdenum trioxide vapor discharged from the firing furnace can be controlled by the amount of the molybdenum oxide precursor compound used, the amount of the metal compound used, the temperature of the firing furnace, the amount of gas supplied into the firing furnace, and the diameter of the firing furnace exhaust port. Although it also depends on the cooling capacity of the cooling pipe, the discharge rate of molybdenum trioxide vapor from the firing furnace to the cooling pipe is preferably 0.001 g / min or more and 100 g / min or less, and more preferably 0.1 g / min or more and 50 g / min or less.

[0215] Furthermore, the molybdenum trioxide vapor content in the gas discharged from the firing furnace is preferably 0.01 mg / L or more and 1000 mg / L or less, and more preferably 1 mg / L or more and 500 mg / L or less.

[0216] Next, the molybdenum trioxide vapor is cooled to atomize it. Cooling of the molybdenum trioxide vapor is achieved by lowering the temperature of the cooling pipe. In this case, cooling methods include cooling by blowing gas into the cooling pipe, cooling by the cooling mechanism of the cooling pipe, and cooling by an external cooling device, as described above.

[0217] Cooling of molybdenum trioxide vapor is preferably carried out in an air atmosphere. By cooling molybdenum trioxide vapor in an air atmosphere and converting it into molybdenum trioxide particles, the ratio (I Ｏ / II Ｏ ) can be made larger than 1.1, and in molybdenum trioxide particles, MoO ３ The β crystal structure is easily obtained.

[0218] The cooling temperature (cooling pipe temperature) is not particularly limited, but is preferably -100 to 600°C, and more preferably -50 to 400°C.

[0219] The cooling rate of molybdenum trioxide vapor is not particularly limited, but is preferably 100°C / second or more and 100,000°C / second or less, and more preferably 1,000°C / second or more and 50,000°C / second or less. It should be noted that the faster the cooling rate of molybdenum trioxide vapor, the more likely it is to yield molybdenum trioxide particles with smaller particle sizes and larger specific surface areas.

[0220] When the cooling means is cooling by blowing gas into a cooling pipe, the temperature of the blown gas is preferably -100 to 300°C, and more preferably -50 to 100°C.

[0221] Furthermore, the gas blowing speed is 0.1 m ３ / min or more 20m ３ Preferably, it should be less than / minute, and 1m ３ / min or more 10m ３ It is more preferable that the gas flow rate is less than or equal to 0.1 m / min. ３ A gas flow rate of 20 m / min or more is preferable because it allows for a high cooling rate and prevents clogging of the cooling pipes. On the other hand, a gas flow rate of 20 m / min is preferable. ３ A rate of less than / minute is preferable because it eliminates the need for an expensive first blowing means (such as an exhaust fan), thereby lowering manufacturing costs.

[0222] The particles obtained by cooling molybdenum trioxide vapor are transported to a recovery machine and collected.

[0223] The method for producing the molybdenum trioxide particles may also involve cooling the molybdenum trioxide vapor to obtain the particles, and then firing them again at a temperature of 100 to 320°C.

[0224] In other words, the molybdenum trioxide particles obtained by the above method for producing molybdenum trioxide particles may be calcined again at a temperature of 100 to 320°C. The calcination temperature may be 120 to 280°C or 140 to 240°C. The time can be, for example, 1 minute to 4 hours, 10 minutes to 5 hours, or 100 minutes to 6 hours. However, by calcining again, a part of the β crystal structure of molybdenum trioxide will disappear, and if calcined at a temperature of 350°C or higher for 4 hours, the β crystal structure in the molybdenum trioxide particles will disappear, the ratio (β(011) / α(021)) will become 0, and the reactivity with sulfur will be impaired. By the method for producing molybdenum trioxide particles described above, molybdenum trioxide particles suitable for the production of the above molybdenum disulfide particles can be produced.

[0225] In the following, an example of a method for producing the particles of the composite according to this embodiment will be described, in which the molybdenum compound is a composite of molybdenum carbide and carbon.

[0226] <Method for producing a composite of molybdenum carbide and carbon> The method for producing the composite of molybdenum carbide and carbon includes calcining molybdenum trioxide and carbon in the presence of at least one inorganic compound selected from the group consisting of inorganic salts and inorganic hydroxides. As the molybdenum trioxide, commercially available molybdenum trioxide may be used, or molybdenum trioxide containing α crystals with an average crystallite size of 50 nm or less may be used.

[0227] The at least one inorganic compound is preferably an alkali metal compound, and more preferably at least one selected from the group consisting of sodium compounds and potassium compounds, such as KCl, NaCl, and Na ２ CO ３ At least one selected from the group consisting of , and KOH is even more preferable.

[0228] The amount of the at least one inorganic compound is not particularly limited, but is preferably 5% to 1000% relative to the mass of molybdenum trioxide and carbon, more preferably 10% to 500%, and even more preferably 20% to 200%. When the amount of the at least one inorganic compound is within the above preferred range, it is easy to form a composite with high conductivity and catalytic activity.

[0229] In the method for producing the composite according to this embodiment, the at least one inorganic compound functions as a flux, promoting the reaction between molybdenum trioxide and carbon. The flux method is characterized by its ability to synthesize inorganic compounds or control their crystal structure and composition at a relatively lower temperature than conventional calcination.

[0230] In the method for producing the composite according to this embodiment, the firing temperature is not particularly limited, but is preferably 400 to 1500°C, more preferably 500 to 1000°C, and even more preferably 750 to 880°C. When the firing temperature is within the above preferred range, it is easier to form a composite with high conductivity and catalytic activity.

[0231] In the method for producing the composite, the heating time is not particularly limited, but should be sufficient for the reaction to proceed sufficiently, and may be 1 to 48 hours, 2 to 24 hours, or 4 to 12 hours.

[0232] The method for producing the composite may include a step of washing the calcined material with water after calcining molybdenum trioxide and carbon in order to remove the at least one inorganic compound.

[0233] In the method for producing the composite material, the carbon is not particularly limited, and commercially available carbon particles such as carbon black, carbon nanotubes, and activated carbon can be used.

[0234] In the method for producing the composite material, the average particle diameter of the primary molybdenum trioxide particles is defined as the average of the particle diameters of 50 randomly selected primary particles when the molybdenum trioxide particles are photographed with a transmission electron microscope (TEM) or scanning electron microscope (SEM), and the major axis (the Ferret diameter of the longest observed part) and minor axis (the shorter Ferret diameter perpendicular to the Ferret diameter of the longest part) of the smallest unit particle constituting the aggregate on the two-dimensional image (i.e., the primary particle) are measured, and the average value of these is taken as the primary particle diameter.

[0235] In the method for producing the composite, MoO2 measured by X-ray fluorescence (XRF) relative to the total mass of molybdenum trioxide particles ３ The content of is preferably 95.0% by mass or more, more preferably 99.0% by mass or more, and even more preferably 99.5% by mass or more, relative to the total detected peak intensity. ３ When the content ratio is within the above preferred range, it is easy to obtain a highly pure composite with good storage stability, free from the risk of generating carbides derived from impurities, by carbonizing molybdenum trioxide particles.

[0236] In the method for manufacturing the composite material, the specific surface area of ​​the molybdenum trioxide particles is 0.5 m². ２ It is preferable that it be 0.8 m or more. ２ It is more preferable that it be 30m or more per gram. ２It is even more preferable that the amount is 100 m or more, as this facilitates the production of composite particles. ２ It is preferable that it be less than or equal to 90m ２ It may be less than / g, and 80m ２ It may be less than / g.

[0237] The following describes the case in which molybdenum trioxide containing α crystals with an average crystallite size of 50 nm or less is used in the production of the composite material. The average crystallite size of the α crystals is 50 nm or less, preferably 5 nm to 50 nm, more preferably 5 nm to 45 nm, even more preferably 10 nm to 40 nm, and particularly preferably 10 nm to 35 nm. When the average crystallite size of the α crystals is within the above range, the reactivity of molybdenum trioxide particles with carbon tends to be better.

[0238] Molybdenum trioxide containing α crystals with an average crystallite size of 50 nm or less may further contain β crystals with an average crystallite size of 50 nm or less. When the crystal structure of molybdenum trioxide contains both α and β crystals, the reactivity of molybdenum trioxide particles with carbon tends to be better.

[0239] The average crystallite size of the β crystal is preferably 5 nm to 50 nm, more preferably 5 nm to 45 nm, even more preferably 10 nm to 40 nm, and particularly preferably 10 nm to 30 nm. When the average crystallite size of the β crystal is within the above preferred range, the reactivity of molybdenum trioxide particles with carbon tends to be better.

[0240] The α-crystal structure of molybdenum trioxide is shown in the profile obtained from powder X-ray diffraction (XRD) using Cu-Kα rays as the X-ray source, MoO ３ The presence of a peak on the (021) plane of the α crystal (around 2θ: 27.32° - No. 166363 (Inorganic Crystal Structure Database, ICSD)) can be confirmed. Furthermore, the β crystal structure can be confirmed in the profile obtained from powder X-ray diffraction (XRD) using Cu-Kα rays as the X-ray source, showing MoO ３This can be confirmed by the presence of a peak (around 2θ: 23.01°, No. 86426 (Inorganic Crystal Structure Database, ICSD)) that is attributed to the (011) plane of the β crystal.

[0241] In the profile obtained from powder X-ray diffraction (XRD) using Cu-Kα rays as the X-ray source, the molybdenum trioxide particles are MoO ３ The peak intensity attributable to the (011) plane of the β crystal of MoO ３ The ratio (β(011) / α(021)) to the peak intensity attributed to the (021) plane of the α crystal is preferably 0.1 or higher, more preferably 0.2 or higher, and even more preferably 0.4 or higher. The ratio (β(011) / α(021)) is preferably 10.0 or lower.

[0242] MoO ３ The peak intensity attributable to the (011) plane of the β crystal, and MoO ３ For the peak intensities attributed to the (021) plane of the α crystal, the maximum peak intensity is read, and the ratio (β(011) / α(021)) is determined.

[0243] The ratio (β(011) / α(021)) is preferably 0.1 to 10.0, more preferably 0.2 to 10.0, and particularly preferably 0.4 to 10.0.

[0244] When using molybdenum trioxide containing α crystals with an average crystallite size of 50 nm or less, the α crystal content of the molybdenum trioxide particles is not particularly limited, but may be 20% or more, 50% or more, 70% or more, 80% or more, or 100%.

[0245] MoO ３ In a mixture of α and β crystals of MoO ３ The α-crystal content can be determined from the obtained profile data using the RIR (Reference Intensity Ratio) method. ３ RIR value K of the α crystal Ａ and MoO ３The integral intensity I of the (021) plane (around 2θ: 27.32° - No. 166363 (Inorganic Crystal Structure Database, ICSD)) of the α crystal Ａ , and MoO ３ RIR value K of the β crystal Ｂ and MoO ３ The integral intensity I of the β crystal attributable to the (011) plane (around 2θ: 23.01°, No. 86426 (Inorganic Crystal Structure Database, ICSD)) Ｂ Using this, from the following equation (2), MoO ３ The α-crystal content (%) can be determined. ３ The α-crystal content (%) = (I Ａ / K Ａ ) / ((I Ａ / K Ａ ) + (I Ｂ / K Ｂ )) × 100 ... (2) Here, the RIR values ​​can be those listed in the ICSD database, and the integrated powder X-ray analysis software (PDXL2, manufactured by Rigaku Corporation) can be used for the analysis.

[0246] (Hydrogen Evolution Catalyst) The composite of this embodiment can be suitably used as a catalyst (sometimes referred to as "hydrogen evolution catalyst" in this specification) in the hydrogen evolution reaction (HER). Furthermore, the composite of this embodiment can also be used as a hydrogen evolution catalyst when used in combination with a conductive material. When the composite of this embodiment is used in combination with a conductive material, the catalytic activity of the hydrogen evolution catalyst in the hydrogen evolution reaction (HER) is further increased.

[0247] The conductive material may be a known material. Examples of the conductive material include highly conductive carbon and metals. The hydrogen generation catalyst may contain only one type of conductive material or two or more types.

[0248] Examples of the conductive material include acetylene black, Cabot carbon black, Ketjenblack and other carbon blacks, graphite, carbon fiber, and metal powders. Ketjenblack is superior in that it has a high specific surface area and conductivity, and can also suppress the aggregation of molybdenum sulfide.

[0249] Examples of the conductive metal include gold, silver, copper, aluminum, rhodium, molybdenum, tungsten, iron, nickel, cobalt, and indium. Unlike the essential metals in the composite of the embodiment, the conductive metal in the hydrogen generation catalyst is simply mixed with the composite of the embodiment.

[0250] The hydrogen generation catalyst may contain only one type of metal as a conductive material, or it may contain two or more types.

[0251] The hydrogen generation catalyst may, for example, contain carbon but no metal as a conductive material, contain metal but no carbon, or contain both metal and carbon.

[0252] In the hydrogen generation catalyst, the content of the conductive material is preferably 0.1 to 100 parts by mass, and more preferably 0.5 to 50 parts by mass, based on the content of 100 parts by mass of the composite of the embodiment.

[0253] In the hydrogen evolution catalyst, the total content ratio of the composite of the embodiment and the conductive material relative to the total mass (100% by mass) of the hydrogen evolution catalyst is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. For example, it may be 97% by mass or more, 99% by mass or more, or 100% by mass. When the ratio is above the lower limit, the catalytic activity of the hydrogen evolution catalyst in the hydrogen evolution reaction (HER) is increased. The ratio may be 100% by mass or less.

[0254] (Catalyst Ink) The catalyst ink of one embodiment contains the composite of this embodiment and a solvent. The catalyst ink of the embodiment may contain the composite of this embodiment, a polymer electrolyte and a solvent.

[0255] The catalyst ink of this embodiment may further contain a conductive material. Examples of the type and content of the conductive material are those exemplified above.

[0256] The catalyst ink can be applied to, for example, a substrate for a working electrode to form a catalyst layer.

[0257] As the polymer electrolyte, those commonly used in the formation of catalyst layers can be used. Specifically, these include perfluorocarbon polymers having sulfonic acid groups (e.g., Nafion®), hydrocarbon polymer compounds having sulfonic acid groups, polymer compounds doped with inorganic acids such as phosphoric acid, organic / inorganic hybrid polymers in which some are substituted with proton-conducting functional groups, and proton conductors in which a polymer matrix is ​​impregnated with a phosphoric acid solution or sulfuric acid solution.

[0258] The solvent can be one that can disperse the composite of the embodiment and can be applied to a substrate for a working electrode to form a catalyst layer. Preferably, the solvent contains alcohols such as 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 1-hexanol, 2-hexanol, 1-heptanol, and 2-heptanol.

[0259] (Electrodes) An electrode according to one embodiment of the present invention is obtained by coating it with the catalyst ink of this embodiment. For example, the electrode can be prepared by coating the electrode surface with a dispersion of the catalyst ink obtained above, allowing the surface liquid to dry naturally, then transferring the electrode to a vacuum dryer and drying it at 30 to 90°C for 2 hours or more. The hydrogen generation activity of the prepared electrode can be evaluated using a three-electrode method. The evaluation conditions were the LSV method, with a scan voltage range from -0.3V to 0V and a scan speed of 5mV / s.

[0260] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0261] (Reference Example 1) "Production and Evaluation of Molybdenum Trioxide Particles" <Production of Molybdenum Trioxide Particles> Molybdenum trioxide was produced using an RHK simulator (manufactured by Noritake Co., Ltd.) as the firing furnace and a VF-5N dust collector (manufactured by Amano Corporation) as the dust collector. 1.5 kg of aluminum hydroxide (manufactured by Nippon Light Metal Co., Ltd.) and 1 kg of molybdenum trioxide (manufactured by Nippon Muki Co., Ltd.) were mixed, then placed in a sagger, and fired at a temperature of 1100°C for 10 hours. During firing, outside air (airflow rate: 150 L / min, outside air temperature: 25°C) was introduced from the sides and bottom of the firing furnace. After the molybdenum trioxide evaporated in the furnace, it was cooled near the dust collector and precipitated as particles, so 900 g of molybdenum trioxide (1) was obtained using the dust collector.

[0262] Median diameter D of the primary particle determined by dynamic light scattering. ５０ The wavelength is 87.8 nm, and the purity of molybdenum trioxide (1) was determined by X-ray fluorescence measurement (MoO ３ The content of (1) was confirmed to be 99.9% by mass. Furthermore, when the crystal structure of molybdenum trioxide (1) was analyzed by X-ray diffraction (XRD), peaks attributed to molybdenum trioxide of the α crystal and molybdenum trioxide of the β crystal were observed, and no other peaks were observed. Next, when the peak intensity ratio of the (011) plane of the β crystal and the (021) plane of the α crystal was compared, β(011) / α(021) was 4. Furthermore, Rigaku Corporation's integrated powder X-ray analysis software PDXL2 was applied, and LaB was used as the standard substance. ６ The XRD instrument constants were determined using a NIST SRM660c LaB6 Standard Powder, and the crystallite size was evaluated using the Scherre method. It was confirmed that molybdenum trioxide (1) has a crystal structure that includes α crystals with an average crystallite size of 15.7 nm and β crystals with an average crystallite size of 16.8 nm.

[0263] <Evaluation of Molybdenum Oxide Powder> [Method for Measuring the Average Particle Size of Primary Molybdenum Trioxide Particles] 0.1 g of molybdenum trioxide (1) obtained in Reference Example 1 was added to 10 ml of ethanol, subjected to sonication in an ice bath for 4 hours, and then further adjusted with ethanol to a concentration within the measurable range of a dynamic light scattering particle size distribution analyzer (Nanotrac Wave II manufactured by MicrotracBEL) to obtain a measurement sample. Using this measurement sample, the particle size distribution in the range of 0.0001 to 10 μm was measured using a dynamic light scattering particle size distribution analyzer (Nanotrac Wave II manufactured by MicrotracBEL), and the median diameter D ５０ The median diameter D was calculated. ５０ For particles larger than 10 μm, prepare the solution similarly and measure the particle size distribution in the range of 0.015 to 500 μm using a laser diffraction particle size distribution analyzer (SALD-7000, Shimadzu Corporation), and determine the median diameter D ５０ The result was calculated.

[0264] [Crystal structure analysis of molybdenum trioxide particles: XRD method] A sample of molybdenum trioxide (1) was packed into a 0.5 mm deep sample holder, and then set in an X-ray diffraction (XRD) apparatus (Ultima IV manufactured by Rigaku Corporation, using a parallel beam method + scintillation counter detector and rotating stage). Measurements were performed under the following conditions: Cu / Kα rays, 40 kV / 40 mA, scan speed (2θ) 2° / min, step (2θ) 0.02°, and scan range (2θ) 10° to 70°.

[0265] [Method for measuring the crystallite size of molybdenum trioxide particles] A SmartLab 9kW X-ray diffractometer (manufactured by Rigaku Corporation) was used as the X-ray diffractometer, a scintillation counter detector was used as the detector, and PDXL2 was used as the analysis software. The measurement method was the 2θ / θ method, and the average crystallite size of molybdenum trioxide was calculated using the Scherrer formula from the full width at half maximum of the peak appearing at 2θ = 12.7° ± 0.5°. The measurement conditions were a scan speed (2θ) of 2.0° / min, a scan range (2θ) of 10 to 70°, a step (2θ) of 0.02°, and no instrument standard width.

[0266] [Purity Measurement of Molybdenum Trioxide: XRF Analysis] Using a Primus IV X-ray fluorescence analyzer (manufactured by Rigaku Corporation), approximately 20-30 mg of the recovered molybdenum trioxide particle sample was placed on filter paper, covered with a PP film, and subjected to compositional analysis. The amount of molybdenum determined from the XRF analysis results was calculated as molybdenum trioxide (mass%) relative to 100% by mass of molybdenum trioxide particles.

[0267] (Synthesis Example 1) "Synthesis of a composite of molybdenum carbide and carbon" 30.0 g of molybdenum trioxide (Sinopharm Group Chemical Reagent Co., LTD, average particle size 5 μm), 15.0 g of activated carbon (Yantai Tongyi Environmental Production Technology Co. LTD.), and 56.3 g of sodium carbonate (Sinopharm Group Chemical Reagent Co., LTD) were mixed and then placed in a crucible and calcined at 850°C for 6 hours under a nitrogen atmosphere. After natural cooling, the calcined material was washed with deionized water to remove salts. According to XRD measurement, the obtained composite was molybdenum carbide (Mo ２ It was confirmed that the composite exhibited the α-crystal structure shown in C). Furthermore, the crystallite size was 47 nm as determined by XRD measurement. The carbon content was 48% of the total mass (100% mass) of the composite. Raman spectroscopy analysis of the composite revealed carbon-derived graphite bands G and disorder bands D, and the ratio of the carbon-derived graphite band G to the disorder band D (G / D) was 0.84. Note that the carbon content and the G / D ratio do not typically change when the composite is combined with metal nanoparticles.

[0268] (Synthesis Example 2) "Synthesis of Molybdenum Disulfide" 40.0 g (277.9 mmol) of molybdenum trioxide (1) obtained in Reference Example 1 and 40.0 g (1250 mmol, 4.5 equivalents to Mo atoms) of sulfur powder (manufactured by Kanto Chemical Co., Ltd.) were added to an alumina crucible and mixed with a stirring rod until the powder was homogeneous. After mixing, a lid was placed on the alumina crucible and it was placed in a high-temperature atmosphere firing furnace (manufactured by Motoyama Co., Ltd., SKM-2030P-OP). The furnace was evacuated and then purged with nitrogen before firing. The firing conditions were to start at room temperature of 25°C, increase the temperature at a rate of 5°C / min, reach 500°C, and hold for 4 hours. Nitrogen gas was blown in at a rate of 0.5 L / min during the firing process. After that, the furnace was cooled by natural cooling to obtain 44.5 g of molybdenum disulfide particles. Furthermore, the presence of a 3R crystal structure was confirmed by XRD measurement.

[0269] (Example 1) 90 mg of the composite obtained in Synthesis Example 1 was dispersed in 20 ml of pure water by ultrasound for 30 minutes to obtain a dispersion. Reagent: NaH, Kanto Chemical Co., Ltd. ２ PO ２ ・H ２ O 14.2 mg was dissolved in 5 ml of pure water to obtain a reducing agent. Kanto Chemical Co., Ltd. Reagent H ２ PtCl ６ 6H ２ O 8 mg, Kanto Chemical Co., Ltd. Reagent Ni (CH ３ COO) ２ 4H ２ 29.7 mg of O and 14.9 mg of Kanto Chemical Co., Ltd.'s reagent polyvinylpyrrolidinone (K=30) were dissolved in 20 ml of pure water by ultrasonic dispersion, and the resulting solution was added to the dispersion with stirring. The mixture was then stirred at room temperature for 0.5 hours. Next, the reducing agent was added to the dispersion with stirring. The dispersion was then refluxed for 2 hours. The precipitate in the dispersion was collected by centrifugation, and the composite powder of this example was obtained by ultrasonic washing three times with water, washing once with ethanol, and vacuum drying.

[0270] (Examples 2-4) Powders of the composites of Examples 2-4 were obtained in the same manner as in Example 1, except that the amounts of the compounds shown in Table 1 were used.

[0271] (Example 5) 90 mg of the composite from Synthesis Example 1 was dispersed in 20 ml of pure water by ultrasound for 30 minutes to obtain a dispersion. Reagent: NaH, Kanto Chemical Co., Ltd. ２ PO ２ ・H ２ A reducing agent was obtained by dissolving 14.7 mg of O in 5 ml of pure water. Kanto Chemical Co., Ltd. Reagent H2PtCl ６ 6H ２ O 5.2 mg, Reagent Na, Kanto Chemical Co., Ltd. ２ PdCl ４ 2.9 mg, Kanto Chemical Co., Ltd. Reagent Ni(CH ３ COO) ２ 4H ２ 29.7 mg of O and 15.5 mg of Kanto Chemical Co., Ltd.'s reagent polyvinylpyrrolidinone (K=30) were dissolved in 20 ml of pure water by ultrasonic dispersion, and the resulting solution was added to the dispersion with stirring. The mixture was then stirred at room temperature for 0.5 hours. Next, the reducing agent was added to the dispersion with stirring. The dispersion was then refluxed for 2 hours. The precipitate in the dispersion was collected by centrifugation, and the composite powder of this example was obtained by ultrasonic washing three times with water, washing once with ethanol, and vacuum drying.

[0272] (Example 6) 90 mg of the composite from Synthesis Example 1 was dispersed in 20 ml of pure water by ultrasound for 30 minutes to obtain a dispersion. Kanto Chemical Co., Ltd. Reagent NaH ２ PO ２ ・H ２ O 14.7 mg was dissolved in 5 ml of pure water to obtain a reducing agent. Kanto Chemical Co., Ltd. Reagent H ２ PtCl ６ 6H ２ O 5.2 mg, Reagent Na, Kanto Chemical Co., Ltd. ２ PdCl ４ 2.9 mg, Kanto Chemical Co., Ltd. reagent CoCl ２ 6H ２28.3 mg of O and 15.5 mg of Kanto Chemical Co., Ltd.'s reagent polyvinylpyrrolidinone (K=30) were dissolved in 20 ml of pure water by ultrasonic dispersion, and the resulting solution was added to the dispersion with stirring. The mixture was then stirred at room temperature for 0.5 hours. Next, the reducing agent was added to the dispersion with stirring. The dispersion was then heated and stirred at 80°C. The precipitate in the dispersion was collected by centrifugation, and the composite powder of this example was obtained by ultrasonic washing three times with water, washing once with ethanol, and vacuum drying.

[0273] (Example 7) NaH ２ PO ２ ・H ２ Instead of 14.7 mg, use Kanto Chemical Co., Ltd. reagent ascorbic acid (C ６ H ８ O ６ The powder of the composite of this example was obtained in the same manner as in Example 6, except that 24.4 mg was used.

[0274] (Example 8) 90 mg of the compound from Synthesis Example 1 was mixed with 10 ml of ethanol (Kanto Chemical Co., Ltd. reagent, C ２ H ５ A dispersion was obtained by dispersing the NaH(OH) in a mixed solvent of 20 ml of pure water using ultrasound for 30 minutes. Kanto Chemical Co., Ltd. Reagent NaH(OH) ２ PO ２ ・H ２ O 14.7 mg was dissolved in 5 ml of pure water to obtain a reducing agent. Kanto Chemical Co., Ltd. Reagent H ２ PtCl ６ 6H ２ O 5.2 mg, Reagent Na, Kanto Chemical Co., Ltd. ２ PdCl ４ 2.9 mg, Kanto Chemical Co., Ltd. reagent CoCl ２ 6H ２ O 28.3 mg, Kanto Chemical Co., Ltd. reagent polyvinylpyrrolidinone (K=30) 15.5 mg in 10 ml ethanol (Kanto Chemical Co., Ltd. reagent, C ２ H ５The OH(OH) was dissolved in a mixed solvent of 20 ml of pure water by ultrasonic dispersion, and the resulting solution was added to the dispersion with stirring. The mixture was then stirred at room temperature for 0.5 hours. Next, the reducing agent was added to the dispersion with stirring. The dispersion was then heated and stirred at 80°C. The precipitate in the dispersion was collected using a centrifuge, and the composite powder of this example was obtained by ultrasonic washing three times with water, washing once with ethanol, and vacuum drying.

[0275] (Example 9) NaH ２ PO ２ ・H ２ Instead of 14.7 mg of O, use Kanto Chemical Co., Ltd. reagent ascorbic acid (C ６ H ８ O ６ The powder of the composite of this example was obtained in the same manner as in Example 8, except that 37.0 mg was used.

[0276] (Example 10) 90 mg of the composite from Synthesis Example 1 was dispersed in 20 ml of pure water by ultrasound for 30 minutes to obtain a dispersion. Kanto Chemical Co., Ltd. Reagent Ascorbic Acid (C ６ H ８ O ６ ) 37.0 mg was dissolved in 5 ml of pure water to obtain a reducing agent. Kanto Chemical Co., Ltd. Reagent H ２ PtCl ６ 6H ２ O 5.2 mg, Reagent Na, Kanto Chemical Co., Ltd. ２ PdCl ４ 2.9 mg, Kanto Chemical Co., Ltd. Reagent CuSO4 ４ ・5H ２ 27.5 mg of O and 16.7 mg of Kanto Chemical Co., Ltd.'s reagent polyvinylpyrrolidinone (K=30) were dissolved in 20 ml of pure water by ultrasonic dispersion, and the resulting solution was added to the dispersion with stirring. Subsequently, the reducing agent was added to the dispersion with stirring. The dispersion was then refluxed for 1.5 hours. The precipitate in the dispersion was collected by centrifugation, and the composite powder of this example was obtained by ultrasonic washing three times with water, washing once with ethanol, and vacuum drying.

[0277] (Example 11) The composite powder of this example was obtained in the same manner as in Example 10, except that the proportions shown in Table 1 were used.

[0278] (Example 12) 90 mg of the composite from Synthesis Example 1 was dispersed in 20 ml of pure water by ultrasound for 30 minutes to obtain a dispersion. Reagent: NaH, Kanto Chemical Co., Ltd. ２ PO ２ ・H ２ O 8.1 mg was dissolved in 5 ml of pure water to obtain a reducing agent. Kanto Chemical Co., Ltd. Reagent H ２ PtCl ６ 6H ２ O 5.2 mg, Reagent Na, Kanto Chemical Co., Ltd. ２ PdCl ４ 2.9 mg, Kanto Chemical Co., Ltd. Reagent RuCl ３ 3H ２ 18.1 mg of O and 9.9 mg of Kanto Chemical Co., Ltd.'s reagent polyvinylpyrrolidinone (K=30) were dissolved in 20 ml of pure water by ultrasonic dispersion, and the resulting solution was added to the dispersion with stirring. The mixture was then stirred at room temperature for 0.5 hours. Next, the reducing agent was added to the dispersion with stirring. The dispersion was then refluxed for 2 hours. The precipitate in the dispersion was collected by centrifugation, and the composite powder of this example was obtained by ultrasonic washing three times with water, washing once with ethanol, and vacuum drying.

[0279] (Example 13) The composite powder of this example was obtained in the same manner as in Example 12, except that the proportions shown in Table 1 were used.

[0280] (Example 14) 90 mg of the composite from Synthesis Example 1 was dispersed in 20 ml of pure water by ultrasound for 30 minutes to obtain a dispersion. Reagent: NaH, Kanto Chemical Co., Ltd. ２ PO ２ ・H ２ O 6.9 mg was dissolved in 5 ml of pure water to obtain a reducing agent. Kanto Chemical Co., Ltd. Reagent H ２ PtCl ６ 6H ２ O 5.2 mg, Reagent Na, Kanto Chemical Co., Ltd. ２ PdCl ４ 2.9mg, Sigma-Aldrich CH ３COOAg 3.2 mg and Kanto Chemical Co., Ltd. reagent polyvinylpyrrolidinone (K=30) 4.4 mg were dissolved in 20 ml of pure water by ultrasonic dispersion, and the resulting solution was added to the dispersion with stirring. The mixture was then stirred at room temperature for 0.5 hours. Next, the reducing agent was added to the dispersion with stirring. The dispersion was then refluxed for 2 hours. The precipitate in the dispersion was collected by centrifugation, and the composite powder of this example was obtained by ultrasonic washing three times with water, washing once with ethanol, and vacuum drying.

[0281] (Example 15) 90 mg of the composite from Synthesis Example 1 was dispersed in 20 ml of pure water by ultrasound for 30 minutes to obtain a dispersion. Reagent: NaH, Kanto Chemical Co., Ltd. ２ PO ２ ・H ２ O 14.7 mg was dissolved in 5 ml of pure water to obtain a reducing agent. Kanto Chemical Co., Ltd. Reagent H ２ PtCl ６ 6H ２ O 5.2 mg, Reagent Na, Kanto Chemical Co., Ltd. ２ PdCl ４ 2.9 mg, Kanto Chemical Co., Ltd. FeCl ２ 4H ２ 24.9 mg of O and 16.1 mg of Kanto Chemical Co., Ltd.'s reagent polyvinylpyrrolidinone (K=30) were dissolved in 20 ml of pure water by ultrasonic dispersion, and the resulting solution was added to the dispersion with stirring. The mixture was then stirred at room temperature for 0.5 hours. Next, the reducing agent was added to the dispersion with stirring. The dispersion was then refluxed for 2 hours. The precipitate in the dispersion was collected by centrifugation, and the composite powder of this example was obtained by ultrasonic washing three times with water, washing once with ethanol, and vacuum drying.

[0282] (Example 16) The powder of the composite of this example was obtained in the same manner as in Example 15, except that 24.4 mg of ascorbic acid was used instead of sodium phosphinate.

[0283] (Example 17) 90 mg of the composite from Synthesis Example 1 was dispersed in 20 ml of pure water by ultrasound for 30 minutes to obtain a dispersion. Reagent C, Kanto Chemical Co., Ltd. ６ H ８ O ６39.0 mg was dissolved in 5 ml of pure water to obtain a reducing agent. Kanto Chemical Co., Ltd. Reagent H ２ PtCl ６ 6H ２ O 5.2 mg, Reagent Na, Kanto Chemical Co., Ltd. ２ PdCl ４ 2.9 mg, Kanto Chemical Co., Ltd. Reagent Ni(CH ３ COO) ２ 4H ２ O 25.4 mg, Kanto Chemical Co., Ltd. Reagent CuSO ４ ・5H ２ 3.9 mg of O and 15.5 mg of Kanto Chemical Co., Ltd.'s reagent polyvinylpyrrolidinone (K=30) were dissolved in 20 ml of pure water by ultrasonic dispersion, and the resulting solution was added to the dispersion with stirring. Subsequently, the reducing agent was added to the dispersion with stirring. The dispersion was then refluxed for 1.5 hours. The precipitate in the dispersion was collected by centrifugation, and the composite powder of this example was obtained by ultrasonic washing three times with water, washing once with ethanol, and vacuum drying.

[0284] (Example 18) 90 mg of the composite from Synthesis Example 1 was dispersed in 20 ml of pure water by ultrasound for 30 minutes to obtain a dispersion. Reagent: NaH, Kanto Chemical Co., Ltd. ２ PO ２ ・H ２ O 11.1 mg was dissolved in 5 ml of pure water to obtain a reducing agent. Kanto Chemical Co., Ltd. Reagent H ２ PtCl ６ 6H ２ O 4.6 mg, Reagent Na, Kanto Chemical Co., Ltd. ２ PdCl ４ 2.6 mg, Kanto Chemical Co., Ltd. Reagent Ni(CH ３ COO) ２ 4H ２ O 26.7 mg, Kanto Chemical Co., Ltd. RuCl ３ 3H ２2.6 mg of O and 14.0 mg of Kanto Chemical Co., Ltd.'s reagent polyvinylpyrrolidinone (K=30) were dissolved in 20 ml of pure water by ultrasonic dispersion, and the resulting solution was added to the dispersion with stirring. Subsequently, the reducing agent was added to the dispersion with stirring. The dispersion was then refluxed for 1.5 hours. The precipitate in the dispersion was collected by centrifugation, and the composite powder of this example was obtained by ultrasonic washing three times with water, washing once with ethanol, and vacuum drying.

[0285] (Examples 19 and 20) Powders of the composites of these examples were obtained in the same manner as in Example 18, except that the proportions shown in Table 1 were used.

[0286] (Example 21) The powder of the composite of this example was obtained in the same manner as in Example 5, except that 90 mg of molybdenum disulfide from Synthesis Example 2 was used instead of the composite of Synthesis Example 1.

[0287] (Comparative Example 1) The composite obtained in Synthesis Example 1 was used as the powder for this comparative example.

[0288] (Comparative Example 2). The molybdenum disulfide obtained in Synthesis Example 2 was used as the powder for this comparative example.

[0289] (Comparative Example 3) A platinum-carbon catalyst with a platinum basis weight of 50%, purchased from Tanaka Precious Metals Co., Ltd., was used as the powder for this comparative example. Hereafter, this powder will be referred to as "commercially available 50% Pt / C".

[0290] (Comparative Example 4) A platinum-carbon catalyst with a platinum basis weight of 20%, purchased from Tanaka Precious Metals Co., Ltd., was used as the powder for this comparative example. Hereinafter, this powder will be referred to as "commercially available 20% Pt / C".

[0291] The following evaluations were performed using the powders from Examples 1 to 21 and Comparative Examples 1 to 4 as samples.

[0292] ≪Evaluation≫ [XRF Analysis] Using a Primus IV X-ray fluorescence analyzer (manufactured by Rigaku Corporation), approximately 20-30 mg of the sample was placed on filter paper, covered with a PP film, and subjected to compositional analysis. Based on the platinum, palladium, molybdenum, and sulfur content determined from the XRF analysis results, the content of palladium and platinum per 100% mass of sample particles ("Pd-Pt content", mass%), and the mass ratio and molar ratio of palladium, platinum, and secondary metal (M) were determined. The results are shown in Table 2.

[0293] [Measurement of BET specific surface area] The specific surface area was measured using a specific surface area meter (Microtrac-Bel, BELSORP-mini) and calculated as the specific surface area per gram of sample, which was determined from the amount of nitrogen gas adsorbed by the BET method. The results are shown in Table 2.

[0294] [Median diameter D] ５０ [Measurement] 0.1 g of sample powder was added to 20 ml of ethanol, and sonicated in an ice bath for 4 hours. Then, the concentration was adjusted with ethanol to the measurable range of a dynamic light scattering particle size distribution analyzer (Microtrac Bell, Nanotrac Wave II) to obtain a measurement sample. Using this measurement sample, the particle size distribution in the range of 0.0001 μm to 10 μm was measured using a dynamic light scattering particle size distribution analyzer, and the median diameter D was determined as the particle size at which the volume integrated percentage was 50%. ５０ The median diameter D was calculated. ５０ For particles larger than 10 μm (Comparative Example 2), the solution was prepared similarly, and the particle size distribution in the range of 0.015 μm to 500 μm was measured using a laser diffraction particle size distribution analyzer (Shimadzu Corporation, SALD-7000), and the median diameter D ５０ The result was calculated and is shown in Table 2.

[0295] [Evaluation of Hydrogen Generation Activity] 4 mg of sample powder, 2 mg of Ketjenblack EC300J (Lion Specialty Chemicals Co., Ltd.), and 40 μl of 5% Nafion dispersion (Nafion dispersion solution, Fujifilm Wako Pure Chemical Corporation) were ultrasonically dispersed in 1 ml of ethanol for more than 1 hour to prepare a dispersion of the catalyst ink. 20 μl of the obtained dispersion was applied to the electrode surface, and after the surface liquid was naturally dried, the electrode was dried in a vacuum dryer at 60°C for 6 hours. The overvoltage of the dried electrode was measured in a three-electrode system to evaluate the hydrogen generation activity. This means the catalyst performance. The measurement conditions were the LSV method, with the scan voltage range from -0.3 V to 0 V and the scan speed at 5 mV / S. Table 2 shows the overvoltage (mV) at a current density of 10 mA / cm ２ 2.

[0296]

[0297]

[0298] Examples 1 to 20 are powders of a composite of molybdenum carbide and carbon and a composite containing the first metal (PM) and the second metal (M). Example 21 is a powder of the composite containing molybdenum disulfide, the first metal (PM), and the second metal (M). From Table 2, it can be seen that the particles of Examples 1 to 20 exhibit excellent catalytic activity compared to a composite of molybdenum carbide and carbon (Comparative Example 1) that does not contain the first metal (PM) and the second metal (M). Also, it can be seen that the particles of Example 21 exhibit excellent catalytic activity compared to molybdenum disulfide (Comparative Example 2) that does not contain the first metal (PM) and the second metal (M). Furthermore, the particles of Examples 1 to 3, 5 to 9, 11, 15, 18, 19 exhibit excellent catalytic activity (overvoltage) at a level equal to or higher than that of Comparative Example 4, even though the total content of platinum and palladium is very low compared to commercially available 20% Pt / C (Comparative Example 4). In particular, it can be seen that the particles of Example 5 exhibit excellent catalytic activity (overvoltage) at a level equivalent to that of commercially available 50% Pt / C (Comparative Example 3).

[0299] Figures 2 to 4 show observation images of the particles obtained in Examples 5, 8, and 14 by a transmission electron microscope (TEM, manufactured by JEOL Ltd., JEM-1400). Figure 8 shows an image obtained by elemental mapping by a high-resolution electron microscopy method (HR-TEM (manufactured by JEOL, JEM-ARM300F)) for the particles obtained in Example 5. The magnification factors are 50K and 250K. The particles of Example 5 contain Pt, Pd, and Ni, the particles of Example 8 contain Pt, Pd, and Co, and the particles of Example 14 contain Pt, Pd, and Ag.

[0300] From Figure 2, it can be seen that in the particles of Example 5, ultra-fine particles with a particle diameter of about 2 nm are dispersed throughout the composite particles of molybdenum carbide and carbon. From Figure 8, it can be seen that in the particles of Example 5, Pt, Pd, and Ni form ultra-fine particles and are dispersed. From Figure 3, it can be seen that in the particles of Example 8, similar to the particles of Example 5, ultra-fine particles with a particle diameter of about 2 nm are dispersed. On the other hand, from Figure 4, it can be seen that in the particles of Example 14, different from the particles of Examples 5 and 8, primary particles of ultra-fine particles are not observed, and aggregated particles with a particle diameter of about 15 nm are formed.

[0301] Figures 5 to 7 show observation images of the particles obtained in Examples 18 to 20 by a transmission electron microscope (TEM, manufactured by JEOL Ltd., JEM-1400). The magnification factor is 250K. Examples 18 to 20 all contain Pt, Pd, Ni, and Ru, but the content of each metal is different.

[0302] From Figure 5, it can be seen that in the particles of Example 18, the metal particles of Pt, Pd, Ni, and Ru are substantially spherical. On the other hand, from Figure 7, it can be seen that in the particles of Example 20, the metal particles of Pt, Pd, Ni, and Ru are connected and form a bead-like shape.

[0303] Further, in the composite according to the present invention, the platinum particles do not show the crystal structure of platinum metal crystals, at least a part of the platinum constitutes the platinum particles, and it is observed that the platinum particles are attached or bonded on the surface of the particles of the molybdenum compound, no change in the interlayer nuclei constituting the molybdenum compound is seen, and the result that the valence of platinum is zero valence has been obtained.

[0304] 1. Manufacturing equipment 2. Firing furnace 3. Cooling piping 4. Recovery machine 5. Exhaust port 6. Opening adjustment damper 7. Observation window 8. Exhaust system 9. External cooling system

Claims

1. A composite comprising a molybdenum compound, a first metal (PM), and a second metal (M), wherein the first metal (PM) is platinum, or a combination of platinum and palladium, and the second metal (M) is one or more selected from the group consisting of metals other than platinum and palladium.

2. The composite according to claim 1, wherein the second metal (M) is one or more selected from the group consisting of Ni, Cu, Ag, Co, Ru, Fe, and Al.

3. The composite according to claim 1 or 2, wherein the first metal (PM) is a combination of platinum and palladium.

4. The composite according to claim 1 or 2, wherein the ratio of the total content of the first metal (PM) to the total mass of the composite, as determined by XRF analysis, is 0.5% by mass or more and 15% by mass or less.

5. The composite according to claim 1 or 2, wherein the ratio of the total content of the second metal (M) to the total mass of the composite, as determined by XRF analysis, is 0.1% by mass or more and 8% by mass or less.

6. The composite according to claim 1 or 2, wherein the ratio of the total content of the first metal (PM) and the second metal (M) to the total mass of the composite, as determined by XRF analysis, is 0.6% by mass or more and 20% by mass or less.

7. The composite according to claim 1 or 2, wherein the molybdenum compound comprises molybdenum sulfide, and the molybdenum sulfide comprises molybdenum disulfide having a 3R structure.

8. The molybdenum compound includes a composite of molybdenum carbide and carbon, wherein the molybdenum carbide is Mo ２ The composite according to claim 1 or 2, having a C crystalline structure, and having a carbon content of 6% or more relative to the total mass (100% by mass) of the composite.

9. The median diameter D of the composite, determined by dynamic light scattering. ５０ The composite according to claim 1 or 2, wherein the wavelength is 1000 nm or less.

10. The specific surface area of ​​the composite, as measured by the BET method, is 10 m². ２ The composite according to claim 1 or 2, wherein the amount is 1 / g or more.

11. The composite according to claim 1 or 2, wherein metal particles are supported on the molybdenum compound, the metal of the metal particles is at least one selected from the group consisting of the first metal (PM) and the second metal (M), and the average particle diameter of the metal particles is 20 nm or less.

12. A hydrogen generation catalyst comprising the composite according to claim 1 or 2.

13. The hydrogen generation catalyst according to claim 12, further comprising a conductive material.

14. A catalyst ink comprising the composite according to claim 1 or 2 and a solvent.

15. An electrode coated with the catalyst ink described in claim 14.

16. A method for producing a composite containing a molybdenum compound, a first metal (PM), and a second metal (M), wherein the molybdenum compound comprises at least one compound selected from the group consisting of molybdenum sulfide, molybdenum carbide, and a composite of molybdenum carbide and carbon; the first metal (PM) is platinum, or a combination of platinum and palladium; the second metal (M) is one or more metals other than platinum and palladium; and the method for producing a composite comprises a mixing step of mixing the molybdenum compound with a metal-containing solution containing the first metal (PM) and the second metal (M) such that the total mass of the first metal (PM) and the second metal (M) is 50 parts by mass or less relative to the total mass (100 parts by mass) of the molybdenum compound.

17. The method for producing a composite according to claim 16, further comprising a reduction step of adding a reducing agent to the mixed liquid obtained in the mixing step.

18. The method for producing the composite according to claim 16 or 17, wherein the molybdenum compound comprises a composite of molybdenum carbide and carbon, and the composite is obtained by calcining molybdenum trioxide and carbon in the presence of at least one inorganic compound selected from the group consisting of inorganic salts and inorganic hydroxides.

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