Method for producing iron carbide nanoparticles, and reduction catalyst containing iron carbide nanoparticles

Abstract

The present invention provides: a method for producing iron carbide nanoparticles of Fe7C3 or Fe5C2 under mild conditions of less than 300°C using iron, which is low in toxicity, stable and easily available, as a starting material; and a catalyst which contains the iron carbide nanoparticles. The present invention relates to a reduction catalyst which contains iron carbide nanoparticles, wherein the iron carbide nanoparticles are Fe7C3 nanoparticles or Fe5C2 nanoparticles, and the average particle diameter of the iron carbide nanoparticles is 30 nm to 800 nm inclusive.

Description

Method for producing iron carbide nanoparticles and reduction catalyst containing iron carbide nanoparticles

[0001] The present invention relates to a method for producing iron carbide nanoparticles and a reduction catalyst containing iron carbide nanoparticles.

[0002] In recent years, there has been widespread research into the properties of metastable materials that do not appear in phase diagrams. Iron carbide, a type of iron-based ceramic, is generally known as cementite, which has a composition of Fe3C, but iron carbide with a metastable phase of Fe7C3 is also known.

[0003] It is known that FeC is produced under ultra-high temperature and pressure conditions, such as 2000 K or higher or 7 GPa or higher. On the other hand, it has been reported in recent years that nano-sized FeC can be synthesized by a gas-phase or liquid-phase method at temperatures below 500 °C (e.g., Non-Patent Document 1).

[0004] In addition, it has been reported that a liquid phase method, which is carried out under milder reaction conditions, produces wire-like FeC with a diameter of 100 nm and an average length of 2 to 3 μm (Non-Patent Document 2), and cauliflower-like FeC with a thickness of 150 nm and an average diameter of 960 nm (Non-Patent Document 3).

[0005] Furthermore, a liquid-phase synthesis method for FeC particles with a particle size of 100 nm or less has been reported (Non-Patent Document 4). In this preparation method, Fe(CO) was thermally decomposed at 350°C in the presence of N,N-dimethyl-n-octadecylamine, and it was reported that FeC particles with an average particle size of 16 nm were synthesized.

[0006] Y. Li, et al., “Relationship between Iron Carbide Phases (ε-Fe2C, Fe7C3, and χ-Fe5C2) and Catalytic Performances of Fe / SiO2 Fischer-Tropsch Catalysts”, ACS Catal., 2018, 8, 4, pp.3304-3316K. Miura, et al., “Surfactant-Assisted Preparation and Magnetic Properties of Iron-Based Nanowires”, Jpn. J. Appl. Phys., 2008, 47, 2342E. E. Carpenter, et al., “Solvothermal synthesis of Fe7C3 and Fe3C nanostructures with phase and morphology control”, J. Appl. Phys., 2016, 120, 033904D. Ma, et al. al., “Synthesis of Iron-Carbide Nanoparticles: Identification of the Active Phase and Mechanism of Fe-Based Fischer-Tropsch Synthesis”, CCS Chem., 2020, 2, pp.2712-2724

[0007] However, the vapor phase preparation method of Non-Patent Document 1 requires a temperature of 300°C or higher, and furthermore, iron carbides of other compositions are also produced, making it impossible to produce a single phase.

[0008] Furthermore, in Non-Patent Document 2, the particles are wire-shaped and cannot be considered nano-sized in terms of length, and in Non-Patent Document 3, the average diameter is about 1 μm, which is too large to be considered nano-sized.

[0009] Furthermore, the method of Non-Patent Document 4 uses Fe(CO)5, which is toxic, unstable, and difficult to obtain, and when prepared at 300°C or less, only Fe2C is obtained, and Fe7C3 cannot be obtained.

[0010] Therefore, a method for synthesizing iron carbide nanoparticles under mild conditions at less than 300° C. using low-toxicity, stable, and easily available iron as a raw material has not yet been achieved.

[0011] Furthermore, in catalytic hydrogenation of unsaturated carbonyl compounds, double bonds are generally hydrogenated preferentially over carbonyl groups, so saturated carbonyl compounds or saturated alcohol compounds are likely to be produced, making it relatively difficult to selectively obtain unsaturated alcohol compounds. In particular, in the case of α,β-unsaturated carbonyl compounds in which the double bond and the carbonyl group are in a conjugated relationship, it is even more difficult to produce unsaturated alcohol compounds, and it has not been possible to selectively obtain unsaturated alcohol compounds from α,β-unsaturated carbonyl compounds using a solid iron catalyst.

[0012] The present invention aims to provide a method for producing iron carbide nanoparticles of FeC or FeC under mild conditions below 300°C using low-toxicity, stable, and easily available iron as a raw material, and a catalyst containing the iron carbide nanoparticles.

[0013] Another object of the present invention is to provide a method for producing an unsaturated alcohol compound, which comprises selectively hydrogenating an α,β-unsaturated carbonyl compound using a solid catalyst containing iron carbide nanoparticles to obtain an unsaturated alcohol compound.

[0014] As a result of extensive research to solve the above problems, the present inventors have found that the above problems can be solved by a method for producing iron carbide nanoparticles, which involves adding iron(III) acetylacetonate and a hydride reducing agent to a solvent to form a mixture, and heating the mixture at a temperature of less than 300°C in the presence of CO gas or CO gas, or by using the obtained iron carbide nanoparticles for other purposes. Based on this finding, the present inventors have conducted further research and have completed the present invention.

[0015] The present invention encompasses the following: [1] A reduction catalyst containing iron carbide nanoparticles, wherein the iron carbide nanoparticles are FeC nanoparticles or FeC nanoparticles, and the average particle size of the iron carbide nanoparticles is 30 nm or more and 800 nm or less. [2] The reduction catalyst according to [1], wherein the iron carbide nanoparticles consist solely of FeC nanoparticles. [3] The reduction catalyst according to [1] or [2], further containing a support. [4] The reduction catalyst according to [3], wherein the support is at least one selected from the group consisting of polymers, chalcogen compounds, metal compounds, metals, and solid carbon materials. [5] A composite containing iron carbide nanoparticles and a support, wherein the iron carbide nanoparticles are FeC nanoparticles or FeC nanoparticles, and the average particle size of the iron carbide nanoparticles is 30 nm or more and 800 nm or less. [6] The composite according to [5], wherein the support is at least one selected from the group consisting of polymers, chalcogen compounds, metal compounds, metals, and solid carbon materials. [7] A method for producing an unsaturated alcohol compound, comprising hydrogenating an α,β-unsaturated carbonyl compound using the reduction catalyst described in [1] or [2] to obtain an unsaturated alcohol compound. [8] A method for producing an unsaturated alcohol compound according to [7], wherein the hydrogenation temperature is 200°C or less. [9] A method for producing an unsaturated alcohol compound according to [7], wherein the hydrogenation is carried out in the presence of a solvent.

[10] A method for producing iron carbide nanoparticles according to [1] or [2], comprising adding an iron compound and a hydride reducing agent to a solvent to form a mixture, and heating the mixture at a temperature of less than 300°C in the presence of a carbon source gas, wherein the iron compound is iron(III) acetylacetonate, iron(II) acetylacetonate, or iron(III) chloride, and the carbon source gas is CO gas or CO2 gas.

[11] The method for producing iron carbide nanoparticles according to

[10] , wherein the iron compound is iron(III) acetylacetonate, the carbon source gas is CO gas, the CO gas pressure is 0.1 MPa or more, and the iron carbide nanoparticles are FeC nanoparticles.

[12] The method for producing iron carbide nanoparticles according to

[11] , wherein the heating time is 2.5 to 50 hours.

[13] The method for producing iron carbide nanoparticles according to

[11] , wherein the solvent is an alcohol solvent.

[14] A method for producing iron carbide nanoparticles according to

[11] , which does not use a surfactant.

[15] FeC nanoparticles having a hexagonal crystalline phase, a spherical shape, and an average particle size of 30 nm to 800 nm.

[0016] The present invention provides a method for producing iron carbide nanoparticles of FeC or FeC under mild conditions below 300°C using low-toxicity, stable, and readily available iron as a raw material, and a catalyst containing the iron carbide nanoparticles. The method for producing iron carbide nanoparticles of the present invention is industrially advantageous in terms of excellent biological safety, since it uses a non-toxic, stable, and readily available iron compound as the iron source. Furthermore, the method for producing iron carbide nanoparticles of the present invention enables the production of single-phase iron carbide nanoparticles (preferably FeC nanoparticles) under mild conditions below 300°C. Furthermore, the method for producing iron carbide nanoparticles of the present invention is industrially advantageous in that it does not require iron pretreatment and the production process is simple.

[0017] The present invention also provides a method for producing an unsaturated alcohol compound by selectively hydrogenating an α,β-unsaturated carbonyl compound using a solid catalyst containing iron carbide nanoparticles to obtain an unsaturated alcohol compound. Furthermore, while conventional techniques require high temperatures of over 200°C when used as a reduction catalyst (e.g., hydrogenation catalyst), the iron carbide nanoparticles of the present invention, when used as a reduction catalyst (e.g., hydrogenation catalyst), can carry out a reduction reaction (e.g., hydrogenation reaction) under milder conditions than those of conventional techniques, which require temperatures of 200°C or less, thereby producing the target compound.

[0018] Furthermore, the iron carbide nanoparticles and reduction catalyst of the present invention use iron, which is also present in living organisms, as a metal source, making them less toxic and safer. Furthermore, given the abundance of iron on Earth (reserves), they are industrially advantageous in terms of cost.

[0019] FIG. 1 shows a transmission electron microscope (TEM) image of FeC nanoparticles according to one embodiment of the present invention. FIG. 2 shows the results of powder X-ray diffraction measurement of the FeC nanoparticles according to Example 1-1 of the present invention, along with the peak positions of the crystal planes corresponding to FeC. FIG. 3 shows the results of powder X-ray diffraction measurement of the FeC nanoparticles according to Example 1-1 of the present invention and the FeC nanoparticles according to Example 1-2. FIG. 4 shows the results of powder X-ray diffraction measurement of the FeC nanoparticles according to Example 1-1 of the present invention and particles according to Comparative Examples 1-1 to 1-3. FIG. 5 shows the results of powder X-ray diffraction measurement of the FeC nanoparticles according to Example 1-1, the FeC nanoparticles according to Example 1-3, and particles according to Comparative Example 1-4. FIG. 6 shows the results of powder X-ray diffraction measurement of the FeC nanoparticles according to Example 1-4, particles according to Comparative Example 1-5, and particles according to Comparative Example 1-6.

[0020] Hereinafter, each embodiment of the present invention will be described. In this specification, the iron carbide nanoparticles of the present invention will be collectively referred to as "nano-Fe x C y (where x represents 5 or 7, y represents 2 or 3; when x is 5, y is 2, and when x is 7, y is 3). In this specification, "under atmospheric conditions" means atmospheric pressure (1 atmosphere) and an oxygen concentration of about 21% in the atmosphere. In this specification, the upper and lower limits of numerical ranges (such as the size of iron carbide nanoparticles, the amount of a certain component (a material such as a compound) used, temperature, pressure, or values ​​calculated from each numerical range and each physical property, etc.) can be combined as appropriate.

[0021] One embodiment of the present invention relates to a reduction catalyst containing iron carbide nanoparticles, wherein the iron carbide nanoparticles are FeC nanoparticles or FeC nanoparticles, and the iron carbide nanoparticles have an average particle size of 30 nm or more and 800 nm or less. Each embodiment will be described below. However, the present invention is not limited to the following embodiments.

[0022] The reduction catalyst of the present invention contains iron carbide nanoparticles. The iron carbide nanoparticles are FeC nanoparticles or FeC nanoparticles, and are preferably composed solely of FeC nanoparticles in terms of superior catalytic activity.

[0023] First, the Fe7C3 nanoparticles used in the reduction catalyst of the present invention will be described.

[0024] The FeC nanoparticles of the present invention have peaks at diffraction angles (2θ±0.5°) of 39.9°, 42.6°, 44.9°, 50.1°, 50.5°, and 53.2° in powder X-ray diffraction measurement using CuKα radiation. The diffraction angles may be 2θ±0.2° or 2θ±0.5°.

[0025] The Fe7C3 nanoparticles of the present invention preferably further have a peak at 45.6° in the powder X-ray diffraction measurement.

[0026] The peaks at diffraction angles of 39.9°, 42.6°, 44.9°, 50.1°, 50.5°, and 53.2° in the X-ray diffraction pattern (hereinafter also referred to as "XRD pattern") of the FeC nanoparticles of the present invention using CuKα radiation correspond to the (210), (102), (211), (301), (202), and (220) crystal planes of FeC, respectively. The peak at a diffraction angle of 45.6° corresponds to the (300) crystal plane of FeC. The FeC nanoparticles of the present invention are preferably hexagonal.

[0027] The FeC nanoparticles of the present invention contain iron atoms in a low valence state (metallic state) and have excellent catalytic activity. "Atomic valence" is a number that represents the ability of an atom of a certain element to bond with atoms of other elements. The iron (Fe) atoms contained in the FeC nanoparticles of the present invention are in a low valence state.

[0028] Furthermore, the FeC nanoparticles of the present invention have peaks at diffraction angles (2θ±0.5°) of 39.0°, 40.6°, 43.2°, 43.7°, and 58.1° in powder X-ray diffraction measurement using CuKα radiation. The diffraction angles may be 2θ±0.2° or 2θ±0.5°.

[0029] The peaks at diffraction angles of 39.0°, 40.6°, 43.2°, 43.7°, and 58.1° in the XRD pattern of the FeC nanoparticles of the present invention using CuKα radiation correspond to the (020), (11-2), (021), (510), and (11-3) planes of FeC, respectively.

[0030] For powder X-ray diffraction analysis (XRD) using CuKα radiation, a known X-ray diffractometer can be used. Examples of the X-ray diffractometer include a commercially available fully automated multipurpose X-ray diffractometer (trade name "Philips X'PERT MPD diffractometer" manufactured by Philips Japan Co., Ltd.).

[0031] The iron carbide nanoparticles (preferably FeC nanoparticles) of the present invention contain low-valent iron atoms and have the property of stably maintaining catalytic activity under atmospheric conditions (hereinafter also referred to as "atmospheric stability"). Therefore, the iron carbide nanoparticles (preferably FeC nanoparticles) of the present invention do not require reduction pretreatment before use as a reduction catalyst. Furthermore, the crystal structure of the iron carbide nanoparticles (preferably FeC nanoparticles) of the present invention can be measured by powder X-ray diffraction measurement in the presence of oxygen.

[0032] Furthermore, the iron carbide nanoparticles (preferably FeC nanoparticles) of the present invention have excellent stability in the presence of oxygen. The oxygen (O) concentration is not particularly limited, and may be about the atmospheric oxygen concentration (approximately 21%) or about 22% to 100%. The iron carbide nanoparticles (preferably FeC nanoparticles) of the present invention have excellent atmospheric stability and can maintain catalytic activity in the presence of oxygen, regardless of the oxygen concentration.

[0033] The peak at the diffraction angle indicates that FeC can be identified, as is clear from the JCPDS card (File 17-0333) in the International Centre for Diffraction Data (ICDD) database (Powder Diffraction File, Level 4 plus 2023). Similarly, the peak at the diffraction angle indicates that FeC can be identified, as is clear from the JCPDS card (File 36-1248) in the ICDD database (Powder Diffraction File, Level 4 plus 2023).

[0034] The shape of the iron carbide nanoparticles (preferably FeC nanoparticles) of the present invention is not particularly limited, but spherical particles are preferred. Spherical particles may be approximately spherical. For approximately spherical particles, the aspect ratio (long axis / short axis) of the particles is preferably 1 to 2.5, more preferably 1 to 2, and even more preferably 1 to 1.5. The aspect ratio refers to the ratio (long axis / short axis) of the long side to the short side of the smallest rectangle (usually called the circumscribed rectangle) when a particle image projected onto a flat surface in an electron microscope photograph or the like is enclosed by a rectangle. The length of the long side is referred to as the "long axis" and the length of the short side is referred to as the "short axis." The closer the aspect ratio is to 1, the more spherical the particle is. The aspect ratio can be calculated as the arithmetic average of 100 particles projected onto a flat surface in an electron microscope photograph or the like. If necessary, the number of particles to be measured may be 200 or 500. The aspect ratio can be calculated using known particle analysis software (e.g., "MultiImageTool" manufactured by System In Frontier, Inc.). The particle morphology of the spherical particles can be confirmed by TEM observation, for example, as shown in Figure 1. Figure 1 shows a TEM image of FeC nanoparticles of the present invention.

[0035] The average particle size of the iron carbide nanoparticles of the present invention is 30 nm or more and 800 nm or less. The average particle size of the iron carbide nanoparticles of the present invention is preferably 50 nm or more, more preferably 60 nm or more, even more preferably 90 nm or more, and particularly preferably 100 nm or more. The average particle size of the iron carbide nanoparticles of the present invention is also preferably 800 nm or less, more preferably 700 nm or less, even more preferably 650 nm or less, and particularly preferably 600 nm or less. A preferred embodiment includes a reduction catalyst in which the average particle size of the iron carbide nanoparticles is 50 nm or more and 800 nm or less. Another preferred embodiment includes FeC nanoparticles having a hexagonal crystalline phase, a spherical shape, and an average particle size of 30 nm or more and 800 nm or less.

[0036] The average particle size of the iron carbide nanoparticles of the present invention can be calculated as the arithmetic mean of the major axis lengths (maximum major axis lengths) of 100 or more (e.g., 200) particles (either primary particles or agglomerated particles, for example, agglomerated particles) observed in an electron microscope photograph. If necessary, the number of particles to be measured may be 400 or 500. Known particle analysis software (e.g., "MultiImageTool" manufactured by System in Frontier) can be used to calculate the average particle size.

[0037] It is believed that the iron carbide nanoparticles (preferably Fe7C3 nanoparticles) of the present invention can maintain catalytic activity in the atmosphere.

[0038] The iron carbide nanoparticles (preferably Fe7C3 nanoparticles) of the present invention have iron atoms in a low valence state and have catalytic activity under atmospheric conditions.

[0039] The valence of iron atoms in the iron carbide nanoparticles (preferably FeC nanoparticles) of the present invention can be analyzed, for example, by X-ray absorption fine structure (XAFS). Specifically, by irradiating metal atoms with high-intensity X-rays, preferably high-intensity X-rays with continuously varying energy, the core electrons of the metal atoms are excited to an energy level equal to or higher than the unoccupied orbitals. The excited metal atoms then emit photoelectrons with a kinetic energy corresponding to the difference between the excitation energy of the incident X-rays and the binding energy of the core electrons. This fine structure appears near the absorption edge in the X-ray absorption spectrum of the metal atoms, and analysis of this fine structure allows the electronic state of the metal atoms to be identified. Within the energy range of XAFS, this fine structure, which appears approximately several tens of eV near the absorption edge, is called the X-ray absorption near edge structure (XANES). On the other hand, the modulation structure that extends from the absorption edge to approximately 1000 eV higher energy within the XAFS energy range is called the extended X-ray absorption fine structure (EXAFS). EXAFS is a vibration structure obtained due to the interaction between excited electrons and scattered electrons from nearby atoms, and the radial distribution function obtained by Fourier transform contains information about the local structure of the metal atom (surrounding atomic species, number of coordinated atoms, and interatomic distance).

[0040] In the iron carbide nanoparticles (preferably FeC nanoparticles) of the present invention, the fact that the iron atoms contained therein are in a low-valent state can also be confirmed by X-ray absorption near edge structure (XANES).

[0041] In the iron carbide nanoparticles (preferably FeC nanoparticles) of the present invention, the iron atoms contained therein exist in a low valence state, and therefore in the XANES spectrum obtained by XANES measurement of the K absorption edge of the Fe atoms, the rise of the peak is the same as the rise of the peak of iron foil (Fe foil). In other words, the fact that the iron atoms constituting the iron carbide nanoparticles (preferably FeC nanoparticles) of the present invention exist in a low valence state can be confirmed by the fact that in the XANES spectrum obtained by the XANES measurement, the rise of the peak is the same as the rise of the peak of iron foil (Fe foil). Iron foil (Fe foil) is zero-valent Fe as a metal. In a preferred embodiment, the iron carbide nanoparticles (preferably FeC nanoparticles) have a ratio of (spectral intensity at 7110 eV of iron carbide nanoparticles (preferably FeC nanoparticles)) / (spectral intensity at 7110 eV of Fe foil) of 0.910 to 1.000 in a XANES spectrum obtained by XANES measurement of the K absorption edge of Fe atoms, where "eV" represents binding energy.

[0042] For XANES measurement of the K absorption edge of Fe atoms, a known measurement device (for example, an X-ray absorption spectrometer (device name "QuantumLeapH2000" (for measurement in atmosphere) or "QuantumLeapV210" (for measurement in vacuum), both manufactured by Canon Inc.)) or known measurement equipment (large-scale synchrotron radiation facility "SPring-8"; beamlines BL01B1 and BL14B2, 1-1 Hikarito, Sayo-cho, Sayo-gun, Hyogo Prefecture, 679-5198) can be used.

[0043] The size of the iron carbide nanoparticles (preferably FeC nanoparticles) of the present invention can be adjusted by adjusting the selection and concentration of raw material compounds, heating temperature, heating conditions (stirring speed, etc.), reaction time, etc. in the method for producing iron carbide nanoparticles described below.

[0044] In the iron carbide nanoparticles (preferably FeC nanoparticles) of the present invention, the abundance ratio of carbon atoms to iron atoms as determined by scanning transmission electron microscope (STEM)-energy dispersive X-ray spectroscopy (EDX) composition analysis is not particularly limited, but from the viewpoint of further enhancing catalytic activity or achieving superior atmospheric stability, it is preferable that C:Fe=20%:80% to 80%:20%, more preferably 30%:70% to 70%:30%, and even more preferably 35%:65% to 65%:35%.

[0045] The ratio of carbon atoms to iron atoms in the iron carbide nanoparticles (preferably FeC nanoparticles) of the present invention can be adjusted by adjusting the degree of iron carbonization. x C y In the formula, x is 7 and y is 3. The iron carbide nanoparticles contain at least one of Fe7C3 and Fe5C2, and preferably contain only Fe7C3 because of their superior catalytic activity. In another embodiment, nano-Fe x C y In the formula, x is 5 and y is 2.

[0046] The degree of iron carbonization can be adjusted by, for example, adjusting the heating temperature in the method for producing iron carbide nanoparticles (e.g., changing the heating temperature, increasing the carbon source gas pressure, or extending the reaction time by one hour). Conversely, to suppress carbonization and limit the progress of the carbonization to a certain extent, the ratio of carbon atoms to iron atoms can be adjusted by conversely adjusting the heating temperature and other conditions (e.g., lowering the heating temperature by 10°C, lowering the carbon source gas pressure, or shortening the reaction time by one hour).

[0047] In the iron carbide nanoparticles of the present invention, the abundance ratio of carbon atoms to iron atoms can be evaluated by elemental analysis (element mapping). A known energy-dispersive X-ray analysis (EDX) can be used for the elemental analysis (element mapping). A known measuring device can be used for EDX. A commercially available measuring device (such as a transmission electron microscope equipped with a Super-X energy-dispersive X-ray spectroscopy (EDX) detector (single atom analysis transmission electron microscope, product name "Titan Cubed G2 60-300", accelerating voltage: 300 kV, manufactured by FEI (now Thermo Fisher Scientific (US)))) can be used.

[0048] Furthermore, while EDX is a method for observing a single particle, the abundance ratio of carbon atoms to iron atoms may be evaluated by observing a plurality of (large number of) iron carbide nanoparticles as a whole, as can be seen under a microscope. One such method is inductively coupled plasma atomic emission spectroscopy (ICP-AES). Known measuring devices can be used for ICP-AES. Commercially available measuring devices (such as an ICP optical emission spectrometer under the trade name "Optima 8300" manufactured by PerkinElmer, Inc.) can be used.

[0049] The abundance ratio of carbon atoms to iron atoms as determined by ICP-AES is not particularly limited, but from the viewpoint of further enhancing catalytic activity or achieving superior atmospheric stability, C:Fe=20%:80% to 80%:20%, more preferably 30%:70% to 70%:30%, and even more preferably 35%:65% to 65%:35%.

[0050] The iron carbide nanoparticles (preferably FeC nanoparticles) of the present invention not only have excellent atmospheric stability, but also maintain their structure even when heated, resulting in excellent thermal stability. Being able to maintain their structure means being able to maintain a low valence state. Whether or not the structure can be maintained when heated can also be confirmed by X-ray absorption fine structure (XAFS) measurement under atmospheric conditions.

[0051] The iron carbide nanoparticles (preferably FeC nanoparticles) of the present invention can maintain their activity after use as a reduction catalyst (e.g., hydrogenation catalyst) and can be recovered. Therefore, they can be recovered and reused. The recovery method is not particularly limited, and known methods such as filtration can be used. Furthermore, the iron carbide nanoparticles (preferably FeC nanoparticles) of the present invention have excellent durability because they retain high catalytic activity even after recovery and reuse.

[0052] The reduction catalyst of the present invention preferably further contains a carrier in order to obtain more excellent catalytic activity.

[0053] Another embodiment of the present invention is a composite containing iron carbide nanoparticles and a carrier, wherein the iron carbide nanoparticles contain FeC nanoparticles or FeC nanoparticles, and the iron carbide nanoparticles have an average particle size of 30 nm or more and 800 nm or less.

[0054] The iron carbide nanoparticles of the present invention (preferably FeC nanoparticles) also have excellent adsorption capacity, so there are no limitations on the type of support, and when used as a composite in a reduction reaction, they are effective as a reduction catalyst. The reason for their excellent adsorption capacity is unclear, but it is thought that part of the reason is that they are nano-sized and stable under atmospheric conditions.

[0055] In the reduction catalyst and composite of the present invention, the iron atoms contained in the iron carbide nanoparticles (preferably, FeC nanoparticles) are in a low-valent state, and the iron carbide nanoparticles (preferably, FeC nanoparticles) are stable under atmospheric conditions. Therefore, unlike the prior art, where catalytically active iron particles must be synthesized on a support and used as a catalyst immediately after synthesis, or where a reduction pretreatment under high temperature and pressure is required to use the iron catalyst in a reduction reaction, the iron carbide nanoparticles (preferably, FeC nanoparticles) of the present invention do not have this requirement. Therefore, unlike the prior art, in which the type of support was limited by the conditions for using the iron particles as an iron catalyst, one of the advantageous effects of the present invention is that the type of support used in combination with the iron carbide nanoparticles (preferably, FeC nanoparticles) when the composite is used as a catalyst is not limited. Thus, the reason for limiting the support is eliminated, and there is no special circumstance that catalytic activity cannot be obtained without a limited support. Therefore, the type of support is not limited in the composite of the present invention, and many types can be used.

[0056] In the reduction catalyst and composite of the present invention, the type of support is not limited as long as it can be used as a support capable of supporting iron carbide nanoparticles (preferably FeC nanoparticles). The support is preferably a liquid or solid at room temperature, more preferably a solid. In another embodiment, the support may not have catalytic activity by itself. By using iron carbide nanoparticles (preferably FeC nanoparticles) together with a support, aggregation of the iron carbide nanoparticles (preferably FeC nanoparticles) can be effectively suppressed, making it easier to recover the composite and increasing reusability.

[0057] The support may be at least one selected from the group consisting of polymers, chalcogen compounds, metal compounds, metals, and solid carbon materials. One support may be used alone, or two or more supports may be used in combination. Commercially available supports may be used.

[0058] The polymer may be either a natural polymer or a synthetic polymer. Examples of natural polymers include organic natural polymers such as natural rubber, protein, starch, and cellulose; and inorganic natural polymers such as quartz, mica, and feldspar. Examples of synthetic polymers include organic synthetic polymers such as polyacrylic acid, polymethacrylic acid, polyvinyl alcohol, polyvinyl chloride, polyvinylpyrrolidone, polyethylene glycol (PEG), polypropylene glycol (PPG), polyethylene terephthalate (PET), polyester, polyethylene, polypropylene, polystyrene, polyurethane, polyethyleneimine, polyethersulfone, polyphenylene sulfide (PPS), polyether ether ketone (PEEK), polyvinylidene fluoride, polylactic acid, epoxy resin, fluorine-based resins (such as PTFE (polytetrafluoroethylene), PFA, FEP, PCTFE, ETFE, and ECTFE), nylon resin, polyamide, polyimide, and rubber (such as silicone rubber, nitrile rubber, butyl rubber, and butadiene rubber); and inorganic synthetic polymers such as glass and silica gel. The polymer may be a homopolymer having one type of monomer as a constituent unit, or a copolymer having two or more types of monomer as constituent units. The polymer may be a thermoplastic resin or a thermosetting resin. The weight-average molecular weight (Mw) of the polymer is not particularly limited, and may be an oligomer or polymer of 1,000 to less than 10,000, 10,000 to less than 1,000,000, or an ultra-high molecular weight polymer of 1,000,000 to 7,000,000. The weight-average molecular weight refers to the weight-average molecular weight in terms of polystyrene determined by gel permeation chromatography (GPC).

[0059] The chalcogen compound refers to a compound containing a Group 16 element (oxygen, sulfur, selenium, tellurium, polonium, livermorium). The Group 16 element contained in the chalcogen compound may be one type alone or two or more types. The chalcogen compound is not particularly limited, and may be H2X 1 O4 (X 1 = chalcogens excluding tellurium), H6TeO6, H2X 2 O3 (X 2= chalcogen) or salts thereof; a compound represented by MX3 (wherein M is Ti, Zr, Hf, V, Nb, Ta, Mo, or W, and X is S or Se); and a metal chalcogenide represented by MPX3 (wherein M is Mg, V, Mn, Fe, Co, Ni, Zn, Cd, or In, and X is S or Se).

[0060] The metal compound is not particularly limited, but examples thereof include oxides of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Si, Zr, Fe, Ti, Al, Mg, Co, Ni, Mn, Cr, Mo, W, V, Zn, and Sn, solid solutions thereof, and composite oxides thereof. Specific examples include SiO, TiO, and AlO. In the present invention, semimetals in the periodic table, such as "Si," are included in the metals.

[0061] Metals include Fe and metal alloys (stainless steel, etc.), which can be used as metallic supports.

[0062] Examples of solid carbon materials include silicon carbide (SiC), activated carbon, graphite, diamond, fullerene, carbon nanotubes, graphene, and amorphous carbon.

[0063] The shape and size of the carrier can be changed depending on the form of use and are not particularly limited. For example, the carrier may be in the form of a sheet, film, or plate. The size of the carrier may be nano-sized, and may be 1 μm or more, 1 mm or more, or 1 cm or more. The carrier may be, for example, a nanosheet (e.g., about 1 nm to 100 nm thick).

[0064] The complex of the present invention contains iron atoms in a low valence state, is stable under atmospheric conditions, and has catalytic activity as a reduction catalyst.

[0065] The composite of the present invention is not particularly limited and can be produced depending on the type of support. An example of an embodiment is a method for producing a composite in which iron carbide nanoparticles are allowed to stand or fixed on a support. The method for fixing the iron carbide nanoparticles on the support is not particularly limited and may be, for example, a heat treatment or a pressure bonding treatment. The heating temperature may be, for example, 100°C or lower. The support may be, for example, a solid support (e.g., sheet-shaped) that is sufficiently larger in size than the iron carbide nanoparticles.

[0066] Because the iron carbide nanoparticles of the present invention have excellent adsorption ability, any known method for supporting the nanoparticles on a carrier can be used without any particular limitations. The method for producing any of the composites is also not particularly limited, and may involve, for example, heat treatment. The heating temperature may be, for example, 150°C or less, or 120°C or less.

[0067] The organic solvent used in the method for producing the composite is not particularly limited, and a polar organic solvent or a non-polar organic solvent can be used. The organic solvent may be used alone or in combination of two or more kinds.

[0068] Examples of organic solvents that can be used in the method for producing a composite include: non-aromatic hydrocarbon solvents (e.g., alkanes such as pentane, hexane, heptane, octane, nonane, decane, dodecane, isododecane, and tridecane; cycloalkanes such as cyclohexane and methylcyclohexane; decahydronaphthalene; and liquid paraffin); aromatic hydrocarbon solvents (e.g., benzene, toluene, xylene, diethylbenzene, mesitylene, tetralin, indene, naphthalene, and methylnaphthalene); halogenated hydrocarbon solvents (e.g., dichloromethane, dichloroethane, chloroform, and chlorobenzene); and alcohol solvents (e.g., monohydric alcohols such as ethanol, propanol, 1-butanol, 2-butanol, 1-heptanol, 2-heptanol, 3-heptanol, 1-hexanol, 2-hexanol, benzyl alcohol, and oleyl alcohol; and polyhydric alcohols such as ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, and glycerin). ether solvents (e.g., diethyl ether, diisopropyl ether, methyl t-butyl ether, diisoamyl ether, ethylene glycol derivatives (e.g., monoglyme (ethylene glycol dimethyl ether), methyl cellosolve, diethyl cellosolve, diglyme, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, triglyme, tetraglyme, diethylene glycol monobutyl ether, triethylene glycol monomethyl ether, ethylene glycol monobenzyl ether, ethylene glycol monophenyl ether, diethylene glycol monobenzyl ether, poly(ethylene glycol) monomethyl ether), propylene glycol derivatives (e.g., 3-etherol propylene glycol monopropyl ether, dipropylene glycol monoethyl ether, tripropylene glycol monomethyl ether), 1,1-dimethoxycyclohexane, phenetole, veratrole, dioxane, tetrahydrofuran); Ester solvents (e.g., ethyl acetate, butyl acetate, isopropyl acetate, 3-methoxy-3-methylbutyl acetate, dimethyl carbonate, diethyl malonate, ethylene carbonate, propylene carbonate, γ-butyrolactone, α-acetyl-γ-butyrolactone);Examples of suitable solvents include ketone solvents (e.g., acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, acetophenone, propiophenone, and isophorone); sulfur-containing solvents (e.g., dimethyl sulfoxide, sulfolane, and diphenyl sulfide); and nitrogen-containing solvents (e.g., amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, 1,3-dimethyl-2-imidazolidinone, N,N-dimethylacrylamide, N,N-dimethylacetoacetamide, N,N-diethylformamide, N,N-diethylacetamide, hexamethylphosphoramide, and methylpyrrolidone, amine solvents such as triethanolamine, and nitrile solvents such as acetonitrile and benzonitrile; nitro solvents such as nitrobenzene and o-nitrotoluene; and quinoline, tetrahydroquinoline and dimethylimidazolidinone).

[0069] Another embodiment of the present invention relates to a method for producing iron carbide nanoparticles.

[0070] The method for producing iron carbide nanoparticles of the present invention includes adding an iron compound and a hydride reducing agent to an alcohol solvent to form a mixture, and heating the mixture at a temperature of less than 300°C in the presence of a carbon source gas, wherein the iron compound is iron(III) acetylacetonate, iron(II) acetylacetonate, or iron(III) chloride, and the carbon source gas is CO gas or CO gas.

[0071] The method for producing iron carbide nanoparticles of the present invention does not require other additives such as surfactants (for example, amine compounds such as alkylamines).

[0072] In the method for producing iron carbide nanoparticles of the present invention, the iron compound used as the iron source can be selected depending on the type of iron carbide nanoparticles desired. The iron compounds may be used alone or in combination. However, when producing FeC nanoparticles, iron(III) acetylacetonate is preferred. When producing FeC nanoparticles, iron(II) acetylacetonate or iron(III) chloride is preferred. The method for producing iron carbide nanoparticles of the present invention can selectively produce the desired iron carbide nanoparticles without using Fe(CO) which is toxic, unstable, and difficult to obtain.

[0073] Examples of hydride reducing agents include borohydride compounds such as potassium borohydride (KBH), sodium borohydride (NaBH), lithium borohydride (LiBH), and lithium triethylborohydride (LiTEBH); aluminum hydride compounds such as lithium aluminum hydride (LiAlH) and sodium tetrahydridoaluminate (NaAlH); and hydrazine (NH), among which borohydride compounds are preferred. One hydride reducing agent may be used alone, or two or more may be used in combination. The hydride reducing agent can be appropriately changed depending on the combination with the solvent.

[0074] The amount of the hydride reducing agent used may be 0.05 to 20 equivalents (molar equivalents), 0.1 to 15 equivalents, or 0.5 to 13 equivalents relative to the amount of the iron compound used.

[0075] From the viewpoint of reactivity, the solvent is preferably one that can dissolve both the iron compound and the hydride reducing agent, and more preferably one that can dissolve both the iron compound and the hydride reducing agent and has a high boiling point. In consideration of the above, the solvent is preferably an alcohol solvent.

[0076] Examples of alcohol solvents include monohydric alcohols such as ethanol, propanol, 1-butanol, 2-butanol, 1-heptanol, 2-heptanol, 3-heptanol, 1-hexanol, 2-hexanol, benzyl alcohol, and oleyl alcohol; and polyhydric alcohols such as ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, tetraethylene glycol, hexylene glycol, 1,5-pentanediol, 1,6-hexanediol, 1,2,6-hexanetriol, 1,2,4-butanetriol, 1,2,3-butanetriol, and glycerin. Polyhydric alcohols are preferred because they are capable of dissolving both the iron compound and the hydride reducing agent and have a high boiling point, thereby providing excellent reactivity. Dihydric alcohols are more preferred because they provide even better reactivity. One type of alcohol solvent may be used alone, or two or more types may be used in combination.

[0077] Examples of the carbon source gas include CO gas or CO2 gas. The carbon source gas used as the carbon source can be selected depending on the type of iron carbide nanoparticles to be produced. When producing Fe7C3 nanoparticles, CO gas is preferred as the carbon source gas because it is easy to produce Fe7C3 nanoparticles in a single phase. When producing Fe5C2 nanoparticles, CO2 gas is preferred as the carbon source gas because it is easy to produce Fe5C2 nanoparticles in a single phase.

[0078] The gas pressure of the carbon source gas is preferably 0.1 MPa or more. The gas pressure of the carbon source gas can be selected depending on the type of iron carbide nanoparticles desired. When producing FeC nanoparticles, the CO gas pressure is preferably 0.2 MPa or more. When producing FeC nanoparticles, the CO gas pressure may be 8 MPa or less, 4 MPa or less, or 2 MPa or less. When producing FeC nanoparticles, the CO gas pressure is preferably 0.1 MPa or more. When producing FeC nanoparticles, the CO gas pressure is preferably less than 0.2 MPa. The upper limit of the gas pressure of the carbon source gas is not particularly limited, but may be 8 MPa or less, or 4 MPa or less.

[0079] In the method for producing iron carbide nanoparticles of the present invention, a mixture obtained by mixing an iron compound, a hydride reducing agent, and an alcohol solvent is heated in the presence of a carbon source gas at a temperature of less than 300°C (hereinafter also referred to as the "heating step"). There are no particular limitations on the heat treatment, and it can be carried out using known methods and devices.

[0080] The heating temperature in the heating step is less than 300°C, preferably 180 to 295°C, more preferably 190 to 290°C, and even more preferably 200 to 280°C.

[0081] The heating step is preferably carried out under stirring, as this promotes the reaction and allows for easier production of the iron carbide nanoparticles of the present invention. In the method for producing iron carbide nanoparticles of the present invention, gas substitution using a carbon source gas (gas substitution can be performed to create an oxygen-free atmosphere from atmospheric conditions) can prevent iron from reacting with oxygen, so while this is not essential, in a preferred embodiment, the heating step may be carried out under vacuum or in an inert gas atmosphere, as this prevents iron from reacting with oxygen and allows for easier production of the iron carbide nanoparticles of the present invention. In either case, the heating step is preferably carried out in the absence of oxygen. Examples of inert gases include argon gas and nitrogen gas.

[0082] The reaction time (heating time) in the heating step is not particularly limited and can be appropriately changed depending on the desired degree of carbonization of the iron carbide nanoparticles. The reaction time is, for example, preferably 2.5 to 50 hours, more preferably 3 to 40 hours, and even more preferably 4 to 30 hours.

[0083] The rate of temperature increase when the temperature is increased to the temperature of the heating step after mixing the iron compound is not particularly limited and can be appropriately changed depending on the desired degree of carbonization of the iron carbide nanoparticles. For example, the rate of temperature increase can be set low to allow the reaction to proceed slowly. The rate of temperature increase is preferably 5 to 150°C / min, more preferably 10 to 100°C / min, and even more preferably 12 to 90°C / min.

[0084] The method for producing iron carbide nanoparticles of the present invention preferably further includes a washing step. An organic solvent can be used as the washing solution used in the washing step. The organic solvent is not particularly limited, and examples thereof include the same organic solvents as those used in the above-mentioned method for producing a composite. One organic solvent may be used alone, or two or more organic solvents may be used in combination. When two or more organic solvents are used in combination, the mixing ratio is not particularly limited, and for example, ethanol and chloroform can be used in a volume ratio of 1:1. An example of the washing step is a method in which the product obtained after the heating step is centrifuged using the organic solvent.

[0085] After the washing step, if necessary, the iron carbide nanoparticles may be dried in a vacuum to obtain powdered iron carbide nanoparticles.

[0086] Another embodiment of the present invention relates to a reduction catalyst comprising any one of the iron carbide nanoparticles described above. Reduction reactions using the reduction catalyst include, for example, hydrogenation reactions.

[0087] In some embodiments, the reduction catalyst of the present invention may contain only iron carbide nanoparticles. Iron carbide nanoparticles may be used as they are as a reduction catalyst. In other embodiments, the reduction catalyst of the present invention may contain iron carbide nanoparticles and a support, and the iron carbide nanoparticles and the support may form a composite.

[0088] The following describes an example in which the reduction catalyst of the present invention is used as a hydrogenation catalyst. Unless otherwise specified, the term "reduction catalyst" can be read as "hydrogenation catalyst" in this specification. One embodiment includes a hydrogenation catalyst containing any of the iron carbide nanoparticles described above. Another embodiment includes a hydrogenation catalyst containing any of the iron carbide nanoparticles described above and a support, wherein the iron carbide nanoparticles and the support form a composite. Note that the reduction catalyst is not limited to a hydrogenation catalyst.

[0089] In one embodiment, there is mentioned a method for producing an unsaturated alcohol compound, in which an α,β-unsaturated carbonyl compound is subjected to hydrogenation treatment using the hydrogenation catalyst described above to obtain an unsaturated alcohol compound.

[0090] A method for producing an unsaturated alcohol compound will be described below, taking as an example a case where the α,β-unsaturated carbonyl compound is an unsaturated aldehyde compound, in which the unsaturated aldehyde compound is hydrogenated using the hydrogenation catalyst (iron carbide nanoparticles (preferably FeC nanoparticles) or a composite containing iron carbide nanoparticles) to obtain an unsaturated alcohol compound.

[0091] Examples of the α,β-unsaturated carbonyl compound include an unsaturated aldehyde compound, an unsaturated ketone compound, an unsaturated carboxylic acid compound, and an unsaturated carboxylic acid ester compound.

[0092] Examples of unsaturated aldehyde compounds include unsaturated aliphatic aldehydes having 3 to 30 carbon atoms and unsaturated aromatic aldehydes having 9 to 30 carbon atoms. The unsaturated aliphatic aldehyde may be linear, branched, or cyclic. The unsaturated aliphatic aldehyde and the unsaturated aromatic aldehyde may be substituted or unsubstituted. The number of carbon atoms contained in the unsaturated aliphatic aldehyde is not particularly limited, but may be 3 to 20 or 3 to 15. The number of carbon atoms contained in the unsaturated aromatic aldehyde is not particularly limited, but may be 9 to 20 or 9 to 15.

[0093] Examples of the substituent include an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a halogen atom, a hydroxyl group, an amino group, a substituted amino group of an alkyl group having 1 to 6 carbon atoms, a formyl group, an acyl group, a cyano group, a nitro group, a sulfo group, an alkylthio group of an alkyl group having 1 to 6 carbon atoms, an azo group, and an azide group, among which an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, and a halogen atom are preferred. The number of substituents can be appropriately selected depending on the structure of the compound and may be, for example, 1 to 6, 1 to 4, or 1 to 3.

[0094] Examples of the unsaturated aldehyde compound include unsaturated aliphatic aldehydes such as 2-butenal, trans-2-hexenal, trans-2-heptenal, trans-2-octenal, trans-2-nonenal, trans-2-decenal, trans-2-undecenal, trans-2-dodecenal, trans-2-tridecenal, 2,4-heptadienal, 2,4-octadienal, 2,4-nonadienal, 2,6-nonadienal, 2,4-decadienal, 2,4-undecadienal, 2,4-dodecadienal, and 3-cyclohexene-1-carboxaldehyde; and unsaturated aromatic aldehydes such as cinnamaldehyde and 2-phenyl-5-methyl-2-hexenal.

[0095] Examples of unsaturated ketone compounds include unsaturated aliphatic ketones having 3 to 30 carbon atoms and unsaturated aromatic ketones having 10 to 30 carbon atoms. The unsaturated aliphatic ketones may be linear, branched, or cyclic. The unsaturated aliphatic ketones and unsaturated aromatic ketones may be substituted or unsubstituted. The number of carbon atoms contained in the unsaturated aliphatic ketones is not particularly limited, but may be 4 to 20 or 4 to 15. The number of carbon atoms contained in the unsaturated aromatic ketones is not particularly limited, but may be 10 to 20 or 10 to 15.

[0096] The substituents of the unsaturated aliphatic ketones and unsaturated aromatic ketones are the same as those exemplified for the substituents of the unsaturated aliphatic aldehydes and unsaturated aromatic aldehydes.

[0097] Examples of the unsaturated ketone compound include linear or branched unsaturated aliphatic ketones such as methyl vinyl ketone, mesityl oxide, methyl (1-cyclohexenyl) ketone, 3-penten-2-one, 3-methyl-3-penten-2-one, 4-methyl-3-penten-2-one, 2-cyclopenten-1-one, 3-methyl-2-cyclopentenone, 3-hexen-2-one, 3-methyl-3-hexen-2-one, 4-hexen-3-one, and 5-methyl-3-hexen-2-one; cyclic unsaturated aliphatic ketones such as 2-cyclohexen-1-one, 2-cyclohepten-1-one, and 2-cycloocten-1-one; and unsaturated aromatic ketones such as 1-phenyl-2-buten-1-one.

[0098] Examples of unsaturated carboxylic acid compounds include unsaturated aliphatic carboxylic acids having 4 to 30 carbon atoms and unsaturated aromatic carboxylic acids having 9 to 30 carbon atoms. The unsaturated aliphatic carboxylic acids may be linear, branched, or cyclic. The unsaturated aliphatic carboxylic acids and unsaturated aromatic carboxylic acids may be substituted or unsubstituted. The number of carbon atoms contained in the unsaturated aliphatic carboxylic acids is not particularly limited, but may be 4 to 20 or 4 to 15. The number of carbon atoms contained in the unsaturated aromatic carboxylic acids is not particularly limited, but may be 9 to 20 or 9 to 15.

[0099] The substituents of the unsaturated aliphatic carboxylic acid and the unsaturated aromatic carboxylic acid are the same as those exemplified for the substituents of the unsaturated aliphatic aldehyde and the unsaturated aromatic aldehyde.

[0100] Examples of the unsaturated carboxylic acid compound include linear or branched unsaturated aliphatic monocarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, tiglic acid, and angelic acid; linear or branched unsaturated aliphatic dicarboxylic acids such as fumaric acid and maleic acid; and unsaturated aromatic monocarboxylic acids such as coumaric acid, benzylidenemalonic acid, and 2-(bromomethyl)-2-phenylethene-1,1-dicarboxylic acid.

[0101] Examples of unsaturated carboxylic acid ester compounds include unsaturated aliphatic carboxylic acid esters having 5 to 30 carbon atoms and unsaturated aromatic carboxylic acid esters having 10 to 30 carbon atoms. The unsaturated aliphatic carboxylic acid esters may be linear, branched, or cyclic. The unsaturated aliphatic carboxylic acid esters and unsaturated aromatic carboxylic acid esters may be substituted or unsubstituted. The number of carbon atoms contained in the unsaturated aliphatic carboxylic acid esters is not particularly limited, but may be 5 to 20 or 5 to 15. The number of carbon atoms contained in the unsaturated aromatic carboxylic acid esters is not particularly limited, but may be 10 to 20 or 10 to 15.

[0102] The substituents possessed by the unsaturated aliphatic carboxylic acid ester and the unsaturated aromatic carboxylic acid ester are the same as those exemplified for the substituents possessed by the unsaturated aliphatic aldehyde and the unsaturated aromatic aldehyde.

[0103] Examples of unsaturated carboxylic acid compound esters include linear or branched unsaturated aliphatic carboxylic acid esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, and isobutyl methacrylate; and unsaturated aromatic monocarboxylic acid esters such as benzylidenemalonate and diethyl 2-(bromomethyl)-2-phenylethene-1,1-dicarboxylate.

[0104] The amount of the hydrogenation catalyst used is preferably 0.1 to 30 mol %, more preferably 0.5 to 25 mol %, and even more preferably 1.0 to 20 mol %, converted into the amount of Fe relative to 100 mol % of the substance amount of the α,β-unsaturated carbonyl compound, in order to have sufficient catalytic activity. Within the above ranges, the hydrogenation reaction proceeds sufficiently. In a preferred embodiment, the method for producing an unsaturated alcohol compound includes the step of using the hydrogenation catalyst in an amount of 2 to 25 mol %, converted into the amount of Fe, relative to 100 mol % of the substance amount of the α,β-unsaturated carbonyl compound, in order to have sufficient catalytic activity.

[0105] The hydrogenation treatment in the method for producing an unsaturated alcohol compound is preferably carried out under heating. The heating temperature is not particularly limited, but in order to carry out the treatment under milder conditions, it is preferably 200°C or lower, more preferably 60 to 200°C, even more preferably 80 to 190°C, and particularly preferably 100 to 180°C.

[0106] The reaction time is not particularly limited, and may be about 5 minutes to 60 hours, about 10 minutes to 30 hours, or about 20 minutes to 15 hours. Depending on the purpose, it may be set to 8 hours or less.

[0107] In the method for producing an unsaturated alcohol compound, it is preferable to carry out hydrogenation treatment under a predetermined hydrogen pressure. In the method for producing an unsaturated alcohol compound, the hydrogen pressure is preferably 8 MPa or less, and when carried out under milder conditions, it may be 5 MPa or less, 4.5 MPa or less, or 4.0 MPa or less. In addition, the hydrogen pressure is preferably 0.05 MPa or more, and more preferably 0.1 MPa or more.

[0108] In a preferred embodiment, a method for producing an unsaturated alcohol compound includes hydrogenation treatment under an inert gas atmosphere. Examples of inert gas include argon gas and nitrogen gas. When hydrogenation treatment is performed under an inert gas atmosphere rather than under a hydrogen atmosphere, the gas pressure is preferably 0.05 MPa or more, more preferably 0.1 MPa or more. The gas pressure is preferably 8 MPa or less, and when hydrogenation is performed under milder conditions, it may be 5 MPa or less, 4.5 MPa or less, or 4.0 MPa or less.

[0109] In the method for producing an unsaturated alcohol compound of the present invention, the hydrogenation treatment is preferably carried out in the presence of a solvent, from the viewpoints of excellent catalytic activity and tendency to high selectivity and yield. As the solvent, an alcohol solvent is preferred from the viewpoint of catalytic activity. Examples of the alcohol solvent include methanol, ethanol, n-propanol, 2-propanol, n-butanol, 2-butanol, and t-butanol.

[0110] In the method for producing an unsaturated alcohol compound, the hydrogenation reaction may be carried out in the presence of a base. By carrying out the hydrogenation reaction in the presence of a base, the yield of the unsaturated alcohol can be increased.

[0111] Examples of the base include, but are not limited to, organic bases ((a) tertiary amines, (b) nitrogen-containing aromatic heterocyclic compounds, (c) compounds having an imine skeleton (-C=N-C-) (in this specification, these compounds are also referred to as "imine bases")), (d) inorganic bases, and (e) tetraalkylammonium hydroxide. One type of base may be used alone, or two or more types may be used in combination.

[0112] (a) Examples of tertiary amines include trimethylamine, triethylamine, N-ethyldiisopropylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, trioctylamine, tridecylamine, triphenylamine, tribenzylamine, tris(2-ethylhexyl)amine, N,N-diisopropylethylamine, N,N-dimethyldecylamine, N-benzyldimethylamine, N-butyldimethylamine, N,N-dimethylcyclohexylamine, N,N,N',N'-tetramethylethylenediamine, N,N-dimethylaniline, N,N-diethylaniline, 1,4-diazabicyclo[2.2.2]octane, and N-methyl Examples of suitable amines include pyrrolidine, N-methylpiperidine, N-methylmorpholine, N-ethylmorpholine, N,N'-dimethylpiperazine, N-methylpyrrolidone, N-vinylpyrrolidone, bis(2-dimethylaminoethyl)ether, N,N,N,N',N''-pentamethyldiethylenetriamine, triethanolamine, tripropanolamine, dimethylethanolamine, dimethylaminoethoxyethanol, N,N-dimethylaminopropylamine, N,N,N',N',N''-pentamethyldipropylenetriamine, tris(3-dimethylaminopropyl)amine, tetramethyliminobis(propylamine), and N-diethylethanolamine.

[0113] (b) Examples of nitrogen-containing aromatic heterocyclic compounds include pyridine, 2,4,6-trimethylpyridine, 4-dimethylaminopyridine, lutidine, pyrimidine, pyridazine, pyrazine, oxazole, isoxazole, thiazole, isothiazole, imidazole, 1,2-dimethylimidazole, 3-(dimethylamino)propylimidazole, pyrazole, furazan, quinoline, isoquinoline, purine, 1H-indazole, quinazoline, cinnoline, quinoxaline, phthalazine, Examples include pteridine, phenanthridine, 2,6-di-t-butylpyridine, 2,2'-bipyridine, 4,4'-dimethyl-2,2'-bipyridyl, 5,5'-dimethyl-2,2'-bipyridyl, 6,6'-t-butyl-2,2'-dipyridyl, 4,4'-diphenyl-2,2'-bipyridyl, 1,10-phenanthroline, 2,7-dimethyl-1,10-phenanthroline, 5,6-dimethyl-1,10-phenanthroline, and 4,7-diphenyl-1,10-phenanthroline.

[0114] (c) Examples of imine bases include 1,8-diazabicyclo[5.4.0]undec-7-ene (diazabicycloundecene), 1,5-diazabicyclo[4.3.0]non-5-ene, and the like.

[0115] (d) Examples of inorganic bases include hydrides of alkali metals or alkaline earth metals (sodium hydride, potassium hydride, lithium hydride, calcium hydride, etc.), hydroxides of alkali metals or alkaline earth metals (sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, etc.), carbonates of alkali metals or alkaline earth metals (sodium carbonate, potassium carbonate, lithium carbonate, calcium carbonate, etc.), hydrogen carbonates of alkali metals (sodium hydrogen carbonate, potassium hydrogen carbonate, lithium hydrogen carbonate, etc.), oxides of alkali metals or alkaline earth metals (lithium oxide, sodium oxide, potassium oxide, Examples of the alkali metal alkoxide include lithium fluoride, sodium fluoride, potassium fluoride, cesium fluoride, magnesium fluoride, calcium fluoride, cesium chloride, and the like; alkali metal alkoxides (lithium methoxide, sodium methoxide, potassium methoxide, lithium ethoxide, sodium ethoxide, potassium ethoxide, lithium isopropoxide, sodium isopropoxide, potassium isopropoxide, lithium tert-butoxide, sodium tert-butoxide, and potassium tert-butoxide); and the like.

[0116] (e) Examples of tetraalkylammonium hydroxides include tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetra-n-propylammonium hydroxide, and tetra-n-butylammonium hydroxide.

[0117] The amount of the base used is preferably 0.01 to 10 mol, more preferably 0.02 to 8 mol, and even more preferably 0.05 to 4 mol, per mol of the α,β-unsaturated carbonyl compound.Within the above range, the hydrogenation reaction proceeds sufficiently.

[0118] The present invention includes embodiments in which some or all of the above configurations are combined in various ways within the scope of the technical idea of ​​the present invention, as long as the effects of the present invention are achieved.

[0119] Next, the present invention will be explained in more detail by way of examples, but the present invention is not limited to these examples in any way, and many modifications within the technical scope of the present invention are possible by those skilled in the art.

[0120] [Example 1: FeC nanoparticles] <Example 1-1> FeC nanoparticles were produced by the following method: First, 2 mmol of iron(III) acetylacetonate and 20 mmol of KBH were added to 60 mL of tetraethylene glycol in a stainless steel autoclave equipped with a glass inner cylinder to prepare a mixed solution, which was then heated to 280°C at a rate of 14°C / min, purged with CO gas, pressurized to 0.2 MPa, and heated at 280°C for 4 hours in a CO gas atmosphere of 0.2 MPa to cause a reaction.

[0121] The mixture was cooled to room temperature, and the product was washed with ethanol and chloroform and dried under vacuum to isolate the FeC nanoparticles. The obtained FeC nanoparticles were evaluated by the following method.

[0122] <Electron Microscope Observation of FeC Nanoparticles> The FeC nanoparticles obtained in Example 1-1 were observed using a field emission transmission electron microscope (trade name "Tecnai (registered trademark) G2 20ST", acceleration voltage: 200 kV, manufactured by FEI (now Thermo Fisher Scientific (US))). The results are shown in Figure 1. Furthermore, it was confirmed from the XRD pattern of the FeC nanoparticles obtained in Example 1-1 that hexagonal crystals of FeC were obtained.

[0123] <Powder X-ray diffraction measurement of FeC nanoparticles> The FeC nanoparticles obtained in the examples were subjected to X-ray diffraction measurement under atmospheric conditions using a fully automatic multipurpose X-ray diffractometer (trade name "Philips X'PERT MPD diffractometer", manufactured by Philips Japan Co., Ltd.) with CuKα radiation (λ: 1.5405 Å) and approximately 10 mg of sample placed on a glass sample plate under the following conditions without pretreatment. The results are shown in Figure 2. [Measurement conditions] Tube voltage: 45 kV Tube current: 40 mA Measurement temperature: room temperature Measurement angle range: 20.00 to 70.00° Sampling interval: 0.013° Scan rate: 0.42° / min

[0124] As shown in Figure 2, in powder X-ray diffraction measurements of the FeC nanoparticles obtained in the examples using CuKα radiation in the presence of oxygen, the maximum intensity was observed for the peak corresponding to the (211) plane of FeC (diffraction angle (2θ): 44.9°). Characteristic peaks corresponding to the (210), (102), (301), (202), and (220) planes of FeC (diffraction angles (2θ): 39.9°, 42.6°, 50.1°, 50.5°, and 53.2°) were also observed. The method for producing iron carbide nanoparticles of the present invention enabled the production of single-phase FeC nanoparticles under mild conditions of less than 300°C.

[0125] Example 1-2 FeC nanoparticles were produced in the same manner as in Example 1-1, except that the amount of KBH was changed to 50 mmol and a 0.1 MPa CO gas atmosphere was used instead of a CO gas atmosphere. Powder X-ray diffraction measurements were performed on the obtained FeC nanoparticles in the same manner as in Example 1-1. The results are shown in Figure 3. Figure 3 confirms that by changing the carbon source gas, FeC nanoparticles and FeC nanoparticles can be easily produced separately.

[0126] Example 1-3 FeC nanoparticles were produced in the same manner as in Example 1-1, except that iron (III) acetylacetonate was replaced with iron (II) acetylacetonate. Powder X-ray diffraction measurements were performed on the obtained FeC nanoparticles in the same manner as in Example 1-1. The results are shown in Figure 5. A peak for FeC was confirmed in Figure 5.

[0127] From FIG. 5, it was confirmed that by changing the iron compound, it is possible to easily produce Fe7C3 nanoparticles and Fe5C2 nanoparticles separately.

[0128] Example 1-4 FeC nanoparticles were produced in the same manner as in Example 1-1, except that iron(III) acetylacetonate was replaced with iron(III) chloride. Powder X-ray diffraction measurements were performed on the obtained FeC nanoparticles in the same manner as in Example 1-1. The results are shown in Figure 6. In Figure 6, a peak for FeC was confirmed.

[0129] Example 1-5 FeC nanoparticles were produced in the same manner as in Example 1-1, except that the heating temperature was changed from 280° C. to 240° C. As in Example 1-1, peaks corresponding to the (210), (102), (211), (301), (202), and (220) planes were observed.

[0130] Example 1-6 FeC nanoparticles were produced in the same manner as in Example 1-1, except that the heating temperature was changed from 280° C. to 200° C. As in Example 1-1, peaks corresponding to the (210), (102), (211), (301), (202), and (220) planes were observed.

[0131] Comparative Example 1-1 Particles were produced in the same manner as in Example 1-1, except that iron(III) acetylacetonate was replaced with iron(III) stearate. Powder X-ray diffraction measurement was performed on the obtained particles in the same manner as in Example 1-1. The results are shown in FIG.

[0132] Comparative Example 1-2 Particles were produced in the same manner as in Example 1-1, except that iron (III) acetylacetonate was replaced with iron 1,3,5-benzenetricarboxylate (product name "Basolite (registered trademark) F300", manufactured by BASF Japan Ltd.). Powder X-ray diffraction measurement was carried out on the obtained particles in the same manner as in Example 1-1. The results are shown in FIG. 4.

[0133] Comparative Example 1-3 Particles were produced in the same manner as in Example 1-1, except that iron (III) acetylacetonate was changed to ferrocene (Fe(C5H5)2). Powder X-ray diffraction measurement was carried out on the obtained particles in the same manner as in Example 1-1. The results are shown in FIG.

[0134] As shown in FIG. 4, FeC nanoparticles could be produced by using iron(III) acetylacetonate, but FeC nanoparticles could not be produced when other iron compounds were used.

[0135] Comparative Example 1-4 Particles were produced in the same manner as in Example 1-1, except that iron (III) acetylacetonate was replaced with iron (II) phthalocyanine. Powder X-ray diffraction measurement was performed on the obtained particles in the same manner as in Example 1-1. The results are shown in FIG.

[0136] As shown in FIG. 5, Fe5C2 nanoparticles and Fe7C3 nanoparticles could not be produced using iron(II) phthalocyanine.

[0137] Comparative Example 1-5 Particles were produced in the same manner as in Example 1-1, except that iron (III) acetylacetonate was replaced with iron (III) nitrate. Powder X-ray diffraction measurement was performed on the obtained particles in the same manner as in Example 1-1. The results are shown in FIG.

[0138] Comparative Example 1-6 Particles were produced in the same manner as in Example 1-1, except that iron(III) acetylacetonate was replaced with iron(III) oxide. Powder X-ray diffraction measurement was performed on the obtained particles in the same manner as in Example 1-1. The results are shown in FIG.

[0139] As shown in FIG. 6, Fe5C2 nanoparticles and Fe7C3 nanoparticles could not be produced using iron(III) nitrate or iron(III) oxide.

[0140] [Example 2: Composite] <Example 2-1: Composite of FeC Nanoparticles and ZrO> A composite was produced using the FeC nanoparticles produced in Example 1-1 and ZrO as a carrier. Specifically, 40 mg of the FeC nanoparticle powder produced in Example 1-1 was dissolved in toluene to obtain a solution. The resulting solution was ultrasonicated at room temperature for 1 hour and further stirred. Next, 1 g of ZrO having an average particle size ranging from 1 μm to 5 μm was added to the solution, and the mixture was stirred at 25°C for 6 hours. After filtration and vacuum drying, a composite of FeC nanoparticles and ZrO was obtained. The average particle size of ZrO can be calculated using a laser diffraction scattering method. Specifically, for example, it can be measured on a volume basis using a laser diffraction particle size distribution analyzer (SALD-2300: manufactured by Shimadzu Corporation) using a 0.2% aqueous sodium hexametaphosphate solution as a dispersion medium.

[0141] Example 2-2: Composite of FeC nanoparticles and SiO A composite of FeC nanoparticles and SiO was obtained in the same manner as in Example 2-1, except that SiO having an average particle size in the range of 0.01 μm to 1 μm was used instead of ZrO. The average particle size of SiO was measured in the same manner as the average particle size of ZrO.

[0142] Example 3: Production of Cinnamyl Alcohol Example 3-1 Cinnamyl alcohol was produced by hydrogenating cinnamaldehyde using the FeC nanoparticles of Example 1-1 as a catalyst. Specifically, 12.2 mg of the FeC nanoparticles of Example 1-1 (Fe content: 0.2 mmol (Fe content: 20 mol% relative to 100 mol% of cinnamaldehyde)), 10 ml of methanol, 1 mmol of cinnamaldehyde, and hydrogen gas were placed in an autoclave, pressurized to 4 MPa, heated to 150°C, and reacted for 1 hour. The results are shown in Table 1 below.

[0143] Examples 3-2 to 3-4 Cinnamyl alcohol was produced in the same manner as in Example 3-1, except that the type of catalyst used was changed to that produced in Examples 2-1 and 2-2, and the reaction time was changed as shown in Table 1 below. The composites of Examples 3-2 and 3-3 used the composite obtained in Example 2-1, and the composite of Example 3-4 used the composite obtained in Example 2-1. The results are shown in Table 1 below.

[0144]

[0145] As shown in Table 1, it was confirmed that the FeC nanoparticles produced in Example 1-1 have catalytic activity as a hydrogenation catalyst. Furthermore, as shown in Table 1, the composite of the present invention was able to selectively obtain the unsaturated alcohol cinnamyl alcohol (compound 2) from the α,β-unsaturated carbonyl compound cinnamaldehyde (compound 1), demonstrating significantly excellent catalytic activity as a hydrogenation catalyst. Furthermore, as shown in Table 1, it was confirmed that the composite of the present invention has significantly excellent catalytic activity even under mild conditions of 200°C or less.

[0146] Example 4: Production of Cinnamyl Alcohol Example 4-1 Cinnamyl alcohol was produced by hydrogenating cinnamaldehyde using the composite (nano-FeC / ZrO) produced in Example 2-1 as a catalyst. Specifically, 0.312 g of the composite (nano-FeC / ZrO) of Example 2-1 (0.2 mmol of Fe (20 mol% Fe relative to 100 mol% cinnamaldehyde)), 10 ml of tetrahydrofuran (THF), 1 mmol of cinnamaldehyde, and hydrogen gas were placed in an autoclave, pressurized to 4 MPa, heated to 150°C, and reacted for 3 hours. The yield was measured in the same manner as in Example 3-1. The results are shown in Table 2 below.

[0147] Examples 4-2 to 4-5 Cinnamyl alcohol was produced in the same manner as in Example 4-1, except that the type of solvent, type of gas, and pressure used were changed to those shown in Table 2 below. The yield was measured in the same manner as in Example 4-1. The yields of the obtained cinnamyl alcohols are shown in Table 2 below.

[0148]

[0149] From the above results, it was confirmed that the reduction catalyst (for example, hydrogenation catalyst) of the present invention has a wide range of catalytic activity when used in many solvents.

[0150] The iron carbide nanoparticles and composites of the present invention are useful as reduction catalysts in reduction reactions (e.g., hydrogenation reactions), and are particularly useful as hydrogenation catalysts in methods for producing amine compounds.

Claims

1. A reduction catalyst comprising iron carbide nanoparticles, the iron carbide nanoparticles being Fe7C3 nanoparticles or Fe5C2 nanoparticles, and the average particle diameter of the iron carbide nanoparticles being 30 nm or more and 800 nm or less.

2. The reduction catalyst according to claim 1, wherein the iron carbide nanoparticles consist solely of Fe7C3 nanoparticles.

3. The reduction catalyst according to claim 1 or 2, further comprising a support.

4. The reduction catalyst according to claim 3, wherein the support is at least one selected from the group consisting of polymers, chalcogen compounds, metal compounds, metals and solid carbon materials.

5. A complex comprising iron carbide nanoparticles and a carrier, the iron carbide nanoparticles comprising Fe7C3 nanoparticles or Fe5C2 nanoparticles, and the average particle diameter of the iron carbide nanoparticles is 30 nm or more and 800 nm or less.

6. The composite according to claim 5, wherein the support is at least one selected from the group consisting of polymers, chalcogen compounds, metal compounds, metals and solid carbon materials.

7. A method for producing an unsaturated alcohol compound, comprising hydrogenating an α,β-unsaturated carbonyl compound using the reduction catalyst according to claim 1 or 2 to obtain an unsaturated alcohol compound.

8. The method for producing an unsaturated alcohol compound according to claim 7, wherein the hydrogenation temperature is 200° C. or lower.

9. The method for producing an unsaturated alcohol compound according to claim 7, wherein the hydrogenation is carried out in the presence of a solvent.

10. A method for producing iron carbide nanoparticles according to claim 1 or 2, comprising adding an iron compound and a hydride reducing agent to a solvent to form a mixture, and heating the mixture at a temperature less than 300°C in the presence of a carbon source gas, wherein the iron compound is iron(III) acetylacetonate, iron(II) acetylacetonate or iron(III) chloride, and the carbon source gas is CO gas or CO2 gas.

11. The method for producing iron carbide nanoparticles according to claim 10, wherein the iron compound is iron(III) acetylacetonate, the carbon source gas is CO gas, the CO gas pressure is 0.1 MPa or more, and the iron carbide nanoparticles are Fe7C3 nanoparticles.

12. The method for producing iron carbide nanoparticles according to claim 11, wherein the heating time is from 2.5 to 50 hours.

13. The method for producing iron carbide nanoparticles according to claim 11, wherein the solvent is an alcohol solvent.

14. The method for producing iron carbide nanoparticles according to claim 11, which does not use a surfactant.

15. Fe7C3 nanoparticles having a hexagonal crystal phase, a spherical shape, and an average particle size of 30 nm or more and 800 nm or less.

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