Metal oxide nanoparticle colloidal dispersion

Abstract

The present invention provides metal oxide nanoparticles with excellent properties. Furthermore, it provides an effective method and apparatus for producing H2, hydrocarbons, and / or alcohols using a metal oxide nanoparticle colloidal dispersion as a catalyst. [Solution] A metal oxide nanoparticle colloidal dispersion is disclosed, comprising metal oxide nanoparticles containing a first metal oxide and a second metal oxide, and a capping agent. A method for producing H2, hydrocarbons, and / or alcohols using the metal oxide nanoparticle colloidal dispersion as a catalyst is also disclosed. Furthermore, an apparatus for producing H2, hydrocarbons, and / or alcohols is disclosed, comprising an electrolytic cell containing the metal oxide nanoparticle colloidal dispersion.

Description

[Technical Field]

[0001] This disclosure relates to a metal oxide nanoparticle colloidal dispersion. It also relates to a method for producing H2, hydrocarbons, and / or alcohols using a metal oxide nanoparticle colloidal dispersion as a catalyst. Furthermore, it relates to an apparatus for producing H2, hydrocarbons, and / or alcohols, which includes an electrolytic cell containing a metal oxide nanoparticle colloidal dispersion. [Background technology]

[0002] Metal oxide nanoparticle colloidal dispersions are used in various industrial fields. For example, Patent Document 1 describes a metal nitride nanoparticle dispersion that can be used for lighting applications. Patent Document 2 describes an aqueous dispersion colloid of metal hydroxide that can be used as a catalyst, coating agent, cosmetic, resin compounding agent, and photofunctional material. Patent Document 3 describes a metal oxide dispersion used in hard masks. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-111493 [Patent Document 2] Japanese Patent Publication No. 2011-121786 [Patent Document 3] Japanese Patent Publication No. 2024-2087 [Overview of the project] [Problems that the invention aims to solve]

[0004] This disclosure aims to provide a metal oxide nanoparticle colloidal dispersion having excellent properties. Another objective is to provide an effective method for producing H2, hydrocarbons, and / or alcohols using the metal oxide nanoparticle colloidal dispersion as a catalyst. Yet another objective is to provide an apparatus for producing H2, hydrocarbons, and / or alcohols, which includes an electrolytic cell containing the metal oxide nanoparticle colloidal dispersion. [Means for solving the problem]

[0005] The inventors discovered that a metal oxide nanoparticle colloidal dispersion with excellent properties can be obtained by reacting a metal carboxylic acid with a higher alcohol in a solvent to produce metal oxide nanoparticles and a capping agent, thus completing the present invention. In other words, the present disclosure discloses, for example, the following aspects: [1] A metal oxide nanoparticle colloidal dispersion comprising metal oxide nanoparticles containing a first metal oxide and a second metal oxide, and a capping agent, wherein the first metal oxide is copper oxide and the second metal oxide is an oxide of a metal other than copper. [Brief explanation of the drawing]

[0006] [Figure 1] Figure 1 shows the fast Fourier transform (FFT) patterns of the transmission electron image and lattice image obtained by transmission electron microscopy (TEM) of the metal oxide nanoparticle colloidal dispersion. The metal oxide nanoparticle colloidal dispersion was prepared using a reaction solvent to which 0.0 vol% (Vol%) (Example 3), 0.0067 vol% (Example 4), or 0.033 vol% (Example 5) of H2O was added. [Figure 2] Figure 2 shows the production rates of ethanol, ethylene, and carbon monoxide generated from carbonate ions using a metal oxide nanoparticle colloidal dispersion as a catalyst. The production rate is the percentage of moles of ethanol, ethylene, or carbon monoxide relative to the number of moles of K2CO3 added to the electrolyte as a carbonate ion source. The metal oxide nanoparticles are those from Example 8 (Zn / (Cu+Zn)=0), Example 7 (Zn / (Cu+Zn)=0.09), Example 6 (Zn / (Cu+Zn)=0.33), or Example 3 (Zn / (Cu+Zn)=0.5). [Figure 3] Figure 3 shows the FT-IR spectrum of the metal oxide nanoparticle colloidal dispersion. The metal oxide nanoparticles are those from Example 3. [Figure 4]Figure 4 shows the powder X-ray diffraction (XRD) pattern of the metal oxide nanoparticle colloidal dispersion. The horizontal axis represents the diffraction angle 2θ (2θ (degrees)), and the vertical axis represents the intensity (intensity (cps)). The metal oxide nanoparticles are those of Example 3. Peaks thought to originate from copper oxide (Cu2O), zinc oxide (ZnO), and copper (Cu) are indicated by *, +, and -, respectively. [Figure 5] Figure 5 shows the optical properties of the metal oxide nanoparticle colloidal dispersion. The metal oxide nanoparticles are those from Example 8 (Zn / (Cu+Zn)=0), Example 7 (Zn / (Cu+Zn)=0.09), Example 6 (Zn / (Cu+Zn)=0.33), or Example 3 (Zn / (Cu+Zn)=0.5). A is a photograph of the metal oxide nanoparticle colloidal dispersion. The concentrations of zinc oleate (M), copper oleate (M), and H2O (volume %) contained in the metal oxide nanoparticles are shown in the figure. B is the optical spectrum of the metal oxide nanoparticle colloidal dispersion. The horizontal axis is wavelength (nm), and the vertical axis is absorption. [Figure 6] Figure 6 shows the structural model of metal oxide nanoparticles. Peaks thought to originate from zinc oxide (ZnO), copper plasmon (Cu plasmon), and copper oxide plasmon (Cu2O plasmon) are shown in the figure. [Modes for carrying out the invention]

[0007] One embodiment of the present disclosure will be described in detail below, but the scope of the present disclosure is not limited to the embodiment described herein, and various modifications can be made without departing from the spirit of the present disclosure. Each embodiment disclosed herein can be combined with any other features disclosed herein. If multiple upper and lower limits are given for a particular parameter, any combination of these upper and lower limits can be used to create a suitable numerical range. The lower and / or upper limits of the numerical ranges described herein may be replaced with numerical values ​​within that range, as shown in the examples. The expression "X~Y" indicating a numerical range means "X or greater and Y or less". If a particular description given for one embodiment also applies to other embodiments, that description may be omitted in the other embodiments.

[0008] [Colloidal dispersion of metal oxide nanoparticles containing metal oxide nanoparticles and a capping agent] In one embodiment, a metal oxide nanoparticle colloidal dispersion is disclosed, comprising metal oxide nanoparticles containing a first metal oxide and a second metal oxide, and a capping agent, wherein the first metal oxide is copper oxide and the second metal oxide is an oxide of a metal other than copper. Metal oxide nanoparticle colloidal dispersions tend to have excellent catalytic activity and can be suitably used, for example, as catalysts in the production methods of H2, hydrocarbons, and / or alcohols described later.

[0009] (Metal oxides) Metal oxides are compounds formed by the bonding of a metal atom and an oxygen atom. They are also called metal oxides. For example, when the metal atom is copper or zinc, the metal oxide is also called copper oxide or zinc oxide, respectively. The first metal oxide is copper oxide, and the second metal oxide is an oxide of a metal other than copper. The metal other than copper may be any metal within the range in which the effects of the invention can be obtained, but preferably it is a metal atom other than copper that is a group 3 to 15 element, more preferably Zn, Fe, Ni, Co, or Zr, and particularly preferably Zn, Fe, or Ni. That is, the second metal oxide may be zinc oxide, iron oxide, nickel oxide, cobalt oxide, or zirconium oxide, and may be zinc oxide, iron oxide, or nickel oxide.

[0010] In the first and second metal oxides, the metal atoms may be bonded to oxygen atoms bonded to the acyl group, but it is preferable that they be bonded to at least one oxygen atom other than the oxygen atom bonded to the acyl group. The acyl group is the remaining atomic group after removing the OH group from the carboxyl group (-COOH) of the carboxylic acid, as described later. That is, the acyl group may preferably be a C6-C24, more preferably a C12-C22, and particularly preferably a C16-C20 acyl group. The carboxylic acid may be an acyl group having an aliphatic hydrocarbon group or an aromatic hydrocarbon group, and preferably an acyl group having an aliphatic hydrocarbon group. The aliphatic hydrocarbon group may be saturated or unsaturated, linear, branched or cyclic, and / or substituted or unsubstituted aliphatic hydrocarbon group. The aromatic hydrocarbon group may be a substituted or unsubstituted aromatic hydrocarbon group. For example, the acyl group may be a saturated or unsaturated C16-C20 aliphatic linear acyl group. Non-limiting examples of acyl groups include hexanenoyl, heptanol, octanoyl, nonanoyl, decanoyl, undecanoyl, dodecanoyl, tridecanoyl, hexadecanoyl, pentadecanoyl, hexadecanoyl, heptadecanoyl, octadecanoyl, oleinoyl, nonadecanoyl, eicosanoyl, henicosanoyl, docosanoyl, tricosanoyl, and tetracosanoyl groups. In a metal oxide, when a metal atom binds to at least one oxygen atom other than the oxygen atom bonded to an acyl group, the at least one oxygen atom may be an oxygen atom contained in a hydroxy group or may be an oxygen atom bonded to another metal atom. Note that two or more metal oxides containing a metal that binds to an oxygen atom contained in a hydroxy group can be converted into a metal oxide containing two or more metal atoms bonded via an oxygen atom by a dehydration reaction.

[0011] (Metal oxide nanoparticles) Metal oxide nanoparticles may contain a first metal oxide and a second metal oxide in one particle, or may contain a first metal oxide and a second metal oxide in two or more particles. The particle size of metal oxide nanoparticles can be determined by a conventional method. For example, the particle size of metal oxide nanoparticles can be determined from a transmission electron microscope image of the metal oxide nanoparticles. In this case, in the transmission electron microscope image, the particle size can be determined based on the projected area criterion in which the diameter of a circle having the same area as the projected area of the particle is defined as the particle size. Also, the particle size of metal oxide nanoparticles can be determined as the average of the particle sizes of each particle in the transmission electron microscope image. The particle size of metal oxide nanoparticles is preferably 0.5 to 100 nm, more preferably 1 to 50 nm, and particularly preferably 2 to 30 nm. Also, the average of the particle sizes of metal oxide nanoparticles is preferably in the range of 0.5 to 100 nm, more preferably 1 to 50 nm, and particularly preferably 2 to 30 nm.

[0012] (Capping agent) A capping agent is a compound or group having an effect of dispersing metal oxide nanoparticles in a medium. The capping agent may contain an ester of a carboxylic acid and a higher alcohol described later, an acyl group bonded to a metal atom via an oxygen atom that may be contained in the above-described metal oxide, or both of them.

[0013] A carboxylic acid is a compound containing a hydrocarbon group and a carboxyl group, and may be any carboxylic acid within the range in which the effects of the present invention are obtained. The carboxylic acid may preferably be a C6-C24, more preferably a C12-C22, and particularly preferably a C16-C20 carboxylic acid. The carboxylic acid may also be an aliphatic or aromatic carboxylic acid, and is preferably an aliphatic carboxylic acid. An aliphatic carboxylic acid may contain saturated or unsaturated, linear, branched, or cyclic, and / or substituted or unsubstituted aliphatic hydrocarbon groups. An aromatic carboxylic acid may contain substituted or unsubstituted aromatic hydrocarbon groups. For example, the carboxylic acid may be a saturated or unsaturated C16-C20 linear carboxylic acid. Non-limiting examples of carboxylic acids include hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanonic acid, hexadecanic acid, pentadecanoic acid, hexadecanic acid, heptadecanic acid, octadecanoic acid, oleic acid, nonadecanic acid, eicosanoic acid, henicosanoic acid, docosanoic acid, tricosanoic acid, and tetracosanoic acid.

[0014] The higher alcohol is a compound containing a higher hydrocarbon group and a hydroxyl group, and may be any higher alcohol within the range in which the effects of the present invention are obtained. The higher alcohol may preferably be a C6-C24, more preferably a C12-C22, and particularly preferably a C16-C20 higher alcohol. The higher alcohol may also be an aliphatic or aromatic higher alcohol, and is preferably an aliphatic higher alcohol. The aliphatic higher alcohol may contain saturated or unsaturated, linear, branched, or cyclic, and / or substituted or unsubstituted aliphatic hydrocarbon groups. The aromatic higher alcohol may contain substituted or unsubstituted aromatic hydrocarbon groups. For example, the higher alcohol may be a saturated or unsaturated C16-C20 aliphatic linear alcohol. Non-limiting examples of higher alcohols include 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, 1-decanol, 1-undecanol, 1-dodecanol, 1-tridecanol, 1-hexadecanol, 1-pentadecanol, 1-hexadecanol, 1-heptadecanol, 1-octadecanol, oleyl alcohol, 1-nonadecanol, 1-icosanol, 1-henicosanol, 1-docosanol, 1-tricosanol, and 1-tetracosanol.

[0015] The ester of a carboxylic acid and a higher alcohol may be any combination of the carboxylic acid and the higher alcohol described above. For example, if the carboxylic acid is oleic acid and the higher alcohol is 1-dodecanol, the ester of the carboxylic acid and the higher alcohol is 1-dodecanyl oleate.

[0016] (Metal oxide nanoparticle colloidal dispersion) A metal oxide nanoparticle colloidal dispersion is a dispersion in which metal oxide nanoparticles are dispersed in a medium. The medium is preferably a liquid, and is preferably the first solvent described above or the second solvent described later. The metal oxide nanoparticle colloidal dispersion may or may not be fluid, and may be in the state of a liquid, gel, sol, or solid. Metal oxide nanoparticle colloidal dispersions can be suitably produced by the method for producing metal oxide nanoparticle colloidal dispersions described later.

[0017] (Infrared absorption spectrum) The metal oxide nanoparticle colloidal dispersion preferably has an infrared absorption spectrum of 700 to 1750 cm⁻¹. -1 , 1100~1200cm -1 , and / or 1200~1270cm -1 It has an absorption peak in the range of [this]. This absorption peak preferably indicates the presence of a carboxylic acid ester. A carboxylic acid ester refers to an ester of a carboxylic acid and an alcohol. In other words, this absorption peak indicates that the capping agent contained in the metal oxide nanoparticle colloidal dispersion contains an ester of a carboxylic acid and a higher alcohol.

[0018] (Powder X-ray diffraction (XRD) pattern) When the first metal oxide is copper oxide and / or the second metal oxide is zinc oxide, the metal oxide nanoparticle colloidal dispersion may preferably have three or more, more preferably five or more, and particularly preferably seven or more diffraction peaks in a powder X-ray diffraction (XRD) pattern with a CuKα source, where the diffraction angle 2θ is 31.2±0.2, 34.2±0.2, 36.8±0.2, 35.7±0.2, 43.6±0.2, 29.5±0.2, 44.1±0.2, or 50.7±0.2. Diffraction peaks with diffraction angles 2θ of 1.2±0.2, 34.2±0.2, or 36.8±0.2 may indicate the presence of zinc oxide (ZnO). Diffraction peaks with diffraction angles 2θ of 35.7±0.2, 43.6±0.2, or 29.5±0.2 may indicate the presence of copper oxide (Cu2O). Diffraction peaks with a diffraction angle 2θ of 44.1±0.2 or 50.7±0.2 may indicate the presence of copper (Cu). Colloidal dispersions of metal oxide nanoparticles exhibiting these diffraction peaks tend to have excellent catalytic activity.

[0019] (Structure of metal oxide nanoparticles) Metal oxide nanoparticles are A core containing metal, A first layer containing a first metal oxide surrounds the nucleus, A second layer containing the second metal oxide surrounds the first layer. Includes, The first metal oxide may be a metal oxide nanoparticle that is an oxide of the metal. Metal oxide nanoparticle colloidal dispersions having this structure tend to possess excellent properties, such as having excellent catalytic activity.

[0020] (Redox potential) The oxidation-reduction potential of the metal oxide nanoparticle colloidal dispersion is preferably -150 to -50 mV, more preferably -140 to -60 mV, and particularly preferably -130 to -70 mV. Metal oxide nanoparticle colloidal dispersions having the redox potential within the range described above tend to exhibit excellent catalytic activity.

[0021] (catalytic activity) The metal oxide nanoparticle colloidal dispersion may have catalytic activity. For example, when one or more raw materials selected from the group consisting of H2O, CO2, CO, and N2 are electrolyzed using the metal oxide nanoparticle colloidal dispersion as a catalyst, it may have catalytic activity to produce H2, hydrocarbons, and / or alcohols in preferably 10 mol% or more, more preferably 15 mol% or more, and particularly preferably 20 mol% or more relative to the raw materials. When CO2 is used as a raw material, the CO2 is preferably a carbonate (CO3 - It is converted into the form of an ion-containing salt before being subjected to electrolysis. Colloidal dispersions of metal oxide nanoparticles possessing such catalytic activity play a crucial role in reducing the cost of CO2 resource utilization or hydrogen production, which are seen as promising steps toward realizing a carbon-neutral society.

[0022] When a metal oxide nanoparticle colloidal dispersion is used as a catalyst for electrolysis, the metal oxide nanoparticle colloidal dispersion may be contained in the catalyst layer formed on the metal substrate as described above. Alternatively, the metal oxide nanoparticle colloidal dispersion may be present in the electrolyte containing the raw materials.

[0023] The hydrocarbon produced by this embodiment may be any hydrocarbon within the range in which the effects of the present invention are obtained, but is preferably a saturated or unsaturated aliphatic hydrocarbon of C1 to C6. Non-limiting examples of hydrocarbons produced by this embodiment include ethylene and methane. The alcohol produced in this embodiment may be any alcohol within the range in which the effects of the present invention are obtained, but is preferably a C1-C6 alcohol, more preferably a C1-C3 alcohol, and particularly preferably methanol or methanol.

[0024] When CO2 is used as a raw material, the metal oxide nanoparticle colloidal dispersion may have catalytic activity to produce alcohol (e.g., ethanol) in an amount of preferably 1 mol% or more, more preferably 15 mol% or more, and particularly preferably 20 mol% or more, relative to the raw material.

[0025] When CO2 is used as a raw material, the metal oxide nanoparticle colloidal dispersion may have catalytic activity to produce 0.5 mol% or more, more preferably 1 mol% or more, and particularly preferably 2 mol% or more of hydrocarbons (e.g., ethylene) relative to the raw material.

[0026] (Resistance of a substrate having a catalyst layer containing a metal oxide nanoparticle colloidal dispersion) A catalyst layer containing metal oxide nanoparticles can be formed by coating a metal oxide nanoparticle colloidal dispersion onto the surface of a metal substrate. The formation of this catalyst layer may reduce the resistance of the metal substrate to preferably 5Ω / □ or higher, more preferably 10Ω / □ or higher, and particularly preferably 15Ω / □ or higher. Furthermore, a substrate with a resistance of 20Ω / □ (e.g., a copper substrate) may have its resistance reduced to 0.1-5Ω / □, more preferably 0.2-2Ω / □, and particularly preferably 0.5-1.5Ω / □ by forming this catalyst layer. This catalyst layer can reduce the resistance of the metal substrate, thereby increasing the current flowing through the metal substrate. Therefore, by using a metal substrate having this catalyst layer as an electrode, the methods for producing H2, hydrocarbons, and / or alcohols described later can be effectively carried out.

[0027] (Molar ratio of the first and second metal oxides) The molar ratio of the second metal oxide to the sum of the first and second metal oxides ((number of moles of the second metal oxide) / (sum of the number of moles of the first and second metal oxides)) may be 0.0 to 1.0, 0.1 to 0.9, 0.2 to 0.8, or 0.3 to 0.7, preferably 0.0 to 1.0, more preferably 0.1 to 0.9, and particularly preferably 0.3 to 0.7. When the molar ratio falls within the range described above, the metal oxide nanoparticle colloidal dispersion tends to exhibit excellent catalytic activity. The molar ratio of the first metal oxide to the sum of the first and second metal oxides can be adjusted in the method for producing the metal oxide nanoparticle colloidal dispersion described later, by adjusting the molar ratio of the first carboxylic acid metal to the sum of the first and second carboxylic acid metals.

[0028] [Method for producing a metal oxide nanoparticle colloidal dispersion] In one embodiment, a method for producing a metal oxide nanoparticle colloidal dispersion is disclosed, which includes reacting a metal carboxylic acid with a higher alcohol in a first solvent to produce metal oxide nanoparticles and a capping agent.

[0029] (Carboxylic acid metals) The metal carboxylate is a compound in which a carboxylic acid and a metal are bonded, and may be any metal carboxylate within the range in which the effects of the present invention are obtained. The metal carboxylate includes a first metal carboxylate and a second metal carboxylate. The carboxylic acid is as described above. The first metal carboxylate may be any combination of the above-mentioned carboxylic acid and copper. For example, the metal carboxylate may be copper carboxylate, which is formed by bonding a C6-C24 aliphatic or aromatic carboxylic acid with copper; it may be metal carboxylate, which is formed by bonding a C12-C22 aliphatic or aromatic carboxylic acid with copper; or it may be metal carboxylate, which is formed by bonding a C16-C20 aliphatic or aromatic carboxylic acid with copper. A non-limiting example of the first metal carboxylate is copper oleate. In the second metal carboxylate, the metal is a metal other than copper and may be the same metal as the metal included in the second metal oxide described above. That is, the second metal carboxylate may be a metal carboxylate in which a C6-C24 aliphatic or aromatic carboxylic acid is bonded to a metal other than copper that is a group 3-15 element, or a metal carboxylate in which a C12-C22 aliphatic or aromatic carboxylic acid is bonded to Zn, Fe, Ni, Co, or Zr, or a metal carboxylate in which a C16-C20 aliphatic or aromatic carboxylic acid is bonded to Zn, Fe, or Ni. Non-limiting examples of the second metal carboxylate include zinc oleate, copper acetate, zinc citrate, iron acetate, and nickel citrate.

[0030] The molar ratio of the second carboxylic acid metal to the sum of the first carboxylic acid metal and the second carboxylic acid metal ((number of moles of the second carboxylic acid metal) / (sum of the number of moles of the first carboxylic acid metal and the number of moles of the second carboxylic acid metal)) may be 0.0 to 1.0, 0.1 to 0.9, 0.2 to 0.8, or 0.3 to 0.7, preferably 0.1 to 0.9, more preferably 0.2 to 0.8, and particularly preferably 0.3 to 0.7. When the molar ratio falls within the range described above, the amount or yield of the metal oxide nanoparticle colloidal dispersion tends to increase. Furthermore, when the molar ratio falls within the range described above, it is easier to obtain a metal oxide nanoparticle colloidal dispersion with excellent catalytic activity.

[0031] (First solvent) The first solvent may be any solvent within the range in which the effects of the present invention are obtained, but is preferably a solvent containing C3-C20, more preferably C6-C19, and particularly preferably C8-C18 aliphatic hydrocarbons, and / or aromatic hydrocarbons containing C5-C20, more preferably C6-C19, and particularly preferably C8-C18 aromatic hydrocarbons. The aliphatic hydrocarbons may be saturated or unsaturated, linear, branched or cyclic, and / or substituted or unsubstituted aliphatic hydrocarbons. The aromatic hydrocarbon groups may be substituted or unsubstituted aromatic hydrocarbons. For example, the first solvent may be a C8-C18 aliphatic unsaturated linear hydrocarbon. Non-limiting examples of the first solvent include solvents containing 1-octadecene, 1-octene, 1-dodecene, etc.

[0032] The first solvent may contain H2O. In this case, the first solvent contains H2O in an amount of preferably 0.001 to 0.2 volume%, more preferably 0.003 to 0.1 volume%, and particularly preferably 0.005 to 0.05 volume%, relative to the total volume. When the first solvent contains H2O in the proportions mentioned above, oxide nanoparticles with the desired particle size are easily obtained.

[0033] The higher alcohols, metal oxides, metal oxide nanoparticles, capping agents, and metal oxide nanoparticle colloidal dispersions are as described above.

[0034] (Reaction time) In the method for producing a metal oxide nanoparticle colloidal dispersion, the reaction time between the metal carboxylic acid and the higher alcohol can be arbitrarily set within the range in which the effects of the present invention can be obtained, but is preferably 5 to 120 minutes, more preferably 10 to 90 minutes, and particularly preferably 15 to 60 minutes.

[0035] (Reaction temperature) In the method for producing a metal oxide nanoparticle colloidal dispersion, the reaction temperature between the metal carboxylic acid and the higher alcohol can be arbitrarily set within the range in which the effects of the present invention can be obtained, but is preferably 100 to 500°C, more preferably 200 to 400°C, and particularly preferably 250 to 350°C.

[0036] (Amount produced) In the method for producing a metal oxide nanoparticle colloidal dispersion, the resulting metal oxide nanoparticle colloidal dispersion contains metal oxide nanoparticles at any concentration within the range in which the effects of the present invention can be obtained. For example, the metal oxide nanoparticle colloidal dispersion may contain metal oxide nanoparticles at a concentration of preferably 1 g / L or more, more preferably 5 g / L or more, particularly preferably 8 g / L or more, or 1 to 30 g / L, more preferably 5 to 25 g / L or more, particularly preferably 8 g / L to 20 g / L.

[0037] (Additional steps including precipitation / redissolution) A method for producing a metal oxide nanoparticle colloidal dispersion may include adding a poor solvent to the first solvent containing metal oxide nanoparticles and a capping agent to precipitate the metal oxide nanoparticles and the capping agent, and / or recovering the precipitated metal oxide nanoparticles and capping agent and dissolving them in a second solvent. By further including these steps, the method for producing a metal oxide nanoparticle colloidal dispersion becomes easier to use for preparing high-concentration metal oxide nanoparticle colloidal dispersions and for changing the solvent to one different from the one used during the reaction.

[0038] A poor solvent is a solvent with lower solubility for metal oxide nanoparticles and capping agents compared to the first solvent, and is not limited to the extent that the effects of the present invention can be obtained. For example, the poor solvent may be a C1-C6 hydrocarbon, ketone, ether, or alcohol. Non-limiting examples of poor solvents include acetone, isopropanol, and ethanol. The poor solvent is added to the first solvent in a volume sufficient to precipitate the metal oxide nanoparticles and the capping agent. For example, the poor solvent may be added to the first solvent in an amount preferably 1 to 15 times, more preferably 1.5 to 10 times, and particularly preferably 2 to 5 times the volume of the first solvent.

[0039] The second solvent is not limited to the extent that the effects of the present invention can be obtained. The second solvent may be the same solvent as the first solvent or a different solvent. If the second solvent is different from the first solvent, the second solvent may be, for example, a C3-C6 hydrocarbon, ketone, ether, or alcohol. When the second solvent is different from the first solvent, non-limiting examples of the second solvent include alcohols (e.g., 1-propanol), hexane, toluene, and diethyl ether.

[0040] [catalyst] In one embodiment, a catalyst comprising a metal oxide nanoparticle colloidal dispersion is disclosed. The catalytic activity and usage of this catalyst are as described above.

[0041] [Methods and apparatus for producing H2, hydrocarbons, and / or alcohols] In one embodiment, a method for producing H2, hydrocarbons, and / or alcohols is disclosed, comprising the step of electrolyzing one or more substances selected from the group consisting of H2O, CO2, CO, and N2 using a metal oxide nanoparticle colloidal dispersion as a catalyst. Furthermore, in one embodiment, a manufacturing apparatus for producing H2, hydrocarbons, and / or alcohols is disclosed, comprising an electrolytic cell for electrolyzing one or more substances selected from the group consisting of H2O, CO2, CO, and N2, which contains a metal oxide nanoparticle colloidal dispersion as a catalyst. The electrolytic cell preferably comprises electrodes and an electrolyte. The metal oxide nanoparticle colloidal dispersion may be contained in the catalyst layer formed on the electrodes and / or in the electrolyte. These manufacturing methods and equipment will play a crucial role in reducing the cost of CO2 resource utilization or hydrogen production, which are seen as promising steps toward realizing a carbon-neutral society. The amounts of CO2, hydrocarbons, and alcohols produced in this manufacturing method, as well as H2, hydrocarbons, and / or alcohols, are as described above.

[0042] A non-limiting list of exemplary embodiments and combinations of exemplary embodiments of this disclosure are disclosed below. [1] A metal oxide nanoparticle colloidal dispersion comprising metal oxide nanoparticles containing a first metal oxide and a second metal oxide, and a capping agent, wherein the first metal oxide is copper oxide and the second metal oxide is an oxide of a metal other than copper. [2] The metal oxide nanoparticle colloidal dispersion according to [1], wherein the capping agent comprises an ester of a carboxylic acid and a higher alcohol. [3] The metal oxide nanoparticle colloidal dispersion according to [2], wherein the carboxylic acid is a C6-C24 aliphatic or aromatic carboxylic acid. [4] The metal oxide nanoparticle colloidal dispersion according to [2] or [3], wherein the higher alcohol is a C6-C24 aliphatic or aromatic alcohol. [5] In the infrared absorption spectrum, 1700–1750 cm⁻¹ -1 , 1100~1200cm -1 , and / or 1200~1270cm -1 A metal oxide nanoparticle colloidal dispersion according to any one of [1] to [4], having an absorption peak in the range of [1]. [6] The metal oxide nanoparticle colloidal dispersion according to any one of [1] to [5], wherein the second metal oxide is an oxide of a metal that is an element of Groups 3 to 15. [7] A metal oxide nanoparticle colloidal dispersion according to any one of [1] to [6], wherein the second metal oxide is zinc oxide. [8] A metal oxide nanoparticle colloidal dispersion according to any one of [1] to [7], having three or more diffraction peaks in a powder X-ray diffraction (XRD) pattern with diffraction angles 2θ of 31.2±0.2, 34.2±0.2, 36.8±0.2, 35.7±0.2, 43.6±0.2, 29.5±0.2, 44.1±0.2, or 50.7±0.2. [9] Metal oxide nanoparticles, A core containing metal, A first layer containing a first metal oxide surrounds the nucleus, A second layer containing the second metal oxide surrounds the first layer. Includes, The first metal oxide is an oxide of the metal. A colloidal dispersion of metal oxide nanoparticles according to any one of [1] to [8]. A catalyst comprising a metal oxide nanoparticle colloidal dispersion as described in any of

[10] , [1] to [9].

[11] A method for producing H2, hydrocarbons, and / or alcohols, comprising the step of electrolyzing one or more substances selected from the group consisting of H2O, CO2, CO, and N2 using a metal oxide nanoparticle colloidal dispersion described in any of [1] to [9] as a catalyst.

[12] A production apparatus for H2, hydrocarbons, and / or alcohols, comprising an electrolytic cell for electrolyzing one or more selected from the group consisting of H2O, CO2, CO, and N2, which contains a metal oxide nanoparticle colloidal dispersion described in any of [1] to [9] as a catalyst. Each configuration and its combination in each embodiment is an example, and additions, omissions, substitutions, and other modifications can be made as appropriate without departing from the spirit of this disclosure. This disclosure is not limited by the embodiments. [Examples]

[0043] [Production of metal oxide nanoparticle colloidal dispersions] In Examples 1 to 8, 3 mL of a 1-octadecene solution containing copper oleate (manufactured by Kanto Chemical Co., Ltd.) and zinc oleate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) at the concentrations and proportions shown in Table 1 was added to 6 mL of 1-dodecanol at room temperature. In Examples 4 and 5, H2O was further added to this 1-octadecene solution. By reacting these at 300°C for 30 minutes, a metal oxide nanoparticle colloidal dispersion containing copper oxide, zinc, and a capping agent was obtained.

[0044] [Table 1]

[0045] By adding 0.5 mL of acetone to 0.5 mL of the obtained metal oxide nanoparticle colloidal dispersion and centrifuging at 15,000 rpm for 20 minutes, the precipitated metal oxide nanoparticles could be recovered. After removing the acetone, 0.5 mL of 1-propanol was added, and the metal oxide nanoparticles could be redispersed.

[0046] [Particle size of metal oxide nanoparticles] In transmission electron microscope (TEM) images of metal oxide nanoparticles, the particle size of the metal oxide nanoparticles was determined as the average particle size of 30 particles using a projection area criterion, where the diameter of a circle with the same area as the projected area of ​​the particle is defined as the particle size. The results are shown in Table 1. Furthermore, for Examples 3-5, the fast Fourier transform (FFT) patterns of the transmission electron and lattice images obtained by transmission electron microscope (TEM) of metal oxide nanoparticles are shown in Figure 1. As shown in Table 1 and Figure 1, the metal oxide nanoparticle colloidal dispersions of the examples had suitable particle sizes in terms of surface area and uniformity. Furthermore, a comparison of Examples 3-5, for example, showed that when H2O was added to the reaction solvent, the particle size of the metal oxide nanoparticles increased in a manner dependent on the increase in H2O concentration. In other words, it was shown that the particle size of the metal oxide nanoparticles could be appropriately adjusted by the presence or absence of H2O addition and the amount of H2O added.

[0047] [Amount of metal oxide nanoparticles produced] The amount of metal oxide nanoparticles generated was measured by the change in recovered weight. The results are shown in Table 1. As shown in Table 1, the amount of metal oxide nanoparticles produced was large. Furthermore, the amount of metal oxide nanoparticles generated was greater when the molar ratio of zinc oleate to the sum of copper oleate and zinc oleate was 0.5 (Example 3) compared to when it was less than or greater than 0.5.

[0048] [Redox potential of metal oxide nanoparticles] The oxidation-reduction potential of metal oxide nanoparticles was measured using an electrochemical analyzer (HA-105A, manufactured by Hokuto Denko). The results are shown in Table 1. As shown in Table 1, the metal oxide nanoparticles in the examples exhibited a low redox potential, which is preferable for use as a catalyst. Furthermore, the oxidation-reduction potential of the metal oxide nanoparticles was lower when the molar ratio of zinc oleate to the sum of copper oleate and zinc oleate was 0.5 (Examples 3-5) compared to when it was less than or greater than 0.5.

[0049] [Resistance of a copper substrate with a catalyst layer of metal oxide nanoparticles formed on its surface] The sheet resistance of the catalyst layer / copper substrate, prepared by applying the metal oxide nanoparticle colloidal dispersion of the example onto an electrolytically mirror-polished copper substrate at 150°C for 30 minutes, was measured using an LCR meter. The results are shown in Table 1. As shown in Table 1, the resistance of the copper substrate with the catalyst layer formed was significantly lower compared to the resistance of the copper substrate (20 Ω / square) before the catalyst layer was formed. Therefore, by forming the catalyst layer with the metal oxide nanoparticle colloidal dispersion of the example, the current flowing through the metal substrate can be increased. This is advantageous in using the substrate as an electrode.

[0050] [Production of ethanol etc. using metal oxide nanoparticles as a catalyst] An aqueous solution containing 1 M K2CO3 as raw material CO2 was used as an electrolyte, and Cu substrates (80 mesh, made by Nilaco) and Pt substrates (80 mesh, made by Nilaco) coated with the metal oxide nanoparticle colloidal dispersions of Examples 3, 6, 7, and 8 were used as the negative electrode and the positive electrode respectively, and a voltage of 8 V was applied (current density 2.7 A / cm 2 ), for 90 minutes (charge amount 10,800 C / cm 2 ) to electrolyze the raw materials. The ethanol, ethylene, and CO obtained thereby were quantified by an FT-IR analyzer and a gas chromatography (GC) analyzer. The results are shown in Figure 2.

[0051] As shown in Figure 2, when electrolyzing by adding the metal oxide nanoparticle colloidal dispersions of Examples 3, 6, 7, and 8, ethanol and ethylene were produced in high yields.

[0052] [Infrared spectrum of metal oxide nanoparticle colloidal dispersion]

[0053] (Infrared absorption spectrum) The infrared absorption spectrum of the metal oxide nanoparticle colloidal dispersion of Example 3 is shown in Figure 3. As shown in Figure 3, the metal oxide nanoparticle colloidal dispersion showed absorption peaks in the ranges of 700~1750 cm -1 , 1100~1200 cm -1 , and 1200~1270 cm -1 . These absorption peaks indicate the presence of carboxylic acid esters in the metal oxide nanoparticle colloidal dispersion. These carboxylic acid esters are thought to be present in the capping agent contained in the metal oxide nanoparticle colloidal dispersion.

[0054] [Powder X-ray diffraction (XRD) patterns of metal oxide nanoparticles] Figure 4 shows the powder X-ray diffraction (XRD) pattern of the metal oxide nanoparticle colloidal dispersion of Example 3, with CuKα as the radiation source. As shown in Figure 4, the metal oxide nanoparticle colloidal dispersion of Example 3 showed diffraction peaks in the powder X-ray diffraction (XRD) pattern with diffraction angles 2θ of 31.2±0.2, 34.2±0.2, 36.8±0.2, 35.7±0.2, 43.6±0.2, 29.5±0.2, 44.1±0.2, and 50.7±0.2. Of these diffraction peaks, those with diffraction angles 2θ of 1.2±0.2, 34.2±0.2, or 36.8±0.2 are thought to originate from the presence of zinc oxide (ZnO), in light of the International Centre for Diffraction Data (ICCD) card. Diffraction peaks with diffraction angles 2θ of 35.7±0.2, 43.6±0.2, or 29.5±0.2 are thought to originate from the presence of copper oxide (Cu2O), considering the ICCD card. Diffraction peaks with diffraction angles 2θ of 44.1±0.2 or 50.7±0.2 are thought to originate from the presence of copper (Cu), considering the ICCD card.

[0055] [Optical properties of metal oxide nanoparticles] Photographs and optical spectra of the metal oxide nanoparticle colloidal dispersions of Examples 3, 6, 7, and 8 are shown in Figures 5A and 5B. As shown in Figures 5A and 5B, the wavelength changed as the molar ratio of zinc oleate to the sum of copper oleate and zinc oleate increased. This change is thought to be due to the increased contribution of ZnO to the spectrum as the concentration of ZnO increases, as well as the red shift in the band gap energy due to the increase in the concentration of Cu2O.

[0056] [Structural model of metal oxide nanoparticles] Figure 6 shows an exemplary model of the structure of the metal oxide nanoparticles, which is expected in light of the XRD patterns and optical spectra described above. In the model shown in Figure 6, the metal oxide nanoparticles have a core containing Cu, a first layer containing Cu2O surrounding the core, and a second layer containing ZnO surrounding the first layer. The capping agent exists either bonded to the metal oxide nanoparticles, not bonded to the metal oxide nanoparticles, or both. [Industrial applicability]

[0057] The metal oxide nanoparticle colloidal dispersions of this disclosure are useful, for example, in the production of H2, hydrocarbons, and / or alcohols, and have industrial applicability.

Claims

1. A metal oxide nanoparticle colloidal dispersion comprising metal oxide nanoparticles containing a first metal oxide and a second metal oxide, and a capping agent, wherein the first metal oxide is copper oxide and the second metal oxide is an oxide of a metal other than copper.

2. The metal oxide nanoparticle colloidal dispersion according to claim 1, wherein the capping agent comprises an ester of a carboxylic acid and a higher alcohol.

3. The metal oxide nanoparticle colloidal dispersion according to claim 2, wherein the carboxylic acid is a C6-C24 aliphatic or aromatic carboxylic acid.

4. The metal oxide nanoparticle colloidal dispersion according to claim 2, wherein the higher alcohol is a C6 to C24 aliphatic or aromatic alcohol.

5. In the infrared absorption spectrum, 1700–1750 cm⁻¹ －１ , 1100-1200cm －１ , and / or 1200-1270 cm －１ The metal oxide nanoparticle colloidal dispersion according to claim 1, having an absorption peak in the range.

6. The metal oxide nanoparticle colloidal dispersion according to claim 1, wherein the second metal oxide is an oxide of a metal belonging to Groups 3 to 15.

7. The metal oxide nanoparticle colloidal dispersion according to claim 1, wherein the second metal oxide is zinc oxide.

8. The metal oxide nanoparticle colloidal dispersion according to claim 1, having three or more diffraction peaks in a powder X-ray diffraction (XRD) pattern, with diffraction angles 2θ of 31.2±0.2, 34.2±0.2, 36.8±0.2, 35.7±0.2, 43.6±0.2, 29.5±0.2, 44.1±0.2, or 50.7±0.

2.

9. Metal oxide nanoparticles, A core containing metal, A first layer containing a first metal oxide surrounds the nucleus, A second layer containing the second metal oxide surrounds the first layer. Includes, The first metal oxide is an oxide of the metal. The metal oxide nanoparticle colloidal dispersion according to claim 1.

10. A catalyst comprising a metal oxide nanoparticle colloidal dispersion according to any one of claims 1 to 9.

11. H ２ A method for producing hydrocarbons and / or alcohols, wherein a metal oxide nanoparticle colloidal dispersion according to any one of claims 1 to 9 is used as a catalyst, H ２ O, CO ２ CO, and N ２ A manufacturing method comprising the step of electrolyzing one or more selected from the group consisting of the following.

12. H ２ , a hydrocarbon, and / or a production apparatus for alcohol, comprising the metal oxide nanoparticle colloidal dispersion according to any one of claims 1 to 9 as a catalyst, H ２ O, CO ２ , CO, and N ２ A production apparatus comprising an electrolytic cell for electrolyzing one or more selected from the group consisting of.

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