High-entropy oxide catalyst and method for ethanol production based on electrochemical methane conversion using same

Abstract

The present invention relates to a high-entropy oxide catalyst for increasing the efficiency of electrochemical methane conversion and a method for alcohol production using same.

Description

High-entropy oxide catalyst and method for producing ethanol based on electrochemical methane conversion using the same

[0001] The present invention relates to a high-entropy oxide catalyst for increasing the efficiency of electrochemical methane conversion and a method for producing alcohol using the same.

[0002] This application claims priority to Korean Patent Application No. 10-2024-0027699, filed on February 27, 2024, the entire contents of which are disclosed in the specification and drawings of the said application are incorporated herein by reference.

[0003] Meanwhile, the present invention was supported by the following national research and development project.

[0004] 1. Assignment ID: 1711131903

[0005] Assignment Number: 2021M3D3A1A01022112

[0006] Ministry of Science and ICT

[0007] Project Management (Professional) Institution Name: National Research Foundation of Korea

[0008] Research Project Name: Climate Change Response Technology Development (R&D)

[0009] Research Project Name: Development of an Electrochemical Catalytic Reaction Process for Methane Conversion

[0010] Project Implementing Institution Name: Korea University

[0011] Research Institute: January 1, 2021 - February 29, 2024

[0012] 2. Assignment ID: 1711191403

[0013] Assignment Number: 2022R1A2C2005228

[0014] Ministry of Science and ICT

[0015] Project Management (Professional) Institution Name: National Research Foundation of Korea

[0016] Research Project Name: Individual Basic Research (Ministry of Science and ICT)

[0017] Research Project Title: Formation of Polymer-Derived Carbon Nanostructures by Controlling Compressive Stress-Adhesion and Their Application to Energy Devices

[0018] Project Implementing Institution Name: Korea University

[0019] Research Institute: March 1, 2022 - February 28, 2025

[0020] Methane, a greenhouse gas, is a very stable substance due to its physical properties, which limits its utilization. Commercial methane-to-methanol synthesis involves indirect conversion via synthesis gas. Most methane conversions require high temperatures and high pressures. Furthermore, synthesis gas conversion is inefficient because it synthesizes carbon monoxide (CO) as an intermediate product. Therefore, research on direct methane conversion is gaining traction.

[0021] Direct electrochemical conversion of methane involves partial oxidation of methane to produce alcohols. This reaction proceeds by directly catalyzing the formation of reactive oxygen species (OH*, O*) in the liquid phase on the catalyst. Furthermore, product selectivity can be controlled by voltage regulation.

[0022] Singh et al. electrochemically converted methane to methanol using a Cu-Ti bimetallic TMO catalyst. They applied the Cu-Ti bimetallic TMO catalyst and obtained a yield of 3.44 μmol / g. cat / hr methanol production and a faradaic efficiency of 6% were achieved.

[0023] The Zhou group synthesized a ZrO2:CuOx catalyst with a capsule structure to convert methane into propanol. In particular, the production of 2-propanol was 2084.3 μmol / g after 18 hours of reaction. cat was achieved, and the selectivity was reported to be approximately 48%.

[0024] A catalyst with Rh atoms dispersed on a Pasquale-grouped NiO, V2O5 mixed oxides nanocomposite support was synthesized. Using this catalyst, methane was electrochemically converted to methanol, with a methanol production yield of 0.13 μmol / g. cat / hr, the selectivity for methanol was reported to be 60%.

[0025] Although the existing reported technologies have the advantage of being able to convert methane at room temperature, they can be considered limited catalytic technologies in that their production rate, faradaic efficiency, and selectivity for target products are low.

[0026] In particular, since the production rate and selectivity for the target product are usually inversely proportional indicators, there is a need to develop a highly efficient catalyst that can induce a rapid reaction while increasing the selectivity for the desired product.

[0027] The present invention was conceived to solve the above-described problem, and aims to provide a high-entropy oxide catalyst capable of directly converting methane, one of the representative greenhouse gases, into a high value-added substance by utilizing a highly efficient electrochemical method without a multi-step process or high energy consumption, and an ethanol production method based on electrochemical methane conversion using the same.

[0028] The electrochemical direct conversion of methane is a process that can not only increase selectivity for products through voltage control, but also stabilize reaction intermediates through liquid-phase reaction and make product separation relatively easy, but has low conversion efficiency and faradaic efficiency as its drawbacks. The purpose of the present invention is to provide a metal oxide catalyst for electrochemical methane conversion that can obtain a high ethanol production rate, conversion efficiency, and selectivity.

[0029] The technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0030] The present invention provides a high-entropy oxide catalyst for electrochemical methane conversion, according to a preferred embodiment, a metal oxide catalyst, wherein the metal comprises metal elements composed of chromium (Cr), cobalt (Co), iron (Fe), manganese (Mn) and nickel (Ni), and the metal oxide catalyst has a single lattice structure, and the metal elements are independently and evenly distributed and randomly (disorderly) arranged throughout the single lattice structure.

[0031] The above metal oxide catalyst may be a spherical particle having a nano-scale diameter, and the diameter may be, but is not limited to, 40 to 100 nm.

[0032] The metal oxide catalyst may be (CoCrFeMnNi)3O4 having a single-lattice spinel structure, and the metal may be composed of 6 to 10 mol% of chromium (Cr), cobalt (Co), iron (Fe), manganese (Mn), and nickel (Ni), respectively, and S of the metal oxide catalyst config The value can be greater than 1.5R.

[0033] The above metal is composed of cobalt (Co) exceeding 10 mol% and chromium (Cr), iron (Fe), manganese (Mn) and nickel (Ni) of 5 to 10 mol%, and S of the metal oxide catalyst config The value can be greater than 1.5R.

[0034] The above metal oxide catalyst has a voltage of 1.4 to 1.8 V RHE Ethanol production rate (μmol / g) under conditions cat / hr) is 6,000 to 13,000, and the selectivity (%) for ethanol among the total products can be 50% or more.

[0035] Alternatively, the metal oxide catalyst has a voltage of 1.5 to 1.7 V RHE Ethanol production rate (μmol / g) under conditions cat / hr) is 8,000 to 13,000, and the selectivity (%) for ethanol among the total products can be 59% or more.

[0036] Alternatively, the metal oxide catalyst has a voltage of 1.5 to 1.6 V RHE Ethanol production rate (μmol / g) under conditions cat / hr) is 8,000 to 13,000, and the selectivity (%) for ethanol among the total products can be 68% or more.

[0037] Meanwhile, the present invention provides a gas diffusion electrode (GDE) including a high-entropy oxide catalyst as described above according to another preferred embodiment, and provides a continuous flow reactor including a reaction tank including the gas diffusion electrode as a working electrode, a counter electrode, and an electrolyte; a voltage applying unit for applying voltage to the reaction tank; a methane supply unit for continuously supplying gaseous methane to the reaction tank; a flow rate controlling unit for controlling the flow rate of the supplied methane; a methane discharge unit for discharging unreacted methane from the reaction tank; and a product obtaining unit for obtaining a reaction product including ethanol.

[0038] At this time, the electrolyte is carbonate (CO3 2- ) may contain ions.

[0039] Meanwhile, the present invention provides an electrochemical methane conversion-based ethanol production method using a continuous flow reaction, comprising the steps of: preparing a reaction vessel including a gas diffusion electrode as a working electrode, a counter electrode, and an electrolyte; applying a voltage to the reaction vessel; supplying gaseous methane to the reaction vessel in a continuous flow to produce a reaction product including ethanol; and obtaining the reaction product.

[0040] At this time, under the condition of a gaseous methane supply flow rate of 50 to 125 sccm, the ethanol production rate (μmol / gcat / hr) may be 15,000 to 27,000, and the selectivity (selectivity, %) for ethanol among the total products may be 60% or more.

[0041] Electrochemical methane conversion is an economical process that consumes less energy than thermochemical reactions because it reacts at room temperature and pressure. During the reaction, methane conversion occurs at the working electrode and hydrogen can be produced simultaneously at the counter electrode.

[0042] The present invention presents a high-entropy oxide catalyst having five metal elements applicable to electrochemical methane conversion, thereby achieving a high ethanol production rate and selectivity.

[0043] The present invention is applicable to the electrochemical methane conversion as described above, and improves the solubility problem of methane and increases the efficiency of the reaction by introducing it into a continuous flow reactor, and confirms the stability of the catalyst even after 100 hours of reaction.

[0044] The high-entropy oxide catalyst of the present invention and the electrochemical methane conversion-based ethanol production method using the same induce an excellent methane oxidation reaction under room temperature and pressure conditions through an electrochemical reaction, thereby enabling alcohol production at low cost. The catalyst can be applied to reduce environmental pollution in industries that generate large amounts of methane gas, such as livestock manure treatment facilities, or to produce alcohol at low cost in alcohol production industries.

[0045] The effects of the present invention are not limited to those mentioned above, and also include other effects that are not explicitly mentioned, although they can be clearly understood by those skilled in the art from the description throughout the specification.

[0046] Figure 1 is a conceptual diagram of a high-entropy oxide catalyst of the present invention.

[0047] Figure 2 is a conceptual diagram explaining the structure of a continuous flow reactor to which the high-entropy oxide catalyst of the present invention is applied, an SEM image analyzing the morphology of the catalyst (left), and a conceptual diagram explaining the chemical reaction within the reactor (right).

[0048] Figure 3 is a conceptual diagram of a continuous flow reactor to which the high-entropy oxide catalyst of the present invention is applied.

[0049] Figure 4 is a chemical reaction mechanism for electrochemical methane conversion within a reactor using a high-entropy oxide catalyst of the present invention.

[0050] Figure 5 is a TEM image of the high-entropy oxide catalyst of the present invention.

[0051] Figure 6 is an EDS analysis image of five metal elements (Cr, Co, Fe, Mn, Ni) of the high-entropy oxide catalyst of the present invention.

[0052] Figure 7 is an HR-TEM (high-resolution TEM) analysis image of the high-entropy oxide catalyst of the present invention.

[0053] Figure 8 is an XRD analysis chart for the high-entropy oxide catalyst of the present invention.

[0054] Figure 9 is a 2p XPS analysis chart of metal elements forming the high-entropy oxide catalyst of the present invention.

[0055] Figure 10 is an EXAFS analysis chart for the high-entropy oxide catalyst of the present invention.

[0056] Figure 11 is a Wavelet-Transform (WT)-EXAFS analysis chart for the high-entropy oxide catalyst of the present invention.

[0057] Figure 12 shows the S based on the ICP-AES analysis results for the high entropy oxide catalyst of the present invention. configuration This is a table of results from analyzing whether a compound is a 'high entropy' oxide by calculating .

[0058] Figure 13 is a TEM (transmission electron microscopy) image of a high-entropy oxide catalyst (high Co content) of the present invention.

[0059] Figure 14 is an EDS (energy dispersive spectroscopy) analysis image of five metal elements (Cr, Co, Fe, Mn, Ni) of the high-entropy oxide catalyst (high Co content) of the present invention.

[0060] Figure 15 is an XRD analysis chart for the high-entropy oxide catalyst (high Co content) of the present invention.

[0061] Figure 16 is an EXAFS analysis chart for a high-entropy oxide catalyst (high Co content) of the present invention.

[0062] Figure 17 is a Wavelet-Transform (WT)-EXAFS analysis chart for the high-entropy oxide catalyst (high Co content) of the present invention.

[0063] Figure 18 is an LSV analysis chart (left) and a photograph of a test specimen (right) for samples with a high content of a specific metal element of the high-entropy oxide catalyst of the present invention.

[0064] Figure 19 shows the voltage-dependent (V) curve for the high-entropy oxide catalyst of the present invention. RHE) Ethanol production rate (μmol / g) cat This is a chart measuring / hr.

[0065] Figure 20 shows the voltage-dependent (V) curve for the high-entropy oxide catalyst of the present invention. RHE ) is a chart measuring product selectivity (Selectivity, %).

[0066] Figure 21 is a comparison chart between two performances (selectivity and alcohol production rate) of the high entropy oxide catalyst (HEO (our work)) of the present invention and the results of previous studies.

[0067] Figure 22 is a chart of isotope analysis results for confirming the conversion of methane to ethanol for the high-entropy oxide catalyst of the present invention.

[0068] Figure 23 is a chart showing the results of measuring the ethanol production rate according to the methane injection flow rate for a continuous flow reactor to which the high-entropy oxide catalyst of the present invention is applied.

[0069] Figure 24 is a chart showing the results of measuring the selectivity of each product according to the methane injection flow rate for a continuous flow reactor to which the high-entropy oxide catalyst of the present invention is applied.

[0070] Figure 25 is a chart showing the results of measuring current density over reaction (operation) time for a continuous flow reactor to which the high-entropy oxide catalyst of the present invention is applied.

[0071] Figure 26 is a chart showing the results of TEM / EDS analysis of a catalyst after 100 hours of reaction through a continuous flow reactor using the high-entropy oxide catalyst of the present invention.

[0072] Figure 27 is a chart showing the XRD analysis results (left) and EIS (electrochemical impedance spectroscopy) analysis results (right) of a catalyst after 100 hours of reaction through a continuous flow reactor using the high-entropy oxide catalyst of the present invention.

[0073] Figure 28 is an XPS valance ratio analysis chart for five elements of a catalyst after 100 hours of reaction through a continuous flow reactor to which the high-entropy oxide catalyst of the present invention is applied.

[0074] Figure 29 is a chart showing the results of conversion rate and alcohol selectivity measurements for a demonstration gas (10% methane / air mixture gas) and a demonstration gas (containing approximately 1% methane) according to Experimental Example 12.

[0075] Figure 30 is a chart showing the results of measuring the methane conversion rate during long-term operation according to Experimental Example 12.

[0076] [Explanation of symbols]

[0077] 10: Membrane

[0078] 20: Working electrode

[0079] 21: Gas diffusion electrode

[0080] 22: High-entropy oxide catalyst (HEO)

[0081] 30: Methane flow plate

[0082] 40: Electrolyte flow plate

[0083] 50: End plate

[0084] 60: Reaction tank

[0085] 70: Voltage application unit

[0086] 100: Continuous flow reactor

[0087] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. The advantages and features of the present invention, and methods for achieving them, will become clear with reference to the embodiments described in detail below together with the attached drawings. However, the present invention is not limited to the embodiments disclosed below, but can be implemented in various different forms. These embodiments are provided only to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

[0088] Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used in a sense commonly understood by those of ordinary skill in the art to which the present invention pertains. Furthermore, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise. The terminology used herein is for the purpose of describing embodiments and is not intended to limit the present invention. In this specification, singular forms also include plural forms, unless specifically stated otherwise.

[0089] The terms "comprises" and / or "comprising" as used in the specification do not exclude the presence or addition of one or more other components, steps, operations and / or elements.

[0090]

[0091] The present invention provides a high-entropy oxide catalyst for electrochemical methane conversion, according to a preferred embodiment, a metal oxide catalyst, wherein the metal comprises metal elements composed of chromium (Cr), cobalt (Co), iron (Fe), manganese (Mn) and nickel (Ni), and the metal oxide catalyst has a single lattice structure, and the metal elements are independently and evenly distributed and randomly (disorderly) arranged throughout the single lattice structure.

[0092] Figure 1 illustrates a conceptual diagram of a high-entropy oxide catalyst according to the present invention. As illustrated in Figure 1, the high-entropy oxide catalyst according to the present invention comprises five types of metal elements uniformly and randomly distributed to form spherical particles overall.

[0093] In this specification, “metal elements are independently distributed evenly and at the same time randomly (disorderly) arranged” means that each of the five metal elements is independently distributed evenly / uniformly throughout the oxide catalyst structure forming a single lattice structure, and at the same time, the metal-metal bonds and metal-oxygen bonds, which are bonds between these metal elements and oxygen elements, are randomly (disorderly) positioned throughout the structure.

[0094] The distribution and arrangement structure of these metal elements forms a high-entropy oxide overall, which is stabilized in terms of entropy, and multiple reaction steps occur simultaneously at each reaction site of the catalyst, which is optimized for ethanol production, enabling high production speed, efficiency, and selectivity to be realized.

[0095] The high-entropy oxide catalyst of the present invention may take the form of spherical particles having a diameter of nanoscale (tens of nm) and may have a single-lattice spinel structure.

[0096] The high-entropy oxide catalyst of the present invention may be composed of five metal elements, chromium (Cr), cobalt (Co), iron (Fe), manganese (Mn), and nickel (Ni), each in an amount of 6 to 10 mol%, and may have a 'high-entropy' property with a configuration entropy value of 1.5R or more (where R is the gas constant).

[0097] According to a preferred embodiment of the present invention, the content of a specific element among five metal elements may exceed 10 mol%. Basically, the high-entropy oxide catalyst of the present invention is manufactured in a form in which precursor materials of the five metal elements are introduced in an equal level of weight during the synthesis process, but a form in which the content of a specific element is high as described above may be manufactured in a manner in which the input weight of the precursor material is additionally introduced in a certain ratio (e.g., 60%, 1.6 times). Even in such an embodiment, the configuration entropy value of the manufactured catalyst may still be 1.5R or more.

[0098] The high entropy oxide catalyst of the present invention has a temperature of 1.4 to 1.8 V RHE Ethanol production rate (μmol / g) under conditions cat / hr) is 6,000 to 13,000, and the selectivity (selectivity, %) for ethanol among the total products can be 50% or more, and 1.5 to 1.7 V RHE Under the conditions, the former can be 8,000 to 13,000 and the latter can be more than 59%, and 1.5 to 1.6 V RHE Under the conditions, the former can be between 8,000 and 13,000 and the latter can be more than 68%.

[0099] The high-entropy oxide catalyst of the present invention can be applied to a gas diffusion electrode (GDE) in the form of a spray injection, and can be applied to a continuous flow reactor using the GDE as a working electrode. Figure 3 illustrates a conceptual diagram of a continuous flow reactor to which the high-entropy oxide catalyst of the present invention is applied.

[0100] Referring to FIG. 3, the continuous flow reactor (100) may be equipped with a reaction tank (60) including a working electrode (20) in which a high-entropy oxide catalyst (22) is formed on at least one surface of a gas diffusion electrode (21), a methane flow plate (30), a counter electrode, and an electrolyte flow plate (40), a voltage application unit (70), an end plate (50) on the methane supply side including a methane supply unit for supplying gaseous methane, a flow rate control unit for methane, a methane discharge unit for unreacted methane, and a product obtaining unit (not shown in the drawing) for obtaining a reaction product including ethanol, wherein the electrolyte is carbonate (CO3) 2- ) can be composed of ions.

[0101] Figure 4 illustrates a schematic diagram illustrating the chemical reaction mechanism by which electrochemical methane conversion occurs within a reactor via a high-entropy oxide catalyst. The mechanism depicted in Figure 4 conceptually demonstrates that metal ions, such as cobalt (Co), induce a redox reaction between methane and water.

[0102] As described above, when the high-entropy oxide catalyst of the present invention is applied to a continuous flow reactor, ethanol can be produced by an electrochemical methane conversion method including a step of applying voltage after preparing a reaction tank, a step of supplying gaseous methane and generating a reaction product, and a step of obtaining the product.

[0103] At this time, under the condition of a methane supply flow rate of 50 to 125 sccm, the ethanol production rate (μmol / gcat / hr) is 15,000 to 27,000, and the selectivity (selectivity, %) for ethanol among the total products can be 60% or more.

[0104]

[0105] Below, specific embodiments and experimental examples of the present invention are examined.

[0106]

[0107] Example 1: Preparation of High Entropy Oxide Catalyst (HEO)

[0108] A sol-gel method was used to synthesize a high entropy oxide (HEO) with a spinel structure. 0.2 g of F127 (a PEO-PPO-PEO triblock copolymer that acts as a surfactant, product name: Pluronic® F-127 (Sigma-aldrich)) was dissolved in a water-ethanol mixture, and 0.025 g of tannic acid and 0.38 ml of formaldehyde solution were added to synthesize the solvent.

[0109] Metal precursors containing five metals (Cobalt nitrate, Manganese nitrate, Nickel nitrate, Iron sulfate, Chromium chloride) were added in equal weights (1 g) to the previously synthesized solvent, and hydrothermal synthesis was performed at a temperature of 100°C for 12 hours. Afterwards, a spinel-structured HEO catalyst was synthesized by sintering for approximately 8 hours under air atmosphere and temperature conditions of 900°C.

[0110]

[0111] Example 2: Preparation of HEO catalyst with increased content of specific metal elements

[0112] The same process as in Example 1 described above was followed, but in the case of the Co 60 catalyst, 1.6 g of cobalt nitrate was added, increasing the weight of the metal precursor by 1.6 times (Example 2-1).

[0113] In the same manner, the Fe precursor, Ni precursor, Cr precursor, and Mn precursor were each added in an amount 1.6 times greater than the input weight to synthesize Examples 2-2 to 2-5, respectively.

[0114]

[0115] Example 3: Continuous flow reactor using HEO catalyst

[0116] To improve the low solubility of methane, a continuous flow reactor based on a gas diffusion electrode (GDE) that can directly inject methane in a gaseous state was introduced.

[0117] Figure 2 is a conceptual diagram explaining the structure of a continuous flow reactor to which the high-entropy oxide catalyst of the present invention is applied, an SEM image analyzing the morphology of the catalyst (left), and a conceptual diagram explaining the chemical reaction within the reactor (right).

[0118] Figure 3 is a conceptual diagram of a continuous flow reactor to which the high-entropy oxide catalyst of the present invention is applied.

[0119] A dispersion solution was prepared by mixing the HEO Co 60 catalyst according to Example 2-1, Nafion, and anhydrous ethanol. The prepared dispersion solution was applied to a gas diffusion electrode (GDE) (21) made of porous carbon material by spraying.

[0120] A continuous flow reactor (100) was manufactured by assembling in the following order: an end plate (50), a methane flow plate (CH4 flow plate) (30), a working electrode (20) composed of a gas diffusion electrode (GDE) (21) manufactured in the manner described above and having a high-entropy oxide catalyst (22) applied to one surface thereof, a separation membrane (10), an electrolyte flow plate (40) made of platinum as a counter electrode, and an end plate (50) on the opposite side.

[0121] The electrolyte is 0.05 M Na2CO3, the working electrode (20) is a carbon electrode (gas diffusion electrode) (21) sprayed with HEO (22), and the counter electrode is Pt, and the reactor is configured as a two-electrode reactor structure, and may additionally be configured with a voltage applying unit (70) for applying voltage, a methane supply unit (methane (CH4) inlet of the left end plate (50) in FIG. 3) for supplying gaseous methane in a continuous flow, a flow rate controlling unit (not shown in the drawing) for controlling the flow rate of the supplied methane, a methane discharge unit (methane (CH4) discharge unit of the left end plate (50) in FIG. 3) for discharging unreacted methane, and a product obtaining unit (not shown in the drawing) for obtaining a product including ethanol, an electrolyte or water supply and discharge unit (electrolyte inlet / outlet of the right end plate (50) in FIG. 3), etc.

[0122]

[0123] Experimental Example 1: Electron Microscope Image Analysis

[0124] Electron microscope image analysis of the HEO catalyst according to Example 1 was performed.

[0125] Figure 5 is a TEM (transmission electron microscopy) image of the high-entropy oxide catalyst of the present invention, confirming that the high-entropy oxide catalyst has spherical particles with a size of about 50 to 55 nm.

[0126] Figure 6 is an EDS (energy dispersive spectroscopy) analysis image of five metal elements (Cr, Co, Fe, Mn, Ni) of the high-entropy oxide catalyst of the present invention, and it can be confirmed that the five metal elements are independently and evenly (uniformly) distributed.

[0127] Fig. 7 is an HR-TEM (high-resolution TEM) analysis image of the high-entropy oxide catalyst of the present invention, through which a lattice spring of 0.28 nm was confirmed, which corresponds to the (220) plane. Referring to Fig. 7, the HEO catalyst according to Example 1 has a single lattice structure, not a composite frame or mixed domain structure like a conventional general composite oxide catalyst, and it can be confirmed that the five metal elements within this single lattice structure are independently and evenly distributed and at the same time randomly (disorderly) arranged.

[0128]

[0129] Experimental Example 2: XRD and XPS Analysis

[0130] XRD analysis (X-ray diffraction analysis) and XPS analysis (X-ray photoelectron spectroscopy analysis) were performed on the HEO catalyst according to Example 1.

[0131] Figure 8 is an XRD analysis chart for the high-entropy oxide catalyst of the present invention, through which it was confirmed that the HEO catalyst according to Example 1 had a peak matching CoFe2O4 of a spinel structure, confirming that a high-entropy oxide having a spinel structure was synthesized.

[0132] Figure 9 is a 2p XPS analysis chart of the metal elements constituting the high-entropy oxide catalyst of the present invention, through which it was confirmed that the elements constituting the HEO catalyst according to Example 1 exist in various oxidation states. This result means that the HEO catalyst is a suitable catalyst for an induced / sensitized current (faradic) reaction.

[0133]

[0134] Experimental Example 3: EXAFS Analysis

[0135] XAS analysis (X-ray absorption analysis) was performed on the HEO catalyst according to Example 1 in the EXAFS (extended X-ray absorption fine structure) region and the Wavelet-Transform (WT)-EXAFS region.

[0136] Figure 10 is an EXAFS analysis chart for the high-entropy oxide catalyst of the present invention, through which it was confirmed that all five metal elements (Co, Cr, Mn, Fe, Ni) exhibit two peaks at similar positions. This corresponds to metal-metal bonds and metal-oxygen bonds.

[0137] FIG. 11 is a Wavelet-Transform (WT)-EXAFS analysis chart for the high-entropy oxide catalyst of the present invention, through which two peaks were observed for all metal elements, which means that all five metal elements were uniformly synthesized within the oxide catalyst lattice structure.

[0138] Thus, it can be confirmed that the five metal elements are independently and evenly distributed throughout the single lattice structure of the metal oxide catalyst according to the present invention, while being randomly (disorderly) arranged.

[0139]

[0140] Experimental Example 4: ICP-AES Analysis

[0141] ICP-AES (inductively coupled plasma-atomic emission spectrometry) analysis was performed on the HEO catalyst according to Example 1.

[0142] Figure 12 shows the S based on the ICP-AES analysis results for the high entropy oxide catalyst of the present invention. configuration This is a table showing the results of analyzing whether a catalyst is a 'high-entropy' oxide by calculating 'HEO'. 'HEO' is a high-entropy oxide catalyst manufactured according to Example 1, and 'Co 60' is a high-entropy oxide catalyst manufactured according to Example 2-1.

[0143] Configuration Entropy(S config ) The calculation method is as follows.

[0144] It can be confirmed that it is a high-entropy substance by calculating the configuration entropy value, and if the value is 1.5R or higher, it can be classified as a high-entropy substance.

[0145] In the equation below, the value corresponding to the anion-site is 0 because it is only oxygen, and the configurational entropy can be calculated based on the number of cation types and the mole fraction of the cation metal at the cation-site.

[0146]

[0147]

[0148] R is the ideal gas constant, which is equal to 8.314 J / (mol K). Using this value, we can consider the entropy change for the total number of particles in the system.

[0149] In the case of the HEO catalyst, the precursor material input amount of each metal element was manufactured in the same way on a weight basis, but it is estimated that the difference in the molar ratio (Atomic %) occurred due to differences in the tendency of each metal element to be arranged / synthesized within the oxide single lattice structure. In particular, manganese (Mn) tends to be mainly synthesized while positioned within the catalyst, so it is understood that the element content is relatively low.

[0150] Referring to Fig. 12, S of the HEO catalyst according to Example 1 config The value is 1.5R or more (S measured experimentally) config The value is 1.606R), and the Co 60 catalyst according to Example 2-1, which increased the input amount (by weight) of the cobalt (Co) precursor by 60%, also had the same level (S measured experimentally). config The value is 1.573R), confirming that both examples are 'high-entropy' oxides.

[0151]

[0152] Experimental Example 5: Analysis of HEO Co 60 electron microscope images

[0153] Electron microscope image analysis was performed on the HEO Co 60 catalyst manufactured according to Example 2-1.

[0154] Figure 13 is a TEM (transmission electron microscope) image of the high-entropy oxide catalyst (high Co content) of the present invention, and it was confirmed that it had spherical particles of about 50 to 55 nm in size, similar to the HEO catalyst manufactured according to Example 1.

[0155] FIG. 14 is an EDS (energy dispersive spectroscopy) analysis image of five metal elements (Cr, Co, Fe, Mn, Ni) of the high-entropy oxide catalyst (high Co content) of the present invention, and it can be confirmed that the five metal elements are independently and evenly (uniformly) distributed, similar to the HEO catalyst manufactured according to Example 1.

[0156] Referring to FIGS. 13 and 14, it can be confirmed that the HEO Co 60 catalyst according to Example 2-1, like the HEO catalyst according to Example 1, has five metal elements independently and evenly distributed within a single lattice structure and arranged randomly (disorderly).

[0157]

[0158] Experimental Example 6: HEO Co 60 XRD and EXAFS Analysis

[0159] XRD analysis (X-ray diffraction analysis) was performed on the HEO Co 60 catalyst manufactured according to Example 2-1.

[0160] Figure 15 is an XRD analysis chart for the high-entropy oxide catalyst (high Co content) of the present invention, through which peaks matching the spinel structure of CoFe2O4 can be confirmed, similar to the HEO catalyst according to Example 1, confirming that the same spinel structure is maintained even when the Co content is increased.

[0161] Next, XAS analysis (X-ray absorption analysis) was performed on the HEO Co 60 catalyst manufactured according to Example 2-1 in the EXAFS (extended X-ray absorption fine structure) region and the Wavelet-Transform (WT)-EXAFS region.

[0162] Figure 16 is an EXAFS analysis chart for the high-entropy oxide catalyst (high Co content) of the present invention, through which it was confirmed that the metal-metal bonds and metal-oxygen bonds of all metal elements appeared in the same vicinity as the HEO catalyst according to Example 1.

[0163] In addition, FIG. 17 is a Wavelet-Transform (WT)-EXAFS analysis chart for the high-entropy oxide catalyst (high Co content) of the present invention, and similarly to the HEO catalyst according to Example 1, two peaks were observed for all metal elements, which means that all five metal elements are uniformly synthesized within the oxide catalyst lattice structure, and that the structure does not change even if the Co content increases.

[0164]

[0165] Experimental Example 7: LSV Analysis by Example

[0166] LSV analysis (linear scanning voltammetry) was performed on the HEO catalyst manufactured according to Example 1 and each HEO catalyst with increased content of a specific element manufactured according to Example 2. Through this experiment, the electrochemical performances of samples with increased content of five metal elements included in the HEO catalyst were compared and analyzed.

[0167] FIG. 18 is an LSV analysis chart (left) and a photograph of a test piece (right) for samples of the high-entropy oxide catalyst of the present invention with a high content of a specific metal element. The Co 60 HEO catalyst sample according to Example 2-1 showed the highest current density value, and the current density values ​​were high in the order of Fe 60 > Ni 60 > Cr 60 > Mn 60.

[0168] 1.6 V RHE Hydrogen was generated at the Pt electrode due to methane oxidation at 1.8 V RHE It was confirmed that O2 was generated on the catalyst surface due to OER, a competitive reaction at voltage.

[0169]

[0170] Experimental Example 8: Voltage-dependent product, selectivity results, and performance comparison with previous studies.

[0171] 1.4 V for the HEO catalyst prepared according to Example 1 RHE ~ 1.8 V RHE Product evaluation and selectivity analysis were performed at voltage.

[0172] Figure 19 shows the voltage-dependent (V) curve for the high-entropy oxide catalyst of the present invention. RHE ) Ethanol production rate (μmol / g) cat / hr) is a chart measuring the voltage (V) for the high-entropy oxide catalyst of the present invention. RHE ) is a chart measuring product selectivity (Selectivity, %).

[0173] The HEO catalyst according to Example 1 has a 1.6 V RHE Maximum ethanol production at voltage 12315.3 μmol / g cat / hr was achieved, and the selectivity for ethanol was confirmed to be 68%. 1.6 V RHE Under voltage conditions, IPA and acetone were partially detected as products.

[0174] Figure 21 is a comparison chart of two performances (selectivity and alcohol production rate) between the high-entropy oxide catalyst (HEO (our work)) of the present invention and the results of previous studies. It can be confirmed that the catalyst exhibits a high alcohol (ethanol) production amount and high selectivity for the target product compared to the results of previous studies.

[0175]

[0176] Experimental Example 9: Isotopic Analysis of Methane to Ethanol Conversion

[0177] Figure 22 is a chart of isotope analysis results for confirming the conversion of methane to ethanol for the high-entropy oxide catalyst of the present invention.

[0178] 13 After the CH4 reaction, the MS spectrum results showed that the m / z value of ethanol shifted by 2, confirming that ethanol was formed from methane. In addition, 18 O was reacted with an oxidizing agent containing 18 It was confirmed that ethanol was produced by oxygen formed in O.

[0179]

[0180] Experimental Example 10: Results of an experiment using a HEO catalyst in a continuous flow reactor

[0181] Performance experiments were conducted on the continuous flow reactor manufactured according to Example 3, including ethanol production rate and selectivity according to methane injection flow rate, and changes in current density over time. The electrolyte flow rate in the reactor was set to 3 ml / min, and the methane gas flow rate was optimized through experiments at different flow rates, and a voltage of 1.5 V was applied.

[0182] Figure 23 is a chart showing the results of measuring the ethanol production rate according to the methane injection flow rate for a continuous flow reactor to which the high-entropy oxide catalyst of the present invention is applied. Through evaluation of the ethanol production amount (rate) according to the flow rate of various methanes, it was confirmed that as the flow rate increases, the partial pressure increases, which not only increases the solubility of methane but also improves mass transfer, thereby increasing the hourly production amount of ethanol.

[0183] Figure 24 is a chart showing the results of measuring the selectivity of each product according to the methane injection flow rate for a continuous flow reactor to which the high-entropy oxide catalyst of the present invention is applied, and is 26553.4 μmol / g at a methane injection flow rate of 125 sccm. cat The maximum ethanol production rate of / hr was achieved, and an ethanol selectivity of approximately 63% was observed.

[0184] Meanwhile, Fig. 25 is a chart showing the results of measuring the current density over the reaction (operation) time for a continuous flow reactor to which the high-entropy oxide catalyst of the present invention is applied. It shows that the current density decreases by only about 14% during a long-term reaction of 100 hours, confirming that stable operation is possible even for a long time.

[0185]

[0186] Experimental Example 11: Analysis of the physical properties of the HEO catalyst before and after the reaction.

[0187] The morphology and electrochemical property changes of the HEO catalyst after 100 hours of reaction were analyzed according to Experimental Example 10 described above.

[0188] Figure 26 is a chart showing the results of TEM / EDS analysis of a catalyst after 100 hours of reaction through a continuous flow reactor using the high-entropy oxide catalyst of the present invention. As a result of the analysis, it was confirmed that a spherical morphology of approximately 50 nm was maintained, and it was confirmed that the five metal elements were still uniformly distributed.

[0189] Figure 27 shows the XRD analysis result chart (left) and the EIS (electrochemical impedance spectroscopy) analysis result chart (right) of the catalyst after 100 hours of reaction through a continuous flow reactor to which the high-entropy oxide catalyst of the present invention is applied. The analysis results show that there is no change in the structure before and after the reaction and that there is almost no change in the charge transfer resistance on the catalyst surface, which means that the catalyst maintains stable characteristics even after long-term operation.

[0190] In addition, the XPS valence ratio of the metal elements before / after 100 hours of reaction was analyzed. Figure 28 is an XPS valence ratio analysis chart for five elements of the catalyst after 100 hours of reaction through a continuous flow reactor using the high-entropy oxide catalyst of the present invention. All five metal elements maintained almost the same ratio before / after the reaction, and in the case of O, only the ratio of adsorbed oxygen increased after the reaction.

[0191]

[0192] Experimental Example 12: Measurement of methane conversion rate of HEO catalyst through a demonstration experiment at a sewage treatment plant.

[0193] Gas generated from the Baekam livestock waste treatment facility in Korea was captured and analyzed for methane composition using gas chromatography (GC). The gas comprised approximately 1% methane (low concentration), with nitrogen (N2) accounting for approximately 78%, oxygen (O2) approximately 20%, and carbon dioxide and carbon monoxide (CO2 / CO) approximately 1%.

[0194] A GC (including a thermal conductivity detector (TCD)) was directly connected to the continuous flow reactor manufactured according to Example 3, and the GC peak according to the presence or absence of voltage application was normalized to the graph for the inert gas N2, and the methane conversion rate was analyzed through the peak area ratio of the reaction gas methane (CH4). At this time, the continuous flow reactor according to Example 3 applied a voltage of 6 V to a 4-stack cell using a HEO Co 60 catalyst (1.5 V applied per cell, and it is a 2-electrode reaction system). The methane flow rate was 50 sccm, and the electrolyte flow rate was 0.5 M Na2CO3 3 ml / min.

[0195] Figure 29 is a chart showing the results of conversion and alcohol selectivity measurements for a demonstration gas (10% methane / air mixture) and a demonstration gas (containing approximately 1% methane) according to this experimental example. The experimental results showed a methane conversion rate of 21.6% for the demonstration gas and a methane conversion rate of 24.6% for the demonstration gas (containing approximately 1% methane). In addition, the selectivity of alcohol according to the methane flow rate was analyzed. Carbon-derived substances such as carbon monoxide and carbon dioxide were not detected in the gaseous product detection using gas chromatography, and the liquid product was measured using gas chromatography-mass spectrometry (GC-MS). As a result, the selectivity for ethanol was approximately 95%.

[0196] Figure 30 is a chart showing the results of long-term methane conversion measurements according to this experimental example. Long-term methane conversion analysis under a 50 sccm gas flow rate confirmed that the methane conversion remained constant at approximately 20% over a 10-hour evaluation. No CO2 was detected in GC analysis of the product, and the selectivity for ethanol also remained at approximately 95%.

[0197] As described above, it can be confirmed that the HEO catalyst according to the present invention and the continuous flow reactor using the same can be effectively applied to reduce environmental pollution in places where methane gas is generated, such as livestock manure treatment facilities.

[0198]

[0199] Although the embodiments and experimental examples of the present invention have been described with reference to the attached drawings, those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical concept or essential features thereof. Therefore, the embodiments described above should be understood to be illustrative in all respects and not restrictive.

Claims

1. As a metal oxide catalyst for electrochemical methane conversion, The above metal includes metal elements composed of chromium (Cr), cobalt (Co), iron (Fe), manganese (Mn) and nickel (Ni), The above metal oxide catalyst is a high-entropy oxide catalyst characterized in that the metal elements are independently and evenly distributed and randomly (disorderly) arranged throughout the single lattice structure, wherein the metal oxide catalyst has a single lattice structure.

2. In paragraph 1, The above metal oxide catalyst is a high-entropy oxide catalyst characterized in that it is a spherical particle having a nano-scale diameter.

3. In paragraph 1, The above metal oxide catalyst is a high-entropy oxide catalyst characterized in that it is (CoCrFeMnNi)3O4 having a single-lattice spinel structure.

4. In paragraph 1, The above metal is a high-entropy oxide catalyst characterized in that it is composed of 6 to 10 mol% of chromium (Cr), cobalt (Co), iron (Fe), manganese (Mn), and nickel (Ni).

5. In paragraph 1, S of the above metal oxide catalyst config A high-entropy oxide catalyst characterized by a value of 1.5R or more (where R is the gas constant).

6. In paragraph 1, The above metal is composed of more than 10 mol% of cobalt (Co) and 5 to 10 mol% of chromium (Cr), iron (Fe), manganese (Mn) and nickel (Ni), S of the above metal oxide catalyst config A high-entropy oxide catalyst characterized by a value of 1.5R or more (where R is the gas constant).

7. In paragraph 1, The above metal oxide catalyst has a voltage of 1.4 to 1.8 V RHE Ethanol production rate (μmol / g) under conditions cat A high-entropy oxide catalyst characterized in that the selectivity (%) for ethanol among the total products is 50% or more and the rate of reaction ( / hr) is 6,000 to 13,000.

8. In paragraph 1, The above metal oxide catalyst has a voltage of 1.5 to 1.7 V RHE Ethanol production rate (μmol / g) under conditions cat A high-entropy oxide catalyst characterized in that the selectivity (%) for ethanol among the total products is 59% or more and the rate of reaction ( / hr) is 8,000 to 13,000.

9. In paragraph 1, The above metal oxide catalyst has a voltage of 1.5 to 1.6 V RHE Ethanol production rate (μmol / g) under conditions cat A high-entropy oxide catalyst characterized in that the selectivity (%) for ethanol among the total products is 68% or more and the rate of reaction ( / hr) is 8,000 to 13,000.

10. A gas diffusion electrode comprising the high-entropy oxide catalyst of paragraph 1.

11. A reaction vessel including a gas diffusion electrode, a counter electrode, and an electrolyte of Article 10 as a working electrode; A voltage application unit for applying voltage to the above reaction tank; A methane supply unit that supplies gaseous methane to the above reactor in a continuous flow; A flow control unit that controls the flow rate of supplied methane; A methane discharge unit for discharging unreacted methane from the above reactor; and A product obtaining unit for obtaining a reaction product including ethanol; A continuous flow reactor comprising:

12. In paragraph 11, The above electrolyte is carbonate (CO3 2- ) A continuous flow reactor characterized by containing ions.

13. A step of preparing a reaction vessel including a gas diffusion electrode, a counter electrode, and an electrolyte of item 10 as a working electrode; A step of applying voltage to the above reaction tank; A step of supplying gaseous methane in a continuous flow to the above reactor to produce a reaction product including ethanol; and A step of obtaining the above reaction product; A method for producing ethanol based on electrochemical methane conversion citing a continuous flow reaction including .

14. In paragraph 13, Ethanol production rate (μmol / g) under the condition of 50 to 125 sccm of methane supply flow rate in the above gaseous state cat A method for producing ethanol based on electrochemical methane conversion using a continuous flow reaction, characterized in that the rate of methane conversion ( / hr) is 15,000 to 27,000 and the selectivity (%) for ethanol among the total products is 60% or more.

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