Catalyst for methane-ethanol conversion and electrochemical methane-ethanol continuous conversion system comprising same

Abstract

The present invention relates to a catalyst for methane-ethanol conversion and an electrochemical methane-ethanol continuous conversion system comprising same. The catalyst for methane-ethanol conversion according to the present invention reduces energy consumption and maximizes ethanol selectivity, ethanol production rate, and Faradaic efficiency in methane-ethanol conversion. In addition, the electrochemical methane-ethanol continuous conversion system according to the present invention significantly improves the mass transfer efficiency of methane, consumes less energy for methane-ethanol conversion, maximizes ethanol selectivity, ethanol production rate, and Faradaic efficiency, and has long-term operation stability.

Description

Catalyst for methane-ethanol conversion and electrochemical methane-ethanol continuous conversion system including the same

[0001] The present invention relates to a catalyst for methane-ethanol conversion and an electrochemical methane-ethanol continuous conversion system including the same, and more specifically, to a catalyst for methane-ethanol conversion that reduces energy consumption and maximizes ethanol selectivity, ethanol production rate, and Faraday efficiency, and an electrochemical methane-ethanol continuous conversion system including the same.

[0002]

[0003] Methane, one of the greenhouse gases, has a global warming potential 20 times greater than carbon dioxide and a greenhouse effect 80 times stronger than that of carbon dioxide; it also has the second-highest contribution to climate change after carbon dioxide. Furthermore, due to its physical and chemical properties, methane is a very stable substance, which limits its utilization. Accordingly, research to reduce methane itself is being conducted simultaneously with research to convert already generated methane into useful substances.

[0004] Traditional chemical methane conversion is carried out indirectly via synthesis gas, a process that generally requires high temperature and pressure conditions. Furthermore, such synthesis gas conversion has low energy efficiency because it involves carbon monoxide (CO) as an intermediate. Consequently, the development of technologies for the direct conversion of methane is considered important.

[0005]

[0006] Recently, research on the direct electrochemical conversion of methane has been actively underway. Direct electrochemical conversion is a method that forms a product directly in the liquid phase by partially oxidizing methane, utilizing active oxygen species (OH) on the catalyst surface. * , O *The reaction is accelerated using ), and product separation is also easy. In addition, the reaction energy barrier can be lowered by applying voltage, which has the advantage of enabling methane conversion even under room temperature and pressure conditions.

[0007] However, conventionally reported electrochemical direct conversion technologies had limitations in commercial application due to low conversion speed and product selectivity.

[0008]

[0009] The present invention is designed to solve the aforementioned problems and aims to provide a catalyst for methane-ethanol conversion that reduces energy consumption and maximizes ethanol selectivity, ethanol production rate, and Faraday efficiency in methane-ethanol conversion.

[0010] In addition, the present invention has another objective of providing a method for manufacturing a methane-ethanol conversion catalyst capable of manufacturing the methane-ethanol conversion catalyst of the present invention.

[0011] In addition, another objective of the present invention is to provide an electrochemical methane-ethanol continuous conversion system that significantly improves the mass transfer efficiency of methane, reduces energy consumption for methane-ethanol conversion, maximizes ethanol selectivity, ethanol production rate, and Faraday efficiency, and provides long-term operational stability.

[0012] In addition, another objective of the present invention is to provide an electrochemical methane-ethanol continuous conversion method that significantly improves the mass transfer efficiency of methane, reduces energy consumption for methane-ethanol conversion, maximizes ethanol selectivity, ethanol production rate, and Faraday efficiency, and provides long-term operational stability.

[0013]

[0014] The problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art to which the present invention belongs from the description below.

[0015]

[0016] To solve the aforementioned problem, OH formed on a catalyst using water as a raw material * Adsorption, O * formation, OOH * Reactive oxygen species (O₂), which are intermediate products formed within the pathway of the four-step oxygen evolution reaction (OER), which involves formation and oxygen (O₂) production. * As a catalyst for converting methane into ethanol via ), it contains ruthenium (Ru) and oxygen (O), and is provided with a Coordinatively Unsaturated Site (CUS) containing ruthenium (Ru) on its surface, and has cross-linked oxygen (O) on its surface Br ) Provides a catalyst for methane-ethanol conversion in which a valence is coordinately bonded to ruthenium (Ru).

[0017] According to one embodiment of the present invention, some of the ruthenium (Ru) and oxygen (O) may be contained as RuO2 crystals.

[0018] In addition, the above-mentioned cross-linking oxygen (O br ) atoms can be coordinately bonded with ruthenium (Ru) on the surface (110) of the above RuO2 crystal.

[0019] In addition, the catalyst can be doped with niobium (Nb).

[0020] In addition, the niobium (Nb) can be doped at 2 to 12 at% based on the total catalyst.

[0021] In addition, the above catalyst may have an average diameter of 14 to 25 nm.

[0022] In addition, the above catalyst is OH * Adsorption, O * formation, OOH *In the four-step oxygen evolution reaction (OER), which involves the formation and production of oxygen (O2), -OOH * The formation phase can be the Rate Determining Step (RDS).

[0023] In addition, the above catalyst is O * The change in free energy (ΔG) during the formation phase is OOH * It can be more than 0.7 eV lower than the change in free energy during the formation phase.

[0024]

[0025] To solve the above-mentioned problem, a method for manufacturing a catalyst for methane-ethanol conversion is provided, comprising: (1) a step of mixing a ruthenium (Ru) precursor and a stabilizer in a solvent to form a mixture; and (2) a step of heat-treating the mixture to produce a catalyst for methane-ethanol conversion.

[0026] In addition, in step (1) above, a niobium (Nb) precursor can be further mixed into the solvent.

[0027] In addition, in step (2) above, the heat treatment is an oxidation heat treatment, and the heat treatment temperature may be 460 to 590 ℃.

[0028]

[0029] To solve the above-mentioned problem, an electrochemical methane-ethanol continuous conversion system for converting ethanol from gaseous methane and a water electrolyzer supplied continuously comprises: a pair of end plate sections; at least one electrochemical cell section fixed between the end plate sections, wherein gaseous methane is supplied and a catalyst layer comprising the above-mentioned methane-ethanol conversion catalyst is disposed on one side, a cathode section to which a water electrolyzer is supplied, and a porous membrane separating the anode section and the cathode section; and a power supply section electrically connected to the anode section and the cathode section.

[0030] According to one embodiment of the present invention, the anode portion may include a gas diffusion electrode having a first flow plate having a methane flow path formed on one surface, a gas diffusion layer disposed to be in contact with the one surface of the first flow plate, and a catalyst layer disposed to be facing a porous membrane on the gas diffusion layer.

[0031] In addition, the above cathode portion may be provided with a second flow plate that functions as a current collector and has a water electrolytic fluid flow path formed on one surface.

[0032] In addition, OH formed on the above-mentioned methane-ethanol conversion catalyst * Adsorption, O * formation, OOH * Reactive oxygen species (O₂), an intermediate product of the four-step oxygen evolution reaction (OER), which involves formation and the production of oxygen (O₂). * ) is generated, but OOH * Voltage can be applied from the voltage supply unit at a level where it is not formed.

[0033] In addition, the voltage applied from the voltage supply unit is 1.27 to 1.48 V based on the reversible hydrogen electrode. RHE It could be.

[0034] In addition, the voltage applied from the voltage supply unit is 1.35 to 1.55 V based on the platinum electrode. Pt It could be.

[0035] The above electrochemical methane-ethanol continuous conversion system may further include a methane supply unit, and the methane supply unit may be controlled so that the methane supplied to the anode side has a flow rate of 30 to 200 sccm.

[0036]

[0037] To solve the above-mentioned problem, an electrochemical methane-ethanol continuous conversion method for converting ethanol from gaseous methane and a water electrolyzer supplied continuously is provided, comprising the steps of: supplying methane to the anode side and supplying a water electrolyzer to the cathode side of an electrochemical cell comprising an anode part, a cathode part, and a porous membrane separating the anode part and the cathode part, wherein a catalyst layer including the methane-ethanol conversion catalyst described above is disposed on one side; and applying a predetermined voltage to the electrochemical cell part so that methane is converted into ethanol on the anode.

[0038] According to one embodiment of the present invention, the production rate of the ethanol may be 15,000 μmol / h or more per 1g of the methane-ethanol conversion catalyst, and the selectivity of the ethanol may be 80% or more.

[0039]

[0040] Meanwhile, it is disclosed that the present invention was developed with the support of the following national research and development project.

[0041] [National R&D Project that supported this invention 1]

[0042] [Project ID] 2710018537

[0043] [Assignment No.] 00466477

[0044] [Ministry Name] Ministry of Science and ICT

[0045] [Name of Project Management (Specialized) Agency] National Research Foundation of Korea

[0046] [Research Project Name] Global C1 Gas Refinery Value-Up (R&D)

[0047] [Research Project Title] Development of Technology for the Production of Lactones and Organic Acids through High Concentration of C1 Off-Gas Species

[0048] [Name of Project Performing Organization] Chung-Ang University

[0049] [Research Period] July 1, 2024 ~ December 31, 2028

[0050]

[0051] [National R&D Project that supported this invention 2]

[0052] [Project ID] 2710006821

[0053] [Assignment No.] 00459242

[0054] [Ministry Name] Ministry of Science and ICT

[0055] [Name of Project Management (Specialized) Agency] Korea Institute for Science and Technology Commercialization

[0056] [Research Project Name] Support Project for Activating Industry-Academic-Research Cooperation

[0057] [Project Title] 2024 University Technology Management Promotion Project (TLO Innovation Type)_Korea University

[0058] [Name of Project Performing Organization] Korea University Industry-Academic Cooperation Foundation

[0059] [Research Period] July 1, 2024 ~ December 31, 2026

[0060]

[0061] The catalyst for methane-ethanol conversion according to the present invention reduces energy consumption in methane-ethanol conversion and maximizes ethanol selectivity, ethanol production rate, and Faraday efficiency.

[0062] In addition, the method for manufacturing a methane-ethanol conversion catalyst according to the present invention can manufacture the methane-ethanol conversion catalyst of the present invention.

[0063] Furthermore, the electrochemical methane-ethanol continuous conversion system and electrochemical methane-ethanol continuous conversion method according to the present invention significantly improve the mass transfer efficiency of methane, reduce energy consumption for methane-ethanol conversion, maximize ethanol selectivity, ethanol production rate, and Faraday efficiency, and possess long-term operational stability.

[0064]

[0065] The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the composition of the invention described in the description or claims of the present invention.

[0066]

[0067] FIG. 1 is a schematic diagram illustrating the mechanism of a catalyst for methane-ethanol conversion according to a preferred embodiment of the present invention, wherein green represents ruthenium, yellow represents CUS (Coordinatively Unsaturated Site) oxygen, and red represents cross-linking oxygen (O Br ) is. FIG. 1a shows the (110) plane of a rutile-phase oxide as a catalyst for methane-ethanol conversion, and FIG. 1b shows OH * Adsorption, O * formation, OOH * In the four-step oxygen evolution reaction (OER), which involves the formation and production of oxygen (O2), O * Figure 1c illustrates the formation stage and the CH bond dissociation process of methane.

[0068] Figure 2 is a TEM (Transmission Electron Microscopy) image showing various catalyst particles according to the sintering temperature during the manufacturing process of a methane-ethanol conversion catalyst according to the present invention.

[0069] FIG. 3 is an HR-TEM (High Resolution-Transmission Electron Microscopy) image showing the (110) and (101) crystal planes of various catalysts according to the sintering temperature in the process of manufacturing a catalyst for methane-ethanol conversion according to the present invention.

[0070] Figure 4 shows the X-ray diffraction (XRD) results of various catalysts according to the sintering temperature during the manufacturing process of a catalyst for methane-ethanol conversion according to the present invention.

[0071] Figure 5 shows the particle size distribution of various catalysts according to the sintering temperature in the manufacturing process of a catalyst for methane-ethanol conversion according to the present invention.

[0072] Figure 6 shows the LSV (Linear Sweep Voltammetry) results of various catalysts according to the sintering temperature in the manufacturing process of a catalyst for methane-ethanol conversion according to the present invention.

[0073] Figures 7a to 7e show the results of cyclic voltammetry (CV) analysis of various catalysts according to the sintering temperature in the manufacturing process of a catalyst for methane-ethanol conversion according to the present invention, and Figure 7f shows the results of electrochemically active surface area (EAS) of various catalysts according to the sintering temperature in the manufacturing process of a catalyst for methane-ethanol conversion according to the present invention.

[0074] FIG. 8 is a TEM image showing catalyst particles when Nb is doped into a catalyst for methane-ethanol conversion according to a preferred embodiment of the present invention.

[0075] Figure 9 is the result of Energy Dispersive X-ray Spectroscopy (EDS) mapping of catalyst particles when Nb is doped into a catalyst for methane-ethanol conversion according to a preferred embodiment of the present invention.

[0076] Figure 10 shows the XANES (X-ray Absorption Near Edge Structure) Ru K-edge analysis results of various methane-ethanol conversion catalysts.

[0077] Figure 11 shows the XRD results of various catalysts according to Nb content when Nb is doped into the methane-ethanol conversion catalyst according to the present invention.

[0078] Figure 12 shows the LSV results of various catalysts according to Nb content when Nb is doped into the methane-ethanol conversion catalyst according to the present invention.

[0079] Figure 13 shows the current density results over a 24-hour period under 0.5M H2SO4 electrolyte conditions for the case where Nb is doped into the methane-ethanol conversion catalyst according to the present invention and the case where it is not doped.

[0080] FIG. 14a is a Gibbs energy diagram of the oxygen evolution reaction (OER) process of a catalyst for methane-ethanol conversion according to the present invention, and FIG. 14b is OH * Adsorption, O * formation, OOH * This is the result of a microkinetic analysis of the four-step oxygen evolution reaction (OER), which includes formation and the production of oxygen (O2).

[0081] Figure 15 shows the results of the analysis of the methane oxidation reaction in the catalyst when Nb is doped into the methane-ethanol conversion catalyst according to the present invention. Figure 15a shows the LSV results when saturated with methane and when methane is absent, and Figure 15b shows the voltage at 1.6 V. RHE This is a photograph of oxygen and hydrogen generation at that time, and Fig. 15c is the result of GC (Gas Chromatography) analysis.

[0082] Figure 16 shows the results of the analysis of liquid oxygen compounds, such as ethanol, produced during the methane oxidation reaction in an Nb-doped catalyst for methane-ethanol conversion. Figure 16a shows the results of the production rate of liquid oxygen compounds, such as ethanol, and Figure 16b shows the results of the selectivity of liquid oxygen compounds, such as ethanol.

[0083] Figure 17 shows the mass spectrometry (MS) results of the liquid phase product generated during the methane oxidation reaction in an Nb-doped catalyst for methane-ethanol conversion.

[0084] FIG. 18 is a schematic diagram of a decomposition of a methane-ethanol continuous conversion system according to a preferred embodiment of the present invention.

[0085] FIG. 19 is a schematic diagram illustrating a methane-ethanol conversion reaction carried out on a methane-ethanol continuous conversion system according to a preferred embodiment of the present invention.

[0086] FIG. 20 is an external photograph of a methane-ethanol continuous conversion system according to a preferred embodiment of the present invention.

[0087] FIG. 21 shows the results of the production rate and selectivity of ethanol produced in a methane-ethanol continuous conversion system according to a preferred embodiment of the present invention, where FIG. 21a is voltage V Pt Figure 21b is the result according to the methane supply flow rate.

[0088] FIG. 22 is a graph of current density over time measured at the anode when operating a methane-ethanol continuous conversion system according to a preferred embodiment of the present invention.

[0089]

[0090] Hereinafter, the present invention will be described in detail with reference to the attached drawings so that those skilled in the art can easily implement it. The present invention may be embodied in various forms and is not limited to the embodiments described herein. In the drawings, parts not directly related to the description have been omitted to clearly explain the present invention, and the same reference numerals are assigned to identical or similar components throughout the specification.

[0091] The terms used in this specification are used merely to describe specific embodiments and are not intended to limit the invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, terms such as “comprising” or “having” should be understood as indicating the presence of the features, numbers, steps, actions, components, or combinations thereof described in the specification, and not as precluding the possibility that one or more other features, numbers, steps, actions, components, or combinations thereof may be present or added.

[0092] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms identical to those defined in commonly used dictionaries should be interpreted in a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined herein.

[0093] When a part such as a layer, membrane, region, or plate is said to be "above," "below," or "next to" another part, this includes not only cases where it is "immediately above," "immediately below," or "immediately next to" the other part, but also cases where there is another part in between. Conversely, when a part is said to be "immediately above," "immediately below," or "immediately next to" another part, it means that there is no other part in between.

[0094]

[0095] As mentioned above, conventional electrochemical direct conversion technologies had limitations in commercial application due to their low conversion speed and product selectivity.

[0096]

[0097] Accordingly, the present invention relates to an OH formed on a catalyst using water as a raw material. * Adsorption, O * formation, OOH * Reactive oxygen species (O₂), which are intermediate products formed within the pathway of the four-step oxygen evolution reaction (OER), which involves formation and oxygen (O₂) production. * As a catalyst for converting methane into ethanol via ), it contains ruthenium (Ru) and oxygen (O), and is provided with a Coordinatively Unsaturated Site (CUS) containing ruthenium (Ru) on its surface, and has cross-linked oxygen (O) on its surface BrA solution to the aforementioned problem was sought by providing a catalyst for methane-ethanol conversion in which a ) atom is coordinately bonded to ruthenium (Ru).

[0098] This allows for lowering energy consumption in methane-ethanol conversion and maximizing ethanol selectivity, ethanol production rate, and Faraday efficiency.

[0099]

[0100] Referring to FIG. 1, the catalyst for methane-ethanol conversion according to the present invention comprises an OH formed on the catalyst using water as a raw material. * Adsorption, O * formation, OOH * Methane is converted into ethanol using a four-step oxygen evolution reaction (OER), which involves the formation and generation of oxygen (O2). Specifically, referring to FIG. 1b, OH supplied from water is applied to the ruthenium site of the coordination unsaturated active site. * is adsorbed, and OH * from O * It can be formed. Referring to Fig. 1c, methane is cross-linked oxygen (O Br Giving H to the ) atom and the above O * It attaches to form CH3O, and generates a synergistic effect with a cross-linking oxygen atom to oxidize methane to CH3O, and CH3O can spontaneously form CH2O through further deprotonation. The CH2O thus formed can combine with methane (CH4) to finally form ethanol. Ultimately, the catalyst of the present invention is the above O * Methane can be effectively converted into ethanol through the synergistic effect of the cross-linked oxygen atoms.

[0101]

[0102] The above catalyst for methane-ethanol conversion contains ruthenium (Ru) and oxygen (O). In this case, some of the ruthenium (Ru) and oxygen (O) may be contained in the catalyst as ruthenium oxide crystals, i.e., RuO2 crystals.

[0103] The above catalyst includes RuO2 crystals, and active oxygen O on the catalyst surface * It can be advantageous to maintain [this], and accordingly, the catalyst can effectively convert methane into ethanol, and since the methane-ethanol conversion reaction is maximized at [this] before the activation of the competing oxygen evolution reaction, the Faraday efficiency can be increased.

[0104]

[0105] The above-described catalyst for methane-ethanol conversion has a coordination unsaturated active site containing ruthenium (Ru) on its surface. Through this, the ruthenium of the coordination unsaturated active site is an intermediate product (O * It is strongly coupled with (etc.), and as a result, the ethanol production efficiency can be very excellent.

[0106] At this time, the ruthenium of the coordination unsaturated active site can be coordinated and fixed by oxygen, and the cross-linking oxygen (O Br It may be in a coordinately unsaturated state by ) atoms.

[0107] In addition, the ruthenium of the coordination unsaturated active site may be present on the (110) surface of the RuO2 crystal.

[0108]

[0109] The above methane-ethanol conversion catalyst has cross-linked oxygen (O) on its surface Br The atom is coordinately bonded with ruthenium (Ru).

[0110] The above-mentioned cross-linked oxygen (O Br The ) atoms can be coordinately bonded with ruthenium (Ru) on the surface (110) of the RuO2 crystal, and the ruthenium bonded to the cross-linking oxygen atoms becomes coordinately unsaturated, resulting in an intermediate product (O * It can be strongly bonded with (etc.), and the ethanol production rate and ethanol selectivity can be excellent. This is because the intermediate (O) coordinated to the cross-linked oxygen atom and ruthenium * This is because steric hindrance is minimized during methane activation by means of (etc.), thereby sufficiently lowering the activation energy for ethanol conversion.

[0111]

[0112] Referring to FIGS. 8 and 9, the methane-ethanol conversion catalyst can be doped with niobium (Nb). The methane-ethanol conversion catalyst is Ru under acidic reaction conditions and high voltage conditions 4+ Problems such as reduced reaction stability and activity may occur due to the peroxidation of ruthenium, but the stability of the reaction process can be improved as electrons from niobium are transferred to ruthenium through niobium doping, thereby increasing the electron density of ruthenium (see Fig. 13).

[0113] When the above niobium is doped, the ruthenium contained in the catalyst may have an oxidation state of +3 to +4 (see Fig. 10), and through this, the stability of the reaction process is increased, so the durability of the catalyst may be excellent (see Fig. 13).

[0114] The niobium can be doped into the catalyst at a concentration of 2 to 12 at% based on the total catalyst, and preferably at a concentration of 6 to 12 at%. Referring to FIGS. 11 and 12, if niobium is doped at less than 2 at%, it is not sufficiently doped, and as the cycle progresses, the stability and activity of the reaction may decrease due to the peroxidation of ruthenium. On the other hand, if niobium is doped at a concentration exceeding 12 at%, the RuO2 crystals expand excessively, causing defects in the crystal structure and reducing crystallinity, which may result in a decrease in the long-term stability of the catalyst. Meanwhile, if the niobium doping content is in the range of 6 to 12 at%, stable current density results can be observed even during long-term operation.

[0115]

[0116] Referring to FIGS. 2 to 7, the catalyst for methane-ethanol conversion may have an average diameter of 14 to 25 nm, preferably 14 to 19 nm. If the average diameter is less than 14 nm, it may not be sufficiently crystallized, resulting in low methane-ethanol conversion reaction activity and thus reduced catalytic performance. On the other hand, if the average diameter exceeds 25 nm, the average diameter of the catalyst particles is excessively large, resulting in a low electrochemically active surface area and thus reduced catalytic performance, such as reduced methane-ethanol conversion efficiency. Meanwhile, when the average diameter is between 14 and 19 nm, the average diameter of the catalyst particles is appropriate, resulting in excellent crystallinity and a sufficiently large electrochemically active surface area, which can lead to excellent catalytic performance.

[0117]

[0118] The above-mentioned catalyst for methane-ethanol conversion is OH * Adsorption, O * formation, OOH * In the four-step oxygen evolution reaction (OER) of formation and oxygen (O2) generation, OOH * The formation step can be the Rate Determining Step (RDS). OOH * When the formation phase is the rate determination phase, O * OOH * Because the conversion speed is slow, O on the surface * There can be many, and O * is produced by extracting hydrogen atoms from methane to form OH * Since it forms and promotes conversion to ethanol, the methane-ethanol conversion performance can be excellent.

[0119] Referring to FIG. 14, the OOH * The formation stage as a rate determining stage, O * The change in free energy (ΔG) during the formation phase is OOH *It can be more than 0.7 eV lower than the free energy change during the formation phase. If there is such a difference in energy change, O on the surface * While there is sufficient existence, O * It extracts hydrogen from methane and OH * As it becomes easier to form, ethanol conversion performance can be maximized.

[0120]

[0121] To solve the above-mentioned problem, a method for manufacturing a catalyst for methane-ethanol conversion is provided, comprising: (1) a step of mixing a ruthenium (Ru) precursor and a stabilizer in a solvent to form a mixture; and (2) a step of heat-treating the mixture to produce a catalyst for methane-ethanol conversion.

[0122] Through this, the methane-ethanol conversion catalyst of the present invention can be manufactured.

[0123]

[0124] First, as step (1), a ruthenium (Ru) precursor and a stabilizer are mixed in a solvent to form a mixture.

[0125] The above ruthenium precursor is not particularly limited as long as it is a material that provides ruthenium, but preferably it may be one or more selected from ruthenium oxide, ruthenium halide, ruthenium nitride, ruthenium carbide, ruthenium sulfide, ruthenium phosphide, and ruthenium acetylacetonate. More preferably it may be a ruthenium halide, and most preferably it may be a ruthenium chloride, for example, ruthenium chloride hydrate.

[0126] The above ruthenium precursor may be 10 to 50 mol / L based on 1 L of the solvent, but is not limited thereto.

[0127]

[0128] The above stabilizer can increase the dispersibility of the ruthenium precursor and control the particle growth of ruthenium metal, thereby enabling the generation of uniform particles.

[0129] The above stabilizer is not particularly limited as long as it can control the growth of ruthenium metal particles formed from a ruthenium precursor, but preferably, the stabilizer may be at least one of polyvinyl pyrrolidone, polyethylene glycol, and polyethylenemine.

[0130] The above stabilizer may be 1 to 20 g / L based on 1 L of the solvent, but is not limited thereto.

[0131]

[0132] The above solvent is not limited as long as it is capable of dispersing the ruthenium precursor and the stabilizer, so the present invention does not specifically limit it. For example, the solvent may be water, methanol, ethanol, propanol, butanol, glycerin, t-butyl alcohol, dimethylformamide (DMF), diethylformamide (DEF), acetonitrile, dimethoxyethane (DME), dioxane, tetrahydrofuran (THF), ethylene glycol, acetone, ethyl acetate, dimethyl sulfoxide (DMSO), or a combination thereof. Preferably, it may be ethanol.

[0133]

[0134] Meanwhile, a niobium (Nb) precursor can be further mixed into the above solvent. Through this, the catalyst for methane-ethanol conversion can be doped with niobium.

[0135] The above niobium precursor is not particularly limited as long as it is a material that provides niobium, but preferably may be one or more selected from niobium oxide, niobium halide, niobium nitride, niobium carbide, niobium sulfide, and niobium phosphide. Most preferably, it may be a niobium halide, and for example, niobium chloride.

[0136] The above niobium precursor may be 1 to 5 mol / L based on 1 L of the solvent, but is not limited thereto.

[0137]

[0138] The above mixing conditions are not particularly limited, but the mixing temperature may be 60 to 100 ℃ and the mixing time may be 2 to 18 hours.

[0139] After forming the above mixture, an additional drying step may be performed, but drying is not mandatory. In this case, any known conditions applicable in the industry may be used for the drying step.

[0140]

[0141] The mixture formed through the above step (1) may include ruthenium ions and a stabilizer. Preferably, it may include ruthenium ions, niobium ions, and a stabilizer.

[0142]

[0143] Next is step (2), in which the mixture formed in step (1) is heat-treated to produce a catalyst for methane-ethanol conversion.

[0144] The above heat treatment may be an oxidative heat treatment, and accordingly, the heat treatment may be performed in an oxygen atmosphere such as an air atmosphere. Through this, a catalyst for methane-ethanol conversion containing ruthenium and oxygen may be formed.

[0145] Referring to FIGS. 2 to 7, the heat treatment temperature may be 460 to 590 ℃. If the heat treatment temperature is less than 460 ℃, the catalyst may not be sufficiently crystallized, which may reduce the catalyst performance and leave behind impurities such as stabilizers. On the other hand, if the heat treatment temperature exceeds 590 ℃, the average diameter of the catalyst particles increases excessively, which reduces the electrochemically active surface area and thus reduces the catalyst performance.

[0146] Preferably, the heat treatment temperature may be 460 to 540 ℃. When within this range, the catalyst for methane-ethanol conversion has a sufficiently small size and excellent crystallinity, so the catalyst performance can be maximized.

[0147] The above heat treatment time may be 1 to 9 hours, but is not limited thereto, and any time that allows ruthenium to be sufficiently oxidized may be selected.

[0148]

[0149] To solve the above-mentioned problem, an electrochemical methane-ethanol continuous conversion system for converting ethanol from gaseous methane and water electrolyzer supplied continuously comprises: a pair of end plate sections (50); at least one electrochemical cell section (60) fixed between the end plate sections (50), wherein a catalyst layer (22) containing the above-mentioned methane-ethanol conversion catalyst is disposed on one side and supplied with gaseous methane, a cathode section (40) to which water electrolyzer is supplied, and a porous membrane (10) separating the anode section (30) and the cathode section (40); and a power supply section electrically connected to the anode section (30) and the cathode section (40).

[0150] Such a continuous methane-ethanol conversion system significantly improves methane mass transfer efficiency, reduces energy consumption for methane-ethanol conversion, maximizes ethanol selectivity, ethanol production rate, and Faraday efficiency, and provides long-term operational stability.

[0151] The electrochemical methane-ethanol continuous conversion system of the present invention will be described below with reference to FIG. 18.

[0152]

[0153] First, a pair of end plate sections (50) will be described.

[0154] The above pair of end plate sections (50) supports the electrochemical cell section (60) from both sides to secure the electrochemical cell section (60) and maintain a constant securing pressure between the cells, and is intended to prevent leakage of the power applied during operation and leakage of the supplied reactants and products. In the case of known end plates used in electrochemical reaction devices, they may be used without limitation. For example, the above end plate section (50) may include a supply section and a discharge section for the converted product (reactant) and the electrolyte, respectively. For example, one end plate section (50) of the pair of end plate sections (50) may include a supply section through which methane, which is the converted product (reactant), is supplied internally, and a discharge section through which the unconverted methane is discharged externally. Additionally, the other end plate section (50) on the other side may include a supply section through which the electrolyte is supplied internally and a discharge section through which the unreacted electrolyte is discharged externally.

[0155] Meanwhile, FIG. 18 illustrates that a supply section and a discharge section are formed in the end plate section (50) to supply the converted product and the electrolyte to the electrochemical cell section (60), but it is not limited thereto. The supply section and the discharge section may be designed so that the converted product (reactant), methane, and the electrolyte, water electrolytic solution, are directly supplied and discharged from the outside to the electrochemical cell section (60), and the present invention is not specifically limited thereto.

[0156]

[0157] Next, the electrochemical cell part (60) is described.

[0158] The electrochemical cell portion (60) includes an anode portion (30), a cathode portion (40), and a porous membrane (10) that separates the anode portion (30) and the cathode portion (40).

[0159] The above anode portion (30) has a catalyst layer (22) comprising a catalyst for methane-ethanol conversion according to one embodiment of the present invention described above disposed on one side, and specifically, the catalyst layer (22) may be provided on a gas diffusion layer (21) and provided within the anode portion (30) as a gas diffusion electrode (20).

[0160] The gas diffusion layer (21) constituting the gas diffusion electrode (20) can provide a diffusion passage for methane, which is the product to be converted (reactant), to move to the catalyst layer, support the catalyst layer, and function as a current collector. The gas diffusion layer (21) can be used without limitation in the case of a gas diffusion layer employed in a known electrochemical reaction device, and for example, a web formed of carbon fibers such as carbon paper, or a porous metal composed of a metal such as titanium can be used for corrosion resistance.

[0161] Additionally, the catalyst layer (22) includes a catalyst for methane-ethanol conversion, and a known binder resin such as Nafion can be used to fix it on the gas diffusion layer (21).

[0162] Additionally, the anode portion (30) may include a first flow plate (23) having a methane flow path formed on one surface, and a gas diffusion layer (21) of a gas diffusion electrode (20) may be arranged to be in contact with one surface of the first flow plate (23), and a catalyst layer (22) may be arranged within the anode portion (30) to face the porous membrane (10).

[0163] The first flow plate (23) may include a methane flow channel on one side formed to allow methane gas supplied from the end plate portion (50) to flow in a planar direction adjacent to the gas diffusion layer (21), and the methane flow channel may be, for example, a serpentine flow channel, but is not limited thereto.

[0164]

[0165] Next, the above cathode section (40) is supplied with an electrolytic solution and may include a second flow plate.

[0166] The water electrolytic solution supplied to the above cathode section (40) may contain water, and such water may serve as an oxygen source for the catalyst for methane-ethanol conversion and the electrochemical methane-ethanol continuous conversion system of the present invention. As such, since no separate oxygen source other than water is required for methane oxidation, the stability of the methane conversion reaction can be increased and the conversion cost reduced. Furthermore, because an intermediate of the oxygen evolution reaction, which is a competing reaction, is utilized, the methane-ethanol conversion efficiency is maximized and a high Faraday efficiency can be achieved.

[0167] The second flow plate above functions as a current collector and thereby can act as a reduction electrode. Additionally, the second flow plate may include a water electrolytic flow channel on one side formed to allow the water electrolytic supplied from the end plate portion (50) to flow in a planar direction adjacent to the porous membrane (10), and the water electrolytic flow channel may be, for example, a serpentine flow channel, but is not limited thereto.

[0168] Meanwhile, the first flow plate (23) and the second flow plate may be one plate constituting a known distribution plate or bipolar plate, and the known materials used therein may be used without limitation, such as metals like stainless steel or aluminum, graphite, or carbon composites in which carbon is dispersed within a polymer matrix.

[0169]

[0170] Next, the porous membrane (10) may be adopted without limitation in the case of a known separation membrane commonly used in the industry, but preferably, it may be adopted without limitation in the case of a known hydrogen separation membrane for suppressing the movement of hydrogen gas formed in the cathode portion (40) to the anode portion (30).

[0171]

[0172] Next, the power supply unit may use a power supply unit employed in a known electrochemical reaction device capable of applying voltage to form a predetermined potential across the anode (30) and cathode (40) described above, and the present invention is not specifically limited thereto.

[0173] The level of voltage applied from the above power supply unit is preferably OH formed on the methane-ethanol conversion catalyst. * Adsorption, O * formation, OOH * Reactive oxygen species (O₂), an intermediate product of the four-step oxygen evolution reaction (OER), which involves formation and the production of oxygen (O₂). *) is generated but OOH * It may be at a level where it is not formed, and through this, it avoids the competing reaction that generates oxygen in the OER reaction, thereby preventing the intermediate product reactive oxygen species (O₂). * It generates and maintains ), and the maintained reactive oxygen species (O * It is advantageous to sustain the reaction of converting methane into ethanol with high efficiency using ).

[0174]

[0175] The voltage applied from the above voltage supply unit is 1.1 to 1.88 V based on the reversible hydrogen electrode. RHE It can be, and through this, by avoiding the competitive reaction that generates oxygen in the OER reaction, the intermediate reactive oxygen species (O₂) * It can generate and maintain ), and at the same time reactive oxygen species (O *Methane can be spontaneously converted into ethanol using ). The water electrolyzer, which has moved toward the catalyst layer (22) side from the Ru atom, which is the active site of the catalyst, on the catalyst layer (22) within the anode (30), at an appropriate anode potential formed by the voltage applied to the electrochemical cell part (60), active oxygen (O * ) is generated and maintained, and active oxygen (O) adsorbed on Ru at an appropriate anodic potential from methane that has passed through the gas diffusion layer (21) * It can be converted into ethanol by reacting with ).

[0176] At this time, as an appropriate anode potential, active oxygen (O₂) from water is first * The anode potential capable of generating and maintaining ) is 1.1 V, referring to Fig. 14. RHE It could be abnormal, but reactive oxygen species is 1.1 V RHE At the anodic potential above this level, it can react with methane to break the CH bond and desorb as methanol, or be further oxidized to ethanol; therefore, through the power supply, 1.1 V RHE It is preferable that a voltage of the above be applied. Accordingly, if the voltage applied from the voltage supply unit is 1.1 V RHE If less than, reactive oxygen species (O * It may be difficult to produce ) or, even if produced, the reaction to convert methane may not occur spontaneously.

[0177] In addition, the applied voltage is 1.88 V RHE If the value exceeds [amount], the oxygen evolution reaction, which is performed competitively rather than being utilized by active oxygen on the anode for the conversion of methane, becomes active and oxygen evolution can become the dominant reaction as oxygen evolution increases rapidly. Consequently, the amount of ethanol produced decreases, and the selectivity for ethanol among the products also decreases. Furthermore, since C3 compounds such as acetone are produced in addition to alcohol and their selectivity increases, a separate separation process may need to be performed to separate ethanol.

[0178] Referring to FIG. 16, preferably, the voltage applied from the voltage supply unit is 1.27 to 1.48 V with respect to the reversible hydrogen electrode. RHE It may be, and in this case, the catalyst may be in a state doped with Nb, but it is not mandatory to dope it. Within this range, it is possible to achieve a high production rate while increasing the selectivity of ethanol. Specifically, the applied voltage is 1.27 V RHE If it becomes less than, almost no ethanol may be produced, and the applied voltage is 1.48 V RHE If exceeded, ethanol selectivity may decrease.

[0179] More preferably, the voltage applied from the voltage supply unit is 1.37 to 1.43 V with respect to the reversible hydrogen electrode. RHE It may be possible, and in this case, the catalyst may be in a state doped with Nb, but it is not mandatory to dope it. Within this range, maximized ethanol selectivity and ethanol production rate can be achieved.

[0180] Meanwhile, the voltage applied from the above voltage supply unit is 1.45 to 1.55 V based on the platinum electrode. Pt It may be possible, and in this case, the catalyst may be in a state doped with Nb, but it is not mandatory to dope it. Within this range, maximized ethanol selectivity and ethanol production rate can be achieved.

[0181]

[0182] The above electrochemical methane-ethanol continuous conversion system may further include a methane supply unit. Through this, the anode unit (30) of the system can receive methane.

[0183] The methane supply unit above can be controlled such that the flow rate of methane supplied to the anode unit (30) is 30 sccm or more, preferably 55 sccm or more, more preferably 80 sccm or more, and even more preferably 105 sccm or more, and can be controlled such that it is 200 sccm or less. When the flow rate is supplied within this range, the solubility of methane can be increased, the mass transferability through the gas diffusion layer (21) to the catalyst layer (22) can be improved, and the ethanol production rate and selectivity can be excellent. In addition, as the flow rate increases within this range, the solubility of methane increases due to the increase in pressure, and the ethanol production rate, etc., can gradually increase. Meanwhile, if the flow rate is less than 30 sccm, the increase in ethanol production may be negligible, and if the flow rate exceeds 200 sccm, the surface area of ​​the interface formed between methane and the water electrolyzer decreases, and the ethanol selectivity and production rate may decrease by destabilizing the flow of the electrolyte at the catalyst surface, and there is a concern that the long-term stability of the provided methane-ethanol conversion catalyst may be reduced.

[0184]

[0185] The above electrochemical methane-ethanol continuous conversion system may have an ethanol production rate of 15,000 μmol / h or more per 1 g of the methane-ethanol conversion catalyst, and preferably 30,000 μmol / h or more.

[0186] In addition, the electrochemical methane-ethanol continuous conversion system may have a selectivity of ethanol of 80% or more, preferably 85% or more, and more preferably 90% or more.

[0187]

[0188] To solve the above-mentioned problem, an electrochemical methane-ethanol continuous conversion method for converting ethanol from gaseous methane and water electrolyzer supplied continuously is provided, comprising: (A) a step of supplying methane to the anode section (30) and supplying water electrolyzer to the cathode section (40) of an electrochemical cell section (60) comprising an anode section (30) and a cathode section (40) having a catalyst layer (22) for methane-ethanol conversion described above disposed on one side, and a porous membrane (10) separating the anode section (30) and the cathode section (40); and (B) a step of applying a predetermined voltage to the electrochemical cell section (60) so that methane is converted into ethanol on the anode (30).

[0189] This electrochemical continuous methane-ethanol conversion method significantly improves methane mass transfer efficiency, reduces energy consumption for methane-ethanol conversion, maximizes ethanol selectivity, ethanol production rate, and Faraday efficiency, and provides long-term operational stability.

[0190]

[0191] Assuming that this methane-ethanol continuous conversion method is performed through the methane-ethanol continuous conversion system described above, the following steps are performed: (A) methane, which is the product to be converted (reactant), is supplied to the anode section (30) of the electrochemical cell section (60), and water electrolytic solution, which is the electrolyte, is supplied to the cathode section (40) of the electrochemical cell section (60).

[0192] FIG. 18 illustrates that methane and water electrolytic solution supplied to the anode section (30) and cathode section (40), respectively, are supplied through different end plate sections (50), but is not limited thereto, and both the supply / discharge of methane and the supply / discharge of water electrolytic solution may be carried out through one end plate section (50). In this case, the first flow plate (23) and the second flow plate may be equipped with a manifold through which the methane and water electrolytic solution supplied from one end plate, and the water electrolytic solution containing unreacted methane and products, can be discharged.

[0193]

[0194] Next, (B) a predetermined voltage is applied to the electrochemical cell to convert methane into ethanol on the anode.

[0195] The applied voltage can be provided through a power supply. In this case, the level of the applied voltage is preferably OH formed on the catalyst for methane-ethanol conversion. * Adsorption, O * formation, OOH * Reactive oxygen species (O₂), an intermediate product of the four-step oxygen evolution reaction (OER), which involves formation and the production of oxygen (O₂). *) is generated but OOH * It may be at a level where it is not formed, and through this, it avoids the competitive reaction that generates oxygen in the OER reaction, thereby preventing the intermediate reactive oxygen species (O₂) * It generates and maintains ), and the maintained reactive oxygen species (O * It is advantageous to sustain the reaction of converting methane into ethanol with high efficiency using ).

[0196]

[0197] The voltage applied from the above voltage supply unit is the same as that described in the electrochemical methane-ethanol continuous conversion system described above, so a detailed explanation will be omitted.

[0198] Meanwhile, since the flow rate of methane supplied through the methane supply unit is the same as that described in the aforementioned electrochemical methane-ethanol continuous conversion system, a detailed explanation will be omitted.

[0199]

[0200] In the above electrochemical methane-ethanol continuous conversion method, the production rate of ethanol may be 15,000 μmol / h or more, preferably 30,000 μmol / h or more, per 1 g of the provided methane-ethanol conversion catalyst.

[0201] In addition, in the above electrochemical methane-ethanol continuous conversion method, the ethanol selectivity may be 80% or more, preferably 85% or more, and more preferably 90% or more.

[0202]

[0203] Meanwhile, the catalyst for methane-ethanol conversion in the electrochemical methane-ethanol continuous conversion system (100) according to one embodiment of the present invention can maintain long-term stability even during a long-term methane-ethanol continuous conversion reaction. Specifically, as shown in FIG. 22, the rate of decrease in current density measured at the anode during a 100-hour continuous conversion reaction is only 5% or less, and there is almost no change in the physical properties and electrochemical characteristics of the catalyst surface after 100 hours of reaction, and through this, it can be expected that a stable reaction will continue even after 100 hours of reaction.

[0204]

[0205] The present invention will be explained more specifically through the following examples, but the following examples are not intended to limit the scope of the invention and should be interpreted as being for the purpose of aiding understanding of the invention.

[0206]

[0207] <Example>

[0208] Example 1

[0209] 0.23 mol of ruthenium chloride hydrate (RuCl3·6H2O) and 60 mg of polyvinyl pyrrolidone were dissolved in 10 mL of ethanol, and then mixed at 80 ℃ for 6 hours to form a mixture.

[0210] The above mixture was heat-treated at 400°C for 3 hours in an air atmosphere to produce a catalyst for methane-ethanol conversion (400°C heat-treated RuO2 catalyst).

[0211]

[0212] Example 2

[0213] A catalyst for methane-ethanol conversion (450 ℃ heat-treated RuO2 catalyst) was prepared by carrying out the same procedure as in Example 1, except that the heat treatment temperature was 450 ℃ instead of 400 ℃.

[0214]

[0215] Example 3

[0216] A catalyst for methane-ethanol conversion (500 ℃ heat-treated RuO2 catalyst) was prepared by carrying out the same procedure as in Example 1, except that the heat treatment temperature was 500 ℃ instead of 400 ℃.

[0217]

[0218] Example 4

[0219] A catalyst for methane-ethanol conversion (550 ℃ heat-treated RuO2 catalyst) was prepared by carrying out the same procedure as in Example 1, except that the heat treatment temperature was 550 ℃ instead of 400 ℃.

[0220]

[0221] Example 5

[0222] A catalyst for methane-ethanol conversion (600 ℃ heat-treated RuO2 catalyst) was prepared by carrying out the same procedure as in Example 1, except that the heat treatment temperature was 600 ℃ instead of 400 ℃.

[0223]

[0224] Example 6

[0225] A catalyst for methane-ethanol conversion (500°C heat treatment and 4 at% Nb-doped RuO2 catalyst) was prepared by carrying out the same procedure as in Example 3, except that niobium chloride (NbCl5) was added to ethanol to dope Nb to 4 at% based on the final catalyst.

[0226]

[0227] Example 7

[0228] A catalyst for methane-ethanol conversion (500°C heat treatment and 8 at% Nb-doped RuO2 catalyst) was prepared by carrying out the same procedure as in Example 3, except that niobium chloride (NbCl5) was added to ethanol to dope Nb to 8 at% based on the final catalyst.

[0229]

[0230] Example 8

[0231] A catalyst for methane-ethanol conversion (500°C heat treatment and 16 at% Nb-doped RuO2 catalyst) was prepared by carrying out the same procedure as in Example 3, except that niobium chloride (NbCl5) was added to ethanol to dope Nb to 16 at% based on the final catalyst.

[0232]

[0233] <Experimental Example>

[0234] Experimental Example 1: TEM-EDS Analysis and Catalyst Average Diameter Analysis

[0235] Transmission Electron Microscopy (TEM) analysis of the catalysts of Examples 1 to 5 was performed using a JEM-ARM200F microscope (JEOL) equipped with a spherical aberration corrector (probe corrector) on a condenser lens, and the results are shown in Figures 2 and 3. In addition, the average diameter distribution of the catalysts of Examples 1 to 5 was determined using the data from Figures 2 and 3, and is shown in Figure 5.

[0236] TEM analysis of the catalyst of Example 7 was performed using the above JEM-ARM200F microscope (JEOL), and the results are shown in Fig. 8. In addition, Energy Dispersive X-ray Spectroscopy (EDS) mapping of the catalyst of Example 7 was analyzed using an Oxford Instruments X-Max SDD detector and is shown in Fig. 9.

[0237]

[0238] Referring to the TEM image in Fig. 2, it can be seen that the average diameter of the RuO2 catalyst is approximately 12 to 20 nm, and that the size of the RuO2 catalyst nanoparticles increases as the heat treatment temperature increases.

[0239] Referring to the HR-TEM image in Fig. 3, lattice spacings of 0.310 nm and 0.253 nm were observed in all catalysts, which correspond to the (110) and (101) planes of the RuO2 crystal, respectively. In particular, (110) plane surface termination was observed on the particle surface, which is attributed to the low bond cleavage density of the (110) plane, as the (110) plane is the most stable.

[0240] Referring to FIG. 5, Example 1 was heat-treated at a low temperature (400 °C) and the average diameter of the catalyst was 6 nm, but as the heat treatment temperature increased, the average diameter increased as the crystals grew. Examples 2 to 5 had average diameters of 13, 16, 20, and 27 nm, respectively.

[0241]

[0242] Referring to Fig. 8, the niobium-doped catalyst of Example 7 (Example 7) did not show a significant difference in particle size compared to the undoped catalyst of Example 3.

[0243] In Fig. 9, a sparse but uniform distribution of niobium was confirmed inside the particles of Example 7.

[0244]

[0245] Experimental Example 2: XRD Analysis

[0246] X-ray diffraction (XRD) analysis of the catalysts of Examples 1 to 5 was performed using an XRD device (Rigaku Miniflex-2005G303, Rigaku) ​​and is shown in Fig. 4. At this time, Cu Kα rays of 20 kV and 10 mA were used, and the analysis was performed in a 2θ range of 10 to 70°.

[0247] XRD analysis of the catalysts of Example 3 and Examples 6 to 8 was performed using the above XRD device, and the results are shown in FIG. 11.

[0248]

[0249] Referring to Fig. 4, the catalyst of Example 1 showed distinct peaks at 26° and 35°, which correspond to the (110) and (101) planes of the rutile RuO2 crystal phase, respectively. As the heat treatment temperature increased, the peak intensity became more distinct, which is because crystallinity improved along with grain growth at high temperatures.

[0250] Referring to Fig. 11, a fine peak shift at a lower angle was observed as the doping content increased, which indicates that the crystal lattice expanded due to substitution caused by niobium doping. However, in the case where 16 at% Nb was doped as in Example 8, the peak broadened, suggesting that the size of the crystalline domain decreased with increasing doping content.

[0251]

[0252] Experimental Example 3: LSV Analysis

[0253] A potentiostat device (Versastat, Ametek) with a three-electrode configuration was used. In this case, a catalyst-coated carbon substrate was used as the working electrode, a platinum wire (Pt wire) as the counter electrode, and a saturated calomel electrode (SCE) as the reference electrode. All potentials were converted to the reversible hydrogen electrode (RHE) reference, and a 0.5 M aqueous H2SO4 solution was used as the electrolyte. Methane saturation was achieved by injecting methane into the electrolyte at 25 °C for 30 minutes.

[0254] Linear Sweep Voltammetry (LSV) analysis was performed on the catalysts of Examples 1 to 5 using the above-mentioned Potentiostat device (Versastat, Ametek), and the results are shown in Fig. 6. In addition, LSV analysis was performed on the catalysts of Examples 3, 6 to 8 using the above-mentioned Potentiostat device (Versastat, Ametek), and the results are shown in Fig. 12. At this time, the analysis was performed at a scan rate of 0.02 V / s.

[0255]

[0256] Referring to FIG. 6, the current densities of Examples 1 to 3 are 30.5, 39.2, and 50.2 mA / cm², respectively. 2 It was shown that the current density increased as the heat treatment temperature increased, but in Examples 4 and 5, it was 45.4 and 42.7 mA / cm², respectively. 2 As shown, it decreased. Example 3, heat-treated at 500 ℃, showed oxidation currents 67% and 17% higher than Examples 1 and 5, heat-treated at 400 ℃ and 600 ℃, respectively. The optimal catalytic activity shown in Example 3 can be explained by the balance between the decrease in surface area due to nanoparticle growth with increasing heat treatment temperature and the improvement in crystallinity.

[0257] Looking at Fig. 12, the anode current density of the undoped catalyst of Example 3 decreased sharply with increasing cycles, which is due to electrochemical instability caused by excessive oxidation of ruthenium. Example 6, doped with 4 at% Nb, showed improved stability compared to Example 3 but still exhibited a gradual decrease in current density during cycling, while Example 7, doped with 8 at% Nb, showed the best stability with cycling. However, a decrease in current density was observed again in Example 8, doped with 16 at% Nb, which is the result of defects in the crystal structure caused by excessive doping.

[0258]

[0259] Experimental Example 4: CV Analysis and EAS (Electrochemically Active Surface Area) Analysis

[0260] Cyclic voltammetry (CV) analysis was performed on the catalysts of Examples 1 to 5 using the above-mentioned potentiostat device (Versastat, Ametek), and the results are shown in Figures 7a to 7e. Based on the CV analysis, the electrochemically active surface area (EAS) was analyzed, and the results are shown in Figure 7f.

[0261]

[0262] In Fig. 7, a decrease in surface area due to nanoparticle growth with increasing heat treatment temperature can be observed. Example 1, which had the lowest heat treatment temperature, showed the highest electrochemically active surface area, but due to poor crystallinity, its electrochemical activity was lower than that of Examples 2 to 5. Consequently, considering Figs. 6 and 7, it was confirmed that Example 3 was the best among Examples 1 to 5.

[0263]

[0264] Experimental Example 5: XANES Analysis

[0265] XANES analysis was performed on the catalyst of Example 3, the catalyst of Example 7, the RuCl3 catalyst, and the Ru foil using a XANES device (7D XAFS beamline, 3.0 GeV storage ring of Pohang Accelerator (PLS-II)), and the results are shown in Fig. 10.

[0266]

[0267] RuO2 crystals are active in the oxygen evolution reaction, but often exhibit instability under acidic electrolyte and high voltage conditions. This is due to the Ru within the crystal. 4+It is known to be caused by excessive oxidation of Ruthenium, and to solve this problem, niobium can be doped into RuO2. Niobium provides electrons to Ruthenium through cross-linked oxygen atoms, increasing the electron density of Ruthenium and suppressing overoxidation by strengthening the Ru-O bond.

[0268] Referring to Fig. 10, the catalyst of Example 7 doped with Nb has a result value that is located between that of the catalyst of Example 3 (RuO2) and the RuCl3 catalyst, which means that electrons from niobium move to ruthenium, and the oxidation state of ruthenium corresponds to between +3 and +4.

[0269] As a result, Example 7 showed superior stability with niobium doping compared to Example 3 (see Experimental Example 6).

[0270]

[0271] Experimental Example 6: Long-term stability test (chronoamperometry measurement)

[0272] Stability analysis of the catalysts of Examples 3 and 7 was performed using the above-mentioned Potentiostat device (Versastat, Ametek) for 24 hours, and the results are shown in Fig. 13.

[0273]

[0274] Referring to Fig. 13, unlike Example 3, Example 7 maintained a stable current density for at least 24 hours.

[0275]

[0276] Experimental Example 7: Microkinetic Analysis of Oxygen Evolution Reaction in RuO2 Catalyst

[0277] Microkinetic analysis was performed to determine the surface coverage of the intermediate of the oxygen evolution reaction (OER) at various anodic potentials in RuO2 catalysts, and the results are shown in Fig. 14.

[0278] OOH in the OER process * It is assumed that the formation step is the rate-determining step (RDS). Under these conditions, the steady-state approximation is OH * and O * It can be applied to intermediate stages related to species formation.

[0279] The velocity equation under steady-state conditions is given as follows:

[0280]

[0281] Here, k1 and k -1 OH from adsorbed species on the catalyst surface, respectively * These are the forward and reverse rate constants of the reaction in which is formed, and k2 and k -2 is OH * From O * Represents the rate constants of the reaction in which is formed and its reverse reaction. θ OH* and θ O* are respectively OH * and O * It refers to the surface coverage rate.

[0282] The equilibrium constants for these reactions are defined as follows:

[0283]

[0284] By introducing the change in Gibbs free energy (ΔGi) associated with each intermediate, this equilibrium constant can be expressed as follows:

[0285]

[0286] In addition, considering the relationship between Gibbs free energy and electrode potential U, the change in free energy at a specific potential (ΔG i (U)) can be expressed as follows:

[0287]

[0288] Here, ΔG i(0) is the change in free energy under standard conditions (U = 0 V), and the eU term reflects the energy transfer according to the applied potential.

[0289] Using this expression, the intermediate OH * and O * The surface coverage ratio can be derived as a function of dislocation. In addition, the overall surface site balance must be considered as follows:

[0290]

[0291] By substituting these equilibrium equations into the site balance equation, nonlinear equations are obtained that allow the coverage rate of each intermediate at a specific potential to be calculated, and the coverage rate can be calculated by interpreting these equations.

[0292]

[0293] Referring to the oxygen evolution reaction diagram in Fig. 14a, the catalyst is OOH * It can be confirmed that the generation step is the Rate Determining Step (RDS).

[0294] Referring to Fig. 14b, 1.1 to 1.88 V RHE Stable reactive oxygen species (O₂) in the voltage range * It is possible to maintain ) and it was confirmed through microkinetic calculations that the coverage rate of reactive oxygen species in that range is 1.

[0295]

[0296] Experimental Example 8: Analysis of Methane Oxidation Reaction

[0297] The methane oxidation reaction is 8 cm at 25 ℃. 2 It was performed for 2 hours in a gas-tight reactor using a catalytic electrode.

[0298] 1) LSV Analysis

[0299] Linear Sweep Voltammetry (LSV) analysis was performed on the catalyst of Example 7 using the above-mentioned Potentiostat device (Versastat, Ametek), and the results are shown in FIG. 15a. At this time, the analysis was performed at a scan rate of 0.02 V / s.

[0300]

[0301] Referring to Fig. 15a, the onset voltage of the oxygen evolution reaction in a methane-free electrolyte (Ar sat.) is 1.4 V RHE Considering that, approximately 1.2 V in methane-saturated electrolyte (CH4sat.) RHE Since the current began to increase from this voltage, it suggests that methane oxidation occurred in the methane-saturated electrolyte starting from this voltage.

[0302] Meanwhile, Fig. 16 shows a voltage of 1.6 V RHE This is an LSV experimental image, and it can be seen that the oxygen evolution reaction occurs very actively in the catalyst of Example 7.

[0303]

[0304] 2) GC Analysis

[0305] Gas chromatography (GC) was performed using a 7820 A GC system (Agilent Technologies, USA) equipped with a flame ionization detector (FID). A PoraPLOT Q column was used for the analysis, and the sample was injected via a gas-sealed syringe with the injection temperature set to 250 °C. The FID was operated under conditions of 300 mL / min argon, 40 mL / min hydrogen fuel, and 25 mL / min nitrogen makeup gas. During this process, the oven temperature was maintained at an initial 40 °C for 2 minutes, then increased to 80 °C at a rate of 20 °C / min, and subsequently increased to 230 °C at a rate of 30 °C / min, and maintained for 3 minutes.

[0306] Using the above gas chromatography, 1.6 V RHE The product gas of the methane oxidation reaction by the catalyst of Example 7 was investigated and is shown in FIG. 15c.

[0307]

[0308] Referring to FIG. 15c, it can be confirmed that the product gases of the methane oxidation reaction by the catalyst of Example 7 are oxygen and hydrogen, respectively. Therefore, 1.6 V RHE In this case, the methane conversion performance is expected to be very poor.

[0309]

[0310] 3) Product Analysis

[0311] Using the above gas chromatography, the rate of product formation and selectivity for the product (particularly ethanol) of the methane oxidation reaction by the catalyst of Example 7 were measured and are shown in FIG. 16.

[0312]

[0313] Referring to Fig. 16a, 1.2 ~ 1.4 V RHE In the range, the rate of ethanol production increased as the potential increased, and in particular, at 1.27 V RHE The rate of ethanol production increased rapidly at . However, at 1.4 V RHE The generation rate decreased from this voltage (1.4 V). RHE ) coincides with the onset voltage of the oxygen evolution reaction, and methane oxidation is inhibited due to the oxidation of adsorbed oxygen, and in particular, 1.48 V RHE It can be observed that the rate of ethanol production decreases sharply from 1.4 V. RHE The production rate of ethanol reached a maximum (7,246 μmol / hr per 1 g of catalyst for methane-ethanol conversion), and this production rate remained stable for several hours and was consistently observed in repeated experiments.

[0314] Meanwhile, 1.4 V RHEThe Faraday efficiency of the oxygen compounds produced in this reached about 90%, which means that the oxygen evolution reaction was significantly inhibited.

[0315] Referring to Fig. 16b, 1.2 V RHE At [location], the selectivity for ethanol was approximately 83%, while the byproduct methanol showed a selectivity of approximately 17%. As the voltage increased, the selectivity for methanol gradually decreased, and the selectivity for ethanol was 1.4 V RHE It peaked at approximately 93%. 1.4 V RHE Significant acetone production was observed from , and at 1.5 V RHE An acetone selectivity of approximately 12% was observed. Conventional photochemical and electrochemical conversion processes generally exhibited high selectivity for oxygen compounds, but the production rate generally remained below approximately 5,000 μmol / hr per g of catalyst. In comparison, the Nb-doped RuO2 catalyst of the present invention (Example 7) achieved a significantly high ethanol production rate while maintaining high selectivity for ethanol.

[0316]

[0317] 4) Mass Spectrometry (MS)

[0318] In isotope analysis 13 CH4(Sigma-Aldrich, 99%, 99 atom% 13 C) and D2O (Sigma-Aldrich, 99.9%, 99.9 atom% D) were used.

[0319] Gas chromatography-mass spectrometry (GC-MS) was performed using a 7890B-5977A GC-MS system (Agilent Technologies, USA) equipped with a mass selector detector (MSD 5975, electron impact ionization 70 eV, Agilent Technologies). A DB-WAX fused silica capillary column (Agilent Technologies, USA) with a poly(ethylene glycol) coating thickness of 0.25 μm was used for the analysis. Samples were introduced via headspace sampling, and 1000 μL of the sample was heated at 70 °C for 30 minutes. The inlet temperature was maintained at 250 °C. The carrier gas used was 99.999% helium at a flow rate of 1 mL / min, and the split ratio was 8:1. The oven temperature was maintained at an initial 40 ℃ for 5 minutes, then increased to 100 ℃ at a rate of 4 ℃ / min, and then increased to 240 ℃ at a rate of 20 ℃ / min and maintained for 3 minutes.

[0320] Using the above gas chromatography-mass spectrometry, the origin of the carbon and oxygen in the product (particularly ethanol) of the methane oxidation reaction by the catalyst of Example 7 was investigated, and the results are shown in Fig. 17.

[0321]

[0322] Referring to Fig. 17, in the case of ethanol among the products, the general 12 A peak shifted by m / z = 2 relative to C ethanol was observed, which is 13 It corresponds to ethanol containing C, confirming that ethanol is derived from methane. Furthermore, considering that water is the sole source of oxygen in the reaction, it can be inferred that methane oxidation occurs due to oxygen derived from water splitting at the anode. Specifically, H218 In a reaction using O, 16 An additional peak shifted by m / z = 2 was observed along with ethanol containing O, and the ratio of the peak intensities was the H2O and H2 used in the experiment 18 It matched the molar ratio of O.

[0323]

[0324] <Preparation Example>

[0325] Preparation Example 1

[0326] A methane-ethanol continuous conversion system was implemented by providing a catalyst for methane-ethanol conversion according to Example 7 in the anode section.

[0327] Specifically, the catalyst for methane-ethanol conversion according to Example 7 was mixed with a Nafion binder and coated onto hydrophobic carbon paper to prepare a gas diffusion electrode. At this time, the catalyst was loaded to 1 mg on the gas diffusion electrode, and the active area of ​​the gas diffusion electrode was 1 (1×1) cm². In addition, commercially available Zirfon, a hydrogen-exclusion porous membrane, was used as the porous membrane. Furthermore, a first flow plate to be placed on the anode side and a second flow plate to be placed on the cathode side were prepared using stainless steel material, with a serpentine flow channel formed on one surface having a cross-section of 239 mm². After assembling the components prepared as shown in FIG. 11, end plates were attached to both sides to create a continuous methane-ethanol conversion system having the appearance shown in FIG. 20.

[0328]

[0329] <Experimental Example>

[0330] Experimental Example 9: Product Analysis According to Voltage

[0331] Using the above gas chromatography with a 7820 A GC system equipped with FID (Agilent Technologies, USA), for the product of the methane oxidation reaction (particularly ethanol) by the system of Preparation Example 1, 1.3 to 1.7 V PtThe production rate and selectivity of the product were measured over a voltage range and are shown in FIG. 21a.

[0332]

[0333] As can be seen from Fig. 21a, the voltage is 1.3 to 1.5 V Pt In the range, the ethanol production rate and ethanol selectivity increased, but 1.5 ~ 1.7 V Pt In this range, the ethanol production rate and ethanol selectivity decreased due to competition with the oxygen evolution reaction. Specifically, 1.45 ~ 1.55 V Pt It showed the best ethanol production rate and ethanol selectivity.

[0334]

[0335] Experimental Example 10: Product Analysis According to Methane Flow Rate

[0336] Using the above gas chromatography with a 7820 A GC system equipped with FID (Agilent Technologies, USA), the production rate and selectivity of the product (particularly ethanol) of the methane oxidation reaction by the system of Preparation Example 1 were measured in the methane flow rate range of 50 to 125 sccm, and the results are shown in FIG. 21b.

[0337]

[0338] Referring to Fig. 21b, the ethanol production rate showed a direct correlation with the increase in methane flow rate, which is because the local pressure within the gas diffusion layer increased, thereby increasing the solubility of methane in the electrolyte. The ethanol selectivity remained constant despite changes in methane flow rate.

[0339]

[0340] Consequently, referring to the aforementioned Experimental Examples 9 and 10, 1.5 V PtAnd under conditions of a methane flow rate of 125 sccm, the ethanol production rate was measured at 33,913 μmol / hr per 1 g of catalyst, and the ethanol selectivity was 95%, which significantly exceeds the previously reported methane conversion rate.

[0341]

[0342] Experimental Example 11: Long-term stability test

[0343] Long-term stability testing was performed by operating the system of Preparation Example 1 for 100 hours and conducting LSV analysis, as shown in FIG. 22. At this time, 1.5 V, which was the best in the aforementioned Experimental Examples 9 and 10, Pt and was performed under conditions of a methane flow rate of 125 sccm.

[0344]

[0345] Referring to Fig. 22, the initial current density is approximately 8 mA / cm². 2 It was and after 100 hours, it decreased slightly to about 7.6 mA / cm², showing a decrease of only 5%. This long-term stability is attributed to the robustness of the Nb-doped RuO2 catalyst, which maintains an oxidized state throughout the reaction process, and no change was observed in the resistance of the catalyst-coated electrode.

[0346]

[0347] Although embodiments of the present invention have been described above, the spirit of the present invention is not limited to the embodiments presented in this specification. Those skilled in the art who understand the spirit of the present invention may easily propose other embodiments within the scope of the same spirit by adding, changing, deleting, or adding components, and such are also to be considered to fall within the scope of the spirit of the present invention.

[0348]

[0349] [Explanation of the symbol]

[0350] 100: Methane-Ethanol Continuous Conversion System

[0351] 10: Porous membrane

[0352] 20: Gas diffusion electrode

[0353] 21: Gas diffusion layer 22: Catalyst layer 23: First flow plate

[0354] 30: Anode

[0355] 40: Cathode

[0356] 50: End plate section

[0357] 60: Electrochemical cell section

Claims

1. OH formed on a catalyst using water as a raw material * Adsorption, O * formation, OOH * Reactive oxygen species (O₂), which are intermediate products formed within the pathway of the four-step oxygen evolution reaction (OER), which involves formation and oxygen (O₂) production. * As a catalyst that converts methane into ethanol via ), Contains ruthenium (Ru) and oxygen (O), It has a Coordinatively Unsaturated Site (CUS) containing ruthenium (Ru) on its surface, Oxygen (O) cross-linked on the surface Br ) Atom coordinately bonded to ruthenium (Ru), Catalyst for methane-ethanol conversion.

2. In Paragraph 1, A catalyst for methane-ethanol conversion characterized in that some of the above ruthenium (Ru) and oxygen (O) are contained as RuO2 crystals.

3. In Paragraph 2, The above-mentioned cross-linked oxygen (O br A catalyst for methane-ethanol conversion characterized in that the ) atom is coordinately bonded with ruthenium (Ru) on the surface (110) of the above RuO2 crystal.

4. In Paragraph 1, The above catalyst is a catalyst for methane-ethanol conversion characterized by being doped with niobium (Nb).

5. In Paragraph 4, A catalyst for methane-ethanol conversion characterized by the above niobium (Nb) being doped at 2 to 12 at% based on the total catalyst.

6. In Paragraph 1, The above catalyst is a catalyst for methane-ethanol conversion characterized by having an average diameter of 14 to 25 nm.

7. In Paragraph 1, The above catalyst is OH * Adsorption, O * formation, OOH * In the four-step oxygen evolution reaction (OER) of formation and oxygen (O2) generation, OOH * A catalyst for methane-ethanol conversion characterized in that the formation step is a rate-determining step (RDS).

8. In Paragraph 7, The above catalyst is O * The change in free energy (ΔG) during the formation phase is OOH * A catalyst for methane-ethanol conversion characterized by having a free energy change of at least 0.7 eV lower than that of the formation stage.

9. (1) A step of mixing a ruthenium (Ru) precursor and a stabilizer in a solvent to form a mixture; and (2) a step of heat-treating the above mixture to produce a catalyst for methane-ethanol conversion; a method for producing a catalyst for methane-ethanol conversion.

10. In Paragraph 9, A method for preparing a catalyst for methane-ethanol conversion, characterized by further mixing a niobium (Nb) precursor into the solvent in step (1) above.

11. In Paragraph 9, A method for manufacturing a catalyst for methane-ethanol conversion, characterized in that, in step (2) above, the heat treatment is an oxidation heat treatment and the heat treatment temperature is 460 to 590 ℃.

12. As an electrochemical methane-ethanol continuous conversion system for converting ethanol from continuously supplied gaseous methane and water electrolyzer, A pair of end plate sections; At least one electrochemical cell portion comprising: an anode portion fixed between the end plate portions, wherein gaseous methane is supplied and a catalyst layer comprising a catalyst for methane-ethanol conversion according to any one of claims 1 to 8 is disposed on one side; a cathode portion supplied with a water electrolytic solution; and a porous membrane separating the anode portion and the cathode portion; and An electrochemical methane-ethanol continuous conversion system comprising: a power supply unit electrically connected to the anode and cathode units.

13. In Paragraph 12, The electrochemical methane-ethanol continuous conversion system is characterized by comprising a gas diffusion electrode having a first flow plate having a methane flow path formed on one surface, a gas diffusion layer disposed in contact with the one surface of the first flow plate, and a catalyst layer disposed on the gas diffusion layer facing a porous membrane.

14. In Paragraph 12, The above-mentioned cathode portion functions as a current collector and is characterized by having a second flow plate having a water electrolytic fluid flow path formed on one surface.

15. In Paragraph 12, OH formed on the above methane-ethanol conversion catalyst * Adsorption, O * formation, OOH * Reactive oxygen species (O₂), an intermediate product of the four-step oxygen evolution reaction (OER), which involves formation and the production of oxygen (O₂). * ) is generated, but OOH * An electrochemical methane-ethanol continuous conversion system characterized by applying voltage from the voltage supply unit at a level where no is formed.

16. In Paragraph 12, The voltage applied from the above voltage supply unit is 1.27 to 1.48 V based on the reversible hydrogen electrode. RHE Electrochemical methane-ethanol continuous conversion system characterized by 17. In Paragraph 12, The voltage applied from the above voltage supply unit is 1.35 to 1.55 V based on the platinum electrode. Pt Electrochemical methane-ethanol continuous conversion system characterized by 18. In Paragraph 12, The above electrochemical methane-ethanol continuous conversion system further includes a methane supply unit, and An electrochemical methane-ethanol continuous conversion system characterized in that the methane supply unit is controlled such that the methane supplied to the anode side has a flow rate of 30 to 200 sccm.

19. An electrochemical methane-ethanol continuous conversion method for converting ethanol from continuously supplied gaseous methane and water electrolyzer, wherein (A) supplying methane to the anode side of an electrochemical cell comprising an anode section, a cathode section, and a porous membrane separating the anode section and the cathode section, wherein a catalyst layer comprising a catalyst for methane-ethanol conversion according to any one of claims 1 to 8 is disposed on one side, and supplying a water electrolytic solution to the cathode side; and (B) a step of applying a predetermined voltage to the electrochemical cell portion so that methane is converted to ethanol on the anode; an electrochemical methane-ethanol continuous conversion method comprising.

20. In Paragraph 19, The production rate of the above ethanol is 15,000 μmol / h or more per 1g of the above methane-ethanol conversion catalyst, and Electrochemical methane-ethanol continuous conversion method having a selectivity of 80% or more for the above ethanol.

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