Plasma-treated catalyst, method for producing the catalyst, and use

Abstract

The present invention relates to a catalytically active material, its preparation and its use in, for example, the catalytic hydrogenation of CO2 to methanol. The catalytically active material comprises a metal oxide doped with a doping metal, said metal oxide being selected from CeO2, ZnO, Ga2O3, In2O3, ZrO2, Fe2O3 and Al2O3, said doping metal being selected from Cu, Pd and Au, and the catalytically active material being obtained by a method comprising a step of a non-thermal plasma treatment.

Description

[Technical Field]

[0001] This application relates to catalytically active materials, their preparation, and the use of such catalytically active materials. [Background technology]

[0002] Sustainable and environmentally friendly methanol production is crucial due to the depletion of fossil fuel resources and the threat of climate change. Methanol can be produced from H2 (green H2 can be produced by electrolysis via water split) and the greenhouse gas CO2. Current methanol synthesis is carried out from a mixture of H2, CO, and CO2 on a Cu / ZnO / Al2O3 catalyst (M. Bukhtiyarova et al., Catal. Letters 147, 416 (2017)). In this method, the CO2 concentration in the starting gas mixture is limited to a maximum of approximately 10%. It has been observed that methanol selectivity decreases as the CO2 concentration increases (J. Zhong et al., Chem. Soc. Rev. 49, 1385 (2020)). Therefore, there is a need for a catalyst that can hydrogenate CO2 into methanol with high reaction rate and high methanol selectivity.

[0003] Furthermore, there is still a need for active materials to catalyze CO2 supply or desulfurization of synthesis gas containing CO, H2, and CO2, using the reverse water-gas shift reaction (CO2 + H2 → CO + H2O; see Y. Daza, JNKuhn, RSC Advances 6, 49675 (2016)) or conventional Cu / ZnO catalysts (M. Breysse et al., Catalysis Today 84, 129 (2003); JW Bae et al., Int. J. Hydrogen Energy 34, 8733 (2009)). [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] An object of the present invention is to provide a catalytically active material that can be effectively used to catalyze the hydrogenation of CO2 to methanol and / or other industrially relevant methods, such as reverse water-gas shift reactions or desulfurization of synthesis gas or CO2 feedstocks. Another object is to provide a catalytically active material suitable for the hydrogenation of CO2 to methanol and / or other industrially relevant methods that exhibit high activity, high selectivity and / or stability in the corresponding reactions. In one other embodiment, another object of the present invention is to provide a simple and effective method for preparing such catalytically active materials that can be suitably used in the present method. [Means for solving the problem]

[0005] The inventors of the present invention have found that the above problem can be solved by the following embodiments (hereinafter referred to as "the matter"). [Matter 1] A catalytically active material containing a metal oxide doped with a doping metal, The aforementioned metal oxide is selected from CeO2, ZnO, Ga2O3, In2O3, ZrO2, Fe2O3, and Al2O3. The doping metal is selected from Cu, Pd, and Au. The catalytically active material is obtained by a method including a non-thermal plasma treatment step. [Matter 2] The catalyst-active material according to item 1, wherein the metal oxide is In2O3. [Matter 3] The catalytically active material according to item 1 or 2, wherein the doping metal is Cu. [Matter 4] The catalytic active material according to any one of claims 1 to 3, wherein the content of the doping metal relative to the metal oxide is 0.01 wt% to 5.0 wt%, preferably 0.01 wt% to 3.0 wt%, and more preferably 0.05 wt% to 0.3 wt%. [Matter 5] A catalytically active material described in any one of items 1 to 4, in the form of particles. [Matter 6] The catalytically active material according to item 5, wherein the catalytically active material is composed of the metal oxide, the doping metal, and an arbitrary negatively charged counterion. [Matter 7] The catalytically active material is the catalytically active material according to item 5 or 6, having an average particle size of 5 nm to 50 nm when measured by a transmission electron microscope (TEM) or scanning transmission electron microscope (STEM). [Matter 8] A catalytically active material described in any one of items 1 to 4, in the form of a film. [Matter 9] The use of a catalytically active material described in any one of items 1 to 8 in the catalytic hydrogenation of CO2 to methanol by reacting a mixed gas composed of H2 and CO2. [Matter 10] The mixed gas containing H2 and CO2 is reacted in the presence of the catalytically active material at a pressure of 10 bar to 150 bar and at a reaction temperature of 100°C to 400°C, preferably 150°C to 350°C, as described in item 9. [Matter 11] The mixed gas has an H2 / CO2 molar ratio of 3.0 or higher, preferably 3.5 or higher, as described in item 9 or 10. [Matter 12] A method for producing a catalytically active material as described in any one of items 5 to 7, (1) Adding an alkaline solution (for example, a Na2CO3 solution) to an aqueous solution containing the doping metal and the metal component of the metal oxide to co-deposit the doping metal and the metal component of the metal oxide as hydroxides; (2) The step of washing and drying the precipitate, (3) The step of calcining the dried precipitate in the presence of O2, (4) The calcined precipitate is subjected to non-thermal plasma treatment to obtain particles of the catalytically active material, A method having [Matter 13] The method according to item 12, wherein the non-thermal plasma treatment is carried out at a pressure of 40 mbar or less. [Item 14] A method for producing the catalyst active material according to item 8, (1) Preferably by a co-deposition method, providing a film containing the metal of the metal oxide and the doping metal; (2) annealing the film in the presence of oxygen; (3) carrying out a non-thermal plasma treatment; comprising the steps of.

[0006] When the present specification refers to preferred embodiments / features, regardless of their levels of preference, combinations of these preferred embodiments / features are considered to be disclosed as long as they are technically meaningful in this combination of preferred embodiments / features.

[0007] In the present specification, the use of the terms "having" or "comprising" should be understood to also disclose the term "consisting of" as a more limited embodiment as long as it is technically meaningful.

[0008] When preferred upper and lower limits are indicated for a particular feature, it should be understood that this discloses any combination of the upper and lower limits.

[0009] Hereinafter, depending on the context, the term "catalyst active material" may be replaceable with "catalyst".

Brief Description of the Drawings

[0010] [Figure 1] A schematic diagram of an experimental apparatus used for plasma treatment of a catalyst active material in the form of a film (a) and a nanoparticle powder (b). [Figure 2]This figure shows the methanol production rates measured after 1 hour (a) and 24 hours (b) on untreated and plasma-treated Cu-In2O3 catalysts and Cu-free In2O3 catalysts according to Comparative Examples 1 to 4, Reference Example 1, and Examples 1 to 3 (CO2:H2:He=1:4:1, 60 bar, 48 mL / min, 280°C). [Figure 3] These are the reaction rates measured using a Cu-In2O3 catalyst containing 0.1 wt% Cu, as described in Examples 1, 4, and 5 (CO2:H2:He = 1:4:1, 60 bar, 48 mL / min, 280°C). [Figure 4] These are the Fourier-transformed CuK-edge extended X-ray absorption fine structure (EXAFS) spectra of Cu-In2O3 catalysts from Example 1 ("Plasma Treatment") and Comparative Example 1 ("Catering"). Spectra were recorded for each catalyst: the untreated (as-prepared) catalyst and the catalyst after the CO2 hydrogenation reaction at 280°C in a CO2+H2+He(1:4:1) mixed gas at a total pressure of 60 bar. Partial contributions of Cu-Cu bonds, obtained from nonlinear least-squares EXAFS data fitted to the catalysts used, are shown as dashed lines. The spectra have been vertically shifted for clarity. [Figure 5] Scanning tunneling microscope images of an In2O3 film catalyst (Reference Example 2) and a plasma-treated In2O3 film catalyst (Reference Example 3), as well as topographic profiles (c, d) along the lines shown in the corresponding images (a, b). [Figure 6] These are the O1s region of the X-ray photoelectron spectra measured for catalysts prepared using Reference Example 2 (untreated with In2O3), Reference Example 3 (In2O3 plasma), Comparative Example 5 (untreated with Cu-In2O3), and Example 6 (Cu-In2O3 plasma). [Modes for carrying out the invention]

[0011] I. Catalytic active material The catalytically active material of the present invention comprises a metal oxide doped with a doping metal. The metal oxide is selected from CeO2, ZnO, Ga2O3, In2O3, ZrO2, Fe2O3, and Al2O3. The doping metal is selected from Cu, Pd, and Au. The catalytically active material is obtained by a method comprising a non-thermal plasma treatment step. This method, for example, includes the steps of co-depositing the metal oxide and the doping metal to obtain a precursor, and calcining this precursor.

[0012] "Atomically dispersed" means that a single doping metal atom (also called a "dopant") is present in the catalytic material and, where necessary, on the surface of the catalytic material, which can be detected by conventional analytical techniques such as extended X-ray absorption fine structure (EXAFS), infrared spectroscopy (IR), or STEM. To avoid ambiguity, and unless otherwise stated, the use of the term "atom" in the specification and claims encompasses both neutral (oxidation state = 0) and charged (ionic, e.g., oxidized) doping metal atoms.

[0013] The form of the catalytically active substance is not particularly limited. For example, it may be in the form of particles (e.g., powder) or a film.

[0014] To optimize its usefulness in industrial processes, the catalytically active material may be applied (supported) on an inert support material. If the catalytically active material exists as a film, it may be supported by a suitable planar support material.

[0015] The present invention is characterized by obtaining a catalytically active material by a method including a non-thermal plasma treatment step. In the present invention, it is preferable to start with a material in which the dopant metal atoms are incorporated into the metal oxide of the catalytically active material (also called the "metal oxide matrix"). In particular, the effect of plasma treatment is considered to be stabilizing the initial "as-prepared" state of the doped metal oxide material, with the doping metal atoms remaining almost entirely within the host metal oxide matrix. While we do not wish to be bound by theory, if the doping metal atoms migrate from the interior of the metal oxide matrix to its surface under reaction conditions, the doping metal atoms are thought to have lower mobility on the metal oxide surface due to their greater plasma-enhanced roughness. On the other hand, in a reference catalyst prepared without plasma treatment, more doping atoms reach the surface (leave the matrix) under reaction conditions, and then sintering occurs. In contrast to having doped metal atoms dispersed in In2O3 (or other claimed metal oxides) or forming very small clusters, this produces an X-ray absorption spectrum (XAS) for, for example, a metallic Cu-Cu signal, corresponding to the formation of relatively large particles.

[0016] In one embodiment, the catalytically active material of the present invention exhibits an additional state of oxygen atoms, characterized by the binding energy of the O1s core level being 1.4 eV to 2.5 eV, preferably 1.6 eV to 2.2 eV higher than the binding energy of the main signal of the metal oxide, as observed by X-ray photoelectron spectroscopy (XPS). See also Figure 6. XPS analysis can be performed according to the method described in the examples. This additional XPS signal may be observed as a shoulder of the main signal. Although not bound by theory, the additional XPS signal is attributed to oxygen from defect sites and is preferably formed on the surface of the metal oxide during non-thermal plasma treatment. For example, in the case of In2O3, the O1s XPS signal of In2O3 appears at 530.2 eV, and the signal for oxygen from defect sites appears at 532.0 eV.

[0017] In this embodiment, the intensity of the additional signal is preferably at least 30% of the intensity of the main peak, and more preferably at least 40%.

[0018] In one embodiment, non-thermal plasma treatment induces the formation of metal oxide nanoclusters on the surface of the catalytically active material. The average diameter of the metal oxide nanoclusters may be 4.0 nm or less, preferably 2.5 nm or less, as measured by scanning tunneling microscopy (STM). See further description below. STM measurements can be performed as described in the examples.

[0019] The catalytically active material of the present invention preferably exhibits one or more of the properties described in the above embodiments.

[0020] In the present invention, the catalytically active material comprises a metal oxide doped with a doping metal, and the metal oxide is selected from CeO2, ZnO, Ga2O3, In2O3, ZrO2, Fe2O3, and Al2O3. Preferably, the metal oxide is selected from ZnO, ZrO2, Ga2O3, In2O3, and Al2O3, more preferably from ZnO, ZrO2, and In2O3, and most preferably In2O3. One metal oxide may be used alone, or two or more may be used in combination.

[0021] In the present invention, the doping metal used to dope the metal oxide is selected from Cu, Pd, and Au. The metal is preferably Cu. In one preferred embodiment, the “doping” metal atoms are atomically dispersed in the host material (metal oxide matrix).

[0022] Preferably, the doping metal is present in the (as-prepared) catalytic material as a single atom (ion) incorporated into the corresponding metal oxide matrix (e.g., Cu in In2O3). It is preferable that the doping metal exists in the as-prepared catalytic material in a positive oxidation state (X), i.e., in an oxidation form. In one embodiment, X is 2+ for Cu and Pd, and 3+ for Au. It should be noted that the oxidation state may depend on various factors. In the case of Cu-In2O3, Cu substitutes In 3+, but may also be in a 2+ state, for example. To balance the net charge, this process may be carried out by forming an O vacancy or by placing a counterion nearby.

[0023] Because the metal oxide is doped with a doping metal, the catalytically active material of the present invention can exhibit excellent catalytic activity in the hydrogenation reaction of CO2 to methanol and / or CO (reverse water-gas shift) and / or in the desulfurization of CO2 or synthesis gas (CO+CO2+H2). Although not bound by theory, it is presumed that the electronic structure of the metal oxide is modified in the presence of the metal dopant, resulting in superior ability to activate the reactants. Furthermore, it is presumed that the presence of the metal dopant alters the crystal structure of the metal oxide, inducing a high surface energy of the metal oxide, which also promotes the activation of the reactants.

[0024] The combination of metal oxide and doping metal is not particularly limited. In one preferred embodiment, the metal oxide is selected from CeO2, ZnO, Ga2O3, In2O3, and Al2O3, and the doping metal is selected from Cu, Pd, or Au. The combination of In2O3 and Cu is more preferred.

[0025] The amount of doping metal to the metal oxide is not particularly limited, but is preferably 0.01 wt% to 5.0 wt%, more preferably 0.01 wt% to 3.0 wt%, and even more preferably 0.01 wt% to 1.0 wt%. The amount of doping metal to the metal oxide is particularly preferably 0.05 wt% to 0.3 wt% because it can further enhance the CO2 hydrogenation activity of the catalytic active material.

[0026] The atmosphere for non-thermal plasma treatment is not particularly limited, but is one or more selected from N2, O2, and Ar, and is preferably O2. Preferably, the non-thermal plasma treatment is carried out in the presence of at least O2.

[0027] In the first embodiment of the present invention, the catalytically active material exists in the form of particles, and may be formed, for example, as a powder. The shape of the particles is not particularly limited and may be selected from, for example, ellipsoidal, cubic, spherical, etc.

[0028] In the first embodiment of the present invention, the average particle size of the catalytically active material is not particularly limited, but is preferably 5 nm to 1 μm, more preferably 5 nm to 500 nm, even more preferably 5 nm to 100 nm, and particularly preferably 5 nm to 50 nm. The average particle size of the metal oxide substrate can be determined by measuring the particle sizes of 20 arbitrarily selected particles using a transmission electron microscope (TEM) or scanning transmission electron microscope (STEM) and calculating the average. The longest visible axis of the particle is used as the "diameter". If further measurement accuracy is desired, measurements can be performed on 100 arbitrarily selected particles. Detailed methods are described in the Examples chapter. When multiple particles are aggregated with each other, the particle size of the primary particle is used for measurement.

[0029] In a first embodiment of the present invention, the catalytically active material is preferably composed of the metal oxide and the doping metal. If the doping metal exists in the form of metal ions, (negatively charged) counterions may also be present to balance the net charge. These counterions may originate, for example, from salts of the doping metal used in the preparation of the catalytically active material.

[0030] In a second embodiment of the present invention, the catalytically active material is in the form of a film.

[0031] Furthermore, a catalytically active material may be provided as a film on a substrate. In one embodiment, the substrate is a flat substrate, and a catalytically active material film can be provided on the substrate by, for example, the deposition of a metal oxide precursor and a metal precursor, and a subsequent oxidation step. The substrate is not particularly limited as long as it does not adversely affect the catalytically active material. For example, a substrate made of metal, alloy, or ceramic may be used. The metal used as the substrate may be a single crystal, and may include, for example, a Ru(0001) single crystal. Examples of alloys that can be used as substrates include, but are not limited to, steel and brass. Examples of ceramics that can be used as substrates include, but are not limited to, silica and silicon carbide. Those skilled in the art can select a substrate suitable for the reaction conditions to which the catalytically active material (coating layer) is exposed.

[0032] In a second embodiment of the present invention, the thickness of the catalytically active material film is not particularly limited, but is preferably 5 nm to 50 nm, more preferably 5 nm to 20 nm. The thickness of the catalytically active material film can be determined, for example, by measuring the attenuation of the XPS signal of the substrate on which the catalytically active material film is provided using XPS. For example, when a catalytically active material film is provided on a Ru substrate, the thickness of the catalytically active material film can be determined by measuring the attenuation of the Ru3d signal in the XPS spectrum. Similarly, when a silica-based material is used, the attenuation of the Si2p signal in the XPS spectrum can be used. Those skilled in the art can appropriately select the signals emanating from elements in the substrate, measure their attenuation, and determine the thickness of the catalytically active material film.

[0033] In a second embodiment of the present invention, the catalytically active material film may have metal oxide clusters on its surface, which may have the same metal oxide. The average diameter of the clusters is 4.0 nm or less, preferably 2.5 nm or less, which may be determined by plotting a topographic profile along a straight line corresponding to, for example, 10 nm in length using a scanning tunneling microscope (STM), measuring the distance between two adjacent minimums, multiplying the measured value by a correction factor of 0.5, recording the obtained value as the diameter, repeating the measurement for 20 arbitrarily selected surface areas showing coating by metal oxide clusters, and calculating the average value. A detailed method is described in the Examples chapter.

[0034] The number of clusters supported on the film surface and normalized per unit area of ​​the metal oxide substrate (surface cluster density) is not particularly limited. The surface cluster density is preferably at least 0.03 clusters / nm 2 , more preferably at least 0.05 clusters / nm 2 More preferably, at least 0.08 clusters / nm 2 Most preferably at least 0.10 clusters / nm 2 The surface cluster density can be determined by STM by counting the number of metal oxide clusters present in an arbitrarily selected region. A detailed method is described in the Examples chapter.

[0035] The catalytically active material of the present invention is particularly suitable as a CO2 hydrogenation catalyst.

[0036] The catalytically active material of the present invention exhibits excellent stability and activity in the hydrogenation of CO2. At least in part, these properties are presumed to be related to, to some extent, to plasma treatment that modifies the surface structure and / or electronic state of the metal oxide, thereby suppressing the formation of large metal clusters (e.g., by aggregation or sintering) during the catalytic reaction and stabilizing or enhancing the high dispersion of doping metal.

[0037] The catalytically active material of the present invention can be prepared by the following method.

[0038] II. Method for producing catalytically active materials A method for producing a catalytically active material according to the first embodiment of the present invention is: (1) Adding an alkaline solution (e.g., Na2CO3 solution) to an aqueous solution containing a salt of the doping metal and the metal component of the metal oxide to co-deposit the doping metal and the metal component of the metal oxide as hydroxides, (2) A step of washing and drying the precipitate, (3) The step of calcining the dried precipitate in the presence of O2, (4) The calcined precipitate is subjected to non-thermal plasma treatment to obtain particles of the catalytically active material, It may have.

[0039] In step (1), the doping metal salt is not particularly limited. Examples include, but are not limited to, nitrates, chlorides, sulfates, acetates, acetylacetonates, tetraamine salts (e.g., copper(II) tetraamine sulfate, palladium(II) tetraamine chloride, etc.), and tetrachloroferrous(III) salts.

[0040] In step (1), the metal element salt of the metal oxide is not particularly limited. Examples, but not limited to, include nitrates, chlorides, sulfates, acetates, acetylacetonates, and tetraamines.

[0041] In step (1), the alkaline solution is not particularly limited as long as its addition increases the pH of the aqueous solution containing the doping metal salt and the metal oxide component. Examples, though not limited to these, include alkaline aqueous solutions such as Na2CO3, K2CO3, NaOH, KOH, Mg(OH)2, Ca(OH)2, and CaCO3.

[0042] As used herein, the terms "calcination" or "calcination" refer to the heat treatment of a solid at a high temperature in the presence of dry O2. The term "dry" as used herein means that no additional water is introduced into the atmosphere in which calcination is performed. For example, calcination in air is understood to be performed under dry conditions.

[0043] The calcination of the catalyst-active material precursor is preferably carried out at a temperature of 200°C to 700°C, more preferably at 200°C to 600°C, and even more preferably at 250°C to 500°C. The calcination is preferably carried out at an O2 concentration of 5 vol% or more, and more preferably at 10 vol% or more. For example, air can be used as the O2 source.

[0044] Non-thermal plasma treatment is performed on a calcined catalytic active material. Before plasma ignition, the pressure is reduced, preferably to 40 mbar or less, more preferably to 20 mbar or less. The pressure during non-thermal plasma treatment is preferably to 40 mbar or less, more preferably to 20 mbar or less. The atmosphere for non-thermal plasma treatment is not particularly limited, but is one or more selected from N2, O2, and Ar, and is preferably O2. Preferably, non-thermal plasma treatment is performed in the presence of at least O2.

[0045] Non-thermal plasma treatment may be carried out under a static atmosphere or under a gas flow. The latter is preferred. When non-thermal plasma treatment is carried out under a gas flow, it is preferable that the calcined catalyst active material precursor is blown up (levitated) by the gas flow during the non-thermal plasma treatment.

[0046] The source of the non-thermal plasma is not limited and includes, for example, inductively coupled plasma, capacitively coupled plasma, DC glow discharge, microwave plasma, radio frequency plasma, cold plasma jet, and dielectric barrier discharge plasma. The source of the non-thermal plasma is preferably microwave plasma or radio frequency plasma.

[0047] When the source of the non-thermal plasma is a microwave plasma, the anode voltage of the plasma source is preferably 0.2kV to 2kV, and the emission current is preferably 0.1μA to 1μA.

[0048] When the source of the non-thermal plasma is a high-frequency plasma, the power of the high-frequency plasma generator is preferably between 20W and 300W.

[0049] The time for non-thermal plasma treatment can be adjusted as desired, and is typically 1 to 300 minutes, preferably 5 to 180 minutes, more preferably 10 to 120 minutes, and even more preferably 30 to 90 minutes.

[0050] A method for producing a catalytically active material according to a second embodiment of the present invention is: (1) Preferably by a co-deposition method, the step of providing a film containing the metal component of a metal oxide and a doping metal, (2) The step of annealing the film in the presence of oxygen, (3) A step of performing non-thermal plasma treatment, It holds.

[0051] In step (1), the method for providing a film containing a metal oxide doped with a doping metal is not particularly limited, and any conventionally known method may be used. For example, but not limited to, co-deposition methods are preferred, including co-deposition, sol-gel methods, and spin coating.

[0052] In step (2), the annealing treatment is preferably carried out at a temperature of 200°C to 400°C, more preferably at 250°C to 350°C, and even more preferably at 280°C to 320°C. The annealing treatment is 10 -4 It is preferable that the procedure be carried out in O2 at a pressure of mbar or higher.

[0053] In step (3), the non-thermal plasma treatment may be carried out as described in the method for producing a catalytically active material according to the first embodiment of the present invention.

[0054] III. Catalytic Reactions The catalytically active material of the present invention can be used in at least one of the following reactions: (i) hydrogenation of CO2 to methanol (also referred to as "catalytic hydrogenation"), (ii) reverse water-gas shift reaction (CO2 + H2 → CO + H2O), or (iii) desulfurization of synthesis gas (CO + CO2 + H2) or a CO2 feedstock. The CO2 feedstock may be from industrial sources such as steel mills, waste incinerators, or cement plants.

[0055] In preferred embodiments, the catalytically active material of the present invention is suitably used in the catalytic hydrogenation of CO2 to methanol. In the catalytic hydrogenation of CO2 to methanol, a reaction gas mixture containing H2 and CO2 is reacted in the presence of the catalytically active material to produce methanol. The pressure of the reaction gas mixture is not particularly limited, but is, for example, 10 bar to 300 bar, preferably 20 bar to 100 bar, and more preferably 30 bar to 80 bar.

[0056] The reaction temperature for catalytic hydrogenation is not particularly limited, but may be between 100°C and 400°C, and preferably between 150°C and 350°C.

[0057] The composition of the reaction gas mixture is not particularly limited, as long as it contains CO2 and H2. The H2 / CO2 molar ratio of the reaction gas mixture is, for example, 3.0 or higher, preferably 3.5 or higher, and more preferably 4.0 or higher. The CO2 content in the reaction gas mixture is not particularly limited, but is, for example, 3% to 25% by volume, preferably 5% to 22% by volume, and more preferably 10% to 20% by volume.

[0058] The reaction gas mixture may further contain an inert gas, such as N2, He, or Ar.

[0059] (Examples) The present invention will be described in more detail below with reference to the following examples. However, the present invention is not limited to the following examples.

[0060] (Analysis method) Scanning transmission electron microscope (STEM) Scanning transmission electron microscope (STEM) images of the powder catalyst were recorded using a 200kV JEOL JEM ARM200F probe / image-corrected TEM (JEOL).

[0061] The average particle size of the catalytically active material was determined by measuring the particle size of 100 arbitrarily selected particles and calculating the average. For selected particles, if the STEM image showed a non-spherical shape, the longest axis was considered the diameter.

[0062] (X-ray photoelectron spectroscopy (XPS)) XPS spectra were measured using an AlKα X-ray source (hν = 1486.6 eV) with a Phoibos 150 analyzer (SPECS GmbH). Spectral analysis (background subtraction and deconvolution) was performed using commercially available CasaXPS software (Casa Software). The procedure was performed using (Ltd; version 2.3.18), and the measured spectrum was subjected to background subtraction using a Shirley background. The core level spectrum of O1s was recorded at a transmission energy of 20 eV. Those skilled in the art can attribute the bond energy to the chemical species using common technical knowledge. For example, a list of bond energy tables, such as the NIST X-ray photoelectron spectroscopy database, is common technical knowledge for those skilled in the art.

[0063] (X-ray absorption spectroscopy (XAS)) The K-edge (8979 eV) X-ray absorption spectrum (XAS) of Cu was measured in total fluorescence yield mode at the ALBA beamline synchrotron radiation facility in Spain using a 4-channel Si drift detector. Measurements were performed at room temperature and in air for catalytically active materials in their "as-prepared" state, and at 280°C and 60 bar (total) in CO2+H2+He(1:4:1) for catalytically active materials after the CO2 hydrogenation reaction, as described below. Extended X-ray absorption fine structure (EXAFS) spectra were fitted using the FEFFIT code, and the contributions induced from Cu-Cu and Cu-O bonds were modeled using theoretical backscatter amplitudes and phases calculated via the FEFF8 code for reference materials (i.e., Cu, CuO), respectively.

[0064] (Scanning tunneling microscope (STM)) STM measurements of In2O3(0001) films grown on Ru(111) were performed with a sample bias of 1.8V and a tunneling current of 0.2 nA.

[0065] To determine the average diameter of metal oxide clusters formed on the surface by plasma treatment, topographic profiles were plotted along lines approximately 10 nm long. In the topographic profiles, the distance between two adjacent local minima was measured, and the measured value was multiplied by an experimentally derived correction factor of 0.5 to correct for chip / cluster convolution effects. Measurements were performed for at least 20 arbitrarily selected metal oxide clusters, and their average corrected value was calculated and used as the "cluster diameter."

[0066] To determine the surface density of metal oxide clusters, i.e., the normalized number of metal oxide clusters per unit area of ​​the film substrate, the number of metal oxide clusters was counted within an arbitrarily selected 100 nm × 100 nm region in the recorded STM image. These measurements were performed on five different sample spots. The average value was defined as the "metal oxide cluster density."

[0067] (CO2 hydrogenation reaction on catalytically active material) The reactivity of a catalytic active material in the CO2 hydrogenation reaction was measured in a tubular packed-bed reactor. 100 mg of the catalytic active material and 100 mg of TiO2 (Alfa Aesar) were physically mixed, and the resulting mixture was packed into the reactor. TiO2 is inert in this reaction and was used for dilution. This catalytic active material was heated at 280°C for 1 hour in 60 bar of He (20 mL / min). Next, the heated catalytic active material was cooled to room temperature in a He gas stream, and then the gas stream was changed to a reaction mixture consisting of CO2, H2, and He (CO2:H2:He = 1:4:1, 48 mL / min, spatial flow rate GHSV = 28800 mL / g). catalyst The pressure was switched to 60 bar, and the reduced catalytic active material was heated to 280°C. The gas mixture at the reactor outlet was analyzed by gas chromatography (Agilent Technologies 7890B).

[0068] (Powdered catalyst) (Comparative Examples 1-3: Preparation of untreated Cu-In2O3 catalysts) The untreated Cu-In2O3 catalyst was prepared according to the process shown below.

[0069] 1) In(NO3)3·xH2O (Sigma Aldrich) and Cu(NO3)2·2.5H2O (Alfa Aesar) were dissolved in 50 ml of deionized water in a 250 ml round-bottom flask to obtain a precursor solution. The amount of In(NO3)3·xH2O used was 2.167 g, and the amount of Cu(NO3)2·2.5H2O was varied as shown in Table 1 below. 2) Dissolve 10.0 g of Na2CO3 in 100 ml of deionized water, and while stirring at room temperature, add the resulting Na2CO3 solution dropwise to the precursor solution. Add the Na2CO3 solution until the pH reaches 9.2. Subsequently, the precursor solution became a turbid liquid due to the formation of In(OH)3 and Cu(OH)2. After letting the slurry stand for 1 hour, add 50 ml of deionized water. 3) The slurry was centrifuged for 5 minutes to separate the precipitate, which was then redispersed in deionized water (50 ml) for washing, and then centrifuged for 5 minutes. This procedure was repeated 5 times to remove any remaining sodium salts. 4) The precipitate was dried in air (70°C, overnight) and then baked at 300°C for 3 hours.

[0070] Table 1 shows the amount of Cu(NO3)2·2.5H2O used in the preparation method and the Cu content of the catalyst. The average particle size of the catalyst, as determined by STEM, was 15±2 nm.

[0071] [Table 1] (Comparative Example 4: Preparation of untreated In2O3 catalyst) An untreated In2O3 catalyst was obtained using the same method as in Comparative Example 1, except that Cu(NO3)2·2.5H2O was not used. The average particle size measured by STEM was 8±1 nm.

[0072] (Examples 1 to 5: Preparation of plasma-treated Cu-In2O3 catalysts) Untreated Cu-In2O3 catalysts were obtained by the same method as in Comparative Examples 1 to 3.

[0073] Next, each Cu-In2O3 catalyst was subjected to plasma treatment in the presence of O2 according to the method described below to obtain plasma-treated Cu-In2O3 catalysts.

[0074] Plasma processing was carried out using an apparatus consisting of a glass tube with frit, a funnel-shaped glass apparatus, a mechanical pump, a high-frequency plasma generator, and a high-voltage power supply. The glass tube was covered with Cu mesh and connected to the high-voltage power supply. The frit was able to hold the calcined powder while allowing gas (O2 was used in this case) to be blown in from the bottom. The funnel-shaped glass apparatus, connected to the top of the tube, and the other three outlets of the funnel-shaped glass apparatus were connected to a pressure gauge, a mechanical pump, and a tungsten rod for grounding. The tungsten rod extended to the bottom of the glass tube, achieving a uniformly distributed plasma. A schematic diagram of the plasma processing configuration is shown in Figure 1b.

[0075] The plasma was generated using a high-voltage power supply (PVM500) with a frequency range of 20 to 60 kHz. Peak voltage was measured with an oscilloscope equipped with a high-voltage probe, and plasma power was the product of the square root of the mean-squared (RMS) voltage and the RMS current, both measured with a multimeter. The power and frequency output of the powder feed were adjusted until a plasma with the desired power was formed.

[0076] The conditions for plasma treatment are as follows: 1) Untreated Cu-In2O3 powder catalyst (100 to 300 mg) was introduced into a glass tube, and the tube was evacuated to below 20 mPa. 2) Oxygen was supplied from the bottom of the tube using a flow rate of 20 mL / min of O2 set by a mass flow controller (MFC). 3) The powder sample began to float in the turbulent flow. 4) The plasma was ignited. The power output and frequency of the power supply were adjusted to achieve the target power shown in Table 2. 5) The plasma treatment time was 1 hour.

[0077] Table 2 shows the untreated Cu-In2O3 catalyst used for plasma treatment, the target plasma output, and the Cu content of the catalyst. The average particle size of the catalyst measured by STEM was 16 ± 2 nm.

[0078] [Table 2] (Reference Example 1: Preparation of Plasma-treated In2O3 Catalyst) The untreated In2O3 catalyst of Comparative Example 4 was plasma-treated in the same manner as in Examples 1 to 3 to prepare a plasma-treated In2O3 catalyst. The average particle size measured by STEM was 10 nm.

[0079] (Evaluation of results) The "untreated" catalyst used in this invention is also called a "calcined" catalyst.

[0080] The prepared Cu-In2O3 catalyst had an average diameter of 16±2 nm, as measured by STEM. The general morphology of the catalyst was not affected by plasma treatment under the conditions used.

[0081] The CO2 hydrogenation activity of the prepared catalytic active materials was measured as described above. Figure 2a shows the methanol production rate measured 1 hour after reaching the reaction temperature of 280°C for the (Cu-)In2O3 catalysts in Comparative Examples 1-4, Reference Example 1, and Examples 1-3. As can be seen, for the untreated (Cu-)In2O3 catalysts of Comparative Examples 1-4, a higher methanol production rate was observed at higher Cu packing. The plasma-treated Cu-free In2O3 catalyst of Reference Example 1 showed a lower methanol production rate than the untreated In2O3 catalyst of Comparative Example 4. In contrast, the plasma-treated Cu-In2O3 catalysts of Examples 1-3 showed a higher methanol production rate than the untreated Cu-In2O3 catalysts of Comparative Examples 1-3 at the same Cu packing. The increase in methanol production rate due to O2-plasma treatment was particularly significant at 0.1 This was particularly noticeable with low wt% Cu filling.

[0082] Figure 2b shows the methanol production rates measured 24 hours after reaching a reaction temperature of 280°C for the (Cu-)In2O3 catalysts of Comparative Examples 1-4, Reference Example 1, and Examples 1-3. As can be seen, the untreated Cu-In2O3 catalysts of Comparative Examples 1-3 showed a higher methanol production rate than the untreated In2O3 catalyst of Comparative Example 4. Among the untreated (Cu-)In2O3 catalysts of Comparative Examples 1-4, the highest methanol production rate was observed with 0.5 wt% Cu packing. The plasma-treated In2O3 catalyst of Reference Example 1 showed a lower methanol production rate than the original In2O3 catalyst of Comparative Example 4. In contrast, the plasma-treated Cu-In2O3 catalysts of Examples 1-3 showed a higher methanol production rate than the untreated Cu-In2O3 catalysts of Comparative Examples 1-3 with the same Cu packing. The increase in methanol production rate due to O2-plasma treatment was particularly pronounced with 0.1 wt% Cu packing.

[0083] Figure 3 shows the measured reaction rates for Cu-In2O3 catalysts containing 0.1 wt% Cu according to Examples 1, 4, and 5, as the target plasma power was varied from 100 W to 200 W. As the plasma power increased from 100 to 200 W, the reaction rate gradually increased.

[0084] Figure 4 shows the Fourier-transformed CuK-edge EXAFS spectra for Cu-In2O3 catalysts prepared by Example 1 (plasma treatment) and Comparative Example 1 (calcination). Measurements were performed on both the "as-prepared" catalyst and the catalyst after the CO2 hydrogenation reaction at 280°C, in CO2+H2+He(1:4:1) at 60 bar (total), as described above ("post-reaction"). The measured spectra of the "as-prepared" Cu-In2O3 catalyst before O2-plasma pretreatment and the treated Cu-In2O3 catalyst show similar structures, which are dominated by the Cu-O distance in the first coordination shell. Another contribution to the CuK-edge EXAFS spectrum of the as-prepared sample is observed at approximately 3.5 Å, its position similar to that of the In-In contribution in In2O3. Thus, the presence of this feature is attributed to the Cu substitution of In atoms in the In2O3 lattice. After the reaction, the calcined Cu-In2O3 catalyst showed a considerable number of Cu-Cu bonds, suggesting aggregation of Cu atoms. On the other hand, the plasma-treated Cu-In2O3 sample retained Cu-O bonds. Experimental CuK-edge The Cu-O and Cu-Cu coordination numbers obtained from fitting EXAFS data are shown in Table 3 below. The uncertainty in the last digit is shown in parentheses. Under the constraint that the bond lengths and disorder factors of the Cu-O and Cu-Cu bonds are the same in all spectra, the spectra of all samples were fitted simultaneously. The obtained Cu-O bond length was 1.944 ± 0.006 Å, the obtained Cu-Cu bond length was 2.542 ± 0.006 Å, and the corresponding disorder factors were 0.005 ± 0.006 Å, respectively. 2 and 0.007±0.002Å 2 The correction of the photoelectron reference energy (ΔE0) obtained by fitting, as well as the value of the R factor for fitting, are shown in Table 3.

[0085] [Table 3] This result represents the difference between the plasma-treated Cu-In2O3 sample and the calcined Cu-In2O3 sample after reaction under the same conditions, and it was confirmed that plasma treatment can suppress the aggregation of Cu atoms that can segregate on the surface of the doped metal oxide during catalyst operation.

[0086] (Membrane catalyst) (Reference Example 2: Preparation of In2O3 membrane catalyst) Experiments were carried out in an ultra-high vacuum (UHV) chamber equipped with a low-energy electron diffraction apparatus (LEED), an X-ray photoelectron spectrometer (XPS), and a scanning tunneling microscope (STM). All of these are available from SPECS GmbH. A regular In2O3(111) film was grown on a Ru(0001) single crystal by the following method. A Ru(0001) single crystal (MaTeck GmbH, 9 mmφ, 1.5 mm thick) was attached to a stainless-steel sample holder with a 9 mmφ hole for heating the sample from the back using an electron beam from a W filament. A K-type thermocouple was spot-welded to the end of the crystal. The Ru(0001) surface was oxidized in O2 at 1000 K, 10 -6 mbar and cooled to room temperature under oxygen. Using an electron beam assist evaporator (Focus EMT3), indium was evaporated onto the oxidized Ru(0001) surface in O2 at 90 K, 10 -6 mbar in an amount equivalent to forming 4 to 5 monolayers (ML) of In2O3(111). Then, the temperature of Ru(0001) was raised at a rate of 1 K / s and maintained at 673 K during the formation of a further In2O3 layer. Next, the sample was oxidized in O2 at 1000 K for 10 -6 mbar to improve the crystallinity of the film. The thickness of the In2O3(111) film was approximately 5 nm. The prepared sample is denoted as "In2O3(111)".

[0087] (Comparative Example 5: Preparation of untreated Cu-In2O3 membrane catalyst) Using two electron beam-assisted evaporators (Omicron EMT3), Cu and In were co-deposited onto an In2O3(111) film from Mo crucibles filled with Cu and In, respectively. Approximately 0.1 ml of Cu and 0.9 ml of In were deposited on the In2O3(111) surface. The 1.0 ml used in this application represents 1 atom per In2O3(111) surface unit cell, i.e., 5.6 × 10⁻¹⁶ atoms. 13 atoms / cm 2 This corresponds to the following. The fluxes for Cu and In were 0.02 ml / min and 0.1 ml / min, respectively. Next, the sample was divided into 10 -5 The sample was oxidized in mbar of O2 at 573 K. The resulting sample is denoted as "Untreated Cu-In2O3".

[0088] (Example 6: Preparation of plasma-treated Cu-In2O3 film catalyst) An untreated Cu-In2O3 film catalyst was prepared by the same method as in Comparative Example 6. Next, the untreated Cu-In2O3 film catalyst was subjected to non-thermal plasma treatment in the presence of O2 by the method shown below, thereby obtaining a plasma-treated Cu-In2O3 film catalyst represented as plasma Cu-In2O3.

[0089] With an anode voltage of 1kV and a discharge current of 0.5μA, 7 × 10 -6 Untreated Cu-In2O3 film catalysts were subjected to oxygen plasma treatment using a microwave plasma generator equipped with a commercially available plasma source (OSPrey, Oxford Scientific, Figure 1a) operating in mbar of O2. The plasma treatment time was 1 hour.

[0090] (Reference Example 3: Preparation of Plasma-treated In2O3 Film Catalyst) The In2O3 film catalyst of Reference Example 2 was subjected to oxygen plasma treatment using the same method as in Example 6.

[0091] (Evaluation of results) The surface morphology of the In2O3 film catalysts of Reference Examples 2 and 3 was evaluated using STM. The STM image of the plasma-treated In2O3 film catalyst from Reference Example 3 (Figure 5b) revealed the formation of randomly distributed In2O3 clusters on the surface of the plasma-treated In2O3 film catalyst, with a wide size distribution ranging from 1 to 4 nm in diameter. The normalized number of In2O3 clusters per unit area in the STM image was 0.08 clusters / nm. 2 Such In2O3 clusters were not observed in the untreated In2O3(111) film catalyst of Reference Example 2 (see Figure 5a).

[0092] The XPS O1s spectrum of the (Cu-)In2O3 catalyst revealed the appearance of a shoulder after plasma treatment (Figure 6). This shoulder is due to a defect site ("O defect This is assigned to oxygen atoms in (represented by "). This result was consistent with the STM image, which shows that plasma treatment generates more clusters and provides a strong shoulder in the O1s spectrum.

Claims

1. A method for producing a catalytically active material for catalytically hydrogenating CO2 to methanol, The catalyst-active material includes a metal oxide doped with a doping metal, The aforementioned metal oxide comprises In₂O₃, The doping metal includes Cu, The method in question is selected from the following methods A and B: Method A described above is, (1) Adding an alkaline solution to an aqueous solution containing the doping metal and the metal component of the metal oxide to co-deposit the doping metal and the metal component of the metal oxide as a hydroxide precipitate, (2) The step of washing and drying the precipitate, (3) The step of calcining the dried precipitate in the presence of O2, (4) The calcined precipitate is subjected to non-thermal plasma treatment to obtain particles of the catalytic active material, It has, Method B described above is, (1) Preferably by a co-deposition method, the step of providing a film containing the metal oxide and the doping metal, (2) The step of annealing the film in the presence of oxygen, (3) A step of performing non-thermal plasma treatment, A method having

2. The method according to claim 1, wherein the content of the doping metal relative to the metal oxide is 0.01 wt% to 5.0 wt%, preferably 0.01 wt% to 3.0 wt%, and more preferably 0.05 wt% to 0.3 wt%.

3. The method according to claim 1, wherein the catalytically active material is in the form of particles.

4. The method according to claim 3, wherein the catalytic active material is composed of the metal oxide, the doping metal, and an arbitrary negatively charged counterion.

5. The method according to claim 3, wherein the catalytically active material has an average particle size of 5 nm to 50 nm when measured by a transmission electron microscope or a scanning transmission electron microscope.

6. The method according to claim 1, wherein the catalytically active material is in the form of a film.

7. The method according to claim 3, wherein the non-thermal plasma treatment is performed at a pressure of 40 mbar or less.

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