Catalyst for carbon dioxide methanation and method for producing the same, catalyst reaction tube for carbon dioxide methanation, and method for producing methane

Abstract

To provide a new catalyst for carbon dioxide methanation capable of achieving at least one of (i) conversion at a lower temperature than in the conventional art, (ii) conversion at a lower pressure than in the conventional art, (iii) enhanced conversion rate, and (iv) enhanced durability.SOLUTION: A catalyst for carbon dioxide methanation according to one embodiment of the present invention comprises a metal oxoacid salt comprising ruthenium. The metal oxoacid salt has a layered structure and is at least one selected from titanate, molybdate, vanadate, tungstate, manganate, nickelate, ferrate, zirconate, germanate, and composite salts thereof.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a catalyst for methanation of carbon dioxide and a methanation catalyst reactor. The present invention also relates to a method for producing the catalyst and a method for producing methane using the catalyst or the methanation catalyst reactor. [Background technology]

[0002] There is a technology that reacts carbon dioxide emitted from industrial facilities with hydrogen to produce methane, the main component of natural gas. This technology is expected to be a carbon-neutral technology aimed at reducing carbon dioxide emissions.

[0003] Ruthenium-based catalysts are known as catalysts for methanation of carbon dioxide. For example, Non-Patent Document 1 describes RuO x C y They have disclosed the methanation of carbon dioxide using a catalyst, and reported that the carbon dioxide conversion rate reached a maximum of 52% under the conditions of a temperature of 180°C, a pressure of 2 MPa, and a catalyst amount of 250 mg (see Figure 9 of the present application). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Carmen Tebar-Soler et al. (2023) "Low-oxidation-state Ru sites stabilized in carbon-doped RuO2 with low-temperature CO2 activation to yield methane", Nature Materials, vol.22, pp.762-768. Summary of the Invention [Problem to be solved by the invention]

[0005] The above-mentioned conventional technologies still require high temperatures and / or high pressures for methanation of carbon dioxide, and there is still room for improvement in the carbon dioxide conversion rate and the durability of the catalyst.

[0006] An object of one aspect of the present invention is to provide a carbon dioxide methanation catalyst that satisfies one or more of the following requirements: - Carbon dioxide can be converted at lower temperatures than conventional technologies. - Carbon dioxide can be converted at lower pressures than conventional technology. -Improved carbon dioxide conversion rate compared to conventional technology. -Improved durability compared to conventional technology. [Means for solving the problem]

[0007] The present invention includes the following aspects. <1> 1. A carbon dioxide methanation catalyst comprising a metal oxoacid salt of ruthenium, The metal oxyacid salt is layered, The metal oxyacid salt is at least one selected from the group consisting of titanates, molybdates, vanadates, tungstates, manganates, nickelates, ferrates, zirconates, germanates, and composite salts thereof. catalyst. <2> The composition of the ruthenium metal oxyacid salt is Ru x A (w-x) B y O z represented by <1> The catalyst described in In the above formula, A is a cation other than a ruthenium ion; B is one or more selected from the group consisting of titanium, molybdenum, vanadium, tungsten, manganese, nickel, iron, zirconium, and germanium; x is 0.01~w; y is 3 to 6; z is 7 to 13; w is the value that makes the total charge zero. <3> It is fibrous, <1> The catalyst according to claim 1. <4> <1> ~ <3> The catalyst according to any one of the preceding claims is contained therein. Methanation catalytic reactor. <5> A method for producing a carbon dioxide methanation catalyst, comprising a step of ion-exchanging at least a portion of cations contained between layers of a layered metal oxyacid salt with ruthenium ions, The metal oxyacid salt is at least one selected from the group consisting of titanates, molybdates, vanadates, tungstates, manganates, nickelates, ferrates, zirconates, germanates, and composite salts thereof. Manufacturing method. <6> The pH of the ion exchange step is 2.5 or higher. <5> The manufacturing method described in <7> The temperature of the ion exchange step is 80 to 220°C. <5> or <6> A method for producing the catalyst described in <8> <1> ~ <3> contacting the catalyst according to any one of the above with carbon dioxide and hydrogen, Methods for producing methane. <9> The temperature in the contacting step is 140 to 200°C. <8> The method for producing methane according to claim 1. <10> The pressure in the contacting step is 0.1 to 1 MPa. <8> or <9> The method for producing methane according to claim 1. <11> <4> The method includes a step of contacting the methanation catalyst reactor tube according to claim 1 with carbon dioxide and hydrogen. Methods for producing methane. <12> The temperature in the contacting step is 100 to 200°C. <11> The method for producing methane according to claim 1. <13> The pressure in the contacting step is 0.1 to 1 MPa. <11> or <12> The method for producing methane according to claim 1. [Effects of the Invention]

[0008] According to one aspect of the present invention, there is provided a carbon dioxide methanation catalyst that satisfies one or more of the following: - Carbon dioxide can be converted at lower temperatures than conventional technologies. - Carbon dioxide can be converted at lower pressures than conventional technology. -Improved carbon dioxide conversion rate compared to conventional technology. -Improved durability compared to conventional technology. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing a predicted structure of a carbon dioxide methanation catalyst according to one embodiment of the present invention. [Figure 2] 1 is a graph showing the electronic state and local structure of ruthenium in a catalyst. [Figure 3] 1 is a graph showing the relationship between the temperature of ion exchange and the activity of the resulting catalyst. [Figure 4] FIG. 1 is a diagram showing the effect of ion-exchange temperature on the composition and structure of the catalyst. [Figure 5] 1 is a graph showing the relationship between the pH of ion exchange and the activity of the resulting catalyst. [Figure 6] 1 is a graph showing the relationship between the concentration of ruthenium precursor in ion exchange and the activity of the resulting catalyst. [Figure 7] 1 is a graph showing the relationship between the temperature of the methanation reaction and the activity of the catalyst. [Figure 8] 1 is a graph showing the durability of the obtained catalyst. [Figure 9] 1 is a graph showing the durability of the catalyst disclosed in Non-Patent Document 1. [Figure 10]1 is a graph examining the effect of changing the type of metal oxoacid salt used as a raw material on the activity of the resulting catalyst. [Figure 11] FIG. 1 is an SEM image of the surface of a methanation catalyst reaction tube. [Figure 12] FIG. 1 is a diagram showing an example of a manufacturing process for a methanation catalyst reactor tube. [Figure 13] 1 is a graph showing the relationship between the temperature of the methanation reaction and the activity of the catalyst. DETAILED DESCRIPTION OF THE INVENTION

[0010] However, the present invention is not limited to the following embodiments and various modifications may be made within the scope of the claims. Embodiments that combine technical means described in different embodiments are also included in the technical scope of the present invention.

[0011] Unless otherwise specified in this specification, "A to B" representing a numerical range means "A or more and B or less." In this specification, the composition of a metal oxyacid salt of ruthenium is expressed as Ru x B y O z (Ru x Ti y O z However, this does not preclude the existence of cations other than ruthenium ions, and Ru x A (w-x) B y O z (Ru x A (w-x) Ti y O z etc.) should be read as follows.

[0012] [1. Carbon dioxide methanation catalyst] A carbon dioxide methanation catalyst according to one embodiment of the present invention contains a metal oxyacid salt of ruthenium. A "metal oxyacid salt" is a salt of a polyatomic anion containing a metal atom and an oxygen atom and a cation. A "metal oxyacid salt of ruthenium" is a substance in which a ruthenium ion and a metal oxyacid anion are bonded by ionic interaction.

[0013] The metal oxyacid salt is one or more selected from the group consisting of titanates, molybdates, vanadates, tungstates, manganates, nickelates, ferrates, zirconates, germanates, and complex salts thereof. Therefore, the metal oxyacid anion is an anion containing (or consisting of) one or more atoms selected from the group consisting of titanium atoms, molybdenum atoms, vanadium atoms, tungsten atoms, manganese atoms, nickel atoms, iron atoms, zirconium atoms, and germanium atoms, and oxygen atoms. In one embodiment, the composition of the metal oxyacid anion is [B n O 2n+1 ] 2- (n is a positive integer). A more specific example is BO3 2- , B2O5 2- , B3O7 2- , B4O9 2- , B5O 11 2- , B6O 13 2- In these formulas, B is one or more atoms selected from the group consisting of titanium atoms, molybdenum atoms, vanadium atoms, tungsten atoms, manganese atoms, nickel atoms, iron atoms, zirconium atoms, and germanium atoms.

[0014] The metal oxyacid anion may contain metal atoms other than the main metal atom (e.g., titanium atom in the case of titanate), and the content of such metal atoms may be 10 atomic % or less, 5 atomic % or less, 3 atomic % or less, or 1 atomic % or less, where the total number of metal atoms contained in the metal oxyacid anion is 100 atomic %.

[0015] Ruthenium oxyacid salts may contain cations other than ruthenium ions. Examples of such cations include H + , Na + , K. + , NH4 + , Mg 2+ , Ni 2+ , Co 2+ , Al 3+ These cations may be included alone or in combination with one another. In one embodiment, the metal oxyacid salt of ruthenium does not contain any cations other than ruthenium ions.

[0016] The metal oxyacid salt of ruthenium may contain anions other than the metal oxyacid anion. Examples of such anions include F - , Cl - , Br - , I - , O.H. - , NO3 - , SO4 2- These anions may be contained alone or in combination of two or more. In one embodiment, the metal oxyacid salt of ruthenium contains no anions other than the metal oxyacid anion.

[0017] In one embodiment, the metal oxyacid salt of ruthenium comprises ruthenium titanate. Ruthenium titanate comprises a titanate ion and a ruthenium ion. The titanate ion is an anion comprising (or consisting of) a titanium atom and an oxygen atom. In one embodiment, the titanate ion is [Ti n O 2n+1 ] 2- (n is a positive integer). A more specific example is TiO3 2- , Ti2O5 2- , Ti3O7 2- , Ti4O9 2- , Ti5O 11 2- , Ti6O 13 2- Examples include:

[0018] Metal oxyacid salts are layered. Typically, ruthenium ions are inserted between layers formed by metal oxyacid anions. Catalysts with this structure tend to be highly stable due to the interaction between the anions and cations.

[0019] The layered structure of the ruthenium metal oxyacid salt may be localized. That is, a uniform layered structure may not be maintained throughout the entire catalyst particle. For example, different layered structures may be in contact with each other via discontinuous surfaces. Alternatively, the catalyst particle may include a portion that does not have a layered structure. In one embodiment, the portion that has a layered structure occupies 50% by volume or more, 70% by volume or more, or 90% by volume or more of the total volume of the catalyst particle.

[0020] In one embodiment, the composition of the ruthenium metal oxyacid salt is Ru x A (w-x) B y O z It is expressed by:

[0021] In the formula, A is a cation other than a ruthenium ion, examples of which are given above.

[0022] In the formula, B is one or more elements selected from the group consisting of titanium, molybdenum, vanadium, tungsten, manganese, nickel, iron, zirconium, and germanium. However, B may contain small amounts of metal atoms other than these. The content of such metal atoms may be 10 atomic % or less, 5 atomic % or less, 3 atomic % or less, or 1 atomic % or less, where the total number of B is 100 atomic %.

[0023] In the formula, x is 0.01 or more. x may be 0.05 or more, 0.1 or more, or 0.5 or more. Theoretically, the upper limit of x is w. x / w represents the degree of ruthenium insertion, and generally, the larger the value, the more preferable.

[0024] wherein y is 3 to 6. z is 7 to 13. In one embodiment, z=2y+1. In one embodiment, (y,z)=(3,7), (4,9), (5,11) or (6,13).

[0025] In the formula, w is the value that makes the total charge 0. y O z Assuming that A is a divalent anion, if A is a monovalent cation, w = 2, if A is a divalent cation, w = 1, and if A is a trivalent cation, w = 2 / 3. If A is composed of multiple cations with different valences, w can also be determined based on the valence and abundance of each cation.

[0026] As described above, the catalyst contains a metal oxyacid salt, and the metal oxyacid salt is microscopically layered. However, the macroscopic shape of the catalyst is not particularly limited. For example, the catalyst may be in the form of a powder or fiber. In one embodiment, a fibrous catalyst is present on the surface of a methanation catalytic reactor tube, which will be described in detail in Section [3] below.

[0027] The aspect ratio (fiber length / fiber diameter) of the fibrous catalyst may be 3 or more, 5 or more, 10 or more, 50 or more, 70 or more, or 100 or more. The lower limit of the fiber length of the fibrous catalyst may be 1 μm or more, 5 μm or more, 10 μm or more, or 20 μm or more. The upper limit of the fiber length of the fibrous catalyst may be 10 mm or less, 1 mm or less, 500 μm or less, 100 μm or less, or 10 μm or less. The lower limit of the fiber diameter of the fibrous catalyst may be 0.5 nm or more, 1 nm or more, 5 nm or more, or 10 nm or more. The upper limit of the fiber diameter of the fibrous catalyst may be 1 mm or less, 0.5 mm or less, 100 μm or less, 50 μm or less, or 10 μm or less. The fiber length and fiber diameter of the catalyst are determined by analysis of SEM images.

[0028] 2. Catalyst Manufacturing Method A method for producing a carbon dioxide methanation catalyst according to one embodiment of the present invention includes a step of ion-exchanging at least a portion of the cations contained in a layered metal oxyacid salt with ruthenium ions.

[0029] The layered metal oxyacid salt is a substance containing (or consisting of) a metal oxyacid anion and a cation other than a ruthenium ion. The metal oxyacid anion has been explained in Section [1], so a detailed explanation will be omitted.

[0030] The ion exchange between the cations contained in the layered metal oxoacid salt and ruthenium ions is carried out, for example, as follows. 1. The layered metal oxyacid salt and ruthenium ions are allowed to coexist in a solvent, such as water. 2. If necessary, mix the reaction system by stirring or the like. 3. The reaction system is heat-treated. The heat treatment time can be 10 to 48 hours.

[0031] The lower limit of the pH of the solvent in step 1 may be 2.5 or higher, 2.7 or higher, or 3.0 or higher. If the pH is within the above range, ion exchange tends to proceed successfully. The upper limit of the pH of the solvent in step 1 may be 10.0 or lower, or 9.5 or lower. If the pH is within the above range, it is easy to prevent the metal oxyacid salt from dissolving in the solvent. Here, the above-mentioned pH is the pH before the metal oxyacid salt and ruthenium ions (or their precursors) are added. In particular, since many metal oxyacid salts are weakly basic substances, adding them to the solvent may increase the pH of the solvent.

[0032] The lower limit of the heat treatment temperature in step 3 may be 80°C or higher, 100°C or higher, 120°C or higher, or 140°C or higher. The upper limit of the heat treatment temperature in step 3 may be 220°C or lower, 200°C or lower, 180°C or lower, or 160°C or lower. In particular, when the heat treatment temperature is 140 to 200°C, a catalyst with high catalytic activity tends to be obtained.

[0033] In this way, a material is obtained in which ruthenium ions are intercalated between the layers of a layered metal oxyacid salt (see FIG. 1 for the production of ruthenium titanate). In one embodiment, the valence of the intercalated ruthenium ions is 4+. In one embodiment, the intercalated ruthenium ions are present in an atomically dispersed state. In one embodiment, the intercalated ruthenium ions do not exhibit the Ru-Ru bonds found in metallic ruthenium or the Ru-O-Ru bonds found in ruthenium dioxide. For example, in EXAFS, the peak intensity of the Ru-O bond is greater than the peak intensity of the Ru-Ru bond or the Ru-O-Ru bond.

[0034] [3. Methanation catalyst reaction tube] One embodiment of the present invention also includes a methanation catalyst reactor tube containing the above-described catalyst. In one embodiment, a fibrous catalyst is present on the surface of the methanation catalyst reactor tube. Figure 11 is an SEM image of the surface of a methanation catalyst reactor tube prepared in Example. As can be seen from the figure, the fibrous catalyst is distributed on the surface of the methanation catalyst reactor tube.

[0035] As an example, a methanation catalyst reactor tube can be manufactured by the following procedure. 1. Provide a substrate comprising one or more selected from the group consisting of titanium, molybdenum, vanadium, tungsten, manganese, nickel, iron, zirconium, and germanium. In one embodiment, the substrate is tubular. In one embodiment, the substrate is not tubular and is later assembled into a tubular shape. 2. The substrate is baked in air to at least partially oxidize it. 3. The oxidized substrate is hydrothermally treated under basic conditions to convert at least a portion of the substrate into a metal oxyacid salt, i.e., the substrate is heated while in contact with a basic aqueous solution. The metal oxyacid salt thus obtained may be in the form of fibers. 4. At least a portion of the cations contained between the layers of the metal oxyacid salt is exchanged with ruthenium ions. The procedure for ion exchange is the same as in Section [2], so a repeated explanation will be omitted.

[0036] In step 2, the lower limit of the firing temperature may be 500°C or more, 550°C or more, 600°C or more, or 650°C or more. The upper limit of the firing temperature may be 1000°C or less, 950°C or less, 800°C or less, or 850°C or less. In step 2, the lower limit of the firing time may be 1 hour or more, 2 hours or more, or 3 hours or more. The upper limit of the firing time may be 12 hours or less, 11 hours or less, or 10 hours or less.

[0037] In step 3, the lower limit of the base concentration in the aqueous solution may be 1 mol / L or more, 3 mol / L or more, or 5 mol / L or more. The upper limit of the base concentration may be 20 mol / L or less, 17 mol / L or less, or 15 mol / L or less. The lower limit of the hydrothermal treatment temperature may be 50°C or more, 100°C or more, or 150°C or more. The upper limit of the hydrothermal treatment temperature may be 500°C or less, 400°C or less, or 300°C or less. The lower limit of the hydrothermal treatment time may be 1 hour or more, 3 hours or more, or 5 hours or more. The upper limit of the hydrothermal treatment time may be 24 hours or less, 18 hours or less, or 12 hours or less.

[0038] The lower limit of the diameter of the methanation catalyst reaction tube may be 5 mm or more, 10 mm or more, or 15 mm or more. The upper limit of the diameter may be 50 mm or less, 45 mm or less, or 30 mm or less. The lower limit of the length of the methanation catalyst reaction tube may be 10 mm or more, 20 mm or more, or 30 mm or more. The upper limit of the length may be 200 mm or less, 150 mm or less, or 100 mm or less.

[0039] The structure of the methanation catalytic reaction tube is not particularly limited. For example, the methanation catalytic reaction tube may have one through-hole or may have multiple through-holes. The more through-holes there are, the larger the surface area of ​​the methanation catalytic reaction tube will be, and therefore, an improvement in the conversion rate of carbon dioxide to methane can be expected.

[0040] 4. Method for producing methane using a catalyst or methanation catalyst reaction tube A method for producing methane according to one embodiment of the present invention includes a step of contacting the above-described catalyst with carbon dioxide and hydrogen. A method for producing methane according to another embodiment of the present invention includes a step of contacting the above-described methanation catalyst reaction tube with carbon dioxide and hydrogen. One molecule of carbon dioxide reacts with four molecules of hydrogen to produce one molecule of methane and two molecules of water.

[0041] By using the above-described catalyst, the methanation reaction of carbon dioxide can proceed even under low temperature and low pressure conditions. In one embodiment, the lower limit of the reaction temperature may be 140°C or higher, 150°C or higher, or 160°C or higher. In one embodiment, the upper limit of the reaction temperature may be 200°C or lower. In one embodiment, the lower limit of the reaction pressure may be 0.1 MPa or higher or 0.2 MPa or higher. In one embodiment, the upper limit of the reaction pressure may be 1 MPa or lower.

[0042] Furthermore, by using the above-mentioned methanation catalyst reaction tube, the methanation reaction of carbon dioxide can proceed under low-temperature, low-pressure conditions. When using a methanation catalyst reaction tube, the lower limit of the reaction temperature can be 100°C or higher, 120°C or higher, or 140°C or higher. In this case, the upper limit of the reaction temperature can be 200°C or lower. When using a methanation catalyst reaction tube, the lower limit of the reaction pressure can be 0.1 MPa or higher or 0.2 MPa or higher. In this case, the upper limit of the reaction pressure can be 1 MPa or lower.

[0043] The use of the catalyst or methanation catalyst reactor described above can increase the conversion rate of carbon dioxide to methane. In one embodiment, the conversion rate can be 10% or more, 20% or more, 30% or more, 40% or more, or 50% or more. In one embodiment, the conversion rate is achieved under the low temperature and low pressure conditions described above. The reaction conditions for measuring the catalyst conversion rate can be those described in Example 5.

[0044] The use of the above-described catalyst can improve the durability of the catalyst. In one embodiment, the conversion rate after 200 hours of continuous reaction can be 50% or more. The reaction conditions for evaluating the durability of the catalyst can be the conditions described in Example 6. [Example]

[0045] [Production Example 1] A catalyst containing layered ruthenium titanate was prepared according to the following procedure. 1. 0.11552 g of ruthenium chloride hydrate (RuCl3·nH2O), 0.10504 g of sodium bicarbonate, and 25 mL of water were mixed with stirring for 30 minutes. The pH of the mixture was 3.05. 2. 0.1 g of sodium titanate (Na2Ti3O7) was added and mixed with stirring for 30 minutes. 3. The resulting mixture was subjected to hydrothermal treatment for 24 hours while stirring at 160°C, thereby exchanging some of the sodium ions contained in the sodium titanate for ruthenium ions. 4. The solids were filtered off and washed with water. 5. The solid was dried for 3 hours at 100° C. In this way, a catalyst containing layered ruthenium titanate was obtained.

[0046] [Production Example 2] The raw material was changed from sodium titanate to potassium titanate to prepare a catalyst containing layered ruthenium titanate. The procedure was as follows: 1. 0.11552 g of ruthenium chloride hydrate (RuCl3·nH2O), 0.12514 g of sodium bicarbonate, and 25 mL of water were mixed with stirring for 30 minutes. 2. 0.126 g of potassium titanate (K2Ti5O7) was added and mixed with stirring for 30 minutes. 5. The resulting mixture was subjected to hydrothermal treatment at 170°C for 20 hours while stirring. This resulted in some of the potassium ions contained in the potassium titanate being exchanged for ruthenium ions. 6. The solid content was filtered off and washed with water. 7. The solid was dried for 3 hours at 100° C. In this way, a catalyst containing layered ruthenium titanate was obtained.

[0047] [Production Example 3] A catalyst was obtained in the same manner as in Production Example 1, except that the amount of ruthenium chloride hydrate was changed to 1.7331 g, the amount of sodium hydrogen carbonate was changed to 1.5751 g, the amount of water was changed to 350 mL, and the amount of sodium titanate added was changed to 1.5 g.

[0048] [Production Example 4] A methanation catalyst reactor tube was prepared according to the following procedure. 1. A tubular member with a diameter of 23 mm and a length of 70 mm was fabricated using a metal 3D printer. The material composition of the tubular member was 89.5% by weight of titanium, 6.35% by weight of aluminum, and 4.15% by weight of vanadium, with the total weight being 100% by weight. 2. The prepared tubular member was sintered in air at 750°C for 6 hours, thus obtaining an oxidized tubular member. 3. The oxidized tubular member was subjected to hydrothermal treatment at 210°C for 8 hours. A 10 mol / L aqueous solution of sodium hydroxide was used as the basic aqueous solution. In this way, fibrous sodium titanate (Na2Ti3O7) was formed on the surface of the tubular member. 4. The tubular member, 1.1554 g of ruthenium chloride hydrate (RuCl3·nH2O) dissolved in 350 mL of distilled water, and 1.5751 g of sodium bicarbonate were hydrothermally treated at 120°C for 24 hours. This exchanged some of the sodium ions contained in the sodium titanate for ruthenium ions. 5. After ion exchange, the tubular member was dried for 3 hours at 100° C. In this way, a methanation catalyst reaction tube with a fibrous catalyst distributed on its surface was obtained.

[0049] Example 1 The state of ruthenium atoms in the catalyst was investigated by X-ray absorption fine structure (XAFS). Specifically, the valence of the ruthenium atoms was investigated by X-ray absorption near edge structure (XANES), and the state of chemical bonds of the ruthenium atoms was investigated by X-ray absorption extended fine structure (EXAFS). The catalyst obtained in Production Example 1 was used as the sample for measurement.

[0050] The results are shown in Figure 2. The XANES spectrum was significantly different from that of ruthenium foil (metallic ruthenium) and nearly identical to that of ruthenium dioxide. This suggests that the valence of the ruthenium atoms in the catalyst is 4+. Furthermore, in the EXAFS spectrum, whether obtained by Fourier transform (FT) or wavelet transform (WT), the peak representing the Ru-O bond was the strongest. On the other hand, the peaks representing the Ru-Ru bond seen in metallic ruthenium and the Ru-O-Ru bond seen in ruthenium dioxide were weaker. From these results, it is believed that the ruthenium atoms in the catalyst exist in an atomically dispersed state.

[0051] Example 2 The effect of the temperature during ion exchange on the catalytic activity of the resulting catalyst was investigated. Specifically, catalysts were prepared by changing the temperature of the hydrothermal treatment in step 3 of Production Example 1. Carbon dioxide was methanated using the resulting catalyst, and the space-time yield of methane was determined. The methanation conditions were as follows: Reaction pressure: 0.1 MPa Reaction temperature: 140℃ ·Catalyst weight: 50mg Composition of raw gas: H2:CO2:N2 = 71.25:23.75:5 (H2:CO2 = 3:1, CO2 concentration = 23.75% by volume) Flow rate of raw gas: 20 mL / min ·Space velocity (GHSV): 24,000 / h

[0052] The results are shown in Figures 3 and 4. Figure 3 also shows the conversion rates (literature values) of previously known ruthenium-based catalysts (for details, see Li et al., Applied Catalysis B: Environmental, vol. 319, (2022) 121903).

[0053] As can be seen from FIG. 3, the catalyst according to one embodiment of the present invention (Ru x Ti y O z -100℃~Ru x Ti y O z The carbon dioxide conversion rate at temperatures between 140 and 200°C was higher than that of conventionally known ruthenium-based catalysts. In particular, the catalyst obtained when the temperature during ion exchange was set to 140 to 200°C had a significantly higher carbon dioxide conversion rate. The ruthenium / titanium dioxide (Ru / TiO2)-based catalyst shown in Figure 3 has a particulate structure. Therefore, it differs from the structure in which ruthenium ions are inserted into layered titanic acid.

[0054] The top panel of Figure 4 is an SEM image showing the microstructure of the catalyst. It can be seen that the microstructure of the catalyst particles changes as the ion exchange temperature is changed. The middle panel of Figure 4 is a graph showing the ruthenium content of the catalyst (measured by X-ray fluorescence analysis). It can be seen that the ruthenium content is highest in the catalyst obtained by ion exchange at 160°C. The bottom panel of Figure 4 is an XRD spectrum of the catalyst. It can be seen that none of the catalysts show peaks characteristic of ruthenium dioxide. It can also be seen that when the ion exchange temperature reaches 200°C, peaks characteristic of anatase titanium dioxide begin to appear.

[0055] Example 3 The effect of pH during ion exchange on the catalytic activity of the resulting catalyst was investigated. Specifically, catalysts were prepared by changing the amount of sodium bicarbonate added in step 1 of Production Example 1. Carbon dioxide was methanated using the resulting catalyst, and the space-time yield of methane was determined. The methanation conditions were the same as in Example 2.

[0056] The results are shown in Figure 5. As can be seen from the figure, if the pH during ion exchange is raised to a certain level (for example, 2.5 or higher), the catalytic activity of the resulting catalyst increases significantly. This is thought to be because if the pH during ion exchange is high enough, the exchange between sodium ions and ruthenium ions proceeds, whereas if the pH is too low, the exchange between sodium ions and hydrogen ions proceeds.

[0057] Example 4 The effect of the ruthenium precursor concentration during ion exchange on the catalytic activity of the resulting catalyst was investigated. Specifically, catalysts were prepared by changing the amount of ruthenium chloride hydrate added in step 1 of Production Example 1. Carbon dioxide was methanated using the resulting catalyst, and the space-time yield of methane and its value per weight of the ruthenium precursor were determined. The methanation conditions were the same as in Example 2.

[0058] The results are shown in Figure 6. As can be seen from the figure, the highest catalytic activity was achieved when the amount of ruthenium precursor during ion exchange was 0.12 g.

[0059] Example 5 The temperature dependency of catalytic activity was investigated for a catalyst according to one embodiment of the present invention. Specifically, a catalyst was prepared according to Production Example 1, and the carbon dioxide conversion rate using the obtained catalyst was measured. The temperature during ion exchange was 160°C. The conditions for measuring the conversion rate were as follows: Reaction pressure: 0.1 MPa Reaction temperature: 100℃, 120℃, 140℃, 160℃ or 180℃ ·Catalyst weight: 50mg Composition of raw gas: H2:CO2:N2 = 71.25:23.75:5 (H2:CO2 = 3:1, CO2 concentration = 23.75% by volume) Flow rate of raw gas: 20 mL / min ·Space velocity (GHSV): 24,000 / h

[0060] The results are shown in Figure 7. As can be seen from the figure, the conversion rate exceeded 10% when the reaction temperature was 140°C, reaching a maximum of nearly 70%. On the other hand, with the catalyst according to the prior art, the conversion rate was less than 10% even when the reaction temperature was increased to 180°C. As such, the catalyst according to one embodiment of the present invention demonstrated catalytic activity even under low-temperature and low-pressure conditions.

[0061] Example 6 The durability of a catalyst according to one embodiment of the present invention was investigated. Specifically, a catalyst was prepared according to Production Example 1, and the time-dependent changes in carbon dioxide conversion rate and methane selectivity of the obtained catalyst were measured. The temperature during ion exchange was 160°C. The conditions for measuring the conversion rate were as follows: Reaction pressure: 0.1 MPa Reaction temperature: 180℃ ·Catalyst weight: 50mg Composition of raw gas: H2:CO2:N2 = 71.25:23.75:5 (H2:CO2 = 3:1, CO2 concentration = 23.75% by volume) Flow rate of raw gas: 20 mL / min ·Space velocity (GHSV): 24,000 / h

[0062] The results are shown in Figure 8. After 220 hours, the carbon dioxide conversion rate was 60.6%, and the methane selectivity was 99.9%. As can be seen from the figure, these values ​​showed almost no decrease from the start of the reaction. Thus, the catalyst according to one embodiment of the present invention maintained high catalytic activity even after continuous reaction.

[0063] For reference, the experimental results of the catalyst durability disclosed in Non-Patent Document 1 are shown in Figure 9 (partially modified from Figure 4 in Non-Patent Document 1). According to this figure, the conversion rate reached only 52% at most. This data is the result at a reaction pressure of 2 MPa and a catalyst weight of 260 mg, so it is estimated that the conversion rate would be further reduced if the measurement conditions were adapted to those of this example.

[0064] Example 7 The influence of different titanates as raw materials on catalytic activity was investigated for a catalyst according to one embodiment of the present invention. Specifically, catalysts were prepared according to Production Example 1 or 2. Carbon dioxide was methanated using the resulting catalyst, and the space-time yield of methane was determined. The methanation conditions were the same as in Example 2.

[0065] The results are shown in Figure 10. The space-time yield of methane was almost the same for both the catalyst made from sodium titanate and the catalyst made from potassium titanate. This demonstrates that a catalyst according to one embodiment of the present invention can be produced using a variety of titanates.

[0066] Example 8 The catalytic activity of a methanation catalyst reactor according to one embodiment of the present invention was investigated. Specifically, a catalyst and a methanation catalyst reactor were prepared according to Production Examples 1, 3, and 4, and the carbon dioxide conversion rate of the resulting catalyst or methanation catalyst reactor was measured. The conditions for measuring the conversion rate were the same as those in Example 5, and therefore will not be repeated here.

[0067] The results are shown in Figure 13. As can be seen from the figure, it was confirmed that the catalyst according to one embodiment of the present invention or the methanation catalyst reactor tube had a higher conversion rate of carbon dioxide to methane than the catalyst according to the prior art. It was also confirmed that the methanation catalyst reactor tube had a conversion rate in the low temperature range that exceeded that of a powdered catalyst. Furthermore, it was confirmed that the catalyst according to one embodiment of the present invention did not affect the catalytic activity under low temperature conditions even when the scale of preparation was increased (generally, catalytic activity can change when preparation is scaled up, but such a phenomenon did not occur with the catalyst according to one embodiment of the present invention). [Industrial Applicability]

[0068] The present invention can be used to produce methane.

Claims

1. 1. A carbon dioxide methanation catalyst comprising a metal oxoacid salt of ruthenium, The metal oxyacid salt is layered, The metal oxyacid salt is at least one selected from the group consisting of titanates, molybdates, vanadates, tungstates, manganates, nickelates, ferrates, zirconates, germanates, and composite salts thereof. catalyst.

2. The composition of the ruthenium metal oxyacid salt is: Ru ｘ A （ｗ－ｘ） B ｙ O ｚ represented by The catalyst of claim 1: In the above formula, A is a cation other than a ruthenium ion; B is at least one selected from the group consisting of titanium, molybdenum, vanadium, tungsten, manganese, nickel, iron, zirconium, and germanium; x is 0.01 to w; y is 3 to 6; z is 7 to 13; w is the value that makes the total charge zero.

3. It is fibrous, The catalyst of claim 1.

4. The catalyst according to any one of claims 1 to 3 is contained. Methanation catalytic reactor.

5. A method for producing a carbon dioxide methanation catalyst, comprising a step of ion-exchanging at least a portion of cations contained between layers of a layered metal oxyacid salt with ruthenium ions, The metal oxyacid salt is at least one selected from the group consisting of titanates, molybdates, vanadates, tungstates, manganates, nickelates, ferrates, zirconates, germanates, and composite salts thereof. Manufacturing method.

6. The pH of the ion exchange step is 2.5 or higher. The method of claim 5.

7. The temperature of the ion exchange step is 80 to 220°C. A method for producing the catalyst according to claim 5.

8. A method comprising a step of contacting the catalyst according to any one of claims 1 to 3 with carbon dioxide and hydrogen. Methods for producing methane.

9. The temperature of the contacting step is 140 to 200°C. The method for producing methane according to claim 8.

10. The pressure in the contacting step is 0.1 to 1 MPa. The method for producing methane according to claim 8.

11. A method for producing a methanation catalyst comprising contacting the methanation catalyst reactor tube according to claim 4 with carbon dioxide and hydrogen. Methods for producing methane.

12. The temperature of the contacting step is 100 to 200°C. The method for producing methane according to claim 11.

13. The pressure in the contacting step is 0.1 to 1 MPa. The method for producing methane according to claim 11.

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