Catalysts for methanation and methods for producing methane

Abstract

To provide a catalyst capable of promoting methanation at temperatures below 500°C, under atmospheric pressure conditions, and even at low hydrogen concentrations, and a method for producing methane. [Solution] The catalyst for methanation according to the present disclosure comprises a first particle, a second particle, and a third particle. The first particle is made of a metal containing at least one selected from the group consisting of nickel, cobalt, and ruthenium. The second particle comprises an oxyfluoride lanthanum-based material represented by the following general formula (1). La 1-x M x OF...(1) (In equation (1), M is a metallic element, and 0 ≤ x ≤ 0.5.) The third particle is made of a ceramic material. The first and second particles are supported on the third particle.

Description

Technical Field

[0001] The present invention relates to a catalyst for methanation and a method for producing methane.

Background Art

[0002] The reaction of producing methane (CH4) from carbon dioxide (CO2) and hydrogen (H2) as raw materials is known as a methanation reaction (sometimes simply referred to as methanation). Methanation is represented by the following reaction formula. CO2 + 4H2 → CH4 + 2H2O Methanation is expected as a technology to achieve carbon neutrality, and catalysts used for methanation have been studied. For example, Patent Document 1 discloses a catalyst for methanation including a carrier and a catalyst component. In the catalyst disclosed in Patent Document 1, the carrier contains one or more selected from the group consisting of elements such as cerium, lanthanum, praseodymium, and neodymium, and the catalyst component contains nickel supported on the carrier.

[0003] Patent Document 2 discloses a catalyst for methanation composed of a carrier and a catalyst metal supported on the carrier. The carrier of the catalyst disclosed in Patent Document 2 contains a metal oxide containing at least one metal element selected from cerium, zirconium, yttrium, aluminum, silicon, and magnesium. The catalyst metal contains at least one metal selected from nickel, ruthenium, rhodium, potassium, calcium, sodium, and iridium.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

[0005] Thermodynamically, methanation reactions are favored at low temperatures and high pressures. However, from a kinetic standpoint, the reaction is difficult to carry out at low temperatures due to the low reaction rate. Therefore, the temperature needs to be raised to a certain extent. However, if the temperature becomes too high, it becomes thermodynamically unfavorable, and above 500°C, the reverse water-gas shift reaction becomes more favorable, producing carbon monoxide. For this reason, the key to promoting methanation is usually to carry out the reaction at high pressure and relatively high temperatures, and to use a catalyst to increase the reaction rate.

[0006] On the other hand, hydrogen gas, which is the raw material for the methanation reaction, is flammable and has an explosive range in air (the explosive concentration range of hydrogen in air is 4-75%). From a safety standpoint, it is preferable that the methanation reaction can be carried out even at hydrogen concentrations below the explosive limit. Therefore, one of the objectives of this disclosure is to provide a catalyst that can carry out methanation even at temperatures of 500°C or less, under atmospheric pressure conditions, and at low hydrogen concentrations, and a method for producing methane using such a catalyst. [Means for solving the problem]

[0007] The methanation catalyst according to this disclosure comprises a first particle, a second particle, and a third particle. The first particle is made of a metal containing at least one selected from the group consisting of nickel, cobalt, and ruthenium. The second particle comprises an oxyfluoride lanthanum-based material represented by the following general formula (1). La 1-x M x OF...(1) (In equation (1), M is a metallic element, and 0 ≤ x ≤ 0.5.) The third particle is made of a ceramic material. The first and second particles are supported on the third particle. [Effects of the Invention]

[0008] According to the above catalyst, methanation can be carried out at temperatures below 500°C, under atmospheric pressure conditions, and even at low hydrogen concentrations. [Brief explanation of the drawing]

[0009] [Figure 1] This graph shows the relationship between reaction temperature and CO2 conversion rate in methanation using the catalysts of Example 1 and Comparative Example 1. [Figure 2] This graph shows the relationship between reaction temperature and methane yield in methanation using the catalysts of Example 1 and Comparative Example 1. [Figure 3] This graph shows the relationship between reaction temperature and CO2 conversion rate in methanation using the catalysts of Examples 1 to 8. [Figure 4] This graph shows the relationship between reaction temperature and methane yield in methanation using the catalysts of Examples 1 to 8. [Figure 5] This graph shows the relationship between reaction temperature and CO2 conversion rate in methanation using the catalysts of Example 5 and Examples 9-12. [Figure 6] This graph shows the relationship between reaction temperature and methane yield in methanation using the catalysts of Example 5 and Examples 9-12. [Figure 7] This graph shows the relationship between reaction temperature and CO2 conversion rate in methanation using the catalysts of Example 10 and Examples 13-14. [Figure 8] This graph shows the relationship between reaction temperature and methane yield in methanation using the catalysts of Example 10 and Examples 13-14. [Figure 9] This graph shows the relationship between reaction temperature and CO2 conversion rate in methanation using the catalysts of Example 10 and Examples 15-16. [Figure 10] This graph shows the relationship between reaction temperature and methane yield in methanation using the catalysts of Example 10 and Examples 15-16. [Figure 11]This flowchart shows a method for producing methane using the catalyst relating to this disclosure. [Modes for carrying out the invention]

[0010] [Summary of the Embodiment] First, the catalysts and manufacturing methods related to this disclosure will be listed and described. The methanation catalyst according to this disclosure comprises a first particle, a second particle, and a third particle. The first particle is made of a metal containing at least one selected from the group consisting of nickel, cobalt, and ruthenium. The second particle comprises an oxyfluoride lanthanum-based material represented by the following general formula (1). La 1-x M x OF...(1) (In equation (1), M is a metallic element, and 0 ≤ x ≤ 0.5.) The third particle is made of a ceramic material. The first and second particles are supported on the third particle.

[0011] Conventionally, catalysts for methanation and methods of using them have been studied. Patent Document 1 discloses a method for carrying out methanation using a catalyst having a specific composition. In the examples of Patent Document 1, it is described that a raw material gas consisting of 80 mol% hydrogen and 20 mol% carbon dioxide, and a raw material gas consisting of 8 mol% hydrogen, 2 mol% carbon dioxide and 90 mol% nitrogen were used.

[0012] Patent Document 2 discloses a method for producing methane by methanation using a specific catalyst. Patent Document 2 discloses a method using a raw material gas containing carbon dioxide, hydrogen, and oxygen. In practical terms, the technology of Patent Document 2 proposes a method for efficiently producing methane even in the presence of oxygen, considering that exhaust gas and other raw material gases used for methanation may contain not only carbon dioxide and hydrogen but also oxygen. In the embodiment of Patent Document 2, a mixed gas consisting of 10% by volume of carbon dioxide, 10% by volume of oxygen, 60% by volume of hydrogen, and the remainder being nitrogen is used as the raw material gas.

[0013] If the concentrations of carbon dioxide and hydrogen in the raw material gas are low, the methanation reaction becomes thermodynamically unfavorable. On the other hand, since hydrogen has an explosive range in air, it is desirable that the methanation reaction proceed even at low hydrogen concentrations below the explosion limit (below 4%). Furthermore, while it is possible to carry out methanation under pressure to increase reaction efficiency, from the viewpoint of energy efficiency and safety, it is desirable that methanation proceeds even under atmospheric pressure. According to the catalyst of this disclosure, even when using raw material gas with a low hydrogen concentration and carrying out the reaction at atmospheric pressure, a sufficient carbon dioxide conversion rate and methane yield can be obtained. Although not bound by any particular theory, it is believed that the catalyst of this disclosure exhibits excellent catalytic activity in methanation due to its configuration in which an oxyfluoride lanthanum-based material that readily conducts oxide ions and can efficiently store and release oxygen within the lattice, and a catalytic metal (typically Ni) with hydrogen dissociation ability are supported on a ceramic material with a high specific surface area, thereby enhancing the oxidation-reduction capacity. Furthermore, this effect is made even more certain if other metals are added to a part of the lanthanum (La) in the structure.

[0014] In the catalyst for methanation, it is preferable that M in the general formula (1) is a transition metal element. When M is a transition metal element, the effects of this disclosure are more clearly obtained.

[0015] In the catalyst for methanation, at least a portion of the first particles may be in contact with the second particles. The content of the first particles may be 3% by mass or more and 40% by mass or less relative to the mass of the catalyst. With these configurations and content ratios, the effects of this disclosure can be reliably obtained.

[0016] In the catalyst for methanation, the content of the second particles may be 5% by mass or more and 60% by mass or less relative to the total mass of the second and third particles. When the content is within this range, the effects of this disclosure can be obtained more reliably.

[0017] In the catalyst for methanation described above, in the general formula (1), M is Ni and x may be 0 ≤ x ≤ 0.1. When this range is observed, the effects of this disclosure can be obtained more reliably.

[0018] A method for producing methane according to this disclosure includes the steps of preparing a raw material gas containing carbon dioxide and hydrogen, and contacting the raw material gas with a catalyst for methanation to produce methane from carbon dioxide and hydrogen. According to the production method according to this disclosure, even when a raw material gas with a low hydrogen concentration is used, the conversion rate of carbon dioxide and the methane yield are high, and methane can be efficiently obtained by methanation.

[0019] In the above method, the hydrogen concentration in the raw material gas may be between 1% by volume and 8% by volume, based on the volume of the raw material gas. When it is within this range, the effects of this disclosure become clearer.

[0020] [Specific examples of embodiments] The following describes in more detail the catalyst and methane production method according to this disclosure, with specific examples of embodiments.

[0021] (catalyst) The catalyst according to this disclosure comprises a first particle, a second particle, and a third particle. The first particle contains a catalytic metal. The second particle contains a lanthanum oxyfluoride-based material. The third particle is a ceramic material. In the catalyst according to this disclosure, the first particle and the second particle are supported on the third particle. At least a portion of the first particle is in contact with the surface of the second particle; that is, at least a portion of the first particle is supported on the second particle. The second particle is in contact with the surface of the third particle. The first particle includes particles that are in contact with the surface of the second particle and the surface of the third particle, and particles that are in contact only with the surface of the second particle and are supported on the third particle via the second particle.

[0022] The first particle can be confirmed to exist as a particle by, for example, confirming its composition using X-ray diffraction (XRD). The second and third particles can be confirmed by, for example, confirming their morphology using a scanning electron microscope (SEM) or transmission electron microscope (TEM), and confirming their composition using X-ray diffraction (XRD) or X-ray fluorescence analysis.

[0023] (1st particle) The first particle is made of a metal containing at least one selected from the group consisting of nickel, cobalt, and ruthenium. The metal constituting the first particle may be one type or may contain two or more types. The metal as the first particle is a catalytic metal that has hydrogen dissociation ability and functions as a catalyst to promote the methanation reaction.

[0024] The first particle preferably contains nickel. The nickel content in the first particle may be 50% by mass or more, preferably 70% by mass or more, and preferably substantially nickel. Substantially nickel means that, excluding unavoidable impurities, the first particle is composed of nickel.

[0025] In the catalyst according to the present disclosure, the content ratio of the first particles, which are the catalytic metal, is not limited as long as it has the effects according to the present disclosure, but may be 3% by mass to 40% by mass, preferably 6% by mass to 30% by mass, based on the mass of the catalyst. If the content of the catalytic metal is 3% by mass or more, the effect of the catalyst of promoting methanation can be obtained by functioning together with the second particles. If the content of the catalytic metal is 40% by mass or less, a sufficient catalytic effect can be obtained.

[0026] (The second particles) The second particles contain a lanthanum oxyfluoride-based material represented by the following general formula (1). La 1-x M x OF···(1) (In formula (1), M is a metal element, and 0 ≦ x ≦ 0.5.) x may be 0, preferably 0 < x ≦ 0.5, more preferably 0 < x ≦ 0.1. That is, the lanthanum oxyfluoride-based material is preferably a composite metal oxyfluoride in which other metal atoms are added as a part of the lanthanum in lanthanum oxyfluoride. When x = 0, it means that no other metal is contained, and the metal oxyfluoride constituting the second particles is LaOF. The second particles of the catalyst according to the present disclosure are not limited to those containing other metals, but the addition of other metals can further improve the redox ability of the catalyst.

[0027] M in formula (1), that is, the metal added as a part of La, is preferably a transition metal, specifically, for example, one or more selected from the group consisting of Mn, Fe, Co, Ni, Cu, and Ce. Among these, when it is Ni, it has excellent redox ability and high effect as a catalyst for methanation.

[0028] In the catalyst according to this disclosure, the content of the second particles is not limited as long as it has the effects described herein, but may be 5% to 60% by mass, and preferably 8% to 53% by mass, relative to the mass of the catalyst. Furthermore, the content of the second particles may be 5% to 60% by mass, and preferably 10% to 60% by mass, relative to the total mass of the second and third particles. If the content of the second particles is 5% by mass or more relative to the total mass of the second and third particles, the effect of converting carbon dioxide in the raw material gas and promoting methanation can be obtained. If the content of the second particles is 60% by mass or less, a sufficient catalytic effect can be obtained.

[0029] (3rd particle) The third particles constituting the catalyst according to this disclosure are ceramic materials that function as a support. The ceramic material may be one or more selected from the group consisting of alumina (Al2O3), silica (SiO2), cordierite (2MgO·2Al2O3·5SiO2), and mullite (3Al2O3·2SiO2). The above materials are suitable as ceramic materials constituting the third particles.

[0030] In particular, cubic γ-alumina can be suitably used. The third particle functions as a dispersion medium. The inclusion of the third particle in the catalyst suppresses aggregation of the first particles with each other and the second particles with each other, thereby suppressing a decrease in the surface area of ​​the first and second particles. The average particle diameter of the third particle is, for example, 5 nm or more, preferably 10 nm or more. There is no particular upper limit to the average particle diameter of the third particle, but for example, it is less than 1 μm.

[0031] The proportion of the third particle in the catalyst according to this disclosure can be appropriately determined according to the proportions of the second and first particles.

[0032] (Function of catalyst) The catalysts described herein are used as catalysts for the production of methane. The catalysts described herein promote the methanation reaction. The activity of the catalyst can be indicated by the CO2 conversion rate, CH4 yield, and CH4 selectivity. The CO2 conversion rate is the percentage decrease in the CO2 concentration in the gas obtained after the reaction relative to the CO2 concentration in the raw material gas, when a raw material gas is brought into contact with a catalyst at a constant amount and temperature. The CH4 yield is the ratio of the CH4 concentration in the gas after the reaction relative to the CO2 concentration in the raw material gas. The CH4 selectivity is the ratio of the CH4 yield to the CO2 conversion rate.

[0033] The catalyst according to this disclosure may have a CO2 conversion rate of 10% or more at a reaction temperature of 250°C to 400°C. Furthermore, the CH4 selectivity may be 54% or more at this temperature. Preferably, the CO2 conversion rate at a reaction temperature of 300°C to 350°C may be 27% or more. Furthermore, the CH4 selectivity may be 67% or more at this temperature. The performance of the catalyst according to this disclosure is not particularly limited, but for example, a CO2 conversion rate of 10% or more and a CH4 selectivity of 55% or more at 250°C. For example, a CO2 conversion rate of 27% or more and a CH4 selectivity of 67% or more at 300°C. For example, a CO2 conversion rate of 42% or more and a CH4 selectivity of 65% or more at 350°C. For example, a CO2 conversion rate of 42% or more and a CH4 selectivity of 54% or more at 400°C. For example, a CO2 conversion rate of 43% or more and a CH4 selectivity of 26% or more at 450°C. For example, the CO2 conversion rate at 500°C is 47% or higher, and the CH4 selectivity is 5% or higher.

[0034] The catalyst according to this disclosure can promote methanation even when the concentrations of carbon dioxide and hydrogen in the source gas are low. For example, it can promote methanation even when the hydrogen concentration in the source gas is 10% or less, or 8% or less, typically 4% or less. Hydrogen gas is a flammable gas, and the explosive concentration range of hydrogen in air is 4.0% to 75%. Using the catalyst according to this disclosure, it is possible to promote methanation even at hydrogen concentrations below the lower limit of the explosive concentration, thus providing high safety in methane production.

[0035] (Method for manufacturing catalyst) The method for manufacturing the catalyst according to the present disclosure is not particularly limited, but can be manufactured, for example, by the following method. First, La which is the second particle 1-x M x OF is produced. La 1-x M x OF can be preferably obtained by a so-called solid-phase reaction method. Specifically, for example, a predetermined amount of lanthanum oxide (La2O3), lanthanum fluoride (LaF3), and nitrate of an additive metal are weighed and mixed, and then molded as necessary and fired under air circulation to produce a lanthanum oxyfluoride with addition of other metals. Next, the obtained second particles and the ceramic material as the third particles are mixed and fired to obtain a composition in which the lanthanum oxyfluoride-based material as the second particles is supported on the ceramic material as the third particles.

[0036] Furthermore, the composition and a nitrate of a catalyst metal (for example, Ni) can be complexed by a carboxylic acid complex polymerization method. More specifically, the composition and an aqueous nitrate solution or an aqueous chloride solution of the catalyst metal are evaporated to dryness to produce a carboxylic acid complex polymer. Next, the obtained carboxylic acid complex polymer is fired. In this way, the catalyst metal as the first particles, the lanthanum oxyfluoride-based material as the second particles, and the ceramic material as the third particles can be complexed.

[0037] Specific examples of the carboxylic acid used in the carboxylic acid complex polymerization include oxalic acid, malonic acid, glycolic acid, lactic acid, malic acid, tartaric acid, glyoxylic acid, citric acid, and gluconic acid, and malic acid is preferably used. The firing step of the carboxylic acid complex polymer can be carried out, for example, in the atmosphere at 400°C to 600°C for 1 to 6 hours. According to these firing temperatures and times, a catalyst having excellent methanation activity can be obtained.

[0038] The resulting catalyst may be used alone or mixed with other materials to form a catalyst composition. Before the calcination step, the catalyst material according to this disclosure and other materials may be mixed and calcined together.

[0039] (Methods for producing methane) A method for producing methane using the catalyst described herein will be explained. Figure 11 is a flowchart showing a method for producing methane using the catalyst described herein.

[0040] Referring to Figure 11, in the method for producing methane using the catalyst according to this disclosure, a preparation step (S10) is first performed in which a raw material gas is prepared. The raw material gas contains carbon dioxide and hydrogen. When using the catalyst according to this disclosure, methanation occurs and methane can be obtained even when the hydrogen concentration in the raw material gas is relatively low.

[0041] The concentration of carbon dioxide in the raw material gas is not particularly limited as long as the effects of this disclosure are obtained, but may be, for example, 1% or more by volume, 2% or more by volume, or 3% or more by volume, and may be 50% or less by volume, 20% or less by volume, or 10% or less by volume, or 8% or less by volume, based on the volume of the raw material gas. The concentration of hydrogen in the raw material gas is not particularly limited as long as the effects of this disclosure are obtained, but may be, for example, 1% or more by volume, 2% or more by volume, or 4% or more by volume, and may be 90% or less by volume, 80% or less by volume, 50% or less by volume, or 10% or less by volume, based on the volume of the raw material gas. Typically, the concentration of hydrogen in the raw material gas may be 1% or more by volume and 8% or less by volume, based on the volume of the raw material gas. Using the catalyst of this disclosure, methanation can be efficiently carried out even when the hydrogen concentration in the raw material gas is low.

[0042] The raw material gas may be, for example, a gas containing carbon dioxide, such as exhaust gas, to which hydrogen has been added. In addition to carbon dioxide and hydrogen, the raw material gas may also contain an inert gas such as nitrogen, or gases such as oxygen and carbon monoxide. In the raw material gas preparation process, pretreatment may be performed to remove specific components such as water and oxygen from the raw material gas.

[0043] Next, a methanation process is carried out (S20). Specifically, methanation can be performed by introducing a raw material gas into a reaction tube filled with the catalyst according to this disclosure and bringing the raw material gas into contact with the catalyst. The flow rate of the raw material gas introduced into the reaction tube is appropriately selected according to the diameter of the reaction tube, but for example, when using a reaction tube with a diameter of 10 mm, the flow rate of the raw material gas can be 1 to 50 mL / min, preferably 10 to 50 mL / min. The catalyst may be directly packed into the reaction tube, or it may be held attached to the surface of a substrate, for example, a ceramic honeycomb structure. When the catalyst is packed into the reaction tube, the amount of catalyst can be appropriately selected according to the diameter of the reaction tube and the flow rate of the reaction gas. For example, the amount of catalyst to be placed in one reaction tube may be 10 mg to 10 g, preferably 10 mg to 1 g. When the catalyst is held on the surface of the substrate, a catalyst layer can be formed on the surface of the substrate by coating the surface of the substrate with a slurry-like catalyst. The amount of catalyst held can be, for example, 0.01 to 10 mg / mm² based on the surface area of ​​the substrate. 2 That's fine.

[0044] The reaction tube is maintained at a temperature at which methanation occurs. The temperature of the reaction tube may be, for example, above 200°C, such as 210°C or higher, 220°C or higher, 250°C or higher, or 270°C or higher. The temperature of the reaction tube may be 400°C or lower, 370°C or lower, or 360°C or lower. The progress of the methanation reaction can be confirmed, for example, by measuring the carbon dioxide concentration in the raw material gas introduced into the reaction tube and the reaction gas discharged from the reaction tube. The heat source for heating the reaction tube is not particularly limited and may be, for example, an electric furnace using an electric heater, or other heat transfer fluids may be used. The temperature of the reaction tube may be constant during the methanation process (S20), or it may be changed according to the progress of the reaction.

[0045] Next, methane is recovered from the reaction gas that flows out of the reaction tube (S30). Any method can be used to recover the methane. The recovered methane can be used, for example, as fuel. In this way, carbon dioxide contained in exhaust gas, etc., can be converted into methane and reused as an energy source. [Examples]

[0046] Next, the present invention will be described in more detail based on examples. However, the present invention is not limited to these examples. The catalyst described herein was prepared as follows, and its structure and the progress of the methanation reaction were confirmed.

[0047] [Example 1] Stoichiometric amounts of La2O3 (0.3123 g) and LaF3 (0.1877 g) were weighed and mixed. Then, under air circulation, the mixture was calcined at 600°C for 12 hours to obtain the metal oxide LaOF. Next, LaOF (0.20 g) and γ-Al2O3 (0.30 g) were mixed in ethanol (25 mL) using a ball mill at 300 rpm for 3 hours. After mixing, the mixture was calcined in air at 500°C for 4 hours. Through these steps, a composition (40 wt% LaOF / γ-Al2O3) in which LaOF was supported on γ-alumina was obtained. Deionized water (20 mL) was placed in a 100 mL beaker, and 40 wt% LaOF / γ-Al2O3 (0.20 g), Ni(NO3)2·6H2O (0.1352 g), and propylene glycol (0.17 mL (5.0 molar equivalents relative to Ni ions)) were added. Next, malic acid (0.1869 g) was added in a molar equivalent ratio of 3.0 relative to Ni ions. Then, the mixture was stirred at 90°C for 4 hours. After stirring, the mixture was heated to 150°C to remove the solvent. After that, it was calcined in air at 500°C for 4 hours. Through the above steps, a catalyst (12 wt% Ni / 40 wt% LaOF / γ-Al2O3) in which LaOF and Ni were supported on γ-alumina was obtained.

[0048] (Methanation device) The catalyst obtained above was used to perform methanation under the following conditions, and the performance of the catalyst was confirmed. A 0.1 g catalyst sample was packed into a reaction tube. To hold the catalyst sample in place within the reaction tube, quartz wool was packed into both ends of the catalyst sample. This reaction tube was placed in an electric furnace and heated until the temperature of the gas introduced into the reaction tube reached a predetermined temperature. Cylinders containing carbon dioxide, hydrogen, and argon gas were prepared, and each gas was extracted in a predetermined ratio and mixed to create the pretreatment gas and the raw material gas. The composition (volume ratio) of the pretreatment gas was 4 vol% H2 - 96 vol% Ar. The composition (volume ratio) of the raw material gas was 1% CO2 - 4% H2 - 95% Ar. As a pretreatment, a pretreatment gas was introduced into a reaction tube maintained at 500°C at a flow rate of 50 mL / min for 1 hour, and then passed through the reaction tube. Subsequently, methanation was carried out by introducing the raw material gas into the reaction tube at a flow rate of 50 mL / min and passing it through the reaction tube. Methanation was performed at reaction temperatures of 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, and 500°C.

[0049] (Analysis of the gas after the reaction) Using a GC-MS (GCMS-QP2010plus, manufactured by Shimadzu Corporation), the composition of the gas that passed through the reaction tube was analyzed, and the CO2 conversion rate, CH4 yield, and CH4 selectivity were calculated using the following formulas.

[0050] CO2 conversion rate (%) = (1 - [CO2] / [CO2]0) × 100 CH4 yield (%) = [CH4] / [CO2] 0 × 100 CH4 selectivity (%) = (CH4 yield) / (CO2 conversion rate) × 100 In the above calculation formula, [CO2]0 represents the initial CO2 concentration in the raw material gas, [CO2] represents the CO2 concentration in the gas after passing through the reaction tube, and [CH4] represents the CH4 concentration in the gas after passing through the reaction tube.

[0051] In the methanation reaction process, the following equilibrium reaction occurs, and the conversion rate and yield at thermodynamic equilibrium were calculated using the NASA-CEA program. [ka]

[0052] [Comparative Example 1] As a comparative example, methanation was performed in the same manner as in Example 1, except that a catalyst of Ni supported on γ-alumina (12 wt% Ni / γ-Al2O3) was used as the catalyst, and the resulting gas was analyzed.

[0053] Table 1 shows the results for Example 1 and Comparative Example 1 when the reaction temperatures were 300°C and 350°C. Figure 1 shows a graph of the CO2 conversion rate at each reaction temperature, and Figure 2 shows a graph of the CH4 yield (%) at each reaction temperature. The dotted lines in the graphs in Figure 1 represent the CO2 conversion rate corresponding to the thermodynamic reaction equilibrium at each temperature. The dotted lines in the graphs in Figure 2 also represent the CO2 conversion rate corresponding to the thermodynamic reaction equilibrium at each temperature. The same applies to Figures 3 and beyond. [Table 1]

[0054] As shown in Table 1, the catalyst of Example 1 showed higher CO2 conversion rates and methane yields at 300°C, and particularly higher selectivity, compared to the catalyst of Comparative Example 1, which did not support lanthanum oxyfluoride (LaOF). Furthermore, the methane yield of Example 1 at 300°C (44.1%) was higher than that of Comparative Example 1 at 350°C (36.3%). Furthermore, as shown in Figures 1 and 2, it was confirmed that the methanation reaction proceeded sufficiently using the catalyst of Example 1 with a raw material gas having a carbon dioxide concentration of 1% and a hydrogen concentration of 4%. In particular, the catalyst of Example 1 showed a higher CO2 conversion rate and methane yield than the catalyst of Comparative Example 1 in the temperature range of 300°C or below.

[0055] (Consideration of added metals) In Examples 2-8, various metals were added to LaOF, and the relationship with methanation was investigated. The Ni loading was fixed at 12 wt%.

[0056] [Example 2] Stoichiometric amounts of La2O3 (0.2821g), LaF3 (0.1834g), and Mn(OCOCH3)2·4H2O (0.0344g) were weighed and mixed. Then, under air circulation, the mixture was calcined at 600°C for 12 hours, and the metal oxide La was formed. 0.95 Mn 0.05 OF was obtained. Next, La 0.95 Mn 0.05 OF (0.20g) and γ-Al2O3 (0.30g) were mixed in ethanol (25mL) using a ball mill at 300rpm for 3 hours. After mixing, the mixture was calcined in air at 500°C for 4 hours. Through the above process, La was obtained from γ-alumina. 0.95 Mn 0.05 OF-supported composition (40 wt% La 0.95 Mn 0.05 OF / γ-Al2O3 was obtained. Add 20 mL of deionized water to a 100 mL beaker, and add 40 wt% La 0.95 Mn 0.05OF / γ-Al2O3 (0.20 g), Ni(NO3)2·6H2O (0.1352 g), and propylene glycol (0.17 mL (5.0 molar equivalents relative to Ni ions)) were added. Next, malic acid (0.1869 g) was added in a molar equivalent ratio of 3.0 relative to Ni ions. Then, the mixture was stirred at 90°C for 4 hours. After stirring, the mixture was heated to 150°C to remove the solvent. After that, it was calcined in air at 500°C for 4 hours. Through the above steps, La was added to γ-alumina. 0.95 Mn 0.05 Catalyst supported with OF and Ni (12wt%Ni / 40wt%La 0.95 Mn 0.05 OF / γ-Al2O3 was obtained.

[0057] [Example 3] The procedure was the same as in Example 2, except that Fe(NO3)3·9H2O was used instead of Mn(OCOCH3)2·4H2O: 12wt%Ni / 40wt%La 0.95 Fe 0.05 OF / γ-Al2O3 was obtained.

[0058] [Example 4] The procedure was the same as in Example 2, except that Co(NO3)2·6H2O was used instead of Mn(OCOCH3)2·4H2O: 12wt%Ni / 40wt%La 0.95 Co 0.05 OF / γ-Al2O3 was obtained.

[0059] [Example 5] The procedure was the same as in Example 2, except that Ni(NO3)2·6H2O was used instead of Mn(OCOCH3)2·4H2O: 12wt%Ni / 40wt%La 0.95 Ni 0.05 OF / γ-Al2O3 was obtained.

[0060] [Example 6] The procedure was the same as in Example 2, except that Cu(NO3)2·3H2O was used instead of Mn(OCOCH3)2·4H2O: 12wt%Ni / 40wt%La 0.95 Cu 0.05 OF / γ-Al2O3 was obtained.

[0061] [Example 7] The procedure was the same as in Example 2, except that Ce(NH4)2(NO3)6 was used instead of Mn(OCOCH3)2·4H2O: 12wt%Ni / 40wt%La 0.95 Ce 0.05 OF / γ-Al2O3 was obtained.

[0062] [Example 8] The procedure was the same as in Example 2, except that Bi2O3 was used instead of Mn(OCOCH3)2·4H2O: 12wt%Ni / 40wt%La 0.95 Bi 0.05 OF / γ-Al2O3 was obtained.

[0063] (Metanation) Using the catalysts from Examples 2 to 8, methanation was performed in the aforementioned methanation apparatus under the same conditions as in Example 1, at reaction temperatures of 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, and 500°C.

[0064] Table 2 shows the methanation results when the catalysts of Examples 2 to 8 were used at reaction temperatures of 300°C and 350°C. The results of Example 1 are also shown again in Table 2. Furthermore, for the catalysts of Examples 2 to 8, graphs of the CO2 conversion rate at each reaction temperature are shown in Figure 3, and graphs of the CH4 yield (%) at each reaction temperature are shown in Figure 4.

[0065] [Table 2]

[0066] As shown in Table 2, using the catalysts of Examples 2-7, which were doped with transition metal elements, resulted in even higher CO2 conversion rates and methane yields than Example 1 at both 300°C and 350°C. In particular, Example 5, which had Ni added, achieved a methane yield of 55.7% at 300°C, the highest methane yield at that temperature. Example 8, which had Bi added, also showed a higher CO2 conversion rate at 300°C than Example 1. Furthermore, as shown in Figures 3 and 4, the methane reaction proceeded even when using a raw material gas with a carbon dioxide concentration of 1% and a hydrogen concentration of 4%, and it was confirmed that the effect was particularly significant below 350°C.

[0067] (Consideration of the proportion of responsibility 1) Examples 9-12 include La 0.95 Ni 0.05 The OF loading ratio was fixed at 40 wt%, and the relationship between the Ni loading ratio and methanation efficiency was examined.

[0068] [Example 9] Except for the amount of Ni supported being 18 wt%, the catalyst (18 wt% Ni / 40 wt% La) was used in the same manner as in Example 5. 0.95 Ni 0.05 OF / γ-Al2O3 was obtained.

[0069] [Example 10] Except for the amount of Ni supported, the catalyst (21 wt% Ni / 40 wt% La) was used in the same manner as in Example 9. 0.95 Ni 0.05 OF / γ-Al2O3 was obtained.

[0070] [Example 11] Except for the amount of Ni supported, the catalyst (24 wt% Ni / 40 wt% La) was used in the same manner as in Example 9. 0.95 Ni 0.05 OF / γ-Al2O3 was obtained.

[0071] [Example 12] Except for the amount of Ni supported being 30 wt%, the catalyst (30 wt% Ni / 40 wt% La) was used in the same manner as in Example 9. 0.95 Ni 0.05 OF / γ-Al2O3 was obtained.

[0072] (Metanation) Using the catalysts from Examples 9 to 12, methanation was performed in the aforementioned methanation apparatus under the same conditions as in Example 1, at reaction temperatures of 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, and 500°C.

[0073] Table 3 shows the methanation results when the catalysts from Examples 9 to 12 were used at reaction temperatures of 300°C and 350°C. Table 3 also includes the results from Examples 1 and 5. Furthermore, Figure 5 shows graphs of the CO2 conversion rate at each reaction temperature for the catalysts from Examples 9 to 12, and Figure 6 shows graphs of the CH4 yield (%) at each reaction temperature.

[0074] [Table 3]

[0075] Referring to Table 3, in all cases where the amount of supported Ni was varied from 12 wt% to 30 wt%, as in Examples 5, 9-12, the CO2 conversion rate and methane yield were equivalent to or higher than those of Example 1 at both 300°C and 350°C. Among these, Examples 5, 9-11, with Ni support ratios from 12 wt% to 24 wt%, showed particularly good results. In particular, Example 10, with 21 wt% Ni supported, achieved a methane yield of 61.6% at 300°C, the highest methane yield at 300°C. Furthermore, as shown in Figures 5 and 6, it was confirmed that the methane reaction proceeds even when using a raw material gas with a carbon dioxide concentration of 1% and a hydrogen concentration of 4%.

[0076] (Consideration of the proportion of responsibility 2) Examples 13 and 14 involved fixing the Ni loading ratio to 12 wt%, and La 0.95 Ni 0.05 We investigated the relationship between the proportion of OF (Functional Oxide) carried and methanation efficiency.

[0077] [Example 13] γ-Alumina and La 0.95 Ni 0.05La for the total amount with OF 0.95 Ni 0.05 Except for setting the proportion of OF to 20 wt%, the procedure was the same as in Example 10, and the catalyst (21 wt% Ni / 20 wt% La) was prepared. 0.95 Ni 0.05 OF / γ-Al2O3 was obtained.

[0078] [Example 14] γ-Alumina and La 0.95 Ni 0.05 La for the total amount with OF 0.95 Ni 0.05 Except for setting the proportion of OF to 60 wt%, the same procedure as in Example 10 was followed, and the catalyst (21 wt% Ni / 60 wt% La) was prepared. 0.95 Ni 0.05 OF / γ-Al2O3 was obtained.

[0079] (Metanation) Using the catalysts of Examples 13 to 14, methanation was performed in the aforementioned methanation apparatus under the same conditions as in Example 1, at reaction temperatures of 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, and 500°C.

[0080] Table 4 shows the methanation results when the catalysts of Examples 13 and 14 were used at reaction temperatures of 300°C and 350°C. Table 4 also includes the results of Examples 10 and 1. Furthermore, Figure 7 shows graphs of the CO2 conversion rate at each reaction temperature for the catalysts of Examples 10, 13, and 14, and Figure 8 shows graphs of the CH4 yield (%) at each reaction temperature.

[0081] [Table 4]

[0082] Referring to Table 4, the supported La is as shown in Examples 10, 13-14. 0.95 Ni 0.05In all cases where the amount of OF was varied from 20 wt% to 60 wt%, the CO2 conversion rate and methane yield were even higher than in Example 1 at both 300°C and 350°C. Furthermore, as shown in Figures 7 and 8, it was confirmed that the methane reaction proceeded even when using a raw material gas with a carbon dioxide concentration of 1% and a hydrogen concentration of 4%, and that the effect was particularly clear below 350°C.

[0083] (Consideration of the metal addition ratio) In Examples 15 and 16, the Ni loading ratio was fixed at 12 wt%, and the relationship between the metal addition ratio and methanation efficiency was investigated by changing the ratio of Ni added to lanthanum oxyfluoride (LaOF).

[0084] [Example 15] In the production of nickel-doped lanthanum oxyfluoride, the procedure was the same as in Example 5, except that the amount of Ni(NO3)2·6H2O added was changed. 0.97 Ni 0.03 OF was obtained. Subsequently, the catalyst (21 wt% Ni / 40 wt% La) was obtained in the same manner as in Example 10. 0.97 Ni 0.03 OF / γ-Al2O3 was obtained.

[0085] [Example 16] In the production of nickel-doped lanthanum oxyfluoride, the procedure was the same as in Example 5, except that the amount of Ni(NO3)2·6H2O added was changed. 0.93 Ni 0.07 OF was obtained. Subsequently, the catalyst (21 wt% Ni / 40 wt% La) was obtained in the same manner as in Example 10. 0.93 Ni 0.07 OF / γ-Al2O3 was obtained.

[0086] (Metanation) Using the catalysts of Examples 15 to 16, methanation was performed in the aforementioned methanation apparatus under the same conditions as in Example 1, at reaction temperatures of 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, and 500°C.

[0087] Table 5 shows the methanation results when the catalysts of Examples 15 and 16 were used at reaction temperatures of 300°C and 350°C. Table 5 also includes the results of Examples 10 and 1. Furthermore, Figure 9 shows graphs of the CO2 conversion rate at each reaction temperature for the catalysts of Examples 10, 15, and 16, and Figure 10 shows graphs of the CH4 yield (%) at each reaction temperature.

[0088] [Table 5]

[0089] Referring to Table 5, in all cases where the proportion of Ni added to lanthanum oxyfluoride was varied from 0.03 to 0.07, as in Examples 10, 15-16, the CO2 conversion rate and methane yield were even higher than in Example 1 at both 300°C and 350°C. In Example 15, the methane selectivity at 350°C was 97.7%, and in Example 16, the methane selectivity at 300°C was 100.8%. Furthermore, as shown in Figures 9 and 10, it was confirmed that the methanation reaction proceeded even when using a raw material gas with a carbon dioxide concentration of 1% and a hydrogen concentration of 4%, and that the effect was particularly clear below 350°C.

[0090] The embodiments and examples disclosed herein are illustrative in all respects and should be understood not to be restrictive in any way. The scope of the present invention is indicated by the claims, not in the sense described above, and all modifications within the sense and scope equivalent to the claims are intended. [Industrial applicability]

[0091] The catalyst of this invention is particularly advantageous as a catalyst for the production of methane using a methanation reaction.

Claims

1. Including a first particle, a second particle, and a third particle, The first particle is made of a metal containing at least one selected from the group consisting of nickel, cobalt, and ruthenium. The second particle comprises an oxyfluoride lanthanum-based material represented by the following general formula (1): La １－ｘ M ｘ OF・・・(1) (In equation (1), M is a metallic element, and 0 ≤ x ≤ 0.5.) The third particle is made of a ceramic material, A catalyst for methanation, wherein the first and second particles are supported on the third particle.

2. In the above general formula (1), M is a transition metal element. The catalyst for methanation according to claim 1.

3. At least a portion of the first particle is in contact with the second particle, The content ratio of the first particles is 3% by mass or more and 40% by mass or less relative to the mass of the catalyst. A catalyst for methanation according to claim 1 or claim 2.

4. The content of the second particle is 5% by mass or more and 60% by mass or less, relative to the total mass of the second particle and the third particle. A catalyst for methanation according to claim 1 or claim 2.

5. In the above general formula (1), M is Ni and x is 0 ≤ x ≤ 0.

1. A catalyst for methanation according to claim 1 or claim 2.

6. The process involves preparing raw material gases containing carbon dioxide and hydrogen, The process includes contacting the catalyst for methanation according to claim 1 or claim 2 with the source gas to produce methane from carbon dioxide and hydrogen, A method for producing methane.

7. The hydrogen concentration in the raw material gas is 1% by volume or more and 8% by volume or less, based on the volume of the raw material gas. A method for producing methane according to claim 6.

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