Carbon dioxide methane catalyst molded body and method for producing the same

Abstract

Provided is a molded body catalyst having high low-temperature activity, sufficient strength for industrial use, and heat resistance under high-temperature and high-vapor-pressure conditions with respect to a methanation catalyst supporting ruthenium as an active metal. Provided is a molded body of a carbon dioxide methanation catalyst which contains an activated alumina molded body and zirconia and ruthenium supported on the activated alumina molded body. The amount of zirconia supported is 3–10 parts by mass with respect to 100 parts by mass of the activated alumina molded body, the amount of ruthenium supported is 0.1–5 parts by mass with respect to 100 parts by mass of the activated alumina molded body, and the molded body has a particle size of 2–20 mm.

Description

[Technical Field]

[0001] The present invention relates to a catalyst molded body for producing a fuel gas mainly composed of methane by reacting hydrogen and carbon dioxide, and to a method for producing the same. [Background technology]

[0002] In recent years, carbon-neutral fuels, which do not substantially increase the concentration of carbon dioxide in the atmosphere when burned, have been attracting attention from the perspective of combating global warming.

[0003] Methane can be obtained by recovering carbon dioxide from exhaust gases generated in industrial processes and thermal power plants, and reacting it with hydrogen obtained through electrolysis using electricity from renewable energy sources such as solar and wind power. Since methane obtained by this method does not generate additional carbon dioxide when burned, it can be considered a carbon-neutral fuel that does not contribute to global warming.

[0004] The methanation reaction (Equation 1), which produces methane by reacting carbon dioxide with hydrogen, is well known. CO2+4H2→ CH4+2H2O (Formula 1)

[0005] Patent Document 1 discloses a method for methane production of a gas containing CO and H2, characterized by using a methane reactor in which a Cu-Zn low-temperature shift catalyst is placed upstream and a methane catalyst is placed downstream. In the upstream low-temperature shift reactor, the CO shift reaction (Equation 2) proceeds, so it is thought that most of the carbon monoxide contained in the raw material gas is converted to carbon dioxide by reacting with water vapor, and the methane reaction of carbon dioxide proceeds on the downstream methane catalyst. CO+H2O → CO2+H2 (Formula 2)

[0006] The methanation reaction has long been used to remove carbon monoxide and carbon dioxide from hydrogen used for ammonia synthesis, and catalysts supported with Ni or Ru are known to exhibit high activity (Non-Patent Documents 1, 2).

[0007] The methane reaction, which produces methane by reacting carbon dioxide and hydrogen, is an industrially established technology (for example, Non-Patent Document 3), but there are still challenges in obtaining fuel gas of a quality that can be used as a raw material for city gas.

[0008] Natural gas is commonly used as a raw material for city gas, and its main component is methane, with small amounts of ethane, propane, and butane. Natural gas does not usually contain hydrogen, and carbon dioxide is removed during the natural gas refining process. In particular, in the case of city gas produced using liquefied natural gas as a raw material, hydrogen and carbon dioxide are almost completely removed during the liquefaction and refining process, so they are practically absent.

[0009] The presence of hydrogen and carbon dioxide in city gas can cause the following problems:

[0010] Carbon dioxide is not only non-flammable, but it also inhibits combustion. Therefore, if it is mixed into fuel gas at high concentrations, it can not only reduce the efficiency of gas transport in pipelines due to a decrease in the calorific value of the fuel gas, but also potentially cause a decrease in the efficiency of combustion equipment.

[0011] Although hydrogen is a fuel gas, its calorific value per unit volume is only about one-third that of methane, the main component of city gas. Therefore, when hydrogen is mixed with a fuel gas that is mainly composed of methane, the calorific value per unit volume decreases. Furthermore, because hydrogen burns quickly, it is known to have a significant impact on combustion equipment.

[0012] The methane reaction of carbon dioxide (Equation 1) is an equilibrium reaction, and under normal industrial operating conditions, it is not possible to completely convert carbon dioxide and hydrogen to methane. When a mixed gas in a stoichiometric ratio (hydrogen:carbon dioxide = 4:1) is reacted at atmospheric pressure (0.1 MPa), the equilibrium conversion rate of carbon dioxide to methane is 95.0% at a reaction temperature of 300°C, 97.5% at a reaction temperature of 250°C, and 98.9% at a reaction temperature of 200°C.

[0013] Thus, at atmospheric pressure, only fuel gas containing a large amount of hydrogen can be obtained. Since the methanation reaction is an exothermic reaction, the equilibrium conversion rate improves as the temperature decreases. However, in the case of a catalytic reaction, the catalytic activity decreases as the temperature decreases. For this reason, there is a lower limit to the reaction temperature, and in the case of a typical methanation catalyst, a temperature of 250°C or higher is required to obtain a practical reaction rate (Non-Patent Document 4, Patent Documents 2 and 3).

[0014] The methane reaction of carbon dioxide (Equation 1) is a reaction in which the amount of substance (number of moles) decreases, so the equilibrium conversion rate increases with higher pressure. While high-pressure methane reactions yield fuel gas with high methane purity, reaction equipment capable of withstanding high pressure is expensive, and there are problems such as the need for a large amount of power to compress the raw material gas. If the methane reaction is carried out using a catalyst with excellent low-temperature activity, fuel gas with high methane purity can be obtained without drastically increasing the reaction pressure, which is economically advantageous.

[0015] Patent Document 4 discloses a catalyst for the hydrogen reduction of carbon dioxide, wherein nanoparticles are dispersed and supported on a powdery carrier, and more than 90% of the nanoparticles have a particle size of less than 10 nm, and the nanoparticles are at least one metal particle selected from the group consisting of Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, and Au, or material particles containing such metal particles. This document describes how, by rotating or pendulum-like a vacuum vessel having a polygonal internal cross-sectional shape with a rotation axis approximately perpendicular to the cross-section, a powdered carrier inside the vacuum vessel can be stirred, rotated, or pendulum-like while sputtering, thereby dispersing and supporting nanoparticles on the surface of the powdered carrier. It also shows that a methanation catalyst prepared in this way can achieve a 100% CO2 conversion rate at a reaction temperature of 200°C, demonstrating superior low-temperature activity compared to methanation catalysts obtained by general impregnation methods.

[0016] Patent Document 5 discloses a catalyst for the hydrogen reduction of carbon dioxide, in which catalytic metal nanoparticles and a metal oxide for suppressing the particle growth of the catalytic metal nanoparticles are dispersed and supported on a carrier.

[0017] This document shows that by using a target containing a metal and a metal oxide, sputtering can be performed while rolling the support to disperse and support the metal-containing nanoparticles and the metal oxide on the surface of the support, and that the methanation catalyst prepared in this way has smaller metal nanoparticle size and higher methanation activity compared to a catalyst that does not contain metal oxides.

[0018] However, while the sputtering method for supporting active metals described in these documents is easy to apply when the support is in powder form, it has the problem that when a support molded into a predetermined shape is used, the active metal can only be supported on the outermost surface of the support.

[0019] Patent Document 6 discloses a methanation catalyst comprising a carrier made of at least one metal oxide selected from the group consisting of titania, zirconia, and alumina, ceria particles supported on the carrier, and ruthenium particles supported on the carrier, wherein the average particle diameter of the ceria particles is 8 nm or less, the amount of ceria particles supported is 0.3 to 10 parts by mass per 100 parts by mass of the carrier, the average particle diameter of the ruthenium particles is 8 nm or less, and the amount of ruthenium particles supported is 0.5 to 5 parts by mass per 100 parts by mass of the carrier.

[0020] According to this document, when the coverage rate of the carrier surface by ceria particles and ruthenium particles is 1 to 80%, preferably 3 to 75%, more preferably 5 to 70%, high catalytic activity is said to be obtained.

[0021] However, none of Patent Documents 4 to 6 describe a method for producing a methanation catalyst for a molded body having practically sufficient strength.

[0022] As methods for molding the catalyst, there are methods such as rolling granulation, tableting molding, and extrusion molding. However, in any case of molding, in order to impart sufficient strength, it is necessary to perform heat treatment after molding, so there is concern that the catalytic activity may decrease during this process.

[0023] Activated alumina can be easily obtained as a molded body with high strength by, for example, rolling granulating boehmite and then firing it in air to obtain activated alumina. Therefore, it is widely used as a carrier for industrial catalysts and is also used as a carrier for methanation catalysts.

[0024] However, it is known that activated alumina changes its crystal structure and the specific surface area decreases at a lower temperature when the temperature is 1000 °C or higher or under conditions with a high water vapor partial pressure. Along with this, the strength of the molded body significantly decreases.

[0025] Patent Document 7 discloses that a catalyst in which ruthenium is supported on an activated alumina carrier containing 0.5 to 10% by weight of silica maintains stable catalytic activity and sufficient strength for a long time under the conditions of the steam reforming reaction of hydrocarbons, and when an activated alumina not containing silica is used as the carrier under the same conditions, a rapid decrease in activity and a significant decrease in strength are observed in a short time.

[0026] Patent Document 8 discloses a method for producing heat-resistant activated alumina, characterized by supporting an organosilicon compound on activated alumina powder or a molded body thereof or an activated alumina-containing molded body, and then oxidizing or thermally decomposing the supported organosilicon compound.

[0027] Patent Document 9 discloses a method for producing highly heat-resistant activated alumina, comprising a fractionation step of contacting a cyclic siloxane with activated alumina in an oxidizing atmosphere of 100°C to 300°C to fractionally extract the cyclic siloxane onto the activated alumina, and a firing step of firing the activated alumina in an oxidizing atmosphere to form a silica coating on the activated alumina.

[0028] Silica-coated activated alumina has excellent heat resistance, but when used as a catalyst support, it has the problem of reduced dispersion of the supported metal. Compared to activated alumina, silica has weaker interaction with the supported metal, and the supported metal tends to coarseen.

[0029] Patent Document 10 discloses a composition comprising zirconium oxide on a carrier based on alumina or aluminum oxyhydroxide, characterized in that the zirconium oxide is in the form of particles attached to the carrier after firing at 900°C for 4 hours, and the particle size of these particles is up to 10 nm.

[0030] This composition is said to be obtained, for example, by mixing a colloidal dispersion of a zirconium compound with alumina or aluminum oxyhydroxide, then drying and calcining it. It has been shown that the decrease in specific surface area after calcination at 1000°C for 4 hours is smaller than that of alumina supported with zirconium oxide prepared by known impregnation methods.

[0031] However, this document does not disclose the effect on the ruthenium dispersion when ruthenium is supported, nor does it describe whether or not the phase change of alumina can be suppressed. Furthermore, there is no specific description of how to obtain molded bodies with sufficient industrial strength.

[0032] Patent Document 11 discloses an impregnation solution for producing a ruthenium catalyst, characterized by being an aqueous solution containing a ruthenium compound and a compound of a Group IVa element of the periodic table, with a pH of 3 or less, and a method for producing a ruthenium catalyst, characterized by contacting the impregnation solution with a carrier to support the ruthenium component and the Group IVa element component on the carrier, drying the resulting ruthenium-supported composition, and then calcining it.

[0033] However, this document only shows the particle size of the supported ruthenium as a result of electron microscopy observations, and although it exemplifies a variety of reactions such as selective hydrogenation catalysts for carbonyl compounds, aromatic compounds, unsaturated compounds such as olefins and dienes, ammonia synthesis catalysts, FT synthesis catalysts, methane catalysts for CO and CO2, hydrogenation catalysts for CO and CO2 into alcohols, hydrogenation catalysts for nitro compounds, hydrocracking catalysts for hydrocarbons, selective hydrogenation catalysts for aromatic amines, reduction and purification catalysts for NOx, steam reforming catalysts for hydrocarbons, low-temperature complete oxidation catalysts, photosemiconductor catalysts, and electrode catalysts, it does not show the specific catalytic activity for any of these reactions.

[0034] Furthermore, Patent Document 11 does not describe the crystalline phase of zirconia supported on alumina, nor its effect on the phase change of alumina.

[0035] This document shows that the ruthenium particle size of a catalyst obtained by impregnating activated alumina with an impregnation solution containing ruthenium and zirconium compounds at a pH of 3 or lower, followed by drying and calcination, is smaller than that of a catalyst obtained by supporting zirconia and then ruthenium on activated alumina. The reason for this is explained as the formation of a complex-like compound between ruthenium and zirconium in the impregnation solution.

[0036] However, with this method, the distribution of ruthenium and zirconium in the molded catalyst must be identical, and it is not possible to control the distribution of ruthenium and zirconium separately. In fact, Patent Document 11 states that ruthenium is supported evenly and uniformly.

[0037] From the perspective of suppressing the phase change of alumina, zirconia needs to be supported at a sufficient concentration all the way to the center of the molded catalyst. In contrast, it is preferable that ruthenium, which serves as the active site of the catalyst, is supported in large quantities near the surface of the molded catalyst. However, in the method described in Patent Document 11, it is difficult to control the distribution of ruthenium and zirconium separately. Patent Document 11 does not offer any insights into the significance of controlling the distribution of ruthenium and zirconium separately, nor does it offer any suggestions on how to achieve this.

[0038] As described above, regarding methanation catalysts supported with ruthenium as the active metal, a molded catalyst possessing high low-temperature activity, sufficient strength for industrial use, and heat resistance under high-temperature and high-water vapor pressure conditions has yet to be established. [Prior art documents] [Patent Documents]

[0039] [Patent Document 1] Japanese Patent Application Publication No. 60-235893 [Patent Document 2] Japanese Patent Publication No. 2015-124217 [Patent Document 3] Japanese Patent Publication No. 2018-135283 [Patent Document 4] Japanese Patent Publication No. 2009-131835 [Patent Document 5] Japanese Patent Publication No. 2019-48249 [Patent Document 6] Japanese Patent Publication No. 2019-76862 [Patent Document 7] Japanese Patent Application Publication No. 57-4232 [Patent Document 8] Japanese Patent Application Publication No. 50-24200 [Patent Document 9] Japanese Patent Publication No. 2020-132514 [Patent Document 10] Special Publication No. 2011-513055 [Patent Document 11] Japanese Patent Application Publication No. 7-116516 [Non-patent literature]

[0040] [Non-Patent Document 1] Compilation of Chemical Processes, edited by the Society of Chemical Engineers, Japan, 1970, p. 153. [Non-Patent Document 2] Catalysis Society of Japan (ed.), Catalysis Handbook, 2008, p. 535. [Non-Patent Document 3] Kawagoe, Matsuda, Matsushima, and Uematsu, Hitachi Review, Vol. 68, No. 10, 1986, p. 73. [Non-Patent Document 4] E. Koytsoumpa and S. Karellas, Renewable and Sustainable Energy Reviews, Vol. 94, 2018, p. 536. [Overview of the project] [Problems that the invention aims to solve]

[0041] In view of the above problems, the present invention aims to provide a molded catalyst and a method for producing the same, relating to a methanation catalyst supported with ruthenium as the active metal, which possesses high low-temperature activity, sufficient strength for industrial use, and heat resistance under high temperature and high water vapor pressure conditions. [Means for solving the problem]

[0042] The characteristic structure of the methanation catalyst molded body according to the present invention is that it contains an activated alumina molded body and zirconia and ruthenium supported on the activated alumina molded body, wherein the amount of zirconia supported is 3 to 10 parts by mass per 100 parts by mass of the activated alumina molded body, and the amount of ruthenium supported is 0.1 to 5 parts by mass per 100 parts by mass of the activated alumina molded body, and the molded body has a particle size of 2 to 20 mm. the law of nature, The ruthenium is supported on the activated alumina molded body in an eggshell shape with a shell thickness of 0.2 to 0.4 mm, and the zirconia is supported in the center at a rate of 50% or more but less than 100% based on the average amount of zirconia supported in the entire activated alumina molded body, and the zirconia is supported in a rate of more than 100% in the shell portion where the ruthenium is supported. It is located at the point.

[0043] According to this characteristic configuration, the methanation catalyst molded body (hereinafter sometimes simply referred to as the catalyst molded body) possesses high low-temperature activity for the methanation reaction, sufficient strength for industrial use, and heat resistance under high temperature and high water vapor pressure conditions. Furthermore, it possesses particularly high low-temperature activity for methanation reactions, sufficient strength for industrial use, and heat resistance under high-temperature and high-water vapor pressure conditions.

[0045] Furthermore, in the aforementioned methanation catalyst molded body, if zirconia is mainly present in a tetragonal crystal structure, it possesses particularly high low-temperature activity for the methanation reaction, sufficient strength for industrial use, and heat resistance under high temperature and high water vapor pressure conditions.

[0046] Furthermore, in the aforementioned methanation catalyst molded body, it is preferable that the cerium oxide content is 5 parts by mass or less per 100 parts by mass of the activated alumina molded body, as this provides high low-temperature activity for the methanation reaction. Also, in the aforementioned methanation catalyst molded body, it is preferable that the degree of alpha-adaptation measured by the procedure of firing the activated alumina molded body with zirconia supported in air at 1050°C for 6 hours in air, and then measuring the degree of alpha-adaptation by X-ray diffraction measurement using Cu-Kα rays as a source, is 10% or less, or that the degree of alpha-adaptation measured by the procedure of firing the methanation catalyst molded body in air at 1050°C for 6 hours in air, and then measuring the degree of alpha-adaptation by X-ray diffraction measurement using Cu-Kα rays as a source, is 10% or less, as this provides sufficient strength for industrial use and particularly improves heat resistance under high temperature and high water vapor pressure conditions. In other words, in the aforementioned methanation catalyst molded body, if the cerium oxide content is 5 parts by mass or less per 100 parts by mass of the activated alumina molded body, and the degree of alpha-adaptation measured by X-ray diffraction using Cu-Kα rays as a source after firing the activated alumina molded body with zirconia supported in air at 1050°C for 6 hours, is 10% or less, or if the degree of alpha-adaptation measured by X-ray diffraction using Cu-Kα rays as a source after firing the methanation catalyst molded body in air at 1050°C for 6 hours, is 10% or less, then the low-temperature activity for the methanation reaction and sufficient strength for industrial use are achieved, and the heat resistance under high temperature and high water vapor pressure conditions is particularly improved.

[0047] The characteristic configuration of the method for producing a methane catalyst molded body of the present invention includes: a zirconium impregnation step to obtain a zirconium-impregnated body by impregnating an activated alumina molded body with a particle size of 2 to 20 mm with an aqueous solution in which a water-soluble compound of zirconium is dissolved; a drying step to obtain a dried body by drying the zirconium-impregnated body; a calcination step to obtain activated alumina with dispersed zirconia supported by calcining the dried body in air at 500 to 800°C; a ruthenium impregnation step to obtain a ruthenium-impregnated body by impregnating the activated alumina with dispersed zirconia supported by an aqueous solution in which a water-soluble compound of ruthenium is dissolved; and a ruthenium immobilization step to fix the ruthenium by drying the ruthenium-impregnated body. fruit, The amount of zirconia supported is 3 to 10 parts by mass per 100 parts by mass of the activated alumina molded body, and the amount of ruthenium supported is 0.1 to 5 parts by mass per 100 parts by mass of the activated alumina molded body. The ruthenium is supported on the activated alumina molded body in an eggshell shape with a shell thickness of 0.2 to 0.4 mm, and the zirconia is supported in the center at a rate of 50% to less than 100% of the average zirconia support in the entire activated alumina molded body, while the zirconia is supported in a rate of more than 100% in the shell portion where the ruthenium is supported. It's at a single point.

[0048] This method makes it possible to produce carbon dioxide methanation catalyst molded bodies that possess high low-temperature activity for methanation reactions, sufficient strength for industrial use, and heat resistance under high-temperature and high-water vapor pressure conditions, in an economically advantageous manner.

[0049] In the method for producing the methanation catalyst molded body described above, when the zirconium impregnation step is carried out using a nitric acid acidic aqueous solution in which a water-soluble zirconium compound is dissolved, a methanation catalyst molded body can be produced that is excellent in terms of low-temperature activity for the methanation reaction, sufficient strength for industrial use, and heat resistance under high temperature and high water vapor pressure conditions. [Brief explanation of the drawing]

[0050] [Figure 1] This is an electron probe microanalysis (EPMA) measurement result showing the distribution of Al, Zr, and Ru in a cross-section of a methane catalyst molded body according to an embodiment of the present invention. [Figure 2] This is an electron probe microanalysis (EPMA) measurement result showing the distribution of Al, Zr, and Ru in a cross-section of a methane catalyst molded body according to an embodiment of the present invention. [Figure 3] This figure shows the X-ray diffraction patterns of catalysts according to examples and comparative examples of the present invention. [Modes for carrying out the invention]

[0051] The following describes embodiments of the methanation catalyst molded body and the method for producing the methanation catalyst molded body according to the present invention.

[0052] The main component of the methanation catalyst molded body of the present invention is activated alumina, which is a transition alumina represented by γ-type and η-type. Activated alumina undergoes a phase transition to α-type by methods such as calcination at a high temperature of 1000°C or higher. However, α-type alumina has a small specific surface area, making it unsuitable as a support for the methanation catalyst molded body of the present invention because it cannot support zirconia and ruthenium in high dispersion. In the methanation catalyst molded body of the present invention, it is preferable that the alumina does not contain α-type alumina, or if it does, its mass ratio to the total alumina is 5% or less.

[0053] The methanation catalyst molded body of the present invention contains zirconia and ruthenium supported on an activated alumina molded body, wherein the amount of zirconia supported is 3 to 10 parts by mass per 100 parts by mass of the activated alumina molded body, and the amount of ruthenium supported is 0.1 to 5 parts by mass per 100 parts by mass of the activated alumina molded body.

[0054] If the amount of zirconia supported is less than 3 parts by mass per 100 parts by mass of the activated alumina molded body, the effect of stabilizing the activated alumina will be reduced, and under the reaction conditions of high temperature and high water vapor partial pressure, which are the reaction conditions for the methanation catalyst molded body, the activated alumina may undergo a phase transition to the α-type, potentially leading to problems such as a decrease in catalytic activity and pulverization of the catalyst.

[0055] If the amount of zirconia supported is greater than 10 parts by mass per 100 parts by mass of the activated alumina molded body, the pores formed in the activated alumina molded body may be blocked by the zirconia, reducing the diffusibility of the gas and potentially decreasing the catalytic activity.

[0056] Zirconia has three crystalline phases: tetragonal, monoclinic, and cubic, with the monoclinic phase being considered stable below 1100°C. However, in the methanation catalyst molded body of the present invention, zirconia is mainly supported in a highly dispersed tetragonal form. While it is acceptable for the methanation catalyst molded body of the present invention to contain monoclinic zirconia, if the zirconia is mainly present in a monoclinic form, the dispersion of zirconia supported on alumina may be low, which may result in insufficient stabilization of the activated alumina.

[0057] If the amount of ruthenium supported is less than 0.1 parts by mass per 100 parts by mass of the activated alumina molded body, sufficient methanation activity cannot be obtained. On the other hand, if the amount of ruthenium supported is greater than 5 parts by mass per 100 parts by mass of the activated alumina molded body, the degree of dispersion of the supported ruthenium becomes low, and methanation activity commensurate with the amount supported cannot be obtained. Furthermore, from the viewpoint of obtaining sufficient methanation activity that is more commensurate with the amount supported, the amount of ruthenium supported is preferably 0.5 to 2 parts by mass per 100 parts by mass of the activated alumina molded body.

[0058] The methane catalyst molded body of the present invention is a molded body with a particle size of 2 to 20 mm. Here, a particle size of 2 to 20 mm means that if the molded body is spherical, its diameter is in the range of 2 to 20 mm; if the molded body is cylindrical, its diameter and length are in the range of 2 to 20 mm; and if it is any other shape, its hydrodynamic equivalent diameter is in the range of 2 to 20 mm.

[0059] If the particle size of the methanation catalyst molded body is smaller than 2 mm, the pressure loss when the reaction gas is passed through the reaction vessel filled with the methanation catalyst molded body increases, worsening the economic efficiency of the methanation process. On the other hand, if the particle size is larger than 20 mm, the geometric surface area of ​​the molded body becomes relatively smaller, resulting in a decrease in methanation activity.

[0060] In a catalyst molded body, it is preferable that ruthenium, which is responsible for catalytic activity, is supported at a higher concentration on the surface than in the center. This is because, due to the diffusivity of the reaction gas within the catalyst molded body, ruthenium near the surface of the catalyst molded body acts more effectively as a catalyst than ruthenium in the center of the catalyst molded body. However, the outermost surface of the catalyst molded body is easily worn down by friction, and if ruthenium is supported only on the outermost surface, the loss of ruthenium due to wear will be large. In addition, considering the need to ensure a certain degree of dispersion, it is preferable to support the ruthenium uniformly from the surface of the catalyst molded body to a certain depth, and either not support it towards the center or reduce its support concentration. This makes it easier to obtain high methanation activity with a small amount of supported ruthenium.

[0061] More specifically, in a catalyst molded body, if ruthenium is supported on the activated alumina molded body in an eggshell shape with a shell thickness of 0.2 to 0.4 mm, in other words, if ruthenium is supported on the shell portion 0.2 to 0.4 mm from the surface of the catalyst molded body, high methanation activity can be easily obtained with a small amount of supported ruthenium.

[0062] On the other hand, zirconia needs to be supported all the way to the center of the catalyst molded body, as it plays a role in both increasing the dispersion of ruthenium and stabilizing activated alumina.

[0063] More specifically, in a catalyst molded body, if the amount of zirconia supported in the center is between 50% and 100% of the average amount of zirconia supported in the entire activated alumina molded body, the activated alumina is more easily stabilized. If the amount of zirconia supported in the shell portion where ruthenium is supported is higher than 100%, the degree of dispersion of ruthenium is increased, making it easier to obtain high methanation activity.

[0064] The present invention provides a method for producing a methane catalyst molded body, comprising: a zirconium impregnation step of impregnating an activated alumina molded body with a particle size of 2 to 20 mm with an aqueous solution in which a water-soluble compound of zirconium is dissolved to obtain a zirconium-impregnated body; a drying step of drying the zirconium-impregnated body to obtain a dried body; a calcination step of calcining the dried body in air at 500 to 800°C to obtain activated alumina on which zirconia is dispersed and supported; a ruthenium impregnation step of impregnating the activated alumina on which zirconia is dispersed and supported with an aqueous solution in which a water-soluble compound of ruthenium is dissolved to obtain a ruthenium-impregnated body; and a ruthenium immobilization step of drying the ruthenium-impregnated body to immobilize ruthenium.

[0065] Activated alumina molded bodies are transition aluminas, such as γ-type and η-type, molded into spherical or cylindrical shapes with diameters ranging from 2 mm to 20 mm. Such molded bodies are obtained by rolling granulation or tableting.

[0066] Water-soluble zirconium compounds that can be used include zirconium nitrate (Zr(NO3)4), zirconium nitrate oxide (Zr(NO3)2O), zirconium acetate (Zr(CH3COO)4), and zirconium acetate oxide (Zr(CH3COO)2O).

[0067] Some water-soluble zirconium compounds have insufficient solubility in water, or their aqueous solutions are not sufficiently stable. In such cases, nitric acid or hydrochloric acid may be added to the aqueous solution. Using a nitric acid-acidified aqueous solution is particularly preferable because it stabilizes the water-soluble zirconium compounds, making it easier to support zirconia in a suitable distribution within the methane catalyst molded body.

[0068] There are no particular restrictions on the temperature or duration of the zirconium impregnation process, but it can be carried out at room temperature for approximately 1 to 20 hours.

[0069] There are no particular restrictions on the temperature or time of the drying process, but it can be carried out at, for example, 80°C to 200°C for 1 to 20 hours.

[0070] If the firing temperature is too low, the zirconium compound may not decompose sufficiently, potentially leading to its leaching during the ruthenium loading process. Conversely, if the temperature is too high, the activated alumina may sinter too quickly, reducing its specific surface area. Therefore, a temperature between 500°C and 800°C is preferable.

[0071] The firing process time should be between 1 hour and 20 hours, as too short a time may result in insufficient decomposition of the zirconium compound, while too long a time may be economically disadvantageous and may reduce the specific surface area of ​​the activated alumina.

[0072] Air is acceptable as the gas used in the firing process, but oxygen or nitrogen may be added as needed to adjust the oxygen concentration.

[0073] Water-soluble ruthenium compounds that can be used include ruthenium chloride (RuCl3) and ruthenium nitrate (Ru(NO3)3).

[0074] There are no particular restrictions on the temperature or duration of the ruthenium impregnation process, but it can be carried out at room temperature for approximately 1 to 20 hours.

[0075] The ruthenium immobilization process, which involves fixing ruthenium, can be carried out by any method as long as the impregnated ruthenium is fixed onto the molded body without flowing out and no residue that inhibits the activity of the catalyst is left on the body. For example, the process can be carried out by immersing the ruthenium-impregnated body in an alkaline solution such as sodium hydroxide to fix the ruthenium as hydroxide, further reducing it with a reducing agent such as hydrazine to obtain metallic ruthenium, washing it to remove sodium ions, chloride ions, nitrate ions, etc., and then drying it in air at around 60°C to 100°C.

[0076] The methanation catalyst molded body of the present invention has high activity in the methanation of carbon dioxide. The reaction to obtain methane by the reaction of hydrogen and carbon dioxide is accompanied by a relatively large amount of heat, so if the reaction is carried out adiabatically, the temperature of the catalyst layer may rise to about 200°C to 400°C. When the temperature of the catalyst layer rises, the supported ruthenium aggregates, which reduces the catalytic activity, and there is a concern that the activated alumina will sinter and undergo a phase change, reducing the strength of the catalyst.

[0077] Therefore, when carrying out the methanation reaction of hydrogen and carbon dioxide, a portion of the reactor outlet gas is recycled to the reactor inlet to mitigate the heat generation. In this case, the gas introduced into the methanation catalyst molded body will include not only hydrogen and carbon dioxide, but also methane, water vapor, and even carbon monoxide produced by the reverse reaction of the CO shift reaction. However, the catalyst of the present invention exhibits high methanation activity even in the presence of water vapor, and also shows activity in the methanation of carbon monoxide, so it can be suitably used even under the conditions of a methanation reaction with recycling.

[0078] The methanation reaction using the methanation catalyst molded body of the present invention is not subject to any particular restrictions on operating conditions as long as the catalyst is within the range in which it exhibits activity, but is usually carried out at a temperature of 200°C to 600°C and a pressure of atmospheric pressure to 10 MPa. [Examples]

[0079] The present invention will be described more specifically below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0080] (Example 1) 40 g of activated alumina (manufactured by Kishida Chemical, catalytic aluminum oxide (activated type), molded spherical bodies of 4-6 mm) was immersed in 40 g of an aqueous solution of zirconium acetate oxide (manufactured by Tokyo Chemical Industry, containing 20% ​​by mass in terms of zirconium oxide) and impregnated for 15 hours to obtain a zirconium-impregnated body. This zirconium-impregnated body was evaporated to dryness on a hot plate, and then dried in a drying oven maintained at 125°C for 1 hour to obtain a dried body. This dried body was loaded into an electric furnace and heated from room temperature to 700°C over 3 hours while circulating air, and then held at 700°C for 4 hours to fire it. After that, it was allowed to cool to room temperature over 3 hours to obtain zirconia-supported alumina A.

[0081] Catalyst A was obtained by impregnating 98 parts by mass of zirconia-supported alumina A with an aqueous ruthenium chloride solution containing 2 parts by mass of ruthenium, drying at 80°C for 4 hours, immersing in a 0.375N-NaOH aqueous solution for 15 hours, liquid-phase reduction with a 0.3% hydrazine aqueous solution, washing with hot water at 80°C, and then drying at 80°C for 4 hours.

[0082] (Example 2) 3.25 g of zirconium nitrate dihydrate (Zr(NO3)2O·2H2O) was dissolved in dilute nitric acid prepared by mixing 2.2 g of 60% nitric acid with 20 g of pure water to obtain an aqueous solution that dissolves zirconium compounds. 30 g of the same activated alumina used in Example 1 was immersed in the aforementioned aqueous solution for 15 hours to obtain a zirconium-impregnated body. This zirconium-impregnated body was evaporated to dryness on a hot plate, and then dried in a drying oven maintained at 125°C for 1 hour to obtain a dried body. This dried body was loaded into an electric furnace and heated from room temperature to 700°C over 3 hours while circulating air, and then held at 700°C for 4 hours for firing. After that, it was allowed to cool to room temperature over 3 hours to obtain zirconia-supported alumina B.

[0083] Catalyst B was obtained by impregnating 98 parts by mass of zirconia-supported alumina B with an aqueous ruthenium chloride solution containing 2 parts by mass of ruthenium, drying at 80°C for 4 hours, immersing in a 0.375N-NaOH aqueous solution for 15 hours, liquid-phase reduction with a 0.3% hydrazine aqueous solution, washing with hot water at 80°C, and then drying at 80°C for 4 hours.

[0084] (Example 3) 6.51 g of zirconium nitrate dihydrate was dissolved in dilute nitric acid prepared by mixing 6.4 g of 60% nitric acid with 18 g of pure water to obtain an aqueous solution that dissolves zirconium compounds. 30 g of the same activated alumina used in Example 1 was immersed in the aforementioned aqueous solution for 15 hours to obtain a zirconium-impregnated body. This zirconium-impregnated body was evaporated to dryness on a hot plate, and then dried in a drying oven maintained at 125°C for 1 hour to obtain a dried body. This dried body was loaded into an electric furnace and heated from room temperature to 700°C over 3 hours while circulating air, and then held at 700°C for 4 hours for firing. After that, it was allowed to cool to room temperature over 3 hours to obtain zirconia-supported alumina C.

[0085] Catalyst C was obtained by impregnating 98 parts by mass of zirconia-supported alumina C with an aqueous ruthenium chloride solution containing 2 parts by mass of ruthenium, drying at 80°C for 4 hours, immersing in a 0.375N-NaOH aqueous solution for 15 hours, liquid-phase reduction with a 0.3% hydrazine aqueous solution, washing with hot water at 80°C, and then drying at 80°C for 4 hours.

[0086] (Comparative Example 1) A borosilicate glass petri dish with an inner diameter of 138 mm and an inner height of 22 mm was placed in the center of another borosilicate glass petri dish with an outer diameter of 60 mm and an outer height of 14 mm. 1.6 g of decamethylcyclopentasiloxane was dropped into the inner petri dish, and 40 g of the same activated alumina as in Example 1 was evenly distributed into the outer petri dish. The outer petri dish was then covered.

[0087] The petri dish was loaded into an electric furnace and heated from room temperature to 200°C over 1.5 hours, held at 200°C for 1 hour, and then allowed to cool to room temperature over approximately 1 hour. During this process, air was circulated into the electric furnace at a flow rate of 1 liter per minute.

[0088] After cooling, the petri dish was removed from the electric furnace, the activated alumina was transferred to an alumina firing container, and the temperature was raised from room temperature to 500°C over 1.5 hours. The alumina was then fired at 500°C for 1 hour to obtain silica-coated alumina D.

[0089] Catalyst D was obtained by impregnating 98 parts by mass of silica-coated alumina D with an aqueous ruthenium chloride solution containing 2 parts by mass of ruthenium, drying at 80°C for 4 hours, immersing in a 0.375N-NaOH aqueous solution for 15 hours, liquid-phase reduction with a 0.3% hydrazine aqueous solution, washing with hot water at 80°C, and then drying at 80°C for 4 hours.

[0090] (Comparative Example 2) Catalyst E was obtained by impregnating 98 parts by mass of the same activated alumina used in Example 1 with an aqueous ruthenium chloride solution containing 2 parts by mass of ruthenium, drying at 80°C for 4 hours, immersing in a 0.375N-NaOH aqueous solution for 15 hours, liquid-phase reduction with a 0.3% hydrazine aqueous solution, washing with hot water at 80°C, and then drying at 80°C for 4 hours.

[0091] (Heat resistance evaluation results) Zirconia-supported aluminas A, B, and C, as well as silica-coated alumina D and untreated activated alumina (referred to as alumina E), were each subjected to high-temperature firing at 1050°C for 6 hours in air. Table 1 shows the ZrO2 or SiO2 content, BET specific surface area (before and after high-temperature firing), and degree of gelatinization for each sample.

[0092] [Table 1] (Note) The BET specific surface area is listed in the format of before high-temperature firing → after high-temperature firing. Also, the degree of gelatinization is the value after high-temperature firing.

[0093] 《Method for measuring SiO2 content and ZrO2 content》 For each sample of zirconia-supported alumina A, B, and C, and silica-coated alumina D, acid decomposition was performed, and Si and Zr were quantified by ICP emission spectrometry. The content was then determined by converting it to oxides.

[0094] 《Method for measuring BET specific surface area》 For each sample before and after high-temperature firing, the BET specific surface area was measured using the BET single-point method, which utilizes the amount of nitrogen adsorbed under the condition of relative pressure (P / P0) = 0.3 at liquid nitrogen temperature.

[0095] Method for measuring the degree of alpha-gelatinization X-ray diffraction measurements were performed on each sample after high-temperature firing, and the degree of alpha-ization was calculated as the ratio of the diffraction line intensity of each sample to the diffraction line intensity of pure α-alumina for the (012) diffraction line (25.6°) of α-alumina. The X-ray diffraction measurements were performed using an X-ray diffractometer equipped with a graphite monochromator (Shimadzu XRD-6100) under the following conditions. X-ray source: Cu-Kα rays (0.1542 nm) emitted from an X-ray tube (Cu target, tube voltage 40kV, tube current 40mA). Measurement conditions: Step scan method, 0.02° step, integration time of 1.2 seconds per step, detection slit 0.15 mm.

[0096] (Evaluation results of Ru dispersion and crushing strength) For each of catalysts A, B, C, D, and E, the degree of metallic dispersion and crushing strength of the supported ruthenium were evaluated. Table 2 shows the Ru, ZrO2, SiO2, and Al2O3 content, BET specific surface area, ruthenium dispersion, and crushing strength of each catalyst.

[0097] [Table 2]

[0098] Methods for measuring the content of Ru, ZrO2, SiO2, and Al2O3 For each sample after ruthenium loading, acid decomposition was performed, and Ru, Si, and Zr were quantified by ICP emission spectrometry. The content of Ru was determined as is, while the content of Si and Zr was calculated by converting them to oxides.

[0099] Method for measuring the surface area of ​​metallic ruthenium For each sample after ruthenium was supported, the amount of CO adsorbed was measured according to the metal surface area measurement method using the CO pulse method (see Catalysis Committee of the Catalysis Society of Japan, "Catalysis", Vol. 31, p. 317, 1989), and is shown as the amount of CO adsorbed per unit of metallic ruthenium (molar ratio of CO / Ru) (i.e., degree of ruthenium dispersion).

[0100] Method for measuring crushing strength The crushing strength of 15 molded catalyst particles was measured using an Aiko Engineering FTN1-13A benchtop load tester, and the average value was used.

[0101] (Evaluation results of methanation activity) The methanation activity of each catalyst, A, B, C, D, and E, was evaluated. The results are shown in Table 3.

[0102] [Table 3]

[0103] 《Method for Evaluating Methanation Activity》 A catalyst layer was formed by filling a stainless steel reaction tube (24 mm inner diameter) with 5 mL of catalyst. While heating the catalyst layer to maintain its temperature at 250°C, a reducing gas (a mixture of nitrogen gas and 10% hydrogen gas by volume) was circulated at a rate of 150 liters per hour (volume at standard conditions of 0°C and 1 atmosphere; the same applies below) for 3 hours to perform the reduction treatment.

[0104] After the reduction treatment described above, the catalyst layer temperature was changed to 225°C, and the pressure inside the reaction tube was maintained at 0.7 MPa (absolute pressure). Nitrogen gas (test gas) containing 2% carbon dioxide and 8% hydrogen (both by volume) was circulated through the catalyst layer at a flow rate of 150 liters per hour. The concentrations of carbon dioxide, hydrogen, nitrogen, and methane in the catalyst layer outlet gas were analyzed using a gas chromatograph (Shimadzu GC-14B, with TCD detector). Subsequently, while the test gas was still circulating, the catalyst layer temperature was changed to 250°C, and the catalyst layer outlet gas was similarly analyzed using a gas chromatograph. The conversion rate of CO2 in the test gas was calculated from the methane and carbon dioxide concentrations (both by volume %) of the catalyst layer outlet gas using the following formula. No carbon monoxide was detected in the catalyst layer outlet gas. (CO2 conversion rate [%]) = 100 × (CH4 concentration) / {(CH4 concentration) + (CO2 concentration)}

[0105] Evaluation of the Examples and Comparative Examples We will examine the results of the heat resistance evaluation. The specific surface area of ​​BET after high-temperature firing is 27.2 m² for alumina E. 2 / g, silica-coated alumina D is 78.6m 2 While the value was / g, zirconia-supported alumina A, B, and C were 64.4m each. 2 / g, 56.3m 2 / g, 61.3m 2 The result was / g. In the zirconia-supported aluminas A, B, and C used in the examples, the decrease in BET specific surface area after high-temperature firing was significantly smaller compared to alumina E, and they maintained a specific surface area at a level close to that of silica-coated alumina D.

[0106] After high-temperature firing, the degree of alpha-gelatinization was 59% for alumina E and 21% for silica-coated alumina D, while it was only 1.5% for zirconia-supported alumina B. In zirconia-supported alumina A and C, no alpha-alumina peaks were observed in X-ray diffraction measurements. In other words, in terms of the degree of alpha-gelatinization, zirconia-supported alumina A, B, and C exhibit superior heat resistance compared to both alumina E and silica-coated alumina D.

[0107] The above results evaluate the heat resistance in the state without ruthenium support. However, since the sintering and phase change of alumina proceed regardless of the presence or absence of ruthenium, the heat resistance in the state with ruthenium support, i.e., the heat resistance of catalysts A, B, C, D, and E, is considered to be the same as described above.

[0108] The ruthenium concentrations supported on catalysts A, B, C, D, and E ranged from 1.61 to 1.66 wt%, showing little difference regardless of whether zirconia-supported alumina A, B, and C, or silica-coated alumina D and E, were used. On the other hand, the dispersion of the supported ruthenium was 0.64 when alumina E was used, while it decreased significantly to 0.42 when silica-coated alumina D was used. This indicates that while coating the surface of alumina with silica improves heat resistance, it also significantly reduces the dispersion of the supported metal. In catalysts A, B, and C of the present invention, which use alumina supported with zirconia, the dispersion degrees of the supported metal were 0.69, 0.61, and 0.73, respectively, which were equivalent to or better than catalyst E. In particular, catalysts A and C, which have a high zirconia content, showed a higher ruthenium dispersion degree than catalyst E.

[0109] Regarding crushing strength, catalysts A, B, and C of the present invention exhibit strength equivalent to or greater than catalyst E, which has only ruthenium supported on activated alumina. In particular, catalysts A and C, which have a high zirconia content, showed improved strength compared to catalyst E.

[0110] The methanation activity of catalysts A, B, and C of the present invention was significantly higher compared to catalyst E, which had ruthenium supported only on activated alumina. On the other hand, the methanation activity of catalyst D, which had ruthenium supported on silica-coated alumina D, was clearly lower than that of catalyst E.

[0111] (Comparative Example 3) 4.04 g of cerium nitrate hexahydrate (Ce(NO3)3·6H2O) was dissolved in 24 g of pure water to obtain an aqueous solution that dissolves cerium compounds. 32 g of the same activated alumina used in Example 1 was immersed in the aforementioned aqueous solution for 15 hours to obtain an impregnated body. This impregnated body was evaporated to dryness on a hot plate, and then dried in a drying oven maintained at 125°C for 1.5 hours to obtain a dried body. This dried body was loaded into an electric furnace and heated from room temperature to 700°C over 3 hours while circulating air, and then held at 700°C for 4 hours to calcinate. After that, it was allowed to cool to room temperature over 3 hours to obtain ceria-supported alumina F.

[0112] Catalyst F was obtained by impregnating 98 parts by mass of ceria-supported alumina F with an aqueous ruthenium chloride solution containing 2 parts by mass of ruthenium, drying at 80°C for 4 hours, immersing in a 0.375N-NaOH aqueous solution for 15 hours, liquid-phase reduction with a 0.3% hydrazine aqueous solution, washing with hot water at 80°C, and then drying at 80°C for 4 hours.

[0113] (Example 4) 3.47 g of zirconium nitrate dihydrate and 4.04 g of cerium nitrate hexahydrate were dissolved in dilute nitric acid prepared by mixing 3.2 g of 60% nitric acid with 24 g of pure water to obtain an aqueous solution that dissolves the zirconium and cerium compounds. 32 g of the same activated alumina used in Example 1 was immersed in the aforementioned aqueous solution for 15 hours to obtain an impregnated body. This impregnated body was evaporated to dryness on a hot plate, and then dried in a drying oven maintained at 125°C for 1.5 hours to obtain a dried body. This dried body was loaded into an electric furnace and heated from room temperature to 700°C over 3 hours while circulating air, and then held at 700°C for 4 hours for firing. After that, it was allowed to cool to room temperature over 3 hours to obtain ceria-zirconia supported alumina G.

[0114] Catalyst G was obtained by impregnating 98 parts by mass of ceria-zirconia-supported alumina G with an aqueous ruthenium chloride solution containing 2 parts by mass of ruthenium, drying at 80°C for 4 hours, immersing in a 0.375N-NaOH aqueous solution for 15 hours, liquid-phase reduction with a 0.3% hydrazine aqueous solution, washing with hot water at 80°C, and then drying at 80°C for 4 hours.

[0115] (Example 5) 3.47 g of zirconium nitrate dihydrate and 8.08 g of cerium nitrate hexahydrate were dissolved in dilute nitric acid prepared by mixing 3.2 g of 60% nitric acid with 24 g of pure water to obtain an aqueous solution that dissolves the zirconium and cerium compounds. 32 g of the same activated alumina used in Example 1 was immersed in the aforementioned aqueous solution for 15 hours to obtain an impregnated body. This impregnated body was evaporated to dryness on a hot plate, and then dried in a drying oven maintained at 125°C for 1.5 hours to obtain a dried body. This dried body was loaded into an electric furnace and heated from room temperature to 700°C over 3 hours while circulating air, and then held at 700°C for 4 hours for firing. After that, it was allowed to cool to room temperature over 3 hours to obtain ceria-zirconia supported alumina H.

[0116] Catalyst H was obtained by impregnating 98 parts by mass of ceria-zirconia-supported alumina H with an aqueous ruthenium chloride solution containing 2 parts by mass of ruthenium, drying at 80°C for 4 hours, immersing in a 0.375N-NaOH aqueous solution for 15 hours, liquid-phase reduction with a 0.3% hydrazine aqueous solution, washing with hot water at 80°C, and then drying at 80°C for 4 hours.

[0117] (Example 6) 13.08 g of zirconium dichloride dihydrate (ZrCl2O·2H2O) was dissolved in 25 g of pure water to obtain an aqueous solution for dissolving the zirconium compound. 50 g of the same activated alumina used in Example 1 was immersed in the aforementioned aqueous solution for 15 hours to obtain an impregnated body. This impregnated body was evaporated to dryness on a hot plate, and then dried in a drying oven maintained at 120°C for 1 hour to obtain a dried body. This dried body was loaded into an electric furnace and heated from room temperature to 500°C over 3 hours while circulating air, and then held at 500°C for 2 hours for firing. After that, it was allowed to cool to room temperature over 3 hours to obtain zirconia-supported alumina I.

[0118] Catalyst I was obtained by impregnating 98 parts by mass of zirconia-supported alumina I with an aqueous ruthenium chloride solution containing 2 parts by mass of ruthenium, drying at 80°C for 4 hours, immersing in a 0.375N-NaOH aqueous solution for 15 hours, liquid-phase reduction with a 0.3% hydrazine aqueous solution, washing with hot water at 80°C, and then drying at 80°C for 4 hours.

[0119] (Heat resistance evaluation results) Ceria-supported alumina F, ceria-zirconia-supported alumina G and H, and zirconia-supported alumina I were each subjected to high-temperature firing at 1050°C for 6 hours in air. Table 4 shows the ZrO2 and CeO2 content, BET specific surface area (before and after high-temperature firing), and degree of gelatinization for each sample.

[0120] [Table 4] (Note) The BET specific surface area is listed in the format of before high-temperature firing → after high-temperature firing. Also, the degree of gelatinization is the value after high-temperature firing.

[0121] 《Measurement method》 For each sample of ceria-supported alumina F, ceria-zirconia-supported alumina G and H, and zirconia-supported alumina I, acid decomposition was performed, and Ce and Zr were quantified by ICP emission spectrometry. The ZrO2 and CeO2 content were then determined by converting them to oxides. The BET specific surface area and degree of gelatinization were measured using the same method as in Table 1.

[0122] (Evaluation Results of Ru Dispersion and Crushing Strength) For each of catalysts F, G, H, and I, the metal dispersion of supported ruthenium and the crushing strength were evaluated. Table 5 shows the Ru, CeO2, ZrO2, and Al2O3 contents, BET specific surface area, ruthenium dispersion, and crushing strength of each catalyst.

[0123]

Table 5

[0124] 《Measurement Method》 For each of catalysts F, G, H, and I, Ru, Ce, Zr, and Al were quantified by acid decomposition and ICP emission spectrometry. The contents of Ru, SiO2, ZrO2, and Al2O3 were determined with Ru as it is and Ce, Zr, and Al converted to oxides. The measurement methods for ruthenium dispersion and crushing strength are the same as those in Table 2.

[0125] (Evaluation Results of Methanation Activity) For each of catalysts F, G, H, and I, the methanation activity was evaluated in the same manner as in Table [3]. The results are shown in Table 6.

[0126]

Table 6

[0127] 《Evaluation of Examples 4 - 6 and Comparative Example 3》 Examine the results of the heat resistance evaluation. The BET specific surface area of ceria - supported alumina F after high - temperature calcination is 46.3 m 2 / g, and that of zirconia - supported aluminas A, B, and C (64.4 m 2 / g, 56.3 m 2 / g, 61.3 m 2The value was lower compared to ( / g). Although an improvement in heat resistance was observed when ceria (cerium oxide) was supported instead of zirconia, it was clear that the effect was not as significant as that of zirconia.

[0128] The BET specific surface area of ​​ceria-zirconia-supported alumina G and H after high-temperature firing is 52.9 m², respectively. 2 / g and 48.7m 2 The value for ceria-supported alumina F was (46.3m). 2 Although it is higher compared to zirconia-supported alumina B (56.3m / g), 2 The values ​​are lower compared to those per g, and the BET specific surface area decreased as the ceria load increased. This indicates that while adding ceria to alumina has some effect on improving heat resistance, the presence of ceria in zirconia-supported alumina reduces heat resistance.

[0129] Zirconia-supported alumina I, which had zirconia supported using zirconium dichloride dihydrate, showed improved heat resistance compared to alumina E. However, compared to zirconia-supported alumina A, B, and C, the decrease in BET specific surface area after high-temperature firing was somewhat greater, and alpha-gelatinization also progressed. Therefore, it is preferable to use a nitric acid solution of zirconium nitrate or an aqueous solution of zirconium acetate for zirconium support.

[0130] The dispersion degrees of ruthenium supported on catalysts F, G, H, and I were 0.46, 0.51, 0.57, and 0.65, respectively. Compared to the value for catalyst E using alumina E (0.64), catalyst I showed a slight improvement, but catalysts F, G, and H showed a decrease, indicating that the presence of ceria reduces the dispersion degree of ruthenium.

[0131] Regarding crushing strength, catalyst H showed improved strength compared to catalyst E, but catalysts F, G, and I showed lower strength than catalyst E.

[0132] The methanation activity of catalysts F, G, H, and I was significantly higher than that of catalyst E, which had only ruthenium supported on activated alumina. However, the methanation activity of catalyst F was significantly lower than that of catalysts B and C, clearly demonstrating the superiority of the catalyst of the present invention, in which zirconia and ruthenium are supported on activated alumina. Furthermore, when comparing the methanation activity of catalysts B, G, and H with the same level of zirconia support, it is understood that the methanation activity decreases as the amount of ceria added increases. While the inclusion of ceria in the catalyst of the present invention is not problematic, from the viewpoint of heat resistance and methanation activity, it is preferable that the amount of ceria be 5 parts by mass or less, and more preferably 1 part by mass or less, per 100 parts by mass of activated alumina.

[0133] (Example 7) 5.4 g of zirconium nitrate dihydrate was dissolved in dilute nitric acid prepared by mixing 4.2 g of 60% nitric acid with 32 g of pure water to obtain an aqueous solution that dissolves zirconium compounds. 50 g of activated alumina (Sumitomo Chemical, KHA-24, 2-4 mm spherical molded body) was immersed in the aforementioned aqueous solution for 15 hours to obtain an impregnated body. This impregnated body was evaporated to dryness on a hot plate, and then dried in a drying oven maintained at 125°C for 1.5 hours to obtain a dried body. This dried body was loaded into an electric furnace and heated from room temperature to 700°C over 3 hours while circulating air, and then held at 700°C for 4 hours to fire it. After that, it was allowed to cool to room temperature over 3 hours to obtain zirconia-supported alumina J.

[0134] Catalyst J was obtained by impregnating 98 parts by mass of zirconia-supported alumina J with an aqueous ruthenium chloride solution containing 2 parts by mass of ruthenium, drying at 80°C for 4 hours, immersing in a 0.375N-NaOH aqueous solution for 15 hours, liquid-phase reduction with a 0.3% hydrazine aqueous solution, washing with hot water at 80°C, and then drying at 80°C for 4 hours.

[0135] (Example 8) 10.8 g of zirconium nitrate dihydrate was dissolved in dilute nitric acid prepared by mixing 11.5 g of 60% nitric acid with 35 g of pure water to obtain an aqueous solution that dissolves zirconium compounds. 50 g of activated alumina (Sumitomo Chemical, KHA-24, 2-4 mm spherical molded body) was immersed in the aforementioned aqueous solution for 15 hours to obtain an impregnated body. This impregnated body was evaporated to dryness on a hot plate, and then dried in a drying oven maintained at 125°C for 1.5 hours to obtain a dried body. This dried body was loaded into an electric furnace and heated from room temperature to 700°C over 3 hours while circulating air, and then held at 700°C for 4 hours to fire it. After that, it was allowed to cool to room temperature over 3 hours to obtain zirconia-supported alumina K.

[0136] Catalyst K was obtained by impregnating 98 parts by mass of zirconia-supported alumina K with an aqueous ruthenium chloride solution containing 2 parts by mass of ruthenium, drying at 80°C for 4 hours, immersing in a 0.375N-NaOH aqueous solution for 15 hours, liquid-phase reduction with a 0.3% hydrazine aqueous solution, washing with hot water at 80°C, and then drying at 80°C for 4 hours.

[0137] (Example 9) 13.09 g of zirconium dichloride dihydrate was dissolved in 22.5 g of pure water to obtain an aqueous solution for dissolving the zirconium compound. 50 g of the same activated alumina used in Example 4 was immersed in the aforementioned aqueous solution for 15 hours to obtain an impregnated body. This impregnated body was evaporated to dryness on a hot plate, and then dried in a drying oven maintained at 120°C for 1 hour to obtain a dried body. This dried body was loaded into an electric furnace and heated from room temperature to 500°C over 3 hours while circulating air, and then held at 500°C for 2 hours for firing. After that, it was allowed to cool to room temperature over 3 hours to obtain zirconia-supported alumina L.

[0138] Catalyst L was obtained by impregnating 98 parts by mass of zirconia-supported alumina L with an aqueous ruthenium chloride solution containing 2 parts by mass of ruthenium, drying at 80°C for 4 hours, immersing in a 0.375N-NaOH aqueous solution for 15 hours, liquid-phase reduction with a 0.3% hydrazine aqueous solution, washing with hot water at 80°C, and then drying at 80°C for 4 hours.

[0139] (Comparative Example 4) Catalyst M was obtained by impregnating 98 parts by mass of the same activated alumina (denoted as alumina M) used in Example 7 with an aqueous ruthenium chloride solution containing 2 parts by mass of ruthenium, drying at 80°C for 4 hours, immersing in a 0.375N-NaOH aqueous solution for 15 hours, liquid-phase reduction with a 0.3% hydrazine aqueous solution, washing with hot water at 80°C, and then drying at 80°C for 4 hours.

[0140] (Heat resistance evaluation results) Zirconia-supported aluminas J, K, and L, as well as alumina M, were subjected to high-temperature firing at 1050°C for 6 hours in air. Table 7 shows the ZrO2 content, BET specific surface area (before and after high-temperature firing), and degree of gelatinization for each sample.

[0141] [Table 7] (Note) The BET specific surface area is listed in the format of before high-temperature firing → after high-temperature firing. Also, the degree of gelatinization is the value after high-temperature firing.

[0142] 《Measurement method》 For each sample of zirconia-supported alumina J, K, and L, and alumina M, Zr was quantified by acid decomposition and ICP emission spectrometry, and the ZrO2 content was determined by converting it to oxide. The method for measuring BET specific surface area and degree of gelatinization was the same as in Table 1.

[0143] (Evaluation results of Ru dispersion and crushing strength) For each of catalysts J, K, L, and M, the metallic dispersion and crushing strength of the supported ruthenium were evaluated. Table 8 shows the Ru, ZrO2, and Al2O3 content, BET specific surface area, ruthenium dispersion, and crushing strength for each catalyst.

[0144] [Table 8]

[0145] 《Measurement method》 For each of catalysts J, K, L, and M, Ru, Zr, and Al were quantified by acid decomposition and ICP emission spectrometry. The content of Ru, ZrO2, and Al2O3 was determined by using Ru directly and converting Zr and Al to their oxide forms. The methods for measuring ruthenium dispersion and crushing strength were the same as in Table 2.

[0146] (Evaluation results of methanation activity) The methanation activity of catalysts J, K, L, and M was evaluated using the same method as in Table 3. The results are shown in Table 9.

[0147] [Table 9]

[0148] (Electron probe microanalysis results) The distribution of ruthenium and zirconia within the catalyst molded body of catalyst K was investigated using electron probe microanalysis. Measurements were performed using a JEOL JXA-8500F field emission electron microanalyzer under the following conditions: accelerating voltage: 15kV, irradiation current: 500nA, analysis range: 3.125mm × 3.125mm, target elements and detected characteristic X-rays: Al(Kβ), Zr(Lα), Ru(Lα). The measurement results for two different molded particle samples of catalyst K are shown in Figures 1 and 2. The measurement results are expressed in mass percent for each element. For example, when explaining Al, the data is color-coded in 4% increments, such as above 0% by mass and below 4% by mass, above 4% by mass and below 8% by mass, and above 8% by mass and below 12% by mass. The grayscale diagram shows that the higher the Al content (AlCn) by mass, the lighter the gray. The Area% column shows the area percentage that the region within that content range occupies within the entire field of view. Note that the edges of the field of view include areas where the catalyst is not present, so the sum of the values ​​shown in the Area% column will not equal 100%.

[0149] As is clear from Figures 1 and 2, in both molded particle forms, ruthenium is concentrated in an eggshell-like support structure within a range of approximately 0.3 mm from the surface. In contrast, zirconia is supported all the way to the center, but in the shell region where ruthenium is supported, it is supported in a higher quantity.

[0150] From the measurement results in Figure 1, when the mass percentage of element Al is converted to the mass percentage of Al2O3 and the amount of Ru supported per 100 parts by mass of alumina (Al2O3) is calculated, an average of 4 parts by mass of ruthenium is supported per 100 parts by mass of alumina in the range of 0.3 mm from the surface of the molded particle, and almost no ruthenium is supported further towards the center (average of 0.1 parts by mass or less).

[0151] Furthermore, from the measurement results in Figure 1, by converting the mass percentage of Al to the mass percentage of Al2O3 and the mass percentage of Zr to the mass percentage of ZrO2, the amount of zirconia (ZrO2) supported per 100 parts by mass of alumina (Al2O3) was calculated. On average, 9 parts by mass of zirconia were supported per 100 parts by mass of alumina in the 0.3 mm range from the surface of the molded particle, and on average, 5 parts by mass of zirconia were supported per 100 parts by mass of alumina closer to the center. From the analysis results shown in Table 8, the amount of zirconia supported by catalyst K is 7 parts by mass per 100 parts by mass of alumina. Therefore, in the central part, the amount of zirconia supported is about 70% of the average amount of molded particle, and in the shell part, the amount of zirconia supported is about 130% of the average amount of molded particle.

[0152] (X-ray diffraction measurement results) X-ray diffraction measurements were performed for catalysts K, L, M, and G. The measurements were performed using an X-ray diffractometer equipped with a graphite monochromator (Shimadzu XRD-6100) under the following conditions: X-ray source: Cu-Kα rays (0.1542 nm) emitted from an X-ray tube (Cu target, tube voltage 40 kV, tube current 40 mA). Measurement conditions: Step scan method, 0.02° step, integration time of 1.2 seconds at each step, detection slit 0.15 mm. The X-ray diffraction patterns of each sample are shown in Figure 3.

[0153] In catalyst K, diffraction lines not observed in catalyst M were detected at 30.3° (±0.5°) and 50.5° (±0.5°). These are diffraction lines of tetragonal zirconia. On the other hand, catalyst L, like catalyst K, contains zirconia and has a similar amount of zirconia, but diffraction lines of tetragonal zirconia were not clearly observed. The significantly higher methanation activity of catalyst K compared to catalyst L, and the results of the X-ray diffraction measurements, suggest that the presence of tetragonal zirconia contributes to the high methanation activity.

[0154] In the X-ray diffraction pattern of catalyst G, diffraction lines not observed in catalyst M were found around 28.8° and 48.0°. These diffraction lines are attributed to the solid solution of cerium oxide and zirconium oxide (zirconia). In other words, in catalyst G, solid solutions are formed with the supported zirconium oxide and cerium oxide, and zirconia does not exist on its own. When cerium was further added to a catalyst in which ruthenium and zirconia were supported on activated alumina, the methanation activity and heat resistance decreased as the amount of cerium added increased. This is presumed to be because the formation of solid solutions with zirconium oxide and cerium oxide prevented the zirconia from exhibiting its original effect.

[0155] (Results of heat resistance evaluation of catalyst) For catalysts K, L, and M, high-temperature firing was performed at 1050°C in air for 6 hours, and the degree of alpha-gelatinization was calculated using the same method as shown in Table 1. The degrees of alpha-gelatinization of catalysts K, L, and M after high-temperature firing were 4.0%, 26%, and 64%, respectively. Compared to the degrees of alpha-gelatinization of zirconia-supported alumina K, L, and alumina M after high-temperature firing, all were slightly higher, indicating that alpha-gelatinization proceeds more easily after ruthenium is supported. However, the improvement in heat resistance due to zirconia support is clear, and it is also clear that catalyst K, with zirconia supported under nitric acid conditions, exhibits particularly excellent heat resistance.

[0156] (Water vapor resistance evaluation results) For catalysts K and M, the stability of alumina under high water vapor partial pressure was evaluated by passing a gas consisting of 0.5 MPa (absolute pressure) water vapor and 0.1 MPa (absolute pressure) nitrogen at 700°C. For samples treated for a predetermined time, BET specific surface area measurements, degree of alpha-gelatinization by X-ray diffraction, and crushing strength measurements were performed. The BET specific surface area measurements and degree of alpha-gelatinization by X-ray diffraction were performed in the same manner as in Table 1, and the crushing strength measurements were performed in the same manner as in Table 2. The results are shown in Table 10.

[0157] [Table 10] (Note) Since catalyst M did not maintain its original shape after 200 hours of treatment, it was analyzed by separating it into granular and powdery portions.

[0158] Catalyst M underwent significant gelatinization after 200 hours, losing its original shape, while catalyst K showed minimal gelatinization even after 200 hours, maintaining a constant BET specific surface area and strength. The degree of gelatinization after treatment under high water vapor pressure corresponds to the degree of gelatinization after high-temperature (1050°C) calcination, indicating that calcination at 1050°C in air for 6 hours is equivalent to treatment at 700°C under high water vapor pressure for 100 to 200 hours. Although gelatinization progresses over time even at lower temperatures, such as around 500°C, under high water vapor pressure conditions, the catalyst of the present invention is resistant to gelatinization even under such conditions, allowing for stable use over long periods.

[0159] From the above results, it is clear that the methanation catalyst molded body of the present invention possesses high low-temperature activity, sufficient strength for industrial use, and heat resistance under high temperature and high water vapor pressure conditions.

[0160] Furthermore, the configurations disclosed in the above embodiments (including other embodiments, the same applies hereinafter) can be applied in combination with configurations disclosed in other embodiments, as long as no inconsistencies arise. Moreover, the embodiments disclosed herein are illustrative, and the embodiments of the present invention are not limited thereto, and can be modified as appropriate without departing from the object of the present invention. [Industrial applicability]

[0161] The present invention can be used, for example, as a catalyst for producing a fuel gas mainly composed of methane, which can be used as city gas, by reacting carbon dioxide and hydrogen.

Claims

1. The material contains an activated alumina molded body and zirconia and ruthenium supported on the activated alumina molded body, wherein the amount of zirconia supported is 3 to 10 parts by mass per 100 parts by mass of the activated alumina molded body, and the amount of ruthenium supported is 0.1 to 5 parts by mass per 100 parts by mass of the activated alumina molded body, and the molded body has a particle size of 2 to 20 mm. A carbon dioxide methanation catalyst molded body, wherein the ruthenium is supported on the activated alumina molded body in an eggshell shape with a shell thickness of 0.2 to 0.4 mm, and the zirconia is supported in the center at a rate of 50% or more but less than 100% based on the average amount of zirconia supported on the entire activated alumina molded body, and the zirconia is supported in a rate of more than 100% in the shell portion on which the ruthenium is supported.

2. A carbon dioxide methane catalyst molded body according to claim 1, wherein zirconia is mainly present in a tetragonal crystal structure.

3. A carbon dioxide methane catalyst molded body according to claim 1 or 2, wherein the cerium oxide content is 5 parts by mass or less per 100 parts by mass of the activated alumina molded body.

4. A carbon dioxide methane catalyst molded body according to any one of claims 1 to 3, wherein the degree of alpha-activation measured by the procedure of firing the activated alumina molded body supporting the zirconia in air at 1050°C for 6 hours, and then measuring the degree of alpha-activation by X-ray diffraction measurement using Cu-Kα rays as a source, is 10% or less.

5. A carbon dioxide methane catalyst molded body according to any one of claims 1 to 3, wherein the degree of alpha-activation, measured by the procedure of firing in air at 1050°C for 6 hours and then measuring the degree of alpha-activation by X-ray diffraction measurement using Cu-Kα rays as a source, is 10% or less.

6. A zirconium impregnation step involves impregnating an activated alumina molded body with a particle size of 2 to 20 mm with an aqueous solution containing a water-soluble zirconium compound to obtain a zirconium-impregnated body. A drying step to dry the zirconium-impregnated material to obtain a dried material, A firing step to obtain activated alumina in which zirconia is dispersed and supported by firing the dried body in air at 500 to 800°C, A ruthenium impregnation step is performed by impregnating the activated alumina, on which the zirconia is dispersed and supported, with an aqueous solution in which a water-soluble compound of ruthenium is dissolved, in order to obtain a ruthenium-impregnated body. The process includes a ruthenium immobilization step of drying the ruthenium-impregnated body to immobilize the ruthenium, The amount of zirconia supported is 3 to 10 parts by mass per 100 parts by mass of the activated alumina molded body, and the amount of ruthenium supported is 0.1 to 5 parts by mass per 100 parts by mass of the activated alumina molded body. A method for producing a carbon dioxide methanation catalyst molded body, wherein the ruthenium is supported on the activated alumina molded body in an eggshell shape with a shell thickness of 0.2 to 0.4 mm, and the zirconia is supported in the center at a rate of 50% or more but less than 100% based on the average amount of zirconia supported on the entire activated alumina molded body, and the zirconia is supported in a rate of more than 100% in the shell portion on which the ruthenium is supported.

7. A method for producing a carbon dioxide methane catalyst molded body, according to claim 6, wherein the zirconium impregnation step is carried out using a nitric acid acidic aqueous solution in which a water-soluble zirconium compound is dissolved.

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