Carbon dioxide storage-reduction catalyst and method for preparing carbon dioxide storage-reduction catalyst

Abstract

To provide a carbon dioxide storage-reduction catalyst exhibiting good carbon dioxide storage density without employing a noble metal, and to provide a method for preparing the carbon dioxide storage-reduction catalyst.SOLUTION: A carbon dioxide storage-reduction catalyst absorbs and reduces carbon dioxide in a carbon dioxide-containing gas, the carbon dioxide storage-reduction catalyst including a carbon dioxide storage-reduction catalyst A composed of Ni and a support C made of a metal oxide, or a mixed catalyst AB composed of the carbon dioxide storage-reduction catalyst A and a carbon dioxide storage material B composed of Li and a support D made of a metal oxide.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a carbon dioxide occlusion-reduction catalyst that occludes and reduces carbon dioxide in a carbon dioxide-containing gas, and a method for preparing the carbon dioxide occlusion-reduction catalyst. [Background technology]

[0002] Methanation reactions using carbon dioxide (CO2) as a raw material have recently attracted attention from the perspective of reducing carbon dioxide emissions to curb global warming.

[0003] As a catalyst used in such a methanation reaction, for example, Patent Document 1 describes a carbon dioxide storage-reduction catalyst that contains a porous carrier made of a metal oxide, ruthenium supported on the porous carrier, and alkaline earth metal oxide and alkali metal oxide supported on the porous carrier, with the mass ratio of alkaline earth metal oxide to alkali metal oxide being alkaline earth metal oxide:alkali metal oxide = 10:1 to 10:5. This carbon dioxide storage-reduction catalyst is said to have high carbon dioxide storage performance.

[0004] Patent Document 2 describes a porous porous material made of a metal oxide, having an average pore diameter of 3 to 50 nm and a pore volume of 0.3 to 1.5 cm 3 The document describes a carbon dioxide storage-reduction catalyst containing a porous carrier having a carbon dioxide absorption capacity of 10 ...

[0005] Non-Patent Document 1 describes the effect of adding alkali metals to methanation catalysts and carbon dioxide storage-reduction catalysts, and also describes Ni-based carbon dioxide storage-reduction catalysts. The catalyst is mainly composed of three components: metal, alkali, and support. The metal is Ni or a mixture of Ni and a noble metal, the alkali is Na2O, KO, CaO, MgO, or La, and the support is Al2O3, ZrO2, MgO-Al2O3, or hydrotalcite.

[0006] Non-Patent Document 2 is a paper on layered double hydroxide-based Ni catalysts for CO2 capture and methanation, and describes that the catalyst was synthesized by coprecipitation of Ni with layered double hydroxides (LDHs) such as MgO and CaO, and that cycle evaluation was performed at 320°C.

[0007] Ru is the most widely known metal that serves as the active site of a methanation catalyst (see Patent Documents 1 and 2 above). Because Ru is expensive, there are concerns that it will increase the introduction cost of the equipment. Catalysts that use transition metals as the metals that serve as the active sites of methanation catalysts are desirable, and Ni catalysts in particular have been actively researched (see Non-Patent Documents 1 and 2 above). However, because Ni has lower activity than Ru, research has been conducted at high operating temperatures (up to 500°C).

[0008] In conventional methane synthesis systems using carbon dioxide derived from waste gas, the size of the carbon dioxide collector is large, raising concerns about restrictions on installation space. Compared to conventional methane synthesis systems, carbon dioxide storage reduction catalysts have a higher carbon dioxide storage density, which represents the amount of carbon dioxide processed per unit volume of catalyst that can process captured carbon dioxide without leaking, and are expected to enable the equipment to be made more compact. Furthermore, reducing the volume is expected to contribute to reducing heat loss. To take advantage of the characteristics of these carbon dioxide storage reduction catalyst systems, it is necessary to aim for a higher carbon dioxide storage density.

[0009] If the operating temperature of a carbon dioxide storage reduction catalyst is high, the exhaust gas to be introduced must be preheated, consuming energy. Lowering the operating temperature has the effect of reducing energy costs during operation. Furthermore, when the catalyst is operated at high temperatures, it is expected that deterioration due to aggregation and oxidation of the catalyst components will progress more easily. Lowering the operating temperature has the effect of suppressing catalyst deterioration and reducing the costs required for catalyst replacement and maintenance. Furthermore, when the catalyst is operated at high temperatures, it is expected that the piping components and heat transfer medium that make up the system will be limited to expensive high-temperature compatible products. As described above, lowering the operating temperature is expected to have the effect of reducing equipment installation costs. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2023-143010 [Patent Document 2] Japanese Patent Publication No. 2023-157643 [Non-patent literature]

[0011] [Non-Patent Document 1] Tsiotsias et al., Catalysts, 10 (2020) 812. [Non-patent document 2] Sakai et al, Applied Catalysis A;General, (2022) 118904. Summary of the Invention [Problem to be solved by the invention]

[0012] An object of the present invention is to provide a carbon dioxide storage-reduction catalyst that has a good carbon dioxide storage density without using a precious metal, and a method for preparing the carbon dioxide storage-reduction catalyst. [Means for solving the problem]

[0013] The present invention is a carbon dioxide storage-reduction catalyst that occludes and reduces carbon dioxide in a carbon dioxide-containing gas, and includes a carbon dioxide storage-reduction catalyst A composed of a carrier C made of Ni and a metal oxide, or a mixed catalyst AB of the carbon dioxide storage-reduction catalyst A and a carbon dioxide storage material B composed of a carrier D made of Li and a metal oxide.

[0014] In the carbon dioxide storage reduction catalyst, the metal oxide of the carrier C and the metal oxide of the carrier D are preferably at least one selected from alumina, ceria, titania, zirconia, silica, and zeolite.

[0015] In the carbon dioxide storage reduction catalyst, the metal oxide of the carrier C is preferably ceria.

[0016] In the carbon dioxide storage reduction catalyst, the metal oxide of the carrier D is preferably alumina.

[0017] In the carbon dioxide storage reduction catalyst, the content of Ni in the carbon dioxide storage reduction catalyst A is preferably in the range of 30 to 90 mass % in terms of NiO relative to the total content of the Ni and the carrier C.

[0018] The present invention is a method for preparing the carbon dioxide occlusion reduction catalyst, comprising: a calcination step of calcining mixed particles in which the Ni is highly dispersed on the carrier C at a calcination temperature in the range of 300 to 500°C to obtain calcined catalyst A, or calcining supported particles in which the Li is supported on the carrier D at a calcination temperature in the range of 300 to 500°C to obtain calcined storage material B; and an activation step of activating the calcined catalyst A obtained in the calcination step at an activation temperature in the range of 300 to 500°C to obtain the carbon dioxide occlusion reduction catalyst A, or activating a mixture of the calcined catalyst A obtained in the calcination step and the calcined storage material B obtained in the calcination step at an activation temperature in the range of 300 to 500°C to obtain the mixed catalyst AB.

[0019] In the method for preparing a carbon dioxide occlusion reduction catalyst, the calcination temperature is preferably in the range of 400 to 450°C.

[0020] In the method for preparing a carbon dioxide storage reduction catalyst, the activation temperature is preferably in the range of 400 to 450°C.

[0021] In the calcination step in the method for preparing the carbon dioxide occlusion reduction catalyst, the calcination is preferably carried out in a reducing atmosphere of 4 to 100 vol % H2.

[0022] In the activation step of the method for preparing a carbon dioxide occlusion reduction catalyst, activation is preferably carried out in a reducing atmosphere of 4 to 100 vol % H2. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide a carbon dioxide occlusion reduction catalyst that has a good carbon dioxide storage density without using a noble metal, and a method for preparing the carbon dioxide occlusion reduction catalyst. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a diagram showing a structural image of a carbon dioxide storage reduction catalyst A, which is a carbon dioxide storage reduction catalyst according to this embodiment, and a mixed catalyst AB of the carbon dioxide storage reduction catalyst A and a carbon dioxide storage material B. FIG. [Figure 2] (i) Carbon dioxide storage reduction catalyst A, (ii) mixed catalyst AB preparation flow, and (iii) catalyst performance evaluation flow [Figure 3] FIG. 1 is a flow diagram of test conditions for catalyst performance evaluation. [Figure 4] FIG. 1 is an image showing the signal intensity of gases (CH4, CO2) after passing through the catalyst, measured by a mass spectrometer in the catalyst performance evaluation. [Figure 5] 1 is a graph showing the correlation between the carbon dioxide storage density (Dcycle, mol-CO2 / L-cat) and the activation temperature Ta (°C) in the carbon dioxide storage reduction catalyst A. [Figure 6] 1 is a graph showing the correlation between the carbon dioxide storage density (D cycle, mol-CO 2 / L-cat) and the NiO composition (mass %) in the carbon dioxide storage reduction catalyst A. [Figure 7] 1 is a graph showing the correlation between the carbon dioxide storage density (Dcycle, mol-CO2 / L-cat) and the calcination conditions in the carbon dioxide storage-reduction catalyst A. [Figure 8] 1 is a graph showing the carbon dioxide storage density (Dcycle, mol-CO2 / L-cat) of various mixed catalysts A and B. [Figure 9] 1 is a graph showing the correlation between the carbon dioxide storage density (D cycle, mol-CO 2 / L-cat) and the NiO composition (mass %) in mixed catalysts AB. [Figure 10] 1 is a graph showing the correlation between the carbon dioxide storage density (D cycle, mol-CO 2 / L-cat) and the NiO composition (mass %) for comparing the mixed catalyst AB and the carbon dioxide storage-reduction catalyst A. [Figure 11] 1 is a graph showing the correlation between the specific surface area (SSA, m2 / g) and NiO (mass%) of carbon dioxide storage reduction catalyst A that has undergone different thermal histories. [Figure 12] 1 is a graph showing the correlation between the crystallite size (nm) of each component contained in the carbon dioxide storage reduction catalyst A and the activation treatment temperature (° C.). DETAILED DESCRIPTION OF THE INVENTION

[0025] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes an embodiment of the present invention. The embodiment is an example of implementing the present invention, and the present invention is not limited to the embodiment.

[0026] <Carbon dioxide storage reduction catalyst> The carbon dioxide storage reduction catalyst according to this embodiment is a catalyst that stores carbon dioxide in a carbon dioxide-containing gas and reduces it to methane. The carbon dioxide storage reduction catalyst includes a carbon dioxide storage reduction catalyst A that is composed of a carrier C that is made of Ni and a metal oxide. Alternatively, the carbon dioxide storage reduction catalyst includes a mixed catalyst AB that includes a carbon dioxide storage reduction catalyst A that is composed of a carrier C that is made of Ni and a metal oxide, and a carbon dioxide storage material B that is composed of a carrier D that is made of an alkali metal or alkaline earth metal and a metal oxide.

[0027] FIG. 1 shows an image of the configuration of a carbon dioxide storage reduction catalyst A, which is a carbon dioxide storage reduction catalyst according to this embodiment, and a mixed catalyst AB of the carbon dioxide storage reduction catalyst A and a carbon dioxide storage material B.

[0028] The carbon dioxide storage reduction catalyst according to this embodiment has a good carbon dioxide storage density without using precious metals. The carbon dioxide storage reduction catalyst according to this embodiment can improve the carbon dioxide storage density without using precious metals, and can lower the operating temperature. By not using precious metals such as Ru in the catalyst, lower equipment costs can be expected. Furthermore, by improving the carbon dioxide storage density, it is expected that the methanation system can be made smaller and the resulting cost reduction can be achieved.

[0029] The methanation reaction of carbon dioxide (CO2) in a carbon dioxide storage reduction catalyst proceeds in two steps as shown in the following formulas (1) and (2). Here, cat is the catalyst (carbon dioxide storage reduction catalyst A or mixed catalyst AB), (CO2) n @cat represents the state in which n units of CO2 are stored in the catalyst. First, as shown in formula (1), when a carbon dioxide-containing gas containing carbon dioxide (CO2) passes through the catalyst (cat), the carbon dioxide (CO2) is stored in the catalyst. Next, as shown in formula (2), when hydrogen (H2) gas, a reducing gas, is passed through the catalyst, the carbon dioxide (CO2) stored in the catalyst reacts with four times the amount of hydrogen (H2) gas to produce n units of methane (CH4). CO2+cat=(CO2) n @cat (1) (CO2) n @cat+4nH2=cat+nCH4+2nH2O (2)

[0030] Regarding the configuration of the carbon dioxide storage reduction catalyst, in the case of carbon dioxide storage reduction catalyst A, Ni is the active site, and the metal oxide acts as both carrier C and carbon dioxide storage material, so it is preferable that both are contained in appropriate amounts. In the case of mixed catalyst AB, carbon dioxide storage material B absorbs and releases a larger amount of carbon dioxide per mass than carrier D, which is made of a metal oxide of an alkali metal or alkaline earth metal. However, since supporting an alkali metal or alkaline earth metal and Ni on the same carrier can result in each acting as an inhibitor, reducing catalytic activity, the alkali metal or alkaline earth metal and Ni can be supported or highly dispersed on separate carriers, and then the particles can be physically mixed to maintain their respective performances.

[0031] The carbon dioxide storage-reduction catalyst A is composed of Ni and a carrier C made of a metal oxide. The Ni is highly dispersed in the carrier C and serves as an active site in the reduction reaction of carbon dioxide. This Ni acts as a methanation catalyst, specifically, it promotes the reduction reaction of carbon dioxide when carbon dioxide stored in the metal oxide carbon dioxide storage material is reduced by reacting with a reducing gas (e.g., hydrogen gas) to produce methane.

[0032] The carrier C constituting the carbon dioxide storage-reduction catalyst A is a carrier made of a metal oxide with highly dispersed Ni. The metal oxide functions as both a carrier and a carbon dioxide storage material that stores carbon dioxide. The carrier C is preferably a porous carrier with a large specific surface area. By using a porous carrier C, Ni is highly dispersed, improving methanation catalytic activity, and the high specific surface area improves carbon dioxide storage performance. In addition, gas components can be favorably diffused within the carrier.

[0033] The metal oxide of the carrier C is not particularly limited as long as it can be used as a carrier for a carbon dioxide storage-reduction catalyst, and examples thereof include alumina (Al2O3), silica (SiO2), ceria (CeO2), titania (TiO2), zirconia (ZrO2), and zeolite. Among these, at least one selected from alumina, ceria, titania, zirconia, and zeolite is preferred from the viewpoint of high methanation catalytic activity, and ceria is more preferred from the viewpoint of higher methanation catalytic activity. The metal oxide of the carrier C may be used alone or in combination of two or more types.

[0034] The Ni content in the carbon dioxide storage-reduction catalyst A is not particularly limited, but is, for example, in the range of 30 to 90 mass% in terms of NiO relative to the total content of Ni and the carrier C. From the viewpoint of increasing the carbon dioxide storage density, the Ni content is preferably in the range of 50 to 70 mass%, and more preferably in the range of 55 to 65 mass%.

[0035] The content of the carrier C in the carbon dioxide storage-reduction catalyst A is not particularly limited, but is, for example, in the range of 10 to 70 mass% relative to the total content of Ni and the carrier C. From the viewpoint of increasing the carbon dioxide storage density, the content is preferably in the range of 30 to 50 mass%, and more preferably in the range of 35 to 45 mass%.

[0036] When the metal oxide of the carrier C in the carbon dioxide storage-reduction catalyst A is ceria, the mass ratio of Ni to ceria is, for example, in the range of 30:70 to 90:10 in terms of NiO:CeO, and from the viewpoint of increasing the carbon dioxide storage density, it is preferably in the range of 50:50 to 70:30, and more preferably in the range of 55:45 to 65:35.

[0037] The mixed catalyst AB is obtained by, for example, physically mixing a carbon dioxide storage reduction catalyst A made of a carrier C made of Ni and a metal oxide with a carbon dioxide storage material B made of a carrier D made of an alkali metal or alkaline earth metal and a metal oxide. The carbon dioxide storage reduction catalyst A contained in the mixed catalyst AB is as described above.

[0038] The carbon dioxide storage material B contained in the mixed catalyst AB is composed of an alkali metal or alkaline earth metal and a carrier D made of a metal oxide. The alkali metal or alkaline earth metal is supported on the carrier D and functions as a carbon dioxide storage material that occludes carbon dioxide. The alkali metal or alkaline earth metal is usually supported on the carrier D in the form of an oxide, carbonate, hydrogencarbonate, hydroxide, or the like.

[0039] Examples of alkali metals include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), etc. Among these, lithium is preferred because of its high carbon dioxide storage capacity.

[0040] The carrier D constituting the carbon dioxide storage material B is a carrier made of a metal oxide that supports an alkali metal or alkaline earth metal. The metal oxide functions as both a carrier and a carbon dioxide storage material that occludes carbon dioxide. The carrier D is preferably a porous carrier with a large specific surface area. By using a porous carrier D, the specific surface area of ​​the carrier is high, and the surface area of ​​the supported alkali metal or alkaline earth metal is increased, thereby improving the carbon dioxide storage performance, or allowing gas components to diffuse smoothly within the carrier.

[0041] The metal oxide of the carrier D is not particularly limited as long as it can be used as a carrier for a carbon dioxide storage material, and examples thereof include alumina (Al2O3), silica (SiO2), ceria (CeO2), titania (TiO2), zirconia (ZrO2), and zeolite. Among these, at least one selected from alumina, ceria, titania, zirconia, and zeolite is preferred in terms of high carbon dioxide storage performance, and alumina is more preferred in terms of higher carbon dioxide storage performance. The metal oxide of the carrier D may be used alone or in combination of two or more types.

[0042] The content of alkali metal or alkaline earth metal in carbon dioxide storage material B is not particularly limited, but is, for example, in the range of 5 to 50 mass% relative to the total content of alkali metal or alkaline earth metal and carrier D. In order to improve carbon dioxide storage performance, it is preferably in the range of 7 to 40 mass%, and more preferably in the range of 10 to 30 mass%.

[0043] When the alkali metal or alkaline earth metal in the carbon dioxide storage material B is lithium, the lithium content is, for example, in the range of 7 to 40 mass% in terms of LiO relative to the total content of lithium and carrier D, and is preferably in the range of 10 to 30 mass% from the viewpoint of improving carbon dioxide storage performance.

[0044] The content of carrier D in carbon dioxide storage material B is not particularly limited, but is, for example, in the range of 50 to 95 mass% of the total content of alkali metal or alkaline earth metal and carrier D. In order to improve carbon dioxide storage performance, the content is preferably in the range of 60 to 93 mass%, and more preferably in the range of 70 to 90 mass%.

[0045] A suitable mixing ratio of the carbon dioxide storage reduction catalyst A and the carbon dioxide storage material B contained in the mixed catalyst AB depends on the compositions of the carbon dioxide storage reduction catalyst A and the carbon dioxide storage material B, but for example, if the carbon dioxide storage reduction catalyst A contains 50 mass % NiO and the carbon dioxide storage material B contains 20 mass % LiO, the mass ratio of the carbon dioxide storage reduction catalyst A:carbon dioxide storage material B is in the range of 20:1 to 1:2, and a range of 20:1 to 1:1 is preferred. If the mixing ratio of the carbon dioxide storage reduction catalyst A and the carbon dioxide storage material B contained in the mixed catalyst AB is less than the mass ratio of the carbon dioxide storage reduction catalyst A:carbon dioxide storage material B = 1:2, the carbon dioxide storage density may be low.

[0046] When the metal oxide of the carrier C in the carbon dioxide storage-reduction catalyst A contained in the mixed catalyst AB is ceria, the alkali metal or alkaline earth metal in the carbon dioxide storage material B is lithium, the carrier D is alumina, the carbon dioxide storage-reduction catalyst A contains 50 mass % NiO and the carbon dioxide storage material B contains 20 mass % LiO, the mass ratio of NiO:ceria:LiO:alumina in the mixed catalyst AB is preferably in the range of 17:17:13:53 to 48:48:1:4, and more preferably in the range of 25:25:10:40 to 48:48:1:4.

[0047] The carbon dioxide-containing gas to be treated is not particularly limited as long as it contains carbon dioxide. Examples of the carbon dioxide-containing gas include air, combustion furnace exhaust gas containing carbon dioxide, and automobile exhaust gas.

[0048] The carbon dioxide content in the carbon dioxide-containing gas is not particularly limited, but is, for example, in the range of 400 ppm to 50 vol %.

[0049] The carbon dioxide occlusion reduction catalyst according to this embodiment can be applied to, for example, a carbon dioxide occlusion reduction methanation system. For example, in a carbon dioxide occlusion reduction methanation system, (i) a carbon dioxide-containing gas containing carbon dioxide (CO2) and (ii) a reducing gas (e.g., hydrogen (H2) gas) are alternately passed through a reactor filled with the carbon dioxide occlusion reduction catalyst according to this embodiment, and the carbon dioxide (CO2) is reduced to methane (CH4). By not using a precious metal (Ru) in the catalyst, low costs for the equipment can be expected. In addition, the carbon dioxide processing capacity (carbon dioxide occlusion density: D cycle By improving this, it is expected that methanation systems can be made smaller and carbon dioxide treatment costs can be reduced.

[0050] The carbon dioxide storage reduction catalyst according to this embodiment has a carbon dioxide storage density (D cycle , mol-CO2 / L-cat) (see "Method for evaluating catalyst performance" in the Examples section) is, for example, 0.02 or more, preferably 0.1 or more, more preferably 0.12 or more, and even more preferably 0.15 or more.

[0051] <Method for preparing carbon dioxide storage reduction catalyst> The method for preparing the carbon dioxide occlusion / reduction catalyst according to this embodiment is a method for preparing the carbon dioxide occlusion / reduction catalyst. The method for preparing the carbon dioxide occlusion / reduction catalyst according to this embodiment includes, for example, a calcination step in which mixed particles in which Ni is highly dispersed on a carrier C are calcined at a calcination temperature in the range of 300 to 500°C to obtain calcined catalyst A, or supported particles in which Ni is supported on a carrier C are calcined at a calcination temperature in the range of 300 to 500°C to obtain calcined catalyst A, and further supported particles in which Li is supported on a carrier D are calcined at a calcination temperature in the range of 300 to 500°C to obtain calcined storage material B; and an activation step in which the calcined catalyst A obtained in the calcination step is activated at an activation temperature in the range of 300 to 500°C to obtain the carbon dioxide occlusion / reduction catalyst A, or a mixture of the calcined catalyst A obtained in the calcination step and the calcined storage material B obtained in the calcination step is activated at an activation temperature in the range of 300 to 500°C to obtain mixed catalyst AB. Here, "highly dispersed" means that Ni is highly dispersed in the carrier C, and for example, this means that the crystallite diameter calculated from the diffraction lines obtained by powder X-ray diffraction measurement is 50 nm or less.

[0052] Carbon dioxide occlusion / reduction catalyst A is prepared, for example, by dissolving a Ni salt and a metal salt that will become the metal oxide in a solvent such as water, adding a solution in which a coprecipitating agent such as sodium carbonate is dissolved in a solvent such as water, heating at a predetermined temperature (e.g., 50-80°C) for a predetermined time (e.g., 30-120 minutes), and then allowing to stand at a predetermined temperature (e.g., 0-30°C) for a predetermined time (e.g., 6-12 hours) to allow coprecipitating, filtering, washing, drying, and calcining at a predetermined temperature (e.g., 300-500°C) for a predetermined time (e.g., 30-240 minutes) in a predetermined calcination atmosphere (e.g., 4-100% H2) to obtain pre-activated catalyst A. After calcination, the mixture may be pressurized, for example, with a room-temperature isostatic press, and then pulverized to form granules, or may be classified. This pre-activated catalyst A can be activated (oxidized NiO is reduced to Ni(0)) at a predetermined temperature (e.g., 300 to 500°C) for a predetermined time (e.g., 30 to 120 minutes) in a predetermined reducing atmosphere (e.g., 4 to 100% H2) to obtain the carbon dioxide storage-reduction catalyst A.

[0053] The carbon dioxide storage-reduction catalyst A can be obtained, for example, by dissolving a Ni salt in a solvent such as water, adding a metal oxide thereto to impregnate and support the mixture, stirring the mixture at a predetermined temperature (e.g., 0-30°C) for a predetermined time (e.g., 10-120 minutes), drying, and calcining the mixture at a predetermined temperature (e.g., 300-500°C) for a predetermined time (e.g., 30-240 minutes) in a predetermined calcination atmosphere (e.g., 4-100% H2). After calcination, the mixture may be pressed, for example, using a room-temperature isostatic press, and then granulated by pulverization or classified. The carbon dioxide storage-reduction catalyst A can be obtained by activating this pre-activation catalyst A (reducing oxidized NiO to Ni(0)) at a predetermined temperature (e.g., 300-500°C) for a predetermined time (e.g., 30-120 minutes) in a predetermined reducing atmosphere (e.g., 4-100% H2).

[0054] Examples of Ni salts that can be used include nickel nitrate (Ni(NO3)2), nickel carbonate (Ni(CO3)), and nickel acetate (Ni(CH3COO)2).

[0055] Examples of metal salts that can be used to form metal oxides include nitrates, carbonates, and acetates of metals such as aluminum (Al), silicon (Si), cerium (Ce), titanium (Ti), and zirconium (Zr).

[0056] Carbon dioxide storage material B can be obtained, for example, by dissolving an alkali metal salt or an alkaline earth metal salt in a solvent such as water, adding a metal oxide thereto to impregnate and support it, heating and concentrating it at a predetermined temperature (e.g., 0 to 30°C) for a predetermined time (e.g., 30 to 120 minutes), drying it, and firing it at a predetermined temperature (e.g., 300 to 500°C) for a predetermined time (e.g., 60 to 240 minutes) in a predetermined firing atmosphere (e.g., air, nitrogen, 4 to 100 vol% H2). After firing, classification may be performed.

[0057] The mixed catalyst AB can be obtained by mixing the pre-activated catalyst A obtained as described above with the carbon dioxide storage material B by physical mixing or the like, and activating the mixture under the above conditions. Alternatively, the mixed catalyst AB can be obtained by mixing the carbon dioxide storage-reduction catalyst A activated as described above with the carbon dioxide storage material B by physical mixing or the like.

[0058] The firing temperature is, for example, in the range of 300 to 500°C, and is preferably in the range of 400 to 450°C in order to increase the carbon dioxide storage density. The firing atmosphere is not particularly limited, and may be, for example, an air atmosphere or a reducing atmosphere. In order to increase the carbon dioxide storage density, the firing atmosphere is preferably a reducing atmosphere. Examples of the reducing atmosphere used in firing include a hydrogen (H2) / nitrogen (N2) mixed atmosphere, a pure hydrogen atmosphere, and a pure nitrogen atmosphere, such as 4 to 100 vol% H2 / 96 to 0 vol% N2.

[0059] The activation temperature is, for example, in the range of 300 to 500°C, and is preferably in the range of 400 to 450°C in view of increasing the carbon dioxide storage density. The activation atmosphere is preferably a reducing atmosphere. Examples of the reducing atmosphere for activation include a hydrogen (H2) / nitrogen (N2) mixed atmosphere and a methane (CH4) atmosphere, for example, 4 to 100 vol% H2 / 96 to 0 vol% N2.

[0060] The specific surface area (SSA) of the carbon dioxide storage reduction catalyst A or the mixed catalyst AB before activation is, for example, 50 m 2 / g or more, and 80m 2 / g or more. The specific surface area of ​​the carbon dioxide storage reduction catalyst A or the mixed catalyst AB before activation is preferably 50 m 2 If the specific surface area is less than 100 m / g, the carbon dioxide storage density may be low. The specific surface area of ​​the carbon dioxide storage / reduction catalyst A or the mixed catalyst AB before activation is preferably as large as possible. There is no particular upper limit, but it may be, for example, 200 m 2 If it exceeds 1 / g, the bulk density decreases, and the carbon dioxide storage density may decrease.

[0061] The specific surface area (SSA) of the carbon dioxide storage reduction catalyst A or the mixed catalyst AB after activation is, for example, 50 m 2 / g or more, and 60m 2 / g or more. The specific surface area of ​​the carbon dioxide storage reduction catalyst A or the mixed catalyst AB before activation is preferably 50 m 2 If the specific surface area is less than 1000 m / g, the pores of the catalyst may be blocked, resulting in a decrease in activity. The specific surface area of ​​the carbon dioxide storage reduction catalyst A or the mixed catalyst AB after activation is preferably as large as possible. There is no particular upper limit, but it may be 200 m, for example. 2 If it exceeds 1 / g, the bulk density decreases, and the carbon dioxide storage density may decrease.

[0062] The bulk density of the carbon dioxide storage-reduction catalyst A or the mixed catalyst AB before activation is, for example, 1 g / mL or more, and preferably in the range of 1 to 2 g / mL. If the bulk density of the carbon dioxide storage-reduction catalyst A or the mixed catalyst AB before activation is less than 1 g / mL, the carbon dioxide storage density may decrease, and if it exceeds 2 g / mL, the pores of the catalyst may become clogged, resulting in a decrease in activity.

[0063] The present specification includes the following embodiments. [1] A carbon dioxide storage / reduction catalyst that stores and reduces carbon dioxide in a carbon dioxide-containing gas, a carbon dioxide storage / reduction catalyst A composed of Ni and a carrier C made of a metal oxide; or a mixed catalyst AB of the carbon dioxide storage reduction catalyst A and a carbon dioxide storage material B composed of a carrier D made of Li and a metal oxide; A carbon dioxide storage reduction catalyst comprising:

[0064] [2] The carbon dioxide storage reduction catalyst according to [1], A carbon dioxide storage-reduction catalyst, wherein the metal oxide of the carrier C and the metal oxide of the carrier D are each at least one selected from alumina, ceria, titania, zirconia, silica, and zeolite.

[0065] [3] The carbon dioxide storage reduction catalyst according to [1] or [2], A carbon dioxide storage reduction catalyst, wherein the metal oxide of the support C is ceria.

[0066] [4] The carbon dioxide storage-reduction catalyst according to any one of [1] to [3], A carbon dioxide storage reduction catalyst, wherein the metal oxide of the carrier D is alumina.

[0067] [5] The carbon dioxide storage reduction catalyst according to any one of [1] to [4], A carbon dioxide storage-reduction catalyst, wherein the content of Ni in the carbon dioxide storage-reduction catalyst A is in the range of 30 to 90 mass % in terms of NiO relative to the total content of the Ni and the carrier C.

[0068] [6] A method for preparing the carbon dioxide storage reduction catalyst according to any one of [1] to [5], a calcination step of calcining the mixed particles in which the Ni is highly dispersed on the carrier C at a calcination temperature in the range of 300 to 500°C to obtain a calcined catalyst A, or calcining the supported particles in which the Li is supported on the carrier D at a calcination temperature in the range of 300 to 500°C to obtain a calcined adsorbent material B; an activation step of activating the calcined catalyst A obtained in the calcination step at an activation temperature in the range of 300 to 500°C to obtain the carbon dioxide storage-reduction catalyst A, or activating a mixture of the calcined catalyst A obtained in the calcination step and the calcined storage material B obtained in the calcination step at an activation temperature in the range of 300 to 500°C to obtain the mixed catalyst AB; A method for preparing a carbon dioxide storage reduction catalyst, comprising:

[0069] [7] A method for preparing the carbon dioxide storage reduction catalyst according to [6], The method for preparing a carbon dioxide occlusion reduction catalyst, wherein the calcination temperature is in the range of 400 to 450°C.

[0070] [8] A method for preparing the carbon dioxide storage reduction catalyst according to [6] or [7], The method for preparing a carbon dioxide storage reduction catalyst, wherein the activation temperature is in the range of 400 to 450°C.

[0071] [9] A method for preparing a carbon dioxide storage reduction catalyst according to any one of [6] to [8], The method for preparing a carbon dioxide occlusion reduction catalyst, wherein the calcination step is carried out in a reducing atmosphere of 4 to 100 vol % H2.

[0072]

[10] A method for preparing the carbon dioxide storage reduction catalyst according to any one of [6] to [9], The method for preparing a carbon dioxide storage reduction catalyst, wherein the activation step is performed in a reducing atmosphere of 4 to 100 vol % H2. [Example]

[0073] EXAMPLES The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0074] [Preparation of carbon dioxide storage / reduction catalyst] Ni-based carbon dioxide storage-reduction catalyst A was prepared by coprecipitation using NiO, which acts as an active site, and ceria (CeO2), which acts as a metal oxide carrier and carbon dioxide storage material.

[0075] The Ni-based carbon dioxide storage-reduction mixed catalyst AB was prepared by physically mixing the Ni-based carbon dioxide storage-reduction catalyst A with the carbon dioxide storage material B, which was made by impregnating and supporting lithium oxide (LiO) as an alkali metal carbon dioxide storage material on alumina (γ-AlO) as a metal oxide.

[0076] The catalysts investigated this time (Examples 1 to 17, Comparative Examples 1 to 6) are shown in Table 1.

[0077] [Table 1]

[0078] FIG. 2 shows (i) the preparation flow of the carbon dioxide storage reduction catalyst A, (ii) the preparation flow of the mixed catalyst AB, and (iii) the catalyst performance evaluation flow.

[0079] <Comparative Example 1> Ruthenium-supported alumina (Ru / Al2O3) was impregnated with calcium oxide (CaO) and prepared as follows:

[0080] 8.0 parts by mass of calcium nitrate (Ca(NO3)2·4H2O: Fujifilm Wako Pure Chemical Industries, Ltd., product number: 039-00735) was dissolved in 250 parts by mass of ion-exchanged water to obtain an aqueous solution, to which 20.0 parts by mass of Ru / Al2O3 powder (N.E. Chemcat Corporation, product number: HYAc-5EN-Type) was added and stirred. After stirring for approximately 1 hour, the mixture was concentrated on a hot plate adjusted to a temperature of 350°C until it became a slurry. The mixture was dried at 110°C for 12 hours and then calcined in an air atmosphere at 500°C for 5 hours. The calcined product was subjected to a pressure of 1000 kg / cm 2 After pressing for 1 minute, the mixture was crushed and sieved to obtain catalyst pellets of 0.5 to 1.0 mm.

[0081] <Comparative Example 2> Activated alumina particles (Al2O3) were impregnated with ruthenium (Ru) and lithium oxide (Li2O). The preparation method is shown below.

[0082] To 44.5 parts by mass of activated alumina granules (Sumika Alchem ​​Co., Ltd., product number: KHO-12), 8.0 parts by mass of an aqueous solution of ruthenium nitrosyl nitrate nitrate (Furuya Metals, 18.73% by mass, metal base) diluted with 40 parts by mass of ion-exchanged water was added. This solid-liquid mixture was placed in a vacuum desiccator and the pressure was reduced at room temperature (20-30°C) using a vacuum pump for 12 hours. After drying at 90°C for 12 hours, it was calcined at 500°C for 5 hours. 18.5 parts by mass of lithium nitrate (LiNO3: Fujifilm Wako Pure Chemical Industries, Ltd., product number: 128-01232) was dissolved in 25 parts by mass of ion-exchanged water and added to the solid obtained by calcination. The pressure was reduced at room temperature for 12 hours using a vacuum pump and vacuum desiccator. After drying at 90°C for 12 hours, it was calcined in an air atmosphere at 500°C for 5 hours. Powder was removed using a 1 mm sieve to obtain a granular catalyst.

[0083] <Comparative Example 3> Nickel oxide (NiO) and calcium oxide (CaO) were impregnated into gamma-alumina powder (gamma-Al2O3). The preparation method is shown below.

[0084] An aqueous solution was prepared by dissolving 16.8 parts by weight of calcium nitrate (Ca(NO3)2·4H2O: Fujifilm Wako Pure Chemical Industries, Ltd., product number 039-00735) in 60 parts by weight of ion-exchanged water, and then added to 6.0 parts by weight of gamma-alumina (W.R. Grace) and stirring. After stirring for approximately 1 hour, the mixture was concentrated on a hot plate adjusted to 350°C until a slurry was formed. The mixture was dried at 110°C for 12 hours and then calcined at 500°C for 2 hours. An aqueous solution was prepared by dissolving 9.9 parts by weight of nickel nitrate (Ni(NO3)2·6H2O: Fujifilm Wako Pure Chemical Industries, Ltd., product number 149-01105) in 10 parts by weight of ion-exchanged water, and then added to the calcined product and stirred. After stirring for approximately 1 hour, the mixture was concentrated on a hot plate adjusted to 350°C until a slurry was formed. After drying at 110°C for 12 hours, the product was fired at 500°C for 2 hours in an air atmosphere. 2 After pressing for 1 minute, the mixture was crushed and sieved to obtain catalyst pellets of 0.5 to 1.0 mm.

[0085] <Examples 1 to 11> A NiO-CeO2 catalyst was prepared by coprecipitation as the carbon dioxide storage / reduction catalyst A. The preparation method is shown below.

[0086] Nickel nitrate (Ni(NO3)2·6H2O; Fujifilm Wako Pure Chemical Industries, Ltd., product number 149-01105) and cerium nitrate (Ce(NO3)3·6H2O; Fujifilm Wako Pure Chemical Industries, Ltd., product number 035-09735) were weighed and dissolved in 500 parts of ion-exchanged water to achieve a NiO:CeO2 mass ratio of 30:70, 50:50, 61:39, 70:30, or 90:10 after calcination of 20 parts of carbon dioxide storage / reduction catalyst A (solution preparation step). While stirring this solution with a magnetic stirrer, 200 parts of ion-exchanged water containing 1.35 equivalents of Ni and Ce (Na2CO3; Fujifilm Wako Pure Chemical Industries, Ltd., product number 199-01585) was added dropwise over 30 minutes. After the dropwise addition was completed, the mixed solution was heated to 70°C, held for 1 hour, and then left to stand overnight (12 hours) (coprecipitation step). The solution was filtered, and the resulting solid was dispersed in 800 parts by mass of 70°C hot water and stirred. Filtration, dispersion in hot water, and stirring were repeated until the sodium ion concentration in the filtrate, measured by the ion electrode method using a compact sodium ion meter (HORIBA, Ltd., LAQUAtwin NA-11), reached 70 ppm or less (filtration and washing step). The mixture was dried at 110°C for 12 hours (drying step), pulverized (pulverization step), and then calcined in an air atmosphere at 500°C for 2 hours (calcination step). The calcined product was subjected to a pressure of 1500 kg / cm. 2 After pressing for 1 minute (granulation step), the mixture was crushed and sieved to obtain catalyst pellets of 0.5 to 1.0 mm.

[0087] <Examples 12 and 13> NiO-CeO2 catalysts were prepared under conditions that were different from those of Examples 1 to 11, except for the calcination conditions.

[0088] A total of 67.1 parts by mass of nickel nitrate (Ni(NO3)2·6H2O: Fujifilm Wako Pure Chemical Industries, Ltd., product number 149-01105) and cerium nitrate (Ce(NO3)3·6H2O: Fujifilm Wako Pure Chemical Industries, Ltd., product number 035-09735) were weighed and dissolved in 500 parts by mass of ion-exchanged water so that the mass ratio of NiO to CeO2 after calcination was 61:39. While stirring this solution with a magnetic stirrer, 200 parts by mass of ion-exchanged water containing 33.1 parts by mass of sodium carbonate (Na2CO3: Fujifilm Wako Pure Chemical Industries, Ltd., product number 199-01585) (1.35 equivalents of Ni and Ce) was added dropwise over 30 minutes. After the addition, the mixture was heated to 70°C, held for 1 hour, and then left to stand overnight (12 hours). The solution was filtered, and the resulting solid was dispersed in hot water at 70°C and stirred. Filtration, dispersion in hot water, and stirring were repeated until the sodium ion concentration in the filtrate reached 70 ppm or less. After drying at 110°C for 12 hours, Example 7 was calcined in an air atmosphere at 500°C for 2 hours. After drying at 110°C for 12 hours, Example 12 was calcined in an air atmosphere at 416°C for 2 hours, and Example 13 was calcined in a 4 vol% H2 / 96 vol% N2 atmosphere at 416°C for 2 hours. The calcined product was subjected to a pressure of 1500 kg / cm2. 2 After pressing for 1 minute, the mixture was crushed and sieved to obtain catalyst pellets of 0.5 to 1.0 mm.

[0089] <Examples 14 and 16, Comparative Examples 4 to 6> A carbon dioxide occlusion / reduction catalyst A prepared by the same method as in Examples 1 to 11 and a carbon dioxide occlusion material B in which an alkali metal is supported on γ-alumina were physically mixed to prepare a mixed catalyst AB.

[0090] Carbon dioxide storage-reduction catalyst A was weighed so that the mass ratio of NiO and CeO2 after calcination was 50:50, and was prepared in the same manner as in Examples 1 to 11 up to the calcination step. Carbon dioxide storage material B (20 parts by mass) was prepared by impregnation so that the mass ratio of oxide to alumina carrier after calcination was 20:80. Lithium nitrate (LiNO3: Fujifilm Wako Pure Chemical Industries, Ltd., product number 122-01235), sodium nitrate (NaNO3: Fujifilm Wako Pure Chemical Industries, Ltd., product number 195-02545), potassium nitrate (KNO3: Fujifilm Wako Pure Chemical Industries, Ltd., product number 160-04035), or calcium nitrate (Ca(NO3)2·4H2O: Fujifilm Wako Pure Chemical Industries, Ltd., product number 039-00735) and gamma-alumina (WR Grace) were weighed out so that the mass ratio (oxide:alumina) after calcination was 20:80. The nitrate was dissolved in 150 parts of ion-exchanged water (solution preparation step), added to the gamma-alumina, and stirred (impregnation step). After stirring for approximately 1 hour, the mixture was concentrated on a hot plate adjusted to 350 °C until a slurry was formed (heat concentration step). The mixture was dried at 110°C for 12 hours (drying step), pulverized (pulverization step), and then calcined in an air atmosphere at 500°C for 2 hours (calcination step). The carbon dioxide occlusion / reduction catalyst A and the carbon dioxide occlusion material B were each pulverized and classified to less than 300 μm using a sieve (classification step). The carbon dioxide occlusion / reduction catalyst A and the carbon dioxide occlusion material B were weighed at a mass ratio of 1:1 and mixed for 10 seconds using a Wonder Blender (WB-1, manufactured by Osaka Chemical Co., Ltd., 25,000 rpm) (mixing step). The mixture was pressurized at 1,500 kg / cm. 2 After pressing for 1 minute (granulation step), the mixture was crushed and sieved to obtain catalyst pellets of 0.5 to 1.0 mm.

[0091] Example 17 The carbon dioxide storage reduction catalyst A prepared in the same manner as in Example 14 and the carbon dioxide storage material B (Li2O / Al2O3) were mixed in a mass ratio of 2:1, and then pelletized in the same manner.

[0092] Example 15 Carbon dioxide storage reduction catalyst A and carbon dioxide storage material B (Li2O / Al2O3) were prepared in the same manner as in Example 14, and then pelletized and mixed to form mixed catalyst AB.

[0093] The carbon dioxide storage reduction catalyst A was crushed and classified into particles of less than 300 μm using a sieve. 2 After pressing for 1 minute, the mixture was crushed and sieved to obtain pellets of 0.5 to 1.0 mm. Carbon dioxide occlusion material B was also similarly classified and pelletized to obtain pellets of 0.5 to 1.0 mm. Carbon dioxide occlusion / reduction catalyst A and carbon dioxide occlusion material B were weighed out so that the mass ratio was 1:1, and the mixture was gently shaken in a plastic container to obtain mixed catalyst AB.

[0094] [Catalyst performance evaluation method] A cycle test was conducted in which a catalyst packed in a reaction tube was alternately supplied with a 10 vol% CO2 + 3 vol% O2 + 87 vol% He mixed gas and a 46 vol% H2 + 54 vol% He mixed gas at 250 °C to evaluate the carbon dioxide treatment capacity per catalyst volume. Details of the test are provided below. Note that the Ni in the carbon dioxide storage / reduction catalyst A or mixed catalyst AB prepared above was in an oxidized state (NiO), so it was activated by reducing it to Ni(0) before it could function as a catalyst. Furthermore, in Example 13, calcination was performed in a reducing atmosphere, and since the NiO was reduced, the surface was oxidized by passing a 1 vol% O2 + 99 vol% N2 mixed gas at room temperature (20–30 °C) for at least one hour before exposure to the outside air.

[0095] A 2.4 mL catalyst was loaded into a stainless steel reactor with an inner diameter of 8 mm and an outer diameter of 10 mm and connected to a temperature-programmed desorption analyzer (Henmi Slide Rule, TP-5000) equipped with a mass spectrometer. The catalyst was activated by heating to the specified activation temperature (Ta) shown in Table 1 in a 40 vol% H2 / 60 vol% N2 atmosphere and maintaining the temperature for 60 minutes (activation step) (see Figure 3). After activation under the specified conditions, the catalyst temperature was adjusted to 250 °C. The following gas cycles were repeated four times: "10 vol% CO2 + 3 vol% O2 + 87 vol% He flow for t1 min," "100 vol% He purge for 1 min," "46% H2 + 54 vol% He flow for t1 min," and "100 vol% He purge for 1 min." Then, t1 was changed to t2 four times, and t2 was changed to t3 four times. The gases (CH4, CO2) after passing through the catalyst were analyzed by a mass spectrometer. The signal intensity of the mass spectrometer in the fourth cycle at each gas switching time (t1 to t3) was extracted (see Figure 4). The concentration of unreacted carbon dioxide that had passed through the catalyst was calculated from the signal intensity of carbon dioxide (CO2 (m / e = 44)), and the carbon dioxide conversion rate (%) from t1 to t3 was obtained (Equation (3) below). The time t99 at which the carbon dioxide conversion rate exceeded 99% was calculated from the correlation between the carbon dioxide conversion rate and t, and the carbon dioxide storage density (D cycle The carbon dioxide storage density (D mol-CO2 / L-cat) was calculated. The carbon dioxide storage density represents the amount of carbon dioxide processed per cycle that can be operated with a carbon dioxide leakage rate of 1%. cycle If the CO2 / L-cat ratio was 0.02 or higher, it was judged to be "good," if it was 0.1 or higher, it was judged to be "excellent," if it was 0.12 or higher, it was judged to be "even better," and if it was 0.15 or higher, it was judged to be "particularly excellent." CO2 conversion rate (%) = (CO2 supply amount - unreacted CO2 amount) / CO2 supply amount × 100 (3)

[0096] A flow diagram of the test conditions for the catalytic performance evaluation is shown in Figure 3. The total gas flow rate was 40 mL / min (He balance), and 100 vol% He was circulated in sections not specified.

[0097] Figure 4 shows an image of the signal intensity of gases (CH4, CO2) after passing through the catalyst, measured by a mass spectrometer in the catalyst performance evaluation.

[0098] [Catalyst performance evaluation results] Figure 5 shows the carbon dioxide storage density (D cycle , mol-CO2 / L-cat) and activation temperature Ta (°C) (Examples 1 to 6).

[0099] The activation treatment temperature before the operation of the carbon dioxide storage reduction catalyst A may be in the range of 300 to 500°C, but by setting the activation treatment temperature to 400 to 450°C, the highest performance (D cycle ) can be obtained. The optimum temperature for activation was calculated to be 416°C by fitting the measurement points with a quadratic curve (y=-2.202E-0.8x 3 +2.047E-05x 2 -5.601E-03x+4.996E-01, R 2 =9.976E-01).

[0100] Figure 6 shows the carbon dioxide storage density (D cycle , mol-CO2 / L-cat) and the NiO composition (mass %) (Examples 7 to 11).

[0101] The performance can be improved by changing the NiO / CeO2 ratio contained in the carbon dioxide storage reduction catalyst A. The Ni content in the carbon dioxide storage reduction catalyst A may be in the range of 30 to 90 mass% in terms of NiO relative to the total content of Ni and the carrier C, and since this increases the carbon dioxide storage density, it is preferable that the content be in the range of 50 to 70 mass%, and more preferably in the range of 55 to 65 mass%. In particular, the highest performance (D cycle ) was obtained.

[0102] Figure 7 shows the carbon dioxide storage density (D cycle , mol-CO2 / L-cat) and the calcination conditions (Examples 9, 12, and 13).

[0103] The performance can be improved by changing the calcination conditions during the preparation of the carbon dioxide storage reduction catalyst A. Calcination at a lower temperature is preferable (Example 12), and a reducing atmosphere is more preferable (Example 13).

[0104] Figure 8 shows the carbon dioxide absorption density (D cycle , mol-CO2 / L-cat) are shown (Examples 14 and 15, Comparative Examples 4 to 6).

[0105] When preparing mixed catalyst AB, Li is most desirable as the carbon dioxide storage site of carbon dioxide storage material B. If the carbon dioxide storage site is Na, K, or Ca, operation without CO2 leakage is not possible at 250°C (Comparative Examples 4 to 6). In Example 14, particles of less than 300 μm were mixed, and in Example 15, particles of 0.5 to 1.0 mm were mixed, and it is desirable that the carbon dioxide storage-reduction catalyst A and carbon dioxide storage material B are finer when mixed (Examples 14 and 15).

[0106] Figure 9 shows the carbon dioxide storage density (D cycle , mol-CO2 / L-cat) and NiO composition (mass%) (Examples 8, 16, and 17).

[0107] The catalytic performance of the mixed catalyst AB also changes depending on the amount of NiO. When 50 mass % NiO is used as the carbon dioxide storage reduction catalyst A, the upper limit of the NiO composition is 50 mass % (Example 8).

[0108] Figure 10 shows the carbon dioxide storage density (D cycle , mol-CO2 / L-cat) and the NiO composition (mass %) (Examples 7 to 11, 16, and 17).

[0109] By using the mixed catalyst AB, it is possible to reduce the amount of Ni used. For example, the mixed catalyst AB (Examples 16 and 17) showed performance that was significantly superior to that of the carbon dioxide storage reduction catalyst A (Example 7), which contained the same amount of NiO.

[0110] (Consideration of why optimal values ​​for catalyst composition and activation temperature exist) Figure 11 shows the specific surface area (SSA, m 2 / g) and NiO (mass %).

[0111] After activation treatment, the specific surface area (SSA) of the carbon dioxide storage reduction catalyst A decreased when the NiO composition was low (30 mass%) or high (90 mass%). Furthermore, the higher the activation treatment temperature, the smaller the specific surface area (SSA) of the carbon dioxide storage reduction catalyst A. This suggests that the NiO or CeO2 particles tend to coarsen due to the bias in the composition. Furthermore, it suggests that the coarsening of the NiO or CeO2 particles reduces the number of active sites for Ni and the carbon dioxide adsorption sites for CeO2. This suggests that the catalyst composition should preferably contain 50 to 70 mass% NiO, and that the activation treatment temperature should preferably be 400 to 450°C.

[0112] FIG. 12 shows the correlation between the crystallite size (nm) of each component contained in the carbon dioxide storage reduction catalyst A and the activation treatment temperature (° C.).

[0113] Without activation treatment, or when the activation treatment temperature is low (300 to 350°C), NiO, which does not have catalytic function, coexists in the carbon dioxide storage reduction catalyst A. When the activation treatment temperature is high (400°C or higher), NiO is reduced and almost completely disappears. It is presumed that when the activation treatment temperature is low, Ni is not sufficiently activated, and catalytic activity remains low. When the activation treatment temperature is too high, Ni is activated but coarsens (see Figure 12), which is presumed to reduce the number of active sites and reduce catalytic activity.

[0114] As described above, the examples provide a carbon dioxide storage reduction catalyst that has a good carbon dioxide storage density without using a precious metal, and a method for preparing the carbon dioxide storage reduction catalyst.

Claims

1. A carbon dioxide storage-reduction catalyst that stores and reduces carbon dioxide in a carbon dioxide-containing gas, A carbon dioxide storage reduction catalyst A composed of Ni and a carrier C made of a metal oxide, or A mixed catalyst AB of the carbon dioxide storage reduction catalyst A and a carbon dioxide storage material B composed of a carrier D made of Li and a metal oxide; A carbon dioxide storage reduction catalyst comprising:

2. The carbon dioxide storage reduction catalyst according to claim 1, A carbon dioxide storage-reduction catalyst, characterized in that the metal oxide of said carrier C and the metal oxide of said carrier D are each at least one selected from alumina, ceria, titania, zirconia, silica, and zeolite.

3. The carbon dioxide storage reduction catalyst according to claim 1, A carbon dioxide storage reduction catalyst, wherein the metal oxide of the carrier C is ceria.

4. The carbon dioxide storage reduction catalyst according to claim 1, A carbon dioxide storage reduction catalyst, wherein the metal oxide of the carrier D is alumina.

5. The carbon dioxide storage reduction catalyst according to claim 1, A carbon dioxide storage-reduction catalyst characterized in that the content of Ni in the carbon dioxide storage-reduction catalyst A is in the range of 30 to 90 mass % in terms of NiO relative to the total content of the Ni and the carrier C.

6. A method for preparing the carbon dioxide storage reduction catalyst according to any one of claims 1 to 5, a calcination step of calcining the mixed particles in which the Ni is highly dispersed on the carrier C at a calcination temperature in the range of 300 to 500°C to obtain a calcined catalyst A, or calcining the supported particles in which the Ni is supported on the carrier C at a calcination temperature in the range of 300 to 500°C to obtain a calcined catalyst A, and further calcining the supported particles in which the Li is supported on the carrier D at a calcination temperature in the range of 300 to 500°C to obtain a calcined absorbent material B; an activation step of activating the calcined catalyst A obtained in the calcination step at an activation temperature in the range of 300 to 500°C to obtain the carbon dioxide storage-reduction catalyst A, or activating a mixture of the calcined catalyst A obtained in the calcination step and the calcined storage material B obtained in the calcination step at an activation temperature in the range of 300 to 500°C to obtain the mixed catalyst AB; A method for preparing a carbon dioxide storage reduction catalyst, comprising:

7. 7. A method for preparing the carbon dioxide storage reduction catalyst according to claim 6, comprising: The method for preparing a carbon dioxide occlusion reduction catalyst is characterized in that the calcination temperature is in the range of 400 to 450°C.

8. 7. A method for preparing the carbon dioxide storage reduction catalyst according to claim 6, comprising: The method for preparing a carbon dioxide storage reduction catalyst is characterized in that the activation temperature is in the range of 400 to 450°C.

9. 7. A method for preparing the carbon dioxide storage reduction catalyst according to claim 6, comprising: In the firing step, 4 to 100 vol% H ２ 2. A method for preparing a carbon dioxide occlusion reduction catalyst, comprising: calcining the catalyst in a reducing atmosphere.

10. 7. A method for preparing the carbon dioxide storage reduction catalyst according to claim 6, comprising: In the activation step, 4 to 100 vol% H ２ 2. A method for preparing a carbon dioxide storage reduction catalyst, comprising: activating the catalyst in a reducing atmosphere;

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