Carbon dioxide storage and reduction catalyst
A CO2 storage and reduction catalyst with a porous metal oxide, ruthenium, and alkali metal support system addresses high-temperature requirements, ensuring efficient CO2 storage and methane production at low temperatures.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- KK TOYOTA CHUO KENKYUSHO
- Filing Date
- 2022-04-15
- Publication Date
- 2026-07-17
AI Technical Summary
Existing CO2 absorption and reduction type catalysts require high operating start temperatures, leading to excessive thermal energy input and reduced energy efficiency, and exhibit decreased methane production with certain CO2 storage materials.
A CO2 storage and reduction catalyst comprising a porous metal oxide carrier with ruthenium and an alkali metal, such as sodium, within specific content ranges, supports excellent CO2 storage and methanation activity at low temperatures.
The catalyst achieves efficient CO2 storage and methane generation without excessive thermal energy input, maintaining high performance even at low temperatures.
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Abstract
Description
Technical Field
[0001] The present invention relates to a carbon dioxide (CO2) absorption and reduction type catalyst, and more particularly to a CO2 absorption and reduction type catalyst containing an alkali metal.
Background Art
[0002] The methanation reaction using carbon dioxide (CO2) as a raw material has attracted attention in recent years from the perspective of reducing CO2 emissions for global warming suppression. As a catalyst used in such a methanation reaction, a CO2 absorption and reduction type catalyst in which calcium oxide (CaO) as a CO2 absorbent and ruthenium (Ru) as a methanation catalyst are supported on a carrier such as alumina (for example, JP 2020-110769 A (Patent Document 1) and A. Bermejo-Lopez et al., Applied Catalysis B: Environmental, 2019, Vol. 256, 117845 (Non-Patent Document 1)) is known. This CO2 absorption and reduction type catalyst absorbs CO2 by flowing a gas containing CO2, and reduces the absorbed CO2 by flowing a reducing gas (for example, H) to generate methane (CH4).
[0003] However, in the CO2 absorption and reduction type catalyst using CaO as a CO2 absorbent, since the operating start temperature during absorption / reduction is as high as 320°C, it is necessary to excessively input thermal energy during the operation of the CO2 absorption and reduction type catalyst system, and there is a problem that the energy efficiency of the system decreases.
[0004] Furthermore, A. Bermejo-Lopez et al., Applied Catalysis B: Environmental, 2019, Vol. 256, pp. 117845 (Non-Patent Literature 1), describes a CO2 storage and reduction type catalyst in which sodium oxide (Na2O) as a CO2 storage material and ruthenium (Ru) as a methanation catalyst are supported on a carrier such as alumina. In this CO2 storage and reduction type catalyst as well, the operating start temperature during storage / reduction is a high 370°C, which means that an excessive amount of thermal energy must be input when operating the CO2 storage and reduction type catalyst system, resulting in a problem of reduced system energy efficiency. Non-Patent Literature 1 also suggests that the amount of methane produced decreases as the Na2O content decreases. [Prior art documents] [Patent Documents]
[0005] [Patent Document 1] Japanese Patent Publication No. 2020-110769 [Non-patent literature]
[0006] [Non-Patent Document 1] A. Bermejo-Lopez et al., Applied Catalysis B: Environmental, 2019, Vol. 256, pp. 117845. [Overview of the Initiative] [Problems that the invention aims to solve]
[0007] This invention has been made in view of the problems of the prior art described above, and aims to provide a CO2 storage and reduction type catalyst that exhibits excellent CO2 storage performance and methanation catalytic activity even at low temperatures. [Means for solving the problem]
[0008] As a result of diligent research to achieve the above objective, the inventors of the present invention have discovered that in a CO2 storage reduction catalyst in which an alkali metal as a CO2 storage material and ruthenium (Ru) as a methanation catalyst are supported on a carrier such as alumina, by keeping the alkali metal content within a specific range, excellent CO2 storage performance and methanation catalytic activity can be exhibited even at low temperatures, thus completing the present invention.
[0009] In other words, the CO2 storage and reduction catalyst of the present invention is made of a metal oxide, has an average pore diameter of 3 to 50 nm, and a pore volume of 0.3 to 1.5 cm³. 3 A catalyst comprising a porous carrier at / g, ruthenium supported on the porous carrier, and an alkali metal supported on the porous carrier, wherein the ruthenium content is such that, relative to 100 parts by mass of the total content of the porous carrier and ruthenium, 5 This is in parts by mass, and the alkali metal content is 2.8 to 4.5% by mass in terms of oxides relative to the entire catalyst. In the X-ray diffraction pattern, there is no diffraction peak corresponding to a crystallite size of 44 nm for the alkali metal oxide. It is characterized by the following:
[0010] In the CO2 storage and reduction catalyst of the present invention, it is preferable that the alkali metal is sodium. stomach. [Effects of the Invention]
[0011] According to the present invention, it is possible to obtain a CO2 storage and reduction type catalyst that exhibits excellent CO2 storage performance and methanation catalytic activity even at low temperatures. [Brief explanation of the drawing]
[0012] [Figure 1] This graph shows the temperature characteristics of the CO2 conversion rate of the catalysts obtained in Examples 1-3 and Comparative Examples 1-7. [Figure 2] This graph shows the relationship between the temperature T50 at which the CO2 conversion rate of the catalysts obtained in Examples 1-3 and Comparative Examples 1-7 reaches 50%, and the CO2 storage material content. [Figure 3] This graph shows the X-ray diffraction patterns of the catalysts obtained in Examples 2-3 and Comparative Examples 3-4.
Mode for Carrying Out the Invention
[0013] Hereinafter, the present invention will be described in detail according to its preferred embodiments.
[0014] 〔CO2 storage and reduction type catalyst〕 The carbon dioxide (CO2) storage and reduction type catalyst of the present invention is a catalyst containing a porous carrier made of a metal oxide, ruthenium supported on the porous carrier, and an alkali metal supported on the porous carrier.
[0015] The carrier used in the present invention is a porous carrier made of a metal oxide. By using a porous carrier, gas components can diffuse well, and the CO2 storage performance and methanation catalytic activity are improved. The metal oxide is not particularly limited as long as it can be used as a carrier for the CO2 storage and reduction type catalyst. For example, known metal oxides such as alumina (Al2O3), silica (SiO2), zirconia (ZrO2), and titania (TiO2) can be mentioned. Among these metal oxides, from the viewpoint of high methanation catalytic activity, alumina and titania are preferred, and alumina is more preferred. Also, such metal oxides may be used alone or in combination of two or more.
[0016] The average pore diameter of the porous carrier is 3 to 50 nm, preferably 5 to 20 nm. When the average pore diameter of the porous carrier is less than the lower limit, gas components cannot diffuse sufficiently, and the CO2 storage performance and methanation catalytic activity tend to decrease. On the other hand, when it exceeds the upper limit, the stability of the pore structure tends to decrease.
[0017] Also, the pore volume of the porous carrier is 0.3 to 1.5 cm 3 / g, and preferably 0.3 to 1.0 cm 3It is preferably / g. When the pore volume of the porous carrier is less than the above lower limit, gas components do not diffuse sufficiently, and the CO2 storage performance and methanation catalytic activity tend to decrease. On the other hand, when it exceeds the above upper limit, the thermal stability of the porous carrier tends to decrease.
[0018] In the CO2 storage reduction type catalyst of the present invention, ruthenium (Ru) is supported on the porous carrier. This Ru acts as a methanation catalyst. Specifically, when CO2 stored in the CO2 storage material reacts with a reducing gas (for example, H2) and is reduced to generate methane (CH4), it promotes the reduction reaction of CO2.
[0019] In the CO2 storage reduction type catalyst of the present invention, the content of Ru is 1 to 5 parts by mass with respect to 100 parts by mass of the total content of the porous carrier and Ru. When the content of Ru is within the above range, the reduction reaction of CO2 is promoted and the methanation catalytic activity is improved. On the other hand, when the content of Ru is less than the above lower limit, the reduction reaction of CO2 is not sufficiently promoted and the methanation catalytic activity decreases. On the other hand, when the content of Ru exceeds the above upper limit, the pores of the porous carrier are blocked and the CO2 storage amount decreases, so the CO2 storage performance decreases, or Ru undergoes grain growth and the methanation catalytic activity decreases.
[0020] Also, in the CO2 storage reduction type catalyst of the present invention, an alkali metal is supported on the porous carrier. This alkali metal acts as a CO2 storage material. Such an alkali metal is usually supported on the porous carrier in the form of an oxide, carbonate, or bicarbonate.
[0021] Examples of the alkali metal include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs). Among them, Na is preferable from the viewpoint of further improving the CO2 storage performance.
[0022] In the CO2 storage and reduction catalyst of the present invention, the alkali metal content is 2.8 to 4.5% by mass in terms of oxides relative to the entire catalyst. When the alkali metal content is within the above range, excellent CO2 storage performance and methanation catalytic activity are exhibited even at low temperatures. On the other hand, when the alkali metal content falls below the lower limit, the number of CO2 storage sites decreases, reducing the amount of CO2 stored, and thus lowering the CO2 storage performance and methanation catalytic activity. Conversely, when the alkali metal content exceeds the upper limit, the pores of the porous support become blocked, reducing the amount of CO2 stored, and thus lowering the CO2 storage performance and methanation catalytic activity. In addition, the crystallite size of the alkali metal oxide increases, reducing the CO2 storage performance and methanation catalytic activity at low temperatures. From the viewpoint of further improving the CO2 storage performance and methanation catalytic activity at low temperatures, the alkali metal content is preferably 2.8 to 4.2% by mass, and more preferably 3.0 to 4.0% by mass, in terms of oxides.
[0023] Furthermore, it is preferable that the CO2 storage-reduction catalyst of the present invention does not contain a diffraction peak corresponding to a crystallite size of 44 nm in its X-ray diffraction pattern, that is, it does not contain alkali metal oxides with a coarse crystallite size. If a diffraction peak corresponding to a crystallite size of 44 nm exists, that is, if alkali metal oxides with a coarse crystallite size are present, the CO2 storage performance and methane catalytic activity at low temperatures tend to decrease. Note that such alkali metal oxides with a coarse crystallite size tend to form when the alkali metal content exceeds the above upper limit.
[0024] [Method for preparing CO2 storage reduction catalyst] The CO2 storage and reduction catalyst of the present invention can be prepared, for example, as follows. That is, an aqueous solution containing an alkali metal salt in a predetermined mass ratio is prepared, a predetermined amount of a porous support made of a metal oxide on which Ru is supported is added to this aqueous solution, and then drying and calcining is performed to obtain a CO2 storage and reduction catalyst on which alkali metal and Ru are supported on the porous support made of the metal oxide. Alternatively, an aqueous solution containing an alkali metal salt in a predetermined mass ratio is prepared, a predetermined amount of a porous support made of a metal oxide is added to this aqueous solution, and then drying and calcining is performed to prepare a CO2 storage material on which alkali metal oxide is supported on the porous support made of the metal oxide, and then adding this CO2 storage material to an aqueous solution in which a predetermined amount of Ru salt is dissolved, and then drying and calcining is performed to obtain a CO2 storage and reduction catalyst on which alkali metal oxide and Ru are supported on the porous support made of the metal oxide. Furthermore, a CO2 storage and reduction catalyst can also be obtained by preparing an aqueous solution containing an alkali metal salt and a Ru salt in a predetermined mass ratio, adding a predetermined amount of a porous support made of a metal oxide to this aqueous solution, and then drying and calcining the solution. In this way, an alkali metal oxide and Ru can be supported on the porous support made of a metal oxide.
[0025] There are no particular restrictions on the firing conditions as long as the alkali metal salts are converted to oxides, carbonates, and bicarbonates, and the Ru salts are converted to Ru. For example, the firing temperature is preferably 400 to 600°C, more preferably 450 to 550°C, and the firing time is preferably 1 to 5 hours, more preferably 2 to 4 hours.
[0026] Examples of alkali metal salts include nitrates, carbonates, and acetates of alkali metals (Li, Na, K, Rb, Cs). Examples of Ru salts include ruthenium nitrosylnitrate, ruthenium nitrate, ruthenium chloride, and ruthenium carbonyl.
[0027] [CO2 storage and reduction treatment] The CO2 storage and reduction catalyst of the present invention can be applied, for example, to the following CO2 storage and reduction treatments. Specifically, by contacting the CO2 storage and reduction catalyst of the present invention with a gas containing CO2 to allow CO2 to be stored, and then contacting the CO2-stored CO2 storage and reduction catalyst with a reducing gas (e.g., H2), the stored CO2 is reduced to produce CH4. Alternatively, by contacting the CO2 storage and reduction catalyst of the present invention with a gas containing both CO2 and H2 to allow CO2 to be stored, and then reacting the stored CO2 with a reducing gas (e.g., H2), the stored CO2 is reduced to produce CH4.
[0028] The CO2 storage and reduction catalyst of the present invention exhibits excellent CO2 storage performance and methanation catalytic activity at low temperatures. Therefore, even in low-temperature conditions such as at the start of the above-mentioned CO2 storage and reduction treatment, it enables the reduction of CO2 and the generation of CH4 without supplying excessive thermal energy. [Examples]
[0029] 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.
[0030] (Example 1) Sodium nitrate (NaNO3, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product code: 192-02555) was dissolved in deionized water, and ruthenium-supported alumina powder (Ru / Al2O3, manufactured by N.E. Chemcat Corporation, product code: HYAc-5E N-Type, Ru content: 5% by mass, alumina content: 95% by mass, average pore size of alumina: 13 nm, pore volume of alumina: 0.38 cm³) was dissolved in the resulting aqueous solution. 3 Na2O was added to the resulting catalyst so that its Na2O content was 2.8% by mass relative to the total catalyst. The resulting dispersion was stirred for about 2 hours, then heated to 250°C and evaporated to dryness. The resulting dry material was dried at 110°C for 12 hours, and then calcined at 500°C for 3 hours. The resulting catalyst powder (approximately 6 g) was subjected to a pressure of 1000 kg / cm². 2After pressurizing for 1 minute, the mixture was pulverized and classified using a sieve to obtain a catalyst powder with a diameter of 0.5 to 1.0 mm, in which Na2O and Ru were supported on Al2O3 [Na2O(2.8) / Ru(4.9) / Al2O3(92.3)].
[0031] (Example 2) Except for adding the Ru / Al2O3 powder so that the Na2O content in the resulting catalyst was 3.7% by mass relative to the total catalyst, the same procedure as in Example 1 was used to obtain a catalyst powder [Na2O(3.7) / Ru(4.8) / Al2O3(91.5)] with a diameter of 0.5 to 1.0 mm, in which Na2O and Ru were supported on Al2O3.
[0032] (Example 3) Except for adding the Ru / Al2O3 powder so that the Na2O content in the resulting catalyst was 4.5% by mass relative to the total catalyst, the same procedure as in Example 1 was used to obtain a catalyst powder [Na2O(4.5) / Ru(4.8) / Al2O3(90.7)] with a diameter of 0.5 to 1.0 mm, in which Na2O and Ru were supported on Al2O3.
[0033] (Comparative Example 1) Except for adding the Ru / Al2O3 powder so that the Na2O content in the resulting catalyst was 1.0% by mass relative to the total catalyst, the same procedure as in Example 1 was used to obtain a catalyst powder [Na2O(1.0) / Ru(4.9) / Al2O3(94.1)] with a diameter of 0.5 to 1.0 mm, in which Na2O and Ru were supported on Al2O3.
[0034] (Comparative Example 2) Except for adding the Ru / Al2O3 powder so that the Na2O content in the resulting catalyst was 5.4% by mass relative to the total catalyst, the same procedure as in Example 1 was used to obtain a catalyst powder [Na2O(5.4) / Ru(4.7) / Al2O3(89.9)] with a diameter of 0.5 to 1.0 mm, in which Na2O and Ru were supported on Al2O3.
[0035] (Comparative Example 3) Except for adding the Ru / Al2O3 powder so that the Na2O content in the resulting catalyst was 8.7% by mass relative to the total catalyst, the same procedure as in Example 1 was used to obtain a catalyst powder [Na2O(8.7) / Ru(4.6) / Al2O3(86.7)] with a diameter of 0.5 to 1.0 mm, in which Na2O and Ru were supported on Al2O3.
[0036] (Comparative Example 4) Except for adding the Ru / Al2O3 powder so that the Na2O content in the resulting catalyst was 12.5% by mass relative to the total catalyst, the same procedure as in Example 1 was used to obtain a catalyst powder [Na2O(12.5%) / Ru(4.4%) / Al2O3(83.1%)] with a diameter of 0.5 to 1.0 mm, in which Na2O and Ru were supported on Al2O3.
[0037] (Comparative Example 5) Except for using calcium nitrate (Ca(NO3)2, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product code: 039-00735) instead of sodium nitrate, and adding the Ru / Al2O3 powder so that the CaO content in the resulting catalyst was 4.5% by mass relative to the total catalyst, the same procedure as in Example 1 was followed to obtain a catalyst powder with a diameter of 0.5 to 1.0 mm [CaO(4.5) / Ru(4.8) / Al2O3(90.7)] in which CaO and Ru were supported on Al2O3.
[0038] (Comparative Example 6) Except for adding the Ru / Al2O3 powder so that the CaO content in the resulting catalyst was 8.7% by mass relative to the total catalyst, the same procedure as in Comparative Example 5 was used to obtain a catalyst powder [CaO(8.7) / Ru(4.6) / Al2O3(86.7)] with a diameter of 0.5 to 1.0 mm, in which CaO and Ru were supported on Al2O3.
[0039] (Comparative Example 7) Except for adding the Ru / Al2O3 powder so that the CaO content in the resulting catalyst was 16.0% by mass relative to the total catalyst, the same procedure as in Comparative Example 5 was used to obtain a catalyst powder [CaO(16.0) / Ru(4.2) / Al2O3(79.8)] with a diameter of 0.5 to 1.0 mm, in which CaO and Ru were supported on Al2O3.
[0040] <Evaluation of Methanation Temperature Characteristics of CO2> The obtained catalyst powder was filled into a stainless steel (SUS) reaction tube (inner diameter: 6 mm) with a volume of 2.4 cm 3 such that the reaction tube was attached to a temperature programmed desorption analyzer (TP-5000 manufactured by Hemmi Calculator Co., Ltd.). While flowing a H2 / CO2-containing gas of H2 (40%) + CO2 (10%) + He (the remainder) through the catalyst bed at a flow rate of 40 ml / min under a pressure of 1 atm, the temperature of the catalyst bed was raised from 50°C to 350°C at a rate of 5°C / min. After cooling the catalyst bed to 50°C or lower, the temperature of the catalyst bed was again raised from 50°C to 350°C at a rate of 5°C / min under the above conditions. At the time of this second temperature increase, the amount of CO2 in the catalyst outlet gas was measured, and the CO2 conversion rate was determined from the amount of CO2 in the catalyst inlet gas and the amount of CO2 in the catalyst outlet gas. The results are shown in Fig. 1. Based on the results shown in Fig. 1, the temperature T50 at which the CO2 conversion rate becomes 50% was determined. The results are shown in Table 1. Also, Fig. 2 shows the results of plotting T50 against the content of the CO2 storage material (Na2O or CaO).
[0041]
Table 1
[0042] As shown in Table 1 and Fig. 2, it was confirmed that by setting the content of the alkali metal (in terms of oxide) within a predetermined range, a CO2 storage reduction type catalyst (Examples 1 to 3) with a low T50 and excellent catalytic activity at low temperatures can be obtained. On the other hand, it was found that when the content of the alkali metal (in terms of oxide) becomes too high, T50 becomes high and the catalytic activity at low temperatures decreases (Comparative Examples 2 to 4).
[0043] Also, the CO2 storage reduction type catalyst obtained in Example 3 was found to have a lower T50 and excellent catalytic activity at low temperatures compared to a catalyst (Comparative Example 5) containing an alkaline earth metal with a content (in terms of oxide) comparable to the content of the alkali metal (in terms of oxide).
[0044] <X-ray Diffraction Measurement> The X-ray diffraction pattern of the obtained catalyst powder was measured using an X-ray diffractometer (UltimaIV, manufactured by Rigaku Corporation) with CuKα as the X-ray source. The results are shown in Figure 3.
[0045] As shown in Figure 3, in catalysts with a Na2O content of 8.7% by mass or more (Comparative Examples 3-4), a diffraction peak corresponding to a Na2O crystallite size of 44 nm was observed, but it was not observed in CO2 storage reduction type catalysts with a Na2O content of 4.5% by mass or less (Examples 2-3). From these results, it is thought that as the alkali metal content increases, coarse particles with a crystallite size of 44 nm or more are generated, leading to a decrease in catalytic activity at low temperatures. [Industrial applicability]
[0046] As described above, the present invention makes it possible to obtain a CO2 storage and reduction type catalyst that exhibits excellent CO2 storage performance and methane catalytic activity even at low temperatures. Therefore, the CO2 storage and reduction type catalyst of the present invention is useful as a catalyst that can efficiently store CO2 and reduce it to CH4 even at low temperatures, such as when starting up a CO2 purification system.
Claims
1. It consists of metal oxides, has an average pore diameter of 3–50 nm, and a pore volume of 0.3–1.5 cm³. ３ The catalyst contains a porous carrier at / g, ruthenium supported on the porous carrier, and an alkali metal supported on the porous carrier. The ruthenium content is 5 parts by mass per 100 parts by mass of the total content of the porous carrier and ruthenium. The alkali metal content is 2.8 to 4.5% by mass in terms of oxides relative to the entire catalyst. In the X-ray diffraction pattern, there is no diffraction peak corresponding to the crystallite size of the alkali metal oxide, which is 44 nm. A carbon dioxide storage and reduction type catalyst characterized by the following features.
2. The carbon dioxide storage and reduction catalyst according to claim 1, characterized in that the alkali metal is sodium.