Method for manufacturing methanation catalyst

Abstract

To provide a method for manufacturing a methanation catalyst improving reactivity of a methanation reaction.SOLUTION: A method for manufacturing a methanation catalyst comprises: a process for acquiring a suspension containing a coprecipitate containing Ce and a rare earth element by adding a neutralizer into a mixture salt solution containing a Ce salt and a rare earth element salt (except for the Ce); a process for generating Ni-containing precipitate in the coprecipitate by adding a Ni salt and the neutralizer to the suspension; and a process for acquiring a methanation catalyst carrying Ni, as a catalyst component on a compound oxide carrier containing the Ce and the rare earth element by calcinating the coprecipitate and the Ni-containing precipitate.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing a methanation catalyst used in a methanation reaction. [Background technology]

[0002] In order to curb global warming, efforts to utilize CO2 through a methanation reaction that produces CH4 from CO2 (carbon dioxide) and H2 (hydrogen) are known. In the methanation reaction, a methanation catalyst is used to promote the reaction. As a catalytic component of a methanation catalyst, Ni (nickel), a transition metal, is inexpensive and highly reactive, and is therefore expected to be a promising component for practical use. Among methanation catalysts that use Ni as a catalytic component, methanation catalysts in which Ni is supported on a support containing CeO2 are known to be more reactive than methanation catalysts in which Ni is supported on other general oxide supports with a high specific surface area (e.g., Al2O3, etc.). A support containing CeO2 has good redox properties and oxygen storage properties. As shown in FIG. 6(a), in the process of methanation reaction in which a methanation catalyst in which Ni is supported on a support containing CeO2 is used, lattice defects generated by reduction of CeO2 attract oxygen from NiO (nickel oxide), promoting Ni reduction of NiO and promoting adsorption of CO2 to CeO2. On the other hand, in a composite oxide support in which a part of Ce in CeO2 is replaced with a rare earth element M, the lattice defects after reduction are increased more than in CeO2, so it is thought that the redox properties and oxygen storage properties of the support are further improved. For this reason, a methanation catalyst in which Ni is supported on the composite oxide support is being studied in order to improve the reactivity of the methanation reaction.

[0003] Known conventional methods for producing such methanation catalysts include, for example, a method in which a solution of a neutralizing agent such as a urea solution is dropped into an aqueous mixed salt solution containing salts of the constituent elements of the methanation catalyst to cause coprecipitate, and then calcining the coprecipitate (Patent Documents 1 and 2). Also known is a method in which a composite oxide support is formed in advance, and Ni is supported on the composite oxide support by an impregnation method (Patent Documents 3 and 4). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] China Patent Application Publication No. 101716513 [Patent Document 2] China Patent Application Publication No. 107376925 [Patent Document 3] Special Publication No. 2016-523182 [Patent Document 4] JP 2019-155227 A Summary of the Invention [Problem to be solved by the invention]

[0005] Among the conventional manufacturing methods, in the method of coprecipitating by dropping a solution of a neutralizing agent into a mixed salt aqueous solution containing salts of the constituent elements of the methanation catalyst and calcining the coprecipitate, the component containing the rare earth element M also interacts with the component containing Ni when simultaneously precipitating the salts of the constituent elements. In the methanation catalyst manufactured by such a method, the surface of NiO may be covered with the oxide of the rare earth element M (M oxide), as shown in Figure 6 (b). As a result, the number of adsorption points of H (hydrogen) on the surface of Ni after reduction of NiO decreases, and improvement of reactivity cannot be expected. On the other hand, in the method of supporting Ni on a composite oxide support by impregnation, the dispersibility of Ni is low and the surface area of ​​Ni is insufficient, so that improvement of reactivity cannot be expected.

[0006] The present invention has been made in view of the above problems, and has as its main object to provide a method for producing a methanation catalyst capable of improving reactivity. [Means for solving the problem]

[0007] In order to solve the above problems, the method for producing a methanation catalyst of the present invention is characterized by comprising the steps of: obtaining a suspension containing a coprecipitate containing Ce and the rare earth element by adding a neutralizing agent to a mixed salt solution containing a Ce salt and a salt of a rare earth element (excluding Ce); adding a Ni salt and a neutralizing agent to the suspension to generate a Ni-containing precipitate in the coprecipitate; and calcining the coprecipitate and the Ni-containing precipitate to obtain a methanation catalyst in which Ni is supported as a catalytic component on a composite oxide support containing the Ce and the rare earth element. Effect of the Invention

[0008] According to the present invention, the reactivity of the methanation reaction can be improved. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2A is a schematic diagram showing a method for producing a methanation catalyst according to an embodiment, and FIG. 2B is a schematic diagram showing a state of the methanation catalyst according to an embodiment during a methanation reaction. [Diagram 2] FIG. 2( a ) is a schematic diagram showing a method for producing a methanation catalyst according to Comparative Example 1, and FIG. 2( b ) is a schematic diagram showing a method for producing a methanation catalyst according to Comparative Examples 2 and 3. [Diagram 3] 1 is a graph showing the maximum CO2 conversion rates of methanation catalysts of Examples and Comparative Examples. [Figure 4] Graph (a) shows the relationship between the Pr or La content and a predetermined lattice constant of the CeO2 crystal lattice in the methanation catalysts of Comparative Example 1, Examples 2, 4, and 6, and Examples 7 to 9. Graph (b) shows the X-ray photoelectron spectroscopy spectra measured by XPS for the methanation catalyst of Example 4 and the methanation catalyst of Comparative Example 1 after reduction. [Diagram 5]Graph (a) shows the amount of CO2 desorbed during the temperature rise process for the methanation catalyst of Comparative Example 1 and the methanation catalysts of Examples 2, 4, and 6. Graph (b) shows the amount of CO2 desorbed during the temperature rise process for the methanation catalyst of Comparative Example 1 and the methanation catalysts of Examples 7, 8, and 9. [Figure 6] 1A is a schematic diagram showing a process of a methanation reaction using a conventional methanation catalyst, and FIG. 1B is a schematic diagram showing the state of a conventional methanation catalyst during a methanation reaction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] FIG. 1(a) is a schematic diagram showing a method for producing a methanation catalyst according to an embodiment, and FIG. 1(b) is a schematic diagram showing a state of the methanation catalyst according to an embodiment in a methanation reaction. In the method for producing a methanation catalyst according to an embodiment, as shown in FIG. 1(a), first, a mixed salt solution (Ce+M solution) containing a Ce salt (cerium salt) and a salt of a rare earth element M (excluding Ce) is prepared (preparation step). Examples of the Ce salt and the salt of a rare earth element M (excluding Ce) include inorganic salts such as nitrates, sulfates, chlorides, and phosphates. The rare earth element M (excluding Ce) is not particularly limited as long as it is an element other than Ce among rare earth elements, and for example, Pr (praseodymium) or La (lanthanum) is preferable. The mixed salt solution is not particularly limited as long as it is a solution in which a Ce salt and a salt of a rare earth element M (excluding Ce) are dissolved in a solvent such as water, and for example, it is an acidic solution, and specifically, for example, a mixed salt aqueous solution in which these salts are dissolved in water is preferable. In the preparation step, the salts of the elements can be added to the solvent in a ratio that will result in the desired ratio of the constituent materials of the methanation catalyst.

[0011] Next, a neutralizer is added to the mixed salt solution to obtain a suspension containing a coprecipitate (Precipitation of Ce+M) containing Ce and the rare earth element M (coprecipitation step). The neutralizer used in the coprecipitation step is a neutralizer that is used to obtain a suspension containing a coprecipitate (Precipitation of Ce+M) containing Ce and the rare earth element M by a coprecipitation method. 3+ ) and ions of rare earth elements M (e.g., Pr3+ , La 3+ The neutralizing agent is not particularly limited as long as it can simultaneously precipitate a salt of Ce and a salt of rare earth element M from the mixed salt solution, and can produce a coprecipitate containing these salts. For example, it is a base, specifically, for example, inorganic bases such as sodium carbonate, sodium hydroxide, potassium hydroxide, and ammonia. In the coprecipitation step, for example, it is preferable to add a neutralizing agent of less than 1 equivalent to the ions of Ce and the ions of rare earth element M contained in the mixed salt solution, and it is particularly preferable to add a neutralizing agent of 0.95 equivalents or less to these to the mixed salt solution. This is because, in the precipitation step described below, Ni-containing precipitates are easily produced so as to adhere to the coprecipitate rather than being produced alone in the suspension. Note that 1 equivalent of the neutralizing agent to the ions of Ce and the ions of rare earth element M contained in the mixed salt solution is the amount of neutralizing agent required to neutralize all of the ions of Ce and the ions of rare earth element M contained in the mixed salt solution and precipitate them as salts of Ce and salts of rare earth element M.

[0012] Next, a Ni salt solution containing Ni salt (nickel salt) and a neutralizer are simultaneously added to the suspension to generate a Ni-containing precipitate (Precipitation Ni) in the coprecipitate (precipitation step). Specifically, the Ni-containing precipitate is generated so as to adhere to the coprecipitate. Examples of Ni salts include inorganic salts such as nitrates, sulfates, chlorides, and phosphates. The Ni salt solution is not particularly limited as long as it is a solution in which a Ni salt is dissolved in a solvent such as water, but for example, an aqueous Ni salt solution in which a Ni salt is dissolved in water is preferred. In the precipitation step, the Ni salt can be added to the suspension at a ratio that results in a desired ratio of the constituent materials of the methanation catalyst. The neutralizer used in the precipitation step is a neutralizer that neutralizes Ni ions (e.g., Ni 2+) to generate Ni salt and generate Ni-containing precipitate containing the salt, but is not particularly limited thereto. For example, the neutralizer may be the same as that used in the coprecipitation step. In the precipitation step, it is preferable to add, for example, 0.4 equivalents or more of a neutralizer to the Ce ions and rare earth element M ions contained in the mixed salt solution and 1.35 equivalents or more of a neutralizer to the Ni ions contained in the Ni salt solution to the suspension. This is because these ions can be reliably neutralized. Note that 1 equivalent of a neutralizer to the Ni ions contained in the Ni salt solution is the amount of neutralizer required to neutralize all of the Ni ions contained in the Ni salt solution and precipitate them as Ni salts.

[0013] Next, the coprecipitate and the Ni-containing precipitate are dried (drying) and then calcined (calcining) to obtain a powdered methanation catalyst (NiO-M / CeO2) in which NiO (nickel oxide) containing Ni (nickel) as a catalytic component is supported on a composite oxide support (composite oxide support containing Ce and rare earth element M) in which a part of Ce in CeO2 is substituted with a rare earth element M (calcination step). The calcination step is not particularly limited as long as a methanation catalyst can be obtained by calcining the coprecipitate and the Ni-containing precipitate, and may be a step of calcining the coprecipitate and the Ni-containing precipitate without drying, but a step of drying and then calcining is preferred. The drying temperature and drying time when the coprecipitate and the Ni-containing precipitate are dried in the air are preferably, for example, 70°C to 200°C and 5 hours to 20 hours. The calcination temperature and calcination time when the coprecipitate and the Ni-containing precipitate are calcined in the air are preferably, for example, 400°C to 600°C and 0.5 hours to 5 hours.

[0014] The methanation catalyst obtained in the calcination step preferably contains Pr as a rare earth element and has a Pr content of 0.5 to 3.6% by weight.Moreover, the methanation catalyst preferably contains La as a rare earth element and has a La content of 1.0 to 3.9% by weight.

[0015] According to the manufacturing method of the embodiment, a neutralizing agent is added to a mixed salt solution containing a Ce salt and a salt of a rare earth element M to obtain a suspension containing a coprecipitate containing Ce and a rare earth element M, and then a Ni salt solution and a neutralizing agent are added to the suspension at the same time to generate a Ni-containing precipitate in the coprecipitate. Then, the coprecipitate and the Ni-containing precipitate are fired to produce a methanation catalyst (NiO-M / CeO2) in which NiO is supported on a composite oxide support in which a part of Ce in CeO2 is replaced with a rare earth element M. Therefore, as shown in FIG. 1(b), the composite oxide support (M / CeO2) of the methanation catalyst has more lattice defects than CeO2. In addition, unlike the manufacturing method in which a solution of a neutralizing agent is dropped into a mixed salt aqueous solution containing salts of the constituent elements (Ce, M, and Ni) of the methanation catalyst to cause coprecipitate and then fired, the methanation catalyst can suppress the surface of NiO from being covered with an oxide of the rare earth element M. This makes it possible to suppress a decrease in the adsorption points of H (hydrogen) on the surface of Ni after reduction of NiO. Furthermore, unlike a manufacturing method in which Ni is supported on a composite oxide support by impregnation, the dispersibility of Ni supported on the composite oxide support can be increased, and the surface area of ​​Ni can be increased. Therefore, in a methanation catalyst in which Ni is supported as a catalytic component on a composite oxide support in which part of Ce in CeO2 is substituted with a rare earth element M, the reactivity of the methanation reaction can be improved.

[0016] The methanation catalyst according to the embodiment is a methanation catalyst in which NiO containing Ni as a catalytic component is supported on a composite oxide support (a composite oxide support containing Ce and a rare earth element M) in which part of Ce in CeO2 is substituted with a rare earth element M. The methanation catalyst according to the embodiment is produced, for example, by using the production method according to the embodiment. EXAMPLES

[0017] The method for producing a methanation catalyst according to the embodiment will be described in more detail below with reference to examples and comparative examples.

[0018] [Examples 1 to 6] An example of a method for producing a methanation catalyst according to the embodiment was carried out. First, cerium nitrate hexahydrate (manufactured by Nacalai Tesque, Inc.) and praseodymium nitrate hexahydrate (manufactured by Kanto Chemical Co., Ltd.) were added to and dissolved in ion-exchanged water to obtain Ce. 3+ and Pr 3+ A precursor aqueous solution (mixed salt solution) containing nickel nitrate hexahydrate (manufactured by Nacalai Tesque, Inc.) was prepared (preparation step). 2+ In preparing the precursor aqueous solution and the Ni salt aqueous solution, the cerium nitrate hexahydrate and praseodymium nitrate hexahydrate to be contained in the precursor aqueous solution and the nickel nitrate hexahydrate to be contained in the Ni salt aqueous solution were weighed out with the aim of producing a catalyst having as its constituent materials CeO2 (ceria), Pr2O3 (praseodymium oxide), and NiO (nickel oxide) as the methanation catalyst, and with the expectation that the contents of CeO2, Pr2O3, and NiO in the catalyst would be in the amounts shown in Table 1 below.

[0019] Next, while stirring the precursor aqueous solution, a Na2CO3 aqueous solution containing Na2CO3 (sodium carbonate) as a precipitant (neutralizer) was added dropwise to the precursor aqueous solution over a period of 30 minutes to obtain a suspension containing a coprecipitate containing carbonates of Ce and Pr (coprecipitation step). 3+ and Pr 3+ An aqueous solution containing 0.95 equivalents of Na2CO3 relative to the amount of the hydrate was used.

[0020] Next, a Ni salt solution and a Na2CO3 solution containing Na2CO3 as a precipitant (neutralizer) were simultaneously dropped into the suspension over a period of 30 minutes. 3+ and Pr 3+ 0.4 equivalents of Na2CO3 and Ni in the Ni salt solution 2+ An aqueous solution containing 1.35 equivalents of Na2CO3 relative to the amount of 1.

[0021] Next, the liquid obtained by dropping the Ni salt aqueous solution and the Na2CO3 aqueous solution into the suspension as described above was heated at 70°C for 1 hour and then left to stand overnight. As a result, a Ni-containing precipitate was formed that adhered to the surface of the coprecipitate contained in the suspension, and a precipitate-containing liquid containing the coprecipitate and the Ni-containing precipitate was obtained (precipitation step). Next, filtration of the precipitate-containing liquid and washing of the precipitate obtained by filtration with warm water at 60°C were repeated seven times to extract Na from the precipitate. + (sodium ions) were removed.

[0022] Next, the precipitate was dried in air at 110°C for 12 hours, and then calcined in air at 500°C for 2 hours. This resulted in a powdered methanation catalyst (NiO-Pr / CeO2) in which NiO was supported on a composite oxide support in which part of the Ce in CeO2 was replaced with Pr (calcination step). The Pr content in the methanation catalyst was measured by ICP-MS (inductively coupled plasma mass spectrometry), and the results are shown in Table 1 below.

[0023] [Examples 7 to 9] An example of a method for producing a methanation catalyst according to the embodiment was carried out. First, cerium nitrate hexahydrate (manufactured by Nacalai Tesque, Inc.) and lanthanum nitrate hexahydrate (manufactured by Nacalai Tesque, Inc.) were added and dissolved in ion-exchanged water to obtain Ce. 3+ and La 3+ A precursor aqueous solution (mixed salt solution) containing nickel nitrate hexahydrate (manufactured by Nacalai Tesque, Inc.) was prepared (preparation step). 2+ In preparing the precursor aqueous solution and the Ni salt aqueous solution, the cerium nitrate hexahydrate and lanthanum nitrate hexahydrate to be contained in the precursor aqueous solution and the nickel nitrate hexahydrate to be contained in the Ni salt aqueous solution were weighed out with the aim of producing a catalyst having CeO2, La2O3 (lanthanum oxide), and NiO as constituent materials as a methanation catalyst, and with the expectation that the contents of CeO2, La2O3, and NiO in the catalyst would be in the amounts shown in Table 1 below.

[0024] Next, while stirring the precursor aqueous solution, a Na2CO3 aqueous solution containing Na2CO3 as a precipitant (neutralizer) was added dropwise to the precursor aqueous solution over a period of 30 minutes to obtain a suspension containing a coprecipitate containing carbonates of Ce and carbonates of La (coprecipitation step). 3+ and La 3+ An aqueous solution containing 0.95 equivalents of Na2CO3 relative to the amount of the hydrate was used.

[0025] Next, a Ni salt solution and a Na2CO3 solution containing Na2CO3 as a precipitant (neutralizer) were simultaneously dropped into the suspension over a period of 30 minutes. 3+ and La 3+ 0.4 equivalents of Na2CO3 and Ni in the Ni salt solution 2+ An aqueous solution containing 1.35 equivalents of Na2CO3 relative to the amount of 1.

[0026] Next, the liquid obtained by dropping the Ni salt aqueous solution and the Na2CO3 aqueous solution into the suspension as described above was heated at 70°C for 1 hour and then left to stand overnight. As a result, a Ni-containing precipitate was formed that adhered to the surface of the coprecipitate contained in the suspension, and a precipitate-containing liquid containing the coprecipitate and the Ni-containing precipitate was obtained (precipitation step). Next, filtration of the precipitate-containing liquid and washing of the precipitate obtained by filtration with warm water at 60°C were repeated seven times to extract Na from the precipitate. + was removed.

[0027] Next, the precipitate was dried in air at 110°C for 12 hours, and then calcined in air at 500°C for 2 hours. This resulted in a powdered methanation catalyst (NiO-La / CeO2) in which NiO was supported on a composite oxide support in which part of the Ce in CeO2 was replaced with La (calcination step). The La content in the methanation catalyst was measured by ICP-MS, and the results are shown in Table 1 below.

[0028] [Comparative Example 1] Fig. 2(a) is a schematic diagram showing a method for producing a methanation catalyst according to Comparative Example 1. As shown in Fig. 2(a), first, cerium nitrate hexahydrate (manufactured by Nacalai Tesque, Inc.) and nickel nitrate hexahydrate (manufactured by Nacalai Tesque, Inc.) are added and dissolved in ion-exchanged water to obtain Ce. 3+ and Ni 2+ In this case, the cerium nitrate hexahydrate and nickel nitrate hexahydrate to be contained in the precursor aqueous solution were weighed out with the aim of producing a catalyst containing CeO2 and NiO as components as a methanation catalyst, and with the expectation that the contents of CeO2 and NiO in the catalyst would be the amounts shown in Table 1 below.

[0029] Next, while stirring the precursor aqueous solution, an aqueous solution of Na2CO3 containing Na2CO3 as a precipitant (neutralizer) was dropped into the precursor aqueous solution over a period of 30 minutes. 3+ and Ni 2+ An aqueous solution containing 1.35 equivalents of Na2CO3 relative to the amount of cerium carbonate was used. The aqueous precursor solution was then heated at 70°C for 1 hour and allowed to stand overnight to obtain a suspension containing a coprecipitate containing a carbonate of cerium and a Ni-containing precipitate.

[0030] Next, the suspension was filtered and the coprecipitate obtained by filtration was washed with hot water at 60°C seven times to separate Na from the coprecipitate. + The coprecipitate was then dried in air at 110°C for 12 hours, and then calcined in air at 500°C for 2 hours. This resulted in a powdered methanation catalyst (NiO-CeO2) in which NiO was supported on an oxide support containing CeO2.

[0031] [Comparative Example 2] Fig. 2(b) is a schematic diagram showing a method for producing the methanation catalyst according to Comparative Examples 2 and 3. As shown in Fig. 2(b), first, cerium nitrate hexahydrate (manufactured by Nacalai Tesque, Inc.), praseodymium nitrate hexahydrate (manufactured by Kanto Chemical Co., Ltd.), and nickel nitrate hexahydrate (manufactured by Nacalai Tesque, Inc.) were added to and dissolved in ion-exchanged water to obtain Ce. 3+ and Pr3+ And Ni 2+ In this case, the cerium nitrate hexahydrate, praseodymium nitrate hexahydrate, and nickel nitrate hexahydrate to be contained in the precursor aqueous solution were weighed out with the aim of producing a catalyst containing CeO2, Pr2O3, and NiO as components as a methanation catalyst, and with the expectation that the contents of CeO2, Pr2O3, and NiO in the catalyst would be in the amounts shown in Table 1 below.

[0032] Next, while stirring the precursor aqueous solution, an aqueous solution of Na2CO3 containing Na2CO3 as a precipitant (neutralizer) was dropped into the precursor aqueous solution over a period of 30 minutes. 3+ and Pr 3+ And Ni 2+ An aqueous solution containing 1.35 equivalents of Na2CO3 relative to the amount of the precursor was used. The aqueous precursor solution was then heated at 70°C for 1 hour and allowed to stand overnight to obtain a suspension containing a coprecipitate containing carbonates of Ce and Pr, as well as a Ni-containing precipitate.

[0033] Next, the suspension was filtered and the coprecipitate obtained by filtration was washed with hot water at 60°C seven times to separate Na from the coprecipitate. + The coprecipitate was then dried in air at 110°C for 12 hours, and then calcined in air at 500°C for 2 hours. This resulted in a powdered methanation catalyst (NiO-Pr / CeO2) in which NiO was supported on a composite oxide support in which part of the Ce in CeO2 was replaced with Pr. The Pr content in the methanation catalyst was measured by ICP-MS, and the results are shown in Table 1 below.

[0034] [Comparative Example 3] As shown in FIG. 2(b), first, cerium nitrate hexahydrate (manufactured by Nacalai Tesque, Inc.), lanthanum nitrate hexahydrate (manufactured by Nacalai Tesque, Inc.), and nickel nitrate hexahydrate (manufactured by Nacalai Tesque, Inc.) were added to ion-exchanged water and dissolved to obtain Ce. 3+ and La 3+ And Ni 2+In this case, the amount of cerium nitrate hexahydrate, lanthanum nitrate hexahydrate, and nickel nitrate hexahydrate to be contained in the precursor aqueous solution was weighed out with the aim of producing a catalyst containing CeO2, La2O3, and NiO as components as a methanation catalyst, and with the expectation that the amounts of CeO2, La2O3, and NiO in the catalyst would be as shown in Table 1 below.

[0035] Next, while stirring the precursor aqueous solution, an aqueous solution of Na2CO3 containing Na2CO3 as a precipitant (neutralizer) was dropped into the precursor aqueous solution over a period of 30 minutes. 3+ and La 3+ And Ni 2+ An aqueous solution containing 1.35 equivalents of Na2CO3 relative to the amount of the precursor was used. The aqueous precursor solution was then heated at 70°C for 1 hour and allowed to stand overnight to obtain a suspension containing a coprecipitate containing carbonates of Ce and La, as well as a Ni-containing precipitate.

[0036] Next, the suspension was filtered and the coprecipitate obtained by filtration was washed with hot water at 60°C seven times to separate Na from the coprecipitate. + The coprecipitate was then dried in air at 110°C for 12 hours, and then calcined in air at 500°C for 2 hours. This resulted in a powdered methanation catalyst (NiO-La / CeO2) in which NiO was supported on a composite oxide support in which part of the Ce in CeO2 was replaced with La. The La content in the methanation catalyst was measured by ICP-MS, and the results are shown in Table 1 below.

[0037] [Table 1]

[0038] [Evaluation of catalytic activity] The catalytic activity of the methanation catalyst of each example was evaluated by measuring the conversion rate of CO2 in a methanation reaction using the methanation catalysts of each example and comparative example.

[0039] In this case, first, 1 ml of the methanation catalyst of each example was placed in the reactor. Next, the methanation catalyst was subjected to reduction pretreatment. In the reduction pretreatment, the following treatment was performed with the pressure in the reactor set to 1 atm. (1) First, the temperature in the reactor was raised from room temperature to 400°C at a rate of 5°C / min while flowing the reaction gas in the reactor. (2) Next, the temperature in the reactor was maintained at 400°C for 30 minutes while continuing to flow the reaction gas. (3) Next, the temperature in the reactor was cooled to 100°C while flowing N2 (nitrogen) gas in the reactor. In the reduction pretreatment, the same gas as that used in the evaluation of catalytic activity described later was used as the reaction gas, and the flow rate of the reaction gas was also the same as that used in the evaluation of catalytic activity described later.

[0040] Next, catalytic activity was evaluated. In the evaluation of catalytic activity, the pressure inside the reactor was set to 1 atm, and the reaction gas was circulated through the reactor to cause a methanation reaction, while the temperature inside the reactor was raised from 100°C to 400°C at a rate of 5°C / min. The reaction gas used was a gas containing 10% by volume of CO2, 40% by volume of H2, and 50% by volume of N2, and the flow rate of the reaction gas was set to 100 ml / min (space velocity SV = 6000 h -1 ) was used. During the temperature rise process, mass analysis of CO2 in the outlet gas of the reactor was performed using a mass spectrometer. From the results of mass analysis, the CO2 conversion rate was calculated by evaluating the CO2 concentration in the outlet gas during the temperature rise process, and the maximum CO2 conversion rate was obtained. The maximum CO2 conversion rates of the methanation catalysts of the examples and comparative examples are shown in Table 2 below. Figure 3 is a graph showing the maximum CO2 conversion rates of the methanation catalysts of the examples and comparative examples.

[0041] [Table 2]

[0042] As shown in Table 2 and FIG. 3, the maximum CO2 conversion of all of the methanation catalysts of Examples 1 to 9 was greater than that of the methanation catalysts of Comparative Examples 1 to 3. Furthermore, among the methanation catalysts of Examples 1 to 6 in which part of Ce was replaced with Pr, the maximum CO2 conversion of the methanation catalyst of Example 4, in which the Pr content was 2.1 wt%, was the highest. It is considered that when the Pr content was low, the effect of improving the oxidation-reduction properties and oxygen storage properties of CeO2 was not sufficiently obtained. Furthermore, when the Pr content was high, Pr could not be fully incorporated into CeO2, and NiO and CeO2 may have been covered with Pr oxide.

[0043] [Evaluation of the crystal structure of composite oxide supports] The methanation catalysts of Comparative Example 1, Examples 2, 4, and 6, and Examples 7 to 9 were evaluated for changes in crystal structure according to the solid solution of Pr or La in CeO2 in the composite oxide carrier. In this case, a powder sample of the composite oxide carrier was taken from the methanation catalyst of each example, and X-ray diffraction measurement was performed on the powder sample to measure the X-ray diffraction pattern. The measurement was performed under conditions of using CuKα radiation in an inert atmosphere. Then, the predetermined lattice constant of the crystal lattice of CeO2 was obtained from the X-ray diffraction pattern. FIG. 4(a) is a graph showing the relationship between the Pr or La content of the methanation catalysts of Comparative Example 1, Examples 2, 4, and 6, and Examples 7 to 9 and the predetermined lattice constant of the crystal lattice of CeO2. As shown in FIG. 4(a), the predetermined lattice constant of the crystal lattice of CeO2 increased with an increase in the Pr or La content. It is considered that Pr or La was solid-solved in CeO2 as intended during the production of the methanation catalyst, resulting in distortion of the crystal lattice of CeO2. It is expected that the amount of lattice defects will increase due to distortion of the CeO2 crystal lattice.

[0044] [Evaluation of lattice defects in composite oxide supports and the reduced state of NiO] The chemical bond state of the methanation catalyst of Example 4 (NiO-Pr / CeO2) and the methanation catalyst of Comparative Example 1 (NiO-CeO2) was investigated by XPS (X-ray photoelectron spectroscopy) after reduction, and the lattice defects and the reduced state of NiO corresponding to the substitution of Ce with Pr in CeO2 were evaluated. Figure 4(b) is a graph showing the X-ray photoelectron spectroscopy spectra measured by XPS after reduction of the methanation catalyst of Example 4 and the methanation catalyst of Comparative Example 1. In each spectrum shown in Figure 4(b), among the peaks corresponding to the valence of Ni (nickel), the peak near 852 eV is Ni. 0 (Ni metal) peak, and the peak at around 855 eV is Ni 2+ As shown in FIG. 4(b), the spectrum of the methanation catalyst of Example 4 is different from the spectrum of the methanation catalyst of Comparative Example 1 in that the peak of Ni 2+ The intensity of the peak of Ni 0 In the methanation catalyst of Example 4, compared with the methanation catalyst of Comparative Example 1, it is considered that the substitution of Ce in CeO2 by Pr in the composite oxide support increases the lattice defects of the support, and oxygen in NiO is effectively attracted to the lattice defects, thereby effectively promoting the reduction of NiO.

[0045] [Evaluation of CO2 adsorption] For the methanation catalysts (NiO-Pr / CeO2) of Examples 2, 4, and 6, the methanation catalysts (NiO-La / CeO2) of Examples 7, 8, and 9, and the methanation catalyst (NiO-CeO2) of Comparative Example 1, the amount of CO2 adsorbed was determined by TPD-MS (thermal evolved gas mass spectrometry) to evaluate the adsorption of CO2 to the methanation catalysts (composite oxide support) in response to the replacement of Ce in CeO2 with Pr and La on the composite oxide support.

[0046] In this case, first, 0.2 ml (about 0.24 g) of the methanation catalyst of each example was placed in the sample cell of the TPD-MS device. Next, the methanation catalyst was subjected to a reduction pretreatment. In the reduction pretreatment, the following treatment was performed with the pressure in the sample cell set to 1 atm. (1) First, He (helium) gas was circulated in the sample cell at a flow rate of 100 ml / min, while the temperature in the sample cell was kept at 25°C for 10 minutes to purge the sample. (2) Next, the gas was switched, and a reducing gas containing 20% ​​by volume of H2 and 80% by volume of He was circulated in the sample cell at a flow rate of 20 ml / min (H2: flow rate of 4 ml / min and He: flow rate of 16 ml / min), while the temperature in the sample cell was kept at 25°C for 30 minutes. (3) Next, while continuing the flow of the reducing gas, the temperature in the sample cell was raised from 30°C to 500°C at a rate of 20°C / min, and then kept at that temperature for 1 hour. (4) Next, the gas was switched, and He gas was circulated through the sample cell at a flow rate of 100 ml / min. The temperature inside the sample cell was then lowered from 500°C to 30°C and held at that temperature for 30 minutes to purge the sample.

[0047] Next, the amount of CO2 adsorbed on the methanation catalyst was calculated. Specifically, the following process was performed with the pressure in the sample cell set to 1 atm. (1) First, a gas containing 20% ​​by volume of CO2 and 80% by volume of He was circulated through the sample cell at a flow rate of 20 ml / min (CO2: flow rate of 4 ml / min and He: flow rate of 16 ml / min), while the temperature in the sample cell was kept at 30°C for 30 minutes. This allowed CO2 to be adsorbed on the methanation catalyst. (2) Next, the gas was switched, and He gas was circulated through the sample cell at a flow rate of 40 ml / min, while the temperature in the sample cell was kept at 30°C for 30 minutes. (3) Next, while continuing the flow of the He gas, the temperature in the sample cell was raised from 30°C to 700°C at a rate of 10°C / min. During the temperature rise process, a mass spectrometer was used to perform mass analysis of CO2 in the gas released from the sample cell. From the results of mass spectrometry, the CO2 concentration in the gas released from the sample cell during the heating process was evaluated, and the amount of CO2 desorbed from the methanation catalyst during the heating process (amount of desorbed CO2) was calculated as the amount of CO2 adsorbed onto the methanation catalyst.

[0048] FIG. 5(a) is a graph showing the amount of CO2 desorbed during the temperature rise process of the methanation catalyst of Comparative Example 1 and the methanation catalysts of Examples 2, 4, and 6. FIG. 5(b) is a graph showing the amount of CO2 desorbed during the temperature rise process of the methanation catalyst of Comparative Example 1 and the methanation catalysts of Examples 7, 8, and 9. As is clear from the graphs shown in FIG. 5(a) and (b), the methanation catalysts of Examples 2, 4, and 6 and the methanation catalysts of Examples 7, 8, and 9 have an increased amount of CO2 adsorption compared to the methanation catalyst of Comparative Example 1. It is believed that the substitution of Ce in CeO2 with Pr or La in the composite oxide support of the methanation catalyst increases the number of lattice defects that become the adsorption sites of CO2.

[0049] Although the embodiments of the method for producing a methanation catalyst of the present invention have been described in detail above, the present invention is not limited to the above-mentioned embodiments, and various design modifications can be made without departing from the spirit of the present invention described in the claims.

Claims

1. A step of adding a neutralizing agent to a mixed salt solution containing a Ce salt and a salt of a rare earth element (excluding Ce) to obtain a suspension containing a coprecipitate containing the Ce and the rare earth element; adding a Ni salt and a neutralizing agent to the suspension to produce a Ni-containing precipitate in the coprecipitate; and calcining the coprecipitate and the Ni-containing precipitate to obtain a methanation catalyst in which Ni is supported as a catalytic component on a composite oxide support containing Ce and a rare earth element.

2. 2. The method for producing a methanation catalyst according to claim 1, wherein the rare earth element is Pr or La.

3. 3. The method for producing a methanation catalyst according to claim 2, wherein the rare earth element is Pr, and the content of Pr in the methanation catalyst is 0.5% by weight to 3.6% by weight.

4. 3. The method for producing a methanation catalyst according to claim 2, wherein the rare earth element is La, and the La content in the methanation catalyst is 1.0% by weight to 3.9% by weight.

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