JP2025030888A - Catalyst for methanation and method for producing methane - Google Patents

Abstract

To provide a catalyst that enables methanation to proceed at temperatures of 500°C or lower under atmospheric pressure and under low hydrogen concentration, and a method for producing methane.SOLUTION: A catalyst for methanation according to the present disclosure comprises first particles, second particles, and third particles. The first particles comprise a metal comprising at least one selected from the group consisting of nickel, cobalt, and ruthenium. The second particles comprise a composite metal oxide represented by the composition formula ZrSn1-xCexO4, satisfying 0≤x≤0.5. The third particles comprise a ceramic material. The first particles and the second particles are carried on the third particles.SELECTED DRAWING: Figure 1

Description

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

The reaction of producing methane using carbon dioxide (CO ₂ ) and hydrogen (H ₂ ) as raw materials is known as the methanation reaction (sometimes simply called methanation). The methanation reaction is represented by the following reaction formula.
CO ₂ +4H ₂ →CH ₄ +2H ₂ O
Catalysts for use in methanation have been studied. For example, Patent Document 1 discloses a catalyst for methanation comprising a carrier and a catalytic component. In the catalyst disclosed in Patent Document 1, the carrier comprises one or more elements selected from the group consisting of elements such as cerium, lanthanum, praseodymium, and neodymium, and the catalytic component comprises nickel supported on the carrier.

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

JP 2019-155227 A JP 2020-33280 A

The methanation reaction is an exothermic reaction, but from about 500°C, carbon monoxide is generated by the reverse water gas shift reaction. For this reason, in consideration of reaction efficiency and safety, it is preferable to be able to carry out methanation at 500°C or less and at normal pressure. In addition, hydrogen gas, which is the raw material, is flammable and has an explosion range in air (the explosion concentration range of hydrogen in air is 4.0 to 75%). From the viewpoint of safety, it is preferable to be able to carry out the methanation reaction at a hydrogen concentration below the explosion limit. Therefore, one of the objectives of the present disclosure is to provide a catalyst and a method for producing methane that can proceed with methanation even at a low hydrogen concentration under normal pressure conditions at a temperature of 500°C or less.

The catalyst for methanation according to the present disclosure includes first particles, second particles, and third particles. The first particles are made of a metal including at least one selected from the group consisting of nickel, cobalt, and ruthenium. The second particles are made of _a composite metal oxide represented by a composition formula of ZrSn1 _{- xCexO4} , where 0≦x≦0.5 is satisfied. The third particles are made of a ceramic material. The first particles and the second particles are supported on the third particles.

The above catalyst allows methanation to proceed even at temperatures below 500°C, under normal pressure conditions, and with low hydrogen concentrations.

1 is a graph showing the relationship between reaction temperature and _CO2 conversion rate in methanation using the catalysts of Example 1 and Comparative Example 1. 1 is a graph showing the relationship between reaction temperature and methane yield in methanation using the catalysts of Example 1 and Comparative Example 1. 1 is a graph showing the relationship between reaction temperature and _CO2 conversion rate in methanation using the catalysts of Examples 2 to 6. 1 is a graph showing the relationship between reaction temperature and methane yield in methanation using the catalysts of Examples 2 to 6. 1 is a graph showing the relationship between reaction temperature and _CO2 conversion rate in methanation using the catalysts of Examples 7 to 11. 1 is a graph showing the relationship between reaction temperature and methane yield in methanation using the catalysts of Examples 7 to 11. 1 is a graph showing the relationship between reaction temperature and _CO2 conversion rate in methanation using the catalysts of Examples 12 to 17. 1 is a graph showing the relationship between reaction temperature and methane yield in methanation using the catalysts of Examples 12 to 17. 1 is a flow chart illustrating a method for producing methane using a catalyst according to the present disclosure.

[Overview of the embodiment]
First, the catalysts and production methods according to the present disclosure will be listed and described.
The catalyst for methanation according to the present disclosure includes first particles, second particles, and third particles. The first particles are made of a metal including at least one selected from the group consisting of nickel, cobalt, and ruthenium. The second particles are made of _a composite metal oxide represented by a composition formula of ZrSn1 _{- xCexO4} , where 0≦x≦0.5 is satisfied. The third particles are made of a ceramic material. The first particles and the second particles are supported on the third particles.

Methanation is a reaction that converts carbon dioxide into methane using hydrogen. Methanation can reduce carbon dioxide and reuse the methane produced as fuel gas. Expectations are high for methanation as a technology that can achieve carbon neutrality, and catalysts for methanation and methods for using them are being studied. Patent Document 1 discloses a method for carrying out methanation using a catalyst with a specific composition. In the examples of Patent Document 1, it is described that a raw material gas consisting of 80 mol % hydrogen and 20 mol % carbon dioxide, and a raw material gas consisting of 8 mol % hydrogen, 2 mol % carbon dioxide, and 90 mol % nitrogen were used as the raw material gas.

Patent Document 2 discloses a method for producing methane by methanation using a specific catalyst. Patent Document 2 discloses a method using a raw material gas containing carbon dioxide, hydrogen, and oxygen. In practice, the technology of Patent Document 2 proposes a method for efficiently producing methane even in the presence of oxygen, taking into consideration that exhaust gases and the like that serve as raw material gas for methanation may contain not only carbon dioxide and hydrogen but also oxygen. In the examples of Patent Document 2, a mixed gas consisting of 10% by volume of carbon dioxide, 10% by volume of oxygen, 60% by volume of hydrogen, and the remainder of nitrogen is used as the raw material gas.

If the concentrations of carbon dioxide and hydrogen contained in the raw gas are low, the methanation reaction is thermodynamically disadvantageous. On the other hand, since hydrogen has an explosive range in air, it is desirable that the methanation reaction proceeds even at a low hydrogen concentration, such as below the explosive limit (4% or less). In addition, in order to increase the reaction efficiency, it is possible to carry out methanation under pressure, but from the viewpoint of energy efficiency and safety, it is desirable that methanation proceeds even at normal pressure. According to the catalyst of the present disclosure, even when a raw gas with a low hydrogen concentration is used and the reaction is carried out at normal pressure, a sufficient carbon dioxide conversion rate and methane yield can be obtained. Although it is not bound by a particular theory, it is believed that the catalyst of the present disclosure has a configuration in which zirconium tin oxide (ZrSnO ₄ ), which is a metal oxide having oxidation-reduction ability because it contains Sn, which is easily changed in valence, and a catalytic metal (typically Ni) having hydrogen dissociation ability are supported on a ceramic material with a high specific surface area, thereby enhancing the oxidation-reduction ability and exhibiting excellent catalytic activity in methanation. Furthermore, this effect is even more pronounced when cerium (Ce) is added to a portion of the tin (Sn).

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

In the catalyst for methanation, the content of the second particles may be 5% by mass or more and 60% by mass or less with respect to the total mass of the second particles and the third particles. When it is in this range, the effects of the present disclosure can be obtained more reliably.

In the catalyst for methanation, the ceramic material may be one or more selected from the group consisting of alumina, silica, cordierite, and mullite. These ceramic materials are known materials with excellent stability, and can stably obtain a catalyst supporting a catalytically active substance including a catalytic metal and a composite metal oxide.

The method for producing methane according to the present disclosure includes the steps of preparing a feed gas containing carbon dioxide and hydrogen, and contacting the feed gas with a catalyst for methanation to produce methane from carbon dioxide and hydrogen. According to the production method according to the present disclosure, even when a feed gas with a low hydrogen concentration is used, the carbon dioxide conversion rate and methane yield are high, and methane can be suitably obtained.

In the method, the hydrogen concentration in the source gas may be 1% by volume or more and 8% by volume or less based on the volume of the source gas. When it is within this range, the effect of the present disclosure becomes more evident.

[Specific Example of the Embodiment]
The catalyst and the method for producing methane according to the present disclosure will be described in more detail below with reference to specific examples of embodiments.

(catalyst)
The catalyst according to the present disclosure is a catalyst including a first particle, a second particle, and a third particle. The first particle includes a catalytic metal. The second particle includes a composite metal oxide. The third particle is a ceramic material. In the catalyst according to the present disclosure, the first particle and the second particle are supported by the third particle. At least a portion of the first particle is in contact with the surface of the second particle. That is, at least a portion of the first particle is supported by the second particle. The second particle is in contact with the surface of the third particle. The first particle includes a particle in contact with the surface of the second particle and the surface of the third particle, and a particle in contact only with the surface of the second particle and supported by the third particle via the second particle.

The composition of the first particles can be confirmed, for example, by X-ray diffraction (XRD), and the existence of the first particles can be confirmed. The particle morphology of the second and third particles can be confirmed, for example, by a scanning electron microscope (SEM) or a transmission electron microscope (TEM), and the composition of the particles can be confirmed by X-ray diffraction (XRD) or X-ray fluorescence analysis.

(First particle)
The first particles are made of at least one metal selected from the group consisting of nickel, cobalt, and ruthenium. The metal constituting the first particles may be one type or may contain two or more types. The metal as the first particles is a catalytic metal that has hydrogen dissociation ability and functions as a catalyst for promoting a methanation reaction.

The first particles preferably contain nickel. The nickel content in the first particles may be 50% by mass or more, preferably 70% by mass or more, based on the entire first particle, and preferably consists essentially of nickel. "Substantially consists of nickel" means that the first particles are composed of nickel, excluding unavoidable impurities.

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

(Second Particle)
The second particles are made of an oxide represented by the composition formula ZrSn _1-x Ce _x O ₄ and satisfy 0≦x≦0.5. That is, the second particles are ZrSnO ₄ or a composite metal oxide to which cerium (Ce) is added as a part of Sn in ZrSnO _4. x is 0 or more and preferably 0.5 or less, more preferably 0.3 or less. When x=0, it means that Ce is not included, and the composite metal oxide constituting the second particles is ZrSnO _4. The second particles of the catalyst according to the present disclosure are not limited to those containing Ce, but the oxidation-reduction ability of the catalyst can be further improved by adding Ce.

In the catalyst according to the present disclosure, the content ratio of the second particles, which are composite metal oxides, is not limited as long as it has the effect according to the present disclosure, but may be 5% by mass to 60% by mass, and preferably 8% by mass to 53% by mass, relative to the mass of the catalyst. The content ratio of the second particles may be 5% by mass to 60% by mass, and preferably 10% by mass to 60% by mass, relative to the total mass of the second particles and the third particles. If the content ratio of the second particles is 5% by mass or more relative to the total mass of the second particles and the third particles, an effect of converting carbon dioxide in the feed gas and promoting methanation is obtained. If the content ratio of the second particles is 60% by mass or less, a sufficient catalytic effect is obtained.

(Third particle)
The third particles constituting the catalyst according to the present disclosure are ceramic materials that function as carriers. The ceramic materials may be, for example, one or more selected from the group consisting of alumina (Al ₂ O ₃ ), silica (SiO ₂ ), cordierite (2MgO.2Al ₂ O _{3.5SiO 2} ) and mullite (3Al ₂ O _{3.2SiO 2} ). The above materials are suitable as ceramic materials constituting the third particles.

Among these, γ-alumina, which is a cubic crystal, can be preferably used. The third particles function as a dispersion medium. When the catalyst contains the third particles, the first particles and the second particles are prevented from agglomerating with each other, and a decrease in the surface area of the first particles and the second particles can be prevented. The average particle size of the third particles is, for example, 5 nm or more, and preferably 10 nm or more. The upper limit of the average particle size of the third particles is not particularly limited, but is, for example, less than 1 μm.

The content ratio of the third particles in the catalyst according to the present disclosure can be appropriately determined according to the content ratio of the second particles and the first particles.

(Catalyst Function)
The catalyst according to the present disclosure is used as a catalyst for producing methane. The catalyst according to the present disclosure promotes a methanation reaction. The activity of the catalyst can be indicated by _CO2 conversion, _CH4 yield, and _CH4 selectivity. The _CO2 conversion is the ratio of the decrease in the _CO2 concentration in the gas obtained after the reaction to the _CO2 concentration in the raw gas when the raw gas is contacted with a constant amount of catalyst at a constant temperature. The _CH4 yield is the ratio of the _CH4 concentration in the gas after the reaction to the _CO2 concentration in the raw gas. The _CH4 selectivity is the ratio of the _CH4 yield to the _CO2 conversion.

The catalyst according to the present disclosure may have a _CO2 conversion rate of 10% or more at a reaction temperature of 250°C to 400°C. At this time, the _CH4 selectivity may be 54% or more. Preferably, the _CO2 conversion rate at a reaction temperature of 300°C to 350°C may be 27% or more. At this time, the _CH4 selectivity may be 67% or more. The performance of such a catalyst according to the present disclosure is not particularly limited, but for example, the _CO2 conversion rate at 250°C is 10% or more and the _CH4 selectivity is 55% or more. For example, the _CO2 conversion rate at 300°C is 27% or more and the _CH4 selectivity is 69% or more. For example, the _CO2 conversion rate at 350°C is 42% or more and the _CH4 selectivity is 67% or more. For example, the _CO2 conversion rate at 400°C is 42% or more and the _CH4 selectivity is 54% or more. For example, the _CO2 conversion rate is 43% or more and the _CH4 selectivity is 26% or more at 450° C. For example, the _CO2 conversion rate is 47% or more and the _CH4 selectivity is 5% or more at 500° C.

The catalyst disclosed herein can cause methanation to proceed even when the carbon dioxide and hydrogen concentrations in the feed gas are low. For example, methanation can proceed even when the hydrogen concentration in the feed gas is 10% or less, typically 4% or less. Hydrogen gas is a flammable gas, and the explosive concentration range of hydrogen in air is 4.0% to 75%. When the catalyst disclosed herein is used, methanation can proceed even when the hydrogen concentration is below the lower explosive concentration limit, making methane production safer.

(Catalyst Manufacturing Method)
The method for producing the catalyst according to the present disclosure is not particularly limited, but it can be produced, for example, by the following method. First, ZrSn _1-x Ce _x O ₄ , which is the second particle, is prepared. ZrSn _1-x Ce _x O ₄ can be suitably obtained by the so-called coprecipitation method. Specifically, for example, an aqueous ammonia solution is slowly added to a nitric acid aqueous solution containing zirconyl nitrate, tin oxalate, and cerium (IV) ammonium nitrate in a predetermined ratio, and the mixture is stirred to obtain a precipitate. This precipitate is recovered, dried, and then fired. Through these steps, ZrSn _1-x Ce _x O ₄ is obtained. Next, the obtained composite metal oxide is mixed with a ceramic material as the third particle, and fired to obtain a composition in which the composite metal oxide as the second particle is supported on the ceramic material as the third particle.

Furthermore, the composition and a nitrate of a catalytic metal (e.g., Ni) can be composited by a carboxylic acid complex polymerization method. More specifically, the composition and an aqueous solution of a nitrate or chloride of the catalytic metal are evaporated to dryness to produce a carboxylic acid complex polymer. The resulting carboxylic acid complex polymer is then fired. In this way, a catalytic metal as the first particle, a composite oxide as the second particle, and a ceramic material as the third particle can be composited.

Specific examples of carboxylic acids used in carboxylic acid complex polymerization include oxalic acid, malonic acid, glycolic acid, lactic acid, malic acid, tartaric acid, glyoxylic acid, citric acid, and gluconic acid, with malic acid being preferred. The calcination process for the carboxylic acid complex polymer can be carried out, for example, in air at 400°C to 600°C for 1 to 6 hours. These calcination temperatures and times result in a catalyst with excellent methanation activity.

The obtained catalyst may be used alone or may be mixed with other materials to be used as a catalyst composition. Prior to the calcination step, the catalyst material according to the present disclosure may be mixed with other materials and calcined together.

(Method of Producing Methane)
A method for producing methane using the catalyst according to the present disclosure will now be described. Figure 9 is a flow chart showing a method for producing methane using the catalyst according to the present disclosure.

Referring to FIG. 9, in the method for producing methane using the catalyst according to the present disclosure, first, a preparation step (S10) is carried out in which a raw material gas is prepared. The raw material gas contains carbon dioxide and hydrogen. When the catalyst according to the present disclosure is used, methanation occurs and methane can be obtained even when the hydrogen concentration in the raw material gas is relatively low.

The concentration of carbon dioxide in the raw gas is not particularly limited as long as the effects of the present disclosure are obtained, but may be, for example, 1 vol.% or more, 2 vol.% or more, or 3 vol.% or more, and 50 vol.% or less, 20 vol.% or less, 10 vol.% or less, or 8 vol.% or less, based on the volume of the raw gas. The concentration of hydrogen in the raw gas is not particularly limited as long as the effects of the present disclosure are obtained, but may be, for example, 1 vol.% or more, 2 vol.% or more, or 4 vol.% or more, and 90 vol.% or less, 80 vol.% or less, 50 vol.% or less, or 10 vol.% or less, based on the volume of the raw gas. The concentration of hydrogen in the raw gas may typically be 1 vol.% or more and 8 vol.% or less, based on the volume of the raw gas.

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

Next, the methanation step is carried out (S20). Specifically, methanation can be carried out by introducing a raw material gas into a reaction tube filled with the catalyst according to the present disclosure and contacting the raw material gas with the catalyst. The flow rate of the raw material gas introduced into the reaction tube is appropriately selected according to the diameter of the reaction tube. For example, when a reaction tube with a diameter of 10 mm is used, the flow rate of the raw material gas can be 1 to 50 mL/min, preferably 10 to 50 mL/min. The catalyst may be directly filled into the reaction tube, or may be held in a state of being attached to the surface of a substrate, for example, a ceramic honeycomb structure. When the catalyst is filled into the reaction tube, the amount of the catalyst can be appropriately selected according to the diameter of the reaction tube and the flow rate of the reaction gas. For example, the amount of catalyst placed in one reaction tube may be 10 mg to 10 g, and preferably 10 mg to 1 g. When the catalyst is held on the surface of the substrate, a catalyst layer can be formed on the surface of the substrate by applying a catalyst slurry to the surface of the substrate. The amount of catalyst carried may be, for example, from 0.01 to 10 mg/mm ² based on the surface area of the substrate.

The reaction tube is maintained at a temperature at which methanation occurs. The temperature of the reaction tube may be, for example, a temperature exceeding 200°C, for example, 210°C or more, 220°C or more, 250°C or more, or 270°C or more. The temperature of the reaction tube may be 400°C or less, 370°C or less, or 360°C or less. The methanation reaction can be confirmed, for example, by measuring the carbon dioxide concentration in the raw material gas introduced into the reaction tube and the reaction gas discharged from the reaction tube. The heat source for heating the reaction tube is not particularly limited, and may be, for example, an electric furnace using an electric heater, or other heat medium. The temperature of the reaction tube may be constant during the methanation step (S20), or may be changed according to the progress of the reaction.

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

The present invention will now be described in more detail with reference to examples, although the present invention is not limited to these examples.
A catalyst according to the present disclosure was prepared as follows, and the structure of the catalyst and the progress of the methanation reaction were confirmed.

[Example 1]
Deionized water (25 mL), ZrO(NO ₃ ) _{2.2H 2} O (0.4864 g), SnC ₂ O ₄ (0.2025 g), and (NH ₄ ) ₂ Ce(NO ₃ ) ₆ (0.2302 g) were mixed. Then, 10 mL of 60% HNO ₃ was added. At room temperature, 28% NH ₃ (20 mL) was slowly added and stirred for 4 hours. After stirring, the precipitate was collected by suction filtration and dried at 80° C. for 1 hour. Then, it was fired at 600° C. for 1 hour under air flow. Through the above process, cerium-doped zirconium tin oxide (ZrSn _0.7 Ce _0.3 O ₄ ), which is a metal oxide, was obtained.
Next, _{ZrSn0.7Ce0.3O4} ( _{0.2 g} ) and γ- _Al2O3 (0.8 _g ) were mixed in ethanol (25 mL) using a ball mill at 300 rpm for 3 hours. After mixing, the mixture was fired in air at ₅₀₀ °C for 4 hours. Through the above steps, a composition in _{which ZrSn0.7Ce0.3O4} was supported on _γ -alumina (20 wt% _{ZrSn0.7Ce0.3O4} / _γ - _{Al2O3 )} was obtained.
0.40 g of this composition was taken and placed in deionized water (40 mL), and Ni(NO ₃ ) _{2.6H 2} O (0.462 g), propylene glycol (0.558 mL), and malic acid (0.590 g, 3 equivalents relative to Ni) were added. The mixture was then stirred at 90°C for 4 hours. After stirring was completed, the mixture was heated to 150°C to remove the solvent. The mixture was then calcined in air at 500°C for 4 hours. In this way, a catalyst (18 wt% Ni/20 wt% ZrSn _0.7 Ce _0.3 O ₄ /γ-Al ₂ O ₃ ) in which ZrSn _0.7 Ce _0.3 O ₄ and Ni were supported on γ-alumina was obtained.

(Methanation device)
Using the catalyst obtained above, methanation was carried out under the following conditions to confirm the performance of the catalyst.
A 0.1 g catalyst sample was filled into a reaction tube. To hold the catalyst sample at a predetermined position in the reaction tube, both ends of the catalyst sample were filled with quartz wool. The reaction tube was placed in an electric furnace and heated so that the temperature of the gas introduced into the reaction tube reached a predetermined temperature.
Cylinders containing carbon dioxide, hydrogen and argon gas were prepared, and the gases were taken out and mixed in a predetermined ratio to prepare a raw material gas. The composition (volume ratio) of the raw material gas was 1% CO ₂ -4% H ₂ -95% Ar. This raw material gas was introduced into the reaction tube at a flow rate of 50 mL/min, and methanation was performed by passing it through the reaction tube. Methanation was performed at reaction temperatures of 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C and 500°C.

(Analysis of gas after reaction)
The composition of the gas passing through the reaction tube was analyzed using GC-MS (Shimadzu Corporation, GCMS-QP2010plus), and the _CO2 conversion rate, _CH4 yield, and _CH4 selectivity were calculated using the following formulas.

_CO2 conversion rate (%) = (1 - [ _CO2 ] / [ _CO2 ] ₀ ) x 100
_CH4 yield (%) = [ _CH4 ] / [ _CO2 ] ₀ × 100
_CH4 selectivity (%) = ( _CH4 yield) / ( _CO2 conversion rate) x 100
In the above formula, [CO ₂ ] ₀ represents the CO ₂ concentration in the raw gas, [CO ₂ ] represents the CO ₂ concentration in the gas after passing through the reaction tube, and [CH ₄ ] represents the CH ₄ concentration in the gas after passing through the reaction tube.

[Comparative Example 1]
As a comparative example, methanation was carried out in the same manner as in Example 1, except that a catalyst in which Ni was supported on γ-alumina (12 wt % Ni/γ-Al ₂ O ₃ ) was used as the catalyst, and the gas after the reaction was analyzed.

The results of Example 1 and Comparative Example 1 when the reaction temperature was 300°C are shown in Table 1. In addition, a graph of the _CO2 conversion rate at each reaction temperature is shown in Figure 1, and a graph of the _CH4 yield (%) at each reaction temperature is shown in Figure 2. The dotted line (indicated as Equilibrium) in Figure 1 indicates the _CO2 conversion rate that thermodynamically corresponds to the reaction equilibrium at each temperature. The dotted line (indicated as Equilibrium) in Figure 2 indicates the _CO2 conversion rate that corresponds to the reaction equilibrium at each temperature.

As shown in Table 1, the catalyst of Example 1 had a significantly higher _CO2 conversion rate and _CH4 yield than the catalyst of Comparative Example 1, which did not support zirconium tin oxide. Also, as shown in Figures 1 and 2, it was confirmed that the methanation reaction proceeded sufficiently when the catalyst of Example 1 was used, even when a raw material gas with a carbon dioxide concentration of 1% and a hydrogen concentration of 4% was used. The effect of the catalyst of Example 1 was particularly clear in the range of less than 400°C.

(Study of cerium doping ratio)
In Examples 2 to 6, the ratio of cerium added to zirconium tin oxide was changed to examine the relationship with methanation. The amount of Ni supported was fixed at 12 wt%.

[Example 2]
Zirconium tin oxide (ZrSnO ₄ ) was obtained in the same manner as in Example 1, except that (NH ₄ ) ₂ Ce(NO ₃ ) ₆ was not used as a raw material. This zirconium tin oxide was supported on γ-alumina by a method similar to Example 1 to obtain a γ-alumina-supported zirconium tin oxide composition. Furthermore, Ni was supported on this composition by a method similar to Example 1 to obtain a catalyst in which ZrSnO ₄ and Ni were supported on γ-alumina (12 wt % Ni/40 wt % ZrSnO ₄ /γ-Al ₂ O ₃ ).

[Example 3]
Cerium-doped zirconium tin oxide (ZrSn _0.95 Ce _0.05 O ₄ ) was obtained in the same manner as in Example 1, except that the amounts of SnC ₂ O ₄ and (NH ₄ ) ₂ Ce(NO ₃ ) ₆ used as raw materials were changed.
In addition, a composition in which ZrSn _0.95 Ce _0.05 O ₄ is supported on γ-alumina (40 wt % ZrSn _0.95 Ce _0.05 O ₄ /γ-Al ₂ O ₃ ) was obtained in the same manner as in Example 1, except that the amount of ZrSn _0.95 Ce _0.05 O ₄ relative to γ-Al ₂ O ₃ was changed.
A catalyst in which _{ZrSn0.95Ce0.05O4} and Ni were supported on γ-alumina ( ₁₂ wt%Ni/40 wt%ZrSn0.95Ce0.05O4/ _γ - _Al2O3 ) was obtained in the same manner as in Example ₁ , except that the amount of Ni( _NO3 ) _2.6H2O relative _{to the composition} was _changed .

[Example 4]
A catalyst in which _{ZrSn0.90Ce0.10O4} and _Ni were supported on γ-alumina _{( 12 wt% Ni/} 40 wt% ZrSn0.90Ce0.10O4/γ- _Al2O3 ) was obtained in the same manner as in Example 3, except that _the amounts _of SnC2O4 and ( _NH4 ) _{2Ce ( NO3} ) ₆ used as raw materials were changed _.

[Example 5]
A catalyst in which _{ZrSn0.80Ce0.20O4} and _Ni were supported on γ-alumina _{( 12 wt% Ni/} 40 wt% ZrSn0.80Ce0.20O4/γ- _Al2O3 ) was obtained in the same manner as in Example 3, except that _the amounts _of SnC2O4 and ( _NH4 ) _{2Ce ( NO3} ) ₆ used as raw materials were changed _.

[Example 6]
A catalyst in which _{ZrSn0.70Ce0.30O4} and _Ni were supported on γ-alumina _{( 12 wt% Ni/} 40 wt% ZrSn0.70Ce0.30O4/γ- _Al2O3 ) was obtained in the same manner as in Example 3, except that the amounts _of SnC2O4 and ( _NH4 ) _{2Ce ( NO3} ) ₆ used as raw materials were _{changed .}

(Methanation)
Using each of the catalysts of Examples 2 to 6, methanation was carried out in the aforementioned methanation apparatus under the same conditions as in Example 1 at reaction temperatures of 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, and 500°C.

Table 2 shows the results of methanation using the catalysts of Examples 3 to 6 at a reaction temperature of 350°C. For the catalysts of Examples 2 to 6, a graph of the _CO2 conversion rate at each reaction temperature is shown in FIG. 3, and a graph of the _CH4 yield (%) at each reaction temperature is shown in FIG. 4. The dotted lines in FIG. 3 show the _CO2 conversion rate corresponding to the reaction equilibrium at each temperature. The dotted lines in FIG. 4 show the _CO2 conversion rate corresponding to the reaction equilibrium at each temperature.

As shown in Table 2, when the catalysts of Examples 3 to 6 were used to carry out the reaction at a reaction temperature of 350°C, the _CO2 conversion rate was about 50%, and it was confirmed that the methanation reaction proceeded even when the hydrogen concentration in the raw gas was 4% and the carbon dioxide concentration was 1%. In addition, the _CH4 selectivity was 70% or more, and in particular, in Example 5, it exceeded 80%, and it was confirmed that the conversion efficiency to methane was excellent. As shown in Figures 3 and 4, it was confirmed that methanation occurred in a temperature range exceeding 200°C when the catalysts of Examples 2 to 6 were used. The _CH4 yield was the best around 350°C.

(Consideration of Support Ratio 1)
In Examples 7 to 11, the Ni loading ratio was fixed at 12 wt %, and the relationship between the ZrSn _0.7 Ce _0.3 O ₄ loading ratio and methanation was examined.

[Example 7]
As in Example 1, cerium-doped zirconium tin oxide (ZrSn _0.7 Ce _0.3 O ₄ ) was obtained.
Next, cerium-doped _zirconium tin oxide ( _{ZrSn0.7Ce0.3O4} ) and nickel (Ni) were supported on γ-alumina in the same manner as in Example ₁ , except that the amount of support relative to γ-alumina was changed, to obtain a catalyst in which _{ZrSn0.7Ce0.3O4} and Ni were supported on γ- _{alumina ( 12} wt% _Ni /10 _wt %ZrSn0.7Ce0.3O4/γ- _Al2O3 ) _.

[Example 8]
A catalyst in which ZrSn _0.7 Ce _0.3 O ₄ and Ni were supported on γ-alumina (12 wt % Ni/20 wt % ZrSn _0.7 Ce _0.3 O ₄ /γ-Al ₂ O ₃ ) was obtained in the same manner as in Example 7, except that the supported amounts were changed.

[Example 9]
A catalyst in which ZrSn _0.7 Ce _0.3 O ₄ and Ni were supported on γ-alumina (12 wt % Ni/30 wt % ZrSn _0.7 Ce _0.3 O ₄ /γ-Al ₂ O ₃ ) was obtained in the same manner as in Example 7, except that the supported amounts were changed.

[Example 10]
A catalyst in which ZrSn _0.7 Ce _0.3 O ₄ and Ni were supported on γ-alumina (12 wt % Ni/40 wt % ZrSn _0.7 Ce _0.3 O ₄ /γ-Al ₂ O ₃ ) was obtained in the same manner as in Example 7, except that the supported amounts were changed.

[Example 11]
A catalyst in which ZrSn _0.7 Ce _0.3 O ₄ and Ni were supported on γ-alumina (12 wt % Ni/60 wt % ZrSn _0.7 Ce _0.3 O ₄ /γ-Al ₂ O ₃ ) was obtained in the same manner as in Example 7, except that the supported amounts were changed.

(Methanation)
Using each of the catalysts of Examples 7 to 11, methanation was carried out in the above-mentioned methanation apparatus under the same conditions as in Example 1 at reaction temperatures of 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, and 500°C.

The results of Examples 7 to 11 when the reaction temperature was 350°C are shown in Table 3. In addition, for the catalysts of Examples 7 to 11, a graph of the _CO2 conversion rate at each reaction temperature is shown in FIG. 5, and a graph of the _CH4 yield (%) at each reaction temperature is shown in FIG. 6. The dotted lines in FIG. 5 show the _CO2 conversion rate corresponding to the reaction equilibrium at each temperature. The dotted lines in FIG. 6 show the _CO2 conversion rate corresponding to the reaction equilibrium at each temperature.

As shown in Table 3, when the catalysts of Examples 7 to 11 were used to carry out the reaction at a reaction temperature of 350°C, the _CO2 conversion rate was 43.3% to 57.7%, and it was confirmed that the methanation reaction proceeded even when the hydrogen concentration in the raw gas was 4% and the carbon dioxide concentration was 1%. In addition, the _CH4 selectivity was 77.5% or more, and in particular, in Examples 9 and 10, it was confirmed that the conversion efficiency to methane was excellent, exceeding 80%. As shown in Figures 5 and 6, it was confirmed that methanation occurred in a temperature range exceeding 200°C when the catalysts of Examples 7 to 11 were used. The _CH4 yield was the best around 350°C.

(Consideration of Support Ratio 2)
In Examples 12 to 17, the supported ratio of ZrSn _0.7 Ce _0.3 O ₄ was fixed at 20 wt %, and the relationship between the supported Ni ratio and the methanation efficiency was examined.

[Example 12]
As in Example 1, cerium-doped zirconium tin oxide (ZrSn _0.7 Ce _0.3 O ₄ ) was obtained.
Next, a catalyst in which _{ZrSn0.7Ce0.3O4} and Ni _were supported on γ-alumina (6 wt% _Ni /20 wt% _{ZrSn0.7Ce0.3O4} /γ- _{Al2O3 )} was obtained by a method similar to that of Example 1, except that the amounts _of cerium-doped zirconium tin oxide _{( ZrSn0.7Ce0.3O4} ) and nickel (Ni) supported on _γ - _alumina were changed.

[Example 13]
A catalyst in which _{ZrSn0.7Ce0.3O4} and _Ni were supported on γ-alumina ( ₁₂ wt% _Ni / ₂₀ wt% _{ZrSn0.7Ce0.3O4} /γ- _Al2O3 ) was obtained in the same manner as in Example 12, except that the amounts of cerium-doped zirconium tin oxide _{( ZrSn0.7Ce0.3O4 )} and nickel (Ni) supported on _γ -alumina were changed.

[Example 14]
A catalyst in which _{ZrSn0.7Ce0.3O4} and Ni _were supported on γ-alumina (15 wt% _{Ni / 20} wt% _{ZrSn0.7Ce0.3O4} /γ- _Al2O3 ) was obtained by a method similar to that of Example 12, except that the amount of cerium-doped zirconium tin oxide _{( ZrSn0.7Ce0.3O4 )} and nickel (Ni) supported on _γ -alumina was changed.

[Example 15]
A catalyst in which _{ZrSn0.7Ce0.3O4} and Ni _were supported on γ-alumina (18 wt% _{Ni / 20} wt% _{ZrSn0.7Ce0.3O4} /γ- _Al2O3 ) was obtained by a method similar to that of Example 12, except that the amount of cerium-doped zirconium tin oxide _{( ZrSn0.7Ce0.3O4 )} and nickel (Ni) supported on _γ -alumina was changed.

[Example 16]
_{A catalyst in which ZrSn0.7Ce0.3O4 and Ni were supported on γ-alumina (24 wt%Ni/20 wt % ZrSn0.7Ce0.3O4 / γ} - _Al2O3 ) was obtained in the same manner as in Example 12, except that the amounts of cerium-doped zirconium tin oxide _{( ZrSn0.7Ce0.3O4 )} and nickel (Ni) supported on _γ -alumina were changed.

[Example 17]
A catalyst in which _{ZrSn0.7Ce0.3O4} and Ni _were supported on γ-alumina (30 wt% _{Ni / 20} wt% _{ZrSn0.7Ce0.3O4} /γ- _Al2O3 ) was obtained by a method similar to that of Example 12, except that the amount of cerium-doped zirconium tin oxide _{( ZrSn0.7Ce0.3O4 )} and nickel (Ni) supported on _γ -alumina was changed.

(Methanation)
Using each of the catalysts of Examples 12 to 17, methanation was carried out in the above-mentioned methanation apparatus under the same conditions as in Example 1 at reaction temperatures of 150°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C, and 500°C.

The results of Examples 12 to 17 when the reaction temperature was 300°C are shown in Table 4. In addition, for the catalysts of Examples 12 to 17, a graph of the _CO2 conversion rate at each reaction temperature is shown in FIG. 7, and a graph of the _CH4 yield (%) at each reaction temperature is shown in FIG. 8. The dotted lines in FIG. 7 show the _CO2 conversion rate corresponding to the reaction equilibrium at each temperature. The dotted lines in FIG. 8 show the _CO2 conversion rate corresponding to the reaction equilibrium at each temperature.

As shown in Table 4, when the catalysts of Examples 12 to 17 were used to carry out the reaction at a reaction temperature of 300°C, the _CO2 conversion rate was 27.7% to 68.4%, and it was confirmed that the methanation reaction proceeded even when the hydrogen concentration in the raw gas was 4% and the carbon dioxide concentration was 1%. In addition, the _CH4 selectivity was 73.8% or more, and it was confirmed that it exceeded 80% in Examples 12, 16, and 17 in particular, and that the conversion efficiency to methane was excellent. As shown in Figures 7 and 8, it was confirmed that methanation occurred in a temperature range of more than 200°C when the catalysts of Examples 12 to 17 were used. The _CH4 yield was the best around 300°C.

It should be understood that the embodiments and examples disclosed herein are illustrative in all respects and are not limiting in any respect. The scope of the present invention is indicated by the claims, not by the meaning described above, and is intended to include all modifications within the meaning and scope of the claims.

The catalyst of the present application is particularly advantageously used as a catalyst for the production of methane using a methanation reaction.

Claims (6)

comprising first particles, second particles, and third particles,
the first particles are made of at least one metal selected from the group consisting of nickel, cobalt, and ruthenium;
The second particles are made of a composite metal oxide represented by a composition formula of ZrSn1 _{-xCexO4 ,} where 0≦x≦0.5 is satisfied _;
the third particles are made of a ceramic material;
A catalyst for methanation, wherein the first particles and the second particles are supported on the third particles. At least a portion of the first particles contact the second particles;
The content ratio of the first particles is 3 mass% or more and 40 mass% or less with respect to the mass of the catalyst.
Catalyst for methanation according to claim 1. The content ratio of the second particles is 5 mass% or more and 60 mass% or less with respect to the total mass of the second particles and the third particles.
Catalyst for methanation according to claim 1 or claim 2. The ceramic material is at least one selected from the group consisting of alumina, silica, cordierite, and mullite.
Catalyst for methanation according to claim 1 or claim 2. Providing a feed gas comprising carbon dioxide and hydrogen;
and contacting the feed gas with the catalyst for methanation according to claim 1 or 2 to produce methane from carbon dioxide and hydrogen.
A method for producing methane. The hydrogen concentration in the source gas is 1 vol% or more and 8 vol% or less based on the volume of the source gas.
6. The method for producing methane according to claim 5.

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