JP2019155227A - Co2 methanation catalyst and carbon dioxide reduction method using the same - Google Patents

Abstract

To provide a catalyst showing a high COmethanation performance in a wide temperature range.SOLUTION: The present invention provides a COmethanation catalyst that converts carbon dioxide into methane using hydrogen, the catalyst containing a support and a catalyst component, the support containing one or more selected from the group consisting of Ce, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, and the catalyst component containing Ni supported on the support.SELECTED DRAWING: Figure 2

Description

The present invention relates to a CO ₂ methanation catalyst and a method for reducing carbon dioxide using the same.

In order to prevent environmental pollution such as global warming, it is important to reduce carbon dioxide emissions. In order to suppress the emission of carbon dioxide (CO ₂ ), means such as storing the separated and recovered CO ₂ in the ground are often taken. In addition, surplus power tends to increase with the introduction of renewable energy.

Since hydrogen (H ₂ ) is mainly obtained by electrolysis of water, a large amount of H ₂ can be synthesized at low cost by using surplus power. By using H ₂ obtained in this way and separated and recovered CO ₂ , it is possible to effectively use the CO ₂ without storing it by converting methane (CH ₄ ) into a fuel such as the beginning.

However, since the conversion of CO ₂ using H ₂ is an exothermic reaction, it is necessary to proceed the reaction at a low temperature in order to improve the production rate of CH _{4 and the} like. Therefore, a catalyst having sufficient activity at a low temperature is demanded.

  Patent Document 1 describes that a catalyst obtained by preparing by spray decomposition from a solution containing at least one active metal compound, alkali metal compound and carrier metal compound enables hydrogenation of carbon dioxide. Has been. In this document, the active metal compound is a nickel compound, and the support metal compound is one or more selected from a zirconium compound, an aluminum compound, a magnesium compound, a zinc compound, a titanium compound, and a niobium compound, and the formation It is stated that the product is methane. Moreover, the case where the actual reaction temperature is 300 degreeC is indicated.

  In Patent Document 2, 90% or more has a particle size of less than 10 nm, and at least one selected from the group consisting of Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, and Au. It is described that a catalyst in which nanoparticles including metal particles are dispersed and supported can hydrogenate carbon dioxide at atmospheric pressure and at a reaction temperature of 200 ° C. or lower.

Patent Document 3 discloses a fuel synthesis catalyst comprising a base material such as Al ₂ O ₃ , a metal such as Ni in contact with the base material, and an oxide such as CeO ₂ , ZrO ₂ , and TiO _2. The oxide has an interface with the metal and the substrate, respectively, on the outer surface of the substrate, on the surface of the substrate in the pores having open ends on the outer surface of the substrate, and on the inside of the substrate. The metal is present, the metal and the oxide are present in the pores, the metal has an interface with the substrate in the pores, and the metal is present in the substrate. Are disclosed. In this document, as a result of experimentally calculating the methane yield between 250 ° C. and 400 ° C., the fuel synthesis catalyst has the metal, the base material integrated with the metal, and the oxide present simultaneously. It is described that the methane yield is improved.

Non-Patent Document 1 describes that the CO ₂ conversion rate when Ni / CeO ₂ was used as a catalyst was 80% or higher at 300 ° C. or higher.

JP-A-7-76528 JP 2009-131835 A JP 2017-170430 A

Uemiya et al .: CeO2 support effect in CO2 methanation: The 66th meeting of the Japan Petroleum Institute (2017)

The catalyst described in Patent Document 2 has improved CO ₂ hydrogenation performance by controlling the dispersity and particle size of the active ingredient. However, since the catalyst preparation method is special, it is difficult to obtain a large amount of catalyst necessary for converting CO ₂ on a large scale.

The catalyst described in Patent Literature 3 includes a metal such as Ni, and an oxide such as CeO ₂ , ZrO ₂ , and TiO ₂ , and also includes a base material such as Al ₂ O ₃ . The proportion of active ingredients is small. For this reason, in order to ensure a processing amount, it is necessary to enlarge the dimension of the reaction tower, which is a practical problem. Moreover, if it is less than 300 degreeC, the conversion rate is low.

The catalyst described in Non-Patent Document 1 has room for improvement in that the CO ₂ conversion is low at less than 300 ° C.

  An object of the present invention is to convert carbon dioxide into a fuel such as methane with high efficiency at a temperature below 300 ° C. using a catalyst obtained by a simple preparation method.

In order to achieve the above object, the CO ₂ methanation catalyst of the present invention is a catalyst for converting carbon dioxide into methane using hydrogen, comprising a support and a catalyst component, and the support is Ce, La , Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu, and the catalyst component includes Ni supported on a support Including.

  According to the present invention, carbon dioxide can be converted to a fuel such as methane with high efficiency at less than 300 ° C. using a catalyst obtained by a simple preparation method.

It is a schematic diagram showing an example of a microscopic structure of the CO ₂ methanation catalyst of the present invention. Another example of a microscopic structure of the CO ₂ methanation catalyst of the present invention is a schematic diagram showing. It is a graph showing the CO ₂ conversion of Example 1 and Comparative Examples 1 and 2. Is a graph showing the CH ₄ selectivity of Example 1 and Comparative Examples 1 and 2. 3 is a graph showing the CO ₂ conversion rates of Examples 2 and 3 and Comparative Example 3. 6 is a graph showing the CH ₄ selectivity of Examples 2 and 3 and Comparative Example 3. 6 is a graph showing the CO ₂ conversion rates of Examples 4 and 5 and Comparative Example 4. 6 is a graph showing the CH ₄ selectivity of Examples 4 and 5 and Comparative Example 4.

  The present invention relates to a novel catalyst suitable for converting carbon dioxide into a fuel such as methane using hydrogen.

FIG. 1A is a conceptual diagram showing the structure of the CO ₂ methanation catalyst (methane synthesis catalyst) of the present invention.

In this figure, the CO ₂ methanation catalyst 100 has a structure in which a catalyst component 2 (first catalyst component) is supported on the surface of a carrier 1. The carrier 1 contains at least one of Ce, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. The catalyst component 2 contains at least Ni.

FIG. 1B shows another example of the CO ₂ methanation catalyst of the present invention.

The CO ₂ methanation catalyst 110 shown in the figure has a configuration in which the catalyst component 2 is supported on the surface of the carrier 1 and the additional component 3 (second catalyst component) is supported. The carrier 1 includes at least one of Ce, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, as in FIG. 1A. Similarly to FIG. 1A, the catalyst component 2 also contains at least Ni. The additional component 3 includes at least one of Pt, Rh, and Pd.

The CO ₂ methanation reaction in the catalyst system of the present invention is considered to proceed by the following mechanism.

First, CO ₂ and H ₂ are adsorbed on the catalyst surface. CO ₂ is oxygen withdrawn by carbon monoxide (CO) becomes as the following reaction formula (1), further CO and _{H 2} as the reaction formula (2) is generated by the reaction CH _4. The reactions of the following reaction formulas (1) and (2) can be combined and expressed as the following reaction formula (3).

When the amount of CO ₂ and H ₂ adsorbed on the catalyst surface is small, the reactions of the above reaction formulas (1) to (3) do not proceed. Further, when the reaction rate of the above reaction formula (1) is slow, CO ₂ is discharged as CO ₂ without being converted into CH ₄ or CO. When the reaction rate of the reaction formula (2) is low, CO converted from CO ₂ is discharged as CO without being converted to CH ₄ .

When containing at least one of Ce, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu as an element constituting the carrier (carrier component) Since the amount of CO ₂ adsorption and oxygen extraction increases, the reaction of the above reaction formula (1) is promoted.

When Ni is contained as the catalyst component 2, the amount of H ₂ adsorption increases, and thus the reactions of the above reaction formulas (1) to (3) are promoted. Further, when at least one of Pt, Rh, and Pd is included as the additional component 3, the rate of extracting oxygen is increased, and thus the reaction of the above reaction formula (1) is promoted.

  The amount of the catalyst component 2 is preferably in the range of 0.1 to 40 parts by mass with respect to 100 parts by mass of the active ingredient of the carrier 1. Here, “parts by mass” represents the content ratio of each component in terms of grams. Moreover, when describing as "0.1-40 mass parts", it shall mean "0.1 mass part or more and 40 mass parts or less."

  Moreover, it is preferable that the quantity of the additional component 3 exists in the range of 0.1-1 mass part with respect to 100 mass parts of active ingredients of the support | carrier 1. As shown in FIG. In the following description, when simply using “parts by mass”, it means a value relative to 100 parts by mass of the active ingredient of the carrier 1. Here, “the active ingredient of the carrier 1” means the component of the carrier 1 excluding the additive when an additive such as a binder component is used to bind the active ingredient contained in the carrier 1. Thus, it refers to the component of the carrier 1 that is essential when preparing the catalyst.

When the amount of the catalyst component 2 or the amount of the additional component 3 is less than 0.1 parts by mass, the effect of adding the component is not sufficiently exhibited, and the CO ₂ methanation performance may be lowered. When the amount of the catalyst component 2 is more than 40 parts by mass, the exposed area of the carrier 1 is reduced, and the CO ₂ methanation performance may not be sufficiently exhibited. Further, when the amount of the additional component 3 is more than 1 part by mass, the exposed area of the carrier 1 or the catalyst component 2 is reduced, and the CO ₂ methanation performance may not be sufficiently exhibited.

In the CO ₂ methanation catalysts 100 and 110, even if a part of the CO ₂ methanation catalysts 100 and 110 is 0.1 to 40 parts by mass, the above effect can be exhibited in that part. Moreover, if the part from which the quantity of the additional component 3 will be 0.1-1 mass part exists in the part, the said effect can be expressed efficiently.

For example, the following cases (1) and (2) can be considered as examples of the forms of the CO ₂ methanation catalysts 100 and 110.

  (1) There is a plate-like or granular carrier 1 as a layer not containing the catalyst component 2 and the additional component 3, and the carrier 1 containing the catalyst component 2 and the additional component 3 is present on the surface thereof.

  (2) The carrier 1 containing the catalyst component 2 and the additional component 3 is present on the surface of the granular carrier 1 not containing the catalyst component 2 and the additional component 3.

  In any of the cases (1) and (2), the amount of the catalyst component 2 is 0.1 to 40 parts by mass with respect to the carrier component contained in the carrier 1 including the catalyst component 2 and the additional component 3. It is preferred that there is a portion where the amount of additional component 3 is 0.1 to 1 part by mass.

  The catalyst component 2 and the additional component 3 are preferably in contact with the carrier 1 containing the carrier component, and the catalyst component 2 and the additional component 3 are preferably provided on the surface of the carrier 1 containing the carrier component.

  As the additional component 3, in addition to Pt, Rh, and Pd, metals such as Ir, Ru, Cr, Mn, Fe, Co, Ni, Cu, and Zn can be used.

The carbon monoxide adsorption amount (CO adsorption amount) on the catalyst component 2 and the additional component 3 is preferably 0.7 cm ³ / g or more. Since CO is selectively adsorbed on the metal surface, it is considered that the larger the amount of CO adsorbed, the greater the amount of exposed metal on the catalyst surface. When metal exposure amount is increased, since the H ₂ adsorption amount increases, an increase in H ₂ amount that can react with CO _2, CO ₂ methanation performance is improved. Further, the average particle diameter of the catalyst component can be calculated based on the CO adsorption amount. The average particle size is preferably 50 nm or less. The smaller the average particle size, the higher the degree of dispersion of the catalyst component, and the reaction between H ₂ and CO ₂ is promoted.

  In addition, as shown in the below-mentioned Example, when producing a catalyst using a liquid phase, the average particle diameter of the catalyst component 2 is often 10 nm or more in practice. However, a catalyst component 2 having a particle size smaller than this may also be generated. Therefore, even if the average particle diameter of the catalyst component 2 is a practical lower limit value of 1 nm or more and less than 10 nm, it is considered that the catalyst component 2 works effectively in a more desirable state. In order to support the catalyst component 2 having a small average particle diameter in this way, for example, a vapor phase method such as chemical vapor deposition (CVD) may be used.

In addition to being a CO ₂ adsorption point, the carrier 1 is considered to play a role of increasing the degree of dispersion of the catalyst component 2 and the additional component 3. The carrier 1 includes a carrier component, and a specific surface area of the carrier component of 50 to 300 m ² / g is preferable for CO ₂ methanation performance. Moreover, it is preferable for the CO ₂ methanation performance that the particle diameter of the carrier component is 0.5 to 15 μm.

  As the support 1, in addition to Ce, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Al, Zr, Ti, Si, Mg, etc. are included. A metal oxide, a complex oxide, or the like can be used.

The shapes of the CO ₂ methanation catalysts 100 and 110 can be applied in various shapes depending on the application. A granular shape, a pellet shape, a plate shape, a powder shape, a honeycomb shape, and the like can be applied. The honeycomb-shaped CO ₂ methanation catalysts 100 and 110 are obtained by coating a catalyst structure carrying various components on a honeycomb structure formed of various materials such as cordierite and stainless steel. In this case, the catalyst component 2 and the additional component 3 may be supported after the carrier 1 is coated on a substrate such as a honeycomb structure, or the substrate 1 may be coated with the catalyst component 2 and the additional component 3 supported thereon. .

The methods for preparing the CO ₂ methanation catalysts 100 and 110 include physical impregnation methods such as an impregnation method, a kneading method, a coprecipitation method, a sol-gel method, an ion exchange method, and a vapor deposition method, and a preparation method using a chemical reaction. Is also applicable. As starting materials for the catalyst component 2 and the additional component 3, various compounds such as nitric acid compounds, acetic acid compounds, complex compounds, hydroxides, carbonate compounds, and organic compounds, metals, and metal oxides can be used.

The ratio of H ₂ and CO ₂ in the reaction gas contacting the CO ₂ methanation catalysts 100 and 110 is preferably the stoichiometric ratio H ₂ / CO ₂ = 4 shown in the above reaction formula (3). if _H 2 _/ CO 2 = 1 to 6 on a molar basis, it is possible to methanation of without CO ₂ to by-produce CO. When H ₂ / CO ₂ is smaller than 1, since the amount of H ₂ is small with respect to CO ₂ , CO may be by-produced. When H ₂ / CO ₂ is larger than 6, the amount of H ₂ discharged without reacting with CO ₂ increases.

Nitrogen (N ₂ ) and oxygen (O ₂ ) may be contained in the reaction gas that contacts the CO ₂ methanation catalysts 100 and 110 in addition to H ₂ and CO ₂ . The N ₂ concentration is preferably 0.1 to 95% on a molar basis. When the N ₂ concentration is higher than 95%, the adsorption of H ₂ and CO _{2 on} the catalyst surface is inhibited, and the reaction may not proceed sufficiently. Further, when O ₂ is contained in the reaction gas, most of the O ₂ reacts with H ₂ to become water, so that the amount of H ₂ that reacts with CO ₂ is reduced, and the amount of CH ₄ produced is reduced. Decrease. However, since there is no CO byproduct, CO ₂ methanation and O ₂ removal can be performed simultaneously. The O ₂ concentration is preferably 0.1 to 20% on a molar basis. When the O ₂ concentration is higher than 20%, a large amount of H ₂ is consumed for the reaction with O _2, and thus the CO ₂ methanation reaction may not proceed.

The maximum CO ₂ conversion rate of the CO ₂ methanation catalysts 100, 110 at less than 300 ° C. is preferably 80% or more. Since the reaction of the above reaction formula (2) is an exothermic reaction, the reaction is likely to proceed at a low temperature. Therefore, the lower the temperature of the reaction gas that contacts the CO ₂ methanation catalysts 100, 110, the easier it is to generate CH ₄ . On the other hand, the reaction of the above reaction formula (1) is an endothermic reaction, so that the reaction is likely to proceed at a high temperature, particularly 300 ° C. Therefore, the higher the temperature of the reaction gas in contact with the CO ₂ methanation catalysts 100, 110, the easier it is for CO to form as a byproduct rather than CH ₄ . Therefore, in order to selectively produce CH ₄ from CO ₂ , it is preferable that the reaction of the above reaction formula (1) in the CO ₂ methanation catalysts 100 and 110 easily proceeds at less than 300 ° C.

Further, it is considered that the product grade CH ₄ concentration is appropriate to be 80% or more on a molar basis. For this reason, it is preferable that the maximum CO ₂ conversion rate of the CO ₂ methanation catalysts 100 and 110 is 80% or more.

  Hereinafter, although it demonstrates using a specific Example and a comparative example, this invention is not restrict | limited by these Examples.

CeO ₂ powder was used as a base material, and this was impregnated with a nickel nitrate aqueous solution (Ni (NO ₃ ) ₂ aqueous solution) as a catalyst component. Thereafter, it was dried at 120 ° C., and then calcined at 500 ° C. for 2 hours. The obtained powder was press-molded and then pulverized. And it sized so that a particle size range might be 0.85 mm-1.7 mm. By the above method, a catalyst sample containing 10 parts by mass of Ni in terms of element with respect to 100 parts by mass of CeO ₂ was obtained.

The obtained catalyst sample was subjected to a CO ₂ methanation performance test under the following conditions.

A catalyst sample with an apparent volume of 3 mL was packed into a quartz glass reaction tube. This reaction tube was installed in an electric furnace, and heating was controlled so that the gas temperature introduced into the reaction tube was 180 to 500 ° C. In the present specification, this gas temperature is referred to as “catalyst inlet temperature”. The reaction tube, a reaction gas and the molar ratio between _{H 2} and CO ₂ were of _H 2 / _CO 2 = 4, was introduced at a space velocity of 19000h ^-1. The composition of the reaction gas was H ₂ : 80% and CO ₂ : 20%.

First, as a pretreatment, H ₂ was passed through the reaction tube at 400 ° C. for 1 hour. Next, a reaction gas was introduced at room temperature, the temperature was raised to 180 to 500 ° C., and CO ₂ methanation performance was measured.

From this result, the CO ₂ conversion rate X _CO2 (unit%) and the CH ₄ selectivity S _CH4 (unit%) were calculated by the following formulas (1) and (2).

_{Wherein, F in, CO2} is the amount of CO ₂ which has flowed into the reaction _{tube, F out, CO2} represents the amount of CO ₂ flowing out of the reaction tube.

In the formula, F _{out, CH4} represents the amount of CH ₄ flowing out of the reaction tube, and F _{out, CO} represents the amount of CO flowing out of the reaction tube.

  The obtained catalyst sample was subjected to a CO adsorption test under the following conditions.

The powder of the catalyst before press molding was filled in a glass cell. First, as pretreatment, He was circulated at 400 ° C. for 15 minutes, and then H ₂ was circulated at 400 ° C. for 15 minutes.

  The amount of CO adsorption was measured by a CO pulse method using a catalyst analyzer (BELCAT (registered trademark) manufactured by Nippon Bell Co., Ltd.). He was used as the carrier gas, and the composition of the adsorbed gas was CO: 3% and He: 97%.

  Furthermore, the average particle diameter of the catalyst component was calculated from the CO adsorption amount using the catalyst analyzer.

(Comparative Example 1)
A catalyst sample was obtained in the same manner as in Example 1 except that Al ₂ O ₃ powder was used instead of CeO ₂ powder. The obtained catalyst sample was subjected to a CO ₂ methanation performance test and a CO adsorption test in the same manner as in Example 1.

(Comparative Example 2)
A catalyst sample was obtained in the same manner as in Example 1 except that NiO powder was used instead of CeO ₂ powder and nickel nitrate solution. The obtained catalyst sample was subjected to a CO ₂ methanation performance test and a CO adsorption test in the same manner as in Example 1.

A catalyst sample was obtained in the same manner as in Example 1. The obtained catalyst samples, a reaction molar ratio of _{H 2} and CO ₂ gases were of _H 2 _/ CO 2 = 5.25, the composition of the reaction gas on a molar basis _{H 2: 84%, CO 2} : 16 % CO ₂ methanation performance test was conducted in the same manner as in Example 1 except that the percentage was changed to%.

Except for using _CeO 2 -ZrO ₂ powder instead of CeO ₂ powder, to obtain a catalyst sample in the same manner as in Example 1. In this case, the carrier is a composite oxide containing CeO _2. The obtained catalyst sample was subjected to a CO ₂ methanation performance test and a CO adsorption test in the same manner as in Example 2.

(Comparative Example 3)
A catalyst sample was obtained in the same manner as in Example 1 except that ZrO ₂ powder was used instead of CeO ₂ powder. The obtained catalyst sample was subjected to a CO ₂ methanation performance test and a CO adsorption test in the same manner as in Example 2.

A catalyst sample was obtained in the same manner as in Example 1. CO ₂ methanation was carried out in the same manner as in Example 1 except that the composition of the reaction gas was changed to H ₂ : 8%, CO ₂ : 2%, and N ₂ : 90% with respect to the obtained catalyst sample. A performance test was performed.

A catalyst sample was obtained in the same manner as in Example 1. Except that the composition of the reaction gas was H ₂ : 8%, CO ₂ : 2%, O ₂ : 1.6%, N ₂ : 88.4% on a molar basis with respect to the obtained catalyst sample. The CO ₂ methanation performance test was conducted in the same manner as in 1.

(Comparative Example 4)
A catalyst sample was obtained in the same manner as in Example 1 except that CeO ₂ powder different from that in Example 1 was used. The catalyst sample of this comparative example has a CO adsorption amount of 0.63 cm ³ / g and is less active than Example 1. The obtained catalyst sample was subjected to a CO ₂ methanation performance test and a CO adsorption test in the same manner as in Example 4.

(Test results)
FIG. 2 is a graph showing the CO ₂ conversion rates of Example 1 and Comparative Examples 1 and 2. The horizontal axis represents the catalyst inlet temperature, and the vertical axis represents the CO ₂ conversion rate.

As shown in the figure, in Example 1, when the temperature exceeds 190 ° C., the CO ₂ conversion rate increases rapidly and reaches a maximum at 200 ° C. On the other hand, in Comparative Example 1, the CO ₂ conversion rate is low up to 290 ° C., and when it exceeds 290 ° C., the CO ₂ conversion rate increases rapidly, and is almost constant at 300 to 360 ° C. The maximum temperature is 340 ° C. Further, the curve of Comparative Example 2 has no steep region up to 400 ° C., indicating that the catalyst is inactive.

FIG. 3 is a graph showing the CH ₄ selectivity of Example 1 and Comparative Examples 1 and 2. The horizontal axis represents the catalyst inlet temperature, and the vertical axis represents the CH ₄ selectivity.

As shown in this figure, in Example 1, the CH ₄ selectivity is approximately 100% at 180 to 260 ° C. On the other hand, in Comparative Example 1, the CH ₄ selectivity is almost 100% up to 240 ° C., but is reduced to about 90% at 260 to 290 ° C. Then, in 300 to 360 ° C., CH ₄ selectivity of is about 95%. Moreover, although the comparative example 2 is almost 100% up to 300 ° C., it is about 50% at 320 to 400 ° C.

Table 1 summarizes the results of FIGS. Here, the maximum CO ₂ conversion is a numerical value representing the maximum value of each curve. The catalyst inlet temperature and CH ₄ selectivity corresponding to the maximum CO ₂ conversion are shown. These terms are the same for other examples and comparative examples. Note that the maximum CO ₂ conversion is a value that varies depending not only on the catalyst inlet temperature but also on the composition of the introduced gas.

From this table, it can be seen that Example 1 has very excellent characteristics in that the CO ₂ conversion rate is maximized at a low temperature of 200 ° C. and the CH ₄ selectivity at that temperature is also high.

The reason for this is thought to be that the use of CeO ₂ as the carrier increased the amount of CO ₂ adsorption and the amount of oxygen extracted compared with the case where no carrier was used and Al ₂ O ₃ was used as the carrier.

FIG. 4 is a graph showing the CO ₂ conversion rates of Examples 2 and 3 and Comparative Example 3. The horizontal axis represents the catalyst inlet temperature, and the vertical axis represents the CO ₂ conversion rate.

As shown in this figure, in Example 2, when the temperature exceeds 180 ° C., the CO ₂ conversion rate increases rapidly and reaches a maximum at 200 ° C. Further, in Example 3, when the temperature exceeds 220 ° C., the CO ₂ conversion rate increases rapidly and reaches a maximum at 230 ° C. In contrast, the curve of Comparative Example 3 does not have a steep region up to 400 ° C., indicating that the catalyst is inactive.

FIG. 5 is a graph showing the CH ₄ selectivity of Examples 2 and 3 and Comparative Example 3. The horizontal axis represents the catalyst inlet temperature, and the vertical axis represents the CH ₄ selectivity.

As shown in this figure, in Example 2, the CH ₄ selectivity is almost 100% at 180 to 260 ° C. In Example 3, the CH ₄ selectivity is almost 100% at 180 to 280 ° C.

In Comparative Example 3, the CH ₄ selectivity is almost 100% at 180 to 400 ° C.

Examples 2 and 3 had higher CO ₂ conversion than Comparative Example 3 in the entire temperature range. This is presumably because the CO ₂ adsorption amount and oxygen extraction amount increased due to the presence of CeO ₂ .

Both Example 3 and Comparative Example 3 contain ZrO ₂ in the carrier, but in Example 3, since CeO ₂ was contained, it is considered that the activity was improved.

  Table 2 summarizes the results of FIGS.

From this table, it can be seen that Example 2 has very excellent characteristics in that the CO ₂ conversion is maximum at 200 ° C. and the CH ₄ selectivity at that temperature is also high.

The catalyst components in Example 2 are the same as in Example 1. In Example 2, the ratio of H ₂ to CO _{2 in the} reaction gas was H ₂ / CO ₂ = 5.25, and H ₂ was added in excess of the stoichiometric ratio. Therefore, the conversion of CO ₂ was promoted, and the maximum CO ₂ conversion rate in Example 2 was improved as compared with Example 1.

In Examples 4 and 5 and Comparative Example 4, unlike the case of Examples 1-3 and Comparative Examples 1-3, and the reaction gas is diluted 10-fold with N _2. Example 5 further includes 1.6% O ₂ .

FIG. 6 is a graph showing the CO ₂ conversion rates of Examples 4 and 5 and Comparative Example 4. The horizontal axis represents the catalyst inlet temperature, and the vertical axis represents the CO ₂ conversion rate.

As shown in this figure, in Example 4, the CO ₂ conversion rate rapidly increases from 180 ° C. to 240 ° C., exceeds 80%, and reaches a maximum at 280 ° C. Above 300 ° C., the CO ₂ conversion rate gradually decreases. Further, the embodiment 5, in the range up to 300 ° C. from 180 ° C., CO ₂ conversion is high, and has a maximum at 260 ° C.. In this range, the CO ₂ conversion is 40% or more. Above 300 ° C., the CO ₂ conversion rate gradually decreases. In contrast, in Comparative Example 4, the CO ₂ conversion rate gradually increased from 180 ° C. to 350 ° C. and reached over 50%. In the range from 350 ° C. to 500 ° C., the CO ₂ conversion is almost constant.

FIG. 7 is a graph showing the CH ₄ selectivity of Examples 4 and 5 and Comparative Example 4. The horizontal axis represents the catalyst inlet temperature, and the vertical axis represents the CH ₄ selectivity.

As shown in this figure, in Example 4, the CH ₄ selectivity is almost 100% at 180 to 350 ° C. In Example 5, the CH ₄ selectivity is almost 100% at 180 to 300 ° C.

In Comparative Example 4, the CH ₄ selectivity at 180 to 260 ° C. is almost 100%.

By diluting the reaction gas with N ₂ , the CO ₂ conversion rate of Example 4 tends to be lower than that of Example 1, but the maximum CO ₂ conversion rate is comparable.

In Comparative Example 4 using CeO ₂ different from Example 4, the maximum CO ₂ conversion rate was lower than that in Example 4, and the temperature at which the maximum CO ₂ conversion rate was reached increased.

In Example 5, a part of H ₂ in the reaction gas due to a reaction with O _2, the reaction of the CO ₂ is reduced, believed to CO ₂ conversion decreased. The CH ₄ selectivity was similar to that in Example 3. Therefore, it can be seen that CO ₂ can be methanated without CO as a by-product even in the presence of O ₂ .

  Table 3 summarizes the results of FIGS.

From this table, Example 4 is an experimental result corresponding to the case where a gas containing a large amount of N ₂ is supplied. Even in this case, the CO ₂ conversion becomes high at less than 300 ° C., and the temperature range thereof. The CH ₄ selectivity in is also high. The maximum CO ₂ conversion is 80% or more at a catalyst inlet temperature of less than 300 ° C. (280 ° C.). From these facts, Example 4 shows very excellent characteristics.

Further, Example 5 is an experimental result corresponding to the case where a gas having a composition that assumes a small amount of O ₂ remaining in the combustion gas is supplied. In this case, compared with Example 4, CO ₂ conversion is performed. The rate is lowered. However, it can be seen that even under such conditions, a CO ₂ conversion of 40% or more can be maintained at less than 300 ° C.

  Table 4 summarizes the supports of Examples 1 to 5 and Comparative Examples 1 to 4, the results of the CO adsorption test, and the average particle diameter of the catalyst particles.

As shown in this table, Examples 1 to 5 have a larger CO adsorption amount and a smaller average particle size than Comparative Examples 1 to 4. Therefore, in Examples 1-5, there is a possibility that the exposure amount of the metal component is large and the dispersity of the active component is high. This is presumably because oxygen bound to the active component was extracted due to the action of CeO ₂ that easily extracts oxygen from the carrier, and the amount existing as a metal increased. As a result, it is considered that the amount of H ₂ adsorbed on the catalyst surface increased and the CO ₂ methanation performance was improved.

In Comparative Example 4, the carrier is composed of CeO ₂ , but unlike the cases of Examples 1, 2, 4 and 5, CeO ₂ which does not easily extract oxygen is used, so that the amount of active ingredient present as a metal is small. It is considered that the CO ₂ methanation performance was reduced.

1: support, 2: catalyst component, 3: additional component, 100, 110: CO ₂ methanation catalyst.

Claims (15)

A catalyst for converting carbon dioxide into methane using hydrogen,
A carrier;
A catalyst component,
The carrier includes one or more selected from the group consisting of Ce, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu,
The catalyst component is a CO ₂ methanation catalyst containing Ni supported on the carrier. The carrier includes Ce and one or more selected from the group consisting of Zr, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. The CO ₂ methanation catalyst according to claim 1. The CO ₂ methanation catalyst according to claim 1 or 2, wherein the support contains an oxide. The CO ₂ methanation catalyst according to any one of claims 1 to 3, wherein the content of Ni as the catalyst component is 0.1 to 40 parts by mass with respect to 100 parts by mass of the active ingredient of the carrier. . 5. The CO ₂ methanation catalyst according to claim 1, wherein the catalyst component further contains one or more kinds selected from the group consisting of Pt, Rh, and Pd as an additional component. 6. The CO ₂ methanation catalyst according to claim 5, wherein the content of the additional component is 0.1 to 1 part by mass with respect to 100 parts by mass of the active ingredient of the carrier. The CO ₂ methanation catalyst according to any one of claims 1 to 6, wherein an adsorption amount of carbon monoxide is 0.7 cm ³ / g or more. The CO ₂ methanation catalyst according to any one of claims 1 to 7, wherein an average particle diameter of the catalyst component is 1 nm or more and 50 nm or less. The CO ₂ methanation catalyst according to any one of claims 1 to 8, wherein the maximum CO ₂ conversion rate under a condition where the catalyst inlet temperature is less than 300 ° C is 80% or more. 9. The maximum CO ₂ conversion rate is 80% or more under the condition that the ratio of nitrogen contained in the supplied gas is 90% on a molar basis and the catalyst inlet temperature is less than 300 ° C. 9. The CO ₂ methanation catalyst according to Item. A method for producing methane by supplying a gas containing hydrogen and carbon dioxide to the CO ₂ methanation catalyst according to any one of claims 1 to 10, and reducing the carbon dioxide.
The concentration ratio between hydrogen and carbon dioxide contained in the gas is 1 to 6 on a molar basis.   The method for reducing carbon dioxide according to claim 11, wherein the gas further contains nitrogen.   The method for reducing carbon dioxide according to claim 12, wherein the concentration of nitrogen contained in the gas is 0.1 to 95% on a molar basis.   The method for reducing carbon dioxide according to any one of claims 11 to 13, wherein the gas further contains oxygen.   The method for reducing carbon dioxide according to claim 13, wherein the concentration of oxygen contained in the gas is 0.1 to 20% on a molar basis.

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