JP7376955B2 - Catalyst and hydrocarbon manufacturing method - Google Patents

Description

The present invention relates to a catalyst and a method for producing hydrocarbons, and more specifically, a catalyst that activates a reaction that produces hydrocarbons having two or more carbon atoms from methane, and a method for producing hydrocarbons having two or more carbon atoms using the same. Concerning how to generate.

Methane exists in abundance as the main component of natural gas, and is also used in hydrogenation reactions of carbon monoxide and carbon dioxide such as reactions of synthesis gas from coal etc., hydrocracking and catalytic cracking of hydrocarbons such as petroleum fractions. It is also obtained in large quantities as a by-product of processes. In this way, methane satisfies the basic requirements as an industrial raw material, such as being able to be supplied stably and being inexpensive, but due to reasons such as low reactivity compared to other hydrocarbons, Most of it is used as fuel. On the other hand, in view of recent petroleum resource problems, there is a need for technology that not only uses methane as a fuel but also converts it into more useful compounds for effective use.

As a reaction technology for the effective use of such methane, a technology of dehydrogenative coupling of methane at extremely high temperatures of 1000° C. or higher to convert it into acetylene or ethylene has been studied for a long time. Particularly recently, the oxidative coupling reaction of methane, a technology in which methane is brought into contact with a catalyst in the presence of oxygen to produce hydrocarbons having two or more carbon atoms such as ethylene and ethane under relatively mild conditions, has attracted attention. ing.

Examples of reactions that synthesize ethylene and ethane from methane under mild conditions include the oxidative coupling of methane (OCM reaction), which synthesizes ethylene and ethane by reacting methane and oxygen. . This reaction is shown in the following formulas (1) and (2).
CH ₄ + 1/2O ₂ → 1/2C ₂ H ₄ +H ₂ O ... (1)
CH ₄ + 1/4O ₂ → 1/2C ₂ H ₆ + 1/2H ₂ O ... (2)

OCM is an attractive reaction that directly converts methane, which has abundant reserves but little use, into ethylene and ethane, which are key compounds in the chemical industry. However, no industrially useful process has been disclosed so far from the viewpoint of cost. This is because the OCM reaction includes complete oxidation of methane, which is a thermodynamically advantageous inhibiting reaction shown in equation (3) below, and has the advantage of converting methane into ethylene and ethane with high selectivity and yield. This is because a suitable catalyst has not yet been discovered.
CH ₄ +2O ₂ →CO ₂ +2H ₂ O...(3)

From the above, practical catalysts are required to have improved CH ₄ conversion and C ₂ compound (ethylene and ethane) selectivity.

Currently, a catalyst in which lithium oxide and tin oxide are supported on a calcium oxide carrier is known as one of the catalysts showing high activity for OCM (see Patent Document 1). This catalyst shows a low yield of _C2 compounds, which is about 15%.

Furthermore, Li/MgO is known as another highly active catalyst (see Non-Patent Document 1). This catalyst has a yield of about 19% of the target products, ethylene and ethane, but has a low activity, with a selectivity of the target products in the product of about 50%.

Furthermore, Mn-Na ₂ WO ₄ /SiO ₂ is also known as a catalyst that exhibits high activity in the OCM reaction (see Non-Patent Documents 2 and 3). This catalyst exhibits relatively high activity, with a yield of the target C ₂ compound of 15 to 25% and a selectivity of the target product of 60 to 80%.

However, there is still room for improvement in order to further improve the yield and selectivity of hydrocarbons with carbon numbers of 2 or more and to more efficiently produce hydrocarbons with carbon numbers of 2 or more from methane compounds. .

Japanese Patent Application Publication No. 5-70372

T. Ito, J. H. Lunsford, Nature 1985, 721-722, 314. S. Arndt, T. Otremba, U. Simon, M. Yildiz, H. Schubert, R. Schomacker, Applied Catalysis A: General 2012, 425-426, 53. E. V. Kondratenko, T. Peppel, D. Seeburg, V. A. Kondratenko, N. Kalevaru, A. Martin, S. Wohlrab, Catalysis Science Technology 2017, 7, 366.

The present invention was made in view of the above circumstances, and an object of the present invention is to provide a new catalyst capable of producing hydrocarbons having a carbon number of 2 or more from methane with high yield and high selectivity. do.

The present inventors have made extensive studies to solve the above-mentioned problems. As a result, Li represented by the general formula Li ₂ ABO ₄ (A is one or more selected from the group consisting of Ca, Sr, Ba and Mg, and B is Si and/or Ge) The present inventors have discovered that hydrocarbons having two or more carbon atoms can be produced from methane with high yield and high selectivity by using the containing composite metal oxide as a catalyst, and have completed the present invention. Specifically, the present invention provides the following.

(1) Li represented by the general formula Li ₂ ABO ₄ (A is one or more selected from the group consisting of Ca, Sr, Ba and Mg, and B is Si and/or Ge) A catalyst containing a composite metal oxide.

(2) The catalyst according to (1), wherein a Ce-containing oxide and/or a W-containing oxide is supported on the surface of the Li-containing composite metal oxide.

(3) The catalyst according to (2), wherein the surface of the Li-containing composite metal oxide includes at least a Ce-containing oxide, and the Ce-containing oxide is _CeO2 .

(4) The surface of the Li-containing composite metal oxide contains at least a W-containing oxide, and the W-containing oxide is a composite metal oxide of W and a metal element constituting the Li-containing composite metal oxide. The catalyst according to (2) or (3).

(5) The content of Ce is 0.5% by mass or more and 5.0% by mass or less based on 100% by mass of the Li-containing composite metal oxide, according to any one of (2) to (4). catalyst.

(6) The catalyst according to any one of (2) to (5), wherein the content of W is 0.5% by mass or more and 10% by mass or less based on 100% by mass of the Li-containing composite metal oxide.

(7) The catalyst according to any one of (1) to (6), for synthesizing a hydrocarbon having two or more carbon atoms from methane.

(8) A method for producing hydrocarbons, which comprises synthesizing hydrocarbons having two or more carbon atoms from methane using the catalyst according to any one of claims 1 to 7.

(9) The method for producing hydrocarbons according to (8), wherein a hydrocarbon having 2 or more carbon atoms is synthesized from methane by bringing methane and oxygen into contact and reacting.

(10) The method for producing hydrocarbons according to (9), wherein methane and oxygen are brought into contact in a reaction system in a temperature range of 600°C or higher and 800°C or lower.

(11) The method for producing hydrocarbons according to (10), wherein the molar ratio of oxygen and methane (oxygen/methane) in the reaction system is 0.12 or more and 0.6 or less.

According to the present invention, it is possible to provide a new catalyst that generates hydrocarbons having two or more carbon atoms in high yield.

1 is an XRD pattern of samples of Example 1 and Example 2. 3 is a SEM image of the sample of Example 1. These are the results of elemental analysis by SEM-EDX of the sample of Example 1, in which (a) is an SEM image, (b) is Sr Lα, (c) is Ge Lα, and (d) is O Kα. 3 is a SEM image of the sample of Example 2. These are the results of elemental analysis by SEM-EDX of the sample of Example 2, where (a) is an SEM image, (b) is Ce Lα, (c) is W Mα, (d) is Sr Lα, and (e) is Ge Lα. , (f) is O Kα. 1 shows the results of catalytic activity evaluation of samples of Example 1, Example 2, and Comparative Example 1. These are the catalyst activity evaluation results of samples of Example 3, Example 4, and Comparative Example 1. These are the catalyst activity evaluation results of samples of Example 5, Example 6, and Comparative Example 1. These are the catalyst activity evaluation results of samples of Example 7, Example 8, and Comparative Example 1. These are the catalyst activity evaluation results of samples of Example 9, Example 10, and Comparative Example 1. These are the catalyst activity evaluation results for samples of Example 5 and Comparative Examples 2 to 4. These are the catalyst activity evaluation results for samples of Comparative Examples 5 to 8. These are the CH ₄ conversion rate, C ₂ selectivity, and C ₂ yield when the sample of Example 1 was held at 800° C. for 2 hours. These are the CH ₄ conversion rate, C ₂ selectivity, and C ₂ yield when the sample of Example 2 was held at 800° C. for 2 hours. These are the CH ₄ conversion rate, C ₂ selectivity, and C ₂ yield when the sample of Example 2 was held at 750° C. for 2 hours. These are the CH ₄ conversion rate, C ₂ selectivity, and C ₂ yield when the sample of Comparative Example 1 was held at 800° C. for 2 hours. FIG. 3 is a diagram showing changes in CH ₄ conversion rate, C ₂ selectivity, and C ₂ yield when changing the oxygen/methane ratio for the sample of Example 5.

Hereinafter, specific embodiments of the present invention will be described in detail. Note that the present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the purpose of the present invention.

<1. Catalyst＞
The catalyst according to the present embodiment has the general formula Li ₂ ABO ₄ (A is one or more selected from the group consisting of Ca, Sr, Ba, and Mg, and B is Si and/or Ge.) It contains a Li-containing composite metal oxide represented by:

Such a catalyst exhibits high catalytic ability due to its unique constituent elements and crystal structure. In particular, when used as a catalyst for OCM reaction, hydrocarbons having two or more carbon atoms can be produced from methane in high yield. More specifically, compared to Li/MgO disclosed in the above-mentioned Non-Patent Document 1 and Mn-Na ₂ WO ₄ /SiO ₂ disclosed in the above-mentioned Non-Patent Documents 2 and 3, It has high OCM reaction catalytic activity and is expected to be used as a new OCM reaction catalyst.

Furthermore, such a catalyst has high thermal stability and does not become deactivated in a short period of time even under high temperature conditions. Therefore, it can be used for a long period of time. Moreover, such a catalyst does not use expensive elements such as noble metals, and can be synthesized with a high yield by a simple method, as will be described in detail later. Thus, it is a useful catalyst also from the viewpoint of achieving an inexpensive process.

As described above, the Li-containing composite metal oxide according to the present embodiment is represented by the general formula Li ₂ ABO ₄ . Here, the A site includes one or more metal elements selected from the group consisting of Ca, Sr, Ba, and Mg (hereinafter referred to as "A site element"). Further, the B site includes a metal element (hereinafter referred to as "B site element") that is Si and/or Ge. The A-site element and the B-site element can each contain one or more of the above-mentioned metal elements.

In addition, the Li site, A site, and B site contain 5% or less of defects or substitutional elements based on the stoichiometric ratio of each metal element, that is, Li:A:B:O=2:1:1:4. be able to. Examples of substitution elements include B, Na, Mg, Al, K, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ga, and the like.

The Li-containing composite metal oxide has high OCM reaction catalytic activity because each element forms a crystal structure as a composite metal oxide in the above-mentioned stoichiometric ratio. The high catalytic activity exhibited in this way cannot be obtained with a mixture of single oxides of each metal element. Therefore, the high OCM reaction catalytic activity of the Li-containing composite metal oxide is due not only to the type of metal element but also to its crystal structure.

Specific _{examples of Li2ABO4 include Li2CaSiO4 , Li2SrSiO4 , Li2BaSiO4 , Li2MgSiO4} , _Li2CaGeO4 , _{Li2SrGeO4 , Li2BaGeO4} , _{Li2M .} gGeO ₄ , _Li2Ca (Si,Ge) _O4 , _Li2Sr (Si,Ge) _O4 , _Li2Ba (Si,Ge) _O4 , _Li2Mg (Si,Ge) _O4 , _Li2 (Ca ,Sr) _SiO4 , _Li2 (Ca,Ba) _SiO4 , _Li2 (Ca,Mg) _SiO4 , _Li2 (Sr,Ba) _SiO4 , _Li2 (Sr,Mg)SiO4 _{, Li2} (Ba) , Mg) _SiO4 , _Li2 (Ca,Sr _{) GeO4} , _Li2 (Ca,Ba)GeO4, _Li2 (Ca,Mg)GeO4 _{, Li2} (Sr,Ba)GeO4 _{, Li2} (Sr) , Mg) _GeO4 , _Li2 (Ba,Mg) _GeO4 , _Li2 (Ca,Sr)(Si,Ge) _O4 , _Li2 (Ca,Ba)(Si,Ge) _O4 , _Li2 (Ca , Mg)(Si,Ge) _O4 , _Li2 (Sr,Ba)(Si,Ge) _O4 , _Li2 (Sr,Mg)(Si,Ge) _O4 , _Li2 (Ba,Mg)(Si , Ge)O ₄ , Li ₂ (Ca, Sr, Ba) SiO ₄ , Li ₂ (Ca, Sr, Mg) SiO ₄ , Li ₂ (Ca, Ba, Mg) SiO ₄ , Li ₂ (Sr, Ba, Mg ) SiO ₄ , Li ₂ (Ca, Sr, Ba) GeO ₄ , Li ₂ (Ca, Sr, Mg) GeO ₄ , Li ₂ (Ca, Ba, Mg) GeO ₄ , Li ₂ (Sr, Ba, Mg) GeO ₄ , Li ₂ (Ca, Sr, Ba) (Si, Ge) O ₄ , Li ₂ (Ca, Sr, Mg) (Si, Ge) O ₄ , Li ₂ (Ca, Ba, Mg) (Si, Ge) O ₄ , Li ₂ (Sr, Ba, Mg) (Si, Ge) O ₄ , Li ₂ (Ca, Sr, Ba, Mg) SiO ₄ , Li ₂ (Ca, Sr, Ba, Mg) GeO ₄ , Li ₂ (Ca, Sr, Ba, Mg) (Si, Ge) O ₄ . In the above chemical formula, it is assumed that the ampholytic ratio of each metal element is greater than 0 and less than 1, and the sum of the ampholytic ratios of each metal element is 1. Specifically, the description of “(W, X, Y, Z)” (W, is greater than 0 and less than 1, and the sum of the theoretical ratios of W, X, Y, and Z is 1.

(Support of Ce-containing oxide and W-containing oxide)
It is preferable that the Li-containing composite metal oxide described above supports a Ce-containing oxide and/or a W-containing oxide.

In this way, by supporting the Ce-containing oxide and/or the W-containing oxide on the Li-containing composite metal oxide, a catalyst exhibiting a higher yield can be obtained. Among these, by supporting a Ce-containing oxide and a W-containing oxide, a catalyst exhibiting a high yield can be obtained.

The Ce-containing oxide is not particularly limited as long as it contains Ce, and for example, it may be combined with CeO ₂ or other metal elements (not limited to the metal elements constituting the Li-containing composite metal oxide). Examples include composite metal oxides, but from the viewpoint of high yield, CeO ₂ is preferable.

The W-containing oxide is not particularly limited as long as it contains W, and examples include WO ₃ , W ₂ O ₃ and other metal elements (including metal elements constituting the Li-containing composite metal oxide). However, from the viewpoint of high yield, it is preferable to use a composite metal oxide of the metal elements constituting the W- and Li-containing composite metal oxide. Examples of such composite metal oxides include SrLi _0.4 W _0.6 O ₃ , Li ₆ WO ₆ , Ba ₂ LiWO _5.5 , Li ₄ WO ₅ and the like. Moreover, a composite metal oxide containing Ce and W can also be used.

The content of the Ce-containing oxide is not particularly limited, and is preferably, for example, 0.5% by mass or more, and preferably 0.7% by mass or more, based on 100% by mass of the Li-containing composite metal oxide. The content is more preferably 1.0% by mass or more, even more preferably 1.2% by mass or more. When the content of the Ce-containing oxide is at least the required amount, the yield of hydrocarbons having 2 or more carbon atoms can be increased. On the other hand, the content of the Ce-containing oxide is preferably 5.0% by mass or less, more preferably 4.5% by mass or less, and even more preferably 4.0% by mass or less. The content is preferably 3.5% by mass or less, particularly preferably 3.5% by mass or less. By keeping the content of the Ce-containing oxide at or below the required amount, it is possible to suppress the amount of Ce, which is a rare metal, and reduce costs.

The content of the W-containing oxide is not particularly limited, and is preferably, for example, 0.5% by mass or more, and preferably 0.7% by mass or more, based on 100% by mass of the Li-containing composite metal oxide. The content is more preferably 1.0% by mass or more, even more preferably 1.2% by mass or more. When the content of the W-containing oxide is at least the required amount, the yield of hydrocarbons having 2 or more carbon atoms can be increased. On the other hand, the content of the W-containing oxide is preferably 10% by mass or less, more preferably 9.0% by mass or less, even more preferably 8.0% by mass or less, It is particularly preferable that the content is 7.0% by mass or less. By keeping the content of the W-containing oxide at or below the required amount, the amount of W, which is a rare metal, used can be suppressed and costs can be reduced.

The catalyst described above exhibits high catalytic ability, and can produce hydrocarbons having two or more carbon atoms from methane in high yield, especially when used as a catalyst for OCM reaction.

Although the above description has mainly been about the use of the catalyst in the OCM reaction, that is, the reaction for synthesizing hydrocarbons having 2 or more carbon atoms from methane, the present invention is not limited to the OCM reaction, but can also be used as a catalyst for other reactions. be able to. Specific applications include, for example, catalysts for conversion reactions from methane to methanol, catalysts for reactions that use methyl radicals (alkyl radicals) as intermediates, such as cross-coupling reactions between methane and toluene, and catalysts for partial oxidation reactions. It can be used for etc.

<2. Catalyst manufacturing method>
Li-containing compound represented by the general formula Li ₂ ABO ₄ (A is one or more selected from the group consisting of Ca, Sr, Ba and Mg, and B is Si and/or Ge). The method for producing the composite metal oxide is not particularly limited, and can be synthesized by, for example, a solid phase method, a sol-gel method, a hydrothermal synthesis method, a coprecipitation method, a citric acid gelation method, etc. Among these, it is preferable to synthesize by a solid phase method or a citric acid gelation method.

In the case of the solid phase method, starting materials suitable for the solid phase method, such as oxides or carbonates of the necessary metals, are mixed in a molar ratio of the compounds to be synthesized, the mixed powder is calcined, and the precursor is get. A Li-containing composite metal oxide can be obtained by main firing the obtained precursor.

In the case of the citric acid gelation method, the starting materials suitable for the citric acid gelation method, such as nitrates of the necessary metals, are dissolved in pure water to the same molar ratio as the compound to be synthesized. Citric acid in an amount equivalent to the total number of moles of metal or in excess is added to the metal solution and heated at low temperature to remove water and form a gel. After the gel is calcined to obtain a precursor, the Li-containing composite metal oxide can be obtained by main firing the precursor.

(Support of Ce-containing oxide and W-containing oxide)
The Ce-containing oxide and W-containing oxide are preferably synthesized by a wet impregnation method.

In the case of the wet impregnation method, the Li composite metal oxide is immersed in an aqueous solution of Ce and/or W nitrate, heated at a low temperature, dried, and then fired at a high temperature to form the Ce-containing oxide and/or the Li composite metal oxide. Alternatively, a Li-containing composite metal oxide supporting a W-containing oxide can be obtained.

In addition, when synthesizing a Li-containing composite metal oxide by a liquid phase method such as a citric acid gelation method, by adding nitrates of Ce and/or W when the starting raw material is purely dissolved, it can be synthesized in one step. A Li-containing composite metal oxide on which a Ce-containing oxide and/or a W-containing oxide is supported can be synthesized. Thereby, the number of manufacturing processes can be reduced.

<3. Hydrocarbon production method>
The method for producing hydrocarbons according to the present embodiment is to synthesize hydrocarbons having two or more carbon atoms from methane using the above-mentioned catalyst.

Specifically, in such a method for producing hydrocarbons, hydrocarbons having two or more carbon atoms are synthesized from methane by bringing methane and oxygen into contact and causing a reaction.

The temperature within the reaction system is not particularly limited, but is preferably 500°C or higher, more preferably 550°C or higher, even more preferably 600°C or higher, particularly 650°C or higher. preferable. By setting the temperature in the reaction system at or above the required temperature, the yield of hydrocarbons having 2 or more carbon atoms can be increased. On the other hand, the temperature within the reaction system is preferably 900°C or lower, more preferably 850°C or lower, and even more preferably 800°C or lower. By keeping the temperature in the reaction system at or below the required amount, it is possible to suppress deactivation of the Li composite metal oxide due to high-temperature sintering, and to suppress an increase in cost due to energy used for heating.

The molar ratio of methane and oxygen (oxygen/methane) in the reaction system is not particularly limited, but is preferably 0.10 or more, more preferably 0.12 or more, and 0.15 or more. More preferably, it is 0.2 or more. When the molar ratio of methane to oxygen in the reaction system is at least the required amount, the yield of hydrocarbons having 2 or more carbon atoms can be increased. On the other hand, the molar ratio of methane to oxygen in the reaction system is preferably 1 or less, more preferably 0.8 or less, even more preferably 0.6 or less, and even more preferably 0.55 or less. It is particularly preferable that When the molar ratio of methane to oxygen in the reaction system is less than or equal to the required amount, the yield of hydrocarbons having 2 or more carbon atoms can be increased.

EXAMPLES Hereinafter, the present invention will be explained in more detail by way of Examples, but the present invention is not limited to these Examples in any way. Note that, hereinafter, the Ce-containing oxide and the W-containing oxide-supported Li ₂ ABO ₄ will be referred to as “Ce-W/Li ₂ ABO ₄ ”.

[Sample preparation]
(Example 1) Li ₂ SrGeO ₄
LiNO ₃ , Sr(NO ₃ ) ₂ , and GeO ₂ were used as raw materials, and these raw materials were mixed in a total metal mole number of 4 so that Li:Sr:Ge=2.3:1:1 (Li: 15 mol% excess). It was added to pure water in which twice the amount of citric acid had been dissolved, and heated and stirred. After gel formation, the obtained gel was calcined in the air at 450° C. for 1 hour to obtain a precursor. The precursor was main fired at 850° C. in the air for 12 hours to synthesize Li ₂ SrGeO ₄ .

(Example 2) Ce-W/Li ₂ SrGeO ₄
In addition to LiNO ₃ , Sr(NO ₃ ) ₂ , and GeO ₂ as raw materials, Ce and W were added to 2% by mass and 5% by mass, respectively, based on 100% by mass of the target Li ₂ SrGeO ₄ . Ce--W/Li ₂ SrGeO ₄ was synthesized by performing the same operation as in Example 1 except that it was prepared by adding.

( _Example 3) _Li2CaGeO4
Li ₂ CaGeO ₄ was synthesized by performing the same operation as in Example 1 except that Ca(NO ₃ ) ₂ was used instead of Sr(NO ₃ ) ₂ .

(Example 4) Ce-W/Li ₂ CaGeO ₄
In addition to LiNO ₃ , Ca(NO ₃ ) ₂ , and GeO ₂ as raw materials, Ce and W were added to 2% by mass and 5% by mass, respectively, based on 100% by mass of the target Li ₂ CaGeO ₄ . Ce-W/Li ₂ CaGeO ₄ was synthesized by performing the same operation as in Example 3 except that it was prepared by adding

(Example 5) Li ₂ CaSiO ₄
A mixed solution using Ca(NO ₃ ) ₂ instead of Sr(NO ₃ ) ₂ and adding C ₃ H ₈ O ₂ and a small amount of HCl to Si(OC ₂ H ₅ ) ₄ instead of GeO ₂ (hereinafter referred to as "Si source solution") was used, but the same operation as in Example 1 was performed to synthesize Li ₂ CaSiO ₄ .

(Example 6) Ce-W/Li ₂ CaSiO ₄
In addition to LiNO ₃ , Ca(NO ₃ ) ₂ , and Si source solution as raw materials, Ce and W were added to 2% by mass and 5% by mass, respectively, based on 100% by mass of the target Li ₂ CaSiO ₄ . Ce--W/Li ₂ CaSiO ₄ was synthesized by carrying out the same operation as in Example 5 except that it was prepared by adding .

(Example 7) Li ₂ SrSiO ₄
Li ₂ SrSiO ₄ was synthesized in the same manner as in Example 1 except that a Si source solution was used instead of GeO ₂ .

(Example 8) Ce-W/Li ₂ SrSiO ₄
In addition to LiNO ₃ , Sr(NO ₃ ) ₂ , and Si source solution as raw materials, Ce and W were added to 2% by mass and 5% by mass, respectively, based on 100% by mass of the target Li ₂ SrSiO ₄ . Ce-W/Li ₂ SrSiO ₄ was synthesized by performing the same operation as in Example 7 except that , was added.

(Example 9) Li ₂ BaSiO ₄
Li ₂ BaSiO ₄ was synthesized by performing the same operation as in Example 1, except that Ba(NO ₃ ) ₂ was used instead of Sr(NO ₃ ) ₂ and a Si source solution was used instead of GeO ₂ . .

(Example 10) Ce-W/Li ₂ BaSiO ₄
In addition to LiNO ₃ , Ba(NO ₃ ) ₂ , and Si source solution as raw materials, Ce and W were added to 2% by mass and 5% by mass, respectively, based on 100% by mass of the target Li ₂ BaSiO ₄ . Ce--W/Li ₂ BaSiO ₄ was synthesized by carrying out the same operation as in Example 9 except that it was prepared by adding .

(Comparative Example 1) Mn-Na ₂ WO ₄ /SiO ₂
Mn-Na ₂ WO ₄ /SiO ₂ was synthesized using a wet impregnation method. Mn(NO ₃ ) _{2.6H 2} O, Na ₂ WO _{4.2H 2} O, and SiO ₂ were used as raw materials. These were dissolved in pure water so that the target substances Mn and Na ₂ WO ₄ were 2% by weight and 5% by weight, respectively, immersed in SiO ₂ as a carrier, heated at 100° C., and dried. The dried product thus obtained was calcined in the air at 850° C. for 5 hours to obtain Mn-Na ₂ WO ₄ /SiO ₂ .

(Comparative Example 2) Li ₂ SiO ₃
Using Li ₂ CO ₃ and SiO ₂ as raw materials, these raw materials were weighed so that Li:Si=2:1, ethanol was added, and they were pulverized and mixed. After mixing, the sample was calcined in the air at 700°C for 1 hour to obtain a precursor. The precursor was main fired at 850°C in the air for 12 hours to synthesize Li ₂ SiO ₃ .

(Comparative Example 3) CaSiO ₃
CaCO ₃ and SiO ₂ were used as raw materials, and these raw materials were weighed so that Ca:Si=1:1, ethanol was added, and they were pulverized and mixed. After mixing, the sample was calcined in the air at 700°C for 1 hour to obtain a precursor. The precursor was main fired at 850° C. in the air for 12 hours to synthesize CaSiO ₃ .

(Comparative Example 4) Mixture of Li ₂ SiO ₃ and CaSiO ₃ Li ₂ SiO ₃ synthesized in Comparative Example 2 and CaSiO _{3 synthesized in Comparative Example 3} were mixed at a mass ratio of 1:1 to form Li ₂ SiO ₃ and CaSiO 3 . A mixture of ₃ was obtained.

(Comparative Example 5) Sr ₂ FeNbO ₆
SrCO ₃ , Fe ₂ O ₃ , and Nb ₂ O ₅ were used as raw materials, and these raw materials were weighed so that Sr:Fe:Nb=2:1:1, ethanol was added, and they were pulverized and mixed. After mixing, the sample was calcined in the air at 1000°C for 12 hours to obtain a precursor. The precursor was main fired at 1200° C. for 12 hours in the air to synthesize Sr ₂ FeNbO ₆ .

(Comparative Example 6) Sr ₂ FeSbO ₆
SrCO ₃ , Fe ₂ O ₃ , and Sb ₂ O ₃ were used as raw materials, and these raw materials were weighed so that Sr:Fe:Nb=2:1:1, ethanol was added, and they were pulverized and mixed. After mixing, the sample was calcined in the air at 1000°C for 12 hours to obtain a precursor. The precursor was main fired at 1200° C. for 12 hours in the air to synthesize Sr ₂ FeSbO ₆ .

(Comparative Example 7) Ca ₂ ZnSi ₂ O ₇
CaCO ₃ , ZnO, and SiO ₂ were used as raw materials, and these raw materials were weighed so that Ca:Zn:Si=2:1:1, and ethanol was added and pulverized and mixed. After mixing, the sample was calcined in the air at 1000°C for 12 hours to obtain a precursor. The precursor was main fired at 1200° C. in the air for 12 hours to synthesize Ca ₂ ZnSi ₂ O ₇ .

(Comparative Example 8) Ba ₂ TiSi ₂ O ₈
BaCO ₃ , TiO ₂ , and SiO ₂ were used as raw materials, and these raw materials were weighed so that Ca:Si=2:1:1, ethanol was added, and they were pulverized and mixed. After mixing, the sample was calcined in the air at 1000°C for 12 hours to obtain a precursor. The precursor was main fired at 1200° C. in the air for 12 hours to synthesize Ba ₂ TiSi ₂ O ₈ .

[Structural evaluation]
(Example 1 and Example 2)
X-ray diffraction (XRD) measurements were performed on the samples of Example 1 and Example 2. FIG. 1 shows XRD patterns of samples of Examples 1 and 2. In the sample of Example 1, only the peak of Li ₂ SrGeO ₄ was confirmed. On the other hand, in the sample of Example 2, in addition to the peak of Li ₂ SrGeO ₄ , peaks of SrLi _0.4 W _0.6 O ₃ , Li ₆ WO ₆ and CeO ₂ as subphases were confirmed. From this, it was found that the sample of Example 2 contained a Ce-containing oxide and a W-containing oxide.

The sample of Example 1 was observed using a scanning electron microscope (SEM). FIG. 2 is a SEM image of the sample of Example 1. Amorphous particles with a particle size of more than 10 μm were confirmed.

Energy dispersive X-ray (EDX) analysis was performed on the sample of Example 1. FIG. 3 shows the results of elemental analysis by SEM-EDX of Example 1, in which (a) is an SEM image, (b) is Sr Lα, (c) is Ge Lα, and (d) is O Kα. Thus, it was found that the Sr element, Ge element, and O element were present throughout the sample particles.

The sample of Example 2 was observed using SEM. FIG. 4 is a SEM image of the sample of Example 2. Amorphous particles with a particle size of 20 μm were confirmed. As shown in FIG. 1, the surface of the sample of Example 1 was smooth, whereas as shown in FIG. 4, the surface of the sample of Example 2 had irregularities.

EDX analysis was performed on the sample of Example 2. Figure 5 shows the results of elemental analysis by SEM-EDX in Example 2, where (a) is an SEM image, (b) is Ce Lα, (c) is W Mα, (d) is Sr Lα, and (e) is Ge Lα, (f) is O Kα. Thus, it was found that Ce element, W element, Sr element, Ge element, and O element were present throughout the particles.

(Example 3 and Example 4)
XRD measurements were performed on the samples of Example 3 and Example 4. In the sample of Example 3, only the peak of Li ₂ CaGeO ₄ was confirmed. On the other hand, in the sample of Example 4, in addition to the peak of Li ₂ CaGeO ₄ , peaks of Li ₄ WO ₅ , CeO ₂ and CaO as subphases were confirmed. From this, it was found that the sample of Example 4 contained a Ce-containing oxide and a W-containing oxide.

(Example 5 and Example 6)
XRD measurements were performed on the samples of Example 5 and Example 6. In the sample of Example 5, in addition to the peak of Li ₂ CaSiO ₄ , peaks of Li ₄ SiO ₄ and CaO as subphases were confirmed. On the other hand, in the sample of Example 6, in addition to the peak of Li ₂ CaSiO ₄ , peaks of Li ₄ WO ₅ , CeO ₂ and Li ₂ O as subphases were confirmed. From this, it was found that the sample of Example 6 contained a Ce-containing oxide and a W-containing oxide.

(Example 7 and Example 8)
XRD measurements were performed on the samples of Example 7 and Example 8. In the sample of Example 7, only the peak of Li ₂ SrSiO ₄ was confirmed. On the other hand, in the sample of Example 8, in addition to the peak of Li ₂ SrSiO ₄ , peaks of SrLi _0.4 W _0.6 O ₃ , CeO ₂ and Li ₄ SiO ₄ as subphases were confirmed. In addition, unidentifiable peaks were also confirmed. From this, it was found that the sample of Example 8 contained a Ce-containing oxide and a W-containing oxide.

(Example 9 and Example 10)
XRD measurements were performed on the samples of Example 9 and Example 10. In the sample of Example 9, in addition to the Li ₂ BaSiO ₄ peak, a SiO ₂ peak was confirmed. On the other hand, in the sample of Example 10, in addition to the Li ₂ BaSiO ₄ peak, BaLiWO _5.5 and CeO ₂ peaks were confirmed. From this, it was found that the sample of Example 10 contained a Ce-containing oxide and a W-containing oxide.

(Comparative Examples 1 to 8)
XRD measurements were performed on the materials of Comparative Examples 1 to 8. In the sample of Comparative Example 1, in addition to the peaks of Na ₂ WO ₄ and crystalline SiO _{2 ,} peaks of Na ₂ WO ₄ , Na ₄ WO ₅ , Na ₂ W ₂ O ₇ , Mn ₂ O ₃ and MnWO ₄ were observed. was confirmed. In the samples of Comparative Example 2 and Comparative Examples 5 to 8, only the peak of each target compound was observed. In the sample of Comparative Example 3, in addition to the peak of CaSiO ₃ , peaks of Ca ₂ SiO ₄ and SiO ₂ as subphases were confirmed.

[Catalytic activity evaluation]
0.3 g of each of the samples of Examples 1 to 10 and Comparative Examples 1 to 7 was filled into a quartz reaction tube with an inner diameter of 4 mm, and 1.0 mL/min of methane, 0.25 mL/min of oxygen, and 8.75 mL/min of nitrogen were charged. The catalytic activity of the OCM reaction was evaluated at 600°C to 800°C. The analysis was performed using a gas chromatograph (GC-8A, GC-TCD, manufactured by SHIMADZU). In addition, in the following method, since the hydrocarbon obtained by the oxidative coupling reaction of methane was mainly C ₂ , only C ₂ was analyzed.

FIG. 6 shows the catalytic activity evaluation results of the samples of Example 1, Example 2, and Comparative Example 1. FIG. 7 shows the catalytic activity evaluation results of samples of Example 3, Example 4, and Comparative Example 1. FIG. 8 shows the catalytic activity evaluation results of samples of Example 5, Example 6, and Comparative Example 1. FIG. 9 shows the catalytic activity evaluation results of samples of Example 7, Example 8, and Comparative Example 1. FIG. 10 shows the catalytic activity evaluation results of the samples of Example 9, Example 10, and Comparative Example 1. FIG. 11 shows the catalytic activity evaluation results of the samples of Example 5 and Comparative Examples 2 to 4. FIG. 12 shows the results of catalytic activity evaluation of samples of Comparative Examples 5 to 8. In these figures, the horizontal axis is the CH ₄ conversion rate (%), and the vertical axis is the C ₂ hydrocarbon selectivity (%). In addition, in these figures, the higher the upper right of the figure, that is, the larger the product of the CH ₄ conversion rate (%) and the selectivity of C ₂ hydrocarbons (%), the higher the yield of C ₂ hydrocarbons. It means that.

Furthermore, Table 1 shows the analysis results when the highest yield was obtained for Examples 1 to 10 and Comparative Examples 1 to 8. Note that the conversion rate, selectivity, and yield in Table 1 are values calculated using the following formulas (4) to (6), respectively.
Methane conversion rate (%)
= [1-(amount of unreacted methane/amount of raw material methane)]×100...(4)
_C2 yield (%)
= (2 x amount of ethylene and ethane produced/amount of raw material methane) x 100 (5)
_C2 selectivity (%) = _C2 yield/methane conversion rate...(6)

As can be seen from FIGS. 6 to 10, the samples of Examples 1 to 10 were all found to have higher selectivity than the existing sample of Comparative Example 1. For example, in the samples of Example 1 and Example 2, the temperature required to obtain the same CH ₄ conversion rate and C ₂ yield as in the existing Comparative Example 1 is about 50° C. lower.

As can be seen from FIG. 11, the sample of Comparative Example 2 contains Li element and Si element, the sample of Comparative Example 3 contains Ca element and Si element, and the sample of Comparative Example 4 contains Li element. , contains Ca element and Si element, but does not have a Li ₂ ABO ₄ crystal structure. Such a compound contains Li element, Ca element, and Si element and has lower selectivity, CH ₄ conversion rate, and C ₂ yield than Example 5, which has a Li ₂ ABO ₄ crystal structure. From this, it was found that the high catalytic activity confirmed in the samples of Examples 1 to 10 could not be achieved only by containing a predetermined metal element.

As can be seen from FIG. 12, the samples of Comparative Examples 5 to 8 are metal composite oxides having a crystal structure different from that of Li ₂ ABO ₄ , but these samples have a lower selectivity than Examples 1 to 10. , _CH4 conversion and _C2 yield are low. From this, it was found that the high catalytic activity observed in the samples of Examples 1 to 10 was achieved with a predetermined crystal structure.

[Thermal stability evaluation]
The samples of Example 1, Example 2, and Comparative Example 1 were held at 800°C for 2 hours in the same apparatus and gas atmosphere as in the above catalyst activity evaluation, and their CH ₄ conversion rate, C ₂ selectivity, and C ₂ yield were evaluated. The rate was measured. Note that in Example 2, measurements were also made at 750°C.

FIG. 13 shows the CH ₄ conversion rate, C ₂ selectivity, and C ₂ yield when the sample of Example 1 was held at 800° C. for 2 hours. FIG. 14 shows the CH ₄ conversion rate, C ₂ selectivity, and C ₂ yield when the sample of Example 2 was held at 800° C. for 2 hours. FIG. 15 shows the CH ₄ conversion rate, C ₂ selectivity, and C ₂ yield when the sample of Example 2 was held at 750° C. for 2 hours. FIG. 16 shows the CH ₄ conversion rate, C ₂ selectivity, and C ₂ yield when the sample of Comparative Example 1 was held at 800° C. for 2 hours. In FIGS. 13 to 16, the horizontal axis represents the elapsed time from the start of the test, and the vertical axis represents the CH ₄ conversion rate, C ₂ selectivity, and C ₂ yield.

As can be seen from FIGS. 13 to 15, the samples of Example 1 and Example 2 maintained high CH ₄ conversion, C ₂ selectivity, and C ₂ yield even after 2 hours, and the thermal It can be said that it is a highly stable material. Furthermore, the _C2 yield at 750°C of Example 2) is comparable to the activity at 800°C of the existing sample of Comparative Example 1, and the sample of Example 2 has a higher activity than the sample of Comparative Example 1. It is considered to be active.

[Effect of oxygen/methane ratio]
Regarding the sample of Example 5, the temperature was fixed at 800 ° C., the total flow rate of methane and oxygen was fixed at 1.25 mL/min, and the oxygen/methane ratio (mole ratio) was changed, under the same conditions as in the above catalyst activity evaluation. The effect of the methane/oxygen ratio was investigated.

FIG. 16 is a diagram showing changes in CH ₄ conversion rate, C ₂ selectivity, and C ₂ yield when changing the oxygen/methane ratio for the sample of Example 5. In FIG. 16, the horizontal axis is the oxygen/methane ratio, and the vertical axis is the CH ₄ conversion rate, C ₂ selectivity, and C ₂ yield.

Claims (5)

Contains a Li - containing composite metal oxide represented by the general formula Li ₂ ABO ₄ (A is Ca and B is Si),
In addition to Li ₂ CaSiO ₄ , it contains Li ₄ SiO ₄ and CaO as subphases.
A catalyst for synthesizing hydrocarbons with two or more carbon atoms from methane. A method for producing hydrocarbons, which comprises synthesizing hydrocarbons having two or more carbon atoms from methane using the catalyst according to claim 1. The method for producing hydrocarbons according to claim 2, wherein hydrocarbons having two or more carbon atoms are synthesized from methane by bringing methane and oxygen into contact and reacting. 4. The method for producing hydrocarbons according to claim 3, wherein methane and oxygen are brought into contact in a reaction system in a temperature range of 600°C or higher and 800°C or lower. The method for producing hydrocarbons according to claim 4, wherein the molar ratio of oxygen and methane (oxygen/methane) in the reaction system is 0.12 or more and 0.6 or less.

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