JP2024144183A - Zeolite catalyst and method for producing synthesis gas - Google Patents

Abstract

The present invention provides a catalyst that suppresses complete oxidation of methane in the reaction between methane and oxygen and highly selectively partially oxidizes methane. The present invention provides a zeolite catalyst used for partial oxidation of light hydrocarbons, containing silicon (Si) and aluminum (Al) as constituent elements and with a content of elements from Groups 8 to 10 of the periodic table of less than 0.1 mass%. [Selected Figures] None

Description

The present invention relates to a zeolite catalyst and a method for producing synthesis gas, and more specifically, to a method for producing carbon monoxide and hydrogen (synthesis gas) using a catalyst and methane as a raw material.

Methane ( _CH4 ) reforming is a commonly used technology for producing a mixed gas (synthetic gas) of carbon monoxide (CO) and hydrogen ( _H2 ). Among the methane reforming reactions, steam reforming of methane ( _CH4 + _H2O → _3H2 + CO, _ΔH0 = + 206 kJ) is the most commonly used technology, but this reaction is a large endothermic reaction, and the large energy consumption in the process is a problem.
On the other hand, the partial oxidation of methane (2CH ₄ +O ₂ →4H ₂ +2CO, ΔH ₀ =-36 kJ) is an exothermic reaction, and therefore, once the reaction starts, it does not require an external energy supply, and is therefore attracting attention as a highly energy-efficient process.

For such partial oxidation of methane, catalytic materials containing transition metals such as Co, Ni, Ru, Rh, Pd, and Pt as active sites have traditionally been used. For example, Patent Document 1 discloses a partial oxidation catalyst for light hydrocarbons that contains cobalt and rhodium-supported zeolite. Patent Document 2 discloses a partial oxidation catalyst for light hydrocarbons in which zeolite supports at least one element selected from the transition metals of Groups 8 to 11 of the periodic table and at least one element selected from the metals of Groups 1 to 3 of the periodic table.

JP 2019-181375 A JP 2021-45722 A

When the catalyst materials disclosed in Patent Documents 1 and 2 are used, a part of methane is likely to be completely oxidized (CH ₄ +2O ₂ →2H ₂ O+CO ₂ , ΔH ₀ =−803 kJ) simultaneously with the partial oxidation of methane. Since the heat generated by the complete oxidation is much larger than that generated during partial oxidation, the catalyst bed is rapidly heated as soon as the reaction starts, forming a hot spot. The formation of such a hot spot not only reduces the yield of carbon monoxide, but also causes aggregation of active metal species at the hot spot. When a hot spot is formed, even if the reaction is stopped and the partial oxidation reaction is resumed, the complete oxidation reaction is likely to occur again, and the aggregation of metals may also cause catalyst deterioration. Therefore, there is a demand for the development of a catalyst that suppresses the complete oxidation of methane and partially oxidizes methane highly selectively by reaction with oxygen.

The present invention aims to solve the above problems by providing a catalyst that suppresses the complete oxidation of methane in the reaction between methane and oxygen and partially oxidizes methane with high selectivity.

The present inventors have conducted studies aimed at solving the above problems, and have found that by activating methane by utilizing the acidic properties of the zeolite surface, the methane can be converted into carbon monoxide and hydrogen, that is, that zeolite can convert methane to carbon monoxide with high selectivity in the partial oxidation of methane.
The present invention was completed based on these findings.

The present invention includes the following gist.
[1] A zeolite catalyst used for partial oxidation of light hydrocarbons, containing silicon (Si) and aluminum (Al) as constituent elements and having a content of elements of Groups 8 to 10 of the Periodic Table of less than 0.1 mass%.
[2] The zeolite catalyst according to the above [1], wherein the molar ratio of silicon to aluminum (Si/Al) contained in the zeolite catalyst is 1 or more and 100 or less.
[3] The zeolite catalyst according to the above [1] or [2], which includes at least one crystal structure selected from the group consisting of AEI, CHA, MFI, and BEA, as defined by the International Zeolite Association (IZA) code.
[4] The zeolite catalyst according to any one of the above [1] to [3], wherein the light hydrocarbons are hydrocarbons having 6 or less carbon atoms.
[5] The zeolite catalyst according to any one of the above [1] to [4], wherein the light hydrocarbon is methane or contains methane as a main component.
[6] A method for producing synthesis gas by a partial oxidation reaction of methane at a reaction temperature of 650°C or higher using a zeolite-based catalyst containing silicon (Si) and aluminum (Al) as constituent elements and having a content of elements from Groups 8 to 10 of the Periodic Table of less than 0.1 mass%.
[7] The method for producing a synthesis gas according to the above [6], wherein a synthesis gas that is a product of the partial oxidation reaction of methane contains carbon monoxide, hydrogen, ethane, ethylene, carbon dioxide, and water, and the selectivity of carbon dioxide relative to methane is 30 mol % or less.
[8] The method for producing a synthesis gas according to the above [6] or [7], wherein the partial oxidation reaction of methane is performed in a molar ratio of methane to oxygen (methane/oxygen) of 1 or more.
[9] The method for producing a synthesis gas according to any one of the above [6] to [8], wherein the partial oxidation reaction of methane is carried out at 1000° C. or less.
[10] The method for producing a synthesis gas according to any one of [6] to [9] above, wherein a molar ratio of silicon to aluminum (Si/Al) contained in the zeolite catalyst is 1 or more and 100 or less.
[11] The method for producing a synthesis gas according to any one of [6] to [10] above, wherein the zeolite in the zeolite-based catalyst has at least one crystal structure selected from the group consisting of AEI, CHA, MFI, and BEA, as defined by the International Zeolite Association (IZA) code.

The present invention provides a catalyst that suppresses complete oxidation of methane in the reaction of methane with oxygen and partially oxidizes methane with high selectivity.

The present invention will be described in detail below. However, the following description of the components is an example (representative example) of an embodiment of the present invention, and the present invention is not limited to these contents, and can be practiced in various modifications within the scope of the gist.

[Zeolite-based catalyst]
The zeolite catalyst of the present invention is a catalyst used for partial oxidation of light hydrocarbons, which contains silicon (Si) and aluminum (Al) as constituent elements and has a content of elements of Groups 8 to 10 of the periodic table of less than 0.1 mass%.
Here, the light hydrocarbon is preferably a hydrocarbon having a carbon number of 6 or less. When the light hydrocarbon is a hydrocarbon having a carbon number of 6 or less, the zeolite catalyst of the present invention effectively functions as a partial oxidation catalyst. In particular, the light hydrocarbon having a carbon number of 6 or less is preferably methane or a hydrocarbon containing methane as a main component.

<Zeolite>
The zeolite used as the catalyst of the present invention contains silicon (Si) and aluminum (Al) as constituent elements. In addition to Si and Al, the constituent elements may contain one or more elements selected from boron (B), titanium (Ti), vanadium (V), iron (Fe), zinc (Zn), gallium (Ga), germanium (Ge), zirconium (Zr), and tin (Sn). The Al and other elements forming the zeolite framework become acid sites and act as reaction sites for catalytic activity.
The molar ratio of silicon to aluminum (hereinafter referred to as "Si/Al ratio") of these zeolites is not particularly limited as long as it is within a range in which the effects of the present invention can be achieved, but is preferably 1 or more and 100 or less.
When the Si/Al ratio is 100 or less, the amount of acid becomes appropriate, and the partial oxidation reaction of methane can be promoted. From the above viewpoints, it is more preferable that the Si/Al ratio is 80 or less. On the other hand, when the Si/Al ratio is 1 or more, dealumination in the partial oxidation reaction of methane can be suppressed, and high activity can be maintained. From the above viewpoints, it is preferable that the Si/Al ratio is 3 or more, and more preferably 8 or more.
The contents of Si, Al, etc. in the zeolite produced by the method of the present invention can usually be measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), etc. The "Si/Al ratio" in the present invention is a value calculated from the value measured by ICP-AES for the produced zeolite, and is not the ratio of Si to Al calculated from the amount of the raw material charged.
The Si _/ Al ratio can be controlled by the _SiO2 / _Al2O3 ratio of the feed when producing the zeolite, and can also be controlled by the production conditions. Furthermore, after the production of the zeolite, the Si/Al ratio can also be controlled by desorbing Al and the like by a steaming treatment or the like.

The crystal structure of the zeolite according to the present invention is not particularly limited as long as it exhibits the effects of the present invention. The codes are defined by the International Nuclear Safety Association (IZA), and include AEI, AEL, AFI, AFX, APC, ATO, BEA, BRE, CDO, CHA, CON, DDR, EAB, EPI, ERI, ESV, EUO, FAU, FER, GIS, GME, HEU, ITH, KFI, LEV, LTA, LTL, MER, MEL, MFI, MON, MOR, MSE, MTF, MTT, MTW, MWW, NES, OFF, PAU, PHI, RHO, RTE, RTH, SOD, STI, STT, SZR, TON, TSC, TUN, UFI, VNI, WEI, and YUG. Among them, it is preferable to use one or more selected from AEI, CHA, MFI, and BEA. These zeolites generate Al species that can exhibit Lewis acidity during the partial oxidation of methane, and are suitable as reaction fields for the partial oxidation of methane. Therefore, they show more favorable activity than MOR and FAU.
The above zeolites may be used alone or in combination of two or more kinds.
The formation of Lewis acid Al species can be confirmed by adsorption IR using CO molecules as a probe.

The pore size of the zeolite is not particularly limited, but is preferably 0.3 nm or more, more preferably 0.35 nm or more. It is also preferably 0.9 nm or less, more preferably 0.8 nm or less, and even more preferably 0.6 nm or less. The pore size referred to here indicates the crystallographic channel diameter defined by the International Zeolite Association (IZA). When the pore size of the zeolite is within the above range, the raw materials methane and oxygen easily enter the zeolite pores, and the reaction easily proceeds at the active sites in the pores. In addition, the product is easily desorbed, and there is no problem such as caulking caused by excessive reaction in the pores.

The ion exchange sites of the zeolite are not particularly limited and may be H-type or may be exchanged with alkali metal ions, alkaline earth metal ions, etc., but H-type is preferred.

In addition, the BET specific surface area of the zeolite is not particularly limited within the range in which the effects of the present invention are exhibited, but is preferably, for example, 200 m ² /g or more. When the BET specific surface area of the zeolite is 200 m ² /g or more, the adsorption sites of the raw material methane are sufficiently secured, and the reaction efficiency can be improved. From the above viewpoints, the BET specific surface area of the zeolite is more preferably 250 m ² /g or more, and even more preferably 300 m ² /g or more. On the other hand, the BET specific surface area of the zeolite is preferably 2000 m ² /g or less. When the BET specific surface area of the zeolite is 2000 m ² /g or less, the synthesis of the zeolite becomes easy. From the above viewpoints, the BET specific surface area of the zeolite is more preferably 1500 m ² /g or less, and even more preferably 1000 m ² /g or less. The BET specific surface area can be measured by a nitrogen adsorption method.

In addition, the pore volume of the zeolite according to the present invention is not particularly limited as long as the effects of the present invention are achieved, but is preferably 0.1 mL/g or more. When the pore volume of the zeolite is 0.1 mL/g or more, sufficient adsorption sites for the raw material methane are secured, and the reaction efficiency can be improved. From the above viewpoints, the pore volume of the zeolite is more preferably 0.2 mL/g or more, and even more preferably 0.3 mL/g or more.
On the other hand, the pore volume of the zeolite is preferably 3 mL/g or less, and more preferably 2 mL/g or less.
The average pore size of the zeolite may be the value of the pore size of each crystal structure published by the IZA, and the pore volume can be measured by a nitrogen adsorption method.

The average primary particle size of the zeolite according to the present invention is not particularly limited as long as the effects of the present invention are achieved, but is preferably 10 μm or less. If the average primary particle size of the zeolite is 10 μm or less, it is advantageous in terms of the diffusion of the reaction substrate and the reaction product. From the above viewpoints, the average primary particle size of the zeolite is more preferably 3 μm or less, and even more preferably 700 nm or less.
On the other hand, the lower limit is not particularly limited as long as it is within a range in which the effects of the present invention can be obtained, and is usually 20 nm or more, preferably 40 nm or more.

The "average primary particle size" can be calculated using a scanning electron microscope (SEM).
Here, "primary particles" refer to the smallest particles for which no grain boundaries are observed. In the present invention, an SEM image of the zeolite catalyst is obtained, and the smallest particles that correspond to the zeolite contained in the SEM image and for which no grain boundaries are observed are determined to be "primary particles." In the present invention, the primary particles do not have to exist as single particles, and may form secondary particles by aggregation or the like. Even if secondary particles are formed, the primary particles on the surfaces of the secondary particles can be identified in the SEM image.
The "average primary particle size" refers to a measurement as follows: 50 primary particles included in a SEM image of a zeolite catalyst are randomly selected, and the major axis (the length of the longest straight line when connecting one end of a primary particle with the other end of a straight line) of each of the selected 50 primary particles is measured, and the arithmetic mean of the major axes of the 50 particles is defined as the "average primary particle size."
However, when the entire zeolite catalyst contains less than 50 primary particles, the major axis of each of all primary particles contained in the zeolite catalyst is measured, and the average value thereof is regarded as the "average primary particle diameter."

The average primary particle size can be set within a specific range, for example, by using zeolite with a small particle size as seed crystals, or by adding a surfactant to the zeolite synthesis raw material gel during the zeolite manufacturing process.

The zeolite according to the present invention has a content of elements from Groups 8 to 10 of the periodic table of less than 0.1% by mass. When the content of elements from Groups 8 to 10 of the periodic table is less than 0.1% by mass, the complete oxidation reaction of methane is not triggered. Therefore, the carbon monoxide yield is not reduced and the formation of hot spots is suppressed, which is preferable.

<Method of manufacturing zeolite>
The method for producing a zeolite of the present invention includes a step of hydrothermally synthesizing a raw material composition.
More specifically, the method includes a step of preparing a raw material gel containing a silica source, an aluminum source, and an alkali metal, and a step of hydrothermally synthesizing the raw material gel at 10 to 240°C.

(Preparation of raw gel)
The raw gel is prepared using a silica source, an aluminum source, and a compound containing an alkali metal. In preparing the raw gel, other components such as a compound containing an alkaline earth metal, an organic structure directing material, and a seed crystal may be further used as long as they do not significantly impair the effects of the present invention.

<<Raw materials, etc.>>
The silica source refers to a raw material compound that becomes silicon atoms that constitute zeolite. Examples of the silica source include fumed silica, silica sol, colloidal silica, water glass, ethyl silicate, methyl silicate, etc., and one or more of these are used. Among these, fumed silica and colloidal silica are preferred because they are easy to handle and highly reactive.

The aluminum source refers to a raw material compound that becomes the aluminum atoms that constitute the zeolite. The aluminum source typically includes aluminum alkoxides such as pseudoboehmite, gibbsite, aluminum isopropoxide, and aluminum triethoxide; aluminum hydroxide; alumina sol, and sodium aluminate, and one or more of these are used. Of these, aluminum hydroxide, aluminum isopropoxide, and pseudoboehmite are preferred because they are easy to handle and highly reactive.

The compound containing an alkali metal may be a hydroxide of an alkali metal such as NaOH or KOH. The type of alkali metal is not particularly limited, and typically includes Na, K, Li, and Rb, and preferably Na and K. Two or more types of compounds containing an alkali metal may be used in combination.
In addition, a compound containing an alkaline earth metal may be used. As the compound containing an alkaline earth metal, Ca(OH) ₂ or the like may be used. The type of alkaline earth metal is not particularly limited, and typically includes Ca, Mg, Sr, and Ba. In addition, two or more types of compounds containing an alkaline earth metal may be used in combination.

As organic structure-directing materials used in the synthesis of zeolites, amines, quaternary ammonium salts, etc. are usually used. For example, when synthesizing CHA-type aluminosilicates, the organic templates described in U.S. Pat. No. 4,544,538 and U.S. Patent Publication No. 2008/0075656 are preferred. However, depending on the composition of the resulting zeolite, an organic structure-directing material is not necessarily required.

The raw gel may be prepared using seed crystals, and zeolite is usually used as the seed crystals.
If the zeolite to be produced is an aluminosilicate, the seed crystals are preferably aluminosilicate zeolite, more preferably aluminosilicate zeolite containing d6r as CBU. The seed crystals may contain an amorphous component as a part thereof.
The zeolite used as the seed crystals may or may not contain an organic structure-directing material. The method for producing the zeolite to be used as the seed crystals is not particularly limited, and the zeolite may be produced by the zeolite production method of the present invention, or may be produced by another method, for example, a general batch method using an autoclave or the like. The amount of the seed crystals is preferably large in terms of the effect of promoting crystallization as the seed crystals being easily exhibited. On the other hand, it is preferable that the amount of the seed crystals is small in terms of the ease of dissolving the seed crystals and the ease of functioning as the seed crystals. Therefore, the amount of the seed crystals is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1.0% by mass or more, and particularly preferably 2% by mass or more, relative to the silica source contained in the raw material composition. On the other hand, it is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 15% by mass or less, and particularly preferably 10% by mass or less.

(Hydrothermal synthesis of raw material gel)
The zeolite of the present invention can be produced by hydrothermal synthesis of the raw material gel described above. The temperature of the hydrothermal synthesis of the raw material gel is usually 10° C. or higher, preferably 50° C. or higher, and more preferably 70° C. or higher. A high temperature is preferable in terms of facilitating the reaction. There is no particular upper limit to the temperature of the hydrothermal synthesis, and it is usually 240° C. or lower, preferably 220° C. or lower, and more preferably 200° C. or lower.

<<Cation exchange>>
The method for producing a zeolite of the present invention may further include a step of exchanging the cation type of the zeolite obtained by the above-mentioned hydrothermal synthesis.
Zeolite obtained by hydrothermal synthesis can be cation-exchanged to a desired cation type as necessary. Cation exchange can be performed using, but is not limited to, nitrates such as NH ₄ NO ₃ , LiNO ₃ , NaNO ₃ , KNO ₃ , RbNO ₃ , CsNO ₃ , Be(NO ₃ ) ₂ , Ca(NO ₃ ) ₂ , Mg(NO ₃ ) ₂ , Sr(NO ₃ ) ₂ , Ba(NO ₃ ) ₂ , or salts of halide ions, sulfate ions, carbonate ions, hydrogen carbonate ions, acetate ions, phosphate ions, and hydrogen phosphate ions instead of the nitrate ions contained in these nitrates, and acids such as nitric acid and hydrochloric acid. The temperature of the cation exchange is not particularly limited as long as it is a general cation exchange temperature, but is usually 10°C or higher and 100°C or lower. Ammonium-type zeolite can also be converted to proton-type zeolite by calcining the zeolite.

After the raw gel crystallizes, the crystallized raw gel is filtered and washed, and the solids are dried at 100 to 200°C and then calcined at 400 to 900°C to obtain zeolite powder.

[Method of producing synthetic gas]
The method for producing a synthesis gas of the present invention is a method for producing a synthesis gas by a partial oxidation reaction of methane, and is characterized in that the synthesis gas is produced by the partial oxidation reaction of methane at a reaction temperature of 650° C. or higher using a zeolite-based catalyst that contains silicon (Si) and aluminum (Al) as constituent elements and has a content of elements from Groups 8 to 10 of the periodic table of less than 0.1 mass %.

<Reaction conditions>
In the synthesis gas production method of the present invention, the reaction temperature must be at least 650° C. By setting the reaction temperature at 650° C. or higher, partial oxidation of methane progresses, and synthesis gas can be efficiently obtained.
On the other hand, there is no particular restriction on the upper limit of the reaction temperature, but in order to suppress complete oxidation of methane, it is preferably 1000°C or lower, and in order to stabilize the activity of the catalyst, it is more preferably 900°C or lower, further preferably 850°C or lower, and most preferably 800°C or lower.
From the above viewpoints, the reaction temperature in this reaction is preferably in the range of 650°C to 1000°C, more preferably in the range of 650°C to 900°C, even more preferably in the range of 650°C to 850°C, and most preferably in the range of 650°C to 800°C.
Since this reaction is an exothermic reaction, even if the reaction start temperature is 500°C, it may reach 650°C or higher when an adiabatic reaction vessel is used. Therefore, the reaction temperature here refers to the temperature of the catalyst layer of the reactor, not the inlet temperature of the reaction gas. The temperature of the catalyst layer can usually be considered to be the same as the internal temperature (not the inlet temperature) of the reactor.

In the partial oxidation process of methane in the present invention, the molar ratio of methane to oxygen in the raw material (methane/oxygen) is preferably 1 or more. When this ratio is 1 or more, complete oxidation of methane can be easily suppressed, and partial oxidation of methane can be promoted. Furthermore, when the methane/oxygen ( _CH4 / _O2 ) ratio is 1 or more, a sufficient reaction rate can be obtained. From the above viewpoints, the methane/oxygen ( _CH4 / _O2 ) ratio in the raw material is preferably 1 or more, more preferably 1.5 or more, and most preferably 2 or more.
On the other hand, there is no particular upper limit to the methane/oxygen (CH ₄ /O ₂ ) ratio, but from the viewpoint of reaction efficiency, it is preferably 6 or less, and more preferably 3 or less.

As the reaction mode in this embodiment, a known gas phase reaction process using a fluidized bed reactor, a moving bed reactor, or a fixed bed reactor can be applied. A fixed bed reactor is advantageous in terms of the equipment cost including auxiliary equipment, catalyst cost, and operation management.
The process may be carried out in any of a batch, semi-continuous or continuous manner, but is preferably carried out in a continuous manner, and may be a process using a single reactor or a process using multiple reactors arranged in series or parallel.

When the above-mentioned catalyst is packed into the fluidized bed reactor, in order to minimize the temperature distribution in the catalyst layer, granular materials inactive to the reaction, such as quartz sand, alumina, silica, silica-alumina, etc., may be mixed with the catalyst and packed. In this case, there is no particular restriction on the amount of granular materials inactive to the reaction, such as quartz sand, used. In addition, it is preferable that the granular materials have a particle size similar to that of the catalyst, from the viewpoint of uniform mixing with the catalyst.
In addition, the reaction substrate (reaction raw material) may be divided and fed to the reactor for the purpose of dispersing heat generated by the reaction.

In addition to methane and oxygen, other gases that can be present in the reactor include helium, argon, nitrogen, carbon monoxide, carbon dioxide, hydrogen, water, paraffins, aromatic compounds, and mixtures thereof. Of these, the coexistence of water (water vapor) and/or carbon dioxide is preferred because it is expected to have the effect of suppressing carbon deposition on the catalyst.
As such a diluent, the impurities contained in the reaction raw materials may be used as they are, or a separately prepared diluent may be mixed with the reaction raw materials. The diluent may also be mixed with the reaction raw materials before being placed in the reactor, or may be supplied to the reactor separately from the reaction raw materials.

It is important that the lower limit of the reaction temperature is 650°C or higher. There is no upper limit to the reaction temperature as long as the effects of the present invention are achieved, but it is preferable that the upper limit is 800°C or lower. If the reaction temperature is 650°C or higher, a sufficient reaction rate can be obtained. On the other hand, if the reaction temperature is 800°C or lower, the activity of the catalyst becomes stable.

The upper limit of the reaction pressure is preferably 3 MPa (absolute pressure, the same applies below). If the reaction pressure is 3 MPa or less, the production of undesirable by-products can be suppressed. From the above viewpoint, the reaction pressure is preferably 1 MPa or less.
The lower limit of the reaction pressure is not particularly limited, but is usually 0.1 kPa or more, preferably 1 kPa or more, and more preferably 10 kPa or more. By keeping the reaction pressure at or above these lower limits, a sufficient reaction rate can be obtained.

The weight hourly space velocity of the reaction raw material is preferably 0.1 hr ^-1 or more, more preferably 0.5 hr ^-1 or more. On the other hand, the weight hourly space velocity is preferably 10 hr ^-1 or less, more preferably 5 hr ^-1 or less. If the weight hourly space velocity is within this range, it is advantageous for the partial oxidation reaction of methane.

According to the method of the present invention, the reaction products include, in addition to synthesis gas (CO+H ₂ ), hydrocarbons having two carbon atoms (by-products) such as ethane and ethylene, carbon dioxide, and water, and among these reaction products, the selectivity of carbon dioxide relative to the raw material methane can be set to 30 mol % or less, more preferably 25 mol % or less. Furthermore, in the present invention, the conversion rate of methane is 8 to 100%, and the selectivities of carbon monoxide and hydrogen are 60 to 90% and 8 to 25%, respectively.
The mixed gas containing the unreacted raw materials, by-products and diluent in the reactor outlet gas can be introduced into a known separation and purification facility and can be recovered, purified, recycled or discharged according to the respective components.

The present invention will be described in more detail below with reference to examples, but the scope of the present invention is not limited to the following examples.
(Evaluation Method)
(1) Physical properties of zeolite <Elemental analysis>
Elemental analysis was performed by inductively coupled plasma atomic emission spectrometry (ICP-AES).
<X-ray diffraction measurement>
The crystal structure of each zeolite was determined by X-ray diffraction measurement (XRD). The measurement was performed using a "D2PHASER" manufactured by BRUKER.
Table 1 shows the crystal structure, Si/Al ratio, and elemental analysis results of the zeolites used in the respective Examples and Comparative Examples.

(2) Reaction evaluation Using a fixed-bed gas-phase flow reactor, 100 mg of the catalyst of each example and comparative example was packed in the middle of a quartz glass reaction tube (catalyst layer part: outer diameter 8.0 mm, inner diameter 6.0 mm, other: outer diameter 6.0 mm, inner diameter 4.0 mm, total length 260 mm). The electric furnace was heated to 500 ° C. under N ₂ flow (10 ml / min). Then, CH ₄ was introduced at a flow rate of 5.0 ml / min, O ₂ at a flow rate of 2.5 ml / min, and N ₂ at a flow rate of 12.5 ml / min, and a partial oxidation reaction test of methane was performed at a reaction temperature range of 500 ° C. to 800 ° C. Downstream of the reactor, condensation of the generated water was prevented by heating at 100 ° C. with a ribbon heater and diluting the reaction gas with N ₂ (100 ml / min). The products were analyzed using a two-channel online Micro-GC (FUSION, manufactured by INFICON). In channel 1 of the Micro-GC, H ₂ , O ₂ , N ₂ , CH ₄ , and CO were quantified using a capillary column Molecular Sieve 5A (trade name) using Ar as the carrier gas. In channel 2, CO ₂ , C ₂ H ₄ , C ₂ H ₆ , and H ₂ O were quantified using a capillary column Porapak (trade name) using He as the carrier gas. A TCD was used as the detector.

The conversion rate of the reactants and the yield of the products were calculated as follows: In the following formula, F means flow rate, in means inlet, and out means outlet. For example, F _CH4,in means the flow rate _{of CH4} at the inlet.

In addition, the following relationship holds in the above formula.

Example 1
A proton-type BEA zeolite (manufactured by Zeolyst, Si/Al ratio = 13) was prepared as a methane partial oxidation catalyst. The reaction evaluation was performed by the above method. As shown in Table 2, the reaction results of the proton-type BEA zeolite at 700 ° C were CH ₄ conversion rate 22%, O ₂ conversion rate 60%, CO selectivity 81%, H ₂ selectivity 20%, and carbon dioxide selectivity 19%.

Examples 2 to 21 and Comparative Examples 1 to 5
A partial oxidation reaction test of methane was carried out in the same manner as in Example 1, except that the catalysts shown in Table 1 were used and the reaction was carried out under the reaction conditions shown in Table 1. The results are shown in Table 2.

From the results shown in Tables 1 and 2, it is clear that by using a zeolite composed of Si and Al and setting the content of transition metals of Groups 8 to 10 of the periodic table to less than 0.1 mass%, it is possible to suppress the complete combustion reaction of methane and improve the selectivity of the partial oxidation of methane. Specifically, it is possible to suppress the selectivity of _CO2 generated by the complete oxidation of methane to 30% or less.
It is also seen that, compared to MOR and FAU, CHA, MFI, and BEA, which have Al sites having Lewis acidity, are preferable.
Furthermore, from a comparison between each of the Examples and Comparative Examples 4 and 5, it is seen that the conversion rate of methane is low when the reaction temperature is 600° C. or lower. Therefore, it is seen that in the present invention, it is essential that the reaction temperature is 650° C. or higher.

According to the production method of the present invention, methane can be partially oxidized with high selectivity, and synthesis gas (CO + H ₂ ) can be efficiently produced. Since synthesis gas is important as a raw material for various reactions, the present invention is a technology that can contribute to industry.

Claims (11)

A zeolite catalyst used for the partial oxidation of light hydrocarbons, containing silicon (Si) and aluminum (Al) as constituent elements and with a content of elements from groups 8 to 10 of the periodic table of less than 0.1 mass%. The zeolite catalyst according to claim 1, wherein the molar ratio of silicon to aluminum (Si/Al) contained in the zeolite catalyst is 1 or more and 100 or less. The zeolite catalyst according to claim 1 or 2, wherein the zeolite catalyst comprises at least one crystal structure selected from the group consisting of AEI, CHA, MFI, and BEA, as defined by the International Zeolite Association (IZA) code. The zeolite catalyst according to claim 1, wherein the light hydrocarbons are hydrocarbons having 6 or less carbon atoms. The zeolite catalyst according to claim 1, wherein the light hydrocarbon is methane or is mainly composed of methane. A zeolite catalyst containing silicon (Si) and aluminum (Al) as constituent elements and having a content of elements of Groups 8 to 10 of the Periodic Table of less than 0.1 mass % is used as a catalyst;
A method for producing synthesis gas by partial oxidation of methane at a reaction temperature of 650°C or higher. The method for producing synthesis gas according to claim 6, wherein the synthesis gas that is the product of the partial oxidation reaction of methane contains carbon monoxide, hydrogen, ethane, ethylene, carbon dioxide, and water, and the selectivity of carbon dioxide relative to methane is 30 mol % or less. The method for producing synthesis gas according to claim 6 or 7, wherein the partial oxidation reaction of methane is performed with a molar ratio of methane to oxygen (methane/oxygen) of 1 or more. The method for producing synthesis gas according to claim 6 or 7, wherein the partial oxidation reaction of methane is carried out at 1000°C or less. The method for producing a synthesis gas according to claim 6 or 7, wherein the molar ratio of silicon to aluminum (Si/Al) contained in the zeolite catalyst is 1 or more and 100 or less. The method for producing a synthesis gas according to claim 6 or 7, wherein the zeolite in the zeolite catalyst includes at least one crystal structure selected from the group consisting of AEI, CHA, MFI, and BEA, as defined by the International Zeolite Association (IZA) code.