Partial oxidation catalyst for light hydrocarbon, method for producing synthesis gas, and method for producing partial oxidation catalyst

Abstract

To provide a partial oxidation catalyst capable of partially oxidizing a light hydrocarbon to a synthesis gas with high oxidation activity of the light hydrocarbon and high gas selectivity, a method for producing the synthesis gas, and a method for producing the partial oxidation catalyst.SOLUTION: Provided are: a partial oxidation catalyst for a light hydrocarbon containing a main catalyst containing boron nitride, and at least one metal selected from the group consisting of transition metals of Groups 4 to 9 of the 4th period, transition metals of Groups 4 to 6 of the 5th to 6th periods, and lanthanoid transition metals of the long-period periodic table, on the surface of the main catalyst; a method for producing synthesis gas using the partial oxidation catalyst; and a method for producing the partial oxidation catalyst.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a partial oxidation catalyst for light hydrocarbons, a method for producing synthesis gas, and a method for producing a partial oxidation catalyst, and more particularly to a partial oxidation catalyst used in a reaction for producing carbon monoxide and hydrogen (synthesis gas) using light hydrocarbons as a raw material, a method for producing synthesis gas, and a method for producing a partial oxidation catalyst. [Background technology]

[0002] Methane (CH4) reforming is a commonly used technology for producing a mixed gas (synthesis 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 (CH4 + 1 / 2O2 → 2H2 + CO, ΔH0 = -36 kJ) is an exothermic reaction, and therefore, once the reaction begins, it does not require external energy supply, and is therefore attracting attention as a highly energy-efficient process.

[0003] Catalyst materials containing transition metals such as Ni, Ru, Rh, Pd, and Pt are used in the partial oxidation of methane. These catalysts are known to produce synthesis gas via either complete methane oxidation (2CH4 + 2O2 → CO2 + 2H2O, ΔH0 = -803 kJ), followed by methane reforming (CH4 + 1 / 2O2 → 2H2 + CO, ΔH0 = -36 kJ, and CH4 + CO2 → 2H2 + 2CO, ΔH0 = +247 kJ), or complete methane oxidation followed by the reverse water-gas shift reaction (RWSS), as shown in equation (1). However, the large heat generated by the complete oxidation of methane creates hot spots, which rapidly deactivate the catalyst. [ka]

[0004] Therefore, the development of catalysts for directly converting methane to synthesis gas is underway. For example, Patent Document 1 and Non-Patent Document 1 describe that boron nitride is active in the direct conversion of methane to synthesis gas. Furthermore, Non-Patent Document 2 describes that boron oxide supported on oxides such as Al2O3 and SiO2 is active in producing CO and formaldehyde from methane. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Chinese Patent No. 107876076 [Non-patent literature]

[0006] [Non-Patent Document 1] Catal. Sci. Technol. 2018, 8, 2051-2055 [Non-patent document 2] Nat. Commun. 2020, 11, 5693. Summary of the Invention [Problem to be solved by the invention]

[0007] However, the catalysts described in Patent Document 1 and Non-Patent Documents 1 and 2 were insufficient in methane oxidation activity and synthesis gas selectivity, and the development of further catalysts was desired. In Non-Patent Document 2, the main products of the partial oxidation of methane were formaldehyde and CO, so high CO selectivity was not obtained.

[0008] The present invention has been made to solve the above-mentioned problems, and provides a partial oxidation catalyst for light hydrocarbons that can partially oxidize light hydrocarbons to synthesis gas with high oxidation activity for light hydrocarbons and high gas selectivity, a method for producing synthesis gas, and a method for producing a partial oxidation catalyst. [Means for solving the problem]

[0009] The present inventors have conducted research to solve the above problems and have found that by using a boron nitride catalyst containing a transition metal, it is possible to improve methane oxidation activity while maintaining high synthesis gas selectivity, thereby achieving a high synthesis gas yield. The present invention was completed based on this finding. [1] A partial oxidation catalyst for light hydrocarbons, comprising: a main catalyst containing boron nitride; and at least one metal selected from the group consisting of transition metals of Groups 4 to 9 of Period 4 of the long form periodic table, transition metals of Groups 4 to 6 of Periods 5 to 6, and lanthanoid transition metals, attached to the surface of the main catalyst. [2] The partial oxidation catalyst according to [1], wherein the metal comprises at least one metal selected from the group consisting of iron (Fe), cobalt (Co), zirconium (Zr), niobium (Nb), molybdenum (Mo), lanthanum (La), cerium (Ce), and tungsten (W). [3] The partial oxidation catalyst according to [1] or [2], wherein the metal comprises at least one metal oxide selected from the group consisting of iron (Fe) oxide, cobalt (Co) oxide, zirconium (Zr) oxide, niobium (Nb) oxide, molybdenum (Mo) oxide, lanthanum (La) oxide, cerium (Ce) oxide, and tungsten (W) oxide. [4] The partial oxidation catalyst according to any one of [1] to [3], wherein the light hydrocarbons are hydrocarbons having 6 or less carbon atoms. [5] The partial oxidation catalyst according to any one of [1] to [4], wherein the light hydrocarbon is methane. [6] The specific surface area of ​​the main catalyst is 10 m 2 / g or more 150m 2 / g or less. [7] The partial oxidation catalyst according to any one of [1] to [6], wherein the content of the metal component calculated by ICP emission spectrometry is 0.5 mass % or more and 20 mass % or less, relative to 100% of the total mass of the partial oxidation catalyst. [8] The partial oxidation catalyst according to any one of [3] to [7], wherein the average crystallite size of the metal oxide is 5 nm or more and 50 nm or less, as calculated based on the Scherrer equation using powder X-ray diffraction with CuKα as an X-ray source. [9] The partial oxidation catalyst according to any one of [1] to [8], wherein the average crystallite size of the main catalyst containing boron nitride is 5 nm or more and 50 nm or less, as calculated based on the Scherrer equation using powder X-ray diffraction with CuKα as an X-ray source.

[10] The partial oxidation catalyst for light hydrocarbons according to any one of [1] to [9], wherein the crystal structure of the boron nitride is hexagonal.

[11] A method for producing a synthesis gas, comprising reacting light hydrocarbons with oxygen gas in the presence of the partial oxidation catalyst according to any one of [1] to

[10] , to produce a synthesis gas containing hydrogen and carbon monoxide.

[12] The method for producing a synthesis gas according to

[11] , wherein the synthesis gas contains at least one of an alkane and an alkene other than the light hydrocarbons that are the raw material.

[13] A method for producing the partial oxidation catalyst according to any one of [1] to

[10] , comprising sequentially carrying out the following steps (1) to (3): Step (1): A step of impregnating a main catalyst containing boron nitride with an aqueous solution containing at least one metal selected from the group consisting of transition metals of Groups 4 to 9 of Period 4 of the long form periodic table, transition metals of Groups 4 to 6 of Periods 5 to 6, and lanthanoid transition metals, to obtain a slurry. Step (2): A step of evaporating the aqueous solvent from the slurry to dryness and drying the slurry to obtain a metal-supported catalyst precursor. Step (3): A step of calcining the obtained metal-supported catalyst precursor to obtain a partial oxidation catalyst.

[14] The method for producing a partial oxidation catalyst according to

[13] , wherein the metal comprises at least one metal selected from the group consisting of iron (Fe), cobalt (Co), zirconium (Zr), niobium (Nb), molybdenum (Mo), lanthanum (La), cerium (Ce), and tungsten (W). [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a partial oxidation catalyst for light hydrocarbons that can partially oxidize light hydrocarbons to synthesis gas with high oxidation activity for light hydrocarbons and high gas selectivity, a method for producing synthesis gas, and a method for producing a partial oxidation catalyst. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in detail below, but the explanation of the constituent elements described below is one example (typical 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. In this specification, "%" and "parts" are based on mass unless otherwise specified. Furthermore, a numerical range specified using the symbol "to" is intended to include the numerical values ​​at both ends (upper and lower limits) of "to".

[0012] [Partial oxidation catalyst for light hydrocarbons] The partial oxidation catalyst for light hydrocarbons of the present invention contains a main catalyst containing boron nitride, and at least one metal selected from the group consisting of transition metals of Groups 4 to 9 of Period 4 of the long form periodic table, transition metals of Groups 4 to 6 of Periods 5 to 6, and lanthanoid transition metals (hereinafter referred to as "transition metals") on the surface of the main catalyst.

[0013] (boron nitride) The boron nitride used as the main catalyst in the partial oxidation catalyst for light hydrocarbons of the present invention can be any of h-BN (hexagonal crystal system), c-BN (cubic crystal system), and w-BN (cubic wurtzite crystal system). Any of these boron nitrides can be used without limitation, including boron nitride prepared by the reduction-nitridation method of a boron compound and ammonia, and boron nitride synthesized from a boron compound and a nitrogen-containing compound such as melamine. However, h-BN, which has a hexagonal crystal structure, is particularly preferred. The shape of the boron nitride particles is not particularly limited, and for example, needle-like, plate-like, or other shapes of boron nitride can be used.

[0014] The specific surface area of ​​the main catalyst is 10m 2 / g or more 150m2 / g or less, and 2 / g or more 120m 2 / g or less is more preferable, and 30m 2 / g or more 90m 2 By setting the specific surface area of ​​boron nitride within the above range, the contact area during the reaction can be increased, and therefore the yield of partial oxidation to CO can be improved.

[0015] The main catalyst may be used in combination with a carrier other than boron nitride, such as alumina, silica, zeolite, zirconia, or titania.

[0016] The average crystallite diameter of the main catalyst is preferably 5 nm or more and 50 nm or less, more preferably 10 nm or more and 45 nm or less, and even more preferably 20 nm or more and 35 nm or less. By setting the average crystallite diameter of the main catalyst within the above range, complete oxidation of light hydrocarbons can be suppressed, and the CO yield can be improved. The average crystallite diameter of the main catalyst can be calculated based on the Scherrer equation using powder X-ray diffraction with CuKα as the X-ray source.

[0017] (transition metal) The partial oxidation catalyst used in the present invention contains, on the surface of the main catalyst, at least one metal selected from the group consisting of transition metals of Groups 4 to 9 of Period 4 of the long-form periodic table, transition metals of Groups 4 to 6 of Periods 5 to 6, and lanthanide transition metals. By containing such a metal on the surface of the main catalyst, complete oxidation of light hydrocarbons is less likely to occur, and partial oxidation can proceed with high selectivity. Therefore, the possibility of localized heat generation, which can cause catalyst degradation, can be suppressed during the reaction process.

[0018] Among the above transition metals, the partial oxidation catalyst of this embodiment preferably contains at least one metal selected from the group consisting of iron (Fe), cobalt (Co), zirconium (Zr), niobium (Nb), molybdenum (Mo), lanthanum (La), cerium (Ce), and tungsten (W).

[0019] The metal may be contained as a metal oxide, and preferably contains at least one metal oxide selected from the group consisting of iron (Fe) oxide, cobalt (Co) oxide, zirconium (Zr) oxide, niobium (Nb) oxide, molybdenum (Mo) oxide, lanthanum (La) oxide, cerium (Ce) oxide, and tungsten (W) oxide. As will be described later, the partial oxidation catalyst of the present invention is produced by impregnating a main catalyst containing boron nitride with an aqueous solution containing a transition metal, followed by drying and calcination. By calcination during production, part or all of the metal is converted to metal oxide, and the partial oxidation catalyst of the present invention contains metal oxide.

[0020] The content of the metal component in the partial oxidation catalyst of this embodiment is preferably 0.5% by mass or more and 20% by mass or less, more preferably 1% by mass or more and 10% by mass or less, and even more preferably 2% by mass or more and 5% by mass or less, relative to 100% by total mass of the partial oxidation catalyst. The content of the metal component in the partial oxidation catalyst can be quantitatively analyzed by ICP emission spectrometry. The content of the metal component refers to the total amount of metal in the metal and metal oxide. By setting the content of the metal component in the partial oxidation catalyst within the above range, the complete oxidation reaction of light hydrocarbons is unlikely to occur, and the partial oxidation reaction can proceed with high selectivity, thereby suppressing the possibility of localized heat generation during the reaction process, which can cause catalyst degradation.

[0021] Furthermore, the average crystallite diameter of the metal oxide or metal is preferably 5 nm or more and 50 nm or less, more preferably 10 nm or more and 45 nm or less, and even more preferably 20 nm or more and 35 nm or less. By setting the average crystallite diameter of the metal oxide within the above range, complete oxidation of light hydrocarbons is unlikely to occur, and partial oxidation can be promoted with high selectivity. Therefore, the possibility of localized heat generation that causes catalyst deterioration during the reaction process can be suppressed. The average crystallite diameter of the metal oxide can be calculated based on the Scherrer equation using powder X-ray diffraction with CuKα as the X-ray source.

[0022] [Synthetic gas production method] The synthesis gas production method of the present invention is a method for producing synthesis gas by a partial oxidation reaction of light hydrocarbons, in which light hydrocarbons are reacted with oxygen gas in the presence of the above-described catalyst for partial oxidation of light hydrocarbons to produce synthesis gas containing hydrogen and carbon monoxide.

[0023] The light hydrocarbons used in the method for producing a synthesis gas of the present invention are preferably hydrocarbons having 6 or less carbon atoms. Specific examples include chain hydrocarbons which may have branches, such as methane, ethane, butane, isobutane, pentane, isopentane, and hexane. Of these, methane is preferred.

[0024] <Reaction conditions> The reaction temperature in the synthesis gas production method of the present invention is preferably 650° C. or higher. A reaction temperature of 650° C. or higher ensures a sufficient reaction rate, promotes partial oxidation of light hydrocarbons, and enables synthesis gas to be efficiently produced. On the other hand, there is no particular upper limit to the reaction temperature, but it is preferably 1000° C. or less in order to prevent complete oxidation of light hydrocarbons. From the above viewpoints, the reaction temperature in this reaction is preferably in the range of 650 to 1000° C., more preferably in the range of 650 to 850° C. By setting the reaction temperature to 850° C. or less, the activity of the catalyst can be stabilized. Since this reaction is exothermic, even if the reaction starting temperature is 500°C, it may reach 650°C or higher if an adiabatic reaction vessel is used. Therefore, the reaction temperature here refers to the temperature of the catalyst layer in 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.

[0025] In the partial oxidation process of light hydrocarbons in the present invention, the ratio of light hydrocarbons to oxygen in the feedstock (C n H 2n+2 It is preferable that the ratio (C / O2) is 1 / 2n or more. When this ratio is 1 / 2n or more, it is possible to easily suppress the complete oxidation of light hydrocarbons and promote the partial oxidation of light hydrocarbons. In addition, the ratio (C / O2) of light hydrocarbons to oxygen is n H 2n+2 From the above viewpoint, the ratio of methane to oxygen in the raw material (C n H 2n+2 / O2) is more preferably 1 / n or more, even more preferably 1.5 / n or more, and most preferably 2 / n or more. On the other hand, the ratio of light hydrocarbons to oxygen (C n H 2n+2 Although there is no particular upper limit for the ratio (O2), from the viewpoint of reaction efficiency, it is preferably 6 / n or less, and more preferably 3 / n or less.

[0026] 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 facility costs including auxiliary facilities, catalyst costs, and operation management. The process may be carried out in any of a batch system, a semi-continuous system, or a continuous system, but is preferably carried out in a continuous system, and the process may use a single reactor or a plurality of reactors arranged in series or parallel.

[0027] When the catalyst is packed into a fluidized bed reactor, particulate matter inert to the reaction, such as quartz sand, alumina, silica, or silica-alumina, may be mixed with the catalyst and packed therein in order to minimize the temperature distribution in the catalyst layer. In this case, there are no particular restrictions on the amount of particulate matter inert to the reaction, such as quartz sand, used. In order to ensure uniform mixing with the catalyst, it is preferable that the particulate matter has a particle size similar to that of the catalyst. Furthermore, the reaction substrates (reaction raw materials) may be supplied to the reactor in divided portions for the purpose of dispersing the heat generated by the reaction.

[0028] In addition to light hydrocarbons 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, 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 introduced into the reactor, or may be supplied to the reactor separately from the reaction raw materials.

[0029] The upper limit of the reaction pressure is preferably 3 MPa (absolute pressure, the same applies hereinafter). 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 pressure at or above these lower limits, a sufficient reaction rate can be obtained.

[0030] According to the synthesis gas production method of the present invention, the reaction products include, in addition to synthesis gas (CO+H), at least one of alkanes and alkenes (by-products) other than the light hydrocarbons used as raw materials, carbon dioxide, and water. The hydrocarbons contained as by-products are at least one of alkanes and alkenes having a carbon number (n+1), where n is the carbon number of the light hydrocarbons used as raw materials. However, according to the synthesis gas production method of the present invention, the yield of CO among these reaction products can be set to 20 to 30%. Furthermore, in the present invention, the conversion of light hydrocarbons is 25 to 45%, and the yield of CO is 2.5% or less. The mixed gas containing unreacted raw materials, by-products, and diluents in the reactor outlet gas can be introduced into known separation and purification equipment, where each component can be recovered, purified, recycled, or discharged according to its composition.

[0031] [Method of manufacturing partial oxidation catalyst] The method for producing a catalyst for partial oxidation of light hydrocarbons of the present invention includes sequentially carrying out the following steps (1) to (3). Step (1): A step of impregnating a main catalyst containing boron nitride with an aqueous solution containing at least one metal selected from the group consisting of transition metals of Groups 4 to 9 of Period 4 of the long form periodic table, transition metals of Groups 4 to 6 of Periods 5 to 6, and lanthanoid transition metals, to obtain a slurry. Step (2): A step of evaporating the aqueous solvent from the slurry to dryness and drying the slurry to obtain a metal-supported catalyst precursor. Step (3): A step of calcining the obtained metal-supported catalyst precursor to obtain a partial oxidation catalyst. Each step will be described below.

[0032] (Process (1)) Step (1) is a step of impregnating a main catalyst containing boron nitride with an aqueous solution containing the transition metal to obtain a slurry. In the method for producing a partial oxidation catalyst of the present invention, the main catalyst, boron nitride, and the transition metal may be the same boron nitride and transition metal used in the partial oxidation catalyst described above.

[0033] The slurry is formed by mixing boron nitride as a raw material, a support other than boron nitride that is used as needed, and an aqueous solution containing a transition metal, and impregnating the support containing boron nitride with the aqueous solution containing the transition metal. The above materials can be mixed by manual stirring and mixing, or by using a general mixer such as an automatic mortar, ball mill, Bonny mixer, internal mixer, three-roll mixer, co-kneader, votator, high-speed fluid mixer, or ultrasonic homogenizer.

[0034] If the amount of water used in the aqueous solution containing a transition metal is too much, the load during drying increases, and if it is too little, uniform mixing becomes difficult. Therefore, the amount of water used in the aqueous solution containing a transition metal is preferably 5 to 20 times, and particularly 5 to 10 times, the mass of boron nitride.

[0035] (Process (2)) Step (2) is a step in which the aqueous solvent of the slurry obtained in step (1) is evaporated to dryness and dried to obtain a metal-supported catalyst precursor. The method for evaporating and drying the aqueous solvent of the slurry is not particularly limited, and methods such as heat drying and heat vacuum drying can be used. Heat drying is generally preferred, but on a small scale, a combination of heat vacuum drying and heat drying is usually used. Heat vacuum drying involves distilling off the aqueous solvent using an evaporator at a temperature of about 50°C. Heat drying is then preferably carried out at 100 to 120°C for about 3 to 24 hours. If the heating temperature is too low or the heating time is too short, sufficient drying cannot be achieved, while if the heating temperature is too high or the heating time is too long, the heating costs increase and are not preferred.

[0036] In step (2), a metal-supported catalyst precursor containing a transition metal on the surface of boron nitride is formed.

[0037] (Step (3)) Step (3) is a step of calcining the metal-supported catalyst precursor obtained in step (2) to obtain a partial oxidation catalyst. The temperature for firing the metal-supported catalyst precursor is usually 300 to 1000 °C, preferably 300 to 800 °C. Also, the firing time is usually 1 to 10 hours, preferably 1 to 5 hours. Also, the firing is preferably carried out by heating in an oxidizing atmosphere such as air. By heating in an oxidizing atmosphere, the metal formed on the surface of the metal-supported catalyst precursor can be made into a metal oxide. The partial oxidation catalyst is produced by the above steps (1) to (3).

Examples

[0038] Hereinafter, the present invention will be described in more detail by way of examples, but the scope of the present invention is not limited by the following examples.

[0039] (Evaluation method) (1) Physical properties of the partial oxidation catalyst <X-ray diffraction measurement> The crystal structure of each catalyst was determined by X-ray diffraction measurement (XRD). The measurement was carried out using a powder X-ray diffractometer "D2PHASER" manufactured by BRUKER with CuKα as the X-ray source. The average crystallite size of boron nitride and metal oxide contained in the catalyst was calculated based on Scherrer's formula. From XRD, the crystal structure of boron nitride was hexagonal. Also, in NbOx / h-BN, the crystal structure of boron nitride was hexagonal, and its crystallite size was 27.4 nm. Furthermore, in NbOx / h-BN, Nb existed as Nb2O5, and its crystallite size was 22.4 nm.

[0040] (2) Reaction evaluation Using a fixed-bed gas-phase flow reactor, 100 mg of the catalyst from each example and comparative example was packed into the middle of a quartz glass reaction tube (catalyst layer: outer diameter 8.0 mm, inner diameter 6.0 mm; remaining portion: outer diameter 6.0 mm, inner diameter 4.0 mm, total length 260 mm). The electric furnace was heated to 500 °C under N flow (10 ml / min). Subsequently, CH was introduced at a flow rate of 5.0 ml / min, O at 2.5 ml / min, and N at 12.5 ml / min, and a partial oxidation reaction test of methane was performed at atmospheric pressure (100 kPa) and a reaction temperature of 800 °C. Downstream of the reactor, the reactor was heated to 100 °C using a ribbon heater, and the reaction gas was diluted with N at 100 ml / min to prevent condensation of the produced water. The product was analyzed using a two-channel online Micro-GC (FUSION, manufactured by INFICON). In channel 1 of the Micro-GC, H2, O2, N2, CH4, and CO were quantified using a capillary column Rt-Molsieve 5A (trade name) with Ar as the carrier gas. In channel 2, CO2, C2H4, C2H6, and H2O were quantified using a capillary column Rt-Q-BOND (trade name) with He as the carrier gas. A TCD was used as the detector.

[0041] 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 inlet CH4 flow rate.

[0042]

number

[0043] Example 1 Niobium ammonium oxalate was used as a precursor to prepare an aqueous solution containing niobium ammonium oxalate. Boron nitride (h-BN) (specific surface area: 50 m 2The catalyst was impregnated with an aqueous solution of niobium ammonium oxalate by impregnation, then dried at 100°C for 6 hours to evaporate the aqueous solvent. It was then calcined at 500°C for 3 hours to obtain NbOx / h-BN, a partial oxidation catalyst. The niobium ammonium oxalate was added so that the amount of Nb was 3 parts by mass per 97 parts by mass of boron nitride. The produced NbOx / h-BN was used to evaluate the reaction using the above-mentioned reaction evaluation method. The reaction results of NbOx / h-BN at 800°C were as shown in Table 1: CH4 conversion 32.0%, O2 conversion 78.4%, CO yield 28.1%, H2 yield 7.0%, and CO2 yield 1.5%.

[0044] <Examples 2 to 7> In Examples 2 to 7, partial oxidation catalysts were produced in the same manner as in Example 1, except that the metal oxide contained in the partial oxidation catalyst was changed from NbOx in Example 1 to the metal oxides shown in Table 1, and a partial oxidation reaction test of methane was carried out.

[0045] <Comparative Example 1> In Comparative Example 1, a partial oxidation reaction test of methane was carried out using only boron nitride as the partial oxidation catalyst, without containing any metal oxide.

[0046] <Comparative Examples 2 to 5> In Comparative Examples 2 to 5, partial oxidation catalysts were produced in the same manner as in Example 1, except that the metal oxide contained in the partial oxidation catalyst was changed from NbOx in Example 1 to the metal oxides shown in Table 1, and a partial oxidation reaction test of methane was carried out.

[0047] <Comparative Examples 6 and 7> In Comparative Examples 6 and 7, the boron nitride used in the partial oxidation catalyst was changed to Al2O3 (Comparative Example 6) and La2O3 (Comparative Example 7), and partial oxidation catalysts were produced in the same manner as in Example 1, except that the metal oxides shown in Table 1 were used, and a partial oxidation reaction test of methane was performed. The results of each example and comparative example are shown in Table 1.

[0048] In each example and comparative example, the metal oxides supported on the catalyst, LaOx (Example 2), CoOx (Example 3), CeOx (Example 4), FeOx (Example 5, Comparative Example 6), ZrOx (Example 6, Comparative Example 7), MoOx (Example 7), YOx (Comparative Example 2), NiOx (Comparative Example 3), CuOx (Comparative Example 4), and ZnOx (Comparative Example 5), were supported using lanthanum nitrate hydrate, cobalt nitrate hydrate, cerium nitrate hydrate, iron nitrate hydrate, zirconyl nitrate hydrate, ammonium molybdate hydrate, yttrium nitrate hydrate, nickel nitrate hydrate, copper nitrate hydrate, and zinc nitrate hydrate, respectively, as precursors.

[0049] [Table 1]

[0050] Comparative Example 1, which used boron nitride without a metal oxide as the partial oxidation catalyst, showed high selectivity in the partial oxidation of CH4 to CO, but the CH4 oxidation activity was insufficient. Examples 1 to 7, which contained at least one metal selected from the group consisting of transition metals of Groups 4 to 9 of Period 4 of the long form periodic table, transition metals of Groups 4 to 6 of Periods 5 to 6, and lanthanoid transition metals on the surface of boron nitride, showed CH4 conversion and CO yield that were up to about 1.4 times higher than those of the partial oxidation catalyst of Comparative Example 1 at a reaction temperature of 800°C. Furthermore, although not shown as an example, in a long-term reaction, the activity of boron nitride not supporting a metal oxide in Comparative Example 1 gradually decreased, while the catalytic activity of boron nitride supporting a metal oxide in Examples 1 to 8 was suppressed.

[0051] Furthermore, Non-Patent Document 1 (Catal. Sci. Technol. 2018, 8, 2051-2055) suggests that surface oxygen species on boron nitride serve as active sites for CH activation of methane. Therefore, the increased oxygen content on the catalyst surface explains the improvement in partial oxidation of methane over metal-supported boron nitride.

[0052] The boron nitride catalysts (Comparative Examples 2 to 5) supporting at least one metal selected from the group consisting of transition metals of Group 3 and Groups 10 to 12 of the long form periodic table did not show any improvement in CH4 conversion rate or CO yield compared to the unsupported boron nitride catalyst (Comparative Example 1). The catalysts (Comparative Examples 6 and 7) that did not use boron nitride as a support also had low CH4 conversion or CO yield. [Industrial Applicability]

[0053] According to the present invention, light hydrocarbons can be partially oxidized with high selectivity, and synthesis gas (CO+H2) can be produced efficiently. Since synthesis gas is an important raw material for various reactions, the present invention is a technology that can contribute to industry.

Claims

1. a main catalyst comprising boron nitride; A partial oxidation catalyst for light hydrocarbons, comprising, on a surface of the main catalyst, at least one metal selected from the group consisting of transition metals of Groups 4 to 9 of Period 4 of the long form periodic table, transition metals of Groups 4 to 6 of Periods 5 to 6 of the long form periodic table, and lanthanoid transition metals.

2. 2. The partial oxidation catalyst according to claim 1, wherein the metal comprises at least one metal selected from the group consisting of iron (Fe), cobalt (Co), zirconium (Zr), niobium (Nb), molybdenum (Mo), lanthanum (La), cerium (Ce), and tungsten (W).

3. 2. The partial oxidation catalyst according to claim 1, wherein the metal comprises at least one metal oxide selected from the group consisting of iron (Fe) oxide, cobalt (Co) oxide, zirconium (Zr) oxide, niobium (Nb) oxide, molybdenum (Mo) oxide, lanthanum (La) oxide, cerium (Ce) oxide, and tungsten (W) oxide.

4. 2. The partial oxidation catalyst according to claim 1, wherein the light hydrocarbons are hydrocarbons having 6 or less carbon atoms.

5. 2. The partial oxidation catalyst of claim 1, wherein the light hydrocarbon is methane.

6. The specific surface area of ​​the main catalyst is 10 m ２ / g or more 150m ２ 2. The partial oxidation catalyst according to claim 1, wherein the Cr content is 0.15 / g or less.

7. 2. The partial oxidation catalyst according to claim 1, wherein the content of the metal component calculated by ICP emission spectrometry is 0.5% by mass or more and 20% by mass or less, relative to 100% by total mass of the partial oxidation catalyst.

8. 4. The partial oxidation catalyst according to claim 3, wherein the metal oxide has an average crystallite size of 5 nm or more and 50 nm or less, calculated based on the Scherrer equation using a powder X-ray diffraction method using CuKα as an X-ray source.

9. 2. The partial oxidation catalyst according to claim 1, wherein the main catalyst containing boron nitride has an average crystallite size of 5 nm or more and 50 nm or less, calculated based on the Scherrer equation using a powder X-ray diffraction method using CuKα as an X-ray source.

10. 2. The partial oxidation catalyst of claim 1, wherein the crystal structure of the boron nitride is hexagonal.

11. A method for producing a synthesis gas, comprising reacting the light hydrocarbons with oxygen gas in the presence of the partial oxidation catalyst according to any one of claims 1 to 10, to produce a synthesis gas containing hydrogen and carbon monoxide.

12. The method for producing a synthesis gas according to claim 11, wherein the synthesis gas contains at least one of an alkane and an alkene other than the light hydrocarbons that are the raw material.

13. A method for producing the partial oxidation catalyst according to any one of claims 1 to 10, A method for producing a partial oxidation catalyst, comprising sequentially carrying out the following steps (1) to (3): Step (1): A step of impregnating a main catalyst containing boron nitride with an aqueous solution containing at least one metal selected from the group consisting of transition metals of Groups 4 to 9 of Period 4 of the long form periodic table, transition metals of Groups 4 to 6 of Periods 5 to 6, and lanthanoid transition metals, to obtain a slurry. Step (2): A step of evaporating the aqueous solvent from the slurry and drying the slurry to obtain a metal-supported catalyst precursor. Step (3): A step of calcining the obtained metal-supported catalyst precursor to obtain a partial oxidation catalyst.

14. 14. The method for producing a partial oxidation catalyst according to claim 13, wherein the metal comprises at least one metal selected from the group consisting of iron (Fe), cobalt (Co), zirconium (Zr), niobium (Nb), molybdenum (Mo), lanthanum (La), cerium (Ce), and tungsten (W).

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