Method for producing a catalyst for alkane gas-phase catalytic oxidation reaction containing complex oxide particles

Abstract

To provide a method for producing a catalyst that can obtain a higher yield of reaction products in a gas-phase catalytic oxidation reaction of alkanes. [Solution] A method for producing a catalyst for a gas-phase catalytic oxidation reaction of an alkane containing composite oxide particles containing Mo and V, comprising the following steps (A) and (B). Step (A): A step of obtaining calcined particles containing a composite oxide containing Mo and V. Step (B): A step of obtaining a calcined particle in which the molar ratio M of sodium to Mo in the calcined particle is 0.005

Description

Technical Field

[0001] The present invention relates to a method for producing a catalyst for gas-phase catalytic oxidation of alkanes, said catalyst comprising composite oxide particles containing Mo and V. Background Art

[0002] The dominant industrial production method for olefins worldwide is pyrolysis of naphtha or alkanes, which consumes high energy and imposes a large environmental burden. In recent years, gas-phase catalytic oxidation of alkanes using catalysts has been expected as a method for producing olefins with low environmental impact, and methods for producing such catalysts have also attracted growing attention.

[0003] Patent Documents 1 to 3 and Non-Patent Document 1 describe treating an oxidation catalyst containing Mo and V with an alkali metal solution.

[0004] Patent Document 4 discloses a method for producing an oxidation catalyst for alkanes containing Mo and V, and describes treating a fired product with hydrogen peroxide.

[0005] Patent Document 5 discloses an oxidation catalyst for alkanes containing Mo and V, and describes washing the fired catalyst with a low-concentration oxalic acid solution. Prior Art Documents Patent Documents

[0006] Patent Document 1 Japanese Patent No. 6125023 Patent Document 2 Japanese Patent No. 7456727 Patent Document 3 Japanese Patent No. 5611206 Patent Document 4 Japanese Patent No. 6947821 Patent Document 5 Japanese Patent No. 7364659 Non-Patent Literature

[0007] [Non-Patent Document 1] Applied Catalysis A, General 660 (2023) 119200 Summary of the Invention Problems to be Solved by the Invention

[0008] Conventional catalysts for the gas-phase catalytic oxidation of alkanes leave much room for performance improvement, and further improvements in the conversion rate of alkanes and the yield of reaction products are demanded.

[0009] The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing a catalyst that can obtain a reaction product at a higher yield in the gas-phase catalytic oxidation reaction of an alkane. Means for Solving the Problems

[0010] The present inventors have conducted studies to solve the above problems, and as a result, found that the above problems can be solved by subjecting calcined particles containing a composite oxide containing Mo and V to a predetermined treatment, and thus completed the present invention.

[0011] That is, the present invention is as follows. [1] A method for producing a catalyst for gas-phase catalytic oxidation reaction of alkane, the catalyst comprising composite oxide particles containing Mo and V, the method comprising the following step (A) and the following step (B). Step (A): a step of obtaining calcined particles containing a composite oxide containing Mo and V Step (B): a step of mixing the calcined particles obtained in the above step (A) with an aqueous solution containing a sodium compound prepared such that the molar ratio M of sodium to molybdenum in the calcined particles satisfies 0.005 < M ≦ 0.08, and impregnating the calcined particles with sodium [2] The method for producing a catalyst according to the above [1], further comprising the following step (C) before the step (B). Step (C): A step in which the calcined particles obtained in step (A) are treated with acid until their BET specific surface area increases by 50% or more. [3] The method for producing a catalyst according to [2] above, wherein the acid used in step (C) contains a dicarboxylic acid. [4] The method for producing a catalyst according to [2] above, wherein the acid used in the treatment of step (C) is an aqueous solution containing 2% to 20% by mass of oxalic acid. [5] The method for producing a catalyst according to [2] or [3] above, wherein the processing temperature of step (C) is 40°C to 70°C. [6] The method for producing a catalyst according to [2] or [3] above, wherein the processing time of step (C) is 10 minutes to 10 hours. [7] The BET specific surface area of ​​the particles obtained by the process in step (C) is 20 m². 2 / g~30m 2 A method for producing the catalyst described in [2] or [3] above, wherein the amount is / g. [8] The method for producing a catalyst according to [2] or [3] above, wherein the proportion of P2 crystals contained in the composite oxide in the particles obtained by the process of step (C) is 55% by mass to 85% by mass, when the total amount of P1 crystals and P2 crystals in the composite oxide is taken as 100% by mass. [9] The BET specific surface area of ​​the calcined particles obtained in step (A) is 10 m². 2 / g~20m 2 A method for producing the catalyst described in [1] or [2] above, wherein the amount is / g.

[10] The method for producing a catalyst according to [1] or [2] above, wherein the calcination temperature in step (A) is 650°C or higher.

[11] The method for producing a catalyst according to [1] or [2] above, wherein step (A) is a step of obtaining calcined particles on which the composite oxide is supported on a carrier.

[12] A method for producing the catalyst according to

[11] , wherein the carrier contains silica.

[13] The method for producing a catalyst according to

[11] , wherein the content of the carrier in the calcined particles obtained in step (A) is 30% by mass to 70% by mass.

[14] A method for producing the catalyst according to [1] or [2] above, wherein the composite oxide further contains Sb.

[15] The method for producing a catalyst according to [1] or [2] above, wherein the composite oxide further contains Nb.

[16] The method for producing a catalyst according to [1] or [2] above, wherein the composite oxide further contains W.

[17] The method for producing a catalyst according to [1] or [2] above, wherein the composite oxide further contains Ce.

[18] The method for producing a catalyst according to [1] or [2] above, wherein the composite oxide does not contain Te.

[19] The composite oxide is represented by the following formula (1): Mo1V a Sb b Nb c T d Z e O n ···(1) (in the formula, T represents at least one element selected from the group consisting of Ti, W, Mn and Bi, Z represents at least one element selected from the group consisting of La, Ce, Yb and Y, a, b, c, d, e and n each represent an atomic ratio of each element when Mo is set to 1, 0.05≦a≦0.35, 0.05≦b≦0.35, 0≦c≦0.25, 0≦d≦0.20, and 0≦e≦0.10 , and n is a value that satisfies valence balance) The method for producing a catalyst according to [1] or [2] above, which is represented by

[20] The method for producing a catalyst according to [1] or [2] above, wherein the BET specific surface area of the composite oxide particles is 20 m 2 / g to 30 m 2 / g.

[21] The method for producing a catalyst according to [1] or [2] above, wherein the alkane includes an alkane having 1 to 6 carbon atoms.

[22] The method for producing the catalyst according to [1] or [2], wherein the catalyst is a catalyst for synthesizing an alkene by a gas-phase catalytic oxidation reaction in which an alkane is reacted with molecular oxygen in the gas phase.

[23] A method for producing an alkene, comprising the step of synthesizing an alkene by a gas-phase catalytic oxidation reaction in which an alkane is reacted with molecular oxygen in the gas phase in the presence of a catalyst produced by the catalyst production method described in [1] or [2] above. [Effects of the Invention]

[0012] The catalyst produced by the manufacturing method of the present invention allows for the acquisition of reaction products in higher yields in the gas-phase catalytic oxidation reaction of alkanes. [Modes for carrying out the invention]

[0013] The following describes embodiments for carrying out the present invention (hereinafter simply referred to as "this embodiment"), but the present invention is not limited to the following embodiments, and various modifications are possible without departing from the spirit thereof.

[0014] This embodiment provides a method for producing a catalyst for the gas-phase catalytic oxidation reaction of alkanes containing composite oxide particles (i.e., particles containing composite oxides) (preferably a catalyst for synthesizing alkenes by a gas-phase catalytic oxidation reaction in which alkanes react with molecular oxygen in the gas phase). Using the catalyst produced by the production method of this embodiment, reaction products can be obtained in higher yields in the gas-phase catalytic oxidation reaction of alkanes.

[0015] The catalyst manufacturing method of this embodiment includes steps (A) and (B). In a preferred embodiment, the catalyst manufacturing method of this embodiment includes step (C) before step (B), in addition to steps (A) and (B). Step (A): Step to obtain calcined particles containing a composite oxide containing Mo and V. Step (B): a step of impregnating sodium by mixing an aqueous solution containing a sodium compound, which is prepared such that the molar ratio M of sodium to Mo in the calcined particles satisfies 0.005 < M ≦ 0.08, with the calcined particles obtained in the above step (A) Step (C): a step of treating the calcined particles obtained in the above step (A) with an acid until the BET specific surface area of the calcined particles increases by 50% or more

[0016] The composite oxide contained in the composite oxide particles included in the catalyst produced by the production method of the present embodiment contains Mo (molybdenum) and V (vanadium). When the atomic ratio of Mo is defined as 1, the content of V in the composite oxide is preferably 0.05 or more and 0.35 or less, more preferably 0.10 or more and 0.30 or less, and still more preferably 0.15 or more and 0.25 or less.

[0017] In one embodiment, the composite oxide contained in the composite oxide particles included in the catalyst produced by the production method of the present embodiment preferably further contains Sb (antimony). When the atomic ratio of Mo is defined as 1, the content of Sb in the composite oxide is preferably 0.05 or more and 0.35 or less, more preferably 0.10 or more and 0.30 or less, and still more preferably 0.20 or more and 0.28 or less.

[0018] In one embodiment, the composite oxide contained in the composite oxide particles included in the catalyst produced by the production method of the present embodiment preferably further contains Nb (niobium), and more preferably further contains both Sb and Nb. When the atomic ratio of Mo is defined as 1, the content of Nb in the composite oxide is preferably more than 0 and 0.25 or less, more preferably 0.02 or more and 0.20 or less, and still more preferably 0.05 or more and 0.15 or less.

[0019] In one embodiment, the composite oxide in the composite oxide particles contained in the catalyst produced by the manufacturing method of this embodiment preferably further contains at least one selected from the group consisting of Ti (titanium), W (tungsten), Mn (manganese), and Bi (bismuth), and more preferably further contains W. The total content of Ti, W, Mn, and Bi in the composite oxide is preferably 0 to 0.20, more preferably 0.005 to 0.10, and even more preferably 0.01 to 0.05, in terms of atomic ratio with Mo set to 1.

[0020] In one embodiment, the composite oxide in the composite oxide particles contained in the catalyst produced by the manufacturing method of this embodiment preferably further contains at least one selected from the group consisting of La (lanthanum), Ce (cerium), Yb (ytterbium), and Y (yttrium), and more preferably further contains Ce. The total content of La, Ce, Yb, and Y in the composite oxide is preferably 0 to 0.10, more preferably 0.001 to 0.03, and even more preferably 0.002 to 0.01, in terms of atomic ratio with Mo being 1.

[0021] From the viewpoint of catalyst durability, the composite oxide in the composite oxide particles contained in the catalyst manufactured by the manufacturing method of this embodiment does not contain Te.

[0022] In one embodiment, the composite oxide in the composite oxide particles contained in the catalyst produced by the manufacturing method of this embodiment is defined by the following formula (1): Mo1V a S b Nb c T d Z e O n ...(1) (In the formula, T represents at least one element selected from the group consisting of Ti, W, Mn, and Bi (preferably W). Z represents at least one element selected from the group consisting of La, Ce, Yb, and Y (preferably Ce). a, b, c, d, e, and n are the atomic ratios of each element when Mo is set to 1, and respectively 0.05 ≤ a ≤ 0.35 (preferably 0.10 ≤ b ≤ 0.30, more preferably 0.15 ≤ b ≤ 0.25), 0.05 ≤ b ≤ 0.35 (preferably 0.10 ≤ b ≤ 0.30, more preferably 0.20 ≤ b ≤ 0.28), 0 ≤ c ≤ 0.25 (preferably 0.02 ≤ c ≤ 0.20, more preferably 0.05 ≤ c ≤ 0.15), 0≦d≦0.20 (preferably 0.005≦d≦0.10, more preferably 0.01≦d≦0.05), and 0 ≤ e ≤ 0.10 (preferably 0.001 ≤ e ≤ 0.03, more preferably 0.002 ≤ e ≤ 0.01) (It is within the range, and n is a value that satisfies the balance of valences.) It is particularly preferable that the composite oxide is represented by [formula].

[0023] The composite oxide in the composite oxide particles contained in the catalyst produced by the manufacturing method of this embodiment preferably contains P2 crystals.

[0024] From the viewpoint of further improving the conversion rate of alkanes, the proportion of P2 crystals contained in the composite oxide particles in the catalyst produced by the manufacturing method of this embodiment is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 55% by mass or more, even more preferably 60% by mass or more, even more preferably 65% ​​by mass or more, and particularly preferably 70% by mass or more, when the total of P1 crystals and P2 crystals in the composite oxide is taken as 100% by mass. From the viewpoint of further improving the yield of the reaction product, the upper limit of the proportion of P2 crystals contained in the composite oxide is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less, and particularly preferably 82% by mass or less, when the total of P1 crystals and P2 crystals in the composite oxide is taken as 100% by mass. The proportion of P2 crystals can be measured and calculated using the method described in "Determination of the proportion of P2 crystals" in Comparative Example 1 below.

[0025] In this specification, a P1 crystal means a crystal having peaks at 22.1±0.5°, 28.1±0.5°, 36.1±0.5°, and 45.2±0.5° in its X-ray diffraction pattern.

[0026] In this specification, a P2 crystal means a crystal having peaks at 7.8±0.5°, 8.9±0.5°, 22.1±0.5°, 27.1±0.5°, 35.2±0.5°, and 45.2±0.5° in its X-ray diffraction pattern.

[0027] From the viewpoint of further improving the conversion rate of alkanes, the BET specific surface area of ​​the composite oxide particles contained in the catalyst produced by the manufacturing method of this embodiment is preferably 10 m². 2 / g or more, more preferably 17m 2 / g or more, more preferably 20m 2 / g or more, particularly preferably 25m 2 The concentration is 1 / g or more. The upper limit of the BET specific surface area of ​​the composite oxide particles is preferably 40m², from the viewpoint of further improving the yield of the reaction product. 2 / g or less, more preferably 32m 2 / g or less, and more preferably 30m2 / g or less, particularly preferably 28m 2 The value is less than / g. The BET specific surface area can be measured by the BET single-point method based on nitrogen adsorption measurement using nitrogen as the adsorbent gas, in accordance with JIS Z 8830:2013.

[0028] The composite oxide particles contained in the catalyst produced by the manufacturing method of this embodiment preferably include particles having a spherical shape. The spherical shape of the catalyst particles can be confirmed, for example, by the circularity of any cross-section of the catalyst particles. Note that circularity means a circularity of 0.80 or higher, preferably 0.90 or higher, and particularly preferably 0.95 or higher.

[0029] The median diameter (average particle diameter) of the composite oxide particles contained in the catalyst produced by the manufacturing method of this embodiment is not particularly limited, but from the viewpoint of catalytic performance, it is preferably 20 μm to 150 μm, more preferably 30 μm to 100 μm, even more preferably 35 μm to 75 μm, and particularly preferably 45 μm to 65 μm. Here, the median diameter (average particle diameter) is the median diameter based on the volume-based particle diameter distribution, and means the particle diameter corresponding to the cumulative frequency of 50% in the particle diameter distribution. The median diameter (average particle diameter) can be measured, for example, by the laser diffraction-scattering method based on Mie scattering theory.

[0030] The composite oxide particles contained in the catalyst produced by the manufacturing method of this embodiment are preferably particles in which the composite oxide is supported on a carrier. The carrier preferably contains silica. The silica is not particularly limited, but examples include silica sol (colloidal silica), powdered silica (dry silica), fumed silica, etc.

[0031] The carrier content in the composite oxide particles contained in the catalyst produced by the manufacturing method of this embodiment is preferably 30% to 70% by mass, and more preferably 40% to 60% by mass, based on 100% by mass of the composite oxide particles, from the viewpoint of abrasion resistance and strength of the catalyst particles. If the carrier content is silica, it can be calculated on a silicon dioxide (SiO2) basis.

[0032] The following describes in detail each step in the method for producing the catalyst of this embodiment.

[0033] Step (A) is a step to obtain calcined particles containing a composite oxide containing Mo and V.

[0034] Step (A) involves calcining a raw material mixture containing, for example, molybdenum compounds such as molybdenum trioxide and ammonium molybdate, and vanadium compounds such as vanadium pentoxide and ammonium metavanadate, to obtain calcined particles containing a composite oxide containing Mo and V.

[0035] In one embodiment, the raw material mixture in step (A) preferably further contains antimony compounds such as diantimony trioxide, diantimony tetroxide, and diantimony pentoxide.

[0036] In one embodiment, the raw material mixture in step (A) preferably further contains niobium compounds such as niobium trichloride, niobium pentachloride, niobium oxide, niobic acid, and niobium-organic acid complexes. Examples of niobium-organic acid complexes include niobium-dicarboxylic acid complexes such as niobium-oxalic acid complex, niobium-malonic acid complex, niobium-succinic acid complex, and niobium-glutaric acid complex; and niobium-oxycarboxylic acid complexes such as niobium-2-hydroxymalonic acid complex, niobium-DL-malic acid complex, niobium-L-malic acid complex, niobium-D-malic acid complex, niobium-tartaric acid complex, and niobium-citric acid complex.

[0037] In one embodiment, the raw material mixture in step (A) preferably further contains at least one selected from the group consisting of titanium compounds such as titanium oxide; tungsten compounds such as ammonium metatungstate, ammonium paratungstate, and tungsten trioxide; manganese compounds such as manganese nitrate; and bismuth compounds such as bismuth trioxide.

[0038] In one embodiment, the raw material mixture in step (A) preferably further contains at least one selected from the group consisting of lanthanum compounds such as lanthanum nitrate; cerium compounds such as cerium nitrate; ytterbium compounds such as ytterbium nitrate; and yttrium compounds such as yttrium oxide.

[0039] It is preferable that step (A) is a step to obtain calcined particles on which a composite oxide is supported on a carrier, and it is preferable that the raw material mixture in step (A) further contains a carrier. It is preferable that the carrier contains silica. The silica is not particularly limited, but examples include silica sol (colloidal silica), powdered silica (dry silica), fumed silica, etc. The raw material mixture in step (A) may further contain hydrogen peroxide.

[0040] The raw material mixture in step (A) may contain water, and the water-containing raw material mixture may be dried before firing in step (A). Drying of the raw material mixture is preferably carried out using a drying device such as a spray dryer (e.g., a centrifugal spray dryer). The inlet temperature of the spray dryer used for drying before firing in step (A) is preferably 150°C to 300°C, and more preferably 200°C to 250°C. The outlet temperature of the spray dryer is preferably 80°C to 160°C, and more preferably 100°C to 150°C.

[0041] The firing temperature in step (A) is preferably 600°C or higher, more preferably 620°C or higher, even more preferably 650°C or higher, and particularly preferably 670°C or higher. The upper limit of the firing temperature in step (A) is preferably 720°C or lower, from the viewpoint of preventing the sublimation of molybdenum oxide. The firing time within the above temperature range is preferably 1 to 15 hours, more preferably 2 to 10 hours, and even more preferably 3 to 7 hours. The firing in step (A) is preferably carried out in an inert atmosphere. The inert gas is not particularly limited, and for example, noble gases such as nitrogen or argon can be used.

[0042] The firing at the above firing temperature may be referred to as the secondary firing, and the primary firing may be performed before the secondary firing. The firing temperature for the primary firing is preferably 300°C to 500°C, more preferably 330°C to 450°C, and even more preferably 350°C to 400°C. The firing time for the primary firing within the above temperature range is preferably 1 hour to 10 hours, more preferably 1 hour to 7 hours, and even more preferably 1 hour to 5 hours. The primary firing is preferably performed in an inert atmosphere. The inert gas is not particularly limited, and for example, noble gases such as nitrogen or argon can be used.

[0043] If crystalline protrusions are present on the particles after firing, these protrusions may be removed. Removal of these protrusions from the particles after firing can be performed, for example, using a vertical tube equipped with a paper filter.

[0044] The carrier content in the calcined particles obtained in step (A) is preferably 30% to 70% by mass, and more preferably 40% to 60% by mass, based on 100% by mass of the calcined particles, from the viewpoint of wear resistance and strength of the calcined particles.

[0045] The proportion of P2 crystals contained in the composite oxide in the calcined particles obtained in step (A) is preferably 30% to 70% by mass, and more preferably 40% to 60% by mass, when the total amount of P1 and P2 crystals in the composite oxide is taken as 100% by mass.

[0046] The BET specific surface area of the calcined particles obtained in step (A) is preferably 5 m 2 / g or more, more preferably 8 m 2 / g or more, and particularly preferably 10 m 2 / g or more. The upper limit of the BET specific surface area of the calcined particles obtained in step (A) is preferably 25 m 2 / g or less, more preferably 20 m 2 / g or less, and particularly preferably 15 m 2 / g or less.

[0047] Step (B) is a step of impregnating sodium by mixing an aqueous solution containing a sodium compound with the calcined particles obtained in step (A).

[0048] In step (B), an aqueous solution containing a sodium compound prepared such that the molar ratio M of sodium to Mo in the calcined particles obtained in step (A) satisfies 0.005 < M ≦ 0.08 is mixed with the calcined particles obtained in step (A). In step (B), the particles are mixed with an aqueous solution prepared such that the molar ratio M of sodium to Mo in the calcined particles obtained in step (A) preferably satisfies 0.006 ≦ M ≦ 0.06, more preferably 0.007 ≦ M ≦ 0.05, and particularly preferably 0.008 ≦ M ≦ 0.04.

[0049] In step (B), the mixing mass ratio of the particles to the aqueous solution, expressed as particles:aqueous solution, is, for example, 10:1 to 1:1, and preferably 7:1 to 3:1. In step (B), the aqueous solution may be added and mixed with the particles in multiple portions (for example, 2 times, 3 times, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times, 10 times, etc.).

[0050] The impregnation method in step (B) is not particularly limited; for example, it may be a method of impregnation by stirring an aqueous solution in which the particles are dispersed, a method of impregnation by leaving an aqueous solution in which the particles are dispersed to stand still without stirring, or a method combining both of these approaches.

[0051] Examples of sodium compounds used in step (B) include sodium salts and sodium hydroxide. Examples of sodium salts include sodium nitrate, sodium chloride, sodium carbonate, sodium sulfate, and sodium acetate. It is preferable that the sodium compound includes a sodium salt. Only one type of sodium compound may be used, or two or more types may be used in combination.

[0052] The sodium impregnation temperature in step (B) is not particularly limited, but is, for example, 0°C to 100°C, preferably 15°C to 75°C. The sodium impregnation time in step (B) is not particularly limited, but is, for example, 1 minute to 5 hours, preferably 10 minutes to 3 hours.

[0053] Step (C), in a preferred embodiment, is performed before step (B), and involves treating the calcined particles obtained in step (A) with acid until their BET specific surface area increases by 50% or more. By performing step (C), both the conversion rate of the alkane and the yield of the reaction product can be further improved.

[0054] In step (C), from the viewpoint of further improving the conversion rate of alkanes, it is preferable to treat the calcined particles with acid until their BET specific surface area increases by 50-100%, more preferably by 60-100%, even more preferably by 70-100%, and particularly preferably by 80-100%. The rate of change in BET specific surface area due to the treatment in step (C) can be calculated by the following formula. BET Specific Surface Area Change Rate (%) = ((Specific surface area of ​​particles obtained by process (C)) - (Specific surface area of ​​calcined particles obtained in process (A))) / (Specific surface area of ​​calcined particles obtained in process (A)) × 100

[0055] The acid used in step (C) may be an inorganic acid or an organic acid, but it is preferably an organic acid. Examples of organic acids include dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, and adipic acid; monocarboxylic acids such as formic acid and acetic acid; oxycarboxylic acids such as malic acid, tartaric acid, and citric acid; and halogenated carboxylic acids such as chloroacetic acid, dichloroacetic acid, trichloroacetic acid, and trifluoroacetic acid. From the viewpoint of further improving the yield of the reaction product, the acid used in step (C) is more preferably a carboxylic acid, even more preferably a dicarboxylic acid, and particularly preferably an oxalic acid. The acid used in step (C) may be just one type of acid, or a mixture of two or more types of acids may be used.

[0056] The acid used in the process of step (C) is preferably an aqueous solution containing an acid. The concentration of the acid in the aqueous solution containing the acid is not particularly limited, but is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, more preferably 0.1% by mass or more, even more preferably 1% by mass or more, even more preferably 2% to 20% by mass, and particularly preferably 3% to 15% by mass. The aqueous solution containing the acid may contain only one type of acid, or it may be a mixture of two or more types of acids.

[0057] The acid used in the process of step (C) is preferably an aqueous solution containing oxalic acid, more preferably an aqueous solution containing 0.01% by mass or more of oxalic acid, even more preferably an aqueous solution containing 0.1% by mass or more of oxalic acid, even more preferably an aqueous solution containing 1% by mass or more of oxalic acid, even more preferably an aqueous solution containing 2% to 20% by mass of oxalic acid, and particularly preferably an aqueous solution containing 3% to 15% by mass of oxalic acid.

[0058] From the viewpoint of processing efficiency, the processing temperature in step (C) is preferably 10°C or higher, more preferably 20°C or higher, even more preferably 30°C or higher, and even more preferably 40°C or higher. From the viewpoint of suppressing excessive processing, the upper limit of the processing temperature in step (C) is preferably 100°C or lower, more preferably 90°C or lower, even more preferably 85°C or lower, even more preferably 80°C or lower, and particularly preferably 45°C to 65°C.

[0059] The processing time for step (C) is not particularly limited, but is preferably 1 minute to 100 hours, more preferably 5 minutes to 30 hours, even more preferably 10 minutes to 10 hours, and most preferably 20 minutes to 5 hours.

[0060] The amount of metal components (i.e., metal oxides in the composite oxide) leached out by the treatment in step (C) is preferably 4% by mass or more, more preferably 7% by mass or more, even more preferably 10% by mass or more, even more preferably 13% by mass or more, and particularly preferably 15% by mass or more, relative to 100% by mass of the composite oxide in the calcined particles obtained in step (A), from the viewpoint of further improving the conversion rate of alkanes. The upper limit of the amount of metal components leached out by the treatment in step (C) is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 35% by mass or less, even more preferably 30% by mass or less, and particularly preferably 25% by mass or less, from the viewpoint of suppressing excessive treatment. The amount of metal components leached out by the treatment in step (C) can be calculated by the following formula. Amount of metal component leached (mass%) = 100 × {(mass ratio of carriers of particles obtained by process (C)) - (mass ratio of carriers of calcined particles obtained by process (A))} / (mass ratio of carriers of particles obtained by process (C))

[0061] After the processing in step (C), it is preferable to wash the particles obtained by the processing in step (C) with water or the like. The particles may be washed by dispersing them in water and stirring. Furthermore, it is preferable to dry the particles after washing.

[0062] From the viewpoint of further improving the conversion rate of alkanes, the proportion of P2 crystals contained in the composite oxide in the particles obtained by the process of step (C) is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 55% by mass or more, even more preferably 60% by mass or more, even more preferably 65% ​​by mass or more, and particularly preferably 70% by mass or more, when the total of P1 crystals and P2 crystals in the composite oxide is taken as 100% by mass. From the viewpoint of further improving the yield of the reaction product, the upper limit of the proportion of P2 crystals contained in the composite oxide in the particles obtained by the process of step (C) is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less, and particularly preferably 82% by mass or less, when the total of P1 crystals and P2 crystals in the composite oxide is taken as 100% by mass.

[0063] From the viewpoint of further improving the conversion rate of alkanes, the BET specific surface area of ​​the particles obtained by the processing in step (C) is preferably 10 m². 2 / g or more, more preferably 17m 2 / g or more, more preferably 20m 2 / g or more, particularly preferably 25m 2 The amount is 1 / g or more. The upper limit of the BET specific surface area of ​​the particles obtained by the processing in step (C) is preferably 40m from the viewpoint of further improving the yield of the reaction product. 2 / g or less, more preferably 32m 2 / g or less, and more preferably 30m 2 / g or less, particularly preferably 28m 2 It is less than / g.

[0064] The catalyst manufacturing method of this embodiment may further include other steps before step (A), after step (A), before step (C), after step (C), before step (B), and after step (B). The catalyst containing the composite oxide particles contained in the catalyst manufactured by the manufacturing method of this embodiment includes composite oxide particles obtained by other steps in step (B) or after step (B). The catalyst containing the composite oxide particles contained in the catalyst manufactured by the manufacturing method of this embodiment may further contain an inorganic binder, an organic binder, a molding aid, etc.

[0065] The method for producing alkenes according to this embodiment includes a step of synthesizing alkenes by a gas-phase catalytic oxidation reaction in which an alkane is reacted with molecular oxygen (i.e., oxygen gas) in the gas phase in the presence of a catalyst containing the complex oxide of this embodiment. When the gas-phase catalytic oxidation reaction of an alkane is carried out using the catalyst of this embodiment, it is possible to achieve both an excellent conversion rate of the alkane and an excellent reaction product, i.e., a high yield of the alkene.

[0066] The gas-phase catalytic oxidation reaction can be carried out, for example, by creating a mixed gas atmosphere in the reactor containing the catalyst of this embodiment, alkanes, and molecular oxygen (oxygen gas), and then increasing the temperature.

[0067] The alkane used as a reaction raw material in the gas-phase catalytic oxidation reaction preferably contains an alkane having 1 to 6 carbon atoms. Examples of alkanes having 1 to 6 carbon atoms include linear alkanes such as methane, ethane, propane, butane, pentane, and hexane; and branched alkanes such as 2-methylpropane (also known as isobutane), 2-methylbutane (also known as isopentane), 2-methylpentane (also known as isohexane), 3-methylpentane, 2,2-dimethylbutane (also known as neohexane), and 2,3-dimethylbutane, with ethane being preferred.

[0068] The alkene reaction product of the gas-phase catalytic oxidation reaction preferably includes an alkene having 2 to 6 carbon atoms. Examples of alkenes having 2 to 6 carbon atoms include linear alkenes such as ethylene, propylene, 1-butene, cis-2-butene, isobutene, 1-pentene, cis-2-pentene, 1-hexene, cis-2-hexene, and cis-3-hexene; and branched alkenes such as 2-methyl-1-butene, 2-methyl-1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 2-methyl-2-pentene, 2,3-dimethyl-1-butene, 3,3-dimethyl-1-butene, 2-ethyl-1-butene, and 2,3-dimethyl-2-butene, with ethylene being preferred.

[0069] The volume ratio of molecular oxygen to alkanes in the raw material mixed gas (molecular oxygen / alkane) is preferably 0.1 to 5.0, more preferably 0.3 to 3.0, and even more preferably 0.5 to 1.5.

[0070] The raw material mixed gas may contain water vapor in addition to alkanes and molecular oxygen. The water vapor content in the raw material mixed gas is preferably 0.1% by volume or more, more preferably 1% by volume or more, and even more preferably 5% by volume or more, based on 100% by volume of the total volume of the raw material mixed gas. The upper limit of the water vapor content is preferably 90% by volume or less, more preferably 60% by volume or less, and even more preferably 50% by volume or less, based on 100% by volume of the total volume of the raw material mixed gas.

[0071] The raw material mixture gas may contain other gases besides water vapor, in addition to alkanes and molecular oxygen. These other gases may be inert gases such as argon or helium. The content of these other gases in the raw material mixture gas is preferably 95% by volume or less, more preferably 90% by volume or less, and even more preferably 85% by volume or less, based on 100% of the total volume of the raw material mixture gas.

[0072] The contact time between the catalyst and the raw material gas in this embodiment is preferably 1 to 6.5 sec·g / cm³. 3More preferably 1.5 to 5.5 sec·g / cm³ 3 The contact time is defined by the following equation. Contact time (sec g / cm 3 ) = (W / F) × 273 / (273 + T) [In the formula, W = mass of the catalyst of this embodiment (g), F = standard conditions (0℃, 1.013 × 10⁻¹⁰] 5 The raw material mixed gas flow rate (Ncm²) at Pa) 3 ( / sec), T = reaction temperature (°C)

[0073] The reaction temperature for the gas-phase catalytic oxidation reaction is preferably 300°C to 500°C, more preferably 350°C to 500°C, even more preferably 400°C to 500°C, even more preferably 420°C to 500°C, even more preferably 430°C to 500°C, and particularly preferably 440°C to 500°C. The reaction pressure for the gas-phase catalytic oxidation reaction is preferably 300 kPa or less, more preferably 20 to 150 kPa.

[0074] For gas-phase catalytic oxidation reactions, known reactors such as fixed-bed reactors, fluidized-bed reactors, and mobile-bed reactors can be used. [Examples]

[0075] The present invention will be described in detail below with reference to examples. The present invention is not limited to these examples. Unless otherwise specified, the temperature condition is room temperature (25°C), and unless otherwise specified, the pressure condition is atmospheric pressure (1 atm).

[0076] <Comparative Example 6: Preparation of Particle F' (without acid treatment - without alkali impregnation)> The chemical formula is Mo1V 0.23 S 0.23 Nb 0.08 W 0.03 Ce 0.005 O n Particle F', represented by / 49.0 mass%-SiO2, was prepared as follows.

[0077] [Preparation of niobium raw material solution] The niobium raw material solution was prepared by the following method: 77.8 kg of water was added to a mixing tank, and then the water was heated to 45°C. Next, while stirring, 72.2 kg of oxalic acid dihydrate [H2C2O4·2H2O] was added, followed by 20.0 kg of niobium acid containing 76.0% by mass as Nb2O5, and the two were mixed in water. The aqueous mixture obtained by heating and stirring this solution at 70°C for 8 hours was allowed to stand, cooled with ice, and the solid was filtered off by suction filtration to obtain a homogeneous niobium raw material solution.

[0078] The molar ratio of oxalic acid to niobium in the obtained niobium raw material solution was 2.11, as determined by the analysis below. The obtained niobium raw material solution was used as the niobium raw material solution in the production of the catalysts in the following examples and comparative examples. The molar ratio of oxalic acid to niobium in the niobium raw material solution was calculated as follows.

[0079] 10 g of niobium starting material solution was accurately weighed into a crucible, dried at 120°C for 2 hours, and then heat-treated at 600°C for 2 hours. The Nb concentration of the niobium starting material solution was calculated from the weight of the resulting solid Nb2O5, which was found to be 0.889 mol / kg. Additionally, 3 g of niobium starting material solution was accurately weighed into a 300 mL glass beaker, 20 mL of hot water at approximately 80°C was added, followed by 10 mL of 1:1 sulfuric acid. The resulting mixture was titrated with 1 / 4 normal KMnO4 under stirring in a water bath while maintaining the liquid temperature at 70°C. The endpoint was defined as the point at which a faint pale pink color due to KMnO4 persisted for approximately 30 seconds or more. The oxalic acid concentration was calculated from the titration volume according to the following formula, and was found to be 1.88 mol / kg. 2KMnO4+3H2SO4+5H2C2O4→K2SO4+2MnSO4+10CO2+8H2O

[0080] Turbidity was measured using a HACH 2100AN Turbidimeter after standing for one day following preparation. 30 mL of niobium raw material was placed in the measurement cell, and the turbidity was measured according to US EPA method 180.1, resulting in a reading of 52 NTU.

[0081] [Preparation of Mixture A] Add ammonium molybdate [(NH4)6Mo7O] to 111 kg of water. 24 16.7 kg of [4H2O], 2.5 kg of ammonium metavanadate [NH4VO3], 3.2 kg of antimony trioxide [Sb2O3], and 0.2 kg of cerium nitrate [Ce(NO3)3·6H2O] were added, and the mixture was heated at 90°C for 2 hours and 30 minutes while stirring to obtain mixture A.

[0082] [Preparation of slurry-like aqueous mixture A] Mixture B was prepared by adding 1.7 kg of hydrogen peroxide solution containing 35.3% by mass of H2O2 to 8.5 kg of niobium raw material solution and stirring the mixture at room temperature for 30 minutes.

[0083] After cooling the obtained mixture A to 70°C, 34.5 kg of silica sol containing 34.1% by mass of SiO2 was added. Next, 4.6 kg of hydrogen peroxide solution containing 35.3% by mass of H2O2 was added, and stirring was continued at 50°C for 1 hour. Mixture B was then added. Subsequently, 1.3 kg of aqueous ammonium metatungstate solution (49.9% purity) and a solution of 7.8 kg of fumed silica dispersed in 78.4 kg of water were added to obtain slurry-like aqueous mixture A.

[0084] [Preparation of dried particles] The resulting slurry-like aqueous mixture A was supplied to a centrifugal spray dryer and dried to obtain micro-spherical dried particles. The inlet temperature of the dryer was 210°C and the outlet temperature was 120°C. The dried particle preparation process was repeated in order to carry out the calcination process described later in a continuous manner.

[0085] [Preparation of calcined particles] The firing process was carried out using a continuous SUS kiln with a diameter of 127 mm and a length of 1150 mm. Specifically, the obtained particles were supplied at a rate of 220 g / hr and subjected to a pre-fired stage at 360°C for 2 hours under a countercurrent nitrogen flow of 3.6 NL / min to obtain the pre-fired product. Next, the pre-fired product was supplied at a rate of 130 g / hr and subjected to a post-fired stage at 680°C for 5 hours under a countercurrent nitrogen flow of 2.3 NL / min to obtain particle F'. Protrusions consisting of protruding oxide crystals were found on the surface of particle F'.

[0086] A vertical tube (41.6 mm inner diameter, 70 cm length) with a perforated disc at the bottom, having three holes with a diameter of 1 / 64 inch, and a paper filter at the top, was used to introduce 50 g of particle F' while air was flowing through it. The length of the airflow in the direction of airflow was 52 mm, and the average linear velocity of the airflow was 310 m / s. When the obtained particle F' was examined by SEM after 24 hours, no protrusions were found on the surface of the particle F'.

[0087] [Specific surface area measurement] The specific surface area was determined by pretreatment of 0.5 g of particles in a glass cell while flowing helium gas at 300°C for 15 minutes, and then by the BET single-point method using nitrogen gas with a Gemini 2360 manufactured by MICROMETRICS.

[0088] The specific surface area of ​​particle F' (after removing the protrusions) is 14.1 m². 2 It was / g.

[0089] [Quantification of the proportion of P2 crystals] (Sample preparation) Approximately 0.5 g of particles were placed in an agate mortar and manually ground for about 1 minute using an agate pestle to obtain a powder. The obtained powder was placed in a circular depression (25 mm in diameter, 1 mm deep) on the surface of the sample stage for XRD measurement, and the surface was leveled using a flat stainless steel spatula.

[0090] (Measurement conditions) X-ray diffraction patterns were obtained using a Bruker AXS D8 Advance under the following conditions. These X-ray diffraction conditions allowed for the acquisition of X-ray diffraction patterns in the range of 2θ = 5° to 85°. X-ray source:CuKα Detector: LYNXEYE XE (1D mode) Tube voltage: 40kV Tube current: 40mA DS (Divergent Slit): 0.3° Solar slit (incident and receiving sides): 2.5° Detector aperture width (PSD aperture width): 2.9° Air scatter screen: Use Measurement mode: Two Theta / Theta Mode: PSD High-Speed ​​Scan Time: 0.5 (s) 2θ / start: 5.0° 2θ / Stop: 80.0° Step width: 0.020°

[0091] (Rielbert analysis) Rietveld analysis is a well-known method for estimating crystal structure. It involves performing X-ray diffraction (XRD) measurements on a given crystal, defining the crystal structure present in the sample based on the information of the measuring instrument (optical system), and then adjusting parameters such as lattice constants and crystal proportions to match the calculated pattern. The resulting particles contain both P1 and P2 crystals within the composite oxide, including Mo, V, and Sb. A "P1 crystal" refers to a crystal that has peaks at 22.1±0.5°, 28.1±0.5°, 36.1±0.5°, and 45.2±0.5° in its X-ray diffraction pattern. A "P2 crystal" refers to a crystal that has peaks at 7.8±0.5°, 8.9±0.5°, 22.1±0.5°, 27.1±0.5°, 35.2±0.5°, and 45.2±0.5° in its X-ray diffraction pattern. By performing Rietveld analysis, crystal structure data for P2 and P1 crystals can be obtained.

[0092] The analysis software used was TOPAS (DIFFRAC.TOPAS Version 6) from Bruker AXS. For the P1 crystal, the structure published in Bulletin de la Societe Chimique de France, 1971, 3459-3463 (EntryWithCollCode26303 in the ICSD database) was used as the initial structure for Rietveld analysis. For the P2 crystal, the structure published in Applied Catalysis A: General, 2007, vol 318, 20, 137-142 (EntryWithCollCode157165 in the ICSD database) was used as the initial structure for Rietveld analysis. Specifically, the Rietveld analysis was performed according to the following procedure.

[0093] (Initial settings) For optical system and instrument information such as "Emission Profile (wavelength)" and "Instrument (instrument constants)," conditions were set according to the measurement conditions, and the background and sample surface height were made variable.

[0094] (Input of sample information) For both the P1 and P2 crystals, the initial structure and refinement conditions were specified as follows. "Refine" means that the corresponding parameter is variable, and refinement is performed to match the measurement data. "Scale" refers to the proportion (weight %) of that crystal to the whole; by refining this, it is possible to determine the proportion of that crystal present in the sample. Enabling Stephens models allows Rietveld analysis to be performed considering crystal anisotropy. Furthermore, enabling Strain G allows Rietveld analysis to be performed considering crystal strain.

[0095] [Table 1-1]

[0096] [Table 1-2]

[0097] The initial structure, as described above, was modified from the database provided. The type, valence, and occupancy rate of elements at each site in the structural information were partially corrected to improve the accuracy of the Rietveld analysis. The modified initial conditions are shown below.

[0098] [Table 2-1]

[0099] [Table 2-2]

[0100] Once the settings were complete as described above, the calculation pattern and measurement data were fitted. Fitting means refining each set parameter, such as the lattice constant and crystal ratio, so that the calculation pattern matches the measurement data. The [amount of P2 crystals] is obtained by refining the scale of the P1 phase and P2 crystals described in Tables 1 and 2.

[0101] Next, in order to further improve the accuracy of the analysis, the following refinement conditions were set for the thermal vibration parameters (BEQ) of each site, the x, y, z coordinates of each site, and the metal occupancy rate of each site for both the P1 and P2 crystals.

[0102] Furthermore, it is desirable to perform fitting of the calculation pattern and measurement data each time the settings for each item described below are changed. This will enable accurate Rietveld analysis.

[0103] Furthermore, in the P2 crystal structure, the "Mo3 site" and "V3 site," "Mo4 site" and "V5 site," "Mo5 site" and "V7 site," and "Mo7 site" and "V9 site" are all located at the same position in the P2 crystal structure, differing only in elemental species. Therefore, their x, y, and z coordinates are specified to be identical (e.g., for "Mo3 site" and "V3 site," their coordinates are set to the same variables x1, y1, and z1). In addition, the variables for these sites are set so that their total occupancy is 1 (e.g., for "Mo3 site" and "V3 site," their respective occupancy is set to the variables n1 and 1-n1).

[0104] Note that "fix" means that the corresponding item is set to a fixed value and no refinement is performed. For sites where the coordinates would be fixed if refinement were performed and the position changed, causing the space group to collapse and preventing proper Rietveld analysis, the coordinates were fixed.

[0105] Furthermore, the fitting process was repeated until the "R_wp" index, which represents the fitting accuracy, was 10 or less, in the fitting results to improve the accuracy of the analysis.

[0106] [Table 3-1]

[0107] [Table 3-2]

[0108] By performing Rietveld analysis using the method described above, an XRD calculation pattern that closely matches the XRD measurement data obtained from the experiment can be obtained. Since this XRD calculation pattern is derived by assuming a certain P1·P2 crystal structure, it can be considered that the [amount of P1 crystals] and [amount of P2 crystals] in that assumed P1·P2 crystal represent the P1·P2 crystals actually present in the measured sample.

[0109] The proportion of P2 crystals in particle F' (after removal of protrusions) was 52.4% by mass.

[0110] <Example 1: Preparation of Particle A (acid-treated - alkali-impregnated)> 750 g of a 5% by mass oxalic acid aqueous solution was prepared by adding oxalic acid and purified water to a 1000 mL Teflon® beaker and heating to 50°C while stirring with a magnetic stirrer. After confirming the dissolution of oxalic acid and the stability of the temperature, 60 g of particles F' (after removing the protrusions) obtained in Comparative Example 6 was added and stirred at 60°C for 0.5 hours. The treated powder was recovered by suction filtration and dispersed in 750 g of purified water for washing, and stirred for 10 minutes. The washed powder was then recovered by suction filtration again and dried at 70°C for 12 hours to obtain acid-treated particles X.

[0111] For the acid-treated particles X, the specific surface area was measured and the proportion of P2 crystals was quantified in the same manner as in Comparative Example 6. The result showed that the specific surface area was 26.5 m². 2 The proportion of P2 crystals per gram was 81.1% by mass.

[0112] [Calculation of the rate of change of specific surface area] For acid-treated particles X, the rate of change in specific surface area was calculated using the following formula. Change in specific surface area (%) = ((Specific surface area after acid treatment) - (Specific surface area before acid treatment)) / (Specific surface area before acid treatment) × 100 Since the acid-treated particles X are made from untreated particles F' obtained in Comparative Example 6, the "specific surface area before acid treatment" is the specific surface area of ​​particles F' (m²). 2 The specific surface area after acid treatment is the specific surface area (m²) of the acid-treated particle X. 2 It is / g).

[0113] The percentage change in the specific surface area of ​​acid-treated particle X was 87.9%.

[0114] [Calculation of the amount of metal components leached out] Approximately 5 g of each catalyst, before and after acid treatment, was placed in a container (made of SUS304, 80 mL capacity) along with 10 stainless steel balls (made of SUS304, Φ10 mm). The mixture was then crushed and mixed at 175 rpm for 15 minutes using a planetary ball mill (made by Ito Seisakusho, LP-4). The resulting powder was pressure-molded into a polyvinyl chloride ring (made by Rigaku Corporation) using a uniaxial press. The resulting pellets were then analyzed semi-quantitatively using wavelength-dispersive X-ray fluorescence spectrometry (XRF, Rigaku Corporation product name "ZSX Primus III", Cr tube, tube voltage 50 kV, tube current 50 mA). The content was determined using the fundamental parameter (FP) method, which uses a sensitivity library pre-registered in the software, to calculate the weight percentage of support silica in the catalyst.

[0115] From the mass ratio of the carrier, where there is almost no increase or decrease in weight before and after treatment, the amount of metal component eluted, with the weight of the catalyst before treatment set to 100%, can be calculated using the following formula. Amount of metal component leached (mass %) = 100 × {(mass percentage of support after acid treatment) - (mass percentage of support before acid treatment)} / (mass percentage of support after acid treatment) Since the acid-treated particles X are made from the untreated particles F' obtained in Comparative Example 1, the "mass ratio of carriers before acid treatment" is the mass ratio of carriers of particles F'. The "mass ratio of carriers after acid treatment" is the mass ratio of carriers of acid-treated particles X.

[0116] The amount of metal components leached from acid-treated particle X was 21.0% by mass.

[0117] The molybdenum content of acid-treated particles X was calculated using XRF. Sodium nitrate, necessary to achieve a Na / Mo ratio of 0.01, was weighed, and purified water was added until 10 g was obtained to prepare an aqueous sodium nitrate solution. The entire amount of the prepared aqueous sodium nitrate solution was added to 50 g of acid-treated particles X in five separate additions, and the mixture was repeated. The resulting powder was dried at 70°C for 12 hours to obtain particles A.

[0118] <Example 2: Preparation of Particle B (no acid treatment - with alkali impregnation (molar ratio to Mo 0.01Na))> The Mo content of particle F' obtained in Comparative Example 6 was calculated using XRF. Sodium nitrate, which is necessary to make the Na / Mo ratio 0.01, was weighed, and purified water was added until 10 g was obtained to prepare an aqueous sodium nitrate solution. The entire amount of the prepared aqueous sodium nitrate solution was added to 50 g of particle F' obtained in Comparative Example 6 in five separate additions, and the mixture was repeated. The resulting powder was dried at 70°C for 12 hours to obtain particle B.

[0119] <Example 3: Preparation of particle C (no acid treatment - with alkali impregnation (molar ratio to Mo 0.03Na))> Particle C was obtained in the same manner as in Example 2, except that sodium nitrate necessary to adjust the Na / Mo ratio to 0.03 was weighed out.

[0120] <Comparative Example 1: Preparation of Particle A' (No Acid Treatment - Alkali Impregnation (Molar Ratio 0.0025Na))> Particle A' was obtained in the same manner as in Example 2, except that sodium nitrate necessary to adjust the Na / Mo ratio to 0.0025 was weighed out.

[0121] <Comparative Example 2: Preparation of Particle B' (No Acid Treatment - Alkali Impregnation (Molar Ratio 0.1Na))> Particle B' was obtained in the same manner as in Example 2, except that sodium nitrate necessary to adjust the Na / Mo ratio to 0.1 was weighed out.

[0122] <Comparative Example 3: Preparation of Particle C' (without acid treatment - with alkali impregnation (molar ratio to Mo 0.01K))> Particle C' was obtained in the same manner as in Example 2, except that potassium nitrate required to make K / Mo 0.01 was weighed to obtain an aqueous potassium nitrate solution, and the obtained aqueous potassium nitrate solution was added in place of the aqueous sodium nitrate solution.

[0123] <Comparative Example 4: Preparation of Particle D' (No Acid Treatment - Alkali Impregnation (Molar Ratio 0.03K))> Particle D' was obtained in the same manner as in Example 2, except that the amount of potassium nitrate required to make the K / Mo ratio 0.03 was weighed, an aqueous potassium nitrate solution was obtained, and the obtained aqueous potassium nitrate solution was added in place of the aqueous sodium nitrate solution.

[0124] <Comparative Example 5: Preparation of Particle E' (without acid treatment - with alkali impregnation (molar ratio to Mo 0.01Rb))> Particles E' were obtained in the same manner as in Example 2, except that the amount of rubidium nitrate required to make Rb / Mo 0.01 was weighed, an aqueous solution of rubidium nitrate was obtained, and the obtained aqueous solution of rubidium nitrate was added in place of the aqueous solution of sodium nitrate.

[0125] <Example Test: Catalyst Performance Test - Oxidation Reaction of Ethane> The catalyst performance test was conducted by filling a fixed-bed reactor (10 mm in diameter) with 2.0 g of particles obtained in the examples and comparative examples, and flowing a mixed gas (20.0 vol% ethane, 20.0 vol% oxygen, 50.0 vol% helium, 10.0 vol% water vapor) at a predetermined temperature (445°C) and pressure (0.06 kg / G).

[0126] First, the ethane conversion rate (%) was calculated by analyzing the samples under conditions where the contact time was 2.0 seconds. Then, the ethylene yield (%) was calculated by adjusting the contact time so that the ethane conversion rate was between 88% and 92% and analyzing the samples again.

[0127] The number of moles of ethane and ethylene produced was determined by first analyzing ethane and ethylene gases of known concentrations using gas chromatography (Shimadzu Corporation "GC2014") to obtain a calibration curve. Then, the reaction product gas 2 hours after the start of the oxidation reaction was quantitatively injected into the gas chromatograph and analyzed. From the measured number of moles of ethane and ethylene, the ethane conversion rate and ethylene yield were calculated according to the following formula. Ethane conversion rate (%) = 100 - (moles of unreacted ethane) / (moles of supplied ethane) × 100 Ethylene yield (%) = (moles of ethylene produced) / (moles of ethane supplied) × 100

[0128] The contact time is defined by the following formula. Contact time (sec g / cm 3 ) = (W / F) × 273 / (273 + T) Here, W, F, and T are defined as follows: W = Amount of particles packed (g) F = Standard conditions (0°C, 1.013 × 10⁻⁶) 5 The raw material mixed gas flow rate (Ncm²) at Pa) 3 / sec) T=reaction temperature (℃)

[0129] The ethane conversion rate (%) and ethylene yield (%) calculated in the test example for the particles obtained in the examples and comparative examples are summarized in the table below, along with the percentage change in specific surface area (%) during the acid treatment step in production, and the type of alkali metal and its molar ratio to Mo during the alkali impregnation step. The ethane conversion rate and ethylene yield were evaluated according to the following criteria.

[0130] (Evaluation criteria for ethane conversion rate) "AA": Ethane conversion rate of 80.0% or higher "A": Ethane conversion rate of 60.0% or more and less than 80.0% "B": Ethane conversion rate of 50.0% or more and less than 60.0% "C": Ethane conversion rate less than 50.0%

[0131] (Evaluation criteria for ethylene yield) "AA": Ethylene yield exceeding 72.5% "A": Ethylene yield between 71.5% and 72.5% "B": Ethylene yield between 70.5% and 71.5% "C": Ethylene yield of 70.5% or less

[0132] [Table 4]

[0133] As shown in the above table, compared with the cases where sodium impregnation treatment is performed by mixing an aqueous solution containing a sodium compound prepared such that the molar ratio M of sodium to Mo satisfies 0.005 < M ≤ 0.08 with the calcined particles obtained in the step (A) (Examples 1 to 3), it was confirmed that the ethylene yield is low when the molar ratio M in the sodium impregnation treatment is outside the above range (Comparative Examples 1 and 2), when impregnation treatment is performed with an alkali metal other than sodium (Comparative Examples 3 to 5), and when no sodium impregnation treatment is performed (Comparative Example 6). It was also confirmed that when acid treatment is performed before sodium impregnation treatment (Example 1), both ethylene yield and ethane conversion can be further improved.

[0134] Although this is an inference, it is considered that containing a specific amount of sodium having appropriate basicity and ionic radius covers decomposition sites without covering effective active sites, thereby making it possible to achieve both ethane conversion and ethylene yield. In addition, since good ethane conversion improves ethane productivity, the catalyst of the present embodiment is advantageous as an industrial catalyst.

Claims

1. A method for producing a catalyst for a gas-phase catalytic oxidation reaction of an alkane containing composite oxide particles containing Mo and V, comprising the following steps (A) and (B). Step (A): Step to obtain calcined particles containing a composite oxide containing Mo and V. Step (B): A step of impregnating the calcined particles obtained in Step (A) with sodium by mixing an aqueous solution containing a sodium compound, prepared so that the molar ratio M of sodium to Mo in the calcined particles is 0.005 < M ≤ 0.

08.

2. A method for producing a catalyst according to claim 1, further comprising the following step (C) before step (B) above. Step (C): A step in which the calcined particles obtained in step (A) are treated with acid until their BET specific surface area increases by 50% or more.

3. The method for producing a catalyst according to claim 2, wherein the acid used in the treatment of step (C) includes a dicarboxylic acid.

4. The method for producing a catalyst according to claim 2, wherein the acid used in the treatment of step (C) is an aqueous solution containing 2% to 20% by mass of oxalic acid.

5. The method for producing a catalyst according to claim 2 or 3, wherein the processing temperature of step (C) is 40°C to 70°C.

6. The method for producing a catalyst according to claim 2 or 3, wherein the processing time for step (C) is 10 minutes to 10 hours.

7. The BET specific surface area of ​​the particles obtained by the process in step (C) is 20 m². 2 / g to 30m 2 A method for producing a catalyst according to claim 2 or 3, wherein the amount is / g.

8. The method for producing a catalyst according to claim 2 or 3, wherein the proportion of P2 crystals contained in the composite oxide in the particles obtained by the process of step (C) is 55% by mass to 85% by mass, when the total amount of P1 crystals and P2 crystals in the composite oxide is taken as 100% by mass.

9. The BET specific surface area of ​​the calcined particles obtained in the above step (A) is 10 m². 2 / g to 20m 2 A method for producing a catalyst according to claim 1 or 2, wherein the amount is / g.

10. The method for producing a catalyst according to claim 1 or 2, wherein the calcination temperature in step (A) is 650°C or higher.

11. The method for producing a catalyst according to claim 1 or 2, wherein step (A) is a step of obtaining calcined particles on which the composite oxide is supported on a carrier.

12. The method for producing a catalyst according to claim 11, wherein the carrier contains silica.

13. The method for producing a catalyst according to claim 11, wherein the content of the carrier in the calcined particles obtained in step (A) is 30% by mass to 70% by mass.

14. The method for producing a catalyst according to claim 1 or 2, wherein the composite oxide further contains Sb.

15. The method for producing a catalyst according to claim 1 or 2, wherein the composite oxide further contains Nb.

16. The method for producing a catalyst according to claim 1 or 2, wherein the composite oxide further contains W.

17. The method for producing a catalyst according to claim 1 or 2, wherein the composite oxide further contains Ce.

18. A method for producing a catalyst according to claim 1 or 2, wherein the composite oxide does not contain Te.

19. The aforementioned composite oxide is given by the following formula (1): Mo 1 V a Sb b Nb c T d Z e O n ・・・(1) (In the formula, T represents at least one element selected from the group consisting of Ti, W, Mn, and Bi. Z represents at least one element selected from the group consisting of La, Ce, Yb, and Y. a, b, c, d, e, and n are the atomic ratios of each element when Mo is set to 1, and respectively 0.05 ≤ a ≤ 0.35, 0.05 ≤ b ≤ 0.35, 0 ≤ c ≤ 0.25, 0 ≤ d ≤ 0.20, and 0 ≤ e ≤ 0.10 (It is within the range, and n is a value that satisfies the balance of valences.) A method for producing a catalyst according to claim 1 or 2.

20. The BET specific surface area of ​​the composite oxide particles is 20 m². 2 / g to 30m 2 A method for producing a catalyst according to claim 1 or 2, wherein the amount is / g.

21. The method for producing a catalyst according to claim 1 or 2, wherein the alkane includes an alkane having 1 to 6 carbon atoms.

22. The method for producing a catalyst according to claim 1 or 2, wherein the catalyst is a catalyst for synthesizing an alkene by a gas-phase catalytic oxidation reaction in which an alkane is reacted with molecular oxygen in the gas phase.

23. A method for producing an alkene, comprising the step of synthesizing an alkene by a gas-phase catalytic oxidation reaction in which an alkane is reacted with molecular oxygen in the gas phase in the presence of a catalyst produced by the method for producing a catalyst according to claim 1 or 2.

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