Catalyst for production of unsaturated carboxylic acid and method for producing unsaturated carboxylic acid

Abstract

The present disclosure relates to a catalyst for the production of an unsaturated carboxylic acid, wherein a catalytically active component has a composition represented by formula (1) described below, and the half-value width of a peak at 22.2° ± 0.3° in the X-ray diffraction pattern obtained using CuKα rays as an X-ray source is 0.65° to 1.60° inclusive. (1): (Mo)12(V)a(W)b(Cu)c(Sb)d(X)e(Y)f(Z)g(O)h

Description

Catalyst for producing unsaturated carboxylic acid and method for producing unsaturated carboxylic acid

[0001] The present invention relates to a catalyst for producing an unsaturated carboxylic acid in high yield by vapor-phase catalytic oxidation of an unsaturated aldehyde in the presence of molecular oxygen or a molecular oxygen-containing gas, a method for producing the same, and a method for producing an unsaturated carboxylic acid using the catalyst.

[0002] Acrylic acid is becoming increasingly important as a raw material for absorbent resins, adhesives, etc. Therefore, in recent years, there has been a demand for improved catalyst performance for producing acrylic acid by gas-phase catalytic oxidation of acrolein as a raw material. Accordingly, various companies have been making various improvements to catalysts that can produce acrylic acid in high yields and stably over the long term. For example, the following proposals have been made:

[0003] Patent Documents 1 to 4 disclose improvements to catalyst composition, etc., focusing on the X-ray diffraction peaks of catalytically active components. These catalysts have been proposed as catalysts that achieve high activity and high yield. Patent Documents 5 and 6 also provide improvement guidelines aimed at improving mechanical strength, and catalytic performance is improved by preventing powdering during packing. Patent Document 7 aims to improve the long-term stability of catalytic reactions by setting the standard deviation of catalyst particle size within a specific range. Patent Document 8 proposes a method for producing a catalyst that combines high catalytic performance and mechanical strength by controlling the relative centrifugal acceleration during molding using a tumbling granulator. Patent Document 9 proposes a method for producing a high-yield catalyst by controlling the density of the catalyst molded body and the roughness of the catalyst surface. Patent Document 10 proposes a production method for obtaining high activity and selectivity by controlling the crystal size of nanocrystalline molybdenum mixed oxide within a specific range.

[0004] However, improving catalytic activity is an important issue, especially in the production of unsaturated carboxylic acids. This not only contributes to improving yields but is also important from the perspective of catalyst life. For example, if the reaction bath temperature at the beginning of the reaction can be lowered by improving catalytic activity in a catalyst-using plant, not only will the energy cost for heating be reduced, but thermal degradation of the catalyst will also be reduced, resulting in less performance degradation from a long-term perspective and enabling stable operation and high yields over a long period of time. For these reasons, there is a demand for highly active catalysts and methods for producing them.

[0005] Japanese Patent Application Publication No. 8-299797 Japanese Patent Application Publication No. 2003-251184 Japanese Patent Application Publication No. 2015-120133 Japanese Patent Application Publication No. 2018-43197 Japanese Patent Application Publication No. 2001-79408 International Publication No. 2012 / 073584 Japanese Patent Application Publication No. 2009-214105 Japanese Patent Application Publication No. 2015-96497 International Publication No. 2020 / 196150 Japanese Patent Publication No. 2011-516378

[0006] In view of the above circumstances, an object of the present invention is to improve the catalytic activity of a catalyst for producing an unsaturated carboxylic acid from an unsaturated aldehyde as a raw material by a vapor-phase catalytic oxidation reaction.

[0007] As a result of extensive research into the current situation and problems described above, the inventors of the present application have found that specific parameters in the X-ray diffraction pattern contribute to improving activity, and have thus made the present invention.

[0008] That is, the present invention relates to the following 1) to 6): 1) A catalyst for producing an unsaturated carboxylic acid, wherein the catalytically active component has a composition represented by the following formula (1), and the half-width of the peak at 22.2°±0.3° in an X-ray diffraction pattern obtained using CuKα radiation as an X-ray source is 0.65° or more and 1.60° or less: (Mo) １２ (V) ａ (W) ｂ (Cu) ｃ (Sb) ｄ (X) ｅ (Y) ｆ (Z) ｇ (O) ｈ(1) (In formula (1), Mo, V, W, Cu, Sb, and O represent molybdenum, vanadium, tungsten, copper, antimony, and oxygen, respectively; X represents at least one element selected from the group consisting of alkali metals and thallium; Y represents at least one element selected from the group consisting of magnesium, calcium, strontium, barium, and zinc; Z represents niobium, cerium, tin, chromium, manganese, iron, cobalt, sulfur, and the like.) Each of the elements represents at least one element selected from the group consisting of marium, germanium, titanium, and arsenic. Furthermore, a, b, c, d, e, f, g, and h represent the atomic ratio of each element, and relative to 12 molybdenum atoms, the ratios are 0<a≦10.0, 0≦b≦10.0, 0<c≦6.0, 0≦d≦10.0, 0≦e≦0.50, 0≦f≦1.0, and 0≦g<6.0. Furthermore, h represents the number of oxygen atoms required to satisfy the valence of each of the components.) 2) A catalyst for producing an unsaturated carboxylic acid according to 1) above, wherein in formula (1) above, the ratios are 1.0≦a≦5.0, 0.50≦b≦3.0, 0.50≦c≦3.0, and 0<d≦2.0. 3) A catalyst for producing an unsaturated carboxylic acid according to 1) above, wherein a catalytically active component is supported on an inert carrier. 4) The catalyst for producing an unsaturated carboxylic acid according to 3) above, wherein the inert carrier is silica, alumina, or a combination thereof. 5) A method for producing an unsaturated carboxylic acid using the catalyst for producing an unsaturated carboxylic acid according to any one of 1) to 4) above. 6) A method for producing an unsaturated carboxylic acid using a reaction tube packed in multiple layers with two or more types of the catalyst for producing an unsaturated carboxylic acid according to any one of 1) to 4) above.

[0009] According to the present invention, high catalytic activity can be maintained when an unsaturated aldehyde, preferably (meth)acrolein, is used as a raw material and an unsaturated carboxylic acid, i.e., (meth)acrylic acid, is produced by subjecting the raw material to a gas-phase catalytic oxidation reaction.

[0010] FIG. 1 is a diagram showing an XRD chart of the catalytically active component of catalyst 1 produced in Example 1.

[0011] [Half-width of the 22.2°±0.3° Peak] The catalyst of the present invention has a half-width of the 22.2°±0.3° peak in an X-ray diffraction (XRD) pattern obtained using CuKα radiation as an X-ray source of 0.65° or more and 1.60° or less. In this specification, "half-width" refers to the full width at half maximum, i.e., the width at half the intensity of the peak value as a quadratic function after fitting, as described below. The details of how the half-width of the 22.2°±0.3° peak in the X-ray diffraction pattern affects activity are unclear, but the clear correlation between the half-width of the 22.2°±0.3° peak and catalytic activity suggests that a specific crystalline structure is responsible for the oxidation reaction of (meth)acrolein. While the majority of the active component of the catalyst for producing (meth)acrylic acid of the present invention has an amorphous structure, it is believed that the presence of some crystals exhibits high catalytic activity. The half-width of the peak at 22.2°±0.3° in the X-ray diffraction pattern decreases when crystals with diffraction planes at 22.2°±0.3° grow. The oxidation reaction of (meth)acrolein is thought to proceed within the crystal structure, and as the crystals grow, the number of reaction sites within the crystal structure increases, which is thought to improve the activity of the catalyst. However, if the crystals become too large, physical resistance occurs, making it difficult for the raw material (meth)acrolein to pass through the crystal structure, which is thought to reduce activity. Furthermore, the half-width of the peak at 22.2°±0.3° also varies depending on the number of crystals. As the proportion of amorphous portions in the active component decreases and the number of crystals increases, the diffraction planes increase, reducing the half-width, and the activity improves due to the increase in highly active components. In addition, the half-width of the peak at 22.2°±0.3° also varies depending on the distortion of the crystal structure. In general, catalytic reactions are believed to proceed more easily in areas with structural defects, and it is believed that catalysts for producing (meth)acrylic acid also become more active when they have a certain degree of structural defects. The presence of structural defects causes distortion in the crystal structure, resulting in a large half-width value for the peak at 22.2°±0.3° in the X-ray diffraction pattern.Generally speaking, the inventors of the present invention believe that a catalyst in which the degree of crystal growth and structural distortion are within a certain range and the number of crystals is large is a preferable form for a catalyst for producing (meth)acrylic acid, and have found that this can be achieved by adjusting the half-value width of the peak at 22.2°±0.3° in the X-ray diffraction pattern to 0.65° or more and 1.60° or less.

[0012] The half-width in the present invention is 0.65° or more and 1.60° or less, and more preferably the lower limit is 0.70°, 0.75°, 0.80°, 0.85°, 0.88°, 0.90°, 0.92°, 0.94°, 0.96°, and particularly preferably 0.98°. Similarly, the upper limit is preferably 1.55°, 1.50°, 1.47°, 1.45°, 1.40°, 1.35°, 1.33°, and particularly preferably 1.31°. Therefore, the half width of the peak at 22.2°±0.3° is preferably 0.70° or more and 1.60° or less, more preferably 0.75° or more and 1.60° or less, more preferably 0.80° or more and 1.60° or less, more preferably 0.85° or more and 1.55° or less, more preferably 0.88° or more and 1.50° or less, more preferably 0.90° or more and 1.47° or less, more preferably 0.92° or more and 1.45° or less, more preferably 0.94° or more and 1.40° or less, more preferably 0.96° or more and 1.35° or less, and most preferably 0.98° or more and 1.31° or less. The half width of the peak at 22.2°±0.3° may be 0.65° or more and 1.47° or less, 0.65° or more and 1.45° or less, 0.65° or more and 1.40° or less, 0.85° or more and 1.60° or less, 0.88° or more and 1.60° or less, or 0.90° or more and 1.60° or less.

[0013] Note that, as a method for measuring the X-ray diffraction angle (2θ), for example, an Ultima IV manufactured by Rigaku Corporation may be used to measure the X-ray diffraction angle (2θ) under the conditions of CuKα X-rays (λ=0.154 nm), output of 40 kV, 30 mA, measurement range of 5 to 60°, and measurement speed of 3° per minute; however, the method is not limited thereto as long as it does not deviate from the measurement principle.

[0014] [Method for calculating the half-width of the peak at 22.2°±0.3°] When calculating the half-width, data that has not been processed, such as baseline smoothing, is used, and OriginPro manufactured by LightStone is used as the analysis software. As an analysis method, a straight line passing through the minimum value of 2θ = 16.0° to 18.0° and the minimum value of 2θ = 39.0° to 42.0° in the X-ray diffraction pattern is used as the baseline, and a quadratic function is fitted to the peak above the baseline, and the full width at half maximum of the fitted quadratic function having a peak in the range of 2θ = 22.2°±0.3° in the X-ray diffraction pattern is read as the half-width of the peak at 2θ = 22.2°±0.3°.

[0015] [Half-width of the 8.3°±0.5° peak] From the viewpoint of catalytic activity, the catalyst of the present invention preferably has a half-width of the 8.3°±0.5° peak that is greater than 0 and not greater than 2.82°. The upper limit of the half-width of the 8.3°±0.5° peak is more preferably 2.75°, 2.70°, 2.65°, 2.60°, 2.55°, 2.50°, 2.45°, or 2.40°, in that order, and particularly preferably 2.37°. Similarly, the lower limit is more preferably 1.00°, 1.50°, 2.00°, 2.10°, or 2.20°, in that order, and particularly preferably 2.30°. Therefore, the half width of the peak at 8.3°±0.5° is more preferably greater than 0 and 2.75° or less, more preferably greater than 0 and 2.70° or less, more preferably greater than 0 and 2.65° or less, more preferably 1.00° or more and 2.60° or less, more preferably 1.50° or more and 2.55° or less, more preferably 2.00° or more and 2.50° or less, more preferably 2.10° or more and 2.45° or less, more preferably 2.20° or more and 2.40° or less, and most preferably 2.30° or more and 2.37° or less.

[0016] [Method for calculating the half width of the peak at 8.3°±0.5°] The method is the same as the method for calculating the half width of the peak at 22.2°±0.3°, except that the half width of the quadratic function after fitting, which has a peak in the range of 2θ=8.3°±0.5°, is read as the half width of the peak.

[0017] [Half-width of the peak at 26.7°±0.3°] From the viewpoint of catalytic activity, the catalyst of the present invention preferably has a half-width of the peak at 26.7°±0.3° of 4.66° or more and 7.40° or less. The upper limit of the half-width of the peak at 26.7°±0.3° is more preferably 7.30°, 7.25°, 7.20°, 7.00°, 6.90°, 6.80°, 6.70°, 6.60°, 6.50°, 6.40°, 6.30°, 6.20°, 6.15°, or 6.10°, and particularly preferably 6.05°. Similarly, the lower limit is more preferably 4.80°, 5.00°, 5.05°, 5.10°, 5.20°, 5.30°, 5.40°, 5.45°, 5.50°, 5.60°, 5.70°, 5.80°, or 5.90°, and is particularly preferably 5.95°. Therefore, the half width of the peak at 26.7°±0.3° is more preferably 4.66° or more and 7.30° or less, more preferably 4.66° or more and 7.25° or less, more preferably 4.80° or more and 7.20° or less, more preferably 5.00° or more and 7.00° or less, more preferably 5.10° or more and 6.90° or less, more preferably 5.20° or more and 6.80° or less, more preferably 5.30° or more and 6.70° or less, more preferably 5.40° or more and 6.60° or less, more preferably 5.45° or more and 6.50° or less, more preferably 5.50° or more and 6.40° or less, more preferably 5.60° or more and 6.30° or less, more preferably 5.70° or more and 6.20° or less, more preferably 5.80° or more and 6.15° or less, more preferably 5.90° or more and 6.10° or less, and most preferably 5.95° or more and 6.05° or less.

[0018] [Method for calculating the half width of the peak at 26.7°±0.3°] The method is the same as the method for calculating the half width of the peak at 22.2°±0.3°, except that the half width of the quadratic function after fitting, which has a peak in the range of 2θ=26.7°±0.3°, is read as the half width of the peak.

[0019] [Half-width of the 45.4°±0.3° peak] From the viewpoint of catalytic activity, the catalyst of the present invention preferably has a half-width of the 45.4°±0.3° peak of 0.64° or more and 1.03° or less. The upper limit of the half-width of the 45.4°±0.3° peak is more preferably 1.00°, 0.99°, or 0.98°, in that order, and particularly preferably 0.97°. Similarly, the lower limit is more preferably 0.65°, 0.67°, 0.70°, 0.75°, 0.80°, 0.85°, or 0.90°, in that order, and particularly preferably 0.95°. Therefore, the half width of the peak at 45.4°±0.3° is more preferably 0.65° or more and 1.03° or less, more preferably 0.67° or more and 1.03° or less, more preferably 0.70° or more and 1.03° or less, more preferably 0.75° or more and 1.03° or less, more preferably 0.80° or more and 1.00° or less, more preferably 0.85° or more and 0.99° or less, more preferably 0.90° or more and 0.98° or less, and most preferably 0.95° or more and 0.97° or less.

[0020] [Method for calculating the half width of the peak at 45.4°±0.3°] The method is the same as the method for calculating the half width of the peak at 22.2°±0.3°, except that the half width of the quadratic function after fitting, which has a peak in the range of 2θ=45.4°±0.3°, is read as the half width of the peak.

[0021] [Catalyst Composition] The catalyst of the present invention has a composition represented by the following formula (1): [Formula (1)] (Mo) １２ (V) ａ (W) ｂ (Cu) ｃ (Sb) ｄ (X) ｅ (Y) ｆ (Z) ｇ (O) ｈ　(1) (In the formula, Mo, V, W, Cu, Sb, and O represent molybdenum, vanadium, tungsten, copper, antimony, and oxygen, respectively; X represents at least one element selected from the group consisting of alkali metals and thallium; Y represents at least one element selected from the group consisting of magnesium, calcium, strontium, barium, and zinc; Z represents bismuth, tellurium, silver, selenium, silicon, aluminum, boron, niobium, cerium, tin, chromium, manganese, iron, cobalt, nickel, samarium, germanium, and arsenic; Each element represents at least one element selected from the group consisting of rumanium, zirconium, titanium, chromium, tantalum, lead, indium, sulfur, palladium, gallium, lanthanum, and arsenic. Furthermore, a, b, c, d, e, f, g, and h represent the atomic ratio of each element, with 0<a≦10.0, 0≦b≦10.0, 0<c≦6.0, 0≦d≦10.0, 0≦e≦0.50, 0≦f≦1.0, and 0≦g<6.0 relative to 12 molybdenum atoms. Furthermore, h represents the number of oxygen atoms required to satisfy the valence of each of the aforementioned components.

[0022] In the above formula (1), the preferred ranges of a to g are as follows: the lower limit of a is, in order of desirability, 0.20, 0.50, 0.80, 1.0, 1.5, 2.0, 2.2, and 2.4, and is most desirably 2.6, and the upper limit of a is, in order of desirability, 9.0, 8.0, 7.0, 6.0, 5.0, 4.5, 4.0, 3.5, 3.3, and 3.1, and is most desirably 2.9. That is, the range of a is preferably 0.20≦a≦9.0, more preferably 0.20≦a≦8.0, more preferably 0.20≦a≦7.0, more preferably 0.50≦a≦6.0, more preferably 0.80≦a≦5.0, more preferably 1.0≦a≦4.5, more preferably 1.5≦a≦4.0, more preferably 2.0≦a≦3.5, more preferably 2.2≦a≦3.3, more preferably 2.4≦a≦3.1, and most preferably 2.6≦a≦2.9. The lower limit of b is, in descending order of desirability, 0.10, 0.20, 0.30, 0.40, 0.50, and 0.60, and most desirably 0.70, and the upper limit of b is, in descending order of desirability, 9.0, 8.0, 7.0, 6.0, 5.0, 4.0, 3.0, 2.5, 2.0, 1.5, and 1.3, and most desirably 1.1. That is, the range of b is preferably 0.10≦b≦9.0, more preferably 0.10≦b≦8.0, more preferably 0.10≦b≦7.0, more preferably 0.10≦b≦6.0, more preferably 0.10≦b≦5.0, more preferably 0.10≦b≦4.0, more preferably 0.20≦b≦3.0, more preferably 0.30≦b≦2.5, more preferably 0.40≦b≦2.0, more preferably 0.50≦b≦1.5, more preferably 0.60≦b≦1.3, and most preferably 0.70≦b≦1.1. The lower limit of c is, in order of desirability, 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, 0.90, and 1.0, and is most desirably 1.3, and the upper limit of c is, in order of desirability, 5.0, 4.0, 3.0, 2.5, 2.0, and 1.8, and is most desirably 1.6.That is, the range of c is preferably 0.10≦c≦5.0, more preferably 0.20≦c≦5.0, more preferably 0.30≦c≦5.0, more preferably 0.40≦c≦5.0, more preferably 0.50≦c≦5.0, more preferably 0.60≦c≦4.0, more preferably 0.70≦c≦3.0, more preferably 0.80≦c≦2.5, more preferably 0.90≦c≦2.0, more preferably 1.0≦c≦1.8, and most preferably 1.3≦c≦1.6. The lower limit of d is, in order of desirability, 0.11, 0.15, 0.18, 0.20, 0.25, 0.30, and 0.35, and most desirably 0.40, and the upper limit of d is, in order of desirability, 9.0, 8.0, 7.0, 6.0, 5.0, 4.0, 3.0, 2.5, 2.0, 1.5, and 1.0, and most desirably 0.70. That is, the range of d is preferably 0.11≦d≦9.0, more preferably 0.11≦d≦8.0, more preferably 0.11≦d≦7.0, more preferably 0.11≦d≦6.0, more preferably 0.11≦d≦5.0, more preferably 0.15≦d≦4.0, more preferably 0.18≦d≦3.0, more preferably 0.20≦d≦2.5, more preferably 0.25≦d≦2.0, more preferably 0.30≦d≦1.5, more preferably 0.35≦d≦1.0, and most preferably 0.40≦d≦0.70. The upper limit of e is, in order of desirability, 0.40, 0.30, 0.20, and 0.10. That is, the range of e is, in order of desirability, 0≦e≦0.40, 0≦e≦0.30, and 0≦e≦0.20, with the most preferred range being 0≦e≦0.10. The upper limit of f is, in order of preference, 0.80, 0.50, 0.20, and 0.15, and most preferably 0.10. That is, the ranges of f are, in order of preference, 0≦f≦0.80, 0≦f≦0.50, 0≦f≦0.20, and 0≦f≦0.15, and the most preferred range is 0≦f≦0.10. The upper limit of g is, in order of preference, 5.0, 4.0, 3.0, 2.0, and 1.0. That is, the ranges of g are, in order of preference, 0≦g≦5.0, 0≦g≦4.0, 0≦g≦3.0, and 0≦g≦2.0, and the most preferred range is 0≦g≦1.0. Note that a particularly preferred embodiment is when e, f, and g are 0.

[0023] When the catalyst of the present invention is used in a reaction for producing a corresponding unsaturated carboxylic acid from an unsaturated aldehyde such as acrolein or methacrolein as a raw material, particularly in a reaction for producing acrylic acid by gas-phase catalytic oxidation of acrolein with molecular oxygen or a molecular oxygen-containing gas, it is possible to achieve improved catalytic activity and a reduced differential pressure compared to known methods, and is therefore very effective. Furthermore, even in the process of a partial oxidation reaction that generates heat, improved stability can be expected due to a reduction in hot spot temperature, etc. Furthermore, the catalyst of the present invention is effective in reducing by-products that have a negative impact on the environment and the quality of the final product, such as carbon monoxide (CO) and carbon dioxide (CO ２ ), and is also effective in reducing acetaldehyde, acetic acid, and formaldehyde.

[0024] [Catalyst Manufacturing Method, etc.] Specific steps for obtaining the catalyst of the present invention are described below. Step a) Preparation: Examples of raw materials for each element constituting the catalyst include the following. The use of ammonium molybdate as the molybdenum component raw material results in a high-performance catalyst. For tungsten, vanadium, antimony, copper, and other elements, raw materials can typically be oxides or ammonium salts that can be converted to oxides upon ignition, carbonates, sulfates, organic acid salts, hydroxides, metal powders, or mixtures thereof. The preferred raw materials vary depending on the type of element, and the half-width of the peak at 22.2°±0.3° in the XRD pattern can also be adjusted accordingly. For example, ammonium salts are preferred for tungsten and vanadium, and sulfates are preferred for copper. For antimony raw materials, compounds with a trivalent valence of antimony are preferred, with salts of acetic acid, carbonic acid, tartaric acid, oxalic acid, and other carboxylic acids being particularly preferred. A vanadium source, a molybdenum source, a tungsten source, and an antimony source are mixed in a desired ratio in an aqueous solvent at 20 to 95°C, heated and stirred for about an hour, and then, if necessary, an X component source, a Y component source, and a Z component source are added. Finally, an aqueous solution containing a dissolved copper source is added. An aqueous solution or slurry containing the catalyst components is obtained, hereinafter referred to as prepared solution (A). When a metal powder is used as the raw material, it is preferably added at the same time as the antimony source. When a divalent copper source is used as the copper source, it is preferably added after the antimony source and metal powder. Adding the divalent copper source before the antimony source and metal powder will result in the formation of low-activity crystals, leading to a decrease in catalytic performance. Here, prepared solution (A) does not necessarily need to contain all of the catalyst constituent elements; some elements or a partial amount of these elements may be added in a subsequent step. Furthermore, when preparing the preparation liquid (A), if the amount of water in which each component raw material is dissolved, or if an acid such as sulfuric acid, nitric acid, hydrochloric acid, tartaric acid, or acetic acid is added for dissolution, is not appropriate, for example, within the range of 5% by mass to 99% by mass, the acid concentration in the aqueous solution sufficient to dissolve the raw materials may not be appropriate, otherwise the preparation liquid (A) may take the form of a clay-like mass, which will not serve as an excellent catalyst.Therefore, the form of the resulting preparation (A) is preferably an aqueous solution or a slurry, in that an excellent catalyst can be obtained.

[0025] Step b) Drying: The preparation (A) obtained above is then dried to obtain a dry powder. The drying method is not particularly limited as long as it can completely dry the preparation (A), and examples include drum drying, freeze drying, spray drying, and evaporation to dryness. Among these, spray drying, which can dry the slurry into powder or granules in a short time, is particularly preferred in the present invention. The drying temperature for spray drying varies depending on the concentration of the slurry, the liquid delivery speed, etc., but is generally 70 to 150°C at the outlet of the dryer. It is also preferable to dry the resulting dry powder so that the average particle size is 20 to 700 μm. In this way, dry powder (B) is obtained.

[0026] Step c) Pre-calcination: The resulting dry powder (B) is calcined under air flow at 200 to 500°C, preferably 300 to 400°C, which tends to improve the moldability, mechanical strength, and catalytic performance of the catalyst. The calcination time is preferably 1 to 12 hours. In this way, a pre-calcined body (C) is obtained.

[0027] Step d) Pulverization The obtained pre-calcined body (C) is obtained as a solid (D) in which the dry powder (B) is agglomerated by pre-calcination. The solid (D) is pulverized to obtain the pre-calcined powder (E) required for the subsequent molding step. The pulverization method is not particularly limited, and examples include a roller mill, jet mill, hammer mill, ball mill, and vibration mill. The average particle size (pre-calcined median diameter) of the pre-calcined powder (E) obtained in this step is preferably 50 μm or less, more preferably 40 μm or less, even more preferably 30 μm or less, and particularly preferably 25 μm or less. In this specification, the pre-calcined powder (E) after pulverization is referred to as a catalyst precursor. However, if there is no agglomeration at the pre-calcined body (C) stage and it can be used without undergoing a pulverization step, the pre-calcined body (C) may be used as a catalyst precursor.

[0028] Step e) Molding There is no particular limitation on the molding method, but when molding into a cylindrical or ring shape, a method using a tablet molding machine, an extrusion molding machine, etc. is preferred. More preferably, when molding into a spherical shape, the pre-sintered powder (E) may be molded into a spherical shape using a molding machine, but a method in which the pre-sintered powder (E) (containing a molding aid and a strength improver, if necessary) is supported on a carrier such as an inert ceramic is preferred. Here, widely known methods of loading include tumbling granulation, methods using centrifugal fluidized coating equipment, washcoating, etc., and are not particularly limited as long as they can uniformly load the pre-calcined powder (E) on the support. However, considering the production efficiency of the catalyst and the performance of the prepared catalyst, a more preferred method is to use an apparatus having a flat or uneven disk at the bottom of a stationary cylindrical container, which is rotated at high speed to vigorously agitate the support charged in the container by the rotation and revolution of the support itself, and to add the pre-calcined powder (E) and, if necessary, a molding aid and / or strength improver and pore former to load the powder components on the support. The tumbling granulation method is the most preferred. It is preferable to use a binder for loading. Specific examples of binders that can be used include water, ethanol, methanol, propanol, polyhydric alcohols, polymeric binders such as polyvinyl alcohol, and inorganic binders such as silica sol aqueous solutions. Ethanol, methanol, propanol, and polyhydric alcohols are preferred, with diols such as ethylene glycol and triols such as glycerin being more preferred. The use of an appropriate amount of glycerin aqueous solution improves moldability and produces a high-performance catalyst with high mechanical strength. Specifically, the use of an aqueous solution with a glycerin concentration of 5% by mass or higher produces a particularly high-performance catalyst. The amount of these binders used is typically 2 to 80 parts by mass per 100 parts by mass of pre-calcined powder (E). An inert carrier typically having a diameter of approximately 2 to 8 mm is used, and the pre-calcined powder (E) is supported on it. The support rate is determined taking into account the catalyst use conditions, such as the space velocity of the reactant materials and the raw material concentrations, and is typically 20 to 80% by mass. When molding aids and strength improvers are used in molding, the support rate is expressed as shown in the following formula (4): In this way, a molded body (F) is obtained.Furthermore, the present inventors have found that the catalyst of the present invention may have poor mechanical strength. Therefore, it is preferable to add inactive inorganic fibers as a strength improver during the support formation. The amount of these fibers used is usually 1 to 30 parts by mass per 100 parts by mass of the pre-calcined powder (E).

[0029] [Regarding Support] Catalysts in which a pre-calcined body (C) obtained by pre-calcining the catalytically active component after preparation, or a pre-calcined powder (E) obtained by further pulverizing the pre-calcined body (C) and supporting it on an inert carrier are particularly effective. Known materials for the inert carrier can be used, such as alumina, silica, titania, zirconia, niobia, silica-alumina, silicon carbide, carbides, and mixtures thereof. The particle size, water absorption, mechanical strength, degree of crystallinity of each crystalline phase, and mixing ratio of the inert carrier are not particularly limited, and should be selected within appropriate ranges taking into account the performance, moldability, production efficiency, etc. of the final catalyst. The shape of the inert carrier is preferably spherical, but is not particularly limited, and pellets, rings, etc. can also be used. The mixing ratio of the carrier and pre-calcined powder is generally calculated as the loading rate using the following formula (4) based on the charged mass of each raw material: In addition, if it is clear that additives such as molding aids and strength improvers remain in the catalyst after the main calcination, they are included in the total amount (denominator). [Formula (4)] Support rate (mass%) = (mass of pre-calcined powder used for molding) / {(mass of pre-calcined powder used for molding) + (mass of support used for molding)} × 100 (4) A preferred upper limit for the support rate is 80 mass%, and more preferred values ​​are 70, 60, 55, 50, 45, and 40 mass%. A preferred lower limit is 10 mass%, and more preferred values ​​are 15, 18, and 20 mass%. That is, the loading rate is preferably 10% by mass or more and 80% by mass or less, more preferably 10% by mass or more and 70% by mass or less, more preferably 10% by mass or more and 60% by mass or less, more preferably 10% by mass or more and 55% by mass or less, more preferably 15% by mass or more and 50% by mass or less, more preferably 18% by mass or more and 45% by mass or less, and the most preferable range is 20% by mass or more and 40% by mass or less.

[0030] [Regarding Inorganic Fibers] The catalyst of the present invention preferably contains inorganic fibers for purposes such as improving mechanical strength. The material of the inorganic fibers is not particularly limited, and examples that can be used include glass fibers (glass fiber), ceramic fibers, metal fibers, mineral fibers, carbon fibers, and various whiskers. Of these, glass fibers treated with silane-based chemicals are particularly preferred. The fiber length is also not particularly limited as long as it does not impair the effects of the present invention, but an average fiber length of approximately 1 to 1,000 μm, more preferably approximately 10 to 500 μm, is preferred. Furthermore, two or more types of inorganic fibers can be used in combination, and they may be two or more types made of different materials, or two types made of the same material but with different average fiber lengths.

[0031] Step f) Calcination Calcining the molded body (F) at a temperature of 100 to 450°C for about 1 to 12 hours tends to improve catalytic activity and effective yield. The calcination temperature is preferably 270 to 420°C, more preferably 350 to 400°C. Air is the preferred gas to be circulated for its simplicity, but other inert gases such as nitrogen, carbon dioxide, argon, helium, nitrogen oxide-containing gases to create a reducing atmosphere, ammonia-containing gases, hydrogen gas, and mixtures thereof can also be used. In this way, catalyst (G) is obtained.

[0032] [Method for adjusting the half width of the peak at 22.2°±0.3°] The value of the half width can be adjusted by changing the types and ratios of raw materials used in the above-mentioned step a), the spray drying conditions in step b), the firing temperature, time, and atmosphere in step c), the pulverization method and median diameter after pulverization in step d), and the relative centrifugal acceleration, loading rate, type of binder, and position of binder addition in step e), but it is difficult to achieve a large change by changing a single condition, and can be achieved by optimizing two or more conditions. Some examples are given below.

[0033] <Types and Ratios of Raw Materials Used in Step a)> The half-width of the peak at 22.2°±0.3° in the XRD pattern can be adjusted by changing the type of raw material used. It is particularly effective to change the compound that can function as a reducing agent. The half-width increases when a trivalent antimony compound is used, while the half-width decreases when metal powders such as molybdenum or copper with an oxidation state of zero or organic substances such as oxalic acid or citric acid are used. The half-width can also be controlled by adjusting the composition ratio of metal elements. The catalyst of the present invention has a basic skeleton of molybdenum and vanadium, and the increase in other elements tends to increase the half-width because distortion occurs in the crystal structure. In particular, tungsten and antimony atoms strongly distort the crystal structure, so the use of larger amounts of these raw materials tends to increase the half-width. Conversely, the use of larger amounts of copper raw materials tends to decrease the half-width. From this viewpoint, for example, the atomic ratio d of antimony to 12 molybdenum atoms in formula (1) may be 0<d<1.0, 0.25≦d≦0.75, or 0.25≦d≦0.50.

[0034] <C) Firing Temperature, Time, and Atmosphere in Step c> As mentioned above, the firing temperature is preferably 200°C to 500°C. Higher temperatures promote crystal growth, tending to reduce the FWHM. However, too high a temperature or too long a time leads to thermal decomposition of the crystals, resulting in a decrease in their number and a larger FWHM. Therefore, from the perspective of adjusting the FWHM, temperatures below 400°C and firing times below 6 hours are preferred. The gas atmosphere during firing can be air, but the presence of oxygen molecules inhibits crystal growth. Therefore, firing under an inert gas atmosphere such as nitrogen or argon, or a reducing gas atmosphere such as hydrogen or ammonia, can reduce the FWHM. <D) Milling Method, Median Diameter, and Centrifugal Acceleration in Step d> While the FWHM can be controlled by the method used in Step d), using a ball mill makes it easier to adjust the FWHM. It can also be adjusted by adjusting the median diameter of the pre-fired powder to a certain value or less. The median diameter of the pre-fired powder is preferably 50 μm or less. The half-value width can also be adjusted by changing the relative centrifugal acceleration when the step e) is performed by rolling granulation, depending on the median diameter of the pre-calcined powder. When the median diameter is smaller than 30 μm, it is recommended to set the relative centrifugal acceleration to 10 G or more.

[0035] [Use of the catalyst] In the production of unsaturated carboxylic acids such as acrylic acid using the catalyst of the present invention, the method of flowing the raw material gas may be a conventional single flow method or a recycle method, and the method may be carried out under commonly used conditions and is not particularly limited. For example, a mixed gas consisting of 1 to 10% by volume, preferably 4 to 9% by volume, of starting raw materials as ideal gases, 3 to 20% by volume, preferably 4 to 18% by volume, of molecular oxygen, 0 to 60% by volume, preferably 4 to 50% by volume, of water vapor, and 20 to 80% by volume, preferably 30 to 75% by volume, of an inert gas such as carbon dioxide or nitrogen is filled in a reaction tube and then heated to 200 to 450°C under a pressure of normal pressure to 10 atmospheres at a space velocity of 300 to 5000 h . －１ The catalyst is introduced into the reaction system and the reaction is carried out. In the above-described method for producing an unsaturated carboxylic acid, a single catalyst may be used alone, or different catalysts may be packed in multiple layers depending on the conditions. Specifically, a method can be employed in which a catalyst layer is formed by dividing the catalyst into n portions in the direction of the raw gas flow in the reaction tube, and the multiple catalysts are arranged so that their activity increases from the raw gas inlet to the outlet in the direction of the raw gas flow. The number of portions n is not particularly limited, but is typically 2 to 5, preferably 2 to 3. The term "different catalysts" does not only refer to catalysts with different compositions, but also includes catalysts with different loading rates on an inert carrier and different dilution rates. Alternatively, a method can be employed in which a highly activated catalyst obtained by adjusting the half-width of the catalyst of the present invention is arranged at the raw gas outlet side, and a catalyst with a relatively lower activity is arranged at the raw gas inlet side.

[0036] The present invention will be explained in more detail below with reference to examples. In the examples, the raw material conversion, yield, and selectivity were calculated according to the following formulas: Raw material conversion (%) = (number of moles of acrolein reacted) / (number of moles of acrolein supplied) x 100 Yield (%) = (number of moles of acrylic acid produced) / (number of moles of acrolein supplied) x 100 Selectivity (%) = (number of moles of acrylic acid produced) / (number of moles of acrolein reacted) x 100

[0037] The following examples are given with specific examples, but the present invention is not limited to these examples as long as they do not deviate from the spirit thereof. The half-width of 2θ=22.2° shown in these examples was obtained by analyzing data obtained by measuring the X-ray diffraction angle (2θ) using an Ultima IV manufactured by Rigaku Corporation under the conditions of X-ray CuKα radiation (λ=0.154 nm), output of 40 kV, 30 mA, measurement range of 5 to 60°, and measurement rate of 3° per minute, using an OriginPro 2022b manufactured by LightStone. As described in the previous section, the analysis method was as follows: a straight line passing through the minimum value of 2θ = 16.0° to 18.0° and the minimum value of 2θ = 39.0° to 42.0° in the X-ray diffraction pattern was used as the baseline, a quadratic function was fitted to the peaks above the baseline, and the half-width of the fitted quadratic function having a peak in the range of 2θ = 22.2° ± 0.3° was read as the half-width of the peak at 2θ = 22.2° ± 0.3° in the X-ray diffraction pattern.

[0038] [Example 1] <Production of Catalyst 1> Mo １２ The composition for V ２．７ W ０．８ Cu １．５ Sb ０．５０ Ammonium molybdate, ammonium paratungstate, ammonium metavanadate, and antimony acetate were weighed and mixed in an aqueous solvent 5.2 times the mass of ammonium molybdate heated to 95 ° C., and then copper sulfate was added to obtain a preparation (A). This preparation (A) was dried by spray drying, and the resulting dried powder (B) was pre-fired at 350 ° C. for 4 hours to obtain a pre-fired body (C). The obtained pre-fired body (C) was pulverized in a ball mill to obtain a pre-fired powder (E). 5% by mass of crystalline cellulose and 5% by mass of glass fibers with an average fiber length of 150 μm were added to the pre-fired powder (E), and after thorough mixing, the mixture was subjected to a tumbling granulation method using a 20% by mass glycerin solution as a binder to an inert spherical carrier composed of a mixture of silica and alumina. The support rate was 33% by mass and the average particle size was 5 mm. A rolling granulator was used for molding, and the centrifugal acceleration was 26.0 G. Next, main calcination was carried out under conditions of 390° C. for 4 hours, to obtain spherical catalyst 1 of the present invention.

[0039] [Example 2] <Production of Catalyst 2> Mo １２ The composition for V ３．０ W １．２ Cu １．５ Sb ０．５０ Ammonium molybdate, ammonium paratungstate, ammonium metavanadate, and antimony acetate were weighed and mixed in an aqueous solvent at 5.2 times the mass of ammonium molybdate heated to 95 ° C., and then copper sulfate was added to obtain a prepared solution (A). This prepared solution (A) was dried by spray drying, and the resulting dried powder (B) was pre-fired at 350 ° C. for 4 hours to obtain a pre-fired body (C). The obtained pre-fired body (C) was pulverized in a ball mill to obtain a pre-fired powder (E). 5% by mass of crystalline cellulose and 5% by mass of glass fibers having an average fiber length of 150 μm were added to the pre-fired powder (E), and after thorough mixing, the mixture was subjected to a tumbling granulation method using a 20% by mass glycerin solution as a binder to form a spherical support on an inert spherical carrier composed of a mixture of silica and alumina, with a loading rate of 33% by mass and an average particle size of 5 mm. A rolling granulator was used for molding, and the centrifugal acceleration was 26.0 G. Next, main calcination was carried out under conditions of 390° C. for 4 hours, to obtain spherical catalyst 2 of the present invention.

[0040] [Example 3] <Production of catalyst 3> Mo １２ The composition for V ３．０ W １．２ Cu １．２ Sb ０．２５ Ammonium molybdate, ammonium paratungstate, ammonium metavanadate, metallic copper powder, and antimony acetate were weighed out so that the weight of the powder was 5.2 times that of the ammonium molybdate in a water solvent heated to 95°C, and then copper sulfate was added to obtain Preparation (A). The metallic copper powder used was copper (powder) (standard: Grade 1, particle size: 75 μm to 150 μm) manufactured by Kanto Chemical Co., Inc., and the amount used was Mo １２The amount was adjusted so that the molar ratio of Cu to SiO2 was 0.25, and copper sulfate was used in the amount corresponding to the remaining 0.95. This preparation (A) was dried by spray drying, and the resulting dry powder (B) was pre-calcined at 350 ° C for 4 hours to obtain a pre-calcined body (C). The resulting pre-calcined body (C) was pulverized in a ball mill to obtain a pre-calcined powder (E). 5% by mass of crystalline cellulose and 5% by mass of glass fibers with an average fiber length of 150 μm were added to the pre-calcined powder (E) and thoroughly mixed. After thorough mixing, the mixture was subjected to a rolling granulation method using a 20% by mass glycerin solution as a binder, and the mixture was shaped into spherical particles on an inert spherical carrier composed of a mixture of silica and alumina so that the loading rate was 33% by mass and the average particle size was 5 mm. A rolling granulator was used for molding, and the centrifugal acceleration was 26.0 G. Next, the main calcination was carried out at 390 ° C for 4 hours to obtain a spherical catalyst 3 of the present invention.

[0041] [Example 4] <Production of Catalyst 4> Mo １２ The composition for V ３．０ W １．２ Cu １．２ Sb ０．５０ Ammonium molybdate, ammonium paratungstate, ammonium metavanadate, and antimony acetate were weighed and mixed in an aqueous solvent 5.2 times the mass of ammonium molybdate heated to 95 ° C., and then copper sulfate was added to obtain a preparation (A). This preparation (A) was dried by spray drying, and the resulting dried powder (B) was pre-fired at 350 ° C. for 4 hours to obtain a pre-fired body (C). The obtained pre-fired body (C) was pulverized in a ball mill to obtain a pre-fired powder (E). 5% by mass of crystalline cellulose and 5% by mass of glass fibers with an average fiber length of 150 μm were added to the pre-fired powder (E), and after thorough mixing, the mixture was subjected to a tumbling granulation method using a 20% by mass glycerin solution as a binder to an inert spherical carrier composed of a mixture of silica and alumina. The support rate was 33% by mass and the average particle size was 5 mm. A rolling granulator was used for molding, and the centrifugal acceleration was 26.0 G. Next, main calcination was carried out under conditions of 390° C. for 4 hours, to obtain spherical catalyst 4 of the present invention.

[0042] [Comparative Example 1] <Production of Catalyst 5> Mo １２The composition for V ３．０ W １．２ Cu １．２ Ammonium molybdate, ammonium paratungstate, ammonium metavanadate, and copper metal powder were weighed and mixed in an aqueous solvent at 5.2 times the mass of the ammonium molybdate heated to 95 ° C., followed by the addition of copper sulfate to obtain a prepared solution (A). The copper metal powder was copper (powder) (specification: Grade 1, particle size: 75 μm to 150 μm) manufactured by Kanto Chemical Co., Ltd., and the amount used was such that the molar ratio of Cu to Mo12 was 0.50, with copper sulfate being used in the remaining 0.70 amount. This prepared solution (A) was dried by spray drying, and the resulting dried powder (B) was pre-fired at 350 ° C. for 4 hours to obtain a pre-fired body (C). The resulting pre-fired body (C) was pulverized in a ball mill to obtain a pre-fired powder (E). 5% by mass of crystalline cellulose and 5% by mass of glass fibers with an average fiber length of 150 μm were added to the pre-calcined powder (E), and after thorough mixing, the mixture was subjected to a tumbling granulation method using a 20% by mass glycerin solution as a binder, and the mixture was shaped into spherical particles on an inert spherical carrier consisting of a mixture of silica and alumina, with a loading rate of 33% by mass and an average particle size of 5 mm. A tumbling granulator was used for shaping, and the centrifugal acceleration was 26.0 G. Next, the catalyst was calcined at 390 ° C for 4 hours, to obtain a spherical catalyst 5 of the present invention.

[0043] [Comparative Example 2] <Production of Catalyst 6> Mo １２ The composition for V ３．０ W １．２ Cu １．２Ammonium molybdate, ammonium paratungstate, ammonium metavanadate, and metallic molybdenum powder were weighed out and mixed in an aqueous solvent at 5.2 times the mass of ammonium molybdate heated to 95 ° C., followed by the addition of copper sulfate to obtain a prepared solution (A). The metallic molybdenum powder used was molybdenum manufactured by SIGMA-ALDRICH (powder, 1-5 μm, ≧99.9% trace metals basis), and the amount used was such that the amount corresponding to 0.50 of Mo12 in molar ratio was metallic molybdenum, and the remaining amount corresponding to 11.5 was ammonium molybdate. This prepared solution (A) was dried by spray drying, and the resulting dried powder (B) was pre-calcined at 350 ° C. for 4 hours to obtain a pre-calcined body (C). The obtained pre-calcined body (C) was pulverized in a ball mill to obtain pre-calcined powder (E). 5% by mass of crystalline cellulose and 5% by mass of glass fibers with an average fiber length of 150 μm were added to the pre-calcined powder (E), and after thorough mixing, the mixture was subjected to a tumbling granulation method using a 20% by mass glycerin solution as a binder, and then shaped into spherical particles on an inert spherical carrier composed of a mixture of silica and alumina, with a loading rate of 33% by mass and an average particle size of 5 mm. A tumbling granulator was used for shaping, and the centrifugal acceleration was 26.0 G. Next, calcination was carried out at 390 ° C. for 4 hours to obtain spherical catalyst 6 of the present invention.

[0044] [Comparative Example 3] <Production of Catalyst 7> Mo １２ The composition for V ３．０ W １．２ Cu １．０ Sb １．０Ammonium molybdate, ammonium paratungstate, ammonium metavanadate, and antimony acetate were weighed and mixed in an aqueous solvent 5.2 times the mass of ammonium molybdate heated to 95 ° C., and then copper sulfate was added to obtain a preparation (A). This preparation (A) was dried by spray drying, and the resulting dried powder (B) was pre-fired at 350 ° C. for 4 hours to obtain a pre-fired body (C). The obtained pre-fired body (C) was pulverized in a ball mill to obtain a pre-fired powder (E). 5% by mass of crystalline cellulose and 5% by mass of glass fibers having an average fiber length of 150 μm were added to the pre-fired powder (E), and after thorough mixing, the mixture was subjected to a tumbling granulation method using a 20% by mass glycerin solution as a binder to an inert spherical carrier composed of a mixture of silica and alumina. The support was formed into a spherical shape so that the support rate was 33% by mass and the average particle size was 5 mm. A rolling granulator was used for molding, and the centrifugal acceleration was 26.0 G. Next, main calcination was carried out under conditions of 390° C. for 4 hours, to obtain spherical catalyst 7 of the present invention.

[0045] Oxidation reactions were carried out using the obtained catalysts 1 to 7. 67.6 ml of catalyst was packed into a reaction tube with an inner diameter of 28.4 mm, and a gas having the following composition, obtained by adding oxygen and nitrogen to a gas obtained by gas-phase catalytic oxidation of propylene using a molybdenum-bismuth catalyst, was introduced, and the reaction was carried out at an SV (space velocity; flow rate of raw material gas per unit time / apparent volume of packed catalyst) of 1020 / hr and a reaction bath temperature of 260°C. Acrolein 5.9 vol% Unreacted propylene + other organic compounds 1.7 vol% Oxygen 4.7 vol% Steam 17.2 vol% Nitrogen-containing inert gas 70.5 vol%

[0046] The reaction results obtained by the oxidation reaction are shown in Table 1, and the half-widths of the respective peaks in the X-ray diffraction patterns are shown in Tables 2 and 3. Table 3 is for reference only.

[0047] From the results in Tables 1 and 2, it was confirmed that the catalyst of the present invention has a high raw material conversion rate, that is, a high catalytic activity.

[0048] [Reference Example 3] The catalyst described in Example 1 of Patent Document 1 was prepared according to the description in the Example of Patent Document 1. That is, ammonium tungstate, ammonium metavanadate, ammonium molybdate, antimony trioxide powder, and copper sulfate were used as raw materials to produce Mo. １２ The composition for V ３ W １．２ Cu １．２ Sb ０．５ A catalyst having a catalytically active component of the formula (I) was obtained. The half-width of the obtained catalyst was measured by the method described in the present invention, and the half-width at 22.2°±0.3° in the X-ray diffraction pattern was 0.52. Furthermore, an oxidation reaction was carried out by the method described in the present invention, and the results were a reaction temperature of 260°C, a raw material conversion of 19.6%, a selectivity of 96.3%, and a yield of 18.9%.

[0049] This application is based on Japanese Patent Application No. 2023-150163, filed on September 15, 2023, the contents of which are incorporated herein by reference.

[0050] According to the present invention, high catalytic activity can be maintained when an unsaturated aldehyde is used as a raw material to produce an unsaturated carboxylic acid by a gas-phase catalytic oxidation reaction, which is extremely useful because it prevents thermal degradation of the catalyst for acrylic acid production and enables the plant to operate stably for a long period of time.

Claims

1. A catalyst for producing an unsaturated carboxylic acid, the catalyst having a catalytically active component having a composition represented by the following formula (1), and an X-ray diffraction pattern obtained using CuKα radiation as an X-ray source has a half-width of a peak at 22.2°±0.3° of 0.65° to 1.60°. (Mo) １２ (V) ａ (W) ｂ (Cu) ｃ (Sb) ｄ (X) ｅ (Y) ｆ (Z) ｇ (O) ｈ (1) (In formula (1), Mo, V, W, Cu, Sb, and O represent molybdenum, vanadium, tungsten, copper, antimony, and oxygen, respectively; X represents at least one element selected from the group consisting of alkali metals and thallium; Y represents at least one element selected from the group consisting of magnesium, calcium, strontium, barium, and zinc; Z represents niobium, cerium, tin, chromium, manganese, iron, cobalt, sulfur, and the like. Each of the elements represents at least one element selected from the group consisting of marium, germanium, titanium, and arsenic. In addition, a, b, c, d, e, f, g, and h represent the atomic ratio of each element, and are 0<a≦10.0, 0≦b≦10.0, 0<c≦6.0, 0≦d≦10.0, 0≦e≦0.50, 0≦f≦1.0, and 0≦g<6.0 relative to 12 molybdenum atoms. In addition, h represents the number of oxygen atoms required to satisfy the valence of each of the components.

2. The catalyst for producing an unsaturated carboxylic acid according to claim 1, wherein in said formula (1), 1.0≦a≦5.0, 0.50≦b≦3.0, 0.50≦c≦3.0 and 0<d≦2.

0.

3. The catalyst for producing an unsaturated carboxylic acid according to claim 1 or 2, which is a catalyst in which a catalytically active component is supported on an inert carrier.

4. The catalyst for producing an unsaturated carboxylic acid according to claim 3, wherein the inert support is silica, alumina or a combination thereof.

5. A method for producing an unsaturated carboxylic acid using the catalyst for producing an unsaturated carboxylic acid according to claim 1 or 2.

6. A method for producing an unsaturated carboxylic acid using a reaction tube packed with two or more types of the catalyst for producing an unsaturated carboxylic acid according to claim 1 or 2 in multiple layers.

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