JP3720625B2 - Method for preparing molybdenum-bismuth-iron-containing composite oxide catalyst - Google Patents

Description

【００３９】
【発明の効果】
本発明の方法により調製されるモリブデン−ビスマス−鉄含有複合酸化物触媒は高活性であり、且つ目的化合物の選択性及び収率が高く、例えばプロピレンのアンモ酸化反応により収率良くアクリロニトリルを得ることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a molybdenum-containing composite oxide catalyst used for an oxidation reaction of an organic compound, and more specifically, selected from the group consisting of nickel, cobalt, magnesium, chromium, manganese and zinc used for a gas phase catalytic oxidation reaction of an organic compound. The present invention also relates to a method for producing a molybdenum-bismuth-iron-containing composite oxide catalyst containing at least one element.
[0002]
[Prior art]
Many molybdenum-bismuth-containing composite oxide catalysts are known as catalysts for oxidation reactions of organic compounds. For example, Japanese Patent Publication No. 36-3563, Japanese Patent Publication No. 36-5870, Japanese Patent Publication No. 38-17967, Japanese Patent Publication No. 39-3670, Japanese Patent Publication No. 39-10111, Japanese Patent Publication No. 42-7774, JP-A-50-64191 and the like are disclosed. Thereafter, these catalysts were improved by adding various additives such as JP-B-47-27490, JP-B-54-22895, and JP-B-60-36812, so that the desired oxidation product was collected. The rate has improved.
[0003]
On the other hand, efforts have been made to improve the yield of the target oxidation product by improving the preparation method. For example, Japanese Patent Publication No. 43-22746 discloses a method of adding a bismuth citrate aqueous solution to an aqueous molybdic acid solution, Japanese Patent Publication No. 53-10387, Japanese Patent Publication No. 53-10388, and Japanese Patent Publication No. 55-12298. Is a method of adding a bismuth compound in a solid state to a molybdic acid aqueous solution, Japanese Patent Publication No. 59-51848 discloses a method of simultaneously adding an aqueous solution of bismuth salt and aqueous ammonia to a molybdic acid aqueous solution having a pH of 6-8, JP-B-59-51849 discloses a method of adding an aqueous solution of a bismuth salt to a suspension of a molybdenum compound, JP-A-55-13187, JP-A-55-47144, and JP-B-60-29536. The gazette includes a method for forming various molybdates in advance, Japanese Patent Publication No. 52-22359, and Japanese Patent Publication No. 52-47435. Are methods for forming various bismuth compounds in advance, Japanese Patent Laid-Open No. 62-23548 uses bismuth oxide or bismuth carbonate as a bismuth source, and Japanese Patent Laid-Open No. 2-59046 discloses iron, bismuth and tellurium. A method of adjusting a slurry containing at least one of the above and a molybdenum compound to a range exceeding pH 7, JP-A-2-214543 discloses a method of adjusting a pH to 6 or more by adding a chelating agent to a molybdenum compound-containing slurry containing silica, JP-A-2-251250 discloses a method of mixing a bismuth compound after setting the slurry containing molybdenum to pH 6 or higher.
[0004]
In order to improve the performance of the catalyst in this way, various methods have been proposed, such as devising a method of mixing an aqueous molybdenum solution and a bismuth compound, or specially selecting a bismuth raw material. However, when these methods are applied to the production of a molybdenum-bismuth-containing composite oxide catalyst containing at least one metal element selected from the group consisting of divalent metal elements and trivalent metal elements, the target oxidation is achieved. The product yield was not always satisfactory.
[0005]
[Problems to be solved by the invention]
The present invention provides a method for preparing a catalyst having high activity and yielding a desired oxidation product in a high yield in a molybdenum-bismuth-iron-containing composite oxide catalyst useful for various oxidation reactions.
[0006]
[Means for solving problems]
As a result of intensive studies to solve the above problems, the present inventors have identified a molybdenum compound and a specific metal compound when producing a molybdenum-bismuth-iron-containing composite oxide catalyst used for an oxidation reaction of an organic compound. The present invention was reached by finding that a catalyst having high activity and a high yield of the desired oxidation product can be obtained by mixing under conditions and then preparing a catalyst by mixing an iron compound.
[0007]
That is, the present invention comprises (1) molybdenum, (2) bismuth, (3) at least one element selected from the group consisting of nickel, cobalt, magnesium, chromium, manganese, and zinc, and (4) iron as a catalyst component. In the method for producing a composite oxide catalyst containing as an essential component, at least part of the raw material of the component (1), at least part of the raw material of the component (2) and at least part of the raw material of the component (3) Containing molybdenum-bismuth-iron, which comprises mixing an aqueous slurry having a pH of 6 or more and a solution or slurry containing the raw material of component (4), and then drying and firing the mixture. The present invention relates to a method for preparing a composite oxide catalyst.
[0008]
An aqueous slurry containing at least a part of the raw material of the component (1), at least a part of the raw material of the component (2) and at least a part of the raw material of the component (3) and having a pH of 6 or more. Is heated at a temperature in the range of 50 to 120 ° C. for at least 10 minutes, and then mixed with a solution containing the raw material of the component (4) or a slurry thereof, and then the mixture is dried and calcined to obtain a higher activity. , Selectivity is obtained.
[0009]
In the method of the present invention, the mechanism of high activity and high selectivity is not clear, but an aqueous slurry containing at least part of the raw material of component (1) and at least part of the raw material of component (3) By adjusting the pH to 6 or more, a compound comprising the component (1) and the component (3) is preferentially produced, and then a preferable catalyst structure is formed by adding a solution containing an iron raw material or a slurry thereof. It is thought to be done. An aqueous slurry containing at least a part of the raw material of component (1) and at least a part of the raw material of component (3) and having a pH of 6 or more is at least 10 minutes at a temperature in the range of 50 ° C to 120 ° C. After the above heat treatment, the activity and selectivity are further improved by mixing the solution containing the raw material of the component (4) or the slurry thereof. This is considered to be because the formation of such a preferable structure is further promoted. .
[0010]
The catalyst to which the present invention is applied has the general formula MoaBibFecQdReXfYgOh
(Wherein Mo, Bi, Fe and O represent molybdenum, bismuth, iron and oxygen, respectively, Q is at least one element selected from the group consisting of nickel, cobalt, magnesium, chromium, manganese and zinc, and R is At least one element selected from the group consisting of beryllium, phosphorus, boron, arsenic, selenium, lithium, sodium, potassium, rubidium, cesium, thallium and tellurium, X is vanadium, tungsten, yttrium, lanthanum, zirconium, hafnium, niobium At least one element selected from the group consisting of tantalum, aluminum, calcium, strontium, barium, lead, copper, cadmium, gallium, indium, germanium, tin, antimony and cerium, Y is praseodymium, neodymium, samarium, yttrium It represents at least one element selected from the group consisting of lopium, gadolinium, thorium, uranium, rhenium, ruthenium, rhodium, palladium, osmium, iridium, platinum, silver and gold, where the subscripts a, b, c, d, e, f, and g represent the atomic ratio of each element. When a = 10, 0.1 ≦ b ≦ 5, 0.1 ≦ c ≦ 10, 0.1 ≦ d ≦ 8, 0 ≦ e ≦ 3, 0 ≦ f ≦ 8, 0 ≦ g ≦ 1, and h is the number of oxygen atoms necessary to satisfy the valence of each component.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The starting material of each element constituting the catalyst of the present invention is not particularly limited. For example, the molybdenum component material is molybdenum oxide such as molybdenum trioxide, molybdic acid, ammonium paramolybdate, and metamolybdenum. Molybdic acid such as ammonium acid or a salt thereof, heteropoly acid containing molybdenum such as phosphomolybdic acid or silicomolybdic acid, or a salt thereof can be used.
[0012]
As raw materials for the bismuth component, bismuth salts such as bismuth nitrate, bismuth carbonate, bismuth sulfate, bismuth acetate, bismuth trioxide, metal bismuth, and the like can be used. These raw materials can be used in the form of a solid or as a slurry of an aqueous solution, a nitric acid solution, or a bismuth compound generated from the aqueous solution, but it is preferable to use nitrate, a solution thereof, or a slurry generated from the solution.
[0013]
Ferrous oxide, ferric oxide, ferric tetroxide, ferrous nitrate, ferric nitrate, iron sulfate, iron chloride, iron organic acid salt, iron hydroxide, etc. are used as raw materials for iron components In addition, metallic iron may be dissolved in heated nitric acid. The solution containing the iron component may be used after adjusting the pH with aqueous ammonia or the like. When adjusting the pH, the presence of a chelating agent in the solution containing the iron component can prevent the iron component from precipitating, and a highly active catalyst can be obtained. Examples of chelating agents that can be used here include ethylenediaminetetraacetic acid, lactic acid, citric acid, tartaric acid, and gluconic acid.
[0014]
The addition amount of the chelating agent is preferably in the range of 0.1 to 10%, more preferably in the range of 0.5 to 8% by weight, based on the weight of the oxide catalyst to be produced. If the addition amount of the chelating agent is less than 0.1% by weight with respect to the weight of the oxide catalyst, the effect is not sufficiently exhibited, and if it exceeds 10% by weight, many cracks may be formed in the completed catalyst. When preparing a solution containing iron ions and a chelating agent, the chelating agent is preferably 0.1 to 2 gram molecules per gram of iron.
[0015]
As raw materials for other elements, usually oxides, nitrates, carbonates, organic acid salts, hydroxides, and the like, which can be converted into oxides when ignited, or mixtures thereof are used.
[0016]
In the method of the present invention, the heat treatment of the aqueous slurry during preparation is not necessarily required, but at least one selected from the group consisting of at least a part of the raw material of molybdenum and nickel, cobalt, magnesium, chromium, manganese and zinc. Properties of the slurry are obtained by heat-treating an aqueous slurry containing at least part of the elemental raw material and having a pH of 6 or more at a temperature of 50 to 120 ° C., preferably 60 to 110 ° C. for at least 10 minutes. Is more stable, and is desirable for improving performance such as activity and physical properties of the finally obtained catalyst.
[0017]
The mixed solution or aqueous slurry containing the predetermined catalyst component is dried, but there is no particular limitation on the method and the state of the obtained dried product. For example, the powder is obtained by using a normal spray dryer, slurry dryer, drum dryer or the like. A dried product in the form of a block may be obtained, or a dried product in the form of a block or flakes may be obtained using a normal box-type dryer, a tunnel-type firing furnace or the like. The drying temperature is preferably in the range of 80 to 350 ° C.
[0018]
There are no particular restrictions on the type and method of the firing furnace when firing the resulting dried product, for example, firing in a state where the dried product is left standing using a normal box-type firing tunnel, tunnel-type firing furnace, or the like. Alternatively, it may be fired while flowing the dried product using a rotary kiln firing furnace or the like. The firing temperature is in the range of 400 to 800 ° C, preferably 500 to 750 ° C. When calcination is performed at a temperature outside this range, a high-performance catalyst may not be obtained. Further, there is no particular limitation on the time for which the heat treatment is continued after reaching a predetermined temperature, but if the heat treatment time is too short, a high-performance catalyst may not be obtained. Is preferred.
[0019]
The catalyst exhibits excellent activity without a support, but may be used by being supported on a suitable support. As the carrier used, silica, alumina, zirconia, silica-alumina, silicon carbide, alundum, inorganic silicate, and the like can be used. It is particularly preferable to use silica as a support for the catalyst in the present invention. The amount of the carrier used is preferably in the range of 10 to 90% of the catalyst weight.
[0020]
The catalyst of the present invention can be used in either a fixed bed or a fluidized bed, and the shape and size of the catalyst particles are not particularly limited, and are in the form of pellets, tablets, spheres, granules, powders depending on the use situation. It can be molded into any shape and size such as a shape.
[0021]
The catalyst of the present invention is used for an oxidation reaction, oxidative dehydrogenation reaction and ammoxidation reaction of an organic compound. Examples of the organic compound subjected to the oxidation reaction using the catalyst of the present invention include propylene, isobutene, methanol, ethanol, tertiary butanol, and methyl tertiary butyl ether, and the corresponding aldehyde, nitrile, conjugated diene, and the like. Obtained in high yield. In particular, favorable results can be obtained by applying to the oxidation reaction of propylene, isobutene and tertiary butanol.
[0022]
【Example】
Hereinafter, the effects of the present invention will be described more specifically by way of examples.
[0023]
The activity test of the activity test catalyst was carried out as follows using a propylene ammoxidation reaction as a representative example.
The catalyst was packed in a fluidized bed reactor having an inner diameter of 25 mmφ and a height of 40 cm so as to have a predetermined contact time, and kept at a reaction temperature of 430 ° C. In this reactor, a mixed gas of propylene, ammonia, air and water vapor having a molar ratio of propylene: ammonia: oxygen: water of 1: 1.2: 2.1: 0.5 was 6.5 l per hour (NTP Conversion). The reaction pressure was 200 kPa. The yield of the ammoxidation product (acrylonitrile) and the conversion rate of the starting organic compound (propylene) in the examples are defined by the following formula.
Acrylonitrile yield (%) = (carbon weight of produced acrylonitrile) / (carbon weight of supplied propylene) × 100
Propylene conversion (%) = (carbon weight of propylene consumed) / (carbon weight of propylene supplied) × 100
[0024]
Example 1
Since the composition is Mo ₁₀ Bi ₁ Fe ₂ Ni _6.5 K _0.4 P _0.2 O _x — (SiO 2) ₆₀ (x is a value naturally determined by the valence of other elements, In the comparative example, the description of oxygen in the catalyst composition is omitted.) A catalyst represented by the following method was prepared by the following method. A solution prepared by dissolving 3.9 g of potassium nitrate in 20 g of pure water was added to 1745.3 g of 20% silica sol. Under stirring, a solution prepared by dissolving 171.0 g of ammonium paramolybdate in 510 g of pure water was added to this solution. Subsequently, a solution in which 183.0 g of nickel nitrate was dissolved in 190 g of pure water, a solution in which 47.0 g of bismuth nitrate was dissolved in 48 g of 10% nitric acid, and 2.2 g of 85% phosphoric acid aqueous solution were sequentially added. 15% aqueous ammonia was added to this slurry to adjust the pH to 8.0, and then a solution in which 20 g of citric acid and 78.2 g of ferric nitrate were dissolved in 100 g of pure water was added.
The obtained slurry was spray dried by controlling the inlet temperature at 320 ° C. and the outlet temperature at 160 ° C. with a rotary disk type spray dryer. The obtained spherical particles were heated at 250 ° C., followed by calcination at 400 ° C. for 2.5 hours and further at 620 ° C. for 3 hours.
[0025]
Example 2
A catalyst having a composition represented by Mo ₁₀ Bi ₁ Fe _0.5 Ni _6.5 Cr ₁ K _0.4 — (SiO 2) ₆₀ was prepared by the following method.
A solution prepared by dissolving 5.5 g of potassium nitrate in 30 g of pure water was added to 2429.3 g of 20% silica sol. Under stirring, a solution prepared by dissolving 238.0 g of ammonium paramolybdate in 650 g of pure water was added to this solution. Subsequently, a solution in which 254.8 g of nickel nitrate and 20.5 g of chromium nitrate were dissolved in 300 g of pure water and a solution in which 65.4 g of bismuth nitrate were dissolved in 66 g of 10% nitric acid were sequentially added. The slurry was adjusted to pH 9.5 by adding 15% aqueous ammonia, and then the slurry was heated at 100 ° C. for 2 hours under reflux, and then 7 g of citric acid and 27.2 g of ferric nitrate were dissolved in 40 g of pure water. The solution was added.
The obtained slurry was spray dried by controlling the inlet temperature at 320 ° C. and the outlet temperature at 160 ° C. with a rotary disk type spray dryer. The obtained spherical particles were heated at 250 ° C., followed by calcination at 400 ° C. for 2.5 hours and further at 600 ° C. for 3 hours.
[0026]
Example 3
The catalyst represented by Mo ₁₀ Bi ₂ Fe ₂ Co _6.5 K _0.2 Te _0.2 — (SiO 2) ₆₀ is used as the tellurium source, followed by ammonium paramolybdate using cobalt nitrate as the cobalt source. It was prepared in the same manner as in Example 2 except that it was added next to potassium nitrate using telluric acid and the final calcination temperature was 550 ° C.
[0027]
Example 4
A catalyst having a composition represented by Mo ₁₀ Bi ₁ Fe ₂ Ni ₅ Mg _1.5 K _0.2 Te _0.2 — (SiO 2) ₆₀ was prepared by the following method.
A solution prepared by dissolving 2.7 g of potassium nitrate in 30 g of pure water was added to 2438.9 g of 20% silica sol. Under stirring, a solution prepared by dissolving 238.9 g of ammonium paramolybdate in 650 g of pure water was added to this solution. Subsequently, a solution in which 196.7 g of nickel nitrate and 52.0 g of magnesium nitrate are dissolved in 300 g of pure water, a solution in which 65.6 g of bismuth nitrate is dissolved in 66 g of 10% nitric acid, and a solution in which 6.2 g of telluric acid are dissolved in 20 g of pure water. Were added sequentially. The slurry was adjusted to pH 8.0 by adding 15% aqueous ammonia, and the slurry was then heated at 100 ° C. for 2 hours under reflux.
Separately, 20 g of citric acid and 109.3 g of ferric nitrate were dissolved in 150 g of pure water, and 15% aqueous ammonia was added to adjust the pH to 7.0. Under stirring, this solution was mixed with the previously heat-treated slurry.
The obtained slurry was spray dried by controlling the inlet temperature at 320 ° C. and the outlet temperature at 160 ° C. with a rotary disk type spray dryer. The obtained spherical particles were heated at 250 ° C., and then calcined at 400 ° C. for 2.5 hours and further at 575 ° C. for 3 hours.
[0028]
Example 5
The catalyst represented by Mo ₁₀ Bi ₂ Fe ₂ Ni ₅ Zn _1.5 K _0.2 Ce _0.2 — (SiO 2) ₆₀ is composed of nickel nitrate using zinc nitrate as the zinc raw material and cerium nitrate as the cerium raw material. Next, it added in order, it prepared by the method similar to Example 2 except having set pH to 8.5 and having made the final calcination temperature 575 degreeC.
[0029]
Example 6
A catalyst having a composition represented by Mo ₁₀ Bi _1.5 Fe _1.5 Ni ₆ Mn ₁ K _0.5 P _0.2 — (SiO 2) ₆₀ is added next to nickel nitrate using manganese nitrate as a manganese raw material, It was prepared in the same manner as in Example 2 except that the pH was 8.5.
[0030]
Example 7
A catalyst whose composition is Mo ₁₀ Bi ₁ Fe ₁ Ni _6.5 K ₁ B _0.5 Sm _0.2 — (SiO 2) ₉₀ , boric acid as a boron raw material, paramolybdic acid next to samarium raw material Was prepared in the same manner as in Example 2 except that samarium nitrate was used and then added to bismuth nitrate, and the final firing temperature was 620 ° C.
[0031]
Example 8
A catalyst having a composition represented by Mo ₁₀ Bi ₁ Fe ₁ Ni _6.5 K _0.2 Te _0.2 W _0.5 — (SiO 2) ₄₀ is used, and ammonium paramolybdate is formed using ammonium paratungstate as a tungsten raw material. Next, telluric acid was used as a tellurium raw material, added next to potassium nitrate, and prepared in the same manner as in Example 2 except that the pH was adjusted to 8.5.
[0032]
Example 9
A catalyst whose composition is Mo ₁₀ Bi ₁ Fe ₁ Ni _6.5 K _0.1 Cs _0.05 V _0.5 — (SiO 2) ₄₀ is used as a cesium raw material, cesium nitrate is used as a cesium raw material, and then potassium nitrate is used as a vanadium raw material. A solution prepared by dissolving ammonium metavanadate in aqueous hydrogen peroxide was added next to ammonium paramolybdate and the pH was adjusted to 8.5.
[0033]
Example 10
A catalyst having a composition represented by Mo ₁₀ Bi ₁ Fe ₁ Ni _6.5 K _0.4 Sn _0.5 Sb _1- (SiO 2) ₆₀ , stannic oxide as a tin raw material, and antimony trioxide as an antimony raw material It was prepared in the same manner as in Example 1 except that ammonium paramolybdate was added in succession and pH was adjusted to 9.5.
[0034]
Comparative Example 1
A catalyst having the same composition as in Example 1 was prepared in the same manner as in Example 1 except that ferric nitrate was added next to nickel nitrate.
[0035]
Comparative Example 2
A catalyst having the same composition as in Example 2 was prepared in the same manner as in Example 2, except that ferric nitrate was added next to nickel nitrate.
[0036]
Comparative Example 3
A catalyst having the same composition as in Example 3 was prepared in the same manner as in Example 3 except that the ferric nitrate solution was added next to the cobalt nitrate solution.
[0037]
Comparative Example 4
A catalyst having the same composition as in Example 4 was prepared by the following method.
A solution prepared by dissolving 2.7 g of potassium nitrate in 30 g of pure water was added to 2438.9 g of 20% silica sol. Under stirring, a solution prepared by dissolving 238.9 g of ammonium paramolybdate in 650 g of pure water was added to this solution. Subsequently, a solution prepared by dissolving 65.6 g of bismuth nitrate in 66 g of 10% nitric acid and a solution prepared by dissolving 6.2 g of telluric acid in 20 g of pure water were sequentially added. The slurry was adjusted to pH 8.0 by adding 15% aqueous ammonia, and the slurry was then heated at 100 ° C. for 2 hours under reflux.
Separately, 20 g of citric acid, 109.3 g of ferric nitrate, 196.7 g of nickel nitrate and 52.0 g of magnesium nitrate were dissolved in 450 g of pure water, and adjusted to pH 7.0 by adding 15% aqueous ammonia. Under stirring, this solution was mixed with the previously heat-treated slurry.
The obtained slurry was spray dried by controlling the inlet temperature at 320 ° C. and the outlet temperature at 160 ° C. with a rotary disk type spray dryer. The obtained spherical particles were heated at 250 ° C., and then calcined at 400 ° C. for 2.5 hours and further at 600 ° C. for 3 hours.
[0038]
The results of the activity tests of the catalysts obtained in the examples and comparative examples are shown in Table 1.
[Table 1]

[0039]
【The invention's effect】
The molybdenum-bismuth-iron-containing composite oxide catalyst prepared by the method of the present invention is highly active and has high selectivity and yield of the target compound. For example, acrylonitrile can be obtained with good yield by ammoxidation of propylene. Can do.

Claims (3)

(1) molybdenum, (2) bismuth, (3) at least one element selected from the group consisting of nickel, cobalt, magnesium, chromium, manganese, and zinc, and (4) complex oxidation containing iron as an essential component. In the method for producing a product catalyst, the component (1) includes at least part of the raw material, at least part of the raw material of the component (2) and at least part of the raw material of the component (3), and has a pH of Preparation of a molybdenum-bismuth-iron-containing composite oxide catalyst, comprising mixing an aqueous slurry of 6 or more with a solution or slurry containing the raw material of component (4), and then drying and calcining the mixture. Law. (1) molybdenum, (2) bismuth, (3) at least one element selected from the group consisting of nickel, cobalt, magnesium, chromium, manganese, and zinc, and (4) complex oxidation containing iron as an essential component. In the method for producing a product catalyst, the component (1) includes at least part of the raw material, at least part of the raw material of the component (2) and at least part of the raw material of the component (3), and has a pH of The aqueous slurry of 6 or more is heat-treated at a temperature of 50 to 120 ° C. for at least 10 minutes, and then mixed with the solution containing the raw material of the component (4) or the slurry thereof, and then the mixture is dried and fired. The method for preparing a molybdenum-bismuth-iron-containing composite oxide catalyst according to claim 1. The composite oxide catalyst has the general formula MoaBibFecQdReXfYgOh
(Wherein Mo, Bi, Fe and O represent molybdenum, bismuth, iron and oxygen, respectively, Q is at least one element selected from the group consisting of nickel, cobalt, magnesium, chromium, manganese and zinc, and R is At least one element selected from the group consisting of beryllium, phosphorus, boron, arsenic, selenium, lithium, sodium, potassium, rubidium, cesium, thallium and tellurium, X is vanadium, tungsten, yttrium, lanthanum, zirconium, hafnium, niobium At least one element selected from the group consisting of tantalum, aluminum, calcium, strontium, barium, lead, copper, cadmium, gallium, indium, germanium, tin, antimony and cerium, Y is praseodymium, neodymium, samarium, yttrium It represents at least one element selected from the group consisting of lopium, gadolinium, thorium, uranium, rhenium, ruthenium, rhodium, palladium, osmium, iridium, platinum, silver and gold, where the subscripts a, b, c, d, e, f, and g represent the atomic ratio of each element. When a = 10, 0.1 ≦ b ≦ 5, 0.1 ≦ c ≦ 10, 0.1 ≦ d ≦ 8, 0 ≦ e ≦ 3, 0 ≦ f ≦ 8, 0 ≦ g ≦ 1, and h is the number of oxygen atoms necessary to satisfy the valence of each component. A process for preparing the molybdenum-bismuth-iron-containing composite oxide catalyst according to claim 1 or 2.