Composite catalyst for preparing acrolein through catalytic oxidation of propylene and preparation method of composite catalyst

Abstract

The invention relates to the technical field of catalysts, and particularly discloses a composite catalyst for preparing acrolein through catalytic oxidation of propylene and a preparation method of the composite catalyst, the composite catalyst comprises an active component I and an active component II, and the use mass ratio of the active component I to the active component II is 1: (1-19); the active component I is bismuth tungstate microspheres obtained by a hydrothermal synthesis method, and the general formula of the active component I is BiaW1Ox; the active component II is a multi-metal oxide obtained by a coprecipitation method, and the general formula of the active component II is Mo < 12 > Bi Co < c > Ni < d > Fe < e > A < f > B < g > O < y >; the bismuth tungstate microspheres obtained by a hydrothermal synthesis method and the multi-metal oxide obtained by a coprecipitation method are mixed to obtain the composite catalyst, so that the bismuth tungstate microspheres with microsphere structures can be used as active phases of reaction, and the specific surface area and the pore volume of the composite catalyst can be increased; the catalyst is suitable for a reaction for preparing acrolein through propylene catalytic oxidation under high load.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts, and particularly relates to a composite catalyst for catalytic oxidation of propylene to produce acrolein and a preparation method thereof. Background Art

[0002] The two-step oxidation of propylene to produce acrylic acid via acrolein is a widely used industrial method for producing acrylic acid. Acrylic acid can be used to produce products such as superabsorbent resins, water-based coatings, and pressure-sensitive adhesives, enjoying a wide range of applications. The catalyst used in the one-step oxidation of propylene to produce acrolein is a Mo-Bi metal oxide catalyst, with the Mo=O site serving as the active center of the reaction. Adding Fe, Co, or Ni to the catalyst can inhibit Mo loss and enhance activity. Adding elements such as W, Cu, and Sb can further enhance catalytic activity. Alkaline additives such as Na, K, Mg, and Ca can suppress non-selective reactions.

[0003] Mo-Bi-based catalysts are widely used industrially for the oxidation of propylene to acrolein due to their high activity, selectivity, and stability. However, catalysts obtained through the coprecipitation method have limited pore structure and specific surface area, resulting in generally low propylene space velocity and low metal element utilization. During the catalyst production process, substances such as urea and carbonates are often added as pore-forming agents. This pore-forming method can easily lead to uneven pore distribution. Residual pore-forming agents can also clog the pores and even contaminate the catalyst. Therefore, it is necessary to propose a composite catalyst for the catalytic oxidation of propylene to acrolein and its preparation method to address these existing problems. Bi2WO6 microspheres can be obtained through a hydrothermal synthesis method and then mixed with Mo-Bi-based metal oxides obtained through the coprecipitation method to obtain a composite catalyst. The microsphere-structured Bi2WO6 not only serves as the active phase in the reaction, but also increases the specific surface area and pore volume of the composite catalyst. Summary of the Invention

[0004] The object of the present invention is to provide a composite catalyst for catalytic oxidation of propylene to produce acrolein and a preparation method thereof. Bi2WO6 microspheres can be obtained by hydrothermal synthesis, and the composite catalyst can be obtained by mixing the microspheres with Mo-Bi metal oxides obtained by coprecipitation. The microspherical Bi2WO6 can serve as the active phase of the reaction and can also increase the specific surface area and pore volume of the composite catalyst, thereby solving the problems raised in the above-mentioned background technology.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A composite catalyst for catalytic oxidation of propylene to produce acrolein, comprising an active component 1 and an active component 2, wherein the mass ratio of the active component 1 to the active component 2 is 1:1-19;

[0007] The active component 1 is bismuth tungstate microspheres obtained by hydrothermal synthesis, with the general formula of Bi a W1O x ;

[0008] The second active component is a multi-metal oxide obtained by co-precipitation method, with the general formula Mo 12 Bi b Co c Ni d Fe e A f B g O y ;

[0009] Wherein, Bi is bismuth, W is tungsten, Mo is molybdenum, Co is cobalt, Ni is nickel, Fe is iron, and O is oxygen; A is at least one element selected from lithium, sodium, potassium, rubidium, and cesium; B is one element selected from beryllium, magnesium, calcium, strontium, and barium;

[0010] a, b, c, d, e, f, and g are the atomic ratios of each element, where a=0.5-2; b=0.8-1.3; c=4-6; d=2-3; e=0.8-2; and f=0.05-0.3.

[0011] Preferably, the process for preparing the active component 1 comprises the following steps:

[0012] A1. Dissolve a tungsten source in deionized water to obtain solution A. Add a bismuth source to deionized water to obtain suspension B. Add solution A dropwise to suspension B under heating conditions and stir at constant temperature for 1 hour.

[0013] A2. Transfer the stirred suspension to a polytetrafluoroethylene-lined stainless steel reactor for hydrothermal synthesis;

[0014] A3. The solid obtained by hydrothermal synthesis is washed with deionized water, centrifuged, dried, and then heat-treated under a nitrogen atmosphere to obtain active component 1.

[0015] Preferably, in step A1, the tungsten source is sodium tungstate or ammonium tungstate, the bismuth source is bismuth nitrate or bismuth subnitrate, and the heating temperature is 60-98°C.

[0016] Preferably, in step A2, the hydrothermal synthesis temperature is 140-200° C., and the hydrothermal synthesis time is 20-28 h.

[0017] Preferably, in step A3, the heat treatment temperature is 600-800°C, the heat treatment time is 1-4 h, the centrifugal separation condition is centrifugation at a speed of 8000 r / min for 3 min, and the drying condition is drying at 80°C for 12 h.

[0018] Preferably, the process for preparing the active component 2 is as follows:

[0019] B1. Under heating conditions, the Mo source, A source, and B source were dissolved in deionized water to obtain solution C, the Co source, Ni source, and Fe source were dissolved in deionized water to obtain solution D, and the Bi source was dissolved in nitric acid to obtain solution E;

[0020] B2. Add solution D and solution E to solution C in sequence to form a slurry;

[0021] B3. Dry the slurry and then grind it to obtain active component 2.

[0022] Preferably, in step B1, the Mo source is ammonium heptamolybdate, the Bi source, Co source, Ni source, and Fe source are nitrates, the A source is nitrate or chloride, and the B source is nitrate or hydroxide.

[0023] Preferably, the total mass ratio of the Mo source, A source, B source, Co source, Ni source, Fe source, and Bi source to the total mass ratio of deionized water is 1:1.5-6.

[0024] Preferably, in step B3, the drying temperature is 110-180° C., and the drying time is 20-30 h.

[0025] Based on the composite catalyst for catalytic oxidation of propylene to produce acrolein described above, the present invention also provides a method for preparing the composite catalyst for catalytic oxidation of propylene to produce acrolein, comprising the following steps:

[0026] S1. Mixing active component 1 and active component 2 in a mass ratio of 1:1-19 to form a mixture;

[0027] S2. calcining the mixture to obtain a finished catalyst product. The calcination temperature is 450-600° C. and the calcination time is 5 h-8 h.

[0028] The composite catalyst for catalytic oxidation of propylene to produce acrolein and its preparation method proposed in the present invention have the following advantages over the prior art:

[0029] 1. The composite catalyst obtained by mixing bismuth tungstate microspheres obtained by hydrothermal synthesis and multi-metal oxides obtained by coprecipitation can make the bismuth tungstate microspheres with microspherical structure serve as the active phase of the reaction and increase the specific surface area and pore volume of the composite catalyst, which is suitable for the catalytic oxidation of propylene to produce acrolein under high load. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a flow chart of the preparation process of the composite catalyst of the present invention;

[0031] Figure 2 This is a flowchart of the preparation process of the active component 1 of the present invention;

[0032] Figure 3 This is a flowchart of the preparation process of the active component 2 of the present invention;

[0033] Figure 4 This is an SEM image of the Bi2WO6 microspheres prepared in the comparative example of the present invention. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0035] The present invention provides Figure 1-3 The composite catalyst for catalytic oxidation of propylene to acrolein comprises an active component 1 and an active component 2, wherein the mass ratio of the active component 1 to the active component 2 is 1:1-19; the active component 1 is bismuth tungstate microspheres obtained by hydrothermal synthesis, and the general formula is Bi a W1O x The active component 2 is a multi-metal oxide obtained by coprecipitation, the general formula is Mo 12 Bi b Co c Ni d Fe e A f B g O y ; Wherein, Bi is bismuth, W is tungsten, Mo is molybdenum, Co is cobalt, Ni is nickel, Fe is iron, and O is oxygen; A is at least one selected from lithium, sodium, potassium, rubidium, and cesium; B is one selected from beryllium, magnesium, calcium, strontium, and barium; a, b, c, d, e, f, and g are the atomic ratios of each element, where a=0.5-2; b=0.8-1.3; c=4-6; d=2-3; e=0.8-2; f=0.05-0.3; By adjusting these ratios, the activity, selectivity, and stability of the catalyst can be optimized.

[0036] The process for preparing the active component 1 comprises the following steps:

[0037] A1. Dissolve a tungsten source in deionized water to obtain solution A. Add a bismuth source to deionized water to obtain suspension B. Add solution A dropwise to suspension B under heating conditions and stir at constant temperature for 1 hour.

[0038] The tungsten source is sodium tungstate or ammonium tungstate, the bismuth source is bismuth nitrate or bismuth subnitrate, and the heating temperature is 60-98°C. The molar ratio of the bismuth source to the tungsten source is 0.5-2:1, for example, 9.46g of sodium tungstate dihydrate and 24.25g of bismuth nitrate pentahydrate are used. The heating temperature is preferably 90°C to ensure uniform mixing of the solution and promote the reaction between the tungsten source and the bismuth source.

[0039] A2. Transfer the stirred suspension to a polytetrafluoroethylene-lined stainless steel reactor for hydrothermal synthesis; the hydrothermal synthesis temperature is 140-200°C, and the hydrothermal synthesis time is 20-28 hours, preferably 180°C, and maintained for 24 hours to form well-crystallized bismuth tungstate microspheres;

[0040] A3. The solid obtained by hydrothermal synthesis is washed with deionized water, centrifuged, dried, and then heat-treated under a nitrogen atmosphere to obtain active component 1. The solid is washed with deionized water until neutral, centrifuged (8000 rpm, 3 min) to remove impurities, and then dried at 80°C for 12 h. The solid is then heat-treated under a nitrogen atmosphere at a temperature of 600-800°C for 1-4 h, preferably at 650°C for 2 h.

[0041] The process for preparing active component 2 is as follows:

[0042] B1. Under heating conditions, the Mo source, A source, and B source were dissolved in deionized water to obtain solution C, the Co source, Ni source, and Fe source were dissolved in deionized water to obtain solution D, and the Bi source was dissolved in nitric acid to obtain solution E;

[0043] The Mo source is ammonium heptamolybdate, the Bi source, Co source, Ni source, and Fe source are nitrates, source A is nitrate or chloride, and source B is nitrate or hydroxide; the total mass ratio of the Mo source, source A, source B, Co source, Ni source, Fe source, and Bi source to the total mass of deionized water is 1:1.5-6; for example, 30 g of ammonium heptamolybdate is used as the Mo source, and the other components are: 0.14 g potassium nitrate (KNO3), 0.36 g magnesium nitrate (Mg(NO3)2·6H2O), 20.61 g cobalt nitrate (Co(NO3)2·6H2O), 9.06 g nickel nitrate (Ni(NO3)2·6H2O), 7.44 g iron nitrate (Fe(NO3)3·9H2O), and 7.56 g bismuth nitrate (Bi(NO3)3·5H2O) (dissolved in 5 mL deionized water and 1 mL nitric acid). The heating temperature is preferably 70°C to ensure that all components are fully dissolved and mixed evenly;

[0044] B2. Add solution D and solution E to solution C in sequence to form a slurry;

[0045] B3. The slurry is dried and then crushed to obtain active component 2. The drying temperature is 110-180°C and the drying time is 20-30 h, preferably 140°C, and maintained for 24 h to remove moisture and form a dry precursor, which is crushed to an appropriate particle size for mixing.

[0046] Based on the composite catalyst for catalytic oxidation of propylene to produce acrolein described above, the present invention also provides a method for preparing the composite catalyst for catalytic oxidation of propylene to produce acrolein, comprising the following steps:

[0047] S1. Active component 1 and active component 2 are mixed in a mass ratio of 1:1-19, preferably in the range of 1:3-9, to form a mixture; grinding or stirring can be used to ensure uniform distribution. After the active component 2 is dried, it is mixed with the active component 1, and the mixture can be roasted without additional drying;

[0048] S2. Calcinate the mixture to obtain a finished catalyst. The calcination temperature is 450-600°C for 5-8 hours. For example, calcination at 500°C for 6 hours can form a stable catalyst structure and promote interaction between active components. The calcination can be performed in atmospheres with varying oxygen concentrations, depending on the catalyst performance requirements.

[0049] It should be noted that the required equipment is as follows:

[0050] A PTFE-lined stainless steel reactor is corrosion-resistant and resistant to high temperatures and pressures, making it suitable for hydrothermal synthesis. During the hydrothermal synthesis process, the reactor must be properly sealed to avoid the dangers of high temperatures and pressures. After the reaction, the reactor should be allowed to cool naturally to room temperature before opening.

[0051] High-speed centrifuge, with a speed of up to 8000 r / min, is used for solid-liquid separation;

[0052] A forced air drying oven or vacuum drying oven with precise temperature control is suitable for drying solid products. The temperature should be strictly controlled during heat treatment and roasting to avoid fire or explosion caused by overheating. During operation, keep away from flammable items and ensure good ventilation conditions.

[0053] High temperature muffle furnace, with precise temperature control and good thermal insulation performance, suitable for heat treatment and roasting of catalysts;

[0054] Exemplarily, according to the method provided above, a specific embodiment verification is performed, and the verification process is as follows:

[0055] Example 1

[0056] (1) Preparation of active component 1

[0057] 9.46 g of ammonium molybdate was dissolved in 300 mL of deionized water to obtain solution A, and 24.25 g of bismuth nitrate was added to 300 mL of deionized water to obtain suspension B. Solution A was added to suspension B at 90°C and stirred at constant temperature for 1 h. The suspension was then transferred to a 1 L polytetrafluoroethylene-lined stainless steel reactor and hydrothermally synthesized at 180°C for 24 h. The solid obtained by hydrothermal synthesis was washed, centrifuged, and dried, and then heat-treated at 650°C under a nitrogen atmosphere for 2 h to obtain active component 1.

[0058] (2) Preparation of active component 2

[0059] At 70 ° C, 30.00 g of ammonium heptamolybdate, 0.14 g of potassium nitrate, and 0.36 g of magnesium nitrate were dissolved in 200 mL of deionized water to obtain solution C. 20.61 g of cobalt nitrate, 9.06 g of nickel nitrate, and 7.44 g of ferric nitrate were dissolved in 30 mL of deionized water to obtain solution D. 7.56 g of bismuth nitrate was dissolved in a solution prepared by 5 mL of deionized water and 1 mL of nitric acid (65 wt%) to obtain solution E. Solution D and solution E were sequentially added dropwise to solution C at 70 ° C to form a slurry. After stirring the slurry for 1 h, it was dried at 140 ° C for 24 h to obtain a block solid, which was crushed to obtain active component 2.

[0060] (3) Preparation of composite catalyst

[0061] Active component 1 and active component 2 (40 g total weight) were thoroughly mixed and then calcined at 500°C for 6 h. The mass ratio of active component 1 to active component 2 was 1:11.5.

[0062] Example 2

[0063] The preparation conditions of active component 1 and active component 2 were the same as those in Example 1. The preparation conditions of the composite catalyst in the third step were changed to: 40 g of active component 1 and active component 2 were fully mixed and then calcined at 500°C for 6 h, wherein the mass ratio of active component 1 to active component 2 was 1:5.67;

[0064] Example 3

[0065] The preparation conditions of active component 1 and active component 2 were the same as those in Example 1. The preparation conditions of the composite catalyst in the third step were changed to: 40 g of active component 1 and active component 2 were fully mixed and then calcined at 500 °C for 6 h, wherein the mass ratio of active component 1 to active component 2 was 1:1.5;

[0066] Example 4

[0067] In the preparation method of active component 2 in Example 1, "0.14 g potassium nitrate" is replaced with "0.21 g potassium nitrate", and the remaining steps are the same as in Example 1;

[0068] Example 5

[0069] The “0.36 g magnesium nitrate” in the preparation method of the active component 2 in Example 1 was replaced with “0.19 g calcium nitrite”, and the remaining steps were the same as in Example 1.

[0070] Example 6

[0071] (1) Preparation of active component 1

[0072] 7.10 g of ammonium molybdate was dissolved in 300 mL of deionized water to obtain solution A, and 24.25 g of bismuth nitrate was added to 300 mL of deionized water to obtain suspension B. Solution A was added to suspension B at 80°C and stirred at constant temperature for 1 h. The suspension was then transferred to a 1 L polytetrafluoroethylene-lined stainless steel reactor and hydrothermally synthesized at 160°C for 20 h. The solid obtained by hydrothermal synthesis was washed, centrifuged, and dried, and then heat-treated at 700°C under a nitrogen atmosphere for 1 h to obtain active component 1.

[0073] (2) Preparation of active component 2

[0074] At 70 ° C, 30.00 g of ammonium heptamolybdate, 0.14 g of potassium nitrate, and 0.36 g of magnesium nitrate were dissolved in 200 mL of deionized water to obtain solution C. 20.61 g of cobalt nitrate, 9.06 g of nickel nitrate, and 7.44 g of ferric nitrate were dissolved in 30 mL of deionized water to obtain solution D. 7.56 g of bismuth nitrate was dissolved in a solution prepared by 5 mL of deionized water and 1 mL of nitric acid (65 wt%) to obtain solution E. Solution D and solution E were sequentially added dropwise to solution C at 70 ° C to form a slurry. After stirring the slurry for 1 h, it was dried at 140 ° C for 24 h to obtain a block solid, which was crushed to obtain active component 2.

[0075] (3) Preparation of composite catalyst

[0076] Active component 1 and active component 2 (40 g total weight) were thoroughly mixed and then calcined at 470°C for 7 h. The mass ratio of active component 1 to active component 2 was 1:4.

[0077] Example 7:

[0078] (1) Preparation of active component 1

[0079] 9.46 g of ammonium molybdate was dissolved in 300 mL of deionized water to obtain solution A, and 24.25 g of bismuth nitrate was added to 300 mL of deionized water to obtain suspension B. Solution A was added to suspension B at 90°C and stirred at constant temperature for 1 h. The suspension was then transferred to a 1 L polytetrafluoroethylene-lined stainless steel reactor and hydrothermally synthesized at 180°C for 24 h. The solid obtained by hydrothermal synthesis was washed, centrifuged, and dried, and then heat-treated at 650°C under a nitrogen atmosphere for 2 h to obtain active component 1.

[0080] (2) Preparation of active component 2

[0081] At 70 ° C, 30.00 g of ammonium heptamolybdate, 0.14 g of potassium nitrate, and 0.36 g of magnesium nitrate were dissolved in 300 mL of deionized water to obtain solution C. 20.61 g of cobalt nitrate, 9.06 g of nickel nitrate, and 7.44 g of ferric nitrate were dissolved in 60 mL of deionized water to obtain solution D. 7.56 g of bismuth nitrate was dissolved in a solution prepared by 5 mL of deionized water and 1 mL of nitric acid (65 wt%) to obtain solution E. Solution D and solution E were sequentially added dropwise to solution C at 70 ° C to form a slurry. After stirring the slurry for 1 h, it was dried at 110 ° C for 28 h to obtain a block solid, which was crushed to obtain active component two.

[0082] (3) Preparation of composite catalyst

[0083] Active component 1 and active component 2 with a total weight of 40 g were fully mixed and calcined at 600 °C for 5 h, wherein the mass ratio of active component 1 to active component 2 was 1:6.69.

[0084] Comparative Example 1:

[0085] 40 g of the active component 1 in Example 1 was calcined at 500 °C for 6 h to obtain the final catalyst. Figure 4 Shown is the SEM image of the prepared Bi2WO6 microspheres.

[0086] Comparative Example 2:

[0087] 40 g of the active component 1 in Example 1 without heat treatment was calcined at 500° C. for 6 h to obtain the final finished catalyst.

[0088] Comparative Example 3:

[0089] 40 g of the active component 2 in Example 1 was calcined at 500° C. for 6 h to obtain the final finished catalyst.

[0090] Comparative Example 4:

[0091] 3.2 g of Comparative Example 1 and 36.8 g of Comparative Example 3 were mixed to prepare the final finished catalyst.

[0092] The catalysts prepared in Examples 1 to 7 and Comparative Examples 1 to 4 were characterized by nitrogen physical adsorption and desorption. The specific surface area ( S BET ) and through P / P The total pore volume obtained by the adsorption of nitrogen when 0=0.99 ( V pore ) The data are shown in Table 1 below:

[0093] Table 1

[0094]

[0095] From the data in the above table, it can be seen that the active component 1 (Comparative Example 1) has a large specific surface area and a large pore volume, and can increase the specific surface area and pore volume of the composite catalyst after being mixed with the active component 2.

[0096] In summary, Bi2WO6 microspheres were obtained by hydrothermal synthesis and mixed with Mo-Bi metal oxides prepared by co-precipitation to obtain a composite catalyst. The microspherical Bi2WO6 can serve as the active phase of the reaction and increase the specific surface area and pore volume of the composite catalyst.

[0097] The catalysts prepared in Examples 1 to 7 and Comparative Examples 1 to 4 were evaluated, and the evaluation data are shown in Table 2 below:

[0098] Table 2

[0099]

[0100] From the evaluation data of Example 1, Example 2, Comparative Example 1 and Comparative Example 3, it can be seen that after the active component 1 and the active component 2 are mixed in an appropriate ratio, the performance of the composite catalyst is significantly improved compared with that of a single active component, among which Example 2 has a significantly improved performance at 900 h. -1 Under the space velocity condition of 1200 h, the propylene conversion rate, acrolein yield and acrylic acid yield of 99.4%, 85.3% and 9.3% can be achieved. -1 Under the space velocity condition of 100 ℃ and 80 ℃, a propylene conversion rate of 98.3%, an acrolein yield of 85.1% and an acrylic acid yield of 8.7% can still be achieved; from the evaluation data of Comparative Examples 1 and 2, it can be seen that heat treatment of the active component one can significantly improve its catalytic activity; from the evaluation data of Example 1 and Comparative Example 4, it can be seen that the catalytic effect of mixing the active component one and the active component two and then calcining is better than that of calcining the two and then mixing them.

[0101] In summary, the composite catalyst of the present invention is -1 Under the space velocity condition of 1200 h, the propylene conversion rate, acrolein yield and acrylic acid yield of 99.4%, 85.3% and 9.3% can be achieved. -1 Under the space velocity conditions, a propylene conversion rate of 98.3%, an acrolein yield of 85.1% and an acrylic acid yield of 8.7% can still be achieved.

[0102] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A composite catalyst for catalytic oxidation of propylene to produce acrolein, characterized in that: The active component comprises an active component 1 and an active component 2, wherein the mass ratio of the active component 1 to the active component 2 is 1:1-19; The active component 1 is bismuth tungstate microspheres obtained by hydrothermal synthesis, with the general formula Bi a W1O x ; The second active component is a multi-metal oxide obtained by co-precipitation method, with the general formula Mo 12 Bi b Co c Ni d Fe e A f B g O y ; Wherein, Bi is bismuth, W is tungsten, Mo is molybdenum, Co is cobalt, Ni is nickel, Fe is iron, and O is oxygen; A is at least one element selected from lithium, sodium, potassium, rubidium, and cesium; B is one element selected from beryllium, magnesium, calcium, strontium, and barium; a, b, c, d, e, f, and g are the atomic ratios of each element, where a=0.5-2; b=0.8-1.3; c=4-6; d=2-3; e=0.8-2; and f=0.05-0.

3.

2. The composite catalyst for catalytic oxidation of propylene to acrolein according to claim 1, characterized in that: The process for preparing the active component 1 comprises the following steps: A1. Dissolve a tungsten source in deionized water to obtain solution A. Add a bismuth source to deionized water to obtain suspension B. Add solution A dropwise to suspension B under heating conditions and stir at constant temperature for 1 hour. A2. Transfer the stirred suspension to a polytetrafluoroethylene-lined stainless steel reactor for hydrothermal synthesis; A3. The solid obtained by hydrothermal synthesis is washed with deionized water, centrifuged, dried, and then heat-treated under a nitrogen atmosphere to obtain active component 1.

3. The composite catalyst for catalytic oxidation of propylene to acrolein according to claim 2, characterized in that: In step A1, the tungsten source is sodium tungstate or ammonium tungstate, the bismuth source is bismuth nitrate or bismuth subnitrate, and the heating temperature is 60-98°C.

4. The composite catalyst for catalytic oxidation of propylene to acrolein according to claim 3, characterized in that: In step A2, the hydrothermal synthesis temperature is 140-200°C, and the hydrothermal synthesis time is 20-28 h.

5. The composite catalyst for catalytic oxidation of propylene to acrolein according to claim 1, characterized in that: In step A3, the heat treatment temperature is 600-800°C, the heat treatment time is 1-4 h, the centrifugal separation condition is centrifugation at a speed of 8000 r / min for 3 min, and the drying condition is drying at 80°C for 12 h.

6. The composite catalyst for catalytic oxidation of propylene to acrolein according to claim 5, characterized in that: The process for preparing the active component 2 is as follows: B1. Under heating conditions, the Mo source, A source, and B source were dissolved in deionized water to obtain solution C, the Co source, Ni source, and Fe source were dissolved in deionized water to obtain solution D, and the Bi source was dissolved in nitric acid to obtain solution E; B2. Add solution D and solution E to solution C in sequence to form a slurry; B3. Dry the slurry and then grind it to obtain active component 2.

7. The composite catalyst for catalytic oxidation of propylene to acrolein according to claim 6, characterized in that: In step B1, the Mo source is ammonium heptamolybdate, the Bi source, the Co source, the Ni source, and the Fe source are nitrates, the A source is nitrate or chloride, and the B source is nitrate or hydroxide.

8. The composite catalyst for catalytic oxidation of propylene to acrolein according to claim 7, characterized in that: The total mass ratio of the Mo source, the A source, the B source, the Co source, the Ni source, the Fe source, the Bi source and the deionized water is 1:1.5-6.

9. The composite catalyst for catalytic oxidation of propylene to acrolein according to claim 8, characterized in that: In step B3, the drying temperature is 110-180° C., and the drying time is 20-30 h.

10. A method for preparing a composite catalyst for catalytic oxidation of propylene to acrolein, based on the composite catalyst for catalytic oxidation of propylene to acrolein according to any one of claims 1 to 9, characterized in that: The steps include: S1. Mixing active component 1 and active component 2 in a mass ratio of 1:1-19 to form a mixture; S2. calcining the mixture to obtain a finished catalyst product. The calcination temperature is 450-600°C and the calcination time is 5 h-8 h.

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