Preparation method of iron-molybdenum formaldehyde catalyst with controllable morphology

Abstract

The application provides a preparation method of a morphology-controllable iron-molybdenum formaldehyde catalyst, and belongs to the technical field of catalyst preparation.The preparation method of the catalyst comprises the following steps: firstly, ammonium heptamolybdate tetrahydrate and ferric nitrate nonahydrate are respectively mixed with a complexing agent to prepare a molybdenum-containing solution and an iron-containing solution; then the molybdenum-containing solution and the iron-containing solution are mixed, pH is adjusted, vacuum rotary evaporation is carried out to form a sol, and finally, the sol is dried to form a dry gel, and the dry gel is calcined to obtain a catalyst product.The Mo and Fe coordination environment in the precursor solution is regulated by the complexing agent in the application, the component distribution is prevented from being uneven, a uniform precursor solution is formed, the precipitation rate of the precursor and the particle growth process are changed by adjusting the pH of the solution, the morphology and particle size of the catalyst are influenced, and a catalyst with different morphology and excellent comprehensive performance is prepared.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalyst preparation, in particular to a preparation method of an iron-molybdenum formaldehyde catalyst with controllable morphology. BACKGROUND

[0002] Formaldehyde is an important basic organic chemical raw material, which is widely used in chemical industry, medicine, textile, wood processing and petroleum industry. Modern industrial formaldehyde production mainly adopts the oxidation method using methanol as raw material, and the iron-molybdenum method is widely used. The related research on iron-molybdenum formaldehyde catalyst is common.

[0003] For example, Chinese patent CN112657504A discloses an iron-molybdenum method for preparing formaldehyde from methanol oxidation coated catalyst and its preparation method. The catalyst is composed of active components and inert carriers, and the structure of the active component is Mo a Fe b Cu c X d O e The catalyst is prepared by co-precipitation reaction of ammonium heptamolybdate and ferric nitrate under the action of ultrasonic and dispersant to obtain Fe-Mo phase suspension system A; ammonium heptamolybdate aqueous solution is prepared, the pH of the solution is adjusted, and the nitrate of metal X is added to obtain system B; under the action of ultrasonic reaction environment and complexing agent, ammonium heptamolybdate and copper salt aqueous solution are subjected to complexing reaction to obtain Cu-Mo sol system, then surface active agent, system B and system A are sequentially added to the system for synthesis reaction, and the obtained slurry is subjected to spray drying and calcination to obtain the active component; the active component is mixed with a binder and a strength improver, the active component is coated on the surface of the spherical inert carrier by rolling coating, and then dried and calcined to obtain the catalyst. However, the catalyst prepared by the above method has low formaldehyde yield.

[0004] And the existing iron-molybdenum formaldehyde catalyst has the following disadvantages:

[0005] 1. The active center of the iron-molybdenum formaldehyde catalyst is Fe2(MoO4)3(Mo / Fe ratio is 1.5), and the Mo / Fe ratio of the industrial iron-molybdenum catalyst is 2.0-2.8. The existence of excess Mo can make up for the loss of Mo during the reaction and improve the catalyst life. However, the existence of excess Mo in the form of free sheet MoO3 will make the catalyst have low activity and poor selectivity.

[0006] 2. Industrially used formaldehyde catalysts have limited morphology, structure, and performance, making it difficult to meet the requirements of different industries. For example, the BDO industry does not require high methanol content in formaldehyde products but has strict requirements for formaldehyde selectivity. Therefore, catalysts with high formaldehyde selectivity should be selected to reduce methanol consumption (methanol consumed to produce one ton of formaldehyde solution) and lower production costs. In aldehyde-aldehyde condensation or ester-aldehyde condensation processes, methanol and water are required as solvents to avoid formaldehyde polymerization. Therefore, methanol conversion rate is not a requirement, and catalysts with extremely high formaldehyde selectivity are suitable to achieve near-complete utilization of methanol molecules. The polyester industry requires high methanol content in formaldehyde products, so highly active catalysts (high methanol conversion rate) should be selected.

[0007] 3. The production process of formaldehyde catalysts using the iron-molybdenum method mostly adopts the co-precipitation method, which has problems such as large wastewater volume and high wastewater treatment costs, resulting in poor environmental protection and economic efficiency. Summary of the Invention

[0008] In view of this, the purpose of the present invention is to provide a method for preparing a formaldehyde catalyst with controllable morphology using the iron-molybdenum method, thereby improving the activity and selectivity of the iron-molybdenum formaldehyde catalyst.

[0009] To solve the above problems, the present invention adopts the following technical solution:

[0010] A method for preparing a formaldehyde catalyst with controllable morphology via the iron-molybdenum process includes the following steps:

[0011] (1) Add ammonium heptamolybdate tetrahydrate to deionized water, and then add a complexing agent to dissolve it completely to obtain a molybdenum-containing solution;

[0012] (2) Add ferric nitrate nonahydrate to deionized water, and then add a complexing agent to dissolve it completely to obtain an iron-containing solution;

[0013] (3) Mix the molybdenum-containing solution and the iron-containing solution to obtain a mixed solution, then add ammonia water to adjust the pH to 4.0-7.0, and stir at room temperature;

[0014] (4) Vacuum rotary evaporate the solution from step (3) to form a sol;

[0015] (5) Dry the sol from step (4) to form a dry gel;

[0016] (6) The dry gel obtained in step (5) is placed in a muffle furnace and calcined to obtain the catalyst product.

[0017] Preferably, the concentration of ammonium heptamolybdate in the molybdenum-containing solution in step (1) is 0.04-0.1 mol / L; the molar ratio of the complexing agent to molybdate is 3:1-1:1.

[0018] Preferably, the concentration of ferric nitrate in the iron-containing solution in step (2) is 0.3-0.5 mol / L; and the molar ratio of the complexing agent to iron ions is 3:1-1:1.

[0019] Preferably, the complexing agent in step (1) and step (2) is any one or several of citric acid, oxalic acid, ethylene glycol, ethylenediamine, ethylenediaminetetraacetic acid, glucose and 8-hydroxyquinoline.

[0020] Preferably, the molar atomic ratio of Mo to Fe in the mixed solution in step (3) is 2.1-2.3.

[0021] Preferably, the stirring time at room temperature in step (3) is 1-2 h.

[0022] Preferably, the temperature of vacuum rotary evaporation in step (4) is 50-75℃.

[0023] Preferably, the temperature of drying in step (5) is 90-100℃; and the drying time is 5-6 h.

[0024] Preferably, the temperature of calcination in step (6) is 500-550℃; and the calcination time is 10-12 h.

[0025] In the present application, the complexing agent can regulate the coordination environment of Fe and Mo in the precursor solution, prevent uneven distribution of components, and form a uniform precursor solution. At the same time, by adjusting the pH of the solution, the precipitation rate of the precursor and the growth process of the particles can be changed, which affects the morphology and particle size of the catalyst.

[0026] For the surface catalytic methanol oxidation to formaldehyde reaction, the larger the specific surface area, the higher the reaction activity. The specific surface area of small-size particulate catalyst (particle size of 20-100 nm) is large, and the activity is the highest. The specific surface area of blocky catalyst is small, and the exposure degree of active center is low, which avoids the excessive oxidation of formaldehyde into CO and CO2, so the selectivity of formaldehyde is higher. The specific surface area of cluster-like catalyst is the smallest, although the methanol conversion rate is very low, but the selectivity of formaldehyde is extremely high, which can greatly reduce the methanol consumption. The specific surface area of large-size particulate catalyst (particle size of 100-300 nm) is moderate, and the comprehensive performance is relatively balanced, which has good activity and selectivity.

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] 1. The iron-molybdenum catalyst prepared by the complex-sol-gel method in the present application can be prepared in different morphologies and particle sizes (blocky, large-size particulate, small-size particulate and cluster-like) by adjusting the type and amount of complexing agent, controlling the pH and drying conditions, and at the same time, the generation of free flaky MoO3 is reduced.

[0029] 2. The catalysts prepared by the present application have different morphology and size, and have excellent comprehensive performance and different performance: the small-size granular catalyst has high methanol conversion rate, and low methanol content in the produced formaldehyde product, and is suitable for industries with high requirement on methanol content; the blocky catalyst has high formaldehyde selectivity and low methanol consumption, and is suitable for industries with high production cost; the cluster-shaped catalyst has very high formaldehyde selectivity, and is suitable for processes using methanol and water as solvent and formaldehyde as raw material; the large-size granular catalyst has excellent comprehensive performance, and can meet the requirements of most industries.

[0030] 3. The sol-gel method is used to prepare the iron molybdate formaldehyde catalyst, and no waste water is produced, which is a green and environmentally friendly process. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 SEM image of the catalyst in Example 1;

[0032] Figure 2 SEM image of the catalyst in Example 2;

[0033] Figure 3 SEM image of the catalyst in Example 3;

[0034] Figure 4 SEM image of the catalyst in Example 4;

[0035] Figure 5 SEM image of the catalyst in Example 5;

[0036] Figure 6 SEM image of the catalyst in Example 8;

[0037] Figure 7 SEM image of the catalyst in Example 11;

[0038] Figure 8 SEM image of the catalyst in Example 14;

[0039] Figure 9 SEM image of the catalyst in Comparative Example 1;

[0040] Figure 10 SEM image of the catalyst in Comparative Example 2;

[0041] Figure 11 SEM image of the catalyst in Comparative Example 3;

[0042] Figure 12 SEM image of the catalyst in Comparative Example 4;

[0043] Figure 13 SEM image of the catalyst in Comparative Example 5;

[0044] Figure 14SEM image of the catalyst of Comparative Example 8;

[0045] Figure 15 SEM image of the catalyst of Comparative Example 11;

[0046] Figure 16 SEM image of the catalyst of Comparative Example 14;

[0047] Figure 17 SEM image of the catalyst of Comparative Example 17;

[0048] Figure 18 SEM image of the catalyst of Comparative Example 18. DETAILED DESCRIPTION

[0049] The present application provides a preparation method of a morphology-controllable iron-molybdenum formaldehyde catalyst, and the steps are as follows:

[0050] (1) Ammonium heptamolybdate tetrahydrate is added to deionized water, and then a complexing agent (the molar ratio of the complexing agent to molybdate is 3:1-1:1) is added thereto to be fully dissolved, to obtain a molybdenum-containing solution with a concentration of 0.04-0.1 mol / L of ammonium heptamolybdate;

[0051] (2) Iron nitrate nonahydrate is added to deionized water, and then a complexing agent (the molar ratio of the complexing agent to iron ions is 3:1-1:1) is added thereto to be fully dissolved, to obtain an iron-containing solution with a concentration of 0.3-0.5 mol / L of iron nitrate;

[0052] (3) The molybdenum-containing solution and the iron-containing solution are mixed to obtain a mixed solution (the molar atomic ratio of Mo to Fe is 2.2), and then ammonia water is added to adjust the pH to 4.0-7.0, and stirring is performed at room temperature for 1-2 h;

[0053] (4) The solution of step (3) is vacuum rotary evaporated at 50-75℃ to form a sol;

[0054] (5) The sol of step (4) is dried in an oven at 90-100℃ for 5-6 h to form a dry gel;

[0055] (6) The dry gel obtained in step (5) is calcined in a muffle furnace at 500-550℃ for 10-12 h to obtain a finished catalyst.

[0056] The complexing agent in steps (1) and (2) is any one or several of citric acid, oxalic acid, ethylene glycol, ethylenediamine, ethylenediaminetetraacetic acid, glucose, and 8-hydroxyquinoline.

[0057] Using the method of this invention, by controlling the coordination environment of Mo and Fe in the precursor solution, the pH of the solution, and the evaporation temperature through a complexing agent, small-sized particulate, large-sized particulate, blocky, and clustered catalysts can be prepared without the formation of free flake-like MoO3. The prepared catalysts each have advantages in catalytic activity and formaldehyde selectivity. Specifically, the blocky catalyst has lower activity but better formaldehyde selectivity; the small-sized particulate catalyst has high activity; the large-sized particulate catalyst has excellent overall performance; and the clustered catalyst has very low activity but extremely good formaldehyde selectivity.

[0058] In a specific embodiment of the present invention

[0059] The preparation method of the bulk catalyst includes the following steps:

[0060] (1) Add ammonium heptamolybdate tetrahydrate to deionized water, and then add citric acid (the molar ratio of the complexing agent to molybdate is 3:1-1:1) to dissolve it completely to obtain a molybdenum-containing solution with a concentration of 0.04-0.1 mol / L.

[0061] (2) Add ferric nitrate nonahydrate to deionized water, and then add citric acid (the molar ratio of the complexing agent to iron ions is 3:1-1:1) to dissolve it completely to obtain an iron-containing solution with a concentration of 0.3-0.5 mol / L.

[0062] (3) Mix the molybdenum-containing solution and the iron-containing solution to obtain a mixed solution (the molar atomic ratio of Mo and Fe is 2.2), then add ammonia water to adjust the pH to 4.0-7.0, and stir at room temperature for 1-2 hours;

[0063] (4) Evaporate the solution from step (3) under vacuum at 50-75°C until a sol is formed;

[0064] (5) Dry the sol from step (4) in an oven at 90-100°C for 5-6 hours to form a dry gel;

[0065] (6) The dry gel obtained in step (5) is placed in a muffle furnace at 500-550°C and calcined for 10-12 hours to obtain the catalyst product.

[0066] The preparation method of the small-sized particulate catalyst includes the following steps:

[0067] (1) Add ammonium heptamolybdate tetrahydrate to deionized water, and then add oxalic acid (the molar ratio of the complexing agent to molybdate is 3:1-1:1) to dissolve it completely to obtain a molybdenum-containing solution with a concentration of 0.04-0.1 mol / L.

[0068] (2) adding nine hydrated ferric nitrate into deionized water, and then adding complexing agent citric acid (mole ratio of complexing agent to ferric ion is 3:1-1:1) into the solution to fully dissolve, to obtain an iron-containing solution with a concentration of 0.3-0.5 mol / L of ferric nitrate;

[0069] (3) mixing the molybdenum-containing solution and the iron-containing solution to obtain a mixed solution (mole atomic ratio of Mo to Fe is 2.2), and then adding ammonia water to adjust the pH to 5.0-6.0, and stirring at room temperature for 1-2 h;

[0070] (4) vacuum rotary evaporation of the solution of step (3) at 75℃ to form a sol;

[0071] (5) drying the sol of step (4) in an oven at 90-100℃ for 5-6 h to form a dry gel;

[0072] (6) calcining the dry gel obtained in step (5) in a muffle furnace at 500-550℃ for 10-12 h to obtain a finished catalyst product.

[0073] The preparation method of the large-size particulate catalyst is as follows:

[0074] (1) adding ammonium heptamolybdate tetrahydrate into deionized water, and then adding complexing agent citric acid (mole ratio of complexing agent to molybdate is 1:1) into the solution to fully dissolve, to obtain a molybdenum-containing solution with a concentration of 0.04-0.1 mol / L of ammonium heptamolybdate;

[0075] (2) adding nine hydrated ferric nitrate into deionized water, and then adding complexing agent ethylene glycol (mole ratio of complexing agent to ferric ion is 1:1) into the solution to fully dissolve, to obtain an iron-containing solution with a concentration of 0.3-0.5 mol / L of ferric nitrate;

[0076] (3) mixing the molybdenum-containing solution and the iron-containing solution to obtain a mixed solution (mole atomic ratio of Mo to Fe is 2.2), and then adding ammonia water to adjust the pH to 5.0-7.0, and stirring at room temperature for 1-2 h;

[0077] (4) vacuum rotary evaporation of the solution of step (3) at 50-75℃ to form a sol;

[0078] (5) drying the sol of step (4) in an oven at 90-100℃ for 5-6 h to form a dry gel;

[0079] (6) calcining the dry gel obtained in step (5) in a muffle furnace at 500-550℃ for 10-12 h to obtain a finished catalyst product.

[0080] The preparation method of the cluster-shaped catalyst is as follows:

[0081] (1) adding ammonium heptamolybdate tetrahydrate into deionized water, and then adding a complexing agent ethylene glycol (mole ratio of complexing agent to molybdate is 2:1-1:1) into the solution to fully dissolve, to obtain a molybdenum-containing solution with a concentration of 0.04-0.1 mol / L of ammonium heptamolybdate;

[0082] (2) adding iron nitrate nonahydrate into deionized water, and then adding a complexing agent ethylene glycol (mole ratio of complexing agent to iron ion is 2:1-1:1) into the solution to fully dissolve, to obtain an iron-containing solution with a concentration of 0.3-0.5 mol / L of iron nitrate;

[0083] (3) mixing the molybdenum-containing solution and the iron-containing solution to obtain a mixed solution (mole atomic ratio of Mo to Fe is 2.2), and then adding ammonia water to adjust pH to 4.0, and stirring at room temperature for 1-2 h;

[0084] (4) vacuum rotary evaporation of the solution of step (3) at 50-70 ℃ to form a sol;

[0085] (5) drying the sol of step (4) in an oven at 90-100 ℃ for 5-6 h to form a dry gel;

[0086] (6) calcining the dry gel obtained in step (5) in a muffle furnace at 500-550 ℃ for 10-12 h to obtain a finished catalyst product.

[0087] The application will be further described below in combination with examples.

[0088] Example 1

[0089] A preparation method of a blocky iron-molybdenum formaldehyde catalyst, the steps being as follows:

[0090] (1) adding 9.8 g of ammonium heptamolybdate tetrahydrate (0.0079 mol) into 200.0 ml of deionized water, and then adding 32.0 g of citric acid (0.167 mol, mole ratio of complexing agent to molybdate is 3:1) into the solution to fully dissolve, to obtain a molybdenum-containing solution with a concentration of 0.04 mol / L of ammonium heptamolybdate;

[0091] (2) adding 10.2 g of iron nitrate nonahydrate (0.025 mol) into 50.8 ml of deionized water, and then adding 14.5 g of citric acid (0.075 mol, mole ratio of complexing agent to iron ion is 3:1) into the solution to fully dissolve, to obtain an iron-containing solution with a concentration of 0.5 mol / L of iron nitrate;

[0092] (3) mixing the molybdenum-containing solution and the iron-containing solution, and then adding ammonia water to adjust pH to 5.0, and stirring at room temperature for 2 h;

[0093] (4) vacuum rotary evaporation of the solution of step (3) at 50 ℃ to form a sol;

[0094] (5) The sol of step (4) was dried in an oven at 100 °C for 6 h to form a xerogel;

[0095] (6) The xerogel obtained in step (5) was calcined in a muffle furnace at 500 °C for 12 h to obtain a bulk iron-molybdenum formaldehyde catalyst. The SEM image of the catalyst is shown in Figure 1. Figure 1 .

[0096] Example 2

[0097] A method for preparing a small-particle iron-molybdenum formaldehyde catalyst, the steps are as follows:

[0098] (1) 9.8 g of ammonium heptamolybdate tetrahydrate was added to 82.5 ml of deionized water, and then 10.0 g of oxalic acid (0.11 mol, the molar ratio of complexing agent to molybdate is 2:1) was added thereto to be fully dissolved, obtaining a molybdenum-containing solution with a concentration of 0.1 mol / L of ammonium heptamolybdate;

[0099] (2) 10.2 g of iron nitrate nonahydrate was added to 83.7 ml of deionized water, and then 9.7 g of citric acid (0.05 mol, the molar ratio of complexing agent to iron ions is 2:1) was added thereto to be fully dissolved, obtaining an iron-containing solution with a concentration of 0.3 mol / L of iron nitrate;

[0100] (3) The molybdenum-containing solution and the iron-containing solution were mixed, and then ammonia water was added to adjust the pH to 6.0, and stirred at room temperature for 2 h;

[0101] (4) The solution of step (3) was vacuum rotary evaporated at 75 °C to form a sol;

[0102] (5) The sol of step (4) was dried in an oven at 100 °C for 6 h to form a xerogel;

[0103] (6) The xerogel obtained in step (5) was calcined in a muffle furnace at 500 °C for 12 h to obtain a small-particle iron-molybdenum formaldehyde catalyst (particle size of 20-100 nm). The SEM image of the catalyst is shown in Figure 2. Figure 2 .

[0104] Example 3

[0105] A method for preparing a large-particle iron-molybdenum formaldehyde catalyst, the steps are as follows:

[0106] (1) 9.8 g of ammonium heptamolybdate tetrahydrate was added to 113.2 ml of deionized water, and then 10.7 g of citric acid (0.055 mol, the molar ratio of complexing agent to molybdate is 1:1) was added thereto to be fully dissolved, obtaining a molybdenum-containing solution with a concentration of 0.07 mol / L of ammonium heptamolybdate;

[0107] (2) 10.2 g of iron nitrate nonahydrate was added to 63.3 ml of deionized water, and then 1.6 g of ethylene glycol (0.025 mol, the molar ratio of the complexing agent to iron ions was 1:1) was added thereto to be sufficiently dissolved, to obtain an iron-containing solution having a concentration of 0.4 mol / L of iron nitrate;

[0108] (3) The molybdenum-containing solution and the iron-containing solution were mixed, and then ammonia water was added to adjust the pH to 6.0, and stirred at room temperature for 2 h;

[0109] (4) The solution of step (3) was vacuum rotary evaporated at 75°C to form a sol;

[0110] (5) The sol of step (4) was dried in an oven at 100°C for 6 h to form a xerogel;

[0111] (6) The xerogel obtained in step (5) was calcined in a muffle furnace at 500°C for 12 h to obtain a large-particle iron-molybdenum formaldehyde catalyst (particle size of 100-300 nm). The SEM image of the catalyst is shown in Figure 3 .

[0112] Example 4

[0113] A method for preparing a cluster-shaped iron-molybdenum formaldehyde catalyst, the steps are as follows:

[0114] (1) 9.8 g of ammonium heptamolybdate tetrahydrate was added to 113.2 ml of deionized water, and then 3.4 g of ethylene glycol (0.055 mol, the molar ratio of the complexing agent to molybdate was 1:1) was added thereto to be sufficiently dissolved, to obtain a molybdenum-containing solution having a concentration of 0.07 mol / L of ammonium heptamolybdate;

[0115] (2) 10.2 g of iron nitrate nonahydrate was added to 63.3 ml of deionized water, and then 1.6 g of ethylene glycol (the molar ratio of the complexing agent to iron ions was 1:1) was added thereto to be sufficiently dissolved, to obtain an iron-containing solution having a concentration of 0.4 mol / L of iron nitrate;

[0116] (3) The molybdenum-containing solution and the iron-containing solution were mixed, and then ammonia water was added to adjust the pH to 4.0, and stirred at room temperature for 2 h;

[0117] (4) The solution of step (3) was vacuum rotary evaporated at 50°C to form a sol;

[0118] (5) The sol of step (4) was dried in an oven at 100°C for 6 h to form a xerogel;

[0119] (6) The xerogel obtained in step (5) was calcined in a muffle furnace at 500°C for 12 h to obtain a cluster-shaped iron-molybdenum formaldehyde catalyst. The SEM image of the catalyst is shown in Figure 4 .

[0120] The catalysts were prepared by changing the raw materials, ratio, reaction parameters, etc. in Example 1, and the specific parameters are shown in Table 1:

[0121] Table 1

[0122]

[0123]

[0124] We used the method of controlling variables to change the preparation conditions of Examples 1-16 above, and conducted comparative example studies. The SEM image of the catalyst of Example 5 is as follows Figure 5 ; the SEM image of the catalyst of Example 8 is as follows Figure 6 ; the SEM image of the catalyst of Example 11 is as follows Figure 7 ; and the SEM image of the catalyst of Example 14 is as follows Figure 8 .

[0125] Comparative Example 1

[0126] A preparation method of a formaldehyde catalyst by iron-molybdenum method, the steps are as follows:

[0127] (1) 9.8 g of ammonium heptamolybdate tetrahydrate was added to 200.0 ml of deionized water, then 32.0 g of citric acid (molar ratio of complexing agent to molybdate is 3:1) was added to it and dissolved thoroughly, to obtain a molybdenum-containing solution with a concentration of 0.04 mol / L of ammonium heptamolybdate;

[0128] (2) 10.2 g of iron nitrate nonahydrate was added to 50.8 ml of deionized water, and dissolved thoroughly without adding a complexing agent, to obtain an iron-containing solution with a concentration of 0.5 mol / L of iron nitrate;

[0129] (3) The molybdenum-containing solution and the iron-containing solution were mixed, then ammonia water was added to adjust the pH to 5.0, and stirred at room temperature for 2 h;

[0130] (4) The solution of step (3) was vacuum rotary evaporated at 50°C to form a sol;

[0131] (5) The sol of step (4) was dried in an oven at 100°C for 6 h to form a dry gel;

[0132] (6) The dry gel obtained in step (5) was calcined in a muffle furnace at 500°C for 12 h to obtain a catalyst with a morphology of agglomerated particles + flakes. The SEM image of the catalyst is as follows Figure 9 .

[0133] Comparative Example 2

[0134] A preparation method of a formaldehyde catalyst by iron-molybdenum method, the steps are as follows:

[0135] (1) 9.8 g of ammonium heptamolybdate tetrahydrate was added to 82.5 ml of deionized water, and then 10.0 g of oxalic acid (molar ratio of complexing agent to molybdate was 2:1) was added thereto to be completely dissolved, to obtain a molybdenum-containing solution having a concentration of 0.1 mol / L of ammonium heptamolybdate;

[0136] (2) 10.2 g of iron nitrate nonahydrate was added to 83.7 ml of deionized water, and then 9.7 g of citric acid (molar ratio of complexing agent to iron ion was 2:1) was added thereto to be completely dissolved, to obtain an iron-containing solution having a concentration of 0.3 mol / L of iron nitrate;

[0137] (3) The molybdenum-containing solution and the iron-containing solution were mixed, and then ammonia water was added to adjust the pH to 6.0, and stirred at room temperature for 2 h;

[0138] (4) The solution of step (3) was vacuum rotary evaporated at 40°C to form a sol;

[0139] (5) The sol of step (4) was dried in an oven at 100°C for 6 h to form a xerogel;

[0140] (6) The xerogel obtained in step (5) was calcined in a muffle furnace at 500°C for 12 h to obtain a catalyst having a morphology of particles + flakes. The SEM image of the catalyst is shown in Figure 10 .

[0141] Comparative Example 3

[0142] A method for preparing a formaldehyde catalyst by an iron-molybdenum method, the steps being as follows:

[0143] (1) 9.8 g of ammonium heptamolybdate tetrahydrate was added to 113.2 ml of deionized water, and then 10.0 g of oxalic acid (molar ratio of complexing agent to molybdate was 2:1) was added thereto to be completely dissolved, to obtain a molybdenum-containing solution having a concentration of 0.07 mol / L of ammonium heptamolybdate;

[0144] (2) 10.2 g of iron nitrate nonahydrate was added to 63.3 ml of deionized water, and then 1.6 g of ethylene glycol (molar ratio of complexing agent to iron ion was 2:1) was added thereto to be completely dissolved, to obtain an iron-containing solution having a concentration of 0.4 mol / L of iron nitrate;

[0145] (3) The molybdenum-containing solution and the iron-containing solution were mixed, and then ammonia water was added to adjust the pH to 6.0, and stirred at room temperature for 2 h;

[0146] (4) The solution of step (3) was vacuum rotary evaporated at 75°C to form a sol;

[0147] (5) The sol of step (4) was dried in an oven at 100°C for 6 h to form a xerogel;

[0148] (6) The dry gel obtained in step (5) was placed in a muffle furnace at 500°C for 12 h to obtain a catalyst with a morphology of granular + flaky. The SEM image of the catalyst is shown in Figure 6. Figure 11 .

[0149] Comparative Example 4

[0150] A preparation method of a formaldehyde catalyst by the iron-molybdenum method, the steps of which are as follows:

[0151] (1) 9.8 g of ammonium heptamolybdate tetrahydrate was added to 113.2 ml of deionized water, and then 3.4 g of ethylene glycol (molar ratio of complexing agent to molybdate is 1:1) was added thereto to be fully dissolved, to obtain a molybdenum-containing solution with a concentration of ammonium heptamolybdate of 0.07 mol / L;

[0152] (2) 10.2 g of iron nitrate nonahydrate was added to 63.3 ml of deionized water, and then 1.6 g of ethylene glycol (molar ratio of complexing agent to iron ions is 1:1) was added thereto to be fully dissolved, to obtain an iron-containing solution with a concentration of iron nitrate of 0.4 mol / L;

[0153] (3) The molybdenum-containing solution and the iron-containing solution were mixed, and then ammonia water was added to adjust the pH to 7.0, and stirred at room temperature for 2 h;

[0154] (4) The solution of step (3) was vacuum rotary evaporated at 50°C to form a sol;

[0155] (5) The sol of step (4) was dried in an oven at 100°C for 6 h to form a dry gel;

[0156] (6) The dry gel obtained in step (5) was placed in a muffle furnace at 500°C for 12 h to obtain a catalyst with a morphology of granular + flaky. The SEM image of the catalyst is shown in Figure 6. Figure 12 .

[0157] Comparative Examples 5-16

[0158] The catalysts were prepared by changing the preparation raw materials, proportions, reaction parameters, etc. in Example 1, and the specific parameters are shown in Table 2:

[0159] Table 2

[0160]

[0161] The SEM image of the catalyst of Comparative Example 5 is shown in Figure 7; Figure 13 ; the SEM image of the catalyst of Comparative Example 8 is shown in Figure 8; Figure 14 ; the SEM image of the catalyst of Comparative Example 11 is shown in Figure 9; Figure 15 ; and the SEM image of the catalyst of Comparative Example 14 is shown in Figure 10. Figure 16 .

[0162] Comparative Example 17

[0163] A method for preparing a formaldehyde catalyst by a coprecipitation method, comprising the following steps:

[0164] (1) 9.8 g of ammonium heptamolybdate tetrahydrate was added to 113.2 ml of deionized water, and fully dissolved without adding a complexing agent to obtain a molybdenum-containing solution with a concentration of 0.07 mol / L of ammonium heptamolybdate;

[0165] (2) 10.2 g of iron nitrate nonahydrate was added to 63.3 ml of deionized water, and fully dissolved without adding a complexing agent to obtain an iron-containing solution with a concentration of 0.5 mol / L of iron nitrate;

[0166] (3) The molybdenum-containing solution and the iron-containing solution were mixed, and then ammonia water was added to adjust the pH to 2.0, and stirred at room temperature for 2 h;

[0167] (4) The solution of step (3) was filtered while hot after stirring at 80°C for 4 h to obtain a filter cake;

[0168] (5) The filter cake of step (4) was dried in an oven at 100°C for 12 h;

[0169] (6) The dry gel obtained in step (5) was calcined in a muffle furnace at 500°C for 12 h to obtain a catalyst with a morphology of granular + flaky. The SEM image of the catalyst is shown in Figure 17 .

[0170] Comparative Example 18

[0171] The FH44 commercial catalyst purchased from Johnson Matthey was used as Comparative Example 18. The SEM image of the catalyst is shown in Figure 18 .

[0172] The catalysts prepared in Examples 1-16 and Comparative Examples 1-17 and the commercial catalyst of Comparative Example 18 were evaluated for reaction in a fixed bed micro-reactor catalytic reaction device to determine the catalyst performance, including catalyst activity (methanol conversion rate) and selectivity (formaldehyde, dimethyl ether, CO and CO2).

[0173] Catalyst evaluation method: 0.5 g of catalyst was loaded in a fixed bed reaction device with an inner diameter of 8.0 mm, and a thermocouple was inserted into the catalyst bed. The raw material anhydrous methanol (flow rate of 0.02 ml / min) was pressurized into the reaction tube by a micro piston pump, and the raw gas was introduced into the reaction tube by a mass flow controller, with a total gas flow rate of 240 ml / min (N2:O2 volume ratio of 7:1). The reaction temperature was measured by the thermocouple inserted into the bed, and the products at the reaction outlet were collected and sampled at 120°C using a ten-way valve, and the contents of each component were analyzed online by gas chromatography. The results are shown in Table 3.

[0174] Table 3

[0175]

[0176]

[0177] The above merely describes the preferred embodiments of the present application, and it should be pointed out that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered as falling within the protection scope of the present application.

Claims

1. A method for preparing a morphology-controllable iron-molybdenum formaldehyde catalyst, characterized in that, The catalyst is in block or cluster shape; The preparation method of the block structure catalyst comprises the following steps: (1) ammonium heptamolybdate tetrahydrate is added into deionized water, and then a complexing agent citric acid is added into the solution to fully dissolve, so as to obtain a molybdenum-containing solution with a concentration of 0.04-0.1 mol / L of ammonium heptamolybdate; the molar ratio of the complexing agent to molybdate is 3:1-1:1; (2) iron nitrate nonahydrate is added into deionized water, and then a complexing agent citric acid is added into the solution to fully dissolve, so as to obtain an iron-containing solution with a concentration of 0.3-0.5 mol / L of iron nitrate; the molar ratio of the complexing agent to iron ions is 3:1-1:1; (3) the molybdenum-containing solution and the iron-containing solution are mixed to obtain a mixed solution, and then ammonia water is added to adjust the pH to 4.0-7.0, and the solution is stirred at room temperature; (4) the solution of step (3) is vacuum rotary evaporated at 50-75 ℃ to form a sol; (5) the sol of step (4) is dried in an oven to form a dry gel; (6) the dry gel obtained in step (5) is calcined in a muffle furnace at 500-550 ℃ for 10-12 h to obtain a finished catalyst; The preparation method of the cluster catalyst comprises the following steps: (1) ammonium heptamolybdate tetrahydrate is added into deionized water, and then a complexing agent ethylene glycol is added into the solution to fully dissolve, so as to obtain a molybdenum-containing solution with a concentration of 0.04-0.1 mol / L of ammonium heptamolybdate; the molar ratio of the complexing agent to molybdate is 2:1-1:1; (2) iron nitrate nonahydrate is added into deionized water, and then a complexing agent ethylene glycol is added into the solution to fully dissolve, so as to obtain an iron-containing solution with a concentration of 0.3-0.5 mol / L of iron nitrate; the molar ratio of the complexing agent to iron ions is 2:1-1:1; (3) the molybdenum-containing solution and the iron-containing solution are mixed to obtain a mixed solution, and then ammonia water is added to adjust the pH to 4.0, and the solution is stirred at room temperature; (4) the solution of step (3) is vacuum rotary evaporated at 50-75 ℃ to form a sol; (5) the sol of step (4) is dried in an oven at 90-100 ℃ for 5-6 h to form a dry gel; (6) the dry gel obtained in step (5) is calcined in a muffle furnace at 500-550 ℃ for 10-12 h to obtain a finished catalyst.

2. The method for preparing a shape-controllable iron-molybdenum formaldehyde catalyst according to claim 1, characterized in that, In the preparation method of the block structure catalyst and the preparation method of the cluster catalyst, the molar atomic ratio of Mo to Fe in the mixed solution of step (3) is 2.1-2.

3.

3. The method for preparing a shape-controllable iron-molybdenum formaldehyde catalyst according to claim 1, characterized in that, In the preparation method of the block structure catalyst and the preparation method of the cluster catalyst, the stirring time of the mixed solution at room temperature of step (3) is 1-2 h.

4. The method for preparing a shape-controllable iron-molybdenum formaldehyde catalyst according to claim 1, characterized in that, In the preparation method of the block structure catalyst, the drying temperature of step (5) is 90-100 ℃; and the drying time is 5-6 h.

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