Molybdenum-iron catalyst for methanol oxidation to formaldehyde with high reaction intensity and preparation method thereof

Abstract

The application belongs to the field of catalytic material preparation, and particularly relates to a molybdenum-iron catalyst for methanol oxidation to formaldehyde with high reaction intensity and a preparation method thereof. The catalyst is prepared by the following steps: adding dry molybdenum trioxide powder and a ferric nitrate solution into a hydrothermal reactor, adding ammonia water into the hydrothermal reactor under stirring to control the pH value of the mixed solution; after uniform stirring, the hydrothermal reactor is sealed and placed into an oven for hydrothermal treatment, and then cooled to room temperature; the obtained precursor is filtered, dried and calcined to obtain the catalyst. The preparation method is simple in operation, low in production cost, small in environmental pollution, and does not require many auxiliary facilities. The hydrothermal treatment can strengthen the contact between the active center and the carrier, and the obtained catalyst is high in crystallinity, good in high-temperature stability, high in formaldehyde selectivity, and can be applied to the reaction condition of methanol oxidation to formaldehyde with high reaction intensity.

Description

Technical Field

[0001] This invention belongs to the field of low-carbon chemical catalytic material preparation, specifically relating to a molybdenum-iron catalyst for methanol oxidation to formaldehyde with high reaction intensity and its preparation method. Background Technology

[0002] Formaldehyde is a common bulk chemical and one of the most important raw materials for chemical production. It can be used to produce thermosetting resins, polyoxymethylene (POM), formalin, pesticides, polyurethane foam, thermoplastics, and adhesives. Industrially, there are two methods for preparing formaldehyde based on the catalytic oxidation of methanol: one uses a silver catalyst to drive the methanol oxidation-dehydrogenation reaction, and the other uses a molybdenum-iron catalyst to directly oxidize methanol to formaldehyde. Compared to silver catalysts, which have shorter lifespans, require harsher reaction conditions, and produce lower purity formaldehyde products, the molybdenum-iron catalyst method is more popular in many applications. Currently, the co-precipitation method is the most studied and widely used method for preparing molybdenum-iron catalysts. Its preparation parameters greatly affect catalyst performance. Furthermore, the co-precipitation method generates large amounts of industrial wastewater containing iron, molybdenum, and ammonium salts, putting pressure on environmental protection. Other preparation methods, such as the sol-gel method, impregnation method, and solid-phase reaction method, have been reported in recent years, but these are not currently suitable for industrial-scale production.

[0003] Ferromolybdenum catalysts consist of ferric molybdate and molybdenum trioxide. Ferric molybdate is generally considered the active center, while molybdenum trioxide is beneficial for catalyst selectivity but has poor activity. Ferric molybdate and molybdenum trioxide exhibit a synergistic effect in the catalytic oxidation of methanol to formaldehyde; the catalyst achieves higher catalytic activity, selectivity, and lifetime when both are present. At high temperatures, molybdenum easily sublimates and is lost, depositing at the bottom of the reactor, increasing bed pressure drop. Simultaneously, the formed iron oxide reduces catalyst selectivity. The catalyst lifetime is only about one year. Summary of the Invention

[0004] The purpose of this invention is to provide a molybdenum-iron catalyst suitable for methanol oxidation to formaldehyde with high reaction intensity and its preparation method. This method features a simple process flow, low production cost, and relatively low wastewater generation, offering certain advantages for industrial production. The molybdenum-iron catalyst prepared using this method can effectively overcome the shortcomings of traditional preparation techniques, such as catalyst active component agglomeration, molybdenum sublimation loss, and low mechanical strength, thereby improving the catalyst's service life.

[0005] To achieve the above-mentioned objectives, the specific technical solution adopted by this invention is as follows:

[0006] A method for preparing a high-reactivity methanol-to-formaldehyde molybdenum ferric catalyst includes the following steps: First, weigh a certain mass of industrial-grade molybdenum trioxide powder, then dry it, and prepare a ferric nitrate solution of a certain mass concentration. Next, add both substances to a hydrothermal reactor. Then, prepare a certain volume fraction of ammonia water and add it to the hydrothermal reactor containing the molybdenum trioxide and ferric nitrate solutions while stirring, controlling the pH value of the mixture. After stirring evenly, seal the hydrothermal reactor and place it in an oven. After hydrothermal treatment at an appropriate temperature for a period of time, remove the hydrothermal reactor, cool it to room temperature, and the resulting precursor is filtered, dried, and calcined to obtain the desired catalyst.

[0007] In a preferred embodiment of the present invention, the specific surface area of ​​the industrial-grade molybdenum trioxide powder is 15-45 m². 2 / g (specifically 15m) 2 / g、20m 2 / g、25m 2 / g、30m 2 / g、35m 2 / g、40m 2 / g、45m 2 / g, etc.; the drying treatment is performed at 80-100℃ (specifically 80℃, 82℃, 84℃, 86℃, 88℃, 90℃, 92℃, 94℃, 96℃, 98℃, 100℃, etc.) for 2.0-3.5h (specifically 2.0h, 2.2h, 2.4h, 2.6h, 2.8h, 3.0h, 3.2h, 3.4h, 3.5h, etc.).

[0008] In a preferred embodiment of the present invention, the ferric nitrate solution has a mass concentration of 0.2-1.5 g / mL (specifically, it can be 0.2 g / mL, 0.4 g / mL, 0.6 g / mL, 0.8 g / mL, 1.0 g / mL, 1.2 g / mL, 1.4 g / mL, 1.5 g / mL, etc.), and the ammonia water has a volume fraction of 30%-65% (specifically, it can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, etc.).

[0009] In a preferred embodiment of the present invention, the stirring speed is 600-1000 r / min and the stirring time is 10-30 min (specifically, it can be 10 min, 15 min, 20 min, 25 min, 30 min, etc.).

[0010] In a preferred embodiment of the present invention, the pH value of the raw material mixture is 2.5-4.0 (specifically, it can be 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, etc.).

[0011] In a preferred embodiment of the present invention, the volume of the solution in the hydrothermal reactor does not exceed 2 / 3 of the reactor volume, the reaction temperature is 120-160℃ (specifically, it can be 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, 160℃, etc.), and the aging time is 15-30h (specifically, it can be 15h, 17h, 19h, 21h, 23h, 25h, 27h, 29h, 30h, etc.).

[0012] In a preferred embodiment of the present invention, the drying temperature is 70-100℃ (specifically, it can be 70℃, 72℃, 74℃, 76℃, 78℃, 80℃, 82℃, 84℃, 86℃, 88℃, 90℃, 92℃, 94℃, 96℃, 98℃, 100℃, etc.), and the drying time is 8-18h (specifically, it can be 8h, 10h, 12h, 14h, 16h, 18h, etc.).

[0013] In a preferred embodiment of the present invention, the calcination temperature is 350-480℃ (specifically, it can be 350℃, 360℃, 370℃, 380℃, 390℃, 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, etc.), the calcination time is 2-6h (specifically, it can be 2h, 3h, 4h, 5h, 6h, etc.), and the calcination atmosphere is air.

[0014] In a preferred embodiment of the present invention, the catalyst is composed of spherical Fe2(MoO4)3 and blocky MoO3, with the contents of the two, in mole fraction, being Fe2(MoO4)3: 15%-38% (specifically, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%). 32%, 33%, 34%, 35%, 36%, 37%, 38%, etc.), MoO3: 62%-85% (specifically 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, etc.).

[0015] This invention provides a method for preparing a molybdenum-iron catalyst suitable for high reaction intensity conditions. The prepared catalyst can be applied to the field of methanol oxidation to formaldehyde.

[0016] Compared with existing technologies, the molybdenum-iron catalyst prepared by the method of this invention has the following advantages:

[0017] (1) Hydrothermal treatment is a method that facilitates catalyst crystal growth. Under hydrothermal treatment conditions, molybdenum trioxide crystals grow continuously, and iron-containing compounds are adsorbed on their surface. During calcination, a solid-phase reaction occurs between the two, and ultimately, Fe2(MoO4)3 particles are uniformly distributed on the surface of the bulk MoO3. This physicochemical process makes the contact between the active center Fe2(MoO4)3 and the MoO3 support closer, enhancing the synergistic catalytic effect and providing abundant active sites. This invention increases the crystallinity of the catalyst, enabling it to support dispersed, fine iron molybdate particles on bulk molybdenum trioxide. This structure can improve the contact ratio at the interface between iron molybdate and molybdenum trioxide and the specific surface area of ​​the catalyst, limiting the formation of iron oxide, which is beneficial to the activity, selectivity, and stability of the catalyst.

[0018] (2) The reaction raw material is industrial-grade molybdenum trioxide, which reduces the production cost. The dried molybdenum trioxide material is more conducive to the adsorption and deposition of iron-containing compounds on its surface. The molybdenum trioxide powder crystallizes and grows into a large block structure in the hydrothermal reactor. On the one hand, it acts as a carrier of the active center to replenish the molybdenum lost due to sublimation in time. On the other hand, the block molybdenum trioxide can improve the mechanical properties of the catalyst material, thereby maintaining the long-term operation of the methanol oxidation reaction.

[0019] (3) The pH value of the reaction system has a great influence on the microstructure of the catalyst. Ammonia water was used as a precipitant to regulate the pH value of the reaction system, so that the iron-containing components, which are Lewis acids, can be better adsorbed on the surface of molybdenum trioxide, which is a Lewis base, thus inhibiting its own aggregation behavior and making the Fe2(MoO4)3 particles of the obtained catalyst have a better dispersion effect.

[0020] (4) Compared with the traditional coprecipitation preparation method, the method of the present invention has simple operation steps, generates less waste liquid, has a simple process device, and the obtained catalyst has a high effective utilization rate of active metal and good stability. It can be applied to the methanol oxidation to formaldehyde reaction with high reaction intensity. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the system changes in a hydrothermal reactor;

[0022] Figure 2 The electron microscopy characterization results are those of the catalyst obtained in Example 1. Detailed Implementation

[0023] A method for preparing a high-reactivity ferromolybdenum catalyst for the methanol oxidation to formaldehyde is illustrated in the following flowchart. Figure 1 The process includes the following steps: adding a certain mass of dried industrial-grade molybdenum trioxide powder and a certain mass concentration of ferric nitrate solution to a hydrothermal reactor. Figure 1 a) Add a certain volume fraction of ammonia water while stirring to adjust the pH value of the system and form a precipitate of iron-containing compounds. Figure 1 b) Then, the hydrothermal reactor is sealed and placed in an oven at a certain temperature for a period of time to form a precursor of ferric molybdate particles adsorbed on the surface of blocky molybdenum trioxide. Figure 1 c) Finally, the reactor is cooled to room temperature, and the precursor is filtered, dried, and calcined to obtain the desired catalyst.

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments and accompanying drawings. It should be understood that all features disclosed in this invention, or steps in all disclosed methods or processes, can be combined in any way, except for mutually exclusive features and / or steps.

[0025] Example 1

[0026] Weigh 28.0 g of industrial-grade molybdenum trioxide powder that has been dried at 100℃ for 2 h, with a specific surface area of ​​35 m². 2 / g, pour into the bottom of the hydrothermal reactor, prepare 0.52g / mL ferric nitrate solution and 45% ammonia water by volume, respectively. Take 50mL of ferric nitrate solution and pour it into the reactor. Then, add ammonia water to the reactor while stirring until the pH of the mixture is 3.6. The stirring speed is 800r / min and the stirring time is 20min. Seal the hydrothermal reactor and place it in an oven. Set the treatment temperature to 140℃ and treat for 28h. After treatment, take out the hydrothermal reactor, cool it to room temperature and filter it. Dry the obtained precursor at 100℃ for 10h and then calcine it in air at 420℃ for 4h to obtain the desired catalyst.

[0027] Example 2

[0028] Weigh 46.6g of industrial-grade molybdenum trioxide powder that has been dried at 90℃ for 2.5h, with a specific surface area of ​​30m². 2 / g, pour into the bottom of the hydrothermal reactor, prepare 1.21g / mL ferric nitrate solution and 30% ammonia water respectively, take 36mL of ferric nitrate solution and pour into the reactor, then add ammonia water to the reactor while stirring until the pH of the mixture is 2.8, the stirring speed is 900r / min and the stirring time is 18min, seal the hydrothermal reactor and place it in an oven, set the treatment temperature to 120℃, treat for 24h, remove the hydrothermal reactor, cool to room temperature and filter, dry the obtained precursor at 80℃ for 15h, and then calcine at 360℃ for 5h in air atmosphere to obtain the desired catalyst.

[0029] Example 3

[0030] Weigh 45.2g of industrial-grade molybdenum trioxide powder that has been dried at 80℃ for 3 hours; its specific surface area is 40m². 2 / g, pour into the bottom of the hydrothermal reactor, prepare 1.13g / mL ferric nitrate solution and 50% ammonia water by volume, respectively. Take 40mL of ferric nitrate solution and pour it into the reactor. Then, add ammonia water to the reactor while stirring until the pH of the mixture is 3.8. The stirring speed is 700r / min and the stirring time is 20min. Seal the hydrothermal reactor and place it in an oven. Set the treatment temperature to 160℃ and treat for 19h. After treatment, take out the hydrothermal reactor, cool it to room temperature and filter it. Dry the obtained precursor at 90℃ for 14h and then calcine it in air at 460℃ for 3h to obtain the desired catalyst.

[0031] Example 4

[0032] Weigh 14.8g of industrial-grade molybdenum trioxide powder that has been dried at 100℃ for 2.5h, with a specific surface area of ​​15m². 2 / g, pour into the bottom of the hydrothermal reactor, prepare 0.36g / mL ferric nitrate solution and 65% ammonia water by volume, respectively. Take 50mL of ferric nitrate solution and pour it into the reactor. Then, add ammonia water to the reactor while stirring until the pH of the mixture is 4.0. The stirring speed is 860r / min and the stirring time is 15min. Seal the hydrothermal reactor and place it in an oven. Set the treatment temperature to 120℃ and treat for 15h. After that, take out the hydrothermal reactor, cool it to room temperature, filter it, dry the obtained precursor at 70℃ for 10h, and then calcine it in air at 350℃ for 5h to obtain the desired catalyst.

[0033] Example 5

[0034] Weigh 180.0 g of industrial-grade molybdenum trioxide powder that has been dried at 100℃ for 1.5 h, with a specific surface area of ​​25 m². 2 / g, pour into the bottom of the hydrothermal reactor, prepare 0.58g / mL ferric nitrate solution and 35% ammonia water respectively, take 230mL of ferric nitrate solution and pour into the reactor, then add ammonia water to the reactor while stirring until the pH of the mixture is 2.5, the stirring speed is 1000r / min and the stirring time is 24min, seal the hydrothermal reactor and place it in an oven, set the treatment temperature to 135℃, treat for 22h, remove the hydrothermal reactor, cool to room temperature and filter, dry the obtained precursor at 89℃ for 13h, and then calcine at 440℃ for 3.5h in air atmosphere to obtain the desired catalyst.

[0035] Example 6

[0036] Weigh 606.9g of industrial-grade molybdenum trioxide powder that has been dried at 100℃ for 3.5h, with a specific surface area of ​​45m². 2 / g, pour into the bottom of the hydrothermal reactor, prepare 0.99g / mL ferric nitrate solution and 58% ammonia water by volume, respectively. Take 400mL of ferric nitrate solution and pour it into the reactor. Then, add ammonia water to the reactor while stirring until the pH of the mixture is 3.2. The stirring speed is 1000r / min and the stirring time is 30min. Seal the hydrothermal reactor and place it in an oven. Set the treatment temperature to 160℃ and treat for 30h. After treatment, remove the hydrothermal reactor, cool it to room temperature and filter it. Dry the obtained precursor at 100℃ for 18h and then calcine it in air at 480℃ for 6h to obtain the desired catalyst.

[0037] Comparative Example 1:

[0038] Weigh 28.0 g of industrial-grade molybdenum trioxide powder that has been dried at 100℃ for 2 h, with a specific surface area of ​​35 m². 2 / g, pour into the bottom of the hydrothermal reactor, prepare 0.52g / mL ferric nitrate solution and 45% ammonia water by volume, respectively. Take 50mL of ferric nitrate solution and pour it into the reactor. Then, add ammonia water to the reactor while stirring until the pH of the mixture is 8.0. The stirring speed is 800r / min and the stirring time is 20min. Seal the hydrothermal reactor and place it in an oven. Set the treatment temperature to 140℃ and treat for 28h. After treatment, take out the hydrothermal reactor, cool it to room temperature and filter it. Dry the obtained precursor at 100℃ for 10h and then calcine it in air at 420℃ for 4h to obtain the desired catalyst.

[0039] Comparative Example 2:

[0040] Weigh 46.6g of industrial-grade molybdenum trioxide powder that has been dried at 90℃ for 2.5h, with a specific surface area of ​​30m². 2 / g, pour into the bottom of the hydrothermal reactor, prepare 1.21g / mL ferric nitrate solution and 30% ammonia water respectively, take 36mL of ferric nitrate solution and pour into the reactor, then add ammonia water to the reactor while stirring until the pH of the mixture is 2.8, the stirring speed is 900r / min and the stirring time is 18min, after the hydrothermal reactor is allowed to stand for 24h, filter, dry the obtained precursor at 80℃ for 15h, and then calcine at 360℃ for 5h in air atmosphere to obtain the desired catalyst.

[0041] Comparative Example 3

[0042] Weigh 19.3g of industrial-grade molybdenum trioxide powder that has been dried at 80℃ for 3 hours; its specific surface area is 40m². 2 / g, pour into the bottom of the hydrothermal reactor, prepare 1.13g / mL ferric nitrate solution and 50% ammonia water by volume, respectively. Take 40mL of ferric nitrate solution and pour it into the reactor. Then, add ammonia water to the reactor while stirring until the pH of the mixture is 3.8. The stirring speed is 700r / min and the stirring time is 20min. Seal the hydrothermal reactor and place it in an oven. Set the treatment temperature to 160℃ and treat for 19h. After treatment, take out the hydrothermal reactor, cool it to room temperature and filter it. Dry the obtained precursor at 90℃ for 14h and then calcine it in air at 460℃ for 3h to obtain the desired catalyst.

[0043] Comparative Example 4

[0044] Weigh 14.8g of industrial-grade molybdenum trioxide powder that has been dried at 100℃ for 2.5h, with a specific surface area of ​​15m². 2 / g, pour into the bottom of the hydrothermal reactor, prepare 0.36g / mL ferric nitrate solution and 65% ammonia water by volume, respectively. Take 50mL of ferric nitrate solution and pour it into the reactor. Then, add ammonia water to the reactor while stirring until the pH of the mixture is 4.0. The stirring speed is 860r / min and the stirring time is 15min. Seal the hydrothermal reactor and place it in an oven. Set the treatment temperature to 120℃ and treat for 15h. After treatment, take out the hydrothermal reactor, cool it to room temperature and filter it. Dry the obtained precursor at 70℃ for 10h and then calcine it in air at 600℃ for 6h to obtain the desired catalyst.

[0045] Comparative Example 5

[0046] Weigh out 220.8g of (NH4)6Mo7O 24·4H2O, prepare a 2000mL aqueous solution with deionized water, add it to the reaction vessel, then prepare a 0.58g / mL ferric nitrate solution and a 35% ammonia solution. While stirring, add 230mL of ferric nitrate solution dropwise to the reaction vessel, followed by the addition of ammonia solution until the pH of the mixture is 2.5. The stirring speed is 1000r / min and the stirring time is 24min. Filter the suspension to obtain the precursor, dry it at 89℃ for 13h, and then calcine it in air at 440℃ for 3.5h to obtain the desired catalyst.

[0047] Key parameters for catalyst performance evaluation

[0048] The calcined catalyst was pressed into hollow cylinders for mechanical strength testing. The shaped catalyst was then crushed into 1mm particles and loaded into a fixed-bed tubular reaction testing apparatus. The reaction temperature was ~330℃, the reaction pressure was atmospheric pressure, and the inlet methanol volume fraction was 10%. The products were analyzed by gas chromatography. The methanol conversion rate, formaldehyde selectivity, and carbon monoxide selectivity were measured at the initial stage of the reaction and after 120 hours of reaction. The catalyst evaluation results are listed in Table 1.

[0049] Table 1. Reactivity and mechanical property data of the catalysts in the examples and comparative examples.

[0050]

[0051] In this invention:

[0052] Methanol conversion rate = (molar amount of methanol feedstock input - molar amount of unreacted methanol) ÷ molar amount of methanol feedstock input × 100%;

[0053] Formaldehyde selectivity = molar amount of formaldehyde ÷ (molar amount of methanol feedstock added - molar amount of unreacted methanol) × 100%;

[0054] Carbon monoxide selectivity = molar amount of carbon monoxide ÷ (molar amount of methanol feedstock added - molar amount of unreacted methanol) × 100%.

[0055] As can be seen from the reaction activity data of Examples 1-6, the catalyst prepared by the method of the present invention has high mechanical strength. When applied to the methanol oxidation to formaldehyde reaction, the methanol conversion rate can reach up to 99.64% and the formaldehyde selectivity can reach up to 96.57% under high reaction intensity conditions. The catalyst still maintains high methanol conversion rate and formaldehyde selectivity after long-term operation for 120 hours, and the catalyst has excellent activity, selectivity and stability.

[0056] Compared to Comparative Example 1, adjusting the pH from 3.6 to 8.0 changed the reaction environment from acidic to alkaline, resulting in a deterioration in catalyst performance. This is because the alkaline environment disrupts the crystal structure of molybdenum trioxide, reducing the dispersibility of the resulting ferric molybdate particles. This leads to insufficient contact between ferric molybdate and molybdenum trioxide, preventing timely replenishment of lost molybdenum and thus decreasing stability. Comparative Example 2 did not employ a hydrothermal treatment process, resulting in a catalyst that was prone to pulverization, exhibiting poor stability, methanol conversion rate, and formaldehyde selectivity. This is because the iron-containing compounds in the prepared catalyst did not maintain sufficient contact with the molybdenum trioxide surface, hindering the replenishment of molybdenum components and the formation of the main formaldehyde product. In Comparative Example 3, the molybdenum atom content was far below the requirements of this invention, failing to obtain sufficient ferric molybdate active centers, significantly reducing reaction performance. In Comparative Example 4, increasing the calcination temperature increased the size of the ferric molybdate particles, decreasing the catalyst's specific surface area and porosity, thus reducing activity. Comparative Example 5 used a traditional co-precipitation method to prepare a ferric molybdenum catalyst; compared to Example 1, the mechanical strength and stability of this catalyst were significantly reduced. The molybdenum-iron catalysts obtained in Comparative Examples 1-5 did not have good microstructure and morphology, and their catalytic performance was significantly lower than that of Examples 1-6. After 120 hours of reaction, the methanol conversion rate and formaldehyde selectivity decreased significantly.

[0057] This invention prepares a highly crystalline ferromolybdenum catalyst. The active centers of this catalyst are small, uniformly distributed ferromolybdate particles, resulting in a large contact area and strong interaction with molybdenum trioxide. Applied to the high-reactivity methanol-to-formaldehyde oxidation reaction, it exhibits good mechanical strength, activity, and stability. The preparation process is simple, low-cost, and produces minimal wastewater, making it a superior approach for industrial production.

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for the preparation of a molybdenum-iron catalyst for the oxidation of methanol to formaldehyde at high reaction intensity, characterized in that, The catalyst is microscopically composed of spherical Fe2(MoO4)3 and block MoO3 crystals; The preparation method comprises the following steps: firstly, drying industrial-grade molybdenum trioxide powder; then, preparing a certain mass concentration of iron nitrate solution; then, adding the dried molybdenum trioxide powder and the iron nitrate solution into a hydrothermal reaction kettle; then, preparing a certain volume fraction of ammonia water, and adding the ammonia water into the hydrothermal reaction kettle containing the molybdenum trioxide and the iron nitrate solution under stirring, and controlling the pH value of the mixed solution to be 2.5-4.0; after stirring uniformly, sealing the hydrothermal reaction kettle into an oven, and hydrothermally treating at a proper temperature for a period of time, taking out the hydrothermal reaction kettle, and cooling to room temperature, the obtained precursor is filtered, dried and calcined to obtain the catalyst; The specific surface area of the industrial-grade molybdenum trioxide powder is 15-45 m 2 / g; the drying treatment is carried out at 80-100 DEG C for 2.0-3.5 h; the hydrothermal temperature is 120-160 DEG C, and the hydrothermal time is 15-30 h; The volume fraction of the ammonia water is 30%-65%.

2. A process for the preparation of a methanol oxidation to formaldehyde molybdenum-iron catalyst for high reaction intensity according to claim 1, characterized by that: The mass concentration of the iron nitrate solution is 0.2-1.5 g / mL.

3. A process for the preparation of a methanol oxidation to formaldehyde molybdenum-iron catalyst for high reaction intensity according to claim 1, characterized by that: The stirring speed is 600-1000 r / min, and the stirring time is 10-30 min.

4. The process for the preparation of a methanol oxidation to formaldehyde molybdenum-iron catalyst for high reaction intensity according to claim 1, characterized by that: The solution volume in the hydrothermal reaction kettle is not more than 2 / 3 of the volume of the reaction kettle.

5. The process for the preparation of a methanol oxidation to formaldehyde molybdenum-iron catalyst for high reaction intensity according to claim 1, characterized by that: The drying temperature is 70-100 ℃, and the drying time is 8-18 h.

6. The process for the preparation of a methanol oxidation to formaldehyde molybdenum-iron catalyst for high reaction intensity according to claim 1, characterized by that: The calcination temperature is 350-480 ℃, the calcination time is 2-6 h, and the calcination atmosphere is air.

7. A molybdenum-iron catalyst for the oxidation of methanol to formaldehyde at high reaction severity, characterized in that: The content of Fe2(MoO4)3 is 15%-38% in terms of mole fraction, and the content of MoO3 is 62%-85% in terms of mole fraction.

8. The molybdenum-iron catalyst obtained by the preparation method in any one of claims 1-6 or the molybdenum-iron catalyst in claim 7 is applied to high reaction intensity methanol oxidation to prepare formaldehyde.

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