Iron-molybdenum catalyst for oxidation of methanol to formaldehyde and preparation method thereof

Abstract

This invention discloses an iron-molybdenum catalyst for the oxidation of methanol to formaldehyde and its preparation method. The method involves uniformly mixing metal oxides; adding silica sol and a pore-forming agent to form a paste, which is then stirred to form a slurry. The slurry is dried, calcined, pulverized, and a lubricant is added. The slurry is then sheeted to obtain a porous SiO2 support. A molybdenum salt solution is impregnated onto the porous SiO2 support to obtain a precursor for the iron-molybdenum catalyst. The precursor is dried and calcined at high temperature to obtain the iron-molybdenum catalyst. The catalyst of this invention exhibits a synergistic effect among its active components, achieving highly efficient methanol conversion in the oxidation of methanol to formaldehyde. It demonstrates excellent catalytic activity, selectivity, and yield, while also exhibiting high stability. The catalyst preparation method of this invention is simple, with low preparation cost and long lifespan, thus showing promising prospects for industrial application.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, specifically relating to an iron-molybdenum catalyst for the oxidation of methanol to formaldehyde and its preparation method. Background Technology

[0002] Formaldehyde is an important basic chemical raw material, widely used in the production of thermosetting resins, polyoxymethylene (POM), pentaerythritol, hexamethylenetetramine, 1,4-butanediol, pyridine, ethylene glycol, trihydroxymethane, and other chemical products. Currently, there is still a significant market demand for it, with a positive growth trend. Industrially, formaldehyde is generally synthesized using the silver method and the iron-molybdenum method. The silver method mainly includes electrolytic silver and supported silver methods. While the silver method has advantages such as low investment and simple production processes, it also has disadvantages such as short catalyst life and low methanol conversion rate. The iron-molybdenum method has advantages such as long catalyst life, high methanol conversion rate, and high product concentration. Since the 1960s, the co-precipitation method has been commonly used industrially for the synthesis of iron-molybdenum catalysts, and this method has been widely applied.

[0003] CN106693981B prepared a catalyst with Fe, Mo, and V as active components by co-precipitation. The catalyst was then extruded with the addition of metal additives and binders, and then calcined to obtain the finished catalyst. The reaction temperature of the catalyst was 240–320℃.

[0004] CN110893344B uses metallic iron, organic acids, and molybdenum acid as raw materials and prepares an iron-molybdenum catalyst by co-precipitation of by-product hydrogen. The catalyst achieves efficient methanol conversion at 200–350°C, but its inlet methanol concentration is low and the actual formaldehyde yield is low.

[0005] CN108435192A discloses a mechanochemical synthesis method for an iron-molybdenum catalyst for the oxidation of methanol to formaldehyde. The catalyst is prepared by ball milling and calcining a mixture of molybdate and iron salt, exhibiting advantages of high selectivity and activity. However, it still suffers from problems such as easy catalyst deactivation.

[0006] Currently, iron-molybdenum catalysts prepared by the co-precipitation method in China have the characteristics of high active center density and good catalyst activity, but they still have defects such as low activity, short service life, many side reactions, and poor stability. Therefore, it is necessary to develop catalysts that can overcome the above defects to meet the requirements of industrial production. Summary of the Invention

[0007] Purpose of the invention: The purpose of this invention is to address the shortcomings of existing technologies by providing an iron-molybdenum catalyst for the oxidation of methanol to formaldehyde and its preparation method.

[0008] This invention provides an iron-molybdenum catalyst supported on a SiO2 doped support and its preparation method, addressing the technical problems of existing iron-molybdenum catalysts such as small specific surface area, poor stability, and low catalytic activity. The method uses an acidic solution of molybdenum salt to impregnate a SiO2 doped support to prepare an iron-molybdenum catalyst for the oxidation of methanol to formaldehyde. The preparation steps are divided into support preparation and impregnation. During support preparation, the active components are effectively dispersed within the support while increasing its specific surface area. By adjusting the pore size of the support, pore blockage during the reaction is avoided, ensuring good dispersion of the molybdenum salt within the support and a more uniform distribution of the active components. This prevents aggregation of active components, which could lead to excessively high local temperatures in the catalyst bed during the catalytic reaction. This enhances the synergistic effect of the active components, increases the reaction rate, ensures effective heat transfer through the support channels, and improves the catalyst's heat dissipation function, thereby effectively reducing the local catalyst bed temperature and preventing the loss of active components such as Mo when the local catalyst bed temperature is too high. This enhances the catalyst's stability and catalytic activity.

[0009] Technical solution: The objective of this invention is achieved through the following technical solution:

[0010] This invention provides a method for preparing an iron-molybdenum catalyst for the oxidation of methanol to formaldehyde, comprising the following steps:

[0011] (1) Mix the metal oxides evenly;

[0012] (2) Add silica sol and pore-forming agent to mix into a paste, continue stirring into a slurry, dry, calcine, pulverize the slurry, add lubricant, and then form into a sheet to obtain a porous SiO2 carrier.

[0013] (3) The molybdenum salt solution is impregnated onto the porous SiO2 support obtained in step (2) to obtain the precursor of the iron-molybdenum catalyst;

[0014] (4) The precursor obtained in step (3) is dried and calcined at high temperature to obtain the iron-molybdenum catalyst.

[0015] Preferably, in step (1), the metal oxide is Fe2O3, NiO, CeO2, or MnO2; wherein the molar ratio of manganese to iron is 0.2 to 0.8:1; the molar ratio of nickel to iron is 0.2 to 0.6:1; and the molar ratio of cerium to iron is 0.1 to 0.3:1.

[0016] Further, the molar ratio of manganese to iron is 0.3 to 0.5:1; the molar ratio of nickel to iron is 0.3 to 0.5:1; and the molar ratio of cerium to iron is 0.1 to 0.2:1.

[0017] Preferably, in step (2), the silica sol is a 40% SiO2 solution; the pore-forming agent is one or more of polyethylene glycol, polyvinyl alcohol, and hydroxypropyl cellulose; the amount of the pore-forming agent added is 2% to 4% of the total mass of the iron-molybdenum catalyst; and the lubricant is one or more of stearic acid, magnesium stearate, zinc stearate, and graphite.

[0018] More preferably, the pore-forming agent is polyethylene glycol; the amount of the pore-forming agent added is 3% of the total mass of the iron-molybdenum catalyst.

[0019] Preferably, in step (2), the drying temperature is 120-150°C and the drying time is 2-4 hours; the calcination temperature is 350-400°C and the calcination time is 4-6 hours.

[0020] Preferably, the molar ratio of molybdenum to iron in the iron-molybdenum catalyst is 1.2 to 2.5:1, and the ratio of the sum of the mass of the metal oxide and the molybdenum salt to the mass of the SiO2 support is 1:9 to 1:4.

[0021] More preferably, the molar ratio of molybdenum to iron in the iron-molybdenum catalyst is 1.6 to 1.9:1.

[0022] Preferably, in step (3), the molybdenum salt in the molybdenum salt solution is one or more of ammonium molybdate, sodium molybdate, lithium molybdate, and potassium molybdate; the concentration of the molybdenum salt solution is 0.01 to 10 g / ml.

[0023] More preferably, the molybdenum salt is sodium molybdate, and the concentration of the molybdenum salt solution is 0.5–5 g / ml.

[0024] Furthermore, the pH of the molybdenum salt solution was adjusted to 1.5–2 using nitric acid solution.

[0025] Preferably, in step (3), the impregnation temperature is 60-80°C; and the pH value of the impregnation is 1-2.5.

[0026] Furthermore, during the impregnation of the SiO2 support with the molybdenum salt solution, ultrasonic oscillation is used, with the power of the ultrasound being 50-100W, until the surface of the support is free of solution.

[0027] Preferably, in step (4), the drying temperature is 100-120°C and the drying time is 6-18 hours; the calcination temperature is 380-450°C and the calcination time is 6-8 hours.

[0028] This invention also provides an iron-molybdenum catalyst prepared by the above method, namely, the Fe2(MoO4)3-Mo2O3-NiO-CeO2-MnO\SiO2 catalyst. The catalyst of this invention has advantages such as low cost, strong catalytic activity, and good environmental performance.

[0029] This invention also provides the application of the above-mentioned iron-molybdenum catalyst in the catalytic oxidation of methanol to formaldehyde.

[0030] The catalyst was added to a tubular fixed-bed reactor with a feed gas inlet temperature of 200–260°C, and anhydrous methanol solution was added with a methanol feed liquid hourly space velocity of 0.6–1.2 h⁻¹. -1 The reaction is carried out by introducing air, with a reaction space velocity of 6000–12000 h⁻¹. -1 The reaction pressure is 0.2–0.6 MPa.

[0031] Beneficial effects:

[0032] (1) In this invention, the porous support and active material can be uniformly dispersed on the surface of the support, and the mass of active material per unit area is greatly reduced. The heat generated locally during the catalytic reaction is significantly reduced, the bed temperature during the reaction is significantly reduced, the sublimation of MoO3 is significantly reduced, and the catalyst becomes more stable. In addition, due to the uniform distribution of active material, the synergistic effect between them is also enhanced. In addition, the synergistic effect between them and the support results in a high conversion rate and yield in the catalytic reaction of methanol to formaldehyde, thereby effectively solving the technical problems of poor stability and low catalytic activity of existing iron-molybdenum catalysts.

[0033] (2) The catalyst preparation method of the present invention is simple, the catalyst has low cost, high stability and long life. It exhibits excellent catalytic activity and selectivity in the methanol oxidation to formaldehyde, effectively reducing industrial production costs. Moreover, it has green and environmentally friendly characteristics, thus possessing a strong competitive advantage. Detailed Implementation

[0034] The technical solution of the present invention will be described in detail below through specific embodiments, but the scope of protection of the present invention is not limited to the embodiments described.

[0035] Experimental Example 1: Preparation of an iron-molybdenum catalyst for the oxidation of methanol to formaldehyde

[0036] 1. Preparation of SiO2 support

[0037] (1) Weigh out 80g of iron oxide, 37.5g of nickel oxide, 34.4g of cerium oxide and 26.1g of manganese oxide respectively, and mix them evenly.

[0038] (2) Add 73g of polyethylene glycol and 5000g of 40% silica sol to the mixture obtained in step (1), stir it into a slurry by a high-speed shearing machine, put the slurry into an oven at 140°C and dry it for 4 hours; put the dried material into a muffle furnace and calcine it at 360°C for 5 hours; crush the calcined material and add 43.6g of magnesium stearate lubricant, and form it into sheets to obtain a porous carrier containing several metal oxides.

[0039] 2. Molybdate-impregnated silica carrier

[0040] A molybdenum salt solution containing 247.2g of sodium molybdate at a concentration of 2g / ml was prepared, and the pH value was adjusted to 1.5 with nitric acid and the temperature was raised to 90℃. The solution was then impregnated onto a silica support under ultrasonic oscillation at a power of 60W until there was no solution on the surface of the support. The precursor of the catalyst was obtained by drying at a temperature of 105℃ for 12 hours. The precursor of the catalyst was then calcined at a temperature of 380℃ for 8 hours to obtain the iron-molybdenum catalyst.

[0041] Experimental Example 2: Preparation of an iron-molybdenum catalyst for the oxidation of methanol to formaldehyde

[0042] 1. Preparation of SiO2 support

[0043] (1) Weigh out 80g of iron oxide, 37.5g of nickel oxide, 34.4g of cerium oxide and 26.1g of manganese oxide respectively, and mix them evenly.

[0044] (2) Add 88g of polyethylene glycol and 6000g of 40% silica sol to the mixture obtained in step (1), stir it into a slurry by a high-speed shearing machine, put the slurry into an oven at 120°C and dry it for 3 hours, put the dried material into a muffle furnace and calcine it at 400°C for 4 hours, crush the calcined material and add 51.6g of magnesium stearate lubricant, and form it into sheets to obtain a porous carrier containing several metal oxides.

[0045] 2. Molybdate-impregnated silica carrier

[0046] The prepared molybdenum salt solution containing 350.2g sodium molybdate with a concentration of 0.5g / ml was adjusted to pH 2 with nitric acid and heated to 80℃. The solution was then impregnated onto a silica support under ultrasonic oscillation at a power of 80W until no solution remained on the support surface. After drying at 120℃ for 6 hours, a catalyst precursor was obtained. The catalyst precursor was then calcined at 420℃ for 7 hours to obtain the iron-molybdenum catalyst.

[0047] Experimental Example 3: Preparation of an iron-molybdenum catalyst for the oxidation of methanol to formaldehyde

[0048] 1. Preparation of SiO2 support

[0049] (1) Weigh out 80g, 37.5g, 34.4g and 26.1g of iron oxide, nickel oxide, cerium oxide and manganese oxide respectively, and mix them evenly.

[0050] (2) Add 102g of polyethylene glycol and 7500g of 40% silica sol to the mixture obtained in step (1). Stir the mixture into a slurry using a high-speed shearing machine. Place the slurry in an oven at 150°C and dry for 2 hours. Place the dried material in a muffle furnace and calcine at 350°C for 6 hours. Crush the calcined material and add 63.5g of magnesium stearate as a lubricant. Form the material into sheets to obtain a porous carrier containing several metal oxides.

[0051] 2. Molybdate-impregnated silica carrier

[0052] The prepared molybdenum salt solution containing 350.2 g of sodium molybdate at a concentration of 5 g / ml was adjusted to pH 1.5 with nitric acid and heated to 60°C. The solution was then impregnated onto a silica support under ultrasonic oscillation at a power of 90 W until no solution remained on the support surface. After drying at 100°C for 18 h, the precursor of the catalyst was obtained. The catalyst precursor was then calcined at 450°C for 6 h to obtain the iron-molybdenum catalyst.

[0053] Example 4: Preparation of an iron-molybdenum catalyst for the oxidation of methanol to formaldehyde

[0054] 1. Preparation of SiO2 support

[0055] (1) Weigh out 80g, 37.5g, 34.4g and 26.1g of iron oxide, nickel oxide, cerium oxide and manganese oxide respectively, and mix them evenly.

[0056] (2) Add 64g of polyethylene glycol and 4000g of 40% silica sol to the mixture obtained in step (1), stir it into a slurry by a high-speed shearing machine, put the slurry into an oven at 140°C and dry it for 3 hours; put the dried material into a muffle furnace and calcine it at 360°C for 5 hours; crush the calcined material and add 35.6g of magnesium stearate lubricant, and form it into sheets to obtain a porous carrier containing several metal oxides.

[0057] 2. Molybdate-impregnated silica carrier

[0058] The prepared molybdenum salt solution containing 350.2 g of sodium molybdate at a concentration of 2 g / ml was adjusted to pH 2 with nitric acid and heated to 80°C. The solution was then impregnated onto a silica support under ultrasonic oscillation at a power of 80 W until no solution remained on the support surface. After drying at 105°C for 12 h, the precursor of the catalyst was obtained. The catalyst precursor was then calcined at 420°C for 7 h to obtain the iron-molybdenum catalyst.

[0059] Example 5: Preparation of an iron-molybdenum catalyst for the oxidation of methanol to formaldehyde

[0060] 1. Preparation of SiO2 support

[0061] (1) Weigh out 80g, 37.5g, 34.4g and 26.1g of iron oxide, nickel oxide, cerium oxide and manganese oxide respectively, and mix them evenly.

[0062] (2) Add 111g of polyethylene glycol and 7500g of 40% silica sol to the mixture obtained in step (1). Stir the mixture into a slurry using a high-speed shearing machine. Place the slurry in an oven and dry it at 150°C for 2 hours. Place the dried material in a muffle furnace and calcine it at 400°C for 4 hours. Crush the calcined material and add 63.5g of magnesium stearate as a lubricant. Shape the material into sheets to obtain a porous carrier containing several metal oxides.

[0063] 2. Molybdate-impregnated silica carrier

[0064] The prepared sodium molybdate solution (515g, 0.5g / ml) was adjusted to pH 1.5 with nitric acid and heated to 80℃. The solution was then impregnated onto a silica support under ultrasonic oscillation at 80W until no solution remained on the support surface. After drying at 120℃ for 8 hours, the catalyst precursor was obtained. The catalyst precursor was then calcined at 380℃ for 9 hours to obtain the iron-molybdenum catalyst.

[0065] Experimental Example 6: Preparation of an iron-molybdenum catalyst for the oxidation of methanol to formaldehyde

[0066] 1. Preparation of SiO2 support

[0067] (1) Weigh out 80g, 37.5g, 34.4g and 43.5g of iron oxide, nickel oxide, cerium oxide and manganese oxide respectively, and mix them evenly.

[0068] (2) Add 88g of polyethylene glycol and 6000g of 40% silica sol to the mixture obtained in step (1), stir it into a slurry by a high-speed shearing machine, put the slurry into an oven and dry it at 120°C for 4 hours; put the dried material into a muffle furnace and calcine it at 350°C for 6 hours; crush the calcined material and add 51.9g of magnesium stearate lubricant, and form it into sheets to obtain a porous carrier containing several metal oxides.

[0069] 2. Molybdate-impregnated silica carrier

[0070] The prepared molybdenum salt solution containing 350.2g of sodium molybdate with a concentration of 2g / ml was adjusted to pH 2 with nitric acid and heated to 90℃. The solution was then impregnated onto a silica support under ultrasonic oscillation at a power of 60W until no solution remained on the support surface. After drying at 105℃ for 12 hours, the precursor of the catalyst was obtained. The catalyst precursor was then calcined at 420℃ for 7 hours to obtain the iron-molybdenum catalyst.

[0071] Experimental Example 7: Preparation of an iron-molybdenum catalyst for the oxidation of methanol to formaldehyde

[0072] 1. Preparation of SiO2 support

[0073] (1) Weigh out 80g of iron oxide, 37.5g of nickel oxide and 34.4g of cerium oxide respectively, and mix them evenly.

[0074] (2) Add 87g of polyethylene glycol and 6000g of 40% silica sol to the mixture obtained in step (1). Stir the mixture into a slurry using a high-speed shearing machine. Place the slurry in an oven and dry it at 150°C for 2 hours. Place the dried material in a muffle furnace and calcine it at 360°C for 5 hours. Crush the calcined material and add 51g of magnesium stearate as a lubricant. Shape the material into sheets to obtain a porous carrier containing several metal oxides.

[0075] 2. Molybdate-impregnated silica carrier

[0076] The prepared molybdenum salt solution containing 350.2g of sodium molybdate (5g / ml) was adjusted to pH 1.5 with nitric acid and heated to 60℃. The solution was then impregnated onto a silica support under ultrasonic oscillation at 90W until no solution remained on the support surface. After drying at 100℃ for 18 hours, the precursor of the catalyst was obtained. The catalyst precursor was then calcined at 450℃ for 6 hours to obtain the iron-molybdenum catalyst.

[0077] Experimental Example 8: Preparation of an iron-molybdenum catalyst for the oxidation of methanol to formaldehyde

[0078] 1. Preparation of SiO2 support

[0079] (1) Weigh out 80g, 22.5g, 34.4g and 26.1g of iron oxide, nickel oxide, cerium oxide and manganese oxide respectively, and mix them evenly.

[0080] (2) Add 87g of polyethylene glycol and 6000g of 40% silica sol to the mixture obtained in step (1), stir it into a slurry by high-speed shearing machine, put the slurry into an oven and dry it at 140°C for 3 hours; put the dried material into a muffle furnace and calcine it at 400°C for 4 hours; crush the calcined material and add 51.3g of magnesium stearate lubricant, and form it into sheets to obtain a porous carrier containing several metal oxides.

[0081] 2. Molybdate-impregnated silica carrier

[0082] The prepared molybdenum salt solution containing 350.2g of sodium molybdate with a concentration of 2g / ml was adjusted to pH 2 with nitric acid and heated to 80℃. The solution was then impregnated onto a silica support under ultrasonic oscillation at a power of 80W until no solution remained on the support surface. After drying at 105℃ for 12 hours, the precursor of the catalyst was obtained. The catalyst precursor was then calcined at 420℃ for 7 hours to obtain the iron-molybdenum catalyst.

[0083] Example 9: Preparation of an iron-molybdenum catalyst for the oxidation of methanol to formaldehyde

[0084] 1. Preparation of SiO2 support

[0085] (1) Weigh out 80g, 37.5g, 17.2g and 26.1g of iron oxide, nickel oxide, cerium oxide and manganese oxide respectively, and mix them evenly.

[0086] (2) Add 87g of polyethylene glycol and 6000g of 40% silica sol to the mixture obtained in step (1), stir it into a slurry by a high-speed shearing machine, put the slurry into an oven and dry it at 120°C for 4 hours; put the dried material into a muffle furnace and calcine it at 360°C for 5 hours; crush the calcined material and add 51.2g of magnesium stearate lubricant, and form it into sheets to obtain a porous carrier containing several metal oxides.

[0087] 2. Molybdate-impregnated silica carrier

[0088] A prepared molybdenum salt solution containing 350.2g of sodium molybdate with a concentration of 0.5g / ml was adjusted to pH 1.5 with nitric acid and heated to 90℃. The solution was then impregnated onto a silica support under ultrasonic oscillation at a power of 60W until no solution remained on the support surface. After drying at 120℃ for 8 hours, a catalyst precursor was obtained. The catalyst precursor was then calcined at 380℃ for 8 hours to obtain the iron-molybdenum catalyst.

[0089] Example 10: Preparation of an iron-molybdenum catalyst for the oxidation of methanol to formaldehyde

[0090] 1. Preparation of SiO2 support

[0091] (1) Weigh out 80g, 22.5g, 34.4g and 43.5g of iron oxide, nickel oxide, cerium oxide and manganese oxide respectively, and mix them evenly.

[0092] (2) Add 87g of polyethylene glycol and 6000g of 40% silica sol to the mixture obtained in step (1), stir it into a slurry by high-speed shearing machine, put the slurry into an oven and dry it at 150°C for 2 hours; put the dried material into a muffle furnace and calcine it at 350°C for 6 hours; crush the calcined material and add 51.6g of magnesium stearate lubricant, and form it into sheets to obtain a porous carrier containing several metal oxides.

[0093] 2. Molybdate-impregnated silica carrier

[0094] The prepared molybdenum salt solution containing 350.2g of sodium molybdate with a concentration of 2g / ml was adjusted to pH 2 with nitric acid and heated to 60℃. The solution was then impregnated onto a silica support under ultrasonic oscillation at a power of 90W until no solution remained on the support surface. After drying at 105℃ for 12 hours, the precursor of the catalyst was obtained. The catalyst precursor was then calcined at 450℃ for 6 hours to obtain the iron-molybdenum catalyst.

[0095] Comparative Example 1

[0096] 1. Preparation of SiO2 support

[0097] (1) Weigh out 80g of iron oxide, 37.5g of nickel oxide, 34.4g of cerium oxide and 26.1g of manganese oxide respectively, and mix them evenly.

[0098] (2) Add 6000g of 40% silica sol to the mixture obtained in step (1), stir it into a slurry by a high-speed shearing machine, put the slurry into an oven at 140°C and dry it for 3 hours; put the dried material into a muffle furnace and calcine it at 360°C for 5 hours; crush the calcined material and add 51.6g of magnesium stearate lubricant, and form it into sheets to obtain a porous carrier containing several metal oxides.

[0099] 2. Molybdate-impregnated silica carrier

[0100] The prepared molybdenum salt solution containing 350.2g sodium molybdate at a concentration of 5g / ml was adjusted to pH 1.5 with nitric acid and heated to 80℃. The solution was then impregnated onto a silica support under ultrasonic oscillation at a power of 80W until no solution remained on the support surface. After drying at 100℃ for 18 hours, the precursor of the catalyst was obtained. The catalyst precursor was then calcined at 420℃ for 7 hours to obtain the iron-molybdenum catalyst.

[0101] Application example:

[0102] The catalysts prepared in the examples and comparative examples, with an initial particle size of 30 ml, were evaluated for activity in a tubular fixed-bed reactor. The feed gas inlet temperature was 235°C, and anhydrous methanol solution was added. The methanol feed liquid hourly space velocity was 1.0 h⁻¹. -1 The reaction is carried out by introducing air, and the reaction space velocity is 10000 h⁻¹. -1 The reaction pressure was 0.3 MPa, and the products were analyzed by online chromatography. The results are shown in Table 1.

[0103] Table 1. Experimental results of catalysts in the examples and comparative examples.

[0104] Methanol conversion rate (%) Formaldehyde yield (%) Example 1 91.5 90.1 Example 2 98.1 97.2 Example 3 97.0 95.8 Example 4 97.2 95.6 Example 5 96.8 95.4 Example 6 98.3. 96.5 Example 7 95.6 94.2 Example 8 96.5 95.8 Example 9 96.7 95.6 Example 10 99.4 96.2 Comparative Example 1 86.2 85.3

[0105] As described above, although the invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the invention itself. Various changes in form and detail may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A process for the preparation of an iron-molybdenum catalyst for the oxidation of methanol to formaldehyde, characterized in that Includes the following steps: (1) Mix the metal oxides evenly; (2) Add silica sol and pore-forming agent to mix into a paste, continue stirring into a slurry, dry, calcine, pulverize the slurry, add lubricant, and then form into a sheet to obtain a porous SiO2 carrier. (3) The molybdenum salt solution is impregnated onto the porous SiO2 support obtained in step (2) to obtain the precursor of the iron-molybdenum catalyst; (4) The precursor obtained in step (3) is dried and calcined at high temperature to obtain the iron-molybdenum catalyst.

2. The production method according to claim 1, characterized by, In step (1), the metal oxide is Fe2O3, NiO, CeO2, MnO2 or Fe2O3, NiO, CeO2; wherein the molar ratio of manganese to iron is 0.2 to 0.8:1; the molar ratio of nickel to iron is 0.2 to 0.6:1; and the molar ratio of cerium to iron is 0.1 to 0.3:

1.

3. The preparation method according to claim 1, characterized in that, In step (2), the silica sol is a 40% SiO2 solution; the pore-forming agent is one or more of polyethylene glycol, polyvinyl alcohol, and hydroxypropyl cellulose; the amount of pore-forming agent added is 2% to 4% of the mass of the iron-molybdenum catalyst; and the lubricant is one or more of stearic acid, magnesium stearate, zinc stearate, and graphite.

4. The method of claim 1, wherein, In step (2), the drying temperature is 120-150℃ and the drying time is 2-4h; the calcination temperature is 350-400℃ and the calcination time is 4-6h.

5. The preparation method according to claim 1, characterized in that, The molar ratio of molybdenum to iron in the iron-molybdenum catalyst is 1.2 to 2.5:1, and the ratio of the total mass of the metal oxide and molybdenum salt to the mass of the SiO2 support is 1:9 to 1:

4.

6. The method of claim 1, wherein, In step (3), the molybdenum salt in the molybdenum salt solution is one or more of ammonium molybdate, sodium molybdate, lithium molybdate, and potassium molybdate; the concentration of the molybdenum salt solution is 0.01 to 10 g / mL.

7. The preparation method according to claim 1, characterized in that, In step (3), the immersion temperature is 60-80°C; the immersion acidity pH value is 1-2.

5.

8. The method of claim 1, wherein, In step (4), the drying temperature is 100-120℃ and the drying time is 6-18h; the calcination temperature is 380-450℃ and the calcination time is 6-8h.

9. An iron-molybdenum catalyst prepared by the preparation method according to any one of claims 1-8, namely, Fe2(MoO4)3-Mo2O3-NiO-CeO2-MnO\SiO2 catalyst.

10. The application of the iron-molybdenum catalyst of claim 9 in the catalytic oxidation of methanol to formaldehyde.

11. The application according to claim 10, characterized in that, The catalyst of claim 9 is added to a fixed bed reactor, the inlet temperature of the raw material gas is 200-260℃, and anhydrous methanol solution is added, the space velocity of the methanol feed liquid is 0.6-1.2h -1 , air is introduced to carry out the reaction, the reaction space velocity is 6000-12000h -1 , and the reaction pressure is 0.2-0.6MPa.