Formaldehyde catalyst as well as preparation method and application thereof

Abstract

The invention relates to a formaldehyde catalyst as well as a preparation method and application thereof. The catalyst is prepared by adopting an impregnation method, by adding monopotassium phosphate and adopting an ultrasonic heating mode, the problem that the molybdenum element of the catalyst is lost along with the prolonging of the reaction time in the conventional process method can be effectively solved, meanwhile, the activity and stability of the catalyst are improved, and the service life of the catalyst is prolonged.

Description

Technical Field

[0001] This invention relates to the field of catalyst preparation, specifically to a formaldehyde catalyst, its preparation method, and its application. Background Technology

[0002] Formaldehyde is an important basic organic chemical raw material, playing a crucial role in adjusting the future energy structure and developing the chemical industry. Currently, my country has become the world's largest producer and consumer of formaldehyde, with domestic demand exceeding 2800 × 10⁻⁶ tons by 2022. 4 Formaldehyde, in quantities exceeding one ton, can be produced from raw materials such as methanol, dimethyl ether, and natural gas, with methanol-to-formaldehyde technology being the most widely used. The methanol-to-air oxidation method is further divided into the silver method and the iron-molybdenum method. Compared to the silver method, the iron-molybdenum method has a lower reaction temperature, resulting in a higher formaldehyde concentration and advantages in cost and yield. Currently, there are many publicly disclosed patents for iron-molybdenum catalysts for formaldehyde production. For example, US4420421A describes using different raw materials, such as sodium molybdate, to achieve a methanol conversion rate of 93%–95% and a selectivity of 92%. Patent CN105457648B prepared a catalyst containing a large number of mesopores and a certain proportion of macropores through co-precipitation, which is beneficial for mass and heat transfer and improves catalyst activity. CN110893344B uses metallic iron, organic acids, and molybdic acid as raw materials, and prepares an iron-molybdenum catalyst through co-precipitation with byproduct hydrogen, achieving efficient methanol conversion at 200–350℃. However, its formaldehyde space-time yield is low when the inlet methanol concentration is low.

[0003] However, existing iron-molybdenum catalysts exhibit varying degrees of deactivation over time, affecting their activity and lifespan. The primary cause of deactivation is the loss of molybdenum, leading to reduced activity and accompanied by deep oxidation reactions that generate CO and CO2, thus decreasing catalyst selectivity. While existing technologies improve catalyst activity and selectivity by adding additives, they do not fundamentally address the catalyst lifespan issue. Summary of the Invention

[0004] This invention provides a method for preparing a formaldehyde catalyst and its application. The catalyst prepared by this invention can effectively solve the problem of molybdenum loss in the catalyst in previous processes, while improving the activity and stability of the catalyst and extending its lifespan.

[0005] To solve the above technical problems, the present invention adopts the following technical solution:

[0006] Firstly, a method for preparing a formaldehyde catalyst includes the following steps:

[0007] a) Co-precipitate aqueous solutions containing molybdenum compounds, cerium compounds, and iron compounds;

[0008] b) After co-precipitation, the filter cake is aged, filtered and washed to obtain a filter cake, which is then dried.

[0009] c) The filter cake is immersed in potassium dihydrogen phosphate solution and subjected to ultrasonic heating treatment. Then the filter cake is dried, shaped, and calcined to obtain formaldehyde catalyst.

[0010] In this invention, the molybdenum-containing compound in step a) is one or more of ammonium polymolybdate, molybdenum trioxide, molybdic acid, and molybdenum disulfide, preferably ammonium polymolybdate, such as ammonium heptamolybdate or ammonium molybdate tetrahydrate; the cerium-containing compound is cerium nitrate; and the iron-containing compound is one or more of ferric chloride, ferric nitrate, iron oxide, and iron powder, preferably ferric chloride or ferric nitrate.

[0011] In this invention, in step a), the pH is controlled at 1-3, preferably 1.5-2.8, and the temperature is controlled at 50-100℃ for a co-precipitation reaction for 3-5 hours.

[0012] In this invention, the molar ratio of molybdenum / iron / cerium in the molybdenum-containing compound, iron-containing compound, and cerium-containing compound in step a) is (0.4-1.35):1:(0.1-0.8); there are no requirements for the concentration of the aqueous solution of the molybdenum-containing compound, cerium-containing compound, and iron-containing compound.

[0013] In this invention, the aging temperature in step b) is 50-100℃ and the time is 24-48h; the drying temperature is 100-130℃ and the time is 6-24h.

[0014] In this invention, the concentration of the potassium dihydrogen phosphate solution in step c) is 0.1-2 mol / L. The molar ratio of phosphorus in the potassium dihydrogen phosphate to iron in the iron-containing compound is (0.1-2):1.

[0015] In this invention, in step c), the frequency range of the ultrasonic waves used in the ultrasonic treatment is 30kHz to 50kHz, the heating temperature is controlled at 30 to 80℃, and the treatment time is 3 to 5 hours.

[0016] This invention modifies iron-molybdenum through ion doping to create lattice defects, thereby reducing molybdenum ion loss efficiency. Molybdenum (Mo) and iron (Fe) are located at the opposing sites of oxygen (O) octahedra, forming deformed MoO6 and FeO6 octahedra; phosphorus (P) atoms are located at the longitudinal sites of oxygen (O) tetrahedra, forming PO4 tetrahedra. Ultrasonic heating connects the FeO6 octahedra through shared vertices, forming a Z-shaped FeO6 octahedral layer. Adjacent molybdenum oxide atoms in the FeO6 octahedral layers are directly connected along the longitudinal axis through shared edges, forming a molybdenum-phosphorus-iron structure and maintaining parallelism, allowing hydrogen ions to move in a two-dimensional direction. Because the PO4 tetrahedra are located between the FeO6 layers, they block the oxygen diffusion channels, preventing molybdenum ions from embedding and detaching within one-dimensional channels, thus reducing the risk of molybdenum precipitation.

[0017] In this invention, in step c), the filter cake is dried at 50℃~100℃ for 10~28 hours, and then dried at 100℃~150℃ for 15h~30h to obtain catalyst powder; the calcination temperature is 450-540℃, and the calcination time is 5~20h.

[0018] In this invention, the molding method in step c) includes, but is not limited to, extrusion, tableting, rolling, etc., and the shape of the resulting molded catalyst includes, but is not limited to, strip, cylindrical, hollow cylindrical, spherical particles, etc.

[0019] The suitable extrusion molding method of the present invention includes the following steps: adding a pore-forming agent and a binder to the catalyst powder and then extruding it to obtain strip-shaped particles.

[0020] In the extrusion molding method of the present invention, the pore-forming agent used is one or more of guar gum powder, cellulose, hydroxymethyl cellulose, and polyvinyl alcohol, preferably one or more of guar gum powder, cellulose, and hydroxymethyl cellulose. The amount of the pore-forming agent is 1% to 6% of the mass of the catalyst powder. The binder used is one or more of water, glycerol, ethanol, graphite, stearic acid, magnesium stearate, and zinc stearate, preferably one or more of water, glycerol, graphite, and magnesium stearate. The amount of the binder is 8% to 15% of the mass of the catalyst powder.

[0021] The suitable tableting method of the present invention includes the following steps: adding a pore-forming agent and a lubricant to the catalyst powder and then pressing it into tablets to obtain cylindrical or hollow cylindrical particles.

[0022] In the tableting method of the present invention, the pore-forming agent used is one or more of guar gum powder, cellulose, polyethylene, polypropylene, and polyvinyl chloride, preferably guar gum powder and / or cellulose, and the amount of the pore-forming agent is 1% to 5% of the mass of the catalyst powder.

[0023] The lubricant used is one or more of stearic acid, magnesium stearate, zinc stearate, and graphite, preferably one or more of magnesium stearate, zinc stearate, and graphite, and the amount of the lubricant used is 0.1% to 1% of the mass of the catalyst powder.

[0024] The suitable rolling molding method of the present invention includes the following steps: adding a pore-forming agent and a binder to the catalyst powder, and rolling it with a spherical carrier.

[0025] In the rolling molding method of the present invention, the pore-forming agent used is one or more of guar gum powder, cellulose, polyvinyl alcohol, polyvinylpyrrolidone, starch, pullulan, preferably one or more of guar gum powder, polyvinylpyrrolidone, and starch, and the amount of the pore-forming agent is 1% to 5% of the mass of the catalyst powder.

[0026] The binder used is one or more of water, ethanol, ethylene glycol, and glycerol, preferably one or more of water, ethanol, and glycerol. The amount of the binder is 20% to 35% of the catalyst powder. The spherical support is preferably a porous alumina support with a diameter of 2.3 to 3.5 mm, and the amount used is 50% to 70% of the mass of the catalyst powder.

[0027] Secondly, the present invention provides a formaldehyde catalyst prepared by the above preparation method, which comprises an iron-containing compound, a molybdenum-containing compound, a phosphorus-containing compound, and a cerium-containing compound, wherein the molar ratio of molybdenum / iron / phosphorus / cerium is 0.4-1.35:1:0.1-0.8:0.1-2;

[0028] In a third aspect, the present invention provides the application of the above-mentioned formaldehyde catalyst in the preparation of formaldehyde by methanol oxidation, wherein methanol and oxygen are oxidized under the conditions of a formaldehyde catalyst to prepare formaldehyde.

[0029] Preferably, the catalyst is pretreated before use; the pretreatment includes the following steps: the catalyst is heated at a volume hourly space velocity (VHSV) of 5000–10000 h⁻¹. -1 In an air or O2 / N2 mixed gas atmosphere, the temperature is raised to 200–400°C at a heating rate of 1–20°C / min and held for 30–180 min, then subjected to a volume hourly space velocity (VHSV) of 2000 h⁻¹. -1 Purge with N2 for 1–180 min.

[0030] Preferably, the reaction temperature for the methanol oxidation method to prepare formaldehyde is 320–420℃; the reaction pressure is 0.05–0.3 MPa absolute; and the gaseous feedstock volume hourly space velocity is 7000–12000 h⁻¹. -1The gaseous raw materials include methanol, dilution gas, and O2, wherein the dilution gas is an inert gas, preferably N2. The molar ratio of methanol to oxygen is 1:0.5-4, and the molar ratio of methanol to dilution gas is 1:7-12. Preferably, the amount of formaldehyde catalyst used is 20g-150g.

[0031] Preferably, the methanol catalyst is pretreated before use; preferably, the pretreatment includes the following steps: the catalyst is heated at a volume hourly space velocity (VHSV) of 5000–10000 h⁻¹. -1 In an air or O2 / N2 mixed gas atmosphere, the temperature is raised to 200–400°C at a heating rate of 1–20°C / min and held for 30–180 min, then heated with a volume hourly space velocity of 1000–2000 h⁻¹. -1 Purge with N2 for 1–180 min.

[0032] Compared with the prior art, the present invention has the following technical effects:

[0033] This invention modifies iron-molybdenum by ion doping to create lattice defects, reducing the molybdenum ion loss efficiency. This allows the catalyst to maintain high activity and selectivity for a long time without the need for additional catalyst additives, thus extending the catalyst's lifespan. Detailed Implementation

[0034] The technical solution of the present invention will be further described below through examples, but it is not limited thereto.

[0035] Unless otherwise specified, all equipment and raw materials used in this invention are commercially available.

[0036] Ultrasonic instrument: Meritek Technology, model UC-6200.

[0037] Elemental analysis: Agilent 5800ICP-OES inductively coupled plasma atomic emission spectrometer.

[0038] Example 1

[0039] 0.06 mol ammonium heptamolybdate, 1 mol ferric chloride hexahydrate, and 0.1 mol cerium nitrate were dissolved in 1000 g of deionized water and stirred thoroughly. All materials were then added concurrently to a reaction vessel, maintaining the solution temperature at 90°C and adjusting the pH to 2.0 for co-precipitation for 3 hours, followed by stirring and aging for 20 hours. The mixture was filtered, washed, and dried at 100°C for 8 hours, then at 120°C for 10 hours. The resulting solid was a blocky material. The dried filter cake was immersed in 1 L of 0.1 mol / L potassium dihydrogen phosphate solution and ultrasonically treated (40 kHz, 30°C) for 5 hours. After ultrasonic treatment, it was dried in situ at 90°C for 24 hours, then at 120°C for 20 hours. The resulting solid was crushed to obtain 30–60 mesh particles. 50 g of these 30–60 mesh particles were mixed with 2.5 g of pore-forming agent (guar gum powder) and 0.5 g of lubricant (graphite), and then shaped into hollow cylindrical particles using a tablet press. The shaped particles were calcined at 460℃ for 5 hours to obtain the catalyst, with a molybdenum-iron ratio of 0.42.

[0040] Example 2

[0041] 0.14 mol ammonium heptamolybdate, 1 mol ferric chloride hexahydrate, and 0.4 mol cerium nitrate were dissolved in 1000 g of deionized water and stirred thoroughly. All materials were then added concurrently to a reaction vessel, maintaining the solution temperature at 80°C and adjusting the pH to 2.0 for co-precipitation for 3 hours, followed by stirring and aging for 20 hours. The mixture was filtered, washed, and dried at 100°C for 8 hours, then at 120°C for 10 hours. The resulting solid was a blocky substance. The dried filter cake was immersed in 1 L of 1 mol / L potassium dihydrogen phosphate solution and ultrasonically treated (40 kHz, 30°C) for 2 hours. After ultrasonication, it was dried in situ at 90°C for 24 hours, then at 120°C for 20 hours. The resulting solid was crushed to obtain 30–60 mesh particles. 50 g of these 30–60 mesh particles were mixed with 2.5 g of pore-forming agent (guar gum powder) and 0.5 g of lubricant (graphite), and then shaped into hollow cylindrical particles using a tablet press. The shaped particles were calcined at 460℃ for 5 hours to obtain the catalyst, with a molybdenum-iron ratio of 0.98.

[0042] Example 3

[0043] 0.19 mol ammonium heptamolybdate, 1 mol ferric chloride hexahydrate, and 0.8 mol cerium nitrate were dissolved in 1000 g of deionized water and stirred thoroughly. All materials were then added concurrently to a reaction vessel, maintaining the solution temperature at 90°C and adjusting the pH to 2.0 for co-precipitation for 4 hours, followed by stirring and aging for 20 hours. The mixture was filtered, washed, and dried at 100°C for 8 hours, then at 120°C for 10 hours. The resulting solid was a blocky substance. The dried filter cake was immersed in 1 L of 2 mol / L potassium dihydrogen phosphate solution and ultrasonically treated (40 kHz, 30°C) for 5 hours. After ultrasonication, it was dried at 90°C for 24 hours, then at 120°C for 20 hours. The resulting solid was crushed to obtain 30–60 mesh particles. 50 g of these 30–60 mesh particles were mixed with 2.5 g of pore-forming agent (guar gum powder) and 0.5 g of lubricant (graphite), and then shaped into hollow cylindrical particles using a tablet press. The shaped particles were calcined at 460℃ for 5 hours to obtain the catalyst, with a molybdenum-iron ratio of 1.33.

[0044] Example 4

[0045] 0.07 mol ammonium heptamolybdate, 1 mol ferric chloride hexahydrate, and 0.2 mol cerium nitrate were dissolved in 1000 g of deionized water and stirred thoroughly. All materials were then added concurrently to a reaction vessel, maintaining the solution temperature at 90°C and adjusting the pH to 2.0 for co-precipitation for 3 hours, followed by stirring and aging for 20 hours. The mixture was filtered, washed, and dried at 100°C for 8 hours, then at 120°C for 10 hours. The resulting solid was a blocky substance. The dried filter cake was immersed in 1 L of 0.5 mol / L potassium dihydrogen phosphate solution and ultrasonically treated (30 kHz, 35°C) for 4 hours. After ultrasonic treatment, it was dried at 90°C for 24 hours, then at 120°C for 20 hours. The resulting solid was crushed to obtain 30–60 mesh particles. 50 g of these 30–60 mesh particles were mixed with 2.5 g of pore-forming agent (guar gum powder) and 0.5 g of lubricant (graphite), and then shaped into hollow cylindrical particles using a tablet press. The shaped particles were calcined at 460℃ for 5 hours to obtain the catalyst, with a molybdenum-iron ratio of 0.49.

[0046] Comparative Example 1

[0047] 0.06 mol ammonium heptamolybdate, 1 mol ferric chloride hexahydrate, and 0.1 mol cerium nitrate were dissolved in 1000 g of deionized water and stirred thoroughly. All materials were then added concurrently to a reaction vessel, maintaining the solution temperature at 90°C and adjusting the pH to 2.0 for co-precipitation for 3 hours, followed by stirring and aging for 20 hours. The mixture was filtered, washed, dried at 100°C for 8 hours, and then dried at 120°C for 10 hours. The resulting solid was crushed to obtain 30–60 mesh particles. 50 g of these 30–60 mesh particles were mixed with 2.5 g of pore-forming agent (guar gum powder) and 0.5 g of lubricant (graphite), and then shaped into hollow cylindrical particles using a tablet press. The shaped particles were calcined at 460°C for 5 hours to obtain a catalyst with a molybdenum-to-iron ratio of 0.42.

[0048] Comparative Example 2

[0049] 0.06 mol ammonium heptamolybdate, 1 mol ferric chloride hexahydrate, and 0.1 mol cerium nitrate were dissolved in 1000 g of deionized water and stirred thoroughly. All materials were then added concurrently to a reaction vessel, maintaining the solution temperature at 90°C and adjusting the pH to 2.0 for co-precipitation for 3 hours, followed by stirring and aging for 20 hours. The mixture was filtered, washed, and dried at 100°C for 8 hours, then at 120°C for 10 hours. The resulting solid was a blocky material. The dried filter cake was then immersed in an aqueous solution and ultrasonically treated (40 kHz, 30°C) for 5 hours. After ultrasonic treatment, it was dried at 90°C for 24 hours, then at 120°C for 20 hours. The resulting solid was crushed to obtain 30–60 mesh particles. 50 g of these 30–60 mesh particles were mixed with 2.5 g of pore-forming agent (guar gum powder) and 0.5 g of lubricant (graphite), and then shaped into hollow cylindrical particles using a tablet press. The shaped particles were calcined at 460℃ for 5 hours to obtain the catalyst, with a molybdenum-iron ratio of 0.42.

[0050] Comparative Example 3

[0051] 0.06 mol ammonium heptamolybdate, 1 mol ferric chloride hexahydrate, and 0.1 mol cerium nitrate were dissolved in 1000 g of deionized water and stirred thoroughly. All materials were then added concurrently to a reaction vessel, maintaining the solution temperature at 90°C and adjusting the pH to 2.0 for co-precipitation for 3 hours, followed by stirring and aging for 20 hours. The mixture was filtered, washed, dried at 100°C for 8 hours, and then dried at 120°C for 10 hours. The resulting solid was a blocky substance. The dried filter cake was immersed in 1 L of 0.1 mol / L potassium dihydrogen phosphate solution, then dried in situ at 90°C for 24 hours, followed by drying at 120°C for 20 hours. The resulting solid was crushed to obtain 30–60 mesh particles. 50 g of these 30–60 mesh particles were mixed with 2.5 g of pore-forming agent (guar gum powder) and 0.5 g of lubricant (graphite), and then shaped into hollow cylindrical particles using a tablet press. The shaped particles were calcined at 460℃ for 5 hours to obtain a catalyst with a molybdenum-iron ratio of 0.42 and phosphorus.

[0052] Comparative Example 4

[0053] 0.06 mol ammonium heptamolybdate, 1 mol ferric chloride hexahydrate, and 0.1 mol cerium nitrate were dissolved in 1000 g of deionized water and stirred thoroughly. All materials were then added concurrently to a reaction vessel, maintaining the solution temperature at 90°C and adjusting the pH to 2.0 for co-precipitation. The mixture was stirred and aged for 20 h. After filtration and washing, the mixture was dried in situ at 100°C for 8 h, followed by drying at 120°C for 10 h. The resulting solid was a blocky substance. The dried filter cake was immersed in 1 L of 0.1 mol / L potassium dihydrogen phosphate solution and ultrasonically treated (40 kHz, 30°C) for 1 h. After ultrasonic treatment, it was dried at 90°C for 24 h, followed by drying at 120°C for 20 h. The resulting solid was crushed to obtain 30–60 mesh particles. 50 g of these 30–60 mesh particles were taken, and 2.5 g of pore-forming agent (guar gum powder) and 0.5 g of lubricant (graphite) were added and mixed thoroughly. The mixture was then pressed into hollow cylindrical particles using a tablet press. The shaped particles were calcined at 460℃ for 5 hours to obtain the catalyst, with a molybdenum-iron ratio of 0.42.

[0054] Application examples

[0055] 25g of the prepared catalyst was loaded into a 50cm long reactor, the reaction tube being a Ф25mm stainless steel tube. The catalyst pretreatment process was as follows: air was first introduced at a volume hourly space velocity (VHSV) of 8000h. -1 The reaction tube temperature was heated from room temperature to 250°C at a rate of 5°C / min and held for 120 min, then purged with nitrogen for 180 min at a volume hourly space velocity (VHSV) of 2000 h⁻¹. -1 After catalyst pretreatment, the mixture was prepared at a methanol:oxygen:nitrogen:water ratio of 1:1.3:10:0.13 (molar ratio) and a volume hourly space velocity (VHSV) of 10000 h⁻¹. -1The oxidation reaction was carried out under standard conditions, at a temperature of 380°C and at atmospheric pressure. The test results of each example and comparative example are shown in the table below.

[0056]

[0057]

[0058] As can be seen from the comparison between Example 1 and Comparative Examples 1-4, this catalyst can effectively solve the problem of molybdenum loss during the reaction process in previous processes, while improving the activity and stability of the catalyst and extending its lifespan.

Claims

1. A formaldehyde catalyst, characterized in that, It includes iron-containing compounds, molybdenum-containing compounds, phosphorus-containing compounds, and cerium-containing compounds; wherein the molar ratio of molybdenum / iron / phosphorus / cerium is 0.4~1.35:1:0.1~2:0.1~0.

8.

2. A method for preparing a formaldehyde catalyst, characterized in that, Includes the following steps: a) Co-precipitate aqueous solutions containing molybdenum compounds, cerium compounds, and iron compounds; b) After co-precipitation, the filter cake is aged, filtered, washed, and dried. c) The filter cake is immersed in potassium dihydrogen phosphate solution and subjected to ultrasonic heating treatment. Then the filter cake is dried, shaped, and calcined to obtain formaldehyde catalyst.

3. The preparation method according to claim 2, characterized in that, In step a), the molybdenum-containing compound is one or more of ammonium polymolybdate, molybdenum trioxide, molybdic acid, and molybdenum disulfide, preferably ammonium polymolybdate, more preferably ammonium heptamolybdate or ammonium molybdate tetrahydrate; the cerium-containing compound is cerium nitrate; the iron-containing compound is one or more of ferric chloride, ferric nitrate, iron oxide, and iron powder, preferably ferric chloride or ferric nitrate. Preferably, in step a), the molar ratio of molybdenum / iron / cerium in the molybdenum-containing compound, iron-containing compound, and cerium-containing compound is 0.4–1.35:1:0.1–0.

8.

4. The preparation method according to claim 2, characterized in that, In step a), the pH is controlled at 1-3, preferably 1.5-2.8, and the co-precipitation reaction is carried out at a temperature of 50-100℃ for 3-5 hours; preferably, in step b), the aging temperature is 50-100℃ and the time is 24-48 hours; the drying temperature is 100-130℃ and the time is 6-24 hours.

5. The preparation method according to claim 2, characterized in that, In step c), the molar ratio of phosphorus in potassium dihydrogen phosphate to iron in the iron-containing compound is 0.1-2:1; preferably, in step c), the ultrasonic frequency is 30 kHz to 50 kHz, the heating temperature is 30 to 80 °C, and the treatment time is 3 to 5 h.

6. The preparation method according to claim 2, characterized in that, In step c), the filter cake is dried at 50℃~100℃ for 10~28h, and then dried at 100℃~150℃ for 15~30h to obtain catalyst powder; preferably, the calcination temperature in step c) is 450-540℃, and the calcination time is 5~20h.

7. The preparation method according to any one of claims 2-6, characterized in that, The forming method in step c) includes extrusion, tableting, or rolling; preferably, the tableting method includes the following steps: adding a pore-forming agent and a lubricant to the catalyst powder and then tableting it to obtain cylindrical or hollow cylindrical particles; the pore-forming agent is preferably one or more of guar gum powder, cellulose, polyethylene, polypropylene, and polyvinyl chloride, and the amount of the pore-forming agent is 1% to 6% of the mass of the catalyst powder; the lubricant is preferably one or more of stearic acid, magnesium stearate, zinc stearate, and graphite, and the amount of the lubricant is 0.1% to 1% of the mass of the catalyst powder.

8. A process for preparing formaldehyde by methanol oxidation, characterized in that, Formaldehyde is prepared by oxidizing methanol and oxygen under formaldehyde catalyst conditions.

9. The process according to claim 8, characterized in that, The oxidation reaction temperature is 320–420℃, the reaction pressure is 0.05–0.3 MPa absolute, and the gaseous feedstock volume hourly space velocity is 7000–12000 h⁻¹.

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