阅读说明：本技术 一种甲醇制甲醛的催化剂、制备方法和应用 (Catalyst for preparing formaldehyde from methanol, preparation method and application ) 是由 汪超 金国杰 杨洪云 丁琳 黄政 康陈军 于 2019-10-08 设计创作，主要内容包括：本发明公开了一种甲醇制甲醛的催化剂、制备方法以及在甲醇氧化制备甲醛工艺中的应用。本发明的催化剂为整体式催化剂,以蜂窝陶瓷为骨架基体,在骨架基体上负载载体涂层,载体涂层包括氧化钼纳米棒,在载体涂层表面,再负载钼酸铁颗粒作为活性组分。该催化剂用于甲醇氧化制备甲醛时,催化剂的活性和选择性高,并且该整体式催化剂在实际应用中具有床层压降低,装填方便,催化剂磨损小等优点。(The invention discloses a catalyst for preparing formaldehyde from methanol, a preparation method and application in a process for preparing formaldehyde by oxidizing methanol. The catalyst is an integral catalyst, honeycomb ceramic is used as a framework substrate, a carrier coating is loaded on the framework substrate, the carrier coating comprises molybdenum oxide nanorods, and iron molybdate particles are loaded on the surface of the carrier coating to serve as active components. When the catalyst is used for preparing formaldehyde by oxidizing methanol, the activity and the selectivity of the catalyst are high, and the monolithic catalyst has the advantages of reduced bed lamination, convenient filling, small catalyst abrasion and the like in practical application.)

1. The catalyst is an integral catalyst, honeycomb ceramic is used as a framework substrate, a carrier coating is loaded on the framework substrate, the carrier coating comprises molybdenum oxide nanorods, and iron molybdate particles are loaded on the surface of the carrier coating to serve as active components.

2. The catalyst of claim 1, wherein: in the catalyst, the total content of molybdenum oxide and iron molybdate accounts for 0.1-20% of the total mass of the catalyst; in the catalyst, the molar ratio of molybdenum atoms to iron atoms is 1-200: 1, preferably 2.0-20: 1.

3. a catalyst according to claim 1 or 2, wherein: in the catalyst, the length of the molybdenum oxide nanorod is 1-10 mu m, and the width of the molybdenum oxide nanorod is 20-500 nm; the diameter of the iron molybdate particles is not more than 100nm, preferably 2-50 nm.

4. The catalyst of claim 1, wherein: the molybdenum oxide nanorods in the carrier coating are randomly distributed.

5. The catalyst of claim 1, wherein: the carrier coating contains a bonding agent besides the molybdenum oxide nano-rods.

6. The catalyst of claim 1, wherein: the honeycomb ceramic is at least one of honeycomb ceramic with cordierite or mullite texture; the size of the pore channel of the honeycomb ceramic is 0.25-2.5 mm according to the hydraulic diameter, and the density of the pore channel is 100-800 meshes per square inch.

7. A process for preparing a catalyst as claimed in any one of claims 1 to 6, comprising:

(1) loading a carrier coating: preparing slurry containing molybdenum oxide nanorods, immersing honeycomb ceramics into the slurry, then taking out the honeycomb ceramics, and carrying out draining and roasting;

(2) loading active components: and (2) adding the substance obtained in the step (1) into an iron salt solution to load an iron-containing component, and then drying and roasting to obtain the catalyst for preparing the formaldehyde from the methanol.

8. The method of claim 7, wherein: in the step (1), slurry containing molybdenum oxide nanorods is prepared, then a binder is added into the slurry and is uniformly stirred, and then the honeycomb ceramic is immersed into the slurry.

9. The method of claim 8, wherein: in the step (1), the roasting conditions are as follows: the roasting temperature is 400-500 ℃, and the roasting time is 1-6 h; in the step (2), the drying is carried out for 1-24 h at 100-150 ℃, and the roasting is carried out for 1-12 h at 350-500 ℃.

10. Use of a catalyst according to any one of claims 1 to 9 in a methanol to formaldehyde reaction.

Technical Field

The invention relates to a catalyst, a preparation method and application, in particular to an integral catalyst for preparing formaldehyde from methanol, a preparation method and application.

Background

Two process routes can be selected for preparing formaldehyde by selective oxidation of methanol, one is to use a silver catalyst to catalyze dehydrogenation of methanol at a higher temperature to generate formaldehyde, and the other is to use an iron-molybdenum catalyst.

The preparation methods of the iron-molybdenum catalyst are various, and the common methods include 1) a coprecipitation method: the solution of molybdenum salt (typically ammonium molybdate) and iron salt (soluble iron salts such as ferric nitrate, ferric chloride, etc.) are mixed and metal ions are precipitated at a suitable pH range. 2) Sol-gel method: firstly, molybdenum salt and iron salt are dissolved and gelatinized by organic acid, and then the mixture is evaporated to dryness to form gel. For example, USP4420421, USP4829042 and CN1100667A adopt a coprecipitation method to prepare the iron-molybdenum catalyst, and GB1282949 and US3846341 adopt a sol-gel method to prepare the iron-molybdenum catalyst. However, whether the coprecipitation method or the sol-gel method is adopted, the obtained iron-molybdenum compound needs to be further shaped to obtain a final finished catalyst so as to be convenient to use. In the above-mentioned patents, the molding methods disclosed are those in which an iron-molybdenum compound is mixed with an auxiliary agent such as a binder and the mixture is molded by extrusion or pressing. The size and shape of the shaped catalyst are determined according to the requirements of the actual industrial process.

In the industrial production of formaldehyde from methanol, a fixed bed reactor is mostly adopted, the factor of bed pressure drop is considered, and the size of the formed catalyst is generally larger. In the case of large particle catalysts, the active components inside the particles are often not effectively utilized during use due to diffusion limitations. Compared with the active component raw powder before forming, the catalytic efficiency and the stability of the formed catalyst are obviously reduced. In addition, the oxidation of methanol to formaldehyde is a strongly exothermic reaction, requiring the mixing of large amounts of inert gases in order to avoid the risk of explosion. The fixed bed reactor of the iron-molybdenum method generally needs to adopt a plurality of tubes, the process of filling catalyst particles is complicated, the catalyst particles are easy to rub and wear under high airspeed and thermal shock, and the phenomenon that the bed layer is blocked by fine powder in the later stage of reaction is common in production.

At present, various iron-molybdenum compounds are loaded on the surface of a shaped carrier (such as a silica carrier), but the performance of the loaded catalyst is found to be greatly influenced. However, it is a research direction of those skilled in the art to overcome the defects of the prior art and to make the prepared catalyst have both reaction performance and convenience in actual operation so as to meet the development requirements of the related fields.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a catalyst for preparing formaldehyde from methanol, a preparation method and application in a process for preparing formaldehyde by oxidizing methanol. The catalyst is an integral catalyst, and when the catalyst is used for preparing formaldehyde by methanol oxidation, the activity and the selectivity of the catalyst are high, and the integral catalyst has the advantages of reduced bed lamination, convenient filling, small catalyst abrasion and the like in practical application.

The invention provides a catalyst for preparing formaldehyde from methanol, which is an integral catalyst, wherein the catalyst takes honeycomb ceramics as a framework substrate, a carrier coating is loaded on the framework substrate, the carrier coating comprises molybdenum oxide nano rods, and iron molybdate particles are loaded on the surface of the carrier coating to serve as active components.

In the catalyst, the total content of molybdenum oxide and iron molybdate is 0.1-20% of the total mass of the catalyst. The content of the iron molybdate is related to the content of molybdenum oxide, and specifically, the molar ratio of molybdenum atoms to iron atoms in the catalyst is 1-200: 1, preferably 2.0-20: 1.

in the catalyst, the length of the molybdenum oxide nanorod is 1-10 mu m, and the width of the molybdenum oxide nanorod is 20-500 nm.

In the catalyst, the diameter of the iron molybdate particles is not more than 100nm, and preferably 2-50 nm.

In the catalyst, the molybdenum oxide nanorods in the carrier coating are randomly distributed.

In the catalyst, the carrier coating contains a binding agent besides the molybdenum oxide nano-rods.

The binder is at least one of silica, alumina, titania, zirconia, etc., and is derived from one or more of silica sol, water glass, alumina sol, and sol of metal oxide such as titania, zirconia, etc., preferably silica and/or alumina.

The honeycomb ceramic of the catalyst of the invention can maintain the mechanical strength at 300-700 ℃, and the thermal expansion coefficient is lower than 2.0 multiplied by 10^-6/° c; the honeycomb ceramic has straight or nearly straight honeycomb regular pore channels, and the cross section of the pore channels can be in various shapes such as square, round, hexagonal and the like.

The size of a pore channel of the honeycomb ceramic is preferably 0.25-2.5 mm in terms of hydraulic diameter, and the density of the pore channel is preferably 100-800 meshes per square inch.

The honeycomb ceramic is preferably cordierite (2 MgO.2A)_l2O₃·5SiO₂) Or mullite (3 Al)₂O₃·2SiO₂) At least one of a textured honeycomb ceramic.

The second aspect of the present invention provides a method for preparing the above catalyst, comprising:

(1) loading a carrier coating: preparing slurry containing molybdenum oxide nanorods, immersing honeycomb ceramics into the slurry, then taking out the honeycomb ceramics, and carrying out draining and roasting;

(2) loading active components: and (2) adding the substance obtained in the step (1) into an iron salt solution to load an iron-containing component, and then drying and roasting to obtain the catalyst.

In the step (1), slurry containing molybdenum oxide nanorods is prepared, then a binder is added into the slurry and is uniformly stirred, and then the honeycomb ceramic is immersed into the slurry.

In the step (1), the added binder is 0.1-10% of the molybdenum oxide in mass in terms of oxide when the slurry containing the molybdenum oxide nanorods are prepared in the step (1).

In the step (1), the honeycomb ceramic can be pretreated as required, and the pretreatment is performed by adopting a conventional pretreatment means in the field, for example, the honeycomb ceramic is cut into a proper size and shape, then is fully washed by hydrochloric acid and deionized water, is dried for 2-12 hours at 80-200 ℃, and is naturally cooled to room temperature for later use.

In the step (1), the specific preparation method of the slurry containing the molybdenum oxide nanorods comprises the following steps: putting molybdenum oxide powder into a hydrogen peroxide solution with the mass concentration of 30-50%, and fully stirring for 6-12 h under the water bath condition of 40-50 ℃ to obtain a peroxymolybdic acid solution; putting the solution of peroxymolybdic acid into a reaction kettle with an exhaust valve, gradually heating to 90-100 ℃, exhausting and reducing pressure, continuously heating to 150-170 ℃, maintaining the pressure at 1.0-2.0 MPa, and keeping for more than 12 hours; and then cooling and depressurizing, and taking out the product in the reaction kettle to be slurry, wherein the solid in the product is the molybdenum oxide nano rod with the length of 1-10 mu m and the width of 20-500 nm.

In the step (1), the honeycomb ceramic is immersed in the slurry, preferably, the honeycomb ceramic is vertically immersed in the slurry along the pore channel direction, and the immersion time of the honeycomb ceramic in the slurry is 5-30 min.

After the step (1) is completed, the honeycomb ceramic can be repeatedly immersed into the slurry according to actual conditions, and the repeated operation is taken as an example, and specifically comprises the following steps: and immersing the honeycomb ceramic into the slurry, taking out the honeycomb ceramic, draining, drying, immersing the honeycomb ceramic into the slurry again, taking out the honeycomb ceramic, draining, roasting and loading the required amount of molybdenum oxide nanorods on the honeycomb ceramic, wherein the drying condition is drying for 1-12 hours at 100-150 ℃.

In the step (1), the slurry in the honeycomb ceramic pore channels is drained, and the roasting conditions are as follows: the roasting temperature is 400-500 ℃, and the roasting time is 1-6 h.

In the step (2), the iron salt is a soluble iron salt, such as one or more of a ferric nitrate solution, a ferric chloride solution and a ferrous chloride solution.

In the step (2), the iron-containing component is loaded by adopting an impregnation method or a deposition precipitation method.

In step (2), the impregnation method is a conventional method in the art, such as: and (3) adding the substance obtained in the step (1) into an iron salt solution, soaking for 1-24 h, and taking out the honeycomb ceramic.

In step (2), the deposition precipitation method is a conventional method in the art, such as: and (2) adding the substance obtained in the step (1) into an iron salt solution, keeping stirring, dropwise adding ammonia water with the mass concentration of 5% -25% into the iron salt solution, stopping stirring and standing for a period of time after the pH of the system is stable, and taking out the honeycomb ceramic.

In the step (2), the drying is carried out for 1-24 h at 100-150 ℃, and the roasting is carried out for 1-12 h at 350-500 ℃.

The third aspect of the invention provides an application of the catalyst in a methanol-to-formaldehyde reaction.

Wherein the reaction temperature of the catalyst in the reaction of preparing formaldehyde from methanol is 200-450 ℃. The raw materials for the reaction are mixed gas of oxygen, methanol steam and inert gas, the raw materials for the reaction are heated to 200-450 ℃, and then the raw materials are contacted with a catalyst for preparing formaldehyde from methanol in a reactor for reaction, so that a reaction product is obtained. Wherein, the mole fraction of the methanol vapor in the mixed gas is 1 to 10 percent, the mole fraction of the oxygen is 5 to 15 percent, and the rest is inert gas; the inert gas includes, but is not limited to, at least one of nitrogen, argon, and water vapor.

Compared with the prior art, the invention has the following advantages:

the catalyst for preparing the formaldehyde from the methanol is an integral catalyst, honeycomb ceramics is used as a framework substrate, a carrier coating comprising molybdenum oxide nano rods is loaded on the framework substrate, and the active component of iron molybdate is loaded on the carrier coating.

Detailed Description

The technical solution of the present invention is further illustrated by the following examples, but the scope of the present invention is not limited by the examples.

In the context of the present specification, the size of the molybdenum oxide nanorods and iron molybdate particles is determined by a Scanning Electron Microscope (SEM) which is determined by a Nova NanoSEM 450(FEI, USA) type scanning electron microscope, during which the relevant sample is directly observed on a sample stage by using a conductive adhesive, the acceleration voltage of the scanning electron microscope is 1.6kV, the magnification is 10000-.

[ example 1 ]

Preparing honeycomb ceramics: cordierite honeycomb ceramic (square cross section, 1.0mm side length, 400 mesh cell density per square inch) is selected, which can maintain its mechanical strength at 300-700 deg.C, and has a thermal expansion coefficient lower than 2.0 × 10^-6Cutting the ceramic block into a (approximate) cylindrical ceramic block with the diameter of 1.8-2 cm and the length of 5cm at the temperature of/° C. The ceramic cake was thoroughly washed with 1mol/L hydrochloric acid and deionized water in this order, and dried at 120 ℃ for 5 hours, and the mass of the honeycomb ceramic was weighed before use. Each time 100g of the honeycomb ceramic was used, the same applies to the following examples.

Hydrothermally preparing slurry containing molybdenum oxide nanorods: 20g of MoO₃Putting the (Chinese medicine reagent) powder into 150mL of hydrogen peroxide solution (Chinese medicine reagent) with the mass concentration of 30%, fully stirring for 12h under the condition of water bath at 40 ℃ to obtain orange transparent peroxymolybdic acid solution, putting the peroxymolybdic acid solution into a reaction kettle with an exhaust valve, gradually heating to 90 ℃, properly exhausting and reducing pressure, further raising the temperature to 150 ℃, maintaining the pressure at 1.0-2.0 MPa, and keeping for 12h to obtain the productThe above. And after cooling and depressurizing, taking out the product in the reaction kettle to be slurry, wherein the solid in the product is the molybdenum oxide nano rod with the length of about 1-10 mu m and the width of about 100 nm.

Loading a carrier coating: the method comprises the steps of directly weighing 160g of slurry containing molybdenum oxide nanorods without separating the molybdenum oxide nanorod particles from hydrothermal mother liquor, adding 5.0g of silica sol (Grace Davison, LUDOX HS-40) with the mass concentration of 40%, stirring for 30min, uniformly mixing, vertically immersing a honeycomb ceramic block into the mixture along the pore channel direction, taking out after immersing for about 30min, properly draining the slurry in the pore channel, and roasting for 4h at 500 ℃. The weight of the honeycomb ceramic block is increased by about 5.1%.

Loading iron molybdate on the surface: 25.4g Fe (NO)₃)₃·9H₂Dissolving O in 20mL of deionized water to prepare a ferric nitrate solution with the weight percent of about 28.5, immersing the honeycomb ceramic block in the ferric nitrate solution and ensuring the inner surfaces of the pore channels to be fully wetted, taking out the honeycomb ceramic after immersing for 12 hours, blowing the liquid in the pore channels to the greatest extent, drying for 2 hours in an air atmosphere at 120 ℃, and further raising the temperature to 500 ℃ for roasting for 4 hours. The molar ratio of molybdenum atoms to iron atoms contained in the catalyst as a whole was 3.7: 1 by ICP-AES analysis. Wherein the diameter of the iron molybdate particles is 10-50 nm. Denoted as catalyst 1.

[ example 2 ]

The concentration of the solution of the impregnated iron salt was varied to increase the ferromolybdenum ratio.

The preparation of the honeycomb ceramic, the hydrothermal preparation of the slurry containing the molybdenum oxide nanorods, and the loading of the washcoat on the honeycomb ceramic were performed as in example 1.

Loading iron molybdate on the surface: mixing 12.7g Fe (NO)₃)₃·9H₂Dissolving O in 100mL of deionized water to prepare about 6.75 wt% of ferric nitrate solution, immersing the honeycomb ceramic block in the deionized water to ensure that the inner surface of the pore channel is fully wetted, taking out the honeycomb ceramic after immersing for 12 hours, blowing the liquid in the pore channel to the greatest extent, drying for 2 hours in 120 ℃ air atmosphere, and further raising the temperature to 500 ℃ for roasting for 4 hours. After calcination, the molar ratio of molybdenum atoms to iron atoms contained in the catalyst as a whole was 12.1: 1 by ICP-AES analysis. Wherein the diameter of the iron molybdate particles is 10-50 nm and is marked as a catalyst 2.

[ example 3 ]

And loading iron molybdate by using a precipitation method.

The preparation of the honeycomb ceramic, the hydrothermal preparation of the slurry containing the molybdenum oxide nanorods, and the loading of the washcoat on the honeycomb ceramic were performed as in example 1.

Loading iron molybdate on the surface: mixing 12.7g Fe (NO)₃)₃·9H₂Dissolving O in 200mL deionized water to obtain 0.157mol/L ferric nitrate solution, and adding the solution coated with MoO₃The ceramic block of (4) was gradually heated to 45 ℃ while maintaining stirring at about 30rpm, and 40mL of 5% by mass aqueous ammonia was added dropwise to the ferric nitrate solution. And after the ammonia water is completely added and the pH value of the system is stable and unchanged, stopping stirring, standing for 3h, and taking out the ceramic block. Draining, drying at 120 deg.C for 2 hr, and roasting at 500 deg.C for 4 hr. After calcination, the molar ratio of molybdenum atoms to iron atoms contained in the catalyst as a whole was 13.6: 1 by ICP-AES analysis. Wherein the diameter of the iron molybdate particles is 2-20 nm and is marked as a catalyst 3.

[ example 4 ]

The amount of silica sol binder used is increased.

Preparation of honeycomb ceramics, hydrothermal preparation of slurry containing molybdenum oxide nanorods, and operation of the slurry were the same as example 1.

When the carrier coating is loaded, 160g of slurry containing molybdenum oxide nanorods is taken out, 20.0g of 40% silica sol (Grace Davison, LUDOX HS-40) is added, the mixture is stirred for 30min and uniformly mixed, the honeycomb ceramic block is vertically immersed into the mixture along the pore channel direction, the honeycomb ceramic block is taken out after being immersed for about 30min, the slurry in the pore channel is properly drained, the honeycomb ceramic block is roasted for 4h at 500 ℃, and when the amount of the silica sol is increased through weighing, the weight gain after coating is slightly increased and reaches about 5.7%.

The subsequent surface loading of iron molybdate was performed in the same manner as in example 1. The molar ratio of molybdenum atoms to iron atoms contained in the catalyst as a whole was 8.7: 1 by ICP-AES analysis. Wherein the diameter of the iron molybdate particles is 10-50 nm. Denoted as catalyst 4.

[ example 5 ]

The type of the replacement binder is alumina sol.

Preparation of honeycomb ceramics, hydrothermal preparation of slurry containing molybdenum oxide nanorods, and operation of the slurry were the same as example 1.

Loading a carrier coating: 2g of pseudo-boehmite powder is mixed with 30mL of deionized water, the mixture is stirred and heated to 80 ℃, concentrated nitric acid is gradually dripped simultaneously, the pH value in the system is maintained to be about 2.0, and semitransparent alumina sol is gradually formed. Directly taking out slurry containing the molybdenum oxide nano-rods, putting the slurry into the aluminum sol, violently stirring for 30min to fully mix, and properly adding nitric acid to maintain the pH. And vertically immersing the honeycomb ceramic block into the mixture along the direction of the pore channel, taking out after about 30min of immersion, properly draining slurry in the pore channel, and roasting for 4h at 500 ℃. The weight of the honeycomb ceramic block is increased by about 5.1%.

The subsequent surface loading of iron molybdate was performed in the same manner as in example 1. The molar ratio of molybdenum atoms to iron atoms contained in the catalyst as a whole was 4.1: 1 by ICP-AES analysis. Wherein the diameter of the iron molybdate particles is 10-50 nm. Denoted as catalyst 5.

[ example 6 ]

Honeycomb ceramics with larger pore diameter are used instead.

Cordierite honeycomb ceramics (with square cross section, 1.8mm side length and 100 meshes per square inch of pore density) are selected and cut into cylindrical ceramic blocks with the diameter of 2cm and the length of 5 cm. The ceramic block was washed thoroughly with 1mol/L hydrochloric acid and deionized water and dried at 120 ℃.

Subsequent hydrothermal preparation of molybdenum oxide nanorods and coating of porous MoO on ceramic blocks₃The coating and surface loading of iron molybdate was performed in the same manner as in example 1. The molar ratio of molybdenum atoms to iron atoms contained in the catalyst as a whole was 3.9: 1 by ICP-AES analysis. Wherein the diameter of the iron molybdate particles is 10-50 nm. Denoted as catalyst 6.

[ example 7 ]

The washcoat loading was repeated.

The honeycomb ceramic was selected similarly to example 6, but after the honeycomb ceramic was immersed in MoO₃Taking out the slurry mixed with silica sol, draining the slurry in the pore canal, drying at 150 deg.C for 4 hr, and soaking in MoO again₃Taking out the mixture of the honeycomb ceramic blocks and the silica sol after 30min, properly draining slurry in pore channels, and roasting at 500 ℃ for 4h to increase the weight of the honeycomb ceramic blocks by about 8%.

The subsequent loading of iron molybdate was performed in the same manner as in example 1. The molar ratio of molybdenum atoms to iron atoms contained in the catalyst as a whole was 6.9: 1 by ICP-AES analysis. Wherein the diameter of the iron molybdate particles is 10-50 nm. Denoted as catalyst 7.

Comparative example 1

The tablets were formed and impregnated with iron molybdate-loaded molybdenum oxide particles.

The hydrothermal preparation of the slurry containing molybdenum oxide nanorods was carried out in a similar manner to example 1, after lowering the temperature and the pressure, the slurry product in the reactor was taken out, the solid was filtered out, and dried at 120 ℃.

12.7g Fe (NO)₃)₃·9H₂O dissolved in 10mL H₂In O, the solution is sprayed on the dried MoO dropwise₃On the nanorod powder, the powder is properly agitated to ensure uniform impregnation. The immersion time was 12h, after which it was dried in an air atmosphere at 120 ℃. Likewise, the mixture was calcined at 500 ℃ for 4 hours. After the calcination, the granules were crushed and mixed with 5.0g of 40% silica sol (Grace Davison, LUDOX HS-40) and 0.5g of sesbania powder, and the mixture was pressed into a wafer having a diameter of 2.0cm and a thickness of 0.5 to 1.0cm, and calcined at 500 ℃ in an air atmosphere for 12 hours. And screening 20-40 meshes of particles after the roasted wafer is crushed, and marking as a catalyst 8. The molar ratio of molybdenum atoms to iron atoms contained in the catalyst as a whole was 12.7: 1 by ICP-AES analysis.

Comparative example 2

The honeycomb ceramics were prepared as in example 1. 24.5g (NH)₄)₆Mo₇O₂₄·4H₂O (national reagent) and 12.7g Fe (NO)₃)₃·9H₂O dissolved in 50mL H₂And stirring the mixture evenly. The solution was sprayed drop by drop onto the surface of the ceramic block, taking care to wet the channel surface sufficiently to ensure uniform impregnation. After the impregnation treatment for 12 hours, the resultant was dried at 120 ℃ for 12 hours in an air atmosphere and then calcined at 500 ℃ for 4 hours. Denoted as catalyst 9. The molar ratio of molybdenum atoms to iron atoms contained in the catalyst as a whole was 4.5: 1 by ICP-AES analysis.

Comparative example 3

Similar to comparative example 2, but selecting pellets of about 2mm in diameter₂As a carrier, 24.5g of (NH)₄)₆Mo₇O₂₄·4H₂O with 12.7g Fe (NO)₃)₃·9H₂O dissolved in 50mL H₂And stirring the mixture evenly. The solution was sprayed dropwise onto 100g of SiO₂The surface of the pellet was carefully wetted thoroughly. After the impregnation treatment for 12 hours, the resultant was dried at 120 ℃ for 12 hours in an air atmosphere and then calcined at 500 ℃ for 4 hours. Denoted as catalyst 10. The molar ratio of molybdenum atoms to iron atoms contained in the catalyst as a whole was 4.4: 1 by ICP-AES analysis.

[ example 8 ]

Catalyst evaluation

The prepared catalyst 1-10 was placed in a quartz tube having an inner diameter of 2 cm. The monolithic catalyst is put in along the direction of the pore channel, and the gap between the tube wall and the ceramic block is filled and compacted by quartz wool, and is pressed into tablets or loaded on SiO in the traditional way₂The catalyst on the surface of the pellets was mixed in the quartz sand to form a fixed bed about 5cm high. The reaction raw material was a mixed gas consisting of 5 mol% methanol vapor, 10 mol% oxygen and 85 mol% nitrogen, heated and passed through the catalyst layer. The flow rate of the feed gas is based on the methanol space velocity of 1.5 g/(h.g catalyst), wherein the mass of the monolithic catalyst is subtracted from the mass of the original ceramic block. The reaction temperature is controlled to be 300-330 ℃. The results of the evaluation test of each catalyst are shown in table 1. From the results, the monolithic catalyst prepared according to the claimed method has high activity and selectivity in catalyzing the reaction of methanol oxidation to formaldehyde, while having the remarkable advantages of low pressure drop and convenient loading, and can substantially approach or exceed the catalyst 8 prepared according to the conventional tablet forming method in comparative example 1. In contrast, in comparative examples 2 and 3, the ferromolybdenum component is directly impregnated and supported on the surface of the ceramic or the silicon oxide, which is far from the effect obtained by the special structure of the ceramic as the framework and the molybdenum oxide as the actual carrier in the invention.

[ TABLE 1 ] Performance of different catalysts in methanol Oxidation reactions

Catalyst and process for preparing same	Conversion of methanol	Selectivity to formaldehyde
			Catalyst 1	92.6％	90.9％
Catalyst 2	86.8％	91.1％
			Catalyst 3	91.8％	93.2％
Catalyst 4	85.1％	92.0％
			Catalyst 5	94.5％	87.6％
Catalyst 6	82.1％	89.0％
			Catalyst 7	90.1％	89.3％
Catalyst 8	88.3％	90.6％
			Catalyst 9	37.1％	72.5％
Catalyst 10	22.3％	51.5％

In the present invention,

methanol conversion rate is 100% -unreacted methanol mol weight in product/input methanol raw material mol weight is multiplied by 100%

Formaldehyde selectivity ═ formaldehyde molar amount ÷ (formaldehyde + dimethyl ether + methyl formate + carbon dioxide + carbon monoxide) molar amount × 100%.