Iron-molybdenum catalyst prepared by deposition-homogenization composite process and use thereof

Abstract

The present application belongs to the technical field of catalysts, and particularly relates to an iron-molybdenum catalyst prepared by a deposition-homogenization composite process and an application thereof. The preparation method of the catalyst comprises the following steps: a certain amount of MoO3 is uniformly mixed with an iron salt solution by stirring, and a certain amount of an alkali solution is added into a homogenizer in parallel flow, a reaction is carried out under a certain precipitation pH value, the precursor obtained by the reaction is added into an aging tank, and the iron-molybdenum catalyst is prepared by aging, filtering, drying, calcining and molding. The molar ratio of Mo to Fe in the iron-molybdenum catalyst is 2.4-2.8. The raw material cost is reduced by the method, the wastewater amount and processing steps are reduced, the active component of the obtained catalyst is highly dispersed and uniform in size, the catalyst has a stable structure in which Fe2(MoO4)3 is embedded in MoO3, and the catalyst exhibits excellent activity, selectivity and stability when used for methanol oxidation to produce formaldehyde.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalysts, and particularly relates to an iron-molybdenum catalyst prepared by a deposition-homogenization composite process and application thereof. BACKGROUND

[0002] Formaldehyde is a very important organic chemical raw material. Due to the active chemical property, formaldehyde can react with almost all compounds, and is widely applied in the production of high-value downstream products such as polyformaldehyde, polyoxymethylene, MDI, etc. Since Germany first realized the industrial production of formaldehyde in 1888, two methods, i.e. a silver method and an iron-molybdenum method, are mainly used to directly oxidize methanol to produce formaldehyde. The iron-molybdenum method gradually dominates the production of formaldehyde due to the low reaction temperature, high formaldehyde yield and long service life.

[0003] In order to promote the application and popularization of domestic iron-molybdenum catalysts, it is urgent to develop iron-molybdenum catalysts with more excellent performance. SUMMARY

[0004] The application aims to provide an iron-molybdenum catalyst prepared by a deposition-homogenization composite process and application thereof. The iron-molybdenum catalyst prepared by the method of the application has excellent activity, selectivity and stability when used in the production of formaldehyde by methanol oxidation.

[0005] In order to achieve the above application purposes, the specific technical scheme of the application is as follows:

[0006] A method for preparing an iron-molybdenum catalyst by a deposition-homogenization composite process, specifically comprising the following steps: uniformly stirring and mixing a certain amount of MoO3 and an iron salt solution, and adding a certain amount of an alkali solution into a homogenizer in parallel flow, reacting at a certain precipitation pH value, then adding the obtained precursor in the reaction into an aging tank, and aging, filtering, drying, calcining and shaping to obtain the iron-molybdenum catalyst.

[0007] As a better embodiment in the application, the iron salt is Fe(NO3)2·6H2O or Fe(NO3)3·9H2O, and the alkali solution is dilute ammonia water.

[0008] As a better embodiment in the application, the component content of the catalyst is Mo / Fe=2.4-2.8 in terms of molar ratio.

[0009] As a better embodiment in the application, the pH value is controlled to be 1.6-2.2.

[0010] As a better embodiment in the application, the method for preparing an iron-molybdenum catalyst by a deposition-homogenization composite process comprises the following specific steps:

[0011] Step one: weigh a certain amount of Fe(NO3)2·6H2O or Fe(NO3)3·9H2O, dissolve in a certain amount of deionized water, stir to fully dissolve and mix evenly, named as salt A;

[0012] Weigh a certain mass of MoO3 accurately;

[0013] Measure a certain volume of concentrated NH3·H2O, dilute with deionized water, prepare into a certain pH value of dilute ammonia water, named as alkali B;

[0014] Step two: take a certain amount of deionized water in the aging tank, named as base solution, preheat the base solution and salt A to the required temperature respectively;

[0015] Step three: slowly add a certain amount of MoO3 to the preheated salt A, stir to mix evenly, and add a certain amount of alkali B into the homogenizer in parallel flow, react at a certain precipitation pH value, add the precursor obtained by reaction into the aging tank, and age for a period of time under constant temperature stirring;

[0016] Step four: after aging, filter, dry, calcine and shape, the iron-molybdenum catalyst described in the application can be obtained.

[0017] As a better embodiment in the application, the pH value of the alkali B is 11.8-13.2 (specifically 11.8, 12.0, 12.2, 12.4, 12.6, 12.8, 13.0, 13.2, etc.), and the precipitation pH value is controlled to 1.6-2.2 (described in the 11th line of the specification) (specifically 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, etc.).

[0018] As a better embodiment in the application, the MoO3 is industrial grade, and the specific surface area is 15-45 m 2 / g.

[0019] As a better embodiment in the application, the preheating temperature of the salt A is controlled to 30-80℃ (specifically 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, etc.), and the preheating temperature of the base solution is controlled to 30-80℃ (specifically 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, etc.).

[0020] As a better embodiment of the present application, the homogenizer has a homogenization time of 5-25 min (specifically, 5 min, 10 min, 15 min, 20 min, 25 min, etc.); and a working pressure of 10-1500 bar (10 bar, 100 bar, 200 bar, 300 bar, 400 bar, 500 bar, 600 bar, 700 bar, 800 bar, 900 bar, 1000 bar, 1100 bar, 1200 bar, 1300 bar, 1400 bar, 1500 bar, etc.).

[0021] As a better embodiment of the present application, the aging temperature is 30-80℃ (specifically, 30℃, 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, etc.), and the time is 1-10 h (specifically, 2 h, 4 h, 6 h, 8 h, 10 h, etc.).

[0022] As a better embodiment of the present application, the calcination temperature is 400-500℃ (specifically, 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, etc.), and the time is 6-12 h (specifically, 6 h, 8 h, 10 h, 12 h, etc.).

[0023] Compared with the existing preparation method, the deposition-homogenization composite process has the following advantages:

[0024] (1) The present application uses industrial-grade MoO3 with large specific surface area as the molybdenum source, which is conducive to the full positioning of Fe and the high dispersion of Fe2(MoO4)3, thereby improving the activity, selectivity and stability of the catalyst in the production of methanol oxidation to formaldehyde. Compared with the prior art using ammonium molybdate as the molybdenum source, the present application not only reduces the cost of raw materials of the catalyst, but also reduces the processing cost and wastewater treatment cost of the catalyst due to the fact that MoO3 does not need to be dissolved and the filter cake does not need to be washed, which is more suitable for industrial production.

[0025] (2) The high-frequency and high-energy circumferential tangential and angular kinetic energy is formed by the high-speed rotation of the rotor of the homogenizer, and the narrow gap between the stator and the rotor provides strong extrusion force, friction force and shear force for the liquid flow. The high-energy, high-density and high-frequency reaction field generated by the homogenizer makes the molecules of iron salt, ammonia, molybdenum trioxide and iron-molybdenum mixture fully collide and combine and highly disperse, so that an iron-molybdenum catalyst with highly dispersed active components and uniform size is obtained. The catalyst has excellent activity and selectivity when used in the production of methanol oxidation to formaldehyde.

[0026] (3) The present application uses large specific surface MoO3 as molybdenum source, adopts deposition-homogeneous composite process to make Fe deposit and combine on the surface of MoO3, and then through special aging and calcination process, Fe2(MoO4)3 is riveted on MoO3. The Fe2(MoO4)3 crystal grain size of the catalyst is uniform, highly dispersed, and closely combined with MoO3. When Mo element of Fe2(MoO4)3 is lost due to the reaction of methanol oxidation to formaldehyde, MoO3 closely combined with Fe2(MoO4)3 can provide supplement, so that the catalyst shows excellent structure and performance stability in the production of methanol oxidation to formaldehyde. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 SEM image of the catalyst described in Example 2;

[0028] Figure 2 SEM image of the catalyst described in Comparative Example 7;

[0029] Figure 3 Preparation process schematic diagram of the catalyst precursor described in the present application. DETAILED DESCRIPTION

[0030] A method for preparing iron-molybdenum catalyst by deposition-homogeneous composite process, the steps of which are as follows: a certain amount of MoO3 is uniformly mixed with iron salt solution, and a certain amount of alkali solution is added into the homogenizer in parallel flow, and the reaction occurs at a certain precipitation pH value, then the obtained precursor is added into an aging tank, and the iron-molybdenum catalyst is prepared by aging, filtering, drying, calcining and molding.

[0031] The iron salt is Fe(NO3)2·6H2O or Fe(NO3)3·9H2O, and the alkali solution is dilute ammonia water.

[0032] The component content of the catalyst is recorded as Mo / Fe=2.4-2.8 in molar ratio.

[0033] The pH value is controlled to be 1.6-2.2.

[0034] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with examples and drawings. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application.

[0035] Example 1

[0036] 50.12g Fe(NO3)3·9H2O is fully stirred and dissolved with deionized water, and the volume is made to be 200mL, which is named as salt A. 200mL deionized water is added into the aging tank as bottom water, and salt A and the bottom water are respectively preheated to 50℃. 42.77g MoO3 with specific surface area of 15m2 / g of MoO3 was slowly added to preheated salt A and stirred until homogeneous. Base B with a pH of 11.8 was prepared using concentrated ammonia. The homogenizer was set to a working pressure of 100 bar and a working time of 5 min. The molybdenum-iron mixture and base B were added to the homogenizer to react and obtain the precursor. During the reaction, the pH of the precipitate was maintained at approximately 1.6 by controlling the amount of base B added. The resulting precursor was added to an aging tank and aged for 6 h under constant temperature and stirring. After aging, the mixture was filtered and dried at 100℃ for 20 h. A portion of the dried sample was calcined at 425℃ for 10 h. The calcined material was shaped to obtain iron-molybdenum catalyst sample 1.

[0037] Example 2

[0038] Dissolve 125.03g of Fe(NO3)3·9H2O thoroughly in deionized water and bring the volume to 600mL, naming this salt A. Add 600mL of deionized water to the aging tank as bottom water, and preheat both salt A and the bottom water to 80℃. Weigh 74.81g of a substance with a specific surface area of ​​45m². 2 / g of MoO3 was slowly added to preheated salt A and stirred until homogeneous. Base B with a pH of 12.3 was prepared using concentrated ammonia. The homogenizer was set to a working pressure of 1200 bar and a working time of 20 min. The molybdenum-iron mixture and base B were added to the homogenizer to react and obtain the precursor. During the reaction, the pH of the precipitate was maintained at approximately 2.0 by controlling the amount of base B added. The resulting precursor was added to an aging tank and aged for 1 h under constant temperature and stirring. After aging, the mixture was filtered and dried at 100℃ for 20 h. A portion of the dried sample was taken and calcined at 500℃ for 6 h. The calcined material was shaped to obtain iron-molybdenum catalyst sample 2.

[0039] Example 3

[0040] Dissolve 100.04g of Fe(NO3)2·6H2O thoroughly in deionized water and bring the volume to 800mL, naming this salt A. Add 800mL of deionized water to the aging tank as bottom water, and preheat both salt A and the bottom water to 45℃. Weigh 135.03g of a substance with a specific surface area of ​​45m². 2 / g of MoO3 was slowly added to preheated salt A and stirred until homogeneous. Alkali B with a pH of 13.2 was prepared using concentrated ammonia. The homogenizer was set to a working pressure of 1500 bar and a working time of 25 min. The molybdenum-iron mixture and alkali B were added to the homogenizer to react and obtain the precursor. During the reaction, the pH of the precipitate was maintained at approximately 2.2 by controlling the amount of alkali B added. The resulting precursor was added to an aging tank and aged for 8 h under constant temperature and stirring. After aging, the mixture was filtered and dried at 100℃ for 20 h. A portion of the dried sample was calcined at 450℃ for 10 h. The calcined material was shaped to obtain iron-molybdenum catalyst sample 3.

[0041] Example 4

[0042] Dissolve 34.70g of Fe(NO3)2·6H2O thoroughly in deionized water and bring the volume to 500mL, naming this salt A. Add 500mL of deionized water to the aging tank as bottom water, and preheat both salt A and the bottom water to 60℃. Weigh 43.37g of a substance with a specific surface area of ​​30m². 2 / g of MoO3 was slowly added to preheated salt A and stirred until homogeneous. Base B with a pH of 12.3 was prepared using concentrated ammonia. The homogenizer was set to a working pressure of 900 bar and a working time of 15 min. The molybdenum-iron mixture and base B were added to the homogenizer to react and obtain the precursor. During the reaction, the pH of the precipitate was maintained at approximately 1.9 by controlling the amount of base B added. The resulting precursor was added to an aging tank and aged for 4 h under constant temperature and stirring. After aging, the mixture was filtered and dried at 100℃ for 20 h. A portion of the dried sample was calcined at 480℃ for 9 h. The calcined material was shaped to obtain iron-molybdenum catalyst sample 4.

[0043] Example 5

[0044] Dissolve 100.03g of Fe(NO3)3·9H2O thoroughly in deionized water and bring the volume to 400mL, naming this salt A. Add 400mL of deionized water to the aging tank as bottom water, and preheat both salt A and the bottom water to 50℃. Weigh 92.64g of a substance with a specific surface area of ​​30m². 2 / g of MoO3 was slowly added to preheated salt A and stirred until homogeneous. Base B with a pH of 12.3 was prepared using concentrated ammonia. The homogenizer was set to a working pressure of 600 bar and a working time of 10 min. The molybdenum-iron mixture and base B were added to the homogenizer to react and obtain the precursor. During the reaction, the pH of the precipitate was maintained at approximately 1.8 by controlling the amount of base B added. The resulting precursor was added to an aging tank and aged for 6 h under constant temperature and stirring. After aging, the mixture was filtered and dried at 100℃ for 20 h. A portion of the dried sample was calcined at 500℃ for 6 h. The calcined material was shaped to obtain iron-molybdenum catalyst sample 5.

[0045] Comparative Example 1

[0046] Dissolve 50.01g of Fe(NO3)3·9H2O in deionized water with thorough stirring, and bring the volume to 200mL. Name this solution salt A. Dissolve 52.40g of (NH4)6Mo7O... 24· 4H2O was dissolved by stirring with deionized water and made up to 200 mL, and named as salt C. 200 mL of deionized water was added into the aging tank as bottom water, and salt A, salt C and the bottom water were preheated to 50°C respectively. Alkali B with pH of 11.8 was prepared by using concentrated ammonia water. The working pressure of the homogenizer was set to 100 bar, and the working time was set to 5 min. Salt A, salt C and alkali B were added into the homogenizer to react to obtain a precursor, and the pH of the precipitate was maintained at about 1.6 by controlling the amount of alkali B added during the reaction. The precursor obtained by the reaction was added into the aging tank, and aged for 6 h under constant temperature stirring. After aging, filtration was performed, and the sample was dried at 100°C for 20 h. Part of the dried sample was calcined at 425°C for 10 h. The calcined material was shaped to obtain iron-molybdenum catalyst sample 6.

[0047] Comparative Example 2

[0048] 125.01 g of Fe(NO3)3·9H2O was dissolved by stirring with deionized water and made up to 600 mL, and named as salt A. 600 mL of deionized water was added into the aging tank as bottom water, and salt A and the bottom water were preheated to 80°C respectively. 74.80 g of MoO3 with specific surface area of 45 m 2 / g was slowly added into the preheated salt A and stirred to mix uniformly. Alkali B with pH of 12.3 was prepared by using concentrated ammonia water. The molybdenum-iron mixture and alkali B were simultaneously added into the aging tank to react, and the reaction time was 20 min, and the pH of the precipitate was maintained at about 2.0 by controlling the amount of alkali B added during the reaction. After the reaction, aging was performed under constant temperature stirring for 1 h. After aging, filtration was performed, and the sample was dried at 100°C for 20 h. Part of the dried sample was calcined at 500°C for 6 h. The calcined material was shaped to obtain iron-molybdenum catalyst sample 7.

[0049] Comparative Example 3

[0050] 100.01 g of Fe(NO3)2·6H2O was dissolved by stirring with deionized water and made up to 800 mL, and named as salt A. 800 mL of deionized water was added into the aging tank as bottom water, and salt A and the bottom water were preheated to 45°C respectively. 100.02 g of MoO3 with specific surface area of 15 m 2 / g was slowly added into the preheated salt A and stirred to mix uniformly. Alkali B with pH of 13.2 was prepared by using concentrated ammonia water. The working pressure of the homogenizer was set to 1500 bar, and the working time was set to 25 min. The molybdenum-iron mixture and alkali B were added into the homogenizer to react to obtain a precursor, and the pH of the precipitate was maintained at about 2.2 by controlling the amount of alkali B added during the reaction. The precursor obtained by the reaction was added into the aging tank, and aged for 8 h under constant temperature stirring. After aging, filtration was performed, and the sample was dried at 100°C for 20 h. Part of the dried sample was calcined at 450°C for 10 h. The calcined material was shaped to obtain iron-molybdenum catalyst sample 8.

[0051] Comparative Example 4

[0052] Dissolve 34.71g of Fe(NO3)2·6H2O thoroughly in deionized water and bring the volume to 500mL, naming this salt A. Add 500mL of deionized water to the aging tank as bottom water, and preheat both salt A and the bottom water to 60℃. Weigh 43.36g of a substance with a specific surface area of ​​30m². 2 / g of MoO3 was slowly added to preheated salt A and stirred until homogeneous. Base B with a pH of 12.3 was prepared using concentrated ammonia. The homogenizer was set to a working pressure of 900 bar and a working time of 15 min. The molybdenum-iron mixture and base B were added to the homogenizer to react and obtain the precursor. During the reaction, the pH of the precipitate was maintained at approximately 1.9 by controlling the amount of base B added. The resulting precursor was added to an aging tank and aged for 4 h under constant temperature and stirring. After aging, the mixture was filtered and dried at 100℃ for 20 h. A portion of the dried sample was calcined at 350℃ for 9 h. The calcined material was shaped to obtain iron-molybdenum catalyst sample 9.

[0053] Comparative Example 5

[0054] Dissolve 100.00g of Fe(NO3)3·9H2O thoroughly in deionized water and bring the volume to 400mL, naming this salt A. Add 400mL of deionized water to the aging tank as bottom water, and preheat both salt A and the bottom water to 50℃. Weigh 92.61g of a substance with a specific surface area of ​​30m². 2 / g of MoO3 was slowly added to preheated salt A and stirred until homogeneous. Base B with a pH of 12.3 was prepared using concentrated ammonia. The homogenizer was set to a working pressure of 600 bar and a working time of 10 min. The molybdenum-iron mixture and base B were added to the homogenizer to react and obtain the precursor. During the reaction, the pH of the precipitate was maintained at approximately 2.5 by controlling the amount of base B added. The resulting precursor was added to an aging tank and aged for 6 h under constant temperature and stirring. After aging, the mixture was filtered and dried at 100℃ for 20 h. A portion of the dried sample was taken and calcined at 500℃ for 6 h. The calcined material was shaped to obtain iron-molybdenum catalyst sample 10.

[0055] Examples and comparative examples of catalyst evaluation methods:

[0056] Granulation: 0.425~0.85mm; Filling volume: 5-10mL.

[0057] Activity testing conditions: reaction temperature controlled at 220–300℃; reaction pressure approximately atmospheric pressure; space velocity approximately 11,000 h⁻¹. -1 .

[0058] The performance of the iron-molybdenum catalysts prepared in the examples and comparative examples was evaluated under the above test conditions, and the data are shown in Table 1.

[0059] Table 1 Performance of catalysts of examples and comparative examples

[0060] Sample No. % CH3OH conversion HCHO selectivity % HCHO yield % 1 98.86 95.03 93.95 2 99.31 96.46 94.37 3 97.57 97.14 94.78 4 97.42 97.55 95.03 5 96.53 96.23 92.89 6 95.87 91.03 87.27 7 96.24 91.42 87.98 8 94.96 93.11 88.41 9 94.72 94.75 89.75 10 93.30 92.80 86.58

[0061] From the data in Table 1, it can be seen that the methanol conversion, formaldehyde selectivity and yield of several example samples are obviously superior to those of the comparative example samples. Sample 1 uses MoO3 as the molybdenum source, and sample 6 uses ammonium tetramolybdate as the molybdenum source. The use of industrial-grade MoO3 with a large specific surface area as the molybdenum source not only reduces production costs, but also is conducive to the full positioning of Fe and the high dispersion of Fe2(MoO4)3. The dispersion and other microstructures of sample 6 are superior to those of sample 1, and thus the catalytic performance of sample 6 is superior to that of sample 1. Sample 2 is prepared using a homogenizer, and sample 7 is not prepared using this process intensification equipment. Since the homogenizer can generate a high-energy, high-density, high-frequency reaction field, the molecules of iron salt, ammonia, molybdenum trioxide and iron-molybdenum mixture can fully collide and combine and are highly dispersed, so that the active components of the catalyst are highly dispersed and uniform in size. Therefore, the performance of sample 7 is inferior to that of sample 2. The Mo / Fe ratio of sample 3 is 2.7, and the Mo / Fe ratio of sample 8 is 2.0. When the Mo / Fe ratio is too low, more active centers Fe2(MoO3)4 cannot be formed in the catalyst, and free Fe2O3 phases exist in the catalyst. When the Mo in the catalyst volatilizes, there is no excess Mo to make up for it, which directly causes the activity, selectivity and stability of the catalyst to decrease. Sample 4 is calcined at 480°C for 9h, and sample 9 is calcined at 350°C for 9h. When the calcination temperature is too low, the Fe deposited on the surface of MoO3 cannot fully react with Mo to form sufficient Fe2(MoO4)3, and the excess Fe exists in the form of Fe2O3, which causes the activity and selectivity of the catalyst to decrease. The precipitation pH value of sample 5 is 1.8, and the precipitation pH value of sample 10 is 2.5. When the precipitation pH value is too high, the surface properties, micro-morphology and phase composition of the catalyst are changed, which further causes the performance of the catalyst to decrease.

[0062] The catalytic performance data of sample 1 and sample 6 after 240h of reaction are listed in Table 2.

[0063] Table 2 Performance of catalysts after 240h of reaction

[0064] Sample No. % CH3OH conversion HCHO selectivity % HCHO yield % 1 98.69 94.97 93.72 6 92.91 87.65 81.43

[0065] As shown in Table 2, when samples 1 and 6 were selected for long-term performance evaluation tests, sample 1 maintained good performance, while sample 6 showed a significant decrease in performance. This is mainly because the present invention uses MoO3 with a large specific surface area as the molybdenum source and employs a deposition-homogenization composite process to deposit and bind Fe onto the surface of MoO3. Then, through a special aging and calcination process, Fe2(MoO4)3 is embedded in the MoO3. The Fe2(MoO4)3 grains in sample 1 are uniform in size, highly dispersed, and tightly interact with MoO3. When the Mo element in Fe2(MoO4)3 is lost due to the catalytic oxidation of methanol to formaldehyde, the tightly bound MoO3 can replenish it, resulting in excellent structural and performance stability of the catalyst in the methanol oxidation to formaldehyde production process. In contrast, sample 6 uses traditional ammonium tetramolybdate as a raw material. The interaction between Fe2(MoO4)3 and MoO3 is not strong enough, leading to easy loss of Mo element that is difficult to replenish, thus resulting in poor catalyst stability.

[0066] At the same time, from Figure 1 and Figure 2 It can be seen that Sample 2, prepared using a deposition-homogenization composite process, exhibits well-distributed small particles on a lamellar structure at the microscopic level. Sample 7, prepared without the homogenization process, lacks a lamellar structure and shows severe particle agglomeration. This invention utilizes the high-energy, high-density, and high-frequency reaction field generated by a homogenizer to fully collide and highly disperse molecules of iron salts, ammonia, molybdenum trioxide, and iron-molybdenum mixtures, resulting in a highly dispersed and uniformly sized iron-molybdenum catalyst. This catalyst demonstrates excellent activity and selectivity when used in the methanol oxidation to formaldehyde production process.

[0067] 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 method for preparing an iron-molybdenum catalyst by a deposition-homogenization process, characterized in that The method comprises the following steps: A certain amount of MoO3 is stirred and mixed with an iron salt solution, and a certain amount of an alkali solution is added into a homogenizer in parallel flow, and the reaction occurs at a precipitation pH value of 1.6-2.2, and then the precursor obtained by the reaction is added into an aging tank, and the iron-molybdenum catalyst is prepared by aging, filtering, drying, calcining and shaping; The component content of the catalyst is expressed by a molar ratio of Mo / Fe=2.4-2.8; MoO3is an industrial grade with a specific surface area of 15 to 45 m 2 / g; The homogenization time of the homogenizer is 5-25 min, and the working pressure of the homogenizer is 10-1500 bar. The calcination temperature is 400-500 DEG C, and the time is 6-12 h.

2. The method of claim 1, wherein the iron-molybdenum catalyst is prepared by a deposition-homogenization composite process, characterized in that, The iron salt is Fe(NO3)2·6H2O or Fe(NO3)3·9H2O, and the alkali solution is dilute ammonia water.

3. The method for preparing iron-molybdenum catalyst by deposition-homogeneous composite process according to claim 1 or 2, characterized in that, The preparation steps are as follows: Step one: a certain amount of Fe(NO3)2·6H2O or Fe(NO3)3·9H2O is weighed and dissolved in a certain amount of deionized water, stirred to fully dissolve and mix uniformly, and named as salt A; A certain amount of MoO3 is accurately weighed; A certain volume of concentrated NH3·H2O is measured, diluted with deionized water, prepared into dilute ammonia water with a certain pH value, and named as alkali B; Step two: a certain amount of deionized water is taken in an aging tank and named as a bottom liquid, and the bottom liquid and the salt A are preheated to the required temperature respectively; Step three: a certain amount of MoO3 is slowly added into the preheated salt A, stirred and mixed uniformly, and a certain amount of alkali B is added into the homogenizer in parallel flow, and the reaction occurs at a certain precipitation pH value, and the precursor obtained by the reaction is added into the aging tank and aged for a period of time under constant temperature stirring; Step four: after aging, the iron-molybdenum catalyst is obtained by filtering, drying, calcining and shaping.

4. The method of claim 3, wherein the iron-molybdenum catalyst is prepared by a deposition-homogenization composite process, characterized in that, In the step one, the pH value of the alkali B is 11.8-13.

2.

5. The method of claim 3, wherein the iron-molybdenum catalyst is prepared by a deposition-homogenization process, characterized in that, In the step two, the preheating temperature of the salt A is 30-80 DEG C, and the preheating temperature of the bottom liquid is 30-80 DEG C.

6. The method of claim 3, wherein the iron-molybdenum catalyst is prepared by a deposition-homogenization composite process, characterized in that, In the step three, the precipitation pH value is controlled to be 1.6-2.2, the aging temperature is 30-80 DEG C, and the aging time is 1-10 h.

7. The method of claim 3, wherein the iron-molybdenum catalyst is prepared by a deposition-homogenization composite process, characterized in that, In the step four, the calcination temperature is 400-500 DEG C, and the time is 6-12 h.

8. Use of an iron-molybdenum catalyst prepared according to the process of any one of claims 1 to 3 or 4 to 7, characterized in that, The catalyst is used for the production of formaldehyde by oxidation of methanol.

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