CN112916019B - Ferromolybdenum catalyst with core-shell structure, preparation and application - Google Patents
Ferromolybdenum catalyst with core-shell structure, preparation and application Download PDFInfo
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- CN112916019B CN112916019B CN202110101681.0A CN202110101681A CN112916019B CN 112916019 B CN112916019 B CN 112916019B CN 202110101681 A CN202110101681 A CN 202110101681A CN 112916019 B CN112916019 B CN 112916019B
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- 239000003054 catalyst Substances 0.000 title claims abstract description 95
- 229910001309 Ferromolybdenum Inorganic materials 0.000 title claims abstract description 35
- 239000011258 core-shell material Substances 0.000 title claims abstract description 29
- 238000002360 preparation method Methods 0.000 title claims abstract description 21
- JKQOBWVOAYFWKG-UHFFFAOYSA-N molybdenum trioxide Chemical compound O=[Mo](=O)=O JKQOBWVOAYFWKG-UHFFFAOYSA-N 0.000 claims abstract description 157
- WSFSSNUMVMOOMR-UHFFFAOYSA-N Formaldehyde Chemical compound O=C WSFSSNUMVMOOMR-UHFFFAOYSA-N 0.000 claims abstract description 89
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 claims abstract description 82
- VCJMYUPGQJHHFU-UHFFFAOYSA-N iron(3+);trinitrate Chemical compound [Fe+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O VCJMYUPGQJHHFU-UHFFFAOYSA-N 0.000 claims abstract description 76
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 50
- 238000000034 method Methods 0.000 claims abstract description 35
- 238000001035 drying Methods 0.000 claims abstract description 28
- 229910052742 iron Inorganic materials 0.000 claims abstract description 25
- 230000008569 process Effects 0.000 claims abstract description 19
- MEFBJEMVZONFCJ-UHFFFAOYSA-N molybdate Chemical compound [O-][Mo]([O-])(=O)=O MEFBJEMVZONFCJ-UHFFFAOYSA-N 0.000 claims abstract description 15
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 claims abstract description 13
- 229910052750 molybdenum Inorganic materials 0.000 claims abstract description 13
- 239000011733 molybdenum Substances 0.000 claims abstract description 13
- 238000005303 weighing Methods 0.000 claims abstract description 13
- 239000002245 particle Substances 0.000 claims abstract description 9
- 230000009471 action Effects 0.000 claims abstract description 5
- 238000006243 chemical reaction Methods 0.000 claims description 36
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 11
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 claims description 10
- 230000003197 catalytic effect Effects 0.000 claims description 9
- 230000003647 oxidation Effects 0.000 claims description 9
- 238000007254 oxidation reaction Methods 0.000 claims description 9
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 6
- 238000004519 manufacturing process Methods 0.000 claims description 4
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- 239000002904 solvent Substances 0.000 claims description 4
- 239000013335 mesoporous material Substances 0.000 claims description 3
- WSFSSNUMVMOOMR-NJFSPNSNSA-N methanone Chemical compound O=[14CH2] WSFSSNUMVMOOMR-NJFSPNSNSA-N 0.000 claims description 3
- 230000001590 oxidative effect Effects 0.000 abstract description 10
- 230000000694 effects Effects 0.000 abstract description 6
- 239000000203 mixture Substances 0.000 abstract description 4
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- 229910002092 carbon dioxide Inorganic materials 0.000 description 12
- 238000012360 testing method Methods 0.000 description 11
- 230000000052 comparative effect Effects 0.000 description 9
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- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 4
- 239000007864 aqueous solution Substances 0.000 description 4
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 3
- 239000001569 carbon dioxide Substances 0.000 description 3
- 229910002091 carbon monoxide Inorganic materials 0.000 description 3
- 238000012512 characterization method Methods 0.000 description 3
- 230000003247 decreasing effect Effects 0.000 description 3
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- 238000002156 mixing Methods 0.000 description 3
- 238000009740 moulding (composite fabrication) Methods 0.000 description 3
- LCGLNKUTAGEVQW-UHFFFAOYSA-N Dimethyl ether Chemical compound COC LCGLNKUTAGEVQW-UHFFFAOYSA-N 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 238000007598 dipping method Methods 0.000 description 2
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- SMZOUWXMTYCWNB-UHFFFAOYSA-N 2-(2-methoxy-5-methylphenyl)ethanamine Chemical compound COC1=CC=C(C)C=C1CCN SMZOUWXMTYCWNB-UHFFFAOYSA-N 0.000 description 1
- NIXOWILDQLNWCW-UHFFFAOYSA-N 2-Propenoic acid Natural products OC(=O)C=C NIXOWILDQLNWCW-UHFFFAOYSA-N 0.000 description 1
- 229910015667 MoO4 Inorganic materials 0.000 description 1
- 239000006004 Quartz sand Substances 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000001354 calcination Methods 0.000 description 1
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- 239000013078 crystal Substances 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 150000002148 esters Chemical class 0.000 description 1
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- -1 iron ions Chemical class 0.000 description 1
- KWUUWVQMAVOYKS-UHFFFAOYSA-N iron molybdenum Chemical compound [Fe].[Fe][Mo][Mo] KWUUWVQMAVOYKS-UHFFFAOYSA-N 0.000 description 1
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/34—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation
- B01J37/341—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation making use of electric or magnetic fields, wave energy or particle radiation
- B01J37/343—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation making use of electric or magnetic fields, wave energy or particle radiation of ultrasonic wave energy
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
- B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
- B01J23/84—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
- B01J23/85—Chromium, molybdenum or tungsten
- B01J23/88—Molybdenum
- B01J23/881—Molybdenum and iron
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- B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
- B01J35/396—Distribution of the active metal ingredient
- B01J35/397—Egg shell like
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- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/02—Impregnation, coating or precipitation
- B01J37/0201—Impregnation
- B01J37/0207—Pretreatment of the support
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C45/00—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds
- C07C45/27—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation
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Abstract
The invention belongs to the field of carbonization chemical engineering, and particularly relates to a ferromolybdenum catalyst with a core-shell structure, and preparation and application thereof. The preparation process comprises the following steps: preparing ferric nitrate solution, weighing dried molybdenum trioxide, completing the process of impregnating the molybdenum carrier by using the iron-containing solution under the action of ultrasonic waves, and then drying, roasting and forming to obtain the ferromolybdenum catalyst with the core-shell structure. The method has the advantages of simple process, few steps and short period, solves the problem of iron loss of the traditional method, and does not generate wastewater in the preparation process. The ferromolybdenum catalyst with the core-shell structure provided by the invention is composed of uniformly distributed iron molybdate and molybdenum trioxide which have a synergistic effect, and the core-shell structure of molybdenum trioxide particles coated by an iron molybdate layer is microscopically formed. The structure effectively inhibits the volatilization loss of molybdenum trioxide, ensures the stability of the composition, physical structure and physical and chemical properties of catalyst elements, and shows excellent activity, selectivity and stability when used for producing formaldehyde by oxidizing methanol.
Description
Technical Field
The invention belongs to the field of carbonization chemical engineering, relates to a ferromolybdenum catalytic material with a novel structure, and preparation and application thereof, and particularly relates to a ferromolybdenum catalyst with a core-shell structure, which is prepared by an ultrasonic-assisted impregnation process, and application thereof in production of high-concentration formaldehyde through methanol oxidation.
Background
China is the first major formaldehyde producing and consuming countries in the world. In the future, with the further increase of the consumption of products such as resin, paint, polyformaldehyde and the like and the rise of novel products such as acrylic acid (ester), polymethoxy dimethyl ether and the like, the demand of high-concentration formaldehyde in China is increasing day by day. As is known, the iron-molybdenum process is an advanced process for producing concentrated formaldehyde, but the ferromolybdenum catalyst used for the process in China seriously depends on import, so that the operation cost of formaldehyde enterprises in China is increased, and the healthy development of the formaldehyde industry in China is hindered to a certain extent. Therefore, under the current situation of the expansion of the global trade war field and the gradual upgrade of the situation, the localization of the ferromolybdenum catalyst is imminent.
The precipitation method is a conventional method for preparing a ferromolybdenum catalyst. Although the catalyst prepared by the method has good activity, molybdenum in the precipitation type bulk catalyst is easy to sublimate and run off due to the structural characteristics of the precipitation type bulk catalyst, so that the physical structure and the catalytic performance of the catalyst are unstable, the service cycle is shortened, and the problems that iron ions cannot be completely precipitated and are lost, the preparation steps and the cycle are long, more waste water is generated and the like exist in the preparation of the ferromolybdenum catalyst by the precipitation method. The sol-gel method is also a more common method for preparing the catalyst, and has the problems of easy volatilization and loss of molybdenum, long preparation steps and period, more generated wastewater and the like of the prepared catalyst, and also has the problems of difficult washing, filtration and forming and the like. The solid phase mixing method, although not having the other problems, still has the problems that the molybdenum of the obtained catalyst is easy to be lost, and the mechanical mixing is a key step, so that the energy consumption for preparing the catalyst is high, and the interphase contact reaction cannot be fully carried out, so that the structure and the performance of the catalyst are relatively poor.
The impregnation method is a simple and efficient catalyst preparation method, but no information is disclosed for the technology for preparing the ferromolybdenum catalyst by the method until now.
Disclosure of Invention
The invention aims to solve the problems in the prior art and provides a preparation method of a ferromolybdenum catalyst with a core-shell structure.
In order to achieve the above object, the technical solution of the present invention is as follows:
a preparation method of a ferromolybdenum catalyst with a core-shell structure comprises the following steps: preparing ferric nitrate solution, weighing dried molybdenum trioxide, completing the process of impregnating the molybdenum carrier by using the iron-containing solution under the action of ultrasonic waves, and then drying, roasting and forming to obtain the ferromolybdenum catalyst with the core-shell structure.
In a preferred embodiment of the present invention, the molar fraction of the solute in the ferric nitrate solution is 1.0 to 5.0mol/L, and the solvent is water, ethanol or acetone.
As a better embodiment in the application, the molybdenum trioxide is a mesoporous material with a large specific surface, and the molybdenum trioxide is dried for 0.5 to 3.0 hours at the temperature of 120 ℃ before use.
As a preferred embodiment in the present application, the process of impregnating the molybdenum carrier with the iron-containing solution is to add molybdenum trioxide to a ferric nitrate solution or to add a ferric nitrate solution dropwise to molybdenum trioxide.
In a preferred embodiment of the present invention, the ultrasonic power is 50-100W, and no solution is applied to the surface of the carrier by oscillation.
As a better embodiment in the application, the drying temperature is 50-120 ℃, and the drying time is 6-18 h.
As a better implementation mode in the application, the roasting temperature is 300-600 ℃, and the roasting time is 1-10 h.
Another object of the present invention is to provide a ferromolybdenum catalyst having a core-shell structure in which molybdenum trioxide particles are coated with an iron molybdate layer, which is prepared by the above method.
In a preferred embodiment of the present invention, the catalyst comprises 50 to 96% by mass, preferably 59 to 88% by mass of an iron molybdate phase and the balance of a molybdenum trioxide phase.
The third invention of the application aims to provide the application of the ferromolybdenum catalyst with the core-shell structure, which is prepared by using an ultrasonic-assisted impregnation process and coated with molybdenum trioxide particles, in the industrial production of preparing high-concentration formaldehyde through methanol oxidation, and specifically aims to generate the high-concentration formaldehyde through the catalytic oxidation of methanol at the reaction temperature of 280-350 ℃.
Compared with the prior art, the invention has the following beneficial effects by adopting the technical scheme:
the first solvent, the water, the ethanol and the acetone are polar solvents, have good affinity adsorption effect on the surface of the molybdenum trioxide, and are ligaments with strong interaction with ferric nitrate molecules dissolved in the molybdenum trioxide. Because the mesoporous molybdenum trioxide with large specific surface is selected as the carrier and is fully dried before dipping, ferric nitrate molecules can fully adsorb and fall on the inner and outer surfaces of the carrier. The dipping process is assisted by continuous oscillation force generated by ultrasonic waves, so that the process that ferric nitrate molecules migrate from a high-density area to a low-density area on the surface of the carrier is strengthened, the preparation effect that the ferric nitrate molecules are uniformly distributed after the ferric nitrate molecules are rearranged on the surface of the molybdenum trioxide carrier is realized, and the prepared catalyst has higher catalytic performance.
Secondly, because ferric nitrate molecules are uniformly distributed on the surface of the molybdenum trioxide and generate strong adhesion with the molybdenum trioxide, the roasted ferric trioxide generated can be fully and closely contacted with the surface of the molybdenum trioxide, and a solid solution reaction is generated to generate an iron molybdate phase, so that a core-shell microstructure with the surface of molybdenum trioxide particles covered by an iron molybdate layer is formed, the physical structure is like a structure that a protective layer is coated on the surface of the molybdenum trioxide, the molybdenum trioxide is not continuously exposed to a reaction material flow containing methanol and water, and the two substances are reported to form a volatile compound with the molybdenum trioxide to cause the loss of the molybdenum trioxide, which is an important reason for causing the loss of the molybdenum trioxide under the normal reaction temperature (the sublimation temperature of the molybdenum trioxide is not reached). The loss of molybdenum not only causes the physical structure of the catalyst to be damaged and the strength to be reduced and gradually pulverized, but also causes the activity, the selectivity and the stability of the catalyst to be reduced and finally deactivated. The invention solves the problem of volatile loss of molybdenum trioxide and ensures the stable physical structure and catalytic performance of the catalyst.
The preparation method of the invention not only has simple process, less steps and short period, but also solves the problem of iron loss in the precipitation method, reduces the production cost of the catalyst and improves the performance of the catalyst. In addition, because washing and filtering are not needed, no wastewater is generated during the preparation of the catalyst, and the production process is more energy-saving and environment-friendly.
Drawings
FIG. 1 is an XRD spectrum before and after a long period test of the catalyst prepared in example 6.
Detailed Description
A preparation method of a ferromolybdenum catalyst with a core-shell structure comprises the following steps: preparing ferric nitrate solution, weighing dried molybdenum trioxide, completing the process of impregnating the molybdenum carrier by the iron-containing solution under the action of ultrasonic waves, and then drying, roasting and forming to obtain the core-shell-shaped ferromolybdenum catalyst.
The molar fraction of solute in the ferric nitrate solution is 1.0-5.0mol/L, and the solvent is water, ethanol or acetone.
The molybdenum trioxide is a mesoporous material with a large specific surface, and is dried for 0.5-3.0h at the temperature of 120 ℃ after being used.
The process for impregnating the molybdenum carrier by the iron-containing solution comprises the following steps: adding molybdenum trioxide to the ferric nitrate solution or adding the ferric nitrate solution dropwise into the molybdenum trioxide.
The ultrasonic power is 50-100W, and no solution exists on the surface of the carrier under the oscillation action.
The drying temperature is 50-120 ℃, and the drying time is 6-18 h.
The roasting temperature is 300-600 ℃, and the roasting time is 1-10 h.
The ferromolybdenum catalyst with the core-shell structure, which is prepared by the preparation method, has a microstructure that molybdenum trioxide particles are coated by an iron molybdate layer.
The mass fraction of the iron molybdate phase in the catalyst is 50-96%, and the balance is a molybdenum trioxide phase.
The application of the ferromolybdenum catalyst with the core-shell structure obtained by the preparation method is suitable for producing high-concentration formaldehyde by catalytic oxidation of methanol, and specifically, the catalyst is used for producing the high-concentration formaldehyde by catalytic oxidation of the methanol at the reaction temperature of 280-350 ℃.
In order to make the objects, technical solutions and advantages of the present invention more clearly apparent, the present invention is further described in detail below with reference to the following embodiments and the accompanying drawings. All of the features disclosed in this specification, or all of the steps in any method or process so disclosed, may be combined in any combination, except combinations of features and/or steps that are mutually exclusive.
Example 1
Drying molybdenum trioxide at 105 ℃ for 2.0 h; preparing 4.5mol/L ferric nitrate aqueous solution; weighing 30.0g of dried molybdenum trioxide, placing the dried molybdenum trioxide in an ultrasonic oscillator with the power set to be 100W, and adding 15.4mL of ferric nitrate solution into the molybdenum trioxide; drying the impregnated carrier without the solution on the surface at 100 ℃ for 15 h; and then roasting at 600 ℃ for 1h to obtain the ferromolybdenum catalyst with the core-shell structure.
The catalyst is used in the reaction of preparing formaldehyde by oxidizing methanol at the reaction temperature of 298 ℃, tail gas is absorbed by water and then trace carbon monoxide and carbon dioxide in the tail gas are analyzed, methanol and formaldehyde in absorption liquid are detected on an Agilent chromatogram, and the performance index of the catalyst is calculated according to the following formula by the obtained data:
YFA＝XMeOH×SFA
note: xMeOHMethanol Single pass conversion, SFASelectivity to formaldehyde, SCOSelectivity to carbon monoxide, SCO2-carbon dioxide selectivity, YFAFormaldehyde yield.
After processing, the following data were obtained:
| XMeOH/％ | SFA/％ | SCO/％ | SCO2/％ | YFA/％ |
| 95.7 | 96.4 | 3.4 | 0.3 | 92.3 |
example 2
Drying molybdenum trioxide at 120 ℃ for 2.5 h; preparing 3.6mol/L ferric nitrate ethanol solution; weighing 30.0g of dried molybdenum trioxide, placing the dried molybdenum trioxide in an ultrasonic oscillator with the power set to 90W, and adding 29.0mL of ferric nitrate solution into the dried molybdenum trioxide; drying the impregnated carrier with no solution on the surface for 8 hours at the temperature of 80 ℃; and then roasting the mixture for 2 hours at the temperature of 450 ℃ to obtain the ferromolybdenum catalyst with the core-shell structure.
The catalyst is used in the reaction of preparing formaldehyde by oxidizing methanol at the reaction temperature of 340 ℃, and the following performance data are obtained by gas-liquid product analysis and experimental data calculation:
| XMeOH/％ | SFA/％ | SCO/％ | SCO2/％ | YFA/％ |
| 99.5 | 93.1 | 6.7 | 0.2 | 92.6 |
example 3
Drying molybdenum trioxide at 110 ℃ for 1.5 h; preparing 3.0mol/L ferric nitrate aqueous solution; weighing 30.0g of dried molybdenum trioxide, placing the dried molybdenum trioxide in an ultrasonic oscillator with the power set to 80W, and adding 31.6mL of ferric nitrate solution into the dried molybdenum trioxide; drying the impregnated carrier without the solution on the surface at 115 ℃ for 12 h; and then roasting at 500 ℃ for 4h to obtain the ferromolybdenum catalyst with the core-shell structure.
The catalyst is used in the reaction of preparing formaldehyde by oxidizing methanol at the reaction temperature of 317 ℃, and the following performance data are obtained by gas-liquid product analysis and experimental data calculation:
| XMeOH/％ | SFA/％ | SCO/％ | SCO2/％ | YFA/％ |
| 99.1 | 95.9 | 3.9 | 0.2 | 95.0 |
example 4
Drying molybdenum trioxide at 115 ℃ for 1.0 h; preparing 1.5mol/L ferric nitrate aqueous solution; weighing 30.0g of dried molybdenum trioxide, placing the dried molybdenum trioxide in an ultrasonic oscillator with the power set to be 50W, and adding 49.6mL of ferric nitrate solution into the dried molybdenum trioxide; drying the impregnated carrier without the solution on the surface at 120 ℃ for 6 hours; and then roasting at 400 ℃ for 7h to obtain the ferromolybdenum catalyst with the core-shell structure.
The catalyst is used in the reaction of preparing formaldehyde by oxidizing methanol at the reaction temperature of 303 ℃, and the following performance data are obtained by gas-liquid phase product analysis and experimental data calculation:
| XMeOH/％ | SFA/％ | SCO/％ | SCO2/％ | YFA/％ |
| 99.5 | 94.2 | 5.5 | 0.3 | 93.7 |
example 5
Drying molybdenum trioxide at 100 ℃ for 3.0 h; preparing 2.0mol/L ferric nitrate acetone solution; weighing 30.0g of dried molybdenum trioxide, placing the dried molybdenum trioxide in an ultrasonic oscillator with power of 70W, and adding 45.3mL of ferric nitrate solution; and drying the impregnated carrier without the solution on the surface at 60 ℃ for 10h, and then roasting at 350 ℃ for 9h to obtain the ferromolybdenum catalyst with the core-shell structure.
The catalyst is used in the reaction of preparing formaldehyde by oxidizing methanol at the reaction temperature of 284 ℃, and the following performance data are obtained by gas-liquid product analysis and experimental data calculation:
| XMeOH/％ | SFA/％ | SCO/％ | SCO2/％ | YFA/％ |
| 99.2 | 92.7 | 6.8 | 0.5 | 92.0 |
example 6
Drying molybdenum trioxide at 120 ℃ for 0.5 h; preparing 2.8mol/L ferric nitrate ethanol solution; weighing 30.0g of dried molybdenum trioxide, placing the dried molybdenum trioxide in an ultrasonic oscillator with the power set to 60W, and adding 29.8mL of ferric nitrate solution into the dried molybdenum trioxide; drying the impregnated carrier without the solution on the surface for 6 hours at 90 ℃, and then roasting the carrier for 2 hours at 550 ℃ to obtain the ferromolybdenum catalyst with the core-shell structure.
The performance of the catalyst for the reaction of preparing formaldehyde by oxidizing methanol is respectively inspected at the following reaction temperatures, and the following performance data are obtained by calculating gas-liquid phase products and experimental data:
| reaction temperature/. degree.C | XMeOH/％ | SFA/％ | SCO/％ | SCO2/％ | YFA/％ |
| 283 | 94.9 | 97.0 | 2.9 | 0.1 | 92.1 |
| 295 | 96.3 | 96.5 | 3.2 | 0.2 | 92.9 |
| 308 | 97.9 | 96.2 | 3.7 | 0.2 | 94.2 |
| 321 | 99.0 | 94.7 | 5.0 | 0.3 | 93.8 |
| 331 | 99.2 | 93.5 | 6.1 | 0.4 | 92.8 |
| 346 | 99.6 | 92.8 | 6.8 | 0.3 | 92.4 |
The catalytic reaction test lasts for about 120 hours, and XRD characterization is carried out on catalyst samples before and after the test, and the result is shown in the attached drawing. XRF characterization of the catalyst before and after the test resulted in the following table:
comparative example 1
Drying molybdenum trioxide at 100 ℃ for 2.5 h; preparing 2.2mol/L ferric nitrate acetone solution; weighing 30.0g of dried molybdenum trioxide, adding 37.7mL of ferric nitrate solution, standing and airing; drying the impregnated carrier without the solution on the surface at 105 ℃ for 9h, and then roasting at 480 ℃ for 6h to obtain the ferromolybdenum catalyst.
The catalyst is used in the reaction of preparing formaldehyde by oxidizing methanol at the reaction temperature of 335 ℃, and the following performance data are obtained by gas-liquid product analysis and experimental data calculation:
| XMeOH/％ | SFA/％ | SCO/％ | SCO2/％ | YFA/％ |
| 94.5 | 87.8 | 11.5 | 0.7 | 83.0 |
comparative example 2
Drying molybdenum trioxide at 120 ℃ for 1.0 h; preparing 1.6mol/L ferric nitrate aqueous solution; weighing 30.0g of dried molybdenum trioxide, placing the dried molybdenum trioxide in an ultrasonic oscillator with power set to 90W, and adding 43.4mL of ferric nitrate solution into the dried molybdenum trioxide; drying the impregnated carrier without the solution on the surface at 110 ℃ for 12h, and then roasting at 290 ℃ for 8h to obtain the ferromolybdenum catalyst.
The temperature of the reactor is kept unchanged, the catalyst is used in the reaction of preparing formaldehyde by oxidizing methanol at the reaction temperature of 326 ℃, the reaction lasts for about 120 hours, and performance data of the catalyst at the beginning and the end of the reaction are obtained by calculating gas-liquid phase products and experimental data:
| reaction time | Reaction temperature/. degree.C | XMeOH/％ | SFA/％ | SCO/％ | SCO2/％ | YFA/％ |
| 12h | 326 | 88.3 | 86.6 | 2.4 | 11.0 | 76.5 |
| 120h | 314 | 82.9 | 83.6 | 3.5 | 12.9 | 69.3 |
XRF characterization of the catalyst before and after this test resulted in the following table:
comparative example 3
Drying molybdenum trioxide at 115 ℃ for 2.0 h; preparing 5.5mol/L ferric nitrate ethanol solution; weighing 30.0g of dried molybdenum trioxide, placing the dried molybdenum trioxide in an ultrasonic oscillator with the power set to 80W, and adding 13.5mL of ferric nitrate solution into the dried molybdenum trioxide; drying the impregnated carrier without the solution on the surface at 75 ℃ for 18h, and then roasting at 420 ℃ for 8h to obtain the ferromolybdenum catalyst.
The catalyst is used in the reaction of preparing formaldehyde by oxidizing methanol at the reaction temperature of 312 ℃, and the following performance data are obtained by gas-liquid product analysis and experimental data calculation:
| XMeOH/％ | SFA/％ | SCO/％ | SCO2/％ | YFA/％ |
| 99.0 | 89.5 | 1.3 | 9.2 | 88.6 |
from the performance evaluation results of the catalysts in examples 1 to 6, it can be seen that the core-shell structure catalyst formed by the molybdenum trioxide particles coated by the iron molybdate layer has excellent performance in the reaction of preparing high-concentration formaldehyde by methanol oxidation, the methanol single-pass conversion rate can reach 99.6%, the formaldehyde selectivity can reach 96.5%, and the formaldehyde yield can reach 95.0%.
As can be seen from the drawing, Fe was detected in the catalysts before and after the reaction in example 62(MoO4)3With MoO3Characteristic peak (SiO appears at a diffraction angle of about 27.1 ℃ in the catalyst after the test)2Characteristic peak caused by mixing quartz sand filler used in the test after the test), and the diffraction angle and the peak intensity of the two characteristic peaks have no obvious change, which indicates that the catalyst consists of two phases of iron molybdate and molybdenum trioxide, and the phase type and the crystal phase structure of the catalyst have no obvious change after the test of about 120 h. From the XRF results for the catalyst of example 6, the elemental composition of the catalyst is essentially unchanged after this longer period of testing, and the catalyst consistently performs well throughout the performance testing, indicating that: the ferromolybdenum catalyst prepared by the ultrasonic-assisted impregnation process generates uniformly-distributed iron molybdate and molybdenum trioxide phases which have a synergistic effect, and a core-shell structure in which an iron molybdate layer coats molybdenum trioxide particles is microscopically formed, so that the volatilization of molybdenum trioxide is effectively inhibited, and the catalyst provided by the invention is stable in composition and structure, and shows excellent and stable performance in a reaction of catalyzing methanol oxidation to prepare formaldehyde.
The performance of the catalysts of comparative examples 1-3 is significantly inferior to the catalysts of examples 1-6. Comparative example 1 no ultrasonic assisted impregnation process was used, but the conventional impregnation method was used, and the conversion of methanol in the obtained catalyst was decreased, the selectivity of carbon monoxide was greatly increased, the selectivity of formaldehyde was greatly decreased, and the yield of formaldehyde was also greatly decreased. Comparative example 3 the prepared ferric nitrate solution with excessive concentration is used for impregnating the carrier, the activity of the obtained catalyst is not influenced, but the selectivity of carbon dioxide is greatly improved, the selectivity of formaldehyde is greatly reduced, and the yield of formaldehyde is also reduced. Comparative example 2 adopts a calcination temperature that is too low, not only greatly reducing the conversion, selectivity and yield of the catalyst, but also greatly reducing the stability of the catalyst by causing the molybdenum in the catalyst to be lost at a rate of 0.72% mass ratio per minute, which is 72 times the rate of molybdenum loss (0.01% mass ratio per minute) of the catalyst in example 6. Since the unfavorable preparation processes in comparative examples 1 to 3 cause a great difference in the performance of the obtained catalysts from those in examples 1 to 6, which is determined by the structure, it is presumed that samples having a structure identical to that of the catalysts in examples 1 to 6, i.e., samples in which the iron molybdate layer covers the microscopic core-shell structure of the molybdenum trioxide particles, were not prepared according to the processes described in comparative examples 1 to 3.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (8)
1. A preparation method of a ferromolybdenum catalyst with a core-shell structure is characterized by comprising the following steps: preparing ferric nitrate solution, weighing dried molybdenum trioxide, completing the process of impregnating the molybdenum carrier with the iron-containing solution under the action of ultrasonic waves, and then drying, roasting and forming to obtain the core-shell-shaped ferromolybdenum catalyst; the mol fraction of solute in the ferric nitrate solution is 1.0-5.0mol/L, and the solvent is water, ethanol or acetone; the roasting temperature is 300-600 ℃, and the roasting time is 1-10 h.
2. The preparation method as claimed in claim 1, wherein the molybdenum trioxide is a mesoporous material with a large specific surface, and is dried at 120 ℃ for 0.5-3.0h before use.
3. The method according to claim 1, wherein the step of impregnating the molybdenum carrier with the iron-containing solution is carried out by adding molybdenum trioxide to a ferric nitrate solution or by adding a ferric nitrate solution dropwise to molybdenum trioxide.
4. The method according to claim 1, wherein the ultrasonic power is 50-100W, and the oscillation is performed until the surface of the carrier is free from the solution.
5. The method according to claim 1, wherein the drying temperature is 50 to 120 ℃ and the drying time is 6 to 18 hours.
6. A ferromolybdenum catalyst having a core-shell structure obtained by the production method according to any one of claims 1 to 4, wherein the catalyst has a microstructure in which molybdenum trioxide particles are coated with an iron molybdate layer.
7. The core-shell structured catalyst according to claim 6, wherein the weight fraction of the iron molybdate phase in the catalyst is 50 to 96%, and the balance is a molybdenum trioxide phase.
8. The use of the ferromolybdenum catalyst with the core-shell structure as claimed in claim 7, wherein the catalyst is suitable for the catalytic oxidation of methanol to produce high-concentration formaldehyde, specifically, the catalyst is suitable for the catalytic oxidation of methanol to produce high-concentration formaldehyde at a reaction temperature of 280-350 ℃.
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