Structural catalyst and preparation method and application thereof
阅读说明：本技术 一种结构型催化剂及其制备方法及应用 (Structural catalyst and preparation method and application thereof ) 是由 万毅 沙宇 孙康 詹吉山 易光铨 李作金 王磊 张永振 黎源 于 2021-01-15 设计创作，主要内容包括：本发明涉及一种结构型催化剂及其制备方法及应用,制备的催化剂具有八面体结构,高活性,热稳定性良好的特点,其应用于低碳醇制备低碳醛的反应过程中,可减少催化剂有效成分的流失,提高催化剂使用寿命,提高反应选择性。该八面体结构型催化剂制备工艺较为特殊,所得催化剂适合于大规模低碳醇制备低碳醛工业化装置应用。(The invention relates to a structural catalyst, a preparation method and application thereof, wherein the prepared catalyst has the characteristics of octahedral structure, high activity and good thermal stability, and can be applied to the reaction process of preparing low-carbon aldehyde from low-carbon alcohol, so that the loss of effective components of the catalyst can be reduced, the service life of the catalyst is prolonged, and the reaction selectivity is improved. The octahedral structure type catalyst is special in preparation process, and the obtained catalyst is suitable for large-scale industrial devices for preparing low-carbon aldehyde from low-carbon alcohol.)
1. A preparation method of a structural catalyst is characterized by comprising the following steps:
a) adding a precursor solution of metal molybdenum and a precursor solution of metal iron into a reaction kettle under the condition of stirring, keeping the temperature of the reaction kettle between 50 and 95 ℃, adjusting the pH value to be 1.0 to 3.0, preferably 1.5 to 2.8, placing the raw material solution into a magnetic field of 100 plus materials of 500A/m, carrying out precipitation and aging under the condition of stirring for 3 to 6 hours, then standing at the temperature of between 50 and 100 ℃, carrying out thermal evaporation for 12 to 48 hours, and drying to obtain a catalyst solid;
b) uniformly mixing the catalyst solid obtained in the step a) and a pore-forming agent, manufacturing and molding, and then roasting at 300-650 ℃, preferably 400-560 ℃ for 10-20 h to obtain a catalyst product.
2. The method for preparing the catalyst according to claim 1, wherein the precursor of the metallic molybdenum is selected from molybdenum element-containing compounds including one or two or more of ammonium polymolybdate, molybdenum trioxide, molybdic acid and molybdenum disulfide, preferably water-soluble molybdenum salt, more preferably ammonium polymolybdate;
preferably, the iron precursor is selected from iron element-containing compounds, including one or more of ferric trichloride, ferric nitrate, ferric oxide and iron powder, preferably ferric trichloride and ferric nitrate.
3. The method for preparing the catalyst according to claim 1, wherein a precursor of another metal is further added in step a), wherein the precursor of another metal is a compound of one or more of the elements bismuth, cobalt, rubidium, cesium, magnesium, strontium and cerium, preferably a water-soluble salt;
preferably, in the metal precursor added in the step a), the molar ratio of molybdenum element, iron element and other metal elements is 0.5-2.2: 0.3-2.8: 0 to 1, preferably 0.5 to 2: 0.3-2.8: 0.1 to 1.
4. The method for preparing a catalyst according to claim 1, wherein the magnetic field strength is preferably 200A/m and 450A/m.
5. The preparation method of the catalyst according to claim 1, wherein the catalyst solid is obtained by filtering and washing after heat evaporation in the step a), drying for 10-28 hours at 50-90 ℃, and then continuously drying for 12-36 hours at 100-300 ℃.
6. The preparation method of the catalyst according to claim 1, wherein the pore-forming agent is one or more of sesbania powder, cellulose, hydroxymethyl cellulose, polyvinyl alcohol, polyethylene, polypropylene, polyvinyl chloride, polyvinylpyrrolidone, starch and pullulan, preferably sesbania powder, cellulose, hydroxymethyl cellulose, polyvinylpyrrolidone and starch;
preferably, the adding amount of the pore-forming agent in the step b) is 1-5% of the mass of the solid catalyst prepared in the step a).
7. The preparation method of the catalyst according to claim 1, wherein a release agent is further added in the step b), wherein the release agent is one or more of stearic acid, magnesium stearate, zinc stearate and graphite, and preferably magnesium stearate, zinc stearate and graphite; the addition amount of the release agent is 0.2-2% of the solid mass of the catalyst prepared in the step a);
preferably, a carrier is also added in the step b), the carrier is a porous alumina carrier, and the addition amount of the carrier is 50-70% of the solid mass of the catalyst prepared in the step a);
preferably, a binder is further added in the step b), the binder is one or more of water, glycol, glycerol, ethanol, graphite, stearic acid, magnesium stearate and zinc stearate, preferably two or more of water, glycerol, graphite and magnesium stearate, and the addition amount of the binder is 10-35% of the solid mass of the catalyst prepared in the step a).
8. The method of claim 1, wherein in the step b), the shaped catalyst is calcined in an atmosphere of one or more of a reducing gas, an oxidizing gas or an inert gas, wherein the reducing gas comprises H2CO, the oxidizing gas comprising O2、H2O and CO2The inert gas comprises He, Ne and N2Ar or Kr;
preferably, the volume fractions of the reducing gas, oxidizing gas and inert gas are 0-50 vol.%, 0-50 vol.% and 0-100 vol.%, respectively.
9. The catalyst prepared by the preparation method according to any one of claims 1 to 8, having a structural formula of: fea+ mBb+ xMoc+ yΔzO4The catalyst is of an octahedral structure, wherein delta is an optional cation vacancy, m, x, y and z are atomic numbers, a, B and c represent ion valence states, B represents other metal elements, and the other metal elements are bismuth, cobalt and rubidiumOne or more of cesium, magnesium, strontium and cerium, wherein z is 3-m-x-y, m × a + x × b + y × c is 8;
preferably, m is more than 0.2 and less than 2.8, x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0.5 and less than or equal to 2, z is more than or equal to 0 and less than 1.2, a is more than or equal to 2 and less than or equal to 3, b is more than or equal to 3 and less than or equal to 5, and c is more than or equal;
more preferably, m is more than or equal to 0.25 and less than or equal to 2.8, x is more than or equal to 0 and less than or equal to 0.5, y is more than or equal to 0.7 and less than or equal to 1.85, and z is more than or equal to 0.5 and less than or equal to 1;
preferably, the cation vacancies are selected from cations of the elements Al, Ca, Co, Cr, Cu, Mg, Mn, Ni, Zn and Ti.
10. Use of the catalyst prepared by the preparation method according to any one of claims 1 to 8, characterized in that the catalyst is used in the reaction for preparing low carbon aldehyde by oxidizing low carbon alcohol, preferably saturated alcohol with five or less carbon atoms, more preferably methanol and ethanol.
Technical Field
The invention relates to the field of catalysts for preparing low-carbon aldehyde by oxidizing low-carbon alcohol, in particular to a structural catalyst and a preparation method and application thereof.
Background
The low-carbon aldehyde is an important basic organic chemical raw material, and plays a significant role in the adjustment of the future energy structure and the development of the chemical industry. The modern industrial low-carbon aldehyde production is mainly produced by a low-carbon alcohol oxidation method. For example, methanol is used for preparing formaldehyde in industrial production, and the ethanol oxidation method is also used for preparing acetaldehyde in industrial production to replace the Wacker method production process.
In the oxide process, aldehydes are generally produced in a tubular reactor. A shell-and-tube reactor usually consists of 10-20000 metal tubes filled with a morphology of solid particulate catalyst and cooled by oil or molten salt as heat transfer fluid. Since the reaction is highly exothermic, it is difficult to obtain a uniform bed temperature profile, and such oxidation reactions typically form hot spots in the reaction zone.
The catalyst used in the oxide process is mainly a molybdenum-based catalyst, e.g. the formaldehyde catalyst is iron molybdate Fe2(MoO4)3And molybdenum trioxide MoO3Wherein the atomic ratio of Mo to Fe is between 0.18 and 6.66. In most respects, the catalytic performance is satisfactory; the formaldehyde yield is high (generally over 93 percent), and the molybdenum and the iron have little toxicity, so the formaldehyde has limited influence on the environment and the human health.
However, molybdenum may volatilize from the catalyst due to the formation of high hot spots of the oxidation reaction, thereby deactivating the catalyst. Molybdenum sublimes from the upper part of the reactor with high methanol concentration and decomposes in the lower part of the reactor to form needle-shaped MoO3And (4) crystals. Due to sublimation and concentration of molybdenumDecomposition, which reduces the catalytic activity and selectivity of the catalyst to aldehydes and can lead to increased pressure drop in the reactor. Therefore, after about 1 to 2 years, or less than 1 year, the catalyst needs to be replaced in view of production economy, and the service life of the catalyst is short.
Disclosure of Invention
The invention provides an octahedral structure type catalyst, a preparation method and application thereof.
The invention provides a preparation method of a structural catalyst, which specifically comprises the following steps:
a) adding a precursor solution of metal molybdenum and a precursor solution of metal iron into a reaction kettle under the condition of stirring, keeping the temperature of the reaction kettle between 50 and 95 ℃, adjusting the pH value to be 1.0 to 3.0, preferably 1.5 to 2.8, placing the raw material solution into a magnetic field of 100 and 500A/m, carrying out precipitation and aging under the condition of stirring for 3 to 6 hours, then standing at the temperature of 50 to 100 ℃, carrying out thermal evaporation for 12 to 48 hours, and drying to obtain a catalyst solid.
b) Uniformly mixing the catalyst solid obtained in the step a) and a pore-forming agent, manufacturing and molding, and then roasting at 300-650 ℃, preferably 400-560 ℃ for 10-20 h to obtain a catalyst product.
The catalyst product can be particles with different shapes such as strip, cylinder, hollow cylinder, sphere and the like, and the catalyst has an octahedral structure.
Preferably, the adding amount of the pore-forming agent in the step b) is 1-5% of the mass of the solid catalyst prepared in the step a).
The precursor of the metal molybdenum in the invention is selected from one or two or more of molybdenum-containing compounds, including ammonium polymolybdate, molybdenum trioxide, molybdic acid, molybdenum disulfide and the like, preferably a water-soluble molybdenum salt, such as ammonium polymolybdate, and usually, the metal molybdenum compound contains a small amount of impurities, and may contain elements such as Al, Ca, Co, Cr, Cu, Mg, Mn, Ni, Zn, Ti and the like.
The precursor of the iron is selected from compounds containing iron elements, including one or more of ferric trichloride, ferric nitrate, ferric oxide and iron powder, preferably ferric trichloride and ferric nitrate.
In step a) of the present invention, precursors of other metals can be optionally added, and the precursors of other metals are compounds of one or more of the elements bismuth, cobalt, rubidium, cesium, magnesium, strontium and cerium, preferably water-soluble salts.
Preferably, in the metal precursor added in the step a), the molar ratio of molybdenum element, iron element and other metal elements is 0.5-2.2: 0.3-2.8: 0 to 1, preferably 0.5 to 2: 0.3-2.8: 0.1 to 1.
To obtain a homogeneous mixing of the elements, the solution may be heated and/or by addition of acids or bases such as ammonia, NaOH, HNO3、H2SO4And HCl and the like.
Preferably, in the step a), the precipitation aging may be performed in ultrasound, and the magnetic field may be generated by using a variable magnetic field generating device, and the magnetic field strength is preferably 200-.
Optionally drying the solid obtained in step a) after thermal evaporation, and if the solid is a dry solid, directly performing step b).
Preferably, the catalyst solid is obtained by filtering and washing after thermal evaporation, drying for 10-28 hours at 50-90 ℃, and then continuously drying for 12-36 hours at 100-300 ℃.
According to the preparation method of the catalyst, the pore-forming agent is one or more of sesbania powder, cellulose, hydroxymethyl cellulose, polyvinyl alcohol, polyethylene, polypropylene, polyvinyl chloride, polyvinylpyrrolidone, starch and pullulan, and preferably sesbania powder, cellulose, hydroxymethyl cellulose, polyvinylpyrrolidone and starch.
In the step b), a release agent can be added, wherein the release agent is one or more of stearic acid, magnesium stearate, zinc stearate and graphite, preferably magnesium stearate, zinc stearate and graphite, and the addition amount of the release agent is 0.2-2% of the solid mass of the catalyst prepared in the step a).
Preferably, a carrier can be further added in the step b), wherein the carrier is a porous alumina carrier, and the addition amount of the carrier is 50-70% of the solid mass of the catalyst prepared in the step a).
Preferably, a binder can be further added in the step b), the binder is one or more of water, glycol, glycerol, ethanol, graphite, stearic acid, magnesium stearate and zinc stearate, preferably two or more of water, glycerol, graphite and magnesium stearate, and the addition amount of the binder is 10-35% of the solid mass of the catalyst prepared in the step a).
Preferably, in the step b), the formed catalyst is calcined in an atmosphere of one or more of reducing gas, oxidizing gas or inert gas, wherein the reducing gas comprises H2CO, the oxidizing gas comprising O2、H2O and CO2The inert gas comprises He, Ne and N2Ar or Kr.
Preferably, the volume fractions of the reducing gas, oxidizing gas and inert gas are 0-50 vol.%, 0-50 vol.% and 0-100 vol.%, respectively.
The invention also provides a catalyst prepared by the preparation method, and the structural formula of the catalyst is as follows: fea+ mBb+ xMoc+ yΔzO4The catalyst has an octahedral structure, wherein delta is an optional cation vacancy, m, x, y and z are atomic numbers, a, B and c represent ionic valence states, and B represents other metal elements, wherein the other metal elements are one or more of bismuth, cobalt, rubidium, cesium, magnesium, strontium and cerium, and z is 3-m-x-y, and m × a + x × B + y × c is 8. Preferably, m is more than 0.2 and less than 2.8, x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0.5 and less than or equal to 2, z is more than or equal to 0 and less than or equal to 1.2, a is more than or equal to 2 and less than or equal to 3, b is more than or equal to 3 and less than or equal to 5, and c is more.
Furthermore, m is more than or equal to 0.25 and less than 2.8, x is more than or equal to 0 and less than or equal to 0.5, y is more than or equal to 0.7 and less than or equal to 1.85, and z is more than or equal to 0.5 and less than or equal to 1.
Preferably, the cation in the cation vacancy can be an impurity metal or nonmetal cation in a precursor of iron, molybdenum or other metals, and preferably, the cation vacancy can be selected from cations of elements such as Al, Ca, Co, Cr, Cu, Mg, Mn, Ni, Zn and Ti.
The catalyst may have cation vacancies in the structure, determined by deviations from the octahedral stoichiometry, determined by the valences of the constituent metals and thus the reaction conditions, i.e. the reaction temperature and the composition of the reaction gases. Cations in composites such as Al, Ca, Co, Cr, Cu, Mg, Mn, Ni, Zn and Ti can also dope with Fe/Mo in an octahedral structure and can successfully fill in cation vacancies.
Preferably, the catalyst has a specific surface area (BET) of 2 to 25m2Per g, preferably 3 to 10m2Per g, more preferably 4 to 6m2/g。
The invention also relates to application of the catalyst prepared by the preparation method disclosed by the invention in the reaction for preparing low-carbon aldehyde by oxidizing low-carbon alcohol, wherein the low-carbon alcohol is preferably saturated alcohol with the carbon number less than five, and more preferably methanol and ethanol.
The catalyst prepared by the method is adopted, and the method for preparing the low-carbon aldehyde by oxidizing the low-carbon alcohol can be carried out by adopting the existing known method.
The invention has the following technical effects:
(1) the octahedral catalyst obtained by the method can be added with metal oxides such as bismuth, cobalt, rubidium, cesium, magnesium, strontium, cerium and the like, so that the reaction temperature can be reduced, and the performance of the catalyst can be improved.
(2) The catalyst prepared by the method has an octahedral structure, the valence state of iron ions is controlled by an external magnetic field in the preparation process of the catalyst, so that the catalyst forms octahedral structure crystals in the processes of precipitation and thermal evaporation, the catalyst with the octahedral structure is more stable, and free iron ions and molybdenum ions can be reduced, so that the activity and the stability of the catalyst are improved, and the service life of the catalyst is prolonged.
Iron, oxygen, molybdenum and other metal ions in the active metal of the catalyst can serve as catalytically active sites in the octahedral sites. The metal cation in octahedral coordination, the 3d orbital crystal field, causes the electron orbital to split into the lower energy t2g orbital and the higher energy eg orbital. When bonded to an oxygen atom, the eg orbital points directly to the electron orbital of oxygen and creates a strong spatial overlap with the 2p of oxygen, creating a strong chemical interaction. The invention can adjust the eg orbital occupancy rate of the metal cations in the octahedral sites by adjusting the types of the metal cations and controlling the synthesis conditions, thereby adjusting the catalytic structure and improving the performance of the catalyst.
(3) The catalyst can oxidize low-carbon saturated alcohol, and is particularly suitable for preparing formaldehyde or acetaldehyde by oxidizing methanol or ethanol. The low-carbon aldehyde prepared by catalytic oxidation of low-carbon alcohol by using the catalyst has the characteristics of high selectivity and low volatility of active elements compared with the traditional iron-molybdenum catalyst.
Description of the drawings:
FIG. 1 is an X-ray diffraction pattern of the catalyst prepared in example 5.
FIG. 2 is an electron micrograph of the catalyst prepared in example 1.
FIG. 3 is an electron micrograph of the catalyst prepared in example 2.
FIG. 4 is an electron micrograph of the catalyst prepared in example 3.
FIG. 5 is an electron micrograph of the catalyst prepared in example 4.
Fig. 6 is an electron micrograph of the catalyst prepared in example 5.
Fig. 7 is an electron micrograph of the catalyst prepared in comparative example 1.
Fig. 8 is an electron micrograph of the catalyst prepared in comparative example 2.
Detailed Description
The present invention is further illustrated by the following examples, but is not limited thereto.
Example 1
36.67g of ammonium heptamolybdate (chemical formula is (NH)4)6Mo7O24·4H2O) is dissolved in 365g of pure water by ultrasonic wave, and solution A is obtained after complete dissolution. 144.29g of iron nitrate (chemical formula is Fe (NO))3)3·9H2O) was dissolved in 360g of pure water to obtain a solution B. Will be provided with1000g of pure water was added as a pot bottom liquid to the reaction pot. Keeping the temperature of the solution in the kettle at 70 ℃, adding the solution B and the solution A into the reaction kettle in a parallel flow manner during stirring, arranging an ultrasonic emission device in the reaction kettle, and generating nano-crystal MoO through ultrasonic precipitation3Then, with MoO3For the core growth octahedral structure, a variable magnetic field generator (model PFMF, Tesister, Suzhou) is adopted, the magnetic field intensity is adjusted to be 450A/m, the precipitation solution is in a constant magnetic field, the pH value is adjusted to be 3 by ammonia water, the precipitation is carried out for 5h under the conditions of stirring and ultrasound, and then the solution is kept stand at 70 ℃ and is subjected to thermal evaporation aging for 42 h. Drying at 80 deg.C for 12 hr, further drying at 150 deg.C for 24 hr to obtain block catalyst solid, and crushing to obtain 50.5g of 60-30 mesh granules.
Taking 50g of granules with 60 meshes to 30 meshes, adding 2.5g of a pore-forming agent sesbania powder and 1g of lubricant magnesium stearate, uniformly mixing, and forming into hollow cylindrical granules by a tablet machine.
And roasting the formed particles at 450 ℃ for 20h to obtain the catalyst.
The octahedral structural formula of the formed catalyst core element is Fe3+ 1.52Mo4+ 0.86Δ0.62O4. The configuration is shown in figure 2
Evaluation of Oxidation test
25g of catalyst is loaded into a 50cm long reactor, wherein the reaction tube is a stainless steel reaction tube with phi 25mm, and the pretreatment process of the catalyst is as follows: firstly, air is fed, and the volume space velocity is 8000h-1Heating the reaction tube from room temperature to 250 ℃ at a heating rate of 5 ℃/min, keeping the temperature for 120min, switching to nitrogen purging for 180min, and purging the volume space velocity for 1000h-1. After the pretreatment of the catalyst is finished, the catalyst is pretreated at a molar ratio of methanol, oxygen, nitrogen and water of 1:1.3:10:0.13 and a volume space velocity of 10000h-1(Standard state), the temperature is 330 ℃, and the oxidation reaction is carried out under the condition of normal pressure. And (3) reaction results: the initial methanol conversion rate was 98.4%, the formaldehyde selectivity was 94.6%, and after 2000h operation, the methanol conversion rate was 97.2%, and the formaldehyde selectivity was 94%.
Example 2
174.59g of ammonium heptamolybdate (chemical formula is (NH)4)6Mo7O24·4H2O) was dissolved in 573g of pure water to obtain a solution A after complete dissolution. 57.71g of iron nitrate (chemical formula is Fe (NO))3)3·9H2O) was dissolved in 140g of pure water to obtain a solution B. 1000g of pure water was added as a pot bottom liquid to the reaction pot. Keeping the temperature of the solution in the kettle at 80 ℃, adding the solution B and the solution A into the reaction kettle in a parallel flow manner during stirring, and generating nanocrystal MoO through ultrasonic precipitation3Then, with MoO3For the core growth octahedral structure, a variable magnetic field generator (model PFMF, Tesister, Suzhou) is adopted, the magnetic field intensity is adjusted to be 150A/m, the precipitation solution is in a constant magnetic field, ammonia water is adopted to adjust the pH value to be 2.1, an ultrasonic emission device is arranged in a reaction kettle, the precipitation is carried out for 5 hours under the conditions of stirring and ultrasonic, and then the precipitation is carried out for 24 hours by standing, thermal evaporation and aging at 90 ℃.
Drying at 80 deg.C for 12 hr, further drying at 150 deg.C for 20 hr to obtain block catalyst solid, and crushing to obtain 58.7g of 60-30 mesh granules.
Taking 50g of particles with 60 meshes to 30 meshes, adding 0.5g of pore-forming agent cellulose and 1g of lubricant graphite, uniformly mixing, and forming into hollow cylindrical particles by a tablet press.
And roasting the formed particles at 400 ℃ for 20h to obtain the catalyst.
The structural formula of the formed catalyst core element is Fe3+ 0.26Mo4+ 1.8Δ0.94O4. The configuration is shown in figure 3
Evaluation of Oxidation test
The evaluation was conducted in the same manner as in example 1, and the evaluation results are shown in Table 1.
Example 3
126.11g of ammonium heptamolybdate (chemical formula is (NH)4)6Mo7O24·4H2O) was dissolved in 417g of pure water to obtain solution A after complete dissolution. 108.22g of iron nitrate (chemical formula is Fe (NO))3)3·9H2O) was dissolved in 270g of pure water to obtain a solution B. 15.96g of bismuth nitrate (Bi (NO)3)3·5H2O) was dissolved in 1000g of 0.2% strength dilute nitric acid as a pot bottom.Keeping the temperature of the solution in the kettle at 85 ℃, adding the solution B and the solution A into the reaction kettle in parallel flow during stirring, arranging an ultrasonic emission device in the reaction kettle, and generating nano-crystal MoO through ultrasonic precipitation3Then, with MoO3For the core growth octahedral structure, a variable magnetic field generator (model PFMF, Tesister, Suzhou) is adopted, the magnetic field intensity is adjusted to 250A/m, the precipitation solution is in a constant magnetic field, the pH value is adjusted to 1.5 by ammonia water, the precipitation is carried out for 4h under the conditions of stirring and ultrasound, and then the solution is stood at 95 ℃ and subjected to thermal evaporation aging for 38 h.
A massive catalyst solid was obtained and crushed to obtain 87.55g of particles of 60 mesh to 30 mesh.
Taking 50g of particles with 60 meshes to 30 meshes, adding 0.5g of pore-forming agent cellulose and 1g of lubricant graphite, uniformly mixing, and forming into hollow cylindrical particles by a tablet press.
And roasting the formed particles at 450 ℃ for 20h to obtain the catalyst.
The octahedral structural formula of the formed catalyst core element is Fe3+ 0.57Bi3+ 0.07Mo4+ 1.52Δ0.84O4. The configuration is shown in figure 4.
Evaluation of Oxidation test
The evaluation was conducted in the same manner as in example 1, and the evaluation results are shown in Table 1.
Example 4
143.31g of ammonium heptamolybdate (chemical formula is (NH)4)6Mo7O24·4H2O) was dissolved in 469g of pure water to obtain solution A after complete dissolution. 72.15g of iron nitrate (chemical formula is Fe (NO))3)3·9H2O) was dissolved in 180g of pure water to obtain a solution B. 89.25g of bismuth nitrate (Bi (NO)3)3·5H2O) is dissolved in 1000g of dilute nitric acid with the concentration of 0.2 percent and added into the reaction kettle as kettle bottom liquid. Keeping the temperature of the solution in the kettle at 60 ℃, adding the solution B and the solution A into the reaction kettle in a parallel flow manner during stirring, arranging an ultrasonic emission device in the reaction kettle, and generating nano-crystal MoO through ultrasonic precipitation3Then, with MoO3Growing octahedral structure as core, and adopting variable magnetic field generator (model PFMF, Suzhou Taisi)Specially), adjusting the magnetic field intensity to 350A/m, enabling the precipitation solution to be in a constant magnetic field, adjusting the pH value to 1.8 by using ammonia water, precipitating for 5 hours under the conditions of stirring and ultrasound, and then standing at 65 ℃ for thermal evaporation and aging for 42 hours.
Drying at 80 deg.C for 18 hr, further drying at 180 deg.C for 18 hr to obtain solid block, and crushing to obtain 74.55g of 60-30 mesh granules.
Taking 50g of particles with 60 meshes to 30 meshes, adding 1.25g of a pore-forming agent sesbania powder and 0.5g of lubricant graphite, uniformly mixing, and forming by using a tablet press to obtain hollow cylindrical particles.
And roasting the formed particles at 450 ℃ for 20h to obtain the catalyst.
The octahedral structural formula of the formed catalyst core element is Fe3+ 0.33Bi3+ 0.34Mo4+ 1.5Δ0.83O4. The configuration is shown in figure 5.
Evaluation of Oxidation test
The evaluation was conducted in the same manner as in example 1, and the evaluation results are shown in Table 1.
Example 5
156.305g of ammonium heptamolybdate (chemical formula is (NH)4)6Mo7O24·4H2O) was dissolved in 521g of pure water to obtain a solution A. 129.86g of iron nitrate (chemical formula is Fe (NO))3)3·9H2O) was dissolved in 320g of pure water to obtain a solution B. 1000g of pure water was added as a pot bottom liquid to the reaction pot. Keeping the temperature of the solution in the kettle at 75 ℃, adding the solution B and the solution A into the reaction kettle in a parallel flow manner during stirring, arranging an ultrasonic emission device in the reaction kettle, and generating nano-crystal MoO through ultrasonic precipitation3Then, with MoO3For the core growth octahedral structure, a variable magnetic field generator (model PFMF, Tesister, Suzhou) is adopted, the magnetic field intensity is adjusted to be 200A/m, the precipitation solution is in a constant magnetic field, the pH value is adjusted to be 2.5 by ammonia water, the precipitation is carried out for 5 hours under the conditions of stirring and ultrasound, and then the solution is kept stand at 75 ℃ and is subjected to thermal evaporation aging for 24 hours. Drying at 80 deg.C for 12 hr, further drying at 200 deg.C for 24 hr to obtain block solid, crushing, and grinding to obtain 10674g of powder.
Taking 50g of powder, adding 2.5g of pore-forming agent polyvinylpyrrolidone, uniformly mixing, weighing 30g of porous alumina carrier with the diameter of 3mm, preparing 15g of glycerol aqueous solution with the concentration of 20% of binder, and performing rolling molding to obtain spherical particles
And roasting the molded particles at 450 ℃ for 20h to obtain the spherical catalyst.
The octahedral structural formula of the formed catalyst core element is Fe3+ 0.57Mo4+ 1.57Δ0.86O4. The configuration is shown in figure 6, and XRD is shown in figure 1.
Evaluation of Oxidation test
The evaluation was conducted in the same manner as in example 1, and the evaluation results are shown in Table 1.
Comparative example 1
174.59g of ammonium heptamolybdate (chemical formula is (NH)4)6Mo7O24·4H2O) was dissolved in 573g of pure water to obtain a solution A after complete dissolution. 57.71g of iron nitrate (chemical formula is Fe (NO))3)3·9H2O) was dissolved in 140g of pure water to obtain a solution B. 1000g of pure water was added as a pot bottom liquid to the reaction pot. Keeping the temperature of the solution in the kettle at 80 ℃, adding the solution B and the solution A into the reaction kettle in a parallel flow manner during stirring, and generating nano-crystal MoO through ultrasonic in the precipitation process3Then, with MoO3Taking the precipitate as a core, adjusting the pH value to be 2.1 by adopting ammonia water, and after the addition of the raw materials is finished, keeping the precipitate solution at 95 ℃, standing, thermally evaporating and aging for 24 hours.
Drying at 80 deg.C for 12 hr, further drying at 150 deg.C for 20 hr to obtain block solid, and crushing to obtain 58g of 60-30 mesh granules.
Taking 50g of particles with 60 meshes to 30 meshes, adding 0.5g of pore-forming agent cellulose and 1g of lubricant graphite, uniformly mixing, and forming into hollow cylindrical particles by a tablet press.
And roasting the formed particles at 500 ℃ for 20 hours to obtain the catalyst.
The structural formula of the formed catalyst core element is Fe3+ 0.26Mo4+ 1.8Δ0.94O4. The configuration is shown in FIG. 7.
Evaluation of Oxidation test
The evaluation was conducted in the same manner as in example 1, and the evaluation results are shown in Table 1.
Comparative example 2
174.59g of ammonium heptamolybdate (chemical formula is (NH)4)6Mo7O24·4H2O) was dissolved in 573g of pure water to obtain a solution A after complete dissolution. 57.71g of iron nitrate (chemical formula is Fe (NO))3)3·9H2O) was dissolved in 140g of pure water to obtain a solution B. 1000g of pure water was added as a pot bottom liquid to the reaction pot. Keeping the temperature of the solution in the kettle at 80 ℃, adding the solution B and the solution A into the reaction kettle in a parallel flow manner during stirring, arranging an ultrasonic emission device in the reaction kettle, and generating nano-crystal MoO through ultrasonic in the precipitation process3Then, with MoO3The method is characterized in that ammonia water is adopted to adjust the pH value to be 2.1, a variable magnetic field generating device (model PFMF, Tesister, Suzhou) is adopted to adjust the magnetic field intensity to be 50A/m, so that the precipitation solution is in a constant magnetic field, and after the raw materials are added, the precipitation solution is kept at 95 ℃ and is kept stand for thermal evaporation and aging for 24 hours.
Drying at 80 deg.C for 12 hr, further drying at 150 deg.C for 20 hr to obtain solid block, and crushing to obtain 59g of 60-30 mesh granules.
Taking 50g of particles with 60 meshes to 30 meshes, adding 0.5g of pore-forming agent cellulose and 1g of lubricant graphite, uniformly mixing, and forming into hollow cylindrical particles by a tablet press.
And roasting the formed particles at 500 ℃ for 20 hours to obtain the catalyst.
The structural formula of the formed catalyst core element is Fe3+ 0.26Mo4+ 1.8Δ0.94O4. The configuration is shown in figure 8.
Evaluation of Oxidation test
The evaluation was conducted in the same manner as in example 1, and the evaluation results are shown in Table 1.
Table 1 evaluation results of catalysts of examples and comparative examples
Table 2 general formula of proportional structure of each element in examples
The proportion structural formula of each element
Example 1
Fe3+ 1.52Mo4+ 0.86Δ0.62O4
Example 2
Fe3+ 0.26Mo4+ 1.8Δ0.94O4
Example 3
Fe3+ 0.57Bi3+ 0.07Mo4+ 1.52Δ0.84O4
Example 4
Fe3+ 0.33Bi3+ 0.34Mo4+ 1.5Δ0.83O4
Example 5
Fe3+ 0.57Mo4+ 1.57Δ0.86O4
Comparative example 1
Fe3+ 0.26Mo4+ 1.8Δ0.94O4
Comparative example 2
Fe3+ 0.26Mo4+ 1.8Δ0.94O4
In addition to showing high selectivity (> 90%) for formaldehyde from methanol and oxygen in an inert medium, the catalysts of the examples failed to detect volatilization of bismuth or molybdenum from the catalysts of the invention after 30 days at 300 ℃ in a stream of flowing gas of 10% methanol and 10% oxygen in nitrogen.
Table 3 example 30 weather flow effect element test results
Mo loss (wt%)
Bi loss (wt%)
Example 1
Not detected out
-
Example 2
Not detected out
-
Example 3
Not detected out
Not detected out
Example 4
Not detected out
Not detected out
Example 5
Not detected out
-
Comparative example 1
0.1
-
Comparative example 2
0.05
-