CN109847762B - Catalyst for reaction of synthesizing p-aminophenol by hydrogenation, preparation method and application - Google Patents
Catalyst for reaction of synthesizing p-aminophenol by hydrogenation, preparation method and application Download PDFInfo
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Abstract
The invention discloses a catalyst for the reaction of synthesizing p-aminophenol by hydrogenation, which comprises the following components: the core comprises a core and a mesoporous silica shell coating the core, and the material of the core comprises a noble metal-magnetic oxide. The core of the catalyst is composed of 'noble metal-magnetic oxide', and the core is wrapped by the shell, so that the strong interaction of the contact interface of 'noble metal and magnetic oxide' can be enhanced under the condition of avoiding agglomeration, the activity and the application range of the catalyst can be greatly improved, and meanwhile, due to the existence of the magnetic oxide, the catalyst can be separated by a magnet, so that the catalyst is convenient to recover, and the utilization rate is improved. Meanwhile, the invention also provides a preparation method of the catalyst, the preparation method is simple and easy to operate, the size and the dimension of the product can be adjusted according to requirements, the catalyst is applied to the hydrogenation reaction of p-nitrophenol, and the conversion rate and the selectivity of the reaction can be improved.
Description
Technical Field
The invention relates to a catalyst for a reaction for synthesizing p-aminophenol by hydrogenation and a preparation method thereof, in particular to a catalyst which can be applied to a reaction for synthesizing p-aminophenol by hydrogenating p-nitrophenol and a preparation method thereof.
Background
The p-nitrophenol is a common intermediate in organic, and is widely applied to the fields of medicines, dye rubber and the like. The prior production methods of p-aminophenol include a reduction method of p-nitro iron powder, a nitrobenzene catalytic hydrogenation method and the like. The catalytic hydrogenation method of nitrobenzene uses nitrobenzene as raw material, and catalytic hydrogenation reduction is carried out in an acid medium, and the method has low reuse rate of noble metal and low selectivity.
Patent publication No. CN106311274A discloses a catalyst in which Ru is supported on silica and magnetic cores can be easily recycled. However, the magnetic core is not completely wrapped by the silica shell layer, so that the particles become large after high-temperature treatment, and the utilization rate of ferroferric oxide is greatly reduced. And no strong interaction interface of the noble metal and the oxide exists, so that the catalytic activity is not further improved.
The patent publication No. CN107952466A discloses a gold-supported h-BN catalyst, the synthesis method is simple, the catalytic flow is easy to operate, but the catalyst has no magnetism and is difficult to recover.
Disclosure of Invention
The invention mainly aims to provide a catalyst for the reaction of synthesizing p-aminophenol by hydrogenation, a preparation method and application thereof, so as to overcome the defects in the prior art.
In order to achieve the purpose, the technical scheme adopted by the invention comprises the following steps:
the embodiment of the invention provides a catalyst for a reaction of synthesizing p-aminophenol by hydrogenation, which comprises the following components: the core comprises a core and a mesoporous silica shell coating the core, and the material of the core comprises a noble metal-magnetic oxide.
The embodiment of the invention also provides a preparation method of the catalyst for the reaction of synthesizing p-aminophenol by hydrogenation, which comprises the following steps:
(1) adding a precursor of noble metal into a first oil phase containing a first surfactant, reacting, adding an alcohol solvent, obtaining a precipitate, centrifuging, washing at least once by using a mixture of the alcohol solvent and alkane to obtain noble metal particles, and dispersing the obtained noble metal particles in an alkane solution to form a first mixed system;
(2) adding the first mixed system into a second oil phase containing a first surfactant and a magnetic oxide precursor, introducing inert gas, reacting, adding an alcohol solvent and chloroform, washing, centrifuging to obtain precious metal-magnetic oxide particles, and dispersing the precious metal-magnetic oxide particles in a chloroform solution to form a second mixed system;
(3) mixing the second mixed system with an aqueous solution containing a second surfactant, heating and stirring, and evaporating chloroform to dryness to obtain an aqueous solution containing precious metal-magnetic oxide particles;
(4) and (2) reacting the aqueous solution containing the noble metal-magnetic oxide particles with ammonia water and TEOS, adding an alcohol solvent, centrifuging to obtain a precipitate, and then carrying out aftertreatment to obtain the catalyst.
The embodiment of the invention also provides application of the catalyst in the reaction of synthesizing p-aminophenol by hydrogenation, in particular to the reaction of synthesizing p-aminophenol by hydrogenating p-nitrophenol.
The embodiment of the invention also provides a method for synthesizing p-aminophenol, which comprises the following steps: the catalyst is adopted to participate in the reaction of synthesizing p-aminophenol by hydrogenation, in particular to the reaction of synthesizing p-aminophenol by hydrogenating p-nitrophenol.
Compared with the prior art, the invention has the advantages that:
1) the catalyst with magnetic particles as the core is synthesized, can be separated by magnet adsorption, and is convenient for collection and recycling, and the interface of the strong interaction of the noble metal and the magnetic oxide can improve the catalytic effect.
2) The preparation method of the catalyst for the reaction of synthesizing p-aminophenol by hydrogenation, provided by the invention, has the advantages of simple process, easiness in operation, convenience in popularization and industrial application. The size and dimension of the product can be adjusted according to requirements, and the product is applied to the hydrogenation reaction of p-nitrophenol, so that the conversion rate and selectivity of the reaction can be improved.
Drawings
Fig. 1 is a schematic structural view of a catalyst for a reaction of synthesizing p-aminophenol by hydrogenation in an exemplary embodiment of the present invention.
Fig. 2 is an SEM image of a catalyst for a reaction of synthesizing p-aminophenol through hydrogenation in an exemplary embodiment of the present invention.
Detailed Description
In view of the defects of the prior art, the inventor of the present invention has made extensive research and practice to propose the technical solution of the present invention, and further explains the technical solution, the implementation process and the principle, etc. as follows. It is to be understood, however, that within the scope of the present invention, each of the above-described features of the present invention and each of the features described in detail below (examples) may be combined with each other to form new or preferred embodiments. Not to be reiterated herein, but to the extent of space.
An aspect of an embodiment of the present invention provides a catalyst for a reaction of synthesizing p-aminophenol by hydrogenation, including: the core comprises a core and a mesoporous silica shell coating the core, and the material of the core comprises a noble metal-magnetic oxide.
Wherein, the core is dumbbell-shaped.
In some embodiments, the noble metal comprises any one or a combination of two or more of Au, Pt, Pd, Ir, Os, Ru, Rh, and Ag.
In some embodiments, the noble metal has a size of 2 to 9 nm.
In some embodiments, the magnetic oxide includes an oxide of any one or two or more elements of Fe, Co, and Ni.
Including oxides in various phases.
In some embodiments, the magnetic oxide is 9-20nm in size.
In some embodiments, the mesoporous silica shell has a thickness of 1 to 20nm and contains pores having a pore size of less than 50 nm.
In some embodiments, the noble metal accounts for 0.01 wt% to 6 wt% of the catalyst, and the magnetic oxide accounts for 0.01 wt% to 20 wt% of the catalyst.
An aspect of an embodiment of the present invention also provides a method for preparing a catalyst for a reaction of synthesizing p-aminophenol by hydrogenation, including:
(1) adding a precursor of noble metal into a first oil phase containing a first surfactant, reacting, adding an alcohol solvent, obtaining a precipitate, centrifuging, washing at least once by using a mixture of the alcohol solvent and alkane to obtain noble metal particles, and dispersing the obtained noble metal particles in an alkane solution to form a first mixed system;
(2) adding the first mixed system into a second oil phase containing a first surfactant and a magnetic oxide precursor, introducing inert gas, reacting, adding an alcohol solvent and chloroform, washing, centrifuging to obtain precious metal-magnetic oxide particles, and dispersing the precious metal-magnetic oxide particles in a chloroform solution to form a second mixed system;
(3) mixing the second mixed system with an aqueous solution containing a second surfactant, heating and stirring, and evaporating chloroform to dryness to obtain an aqueous solution containing precious metal-magnetic oxide particles;
(4) and (2) reacting the aqueous solution containing the noble metal-magnetic oxide particles with ammonia water and TEOS, adding an alcohol solvent, centrifuging to obtain a precipitate, and then carrying out aftertreatment to obtain the catalyst.
In some embodiments, the reaction temperature in step (1) is 110-.
In some embodiments, the reaction temperature in step (2) is 230-300 ℃ and the reaction time is 1-3 h.
In some embodiments, the heating temperature in step (3) is 65-70 ℃.
In some embodiments, the reaction time in step (4) is 1 to 3 hours.
In some embodiments, the post-treatment comprises: drying the obtained precipitate, and then calcining for 1-3h at the temperature of 450-550 ℃.
In some embodiments, the first surfactant comprises at least one or both of oleic acid and oleylamine.
In some embodiments, the alcohol solvent comprises at least one or both of ethanol and isopropanol.
In some embodiments, the first oil phase comprises at least one or both of octadecene and diphenyl ether.
In some embodiments, the second oil phase comprises at least one or both of octadecene and diphenyl ether.
In some embodiments, the alkane comprises hexane.
In some embodiments, the second surfactant comprises a cationic surfactant.
Further, the cationic surfactant includes any one or a combination of two or more of dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide.
In some embodiments, the mass ratio of the precursor of the noble metal to the first oil phase in step (1) is from 0.004 to 0.02: 1.
In some embodiments, the mass ratio of the first surfactant to the first oil phase in step (1) is from 0.0012 to 0.01: 1.
In some embodiments, the mass ratio of the alcoholic solvent to the first oily phase in step (1) is from 1-4: 1.
In some embodiments, the mass ratio of alcohol solvent to alkane in the mixture in step (1) is 1-2: 1.
In some embodiments, the mass ratio of the precursor of the noble metal to the second oil phase in step (2) is 0.002 to 0.01: 1.
In some embodiments, the mass ratio of the magnetic oxide precursor to the second oil phase in step (2) is from 0.15 to 0.5: 1.
In some embodiments, the mass ratio of the first surfactant to the second oil phase in step (2) is from 0.0012 to 0.01: 1.
In some embodiments, the mass ratio of the alcoholic solvent to chloroform in step (2) is 1-2: 1.
In some embodiments, the mass ratio of the second surfactant to water in step (3) is 0.02 to 0.3: 1.
In some embodiments, the mass ratio of the aqueous ammonia to water in step (4) is 0.02-0.3: 1.
In some embodiments, the mass ratio of TEOS to water in step (4) is 0.02-0.1: 1.
For example, in an exemplary embodiment of the present invention, a method for preparing a catalyst for a reaction of synthesizing p-aminophenol by hydrogenation, comprises the steps of:
(1) adding chloroauric acid into the first oil phase containing the first surfactant, magnetically stirring, reacting at 130 ℃ for 1h, adding an alcohol solvent to obtain a precipitate, centrifuging, and washing with a mixture of the alcohol solvent and the alkane for multiple times. Finally, dispersing the particles in an alkane solution to form a first mixed system;
(2) adding the first mixed system into a second oil phase containing a first surfactant and a precursor of the magnetic oxide, introducing inert gas, and blowing out alkane and other impurities for a period of time. Then heated to 300 ℃. Keeping the reaction time for 1h, cooling to room temperature, adding an alcohol solvent and chloroform for washing, centrifuging to obtain a precipitate, and finally dispersing the particles in a chloroform solution to form a second mixed system;
(3) mixing the second mixed system with an aqueous solution containing a second surfactant, heating and stirring at 65-70 ℃, and evaporating chloroform to dryness to obtain an aqueous solution containing magnetic particles;
(4) adding a certain amount of ammonia water and TEOS into an aqueous solution containing magnetic particles, reacting for 3h, adding an alcohol solvent into the solution, centrifuging to obtain a precipitate, and drying;
(5) calcining the dried particles for 1-2h at the temperature of 450-550 ℃ to finally obtain the composition: a dumbbell-shaped core of 'noble metal-magnetic oxide' and magnetic particles of mesoporous silica shells.
In the exemplary embodiment, the structure of the catalyst obtained can be seen in FIG. 1, and the SEM is seen in FIG. 2. The catalyst comprises the following components: the core is dumbbell-shaped, wherein the core comprises noble metal 1, magnetic oxide 2 and mesoporous silica shell 3 coating the core, and the mesoporous silica shell 3 is provided with a pore passage 4.
In the typical embodiment of the invention, the dumbbell-shaped core is composed of the precious metal-magnetic oxide, and after high-temperature calcination, the shell is used for wrapping, so that the strong interaction of the contact interface of the precious metal and the magnetic oxide can be enhanced under the condition of avoiding agglomeration, the activity and the application range of the catalyst can be greatly improved, and meanwhile, due to the existence of the magnetic oxide, the dumbbell-shaped core can be separated by a magnet, is convenient to recover and improves the utilization rate.
An aspect of an embodiment of the present invention also provides a use of the catalyst in a reaction for synthesizing p-aminophenol by hydrogenation, particularly a reaction for synthesizing p-aminophenol by hydrogenation of p-nitrophenol.
An aspect of an embodiment of the present invention also provides a method for synthesizing p-aminophenol, including: the catalyst is adopted to participate in the reaction of synthesizing p-aminophenol by hydrogenation, in particular to the reaction of synthesizing p-aminophenol by hydrogenating p-nitrophenol.
The reaction for synthesizing p-aminophenol by hydrogenating p-nitrophenol can be low-temperature liquid-phase catalytic hydrogenation reaction and the like
For example, a method for synthesizing p-aminophenol by hydrogenation may specifically include: adding the catalyst and the p-nitrophenol aqueous solution into a reactor, adding hydrogen, and controlling the reaction temperature to be normal temperature and the pressure to be normal pressure. The mass ratio of the catalyst to the p-nitrophenol is about 3:1, and the reaction time is about 30 minutes. After the reaction is completed, the product can be detected and analyzed by a conventional means such as gas chromatography. The method can also be used to perform activity tests of the catalyst.
The technical solution of the present invention is further described in detail by the following examples. However, the examples are chosen only for the purpose of illustrating the invention and are not to be construed as limiting the scope of the invention.
Example 1
The preparation process of the catalyst according to this example includes the following steps:
(1) preparation of noble metal particles:
40mg of chloroauric acid was added to 10g of octadecene containing 12mg of oleic acid, 12mg of oleylamine as both surfactants, magnetically stirred, reacted at 110 ℃ for 0.5h, then 10g of hexanol was added to obtain a precipitate and centrifuged, and then washed with a mixture of 10g of hexanol and 10g of hexane several times. Finally, the particles were dispersed in 10g of hexane (described as solution A) for further use.
(2) Preparation of a "noble metal-magnetic oxide" dumbbell-shaped core:
adding the solution A in the step (1) into 10g of octadecene containing 12mg of oleic acid, 12mg of oleylamine, two surfactants and 1.5g of iron oleate, introducing inert gas, and blowing out hexane and other impurities for a period of time. Then heated to 230 ℃. The reaction time is kept for 1h, the reaction temperature is reduced to room temperature, 10g of ethanol and 10g of chloroform are added for washing, the precipitate is obtained by centrifugation, and finally the particles are dispersed in 10mL of chloroform solution for standby (recorded as solution B).
(3) The particles were changed from oil phase to water phase:
"solution B" in (2) above was mixed with 50mL of an aqueous solution containing 1g of cetyltrimethylammonium bromide surfactant, and heated and stirred at 65 ℃ to evaporate chloroform to dryness. An aqueous solution containing magnetic particles (denoted as solution C) was obtained.
(4) Wrapping the shell:
1g of ammonia water and 1g of TEOS were added to the "solution C" of the above (3), and after reaction h, 25mL of ethanol was added to the solution, followed by centrifugation to obtain a precipitate and drying.
(5) High-temperature calcination:
and (4) calcining the dried particles in the step (4) at 450 ℃ for 1h to finally obtain the catalyst.
ICP data indicated that the catalyst had an Au content of 0.01 wt% and an Fe content of 0.01 wt%. TEM test data show that the thickness of the silicon dioxide mesoporous layer in the catalyst is 1nm, the particle size of gold particles is about 2nm, and the particle size of ferroferric oxide particles is about 9 nm. N is a radical of2Adsorption and desorption tests show that the pore diameter of the pore canal in the silicon dioxide mesoporous layer is about 2 nm.
Adding the catalyst and the aqueous solution of p-nitrophenol into a reactor, introducing hydrogen, and introducing hydrogen at normal temperature and normal pressure. The mass ratio of the catalyst to the p-nitrophenol is 3:1, and the reaction time is 30 min. After the reaction is finished, the product is detected and analyzed by adopting gas chromatography, the conversion rate of the p-nitrophenol is calculated to be 73.1 percent, and the selectivity of the generated p-aminophenol is 78.3 percent. After the reaction is finished, the catalyst can be separated from the mixed reaction product by using a magnet for recycling, and good catalytic activity can be kept.
Example 2
(1) Preparation of noble metal particles:
200mg of chloroauric acid was added to 10g of octadecene containing 100mg of oleic acid, 100mg of oleylamine, both surfactants, and the mixture was magnetically stirred, reacted at 130 ℃ for 2.5 hours, and then 40g of hexanol was added to obtain a precipitate and centrifuged, and then washed with a mixture of 20g of hexanol and 10g of hexane several times. Finally, the particles were dispersed in 10g of hexane (described as solution A) for further use.
(2) Preparation of a "noble metal-magnetic oxide" dumbbell-shaped core:
adding the solution A in the step (1) into 10g of octadecene containing 100mg of oleic acid, 100mg of oleylamine, two surfactants and 5g of iron oleate, introducing inert gas, and blowing out hexane and other impurities for a period of time. Then heated to 300 ℃. The reaction time is kept for 3h, the temperature is reduced to room temperature, 20g of ethanol and 10g of chloroform are added for washing, the precipitate is obtained by centrifugation, and finally the particles are dispersed in 10mL of chloroform solution for standby (recorded as solution B).
(3) The particles were changed from oil phase to water phase:
"solution B" in (2) above was mixed with 50mL of an aqueous solution containing 15g of cetyltrimethylammonium bromide surfactant, and heated and stirred at 70 ℃ to evaporate chloroform to dryness. An aqueous solution containing magnetic particles (denoted as solution C) was obtained.
(4) Wrapping the shell:
to the "solution C" of the above (3), 15g of ammonia water and 5g of TEOS were added, and after reacting for 3 hours, 25mL of ethanol was added to the solution, followed by centrifugation to obtain a precipitate and drying.
(5) High-temperature calcination:
and (4) calcining the dried particles in the step (4) at 550 ℃ for 3h to finally obtain the catalyst.
ICP data indicated that the catalyst had an Au content of 6 wt% and an Fe content of 20 wt%. TEM test data show that the thickness of the silicon dioxide mesoporous layer in the catalyst is 20nm, the particle size of gold particles is about 9nm, and the particle size of ferroferric oxide particles is about 20 nm. N is a radical of2Adsorption and desorption tests show that the pore diameter of the pore canal in the silicon dioxide mesoporous layer is about 2 nm.
Adding the catalyst and the aqueous solution of p-nitrophenol into a reactor, introducing hydrogen, and introducing hydrogen at normal temperature and normal pressure. The mass ratio of the catalyst to the p-nitrophenol is 3:1, and the reaction time is 30 min. After the reaction is finished, the product is detected and analyzed by adopting gas chromatography, the conversion rate of the p-nitrophenol is calculated to be 85.3 percent, and the selectivity of the generated p-aminophenol is 83.4 percent. After the reaction is finished, the catalyst can be separated from the mixed reaction product by using a magnet for recycling, and good catalytic activity can be kept.
Example 3
(1) Preparation of noble metal particles:
120mg of chloroauric acid was added to 10g of octadecene containing 56mL of oleic acid, 56mL of oleylamine, both surfactants, and reacted at 120 ℃ for 1.5 hours with magnetic stirring, then 25g of hexanol was added to obtain a precipitate and centrifuged, and then washed with a mixture of 15g of hexanol and 10g of hexane several times. Finally, the particles were dispersed in 10mL of hexane (noted: solution A) for further use.
(2) Preparation of a "noble metal-magnetic oxide" dumbbell-shaped core:
adding the solution A in the step (1) into 10g of octadecene containing 56mg of oleic acid, 56mg of oleylamine and 3.25g of iron oleate, introducing inert gas, and blowing out hexane and other impurities for a period of time. And then heated to 265 ℃. The reaction time is kept for 2h, the temperature is reduced to room temperature, 15g of ethanol and 10g of chloroform are added for washing, the precipitate is obtained by centrifugation, and finally the particles are dispersed in 10mL of chloroform solution for standby (recorded as solution B).
(3) The particles were changed from oil phase to water phase:
"solution B" in (2) above was mixed with 50mL of an aqueous solution containing 8g of cetyltrimethylammonium bromide surfactant, and heated and stirred at 67.5 ℃ to evaporate chloroform. An aqueous solution containing magnetic particles (denoted as solution C) was obtained.
(4) Wrapping the shell:
to the "solution C" of the above (3), 8g of ammonia water and 3g of TEOS were added, and after reacting for 2 hours, 25mL of ethanol was added to the solution, followed by centrifugation to obtain a precipitate and drying.
(5) High-temperature calcination:
and (4) calcining the dried particles in the step (4) at 475 ℃ for 2h to finally obtain the catalyst.
The ICP data indicated that the catalyst had a 3 wt% Au content and a 10 wt% Fe content. TEM test data show that the thickness of the silicon dioxide mesoporous layer in the catalyst is 10nm, the particle size of gold particles is about 5.5nm, and the particle size of ferroferric oxide particles is about 14.5 nm. N is a radical of2Adsorption and desorption tests show that the pore diameter of the pore canal in the silicon dioxide mesoporous layer is about 2 nm.
Adding the catalyst and the aqueous solution of p-nitrophenol into a reactor, introducing hydrogen, and introducing hydrogen at normal temperature and normal pressure. The mass ratio of the catalyst to the p-nitrophenol is 3:1, and the reaction time is 30 min. After the reaction is finished, the product is detected and analyzed by adopting gas chromatography, and the conversion rate of the p-nitrophenol is calculated to be 82.1 percent, and the selectivity of the generated p-aminophenol is 84.3 percent. After the reaction is finished, the catalyst can be separated from the mixed reaction product by using a magnet for recycling, and good catalytic activity can be kept.
Example 4
(1) Preparation of noble metal particles:
80mg of chloroauric acid was added to 10g of octadecene containing 34mL of oleic acid, 34mL of oleylamine, both surfactants, and reacted at 115 ℃ for 1.25 hours with magnetic stirring, then 16g of hexanol was added to obtain a precipitate and centrifuged, and then washed with a mixture of 12.5g of hexanol and 10g of hexane several times. Finally, the particles were dispersed in 10mL of hexane (noted: solution A) for further use.
(2) Preparation of a "noble metal-magnetic oxide" dumbbell-shaped core:
adding the solution A in the step (1) into 10g of octadecene containing 34mg of oleic acid, 34mg of oleylamine, two surfactants and 2.4g of iron oleate, introducing inert gas, and blowing out hexane and other impurities for a period of time. Then heated to 247 ℃. The reaction time is kept for 1.5h, the reaction solution is cooled to room temperature, 12.5g of ethanol and 10g of chloroform are added for washing, the precipitate is obtained by centrifugation, and finally the particles are dispersed in 10mL of chloroform solution for later use (recorded as solution B).
(3) The particles were changed from oil phase to water phase:
"solution B" of the above (2) was mixed with 50mL of an aqueous solution containing 4.5g of cetyltrimethylammonium bromide surfactant, and heated and stirred at 66 ℃ to evaporate chloroform. An aqueous solution containing magnetic particles (denoted as solution C) was obtained.
(4) Wrapping the shell:
to the "solution C" of the above (3), 4.5g of ammonia water and 2g of TEOS were added, and after 1.5 hours of reaction, 25mL of ethanol was added to the solution, followed by centrifugation to obtain a precipitate and drying.
(5) High-temperature calcination:
and (4) calcining the dried particles in the step (4) at 462 ℃ for 1.5h to finally obtain the catalyst.
The ICP data indicated that the catalyst had an Au content of 1.5 wt% and an Fe content of 5 wt%. TEM test data show that the thickness of the silicon dioxide mesoporous layer in the catalyst is 5nm, the particle size of gold particles is about 2.7nm, and the particle size of ferroferric oxide particles is about 12 nm. N is a radical of2Adsorption and desorption tests show that the pore diameter of the pore canal in the silicon dioxide mesoporous layer is about 2 nm.
Adding the catalyst and the aqueous solution of p-nitrophenol into a reactor, introducing hydrogen, and introducing hydrogen at normal temperature and normal pressure. The mass ratio of the catalyst to the p-nitrophenol is 3:1, and the reaction time is 30 min. After the reaction is finished, the product is detected and analyzed by adopting gas chromatography, the conversion rate of the p-nitrophenol is calculated to be 78.3 percent, and the selectivity of the generated p-aminophenol is 82.4 percent. After the reaction is finished, the catalyst can be separated from the mixed reaction product by using a magnet for recycling, and good catalytic activity can be kept.
Example 5
(1) Preparation of noble metal particles:
160mg of chloroauric acid were added to 10g of octadecene containing 78mL of oleic acid, 78mL of oleylamine, both surfactants, magnetically stirred, reacted at 125 ℃ for 2h, then 32.5g of hexanol was added to obtain a precipitate and centrifuged, and then washed with a mixture of 17.5g of hexanol and 10g of hexane several times. Finally, the particles were dispersed in 10mL of hexane (noted: solution A) for further use.
(2) Preparation of a "noble metal-magnetic oxide" dumbbell-shaped core:
adding the solution A in the step (1) into 10g of octadecene containing 78mg of oleic acid, 78mg of oleylamine and 4.2g of iron oleate, introducing inert gas, and blowing out hexane and other impurities for a period of time. Then heated to 283 ℃. The reaction time is kept for 2.5h, the reaction solution is cooled to room temperature, 17.5g of ethanol and 10g of chloroform are added for washing, the precipitate is obtained by centrifugation, and finally the particles are dispersed in 10mL of chloroform solution for later use (recorded as solution B).
(3) The particles were changed from oil phase to water phase:
"solution B" of the above (2) was mixed with 50mL of an aqueous solution containing 10.5g of cetyltrimethylammonium bromide surfactant, and heated and stirred at 68.5 ℃ to evaporate chloroform. An aqueous solution containing magnetic particles (denoted as solution C) was obtained.
(4) Wrapping the shell:
to the "solution C" of the above (3), 10.5g of ammonia water and 4g of TEOS were added, and after reacting for 2.5 hours, 25mL of ethanol was added to the solution, followed by centrifugation to obtain a precipitate and drying.
(5) High-temperature calcination:
and (4) calcining the dried particles in the step (4) at 487 ℃ for 2.5 hours to finally obtain the catalyst.
The ICP data indicated that the catalyst had an Au content of 4.5 wt% and an Fe content of 15 wt%. TEM test data show that the thickness of the silicon dioxide mesoporous layer in the catalyst is 15nm, the particle size of gold particles is about 7.5nm, and the particle size of ferroferric oxide particles is about 17 nm. N is a radical of2Adsorption and desorption tests show that the pore diameter of the pore canal in the silicon dioxide mesoporous layer is about 2 nm.
Adding the catalyst and the aqueous solution of p-nitrophenol into a reactor, introducing hydrogen, and introducing hydrogen at normal temperature and normal pressure. The mass ratio of the catalyst to the p-nitrophenol is 3:1, and the reaction time is 30 min. After the reaction is finished, the product is detected and analyzed by adopting gas chromatography, the conversion rate of the p-nitrophenol is calculated to be 87.7 percent, and the selectivity of the generated p-aminophenol is 84.3 percent. After the reaction is finished, the catalyst can be separated from the mixed reaction product by using a magnet for recycling, and good catalytic activity can be kept.
Example 6
(1) Preparation of noble metal particles:
70mg of chloroauric acid was added to 10g of octadecene containing 30mL of oleic acid, 30mL of oleylamine, both surfactants, and the mixture was magnetically stirred, reacted at 112 ℃ for 1.2h, then 15g of hexanol was added to obtain a precipitate and centrifuged, and then washed with a mixture of 12g of hexanol and 10g of hexane several times. Finally, the particles were dispersed in 10mL of hexane (noted: solution A) for further use.
(2) Preparation of a "noble metal-magnetic oxide" dumbbell-shaped core:
adding the solution A in the step (1) into 10g of octadecene containing 70mg of oleic acid, 70mg of oleylamine and 4g of iron oleate, introducing inert gas, and blowing out hexane and other impurities for a period of time. And then heated to 280 deg.c. The reaction time is kept for 2h, the temperature is reduced to room temperature, 17g of ethanol and 10g of chloroform are added for washing, the precipitate is obtained by centrifugation, and finally the particles are dispersed in 10mL of chloroform solution for standby (recorded as solution B).
(3) The particles were changed from oil phase to water phase:
"solution B" in (2) above was mixed with 50mL of an aqueous solution containing 6g of cetyltrimethylammonium bromide surfactant, and heated and stirred at 68 ℃ to evaporate chloroform to dryness. An aqueous solution containing magnetic particles (denoted as solution C) was obtained.
(4) Wrapping the shell:
to the "solution C" of the above (3), 7g of ammonia water and 2.5g of TEOS were added, and after 1.8 hours of reaction, 25mL of ethanol was added to the solution, followed by centrifugation to obtain a precipitate and drying.
(5) High-temperature calcination:
and (4) calcining the dried particles in the step (4) at 470 ℃ for 1.8h to finally obtain the catalyst.
The ICP data indicated that the catalyst had an Au content of 1.6 wt% and an Fe content of 9 wt%. TEM test data show that the thickness of the silicon dioxide mesoporous layer in the catalyst is 12nm, the particle size of gold particles is about 4.5nm, and the particle size of ferroferric oxide particles is about 16 nm. N is a radical of2Adsorption and desorption tests show that the pore diameter of the pore canal in the silicon dioxide mesoporous layer is about 2 nm.
Adding the catalyst and the aqueous solution of p-nitrophenol into a reactor, introducing hydrogen, and introducing hydrogen at normal temperature and normal pressure. The mass ratio of the catalyst to the p-nitrophenol is 3:1, and the reaction time is 30 min. After the reaction is finished, the product is detected and analyzed by adopting gas chromatography, the conversion rate of the p-nitrophenol is calculated to be 95.5%, and the selectivity of the generated p-aminophenol is 91.2%. After the reaction is finished, the catalyst can be separated from the mixed reaction product by using a magnet for recycling, and good catalytic activity can be kept.
The results of the catalytic performance tests of the catalysts obtained in examples 1 to 6 are shown in Table 1.
Table 1.
In addition, the inventor also carries out corresponding experiments by using other raw materials and other process conditions listed above instead of various raw materials and corresponding process conditions in the examples 1 to 6, and the contents to be verified are similar to the products in the examples 1 to 6. Therefore, the contents of the verification of each example are not described herein one by one, and only examples 1 to 6 are used as representatives to describe the excellent points of the present invention.
It should be understood that the above-mentioned embodiments are merely illustrative of the technical concepts and features of the present invention, and are intended to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Claims (8)
1. A method for synthesizing p-aminophenol, comprising:
preparing a catalyst for the reaction of synthesizing p-aminophenol by hydrogenation, comprising:
(1) adding a precursor of a noble metal into a first oil phase containing a first surfactant for reaction at the temperature of 110-130 ℃, reacting for 0.5-2.5h, adding an alcohol solvent, obtaining a precipitate, centrifuging, washing at least once by using a mixture of the alcohol solvent and alkane with the mass ratio of 1-2:1 to obtain noble metal particles, dispersing the obtained noble metal particles into the alkane solution to form a first mixed system, wherein the mass ratio of the precursor of the noble metal to the first oil phase is 0.004-0.02:1, the mass ratio of the first surfactant to the first oil phase is 0.0012-0.01:1, and the mass ratio of the alcohol solvent to the first oil phase is 1-4: 1;
(2) adding the first mixed system into a second oil phase containing a first surfactant and a magnetic oxide precursor, introducing inert gas, reacting at the temperature of 230-300 ℃ for 1-3h, adding an alcohol solvent and chloroform in a mass ratio of 1-2:1, washing, centrifuging to obtain precious metal-magnetic oxide particles, dispersing the obtained precious metal-magnetic oxide particles in a chloroform solution to form a second mixed system, wherein the mass ratio of the precious metal precursor to the second oil phase is 0.002-0.01:1, the mass ratio of the magnetic oxide precursor to the second oil phase is 0.15-0.5:1, and the mass ratio of the first surfactant to the second oil phase is 0.0012-0.01: 1;
(3) mixing the second mixed system with an aqueous solution containing a second surfactant, wherein the mass ratio of the second surfactant to water is 0.02-0.3:1, then heating to 65-70 ℃, stirring, and evaporating chloroform to dryness to obtain an aqueous solution containing precious metal-magnetic oxide particles;
(4) reacting the aqueous solution containing the noble metal-magnetic oxide particles with ammonia water and TEOS for 1-3h, wherein the mass ratio of the ammonia water to the water is 0.02-0.3:1, the mass ratio of the TEOS to the water is 0.02-0.1:1, adding an alcohol solvent, centrifuging to obtain a precipitate, and then carrying out aftertreatment to obtain the catalyst, wherein the aftertreatment comprises the following steps: drying the obtained precipitate, and calcining for 1-3h at the temperature of 450-550 ℃;
the catalyst comprises a dumbbell-shaped core and a mesoporous silica shell coating the core, wherein the core is made of precious metal-magnetic oxide, the size of the precious metal is 2-9nm, the size of the magnetic oxide is 9-20nm, the precious metal is selected from any one or the combination of more than two of Au, Pt, Pd, Ir, Os, Ru, Rh and Ag, the catalyst comprises 0.01-6 wt% of precious metal and 0.01-20 wt% of magnetic oxide, the thickness of the mesoporous silica shell is 1-20nm, and the aperture of the contained hole is smaller than 50 nm; and
the catalyst participates in the reaction of synthesizing p-aminophenol by hydrogenating p-nitrophenol.
2. A method for the synthesis of p-aminophenol, according to claim 1, characterized in that: the magnetic oxide is selected from one or more than two oxides of Fe, Co and Ni.
3. A method for the synthesis of p-aminophenol, according to claim 1, characterized in that: the first surfactant is selected from any one or two of oleic acid and oleylamine.
4. A method for the synthesis of p-aminophenol, according to claim 1, characterized in that: the alcohol solvent is selected from any one or two of ethanol and isopropanol.
5. A method for the synthesis of p-aminophenol, according to claim 1, characterized in that: the first oil phase is selected from one or two of octadecene and diphenyl ether.
6. A method for the synthesis of p-aminophenol, according to claim 1, characterized in that: the second oil phase is selected from one or two of octadecene and diphenyl ether.
7. A method for the synthesis of p-aminophenol, according to claim 1, characterized in that: the alkane is hexane.
8. A method for the synthesis of p-aminophenol, according to claim 1, characterized in that: the second surfactant is selected from one or the combination of more than two of dodecyl trimethyl ammonium bromide, tetradecyl trimethyl ammonium bromide, hexadecyl trimethyl ammonium bromide and octadecyl trimethyl ammonium bromide.
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