CN113019393B - Platinum nano catalyst, preparation method thereof and method for synthesizing aromatic amine by selective hydrogenation of aromatic nitro compound - Google Patents

Platinum nano catalyst, preparation method thereof and method for synthesizing aromatic amine by selective hydrogenation of aromatic nitro compound Download PDF

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CN113019393B
CN113019393B CN202110294570.6A CN202110294570A CN113019393B CN 113019393 B CN113019393 B CN 113019393B CN 202110294570 A CN202110294570 A CN 202110294570A CN 113019393 B CN113019393 B CN 113019393B
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platinum
metal salt
surfactant
catalyst
hydrotalcite
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CN113019393A (en
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赵建波
袁海丰
秦肖雲
贾晓东
刘应凡
王国庆
周立明
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Zhengzhou University of Light Industry
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Abstract

The invention belongs to the technical field of aromatic amine preparation by catalytic reduction of aromatic nitro compounds, and relates to a platinum nano catalyst and a preparation method thereof, and a method for synthesizing aromatic amine by selective hydrogenation of aromatic nitro compounds. The platinum nano catalyst comprises a carrier and an active component dispersed on the surface of the carrier in a nano particle form, wherein the carrier is an oxide obtained by calcining hydrotalcite modified by a surfactant, and the active component is platinum. The platinum nano catalyst provided by the invention has excellent catalytic activity, selectivity, recycling performance and substrate universality in the reaction process of preparing aromatic amine by reducing aromatic nitro-compound, the conversion rate of the aromatic nitro-compound can reach 100% at the highest, the selectivity of the aromatic amine can reach 100% at the highest, the catalyst can be recycled for many times, and the performance of the catalyst is basically unchanged.

Description

Platinum nano catalyst, preparation method thereof and method for synthesizing aromatic amine by selective hydrogenation of aromatic nitro compound
Technical Field
The invention belongs to the technical field of aromatic nitro-compound catalytic reduction for preparing aromatic amine, and in particular relates to a platinum nano-catalyst taking an oxide obtained by calcining hydrotalcite modified by a surfactant as a carrier and a preparation method thereof, and a method for synthesizing aromatic amine by catalyzing aromatic nitro-compound hydrogenation by using the platinum nano-catalyst.
Background
In the fine chemical catalysis process, aromatic amine compounds (abbreviated as aromatic amine) and derivatives thereof are important organic chemical intermediates, for example, the para-chloroaniline has very wide application in industries such as pesticides, medicines, dyes, additives and the like, and the development and production of the aromatic amine have wide market prospect in China. At present, a liquid phase catalytic hydrogenation method is favored in the method for reducing the aromatic nitro compound into the aromatic amine, and the method has simple and clean process, can realize continuous large-scale production, is regarded as a green, efficient and advanced production process for preparing the aromatic amine and the derivatives thereof from the aromatic nitro compound, and has great application value.
In the prior art, the catalyst used for hydrogenation of aromatic nitro compounds is basically a supported nano catalyst, and the supported catalyst has a high reactivity, particularly, the supported catalyst has a noble metal such as Pt, pd, au, co, ni as an active component. However, the conventional catalytic hydrogenation method has disadvantages such as complicated preparation process of the catalyst, poor universality, and high requirement of equipment because the hydrogenation reaction condition is carried out under high pressure and high temperature. In particular, when the substrate molecule contains other groups such as halogen, side reactions such as dehalogenation often occur, and the selectivity of the product decreases. Related researches are carried out around the preparation of aromatic amine by hydrogenation of aromatic nitro compounds at home and abroad.
PtNi@mSiO was synthesized in document 1 (RSCAdv., 2015, 5:20238) 2 And Pt-NiO@mSiO 2 Mesoporous core-shell nano catalyst and its application in selective hydrogenation of p-chloronitrobenzene to prepare p-chloroaniline. Research shows that with Pt@mSiO 2 Compared with nano catalyst, ptNi@mSiO 2 And Pt-NiO@mSiO 2 The p-chloroaniline selectivity is obviously improved. However, the catalyst is only suitable for preparing p-chloroaniline by hydrogenating p-chloronitrobenzene, is not suitable for other aromatic nitro compounds, and has low universality. Document 2 (Chemical Engineering Science,2019, 196:402-413) synthesized intermetallic compounds CuM (m=pt, pd and Au) by a butyllithium co-reduction method. Research shows that compared with a monometal Pt catalyst, the synthesized PtCu ordered intermetallic compound shows better selectivity in a series of substituted nitrobenzene hydrogenation reactions. Ordered PtCu has higher selectivity than disordered PtCu and retains the same catalytic activity as disordered PtCu. DFT calculation shows that the ordered structure is favorable for reactant adsorption and product desorption, and coordination of Cl on an active site can be avoided, so that the catalytic selectivity is improved. However, the catalyst is costly to produce and the preparation process is cumbersome. Document 3 (adv. Mater.2019,31 (11): 1808341) discloses that nitrogen-doped carbon nanotube-confined Co nanoparticles derived from organic framework materials (ZIF-67) are useful for catalyzing nitro selective hydrogenation reactions, but have lower intrinsic activity.
CN101745382A discloses a catalyst for synthesizing p-chloroaniline by hydrogenating p-chloronitrobenzene and a preparation method thereofThe catalyst takes attapulgite as a carrier and platinum as an active component, and is prepared at 40 ℃ and 2.0MPa H 2 The catalyst has excellent activity and good stability in the hydrogenation reaction of p-chloronitrobenzene. However, the reaction needs to be carried out under higher pressure, the requirement on equipment is higher, and the catalyst is only suitable for preparing the parachloroaniline by hydrogenating the parachloronitrobenzene, is not suitable for other aromatic nitro compounds and has low universality.
CN105562032a discloses a catalyst for synthesizing p-chloroaniline by hydrogenation, a preparation method and application thereof, the catalyst comprises a magnetic core and platinum nano particles loaded on the magnetic core, and the magnetic core is a microporous zirconium dioxide layer. Although the catalyst can efficiently catalyze the hydrogenation of the p-chloronitrobenzene to synthesize the p-chloroaniline, the selectivity of the p-chloroaniline still needs to be improved, and the preparation process of the catalyst is complex, the period is long, and the mass production is difficult. In addition, the catalyst is only suitable for preparing p-chloroaniline by hydrogenating p-chloronitrobenzene, is not suitable for other aromatic nitro compounds, and has low universality.
Disclosure of Invention
The invention aims to solve the problems of complicated preparation process, low universality and severe corresponding hydrogenation reaction conditions of the existing catalyst for synthesizing aromatic amine by hydrogenating aromatic nitro compounds, and provides a platinum nano catalyst which is simple in preparation process and good in substrate universality.
The inventor of the present invention has found after intensive studies that a platinum nano catalyst using hydrotalcite modified with a surfactant as a carrier precursor and platinum as an active component has excellent catalytic activity, selectivity, stability and substrate universality in a reaction for preparing aromatic amine by reduction of an aromatic nitro compound. Based on this, the present invention has been completed.
The first aspect of the invention provides a platinum nano-catalyst, wherein the platinum nano-catalyst comprises a carrier and an active component dispersed on the surface of the carrier in a nano particle form, the carrier is an oxide obtained by calcining hydrotalcite modified by a surfactant, and the active component is platinum.
The second aspect of the present invention provides a preparation method of the platinum nano-catalyst, wherein the method comprises the following steps:
s1, uniformly mixing a metal mixed salt solution, an alkali mixed solution, a surfactant and a dispersing agent, wherein the metal mixed salt solution contains divalent metal salt and trivalent metal salt at the same time, and then carrying out solid-liquid separation after precipitation and crystallization on the obtained mixture, washing the obtained solid product to be neutral, and then drying to obtain hydrotalcite modified by the surfactant;
s2, dispersing the hydrotalcite modified by the surfactant obtained in the step S1 in water, uniformly mixing the obtained suspension with a platinum precursor and alkali liquor, then heating for reaction, and sequentially centrifuging, drying and roasting the obtained heating reaction product to obtain the platinum nano catalyst.
In a third aspect, the present invention provides a method for synthesizing aromatic amine by selective hydrogenation of aromatic nitro compound, wherein the method comprises the step of performing hydrogenation reaction on aromatic nitro compound and the platinum nano catalyst in a solvent.
Compared with the prior art, the invention has the following advantages and beneficial effects:
(1) The preparation process of the platinum nano catalyst provided by the invention is simple, and is beneficial to large-scale production.
(2) The platinum nano catalyst provided by the invention has excellent catalytic activity, selectivity, recycling performance and substrate universality in the reaction process of preparing aromatic amine by reducing aromatic nitro-compound, the conversion rate of the aromatic nitro-compound can reach 100% at the highest, the selectivity of the aromatic amine can reach 100%, the catalyst can be recycled for multiple times, and the performance of the catalyst is basically unchanged.
Drawings
FIG. 1 is a HAADF-STEM diagram of a Pt/NiAlO-SDS platinum nanocatalyst obtained in example 1.
FIG. 2 is a graph showing the particle size distribution of Pt nanoparticles in Pt/NiAlO-SDS as a platinum nanocatalyst obtained in example 1.
FIG. 3 is an X-ray diffraction pattern of the surfactant-modified hydrotalcite NiAl-LDH-SDS obtained in example 1 and the platinum nanocatalyst Pt/NiAlO-SDS, and the reference hydrotalcite NiAl-LDH obtained in comparative example 1.
FIG. 4 is a graph showing the reaction time of the platinum nanocatalyst Pt/NiAlO-SDS obtained in example 1 for hydrogenation of p-chloronitrobenzene.
FIG. 5 is a graph showing the cyclic use of the Pt/NiAlO-SDS catalyst obtained in example 1 for the hydrogenation of p-chloronitrobenzene.
Detailed Description
The platinum nano catalyst provided by the invention comprises a carrier and an active component dispersed on the surface of the carrier in a nano particle form, wherein the carrier is an oxide obtained by calcining hydrotalcite modified by a surfactant, and the active component is platinum.
In a preferred embodiment of the present invention, the platinum nano-catalyst has a platinum loading of 0.5 to 2.0wt%, for example, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2.0wt%, etc.
In a preferred embodiment of the present invention, the hydrotalcite is selected from at least one of NiAl hydrotalcite, coAl hydrotalcite, znAl hydrotalcite and NiFe hydrotalcite.
In a preferred embodiment of the present invention, the surfactant-modified hydrotalcite is prepared in the following manner: and uniformly mixing a metal mixed salt solution, an alkali mixed solution, a surfactant and a dispersing agent, wherein the metal mixed salt solution contains divalent metal salt and trivalent metal salt at the same time, and then carrying out solid-liquid separation after precipitating and crystallizing the obtained mixture, washing the obtained solid product with water to be neutral, and then drying to obtain the surfactant modified hydrotalcite.
In a preferred embodiment of the present invention, the molar ratio of divalent metal salt to trivalent metal salt is (1.5-3.0): 1, for example, may be 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, 3.0:1, etc.
In a preferred embodiment of the invention, the alkali mixture solution is used in such an amount that the pH of the system is 8.5 to 10.0, for example, 8.5, 8.6, 8.7, 8.8, 8.9, 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9, 10.0, etc. Wherein, the alkali mixed solution is used for adjusting the pH value, and the purpose of adopting a plurality of alkalis for matching use is to enhance the exchangeable property of interlayer anions while increasing the binding force of hydrotalcite laminae to anions.
In a preferred embodiment of the present invention, the molar ratio of the trivalent metal salt, the surfactant and the dispersant is 1 (0.5 to 20): 0.1 to 0.5. For example, the molar ratio of trivalent metal salt to surfactant can be 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, and the like. The molar ratio of the trivalent metal salt to the dispersant may be 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, etc.
In a preferred embodiment of the present invention, the anions in the divalent metal salt and the trivalent metal salt are NO 3 - And/or Cl - . In particular, specific examples of the divalent metal salt include, but are not limited to: at least one of nickel nitrate, zinc nitrate, nickel chloride and zinc chloride. Specific examples of the trivalent metal salt include, but are not limited to: at least one of aluminum nitrate, iron nitrate, cobalt nitrate, aluminum chloride, iron chloride, and cobalt chloride.
In a preferred embodiment of the present invention, the alkali mixed solution is selected from CH 4 N 2 O、NaOH、KOH、NH 3 ·H 2 O and Na 2 CO 3 At least two of them.
In the present invention, the surfactant may be various existing cationic surfactants, anionic surfactants, nonionic surfactants, amphoteric surfactants, specific examples of which include but are not limited to: at least one of sodium dodecyl sulfonate, sodium lignin sulfonate, metanilic acid and amino acid.
In a preferred embodiment of the present invention, the dispersant is selected from at least one of n-butanol, formamide, isooctane, and toluene.
In a preferred embodiment of the present invention, the conditions for the precipitation crystallization include a temperature of 120 to 140℃for 20 to 50 hours.
The invention also provides a preparation method of the platinum nano catalyst, which comprises the following steps:
s1, uniformly mixing a metal mixed salt solution, an alkali mixed solution, a surfactant and a dispersing agent, wherein the metal mixed salt solution contains divalent metal salt and trivalent metal salt at the same time, and then carrying out solid-liquid separation after precipitation and crystallization on the obtained mixture, washing the obtained solid product to be neutral, and then drying to obtain hydrotalcite modified by the surfactant;
s2, dispersing the hydrotalcite modified by the surfactant obtained in the step S1 in water, uniformly mixing the obtained suspension with a platinum precursor and alkali liquor, then heating for reaction, and sequentially centrifuging, drying and roasting the obtained heating reaction product to obtain the platinum nano catalyst.
In a preferred embodiment of the present invention, in step S1, the molar ratio of the divalent metal salt to the trivalent metal salt is (1.5 to 3.0): 1, for example, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, 3.0:1, etc. may be mentioned.
In a preferred embodiment of the invention, in step S1, the alkali mixture solution is used in such an amount that the pH of the system is 8.5 to 10.0, for example, 8.5, 8.6, 8.7, 8.8, 8.9, 9.0, 9.1, 9.2, 9.3, 9.4, 9.5, 9.6, 9.7, 9.8, 9.9, 10.0, etc.
In a preferred embodiment of the present invention, in step S1, the molar ratio of the trivalent metal salt, the surfactant and the dispersant is 1 (0.5 to 2.0): 0.1 to 0.5. For example, the molar ratio of trivalent metal salt to surfactant can be 1:0.5, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, and the like. The molar ratio of the trivalent metal salt to the dispersant may be 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, etc.
In a preferred embodiment of the present invention, in step S1, the anions of the divalent metal salt and the trivalent metal salt are NO 3 - And/or Cl-. In particular, specific examples of the divalent metal salt include, but are not limited to: at least one of nickel nitrate, zinc nitrate, nickel chloride and zinc chloride. Specific examples of the trivalent metal salt include, but are not limited to: at least one of aluminum nitrate, iron nitrate, cobalt nitrate, aluminum chloride, iron chloride, and cobalt chloride.
In a preferred embodiment of the present invention, in step S1, the alkali mixed solution is selected from CH 4 N 2 O、NaOH、KOH、NH 3 ·H 2 O and Na 2 CO 3 At least two of them.
In the present invention, in step S1, the surfactant may be various existing cationic surfactants, anionic surfactants, nonionic surfactants, amphoteric surfactants, specific examples of which include, but are not limited to: at least one of sodium dodecyl sulfonate, sodium lignin sulfonate, metanilic acid and amino acid.
In a preferred embodiment of the present invention, in step S1, the dispersant is selected from at least one of n-butanol, formamide, isooctane, and toluene.
In a preferred embodiment of the present invention, in the step S1, the conditions for the precipitation crystallization include a temperature of 120 to 140 ℃ for 20 to 50 hours.
In a preferred embodiment of the present invention, in step S2, the platinum precursor is selected from the group consisting of H 2 PtCl 6 、Na 2 PtCl 4 And PtCl 4 At least one of them.
In a preferred embodiment of the present invention, the platinum precursor is used in an amount such that the platinum loading in the resulting platinum nanocatalyst is 0.5 to 2.0wt%, for example, may be 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1.0wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2.0wt%, etc. in step S2.
In a preferred embodiment of the present invention, in step S2, the mass ratio of the surfactant-modified hydrotalcite to the lye is 1 (0.1-1), for example, may be 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.0, etc.
In a preferred embodiment of the present invention, in step S2, the lye is CH 4 N 2 O and/or NH 3 ·H 2 O。
In a preferred embodiment of the present invention, in the step S2, the heating reaction is performed at a temperature of 60 to 100 ℃ for a time of 1 to 20 hours.
In a preferred embodiment of the present invention, in step S2, the drying temperature is 50 to 70 ℃ for 4 to 6 hours.
In a preferred embodiment of the present invention, in step S2, the baking temperature is 400 to 700 ℃ and the time is 1 to 5 hours, and the baking atmosphere is selected from any one of argon and hydrogen/argon mixture.
The invention also provides a method for synthesizing aromatic amine by selective hydrogenation of the aromatic nitro-compound, which comprises the step of carrying out hydrogenation reaction on the aromatic nitro-compound and the platinum nano-catalyst in a solvent.
In a preferred embodiment of the present invention, the hydrogenation reaction conditions include a temperature of 25 to 80℃and a pressure of from atmospheric to 1.5MPa H 2 The time is 10 min-200 min. In the invention, the pressures refer to gauge pressure.
In the present invention, specific examples of the aromatic nitro compound include, but are not limited to: at least one of nitrobenzene, p-chloronitrobenzene, p-nitrotoluene, 3, 5-dimethylnitrobenzene, p-nitrostyrene, m-nitrostyrene and p-nitrobenzaldehyde.
In a preferred embodiment of the present invention, the molar ratio of the active component to the aromatic nitro compound in the platinum nanocatalyst is (0.01 to 1): 1, and for example, may be 0.01:1, 0.05:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1.0:1, etc.
In a preferred embodiment of the present invention, the solvent is selected from at least one of water, methanol, ethanol, isopropanol, acetonitrile, n-hexane and toluene.
The present invention will be described in detail by examples. The examples of embodiments are intended to illustrate the invention and are not to be construed as limiting the invention. The experimental methods for which specific conditions are not specified in the examples are generally conducted under conventional conditions or under conditions recommended by the manufacturer. Percentages and parts are by weight unless otherwise indicated.
Example 1
S1, preparing surfactant modified hydrotalcite NiAl-LDH-SDS:
the co-precipitation method is adopted to prepare hydrotalcite carrier, and the mole ratio of Ni/Al is 2/1. Ni (NO) 3 ) 2 And Al (NO) 3 ) 3 Dissolving in deionized water to obtain 0.08mol/LNi (NO) 3 ) 2 And 0.04mol/LAl (NO) 3 ) 3 Is prepared from NaOH and Na 2 CO 3 Dissolving in deionized water to obtain 0.26mol/LNaOH and 0.08mol/LNa 2 CO 3 13.4g Sodium Dodecyl Sulfate (SDS), 160mL isooctane, 5mL n-butanol and 3.5mL deionized water were stirred and mixed to obtain a mixed slurry A. At room temperature, 100mL of Ni/Al mixed salt solution and alkali mixed solution are slowly added dropwise into a three-neck flask containing 50mL of deionized water at the same time, the dosage of the alkali mixed solution is such that the pH value in the flask is kept at about 9.0 during the period of adding the solution dropwise, and the mixed slurry B is obtained by stirring and uniformly mixing. The mixed slurry B and the mixed slurry A are stirred and mixed uniformly, then transferred into a hydrothermal kettle to react for 48 hours at 120 ℃, the obtained reaction product is taken out of the hydrothermal kettle and cooled to room temperature, and the sample is centrifugally washed by deionized water until the pH value of supernatant is about 7.0. The obtained precipitate is dried for 6 hours at 60 ℃, and the powder sample obtained by grinding is the hydrotalcite NiAl-LDH-SDS modified by the surfactant.
S2, preparing a platinum nano catalyst:
1.0g of surfactant-modified hydrotalcite NiAl-LDH-SDS was weighed and added to 100mL of a calcined cakeInto the cup, 80mL of deionized water was added again, and the mixture was stirred to form a suspension, followed by addition of 3.1mL of 0.025mol/LH 2 PtCl 6 After the solution and 0.3g of urea are stirred and mixed, an oil bath at 80 ℃ is heated for 16 hours, the suspension is centrifuged, deionized water is washed for 3 times, the obtained sample is dried in a vacuum drying oven at 60 ℃ for 6 hours, and then calcined in a hydrogen/argon mixed atmosphere at 500 ℃ for 2 hours, so that a platinum nano catalyst Pt/NiAlO-SDS with a Pt load of 1.09wt% is obtained, and the platinum nano catalyst is marked as a 1# catalyst. The HAADF-STEM diagram of the Pt/NiAlO-SDS platinum nano catalyst is shown in figure 1, and as can be seen from figure 1, the platinum nano particles are uniformly dispersed and have smaller particle size. The particle size distribution diagram of Pt nano particles in the Pt/NiAlO-SDS of the platinum nano catalyst is shown in figure 2, and as can be seen from figure 2, the platinum nano particles have smaller size and the average particle size is 1.2nm.
Comparative example 1
Hydrotalcite and a platinum nanocatalyst were prepared according to the method of example 1, except that Sodium Dodecyl Sulfate (SDS) in step S1 was replaced with the same parts by weight of deionized water, i.e., no surfactant was added, and the other conditions were the same as in example 1, to obtain a reference hydrotalcite NiAl-LDH and a reference platinum nanocatalyst Pt/NiAlO, designated d1# catalyst.
The X-ray diffraction patterns of the surfactant-modified hydrotalcite NiAl-LDH-SDS obtained in example 1 and the platinum nanocatalyst Pt/NiAlO-SDS and the reference hydrotalcite NiAl-LDH obtained in comparative example 1 are shown in FIG. 3. As can be seen from fig. 3, the diffraction peak shape of NiAl-LDH-SDS was broadened compared to hydrotalcite NiAl-LDH, indicating that the thickness thereof was thinned, indicating that hydrotalcite has been successfully modified by SDS, and that no diffraction peak of platinum was observed.
Example 2
S1, preparing surfactant modified hydrotalcite ZnAl-LDH-SDS:
the hydrotalcite carrier is prepared by adopting a coprecipitation method, and the molar ratio of Zn/Al is 2/1. Zn (NO) 3 ) 2 And Al (NO) 3 ) 3 Dissolving in deionized water to obtain 0.08mol/LZn (NO) 3 ) 2 And 0.04mol/LAl (NO) 3 ) 3 The Zn/Al mixed salt solution of (2) is prepared by mixing NaOH and Na 2 CO 3 Dissolving in deionized water to obtain 0.26mol/LNaOH and 0.08mol/LNa 2 CO 3 13.0g sodium lignin sulfonate, 80mL formamide and 3.0mL deionized water are uniformly stirred to obtain a mixed slurry A. At room temperature, 100mL of Zn/Al mixed salt solution and alkali mixed solution are slowly added dropwise into a three-neck flask containing 50mL of deionized water at the same time, the dosage of the alkali mixed solution is such that the pH value in the flask is kept at about 9.5 during the period of adding the solution dropwise, and the mixed slurry B is obtained by stirring and uniformly mixing. The obtained mixed slurry B and the mixed slurry A are stirred and mixed uniformly, then transferred into a hydrothermal kettle to react for 36 hours at 120 ℃, the obtained reaction product is taken out of the hydrothermal kettle and cooled to room temperature, and the sample is centrifugally washed by deionized water until the pH value of supernatant is about 7.0. The obtained precipitate is dried for 6 hours at 60 ℃, and the powder sample obtained by grinding is the hydrotalcite ZnAl-LDH-SDS modified by the surfactant.
S2, preparing a platinum nano catalyst:
1.0g of surfactant-modified hydrotalcite ZnAl-LDH-SDS is weighed into a 100mL beaker, 80mL of deionized water is added, and after the mixture is fully stirred to form a suspension, 3.0mL of 0.025mol/L H is added 2 PtCl 6 After the solution and 0.3g of urea are stirred and mixed, an oil bath at 85 ℃ is heated for 16 hours, the suspension is centrifuged, deionized water is washed for 5 times, the obtained sample is dried in a vacuum drying oven at 60 ℃ for 6 hours, and then calcined in an argon atmosphere at 500 ℃ for 2 hours, so that a platinum nano catalyst Pt/ZnAlO-SDS with Pt loading of 1.06wt% is obtained, and the platinum nano catalyst is marked as a No. 2 catalyst. The Pt nano particle size of the Pt/ZnAlO-SDS nano catalyst is 1.1-1.3 nm.
Example 3
S1, preparing surfactant modified hydrotalcite NiFe-LDH-SDS:
the co-precipitation method is adopted to prepare hydrotalcite carrier, and the mole ratio of Ni/Fe is 2/1. Ni (NO) 3 ) 2 And Fe (NO) 3 ) 3 Dissolving in deionized water to obtain 0.08mol/L Ni (NO) 3 ) 2 And 0.04mol/L Fe (NO) 3 ) 3 NaOH and Na 2 CO 3 Dissolving in deionized water to prepare 0.26mol/LNaOH and 0.08mol/LNa 2 CO 3 13.4g of metanilic acid, 160mL of isooctane, 5mL of n-butanol and 3.5mL of deionized water are stirred and mixed uniformly to obtain a mixed slurry A. At room temperature, 150mL of LNi/Fe mixed salt solution and alkali mixed solution are slowly added into a three-neck flask containing 50mL of deionized water in a dropwise manner at the same time, the dosage of the alkali mixed solution is such that the pH value in the flask is kept at about 8.5 during the period of adding the solution in the dropwise manner, and the mixed slurry B is obtained by stirring and uniformly mixing. The obtained mixed slurry B and the mixed slurry A are stirred and mixed uniformly, then transferred into a hydrothermal kettle to react for 48 hours at 140 ℃, then the obtained reaction product is taken out of the hydrothermal kettle and cooled to room temperature, and the sample is centrifugally washed by deionized water until the pH value of supernatant is about 7.0. The obtained precipitate is dried for 6 hours at 60 ℃, and the powder sample obtained by grinding is the hydrotalcite NiFe-LDH-SDS modified by the surfactant.
S2, preparing a platinum nano catalyst:
1.0g of surfactant-modified hydrotalcite NiFe-LDH-SDS was weighed into a 100mL beaker, 80mL of deionized water was added thereto, and after stirring sufficiently to form a suspension, 3.0mL of 0.025mol/L H was added thereto 2 PtCl 6 The solution and 0.2g of ammonia water are stirred and mixed, then the solution is heated for 12 hours in an oil bath at 80 ℃, the suspension is centrifuged, deionized water is washed for 4 times, the obtained sample is dried for 6 hours at 60 ℃ in a vacuum drying oven, and then calcined for 2 hours in a hydrogen/argon mixed atmosphere at 600 ℃ to obtain a platinum nano catalyst Pt/NiFeO-SDS with Pt loading of 1.12wt%, and the platinum nano catalyst is marked as a 3# catalyst. The Pt nano particle size of the Pt/NiFeO-SDS nano catalyst is 1.1-1.2 nm.
Test case
100mg of the No. 1-3 catalyst was weighed and added into a high-pressure reaction kettle containing 8mL of toluene and 5.1mol of p-chloronitrobenzene, and 1.0MPa H was introduced 2 Stirring at a certain temperature for reacting for a period of time, cooling to room temperature after the reaction is finished, discharging residual hydrogen, centrifuging the catalyst, and carrying out qualitative and quantitative analysis on the reaction liquid by using GC and GC-MS, wherein the result is shown in table 1. From table 1, it can be seen that the platinum nano-catalyst provided by the invention has excellent catalytic activity and selectivity in the reaction process of preparing aromatic amine by reducing aromatic nitro-compound. In additionThe reaction time of the p-chloronitrobenzene hydrogenation reaction product of the catalyst # 1 is shown in the graph of fig. 4, and it can be seen from fig. 4 that the p-chloronitrobenzene conversion rate and the p-chloroaniline selectivity both increase with the increase of the reaction time under the mild reaction conditions. When the reaction is carried out for 90min, the conversion rate of the p-chloronitrobenzene is more than 99 percent, and the selectivity of the p-chloroaniline is 100 percent. And the reaction time is prolonged to 180min, and the distribution of the product is not obviously changed. The above case shows that the catalyst # 1 is a p-chloronitrobenzene hydrogenation catalyst with excellent performance.
100mg of the No. 2 catalyst was weighed and added to a high-pressure reaction kettle containing 8mL of toluene and 5.1mol of an aromatic nitro compound, and 1.0MPa H was introduced 2 After stirring and reacting for a period of time at a certain temperature, cooling to room temperature after the reaction is finished, discharging residual hydrogen, centrifuging and separating the catalyst, and carrying out qualitative and quantitative analysis on the reaction liquid product by using GC and GC-MS, wherein the result is shown in Table 2. From table 2, it can be seen that the platinum nano-catalyst provided by the invention has excellent catalytic activity, selectivity and substrate universality in the reaction process of preparing aromatic amine by reducing aromatic nitro-compound.
100mg of the No. 2 catalyst was weighed and added into a high-pressure reaction kettle containing 8mL of toluene and 5.1mol of p-chloronitrobenzene, and 1.0MPa H was introduced 2 The reaction was stirred at 50℃for 90min. After the reaction, the catalyst was separated from the reaction solution by centrifugation, and 8mL of fresh toluene and a certain amount of p-chloronitrobenzene were continuously added to the separated catalyst to perform the next reaction. The catalyst is continuously used for 6 times, and the reaction result is shown in figure 5, wherein P-CNB represents P-chloronitrobenzene, and P-CAN represents P-chloroaniline. As can be seen from FIG. 5, the platinum nano-catalyst provided by the invention has good recycling performance in the reaction process of preparing aromatic amine by reducing aromatic nitro-compounds.
TABLE 1
Figure BDA0002983825620000121
TABLE 2
Figure BDA0002983825620000122
Although embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and not to be construed as limiting the invention, and that variations, modifications, alternatives, and variations may be made in the above embodiments by those skilled in the art without departing from the spirit and principles of the invention.

Claims (11)

1. The platinum nano catalyst is characterized by comprising a carrier and an active component dispersed on the surface of the carrier in a nano particle form, wherein the carrier is an oxide obtained by calcining hydrotalcite modified by a surfactant, and the active component is platinum;
the surfactant-modified hydrotalcite is prepared in the following manner: uniformly mixing a metal mixed salt solution, an alkali mixed solution, a surfactant and a dispersing agent, wherein the metal mixed salt solution contains divalent metal salt and trivalent metal salt at the same time, and then carrying out solid-liquid separation after precipitation and crystallization on the obtained mixture, washing the obtained solid product to be neutral, and drying to obtain the surfactant modified hydrotalcite; the surfactant is at least one selected from sodium dodecyl sulfonate, sodium lignin sulfonate, metanilic acid and amino acid;
the hydrotalcite is at least one of NiAl hydrotalcite, coAl hydrotalcite, znAl hydrotalcite and NiFe hydrotalcite.
2. The platinum nanocatalyst of claim 1, wherein the platinum nanocatalyst has a platinum loading of 0.5wt% to 2.0wt%.
3. The platinum nanocatalyst of claim 1, characterized in that the molar ratio of divalent metal salt to trivalent metal salt is (1.5-3.0): 1; the dosage of the alkali mixed solution enables the pH value of the system to be 8.5-10.0; the mole ratio of the trivalent metal salt to the surfactant to the dispersant is 1 (0.5-20): 0.1-0.5; the conditions of precipitation crystallization comprise the temperature of 120-140 ℃ and the time of 20-50 h.
4. The platinum nanocatalyst of claim 1, wherein the anions of the divalent metal salt and the trivalent metal salt are NO 3 - And/or Cl - The method comprises the steps of carrying out a first treatment on the surface of the The alkali mixed solution is selected from CH 4 N 2 O、NaOH、KOH、NH 3 ·H 2 O and Na 2 CO 3 At least two of (a) and (b); the dispersing agent is at least one selected from n-butanol, formamide, isooctane and toluene.
5. The platinum nanocatalyst of claim 1, wherein the divalent metal salt is selected from at least one of cobalt nitrate, cobalt chloride, nickel nitrate, zinc nitrate, nickel chloride, and zinc chloride; the trivalent metal salt is selected from at least one of aluminum nitrate, ferric nitrate, aluminum chloride and ferric chloride.
6. The method for preparing the platinum nano-catalyst according to any one of claims 1 to 5, characterized in that the method comprises the following steps:
s1, uniformly mixing a metal mixed salt solution, an alkali mixed solution, a surfactant and a dispersing agent, wherein the metal mixed salt solution contains divalent metal salt and trivalent metal salt at the same time, and then carrying out solid-liquid separation after precipitation and crystallization on the obtained mixture, washing the obtained solid product to be neutral, and then drying to obtain hydrotalcite modified by the surfactant;
s2, dispersing the hydrotalcite modified by the surfactant obtained in the step S1 in water, uniformly mixing the obtained suspension with a platinum precursor and alkali liquor, then heating for reaction, and sequentially centrifuging, drying and roasting the obtained heating reaction product to obtain the platinum nano catalyst.
7. The method for preparing a platinum nanocatalyst according to claim 6, wherein in step S1, the molar ratio of the divalent metal salt to the trivalent metal salt is (1.5-3.0): 1; by a means ofThe dosage of the alkali mixed solution enables the pH value of the system to be 8.5-10.0; the mole ratio of the trivalent metal salt to the surfactant to the dispersant is 1 (0.5-20): 0.1-0.5; the conditions of the precipitation crystallization comprise the temperature of 120-140 ℃ and the time of 20-50 h; the anions in the divalent metal salt and the trivalent metal salt are NO 3 - And/or Cl - The method comprises the steps of carrying out a first treatment on the surface of the The alkali mixed solution is selected from CH 4 N 2 O、NaOH、KOH、NH 3 ·H 2 O and Na 2 CO 3 At least two of (a) and (b); the surfactant is at least one selected from sodium dodecyl sulfonate, sodium lignin sulfonate, metanilic acid and amino acid; the dispersing agent is at least one selected from n-butanol, formamide, isooctane and toluene.
8. The method for preparing a platinum nanocatalyst according to claim 6, wherein the divalent metal salt is selected from at least one of cobalt nitrate, cobalt chloride, nickel nitrate, zinc nitrate, nickel chloride and zinc chloride; the trivalent metal salt is selected from at least one of aluminum nitrate, ferric nitrate, aluminum chloride and ferric chloride.
9. The method for preparing a platinum nanocatalyst according to claim 6 or 7, characterized in that in step S2, the platinum precursor is selected from the group consisting of H 2 PtCl 6 、Na 2 PtCl 4 And PtCl 4 At least one of (a) and (b); the dosage of the platinum precursor enables the platinum loading capacity of the obtained platinum nano catalyst to be 0.5-2.0wt%; the mass ratio of the hydrotalcite modified by the surfactant to the alkali liquor is 1 (0.1-1); the alkali liquor is CH 4 N 2 O and/or NH 3 ·H 2 O; the temperature of the heating reaction is 60-100 ℃ and the time is 1-20 h; the drying temperature is 50-70 ℃ and the drying time is 4-6 hours; the roasting temperature is 400-700 ℃ and the time is 1-5 h, and the roasting atmosphere is any one of argon and hydrogen/argon mixed gas.
10. A method for synthesizing aromatic amine by selectively hydrogenating an aromatic nitro compound, which is characterized by comprising the step of carrying out hydrogenation reaction on the aromatic nitro compound and a catalyst in a solvent, wherein the catalyst is the platinum nano catalyst according to any one of claims 1-5.
11. The method for synthesizing aromatic amine by selective hydrogenation of aromatic nitro compound according to claim 10, wherein the conditions of hydrogenation reaction comprise a temperature of 25-80 ℃ and a pressure of normal pressure-1.5 MPa H 2 The time is 10 min-200 min; the aromatic nitro compound is at least one selected from nitrobenzene, p-chloronitrobenzene, p-nitrotoluene, 3, 5-dimethylnitrobenzene, p-nitrostyrene, m-nitrostyrene and p-nitrobenzaldehyde; the molar ratio of the active component in the platinum nano catalyst to the aromatic nitro compound is (0.01-1): 1.
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