CN115337960A - Preparation of platinum metal nanocluster NaA molecular sieve and application of platinum metal nanocluster NaA molecular sieve in 1,2,3,4-tetrahydroquinoline synthesis - Google Patents

Preparation of platinum metal nanocluster NaA molecular sieve and application of platinum metal nanocluster NaA molecular sieve in 1,2,3,4-tetrahydroquinoline synthesis Download PDF

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CN115337960A
CN115337960A CN202210999117.XA CN202210999117A CN115337960A CN 115337960 A CN115337960 A CN 115337960A CN 202210999117 A CN202210999117 A CN 202210999117A CN 115337960 A CN115337960 A CN 115337960A
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陈强
韩孟熹
谭耀棕
彭湃
孙宗宇
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Sun Yat Sen University
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    • C07D215/04Heterocyclic compounds containing quinoline or hydrogenated quinoline ring systems having no bond between the ring nitrogen atom and a non-ring member or having only hydrogen atoms or carbon atoms directly attached to the ring nitrogen atom with only hydrogen atoms or radicals containing only hydrogen and carbon atoms, directly attached to the ring carbon atoms
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Abstract

The invention belongs to the technical field of organic chemical synthesis, and particularly relates to preparation of a platinum metal nanocluster NaA molecular sieve and application of the platinum metal nanocluster NaA molecular sieve in 1,2,3,4-tetrahydroquinoline synthesis. The invention uses silicon source, aluminum source and alkali source, polyethylene glycol, noble metal precursor and the like as raw materials, uses (3-mercaptopropyl) trimethoxysilane as a ligand, and is prepared by hydrothermal standing crystallization, roasting and hydrogen reduction. And the prepared platinum metal nanocluster NaA molecular sieve, wherein the size of the platinum metal cluster is nanoscale, and the NaA molecular sieve belongs to an alpha cage-limited platinum nanometal cluster, and when the NaA molecular sieve is used as a catalyst for selective catalytic hydrogenation, the high selectivity of preparing 1,2,3,4-tetrahydroquinoline by selective hydrogenation can be realized by utilizing the hydrogen overflow effect of the NaA molecular sieve and the alpha cage-limited effect.

Description

Preparation of platinum metal nanocluster NaA molecular sieve and application of platinum metal nanocluster NaA molecular sieve in 1,2,3,4-tetrahydroquinoline synthesis
Technical Field
The invention belongs to the technical field of organic chemical synthesis, and particularly relates to preparation of a platinum metal nanocluster NaA molecular sieve and application of the platinum metal nanocluster NaA molecular sieve in 1,2,3,4-tetrahydroquinoline synthesis.
Background
Since 1,2,3,4-tetrahydroquinoline and its derivatives are widely used in the fields of medicines, agrochemicals, fine chemicals and the like, the preparation of 1,2,3,4-tetrahydroquinoline is also of great interest. At present, selective hydrogenation of quinoline is one of the most effective ways to obtain 1,2,3,4-tetrahydroquinoline, because the reaction is simple and convenient, and has high atomic efficiency. However, the selective hydrogenation of quinoline presents the following difficulties: the energy barrier of quinoline hydrogenation is high, so the reaction rate is low, and harsh reaction conditions are required; the hydrogenation process is accompanied by other byproducts, such as 5,6,7,8-tetrahydroquinoline and decahydroquinoline; the metal catalyst has strong coordination with nitrogen atoms in the N-heterocyclic ring of quinoline, so that the metal is easy to be poisoned, and the sustainability of the catalytic system is greatly reduced.
In view of the above-mentioned drawbacks of quinoline and its derivatives in the selective hydrogenation process, researchers have proposed many improvements, and among them, alternative metal catalysts such as transition metal or noble metal supported catalysts have attracted the most attention. There are studies using the iridium/phosphine/iodine system as an initial model for asymmetric reduction of quinoline derivatives, with selective hydrogenation of quinoline derivatives catalyzed by iridium catalysts in the presence of bidentate phosphorus ligands, where iodine has the main role of converting iridium (I) to iridium (III). However, transition metal phosphine catalysts are sensitive to air, which can lead to catalyst deactivation. The research also shows that sub-nanometer palladium metal clusters are loaded in random copolymer micelles, a plurality of palladium-containing micelles with different forms can be obtained through the crosslinking of the copolymer, the obtained latticed palladium micelles can catalyze quinoline to selectively hydrogenate to obtain 1,2,3,4-tetrahydroquinoline at room temperature and normal pressure in hydrogen atmosphere, the reaction lasts for 24 hours, and the conversion rate can reach 80%. Although the method solves the problem of easy deactivation of the catalyst to a certain extent, the required reaction time is longer. Research also shows that the Fe/Pt nanowire is subjected to acid etching in the air and then washed in methanol for multiple times to synthesize the ultrafine Pt nanowire catalyst, the catalyst is used for synthesizing 1,2,3,4-tetrahydroquinoline, the quinoline conversion rate in solvents such as water, methanol, ethanol and the like can reach 91-98%, and the selectivity of 1,2,3,4-tetrahydroquinoline can reach 93-97%. Although the conversion rate and the selectivity of the method are high, the platinum nanowire has poor tolerance to complex chemical environment and is easy to be poisoned and inactivated. Therefore, it is necessary to develop a new preparation method of 1,2,3,4-tetrahydroquinoline to overcome the above disadvantages.
Disclosure of Invention
In order to overcome the defects of the prior art, the preparation method of the platinum metal nanocluster NaA molecular sieve is used for selectively hydrogenating quinoline to generate 1,2,3,4-tetrahydroquinoline, and the selectivity of hydrogenating quinoline to generate 1,2,3,4-tetrahydroquinoline is improved.
In order to realize the purpose, the invention is realized by the following technical scheme:
the invention provides a preparation method of a platinum metal nanocluster NaA molecular sieve, which comprises the following steps: heating and stirring an alkali source, a silicon source, (3-mercaptopropyl) trimethoxysilane, a platinum metal precursor and polyethylene glycol in a water bath, adding an aluminum source, uniformly mixing, and then sequentially carrying out hydrothermal standing crystallization, roasting and hydrogen reduction to prepare the platinum metal nanocluster NaA molecular sieve.
According to the invention, polyethylene glycol is added into a system for synthesizing the NaA molecular sieve by using a silicon source, an aluminum source and an alkali source, and the mixture is uniformly stirred; adding a noble metal precursor in the synthesis process, and adding (3-mercaptopropyl) trimethoxysilane as a ligand to protect the platinum metal precursor; all raw materials are fully mixed and then are subjected to hydrothermal standing crystallization, roasting and hydrogen reduction treatment. The (3-mercaptopropyl) trimethoxy silane can protect the precious platinum metal precursor in the hydrothermal crystallization process of the molecular sieve, promote the growth and molding characteristics of the molecular sieve framework around the platinum metal precursor and ensure thatThe platinum metal precursor may be confined to the alpha cage of the NaA molecular sieve. The Na-type molecular sieve loaded with the noble metal nanocluster and obtained by the preparation method is an alpha-cage-limited platinum metal nanocluster NaA molecular sieve, the mass content of platinum metal is 0.1-2%, and SiO is used 2 :Al 2 O 3 The silicon-aluminum ratio is 1-2.
Preferably, the silicon source is SiO 2 The aluminum source is NaAlO 2 In terms of NAOH, the molar ratio of the silicon source to the aluminum source to the alkali source is 1.0:0.5 to 2:0.25 to 0.8.
Preferably, the platinum metal precursor is calculated by platinum metal element, the polyethylene glycol is calculated by average molecular weight of 1450g/mol, and the silicon source is calculated by SiO 2 The molar ratio of the (3-mercaptopropyl) trimethoxysilane to the platinum metal precursor to the polyethylene glycol to the silicon source is 0.03-0.1: 0.005-0.05: 0.01 to 0.1:1, the platinum metal precursor comprises chloroplatinic acid hexahydrate.
Preferably, the temperature of the hydrothermal standing crystallization is 70-110 ℃, and the time is 1-3 days.
In order to avoid the platinum metal nanocluster from being agglomerated due to overhigh temperature while ensuring the roasting effect. Preferably, the roasting temperature is 300-500 ℃, the heating rate is 20-60 ℃/h, and the time is 3-5 days; the temperature of the hydrogen reduction is 350-450 ℃, the heating rate is 60-100 ℃/h, and the time is 3-5 days.
Preferably, the water bath heating and stirring is carried out for 0.5 to 1 hour at the temperature of between 70 and 90 ℃.
The invention provides a platinum metal nanocluster NaA molecular sieve prepared by the preparation method of the first aspect.
The third aspect of the invention provides an application of the platinum metal nanocluster NaA molecular sieve in preparation of 1,2,3,4-tetrahydroquinoline.
The fourth aspect of the invention provides a method for preparing 1,2,3,4-tetrahydroquinoline, which is characterized in that under a hydrogen atmosphere, the platinum metal nanocluster NaA molecular sieve of claim 6 is used as a catalyst to catalyze selective hydrogenation of quinoline to generate 1,2,3,4-tetrahydroquinoline.
The aperture of the NaA molecular sieve is smaller than the diameter of a quinoline molecule (the NaA molecular sieve consists of a benzene ring and a pyridine ring, wherein the diameter of the benzene ring is about 0.55nm, namely the diameter of the quinoline molecule is larger than that of the benzene ring and is also larger than that of the NaA molecular sieve), so that the quinoline molecule cannot enter the NaA molecular sieve to be directly contacted with the platinum metal nanocluster and can only be subjected to catalytic hydrogenation through hydrogen overflow of the molecular sieve, and when the selective catalytic hydrogenation is carried out on quinoline, the hydrogen overflow effect of the NaA molecular sieve and the domain-limited effect of an alpha cage can be utilized, and the selectivity of 3262 zxft 3238-tetrahydroquinoline is obviously improved. In addition, because the aperture of the NaA molecular sieve is smaller than the diameter of a quinoline molecule, the framework structure of the molecular sieve can effectively prevent the direct contact of the quinoline molecule and metal platinum, and the problem of strong coordination of nitrogen atoms in quinoline and metal is avoided, so that the problems of poor tolerance and easy poisoning and inactivation of the catalyst are solved.
Preferably, the molar ratio of quinoline to metal platinum in the platinum metal nanocluster NaA molecular sieve is 30-70.
Preferably, the temperature of the catalytic reaction is 100-160 ℃, the pressure of the hydrogen is 1.5-2.5 MPa, and the time is 40-90 min.
Preferably, the catalytic reaction takes ethanol as a solvent, and the mass of the ethanol is 100 to 300 times of that of quinoline.
Compared with the prior art, the invention has the beneficial effects that:
the invention discloses a preparation method of a platinum metal nanocluster NaA molecular sieve, which is prepared by using a silicon source, an aluminum source, an alkali source, polyethylene glycol, a precious metal precursor and the like as raw materials and (3-mercaptopropyl) trimethoxysilane as a ligand through hydrothermal standing crystallization, roasting and hydrogen reduction. And the prepared platinum metal nanocluster NaA molecular sieve is nanoscale, belongs to an alpha cage limited platinum nanocluster, and can be used as a catalyst for selective catalytic hydrogenation to realize high selectivity of 1,2,3,4-tetrahydroquinoline by utilizing the hydrogen overflow effect and the alpha cage limited effect of the NaA molecular sieve.
Drawings
FIG. 1 is a schematic view of a model of the microcell structure of a sample of example 1;
FIG. 2 is a schematic diagram of the structure of an alpha cage in a NaA molecular sieve;
FIG. 3 is an XRD spectrum of a sample of example 1;
FIG. 4 is a TEM photograph and a particle size distribution chart of a sample of example 1;
FIG. 5 is a TEM photograph and a particle size distribution chart of a sample of comparative example 1.
Detailed Description
The following further describes the embodiments of the present invention. It should be noted that the description of the embodiments is provided to help understanding of the present invention, and is not intended to limit the present invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The experimental procedures in the following examples were carried out by conventional methods unless otherwise specified, and the test materials used in the following examples were commercially available by conventional methods unless otherwise specified.
Example 1 Synthesis of platinum Metal nanocluster NaA molecular sieves
(1) 11.5g of sodium metaaluminate (NaAlO) are taken 2 ) Dissolved in 16g H 2 O to obtain solution A; 2.3g of sodium hydroxide (NaOH) is dissolved in 8.0g H 2 Adding 0.8g of (3-mercaptopropyl) trimethoxy silane into the solution O to prepare a solution B; dissolving chloroplatinic acid hexahydrate 0.5g in 4g H 2 O, to obtain solution C.
(2) Stirring solution B at room temperature for 10min, adding solution C, 3.54g polyethylene glycol and 18g silica sol (LUDOX-30) under vigorous stirring, heating in water bath to 80 deg.C, and stirring for 30min until the solution is clear. And slowly dripping the solution A after the mixed solution is cooled, and uniformly stirring at room temperature to obtain the synthesized mixed solution, namely the platinum metal nanocluster NaA molecular sieve system.
In the platinum metal nanocluster NaA molecular sieve system: siO 2 2 、NaAlO 2 The molar ratio of NaOH is 1.0:1.56:0.64; (3-mercaptopropyl) trimethoxysilane, chloroplatinic acid hexahydrate, polyethylene glycol and silica sol (made of SiO) 2 Calculated) was 0.045:0.01:0.027:1.
(3) Placing the mixed solution into a stainless steel hot kettle with a polytetrafluoroethylene lining, and standing and crystallizing for 2 days at 80 ℃. And after crystallization, centrifuging, washing and drying the crystallized product. And roasting the obtained sample in a tubular furnace in an air atmosphere at the roasting temperature of 400 ℃ for 4h at the heating rate of 40 ℃/h. And finally, reducing in a hydrogen atmosphere at 400 ℃ for 4h at the heating rate of 80 ℃/h to obtain the NaA molecular sieve sample A1. In sample A1, the silicon to aluminum ratio (SiO) 2 :Al 2 O 3 ) Is 1.28:1, the mass fraction of platinum is about 1.5%. As shown in figure 1, the prepared NaA molecular sieve is of a three-dimensional porous structure with eight-membered rings.
Fig. 3 is an XRD spectrogram of the sample A1, which shows that the prepared molecular sieve is a platinum-loaded NaA molecular sieve, and the spectrogram of the platinum-loaded molecular sieve has no significant characteristic peak of platinum element, and indirectly shows that the platinum loaded by the molecular sieve has no significant agglomeration, and the structure of the NaA molecular sieve itself is not significantly damaged.
Fig. 4 is a TEM photograph and a particle size distribution diagram of the sample A1, in which white bright spots are platinum nanoclusters, and it can be seen from fig. 4 that the platinum nanoclusters are uniformly dispersed in the crystal of the NaA molecular sieve. From the particle size analysis result, it can be seen that the diameter distribution of the platinum nanoclusters is relatively uniform, the average diameter is about 1.1nm, the diameter of the platinum nanoclusters is close to that of an alpha cage (as shown in fig. 2) of the NaA molecular sieve, but the pore diameter is only about 0.4nm, which indirectly indicates that the sample A1 is the platinum metal nanocluster NaA molecular sieve with an alpha cage confinement.
Example 2 Synthesis of platinum Metal nanocluster NaA molecular sieves
The preparation method is the same as in example 1, except that the calcination temperature in step (3) is 350 ℃ and the reduction temperature is 350 ℃, and the obtained sample is denoted as A2.
The sample A2 also has the structural features of fig. 1 and 2, and the XRD spectrum and TEM photograph of the sample A2 also have the features of fig. 3 and 4.
Comparative example 1 preparation of platinum Metal nanocluster NaA molecular sieves
Unlike example 1, in this comparative example, the platinum metal nanocluster NaA molecular sieve is prepared without in-situ encapsulation, that is, no metal precursor is added during the crystallization of the molecular sieve, and the platinum nanocluster is loaded by impregnation after the molecular sieve is synthesized. The preparation method of the comparative example comprises the following steps:
(1) In the mixing stage of raw materials, chloroplatinic acid hexahydrate and (3-mercaptopropyl) trimethoxysilane are not added, and a pure NaA molecular sieve is firstly prepared: 11.5g of sodium metaaluminate (NaAlO) are taken 2 ) Dissolved in 16g H 2 O to obtain solution A; 2.3g of sodium hydroxide (NaOH) is dissolved in 8.0g H 2 Preparing solution B in O;
adding the solution B, 3.54g of polyethylene glycol and 18g of silica sol (LUDOX-30) into the solution A in sequence, heating the mixture to 80 ℃ in a water bath, and stirring the mixture for 30min until the solution is clear.
(2) After the same crystallization, calcination and hydrogen atmosphere reduction as in the step (3) of example 1, the prepared NaA molecular sieve was dehydrated and degassed in a vacuum oven at 80 ℃, and then a chloroplatinic acid hexahydrate solution (0.5 g chloroplatinic acid hexahydrate in 4g H) was used 2 O), carrying out impregnation treatment, sealing and stirring for 1h under the condition of heating in a water bath at 60 ℃, and evaporating the solution at the same temperature to obtain an impregnated product. The impregnated product was again subjected to the same calcination and hydrogen atmosphere reduction operation as in the step (3) of example 1, to obtain a surface-supported platinum metal nanocluster NaA molecular sieve, denoted as D1. Sample D1, silicon to aluminum ratio (SiO) 2 :Al 2 O 3 ) Is 1.28:1, the mass fraction of platinum is about 1.5%.
Fig. 5 is a TEM photograph and a particle size distribution diagram of the sample D1, and it can be seen from the drawing that the platinum nanoclusters in the sample D1 are not uniformly distributed, and have an average diameter of about 2nm, and meanwhile, there exist large-sized nanoparticles with a diameter close to 5nm, which are larger than the diameter of the α cage in the NaA molecular sieve, which indicates that the platinum metal nanoclusters NaA molecular sieve with α cage domains are not obtained in this comparative example.
This comparative example illustrates that the present invention uses in-situ encapsulation technology to play a key role in the alpha-caged platinum metal nanocluster by participating (3-mercaptopropyl) trimethoxysilane in the preparation process of the noble metal supported NaA molecular sieve.
Experimental example 1 application of platinum metal nanocluster NaA molecular sieve in synthesis of 1,2,3,4-tetrahydroquinoline
(1) Taking 0.1mmol of quinoline, adding the molecular sieve sample A1 prepared in example 1 according to the molar ratio of the quinoline to platinum in the platinum metal nanocluster NaA molecular sieve catalyst being 50 2 And (3) carrying out catalytic reaction for 60min under the condition, centrifuging after reaction, taking supernate, diluting, and detecting by using GC-MS (gas chromatography-mass spectrometry), wherein the obtained conversion rate is about 50% and the selectivity is about 98%. It can be seen that the conversion rate has reached 50% under the condition of 1 hour of reaction time, and it can be presumed that the conversion rate can reach more than 95% under the condition of 3 to 5 hours of reaction time, and that the selectivity of more than 98% is ensured.
(2) Taking 0.1mmol of quinoline, adding the molecular sieve sample D1 prepared in the comparative example 1 according to the molar ratio of the quinoline to the platinum in the catalyst of 50 2 After the conditional catalytic reaction is carried out for 60min, the supernatant is centrifuged and diluted, and then GC-MS is used for detection, so that the conversion rate is about 91 percent, and the selectivity is about 55 percent. Furthermore, the selectivity remained essentially unchanged with increasing reaction time, with no tendency to increase.
The embodiments of the present invention have been described in detail, but the present invention is not limited to the described embodiments. It will be apparent to those skilled in the art that various changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, and the scope of protection is still within the scope of the invention.

Claims (10)

1. A preparation method of a platinum metal nanocluster NaA molecular sieve is characterized in that an alkali source, a silicon source, (3-mercaptopropyl) trimethoxysilane, a platinum metal precursor and polyethylene glycol are heated in a water bath, stirred and mixed uniformly, then an aluminum source is added and mixed uniformly, and then the platinum metal nanocluster NaA molecular sieve is prepared through hydrothermal standing crystallization, roasting and hydrogen reduction successively.
2. The method for preparing a platinum metal nanocluster NaA molecular sieve as claimed in claim 1, wherein the silicon source is SiO 2 The aluminum source is NaAlO 2 In terms of NAOH, the molar ratio of the silicon source to the aluminum source to the alkali source is 1.0:0.5 to 2:0.25 to 0.8.
3. The method of claim 1, wherein the platinum metal precursor is platinum metal, the polyethylene glycol is polyethylene glycol with an average molecular weight of 1450g/mol, and the silicon source is SiO 2 In 0.4, the molar ratio of the (3-mercaptopropyl) trimethoxysilane to the platinum metal precursor to the polyethylene glycol to the silicon source is 0.03-0.1: 0.005-0.05: 0.01 to 0.1:1, the platinum metal precursor comprises chloroplatinic acid hexahydrate.
4. The method for preparing the platinum metal nanocluster NaA molecular sieve as claimed in claim 1, wherein the temperature of the hydrothermal standing crystallization is 70-110 ℃ and the time is 1-3 days.
5. The method for preparing the platinum metal nanocluster NaA molecular sieve as claimed in claim 1, wherein the roasting temperature is 300-500 ℃, the heating rate is 20-60 ℃/h, and the time is 3-5 days; the temperature of the hydrogen reduction is 350-450 ℃, the heating rate is 60-100 ℃/h, and the time is 3-5 days.
6. The platinum metal nanocluster NaA molecular sieve prepared by the preparation method of any one of claims 1 to 5.
7. The use of the platinum metal nanocluster NaA molecular sieve as claimed in claim 6 for the preparation of 1,2,3,4-tetrahydroquinoline.
8. A method for preparing 1,2,3,4-tetrahydroquinoline, which is characterized in that under hydrogen atmosphere, the platinum metal nanocluster NaA molecular sieve of claim 6 is used as a catalyst to catalyze selective hydrogenation of quinoline to 1,2,3,4-tetrahydroquinoline.
9. The method for preparing 1,2,3,4-tetrahydroquinoline of claim 8, wherein the molar ratio of quinoline to platinum in the platinum metal nanocluster NaA molecular sieve is 30 to 70.
10. The method for preparing 1,2,3,4-tetrahydroquinoline according to claim 8, wherein the temperature of the catalytic reaction is 100-160 ℃, the pressure of hydrogen is 1.5-2.5 MPa, and the time is 40-90 min.
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Citations (8)

* Cited by examiner, † Cited by third party
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