阅读说明：本技术 一种Pt/CoFe-LDH负载型纳米固体催化剂及其制备方法和应用 (Pt/CoFe-LDH supported nano solid catalyst and preparation method and application thereof ) 是由 瞿永泉 张赛 张铭凯 于 2021-09-22 设计创作，主要内容包括：本发明公开了一种Pt/CoFe-LDH负载型纳米固体催化剂及其制备方法和应用,其制备方法包括以下步骤：将CoFe-LDH载体溶解于去离子水中,加入Na-(2)PtCl-(6)·6H-(2)O溶液,再加入尿素,搅拌均匀后,加热回流,待所得溶液冷却后,加入NaBH-(4)溶液,最后离心、清洗和干燥,得到Pt/CoFe-LDH负载型纳米固体催化剂。本发明制备的催化剂高效、稳定,可以防止还原胺化反应中副产物的生成、实现伯胺的高选择性合成。(The invention discloses a Pt/CoFe-LDH supported nano solid catalyst and a preparation method and application thereof, wherein the preparation method comprises the following steps: dissolving CoFe-LDH carrier in deionized water, adding Na 2 PtCl 6 ·6H 2 Adding urea into O solution, stirring, heating and refluxing, cooling, adding NaBH 4 And finally centrifuging, washing and drying the solution to obtain the Pt/CoFe-LDH supported nano solid catalyst. The catalyst prepared by the method is efficient and stable, can prevent the generation of byproducts in reductive amination reaction, and realizes the high-selectivity synthesis of primary amine.)

1. A preparation method of a Pt/CoFe-LDH supported nano solid catalyst is characterized by comprising the following steps:

(1) the CoFe-LDH carrier is dissolved in deionized water, and then Na is added₂PtCl₆·6H₂Adding urea into the O solution, uniformly stirring, and heating and refluxing for 0.8-1.2h at 58-62 ℃;

(2) after the solution obtained in the step (1) is cooled, adding NaBH₄The solution is stirred evenly, wherein, NaBH₄The concentration of the solution is 2-4 g/L;

(3) and (3) centrifuging the solution obtained in the step (2), and then cleaning and drying the solid obtained by centrifuging to obtain the Pt/CoFe-LDH supported nano solid catalyst.

2. The preparation method of Pt/CoFe-LDH supported nano-solid catalyst as claimed in claim 1, wherein the CoFe-LDH support in step (1) is prepared by the following preparation method:

(1) mixing Fe (NO)₃)₃·9H₂O and Co (NO)₃)₂·6H₂Dissolving O in deionized water to obtain a first solution; wherein, Fe (NO)₃)₃·9H₂O concentration of 0.2-0.4mol/L, Co (NO)₃)₂·6H₂The concentration of O is 0.5-0.7 mol/L;

(2) mixing NaOH and Na₂CO₃Dissolving in deionized water to obtain a solution II; wherein the concentration of NaOH is 1.8-2mol/L, Na₂CO₃The concentration of (A) is 0.7-0.9 mol/L;

(3) uniformly mixing the solution I and the solution II according to the volume ratio of 1 (0.9-1.5), and reacting at 75-85 ℃ for 45-50 h;

(4) and (4) centrifuging the solution obtained in the step (3), and then cleaning and drying the solid obtained by centrifugation to obtain the CoFe-LDH carrier.

3. The method for preparing the Pt/CoFe-LDH supported nano solid catalyst as claimed in claim 2, wherein the solution one and the solution two are mixed in a volume ratio of 1:1 in the step (3).

4. The method for preparing Pt/CoFe-LDH supported nano-solid catalyst as claimed in claim 1, wherein the concentration of CoFe-LDH support in deionized water in step (1) is 8-12 g/L.

5. The Pt/CoFe-LDH supported nano-solid as claimed in claim 1The preparation method of the catalyst is characterized in that the step (1) is Na₂PtCl₆·6H₂The concentration of the O solution is 1.5-2.5g/L, Na is added₂PtCl₆·6H₂The volume of the O solution is 2-3% of the volume of the deionized water.

6. The method for preparing Pt/CoFe-LDH supported nano-solid catalyst as claimed in claim 1, wherein the mass ratio of urea to CoFe-LDH support in step (1) is 1 (0.9-1.5).

7. The method for preparing Pt/CoFe-LDH supported nano-solid catalyst of claim 6, wherein the mass ratio of urea to CoFe-LDH support is 1:1.

8. The Pt/CoFe-LDH supported nano solid catalyst prepared by the preparation method of the Pt/CoFe-LDH supported nano solid catalyst as set forth in any one of claims 1 to 7.

9. Use of the Pt/CoFe-LDH supported nano-solid catalyst of claim 8 in the synthesis of primary amines.

Technical Field

The invention relates to the technical field of catalyst preparation, in particular to a Pt/CoFe-LDH supported nano solid catalyst and a preparation method and application thereof.

Background

The primary amine compound is an important amine chemical, is an indispensable substance for forming a living organism, can be used as a raw material or an intermediate to synthesize a fine chemical product with high added value, and is widely applied to industries such as textile, biology, medicine and the like. In the common process for producing primary amine chemicals, reductive amination reactions are widely studied. The reductive amination reaction takes aldehyde or ketone organic matters as a substrate and organic amine or inorganic ammonia as a nitrogen source, and realizes the synthesis of primary amine through the steps of substrate amination, hydrogenation and the like in the atmosphere of hydrogen. The reaction has high atom utilization rate, relatively cheap and easily available raw materials, mild reaction conditions and certain advantages in industrial production. However, in the reductive amination reaction, side reactions such as direct substrate hydrogenation, excessive imine intermediate hydrogenation and the like can result in the generation of byproducts such as alcohol and secondary amine, thereby greatly reducing the yield of the target product primary amine and also increasing the separation cost of the product. In addition, the presence of inorganic ammonia in the reaction system may result in catalyst deactivation, thereby reducing the conversion rate of the reaction. Therefore, the synthesis of the efficient and stable catalyst for preventing the generation of byproducts in the reductive amination reaction and realizing the high-selectivity synthesis of primary amine has important research value.

Disclosure of Invention

In order to solve the technical problems, the invention aims to provide a Pt/CoFe-LDH supported nano solid catalyst, a preparation method and an application thereof, so as to solve the problems that the yield of primary amine of the existing reductive amination reaction is not high, a byproduct is easily generated, and the catalyst is easily deactivated.

The technical scheme for solving the technical problems is as follows: provides a preparation method of a Pt/CoFe-LDH supported nano solid catalyst, which comprises the following steps:

(1) the CoFe-LDH carrier is dissolved in deionized water, and then Na is added₂PtCl₆·6H₂Adding urea into the O solution, uniformly stirring, and heating and refluxing for 0.8-1.2h at 58-62 ℃;

(2) after the solution obtained in the step (1) is cooled, adding NaBH₄The solution is stirred evenly, wherein, NaBH₄The concentration of the solution is 2-4 g/L;

(3) and (3) centrifuging the solution obtained in the step (2), and then cleaning and drying the solid obtained by centrifuging to obtain the Pt/CoFe-LDH supported nano solid catalyst.

The invention has the beneficial effects that: the invention synthesizes the nano solid catalyst with platinum loaded on cobalt iron hydrotalcite (Pt/CoFe-LDH), and adjusts the electron density of metal through the interaction between the loaded metal and the carrier, thereby changing the absorption of reaction substrates, inhibiting the generation of benzyl alcohol and dibenzylamine and ensuring that the yield of the target product benzylamine is more than 95 percent.

On the basis of the technical scheme, the invention can be further improved as follows:

further, the CoFe-LDH carrier of the step (1) is prepared by the following preparation method:

(1) mixing Fe (NO)₃)₃·9H₂O and Co (NO)₃)₂·6H₂Dissolving O in deionized water to obtain a first solution; wherein, Fe (NO)₃)₃·9H₂O concentration of 0.2-0.4mol/L, Co (NO)₃)₂·6H₂The concentration of O is 0.5-0.7 mol/L;

(2) mixing NaOH and Na₂CO₃Dissolving in deionized water to obtain a solution II; wherein the concentration of NaOH is 1.8-2mol/L, Na₂CO₃The concentration of (A) is 0.7-0.9 mol/L;

(3) uniformly mixing the solution I and the solution II according to the volume ratio of 1 (0.9-1.5), and reacting at 75-85 ℃ for 45-50 h;

(4) and (4) centrifuging the solution obtained in the step (3), and then cleaning and drying the solid obtained by centrifugation to obtain the CoFe-LDH carrier.

Further, in the preparation method of the CoFe-LDH carrier, the solution I and the solution II in the step (3) are mixed according to the volume ratio of 1:1.

Further, in the preparation method of the Pt/CoFe-LDH supported nano solid catalyst, the concentration of the CoFe-LDH carrier in the step (1) in deionized water is 8-12 g/L.

Further, step (1) Na in the preparation method of the Pt/CoFe-LDH supported nano solid catalyst₂PtCl₆·6H₂The concentration of the O solution is 1.5-2.5g/L, and Na is added₂PtCl₆·6H₂The volume of the O solution is 2-3% of the volume of the deionized water.

Further, in the preparation method of the Pt/CoFe-LDH supported nano solid catalyst, the mass ratio of the urea in the step (1) to the CoFe-LDH carrier is 1 (0.9-1.5).

Further, the mass ratio of urea to CoFe-LDH carrier was 1:1.

The beneficial effect of adopting the further technical scheme is as follows:

the method for preparing the catalyst is simple and convenient, the raw materials are easy to obtain, the operation is flexible and feasible, and the repeatability is good.

The invention also provides the Pt/CoFe-LDH supported nano solid catalyst prepared by the preparation method.

The invention also provides application of the Pt/CoFe-LDH supported nano solid catalyst in the aspect of synthesizing primary amine.

The invention has the following beneficial effects:

(1) the catalyst is used for carrying out reductive amination reaction of benzaldehyde and ammonia water, the reaction temperature is mild, and the complete conversion of benzaldehyde can be realized after the reaction is carried out for 15 hours at 80 ℃;

(2) under the optimized reaction conditions, the yield of the target product benzylamine can reach 95.1%, and the generation of benzyl alcohol and dibenzylamine as byproducts can hardly be detected.

(3) The catalyst has better stability, and the yield of benzylamine can still be over 86 percent after the reaction is circulated for 5 times.

(4) The catalyst has low Pt loading capacity and reduces the preparation cost.

(5) The catalyst is widely applicable to substrates, and can realize high-selectivity synthesis of corresponding primary amine when substituents such as methyl, methoxy, halogen and the like exist on a benzene ring besides benzaldehyde; in addition to aromatic aldehydes, efficient synthesis of primary amines can also be achieved with aliphatic aldehydes as substrates.

Drawings

FIG. 1 is a graph of the reaction conversion and product selectivity over time for the catalyst prepared in example 1;

FIG. 2 is a graph of the reaction cycle stability of the catalyst prepared in example 1.

Detailed Description

The principles and features of this invention are described below in conjunction with the following drawings, which are set forth by way of illustration only and are not intended to limit the scope of the invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

Example 1:

a preparation method of a Pt/CoFe-LDH supported nano solid catalyst comprises the following steps:

(1) mixing Fe (NO)₃)₃·9H₂O and Co (NO)₃)₂·6H₂Dissolving O in deionized water uniformly to obtain a first solution; wherein, Fe (NO)₃)₃·9H₂O concentration of 0.3mol/L, Co (NO)₃)₂·6H₂The concentration of O is 0.6 mol/L;

(2) mixing NaOH and Na₂CO₃Uniformly dissolving the mixture in deionized water to obtain a solution II; wherein the concentration of NaOH is 1.92mol/L, Na₂CO₃The concentration of (A) is 0.8 mol/L;

(3) uniformly mixing the solution I and the solution II according to the volume ratio of 1:1, adding the mixture into a stainless steel kettle with a polytetrafluoroethylene lining, placing the stainless steel kettle into a high-temperature furnace, and reacting at the high temperature of 80 ℃ for 48 hours;

(4) centrifuging the solution obtained in the step (3), then respectively washing the solid obtained by centrifuging for 3 times by using water and ethanol, and drying in a drying oven at the temperature of 60 ℃ to obtain a CoFe-LDH carrier;

(5) dissolving CoFe-LDH carrier in deionized water, carrying out ultrasonic treatment for 30min, and then adding Na with the concentration of 2g/L₂PtCl₆·6H₂Adding urea into O solution, stirring uniformly, heating and refluxing for 1h at 60 ℃, wherein the concentration of CoFe-LDH carrier in deionized water is 10g/L, and adding Na₂PtCl₆·6H₂The volume of the O solution is 2.5 percent of the volume of the deionized water, and the mass ratio of the urea to the CoFe-LDH carrier is 1: 1;

(6) after the solution obtained in the step (5) is cooled, adding NaBH₄The solution is stirred evenly, wherein, NaBH₄The concentration of the solution is 3g/L, NaBH₄The solution is prepared by dissolving NaBH₄Dissolving in deionized water to obtain;

(7) and (4) after the solution obtained in the step (6) is subjected to centrifugal treatment, washing the solid obtained by the centrifugal treatment for 3 times by using ionized water, and drying in a drying box at the temperature of 60 ℃ to obtain the Pt/CoFe-LDH supported nano solid catalyst.

Example 2:

a preparation method of a Pt/CoFe-LDH supported nano solid catalyst comprises the following steps:

(1) mixing Fe (NO)₃)₃·9H₂O and Co (NO)₃)₂·6H₂Dissolving O in deionized water uniformly to obtain a first solution; wherein, Fe (NO)₃)₃·9H₂O concentration of 0.2mol/L, Co (NO)₃)₂·6H₂The concentration of O is 0.5 mol/L;

(2) mixing NaOH and Na₂CO₃Uniformly dissolving the mixture in deionized water to obtain a solution II; wherein the concentration of NaOH is 1.8mol/L, Na₂CO₃The concentration of (A) is 0.7 mol/L;

(3) uniformly mixing the solution I and the solution II according to the volume ratio of 1:0.9, adding the mixture into a stainless steel kettle with a polytetrafluoroethylene lining, placing the stainless steel kettle into a high-temperature furnace, and reacting at the high temperature of 75 ℃ for 50 hours;

(4) centrifuging the solution obtained in the step (3), then respectively washing the solid obtained by centrifuging for 3 times by using water and ethanol, and drying in a drying oven at the temperature of 60 ℃ to obtain a CoFe-LDH carrier;

(5) dissolving CoFe-LDH carrier in deionized water, carrying out ultrasonic treatment for 30min, and then adding Na with the concentration of 1.5g/L₂PtCl₆·6H₂Adding urea into O solution, stirring uniformly, heating and refluxing for 1.2h at 58 ℃, wherein the concentration of CoFe-LDH carrier in deionized water is 8g/L, and adding Na₂PtCl₆·6H₂The volume of the O solution is 2 percent of the volume of the deionized water, and the mass ratio of the urea to the CoFe-LDH carrier is 1: 0.9;

(6) after the solution obtained in the step (5) is cooled, adding NaBH₄The solution is stirred evenly, wherein, NaBH₄The concentration of the solution is 2g/L, NaBH₄The solution is prepared by dissolving NaBH₄Dissolving in deionized water to obtain;

(7) and (4) after the solution obtained in the step (6) is subjected to centrifugal treatment, washing the solid obtained by the centrifugal treatment for 3 times by using ionized water, and drying in a drying box at the temperature of 60 ℃ to obtain the Pt/CoFe-LDH supported nano solid catalyst.

Example 3:

a preparation method of a Pt/CoFe-LDH supported nano solid catalyst comprises the following steps:

(1) mixing Fe (NO)₃)₃·9H₂O and Co (NO)₃)₂·6H₂Dissolving O in deionized water uniformly to obtain a first solution; wherein, Fe (NO)₃)₃·9H₂O concentration of 0.4mol/L, Co (NO)₃)₂·6H₂The concentration of O is 0.7 mol/L;

(2) mixing NaOH and Na₂CO₃Uniformly dissolving the mixture in deionized water to obtain a solution II; wherein the concentration of NaOH is 2mol/L, Na₂CO₃The concentration of (A) is 0.9 mol/L;

(3) uniformly mixing the solution I and the solution II according to the volume ratio of 1:1.5, adding the mixture into a stainless steel kettle with a polytetrafluoroethylene lining, placing the stainless steel kettle into a high-temperature furnace, and reacting for 45 hours at the high temperature of 85 ℃;

(4) centrifuging the solution obtained in the step (3), then respectively washing the solid obtained by centrifuging for 3 times by using water and ethanol, and drying in a drying oven at the temperature of 60 ℃ to obtain a CoFe-LDH carrier;

(5) dissolving CoFe-LDH carrier in deionized water, carrying out ultrasonic treatment for 30min, and then adding Na with the concentration of 2.5g/L₂PtCl₆·6H₂Adding urea into O solution, stirring, heating and refluxing at 62 deg.C for 0.8h, wherein the concentration of CoFe-LDH carrier in deionized water is 12g/L, and adding Na₂PtCl₆·6H₂The volume of the O solution is 3 percent of the volume of the deionized water, and the mass ratio of the urea to the CoFe-LDH carrier is 1: 1.5;

(6) after the solution obtained in the step (5) is cooled, adding NaBH₄The solution is stirred evenly, wherein, NaBH₄The concentration of the solution is 4g/L, NaBH₄The solution is prepared by dissolving NaBH₄Dissolving in deionized water to obtain;

(7) and (4) after the solution obtained in the step (6) is subjected to centrifugal treatment, washing the solid obtained by the centrifugal treatment for 3 times by using ionized water, and drying in a drying box at the temperature of 60 ℃ to obtain the Pt/CoFe-LDH supported nano solid catalyst.

Comparative example 1

A preparation method of a Pt/C catalyst comprises the following steps:

(1) dissolving carbon black carrier treated by nitric acid in deionized water, performing ultrasonic treatment for 30min, and adding Na with concentration of 2g/L₂PtCl₆·6H₂Adding urea into the O solution, stirring uniformly, heating and refluxing for 1h at 60 ℃, wherein the concentration of the carbon black carrier in deionized water is 10g/L, and adding Na₂PtCl₆·6H₂The volume of the O solution is 2.5 percent of the volume of the deionized water, and the mass ratio of the urea to the carbon black carrier is 1: 1;

(2) after the solution obtained in the step (1) is cooled, adding NaBH₄The solution is stirred evenly, wherein, NaBH₄The concentration of the solution is 3g/L, NaBH₄The solution is prepared by dissolving NaBH₄Dissolving in deionized water to obtain;

(3) and (3) after the solution obtained in the step (2) is subjected to centrifugal treatment, washing the solid obtained by the centrifugal treatment for 3 times by using ionized water, and drying in a drying box at the temperature of 60 ℃ to obtain the Pt/C catalyst.

And (4) detecting a result:

1. catalytic efficiency of Pt/CoFe-LDH supported nano solid catalyst

(1) 20mg of the Pt/CoFe-LDH supported nano solid catalyst prepared in example 1, 51.2uL of benzaldehyde, 2mL of ammonia water (25 wt%) and 4mL of isopropanol were added to a stainless steel reaction kettle, and then 2MPa of hydrogen was charged to react at 80 ℃ for 15 hours. The results of the experiment are shown in FIG. 1, and it is understood from FIG. 1 that the yield of benzylamine is 95.1%, and formation of benzyl alcohol and dibenzylamine as by-products is hardly detected.

(2) 20mg of the Pt/C catalyst prepared in comparative example 1, 51.2uL of benzaldehyde, 2mL of ammonia (25 wt%) and 4mL of isopropanol were charged in a stainless steel reaction vessel, and then charged with 2MPa of hydrogen to react at 80 ℃ for 15 hours. The experimental results are as follows: the yield of benzylamine was 30%.

According to the experimental detection, the Pt/CoFe-LDH supported nano solid catalyst prepared by the invention is used for catalyzing the reductive amination reaction of benzaldehyde and ammonia water, the reaction temperature is mild, the benzaldehyde can be completely converted after the reaction is carried out for 15 hours at 80 ℃, the yield of a target product benzylamine can reach 95.1%, and the generation of byproducts benzyl alcohol and dibenzylamine can not be detected almost.

2. Application range of Pt/CoFe-LDH supported nano solid catalyst

(1) Adding 20mg of the Pt/CoFe-LDH supported nano solid catalyst prepared in the example 2, 2-methylbenzaldehyde, ammonia water (28 wt%) and isopropanol into a stainless steel reaction kettle, then filling 2MPa hydrogen, and reacting for 15h at 80 ℃; wherein the amount of the substance of 2-methylbenzaldehyde was 0.5mmol, and the volume ratio of 2-methylbenzaldehyde, aqueous ammonia (28 wt%) and isopropyl alcohol was 1:40: 80.

Experiments were conducted according to the above-mentioned procedures by replacing 2-methylbenzaldehyde in the above-mentioned reaction with 3-methylbenzaldehyde, 4-methylbenzaldehyde or 4-methoxybenzaldehyde, respectively. The experimental results are as follows: the yields of 2-methylbenzylamine, 3-methylbenzylamine and 4-methylbenzylamine were 81.4%, 85.7%, 88.4% and 95.9%, respectively.

(2) Adding 20mg of the Pt/CoFe-LDH supported nano solid catalyst prepared in the example 3, 4-chlorobenzaldehyde, ammonia water (25 wt%) and isopropanol into a stainless steel reaction kettle, then filling 2MPa hydrogen, and reacting for 15h at 100 ℃; wherein the content of 4-chlorobenzaldehyde is 0.5mmol, and the volume ratio of 4-chlorobenzaldehyde, ammonia water (25 wt%) and isopropanol is 1:40: 80.

The 4-chlorobenzaldehyde in the above reaction was replaced with 4-bromobenzaldehyde, and the experiment was carried out according to the above reaction procedure. The experimental results are as follows: the yields of 4-chlorobenzylamine and 4-bromobenzylamine were 88.5% and 86.3%.

(3) Adding 20mg of the Pt/CoFe-LDH supported nano solid catalyst prepared in the example 3, hexanal, ammonia water (28 wt%) and isopropanol into a stainless steel reaction kettle, then filling 2MPa hydrogen, and reacting for 15h at 80 ℃; wherein the amount of hexanal substance is 0.5mmol, and the volume ratio of hexanal, ammonia (28 wt%) and isopropanol is 1:40: 80. The experimental results are as follows: the hexylamine yield was 96.3%.

(4) 20mg of the Pt/CoFe-LDH supported nano solid catalyst prepared in example 1, 51.2uL of benzaldehyde, 409.6uL of ammonium nitrate and 6.1mL of isopropanol are added into a stainless steel reaction kettle, and then 2MPa of hydrogen is charged into the stainless steel reaction kettle to react for 15h at 110 ℃. The experimental results are as follows: the benzylamine yield was 91.5%.

The experimental results show that the Pt/CoFe-LDH supported nano solid catalyst prepared by the invention has wide application substrates in the amine catalytic reduction reaction, and can realize high-selectivity synthesis of corresponding primary amine when substituents such as methyl, methoxy, halogen and the like exist on a benzene ring besides benzaldehyde; besides aromatic aldehyde, the high-efficiency synthesis of primary amine can be realized by taking aliphatic aldehyde as a substrate; when the nitrogen source is organic amine or inorganic ammonia, the high-efficiency synthesis of the primary amine can be realized, and the catalytic efficiency is higher.

3. Stability of Pt/CoFe-LDH supported nano solid catalyst

20mg of the Pt/CoFe-LDH supported nano solid catalyst prepared in example 1, 51.2uL of benzaldehyde, 2mL of ammonia water (28 wt%) and 4mL of isopropanol were added to a stainless steel reaction kettle, and then 2MPa of hydrogen was charged to react at 80 ℃ for 15 hours. The catalyst is used for cyclic reaction for 5 times. The results of the detection of the benzylamine are shown in figure 2, and it can be seen from figure 2 that the benzylamine yield can still be above 86% after 5 times of reaction circulation, and the Pt/CoFe-LDH supported nano solid catalyst prepared by the invention has better stability.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.