CN104998631A - Nitrogen-doped graphene, Pd-loaded nitrogen-doped graphene catalyst and preparation method and application thereof - Google Patents

Abstract

The invention provides an azagraphene, a Pd-loaded azagraphene catalyst, a preparation method and an application thereof. Wherein, the preparation method of the Pd-loaded azagraphene catalyst comprises: mixing graphene oxide, urea and water, and ultrasonically treating for 3 hours. Transferred to the reaction kettle, stirred and reacted at 180°C for 10h. suction filtration, washing and drying to obtain NRGO- _x . Mix NRGO- _x , palladium chloride solution and water, and sonicate for 1 h. Put it into the reaction kettle, raise the temperature to 40°C, and stir the reaction for 8h under 2MPaH ₂ . After the reaction, suction filtration, washing, and vacuum drying at 60° C. for 12 h yielded Pd/NRGO _-x . Compared with the Pd catalyst supported by traditional carbon materials, the Pd catalyst supported by azagraphene of the present invention has higher catalytic activity and stability. The method for preparing nitrogen-doped graphene avoids the use of high temperature and high pressure, and the content of nitrogen is easy to adjust.

Description

Azagraphene, Pd-loaded azagraphene catalyst, preparation method and application thereof

technical field

The invention relates to the technical field of chemical industry, in particular to azagraphene, a Pd-loaded azagraphene catalyst, a preparation method and an application thereof.

Background technique

Recently, a new type of single-atom-thick carbon nanosheets—graphene—has been the focus of intense research. From the current research, it is found that graphene not only has a larger theoretical specific surface area (up to 2630m ² /g) than activated carbon and carbon nanotubes, but also has better electrical and thermal conductivity. At the same time, since the upper and lower layers of the graphene nanosheet are easily exposed, it has a high specific surface area utilization efficiency. In addition, there are many oxygen-containing groups and defects such as carbon or oxygen on the surface of graphene. This will bring many chemically active sites, or serve as anchor sites for metal particles. However, compared with carbon nanotubes, graphene is an easy-to-synthesize, low-cost carbon material, so it is easier to produce on a large scale. It can be predicted that graphene can be used as a superior catalyst support for heterogeneous catalytic reactions.

With the gradual expansion of research, it was found that the physical and chemical properties of graphene can be further changed by introducing heteroelements (N, B, and P). For example, the introduction of N atoms into the graphene framework can not only suppress its re-graphitization during drying and use, but also act as defect-enhanced particle nucleation and particle size reduction. Compared with pure graphene, azagraphene is a kind of catalyst carrier with obvious advantages. It is of great significance and value to develop new azacarbon materials and explore their application in heterogeneous catalytic reactions.

In recent years, a variety of methods can be used to prepare various new nitrogen-doped graphene, such as organic pyrolysis, high-voltage arc method, laser lift-off method or chemical vapor deposition method, etc., but harsh preparation conditions and expensive prices restrict its Large-scale practical application. With the deepening of the concept of green chemistry and the continuous improvement of people's requirements for energy conservation and emission reduction, it is inevitable to find a method for the preparation of environmentally friendly and easy-to-synthesize azacarbon graphene.

Contents of the invention

The purpose of the present invention is to solve the above-mentioned defects in the prior art, a simple and easy preparation method of azagraphene, a highly active supported Pd catalyst and a preparation method thereof. This azagraphene-supported Pd catalyst has higher catalytic activity and stability than traditional carbon material-supported Pd catalysts. The method for preparing nitrogen-doped graphene avoids the use of high temperature and high pressure, and the content of nitrogen is easy to adjust. In the process of loading palladium, hydrogen is used as a reducing agent, avoiding the use of protective agents and non-green reducing agents, and the conditions are mild, which is convenient for washing and exposure of active sites. The catalyst uses azagraphene as a carrier and palladium as an active center. Calculated on the basis of its weight, the composition is as follows: the loading amount of palladium is 0-20wt%, and the content of nitrogen is 0-7.5wt%.

A preparation method of azagraphene, comprising the following steps;

(1), GO is added to a certain amount of water, and treated in an ultrasonic generator for 1-3h; the mass volume ratio of the GO to water is (10-90)mg:(10-80)mL;

(2), then transferred to the reaction kettle, stirred and reacted at 150-200°C for 5-24h;

(3) Vacuum drying at 30-60° C. for 12-24 hours after suction filtration and washing to obtain sample RGO.

Further, the preparation method of azagraphene as described above, said step 1 comprises:

GO, a certain amount of urea, and water are treated in an ultrasonic generator for 1-3h to finally obtain a sample NRGO- _x , and the mass-volume ratio of GO, urea, and water is: A mg:B g:C mL, where , 10≤A≤90, 0<B≤27, 10≤C≤80, the x represents the mass ratio of urea to graphene oxide, 0<X<300.

Further, the preparation method of azagraphene as described above comprises the following steps:

(1) Take a certain amount of NRGO- _x and disperse it into water, and treat it in an ultrasonic generator for 1 hour, wherein the mass-volume ratio of NRGO- _x to water is (5-100)mg:(10-200)mL;

(2), take 0-0.84mL of PdCl ₂ aqueous solution, stir at room temperature for 10-120min;

(3), then transferred to the reaction kettle, stirred and reacted at 20-50°C and 0.5-3MPa H ₂ for 2-12h;

(4) Suction filtration, fully washed with distilled water, and vacuum drying at 30-80° C. for 12-24 hours to obtain Pd/NRGO _-x .

Further, in the preparation method of azagraphene as described above, the palladium content in the palladium chloride solution in step (2) is 1-24 mg/mL.

The azagraphene catalyst loaded with Pd prepared by the preparation method as described above.

Application of the azagraphene catalyst loaded with Pd in carbon-carbon coupling synthesis of biphenyl as described above.

The present invention aims at the current difficult situation in the preparation and use of azagraphene, uses cheap urea and graphene oxide as raw materials, and obtains nitrogen with different nitrogen contents under hydrothermal treatment by adjusting the ratio of the two miscellaneous graphene. Highly dispersed nano-palladium particles (Pd/NRGO) were prepared by in situ reduction with hydrogen on the surface of azagraphene. It was applied to the Suzuki carbon-carbon coupling reaction, which showed significantly better catalytic activity than ordinary activated carbon and traditional oxide-supported Pd catalysts. The method for preparing nitrogen-doped graphene avoids the use of high temperature and high pressure, and the content of nitrogen is easy to adjust. The process of loading palladium avoids the use of protective agents and non-green reducing agents, and the conditions are mild, which is convenient for washing and exposure of active sites. The method of aza-graphene supported palladium catalyst provides the possibility to try the possible development direction of this field and realize the industrialization of graphene catalysis.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention clearer, the following technical solutions in the present invention are clearly and completely described. Obviously, the described embodiments are some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

The present invention provides a kind of preparation method of azagraphene, comprises the following steps;

(1), GO is added to a certain amount of water, and treated in an ultrasonic generator for 1-3h; the mass volume ratio of the GO to water is (10-90)mg:(10-80)mL;

(2), then transferred to the reaction kettle, stirred and reacted at 150-200°C for 5-24h;

(3) Vacuum drying at 30-60° C. for 12-24 hours after suction filtration and washing to obtain sample RGO.

Further, the preparation method of azagraphene as described above also needs to add urea in step 1, specifically:

GO, a certain amount of urea, and water are treated in an ultrasonic generator for 1-3h to finally obtain a sample NRGO- _x , and the mass-volume ratio of GO, urea, and water is: A mg:B g:C mL, where , 10≤A≤90, 0<B≤27, 10≤C≤80, the x represents the mass ratio of urea to graphene oxide, 0<X<300.

Further, the preparation method of azagraphene as described above comprises the following steps:

(1) Take a certain amount of NRGO- _x and disperse it into water, and treat it in an ultrasonic generator for 1 hour, wherein the mass-volume ratio of NRGO- _x to water is (5-100)mg:(10-200)mL;

(2), take 0-0.84mL of PdCl ₂ aqueous solution, stir at room temperature for 10-120min; palladium content in the palladium chloride solution is 1-24mg/mL;

(3), then transferred to the reaction kettle, stirred and reacted at 20-50°C and 0.5-3MPa H ₂ for 2-12h;

(4) Suction filtration, fully washed with distilled water, and vacuum drying at 30-80° C. for 12-24 hours to obtain Pd/NRGO _-x .

The catalyst prepared by the above preparation method uses azagraphene as a carrier, palladium as an active center, and is calculated on the basis of its weight. 7.5 wt%.

Example 1:

Preparation of Graphene Oxide (GO)

1) Add an appropriate amount of 98% concentrated sulfuric acid into a 500mL beaker, and control the temperature to 0°C.

2) Add 10g of graphite powder and 5g of sodium nitrate, and stir for 1h.

3) Add 30 g of potassium permanganate powder under vigorous stirring (the addition speed should be well controlled, and it is best not to make the temperature exceed 20° C.).

4) Remove the low-temperature ice bath, and stir in a water bath at 35°C for 30 min.

5) Add 460mL of deionized water under stirring, raise the temperature of the reaction solution to about 98°C, and continue stirring for 1h.

6) Dilute the reaction solution with 1.4L deionized warm water, and then add a certain amount of 3% hydrogen peroxide solution.

7) Filtrate while it is hot, and fully wash the filter cake with a pre-prepared 5% hydrochloric acid aqueous solution (warm) until there is no sulfate ion in the filtrate.

8) The naturally drained filter cake is evenly distributed in five airtight glass bottles.

Example 2:

Preparation process of nitrogen-doped graphene

(1) GO (containing about 81mg C) and a certain amount of urea were added to 70mL water, and treated in an ultrasonic generator (200W) for 3h.

(2) Then transfer to a 100mL reactor and stir the reaction at 180°C for 10h.

(3) Vacuum-dry at 30° C. for 12 hours after suction filtration and washing. The sample is marked as NRGO- _x (x represents the weight ratio of urea and GO = 10, 75, 150, 300, etc.), and the value of x can be adjusted to prepare azagraphene with different nitrogen contents.

Example 3:

Preparation Technology of Supported Pd Catalyst (2.5%Pd/NRGO _-x )

(1) Take 50mg of NRGO- _x , disperse it into 43mL of water, and treat it in an ultrasonic generator (200W) for 1h.

(2) 0.21 mL of PdCl ₂ (12 mg Pd/mL) aqueous solution was stirred at room temperature for 30 min.

(3) Then transfer to the reaction kettle, stir and react at 40°C and 2MPa H ₂ for 8h.

(4) Suction filtration, fully washed with distilled water, and vacuum-dried at 60° C. for 12 hours. This sample is labeled 5%Pd/NRGO- _x .

Example 4:

Suzuki carbon-carbon coupling reaction process under the action of azagraphene:

Carbon-carbon coupling reactions were carried out in 10 mL test tubes with rubber stoppers. Add 0.5mmol halobenzene to the mixed solution of 6mL ethanol/water (V/V=1), add 0.55mmol phenylboronic acid, 1.0mmol K ₂ CO ₃ and a certain amount of catalyst, then stir at 80°C (2600 rpm /point). After the reaction, a small amount of the reaction solution was taken and extracted three times with ethyl acetate (3×10mL), and the resulting organic phase was dried with anhydrous Na ₂ SO ₄ , and then analyzed by gas chromatography by internal standard method (HP 5890, USA) . All reaction products were confirmed by GC-MS (Agilent 6890-5973N).

Example 5

Take 0.5mmol bromobenzene, 0.55mmol phenylboronic acid, 1.0mmol K ₂ CO ₃ and a certain amount of Pd/NRGO- ₃₀₀ catalyst (0.023mol% Pd) into a 10mL test tube with a rubber stopper, add 6mL ethanol/water ( V/V=1) mixed solution. Then it was stirred (2600 rpm) at 80 °C for 0.5 h. After the reaction, a small amount of the reaction solution was taken and extracted three times with ethyl acetate (3×10 mL), and the obtained organic phase was dried with anhydrous Na ₂ SO ₄ and analyzed by gas chromatography. The results showed that the yield of biphenyl was 99.1%.

Example 6

Referring to the preparation method and steps of Example 5, the difference is that the catalyst is changed to Pd/NRGO- ₁₅₀ . The results show that:

Example 7

Referring to the preparation method and steps of Example 5, the difference is that the catalyst is changed to Pd/NRGO- ₇₅ . The results show that:

Example 8

Referring to the preparation method and steps of Example 5, the difference is that the catalyst is changed to Pd/NRGO _-10 . The results show that:

Example 9

Referring to the preparation method and steps of Example 5, the difference is that the catalyst is changed to Pd/GO. The results show that:

Example 10

Referring to the preparation method and steps of Example 5, the difference is that the catalyst is changed to Pd/RGO. The results show that:

Example 11

Referring to the preparation method and steps of Example 5, the difference is that the catalyst is changed to commercial Pd/C. The results showed that the yield of biphenyl was 42.3%.

Example 12

Referring to the preparation method and steps of Example 5, the difference is that the substrate is changed to chlorobenzene. The results show that:

Example 13

With reference to the evaluation conditions of Example 12, the difference is that the catalyst is changed to commercial Pd/C. The results show that:

Example 14

Referring to the preparation method and steps of Example 5, the catalyst was reused. The results show that:

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: it can still be Modifications are made to the technical solutions described in the foregoing embodiments, or equivalent replacements are made to some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims (6)

1. a preparation method of azagraphene, is characterized in that, comprises the following steps; (1), GO is added to a certain amount of water, and treated in an ultrasonic generator for 1-3h; the mass volume ratio of the GO to water is (10-90)mg:(10-80)mL; (2), then transferred to the reaction kettle, stirred and reacted at 150-200°C for 5-24h; (3) Vacuum drying at 30-60° C. for 12-24 hours after suction filtration and washing to obtain sample RGO. 2. the preparation method of azagraphene according to claim 1, is characterized in that, described step 1 comprises: GO, a certain amount of urea, and water are treated in an ultrasonic generator for 1-3h to finally obtain a sample NRGO- _x , and the mass-volume ratio of GO, urea, and water is: A mg:B g:C mL, where , 10≤A≤90, 0<B≤27, 10≤C≤80, the x represents the mass ratio of urea to graphene oxide, 0<X<300. 3. a method for preparing a Pd-loaded azagraphene catalyst, characterized in that it may further comprise the steps: (1) Take a certain amount of NRGO- _x and disperse it into water, and treat it in an ultrasonic generator for 1 hour, wherein the mass-volume ratio of NRGO- _x to water is (5-100)mg:(10-200)mL; (2), take 0-0.84mL of PdCl ₂ aqueous solution, stir at room temperature for 10-120min; (3), then transferred to the reaction kettle, stirred and reacted at 20-50°C and 0.5-3MPa H ₂ for 2-12h; (4) Suction filtration, fully washed with distilled water, and vacuum drying at 30-80° C. for 12-24 hours to obtain Pd/NRGO _-x . 4. the preparation method of the azagraphene catalyst of loaded Pd according to claim 3, is characterized in that, in the palladium chloride solution in step (2), palladium content is 1-24mg/mL. 5. the azagraphene catalyst of the loaded Pd that utilizes the preparation method described in claim 3 to prepare. 6. the application of the azagraphene catalyst of loaded Pd as claimed in claim 5 in carbon-carbon coupling synthesis biphenyl.