Nitrogen-doped carbon-coated copper catalyst and preparation method thereof, and method for preparing nitrile through aldehyde ammoxidation

Abstract

The invention discloses a nitrogen-doped carbon-coated copper catalyst as well as a preparation method and application thereof, and aims to provide a nitrogen-doped carbon-coated copper catalyst for preparing nitrile through aldehyde ammoxidation. The catalyst is prepared by taking copper chloride, melamine and sodium lignin sulfonate as raw materials to prepare a precursor and then performing pyrolysis and carbonization on the precursor, when the nitrogen-doped carbon-coated copper catalyst prepared by the preparation method disclosed by the invention is applied to a reaction for preparing nitrile by catalyzing aldehyde ammoxidation, the nitrogen-doped carbon-coated copper catalyst not only has high catalytic activity, but also has high selectivity to nitrile, and more importantly, good stability can be kept; belongs to the technical field of catalysts.

Description

Technical Field

[0001] The present invention discloses a catalyst, specifically, a nitrogen-doped carbon-coated copper catalyst. The present invention also discloses a preparation method and application of the nitrogen-doped carbon-coated copper catalyst, belonging to the technical field of catalysts. Background Art

[0002] With the enhancement of environmental awareness and the implementation of the sustainable development strategy, the concept of green chemistry has received increasing attention in chemical production. Aldehydes are an important class of biomass derivatives, and the ammoxidation of aldehydes to nitriles is an important way to realize the high-value utilization of biomass, which is in line with the sustainable development goal. Nitrile compounds are a class of high-value important chemicals and are widely used in fields such as pharmaceuticals, polymer industry, and agrochemicals. More importantly, nitriles are highly reactive entities that can participate in various chemical reactions. Therefore, in recent years, the synthesis of nitriles has attracted great interest in both academia and industry. Among various nitrile synthesis methods, the ammoxidation of aldehydes using molecular oxygen (or air) as the sole oxidant and NH3 as the sole nitrogen source is a green and sustainable way to obtain nitriles. This method has high atomic and step economy because water is the only by-product in the whole process.

[0003] Although a series of homogeneous catalysts such as Cu / TEMPO and Fe / TEMPO have been developed, and these systems show excellent catalytic activity, there are still problems in catalyst recovery and product separation. In this regard, heterogeneous catalysts have advantages due to their excellent recyclability, separability, and stability. Therefore, a series of noble metal heterogeneous catalysts have been used for the ammoxidation of aldehydes to nitriles. However, their inherent high cost, limited availability, and toxicity require replacing them with more earth-abundant metal catalysts.

[0004] Cu-based catalysts have the advantages of rich resources, low price, high activity, and good selectivity. In the reaction of ammoxidation of aldehydes to nitriles, Cu-based catalysts can effectively promote the oxidative coupling reaction of aldehydes and ammonia to produce the target nitrile compounds, and at the same time have good substrate adaptability and mild reaction conditions.

[0005] However, due to the structural problems of copper itself, its hydrothermal stability is poor and it is easy to sinter and deactivate. To solve the problem of hydrothermal stability, the prior art attempts to coat the catalyst with a carbon support and utilize the hydrothermal stable characteristics of the carbon layer to improve the poor hydrothermal stability of copper. However, on the one hand, the dispersion of the carbon-coated catalyst obtained by the current related preparation methods is still insufficient, and on the other hand, the selectivity of the by-product amide is relatively high.

[0006] For example, the prior art discloses a coated copper oxide nanoparticle material (Senthamarai, T. et al. Cu-Oxide Nanoparticles Catalyzed Synthesis of Nitriles and Amides from Alcohols and Ammonia in Presence of Air. Advanced Sustainable Systems 6, 2200263 (2022)). This material is prepared using DMF (N,N-dimethylformamide) and copper nitrate trihydrate as the main raw materials and is used in the ammoxidation reaction to produce nitriles, which can improve the selectivity for nitriles. However, the preparation process of this catalyst is complex, with high energy consumption, and the reaction conditions are harsh, requiring a relatively high reaction temperature and a long reaction time. Summary of the Invention

[0007] To this end, the first object of the present invention is to provide a method for preparing a nitrogen-doped carbon-coated copper catalyst. This method first uses copper chloride, melamine, and sodium lignosulfonate as raw materials to prepare a precursor, and then pyrolyzes and carbonizes the precursor to obtain the catalyst. The preparation process of this method is simple, and the raw materials are easily available.

[0008] The second object of the present invention is to provide a nitrogen-doped carbon-coated copper catalyst, which has high catalytic activity and excellent stability for the ammoxidation of aldehydes to nitriles, and also has high selectivity for the reaction.

[0009] Another object of the present invention is to provide the application and method of the nitrogen-doped carbon-coated copper catalyst in the catalytic reaction of aldehyde compounds with ammonia to produce nitrile compounds.

[0010] To achieve the above objects, the technical solutions adopted by the present invention are as follows:

[0011] The first aspect of the present invention provides a method for preparing a nitrogen-doped carbon-coated copper catalyst, including the following steps:

[0012] S1. Ball-mill and mix copper chloride, melamine, and sodium lignosulfonate evenly and complex them to obtain a catalyst precursor; the mass ratio of copper chloride, melamine, and sodium lignosulfonate is 1:(5-8):(5-8).

[0013] S2. Ball-mill the mixture obtained in step S1 to obtain a catalyst precursor, and pyrolyze the precursor in an inert atmosphere, and then wash and dry it to obtain a nitrogen-doped carbon-coated copper catalyst.

[0014] In step S2, the pyrolysis process aims to convert the carbon source into a carbon support complex, and at the same time reduce Cu 2+ to Cu 0 or Cu+ 。The catalytic performance of the multi-valent state characteristic material of Cu provides additional advantages. The purpose of washing is to remove the impurities on the surface of the solid obtained after pyrolysis.

[0015] Preferably, in the S1, the mass ratio of copper chloride, melamine and sodium lignosulfonate is 1:5:5.

[0016] By adjusting the mass ratio of copper chloride, melamine and sodium lignosulfonate, the ratios of Cu, N and C sources are regulated. When the step S2 is fully carried out, the Cu nanoparticles can be completely coated on the carbon support. It should be noted that although carbon itself does not directly participate in the catalytic reaction of aldehyde-ammonia oxidation to nitrile, its appropriate content in the catalyst is crucial for maintaining the catalytic activity. If the addition amount of the carbon source is too large, it will lead to too thick a carbon layer, which may have a negative impact on the activity of the catalyst; on the contrary, if the addition amount of the carbon source is insufficient, the isolation effect of the carbon layer cannot be fully utilized, thus the aggregation of the active components cannot be effectively prevented. In addition, when the carbon content is too low, in addition to being unfavorable for the dispersion of Cu, it will also reduce the stability of the catalyst, but too high a carbon content will reduce the exposure of the active components and lower the selectivity and catalytic efficiency of the catalyst.

[0017] Preferably, in the step S2, the pyrolysis temperature is 800-1000 °C, and more preferably, the pyrolysis temperature is 900 °C.

[0018] Preferably, in the step S2, the pyrolysis time is 1-2 h, and more preferably 1 h.

[0019] During the pyrolysis process, the control of temperature and time is crucial for the performance of the catalyst. Appropriate pyrolysis temperature and pyrolysis time can ensure the effective coating of the carbon content and the active components. When the pyrolysis temperature is too low, the copper salt and the carbon source cannot undergo a sufficient pyrolysis reaction, and a catalyst with a high coating amount cannot be formed, and at the same time, the compactness of the carbon layer particles is also affected. When the pyrolysis temperature is too high, the copper metal may sinter and form larger particles. Both situations will greatly reduce the catalytic activity of the catalyst.

[0020] Preferably, the inert atmosphere in the step S2 includes but is not limited to a nitrogen atmosphere.

[0021] The second aspect of the present invention provides a catalyst of nitrogen-doped carbon-coated copper prepared by using the preparation method described in the first aspect. Its active components include Cu nanoparticles, a carbon support and nitrogen.

[0022] Preferably, the Cu nanoparticles in the present invention are from copper chloride; the nitrogen source is from melamine, and the carbon source is mainly from sodium lignosulfonate.

[0023] The third aspect of the present invention provides the application of the catalyst of nitrogen-doped carbon-coated copper described in the second aspect in the ammoxidation of aldehydes to nitriles.

[0024] Preferably, the aldehyde is one of benzaldehyde, p-chlorobenzaldehyde, p-methylbenzaldehyde, p-anisaldehyde, 2-naphthaldehyde, and furfural.

[0025] The fourth aspect of the present invention provides a method for catalytic ammoxidation of aldehydes to nitriles, specifically: adding aldehydes and ammonia water into an acetonitrile solvent, then adding the catalyst of nitrogen-doped carbon-coated copper described in the second aspect, and then reacting the obtained mixture under 0.5-1 MPa of oxygen for 6-10 h.

[0026] Preferably, the reaction temperature is 35 °C.

[0027] Preferably, the addition ratio of the catalyst of nitrogen-doped carbon-coated copper, aldehyde compound, and ammonia water is 90-110 mg: 0.5 mmol: 100-200 μL.

[0028] Compared with the prior art, the technical solution provided by the present invention has the following technical advantages:

[0029] 1. The catalyst of nitrogen-doped carbon-coated copper prepared by the present invention includes active component Cu nanoparticles, carbon carrier, and nitrogen; the carbon carrier can effectively prevent the migration and aggregation of active component Cu nanoparticles, ensuring the uniform dispersion of Cu nanoparticles on the carbon carrier. The doping of nitrogen introduces defect sites and nitrogen species, and these defect sites and nitrogen species can serve as the growth sites of metallic Cu. Through the anchoring effect of N atoms on Cu, the interaction between the Cu active component and the carrier is enhanced, thereby promoting the stability of the catalyst.

[0030] 2. The technical solution provided by the present invention successfully prepares the catalyst of nitrogen-doped carbon-coated copper by ball milling method and pyrolysis method. The Cu metal coated on the obtained catalyst is evenly distributed. Due to the highly dispersed Cu nanoparticles in the prepared catalyst, more catalytic active sites can be provided, thereby effectively improving the activation ability of oxygen and enabling it to efficiently catalyze the ammoxidation of aldehydes to nitriles.

[0031] 3. When the catalyst of nitrogen-doped carbon-coated copper provided by the present invention is applied to the ammoxidation of aldehydes to nitriles, it has high catalytic activity and high selectivity for nitriles. More importantly, it can maintain good stability, solving the problems of unstable catalyst and low nitrile selectivity existing in the prior Cu-based catalysts in the ammoxidation of aldehydes to nitriles, and has broad application prospects. In addition, the catalyst of nitrogen-doped carbon-coated copper of the present invention realizes the efficient catalysis of the ammoxidation of aldehydes to nitriles at a low temperature of 35 °C using a non-noble metal catalyst, which plays an important role in promoting the development and application of the technology of ammoxidation of aldehydes to nitriles. Description of the Drawings

[0032] Figure 1 TEM images of the catalyst prepared in Example 1;

[0033] Figure 2 TEM images of the catalyst prepared in Example 2;

[0034] Figure 3 TEM images of the catalyst prepared in Example 3;

[0035] Figure 4 TEM images of the catalyst prepared in Example 4;

[0036] Figure 5 TEM images of the catalyst prepared in Example 5;

[0037] Figure 6 TEM images of the catalyst prepared in Example 6;

[0038] Figure 7 TEM images of the catalyst prepared in Comparative Example 2;

[0039] Figure 8 TEM images of the catalyst prepared in Comparative Example 3;

[0040] Figure 9 TEM images of the catalyst prepared in Comparative Example 4;

[0041] Figure 10 TEM images of the catalyst prepared in Comparative Example 5;

[0042] Figure 11 XPS full spectrum of the catalyst obtained in Example 2;

[0043] Figure 12 Cyclic stability test diagram of the catalyst obtained in Example 2. Detailed Description of the Invention

[0044] The following is a detailed description in conjunction with the accompanying drawings, but it should be understood that the protection scope of the present invention is not limited by the detailed description.

[0045] The experimental methods in the following examples are all conventional methods unless otherwise specified, and the test materials used in the following examples can all be obtained through conventional commercial channels unless otherwise specified.

[0046] Example 1 Preparation Method of a Nitrogen-Doped Carbon-Coated Copper Catalyst

[0047] (1) Copper chloride, melamine, and sodium lignosulfonate were placed in an agate ball milling jar (equipped with an appropriate amount of agate ball milling beads) at a mass ratio of 1:5:5. Then, the agate ball milling jar was placed in a planetary ball mill and rotated alternately forward and backward at a speed of 300 rmp for 10 h (specifically, rotating forward for 30 min, stopping for 5 min, and then rotating backward for 30 min, with the total forward and backward rotation time being 10 h) to obtain a catalyst precursor;

[0048] (2) The precursor obtained in step (1) was placed in a nitrogen atmosphere and heated to 800 °C at a heating rate of 5 °C / min for pyrolysis for 1 h. After the pyrolysis was completed, a copper-doped carbon material composite was obtained.

[0049] (3) The copper-doped carbon material composite prepared in step (2) was centrifuged and washed with ultrapure water 5 times, 4 min each time, to remove impurities on the solid surface, and then dried in a vacuum drying oven at -0.08 MPA and 60 °C for 12 h to obtain a catalyst with nitrogen-doped carbon-coated copper.

[0050] Example 2

[0051] The reaction steps, reaction substrates, and process conditions of Example 2 were the same as those of Example 1, except that the pyrolysis temperature was 900 °C.

[0052] Example 3

[0053] The reaction steps, reaction substrates, and process conditions of Example 3 were the same as those of Example 1, except that the pyrolysis temperature was 1000 °C.

[0054] The main process parameters of the catalysts with nitrogen-doped carbon-coated copper in Examples 1-3 are shown in Table 1.

[0055] Table 1

[0056] Example Copper chloride: Melamine: Sodium lignosulfonate (mass ratio) Pyrolysis temperature / °C Example 1 1:5:5 800 Example 2 1:5:5 900 Example 3 1:5:5 1000

[0057] Example 4

[0058] The reaction steps, reaction substrates, and process conditions of Example 3 were the same as those of Example 1, except that the mass ratio of copper chloride:melamine:sodium lignosulfonate was 1:8:8.

[0059] Example 5

[0060] The reaction steps, reaction substrates, and process conditions of Example 2 were the same as those of Example 1, except that the mass ratio of copper chloride:melamine:sodium lignosulfonate was 1:8:8.

[0061] Example 6

[0062] Example 6 is the same as Example 1 in terms of reaction steps, reaction substrates, and process conditions, except that the mass ratio of copper chloride: melamine: sodium lignosulfonate is 1:8:8.

[0063] For the main process parameters of the nitrogen-doped carbon-coated copper catalyst in Examples 4-6, refer to Table 2.

[0064] Table 2

[0065] Example Copper chloride: Melamine: Sodium lignosulfonate (mass ratio) Pyrolysis temperature / °C Example 4 1:8:8 800 Example 5 1:8:8 900 Example 6 1:8:8 1000

[0066] Example 7

[0067] Example 7 is the same as Example 1 in terms of reaction steps, reaction substrates, and process conditions, except that the rotation speed of ball milling is 200 rmp.

[0068] Example 8

[0069] Example 8 is the same as Example 1 in terms of reaction steps, reaction substrates, and process conditions, except that the rotation speed of ball milling is 400 rmp.

[0070] Example 9

[0071] Example 9 is the same as Example 1 in terms of reaction steps, reaction substrates, and process conditions, except that the ball milling time is 6 h.

[0072] Example 10

[0073] Example 10 is the same as Example 1 in terms of reaction steps, reaction substrates, and process conditions, except that the ball milling time is 8 h.

[0074] Comparative Example 1

[0075] This comparative example provides a commercial platinum-carbon catalyst, specifically a 5% Pt / C catalyst, purchased from Aladdin Reagent (Shanghai) Co., Ltd.

[0076] Comparative Example 2

[0077] This comparative example is the same as Example 1 in terms of reaction steps, reaction substrates, and process conditions, except that the pyrolysis temperature is 600 °C.

[0078] Comparative Example 3

[0079] This comparative example is the same as Example 1 in terms of reaction steps, reaction substrates, and process conditions, except that the pyrolysis temperature is 700 °C.

[0080] Comparative Example 4

[0081] (1) Melamine and sodium lignosulfonate were placed in an agate ball milling jar (equipped with an appropriate amount of agate ball milling beads) at a mass ratio of 5:5. Then, the agate ball milling jar was placed in a planetary ball mill and rotated alternately forward and backward at a speed of 300 rmp for 10 h (specifically, rotating forward for 30 min, stopping for 5 min, and then rotating backward for 30 min, with the total forward and backward rotation time being 10 h) to obtain a catalyst precursor;

[0082] (2) The precursor obtained in step (1) was placed in a nitrogen atmosphere and heated to 900 °C at a heating rate of 5 °C / min for pyrolysis for 1 h. After pyrolysis, a doped carbon material composite was obtained.

[0083] (3) The doped carbon material composite prepared in step (2) was centrifugally washed with ultrapure water 5 times, 4 min each time, to remove impurities on the solid surface, and then dried in a vacuum drying oven at -0.08 MPA, 60 °C for 12 h to obtain a nitrogen-doped carbon-coated catalyst.

[0084] Comparative Example 5

[0085] (1) Copper chloride and sodium lignosulfonate were placed in an agate ball milling jar (equipped with an appropriate amount of agate ball milling beads) at a mass ratio of 1:10. Then, the agate ball milling jar was placed in a planetary ball mill and rotated alternately forward and backward at a speed of 300 rmp for 10 h (specifically, rotating forward for 30 min, stopping for 5 min, and then rotating backward for 30 min, with the total forward and backward rotation time being 10 h) to obtain a catalyst precursor;

[0086] (2) The precursor obtained in step (1) was placed in a nitrogen atmosphere and heated to 900 °C at a heating rate of 5 °C / min for pyrolysis for 1 h. After pyrolysis, a copper-doped carbon material composite was obtained.

[0087] (3) The copper-doped carbon material composite prepared in step (2) was centrifugally washed with ultrapure water 5 times, 4 min each time, to remove impurities on the solid surface, and then dried in a vacuum drying oven at -0.08 MPA, 60 °C for 12 h to obtain a nitrogen-doped carbon-coated copper catalyst.

[0088] To study the performance of the catalyst provided in this application, the catalyst characterization test results provided in this application are given below.

[0089] The TEM images of the catalysts prepared in Examples 1-3 are referred to Figures 1 to 3 , from Figures 1 to 3 it can be seen that the Cu nanoparticles are uniformly dispersed on the nitrogen-carbon sheet, indicating that the nitrogen-doped carbon-coated copper catalyst is a high-density and highly dispersed copper-based catalyst. The high-density and highly dispersed Cu sites efficiently promote the ammoxidation reaction of aldehydes.

[0090] The TEM images of the catalysts prepared in Examples 4-6 are referred to Figures 4 - 6 , from Figures 4 to 6It can be seen that the Cu nanoparticles of the prepared catalyst are anchored on the carbon support in a highly dispersed form. The highly dispersed feature ensures the full exposure of a large number of active sites, promoting the ammoxidation of aldehydes.

[0091] The full XPS spectrum of the catalyst obtained in Example 2 is referred to Figure 11 , and it can be seen from the figure that the elements Cu, C, N, and O exist in the catalyst.

[0092] The TEM images of the catalysts prepared in Comparative Examples 2 and 3 are referred to Figures 7 - 8 , and it can be known from Figures 7 - 8 that there are few or almost no Cu nanoparticles on the carbon support, indicating that at a relatively low calcination temperature, the catalyst will not be completely pyrolyzed, resulting in a low coating amount of Cu, and thus having a low reaction activity in the reaction.

[0093] The TEM image of the catalyst prepared in Comparative Example 4 is referred to Figure 9 , and it can be known from Figure 9 that there are no Cu nanoparticles in the catalyst.

[0094] The TEM image of the catalyst prepared in Comparative Example 5 is referred to Figure 10 , and it can be known from Figure 10 that the Cu nanoparticles are agglomerated together, indicating that the introduction of nitrogen species can disperse the Cu nanoparticles on the carbon support.

[0095] Ammoxidation of aldehydes to nitriles using the nitrogen-doped carbon-coated Cu catalyst in Application Example 1

[0096] 0.5 mmol of the substrate (benzaldehyde) and 150 μL of ammonia water were added to 3 mL of acetonitrile. Subsequently, 100 mg of the nitrogen-doped carbon-coated Cu catalyst prepared in Example 1 was added. Then, the above mixture was placed in a 25 mL high-temperature and high-pressure reactor and reacted at 35 °C and 1 MPa of oxygen for 8 h. Finally, the reaction solution after the reaction was analyzed by gas chromatography, and the results are referred to Table 3.

[0097] Application Examples 2 - 10

[0098] For the ammoxidation of aldehydes to nitriles using the nitrogen-doped carbon-coated Cu catalyst given in Application Examples 2 - 10, the reaction process, process parameters, and the amounts of each substance used are the same as those in Application Example 1. The difference is that the ammoxidation of aldehydes to nitriles using the nitrogen-doped carbon-coated Cu catalyst prepared by any one of the preparation methods in Examples 2 - 10 is used to replace the ammoxidation of aldehydes to nitriles using the nitrogen-doped carbon-coated Cu catalyst prepared in Example 1. The specific parameters and their results are referred to Table 3.

[0099] Application Examples 11 - 14

[0100] Application Example 11 - 14 provide the reaction of catalytic oxidation of aldehyde and ammonia to nitrile using the nitrogen-doped carbon-coated Cu catalyst prepared in Example 2. The reaction process, process parameters, and the amounts of each substance used are the same as those in Application Example 1, except that the specific substrates used are different. The specific parameters and their results are shown in Table 3.

[0101] Application Example 15

[0102] Application Example 15 has the same reaction steps, reaction substrates, reaction conditions, and catalysts as those in Application Example 2, except that the reaction temperature is 30°C; the specific parameters and their results are shown in Table 3.

[0103] Application Example 16

[0104] Application Example 16 has the same reaction steps, reaction substrates, reaction conditions, and catalysts as those in Application Example 2, except that the reaction temperature is 40°C; the specific parameters and their results are shown in Table 3.

[0105] Application Example 17

[0106] Application Example 17 has the same reaction steps, reaction substrates, reaction conditions, and catalysts as those in Application Example 2, except that the reaction time is 6 hours; the specific parameters and their results are shown in Table 3.

[0107] Application Example 18

[0108] Application Example 18 has the same reaction steps, reaction substrates, reaction conditions, and catalysts as those in Application Example 2, except that the reaction time is 10 hours; the specific parameters and their results are shown in Table 3.

[0109] Application Example 19

[0110] Application Example 19 has the same reaction steps, reaction substrates, reaction conditions, and catalysts as those in Application Example 2, except that the amount of catalyst used is 90 mg; the specific parameters and their results are shown in Table 3.

[0111] Application Example 20

[0112] Application Example 20 has the same reaction steps, reaction substrates, reaction conditions, and catalysts as those in Application Example 2, except that the amount of catalyst used is 110 mg; the specific parameters and their results are shown in Table 3.

[0113] Application Example 21

[0114] Application Example 21 has the same reaction steps, reaction substrates, reaction conditions, and catalysts as those in Application Example 2, except that the amount of ammonia water used is 100 μl; the specific parameters and their results are shown in Table 3.

[0115] Application Example 22

[0116] Application Example 22 has the same reaction steps, reaction substrates, reaction conditions, and catalysts used as Application Example 2. The difference lies in that the amount of ammonia water used is 200 μl; for specific parameters and their results, refer to Table 3.

[0117] Comparative Application Example 1

[0118] Comparative Application Example 1 provides a nitrogen-doped carbon-coated Cu catalyst for the catalytic oxidation of aldehyde and ammonia to nitrile. The reaction process, process parameters, and the amount of each substance used are the same as those in Application Example 1. The difference lies in that the catalyst provided in Comparative Example 1 is used instead of the catalyst in Application Example 1. For specific parameters and their results, refer to Table 3.

[0119] Comparative Application Example 2

[0120] Comparative Application Example 2 provides a nitrogen-doped carbon-coated Cu catalyst for the catalytic oxidation of aldehyde and ammonia to nitrile. The reaction process, process parameters, and the amount of each substance used are the same as those in Application Example 1. The difference lies in that the catalyst provided in Comparative Example 2 is used instead of the catalyst in Application Example 1. For specific parameters and their results, refer to Table 3.

[0121] Comparative Application Example 3

[0122] Comparative Application Example 3 provides a nitrogen-doped carbon-coated Cu catalyst for the catalytic oxidation of aldehyde and ammonia to nitrile. The reaction process, process parameters, and the amount of each substance used are the same as those in Application Example 1. The difference lies in that the catalyst provided in Comparative Example 3 is used instead of the catalyst in Application Example 1. For specific parameters and their results, refer to Table 3.

[0123] Comparative Application Example 4

[0124] Comparative Application Example 4 provides a nitrogen-doped carbon-coated Cu catalyst for the catalytic oxidation of aldehyde and ammonia to nitrile. The reaction process, process parameters, and the amount of each substance used are the same as those in Application Example 1. The difference lies in that the catalyst provided in Comparative Example 4 is used instead of the catalyst in Application Example 1. For specific parameters and their results, refer to Table 3.

[0125] Comparative Application Example 5

[0126] Comparative Application Example 5 provides a nitrogen-doped carbon-coated Cu catalyst for the catalytic oxidation of aldehyde and ammonia to nitrile. The reaction process, process parameters, and the amount of each substance used are the same as those in Application Example 1. The difference lies in that the catalyst provided in Comparative Example 5 is used instead of the catalyst in Application Example 1. For specific parameters and their results, refer to Table 3.

[0127] Comparative Application Example 6

[0128] Comparative Application Example 6 provides a nitrogen-doped carbon-coated Cu catalyst for the catalytic oxidation of aldehyde and ammonia to nitrile. The reaction process, process parameters, and the amount of each substance used are the same as those in Application Example 1. The difference lies in that the reaction time is 2 h. For specific parameters and their results, refer to Table 3.

[0129] Table 3

[0130]

[0131]

[0132] As can be seen from Table 3, when the ratio of raw materials copper chloride, melamine and sodium lignosulfonate is controlled at 1:5:5, a catalyst of nitrogen-doped carbon-coated copper with excellent catalytic activity can be successfully prepared. However, if the amount of Cu source added is less, the performance of the obtained catalyst will decline. In addition, if the pyrolysis temperature is too low, the Cu salt and carbon source cannot be fully pyrolyzed, and a catalyst with a high coating amount cannot be formed, reducing the catalytic activity of the catalyst. If the pyrolysis temperature is too high, the carbon content decreases, and the Cu metal will sinter to form large particles, reducing the conversion rate of the final reactants and the nitrile yield.

[0133] Through Application Example 1 and Comparative Application Example 1, it can be seen that the nitrogen-doped carbon-coated copper catalyst is superior to the commercial platinum-carbon catalyst (5% Pt / C). Its catalytic performance is more excellent, realizing the efficient catalytic oxidation of aldehyde and ammonia to nitrile using a non-precious metal catalyst at 35°C, improving the nitrile yield while ensuring the catalytic efficiency, and achieving a major technological breakthrough.

[0134] To verify the reusability of the nitrogen-doped carbon-coated Cu catalyst provided in this application, according to the method of Application Example 2, the nitrogen-doped carbon-coated Cu catalyst was used to catalyze the oxidation of aldehyde and ammonia to nitrile. After the reaction, the catalyst and solution mixture were placed in a 50 mL centrifuge tube and then centrifuged in a centrifuge for 3 - 5 min for solid-liquid separation. Ultra-pure water was added to the separated solid, stirred for 3 min and then centrifuged for solid-liquid separation. After centrifugal washing with ultra-pure water 3 times, it was then washed 2 times with absolute ethanol, and then the catalyst was placed in a vacuum drying oven at 60°C for 12 h to obtain the catalyst after 1 reaction; the previous reaction process and the catalyst recovery process were repeated 5 times, and the conversion rate of benzaldehyde and the yield of benzonitrile were detected after each reaction. The results are shown in Figure 12 , Figure 12 The data in show that the catalyst still has high catalytic activity and stability after 5 consecutive reactions.

[0135] In summary, the nitrogen-doped carbon catalyst prepared by the method of the present invention has both high catalytic activity and high selectivity for nitrile. More importantly, it can maintain good stability, solving the problems of unstable catalyst and low nitrile selectivity existing in the existing precious metal catalysts in the aldehyde-ammonia oxidation reaction, and has broad application prospects.

[0136] The above has described the embodiments of the present invention in detail, but the present invention is not limited to the described embodiments. For those skilled in the art, without departing from the principles and spirit of the present invention, various changes, modifications, substitutions, and variations made to these embodiments still fall within the protection scope of the present invention.

Claims

1. A method for preparing a nitrogen-doped carbon-coated copper catalyst, characterized in that: The following steps are involved: S1, copper chloride, melamine and sodium lignin sulfonate solids are mixed and evenly complexed by ball milling to obtain a catalyst precursor; S2, pyrolyzing the catalyst precursor in S1 under an inert atmosphere, washing and drying the obtained solid powder to obtain a nitrogen-doped carbon-coated copper catalyst; The mass ratio of the copper chloride, melamine and sodium lignin sulfonate is 1:(5-8):(5-8).

2. The method for preparing a nitrogen-doped carbon-coated copper catalyst according to claim 1, characterized in that: In step S1, the ball milling is to first place the mixture of copper chloride, melamine and sodium lignin sulfonate in an agate ball milling jar equipped with agate ball milling beads, and then place the ball milling jar in a planetary ball mill for forward and reverse alternating interval ball milling; the ball milling speed is 200-400rmp, and the ball milling time is 6-10h.

3. The method for preparing a nitrogen-doped carbon-coated copper catalyst according to claim 1, characterized in that: In step S2, the pyrolysis temperature is 800-1000°C, the inert flow rate is 100 mL / min, and the pyrolysis time is 1-2 h.

4. The method for preparing a nitrogen-doped carbon-coated copper catalyst according to claim 1, characterized in that: In step S2, the washing is performed by centrifugation washing with ultrapure water for 3-5 times, each time for 3-5 minutes; and the drying is performed in a vacuum drying oven at 60° C. for 12 hours.

5. A nitrogen-doped carbon-coated copper catalyst, characterized in that: A nitrogen-doped carbon-coated copper catalyst obtained by the preparation method according to any one of claims 1 to 4.

6. Use of the nitrogen-doped carbon-coated copper catalyst according to claim 5 in catalyzing the oxidation reaction of aldehyde compounds with ammonia to produce nitrile compounds.

7. A method for preparing nitrile compounds by oxidation of aldehyde compounds with ammonia, characterized in that: The aldehyde compound, solvent, ammonia water and the nitrogen-doped carbon-coated copper catalyst according to claim 5 are placed in a reaction kettle, and reacted at an oxygen pressure of 0.5-1Mpa and a temperature of 30-40°C for 6-10 hours to obtain the target product.

8. The method for preparing nitrile compounds by oxidation of aldehyde compounds with ammonia according to claim 7, characterized in that: The aldehyde compound is one of benzaldehyde, p-tolualdehyde, p-anisaldehyde, 2-methoxybenzaldehyde, p-chlorobenzaldehyde, and 2-naphthaldehyde, or any combination thereof.

9. The method for preparing nitrile compounds by oxidation of aldehyde compounds with ammonia according to claim 7, characterized in that: The nitrogen-doped carbon-coated copper catalyst, aldehyde compound, and ammonia water added in a ratio of 90-110 mg: 0.5 mmol: 100-200 μL as described in claim 5.

10. The method for preparing nitrile compounds by oxidation reaction of aldehyde compounds with ammonia according to claim 7, characterized in that: The solvent is acetonitrile.

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