A Co 1-NP / CNT@CN catalysts, their preparation methods, and applications

Abstract

The application discloses a Co 1‑NP / CNT@CN catalyst, a preparation method and application thereof. The catalyst has Co NP and Co1 double active sites, and the catalyst takes CNT as a carrier, the surface of the CNT is attached with a CN layer, Co NP is mainly loaded on the CNT, and Co1 is mainly loaded on the CN layer. The preparation method comprises the following steps: (1) dispersing multi-walled carbon nanotubes, Co(acac)2 and carbon nitride precursors in water, and stirring and heating until the dispersion is uniform; (2) first performing liquid nitrogen freezing on the dispersion system, and then performing freeze drying to obtain a catalyst precursor; and (3) annealing the catalyst precursor in a hydrogen / inert gas mixed gas atmosphere at 500-600 DEG C for 2-4 h to obtain the target catalyst Co 1‑NP / CNT@CN. The Co 1‑NP / CNT@CN catalyst is applied to hydrogen production by ammonia borane hydrolysis or preparation of arylamines by selective hydrogenation of nitroaromatics. The Co 1‑NP / CNT@CN catalyst prepared in the application contains double active sites, shows excellent synergistic effect, and exhibits excellent catalytic activity in hydrogen production by ammonia borane hydrolysis and transfer hydrogenation of various nitroaromatics.

Description

Technical Field

[0001] This invention belongs to the field of selective hydrogenation of nitroaromatics to prepare aromatic amines, specifically relating to a Co 1-NP / CNT@CN catalysts, their preparation methods, and applications. Background Technology

[0002] Aromatic amines are important chemical raw materials and intermediates, widely used in the synthesis of dyes, polymers, antioxidants, and pesticides. Therefore, the selective hydrogenation of nitroaromatics to produce aromatic amines, as a large-scale industrial process, is of significant research importance. Industrially, high-pressure H2 gas is generally used as a reducing agent, and supported noble metal nanoparticles are used as catalysts to catalyze the hydrogenation of nitroaromatics to produce aromatic amines. However, this method has inherent drawbacks such as expensive catalysts, high risk of explosive gases, and poor selectivity. Therefore, developing novel nitroaromatic reduction catalysts with high activity and selectivity under safer and more environmentally acceptable conditions is of great importance and has attracted widespread attention from researchers worldwide.

[0003] Over the past decade, the transfer hydrogenation reaction of nitroaromatics using hydrogen storage molecules as reducing agents has attracted widespread attention as a safe and efficient method for preparing functional aromatic amines. Among various hydrogen storage molecules, ammonia borane (AB) is considered one of the most promising candidate hydrogen sources due to its high hydrogen storage capacity (19.6 wt%), good stability, and relatively low cost. In fact, this complex transfer hydrogenation process is a typical tandem reaction consisting of two elementary steps: the hydrolysis of hydrogen storage molecules to produce hydrogen or the adsorption-hydrogenation of active hydrogen with nitroaromatics. Excitingly, non-precious metal catalysts, especially cobalt-based catalysts, typically exhibit some activity in both steps of the reaction. Due to the abundance, low cost, and high selectivity of cobalt for aromatic amines, cobalt-based catalysts are considered an indispensable key technology for future industry. However, due to the diversity of metal species and the unclear active sites in single transition metal catalysts, the actual mechanism of action of non-precious metal catalysts in the complex transfer hydrogenation reaction of nitroaromatics remains unclear, which limits the development of highly efficient catalysts. Therefore, there is an urgent need to develop more efficient non-precious metal catalysts to meet the needs of industrial production. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, the present invention aims to provide a Co 1-NP / CNT@CN catalysts, their preparation methods, and applications.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A Co 1-NPThe / CNT@CN catalyst has two active sites, Co NP and Co1. The catalyst uses CNT as a support, with a CN layer attached to the surface of the CNT. Co NP is mainly supported on the CNT, and Co1 is mainly supported on the CN layer. CNT is carbon nanotube, CN is carbon nitride, Co NP is cobalt nanoparticle, and Co1 is cobalt single atom.

[0006] The Co 1-NP The preparation method of / CNT@CN catalyst is as follows: (1) Disperse multi-walled carbon nanotubes, Co(acac)2 and carbon nitride precursor in water and heat and stir until uniformly dispersed; wherein, by mass ratio, multi-walled carbon nanotubes: Co(acac)2 = 5: (0.1~1), carbon nitride precursor: multi-walled carbon nanotubes = (0.1~5.0): 1; (2) The dispersion system is first frozen with liquid nitrogen and then freeze-dried to obtain the catalyst precursor; (3) Anneal the catalyst precursor at 500-600 °C for 2-4 h in a hydrogen / inert gas mixed atmosphere to obtain the target catalyst Co. 1-NP / CNT@CN.

[0007] Preferably, the carbon nitride precursor is dicyandiamide, melamine, or urea.

[0008] Preferably, by mass ratio, the ratio of multi-walled carbon nanotubes to water is 5: (500~2000), and the ratio of carbon nitride precursor to multi-walled carbon nanotubes is (2.0~4.5): 1.

[0009] Preferably, the heating and stirring temperature is 40~60 ℃, and the time is 4~12 h; in the hydrogen / inert gas mixed atmosphere, the volume percentage of hydrogen is 5~10%; and the temperature is increased to the annealing temperature at a heating rate of 2~10 ℃ / min.

[0010] The Co 1-NP Application of / CNT@CN catalyst in hydrogen production from ammonia borane hydrolysis.

[0011] Better, Co 1-NP The CNT@CN catalyst, ammonia borane, and solvent are reacted at 10–40 °C and 300–600 rpm for 1–3 h; the solvent is a mixture of water and methanol in a volume ratio of (1–3):1 or water alone; wherein, the raw material dosage ratio is Co 1-NP / CNT@CN catalyst∶ammoniaborane∶solvent = 10 mg∶(1~2) mmol∶(5~10) mL.

[0012] The Co 1-NPApplication of / CNT@CN catalyst in the selective hydrogenation of nitroaromatics to prepare aromatic amines.

[0013] Better, Co 1-NP The CNT@CN catalyst, ammonia borane, nitroaromatic hydrocarbons, and solvent are reacted at 10–40 °C and 300–600 rpm for 1–3 h; the solvent is a mixture of water and methanol in a volume ratio of (1–3):1; wherein, the raw material dosage ratio is Co. 1-NP / CNT@CN catalyst∶ammoniaborane∶nitroaromatics∶solvent = 10 mg∶(1~2) mmol∶(0.1~0.2) mmol∶(5~10) mL.

[0014] Preferably, the nitroaromatic hydrocarbon is nitrobenzene, 3-nitrotoluene, 4-nitrotoluene, 4-nitroethylbenzene, 4-fluoronitrobenzene, 4-chloronitrobenzene, 4-bromonitrobenzene, 2-chloronitrobenzene, 3-chloronitrobenzene, or 2-chloro-4-nitrotoluene.

[0015] Beneficial effects: The Co prepared by this invention 1-NP The / CNT@CN catalyst contains dual active sites (metal NP and single atom), exhibiting excellent synergistic effects. This catalyst demonstrates excellent catalytic activity and significant selectivity (yield > 99%) in the hydrolysis of ammonia borane to produce hydrogen and in the transfer hydrogenation of various nitro aromatics. Attached Figure Description

[0016] Figure 1 TEM images of pure CNT (a) and CNT@CN (b) prepared in Control Example 1.

[0017] Figure 2 Co prepared in Example 1 1-NP (a) TEM image and corresponding particle size distribution histogram of / CNT@CN-2.5; (b) high HRTEM image; (c) HRTEM image of a single Co NP and corresponding IFFT image; (de) AC-HADDF-STEM image; (f) AC-HADDF-STEM image and corresponding IFFT image of a single Co atom; (g) HAADF-STEM and elemental mapping image.

[0018] Figure 3 Co prepared for control example 2 NP (a) TEM image of / CNT; (b) HRTEM image and corresponding (c) HRTEM image of Co NP and corresponding IFFT image; (d) HAADF-STEM image and corresponding element-mapped image.

[0019] Figure 4(a) TEM image of Co1 / CNT@CN prepared for Comparative Example 3; (b) HRTEM image and (cd) related magnified local image; (e) HAADF-STEM image and corresponding elemental mapping image.

[0020] Figure 5 Catalytic transfer hydrogenation reaction route for nitrobenzene (a), catalytic performance of different catalysts for nitrobenzene transfer hydrogenation (b), and Co 1-NP Catalytic performance of / CNT@CN-X for the transfer hydrogenation of p-nitrobenzene (c).

[0021] Figure 6 For Co 1-NP Cyclic performance test results of / CNT@CN-2.5 catalyst in nitrobenzene hydrogenation reaction.

[0022] Figure 7 For Co 1-NP / CNT@CN-2.5 after four reactions: (a) TEM image and corresponding particle size distribution histogram; (b) HRTEM image and (c) corresponding IFFT image of a single Co NP; (d) HAADF-STEM image and corresponding elemental mapping image. Detailed Implementation

[0023] To make the present invention clearer and more explicit, the present invention will be further described in detail below. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0024] Example 1

[0025] Co 1-NP Preparation method of / CNT@CN-X catalyst: First, 200 mg of commercially available multi-walled carbon nanotubes (CNTs), 35 mg of Co(acac)2, and a certain mass of dicyandiamide (DCD) were dispersed in 50 mL of deionized water, and then stirred and dispersed in a 50 ℃ water bath for 8 h. The dispersion system was rapidly frozen with liquid nitrogen, and then freeze-dried in a freeze dryer to obtain the catalyst precursor CNT@DCD-Co. Finally, CNT@DCD-Co was heated to the annealing temperature of 600 ℃ in a 10 v% hydrogen / argon mixed atmosphere at a heating rate of 2 ℃ / min, and annealed for 2 h. The synthesized catalyst was named Co. 1-NP / CNT@CN-X, where the synthesis parameter X is the mass ratio of DCD to CNT, X = 0.1, 0.4, 0.5, 1.5, 2.0, 2.5, 3.0, 4.0, 4.5 and 5.0.

[0026] Compare with Example 1 Preparation method of CNT@CN: First, 200 mg of commercially available carbon nanotubes (CNTs) and 500 mg of dicyandiamide (DCD) were dispersed in 50 mL of deionized water, and then stirred and dispersed in a water bath at 50 °C for 8 h. The dispersion system was rapidly frozen with liquid nitrogen and then freeze-dried in a freeze dryer to obtain the catalyst precursor CNT@DCD. Finally, CNT@DCD was heated to the annealing temperature of 600 °C at a heating rate of 2 °C / min in a 10 v% hydrogen / argon mixed atmosphere and annealed for 2 h. The synthesized catalyst was named CNT@CN.

[0027] Compare with Example 2 Co NP Preparation method of CNT catalyst: First, 200 mg of commercially available multi-walled carbon nanotubes (CNTs) and 35 mg of Co(acac)₂ were dispersed in 50 mL of deionized water, and then stirred and dispersed in a 50 °C water bath for 8 h. The dispersion system was rapidly frozen with liquid nitrogen, and then freeze-dried in a freeze dryer to obtain the catalyst precursor CNT-Co. Finally, CNT-Co was heated to the annealing temperature of 600 °C at a heating rate of 2 °C / min in a 10 v% hydrogen / argon mixed atmosphere and annealed for 2 h. The resulting catalyst was named Co. NP / CNT.

[0028] Compare with Example 3 Preparation method of Co1 / CNT@CN: First, Co was prepared using the same method as in Example 1. 1-NP / CNT@CN-2.5, then use 2 M hydrochloric acid solution to treat Co 1-NP The etching process for / CNT@CN-2.5 involved heating in a 50 ℃ water bath for 6 h, followed by centrifugation, discarding the supernatant, adding fresh 2 M hydrochloric acid solution, and heating again at 50 ℃ for 6 h. After centrifugation and vacuum drying, the resulting catalyst was named Co1 / CNT@CN.

[0029] Figure 1 TEM images of pure CNTs (a) and CNT@CN (b) prepared as control example 1. From Figure 1 As can be seen, the surface of pure CNTs (i.e., raw carbon nanotubes) is relatively smooth, and most of the carbon has good crystallinity. In contrast, the surface of CNT@CN has an amorphous carbon layer belonging to the CN layer (g-C3N4), such as... Figure 1 The light red portion in b is shown; furthermore, the carbon nanotubes in CNT@CN retain their original morphology and structure.

[0030] Figure 2Co prepared in Example 1 1-NP (a) TEM image and corresponding particle size distribution histogram of / CNT@CN-2.5; (b) high HRTEM image; (c) HRTEM image and corresponding IFFT image of a single Co NP; (de) AC-HADDF-STEM image; (f) AC-HADDF-STEM image and corresponding IFFT image of a single cobalt atom; (g) HAADF-STEM and elemental mapping image. Figure 2 As shown in a, a typical Co 1-NP / CNT@CN exhibits a hollow tube morphology similar to the raw material carbon nanotubes, with no significant increase in diameter. Besides the carbon nanotubes, a large amount of amorphous carbon was found attached to the surface of the carbon nanotubes or forming thin sheets. This amorphous carbon belongs to the poorly crystallized CN. Most of the metal nanoparticles are exposed on the surface of the carbon nanotubes, with an average size of approximately 10.2 nm. A small number of nanoparticles exist alone on the amorphous CN layer. Co 1-NP High-resolution transmission electron microscopy (HRTEM) images and corresponding inverse fast Fourier transform (IFFT) images of / CNT@CN-2.5 show that the interplanar spacing of the crystal is 0.205 nm, corresponding to the Co(111) plane, indicating that the nanoparticles are elemental cobalt. Figure 2 bc). It is worth noting that the presence of cobalt single atoms and Co NPs in the carbon framework can be directly observed using aberration-corrected high-angle circular dark-field scanning electron microscopy (AC-HAADF-STEM). Figure 2 d) The cobalt nanoparticles (enclosed by the yellow dashed line) are surrounded by a large number of cobalt single atoms (highlighted by the red circle), and the two are in close contact, which is beneficial for subsequent synergistic catalysis. Analysis of AC-HAADF-STEM images of the carbon nanotube edges reveals that the CNTs exhibit a typical graphite structure, with a thinner CN layer in the middle and a very small number of cobalt single atoms on the surface; while the thicker CN layer at the CNT edges contains a large number of cobalt single atoms. Figure 2 (e) This is because simple graphene-based supports are difficult to stabilize single atoms, easily leading to agglomeration of single atoms. Dopants (such as N, S, P) or defects are usually needed to stabilize the single atoms. Therefore, the single atoms mainly exist on the nitrogen-rich CN layer, which is consistent with previous reports. AC-HAADF-STEM images and corresponding IFFT images of cobalt single atoms show that the size of the cobalt single atom is 0.12 nm, further confirming the formation of the cobalt single atom (e). Figure 2 f). HAADF-STEM-EDS map ( Figure 2 g) The results show that Co, C, and N elements are uniformly distributed throughout the catalyst. Therefore, in Co... 1-NP In / CNT@CN-2.5, cobalt exists mainly in the form of cobalt nanoparticles and cobalt single atoms.

[0031] Figure 3 Co prepared for control example 2 NP (a) TEM image of / CNT; (b) HRTEM image and corresponding (c) HRTEM image of Co NP and corresponding IFFT image; (d) HAADF-STEM image and corresponding element-mapped image. Figure 3 As shown in figure a, there are Co NPs of similar size and uniform distribution on the surface of carbon nanotubes, with an average particle size of 10.6 nm. NP HRTEM and corresponding IFFT images of / CNT show that the interplanar spacing of the crystal is 0.205 nm, corresponding to the Co(111) plane, indicating that the nanoparticles are metallic cobalt ( Figure 3 bc). For example Figure 3 As shown in d, Co NP The overlay of the HAADF-STEM image and corresponding elemental mapping image of / CNT shows that Co mainly exists in the NP form. As mentioned earlier, cobalt single atoms are difficult to exist stably in the absence of nitrogen dopants. Therefore, it can be considered that Co... NP In / CNT, cobalt exists mainly in the form of cobalt nanoparticles, and cobalt single atoms are negligible.

[0032] Figure 4 (a) TEM image of Co1 / CNT@CN prepared for control example 3; (b) HRTEM image and (cd) related magnified local image; (e) HAADF-STEM image and corresponding elemental mapping image. Figure 4 As shown in image a, the catalyst after acid washing did not exhibit obvious NP. This was confirmed by HRTEM images ( Figure 4 As shown in bc), the indentations left by the etching of cobalt nanoparticles can be clearly seen, and only about 0.370 nm of C(002) spatial lattice fringes were measured. Figure 4 d). As shown in the HAADF-STEM image of Co1 / CNT@CN and the corresponding elemental mapping image ( Figure 4 (e) Cobalt is still present after acid washing, and it is uniformly distributed on the catalyst surface, indicating that metallic cobalt mainly exists in the form of single cobalt atoms. The corresponding elemental mapping shows that nitrogen (N) is still present in the sample after acid washing, and it is uniformly distributed on the catalyst surface, indicating that acid washing does not significantly damage the CN layer. Meanwhile, the distribution of N and Co elements is relatively consistent. Therefore, acid washing removes CoNPs from the catalyst, while the cobalt single atoms are well preserved. These results demonstrate the successful preparation of Co1 / CNT@CN containing a CN layer and cobalt primarily composed of single Co atoms.

[0033] Application Example 1 (I) Nitrobenzene transfer hydrogenation reaction: 10 mg catalyst, 1 mmol ammonia borane, 0.1 mmol nitrobenzene and 10 mL mixed solvent (6 mL water + 4 mL methanol) were reacted at 30 °C and 600 rpm for 1 h.

[0034] (ii) Hydrolysis of ammonia borane: 10 mg catalyst, 1 mmol ammonia borane and 10 mL mixed solvent (6 mL water + 4 mL methanol) or 10 mL water are reacted at 30 °C and 600 rpm.

[0035] Figure 5 Catalytic transfer hydrogenation reaction route for nitrobenzene (a), catalytic performance of different catalysts for nitrobenzene transfer hydrogenation (b), and Co 1-NP The catalytic performance of / CNT@CN-X for the transfer hydrogenation of p-nitrobenzene (c), whereby... Figure 5 Catalyst Co in b 1-NP / CNT@CN is the Co prepared in Example 1. 1-NP / CNT@CN-2.5, the catalyst CNT@CN was prepared as in Control Example 1, and the catalyst Co NP / CNT was prepared as in Comparative Example 2, and the catalyst Co1 / CNT@CN was prepared as in Comparative Example 3; Figure 5 The illustration in b shows the catalytic performance of ammonia borane hydrolysis; Figure 5 Catalyst Co in c 1-NP / CNT@CN-X was prepared in Example 1. It can be seen that during the catalytic transfer hydrogenation of nitrobenzene, Co... 1-NP / CNT@CN catalyst yields higher aniline yields (>99%); while Co1 / CNT@CN, CNT@CN, and Co NP / CNT catalysts were inactive under the same reaction conditions. Figure 5 b). Furthermore, we found Co NP / CNT exhibits high catalytic activity for the hydrolysis of ammonia borane to produce hydrogen, while Co1 / CNT@CN shows no activity (see...). Figure 5 (b) It can be inferred that Co NP is the actual active site for the hydrolysis of ammonia borane, and the Co single atom is the actual active site for the hydrogenation of nitrobenzene. It is noteworthy that, with the increase of X, these Co... 1-NP The / CNT@CN-X catalyst exhibits volcanic catalytic activity in the transfer hydrogenation of nitrobenzene. Figure 5c). Within a certain range (X ≤ 2), the aniline yield initially increases from 27% to 100% with increasing nitrogen content; however, when the nitrogen content exceeds a certain value (X ≥ 4.5), the aniline yield decreases from 100% to 72% with increasing nitrogen content. This specific yield distribution is likely a result of the matching catalytic efficiency of Co NPs and Co single atoms in hydrogen production and consumption. Increased N content favors the formation of Co single atoms, but decreases the ratio of Co NPs to Co single atoms, accelerating the catalytic hydrogenation of nitrobenzene but reducing the hydrolysis rate of ammonia borane. Therefore, since Co NPs and Co single atoms exhibit a significant relay catalytic effect, the yield of Co can be increased by matching the rates of the two-step reaction. 1-NP The catalytic efficiency of / CNT@CN-X in the transfer hydrogenation reaction of nitrobenzene hinges on the appropriate ratio of Co NPs to Co single atoms. By simply altering the DCD content to adjust the Co single atom content, a series of Co-containing catalysts were prepared. 1-NP / CNT@CN-X catalyst, Co 1-NP The / CNT@CN-X catalysts (X = 2.0, 2.5, 3.0, 4.0 and 4.5) exhibited the highest catalytic efficiency.

[0036] (iii) Stability testing of catalysts Catalyst stability is an important criterion for evaluating catalyst performance. To further explore catalyst lifetime and stability, the conversion rate of repeated reactions was recorded every 1 hour. After each cycle, the catalyst was washed, centrifuged, and dried. Reaction conditions: 10 mg Co 1-NP / CNT@CN-2.5 catalyst (prepared in Example 1), 0.1 mmol nitrobenzene, 1 mmol ammonia borane, 4 mL methanol and 6 mL water, 303 K, reaction time 1 h, stirring rate 600 rpm; after the third cycle, the catalyst was regenerated by high-temperature annealing, specifically by deactivating and regenerating the catalyst by annealing it at 600 °C at a heating rate of 2 °C / min in a 10 v% hydrogen-argon mixed atmosphere for 2 h.

[0037] Figure 6 For Co 1-NP Cyclic performance test results of / CNT@CN-2.5 catalyst in nitrobenzene hydrogenation reaction. Figure 6 The results showed that the catalyst activity decreased to 54% after three repetitions. Based on previous reports, the relatively exposed Co single-atom species were likely influenced by surrounding species, leading to this reversible deactivation. The loss of catalytic activity is likely attributed to the blockage of active sites, rather than changes in state or other properties. Figure 7 For Co 1-NP / CNT@CN-2.5 after four reactions: (a) TEM image and corresponding particle size distribution histogram; (b) HRTEM image and (c) corresponding IFFT image of a single Co NP; (d) HAADF-STEM image and corresponding elemental mapping image. Figure 7 As shown, TEM results indicate that, compared with the newly prepared Co 1-NP Compared to the / CNT@CN-2.5 catalyst, the morphology and structure of the catalyst did not change significantly, with the cobalt nanoparticles slightly increasing to 10.8 nm. The catalyst was regenerated by high-temperature annealing, and the catalytic performance of the regenerated catalyst was subsequently tested. The catalytic activity recovered to 95% of the yield, and the yield in a second cycle was 72%, similar to the activities of the first two cycles. Therefore, the decrease in catalyst activity can be mainly attributed to the adsorbate occupying exposed Co single-atom sites, hindering the hydrogenation of nitrobenzene. Therefore, regeneration through annealing treatment can effectively restore the Co nanoparticles' activity. 1-NP The / CNT@CN-2.5 catalyst exhibits excellent reusability and stability.

[0038] Application Example 2 Co prepared in Example 1 1-NP / CNT@CN-2.5 was used as a catalyst, and other nitroaromatic hydrocarbons were used instead of nitrobenzene in Application Example 1 for the hydrogenation reaction.

[0039] The catalytic results are shown in Table 1. Table 1 shows that the prepared Co... 1-NP The / CNT@CN-2.5 catalyst also exhibits excellent catalytic performance in the transfer hydrogenation reactions of nitrotoluene series (3-nitrotoluene, 4-nitrotoluene, and 4-nitroethylbenzene), nitrobenzene halides (4-fluoronitrobenzene, 4-chloronitrobenzene, 2-chloronitrobenzene, 3-chloronitrobenzene, and 4-bromonitrobenzene), and 2-chloro-4-nitrotoluene. Overall, Co... 1-NP The / CNTs@CN-2.5 dual-active-site catalyst exhibits significant selectivity for nitro hydrogenation, with high yields (>99%) of the corresponding functionalized aromatic amines, a feat often unattainable by noble metal-based catalysts. Furthermore, under mild conditions, almost all 10 reaction substrates were converted to their corresponding amino products within 3 h (conversion >99%). Notably, no dehalogenation or dealkylation products were observed during the hydrogenation of these bifunctional nitro compounds after transfer hydrogenation. These extended catalytic results strongly support the successful preparation of Co... 1-NP The application value of / CNT@CN catalyst in the selective hydrogenation of nitroaromatics.

[0040]

Claims

1. A Co 1-NP / CNT@CN catalyst, characterized in that: The catalyst has two active sites, Co NP and Co1. It uses CNT as a support, with a CN layer attached to the surface of the CNT. Co NP is mainly supported on the CNT, and Co1 is mainly supported on the CN layer. CNT is carbon nanotube, CN is carbon nitride, Co NP is cobalt nanoparticle, and Co1 is cobalt single atom.

2. A Co as described in claim 1 1-NP The method for preparing / CNT@CN catalyst is characterized by, The steps are as follows: (1) Disperse multi-walled carbon nanotubes, Co(acac)2 and carbon nitride precursor in water and heat and stir until uniformly dispersed; wherein, by mass ratio, multi-walled carbon nanotubes: Co(acac)2 = 5: (0.1~1), carbon nitride precursor: multi-walled carbon nanotubes = (0.1~5.0): 1; (2) The dispersion system is first frozen with liquid nitrogen and then freeze-dried to obtain the catalyst precursor; (3) Anneal the catalyst precursor at 500-600 °C for 2-4 h in a mixed atmosphere of hydrogen and inert gas to obtain the target catalyst Co. 1-NP / CNT@CN.

3. The Co as described in claim 2 1-NP The method for preparing / CNT@CN catalyst is characterized by: The carbon nitride precursor is dicyandiamide, melamine, or urea.

4. The Co as described in claim 2 1-NP The method for preparing / CNT@CN catalyst is characterized by: By mass ratio, the ratio of multi-walled carbon nanotubes to water is 5: (500~2000), and the ratio of carbon nitride precursor to multi-walled carbon nanotubes is (2.0~4.5):

1.

5. The Co as described in claim 2 1-NP The method for preparing / CNT@CN catalyst is characterized by: The heating and stirring temperature is 40~60 ℃, and the time is 4~12 h; in the mixed atmosphere of hydrogen and inert gas, the volume ratio of hydrogen is 5~10%; the temperature is increased to the annealing temperature at a heating rate of 2~10 ℃ / min.

6. A Co as described in claim 1 1-NP Application of / CNT@CN catalyst in hydrogen production from ammonia borane hydrolysis.

7. The Co as described in claim 6 1-NP The application of / CNT@CN catalyst in hydrogen production from ammonia borane hydrolysis is characterized by: Co 1-NP The CNT@CN catalyst, ammonia borane, and solvent are reacted at 10–40 °C and 300–600 rpm for 1–3 h; the solvent is a mixture of water and methanol in a volume ratio of (1–3):1 or water alone; wherein, the raw material dosage ratio is Co 1-NP / CNT@CN catalyst∶ammoniaborane∶solvent = 10 mg∶(1~2) mmol∶(5~10) mL.

8. A Co as described in claim 1 1-NP Application of / CNT@CN catalyst in the selective hydrogenation of nitroaromatics to prepare aromatic amines.

9. The Co as described in claim 8 1-NP The application of / CNT@CN catalyst in the selective hydrogenation of nitroaromatics to prepare aromatic amines is characterized by: Co 1-NP The CNT@CN catalyst, ammonia borane, nitroaromatic hydrocarbons, and solvent are reacted at 10–40 °C and 300–600 rpm for 1–3 h; the solvent is a mixture of water and methanol in a volume ratio of (1–3):1; wherein, the raw material dosage ratio is Co. 1-NP / CNT@CN catalyst∶ammoniaborane∶nitroaromatics∶solvent = 10 mg∶(1~2) mmol∶(0.1~0.2) mmol∶(5~10) mL.

10. The Co as described in claim 9 1-NP The application of / CNT@CN catalyst in the selective hydrogenation of nitroaromatics to prepare aromatic amines is characterized by: The nitroaromatic hydrocarbon is nitrobenzene, 3-nitrotoluene, 4-nitrotoluene, 4-nitroethylbenzene, 4-fluoronitrobenzene, 4-chloronitrobenzene, 4-bromonitrobenzene, 2-chloronitrobenzene, 3-chloronitrobenzene, or 2-chloro-4-nitrotoluene.

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