CN113070086B - Nitrogen-doped carbon-loaded molybdenum carbide nano composite material and preparation method and application thereof - Google Patents

Nitrogen-doped carbon-loaded molybdenum carbide nano composite material and preparation method and application thereof Download PDF

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CN113070086B
CN113070086B CN202110354917.1A CN202110354917A CN113070086B CN 113070086 B CN113070086 B CN 113070086B CN 202110354917 A CN202110354917 A CN 202110354917A CN 113070086 B CN113070086 B CN 113070086B
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nitrogen
molybdenum carbide
doped carbon
molybdate
composite material
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CN113070086A (en
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刘又年
王瑾
王立强
马凌
赵晓君
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Central South University
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    • C07C209/36—Preparation of compounds containing amino groups bound to a carbon skeleton by reduction of nitrogen-to-oxygen or nitrogen-to-nitrogen bonds by reduction of nitro groups by reduction of nitro groups bound to carbon atoms of six-membered aromatic rings in presence of hydrogen-containing gases and a catalyst
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    • C07C209/32—Preparation of compounds containing amino groups bound to a carbon skeleton by reduction of nitrogen-to-oxygen or nitrogen-to-nitrogen bonds by reduction of nitro groups
    • C07C209/36—Preparation of compounds containing amino groups bound to a carbon skeleton by reduction of nitrogen-to-oxygen or nitrogen-to-nitrogen bonds by reduction of nitro groups by reduction of nitro groups bound to carbon atoms of six-membered aromatic rings in presence of hydrogen-containing gases and a catalyst
    • C07C209/365—Preparation of compounds containing amino groups bound to a carbon skeleton by reduction of nitrogen-to-oxygen or nitrogen-to-nitrogen bonds by reduction of nitro groups by reduction of nitro groups bound to carbon atoms of six-membered aromatic rings in presence of hydrogen-containing gases and a catalyst by reduction with preservation of halogen-atoms in compounds containing nitro groups and halogen atoms bound to the same carbon skeleton
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    • C07C213/00—Preparation of compounds containing amino and hydroxy, amino and etherified hydroxy or amino and esterified hydroxy groups bound to the same carbon skeleton
    • C07C213/02—Preparation of compounds containing amino and hydroxy, amino and etherified hydroxy or amino and esterified hydroxy groups bound to the same carbon skeleton by reactions involving the formation of amino groups from compounds containing hydroxy groups or etherified or esterified hydroxy groups
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    • C07—ORGANIC CHEMISTRY
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    • C07C221/00—Preparation of compounds containing amino groups and doubly-bound oxygen atoms bound to the same carbon skeleton
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    • C07—ORGANIC CHEMISTRY
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    • C07C227/00—Preparation of compounds containing amino and carboxyl groups bound to the same carbon skeleton
    • C07C227/04—Formation of amino groups in compounds containing carboxyl groups
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    • C07C319/00—Preparation of thiols, sulfides, hydropolysulfides or polysulfides
    • C07C319/14—Preparation of thiols, sulfides, hydropolysulfides or polysulfides of sulfides
    • C07C319/20—Preparation of thiols, sulfides, hydropolysulfides or polysulfides of sulfides by reactions not involving the formation of sulfide groups
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    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D213/00—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members
    • C07D213/02—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members having three double bonds between ring members or between ring members and non-ring members
    • C07D213/04—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members having three double bonds between ring members or between ring members and non-ring members having no bond between the ring nitrogen atom and a non-ring member or having only hydrogen or carbon atoms directly attached to the ring nitrogen atom
    • C07D213/24—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members having three double bonds between ring members or between ring members and non-ring members having no bond between the ring nitrogen atom and a non-ring member or having only hydrogen or carbon atoms directly attached to the ring nitrogen atom with substituted hydrocarbon radicals attached to ring carbon atoms
    • C07D213/36—Radicals substituted by singly-bound nitrogen atoms
    • C07D213/38—Radicals substituted by singly-bound nitrogen atoms having only hydrogen or hydrocarbon radicals attached to the substituent nitrogen atom
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D215/00—Heterocyclic compounds containing quinoline or hydrogenated quinoline ring systems
    • C07D215/02—Heterocyclic compounds containing quinoline or hydrogenated quinoline ring systems having no bond between the ring nitrogen atom and a non-ring member or having only hydrogen atoms or carbon atoms directly attached to the ring nitrogen atom
    • C07D215/16—Heterocyclic compounds containing quinoline or hydrogenated quinoline ring systems having no bond between the ring nitrogen atom and a non-ring member or having only hydrogen atoms or carbon atoms directly attached to the ring nitrogen atom with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached to ring carbon atoms
    • C07D215/38—Nitrogen atoms
    • C07D215/40—Nitrogen atoms attached in position 8

Abstract

The invention discloses a nitrogen-doped carbon-loaded molybdenum carbide nano composite material as well as a preparation method and application thereof. Dissolving molybdate and protein in water, forming protein-molybdate cross-linked network by self-assembly, andsequentially carrying out freeze drying and pyrolysis to obtain Mo 2 C/NC nano composite material. Mo 2 C/NC nanocomposites with nitrogen doping for Mo tuning 2 The interaction between C and a carbon carrier changes the electron density of Mo sites, so that the d-band center of the metal molybdenum is closer to the Fermi level, the activation of hydrogen (including the cracking of hydrogen and the desorption of active hydrogen) is promoted, and the catalyst shows high catalytic activity and high selectivity in the hydrogenation reduction reaction of the nitroaromatic. Furthermore, Mo 2 The C/NC nano composite material has the advantages of simple synthesis method, mild conditions and low cost, and is beneficial to large-scale production.

Description

Nitrogen-doped carbon-loaded molybdenum carbide nano composite material and preparation method and application thereof
Technical Field
The invention relates to a hydrogenation catalytic material, in particular to a nitrogen-doped carbon-loaded molybdenum carbide nano composite material, a preparation method thereof and application of the nitrogen-doped carbon-loaded molybdenum carbide nano composite material in catalyzing nitryl aromatic hydrocarbons to be hydrogenated and reduced into aromatic amine, and belongs to the technical field of hydrogenation catalysis.
Background
Catalytic hydrogenation is of vital importance in the chemical industry for the synthesis of fine and bulk chemicals. The noble metal-based catalyst is widely applied to hydrogenation reaction. However, the high cost and susceptibility to poisoning limit its large-scale application. Transition Metal Carbides (TMC) are of great interest due to their electronic structure and catalytic properties similar to those of noble metals. For example, molybdenum carbide (MoC) x ) The catalyst shows good activity in various hydrogenation reactions such as hydrodesulfurization, biomass conversion, dry reforming of methane, CO hydrogenation and the like. However, H of TMCs catalyst 2 Activation (including H) 2 Dissociation and desorption of active hydrogen) is the rate control step that determines the catalytic hydrogenation performance. Thus, increasing H in catalytic hydrogenation of TMCs 2 The activation capacity is very important.
H 2 The activation on the transition metal depends mainly on the d-orbital of the metal, and for supported catalysts, metal-support interactions (MSI) can modulate the transition goldD orbitals of genus, improvement H 2 The activation capacity, and thus the catalytic activity. MSI can be adjusted by (but is not limited to) changing the composition and structure of the support, especially for carbon supported catalysts. The physical and chemical properties of the carbon matrix can be adjusted by doping, introducing defects, pore formation, and the like. For example, nitrogen doping can make the carbon matrix an excellent support for supporting the transition metal catalyst. Nitrogen has a smaller atomic radius and a higher electronegativity than carbon. Meanwhile, the interaction between the p orbital of N and the d orbital of metal is stronger than that of C. Thus, when an N-doped Carbon matrix, the interaction between the Carbon support and the metal sites inevitably changes significantly, for example, the wu jun theme group prepared iridium nanoparticles supported on N-doped graphene sheets (Ir @ N-G-750), and Density Functional Theory (DFT) calculations showed that N can stabilize the iridium nanoparticles and enhance the metal-support interaction between the iridium nanoparticles and the graphene support (Shi, r.; Zhao, j.; Liu, s., Carbon 2018,130, 185-195.). The Li Longming group discovered that in N-doped graphene-supported Cu, N can enhance the interaction between Cu and a carbon matrix, thereby promoting the adsorption of CO on the carbon surface (Wu, X.; Feng, B.; Li, W., Nano Energy 2019,62, 117-.
Disclosure of Invention
Aiming at the defects of the prior nitroaromatic catalytic hydrogenation technology, the invention aims to provide nitrogen-doped carbon-loaded Mo 2 C nanocomposite material using nitrogen doping to adjust Mo 2 The interaction between C and a carbon carrier changes the electron density of Mo sites, so that the center of a d-band of metal molybdenum is closer to a Fermi level, the activation of hydrogen (including the cracking of hydrogen and the desorption of active hydrogen) is promoted, and the excellent performance is shown in the hydrogenation reduction reaction of nitro compounds.
The second purpose of the invention is to provide a method for preparing the nitrogen-doped carbon-loaded molybdenum carbide nano composite material, which has the advantages of mild conditions, simple steps and low cost.
The third purpose of the invention is to provide application of the nitrogen-doped carbon-supported molybdenum carbide nanocomposite, wherein the nitrogen-doped carbon-supported molybdenum carbide nanocomposite is used for hydrogenation reduction of nitroarene to aromatic amine, and shows high-efficiency catalytic activity and selectivity.
In order to achieve the technical purpose, the invention provides a preparation method of a nitrogen-doped carbon-loaded molybdenum carbide nano composite material, which comprises the steps of dissolving molybdate and protein into water, forming a protein-molybdate radical cross-linked network through self-assembly, and then sequentially carrying out freeze drying and pyrolysis to obtain the nitrogen-doped carbon-loaded molybdenum carbide nano composite material.
The key point of the preparation of the nitrogen-doped carbon-loaded molybdenum carbide nanocomposite is that the protein with high nitrogen content is used as a carbon source and a nitrogen source at the same time, the protein contains polar groups and can form a protein-molybdate crosslinking network with molybdate after self-assembly in a solution system, the original structure of the precursor of the protein-molybdate crosslinking network can be maintained after freeze drying, and high-temperature pyrolysis is carried out on the basis, so that the precursor is converted into the nitrogen-doped carbon-loaded molybdenum carbide nanocomposite in situ. In the high-temperature pyrolysis process, the conversion of protein into nitrogen-doped carbon carriers and the conversion of molybdenum sources into nano-grade molybdenum carbide particles are realized simultaneously, the in-situ compounding of the protein and the molybdenum sources is realized, a very thin nano nitrogen-doped carbon coating layer is generated on the surfaces of the generated nano-grade molybdenum carbide particles in situ, and the molybdenum carbide particles are uniformly dispersed in the nitrogen-doped carbon carriers. Nitrogen in nitrogen-doped carbon can change the electron density of molybdenum sites to make the d-band center of the metal closer to the Fermi level, thereby promoting H 2 The adsorption and the dissociation of active hydrogen of the molybdenum carbide can greatly improve the catalytic activity of the molybdenum carbide, and the catalyst is found to have no hydrogenation catalytic activity on alkynyl, carbonyl, carboxyl and other groups and show high-selectivity hydrogenation catalysis on nitro, which is unexpected. In addition, protein molecules and molybdate are self-assembled in a solution system to form a protein-molybdate crosslinked network, and the structure of a precursor of the protein-molybdate crosslinked network can be basically maintained through freeze drying and high-temperature carbonization, so that an additional template agent is not required to be introduced, and the preparation process is simplified.
As a preferred embodiment, the molybdate is a conventional water-soluble molybdate, such as ammonium molybdate, sodium molybdate and the like, which are common, and specifically (NH) 4 ) 6 Mo 7 O 24 、Na 2 MoO 4 、Li 2 MoO 4 、K 2 MoO 4 And so on.
As a preferred embodiment, the protein is a nitrogen-rich protein, such as bovine serum albumin, egg white, whey protein, silk protein, and other proteins.
In a preferred embodiment, the weight ratio of molybdate to protein is 1 (1-10), and most preferably 1 (1-1.5).
As a preferred embodiment, the pyrolysis conditions are: in N 2 Under protection, heating to 700-900 ℃ at a heating rate of 5-30 ℃/min, and preserving heat for 2-7 h. The further preferable pyrolysis temperature is 700-900 ℃. The nitrogen doping amount can be reduced when the temperature is too high, so that the catalytic activity of the nitrogen-doped carbon-loaded molybdenum carbide nano composite material can be influenced, and the carbonization degree is low when the temperature is too low, so that the composite material is not easy to generate.
The invention also provides a nitrogen-doped carbon-loaded molybdenum carbide nano composite material, which is prepared by the preparation method.
As a preferable scheme, the nitrogen-doped carbon-loaded molybdenum carbide nanocomposite is formed by uniformly distributing nano molybdenum carbide particles coated by a nano carbon layer in a nitrogen-doped carbon matrix; the average particle size of the nano molybdenum carbide particles is within the range of 4-14 nanometers. The nitrogen-doped carbon-loaded molybdenum carbide nano composite material (Mo) of the invention 2 C/NC) of Mo 2 The average particle size of the C nano particles is smaller, and the distribution is more uniform. Mo 2 The surface of the C particle is covered with a thin carbon layer which can prevent Mo 2 The aggregation of the C nano particles can also induce the MSI effect, which is beneficial to improving the hydrogenation catalytic activity.
The invention also provides application of the nitrogen-doped carbon-loaded molybdenum carbide nano composite material in catalyzing hydrogenation reduction of nitroarene into arylamine.
As a preferred scheme, the conditions of the hydrogenation reaction are as follows: the pressure is 8-12 bar, and the reaction is carried out for 2-4 h at 105-115 ℃.
The specific structural formula of the nitroarene is as follows:
ArNO 2
ar is phenyl or substituted phenyl, or aromatic condensed ring group, or aromatic heterocyclic group, or benzoaromatic heterocyclic group. The substituted phenyl is a substituent containing common substituent on a benzene ring, such as alkynyl, acyl, cyano and C 1 ～C 10 Alkyl, halogen substituents, carboxyl, C 1 ～C 10 Alkoxy radical, C 1 ～C 10 Alkylthio, hydroxyl, amido, and the like. Aromatic condensed rings such as naphthalene and the like, and benzoaromatic heterocyclic groups such as quinoline and the like. The high selectivity reduction of the nitro group in the nitro aromatic hydrocarbon by the nitrogen-doped carbon-loaded molybdenum carbide nano composite material is not influenced by the selection of the aromatic hydrocarbon group in the nitro aromatic hydrocarbon and the introduction of various substituents in the aromatic hydrocarbon group. Of particular interest is the controlled highly selective reduction of a nitro group when the phenyl ring contains two nitro groups.
The nitrogen-doped carbon-supported Mo of the invention 2 C nanocomposite (Mo) 2 C/NC) preparation method, comprising the following steps: weighing 1g of BSA in a beaker, adding 10mL of deionized water, and stirring for dissolving; weighing 1g (NH) 4 ) 6 Mo 7 O 24 ·4H 2 Adding 10mL of deionized water into a centrifugal tube, performing ultrasonic dissolution, dropwise adding the formed molybdate solution into BSA while stirring until the mixture is completely and uniformly stirred; transferring the solution into a beaker after stirring, putting the beaker into a freeze drying box until the solvent is completely freeze-dried to obtain a yellow solid after freeze-drying, fully grinding the yellow solid to obtain powder, putting the powder into a porcelain boat, covering the porcelain boat with a cover (another porcelain boat), putting the porcelain boat into a tube furnace, and performing N reaction 2 Heating to 800 ℃ at the speed of 5 ℃/min in the atmosphere to perform calcination treatment, keeping the temperature for 3 hours, and then cooling to room temperature to obtain black powder named as Mo 2 C/NC。
Mo of the invention 2 Use of C/NC nanocomposites for H 2 The catalytic nitrobenzene hydrogenation reduction reaction is specifically implemented as follows: a mixture of 0.25mmol nitrobenzene, 20mg catalyst and 4mL deionized water was placed in a 50mL stainless steel autoclave with H 2 Purging three times to remove air, then pressurizing to 10bar at 1The reaction was carried out at 10 ℃ for 3 h. After the reaction is finished, naturally cooling to room temperature, and adding the rest H 2 And (4) discharging. The mixture was collected in a centrifuge tube, extracted with ethyl acetate and analyzed by gas chromatography.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
1) according to the technical scheme, the protein contains polar groups, the protein and molybdate can form a protein-molybdate crosslinking network in a solution system through self-assembly, the original structure of the protein-molybdate crosslinking network precursor can be maintained through freeze drying, a template agent does not need to be additionally introduced, a template removing machine does not need to be subjected to acid or alkali post-treatment, and the process steps are simplified.
2) The nitrogen-doped carbon-loaded molybdenum carbide nano composite material is prepared from Mo 2 The C nano-particle surface is coated with a thin carbon layer, and the characteristic can prevent Mo 2 Aggregation of C, MSI effect can also be induced, and Mo 2 The C nano-particles are uniformly dispersed in the nitrogen-doped carbon carrier, and the N in the nitrogen-doped carbon carrier can also adjust Mo 2 MSI between C and carbon support can promote hydrogen activation.
3) The nitrogen-doped carbon-loaded molybdenum carbide nano composite material is used as a hydrogenation catalyst, can catalyze the hydrogenation reduction reaction of nitro compounds under the action of hydrogen, and has good catalytic activity, selectivity and stability. The nitrogen-doped carbon-loaded molybdenum carbide nano composite material is mainly based on MSI effect, utilizes N doping to adjust the interaction between a p orbit of N and a d orbit of Mo, increases the electron density of Mo, and is beneficial to H 2 In the presence of Mo 2 Activation on C, Mo 2 The performance of C/NC in hydrogenation catalysis is obviously superior to that of Mo 2 C and Mo 2 C/C。
4) The preparation method of the nitrogen-doped carbon-loaded molybdenum carbide nano composite material is simple, easy to operate, environment-friendly and applicable to industrialization, and adopts nontoxic and cheap raw materials without large-scale complex devices.
Drawings
FIG. 1 shows Mo prepared in example 1 of the present invention 2 Synthesis procedure of C/NC sampleIntention, Mo 2 Transmission Electron Microscope (TEM) image, HR-TEM image and Mo of C nanoparticles 2 Element Mapping (Mapping) graph of C/NC: (a) mo prepared for example 1 2 A manufacturing process schematic diagram of the C/NC sample; (b) is Mo 2 TEM and Mo of C nanoparticles 2 A C NP size distribution map; (c) and (d) Mo prepared in example 1 2 HR-TEM image of C/NC sample; (e) is Mo 2 Element Mapping (Mapping) graph of C/NC.
FIG. 2 shows Mo prepared in examples 1 and 2 of the present invention 2 C/NC、Mo 2 C/C sample and commercial Mo 2 X-ray photoelectron Spectroscopy (XPS) graph of C, H 2 TPR graph and H 2 -TPD map: (a) sample Mo prepared for example 1 2 N1s XPS peak for C/NC; (b) sample Mo prepared for examples 1,2 2 C/NC、Mo 2 C/C and Mo commercial products 2 Mo 3d XPS peak of C; (c) sample Mo prepared for examples 1,2 2 C/NC、Mo 2 C/C and Mo Commodity 2 H of C 2 -a TPR map; (d) sample Mo prepared for examples 1,2 2 C/NC、Mo 2 C/C and Mo Commodity 2 H of C 2 -TPD map.
FIG. 3 shows Mo prepared in example 1 of the present invention 2 Hydrogenation performance diagram of C/NC sample under different conditions: (a) nitrobenzene concentration vs. 8bar H 2 The effect of the initial hydrogenation rate at 110 ℃, the initial reaction rate was calculated at a conversion below 20%; (b) h at 110 DEG C 2 Influence of pressure on nitrobenzene hydrogenation rate; the concentration of nitrobenzene is 5mmol/L, and the dosage of the catalyst is 0.55 mg/mL; the content of the mixture was determined by gas chromatography.
FIG. 4 shows Mo prepared in example 1 of the present invention 2 Charge density difference map, PDOS map and H for different N configurations in C/NC samples 2 Free energy profile of dissociation: (a) is Mo 2 C/NC-0、Mo 2 C/NC-1、Mo 2 C/NC-2 and Mo 2 Charge density differences for the C/NC-3 configuration (yellow and cyan regions represent electron accumulation and depletion, respectively); (b) is Mo 2 Calculation of predicted density of states of Mo atoms in C/NCs, and (C) predicted density of states of carbon, graphite-N, pyridine-N, and pyrrole-N; (d) is composed ofMo 2 C/NC-0、Mo 2 C/NC-1、Mo 2 C/NC-2 and Mo 2 C/NC-3 upper H 2 The free energy distribution of dissociation.
Detailed Description
The technical solution of the present invention is further illustrated by the following specific examples, but the scope of the present invention is not limited to the following examples.
Example 1
Catalyst sample Mo 2 C/NC preparation: 1g BSA and 1g (NH) 4 ) 6 Mo 7 O 24 ·4H 2 O was dissolved in 10mL of deionized water, respectively. Then, the (NH) is added 4 ) 6 Mo 7 O 24 ·4H 2 And dropwise adding the O solution into the bovine serum albumin aqueous solution, and stirring to form a BSA-Mo network. After stirring was complete, the solution was transferred to a beaker and placed in a freeze drying oven until the solvent was completely lyophilized. Grinding the freeze-dried solid to obtain powder, placing into a porcelain boat, covering with a cover (another porcelain boat), transferring into a tube furnace, pyrolyzing under nitrogen flow at 5 deg.C for min -1 Heating the sample to 800 ℃ at a heating rate of (2) and maintaining at 800 ℃ for 3h, and then cooling to room temperature, the obtained sample was named Mo 2 C/NC。
Example 2 (comparative example)
Catalyst sample Mo 2 C/C preparation: mixing 1g sucrose and 1g Na 2 MoO 4 Dissolved in 10mL of deionized water. Subsequently, Na is added 2 MoO 4 The solution is dripped into a sucrose aqueous solution and stirred to form a sucrose-Mo network. After stirring was complete, the solution was transferred to a beaker and placed in a freeze drying oven until the solvent was completely lyophilized. Grinding the freeze-dried solid to obtain powder, placing into a porcelain boat, covering with a cover (another porcelain boat), transferring into a tube furnace, pyrolyzing under nitrogen flow at 5 deg.C for one minute 1 Heating the sample to 800 ℃ at a heating rate of (2) and maintaining at 800 ℃ for 3h, and then cooling to room temperature, the obtained sample was named Mo 2 C/C。
N-doped carbon-loaded molybdenum carbide (Mo) 2 C/NC) is shown in FIG. 1 (a). As shown in FIG. 1(b) isMo 2 Transmission Electron Microscope (TEM) image of C/NC, Mo 2 The average particle size of the C nanoparticles was 8.23 nm. Shown in FIG. 1(c) is Mo 2 High resolution transmission electron microscopy (HR-TEM) of C/NC, the surface of these particles being covered with a thin carbon layer, which not only prevents Mo 2 Aggregation of C, may also induce MSI effects. As shown in FIG. 1(d), the interplanar spacing of these particles was 0.228nm, pointing to the (101) plane of Mo 2C. Shown in FIG. 1(e) is Mo 2 High angle annular dark field scanning transmission electron microscope (HAADF-STEM) and corresponding Energy Dispersive Spectroscopy (EDS) mapping images of C/NC, Mo can be seen 2 The size of C is small. Meanwhile, the Mo element is uniformly distributed in the whole carbon matrix.
Shown as Mo in FIG. 2(a) 2 High resolution XPS spectra of the N1s peak for C/NC, 398.3eV, 399.6eV, 401.3eV correspond to pyridine N, pyrrole N, and graphite N, respectively. Mo in FIG. 2(b) 2 High resolution XPS spectra of Mo 3d peak of C/NC. And Mo 2 C/NC ratio, Mo 2 C and Mo 2 The Mo 3d binding energy of C/C exhibits positive movement due to the interaction of Mo and doped N in the carbon support. N doping can change the electron density of Mo sites, which is in contrast to H 2 Are closely related to adsorption and desorption. As shown in FIG. 2(c), H is used 2 TPR temperature programmed reduction method studies the interaction between hydrogen and different catalysts. In addition, the position of the reduction peak may reflect the strength of the metal-support interaction. Mo 2 C/NC and Mo 2 There are two peaks in the TPR profile of C/C, and Mo 2 C has only one peak. Specifically, the peak of the low temperature region is due to reduction of the passivation layer. The higher temperature region corresponds to Mo 2 C and containing Mo 2 And (4) decomposing the substance C. With Mo 2 C and Mo 2 C/C ratio, Mo 2 C/NC at 232 ℃ (Mo) 2 C:243℃、Mo 2 A first peak of decrease occurs at a lower temperature of 281 ℃ C/C. This indicates that in Mo 2 C/NC on H 2 Activation is easier. For higher reduction temperatures (Mo) 2 C/NC:736℃、Mo 2 C/C:640 ℃ C.), indicating that Mo is present 2 There is a strong interaction between C and N-doped carbon carriers. These results are consistent with the results of XPS analysis. As shown in FIG. 2(d), H is used 2 The adsorption capacity of the catalyst to hydrogen was investigated in a TPD temperature programmed desorption experiment. Mo 2 C/NC and Mo 2 H of C/C 2 Two peaks in the TPD spectrum, Mo 2 H of C 2 -none in the TPD spectrum. Generally, the low temperature signal results from desorption of chemisorbed hydrogen at the metal sites, while the high temperature signal is associated with hydrogen species breakthrough. And Mo 2 C/C ratio, Mo 2 C/NC desorption of H at higher temperatures (75 ℃ and 103 ℃) 2 This means that Mo is 2 C/NC has stronger hydrogen adsorption capacity. Mo 2 H overflow temperature of C/NC is lower than Mo 2 C/C(Mo 2 C/NC:249℃；Mo 2 C/C:260 ℃ C.), which means that dissociated H species are more readily removed from Mo 2 C/NC desorption, which shows that N doping can promote H 2 Adsorption and dissociation of (2). In summary, H 2 TPD and H 2 TPR results show that N in the carbon support can regulate Mo 2 MSI between C and carbon support, which may promote hydrogen activation.
As shown in table 1, the hydrogenation activity of the catalyst was examined by using the nitrobenzene reduction reaction as a model reaction. In particular, whether it is Mo 2 C itself or N-doped carbon (NC) shows activity to nitrobenzene hydrogenation catalysis. In contrast, the load type Mo 2 C shows better catalytic performance. Notably, Mo 2 The C/C conversion and selectivity were 18% and 90%, respectively; mo 2 The C/NC performance is better, and the conversion rate and the selectivity reach 99 percent. Can reasonably obtain Mo 2 C reactivity was highly correlated with the support. Wherein, Mo 2 When the C carrier is on the carbon matrix, the hydrogenation activity of Mo2C is improved mainly by MSI, and the introduction of N in the carbon matrix can further improve Mo 2 The hydrogenation activity of C is improved, thereby improving the catalytic performance of C. Examine Mo as solvent 2 Influence of C/NC catalytic Activity. In various solvents, including water and various alcohols, Mo 2 The best performance of C/NC in water.
As shown in Table 2, Mo was investigated 2 The application range and the universality of the C/NC for hydrogenation of nitro compounds. Mo 2 C/NC has very high activity, soIt was evaluated that the substrate (17 examples) could be selectively hydrogenated to the corresponding amine compound with high conversion. In general, aldehyde groups are susceptible to hydrogenation reactions and are readily converted to hydroxyl compounds on noble metal catalysts such as Pt/C. In contrast, for Mo 2 The C/NC catalyst, 4-nitrobenzaldehyde, was efficiently hydrogenated to 4-aminobenzaldehyde (Table 2, item 2) with 99% conversion and 99% selectivity (selectivity in parentheses). Other unsaturated groups such as halogens, ketones, amides, alkynes, and the like remain during hydrogenation. For example, halonitro compounds can be hydrogenated with up to 99% conversion and 99% selectivity without dehalogenation (table 2, items 6, 7). Mo 2 The hydrogenation of C/NC para-nitro substituted N heterocycles also showed very high selectivity (Table 2, items 15, 17).
TABLE 1
Figure BDA0003001537240000081
TABLE 2
Figure BDA0003001537240000082
Figure BDA0003001537240000091
As shown in FIG. 4, the Density Functional Theory (DFT) is used to calculate Mo in N-doped pair 2 MSI and H between C and carrier 2 Influence of activation and hydrogenation activity. In the presence of Mo 2 In C/NC, N exists mainly in 3 forms, graphite-N, pyridine-N and pyrrole-N, respectively. First, Mo is compared 2 The difference in charge density of the C site interaction with N or C. Under the action of N, Mo 2 The electron transfer between C and the carbon carrier is significantly enhanced, as both the electron accumulation and depletion regions are scaled up, indicating that N-doped carbon and Mo are comparable to pure carbon 2 The interaction of C is stronger, which is beneficial to the adsorption of hydrogen. As shown in FIGS. 4(b) and (c), Mo was investigated 2 Predicted state density of C/NCs (PDOS).For Mo 2 C/NCs, the d-orbital of Mo contributes most to DOS near the Fermi level. Mo 2 C/NC-X (X ═ 1,2,3) ratio Mo 2 C/NC-0 has a higher PDOS; while near the fermi level, the p-orbital of N exhibits a higher DOS than the p-orbital of carbon. This indicates that N doping can enhance the DOS of Mo, thereby providing higher active electrons. Mo 2 C/NC-0 d band center (E) d ) Is 1.93eV, Mo 2 C/NC-1 is 1.88eV, Mo 2 C/NC-2 is 1.85eV, Mo 2 C/NC-3 was 1.84 eV. Obviously, the center of the d-band is closer to the Fermi level after the interaction with N, which is beneficial to the adsorption of hydrogen. In summary, the N dopant can adjust Mo 2 The initial MSI and carbon support between C is through the interaction between the p orbitals incorporating the N and d orbitals. The interaction can improve the electron density of the molybdenum, and is beneficial to hydrogen adsorption/dissociation, thereby improving the Mo 2 The catalytic performance of C.
By way of example, the applicant has demonstrated Mo 2 The preparation method of the C/NC nano composite material and the influence of the preparation method on the hydrogenation reduction reaction of the nitro compound. The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments, and all equivalent changes and modifications made according to the claims of the present invention should be covered by the present invention, and the protection scope claimed in the present invention is as shown in the claims of the present application.

Claims (5)

1. The application of the nitrogen-doped carbon-loaded molybdenum carbide nano composite material is characterized in that: the catalyst is applied to catalyzing hydrogenation reduction of nitroarene into aromatic amine; the solvent for catalyzing the hydrogenation reduction reaction of the nitroaromatic is one of water, ethanol, isopropanol, ethyl acetate or cyclohexane; the nitrogen-doped carbon-loaded molybdenum carbide nano composite material is prepared by the following preparation method: and dissolving molybdate and protein into water, forming a protein-molybdate cross-linked network through self-assembly, and then sequentially carrying out freeze drying and pyrolysis to obtain the molybdate-molybdate cross-linked network.
2. The use of the nitrogen-doped carbon-supported molybdenum carbide nanocomposite material according to claim 1, wherein the nitrogen-doped carbon-supported molybdenum carbide nanocomposite material is characterized in thatCharacterized in that: the molybdate is (NH) 4 )6Mo 7 O 24 、Na 2 MoO 4 、Li 2 MoO 4 、K 2 MoO 4 At least one of (1); the protein is at least one of bovine serum albumin, egg white, whey protein and silk protein.
3. The use of the nitrogen-doped carbon-supported molybdenum carbide nanocomposite material according to claim 1 or 2, wherein: the mass ratio of the molybdate to the protein is 1 (1-10).
4. The use of the nitrogen-doped carbon-supported molybdenum carbide nanocomposite material according to claim 1, wherein: the pyrolysis conditions are as follows: at N 2 Under protection, heating to 700-900 ℃ at a heating rate of 5-30 ℃/min, and preserving heat for 2-7 h.
5. The use of the nitrogen-doped carbon-supported molybdenum carbide nanocomposite material according to claim 1, wherein: the nitrogen-doped carbon loaded molybdenum carbide nano composite material is formed by uniformly distributing nano molybdenum carbide particles coated by a nano carbon layer in a nitrogen-doped carbon matrix; the average particle size of the nanometer molybdenum carbide particles is within the range of 4-14 nanometers.
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