Inorganic carbon supported iron-based catalyst and preparation method and application thereof

Abstract

The invention discloses an inorganic carbon supported iron-based catalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: carrying out surface treatment on a carbon carrier to form an oxygen-containing functional group, introducing the oxygen-containing functional group into a mixed solution containing an iron-based metal salt and an inorganic ammonium salt, fully dispersing, and sequentially drying and sintering to obtain the catalyst, the mass ratio of the carbon carrier to the iron-based metal salt to the inorganic ammonium salt is (5-8): (1-5): (20-25). According to the catalyst, based on the synergistic effect of the carbon carrier, the inorganic ammonium salt and the iron-based metal salt, the inorganic ammonium salt provides nitrogen for a catalyst system and forms fixed-point nitrogen doping with the carbon carrier, so that the binding property between the carrier and cobalt is improved, and the cobalt is ensured to be exposed on the surface of the catalyst; in addition, the blending of the inorganic ammonium salt and the iron-based metal salt can promote the dispersibility of the inorganic ammonium salt and the iron-based metal salt, so that the activity and the cycling stability of the catalyst are improved.

Description

Technical Field

[0001] The invention relates to an iron-based catalyst, in particular to an inorganic carbon-supported iron-based catalyst and a preparation method and application thereof, and belongs to the field of hydrogenation catalyst preparation. Background Art

[0002] Aromatic amine compounds are important fine chemicals and also important bulk chemicals. In 2020, the market demand is more than 6 million tons, and it is showing an increasing trend year by year. It plays an irreplaceable role in high-end chemical fields such as medicine, pesticides, dyes and electronic materials. Reduction of nitro compounds is an important method for preparing amine compounds and their derivatives. Hydrogen is a renewable resource and is green, environmentally friendly and widely available. Catalytic hydrogenation technology using hydrogen as a reducing agent has gradually developed into an important means of nitro reduction and has received widespread attention from academia and industry. However, in the actual production process, the current catalytic hydrogenation technology still has a lot of room for improvement in terms of atomic economics, efficient and green production, etc. It is mainly manifested in the high energy consumption caused by high temperature and high pressure reaction environment; the increase of three wastes and energy consumption caused by by-product separation and product purification. Precious metal (platinum, palladium) based catalysts are still the fastest growing and most widely used catalysts. The disadvantages of precious metal catalysts are poor availability, high cost, and poor toxicity tolerance to molecules such as CO and S. Therefore, in the catalytic hydrogenation reduction reaction of nitro compounds, people urgently need low-cost, high-performance non-precious metal catalysts to replace precious metal catalysts.

[0003] Carbon-supported catalysts with MNC (nitrogen-doped carbon-supported iron-based metal catalyst, M represents iron-based metal) structure show excellent hydrogenation activity during nitro hydrogenation reactions. However, the traditional preparation method is mainly achieved by in-situ cracking, that is, cracking a precursor composed of organic small molecules containing nitrogen atoms and metal ions. However, the active sites of the MNC structure prepared by this method are usually located in the pore structure. Due to the large molecular volume and limited solubility of aromatic nitro compounds, the active sites are buried in the pore structure due to the blocking of the pores by reactants or substrates during the gas-solid-liquid three-phase catalytic reaction, resulting in a serious decrease in its catalytic activity after multiple cycles, showing poor cyclic stability. Therefore. How to change the limitations of the confined distribution of active sites is the key to improving the hydrogenation stability of MNC structure catalysts.

[0004] By introducing pre-prepared carbon materials into the precursor, the precursor cracking process occurs on the surface of the carrier, which can improve the distribution of active sites to a certain extent and make more active sites distributed on the surface of the carrier carbon. However, in order to promote better dispersion of metal centers and increase the density of single-atom sites, ligands are usually required to be introduced. However, previous organic ligands are mostly carbon-rich organic ligands containing nitrogen atoms. During the cracking process, the active centers are mostly nanoscale and coated with carbon. At the same time, the ligands can produce a carbon deposition effect and block the pores of the porous carrier. While increasing the internal diffusion resistance, some of the active sites inside the pores are inactivated due to embedding, so the catalysts mostly show low catalytic activity. Therefore, how to overcome the confined distribution of active sites while improving the intrinsic performance of the sites is the key to constructing a MNC structure and a structure-effective nitro hydrogenation catalyst. Summary of the invention

[0005] In view of the problems existing in the prior art, the first object of the present invention is to provide an inorganic carbon-supported iron-based catalyst. The catalyst is based on the synergistic effect between a carbon carrier, an inorganic ammonium salt and an iron-based metal salt. The inorganic ammonium salt is used to provide nitrogen elements for the catalyst system, and nitrogen doping is formed at a fixed point with the carbon carrier, thereby improving the binding between the carrier and the cobalt element, ensuring that the cobalt element is exposed to the catalyst surface, and avoiding the carbon deposition effect of traditional organic molecules during high-temperature cracking and clogging the pore structure of the carrier. In addition, the blending of the inorganic ammonium salt and the iron-based metal salt can promote the dispersion of the two, thereby improving the activity and cycle stability of the catalyst.

[0006] The second object of the present invention is to provide a method for preparing an inorganic carbon-supported iron-based catalyst, which has the advantages of simple process and easy operation, and uses non-precious metal iron-based catalysts, greatly reducing the cost of the catalyst, and does not require large and complex devices, which is more environmentally friendly and can meet the requirements of industrial production.

[0007] The third object of the present invention is to provide an application of an inorganic carbon-supported iron-based catalyst for catalytic hydrogenation of nitro compounds. The use of carbon-supported iron-based catalysts for catalytic hydrogenation of nitro compounds not only has milder reaction conditions, but also has excellent selectivity and cycle stability. According to tests, the catalyst provided by the present invention has a selectivity of >99% and a conversion rate of >99% for catalytic hydrogenation of nitro compounds to corresponding amine compounds. After 16 cycles of use, the conversion rate of the catalyst is still >90% and the selectivity is >99%.

[0008] In order to achieve the above technical objectives, the present invention provides a method for preparing an inorganic carbon-supported iron-based catalyst, wherein the carbon carrier is surface-treated to form oxygen-containing functional groups, and then introduced into a mixed solution containing an iron-based metal salt and an inorganic ammonium salt to be fully dispersed, and then dried and sintered in sequence to obtain;

[0009] The mass ratio of the carbon carrier, the iron-based metal salt and the inorganic ammonium salt is 5-8:1-5:20-25.

[0010] As a preferred solution, the surface treatment process of the carbon carrier is: placing the carbon carrier in an inorganic acid for surface activation treatment, and then drying it to neutrality through washing and extraction.

[0011] As a preferred solution, the inorganic acid is at least one of sulfuric acid, nitric acid, hydrochloric acid and perchloric acid; the pH of the inorganic acid is 1-3.

[0012] As a preferred solution, the mass volume ratio of the carbon carrier to the inorganic acid is 0.05 to 0.15 g / ml. More preferably, the mass volume ratio of the carbon carrier to the inorganic acid is 0.1 g / ml.

[0013] As a preferred solution, the iron-based metal salt is at least one of an iron salt, a cobalt salt and a nickel salt.

[0014] As a preferred embodiment, the inorganic ammonium salt is at least one of ammonium chloride, ammonium sulfate and ammonium bicarbonate.

[0015] As a preferred solution, the carbon carrier is one of activated carbon, coconut shell charcoal, microsphere carbon and carbon nanotube.

[0016] As a preferred solution, the sufficient dispersion method is one of ultrasonic dispersion, stirring dispersion and oscillation dispersion.

[0017] As a preferred solution, the sufficient dispersion time is 1 to 10 hours.

[0018] As a preferred solution, the drying method is oven drying, and the conditions are: temperature of 50 to 120° C. and drying time of 1 to 10 hours.

[0019] As a preferred solution, the sintering process is carried out under a protective atmosphere, and the process is: heating to 400-1000° C. at a heating rate of 4-20° C. / min, and keeping the temperature for 1.5-10 hours.

[0020] As a preferred solution, the protective atmosphere is nitrogen and / or helium.

[0021] The present invention also provides an inorganic carbon-supported iron catalyst, which is prepared by any one of the preparation methods described above, and the specific surface area of ​​the iron catalyst is 850 to 1000 m 2 g -1 .

[0022] The present invention also provides an application of an inorganic carbon-supported iron-based catalyst for catalytic hydrogenation of nitro compounds.

[0023] As a preferred solution, the reaction conditions of the catalytic hydrogenation are: H2 pressure ≤ 10 bar, temperature ≤ 200°C, time 1 to 10 hours, and the mass ratio of the catalyst to the nitro compound is 1:2 to 4. More preferably, the mass ratio of the catalyst to the nitro compound is 1:3.

[0024] Compared with the prior art, the beneficial technical effects of the technical solution of the present invention are:

[0025] 1) The carbon-supported iron-based catalyst provided by the present invention is based on the synergistic effect between the carbon carrier, the inorganic ammonium salt and the iron-based metal salt. The inorganic ammonium salt is used to provide nitrogen elements for the catalyst system, and forms fixed-point nitrogen doping with the carbon carrier, thereby improving the binding between the carrier and the cobalt element, ensuring that the cobalt element is exposed to the catalyst surface, and avoiding the carbon deposition effect of traditional organic molecules during high-temperature cracking and clogging the pore structure of the carrier. In addition, the blending of the inorganic ammonium salt and the iron-based metal salt can promote the dispersibility of the two, thereby improving the activity and cycle stability of the catalyst.

[0026] 2) The preparation method provided by the present invention has the advantages of simple process and easy operation, and adopts non-precious metal iron-based raw materials, which greatly reduces the cost of catalysts, does not require large and complex devices, is more environmentally friendly, and can meet the requirements of industrial production.

[0027] 3) In the technical solution provided by the present invention, the carbon-supported iron catalyst is used to carry out the catalytic hydrogenation reaction of the nitro compound. Not only the reaction conditions are milder, but also the catalyst has excellent selectivity and cycle stability. According to the test, the selectivity of the catalyst provided by the present invention for the catalytic hydrogenation of the nitro compound into the corresponding amine compound is greater than 99%, and the conversion rate is greater than 99%. After 16 cycles of use, the conversion rate of the catalyst is still greater than 90%, and the selectivity is greater than 99%. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 X-ray diffraction patterns of the Co / AC-AP, Co / AC and AC-AP catalysts provided by the present invention;

[0029] Figure 2 A high-resolution transmission electron microscope image of the Co / AC-AP catalyst prepared in Example 1 of the present invention;

[0030] Figure 3 Transmission electron microscope image and particle size distribution image of the Co / AC-AP catalyst prepared in Example 1 of the present invention;

[0031] Figure 4 This is the XPS spectrum of the Co / AC-AP catalyst prepared in Example 1 of the present invention;

[0032] Figure 5 This is a graph showing the recoverable performance of the Co / AC-AP catalyst prepared in Example 1 of the present invention;

[0033] Figure 6 Schematic diagram of the conversion rate and selectivity of the Co / AC-AP catalyst prepared in Example 1 of the present invention in catalytic hydrogenation of nitro compounds into corresponding amine compounds. DETAILED DESCRIPTION

[0034] The technical solution of the present invention is further illustrated by specific embodiments below. It should be understood that the protection scope of the present invention is not limited to the following embodiments; it should be understood that the multiple method steps mentioned in the present invention do not exclude the addition of other method steps before and after the combination steps or the insertion of other method steps between the combination steps; it should be understood that the enumerated embodiments are only used to illustrate the present invention but not to limit the scope of the present invention; it should be understood that the numbering of each method step involved in the present invention is only an effective tool for facilitating the identification of each step, but does not limit the arrangement order of each method step or limit the scope of the present invention; it should be understood that in the case of no substantial change in the technical content, it should also be regarded as the scope of the present invention.

[0035] Example 1

[0036] The carbon-supported iron-based catalyst provided in this embodiment is a cobalt catalyst, and its preparation process is as follows:

[0037] 1. 10.0 g of activated carbon was activated in 100 ml of nitric acid at pH 1, and after washing and drying, a carbon carrier rich in oxygen-containing functional groups on the surface was obtained, which was recorded as NAC;

[0038] 2. Add 0.5g ammonium persulfate and 0.02g cobalt salt into a 10ml flask, add 1.0g NAC after dissolving evenly, disperse for 2h, and then dry at 100℃ for 6h to obtain a black precursor;

[0039] 3. The precursor was transferred to a tube furnace, heated to 800°C at a heating rate of 5°C / min, and kept at this temperature for 3 h to obtain a carbon-supported cobalt catalyst, which was recorded as Co / AC-AP.

[0040] Comparative Example 1

[0041] The preparation process of this comparative example is exactly the same as that of Example 1, except that no ammonium salt is added, and the obtained catalyst is recorded as Co / AP.

[0042] Comparative Example 2

[0043] The preparation process of this comparative example is exactly the same as that of Example 1, except that no cobalt salt is added, and the obtained catalyst is recorded as AC-AP.

[0044] The above three catalysts were subjected to XRD test, and the results are as follows Figure 1 As shown in the figure, no identifiable peaks of elemental metal cobalt nanocrystals were found in the peak spectra of the three catalysts, while obvious broad peaks could be observed at 25° and 44°, which corresponded to 002 and 001 of the carbon support respectively; peaks of cobalt element could be observed at 44° and 51° on both Co / AC and Co / AP-AC, but it was obvious that the cobalt peak of Co / AC was sharper. Preliminary analysis showed that this might be due to the agglomeration of some cobalt elements.

[0045] In order to observe the morphology and microstructure of the catalyst more clearly, the present invention also conducted a high-resolution transmission electron microscope test on the catalyst. The test results are as follows: Figure 2 As shown in the figure, after statistics, all the cobalt nanoclusters of the Co / AC-AP catalyst are very small, about 10 nanometers. Compared with the catalyst Co / AC without adding inorganic heteroatom salts, the particle size of the active metal is reduced by 10 times and is highly dispersed. The Co atoms highlighted by the white circles are dispersed in the N / C matrix in atomic form without aggregated particles. From the above characterization, it can be seen that there is a CN-bound matrix in the Co / AC-AP catalyst. The XPS spectrum test of the Co / AC-AP catalyst is further performed, and the existence of the Co-NC center can be seen from the figure.

[0046] Furthermore, the present invention also conducted a catalytic hydrogenation experiment on the above three catalysts, and the process was as follows:

[0047] The above catalyst was loaded into a tank reactor, and the substrate p-chloronitrobenzene, hydrogen and a mixed solvent were introduced, wherein the mass ratio of the catalyst to the substrate was 1:33, the hydrogen partial pressure was 0.5 MPa, and the mixed solvent was a mixture of water and ethanol in a volume ratio of 1:1. The conditions of the above catalytic hydrogenation reaction were: reaction temperature of 120°C, reaction time of 3h, and after the reaction was completed, the conversion rate of the substrate and the selectivity of aniline were recorded. The results are shown in Table 1.

[0048] Table 1

[0049] Case Conversion rate Selectivity Example 1 ＞99.9％ ＞99.9％ Comparative Example 1 20％ 99％ Comparative Example 2 / /

[0050] As can be seen from Table 1, the catalyst provided in Comparative Example 1 does not add ammonium salt, and its conversion rate is only 20%, while the catalyst provided in Example 1 of the present invention has a conversion rate and selectivity of ≥99.9% for catalytic hydrogenation of p-chloronitrobenzene to aniline, and has an excellent catalytic effect. This is because the ammonium salt can provide nitrogen elements on the one hand, and form fixed-point nitrogen doping with the carbon carrier, thereby improving the binding between the carrier and the cobalt element, ensuring that the cobalt element is exposed to the catalyst surface, and avoiding the carbon deposition effect of traditional organic molecules during high-temperature cracking and blocking the pore structure of the carrier. On the other hand, the inorganic ammonium salt can also play a good dispersing effect on the cobalt element, improve the activity and cycle stability of the catalyst, thereby greatly improving the conversion rate and selectivity of the catalyst; the catalyst obtained in Comparative Example 2 does not add cobalt salt, and the product output is too small to accurately test the reaction conversion rate and selectivity. It proves that the catalyst provided by the present invention uses iron-based metal salts as catalytic active components, and only under the synergistic effect of iron-based metal salts, inorganic ammonium salts and carbon carriers can the excellent catalytic performance of the catalyst be achieved.

[0051] The catalyst provided in Example 1 of the present invention also has excellent lifespan and cycle stability. Figure 5 As shown, after 16 cycles, the conversion rate of the Co / AC-AP catalyst for the catalytic hydrogenation reaction of p-chloronitrobenzene is still greater than 90%, and the selectivity is greater than 99%.

[0052] In order to verify the applicability of the catalyst provided by the present invention for the hydrogenation reaction of nitro compounds, the present invention also used Co / AC-AP catalyst to carry out catalytic hydrogenation reaction of different nitro compounds, and the reaction conditions and process were exactly the same as those of the hydrogenation reaction of p-chloronitrobenzene. The results are as follows: Figure 6 As shown, the test shows that the conversion rate and selectivity of the Co / AC-AP catalyst for catalytic hydrogenation of other nitro compounds with sensitive groups into corresponding amine compounds are both greater than 99%, and it is generally applicable in the hydrogenation reaction of nitroaromatics.

Claims

1. A method for preparing an inorganic carbon-supported iron-based catalyst, characterized in that: The carbon carrier is surface treated to form oxygen-containing functional groups, and then introduced into a mixed solution containing an iron-based metal salt and an inorganic ammonium salt to be fully dispersed, and then dried and sintered in sequence to obtain; The mass ratio of the carbon carrier, the iron-based metal salt and the inorganic ammonium salt is 5-8:1-5:20-25.

2. The method for preparing an inorganic carbon-supported iron catalyst according to claim 1, characterized in that: The surface treatment process of the carbon carrier is as follows: placing the carbon carrier in an inorganic acid for surface activation treatment, and then washing and drying to neutrality by an extraction method to obtain the carbon carrier.

3. The method for preparing an inorganic carbon-supported iron-based catalyst according to claim 2, characterized in that: The inorganic acid is at least one of sulfuric acid, nitric acid, hydrochloric acid and perchloric acid; the pH of the inorganic acid is 1-3; the mass volume ratio of the carbon carrier to the inorganic acid is 0.05-0.15 g / ml.

4. The method for preparing an inorganic carbon-supported iron catalyst according to claim 1, characterized in that: The iron-based metal salt is at least one of iron salt, cobalt salt and nickel salt; the inorganic ammonium salt is at least one of ammonium chloride, ammonium sulfate and ammonium bicarbonate; the carbon carrier is one of activated carbon, coconut shell charcoal, microsphere carbon and carbon nanotube.

5. The method for preparing an inorganic carbon-supported iron catalyst according to claim 1, characterized in that: The method of sufficient dispersion is one of ultrasonic dispersion, stirring dispersion and oscillation dispersion; and the time of sufficient dispersion is 1 to 10 hours.

6. The method for preparing an inorganic carbon-supported iron catalyst according to claim 1, characterized in that: The drying method is oven drying, and the conditions are: temperature of 50-120° C., and drying time of 1-10 hours.

7. The method for preparing an inorganic carbon-supported iron-based catalyst according to claim 1, characterized in that: The sintering process is carried out under a protective atmosphere, and the process is: heating to 400-1000° C. at a heating rate of 4-20° C. / min, and keeping the temperature for 1.5-10 hours; the protective atmosphere is nitrogen and / or helium.

8. An inorganic carbon-supported iron catalyst, characterized in that: Prepared by the preparation method according to any one of claims 1 to 7, the specific surface area of ​​the iron-based catalyst is 850 to 1000 m 2 g -1 .

9. The use of an inorganic carbon-supported iron-based catalyst according to claim 8, characterized in that: Used for catalytic hydrogenation of nitro compounds.

10. The use of an inorganic carbon-supported iron-based catalyst according to claim 8, characterized in that: The reaction conditions of the catalytic hydrogenation are: H2 pressure ≤ 10 bar, temperature ≤ 200°C, time 1 to 10 hours, and a mass ratio of catalyst to nitro compound of 1:2 to 4.

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