Preparation method and application of iron-doped carbon nitride H2S high-value catalyst

Abstract

The application discloses a preparation method of an iron-doped carbon nitride H2S high-value catalyst and application thereof, and belongs to the technical field of material preparation and environmental catalysis. The method takes melamine, dopamine hydrochloride and iron salt as raw materials, and obtains the product iron-doped carbon nitride through ultrasonic treatment, stirring, calcination and drying and grinding treatment. x The Fe metal is loaded on the carbon nitride carrier through the action of the chemical bond bonding, the electronic structure and the steric hindrance of the catalyst can be regulated and optimized, a large number of active sites are provided for the reaction, the Fe-based catalyst exhibits high catalytic activity and target product selectivity in the reaction of reducing aromatic nitro compounds into aromatic amines by H2S, the Fe-based catalyst prepared in the application can remove H2S at the source and realize high-value utilization of H2S, compared with traditional g-C3N4 and Fe2O3 catalysts, the Fe-based catalyst has better catalytic performance and is not easy to be poisoned and inactivated, can be recycled, has wide substrate applicability, and has a large industrial application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of material preparation and environmental catalysis, and particularly relates to a preparation method of an iron-doped carbon nitride H2S high-value catalyst and application thereof. BACKGROUND

[0002] Hydrogen sulfide (H2S) generated in natural gas refineries, biogas purification and coal chemical industry processes is a highly toxic and corrosive gas, which not only corrodes chemical equipment and endangers human health, but also seriously pollutes the ecological environment. Therefore, in order to ensure safe production and prevent environmental risks, H2S must be removed efficiently.

[0003] At present, the Claus method is the most commonly used technology for treating industrial associated H2S waste gas. However, due to the limitation of thermodynamic equilibrium, about 3%-5% of H2S remains in the tail gas, which is difficult to meet the increasingly stringent environmental protection requirements of the country. In addition, the traditional Claus process can only recover sulfur resources in H2S, while the hydrogen in H2S is wasted. In fact, H2S can be directly used as a "hydrogen donor", and from the perspective of atom economy, the H and S elements in H2S can be converted into high-value chemicals. Therefore, exploring the removal of H2S from the source and realizing the high-value utilization of H2S not only can meet the important needs of chemical safety production, but also can produce huge economic benefits, which is a front topic and a key development direction in the field of environmental chemical engineering.

[0004] Aromatic amines are an important class of industrial materials and play an important role in many fields. On the other hand, aryl nitro compounds are inexpensive and easy to obtain, and the corresponding aryl amines can be synthesized using the corresponding aryl nitro compounds as substrates, which improves the added value of the products. Currently, aryl nitro compounds can be aminated by catalytic hydrogenation, hydrazine hydrate reduction, metal reduction, sulfidation-alkali reduction, electrochemical reduction, and catalytic hydrogen transfer. However, the developed methods still have some shortcomings, such as catalytic hydrogenation reaction which often needs to be carried out under high pressure, requiring high equipment and large investment, and being prone to dehalogenation. The product of hydrazine hydrate reduction is nitrogen and water, but its cost is high, it needs to be stored at low temperature, and it is only suitable for the reduction of a small amount of specific nitro compounds; in the production process of metal reduction and sulfidation-alkali method, there is a lot of waste water and waste residue, which is difficult to recover.

[0005] Catalytic hydrogen transfer reduction is a widely used hydrogenation process in organic synthesis. It is a method that uses hydrogen donor as hydrogen source and realizes the reduction of specific functional groups in the presence of catalyst. This method does not need to use hydrogen directly, and the reaction can be carried out under relatively mild conditions. In addition, the hydrogen resource in the catalytic hydrogen transfer reduction method is abundant, which can also provide new ideas for further improving the selectivity of the reaction. Among them, H2S has reducing property and can also be used as a kind of "hydrogen donor". By transferring the hydrogen in H2S to aromatic nitro, not only the efficient utilization of hydrogen resource can be realized, but also the sulfur resource can be recycled and co-produced aromatic amine compounds. The reaction has high atom economy and can realize the high value utilization of H2S, which is an ideal way to deal with industrial H2S waste gas. The development of new type of efficient catalyst is the key to realize this process.

[0006] The g-C3N4 material is composed of 2D layers of repeating heptazine skeleton, which has unique electronic structure and high physical and chemical stability. Due to the high nitrogen content (~ 55%-62%) and the existence of sp 2 Hybrid nitrogen and carbon, chemical stability, is a suitable scaffold for building hybrid materials. Most importantly, CN has 6 pairs of "nitrogen cavity" of nitrogen lone pair, which can capture single metal atoms by forming metal-Nx bond to construct functional catalysts. In addition, the defects and / or edges of triazine framework can provide sites for the integration of metal atoms. Based on this, the inventors creatively developed a simple method to prepare iron-doped carbon nitride catalyst and applied it to the reduction of aromatic nitro to amine reaction by H2S. We used dopamine hydrochloride as carbon source, through its self-polymerization in alkaline conditions, and added melamine as nitrogen source, and added ferric chloride solution as the source of iron atoms. After ultrasonic treatment, stirring, calcination, drying and grinding treatment, Fe atoms were highly dispersedly anchored on the carbon-nitrogen carrier, and finally iron-doped carbon nitride material was obtained. The material shows high catalytic activity and selectivity in the catalysis of aromatic nitro compounds to aromatic amine reaction. The present application provides a simple and green method for the preparation of single-atom dispersed iron-doped carbon nitride catalyst. At the same time, the prepared iron-doped carbon nitride catalyst can efficiently realize the reduction of aromatic nitro to amine by H2S, which further expands the application field of iron-doped carbon nitride catalyst and provides a new idea for the removal and high value utilization of H2S. SUMMARY

[0007] The application aims at solving the problems of waste of hydrogen resources in H2S and low product added value in the prior art, and provides a synthesis method of iron-doped carbon nitride material and application thereof.

[0008] To achieve the above object, the application adopts the following technical scheme:

[0009] A synthesis method of iron-doped carbon nitride high-value catalyst, comprising the following steps:

[0010] a. A carbon source and a certain amount of alkali solution, organic solvent and deionized water are weighed and measured, and stirred at room temperature for 30 min;

[0011] b. Then a certain proportion of nitrogen source and iron salt is added to the solution obtained in step a, wherein the iron salt is dissolved in 50 mL of deionized water, and then the above solution is added under ultrasonic, and the obtained precipitate is washed and dried after stirring at room temperature for 12 h;

[0012] c. After calcination at 600 DEG C for 2 h, the final product of iron-doped carbon nitride high-value catalyst is obtained.

[0013] In step a, the alkali solution is ammonium hydroxide, the organic solvent is anhydrous ethanol, the carbon source is dopamine hydrochloride, the ammonia water is 0.75 mL, the anhydrous ethanol is 40 mL, and the deionized water is 40 mL.

[0014] Further, the volume ratio of the alkali solution, the organic solvent and the deionized water in step a is 1:53:53. The carbon source is preferably dopamine hydrochloride, and the organic solution is preferably anhydrous ethanol.

[0015] In step b, the nitrogen source is melamine, the iron salt is ferric chloride, and the mass ratio of the nitrogen source to the iron salt is 60:1-300:1.

[0016] In step b, the obtained precipitate is washed with deionized water and anhydrous ethanol for two times respectively.

[0017] In step b, the drying is vacuum drying at 60 DEG C for 12 h.

[0018] In step c, the heating rate of the calcination is 5 DEG C / min.

[0019] The iron-doped carbon nitride material synthesized by the synthesis method described above is applied in the reaction of catalyzing H2S to reduce aromatic nitro compounds.

[0020] The obtained iron-doped carbon nitride can be used in the reaction of converting H2S to aryl nitro compounds, and the reaction temperature is 80-110 DEG C.

[0021] In the reaction of catalyzing H2S to reduce aryl nitro compounds to prepare aromatic amines, the amount of the iron-doped carbon nitride material is 40 mg; the components and contents of the raw gas are 5 wt% H2S and 95 wt% N2 balance gas; the flow rate is 30 mL / min; and the reaction time is 2 h.

[0022] Further, the specific conditions of using the iron-doped carbon nitride to catalyze H2S to convert nitroaromatics are as follows: the reaction substrate is 1 mmol of nitrobenzene; the amount of the catalyst is 40 mg; the assistant is 1 mL of isopropylamine; the components and contents of the raw gas are 5 wt% H2S and N2 balance gas; the flow rate of the raw gas is 30 mL / min; and the reaction temperature is 80-110 DEG C. -1

[0023] The present application has the following advantages and beneficial effects:

[0024] 1. The nitrogen content of the carbon nitride synthesized in the present application is high (about 55%-62%), sp 2 hybridization exists, the chemical property is stable, the defects and / or edges of the triazine framework can provide sites for the integration of metal atoms, and the triazine framework is a suitable scaffold for constructing hybrid materials. On this basis, the iron-doped carbon nitride is prepared by doping iron elements, and the coordination structure of the iron elements can be regulated by adjusting the amount of the added iron salt. In addition, the basic groups in the matrix can promote the adsorption and activation of the reaction substrate, and improve the catalytic activity.

[0025] 2. The iron-doped carbon nitride prepared in the present application is dispersed on a larger specific surface area by high-temperature pyrolysis, which is beneficial to the full exposure of the active components and further improves the catalytic activity. In addition, the catalyst has the advantages of small amount of metal doping, low price of raw materials, simple preparation process, easy industrialization, and wide application prospect.

[0026] 3. The iron-doped carbon nitride obtained in the present application can provide a large number of active sites, which can reduce the activation energy of the reaction and improve the reaction rate on the one hand, and make the sulfur intermediate quickly desorb and release hydrogen atoms to participate in the reduction reaction of aryl nitro, thereby obtaining the target product aromatic amine.

[0027] 4. The Fe-based sulfur high-value catalyst provided in the present application has good catalytic activity and selectivity, and can be recycled. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 X-ray powder diffraction spectrum of Fe-CN-x prepared for Examples 1-3 and Comparative Example 1 of the present application; ​

[0029] Figure 2 Mapping of Fe-doped carbon nitride prepared for Example 2 of the present application;

[0030] Figure 3 SEM of Fe-CN-x prepared for Examples 1-3 and Comparative Example 1 of the present application;

[0031] Figure 4 Raman of Fe-doped carbon nitride prepared for Example 2 of the present application;

[0032] Figure 5 FTIR of Fe-doped carbon nitride prepared for Example 2 of the present application;

[0033] Figure 6 Selectivity, conversion and yield of Fe-CN-x prepared for Examples 1-3 and Comparative Example 1 of the present application in the reaction of catalyzing H2S conversion of nitroarenes for 2h;

[0034] Figure 7 Activity of Fe-CN-3 prepared for Example 2 of the present application in five cycles of regeneration test. DETAILED DESCRIPTION

[0035] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application is described in detail below with reference to the examples and drawings, and the examples described are further descriptions of the present application, but not limitations of the content of the present application.

[0036] Example 1

[0037] A method for synthesizing a Fe-doped carbon nitride material: 0.75 mL of ammonium hydroxide and 40 mL of anhydrous ethanol were dissolved in 40 mL of deionized water to obtain a solution, then a 0.52 mM (4.9 mg / 50 mL) dopamine hydrochloride solution was prepared by dissolving in deionized water, and then injected into the above solution, and stirred vigorously at room temperature for 30 min to form a black solution A. 4.056 g of melamine was added to solution A. During ultrasonic treatment, a low-concentration 1 mmol / L FeCl3 solution was added dropwise, and continuously stirred for 12 h. After centrifugation, each was washed twice with ethanol and deionized water, and vacuum dried at 60°C for 12 h. The obtained product was centrifuged, dried, ground, and pyrolyzed at 600°C for 2 hours at a heating rate of 5°C / min under an argon atmosphere to obtain the final product Fe-doped carbon nitride material Fe-CN-1. -1 A method for synthesizing a Fe-doped carbon nitride material: 0.75 mL of ammonium hydroxide and 40 mL of anhydrous ethanol were dissolved in 40 mL of deionized water to obtain a solution, then a 0.52 mM (4.9 mg / 50 mL) dopamine hydrochloride solution was prepared by dissolving in deionized water, and then injected into the above solution, and stirred vigorously at room temperature for 30 min to form a black solution A. 4.056 g of melamine was added to solution A. During ultrasonic treatment, a low-concentration 1 mmol / L FeCl3 solution was added dropwise, and continuously stirred for 12 h. After centrifugation, each was washed twice with ethanol and deionized water, and vacuum dried at 60°C for 12 h. The obtained product was centrifuged, dried, ground, and pyrolyzed at 600°C for 2 hours at a heating rate of 5°C / min under an argon atmosphere to obtain the final product Fe-doped carbon nitride material Fe-CN-1.

[0038] Example 2

[0039] A method for synthesizing an iron-doped carbon nitride material: 0.75 mL of ammonium hydroxide and 40 mL of anhydrous ethanol were dissolved in 40 mL of deionized water to obtain a solution, then a 0.52 mM (4.9 mg / 50 mL) dopamine hydrochloride solution was dissolved in deionized water, and then injected into the above solution, stirred vigorously at room temperature for 30 min, forming a black solution A. 4.056 g of melamine was added to solution A. During ultrasonic treatment, a low-concentration 3 mmol / L FeCl3 solution was added dropwise, and continuously stirred for 12 h. After centrifugation, washed with ethanol and deionized water twice, vacuum dried at 60°C for 12 h. The obtained product was centrifuged, dried, ground, and pyrolyzed at a heating rate of 5°C / min at 600°C for 2 hours under an argon atmosphere to obtain the final product iron-doped carbon nitride material Fe-CN-3. -1

[0040] Example 3

[0041] A method for synthesizing an iron-doped carbon nitride material: 0.75 mL of ammonium hydroxide and 40 mL of anhydrous ethanol were dissolved in 40 mL of deionized water to obtain a solution, then a 0.52 mM (4.9 mg / 50 mL) dopamine hydrochloride solution was dissolved in deionized water, and then injected into the above solution, stirred vigorously at room temperature for 30 min, forming a black solution A. 4.056 g of melamine was added to solution A. During ultrasonic treatment, a low-concentration 3 mmol / L FeCl3 solution was added dropwise, and continuously stirred for 12 h. After centrifugation, washed with ethanol and deionized water twice, vacuum dried at 60°C for 12 h. The obtained product was centrifuged, dried, ground, and pyrolyzed at a heating rate of 5°C / min at 600°C for 2 hours under an argon atmosphere to obtain the final product iron-doped carbon nitride material Fe-CN-3. -1

[0042] Comparative Example 1

[0043] 0.75 mL of ammonium hydroxide and 40 mL of anhydrous ethanol were dissolved in 40 mL of deionized water to obtain a solution, then a 0.52 mM (4.9 mg / 50 mL) dopamine hydrochloride solution was dissolved in deionized water, and then injected into the above solution, stirred vigorously at room temperature for 30 min, forming a black solution A. 4.056 g of melamine was added to solution A. 12 h of continuous stirring. After centrifugation, washed with ethanol and deionized water twice, vacuum dried at 60°C for 12 h. The obtained product was centrifuged, dried, ground, and pyrolyzed at a heating rate of 5°C / min at 600°C for 2 hours under an argon atmosphere to obtain the final product bulk-CN. -1

[0044] ​​​X-ray powder diffraction (XRD): The phase characterization of the samples was performed using an X'pert pro powder diffractometer from Panalytical, with an X'celerator as the detector, a copper target (Cu Kα, λ = 0.154 nm) as the excitation source, an operating voltage of 45 kV, and an operating current of 40 mA.

[0045] Field emission scanning electron microscopy (SEM): SEM images of the samples were observed on an S-4800 scanning electron microscope, with a test current of 7 μA and a voltage of 5 kV.

[0046] Figure 1 The images show the X-ray powder diffraction patterns of iron-doped carbon nitride prepared in Examples 1-3 and Comparative Example 1 of this invention. Figure 1 As shown, all samples exhibit two peaks at 13.0° and 27.8°, belonging to the in-plane order (100) of the 3S triazine unit and the interlayer stacking (002) of the aromatic segment, respectively. Compared to bulk-CN, the peaks of the Fe-CN-x samples broadened and weakened with increasing Fe content. The results indicate that the introduction of iron affects the thermal polymerization of CN, leading to increased interplanar spacing and graphite perturbation. Furthermore, no diffraction peaks attributed to iron, such as iron oxide, were detected. The absence of iron-related peaks suggests that iron is highly dispersed and / or chemically coordinated with CN.

[0047] Figure 2 This is a mapping diagram of the iron-doped carbon nitride prepared in Example 2 of the present invention. As can be seen from the diagram, the distribution of O, C, N, and Fe in the material indicates that these elements are relatively uniformly distributed in the catalyst.

[0048] Figure 3 The images show SEM images of the iron-doped carbon nitride prepared in Examples 1-3 and Comparative Example 1 of this invention. As can be seen from the images, the iron-doped carbon nitride prepared in Examples 1-3 and Comparative Example 1 is all sheet-like, and the examples are coarser and thinner than Comparative Example 1.

[0049] Figure 4 This is the Raman spectroscopy diagram of iron-doped carbon nitride prepared in Example 2 of this invention. As shown in the diagram, 1250–1700 cm⁻¹ -1 The band can be attributed to the stretching vibration of the CN element. 975cm -1 and 760cm -1 The peak values ​​at these locations correspond to the breathing mode of the 3s triazine unit and the bending vibration of the CNC, respectively. XRD analysis revealed that the intensity of all peaks decreased with increasing Fe content, indicating that the host-guest interaction caused a slight disruption in the CN structure.

[0050] Figure 5FTIR spectra of Fe-doped carbon nitride prepared for Example 2 of the present application. As shown in the figure, the CN sample exhibits typical bands at 802 cm -1 and 889 cm -1 , which are attributed to the breathing mode of 3s-triazine group and cross-linking deformation mode of N-H, respectively. In addition, the absorption band between 1200 and 1630 cm -1 belongs to the typical stretching mode of CN heterocycle. With the increase of Fe doping amount, the peak intensity of these peaks gradually increases, and the amino peak intensity between 3000 and 3360 cm -1 also gradually increases.

[0051] Reaction test of H2S converting nitrobenzene: the Fe-doped carbon nitride materials prepared in Examples 1-3 and Comparative Example 1 were used for evaluating the catalytic activity of converting nitrobenzene after simple grinding. The test conditions are as follows: the catalyst loading amount is 0.04 g, the raw gas is composed of 5% H2S and balance nitrogen, the raw gas flow rate is 30 mL·min -1 , the reaction temperature is 110°C, and the reaction time is 2 h.

[0052] The catalysts prepared in each example were applied to the catalytic reaction of H2S converting nitrobenzene, and quantitative analysis was performed by gas chromatography. The peak area at the corresponding retention time of the organic phase product at the end of the reaction and the aniline solution with a known prepared concentration was calculated to obtain the aniline yield I a of the reaction, and then the peak area I0 corresponding to 100% conversion of the reactant nitrobenzene to aniline at the retention time was calculated to obtain the aniline yield in the reaction.

[0053] The aniline yield calculation formula is as follows:

[0054]

[0055] Figure 6 The catalytic activity curve of the Fe-doped carbon nitride materials prepared in Examples 1-3 and Comparative Example 1 of the present application in the catalytic reaction of H2S converting nitrobenzene at 110°C. The conversion rate and selectivity of the Fe-CN-3 sample prepared in Example 2 of the present application at normal pressure and 110°C reached 91.97% and 94.09%, respectively, while the conversion rate and selectivity of Examples 1 and 3 at normal pressure and 110°C were 80.21% and 93.54%, 76.45% and 93.85%, respectively. The conversion rate and selectivity of Comparative Example 1 at normal pressure and 110°C were 76.29% and 95.75%, respectively. In addition, the Fe-CN-x catalyst synthesized in the present application has good catalytic activity and selectivity. After five cycles of regeneration test, the activity did not decrease significantly Figure 7), which can be recycled. It is found that the performance of the iron-doped carbon nitride material is superior to that of bulk-CN, commercial activated carbon and commercial iron oxide yellow (Table 1). More importantly, the catalyst can be applied to different aryl nitro substrates and exhibits good amine synthesis activity, and the substrate applicability is wide (Table 2).

[0056] Table 1 Statistical table of H2S reduction of aryl nitro substrate to aryl amine activity of examples 1-3 and comparative example 1 of the present application, commercial activated carbon and commercial iron oxide yellow

[0057] Catalyst Conversion (%) Selectivity (%) Example 1 80.21 93.54 Example 2 91.97 94.09 Example 3 76.45 93.85 Bulk-CN 76.29 95.57 Commercial activated carbon 65.19 99.99 Commercial iron oxide yellow 76.57 99.99

[0058] Table 2 Statistical table of H2S reduction of different aryl nitro substrates to aryl amine activity of example 2 of the present application

[0059] Aryl nitro substrate Conversion (%) Selectivity (%) Nitrobenzene 91.97 93.54 p-Chloronitrobenzene 98.69 11.00 o-Chloronitrobenzene 80.51 67.72 m-Chloronitrobenzene 99.99 99.99 p-Nitrophenol ＜1 ＞99 1-Fluoro-4-nitrobenzene 99.96 0.98 p-Nitroaniline ＜1 ＞99 p-Nitroacetophenone ＜1 ＞99 p-Nitrotoluene 49.29 99.99 p-Aminobenzamide 99.99 99.99

[0060] From the above, it can be seen that the iron-doped carbon nitride with different iron doping amounts prepared by the present application has good catalytic performance in the reaction of converting nitrobenzene by H2S, and the catalytic activity of the Fe-CN-3 sample is the highest.

[0061] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for synthesizing an iron-doped carbon nitride H2S high-value catalyst, characterized by comprising the following steps: The method comprises the following steps: ​ a. Measure or weigh a certain amount of alkali solution, organic solvent and carbon source, and dissolve them in a certain amount of deionized water, and stir at room temperature for 30 min to obtain a solution; wherein the alkali solution is ammonium hydroxide, the organic solvent is anhydrous ethanol, and the carbon source is dopamine hydrochloride; b. Weigh a certain proportion of nitrogen source and iron salt, wherein the nitrogen source is melamine and the iron salt is ferric chloride, and the mass ratio of the nitrogen source and the iron salt is 60:1-300:1; add the nitrogen source into the solution obtained in step a to obtain a mixture solution, dissolve the iron salt in a certain amount of deionized water, and then add the mixture solution while ultrasonic stirring, and ultrasonic stir at room temperature for 12 h; wash the obtained precipitate with deionized water and anhydrous ethanol twice respectively, and then vacuum dry at 60℃ for 12 h to obtain a powder sample; c. Move the powder sample obtained in step b into a tube furnace, and calcine at 600℃ for 2 hours to obtain an iron-doped carbon nitride material.

2. The method of synthesis according to claim 1, characterized in that: The heating rate of the calcination in step c is 5℃ / min.

3. The application of the iron-doped carbon nitride material synthesized by the synthesis method of any one of claims 1-2 in the reaction of catalyzing H2S to reduce aromatic nitro compounds.

4. Use according to claim 3, characterized in that: The iron-doped carbon nitride material is used as a catalyst in the reaction of catalyzing H2S to reduce aromatic nitro compounds to prepare aromatic amines, and the reaction temperature is 80-110℃.

5. Use according to claim 4, characterized in that: In the reaction of catalyzing H2S to reduce aromatic nitro compounds to prepare aromatic amines, the amount of the iron-doped carbon nitride material is 40 mg; the components and contents of the raw gas are 5wt % H2S and 95wt % N2 balance gas in sequence; the flow rate is 30 mL / min; and the reaction time is 2 h.

Images