Preparation method of hierarchical pore carbon-doped boron nitride catalyst
Through the preparation of multi-stage porous carbon doped boron nitride catalyst, the problem of poor performance of traditional h-BN materials in catalytic reactions was solved, the activity and stability of propane oxidation and dehydrogenation reaction was significantly improved, and high-efficiency propylene was achieved Production and low carbon emissions.
Patent Information
- Application Number
- CN202410948655.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-07-16
- Publication Date
- 2024-12-10
AI Technical Summary
Traditional hexagonal boron nitride (h-BN) materials have poor performance in catalytic reactions due to their low specific surface area and chemically inert surfaces, especially in propylene production, which is difficult to effectively activate the oxidative dehydrogenation of alkanes and inhibit low Deep oxidation of carbon olefins.
The preparation method of multi-stage pore carbon doped boron nitride catalyst is adopted to form multi-stage pore structures and surfactant functional groups through the soy protein flocculation-aminolysis process to improve the catalytic performance of boron nitride.
It significantly improves the activity and reaction stability of the propane oxidative dehydrogenation reaction, achieves efficient propylene production, and reduces energy consumption and high-carbon compound emissions.
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Figure CN119098199A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of catalyst material preparation and heterogeneous catalysis, and in particular relates to a method for preparing a multi-level porous carbon-doped boron nitride catalyst. Background Art
[0002] As an important organic chemical raw material, propylene is widely used in the synthesis of polymers, fibers, plastics and other products. The industrial production processes of propylene mainly include catalytic cracking, naphtha steam cracking, coal-to-olefins and direct propane dehydrogenation, but these processes have disadvantages such as high energy consumption and easy catalyst deactivation. In recent years, the large-scale exploitation of shale gas and natural gas has greatly promoted the lightweight process of low-carbon olefin raw materials. Among them, the oxidative dehydrogenation of propane to produce propylene can not only achieve high-value conversion of low-carbon alkanes, but also help to reduce the energy consumption of propylene production and reduce the emission of high-carbon compounds. However, propylene is easily deeply oxidized to produce CO under oxygen conditions. x , resulting in a decrease in product yield, and a catalyst is needed to regulate the reaction process. Compared with traditional metal-based catalysts, non-metallic boron-based catalysts represented by hexagonal boron nitride (h-BN) can effectively activate the oxidative dehydrogenation of alkanes and inhibit the deep oxidation of low-carbon olefins, showing high olefin selectivity.
[0003] h-BN is a crystal with a graphite-like structure. Due to its special thermochemical stability and high thermal conductivity, it has attracted the interest of researchers. They found that h-BN materials with special structures (such as 1D nanotubes, 2D nanosheets, and 3D nanoscale hierarchical pore structures) have shown great application prospects in various fields (such as sensing, pollutant removal, heat conduction, and energy storage). At the end of 2016, the Hermans group and the Lu Anhui group almost simultaneously discovered that h-BN materials can be applied to propane oxidative dehydrogenation reactions, showing excellent olefin selectivity and negligible carbon dioxide selectivity (Science, 2016, 354:1570; ChemCatChem, 2017, 9:1718). Since then, the application of h-BN materials in heterogeneous catalytic reactions has been increasing. However, due to the low specific surface area and chemically inert surface of traditional h-BN materials, the active sites on the surface cannot be better exposed, resulting in unsatisfactory performance of such materials in catalytic reactions.
[0004] In order to solve the above problems, designing and synthesizing h-BN materials with large specific surface area, rich pore structure and rich surface functional groups is an effective strategy to improve its catalytic performance. Materials with multi-level pores have the advantages of improving mass transfer, reducing internal diffusion and external diffusion, and exposing a large number of active sites, so they are favored by researchers. So far, many types of pore materials have been reported, such as mesoporous silica, multi-level porous metal oxides, carbon materials and molecular sieves, which are often used as catalyst supports or catalysts. However, there are few reports on the application of multi-level porous h-BN in catalytic reactions.
[0005] Therefore, it is of theoretical and practical significance to find a simple, green and efficient synthesis method to prepare h-BN materials with multi-level pores and rich in surface active functional groups. Summary of the invention
[0006] In view of this, the present invention provides a multi-level porous carbon-doped boron nitride catalyst and a preparation method and application thereof, so as to prepare a boron nitride catalyst with excellent performance, good reaction stability and high performance in propane oxidative dehydrogenation reaction.
[0007] In one aspect, the present invention provides a method for preparing a hierarchical porous carbon-doped boron nitride catalyst, comprising the following steps:
[0008] Step 1: preparing raw soy milk;
[0009] Step 2: Add water to the raw soy milk and boil the raw soy milk and water together;
[0010] Step 3: Add boric acid to the mixture of boiled raw soy milk and water to obtain solution A.
[0011] Step 4: Cool solution A, and after complete flocculation, filter out excess water to obtain floccules;
[0012] Step 5: freeze-drying the floccules;
[0013] Step 6: The fully dried flocculants are subjected to ammonolysis in an ammonia atmosphere to obtain a hierarchical porous carbon-doped boron nitride catalyst MA-CBN-x, wherein x represents the amount of boric acid added.
[0014] Preferably, the raw beans used to prepare raw soy milk in step 1 are any one of soybeans, mung beans and black beans.
[0015] Preferably, the amount of raw soy milk in step 2 is 50-500 mL, and the volume ratio of raw soy milk to water is 1:1-1:3.
[0016] Preferably, the amount of boric acid added in step 3 is 5 to 50 g.
[0017] Preferably, the freeze-drying method in step 5 is: placing the floccules in a freeze dryer for freeze drying, and the freeze drying time is 24 to 72 hours.
[0018] Preferably, the temperature of the ammonolysis in step 6 is 800-1300° C., and the ammonolysis time is 5-10 h.
[0019] The present invention also provides a multi-level porous carbon-doped boron nitride catalyst, which is prepared by the above preparation method.
[0020] Finally, the present invention also provides an application of a multi-level porous carbon-doped boron nitride catalyst, wherein the catalyst is applied in the propane oxidative dehydrogenation reaction.
[0021] Specifically, the amount of boron nitride catalyst used in the propane oxidative dehydrogenation reaction is 0.05-0.5 g, the volume ratio of propane to oxygen is 1-3, the reaction temperature is 450-520° C., and the reaction flow rate is 15-30 mL / min.
[0022] The present invention provides a multi-level porous carbon-doped boron nitride catalyst and a preparation method and application thereof. The preparation method is based on the idea of "marinade with tofu", takes soybean protein as the carbon source, and introduces heteroatom carbon into the boron nitride skeleton through the protein flocculation-ammonolysis method, while forming a multi-level pore structure, so as to achieve the purpose of regulating the defects and surface active functional groups in the boron nitride, thereby improving the activity and reaction stability of the catalyst in the reaction of propane oxidative dehydrogenation to propylene.
[0023] The raw materials for the preparation are widely available and green; the synthesis process is novel, green, simple and efficient; the prepared boron nitride has excellent performance and good reaction stability, achieving a significant improvement in the performance of the propane oxidative dehydrogenation reaction. BRIEF DESCRIPTION OF THE DRAWINGS
[0024] Figure 1 SEM photos of the MA-CBN-x catalyst provided by the present invention (a, b) MA-CBN-5, (c, d) MA-CBN-10, (e, f) MA-CBN-15;
[0025] Figure 2 The X-ray diffraction spectrum of the MA-CBN-x catalyst provided by the present invention;
[0026] Figure 3 Comparison of propane conversion and product selectivity on different catalysts at 500°C (a) and stability test results of MA-CBN-10 catalyst. Reaction conditions: C3H8:O2:N2=1 / 1 / 4, total flow rate=18mL / min. DETAILED DESCRIPTION
[0027] In order to make the purpose, technical solution and advantages of the present invention more clear, the technical content of the present invention is further explained in conjunction with specific embodiments. It should be understood that the specific examples described are only used to explain the present invention and are not used to limit the present invention.
[0028] In order to provide a simple, green and efficient synthesis method to prepare h-BN materials with multi-level pores and rich in surface active functional groups; firstly, this embodiment provides a method for preparing a multi-level porous carbon-doped boron nitride catalyst, comprising the following steps:
[0029] Step 1: preparing raw soy milk;
[0030] The following method can be preferably used for preparation: soak soybeans in water for a period of time, then put the soaked soybeans in a wall breaking machine, add appropriate amount of clean water for grinding, and after grinding, filter out the bean dregs to obtain raw soy milk.
[0031] Step 2: Add water to the raw soy milk and boil the raw soy milk and water together;
[0032] Preferably, the beans used are any one of soybeans, mung beans and black beans. The amount of raw soybean milk is 50 to 500 mL. The volume ratio of raw soybean milk to water is 1:1 to 1:3.
[0033] Step 3: Adding boric acid to a mixture of boiled raw soy milk and water to obtain a solution A;
[0034] Preferably, the amount of boric acid added is 5 to 50 g.
[0035] Step 4: Cool solution A, and after complete flocculation, filter out excess water to obtain floccules;
[0036] Step 5: freeze-drying the floccules;
[0037] Preferably, the flocculent is placed in a freeze dryer for freeze drying for 24 to 72 hours.
[0038] Step 6: The fully dried flocculants are subjected to ammonolysis in an ammonia atmosphere to obtain a hierarchical porous carbon-doped boron nitride catalyst MA-CBN-x, wherein x represents the amount of boric acid added.
[0039] Preferably, the temperature of the ammonolysis is 800-1300° C., and the ammonolysis time is 5-10 h.
[0040] The novel preparation method of carbon-doped boron nitride provided in this embodiment is a carbon-doped boron nitride catalyst with multi-level pores obtained based on the idea of "brine dotting tofu". On the one hand, since the electronegativity of carbon is greater than that of boron, the CN bond formed by replacing the boron atom is easier to donate electrons than the BN bond, which is conducive to the formation of nitrogen defects; on the other hand, in the process of preparing carbon-doped boron nitride using flocculated soy protein as a carbon source, the macroscopic structure of the flocculated protein will be retained, and the surface oxygen-containing functional groups of the soy protein-derived carbon will also enter the structure of the boron nitride with carbon doping. It has been verified that the above carbon doping method can not only promote the large-scale generation of defects in boron nitride, but also increase the specific surface area of the catalyst, and generate a large number of boron oxygen active species in situ.
[0041] In addition, the above method uses raw soy milk as the carbon precursor, which expands the raw material source of the carbon precursor. The carbon precursor is cheap and easy to obtain, and the preparation process does not require expensive equipment, so the preparation cost is low.
[0042] This embodiment also provides a multi-level porous carbon-doped boron nitride catalyst prepared by the above method, and the multi-level porous carbon-doped boron nitride catalyst is applied to the propane oxidative dehydrogenation reaction. On the one hand, the multi-level porous carbon-doped boron nitride catalyst prepared above has a large specific surface area and can expose more active sites. On the other hand, the surface of the multi-level porous carbon-doped boron nitride catalyst has abundant active functional groups, which can fully realize the efficient activation and conversion of propane molecules.
[0043] The experimental methods in the following examples are all conventional methods unless otherwise specified.
[0044] Unless otherwise specified, the test materials used in the following examples were purchased from conventional reagent stores and were not further purified.
[0045] The quantitative tests in the following examples were all performed three times, and the data are the average values or the average values ± standard deviations of the three repeated experiments.
[0046] The analysis method in the examples of this application is as follows:
[0047] The catalyst performance evaluation calculation is as follows:
[0048] The target product of propane oxidative dehydrogenation is propylene (C3H8), and the by-products are carbon monoxide (CO), carbon dioxide (CO2) and methane (CH4).
[0049] The evaluation process of the catalyst in the propane oxidative dehydrogenation reaction to propylene is as follows:
[0050] 100 mg of catalyst was placed in a quartz tube fixed with quartz wool at the top and bottom. A thermocouple was placed in the center of the catalyst bed to achieve precise reaction temperature control. Under normal pressure, the reaction gas was kept at a volume ratio (V C3H8 :V O2 :V N2 ) was introduced into the reactor at a flow rate of 1:1:4. The reaction temperature was first raised to 450°C, and data were collected after stabilization for 30 minutes. Data were collected at intervals of 10°C in the temperature range of 450-520°C, and the heating rate was 2°C / min. The reactants and products entered the gas chromatograph through a constant temperature pipeline for online analysis.
[0051] Experimental data analysis:
[0052] The propane conversion (Conv(C3H8)), product selectivity (S i ) and yield (Y i ). The calculation formula is as follows:
[0053]
[0054]
[0055] Y i (%) = Conv(C3H8) × S i / 100
[0056] Where i represents any product, Carbi is the number of carbon atoms in component i, [n C3H8 ] in and [n C3H8 ] out are the moles of propane input and output.
[0057] Embodiment 1:
[0058] A method for preparing a hierarchical porous carbon-doped boron nitride catalyst with different morphologies comprises the following steps:
[0059] S1: Soak a certain amount of soybeans in water for a period of time, then put them in a wall-breaking machine, add appropriate amount of clean water to grind them, and after grinding, filter out the bean dregs to obtain raw soy milk.
[0060] S2: Add an equal volume of water to 100 mL of raw soy milk and boil, then add 5 g, 10 g, and 15 g of boric acid.
[0061] S3: After cooling and complete flocculation, filter out excess water and then freeze-dry the flocs in a freeze dryer for 24 hours.
[0062] S4: The fully dried flocculants were subjected to ammonolysis in an ammonia atmosphere at 1000° C. for 7 h to obtain hierarchical porous carbon-doped boron nitride MA-CBN-x catalysts with different morphologies, where x represents the amount of boric acid added.
[0063] like Figure 1 As shown in the scanning electron microscope photos, it can be seen that when the amount of boric acid is 5g ( Figure 1 a and b), the MA-CBN-5 catalyst has neither a special morphology nor abundant pores; as the amount of boric acid increases to 10 g ( Figure 1 c and d), the MA-CBN-10 catalyst presents the shape of a "dinosaur egg". From the broken "dinosaur egg" photos, it can be found that the catalyst has a rich pore structure; when the boric acid addition amount is 15g ( Figure 1 In (e) and (f), the MA-CBN-15 catalyst has a "cauliflower"-like appearance, and some pores can be found inside it through the cross-sectional photos.
[0064] Example 2
[0065] A method for preparing a multi-level porous carbon-doped boron nitride catalyst with different structures, comprising the following steps:
[0066] Same as Example 1, except that the ammonolysis temperature and time are 900° C. and 5 h, respectively.
[0067] pass Figure 2 The X-ray diffraction patterns shown show that all catalysts have characteristic diffraction peaks at 2θ=25.7° and 42.1°, which are attributed to the (002) and (100) crystal planes of h-BN. However, characteristic diffraction peaks of carbon species were detected in the MA-CBN-5 sample, indicating that h-BN and C coexist in this sample. With the increase of boric acid addition, the diffraction peaks of carbon species disappear, but the intensity of the characteristic diffraction peaks attributed to h-BN decreases and gradually broadens.
[0068] Comparative Example 1:
[0069] Preparation of activated commercial boron nitride catalyst Activated Bulk BN:
[0070] Commercial boron nitride is placed in a fixed bed reactor, and propane, oxygen and nitrogen are introduced, maintaining the volume ratio of the three gases at V C3H8 :V O2 :V N2 =1:1:4, and at the same time, the temperature is raised to 450°C for activation for 2 hours to obtain an activated commercial boron nitride catalyst.
[0071] Taking the multi-level porous MA-CBN-10 catalyst prepared in Example 1 as a typical example, the propane oxidative dehydrogenation performance was tested using a fixed bed micro multiphase reaction device. Figure 3 The following is a comparison chart of the propane oxidative dehydrogenation performance evaluation results and stability test results of the catalysts prepared in Example 1 and Comparative Example 1. Figure 3 It can be seen from a that the propane conversion rate on the MA-CBN-10 catalyst is much higher than that on the commercial boron nitride Bulk BN and activated commercial boron nitride Activated Bulk BN catalysts. At the same time, the MA-CBN-10 catalyst can still maintain a high overall olefin selectivity. Figure 3 b It can be seen that during the continuous 100h test process, the propane conversion rate on the MA-CBN-10 catalyst was about 23%, and the selectivity of propylene and ethylene was maintained at 72%±3% and 12%±3%, respectively, indicating that the catalyst has good stability.
[0072] The detailed description of the embodiments of the invention is written in a progressive manner, emphasizing the differences between the various implementation schemes, and similar parts thereof can be referred to each other.
[0073] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.
Claims
1. A method for preparing a hierarchical porous carbon-doped boron nitride catalyst, characterized in that: The steps include: Step 1: preparing raw soy milk; Step 2: Add water to the raw soy milk and boil the raw soy milk and water together; Step 3: Add boric acid to the mixture of boiled raw soy milk and water to obtain solution A. Step 4: Cool solution A, and after complete flocculation, filter out excess water to obtain floccules; Step 5: freeze-drying the floccules; Step 6: The fully dried flocculants are subjected to ammonolysis in an ammonia atmosphere to obtain a hierarchical porous carbon-doped boron nitride catalyst MA-CBN-x, wherein x represents the amount of boric acid added.
2. The method for preparing a hierarchically porous carbon-doped boron nitride catalyst according to claim 1, characterized in that: The raw beans used to prepare the raw soy milk in step 1 are any one of soybeans, mung beans and black beans.
3. The method for preparing a hierarchically porous carbon-doped boron nitride catalyst according to claim 1, characterized in that: In step 2, the amount of raw soy milk is 50-500 mL, and the volume ratio of raw soy milk to water is 1:1-1:
3.
4. The method for preparing a hierarchically porous carbon-doped boron nitride catalyst according to claim 1, characterized in that: In step 3, the amount of boric acid added is 5 to 50 g.
5. The method for preparing a hierarchically porous carbon-doped boron nitride catalyst according to claim 1, characterized in that: The freeze-drying method in step 5 is: placing the floccules in a freeze dryer for freeze drying, and the freeze drying time is 24 to 72 hours.
6. The method for preparing a hierarchically porous carbon-doped boron nitride catalyst according to claim 1, characterized in that: In step 6, the temperature of the ammonolysis is 800-1300° C., and the ammonolysis time is 5-10 hours.
7. A hierarchical carbon-doped boron nitride catalyst, characterized in that: The invention is prepared by the preparation method described in any one of claims 1 to 7.
8. The use of a hierarchical porous carbon-doped boron nitride catalyst according to claim 7, characterized in that: The catalyst is used in propane oxidative dehydrogenation reaction.
9. The use of a hierarchical porous carbon-doped boron nitride catalyst according to claim 8, characterized in that: The amount of boron nitride catalyst used in the propane oxidative dehydrogenation reaction is 0.05-0.5 g, the volume ratio of propane to oxygen is 1-3, the reaction temperature is 450-520° C., and the reaction flow rate is 15-30 mL / min.