A nitrogen-doped carbon-coated nano-zinc oxide catalyst, its preparation method and application

Abstract

The present invention belongs to the technical field of catalysts, and particularly relates to a nitrogen-doped carbon-coated nano-zinc oxide catalyst, a preparation method thereof, and an application thereof. In the present invention, a nano-zinc oxide is modified by a silane coupling agent capped with a primary amine, so that the nano-zinc oxide is effectively wrapped by the silane coupling agent. The terminal amino functional group of the silane coupling agent participates in the polycondensation reaction of an organic anhydride monomer and an organic amine monomer, which can effectively improve the dispersion uniformity of the nano-zinc oxide in the polymer. After curing and calcination, the coating efficiency of the nano-zinc oxide and the interfacial interaction strength between the nano-zinc oxide and the nitrogen-doped carbon carrier are significantly improved, and the aggregation and loss of the active components of the catalyst during the propane dehydrogenation to propylene reaction can be effectively inhibited, avoiding the generation of phenomena such as high-temperature sintering, agglomeration, and carbon deposition, solving the problem of short-term deactivation of the zinc oxide catalyst. The nitrogen-doped carbon-coated nano-zinc oxide catalyst has high catalytic activity for the propane dehydrogenation to propylene reaction and strong catalyst stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and particularly relates to a nitrogen-doped carbon-coated nano zinc oxide catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] The technology for propane dehydrogenation to propylene is one of the important ways to increase the production of propylene, mainly including direct dehydrogenation and oxidative dehydrogenation. Direct dehydrogenation is a strongly endothermic reaction and needs to be carried out at a relatively high temperature. However, high temperature often leads to catalyst sintering and carbon deposition, resulting in poor catalytic performance and stability. The catalysts for industrial production in the direct dehydrogenation technology mainly include two categories: Cr-based and Pt-based catalysts. Cr-based catalysts are inexpensive but easily deactivate, and at the same time, they cause serious environmental pollution; Pt-based catalysts have high activity, good selectivity and stability, but are expensive and have high catalytic costs. Therefore, the development of catalysts with high efficiency, environmental protection, low cost and stable performance has great application value and strategic significance for the industrial production of propane dehydrogenation to propylene in China.

[0003] In recent years, the newly developed oxide ZnO-based catalysts are inexpensive and have attracted much attention due to their good dehydrogenation activity in the dehydrogenation of propane to propylene. For example, the prior art (Angew. Chem. Int. Ed., 2020, 59, 2-11; Chem. Sci., 2020, 11, 1549-1555; Fuel Process. Technol., 2012, 96, 220-227; RSC Adv., 2019, 9, 9828-9837.) has all disclosed ZnO-based catalysts. However, the existing ZnO-based catalysts are prone to sintering, aggregation and carbon deposition under the high-temperature conditions of propane dehydrogenation to propylene, resulting in a decrease in catalytic activity and even deactivation. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a nitrogen-doped carbon-coated nano zinc oxide catalyst, a preparation method thereof, and an application thereof. The nitrogen-doped carbon-coated nano zinc oxide catalyst prepared by the present invention using an in-situ polycondensation reaction has uniformly dispersed nano zinc oxide, high catalytic activity for propane dehydrogenation to propylene and good catalyst stability.

[0005] In order to achieve the above-mentioned invention purpose, the present invention provides the following technical solutions.

[0006] The present invention provides a preparation method of a nitrogen-doped carbon-coated nano zinc oxide catalyst, comprising the following steps:

[0007] Modifying nano zinc oxide with a silane coupling agent capped with a primary amine to obtain modified nano zinc oxide;

[0008] The modified nano-zinc oxide, organic amine monomer and organic anhydride monomer are subjected to in-situ polycondensation reaction under an anhydrous and anaerobic environment to obtain a precursor;

[0009] The precursor is successively cured and calcined to obtain a nitrogen-doped carbon-coated nano-zinc oxide catalyst.

[0010] Preferably, the primary amine-terminated silane coupling agent includes one or more of γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldimethoxysilane, γ-aminopropyltriethoxysilane, and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane;

[0011] The mass of the primary amine-terminated silane coupling agent is 5-10% of the mass of nano-zinc oxide.

[0012] Preferably, the modification temperature is 30-50 °C and the time is 3-8 h.

[0013] Preferably, the organic amine monomer includes one or more of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 1,3-bis(3-aminophenoxy)benzene, and 1,4-bis(4-aminophenoxy)benzene;

[0014] The organic anhydride monomer includes one or more of pyromellitic dianhydride, 1,2,4,-trimellitic anhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, and 2,3,3',4'-diphenyl ether dianhydride;

[0015] The molar ratio of the modified nano-zinc oxide, organic anhydride monomer and organic amine monomer is 1:(3-5):(1-4).

[0016] Preferably, the temperature of the in-situ polycondensation reaction is 10-40 °C and the time is 2-5 h.

[0017] Preferably, the curing is program curing, and the program curing successively includes: heat preservation and curing for 0.5-3 h at 60-100 °C, heat preservation and curing for 0.5-3 h at 100-150 °C, and heat preservation and curing for 0.5-3 h at 200-300 °C.

[0018] Preferably, the calcination temperature is 500-700 °C and the heat preservation time is 5-8 h.

[0019] The present invention provides a nitrogen-doped carbon-coated nano-zinc oxide catalyst prepared by the preparation method described in the above technical solution, which includes nano-zinc oxide and amorphous carbon doped with nitrogen element coated on the surface of the nano-zinc oxide.

[0020] Preferably, in the nitrogen-doped carbon-coated nano-zinc oxide catalyst, the content of nano-zinc oxide is 8-15 wt%, and the content of nitrogen-doped amorphous carbon is 85-92%;

[0021] The particle size of the nano-zinc oxide is 10-20 nm.

[0022] The present invention provides an application of the nitrogen-doped carbon-coated nano-zinc oxide catalyst described in the above technical solution in the dehydrogenation of propane to propylene.

[0023] In the present invention, nano-zinc oxide is modified by a silane coupling agent capped with a primary amine. On the one hand, the nano-zinc oxide is effectively encapsulated by the silane coupling agent capped with a primary amine; on the other hand, the terminal amino functional group of the silane coupling agent capped with a primary amine participates in the polycondensation reaction of organic anhydride monomers and organic amine monomers, which can effectively improve the dispersion uniformity of nano-zinc oxide in the polymer. The combined action of the above two aspects can improve the coating efficiency of nano-zinc oxide after calcination and the interfacial interaction strength between nano-zinc oxide and the nitrogen-doped carbon carrier, and can effectively inhibit the aggregation and loss of the active components of the catalyst during the dehydrogenation reaction of propane to propylene, avoiding the generation of phenomena such as high-temperature sintering, agglomeration, and carbon deposition, and solving the problem of short-term inactivation of the zinc oxide catalyst. The nitrogen-doped carbon-coated nano-zinc oxide catalyst prepared by the present invention has high catalytic activity for the dehydrogenation reaction of propane to propylene and strong catalyst stability. Description of the Drawings

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0025] Figure 1 It is a TEM image of the nitrogen-doped carbon-coated nano-zinc oxide catalyst prepared by the in-situ polycondensation reaction method in Example 1;

[0026] Figure 2 It is a TEM image of the nitrogen-doped carbon-coated nano-zinc oxide catalyst prepared by directly blending nano-zinc oxide in Comparative Example 1. Detailed Embodiments

[0027] The present invention provides a preparation method of a nitrogen-doped carbon-coated nano-zinc oxide catalyst, including the following steps:

[0028] Modify the nano-zinc oxide with a silane coupling agent capped with a primary amine to obtain modified nano-zinc oxide;

[0029] Perform an in-situ polycondensation reaction on the modified nano-zinc oxide, organic amine monomer, and organic anhydride monomer under an anhydrous and anaerobic environment to obtain a precursor;

[0030] Cure and calcine the precursor in sequence to obtain a nitrogen-doped carbon-coated nano-zinc oxide catalyst.

[0031] In the present invention, unless otherwise specified, the materials and equipment used are all commercially available products in the art.

[0032] The present invention modifies nano-zinc oxide with a silane coupling agent capped with a primary amine to obtain modified nano-zinc oxide.

[0033] In the present invention, the nano-zinc oxide is preferably prepared by a hydrothermal reaction. The present invention has no special limitation on the preparation conditions of the nano-zinc oxide, and it is sufficient to obtain nano-zinc oxide with a particle size of 10-20 nm; the nano-zinc oxide is preferably spherical nano-zinc oxide.

[0034] In a specific embodiment of the present invention, the preparation method of the nano-zinc oxide preferably includes the following steps: Mix an aqueous solution of zinc chloride and an ethanol solution of dodecylamine, adjust the pH value to 7-9 with ammonia water and then perform a hydrothermal reaction to obtain nano-zinc oxide. In the present invention, the molar ratio of zinc chloride in the aqueous zinc chloride solution to dodecylamine in the ethanol solution of dodecylamine is preferably 1:(6-15), more preferably 1:9; the concentration of the aqueous zinc chloride solution is preferably 0.1-0.4 mol / L, more preferably 0.143 mol / L; the concentration of dodecylamine in the ethanol solution of dodecylamine is preferably 0.2-0.8 mol / L, more preferably 0.45 mol / L. The present invention has no special limitation on the concentration of the ammonia water, and it is sufficient to adjust the pH value to 8. In the present invention, the temperature of the hydrothermal reaction is preferably 150-230 °C, more preferably 160 °C, and the time of the hydrothermal reaction is preferably 20-48 h, more preferably 24 h. After the hydrothermal reaction is completed, the present invention preferably further includes performing solid-liquid separation on the obtained hydrothermal reaction solution, washing the obtained precipitate alternately with water and ethanol and then drying to obtain nano-zinc oxide; the present invention has no special limitation on the solid-liquid separation, and any solid-liquid separation method well-known to those skilled in the art can be used, such as centrifugal separation, filtration, or suction filtration; the number of alternate washings is preferably 3-8 times, more preferably 4 times, and the alternate washing is preferably centrifugal alternate washing; the drying temperature is preferably 30-80 °C, more preferably 50 °C, and the drying is preferably vacuum drying. The present invention has no special limitation on the drying time, and it is sufficient to dry to a constant weight.

[0035] In the present invention, the primary amine-terminated silane coupling agent preferably includes one or more of γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldimethoxysilane, γ-aminopropyltriethoxysilane, and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, and more preferably includes γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldimethoxysilane, γ-aminopropyltriethoxysilane, or N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane. In the present invention, the mass of the primary amine-terminated silane coupling agent is preferably 5-10% of the mass of the nanozinc oxide, and more preferably 5-8%.

[0036] In the present invention, the modification temperature is preferably 30-50°C, more preferably 40-45°C, and the modification time is preferably 3-8 h, more preferably 5-6 h. In the present invention, during the modification process, the nanozinc oxide is effectively encapsulated by the primary amine-terminated silane coupling agent.

[0037] In a specific embodiment of the present invention, the modification is preferably as follows: The nanozinc oxide is dispersed in an ethanol aqueous solution, and a primary amine-terminated silane coupling agent is added dropwise to the obtained nanozinc oxide dispersion for modification. In the present invention, the volume fraction of water and ethanol in the ethanol aqueous solution is preferably 1:(8-10), and more preferably 1:9. In the present invention, the dispersion is preferably ultrasonic dispersion, and the ultrasonic dispersion time is preferably 60-120 min, more preferably 90 min; the mass fraction of nanozinc oxide in the nanozinc oxide dispersion is preferably 2-8%, and more preferably 4%. The present invention has no special limitation on the dropping, and it can be added dropwise evenly.

[0038] After the modification is completed, the present invention preferably further includes solid-liquid separation of the obtained modified system, drying the obtained solid component and then crushing it to obtain modified nanozinc oxide. The present invention has no special limitation on the solid-liquid separation, and any solid-liquid separation method well-known to those skilled in the art can be used, such as centrifugal separation, filtration, or suction filtration. In the present invention, the drying temperature is preferably 30-80°C, more preferably 40-60°C, and the drying is preferably vacuum drying. The present invention has no special limitation on the drying time, and it can be dried to constant weight. In the present invention, the crushing is preferably grinding, and the particle size of the modified nanozinc oxide is preferably 5-60 nm, more preferably 10-20 nm.

[0039] After obtaining the modified nanozinc oxide, the present invention carries out an in-situ polycondensation reaction on the modified nanozinc oxide, organic amine monomer, and organic anhydride monomer in an anhydrous and oxygen-free environment to obtain a precursor.

[0040] In the present invention, the organic amine monomer preferably includes one or more of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 1,3-bis(3-aminophenoxy)benzene, and 1,4-bis(4-aminophenoxy)benzene, more preferably includes one or two of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 1,3-bis(3-aminophenoxy)benzene, and 1,4-bis(4-aminophenoxy)benzene. In the present invention, the organic anhydride monomer includes one or more of pyromellitic dianhydride, 1,2,4,-trimellitic anhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, and 2,3,3',4'-diphenyl ether dianhydride, more preferably includes one or two of pyromellitic dianhydride, 1,2,4,-trimellitic anhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, and 2,3,3',4'-diphenyl ether dianhydride. In the present invention, the molar ratio of the modified nano-zinc oxide, the organic anhydride monomer, and the organic amine monomer is preferably 1:(3-5):(1-4), more preferably 1:(4-5):(2-3), and further preferably 1:5:2.

[0041] In the present invention, the temperature of the in-situ polycondensation reaction is preferably 10-40°C, more preferably 20-30°C, and further preferably 25°C. The time of the in-situ polycondensation reaction is preferably 2-5 h, more preferably 3-4 h. In the present invention, the solvent used in the in-situ polycondensation reaction preferably includes dimethylformamide (DMF) and / or dimethylacetamide. In the present invention, during the in-situ polycondensation reaction, the terminal amine functional group of the silane coupling agent capped with primary amine in the modified nano-zinc oxide participates in the polycondensation reaction of the organic anhydride monomer and the organic amine monomer, so that the nano-zinc oxide is in-situ anchored on the molecular chain of the polyimide prepolymer (polyamic acid), effectively improving the dispersion uniformity of the nano-zinc oxide in the polyimide prepolymer.

[0042] In a specific embodiment of the present invention, the in-situ polycondensation reaction is preferably as follows: the modified nano-zinc oxide and the organic amine monomer are dispersed in a solvent to obtain a modified zinc oxide-organic amine mixture; the organic anhydride monomer is dissolved in a solvent to obtain an organic anhydride solution; under a protective atmosphere, the organic anhydride solution is dropped into the modified zinc oxide-organic amine mixture for in-situ polycondensation reaction. In the present invention, the concentration of the modified nano-zinc oxide in the modified zinc oxide-organic amine mixture is preferably 0.1-0.8 mol / L, more preferably 0.5 mol / L. In the present invention, the concentration of the organic anhydride solution is preferably 0.4-1.0 mol / L, more preferably 0.6-0.7 mol / L. In the present invention, the protective atmosphere preferably includes nitrogen, argon, or helium. The present invention has no special limitation on the dropping, and it can be added drop by drop at a uniform speed.

[0043] After obtaining the precursor, the present invention cures and calcines the precursor in sequence to obtain a nitrogen-doped carbon-coated nano-zinc oxide catalyst.

[0044] In the present invention, the curing is preferably programmed curing, and the programmed curing preferably includes in sequence: heat preservation curing at 60-100°C for 0.5-3 h, heat preservation curing at 100-150°C for 0.5-3 h, and heat preservation curing at 200-300°C for 0.5-3 h. More preferably, it includes in sequence: heat preservation curing at 70-90°C for 0.5-2 h, heat preservation curing at 110-130°C for 0.5-2 h, and heat preservation curing at 260-290°C for 0.5-2 h. Further preferably, it includes in sequence heat preservation curing at 80°C for 1 h, heat preservation curing at 120°C for 1 h, and heat preservation curing at 280°C for 1 h. In the present invention, the heating rate during the programmed curing process is preferably independently 5-8°C / min, more preferably 7-8°C / min.

[0045] The present invention preferably cools the cured product obtained by curing to room temperature before calcining. The present invention has no special limitation on the cooling, and a cooling method well-known to those skilled in the art can be used, such as natural cooling.

[0046] In the present invention, the temperature of the calcination is preferably 500-700°C, more preferably 600-700°C, and further preferably 650°C; the heat preservation time of the calcination is preferably 5-8 h, more preferably 5.5-7.5 h, and further preferably 6-7 h; the atmosphere of the calcination is preferably nitrogen, helium or argon; the calcination is preferably carried out in a tubular furnace. In the present invention, the calcination can significantly improve the coating efficiency of nano-zinc oxide and the interfacial interaction strength between zinc oxide and the nitrogen-doped carbon support, and can effectively inhibit the aggregation and loss of the active components of the catalyst during the propane dehydrogenation to propylene reaction, thereby effectively ensuring the long-term high activity and catalytic stability of the nitrogen-doped carbon-coated nano-zinc oxide catalyst.

[0047] After the calcination, the present invention preferably further includes crushing the obtained calcined product to obtain a nitrogen-doped carbon-coated nano-zinc oxide catalyst; the crushing is preferably grinding, and the grinding is preferably carried out in an agate mortar.

[0048] The present invention provides a nitrogen-doped carbon-coated nano-zinc oxide catalyst prepared by the preparation method described in the above technical solution, which comprises nano-zinc oxide and amorphous carbon doped with nitrogen element coated on the surface of the nano-zinc oxide. In the present invention, in the nitrogen-doped carbon-coated nano-zinc oxide catalyst, the content of nano-zinc oxide is preferably 8-15 wt%, more preferably 10-12 wt%; the content of nitrogen-doped amorphous carbon in the nitrogen-doped carbon-coated nano-zinc oxide catalyst is preferably 85-92%, more preferably 88-90%. In the present invention, the particle size of the nano-zinc oxide is preferably 5-60 nm, more preferably 10-20 nm.

[0049] The present invention provides the application of the nitrogen-doped carbon-coated nano-zinc oxide catalyst described in the above technical solution in the dehydrogenation of propane to propylene.

[0050] In order to further illustrate the present invention, the nitrogen-doped carbon-coated nano-zinc oxide catalyst of the present invention, its preparation method and application will be described in detail below with reference to the drawings and examples, but they should not be construed as limiting the protection scope of the present invention.

[0051] Example 1

[0052] (1) 10 mmol of ZnCl2·6H2O was added to 70 mL of deionized water and stirred until completely dissolved to obtain a zinc chloride solution; 9.0 mmol of dodecylamine was dissolved in 20 mL of absolute ethanol to obtain an ethanol solution of dodecylamine; the zinc chloride solution was mixed with the ethanol solution of dodecylamine, the pH value was adjusted to 8 with ammonia water, and then transferred to a hydrothermal reaction kettle, and hydrothermally reacted at 160 °C for 24 h. The obtained precipitate was centrifugally washed 4 times with deionized water and ethanol alternately, and then vacuum dried at 60 °C until constant weight to obtain nano-zinc oxide with a particle size of 10-20 nm.

[0053] (2) The nano-zinc oxide was ultrasonically dispersed in an ethanol aqueous solution (volume ratio of deionized water to absolute ethanol = 1:9) for 90 min. The obtained nano-zinc oxide dispersion (mass fraction of nano-zinc oxide was 4.0%) was transferred to a three-necked flask, and 5% of γ-aminopropyltriethoxysilane based on the mass fraction of zinc oxide was slowly added dropwise. After the addition, it was modified at 80 °C for 6 h, and then centrifuged and separated. The obtained solid component was vacuum dried at 50 °C until constant weight and then ground to obtain modified nano-zinc oxide with a particle size of 10-20 nm.

[0054] (3) In a three-necked flask, 4.38 g of 1,3-bis(3-aminophenoxy)benzene and 1.46 g of modified nano-zinc oxide were dispersed in 30 mL of DMF, and then nitrogen was introduced. After stirring at room temperature for 30 min, a modified zinc oxide-organic amine mixed solution was obtained. 6.2 g of 3,3',4,4'-diphenylether tetracarboxylic dianhydride was dissolved in 30 mL of DMF under stirring at room temperature, and nitrogen was introduced. Then it was transferred to a constant pressure funnel and slowly added dropwise to the three-necked flask and added dropwise to the modified zinc oxide-organic amine mixed solution. After the addition was completed, stirring was continued for 3 h to obtain a precursor solution. The precursor solution was spread on a clean glass plate and heated at a gradient temperature in a forced-air drying oven, and was taken out after being cured at 80 °C, 120 °C and 280 °C for 1 h each, and then calcined in a nitrogen atmosphere tube furnace at 650 °C for 6 h and ground in an agate mortar to obtain a nitrogen-doped carbon-coated nano-zinc oxide catalyst; wherein, the heating rate during the curing process was 8 °C / min for each stage.

[0055] Example 2

[0056] The nitrogen-doped carbon-coated nano-zinc oxide catalyst was prepared according to the method of Example 1, and the difference from Example 1 was only that: in step (3), the amount of the modified nano-zinc oxide used was 3.25 g.

[0057] Example 3

[0058] The nitrogen-doped carbon-coated nano-zinc oxide catalyst was prepared according to the method of Example 1, and the difference from Example 1 was only that: in step (2), γ-aminopropyltriethoxysilane was replaced by γ-aminopropyltrimethoxysilane; in step (3), the amount of the modified nano-zinc oxide used was 4.58 g.

[0059] Comparative Example 1

[0060] The nitrogen-doped carbon-coated nano-zinc oxide catalyst was prepared according to the method of Example 1, and the difference from Example 1 was only that: step (2) was omitted; in step (3), the modified nano-zinc oxide was replaced by nano-zinc oxide.

[0061] Comparative Example 2

[0062] The nitrogen-doped carbon-coated nano-zinc oxide catalyst was prepared according to the method of Example 1, and the difference from Example 1 was only that: step (2) was omitted; in step (3), 1.46 g of the modified nano-zinc oxide was replaced by 6.64 g of nano-zinc oxide.

[0063] Figure 1 It is the TEM image of the nitrogen-doped carbon-coated nano-zinc oxide catalyst prepared by the in-situ polycondensation reaction method in Example 1. Figure 2 It is the TEM image of the nitrogen-doped carbon-coated nano-zinc oxide catalyst prepared by directly blending nano-zinc oxide in Comparative Example 1. By comparison Figure 1and Figure 2 It can be seen that the dispersion of zinc oxide in the catalyst prepared by in-situ polycondensation reaction is better, and almost no agglomeration of nano-zinc oxide can be observed. However, the agglomeration of nano-zinc oxide in the catalyst prepared by direct blending is serious, and the overall dispersion of zinc oxide is poor.

[0064] Application Example 1

[0065] The nitrogen-doped carbon-coated nano-zinc oxide catalysts prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were used for catalytic propane dehydrogenation reaction. The specific reaction conditions were as follows: The propane dehydrogenation reaction was carried out on a fixed-bed micro-reactor. Weigh 0.4 g of the nitrogen-doped carbon-coated nano-zinc oxide catalyst and place it in the constant-temperature section of the reaction tube. The lower part of the bed was filled with 1.0 g of quartz sand with a particle size of 60 - 80 mesh as a support. After the catalyst was heated to the reaction temperature (550 °C) under a nitrogen atmosphere, propane was introduced into the reactor at atmospheric pressure. After the reaction system was stabilized for 0.5 h, the products were analyzed online. The reaction products were analyzed by a gas chromatograph (Shimadzu GC2014) with a dual-column and dual-detector system; hydrocarbon products were separated by γ-Al2O3 (30 m × 0.53 mm × 10.0 μm) and detected by FID; CO x was separated by a TDX packed column and detected by TCD. The catalytic performance test results of the catalyst were the average values within 3.5 h. The results of the catalyst for catalytic propane dehydrogenation reaction are shown in Table 1:

[0066] Table 1 Results of the catalysts prepared in Examples and Comparative Examples for catalytic propane dehydrogenation reaction

[0067]

[0068] As can be seen from Table 1, the nitrogen-doped carbon-coated nano-zinc oxide catalyst prepared in the present invention has good propylene selectivity and conversion rate. Comparing Examples 1 to 3 with Comparative Examples 1 to 2, it can be seen that since nano-zinc oxide did not participate in the chemical reaction during the catalyst preparation process and was only blended in the polyimide continuous phase, the dispersion of nano-zinc oxide was poor, and its propane conversion rate and propylene selectivity were both weaker than those of the catalysts prepared by the in-situ polycondensation reaction of modified nano-zinc oxide in the examples.

[0069] The reaction results of propane dehydrogenation with time under the action of the catalysts prepared in Example 1 and Comparative Example 2 are shown in Table 2:

[0070] The stability test results are shown in Table 2:

[0071] Table 2 Stability test results of the catalysts prepared in Example 1 and Comparative Example 2

[0072]

[0073] As can be seen from Table 2, at the same reaction time, compared with the catalyst prepared by direct blending with nano-zinc oxide, the catalyst prepared by in-situ polycondensation of modified nano-zinc oxide according to the present invention has more excellent catalytic reaction stability.

[0074] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, rather than all embodiments. People can also obtain other embodiments according to the embodiments of the present invention without creative work, and these embodiments all belong to the protection scope of the present invention.

Claims

1. A preparation method of a nitrogen-doped carbon-coated nano-zinc oxide catalyst for propane dehydrogenation to propylene, comprising the following steps: Modifying nano-zinc oxide with a primary amine-terminated silane coupling agent to obtain modified nano-zinc oxide; Carrying out an in-situ polycondensation reaction on the modified nano-zinc oxide, an organic amine monomer and an organic acid anhydride monomer in an anhydrous and oxygen-free environment to obtain a precursor; Successively curing and calcining the precursor to obtain a nitrogen-doped carbon-coated nano-zinc oxide catalyst; In the nitrogen-doped carbon-coated nano-zinc oxide catalyst, the content of nano-zinc oxide is 8-15 wt%, and the content of nitrogen-doped amorphous carbon is 85-92 wt%.

2. The preparation method according to claim 1, characterized in that, The primary amine-terminated silane coupling agent includes one or more of γ-aminopropyltrimethoxysilane, γ-aminopropylmethyldimethoxysilane, γ-aminopropyltriethoxysilane and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane; The mass of the primary amine-terminated silane coupling agent is 5-10% of the mass of nano-zinc oxide.

3. The preparation method according to claim 1 or 2, characterized in that, The temperature of the modification is 30-50 °C, and the time is 3-8 h.

4. The preparation method according to claim 1, characterized in that, The organic amine monomer includes one or more of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 1,3-bis(3-aminophenoxy)benzene and 1,4-bis(4-aminophenoxy)benzene; The organic acid anhydride monomer includes one or more of pyromellitic dianhydride and 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride; The molar ratio of the modified nano-zinc oxide, the organic acid anhydride monomer and the organic amine monomer is 1:(3-5):(1-4).

5. The preparation method according to claim 1 or 4, characterized in that, The temperature of the in-situ polycondensation reaction is 10-40 °C, and the time is 2-5 h.

6. The preparation method according to claim 1, characterized in that, The curing is programmed curing, and the programmed curing successively includes: heat preservation curing for 0.5-3 h at 60-100 °C, heat preservation curing for 0.5-3 h at a temperature greater than 100 °C and less than or equal to 150 °C, and heat preservation curing for 0.5-3 h at 200-300 °C.

7. The preparation method according to claim 1, characterized in that The temperature of the calcination is 500-700 °C, and the heat preservation time is 5-8 h.

8. The nitrogen-doped carbon-coated nano-zinc oxide catalyst prepared by the preparation method according to any one of claims 1-7, comprising nano-zinc oxide and nitrogen element-doped amorphous carbon coated on the surface of the nano-zinc oxide.

9. The nitrogen-doped carbon-coated nano-zinc oxide catalyst according to claim 8, wherein, In the nitrogen-doped carbon-coated nano-zinc oxide catalyst, the content of nano-zinc oxide is 8-15 wt%, and the content of nitrogen-doped amorphous carbon is 85-92 wt%; The particle size of the nano-zinc oxide is 10-20 nm.

10. Application of the nitrogen-doped carbon-coated nano-zinc oxide catalyst according to claim 8 or 9 in propane dehydrogenation to propylene.

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