Composite catalyst for oxidative dehydrogenation of ethane and preparation method thereof

Abstract

The application discloses a composite catalyst for ethane oxidative dehydrogenation, which comprises a molybdenum-vanadium-tellurium-niobium catalyst and a molecular sieve; the molecular sieve is a phosphorus-aluminum molecular sieve or a transition metal modified phosphorus-aluminum molecular sieve. By compounding the phosphorus-aluminum molecular sieve or the transition metal modified phosphorus-aluminum molecular sieve with the molybdenum-vanadium-tellurium-niobium catalyst, on one hand, the structure of the molecular sieve and the molybdenum-vanadium-tellurium-niobium catalyst is not damaged, and the molecular sieve and the molybdenum-vanadium-tellurium-niobium catalyst can be directly used for catalyzing ethane oxidative dehydrogenation to ethylene reaction, and the unique oxidation-reduction capacity of the molecular sieve is utilized to improve the reaction performance of the catalytic ethane oxidative dehydrogenation. On the other hand, the phosphorus-aluminum molecular sieve / transition metal modified phosphorus-aluminum molecular sieve as a diluent can play a role in dispersing and transferring reaction heat, effectively avoiding the occurrence of local high temperature in the reaction process to cause a side reaction, and then improving the ethylene selectivity and the operation stability of the catalyst.

Description

Technical Field

[0001] This invention relates to the field of ethane oxidative dehydrogenation to ethylene technology, specifically to a composite catalyst for ethane oxidative dehydrogenation and its preparation method. Background Technology

[0002] Ethylene is an important basic feedstock in the petrochemical industry, mainly produced through the traditional steam thermal cracking method. In a typical ethane steam cracking plant for ethylene production, energy costs account for approximately 70% of the production cost. Compared to high-temperature cracking, the oxidative dehydrogenation of ethane to ethylene (ODHE) technology produces a single, easily separable product with a simple separation system. It is a low-energy-consumption route with enormous application potential and has become one of the research hotspots in recent years.

[0003] The MoVNbTeOx composite metal oxide (M1 catalyst) exhibits good catalytic performance for the ODHE reaction and operates under mild conditions, generally requiring a reaction temperature below 450℃, making it a current research hotspot for the oxidative dehydrogenation of low-carbon alkanes.

[0004] For example, Chinese patent document CN 108503529 B discloses a method for preparing acrylic acid from propane. The catalyst used is a composite catalyst composed of a molybdenum-vanadium-tellurium-niobium catalyst and a stabilizer. The stabilizer is selected from at least one of SiC, Al2O3, or SiO2. The stabilizer accounts for 5%–95% by mass in the composite catalyst, preferably 20%–70%, and more preferably 30%–50%. This method uses a composite catalyst composed of molybdenum-vanadium-tellurium-niobium catalyst powder and a stabilizer. The innovative introduction of a stabilizer into the catalyst has several advantages: first, it can stabilize the catalyst under harsh reaction conditions because the stabilizer facilitates the dispersion and transfer of reaction heat, thus avoiding high hot spots inside the catalyst; second, the stabilizer itself, as a low-cost diluent, can significantly reduce the production cost of the catalyst. While the stabilizers such as SiC, Al2O3, or SiO2 added to the composite catalyst disclosed in this document reduce costs and improve catalyst stability, they have a significant negative impact on the reaction activity when used in the ODHE reaction. Summary of the Invention

[0005] In view of this, the present invention provides a composite catalyst for the oxidative dehydrogenation of ethane and its preparation method. The composite catalyst comprises a molybdenum-vanadium-tellurium-niobium catalyst (M1 catalyst) and a molecular sieve, wherein the molecular sieve is a phosphorus-aluminum molecular sieve or a transition metal-modified phosphorus-aluminum molecular sieve. This composite catalyst for the oxidative dehydrogenation of ethane utilizes the unique redox capabilities of the phosphorus-aluminum molecular sieve / transition metal-modified phosphorus-aluminum molecular sieve to improve the performance of the composite catalyst in catalyzing the oxidative dehydrogenation reaction of ethane, while also dispersing and transferring the heat of reaction.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A composite catalyst for the oxidative dehydrogenation of ethane, the composite catalyst comprising an M1 catalyst and a molecular sieve; the molecular sieve is a phosphorus-aluminum molecular sieve or a transition metal-modified phosphorus-aluminum molecular sieve.

[0008] Optionally, in the composite catalyst for ethane oxidative dehydrogenation provided by the present invention, the general formula of the M1 catalyst is MoV. a Te b Nb c Where a is 0.25–0.32, b is 0.16–0.23, and c is 0.08–0.15. By further defining the general formula of the M1 catalyst, the catalytic performance of the composite catalyst can be further improved.

[0009] Optionally, in the composite catalyst for ethane oxidative dehydrogenation provided by the present invention, the phosphorus aluminum molecule is screened from AlPO4-18.

[0010] Optionally, in the composite catalyst for ethane oxidative dehydrogenation provided by the present invention, the transition metal is selected from at least one of Mn, Fe, Ce and Co.

[0011] Optionally, in the composite catalyst for ethane oxidative dehydrogenation provided by the present invention, the content of the molybdenum-vanadium-tellurium-niobium catalyst is 70wt% to 90wt% and the content of the molecular sieve is 10wt% to 30wt%, based on the mass of the composite catalyst as 100%.

[0012] The present invention also provides a method for preparing the above-mentioned composite catalyst for ethane oxidative dehydrogenation, comprising the step of physically mixing a phosphorus aluminum molecular sieve or a transition metal modified phosphorus aluminum molecular sieve with a molybdenum vanadium tellurium niobium catalyst.

[0013] The M1 catalyst can be prepared using conventional methods in the industry, such as hydrothermal synthesis, including the following steps:

[0014] (1) Dissolve ammonium heptamolybdate tetrahydrate, ammonium metavanadate and telluric acid in deionized water to obtain the first mixed solution;

[0015] (2) Add an aqueous solution of niobium oxalate to the first mixed solution within 15 to 50 min to form a suspension. After aging, hydrothermal crystallization, drying, calcination, and removal of the M2 phase, a molybdenum-vanadium-tellurium niobium catalyst is obtained.

[0016] Optionally, in the method for preparing M1 catalyst by hydrothermal synthesis provided by the present invention, the aqueous solution of niobium oxalate is added dropwise to the first mixed solution.

[0017] In step (1) of the hydrothermal synthesis method for preparing the M1 catalyst recommended in this invention, it is sufficient to dissolve ammonium heptamolybdate tetrahydrate, ammonium metavanadate, and telluric acid in deionized water. The specific method is not limited; for example, ammonium heptamolybdate, ammonium metavanadate, and telluric acid can be added to deionized water and stirred at 70℃~100℃ for 60~180min until dissolved to form a first mixed solution. In the hydrothermal synthesis method for preparing the M1 catalyst recommended in this invention, the niobium oxalate aqueous solution is formed by adding niobium oxalate to deionized water. For example, it can be stirred at 60~90℃ for 20~60min until niobium oxalate dissolves to form an aqueous solution of niobium oxalate. The specific stirring time and stirring rate can be adjusted according to the actual situation, as long as all substances are completely dissolved and mixed evenly.

[0018] Optionally, in the method for preparing M1 catalyst via hydrothermal synthesis recommended by this invention, the aging temperature recommended by this invention is 20–90°C, and the time is 20–180 min. The hydrothermal crystallization reaction temperature recommended by this invention is 150°C–200°C; the time is 12–60 h. The drying temperature recommended by this invention is 70–120°C, and the time is 6–30 h. The calcination procedure recommended by this invention is a two-stage calcination, specifically as follows: first, calcination in air at 200–400°C for 2–6 h, and then calcination in an inert atmosphere at 550–650°C for 1–4 h. The inert atmosphere is at least one of nitrogen, argon, and helium. The method recommended by this invention for removing the M2 phase is to use 5wt% to 15wt% hydrogen peroxide and purify at 30 to 80°C for 30 to 240 minutes to remove the M2 phase; preferably, after removing the M2 phase, dry at 60 to 150°C for 5 to 18 hours.

[0019] Optionally, in the preparation method of the above-mentioned molybdenum-vanadium-tellurium-niobium catalyst provided by the present invention, the first mixed solution further includes a dispersant; preferably, the dispersant is selected from any one of propylene glycol, polymethyl cellulose, polyvinyl alcohol, guar gum, polyethylene glycol, and polyvinylpyrrolidone.

[0020] The mass ratio of ammonium heptamolybdate tetrahydrate to the dispersant is 100:0.005-0.1. By further adding the dispersant to the first mixed solution, the components such as molybdenum, vanadium, tellurium, and niobium can be dispersed and supported, improving the pore structure and specific surface area of ​​the molybdenum-vanadium-tellurium-niobium catalyst, and further enhancing the catalytic activity of the composite catalyst.

[0021] Optionally, in the preparation method of the composite catalyst for ethane oxidative dehydrogenation provided by the present invention, the preparation of the phosphorus-aluminum molecular sieve can be carried out using conventional methods in the industry. The preparation method of the phosphorus-aluminum molecular sieve recommended by the present invention includes the following steps:

[0022] An aluminum source, a phosphorus source, and a template agent are mixed to form a gel. This gel is then crystallized, filtered, washed, and dried to obtain a phosphorus-aluminum molecular sieve precursor. The precursor is then calcined to obtain the phosphorus-aluminum molecular sieve. The specific amounts of each material and the reaction parameters for each step can be adjusted according to actual conditions. For example, the mass ratio of aluminum source (calculated as oxide), phosphorus source (calculated as oxide), and template agent is 1:0.8-1.7:0.4-2.0; the crystallization temperature is 170-220℃, and the time is 5-30 hours; the drying temperature is 80-120℃, and the time is 4-10 hours; the calcination temperature is 520-600℃, and the time is 3-8 hours.

[0023] Optionally, in the preparation method of the composite catalyst for ethane oxidative dehydrogenation provided by the present invention, the preparation method of the transition metal modified phosphorus aluminum molecular sieve recommended by the present invention includes the following steps:

[0024] An aluminum source, a precursor salt of a transition metal, a phosphorus source, and a template agent are mixed to form a gel. The gel is then crystallized, dried, and calcined to obtain the transition metal-modified phosphorus-aluminum molecular sieve.

[0025] Optionally, in the preparation method of the transition metal modified phosphorus aluminum molecular sieve provided by the present invention, the precursor salt of the transition metal is selected from the nitrate or acetate of the transition metal; such as manganese acetate, cobalt nitrate hexahydrate, ferric nitrate, cerium nitrate, etc.

[0026] The molar ratio of the aluminum source to the precursor salt of the transition metal is 1 to 20, calculated as a metal oxide (the aluminum source is calculated as alumina, and the precursor salt of the transition metal is calculated as a transition metal oxide).

[0027] Optionally, in the preparation methods of the phosphorus-aluminum molecular sieve and the above-mentioned transition metal modified phosphorus-aluminum molecular sieve provided by the present invention, the aluminum source, the phosphorus source, and the template agent can be conventional in the industry, and the types of aluminum source, phosphorus source, and template agent will not affect the implementation and effect of the present invention. For example, the aluminum source can be selected from aluminum isopropoxide, boehmite, etc.; the phosphorus source is selected from 85% phosphoric acid; and the template agent can be selected from N,N-diisopropylethylamine, tri-n-propylamine, triethylamine, diisopropylamine, etc.

[0028] The composite catalyst for ethane oxidative dehydrogenation provided by this invention can catalyze the reaction under conventional ethane oxidative dehydrogenation reaction conditions. The reaction conditions recommended by this invention for ethane oxidative dehydrogenation to ethylene using the above-mentioned composite catalyst are as follows: reaction temperature 350–400°C, atmospheric pressure, and feed space velocity of the reactant gas 200–500 h⁻¹. -1 The molar ratio of ethane:oxygen:nitrogen in the reaction gas is 1:0.4-0.8:1.2-2.0.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] 1. The composite catalyst for ethane oxidative dehydrogenation provided by this invention comprises a molybdenum-vanadium-tellurium-niobium catalyst and a molecular sieve; the molecular sieve is a phosphorus-aluminum molecular sieve or a transition metal-modified phosphorus-aluminum molecular sieve. By combining the phosphorus-aluminum molecular sieve or the transition metal-modified phosphorus-aluminum molecular sieve with the molybdenum-vanadium-tellurium-niobium catalyst (physical mixing), on the one hand, the structure of the molecular sieve and the molybdenum-vanadium-tellurium-niobium catalyst is not destroyed, and both the molecular sieve and the molybdenum-vanadium-tellurium-niobium catalyst can be directly used to catalyze the ethane oxidative dehydrogenation to ethylene reaction. Simultaneously, the unique redox capabilities of the phosphorus-aluminum molecular sieve / transition metal-modified phosphorus-aluminum molecular sieve are utilized to improve the catalytic performance of the composite catalyst for ethane oxidative dehydrogenation. On the other hand, the ethane oxidative dehydrogenation to ethylene reaction is exothermic. The phosphorus-aluminum molecular sieve / transition metal-modified phosphorus-aluminum molecular sieve can act as a diluent to dilute the molybdenum-vanadium-tellurium-niobium catalyst, playing a role in dispersing and transferring the heat of reaction, effectively avoiding excessively high local temperatures during the reaction process that could trigger side reactions (avoiding excessive oxidation of the product ethylene to form carbon oxides), thereby improving ethylene selectivity and catalyst operational stability.

[0031] 2. In the preparation method of the composite catalyst for ethane oxidative dehydrogenation provided by this invention, during the preparation of the molybdenum-vanadium-tellurium-niobium catalyst, the rate at which the heteropolyacid anions formed in the initial mixed aqueous solution of Mo, V, and Te and the Nb precursor form a complex is controlled by limiting the time of addition of the niobium oxalate aqueous solution to the first mixed solution, thereby generating more active species and improving the catalyst's reactivity. The molybdenum-vanadium-tellurium-niobium catalyst prepared by this method, when combined with phosphorus aluminum molecular sieves or transition metal-modified phosphorus aluminum molecular sieves, can significantly improve the activity and stability of the composite catalyst while reducing its cost. Detailed Implementation

[0032] The present invention will now be described in detail through embodiments. It should be noted that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0033] For any experimental steps or conditions not specified in the examples and comparative examples, the procedures and conditions described in the literature in this field can be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0034] Raw material sources: All raw materials involved in the preparation of the composite catalyst in the embodiments of this invention are analytical grade (AR). The raw materials are: ammonium heptamolybdate tetrahydrate, polyethylene glycol, polyvinylpyrrolidone, polymethyl cellulose, polyvinyl alcohol, phosphoric acid, N,N-diisopropylethylamine, hydrogen peroxide, propylene glycol, manganese acetate, cobalt nitrate hexahydrate, ferric nitrate, cerium nitrate, SiC, silica sol, NaAlO2, and tetrapropylammonium bromide, which were purchased from Sinopharm Reagent Co., Ltd.; tri-n-propylamine, ammonium metavanadate, and telluric acid, which were purchased from Maclean's Reagent Co., Ltd.; and niobium oxalate, aluminum isopropoxide, and guar gum powder, which were purchased from Aladdin Reagent Co., Ltd.

[0035] Evaluation and analysis method: The catalyst was tableted and crushed, sieved to 20-40 mesh, and packed into a 10 mL fixed-bed microreactor with an inner diameter of 5 mm. The reaction was carried out at a reaction temperature of 360℃, atmospheric pressure, and a feed space velocity of 300 h⁻¹. -1 The reaction was carried out under conditions where the molar ratio of ethane:oxygen:nitrogen in the reaction gas was 1:0.6:1.5, yielding ethylene as the product. The reaction product was detected by gas chromatography.

[0036] Example 1

[0037] This embodiment provides a composite catalyst for the oxidative dehydrogenation of ethane, and its specific preparation method is as follows:

[0038] Molybdenum-vanadium-tellurium-niobium catalyst (M1 catalyst)

[0039] (1) A certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and polyvinyl alcohol are added to deionized water and heated and stirred at 80°C for 120 min to form a first mixed solution; wherein, the amount of polyvinyl alcohol added is 0.01 wt% of the mass of ammonium heptamolybdate tetrahydrate.

[0040] (2) Add a certain amount of niobium oxalate to deionized water and heat and stir at 80°C for 30 min to form a second mixed solution;

[0041] (3) The second mixed solution was added dropwise to the first mixed solution to form a suspension (added over 20 min). After aging at 80°C for 180 min, the suspension was transferred to a hydrothermal synthesis reactor and hydrothermally crystallized at 175°C for 48 h, followed by drying at 80°C for 20 h. The catalyst was then calcined at 300°C in air for 3 h, and then calcined at 600°C in helium for 2 h to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst was then purified in 7.5 wt% hydrogen peroxide to remove the M2 phase. After heating and stirring at 60°C for 180 min, the solution was filtered and finally dried at 120°C for 12 h to obtain the M1 catalyst, with a composition of MoV1. 0.3 Te 0.18 Nb 0.12 .

[0042] AlPO4-18 molecular sieve (using hydrothermal crystallization method)

[0043] Phosphoric acid was diluted with distilled water, and aluminum isopropoxide was added under vigorous stirring and stirred continuously for 1 hour. Then, N,N-diisopropylethylamine (DIPEA) was added and stirring was continued for 48 hours to form a homogeneous gel. The gel composition was: n(Al2O3):n(P2O5):n(DIPEA):n(H2O) = 1:1:1:50. The gel was crystallized in a crystallization vessel at 180℃ for 20 days, filtered, washed with distilled water, and dried in a constant temperature oven at 100℃ for 6 hours to obtain a molecular sieve precursor. The molecular sieve precursor was calcined at 250℃ for 1 hour, and then calcined at 550℃ for 5 hours to obtain a mesoporous AlPO4-18 molecular sieve.

[0044] Composite catalyst

[0045] After mixing 0.90g of the above molybdenum-vanadium-tellurium-niobium catalyst with 0.10g of the above AlPO4-18 phosphorus-aluminum molecular sieve, the mixture was loaded into a fixed-bed microreactor. Ethane, oxygen and nitrogen were introduced to carry out the ethane oxidative dehydrogenation to ethylene reaction according to the above evaluation method. The activity evaluation results are shown in Table 1.

[0046] Example 2

[0047] This embodiment provides a composite catalyst for the oxidative dehydrogenation of ethane, and its specific preparation method is as follows:

[0048] Molybdenum-vanadium-tellurium-niobium catalyst (M1 catalyst)

[0049] (1) A certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and guar gum powder were added to deionized water and heated and stirred at 90°C for 100 min to form a first mixed solution; wherein, the amount of guar gum powder added was 0.008 wt% of the mass of ammonium heptamolybdate tetrahydrate.

[0050] (2) Add a certain amount of niobium oxalate to deionized water and heat and stir at 90°C for 20 min to form a second mixed solution;

[0051] (3) The second mixed solution was added dropwise to the first mixed solution to form a suspension (added over 25 min). After aging at 90°C for 20 min, the suspension was transferred to a hydrothermal synthesis reactor and hydrothermally crystallized at 180°C for 24 h, followed by drying at 100°C for 10 h. The catalyst was then calcined at 280°C in air for 4 h, and then calcined at 570°C in helium for 2.5 h to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst was then purified in 10.0 wt% hydrogen peroxide to remove the M2 phase. After heating and stirring at 70°C for 120 min, the solution was filtered and finally dried at 120°C for 6 h to obtain the M1 catalyst, with a composition of MoV. 0.3 Te 0.20 Nb0.10 .

[0052] CoAlPO4-18 molecular sieve:

[0053] Aluminum isopropoxide, cobalt nitrate hexahydrate, phosphoric acid, and tri-n-propylamine were added to a reaction vessel in a molar ratio of n(Al2O3):n(CoO):n(P2O5):n(TPrA):n(H2O) = 0.9:0.1:0.8:1:50 and mixed thoroughly. The mixture was then aged at 90°C for 2 hours to form a homogeneous gel. The gel was then stirred and crystallized at 200°C for 24 hours. The resulting solid was washed with deionized water until neutral, dried in an oven at 80°C for 10 hours, and calcined in a muffle furnace at 520°C for 6 hours to obtain CoAlPO4-18 molecular sieve.

[0054] Composite catalyst

[0055] After mixing 0.70g of the above molybdenum-vanadium-tellurium-niobium catalyst and 0.30g of CoAlPO4-18 molecular sieve evenly, the mixture was loaded into a fixed-bed microreactor. Ethane, oxygen and nitrogen were introduced to carry out the ethane oxidative dehydrogenation to ethylene reaction according to the evaluation method described above. The activity evaluation results are shown in Table 1.

[0056] Example 3

[0057] This embodiment provides a composite catalyst for the oxidative dehydrogenation of ethane, and its specific preparation method is as follows:

[0058] Molybdenum-vanadium-tellurium-niobium catalyst (M1 catalyst)

[0059] (1) A certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and polyethylene glycol are added to deionized water and heated and stirred at 70°C for 180 min to form a first mixed solution; wherein, the amount of polyethylene glycol added is 0.015 wt% of the mass of ammonium heptamolybdate tetrahydrate.

[0060] (2) Add a certain amount of niobium oxalate to deionized water and heat and stir at 60°C for 60 min to form a second mixed solution;

[0061] (3) The second mixed solution was added dropwise to the first mixed solution to form a suspension (added over 30 min). After aging at 40°C for 180 min, the suspension was transferred to a hydrothermal synthesis reactor and hydrothermally crystallized at 200°C for 20 h, followed by drying at 90°C for 15 h. The catalyst was then calcined at 260°C for 5 h in air and then calcined at 650°C for 2 h in nitrogen to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst was then purified in 8.0 wt% hydrogen peroxide to remove the M2 phase. After heating and stirring at 50°C for 60 min, the solution was filtered and finally dried at 100°C for 12 h to obtain the M1 catalyst, with a composition of MoV1. 0.28 Te 0.18Nb 0.13 .

[0062] MnAlPO4-18 molecular sieve:

[0063] Aluminum isopropoxide, manganese acetate, phosphoric acid, and N,N-diisopropylethylamine were added to a reaction vessel in a molar ratio of n(Al2O3):n(MnO):n(P2O5):n(DIPEA):n(H2O) = 0.9:0.1:1.2:0.8:50. After mixing thoroughly, the mixture was aged at 80°C for 2 hours to form a homogeneous gel. The gel was then stirred and crystallized at 190°C for 15 hours. The resulting solid was washed with deionized water until neutral, dried in a constant temperature oven at 90°C for 8 hours, and calcined in a muffle furnace at 550°C for 6 hours to obtain MnAlPO4-18 molecular sieve.

[0064] Composite catalyst

[0065] After thoroughly mixing 0.85g of the above-mentioned molybdenum-vanadium-tellurium-niobium catalyst and 0.15g of MnAlPO4-18 molecular sieve, the mixture was loaded into a fixed-bed microreactor. Ethane, oxygen, and nitrogen were introduced to carry out the ethane oxidative dehydrogenation to ethylene reaction according to the evaluation method described above. The activity evaluation results are shown in Table 1.

[0066] Example 4

[0067] This embodiment provides a composite catalyst for the oxidative dehydrogenation of ethane, and its specific preparation method is as follows:

[0068] Molybdenum-vanadium-tellurium-niobium catalyst (M1 catalyst)

[0069] (1) A certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and propylene glycol are added to deionized water and heated and stirred at 100°C for 60 min to form a first mixed solution; wherein, the amount of propylene glycol added is 0.02 wt% of the mass of ammonium heptamolybdate tetrahydrate.

[0070] (2) Add a certain amount of niobium oxalate to deionized water and heat and stir at 70°C for 40 min to form a second mixed solution;

[0071] (3) The second mixed solution was added dropwise to the first mixed solution to form a suspension (added over 40 min). After aging at 70°C for 120 min, it was transferred to a hydrothermal synthesis reactor and hydrothermally crystallized at 180°C for 50 h, then dried at 100°C for 15 h. Afterward, it was calcined at 350°C in air for 3 h, and then calcined at 550°C in argon for 3 h to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst was then purified in 7.0 wt% hydrogen peroxide to remove the M2 phase. After heating and stirring at 60°C for 120 min, it was filtered and finally dried at 150°C for 5 h to obtain the M1 catalyst with the composition MoV. 0.32 Te0.16 Nb 0.15 .

[0072] FeAlPO4-18 molecular sieve:

[0073] Aluminum isopropoxide, ferric nitrate, phosphoric acid, and N,N-diisopropylethylamine were added to a reaction vessel in a molar ratio of n(Al2O3):n(FeO):n(P2O5):n(DIPEA):n(H2O) = 0.92:0.08:1.5:1.2:50. After mixing thoroughly, the mixture was aged at 80°C for 2 hours to form a homogeneous gel. The gel was then stirred and crystallized at 200°C for 10 hours. The resulting solid was washed with deionized water until neutral, dried in a constant temperature oven at 100°C for 5 hours, and calcined in a muffle furnace at 580°C for 4 hours to obtain FeAlPO4-18 molecular sieve.

[0074] Composite catalyst

[0075] After thoroughly mixing 0.75g of the above-mentioned molybdenum-vanadium-tellurium-niobium catalyst and 0.25g of FeAlPO4-18 molecular sieve, the mixture was loaded into a fixed-bed microreactor. Ethane, oxygen, and nitrogen were introduced according to the evaluation method described above to carry out the ethane oxidative dehydrogenation to ethylene reaction. The activity evaluation results are shown in Table 1.

[0076] Example 5

[0077] This embodiment provides a composite catalyst for the oxidative dehydrogenation of ethane, and its specific preparation method is as follows:

[0078] Molybdenum-vanadium-tellurium-niobium catalyst (M1 catalyst)

[0079] (1) A certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and guar gum powder were added to deionized water and heated and stirred at 80°C for 90 min to form a first mixed solution; wherein, the amount of guar gum powder added was 0.08 wt% of the mass of ammonium heptamolybdate tetrahydrate.

[0080] (2) Add a certain amount of niobium oxalate to deionized water and heat and stir at 80°C for 25 min to form a second mixed solution;

[0081] (3) The second mixed solution was added dropwise to the first mixed solution to form a suspension (added over 25 min). After aging at 80°C for 100 min, the suspension was transferred to a hydrothermal synthesis reactor and hydrothermally crystallized at 170°C for 36 h, followed by drying at 120°C for 6 h. The catalyst was then calcined at 200°C in air for 6 h, and then calcined at 580°C in helium for 1 h to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst was then purified in 15.0 wt% hydrogen peroxide to remove the M2 phase. After heating and stirring at 70°C for 150 min, the solution was filtered and finally dried at 120°C for 10 h to obtain the M1 catalyst, with a composition of MoV1.0.25 Te 0.23 Nb 0.10 .

[0082] CeAlPO4-18 molecular sieve:

[0083] Aluminum isopropoxide, cerium nitrate, phosphoric acid, and N,N-diisopropylethylamine were added to a reaction vessel in a molar ratio of n(Al2O3):n(CeO):n(P2O5):n(DIPEA):n(H2O) = 0.92:0.08:1:0.6:50. After mixing thoroughly, the mixture was aged at 80°C for 2 hours to form a homogeneous gel. The gel was then stirred and crystallized at 220°C for 5 hours. The resulting solid was washed with deionized water until neutral, dried in an oven at 80°C for 8 hours, and calcined in a muffle furnace at 550°C for 5 hours to obtain CeAlPO4-18 molecular sieve.

[0084] Composite catalyst

[0085] After thoroughly mixing 0.75g of the above-mentioned molybdenum-vanadium-tellurium-niobium catalyst and 0.25g of CeAlPO4-18 molecular sieve, the mixture was loaded into a fixed-bed microreactor. Ethane, oxygen, and nitrogen were introduced to carry out the ethane oxidative dehydrogenation to ethylene reaction according to the evaluation method described above. The activity evaluation results are shown in Table 1.

[0086] Example 6

[0087] This embodiment provides a composite catalyst for the oxidative dehydrogenation of ethane, and its specific preparation method is as follows:

[0088] Molybdenum-vanadium-tellurium-niobium catalyst (M1 catalyst)

[0089] (1) A certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and polyvinylpyrrolidone were added to deionized water and heated and stirred at 75°C for 150 min to form a first mixed solution; wherein, the amount of polyvinylpyrrolidone added was 0.1 wt% of the mass of ammonium heptamolybdate tetrahydrate.

[0090] (2) Add a certain amount of niobium oxalate to deionized water and heat and stir at 75°C for 50 min to form a second mixed solution;

[0091] (3) The second mixed solution was added dropwise to the first mixed solution to form a suspension (added over 50 min). After aging at 20°C for 150 min, the suspension was transferred to a hydrothermal synthesis reactor and hydrothermally crystallized at 190°C for 60 h, followed by drying at 80°C for 18 h. The catalyst was then calcined at 320°C in air for 2 h, and then calcined at 600°C in nitrogen for 2.5 h to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst was then purified in 12.0 wt% hydrogen peroxide to remove the M2 phase. After heating and stirring at 80°C for 30 min, the solution was filtered and finally dried at 60°C for 15 h to obtain the M1 catalyst, with a composition of MoV1. 0.32 Te 0.21 Nb 0.08 .

[0092] MnAlPO4-18 molecular sieve:

[0093] Aluminum isopropoxide, manganese acetate, phosphoric acid, and N,N-diisopropylethylamine were added to a reaction vessel in a molar ratio of n(Al2O3):n(MnO):n(P2O5):n(DIPEA):n(H2O) = 0.85:0.15:0.8:0.4:50. After mixing thoroughly, the mixture was aged at 60°C for 2 hours to form a homogeneous gel. The gel was then stirred and crystallized at 180°C for 12 hours. The resulting solid was washed with deionized water until neutral, dried in a constant temperature oven at 120°C for 3 hours, and calcined in a muffle furnace at 575°C for 6 hours to obtain MnAlPO4-18 molecular sieve.

[0094] Composite catalyst

[0095] After thoroughly mixing 0.80 g of the above-mentioned molybdenum-vanadium-tellurium-niobium catalyst and 0.20 g of MnAlPO4-18 molecular sieve, the mixture was loaded into a fixed-bed microreactor. Ethane, oxygen, and nitrogen were introduced to carry out the ethane oxidative dehydrogenation to ethylene reaction according to the evaluation method described above. The activity evaluation results are shown in Table 1.

[0096] Example 7

[0097] This embodiment provides a composite catalyst for the oxidative dehydrogenation of ethane, and its specific preparation method is as follows:

[0098] Molybdenum-vanadium-tellurium-niobium catalyst (M1 catalyst)

[0099] (1) A certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and polyvinylpyrrolidone were added to deionized water and heated and stirred at 90°C for 90 min to form a first mixed solution; wherein, the amount of polyvinylpyrrolidone added was 0.06 wt% of the mass of ammonium heptamolybdate tetrahydrate.

[0100] (2) Add a certain amount of niobium oxalate to deionized water and heat and stir at 90°C for 30 min to form a second mixed solution;

[0101] (3) The second mixed solution was added dropwise to the first mixed solution to form a suspension (added completely over 35 min). After aging at 60°C for 90 min, the suspension was transferred to a hydrothermal synthesis reactor and hydrothermally crystallized at 150°C for 30 h, followed by drying at 70°C for 20 h. The catalyst was then calcined at 400°C in air for 3 h, and then calcined at 600°C in helium for 3 h to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst was then purified in 5.0 wt% hydrogen peroxide to remove the M2 phase. After heating and stirring at 30°C for 90 min, the solution was filtered and finally dried at 70°C for 8 h to obtain the M1 catalyst, with a composition of MoV1. 0.25 Te 0.20 Nb 0.08 .

[0102] CeAlPO4-18 molecular sieve:

[0103] Aluminum isopropoxide, cerium nitrate, phosphoric acid, and N,N-diisopropylethylamine were added to a reaction vessel in a molar ratio of n(Al2O3):n(CeO):n(P2O5):n(DIPEA):n(H2O) = 0.8:0.2:1:1.5:50. After mixing thoroughly, the mixture was aged at 90°C for 2 hours to form a homogeneous gel. The gel was then stirred and crystallized at 170°C for 20 hours. The resulting solid was washed with deionized water until neutral, dried in a constant temperature oven at 90°C for 10 hours, and calcined in a muffle furnace at 560°C for 4 hours to obtain CeAlPO4-18 molecular sieve.

[0104] Composite catalyst

[0105] After thoroughly mixing 0.80 g of the above-mentioned molybdenum-vanadium-tellurium-niobium catalyst and 0.20 g of CeAlPO4-18 molecular sieve, the mixture was loaded into a fixed-bed microreactor. Ethane, oxygen, and nitrogen were introduced to carry out the ethane oxidative dehydrogenation to ethylene reaction according to the evaluation method described above. The activity evaluation results are shown in Table 1.

[0106] Example 8

[0107] This embodiment provides a composite catalyst for the oxidative dehydrogenation of ethane, and its specific preparation method is as follows:

[0108] Molybdenum-vanadium-tellurium-niobium catalyst (M1 catalyst)

[0109] (1) A certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and polymethylcellulose were added to deionized water and heated and stirred at 80°C for 120 min to form a first mixed solution; wherein, the amount of polymethylcellulose added was 0.05 wt% of the mass of ammonium heptamolybdate tetrahydrate.

[0110] (2) Add a certain amount of niobium oxalate to deionized water and heat and stir at 80°C for 30 min to form a second mixed solution;

[0111] (3) The second mixed solution was added dropwise to the first mixed solution to form a suspension (added completely over 35 min). After aging at 80°C for 60 min, the suspension was transferred to a hydrothermal synthesis reactor and hydrothermally crystallized at 175°C for 24 h, followed by drying at 100°C for 10 h. The catalyst was then calcined at 300°C for 4 h in air and then calcined at 620°C for 2 h in nitrogen to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst was then purified in 8.0 wt% hydrogen peroxide to remove the M2 phase. After heating and stirring at 60°C for 180 min, the solution was filtered and finally dried at 80°C for 10 h to obtain the M1 catalyst, with a composition of MoV1. 0.30 Te 0.18 Nb 0.10 .

[0112] CeAlPO4-18 molecular sieve:

[0113] Aluminum isopropoxide, cerium nitrate, phosphoric acid, and N,N-diisopropylethylamine were added to a reaction vessel in a molar ratio of n(Al2O3):n(CeO):n(P2O5):n(DIPEA):n(H2O) = 0.95:0.05:1.2:1.2:50. After mixing thoroughly, the mixture was aged at 70°C for 2 hours to form a homogeneous gel. The gel was then stirred and crystallized at 170°C for 24 hours. The resulting solid was washed with deionized water until neutral, dried in an oven at 80°C for 6 hours, and calcined in a muffle furnace at 570°C for 5 hours to obtain CeAlPO4-18 molecular sieve.

[0114] Composite catalyst

[0115] After thoroughly mixing 0.875g of the above-mentioned molybdenum-vanadium-tellurium-niobium catalyst and 0.125g of CeAlPO4-18 molecular sieve, the mixture was loaded into a fixed-bed microreactor. Ethane, oxygen, and nitrogen were introduced to carry out the ethane oxidative dehydrogenation to ethylene reaction according to the evaluation method described above. The activity evaluation results are shown in Table 1.

[0116] Example 9

[0117] This embodiment provides a composite catalyst for the oxidative dehydrogenation of ethane, and its specific preparation method is as follows:

[0118] Molybdenum-vanadium-tellurium-niobium catalyst (M1 catalyst)

[0119] (1) A certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and polymethylcellulose were added to deionized water and heated and stirred at 85°C for 150 min to form a first mixed solution; wherein, the amount of polymethylcellulose added was 0.03 wt% of the mass of ammonium heptamolybdate tetrahydrate.

[0120] (2) Add a certain amount of niobium oxalate to deionized water and heat and stir at 85°C for 30 min to form a second mixed solution;

[0121] (3) The second mixed solution was added dropwise to the first mixed solution to form a precipitate (added over 40 min). After aging at 85°C for 90 min, the precipitate was transferred to a hydrothermal synthesis reactor and hydrothermally crystallized at 185°C for 22 h, followed by drying at 100°C for 10 h. The catalyst was then calcined at 350°C in air for 3 h, and then calcined at 590°C in helium for 2.5 h to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst was then purified in 8.5 wt% hydrogen peroxide to remove the M2 phase. After heating and stirring at 65°C for 240 min, the catalyst was filtered and finally dried at 70°C for 18 h to obtain the M1 catalyst, with a composition of MoV1. 0.30 Te 0.18 Nb 0.10 .

[0122] Co-CeAlPO4-18 molecular sieve

[0123] Aluminum isopropoxide, cerium nitrate, cobalt nitrate hexahydrate, phosphoric acid, and N,N-diisopropylethylamine were added to a reaction vessel in a molar ratio of n(Al₂O₃):n(CeO):n(CoO):n(P₂O₅):n(DIPEA):n(H₂O) = 0.85:0.1:0.05:1.3:1:50. After being mixed evenly, the mixture was aged at 80°C for 2 hours to form a homogeneous gel. The gel was then stirred and crystallized at 200°C for 24 hours. The resulting solid was washed with deionized water until neutral, dried in an oven at 80°C for 6 hours, and calcined in a muffle furnace at 550°C for 6 hours to obtain Co-CeAlPO₄-18 molecular sieve.

[0124] Composite catalyst

[0125] After thoroughly mixing 0.85g of the above-mentioned molybdenum-vanadium-tellurium-niobium catalyst and 0.15g of Co-CeAlPO4-18 molecular sieve, the mixture was loaded into a fixed-bed microreactor. Ethane, oxygen, and nitrogen were introduced to carry out the ethane oxidative dehydrogenation to ethylene reaction according to the evaluation method described above. The activity evaluation results are shown in Table 1.

[0126] Example 10

[0127] This embodiment provides a composite catalyst for the oxidative dehydrogenation of ethane, and its specific preparation method is as follows:

[0128] Molybdenum-vanadium-tellurium-niobium catalyst (M1 catalyst)

[0129] (1) A certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and propylene glycol are added to deionized water and heated and stirred at 75°C for 100 min to form a first mixed solution; wherein, the amount of propylene glycol added is 0.005 wt% of the mass of ammonium heptamolybdate tetrahydrate.

[0130] (2) Add a certain amount of niobium oxalate to deionized water and heat and stir at 75°C for 30 min to form a second mixed solution;

[0131] (3) The second mixed solution was added dropwise to the first mixed solution to form a precipitate (added over 15 min). After aging at 75°C for 60 min, the precipitate was transferred to a hydrothermal synthesis reactor and hydrothermally crystallized at 165°C for 20 h, followed by drying at 90°C for 25 h. The precipitate was then calcined at 380°C in air for 3.5 h, and then calcined at 600°C in nitrogen for 3.5 h to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst was then purified in 7.5 wt% hydrogen peroxide to remove the M2 phase. After heating and stirring at 60°C for 100 min, the catalyst was filtered and finally dried at 80°C for 14 h to obtain the M1 catalyst, with a composition of MoV1. 0.32 Te 0.18 Nb 0.13 .

[0132] Co-MnAlPO4-18 molecular sieve: Aluminum isopropoxide, manganese acetate, cobalt nitrate hexahydrate, phosphoric acid, and N,N-diisopropylethylamine were added to a reaction vessel in a molar ratio of n(Al2O3):n(MnO):n(CoO):n(P2O5):n(DIPEA):n(H2O) = 0.90:0.08:0.02:1.7:1:50 and mixed thoroughly. The mixture was then aged at 70°C for 2 hours to form a homogeneous gel. The gel was then stirred and crystallized at 200°C for 24 hours. The resulting solid was washed with deionized water until neutral. The separated solid was dried in an 80°C oven for 6 hours and then calcined in a muffle furnace at 550°C for 6 hours to obtain Co-MnAlPO4-18 molecular sieve.

[0133] Composite catalyst

[0134] After thoroughly mixing 0.9 g of the above-mentioned molybdenum-vanadium-tellurium-niobium catalyst and 0.1 g of Co-MnAlPO4-18 molecular sieve, the mixture was loaded into a fixed-bed microreactor. Ethane, oxygen, and nitrogen were introduced to carry out the ethane oxidative dehydrogenation to ethylene reaction according to the evaluation method described above. The activity evaluation results are shown in Table 1.

[0135] Example 11

[0136] This embodiment provides a composite catalyst for the oxidative dehydrogenation of ethane, and its specific preparation method is as follows:

[0137] Molybdenum-vanadium-tellurium-niobium catalyst (M1 catalyst)

[0138] (1) A certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and guar gum powder were added to deionized water and heated and stirred at 80°C for 150 min to form a first mixed solution; wherein, the amount of guar gum powder added was 0.02 wt% of the mass of ammonium heptamolybdate tetrahydrate.

[0139] (2) Add a certain amount of niobium oxalate to deionized water and heat and stir at 80°C for 40 min to form a second mixed solution;

[0140] (3) The second mixed solution was added dropwise to the first mixed solution to form a precipitate (added completely over 30 min). After aging at 80°C for 100 min, the precipitate was transferred to a hydrothermal synthesis reactor and hydrothermally crystallized at 175°C for 30 h, followed by drying at 120°C for 10 h. The precipitate was then calcined at 340°C in air for 4.5 h, and then calcined at 620°C in nitrogen for 2 h to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst was then purified in 10.0 wt% hydrogen peroxide to remove the M2 phase. After heating and stirring at 75°C for 200 min, the catalyst was filtered and finally dried at 80°C for 10 h to obtain the M1 catalyst, with a composition of MoV1. 0.28 Te 0.18 Nb 0.12 .

[0141] Mn-CeAlPO4-18 molecular sieve: Aluminum isopropoxide, manganese acetate, cerium nitrate, phosphoric acid, and N,N-diisopropylethylamine were added to a reaction vessel in a molar ratio of n(Al2O3):n(MnO):n(CeO):n(P2O5):n(DIPEA):n(H2O) = 0.9:0.05:0.05:1:1:50. After mixing, the mixture was aged at 60℃ for 2 hours to form a homogeneous gel. The gel was then stirred and crystallized at 200℃ for 24 hours. The resulting solid was washed with deionized water until neutral, dried in an oven at 80℃ for 6 hours, and calcined in a muffle furnace at 550℃ for 6 hours to obtain Mn-CeAlPO4-18 molecular sieve.

[0142] Composite catalyst

[0143] After thoroughly mixing 0.85g of the above-mentioned molybdenum-vanadium-tellurium-niobium catalyst and 0.15g of Mn-CeAlPO4-18 molecular sieve, the mixture was loaded into a fixed-bed microreactor. Ethane, oxygen, and nitrogen were introduced to carry out the ethane oxidative dehydrogenation to ethylene reaction according to the evaluation method described above. The activity evaluation results are shown in Table 1.

[0144] Example 12

[0145] This embodiment provides a composite catalyst for the oxidative dehydrogenation of ethane, and its specific preparation method is as follows:

[0146] Molybdenum-vanadium-tellurium-niobium catalyst (M1 catalyst)

[0147] (1) Add a certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate and telluric acid to deionized water, and heat and stir at 80°C for 120 min to form the first mixed solution;

[0148] (2) Add a certain amount of niobium oxalate to deionized water and heat and stir at 80°C for 30 min to form a second mixed solution;

[0149] (3) The second mixed solution was added to the first mixed solution to form a precipitate (the second mixed solution was added in batches, all within 35 minutes). After aging at 80°C for 60 minutes, the precipitate was transferred to a hydrothermal synthesis reactor and hydrothermally crystallized at 175°C for 24 hours, followed by drying at 100°C for 10 hours. Then, it was calcined at 300°C in air for 3 hours, and then calcined at 620°C in helium for 2 hours to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst was then purified in 8.0 wt% hydrogen peroxide to remove the M2 phase. After heating and stirring at 60°C for 180 minutes, the catalyst was filtered and finally dried at 80°C for 10 hours to obtain the M1 catalyst, with a composition of MoV. 0.30 Te 0.18 Nb 0.10 .

[0150] CeAlPO4-18 molecular sieve:

[0151] Aluminum isopropoxide, cerium nitrate, phosphoric acid, and N,N-diisopropylethylamine were added to a reaction vessel in a molar ratio of n(Al2O3):n(CeO):n(P2O5):n(DIPEA):n(H2O) = 0.95:0.05:1:1:50. After mixing thoroughly, the mixture was aged at 70°C for 2 hours to form a homogeneous gel. The gel was then stirred and crystallized at 170°C for 24 hours. The resulting solid was washed with deionized water until neutral. The separated solid was dried in an oven at 80°C for 6 hours and then calcined in a muffle furnace at 570°C for 5 hours to obtain CeAlPO4-18 molecular sieve.

[0152] Composite catalyst

[0153] After thoroughly mixing 0.875g of the above-mentioned molybdenum-vanadium-tellurium-niobium catalyst and 0.125g of CeAlPO4-18 molecular sieve, the mixture was loaded into a fixed-bed microreactor. Ethane, oxygen, and nitrogen were introduced to carry out the ethane oxidative dehydrogenation to ethylene reaction according to the evaluation method described above. The activity evaluation results are shown in Table 1.

[0154] Comparative Example 1

[0155] This comparative example provides a catalyst (M1 catalyst) for the oxidative dehydrogenation of ethane, and its specific preparation method is as follows:

[0156] (1) A certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and guar gum powder were added to deionized water and heated and stirred at 80°C for 150 min to form a first mixed solution; wherein, the amount of guar gum powder added was 0.02 wt% of the mass of ammonium heptamolybdate tetrahydrate.

[0157] (2) Add a certain amount of niobium oxalate to deionized water and heat and stir at 80°C for 40 min to form a second mixed solution;

[0158] (3) The second mixed solution was added to the first mixed solution to form a precipitate (dropping time was 30 min). After aging at 80 °C for 100 min, the precipitate was transferred to a hydrothermal synthesis reactor and hydrothermally crystallized at 175 °C for 30 h, followed by drying at 120 °C for 10 h. The precipitate was then calcined at 340 °C for 4.5 h in air, followed by calcination at 620 °C for 2 h in nitrogen to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst was then purified in 10 wt% hydrogen peroxide to remove the M2 phase. After heating and stirring at 75 °C for 200 min, the catalyst was filtered and finally dried at 80 °C for 10 h to obtain the M1 catalyst, with a composition of MoV1. 0.28 Te 0.18 Nb 0.12 .

[0159] 1.0 g of the above-mentioned molybdenum-vanadium-tellurium-niobium catalyst was loaded into a fixed-bed microreactor, and ethane, oxygen, and nitrogen were introduced to carry out the ethane oxidative dehydrogenation to ethylene reaction according to the evaluation method described above. The activity evaluation results are shown in Table 1.

[0160] Comparative Example 2

[0161] This comparative example provides a catalyst (Mn-CeAlPO4-18 molecular sieve) for the oxidative dehydrogenation of ethane, and its specific preparation method is as follows:

[0162] Aluminum isopropoxide, manganese acetate, cerium nitrate, phosphoric acid, and N,N-diisopropylethylamine were added to a reaction vessel in a molar ratio of n(Al₂O₃):n(MnO):n(CeO):n(P₂O₅):n(DIPEA):n(H₂O) = 0.9:0.05:0.05:1:1:50. After being mixed evenly, the mixture was aged at 60°C for 2 hours to form a homogeneous gel. The gel was then stirred and crystallized at 200°C for 24 hours. The resulting solid was washed with deionized water until neutral, dried in an oven at 80°C for 6 hours, and calcined in a muffle furnace at 550°C for 6 hours to obtain Mn-CeAlPO₄-18 molecular sieve.

[0163] 1.0 g of the above-mentioned Mn-CeAlPO4-18 molecular sieve was loaded into a fixed-bed microreactor, and ethane, oxygen, and nitrogen were introduced to carry out the ethane oxidative dehydrogenation to ethylene reaction according to the evaluation method described above. The activity evaluation results are shown in Table 1.

[0164] Comparative Example 3

[0165] The composite catalyst for ethane oxidative dehydrogenation provided in this comparative example is similar to that in Example 1, except that a different molecular sieve is used. The specific preparation method of the composite catalyst for ethane oxidative dehydrogenation provided in this comparative example is as follows:

[0166] Molybdenum vanadium tellurium niobium catalyst (M1 catalyst): Same as in Example 1;

[0167] ZSM-5 molecular sieves were prepared according to the following steps:

[0168] An in-situ hydrothermal synthesis method was adopted, using silica sol as the silicon source, NaAlO2 as the aluminum source, and TPABr (tetrapropylammonium bromide) as the template agent, with the addition of NaOH and deionized water. The material ratio was n(SiO2):n(Al2O3):n(TPABr):n(NaOH):n(H2O) = 1:0.003:0.05:0.01:5. After stirring for 4 hours, the gel was transferred to a crystallization vessel and crystallized at 160℃ for 48 hours. The product was filtered, washed until neutral, dried at 120℃ for 12 hours, and calcined at 550℃ for 6 hours to obtain Na-type ZSM-5 molecular sieve. Na-type ZSM-5 molecular sieve was treated with 1 mol / L NH4Cl solution (liquid-to-solid mass ratio 20) at 85℃ for 2 h, followed by washing, drying (drying at 120℃ for 12 h) and calcination (calcination at 550℃ for 6 h), and the process was repeated 3 times to obtain H-type ZSM-5 molecular sieve.

[0169] Composite catalyst

[0170] After mixing 0.90g of the above molybdenum-vanadium-tellurium-niobium catalyst with 0.10g of the above ZSM-5 molecular sieve, the mixture was loaded into a fixed-bed microreactor. Ethane, oxygen and nitrogen were introduced to carry out the ethane oxidative dehydrogenation to ethylene reaction according to the above evaluation method. The activity evaluation results are shown in Table 1.

[0171] Comparative Example 4

[0172] The composite catalyst for ethane oxidative dehydrogenation provided in this comparative example is similar to that in Example 11, except that silicon carbide is used instead of molecular sieve in this comparative example. The specific preparation method of the composite catalyst for ethane oxidative dehydrogenation provided in this comparative example is as follows:

[0173] Molybdenum-vanadium-tellurium-niobium catalyst (M1 catalyst): Same as in Example 11.

[0174] Composite catalyst

[0175] 0.85g of the above-mentioned molybdenum-vanadium-tellurium-niobium catalyst and 0.15g of commercially available SiC were mixed evenly and then loaded into a fixed-bed microreactor. Ethane, oxygen, and nitrogen were introduced to carry out the ethane oxidative dehydrogenation to ethylene reaction according to the evaluation method described above. The activity evaluation results are shown in Table 1.

[0176] Comparative Example 5

[0177] The composite catalyst for oxidative dehydrogenation of ethane provided in this comparative example is similar to that in Example 8, except that the addition time of the niobium oxalate solution is different. The specific preparation method of the composite catalyst for oxidative dehydrogenation of ethane provided in this comparative example is as follows:

[0178] Molybdenum-vanadium-tellurium-niobium catalyst (M1 catalyst)

[0179] (1) A certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and polymethylcellulose were added to deionized water and heated and stirred at 80°C for 120 min to form a first mixed solution; wherein, the amount of polymethylcellulose added was 0.05 wt% of the mass of ammonium heptamolybdate tetrahydrate.

[0180] (2) Add a certain amount of niobium oxalate to deionized water and heat and stir at 80°C for 30 min to form a second mixed solution;

[0181] (3) The second mixed solution was added dropwise to the first mixed solution to form a suspension (added over 5 min). After aging at 80°C for 60 min, the suspension was transferred to a hydrothermal synthesis reactor and hydrothermally crystallized at 175°C for 24 h, followed by drying at 100°C for 10 h. The catalyst was then calcined at 300°C in air for 4 h, and then calcined at 620°C in nitrogen for 2 h to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst was then purified in 8.0 wt% hydrogen peroxide to remove the M2 phase. After heating and stirring at 60°C for 180 min, the solution was filtered and finally dried at 80°C for 10 h to obtain the M1 catalyst, with a composition of MoV1. 0.30 Te 0.18 Nb 0.10 .

[0182] CeAlPO4-18 molecular sieve:

[0183] Aluminum isopropoxide, cerium nitrate, phosphoric acid, and N,N-diisopropylethylamine were added to a reaction vessel in a molar ratio of n(Al2O3):n(CeO):n(P2O5):n(DIPEA):n(H2O) = 0.95:0.05:1:1.2:50. After mixing thoroughly, the mixture was aged at 70°C for 2 hours to form a homogeneous gel. The gel was then stirred and crystallized at 170°C for 24 hours. The resulting solid was washed with deionized water until neutral, dried in an oven at 80°C for 6 hours, and calcined in a muffle furnace at 570°C for 5 hours to obtain CeAlPO4-18 molecular sieve.

[0184] Composite catalyst

[0185] After thoroughly mixing 0.875g of the above-mentioned molybdenum-vanadium-tellurium-niobium catalyst and 0.125g of CeAlPO4-18 molecular sieve, the mixture was loaded into a fixed-bed microreactor. Ethane, oxygen, and nitrogen were introduced to carry out the ethane oxidative dehydrogenation to ethylene reaction according to the evaluation method described above. The activity evaluation results are shown in Table 1.

[0186] The catalyst evaluation results are shown in the table below.

[0187] Table 1

[0188]

[0189] As can be seen from the data in the table above, the composite catalyst formed by mixing the M1 catalyst provided by this invention with phosphorus aluminum molecular sieve / modified phosphorus aluminum molecular sieve has a certain degree of improved catalytic performance in the ethane oxidative dehydrogenation to ethylene reaction compared with the prior art.

[0190] (1) Compared with the use of M1 phase catalyst alone in Comparative Example 1, the combination of Mn-Ce bimetallic modified phosphorus aluminum molecular sieve and M1 phase catalyst in Example 11 increased the ethylene selectivity by about 2 points under the condition of improving ethane conversion. Moreover, after 500 h of reaction, the ethylene selectivity of the composite catalyst decreased by only 1 point. In contrast, the ethylene selectivity of the M1 phase catalyst in Comparative Example 1 decreased by about 4 points after 500 h of operation. This indicates that mixing phosphorus aluminum molecular sieve or transition metal modified phosphorus aluminum molecular sieve with molybdenum vanadium tellurium niobium catalyst by physical mixing not only does not damage the structure of molecular sieve and M1 catalyst, but also allows both molecular sieve and M1 catalyst to be directly used to catalyze the oxidative dehydrogenation of ethane to ethylene. At the same time, molecular sieve also has the excellent effect of diluting M1 catalyst and thus avoiding side reactions caused by excessive local temperature.

[0191] (2) Compared with Example 11, Comparative Example 2 only used Mn-CeAlPO4-18 molecular sieve as catalyst. The results show that Mn-CeAlPO4-18 molecular sieve has a certain oxidative dehydrogenation effect, but the effect is average. In contrast, the Mn-CeAlPO4-18 molecular sieve in Example 11 can play a synergistic role with the M1 phase catalyst, and the reaction performance is better.

[0192] (3) Compared with Example 1, Comparative Example 3 used ZSM-5 molecular sieve. From the perspective of the reaction performance of the composite catalyst, the addition of ZSM-5 molecular sieve not only affected the conversion rate of ethane, but also significantly reduced the selectivity of ethylene. This is mainly because ZSM-5 molecular sieve is highly acidic and easily causes product cracking and excessive oxidation.

[0193] (4) Compared with Comparative Example 1, although the selectivity of ethylene was improved when the M1 phase catalyst was combined with inactive SiC in Comparative Example 4, the ethane conversion rate decreased significantly. This was mainly because the inactive SiC diluted the M1 phase catalyst, thus reducing its activity. Compared with Example 11, the selectivity of ethylene and the ethane conversion rate were both improved when the M1 phase catalyst was combined with Mn-CeAlPO4-18 molecular sieve.

[0194] (5) Compared with Example 8, in Comparative Example 5, the catalyst reaction performance was significantly reduced when the addition time of niobium oxalate solution was shortened to 5 min. This is mainly because the addition rate of niobium oxalate solution is too fast, which has a significant negative impact on the formation of the microstructure of Mo, V, Te, and Nb complexes in the solution. At the same time, the addition rate is too fast, resulting in larger crystal nuclei and severe crystal phase encapsulation. Therefore, it is necessary to strictly control the addition time of niobium oxalate solution.

[0195] In summary, phosphorus-aluminum molecular sieves with suitable acidity and redox capabilities, or phosphorus-aluminum molecular sieves modified with transition metals, can be combined with molybdenum-vanadium-tellurium-niobium catalysts to significantly improve the ethylene selectivity and stability of the catalysts while reducing the cost of the catalysts.

[0196] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A composite catalyst for the oxidative dehydrogenation of ethane, characterized in that, The composite catalyst includes a molybdenum-vanadium-tellurium-niobium catalyst and a molecular sieve; the molecular sieve is a phosphorus-aluminum molecular sieve or a transition metal-modified phosphorus-aluminum molecular sieve. The general formula of the molybdenum-vanadium-tellurium-niobium catalyst is MoV. a Te b Nb c Where a is 0.25~0.32, b is 0.16~0.23, and c is 0.08~0.15; The phosphorus aluminum molecules were screened from AlPO4-18; The transition metal is selected from at least one of Mn, Fe, Ce, and Co; Based on the mass of the composite catalyst as 100%, the content of the molybdenum-vanadium-tellurium-niobium catalyst is 70wt%~90wt%, and the content of the molecular sieve is 10wt%~30wt%.

2. A method for preparing the composite catalyst for ethane oxidative dehydrogenation as described in claim 1, characterized in that, This includes the step of physically mixing phosphorus aluminum molecular sieves or transition metal modified phosphorus aluminum molecular sieves with molybdenum vanadium tellurium niobium catalysts. The molybdenum-vanadium-tellurium-niobium catalyst is prepared by a hydrothermal synthesis method, including the following steps: (1) Dissolve ammonium heptamolybdate tetrahydrate, ammonium metavanadate and telluric acid in deionized water to obtain the first mixed solution; (2) Add an aqueous solution of niobium oxalate to the first mixed solution within 15 to 50 min to form a suspension. After aging, hydrothermal crystallization, drying, calcination, and removal of the M2 phase, a molybdenum-vanadium-tellurium niobium catalyst is obtained.

3. The preparation method according to claim 2, characterized in that, The aqueous solution of niobium oxalate is added dropwise to the first mixed solution.

4. The preparation method according to claim 2, characterized in that, The first mixed solution also includes a dispersant; the dispersant is selected from any one of propylene glycol, polymethyl cellulose, polyvinyl alcohol, guar gum powder, polyethylene glycol, and polyvinylpyrrolidone; The mass ratio of ammonium heptamolybdate tetrahydrate to the dispersant is 100:0.005~0.

1.

5. The preparation method according to claim 2, characterized in that, The preparation of the transition metal modified phosphorus aluminum molecular sieve includes the following steps: An aluminum source, a precursor salt of a transition metal, a phosphorus source, and a template agent are mixed to form a gel. The gel is then crystallized, dried, and calcined to obtain the transition metal-modified phosphorus-aluminum molecular sieve.

6. The preparation method according to claim 5, characterized in that, The precursor salt of the transition metal is selected from the nitrate or acetate of the transition metal; The molar ratio of the aluminum source to the precursor salt of the transition metal, calculated as a metal oxide, is 1 to 20.

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