Composite catalyst for oxidative dehydrogenation of ethane and preparation method thereof

Abstract

The invention discloses a composite catalyst for oxidative dehydrogenation of ethane. The composite catalyst 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 structures of the molecular sieve and the molybdenum-vanadium-tellurium-niobium catalyst are not destroyed, and the molecular sieve and the molybdenum-vanadium-tellurium-niobium catalyst can be directly used for catalyzing the reaction for preparing ethylene by oxidative dehydrogenation of ethane, and by utilizing the unique oxidation-reduction capability of the molecular sieve, the ethylene yield is improved; the reaction performance of catalyzing oxidative dehydrogenation of ethane is improved. On the other hand, as a diluent, the phosphorus-aluminum molecular sieve / transition metal modified phosphorus-aluminum molecular sieve can play roles in dispersing and transferring reaction heat, so that side reaction caused by overhigh local temperature in the reaction process is effectively avoided, and the ethylene selectivity and the operation stability of the catalyst are further improved.

Description

Technical Field

[0001] The invention relates to the technical field of ethane oxidative dehydrogenation to ethylene, and in particular to a composite catalyst for ethane oxidative dehydrogenation and a preparation method thereof. Background Art

[0002] Ethylene is an important petrochemical raw material, which is mainly produced by traditional steam thermal cracking. In a typical ethane steam cracking plant to produce ethylene, energy consumption costs account for about 70% of the production cost. Compared with high-temperature cracking, the product of ethane oxidative dehydrogenation to ethylene (ODHE) technology is single and easy to separate, and the separation system is simple. It is a low-energy consumption approach with great application prospects and has been one of the research hotspots in recent years.

[0003] MoVNbTeOx composite metal oxide (M1 catalyst) has good catalytic performance in ODHE reaction under mild conditions. The reaction temperature required is generally lower than 450°C. It is currently a research hotspot in the oxidative dehydrogenation of low-carbon alkanes.

[0004] For example, Chinese patent document CN 108503529 B provides a method for preparing acrylic acid from propane, wherein the catalyst used is a composite catalyst, which is composed of a molybdenum, vanadium, tellurium, and niobium catalyst and a stabilizer, and the stabilizer is selected from at least one of SiC, Al2O3, or SiO2. In the composite catalyst, the mass percentage of the stabilizer is 5% to 95%, preferably 20% to 70%, and more preferably 30% to 50%. In this method, a composite catalyst composed of a molybdenum, vanadium, tellurium, and niobium catalyst powder and a stabilizer is used, and a stabilizer is creatively introduced into the catalyst. First, the catalyst can be stabilized under harsh reaction conditions, because the stabilizer is conducive to the dispersion and transfer of reaction heat, thereby avoiding the generation of a high hot spot temperature inside the catalyst; second, the stabilizer itself, as a low-cost diluent, can also significantly reduce the production cost of the catalyst. Although the stabilizers such as SiC, Al2O3, or SiO2 added to the composite catalyst disclosed in the document reduce the cost and improve the stability of the catalyst, they have a significant negative impact on the reaction activity when used for the ODHE reaction. Summary of the invention

[0005] In view of this, the present invention provides a composite catalyst for ethane oxidative dehydrogenation and a preparation method thereof, wherein 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 phosphorus-aluminum molecular sieve modified by a transition metal. The composite catalyst for ethane oxidative dehydrogenation utilizes the unique redox ability of the phosphorus-aluminum molecular sieve / transition metal-modified phosphorus-aluminum molecular sieve to improve the performance of the composite catalyst in catalyzing the ethane oxidative dehydrogenation reaction, and at the same time, can also play a role in dispersing and transferring reaction heat.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A composite catalyst for ethane oxidative dehydrogenation, 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 , wherein a is 0.25 to 0.32, b is 0.16 to 0.23, and c is 0.08 to 0.15. By further limiting 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 molecules are selected 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, based on the mass of the composite catalyst being 100%, the content of the molybdenum-vanadium-tellurium-niobium catalyst is 70wt% to 90wt%, and the content of the molecular sieve is 10wt% to 30wt%.

[0012] The present invention also provides a method for preparing the composite catalyst for ethane oxidative dehydrogenation, comprising the steps 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 by conventional methods in the industry, such as by hydrothermal synthesis, including the following steps:

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

[0015] (2) adding an aqueous solution of niobium oxalate to the first mixed solution within 15 to 50 minutes to form a suspension, and subjecting the suspension to aging, hydrothermal crystallization, drying, calcination, and removal of the M2 phase to obtain a molybdenum, vanadium, tellurium, and niobium catalyst.

[0016] Optionally, in the method for preparing the 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 the step (1) of preparing the M1 catalyst by the hydrothermal synthesis method recommended by the present invention, it is sufficient to dissolve ammonium heptamolybdate tetrahydrate, ammonium metavanadate and telluric acid in deionized water, and there is no specific limitation. For example, ammonium heptamolybdate, ammonium metavanadate and telluric acid can be added to deionized water, and then stirred at 70°C to 100°C for 60 to 180 minutes until dissolved to form a first mixed solution. In the step (1) of preparing the M1 catalyst by the hydrothermal synthesis method recommended by the present invention, the aqueous solution of niobium oxalate is formed by adding niobium oxalate to deionized water, such as stirring at 60 to 90°C for 20 to 60 minutes until niobium oxalate is dissolved 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 each substance can be completely dissolved and mixed evenly.

[0018] Optionally, in the method for preparing M1 catalyst by hydrothermal synthesis recommended by the present invention, the aging temperature recommended by the present invention is 20-90°C and the time is 20-180min. The reaction temperature of the hydrothermal crystallization recommended by the present invention is 150°C-200°C; the time is 12-60h. The drying temperature recommended by the present invention is 70-120°C and the time is 6-30h. The calcination procedure recommended by the present invention is a two-stage calcination, and the specific steps are as follows: first calcining at 200-400°C in air for 2-6h, and then calcining at 550-650°C in an inert atmosphere for 1-4h. The inert atmosphere is at least one of nitrogen, argon, and helium. The method recommended by the present 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 molybdenum, vanadium, tellurium, and 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, sesbania powder, polyethylene glycol, and polyvinyl pyrrolidone;

[0020] The mass ratio of the tetrahydrated ammonium heptamolybdate to the dispersant is 100:0.005-0.1. By further adding the dispersant to the first mixed solution, it can disperse and support components such as molybdenum, vanadium, tellurium, and niobium, improve the pore structure and specific surface area of ​​the molybdenum-vanadium-tellurium-niobium catalyst, and further improve 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 by conventional methods in the industry. The preparation method of the phosphorus-aluminum molecular sieve recommended by the present invention comprises the following steps:

[0022] The aluminum source, phosphorus source and template are mixed to form a gel, and then the phosphorus aluminum molecular sieve precursor is obtained by crystallization, filtration, washing and drying, and then the phosphorus aluminum molecular sieve precursor is calcined to obtain the phosphorus aluminum molecular sieve. The specific amount of each material and the reaction parameters of each step can be adjusted according to the actual situation. For example, the mass ratio of the aluminum source (in terms of oxide), the phosphorus source (in terms of oxide) and the template is 1:0.8-1.7:0.4-2.0; the crystallization temperature is 170-220°C, and the time is 5-30h; the drying temperature is 80-120°C, and the time is 4-10h; the calcination temperature is 520-600°C, and the time is 3-8h.

[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 aluminum-phosphorus molecular sieve recommended by the present invention comprises the following steps:

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

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

[0026] Calculated on the basis of metal oxides (the aluminum source is calculated on the basis of aluminum oxide, and the precursor salt of the transition metal is calculated on the basis of transition metal oxides), the molar ratio of the aluminum source to the precursor salt of the transition metal is 1-20.

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

[0028] The composite catalyst for ethane oxidative dehydrogenation provided by the present invention can be used for catalytic reaction under conventional ethane oxidative dehydrogenation reaction conditions. The present invention recommends that the composite catalyst be used to catalyze the ethane oxidative dehydrogenation to ethylene reaction under the following reaction conditions: reaction temperature of 350-400°C, atmospheric pressure, and feed space velocity of reaction gas of 200-500h / min. -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 present invention has the following beneficial effects:

[0030] 1. The composite catalyst for ethane oxidative dehydrogenation provided by the present 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 compounding (physical mixing) the phosphorus aluminum molecular sieve or the transition metal modified phosphorus aluminum molecular sieve with the molybdenum vanadium tellurium niobium catalyst, on the one hand, the structure of the molecular sieve and the molybdenum vanadium tellurium niobium catalyst will not be destroyed, and the molecular sieve and the molybdenum vanadium tellurium niobium catalyst can be directly used to catalyze the oxidative dehydrogenation of ethane to produce ethylene, while utilizing the unique redox ability of the phosphorus aluminum molecular sieve / transition metal modified phosphorus aluminum molecular sieve to improve the reaction performance of the composite catalyst in catalyzing the oxidative dehydrogenation of ethane. On the other hand, ethane oxidative dehydrogenation to produce ethylene is an exothermic reaction, and the phosphorus aluminum molecular sieve / transition metal modified phosphorus aluminum molecular sieve can be used as a diluent to dilute the molybdenum vanadium tellurium niobium catalyst, which plays a role in dispersing and transferring the reaction heat, effectively avoiding the local temperature that is too high during the reaction to cause side reactions (avoiding excessive oxidation of the product ethylene to produce carbon oxides), thereby improving the ethylene selectivity and the operating stability of the catalyst.

[0031] 2. In the preparation method of the composite catalyst for ethane oxidative dehydrogenation provided by the present invention, during the preparation of the molybdenum, vanadium, tellurium, and niobium catalyst, by limiting the time for adding the aqueous solution of niobium oxalate to the first mixed solution, the rate of forming a complex after mixing the heteropolyacid anions and Nb precursors formed in the initial mixed aqueous solution of Mo, V, and Te is regulated, thereby generating more active species and improving the reaction activity of the catalyst. The molybdenum, vanadium, tellurium, and niobium catalyst prepared by the method cooperates with the phosphorus aluminum molecular sieve or the transition metal-modified phosphorus aluminum molecular sieve, which can significantly improve the activity and stability of the composite catalyst and reduce the cost of the composite catalyst. DETAILED DESCRIPTION

[0032] The present invention is described in detail below by way of examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Those skilled in the art in this field can make some non-essential improvements and adjustments to the present invention based on the above content of the present invention.

[0033] If no specific experimental steps or conditions are specified in the examples and comparative examples, the conventional experimental steps or conditions described in the literature in the art can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be purchased commercially.

[0034] Source of raw materials: The raw materials involved in the preparation process of the composite catalyst in the embodiment of the present invention are all analytically pure (AR). Raw materials: ammonium heptamolybdate tetrahydrate, polyethylene glycol, polyvinyl pyrrolidone, 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, tetrapropylammonium bromide were purchased from Sinopharm Reagent Co., Ltd.; tri-n-propylamine, ammonium metavanadate, and telluric acid were purchased from MacLean Reagent Company; niobium oxalate, aluminum isopropoxide, and sesbania powder were purchased from Aladdin Reagent Company.

[0035] Evaluation and analysis method: The catalyst was tableted and crushed, and 20-40 mesh was screened and loaded into a 10 mL fixed bed microreactor with an inner diameter of 5 mm. The reaction temperature was 360 ° C, atmospheric pressure, and the feed space velocity of the reaction gas was 300 h -1 ; The reaction is carried out under the condition that the molar ratio of ethane: oxygen: nitrogen in the reaction gas is 1: 0.6: 1.5 to obtain ethylene product. The reaction product is detected by gas chromatography analysis.

[0036] Example 1

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

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

[0039] (1) adding a certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and polyvinyl alcohol into deionized water, heating and stirring 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) adding a certain amount of niobium oxalate into deionized water, heating and stirring at 80° C. for 30 minutes to form a second mixed solution;

[0041] (3) The second mixed solution is added dropwise to the first mixed solution to form a suspension (addition is completed in 20 minutes), and after aging at 80°C for 180 minutes, it is transferred to a hydrothermal synthesis reactor, hydrothermally crystallized at 175°C for 48 hours, and then dried at 80°C for 20 hours; thereafter, it is calcined at 300°C in an air atmosphere for 3 hours, and then calcined at 600°C in helium for 2 hours to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst is then purified in 7.5wt% hydrogen peroxide to remove the M2 phase, heated and stirred at 60°C for 180 minutes, filtered, and finally dried at 120°C for 12 hours to obtain an M1 catalyst with a composition of MoV 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, aluminum isopropoxide was added under vigorous stirring and stirred for 1 hour, then N,N-diisopropylethylamine (DIPEA) was added and stirred for 48 hours to form a uniform gel. The composition of the gel is: n(Al2O3): n(P2O5): n(DIPEA): n(H2O) = 1:1:1:50. The gel was crystallized in a crystallization kettle at 180°C for 20 days, filtered, washed with distilled water, and dried in a 100°C thermostat for 6 hours to obtain a molecular sieve precursor; the molecular sieve precursor was calcined at 250°C for 1 hour, and then heated to 550°C for 5 hours to obtain a mesoporous AlPO4-18 molecular sieve.

[0044] Composite catalyst

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

[0046] Example 2

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

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

[0049] (1) adding a certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and sesbania powder into deionized water, heating and stirring at 90° C. for 100 min to form a first mixed solution; wherein the amount of sesbania powder added is 0.008 wt % of the mass of ammonium heptamolybdate tetrahydrate;

[0050] (2) adding a certain amount of niobium oxalate into deionized water, heating and stirring at 90° C. for 20 min to form a second mixed solution;

[0051] (3) The second mixed solution is added dropwise to the first mixed solution to form a suspension (addition is completed in 25 minutes), and after aging at 90°C for 20 minutes, it is transferred to a hydrothermal synthesis reactor, hydrothermally crystallized at 180°C for 24 hours, and then dried at 100°C for 10 hours; thereafter, it is calcined at 280°C in an air atmosphere for 4 hours, and then calcined at 570°C in helium for 2.5 hours to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst is then purified in 10.0wt% hydrogen peroxide to remove the M2 phase, heated and stirred at 70°C for 120 minutes, filtered, and finally dried at 120°C for 6 hours to obtain an 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 into a reactor at a molar ratio of n(Al2O3):n(CoO):n(P2O5):n(TPrA):n(H2O)=0.9:0.1:0.8:1:50 and mixed evenly, and then aged at 90°C for 2 hours to form a uniform gel. The gel was then stirred and crystallized at 200°C for 24 hours. The obtained solid was washed with deionized water until it was neutral, dried in a thermostat 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] 0.70 g of the above-mentioned molybdenum vanadium tellurium niobium catalyst and 0.30 g of CoAlPO4-18 molecular sieve were mixed evenly and loaded into a fixed bed microreactor. Ethane, oxygen and nitrogen were introduced according to the above-mentioned evaluation method to carry out ethane oxidative dehydrogenation to ethylene reaction. The activity evaluation results are shown in Table 1.

[0056] Example 3

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

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

[0059] (1) adding a certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and polyethylene glycol to deionized water, heating and stirring 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) adding a certain amount of niobium oxalate into deionized water, heating and stirring at 60° C. for 60 min to form a second mixed solution;

[0061] (3) The second mixed solution is added dropwise to the first mixed solution to form a suspension (addition is completed in 30 minutes), and after aging at 40°C for 180 minutes, it is transferred to a hydrothermal synthesis reactor, hydrothermally crystallized at 200°C for 20 hours, and then dried at 90°C for 15 hours; thereafter, it is calcined at 260°C in an air atmosphere for 5 hours, and then calcined at 650°C in nitrogen for 2 hours to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst is then purified in 8.0wt% hydrogen peroxide to remove the M2 phase, heated and stirred at 50°C for 60 minutes, filtered, and finally dried at 100°C for 12 hours to obtain an M1 catalyst with a composition of MoV 0.28 Te 0.18Nb 0.13 .

[0062] MnAlPO4-18 molecular sieve:

[0063] Aluminum isopropoxide, manganese acetate, phosphoric acid, and N,N-diisopropylethylamine are added into a reactor at a molar ratio of n(Al2O3):n(MnO):n(P2O5):n(DIPEA):n(H2O)=0.9:0.1:1.2:0.8:50, mixed evenly, and aged at 80°C for 2 hours to form a uniform gel, which is stirred and crystallized at 190°C for 15 hours. The obtained solid is washed with deionized water to neutrality, dried in a constant temperature box 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] 0.85 g of the above molybdenum-vanadium-tellurium-niobium catalyst and 0.15 g of MnAlPO4-18 molecular sieve were mixed evenly and loaded into a fixed bed microreactor, and ethane, oxygen and nitrogen were introduced according to the above evaluation method to carry out ethane oxidative dehydrogenation to ethylene reaction. The activity evaluation results are shown in Table 1.

[0066] Example 4

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

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

[0069] (1) adding a certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and propylene glycol to deionized water, heating and stirring 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) adding a certain amount of niobium oxalate into deionized water, heating and stirring at 70° C. for 40 minutes to form a second mixed solution;

[0071] (3) The second mixed solution is added dropwise to the first mixed solution to form a suspension (addition is completed in 40 minutes), and after aging at 70°C for 120 minutes, it is transferred to a hydrothermal synthesis reactor, hydrothermally crystallized at 180°C for 50 hours, and then dried at 100°C for 15 hours; thereafter, it is calcined at 350°C in an air atmosphere for 3 hours, and then calcined at 550°C in argon for 3 hours to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst is then purified in 7.0wt% hydrogen peroxide to remove the M2 phase, heated and stirred at 60°C for 120 minutes, filtered, and finally dried at 150°C for 5 hours to obtain an M1 catalyst with a composition of MoV 0.32 Te0.16 Nb 0.15 .

[0072] FeAlPO4-18 molecular sieve:

[0073] Aluminum isopropoxide, ferric nitrate, phosphoric acid, and N,N-diisopropylethylamine are added to a reactor at a molar ratio of n(Al2O3):n(FeO):n(P2O5):n(DIPEA):n(H2O)=0.92:0.08:1.5:1.2:50. After being evenly mixed, the mixture is aged at 80°C for 2 hours to form a uniform gel. The gel is stirred and crystallized at 200°C for 10 hours. The obtained solid is washed with deionized water until it is neutral, dried in a constant temperature box 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] 0.75 g of the above molybdenum-vanadium-tellurium-niobium catalyst and 0.25 g of FeAlPO4-18 molecular sieve were mixed evenly and loaded into a fixed bed microreactor, and ethane, oxygen and nitrogen were introduced according to the above evaluation method to carry out 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 ethane oxidative dehydrogenation, and its specific preparation method is as follows:

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

[0079] (1) adding a certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and sesbania powder into deionized water, heating and stirring at 80° C. for 90 min to form a first mixed solution; wherein the amount of sesbania powder added is 0.08 wt % of the mass of ammonium heptamolybdate tetrahydrate;

[0080] (2) adding a certain amount of niobium oxalate into deionized water, heating and stirring at 80° C. for 25 minutes to form a second mixed solution;

[0081] (3) The second mixed solution is added dropwise to the first mixed solution to form a suspension (addition is completed in 25 minutes), and after aging at 80°C for 100 minutes, it is transferred to a hydrothermal synthesis reactor, hydrothermally crystallized at 170°C for 36 hours, and then dried at 120°C for 6 hours; thereafter, it is calcined at 200°C in an air atmosphere for 6 hours, and then calcined at 580°C in helium for 1 hour to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst is then purified in 15.0wt% hydrogen peroxide to remove the M2 phase, heated and stirred at 70°C for 150 minutes, filtered, and finally dried at 120°C for 10 hours to obtain an M1 catalyst with a composition of MoV0.25 Te 0.23 Nb 0.10 .

[0082] CeAlPO4-18 molecular sieve:

[0083] Aluminum isopropoxide, cerium nitrate, phosphoric acid, and N,N-diisopropylethylamine were added into a reactor at a molar ratio of n(Al2O3):n(CeO):n(P2O5):n(DIPEA):n(H2O)=0.92:0.08:1:0.6:50. After being evenly mixed, the mixture was aged at 80°C for 2 hours to form a uniform gel. The gel was stirred and crystallized at 220°C for 5 hours. The obtained solid was washed with deionized water until it was neutral, dried in a thermostat 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] 0.75 g of the above molybdenum-vanadium-tellurium-niobium catalyst and 0.25 g of CeAlPO4-18 molecular sieve were mixed evenly and loaded into a fixed bed microreactor, and ethane, oxygen and nitrogen were introduced according to the above evaluation method to carry out ethane oxidative dehydrogenation to ethylene reaction. The activity evaluation results are shown in Table 1.

[0086] Example 6

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

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

[0089] (1) adding a certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and polyvinyl pyrrolidone into deionized water, heating and stirring at 75° C. for 150 min to form a first mixed solution; wherein the amount of polyvinyl pyrrolidone added is 0.1 wt % of the mass of ammonium heptamolybdate tetrahydrate;

[0090] (2) adding a certain amount of niobium oxalate into deionized water, heating and stirring at 75° C. for 50 min to form a second mixed solution;

[0091] (3) The second mixed solution is added dropwise to the first mixed solution to form a suspension (addition is completed in 50 minutes), and after aging at 20°C for 150 minutes, it is transferred to a hydrothermal synthesis reactor, hydrothermally crystallized at 190°C for 60 hours, and then dried at 80°C for 18 hours; thereafter, it is calcined at 320°C in an air atmosphere for 2 hours, and then calcined at 600°C in nitrogen for 2.5 hours to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst is then purified in 12.0wt% hydrogen peroxide to remove the M2 phase, heated and stirred at 80°C for 30 minutes, filtered, and finally dried at 60°C for 15 hours to obtain an M1 catalyst with a composition of MoV 0.32 Te 0.21 Nb 0.08 .

[0092] MnAlPO4-18 molecular sieve:

[0093] Aluminum isopropoxide, manganese acetate, phosphoric acid, and N,N-diisopropylethylamine are added into a reactor at a molar ratio of n(Al2O3):n(MnO):n(P2O5):n(DIPEA):n(H2O)=0.85:0.15:0.8:0.4:50. After being evenly mixed, the mixture is aged at 60°C for 2 hours to form a uniform gel. The gel is stirred and crystallized at 180°C for 12 hours. The obtained solid is washed with deionized water until it is neutral, dried in a constant temperature box at 120°C for 3 hours, and calcined in a muffle furnace at 575°C for 6 hours to obtain a MnAlPO4-18 molecular sieve.

[0094] Composite catalyst

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

[0096] Example 7

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

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

[0099] (1) adding a certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and polyvinyl pyrrolidone into deionized water, heating and stirring at 90° C. for 90 min to form a first mixed solution; wherein the amount of polyvinyl pyrrolidone added is 0.06 wt % of the mass of ammonium heptamolybdate tetrahydrate;

[0100] (2) adding a certain amount of niobium oxalate into deionized water, heating and stirring at 90° C. for 30 minutes to form a second mixed solution;

[0101] (3) The second mixed solution is added dropwise to the first mixed solution to form a suspension (addition is completed in 35 minutes), and after aging at 60°C for 90 minutes, it is transferred to a hydrothermal synthesis reactor, hydrothermally crystallized at 150°C for 30 hours, and then dried at 70°C for 20 hours; thereafter, it is calcined at 400°C in an air atmosphere for 3 hours, and then calcined at 600°C in helium for 3 hours to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst is then purified in 5.0wt% hydrogen peroxide to remove the M2 phase, heated and stirred at 30°C for 90 minutes, filtered, and finally dried at 70°C for 8 hours to obtain an M1 catalyst with a composition of MoV 0.25 Te 0.20 Nb 0.08 .

[0102] CeAlPO4-18 molecular sieve:

[0103] Aluminum isopropoxide, cerium nitrate, phosphoric acid, and N,N-diisopropylethylamine are added to a reactor at a molar ratio of n(Al2O3):n(CeO):n(P2O5):n(DIPEA):n(H2O)=0.8:0.2:1:1.5:50. After being evenly mixed, the mixture is aged at 90°C for 2 hours to form a uniform gel. The gel is stirred and crystallized at 170°C for 20 hours. The obtained solid is washed with deionized water until it is neutral, dried in a constant temperature box 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] 0.80 g of the above molybdenum-vanadium-tellurium-niobium catalyst and 0.20 g of CeAlPO4-18 molecular sieve were mixed evenly and loaded into a fixed bed microreactor, and ethane, oxygen and nitrogen were introduced according to the above evaluation method to carry out ethane oxidative dehydrogenation to ethylene reaction. The activity evaluation results are shown in Table 1.

[0106] Example 8

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

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

[0109] (1) adding a certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and polymethyl cellulose to deionized water, heating and stirring at 80° C. for 120 min to form a first mixed solution; wherein the amount of polymethyl cellulose added is 0.05 wt % of the mass of ammonium heptamolybdate tetrahydrate;

[0110] (2) adding a certain amount of niobium oxalate into deionized water, heating and stirring at 80° C. for 30 minutes to form a second mixed solution;

[0111] (3) The second mixed solution is added dropwise to the first mixed solution to form a suspension (addition is completed in 35 minutes), and after aging at 80°C for 60 minutes, it is transferred to a hydrothermal synthesis reactor, hydrothermally crystallized at 175°C for 24 hours, and then dried at 100°C for 10 hours; thereafter, it is calcined at 300°C in an air atmosphere for 4 hours, and then calcined at 620°C in nitrogen for 2 hours to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst is then purified in 8.0wt% hydrogen peroxide to remove the M2 phase, heated and stirred at 60°C for 180 minutes, filtered, and finally dried at 80°C for 10 hours to obtain an M1 catalyst with a composition of MoV 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 into a reactor at a molar ratio of n(Al2O3):n(CeO):n(P2O5):n(DIPEA):n(H2O)=0.95:0.05:1.2:1.2:50. After being evenly mixed, the mixture was aged at 70°C for 2 hours to form a uniform gel. The gel was stirred and crystallized at 170°C for 24 hours. The obtained solid was washed with deionized water until it was neutral, dried in a thermostat 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] 0.875 g of the above molybdenum-vanadium-tellurium-niobium catalyst and 0.125 g of CeAlPO4-18 molecular sieve were mixed evenly and loaded into a fixed bed microreactor, and ethane, oxygen and nitrogen were introduced according to the above evaluation method to carry out ethane oxidative dehydrogenation to ethylene reaction. The activity evaluation results are shown in Table 1.

[0116] Example 9

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

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

[0119] (1) adding a certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and polymethyl cellulose to deionized water, heating and stirring at 85° C. for 150 min to form a first mixed solution; wherein the amount of polymethyl cellulose added is 0.03 wt % of the mass of ammonium heptamolybdate tetrahydrate;

[0120] (2) adding a certain amount of niobium oxalate into deionized water, heating and stirring at 85° C. for 30 minutes to form a second mixed solution;

[0121] (3) The second mixed solution is added dropwise to the first mixed solution to form a precipitate (addition is completed in 40 minutes), and after aging at 85°C for 90 minutes, it is transferred to a hydrothermal synthesis reactor, hydrothermally crystallized at 185°C for 22 hours, and then dried at 100°C for 10 hours; thereafter, it is calcined at 350°C in an air atmosphere for 3 hours, and then calcined at 590°C in helium for 2.5 hours to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst is then purified in 8.5wt% hydrogen peroxide to remove the M2 phase, heated and stirred at 65°C for 240 minutes, filtered, and finally dried at 70°C for 18 hours to obtain an M1 catalyst with a composition of MoV 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 are added into a reactor at 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 and mixed evenly. The mixture is aged at 80°C for 2 hours to form a uniform gel. The gel is stirred and crystallized at 200°C for 24 hours. The obtained solid is washed with deionized water until it is neutral, dried in a thermostat 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] 0.85 g of the above molybdenum-vanadium-tellurium-niobium catalyst and 0.15 g of Co-CeAlPO4-18 molecular sieve were mixed evenly and loaded into a fixed bed microreactor, and ethane, oxygen and nitrogen were introduced according to the above evaluation method to carry out ethane oxidative dehydrogenation to ethylene reaction. The activity evaluation results are shown in Table 1.

[0126] Example 10

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

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

[0129] (1) adding a certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and propylene glycol to deionized water, heating and stirring 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) adding a certain amount of niobium oxalate into deionized water, heating and stirring at 75° C. for 30 minutes to form a second mixed solution;

[0131] (3) The second mixed solution is added dropwise to the first mixed solution to form a precipitate (addition takes 15 minutes), and after aging at 75°C for 60 minutes, it is transferred to a hydrothermal synthesis reactor, hydrothermally crystallized at 165°C for 20 hours, and then dried at 90°C for 25 hours; then calcined at 380°C in an air atmosphere for 3.5 hours, and then calcined at 600°C in nitrogen for 3.5 hours to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst is then purified in 7.5wt% hydrogen peroxide to remove the M2 phase, heated and stirred at 60°C for 100 minutes, filtered, and finally dried at 80°C for 14 hours to obtain an M1 catalyst with a composition of MoV 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 are added into a reactor at 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 evenly. The mixture is aged at 70°C for 2 hours to form a uniform gel. The gel is stirred and crystallized at 200°C for 24 hours. The obtained solid is washed with deionized water until it is neutral. The separated solid is dried in a thermostat at 80°C for 6 hours, and calcined in a muffle furnace at 550°C for 6 hours to obtain Co-MnAlPO4-18 molecular sieve.

[0133] Composite catalyst

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

[0135] Embodiment 11

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

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

[0138] (1) adding a certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and sesbania powder into deionized water, heating and stirring at 80° C. for 150 min to form a first mixed solution; wherein the amount of sesbania powder added is 0.02 wt % of the mass of ammonium heptamolybdate tetrahydrate;

[0139] (2) adding a certain amount of niobium oxalate into deionized water, heating and stirring at 80° C. for 40 minutes to form a second mixed solution;

[0140] (3) The second mixed solution is added dropwise to the first mixed solution to form a precipitate (addition is completed in 30 minutes), and after aging at 80°C for 100 minutes, it is transferred to a hydrothermal synthesis reactor, hydrothermally crystallized at 175°C for 30 hours, and then dried at 120°C for 10 hours; thereafter, it is calcined at 340°C in an air atmosphere for 4.5 hours, and then calcined at 620°C in nitrogen for 2 hours to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst is then purified in 10.0wt% hydrogen peroxide to remove the M2 phase, heated and stirred at 75°C for 200 minutes, filtered, and finally dried at 80°C for 10 hours to obtain an M1 catalyst with a composition of MoV 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 are added into a reactor at 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, and mixed evenly. The mixture is aged at 60°C for 2 hours to form a uniform gel. The gel is stirred and crystallized at 200°C for 24 hours. The obtained solid is washed with deionized water until it is neutral, dried in a thermostat 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.

[0142] Composite catalyst

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

[0144] Example 12

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

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

[0147] (1) adding a certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate and telluric acid into deionized water, heating and stirring at 80° C. for 120 min to form a first mixed solution;

[0148] (2) adding a certain amount of niobium oxalate into deionized water, heating and stirring at 80° C. for 30 minutes to form a second mixed solution;

[0149] (3) The second mixed solution is added to the first mixed solution to form a precipitate (the second mixed solution is added in batches and added in 35 minutes), and after aging at 80°C for 60 minutes, it is transferred to a hydrothermal synthesis reactor, hydrothermally crystallized at 175°C for 24 hours, and then dried at 100°C for 10 hours; then calcined at 300°C in an air atmosphere 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 is then purified in 8.0wt% hydrogen peroxide to remove the M2 phase, heated and stirred at 60°C for 180 minutes, filtered, and finally dried at 80°C for 10 hours to obtain an 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 into a reactor at a molar ratio of n(Al2O3):n(CeO):n(P2O5):n(DIPEA):n(H2O)=0.95:0.05:1:1:50, mixed evenly, and aged at 70°C for 2 hours to form a uniform gel. The gel was stirred and crystallized at 170°C for 24 hours to obtain a solid that was washed with deionized water until it was neutral. The separated solid was dried in a thermostat at 80°C for 6 hours, and calcined in a muffle furnace at 570°C for 5 hours to obtain CeAlPO4-18 molecular sieve.

[0152] Composite catalyst

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

[0154] Comparative Example 1

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

[0156] (1) adding a certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and sesbania powder into deionized water, heating and stirring at 80° C. for 150 min to form a first mixed solution; wherein the amount of sesbania powder added is 0.02 wt % of the mass of ammonium heptamolybdate tetrahydrate;

[0157] (2) adding a certain amount of niobium oxalate into deionized water, heating and stirring at 80° C. for 40 minutes to form a second mixed solution;

[0158] (3) The second mixed solution is added to the first mixed solution to form a precipitate (the dropping time is 30 minutes), and after aging at 80°C for 100 minutes, it is transferred to a hydrothermal synthesis reactor, hydrothermally crystallized at 175°C for 30 hours, and then dried at 120°C for 10 hours; then calcined at 340°C in an air atmosphere for 4.5 hours, and then calcined at 620°C in nitrogen for 2 hours to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst is then purified in 10wt% hydrogen peroxide to remove the M2 phase, heated and stirred at 75°C for 200 minutes, filtered, and finally dried at 80°C for 10 hours to obtain an M1 catalyst with a composition of MoV 0.28 Te 0.18 Nb 0.12 .

[0159] 1.0 g of the above molybdenum-vanadium-tellurium-niobium catalyst was placed in a fixed bed microreactor, and ethane, oxygen and nitrogen were introduced according to the above evaluation method to carry out ethane oxidative dehydrogenation to ethylene reaction. 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 ethane oxidative dehydrogenation, and its specific preparation method is as follows:

[0162] Aluminum isopropoxide, manganese acetate, cerium nitrate, phosphoric acid, and N,N-diisopropylethylamine are added into a reactor at 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 and mixed evenly. The mixture is aged at 60°C for 2 hours to form a uniform gel. The gel is stirred and crystallized at 200°C for 24 hours. The obtained solid is washed with deionized water until it is neutral, dried in a thermostat at 80°C for 6 hours, and calcined in a muffle furnace at 550°C for 6 hours to obtain a Mn-CeAlPO4-18 molecular sieve.

[0163] 1.0 g of the above-mentioned Mn-CeAlPO4-18 molecular sieve was placed in a fixed bed microreactor, and ethane, oxygen and nitrogen were introduced according to the above-mentioned evaluation method to carry out ethane oxidative dehydrogenation to ethylene reaction. 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): the same as in Example 1;

[0167] ZSM-5 molecular sieve is prepared according to the following steps:

[0168] An in-situ hydrothermal synthesis method was adopted, with silica sol as the silicon source, NaAlO2 as the aluminum source, TPABr (tetrapropylammonium bromide) as the template, and NaOH and deionized water were added. 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 kettle and crystallized at 160°C for 48 hours. The product was filtered and washed to neutrality, dried at 120°C for 12 hours, and calcined at 550°C for 6 hours to obtain Na-type ZSM-5 molecular sieve. At 85°C, the Na-type ZSM-5 molecular sieve was treated with 1 mol / L NH4Cl solution (liquid-to-solid mass ratio 20) for 2 hours, and then washed, dried (dried at 120°C for 12 hours) and calcined (calcined at 550°C for 6 hours), and the process was repeated 3 times to obtain the H-type ZSM-5 molecular sieve.

[0169] Composite catalyst

[0170] 0.90 g of the above-mentioned molybdenum vanadium tellurium niobium catalyst and 0.10 g of the above-mentioned ZSM-5 molecular sieve were mixed evenly and loaded into a fixed bed microreactor. Ethane, oxygen and nitrogen were introduced according to the above-mentioned evaluation method to carry out ethane oxidative dehydrogenation to ethylene reaction. 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): the same as Example 11.

[0174] Composite catalyst

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

[0176] Comparative Example 5

[0177] The composite catalyst for ethane oxidative dehydrogenation 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 ethane oxidative dehydrogenation provided in this comparative example is as follows:

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

[0179] (1) adding a certain amount of ammonium heptamolybdate tetrahydrate, ammonium metavanadate, telluric acid and polymethyl cellulose to deionized water, heating and stirring at 80° C. for 120 min to form a first mixed solution; wherein the amount of polymethyl cellulose added is 0.05 wt % of the mass of ammonium heptamolybdate tetrahydrate;

[0180] (2) adding a certain amount of niobium oxalate into deionized water, heating and stirring at 80° C. for 30 minutes to form a second mixed solution;

[0181] (3) The second mixed solution is added dropwise to the first mixed solution to form a suspension (addition is completed in 5 minutes), and after aging at 80°C for 60 minutes, it is transferred to a hydrothermal synthesis reactor, hydrothermally crystallized at 175°C for 24 hours, and then dried at 100°C for 10 hours; thereafter, it is calcined at 300°C in an air atmosphere for 4 hours, and then calcined at 620°C in nitrogen for 2 hours to obtain a molybdenum-vanadium-tellurium-niobium catalyst. The molybdenum-vanadium-tellurium-niobium catalyst is then purified in 8.0wt% hydrogen peroxide to remove the M2 phase, heated and stirred at 60°C for 180 minutes, filtered, and finally dried at 80°C for 10 hours to obtain an M1 catalyst with a composition of MoV 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 into a reactor at a molar ratio of n(Al2O3):n(CeO):n(P2O5):n(DIPEA):n(H2O)=0.95:0.05:1:1.2:50. After being evenly mixed, the mixture was aged at 70°C for 2 hours to form a uniform gel. The gel was stirred and crystallized at 170°C for 24 hours. The obtained solid was washed with deionized water until it was neutral, dried in a thermostat 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] 0.875 g of the above molybdenum-vanadium-tellurium-niobium catalyst and 0.125 g of CeAlPO4-18 molecular sieve were mixed evenly and loaded into a fixed bed microreactor, and ethane, oxygen and nitrogen were introduced according to the above evaluation method to carry out ethane oxidative dehydrogenation to ethylene reaction. The activity evaluation results are shown in Table 1.

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

[0187] Table 1

[0188]

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

[0190] (1) Compared with the M1 phase catalyst used alone in Comparative Example 1, after the Mn-Ce bimetallic modified aluminum phosphorus molecular sieve and the M1 phase catalyst were composited in Example 11, the ethylene selectivity was increased by about 2 points under the condition of improving the ethane conversion rate, and after 500 hours of reaction, the ethylene selectivity of the composite catalyst only decreased by 1 point, while the M1 phase catalyst in Comparative Example 1, after 500 hours of operation, the ethylene selectivity decreased by about 4 points. This shows that the mixing of aluminum phosphorus molecular sieve or transition metal modified aluminum phosphorus molecular sieve with molybdenum vanadium tellurium niobium catalyst by physical mixing not only does not destroy the structure of the molecular sieve and the M1 catalyst, but also the molecular sieve and the M1 catalyst are directly used to catalyze the ethylene production reaction of ethane oxidative dehydrogenation. At the same time, the molecular sieve also has the excellent effect of diluting the M1 catalyst and thus avoiding the side reaction caused by excessive local temperature.

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

[0192] (3) Compared with Example 1, ZSM-5 molecular sieve was used in Comparative Example 3. From the reaction performance of the composite catalyst, the addition of ZSM-5 molecular sieve not only had a certain impact on the conversion rate of ethane, but also significantly reduced the selectivity of ethylene. This is mainly because the ZSM-5 molecular sieve has a strong acidity and is prone to cause cracking and over-oxidation of the product.

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

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

[0195] In general, the combination of phosphate-aluminum molecular sieves or transition metal-modified phosphate-aluminum molecular sieves with suitable acidity and redox ability and molybdenum-vanadium-tellurium-niobium catalysts can significantly improve the ethylene selectivity and stability of the catalyst while reducing the cost of the catalyst.

[0196] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, technicians familiar with the field may make various corresponding changes and deformations based on the present invention, but these corresponding changes and deformations should all fall within the scope of protection of the claims of the present invention.

Claims

1. A composite catalyst for ethane oxidative dehydrogenation, characterized in that: The composite catalyst comprises a molybdenum-vanadium-tellurium-niobium catalyst and a molecular sieve; the molecular sieve is a phosphorus-aluminum molecular sieve or a phosphorus-aluminum molecular sieve modified by a transition metal.

2. The composite catalyst for ethane oxidative dehydrogenation according to claim 1, characterized in that: The general formula of the molybdenum-vanadium-tellurium-niobium catalyst is MoV a Te b Nb c , where a is 0.25 to 0.32, b is 0.16 to 0.23, and c is 0.08 to 0.

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3. The composite catalyst for ethane oxidative dehydrogenation according to claim 1, characterized in that: The phosphorus aluminum molecules are selected from AlPO4-18.

4. The composite catalyst for ethane oxidative dehydrogenation according to claim 1, characterized in that: The transition metal is selected from at least one of Mn, Fe, Ce and Co.

5. The composite catalyst for ethane oxidative dehydrogenation according to claim 1, characterized in that: Taking 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%.

6. A method for preparing a composite catalyst for ethane oxidative dehydrogenation according to any one of claims 1 to 5, characterized in that: The method comprises the steps of physically mixing a phosphorus aluminum molecular sieve or a phosphorus aluminum molecular sieve modified by a transition metal with a molybdenum vanadium tellurium niobium catalyst; The molybdenum, vanadium, tellurium and niobium catalyst is prepared by a hydrothermal synthesis method, comprising the following steps: (1) dissolving ammonium heptamolybdate tetrahydrate, ammonium metavanadate and telluric acid in deionized water to obtain a first mixed solution; (2) adding an aqueous solution of niobium oxalate to the first mixed solution within 15 to 50 minutes to form a suspension, and subjecting the suspension to aging, hydrothermal crystallization, drying, calcination, and removal of the M2 phase to obtain a molybdenum, vanadium, tellurium, and niobium catalyst.

7. The preparation method according to claim 6, characterized in that: The aqueous solution of niobium oxalate is added dropwise into the first mixed solution.

8. The preparation method according to claim 6, characterized in that: The first mixed solution also includes a dispersant; preferably, the dispersant is selected from any one of propylene glycol, polymethyl cellulose, polyvinyl alcohol, sesbania powder, polyethylene glycol, and polyvinyl pyrrolidone; The mass ratio of the ammonium heptamolybdate tetrahydrate to the dispersant is 100:0.005-0.

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9. The preparation method according to claim 6, characterized in that: The preparation of the transition metal modified aluminum phosphorus molecular sieve comprises the following steps: An aluminum source, a transition metal precursor salt, a phosphorus source and a template agent are mixed to form a gel, and the gel is crystallized, dried and calcined to obtain the transition metal-modified phosphorus aluminum molecular sieve.

10. The preparation method according to claim 9, characterized in that: The transition metal precursor salt is selected from nitrates or acetates of transition metals; The molar ratio of the aluminum source to the precursor salt of the transition metal is 1 to 20 based on the metal oxide.

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