Preparation method of differential Mo-Ce / HZSM-5 oxidation regeneration catalyst based on oxygen storage

Abstract

The invention belongs to the technical field of catalyst preparation, and particularly relates to a preparation method of a differential Mo-Ce / HZSM-5 oxidation regeneration catalyst based on oxygen storage. According to the preparation method, differential oxidation regeneration conditions are constructed by using the oxygen storage material, oxidation conditions are changed on the outer surface of the catalyst through oxygen storage / oxygen release characteristics of the oxygen storage material, and polycyclic aromatic hydrocarbon carbon deposition and graphite selective elimination are realized. According to the Mo-Ce / HZSM-5 catalytic system constructed by the invention, the oxygen storage material loaded on the surface of the Mo-Ce / HZSM-5 catalytic system can effectively adsorb oxygen in an oxygen regeneration stage, so that the oxidation regeneration atmosphere is accurately regulated and controlled; the catalytic system has the capacity of adjusting the oxidation state of MoCy clusters on the surface of the catalyst, abnormal growth of MoO3 crystal grains is effectively inhibited, high dispersity of molybdenum oxide microcrystals is guaranteed, and the molybdenum oxide microcrystals are promoted to be embedded into the inner layer of a molecular sieve framework again.

Description

Technical Field

[0001] The invention belongs to the technical field of catalyst preparation, and in particular relates to a method for preparing a differentiated Mo-Ce / HZSM-5 oxidation regeneration catalyst based on oxygen storage. Background Art

[0002] Methane dehydrogenation aromatization is considered to be a promising natural gas direct conversion technology, which can not only provide pure hydrogen (H 2 ), and hydrocarbon chemical products without carbon dioxide emissions can be obtained, making it extremely valuable in the fields of carbon-one chemistry, natural gas conversion, clean energy utilization, and hydrogen energy utilization. High-temperature activation of methane makes it easy for the optimized Mo / HZSM-5 catalyst to form polycyclic aromatic hydrocarbons carbon deposits in the pores, resulting in rapid deactivation of the catalyst. Domestic and foreign scholars have adopted a variety of research strategies, including optimizing active components, adding additives, molecular sieve modification, silanization of the catalyst's outer surface, adjusting the catalyst's pore structure and acid properties, optimizing the interaction between metals and carriers, co-feeding light hydrocarbons and oxygen-containing components, reaction coupling, membrane reactors, process intensification, etc., to inhibit the formation of polycyclic aromatic hydrocarbons, reduce coke deposition, and extend the catalyst's reaction life, but the results are not significant. So far, Mo / HZSM-5 is still considered to be the most active catalyst for methane dehydrogenation aromatization.

[0003] Since the dissociation of the CH bond requires high temperature, methane reacts with oxidized Mo at high temperature to generate highly active carbon-containing MoO x C y 、Mo 2 C molybdenum species. Under the action of active molybdenum species, the CH bond of methane molecules dissociates to form CHx species, which then couples to form C 2 H y According to the bifunctional reaction and hydrocarbon pool mechanism, CH x Species or C 2 The species cyclizes in the pores of the shape-selective molecular sieves (ZSM-5, MCM-22 and MCM-49) to generate benzene and aromatics with high selectivity. In the later stage of the reaction, carbon deposits of condensed ring aromatics will quickly deposit and clog the pores of the molecular sieve, resulting in inactivation of the reaction.

[0004] Podkolzin reported the regeneration of methane dehydrogenation aromatization catalyst in science (science, 2015, 348: P.686-690), pointing out that the use of molecular oxygen can achieve effective regeneration of Mo / HZSM-5 catalyst, making oxidation regeneration considered by the scientific community to be an economical and efficient method for achieving long-term operation of methane dehydrogenation aromatization reaction; the redistribution (re-location) of molybdenum oxide on the regenerated catalyst in the molecular sieve pores forms Mo-oxo species. Conventional air calcination regeneration can make MoCx is completely oxidized to form MoO 3 ; however, air calcination cannot avoid the aggregation of MoO on the outer surface of the catalyst 3 . After aggregation, the oxidized Mo microcrystals are difficult to re-enter the zeolite pores to form highly dispersed MoOx species, but tend to combine with the framework aluminum of the zeolite to form aluminum molybdate. After multiple oxidative regenerations of the Mo / HZSM-5 catalyst, the free MoO 3 will gradually converge and increase in size, which accelerates the removal of aluminum from the zeolite framework and the formation of aluminum molybdate, ultimately leading to the collapse of the zeolite pores and making the oxidative regeneration deactivation irreversible. In recent years, researchers have used short regeneration times, periodically pulsed oxygen into the methane feed, and low regeneration reaction temperatures (450 °C) in a continuous regeneration cycle mode to extend the life of the Mo / zeolite catalyst and improve the aromatic hydrocarbon yield in the methane dehydrogenation aromatization reaction; however, so far, oxidative regeneration can timely remove the carbon deposition in the catalyst pores, but achieving the complete recovery of the Mo species on the outer surface is a challenge for the Mo / HZSM-5 catalyst to maintain the structural stability of the catalyst and achieve long-term operation of the methane dehydrogenation aromatization reaction.

[0005] Dalian Institute of Chemical Physics (CN1590352, CN1401431) applied for Chinese patents on the preparation method and application of methane dehydrogenation aromatization catalysts a long time ago, indicating that Mo or W loaded in HZSM-5, ZSM-11, MCM-22, MCM-49, MCM-56 zeolites can show good methane dehydrogenation aromatization reaction activity, but did not mention the reaction deactivation caused after multiple reactions. Shanghai Research Institute of Petrochemical Technology, Sinopec (CN104447172A) disclosed a regeneration method for a methane non-oxidative dehydrogenation aromatization catalyst, adopting a technical solution of periodic continuous switching and in-situ regeneration of a regenerating gas composed of methane raw gas and oxidizing gases carbon dioxide and hydrogen, which solved the above problems. Korean scholars believe through theoretical calculations that methane CO 2 co-addition is a relatively economical and effective carbon-neutral method; however, later studies by scholars in multiple countries have shown that the addition of oxygen-containing gases currently cannot achieve continuous operation of the reaction. Qingdao Institute of the Chinese Academy of Sciences (CN107774299A) disclosed a bifunctional mixed catalyst for methane dehydrogenation aromatization reaction and its preparation and regeneration method, introducing an oxygen storage material into the methane dehydrogenation aromatization reaction process for the first time. Its catalytic system consists of an oxygen carrier and a molybdenum-based zeolite. The molybdenum-based zeolite is used for the methane dehydrogenation aromatization step, while the oxygen carrier is used to selectively convert the hydrogen generated by the aromatization reaction into water, improving the life and reaction activity of the catalyst; however, this method does not mention how to avoid the formation of aluminum molybdate that causes the collapse of the zeolite pores. Therefore, a catalytic oxidation regeneration method that can inhibit the collapse of the zeolite pores is needed to solve the problems of the existing technology. Summary of the Invention

[0006] In view of the above-mentioned existing technical problems, the present invention provides a preparation method of a differential Mo-Ce / HZSM-5 oxidation regeneration catalyst based on oxygen storage. By using an oxygen storage material to construct differential oxidation regeneration conditions, the oxidation conditions are changed through the oxygen storage / oxygen release characteristics of the oxygen storage material on the outer surface of the catalyst, so as to selectively eliminate polycyclic aromatic hydrocarbon (high temperature) carbon deposition and graphite-like (low temperature carbon deposition).

[0007] To achieve the above object, the present invention adopts the following technical solutions.

[0008] A preparation method of a differential Mo-Ce / HZSM-5 oxidation regeneration catalyst based on oxygen storage, comprising the following steps: Step 1, preparing a conventional Mo / HZSM-5 catalyst: dissolving ammonium molybdate in deionized water to obtain a solution containing Mo ions; impregnating the solution containing Mo ions on HZSM-5 zeolite, standing and drying to obtain a Mo / HZSM-5 catalyst precursor, and calcining the dried catalyst precursor to obtain a Mo / HZSM-5 catalyst; Step 2, blocking the pores of the Mo / HZSM-5 catalyst with macromolecular polycyclic aromatic hydrocarbons: dissolving polycyclic aromatic hydrocarbons in a solution, impregnating the solution on the above-mentioned Mo / HZSM-5, standing and drying to obtain a Mo@Ar / HZSM-5 catalyst precursor containing aromatic hydrocarbons, and calcining the dried catalyst precursor in an inert gas atmosphere to obtain a Mo@Ar / HZSM-5 catalyst; Step 3, introducing an oxygen storage material on the outer surface of the catalyst: dissolving an oxygen storage material precursor in a solvent, impregnating the solution on Mo@Ar / HZSM-5, standing and drying to obtain a Mo-Ce@Ar / HZSM-5 catalyst precursor containing aromatic hydrocarbons, and removing the macromolecular polycyclic aromatic hydrocarbons blocking the pores by calcination to obtain a Mo-Ce / HZSM-5 catalyst with an oxygen storage material covering the outer surface.

[0009] Further, in step 1, based on MoO 3 the molybdenum content is 0.1%-40 w% by weight in the catalyst.

[0010] Further, in step 1, when impregnating the solution containing Mo ions on HZSM-5 zeolite, either equal-volume impregnation (the volume of the solution containing Mo is approximately equal to the saturated water absorption of HZSM-5), or excessive impregnation (the volume of the solution containing Mo is greater than the saturated water absorption of HZSM-5) and unsaturated impregnation (the volume of the solution containing Mo is less than the saturated water absorption of HZSM-5) can be used.

[0011] Further, in step 1, either short-time standing or no standing (standing for 0-6 hours) can be adopted, or relatively long-time standing (6-120 hours) can be adopted.

[0012] Further, in step 1, the roasting speed is within 0.1 - 50 °C / min; the roasting temperature is 200 - 1000 °C.

[0013] Further, in step 1, the roasting time is 0.1 - 1000 minutes.

[0014] Further, in step 2, the polycyclic aromatic hydrocarbons refer to aromatic hydrocarbons with more than 2 aromatic rings, including monocyclic aromatic hydrocarbon polymers and their derivatives (including those containing side chains, branched chains, cycloalkanes, etc.).

[0015] Further, in step 2, the solution is one of deionized water, inorganic solvent, organic solvent, or a mixture of inorganic solvent and organic solvent.

[0016] Further, in step 2, either equal - volume impregnation (the volume of the polycyclic aromatic hydrocarbon solution is similar to the saturated adsorption capacity of Mo / HZSM - 5) can be used, or excess impregnation (the volume of the polycyclic aromatic hydrocarbon solution is greater than the saturated adsorption capacity of Mo / HZSM - 5) and unsaturated impregnation (the volume of the polycyclic aromatic hydrocarbon solution is less than the saturated adsorption capacity of Mo / HZSM - 5) can be used.

[0017] Further, in step 2, either short - time static or no static (static for 0 - 6 hours) can be used, or relatively long - time static (6 - 120 hours) can be used.

[0018] Further, in step 2, the drying temperature can be higher than the boiling point of the solvent, or can be dried for a long time below the boiling point of the solvent.

[0019] Further, in step 2, static drying can be carried out in air (low - temperature drying in an oven), or can be carried out under reduced pressure (such as in a vacuum drying oven), or can be carried out in an inert gas atmosphere (such as nitrogen, helium, argon, etc.) to ensure experimental safety.

[0020] Further, in step 2, the catalyst precursor is calcined in an inert gas atmosphere to avoid oxidation of polycyclic aromatic hydrocarbons, etc.; the inert gas can be nitrogen, helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn, radioactive).

[0021] Further, in step 2, the calcination speed is within 0.1 - 50 °C / min; the calcination temperature range is room temperature - 1000 °C; the calcination time is 0.1 - 1000 minutes.

[0022] Further, in step 3, the oxygen storage material precursor mainly includes mono - component, binary, or multi - component composite oxides composed of rare earth elements, alkaline earth metal elements, or transition metal elements. These materials are mainly based on cerium oxide and can reversibly store and release oxygen.

[0023] Further, in Step 3, when the solvent is deionized water, the oxygen storage material precursor can be water-soluble nitrates, sulfates, chlorides, or other water-soluble precursor salts; when the solvent is non-deionized water (such as organic solvents), the oxygen storage material precursor can be non-water-soluble precursor salts; the solvent can be an organic solvent, or a mixture of an inorganic solvent and an organic solvent.

[0024] Further, in Step 3, either equal-volume impregnation (the solution volume is similar to the saturated adsorption capacity of Mo@Ar / HZSM-5) can be used, or excess impregnation (the solution volume is greater than the saturated adsorption capacity of Mo@Ar / HZSM-5) and unsaturated impregnation (the solution volume is less than the saturated adsorption capacity of Mo@Ar / HZSM-5) can be used.

[0025] Further, in Step 3, either short-time static or non-static (static for 0 - 6 hours) can be used, or relatively long-time static (static for 6 - 120 hours) can be used.

[0026] Further, in Step 3, the calcination rate is within 0.1 - 50 °C / min; the calcination temperature range is 200 °C - 1000 °C; the calcination time is 0.1 - 1000 minutes.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows.

[0028] The Mo-Ce / HZSM-5 catalytic system constructed by the present invention has an oxygen storage material loaded on its surface that can effectively adsorb oxygen during the oxygen regeneration stage, thereby precisely regulating the oxidative regeneration atmosphere. This catalytic system has the ability to adjust the oxidation state of MoCy clusters on the catalyst surface, effectively inhibiting the abnormal growth of MoO 3 grains, ensuring a high degree of dispersion of molybdenum oxide microcrystals, and promoting their re-embedding into the inner layer of the molecular sieve framework. In addition, the Mo-oxo species combined with the Brönsted acidic hydroxyl groups of the molecular sieve can prevent molybdenum from reacting with the framework aluminum of the molecular sieve to form aluminum molybdate, ensuring the reversible cyclicity of molybdenum species during the catalytic process. The catalyst prepared according to this technical solution is expected to maintain the structural stability of the Mo / HZSM-5 catalyst during long-term operation. Description of the Drawings

[0029] Figure 1 Methane dehydrogenation aromatization methane conversion rate and benzene yield curve diagrams on different catalysts (a, methane conversion rate; b, benzene yield).

[0030] Figure 2TPO result diagrams of catalytic materials under different conditions (a, TPO of Mo / HZSM-5 catalyst; b, TPO of Mo / HZSM-5 catalyst after 3.5 hours of air pulse; c, TPO of Mo-Ce / HZSM-5 catalyst; d, TPO of Mo-Ce / HZSM-5 catalyst after 3.5 hours of air pulse) Detailed implementation manners

[0031] The technical solutions in the present invention will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0032] A preparation method of a differential Mo-Ce / HZSM-5 oxidation regeneration catalyst based on oxygen storage includes the following steps: Step 1: Prepare a conventional Mo / HZSM-5 catalyst: Dissolve ammonium molybdate in deionized water to obtain a solution containing Mo ions; Immerse the solution containing Mo ions on HZSM-5 molecular sieve, stand still and dry to obtain a Mo / HZSM-5 catalyst precursor, and calcine the dried catalyst precursor to obtain a Mo / HZSM-5 catalyst; Step 2: Block the pores of the Mo / HZSM-5 catalyst with macromolecular polycyclic aromatic hydrocarbons: Dissolve the polycyclic aromatic hydrocarbons in a solution, immerse them on the above Mo / HZSM-5, stand still and dry to obtain a Mo@Ar / HZSM-5 catalyst precursor containing aromatic hydrocarbons, and calcine the dried catalyst precursor in an inert gas atmosphere to obtain a Mo@Ar / HZSM-5 catalyst; Step 3: Introduce an oxygen storage material on the outer surface of the catalyst: Dissolve the oxygen storage material precursor in a solvent, immerse it on Mo@Ar / HZSM-5, stand still and dry to obtain a Mo-Ce@Ar / HZSM-5 catalyst precursor containing aromatic hydrocarbons, and remove the macromolecular polycyclic aromatic hydrocarbons blocking the pores by calcination to obtain a Mo-Ce / HZSM-5 catalyst with an oxygen storage material covering the outer surface.

[0033] Further, in Step 1, based on MoO 3 the molybdenum content is 0.1%-40 w% by weight in the catalyst; preferably 0.1%-20 w%, more preferably 0.1%-10 w%.

[0034] Further, in step 1, the solution containing Mo ions is impregnated on the HZSM-5 molecular sieve. Either equal-volume impregnation (the volume of the Mo-containing solution is approximately equal to the saturated water absorption of HZSM-5), or excess impregnation (the volume of the Mo-containing solution is greater than the saturated water absorption of HZSM-5) and unsaturated impregnation (the volume of the Mo-containing solution is less than the saturated water absorption of HZSM-5) can be used.

[0035] Further, in step 1, either short-time static or no static (static for 0 - 6 hours) can be adopted, or relatively long-time static (6 - 120 hours), preferably 2 - 12 hours, can be used to make Mo evenly distributed in the molecular sieve pores.

[0036] Further, in step 1, the calcination rate is within 0.1 - 50 °C / minute, preferably 0.5 - 10 °C / minute; in order to decompose ammonium molybdate into MoOx (x = 0.1 - 3), the calcination temperature is 200 - 1000 °C, preferably 300 - 800 °C.

[0037] Further, in step 1, in order to decompose ammonium molybdate into MoOx (x = 0.1 - 3), the calcination time is 0.1 - 1000 minutes, preferably 10 - 600 minutes.

[0038] Further, in step 2, the polycyclic aromatic hydrocarbon refers to an aromatic hydrocarbon with more than 2 aromatic rings, including monocyclic aromatic hydrocarbon polymers and their derivatives (including those containing side chains, branched chains, cycloalkanes, etc.).

[0039] Further, in step 2, the solution is one of deionized water, inorganic solvent, organic solvent or a mixture of inorganic solvent and organic solvent.

[0040] Further, in step 2, either equal-volume impregnation (the volume of the polycyclic aromatic hydrocarbon solution is similar to the saturated adsorption capacity of Mo / HZSM-5), or excess impregnation (the volume of the polycyclic aromatic hydrocarbon solution is greater than the saturated adsorption capacity of Mo / HZSM-5) and unsaturated impregnation (the volume of the polycyclic aromatic hydrocarbon solution is less than the saturated adsorption capacity of Mo / HZSM-5) can be used.

[0041] Further, in step 2, either short-time static or no static (static for 0 - 6 hours) can be adopted, or relatively long-time static (6 - 120 hours), preferably 2 - 12 hours, can be used to make Mo evenly distributed in the molecular sieve pores.

[0042] Further, in step 2, the drying temperature can be higher than the boiling point of the solvent, or can be dried for a long time below the boiling point of the solvent to keep the polycyclic aromatic hydrocarbon evenly dispersed.

[0043] Further, in Step 2, the static drying can be carried out in air (low-temperature drying in an oven), under reduced pressure (such as in a vacuum drying oven), or in an inert gas atmosphere (such as nitrogen, helium, argon, etc.) to ensure experimental safety.

[0044] Further, in Step 2, the catalyst precursor is calcined in an inert gas atmosphere to avoid oxidation of polycyclic aromatic hydrocarbons, etc.; the inert gas can be nitrogen, helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn, radioactive).

[0045] Further, in Step 2, the calcination time depends on the decomposition of polycyclic aromatic hydrocarbons by the calcination equipment. Generally, the calcination time is 0.1 - 1000 minutes, preferably 10 - 600 minutes.

[0046] Further, in Step 2, the calcination rate depends on the combination of polycyclic aromatic hydrocarbons and the catalyst by the calcination equipment. The calcination rate can be within 0.1 - 50 °C / minute, preferably 0.5 - 10 °C / minute.

[0047] Further, in Step 2, to make the polycyclic aromatic hydrocarbons adhere to the catalyst, the calcination temperature range is room temperature - 1000 °C, preferably 300 °C - 800 °C.

[0048] Further, in Step 3, the oxygen storage material precursor mainly includes single-component, binary, or multi-component composite oxides composed of rare earth elements, alkaline earth metal elements, or transition metal elements. These materials are mainly based on cerium oxide and can reversibly store and release oxygen.

[0049] Further, in Step 3, when the solvent is deionized water, the oxygen storage material precursor can be water-soluble nitrates, sulfates, chlorides, or other water-soluble precursor salts; when the solvent is non-deionized water (such as organic solvents), the oxygen storage material precursor can be water-insoluble precursor salts; the solvent can be organic solvents, inorganic solvents, or a mixture of organic solvents and inorganic solvents.

[0050] Further, in Step 3, either equal-volume impregnation (the solution volume is similar to the saturated adsorption capacity of Mo@Ar / HZSM-5) can be used, or excess impregnation (the solution volume is greater than the saturated adsorption capacity of Mo@Ar / HZSM-5) and unsaturated impregnation (the solution volume is less than the saturated adsorption capacity of Mo@Ar / HZSM-5) can be used.

[0051] Further, in Step 3, either short-term static or non-static (static for 0 - 6 hours) can be used, or relatively long-term static (6 - 120 hours), preferably 2 - 12 hours, to disperse the oxygen storage material on the catalyst surface.

[0052] Further, in Step 3, the roasting speed is within 0.1 - 50 °C / minute, preferably 0.5 - 10 °C / minute; the roasting temperature range is 200 °C - 1000 °C, preferably 300 °C - 800 °C.

[0053] Further, in Step 3, the roasting time is 0.1 - 1000 minutes, preferably 10 - 600 minutes.

[0054] Example 1.

[0055] Step 1: Dissolve analytical pure ammonium molybdate in deionized water to obtain a solution containing Mo ions with a solution concentration of 0.06 g / L. Immerse 10 mL of the above solution and 10 g of HZSM-5 molecular sieve at room temperature, stir evenly repeatedly, and then let it stand overnight at room temperature. Dry the above materials at 120 °C in an oven for 6 hours to obtain a Mo / HZSM-5 catalyst precursor. Roast the dried catalyst precursor in a muffle furnace at 3 °C / min to 550 °C and calcine at this temperature for 4 hours to obtain a 6 wt% Mo / HZSM-5 catalyst.

[0056] Step 2: Dissolve 4 g of pyrene in 8 mL of toluene. Mix 10 g of the above 6 wt% Mo / HZSM-5 catalyst and the toluene solution containing pyrene at room temperature, stir evenly repeatedly, and then let it stand overnight. Dry the above materials in a vacuum drying oven at 60 °C for 4 hours to obtain a Mo@Ar / HZSM-5 catalyst precursor; Place the above precursor in a quartz boat and place it in the center of a quartz tube. Under a nitrogen atmosphere of 100 ml / min, heat the tube furnace from 3 °C / min to 500 °C and calcine at this temperature for 4 hours to obtain a Mo@Ar / HZSM-5 catalyst.

[0057] Step 3: Dissolve analytical pure cerium nitrate in deionized water to obtain a solution containing Ce ions with Ce / Mo = 1:1 and a solution concentration of 0.06 g / L. Immerse 10 mL of the solution containing Ce ions and 10 g of Mo@Ar / HZSM-5 at room temperature, stir evenly repeatedly, and then let it stand overnight at room temperature. Dry the above materials at 120 °C in an oven for 6 hours to obtain a Mo / HZSM-5 catalyst precursor. Roast the dried catalyst precursor in a muffle furnace at 3 °C / min to 500 0 °C and calcine at this temperature for 4 hours to obtain a Mo-Ce / HZSM-5 catalyst.

[0058] Example 2.

[0059] Step 1: Dissolve analytical pure ammonium molybdate in deionized water to obtain a solution containing Mo ions with a solution concentration of 0.06 g / L. Immerse 10 mL of the above solution and 10 g of HZSM-5 molecular sieve at room temperature, stir evenly repeatedly, and then let it stand overnight at room temperature. Dry the above materials at 120 °C in an oven for 6 hours to obtain a Mo / HZSM-5 catalyst precursor. Calcinate the dried catalyst precursor in a muffle furnace at 3 °C / min to 550 °C and calcine at this temperature for 4 hours to obtain a 6 wt% Mo / HZSM-5 catalyst.

[0060] Step 2: Dissolve 4 g of anthracene in 8 mL of toluene. Mix 10 g of the above 6 wt% Mo / HZSM-5 catalyst and the toluene solution containing anthracene and immerse them at room temperature. Stir evenly repeatedly and then let it stand overnight. Dry the above materials in a vacuum drying oven at 60 °C for 4 hours to obtain a Mo@Ar / HZSM-5 catalyst precursor. Place the above precursor in a quartz boat and place it in the center of a quartz tube. Under a nitrogen atmosphere of 100 ml / min, heat the tube furnace at 3 °C / min to 500 °C and calcine at this temperature for 4 hours to obtain a Mo@Ar / HZSM-5 catalyst.

[0061] Step 3: Dissolve analytical pure cerium nitrate in deionized water to obtain a solution containing Ce ions with Ce / Mo = 1:1 and a solution concentration of approximately 0.06 g / L. Immerse 10 mL of the above solution and 10 g of Mo@Ar / HZSM-5 at room temperature, stir evenly repeatedly, and then let it stand overnight at room temperature. Dry the above materials at 120 °C in an oven for 6 hours to obtain a Mo / HZSM-5 catalyst precursor. Calcinate the dried catalyst precursor in a muffle furnace at 3 °C / min to 500 °C and calcine at this temperature for 4 hours to obtain a Mo-Ce / HZSM-5 catalyst.

[0062] Example 3.

[0063] Step 1: Dissolve analytical pure ammonium molybdate in deionized water to obtain a solution containing Mo ions with a solution concentration of 0.06 g / L. Immerse 10 mL of the above solution and 10 g of HZSM-5 molecular sieve at room temperature, stir evenly repeatedly, and then let it stand overnight at room temperature. Dry the above materials at 120 °C in an oven for 6 hours to obtain a Mo / HZSM-5 catalyst precursor. Calcinate the dried catalyst precursor in a muffle furnace at 3 °C / min to 550 °C and calcine at this temperature for 4 hours to obtain a 6 wt% Mo / HZSM-5 catalyst.

[0064] Step 2: Dissolve 4 g of phenanthrene in 8 mL of toluene. Mix 10 g of the above 6 wt% Mo / HZSM-5 catalyst with the toluene solution containing phenanthrene and impregnate at room temperature. After repeatedly stirring evenly, let it stand overnight. Dry the above materials in a vacuum drying oven at 60 °C for 4 hours to obtain the Mo@Ar / HZSM-5 catalyst precursor. Place the above precursor in a quartz boat and place it in the center of a quartz tube. Under a nitrogen atmosphere of 100 ml / min, heat the tube furnace from 3 °C / min to 500 °C and calcine at this temperature for 4 hours to obtain the Mo@Ar / HZSM-5 catalyst.

[0065] Step 3: Dissolve analytical pure cerium nitrate in deionized water to obtain a solution containing Ce ions, with Ce / Mo = 1:1 and a solution concentration of approximately 0.06 g / L. Mix 10 mL of the above solution with 10 g of Mo@Ar / HZSM-5 and impregnate at room temperature. After repeatedly stirring evenly, let it stand overnight at room temperature. Dry the above materials after standing in an oven at 120 °C for 6 hours to obtain the Mo / HZSM-5 catalyst precursor. Calcinate the dried catalyst precursor in a muffle furnace from 3 °C / min to 500 0 °C and calcine at this temperature for 4 hours to obtain the Mo-Ce / HZSM-5 catalyst.

[0066] Reaction performance evaluation test The reaction performance evaluation method is as follows: Put 400 mg of 20–40 mesh conventional Mo / HZSM-5 catalyst and the methane dehydroaromatization Mo-Ce / HZSM-5 catalyst of Examples 1-3 into a tubular quartz reactor with an inner diameter of 0.8 mm. Place the catalyst in the constant temperature zone oven and put quartz wool on both sides. Use a flow controller to control the individual feed gases. Raise the reaction temperature to 973 K at a rate of 10 K / min, with a gas hourly space velocity of 1500 ml / (G.H) under a flow rate of 90% CH 4 / 10% N 2 ; Then stabilize at 973 K and analyze the effluent through an on-line gas chromatograph equipped with a flame ionization detector (FID) and a thermal conductivity detector (TCD); FID is used to analyze CH 4 , C 6 H 6 , C 7 H 8 and C 10 H 8 , while TCD is used to analyze H 2 , N 2 , O 2 , CH 4 , Co, CO 2 , C 2 H 4 and C 2 H 6; Using N 2 as the internal standard, the methane conversion rate was calculated using the TCD results; the C 6 H 6 aromatic products such as etc. were detected by FID, and the methane conversion rate and the aromatic conversion rate were obtained by calculation. The results of the methane dehydroaromatization reaction are as Figure 1 shown.

[0067] From Figure 1 it can be seen that in the methane dehydroaromatization at 973K, the methane conversion rate was about 10% or so, and the aromatic yield was 6%. As the reaction proceeded, the methane conversion rate and the aromatic yield gradually decreased, which was similar to the results reported in the literature. When the catalyst contained pyridine, anthracene, and phenanthrene, the methane conversion rate was significantly increased to 20 - 45%, while the aromatic yield was increased to 6.5 - 8.5%. Previous studies have shown that the Mo / HZSM-5 catalyst deposited with oxygen storage materials showed high catalytic activity mainly due to its redox characteristics, which promoted the controllable combustion of hydrogen. This process has been indirectly verified by RGA-MS, O 2 -TPD and H 2 -TPR analysis methods. Through selective hydrogen combustion, the over-oxidation of aromatic substances generated in the reaction was effectively avoided. Therefore, the combination of oxygen storage materials and Mo / HZSM-5 can shift the reaction equilibrium towards the MDA reaction direction favorable for benzene formation. Figure 1 The results shown indicate that after the oxygen storage materials were covered with different macromolecular compounds (pyridine, anthracene, phenanthrene), they did cover the catalyst surface and affected the reaction performance of the catalyst.

[0068] Differentiated carbon deposition elimination evaluation experiment By combining the O 2 pulse partial oxidation technology and the temperature-programmed oxidation (TPO) test method, to evaluate whether the Mo-Ce / HZSM-5 catalyst achieved differentiated oxidation effect during the regeneration process. The catalyst used was the Mo-Ce / HZSM-5 catalyst synthesized with the assistance of pyrene. The TPO test was completed in a self-made high-efficiency multi-purpose adsorption instrument and an on-line mass spectrometry combined system in the laboratory. The air pulse experiment was carried out using a self-made gas pulse instrument in the laboratory. Each pulse lasted for 45 seconds, and the pulse interval was also 45 seconds. The reaction temperature was set at 550°C. The TPO detection channels included 32, 28, and 44, corresponding to oxygen, carbon monoxide, and carbon dioxide respectively. Figure 2 a shows the TPO analysis results of the carbon deposition after the reaction of the Mo / HZSM-5 catalyst, Figure 2 c is the TPO analysis result of the carbon deposition after the reaction of the Mo-Ce / HZSM-5 catalyst; Figure 2 b and Figure 2d shows the TPO analysis results of carbon deposition on Mo / HZSM-5 catalyst and Mo-Ce / HZSM-5 catalyst after 3.5-hour air pulse treatment. Specific characterization data can be found in Figure 2 a- Figure 2 d.

[0069] Analysis Figure 2 From the data shown in a, it can be observed that the Mo / HZSM-5 catalyst mainly forms high-temperature carbon deposition after the reaction; Figure 2 As shown in b, after multiple pulse treatments, the types of carbon deposition on the Mo / HZSM-5 catalyst did not change, and the partial oxidation of the pulsed air mainly led to a significant reduction in the total amount of carbon deposition.

[0070] Further investigation Figure 2 c shows that the carbon deposition types on the Mo-Ce / HZSM-5 (pyrene) catalyst can be divided into two types: one is high-temperature carbon deposition with a central temperature of about 520 °C, belonging to polycyclic aromatic hydrocarbons; the other is low-temperature carbon deposition with a slightly lower central temperature, namely graphite. Among them, the amount of high-temperature carbon deposition is significantly higher than that of low-temperature carbon deposition; from Figure 2 d, it can be seen that after multiple air pulse treatments, the quantity ratio of different carbon depositions on the Mo-Ce / HZSM-5 (pyrene) catalyst changed significantly, and the reduction amount of high-temperature carbon deposition was significantly greater than that of low-temperature carbon deposition.

[0071] The research results show that after adding oxygen storage materials, the Mo-Ce / HZSM-5 catalyst exhibits selective regeneration characteristics. Under air regeneration conditions, the catalyst can selectively eliminate high-temperature carbon deposition on the inner surface. At the same time, due to the presence of oxygen storage materials on the outer surface, the regeneration conditions on the outer surface of the catalyst are reduced, thus retaining more low-temperature carbon deposition.

Claims

1. A method for preparing a differentiated Mo-Ce / HZSM-5 oxidation regeneration catalyst based on oxygen storage, characterized in that: The steps include: Step 1, preparing a conventional Mo / HZSM-5 catalyst: dissolving ammonium molybdate in deionized water to obtain a solution containing Mo ions; impregnating the solution containing Mo ions on a HZSM-5 molecular sieve, standing and drying to obtain a Mo / HZSM-5 catalyst precursor, and calcining the dried catalyst precursor to obtain a Mo / HZSM-5 catalyst; Step 2, macromolecular polycyclic aromatic hydrocarbons block the pores of the Mo / HZSM-5 catalyst: dissolving polycyclic aromatic hydrocarbons in a solution, impregnating the solution on the Mo / HZSM-5, standing and drying to obtain a Mo@Ar / HZSM-5 catalyst precursor containing aromatic hydrocarbons, and calcining the dried catalyst precursor under an inert gas atmosphere to obtain a Mo@Ar / HZSM-5 catalyst; Step 3, introducing oxygen storage material on the outer surface of the catalyst: dissolving the oxygen storage material precursor in a solvent, impregnating it on Mo@Ar / HZSM-5, and drying it to obtain a Mo-Ce@Ar / HZSM-5 catalyst precursor containing aromatics. The large molecular polycyclic aromatic hydrocarbons that block the pores are removed by calcination to obtain a Mo-Ce / HZSM-5 catalyst covered with oxygen storage material on the outer surface.

2. The method for preparing a differentiated Mo-Ce / HZSM-5 oxidation regeneration catalyst based on oxygen storage according to claim 1, characterized in that: In the step 1, based on MoO3, the molybdenum content in the catalyst is 0.1%-40w%.

3. The method for preparing a differentiated Mo-Ce / HZSM-5 oxidation regeneration catalyst based on oxygen storage according to claim 1, characterized in that: In the step 1, the impregnation is equal volume impregnation, excess impregnation or non-saturated impregnation.

4. The method for preparing a differentiated Mo-Ce / HZSM-5 oxidation regeneration catalyst based on oxygen storage according to claim 1, characterized in that: In the step 1, the calcination rate is within the range of 0.1-50°C / min; the calcination temperature is 200-1000°C; and the calcination time is 0.1-1000 minutes.

5. The method for preparing a differentiated Mo-Ce / HZSM-5 oxidation regeneration catalyst based on oxygen storage according to claim 1, characterized in that: In step 2, condensed ring aromatic hydrocarbons refer to aromatic hydrocarbons with more than 2 aromatic rings, including single-ring aromatic hydrocarbon polymers and their derivatives.

6. The method for preparing a differentiated Mo-Ce / HZSM-5 oxidation regeneration catalyst based on oxygen storage according to claim 1, characterized in that: In the step 2, the calcination rate is within the range of 0.1-50°C / min; the calcination temperature ranges from room temperature to 1000°C; and the calcination time is 0.1-1000 minutes.

7. The method for preparing a differentiated Mo-Ce / HZSM-5 oxidation regeneration catalyst based on oxygen storage according to claim 1, characterized in that: In step 2, the inert gas is one of nitrogen, helium, neon, argon, krypton, xenon or radon.

8. The method for preparing a differentiated Mo-Ce / HZSM-5 oxidation regeneration catalyst based on oxygen storage according to claim 1, characterized in that: In step 3, the oxygen storage material mainly includes mono-, di- or multi-component composite oxides composed of rare earth elements, alkaline earth metal elements or transition metal elements, and these materials are mainly composed of cerium oxide.

9. The method for preparing a differentiated Mo-Ce / HZSM-5 oxidation regeneration catalyst based on oxygen storage according to claim 1, characterized in that: In step 3, the solvent is a mixture of deionized water, deionized water, an organic solvent, an inorganic solvent and an organic solvent; when the solvent is deionized water, the oxygen storage material precursor is a water-soluble nitrate, sulfate, chloride, or other water-soluble precursor salt; when the solvent is deionized water, the oxygen storage material precursor is a water-insoluble precursor salt.

10. The method for preparing a differentiated Mo-Ce / HZSM-5 oxidation regeneration catalyst based on oxygen storage according to claim 1, characterized in that: In the step 3, the calcination rate is within the range of 0.1-50°C / min; the calcination temperature range is 200°C-1000°C; and the calcination time is 0.1-1000 minutes.

Images