Flaky HZSM-5 molecular sieve catalyst, preparation method thereof and application of flaky HZSM-5 molecular sieve catalyst in preparation of aromatic hydrocarbon through carbon dioxide hydrogenation

Abstract

The invention provides a flaky HZSM-5 molecular sieve catalyst, a preparation method thereof and application of the flaky HZSM-5 molecular sieve catalyst in preparation of aromatic hydrocarbon through carbon dioxide hydrogenation, and belongs to the technical field of molecular sieve catalysts. The preparation process of the catalyst comprises the following steps: sequentially adding a silicon source, a template agent, an aluminum source and an additive into water, stirring to obtain mixed gel, carrying out heating crystallization, centrifuging, washing to be neutral, drying, roasting and carrying out ion exchange to obtain the flaky HZSM-5 molecular sieve catalyst, wherein the silicon source and the aluminum source are respectively metered by SiO2 and Al2O3, and the molar ratio of SiO2 to the template agent to Al2O3 to the additive to H2O is controlled to be 1: (0.2-0.3): (0.02-0.04): (0.4-0.6): (35-45). The catalyst preparation method is simple and easy to operate, and raw materials are cheap and easily available; and the catalyst has excellent catalytic activity and relatively high aromatic hydrocarbon selectivity in preparation of aromatic hydrocarbon through CO2 hydrogenation.

Description

Technical Field

[0001] The invention belongs to the technical field of molecular sieve catalysts, and in particular relates to a sheet-like HZSM-5 molecular sieve catalyst, a preparation method thereof, and an application thereof in the hydrogenation of carbon dioxide to aromatics. Background Art

[0002] At present, the main means to solve CO2 emissions is to use CO2 to directly or indirectly hydrogenate to obtain high-added chemicals (such as olefins, aromatics, alcohols, gasoline, etc.). Aromatics are one of the important basic chemical raw materials in the synthesis of organic materials, and are important synthetic raw materials for many polymer materials (such as polystyrene, phenol resin, nylon, and polyethylene terephthalate resin, etc.). Therefore, converting CO2 into aromatics is an important way to solve the environmental problems caused by excessive CO2 emissions and reduce fossil energy. At the same time, it provides an important source of raw materials for the chemical industry and realizes resource recycling. The key point of this conversion is how to prepare a catalyst with low cost, high efficiency, stability and simple process.

[0003] ZSM-5 molecular sieve plays an important role in aromatization reaction due to its unique pore structure, shape selectivity, adjustable acidity and specific surface area. However, the traditional ZSM-5 molecular sieve has a long residence time in the pores of the guest molecules, which hinders the diffusion of the product, not only causing the blockage of the molecular sieve pores, but also leading to the occurrence of side reactions, and also causing the increase in the rate of carbon deposition, reducing the life of the catalyst. Short b-axis ZSM-5 molecular sieve has many advantages such as ultra-thin molecular sieve skeleton, high specific surface area, accessible acid sites and adjustable mesopore size. It has better catalytic performance for specific reactions, and the exploration of its synthesis method and application field is of great significance.

[0004] At present, the synthesis of short b-axis ZSM-5 molecular sieves mainly adopts the structure-directed method using quaternary ammonium salts, triethylenediamine and tetrabutylphosphonium hydroxide as structure-directing agents; and the growth modification method assisted by additives such as urea, fluorine, sugars, alcohols and guanidines.

[0005] Chinese invention patent CN105000574A discloses a HASM-5 molecular sieve with special morphology and its preparation method, which is prepared by using aluminum source, silicon source, alkali source and template agent as raw materials to prepare mixed mother liquor, and is obtained by first-stage and second-stage crystallization and ion exchange, but is mainly used in methanol to olefin reaction.

[0006] Chinese invention patent CN114160183B discloses the preparation of a flaky HZSM-5 molecular sieve catalyst and its application in the hydrogenation of carbon dioxide to aromatics. By adding the mineralizer NH4F and adjusting the molar addition ratio of urea and NH4F, precise control of the synthetic thickness of the HZSM-5 molecular sieve is achieved. It has a large specific surface area, a large total acid content, and a high aromatics selectivity, but its CO2 conversion rate is low.

[0007] However, HZSM-5 molecular sieve still has defects such as small pore size and uneven acid distribution, which leads to reduced selectivity of target products. Therefore, it is of great significance to study the structural regulation and catalytic performance of HZSM-5 molecular sieve. In addition, metal catalysts formed with flake HZSM-5 molecular sieve as components have good application prospects in terms of catalytic activity and stability. Summary of the invention

[0008] The present invention aims at the problems existing in the prior art and provides a sheet-like HZSM-5 molecular sieve catalyst, a preparation method thereof and an application thereof in the hydrogenation of carbon dioxide to aromatics. By adding NH4F to inhibit the growth of straight pore channels (b axis), an HZSM-5 molecular sieve with an average b axis length of less than 100 nm is synthesized. The preparation method is simple and easy to operate, and the raw materials are cheap and readily available. The catalyst has excellent catalytic activity and high aromatics selectivity in the direct production of aromatics by hydrogenation of CO2.

[0009] The technical solution of the present invention is as follows:

[0010] The present invention relates to a method for preparing a flaky HZSM-5 molecular sieve catalyst, comprising the following steps:

[0011] (1) adding a silicon source, a template, an aluminum source and an additive into water in sequence, heating and stirring, to obtain a mixed gel;

[0012] (2) raising the temperature to allow the mixed gel to crystallize;

[0013] (3) After the crystallization is completed, the flaky ZSM-5 molecular sieve is obtained by centrifugation, washing to neutrality, drying, and calcination;

[0014] (4) performing ion exchange on the ZSM-5 molecular sieve to obtain the flaky HZSM-5 molecular sieve catalyst;

[0015] The silicon source and the aluminum source are measured with SiO2 and Al2O3 respectively, and the molar ratio of each raw material is controlled to be SiO2: template: Al2O3: additive: H2O = 1: 0.2-0.3: 0.02-0.04: 0.4-0.6: 35-45.

[0016] Furthermore, the template agent is selected from one or more of tetrapropylammonium hydroxide (TPAOH) and tetrapropylammonium bromide (TPABr); preferably tetrapropylammonium hydroxide (TPAOH).

[0017] Furthermore, the additive is NH4F. The additive used in the present invention can effectively inhibit the growth of the b-axis of the molecular sieve and obtain a molecular sieve with a short b-axis.

[0018] Furthermore, the silicon source is selected from one or more of tetraethyl orthosilicate (TEOS), white carbon black, silica sol, solid silica gel, sodium silicate crystals, C-type silica gel and water glass; preferably tetraethyl orthosilicate (TEOS).

[0019] Furthermore, the aluminum source is selected from one or more of sodium aluminate (Al2Na2O4), sodium aluminate (NaAlO2), aluminum sulfate (Al2(SO4)3), boehmite (γ-AlOOH), aluminum nitrate (Al(NO3)3), aluminum isopropoxide (Al(OPri)3), aluminum hydroxide (Al(OH)3) and aluminum sulfate 18hydrate (Al2(SO4)3·18H2O), preferably sodium aluminate (NaAlO2).

[0020] Furthermore, in step (1), the heating temperature is 30-90° C., the stirring speed is 300-500 r / min, and the stirring time is 12-24 h.

[0021] Furthermore, in step (2), the crystallization temperature is 170° C. and the crystallization time is 48-72 h.

[0022] Furthermore, in step (3), the drying temperature is 100-120°C, the drying time is 12-24h, the roasting temperature is 500-650°C, and the roasting time is 4-8h.

[0023] Furthermore, in step (4), the ion exchange process is: dissolving the flaky ZSM-5 molecular sieve in NH4Cl or NH4NO3 solution under heating and stirring, centrifuging with stirring, adjusting the pH to neutral, drying, and calcining; repeating 2-5 times.

[0024] Furthermore, the concentration of the NH4Cl or NH4NO3 solution is 1-5 mol / L.

[0025] Furthermore, the heating temperature is 30-90° C., the stirring speed is 300-500 r / min, and the heating stirring time is 4-6 h.

[0026] Furthermore, the drying temperature is 100-120° C., and the drying time is 12-24 hours; the roasting temperature is 500-650° C., and the roasting time is 4-8 hours.

[0027] The present invention also relates to a sheet-like HZSM-5 molecular sieve catalyst prepared by any of the above-mentioned preparation methods.

[0028] Furthermore, the b-axis length of the flaky HZSM-5 molecular sieve catalyst is ≤100 nm.

[0029] The present invention also relates to a flaky HZSM-5 molecular sieve catalyst prepared by the preparation method or application of the flaky HZSM-5 molecular sieve catalyst in the hydrogenation of carbon dioxide to aromatics.

[0030] Furthermore, the flaky HZSM-5 molecular sieve catalyst is mixed with a metal oxidant catalyst and used in a process of hydrogenating carbon dioxide to produce aromatics.

[0031] Furthermore, the mass ratio of the flaky HASM-5 molecular sieve catalyst to the metal oxide catalyst is 1-5:1-5.

[0032] Furthermore, the metal catalyst is a Fe / Mn / Na metal oxide catalyst and / or a Fe / Co / K metal oxide catalyst.

[0033] Furthermore, the molar ratio of each metal in the Fe / Mn / Na metal oxide catalyst is Fe:Mn:Na=3-6:1-3:1.5-4.5; and / or the molar ratio of each metal in the Fe / Co / K metal oxide catalyst is Fe:Co:K=3-6:1-3:1.5-4.5.

[0034] Furthermore, the specific process conditions for producing aromatics by hydrogenating carbon dioxide include:

[0035] The reduction temperature is 300-500°C and the reduction time is 2-10h;

[0036] And / or the reaction gas is a mixture of H2 / CO2 with a volume ratio of 3-5:1;

[0037] and / or the reaction temperature is 300-400°C;

[0038] and / or the reaction pressure is 2-6 MPa;

[0039] And / or the reaction space velocity is 500-20000h -1 .

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] The invention realizes the growth of the b-axis of the HZSM5 molecular sieve during the synthesis process by regulating the dosage of the additive NH4F, the silicon source, the aluminum source, the template agent and water. The prepared flaky HZSM5 molecular sieve has a typical MFI topological structure, high crystallinity, an average thickness of less than 100 nm and a large specific surface area.

[0042] The present invention also finds that in the synthesis process of the HZSM-5 molecular sieve catalyst, appropriately increasing the proportion of water in the material mixing ratio is more conducive to the synthesis of a sheet structure with a shorter b axis.

[0043] In addition, the raw material feeding sequence and the crystallization process during the preparation of the molecular sieve catalyst also have a great influence on the formation of its structure. Generally speaking, the present invention achieves a significant improvement in catalyst performance by regulating the raw material ratio and the preparation process.

[0044] The short b-axis HASM-5 molecular sieve catalyst reduces the residence time of guest molecules in the pores and has a certain inhibitory effect on the occurrence of side reactions. At the same time, the shorter straight pore channels are more conducive to material transport and diffusion, making it easier for guest molecules to enter the active sites, resulting in better catalytic activity. It also prolongs the carbon deposit generation rate to a certain extent and improves the catalyst life.

[0045] The metal oxide catalyst is simply mechanically mixed with the flaky HZSM-5 molecular sieve prepared by the present invention and used in the CO2 hydrogenation reaction to produce aromatics. The catalyst not only has high reaction activity, but also has high aromatics selectivity and low low carbon alkane and olefin selectivity. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. It is worth noting that the raw materials used in the present invention are all common commercial products, and their sources are not specifically limited. The following is an exemplary description:

[0047] The preparation method of the metal oxide catalyst with a molar ratio of Fe:Mn:Na of 3:1:1.5 used in the embodiment of the present invention is as follows:

[0048] (1) Under the conditions of 60°C water bath heating and 300 r / min stirring speed, 32 g of Fe source and 6.63 g of Mn source were added into 200 mL of deionized water in sequence, and the resulting mixture was fully dissolved for 4 h;

[0049] (2) After being fully dissolved, 1.5 mol / L NaOH solution was added dropwise using a peristaltic pump at the same temperature to precipitate the mixture in (1) until the pH value was 10;

[0050] (3) stirring the mixture obtained in (2) at 60° C. for 1 h, and centrifuging at 4000 r / min to precipitate;

[0051] (4) washing the solid obtained after centrifugation of (3) twice with 400 mL of deionized water, and centrifuging again under the same conditions after each washing;

[0052] (5) The solid obtained after washing and centrifugation in (4) was dried in a drying oven at 110° C. for 15 h to obtain a metal oxide catalyst with a molar ratio of Fe:Mn:Na of 3:1:1.5.

[0053] In this preparation process, the Fe source is Fe(NO3)3·9H2O, and the Mn source is Mn(NO3)2·4H2O.

[0054] The preparation method of the metal oxidant with a Fe:Co:K molar ratio of 3:1:1.5 used in the embodiment of the present invention is the same as above, except that a Co source is used instead of a Mn source, and the Co source is Co(NO3)2·6H2O.

[0055] Those skilled in the art should understand that the preparation method of the metal oxide catalyst has no effect or little effect on the catalytic effect, and does not constitute a limitation on the technical solution of the present invention; the metal oxide catalyst of the present invention can be prepared by other alternative preparation methods in the art, or purchased commercially.

[0056] Example 1

[0057] 1. Preparation of flaky HZSM-5 molecular sieve:

[0058] The silicon source and the aluminum source are measured as SiO2 and Al2O3, and the molar ratio of the raw materials is: SiO2:TPAOH:Al2O3:NH4F:H2O=1:0.3:0.04:0.6:45.

[0059] (1) Under the conditions of heating in a water bath at 60° C. and stirring at a speed of 300 r / min, tetraethyl orthosilicate, tetrapropylammonium hydroxide, NaAlO2 and NH4F were added to deionized water in sequence to complete preliminary material mixing, and then the mouth of the beaker was sealed with plastic wrap to prevent excessive evaporation of water;

[0060] (2) stirring for 12 h in a water bath at 60 °C and a stirring speed of 300 r / min, then transferring the mixed gel to a polytetrafluoroethylene liner, and then transferring it to a stainless steel reactor and crystallizing it at 170 °C for 72 h;

[0061] (3) taking out the reactor and cooling it naturally to room temperature, washing it with deionized water until it is neutral, and then drying it at 110° C. for 12 h, and then calcining it at 550° C. for 4 h to remove the template, thereby obtaining a flaky Na-ZSM-5 molecular sieve;

[0062] (4) Take 100 mL of 1 mol / L NH4Cl solution, heat it to 60°C in a water bath, dissolve the Na-ZSM-5 molecular sieve in the NH4Cl solution, stir it at 400 r / min for 5 h, centrifuge it, adjust the pH to neutral, dry it at 110°C for 12 h, and calcine it at 550°C for 4 h. Repeat this process 3 times to obtain a flaky HZSM-5 molecular sieve.

[0063] 2. CO2 hydrogenation to produce aromatics:

[0064] The obtained flaky HZSM-5 molecular sieve catalyst was mixed with a metal oxide catalyst of Fe:Mn:Na=3:1:1.5 prepared by a co-precipitation method in a mass ratio of 1:1 and then used in the process of CO2 hydrogenation to produce aromatics. The process conditions were: reduction temperature 350℃, reduction time 8h; reaction gas was a mixture of H2 / CO2=3 / 1 (volume ratio), reaction temperature 315℃, reaction pressure 3MPa, reaction space velocity 20000h -1 .

[0065] Example 2

[0066] 1. Preparation of flaky HZSM-5 molecular sieve:

[0067] The silicon source and the aluminum source are measured as SiO2 and Al2O3, and the molar ratio of the raw materials is: SiO2:TPAOH:Al2O3:NH4F:H2O=1:0.3:0.04:0.6:45.

[0068] (1) Under the conditions of 60° C. water bath heating and 300 r / min stirring speed, tetraethyl orthosilicate, tetrapropylammonium hydroxide, Al(OPri)3 and NH4F were added to deionized water in sequence to complete the preliminary material mixing, and then the beaker mouth was sealed with plastic wrap to prevent excessive evaporation of water;

[0069] (2) stirring for 12 h in a water bath at 60 °C and a stirring speed of 300 r / min, then transferring the mixed gel to a polytetrafluoroethylene liner, and then transferring it to a stainless steel reactor and crystallizing it at 170 °C for 72 h;

[0070] (3) taking out the reactor and cooling it naturally to room temperature, washing it with deionized water until it is neutral, and then drying it at 110° C. for 12 h, and then calcining it at 550° C. for 4 h to remove the template, thereby obtaining a flaky Na-ZSM-5 molecular sieve;

[0071] (4) Take 100 mL of 1 mol / L NH4Cl solution, heat it to 60°C in a water bath, dissolve the Na-ZSM-5 molecular sieve in the NH4Cl solution, stir at 400 r / min for 4 h, centrifuge, adjust the pH to neutral, dry at 110°C for 12 h, and calcine at 550°C for 4 h. Repeat this process 3 times to obtain a flaky HZSM-5 molecular sieve.

[0072] 2. CO2 hydrogenation to produce aromatics:

[0073] The obtained flake HZSM-5 molecular sieve catalyst was mixed with Fe:Mn:Na=3:1:1.5 metal oxide catalyst in a mass ratio of 1:1 and used in the process of CO2 hydrogenation to produce aromatics. The process conditions were: reduction temperature 350℃, reduction time 8h. The reaction gas was a mixture of H2 / CO2=3 / 1 (volume ratio), the reaction temperature was 315℃, the reaction pressure was 3MPa, and the reaction space velocity was 20000h -1 .

[0074] Example 3

[0075] 1. Preparation of flaky HZSM-5 molecular sieve:

[0076] The silicon source and the aluminum source are measured as SiO2 and Al2O3, and the molar ratio of the raw materials is: SiO2:TPAOH:Al2O3:NH4F:H2O=1:0.2:0.04:0.4:45.

[0077] (1) Under the conditions of heating in a water bath at 60° C. and stirring at a speed of 300 r / min, silica sol, tetrapropylammonium hydroxide, NaAlO2 and NH4F were added to deionized water in sequence to complete preliminary material mixing, and then the mouth of the beaker was sealed with plastic wrap to prevent excessive evaporation of water;

[0078] (2) stirring for 12 h in a water bath at 60 °C and a stirring speed of 300 r / min, then transferring the mixed gel to a polytetrafluoroethylene liner, and then transferring it to a stainless steel reactor and crystallizing it at 170 °C for 72 h;

[0079] (3) taking out the reactor and cooling it naturally to room temperature, washing it with deionized water until it is neutral, and then drying it at 110° C. for 12 h, and then calcining it at 550° C. for 4 h to remove the template, thereby obtaining a flaky Na-ZSM-5 molecular sieve;

[0080] (4) Take 100 mL of 1 mol / L NH4Cl solution, heat it to 60°C in a water bath, dissolve the Na-ZSM-5 molecular sieve in the NH4Cl solution, stir at 300-500 r / min for 4-6 h, centrifuge, adjust the pH to neutral, dry at 110°C for 12 h, and calcine at 550°C for 4 h. Repeat this process 3 times to obtain a flaky HZSM-5 molecular sieve.

[0081] 2. CO2 hydrogenation to produce aromatics:

[0082] The obtained flake HZSM-5 molecular sieve catalyst was mixed with Fe:Mn:Na=3:1:1.5 metal oxidant catalyst in a mass ratio of 1:1 and used in the process of CO2 hydrogenation to produce aromatics. The process conditions were: reduction temperature 350℃, reduction time 8h. The reaction gas was a mixture of H2 / CO2=3 / 1 (volume ratio), the reaction temperature was 315℃, the reaction pressure was 3MPa, and the reaction space velocity was 20000h -1 .

[0083] Example 4

[0084] 1. Preparation of flaky HZSM-5 molecular sieve:

[0085] The silicon source and the aluminum source are measured as SiO2 and Al2O3, and the molar ratio of the raw materials is: SiO2:TPAOH:Al2O3:NH4F:H2O=1:0.2:0.02:0.6:35.

[0086] (1) Under the conditions of heating in a water bath at 60° C. and stirring at a speed of 300 r / min, tetraethyl orthosilicate, tetrapropylammonium hydroxide, NaAlO2 and NH4F were added to deionized water in sequence to complete preliminary material mixing, and then the mouth of the beaker was sealed with plastic wrap to prevent excessive evaporation of water;

[0087] (2) stirring for 12 h in a water bath at 60 °C and a stirring speed of 300 r / min, then transferring the mixed gel to a polytetrafluoroethylene liner, and then transferring it to a stainless steel reactor and crystallizing it at 170 °C for 72 h;

[0088] (3) taking out the reactor and cooling it naturally to room temperature, washing it with deionized water until it is neutral, and then drying it at 110° C. for 12 h, and then calcining it at 550° C. for 4 h to remove the template, thereby obtaining a flaky Na-ZSM-5 molecular sieve;

[0089] (4) Take 100 mL of 1 mol / L NH4NO3 solution, heat it to 60°C in a water bath, dissolve the Na-ZSM-5 molecular sieve in the NH4NO3 solution, stir it at 400 r / min for 4 h, centrifuge it, adjust the pH to neutral, dry it at 110°C for 12 h, and calcine it at 550°C for 4 h. Repeat this process 3 times to obtain a flaky HZSM-5 molecular sieve.

[0090] 2. CO2 hydrogenation to produce aromatics:

[0091] The obtained flake HZSM-5 molecular sieve catalyst was mixed with Fe:Mn:Na=3:1:1.5 metal oxidant catalyst prepared by coprecipitation method in a mass ratio of 1:1 and then used in the process of CO2 hydrogenation to produce aromatics. The process conditions were: reduction temperature 350℃, reduction time 8h. The reaction gas was a mixture of H2 / CO2=3 / 1 (volume ratio), the reaction temperature was 315℃, the reaction pressure was 3MPa, and the reaction space velocity was 20000h -1 .

[0092] Example 5

[0093] 1. Preparation of flaky HZSM-5 molecular sieve:

[0094] The silicon source and the aluminum source are measured as SiO2 and Al2O3, and the molar ratio of the raw materials is: SiO2:TPAOH:NH4F:Al2O3:H2O=1:0.3:0.04:0.6:45.

[0095] (1) Under the conditions of heating in a water bath at 60° C. and stirring at a speed of 300 r / min, tetraethyl orthosilicate, tetrapropylammonium hydroxide, NaAlO2 and NH4F were added to deionized water in sequence to complete preliminary material mixing, and then the mouth of the beaker was sealed with plastic wrap to prevent excessive evaporation of water;

[0096] (2) stirring for 12 h in a water bath at 60 °C and a stirring speed of 300 r / min, then transferring the mixed gel to a polytetrafluoroethylene liner, and then transferring it to a stainless steel reactor and crystallizing it at 170 °C for 72 h;

[0097] (3) taking out the reactor and cooling it naturally to room temperature, washing it with deionized water until it is neutral, and then drying it at 110° C. for 12 h, and then calcining it at 550° C. for 4 h to remove the template, thereby obtaining a flaky Na-ZSM-5 molecular sieve;

[0098] (4) Take 100 mL of 1 mol / L NH4NO3 solution, heat it to 60°C in a water bath, dissolve the Na-ZSM-5 molecular sieve in the NH4NO3 solution, stir it at 400 r / min for 5 h, centrifuge it, adjust the pH to neutral, dry it at 110°C for 12 h, and calcine it at 550°C for 4 h. Repeat this process 3 times to obtain flaky HZSM-5 molecular sieve.

[0099] 2. CO2 hydrogenation to produce aromatics:

[0100] The obtained flake HZSM-5 molecular sieve catalyst was mixed with Fe:Co:K=3:1:1.5 metal oxidant catalyst in a mass ratio of 1:1 and used in the process of CO2 hydrogenation to produce aromatics. The process conditions were: reduction temperature 350℃, reduction time 8h. The reaction gas was a mixture of H2 / CO2=3 / 1 (volume ratio), the reaction temperature was 315℃, the reaction pressure was 3MPa, and the reaction space velocity was 20000h -1 .

[0101] Comparative Example 1

[0102] 1. Preparation of flaky HZSM-5 molecular sieve:

[0103] The silicon source and the aluminum source are measured as SiO2 and Al2O3, and the molar ratio of the raw materials is: SiO2:TPAOH:Al2O3:NH4F:H2O=1:0.3:0.04:0.1:45.

[0104] (1) Under the conditions of heating in a water bath at 60° C. and stirring at a speed of 300 r / min, tetraethyl orthosilicate, tetrapropylammonium hydroxide, NaAlO2 and NH4F were added to deionized water in sequence to complete preliminary material mixing, and then the mouth of the beaker was sealed with plastic wrap to prevent excessive evaporation of water;

[0105] (2) stirring for 12 h in a water bath at 60 °C and a stirring speed of 300 r / min, then transferring the mixed gel to a polytetrafluoroethylene liner, and then transferring it to a stainless steel reactor and crystallizing it at 170 °C for 48 h;

[0106] (3) taking out the reactor and cooling it naturally to room temperature, washing it with deionized water until it is neutral, and then drying it at 110° C. for 12 h, and then calcining it at 550° C. for 4 h to remove the template, thereby obtaining a flaky Na-ZSM-5 molecular sieve;

[0107] (4) Take 100 mL of 1 mol / L NH4Cl solution, heat it to 60°C in a water bath, dissolve the Na-ZSM-5 molecular sieve in the NH4Cl solution, stir it at 400 r / min for 5 h, centrifuge it, adjust the pH to neutral, dry it at 110°C for 12 h, and calcine it at 550°C for 4 h. Repeat this process 3 times to obtain a flaky HZSM-5 molecular sieve.

[0108] 2. CO2 hydrogenation to produce aromatics:

[0109] The obtained flake HZSM-5 molecular sieve catalyst was mixed with Fe:Mn:Na=3:1:1.5 metal oxidant catalyst prepared by coprecipitation method in a mass ratio of 1:1 and then used in the process of CO2 hydrogenation to produce aromatics. The process conditions were: reduction temperature 350℃, reduction time 8h. The reaction gas was a mixture of H2 / CO2=3 / 1 (volume ratio), the reaction temperature was 315℃, the reaction pressure was 3MPa, and the reaction space velocity was 20000h -1 .

[0110] Comparative Example 2

[0111] 1. Preparation of flaky HZSM-5 molecular sieve:

[0112] The silicon source and the aluminum source are measured as SiO2 and Al2O3, and the molar ratio of the raw materials is: SiO2:TPAOH:Al2O3:NH4F:H2O=1:0.3:0.04:0.8:45.

[0113] (1) Under the conditions of heating in a water bath at 40° C. and stirring at a speed of 300 r / min, tetraethyl orthosilicate, tetrapropylammonium hydroxide, NaAlO2 and NH4F were added to deionized water in sequence to complete preliminary material mixing, and then the mouth of the beaker was sealed with plastic wrap to prevent excessive evaporation of water;

[0114] (2) stirring for 12 h in a water bath at 60 °C and a stirring speed of 300 r / min, then transferring the mixed gel to a polytetrafluoroethylene liner, and then transferring it to a stainless steel reactor and crystallizing it at 170 °C for 72 h;

[0115] (3) taking out the reactor and cooling it naturally to room temperature, washing it with deionized water until it is neutral, and then drying it at 110° C. for 12 h, and then calcining it at 550° C. for 4 h to remove the template, thereby obtaining a flaky Na-ZSM-5 molecular sieve;

[0116] (4) Take 100 mL of 1 mol / L NH4Cl solution, heat it to 60°C in a water bath, dissolve the Na-ZSM-5 molecular sieve in the NH4Cl solution, stir it at 400 r / min for 5 h, centrifuge it, adjust the pH to neutral, dry it at 110°C for 12 h, and calcine it at 550°C for 4 h. Repeat this process 3 times to obtain a flaky HZSM-5 molecular sieve.

[0117] 2. CO2 hydrogenation to produce aromatics:

[0118] The obtained flake HZSM-5 molecular sieve catalyst was mixed with Fe:Mn:Na=3:1:1.5 metal oxidant catalyst in a mass ratio of 1:1 and used in the process of CO2 hydrogenation to produce aromatics. The process conditions were: reduction temperature 350℃, reduction time 8h. The reaction gas was a mixture of H2 / CO2=3 / 1 (volume ratio), the reaction temperature was 315℃, the reaction pressure was 3MPa, and the reaction space velocity was 20000h -1 .

[0119] Comparative Example 3

[0120] 1. Preparation of flaky HZSM-5 molecular sieve:

[0121] The silicon source and the aluminum source are measured as SiO2 and Al2O3, and the molar ratio of the raw materials is SiO2:TPAOH:Al2O3:NH4F:H2O=1:0.3:0.04:0.6:30.

[0122] (1) Under the conditions of heating in a water bath at 60° C. and stirring at a speed of 300 r / min, tetraethyl orthosilicate, tetrapropylammonium hydroxide, NaAlO2 and NH4F were added to deionized water in sequence to complete preliminary material mixing, and then the mouth of the beaker was sealed with plastic wrap to prevent excessive evaporation of water;

[0123] (2) stirring for 12 h in a water bath at 40 °C and a stirring speed of 300 r / min, then transferring the mixed gel to a polytetrafluoroethylene liner, and then transferring to a stainless steel reactor and crystallizing at 170 °C for 72 h;

[0124] (3) taking out the reactor and cooling it naturally to room temperature, washing it with deionized water until it is neutral, and then drying it at 110° C. for 12 h, and then calcining it at 550° C. for 4 h to remove the template, thereby obtaining a flaky Na-ZSM-5 molecular sieve;

[0125] (4) Take 100 mL of 1 mol / L NH4Cl solution, heat it to 40°C in a water bath, dissolve the Na-ZSM-5 molecular sieve in the NH4Cl solution, stir at 400 r / min for 5 h, centrifuge, adjust the pH to neutral, dry at 110°C for 12 h, and calcine at 550°C for 4 h. Repeat this process 3 times to obtain a flaky HZSM-5 molecular sieve.

[0126] 2. CO2 hydrogenation to produce aromatics:

[0127] The obtained flake HZSM-5 molecular sieve catalyst was mixed with Fe:Mn:Na=3:1:1.5 metal oxidant catalyst prepared by coprecipitation method in a mass ratio of 1:1 and then used in the process of CO2 hydrogenation to produce aromatics. The process conditions were: reduction temperature 350℃, reduction time 8h. The reaction gas was a mixture of H2 / CO2=3 / 1 (volume ratio), the reaction temperature was 315℃, the reaction pressure was 3MPa, and the reaction space velocity was 20000h -1 .

[0128] Comparative Example 4

[0129] 1. Preparation of flaky HZSM-5 molecular sieve:

[0130] The silicon source and the aluminum source are measured as SiO2 and Al2O3, and the molar ratio of the raw materials is: SiO2:TPAOH:Al2O3:NH4F:H2O=1:0.1:0.04:0.6:45.

[0131] (1) Under the conditions of heating in a water bath at 60° C. and stirring at a speed of 300 r / min, tetraethyl orthosilicate, tetrapropylammonium hydroxide, NaAlO2 and NH4F were added to deionized water in sequence to complete preliminary material mixing, and then the mouth of the beaker was sealed with plastic wrap to prevent excessive evaporation of water;

[0132] (2) stirring for 12 h in a water bath at 60 °C and a stirring speed of 300 r / min, then transferring the mixed gel to a polytetrafluoroethylene liner, and then transferring it to a stainless steel reactor and crystallizing it at 170 °C for 72 h;

[0133] (3) taking out the reactor and cooling it naturally to room temperature, washing it with deionized water until it is neutral, and then drying it at 110° C. for 12 h, and then calcining it at 550° C. for 4 h to remove the template, thereby obtaining a flaky Na-ZSM-5 molecular sieve;

[0134] (4) Take 100 mL of 1 mol / L NH4Cl solution, heat it to 60°C in a water bath, dissolve the Na-ZSM-5 molecular sieve in the NH4Cl solution, stir it at 400 r / min for 5 h, centrifuge it, adjust the pH to neutral, dry it at 110°C for 12 h, and calcine it at 550°C for 4 h. Repeat this process 3 times to obtain a flaky HZSM-5 molecular sieve.

[0135] 2. CO2 hydrogenation to produce aromatics:

[0136] The obtained flake HZSM-5 molecular sieve catalyst was mixed with Fe:Mn:Na=3:1:1.5 metal oxidant catalyst in a mass ratio of 1:1 and used in the process of CO2 hydrogenation to produce aromatics. The process conditions were: reduction temperature 350℃, reduction time 8h. The reaction gas was a mixture of H2 / CO2=3 / 1 (volume ratio), the reaction temperature was 315℃, the reaction pressure was 3MPa, and the reaction space velocity was 20000h -1 .

[0137] Comparative Example 5

[0138] 1. Preparation of flaky HZSM-5 molecular sieve:

[0139] The silicon source and the aluminum source are measured as SiO2 and Al2O3, and the molar ratio of the raw materials is: SiO2:TPAOH:Al2O3:NH4F:H2O=1:0.3:0.01:0.6:45.

[0140] (1) Under the conditions of heating in a water bath at 60° C. and stirring at a speed of 300 r / min, tetraethyl orthosilicate, tetrapropylammonium hydroxide, NaAlO2 and NH4F were added to deionized water in sequence to complete preliminary material mixing, and then the mouth of the beaker was sealed with plastic wrap to prevent excessive evaporation of water;

[0141] (2) stirring for 12 h in a water bath at 60 °C and a stirring speed of 300 r / min, then transferring the mixed gel to a polytetrafluoroethylene liner, and then transferring it to a stainless steel reactor and crystallizing it at 170 °C for 72 h;

[0142] (3) taking out the reactor and cooling it naturally to room temperature, washing it with deionized water until it is neutral, and then drying it at 110° C. for 12 h, and then calcining it at 550° C. for 4 h to remove the template, thereby obtaining a flaky Na-ZSM-5 molecular sieve;

[0143] (4) Take 100 mL of 1 mol / L NH4Cl solution, heat it to 60°C in a water bath, dissolve the Na-ZSM-5 molecular sieve in the NH4Cl solution, stir it at 400 r / min for 5 h, centrifuge it, adjust the pH to neutral, dry it at 110°C for 12 h, and calcine it at 550°C for 4 h. Repeat this process 3 times to obtain a flaky HZSM-5 molecular sieve.

[0144] 2. CO2 hydrogenation to produce aromatics:

[0145] The obtained flake HZSM-5 molecular sieve catalyst was mixed with Fe:Mn:Na=3:1:1.5 metal oxidant catalyst in a mass ratio of 1:1 and used in the process of CO2 hydrogenation to produce aromatics. The process conditions were: reduction temperature 350℃, reduction time 8h. The reaction gas was a mixture of H2 / CO2=3 / 1 (volume ratio), the reaction temperature was 315℃, the reaction pressure was 3MPa, and the reaction space velocity was 20000h -1 .

[0146] Comparative Example 6

[0147] 1. Preparation of flaky HZSM-5 molecular sieve:

[0148] The silicon source and the aluminum source are measured as SiO2 and Al2O3, and the molar ratio of the raw materials is: SiO2:TPAOH:Al2O3:NH4F:H2O=1:0.3:0.04:0.6:45.

[0149] (1) Tetrapropylammonium hydroxide, tetraethyl orthosilicate, NaAlO2 and NH4F were added to deionized water in sequence, stirred at room temperature for pre-crystallization, and the initial material mixing was completed. Then, the beaker was sealed with plastic wrap to prevent excessive evaporation of water; and stirred at 90°C for 12 hours;

[0150] (2) adding NH4F to the obtained mixed sol and stirring at 90°C for 12 hours; transferring the mixed gel to a polytetrafluoroethylene liner, and then transferring to a stainless steel reactor, and crystallizing at 170°C for 72 hours;

[0151] (3) taking out the reactor and cooling it naturally to room temperature, washing it with deionized water until it is neutral, and then drying it at 110° C. for 12 h, and then calcining it at 550° C. for 4 h to remove the template, thereby obtaining a flaky Na-ZSM-5 molecular sieve;

[0152] (4) Take 100 mL of 1 mol / L NH4Cl solution, heat it to 60°C in a water bath, dissolve the Na-ZSM-5 molecular sieve in the NH4Cl solution, stir it at 400 r / min for 5 h, centrifuge it, adjust the pH to neutral, dry it at 110°C for 12 h, and calcine it at 550°C for 4 h. Repeat this process 3 times to obtain a flaky HZSM-5 molecular sieve.

[0153] 2. CO2 hydrogenation to produce aromatics:

[0154] The obtained flaky HZSM-5 molecular sieve catalyst was mixed with a metal oxide catalyst of Fe:Mn:Na=3:1:1.5 prepared by a co-precipitation method in a mass ratio of 1:1 and then used in the process of CO2 hydrogenation to produce aromatics. The process conditions were: reduction temperature 350℃, reduction time 8h; reaction gas was a mixture of H2 / CO2=3 / 1 (volume ratio), reaction temperature 315℃, reaction pressure 3MPa, reaction space velocity 20000h -1 .

[0155] The catalytic performance parameters (CO2 conversion rate, low carbon alkane (C 1-4 ) selectivity, light olefins (C 2-4 =) selectivity and aromatics (Aro) selectivity) were compared, and the comparison results are shown in Table 1.

[0156] Table 1 Catalytic CO2 hydrogenation results

[0157]

[0158] As can be seen from the above table, the flaky HZSM-5 molecular sieve catalyst prepared in the embodiment of the present invention has a high CO2 conversion rate for catalyzing CO2 hydrogenation, and at the same time, the aromatics selectivity is high, and the low carbon alkane and olefin selectivity is low, which is conducive to the synthesis of aromatics. Compared with Example 1, the CO2 conversion rate of Comparative Examples 1-5 decreased significantly, the conversion rate of low carbon alkanes and low carbon olefins increased, and the aromatics conversion rate decreased, indicating that too much or too little additive is not conducive to the formation of short b-axis flaky HZSM-5 molecular sieves; and appropriately increasing the proportion of water in the material mixing ratio is more conducive to the synthesis of a flaky structure with a shorter b axis; at the same time, it is also necessary to ensure that the amount of silicon source, aluminum source and template agent is within a suitable range to achieve the HZSM-5 molecular sieve catalyst with the best catalytic performance. In addition, it was unexpectedly discovered during the experiment that the preparation process of the flaky HZSM-5 molecular sieve catalyst, such as the feeding sequence of raw materials and the pre-crystallization conditions (for example, Comparative Example 6 adjusted the feeding sequence and temperature based on Example 1), had an impact on the performance of the catalyst - CO2 conversion rate and aromatics selectivity decreased, while olefin selectivity increased, and the catalytic effect decreased to a certain extent.

[0159] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Simple modifications or equivalent substitutions of the technical solution of the present invention by ordinary technicians in this field do not deviate from the essence and scope of the technical solution of the present invention.

Claims

1. A method for preparing a flaky HZSM-5 molecular sieve catalyst, characterized in that: The following steps are involved: (1) adding a silicon source, a template, an aluminum source and an additive into water in sequence, heating and stirring, to obtain a mixed gel; (2) raising the temperature to allow the mixed gel to crystallize; (3) After the crystallization is completed, the flaky ZSM-5 molecular sieve is obtained by centrifugation, washing to neutrality, drying, and calcination; (4) performing ion exchange on the ZSM-5 molecular sieve to obtain the flaky HZSM-5 molecular sieve catalyst; The silicon source and the aluminum source are measured with SiO2 and Al2O3 respectively, and the molar ratio of each raw material is controlled to be SiO2: template: Al2O3: additive: H2O = 1: 0.2-0.3: 0.02-0.04: 0.4-0.6: 35-45.

2. The preparation method according to claim 1, characterized in that: The template agent is selected from one or more of tetrapropylammonium hydroxide and tetrapropylammonium bromide; preferably tetrapropylammonium hydroxide; and the additive is NH4F.

3. The preparation method according to claim 1, characterized in that: The silicon source is selected from one or more of tetraethyl orthosilicate, white carbon black, silica sol, solid silica gel, sodium silicate crystals, C-type silica gel and water glass; preferably tetraethyl orthosilicate; The aluminum source is selected from one or more of sodium aluminate, sodium metaaluminate, aluminum sulfate, boehmite, aluminum nitrate, aluminum isopropoxide, aluminum hydroxide and aluminum sulfate 18hydrate, preferably sodium aluminate.

4. The preparation method according to claim 1, characterized in that: In step (1), the heating temperature is 30-90° C., the stirring speed is 300-500 r / min, and the stirring time is 12-24 h; In step (2), the crystallization temperature is 150-180° C. and the crystallization time is 48-72 h; In step (3), the drying temperature is 100-120° C., the drying time is 12-24 hours, the roasting temperature is 500-650° C., and the roasting time is 4-8 hours.

5. The preparation method according to claim 1, characterized in that: In step (4), the ion exchange process is: dissolving the flaky ZSM-5 molecular sieve in NH4Cl or NH4NO3 solution under heating and stirring, centrifuging with stirring, adjusting the pH to neutral, drying, and calcining; repeating 2-5 times.

6. The preparation method according to claim 5, characterized in that: The concentration of the NH4Cl or NH4NO3 solution is 1-5 mol / L; The heating temperature is 30-90°C, the stirring speed is 300-500r / min, and the heating and stirring time is 4-6h; The drying temperature is 100-120°C and the drying time is 12-24h; The calcination temperature is 500-650°C and the calcination time is 4-8h.

7. The sheet-like HZSM-5 molecular sieve catalyst prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The b-axis length of the flaky HZSM-5 molecular sieve catalyst is ≤100 nm.

8. Use of the flaky HZSM-5 molecular sieve prepared by the preparation method according to any one of claims 1 to 6 or the flaky HZSM-5 molecular sieve catalyst according to claim 7 in the hydrogenation of carbon dioxide to aromatics.

9. The use according to claim 8, characterized in that: The flaky HZSM-5 molecular sieve catalyst is mixed with a metal oxide catalyst and used in a process for hydrogenating carbon dioxide to produce aromatics; Preferably, the mass ratio of the flaky HASM-5 molecular sieve to the metal oxide catalyst is 1-5:1-5; More preferably, the metal catalyst is a Fe / Mn / Na metal oxide catalyst and / or a Fe / Co / K metal oxide catalyst; Further preferably, the molar ratio of each metal in the Fe / Mn / Na metal oxide catalyst is Fe:Mn:Na=3-6:1-3:1.5-4.5; and / or the molar ratio of each metal in the Fe / Co / K metal oxide catalyst is Fe:Co:K=3-6:1-3:1.5-4.

5.

10. The use according to claim 8, characterized in that: The specific process conditions for the carbon dioxide hydrogenation to aromatics include: a reduction temperature of 300-500°C; and / or the time of reduction is 2-10h; And / or the reaction gas is a mixture of H2 / CO2 with a volume ratio of 3-5:1; and / or the reaction temperature is 300-400°C; and / or the reaction pressure is 2-6 MPa; And / or the reaction space velocity is 500-20000h -1 .

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