CN116078421A - A kind of preparation method and application of high stability nanoscale ZSM-5 catalyst - Google Patents

Abstract

The invention provides a preparation method and application of a high-stability nanoscale ZSM-5 catalyst, wherein the preparation method comprises the following steps: (1) Preparing a full-silicon molecular sieve silicalite-1 by taking a template agent, a silicon source and water as raw materials through a pre-crystallization method; (2) The ZSM-5 catalyst is prepared by adopting a seed crystal method, taking the all-silicon molecular sieve silicalite-1 as a seed crystal, mixing the seed crystal with reaction raw materials including a template agent, a silicon source, an aluminum source and water, treating the mixture by a pre-crystallization method, crystallizing the mixture sequentially, exchanging ammonia, and loading metal. The ZSM-5 catalyst for aromatization of light alkane with high stability, which is formed by stacking secondary small particles with the size of about 50nm, is obtained by the preparation method. The catalyst can keep activity for a long time in the process of propane anaerobic aromatization reaction, has low surface carbon, and has high aromatic hydrocarbon selectivity and propane conversion rate; the synthesis method reduces the use of the template agent, is environment-friendly, and has good application prospect in the field of preparation of propane aromatization catalysts.

Description

A kind of preparation method and application of high stability nanoscale ZSM-5 catalyst

technical field

The invention belongs to the technical field of catalyst and reaction optimization, and in particular relates to a preparation method and application of a high-stability nanoscale ZSM-5 catalyst.

Background technique

As a widely used chemical raw material, light aromatics (BTX) can not only be used to reduce the octane number of gasoline, but also an important intermediate of organic chemical raw materials such as surfactants, pesticides, pigments and dyes. In industry, BTX is mainly obtained by catalytic reforming of naphtha. However, with the rapid development of the petrochemical industry and the shortage of fossil fuels, traditional BTX production methods have been unable to meet the growing market demand for BTX. In this context, new processes for producing BTX from light paraffins (C2-C6), such as propane aromatization, have received extensive attention; , low process cost and other characteristics, has broad application prospects.

Zeolite molecular sieves such as H-ZSM-5, H-ZSM-8, H-ZSM-11, MCM-22, L-type zeolite, etc., are beneficial to the aromatization of light alkanes due to their two-dimensional structure and pore size. There have been many studies. Among them, the ZSM-5 catalyst is considered to be the most effective catalyst in the propane aromatization reaction because its pores only allow molecules below trimethylbenzene to pass through, which is more beneficial to the selectivity of BTX. And the B acid of low silicon aluminum ratio HZSM-5 catalyst is stronger, can promote the generation of side reactions such as hydrogen transfer, and the productive rate of _C1 to _C3 is higher, so the selectivity of BTX is not ideal, and the stability of catalyst is also poor. relatively poor; and the total acid content of the HZSM-5 catalyst with a high silicon-aluminum ratio is relatively low, so the reactivity is not high; The reactivity in the aromatization system is also low.

Therefore, researchers are committed to improving the conversion rate of the reaction and the stability of the catalyst through the study of the structural change of the zeolite molecular sieve, the regulation of the amount of acid and the acid site, so as to find a light-weight catalyst with both stability and selectivity. Alkanes aromatization catalyst.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies in the prior art, to provide a preparation method and application of a highly stable nano-scale ZSM-5 catalyst, the preparation method is environmentally friendly, low equipment requirements, the prepared catalyst in light alkanes The conversion rate of raw materials in the aromatization system is high, the selectivity of aromatics is high, and the stability is good.

In order to achieve the above object, the present invention adopts the following technical solutions:

A kind of preparation method of high stability nano-scale ZSM-5 catalyst, described preparation method comprises the following steps:

(1) Prepare all-silicon molecular sieve silicalite-1 with template agent, silicon source and water as raw materials;

(2) Using the seed crystal method, the all-silicon molecular sieve silicalite-1 prepared in step (1) is used as the seed crystal, mixed with the reaction raw materials, including template agent, silicon source, aluminum source and water, after the pre-crystallization stage, passed through The ZSM-5 catalyst was prepared after crystallization, ammonia exchange and metal loading.

The present invention adopts the method of using all-silicon molecular sieve silicalite-1 as the seed crystal, and crystallizes the mother liquor obtained after pre-crystallization under water bath conditions in a hydrothermal kettle to obtain a catalyst with a diameter of tens of nanometers, which is used in ammonia exchange and metal loading After that, it has a high conversion rate of light alkanes and maintains excellent reaction stability, thereby realizing the preparation of a highly stable nano-scale aromatization ZSM-5 catalyst.

The present invention is further set as, described templating agent is preferably tetrapropyl ammonium hydroxide (TPAOH), and described silicon source is preferably tetraethoxysilane (TEOS), and described aluminum source is preferably sodium metaaluminate; Step ( 1) and the selection of template agent and silicon source in step (2) can be the same or different.

The present invention is further set as, adopt precrystallization method to prepare all-silicon molecular sieve silicalite-1 in step (1), specifically comprise the following steps:

S1. Pre-crystallization stage: mix the raw material template agent, silicon source and water, and age in a water bath at 70-90°C for 1-3 hours. to the quality before aging;

S2. Crystallization stage: transfer the aged mixed solution to a crystallization kettle for crystallization reaction, the reaction temperature is 160-180°C, and the reaction time is 48-96h;

S3. Separation and washing: centrifuging and washing the crystallized product;

S4. Roasting stage: Roast the separated and washed product at a heating rate of 1-5° C./min, a calcination temperature of 500-600° C., and a holding time of 4-8 hours to obtain the all-silicon molecular sieve silicalite-1.

Further, in the step (1), the molar ratio of raw material silicon source, templating agent and water is 30SiO ₂ :x TPAOH:900H ₂ O, x=3-12, preferably 3,6,9 or 12.

Preferably, in the S1 pre-crystallization stage of step (1), the aging temperature is 80°C and the aging time is 2h; the crystallization reaction temperature in the S2 crystallization stage is 170°C and the reaction time is 72h.

Preferably, in step (1) of S3 separation and washing, the crystallized product is centrifuged at 5000-10000 r/min, more preferably at 10000 r/min, and washed three times with ultrapure water.

Preferably, in the S4 calcination stage of step (1), the heating rate of the product in the muffle furnace is 2°C/min, the calcination temperature is 550°C, and the holding time is 6h.

The present invention is further set to, adopts seed crystal method to prepare ZSM-5 catalyst in step (2), specifically comprises the following steps:

S1. Pre-crystallization stage: mix template agent, silicon source, aluminum source and water, and add all-silicon molecular sieve silicalite-1 with a mass fraction of 2.5% to 10%, aging in a water bath at 70 to 90°C for 1 to 3 hours, and aging Add water to the initial mass after the end; the mass fraction of the all-silicon molecular sieve silicalite-1 is the mass percent of the total silicon source (in SiO ₂ ) in the raw material;

S2. Crystallization stage: transfer the aged mixed solution to a crystallization kettle for crystallization reaction, the reaction temperature is 160-180°C, and the reaction time is 36-96h;

S3. Separation and roasting: the product obtained by crystallization is centrifuged, washed, and roasted;

S4. Ammonia exchange: the product obtained in S3 is ammonium exchanged in an ammonium chloride solution, and roasted after the ammonium exchange;

S5. Metal loading: The product obtained in S4 is impregnated with an equal amount of active metal in a metal compound, and then calcined after impregnation.

Further, in the step (2), the molar ratio of raw material silicon source, aluminum source, templating agent and water is _60SiO2 :xAl:12TPAOH: _1800H2O , x=1~5, preferably 1~3, more preferably 1.5-2.

Preferably, in the S1 precrystallization stage of step (2), the aging temperature is 80° C., and the aging time is 2 hours.

Preferably, the crystallization reaction temperature in the S2 crystallization stage of step (2) is 170° C., and the reaction time is 72 hours.

Preferably, in step (2) of S3 separation and roasting, the crystallized product is centrifuged at 5000-10000r/min, more preferably at 10000r/min, and washed three times with ultrapure water.

Preferably, in the S4 ammonia exchange of step (2), the concentration of the ammonium chloride solution is 0.5-2 mol·L ^-1 , more preferably 1 mol·L ^-1 ; the ammonia exchange time is 20-30 h, more preferably 24h.

Further, in the S5 metal loading of step (2), the metal compound used for loading is selected from at least one of zinc nitrate, gallium nitrate, copper nitrate, and iron nitrate, and the loading is 0.5-6% by mass fraction, and the immersion time is 20-30h, more preferably 24h.

Preferably, in the roasting treatment of S3-S5 in step (2), the heating rate in the muffle furnace is 1-5°C/min, the roasting temperature is 500-600°C, and the holding time is 4-8h; more preferably , the heating rate is 2°C/min, the calcination temperature is 550°C, and the holding time is 6h.

A second aspect of the present invention is to provide the high-stability nano-scale ZSM-5 catalyst prepared by the preparation method of the high-stability nano-scale ZSM-5 catalyst, and the ZSM-5 catalyst has a particle diameter of 50nm The accumulation of secondary small particles (30-80nm) is rich in intercrystalline mesopores, its acidity is well preserved and its specific surface area is large, its diffusion performance is good, and its stability is high. Its specific surface area is as high as 395m ² ·g ^-1 .

The third aspect of the present invention is to provide the application of the high-stability nano-scale ZSM-5 catalyst for the aromatization reaction of light alkanes, including the aromatization reaction of propane. In the oxygen-free aromatization reaction of propane, the high-stable nano-scale ZSM-5 catalyst has the propane 5h conversion rate > 80%, aromatics selectivity > 85%, carbon deposition rate < 5%, and activity drop < 5%.

Compared with prior art, the beneficial effect of the present invention is:

In the present invention, the all-silicon molecular sieve Silicalite-1 is firstly synthesized under the assistance of precrystallization, and the nanometer ZSM-5 molecular sieve is synthesized again through the precrystallization method with the assistance of the Silicalite-1 seed crystal. During the precrystallization process, steam alcohol and The operation of replenishing water makes it possible to synthesize the nano ZSM-5 molecular sieve formed by the accumulation of secondary small particles of about 50nm, compared with the micron-sized ZSM-5 molecular sieve synthesized by the traditional method.

Nano ZSM-5 molecular sieves loaded with metals showed good reaction performance in propane aromatization reaction, high aromatics selectivity and propane conversion rate, and its 5-hour propane conversion rate and total aromatics selectivity were as high as 88.4% and 86.8%, and It is basically not deactivated within 5 hours, and can maintain activity for a long time in the process of propane oxygen-free aromatization reaction. The surface area of carbon is low, and the catalytic effect is significantly better than that of ZSM synthesized by micron-sized or not using the seed crystal method plus pre-crystallization method. -5 catalyst; and the synthesis method reduces the use of template agents, is green and environmentally friendly, and has good application prospects in the field of propane aromatization catalyst preparation.

Description of drawings

Fig. 1 is the TEM figure of the ZSM-5 molecular sieve catalyst that embodiment 1 prepares;

Fig. 2 is the TEM figure of the ZSM-5 molecular sieve catalyst that comparative example 1 prepares;

Fig. 3 is the TEM figure of the ZSM-5 molecular sieve catalyst that comparative example 2 prepares;

Figure 4 is a TEM image of the ZSM-5 molecular sieve catalyst prepared in Comparative Example 3.

Detailed ways

The technical solutions of the present invention are clearly and completely described below with specific examples. It should be understood that the described embodiments are only some of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the scope of the present invention.

Example 1

The all-silicon molecular sieve Silicalite-1 was synthesized by precrystallization method, and the feed ratio was 30SiO ₂ : 9TPAOH: 900H ₂ O. The specific operation is to add 32.4g ultrapure water and 9.15gTPAOH (40wt%) into a 200ml beaker, and slowly add 12.5g TEOS solution dropwise under the condition of stirring, and stir for 2 hours in a water bath at 80°C until the alcohol is basically evaporated to dryness, and replenish Add water to initial mass. Then it was transferred into a polytetrafluoroethylene reactor for static crystallization at 170°C for 72h. The obtained mother liquor was centrifuged, washed three times and then dried at 110° C. for 12 hours. Finally, it was calcined at 550°C for 6 hours in a muffle furnace to obtain Silicalite-1, an all-silicon molecular sieve.

Use all-silicon molecular sieve Silicalite-1 as the seed crystal, the addition amount is 5wt%, and the pre-crystallization method is adopted with the assistance of the seed crystal. The feeding ratio is 30SiO ₂ : 1Al: 6TPAOH: 900H ₂ O. The specific operation is to add in a 200ml beaker 32.4g ultrapure water, 6.1gTPAOH (40wt%), 0.248gNaAlO ₂ (the content of Al ₂ O ₃ is 41%) and 0.18gSilicalite-1, and slowly add 11.875gTEOS solution dropwise under the situation of stirring, in 80 ℃ water bath Under the circumstances, stir for 2h until the alcohol is basically evaporated to dryness, and add water to the original mass. Then it was transferred into a polytetrafluoroethylene reactor for static crystallization at 170°C for 72h. The obtained mother liquor was centrifuged, washed three times and then dried at 110° C. for 12 hours. After drying, it was calcined at 550°C for 6 hours in a muffle furnace, and the obtained sample was exchanged for ammonia with 1M NH ₄ Cl for 24 hours, and then calcined at 550°C for 6 hours in a muffle furnace to obtain nanoscale HZSM-5.

Use a certain concentration of zinc nitrate solution (Zn(NO ₃ ) ₂ ) to prepare 2wt% Zn/HZSM-5 by equal volume impregnation. The impregnated catalyst was dried at 110°C for 12h, and then baked in a muffle furnace at 550°C for 6h. The high-stability nanoscale catalyst is obtained.

Example 2

Using the all-silicon molecular sieve silicalite-1 in Example 1 as the seed crystal, the addition amount is 5wt%, and the pre-crystallization method is adopted with the assistance of the seed crystal, and the feeding ratio is 30SiO ₂ : 1Al: 6TPAOH: 900H ₂ O. The specific operation is as follows Add 32.4g ultrapure water, 6.1gTPAOH (40wt%), 0.248gNaAlO ₂ (the content of Al ₂ O ₃ is 41%) and 0.18g Silicalite-1 in a 200ml beaker, and slowly add 11.875gTEOS solution dropwise under stirring , Stir in a water bath at 70°C for 2h until the alcohol is basically evaporated to dryness, and add water to the original mass. Then it was transferred into a polytetrafluoroethylene reactor for static crystallization at 170°C for 72h. The obtained mother liquor was centrifuged, washed three times and then dried at 110° C. for 12 hours. After drying, it was calcined at 550°C for 6 hours in a muffle furnace, and the obtained sample was exchanged for ammonia with 1M NH ₄ Cl for 24 hours, and then calcined at 550°C for 6 hours in a muffle furnace to obtain nanoscale HZSM-5. Use a certain concentration of zinc nitrate solution (Zn(NO ₃ ) ₂ ) to prepare 2wt% Zn/HZSM-5 by equal volume impregnation. The impregnated catalyst was dried at 110°C for 12h, and then baked in a muffle furnace at 550°C for 6h. The high-stability nanoscale catalyst is obtained.

Example 3

Using the all-silicon molecular sieve Silicalite-1 in Example 1 as the seed crystal, the addition amount is 5wt%, and the pre-crystallization method is adopted with the assistance of the seed crystal, and the feeding ratio is 30SiO ₂ : 1Al: 6TPAOH: 900H ₂ O. The specific operation is as follows Add 32.4g ultrapure water, 6.1gTPAOH (40wt%), 0.248g NaAlO ₂ (the content of Al ₂ O ₃ is 41%) and 0.18g Silicalite-1 in a 200ml beaker, and slowly add 11.875gTEOS dropwise while stirring The solution was stirred in a water bath at 90°C for 2h until the alcohol was basically evaporated to dryness, and water was added to the original mass. Then it was transferred into a polytetrafluoroethylene reactor for static crystallization at 170°C for 72h. The obtained mother liquor was centrifuged, washed three times and then dried at 110° C. for 12 hours. Drying was performed in a muffle furnace at 550°C for 6 hours, and the obtained samples were exchanged for ammonia with 1M NH ₄ Cl for 24 hours, and then fired in a muffle furnace at 550°C for 6 hours to obtain nanoscale HZSM-5. Use a certain concentration of zinc nitrate solution (Zn(NO ₃ ) ₂ ) to prepare 2wt% Zn/HZSM-5 by equal volume impregnation. The impregnated catalyst was dried at 110°C for 12h, and then baked in a muffle furnace at 550°C for 6h. The high-stability nanoscale catalyst is obtained.

Example 4

Using the all-silicon molecular sieve Silicalite-1 in Example 1 as the seed crystal, the addition amount is 5wt%, and the pre-crystallization method is adopted with the assistance of the seed crystal, and the feeding ratio is 60SiO ₂ : 1.5Al: 12TPAOH: 1800H ₂ O. The specific operation In order to add 32.4g ultrapure water, 6.1gTPAOH (40wt%), 0.186g NaAlO ₂ (the content of Al ₂ O ₃ is 41%) and 0.18g Silicalite-1 in a 200ml beaker, and slowly dropwise add 11.875 gTEOS solution, stirred in a water bath at 80°C for 1 h until most of the alcohol evaporated to dryness, and added water to the original mass. Then it was transferred into a polytetrafluoroethylene reactor for static crystallization at 170°C for 72h. The obtained mother liquor was centrifuged, washed three times and then dried at 110° C. for 12 hours. After drying, it was calcined at 550°C for 6 hours in a muffle furnace, and the obtained sample was exchanged for ammonia with 1M NH ₄ Cl for 24 hours, and then calcined at 550°C for 6 hours in a muffle furnace to obtain nanoscale HZSM-5. Use a certain concentration of zinc nitrate solution (Zn(NO ₃ ) ₂ ) to prepare 2wt% Zn/HZSM-5 by equal volume impregnation. The impregnated catalyst was dried at 110°C for 12h, and then baked in a muffle furnace at 550°C for 6h. The high-stability nanoscale catalyst is obtained.

Example 5

Using the all-silicon molecular sieve Silicalite-1 in Example 1 as the seed crystal, the addition amount is 5wt%, and the pre-crystallization method is adopted with the assistance of the seed crystal, and the feeding ratio is 30SiO ₂ : 1Al: 6TPAOH: 900H ₂ O. The specific operation is as follows Add 32.4g ultrapure water, 6.1gTPAOH (40wt%), 0.248gNaAlO ₂ (the content of Al ₂ O ₃ is 41%) and 0.18g Silicalite-1 in a 200ml beaker, and slowly add 11.875gTEOS solution dropwise under stirring , stirred for 3h in a water bath at 80°C until the alcohol was evaporated to dryness, and added water to the original mass. Then it was transferred into a polytetrafluoroethylene reactor for static crystallization at 170°C for 72h. The obtained mother liquor was centrifuged, washed three times and then dried at 110° C. for 12 hours. After drying, it was calcined at 550°C for 6 hours in a muffle furnace, and the obtained sample was exchanged for ammonia with 1M NH ₄ Cl for 24 hours, and then calcined at 550°C for 6 hours in a muffle furnace to obtain nanoscale HZSM-5. Use a certain concentration of zinc nitrate solution (Zn(NO ₃ ) ₂ ) to prepare 2wt% Zn/HZSM-5 by equal volume impregnation. The impregnated catalyst was dried at 110°C for 12h, and then baked in a muffle furnace at 550°C for 6h. The high-stability nanoscale catalyst is obtained.

Comparative example 1

Taking the commercial ZSM-5 catalyst (silicon-aluminum ratio Si/Al=30) purchased by Nankai University as an example, it was impregnated with a certain concentration of zinc nitrate solution (Zn(NO ₃ ) ₂ ) to make 2wt% Zn/HZSM-5, impregnated The final catalyst was dried at 110°C for 12 hours, and calcined in a muffle furnace at 550°C for 6 hours to obtain Comparative Sample 1.

Comparative example 2

In this comparative example, only the seed crystal method was used, but the pre-crystallization method was not used in the preparation of the ZSM-5 molecular sieve catalyst.

Using the all-silicon molecular sieve silicalite-1 in Example 1 as the seed crystal, the addition amount is 5wt%, and the feed ratio is 30SiO ₂ : 1Al: 6TPAOH: 900H ₂ O. The specific operation is to add 32.4g of ultrapure water into a 200ml beaker, 6.1g TPAOH (40wt%), 0.248g NaAlO ₂ (the content of Al ₂ O ₃ is 41%) and 0.18g Silicalite-1, and slowly add 11.875g TEOS solution dropwise while stirring, and stir at room temperature for 6h. Then it was transferred into a polytetrafluoroethylene reactor for static crystallization at 170°C for 72h. The obtained mother liquor was centrifuged, washed three times and then dried at 110° C. for 12 hours. After drying, it was calcined at 550°C for 6 hours in a muffle furnace, and the obtained sample was exchanged for ammonia with 1M NH ₄ Cl for 24 hours, and then calcined at 550°C for 6 hours in a muffle furnace to obtain nanoscale HZSM-5. Use a certain concentration of zinc nitrate solution (Zn(NO ₃ ) ₂ ) to prepare 2wt% Zn/HZSM-5 by equal volume impregnation, bake the impregnated catalyst at 110°C for 12h, and bake it in a muffle furnace at 550°C for 6h to obtain Comparative sample 2.

Comparative example 3

In this comparative example, only the pre-crystallization method was used, and no all-silicon molecular sieve silicalite-1 was added as the seed crystal.

Prepare the sample with a feed ratio of 30SiO ₂ : 1Al: 6TPAOH: 900H ₂ O. The specific operation is to add 32.4g ultrapure water, 6.1gTPAOH (40wt%), 0.248g NaAlO ₂ (the content of Al ₂ O ₃ is 41 %), and slowly dropwise added 12.5g of TEOS solution while stirring, stirred for 2h in a water bath at 80°C until the alcohol was basically evaporated to dryness, and added water to the original mass. Then it was transferred into a polytetrafluoroethylene reactor for static crystallization at 170°C for 72h. The obtained mother liquor was centrifuged, washed three times and then dried at 110° C. for 12 hours. After drying, it was calcined at 550°C for 6 hours in a muffle furnace, and the obtained sample was exchanged for ammonia with 1M NH ₄ Cl for 24 hours, and then calcined at 550°C for 6 hours in a muffle furnace to obtain nanoscale HZSM-5. Use a certain concentration of zinc nitrate solution (Zn(NO ₃ ) ₂ ) to prepare 2wt% Zn/HZSM-5 by equal volume impregnation, bake the impregnated catalyst at 110°C for 12h, and bake it in a muffle furnace at 550°C for 6h to obtain Comparative sample 3.

Example 6 Catalyst Evaluation

The catalyst microscopic appearance in embodiment 1-5 and comparative example 1-3 is analyzed, and result is shown in Fig. 1 and Fig. 2-4 respectively, is respectively the TEM figure of embodiment 1 and comparative example 1-3, implements The microscopic morphology of the catalyst obtained in Example 2-5 is similar to that of Example 1. The particle size of the catalyst prepared by using the seed crystal method and the pre-crystallization method in the present invention changes obviously, and the nanometer ZSM-5 molecular sieve is formed by accumulating secondary small particles with a particle size of tens of nanometers. However, the diameters of the catalyst particles prepared without using the seed crystal method and the pre-crystallization method of the present invention all exceed hundreds of nanometers.

The above catalysts were evaluated in the aromatization of propane in a fixed bed reactor at 550°C under normal pressure. 0.3 g of 20-40 mesh catalyst was loaded into a quartz tube reactor, and the temperature of the reactor was raised from room temperature to 550 °C under the protection of 20 mL·min ⁻¹ N ₂ flow. Inject the sample at a space velocity of 3000mL·g ^-1 ·h ^-1 at a ratio of propane: nitrogen of 3:7. The reaction products were analyzed by gas phase and liquid chromatography, and the results are shown in Table 1.

The reaction result of the catalyst 5h that table 1 embodiment 1-5 and comparative example 1-3 make

As shown in Table 1, compared with the comparative example, the catalyst prepared by the example of the present invention not only ensures high selectivity of aromatics, but also significantly increases the conversion rate of propane, and has a very low decrease in activity after 5 hours. Propane 5h conversion rate > 80%, aromatics selectivity > 85%, carbon deposition rate < 5%, activity drop < 5%, and the effect of the catalyst prepared by reacting under the conditions of Example 1 is the best, 5 hours propane conversion rate Up to 88.4%. The invention prepares the ZSM-5 molecular sieve formed by the accumulation of secondary small particles with a particle size of tens of nanometers. Compared with the ZSM-5 molecular sieve with a larger particle size in the prior art, the smaller particle size brings higher Excellent diffusion performance and reduced carbon deposition, thus further improving the stability of the catalyst.

This application has made a detailed description, the purpose of which is to enable those skilled in the art to understand and implement the content of this application, and not to limit the scope of protection of this application. Effect changes or modifications should be covered within the protection scope of the present application.

Claims (10)

1. The preparation method of the high-stability nanoscale ZSM-5 catalyst is characterized by comprising the following steps of:

(1) Preparing a full-silicon molecular sieve silicalite-1 by taking a template agent, a silicon source and water as raw materials;

(2) The ZSM-5 catalyst is prepared by mixing the all-silicon molecular sieve silicalite-1 serving as a seed crystal with reaction raw materials including a template agent, a silicon source, an aluminum source and water, performing a pre-crystallization stage, sequentially performing crystallization, ammonia exchange and metal loading.

2. The method of claim 1, wherein the template is tetrapropylammonium hydroxide, the silicon source is tetraethoxysilane, and the aluminum source is sodium metaaluminate.

3. The preparation method according to claim 2, wherein the preparation of all-silicon molecular sieve silicalite-1 in the step (1) by a pre-crystallization method comprises the following steps:

s1, a pre-crystallization stage: mixing a raw material template agent, a silicon source and water, aging for 1-3 hours in a water bath at 70-90 ℃, and adding water to the initial mass after the aging is finished;

s2, crystallization: transferring the aged mixed solution into a crystallization kettle for crystallization reaction, wherein the reaction temperature is 160-180 ℃ and the reaction time is 48-96 h;

s3, separating and washing: centrifugally separating and washing the crystallized product;

s4, roasting: and roasting the separated and washed product to obtain the all-silicon molecular sieve silicalite-1.

4. The method according to claim 3, wherein the raw material silicon source, the template agent and water in the step (1) are fed in a molar ratio of 30SiO ₂ ：x TPAOH：900H ₂ O，x＝3～12。

5. The preparation method according to claim 2, wherein the step (2) comprises the steps of:

s1, a pre-crystallization stage: mixing a template agent, a silicon source, an aluminum source and water, adding 2.5-10% of total silicon molecular sieve silicalite-1 by mass percent, aging for 1-3 hours in a water bath at 70-90 ℃, and adding water to the initial mass after the aging is finished;

s2, crystallization: transferring the aged mixed solution into a crystallization kettle for crystallization reaction, wherein the reaction temperature is 160-180 ℃ and the reaction time is 36-96 h;

s3, separating and roasting: centrifugally separating and washing the crystallized product, and roasting;

s4, ammonia exchange: ammonia exchange is carried out on the product obtained in the step S3 in an ammonium chloride solution, and roasting treatment is carried out after the ammonia exchange;

s5, metal loading: and (3) loading active metals into the product obtained in the step (S4) through equivalent impregnation, and roasting after impregnation.

6. The method according to claim 5, wherein the raw material silicon source, aluminum source, template agent and water in step (2) are added in a molar ratio of 60SiO ₂ ：x Al：12TPAOH：1800H ₂ O，x＝1～5。

7. The method according to claim 5, wherein in the step (2) S1 pre-crystallization stage, the aging temperature is 80 ℃ and the aging time is 2 hours; the crystallization reaction temperature in the S2 crystallization stage is 170 ℃ and the reaction time is 72 hours.

8. The method according to claim 5, wherein the concentration of the ammonium chloride solution in the S4 ammonia exchange of step (2) is 0.5 to 2 mol.L ^-1 The method comprises the steps of carrying out a first treatment on the surface of the The ammonia exchange time is 20-30 h;

in the S5 metal load, the metal compound used for the load is at least one of zinc nitrate, gallium nitrate, copper nitrate and ferric nitrate, the load is 0.5-6wt% and the dipping time is 20-30 h;

in the roasting treatment of S3-S5, the temperature rising rate in a muffle furnace is 1-5 ℃/min, the roasting temperature is 500-600 ℃, and the heat preservation time is 4-8 h.

9. A high stability nanoscale ZSM-5 catalyst, characterized in that the catalyst is prepared by the preparation method according to any one of claims 1-8.

10. The use of the high stability nanoscale ZSM-5 catalyst of claim 9, for light alkane aromatization reactions, including propane aromatization reactions.

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