CN113751055A

CN113751055A - A kind of in-situ preparation method of high stability molecular sieve supported metal catalyst

Info

Publication number: CN113751055A
Application number: CN202111120573.4A
Authority: CN
Inventors: 刘民; 郭新闻; 倪婉萍
Original assignee: Dalian University of Technology
Current assignee: Dalian University of Technology
Priority date: 2021-09-24
Filing date: 2021-09-24
Publication date: 2021-12-07

Abstract

The invention provides a molecular sieve supported metal catalyst and a preparation method thereof. The steps include: uniformly mixing deionized water, a template agent and a silicon source; uniformly mixing a metal source, a complexing agent and H ₂ O; ₂ O is mixed with Na ion and alkali source evenly; after crystallization, it is washed to neutrality and then roasted; after ammonium exchange treatment, it becomes hydrogen form. The invention adopts an in-situ synthesis method to synthesize a molecular sieve supported metal catalyst, encapsulates metals with higher dehydrogenation activity, can improve aromatics selectivity, can also control the size of metal particles and effectively suppress particle aggregation at high temperature; It is more uniform, so that the catalyst has higher stability and longer catalytic life; the aromatics selectivity of the present invention is as high as 54.7%; and the duration of the methanol conversion rate of the present invention above 90% can reach 220h.

Description

In-situ preparation method of high-stability molecular sieve loaded metal catalyst

Technical Field

The invention relates to the field of catalyst preparation, in particular to an in-situ preparation method of a high-stability molecular sieve supported metal catalyst.

Background

The process of preparing aromatic hydrocarbon (MTA) from methanol can prepare aromatic hydrocarbon compounds such as benzene (B), toluene (T), xylene (X) and the like from methanol with high selectivity, and the aromatic hydrocarbon with high added value is produced by producing methanol with excessive capacity, so that the dependence of the produced aromatic hydrocarbon on petroleum resources can be reduced, the problem of insufficient supply of the aromatic hydrocarbon is solved, the utilization efficiency of coal resources in China can be improved, the source of the aromatic hydrocarbon is enriched, and the method has important practical significance and industrial application value for extending the industrial chain of coal chemical industry. However, the MTA technology is still not mature enough, and the main problems existing at present are low aromatic hydrocarbon yield, short catalyst life and poor stability, and the requirements of large-scale industrial application cannot be met. The key point for solving the problem is to develop a catalyst with higher arene selectivity and longer stability, while the metal modified ZSM-5 molecular sieve is considered as the most suitable catalyst due to the excellent dehydrogenation performance, shape selectivity and adjustable acidity, the metal is mainly used as a dehydrogenation active center and is beneficial to dehydrogenation and aromatization of cycloalkane, and the commonly used metals comprise zinc, silver, gallium, nickel and the like. The molecular sieve is used as a carrier and provides an acid center, which is beneficial to reactions such as methanol conversion, cyclization, hydrogen transfer and the like, and the molecular sieve usually adopts ZSM-5, and has excellent shape selectivity because of having a special pore channel structure and the pore size being equivalent to the size of low-carbon aromatic hydrocarbon molecules such as benzene, toluene and the like.

However, the microporous pore channel structure of ZSM-5 is not favorable for the diffusion of macromolecular intermediate products, and carbon deposits are easy to block the pore channels and cover active sites, so that the catalyst is quickly inactivated. Therefore, modification of ZSM-5 is required to increase the selectivity of aromatics in the product.

However, when the existing metal modified ZSM-5 catalyst is used for methanol aromatization reaction, high aromatic selectivity and long catalyst life cannot be considered at the same time (Chinese patent, application number: 2019113872059, a preparation method of a flaky Zn/ZSM-5 molecular sieve for methanol aromatization), in the prior art, the catalyst life is obviously reduced while the aromatic selectivity is improved by modification, and the selectivity is reduced rapidly along with the reaction. Therefore, on the basis of modifying the catalyst metal, the selectivity of the catalyst in the methanol aromatization reaction is improved by regulating and controlling the structure and the morphology of the catalyst, and the key problem is to maintain high activity and high stability.

Disclosure of Invention

The invention provides an in-situ synthesis method of a high-stability molecular sieve supported metal catalyst, which aims to solve the problems of short service life of the catalyst, unstable selectivity and uneven distribution of metal active species in the MTA reaction in the prior art.

In order to achieve the above object, the present invention provides a method for preparing a molecular sieve supported metal catalyst, comprising the steps of:

s1, uniformly mixing deionized water, a template agent and a silicon source, and stirring for 0.5-24 hours at 20-80 ℃;

s2, mixing a metal source, a complexing agent and H₂Mixing O uniformly, adding the mixture into the solution prepared by S1, heating to 40-120 ℃, and continuing stirring for 1-24 hours;

s3, mixing an aluminum source and H₂Uniformly mixing O, Na ions and an alkali source, adding the mixture into the mixed solution obtained in the step S1 and the step S2, and continuously stirring for 0.5-24 hours;

s4, crystallizing at 170-200 ℃ for 12-96 h;

s5, washing with deionized water until the filtrate is neutral, drying at 80-100 ℃, and roasting at 540-560 ℃ for 6-8 h to obtain a Na-type molecular sieve supported metal catalyst;

s6, placing the Na-type molecular sieve loaded metal catalyst into an ammonium nitrate aqueous solution, and stirring at 80-100 ℃ until ammonium exchange is completed; washing the solid until the filtrate is neutral, drying at 80-100 ℃, and roasting at 540-560 ℃ for 4-6H to obtain an H-type molecular sieve supported metal catalyst;

the catalyst molecular sieve is any one of a ZSM-5 molecular sieve, a Beta molecular sieve or a mercerized molecular sieve; the metal source is any one of zinc, silver or gallium;

wherein the molar content ratio of water molecules to silicon atoms is 62.1-79.4; the molar content ratio of the template agent to the silicon atoms is 0.15-0.34; the molar content ratio of the metal source atoms to the silicon atoms is 0.004-0.05; the molar ratio of the sodium ions to the silicon atoms is 0.04-0.12; the molar content ratio of the aluminum atoms to the silicon atoms is 0.0017-0.010.

Preferably, the template agent is any one of tetrapropylammonium hydroxide, tetrapropylammonium bromide or ethylamine.

Preferably, the silicon source is any one of ethyl orthosilicate, silica sol and water glass.

Preferably, the complexing agent is any one of anhydrous ethylenediamine and ethylene diamine tetraacetic acid metal complexing agent.

Preferably, the alkali source is any one of NaOH and ammonia water alkaline substances.

Preferably, the Na ion is any one of a sodium salt and a sodium base.

Preferably, the preparation method of the H-type Zn @ ZSM-5 comprises the following steps:

s1, stirring 84.50-88.50 g of deionized water, 14.88-26.40 g of 25 wt% tetrapropylammonium hydroxide and 19.38g of tetraethoxysilane at 20-80 ℃ for 0.5-24 h;

s2, 0.06-0.48 g of ZnCl₂0.43 to 3.62g of anhydrous ethylenediamine and 1.66 to 12.72g of H₂Mixing O uniformly, adding the mixture into the solution prepared by S1, heating to 40-120 ℃, and continuing stirring for 1-24 hours;

s3, mixing 0.15-0.45 g NaOH, 0.06-0.35 g Al (NO)₃)₃·9H₂O and 3.17-18.65 g of H₂Mixing O uniformly, adding the mixture into the mixed solution obtained in the step S1 and the step S2, and stirring for 0.5-24 hours;

s4, crystallizing at 170-200 ℃ for 12-96 h;

s5, washing with deionized water until the filtrate is neutral, drying at 80-100 ℃, and roasting at 540-560 ℃ for 6-8 h to obtain Na-type Zn @ ZSM-5;

s6, placing the Na type Zn @ ZSM-5 in 0.4-1 mol/L ammonium nitrate aqueous solution with the solid-liquid mass volume ratio of 1:10, and stirring at 80-100 ℃ until ammonium exchange is completed; and filtering the deionized water, washing the solid until the filtrate is neutral, drying the filtrate at 80-100 ℃, and roasting the dried filtrate at 540-560 ℃ for 4-6 hours to obtain the H-type Zn @ ZSM-5.

The invention has the beneficial effects that:

aiming at the problems of short service life and unstable selectivity of the catalyst in the MTA reaction, the invention synthesizes the molecular sieve supported metal catalyst by adopting an in-situ synthesis method, can improve the selectivity of aromatic hydrocarbon by encapsulating metal with higher dehydrogenation activity, and can play a role in controlling the size of metal particles and effectively inhibiting the aggregation of the particles at high temperature. Compared with other metal loading modes, the in-situ synthesis method adopted by the invention can ensure that the distribution of metal active species is more uniform, so that the catalyst has higher stability and longer catalytic life. Compared with Zn/ZSM-5 prepared by the prior art, the aromatic selectivity of samples with different metal contents is lower than 30 percent, and the aromatic selectivity of the invention is as high as 54.7 percent; compared with the service life of 70h of the Zn/HZSM-5 catalyst prepared by the prior art, the duration time of the methanol conversion rate of the invention of more than 90 percent can reach 220 h.

Drawings

FIG. 1 is an XRD pattern of Zn @ ZSM-5 of example 1 of the present invention;

FIG. 2 is an SEM image of Zn @ ZSM-5 of example 1 of the present invention;

FIG. 3 is a plot of the methanol conversion for the Zn @ ZSM-5 reaction of example 1 of the present invention.

Detailed Description

The present invention is further illustrated by the following specific examples.

The invention provides a synthesis method of a molecular sieve supported metal catalyst, which comprises the following steps:

s2, mixing a metal source, a complexing agent and H₂Mixing O, adding S1Heating the prepared solution to 40-120 ℃, and continuously stirring for 1-24 hours;

s4, crystallizing at 170-200 ℃ for 12-96 h;

s6, placing the Na-type molecular sieve-loaded metal catalyst into an ammonium nitrate aqueous solution, stirring for 0.5-3 hours at 80-100 ℃ with the solid-liquid mass-volume ratio of 1:10, and repeating for 1-3 times; and washing the solid until the filtrate is neutral, drying at 80-100 ℃, and roasting at 540-560 ℃ for 4-6H to obtain the H-type molecular sieve supported metal catalyst.

Wherein the metal can be zinc, silver, gallium, etc.; the molecular sieve can be ZSM-5 molecular sieve, Beta molecular sieve, mercerized molecular sieve, etc.; the template agent can be tetrapropylammonium hydroxide, tetrapropylammonium bromide and ethylamine; the silicon source can be tetraethoxysilane, silica sol and water glass; the complexing agent can be metal complexing agents such as anhydrous ethylenediamine, disodium ethylene diamine tetraacetate and the like; the alkali source can be alkaline substances such as ammonia water besides NaOH.

Wherein the molar content ratio of water molecules to silicon atoms is 62.1-79.4; the molar content ratio of the template agent TPAOH to the silicon atoms is 0.15-0.34; the molar content ratio of the metal atoms to the silicon atoms is 0.004-0.05; the molar ratio of the sodium ions to the silicon atoms is 0.04-0.12; the molar content ratio of the aluminum atoms to the silicon atoms is 0.0017-0.010.

TABLE 1 molar content ratio of each substance to silicon atom during synthesis

Taking Zn @ ZSM-5 as an example, the preparation method is as follows:

s1, preparing a solution A from 84.50-88.50 g of deionized water, 14.88-26.40 g of tetrapropylammonium hydroxide (25 wt%) and 19.38g of tetraethoxysilane, and stirring at 20-80 ℃ for 0.5-24 hours;

s2, 0.06-0.48 g of ZnCl₂0.43 to 3.62g of anhydrous ethylenediamine and 1.66 to 12.72g of H₂Mixing O uniformly to prepare a solution B, adding the solution B into the solution A, heating to 40-120 ℃, and continuously stirring for 1-24 hours;

s3, mixing 0.15-0.45 g NaOH, 0.06-0.35 g Al (NO)₃)₃·9H₂O and 3.17-18.65 g of H₂Mixing O uniformly to prepare a solution C, adding the solution C into the solution, and stirring for 0.5-24 hours;

s4, after the stirring is finished, the mixture is put into a crystallization kettle and crystallized for 12-96 hours at the temperature of 170-200 ℃; and the degree of crystallization was judged by XRD.

And S5, washing with deionized water after crystallization is finished until the filtrate is neutral (pH is 7-8), drying the filter cake at 80-100 ℃, and roasting at 540-560 ℃ for 6-8 h to obtain the Na-type Zn @ ZSM-5 sample.

S6, putting a powdery Na type Zn @ ZSM-5 sample into 0.4-1 mol/L ammonium nitrate aqueous solution with the solid-liquid mass volume ratio of 1:10, stirring for 0.5-3 h at 80-100 ℃, and repeating for 1-3 times. And filtering the deionized water, washing the solid until the filtrate is neutral, drying the filtrate at 80-100 ℃, and roasting the dried filtrate at 540-560 ℃ for 4-6 hours to obtain an H-shaped Zn @ ZSM-5 sample.

Example 1:

86.50g of deionized water, 18.6g of tetrapropylammonium hydroxide (25 wt%) and 19.38g of ethyl orthosilicate are prepared into solution A, and the solution A is stirred for 3 hours at 35 ℃;

0.23g of ZnCl₂1.63g of anhydrous ethylenediamine and 6.36g of H₂Mixing O uniformly to prepare a solution B, adding the solution B into the solution A, heating to 80 ℃, and continuing stirring for 3 hours;

0.37g of NaOH, 0.116g of Al (NO)₃)₃·9H₂O and 6.2g of H₂Mixing O uniformly to prepare a solution C, adding the solution C into the solution, and stirring for 1.5 h;

after the stirring is finished, the mixture is put into a crystallization kettle and is statically crystallized for 24 hours at the temperature of 170 ℃.

Putting a powdery Na type Zn @ ZSM-5 sample into a 1mol/L ammonium nitrate aqueous solution with the solid-to-liquid ratio of 1:10, stirring for 1.5h at 80 ℃, and repeating for 3 times. And (3) washing the solid until the pH value of the filtrate is 7, drying at 80 ℃, and roasting at 540 ℃ for 4H to obtain an H-type Zn @ ZSM-5 sample.

TABLE 2 product average Selectivity of Zn @ ZSM-5 of inventive example 1

As shown in fig. 1, the molecular sieve supported metal catalyst prepared by the invention has a typical MFI structure, and no characteristic diffraction peak of Zn is observed, which indicates that the metal dispersion degree of the method of the invention is higher. As shown in figure 2, the catalyst is uniform in size and is in a short column shape. As shown in fig. 3, the methanol conversion was above 90% for a duration of about 220 hours, indicating a longer reaction life for the catalyst prepared according to the invention.

Compared with the prior art, the invention has better methanol aromatization performance; in addition, the method of the invention saves an inducer (urea) and seed crystals, and has simpler synthetic process and lower cost; better performance and higher selectivity of aromatic hydrocarbon and propylene.

Example 2:

86.50g of deionized water, 18.6g of tetrapropylammonium hydroxide (25 wt%) and 19.38g of ethyl orthosilicate are prepared into solution A, and the solution A is stirred for 4 hours at 20 ℃;

0.06g of ZnCl₂0.43g of anhydrous ethylenediamine and 1.66g of H₂Mixing O uniformly to prepare a solution B, adding the solution B into the solution A, heating to 60 ℃, and continuing stirring for 24 hours;

0.15g of NaOH, 0.35g of Al (NO)₃)₃·9H₂O and 18.65g of H₂Mixing O uniformly to prepare a solution C, adding the solution C into the solution, and stirring for 3 hours;

after the stirring is finished, the mixture is put into a crystallization kettle and is statically crystallized for 48 hours at the temperature of 170 ℃.

Putting a powdery Na type Zn @ ZSM-5 sample into 0.6mol/L ammonium nitrate aqueous solution with the solid-liquid mass-volume ratio of 1:10, stirring for 1h at 80 ℃, and repeating for 3 times. And (3) washing the solid until the pH value of the filtrate is 7, drying at 100 ℃, and roasting at 540 ℃ for 4H to obtain an H-type Zn @ ZSM-5 sample.

Example 3:

88.50g of deionized water, 18.6g of tetrapropylammonium hydroxide (25 wt%) and 19.38g of ethyl orthosilicate are prepared into solution A, and the solution A is stirred for 2 hours at 40 ℃;

0.06g of ZnCl₂0.43g of anhydrous ethylenediamine and 1.66g of H₂Mixing O uniformly to prepare a solution B, adding the solution B into the solution A, heating to 120 ℃, and continuing stirring for 1 h;

0.45g of NaOH, 0.06g of Al (NO)₃)₃9H2O and 3.17g of H₂Mixing O uniformly to prepare a solution C, adding the solution C into the solution, and stirring for 1 h;

after the stirring is finished, the mixture is put into a crystallization kettle and is statically crystallized for 72 hours at the temperature of 170 ℃.

Putting a powdery Na type Zn @ ZSM-5 sample into a 1mol/L ammonium nitrate aqueous solution with the solid-to-liquid ratio of 1:10, stirring for 2 hours at 80 ℃, and repeating the steps for 3 times. And (3) washing the solid until the pH value of the filtrate is 7, drying at 80 ℃, and roasting at 540 ℃ for 5H to obtain an H-type Zn @ ZSM-5 sample.

Example 4:

preparing solution A from 84.50g of deionized water, 18.6g of tetrapropylammonium hydroxide (25 wt%) and 19.38g of tetraethoxysilane, and stirring at 40 ℃ for 2 hours;

0.48g of ZnCl₂3.62g of anhydrous ethylenediamine and 12.72g of H₂Mixing O uniformly to prepare a solution B, adding the solution B into the solution A, heating to 80 ℃, and continuing stirring for 21 hours;

Putting a powdery Na type Zn @ ZSM-5 sample into a 1mol/L ammonium nitrate aqueous solution with the solid-liquid mass-volume ratio of 1:10, stirring for 1.5h at 80 ℃, and repeating for 3 times. And (3) washing the solid until the pH value of the filtrate is 7, drying at 80 ℃, and roasting at 540 ℃ for 4H to obtain an H-type Zn @ ZSM-5 sample.

Example 5:

90.22g of deionized water, 14.88g of tetrapropylammonium hydroxide (25 wt%) and 19.38g of ethyl orthosilicate are prepared into solution A, and the solution A is stirred for 3 hours at the temperature of 35 ℃;

Example 6:

80.65g of deionized water, 26.40g of tetrapropylammonium hydroxide (25 wt%) and 19.38g of tetraethoxysilane are prepared into solution A, and the solution A is stirred for 3 hours at the temperature of 35 ℃;

Example 7:

0.11g of Ni (NO)₃)₂·6H₂O, 1.63g of anhydrous ethylenediamine and 6.36g of H₂Mixing O uniformly to prepare a solution B, adding the solution B into the solution A, heating to 80 ℃, and continuing stirring for 21 hours;

The method for modifying the ZSM-5 also comprises the steps of changing the properties of the ZSM-5 such as particle size, pore channel structure and the like, thereby improving the diffusion performance of macromolecules; the metal is loaded on the ZSM-5 through the modes of dipping, in-situ synthesis, deposition, ion exchange and the like, so that the acidity distribution is changed, and the selectivity of the aromatic hydrocarbon in the product can be improved by utilizing the shape selectivity.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be able to cover the technical solutions and the inventive concepts of the present invention within the technical scope of the present invention.

Claims

1. a preparation method of molecular sieve supported metal catalyst, is characterized in that, comprises the following steps:

S1. Mix the deionized water, the template agent and the silicon source evenly, and stir at 20 to 80°C for 0.5 to 24 hours;

S2. Mix the metal source, complexing agent and H ₂ O evenly, add it to the solution prepared in S1, heat up to 40-120°C, and continue stirring for 1-24h;

S3. Mix the aluminum source, H ₂ O, Na ion and alkali source evenly, add them to the mixed solution of steps S1 and S2, and continue to stir for 0.5-24 h;

S4, crystallize at 170℃～200℃ for 12～96h;

S5, washing with deionized water until the filtrate is neutral, drying at 80°C to 100°C, and then calcining at 540°C to 560°C for 6 to 8 hours to obtain a Na-type molecular sieve supported metal catalyst;

S6, placing the Na-type molecular sieve supported metal catalyst in an aqueous solution of ammonium nitrate, stirring at 80-100 °C until the ammonium exchange is completed; washing the solid until the filtrate is neutral, drying at 80-100 °C, and calcining at 540-560 °C 4～6h, obtain H type molecular sieve supported metal catalyst;

The molecular sieve of the catalyst is any one of ZSM-5 molecular sieve, Beta molecular sieve or mercerized molecular sieve; the metal source is any one of zinc, silver or gallium;

The molar content ratio of water molecules to silicon atoms in the H-type molecular sieve supported metal catalyst is 62.1 to 79.4; the molar content ratio of template agent to silicon atoms is 0.15 to 0.34; the molar content ratio of metal source atoms to silicon atoms is 0.004 to 0.004 0.05; the molar ratio of sodium ions to silicon atoms is 0.04 to 0.12; the molar content ratio of aluminum atoms to silicon atoms is 0.0017 to 0.010.

2. the preparation method of the molecular sieve supported metal catalyst according to claim 1, is characterized in that, described templating agent is any one in tetrapropylammonium hydroxide, tetrapropylammonium bromide or ethylamine.

3 . The method for preparing a molecular sieve supported metal catalyst according to claim 1 , wherein the silicon source is any one of ethyl orthosilicate, silica sol and water glass. 4 .

4 . The preparation method of the molecular sieve supported metal catalyst according to claim 1 , wherein the complexing agent is any one of anhydrous ethylenediamine and disodium EDTA metal complexing agent. 5 .

5 . The method for preparing a molecular sieve supported metal catalyst according to claim 1 , wherein the alkali source is any one of NaOH and ammonia water alkaline substances. 6 .

6. The preparation method of the molecular sieve supported metal catalyst according to claim 1, wherein the Na ion is any one of sodium salt and sodium alkali.

7. The preparation method of the molecular sieve supported metal catalyst according to any one of claims 1 to 6, wherein the preparation method of H-type Zn@ZSM-5 comprises the following steps:

S1. Stir 84.50-88.50g of deionized water, 14.88-26.40g of 25wt% tetrapropylammonium hydroxide and 19.38g of ethyl orthosilicate at 20-80°C for 0.5-24h;

S2. Mix 0.06-0.48g of ZnCl ₂ , 0.43-3.62g of anhydrous ethylenediamine and 1.66-12.72g of H ₂ O evenly, add to the solution prepared in S1, heat up to 40-120°C, and continue stirring for 1 ~24h;

S3. Mix 0.15-0.45g of NaOH, 0.06-0.35g of Al(NO ₃ ) ₃ .9H ₂ O and 3.17-18.65g of H ₂ O evenly, add it to the mixed solution of steps S1 and S2, and stir for 0.5 ~24h;

S4, crystallize at 170℃～200℃ for 12～96h;

S5, washing with deionized water until the filtrate is neutral, and drying at 80℃～100℃, and then calcining at 540℃～560℃ for 6～8h to obtain Na-type Zn@ZSM-5;

S6. Place the Na-type Zn@ZSM-5 in a 0.4-1 mol/L ammonium nitrate aqueous solution, with a solid-liquid mass-volume ratio of 1:10, and stir at 80-100° C. until the ammonium exchange is completed; deionization Filter with water and wash the solid until the filtrate is neutral, dry at 80-100 °C, and calcinate at 540-560 °C for 4-6 h to obtain H-type Zn@ZSM-5.