CN113649064B - Zeolite molecular sieve supported metal catalyst and synthesis method and application thereof - Google Patents

Zeolite molecular sieve supported metal catalyst and synthesis method and application thereof Download PDF

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CN113649064B
CN113649064B CN202110831222.8A CN202110831222A CN113649064B CN 113649064 B CN113649064 B CN 113649064B CN 202110831222 A CN202110831222 A CN 202110831222A CN 113649064 B CN113649064 B CN 113649064B
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zeolite
molecular sieve
metal catalyst
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supported metal
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CN113649064A (en
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吴志杰
刘萌
杨江蒨
苗彩霞
葛思达
潘涛
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China University of Petroleum Beijing
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    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • B01J29/70—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups B01J29/08 - B01J29/65
    • B01J29/72—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups B01J29/08 - B01J29/65 containing iron group metals, noble metals or copper
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    • B01J29/42—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively containing iron group metals, noble metals or copper
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Abstract

The invention relates to the technical field of synthesis of modified zeolite molecular sieves, in particular to a zeolite molecular sieve supported metal catalyst and a synthesis method and application thereof. The synthesis method of the zeolite molecular sieve supported metal catalyst provided by the invention is a two-step crystallization method; the method comprises the following steps: the silica-alumina gel is pre-crystallized at low temperature, and then metal salt solution is added for high temperature crystallization. The zeolite molecular sieve is directly introduced in the process of synthesizing the zeolite molecular sieve, the problem that the growth difficulty of crystals is increased due to the doping of a metal salt solution in the conventional in-situ coating method is solved through a two-step crystallization method, and meanwhile, the step of adjusting the pH of a system for the second time or additionally adding seed crystals is avoided, so that the process flow is simplified, the production efficiency is improved and the cost is reduced. In addition, the zeolite supported metal catalyst obtained by the two-step crystallization method has smaller metal particle size and higher dispersity, and has higher hydrogenation activity and target product selectivity when used in hydrogenation reaction.

Description

Zeolite molecular sieve supported metal catalyst and synthesis method and application thereof
Technical Field
The invention relates to the technical field of zeolite molecular sieve synthesis, in particular to a zeolite molecular sieve supported metal catalyst and a synthesis method and application thereof.
Background
Metals are an important class of industrial catalysts and have been widely used in hydrogenation, oxidation, coupling, and other reactions over the past few decades. As the metal particle size decreases, the number of atoms at the corners and edges increases, which atoms have the effect of activating the substrate and are particularly susceptible to participating in catalytic reactions to increase catalytic activity, with the most active catalyst particles typically having a size less than 5nm. The metal catalyst with small particle size has high surface free energy, and is easy to migrate and agglomerate, so that the catalytic activity is reduced. The aggregation deactivation of the metal particles can be suppressed by loading the metal particles on the carrier.
Currently, methods for preparing zeolite supported metal catalysts mainly include impregnation methods and ion exchange methods (CN 101497047B. The loading of metal in the impregnation process is limited by the pore volume and, in theory, the metal precursor can completely fill the zeolite channels. However, in solution, the radius of the hydrated metal cations is large and cannot enter the medium or small pore zeolite by diffusion, so that most of the metal species introduced by this method are concentrated on the surface of the zeolite and aggregate at high temperature to form large particles (New Journal of Chemistry,2016,40 (5): 3933-3949.). The exchange amount of the ion exchange method depends on the number of Al atoms in each unit cell, and therefore the ion exchange method is not suitable for all-silica zeolites or high-silica zeolites (Advanced Materials,2019,31 (1): 1803966-1803989.).
The in-situ coating method refers to a method of introducing a metal precursor into zeolite and performing hydrothermal crystallization. By the in-situ coating method, the metal particles can be uniformly distributed throughout the zeolite crystals without being limited by the pore size of the zeolite. However, in the actual synthesis process, the difficulty of crystal growth is increased due to the doping of the metal salt solution.
For this reason, the prior art proposes to reduce the difficulty of crystal nucleation of the system by adjusting the pH value of the system twice or adding seed crystals.
Patent (CN 108160103A) discloses a preparation method of a highly dispersed transition metal particle supported hierarchical pore zeolite aggregate. Mixing a transition metal salt solution with an aluminum source, then dropwise adding the mixture into a silicon source solution to obtain a transition metal-silicon aluminum sol-gel solution, then adding a seed crystal, and crystallizing at a proper temperature; the metal particle diameter of the finally obtained catalyst is 1.5-2 nm.
A patent (CN 103551184A) discloses a zeolite-coated metal oxide catalyst for preparing olefin by methanol conversion, which is prepared by mixing a metal salt solution with a prepared zeolite silica-alumina sol, and crystallizing to obtain the catalyst with high selectivity and yield.
Otto et al (microporus and mesopouus Materials,2018, 270.. The metal particles in the obtained catalyst have good dispersibility, and the size of the metal particles is less than 2.5nm.
CN201510847939.6 and CN201510849101.0 disclose a method for preparing a zeolite-supported metal or metal oxide catalyst, which mainly comprises mixing silicon and aluminum raw materials synthesized by zeolite molecular sieves with a metal salt to form a gel, and then performing conversion by a dry gel method to obtain the zeolite-coated metal catalyst. However, the dry glue method is adopted for synthesis, so that a large amount of steam is needed in large-scale batch preparation, the energy consumption is high, and the industrial implementation is not facilitated.
CN201910389284.0 discloses a method for directly adding metal salts such as metal molybdenum, metal nickel, metal zinc and the like in a synthesis process of ZSM-5 zeolite to form a silicon-aluminum gel containing metal ions, and then directly performing hydrothermal crystallization to produce a metal-containing ZSM-5 zeolite with a multilevel structure, wherein the metal-ZSM-5 zeolite has excellent activity in catalytic gasoline desulfurization-olefin reduction reactions. The method requires specific mixing and aging treatment of different metal salt precursors and silicon sources or aluminum sources, and proper pH value is established, so that the process flow is complex and time is long.
Although the technical contents disclosed in the above patents and documents can obtain a catalyst with relatively small size and relatively good dispersibility, the process flow is complicated or the cost is increased due to the need of adjusting the pH of the system or adding additional seed crystals, which is not favorable for industrial synthesis.
Disclosure of Invention
The invention provides a method for directly synthesizing a zeolite molecular sieve loaded metal catalyst in situ, which reduces the links of zeolite molecular sieve impregnation or ion exchange of metal ions.
The second aspect of the invention provides a zeolite molecular sieve supported metal catalyst obtained by the synthesis method.
In a third aspect, the invention provides the use of the above zeolite molecular sieve supported metal catalyst in a hydrogenation reaction.
Specifically, the synthesis method of the zeolite molecular sieve supported metal catalyst provided by the invention is a two-step crystallization method; the method comprises the following steps: the silicon-aluminum gel is pre-crystallized at low temperature, and then the metal salt solution is added for high temperature crystallization.
The traditional method for loading a metal catalyst on a zeolite molecular sieve generally comprises the steps of synthesizing zeolite and then loading; the zeolite molecular sieve is directly introduced in the process of synthesizing the zeolite molecular sieve. The research of the invention discovers that the problem that the growth difficulty of the crystal is increased due to the doping of the metal salt solution in the existing in-situ coating method can be solved by the two-step crystallization method, and meanwhile, the step of adjusting the pH value of the system for the second time or adding the seed crystal additionally is avoided, the process flow is simplified, the production efficiency is improved and the cost is reduced.
In addition, the zeolite supported metal catalyst obtained by the two-step crystallization method has smaller metal particle size and higher dispersity, and has higher hydrogenation activity and target product selectivity when used in hydrogenation reaction.
In the synthesis process, the conditions of pre-crystallization are as follows: crystallizing at 60-100 deg.c for 12-48 hr. By controlling the pre-crystallization temperature and time range, the method is more favorable for crystal nucleation and is also favorable for the growth of crystals in the subsequent crystallization process of formed crystal nuclei, thereby reducing the growth difficulty of zeolite crystals after the addition of metal salt; in addition, reasonable control of the pre-crystallization temperature and time can avoid the influence of premature precipitation of metal cations into colloidal hydroxide on the dispersibility of the metal ions in the zeolite.
The silicon-aluminum gel is obtained by the following method: mixing the microporous organic template agent, water and an alkali source, adding an aluminum source after stirring, stirring until the mixture is clear, adding a silicon source, and stirring uniformly.
Wherein the microporous organic template agent is one of tetraethylammonium hydroxide (TEAOH), tetraethylammonium bromide (TEABr), tetrapropylammonium hydroxide (TPAOH), tetrapropylammonium bromide (TPABr), n-butylamine, adamantane, 1, 6-hexamethylenediamine or hexamethonium bromide.
The alkali source is NaOH or KOH.
The aluminum source is one of sodium aluminate, pseudo-boehmite, aluminum sulfate or aluminum isopropoxide.
The silicon source is one of silica sol, water glass, coarse pore silica gel or white carbon black.
Using SiO in silicon source 2 Al in aluminum source 2 O 3 When tetraethyl ammonium hydroxide is used as a microporous organic template agent, the mass ratio of tetraethyl ammonium hydroxide, water, an aluminum source, a silicon source and an alkali source is (1.5-2.0): (0.66-0.80): (0.020-0.030): 1: (0.023-0.034);
when tetrapropylammonium bromide is used as the microporous organic template agent, the mass ratio of the tetrapropylammonium bromide to the water to the aluminum source to the silicon source to the alkali source is (0.35-0.46): (2.2-3.0): (0.036-0.045): 1: (0.1-0.15);
when the ammonium hexametaphosphate is used as the microporous organic template agent, the mass ratio of the ammonium hexametaphosphate, the water, the aluminum source, the silicon source and the alkali source is (0.10-0.15): (5.5-6.8): (0.018-0.019): 1: (0.08-0.09).
In the synthesis process, the high-temperature crystallization conditions are as follows: crystallizing at 100-170 deg.c for 12-36 hr. By controlling the pre-crystallization temperature and time range, the method is more favorable for crystal nucleation and is also favorable for the growth of crystals in the subsequent crystallization process of formed crystal nuclei, thereby reducing the growth difficulty of zeolite crystals after the addition of metal salts; in addition, the temperature and time of the pre-crystallization are reasonably controlled, so that the influence on the dispersibility of metal species in the zeolite caused by the early precipitation of metal cations into colloidal hydroxide can be avoided, the metal species can enter the inside of the pore channels of the zeolite, and the small-scale metal catalyst can be obtained after the reduction.
Wherein the metal salt solution is one or two of soluble salts containing transition metals or noble metals such as Fe, co, ni, cu, ru, rh, pt, pd and the like.
The synthesis method further comprises the following steps: further roasting the product obtained by high-temperature crystallization in an air atmosphere, and then reducing the product in a hydrogen atmosphere;
the roasting temperature is 500-600 ℃.
The reduction temperature can be specifically determined according to different metals, such as 300-400 ℃, so as to avoid that the metal cannot be effectively reduced due to too low temperature or the metal is sintered due to too high temperature.
The zeolite molecular sieve supported metal catalyst obtained by the synthesis method is adopted in the invention. The metal ions in the catalyst are uniformly dispersed in zeolite pore channels, the metal size is small, and the hydrogenation performance of the catalyst is remarkably improved.
The zeolite of the zeolite molecular sieve supported metal catalyst is zeolite with a one-dimensional pore channel or a three-dimensional pore channel structure.
The zeolite with the one-dimensional pore channel structure refers to zeolite with one-dimensional pore channels, such as TON, MTT, AEL, MOR or EUO and the like, and preferably twelve-membered ring channel EUO structure zeolite ZSM-48; compared with other zeolites, the preferred zeolite has the advantages of good hydrothermal stability, thermal stability, pore structure, proper acidity and the like, and has a wide application range.
The zeolite with a three-dimensional channel structure refers to zeolite with three-dimensional channels such as MFI, BEA, CHA or FAU and the like, preferably zeolite ZSM-5 with an MFI structure of ten-membered ring channel and zeolite Beta with a BEA structure of twelve-membered ring channel; compared with other zeolites, the preferred zeolite Beta zeolite with the twelve-membered ring channel BEA structure has the advantages of high silicon-aluminum ratio, high stability and wide application range of the MFI structure zeolite ZSM-5 with the ten-membered ring channel, and the preferred zeolite Beta zeolite with the twelve-membered ring channel BEA structure has the advantage of large adjustable range of silicon-aluminum ratio.
The third aspect of the invention provides the application of the catalyst obtained by the synthesis method in hydrogenation reaction.
For example, in the hydrogenation reaction of toluene and triisopropylbenzene, the hydrogenation conditions are as follows: p H2 =2.75MPa, reaction temperature 150 ℃; or applied to furfural hydrogenation reaction, and the reaction conditions are as follows: at a temperature of 110 ℃ P H2 =10bar, rotation speed 1000rpm, reaction time 1h or 2h; or the method is applied to the phenol hydrodeoxygenation reaction, and the reaction conditions are as follows: p H2 =5.0MPa, T =150 ℃, and the reaction time is 2h.
The beneficial effects obtained by the invention are as follows:
the invention solves the problem that the growth difficulty of the crystal is increased due to the doping of the metal salt solution in the existing in-situ coating method by a two-step crystallization method, simultaneously avoids the step of adjusting the pH of the system for the second time or additionally adding the seed crystal, simplifies the process flow, improves the production efficiency and reduces the cost.
Meanwhile, the synthesis method can obviously improve the dispersion degree of metal particles in zeolite, reduce the particle size of metal and further improve the hydrogenation-dehydrogenation performance of the catalyst.
In addition, by zeolite coating, the selective conversion of the primary product can be inhibited and the selectivity of the primary product can be improved by utilizing the pore structure of zeolite.
Drawings
FIG. 1 is Ni @ beta-NO 3 - XRD pattern of (a).
FIG. 2 shows Ni @ beta-NO 3 - TEM image of (a).
FIG. 3 shows Ni @ beta-Cl - XRD pattern of (a).
FIG. 4 shows Ni @ beta-Cl - A TEM image of (a).
Fig. 5 is an XRD pattern of the sample obtained in comparative example 1.
Fig. 6 is an XRD pattern of the sample obtained in comparative example 2.
FIG. 7 is an XRD pattern of Ni/Beta.
FIG. 8 is a TEM image of Ni/Beta.
FIG. 9 is an XRD pattern for Ru @ ZSM-5.
FIG. 10 is a TEM image of Ru @ ZSM-5.
FIG. 11 is an XRD spectrum of Ru/ZSM-5-HT.
FIG. 12 is a TEM spectrum of Ru/ZSM-5-HT.
FIG. 13 is an XRD spectrum of Ru/ZSM-5-CN.
FIG. 14 is a TEM spectrum of Ru/ZSM-5-CN.
FIG. 15 is an XRD spectrum of Ru/ZSM-5.
FIG. 16 is a TEM spectrum of Ru/ZSM-5.
FIG. 17 is an XRD spectrum of Pt @ Y.
FIG. 18 is a TEM spectrum of Pt @ Y.
FIG. 19 is an XRD spectrum of Pt/Y.
FIG. 20 is a TEM spectrum of Pt/Y.
FIG. 21 is an XRD spectrum of Pt @ ZSM-48.
Detailed Description
The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.
Each of the components in the following examples is commercially available.
Example 1
This example provides a method for synthesizing Beta zeolite with BEA structure (catalyst a and catalyst B) containing Ni, which specifically includes the following steps:
firstly, 11.48g of water and 27.90g of TEAOH and 0.45g of NaOH are mixed and stirred to form a clear solution, then 0.8g of sodium aluminate is added and stirred until the solution is clear, 15g of coarse silica gel is added and stirred for 3h to form the silica-alumina gel.
The silicon-aluminum gel comprises the following components in percentage by mass: 1.86TEAOH:0.77H 2 O：0.024Al 2 O 3 ：SiO 2 ：0.03NaOH。
Transferring the silicon-aluminum gel into a crystallization kettle, and pre-crystallizing for 24 hours at 100 ℃; taking out the pre-crystallized product and stirring uniformly.
0.75g of nickel nitrate was dissolved in 1ml of water to prepare a metal salt solution. And dropwise adding the metal salt solution into the pre-crystallized product, uniformly stirring, transferring to a crystallization kettle, and recrystallizing for 36 hours at 140 ℃.
Washing and drying the obtained sample, roasting for 6h at 550 ℃ in an air atmosphere, and then reducing 2 at 400 ℃ in a hydrogen atmosphereh, to obtain Ni @ beta-NO 3 - (catalyst A).
Changing 0.75g of nickel nitrate into 0.34g of nickel chloride under the same other synthesis conditions to obtain Ni @ beta-Cl - (catalyst B).
FIG. 1 and FIG. 3 are respectively Ni @ beta-NO 3 - And Ni @ beta-Cl - XRD pattern of (a). From the figure, it can be seen that Ni @ beta-NO 3 - And Ni @ beta-Cl - The method has obvious Beta zeolite characteristic diffraction peak and no other miscellaneous peaks, and indicates that the sample phase is good. XRF results show that the prepared Ni @ beta-NO 3 - And Ni @ beta-Cl - The loading of medium Ni is about 1.3 wt.%.
FIGS. 2 and 4 are respectively Ni @ beta-NO 3 - And Ni @ beta-Cl - The TEM images of (a) show that no significant metal particles are observed, indicating that the metal particles are highly dispersed and small in size.
Comparative example 1
For comparison, the Ni-containing Beta zeolite (without pH adjustment or with seed crystal addition) was prepared by a one-step crystallization method, comprising the following steps:
firstly, 11.48g of water and 27.90g of TEAOH and 0.45g of NaOH are mixed and stirred to form a clear solution, then 0.8g of sodium aluminate is added and stirred until the solution is clear, 15g of coarse silica gel is added and stirred for 3h to form the silica-alumina gel.
0.75g of nickel nitrate was dissolved in 1ml of water to prepare a metal salt solution. And dropwise adding the metal salt solution into the silicon-aluminum gel, uniformly mixing, transferring to a crystallization kettle, and crystallizing for 60 hours at 140 ℃.
The mass ratio of the obtained mixture is as follows: 1.86TEAOH:0.77H 2 O：0.024Al 2 O 3 ：SiO 2 ：0.03NaOH。
The obtained sample is washed, dried, roasted for 6h at 550 ℃ in an air atmosphere and then reduced for 2h at 400 ℃ in a hydrogen atmosphere.
Fig. 5 is an XRD pattern of the resulting sample. The characteristic diffraction peak of Beta zeolite is not observed in the figure, and the Beta zeolite is in an amorphous structure. This is because the addition of the metal salt solution increases the difficulty of crystal growth.
Comparative example 2
For comparison, the formula of the metal-containing silica-alumina gel synthesized in comparative example 1 is used for reference of the synthesis method of patent CN201910389284.0, and the Ni-containing Beta zeolite is prepared by a two-step crystallization method.
Firstly, adding 27.90g of TEAOH into 8g of water at 25 ℃, uniformly stirring, adding 15g of coarse silica gel, and continuously stirring for about 30min to obtain a silicon source solution;
secondly, adding 0.8g of sodium aluminate into 4g of water at 25 ℃, stirring for 5min, then adding 0.75g of nickel nitrate, adding 0.45g of sodium hydroxide, continuously stirring for about 40min to be in a clear state to obtain an aluminum source and nickel source solution, and then aging for 5 hours at 50 ℃ to obtain a uniform solution;
and finally, adding the silicon source solution into the aluminum source and nickel source solution, and aging for 2 hours at 50 ℃ to obtain a hydrothermal synthesis system. The mass ratio of the obtained mixture is as follows: 1.86TEAOH:0.8H 2 O：0.024Al 2 O 3 ：SiO 2 ：0.03NaOH。
The raw material preparation liquid is transferred to a reaction kettle and is pre-crystallized in an oven at 100 ℃ for 24 hours, and then the temperature is raised to 140 ℃ again for crystallization for 36 hours.
The obtained sample is washed, dried, roasted for 6h at 550 ℃ in an air atmosphere and then reduced for 2h at 400 ℃ in a hydrogen atmosphere.
Fig. 6 is an XRD pattern of the resulting sample. No characteristic diffraction peaks of zeolite Beta were observed from the figure. This indicates that the presence of metal ions in the silica-alumina gel affects the nucleation process, and the sequence and timing of the metal ions addition can significantly affect the zeolite formation by adopting the two-step crystallization method.
Comparative example 3
For comparison, a conventional impregnation method was used to prepare a zeolite Beta containing Ni (catalyst C) by the following steps:
firstly, 11.48g of water and 27.90g of TEAOH and 0.45g of NaOH are mixed and stirred to form a clear solution, then 0.8g of sodium aluminate is added and stirred until the solution is clear, 15g of coarse silica gel is added and stirred for 3h to form the silica-alumina gel.
The silicon-aluminum gel comprises the following components in percentage by mass: 1.86TEAOH:0.77H 2 O：0.024Al 2 O 3 ：SiO 2 :0.03NaOH. And transferring the silicon-aluminum gel into a crystallization kettle, and crystallizing for 48 hours at 140 ℃.
Washing and drying the obtained sample, and roasting at 550 ℃ for 6h in the air atmosphere to obtain Beta zeolite; 2g of Beta zeolite was dissolved in 14g of water and stirred well.
Dissolving 0.1g of nickel nitrate in 5ml of water to obtain a metal salt solution, dropwise adding the metal salt solution into the solution of Beta zeolite, stirring for 3 hours in a water bath at 60 ℃, evaporating water, and drying.
The dried sample was calcined at 550 ℃ for 6h and then reduced at 400 ℃ for 2h in a hydrogen atmosphere to give Ni/Beta (catalyst C).
FIG. 7 is an XRD pattern of Ni/Beta. From the figure, ni/Beta can be seen to have a diffraction peak characteristic to zeolite Beta, and no other miscellaneous peaks, indicating that the sample phase is good. XRF results showed Ni loading in Ni/Beta produced to be 1.1wt.%.
FIG. 8 is a TEM image of Ni/Beta. From the figure, it can be observed that the metal particles are obvious, the size of the metal particles is larger, which indicates that the Ni particles are agglomerated because the hydrate size of Ni ions is close to the pore size (0.64 nm) of Beta zeolite, and Ni ions are not easy to enter the inside of zeolite pores during the impregnation process and are loaded on the outer surface to be agglomerated.
Example 2
The embodiment provides a synthetic method of MFI structure ZSM-5 zeolite (catalyst D) containing Ru, which specifically comprises the following steps:
firstly, 18.75g of water and 3g of TPABr and 0.85g of NaOH are mixed and stirred to form a clear solution, then 0.45g of pseudo-boehmite is added and stirred until the solution is clear, 7.5g of white carbon black is added and stirred for 3 hours to form the silicon-aluminum gel.
The silicon-aluminum gel comprises the following components in percentage by mass: 0.4TPABr:2.5H 2 O：0.04Al 2 O 3 ：SiO 2 ：0.1NaOH。
Transferring the silicon-aluminum gel into a crystallization kettle, and pre-crystallizing for 24 hours at 100 ℃; taking out the pre-crystallized product and stirring uniformly. A metal salt solution was prepared by dissolving 0.22g of ruthenium chloride in 1ml of water.
And dropwise adding the metal salt solution into the pre-crystallized product, uniformly stirring, transferring to a crystallization kettle, and crystallizing for 24 hours at 170 ℃.
The obtained sample is washed, dried, roasted at 550 ℃ for 6h in an air atmosphere, and then reduced at 350 ℃ for 2h in a hydrogen atmosphere to obtain Ru @ ZSM-5 (catalyst D).
FIG. 9 is an XRD pattern of Ru @ ZSM-5. XRD proves that the obtained catalyst has a ZSM-5 zeolite characteristic diffraction peak and no other impurity peaks, which indicates that the sample phase is good. The XRF results showed a Ru loading of 0.53wt.% in the prepared Ru @ ZSM-5.
FIG. 10 is a TEM image of Ru @ ZSM-5. It can be seen from the figure that the Ru metal particles are small and have an average particle size of 1.1nm.
Comparative example 4
For comparison, ZSM-5 zeolite (catalyst E) containing Ru was prepared by a one-step crystallization method, comprising the following steps:
firstly, 18.75g of water and 3g of TPABr and 0.85g of NaOH are mixed and stirred to form a clear solution, then 0.45g of pseudo-boehmite is added and stirred until the solution is clear, 7.5g of white carbon black is added and stirred for 3 hours to form the silica-alumina gel.
A metal salt solution was prepared by dissolving 0.22g of ruthenium chloride in 1ml of water. And dropwise adding the metal salt solution into the silicon-aluminum gel, uniformly mixing, transferring to a crystallization kettle, and crystallizing for 48 hours at 170 ℃.
The mass ratio of the obtained mixture is as follows: 0.4TPABr:2.5H 2 O：0.04Al 2 O 3 ：SiO 2 ：0.1NaOH。
The obtained sample is washed, dried, roasted for 6h at 550 ℃ in the air atmosphere and then reduced for 2h at 350 ℃ in the hydrogen atmosphere to obtain Ru/ZSM-5-HT (catalyst E).
FIG. 11 is an XRD pattern of Ru/ZSM-5-HT. The XRD results showed the resulting sample to have characteristic diffraction peaks of ZSM-5 zeolite, and the XRF results showed the loading of Ru in the sample to be 0.46wt.%.
FIG. 12 is a TEM image of Ru/ZSM-5-HT. TEM results show that the metal Ru has large particle size and non-uniform size (1-20 nm), which indicates that the metal Ru is mainly deposited on the outer surface of the zeolite and can not enter the pore channels.
Comparative example 5
For comparison, a formula of the metal-containing silica-alumina gel synthesized in comparative example 4 was used to prepare a Ru-containing ZSM-5 zeolite (catalyst F) by a two-step crystallization method with reference to the synthesis method of patent CN 201910389284.0.
Firstly, adding 3g of TPABr into 10g of water at 25 ℃, uniformly stirring, adding 7.5g of white carbon black, and continuously stirring for about 30min to obtain a silicon source solution;
secondly, adding 0.45g of pseudo-boehmite into 8.75g of water at 25 ℃, stirring for 5min, adding 0.22g of ruthenium chloride, adding 0.85g of sodium hydroxide, continuously stirring for about 40min to be in a clear state to obtain an aluminum source and ruthenium source solution, and then aging for 5 hours at 50 ℃ to obtain a uniform solution;
and finally, adding the silicon source solution into the aluminum source and ruthenium source solution, and aging for 2 hours at 50 ℃ to obtain a hydrothermal synthesis system. The mass ratio of the obtained mixture is as follows: 0.4TPABr:2.5H 2 O：0.04Al 2 O 3 ：SiO 2 ：0.1NaOH。
The raw material preparation liquid is transferred to a reaction kettle and is pre-crystallized in an oven at 100 ℃ for 24 hours, and then the temperature is raised to 170 ℃ again for crystallization for 24 hours.
The obtained sample is washed, dried, roasted for 6h at 550 ℃ in the air atmosphere and then reduced for 2h at 350 ℃ in the hydrogen atmosphere to obtain Ru/ZSM-5-CN (catalyst F).
FIG. 13 is an XRD pattern of Ru/ZSM-5-CN. The XRD results showed the resulting sample to have characteristic diffraction peaks of ZSM-5 zeolite, and the XRF results showed the loading of Ru in the sample to be 0.52wt.%.
FIG. 14 is a TEM image of Ru/ZSM-5-CN. TEM results showed that the metal Ru had a large particle size and a uniform size, but the crystal grain size was 20 to 30nm, indicating that the metal Ru was mainly deposited on the outer surface of the zeolite and that the particle size of the supported metal was large. This indicates that, when the growth process of zeolite crystals is carried out in the presence of metal ions in the silica-alumina gel, the metal ions cannot enter the microporous pores of the zeolite, and thus small-sized metal particles cannot be obtained as a highly active catalyst. This further illustrates that the order and timing of the addition of metal ions can affect the distribution of metal particles on the zeolite and their size using a two-step crystallization process.
Comparative example 6
For comparison, a conventional impregnation method was used to prepare a Ru-containing ZSM-5 zeolite (catalyst G) by the following steps:
firstly, 18.75g of water and 3g of TPABr and 0.85g of NaOH are mixed and stirred to form a clear solution, then 0.45g of pseudo-boehmite is added and stirred until the solution is clear, 7.5g of white carbon black is added and stirred for 3 hours to form the silicon-aluminum gel.
The silicon-aluminum gel comprises the following components in percentage by mass: 0.4TPABr:2.5H 2 O：0.04Al 2 O 3 ：SiO 2 :0.1NaOH. And transferring the silicon-aluminum gel into a crystallization kettle, and crystallizing for 48 hours at 170 ℃.
Washing and drying the obtained sample, and roasting at 550 ℃ for 6 hours in the air atmosphere to obtain ZSM-5 zeolite; 2g of ZSM-5 zeolite was dissolved in 14g of water and stirred well.
Dissolving 0.06g of ruthenium chloride in 4g of water to obtain a metal salt solution, dropwise adding the metal salt solution into a ZSM-5 zeolite solution, stirring in a water bath at 60 ℃ for 3 hours, evaporating water, and drying.
The dried sample was calcined at 550 ℃ for 6h and then reduced at 350 ℃ for 2h in a hydrogen atmosphere to give Ru/ZSM-5 (catalyst G).
FIG. 15 is an XRD pattern of Ru/ZSM-5. The XRD results showed that the resulting sample had characteristic diffraction peaks of ZSM-5 zeolite, and the XRF results showed that the loading of Ru in the sample was 0.45wt.%.
FIG. 16 is a TEM image of Ru/ZSM-5. TEM results show that the metal Ru has larger particle size and uneven size, which indicates that the metal Ru is mainly deposited on the outer surface of the zeolite and can not enter the pore channels.
Example 3
The coating of the metal nanoparticles in the ZSM-5 zeolite channels was demonstrated by the hydrogenation reaction of toluene (molecular size: 0.55 nm) and triisopropylbenzene (molecular size: 0.85 nm).
Example 2 (Ru @ ZSM-5, catalyst D), comparative example 4 (Ru/ZSM-5-HT, catalyst E), comparative example 5 (Ru/ZSM-5-CN, catalyst F), comparative example 6 (Ru/ZSM-5, catalyst G) for toluene and triisoiso-triiso-tolueneAnd (3) hydrogenation reaction of propyl benzene. For comparison, 0.5wt.% Ru/SiO was prepared by the dipping method 2 。
The hydrogenation reaction conditions were as follows: 15mg of catalyst, 111kPa toluene and 6.8kPa cumene, P H2 =2.75MPa, reaction temperature 150 ℃. The TOF values of toluene and triisopropylbenzene were as follows: ru @ ZSM-5 (0.71, 0.06), ru/ZSM-5-HT (catalyst E) (0.85, 0.52), ru/ZSM-5-CN (catalyst F (0.82, 0.67), ru/ZSM-5 (catalyst G) (0.84, 0.65), ru/SiO 2 (0.82,1.02)。
The results show that toluene can enter the pore channels of the ZSM-5 molecular sieve, so that the TOF value of toluene is higher in all the catalysts. The triisopropylbenzene has larger size and can not enter the pore channels of the ZSM-5 zeolite, so the TOF value of the Ru @ ZSM-5 is very low, but most of Ru particles in the Ru/ZSM-5-HT and Ru/ZSM-5 are positioned outside the pore channels, and the TOF value is second to that of the Ru/SiO 2 . This demonstrates that in Ru @ ZAM-5 the Ru particles are substantially coated in the ZSM-5 zeolite channels.
Example 4
The embodiment provides a synthesis method of FAU structure Y zeolite (Pt @ Y) containing Pt, which specifically comprises the following steps:
first, 6.4g of water and 1.28g of NaOH were mixed and stirred to form a clear solution, then 0.77g of sodium aluminate was added and stirred until clear 7.69g of sodium silicate solution (10.6 wt.% Na) was added 2 O，26.5wt.％SiO 2 ) Stirring for more than 10min, and standing at room temperature for 24h to obtain the guiding agent.
Next, 44g of water and 0.044g of NaOH were mixed and stirred to form a clear solution, then 4.82g of sodium aluminate were added and stirred until clear 42.80g of sodium silicate solution (10.6 wt.% Na) was added 2 O，26.5wt.％SiO 2 ) Stirring to be emulsion, then slowly adding 5.6g of guiding agent aged for 24h, and stirring vigorously for 20min to form the silica-alumina gel.
The silicon-aluminum gel comprises the following components in percentage by mass: 3.9H 2 O：0.20Al 2 O 3 ：SiO 2 ：0.1NaOH。
And transferring the silicon-aluminum gel to a crystallization kettle, and stirring and pre-crystallizing for 12 hours at 60 ℃. Taking out the pre-crystallized product and stirring uniformly.
0.38g of ammonium platinum nitrate was dissolved in 1ml of water to obtain a metal salt solution, and the metal salt solution was dropwise added to the pre-crystallized product.
Stirring evenly, transferring to a crystallization kettle, standing at room temperature for 24h, and then crystallizing at 100 ℃ for 6h.
The obtained sample is washed, dried, roasted for 6h at 550 ℃ in the air atmosphere, and then reduced for 2h at 350 ℃ in the hydrogen atmosphere to obtain Pt @ Y.
FIG. 17 is an XRD pattern of Pt @ Y. XRD proves that the obtained catalyst has a characteristic diffraction peak of Y zeolite and no other miscellaneous peaks, which indicates that the sample phase is good.
FIG. 18 is a TEM image of Pt @ Y. It can be seen from the figure that the Pt metal particles are small and the dispersion is high.
Comparative example 5
For comparison, a Y zeolite containing Pt was prepared by ion exchange, the procedure was as follows:
first, 6.4g of water and 1.28g of NaOH were mixed and stirred to form a clear solution, then 0.77g of sodium aluminate was added and stirred until clear 7.69g of sodium silicate solution (10.6 wt.% Na) was added 2 O，26.5wt.％SiO 2 ) Stirring for more than 10min, and standing at room temperature for 24h to obtain the guiding agent.
Next, 44g of water and 0.044g of NaOH were mixed and stirred to form a clear solution, followed by the addition of 4.82g of sodium aluminate, stirred until clear 42.80g of sodium silicate solution (10.6 wt.% Na) 2 O，26.5wt.％SiO 2 ) Stirring to be emulsion, then slowly adding 5.6g of guiding agent aged for 24h, and stirring vigorously for 20min to form the silica-alumina gel.
The silicon-aluminum gel comprises the following components in percentage by mass: 3.9H 2 O：0.20Al 2 O 3 ：SiO 2 :0.1NaOH. And transferring the silicon-aluminum gel into a crystallization kettle, standing at room temperature for 24 hours, and then crystallizing at 100 ℃ for 6 hours.
Washing and drying the obtained sample, and roasting at 550 ℃ for 6 hours in the air atmosphere to obtain Y zeolite; 2g of Y zeolite was dissolved in 14g of water and stirred well.
0.38g of ammonium nitrate platinum was dissolved in 4g of water to obtain a metal salt solution, the metal salt solution was dropwise added to the solution of Y zeolite, stirred in an oil bath at 100 ℃ under reflux for 6 hours, and after completion, washed and dried.
The dried sample was calcined at 550 ℃ for 6h and then reduced in a hydrogen atmosphere at 350 ℃ for 2h to Pt/Y.
FIG. 19 is an XRD pattern of Pt/Y. XRD proves that the obtained catalyst has a characteristic diffraction peak of Y zeolite and no other miscellaneous peaks, which indicates that the sample phase is good.
FIG. 20 is a TEM image of Pt/Y. It can be seen from the figure that the Ru metal particles are agglomerated and have a large particle size.
Example 5
The embodiment provides a synthesis method of Pt-containing ZSM-48 zeolite with an EUO structure, which specifically comprises the following steps:
firstly, 36.0g of water and 0.72g of hexamethonium bromide and 0.53g of NaOH are mixed and stirred to form a clear solution, then 0.26g of sodium aluminate is added, stirring is carried out until the solution is clear, 6g of coarse silica gel is added, and stirring is carried out for 3 hours to form the silicon-aluminum gel. The silicon-aluminum gel comprises the following components in percentage by mass: 0.12 hexamethonium bromide: 6H 2 O：0.019Al 2 O 3 ：SiO 2 ：0.088NaOH。
Transferring the silicon-aluminum gel into a crystallization kettle, and pre-crystallizing for 48 hours at 100 ℃; taking out the pre-crystallized product and stirring uniformly.
0.12g of platinum ammonium nitrate was dissolved in 2g of water to prepare a metal salt solution. And dropwise adding the metal salt solution into the pre-crystallized product, uniformly stirring, transferring to a crystallization kettle, and crystallizing for 48 hours at 160 ℃.
The obtained sample is washed, dried, roasted for 6h at 550 ℃ in the air atmosphere, and then reduced for 2h at 350 ℃ in the hydrogen atmosphere to obtain Pt @ ZSM-48.
FIG. 21 is an XRD pattern of Pt @ ZSM-48. XRD proves that the obtained catalyst has a ZSM-48 zeolite characteristic diffraction peak and no other impurity peaks, which indicates that the sample phase is good.
Application example 1
The catalysts synthesized in example 1 (catalyst a and catalyst B) and comparative example 2 (catalyst C) were used in furfural hydrogenation reaction. For comparison, commercial SiO was used 2 Prepared by the dipping method to 1.0wt% Ni/SiO 2 。
The reactants are: 0.3g furfural and 23.56g isopropanol.
The reaction conditions are as follows: 0.3g of catalyst, temperature 110 ℃ 10bar H 2 The rotating speed is 1000rpm, and the reaction time is 1h or 2h.
The reaction results were as follows:
TABLE 1 Furfural hydrogenation results
Figure BDA0003175627440000151
The results of tests 1, 2, 3 and 4 in table 1 show that the furfural conversion rate of the catalyst obtained by the two-step crystallization method is higher than that of the catalyst prepared by the impregnation method.
This shows that the catalyst Ni obtained by the two-step crystallization method has higher dispersity, stronger hydrogen activating capability and higher hydrogenation activity.
The results of tests 3, 4, 5 and 6 in Table 1 show that when the hydrogenation reaction is not in equilibrium, the selectivity of the secondary hydrogenation product of the catalyst obtained by the two-step crystallization method is significantly lower than that of the catalyst obtained by the impregnation method, and that Ni/SiO 2 At lower conversion, the selectivity of the secondary hydrogenation product is highest.
This indicates that 2 In contrast, when the active metal Ni is present in the Beta zeolite pore channels, the activation of the primary hydrogenation product molecules becomes more difficult due to the space limitation of the zeolite micropores, and particularly, when all the metal Ni species are coated in the micropores, such as the catalyst obtained by the two-step crystallization method, the selectivity of the secondary hydrogenation product is reduced from 11.1% of the catalyst obtained by the impregnation method to 5.4% and 3.7%.
This result is sufficient to show that the selective conversion of the primary product can be suppressed and the selectivity of the primary product can be improved by the zeolite coating by utilizing the pore structure of the zeolite.
Application example 2
Catalyst D synthesized in example 2 and catalysts E to G synthesized in comparative examples 4 to 6 were prepared as hydrogen-form zeolite by ion exchange and used for the phenol hydrodeoxygenation reaction.
By way of comparison, commercially available SiO was used 2 0.5wt.% Ru/SiO by impregnation 2 And Ru/SiO are mixed mechanically 2 Mixing with H-ZSM-5 to obtain Ru/SiO 2 +H-ZSM-5。
The reaction conditions are as follows: 200mg catalyst, 2.13mmol phenol, 10mL water, P H2 =5.0MPa, T =150 ℃ and reaction time 2h.
The reaction results were as follows:
TABLE 2 phenol hydrodeoxygenation reaction results
Catalyst and process for producing the same Conversion (wt.%) Cyclohexane Selectivity (wt.%)
Catalyst D ～100 90
Catalyst E 80 75
Catalyst F 78 76
Catalyst G 72 75
Ru/SiO 2 +H-ZSM-5 80 83
Ru/SiO 2 70 8.0
Ru @ H-ZSM-5 showed higher phenol conversion and higher selectivity to cyclohexane than all catalysts. Indicating that the coating promotes metal-acid affinity and thus improves catalyst activity and product selectivity.
Although the invention has been described in detail hereinabove with respect to a general description and specific embodiments thereof, it will be apparent to those skilled in the art that modifications or improvements may be made thereto based on the invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.

Claims (8)

1. A synthetic method of a zeolite molecular sieve supported metal catalyst is characterized by adopting a two-step crystallization method: pre-crystallizing the silica-alumina gel at low temperature, and then adding a metal salt solution for high-temperature crystallization; the low-temperature pre-crystallization conditions are as follows: crystallizing at 60-100 deg.c for 12-48 hr; the high-temperature crystallization conditions are as follows: crystallizing at 100-170 deg.c for 12-36 hr;
the silicon-aluminum gel is obtained by the following method:
mixing the microporous organic template agent, water and an alkali source, adding an aluminum source after stirring, stirring until the mixture is clear, adding a silicon source, and uniformly stirring;
wherein the microporous organic template agent is one of tetraethylammonium hydroxide, tetraethylammonium bromide, tetrapropylammonium hydroxide, tetrapropylammonium bromide, n-butylamine, adamantane, 1, 6-hexamethylenediamine or hexamethonium bromide;
the alkali source is NaOH or KOH;
the metal salt solution is one or two of soluble salts containing Fe, co, ni, cu, ru, rh, pt or Pd.
2. A method of synthesizing a zeolitic molecular sieve-supported metal catalyst according to claim 1, wherein said method of synthesizing further comprises: roasting the product obtained by high-temperature crystallization in an air atmosphere, and then reducing in a hydrogen atmosphere;
the roasting temperature is 500-600 ℃; the reduction temperature is 300-400 ℃.
3. A method for synthesizing a zeolite molecular sieve supported metal catalyst as claimed in claim 1 or 2, wherein the aluminum source is one of sodium aluminate, pseudo-boehmite, aluminum sulfate or aluminum isopropoxide;
the silicon source is one of silica sol, water glass, coarse-pore silica gel or white carbon black.
4. A synthesis method of a zeolite molecular sieve supported metal catalyst according to claim 3, characterized in that SiO in silicon source is used 2 Al in aluminum source 2 O 3 When tetraethyl ammonium hydroxide is used as a microporous organic template agent, the mass ratio of tetraethyl ammonium hydroxide, water, an aluminum source, a silicon source and an alkali source is (1.5-2.0): (0.66-0.80): (0.020-0.030): 1: (0.023-0.034);
when tetrapropyl ammonium bromide is adopted as the microporous organic template agent, the mass ratio of the tetrapropyl ammonium bromide to the water to the aluminum source to the silicon source to the alkali source is (0.35-0.46): (2.2-3.0): (0.036-0.045): 1: (0.1-0.15);
when the ammonium hexametaphosphate is used as the microporous organic template agent, the mass ratio of the ammonium hexametaphosphate, the water, the aluminum source, the silicon source and the alkali source is (0.10-0.15): (5.5-6.8): (0.018-0.019): 1: (0.08-0.09).
5. A zeolitic molecular sieve-supported metal catalyst obtainable by a synthesis process according to any one of claims 1 to 4.
6. A zeolite molecular sieve supported metal catalyst according to claim 5, wherein the zeolite of the zeolite molecular sieve supported metal catalyst is a zeolite having a one-dimensional or three-dimensional pore structure;
the zeolite with the one-dimensional pore channel structure refers to zeolite with one-dimensional pore channels, the topological structure of which is TON, MTT, AEL, MOR or EUO;
the zeolite with a three-dimensional pore channel structure refers to a zeolite with three-dimensional pore channels and with a topological structure of MFI, BEA, CHA or FAU.
7. The zeolite molecular sieve supported metal catalyst of claim 6, wherein said zeolite with three-dimensional channel structure is zeolite ZSM-5 with ten-membered ring channel MFI structure and zeolite Beta with twelve-membered ring channel BEA structure in topology.
8. Use of a zeolitic molecular sieve-supported metal catalyst according to any of claims 5 to 7 in a hydrogenation reaction.
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CN114904563B (en) * 2022-06-08 2024-02-09 江苏扬农化工集团有限公司 ZSM-5 supported noble metal catalyst, preparation method and application
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