CN113385222A - Monodisperse mesoporous silica composite zeolite core-shell material and preparation method thereof - Google Patents

Monodisperse mesoporous silica composite zeolite core-shell material and preparation method thereof Download PDF

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CN113385222A
CN113385222A CN202110682365.7A CN202110682365A CN113385222A CN 113385222 A CN113385222 A CN 113385222A CN 202110682365 A CN202110682365 A CN 202110682365A CN 113385222 A CN113385222 A CN 113385222A
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zeolite
shell
core
mesoporous
phase
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赵东元
洪锦德
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Fudan University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J29/00—Catalysts comprising molecular sieves
    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/03—Catalysts comprising molecular sieves not having base-exchange properties
    • B01J29/035—Microporous crystalline materials not having base exchange properties, such as silica polymorphs, e.g. silicalites
    • B01J35/396—
    • B01J35/40—
    • B01J35/51—
    • B01J35/617—
    • B01J35/638—
    • B01J35/647—
    • C—CHEMISTRY; METALLURGY
    • C11—ANIMAL OR VEGETABLE OILS, FATS, FATTY SUBSTANCES OR WAXES; FATTY ACIDS THEREFROM; DETERGENTS; CANDLES
    • C11C—FATTY ACIDS FROM FATS, OILS OR WAXES; CANDLES; FATS, OILS OR FATTY ACIDS BY CHEMICAL MODIFICATION OF FATS, OILS, OR FATTY ACIDS OBTAINED THEREFROM
    • C11C3/00—Fats, oils, or fatty acids by chemical modification of fats, oils, or fatty acids obtained therefrom
    • C11C3/003—Fats, oils, or fatty acids by chemical modification of fats, oils, or fatty acids obtained therefrom by esterification of fatty acids with alcohols

Abstract

The invention belongs to the technical field of zeolite molecular sieve catalysts, and particularly relates to a monodisperse mesoporous silica composite zeolite core-shell material and a preparation method thereof. The composite material of the present invention comprises: the zeolite crystal grain serving as the core is formed into a multi-level grading pore zeolite material with a core-shell structure by utilizing a silicon dioxide layer with a divergent mesoporous pore canal, which is constructed on the outer surface of the zeolite crystal grain by an oil-water two-phase layered interface assembly method, wherein the multi-level grading pore zeolite material comprises inner core zeolite micropores, shell layer mesopores and block material gap stacking holes, and the number of the holes is up to 4; the shell layer pore canal pattern is a gradient mesoporous pore canal which is radially developed; the material itself still ensures the high crystalline phase and strong acidity of the original zeolite grains. The invention adopts a brand new synthesis strategy-oil-water two-phase interface assembly method and adopts organic amine catalysis synthesis, thereby avoiding the etching decomposition of the stone crystal grains in the coating process, retaining the high crystal phase and strong acidity of the original zeolite crystal grains, being used as a catalyst for macromolecular catalysis or multistage series catalytic reaction and having quite strong applicability.

Description

Monodisperse mesoporous silica composite zeolite core-shell material and preparation method thereof
Technical Field
The invention belongs to the technical field of zeolite molecular sieve catalysts, and particularly relates to a monodisperse mesoporous silica composite zeolite core-shell material and a preparation method thereof.
Background
Zeolite is an important micro-mesoporous material, has the characteristics of high porosity, large specific surface area, stable chemical property, high strong acidity and the like, and has an irreplaceable position in chemical catalysis, particularly petroleum refining and petrochemical product synthesis. From the structural point of view, the zeolite framework is mostly aluminosilicate and is characterized by silicon oxide (SiO)4) Tetrahedron and aluminum oxide (AlO)4) Two tetrahedral units are constructed into a net structure, and some zeolites are composed of aluminophosphates; the structure is open, and the crystal structure has a plurality of cavities and channels connecting the cavities, so that the special porous structure of the cavities and the channels of the cavities is benefited, the special capacity of sieving substances on a molecular level is realized, and molecules of other substances can be absorbed or filtered, and the structure is also called as a zeolite molecular sieve. Because the aluminum ion is trivalent (Al)3+) And the silicon ion is tetravalent (Si)4+) When forming a silicoaluminophosphate tetrahedron, the negative charge of aluminum requires the adsorption of cations in its space and channels to neutralize its electrical properties, so that the zeolite has cation exchange properties and can accommodate a variety of metal cations in its internal cavity. This property also tends to promote the adsorption of large amounts of crystal water thereto, and the charge imbalance of the alumino-silica tetrahedra in its own structure makes the zeolite highly acidic active sites, making it very suitable for use as a catalyst for chemical reactions. There are many kinds of zeolite classification methods, and the classification method can be classified into three types according to the silicon/aluminum ratio of the components: (1) low silicon zeolites (Si/Al = 1-1.5), are mostly used in ion exchange; (2) medium silicon zeolite (Si/Al = 1.5-5.0), which is mostly applied to catalytic reaction in petrochemical industry, namely, a catalyst for reaction; (3) high silicon zeolite (Si/Al)>5) It is mostly applied to fine oil refining industries such as catalytic cracking of petroleum.
The suitability of a zeolite molecular sieve for the choice of adsorption catalysis application depends primarily on its own composition silicon/aluminum ratio and the size of the cavities and the channel pores connecting the cavities. Basically, the stability of zeolites increases with increasing silicon content, but the ion exchange capacity and the catalytic conversion decrease. The size of the holes of the zeolite molecular sieve is mainly concentrated between 0.3 and 1.5 nm, the requirements of adsorption, catalysis and diffusion of reaction species with smaller molecular size are fully met, and the high specific surface area characteristic of the zeolite molecular sieve can be fully utilized. However, for larger molecular size reaction species, such as high molecular polymer, high carbon ring aromatic hydrocarbon, low volatile high boiling point organic substance, polypeptide linear polymer or protein, the influence of zeolite pore diffusion limitation is significant, so that the adsorption catalysis can only be concentrated on the outer surface of the zeolite molecular sieve, and the pore channels of the internal pores cannot be used. For example, aiming at the refinement of the petroleum crude oil refining process and the improvement of the overall utilization rate of crude oil, the re-refining of waste oil is a key topic of many advanced countries at present, but the key core of the re-refining at present is that no zeolite molecular sieve catalyst with good adaptability exists, the super-high viscosity macromolecules are limited in residual oil, microporous pore channels of zeolite are easily blocked, or in the catalysis process, a plurality of carbon deposits are generated to fill up pores (cage) of zeolite, so that the service life of the molecular sieve zeolite is greatly reduced, and high-frequency addition and regeneration activation are needed. Therefore, the importance of exploring the preparation of the novel zeolite with the mesoporous size dimension, controllable pore structure, simplicity and easiness for large-scale production is more obvious.
The monodisperse mesoporous silica composite zeolite core-shell material prepared by the method fully retains the catalytic capability of the original zeolite; the oil-water interface assembly is adopted, the mineralization rate of a silicon source is effectively controlled, the interaction between the silicon source and surfactant molecules is enhanced, and the purpose of adjustable and controllable mesoporous divergent pore channels is successfully achieved; the shell layer composition has diversity, silicon dioxide is removed to be used as a main material body, inorganic metal sources such as aluminum, titanium or zirconium and the like or organic and inorganic carbon sources can be introduced to form a hybrid mesoporous silicon dioxide shell layer, the hybrid mesoporous silicon dioxide shell layer can be introduced to be used as a primary adsorption catalytic active site, the hybrid mesoporous silicon dioxide shell layer is matched with zeolite of an inner core, so that the hybrid mesoporous silicon dioxide shell layer has time and space guiding capacity, can be constructed into a multi-level catalytic interlocking type nano reactor, realizes multi-level series reaction and macromolecular catalysis, and shows multiple application values of the hybrid mesoporous silicon dioxide shell layer.
Disclosure of Invention
The invention aims to provide a monodisperse mesoporous silica composite zeolite core-shell material and a preparation method thereof, which are used for solving the problems of smaller surface pore channels, dealumination, desiliconization and crystal decomposition inactivation of zeolite in the prior art and realizing the free regulation and control of the pore diameter of the mesoporous silica composite zeolite material.
The invention provides a monodisperse mesoporous silica composite zeolite core-shell material, which comprises the following components: forming a multi-level graded pore zeolite material with a core-shell structure by utilizing a silicon dioxide shell layer with divergent mesoporous pore channels, which is constructed on the outer surface of a zeolite crystal grain by an oil-water two-phase layered interface assembly method and is used as a core, wherein the size range is 20 nm-30 mu m, the shell layer thickness is 10 nm-10 mu m, and the specific surface area is 750-1000 m2The pore diameter of the mesoporous shell is 3-30 nm, and the pore volume is 0.4-2.4 cm3(ii)/g; the material comprises inner core zeolite micropores, shell mesoporous and block gap stacking holes, wherein the shell pore canal pattern is a gradient mesoporous pore canal which is radially developed, the number of the pore canals is 4, and the material still ensures high crystalline phase and strong acidity of original zeolite grains.
In the present invention, the zeolite type as the core is selected from one or more of silicate type zeolite, aluminosilicate type zeolite, and aluminophosphate type zeolite; including but not limited to LTA, FAU, MFI, MOR, CHA-type zeolites.
In the present invention, the material for the shell layer is not limited to silica, and may include alumina, aluminosilicate, titania, zirconia, carbon, and the like.
The preparation method of the monodisperse mesoporous silica composite zeolite core-shell material comprises the following specific steps:
(1) dissolving a surfactant and a catalyst into water, and stirring to obtain a clear solution; the concentration of the surfactant in the clear solution is 0.5-10 wt%, and the concentration of the catalyst is 0.2-0.5 wt%; adding the nano-scale zeolite crystal particles into the clarified solution, performing ultrasonic dispersion, and continuously stirring to obtain a homogeneous water phase solution;
(2) dissolving a silicon source, a pre-prepared metal-doped silicon source or a pre-prepared carbon-doped silicon source in an organic solvent to obtain an organic solution of the silicon source; wherein the concentration of the silicon source is 2.5-30 wt%; slowly adding the organic solution into the upper layer of the aqueous phase solution obtained in the step (1) to form an upper oil phase, so as to obtain an oil-water two-phase layered system; the mass ratio of the nano-scale zeolite crystal grains to the silicon source is 0.01-0.05, and the mass ratio of the surfactant to the silicon source is 0.25-10.0;
(3) reacting the oil-water two-phase layered system obtained in the step (2) at the temperature of 0-120 ℃; obtaining a monodisperse mesoporous silica composite zeolite core-shell material;
(4) roasting in air atmosphere to remove the surfactant in the monodisperse mesoporous silica composite zeolite core-shell material, and obtaining the high-dispersion core-shell material with the zeolite grains coated by the disperse mesoporous silica.
Preferably, the surfactant in step (1) is selected from one or more of quaternary ammonium salt cationic surfactant, organic/inorganic acid salt anionic surfactant and nonionic surfactant; including but not limited to cetyltrimethylammonium chloride (CTAC), cetyltrimethylammonium bromide (CTAB), octadecyltrimethylammonium chloride, octadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, sodium hexadecylbenzenesulfonate, sodium hexadecylsulfonate, sodium lauryl sulfate, polyalkylene oxide olefin block copolymers, oligomeric alkyl polyethylene oxides, alkylphenol polyethylene oxides, sorbitan esters.
Preferably, the catalyst in step (1) is selected from one or more of organic amine molecules, aliphatic amine, alcohol amine, aromatic amine, amide, aromatic amine and alicyclic amine; including but not limited to octylamine, dodecylamine, triethanolamine, diethanolamine.
Preferably, the stirring in step (1) is carried out at a speed of 50-1000 rpm for 6-24 hours.
Preferably, the volume ratio of the organic solvent phase to the aqueous phase in step (2) is 0.2 to 1.0.
Preferably, the organic solvent in step (2) is selected from liquid organic species having hydrophobicity; including but not limited to one or more of cyclohexane, n-hexane, decalin, olefin, high carbon number naphthene and high carbon number alkane.
Preferably, the silicon source is selected from one or more of sodium silicate, sodium metasilicate, gas-phase silicon dioxide, ethyl orthosilicate, aluminosilicate oxide and organosilane; the aluminum source is selected from one or more of aluminum isopropoxide, sodium metaaluminate, alumina, aluminosilicate and aluminum acetylacetonate; the titanium source is selected from one or more of isopropyl titanate, tetrabutyl titanate, titanium tetrachloride, titanyl sulfate and metatitanic acid; the zirconium source is selected from one or more of tetraethoxy zirconium, normal propyl zirconium, iso propyl zirconium, tetra iso propyl zirconium, normal butyl zirconium, tertiary butyl zirconium and zirconium nitrate.
Preferably, the heating rate of the calcination used in the step (4) is 0.1 to 10 degrees/minute (preferably, the heating rate is 2 to 6 degrees/minute). The roasting temperature is 400-600 ℃. The calcination time is 5 to 7 hours, preferably 6 hours.
Preferably, the prepared material is a coated mesoporous nano zeolite ball formed by silicon dioxide close packing, the size of the mesoporous nano zeolite ball is 20 nm-30 mu m, the thickness of a shell layer is 10 nm-10 mu m, and the specific surface area is 750-1000 m2The pore diameter of the mesoporous shell is 3-30 nm, and the pore volume is 0.4-2.4 cm3/g。
The material prepared by the invention still keeps the original high crystalline phase property and high strong acid property of zeolite crystal grains27Solid-state nmr and powder diffraction analysis of Al revealed only less than about 1% aluminum removal.
The invention has the following characteristics and advantages:
(1) the invention adopts an oil-water two-phase layered interface assembly reaction system, which is different from a homogeneous reaction system frequently adopted in the prior art, and introduces an organic phase component; due to the hole expanding effect of the organic phase, the aperture of the obtained mesoporous silica nanosheet is much higher than that reported in the literature (less than 4 nm), and can reach 30 nm at most; meanwhile, the aperture of the mesoporous silica shell layer can be regulated and controlled by regulating the type of the organic phase or the amount of the silicon source, so that the aperture can be freely regulated and controlled between 3 nm and 30 nm;
(2) in the reaction process, organic amine is used as a catalyst, so that the crystal decomposition phenomenon of dealuminization and desilication of zeolite can be greatly relieved; therefore, the nuclear zeolite in the obtained composite material can still keep the characteristics of the pore structure, the specific surface area, the high crystalline phase, the strong acidity and the like;
(3) the invention provides a novel oil-water two-phase interface assembly synthesis method, which is suitable for constructing surface mesoporous shell layers of full-series zeolites, and comprises silicate type zeolite, aluminosilicate type zeolite and phosphoaluminate type zeolite;
(4) the constructed mesoporous shell has variable composition, the hybrid mesoporous silica shell can be formed by removing silica as a main material body and introducing inorganic metal sources such as aluminum, titanium or zirconium and the like, and even the mesoporous shell of alumina, titanium oxide, zirconium oxide or carbon can be directly constructed;
(5) the invention fully utilizes the time-space guiding capability of a core-shell structure, and a monodisperse mesoporous silica composite zeolite core-shell material is constructed into a multi-level catalytic interlocking nano reactor; in the aspect of the application of the catalytic synthesis of the biodiesel in the embodiment 4, the design advantages of the material of the invention are shown and highlighted: the mesoporous shell can allow macromolecular biomass to smoothly and quickly diffuse to the catalytic active sites on the surfaces of the holes; the arrangement of the inner core zeolite exerts the powerful water molecule adsorption and capture functions, and water molecules generated after the reaction of the shell acid active sites are accurately and quickly removed, so that the passivation phenomenon of the active sites caused by the hydration effect is avoided, the chemical balance trend is changed, and the catalytic reaction is accelerated; the biodiesel catalytic application of example 4 clearly reveals the effective improvement of catalytic ability (fig. 3), the experimental group is the monodisperse mesoporous silica composite zeolite core-shell material of the present invention, the control group is the monodisperse mesoporous silica spheres, and the improvement advantage of nearly 1.4 times in biodiesel catalytic synthesis yield is obtained.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without inventive exercise.
Fig. 1 is a transmission electron microscope image of the monodisperse mesoporous silica composite zeolite core-shell nanosphere material in example 1. Wherein the upper scale is 200 nm and the lower scale is 50 nm.
Fig. 2 is a characteristic nitrogen adsorption-desorption isotherm and a pore size distribution curve of the monodisperse mesoporous silica composite zeolite core-shell nanosphere material of example 1.
FIG. 3 shows the results of the biodiesel catalyzed synthesis reaction evaluation in example 4.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
A monodisperse mesoporous silica composite zeolite core-shell nanosphere material, wherein the core is a nano-scale zeolite crystal grain, and the shell layer is radiation-shaped mesoporous channel silica. Is prepared by the following steps:
completely dissolving 5 g of tetramethylammonium hydroxide and 0.75 g of aluminum isopropoxide in 7 g of water, adding a prepared tetraethoxysilane aqueous solution (2.25 g of tetraethoxysilane mixed with 2 g of water) into the solution, stirring the solution at normal temperature for 5 minutes, adding 0.6 g of 1M sodium hydroxide aqueous solution, continuously stirring the solution at normal temperature for 5 hours, and moving the solution into a hydrothermal kettle. The mixture was heated in an oven at 80 ℃ for 72 hours. After the reaction is finished, naturally cooling to room temperature, washing with ethanol and water for three times to obtain LTA type zeolite crystal grains, and drying for later use.
10 g of cetyltrimethylammonium bromide, 100 mg of LTA-type zeolite crystallitesDissolving the mixture and 0.8 mL of triethanolamine into 180 mL of deionized water in sequence, and uniformly stirring by ultrasonic to form a light white homogeneous transparent aqueous phase solution; putting the solution into a reactor, and stirring for 0.5 hour at 60 ℃; dissolving 1 ml of tetraethoxysilane in 50 ml of cyclohexane to obtain an organic oil phase solution, wherein the concentration of the tetraethoxysilane is 2 wt%; adjusting the stirring speed of the aqueous phase solution to 300 revolutions per minute, and dropwise adding the organic oil phase solution onto the aqueous phase solution to form an oil-water two-phase layered system; reacting for 24 hours in an oil bath at the temperature of 60 ℃ to obtain the monodisperse mesoporous silica composite zeolite core-shell nanosphere material; the mesoporous silica composite zeolite nano material is placed in a muffle furnace, the temperature is raised from room temperature to 550 ℃ at the speed of 1 ℃/min under the air atmosphere, the temperature is kept for 6 hours, a surfactant and a structure directing agent are removed, and a product obtained after roasting is the monodisperse mesoporous silica composite zeolite core-shell nanosphere material (shown in figure 1). The appearance of the whole material is highly monodisperse and uniform-sized nanospheres, and the size of the nanospheres is 300 nm. The sphere is of a core-shell structure, the inner core is zeolite crystal grains with the size of 100 nm, the size of the hole is 0.5 nm, a silicon dioxide layer with divergent mesoporous channels is constructed on the outer surface of the zeolite crystal grains, the thickness of the mesoporous shell layer is 100 nm, and the aperture of the mesoporous shell layer is 10 nm. The overall specific surface area is 780 m2Per g, pore volume of 2.0 cm3(ii) in terms of/g. The zeolite material comprises inner core zeolite micropores, shell mesoporous and bulk clearance stacking holes to form a multilevel gradation hole zeolite material. Material itself by X-ray diffraction spectroscopy and27after the Al solid-state nuclear magnetic resonance spectrum identification, the monodisperse mesoporous silica composite zeolite core-shell nanosphere material is ensured to still have the high crystalline phase and strong acidity of the original zeolite crystalline grains.
Example 2
A preparation method of a monodisperse mesoporous silica composite zeolite core-shell nanosphere material comprises the following steps:
0.63 g of tetrapropylammonium hydroxide and 1.6 g of ethanol were completely dissolved in 4.2 g of water, and then 1.8 g of ethyl orthosilicate was added thereto, stirred at normal temperature for 24 hours, and transferred to a hydrothermal reactor. The mixture was heated in an oven at 90 ℃ for 48 hours. After the reaction is finished, naturally cooling to room temperature, washing with ethanol and water for three times to obtain MFI type zeolite crystal grains with the size of 40 nm, and re-dispersing in water for later use.
Sequentially dissolving 8 g of hexadecyl trimethyl ammonium chloride, 120 mg of MFI type zeolite crystal grains and 0.75 mL of triethanolamine into 150 mL of deionized water, and uniformly stirring by ultrasonic waves to form a light white homogeneous transparent aqueous phase solution; putting the solution into a reactor, and stirring for 0.5 hour at 80 ℃; dissolving 1 ml of fumed silica in 50 ml of n-hexane to obtain an organic oil phase solution, wherein the concentration of the fumed silica is 2 wt%; adjusting the stirring speed of the aqueous phase solution to 400 revolutions per minute, and dropwise adding the organic oil phase solution onto the aqueous phase solution to form an oil-water two-phase layered system; reacting for 48 hours in an oil bath at the temperature of 80 ℃ to obtain the monodisperse mesoporous silica composite zeolite core-shell nanosphere material; and (2) placing the mesoporous silica composite zeolite nano material in a muffle furnace, heating the mesoporous silica composite zeolite nano material to 550 ℃ from room temperature at the speed of 1 ℃/min in the air atmosphere, keeping the temperature for 6 hours, removing a surfactant and a structure directing agent in the mesoporous silica composite zeolite nano material, and obtaining a product, namely the monodisperse mesoporous silica composite zeolite core-shell nano sphere material after roasting. The resulting material was highly monodisperse and uniformly sized nanospheres with a sphere size of 500 nm in appearance. The sphere is in a core-shell structure, the inner core is MFI zeolite crystal grains, the size is 40 nm, the size of the hole is 0.8 nm, a silicon dioxide layer with divergent gradient mesoporous channels is constructed on the outer surface of the zeolite crystal grains, the thickness of a mesoporous shell layer is 230 nm, and the aperture of the mesoporous shell layer is 16 nm. The whole specific surface area is 810 m2G, pore volume of 2.2 cm3(ii) in terms of/g. Material itself by X-ray diffraction spectroscopy and27after the Al solid-state nuclear magnetic resonance spectrum identification, the monodisperse mesoporous silica composite zeolite core-shell nanosphere material is ensured to still have the high crystal phase and strong acidity of the original MFI zeolite crystal grains.
Example 3
A preparation method of a monodisperse mesoporous silica composite zeolite core-shell nanosphere material comprises the following steps:
after 8.1 g of tetrapropylammonium hydroxide was completely dissolved in 40 g of water, 23 g of ethyl orthosilicate was added thereto, and the mixture was stirred at room temperature for 3 hours and transferred to a hydrothermal reactor. Heating in a 120 deg.C oven for 2 hr, and heating to 170 deg.C for 24 hr. After the reaction is finished, naturally cooling to room temperature, washing with ethanol and water for three times to obtain MFI type zeolite crystal grains with the size of 100 nm, and drying for later use.
Sequentially dissolving 2 g of octadecyl trimethyl ammonium chloride, 20 mg of MFI type zeolite crystal grains and 0.5 mL of triethanolamine into 36 mL of deionized water, and uniformly stirring by ultrasonic waves to form a light white homogeneous transparent aqueous phase solution; putting the solution into a reactor, and stirring for 0.5 hour at 70 ℃; dissolving 0.6 ml of tetraethoxysilane in 4 ml of decalin to obtain an organic oil phase solution, wherein the concentration of tetraethoxysilane is 13.04 wt%; adjusting the stirring speed of the aqueous phase solution to 200 revolutions per minute, and dropwise adding the organic oil phase solution onto the aqueous phase solution to form an oil-water two-phase layered system; reacting for 24 hours in an oil bath at the temperature of 70 ℃ to obtain the monodisperse mesoporous silica composite zeolite core-shell nanosphere material; and (3) placing the mesoporous silica composite zeolite nano material in a muffle furnace, heating the mesoporous silica composite zeolite nano material to 550 ℃ from room temperature at the speed of 1 ℃/min in the air atmosphere, keeping the temperature for 7 hours, removing a surfactant and a structure directing agent in the mesoporous silica composite zeolite nano material, and obtaining a product, namely the monodisperse mesoporous silica composite zeolite core-shell nano sphere material after roasting. The resulting material was highly monodisperse and uniformly sized nanospheres with a sphere size of 800 nm. The sphere is in a core-shell structure, the inner core is MFI zeolite crystal grains, the size is 100 nm, the size of the hole is 0.8 nm, a silicon dioxide layer with divergent gradient mesoporous channels is constructed on the outer surface of the zeolite crystal grains, the thickness of a mesoporous shell layer is 350 nm, and the aperture of the mesoporous shell layer is 6 nm. The whole specific surface area is 920 m2Per g, pore volume of 2.34 cm3(ii) in terms of/g. Material itself by X-ray diffraction spectroscopy and27after the Al solid-state nuclear magnetic resonance spectrum identification, the monodisperse mesoporous silica composite zeolite core-shell nanosphere material is ensured to still have the high crystal phase and strong acidity of the original MFI zeolite crystal grains.
Example 4
The monodisperse mesoporous silica composite zeolite core-shell nanosphere material prepared in example 1 is subjected to surface sulfonation modification and then is used for esterification reaction of saturated higher fatty acid on a batch reactor to synthesize biomass diesel, wherein palmitic acid (hexadecanoic acid) and methanol are used as raw materials, the reaction temperature is 60 ℃, the total reaction time is 70 hours, and the evaluation result is shown in fig. 3. And a control group is set as a control group, and the catalyst adopted by the control group is the sulfonated and modified monodisperse mesoporous silica nanospheres. The evaluation result shows that the monodisperse mesoporous silica composite zeolite core-shell material has nearly 1.4 times of improvement advantage in the catalytic synthesis yield of the biodiesel compared with the monodisperse mesoporous silica nanospheres. The time-space guiding capability of the core-shell structure is fully utilized, and the advantages of hole space macromolecule diffusion of the mesoporous shell layer and rapid and strong water molecule adsorption and capture of the core zeolite are combined, so that the overall yield of the esterification reaction of the saturated high-grade fatty acid is greatly improved.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (10)

1. A monodisperse mesoporous silica composite zeolite core-shell material, comprising: forming a silica layer with divergent mesoporous channels on the outer surface of the zeolite crystal grains by using an oil-water two-phase layered interface assembly method to form a multi-level pore distribution zeolite material with a core-shell structure, wherein the size range is 20 nm-30 mu m, the shell thickness is 10 nm-10 mu m, and the specific surface area is 750-1000 m2The pore diameter of the mesoporous shell is 3-30 nm, and the pore volume is 0.4-2.4 cm3(ii)/g; the porous zeolite core comprises core zeolite micropores, shell mesoporous pores and bulk material gap stacking pores, wherein the shell pore canal pattern is a gradient mesoporous pore canal which is radially developed; the material itself still ensures the high crystalline phase and strong acidity of the original zeolite grains.
2. The monodisperse mesoporous silica composite zeolite core-shell material of claim 1, wherein the zeolite type as the core is one or more of silicate type zeolite, aluminosilicate type zeolite, and aluminophosphate type zeolite.
3. The monodisperse mesoporous silica composite zeolite core-shell material of claim 1, wherein the shell layer material further comprises alumina, alumina silicate, titania, zirconia, or carbon.
4. A preparation method of a monodisperse mesoporous silica composite zeolite core-shell material is characterized by comprising the following specific steps:
(1) dissolving a surfactant and a catalyst into water, and stirring to obtain a clear solution; the concentration of the surfactant in the clear solution is 0.5-10 wt%, and the concentration of the catalyst is 0.2-0.5 wt%; adding the nano-scale zeolite crystal particles into the clarified solution, performing ultrasonic dispersion, and continuously stirring to obtain a homogeneous water phase solution;
(2) dissolving a silicon source, a pre-prepared metal-doped silicon source or a pre-prepared carbon-doped silicon source in an organic solvent to obtain an organic solution of the silicon source; wherein the concentration of the silicon source is 2.5-30 wt%; slowly adding the organic solution into the upper layer of the aqueous phase solution obtained in the step (1) to form an upper oil phase, so as to obtain an oil-water two-phase layered system; the mass ratio of the nano-scale zeolite crystal grains to the silicon source is 0.01-0.05, and the mass ratio of the surfactant to the silicon source is 0.25-10.0;
(3) reacting the oil-water two-phase layered system obtained in the step (2) at the temperature of 0-120 ℃; obtaining a monodisperse mesoporous silica composite zeolite core-shell material;
(4) roasting in air atmosphere to remove the surfactant in the monodisperse mesoporous silica composite zeolite core-shell material, and obtaining the high-dispersion core-shell material with the zeolite grains coated by the disperse mesoporous silica.
5. The preparation method according to claim 4, wherein the surfactant in step (1) is one or more selected from quaternary ammonium salt cationic surfactant, organic/inorganic acid salt anionic surfactant and nonionic surfactant; the catalyst is selected from one or more of organic amine molecules, aliphatic amine, alcohol amine, aromatic amine, amide, aromatic amine and alicyclic amine.
6. The method according to claim 4, wherein the stirring in the step (1) is carried out at a speed of 50 to 1000 rpm for 6 to 24 hours.
7. The preparation method according to claim 4, wherein the organic solvent in step (2) is one or more selected from cyclohexane, n-hexane, decalin, olefin, high-carbon cycloalkane, and high-carbon alkane; the ratio of organic solvent phase to aqueous phase is 0.2-1.0 by volume.
8. The preparation method according to claim 4, wherein the silicon source in step (2) is selected from one or more of sodium silicate, sodium metasilicate, fumed silica, ethyl orthosilicate, oxidized aluminosilicate and organosilane; the aluminum source is selected from one or more of aluminum isopropoxide, sodium metaaluminate, alumina, aluminosilicate and aluminum acetylacetonate; the titanium source is selected from one or more of isopropyl titanate, tetrabutyl titanate, titanium tetrachloride, titanyl sulfate and metatitanic acid; the zirconium source is selected from one or more of tetraethoxy zirconium, normal propyl zirconium, iso propyl zirconium, tetra iso propyl zirconium, normal butyl zirconium, tertiary butyl zirconium and zirconium nitrate.
9. The production method according to claim 4, wherein in the step (4), the temperature rise rate at the time of the calcination is 0.1 to 10 degrees/minute; the roasting temperature is 400-600 ℃, and the roasting time is 5-7 hours.
10. The preparation method according to one of claims 4 to 9, characterized in that the prepared material is a coated mesoporous nano zeolite ball formed by silicon dioxide close packing, the size of the coated mesoporous nano zeolite ball is 20 nm to 30 mu m, the thickness of a shell layer is 10 nm to 10 mu m, and the specific surface area is 750 to 1000 m2A/g, mThe pore diameter of the porous shell layer is 3-30 nm, and the pore volume is 0.4-2.4 cm3/g。
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