CN112387306A - Preparation method of silver-silicon catalyst, silver-silicon catalyst and application thereof - Google Patents

Preparation method of silver-silicon catalyst, silver-silicon catalyst and application thereof Download PDF

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CN112387306A
CN112387306A CN201910759318.0A CN201910759318A CN112387306A CN 112387306 A CN112387306 A CN 112387306A CN 201910759318 A CN201910759318 A CN 201910759318A CN 112387306 A CN112387306 A CN 112387306A
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silver
mesoporous silica
catalyst
silicon catalyst
silica nano
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周静红
董桂霖
李伟
曹约强
沈荣春
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East China University of Science and Technology
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East China University of Science and Technology
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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
    • B01J31/00—Catalysts comprising hydrides, coordination complexes or organic compounds
    • B01J31/02—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides
    • B01J31/0272—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides containing elements other than those covered by B01J31/0201 - B01J31/0255
    • B01J31/0274—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides containing elements other than those covered by B01J31/0201 - B01J31/0255 containing silicon
    • 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
    • B01J31/00—Catalysts comprising hydrides, coordination complexes or organic compounds
    • B01J31/02—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides
    • B01J31/0272—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides containing elements other than those covered by B01J31/0201 - B01J31/0255
    • B01J31/0275—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides containing elements other than those covered by B01J31/0201 - B01J31/0255 also containing elements or functional groups covered by B01J31/0201 - B01J31/0269
    • B01J35/394—
    • B01J35/40—
    • B01J35/51—
    • B01J35/617—
    • B01J35/633—
    • B01J35/647—
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C67/00—Preparation of carboxylic acid esters
    • C07C67/30—Preparation of carboxylic acid esters by modifying the acid moiety of the ester, such modification not being an introduction of an ester group
    • C07C67/31—Preparation of carboxylic acid esters by modifying the acid moiety of the ester, such modification not being an introduction of an ester group by introduction of functional groups containing oxygen only in singly bound form
    • 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
    • B01J2231/00—Catalytic reactions performed with catalysts classified in B01J31/00
    • B01J2231/60—Reduction reactions, e.g. hydrogenation
    • B01J2231/64—Reductions in general of organic substrates, e.g. hydride reductions or hydrogenations
    • B01J2231/641—Hydrogenation of organic substrates, i.e. H2 or H-transfer hydrogenations, e.g. Fischer-Tropsch processes

Abstract

The invention discloses a preparation method of a silver-silicon catalyst, the silver-silicon catalyst and application thereof, which take mesoporous silica nano microspheres with large specific surface area, uniform pore size distribution and nano-scale center divergent short pore channels as carriers, functionalize amino on the surfaces of the mesoporous silica nano microspheres by adopting a silane coupling agent, then connect silver ions to functional groups of the pore channels through the action of coordinate bonds, and finally reduce the silver ions absorbed in the pore channels into nano-silver particles in situ under the action of a reducing agent. Compared with the traditional catalyst taking silver as an active component, the catalyst prepared by the invention has the characteristics of remarkably reduced consumption of noble metal silver, high dispersion degree, high activity and good stability, shows excellent catalytic performance in the preparation of methyl glycolate by dimethyl oxalate hydrogenation, has a conversion rate of dimethyl oxalate of more than 99 percent, a selectivity of methyl glycolate of not less than 94.9 percent and a yield of not less than 94.3 percent, and has good industrial application prospect.

Description

Preparation method of silver-silicon catalyst, silver-silicon catalyst and application thereof
Technical Field
The invention belongs to the technical field of catalyst preparation, and particularly relates to a preparation method of a silver-silicon catalyst, the silver-silicon catalyst and application thereof.
Background
Methyl glycolate is an important organic chemical raw material, has good biocompatibility and degradability, and is widely applied to the fields of chemical industry, medicines, spices, high polymer materials and the like. The existing industrialized synthetic route of methyl glycolate mainly comprises a formaldehyde carbonylation method, a methyl formate coupling method, a chloroacetic acid esterification method and the like which take petroleum and derivatives thereof as raw materials, and synthesis gas is prepared by hydrogenation of dimethyl oxalate by using an efficient catalyst. The latter is a more economical and environmentally friendly non-petroleum based process route due to the wider sources of synthesis gas, and has significant economic benefits and broad market prospects.
At present, catalysts for preparing methyl glycolate by hydrogenating dimethyl oxalate are mainly divided into copper-based catalysts taking Cu as a main active component and silver-based catalysts taking Ag as a main active component. When the conventional copper-based catalyst is used for catalyzing hydrogenation of dimethyl oxalate to prepare methyl glycolate, the yield of the methyl glycolate is lower than 90 percent, for example, the copper-based catalysts prepared in patents CN101954288A, CN108499564A and CN 108325532A. Wherein: CN101954288A best example 17 20% Cu-12% Ag-0.2% Pt/SiO2Under the optimal condition, the conversion rate of dimethyl oxalate is 94.5 percent, and the selectivity and the yield of methyl glycolate are 91.2 percent and 86.2 percent respectively. The silver-based catalyst has a mild hydrogenation performance, a low hydrogenation reaction rate and a high selectivity and yield of methyl glycolate in the dimethyl oxalate hydrogenation reaction, and is thus valued by more and more researchers. However, in the prior art, silver loadings of greater than 10 wt% are generally required in order to ensure yields of methyl glycolate of greater than 90%. For example: CN102336666A reports a preparation method for synthesizing methyl glycolate and ethylene glycol by hydrogenation of dimethyl oxalate, the catalyst is prepared by taking Ag as a main active component, one or more of Cu, Mg, Ca, Ba, Zn, Zr, Co, Cr, Ni, Mn, Sn, Au, Pt, Pd, Ru and Re as an auxiliary agent, and one or more of mesoporous silica SBA-15, MCM-41, MCM-48, HMS and MSU as a carrier through an impregnation method or a sol-gel method. At an Ag loading of 5 wt%, under optimal conditions (example 18, S2 catalyst), the dimethyl oxalate conversion was 96% and the methyl glycolate selectivity and yield were 90% and 86.4%, respectively.
CN104492429A reports a catalyst and a method for synthesizing methyl glycolate and ethylene glycol by hydrogenation of dimethyl oxalate, wherein the catalyst is prepared by taking Ag as a main active component, one or more of Cu, Mg, Ca, Ba, Zn, Zr, Ni, Au, Pt, Pd, Ru and Rh as an auxiliary agent and at least one of titanium dioxide and a carbon carrier as a carrier through an impregnation method or a deposition precipitation method. All the examples in CN104492429A adopt Ag loading of more than 10 wt%, and under different conditions of the carrier and the preparation method, the yield of most examples is less than 90%. Although the catalyst prepared in example 3 had a dimethyl oxalate conversion of 99.3% and methyl glycolate selectivity and yield of 97.1% and 96.4%, respectively, the Ag loading was 13 wt%, and carbon nanotubes were used as the support.
From this, it can be seen that although a catalyst prepared using Ag as a main active component can improve the selectivity and yield of methyl glycolate, the amount of noble metal used is large because the supported amount of Ag is generally 10 wt% or more while maintaining the yield of methyl glycolate > 90%, which significantly increases the cost for industrial application.
On the other hand, the existing silver-based catalyst has the following technical defects:
the preparation of the silver-based catalyst needs high-temperature calcination to reduce Ag, which is easy to cause silver particle agglomeration, and the obtained Ag particles have fewer lattice defects and are not beneficial to the activation and diffusion of hydrogen (Nanoscale,2016,8, 5959-5967), so that the catalytic activity is low; and the high-temperature calcination process strengthens the action of the silver precursor and the carrier, and is not beneficial to the reduction of silverSo that the silver-based catalyst also contains unreduced Ag+Resulting in a reduction in the number of silver active sites on the surface of the catalyst (chem. Commun.,2010,46,4348-4350.), resulting in low catalytic activity.
And (II) the Ag-based catalyst with high loading also has the phenomenon of sintering increase of Ag particles in the reaction, thereby influencing the stability of the catalyst (JP 06135895 and ChemComm,2010,46(24): 4348-4350).
And (III) selecting a traditional mesoporous material as a carrier, such as SBA-15, MCM-41, activated carbon, a carbon nano tube and the like, wherein the limit function of the mesopores can effectively prevent the agglomeration and sintering of metal particles, but the metal nano particles are easy to penetrate into the pore channels due to the long (micron-sized) pore channels, so that the dispersion degree of Ag on the surface of the catalyst is low (less than 0.2, which is measured by a chemical adsorption method), the utilization rate of Ag is low, and the loading capacity of Ag is required to be large, so that the cost of the silver-based catalyst is high, and the industrial application of the silver-based catalyst is not facilitated.
In conclusion, the development of a novel silver-based catalyst with low load applied to the preparation of methyl glycolate by dimethyl oxalate hydrogenation realizes high yield of methyl glycolate and high stability of the catalyst, and has great significance for industrial application of a methyl glycolate process in a synthesis gas route.
Disclosure of Invention
The invention provides a preparation method of a silver-silicon catalyst, which takes amino functionalized mesoporous silica nano microspheres as a carrier, so that an active component silver is reduced on the surface layer of the carrier to the maximum extent in situ, and silver nano particles are formed; the prepared silver-silicon catalyst has the advantages of low Ag loading capacity, high dispersity, high catalytic activity, good selectivity and long service life.
In order to realize the purpose, the following technical scheme is adopted:
the preparation method of the silver-silicon catalyst is characterized by comprising the following steps:
(1) carrying out amination treatment on the mesoporous silica nano-microspheres to obtain aminated mesoporous silica nano-microspheres;
(2) loading nano silver particles on the aminated mesoporous silica nano microspheres obtained in the step (1) by adopting an in-situ reduction method: ultrasonically dispersing the aminated mesoporous silica nano microsphere in the step (1) in ethanol according to the formula, adding an ethanol solution of silver salt, stirring for 1-6 hours at 10-40 ℃, reducing by using a reducing agent at-10-90 ℃, and finally performing centrifugal separation, washing and drying to obtain a nano-silver-loaded silver-silicon catalyst of the aminated mesoporous silica nano microsphere;
the silver salt is selected from one or more of silver nitrate, silver acetate, silver sulfate or silver lactate, and the reducing agent is selected from one of sodium borohydride, hydrazine hydrate, formaldehyde, ascorbic acid, glycol and ethanol;
the mass-volume ratio of the aminated mesoporous silica nano microsphere to ethanol for ultrasonic dispersion is 1g:
(50-100) ml; the mass ratio of the aminated mesoporous silica nano microsphere to the silver salt is 1 (0.03-0.1); the molar ratio of silver element to reducing agent in the silver salt is 1 (2-10).
The temperature of the reduction reaction is reasonably selected within the range of-10 to 90 ℃ according to the difference of the reducing agent, and the time of the reduction reaction is properly adjusted within 1 to 24 hours according to the difference of the reducing agent and the selection of the reduction temperature. When the reduction reaction is complete, the color of the suspension does not change any more, and thus the color of the suspension can no longer change to the end point of the reduction reaction. It is also possible to suitably prolong the reaction time on the basis of this.
Preferably, the mass volume ratio of the aminated mesoporous silica nano-microsphere to ethanol for ultrasonic dispersion is 1g:90 ml; the mass ratio of the aminated mesoporous silica nano microsphere to the silver salt is 1 (0.048-0.089).
Preferably, the silver salt is silver nitrate, the reducing agent is ethanol, and the reduction temperature is 60-90 ℃.
Further preferably, the reduction temperature is 70 ℃.
It should be noted that when the reduction temperature is set to 70 ℃, the reaction speed is moderate, the obtained Ag particles are uniformly loaded on the surface of the carrier, the dispersion degree measured by chemical adsorption is highest, the number of active sites on the surface of the catalyst is the largest, and the catalytic effect is good; when the reduction temperature is 60 ℃, the reaction speed is slow, the Ag particles grow slowly, the particle size is minimum, the smaller Ag particles easily penetrate into the pore channels of the carrier, the dispersity measured by chemical adsorption is reduced, the number of active sites on the surface of the catalyst is reduced, and the catalytic effect is good when the reduction temperature is not 70 ℃. When the reduction temperature is 90 ℃, the reaction speed is high, the Ag particles grow fast, the particle size is maximum, the dispersity measured by chemical adsorption is reduced, the number of active sites on the surface of the catalyst is reduced, and the relative reduction temperature of the catalytic effect is 70 ℃.
According to some preferred embodiments of the present invention, the mesoporous silica nanospheres are prepared by the following method:
adding triethanolamine with the formula amount into a deionized water solution of a cationic surfactant to serve as a water phase; dissolving tetraethoxysilane in cyclohexane to obtain an oil phase; adding the oil phase into the water phase, and stirring to react for 12-36 h; after the reaction is finished, carrying out centrifugal separation, washing, drying and roasting to obtain the mesoporous silica nano-microsphere;
the mass volume ratio of the cationic surfactant to the deionized water is 1g (6-20) ml; the mass ratio of the cationic surfactant to the triethanolamine is 1 (0.02-0.04); the mass ratio of the cationic surfactant to the tetraethoxysilane and the cyclohexane is 1 (0.4-0.6) to 1.5-2.5.
Preferably, the mass ratio of the cationic surfactant to the tetraethoxysilane and the cyclohexane is 1:0.5 (1.25-2.08).
Further preferably, the mass volume ratio of the cationic surfactant to the deionized water is 1g:8 ml; the mass ratio of the cationic surfactant to the triethanolamine is 1: 0.027; the mass ratio of the cationic surfactant to the tetraethoxysilane and the cyclohexane is 1:0.5: 2.
Preferably, the cationic surfactant is selected from one or both of cetyltrimethylammonium chloride and cetyltrimethylammonium bromide.
Further preferably, the cationic surfactant is cetyltrimethylammonium chloride.
According to some preferred embodiments of the present invention, the amination step comprises:
ultrasonically dispersing the mesoporous silica nano microspheres in toluene according to the mass ratio of 1 (10-100), then adding a silane coupling agent according to the mass ratio of 1 (0.2-1), refluxing for 8-24 hours at 100-120 ℃, and then performing centrifugal separation, washing and drying to obtain the aminated mesoporous silica nano microspheres.
Preferably, the mass ratio of the mesoporous silica nano microspheres to the toluene is 1 (30-100); the mass ratio of the mesoporous silica nano microspheres to the silane coupling agent is 1 (0.33-1), and the mesoporous silica nano microspheres are refluxed for 8-12 hours at the temperature of 110-120 ℃.
Preferably, the silane coupling agent is selected from one or two of 3-aminopropyltrimethoxysilane and 3-aminopropyltriethoxysilane. Further preferably, the silane coupling agent is 3-aminopropyltriethoxysilane.
The second aspect of the present invention provides a silver-silicon catalyst prepared by the above-mentioned preparation method.
According to the invention, the mesoporous silica nano-microspheres have uniform size, high sphericity, controllable range of diameter of 150-500 nm and controllable range of pore diameter of 4-10 nm; the pore canal of the mesoporous silica nano microsphere is in a central divergent slit shape, and the controllable range of the pore canal length is 75-250 nm.
According to the invention, the controllable range of the particle size of the nano silver particles is 3-14 nm.
According to the invention, the specific surface area of the mesoporous silica nano-microspheres ranges from 350 m to 1000m2·g-1. Preferably, the specific surface area of the mesoporous silica nano-microsphere ranges from 479m to 906m2·g-1。
The third aspect of the invention provides the application of the silver-silicon catalyst, which is used for catalyzing the reaction of preparing methyl glycolate by hydrogenating dimethyl oxalate.
According to the invention, the reaction for preparing methyl glycolate by hydrogenation of dimethyl oxalate,a fixed bed reactor is adopted, the reaction temperature is 180-250 ℃, the reaction pressure is 2.0-4.0 MPa, the molar ratio of hydrogen to dimethyl oxalate is (60-120): 1, and the liquid hourly space velocity of the dimethyl oxalate is 0.2-3 h-1。
According to a specific example of the invention, the reaction for preparing methyl glycolate by hydrogenating dimethyl oxalate adopts a fixed bed reactor, the reaction temperature is 200 ℃, the reaction pressure is 2.8MPa, the molar ratio of hydrogen to dimethyl oxalate is 80:1, and the liquid hourly space velocity of dimethyl oxalate is 1.0h-1。
Compared with the prior art, the invention has the following beneficial technical effects:
according to the preparation method of the silver-silicon catalyst, amination treatment is carried out on the surface of the mesoporous nano-silica microsphere, the obtained aminated mesoporous silica microsphere is used as a carrier, and nano-silver particles are reduced and loaded in situ, so that the silver-silicon catalyst with high dispersity is obtained. The aminated mesoporous silica carrier is characterized in that silver ions are complexed through surface amino groups, the adsorbed silver ions are reduced to be in a metal state in situ by a reducing agent, the metal state is used as a seed crystal and is continuously increased to be silver nano particles, the dispersity of silver is high, the phenomenon of silver particle agglomeration caused by high-temperature roasting and high-temperature reduction in the traditional preparation method is avoided, the utilization rate of silver can be improved, the silver loading capacity is reduced, and the catalytic activity is improved. In addition, the amination treatment of the carrier changes the electronic valence state of partial silver atoms of the obtained nano silver particles, and an electron-rich silver species exists, so that the adsorption and activation of dimethyl oxalate are facilitated, and the nano silver particles have higher catalytic activity.
The silver-silicon catalyst adopts the mesoporous silica nano microspheres with large specific surface area, uniform pore size distribution and nano-scale center divergent short pore passages as the carrier, so that the active component silver is dispersed on the surface layer of the microspheres to the maximum extent, silver particles are prevented from penetrating into the carrier bulk phase to a great extent, and the silver is maintained to have higher dispersity on the surface of the carrier, thereby improving the utilization rate of the silver, further reducing the loading capacity of the silver and improving the catalytic activity. Meanwhile, the nano-aperture on the surface of the carrier can limit the silver particles, so that the silver particles are prevented from agglomerating, and the nano-silver particles have more lattice defects, so that the activation and diffusion of hydrogen are facilitated, and the catalytic activity is high.
The silver-silicon catalyst prepared by the invention has the characteristics of obviously reduced silver loading capacity, high dispersity, high catalytic activity, good selectivity and long service life, greatly reduces the cost of the existing catalyst for preparing methyl glycolate by hydrogenating dimethyl oxalate, and has good industrial application prospect.
Drawings
FIG. 1 is a transmission electron micrograph of mesoporous silica nanospheres prepared in example 1 of the present invention.
FIG. 2 is a transmission electron micrograph of the amino functionalized mesoporous silica nanospheres prepared in example 4 of the present invention.
FIG. 3 is a Fourier transform infrared spectrum of the mesoporous silica nanospheres M1 prepared in example 1 and the amino functionalized mesoporous silica nanospheres N1M1 prepared in example 4. Wherein curve A represents the Fourier transform infrared spectrum of M1, and curve B represents the Fourier transform infrared spectrum of N1M 1.
FIG. 4 is a transmission electron micrograph of a silver silicon catalyst prepared according to example 7 of the present invention.
Fig. 5 is a transmission electron micrograph of nano silver particles of the silver silicon catalyst prepared in example 7 of the present invention.
FIG. 6 is an XPS spectrum of Ag3d of Ag silicon catalyst 3Ag1/N1M1 prepared in example 7 of the present invention.
FIG. 7 is a transmission electron micrograph of a silver silicon catalyst prepared according to example 8 of the present invention.
FIG. 8 is a TEM image of the Ag-Si catalyst prepared in example 9 of the present invention.
Detailed Description
The present invention will be further described with reference to the following examples. It should be understood that the following examples are illustrative only and are not intended to limit the scope of the present invention.
The technical solution of the present invention will be described below by way of preferred examples.
Example 1 preparation of mesoporous silica nanospheres
The preparation of the mesoporous silica nanosphere of the present embodiment comprises the following steps:
(1) dissolving 15g of surfactant cetyl trimethyl ammonium chloride in 120ml of deionized water, adding 0.4g of triethanolamine, heating to 60 ℃, and stirring for 1 hour at the rotating speed of 150r/min to obtain a surfactant-water solution serving as a water phase; 7.5g of tetraethoxysilane was dissolved in 25g of cyclohexane to prepare an oil phase.
(2) Dropwise adding the oil phase obtained in the step (1) into the water phase, controlling the temperature at 60 ℃ and the rotating speed at 100r/min, and continuously stirring for 20 hours; after stirring, carrying out centrifugal separation, and washing the precipitate with 120ml of ethanol to remove residues to obtain a white solid;
(3) and (3) drying the white solid obtained in the step (2) at 120 ℃ for 4 hours, and then roasting at 550 ℃ for 4 hours to remove hexadecyl trimethyl ammonium chloride, so as to obtain the mesoporous silica nano microsphere marked as M1.
The microscopic morphology of the M1 was observed by transmission electron microscopy and is shown in FIG. 1. As can be seen from FIG. 1, M1 prepared in this example has good dispersibility, uniform particle size, diameter of about 370nm, and a pore channel in the shape of a central divergent slit. The BET specific surface area of M1 was 665M as measured by nitrogen physisorption2g-1Pore volume of 0.80m3g-1The average pore diameter was 6.61 nm.
Example 2 preparation of mesoporous silica nanospheres
The preparation method of this example is substantially the same as that of example 1, except that:
in the step (1), 15g of surfactant cetyl trimethyl ammonium chloride is dissolved in 300ml of deionized water, and 0.6g of triethanolamine is added to serve as a water phase; 7.5g of tetraethoxysilane was dissolved in 18.75g of cyclohexane to prepare an oil phase.
In the step (2), the temperature is controlled at 50 ℃, the rotating speed is 150r/min, and the stirring is continued for 36 hours.
Obtaining the mesoporous silica nano microsphere marked as M2.
Observing the M2 by a transmission electron microscope, and obtaining the micro morphologyFig. 1 is similar. The M2 prepared in this example has a diameter of about 490nm and a BET specific surface area of 479M2g-1Pore volume of 1.14m3g-1The average pore diameter was 9.37 nm.
Example 3 preparation of mesoporous silica nanospheres
The preparation method of this example is substantially the same as that of example 1, except that:
in the step (1), 15g of surfactant cetyl trimethyl ammonium chloride is dissolved in 90ml of deionized water, and 0.3g of triethanolamine is added to serve as a water phase; 7.5g of tetraethoxysilane was dissolved in 31.25g of cyclohexane to prepare an oil phase.
In the step (2), the temperature is controlled at 70 ℃, the rotating speed is 50r/min, and the stirring is continued for 12 hours.
Obtaining the mesoporous silica nano microsphere marked as M3.
The microscopic morphology of the M3 was similar to that of FIG. 1 when observed by transmission electron microscopy. The M3 prepared in this example had a diameter of about 220nm and a BET specific surface area of 906M2g-1Pore volume of 0.49m3g-1The average pore diameter was 4.12 nm.
The mesoporous silica nanospheres prepared under the process conditions of the embodiments 1-3 have uniform size, controllable diameter range of 150-500 nm, pore size distribution of 4-10 nm, central divergent slit-shaped pore channels, and controllable length range of 75-250 nm.
Example 4 preparation of amino-functionalized mesoporous silica nanospheres
In this embodiment, the amination treatment of the mesoporous silica nanosphere M1 includes the following specific steps:
(1) 1.5g M1 was dispersed in 45g of toluene, then 0.5g of 3-aminopropyltriethoxysilane was added, refluxed at 110 ℃ for 12 hours, then cooled to room temperature, centrifuged, and the precipitate was washed with ethanol to remove the residue, yielding a white solid.
(2) And (2) drying the white solid prepared in the step (1) at 120 ℃ for 4 hours to obtain the mesoporous silica microsphere with the aminated surface, wherein the label is N1M 1.
For N1M1, the sample was subjected to transmission electron microscopyThe microscopic morphology is shown in FIG. 2. As can be seen from the comparison between fig. 1 and fig. 2, the morphology of N1M1 is not significantly changed, i.e., the surface amination of M1 does not destroy the original microstructure. N1M1BET specific surface area 323M2g-1Pore volume of 0.41m3g-1The average pore diameter was 6.17 nm.
FIG. 3 is a Fourier transform infrared spectrum of M1 and N1M1, comparing M1 and finding that N1M1 is 1562cm-1And 700cm-1The absorption peaks at (A) are respectively attributed to the plane shear vibration and the out-of-plane rocking vibration of NH, which indicates that the surface of M1 contains-NH2The group was successfully amino-functionalized.
Example 5 preparation of amino-functionalized mesoporous silica nanospheres
In this embodiment, the amination treatment of the mesoporous silica nanosphere M2 includes the following specific steps:
(1) 0.5g M2 was dispersed in 50g of toluene, then 0.5g of 3-aminopropyltriethoxysilane was added, refluxed at 120 ℃ for 8 hours, then cooled to room temperature, centrifuged, and the precipitate was washed with ethanol to remove the residue, yielding a white solid.
(2) And (2) drying the white solid prepared in the step (1) at 120 ℃ for 4 hours to obtain the mesoporous silica microsphere with the aminated surface, wherein the label is N2M 2.
The microscopic morphology of N2M2 was similar to that of FIG. 2 when observed using a transmission electron microscope. The BET specific surface area of N2M2 prepared in this example was 287M2g-1Pore volume of 0.69m3g-1The average pore diameter was 8.95 nm.
Fourier transform infrared spectroscopy similar to that of FIG. 3 shows that N2M2 is 1562cm-1And 700cm-1The absorption peaks at (A) are respectively attributed to the plane shear vibration and the out-of-plane rocking vibration of NH, which indicates that the surface of M2 contains-NH2The group was successfully amino-functionalized.
Example 6 preparation of amino-functionalized mesoporous silica nanospheres
In this embodiment, the amination treatment of the mesoporous silica nanosphere M3 includes the following specific steps:
(1) 5g M3 was dispersed in 50g of toluene, 1.0g of 3-aminopropyltriethoxysilane was then added, refluxed at 100 ℃ for 24 hours, then cooled to room temperature, centrifuged, and the precipitate was washed with ethanol to remove the residue, yielding a white solid.
(2) And (2) drying the white solid prepared in the step (1) at 120 ℃ for 4 hours to obtain the mesoporous silica microsphere with the aminated surface, wherein the label is N3M 3.
The microscopic morphology of N3M3 was similar to that of FIG. 2, as observed by transmission electron microscopy. The BET specific surface area of N3M3 prepared in this example was 634M2g-1Pore volume of 0.36m3g-1The average pore diameter was 3.98 nm.
Fourier transform infrared spectroscopy similar to that of FIG. 3 shows that N3M3 is 1562cm-1And 700cm-1The absorption peaks at (A) are respectively attributed to the plane shear vibration and the out-of-plane rocking vibration of NH, which indicates that the surface of M3 contains-NH2The group was successfully amino-functionalized.
Example 7 preparation of silver-silicon catalyst by in-situ reduction
In this embodiment, the N1M1 prepared in example 4 is used as a carrier, an in-situ reduction method is used to prepare a silver-silicon catalyst with an Ag loading of 3 wt%, and ethanol is used as a reducing agent to perform in-situ reduction on silver nitrate, and the specific steps are as follows:
(1) 1.0g N1M1 was immersed in 90ml of ethanol and dispersed ultrasonically to a homogeneous suspension; 0.049g of AgNO3Dissolving in 24.5ml ethanol to obtain silver salt-ethanol solution; controlling the temperature of the suspension to be 30 ℃, controlling the stirring speed to be 100r/min, dropwise adding a silver salt-ethanol solution into the suspension at the speed of 2ml/min, stirring for 4 hours, then heating the reaction system to 70 ℃ to perform in-situ reduction reaction, and continuously stirring until the color of the suspension is not changed any more, wherein the time is about 12 hours.
(2) And (2) centrifugally separating the reaction system in the step (1), washing precipitates with ethanol to remove residues, and drying the separated brown yellow solid at 60 ℃ for 12 hours under the protection of nitrogen to obtain the final product catalyst which is marked as 3Ag1/N1M 1.
The transmission electron microscope is used for observing the 3Ag1/N1M1 catalyst, and the micro morphology is shown in FIG. 4. As shown in fig. 4, in the 3Ag1/N1M1 catalyst prepared in this example, Ag nanoparticles are uniformly supported in the nanopores of N1M1, and no large silver particle agglomeration is found on the outer surface. The average diameter of the Ag particles was 5.5nm, and the dispersion of Ag was 0.317.
Fig. 5 is a transmission electron micrograph of Ag nanoparticles in the 3Ag1/N1M1 catalyst, which shows that the degree of ordered arrangement of particles of Ag nanoparticles is greatly reduced, the surface is distributed with many crystal domains, and there are a lot of grain boundaries, lattice defects and non-uniform surfaces.
FIG. 6 is an XPS spectrum of Ag3d in 3Ag1/N1M1 catalyst: ag3d compared to metallic Ag3/2(374.1eV) and Ag3d5/2(368.1eV) characteristic peak, Ag3d in 3Ag1/N1M1 catalyst3/2And Ag3d5/2The characteristic peak is shifted positively by 0.3eV, indicating that the electronic valence state of part of the silver atoms is changed and that there is an electron-rich silver species.
Example 8 preparation of silver silicon catalyst by in situ reduction
In this embodiment, the N2M2 prepared in example 5 is used as a carrier, an in-situ reduction method is used to prepare a silver-silicon catalyst with an Ag loading of 3 wt%, and ethanol is used as a reducing agent to perform in-situ reduction on silver nitrate, and the specific steps are as follows:
(1) 1.0g N2M2 was immersed in 50ml of ethanol and ultrasonically dispersed to a homogeneous suspension; 0.089g of Ag2SO4Dissolving in 24.5ml ethanol to obtain silver salt-ethanol solution; controlling the temperature of the suspension to be 40 ℃, controlling the stirring speed to be 100r/min, dropwise adding a silver salt-ethanol solution into the suspension at the speed of 2ml/min, stirring for 1 hour, heating to 90 ℃ to perform in-situ reduction reaction, and continuously stirring until the color of the suspension is not changed any more, wherein the time is about 8 hours.
(2) And (2) centrifugally separating the reaction system in the step (1), washing precipitates with ethanol to remove residues, and drying the separated brown yellow solid at 60 ℃ for 12 hours under the protection of nitrogen to obtain the final product catalyst which is marked as 3Ag2/N2M 2.
The transmission electron microscope is used for observing the 3Ag2/N2M2 catalyst, and the micro morphology is shown in FIG. 7. In the 3Ag2/N2M2 catalyst prepared in this example, the reduction reaction is accelerated due to the increase of the reduction temperature, so that Ag nanoparticles grow faster, and large-particle silver appears on the surface of N2M 2. The average diameter of the Ag particles was 14.1nm, and the dispersity of Ag was 0.184.
Example 9 preparation of silver silicon catalyst by in situ reduction
In this embodiment, the N3M3 prepared in example 6 is used as a carrier, an in-situ reduction method is used to prepare a silver-silicon catalyst with an Ag loading of 3 wt%, and ethanol is used as a reducing agent to perform in-situ reduction on silver nitrate, and the specific steps are as follows:
(1) 1.0g N3M3 was immersed in 100ml of ethanol and dispersed ultrasonically to a homogeneous suspension; 0.048g C2H3AgO2Dissolving in 24.5ml ethanol to obtain silver salt-ethanol solution; controlling the temperature to be 10 ℃, stirring the mixture at the rotating speed of 100r/min, dropwise adding a silver salt-ethanol solution into the suspension at the speed of 2ml/min, stirring the mixture for 6 hours, heating the mixture to 60 ℃ to perform in-situ reduction reaction, and continuously stirring the mixture until the color of the suspension is not changed any more, wherein the time is about 24 hours.
(2) And (2) centrifugally separating the reaction system in the step (1), washing precipitates with ethanol to remove residues, and drying the separated brown yellow solid at 60 ℃ for 12 hours under the protection of nitrogen to obtain the final product catalyst which is marked as 3Ag3/N3M 3.
The transmission electron microscope is used for observing the 3Ag3/N3M3 catalyst, and the micro morphology is shown in FIG. 8. In the 3Ag3/N3M3 catalyst prepared in the example, Ag nanoparticles are uniformly loaded in nanopores of N3M3, and no large silver particle agglomeration is found on the outer surface. The average diameter of Ag particles was 3.2nm, and the dispersion degree of Ag was 0.281.
Example 10 preparation of silver silicon catalyst by in situ reduction
In this embodiment, the N1M1 prepared in example 4 is used as a carrier, and an in-situ reduction method is used to prepare a silver-silicon catalyst with an Ag loading of 3 wt%, which includes the following steps:
(1) 1.0g of N1M1 was immersed in 90ml of ethanol and ultrasonically dispersed to a homogeneous suspension; 0.049g of AgNO3Dissolving in 24.5ml ethanol to obtain silver salt-ethanol solution; controlling the temperature of the suspension to be 30 ℃, and stirringThe rotating speed is 100r/min, silver salt-ethanol solution is dripped into the suspension at the speed of 2ml/min, the suspension is stirred for 4 hours, and then the reaction system is cooled to 5 ℃; 0.1g of NaBH4Dissolving in 25ml ethanol to obtain reducing agent-ethanol solution; and (3) dripping the reducing agent-ethanol solution into the cooled reaction system at the speed of 0.75ml/min for in-situ reduction reaction, and stirring until the color of the suspension is not changed any more, wherein the reduction time is about 1 h.
(2) And (2) centrifugally separating the reaction system in the step (1), washing precipitates with ethanol to remove residues, and drying the separated brown yellow solid at 60 ℃ for 12 hours under the protection of nitrogen to obtain the final product catalyst which is marked as 3Ag4/N1M 1.
In the 3Ag4/N1M1 catalyst prepared in this example, the average diameter of Ag particles was 9.5nm, and the dispersity of Ag was 0.224.
Example 11 preparation of silver silicon catalyst by in situ reduction
The basic steps of this example are the same as example 10, except that: the in-situ reduction temperature is-10 ℃, the reduction time is about 5 hours, and the finally obtained catalyst is marked as 3Ag5/N1M 1.
In the 3Ag5/N1M1 catalyst prepared in this example, the average diameter of Ag particles was 6.9nm, and the degree of dispersion of Ag was 0.271.
Example 12 preparation of silver silicon catalyst by in situ reduction
The basic steps of this example are the same as example 7, except that: the Ag loading was 5 wt% and the final catalyst was labeled 5Ag6/N1M 1.
In the 5Ag6/N1M1 catalyst prepared in this example, the average diameter of Ag particles was 7.1nm, and the degree of dispersion of Ag was 0.266.
Example 13 preparation of silver silicon catalyst by in situ reduction
The basic steps of this example are the same as example 11, except that: the Ag loading was 5 wt% and the final catalyst was labeled 5Ag7/N1M 1.
In the 5Ag7/N1M1 catalyst prepared in this example, the average diameter of Ag particles was 7.9nm, and the dispersity of Ag was 0.248.
Example 14 preparation of silver-silicon catalyst by in-situ reduction
The basic steps of this example are the same as example 7, except that:
when the mesoporous silica nano-microsphere is subjected to amination treatment, the silane coupling agent is 3-aminopropyltrimethoxysilane, and the finally obtained catalyst is marked as 3Ag1/N2M 1.
In the 3Ag1/N2M1 catalyst prepared in this example, the average diameter of Ag particles was 5.8nm, and the degree of dispersion of Ag was 0.303.
Example 15 preparation of silver silicon catalyst by in situ reduction
The basic steps of this example are the same as example 7, except that:
when the mesoporous silica nano-microsphere is prepared, the used surfactant is 17g of hexadecyl trimethyl ammonium bromide, and the finally obtained catalyst is marked as 3Ag1/N1M 2.
In the 3Ag1/N1M2 catalyst prepared in this example, the average diameter of Ag particles was 6.3 nm. The Ag dispersion was 0.287.
Example 16 preparation of silver silicon catalyst by in situ reduction
The basic steps of this example are the same as example 7, except that:
the reducing agent is hydrazine hydrate, the in-situ reduction temperature is 30 ℃, the reduction time is 4h, and the method comprises the following specific steps:
1.0g N1M1 was ultrasonically dispersed in 90ml ethanol to make a uniformly dispersed suspension. 0.049g of AgNO3Dissolved in 24.5ml of ethanol, added dropwise to the above suspension at a rate of 2ml/min, stirred at 30 ℃ for 4 hours, and maintained at 30 ℃.
Then 0.07g of hydrazine hydrate is dissolved in 25ml of ethanol, the solution is dripped at the speed of 0.75ml/min for in-situ reduction, the solution is continuously stirred for 4 hours, then centrifugal separation is carried out, precipitates are washed by ethanol to remove residues, brownish yellow solids obtained by separation are dried for 12 hours at the temperature of 60 ℃ under the protection of nitrogen, and finally the obtained catalyst is marked as 3Ag8/N1M 1.
In the 3Ag8/N1M1 catalyst prepared in this example, the average diameter of Ag particles was 8.3nm, and the dispersity of Ag was 0.242.
Example 17 preparation of silver silicon catalyst by in situ reduction
The basic steps of this example are the same as example 7, except that:
the used reducing agent is formaldehyde, the in-situ reduction temperature is 50 ℃, the reduction time is 8h, and the method comprises the following specific steps:
1.0g N1M1 was ultrasonically dispersed in 90ml ethanol to make a uniformly dispersed suspension. 0.049g of AgNO3Dissolved in 24.5ml of ethanol, added dropwise to the suspension at a rate of 2ml/min, stirred at 30 ℃ for 4 hours, and warmed to 50 ℃.
Then 0.15g of 37 wt% formaldehyde is dissolved in 25ml of ethanol, the solution is dripped at the speed of 0.75ml/min for in-situ reduction, the solution is continuously stirred for 8 hours, then centrifugal separation is carried out, precipitates are washed by ethanol to remove residues, brownish yellow solids obtained by separation are dried for 12 hours at the temperature of 60 ℃ under the protection of nitrogen, and finally the obtained catalyst is marked as 3Ag9/N1M 1.
In the 3Ag9/N1M1 catalyst prepared in this example, the average diameter of Ag particles was 7.8nm, and the degree of dispersion of Ag was 0.251.
Example 18 preparation of silver silicon catalyst by in situ reduction
The basic steps of this example are the same as example 7, except that:
the reducing agent is ascorbic acid, the in-situ reduction temperature is 60 ℃, the reduction time is 10h, and the method comprises the following specific steps:
1.0g N1M1 was ultrasonically dispersed in 90ml ethanol to make a uniformly dispersed suspension. 0.049g of AgNO3Dissolved in 24.5ml of ethanol, added dropwise to the suspension at a rate of 2ml/min, stirred at 30 ℃ for 4 hours, and warmed to 60 ℃.
Then 0.5g ascorbic acid is dissolved in 25ml ethanol, the solution is dripped at the speed of 0.75ml/min for in-situ reduction, the solution is continuously stirred for 10 hours, then centrifugal separation is carried out, precipitates are washed by ethanol to remove residues, brownish yellow solids obtained by separation are dried for 12 hours at the temperature of 60 ℃ under the protection of nitrogen, and finally the obtained catalyst is marked as 3Ag10/N1M 1.
In the 3Ag10/N1M1 catalyst prepared in this example, the average diameter of Ag particles was 7.2nm, and the degree of dispersion of Ag was 0.264.
Example 19 preparation of silver silicon catalyst by in situ reduction
The basic steps of this example are the same as example 7, except that:
the reducing agent is ethylene glycol, the in-situ reduction temperature is 60 ℃, the reduction time is 12h, and the method comprises the following specific steps:
1.0g N1M1 was ultrasonically dispersed in 90ml ethanol to make a uniformly dispersed suspension. 0.049g of AgNO3Dissolved in 24.5ml of ethanol, added dropwise to the suspension at a rate of 2ml/min, stirred at 30 ℃ for 4 hours, and warmed to 60 ℃.
Then 0.18g of ethylene glycol is dissolved in 25ml of ethanol, the solution is dripped at the speed of 0.75ml/min for in-situ reduction, the solution is continuously stirred for 12 hours, then the solution is centrifugally separated, precipitates are washed by ethanol to remove residues, the separated brownish yellow solid is dried for 12 hours at the temperature of 60 ℃ under the protection of nitrogen, and the finally obtained catalyst is marked as 3Ag11/N1M 1.
In the 3Ag11/N1M1 catalyst prepared in this example, the average diameter of Ag particles was 6.7nm, and the degree of dispersion of Ag was 0.276.
The properties of the 3Ag4/N1M 1-3 Ag4/N1M1 catalysts prepared in examples 10-19, such as micro-morphology, are similar to those of the 3Ag2/N1M1 catalyst prepared in example 7, and further description is omitted here for the sake of reducing redundancy.
Example 20 evaluation of catalytic Performance of catalyst
Dimethyl oxalate conversion (C) by testing the silver silicon catalysts prepared in examples 7-19DMO) Selectivity to methyl glycolate (S)MG) Yield (Y)MG) The catalytic performance of the catalyst on the hydrogenation reaction of dimethyl oxalate was evaluated, wherein:
CDMOthe amount of DMO converted (mol)/the amount of DMO initiated (mol);
SMGthe amount of DMO consumed (mol)/the amount of DMO converted (mol) to MG;
YMG＝CDMO×SMG。
evaluation of catalytic hydrogenation Activity of silver silicon catalyst prepared in examples 7 to 19 on dimethyl oxalate on stainless steel with inner diameter of 8mmOn a steel fixed bed reactor. The evaluation conditions were: the loading of the catalyst is 0.2g, the reaction temperature is 200 ℃, and the liquid hourly space velocity is 1.0h-1The molar ratio of the hydrogen to the dimethyl oxalate is 80:1, and the reaction pressure is 2.8 MPa. The specific evaluation method is as follows:
0.2g of catalyst (40-60 meshes) is loaded into the isothermal section of the fixed bed reactor, and then 100ml/min of H is added at 350 DEG C2The atmosphere was reduced for 4h to activate the Ag due to oxidation during storage. H with a hydrogen-ester ratio of 80 at 200 ℃ and 2.8MPa2And a methanol solution of dimethyl oxalate (the content of dimethyl oxalate is 15 wt%) respectively enters an evaporator through a mass flow meter and a high performance liquid chromatography constant flow pump, is fully mixed by a gas mixer and then enters a reactor for reaction, and the liquid hourly space velocity is controlled to be 1.0h-1. The exit gas stream was sampled using an automatic six-way valve system and then quantitatively analyzed using an on-line gas chromatograph, a hydrogen flame ionization detector, a KB-Wax capillary column (30m x 0.32mm x 0.25 μm) with 30min intervals. Calculating CDMO、SMGAnd YMGAs shown in table 1.
This example uses the following two references of catalysts and their catalytic performance compared to the catalysts and their catalytic performance of the invention prepared in examples 7-19. In the two documents, carriers different from the present invention are respectively adopted to prepare a silver-based catalyst with a silver loading of not less than 10 wt% by an impregnation method. Wherein:
the first document: patent CN105363438A, example 7 of which is that a mixed carrier composed of silica, titania, zirconia and molecular sieve alumina is loaded with 10.03 wt% of Ag by an impregnation method to obtain a catalyst Ag/M-SiO2. Catalyst Ag/M-SiO2The average diameter of the medium Ag particles was 22 nm. According to the description of the patent, the evaluation conditions of the catalyst of example 7 are: the loading of the catalyst is 0.2g, the reaction temperature is 205 ℃, and the liquid hourly space velocity is 0.9h-1The molar ratio of the hydrogen to the dimethyl oxalate is 80:1, and the reaction pressure is 2.8 MPa. And (3) reaction results: the conversion of dimethyl oxalate was 98.5% and the selectivity of methyl glycolate was 89.1%.
The second document: journal articles CATAL COMMON, 2013,40(19),129-13And 3, loading 10 wt% of Ag on the SBA-15 mesoporous molecular sieve carrier by the catalyst preparation part through an impregnation method to obtain the catalyst Ag/SBA-15. According to the journal literature, the catalyst was evaluated under the following conditions: the loading of the catalyst is 0.2g, the reaction temperature is 200 ℃, and the liquid hourly space velocity is 0.6h-1The molar ratio of the hydrogen to the dimethyl oxalate is 80:1, and the reaction pressure is 3 MPa. And (3) reaction results: the conversion rate of dimethyl oxalate was 100% and the selectivity of methyl glycolate was 94.0%.
The data of the results of the evaluation of the catalytic performance of the relevant catalysts of the above two documents are also shown in Table 1.
TABLE 1 evaluation results of catalytic Performance of catalysts
Figure BDA0002169746200000151
The average particle size of Ag in examples 7-19 in Table 1 was determined by TEM photograph analysis and dispersion of Ag by dynamic chemisorption hydroxide titration.
As can be seen from the results in table 1, the Ag dispersion degree of the silver-silicon catalyst of the present invention is large, and the utilization rate of Ag particles in the catalytic reaction is high. The silver loading of the catalyst is only 3 wt% and 5 wt%, but the DMO conversion rate is high and almost reaches 100%, the MG selectivity is more than or equal to 94.9%, the highest MG selectivity can reach 97.2%, the yield is more than or equal to 94.3, and the highest DMO conversion rate can reach 97.2%.
Under the conditions of same catalyst filling amount and similar reaction conditions, the catalyst Ag/M-SiO2The DMO conversion rate, the MG selectivity and the yield of the catalyst are obviously lower than those of the catalyst, and the Ag loading is far higher than that of the catalyst. Under the conditions of the same catalyst loading and similar reaction conditions, although the Ag loading of the catalyst Ag/SBA-15 reaches 10 wt%, the MG selectivity and the yield are still lower than those of the catalyst prepared by the invention.
It is readily understood by those skilled in the art that lower catalytic temperature and higher liquid hourly space velocity conditions will result in lower DMO conversion and lower MG yield under otherwise identical catalytic conditions. Whereas the Ag loading of the present invention is no greater than 5 wt% and even moreThe selectivity and the yield of the obtained methyl glycolate are higher than those of the catalyst Ag/M-SiO2And selectivity and yield of catalyst Ag/SBA-15 to methyl glycolate.
In conclusion, the catalyst Ag/M-SiO2And the utilization rate of Ag particles in Ag/SBA-15 in catalytic reaction is lower, while the utilization rate of the Ag particles in the catalytic reaction is higher, and the silver-silicon catalyst has very excellent catalytic activity. And because the loading capacity of the noble metal silver is obviously reduced, the cost for preparing the silver-silicon catalyst is obviously reduced, and the silver-silicon catalyst is more beneficial to the industrial application of the silver-based catalyst, thereby providing a good way for the industrial application of the silver-based catalyst.
Example 21 evaluation of catalyst stability
Using the 3Ag1/N1M1 catalyst prepared in example 7 and the 3Ag2/N2M2 catalyst prepared in example 8, the stability of each of the two catalysts was evaluated according to the catalytic performance test method of example 20, CDMO、SMG、YMGThe results are shown in tables 2 and 3:
TABLE 2 evaluation of catalyst stability with 3Ag1/N1M1
Figure BDA0002169746200000161
Figure BDA0002169746200000171
As shown in Table 2, the silver silicon catalyst 3Ag1/N1M1 prepared in example 7 still maintained a methyl glycolate yield of 95.0% or more after 240h reaction evaluation. Analysis of the catalyst 3Ag1/N1M1 after 240h reaction found: the Ag dispersion was 0.310. The above results show that the silver silicon catalyst 3Ag1/N1M1 prepared in example 7 has good stability.
TABLE 3 evaluation of stability of 3Ag2/N2M2 catalyst
Time (h) CDMO SMG YMG
8 100 96.1 96.1
24 99.8 95.9 95.7
48 99.5 95.8 95.3
72 99.1 95.6 94.7
96 98.8 95.5 94.4
120 98.6 95.4 94.1
144 98.4 95.2 93.7
168 98.1 95.0 93.2
192 98.0 95.1 93.2
216 98.1 95.2 93.4
240 98.1 95.1 93.3
As seen from Table 3, the silver silicon catalyst 3Ag2/N2M2 prepared in example 8 still maintained a methyl glycolate yield of 93.0% or more after 240h reaction evaluation. Analysis of the catalyst 3Ag2/N2M2 after 240h reaction found: the dispersity of Ag is 0.181. The above results show that the silver silicon catalyst 3Ag2/N2M2 prepared in example 8 has good stability.
The stability test shows that the silver-silicon catalyst prepared by the invention has good catalytic stability and long service life, reduces the use cost of the catalyst and is beneficial to the industrial application of the silver-based catalyst.
The embodiments of the present invention have been described in detail, but the embodiments are merely examples, and the present invention is not limited to the embodiments described above. Any equivalent modifications or alterations to this practice will occur to those skilled in the art and are intended to be within the scope of this invention. Accordingly, equivalent changes and modifications made without departing from the spirit and scope of the present invention should be covered by the present invention.

Claims (10)

1. The preparation method of the silver-silicon catalyst is characterized by comprising the following steps:
(1) carrying out amination treatment on the mesoporous silica nano-microspheres to obtain aminated mesoporous silica nano-microspheres;
(2) loading nano silver particles on the aminated mesoporous silica nano microspheres obtained in the step (1) by adopting an in-situ reduction method: ultrasonically dispersing the aminated mesoporous silica nano microsphere in the step (1) in ethanol according to the formula, adding an ethanol solution of silver salt, stirring for 1-6 hours at 10-40 ℃, reducing by using a reducing agent at-10-90 ℃, and finally performing centrifugal separation, washing and drying to obtain a nano-silver-loaded silver-silicon catalyst of the aminated mesoporous silica nano microsphere;
the silver salt is selected from one or more of silver nitrate, silver acetate, silver sulfate or silver lactate; the reducing agent is selected from one of sodium borohydride, hydrazine hydrate, formaldehyde, ascorbic acid, ethylene glycol and ethanol;
the mass-to-volume ratio of the aminated mesoporous silica nano microsphere to ethanol for ultrasonic dispersion is 1g (50-100) ml; the mass ratio of the aminated mesoporous silica nano microsphere to the silver salt is 1 (0.03-0.1); the molar ratio of silver element in the silver salt to the reducing agent is 1 (2-10).
2. The method for preparing the silver-silicon catalyst according to claim 1, wherein the mesoporous silica nanospheres are prepared by the following method:
adding triethanolamine with the formula amount into a deionized water solution of a cationic surfactant to serve as a water phase; dissolving tetraethoxysilane in cyclohexane to obtain an oil phase; adding the oil phase into the water phase, and stirring to react for 12-36 h; after the reaction is finished, carrying out centrifugal separation, washing, drying and roasting to obtain the mesoporous silica nano-microsphere;
the mass volume ratio of the cationic surfactant to the deionized water is 1g (6-20) ml; the mass ratio of the cationic surfactant to the triethanolamine is 1 (0.02-0.04); the mass ratio of the cationic surfactant to the tetraethoxysilane and the cyclohexane is 1 (0.4-0.6) to 1.5-2.5.
3. The method of preparing a silver silicon catalyst according to claim 2, wherein the cationic surfactant is one or two selected from the group consisting of cetyltrimethylammonium chloride and cetyltrimethylammonium bromide.
4. The method for preparing a silver-silicon catalyst according to claim 1, wherein the amination step comprises:
ultrasonically dispersing the mesoporous silica nano microspheres in toluene according to the mass ratio of 1 (10-100), then adding a silane coupling agent according to the mass ratio of 1 (0.2-1), refluxing for 8-24 hours at 100-120 ℃, and then performing centrifugal separation, washing and drying to obtain the aminated mesoporous silica nano microspheres.
5. The preparation method of the silver-silicon catalyst according to claim 4, wherein the mass ratio of the mesoporous silica nano-microspheres to toluene is 1 (30-100); the mass ratio of the mesoporous silica nano microspheres to the silane coupling agent is 1 (0.33-1), and the mesoporous silica nano microspheres are refluxed for 8-12 hours at the temperature of 110-120 ℃.
6. The method for preparing the silver-silicon catalyst according to claim 4, wherein the silane coupling agent is one or two selected from the group consisting of 3-aminopropyltrimethoxysilane and 3-aminopropyltriethoxysilane.
7. The silver silicon catalyst prepared by the method for preparing a silver silicon catalyst according to any one of claims 1 to 6.
8. The silver-silicon catalyst of claim 7, wherein the diameter of the mesoporous silica nanospheres is controllable in the range of 150-500 nm, and the pore diameter is controllable in the range of 4-10 nm; the pore canal of the mesoporous silica nano microsphere is in a central divergent slit shape, and the controllable range of the pore canal length is 75-250 nm.
9. The silver-silicon catalyst as recited in claim 7, wherein the particle size of the nano silver particles is controllable within a range of 3 to 14 nm.
10. Use of the silver silicon catalyst according to any one of claims 7 to 9 for catalyzing the reaction of hydrogenation of dimethyl oxalate to methyl glycolate.
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CN114225900A (en) * 2021-12-22 2022-03-25 卡兰途(浙江)环保科技有限公司 Functionalized HMS molecular sieve adsorbent for removing impurities from automobile urea aqueous solution and preparation method and application thereof
CN114225900B (en) * 2021-12-22 2024-01-23 卡兰途(浙江)环保科技有限公司 Functional HMS molecular sieve adsorbent for removing impurities from vehicle urea aqueous solution and preparation method and application thereof
CN114917900A (en) * 2022-04-15 2022-08-19 华东理工大学 Eggshell type silver-silicon catalyst and preparation method and application thereof
CN114917900B (en) * 2022-04-15 2023-12-01 华东理工大学 Eggshell type silver-silicon catalyst and preparation method and application thereof

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