CN116959599A - Method for designing and calculating reaction mechanism model of supported molecular sieve for catalytic synthesis of propylene carbonate - Google Patents

Method for designing and calculating reaction mechanism model of supported molecular sieve for catalytic synthesis of propylene carbonate Download PDF

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CN116959599A
CN116959599A CN202310921071.4A CN202310921071A CN116959599A CN 116959599 A CN116959599 A CN 116959599A CN 202310921071 A CN202310921071 A CN 202310921071A CN 116959599 A CN116959599 A CN 116959599A
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耿赛
牛世元
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Qingdao University of Science and Technology
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    • B01J2229/10—After treatment, characterised by the effect to be obtained
    • B01J2229/18—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself
    • B01J2229/186—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself not in framework positions

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Abstract

The invention provides a method for designing and calculating a reaction mechanism model of a supported molecular sieve for catalyzing and synthesizing propylene carbonate. The invention provides a synthesis method for loading single metal on an SBA-15 molecular sieve, which can be used as an ideal heterogeneous catalyst for catalyzing Propylene Oxide (PO) and carbon dioxide to synthesize cyclic carbonate, so as to realize the green conversion of carbon dioxide. Compared with the traditional method for synthesizing the cyclic carbonate, the synthesis process does not use toxic and harmful reagents, has mild reaction conditions, higher synthesis yield and selectivity and is economicalGood and has better industrial application prospect. Meanwhile, the invention also provides a method for researching CeO 2 Catalytic CO 2 A simulation method for researching reaction mechanism and performance of propylene carbonate directly synthesized by propylene oxide. Establishing CeO by using Gaussian software 2 All reactants, transition states and molecular models of products in the catalytic process infer possible reaction mechanisms, and the final reaction mechanism is determined by calculating energy barriers, namely, the supported metal activates propylene oxide to form an alkyl carbonate intermediate, and the cyclic carbonate is finally formed by ring closure. The invention realizes the green conversion of carbon dioxide and simultaneously determines CO 2 Has important significance in the aspect of reaction mechanism for directly synthesizing propylene carbonate with propylene oxide, and is designed to be efficient CeO 2 The base catalyst provides a theoretical basis.

Description

Method for designing and calculating reaction mechanism model of supported molecular sieve for catalytic synthesis of propylene carbonate
Technical Field
The invention belongs to the technical field of carbonate materials, and particularly relates to a method for calculating a supported molecular sieve design and a reaction mechanism model for catalyzing and synthesizing propylene carbonate.
Background
With the rapid development of industry and economy, the human living standard is increasingly improved, the demand for energy is increasingly greater, and fossil fuels such as coal, petroleum, natural gas and the like are main sources of energy acquired by human beings. Combustion of fossil fuels produces large amounts of carbon dioxide. CO 2 The greenhouse effect is directly exacerbated by the increase in emissions. In the 20 th century, CO 2 The annual average air temperature increases by 0.5-0.8 ℃, and the global sea level rises by 1-2 mm each year on average. In the last century, the actual temperature rise rate of the earth was increased by more than 30 times over the past. At the current rate of climate warming, himalayan glaciers will disappear by 2035. Therefore, global climate warming causes the melted glacier sea level to rise, land drought and desertification area to increase, extreme weather such as extremely hot in summer and extremely cold in winter increases, animals lose living natural families, human beings, animals and plants are threatened by diseases, insects and poison, and natural disasters on the earth are dramatically increased. CO 2 As a culprit for causing greenhouse effect, the reduction of the emission is urgent, and scientists are urgent to recycle the waste water to suppress CO 2 And no emission is controlled.
Based on CO 2 As the characteristics of low cost and abundant resources of carbon resources, the utilization of carbon dioxide is becoming more and more widespread, and the carbon dioxide is converted into valuable fuels and chemicals, so that not only can the environmental pollution be reduced, but also the economic value of the carbon dioxide can be realized, and the sustainable development strategy of the current society is followed. CO 2 The chemical utilization of (a) mainly comprises solar thermochemical conversion, plasma chemical conversion, electrochemical conversion, photochemical conversion, catalytic conversion and the like. Currently, CO 2 The catalytic conversion of (C) is a research hotspot, various fuels can be generated by carrying out catalytic hydrogenation on the catalyst, and the catalyst can be reacted with an epoxy compound to prepare a high polymer material and a fine chemical product.
Propylene carbonate has the molecular formula C 4 H 6 O 3 PC for short, wherein the molecular structure contains carbonyl, ester group and methylFunctional groups such as a group. Propylene carbonate is a non-toxic, readily biodegradable and environmentally friendly commodity chemical. The oxygen content in the molecule is higher, and can participate in various chemical reactions. PC is a very versatile fine chemical that can be used industrially as a polar aprotic solvent, an electrolyte solution in a battery, a precursor for forming polycarbonate, a pharmaceutical intermediate, etc., wherein the synthesized PC can be used as an intermediate for a chemical combination reaction and continues to undergo transesterification with various alcohols having an alkyl group to form dialkyl carbonates. At present for CO 2 Maximizing resource utilization is achieved by using propylene oxide and CO 2 PC is synthesized for the reaction raw material, and the reaction is a green and economic synthesis path with 100% of atom utilization rate. But due to CO 2 Is extremely inactive, activates CO 2 The process is very difficult. The forward progress of cycloaddition reactions therefore generally requires the addition of a certain amount of catalyst, and it is therefore of great research importance to try to synthesize a catalyst with a high catalytic effect. Heterogeneous catalysts are widely used because of their simple separation and ease of flow operations. Several methods have been reported using metal supported molecular sieve catalysis, but the reaction mechanism of Ce metal supported molecular sieve catalysts is not well understood. CO determined by the invention 2 The reaction mechanism for directly synthesizing propylene carbonate with propylene oxide is to design high-efficiency CeO 2 The base catalyst provides a theoretical basis.
To sum up, CO 2 The propylene carbonate synthesized directly with propylene oxide can not only effectively utilize CO 2 The resources can reduce the emission of greenhouse gases, and can also produce organic green chemical products PC. CeO (CeO) 2 The surface of the catalyst has double functional acid-base sites and has certain catalytic activity for the reaction. According to the current research situation, for CeO 2 The reaction mechanism of (2) has been studied only slightly. The subject mainly adopts a Density Functional Theory (DFT) method to reveal CeO 2 The mechanism of the catalytic reaction is clarified, and the influence of electrostatic potential and weak interaction in the reaction process is clarified so as to obtain the CeO with high activity 2 A base catalyst.
Disclosure of Invention
The invention aims to provide a synthesis method of a supported active single-metal molecular sieve catalyst, which is characterized in that a single-metal in metal salt and Si element in a molecular sieve are heated in absolute ethyl alcohol according to a molar ratio of 1:4-20, stirred and fully reacted, and separated, dried and calcined to obtain the supported active single-metal molecular sieve catalyst.
The synthesis steps of the metal element loaded molecular sieve are as follows:
(1) Adding weighed cerium nitrate hexahydrate and SBA-15 molecular sieve into 20mL absolute ethyl alcohol at one time, wherein the molar ratio of metal elements in the cerium nitrate hexahydrate to Si elements in the SBA-15 molecular sieve is 1:4-20, stirring for 12h in a constant-temperature water bath at 78 ℃, then sending into a drying oven at 100 ℃ for drying for 3-6 h, and finally sending into a muffle furnace with a set calcination program for calcination to obtain the active single metal loaded molecular sieve catalyst. After synthesis, the mixture is placed in a shady environment for sealing storage.
(2) And the temperature of the muffle furnace is raised to 550 ℃ at the speed of 2 ℃/min, and the temperature is kept for 4 hours.
The second object of the invention is to provide a method for synthesizing cyclic carbonate by catalyzing carbon dioxide and propylene oxide by a supported monometal molecular sieve catalyst, which comprises the following steps:
(1) Sequentially placing the prepared metal-loaded molecular sieve catalyst, tetrabutylammonium iodide and epoxypropane into a reaction kettle, introducing carbon dioxide, and sealing the reaction kettle;
(2) Then placing the reaction kettle on a magnetic stirring table, and starting magnetic stirring;
(3) After the reaction is finished, transferring all reagents in the reaction kettle into a reagent tube, and performing ultrasonic oscillation;
(4) Placing the product obtained after ultrasonic oscillation into a centrifuge for separation, wherein the obtained supernatant is a reaction product and a reactant, and the precipitate is the active monometal-loaded molecular sieve catalyst;
(5) And (3) carrying out regeneration and recycling on the active single-metal supported molecular sieve catalyst after the reaction is finished.
Preferably, the SBA-15 has a purity of 99.99% in the feedstock of the active single metal supported molecular sieve catalyst.
Preferably, in the raw material of the active single metal supported molecular sieve catalyst, the purity of the active single metal salt is 99% or more.
Preferably, the active monometal salt and SBA-15 molecular sieve are placed in 20mL absolute ethanol and stirred for 12h at 78℃in a constant temperature water bath.
Preferably, the product of the reaction of the active monometal salt and the SBA-15 molecular sieve is sent to a drying oven at 100 ℃ to be dried for 3 to 6 hours.
Preferably, the muffle furnace calcination procedure is set to heat up to 550 ℃ at a rate of 2 ℃/min, and the temperature is kept for 4 hours.
Preferably, the saturation magnetization of the magnetic imidazole-based iron-based ionic liquid is 0.4emu g -1 。
Preferably, the supported active monometal molecular sieve catalyst is insoluble in a catalytic reaction system, catalyst solid particles are separated by a method of centrifugation, sedimentation and filtration, and the catalyst can be recycled.
The third purpose of the invention is to obtain possible reaction mechanism through theoretical calculation and verify the obtained reaction mechanism through visual software.
The calculation steps are as follows:
(1) Referring to the relevant paper, a calculation method and a mixed group using PEB0 are determined, wherein the I atom adopts an SDD pseudopotential, the Ce atom adopts an MWB47 pseudopotential, and other atoms adopt a 6-31G (d) group. And establishing a molecular layer model aiming at reactants in the reaction process, and carrying out structural optimization and vibration frequency calculation on the molecular layer model.
(2) According to the presumed reaction mechanism, flexible scanning is carried out on O and C of propylene oxide by utilizing a method that a keyword is opt=modred, so that C atoms are gradually far away from O atoms, calculated potential energy is firstly increased and then decreased, the highest point of the potential energy is an unstable transition state, the transition state is calculated by utilizing a TS method, and reactants and products are determined by utilizing a irc method.
(3) Repeating the steps to obtain all the molecular structures of the reaction transition state and the product; wherein CO is 2 The coupling process is to CO 2 C atom of (C) and epoxyFlexible scanning of propane O atom, molecular ring forming process of CO 2 Flexible scanning between the oxygen atom and the C atom attached to I.
(4) The energy of the energy barrier, the energy of the LUMO and the energy of the HOMO orbits are searched, an energy barrier diagram is statistically drawn, a static potential diagram, a weak interaction diagram and the like of the system are obtained by using visual software such as Multiwfn, gnuplot, VMD, and the obtained reaction mechanism is verified.
The result of the calculation is: ce and O atoms are mutually complexed, and I-in the first step transition state nucleophilic attack the second carbon atom with smaller hollow in propylene oxide through an SN1 mechanism, so that the ring opening process is promoted. The main role of KI is to promote ring opening and as a stabilizer for the intermediate product. 28.6kcal/mol. The next step is CO 2 Coupling with activated intermediate product, CO 2 All adsorb on ring-opened O, the energy of the calculated transition state is obviously higher than that of the product, which indicates that the metal-supported catalyst is suitable for catalyzing CO 2 Since this transition state has an energy barrier protection against CO generation by decomposition 2 。CO 2 The last step of the cycloaddition reaction is the ring closure of the molecule, in the course of which O attacks the iodide bound C atom, I - Anions close to K + The cation generates PC molecules, and the regeneration of the catalyst is completed. The energy barrier of this process is 22.7kcal/mol. And meanwhile, the conclusion that the LUMO-HOMO energy gap has positive correlation with the energy barrier is drawn, which shows that the obtained transition state is unstable.
In the open loop process, I - Obviously negatively charged and nucleophilic attack on positively charged carbon atoms. In the intramolecular ring closure process, CO 2 The O atom of (C) attacks the positively charged C atom in the ring-opened intermediate product, while I-is removed. The local maximum average ESP value of Ce atoms of Ce-SBA-15/KI is determined to be 2040.14kcal/mol. The interaction force between I-and C of PO approaches-0.03 au in the ring opening process, which indicates that the attraction effect exists between I-and C, and the I-plays a role in promoting ring opening. While CO in a closed loop process 2 Has only a weak van der Waals effect on the intermediate product C and has a strength of only-0.01 au.
Detailed Description
It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the invention. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
The invention aims to provide a synthesis method of a supported active single-metal molecular sieve catalyst, which is characterized in that a single-metal in metal salt and Si element in a molecular sieve are heated in absolute ethyl alcohol according to a molar ratio of 1:4-20, stirred and fully reacted, and separated, dried and calcined to obtain the supported active single-metal molecular sieve catalyst.
The synthesis steps of the metal element loaded molecular sieve are as follows:
(1) Adding weighed cerium nitrate hexahydrate and SBA-15 molecular sieve into 20mL absolute ethyl alcohol at one time, wherein the molar ratio of metal elements in the cerium nitrate hexahydrate to Si elements in the SBA-15 molecular sieve is 1:4-20, stirring for 12h in a constant-temperature water bath at 78 ℃, then sending into a drying oven at 100 ℃ for drying for 3-6 h, and finally sending into a muffle furnace with a set calcination program for calcination to obtain the active single metal loaded molecular sieve catalyst. After synthesis, the mixture is placed in a shady environment for sealing storage.
(2) And the temperature of the muffle furnace is raised to 550 ℃ at the speed of 2 ℃/min, and the temperature is kept for 4 hours.
The second object of the invention is to provide a method for synthesizing cyclic carbonate by catalyzing carbon dioxide and propylene oxide by a supported single-metal molecular sieve catalyst, which comprises the following steps:
(1) Sequentially placing the prepared molecular sieve catalyst with metal load, tetrabutylammonium iodide and epoxypropane into a reaction kettle, introducing carbon dioxide, and sealing the reaction kettle;
(2) Placing the reaction kettle on a magnetic stirring table, and starting magnetic stirring;
(3) After the reaction is finished, transferring all reagents in the reaction kettle into a reagent tube, and performing ultrasonic oscillation;
(4) Placing the product obtained after ultrasonic oscillation into a centrifuge for separation, wherein the obtained supernatant is a reaction product and a reactant, and the precipitate is an active single-metal supported molecular sieve catalyst;
(5) And (3) carrying out regeneration and recycling on the active single-metal supported molecular sieve catalyst after the reaction is finished.
Preferably, the purity of the SBA-15 in the feedstock of the active single metal supported molecular sieve catalyst is 99.99%.
Preferably, in the raw material of the active single metal supported molecular sieve catalyst, the purity of the active single metal salt is 99% or more.
Preferably, the active monometal salt and SBA-15 molecular sieve are placed in 20mL absolute ethanol and stirred for 12h at 78℃in a constant temperature water bath.
Preferably, the product of the reaction of the active monometal salt and the SBA-15 molecular sieve is sent to a drying oven at 100 ℃ to be dried for 3 to 6 hours.
Preferably, the muffle furnace calcination procedure is set to heat up to 550 ℃ at a rate of 2 ℃/min, and the temperature is kept for 4 hours.
Preferably, the saturation magnetization of the magnetic imidazole-based iron-based ionic liquid is 0.4emu g -1 。
Preferably, the supported active monometal molecular sieve catalyst is insoluble in a catalytic reaction system, catalyst solid particles are separated by a method of centrifugation, sedimentation and filtration, and the catalyst can be recycled.
The third purpose of the invention is to obtain possible reaction mechanism through theoretical calculation and verify the obtained reaction mechanism through visual software.
The calculation steps are as follows:
(1) Referring to the relevant paper, a calculation method and a mixed group using PEB0 are determined, wherein the I atom adopts an SDD pseudopotential, the Ce atom adopts an MWB47 pseudopotential, and other atoms adopt a 6-31G (d) group. And establishing a molecular layer model aiming at reactants in the reaction process, and carrying out structural optimization and vibration frequency calculation on the molecular layer model.
(2) According to the presumed reaction mechanism, flexible scanning is carried out on O and C of propylene oxide by utilizing a method that a keyword is opt=modred, so that C atoms are gradually far away from O atoms, calculated potential energy is firstly increased and then decreased, the highest point of the potential energy is an unstable transition state, the transition state is calculated by utilizing a TS method, and reactants and products are determined by utilizing a irc method.
(3) Repeating the steps to obtain all the molecular structures of the reaction transition state and the product; wherein CO is 2 The coupling process is to CO 2 Is flexibly scanned by C atoms of propylene oxide and O atoms of propylene oxide, and the molecular ring forming process is to CO 2 Flexible scanning between the oxygen atom and the C atom attached to I.
(4) The energy of the energy barrier, the energy of the LUMO and the energy of the HOMO orbits are searched, an energy barrier diagram is statistically drawn, a static potential diagram, a weak interaction diagram and the like of the system are obtained by using visual software such as Multiwfn, gnuplot, VMD, and the obtained reaction mechanism is verified.
The result of the calculation is: ce and O atoms are complexed with each other, I in the first transition state - Nucleophilic attack of the secondary carbon atom with smaller hollow space in propylene oxide is performed through an SN1 mechanism, so that the ring opening process is promoted. The main role of KI is to promote ring opening and as a stabilizer for the intermediate product. 28.6kcal/mol. The next step is CO 2 Coupling with activated intermediate product, CO 2 All adsorb on ring-opened O, the energy of the calculated transition state is obviously higher than that of the product, which indicates that the metal-supported catalyst is suitable for catalyzing CO 2 Since this transition state has an energy barrier protection against CO generation by decomposition 2 。CO 2 The last step of the cycloaddition reaction is the ring closure of the molecule, in the course of which O attacks the iodide bound C atom, I - Anions close to K + The cation generates PC molecules, and the regeneration of the catalyst is completed. The energy barrier of this process is 22.7kcal/mol. And meanwhile, the conclusion that the LUMO-HOMO energy gap has positive correlation with the energy barrier is drawn, which shows that the obtained transition state is unstable.
During the ring opening process, I-is significantly negatively charged and nucleophilic attacks the positively charged carbon atom. In the intramolecular ring closure process, CO 2 The O atom of (2) attacks the positively charged C atom in the ring-opened intermediate product while removing I - . Determining the Ce atom local maximum of Ce-SBA-15/KIThe large average ESP value was 2040.14kcal/mol. In the open loop process I - Interaction with C of PO was approximately-0.03 au, indicating I - There is attraction between C and I - Plays a role in promoting ring opening. While CO in a closed loop process 2 Has only a weak van der Waals effect on the intermediate product C and has a strength of only-0.01 au.
The method for catalyzing carbon dioxide and propylene oxide to synthesize cyclic carbonate by using the supported active metal molecular sieve catalyst is detailed below, and specific embodiments for calculating the relevant reaction mechanism are described in detail.
Example 1
Absolute ethanol (about 20 mL), ce (NO) were sequentially added to a 250mL Erlenmeyer flask 3 ) 3 ·6H 2 O (0.138 g,0.0006mol, 99% purity) and SBA-15 (0.25 g, 0.04 mol, 99.9% purity) were placed in a constant temperature water bath set at 78℃and stirred for about 12 hours, with a molar ratio of Ce element to Si element of 1:6.7 (0.15) being ensured. Completely removing liquid phase of the product in a drying oven at 100deg.C, taking out, grinding, calcining in a muffle furnace at a speed of 2deg.C/min to 550deg.C, maintaining the temperature for 4 hr, cooling, and taking out to obtain Ce (NO) 3 ) 3 SBA-15 (0.15) catalyst.
0.05g of synthesized Ce (NO) was added to the reaction vessel in this order 3 ) 3 SBA-15 (0.15) catalyst, 0.1g tetrabutylammonium iodide and 2.4mL propylene oxide, a rotor is added into a reaction kettle, the reaction kettle with the added reagent and the rotor is sealed, a high-pressure carbon dioxide gas cylinder is connected, a proper amount of carbon dioxide gas is introduced for replacing the gas in the kettle in four times, and after the gas replacement is completed, the carbon dioxide gas of 1.0MPa is introduced into the kettle. Placing the reaction kettle on a magnetic stirring table with the temperature of 80 ℃ set, starting magnetic stirring for about 8 hours, taking down the reaction kettle after the reaction is finished, taking out all reagents in the reaction kettle after pressure relief, filling the reagents into a reagent tube, carrying out ultrasonic vibration on the reagents obtained by the reaction, putting the reagents into a centrifugal machine, centrifuging for 4 minutes at 8000r/min, taking a supernatant product after the centrifugation is finished, bottling, and storing the obtained precipitate.
The resulting precipitate was regarded as a pure catalyst component, the carbon dioxide synthesis reaction was repeated again, and the centrifuged product was obtained in the same operation, and the analysis product was tested again.
The obtained supernatant is subjected to gas chromatography analysis, TEM characterization and infrared spectrum analysis, which proves that the yield of the obtained product is higher, and CeO 2 Has been successfully supported on the surface of SBA-15 molecular sieves, and Ce is supported on the surface of SBA-15 at the expense of silanol groups.
The following is done by means of software Gaussian: a. and (3) a model is newly built in Gaussview according to the structure of Ce/SBA-15, a reasonable molecular coordinate is obtained, the spin severity of the system is 1, dispersion correction is carried out by using a keyword em=g3bj, a keyword genecp is input by using a mixed base group, the mixed base group is input, and structural optimization and frequency calculation are carried out. b. And adopting an opt=modred flexible scanning method to scan the bond length between O and C of the epoxypropane, and obtaining the highest potential energy value through calculation. c. And searching a transition state for the model and the inferred reaction mechanism by using a TS method, determining a transition state model, and perfecting the reaction mechanism process through a plurality of transition state models. Wherein the CO2 coupling process is a flexible scanning of the C atoms of CO2 and the O atoms of propylene oxide, and the molecular looping process is a flexible scanning between one oxygen atom of CO2 and the C atom connected with I. d. On the basis, the cerium oxide model and a plurality of transition state energies are calculated, the surface energy, the adsorption energy and the energy barrier are calculated by using a formula, and finally a reasonable reaction mechanism is obtained. e. And analyzing electrostatic potential and weak interaction of the system by utilizing various visualization software, and verifying the obtained reaction mechanism based on the electrostatic potential and weak interaction.
Example 2
Absolute ethanol (about 20 mL), ce (NO) were sequentially added to a 250mL Erlenmeyer flask 3 ) 3 ·6H 2 O (0.138 g,0.0006mol, 99% purity) and SBA-15 (0.25 g,0.004mol, 99.9% purity) were placed in a constant temperature water bath set at 78℃and stirred for about 12 hours, with a molar ratio of Ce element to Si element of 1:4 (0.25) being ensured. Completely removing liquid phase of the product in a drying oven at 100deg.C, taking out, grinding, calcining in a muffle furnace at a speed of 2deg.C/min to 550deg.C, maintaining the temperature for 4 hr, cooling, and taking out to obtain Ce (NO) 3 ) 3 SBA-15 (0.25) catalyst.
0.05g of synthesized Ce (NO) was added to the reaction vessel in this order 3 ) 3 SBA-15 (0.25) catalyst, 0.1g tetrabutylammonium iodide and 2.4mL propylene oxide, a rotor is added into a reaction kettle, the reaction kettle with the added reagent and the rotor is sealed, a high-pressure carbon dioxide gas cylinder is connected, a proper amount of carbon dioxide gas is introduced for replacing the gas in the kettle in four times, and after the gas replacement is completed, the carbon dioxide gas of 1.0MPa is introduced into the kettle. Placing the reaction kettle on a magnetic stirring table with the temperature of 80 ℃ set, starting magnetic stirring for about 8 hours, taking down the reaction kettle after the reaction is finished, taking out all reagents in the reaction kettle after pressure relief, filling the reagents into a reagent tube, carrying out ultrasonic vibration on the reagents obtained by the reaction, putting the reagents into a centrifugal machine, centrifuging for 4 minutes at 8000r/min, taking a supernatant product after the centrifugation is finished, bottling, and storing the obtained precipitate.
The resulting precipitate was regarded as a pure catalyst component, the carbon dioxide synthesis reaction was repeated again, and the centrifuged product was obtained in the same operation, and the analysis product was tested again.
The obtained supernatant is subjected to gas chromatography analysis, TEM characterization and infrared spectrum analysis, which proves that the yield of the obtained product is higher, and CeO 2 Has been successfully supported on the surface of SBA-15 molecular sieves, and Ce is supported on the surface of SBA-15 at the expense of silanol groups.
The following is done by means of software Gaussian: a. and (3) a model is newly built in Gaussview according to the structure of Ce/SBA-15, a reasonable molecular coordinate is obtained, the spin severity of the system is 1, dispersion correction is carried out by using a keyword em=g3bj, a keyword genecp is input by using a mixed base group, the mixed base group is input, and structural optimization and frequency calculation are carried out. b. The flexible scanning method of opt=modred is adopted to scan the bond length of O-ion and I-ion of KI of propylene oxide, and the highest potential energy value is obtained through calculation. c. And searching a transition state for the model and the inferred reaction mechanism by using a ts method, determining a transition state model, and perfecting the reaction mechanism process through a plurality of transition state models. Wherein the CO2 coupling process is a flexible scanning of the C atoms of CO2 and the O atoms of propylene oxide, and the molecular looping process is a flexible scanning between one oxygen atom of CO2 and the C atom connected with I. d. On the basis, the cerium oxide model and a plurality of transition state energies are calculated, the surface energy, the adsorption energy and the energy barrier are calculated by using a formula, and finally a reasonable reaction mechanism is obtained. e. And analyzing electrostatic potential and weak interaction of the system by utilizing various visualization software, and verifying the obtained reaction mechanism based on the electrostatic potential and weak interaction.
Example 3
Absolute ethanol (about 20 mL), ce (NO) were sequentially added to a 250mL Erlenmeyer flask 3 ) 3 ·6H 2 O (0.138 g,0.0006mol, 99% purity) and SBA-15 (0.25 g, 0.04 mol, 99.9% purity) were placed in a constant temperature water bath set at 78℃and stirred for about 12 hours, with a molar ratio of Ce element to Si element of 1:6.7 (0.15) being ensured. Completely removing liquid phase of the product in a drying oven at 100deg.C, taking out, grinding, calcining in a muffle furnace at a speed of 2deg.C/min to 550deg.C, maintaining the temperature for 4 hr, cooling, and taking out to obtain Ce (NO) 3 ) 3 SBA-15 (0.15) catalyst.
0.05g of synthesized Ce (NO) was added to the reaction vessel in this order 3 ) 3 SBA-15 (0.15) catalyst, 0.1g tetrabutylammonium iodide and 2.4mL propylene oxide, a rotor is added into a reaction kettle, the reaction kettle with the added reagent and the rotor is sealed, a high-pressure carbon dioxide gas cylinder is connected, a proper amount of carbon dioxide gas is introduced for replacing the gas in the kettle in four times, and after the gas replacement is completed, 2.0MPa of carbon dioxide gas is introduced into the kettle. Placing the reaction kettle on a magnetic stirring table with the temperature of 80 ℃ set, starting magnetic stirring for about 8 hours, taking down the reaction kettle after the reaction is finished, taking out all reagents in the reaction kettle after pressure relief, filling the reagents into a reagent tube, carrying out ultrasonic vibration on the reagents obtained by the reaction, putting the reagents into a centrifugal machine, centrifuging for 4 minutes at 8000r/min, taking a supernatant product after the centrifugation is finished, bottling, and storing the obtained precipitate.
The resulting precipitate was regarded as a pure catalyst component, the carbon dioxide synthesis reaction was repeated again, and the centrifuged product was obtained in the same operation, and the analysis product was tested again.
Subjecting the obtained supernatant to gas chromatography, TEM characterization and infrared spectrum analysis, and provingThe yield of the obtained product is higher, and CeO 2 Has been successfully supported on the surface of SBA-15 molecular sieves, and Ce is supported on the surface of SBA-15 at the expense of silanol groups.
The following is done with the aid of software Gaussian and Gaussian: a. and (3) a model is newly built in Gaussview according to the structure of Ce/SBA-15, a reasonable molecular coordinate is obtained, the spin severity of the system is 1, dispersion correction is carried out by using a keyword em=g3bj, a keyword genecp is input by using a mixed base group, the mixed base group is input, and structural optimization and frequency calculation are carried out. b. The flexible scanning method of opt=modred is adopted to scan the bond length of O-ion and I-ion of KI of propylene oxide, and the highest potential energy value is obtained through calculation. c. And searching a transition state for the model and the inferred reaction mechanism by using a ts method, determining a transition state model, and perfecting the reaction mechanism process through a plurality of transition state models. Wherein the CO2 coupling process is a flexible scanning of O atoms and Ce atoms of propylene oxide, and the molecular ring forming process is a flexible scanning between one oxygen atom of CO2 and a C atom connected with I. d. On the basis, the cerium oxide model and a plurality of transition state energies are calculated, the surface energy, the adsorption energy and the energy barrier are calculated by using a formula, and finally a reasonable reaction mechanism is obtained. e. And analyzing electrostatic potential and weak interaction of the system by utilizing various visualization software, and verifying the obtained reaction mechanism based on the electrostatic potential and weak interaction.
Finally, it should be noted that the above-mentioned embodiments are only preferred embodiments of the present invention, and the present invention is not limited to the above-mentioned embodiments, but may be modified or substituted for some of them by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention. While the foregoing has been described in conjunction with specific examples, it will be understood that they are not intended to limit the scope of the invention, but that various modifications or variations can be made by those skilled in the art without the benefit of the teachings of this invention.

Claims (9)

1. The method for designing and calculating the reaction mechanism model of the supported molecular sieve for catalyzing and synthesizing propylene carbonate is characterized by comprising the following steps:
(1) Adopting an impregnation method, putting a metal salt containing cerium element and an SBA-15 molecular sieve into ethanol for heating, and simultaneously stirring in a water bath for reaction;
(2) Completely removing the liquid phase of the substance after solvent evaporation in a drying oven, and grinding the obtained product;
(3) The obtained product is sent into a muffle furnace for calcination, the muffle furnace is provided with a calcination program, and the loaded single-metal molecular sieve catalyst is obtained after cooling;
(4) Loading Ce-loaded monometal molecular sieve catalyst powder, ethylene oxide and tetrabutylammonium iodide into a reaction kettle together, introducing carbon dioxide, pressurizing and sealing for reaction to generate cyclic carbonate;
(5) And after the catalytic synthesis reaction is finished, separating the supported single-metal molecular sieve catalyst, and carrying out regeneration and recycling.
(6) And establishing a molecular layer model aiming at reactants in the reaction process, carrying out structural optimization and vibration frequency calculation on the molecular layer model, and adopting a reasonable mode to infer a reaction mechanism to determine a transition state structure and a vibration trend. And finally obtaining the molecular level model of the reactant, the transition state and the product.
(7) And (3) counting the energy barrier of the reaction, namely, the difference between the LUMO and HOMO orbits, and establishing a static potential diagram, a weak interaction diagram and the like of the molecules by utilizing various visualization software to establish a final reaction mechanism.
2. The process of claim 1, wherein the active monometal salt and SBA-15 molecular sieve are stirred in 20mL of absolute ethanol heated in a 78 ℃ water bath for 1-3 hours.
3. The process of claim 1, dried in an oven at 100 ℃ for 4-6 hours to completely remove the liquid phase from the catalyst powder. The muffle furnace was set to calcine at a rate of 2 ℃/min to 550 ℃ and incubated for 4 hours.
4. The method of claim 1, wherein the single metal loaded molecular sieve is prepared by the following steps: taking active monometal salt and SBA-15 as raw materials, mixing the raw materials, wherein the molar ratio of the monometal salt to Si element in the molecular sieve is 1:4-20, and heating in a water bath in a reaction container containing 20mL of absolute ethyl alcohol; the water bath set temperature is 78 ℃, the reaction is continuously carried out for 12 hours under constant stirring, the obtained reaction product is sent into a normal pressure drying oven at 100 ℃ for drying for 4-6 hours, the product obtained in the drying oven is sent into a muffle furnace with the set calcination program of 2 ℃/min and the temperature is raised to 550 ℃, and the muffle furnace is kept for 4 hours for calcination, thus obtaining the supported monometal molecular sieve catalyst.
5. The method according to claim 1, wherein the metal element in the single metal salt selected in the preparation of the single metal supported molecular sieve raw material is lanthanide metal represented by Ce.
6. The method according to claim 1, wherein tetrabutylammonium iodide added in the reaction is used as a reaction auxiliary agent, the added mass is 0.05-0.1 g, the actual reaction process is not participated, the carbon dioxide pressure in the reaction kettle is in the range of 0.5-3.0 Mpa, and the reaction temperature is 60-100 ℃.
7. The method of claim 1, wherein the single metal supported molecular sieve catalyst is used in a yield of greater than 90% for the first time and greater than 80% after 3 times of repeated use.
8. The method of claim 1, wherein the single metal supported molecular sieve catalyst is insoluble in reactants and products and can be recycled by direct physical separation.
9. The method of claim 1 wherein the system employs a PBE0 method, wherein SDD pseudopotential is employed for I, MWB47 pseudopotential is employed for Ce and 6-31G (d) mixed-basis set is employed for other atoms. The mechanism is guessed based on the previous study, the transition state is calculated by using a Ts method, the energy of the energy barrier and the energy of the LUMO and HOMO orbits are searched by using the basic function of Gaussview, and the analysis is carried out by using the visualization software such as Multiwfn, gnuplot, VMD.
CN202310921071.4A 2023-07-26 2023-07-26 Method for designing and calculating reaction mechanism model of supported molecular sieve for catalytic synthesis of propylene carbonate Pending CN116959599A (en)

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