Construction Of Composite Catalysts With Different Dimensional Channels And Study Of Their Carbon-carbon Double Bond Epoxidation Performanc

Epoxidation products are an important class of compounds that provide key raw materials for the synthesis of perfumes,drugs,plasticizers,lubricants and fine chemicals.So far,a large number of multiphase catalytic systems have been developed for carbon-carbon double bond epoxidation,among which,silver-based catalysts have shown excellent catalytic activity in olefin epoxidation reactions.In addition,heteropolyacids are widely used for carbon-carbon double bond epoxidation reactions,especially for the epoxidation of unsaturated fatty acid methyl esters,due to their easy dispersion and high catalytic activity.However,these catalytically active components often need to rely on suitable carriers to exert their excellent and stable catalytic activities.Based on this,in this thesis,three different types of multiphase catalysts for carbon-carbon double bond epoxidation were prepared using silica with different dimensional pores（zero-dimensional,one-dimensional and two-dimensional）as carriers and applied to the corresponding carbon-carbon double bond epoxidation reactions.The details are as follows:（1）Preparation of amino-functionalized zero-dimensional（0D）pore hierarchical hollow silica spheres（HHSS）composite catalysts（Ag-NH₂-HHSS）loaded with Ag nanoparticles and their styrene epoxidation performance studies.In this work,the highly dispersed Ag nanoparticles multiphase catalyst for styrene epoxidation（Ag-NH₂-HHSS）was successfully synthesized using amino-functionalized 0D pore HHSS as a carrier,and the effects of Ag loading,molar ratio of C=C to tert-butyl hydroperoxide（TBHP）,catalyst dosage,reaction temperature and reaction time on the styrene epoxidation reaction were investigated.Under the optimal experimental conditions,the conversion of styrene could reach 70.58%and the selectivity of styrene oxidation could reach 80.17%.Based on a series of catalyst characterization results,it is known that the Ag nanoparticles are uniformly dispersed in the 0D pore HHSS,exposing a large amount of metal active components,such that the catalyst has excellent catalytic styrene epoxidation ability.The catalyst cycling stability test revealed that the Ag-NH₂-HHSS could be recycled for five times under the same conditions without any significant degradation in catalytic performance.In addition,the morphological structure of the catalyst did not change throughout the reaction,and the confining effect of the 0D pore HHSS on Ag nanoparticles was retained.This work provides a new idea and method for the development of metal nanoparticles solidly loaded on 0D pore carrier materials to design efficient multiphase catalysts.（2）Preparation of amino-functionalized one-dimensional（1D）pore tubular silica（HSNT）composite catalyst（Ag-NH₂-HSNT）loaded with Ag nanoparticles and its performance study for styrene epoxidation.In this work,highly dispersed Ag nanoparticles were successfully synthesized as a multiphase catalyst for styrene epoxidation（Ag-NH₂-HSNT）using amino-functionalized 1D pore HSNT as a carrier,and the effects of these factors on the catalyst Ag-NH₂-HSNT catalyzed styrene epoxidation were investigated by modulating the Ag loading,C=C to TBHP molar ratio,catalyst dosage,reaction temperature and reaction time.epoxidation.The Ag-NH₂-HSNT catalyst was subjected to a series of characterization and performance tests,and the results showed that the Ag-NH₂-HSNT catalyst exhibited the most excellent epoxidation performance in the styrene epoxidation reaction when the loading of Ag was 7.5%,and the catalyst maintained excellent catalytic performance with good cycling stability after five cycles of use.In addition,characterization of the recycled catalysts showed that the catalysts still maintained good structure and morphology after the reaction,indicating that the prepared 1D pore HSNT carriers have good stability.This work has implications for the design of efficient styrene epoxidation catalysts with1D pore materials loaded with metal nanoparticles.（3）Preparation of layered silica（2D-CS_x）composite catalysts（2D-CS_x-NH₂-HPW）loaded with phosphotungstic acid（HPW）and its performance study of catalytic epoxidation of methyl oleate.In this work,the layered silica composite catalyst（2D-CS_x-NH₂-HPW）with easily accessible,open two-dimensional（2D）transport channels was obtained by uniformly dispersing HPW on layered silica through the positive charge interactions of phosphotungstic acid（PW^-）and amino groups(-NH³⁺).As shown by performance tests,2D-CS_3.5-NH₂-HPW with a length of 300 nm and a diameter of150 nm exhibited significant methyl oleate（MO）epoxidation activity(X_MO=91.68%)and epoxidized methyl oleate（EMO）selectivity(S_EMO=90.03%)in only 4 h,which is better than most of the currently reported epoxidation catalysts in terms of catalytic efficiency and selectivity.The open 2D transport channel greatly improves the material transfer efficiency,and the high dispersion of HPW enhances the utilization of active components.The positive charge interactions between phosphotungstic acid（PW^-）and amino groups(-NH³⁺)greatly improved the cycling stability of the catalyst,resulting in the 2D-CS_x-NH₂-HPW catalyst with excellent catalytic performance and good cycling stability for the epoxidation of methyl oleate.This work effectively shortens the reaction time of methyl oleate epoxidation by using the 2D channel of the catalyst,which provides a new way to develop a more efficient catalyst for methyl oleate epoxidation.