Multifunctionalized Silica Supports: Design,Synthesis And Applications In Catalysis

Nowadays,we live in a prosperous world.While people are constantly improving their quality of life,it is inevitable that greater pressure will be brought to energy supply and environmental protection.Traditional extensive development is no longer in line with today's social concept.In order to achieve the goal of sustainable development,we need to start from the perspective of energy conservation and environmental protection,design more new materials to solve the above problems.Since silica materials can be prepared by different synthesis methods to produce a variety of spatial structures,different silicon source precursors can be selected to change the composition of silica skeleton,and silica materials have high chemical and thermal stability.Therefore,it has been widely used in industrial production and environmental protection in recent years.By designing high activity mesoporous silica supports catalysts,researchers can effectively reduce energy consumption and pollutant emission in chemical production.Mesoporous silica materials have high specific surface area and pore volume,and the active nanoparticles can be loaded into the pores or cavities of the materials to prevent the agglomeration of the active sites in the catalytic reaction.Moreover,due to the rich spatial structure and chemical composition of mesoporous silica materials,supports materials can be designed according to the demand of catalytic reactions.In this paper,from the perspective of functionalized mesoporous silica materials,the spatial structure and skeleton composition of mesoporous silica materials were designed in a diversified way,and new synthesis methods of mesoporous silica materials were explored.In addition,multiple active components were attempted to integrate and prepare new catalysts,and the catalytic performance of these catalysts was studied.In the second chapter,yolk-shell structural mesoporous silica was introduced as materials for limiting the growth of Au nanoparticles.The materials consist of the amino modified core,the inorganic-organic hybrid silica shell,and a narrow space between the core and shell.Because of the presence of amino groups,anions of chloroauric acid are adsorbed to the surface of core.In a hydrogen atmosphere,the reduced gold nanoparticles exist in the narrow space between cores and shells.In this work,the size of metal nanoparticles is small,and the catalyst has high reactivity.At the same time,due to the spatial restriction of the narrow space between the core and shell and the coordination of amino groups,gold nanoparticles are well confined in the narrow space,and no obvious agglomeration occurs during the catalytic reaction.The as-prepared catalyst can completely transform the product in five cycles and maintain good stability.By adjusting the amount of tetraethyl orthosilicate in the synthesis process,we successfully controlled the average size of the narrow space between the core and shell from 1 nm to 6 nm.We found that the diameter of gold nanoparticles with narrower space in the catalysts was smaller,the distribution was more uniform,and the catalytic activity was higher.In the third chapter,we designed a catalyst which is composed of Mn O_x and dendritic mesoporous silica nanoparticle(DMSN)and it can catalyze toluene oxidation at low temperatre.We synthesized dendritic mesoporous silica materials with 30 nm open channels by using surfactants and organic small molecule pore-enlarging agent.The as-prepared dendritic mesoporous materials were calcined at different temperatures.It was found that the amount of hydroxyl group on the surface of mesoporous silica materials decreased with the increase of calcining temperature,and the hydrophobicity of mesoporous materials increased significantly.Mn O_x/DMSN catalysts were prepared by surface adsorption and in-situ oxidation-reduction deposited.Mn O_x particles have good dispersion on the surface of dendritic mesoporous materials,and the mesoporous silica supports at different calcination temperatures has no obvious influence on the chemical properties of Mn O_x.In the catalytic oxidation of toluene,the catalytic activity of Mn O_x/DMSN catalysts which supports were treated at three temperatures is much higher than that of pure Mn O_x,and Mn O_x/DMSN-800 catalysts show the best catalytic activity under a space velocity of 60000 m L/(g h).When the concentration of toluene is 600 ppm,above 90%toluene can be eliminated at 199?,and the conversion temperature of T₅₀ and T₉₀ is obviously lower than that of other catalysts.This indicates that improving the hydrophobicity of the DMSN supports can effectively improve the catalytic activity of Mn O_x catalysts.In the fourth chapter,we designed a photoactive amphiphilic nanoreactor Pt/CDs@PMO.The synthesis routes:(1)the synthesis of inorganic-organic hybrid silica hollow nanotubes,(2)impregnation of carbon dots(CDs)into the nanotubes by solvothermal method,(3)preparing the chloroplast-like catalyst Pt/CDs@PMO by a photo-reduction method.The photoactive nanoreactor is capable of enriching organic substrate from aqueous solution due to its good amphiphilicity.Under natural light conditions,the internal carbon dots can be excited to generate electrons,which directly transferred to the active sites of Pt nanoparticles located on the surface of CDs.The O₂molecules dissolved in the solution were activated by Pt nanoparticles to form singlet oxygen(¹O₂),which selectively oxidized the alcohol to the corresponding aldehyde,and the TOF value of this reaction was 306 h^-1.The photoactivity of the catalyst can be regulated by the loading amount of CDs.The catalysts can be recycled after the reaction.The conversion and selectivity were more than 90%after 10 cycles.The nanoreactor exhibited excellent photocatalytic activity and stability due to the synergistic effect of the amphiphilic mesoporous supports framework,abundant light energy absorption sites and high efficiency catalytic active sites.