Controllable Synthesis Of Mesoporous Metal-doped Silica Microparticles Based On Spray Drying Technology And Their Catalytic Applications

Mesoporous silica materials have attracted considerable interest due to its high specific surface area,ordered pore structures,adjustable pore size and available functional properties.Therefore,it is widely used in the fileds of heterogeneous catalysis,adsorption and separation and so on.The discovery of mesoprous silica SB A-15 with thick pore walls and high stability has become the key research objective in the field of mesoporous materials.However,it is difficult to directly use SBA-15 material in practical catalysis and adsorption,because it is mainly an amorphous form of silica material with a very low active density.Therefore,tremedious efforts have been devoted to the controllable synthesis of functional SBA-15,such as metal doping,nanoparticle loading,and so forth.Generally,direct synthes is and post modification can be applied for the production of functional porous silica materials with acid sites or metal active centers.However,during the preparation of metal-substituted mesoporous SBA-15,Si-O-M(M refers to metal)bonds can be easily dissociated under acidic mediums,inducing formation of "extra-frame work”species.Besides,the synthesis process is usually complicated,and the morphology control and particle size adjustment need to be improved.In the preparation of metal nanoparticles loaded mesoporous silica,metal species tend to be easily aggregated.Complicated processes and special solvents are acquired to achieve high metal dispersion and small size.In order to address these issues,this thesis demonstrated a detailed study about using a novel micro-fluidic-jet spray drying technology(MFJSD)to prepare metal-doped mesoporous silica materials.Functional mesoporous silica microspheres with controllable mogphology,uniform particle size and highly dispersed metal species have been successfully synthesized through adjusting experimental parameters and process conditions.The main research contents of the thesis are as follows.In chapter 3,the focus is ethat how to synthesize mesoporous aluminosilicates with controllable surface morphorlogy,uniform particles size and high hydrothermal stability.Al-SBA-15 microspheres with controllable physicochemical properties and high hydrothermal stability has been successfully prepared by combining the MFJSD technology and and self-assemble method,and this technique process could achieve a large-scale production.The effects of Si/Al molar ratio,solid content,spray drying and calcination temperature on the structure and acid porperties of the resultant Al-SBA-15 microparticles were explred.Al-SBA-15 microspheres with adjustable particle size and porosity were obtained.In addition,the effects of Si/Al molar ratio and solid content on particle formation and morphology transition mechanism were also investigated.The obtained Al-SBA-15 microspheres possess plenty of acid sites,high surface areas and excellent hydrothermal stability,showing efficient acid catalytic performance toward the aldol condensation reaction between benzaldehyde and ethyl alcoholIn chapter 4,the focus is that how to solve the problems that metal species loaded on Al-SBA-15 is prone to migration and agglomeration and it is difficult to synthesize on a large scale.A one-pot spray-drying-assisted assembly methos was adopted to prepare transition and noble metals doped Al-SBA-15 microspheres.The metal dispersion can be improved based on the high surface areas,uniform pore sizes and abundant acid sites of Al-SBA-15 microspheres.No effect of the metal doping on the mesoporous structure of Al-SBA-15 can be observed when doped with different metals.The obtained materials showed high metal dispersion and uniform particle distribution In addition,the surface morphology of Al-SBA-15 particles could be changed from a smooth microsphere to a wrinkled spherical shape when doped with metals of Fe or Pd.In chapter 5,the focus is that how to strengthen the interaction between the support and metals,limit the growth of metal nanoparticles and achieve rapid alloying.Mesoporous silica loaded with highly dispersed metal nanoparticles were successfully synthesized by spray drying assisted post impregantion method.This method is a universal approach,and a variety of mono and bi-metallic nanoparticles can be supported on mesoporous silica.XRD,HRTEM,H2-TPR,XPS and FT-IR show that the spray-drying loading method can produce smaller metal nanoparticle slize,higher dispersity and degree of alloying compared with the traditional wet-impregnation method.The catalytic performance of the typical catalysts PtxNiy/SiO2 in 3-nitrostyrene selective hydrogenation reaction and the effect of catalyst's composition on performance were also explores.