Synthesis Of Functional Mesoporous Materials And Study For Their Catalytic Properties

Mesoporous materials have been widely studied in the fields of biomedicine,energy and environment due to their unique advantages such as different skeleton composition,flexible surface chemical properties and rich and diverse mesoscopic structures.At present,the most mature mesoporous materials are mesoporous carbon and mesoporous silica.Because of its high specific surface area,large pore volume,uniform and adjustable pore size and good stability,mesoporous materials have broad application prospects in many fields such as catalysis,sensing,adsorption and separation,drug loading and so on.However,it is still challenging to design and synthesize functional mesoporous materials according to the needs of practical applications.In this paper,mesoporous carbon and silica materials with hollow structure and specific surface chemical structure were prepared by the combination of template method,selective etching and surface modification,and metal nanoparticles were successfully supported by unique pore and surface chemical structure of these materials to prepare supported metal nano catalysts.The synthesized supported metal nano catalyst was used in the dehydrogenation of formic acid.The catalytic activity of metal nanoparticles was improved through the host-guest interaction between the carrier and metal nanoparticles.In Chapter 2,hollow mesoporous carbon nanospheres(HMCS)were synthesized by in-situ self-assembly method,which has the advantages of large pore size and large cavity structure.On this basis,amino and impurity atomic nitrogen were introduced through multi-step surface modification to prepare mesoporous carbon nanospheres with both amino functionalization and nitrogen doping(NH₂-N-HMCS),and Au Pd nanoparticles were successfully introduced into the material by wet chemical method,and finally the mesoporous composite material Au Pd/NH₂-N-HMCS with catalytic activity for dehydrogenation of formic acid was obtained.The introduction of heteroatomic nitrogen makes the carbon surface obtain more active?electrons,which enhanced the interaction between metal and support to the maximum extent,and thus improved the catalytic activity of the catalyst for dehydrogenation of formic acid.At the same time,the polar group-NH₂makes the carbon surface hydrophilic and inhibits the agglomeration of loaded metal nanoparticles.In addition,-NH₂ can also accelerate the breaking of O-H bond in formic acid,so as to accelerate the decomposition rate of formic acid and significantly improve the hydrogen evolution activity of the catalyst.At 298 K without any additives,the Au_0.3Pd_0.7/NH₂-N-HMCS showed excellent catalytic activity in the dehydrogenation of formic acid,and its initial TOF value was as high as 7747 mol H₂ mol catalyst^-1 H^-1.The catalyst still has good catalytic activity after 4 times of catalytic reaction test.In Chapter 3,hollow mesoporous silica nanospheres(HMSS)were synthesized using sSiO₂@CTAB/SiO₂ nanospheres as the core by cationic surfactant induced selective etching,and amino groups were introduced into the surface of the obtained material by surface grafting method.Finally,Au Pd nanoparticles were introduced by wet chemical method to synthesize amino modified supported metal nano catalyst Au_0.3Pd_0.7/NH₂-HMSS.The material has a hollow structure,and the shell has obvious open and vertical mesoporous channels,which provides more space for catalytic reaction.The introduction of-NH₂ in the material can significantly affect the nucleation and growth of Au Pd nanoparticles on the support surface,promote the adsorption of formic acid,and then improve the catalytic performance of the catalyst for dehydrogenation of formic acid.In Chapter 4,using 3-aminopropyl trimethoxysilane and monochlorotriazine-?-Cyclodextrin reacted to form cyclodextrin derivatives,which were modified on the surface of hollow mesoporous silica microspheres HMSS by grafting method.Finally,Au Pd nanoparticles were introduced by wet chemical method to obtain cyclodextrin modified supported metal nano catalyst Au_0.3Pd_0.7/?-CD-HMSS.The catalyst has good dispersion,hollow structure and vertical mesoporous structure.Cyclodextrin derivatives are beneficial to immobilize metal nanoparticles and form highly dispersed metal nanoparticles.At the same time,pyrrole nitrogen in its structure can further optimize the catalytic activity of the obtained material for formic acid,the initial theoretical TOF value of Au_0.3Pd_0.7/?-CD-HMSS catalyst for dehydrogenation of formic acid is 272 mol H₂ mol catalyst^-1 H^-1.