Nanostructure Control Of Heterogeneous Hydrosilylation Catalyst

Hydrosilylation,the addition reaction of C=C with Si-H by employing appropriate catalysts to form Si-C bond,is one of the commonly used strategies to synthesize organosilicon compound.The homogeneous Karstedt catalyst,which is commonly used for the hydrosilylation,is highly active with high selectivity and less by-products.Nonetheless,the platinum atom can be hardly recycled due to its homogeneous nature,leading to the high cost of Karstedt catalyst.In order to reduce the loss of precious metals,the heterogeneous-type hydrosilylation catalyst have been studied,which can be commonly recovered by filtration and chromatography.Mesoporous silica?SiO₂?holds a high specific surface area,large pore volume and adjustable pore size,which has been widely used in medicine,organic catalysis and other fields.However,for macromolecular reaction system commonly with high viscosity,the filtration efficiency of these heterogeneous catalysts fairly low.To solve the problems,this thesis objects to design a catalyst which can efficiently catalyze the hydrosilylation reaction and quickly recover.By designing a superparamagnetic core-shell nano-structured supporting material with Fe₃O₄ as core and mesoporous SiO₂ as shell,and then anchoring molecular Karstedt catalyst with atomic Pt on SiO₂ as well as in their pores,the heterogeneous-type Karstedt catalyst retains the high catalytic activities of their homogeneous counterpart.Superparamagnetic core nanoparticles are designed to facilitate magnetic response,while mesoporous SiO₂ shell plays as a high-specific-surface catalyst carrier,both of which contribute to unique performance of the catalyst.Inthiswork,thecore-shellnano-structuredM-SiO₂/Fe₃O₄with mesoporous-SiO₂-coated superparamagnetic particles are prepared in a straightforward approach.It is found that the morphology of the particles could be effectively adjusted by changing the pH value of the system,the proportion of precursors and the surface polarity,and the supporting nanoparticles could be quickly separated by applying magnetic field.This work utilizes vinyltriethoxysilane as a coupling agent to modify M-SiO₂/Fe₃O₄ surface and coordinate with Pt atoms through complexation between the C=C bond and atomic Pt.By using various templates,the M-SiO₂/Fe₃O₄ nanoparticles with different pore sizes are prepared,and thus the corresponding Pt/Vinyl/M-SiO₂/Fe₃O₄ catalysts with various pore size and loading.The catalysts show high activities for the hydrosilylation of allyl-terminated polyether with polymethylhydrosiloxane a 94.1%conversion can be achieved for the reaction carried out at 100?using 5 ppm catalyst.In addition,it is found that when pore size shrinks,the catalyst shows better recyling performance.The catalysts still show activities after 4times of catalytic reaction.Even if the catalyst fails,its activity can be recovered by loading Pt atoms again.In addition,the M-SiO₂/Fe₃O₄ particles are also functionalized by using aminopropyltriethoxysilane as the coupling agent to prepared Pt/Azyl/M-SiO₂/Fe₃O₄ catalysts,which could further improve the activity of the catalyst and reusable performance.This thesis has achieved the high performance and recycling performance of the catalyst.It is expected that by increasing the recycling numbers,the cost of the catalysts,as well as the hydrosilylation reaction,can be further reduced.