Preparation And Catalytic Performance Of A Bilayer Mesoporous Silica Nanoreactor Loaded With Palladium

Pd catalyzed coupling reaction is one of the most widely used reactions in organic synthesis.For example,Pd catalyzed Heck reaction,Sonogashira reaction,Stille reaction and Suzuki reaction have been brilliant in organic synthesis.However,currently,the vast majority of palladium catalyzed reactions are carried out in homogeneous systems,which also brings a series of problems.For example,the difficulty in separating palladium from the reaction system makes it difficult to recover the precious metal palladium,which not only increases the synthesis cost and consumption of rare metals,but also may lead to a series of problems such as affecting product quality due to the residue of palladium in the product or polluting the environment due to entering the waste liquid.The heterogeneous reaction of anchoring Pd onto a suitable carrier can to some extent solve these problems.However,this heterogeneous catalyst must have high catalytic activity,high stability and easy recovery.Therefore,the selection of support and the method of palladium loading are the key to the synthesis of heterogeneous catalysts.Based on the above ideas,this paper studies heterogeneous palladium catalysts with mesoporous silica as the carrier,and studies their catalytic performance through suzuki coupling reaction.The main work includes the following two aspects:1.A novel heterogeneous nano palladium catalyst was synthesized,and a nano palladium catalyst based on silica material was prepared through soft template method and alkali etching strategy.The basic method is to use mesoporous silica as the "core",and then fix Pd nanoparticles on the "core" by chemical reduction.The choice of this mesoporous silica core is to control the particle size of palladium particles on the one hand,and disperse palladium particles in the mesoporous channels on the other hand to prevent palladium agglomeration in the reaction process.Next,encapsulate silicon dioxide on the outer surface of the core.By alkali selective etching of the "shell" surface,on the one hand,Pd nanoparticles are all encapsulated in the "shell",which can reduce the loss of palladium particles in the reaction process to a certain extent;On the other hand,the pores formed by alkali etching leave space for the entry and exit of organic molecules,ensuring mass transfer efficiency.The new heterogeneous catalyst was characterized by SEM,XRD,TEM and XPS.A pore with a diameter of around 7nm can firmly fix metal particles in the core,while a macroporous structure with a pore size of around 15 nm allows for the free entry and exit of reactant molecules.Subsequently,the obtained catalyst was used to catalyze Suzuki coupling reaction,and it was found that it had good catalytic performance,with a reaction efficiency of more than 95%.And repeated use did not show a significant decrease in catalytic efficiency.2.Palladium is one of the rarest precious metals in the world,with a content of approximately one hundred million parts in the Earth’s crust.Therefore,reducing the amount of palladium by doping other non precious metals while maintaining their catalytic performance is one of the ways to save resources.In addition,by incorporating another metal,the synergistic effect between bimetallics can be achieved by adjusting the spatial and electronic relationships between the metals,enhancing their catalytic activity.Therefore,based on the pre prepared nano palladium catalyst,a Pd-Ni bimetallic catalyst was synthesized.Similarly,through the catalytic Suzuki coupling reaction,it was found that although the Pd load of the bimetallic catalyst was lower than that of the single metal Pd catalyst,the catalytic activity of the Pd Ni bimetallic catalyst still remained extremely high.After repeated recycling,the catalytic activity of the catalyst did not decrease significantly.