Preparation Of Hollow Multinuclear Multi-Pd@HCS Catalyst And Application On Direct Synthesis Of H₂O₂

The direct catalytic synthesis of H₂O₂ with palladium based catalysts,using H₂ and O₂ as raw materials,has become a hot field of research due to its high-efficiency solutions and the advantages of environmental protection.Scholars have discovered in the research on catalysts with various structures that among the core-shell,the abundant pores on the shell of the hollow single-core catalyst and the internal mechanism of the catalyst microreactor provide an alternative reaction place for the products and raw materials of the catalytic reaction.And channel.However,the disadvantage of this catalyst is that due to its one-core-one-shell structure,the Pd active surface it provides is limited,resulting in increased H₂ adsorption,but the synthesis of H₂ activity still decreases.Therefore,it is very necessary to increase the exposed area of Pd in the oxide catalyst.In view of the above problems,this thesis designs and prepares a new type of hollow multi-core one-shell catalyst Multi-Pd@HCS,which is an embedded multi-Pd hollow carbon sphere catalyst,forming multi-core Pd nanoparticles as the active core and porous carbon as the shell structure.catalyst.The outer shell layer of the catalyst can prevent the substitution and agglomeration of the active component Pd,and at the same time,multiple active nuclei also maximize the area of active sites and improve the catalytic activity.Therefore,a series of hollow multi-core one-shell catalysts,Multi-Pd@HCS,are prepared from three aspects of in-situ reduced Pd particle size,particle size,and shell properties,through various characterization methods such as TEM,XRD,FTIR,TPO-MS,etc.The catalyst was analyzed,and the performance of the catalyst for H₂O₂ synthesis was measured under normal conditions.The specific research content is as follows:1.The hollow multi-core one-shell catalyst Multi-Pd@HCS is designed and prepared.The synthesis route is:SiO2 microspheres are prepared by the St?ber method,and the SiO₂ surface is modified with the siloxane coupling agent APTES,grafted with amino functional groups,based on amino and The complexation of Pd²⁺grafts the negatively charged Pd2+onto the amino radical group,and the reducing agent is added to reduce the Pd²⁺in situ to obtain Multi-Pd/SiO₂-NH₂,with Pd nanoparticles grafted and anchored on the surface of Si O₂-NH₂,then CTAB as the pore former,resorcinol and formaldehyde as the carbon source,through the self-assembly method,insert a phenolic resin shell in the outer layer,high temperature carbonization to obtain porous carbon-doped Multi-Pd/SiO₂@C;The etching agent removes SiO₂,and the hollow multi-core one-shell catalyst Multi-Pd@HCS is obtained after activation treatment.TEM,XRD,FTIR,TPO-MS and other characterization results show that the multi-core structure of the catalyst is clear,Pd is anchored on the inner wall of the carbon shell,the shell is completely covered,the average particle size of the Pd core is 5.27±0.12 nm,and the catalyst particles are average The diameter is 104.58±1.93 nm.Through the exploration of solvent types,precursor H₂PdCl₄ concentration,reducing agent types,and reduction time factors,the study of nucleus formation and particle growth on nanoparticles is studied.The results show that the Alternating Alcohol is used as the modified solvent,the precursor H₂PdCl₄ concentration is 0.075 mol/L,and the synthesis conditions of sodium borohydride reduction for 0.5h,the average Pd generated by in-situ reduction is 5.01nm,and the catalyst activity is the highest.,H₂O₂ selectivity and production accounted for 81%respectively,1728 mmol gh-1（activity evaluation experiment）environment:0℃,1atm,the same below).3.By studying SiO2 microspheres of different diameters to prepare catalysts with different particle sizes and Pd nanoparticle scales,the effect of the studied diameter and Pd on the structure and performance of the hollow multi-core catalyst Multi-Pd@HCS is used.TEM,XRD,BET,laser particle size analyzer for characterization and analysis.The results of the study showed that the diameter of the transformed SiO₂ microspheres increased from 103.91 nm to 446.54 nm,and the average Pd core changed from 6.17 nm to 4.75.nm,the carbon shell layer of the catalyst contains abundant micropores.As the diameter increases,the size of Pd nanoparticles gradually decreases,and the catalytic activity first increases and then decreases.When the diameter is reduced to 308.74 nm,Pd must be 5.07 nm,which has the highest catalytic activity.The selectivity and representativeness of H₂O₂ are respectively 91%,2013 mmol g_pd^-1h^-1,and better stability.4.Study the effect of carbon shell structure properties on hollow multi-core catalyst Multi-Pd@HCS and its catalytic activity.The pore structure of the shell layer was changed by the amount of the porogen CTAB,and the thickness of the shell layer was changed by the amount of the hard template SiO₂.The results show that when the addition amount of CTAB is 2.0g and the addition amount of SiO₂ is 1.0g,the properties of the prepared catalyst shell are most conducive to the catalytic synthesis activity.The H₂O₂selectivity and production volume are 81%,1728 mmol g_pd^-1h^-1.