Preparation Of Cobalt/Nitrogen/Carbon Modified Mesoporous Silica Hollow Nanoreactor As Highly Efficient Catalysts For Ethylbenzene Oxidation

Mesoporous silica hollow spheres are well known for their large specific surface area and large pore volume.In addition,the advantages of easy surface modification and good stability have also attracted the attention of nanomaterials researchers.Generally,the mesoporous silica hollow spheres are functionalized via methods such as surface grafting,polymer modification,loading of metals or oxides.As a result,the as-synthesized hollow mesoporous nanoreactors widely used in the fields of catalysis,energy storage and medicine are obtained.In the field of catalysis,the main factors that directly affect the catalytic performance of the nanoreactor are the inherent surface area,the size of the mesopores and the active sites introduced.In addition,existing studies have proved that transition metal porphyrins have a good M-N4 structure,which prevents the sintering of the metal during pyrolysis and converting into active sites M-Nx.And the active sites M-Nx promote the selective oxidation of ethylbenzene.Therefore,the nanoreactors based on mesoporous silica hollow spheres were designed.Different methods were used to assemble mesoporous silica hollow spheres and metal porphyrins and form a nanoreactor of cobalt/nitrogen/carbon modified mesoporous silica hollow spheres.And the catalytic performance of over the nanoreactors for selective ethylbenzene oxidation were investigated.The specific research content is as follows:1.A hollow mesoporous nanoreactor with Co-Nx-C loaded inside mesoporous silica hollow spheres was prepared by the dipping method.First,according to the improved Stober method,mesoporous silica hollow spheres with a specific surface area increased from 373.9 cm2/g to 943.6 cm2/g could be obtained by adjusting the density of the silicon precursor.Then the cobalt porphyrin was used as the Co-Nx-C precursor,and introduced into the inner wall and cavity of the mesoporous silica hollow sphere by dipping.And finally,a hollow mesoporous silica nanoreactor with Co-Nx-C loaded inside(Co-NxC@mSiO2)was obtained.In addition,the catalytic performance of nanoreactors with different specific surface areas for the oxidation of ethylbenzene was studied.Among them,Co-Nx-C@mSiO2-1 showed higher catalytic activity and stability.Through a series of characterization and analysis,it was determined that the excellent catalytic performance of the Co-Nx-C@mSiO2-1 nanoreactor was due to its relatively regular mesoporous structure,large specific surface area(707.6 cm2/g)and distribution in the microspheres uniform Co-Nx-C active sites.2.Similarly,the mesoporous silica hollow spheres were modified and functionalized.And the in-situ synthesis was used to obtain a sandwich-like CoNx modified carbon@silicon@carbon nanoreactor(Co-Nx-C/C@mSiO2).The carbon precursor phenolic resin and the metal precursor cobalt porphyrin were simultaneously introduced on the inner and outer walls of the mesoporous silica hollow spheres with large specific surface area.And then the hollow mesoporous nanoreactor was obtained through a high-temperature pyrolysis process.The advantage of this method was that the carbon material doped in situ with active sites was formed and uniformly coated on the inner and outer walls of the mesoporous silica hollow sphere.In addition,the structure of carbon-coated solid silica microspheres and hollow mesoporous silica microspheres without carbon modification were also prepared.The regular hollow mesoporous structure and hydrophobicity structure of the obtained hollow mesoporous nanoreactor Co-Nx-C/C@mSiO2 were beneficial to improve the catalytic activity of the catalyst.In addition,the influence of the doping amount of cobalt porphyrin on the catalytic performance was explored.When the doping amount of cobalt porphyrin was 0.03 g,the obtained 0.03-Co-NxC/C@mSiO2 hollow nanoreactor showed outstanding performance.Acetophenone yield and catalytic stability.3.A one-pot method was used to prepare a raspberry-shaped Co-N,modified carbon/silicon nanoreactor(Co-Nx-C-m SiO2).First,cobalt porphyrinis loaed in the solution containing resorcinol,formaldehyde and 1,6hexanediamine substrate to prepare the polymer polybenzoxazine containing cobalt porphyrin.After the reaction was complete,adding silica precursor to the solution.During the N2 atmosphere pyrolysis process,polybenzoxazine gradually decomposed from the inside to the outside,and was continuously coated in the pores of the mesoporous silica to form a hydrophobic hollow carbon/silicon reactor.When the pyrolysis temperature is 900℃,the degree of defects of the nanoreactor is the largest,and it shows the best catalytic activity.In addition,the active sites in 900-Co-Nx-C-C/mSiO2 are Co-Nx uniformly distributed on the shell of microspheres assembled by carbon and silica.Compared with the catalyst(Co-Nx-C@C/mSiO2)prepared by impregnating the cobalt porphyrin in the prepared the carbon/silicon nanoreactor before,900-CoNx-C-C/mSiO2 has better yield of ketone,which is attributed to its higher proportion of Co-Nx active sites.