Synthesis of wormhole mesoporous silica by compressed carbon dioxide and application in catalytic hydrogenation

Mesoporous silica materials were prepared by infusion and selective condensation of silicon alkoxides within self-assembly formed from protonated hexadecylamine by CO2 in aqueous media. Compared to the conventional synthesis approach, the introduction of CO2 facilitates the hydrolysis of silicon alkoxide precursor and does not need adding any co-solvent in the course of the synthesis of mesoporous material. Moreover, CO2 can be used as a swelling agent increasing the average pore size form 3.2-5.4 nm with expansion rate of approximately 69 %. The influence of CO2 pressure and temperature were carefully investigated. During the preparation, nonionic surfactant hexadecylamine can turn into cationic surfactant in situ as mesostructure-directing template under pressurized CO2 condition, which is the key factor for the formation of ordered mesoporous silica. In addition, the supported Pd catalysts were prepared and characterized thoroughly by X-ray diffraction, H-1 NMR, C-13 NMR, ICP-AES analysis, scanning electron microscopy, transmission electron microscopy and nitrogen adsorption measurements. On the basis of the characterization and hydrogenation performance of the catalysts, the roles of different supports were discussed.