Post-synthesis grafting of metal oxide onto mesoporous silica and synthesis of mesoporous carbon

• Main Authors: Yi-Shuang Pan, 潘易霜
• Other Authors: Hong-Ping Lin
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/40506729915641016800

碩士 === 國立成功大學 === 化學系碩博士班 === 94 === In this thesis, there are two major researching parts. 1. Chemical coating of metal oxides onto as-synthesized mesoporous silicas; 2. Synthesis of mesoporous carbons. The first part is chemical coating of metal oxides onto the as-synthesized mesoporous silicas. The mesoporous silicas of high surface area, tunable pore size and large pore volume are desirable for catalytic processes involving large molecules. However, the amorphous silica framework of weak acidity hinders the applications in acidic-catalytic reactions. The mesoporous silicas as potential catalysts can be enhanced by a modification of their surface with other metal oxides. To increase the acidity, grafting Al2O3 onto mesoporous silica is a very promising method. In typical grafting processes, the calcined mesoporous silicas have been widely used. While, there exist two disadvantages in using calcined mesoporous silica: 1. The calcined mesoporous silica has high absorption capability for water, which can lead to a serious self-clustering of metal oxides. 2. Removal of surfactants is a time- and energy-consuming process and the surface silanol group density is considerably reduced during high-temperature calcinations. In this thesis, we proposed a new method to coat the metal oxides layer onto the mesoporous silica by directly refluxing the as-synthesized mesoporous silica in a 1-propanol solution of the metal alkoxide. After calcination, the metal oxide-coated mesoporous silicas with high surface area, large porosity were obtained. In the second part, we used mesoporous silicas–SBA-15 as a solid template to prepare the mesoporous carbons – CMK-3 or CMK-5 by using phenol-formaldehyde resin or furfuryl alcohol as carbon source. When using phenol-formaldehyde resin, a simple impregnation in ethanol solution was perform to introduce the phenol-formaldehyde polymer into mesoporous silicas. Cuing at 100 oC, carbonization at 1000 oC and silica etching by HF solution gave the CMK-3 mesoporous carbon. A typical incipient-wetness process was used to fill the mesopores of the acidic Al2O3-coated or pure silica mesoporous silicas with the furfuryl alcohol. Due to the high acidity of the Al2O3-coated mesoporous, polymerization of the furfuryl alcohol was achieved at relatively lower (~60–80 oC). In contrast, higher polymerizing temperature (~100 oC) was required for the pure-silica mesoporous silicas. After pyrolysis at 1000 oC under N2 environment and silica removal by HF-etching, the CMK-3 mesoporous carbons were synthesized. With a careful control on the furfuryl alcohol content, the CMK-5 consisted of carbon tube were generated instead. These mesoporous carbons possess the properties of high surface area (1700~1000 m2g-1), and large volume (1.5~ 0.7 cm3g-1).