鹼性條件下合成含磺酸根官能基之介孔材料催化反應研究

Abstract

介孔二氧化矽在吸附、觸媒、光學材料與薄膜等方面都有相當的應用性，而介孔材料的孔洞結構與穩定性是決定其應用價值的關鍵。本篇論文的研究為，在鹼性條件下(pH ~ 10)，利用共沉澱法以cetyltriethylammonium (CTEA+)作為模版試劑，矽源為 sodium silicate (Na2SiO3)，有機矽烷前驅物為(3-mercaptopropyl)trimethoxysilane (MPTMS)。初合成樣品經過乙醇萃取移除模板試劑後，再使用H2O2將硫醇官能基做進一步的氧化，產生磺酸化官能基。在不同陰離子(Cl-與NO3-)條件下可得到具有三維立方堆積孔洞結構(3D-cubic，Pm3n)與二維六方堆積孔洞結構(2D-hexagonal，p6mm)之介孔材料，且加入的官能基含量可達S/Si = 15 mol%。催化反應部份，將不同長碳鏈羧酸(lauric acid與醋酸)與醇類(甲醇與苯甲醇)在50℃下進行脂化反應，以所合成的固體酸觸媒作為催化劑，且與具有磺酸根官能基的MCM-41材料比較其催化活性。催化結果顯示具有3D-cubic (Pm3n)的孔洞結構具有較高的初始速率，此結果可說明三維的孔洞結構與二維隧道型孔洞比較起來，有利於反應物與產物在孔洞內擴散。

Mesoporous silica materials have potential applications in sorption, catalysis and optoelectronic devices. For practical applications, the porous structure and framework stability are the main concerns. In this study, two sulfonic acid-functionalized mesoporous materials were synthesized using cetyltriethylammonium (CTEA+) ion as pore-directing agent by one-pot co-condensation of sodium silicate (Na2SiO3) and (3-mercaptopropyl)trimethoxysilane (MPTMS) in alkaline condition (pH~10). After the templating surfactants were removed, the thiol groups were oxidized to sulfonic acid groups by H2O2. Well-ordered functionalized mesoporous silica materials of 2D-hexagonal (p6mm) and 3D-cubic (Pm3n) structures with sulfonic acid contents (S/Si molar ratio) up to 1.53 mmol H+/g were obtained in the presence of NO3- and Cl- anions, respectively. . The catalytic properties of these materials in esterifications of carboxylic acids of different chain lengths (lauric acid or acetic acid) with methanol or benzylalcohol were examined, and the results were compared with that of sulfonic acid-functionalized MCM-41. The initial rates of esterification over cubic Pm3n material were faster than that over 2D-hexagonal materials, attributing to the easier diffusion of the reactants in the 3D-pores than 2D-channels.