SBA-15 with Crystalline Walls Produced via Thermal Treatment with the Alkali and Alkali Earth Metal Ions

Crystalline walled SBA-15 with large pore size were prepared using alkali and alkali earth metal ions (Na(+), Li(+), K(+) and Ca(2+)). For this work, the ratios of alkali metal ions (Si/metal ion) ranged from 2.1 to 80, while the temperatures tested ranged from 500 to 700 °C. The SBA-15 prepared with Si/Na(+) ratios ranging from 2.1 to 40 at 700 °C exhibited both cristobalite and quartz SiO(2) structures in pore walls. When the Na(+) amount increased (i.e., Si/Na increased from 80 to 40), the pore size was increased remarkably but the surface area and pore volume of the metal ion-based SBA-15 were decreased. When the SBA-15 prepared with Li(+), K(+) and Ca(2+) ions (Si/metal ion = 40) was thermally treated at 700 °C, the crystalline SiO(2) of quartz structure with large pore diameter (i.e., 802.5 Å) was observed for Ca(+2) ion-based SBA-15, while no crystalline SiO(2) structures were observed in pore walls for both the K(+) and Li(+) ions treated SBA-15. The crystalline SiO(2) structures may be formed by the rearrangement of silica matrix when alkali or alkali earth metal ions are inserted into silica matrix at elevated temperature.