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

Chang-Sik Ha,Sang-Wook Chu,Shuai Yuan,Sung Soo Park,Liyi Shi

doi:10.3390/ma14185270

Chang-Sik Ha, Sang-Wook Chu + Show 3 more

Open Access

https://doi.org/10.3390/ma14185270

Copy DOI

Abstract

Crystalline walled SBA-15 with large pore size were prepared using alkali and alkali earth metal ions (Na+, Li+, K+ and Ca2+). 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 SiO2 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 Ca2+ ions (Si/metal ion = 40) was thermally treated at 700 °C, the crystalline SiO2 of quartz structure with large pore diameter (i.e., 802.5 Å) was observed for Ca+2 ion-based SBA-15, while no crystalline SiO2 structures were observed in pore walls for both the K+ and Li+ ions treated SBA-15. The crystalline SiO2 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.

Highlights

With Na+ as source of alkali metal ion, mesoporous silica SBA-15 showed clearly the production of crystalline silica walls when the Na+ content of Si/Na = 20 or more was used at the temperature of 650 ◦ C or higher
When the Na+ amount was increased up to Si/Na = 2.1 at 700 ◦ C (SBA15-Na-2.1-700), the crystalline silica was dominated by cristobalite
Pore diameter was increased with dual size (18.3 and 972.7 Å) compared to the pristine SBA15, but the surface area and pore volume were decreased to 11 m2 ·g−1 and 0.03 cm3 ·g−1, respectively

Summary

Introduction

Mesoporous silica materials with metal (i.e., Al, Ga, In, Ti, Zr and Zn, etc.) oxide incorporated frameworks have greatly expanded and advanced their applications such as catalysis and magnetics [6]. Periodic mesoporous organosilicas (PMOs) with crystal-like layered structures in frameworks were synthesized using bridged organosilica precursors including aromatic groups such as benzene and biphenyl groups as silica sources [26,39,40]. Mesoporous materials with inorganic crystalline frameworks were synthesized with zeolite, which was well-known as microporous material with well-defined structure [41,42,43]. The resulting zeolite materials with hierarchical pore size distributions exhibit significantly improved catalytic properties for various reactions with respect to microporous zeolite materials [41,42,43]

Methods

Results

Discussion

Conclusion