Incorporation of Al3+ ions to promote the stabilization effect of (NH4)2SiF6 treatment on the hydrothermal stability of mesoporous SBA-15 zeolite

This work demonstrates an improved (NH4)2SiF6 treatment to enhance the hydrothermal stability of mesoporous SBA-15 zeolite. In this treatment, Al3+ ions are incorporated into SBA-15 zeolite first, then it is treated with 5% (NH4)2SiF6 solution according to 1% SiO2 of SBA-15 and finally washed with HCl (2 mol/L) to remove the pre-incorporated Al3+ ions. The obtained SBA-15 exhibits higher hydrothermal stability than that without pre-incorporated Al3+. Compared with the latter, the sample maintains a better ordered mesostructure and a larger surface area (271 m2/g) after hydrothermal treatment at 800 °C for 12 h in 100% steam. The results show that incorporating Al3+ ions into SBA-15 zeolite before (NH4)2SiF6 treatment obviously promotes the stabilization effect of (NH4)2SiF6 treatment. The mechanism suggests that the incorporated Al3+ ions can effectively capture F− ions that have been released from (NH4)2SiF6, and thus reduce their etching into the SBA-15 zeolite framework. This ensures that the positive factors of (NH4)2SiF6 treatment, such as silicon insertion and surface hydrophobization by F− ions, play effective roles in the improvement of the hydrothermal stability of SBA-15 zeolite. This promoting effect of the Al3+ ions is closely related to the method that is used to introduce the Al3+ and the SBA-15 zeolite processing temperature.

Graphical AbstractAn improved (NH4)2SiF6 treatment by pre-incorporating with Al3+, which can capture F− and reduce its etching into SBA-15 framework, finally promote the stabilization effect of (NH4)2SiF6 treatment on SBA-15 zeolite.Figure optionsDownload full-size imageDownload as PowerPoint slide