S+X−I+ route to mesostructured materials from Fau and Beta zeolite precursors: A comparative study of their assembly behaviors in extremely acidic media

Mesoporous molecular sieves were synthesized from Beta and Fau zeolite precursors through S+X−I+ route under extremely acidic conditions in parallel (designated as MBeta and MFau, respectively). The textural properties of MFau were different from its MBeta counterpart but resembled normal MCM-41 silica from TEOS. Al content in MBeta was almost equivalent to that in the initial Beta zeolite precursors, whereas only trace Al species was present in MFau from elemental analysis results. The hydrothermal stability of MBeta after post-synthesis ammonia treatment was considerably improved compared with normal MCM-41 aluminosilicates, whereas the MFau after the same procedure was as unstable as normal MCM-41 silica. Thus, the assembly behaviors of Beta and Fau zeolite precursors were comparatively studied based on these results. The microstructure of Fau zeolite precursors were degraded by the extremely acidic condition, and Al species was dissolved into the synthesis mixture. However, Beta zeolite precursors survived the chemical attack of extremely acidic media and were incorporated into mesostructured framework as primary building units.