The influence of surfactanthilica molar ratio (Sur/Si) in the synthesis of the mesoporous molecular sieve materials (M41S) was studied in a simple ternary synthesis system containing tetraethylorthosilicate (TEOS), water, and the cetyltrimethylammonium (CTMA) cation at 100 "C. The resulting silicate materials were characterized by X-ray diffraction, 29Si NMR, and FTIR. As the Sur/Si molar ratio increased from 0.5 to 2, the siliceous products obtained could be classified into four separate groups: MCM-41 (hexagonal), MCM-48 (cubic), thermally unstable M41S, and a molecular species, the cubic octamer [(CTMA)SiO2.5]8. One of the thermally unstable structures has been identified as a lamellar phase. These results are consistent with known micellar phase transformations that occur a t various surfactant concentrations and reinforce the concept that liquid-crystal structures serve as templating agents for the formation of M41S type materials.

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Trimethyloxonium cation (TMO) in zeolite ZSM-5 reacts principally as a surface methylating agent, similar to TMO salt decomposition with other weak conjugate bases (e.g. BFl, arenesulphonates); recent reports of C2 product formation from dimethyloxonium methylide generated by heating TMO salts with strong, poorly nucleophilic bases such as NaH and Li(2,2,6, do not accurately model the actual behaviour of this cation in ZSM-5.

High-silica ZSM-5 and [BIZSM-5 (both containing ca. 600 ppm Al) are catalytically activated by hydrothermal treatment in the presence of alumina. Aluminium is transported as an aquospecies from A1,0, into the zeolite and enters the framework in the tetrahedral conformation. The presence of framework B induces enhanced activation, the degree of activation increasing with B content. This is due to the hydrolytic instability of framework B and hence its ready substitution by Al.