Imidazolium structure directing agents in zeolite synthesis: Exploring guest/host relationships in the synthesis of SSZ-70

Abstract

The synthesis of high-silica molecular sieve SSZ-70 is investigated using a variety of imidazolium structure directing agents (SDAs) that are designed to explore the nature of the guest (SDA)/host (SSZ-70) interactions. The SDAs are symmetric 1,3-disubstituted imidazoliums that span a wide range of hydrophobicity from 1,3-dimethylimidazolium (Σ(C + N) = 7) to 1,3-bis(2,6-diisopropylphenyl)imidazolium (Σ(C + N) = 29). Reactions with fluoride or hydroxide as mineralizing agent are investigated in pure-silica, borosilicate, and aluminosilicate inorganic compositions. The original borosilicate synthesis is extended to pure-silica and aluminosilicate compositions using five SDAs. The five SDAs span Σ(C + N) = 13 (1,3-bis(isobutyl)imidazolium) to Σ(C + N) = 19 (1,3-bis(cycloheptyl)imidazolium and 1,3-bis(norborn-2-yl)imidazolium) and four contain cycloalkyl groups. Thirteen screening reaction conditions (total of 160 syntheses) produced 11 different known molecular sieves.