High-silica molecular sieve syntheses using the sparteine related compounds as structure-directing agents

Abstract

Three quaternary ammonium compounds are synthesized from sparteine and their performances in high-silica molecular sieve syntheses investigated. N(1)-Methyl- α-isosparteinium (compound A) is found to form the pure-silica molecular sieve with the CFI topology that was first synthesized with its diastereomer N(16)-methylsparteinium (B). The crystallization time for the synthesis of pure-silica CFI using A as an organic agent is shorter than that with B. The crystal size of the product obtained with A is much smaller than that recovered when using B. These results indicate that A is a better structure-directing agent for the formation of the CFI than B. Molecular modeling studies suggest that the reason A is a better structure-directing agent for CFI than B is that A can form a greater number of Van der Waals interactions with the silica framework of CFI. The very rigid and bulky compound, N(1), N′(16)-endo- methylenesparteinium (compound C) does not yield any crystalline molecular sieves over a range of the reaction conditions. The lack of success with C could be due to its decreased hydrophobicity and hydrothermal stability compared to A and B.