THE ROLE OF DIQUATERNARY CATIONS AS DIRECTING AGENTS IN ZEOLITE SYNTHESIS

A systematic study was carried out in which the formation of various zeolitic phases from diquaternary cations was monitored. The chain length of the diquats was found to play a key role in the nature of the final products. In a specific composition regime, an ''oscillatory'' pattern was observed, where, by varying the diquat chain length, the unidimensional 10-ring zeolite ZSM-23 or a 12-ring containing system, i.e., ZSM-50, NU-87, or ZSM-12, was obtained. Molecular modeling studies led to a proposed orientation of the respective diquats in the 12-ring pores/channels of ZSM-50 and NU-87. It is concluded that specific chain lengths provide an ideal fit for the formation of these ''2-dimensional'' pore systems. When the fit is less than ideal, ZSM-23 appears as the default phase under the conditions studied.