Control of Competitive Structure-Directing Effect in CON-Type Zeolite Synthesis via Intermediate Addition Method

The development of efficient and economical synthesis methods for CON-type aluminoborosilicate zeolite, a promising catalyst for methanol-to-olefins reactions, is in high demand. Herein, we propose the dual use of organic structure-directing agents that have different roles in the formation of CON-type zeolite. Although N,N,N-trimethyl-(-)-cis-myrtanylammonium hydroxide (TMMAOH) has a strong structure-directing effect on the formation of CON-type zeolite, it is considerably expensive. Conversely, the relatively inexpensive tetraethylammonium hydroxide (TEAOH) has a weak structure-directing effect on the formation of CON-type zeolite and/or even directs the formation of other impurity phases. The intermediate addition method of TEAOH, developed herein, could control these competitive structure-directing effects and enhance the crystallization of CON-type zeolite from economically viable raw materials. The timing of intermediate TEAOH addition was found to be a critical factor to obtain a pure CON phase, and TEA+ was occluded in the final product, suggesting the pore filler role of TEAOH, while TMMAOH is required in the early stage of crystallization.