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

Abstract

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.

Zeolite Crystal Engineering

“…This virtual special issue also includes nonconventional methods of synthesizing nonzeolititc porous materials, such as metal–organic frameworks (MOFs) and mixed metal oxides . Synthesis methods employing low quantities of solvent have shown promise for preparing materials with unique properties, whereas staged syntheses, when either a reagent or reaction condition is altered midsynthesis, can offer a unique route to control processes of crystallization . In this virtual special issue, there are also studies focusing on new methods of characterization, both ex-situ and in situ, to improve our understanding of crystallization processes and offer better diagnostic tools …”