Di- and trioxacyclohexane as structure directing molecules in the synthesis of zeolites omega and ECR-1

Abstract

Six-membered ring cyclohexane derivatives with 2 oxygen (1,4-dioxane or p -dioxane) and 3 oxygen (1,3,5-trioxane) atoms have been used as organic molecules in the synthesis of zeolites omega ( MAZ framework type) and ECR-1 ( EON framework type). Both molecules yield zeolite omega at moderate temperatures with a composition and aluminum distribution similar to those obtained with more standard organics such as the tetramethylammonium cation. If the preparation of zeolite omega with p -dioxane was previously known, the use of 1,3,5-trioxane had never been reported in the literature. The most interesting feature of 1,3,5-trioxane is that these molecules could be released from the structure at very low temperature, typically 300 °C below the temperature observed with p -dioxane. When the alkalinity of synthesis gels was decreased, zeolite omega was progressively replaced by ECR-1 in the presence of 1,3,5-trioxane but not in the presence of p -dioxane. The relative proportion of omega and ECR-1 in the different solids has been monitored by X-ray diffraction (XRD) and solid-stare nuclear magnetic resonance (NMR). 23 Na NMR of calcined rehydrated solids was found to be particularly adapted to discriminate ECR-1 from zeolites omega in MAZ / EON mixtures with poorly resolved XRD patterns. • 1,3,5-trioxane directs the crystallization of zeolites omega and ECR-1. • The nature of the zeolite formed depend on the alkalinity of the synthesis gel. • Organic molecules are removed from the framework at very low temperature. • 23 Na solid state NMR is a powerful tool to discriminate between the two zeolites.