(349b) Unique Roles of Heteroatoms in the Zeolite Synthesis

The incorporation of heteroatoms has opened up various new and exciting avenues for the synthesis and applications of traditional (alumino)silicate zeolites. The role of metals in zeolite synthesis ranges from adjusting catalyst acidity by isomorphous substitution of atoms like B, P, Fe, Sn and Ti, to directing crystal structure and/or acid siting within the zeolite framework. Heteroatoms in zeolites have also led to the development of bifunctional catalysts where heteroatoms typically act as primary active sites while framework aluminum and nanopores of zeolites provide Brønsted acid sites and shape selectivity, respectively. Here, we present two cases where incorporation of heteroatoms in zeolite synthesis leads to significant improvements in their physiochemical properties in unexpected ways.

The first example will highlight a facile and generalizable strategy to synthesize nano-sized zeolites using inexpensive metals as heteroatoms. The latter act as zeolite growth modifiers to reduce crystal size (<100 nm) and/or change the morphology of various framework types (e.g. MEL, MFI and MOR). We will show how these unique features lead to significant improvement in their diffusion properties and hence, their performance in different catalytic applications.

The synthesis of high silica faujasite (FAU) has been a challenge via organic-free routes. We have developed an organic-free method to generate a FAU zeolite (HOU-3) with the highest Si/Al ratio (~ 3). In this presentation, we will discuss a new method to achieve FAU with Si/Al = 3.5 via the addition of zinc oxide in the synthesis gel. In addition, we will demonstrate how this high-silica FAU material performs as a bifunctional catalyst compared to conventional zeolite Y analogues.

Overall, we will show how the judicious selection of heteroatoms can be used to tailor the properties and performance of zeolite catalysts, leading to significant improvements in zeolite properties that extend beyond those obtained by conventional zeolite syntheses.