Crystallization of One-Dimensional Zeolites: Elucidating Mechanisms of Growth and the Role of Structure Direction

            Crystallization of One-dimensional Zeolites: Elucidating Mechanisms of Growth and the Role of Structure Direction

Rui Li and Jeffrey D. Rimer

 

Department of Chemical and Biomolecular Engineering, University of Houston, 4726 Calhoun Road, Houston, TX, 77204, jrimer@central.uh.edu

 

Zeolites possess well-defined pore systems that give rise to shape selectivity for chemical reactions, thus providing an essential advantage for their use as catalysts in commercial applications. The performance of zeolites (i.e., activity and lifetime) is closely aligned with the selection of internal pore geometry and dimensions, which can influence diffusion, adsorption, and reaction pathways. Design of optimized zeolite catalysts a priori is challenging owing to the complexity of synthesis that is derived in part from the unknown role of amorphous precursors, organic structure-directing agents (OSDAs), and the pathways of crystallization. Previous studies have demonstrated that one-dimensional (1D) zeolites, such as zeolite L (LTL type), grow via nonclassical mechanisms involving the assembly of so-called worm-like particles (WLPs), which are bulk amorphous precursors that serve as growth units during crystallization.¹ Evidence of crystallization by particle attachment (or CPA) is mounting for a range of materials that include biominerals², metal oxides,³ and zeolites.⁴ In this relatively new area of research, there are many knowledge gaps between the design of synthesis conditions and the resulting physicochemical properties of the materials.⁵ One interesting phenomenon regarding nonclassical crystallization of zeolites is the existence of WLPs, which are common to many different framework types.¹ Here, we will discuss how two widely-used 1D zeolites,^6,7 LTL and TON, crystallize from similar growth solutions that comprised of amorphous WLP precursors. Despite the similarity of their precursor solutions, we will show how these two structures involve distinct growth pathways that can be manipulated by the judicious selection of synthesis parameters (e.g., temperature, alkaline content, OSDA, etc.). We will present our work on the design of OSDAs for zeolite TON crystallization. Moreover, we will discuss mechanisms of LTL and TON crystallization and demonstrate how facile, economically-viable methods can be used to produce zeolites with improved properties for a wide range of industrial applications.

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(7) Perego, C.; Carati, A. Zeolites and zeolite-like materials in industrial catalysis; In Zeolites: From Model Materials to Industrial Catalysts; Čejka, J., Per¨¦z-Pariente, J., Eds.; Transworld Research Network: 2008, p 357-389.