Chapter 6 - Theoretical and Practical Aspects of Zeolite Nucleation

Abstract

This chapter critically evaluates numerous concepts of zeolite nucleation. Although most of applications of zeolites are closely related to their structural and chemical properties (i.e., type of zeolite, modification by ion exchange, and/or isomorphous substitution), size of zeolite crystals may play a crucial role in the mode and efficiency of their application as catalysts, adsorbents, and cation exchangers. Large zeolite crystals with well defined morphology are used not only for fundamental studies, such as spatially resolved measurements of molecular diffusion in micropores, electron microscopic observations of crystal surface growing processes, single crystal structure determinations, determination of anisotropic magnetic, and optical properties, but also they have a number of potential applications such as advanced functional materials in microelectronic and optics, materials for anisotropic ionic conductivity, matrices for creation of arraying micro clusters, catalysts, and adsorbents. Because of the great influence of zeolite crystal size on the mode and efficiency of their applications, the knowledge on the nucleation of zeolites has a crucial importance in the designing of the products having desired particulate properties needed for specific applications. For this reason, the existing concepts of zeolite nucleation are overviewed and critically evaluated. Since the final size of zeolite crystals obtained in a typical batch crystallization strongly depends on the total number of nuclei formed during the crystallization and on the rate of their formation, it is quite clear that the knowledge on the nucleation events has a crucial importance in the control of particulate properties of zeolites, and thus on the designing of the products having desired particulate properties needed for specific applications.