In zeolite synthesis, metastable zeolites are those that form at lower temperatures and have a high tendency to undergo interzeolite transformation. The most common among them is faujasite (FAU), which is heavily utilized in commercial fluid catalytic cracking (FCC). Approximately 14.5 million barrels of feedstock are treated every day in FCC units in over 300 oil refineries worldwide. Approximately 8400,000 tons of FCC catalysts are produced and used every year. Zeolite FAU catalysts are prone to severe deactivation owing in part to their large pores that facilitate coke formation. To this end, creating hierarchical FAU to modify the mesoporosity is a promising route to improve FAU catalyst performance. Intergrowths of FAU with zeolite EMT (a similar crystal structure) has been shown to generate a house-of-card hierarchical structure, which introduces mesoporosity using organic-free (i.e., economical) synthesis conditions. There have been studies showing that EMT can be synthesized with organics, such as crown ethers, as well as organic-free conditions; however, the current understanding of zeolite EMT crystallization mechanisms is limited.
In this presentation, we will highlight our parametric studies of EMT synthesis conditions and the optimization of FAU/EMT intergrowth materials. To better understand how each synthesis parameter influences zeolite crystallization, we have employed high-temperature atomic force microscopy (AFM) to characterize the surface growth of both FAU and EMT crystals. Our findings reveal distinct modes of growth despite similarities in their crystal structure. Recently, we reported the use of AFM to monitor FAU surface growth in situ wherein we confirmed a pathway that markedly varies from another similar zeolite structure (LTA) under nearly identical synthesis conditions. Here, we will discuss how in situ AFM in combination with other state-of-the-art characterization techniques can be used to provide a deeper understanding of zeolite surface growth under different crystallization environments; and how these conditions can be tailored to alter the physicochemical properties of the zeolite materials.
