(371l) Diffusion Studies of Hydrocarbons in Ill-Crystallized or Desilicated ZSM-5 Catalysts

The physical and chemical properties of zeolites may be tuned by modification of their synthesis (bottom-up methods) or post-synthesis procedures (top-down). These may involve embryonic zeolites, partially formed or ill-crystallized structures, and desilication of consolidated zeolites by consuming part of the zeolitic structure in an alkaline solution. These modifications would form secondary porosity, mainly for applications as catalysts in reactions that form deactivating coke, as usually seen in the conversion of methanol to hydrocarbons (MTH), for example.

In this study amorphous, partially crystallized, and fully-grown ZSM-5 zeolites were prepared and characterized. Also, fully crystallized ZSM-5 zeolite samples were desilicated and acid leached to create different structural and morphological properties and correlate them with the accessibility to catalytic sites and their effect on catalyst deactivation. The diffusional behavior of hydrocarbons in these samples was evaluated using the Zero-Length Column (ZLC) method and compared to catalytic results in model reactions such as MTH.