(704h) Enhancing Mass Transport Properties and Catalyst Performance of Low-Dimensional Zeolites

Reducing limitations for internal molecular diffusion in zeolites is critical to improving catalyst activity and stability for commercial applications such as hydrocarbon cracking and methanol-to-hydrocarbons (MTH) reactions. The intrinsic confined pore networks in zeolite structures give rise to well-defined shape-selectivity, which can result in highly selective products, but oftentimes at the expense of reduced activity and lifetime owing to the large crystal sizes of conventional zeolites that impose mass transport restrictions. This is particularly relevant for zeolites with one-dimensional pores, which are highly selective to propylene in naptha cracking, but deactivate faster than higher dimensional (2D or 3D) analogues due to extensive coking and pore mouth blockage. Such limitations can be overcome via a facile post-synthesis treatment to produce fins, which are small protrusions on external surfaces of seed crystals. This secondary growth technique has been demonstrated for zeolites with 3D (MFI, MEL) and 2D (FER) pore networks wherein finned catalysts markedly outperform their parent seeds in MTH and butene isomerization reactions, respectively. Here, we will discuss how this approach can be used to design finned MTT – a 1D zeolite with straight medium-pores that mimic those of commercial ZSM-5. Our findings show that molecular diffusion in finned MTT zeolites is faster, resulting in reduced rates of coking and longer catalyst lifetime relative to the conventional counterparts. Zeolites are also known to be prone to intrinsic defects during synthesis. We will show how facile post-synthesis treatment methods can be used to reduce defects in zeolites thereby improving their diffusion properties and catalytic performance (e.g. total turnovers and lifetime) beyond what can be achieved with conventional as-synthesized materials.