(363aj) Enhanced Stability of Finned Zeolite SSZ-13 Catalysts in the Methanol to Olefins Reaction

Zeolite SSZ-13 (chabazite, CHA) and its zeotype SAPO-34 are typical catalysts for methanol to olefins (MTO) reactions owing to their high selectivity for light olefins. However, the pore topology of CHA-type crystals consists of large cages that enable the formation of heavy hydrocarbons and small pore aperture that restrict their removal from internal pores, which expedites catalyst deactivation by coke accumulation. In order to improve catalyst stability, methods to reduce internal diffusion limitations can facilitate the rapid removal of products, thereby suppressing the rate of coke formation. Among the methods reported in literature are the synthesis of nano-sized or hierarchical catalysts. In this presentation, we will discuss how we have achieved superior CHA-type zeolites by introducing fins, which are small protrusions (30 – 180 nm) that epitaxially grow on the surface of SSZ-13 seed crystals. We have demonstrated for a variety of zeolites (MFI, MEL, FER) that fins enhance catalyst stability by improving internal mass transport; however, the relationship between the size of the original seed and the fin has remained elusive.

Here we will discuss our recent efforts to synthesize the first library of finned SSZ-13 catalysts. We have identified synthesis conditions that allow for the preparation of finned SSZ-13 with different seed/fin sizes to assess scaling relationships as a means of establishing structure-performance relationships using MTO as a benchmark reaction. We prepared fins on seed crystals ranging in size from 700 to 5000 nm and conducted parametric studies to assess what synthesis conditions can tailor fin properties (e.g., size and distribution). Our findings reveal that fins reduce the rate of coke formation and extend catalyst lifetime compared to the parent SSZ-13 catalysts. These studies will be discussed in relation to the effects of fins on zeolites with medium-sized pores (e.g., ZSM-5) that are conventionally used as methanol to hydrocarbon catalysts, and the optimal scaling relations for designing fins on small-pore zeolites.