(544cd) Controlled Post-Synthesis Modification Enables Tuning of ZSM-11 Catalyst Performance in the Methanol-to-Hydrocarbon Reaction

ZSM-11 (MEL framework) is a zeolite with potential in a wide range of catalytic applications. The structure of ZSM-11 is closely related to ZSM-5 (MFI framework), which is a well-known industrial catalyst; however, ZSM-11 has straight channels compared to more tortuous ones of its counterpart. This factor is posited to be one of the key reasons for the reduced diffusion limitations in ZSM-11 and its improved catalyst lifetime compared to ZSM-5,^1-3 yet there are relatively few published studies of ZSM-11 synthesis. In this talk, we will discuss the ability to alter the physiochemical properties of ZSM-11 through post-synthesis modification methods and convey how these changes (i) influence methanol-to-hydrocarbon (MTH) reactions and (ii) improve our understanding of zeolite property-performance relationships. The first method that will be described is the passivation of external acid sites, which is a proven method for improving product selectivity.⁴ Reactions at external surface sites are non-shape-selective, and thus do not fully utilizing the benefit of confined sites within zeolite pores and channels.⁵ Another problem associated with external acid sites is pore blockage due to the formation of polyaromatic molecules (i.e., coke precursors).⁶ Therefore, it is hypothesized that catalyst lifetime and selectivity can be improved by surface passivation techniques. Many reported methods lead to the narrowing of external pore openings, thereby decreasing catalytic activity.^7,8 In this talk, we will discuss an alternative method developed by our group⁹ to generate core-shell structures in which siliceous ZSM-11 (silicalite-2) is epitaxially grown over the aluminosilicate zeolite to create ZSM-11@silicalite-2 with continuous core-shell pore alignment and tunable shell thickness (5 - 20 nm). We show that controllable surface modification allows for in-depth evaluation of the effects of surface passivation on catalyst performance in MTH.

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