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

Le, T. T. - Presenter, University of Houston
Dai, H., University of Houston
Rimer, J. D., University of Houston
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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