Coupled diffusion and acid-catalyzed reactions in zeolites control a multitude of industrially-important chemistries that exert huge impact on the planetary ecosystem and the society. In this study, macroscopic diffusion in the well-defined Knudsen regime is used as a transport standard to characterize the diffusion within meso- and micropores of zeolites (zeotypes) as well as to measure the intrinsic kinetics of olefin methylation, a key step in the Methanol-To-Olefins (MTO) chemistry. Temporal Analysis of Products (TAP) pulse-response experiments provide time-resolved (Δt=1 ms) kinetic data which are then interpreted within a 1D reaction-diffusion model to yield the transport and reaction characteristics of investigated materials.<br/>The molecular transport of various low weight guest molecules (4-84 amu range, inert gases and hydrocarbons) was characterized in ALPO-5 (AFI), SAPO-34 (CHA), ZSM-22 (TON), ZSM-5 (MFI), and self-pillared pentasils (MFI) materials. For several materials, novel TAP experiments with <i>in situ</i> template removal were performed to characterize, separately, mesoporous and microporous transport. These precise measurements of diffusional properties, in turn, provided means to characterize physico-chemical interactions of various gases with the host frameworks, e.g. Henry constants of molecular uptake by the framework. With the insights gained into the transport properties of microporous frameworks under low-pressure TAP conditions, the intrinsic kinetics of olefin methylation was studied in selected materials and the resulting parameters were compared to theoretical (DFT) estimates. These results contribute to our fundamental understanding of and the practical ability to control shape-selective MTO chemistry occurring in zeolites (and zeotypes) under confinement.

Time-resolved characterization of hierarchical diffusion and reactions in acidic zeolites and zeotypes with Temporal Analysis of Products (TAP) experiments

253rd National Meeting (2017)

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