Authors:

David W Ball

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About Paper:

Zeolites are catalysts widely used in industrial chemical processes for upgrading raw feedstocks into value-added products. These catalysts contain active (H+) sites, confined within molecular-sized voids (<2 nm), that shape-selectively stabilize desired reactive intermediates. Their structure comprises a porous framework of interconnected silicon oxide (Si4+) tetrahedra occasionally substituted by aluminum (Al4+) that generate net-negative charges, which are charge-compensated by active Brønsted (H+) sites. When operating as industrial catalysts, zeolites are routinely exposed to steam at high temperatures (>700 K), leading to loss of H+ sites via hydrolysis of framework aluminum. To mitigate H+ site loss, commercially available MFI (framework type) zeolites are commonly treated with phosphorus species, which results in higher H+ site retention upon exposure to steam at high temperature (hydrothermal treatments). However, the amount of phosphorus required to retain the maximum number of H+ sites varies with active site content and precursor identity, requiring empirical models for catalyst design. Herein, we elucidate molecular interactions between phosphorus and H+ sites that govern hydrothermal stability by studying model MFI zeolites impregnated with gradually increasing phosphorus content. H+ site counts before and after hydrothermal treatments will be used as a proxy to quantify hydrothermal stability, and will be complemented by kinetic studies of H+ site-catalyzed probe reactions to evaluate reactivity of pristine and steam-aged phosphorus-MFI samples. Together, these data elucidate the interactions between phosphorus species and H+ sites in MFI zeolites that govern their hydrothermal stability and reactivity, allowing the design of phosphorus-stabilized zeolites that account for these site-specific interactions. Keywords: Hydrocarbon Upgrading; Zeolites; Acid Catalysis; Hydrothermal Stability; Phosphorus Modification † Presenting Undergrad Author; ‡ Contributing Undergrad Author; * Undergrad Acknowledgment

Source:

Purdue University / 2025

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Co-authors:

David W Ball