2025 AIChE Annual Meeting

(118b) Role of Phosphorus Precursors in Zeolite Catalyst Modification: Diffusion Constraints and Reaction Implications

Authors

Farzad Jokar, The University of Oklahoma
M Sri Abey Vignesh, The University of Oklahoma
Jeffery L. White, Oklahoma State University
Steven P. Crossley, University of Oklahoma
Phosphorus (P) incorporation into zeolites has been explored since the 1970s as a simple, cost-effective strategy for modifying zeolite properties in industrial catalytic applications. P-modified zeolites have demonstrated improved hydrothermal stability during regeneration cycles, altered pore environments that influence product selectivity, and modulated acidity that slows coke formation1. While the catalytic behavior of P-modified zeolites is often correlated with phosphorus loading and incorporation methods, the role of the phosphorus precursor itself remains underexplored. In this study, we investigate the catalytic implications of using two distinct phosphorus precursors, an inorganic source, ammonium dihydrogen phosphate ((NH₄)H₂PO₄, ADP), and an organic source, trimethyl phosphate ((CH₃)₃PO₄, TMP), to modify a low-aluminum MFI zeolite (Si/Al = 140) via incipient wetness impregnation. This technique can yield different phosphate species prior to incorporation into the zeolite framework, ultimately influencing physicochemical properties and catalytic performance. Textural analysis reveals a significant difference between the two treatments, with TMP-modified MFI showing minimal loss in BET surface area and micropore volume, suggesting less pore blockage. In contrast, ADP-treated samples exhibit increased diffusional constraints, as supported by constraint index measurements2. These structural differences translate into distinct catalytic behaviors across various reactions, including acylation,3alkylation, cracking, etherification, and esterification. Notable variations were observed in activity, stability, and product selectivity, underscoring the critical role of the phosphorus precursor in tuning catalyst performance. These findings highlight the significance of precursor selection in phosphorus modification of zeolites and offer new insights for optimizing catalyst design in industrially relevant processes.

References

  1. van der Bij, H. E., & Weckhuysen, B. M. Chemical Society Reviews 44.20 (2015): 7406-7428.
  2. Zones, S.I. and T.V. Harris, Microporous and Mesoporous Materials. 2000 Apr 1;35:31-46
  3. Alalq, I. et al. Journal of Catalysis, accepted (2025) https://doi.org/10.1016/j.jcat.2025.116096