Acid Catalysis over Low-Silica Faujasite Zeolites

Xinyu Li; He Han; Wenqian Xu; Son-Jong Hwang; Zhichen Shi; Peng Lu; Aditya Bhan; Michael Tsapatsis

doi:10.1021/jacs.2c01022

Acid Catalysis over Low-Silica Faujasite Zeolites

J Am Chem Soc. 2022 Jun 1;144(21):9324-9329. doi: 10.1021/jacs.2c01022. Epub 2022 May 17.

Authors

Xinyu Li¹, He Han^{1

2}, Wenqian Xu³, Son-Jong Hwang⁴, Zhichen Shi¹, Peng Lu⁵, Aditya Bhan¹, Michael Tsapatsis^{1

5

6}

Affiliations

¹ Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Avenue SE, Minneapolis, Minnesota 55455, United States.
² State Key Laboratory of Fine Chemicals, PSU-DUT Joint Center for Energy Research, School of Chemical Engineering, Dalian University of Technology, Dalian 116024, Liaoning Province, China.
³ X-ray Science Division, Advanced Photon Source, Argonne National Laboratory, Lemont, Illinois 60439, United States.
⁴ Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States.
⁵ Department of Chemical and Biomolecular Engineering & Institute for NanoBioTechnology, Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, United States.
⁶ Applied Physics Laboratory, Johns Hopkins University, 11100 Johns Hopkins Road, Laurel, Maryland 20723, United States.

PMID: 35580033
DOI: 10.1021/jacs.2c01022

Abstract

Low-silica faujasite (FAU) zeolites (with Si/Al ratio of ca. 1.2-1.8) sustain framework integrity and porosity upon moderate ion exchange (0.01 M NH₄NO₃ solution for 1 h at ambient temperature), which introduces two kinds of protons, distinctive in reactivity and coordination to the zeolite framework, within supercages (H_SUP). Moderate ion exchange limited within supercages transpires while maintaining full occupancy of Na⁺ cations within associated sodalite cages; this in turn helps stabilize the framework of low-silica H-FAU zeolites. Protons located on site II (H₃₆₃₀) and site III (H₃₆₅₀) within supercages on low-silica FAU zeolites can be classified and enumerated by virtue of infrared spectroscopy, providing an opportunity to compare reactivities of these distinct protons for monomolecular protolytic reactions of propane. Protons on site II exhibit prominently higher reactivity for monomolecular propane dehydrogenation and cracking than protons on site III. Low-silica proton-form FAU zeolites (zeolite X) upon moderate ion exchange possess protons on site III that are unavailable on high-silica FAU zeolites (zeolite Y) and limit ion exchange within supercages, providing unprecedented high-temperature structural and chemical stability (>773 K) and enabling their application as solid-acid catalysts.