AI Article Synopsis
- Low-silica faujasite zeolites maintain their structure and porosity after a mild ion exchange process, which introduces reactive protons within their supercages.
- This ion exchange occurs without displacing sodium ions in associated sodalite cages, helping to stabilize the zeolite's framework.
- The distinct reactivities of the protons can be analyzed using infrared spectroscopy, showing that protons in one location (site II) are significantly more reactive for propane reactions compared to those in another location (site III), which enhances the zeolite's effectiveness as a solid-acid catalyst at high temperatures.
Article 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 NHNO 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). 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 (H) and site III (H) 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.
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| http://dx.doi.org/10.1021/jacs.2c01022 | DOI Listing |
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