Accessibility and Reactivity of Protons in Sodalite Cages of Faujasite Zeolites

Faujasite (FAU) zeolites undergo mild dealumination at moderate ion exchange conditions (0.01 to 0.6 M of NH₄NO₃ solutions) resulting in protons circumscribed by sodalite cages becoming accessible for reaction. Accessibility of protons in the sodalite cages on FAU zeolites can be systematically manipulated by varying ammonium concentrations, and distribution of accessible protons can be quantified based on the band area ratio of OD_SOD/OD_SUP (OD₂₈₂₀/OD₂₈₆₀) by virtue of infrared spectra for H-D exchange of deuterated propane operated in batch mode. Protons in sodalite cages (H_SOD) show higher H-D exchange rates than protons in supercages (H_SUP) plausibly due to confinement effects being more prominent in smaller voids. Rate constants of propane dehydrogenation (k_D) and cracking (k_C) are also augmented as the fraction of accessible protons in the sodalite cages is enhanced, and these data in turn inform that both k_D and k_C are higher on a per proton basis in sodalite cages than in supercages. These effects of accessibility and reactivity of protons in sodalite cages are revealed herein via methods that systematically increase accessibility of sodalite cages.