4.6 Article

Spatial Proximities between Bronsted Acid Sites, AlOH Groups, and Residual NH4+Cations in Zeolites Mordenite and Ferrierite

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JOURNAL OF PHYSICAL CHEMISTRY C
卷 127, 期 1, 页码 736-745

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AMER CHEMICAL SOC
DOI: 10.1021/acs.jpcc.2c07346

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The interaction between Bri nsted acid sites, AlOH groups, and residual NH4+ cations in zeolites mordenite and ferrierite was investigated. High temperatures are required to eliminate NH4+. NMR data reveal NH4+ cations primarily in the vicinity of BAS and other NH4+ in mordenite, while AlOH groups in ferrierite.
The interaction between Bri nsted acid sites (BAS), AlOH groups, and residual NH4+ cations in zeolites mordenite and ferrierite was investigated by solid-state 1H magic-angle spinning and 1H-27Al rotational-echo adiabatic-passage double-resonance (REAPDOR) nuclear magnetic resonance (NMR) techniques in combination with density functional theory (DFT) cluster calculations. Higher temperatures are needed for the full elimination of NH4+ (853 K instead of 723 K compared to other high-silica zeolites). NMR data reveal that residual NH4+ cations are primarily in the vicinity of BAS and other NH4+ in the case of mordenite and AlOH groups in ferrierite materials. DFT calculations for a variety of cluster models with BAS and NH4+ ions embedded in their zeolite environment rationalize the experimental data. It is suggested that NH4+ ions are preferably stabilized within 8-ring pores, explaining the higher temperature required to decompose them.

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