IR study of dynamic behavior of Brønsted acid sites on zeolites at high temperatures

Osuga Ryota, N. Kondo Junko

doi:10.20731/zeoraito.35.3.101

Zeolites have been widely used as solid acid catalysts, and infrared spectroscopy is one of the powerful methods for characterization of acidity of that. However, the conventional characterization method using probe molecules have some disadvantages, which is the difference of temperatures between characterization and catalytic reaction. Hence, we cannot directly relate the result of characterization to the catalytic activity under real reaction conditions. In this study, dynamic behavior of acidic OH groups on zeolites was directly observed using IR, and dissociation enthalpy of acidic OH groups was estimated to use for one of the factors of a characterization of zeolite acidity at high temperatures. Moreover, the mechanism of proton-hopping on zeolites was investigated combined with DFT calculation. The dissociation enthalpy was dramatically affected by the zeolite topology, which was different between over 573 K and under of that. In results of DFT calculation, it revealed that protons delocalized around the T site under 573 K, and it hopped over all of the structures of zeolite at higher temperatures.

IR study of dynamic behavior of Brønsted acid sites on zeolites at high temperatures

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