Speaker
Description
Acid forms of zeolites have been used in industry for several decades but scaling the strength of their acid centers is still an unresolved and intensely debated issue. The Brønsted acidity strength in aluminosilicates measured by their deprotonation energy was investigated for FAU, CHA, IFR, MOR, FER, MFI, and TON zeolites by means of periodic and cluster calculations at the density functional theory (DFT) level resulting into a novel approach to calculate acidity strength of aluminosilicate materials. Moreover, large diversity of the IR band shapes in the OH stretching region were investigated by combined use of FT-IR spectroscopy and DFT calculations. The analysis of various isolated Brønsted acid sites was performed with a model based on Boltzmann weighted relative energies and OH frequencies obtained by the ω/r correlation method. The model correctly predicts the band shapes of H-FER and H-TON zeolites in the free OH region of the FT-IR spectra. For H-CHA and H-IFR, however, the mutual BAS interactions cannot be ignored even for high Si/Al ratios, which renders the concept of isolated BAS inadequate.
