Quantum Chemical Calculation Of The Acidity Of Zeolites

In this dissertation, quantum chemistry computations and NMR experimental results based on probe molecules were combined to study acidity of several industrially used zeolites and the interactions between Br?nsted acid sites and probe molecules. We used 8T cluster to study Br?nsted acid sites by proton affinity, adsorption energy, chemical shift and quadrupole coupling constant.(1) Trimethylphosphine oxide (TMPO), pyridine and trimethylphosphine (TMP) were selected as NMR probe molecules to theoretically study the acid strength of several industrially used zeolites (H-Y, H-ZSM5 and H-MOR). The relationship between chemical shifts of these probe molecules and acid strength of zeolites was revealed. Meanwhile, the applicability of probe molecules on the characterization of Br?nsted acidity was discussed.(2) Density functional theory (DFT) method was employed to optimize the geometries of several probe molecules adsorption complexes on a Br?nsted acid site of H-Y. The relationship between proton affinity (PA) of these probe molecules and quadrupole coupling constant of 17O and 27Al atoms was revealed. The theoretical calculation suggested that the quadrupolar coupling constants of 17O and 27Al atoms of HY-adsorbates had a negative correlation with the basicity of probe molecules.