Teoretické studium kyselých zeolitů

The acidic zeolite H-FER with Si:Al ratios of 71, 35 and 8 was investigated employing a periodic DFT model, as well as cluster models and the CCSD(T) level of theory. The computational study of the H- FER in a high silica form (Si:Al = 71) accompanied by the investigation of the interaction of the CO and N2 probe molecules with the H-FER sample was supplemented with the experimental data obtained from the variable temperature infrared spectroscopy (VTIR). The H-FER samples with different Si:Al ratios were characterized by the structure, location and relative stabilities of the Brønsted acid groups. Relative stability of these sites was found to be dependent on Si:Al ratio, which is the main factor dictating the relative concentration of Brønsted acid sites having different types of local configuration. The number of AlO4 tetrahedra sharing an oxygen with the SiO4 tetrahedron involved in the Brønsted acid site determines the Si-O(H)-Al angle, O-H stretching frequency and deprotonation energy (and hence acid strength). Furthermore, the theoretical results obtained for the CO and N2 interaction with the H-FER were found to be in a good agreement with the experimental VTIR data. Several types of hydrogen-bonded OH···CO and OH···N2 complexes were characterized, formed by interaction between the adsorbed..