Abstract
Density functional and ONIOM calculations were carried out to investigate the possible active sites of Au(I) ion-exchanged ZSM-5 catalysts. Adsorption energies and vibrational frequencies of CO, NO, NO 2, SO 2, H 2O, NH 3, CH 3NH 2 and CH 3SH molecules were analyzed. For first time the existence of two active sites in Au/ZSM-5 is shown; one of them is responsible for the high and the other for the low CO and NO adsorption frequencies. The analysis of adsorption Δ G shows that Au(I) behaves like a soft acid; therefore, there will be a preferential adsorption of soft bases over hard bases. The interaction with NH 3 is thermodynamically very favored, mainly due to the hydrogen bond formation between the NH 3 hydrogen atoms and the oxygen atoms of the zeolitic framework.
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