Effect of Ag loading on the adsorption/desorption properties of ZSM-5 towards toluene

A series of Ag-ZSM-5 samples with different Ag loading (0-10 wt%) was prepared via ion exchange. All samples were characterized by similar adsorption behavior towards toluene vapors. The concentration of Ag as well as the nature of Ag species were found to affect strongly the strength of toluene adsorption thus resulting in different profiles of temperature programmed desorption. The water vapors were shown to have a negative effect on adsorption properties of low Ag samples. It was suggested that the increase of Ag loading leads to the appearance of Ag (n) (delta+) (n = 2-8) clusters instead of monoatomic Ag+ sites predominantly existed in the case of the samples with low silver loading. It was found experimentally and explained theoretically by means of DFT calculations that these clusters exceed the monoatomic species by the strength of toluene adsorption even in the presence of water vapors. At the same time, SiO2/Al2O3 ratio in Ag-ZSM-5 samples was found to have no significant effect on adsorption/desorption properties of the zeolites.