Effect of Silver Cations on Propene Aromatization on H-ZSM-5 Zeolite Investigated by 13C MAS NMR and FTIR Spectroscopy

Silver-modified zeolites exhibit high selectivity foralkene transformationto aromatic hydrocarbons. To inquire into the effect of silver cationsin zeolite on the pathways of propene aromatization, the transformationsof propene on H-ZSM-5 and Ag/H-ZSM-5 zeolites have been investigatedby C-13 MAS NMR and Fourier-transform infrared spectroscopy.It is established that propene transformation on H-ZSM-5 at 296-773K occurs on Bronsted acid sites (BAS) by the mechanism of conjunctpolymerization, as evidenced by the detection of cyclopentenyl cationintermediates. On the contrary, propene forms very stable & pi;-complexeswith Ag+ sites on Ag/H-ZSM-5, which prevents the alkenefrom converting on BAS at 296-623 K. At T & GE;623 K, transformation proceeds with the assistance of silver cationsvia carbanionic allyl-like intermediate formation. Thus, the changein the reaction mechanism from conjunct polymerization on BAS to themechanism with Ag+ ion involvement provides high selectivityfor aromatic hydrocarbons on Ag+/H-ZSM-5 zeolite.

Automated summary

Silver-modified zeolites with high selectivity for alkene transformation to aromatic hydrocarbons were studied. The effect of silver cations in zeolite on the pathways of propene aromatization was investigated using C-13 MAS NMR and Fourier-transform infrared spectroscopy. Results showed that propene on H-ZSM-5 transformed via conjunct polymerization while being influenced by Ag+ sites on Ag/H-ZSM-5, resulting in high selectivity for aromatic hydrocarbons.