Study of the role of Zn in aromatization of light alkanes with probe molecules

The role of Zn2+ in ZnZSM-5 catalyst in the process of aromatization of alkanes has been studied with the probe molecules n-hexane, cyclohexane and 1-hexene. IR measurements showed that the parent HZSM-5 zeolite contains predominantly Bronsted acid sites, while Zn cations in ZnZSM-5 catalyst represent Lewis sites. From the results it follows, that Zn cations in ZnZSM-5 catalyst as Lewis acid sites have strong hydro-dehydrogenation activity and they catalyze the dehydrogenation of n-hexane as well as of cyclic intermediates into the corresponding aromatics. From the results of catalytic tests we conclude that the hydro-dehydrogenation activity of the catalyst plays an essential role in aromatization of light alkanes. The results indicate that for improving the yields of aromatics in aromatization of light alkanes on bifunctional catalysts it is inevitable to increase the participation of the dehydrogenation reactions in the activation of alkane as well as in the formation of the corresponding aromatics from cyclic intermediates.