Abstract
The peculiar role of either Zn2+ cations or small ZnO clusters located inside the zeolite pores in propylene transformation to aromatic hydrocarbons on Zn2+/H-ZSM-5 and ZnO/H-BEA zeolites has been analyzed. 13C MAS NMR and FTIR spectroscopic investigation has revealed similar properties of different Zn-sites with respect to propylene oligomerization. Both Zn2+ cations and ZnO species are capable to convert propylene to higher C6–C9 olefins which represent the precursors of simple benzene-based aromatics. The mechanism of such oligomerization has been inferred to include the following stages: (a) adsorption of propylene on the Zn-sites in the form of a π-complex; (b) transformation of the π-complex of propylene to σ-allylzinc surface species at elevated temperature; (c) formation of C6+ olefins; (d) transformation of oligomeric C6+ olefins to simple aromatic molecules (benzene, toluene, and xylenes). NMR evidences that Bronsted acid sites (BAS) of both zeolite samples are not involved in the oligomerizatio...
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