Transformation of but-1-ene into aromatic hydrocarbons over ZSM-5 zeolites

The yield of aromatic hydrocarbons from but-1-ene increases greatly when zinc cations are incorporated into ZSM-5 zeolites. Thus, the selectivities to aromatics were 38.6% and 77.8% over H-ZSM-5 and Zn-ZSM-5, respectively, at 773 K. For both zeolites, the main aromatic products are benzene, toluene and xylenes. A variety of aromatic products implies that the interconversion among alkenes precedes their aromatization over ZSM-5 zeolites. The ratio of alkanes to aromatics was close to 3 over H-ZSM-5, indicating that aromatics are formed by the successive deprotonation and hydride transfer to carbenium ions from oligomerized products. On the other hand, the ratio was 0.9 over Zn-ZSM-5, indicating that the direct dehydrogenation of intermediate alkenes is involved in aromatization. Over H-borosilicate, the formation of alkanes and aromatics is negligible. The aromatization activity developed on incorporating zinc cations into the borosilicate, indicating the essential role of zinc species in aromatization. The dehydrogenation activity of zinc species is further confirmed by the high selectivity to butadiene from but-1-ene at low contact time over Zn-borosilicate.