(175e) Aromatization of N-Octane over Zsm-5 Zeolite Catalysts and Its Reaction Pathways

Much attention has been focused on the transformation of naphtha into aromatics utilized as fundamental raw materials for many petrochemical industries. In this contribution, aromatization of n-octane, one of the main components of light naphtha, has been investigated over HZSM-5 (Si/Al = 10, 36, 50, 100) and Zn/HZSM-5 catalysts prepared by ion exchange method. The catalytic activity measurement was performed at 500 ^oC under atmospheric pressure. Results exhibited that the lower Si/Al ratio of HZSM-5 catalysts provided for the higher selectivity to total aromatics since an increase in BrØnsted acid sites would enhance the greater availability of cracking intermediates for aromatics. The presence of zinc in Zn/HZSM-5 provided a significant increase in total aromatics selectivity due to the improvement in dehydrogenation activity by Zn incorporation. Zn species facilitated the aromatization by converting the paraffins into corresponding olefins which, in turn, were the aromatics precursors. Therefore, both acidity and zinc incorporation played important roles in aromatization of n-octane. The results revealed that the aromatics were generated from small olefins. The reaction pathways could be proposed based on the preliminary results as follows: the n-octane would be first decomposed to small olefins, followed by oligomerization and cyclization. In addition, toluene disproportionation and benzene alkylation would also take place for C₈ aromatics production. However, the direct dehydrocyclization of n-octane was not observed over Zn/HZSM-5.