Effect of Type of Matrix on Formation of Aromatics by Cracking and Dehydrocyclization of n-Pentane Using ZnZSM-5 Metal Oxide Hierarchical Composite Catalysts

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ZnZSM-5 metal oxide hierarchical composite catalysts were made using Zn-exchanged ZSM-5 and various oxides by the conventional kneading method. The effects of these oxides as matrices on the activity and selectivity for aromatics in cracking and dehydrocyclization of n-pentane were investigated. ZnZSM-5 50-85 wt% was mixed with oxide 0-35 wt% and alumina-sol binder 15 wt% using the kneading method. Al2O3 (A), TiO2 (T), ZrO2 (Zr) and kaolin (ka) were used as the oxide. Cracking and successive dehydrocyclization of n-pentane was carried out in a fixed-bed reactor under atmospheric H2 in the range 450-550 °C. Conversions of n-pentane at 550 °C decreased in the order ZnZSM/0A (85 wt% ZnZSM-5, 0 wt% Al2O3, 15 wt% binder) ≥ ZnZSM/10A > ZnZSM/10T > ZnZSM/10Zr > ZnZSM/10ka ≥ ZnZSM/35A. The selectivity for aromatics at 550 °C decreased in the order ZnZSM/10A > ZnZSM/0A > ZnZSM/10Zr = ZnZSM/10T = ZnZSM/10ka > ZnZSM/35A. These results suggested that the use of both ZnZSM-5 and matrix with large porosity for this reaction would optimize the catalytic functions. The product distribution indicated that aromatization of olefins to benzene, toluene, and xylene occurred through the Diels-Alder reaction on Zn species in the ZSM-5.