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

Abstract

The effects of the matrix oxides activity, selectivity of 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. Al 2 O 3 (A), TiO 2 (T), ZrO 2 (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 H 2 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% Al 2 O 3 , 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.