Are olefin aromatization reactions structure sensitive over Al pairs and single Al in H-ZSM-5 Zeolite?

Understanding the catalytic structure–activity relationship over active sites is of fundamental importance in heterogeneous catalysis field. Herein, a series of H-ZSM-5 zeolites with Al pairs contents in the range of 31% to 82% are used to explore the structure sensitivity of olefin aromatization reaction. Compared with high reaction temperatures (385 ℃ and above), prominently different initial aromatic yields are observed over the samples at 150 ℃. In addition, the 1-octene temperature-programmed surface reaction (TPSR) and theoretical calculation results give a thorough understanding on active site dependent activation temperature (100 vs 150 ℃ over Al pairs and single Al). However, the catalytic cycle of olefin aromatization is not sustainable at low reaction temperature, which is due to the formation and blocking of big molecules in the micropores (e.g., trimethylbenzene etc.). In conclusion, the desorption of big molecules is the rate-determining step for olefin aromatization reaction over H-ZSM-5, which masks the structure sensitivity over Al pairs and single Al.