CO2-Assisted in situ hydrogen extraction for highly selective aromatization of n-Hexane over Zn modified HZSM-5 catalyst

Controlling the evolution of H species in CO2-assisted alkane activation represents an opportunity for simultaneously upgrading light alkanes and greenhouse gas CO2. Herein, we successfully realized the highly selective aromatization of n-hexane by the assistance of CO2 over Zn modified HZSM-5 catalyst. Multi-characterizations demonstrated that the introduction of CO2 could timely remove the in situ H originated from the C-H activation of n-hexane and cyclohexane through the dynamic evolution of the pentagonal coordination Zn-OH+-(CO)-O-Zn structure. On this basis, hydrogen transfer between olefins and aromatics is effectively inhibited, and the binding between π electrons of benzene ring and hydrogen proton is weakened, accelerating the generation and desorption of BTEX. Therefore, the Zn/ZSM-5-CO2 displays a record high 49.7% BTEX yield, which is nearly 10% higher than that of the Zn/ZSM-5-N2 (40.3%). In addition, the loss of medium strength Lewis acid caused by in situ H reduction of Si(Al)-O-Zn structure is significantly reduced, ensuring its superior catalytic stability under long-term conditions. These results may provide some insights for the profitable utilization of petrochemical resources to aromatics over zeolites.