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 simulta-neously 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 activa-tion 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 pi 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.

Automated summary

The selective aromatization of n-hexane was achieved by using CO2 over a Zn modified HZSM-5 catalyst, which effectively suppressed the hydrogen transfer between olefins and aromatics. This was achieved by the dynamic evolution of the Zn-OH+-(CO)-O-Zn structure, which removed in situ H originated from C-H activation. As a result, the Zn/ZSM-5-CO2 catalyst exhibited a record high BTEX yield of 49.7%, nearly 10% higher than the Zn/ZSM-5-N2 catalyst (40.3%), indicating its potential for profitable utilization of petrochemical resources.