Elucidating the Role of CO ₂ in the Oxidative Cracking of <i>n</i> -Hexane to Olefin Using a Tandem VO _<i>x</i> /Z

This study investigates the role of CO 2 as a soft oxidant in the oxidative cracking of n -hexane to light olefins over a tandem VO x /ZSM-5 catalyst. The goal is to reduce CO 2 emissions in petroleum refining by integrating its use into catalytic processes while simultaneously boosting olefin production and reducing coke formation. The VO x /ZSM-5 catalyst combines redox-active vanadium sites for oxidative dehydrogenation and acidic ZSM-5 sites for cracking, creating a synergistic system. Various characterization techniques, including X-ray diffraction (XRD), temperature-programmed reduction (TPR), NH 3 -TPD, Fourier transform infrared (FTIR), and thermogravimetric analysis (TGA), were employed to analyze the catalyst’s structure, reducibility, and regeneration behavior. Activity tests conducted in a riser simulator showed that CO 2 regeneration resulted in higher olefin selectivity (68%) and improved catalyst stability compared to O 2 regeneration (58%). However, CO 2 regeneration exhibited a slightly lower conversion (55%) than the conventional O 2 regeneration process (65%). Additionally, excess CO 2 enhances the regeneration of isolated VO x species, thereby improving oxidative dehydrogenation, particularly for longer-chain alkanes. The proposed mechanism highlights CO 2 ’s dual role in replenishing lattice oxygen and removing coke, supporting its use as a sustainable alternative oxidant in fluid catalytic cracking systems. These findings contribute to the development of greener refining methods and productive utilization of CO 2 in petrochemical applications.