第二届中国化学链会议

Chemical looping oxidative dehydrogenation (CL-ODH) has been extensively investigated as a green strategy for light olefins production from alkanes/naphtha without thermodynamic equilibrium constraints. However, achieving high ethylene selectivity as well as promising ethane conversion at relatively low-temperature (≤ 600 °C) remains challenging so far in chemical looping oxidative dehydrogenation (CL-ODH) of ethane. Dual-metal oxides (especially non-expensive ones) supported zeolite may possess promising ethane ODH performance due to the tunable acidity and redox property, which has rarely been investigated under the context of CL-ODH. Herein, we show that Fe-Co dual-metal oxides supported HZSM-5 can be used as appropriate redox catalyst for CL-ODH of ethane. By adjusting the Fe: Co ratio in the mixed oxides as well as the Si: Al ratio in the HZSM-5 support, the synergy of dual-metal oxides and the role of sample acidity in ethane ODH reaction were systematically investigated. In addition, the effects of reaction temperature and gas hourly space velocities (GHSV) on the ethane ODH performance of 8Fe-2Co/HZ5(200) were investigated. As it turned out, the best-performing sample, i.e., 8Fe-2Co/HZ5(200), demonstrated ~87% ethylene selectivity at 23% ethane conversion under reaction temperature of 600 °C and the GHSV of 4800 mL·h^-1·g^-1. The stable ethane ODH performance achieved over 100 redox cycles without coking further indicated the feasibility of its utilization in CL-ODH. Physicochemical characterization techniques including XRD, SEM, TEM-EDS, NH₃-TPD, H₂-TPR, XPS, and C₂H₆-TPR were used to elucidate the structure-function relationship of the redox catalysts. Comparison testing and physicochemical characterization results showed that both sample acidity and dual-metal oxides synergy are pivotal for ethane ODH to yield ethylene, in which dual-metal oxides are responsible for low-temperature ethane activation while sample acidity is critical for ethylene selectivity as well as activity. The present work demonstrates the feasibility of using dual-metal oxides supported HZSM-5 for low-temperature CL-ODH of ethane, and provides sights for redox catalyst design to achieve a good balance between sample activity and selectivity.

Oxidative dehydrogenation, chemical looping, ethylene production, dual-metal oxides, HZSM-5