Temperature-dependent reaction mechanisms of ethane oxidative dehydrogenation to ethylene with CO2 on cobalt based catalysts

CO 2 -assisted oxidative dehydrogenation of ethane (CO 2 -ODHE) has attracted growing attention as a promising route for the effective utilization of shale gas and CO 2 to produce ethylene. A 1.5 wt% Co/TiZrO 4 catalyst was identified highly effective for the CO 2 -ODHE reaction, achieving an ethane conversion of 43.7%, an ethylene yield of 27.9% and a CO 2 conversion of 20.1% at 650 ℃ − performances that surpasses many reported non-Cr-based transition metal catalysts. Based upon our recently developed analytical method for quantitative elucidation of ethane-CO 2 reaction pathways, combined characterization using powder X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H 2 -TPR), in-situ Raman, in-situ NO adsorption diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and quasi in-situ X-ray photoelectron spectroscopy (XPS) revealed that Co 3+ species exhibited higher intrinsic activity than Co 2+ for ethane dehydrogenation. More importantly, this study provide first evidence for a temperature dependent reaction mechanism- from a Mars-van Krevelen mechanism at low temperature, to a coupled direct dehydrogenation (DDHE) and reverse water gas shift (RWGS) mechanism at intermediate temperatures, and finally to dry reforming of ethane (DRE) at high temperature. These mechanistic insights establised a robust foundation for the rational design of highly selective and thermally stable catalysts for efficient ethylene production via CO 2 -ODHE.