Cobalt catalyzed ethane dehydrogenation to ethylene with CO2: Relationships between cobalt species and reaction pathways
TiO 2 , ZrO 2 and a series of TiO 2 -ZrO 2 (TxZ1, x means the atomic ratio of Ti/Zr = 10, 5, 1, 0.2 and 0.1) composite oxide supports were prepared through co-precipitation, and then 3 wt% Co was loaded through wetness impregnation methods. The obtained 3 wt% Co/TiO 2 (3CT), 3 wt% Co/ZrO 2 (3CZ) and 3 wt% Co/TxZ1 (3CTxZ1) catalysts were evaluated for the oxidative ethane dehydrogenation reaction with CO 2 (CO 2 -ODHE) as a soft oxidant. 3CT1Z1 catalyst exhibits excellent catalytic properties, with C 2 H 4 yield, C 2 H 6 conversion and CO 2 conversion about 24.5 %, 33.8 % and 18.0 % at 650 °C, respectively. X-Ray Diffraction (XRD), in-situ Raman, UV–vis diffuse reflectance spectra (UV–vis DRS), H 2 temperature-programmed reduction (H 2 -TPR), Electron paramagnetic resonance (EPR) and quasi in-situ X-ray Photoelectron Spectroscopy (XPS) have been utilized to thoroughly characterize the investigated catalysts. The results revealed that 3CT1Z1 produced TiZrO 4 solid solution with more metal defect sites and oxygen vacancies (Ov), promoting the formation of Co 2+ -TiZrO 4 structure. Furthermore, the presence of Ov and Ti 3+ can facilitate the high dispersion and stabilization of Co 2+ , as well as suppressing the severe reduction of Co 2+ , leading to superior ethane oxidative dehydrogenation activity. Besides, less Co 0 is beneficial to ODHE reaction, because of its promotion effects for reverse water gas shift reaction ; however, more Co 0 results in dry reforming reaction (DRE). This work will shed new lights for the design and preparation of highly efficient catalysts for ethylene production.
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