Fluidized bed oxidative dehydrogenation of ethane to ethylene over VO_x/Ce-ΓAl₂O₃ catalysts: Reduction kinetics and catalyst activity

Cerium-doped γ-Al₂O₃ (Ce-γAl₂O₃) catalyst supports are prepared with various amounts of cerium (0.2–5 wt.%). An excess solvent impregnation method is used to saturate the vanadium (5 wt%) on the cerium-modified supports. The XRD and FTIR characterization techniques indicate the presence of crystalline CeO₂ phase, and amorphous VO_x phases on the γAl₂O₃. Raman analysis shows the coexistence of poly-vanadate and mono-vanadate species. BET analysis reveals a high surface area for the synthesized catalysts with a type-IV adsorption isotherm. TPR/TPO analyses show that VO_x/Ce-γAl₂O₃ catalysts are very active and stable over repeated reduction/oxidation cycles. The stability/purity of the synthesized catalyst is also confirmed by TGA analysis. NH₃-TPD characterization shows mild acidity while the TPR kinetics predicts lower activation energy for reduction. Oxidative dehydrogenation (ODH) of ethane experiments are developed over VO_x/Ce-γAl₂O₃ catalysts under gas-phase oxygen-free conditions in a fluidized CREC Riser Simulator. Temperatures and residence times are varied between 450 and 600 °C and 10–50 s, respectively. A maximum ethylene selectivity of 87.9% with 10.0% ethane conversion is achieved at 550 °C using the 1.0 wt.% cerium-doped VO_x/γ-Al₂O₃ catalyst. The successive ethane injections and subsequent catalyst regeneration show the stable redox characteristics of the prepared ODH catalysts.