Reduction kinetics and catalytic activity of VO_x/γ-Al₂O₃-ZrO₂ for gas phase oxygen free ODH of ethane

Oxidative dehydrogenation (ODH) of ethane is investigated using VO_x/Al₂O₃-ZrO₂ catalysts in absence of gas phase oxygen under circulating fluidized conditions. In this approach, the catalyst particles also serve as a source of lattice oxygen. The fluidizable VO_x/Al₂O₃-ZrO₂ catalysts are prepared with various amount of VO_x using a successive impregnation technique. XRF measurement confirms the consistency between the targeted and actual metal loading. Nitrogen adsorption shows type-v monolayer adsorption on VO_x/Al₂O₃-ZrO₂ surface. XRD and Raman confirm the presence of VO_x species on the Al₂O₃-ZrO₂ as a crystal phase. NH₃-TPD measurement shows that the acidity of the catalysts decreases slightly with VO_x loading. The VO_x/Al₂O₃-ZrO₂ catalysts are stable over repeated reduction (TPR) and oxidation (TPO) cycles. The TPR kinetics modeling reveals that the activation energy of catalyst reduction (oxygen release) increases with increasing the VO_x loading. This is an indication of increasing difficulties of VO_x reduction at higher VO_x loading. The ODH of ethane experiments are established in a fluidized CREC-riser simulator at different temperatures (525-600°C) and reaction times (20-50s). Approximately, 89% ethylene selectivity is achieved with 10% VO_x on Al₂O₃-ZrO₂. The ethylene selectivity also remains stable over repeated ODH and catalyst regeneration cycles.