Fluidized bed ODH of ethane to ethylene over VO_x-MoO_x/γ-Al₂O₃ catalyst: Desorption kinetics and catalytic activity

(Graph Presented) Oxidative dehydrogenation (ODH) of ethane is studied in a gas phase oxygen free conditions using a VO_x-MoO_x/γ-Al₂O₃ catalyst which also acts as a carrier of lattice oxygen. The prepared catalyst and the support γ-Al₂O₃ are characterized using various physicochemical techniques. XRD, Raman, and FTIR analysis show the availability of VO_x and MoO_x species on the alumina support. The TPR analysis gives two distinct peaks for the reduction of VO_x and MoO_x species, respectively. The cyclic TPR/TPO shows consistent reduction behavior of the catalyst over repeated reduction and oxidation cycles. Desorption kinetics analysis reveals low activation energy for ammonia desorption from VO_x-MoO_x/γ-Al₂O₃ surface. This indicates a minimum interaction between VO_x-MoO_x and γ-Al₂O₃ confirming easy availability of lattice oxygen for reaction. The ODH of ethane experiments are conducted in a fluidized CREC Riser Simulator at temperature range of 500-650 ΰC. The contact time is varied between 10 and 50 s. Under the studied reaction conditions, ethylene, carbon dioxide, carbon monoxide and water are the major products. At fluidized condition, VO_x-MoO_x/γ-Al₂O₃ shows significant higher ethane conversion due to the intense mixing between the catalyst and the feed. High temperature and longer contact times lead to further oxidation of the desired product ethylene to give undesired products CO_x. In repeated ODH of ethane and re-oxidation cycles, VO_x-MoO_x/γ-Al₂O₃ shows stable ethane conversion and product selectivity which is consistent to the TPR/TPO evaluation results.