Fluidized bed ODH of ethane to ethylene over VOx–MoOx/γ-Al2O3 catalyst: Desorption kinetics and catalytic activity

Abstract

Oxidative dehydrogenation (ODH) of ethane is studied in a gas phase oxygen free conditions using a VOx–MoOx/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 VOx and MoOx species on the alumina support. The TPR analysis gives two distinct peaks for the reduction of VOx and MoOx 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 VOx–MoOx/γ-Al2O3 surface. This indicates a minimum interaction between VOx–MoOx 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°C. The contact time is varied between 10 and 50s. Under the studied reaction conditions, ethylene, carbon dioxide, carbon monoxide and water are the major products. At fluidized condition, VOx–MoOx/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 COx. In repeated ODH of ethane and re-oxidation cycles, VOx–MoOx/γ-Al2O3 shows stable ethane conversion and product selectivity which is consistent to the TPR/TPO evaluation results.