Fluidized bed oxidative dehydrogenation of ethane to ethylene over VOx/Ce-γAl2O3 catalysts: Reduction kinetics and catalyst activity

Abstract

Cerium-doped γ-Al2O3 (Ce-γAl2O3) catalyst supports are prepared with various amounts of cerium (0.2–5wt.%). An excess solvent impregnation method is used to saturate the vanadium (5wt%) on the cerium-modified supports. The XRD and FTIR characterization techniques indicate the presence of crystalline CeO2 phase, and amorphous VOx 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 VOx/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 VOx/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 10–50s, respectively. A maximum ethylene selectivity of 87.9% with 10.0% ethane conversion is achieved at 550°C using the 1.0wt.% cerium-doped VOx/γ-Al2O3 catalyst. The successive ethane injections and subsequent catalyst regeneration show the stable redox characteristics of the prepared ODH catalysts.