American Chemical Society
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Oxidative Dehydrogenation of Ethane to Ethylene over Potassium Tungstate Catalysts

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journal contribution
posted on 2024-03-22, 23:43 authored by Duanxing Li, Zenghao Wei, Kazuhiro Takanabe
This study elucidated the mechanism of catalytic oxidative dehydrogenation (ODH) of ethane over K2WO4/SiO2 by using microkinetic analysis and simulation with gas-phase chemistry. The K2WO4/SiO2 catalyst prepared with amorphous silica as starting material and cristobalite produced during 900 °C calcination exhibited better performance than catalysts prepared with crystallized silica (cristobalite). The kinetic analysis suggested that both C2H6 and O2 show positive dependences and the reaction proceeds by C–H activation via surface O species (O*, likely peroxide species)-mediated H-abstraction at low conversion. Upon addition of H2O in the reactant stream, the conversion rate drastically improved. Kinetic orders with respective to O2 and H2O pressure are consistent with OH radical formation through the reaction of O* species with H2O, which would then activate the C–H of C2H6 molecules in the gas phase. The experimentally observed C2H6 conversion rate involved contributions from both O*-mediated (dry) and OH radical-mediated (wet) parallel pathways. By assuming that the main kinetic consequence of cofed H2O was generating OH radicals, kinetic simulation illustrated the promotional effect of cofed H2O on C2H6 activation while not affecting the product distribution, which matched well with experimentally observed trends.