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.

中文翻译：

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钨酸钾催化剂上乙烷氧化脱氢制乙烯

本研究通过微动力学分析和气相化学模拟，阐明了乙烷在 K ₂ WO ₄ /SiO ₂上催化氧化脱氢（ODH）的机理。以无定形二氧化硅为原料，900 ℃煅烧生成方英石制备的K ₂ WO ₄ /SiO ₂催化剂表现出比结晶二氧化硅（方英石）制备的催化剂更好的性能。动力学分析表明，C ₂ H ₆和O ₂均表现出正依赖性，并且反应通过表面O物种（O*，可能是过氧化物物种）介导的H-抽象在低转化率下通过C-H激活进行。在反应物流中添加H ₂ O后，转化率显着提高。相对于O ₂和H _{2 O压力的动力学顺序与通过O*物质与H 2} O反应形成OH自由基一致，该自由基随后将激活气相中C ₂ H ₆分子的C-H 。实验观察到的C ₂ H ₆转化率涉及O*介导（干）和OH自由基介导（湿）平行途径的贡献。通过假设cofed H _{2 O的主要动力学后果是产生OH自由基，动力学模拟说明了cofed H 2} O对C ₂ H ₆活化的促进作用，同时不影响产物分布，这与实验观察到的趋势非常吻合。