Reaction Mechanism and Kinetics of Olefin Metathesis by Supported ReOx/Al2O3 Catalysts

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• 作者：Soe Lwin ; Israel E. Wachs
• 刊名：ACS Catalysis
• 出版年：2016
• 出版时间：January 4, 2016
• 年：2016
• 卷：6
• 期：1
• 页码：272-278
• 全文大小：447K
• ISSN：2155-5435

文摘

The self-metathesis of propylene by heterogeneous supported ReO_x/Al₂O₃ catalysts was investigated with in situ Raman spectroscopy, isotopic switch (D–C₃⁼ → H–C₃⁼), temperature-programmed surface reaction (TPSR) spectroscopy, and steady-state kinetic studies. The in situ Raman studies showed that two distinct surface ReO₄ sites are present on alumina and that the olefins preferentially interact with surface ReO₄ sites anchored at acidic surface sites of alumina (olefin adsorption: C₄⁼ > C₃⁼ > C₂⁼). The isotopic switch experiments demonstrate that surface Re*═CH₃ and Re*═CHCH₃ are present during propylene metathesis, with Re* representing activated surface rhenia sites. At low temperatures (<100 °C), the rate-determining step is adsorption of propylene on two adjacent surface sites (rate ≈ [C₃⁼][Re*]². At high temperatures (>100 °C), the rate-determining step is the recombination of two surface propylene molecules (rate ≈ [C₃⁼]²[Re*]). To a lesser extent, the recombination of surface Re*═CH₃ and Re*═CHCH₃ intermediates also contributes to self-metathesis of propylene at elevated reaction temperatures.