Enhanced reaction rate for gas-phase epoxidation of propylene using H₂ and O₂ by Cs promotion of Au/TS-1

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• 作者：Wen-Sheng Lee ; M. Cem Akatay ; Eric A. Stach ; Fabio H. Ribeiro ; W. Nicholas Delgass
• 关键词：Au/TS-1 ; Cs promotion ; Gold clusters ; Propylene epoxidation ; Nanoporous materials
• 刊名：Journal of Catalysis
• 出版年：December, 2013
• 年：2013
• 卷：308
• 期：Complete
• 页码：98-113
• 全文大小：2687 K

文摘

Gold clusters supported on titanium silicalite-1 (hereafter denoted as Au/TS-1) with high gold loading at 鈭?.1-0.16 wt%, prepared by the deposition precipitation (DP) method, showed about two times enhancement in the PO rate ( at 200 掳C), 鈭?0% increase in PO selectivity (鈭?0% versus 鈭?0%) and 鈭?-10% increase in H₂ selectivity (鈭?0% versus 鈭?0%) when Cs₂CO₃ instead of Na₂CO₃ was used as the precipitation agent. Using Cs₂CO₃ as the precipitation agent caused a fourfold increase in Au uptake efficiency, indicating a strong interaction between Cs and Au in the Au/TS-1 system. XPS/TEM analyses for two Au/TS-1 samples with the same gold loading at 鈭?.16 wt% but different alkali metals (Cs versus Na) indicate that more Au was retained inside the TS-1 nanopores for the Cs sample. The presence of Cs is, therefore, proposed to help stabilize small gold clusters (<1 nm) inside the TS-1 nanoporous channels at the high gold loading (>0.1 wt%) due to the Cs/Au interaction, resulting in the promotion of PO rate per gram of catalyst. Furthermore, similar apparent activation energy at 鈭?0 kJ mole^鈭? observed for the Au/TS-1 catalysts with the presence of either Cs or Na suggests that the number, but not the nature of the active sites, is changed in the Cs-promoted samples. Finally, regardless of the type of alkali metal (Na or Cs) present in the catalysts, lower Ti content (Si/Ti molar ratio 鈭?00) for Au/TS-1 catalysts was found to favor PO catalytic performance.