Enhanced reaction rate for gas-phase epoxidation of propylene using H-2 and O-2 by Cs promotion of Au/TS-1
Date of this Version
12-2013Abstract
Gold clusters supported on titanium silicalite-1 (hereafter denoted as Au/TS-1) with high gold loading at 0.1-0.16 wt%, prepared by the deposition precipitation (DP) method, showed about two times enhancement in the PO rate (similar to 300 versus similar to 150 gpo h(-1) kg(cat)(-1), at 200 degrees C), similar to 10% increase in PO selectivity (similar to 80% versus similar to 70%) and similar to 5-10% increase in H-2 selectivity (-20% versus similar to 10%) 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 similar to 0.16 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 30 kJ mole(-1) 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 100) for Au/TS-1 catalysts was found to favor PO catalytic performance. (C) 2013 Elsevier Inc. All rights reserved.
Discipline(s)
Nanoscience and Nanotechnology
Link to Full Text
Comments
Publisher's version can be found at
http://www.sciencedirect.com/science/article/pii/S0021951713001966)
DOI: 10.1016/j.jcat.2013.05.023