(113e) Metal-Exchanged Ordered Mesoporous Silicates As Olefin Epoxidation Catalysts

With the increasing demand for plastics and increased availability of ethylene in the United States from shale gas, resource-efficient technologies for converting ethylene to chemical intermediates assume increased importance.  In this context, the selective epoxidation of ethylene with no CO₂ formation continues to attract interest from both academia and industry. Previously, we had shown that methyltrioxorhenium is an active homogeneous catalyst for selective ethylene epoxidation with hydrogen peroxide ^{[1, 2]}. In our quest to find inexpensive alternatives, we are investigating metal-incorporated mesoporous silicates such as tungsten-exchanged KIT-5^[3] and KIT-6^[4] materials, and Ce-TUD-1 as selective epoxidation catalysts for converting ethylene to ethylene oxide using aqueous hydrogen peroxide (H₂O₂) as the oxidant. Most interestingly, all these catalysts show reasonable ethylene epoxidation activity (~150-1400 mg EO/h g metal) with no CO₂ formation at mild conditions (25-40°C, ~50 bars). However, significant H₂O₂ decomposition and metal leaching are problems that must be overcome for these catalysts to be practically viable. This talk will discuss the synthesis and detailed characterization of these catalysts along with the epoxidation activity results and plausible mechanisms for H₂O₂ decomposition and metal leaching. Steps to mitigate these drawbacks (such as silylation of the catalysts) will also be discussed.

1. Ghanta, M., et al., Highly Selective Homogeneous Ethylene Epoxidation in Gas (Ethylene)-Expanded Liquid: Transport and Kinetic Studies. AIChE Journal, 2013. 59(1): p. 180-187.

2. Ghanta, M., et al., Is the Liquid-Phase H₂O₂-Based Ethylene Oxide Process More Economical and Greener Than the Gas-Phase O-2-Based Silver-Catalyzed Process? Industrial & Engineering Chemistry Research, 2013. 52(1): p. 18-29.

3. Ramanathan, A., et al., Tungsten-incorporated cage-type mesoporous silicate: W-KIT-5. Microporous and Mesoporous Materials, 2013. 175: p. 43-49.

4. Ramanathan, A., et al., Direct incorporation of tungsten into ultra-large-pore three-dimensional mesoporous silicate framework: W-KIT-6. Journal of Porous Materials, 2012. 19(6): p. 961-968.