(513dl) Aqueous Phase Hydrodechlorination of TCE with Pd Supported Swellable Organically Modified Silica(SOMS): Effect of Ethanol on Reaction Kinetics

Trichloroethylene is one of the major contaminants found in groundwater. The concentration of TCE in groundwater is strictly regulated to be less than 5 ppb by US EPA due to its acute toxicity. Physical and biological techniques of eliminating TCE are limited by their efficiency and high cost of operation. Catalytic hydrodechlorination (HDC) of TCE is known to be a promising option. However, the catalyst suffers from inhibiton by HCl formed in the reaction. Furthermore, low concentration of TCE due to its low water solubility hampers reaction kinetics. In this study, we have used swellable organically modified silica (SOMS) as the catalyst support to overcome these issues.

SOMS is a novel hybrid organic-inorganic hydrophobic mesoporous material synthesized by sol-gel method. Its affinity for organics helps in increasing the local concentration of TCE near the active sites. Swellability of SOMS in presence of organics, provides high surface area for the reaction and improves metal dispersion. We have reported an active Pd/SOMS catalyst for HDC of TCE earlier. Swellability of SOMS was demonstrated using cryogenic scanning electron microscopy (Cryo-SEM) and near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS).

In this work, the effect of ethanol, used as a swelling agent, on catalyst performance and reaction kinetics is explored. Experiments under varied reaction conditions and degree of catalyst swelling were performed to study the dynamic nature of SOMS. Removal of HCl formed in the reaction was found to be a function of swelling. Effect of ethanol concentration on accessibility of hydrogen was studied by performing time resolved in-situ X-ray absorption near edge structure (XANES) under liquid phase conditions. Furthermore, opening of pores under rising ethanol pressures revealed an increase in the Pd/Si ratio obtained by NAP-XPS. Information about the role of ethanol obtained by the above experiments provided mechanistic insight into the reaction.