(178e) Aqueous Phase Hydrodechlorination of Trichloroethylene Using Pd Supported on Swellable Organically Modified Silica (SOMS): Effect of Support Derivatization

Hydrodechlorination (HDC) using Pd catalysts has been demonstrated to be an effective approach to convert TCE present in groundwater, into benign products, ethane and HCl. However, HCl formed during the reaction is known to deactivate conventional Pd/Al₂O₃ catalysts. This prompted development of strategies for enhancing the deactivation resistance of HDC catalysts. Our group reported the superior deactivation resistance of Pd supported on a novel animated material known as swellable organically modified silica (SOMS). SOMS is a hydrophobic organic-inorganic hybrid material with a high affinity for organics and an ability to swell up to 6 times its dry volume on exposure to organics. In this study, we investigated the high deactivation resistance of Pd/SOMS to HCl to determine if it was due to hydrophobicity of SOMS or swellability or a combination of both. To that end, samples with varying degrees of hydrophobicity and swellability were synthesized by changing the extent of surface derivatization during sol-gel synthesis of SOMS. The impact of surface derivatization on hydrophobicity, swellability and surface area was confirmed by infrared spectroscopy and N₂ physisorption, respectively. Furthermore, after Pd impregnation, it was found that the resultant particle size, location, and atomic environment of Pd were also governed by the extent of support derivatization. The sample with the least derivatization material provided lowest protection to Pd from HCl. To study the interaction of HCl with Pd, the pristine catalysts were treated with HCl solutions. For these HCl-treated samples, the batch activity rate constants decreased by 66% for the least derivatized sample and 17% for the most derivatized one, suggesting that hydrophobicity and swellability are essential for obtaining high resistance to HCl which could potentially impact the economic viability of HDC of TCE process.