(14g) Swellable Organically Modified Silica (SOMS): A Novel Support for Pd Catalyzed Hydrodechlorination of Trichloroethylene in Aqueous Phase

Trichloroethylene (TCE) is a major groundwater contaminant which is strictly regulated by U.S. E.P.A. The maximum allowable concentration of TCE in water is 5 ppb, which demands complete removal of TCE from groundwater[1]. As of today, several techniques have been explored for degradation of TCE, among which, the catalytic hydrodechlorination (HDC) appears to be promising[2, 3]. Nonetheless, the challenges that need to be overcome in the use of catalytic HDC of TCE include slow kinetics, product inhibition and deactivation due to anionic species such as chloride and sulfites.

Our studies focus on the application of swellable organically modified silica (SOMS) as a novel catalyst support for HDC of TCE. SOMS belongs to the class of bridged polysilsesquioxanes, which are hybrid organic-inorganic materials, synthesized by sol-gel technique. A unique quality of SOMS is that it swells to almost 3 times it’s dry volume, in presence of organic solvents. Apart from this, properties such as hydrophobicity, mesoporosity, high surface area and absorptivity, also make SOMS an attractive choice for a catalyst support[4]. Furthermore, catalysts involving SOMS as the support were synthesized by impregnation of Pd in its pores[5]. This study aims at investigating the effects of swelling and hydrophobicity of SOMS on the kinetics of HDC of TCE. The deactivation resistance of SOMS towards the anionic species in groundwater is also being studied.

Various techniques such as, near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), in-situ X-ray absorption near edge structure (XANES), in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and laser Raman spectroscopy were used to investigate different characteristics of Pd/SOMS and their role in HDC of TCE. Additionally, techniques such as extended X-ray absorption fine structure (EXAFS), inductively coupled plasma optical emission spectrometry (ICP-OES), transmission electron microcopy (TEM) and mass spectrometry were employed to determine the deactivation resistance of Pd/SOMS. For this study, Pd/Al₂O₃was used as the basis of comparison. The results indicate that SOMS has great potential to serve as a catalyst support for HDC of TCE.

[1] National Primary Drinking Water Regulations: EPA 816-F-09-004, in, United States Environmental Protection Agency, 2009.

[2] C.G. Schreier, M. Reinhard, Catalytic hydrodehalogenation of chlorinated ethylenes using palladium and hydrogen for the treatment of contaminated water, Chemosphere, 31 (1995) 13.

[3] H.H. Russell, J.E. Matthews, W.S. Guy, TCE removal from contaminated soil and groundwater, EPA Environmental Engineering Sourcebook, (1992).

[4] C.M. Burkett, L.A. Underwood, R.S. Volzer, J.A. Baughman, P.L. Edmiston, Organic–Inorganic Hybrid Materials that Rapidly Swell in Non-Polar Liquids: Nanoscale Morphology and Swelling Mechanism, Chemistry of Materials, 20 (2008) 10.

[5] H. Sohn, G. Celik, S. Gunduz, S.L. Dean, E. Painting, P.L. Edmiston, U.S. Ozkan, Hydrodechlorination of trichloroethylene over Pd supported on swellable organically-modified silica (SOMS), Applied Catalysis B: Environmental, 203 (2017) 641-653.