(617gp) Aqueous-Phase Hydrodechlorination of Trichloroethene over Pd-Supported on Swellable Organically-Modified Silica (SOMS)

Gokhan Celik¹, Hyuntae Sohn¹, Seval Gunduz¹, Saurabh A. Ailawar¹, Paul Edmiston², Umit. S. Ozkan^1*

¹The Ohio State University, Columbus, Ohio 43210 (United States)

²The College of Wooster, Wooster, Ohio, 44691 (United States)

^*ozkan.1@osu.edu

The widespread contamination of water by chlorinated ethenes such as trichloroethene (TCE) and perchloroethene (PCE) is a growing environmental concern [1]. The high level of toxicity and the carcinogenic effects of TCE pose a serious threat to human health and the environment. According to a study conducted by Environmental Protection Agency, TCE was detected in 91 out of 945 drinking-water and groundwater samples [2]. Hydrodechlorination (HDC) is an efficient way of removing chlorinated compounds from water. It is an elimination-based remediation technique in which chlorinated compounds react with hydrogen and are catalytically converted to Cl-free hydrocarbons and hydrogen chloride. There has been on-going research on HDC of chlorinated compounds where promising catalytic activities have been obtained with the palladium-based state-of-the-art catalysts. However, catalyst deactivation due to anionic groundwater constituents such as sulfur species, nitrates, carbonates, and chlorides is a recurring problem [3, 4]. For industrial organizations to adapt catalytic HDC as their remediation technique, deactivation issues due to the anionic species need to be addressed.

Herein, we report the use of a new class of materials, namely swellable organically-modified silica (SOMS) as a catalyst support for HDC reactions. SOMS is extremely hydrophobic and has a high affinity for absorbing organics. While absorption of organics is in progress, SOMS swells in such a way that its volume physically expands to more than 3-6 times of its original size [5-7]. Active metals incorporated within the SOMS matrix in its expanded state are protected from dissolved anions present in water. Hydrophobic nature of these materials will also create a repulsive force against water and its constituents. This will result in an additional level of protection of active sites. SOMS can have the potential to address the deactivation issues involved in catalytic HDC.

In this study, Pd-incorporated SOMS (Pd/SOMS) and Pd/Al₂O₃, for comparison purposes, have been tested for HDC of TCE. Reaction experiments and characterization studies including N₂ physisorption, solid-state NMR, laser RAMAN and infrared spectroscopy, extended X-ray absorption fine structure (EXAFS), and inductively coupled plasma optical emission spectrometer (ICP-OES) have been performed to understand the poison-resistant characteristics of Pd/SOMS.

References

[1] R.E. Doherty, A History of the Production and Use of Carbon Tetrachloride, Tetrachloroethylene, Trichloroethylene and 1,1,1-Trichloroethane in the United States: Part 1--Historical Background; Carbon Tetrachloride and Tetrachloroethylene, Environmental Forensics, 1 (2000) 69-81.

[2] Toxilogical Profile for Trichloroethylene, in, Public Health Service,Agency for Toxic Substances and Disease Registry, U.S. Department of Health and Human Services, 2014.

[3] N. Munakata, M. Reinhard, Palladium-catalyzed aqueous hydrodehalogenation in column reactors: Modeling of deactivation kinetics with sulfide and comparison of regenerants, Applied Catalysis B: Environmental, 75 (2007) 1-10.

[4] G.V. Lowry, M. Reinhard, Pd-Catalyzed TCE Dechlorination in Water: Effect of [H2](aq) H2-Utilizing Competitive Solutes on the TCE Dechlorination Rate and Product Distribution, Environmental Science & Technology, 35 (2001) 696-702.

[5] C.M. Burkett, P.L. Edmiston, Highly swellable solâ??gels prepared by chemical modification of silanol groups prior to drying, Journal of Non-Crystalline Solids, 351 (2005) 3174-3178.

[6] C.M. Burkett, L.A. Underwood, R.S. Volzer, J.A. Baughman, P.L. Edmiston, Organicâ??Inorganic Hybrid Materials that Rapidly Swell in Non-Polar Liquids: Nanoscale Morphology and Swelling Mechanism, Chemistry of Materials, 20 (2008) 1312-1321.

[7] P.L. Edmiston, L.A. Underwood, Absorption of dissolved organic species from water using organically modified silica that swells, Separation and Purification Technology, 66 (2009) 532-540.