Investigation of Palladium Catalyzed Hydrodehalogenation for the Removal of Chlorinated Groundwater
Contaminants: Surface Chemistry of Catalyst Deactivation and Regeneration
Goal
This project aims to (1) evaluate surface chemical reactions of commonly found natural groundwater solutes at the surface of supported
palladium catalysts, particularly the effects of carbonate, nitrate, sulfate, and pH; (2) elucidate the deactivation and reactivation mechanisms,
chemical and physical, for these solutes; (3) investigate the potential biofouling and catalyst deactivation that may result from biological activity
expected in long-term treatment applications; (4) develop custom catalyst supports to circumvent chemical catalyst deactivation and fouling
through ion exclusion or repulsion; (5) develop convenient and economical methods to regenerate catalysts in situ.
Rationale
Batch studies with supported palladium catalysts have demonstrated the potential of the palladium/hydrogen process for treating
groundwaters or effluent streams that are contaminated with halogenated compounds. These studies yielded virtually complete reductive
dehalogenation of chlorinated ethylenes to ethane at room temperature in short contact times, with reaction rates that are orders of magnitude
higher than zero-valent iron. Other batch studies have shown the ability of palladium to catalyze the reaction of a range of compounds: all 6
species of chlorinated ethylenes, carbon tetrachloride, chloroform, 1,2-dibromo-3-chloropropane, Freon 113, chlorobenzene, naphthalene and
lindane. However, laboratory column studies and field tests have indicated that catalyst activity may decline under some conditions, thereby
potentially affecting the economic competitiveness of this process. Research is needed to optimize the catalyst and operating parameters for the
field, by determining the causes of activity loss and preventing or minimizing such effects.
Approach
Advanced surface spectroscopic techniques will be used for characterizing processes that occur at the catalyst surface. The surface
of the fresh catalyst will be compared to that of samples taken throughout the duration of column tests run with natural and synthetic
groundwaters. The surface of catalyst that was subjected to different treatments will be characterized by chemical and crystal analysis, and the
long-term effects of biological growth on catalyst activity will be evaluated. With this understanding of catalyst deactivation mechanisms,
custom catalyst supports will be designed to circumvent the competition, inhibition, fouling, and poisoning effects of naturally found
groundwater solutes. Finally, convenient methods for regenerating the catalyst beds in situ will be developed and evaluated.
Status
Samples of dispersed Pd/alumina for analysis were obtained. These samples consist of fresh catalyst; catalyst exposed to DI waters
containing carbonate, bicarbonate, carbon dioxide, and sulfite, and groundwater with high-sulfate concentrations; and deactivated catalyst
regenerated by exposure to air, air at 100¡C, or to Clorox bleach. These samples will be analyzed with XRD, XPS and SEM. This study
commenced 1 October 1999 and is authorized for a two-year period terminating 30 September 2001.
Copyright © Georgia Tech Research Corporation, 2000.
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Make comments to: mark.hodges@gtri.gatech.edu
Last modified on: March 16, 2000.
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