Hydrodechlorination Of Trichloroethylene Research Articles

Trichloroethene Hydrodechlorination in Water by Highly Disordered Monometallic Nanoiron

The small size and high surface-to-volume ratio makes nanoiron attractive for in situ remediation of groundwater contaminants that are susceptible to reductive transformation, e.g. trichloroethylene (TCE). Nanoiron synthesized from borohydride reduction of dissolved iron is the most widely studied. Its reactivity with chlorinated organics such as trichloroethylene (TCE) is unique compared to other nanoiron and to iron filings that are typically used for in situ groundwater remediation, e.g. (1) higher surface-area normalized TCE dechlorination reaction rate constants, (2) the formation of saturated reaction products, and (3) higher reaction rates in the presence of H2. The objectives of this study were to confirm the ability of monometallic Fe(B) to activate and use H2 for TCE hydrodechlorination and to determine how the nanoiron chemical composition and the degree of crystallinity influence nanoiron reactivity with TCE. Fresh (Fe(B)), partially oxidized (Fe(B)ox), and annealed (Fe(B)cr) nanoiron samples made from borohydride reduction of dissolved Fe(II) in a water/methanol solution were characterized by HRTEM, XRD, XPS, and N2-BET. The TCE dechlorination rate and products and the dissolved iron and boron released during reaction with TCE were measured. Fe(B) and Fe(B)ox were poorly ordered and could activate and use H2 to reduce TCE to ethane. Fe(B)cr was crystalline and could not activate and use H2 and reduced TCE to acetylene. The poorly ordered structure rather than the presence of boron (up to 5 wt %) provided the ability of Fe(B) and Fe(B)ox to activate and use H2 for TCE dechlorination. Fe(B) and Fe(B)ox underwent oxidative dissolution during TCE dechlorination, and the Fe0 in the particles was fully accessible. Particle dissolution suggests that normalizing the observed reaction rate constants with the measured specific surface area for comparison with other types of Fe0 may be inappropriate.

Designing Pd-on-Au Bimetallic Nanoparticle Catalysts for Trichloroethene Hydrodechlorination

Alumina-supported palladium (Pd) catalysts have previously been shown to hydrodechlorinate trichloroethene (TCE) and other chlorinated compounds in water, at room temperature, and in the presence of hydrogen. The feasibility of this catalytic technology to remediate groundwater of halogenated compounds can be improved by re-designing the Pd material in order to increase catalytic activity. We synthesized and characterized Pd supported on gold nanoparticles (Au NPs) of different Pd loadings. In all cases, we found that these catalysts were considerably more active than Pd NPs, alumina-supported Pd, ard Pd-black (62.0, 12.2, and 0.42 L x g(Pd)(-1) x min(-1), respectively). There is a synergistic effect of the Pd-on-Au bimetallic structure, with the material with the highest TCE hydrodechlorination activity (943 L x g(Pd)(-1) x min(-1)) comprised of Au NPs partially covered by Pd metal. The Pd-on-Au bimetallic catalyst structure provides a new synthesis approach in improving the catalytic properties of monometallic Pd materials. The resulting nanoparticle-based materials should be highly suitable as hydrodehalogenation and reduction catalysts for the remediation of various organic and inorganic groundwater contaminants.

Kinetic study of the hydrodechlorination of trichloroethene in water using a platinum catalyst and hydrazine.

Column experiments were used to measure the hydrodechlorination rate of relatively high concentrations of trichloroethene (TCE) (approximately 100 mg L(-1)). Trichloroethene in water was treated with a platinum on titania (Pt-TiO2) catalyst and hydrazine. The influence of some experimental conditions (i.e., flowrate, temperature, and pH) on the catalytic conversion of TCE was studied. The pseudo-first-order rate constant of the overall hydrodechlorination of TCE was approximately 1 x 10(-3) to 1 x 10(-2) s(-1) in the temperature range of 283 to 328 K and was determined from the dependence of the TCE conversion on the contact time of the feed water with the catalyst by assuming first-order kinetics. The activation energy of the catalytic hydrodechlorination of TCE was calculated as approximately 34 kJ/mol from the temperature dependence of the rate constant. The TCE conversion increases with increasing pH, and probably correlates with the presence of un-ionized hydrazine.