2000 Progress Report: Palladium Catalyzed Reductions of Water Contaminants under Environmental ConditionsEPA Grant Number: R825421
Title: Palladium Catalyzed Reductions of Water Contaminants under Environmental Conditions
Investigators: Reinhard, Martin
Institution: Stanford University
EPA Project Officer: Lasat, Mitch
Project Period: November 1, 1996 through October 31, 1999 (Extended to October 31, 2001)
Project Period Covered by this Report: November 1, 1999 through October 31, 2000
Project Amount: $366,667
RFA: Exploratory Research - Water Engineering (1996) RFA Text | Recipients Lists
Research Category: Water , Land and Waste Management , Engineering and Environmental Chemistry
Objective:The objectives are to evaluate the effect of hydrogen limitation on the rate and intermediate formation and to develop a model catalyst suitable for surface chemical studies.
Progress Summary:The effect of the aqueous hydrogen concentration ([H2](aq)) and H2-utilizing competing solutes (cis-DCE, trans-DCE, 1,1-DCE, dissolved oxygen (DO), nitrite, nitrate) on the TCE transformation rate and product distribution were evaluated using 100 mg/L of a powdered Pd-on-Al2O3 catalysts in batch reactors or 1.0 g of a 1.6-mm Pd-on-g-Al2O3 catalyst in column reactors. The TCE dechlorination rate constant decreased by 55 percent from 0.034 ?0.006 min-1 to 0.015 ?0.001 min-1 when the ([H2](aq)) decreased from 1000 to 100 µM, and decreased sharply to 0.0007 ?0.0003 min-1 when the [H2](aq) decreased from 100 to 10 µM. Production of reactive chlorinated intermediates and C4-C6 radical coupling products increased with decreasing [H2](aq). At an [H2](aq) of 10 µM (P/Po=0.01), DCE isomers and vinyl chloride accounted for as much as 9.8 percent of the TCE transformed at their maximum, but disappeared thereafter, and C4-C6 radical coupling products accounted for as much as 18 percent of TCE transformed. The TCE transformation rate was unaffected by the presence of c-DCE (202 µM), t-DCE (89 µM), and 1,1-DCE (91 µM), indicating that these compounds do not compete with TCE for catalyst active sites. DO is twice as reactive as TCE, but had no effect on TCE conversion in the column below a concentration of 370 µM (11.8 mg/L), indicating that DO and TCE will not compete for active catalyst sites at typical groundwater DO concentrations. TCE conversion in the column was reduced by as much as a factor of 10 at influent DO levels greater than 450 µM (14.3 mg/L) because the [H2](aq) fell below 100 µM due to H2 utilized in DO conversion. Nitrite reacts 2 to 5 times slower than TCE and reduced TCE conversion by less than 4 percent at a concentration of 6630 µM (305 mg/L). Nitrate was not reactive and did not effect TCE conversion at a concentration of 1290 µM (80 mg/L). To study surface chemical reactions under treatment conditions, a model catalyst has been developed consisting of flat Al2O3 plates (1cn x 1 cm) coated with a thin layer of palladium. The palladium-coated plates will be mounted in a specially designed flow-through reactor and exposed to real or synthetic groundwater.
Future Activities:For the final project year, we will study the surface chemistry of catalyst deactivation and regeneration. The model catalyst will be run in a specially designed reactor under groundwater conditions. The model catalyst will be exposed to groundwater enriched with different poisons, including hydrogen sulfide, and analyzed using surface spectroscopic methods. A correlation will be established between surface chemical properties and catalyst activity.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
|Other project views:||All 20 publications||5 publications in selected types||All 5 journal articles|
||Lowry GV, Reinhard M. Pd-catalyzed TCE dechlorination in groundwater: solute effects, biological control, and oxidative catalyst regeneration. Environmental Science & Technology 2000;34(15):3217-3223.||
||Schuth C, Disser S, Schuth F, Reinhard M. Tailoring catalysts for hydrodechlorinating chlorinated hydrocarbon contaminants in groundwater. Applied Catalysis B:Environmental 2000;28(3-4):147-152.||