Effects of methyl orange on nitrate reduction by a Pd-In/γ-Al2O3 catalyst

ENVR 199

Danmeng Shuai, dshuai2@uiuc.edu, Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 205 N. Mathews Ave., Newmark Civil Engineering Laboratory, Urbana, IL 61801, Stan Wojnar, cwojnar2@uiuc.edu, Department of Aerospace Engineering, University of Illinois at Urbana-Champaign, 1206 W Green, Urbana, IL 61801, Brian P. Chaplin, chaplin1@email.arizona.edu, Department of Chemical and Environmental Engineering, University of Arizona, 1133 E James E Rogers Way, Tucson, AZ 85721, John R. Shapley, shapley@uiuc.edu, Department of Chemistry and Center of Advanced Materials for the Purification of Water with Systems, University of Illinois at Urbana-Champaign, 505 S. Mathews, Urbana, IL 61801, and Charles J. Werth, werth@uiuc.edu, Department of Civil and Environmental Engineering and Center of Advanced Materials for Purification of Water with Systems, University of Illinois at Urbana-Champaign, 3215 Newmark Civil Engineering Laboratory, 205 N. Mathews Ave., Urbana, IL 61801.
The effects of methyl orange on nitrate reduction were determined using a γ-Al2O3-supported Pd/In catalyst with hydrogen in a batch reactor. Different concentrations of methyl orange, solution pH values and interval times between methyl orange and nitrate addition to the reactor (in the presence of H2) were evaluated. It was found that nitrate reduced faster with higher concentrations of methyl orange. Also, nitrate reduction was faster when methyl orange and nitrate were injected into the reactor simultaneously; nitrate reduction rates decreased with greater lag times between methyl orange and nitrate addition. We hypothesize that methyl orange and its reduced form, N,N'-dihydro methyl orange, act as a hydrogen atom shuttle and, thus, accelerate nitrate reduction. The cleaved reduced forms of methyl orange, sulfanilic acid (SA) and dimethyl-p-phenylenediamine (DMPPD) were detected in solution. Deliberate addition of SA and DMPPD had little or no effect on nitrate reduction rates. Therefore, formation of these fully reduced cleavage products will diminish the capacity of methyl orange to affect nitrate reduction. These results, as well as those that explore the mechanism of hydrogen atom shuttling and product selection, will be presented.
 

Advances in Abiotic Transformation Processes for Micropollutants in Drinking Water and for Sourcewater Protection
1:30 PM-3:15 PM, Wednesday, April 9, 2008 Morial Convention Center -- Rm. 237, Oral

Sci-Mix
8:00 PM-10:00 PM, Monday, April 7, 2008 Morial Convention Center -- Hall A, Sci-Mix

Division of Environmental Chemistry

The 235th ACS National Meeting, New Orleans, LA, April 6-10, 2008