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Development of sustainable Pd-based catalysts for removal of persistent contaminants from drinking water

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Title: Development of sustainable Pd-based catalysts for removal of persistent contaminants from drinking water
Author(s): Shuai, Danmeng
Director of Research: Werth, Charles J.
Doctoral Committee Chair(s): Werth, Charles J.
Doctoral Committee Member(s): Shapley, John R.; Strathmann, Timothy J.; Schneider, William F.
Department / Program: Civil & Environmental Eng
Discipline: Environ Engr in Civil Engr
Degree Granting Institution: University of Illinois at Urbana-Champaign
Degree: Ph.D.
Genre: Dissertation
Subject(s): catalyst palladium water treatment nitrate nitrite nitrosodimethylamine (NDMA) diatrizoate azo dyes carbon nanofibers shape-control
Abstract: Pd-based catalytic reduction has emerged as an advanced treatment technology for drinking water decontamination, and a suite of persistent contaminants including oxyanions, N-nitrosoamines, and halogenated compounds are amenable to catalytic reduction. The primary goal of this study is to develop novel Pd-based catalysts with enhanced performance (i.e., activity, selectivity, and sustainability) to remove contaminants from drinking water. The effects of water quality (i.e., co-contaminants in water matrix), catalyst support, and catalyst metal were explored, and they provide insights for preparing catalysts with faster kinetics, higher selectivity, and extended lifetime. Azo dyes are wide-spread contaminants, and they are potentially co-exisiting with target contaminants amenable for catalytic removal. The probe azo dye methyl orange (MO) enhanced catalytic reduction kinetics of a suite of oxyanions (i.e., nitrate, nitrite, bromate, chlorate, and perchlorate) and diatrizoate significantly but not N-nitrosodimethylamine (NDMA) with a variety of Pd-based catalysts. Nitrate was selected as a probe contaminant, and several different azo dyes (i.e., (methyl orange, methyl red, fast yellow AB, metanil yellow, acid orange 7, congo red, eriochrome black T, acid red 27, acid yellow 11, and acid yellow 17) were evaluated for their ability to enhance reduction. A hydrogen atom shuttling mechanism was proposed and a kinetic model was proposed based on Brønsted–Evans–Polanyi (BEP) theory, and they suggest sorbed azo dyes and reduced hydrazo dyes shuttle hydrogen atoms to oxyanions or diatrizoate to enhance their reduction kinetics. Next, vapor-grown carbon nanofiber (CNF) supports were used to explore the effects of Pd nanoparticle size and interior versus exterior loading on nitrite reduction activity and selectivity (i.e., dinitrogen over ammonia production). In order to evaluate the amount of interior versus exterior loading of Pd nanoparticles, a fast and accurate geometric model was developed based on two-dimensional transmission electron microscopy (2D TEM). Results from my method agree adequately with 3D scanning transmission electron microscopy (3D TEM), which is recognized as a convincing method to evaluate interior versus exterior loading. By using Pd CNF catalysts for nitrite reduction, results show that both activity and selectivity are not significantly impacted by Pd interior versus exterior loading. Turnover frequencies (TOFs) among all CNF catalysts are consistent, suggesting faster kinetics are achieved on catalysts with smaller Pd nanoparticles, and suggesting nitrite reduction is neither sensitive to Pd location on CNFs nor Pd structure. However selectivity to dinitrogen is more favorable on larger Pd nanoparticles. Therefore, an optimum Pd nanoparticle size on CNFs balances high reduction kinetics and selectivity to dinitrogen. CNF Pd catalysts perform better than conventional activated or alumina supported Pd catalysts in term of kinetics and selectivity for nitrite reduction, and they maintain consistent activity during multiple reduction cycles. Lastly, the structure-sensitivity of catalytic activity and selectivity for contaminant nitrite, NDMA, and diatrizoate removal were investigated on shape- and size-controlled Pd nanoparticles. Results show that TOFs for nitrite, NDMA, and diatrizoate are dependent on coordination numbers of surface Pd sites at low contaminant concentration, but TOFs for nitrite at high concentration are consistent. Selectivity to ammonia for nitrite reduction decreases with increasing surface Pd sites, i.e., decreasing Pd nanoparticle size irrespective of nitrite concentration, but NDMA reduction is neither shape- nor size-specific, and it exclusively proceeds to ammonia and dimethylamine. Diatrizoate reduction selectivity is also likely to be nonspecific to shape and size, and a series of deiodinated intermediates, 3,5-diacetamidobenzoic acid, and iodide are the produced. Hence, this study suggests that contaminant reduction kinetics and selectivity are Pd shape and size dependent, and the dependence varies by contaminant type and concentration. In summary, Pd-based catalysts can be tailored for enhanced activity, selectivity, and longevity, and catalytic treatment holds the promise for advanced drinking water treatment.
Issue Date: 2012-09-18
URI: http://hdl.handle.net/2142/34377
Rights Information: Copyright 2012 Danmeng Shuai
Date Available in IDEALS: 2012-09-18
Date Deposited: 2012-08
 

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