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oai:www.ideals.illinois.edu:2142/24421 2023-07-10 col_2142_14770 col_2142_5131 com_2142_3518 com_2142_234 com_2142_5130

Strathmann, Timothy J. Werth, Charles J. Zhang, Rui 2011-05-25T14:40:23Z 2013-05-26T10:00:25Z 2011-05-25T14:40:23Z 2011-05 Catalytic hydrogenation over Pd-based catalysts has emerged as an effective treatment approach for nitrate (NO3-) removal, but its full-scale application for direct treatment of drinking water or ion exchange regenerant brines requires improved selectivity for the end-product dinitrogen (N2) over toxic ammonia species (NH4+, NH3). A key to improving N2 versus NH4+ production is to elucidate nitrate reduction pathways and identify the key intermediate(s) that determine selectivity. To address this challenge, aqueous reduction experiments with an Al2O3-supported Pd/In bimetallic catalyst were conducted using isotope-labeled nitrite (15NO2-), the first reduction intermediate of NO3-, alone and in combination with unlabeled proposed reduction intermediates (N2O, NO), and using N2O and NO alone, each as a starting reactant. Use of 15N-labeled species eliminated interference from ambient 14N2 when assessing mass balances and product distributions. Simultaneous catalytic reduction of 15NO2- and 14N2O showed no isotope mixing in the final N2 product, demonstrating that N2O does not react with other NO2- reduction intermediates. N2O reduction alone also yielded only N2, verifying that N2O reduction occurs after the reaction step controlling final N2/NH4+ product distribution. In contrast, simultaneous catalytic reduction of 15NO2- and 14NO yielded mixed-labeled N2 (mass 29), and 15NO reduction alone yielded both N2 and NH4+, indicating that NO is a key intermediate involved in determining final product selectivity. N2/NH4+ product selectivity was also evaluated as a function of varying initial 15NO concentration, and results show that selectivity for N2 increases with initial NO concentration to a point, above which product selectivity remains unchanged. This trend is attributed to the increasing importance of N-N pairing reactions leading to N2O formation as the concentration of catalyst-adsorbed NO (NOads) increases to a point of saturating available adsorption sites, above which no further increases in N2 selectivity occur. These results are important because they yield mechanistic insights into the NO3- reduction pathway and information on how catalytic reduction processes can be optimized to maximize N2 production over NH4+. Item withdrawn by Alexis Thompson (athmpsn1@illinois.edu) on 2011-04-20T21:47:33Z Item was in collections: University of Illinois Theses & Dissertations (ID: 1) No. of bitstreams: 2 Zhang_Rui.pdf: 280951 bytes, checksum: e3c177a007733fdd1c3167f6a37d74a4 (MD5) Zhang_Rui.pdf: 280951 bytes, checksum: e3c177a007733fdd1c3167f6a37d74a4 (MD5) Made available in DSpace on 2011-05-25T14:40:23Z (GMT). No. of bitstreams: 2 Zhang_Rui.pdf: 280951 bytes, checksum: e3c177a007733fdd1c3167f6a37d74a4 (MD5) license.txt: 4059 bytes, checksum: 1bdc58b091c7ae9211206c9d656e4396 (MD5) Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by William Ingram (wingram2@illinois.edu) on 2011-05-25T14:42:11Z Item is restricted until 2013-05-25T14:41:28Z Item reinstated by Sarah Shreeves (sshreeve@illinois.edu) on 2013-05-26T10:00:25Z Item was in collections: Dissertations and Theses - Civil and Environmental Engineering (ID: 672) University of Illinois Dissertations and Theses (ID: 204) No. of bitstreams: 3 Zhang_Rui.pdf.txt: 61025 bytes, checksum: e9b3a2030f9236bb7bee4d8009102d7d (MD5) Zhang_Rui.pdf: 280951 bytes, checksum: e3c177a007733fdd1c3167f6a37d74a4 (MD5) license.txt: 4059 bytes, checksum: 1bdc58b091c7ae9211206c9d656e4396 (MD5) Item released from any restrictions by Sarah Shreeves (sshreeve@illinois.edu) on 2013-05-26T10:00:25Z http://hdl.handle.net/2142/24421 en Copyright 2011 Rui Zhang catalytic hydrogenation nitrate reduction selectivity intermediates Elucidation of nitrate reduction mechanisms on a Pd/In bimetallic catalyst using isotope labeled nitrogen species Civil & Environmental Eng 1251 Environ Engr in Civil Engr 0231 University of Illinois at Urbana-Champaign Thesis M.S. MS:Env Engr Civil Engr -UIUC 10KS0231MS