Elucidation of Nitrate Reduction Mechanisms on a Pd‐In Bimetallic Catalyst using Isotope Labeled Nitrogen Species. Issue 1 (23rd November 2012)

• Record Type: Journal Article
• Authors: Zhang, Rui; Shuai, Danmeng; Guy, Kathryn A.; Shapley, John R.; Strathmann, Timothy J.; Werth, Charles J.
• Is Part Of: ChemCatChem. Volume 5:Issue 1(2013:Jan.)
• Page Start: 313
• Page End: 321
• Publication Date: 2012-11-23
• Subjects: Catalysis -- Periodicals; 541.39505
• DOI: 10.1002/cctc.201200457
• Languages: English
• ISSNs: 1867-3880

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>To understand nitrate reduction pathway and to improve selectivity towards dinitrogen (N<sub>2</sub>) over toxic ammonia species (NH<sub>4</sub><sup>+</sup>, NH<sub>3</sub>), aqueous reduction experiments with an Al<sub>2</sub>O<sub>3</sub>‐supported Pd‐In bimetallic catalyst were conducted by using isotope‐labeled nitrite (<sup>15</sup>NO<sub>2</sub><sup>−</sup>). Nitrite is the first reduction intermediate of nitrate. Experiments were performed using nitrite alone and in combination with unlabeled proposed reduction intermediates (N<sub>2</sub>O, NO), and using only N<sub>2</sub>O and NO alone, each as a starting reactant. Use of <sup>15</sup>N‐labeled species eliminates interference from ambient N<sub>2</sub> when assessing mass balances and product distributions. Simultaneous catalytic reduction of <sup>15</sup>NO<sub>2</sub><sup>−</sup> and <sup>14</sup>N<sub>2</sub>O shows no isotope mixing in the final N<sub>2</sub> product, demonstrating that N<sub>2</sub>O does not react with other NO<sub>2</sub><sup>−</sup> reduction intermediates; N<sub>2</sub>O reduction alone yielded only N<sub>2</sub>. In contrast, simultaneous catalytic reduction of <sup>15</sup>NO<sub>2</sub><sup>−</sup> and <sup>14</sup>NO yielded mixed‐labeled <sup>15/14</sup>N<sub>2</sub> (MW: 29), whereas reduction of <sup>15</sup>NO alone yields a mixture N<sub>2</sub> and NH<sub>4</sub><sup>+</sup>, the ratio of which varies with initial <sup>15</sup>NO concentration. These findings, along with those from a new kinetic model we propose, indicate that highly reactive adsorbed NO (NO*), or other unspecified adsorbed N species (N<sub>ads</sub>), is a key intermediate involved in determining final product selectivity.</p> </abstract>