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Fundamental Studies of Nitrogen and Hydrocarbons on Metal Surfaces

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Title: Fundamental Studies of Nitrogen and Hydrocarbons on Metal Surfaces
Author(s): Yin, Jun
Advisor(s): Meyer, Randall
Contributor(s): Trenary, Michael; Chan, Ally; Klie, Robert
Department / Program: Chemical Engineering
Graduate Major: Chemical Engineering
Degree Granting Institution: University of Illinois at Chicago
Degree: PhD, Doctor of Philosophy
Genre: Doctoral
Subject(s): NOx storage-reduction Physical vapor deposition Reflection absorption infrared spectroscopy Selective catalytic reduction Scanning tunneling microcopy Temperature programmed desorption Pt(111) Quadruple mass spectrometry Ultrahigh vacuum surface science Auger electron spectroscopy Infrared reflection absorption spectroscopy Low energy electron diffraction Langmuir
Abstract: The selective catalytic reduction (SCR) of NOx by hydrocarbons on noble metals is critically important to the implementation of leaner-burning, more fuel-efficient combustion engines in order to handle the increased amount of NOx that is produced. Understanding the reaction mechanisms and pathways is essential for designing an effective catalytic system for exhaust treatment. As one small part of this effort, we focus on the interaction of nitrogen atoms and simple unsaturated hydrocarbons such as ethylene and acetylene on the Pt(111) surface under ultra high vacuum conditions to understand the potential intermediates in NOx reduction. In this study, we employ a variety of surface techniques, including temperature programmed desorption (TPD), and reflection absorption infrared spectroscopy (RAIRS) in an attempt to identify reaction pathways in hydrocarbon SCR. Three interesting observations have been made. First, we observed the presence of π-bonded ethylene below 220 K, indicating a switch in the preferred binding site for ethylene on N-Pt(111) as compared to the clean surface. This result suggests that nitrogen could potentially serve as a promoter in metal catalyzed hydrogenation reactions. Second, the formation of ammonia is observed through ND3 desorption by using isotopically labeled ethylene or acetylene at 500 K. Because direct reaction between nitrogen atoms and hydrogen does not proceed to form ammonia, the appearance of ammonia is believed to be the result of a reaction between N atoms with coadsorbed ethynyl (CCH). This route to ammonia synthesis has not been previously observed under UHV conditions. Third, above 560 K, CN coupling occurs as indicated by the desorption of HCN and the identification of CNH2 with RAIRS. In addition, a new dual UHV/“high-pressure” chamber has been constructed and tested through two proof of principle experiments. First, nitrogen adsorption on Ni(110) has been examined at pressures ranging up to the torr level. Second, we have studied the hydrogenation of a nitrogen layer on Pt(111) at room temperature to determine the effects of pressure on the ability to achieve a higher coverage of NH than what can be achieved under UHV conditions. A detailed discussion about the system limitations are provided and possible improvements are suggested.
Issue Date: 2012-12-07
Genre: thesis
Rights Information: Copyright 2011 Jun Yin
Date Available in INDIGO: 2012-12-07
Date Deposited: 2011-08

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