<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; color: rgb(0, 0, 0); font-size: 14px; font-family: Calibri, sans-serif; "><div><br></div><span id="OLK_SRC_BODY_SECTION"><div xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"><div lang="EN-US" link="blue" vlink="purple" style="text-justify-trim:punctuation"><div class="WordSection1" style="layout-grid:15.6pt"><p class="MsoNormal"><o:p> </o:p></p><p class="MsoNormal" align="center" style="mso-margin-top-alt:auto;margin-bottom:6.0pt;text-align:center;line-height:18.0pt"><b><span style="font-size:14.0pt;color:black">PhD DEFENSE STUDENT: </span></b><span style="font-size:14.0pt;color:black">Yang Zheng</span><span style="font-family: PMingLiU, serif; color: black; "><o:p></o:p></span></p><p class="MsoNormal" align="center" style="mso-margin-top-alt:auto;margin-bottom:6.0pt;text-align:center;line-height:18.0pt"><b><span style="font-size:14.0pt;color:black">DATE: </span></b><span style="font-size:14.0pt;color:black">September 24, 2015</span><span style="color:black"><o:p></o:p></span></p><p class="MsoNormal" align="center" style="mso-margin-top-alt:auto;margin-bottom:6.0pt;text-align:center;line-height:18.0pt"><b><span style="font-size:14.0pt;color:black">TIME: </span></b><span style="font-size:14.0pt;color:black">9:00 AM</span><span style="color:black"><o:p></o:p></span></p><p class="MsoNormal" align="center" style="mso-margin-top-alt:auto;margin-bottom:6.0pt;text-align:center;line-height:18.0pt"><b><span style="font-size:14.0pt;color:black">PLACE: </span></b><span style="font-size:14.0pt;color:black">Mechanical Engineering Large Conference Room</span><span style="color:black"><o:p></o:p></span></p><p class="MsoNormal" align="center" style="mso-margin-top-alt:auto;margin-bottom:6.0pt;text-align:center;line-height:18.0pt"><b><span style="font-size:14.0pt;color:black">DISSERTATION CHAIRS: </span></b><span style="font-size:14.0pt;color:black">Dr. Michael Harold and Dr. Dan Luss</span><span style="color:black"><o:p></o:p></span></p><div class="MsoNormal" align="center" style="text-align:center;line-height:24.0pt"><b><span style="font-size: 14pt; font-family: Calibri, sans-serif; color: black; "><hr size="2" width="100%" align="center"></span></b></div><p class="MsoNormal" align="center" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;text-align:center"><b><span style="font-size:14.0pt;line-height:200%;color:black">TITLE:<o:p></o:p></span></b></p><p class="MsoNormal" align="center" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;text-align:center"><b><span style="font-size:14.0pt;line-height:200%">Applied and Fundamental Studies of LNT-SCR Dual-layer Monolithic Catalysts for Lean NOx Emission Control<span style="color:black"><o:p></o:p></span></span></b></p><p class="MsoNormal" style="text-align:justify;text-indent:.5in;line-height:150%">
The increasingly stringent both greenhouse gas (GHG) and tailpipe NOx emission standards have driven the continuous improvement of commercial deNOx technologies, NOx reduction & storage (NSR, also referred to as lean NOx trap (LNT)) and selective catalytic
reduction (SCR) technologies. This dissertation conducts applied and fundamental studies of coupled LNT-SCR dual-layer catalysts with the aim of expanding the operating temperature window of a conventional NSR system at lower cost. This is accomplished by
a systems approach to identify the influencing factors such as catalyst composition and architecture, types of reducing agents, operating and regeneration strategies, as well as synergistic interactions between the LNT and SCR.
<o:p></o:p></p><p class="MsoNormal" style="text-align:justify;text-indent:.5in;line-height:150%">
We start with performance evaluation of dual-layer catalysts under different regeneration conditions such as H<sub>2</sub> alone, CO/H<sub>2</sub> mixture and a simulated diesel exhaust containing the CO/H<sub>2</sub>/C<sub>3</sub>H<sub>6
</sub>mixture. Spatial analyses of NH<sub>3</sub> yield and NOx conversion along the LNT monolith identify the upstream zone as major NH<sub>3</sub> generator and NOx reducer, especially at temperatures exceeding 300
<sup>o</sup>C. <span style="color:black">Zoning of either or both the SCR and LNT having a dual-layer structure enables an increase in the low-temperature (200-250</span><sup> o</sup>C)<span style="color:black"> NO<sub>x</sub> conversion, and minimizes the
high temperature (300-400<sup> o</sup>C) conversion loss caused by the SCR diffusion resistance and undesired NH<sub>3</sub> oxidation by the LNT.
</span><o:p></o:p></p><p class="MsoNormal" style="text-align:justify;text-indent:.5in;line-height:150%"><span style="color:black">The hydrocarbon (HC) reductant leads to an alternative LNT-SCR synergy to classical NH<sub>3</sub>-pathway; a LNT-assisted HC-SCR pathway. The LNT promotes the formation of partially oxidized HC intermediates during the rich purge
which are otherwise difficult to be generated by the Cu-zeolite layer at low temperatures. These activated intermediates can be captured and utilized by the SCR catalyst via HC-SCR during the ensuing lean phase.</span><span style="color:black;mso-fareast-language:ZH-CN">
This pathway plays a major role at low temperatures (<= 225 <sup>o</sup>C) using the simulated diesel exhaust feed.
<o:p></o:p></span></p><p class="MsoNormal" style="text-align:justify;text-indent:.5in;line-height:150%">
We investigated the steady-state and transient effects of reductants (CO, H<sub>2</sub> and C<sub>3</sub>H<sub>6</sub>) on Cu-SSZ-13 catalyzed NH<sub>3</sub>-SCR as the SCR component in
<span style="color:black;mso-fareast-language:ZH-CN">the combined system is periodically exposed to a rich exhaust.
</span>The three reductants affect to different extent the NH<sub>3</sub>-SCR reactions. Propylene is most effective in promoting NO<sub>2</sub> reduction to NO by formation of organic intermediates. CO effectively reduces nitrates to nitrites that react with
NO<sub>2</sub>, releasing NO. H<sub>2</sub> follows a similar pathway as CO but is less effective.<o:p></o:p></p><p class="MsoNormal" style="text-align:justify;text-indent:.5in;line-height:150%">
Finally, the effects of the lean/rich cycling frequency on both LNT and combined catalysts are investigated.
<span style="mso-fareast-language:ZH-CN">Rapid C<sub>3</sub>H<sub>6</sub> pulsing into a lean exhaust steam
</span>expands the operating temperature window of a conventional NSR system in both low and high-temperature regions. The combination of rapid propylene pulsing and the dual-layer catalyst architecture achieves the highest low-temperature NOx conversion. The
working mechanisms of rapid propylene pulsing on both LNT and LNT-SCR catalysts are elucidated. Optimization of top-layer material and catalyst configuration like SCR and PGM zoning can improve system performance at lower cost.<span style="mso-fareast-language:X-NONE"><o:p></o:p></span></p></div></div></div></span><style><!--
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