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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal align=center style='text-align:center'><b><span style='font-size:16.0pt;line-height:115%;font-family:"Tahoma","sans-serif"'>PhD Dissertation Defense<o:p></o:p></span></b></p><p class=MsoNormal align=center style='text-align:center;line-height:150%'><b><span style='font-size:14.0pt;line-height:150%;font-family:"Tahoma","sans-serif"'>NO</span></b><b><span style='font-size:12.0pt;line-height:150%;font-family:"Tahoma","sans-serif"'>x</span></b><b><span style='font-size:14.0pt;line-height:150%;font-family:"Tahoma","sans-serif"'> Removal by LNT-SCR Dual-Layer Catalysts</span></b><span style='font-size:14.0pt;line-height:150%;font-family:"Tahoma","sans-serif"'><o:p></o:p></span></p><p class=MsoNormal align=center style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;text-align:center;line-height:150%'><b><span style='font-size:14.0pt;line-height:150%;font-family:"Tahoma","sans-serif"'>Yi Liu</span></b><b><span style='font-size:12.0pt;line-height:150%;font-family:"Tahoma","sans-serif"'><o:p></o:p></span></b></p><p class=MsoNormal align=center style='margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal'><b><span style='font-size:12.0pt'>Date:</span></b><span style='font-size:12.0pt'> <b>Thursday, September 27, 2012</b><o:p></o:p></span></p><p class=MsoNormal align=center style='margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal'><span style='font-size:12.0pt'><o:p> </o:p></span></p><p class=MsoNormal align=center style='margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal'><b><span style='font-size:12.0pt'>Location:</span></b><span style='font-size:12.0pt'> Mechanical Engineering Conference Room - 202<o:p></o:p></span></p><p class=MsoNormal align=center style='margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal'><b><span style='font-size:12.0pt'>Time:</span></b><span style='font-size:12.0pt'> 2:00 pm<o:p></o:p></span></p><p class=MsoNormal align=center style='margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal'><span style='font-size:12.0pt'><o:p> </o:p></span></p><p class=MsoNormal align=center style='margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal'><b><span style='font-size:12.0pt'>Committee Co-Chair: </span></b><span style='font-size:12.0pt'>Dr. Dan Luss<o:p></o:p></span></p><p class=MsoNormal align=center style='margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal'><b>Committee Co-Chair:</b> Dr. Michael P. Harold<o:p></o:p></p><p class=MsoNormal align=center style='margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal'><b>Committee Members:</b> <o:p></o:p></p><p class=MsoNormal align=center style='margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal'>Dr. Vemuri Balakotaiah<o:p></o:p></p><p class=MsoNormal align=center style='margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal'>Dr. Shankar Chellam<o:p></o:p></p><p class=MsoNormal align=center style='margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal'>Dr. Allan Jacobson<o:p></o:p></p><p class=MsoNormal align=center style='margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal'><span style='font-size:12.0pt'><o:p> </o:p></span></p><p class=MsoNormal align=center style='margin-bottom:0in;margin-bottom:.0001pt;text-align:center;line-height:normal'><o:p> </o:p></p><p class=MsoNormal style='margin-bottom:12.0pt;line-height:normal'>The increasingly strict emission standards have driven the progress of NOx storage and reduction (NSR) technology. NOx is stored in a lean NOx trap (LNT) catalyst during fuel-lean mode and reduced to N2 during fuel-rich mode.<o:p></o:p></p><p class=MsoNormal style='margin-bottom:12.0pt;line-height:normal'>First, we investigated the impact of ceria on NSR in a Pt/Ce LNT catalyst. The physisorbed oxygen over the ceria-containing LNT catalyst led to a spatio-temporal temperature rise in the monolith upstream after the cyclic introduction of H2/CO to a pre-oxidized catalyst. The stored oxygen over ceria enhanced NO storage by in-situ NO2 formation, while it competed with NO2 for storage sites. During the NOx reduction over the Pt/Ceria, the Pt surface purgation was the first step and the oxygen reduction preceded the NOx reduction. <o:p></o:p></p><p class=MsoNormal style='margin-bottom:12.0pt;line-height:normal'>Second, we studied the NSR by dual-layer catalysts consisting of a selective catalytic reduction (SCR) catalyst layer on top of a LNT catalyst. During periodic switching between lean and rich feeds, the LNT layer reduced NOx to N2 and NH3. The SCR layer trapped the latter leading to additional NOx reduction. <o:p></o:p></p><p class=MsoNormal style='margin-bottom:12.0pt;line-height:normal'>The dual-layer catalysts exhibited high N2 selectivity and low NH3 selectivity over the temperature range of 150-400 ºC. The NOx conversion was incomplete due to undesired NH3 oxidation. The dual-layer catalyst has a higher NOx conversion and N2 selectivity than the LNT catalyst when H2O and CO2 were present in the feed. <o:p></o:p></p><p class=MsoNormal style='margin-bottom:12.0pt;line-height:normal'>Ceria was used to adjust the dual-layer catalyst performance. The ceria addition increased NOx storage capacity, promoted hydrothermal durability and mitigated CO poisoning. However, ceria decreased the high-temperature NOx conversion by promoting NH3 oxidation. Ceria zoning led to the highest NOx reduction for both low- and high- temperatures due to the beneficial interaction of ceria and H2. <o:p></o:p></p><p class=MsoNormal style='margin-bottom:12.0pt;line-height:normal'>The impact of catalyst design and operation strategy was evaluated. The low-temperature NOx conversion of an aged dual-layer catalyst was increased by a high SCR catalyst loading. The ratio of lean to rich feed duration and the total cycle time were optimized to improve the NOx conversion. The results suggest the dual-layer catalyst could be used to reduce precious metal loading and improve the fuel economy.<o:p></o:p></p><p class=MsoNormal style='margin-bottom:12.0pt;line-height:normal'><o:p> </o:p></p></div></body></html>