A non-NH3 pathway for NOx conversion in coupled LNT-SCR systems
A non-NH3 pathway for NOx conversion in coupled LNT-SCR systems
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DOI：
10.1016/j.apcatb.2011.11.008
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发表时间：
2012-01
影响因子：
22.1
通讯作者：
Jin Wang;Yaying Ji;Zhengwang He;M. Crocker;M. Dearth;R. McCabe
中科院分区：
文献类型：
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作者：
Jin Wang;Yaying Ji;Zhengwang He;M. Crocker;M. Dearth;R. McCabe
使用由低贵金属负载的Pt/Rh LNT催化剂和商业Cu-沸石SCR催化剂组成的耦合LNT-SCR系统进行NOx储存-还原实验。循环实验表明，当CO+H2+ C3 H6混合物或C3 H6本身用作还原剂时，SCR催化剂上的NOx转化率超过相同催化剂上的NH3转化率。这可以通过丙烯的存在来解释，丙烯滑过LNT催化剂并与LNT NOxslip反应。在连续流动和贫-富循环条件下进行的单独实验证实了丙烯以及乙烯在SCR催化剂上充当NOx还原剂的能力。循环实验还揭示了SCR催化剂能够储存丙烯，使得通过储存的丙烯的NOx还原继续进入贫相（在从富条件切换之后）。吸附实验表明，SCR催化剂中NH3和丙烯发生了显著的共吸附，而在贫-富循环条件下，NH3和C3 H6对NOx转化率的贡献基本上是相加的。这些研究结果表明，在实际驾驶条件下，NOx还原的非NH3还原剂（烯烃和可能的其他碳氢化合物）的SCR催化剂可以有助于减轻贫相和富相NOx。
NOxstorage-reduction experiments were performed using a coupled LNT-SCR system consisting of a low-precious metal loaded Pt/Rh LNT catalyst and a commercial Cu–zeolite SCR catalyst. Cycling experiments revealed that when a CO+H2+C3H6mixture or C3H6by itself was used as the reductant, the NOxconversion over the SCR catalyst exceeded the conversion of NH3over the same catalyst. This is explained by the presence of propene, which slipped through the LNT catalyst and reacted with the LNT NOxslip. Separate experiments, conducted under continuous flow and lean-rich cycling conditions, confirmed the ability of propene, as well as ethene, to function as a NOxreductant over the SCR catalyst. Cycling experiments also revealed that the SCR catalyst was able to store propene, such that NOxreduction by stored propene continued into the lean phase (after the switch from rich conditions). According to adsorption experiments, significant co-adsorption of NH3and propene occured in the SCR catalyst, while under lean-rich cycling conditions the contributions of NH3and C3H6to NOxconversion were found to be essentially additive. These findings suggest that under actual driving conditions, NOxreduction by non-NH3reductants (olefins and possibly other hydrocarbons) in the SCR catalyst can contribute to the mitigation of lean and rich phase NOx.