Hydrotalcite-Derived MnxMg3−xAlO Catalysts Used for Soot Combustion, NOx Storage and Simultaneous Soot-NOx Removal

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• 作者：Qian Li ; Ming Meng ; Hui Xian ; Noritatsu Tsubaki ; Xingang Li ; Yaning Xie ; Tiandou Hu ; Jing Zhang
• 刊名：Environmental Science & Technology
• 出版年：2010
• 出版时间：June 15, 2010
• 年：2010
• 卷：44
• 期：12
• 页码：4747-4752
• 全文大小：254K
• 年卷期：v.44,no.12(June 15, 2010)
• ISSN：1520-5851

文摘

The hydrotalcite-based Mn<sub>xsub>Mg<sub>3−xsub>AlO catalysts with different Mn:Mg atomic ratios were synthesized by coprecipitation, and employed for soot combustion, NOx storage and simultaneous soot-NO<sub>xsub> removal. It is shown that with the increase of Mn content in the hydrotalcite-based Mn<sub>xsub>Mg<sub>3−xsub>AlO catalysts the major Mn-related species vary from MnAl<sub>2sub>O<sub>4sub> and Mg<sub>2sub>MnO<sub>4sub> to Mn<sub>3sub>O<sub>4sub> and Mn<sub>2sub>O<sub>3sub>. The catalyst Mn<sub>1.5sub>Mg<sub>1.5sub>AlO displays the highest soot combustion activity with the temperature for maximal soot combustion rate decreased by 210 °C, as compared with the Mn-free catalyst. The highly reducible Mn<sup>4+sup> ions in Mg<sub>2sub>MnO<sub>4sub> are identified as the most active species for soot combustion. For NO<sub>xsub> storage, introduction of Mn greatly influences bulk NO<sub>xsub> storage, with the adsorbed NO<sub>xsub> species varying from linear nitrites to ionic and chelating bidentate nitrates gradually. The coexistence of highly oxidative Mn<sup>4+sup> and highly reductive Mn<sup>2+sup> in Mn<sub>1.0sub>Mg<sub>2.0sub>AlO is favorable to the simultaneous soot-NO<sub>xsub> removal, giving a NO<sub>xsub> reduction percentage of 24%. In situ DRIFTS reveals that the ionic nitrate species are more reactive with soot than nitrites and chelating bidentate nitrates, showing higher NO<sub>xsub> reduction efficiency.