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_xMg_3−xAlO catalysts with different Mn:Mg atomic ratios were synthesized by coprecipitation, and employed for soot combustion, NOx storage and simultaneous soot-NO_x removal. It is shown that with the increase of Mn content in the hydrotalcite-based Mn_xMg_3−xAlO catalysts the major Mn-related species vary from MnAl₂O₄ and Mg₂MnO₄ to Mn₃O₄ and Mn₂O₃. The catalyst Mn_1.5Mg_1.5AlO 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 Mn⁴⁺ ions in Mg₂MnO₄ are identified as the most active species for soot combustion. For NO_x storage, introduction of Mn greatly influences bulk NO_x storage, with the adsorbed NO_x species varying from linear nitrites to ionic and chelating bidentate nitrates gradually. The coexistence of highly oxidative Mn⁴⁺ and highly reductive Mn²⁺ in Mn_1.0Mg_2.0AlO is favorable to the simultaneous soot-NO_x removal, giving a NO_x 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_x reduction efficiency.