Determination of Intermediates and Mechanism for Soot Combustion with NOx/O2 on Potassium-Supported Mg−Al Hydrotalcite Mixed Oxides by In Situ FTIR

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• 作者：Zhaoliang Zhang ; Yexin Zhang ; Qingyun Su ; Zhongpeng Wang ; Qian Li ; Xiyan Gao
• 刊名：Environmental Science & Technology
• 出版年：2010
• 出版时间：November 1, 2010
• 年：2010
• 卷：44
• 期：21
• 页码：8254-8258
• 全文大小：317K
• 年卷期：v.44,no.21(November 1, 2010)
• ISSN：1520-5851

文摘

The soot combustion with NO_x and/or O₂ on potassium-supported Mg−Al hydrotalcite mixed oxides under tight contact condition was studied using temperature-programmed oxidation (TPO), isothermal reaction and in situ FTIR techniques. The presence of NO_x in O₂ favors the soot combustion at lower temperatures (<300 °C). However, a little suppression was observed at higher temperatures (>300 °C), which was accompanied by a substantial NO_x reduction. The ketene (C═C═O) and isocyanate (NCO⁻) species were determined as the reaction intermediates. In NO_x + O₂, NO₂ directly interacts with the free carbon sites (C═C*) through two parallel reactions: (1) NO₂ + C═C* → C═C═O + NO; (2) NO₂ + C═C* → NCO⁻ + CO₂. The two reactions can proceed easily, which accounts for the promotion effect of NO_x on soot combustion at lower temperatures. The further oxidation of NCO⁻ by NO₂ or O₂ is responsible for the simultaneous reduction of NO_x. However, the reactions between NO₂ and C═C* are limited by the amount of free carbon sites, which can be provided by the oxidation of soot by O₂ at higher temperatures. The interaction of NO_x and catalyst results in the formation of nitrates and nitrites, which poisoned the active K sites.