Superior low temperature activity over α-MnO2/β-MnOOH catalyst for selective catalytic reduction of NO with ammonia
Masanori Takemoto1, Haruko Fujinuma1, Yoshihiro Sugawara2
1Department of Chemical System Engineering, School of Engineering, The University of Tokyo 7-3-1 Hongo Bunkyo-ku Tokyo 113-8656 Japan wakihara@chemsys.t.u-tokyo.ac.jp.
Abstract:
Manganese octahedral molecular sieves with an α-MnO2 crystal structure (OMS-2) and their related materials have attracted significant attention for the selective catalytic reduction of NO using NH3 (NH3-SCR) at low temperatures. Further lowering their operating temperature should be an effective method to develop an environmentally friendly de-NO system; however, their catalytic activity at low temperatures, especially below 100 °C, remains poor. This study describes a post-synthetic approach to develop Mn-based catalysts superior to those in the literature that operate at ultralow temperatures. Post-synthetic planetary ball milling for OMS-2 caused the partial conversion of OMS-2 into β-MnOOH. The obtained nanocomposite catalysts possessed abundant surface oxygen vacancies and strong surface acidity, allowing the milled catalyst to exhibit higher NO conversion at 90 °C (91%) than that in freshly prepared OMS-2 without planetary ball milling (29%). Lowering the operation temperature of OMS-2 catalysts contributed to the suppression of N2O evolution during NH3-SCR over manganese-based catalysts, resulting in high N2 selectivity over the milled OMS-2 catalyst (93%).
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