Superior low temperature activity over α-MnO/β-MnOOH catalyst for selective catalytic reduction of NO with ammonia

• Published in: RSC advances 2024-11, Vol.14 (48), p.35498-3554
• Main Authors: Takemoto, Masanori, Fujinuma, Haruko, Sugawara, Yoshihiro, Sasaki, Yukichi, Iyoki, Kenta, Okubo, Tatsuya, Yamaguchi, Kazuya, Wakihara, Toru
• Format: Article
• ISSN: 2046-2069
• DOI: 10.1039/d4ra05934d

Manganese octahedral molecular sieves with an α-MnO 2 crystal structure (OMS-2) and their related materials have attracted significant attention for the selective catalytic reduction of NO x using NH 3 (NH 3 -SCR) at low temperatures. Further lowering their operating temperature should be an effective method to develop an environmentally friendly de-NO x 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 N 2 O evolution during NH 3 -SCR over manganese-based catalysts, resulting in high N 2 selectivity over the milled OMS-2 catalyst (93%). α-MnO 2 /β-MnOOH catalysts were synthesized by post-synthetic planetary ball milling for OMS-2, enhancing catalytic activity in low-temperature NH 3 -SCR.