Insight into structure defects and catalytic mechanism for NO oxidation over Ce_0.6Mn_0.4O_x solid solutions catalysts: Effect of manganese precursors

The effects of Mn precursors on structure defects and NO catalytic mechanism over Ce_0·6Mn_0.4O_x catalysts were fully investigated. The Ce_0·6Mn_0.4O_x-Ac catalyst, synthesized by using MnAc₂ as a Mn precursor, showed the best catalytic activity for NO conversion (86.9%) at 250 °C under high space velocity (40,000 mL g^-1 h^-1). Detailed structure-activity relationship reveals that the abundant oxygen vacancies and the highly migratory oxygen species formed on Ce_0·6Mn_0.4O_x are the crucial factors that leading to the better NO oxidation activity than that of the other Ce_0·6Mn_0.4O_x-Y (YNO₃, SO₄, Cl) catalysts. In situ DRIFTS technique confirms that the differences in formation mode and desorption ability of N-based (nitrates, nitrites, and dimer nitroso) intermediate species are the vital factors for NO high-efficiency catalytic oxidation. The highly reactive surface intermediate species, like monodentate nitrates, were observed particularly on Ce_0·6Mn_0.4O_x-Ac catalyst, so that the NO oxidation performance on Ce_0·6Mn_0.4O_x-Ac catalyst was more active comparing with other Ce_0·6Mn_0.4O_x-Y catalysts. This study can broaden the horizons for understanding NO catalytic oxidation mechanism on serial Ce_0·6Mn_0.4O_x catalysts and serve as a reference guide in design of structure defects for functional materials by modulating precursor species.