Spinel structured CoaMnbOx mixed oxide catalyst for the selective catalytic reduction of NOx with NH3

Abstract A highly efficient catalyst of a Co a Mn b O x mixed oxide prepared by the co-precipitation method was developed for the selective catalytic reduction (SCR) of NO x with ammonia. With an increase in the Mn content, the catalytic activity of the Co a Mn b O x mixed oxide exhibited a volcano-type tendency, and when Co/Mn molar ratio reached 7:3 (Co 7 Mn 3 O x ), the operation temperature for achieving >80% NO x conversion was 170 °C (116–285 °C window). The formation of spinel structured MnCo 2 O 4 is highly important, and the presence of the spinel structure in Co 7 Mn 3 O x contributes to the increase in active sites and thermal stability and promotes SO 2 and/or H 2 O resistance. In comparison with MnO x or CoO x alone, the Co a Mn b O x catalysts possess improved redox properties and more surface acid sites due to synergistic effects between the Co and Mn species. Among the Co a Mn b O x catalysts with different Co/Mn molar ratios, a higher NH 3 and NO + O 2 adsorption ability was found for the Co 7 Mn 3 O x catalyst, originating from its MnCo 2 O 4.5 phase and higher surface area, which leads to the higher activity of the Co 7 Mn 3 O x catalyst. In situ DRIFTs indicated that bridging nitrate and bidentate nitrate are the intermediate species in the NH 3 -SCR reaction, and the high NO adsorption ability and improved redox properties of the Co 7 Mn 3 O x catalyst are beneficial for the formation of nitrate species on the catalyst surface. Furthermore, NH 3 species adsorbed at Lewis acid sites taken part in SCR reaction, while the reactivity of NH 3 species adsorbed at Bronsted acid was not definitized.