The formation of CuO/OMS-2 nanocomposite leads to a significant improvement in catalytic performance for NO reduction by CO

Abstract

CuO/OMS-2 nanocomposites with different Cu/Mn molar ratios of 0.148, 0.332, 0.569, and 0.886 were prepared by loading cupric oxide on OMS-2 nanorods. The formation of the CuO/OMS-2 nanocomposites significantly increases NO conversion and N2 yield for the reduction of NO by CO. The CuO/OMS-2 nanocomposite with the optimum Cu/Mn molar ratio of 0.569 (CuO/OMS-2-C) exhibited excellent catalytic activity at lower temperature below 300°C, which is much better than a commercial precious metal catalyst (0.84wt% Pd/MgO-Al2O3-SiO2). Compared to the commercial precious metal catalyst, T50 and T90 (the reaction temperature corresponding to 50% and 90% of NO conversion) of CuO/OMS-2-C are significantly reduced by ΔT50=126°C, ΔT90=100°C, respectively. Even at the low temperature of 240°C, the N2 yield of CuO/OMS-2-C is as high as 93.8%. In striking contrast, the N2 yield of the pure OMS-2 nanorod sample and the commercial precious metal catalyst is as low as 3.6%, 8.0% at 240°C, respectively. CuO/OMS-2-C exhibited excellent durability for the reduction of NO by CO. Even after operated at 300°C for 140h, the catalytic activity almost remained unchanged. The evolution of the catalytic active phases or sites for CuO/OMS-2-C with the elevation of the reaction temperature was investigated by CO temperature-programmed reduction, TEM, XRD, and XPS. When the temperature increases above 240°C, the catalytic active phases of the CuO/OMS-2 nanocomposites are reconstructed to metallic Cu and Mn3O4. These characterizations reveal that the formation of the CuO/OMS-2-C nanocomposite considerably promotes the reduction of OMS-2 to catalytic active phase of Mn3O4 as well as the reduction of CuO to catalytic active phase of metallic Cu. The more active catalytic sites of Mn3+ ions and metallic Cu in the CuO/OMS-2-C nanocomposite produced at lower temperature together with the synergetic effect between Mn3O4 and metallic Cu significantly improve the NO conversion and N2 yield as compared to pure OMS-2 and nano CuO.