Abstract
A series of MnOx–CeO2 and MnOx–TiO2 catalysts were prepared by a homogeneous precipitation method and their catalytic activities for the NO oxidation in the absence or presence of SO2 were evaluated. Results show that the optimal molar ratio of Mn/Ce and Mn/Ti are 0.7 and 0.5, respectively. The MnOx–CeO2 catalyst exhibits higher catalytic activity and better resistance to SO2 poisoning than the MnOx–TiO2 catalyst. On the basis of Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), and scanning transmission electron microscope with mapping (STEM-mapping) analyses, it is seen that the MnOx–CeO2 catalyst possesses higher BET surface area and better dispersion of MnOx over the catalyst than MnOx–TiO2 catalyst. X-ray photoelectron spectroscopy (XPS) measurements reveal that MnOx–CeO2 catalyst provides the abundance of Mn3+ and more surface adsorbed oxygen, and SO2 might be preferentially adsorbed to the surface of CeO2 to form sulfate species, which provides a protection of MnOx active sites from being poisoned. In contrast, MnOx active sites over the MnOx–TiO2 catalyst are easily and quickly sulfated, leading to rapid deactivation of the catalyst for NO oxidation. Furthermore, temperature programmed desorption with NO and O2 (NO + O2-TPD) and in situ diffuse reflectance infrared transform spectroscopy (in situ DRIFTS) characterizations results show that the MnOx–CeO2 catalyst displays much stronger ability to adsorb NOx than the MnOx–TiO2 catalyst, especially after SO2 poisoning.
Highlights
Nitrogen oxides (NOx ) emitted from stationary and mobile sources are some of the main air pollutants, which cause a variety of serious environmental problems, such as photochemical smog, acid rain, and greenhouse effect [1]
X-ray photoelectron spectroscopy (XPS) measurements reveal that MnOx –CeO2 catalyst provides the abundance of Mn3+ and more surface adsorbed oxygen, and SO2 might be preferentially adsorbed to the surface of CeO2 to form sulfate species, which provides a protection of MnOx active sites from being poisoned
The maximum NO oxidation efficiency of 72% over MnOx –CeO2 -0.7 catalyst is obtained at 325 ◦ C, while that of 62% over MnOx –TiO2 -0.5 catalyst is obtained at 375 ◦ C the MnO
Summary
Nitrogen oxides (NOx ) emitted from stationary and mobile sources are some of the main air pollutants, which cause a variety of serious environmental problems, such as photochemical smog, acid rain, and greenhouse effect [1]. NOx are the primary precursors of haze occurring in. NOx removal has become the focus of recent environmental protection. The most effective and mature technology is the selective catalytic reduction using ammonia as a reducing agent (NH3 -SCR). There still exist some problems, such as high reaction temperature, sophisticated system design, and high operation cost. It is possible to cause secondary pollution due to the leakage of ammonia [2]
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