In Situ DRIFTs Investigation of Promotional Effects of Tungsten on MnO_<i>x</i>-CeO₂/meso-TiO₂ Catalysts for NO_<i>x</i> Reduction

Abstract

In this work, mesoporous TiO2 spheres supported MnCeW mixed oxide catalysts (MnCeW/m-TiO2) for selective catalytic reduction of NOx with NH3 were prepared by a wet impregnation method. It is interesting that the MnCeW/m-TiO2 catalysts exhibited excellent SCR activity and N2 selectivity in a wide temperature range, even under the high gas hourly space velocity. From in situ diffuse reflectance infrared transform spectroscopy (in situ DRIFTs) studies of desorption, it could be concluded that the addition of tungsten brought about more Brønsted acid sites and reduced the energy barrier of NOx species adsorbed on the surface. At high temperature range, there were still some Brønsted acid sites and NOx species including bidentate nitrate and nitro compounds in MnCeW/m-TiO2, therefore more intermediates could take part in the SCR reactions as well as better catalytic performance. Besides, the in situ DRIFTs of transient reactions indicated that the formed NH3 species and NOx species of MnCeW/m-TiO2 were more reactive due to the promotional effects of tungsten. A series of traditional characterizations also revealed the promotional effects of tungsten for surface active elements, catalytic redox properties, and acid sites of NH3 adsorption. In a word, all the results confirmed that the introduction of W could enhance active NH3 and NOx species as well as surface active elements, thus contributing to the catalytic performance. The present investigations may open a path for design and application of catalysts with outstanding catalytic activity and selectivity.