Influence of tungsten on the NH3-SCR activity of MnWOx/TiO2 catalysts

Abstract

A series of bulk MnWO_x and supported MnWO_x/TiO₂ catalysts with MnWO₄ structure were prepared via self-propagating high-temperature synthesis (SHS), co-precipitation and impregnation methods. The catalysts were characterized using X-ray diffraction (XRD), N₂ adsorption/desorption, hydrogen-temperature programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS) and transmission electron microcopy (TEM). The performance of MnWO_x and MnWO_x/TiO₂ and the relation between the tungsten and manganese oxide species in MnWO_x and MnWO_x/TiO₂ catalysts were investigated. The supported MnWO_x/TiO₂ catalysts exhibited the activity improvement of the SCR reaction via the promotion of tungsten. The XRD pattern and the TEM images revealed that the presence of tungsten induces the formation of a MnWO₄ oxide phase, thus weakening the interaction between MnO₂ and TiO₂, which is favorable for the specific surface area of MnWO_x/TiO₂. The MnWO₄ phase also has a positive effect for the activity and N₂ selectivity of MnWO_x/TiO₂ in the high temperature range. In a feed gas that contains 500 ppm NO, 500 ppm NH₃, 5 vol% O₂ and N₂ as the balance gas, Mn₂WO_x/TiO₂-SHS shows the best deNO_x performance and the NO_x conversion reaches 100% in the temperature range of 130–300 °C under the reaction condition of 30 000 h⁻¹.