Tungsten modified MnOx–CeO2/ZrO2 monolith catalysts for selective catalytic reduction of NOx with ammonia

A series of WO3–ZrO2 carriers were prepared by co-precipitation method with different mass fractions (0 wt%, 5 wt%, 10 wt%, 15 wt% and 20 wt%) of WO3, and MnOx–CeO2/WO3–ZrO2 monolith catalysts were prepared for selective catalytic reduction of NOx with ammonia (NH3-SCR) in the presence of excessive O2. The catalysts were characterized by N2 adsorption–desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and NH3/NO temperature-programmed desorption (NH3/NO-TPD). The experimental results showed that, the tungsten modified monolith catalyst MnOx–CeO2/WO3–ZrO2 with the WO3 content 10 wt% had the best catalytic activity and the widest reaction window; it possessed a better thermal stability than V2O5/WO3/TiO2 catalyst, and showed a better H2O and SO2 tolerance than MnOx–CeO2/ZrO2. The characterization results indicated that MnOx–CeO2/10% WO3–ZrO2 had the best textural properties, a well-dispersed state of WO3, the lowest binding energy of Ce3+ 3d5/2, the maximum value of Ce3+:Ce=20.7%, the suitable molar ratio of Mn:Ce≈1, and a co-existence state of MnO2–Mn2O3. In addition, it had the most adsorbed sites of NH3 or NO species. The NOx conversion was more than 80% in the temperature range of 150 °C to 380 °C at the space velocity of 10,000 h−1. It possessed better potential for practical application.

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► WO3 modified MnOx–CeO2/ZrO2 catalysts evidently improved the SCR performance.
► An optimal WO3 loading exists providing high activity and broad reaction window.
► MnOx–CeO2/10%WO3–ZrO2 shows excellent NOx activity and thermal stability.
► The catalyst presents a better tolerance to H2O and SO2 than MnOx–CeO2/ZrO2.