Synthesis of W-modified CeO 2 /ZrO 2 catalysts for selective catalytic reduction of NO with NH 3 .

In this paper, a series of tungsten-zirconium mixed binary oxides (denoted as W m ZrO x ) were synthesized via co-precipitation as supports to prepare Ce 0.4 /W m ZrO x catalysts through an impregnation method. The promoting effect of W doping in ZrO 2 on selective catalytic reduction (SCR) performance of Ce 0.4 /ZrO 2 catalysts was investigated. The results demonstrated that addition of W in ZrO 2 could remarkably enhance the catalytic performance of Ce 0.4 /ZrO 2 catalysts in a broad temperature range. Especially when the W/Zr molar ratio was 0.1, the Ce 0.4 /W 0.1 ZrO x catalyst exhibited the widest active temperature window of 226-446 °C (NO x conversion rate > 80%) and its N 2 selectivity was almost 100% in the temperature of 150-450 °C. Moreover, the Ce 0.4 /W 0.1 ZrO x catalyst also exhibited good SO 2 tolerance, which could maintain more than 94% of NO x conversion efficiency after being exposed to a 100 ppm SO 2 atmosphere for 18 h. Various characterization results manifested that a proper amount of W doping in ZrO 2 was not only beneficial to enlarge the specific surface area of the catalyst, but also inhibited the growth of fluorite structure CeO 2 , which were in favor of CeO 2 dispersion on the support. The presence of W was conducive to the growth of a stable tetragonal phase crystal of ZrO 2 support, and a part of W and Zr combined to form W-Zr-O x solid super acid. Both of them resulted in abundant Lewis acid sites and Brønsted acid sites, enhancing the total surface acidity, thus significantly improving NH 3 species adsorption on the surface of the Ce 0.4 /W 0.1 ZrO x catalyst. Furthermore, the promoting effect of adding W on SCR performance was also related to the improved redox capability, higher Ce 3+ /(Ce 3+ + Ce 4+ ) ratio and abundant surface chemisorbed oxygen species. The in situ DRIFTS results indicated that nitrate species adsorbed on the surface of the Ce 0.4 /W 0.1 ZrO x catalyst could react with NH 3 due to the activation of W. Therefore, the reaction pathway over the Ce 0.4 /W 0.1 ZrO x catalyst followed both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms at 250 °C.