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

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