Abstract
To meet stringent emission standard above European VI, the hydrothermal stability of NH3-SCR catalyst is very important for removal of NOx from diesel engines. In this work, V2O5-WO3/TiO2 (denotes as V-W/Ti) and CeO2-WO3/TiO2 (denotes as Ce-W/Ti) catalysts were prepared by impregnation method. The NH3-SCR activity of fresh and hydrothermal aged catalysts was studied. Comparing with traditional V-W/Ti catalyst, the novel Ce-W/Ti catalyst exhibited much better resistance to hydrothermal aging. More than 80% of NO conversion was obtained over Ce-W/Ti catalyst in the temperature range of 238–573°C even after hydrothermal treatment at 670°C in 5% H2O/air for 64h. The characterization results revealed that the existence of Ce4+-Ce3+ couple contribute to provide more oxygen vacancies and improve the surface Lewis acid of catalyst and affect the surface adsorbed NH3 species. CeO2 could inhibit the segregation and crystallization of WOx species due to the solid state reactions (Ce2(WO4)3) provided more Brønsted acid sites (W-O-W or WO modes of Ce2(WO4)3). In addition, CeO2 inhibit the sintering or phase transition of anatase TiO2 and make the catalyst keep the high surface area, which was favorable to keep more acid sites.
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