Ultra-high hydrothermal stability of Ce-based NH3-SCR catalyst for diesel engines: A substitute for Cu zeolites

Abstract

Hydrothermal stability is one of the important bottlenecks limiting the application of NH3-SCR catalysts in NOx abatement. Different acid groups are used to modify CeO2 which can greatly increase the number of surface oxygen vacancies and acid sites, thus improving the redox properties and acidity of Ce-based catalysts. Therefore, all the Ce-PO43-, Ce-SO42- and Ce-WO3 catalysts demonstrate excellent catalytic activities. However, only the Ce-PO43- catalyst shows superior hydrothermal stability and achieves > 80 % NOx conversion between 325 °C and 475 °C after hydrothermal treatment at 800 °C and 850 °C. The hydrothermal process resulted in the decomposition of sulfates and the sintering of WO3, leading to the decrease of oxygen vacancies and the weakness of acid sites. Nevertheless, the Ce-PO43- catalyst could maintain these properties due to the ultra-high stable structure P-Ce-Ov, which has the potential to replace the commercial Cu-SSZ-13. It provides a strategy to improve the hydrothermal stability of metal oxide SCR catalysts to satisfy the application in removing NOx from vehicles.